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August 28

invisibility

if a suit emmits a spectrum of light which can't be seen by the human eye i.e. infra red or ultra violet will it be invisible or will it produce a wave like affect or distorted image.--Meloxicam (talk) 01:48, 28 August 2009 (UTC)

It won't make any difference at all. It would still block the visible light from behind it and would probably reflect visible light from in front of it as well. What is happening in parts of the spectrum we can't see is pretty much completely irrelevant for determining what we will see. --Tango (talk) 01:59, 28 August 2009 (UTC)

A suit emitting IR might, like a red hot stove, produce distortion of light waves passing near it, by heating of the air. A suit emitting UV migh cause other objects in the scene to fluoresce, just like a black light bulb. Parts of the spectrum we cannot see can have visible effects. Edison (talk) 02:32, 28 August 2009 (UTC)

"IR" and "heat" are not the same thing. All objects at any temperature emit EM radiation, objects are every day temperatures happen to emit IR. It isn't IR that distorts light near hot objects, it is the hot air caused by the actual heat of the object. Any frequency of EM radiation will heat up anything that absorbs it, what matters is just the total energy being emitted, not the frequency (although the frequency will affect how much it is absorbed). A suit will only cause heat distortions if it is very hot. I don't think the OP intended the suit to emit the radiation by being at the appropriate temperature (which, for UV, would be thousands of degrees C), it would just use bulbs (which may involve a filament at that temperature, of course). --Tango (talk) 02:50, 28 August 2009 (UTC)

The front of most remote controls emit IR when a button is pressed, they get neither hot, nor invisible. Admittedly those are only small amounts but I've seen high power IR spotlights for night time security cameras and to the naked eye they appear just as cold and visible. Vespine (talk) 05:11, 28 August 2009 (UTC)

What clothes look like in infra-red! [through an image intensifier that has nothing to do with IR - wrong type of night vision! --Tango (talk) 14:15, 28 August 2009 (UTC)] (Tango is incorrect: Modern NVG's see almost entirely in the near infra-red. SteveBaker (talk) 18:05, 28 August 2009 (UTC)) Tango is never incorrect, you should know better than to say such things! Look at the image description, it is from an image intensifier, not IR goggles. If it was IR you would be able to see that it was lit by an IR bulb somewhere near the camera - it clearly isn't passive IR - and it doesn't look like that to me. --Tango (talk) 18:32, 28 August 2009 (UTC) Near-IR looks like that - and modern image-intensifiers such as found in military NVG's (which is what was used to take this picture) see predominantly in the IR. Mid to Far IR correlates better with 'heat' and those look quite different (eg faces glow more than clothing). This is 'near' IR. SteveBaker (talk) 19:55, 29 August 2009 (UTC) Near-IR night vision is active, yes? It should be lit by an IR bulb near the camera, that images looks like it is lit by something off to the left. --Tango (talk) 15:37, 30 August 2009 (UTC) No - when used by the military, it's generally passive. The last thing you want to do at night is to be shining lights around the place (even if they are IR lights). There is enough near IR produced by the moon and stars for these light amplifiers to cope with. The directional lighting in that image is probably moonlight. SteveBaker (talk) 17:55, 30 August 2009 (UTC)

More than that - you and your clothes DO emit infra-red light. You are very visible on an infra-red "night vision" camera because of that. You certainly aren't invisible - and because human eyes can't see into the infra-red, we can't see that light without help from some high-tech gear. SteveBaker (talk) 13:26, 28 August 2009 (UTC)

(I think you have swapped visible/invisible there.) But yeah, this is a good example. When you press the button on your remote, you don't see anything coming out of that little light bulb on the front. That's what IR looks like. If you view it through something sensitive to that band of frequencies—like a cell-phone camera—you can see it as if it were regular light (which is a neat trick to pull on those who otherwise don't know about that). Nothing fancy to it, but you can't see it with your naked eyes. --68.50.54.144 (talk) 13:17, 28 August 2009 (UTC)

No, SB's usage was correct. You're visible on an infra-red camera not invisible. Nil Einne (talk) 18:36, 28 August 2009 (UTC)

What clothes may look like in infrared no dispute, hopefully (colouring is artificial of course, you can't visualise what humans look like in infrared naturally since we can't see infrared) Nil Einne (talk) 18:44, 28 August 2009 (UTC) [Thermal IR, yes. Near-IR is rather different and that is what I expect the OP was talking about. --Tango (talk) 18:50, 28 August 2009 (UTC)]

• When you see a suit, what you actually see is a reflection from light around it, usually this light has all colors, so you can see a wide spectrum of different colors. For a red suit, almost all the visible non-red light is absorbed by the suit, while only the red light is reflected back to your eye, and the suit looks red. If the light shining on the red suit was completely blue only, with no red in its spectrum, that same suit would look black. A suit which only reflects back IR and UV, and nothing in the visible spectrum, would simply look pitch black, but since it is opaque, it would not function like an invisibility cloak. Sjakkalle (Check!) 09:07, 28 August 2009 (UTC)

No one has addressed my comment about a suit that emitted UV causing fluorescence of objects. For the sake of argument, I would assume the suit emits the equivalent of a 20 watt "blacklight" compact fluorescent bulb. And the OP did not specify that the suit emits the limited IR energy of a remote control or the normal clothing on a non-cloaked individual. Perhaps it radiates all the heat generated by the wearer, which is perhaps 60 watts, in the IR and UV regions, while absorbing incident light in the visible spectrum. It would be black to normal vision, it would be bright when viewed in IR sensitive optics such as security cameras, and it might well cause dayglo paint, tonic water, white paper, cleaning products, clothing washed in certain detergents or a white shirt to glow due to the UV. Thus emitting UV would be more likely to make the wearer easily detectable to the unaided eye at night than just emitting IR. Note: many years ago my rock band would sometimes kill the lights except for a couple of UV fluorescent tubes. Teeth, shirts,and other parts of clothing would fluoresce brightly, as would some of the image on advertising signs or labels or beverages. A cloaked person emitting similar UV would have been easily detected making his way through the room. Edison (talk) 14:58, 28 August 2009 (UTC)

The UV light would attract small flying insects (but not mosquitoes) like a Bug zapper without the zap. The wearer would see interesting UV watermarks on some stamps, banknotes, passports, credit cards and other documents, as well as any stains of body fluids such as semen, blood, bile and urine. Ultraviolet#Human health-related effects of UV radiation gives information that suggests (s)he should wear both insect repellant and sunblock creams and not bite on anything that looks like a candy[1].Cuddlyable3 (talk) 15:46, 28 August 2009 (UTC)

If you want an invisible cloak, you would likely want to consider Broadband Exterior Cloaking. [2][3] They haven't got it scaled up to humans at visible light frequencies quite yet though. ;) Franamax (talk) 17:54, 28 August 2009 (UTC)

People who have had cataract surgery can see a little way into the ultra-violet. My mother noted that some flowers which had been plain before had blue spots or stripes visible on their petals after her surgery. It's believed that plants do this to attract bees (which can see into the ultra-violet). SteveBaker (talk) 18:25, 28 August 2009 (UTC)

v

Gravitational wave triangulation

LIGO says:

These sites are separated by 3,002 kilometers (1,865 miles). Since gravitational waves are expected to travel at the speed of light, this distance corresponds to a difference in gravitational wave arrival times of up to ten milliseconds. Through the use of triangulation, the difference in arrival times can determine the source of the wave in the sky.

How can a single piece of information (the difference between two times) determine the source of the wave? You need three pieces of information to determine a position in 3D space (hence the name). I can imagine two pieces of information being useful since the universe is fairly sparsely populated so there is likely to be very few potential sources along the line (or curve) that you can narrow the source down to, but there being only one source on an entire plane (or surface) seems unlikely to me. --Tango (talk) 01:57, 28 August 2009 (UTC)

From the papers I'm reading (original 1991 LIGO paper in Science and 1999 publication in Physics Today) the purpose for two distant laboratories 3000 km apart is to filter out local noise sources. However, the latter source also states that "one determines the direction and polarization of a gravitational wave by measuring arrival-time differences between geographically dispersed detectors." So, this may also have been a design goal. Two arrival-times define two spheres; the intersection of two spheres is a circle (I think? Somebody check me on that). If so, the source must lie on that circle of intersection. Furthermore, there is polarization information because the two sites also have two arms each - so that can further narrow the possible source locations on that locus. I have not, however, found any papers which specifically discuss techniques or examples of such source location using the LIGO. My experience with electromagnetic waves source-determination suggests that you would still need three geographically-dispersed receivers; but there are a lot of games that you can play (also, space is pretty sparse, so there's only a few black holes that would even be candidates as sources for detectable waves - that can help narrow down the source locations). Nimur (talk) 05:20, 28 August 2009 (UTC)

The intersection of two spheres is a circle (or a point or empty), but that's irrelevant. You would only get a sphere if you knew the emission time as well as the arrival time (so you could calculate travel time, which gives you distance). With just the arrival time you have no information at all, with two arrival times you can calculate the difference and that is useful information, but only one piece of it. --Tango (talk) 14:19, 28 August 2009 (UTC)

In N dimensions, you need N pieces of independent information in order to identify a point uniquely. Hence, in 3D space, you need three pieces of information to determine a position unambiguously. With just the difference between two times - you have only one piece of information. For example - if the pulse were to arrive at exactly the same time at both places, you'd know that the source was equidistant from the two receivers...but that's all you'd know. That means that the source could be any point on a vertical plane that's at right angles to the line between the two receivers. Assuming that the point lies in the plane of the galactic disk narrows it down to a line - and because the solar system is on one of the outer arms of the galaxy, one might guess that the direction lies towards the center of the galaxy - which narrows the search down to a single direction...but those are assumptions that might not be true.

If they had a third receiver, they could unambiguously narrow the source down to any point on a line - and only with a fourth receiver could they determine the position exactly in 3D space. That's why your GPS reciever can't tell you where you are unless it can see four satellites. SteveBaker (talk) 13:20, 28 August 2009 (UTC)

GPS receivers do not need to see 4 satellites if they have a very good clock as the satellites themselves broadcast timestamps for the signals they send out. For an 'average' GPS receiver 4 satellites are required though to determine (x,y,z) and t to an accuracy better than the internal clock can provide. JMiall₰ 17:35, 28 August 2009 (UTC)

First I want to point out that pinpointing a source in the sky in that context means only the two coordinates of a point in the celestial sphere, namely right ascension and declination. Second, the time difference can be suplemented, as pointed out above, by the polarization information which helps pinpoint the source. Dauto (talk) 14:24, 28 August 2009 (UTC)

But they're not looking for a dirac-function, they're looking for a periodic wave (emanating from black hole rotations, for example). This gives phase and timing information (assuming a sub-wavelength separation); so two locations + timing information + phase information may be sufficient to uniquely identify the source (meaning that the N pieces of information criteria is satisfied - as long as the phase assumptions hold). Needless to say, I can't find any documentation of successful identification by this technique in the above papers. Nimur (talk) 15:52, 28 August 2009 (UTC)

Also if they find a source that lasts more than a few hours then they can use the fact that the baseline is moving to triangulate from different orientations of the baseline and get a better directional fix. Gandalf61 (talk) 16:01, 28 August 2009 (UTC)

Relatively local area network

Can I join the wireless home network of my friend who lives on a nearby street about 800 meters away? (Uh, half a mile, isn't it.) I asked this question in an electronics shop and the man said no, not unless I built a tall tower to provide line of sight over the intervening houses for the radio signal. Is there no better way? 81.131.51.80 (talk) 02:31, 28 August 2009 (UTC)

I don't think you need a tower, just an aerial on the roof of each house with some appropriate kind of booster. The Computing desk might be a better place to find out what you need to boost the signal. --Tango (talk) 02:42, 28 August 2009 (UTC)

OK, but just to squeeze every drop of science out of the question while I'm here - would this work even if I can't see his roof from my roof due to other people's roofs being in the way? I think the signal would have to go through about six of the things.81.131.51.80 (talk) 02:45, 28 August 2009 (UTC)

Yes. The signal will spread out from his house (or yours for the return journey) and then diffract around the roofs. Those roofs may weaken the signal, but shouldn't block it entirely. --Tango (talk) 03:06, 28 August 2009 (UTC)

In fact, for that reason, an aerial on the roof isn't strictly necessary at all, the aerial could be inside, but you'll get better signal strength with it on the roof. --Tango (talk) 03:07, 28 August 2009 (UTC)

Thanks! That was what I was hoping, having seen diffraction mentioned further up the page, but I wasn't sure if it would work over such large obstacles so many times in a row. (If I imagine water waves instead of radio waves, it seems less extraordinary.) 81.131.51.80 (talk) 03:16, 28 August 2009 (UTC)

Diffraction happens most when the wavelength and the size of the object being diffracted around are comparable. The wavelength for wireless networks is (I believe) on the scale of millimetres, the roofs are on the scale of metres, that is close enough to get significant diffraction. (You won't, however, get much diffraction of visible light (which is on the scale of 100s of nanometres), which is why you can't see the sun when it goes beneath the skyline.) I rather suspect I am oversimplifying the situation here (optics isn't really my area), but I think the general idea is right and that is all you need. --Tango (talk) 03:30, 28 August 2009 (UTC)

Ha, I like the relaxed notion of "comparable". In most situations I encounter, millimeters are not comparable with meters, but I'll take your word for it. I just went and looked up radio waves and saw that amateur radio wavelengths can be exactly house-sized, so I thought maybe that would be good to aim for, but perhaps converting LAN data to ham radio is not a practical idea, I couldn't say, I know nothing. Leaving it at the same frequency is undoubted cheaper, anyway. 81.131.51.80 (talk) 03:58, 28 August 2009 (UTC)

You may also need a license to use those wavelengths. It would certainly work, though - ham radios definitely work over 800m! The notion of "comparable" can be made precise, but for this kind of thing anything within a few orders of magnitude is close enough. --Tango (talk) 04:15, 28 August 2009 (UTC)

Typical consumer wi-fi gear has a range of only about 100m outdoors, you can get amps and directional antennas and stuff, but I think they claim to improve the signal by 50%-200%, not by 800%. I don't think you'll get 800m out of consumer gear without repeaters in between. There are things like Long-range Wi-Fi but I don't know how cheap and easy that would be to set up. Vespine (talk) 04:22, 28 August 2009 (UTC)

That's an excellent article. "just placing standard USB WLAN hardware at the focal point of modified parabolic cookware" is an inspiring phrase. (Does seem to want line of sight, though.) 81.131.51.80 (talk) 04:42, 28 August 2009 (UTC)

Converting "LAN data" into "HAM data" is commonly done. See AX.25, packet radio, and this great web resource from Tucson Area Packet Radio. With UHF (and a HAM license - you need a powerful transmitter, and you should be licensed to operate it!), UHF-based IP networks have been established with wireless ranges over 25 miles. Nimur (talk) 05:23, 28 August 2009 (UTC)

The 25-mile range isn't because of technical limitations, right? By transmitting LAN data at a shortwave wavelength and bouncing it off the ionosphere, I don't see why you can't transmit to the other side of the world. --99.237.234.104 (talk) 06:13, 28 August 2009 (UTC)

You will not be able to get anywhere near enough bandwidth to bounce off the ionosphere at high frequency. Also the ionosphere adds multipath distortion and is constantly changing. There are special HF modems that can do this job, but you will be lucky to get 9600 bps. You can certainly get multiple kilometers out of wifi. Both ends need a wire parabolic dish, you can get about 26 dBi from each antenna. You have to match polarization and line of site really is required. You could perhaps survive one roof in the way, but 10 or twenty will give you a total loss. Not only do you have to get your signal through, you also have to separate it from all the other WiFi signals around. Graeme Bartlett (talk) 09:21, 28 August 2009 (UTC)

Normal wifi gear operates at 2.4GHz or higher. This is strictly line-of-sight and will be attenuated by intervening walls: diffraction will not help. If you cannot see the neighbor's house, you are stuck. If you do have LOS, then you can get or make a pair of directional antennas that will work. The classical one is the "Pringle's can antenna." See [4] -Arch dude (talk) 13:12, 28 August 2009 (UTC)

Do directional antennas and diffraction mix, if you see what I mean? Can you have a situation where you're pointing a directional antenna at the edge of an object the waves are diffracting round, or is that just silly? 213.122.66.56 (talk) 14:08, 28 August 2009 (UTC)

You can get ranges as far as this from a pair of home WiFi units using the "Pringle can antenna" approach (just Google for that exact term). "Pringles" cans are foil-lined cardboard tubes - but for some (almost magical) reason, they work extremely well as highly-directional WiFi antennae. HOWEVER - you will definitely need a line-of-sight over the rooftops because you can only get that kind of a signal boost using very directional signals that would be disrupted by the intervening rooftops. SPECIFICALLY: You're going to need to be able to see his Pringle-can antenna from your Pringle-can antenna with nothing but air in-between - you'll need to tape a laser-pointer inside the can-antenna of one of them and have it shine onto the bottom of the can-antenna of the other. You'll need to mount them quite firmly (and obviously, waterproof them somehow) in order that the wind doesn't blow them out of alignmnent. If you manage that then you have a really good chance to make this work - even at 8 times the range the thing is designed to work at. However, if you don't make the antennae just right - and if they don't accurately line up - you definitely won't succeed. SteveBaker (talk) 13:04, 28 August 2009 (UTC)

As I understand it, Pringles cantennas aren't actually as good as people seem to think despite the hype and popularity. You're better off choosing a different can and doing things somewhat differently without really raising cost or difficult. This isn't something I've ever done myself or look into in depth, so I could easily be wrong but what I have seen before and re-reading thing things now, the theory and evidence seems fair enough [5] [6] [7] and in particular, I've never come across anyone claiming the opposite whether in theory or evidence/testing (although that doesn't always say much) Nil Einne (talk) 18:31, 29 August 2009 (UTC)

A more reliable alternative is an off-the-shelf microwave transmitter and receiver (this reply is being sent via one of these), but it still needs line-of-sight and is more expensive than the above solutions. I suppose wi-fi is microwave anyway, so the technology is the same, even if the name is different This range of frequencies uses a tiny dish as an aerial. Dbfirs 02:15, 3 September 2009 (UTC)

how to interpret

work done in a compression process in int(pdv).and shaft work in a compression process in int(vdp). how?how its possible? 220.225.98.251 (talk)

Consider some quantity of gas moving through the system and doing some mechanical work as it goes. The gas enters at volume V₁ and pressure P₁ and leaves at volume V₂, pressure P₂. The work it does is $\int _{V_{1}}^{V_{2}}{PdV}$ using the usual work forumla. Using integration by parts, $\int _{V_{1}}^{V_{2}}{PdV}=V_{2}P_{2}-V_{1}P_{1}-\int _{P_{1}}^{P_{2}}{VdP}$.

The $-\int _{P_{1}}^{P_{2}}{VdP}$ part is the shaft work and the $V_{2}P_{2}-V_{1}P_{1}$ part is the flow work. (Edit: I'm not sure this is right. I need to think about it.) Rckrone (talk) 06:48, 28 August 2009 (UTC)

This must relate to http://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Archives/Science/2009_August_2#why_so.3F.3F.2F

(removed confused stuff)83.100.250.79 (talk) 12:16, 28 August 2009 (UTC)

Ok, I think I understand this better now. Enthalpy#Open_systems talks about it a little. The total work that the apparatus does can be divided into two types: flow work, which is the work done to force the gas through, and shaft work which is mechanical work done on an external object like a turbine. The energy that the apparatus gets to do its work comes from energy donated by the gas passing through and heat added to the system ΔQ. For a steady-state process (internal energy in the control volume isn't changing) that's adiabatic (ΔQ = 0), the total work done by the apparatus is equal to the work done by the gas, so W_shaft = W_gas - W_flow = $\int _{V_{1}}^{V_{2}}{PdV}-(V_{2}P_{2}-V_{1}P_{1})=-\int _{P_{1}}^{P_{2}}{VdP}$. This is only true for a steady state adiabatic process. Rckrone (talk) 17:19, 28 August 2009 (UTC)

But the PV terms are not equal to the energy of the gas - the energy of the gas is kPV where k is a dimensionless constant relating to the number of degrees of freedom of the gas (I think)

ie δW = d(poutVout) − d(pinVin) + δWshaft

does not integrate to Work = change(PV) + shaft energy

The questioner has already asked a question based on a false supposition (linked above) - I would not be surprised that they are doing the same here.

I wouldn't waste any time on attempting to reverse engineer unfounded statements.

The PV terms aren't supposed to represent the internal energy of the gas, but the energy required to move the gas out of the control volume (and the energy gained when gas forces itself in). To push a volume of V out against a pressure of P requires work PV. This is called flow work or pV work. Here's a source I found on it [8]. The change in internal energy of the gas is measured by the work that the gas does (since in an adiabatic process the two are equal). Some of the internal energy that the gas is donating goes toward pushing itself out of the control volume (flow work) and the remainder is shaft work. δW = d(poutVout) − d(pinVin) + δWshaft does integrate to Work = change(PV) + shaft energy. You might be right about the OP trying to waste everyone's time though (but maybe not). Rckrone (talk) 18:01, 28 August 2009 (UTC)

To the OP:

Can you give a single example (such as a book reference or web page) where this formulation int(VdP) is used?

You've already asked one question that assumed something was true when it wasn't ie your question linked to above.

Please don't expect others to do your work for you.

I have suspicions that you are deliberately wasting other peoples time - Can you please prove me wrong and give a source from where you are getting these statements?

If you do not I will treat any further posts as vandalism - if you feel this is unfair then feel free to complain about it.

83.100.250.79 (talk) 17:35, 28 August 2009 (UTC)

Firefighting with seaplanes

Recently, in the fires that desolated Greece, I got the impression that the fire fighting seaplanes were picking up water directly from the sea. Do they really use seawater against fire? Quest09 (talk) 10:21, 28 August 2009 (UTC)

Sure. But they prefer fresh water, if that's handy. Our article on aerial firefighting doesn't really address this, but salt water is more likely to lead to corrosion and other conditions that require extra maintenance hours, so sea water isn't the preferred source of water. Still, if sea water's what they've got, that's what they'll use; an emergency is an emergency, after all. -- Captain Disdain (talk) 11:01, 28 August 2009 (UTC)

However, would they use this water on forest fires too? And, wouldn't that ruin the ground for many years? It seems less damaging to let it burn... Quest09 (talk) 11:34, 28 August 2009 (UTC)

The salting the earth question is interesting: but how long would it take to leach out the salt added in the firefighting operation? And for practical purposes, is the amount of salt deposited of real moment, in comparison with, for instance, wind-blown spray over the millennia, or the salts deposited by the conflagration? --Tagishsimon (talk) 11:49, 28 August 2009 (UTC)

This page says salt contamination is taken into consideration for sensitive vegetation and water supply areas. I guess several things need to be considered: how much damage the fire would cause, how far away a fresh water supply is, how much water (and thus salt) would be needed, and what the effects of that amount of salt will be on the land type in question. 88.114.222.252 (talk) 11:56, 28 August 2009 (UTC)

one way salb

i looked evry where , without any use . now designing a one way slab we put the main reinforcement in the short direction but when you take astripe in each direction you will find that the one in the long direction is carrieng more load and resisting more moment . so shouldnt we be putting the main reinforcement in the long direction.please dont use math i need avery clear exponation even other people beside engineers can figure it out ....? —Preceding unsigned comment added by Mjaafreh2008 (talk • contribs) 12:09, 28 August 2009 (UTC)

Usually reinforcement is put in any part that is too weak as it is to carry, support, or withstand an expected load.

Also what is the "one way slab" for, what is it for?83.100.250.79 (talk) 12:21, 28 August 2009 (UTC)

Without further details it's impossible to say where the reinforcement should go in your example.83.100.250.79 (talk) 12:19, 28 August 2009 (UTC)

will the way i visualized it like this ... assuming a two beams crossing each other at midspan now to carry a specified load applied at that point of intersection then which one of the two beams need the biggest reinforce steel ratio to support that load ... —Preceding unsigned comment added by Mjaafreh2008 (talk • contribs) 12:47, 28 August 2009 (UTC)

It's still not clear, please supply a diagram, or actual dimensions.83.100.250.79 (talk) 12:50, 28 August 2009 (UTC)

This sounds like a civil engineering matter where some mathematics is unavoidable and viability of the resulting structure could have legal consequences. I don't think we can provide the kind of consultation that requires. Cuddlyable3 (talk) 12:53, 28 August 2009 (UTC)

If the slab is long but not very wide, then obviously the main tendancy to bend will be along the long direction - so the main reinforcement beams need to go along the length to resist that bending. However, I presume you need some reinforcement across the width too - resulting in a "waffle-slab" approach. The trouble is that the spacing and depth of the beams and the degree of post-tensioning that goes on does indeed require some math - and it depends on the results of a proper soil survey too. I would have thought that you'd either have a book or table of some kind that specified what you need for different shapes and sizes and under different soil conditions - or that you'd employ a structural engineer to design the slab properly using math and stuff. The consequences of a slab cracking years after the building is completed are pretty severe for the owners (I know - it's happened to me!) and I'd be horrified if someone was just guessing how much reinforcement the thing needed on the basis of asking a question to a bunch of unknown people on the Internet! SteveBaker (talk) 12:53, 28 August 2009 (UTC)

But a one-way slab is by definition supported across the short way. What you're thinking of is a case where you can only support at the distant ends. Or in the case of a two-way slab (W > 0.5L), you would need to consider the long direction as well as the short one. Franamax (talk) 18:55, 28 August 2009 (UTC)

And isn't there another option: diagonal reinforcement ? Those would have the advantages of providing more rigidity and stopping cracks parallel to any of the walls, but some would need to be somewhat longer than a straight reinforcement, in order to reach from one corner to another, and others would be shorter. If the reinforcement is free-floating, this might work fairly well. However, if attached to the frame at the ends, this would be a bit trickier (if the components don't meet at a right angle).

If we're still discussing length-wise or cross-wise reinforcements, the site will make a big difference. Is this on a hill ? If so, I'd put the reinforcement in the direction going up and down the hill. But, better yet, put in reinforcement in both directions, so you're covered no matter what the stresses are. StuRat (talk) 14:52, 28 August 2009 (UTC)

will .... first of all in engineering they call it one way slab and the wright way is to provide steel reinforcement along the short dimension , so its known where to put the steel . what iam asking for is why ,,, i think we should provide the steel along the long direction . and we cannt provide steel reinforcement along both directions because it wont be economical at all .

How do you know one way is the right way - give a reference for your statements or stop wasting peoples time. ok? Why do you think the short reinforcement is supposed to be the right way to do it -does it say so somewhere? Where?

Stop wasting peoples time with you unfounded statements ok?.83.100.250.79 (talk) 17:24, 28 August 2009 (UTC)

You need to provide some reference for your statements that

the wright way is to provide steel reinforcement along the short dimension

This seems wrong - please provide evidence showing from where you got this statement. Otherwise I will assume that you, like others are making up false statements in an attempt to waste other peoples time. I view that sort of behaviour as vandalism and will treat it accordingly.

You should realise that disruptive behaviour is vandalism.

If you feel have been falsely accused of disruptive behaviour by me please provide evidence that your statements have a legitimate basis, if you feel I am treating you unfairly then please feel free to complain.

83.100.250.79 (talk) 17:41, 28 August 2009 (UTC)

Iam acivil engineer ... thats how i know ... because we design it ... but i need a full understanding about it theres alot of terms that we use all the time but we didnt have afull understanding for it ...?? and i think you should cool alittle bit ... iam not intersted in wasting your time ... ????????????????????????????????/ —Preceding unsigned comment added by Mjaafreh2008 (talk • contribs) 17:52, 28 August 2009 (UTC)

You know what - I don't believe you. Why is a civil engineer asking simple questions on the internet - you should already know the answer. You should also know as an engineer that you need to communicate the problem clearly to other people - something you have failed to do - You have not supplied any information about dimensions, material, points of attatchment, etc despite being asked. You have failed to provide any source for your statement that "reinforcement should be across the short length".

Why should people waste their time (which is what you are doing) trying to justify statements that you have not provided a source for, and may not even be true.83.100.250.79 (talk) 18:04, 28 August 2009 (UTC)

83.100, you seem to enjoy hectoring posters here more than actually answering their questions. If you wanted to know what a one way slab is, you could have tried that handy new thing called Google. If you want a source that short way is the right way, you could have looked that up pretty easily too, since the answer is "all of them". But if it will make you feel any better, here's a nice Powerpoint with lots of pictures.[9] Now please try to provide answers in a polite and helpful way, and if you're worried about people's time being wasted, well, the only time you control is your own. I didn't have any trouble understanding the question or giving a simple non-numeric answer. Franamax (talk) 18:45, 28 August 2009 (UTC)

Also 83.100.250.79, please consider that an OP's first language might not be English. Not all the other language wikis have reference desks. If you don't understand what the person is asking, then tell them so politely and ask them to clarify. Also there is no requirement for questioners to produce sources for their statements, you may ask for them politely, but they don't have to give you any. Asking or answering questions on the ref desk isn't like editing an article. Also please assume good faith. 152.16.15.144 (talk) 06:15, 30 August 2009 (UTC)

Your problem is that the slab is supported all around, so your assumption that there is more stress in the long direction is incorrect. The load is borne primarily in the short direction. Think of it as the load wants to find something to hold it up as quickly as possible, so it "looks" for whatever support is closest. Franamax (talk) 18:08, 28 August 2009 (UTC)

Or for another way to think about it, why does the slab care how long it is? If it 1 meter wide and 10 meters long, why is that any different than if it was 10 kilometers long? It would only be important if you were supporting the slab only at the widely separated ends, in which case you would definitely need to reinforce it the long way (and if it's 10km long, you will need an awful lot of rebar;). Franamax (talk) 18:12, 28 August 2009 (UTC)

you could look at it like this ... at midspan where the moment is maximum and assuming that the slab is consist of two strips crossing each other at midspan now ,,, deflection will be the same amount at midspan because as we know both strips are attached at that point . and using this info that elastic strain in ex. concrete is 0.003 then the short side need more steel to prevent strain from exceed this value where cracks could start to form . so if you provide enough steel in the short direction to prevent cracks cracks surly wont form along the long direction. mabey this is the answer. and mr 83.100.250.79 please dont call people lair ... unless ofcoarse if its make you feel good .--Mjaafreh2008 (talk) 18:43, 28 August 2009 (UTC)

Or here's yet another way of looking at it, related to the first thought experiment of two crossing beams: pretend you have two beams of equal cross-section, one (beam A) 3 times longer than the other (beam B), with no load, just their own weight. We know for sure that A will have a higher deflection than B. But we also know that if the beams are joined at the centre, they must have the same deflection, so in effect, beam B is supporting A, and A is actually two beams of length A/2 (actually it's a compound beam with two spans, but whatever). Now stick in a few more "B" beams across the width. Now you have A as a compound beam with four spans of length A/4. Since deflection varies as L^3 and stress varies as L^2, pretty soon you don't have to worry at all about A. Everything is carried by the "B" beams, except right at the very ends of the slab. Don't know if that makes it clearer or not... Franamax (talk) 19:12, 28 August 2009 (UTC)

thank you very mush ... will as you said i could google it , but its better to disscus it with someone , soory for wasting your time .--Mjaafreh2008 (talk) 20:11, 28 August 2009 (UTC)

Not a problem, and I don't think you wasted anyone's time. We all choose how to use our time here. It's easy enough to search for things on Google or look them up in books, and you can always find the equations. But when you get stuck on why the equations are the way they are and need help in understanding the conceptual basis, well, that's exactly what we're here for. Hopefully at least some of us helped you, and feel free to ask more questions. (And I see that our concrete slab could use a bit of work, I'll put that on my list) Franamax (talk) 22:56, 28 August 2009 (UTC)

Comparing male/female weight loss on The Biggest Loser

Sorry about this banal question, but I'm going to be competing with some female friends in a weight loss race, and I want to make it fair so they cant complain when I win. I see in The Biggest Loser that it's proportional - they use percentage of body weight lost - is that how they deal with the fact that males tend to lose weight faster than females?

thanks Adambrowne666 (talk) 12:20, 28 August 2009 (UTC)

I suggest you agree with your friends about how your weight changes will be compared before starting the race. Then there need be no complaints afterwards. Cuddlyable3 (talk) 12:48, 28 August 2009 (UTC)

If that's all they do then that's all they do, so there's your answer. One of the reasons why men and women tend to lose weight differently is that, when working out, women often gain a fair portion of muscle mass. That dulls the weight loss they might otherwise notice. So if you wanted to be completely correct about it, percentage wouldn't inherently be correct, but it should be more than sufficient for your purposes. ~ Amory (user • talk • contribs) 13:11, 28 August 2009 (UTC)

Exercise increase the basal metabolic rate, what fat you burn at rest on a fasting stomach. According to our dieting article, this increase accounts for a lot of the weight loss from exercising. With equal heights the BMR is roughly BMR = 10*weight + s where s is a constant. Depending on whether you'r male or female s is +5 or -161. This means that the weight-term dominates the equation. Given two people who exercise equally, the fattest will loose the most weight. So as a measure of who's exercising most during a diet, percentage loss is a good measure and gender can be ignored. EverGreg (talk) 13:13, 28 August 2009 (UTC)

You have neglected to say what units you are measuring weight in... --Tango (talk) 14:28, 28 August 2009 (UTC)

I think on the biggest loser, it's not done that way just to compare male and females, but also people that are different amounts over weight. It's much more feasable to lose 100 lbs if you're 350lbs than if you're 250lbs to start with, for example. The % loss is probably a fairly fair way to go about it (although as pointed out it ignores muscle gains). Perhaps you could also compare BMIs (which will suffer from the same problem). TastyCakes (talk) 14:50, 28 August 2009 (UTC)

Doesn't this question request medical advice? You should consult your doctor before participating in a "weight loss race." Wikipedia can't specifically advise you on what a safe or desirable weight should be; nor what weight-loss regimen is healthy. Nimur (talk) 15:54, 28 August 2009 (UTC)

But we can speculate on what makes a fair competition, no? An egg eating contest might well have health implications, but we could still pontificate on the best way to judge such a competition (clearly most eggs as a percentage of body weight would be fairest). TastyCakes (talk) 16:00, 28 August 2009 (UTC)

This isn't medical advice, it is advice about judging a competition. There is no diagnosis, prognosis or treatment suggestion involved. --Tango (talk) 16:02, 28 August 2009 (UTC)

A lot of the time, it's the skinny ones who cram down the most eggs in absolute terms, so judging based on % body wt. might just skew things even farther in their favour. And I agree this is not a mediq per se, but a warning that rapid weight loss can be quite dangerous is certainly appropriate. Franamax (talk) 19:19, 28 August 2009 (UTC)

Yeah, look how many skinny people are champion gurgitators. Body mass has little to do with it, if anything it should be handicapped by height but even that's hard to correlate. --66.195.232.121 (talk) 20:28, 28 August 2009 (UTC)

I think those people are skinny precisely because they have an overactive metabolism (which also leads to their increased appetite). I should know, because I'm thin as a stick but I absolutely devour buffets and am constantly hungry. (Perhaps I have an enzyme deficiency or something...) John Riemann Soong (talk) 21:56, 28 August 2009 (UTC)

Possibly true, but when you're ingesting eggs at a rate of one a second, your metabolic rate isn't really going to help you fit more in, since the contest is over basically before the digestive process has even begun. I would rather speculate that a relative lack of fatty tissue around the stomach allows it to expand more in a short period of time. (And if you are able to enjoy eating lots of food while avoiding weight gain, I'd be thinking enjoy it while it lasts! Good food is one of the true pleasures of life. :) Franamax (talk) 22:42, 28 August 2009 (UTC)

Thanks, all, for your informative answers. Adambrowne666 (talk) 08:01, 31 August 2009 (UTC)

Recharging Electronics in Different Countries

If I take my iPhone to different countries around the world and plug it in to recharge from empty will the charge time vary based on the local electric power standards? TheFutureAwaits (talk) 16:35, 28 August 2009 (UTC)

Probably not, but make sure you have an adapter that can cope with all the different voltages you may encounter (ie 110V and 230V). SpinningSpark 17:26, 28 August 2009 (UTC)

And in addition to the voltage difference, be aware that plug configuration varies a lot around the world, beyond just the standard North American and European shapes. Franamax (talk) 20:53, 28 August 2009 (UTC)

Assuming everything works correctly, the wall voltage goes through a transformer which changes it to the proper voltage for the iPhone to use (and converts it to DC). At that point there's no difference in what the phone is receiving. Rckrone (talk) 17:39, 28 August 2009 (UTC)

Ah, thanks this makes sense. Though I was hoping higher voltage meant faster charge time... TheFutureAwaits (talk) 21:34, 28 August 2009 (UTC)

I hate to pass on rumours[10] but they say there is a problem of iphones exploding. Cuddlyable3 (talk) 13:37, 29 August 2009 (UTC)

what is the counterion for DNA?

Okay, I should prolly know this, but they don't ever mention where the positive counterion for the phosphate in DNA goes! I mean, if you have millions or billions of basepairs of this stuff in a single chromosome, it seems to me you have some major charge separation ... is it like sodium and potassium ions around the DNA? And when you're during agarose gel electrophoresis and you do DNA extraction, I assume these counterions are still hanging around in solution (or you'd have a major test tube of negativity, lol...), and it is these ions that flow in opposite direction of the DNA? But I'm really amazed, because chromatin gets wound into these megadense structures and I would think there would be some major electrostatic repulsion. John Riemann Soong (talk) 17:32, 28 August 2009 (UTC)

At first I was thinking that, the phophates may be protonated at physiologic pH, which would mean that counterions would be unneccessary. Upon actual research, that turns out not to be the case. However, This 2004 study implies that the DNA is actually in a diffuse sea of sodium and potassium cations, which provides the charge balance; however the counterions don't actually bond to the phosphates directly. This google search turns up LOTS of material on this topic. --Jayron32 18:44, 28 August 2009 (UTC)

Hmm, I'm just perplexed at why everyone seems to neglect to mention where the counterions go (or how they affect things) at the elementary level. The paper you cite gives short-length DNA chains -- but let's take say, a chromosome. Why don't the negative phosphates generate some major repulsion? I'm sure that the K+ and Na+ will have hard time reaching the phosphate groups deep within the chromosome. For that matter, I'm kind of perplexed at why DNA is called an "acid", when the NH2 groups and phosphate groups would seem to make it at least weakly basic. If DNA is already negatively charged, I'm sure that the pKa of DNA (or of one base pair unit) must make it a weaker acid (and a stronger base) than water. John Riemann Soong (talk) 21:46, 28 August 2009 (UTC)

Have a look at the histone article. There is a discussion of exactly what you are asking under the sub-heading "Structure". From the article: "Helix-dipoles from alpha-helices in H2B, H3, and H4 cause a net positive charge to accumulate at the point of interaction with negatively charged phosphate groups on DNA". --- Medical geneticist (talk) 00:54, 29 August 2009 (UTC)

I don't really know the answer to that question. I have always assumed that there would be enough hydrogen atoms around to balance the charges. Isn't that why DNA is considered an acid? Dauto (talk) 03:30, 29 August 2009 (UTC)

Well shouldn't it be called deoxyribonucleic conjugate base then? Are Na+ / K+ really the primary counterions, or is it H+? John Riemann Soong (talk) 20:04, 29 August 2009 (UTC)

If you get full dissociation in aqueous solution, there isn't really any "possession" of counter ions - that is, you can't say "these ions are associated with DNA, these with these acidic metabolites, these with acidic protein sidechains, etc." The neutralization of charge is a bulk effect - all positively charged species contribute to countering all negatively charged species, and vice versa. The closest you come to is when histones and other proteins bind to the DNA. The remaining charges are neutralized by whatever else is around. In large part this depends on the pH and what else is dissolved. At pH 7-8, there isn't a lot of H⁺ around, and other ions are needed (indeed - if the other ions haven't been added, you wouldn't *be* at pH 7-8). Inside the cell there are some positively charged amines floating around, but I imagine that most of the cations would be potassium rather than sodium (cytosol concentrations of ~200 mM vs. 5 mM - for E. coli, from Bionumbers). In an agarose gel, it will be countered by whatever counterion you've placed in the buffer. For TAE buffer/TBE buffer, that would be Tris. -- 128.104.112.102 (talk) 20:01, 31 August 2009 (UTC)

t--

Is K+ (as well as Ca++, Mg++ and whatever cations happen to be there) at a higher concentration in the nucleus? Basically the issue is that DNA would seem to be a pretty concentrated mass of negative charges, and a neutral histone could probably form polar bonds with DNA, helping to delocalise some of the charge, but this means negative charge areas would be created on "another" side (inside the histone?). DNA must create a pretty strong electric field inside the cell that would probably pull cations towards it! So these cations could be "associated" with DNA, roughly speaking. John Riemann Soong (talk) 00:49, 1 September 2009 (UTC)

Also, bacteria don't have histones, but I imagine that with a circular chromosome you're still going to get quite the localisation of negative charge .... wouldn't it be in quite a high energy conformation? John Riemann Soong (talk) 00:56, 1 September 2009 (UTC)

Histones aren't neutral. They usually contain a large number of lysine and arginine residues, which are positively charged at physiological pH. In fact, this is generally true of all nucleic acid binding proteins - overall, they have a net positive charge. The coulombic attraction between the positively charged proteins and the negatively charged nucleic acid adds to the binding affinity, and also serves to neutralize the negative charge on the phosphate backbone. I don't know about the difference in ion concentrations in the nucleus and cytoplasm, but it could be slightly different, although there is a bunch of other negatively charged items in the cytoplasm (ribosomes, mRNA, ATP, various small molecule and protein phosphates, various organic acid metabolites) which may boost the amount of cations in the cytoplasm. Remember also that water has a pretty strong dipole moment, and as such can shield/solvate charged particles quite well, so strict neutrality isn't needed. (Indeed, there is usually an electrostatic membrane potential that is maintained by the cell.) Also, while bacteria don't have histones per se, they do have histone like DNA binding proteins, as well as a host of other DNA binding proteins. -- 128.104.112.102 (talk) 15:30, 1 September 2009 (UTC)

Brain Development

Am I right in thinking that the brain stops developing at age 18 and the between the ages of 18 and 24, the brain only changes in the way it works in order to adapt to the adult social environment. In other words the brain of an 18 year old brain is fully developed structurally and has the same capabilities as a 25 year old brain but has just not yet adjusted to the adult environment. Thanks in advance for any answers. 86.139.54.213 (talk) 20:44, 28 August 2009 (UTC)

Neuroplasticity drops off sharply before puberty (and this seems related to the linguistic critical window). Neural stem cells continue to be active for most of the adult life (though neural stem cells are more active in children). Are you in an argument about maturity of 18-year-olds or something? "Structure" and "social environment" are all pretty vague terms. If you amputated an adult arm, the part of the brain that used to control that arm will be restructured to do something else. (though not perfectly -- sometimes you get phantom limbs.) John Riemann Soong (talk) 21:26, 28 August 2009 (UTC)

I've been reading around this area and alot of research suggests that the brainc ontinues to develop after age 18 up to about 25. However I don't quite understand how. The assumption I made above was that by age 18 the structuring process of the brain which occurs during adolescence has finished and the brain has its full capabilities and that after that the change is more of a change like you described with phantom limbs to adapt to the adult environment. 86.139.54.213 (talk) 21:35, 28 August 2009 (UTC)

As far as I understand, the brain was thought to stop developing at around 18, but more recent thinking is that it can continue to change or develop at any age. One example is registered London taxi drivers who have to memorise a lot of streets - known as "The Knowledge" - and the part of their brain that remembers things grows larger. 89.240.194.145 (talk) 22:54, 28 August 2009 (UTC)

Brain development has many aspects, and some of them continue throughout life, although most of the structure is in place by ages 5-6. Most of the brain's nerve cells are created before birth, and there is actually a drop in numbers after birth as redundant cells are eliminated, but there are a couple of special areas where new neurons are apparently created throughout life. One is the dentate gyrus of the hippocampus, and there is evidence that the newly created neurons play a role in storing new memories. This is just one aspect; a complete answer to the question would be very long. Looie496 (talk) 23:23, 28 August 2009 (UTC)

There was a mid-decade newsmagazine article that said the body pretty much reaches adultivity at 18, but brain development isn't really complete until about 22, and somewhat even until way into the 20s, so the traditional 21 age of complete majority would really be 22 psychologically. (though some things about wisdom teeth and bones aren't until 22) Does anyone know the paper(s) this was based on? Sagittarian Milky Way (talk) 00:07, 29 August 2009 (UTC)

I'm not quite sure what everybody means when they say the brain "stops developing". The brain continues to have the ability to learn throughout your life, which requires the formation of new connections between neurons. StuRat (talk) 14:30, 29 August 2009 (UTC)

I'd say your assessment is quite accurate. The brain stops 'expanding horizons' at about 18, and after that it's filling in the gaps left by that expansion, so to speak. Vranak (talk) 16:42, 29 August 2009 (UTC)

(Wrote this while ago but got distracted and never posted) As most of the discussions above indicate, this is a rather complicated and in some ways I would say unanswerable question since it depends by what you mean by structural brain development, stops etc. Generally speaking your brain is going to be changing until you die. Precisely how will depend of course on a variety of factors particularly how you train it. Size wise (well weight), the brain is already about 25% of the adult brain at birth [11] and broadly speaking is structurally very similar. Of course human brain development is much more then just getting larger and taking on the right structure. As said earlier, the brain is always changing and I'm pretty sure there are some quite significant changes past 18. For example, one thing that often comes up particularly when it comes to driving is that the parts of the brain involved in risk taking continue to change significantly until about 25 [12] [13] [14] [15]. It's sometimes said that the brain reaches maturity or adulthood at 25, but as I've indicated this is really overtly simplistic Nil Einne (talk) 20:23, 30 August 2009 (UTC)

Kirchhoff current law validity

It was quiet interesting when I had a discussion with some friends about Kirchhoff current law. Someone told me that there is some current lost in the case of a lamp/bulb due to electrons-ions effect. I'd like to verify this, and how can I restate Kirchhoff current law?--Email4mobile (talk) 21:44, 28 August 2009 (UTC)

It sounds like somebody is playing games with the definition of a closed system. Kirchoff's current law always holds, because conservation of current is equivalent to conservation of particles (# electrons in = # electrons out). There are no relevant electronic processes which create or destroy electrons; photon radiation by incandescent heating certainly does not create or destroy electrons. It might be *remotely* possible that some electrons thermally escape from the hot filament, and result in a static charge buildup on the exterior of the lightbulb; this is a very minor effect, if it is even measurably present in a lightbulb. Anyway, current is still conserved, if you count the flow of electrons via thermionic emission as part of the wire-in, wire-out system. A more general way of stating Kirchoff's law is in the form of the displacement continuity equation, $\nabla J=-{\frac {\partial \rho }{\partial t}}$; most people consider the charge buildup to constitute current (by definition). Nimur (talk) 22:16, 28 August 2009 (UTC)

In fact, Kirchoff's current law holds even if electrons are created or annihilated since electrical charge is always conserved. Rckrone (talk) 01:13, 29 August 2009 (UTC)

General fomula for electric fusing

Given a material's characteristics (type, length, cross sectional area) is there a formula to relate time-current fusion assuming normal conditions?--Email4mobile (talk) 21:49, 28 August 2009 (UTC)

Yes there is, the resistance of the material is a major factor, you need to make assumptions about how fast it will radiate heat, (and whether or not it's local surroundings form insulate the heat produced.

You also need a formula for Thermal_radiation - when the heat (due to resistance, dependent on current) generated is greater than the heat that can be dissapated at the fuse melting point the fuse fails. Note that the resistance depends on temperature too.83.100.250.79 (talk) 22:01, 28 August 2009 (UTC)

By "fusing" do you mean "melting?" Model the energy dissipated in a unit length of the material versus the heat radiated or conducted, along with the ambient temperature and tension on it. A bare conductor would carry more current without melting than an insulated conductor, and a conduit filled with conductors would lead to melting at lower current than the same conduit with one pair of conductors. Conductors at a very high ambient temperature would melt at lower current than conductors at low ambient temperature. Even the surface color or emmisivity of a conductor would affect the current it could carry before melting. In some household plug fuses, the spring tension on a fuse element causes it to open at a lower current than if it were not under tension. Edison (talk) 00:34, 30 August 2009 (UTC)

Yes I do mean "melting". The reason I raise this question is to estimate an approximate but general formula for the fuses melting curve given in data sheets, thanks..--Email4mobile (talk) 21:55, 31 August 2009 (UTC)

why is ammonia more acidic than water?

Is it because it has more protons to donate? It's kind of curious to me, because shouldn't oxygen tolerate the negative charge better than the ammonia? Or does having more hydrogens to delocalise the negative charge improve ammonia's acidity? If NH2- is a stronger base than OH-, why is NH3 more acidic? John Riemann Soong (talk) 21:52, 28 August 2009 (UTC)

Ammonia is a weak base. It is not more acidic than water. You should read that article, which describes its ionization process, and Ammonium for some electrochemical properties of the ion that forms. This MSDS from Texas A&M Chemistry says Ammonia has a pH of 11.6 at 1M and describes it as a dangerously corrosive alkaline. Ammonia also has interesting properties when mixed in low concentrations with chemical solvents at other net pH 's - it can become dramatically more dangerous and can create hazardous fumes. Nimur (talk) 22:06, 28 August 2009 (UTC)

I just did. I was actually curious about its pKa, and I note its value (9.75) is even lower than that of phenol (9.95). But NH2- has no resonance stabilisation! Why is it so acidic? I know it's a weak base, but ammonia seems to have some significant (though not symmetric) amphoterism. Water is usually known as an amphoteric substance, but ammonia seems to give water a run for its money. John Riemann Soong (talk) 22:11, 28 August 2009 (UTC)

What do you mean ammonia is not more acidic than water? Water's pKa is 15.74 ... a drastically weaker acid than ammonia. In fact, I'm wondering why hydrogen bonding doesn't form between ammonia molecules as it does for HOH molecules, since ammonia has a lone pair to donate, and it also has protic hydrogens to donate as well. Is it the lack of symmetry (3 protic hydrogens and 1 lone pair versus 2 protic hydrogens and 2 lone pairs)? Here's my working hypothesis: ammonia's 3 protic hydrogens give it an advantage over water, which only has two, resulting in a higher pKa. But nitrogen isn't as good at handling negative charge, so I wonder why those two effects don't cancel out. (I note that water is only an order of magnitude or two more acidic than alcohols, when it has twice the number of acidic hydrogens, so surely ammonia having 50% more acidic hydrogens can't lower the pKa that much??) John Riemann Soong (talk) 22:18, 28 August 2009 (UTC)

There are multiple definitions of acid and base. I think you're using an uncommon definition, and incorrectly applying it to compare Ammonia's dissociation constant to that of water. See also this detailed description of Ammonia and its pKa. You might also want to read Amphoterism about chemicals which have both acidic- and alkaline- properties, simultaneously. Nimur (talk) 22:19, 28 August 2009 (UTC)

It's uncommon to define acidity as a function of pKa? I suppose I don't know what the solvent context for the reported pKa value in question. If the 9.75 value is the self-ionization value, then the pKb of ammonia (in ammonia) should also be 9.75, shouldn't it? (Since there would always be equal amounts of NH2- and NH4+ with pure ammonia). Plus, I'm not sure how you would measure the self-dissociation constant of a gas...so I'm guessing the 9.75 value is that of ammonia in water? I don't see how I'm using pKa incorrectly here. If ammonia's pKa in water is 9.75, and water's pKa in water is 15.76, surely ammonia must be more acidic than water? John Riemann Soong (talk) 22:37, 28 August 2009 (UTC)

Also, what is the mathematical relationship between the number of acidic hydrogens (assuming that they are chemically equivalent) and pKa? I note that ethylene glycol has a pKa of 14.22 whereas ethanol has a pKa of 15.9. I actually suspect that the (straight-chain) alkyl group stabilises the negative charge on a deprotonated alcohol via hyperconjugation, so perhaps a 50% decrease in the amount of acidic hydrogens by itself should actually result in a much greater pKa difference than the pKa of alcohols would suggest? (Having a tert alcohol increases the partial negative charge on the carbon next to the alkoxy oxygen, but would probably only negate a minority of the stabilising effect, so perhaps it's possible that having more or less protic hydrogens can affect pKa that drastically, an effect which the alkyl group mostly masks?) And is it true that NH2- enjoys some hyperconjugative stabilisation? John Riemann Soong (talk) 22:37, 28 August 2009 (UTC)

Sorry for the 3 posts in a row, but can I double check to ensure that the 9.75 value is correct? A google search is telling me that some people think ammonia has a pKa of 9.25, which makes it even more acidic than I thought it was. John Riemann Soong (talk) 22:39, 28 August 2009 (UTC)

(see below) Basically google is giving you the wrong figure. It pKa ammonia =34

The OP (J R S) is talking about this acidity

NH3 >>> NH2- + H+

not the acidity/basicity in water -

I think there must be some wrong figures somewhere - Sodium amide definately deprotonates water.

I think you may have got the pKa for ammonium, not ammonia - that's an error on the part of the people who write the books/web pages - they say the pKa of ammonia when they are describing the pKa of NH4+

This is better [16] pKa ammonia/amide is 34 , (ammonium is 9.24) I assume this is near enough to 9.75 to not cause any problems

The 3 H's on N should add slightly to the acidity (compared to a hypothetical NH2, or an OH2 were the N and O have the same electronegativities), but this won't be a major factor. Less than 1 pKa unit.

83.100.250.79 (talk) 22:48, 28 August 2009 (UTC)

Wow, thank you .... I've gone back and fixed the article. It makes me so mad when people are sloppy and end up describing the pka's or pkb's of the ions instead. I was guessing solvent acidity because it's kind of hard to self-dissociate as a gas. How do you measure the self-dissociation constant of a pure gas anyway? One more question though ... I assume a 50% increase in the number of protic hydrogens results in a pKa decrease of around (or less than 1), but a 50% decrease (ceteris paribus) seems to affect the pKa way more than this (in alcohols the alkyl group's hyperconjugation probably masks this somewhat). Am I right in thinking that the relationship of the number of protic hydrogens to (pKa1) acidity isn't linear? John Riemann Soong (talk) 22:53, 28 August 2009 (UTC)

Wait a minute - alcohol hyperconjugation - you mean like in ethylene glycol? There's a much simpler thing going on here which is the stabilisation of -O^- by an 'adjacent' OH group

     H
    /
   O   O-
   |   |
 2HC---CH2

You can see how the H can be 'shared' by the two O groups - think resonant hybrids - is this what you meant - I don't think that is usually termed hyperconjugation. (I might have forgotten)

The effect of having more H's is complex - you can view it theorectically as having N times more hydrogen (ie equivalent to the concentration being N times more concentrated). As a first approximation this would change the pKa by log(N). (does this make sense to you?)

It's possible to draw up more complex models - but they usually fall apart outside a narrow range of compounds - because of all the other things that can alter acidity.83.100.250.79 (talk) 23:05, 28 August 2009 (UTC)

Wow, thanks for addressing ethylene glycol. I guess I don't have to make a new question after all! Is the inductive effect also at play in ethylene glycol? (Or is the single oxygen too far away?) I'm thinking something analogous to what happens in trichloroacetic acid. Would making the OH groups further apart basically weaken this "H+ delocalisation" significantly? If I had OH groups substituted on opposite ends of n-octane, for instance, would approximately see a pKa decrease of log 2 compared to n-octanol? John Riemann Soong (talk) 23:15, 28 August 2009 (UTC)

Also, by "hyperconjugative stabilisation" I was referring to the possibility that the alkyl group on ethanol for instance, helps delocalise some of the negative charge of the EtO- anion. Theoretically the difference in pKa between water and ethanol should be 0.30, right? But we observe a pKa difference of 0.14. The alkyl group seems to mitigate half of the lost acidity. John Riemann Soong (talk) 23:18, 28 August 2009 (UTC)

And does a tert alkyl group actually destabilise the conjugate base because the tert-carbon is likely to have more partial negative charge than say, a methylene carbon? What would explain say, isopropyl alcohol's increased acidity compared to n-propanol? Interestingly, methanol has a pKa of 15.5 -- it's more acidic than water! So the hyperconjugative stabilisation seems to have some observable effects (pKa stabilisation of 0.56? theoretically methanol's pKa should be 16.06 compared to water if the alkyl group didn't do anything...) John Riemann Soong (talk) 23:28, 28 August 2009 (UTC)

The inductive effect always works a bit, even 4 atoms away - but it gets weaker an weaker.. So 3chloro propanol will be ever so slightly more acidic than plain propanol. etc. Same goes for OH groups..

The log 2 effect I think would appply to any di-alcohol, that's just the effect of having more OH groups (don't quote me on that because I haven't got a reference - but I'm sure the reality isn't far off)

The H+ delocalisation should work best when the compound can make 5 and 6 membered rings (eg 1,2 and 1,3 diols) - (5 and 6 membered rings are the best - anything over get's a bit 'wobbly')

The difference in pKa between water and alcohol - the 0.3 figure is a very rough estimate (ie the value should be the same order of magnitude) - but maybe yes.

t-butanol is less acidic than s-propanol - this could be the electronic effect of the alkyl group - BUT - the larger the size of the alkyl group the more sterically hindered the O- is - which affects solvation - in other words in t-butanol the O- anion of the base is more difficult to solvate - I would expect this to have quite a significant effect in this case (the relative electron withdrawing abilities of the different plain alkyl groups being about the same.) In the absence of the solvation effect t-butanol might be expected to be as acidic as ethanol - because the larger molecule can very weakly stabilise the anion very slightly, and the other factors (excluding solvation) are nearly the same.

I think the difficult of solvation effect must be greater than the stabilisation due to hyperconjugation in t-butanol - as you mentioned above - measuring gas phase acidities would cut out the solvation effect - I don't know much about gas phase methods - if you want to know I suggest a separate question for it.

Yes methanol is a good example of hyperconjugation .

There's actually one book that covers all this (and super acids) very well - it's called "Physical and mechanistic organic chemistry" by R.A.Y Jones . Don't know if it's still in print - but you can get it from amazoncom from $1.40 (used)! (academic books are always expensive - typically about £30 for this new = ~50US $.) It should be library gettable - it's quite a common text for higher level chemistry. It's the size of a paperback novel, It may or may not be too complex - I haven't got a copy so this is from memory. But it definately covers all these topics.83.100.250.79 (talk) 00:14, 29 August 2009 (UTC)

I've given a link [17] - it seems to be out of print which may explain why some people are asking $150 for one on amazon. 83.100.250.79 (talk) 00:18, 29 August 2009 (UTC)

There's a link here [ http://books.google.co.uk/books?id=z3jXKOYuqQAC&pg=PA245&lpg=PA245&dq=methanol+acidity&source=bl&ots=dKaix0e3Or&sig=6jNkscLbVbfbwPrr1jPbfMXI6VU&hl=en&ei=Q3qYSs_ICpPajQet1IW3BQ&sa=X&oi=book_result&ct=result&resnum=8#v=onepage&q=methanol%20acidity&f=false] for the gas phase acidities of alcohols - page 245. It doesn't use the term hyperconjugation - but the data can be explained in terms of hyperconjugation quite well. It also covers solvation effects on page 246. It should go some way to answering most of your alchohol questions.83.100.250.79 (talk) 00:50, 29 August 2009 (UTC)

August 29

Alpha particle scattering experiment

If we perform alpha particle scattering experiment what will happen if electrons come across alpha particles? —Preceding unsigned comment added by Tipusultan11 (talk • contribs) 00:36, 29 August 2009 (UTC)

Electrons are not alive, so they cannot "come across" anything. They can be scattered elastically, though. Since the rest mass of an alpha-particle is much larger than that of an electron, the momentum of an alpha-particle in laboratory frame does not change significantly in that process. I assume you are talking about Rutherford experiment (a.k.a. Geiger–Marsden experiment), and you have read the article. --Dr Dima (talk) 01:26, 29 August 2009 (UTC)

An alpha particle is just a positively charged helium ion, He²⁺. So an alpha particle attracts electrons, and can bind with one electron to form an He¹⁺ ion, or bind with two of them to form a neutral He atom. Red Act (talk) 01:32, 29 August 2009 (UTC)

I think the alpha particles are moving too fast in this kind of experiment to stand much chance of capturing electrons. It is not impossible, though. --Tango (talk) 17:31, 29 August 2009 (UTC)

Unless the He++ e- pair can transfer energy to something the resultant He+ will be of such high energy that it would break apart again - the common method of losing energy would be to emit raditation, thus:

He2+ + e- >>> He+ + hv

83.100.250.79 (talk) 18:51, 29 August 2009 (UTC)

It is not easy to calculate rates of various He²⁺ + X <==> He⁺ + Y⁺ processes (photoionization and photorecombination, electron impact ionization and three-body recombination, charge transfer, etc.) even in a dilute gas or plasma; in a solid foil it is almost hopeless. However, Rutherford and his students used a foil so thin that electromagnetic interaction of an alpha-particle with electrons in the foil did not appreciably change the alpha-particle momentum, no matter what the end states were of that interaction. --Dr Dima (talk) 22:39, 29 August 2009 (UTC)

Parallax method

What is Parallax method? Please explain its use. —Preceding unsigned comment added by Tipusultan11 (talk • contribs) 00:46, 29 August 2009 (UTC)

The Parallax method is the use of two different vantage points to calculate the distance to an object. For example, if you stick a finger in front of you and open your eyes alternately, your finger moves with respect to the more distant objects in the background. It can be used to measure the distance to faraway objects, but the Parallax article does a very good job of explaining it (with diagrams), so I won't repeat that here. Awickert (talk) 00:55, 29 August 2009 (UTC)

I once saw a cow move its head from side to side while looking at me across a fence, as if it was using the parallax method to see how far I was away. I have done this myself in exactly the same way. Poor genius cow - turned into beefburgers. 89.243.198.115 (talk) 19:00, 29 August 2009 (UTC)

Uncertainty principle-another question

Uncertainty principle#Wave mechanics explains uncertainty principle of position and momentum of a particle.

It says: "If the wave (note by the poster: the wavefunction of the particle) extends over a region of size L and the wavelength is approximately λ, the number of cycles in the region is approximately L / λ. The inverse of the wavelength can be changed by about 1 / L without changing the number of cycles in the region by a full unit, and this is approximately the uncertainty in the inverse of the wavelength"

I think this is about one particle, but the above process includes changing the inverse of the wavelength without changing the number of cycles in the region by a full unit. If we are to measure only one particle, there seem to be no way of knowing the number of cycles in the region, on the other hand, if we are to measure a bunch of particles, capturing the shape of the wave seems possible, and therefore the wavelength and position. How should I understand this? Like sushi (talk) 08:35, 29 August 2009 (UTC)

You do need to repeat your measurement on many "identically prepared systems" in order to see evidence of the uncertainty principle, and you can by such repeated experiments build up a picture of the whole wavefunction. But knowing the whole wavefunction doesn't tell you the position and momentum because that information simply isn't there. Actual experiments aside, position and momentum can't be mathematically encoded in the wave function to better precision than what's given by the uncertainty principle. That's what the argument you quoted is meant to illustrate, I think.

Think in terms of systems, not particles. There's almost nothing that distinguishes the "fundamental" particles from any other system in quantum mechanics. The uncertainty principle applies to quantum systems regardless of the fundamental particles in them. I don't mean that it applies to the system indirectly by way of its constituent particles, I mean that it applies directly to the system as a whole. It's systems that are described by wavefunctions, not particles. Unless your system happens to consist of exactly one particle, the wavefunction of the system is not made up of wavefunctions of constituent particles. -- BenRG (talk) 13:17, 29 August 2009 (UTC)

You seem to be under the impression that the uncertainty comes from some difficulty in measuring the shape of the wavefunction. That's not the case. The uncertainty is an intrinsic property of the wavefunction even if we have a full knowlege of its shape. Dauto (talk) 13:23, 29 August 2009 (UTC)

Thank you for both. If we can build up the picture of the whole wavefunction, can we not tell the wavelength by measuring the distance between the peaks?

Like sushi (talk) 03:51, 30 August 2009 (UTC)

Only if the wavefunction is exactly periodic like a sine function in which case it would have infinite extension and you would pay your exact knowlege of the wavelength (and momentum) with complete uncertainty about the position. The particle could be anywhere along that sine wave. Simply cutting the sine function after some finite extension and setting the wavefunction to zero outside of that "box" doesn't solve the problem bacause you introduce other wavelegths into the fourier analysis of that modified wavefunction other than the original wavelength.In other words, you pay for your partial determination of the position of the particle with uncertainty about the wavelength (and momentum). That unavoidable feature of the fourier analysis is very much the spirit behind the uncertainty principle. Dauto (talk) 06:50, 30 August 2009 (UTC)

Sorry to bring up once more the constituent particles, but doesn't determining the shape of the wavefunction include determining the positions of each particles? I mean as parts of the picture like dots. ! I might have got it. The wavelength of the system can be known with the positions of particles, but not with the distribution of the positions of all particles in the system? That is what Mr. BenRG (I guess he is a man) means by "it applies directly to the system as a whole"?

(But where has "changing the inverse of the wavelength without changing the number of cycles in the region by a full unit" gone? I thought change in this limitation in the wavelength and the size of the wavefront at the distance have something to do with it.)

Mmmm... I don't know, but wavefunctions of particles are changes of some fields, right? Then as the field has no end, the wavefunction must have an infinite possibility of positions of particles, or have infinite areas of value zero? How does infinite areas of value zero influence the accuracy of determining wavelength?

Like sushi (talk) 08:01, 30 August 2009 (UTC)

I'm afraid I can't make head or tail of most of what you just wrote. I think you need to get all these wrong ideas out of your head and start from scratch. The wave function is not a wave in space. Particles don't have wave functions. Particles don't appear as dots or bumps in wave functions. A wave function and a quantum field are different things. You still seem to think that there's something special about particles and that you'll get a better understanding of quantum physics by starting with the particles. That's not true either. Forget about particles. In fact, forget about quantum mechanics for the time being. The uncertainty principle is a property of any kind of wave, not just a quantum wave function. To the extent that the frequency of a wave is well defined, the "position" (effectively the region where it's nonzero) is spread out, and vice versa. -- BenRG (talk) 10:31, 30 August 2009 (UTC)

I thought I might have got something, but that (you say) is wrong.

(Skip this if you are not interested in what I thought)I thought wavefunction spread in space (which has no end) and when observed, had one position like a dot (and can be seen as a particle). I thought observing a wavefunction might leave different dots and they could form a shape of the wavefunction.

So, what is Uncertainty principle?

It is a property of any kind of wave. And it is that "to the extent that the frequency of a wave is well defined, the "position" (effectively the region where it's nonzero) is spread out, and vice versa".

I don't know where to ask you to start, but one thing I feel not clear is what "position" is.

Like sushi (talk) 12:03, 30 August 2009 (UTC)

Okay, that paragraph (the one you believed) is pretty accurate, except that the wave function isn't defined in 3D space, it's defined in a "configuration space" where the points are different configurations of the system. When you do a measurement to find the state of the system you find some configuration where the wavefunction was nonzero. After the measurement you can treat the wavefunction as having "collapsed" such that it's zero everywhere except for a narrow peak around the configuration you actually got. This doesn't mean the system has collapsed to a point in 3D space, it means that the parts are fairly definitely in a particular arrangement, which might be spread out over a large area in 3D space. The dimensions of the configuration space are degrees of freedom (mechanics), arbitrary parameters that describe the arrangement of the system. You could call this the "position of the system", but it's not a point in 3D space; the system might occupy a large region of space. A point particle of the sort they talk about in undergraduate quantum mechanics (which is not quite the same as a particle-physics particle) can be described by three numbers giving a spatial position, so in a single-particle system you can identify the configuration space with 3D space. With two particles, though, the configuration space has six dimensions. With one rigid body it has six dimensions (three for position and three for angular orientation). With two rigid bodies it has twelve dimensions, and so on.

The classical time derivatives of the position and the angular orientation (momentum and angular momentum respectively) are not independent coordinates in the configuration space. Instead, they are the derivatives of the wave function with respect to the position or angular orientation. That means you can't have an object in a definite position or definite orientation, because then the derivatives don't exist and the momenta aren't well defined. There has to be some spread in the position. But the narrower the spread, the more the derivative varies, and so the less precisely the momentum or angular momentum is defined.

You can't work out the whole shape of the wavefunction by consecutive measurements on the same system because of the collapse, but you can work it out with independent measurements on a bunch of "identically prepared systems" (meaning, effectively, systems that all have the same wave function). However, even knowing the whole wave function you can't work out both the precise configuration and the precise time derivative of the configuration because they aren't both present in the wave function. Also, if you measure the "position of the system" then the wave function collapses to a narrow peak, meaning the momentum becomes very uncertain. If you measure the momentum then the position becomes very uncertain. -- BenRG (talk) 13:54, 30 August 2009 (UTC)

Well, it's true that in general a wave function can't be thought of as a function on 3D space, but for the simplest case of a single particle ignoring spin the only degrees of freedom are its position, so you can view the wave function as a function on space (or as a function on the momentum space).

To the OP: Uncertainty is as you said a property of any wave function. It follows mathematically from the way we define the momentum operator relative to the position operator. The Uncertainty principle#Derivations part goes into how you might prove that. Rckrone (talk) 19:17, 30 August 2009 (UTC)

I haven't thought that wavefunctions can have so many dimensions. So it has dimensions for positions plus dimensions for angular orientaions. What are these angular orientations? Do they have something to do with uncertainty?

I don't know what you mean by "parts" and "arrangement" in "...the parts are fairly definitely in a particular arrangement, which might be spread out over a large area in 3D space. The dimensions of the configuration space are degrees of freedom (mechanics), arbitrary parameters that describe the arrangement of the system."

And why collapse into "a narrow peak around the configuration" may not result in fairly accurate position and the wavefunction "might be spread out over a large area in 3D space"?

"you can't have an object in a definite position or definite orientation, because then the derivatives don't exist and the momenta aren't well defined". Derevatives are like, for example, tangent lines for a parabola, right? Then derivatives in the case of a definite position or definite orientation are not 0?

Like sushi (talk) 03:15, 31 August 2009 (UTC)

'Hottest' chilli pepper

We've been given a plant that is claimed to be the worlds hottest chilli pepper (not 100% sure though) and were wondering how to know when it's ripe?... They're green at the moment and look big enough but we're not sure whether that's the right colour and we don't know what variety it is... If anyone knows anything about the matter any help would be appreciated... Thanks —Preceding unsigned comment added by 83.33.75.101 (talk) 12:55, 29 August 2009 (UTC)

The "worlds hottest pepper" plants sold in department stores will turn orange or bright yellow when fully ripe. You can use them when still green as they're already very hot. --Digrpat (talk) 17:09, 29 August 2009 (UTC)

Bhut jolokia? Axl ¤ [Talk] 00:02, 1 September 2009 (UTC)

Hottest pepper

The above question inspired a desire in me to know what the spiciest pepper and spiciest foods are. Ks0stm ^(T•C) 17:18, 29 August 2009 (UTC)

See Scoville#List_of_Scoville_ratings. --Tango (talk) 17:32, 29 August 2009 (UTC)

Other flavours comparied with spiciness are substances like piperine from ground pepper and whatever it is that gives wasabi its flavour. I don't know what the most peppery/wasabi-y foods are, mind. Vimescarrot (talk) 17:51, 29 August 2009 (UTC)

Scoville scale generally measures only Capsaicin heat, and not piperidine (pepper corn) or Isothiocyanate (horseradish, mustard, and wasabi) are not generally measured on that scale. The methodology used to develop the Scoville scale could could be used seperately for piperidines and isothiocyanates, but it generally isn't necessary to develop a "mustard" scale or a "peppercorn" scale, since the botanical variation in these types of foods aren't as great as in the Chili peppers. Horseradish and peppercorn are just not known for having dozens of varieties, each with unique culinary uses, which would necessitate a "scale" for measuring them on. When you use peppercorn or Wasabi in a dish, you pretty much know exactly what you are getting. Chili peppers are a MUCH different sort of thing, and it is important to recognize the difference between a Poblano pepper, a Jalapeno pepper, and a Habenero pepper, lest you screw up a dish horibly... --Jayron32 19:27, 29 August 2009 (UTC)

Going off on a slight tangent here — does it strike anyone else as strange that most languages have no exact translation for hot as in spicy? In Italian, for example, the closest word is piccante, but that can also apply to spices that are definitely not hot (such as garlic).

I really don't think this is a culturally constructed category -- hot spices (the ones mentioned above, plus ginger) genuinely produce a sensation of heat, as in temperature, and non-hot ones don't. So why isn't there a word? --Trovatore (talk) 19:35, 29 August 2009 (UTC)

It's also intriguing that English doesn't have two separate words for knowledge: a word for knowledge that resulting from recognition and knowledge resulting from understanding...it's a trait that the German language has, yet English is lacking. Ks0stm ^(T•C) 19:43, 29 August 2009 (UTC)

Well, that's a little different — English is unusual in conflating kennen and wissen, conoscere and sapere. That can be seen as a quirk of English. In the hot case, though, English has a word for a natural, biologically based category, where no other language I'm aware of has such a word. So that's a "quirk" of all other languages, which is something that needs explanation. --Trovatore (talk) 19:47, 29 August 2009 (UTC)

I suppose that's like Irish where you're supposed to say if you know something from experience, from reading it in a book, or because somebody told you. But as to spices, I don't experience hot spices as hot in the sense of boiling water or burning as in the sense of a burn. So I see no reason at all why any other language should use the corresponding word for hot. Actually I think the Italian grouping is better though still not very good. In short I think it is a cultural construct. Dmcq (talk) 21:09, 29 August 2009 (UTC)

Well, I think you're just wrong on the facts here. The sensation of hot spices is not hot as in a burn, no, but it is definitely hot as in temperature. This is probably measurable — hook up some sort of sensor to the thermoreceptors in the tongue and the bucal epithelium, and you'll see a response. --Trovatore (talk) 00:50, 30 August 2009 (UTC)

Capsaicin may be of relevance hear, particularly Capsaicin#Mechanism of action. Capsaican does indeed activate one of the known temperature sensors. However I don't know whether you can say the stimulation is exact, as there are other sensors which are not activated including probably some we don't know about which are likely essential for our perception of normal temperature Nil Einne (talk) 08:51, 30 August 2009 (UTC)

One significant factor would be that spices (mild or hot) found their way to Europe rather late and people just "tweaked" exsting words to fit the novel sensation. I have no knowledge of languages on the Indian subcontinent or in SE-Asia, but I would not be surprised if "proper" terms existed for "hot" and "spicey" ingredients. --Cookatoo.ergo.ZooM (talk) 21:53, 29 August 2009 (UTC)

I think so. "Bedus" means "hot" in Javanese. I don't know how one would say spicy, but I'm fairly certain "bedus" isn't it. AlmostReadytoFly (talk) 22:31, 29 August 2009 (UTC)

In Malay wiktionary:pedas means spicy hot and wiktionary:panas means temperature hot (see also [18]). I don't think the word would be used for something like garlic, but perhaps that's partly because the effect is weak. I'm not sure you'd say it in relation to ginger either for that matter. ([19] says pedas means has a Chilli feeling/taste but I can't imagine any other word you'd use for something like Wasabi and the Malay Wikipedia article Ms:Wasabi does indeed use pedas.) I've always been intrigued by the lack of such a distinction in English and wondered how common it was and have even thought of asking it on the RD (WP:RD/L obviously) but never got around to it. As with Cookatoo, I've always expected it was because of the late introduction of hot spicy food into most English speaking cultures. This issue is always going to be complicated by the fact that most cultures lack a history of all the various foods that can be called 'hot' and for some cultures if the sensation is mild and/or overridden by other sensations and tastes that it may not be enough that it's likely to be called 'hot'. Actually personally I think a distinction between wasabi hot and chilli+pepper (or capsacain+piperine) hot is not unreasonable as their sensation is IMHO clearly different and from what I can tell from a brief glance at [20] and [21] (both need subscription) the receptors involved are different too. Interesting enough, it looks like garlic does in fact activate both the wasabi and capsacian receptors (second link) so perhaps it should be called 'hot' and the Italian usage is better then it seems. The entry at wiktionary:hot provides some clue on other languages but it's very incomplete and also could be wrong in some instances. Interesting enough Finnish appears to have a distinction but Hindi and Marathi appear to lack it. The lack of a distinction can of course be problematic e.g. when someone says their food is hot in some circumstances it's unclear what they mean. Nil Einne (talk) 08:26, 30 August 2009 (UTC)

In English, there is "to know", "to understand", and "to grok", in order of increasing understanding. We also have an article on Knowledge by acquaintance which goes over some of the kennen/wissen duality. As for the description of taste, Hebrew has distinct words for hot: "kham" for temperature and "khariff" for taste. It is the same in Russian, too: "goryachiy" is for temperature and "ostryi" or "perchennyi" are for taste. --Dr Dima (talk) 23:00, 29 August 2009 (UTC)

I'm not sure I think kennen/wissen is really about degree of understanding. You kennst a person; you weisst (or is it wisst? I've forgotten) a fact. I suspect that to wissen a person would have a Biblical meaning, the way Adam knew Eve. But I'm out of my depth here -- just speculating, really. I do think I've heard that Adam seppe Eve in Italian. --Trovatore (talk) 01:28, 30 August 2009 (UTC)

What's it mean "to grok"? I've never heard that word before. BTW, in Russian, "ostryy" literally means "sharp" (as of a knife, for instance), and "perchennyy" means "peppery" -- which would relate to spiciness on the Scoville scale. FWIW 98.234.126.251 (talk) 05:10, 30 August 2009 (UTC)

"Grok" is a word made up by Robert Heinlein and first used in the novel Stranger in a Strange Land in 1961. If you didn't grow up in the sixties doing magic 'shrooms and LSD, it's not at all surprising that it's unfamiliar. Its meaning is "to understand profoundly". - Nunh-huh 06:25, 30 August 2009 (UTC)

Incidentally — is it possible to damage one's tongue (whether you want to call it "burning" or otherwise) by eating overly spicy foods? Not a request for medical advice. Nyttend (talk) 13:41, 30 August 2009 (UTC)

I have two things to say here. Firstly, on the language issue noted above, Japanese uses 'karai' for 'hot' (as in spicy), but this can also mean 'salty' (even though there is also another more specific word for that). Secondly, I think garlic can be considered hot. Have you ever bitten into a piece of raw garlic (very common in Korean food)? I would say that is definitely hot as in the spicy sense of the word, so the Italian word definitely fits for me. --KageTora - (영호 (影虎)) (talk) 14:32, 30 August 2009 (UTC)

Ohm's law and Johnson–Nyquist_noise

I was just wondering how Ohm's law is valid given that resistance is related to the temperature of something. I mean it would be valid at any given instance but how would it work over time? Suppose you took something like a circuit with the light bulb. When the filament in the light bulb is cool its resistance is "x" ohms. However doesn't the resistance increase when you increase the temperature of the substance? When you completed the circuit and the light bulb lit up it's resistance would increase, which would make the current across the light bulb filament decrease. (EDIT:) Forgot to include that the current would then go down, causing the temperature to go down, and causing the resistance to go down, thus increasing the current and repeating the cycle. It seems like it would never reach a equilibrium. Is this fluctuation the Johnson–Nyquist_noise mentioned in the Ohm's law article? 66.133.196.152 (talk) 17:37, 29 August 2009 (UTC)

No, the filament will quickly reach an equilibrium point where the heat generated by ohmic resistance exactly matches the heat lost by radiation. Johnson-Nyquist noise, more commonly known as thermal noise does not represent any kind of oscillation by the applied current and is present even when the applied current is zero. It is, however, dependent on the resistance (as well as temperature) which is increasing with increased current. SpinningSpark 18:09, 29 August 2009 (UTC)

Lots of conductors have the resistance change when the temperature changes, or even when the current flow changes. Many conductors and semiconductors , diodes, transistors, vacuum tubes, mercury arc rectifiers, or arcs in general cannot be analyzed as simple Ohmic resistances. Edison (talk) 19:51, 29 August 2009 (UTC)

Exactly. In the case that the voltage-current relationship is not linear, the "resistance" is not constant, so generally it is said that the circuit is "non-ohmic" or that Ohm's law doesn't apply (at least, not with a constant R. Terms and definitions can be minced here). However, this is not really the cause for thermal noise; the theoretical basis for Johnson noise is usually attributable to the statistical, but non-deterministic, electron flow pathways at the atomic level. The mathematics of Brownian motion and Johnson noise discusses the necessary modeling from a pedagogical point of view. J. B. Johnson's original 1928 paper, Thermal Agitation of Electricity in Conductors, attributes the noise to thermodynamic equilibrium of the electrons and the atoms of the conductor material. Simple approximations can relate the thermal noise to the observed ohmic resistivity, but an in-depth analysis reveals that they have different causes and are separate effects. Nimur (talk) 00:50, 30 August 2009 (UTC)

Temperature dependent resistors, thermistors, sensistors etc do not obey Ohm's law. —Preceding unsigned comment added by 79.75.25.53 (talk) 00:57, 31 August 2009 (UTC)

Le Chatelier's principle

Hello. Why does the equilibrium shift in the reverse direction if the pressure increased by decreasing the volume for the following reaction: 6CO_2(g) + 6H₂O_(l) ↔ C6H12O6(s) + 6O2(g)? Thanks in advance. --Mayfare (talk) 18:20, 29 August 2009 (UTC)

Does it not follow the nitrogen hydrogen example in Le Chatelier's principle#Pressure? But I don't know in this case which is the greater volume of the two sides of the reaction. --Tagishsimon (talk) 18:27, 29 August 2009 (UTC)

I imagine H20 constributes to the vapour press, but only slightly. At very high pressures the CO2 will liquify first.

Mayfare, can you explain where you got the idea that the supposition you provided is actually true? Or at least give some other indication of the conditions?83.100.250.79 (talk) 18:47, 29 August 2009 (UTC)

According to the basic premises of LeChatelier's principle, this equilibrium should not be pressure dependent to a first approximation. The hypothetical solution to changes in pressure should be no change since there are the same number of moles of gas on both sides of the reaction (6 vs. 6) so NEITHER direction actually reduces the stress, so the reaction should favor neither direction in the case of increasing pressure. In actual practice, there are LOTS of factors that LeChatelier's Principle does not take into account, so there is a very good chance that changing pressure WILL cause an equilibrium shift, slightly, but that is largely due to a gap between the rather simplistic model that LeChatelier's Principle is based on, and the actual reality of the effects off pressure changes on all sorts of processes. --Jayron32 19:19, 29 August 2009 (UTC)

83.100.250.79, my tutor taught me this. I myself am as confused as you are. --Mayfare (talk) 02:28, 30 August 2009 (UTC)

The important thing is you understand the principle, which it seems you do. As for your tutor - do they make mistakes often - possibly the forgetful type? I hope they're not just incompetent :)

83.100.250.79 (talk) 12:25, 30 August 2009 (UTC)

This reaction is extremely unlikely to go in the forward direction unless there are some serious help involved, such as imput of energy and enzymes. In nature this would involve many other reactions that would have different rates and equilibria and competing side products. Graeme Bartlett (talk) 22:44, 30 August 2009 (UTC)

The other issue is that at a given air pressure the oxygen level partial pressure is constant, whereas the carbon dioxide partial pressure can vary a lot in the environment. So in a green house for example an enhanced carbon dioxide level can help plants grow faster. Graeme Bartlett (talk) 22:49, 30 August 2009 (UTC)

Bathroom scales inaccurate

The big disadvantage with the bathroom scales I've used are that the recorded weight varies by a large amount according to whether you lean slightly forward or slightly back. This is no good for precision weighing while dieting. Perhaps this problem has been due to always buying the cheapest bathroom scales available. Are there any types or brands of bathroom scales that do not have this problem please? Or do even the most expensive scales have this problem? 89.243.198.115 (talk) 18:54, 29 August 2009 (UTC)

If the reading is varying when you lean, that's probably because you're tilting the platform so that part of it is resting on the frame of the scale and taking some weight off the mechanism. If you want an accurate measurement you should look for the highest reading, which is probably going to be when your weight is centered. I don't have any good advice for finding a more accurate brand of scale though. Rckrone (talk) 19:08, 29 August 2009 (UTC)

This problem is easily solved with the 4-point scales. Often, they look like a glass plate on 4 rather chunky feet. Each foot is actually a miniature scale. Shifting weight off one foot will increase weight on another foot and the measured overall weight will not change. -- kainaw™ 19:12, 29 August 2009 (UTC)

Do you have any brand names for 4-point scales please? My Google search found nothing. 89.243.198.115 (talk) 19:24, 29 August 2009 (UTC)

Try this. Those are all glass, but you can see the manufacturers and locate more models. -- kainaw™ 19:33, 29 August 2009 (UTC)

The important feature is 4 load-cell technology (see this). The reason for inaccuracies (when leaning etc.) is that the weight distribution "web" for either a spring or a single load-cell scale is notoriously inaccurate particularly after exposure to a steamy bathroom for a few months (primarily due to friction at the pivot points). A four load-cell system truly applies the correct weight at each corner and sums those weights. hydnjo (talk) 20:26, 29 August 2009 (UTC)

Wikipedia as Education

Could Wikipedia and Wikiversity educate a child, without access to any other learning tools, to a university level? TheFutureAwaits (talk) 19:37, 29 August 2009 (UTC)

In the United States, you only need to score well on either the SAT or ACT to be considered "University Level". Those have a little mathematics, which is covered in both Wikipedia and Wikiversity. Mostly, they are reading comprehension problems, which is a skill that anyone can learn by reading Wikipedia and attempting to recall what was read. -- kainaw™ 19:41, 29 August 2009 (UTC)

If I had sought to educate myself with these tools, I would have studied what delighted me and avoided what I disliked. I speak mostly of Wikipedia and not Wikiversity. There would have been gaps, as is common among autodidacts. Who would enforce general distribution requirements in the curriculum? The student would have to be a glutton for punishment to learn science and math if only interested in art and music, or contrariwise. And reading an article about calculus, differential equations, matrix algebra, electrical engineering, physics or chemistry would not leave the pupil capable of solving problems in those fields. Reading the best articles that could be written about art or music would not produce a student whose performance level was high. Some subjects, like chorus, band or orchestra require a group. Group study can be very helpful in diverse fields such as math, the sciences, philosophy or law. Most self-taught scholars are weak on doing difficult homework in technical subjects. How would an autodidact do writing and learn from thoughtful criticism? Edison (talk) 19:49, 29 August 2009 (UTC)

The SAT is a test for admission to university. "University level" usually refers to things that are taught at university. --Tango (talk) 20:02, 29 August 2009 (UTC)

Starting from what level? You can't learn to read from Wikipedia. Once you've reached a reasonable level with the key skills you could learn quite a lot from Wikipedia, but generally it would just be learning facts. Wikipedia doesn't teach you how to do things. Wikiversity does, but it isn't anywhere near developed enough to be used in isolation yet. --Tango (talk) 20:02, 29 August 2009 (UTC)

Wikipedia and Wikiversity could probably be used as the only study materials as part of homeschooling. The parent or tutor would need some separate material to guide the student as to what to study in order to pass . Using Wikipedia (even the simple enghish version) as the only material to teach kindergarden and first grade would be impractical but not impossible. If you mean "to the level of a university graduate" I think you will need to allow for theuse of th erest of the internet, not just Wikipedia. A well-rounded student must also have some social interaction, of course, and sports and music are hard to do by yourself. -Arch dude (talk) 20:36, 29 August 2009 (UTC)

This case-study points out some of the flaws and limitations of web-based education. The case in question was using a web-based distance-education software (not Wikipedia), but the lack of interaction and feedback were found to be a source of frustration and impaired learning. Information-seeking strategies of novices using a full-text electronic encyclopedia, published in 1989, analyzes the case of encyclopedia-based learning. It is found that novice users have a very different strategy for learning than experienced learners. "The results demonstrated that, in general, young novice users could successfully use a full-text, electronic encyclopedia with minimal introductory training. Subjects in third or fourth grade were less successful and took more time than subjects in the sixth grade. ... Many, especially the younger searchers, used sentences or phrases as queries, reflecting an ill-defined mental model of the search-system, a kind of hybrid between a print-encyclopedia and an interactive computer program." Again, though, this assumes basic literacy as a prerequisite. Further, there is a big difference between being able to use an encyclopedia/ information database, and being a well-rounded student equipped for further academic study or career productivity. Nimur (talk) 01:04, 30 August 2009 (UTC)

You say that "there is a big difference between being able to use an encyclopedia/ information database, and being a well-rounded student." I would very much so argue that life with Wikipedia has allowed me to give myself a much more well-rounded body of knowledge than I would have gotten through traditional schooling. Mac Davis (talk) 04:30, 30 August 2009 (UTC)

That is a false dicotomy. You don't have to choose between Wikipedia and traditional schooling. I have made use of both and therefore have the problem solving skills, social skills, useful but boring skills and knowledge that come from school and the very broad body of knowledge that comes from spending far more time than is healthy on the Wikipedia reference desks. --Tango (talk) 16:00, 30 August 2009 (UTC)

I like Wikipedia just fine (and don't know Wikiversity well), but I don't really seem how they would replicate a "real" education. You need interactivity, you need assignments, you need more than lists of facts however well written. Sometimes, though it is miserable, you need drilling and route memorization. Sometimes you need someone to push you on your writing and on your performance. I don't really see how these sources can do it, any more than a giant Encyclopedia Brittannica would. Obviously such a thing could supplement an education periodically but the education is the method, not the specific tool. --98.217.14.211 (talk) 01:25, 30 August 2009 (UTC)

Education involves a lot more than a collection of facts organized for easy consumption. Wikipedia can never be more than such a collection of facts, and it and other print media can be a VERY IMPORTANT part of education, but it cannot and should not be the only tool. Lots of education, such as interpersonal feedback; which includes the ability to get questions answered AND the ability to have someone watch you learn and interpret the problems you are having and help correct those problems without you even realizing you had a problem that you needed to ask a question about. Also, the ability to practice a skill, to watch others with expertise perform a skill, to have someone watch you perform a skill wrong and provide correction; the ability to provide appropriate approximations which build your knowledge from the superficial to the deep learning, the ability to provide context to facts and to connect them to each other in ways that have meaning. All of that needs another person to do for you. Wikipedia certainly contains all of the raw facts covered in any typical university program; but it does not have any ability to provide you with any of the skills and activities that are the real core of any education. --Jayron32 01:47, 30 August 2009 (UTC)

St Augustine, in his "Confessions" from the 4th century or so, emphasized the importance to his early education of having the teacher beat the student when he preferred playing outside to learning things such as Greek and Latin grammar, which are not "fun." It is hard to get the encyclopedia to wield the cane in the form of grading or report cards or evaluations of any form, or directing the attention to things which "should" be learned rather than things which are intrinsically rewarding. Edison (talk) 03:28, 30 August 2009 (UTC)

When those argue that it is important to be beaten when you prefer to learn about some subjects and not other ones, they are arguing against freedom over your own education. They argue that each student needs a fine structure—all to often every student gets almost exactly the same structure and we definitely do not "take them seriously." Some children may need to be schooled, and some need to be unschooled. There is no specific body of knowledge that is, or should be, required of a child just as there is no one right way to live. Mac Davis (talk) 04:26, 30 August 2009 (UTC)

The flaw in your argument (actually, a great gaping chasm in your argument) is that an undeveloped brain without the necessary knowledge is ill-placed to decide which things are important and which are not - an untutored mind - given complete freedom to pick and choose what is learned - doesn't even know of all of the wonderful things they might want to learn about. Children require the guidance of someone who has already learned the material to guide them as to what needs to be learned (even if it's a pain to do that). A child is unlikely to voluntarily subject her/himself to the rigors of memorizing the multiplication tables - but without that, you're unable to perform any kind of arithmetic - and without that, most of science and mathematics would be shut out from their attention. Even a child who might otherwise grow into an adult with a passion for math would be exceedingly unlikely to simply stumble on that without guidance - and indeed some pressure to learn things that he/she seems to dislike. No matter how much the child resists - the multiplication tables have to be learned as a 'gateway' to giving that child the option to learn physics/chemistry/biology/etc in the future. There are also things that people have to learn to do despite hating to do it. People NEED to be able to read. Learning to read is not an option - it's a requirement. Your conclusions sound great - but are ludicrously over-simplistic in practice. SteveBaker (talk) 14:29, 30 August 2009 (UTC)

I agree with your main point, but I disagree with your example - I recently graduated with a 1st class MMath having never learned multiplication tables. I still don't know them. I do, however, know how to multiply. That is far more useful. I have no idea what 6x8 is, but I know that I can work it out very quickly because I know various landmarks (for example, I know my squares) and I know the rules of arithmetic, so I can do 6x8=6x(2+6)=6x2+6x6=12+36=48. I can do that in a fraction of a second, it doesn't really take any longer than it probably takes for you to recall that fact and use it (using it is generally so much slower than calculating/remembering it that is the only relevant part for the total time taken). My example (which applies to me, it won't apply to everyone - that is a key point in itself) is writing. I used to hate writing. I wasn't very good at it and I didn't enjoy it (the two are undoubtedly related, but I don't know what direction the causal link is in). I was, however, forced to do it. I can now confidently express myself in writing (although my handwriting is still terrible - just about legible, though!), which is a skill I now realise is extremely important for pretty much any application of those skills I did enjoy (maths, say). Had I been allowed to choose what I wanted to learn I would now know lots of maths but not being able to do anything with it. --Tango (talk) 16:00, 30 August 2009 (UTC)

A certain third grader I once taught the multiplication tables to could have furnished the answer faster than your claimed "fraction of a second," by learning 1x1 through 12x12, then speeding the recitation until it was as fast as the numbers could be spoken, then learning them backwards and sideways (breaking up the use of one rote order). It was something the student wanted to do, and not something externally required. The student went on in later years to far surpass my math accomplishments. Edison (talk) 18:50, 31 August 2009 (UTC)

Being able to recite them all in order is a completely useless skill. What is useful is being able to get the right answer to a specific question. I don't claim that knowing your multiplication tables by rote is useless, but I think the time would be better spent learning how to multiply. Tell me, how good was this third grader at his 13 times table? --Tango (talk) 22:50, 31 August 2009 (UTC)

Tango, I'm not sure if you, not having learned the "times tables", really appreciate how use of them works, and Edison's description is I think unclear. Once you've thoroughly learned them at age 7 or whatever (by admittedly tedious recitation practice) you don't have to recite all the way through, say, "Once six is six, two sixes are twelve . . ." to get up to 7 x 6 = 42: instead, as soon as "7 x 6" is articulated or read, "42" flashes instantly into the mind. This was and still is the case not just for myself, a far-from-brilliant 50-odd-y-o Brit, but for almost everyone else of my generation educated in Britain that I've met for whom the subject has arisen. Moreover, although the default maximum was usually 12 x 12, it was not uncommon for the 13- and 14-times tables to be learned, and of course higher numbers can be readily factorised in the manner you describe. None of this works as a substitute for "knowing how to multiply", it's merely a (significantly) time-saving aid. 87.81.230.195 (talk) 21:41, 1 September 2009 (UTC)

Yes, as long as the only thing they needed to learn about was Family Guy. DJ Clayworth (talk) 20:14, 31 August 2009 (UTC)

Fruit beginning with U

Are there any fruits (of the culinary or botanical definition) whose names start with U in English, other than the Ugli fruit? --✶♏‭ݣ 20:49, 29 August 2009 (UTC)

Did you mean Ugni molinae? --Tagishsimon (talk) 20:51, 29 August 2009 (UTC)

No, I really did mean the ugli fruit but that's another good one. :) --✶♏‭ݣ 20:53, 29 August 2009 (UTC)

Ulster cherry, Uva di Troia, Usakhelauri, Ume --Tagishsimon (talk) 20:55, 29 August 2009 (UTC)

Well, the fruit of almost any flowering plant who's name begins with a 'U' would strictly meet your need. There are about a quarter million species of flowering plants - many of which are known by several common names - so there could easily be a million possible 'fruit names' - which probably means there are tens of thousands of candidates - vastly too many for us to list or even research! (For example: The Elm tree has the scientific name Ulmus - so it's fruit is an "Ulmus fruit".) But in terms of edible fruit - we'd have to refer you to List of culinary fruits - which lists only one - the Ugniberry - the Ugni molinae, which Tagishsimon already mentioned. I bet there are lots of others - but they'll be hard to track down. SteveBaker (talk) 14:15, 30 August 2009 (UTC)

Smell after rain

What does the smell after rain consist of? Mac Davis (talk) 21:31, 29 August 2009 (UTC)

See http://science.howstuffworks.com/question479.htm Who then was a gentleman? (talk) 22:05, 29 August 2009 (UTC)

They didn't list one of the bad smells, drowned worms decaying on the sidewalks. StuRat (talk) 13:00, 30 August 2009 (UTC)

I wonder (without proof) whether this is a Neural adaptation kind of phenomena - like the illusion where you stare at a brightly colored object for 30 seconds - then look at a blank, white sheet of paper and see the same image in complementary colors. Is it possible that we've become 'adapted' to the smells of our normal environment and have stopped registering them - then the rain washes those smells away, leaving behind 'pure' air - and (like the white paper) causing us to smell the complement of the smells that we've been ignoring. Just like an optical afterimage. Hence the air might seem sweet even though there is no substance in the air producing that smell. I have no idea whether that's really the reason - but I can see no reason why it shouldn't be true - and it fits with the smell seeming to dissipate very soon after it first appears. SteveBaker (talk) 13:59, 30 August 2009 (UTC)

An example: During a cross-country drive, I once stayed in a hotel in Sterling, Colorado (I had reserved the room from out-of-town because their rates were half of the surrounding towns). When I arrived, I found a huge cattle feed lot next door, and the whole town stank of manure. I asked the desk clerk if it always smells like this, and she said "Smells like what ?". StuRat (talk) 15:31, 31 August 2009 (UTC)

An interesting idea, and we certainly do stop noticing smells after a while and notice sudden changes in smells, however I don't see how a smell can have a complement. Eyes convert stimuli to a 3D space, the nose converts stimuli to a far larger space (about 400D according to Olfactory receptor). The concept of complements doesn't really work in that context. (Interesting fact of the day that I've just learned from that article: About 3% of the mammalian genome is devoted to genes for different olfactory receptors. That's an enormous amount!) --Tango (talk) 16:09, 30 August 2009 (UTC)

Well, if you agree that we stop noticing smells after a while - and yet we still notice when that smell goes away - isn't that the exact effect I'm speculating about here? There is an analogy with sound too - you can sit in an office all day with the fan running on your PC and not notice it. You'd swear there were no noises - but notice a more profound silence when you turn it off. If it works for sound and vision - it would be surprising if it didn't work for smell also. SteveBaker (talk) 17:47, 30 August 2009 (UTC)

With vision we see the absence of red as cyan, a colour in its own right. With smell and hearing we just perceive the absence of a given smell or sound as an absence (as you say, you hear a profound silence, you don't suddenly start hearing a different sound). --Tango (talk) 23:38, 30 August 2009 (UTC)

Severed vine

I have severed a vine that leads to a nice pumpkin I am growing in my garden. Oops. Is there any way to patch together the vine and save the pumpkin? Panasonic phones (talk) 22:01, 29 August 2009 (UTC)

Grafting might have some information on effective ways to do this. Rckrone (talk) 22:56, 29 August 2009 (UTC)

Proximate the severed ends, ensure they are tightly connected, and hope for the best. Time is of the essence. Also Google "milk fed pumpkin." Maybe additional nutrients would help. Edison (talk) 00:21, 30 August 2009 (UTC)

Done, and hoping. Thanks. Panasonic phones (talk) 00:05, 31 August 2009 (UTC)

Hurricanes in Southern California

weather.com is warning that Hurricane Jimena may hit Baja California in 3 or 4 days. Has a hurricane ever hit Southern California (note - I'm talking about Southern California, not Baja) while still at hurricane strength? Who then was a gentleman? (talk) 22:04, 29 August 2009 (UTC)

List of California hurricanes. -Atmoz (talk) 22:27, 29 August 2009 (UTC)

Great, thanks. Who then was a gentleman? (talk) 22:30, 29 August 2009 (UTC)

No known TC has officially struck California at hurricane strength, though the 1858 San Diego hurricane may have done so. –Juliancolton | ^Talk 19:29, 31 August 2009 (UTC)

Engineering - 'agricultural drain"

I am looking for details on how to make an 'agricultural drain'. What I understand so far: These 2 words do not seem to appear together as a phrase on wiki - only as 2 separate words in an article. It may have a more technical name and maybe that's why I can't find it.

It involves plastic sheeting with some sort of tube or foam which is buried underground where water normally collects and doesn't drain ie. next to a wall. This 'system' channels the water away to a desired area. I believe landscapers use it. I really want all the details possible... the depth, the slope, covering.

looking forward to seeing something about this on the website soon. —Preceding unsigned comment added by 41.208.48.176 (talk) 22:58, 29 August 2009 (UTC)

Try Tile drainage and Drainage system (agriculture) and the articles they link to. This has been an important, but expensive part of U.S. farming since the early 20th century. It makes muck into productive farmland. I am not sure that plastic sheeting is part of it. Landscaping also involves ditches, swales and berms. Try Googling those terms. Edison (talk) 00:15, 30 August 2009 (UTC)

It could be a varient of a French drain, which IS a common landscaping tool for keeping water off of the surface of an area, and it matches the OP's description almost exactly. French drains are very commonly installed next to structural walls to prevent water from resting next to a wall and damaging it. Our article describes their construction and use quite well, and also contains links to external sites. There's lots of good DIY websites describing how to construct and maintain a french drain... --Jayron32 01:38, 30 August 2009 (UTC)

Another option, for those with fields which are perpetually flooded, is to just plant crops which thrive in such an environment, such as rice. StuRat (talk) 12:55, 30 August 2009 (UTC)

Assuming there is infrastructure and demand to support such crops. They would also need to have a suitable climate to grow.

That can be impractical against a foundational wall; and may lead to other problems as planting directly next to a house can produce "root pry" problems. While in the open, carefully chosen plants may be a better solution than a French drain, against the foundation of ones house, a french drain is often a very efficient means of draining away water. --Jayron32 03:41, 31 August 2009 (UTC)

August 30

QUANTUM NUMBERS

What is quantum and quantum number? How electrons move around the nucleus? Explain.

Please do your own homework, as we will not do it for you. However, I will suggest the following articles: Bohr model, Bohr Theory and Balmer–Rydberg Equation, Quantum number, Principal quantum number, and Spectroscopic notation. ~ Amory (user • talk • contribs) 02:34, 30 August 2009 (UTC)

'Explain'? Readjust your attitude. And your grammar. Seriously, this is a volunteer reference desk. It's also part of an encyclopedia that you can search. Awickert (talk) 06:56, 31 August 2009 (UTC)

Blood pH

I was thinking about this and wondering: What substance in the blood keeps it slightly alkaline (7.35-7.45)? Why does the body maintain a slightly alkaline pH? bibliomaniac15 04:30, 30 August 2009 (UTC)

The major system used by most living things to is the bicarbonate buffering system. This, combined with the ability of the kidneys to filter extra H⁺ ions from the blood, and you have a pretty solidly maintained pH. – ClockworkSoul 04:43, 30 August 2009 (UTC)

As for the second question: the binding of O2 to hemoglobin is influenced by pH level, so the blood pH is maintained at a level that optimizes both the O2 binding in the lungs, and its unbinding in tissue capillaries. (Note that O2 binding decreases with lower pH, so an increase in blood CO2 concentration, which lowers pH ever so slightly, causes oxygen to unbind from hemoglobin exactly when and where it's needed most. Neat, huh?) 98.234.126.251 (talk) 04:51, 30 August 2009 (UTC)

That's a cool mechanism! DMacks (talk) 17:52, 30 August 2009 (UTC)

No single substance, though it all gets conceptualized as concentration of [H⁺]. Blood pH is maintained by a number of mechanisms, the most important of which are respiratory regulation (blowing off CO₂ by breathing more rapidly, or retaining it by breathing more slowly) and the bicarbonate-carbonic acid and dihydrogen phosphate-hydrogen phosphate-hydrogen blood buffer systems. Hemoglobin also has some effect as a pH buffer. See the Henderson-Hasselbalch equation, respiratory acidosis, respiratory alkalosis, metabolic acidosis, metabolic alkalosis articles for more detail. Your "why" question, taken locally, is that if the blood becomes too acidic, you die, and if the blood become too alkalotic, you die (because enyzmatic reactions necessary for life are pH-dependent). Taken more broadly, because that's how the system evolved: the blood's pH mimics that of the primeval sea in which it was evolved, in order to maintain the functioning of the enzymes that require that pH. Specifically, the transition to air-breathing led to relatively high CO₂ plasma tension and led to the development of the bicarbonate buffer system. See Some Aspects of the Evolution of Vertebrate Acid-Base Regulation. - Nunh-huh 05:06, 30 August 2009 (UTC)

Cell phone jamming

Here's a question related to the discussion about "White noise generator": Where I live, you always see drivers yakkin' (or textin', or even worse, readin' stuff on the internet) on their cell phones and not paying attention to the road ahead (that's how that big rig rear-ended my Mustang, the driver was talkin' on his cell phone and didn't see me stop at a crosswalk to let a lady with a little kid get across the road). So when I saw the discussion about "White noise generator", it got me thinking: is it possible to rig up some device that would prevent cell phones inside the car from transmitting / receiving any signals, while at the same time having minimal effect on cell phones outside the car? 98.234.126.251 (talk) 06:19, 30 August 2009 (UTC)

Theoretically. Cars can potentially act as Faraday cages. The pragmatic issue is that the cellphone frequency band prolly wouldn't be ideal. John Riemann Soong (talk) 06:49, 30 August 2009 (UTC)

And also you'd probably have to figure out a way to disable it when the car isn't running! 124.154.253.31 (talk) 08:00, 30 August 2009 (UTC)

I really doubt that this would be practically possible - and it would certainly be illegal. SteveBaker (talk) 13:47, 30 August 2009 (UTC)

Passive interference is legal, in the US anyway (which it sort of has to be—you can't blame an architect for happening to make a structure that doesn't conduct cell phone signals efficiently). Active interference (e.g. saturating a spectrum with noise) is prohibited by the FCC. --98.217.14.211 (talk) 14:00, 30 August 2009 (UTC)

Again, as I've pointed out numerous times, calling anything that is made of metal a "faraday cage" is a stretch at best. All you have to do is sit in your car and make a cell phone call to demonstrate, beyond reasonable doubt, that the car's metal frame is not a faraday cage - it's just a bunch of metal. It isn't attenuating the mobile telephone radio signal. It's probably not attenuating any radio signal (except maybe when you get towards the visible light frequencies - solid bodies are good at attenuating those!) A faraday cage needs to be specifically designed if it's going to be even slightly effective. It's going to have a specific frequency response. Even if it actually did suppress a particular frequency, the cell phone probably will be able to decode its signal anyway, because it uses a complicated digital spreading code. If you go around calling every piece of metal a "Faraday cage", you're devaluing the design and complexity of actual Faraday cages. Attenuation isn't a "qualitative thing" - it can be quantitatively analyzed, and I suspect that the attenuation of UHF radio through a car body is so close to zero that it's really creative application of terminology to call it a "shielding" effect. Nimur (talk) 14:45, 30 August 2009 (UTC)

I would point out as I did last time that GSM (and in fact the vast majority of 2G systems) doesn't use CDMA but TDMA. I appreciate that this discussion appears to relate to the US but your answer didn't clearly specify you were only referring to the US. Whether this makes a difference to the answer or not, I don't know but given a large percentage of the world uses GSM; with cdmaOne and 3G networks like CDMA2000, UMTS and others combined I strongly suspect remaining a minority I don't think it's wise to discuss this as if most mobile phones use CDMA. (My suspicions are supported by this [22] although it's hardly a neutral source.) Of course when we move to 4G we'd likely be using FDMA based on current proposals but it's a long way away before they take over given that 3G networks are still a distinct minority. Nil Einne (talk) 16:20, 30 August 2009 (UTC)

I think you are mistaken. GSM does use TDMA for packet scheduling and collision avoidance, but individual packets are coded with MSK, which is effectively a digital frequency spreading code. In fact, it's a more sophisticated frequency spreader than CDMA. I am not aware of any mobile telephony systems in operation, worldwide, that do not use a frequency spreading scheme for the digital encoding. We should make clear the difference between CDMA, the marketing-ese word for US-standard-radiotelephony, and CDMA, the technically-correct-description-for-code-spreading. The first paragraph of the CDMA article makes this distinction clear. Nimur (talk) 16:47, 30 August 2009 (UTC)

It may use spread spectrum. But that's irrelevant to me since the issue I raised was whether it used code division multiple access (which was the article you linked to, and also what you mentioned in a previous question). Although [23] appears to suggest to me (see below) that it's inaccurate to say GSM uses CDMA and our article doesn't seem to say it does either, if you say it does, then I accept that, since it's not something I understand very well. But if not, I feel my point still stands. And just to be clear, my point is that GSM doesn't use CDMA. I think the US marketing issue is somewhat irrelevant here since W-CDMA is commonly marketed as UMTS despite the fact it uses CDMA without dispute (actually it appears it's possible to use something other then W-CDMA, but all of them are CDMA and in any case, all use W-CDMA AFAIK) so I don't think there's any real confusion about what CDMA is, simply whether all spread spectrum techniques used by mobile phone networks are correctly called CDMA. P.S. I appreciate you did not specifically mention CDMA earlier on in this thread even if you did link to it, but I think it's inherently confusing to solely link to an article on CDMA (and not even as a sublink to the specifics) if (since I don't know) GSM doesn't use CDMA. It would be better to link to an article on spread spectrum (or multiple articles if you feel it's necessary, e.g. because our other articles don't explain it so well) since my understanding at the moment is that while CDMA is inherently a form of spread spectrum and is used by multiple mobile phone network systems, many 2G ones don't use it but use TDMA with spread spectrum techniques and possibly most 4G ones won't use it either, so solely linking to a CDMA article to explain spread spectrum techniques used by mobile networks is problematic. Again, if I'm wrong on this, apologies but I feel it's worth clearing up.

• Note that spread spectrum is not a modulation scheme, and should not be confused with other types of modulation. One can, for example, use spread-spectrum techniques to transmit a signal modulated by FSK or BPSK. Thanks to the coding basis, spread spectrum can also be used as another method for implementing multiple access + GSM, for instance, combines TDMA and FDMA. GSM defines the topological areas (cells) with different carrier frequencies, and sets time slots within each cell etc

Nil Einne (talk) 21:05, 30 August 2009 (UTC)

This is an issue that's worth further investigation; let's take this discussion offline since it's really peripheral to the OP's question anyway. I'll do some reading and follow up later in the week; I've been repeating this claim because I'm pretty sure it's correct; but if there's any doubt about it, then I should re-check my terminology and my facts before proceeding. Nimur (talk) 01:06, 31 August 2009 (UTC)

Nimur it is wrong to say: "MSK...is effectively a digital frequency spreading code. In fact, it's a more sophisticated frequency spreader than CDMA". Far from being a spreading code, MSK is a narrow band digital modulation method. Cuddlyable3 (talk) 16:00, 31 August 2009 (UTC)

This source, from our article: from Aerospace Corporation, has power spectral density plots for several variants of MSK and GMSK. I suppose it's up to the reader to decide whether 1 MHz consitutes "wide" or "narrow" bandwidth. I would put 1MHz channel width solidly in the realm of wide-band spectrum-spreading signal (considering the audio data is 3 kHz). Nimur (talk) 01:49, 1 September 2009 (UTC)

It would be technically straightforward to re-program the cell towers to refuse to connect to a moving cell phone. This requires no on-vehicle electronics other than the cell phone, and it allows you to pull over and stop and use your cell phone. It would even be possible to add specialized systems inside busses and trains to re-enable cell phones for their occupants. Harder, but not impossible, to permit the passengers but not the drivers in busses and trains. Very difficult or impossible to disable for car drivers but not for their passengers. The problem is that the voters will resist such a system. Similarly, it is technically straightforward to catch all speeders, but it's politically impossible. -Arch dude (talk) 14:59, 30 August 2009 (UTC)

I believe most of the signals you receive on the phone in the car now come through the windows of the car, other than that they should act as pretty good faraday cages as pointed out above. So I would think applying a film like they use on some trains to block out signals through the windows (see this article) would probably work about as well as it works in these trains (I don't know how well they work). TastyCakes (talk) 16:39, 30 August 2009 (UTC)

Excellent idea, TastyCakes -- a conductive film on the windows would work much better than an active jammer (which is expensive and can cause harmful interference) or reprogramming the cell towers (which can cause erroneous applications of the protocol). As they say, the simplest solution works best. (BTW, a wire mesh embedded in the windows could work just as well.) 98.234.126.251 (talk) 07:29, 31 August 2009 (UTC)

Programming cell towers to drop moving signals would not be a very good solution. The problem is drivers yakking on the phone. Passengers in all kinds of vehicles should not be limited as they are not operating the vehicle. Googlemeister (talk) 13:13, 31 August 2009 (UTC)

Is it not illegal to use a mobile while driving in the US? It certainly is in the UK (3 points on licence and £60 penalty) - unless it's 100% hands free. As regard signals getting in the car - I think it's the large amount of windows. On my metal boat - it kills the signal, unless you stand next to the window (or outside!)  Ronhjones  ^(Talk) 18:49, 31 August 2009 (UTC)

To address the question of the legality of using a cell while driving in the US, that depends on where you are. I think that it is legal most places, but I do know of at least one city where it is not. Googlemeister (talk) 20:12, 31 August 2009 (UTC)

One obvious effect of your question, if it would succeed, is the passenger who wants to use a cellphone and couldn't because the phone was jammed. Nyttend (talk) 01:14, 4 September 2009 (UTC)

Education is the answer, not cell phone jamming, which is illegal. See the recent road safety video made by Gwent police http://www.guardian.co.uk/uk/2009/sep/03/gwent-road-safety-film Jdrewitt (talk) 09:49, 5 September 2009 (UTC)

Single celled organisms and evolution

Until I gave it a good think, I had previously assumed that simpler microorganisms (particularly single-celled varieties such as the amoeba) had survived essentially unchanged since the emergence of more complex/multi-celled organisms. But this shouldn't be the case right? It doesn't make sense to me that an Amoeba proteus from 2009 would look the same as an amoeba 10 million years ago, or that the flagella of Giardia lamblia hasn't changed in the past million years or so. But certain things I've been reading seem to hint at the contrary. Chlorophyceae seems to be organised according to the type of flagella each species/family has, which implies that the same flagella is ancestral to all species within that class. This seems incredible, considering the fact that larger species such as humans have structurally very little evidence of having ever been water-breathers, and water mammals have little evidence of ever having had legs! Could it be that there are many simple organisms that have been mis-classified because of such re-evolutions, or is there really a fundamental difference in the way simple organisms evolve?

Lastly, are there any single-celled organisms that (for example) show signs of having evolved into single-celled organisms after having been multi-celled? I can imagine the analysis of the genome of such an organism showing it as a member of a group exclusive to multi-cellular organisms, despite the obvious structural differences. Sorry for asking so many questions! 124.154.253.31 (talk) 08:00, 30 August 2009 (UTC)

I think you really want the distinction eukaryote versus prokaryote. The eukaryotes include single celled animals and plants and the multicellular animals and plants evolved independently. Amoeba is a eukaryote. You're probably thinking of bacteria and archaea which are much less complex and have had a very long time to evolve into something fairly optimal. They have changed of course and continue to do so but it's a bit like frogs - they look alike to us but genetically there's probably more difference between two random types of frogs than there is between us and the birds. Dmcq (talk) 12:27, 30 August 2009 (UTC)

Yes, sorry, I meant to refer exclusively to single-celled eukaryotes, as well as prokaryotes actually. I guess I didn't realize that there could be so many significant changes genetically without much physical evidence of it. 124.154.253.31 (talk) 03:51, 31 August 2009 (UTC)

"...water mammals have little evidence of ever having had legs" ? Sure they do. Whales have non-functional, residual rear legs, which don't protrude beyond the skin, even to this day: [24]. Their front legs, fingers included, are now their fins. StuRat (talk) 12:47, 30 August 2009 (UTC)

Argh. I recently watched a video about this and they made a lot of fuss about the discovery of residual legs in a primitive whale found in Egypt; the way they worded it made it sound like the bones no longer existed in modern whales. I guess all I can say then is that they no longer have toes? 124.154.253.31 (talk) 03:51, 31 August 2009 (UTC)

Micro-organisms certainly evolve. They do it continuously and rapidly. That's why we have so much trouble with drug resistance - we treat simple organisms with drugs that are supposed to kill them - the few that survive go on to become the whole population. Over many generations of micro-organisms, you have a drug that no longer works anymore. This is an extremely common phenomenon. But our ability to track that evolution into the distant past is limited. Looking at the appearance of bacteria doesn't tell you much about what's going on biochemically inside - and we don't have that detailed information about bacteria from the distant past. It's not like a large organism like (say) a horse. We can find the fossilised bones of ancient proto-horses and deduce a lot about how they evolved - but our ability to do that kind of thing for micro-organisms is extremely limited. SteveBaker (talk) 13:41, 30 August 2009 (UTC)

True, but we can compare the genes of single-celled organisms with those of multicellular organisms. To the extent that they are the same, it's reasonable to conclude that both groups have preserved an ancestral structure. Looie496 (talk) 00:28, 31 August 2009 (UTC)

The bacterial flagellum is a favourite of creationists. Because it is fairly complex they think it couldn't have evolved. Cilia are a similar thing. Richard Dawkin's book The Ancestor's Tale has a bit about them, especially the Mixotricha paradoxa, it's a pity wiki doesn't have a nice picture of that. Dmcq (talk) 16:41, 30 August 2009 (UTC)

You can also check out Kenneth Miller's The Flagellum Unspun, published in 2004 by Cambridge University Press. DRosenbach ^{(Talk | Contribs)} 20:35, 30 August 2009 (UTC)

The concept of punctuated equilibrium is probably relevant to the original question. Single celled organisms evolve so rapidly that they quickly reach highly optimized forms, which can persist with only minimal changes for a very long time. Looie496 (talk) 00:28, 31 August 2009 (UTC)

Wow! If punctuated equilibrium is true, than that explains a lot to me. I understand that there are competing controvercial theories, and that of course as SteveBaker says the micro-organisms are evolving, but due to the extremely specific niches that most of these organisms have evolved to occupy it makes sense that they would give appearances of having met some sort of equilibrium, a cancelling out of multiple evoluctionary changes. Dmcq made the point about frogs, but have they really changed functionally that much? It seems like an example of genetic rearrangement over enormous spans of time only to result in an organism that does virtually the same thing maybe more efficiently but without any extra tricks (of course, most individual species of frog have developed lots of tricks, but I'm attempting to refer to frogs as a group of species).

I have previously thought of the idea of "highly optimized" or "perfectly evolved" forms as silly, almost narcissistic, but now I can see how it might not be such a strange concept. 124.154.253.31 (talk) 03:51, 31 August 2009 (UTC)

An organism can be perfectly evolved for a given environment, but a change in the environment would tend to necessitate a change in the organism. Generalists like humans are more likely to be able to adapt behaviorally, like by wearing more or less clothes, as the climate changes, while specialists like finches must evolve physically, such as the shape of their beaks as their food source changes. StuRat (talk) 19:00, 31 August 2009 (UTC)

Micro-organisms can generally evolve much more rapidly though - their extremely short life-cycles (some can produce a new generation every 10 minutes!) allows them to evolve vastly more quickly than (say) humans who require 16 to 30 years to do the same thing. Large animals have to be at least somewhat generalists because there simply isn't time for them to evolve. But bacteria could conceivably be so super-specialised that they might suite an environment that changes so often that the bacteria are continuously evolving to fit its changes. But whether you'd say that a generalist was "well suited" to any particular environment is a tough call. SteveBaker (talk) 05:33, 1 September 2009 (UTC)

That brings up a good point then, what is it about bacteria that prevents them from becoming generalists? Isn't being generalist always evolutionarily beneficial? The Why is it, for example, that many organisms in the body have not evolved to respond to changes in body temperature of a couple degrees, whereas others can survive in environments with incredible ranges of temperature? Is the length of the genome a factor, i.e. are the organisms forced to compromise more, as a 64k demo programmer might be forced to sacrifice sound complexity in order to produce a pretty looking program? 124.154.253.31 (talk) 02:12, 2 September 2009 (UTC)

Um why do you think being a generalist is always evolutionary beneficial? If you have two bacteria species competing to live in your gut, one producing a large number of enzymes to digest stuff they never encounter, one producing only the enzymes to digest stuff they are likely to encounter, which one do you think is likely to have the evolutionary advantage? The phrase 'jack of all trades, master of none' comes to mind. For something like a bacterium, given their small size etc it rarely pays to be a jack of all trades. Remember also, even if a bacterium could eventually evolve to be an ultimate machine for all environments (which I think is usually unlikely), if all the evolutionary forms in between are worse off there's a fair chance this will never happen. Nil Einne (talk) 23:04, 3 September 2009 (UTC)

So you're basically saying that yes, the size of the genome is the factor in limiting the generalization of small bacteria. I don't see any reason why a large-genomed bacteria wouldn't generalize, nor why intermediate evolutionary forms need be "worse off". 124.154.253.31 (talk) 23:20, 3 September 2009 (UTC)

Genus Canis

What are the best sources for up-to-date information on the coywolf and other contorversies surrounding the family tree and phylogenetics of the genus Canis? NeonMerlin 08:01, 30 August 2009 (UTC)

It looks like the Journal of Mammology, the Journal of Systematic Zoology, and Conservation Biology have all published articles. The articles I found were The Taxonomic Status of Wild Canis (Canidae) in the South Central United States, The Taxonomic Status of Wild Canis in Arkansas, etc. You can find these sorts of journals in a university library, or online (if you have subscription access through your school, library, etc). Nimur (talk) 14:56, 30 August 2009 (UTC)

Parameters of Planet Habitability for people? (not Extremophiles)

There is an article that refers to habitabilty of Extremophiles "ETs" but I was wondering if there is any matter or thought on the parameters of survivability of a planet for Human Beings? I know the Habitable zone article talks about one dimension there, temperature ranges from 0°C to 100°C but most people wouldn't survive through 70% of that range. Also gravity, atmosphere composition and emissivity, atmosphere pressure, hydrosphere size, magnetosphere strength, irradiance, eccentricity, axial tilt, albedo, etc. must have referable boundry limits were people are concerned, does anyone know what these ranges are?? Cpt. J. Tiberio Kirk (talk) 08:31, 30 August 2009 (UTC)

There's a difference for people, where we can live in a place that doesn't meet all our survival needs, by trading with others who have those items we lack. Thus people can live in a wider variety of places than we could if we were all hermits. Remote whaling villages are one example from a couple centuries back, and people living at the South Pole or on the International Space Station are some extreme examples from today, where they are provided with everything they need, in this case in exchange for research. So, do you mean to ask where people can survive if provided with all their needs from outside, or where they can live in total isolation ? StuRat (talk) 12:37, 30 August 2009 (UTC)

We don't even need to trade, technology (even something as simple as a warm coat) can dramatically increase the range of environments we can survive in. --Tango (talk) 15:42, 30 August 2009 (UTC)

Sure, but where did you get that warm coat? Unless you single-handedly grew the plant fiber; smelted the steel and forged the industrial sewing machine; operated the vertically integrated fiber-to-cotton-to-coat industry... you had to trade something to get that coat. Chances are, much of the material and labor for that industrial chain came from a more habitable region, depending on how far back into the supply-chain you look. Nimur (talk) 18:11, 30 August 2009 (UTC)

In modern times, yes, but specialisation on a large scale is a fairly recent part of human history (just since the industrial revolution, really, it existed to a lesser extent for a few millennia before that). A caveman could have killed a large animal and turned its skin and fur into a coat without any trade involved. --Tango (talk) 19:23, 30 August 2009 (UTC)

Agreed. So a human with some basic technology, like the ability to make animal skin clothes, has a wider range than one without. We can see that by where Inuits and other similar people live (which doesn't extend all the way to the poles, however). Without any technology at all, people would be forced to live only in tropical areas near a food and fresh water supply. But once a high level of technology and trading is added, people could live just about anywhere on Earth, and even in space, provided that those who remain on Earth are willing to send them what they need to survive in exchange for the research/exploration/experimentation they do. StuRat (talk) 15:04, 31 August 2009 (UTC)

Just as we are if you will, not a space station or "technology:"

(Human Environmental Tolerances.)

Attribute	Minimum	to	Maximum	Earth eg./avg.
Temperature:	0°C	to	30°C	14°C
Gravity:	0g	to	??g	1.0g
Atmosphere composition:
Oxygen	??% min		??% max	21%
Nitrogen	??% min		??% max	78%
??	??% min		??% max
??	??% min		??% max
Emissivity:	from ??	to	??
Atmosphere pressure:	?? mb min	to	?? mb max.	1013.25
Hydrosphere size:	??% min	to	100% max.	71%
Magnetosphere strength:	?? min		?? max	0.3-0.6 gauss
Irradiance:	???? W/m2	to	???? W/m2	1366.078 W/m2
Eccentricity:	0 min	to	0.3022 max.	0.016710219
Axial tilt:	0 °	to	??° max	23.44°
Albedo:	0.?? min	to	0.?? min	1.0 = Absolue zero

I'm looking mostly for help with references... ...does anyone know what these ranges are, for ANY planet Habitation?? Cpt. J. Tiberio Kirk (talk) 08:31, 30 August 2009 (UTC)

Some of these terms are poorly defined, e.g. magnetosphere strength, and even incident radiation (What does this mean - total radiation? Blackbody-style radiation with a peak near visible light? I'm pretty sure that 1 kW of gamma radiation is much more hazardous than 1 kW of visible-light!) Atmospheric composition will have varying effects ranging from temporary to permanent health problems; do you have a criteria for quantifying these? Are you seeking the LD50 or something similar for these parameters? How long do the humans have to survive (a few hours, weeks, months, years?) It seems unlikely we can find habitability data for humans regarding the orbital parameters, as we have only experienced life on Earth; but I can't imagine what an eccentricity has to do with anything (except its effect on other planet parameters, like temperature and radiation). Nimur (talk) 06:07, 1 September 2009 (UTC)

• IS THIS THE SCIENCE REFERENCE DESK or the "I can't imagine" so I'll bash the question desk??

You need an English lesson? -> Habitability and Habitation,

How do you confuse "Median lethal dose" with "Habitiability" and still think you should comment here?

If you don't understand the question should you be commenting with ignorant questions?Cpt. J Tiberio Kirk (talk) 08:34, 1 September 2009 (UTC)

This is the Science Reference Desk, not the wild speculation/colorful imagination desk. LD50 is as good a measure as any for determining habitability. You want to know what conditions humans can survive; but you failed to define "survival" in a way that allows a scientific answer to your question. Nimur (talk) 18:20, 1 September 2009 (UTC)

I resent that. There has been a lot of healthy "wild speculation" and "colorful imagining" performed on the science RD over the years, and I find it slightly arrogant of you to debase that what ever reason you may have. Many of the OPs queries seem to have perfectly reasonable scientific answers, whether they're suitable for an encyclopaedic article is another story (and not one that need be discussed here). 124.154.253.31 (talk) 02:21, 2 September 2009 (UTC)

Didn't we come to the conclusion in a thread some time ago that humans could probably/possibly survive at 2x earth gravity? --Kurt Shaped Box (talk) 11:34, 1 September 2009 (UTC)

A few comments on the table:

1) 0°C seems questionable for a naked human, I'd expect him to quickly freeze to death. And I suspect that a naked human could take more than 30°C, especially if there is water around for cooling off. So, I'd raise both by 10°C, to get a range of 10°C - 40°C.

• 0°C to 30°C are referenced values.

2) I doubt if naked humans could survive long term at 0g, due to bone and circulatory system degradation. Even in the short term, doing everything necessary for life in zero gravity could be quite difficult, without technology. I'd raise that minimum to at least 0.1g.

• More reasonable is the minimum gravity needed to support a breathable (surface pressure) atmosphere.

3) I don't believe we need any atmospheric nitrogen. We do need some nitrogen, but we get that from our diet, not from the air.

• "The unfortunate problem is the flammability. For this reason, McKay et al. 1991 sets the upper limit on O₂ at 300 mbar. The lower limit of 130 mbar is set by hypoxia. They estimate that the partial pressure of N₂ needs to be greater than 300 mbar. Although nitrogen is not widely thought of as an important gas, it makes up 78% of Earth’s atmosphere. It is needed as a as a buffer gas to prevent O₂ combustion in the atmosphere. The partial pressure of CO₂ is set by toxicity. The overall mixture is estimated to be between 500 and 5000 mbar, with the upper limit shown by inhabitants of high elevations on Earth. The lower limit of the overall mixture is set to 500 mbar based on buffer gas narcosis. If the buffer gas, N₂ in this case, is set to be >300 mbar, that leaves the O₂ content dangerously close to the lower limit set by hypoxia. McKay et al. 1991 suggest that the high concentration of buffer gas to O₂ is toxic. Temperatures and pressures needed for habitability are set by the triple point of water. This is the point where water can exists as a solid, liquid and gas. It is defined as 273K at 6.11 mbar. If we are to have liquid water on the surface, the temperature and pressure must not lie far off above or below the triple point.

4) We actually don't directly need any of the trace elements in the atmosphere, either. Of course, the plants we eat need atmospheric carbon dioxide, so you could argue that we need it, too, since we need plants to eat. This is unless we had another food source that didn't require atmospheric CO₂.

5) I don't believe we need any oceans, seas, or lakes to survive, as people can survive on underground water reservoirs only, if necessary.

• Actually, I have read a breathable atmosphere has to have some moisture. And that rain washes away suspended silica dust that would make the atmosphere unbreathable. GabrielVelasquez (talk) 09:05, 3 September 2009 (UTC)

6) I don't believe we need seasonal variations to survive, which means we don't require any axial tilt (or eccentricity of our planet's orbit, which could be an alternate means of achieving seasons. StuRat (talk) 13:58, 1 September 2009 (UTC)

This is an amusing comment as you refer to "needed" axial tilt or eccentricity and assume minimums, but there there would have to be maximum limits. Planets of Larger stars would have larger habitable zone orbits (ie. longer periods) and with a 90° axial tilt one entire hemisphere could freeze over seasonally. GabrielVelasquez (talk) 09:03, 3 September 2009 (UTC)

The atmospheric pressure that humans need to survive will be a function of the O2 content of said atmosphere. Should probably note that we need there to be an absence of toxic elements as well. It would not work if there was an arsenic desert nearby with dust storms hitting the settlement frequently. Googlemeister (talk) 14:37, 1 September 2009 (UTC)

We need a partial pressure of oxygen of about 0.2 atm, neither the total pressure of the atmosphere or the proportion of oxygen are particularly important, it is that partial pressure. Total pressure of 0.2 atm ought to be fine, or we can have some kind of buffer gas up to a total of somewhere more than 1 atm, but I don't know how much more. --Tango (talk) 21:12, 1 September 2009 (UTC)

With Nitrox or TriMix, SCUBA divers can breathe up to almost 40% oxygen. In fact, utility divers will breathe some pretty exotic air mixtures - helium, argon, you name it. You can even go to very low percentages of oxygen if the partial pressure is high enough - but that requires a very high pressure gas mix (certainly not recommended for long-duration exposure, or consumption at sea-level). There are severe health ramifications and the gas levels and pressures need to be properly monitored by a trained diver. Nimur (talk) 23:55, 1 September 2009 (UTC)

Let's say for the sake of argument that we are talking about a resettled Inuit (mentioned above), on some Arctic/Tundra planet... Would you expect them to leave their shelter to go hunting in a scuba suit and still call that habitiable?? - GabrielVelasquez (talk) 12:43, 3 September 2009 (UTC)

Re item 2): FWIW, I recall from discussions at Mars Society conferences that the minimum gravity needed to avoid long-term skeletal, etc, degredation problems is currently thought to be about 1/3g - for obvious reasons, experimental investigations of this consideration are not easy to carry out. This means that long-term habitation (by terrestrial humans, of course) in the Moon's 0.165g would be problematic without appropriate countermeasures (such as drugs, exercises, centrifuge sessions), but that extended or permanent Martian habitation in 0.379g should be just about tolerable in this regard. 87.81.230.195 (talk) 20:54, 1 September 2009 (UTC)

The Mars Society just happened to come across a figure that is just under the gravity of Mars? I would take that with a pinch of salt. We know what happens to humans at 1g, 0g and a little at >1g. We know next to nothing about anything between 0 and 1. There have been no direct experiments, so it is all guesswork. --Tango (talk) 21:12, 1 September 2009 (UTC)

Having had no little interaction with the Mars Society (though I'm not currently a member), Tango, I'm prepared to believe it does not favour self-serving spin over facts; it is after all composed of numerous articulate scientists and others who aren't required to toe any party line - not everyone is intellectually corrupt. In this case they say (or said when I was participating) merely that yes, absent direct observations, the best estimates available were "about 1/3g", and precisely in order to investigate this question, the Society has been collaborating with NASA to design an experiment to raise generations of mice in tethered centrifugal microsatellites simulating Martian gravity: regrettably this is currently a victim of budget cuts, but in the longer term such experiments will doubtless be performed. The more immediate worry for Mars expeditions is in fact not the toleration of Martian gravity, but the effects of zero-g for the months it will take getting there and back; again, tethered centrifugal craft may be an answer (OK, that kind of spin they favour :-) ). 87.81.230.195 (talk) 13:28, 3 September 2009 (UTC)

As for maximum gravity humans can tolerate, I think 4-5 g's would be the upper limit due to cardiovascular effects (blood draining away from the brain, blackouts, lower body edema, stuff like that). Although some people could briefly tolerate much higher gravity, the maximum continuous gravity force they can tolerate (for more than a few minutes) is no more than that. Also, the maximum tolerable temperature is 70 C (I looked it up in the Science Encyclopedia). FWiW 98.234.126.251 (talk) 05:23, 2 September 2009 (UTC)

Yes, without g-suits and special training, 5g seems to be the maximum for more than a few seconds. --Tango (talk) 18:18, 2 September 2009 (UTC)

But then again, that's for an adult, isn't it? And probably a pretty healthy one. For these figures, fetuses would have to be able to survive birth as well, right? 124.154.253.31 (talk) 06:08, 4 September 2009 (UTC)

Yeah, I agree, 5g is a bit too much. Also, I realized, with a gravity of 3-5g, it would make basic everyday activities difficult or impossible even without cardiovascular effects. So with that in mind, 1.5-2g seems about right for a maximum limit. 98.234.126.251 (talk) 04:40, 5 September 2009 (UTC)

Did I forget to mention that according to the article on oxygen toxicity, the maximum tolerable oxygen partial pressure is 0.5 bar? 98.234.126.251 (talk) 05:27, 2 September 2009 (UTC)

Well found. --Tango (talk) 18:18, 2 September 2009 (UTC)

The original source for that number indicates that 0.5 bar of oxygen is not fatal, only that it induces clinical symptoms of tracheobronchitis. Again, this highlights the necessary definition of "habitible" - humans seem to be able to survive up to 1.8 to almost 3 bar of oxygen without major damage to the central nervous system, depending on other conditions. Even this damage, which ranges from dizziness and nausea to more serious problems, is considered mostly reversable. [25]. So, what level of discomfort is acceptable, or are these terms meant strictly to refer to fatality limits? Nimur (talk) 05:51, 3 September 2009 (UTC)

You irrationally insist on ignoring the clarification "Just as we are..." and "Habitability" to continue your criticism.
Obviously torture isn't a "habitable" situation. Here is a "definition of habitiable" that you might appreciate:

• http://en.wikipedia.org/wiki/User:Explodicle/Planetary_human_habitability
  

and I hope this article gets finished some time this year as it is obviously needed!
Also just because dimensions are connected doesn't mean that they don't have limits, for people.
GabrielVelasquez (talk) 08:54, 3 September 2009 (UTC)

Habitability defines the term in accordance with a few state legal statutes - more along the lines of a building code. I'm only asking for clarification because your question is phrased in a way that requests very specific numbers to a very vaguely defined concept - so in its present form, there is no way to answer this question. Nimur (talk) 16:39, 3 September 2009 (UTC)

"And you are lynching Negroes" - You deliberately ignore the clarification, you make me suspect you are just mocking.
I quote from the link right above "...Dole and Asimov (1963) and they defined a "habitable planet" as "one on which large numbers of people can live comfortably and enjoyably without needing unreasonable protection from the natural environment and without dependance on materials brought in from other planets." They added that in discussing habitability the planet in question must be at least 10% habitable. In their book they went on to list more specific parameters for said habitability."

Please edit table at will, but comment above this subsection

---

"Human Habitability Environmental Requirements and Tolerances."

• NEW TABLE BASED ON ANSWERS:

Attribute	Minimum	...to...	Maximum	Useful References
Mean Annual Temperature:	0°C	to	30°C	Planets for Man, 2nd Ed. page 16
Seasonal Temperatures:	-10°C	to	40°C	Planets for Man, 2nd Ed. page 16
Gravity:	0.5 g	to	1.5 g	Planets for Man, 2nd Ed. page 24.
Atmosphere composition:				??
Oxygen	??% min		??% max	??
Nitrogen	??% min		??% max	??
??	??% min		??% max	??
??	??% min		??% max	??
Emissivity:	from ??	to	??	??
Atmosphere pressure:	?? mb min	to	?? mb max.	??
Hydrosphere size:	??% min	to	100% max.	??
Magnetosphere strength:	?? min		?? max	??
Irradiance:	???? W/m2	to	???? W/m2	??
Eccentricity:	0 min	to	0.3022 max.	ie ± 50°C.  ??
Axial tilt:	0 °	to	??° max	??
Albedo:	0.?? min	to	0.?? min	??

GabrielVelasquez (talk) 09:30, 3 September 2009 (UTC)

"NOx" written in expanded form as...?

Is "oxides of nitrogen" or "nitrogen oxides" appropriate for a research paper to be published in an international journal? I'm cleaning up a manuscript for a Chinese professor and the original has "oxides of nitrogen" which seemed a bit off to me.

Google shows both are present in the vernacular, so I'm wondering if anyone with direct experience in a related field could give me a definitive answer (or even a definitive "they're both ok")...

Thank you, 61.189.63.152 (talk) 13:37, 30 August 2009 (UTC)

Both are fine. Nitrogen oxides may be better, especially if it is to be indexed by a computer.83.100.250.79 (talk) 14:27, 30 August 2009 (UTC)

I'm not a chemist. To me, between the two, I'd prefer "oxides of nitrogen", as it communicates very clearly that we're talking about a group of compounds. For retrieval purposes, I'd suggest including both as index terms. --98.114.146.57 (talk) 14:51, 30 August 2009 (UTC)

NOx is a perfectly acceptable "technojargon" term in certain communities, and does not need expanding. While in a strictly chemical context, an expanded form may be more appropriate, I think it would confuse readers from other disciplines (like atmospheric research, combustion research) who are more used to seeing "NOx" and knowing unambiguously what is meant. Nimur (talk) 15:00, 30 August 2009 (UTC)

Highly dependent on the conventions for the specific journal (some have style-guides with lists of accepted/standard abbreviations) and/or the target audience. DMacks (talk) 17:51, 30 August 2009 (UTC)

I agree. Check the manual of style for the particular journal. Google Scholar found 477,000 usages. Nimur (talk) 17:59, 30 August 2009 (UTC)

Coal & Fossils

Coal, like oil, as I am lead to believe, is formed from the compression of carbon based material (i.e. animals and plants) over time. Why is it that some animals become fossils, yet others become coal? Also, related question, why do we have coal and oil fields? It seems like all these animals all died in the same place. Any info would be appreciated. --KageTora - (영호 (影虎)) (talk) 14:17, 30 August 2009 (UTC)

Fossils in coal are actually very common - search for "fossils coal" - here's a fish [26], and image search may be even better.83.100.250.79 (talk) 14:24, 30 August 2009 (UTC)

Thanks. So, if there are fossils even in coal, where does all the rest of the coal come from? --KageTora - (영호 (影虎)) (talk) 14:36, 30 August 2009 (UTC)

Ah, I think that last question has just been answered by an Gimage search. It said that in the case of that particular image, the coal in question was fossilized peat, which would lead me to believe that the surrounding coal on the image of the fish in your answer would also be some such similar thing, such as vegetation. --KageTora - (영호 (影虎)) (talk) 14:41, 30 August 2009 (UTC)

Fossil forming requires circumstances conducive to it. Fossils are by no means a certainty when you have organic matter entombed in mineral matter. See rarity of fossils. Bus stop (talk) 15:15, 30 August 2009 (UTC)

(ec) Fossils can be present in coal, but most coal is not made of decayed animal. It is made from Type III kerogen, "terrestrial plant matter that is lacking in lipids or waxy matter" like peats and grasses (and trees, maybe). Different kinds of plant matter (like marine algae, lake plants, and terrestrial plants) are different kerogen material, and typically result in different kinds of fossil-fuel. However, few fossil-fuels are actually made of animal fossil. Nimur (talk) 15:17, 30 August 2009 (UTC)

Thanks, Nimur, but in my original question, I did actually mention plants, too. --KageTora - (영호 (影虎)) (talk) 16:28, 30 August 2009 (UTC)

Ok, but it seems like the kerogen article will link you to the information you want. Why do certain regions form oil or coal, while others do not? See petroleum geology for an in-depth answer. To summarize: you need several conditions to occur - presence of a kerogen source (meaning the correct type of plant or organic matter), and the presence of a reservoir rock that can hold that matter; presence of a seal rock; and mild seismic activity (geothermal energy) to cook the kerogen without fracturing the seal. This is a rare combination, so only certain regions result in liquid hydrocarbon or economically extractable natural gas. Coal, on the other hand, doesn't need a seal rock; and is less sensitive to seismic activity; so it is much more common. I might have misinterpreted one of your original questions, "Why is it that some animals become fossils, yet others become coal?" In truth, no animals become coal; only certain plants can become coal; but even those must be subjected to the proper geological conditions (as I described above), so coal will only form in certain regions. Nimur (talk) 17:21, 30 August 2009 (UTC)

I see, thanks. You have cleared it up. Basically, the reason why we have coal fields is because those conditions only exist in certain places. Animals don't become coal, so that is why we have fossilized animals in coal. I get it, now. Thanks. --KageTora - (영호 (影虎)) (talk) 17:58, 30 August 2009 (UTC)

As an extra tidbit, the two main depositional enviornments that I think of for coal are (a) oxbow lakes in subtropical to tropical meander belts that slowly fill up with sediment, and (b) costal/tidal plains. Awickert (talk) 06:51, 31 August 2009 (UTC)

Puzzling Puzzle

This is already on the Miscellaneous desk. We discourage cross-posting of questions. // BL \\ (talk) 16:22, 30 August 2009 (UTC)

Wouldn't it fit better on the Math desk? -GTBacchus^(talk) 16:26, 30 August 2009 (UTC)

Transparent objects

Why transparent objects are transparent.? —Preceding unsigned comment added by 121.245.107.152 (talk) 18:13, 30 August 2009 (UTC)

At the risk of sounding glib, because you can see light through them. The article Transparent materials is reasonably clear even for a non-scientist. // BL \\ (talk) 18:30, 30 August 2009 (UTC)

The article is reasonably clear? How fitting to the subject matter! No wonder the article on black holes seems a bit less enlightening to me. --Cookatoo.ergo.ZooM (talk) 19:24, 30 August 2009 (UTC)

It is important to remember that transparency is dependant on the wavelength of light in question. We usually mean the visible part of the EM spectrum, but something being transparent in that part (or not) does not mean it is necessary transparent (or not transparent) in other parts. For example, the glass in a greenhouse is transparent to visible light but not to far infra-red light (that's part of why it traps heat). A bin bag is opaque to visible light, but transparent to far IR (there is a picture of that further up this page in the "invisibility" section). I believe it is all to do with electron energy levels - to absorb a photon there has to be en electron in the substance that can rise to another energy level an amount of energy higher equal to the energy of the photon (which is inversely proportional to wavelength). --Tango (talk) 19:19, 30 August 2009 (UTC)

Greenhouses mostly trap heat by trapping hot air. The greenhouse effect isn't very significant in greenhouses. — DanielLC 22:45, 31 August 2009 (UTC)

Have you considered why non-transparent things are like they are - once you understand this you may be able to come to terms with transparency.83.100.250.79 (talk) 21:20, 30 August 2009 (UTC)

That is essentially exactly the same question, so how is that helpful? --Tango (talk) 22:38, 30 August 2009 (UTC)

No it isn't - I was suggesting that they look at why things absorb light. Once that is understood transparent things should be obvious.83.100.250.79 (talk) 00:01, 31 August 2009 (UTC)

Of course it will be - you'll already have the answer because it is the same question. Something is transparent if it doesn't absorb (or reflect - don't forget that possibility, although arguably it is temporary absorption) light, so if you know why something absorbs light you also know why other things don't. They are the same question, just from a different direction. --Tango (talk) 00:11, 31 August 2009 (UTC)

The question is "why do these things let light through" - I thought it might help to consider "why do some things not let light through" - obviously they are two sides of the same coin. - Non tranparency is (in my opinion) less 'mysterious' (in a psychological sense consider how excited people get about gadgets with transparent bits)than transparency at a very basic level, which is where we are.83.100.250.79 (talk) 00:44, 31 August 2009 (UTC)

What gadgets? Cuddlyable3 (talk) 15:38, 31 August 2009 (UTC)

Controllers for games consoles, and some handhelds, come in semitransparent versions. Vimescarrot (talk) 15:52, 31 August 2009 (UTC)

Hair follicle imitator

Is there a plant or animal that looks like a hair follicle, including the root (white or clear "bulb")when pulled out that is much stiffer and thicker than surrounding follicles and which does not soften or react to isotropy alcohol but dies or dissolves when iodine is applied as an antiseptic? 71.100.5.63 (talk) 19:39, 30 August 2009 (UTC)

Are you asking if an animal or plant exists that would be lodged into a human scalp, so that when plucked it would resemble a hair and its follicle? DRosenbach ^{(Talk | Contribs)} 20:28, 30 August 2009 (UTC)

Why did you say scalp??? ...but yes. 71.100.5.63 (talk) 21:16, 30 August 2009 (UTC)

I'm curious if you mean what is sometimes called in slang "fledges" - a form of 'pubic' like hair that grows on the shoulders etc, as people get older - this is thicker and stiffer that normal hair.?

What exactly happens when you add iodine ?83.100.250.79 (talk) 21:18, 30 August 2009 (UTC)

The original one I found was about 1.5" from the corner of my mouth. I thought at first it was a petrified blackhead. The end looked more like a glob of grease than a root. The one on my scalp that I put iodine on simply vanished. The third one I have now became much softer after the iodine but has not dissolved completely yet or gone away. Never heard of "fledges." What is it? 71.100.5.63 (talk) 21:31, 30 August 2009 (UTC)

It sounds to me like an ingrown hair, which may grow much thicker than a normal hair and have the appearance of a pimple before it emerges. Unpleasant, but not a sign of disease or infestation. I've had them along the jawline, and when they emerge they have an appearance like what you're describing. --FOo (talk) 22:23, 30 August 2009 (UTC)

No curling or folding backwards. I've had ingrown hairs but none that were thick, tough, and straight. This is definitely a species that has come here from outer space to infiltrate Earth to spy on us by pretending to be a hair. 71.100.5.63 (talk) 23:22, 30 August 2009 (UTC)

Morgellons syndrome. --TammyMoet (talk) 08:56, 31 August 2009 (UTC)

Fish safety

For years I've enjoyed tunafish - both as BBQed steaks and also raw in sushi. A while ago I saw sushi grade tuna for sale at a fish place, and for the first time enjoyed raw fish as a meal in its own right rather than with rice. Delicious. I've bought tunafish steaks a couple of times since.

My question is, isn't raw meat (including fish) supposed to be extremely prone to food poisoning? Is this safe? What is the difference between "safe" raw fish (used worldwide in sushi) and "unsafe" raw fish if any? (assuming it's from a reputable source, fresh, washed, cold, etc)

What's the risk if I carry on indulging myself by buying raw fish at reputable stores and taking it home to make my own sushi and raw fish meals at leisure? What precautions and other safety rules do I need to be aware of?

Thanks for any answers.

FT2 ^{(Talk | email)} 19:51, 30 August 2009 (UTC)

This might help -- you can google "raw fish safety" yourself for more info. DRosenbach ^{(Talk | Contribs)} 20:27, 30 August 2009 (UTC)

Thanks :) FT2 ^{(Talk | email)} 21:39, 30 August 2009 (UTC)

It's not a good idea to overdo the tuna, even if it's cooked. From the mercury poisoning article: "the consumption of fish is by far the most significant source of ingestion-related mercury exposure in humans" and "larger species of fish, such as tuna or swordfish, are usually of greater concern than smaller species". This is especially true for certain at-risk groups (see the article), for whom the FDA recommends limiting the consumption of albacore tuna to no more than 6 oz per week, and all other fish and shellfish to no more than 12 oz. per week. My niece developed mercury poisoning a few years ago, while in her late teens, after eating nothing but tuna fish and blueberries for 6 months (she had an eating disorder). The symptoms of mercury poisoning have pretty much ruined her life. Red Act (talk) 11:59, 31 August 2009 (UTC)

So far parasites have been mentioned, as has mercury (which is just as much of a problem in cooked fish). The other major threat of raw fish is bacteria, which is worse when they have started to decay. This would result in the classic food poisoning symptoms of nausea, vomiting, and diarrhea. Cooking fish properly should kill of all (or almost all) of the bacteria, but then they can regrow if it's left around too long. There may also be some virus which can be passed from fish to a person, that I'm not sure about. In short, cooking meat and fish is one of the best ideas humans ever invented, and skipping it seems too risky for me. StuRat (talk) 14:47, 31 August 2009 (UTC)

When you say 12 oz. per week, how many ounces in a normal meal, say at a seafood place down in Florida, with dinner sized fish & a side dish or two?4.68.248.130 (talk) 18:57, 31 August 2009 (UTC)

A typical fillet of flounder is four to six ounces, for example. --Sean 19:10, 31 August 2009 (UTC)

I've filets 3-4 times in a week-long vacation, but then hardly ever eat it throughout the year. that's probably safe. Your mileage may vary, though some may depend on how deep the water is it comes from, and your size; I'm pretty much average build and close to ideal weight. I love mahi mahi and grouper myself.Somebody or his brother (talk) 23:18, 31 August 2009 (UTC)

If you are looking for reading to put you off raw fish, this might do http://www.chow.com/stories/10163 -71.236.26.74 (talk) 16:39, 1 September 2009 (UTC)

Thanks, and ewww, gross.4.68.248.130 (talk) 19:01, 1 September 2009 (UTC)

I did a school project on sushi some years ago, and one of the more interesting tidbits was that sushi didn't emerge in Japan until the advent of refrigeration. Vranak (talk) 01:23, 2 September 2009 (UTC)

Trying to figure out the name of a car part

Hi. I was looking at a Volkswagen Passat yesterday and there seemed to be rust on part of the wheel/axle but I am not sure what the part is so I can look it up (the salesman told me that it was caused by brake dust and wasn't a problem). I can't find a clear picture of the part but it was basically a drum shape that seems to be at the very end of the axle, and has the wheel bolted to it (so it sits ust behind the hub cap). It is circular, maybe six inches deep and nine inches in diameter (very rough estimates). I wondered if anybody could help me find the name please, so that I can investigate the rust issue more thoroughly. Thanks HungryAvocado (talk) 19:55, 30 August 2009 (UTC)

red calipers, brake disk and the rotating plate of the wheel hub

In that area, you tend to have the wheel hub (comprising wheel bearings and a plate for mounting the wheel itself - good engineering drawings); attached to the static part of the hub are brake calipers; attached to the rotatable wheel mounting plate is the brake disk ... the calipers fit around the disk and brake pads sit within caliper. The whole thing then tends to have a metal shroud around the back of it (at least in my memory it does), and, err, that's about all there is. Any other parts in the vicinity will be suspension or steering. Does this help any? --Tagishsimon (talk) 20:06, 30 August 2009 (UTC)

Thanks very much, that is very helpful. The specific part where the rust was seemed to be was the cylinder that protudes from the large disk in the photo and has the holes in the end of it. Is there a specific name for that, or is it just part of the brake disk? Thanks again for your help. Thanks HungryAvocado (talk) 20:44, 30 August 2009 (UTC)

Normal rusting on a wheel hub

I think it would be described it as the moving part of the wheel hub. Compare with this car part advert. However elsewhere it appears to be an integral parl of the brake disc (brake rotos in USian) - see here. Your's probably looks much more like the second photo I've posted. IMO surface rusting here does go with the territory and in general is nothing to worry about. If the metal has started flaking away, that's another thing entirely. --Tagishsimon (talk) 21:06, 30 August 2009 (UTC)

And in closing the part you pointed to, on a Passat, does appear to be integral to the brake disk - and costs $36. --Tagishsimon (talk) 21:13, 30 August 2009 (UTC)

Thanks for all this help. For some reason the part that I saw doesn't actually look very similar to the brake disk on partstrain.com. It looks more like the original image you linked to, in the sense that the cylinder was much deeper (maybe even deeper than your original photo). I have slightly doctored the original photo here to show was the rust looked like (it was in patches and looked quite superficial). Thanks again HungryAvocado (talk) 21:27, 30 August 2009 (UTC)

No probs. The part you coloured plays no direct functional role; sounds like it's fine. --Tagishsimon (talk) 22:33, 30 August 2009 (UTC)

I know very little about car specifics - but with localised rust like that - would it be worth looking for a source - perhaps the car has been left standing for a long time and some water found a way to drip through the bodywork - hole in the wheel arch.?83.100.250.79 (talk) 00:39, 31 August 2009 (UTC)

Cars which have been idle (not driven at all) for even just a few days (depending on climate) will develop a rust film on their brake discs. This is extremely common, and disappears within a few miles of driving as the brakes are used again. Here are some forums where this is discussed: [27] [28] [29] [30] with some posters reporting rust appearing within days or hours after the discs get wet. Nimur (talk) 01:17, 31 August 2009 (UTC)

I wish there was a International Standard Part Number (ISPN) that was stamped on every manufactured item, not just for car parts, like an ISBN number for books. This would make getting a replacement part from eBay or whereever so much easier - I speak from experience. If a non-standard alphabet was used that had 50 or 60 characters rather than the traditional 10 or 24+9, then the ISPN need not be very long. 78.147.28.17 (talk) 10:31, 1 September 2009 (UTC)

August 31

Why do dogs sometimes chase their own tails?

I am not a dog owner, nor have I ever owned a dog - but I have noticed dogs doing the tail chasing thing when I've been out and about. Sometimes I've even seen them manage to successfully bite their own tails - quite hard, if the dog's pained yelp and jump immediately afterwards is anything to go by.

Now, I'd always put it down to dogs not being particularly smart and failing to realize that their tails are part of their own body - but thinking about it now, that doesn't really make any sense at all. Presumably the dog receives sensory feedback from its tail telling the brain where the tail is in relation to the rest of the body, so even if the dog saw its tail in its peripheral vision it would have a good idea that it belonged to its body and wasn't a prey animal/chew toy to pursue and attack...

So, what's really going on here? Some sort of canine body integrity identity disorder or other neurological/psychological issue? Too many recessive genes due to inbreeding? --Kurt Shaped Box (talk) 00:44, 31 August 2009 (UTC)

Dogs may not be anywhere close to the intelligence level of humans, but they're much smarter than people often give them credit for. I suspect it's more likely a form of play. – ClockworkSoul 01:00, 31 August 2009 (UTC)

I'd say it's exactly that. Cats often do it as well (and they're much smarter than dogs :D). Next time you see an animal do this, take a look at it - usually, you can tell there's an element of playfulness there as it chases its tail around. Young cats and dogs will often play fight - it's more common in wild cats like lions - training to hunt and survive on their own. You might also ask why children play with dolls are pretend to be superheros. It's creative entertainment. ~ Amory (user • talk • contribs) 01:28, 31 August 2009 (UTC)

Don't think that I hadn't considered that myself - but is it really normal to bite one's own body parts hard enough to cause what appears to be significant pain during play activities (excluding certain human sexual practices... ^_^)? --Kurt Shaped Box (talk) 01:33, 31 August 2009 (UTC)

One of our cats does it frequently (once a week that we see). Perhaps it is some form of pleasure, sexual or otherwise. -hydnjo (talk) 02:12, 31 August 2009 (UTC)

The fundamental error here is to assume that everything an animal does is for a reason. Every action has a cause, but not every action needs to have a reason -- that is, not every action needs to result from a plan formulated with the aim of accomplishing an understood goal. It seems likely to me that the dog is responding automatically to a certain type of movement, just as you or I automatically look toward a bright light that flashes in front of us. Looie496 (talk) 02:58, 31 August 2009 (UTC)

Even if there was no real reason to chase a tail in the first place, a dog may learn that chasing his tail grabs a lot of attention from humans (who usually consider it funny), which may reinforce the behavior. Unilynx (talk) 22:12, 31 August 2009 (UTC)

How about drinking? What's the percentage of people that "hurt" themselves while drinking in a "playful" manner? And how many do it again the next weekend? Roughly 98.63% of college students, at my last count. It's a different situation, we could also look at punching a wall or pounding a table in anger or frustration. I've seen no research on it, but it's probably a feature of highly intelligent creatures to be able to do things that seem to cause themselves immediate pain and harm (mind over matter). ~ Amory (user • talk • contribs) 03:19, 31 August 2009 (UTC)

I disagree with the above, i think dogs might not be aware that the tail is their own when they are chasing it. I can't see any reason to doubt it apart from our human interpretation of how "dumb" that would be and how "smart" we think dogs are. Not suggesting it is directly related but most animals, including dogs do not pass the Mirror test. Vespine (talk) 04:02, 31 August 2009 (UTC)

OR here, but I always thought that, similar to Looie496's comment, the chasing of tails is related to dogs' built-in chase reaction. Dogs will react to a fleeing squirrel (or dog, or cat, or human) by chasing it, and my belief is that tail chasing is related. Tempshill (talk) 06:29, 31 August 2009 (UTC)

I'd say that they are aware that it's their tail at a certain level, but that's not enough to overcome the instinct to chase and bite at wiggling objects. For a similar example in humans, if I see a bunch of bugs on TV, my skin gets itchy and I just have to scratch, even though I'm fully aware that those bugs aren't actually on me. StuRat (talk) 12:01, 31 August 2009 (UTC)

Young dogs almost always do it occasionally - but if your dog does it a lot - or fails to grow out of the habit - then you have a seriously bored dog who needs more stimulation - either from human contact - or perhaps with some chew toys or something. SteveBaker (talk) 18:16, 31 August 2009 (UTC)

If your dog need more stimulation, get him a humpy toy. StuRat (talk) 18:54, 31 August 2009 (UTC)

World Drug List

About a year ago, I found a file online that had every prescription drug name (both brand name and generic name) for the entire world. I remember it being hosted by the WHO. However, I simply cannot find it anymore. Can someone provide a link to such a file? I already have the NDC file from the FDA. That file is so full of typos and omissions that it is useless. I'm looking for a file that has all brand names and generic names without typos and without omissions. -- kainaw™ 01:59, 31 August 2009 (UTC)

http://www.who.int/medicines/publications/essentialmedicines/en/ - this one? - use Google with a site limiter e.g. list of drug site:www.who.int  Ronhjones  ^(Talk) 18:39, 31 August 2009 (UTC)

Thanks. That is not what I am looking for, but it is a list of medications (a list of what is considered "essential" for a proper health care system). I meant to use this list for another project and forgot about it. According to the WHO, these medications are "essential". I wanted to match them up against what different insurance agencies and drug programs consider to be "essential". -- kainaw™ 02:05, 1 September 2009 (UTC)

Carl Linnaeus translated to English?

Can anyone point me to some of Linnaeus's scientific writings translated to English please? Thanks Adambrowne666 (talk) 08:05, 31 August 2009 (UTC)

The Wikipedia article is Carl Linnaeus. This[31] gives some of his writing in Latin with English translation.Cuddlyable3 (talk) 14:16, 31 August 2009 (UTC)

I'd imagine that most of the translations of his major works are in printed form (such as this). Online, things are probably more difficult: There's an old translation of the Ordines et genera insectorum, so disfigured by scanning errors as to be practically unreadable, here; and a few other things are available behind subscription walls. Wikisource has a (very) partial text of an Introduction to Botany that seems to be an exposition in English of Linnaeus' systematic work. Just search for Linnaeus English translation and poke around. Deor (talk) 15:38, 31 August 2009 (UTC)

Just a note: there are not a lot of English translations of Linnaeus around. It took me ages to find a good English translation of the first edition of Systema Naturae, ages ago, and I finally did find one as a very rare manuscript. The works are dry and dull; if you are a historian who really wants to know about Linnaeus, you usually already must learn Latin anyway. --98.217.14.211 (talk) 13:23, 1 September 2009 (UTC)

Ground

If there is no solid ground on the giant planets, what stops you from going underneath their surfaces? —Preceding unsigned comment added by Jc iindyysgvxc (talk • contribs) 08:21, 31 August 2009 (UTC)

At a certain distance, it might be hard to push through the heavily-compressed gas, but otherwise nothing prevents you from going underneath their surface. --99.237.234.104 (talk) 08:30, 31 August 2009 (UTC)

Extreme pressures, winds, and, in some cases, temperatures. StuRat (talk) 11:49, 31 August 2009 (UTC)

Galileo (spacecraft) sent a probe beneath the atmospheric surface of Jupiter. It certainly vaporized before hitting the metallic hydrogen interior. -- kainaw™ 11:57, 31 August 2009 (UTC)

In my case a lack of transport. Cuddlyable3 (talk) 13:56, 31 August 2009 (UTC)

Or, as a linguistic exercise, if there is no solid ground, what does "underneath the surface" even mean? — Lomn 13:59, 31 August 2009 (UTC)

Not a thing. You'd sink right in. Probably not all the way to the core, but you'd sink for many many miles. Until you got so deep that the air pressure was high enough to crush you like a tomato. APL (talk) 14:47, 31 August 2009 (UTC)

OMG! I had no idea tomatoes were so likely to crush me! I need to be MUCH more careful near my refrigerator. SteveBaker (talk) 18:12, 31 August 2009 (UTC)

Yes, that's why they are called "rotten tomatoes" ... those evil fruits masquerading as innocent veggies ! StuRat (talk) 18:40, 31 August 2009 (UTC)

No, no, "rot10 tomatoes" would be dywkdyoc, which stands for "Do You Want Ketchup? Do You? Or Catsup?" --Anonymous, 20:08 UTC, August 31, 2009.

If you have a way to slow down (e.g. re-entry shield and then a parachute. You will eventually begin descending slowly and approximately vertically. Your descent will stop at the point where the density of your spacecraft equals the density of the gas, assumiig that your spacecraft is strong enough to resist crushing. You can go deeperby usig power or by increasing your denisty (e.g., by compressing some of your internal atmosphere) similar to the way a submarine operates. -Arch dude (talk) 15:24, 31 August 2009 (UTC)

You must be using an ablative shield, as atmospheric pressure has apparently blown away the closing parenthesis for that first sentence, the "n" in "assuming" (where the existing "i" was also split into two), the space between "deeper" and "by", and the "n" in "using". The letters in "density" were apparently also shaken out of position. I'm just glad that any of your paragraph managed to survive at all. :-) StuRat (talk) 18:51, 31 August 2009 (UTC)

This is what happens when every component of your paragraph lander has been made by the lowest bidder. ;) Franamax (talk) 20:07, 31 August 2009 (UTC)

It would be a straightforward engineering exercise to calculate how large a gas bag would support a small pressure cabin, so that a vessel could descend in the atmosphere of a gas giant to a level where the pressure would not crush the pressure cabin and the gas bag would give the entire craft neutral bouyancy. For extra credit, could it jettiston ballast, expand the gas bag and ascend to a higher altitude, then launch a rocket to escape the planet? Edison (talk) 18:40, 31 August 2009 (UTC)

Isn't Jupiter also highly radioactive? Googlemeister (talk) 20:09, 31 August 2009 (UTC)

not especially so radioactive in the body of the planet, it is the magnetosphere of Jupiter that is full of radiation. Graeme Bartlett (talk) 21:41, 31 August 2009 (UTC)

Moon

Why doesn't the Moon have an official name? Jc iindyysgvxc (talk) 08:50, 31 August 2009 (UTC)

What about Luna? -- Aeluwas (talk) 10:48, 31 August 2009 (UTC)

The other earth moon is called Cruithne —Preceding unsigned comment added by 79.75.25.53 (talk) 10:57, 31 August 2009 (UTC)

The Moon does have an official name. According to the IAU, it is called "Moon", alternatively "Earth I". Perhaps you are thinking of other natural satellites, which are commonly called moons, with a lower-case "m"? There is only one Moon, the one in our sky. Sorry I can't pop up the link just now, this is my last post before bed. Franamax (talk) 11:47, 31 August 2009 (UTC)

Nahh, I lied, I have one more post in me. From the IAU page, you go to the link they supply and voila - it's called "Moon"! Franamax (talk) 11:56, 31 August 2009 (UTC)

An etymological dictionary[32] implies that until 1665 the only moon to consider was the Moon. The first non-earth moon identified as such was Titan in 1655. (Galileo saw 4 of Jupiter's moons in 1610 but called them the Medician Stars.)Cuddlyable3 (talk) 13:53, 31 August 2009 (UTC)

This is going to get confusing if we ever start communicating with other civilisations. I'll bet everyone calls their moon "Moon". APL (talk) 14:44, 31 August 2009 (UTC)

And I bet everyone also calls their own planet some variation of the theme of "Earth." Thankfully, they probably won't speak English, so we can just call their moon "J'klorb" or whatever their word is. ~ Amory (user • talk • contribs) 15:42, 31 August 2009 (UTC)

• It works for countries here. There are several countries or ethnic groups whose names mean "the people" or "people who can talk" (i.e. in a comprehensible language), but we just use their words for that, or a form of them. Two examples that come to mind are the Slavs and the Inuit. --Anonymous, 20:17 UTC, August 31, 2009.

"They" will probably communicate in high frequency, highly directional pure sound tones that cause your eyeballs to burst when spoken to...83.100.250.79 (talk) 18:35, 31 August 2009 (UTC)

Similar question came up before http://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Archives/Science/2007_September_5#Names_of_Sun_and_Moon

83.100.250.79 (talk) 14:52, 31 August 2009 (UTC)

To sum it up, "There's a moon in the sky; it's called the Moon." --98.217.14.211 (talk) 15:11, 1 September 2009 (UTC)

In English the Earth's natural satellite's name is 'The Moon.' Although Gallleo tried sucking up to the Medicis, Johannes Kepler denominated all secondary objects as 'satellites,' from the Latin for the hangers-on of a famous man (ie the "posse").

"Luna" is incorrect, as it is Latin, not English. Calling the satellites of other planets "moons," while nor absolutely right, only bothers the very pickiest folk.

{{B00P (talk) 01:25, 2 September 2009 (UTC)

Genetic modification of pubic hair for transplant?

Could pubic or body hair be modified by genetic or chemical methods to permanently resemble head hair, and then be transplanted on to balding mans scalps?80.2.197.71 (talk) 10:54, 31 August 2009 (UTC)

Pubic hair (and armpit hair) is about as far from head hair as you can get, but arm hair and leg hair is a bit closer. However, if we could do that level of genetic manipulation, we could convince the hair follicles on the head to produce more hair. StuRat (talk) 11:47, 31 August 2009 (UTC)

The Wikipedia article Hair transplantation reports that transplanted hairs grow and last just as they would have at their original home. It mentions that donor hairs may be extracted from the chest, legs or beard. It does not mention Pubic hair that is often closer in colour to the eyebrows than to scalp hair, but I find no suggestion that genetic modification would be needed to transplant them.Cuddlyable3 (talk) 13:29, 31 August 2009 (UTC)

Spider identification

Unknown green spider.

I don't think I've ever seen a green spider, much less one that was pale and translucent. Anybody know what species this thing is? --ErgoSum•talk•trib 14:11, 31 August 2009 (UTC)

Hmmm, so far it looks like a close match to the green lynx spider, perhaps a juvenile? I'm not an expert on spiders. --ErgoSum•talk•trib 15:02, 31 August 2009 (UTC)

Where (geographically speaking) was this taken? What region/country/state/etc.? Might help narrow down the species. The Seeker 4 Talk 17:44, 31 August 2009 (UTC)

Arkansas. I think the photo of the green lynx spider in the article closely resembles my photo. I'll probably just delete the picture since there is already a better quality photo of the spider in place. I was under the assumption that all spiders were black or brown, so I was quite surprised to see a green spider. Thanks anyway! --ErgoSum•talk•trib 22:33, 31 August 2009 (UTC)

I think your photograph is great. It very clearly shows in detail the structure of the legs. Beautiful. Bus stop (talk) 22:43, 31 August 2009 (UTC)

Yup. I voted keep on Ergo talk page, and have boldly added the image to the article's gallery. --Tagishsimon (talk) 22:49, 31 August 2009 (UTC)

Thanks guys, this is why I love this place! I'll leave the photo uploaded. Happy editing. --ErgoSum•talk•trib 00:19, 1 September 2009 (UTC)

I'm wondering whether the three photographs taken in India oughtn't be removed from that gallery. According to the article, the Indian critter is a different species, P. viridana, which has its own article (albeit a one-sentence substub); and according to the descrptions on the image pages, they are purported to depict still another species, Oxyopes viridanus (which does not appear in List of Oxyopidae species). Deor (talk) 14:17, 1 September 2009 (UTC)

I was wondering the same thing, the spiders in those photos look much larger than the one I saw, which made me think it was a juvenile. I see what you are saying though, the other images are obviously of a different species so I have boldly removed them for now, until somone can confirm they are the same species. --ErgoSum•talk•trib 22:10, 1 September 2009 (UTC)

Swine flu - dead birds

Anyone know of a link between "swine flu", and large apparently healthy looking birds dropping out of trees stone dead - I ask because swine flu has recently been identified in my area, and I have recently noticed an unusually large number of dead birds on the grass verges near to where I live, seemingly not the victims of "road kill" ?

thanks.83.100.250.79 (talk) 15:36, 31 August 2009 (UTC)

I don't think Swine flu infects birds. Here in central California the West Nile virus (carried by mosquitoes) has kille a lot of birds that way, but I don't know whether that could happen in the Sheffield area. Looie496 (talk) 15:41, 31 August 2009 (UTC)

Looie is right. Birds cannot catch swine flus (although pigs can be infected with avian flus, potentially making them very dangerous) so you don't have to worry about that. ~ Amory (user • talk • contribs) 16:33, 31 August 2009 (UTC)

A little followup research shows that there have been reports of West Nile in British birds this year. In California corvids such as crows and magpies have been most strongly affected -- do you know what types of dead birds you are seeing? Looie496 (talk) 16:52, 31 August 2009 (UTC)

All pigeon type birds, probably Wood Pigeons rather than "town pigeons". No dead crows as yet.83.100.250.79 (talk) 18:11, 31 August 2009 (UTC)

If H1N1 ("Swine flu") had indeed crossed over to birds, that would be a rather worrying thing because that would increase the chances of a gene exchange with H5N1 ("Bird flu") resulting in H5N1 variants being able to be passed from human to human rather than only from birds to humans as currently is the case. SteveBaker (talk) 18:10, 31 August 2009 (UTC)

Of course there a numerous other explanations which don't involve a global human catastrophe, I'm still panicking though, just to be on the safe side...83.100.250.79 (talk) 19:20, 31 August 2009 (UTC)

You could always call your local health authority and ask. When West Nile first came to my region, the public was asked to report any dead crows, jays, other large birds. They might be interested in getting a recent corpse for testing. (And we were told not to handle them ourselves) Franamax (talk) 20:25, 31 August 2009 (UTC)

Yes, already e-mailed local "enviromental health department" as they are called here.83.100.250.79 (talk) 20:34, 31 August 2009 (UTC)

Well, H5N1 had been found in pigs years ago, and while it may not be perceived as as big of a threat as it once was, H5N1 is definitely still around so the possibility certainly exists. ~ Amory (user • talk • contribs) 19:54, 31 August 2009 (UTC)

H1N1 is not synonymous with "Swine flu". There are loads of strains of H1N1, some of which are probably definitely (Avian flu#Subtypes) already in birds. The current outbreak is just one strain of H1N1. --Tango (talk) 20:21, 31 August 2009 (UTC)

This year's pandemic novel swine flu H1N1 virus has indeed been detected in turkeys at a farm in Chile[33] and in pigs in several countries. 75.41.110.200 (talk) 03:26, 1 September 2009 (UTC)

Bug control with garlic water?

Is this advice (found on the Internet) useful or merely wishful thinking? Thanks. Wanderer57 (talk)

"Get rid of bugs on plants by spraying them with garlic water.

Peel and chop three garlic cloves, put them in a mason jar and fill 3/4 full with water. Put on the lid and shake then let soak for a week or two. Place water in a spray bottle and spray directly onto your plants. Do not soak, just mist. Do this for a few days in a row and this should get rid of your problem. Repeat as needed. "

It sounds like a harmless experiment. Why not do it yourself and report the results? It should be a fairly easy thing to check out. It is at least possible that chemicals in the garlic may act as a natural deterrant to some insects. But if you actually do them experiment, you may find out yourself... --Jayron32 18:12, 31 August 2009 (UTC)

And, if it does work, it's possible that garlic developed those strong smelling chemicals exactly because they kept bugs from eating it. I believe many spices developed their flavors that way. While those spices might taste nice when properly diluted, mixed with sugar, etc., the straight plants would also seem noxious to us, in many cases. StuRat (talk) 18:31, 31 August 2009 (UTC)

I will try a experiment at the next opportunity. My sense if that this method actually worked it would be well known that it works and I would not have to ask. Thanks Wanderer57 (talk)

Do snakes has vision

Yes it is true that snakes has eyes but can they see. Or they sence through there toung. —Preceding unsigned comment added by 125.18.239.135 (talk) 18:06, 31 August 2009 (UTC)

See Snake#Perception. -- Coneslayer (talk) 18:07, 31 August 2009 (UTC)

(edit conflict)Sure they can see. Some snakes may not be able to see well, or may use other senses more to help them navigate, but I am fairly certain that nearly all snakes have some sense of vision of some sort. --Jayron32 18:10, 31 August 2009 (UTC)

Many snakes (like rattlesnakes) can also see in infrared... 98.234.126.251 (talk) 05:37, 2 September 2009 (UTC)

The smallest hole water can penetrate

How can I calculate the minimal diameter of hole in flat surface water can penetrate in standart conditions? Renaldas Kanarskas (talk) 20:48, 31 August 2009 (UTC)

You would need to more clearly define what standard conditions are. Water that is under pressure can go through a smaller hole because surface tension is less of an impact, and your pressure is going to probably be determined by how deep the water is at the level of your hole. Shape would also play a part, however, the use of the word diameter would indicate a circular hole? Googlemeister (talk) 21:15, 31 August 2009 (UTC)

20C temperature, 1 atm. pressure. Lets take the heigth of water in, e.g., cylinder, as variable, which we will use in formula. As I understand, it will depend not only on water surface tension but also on contact angle with the the material where the hole is made. Renaldas Kanarskas (talk) 22:17, 31 August 2009 (UTC)

Do you know the relationship between contact angle and 'surface energy'? There is one, but I don't have it to hand - it can be derived however. You can use the surface energy of water/hole material to work out how much energy the H2O will need to leave the bulk water, and enter the hole.

Using an energy distribution equation you can work out what percentage of water molecules have enough energy to enter the hole.

The height of water converts to increased pressure - which gives a change in relative energies on either side of the hole. I'm not sure how to directly relate this to rate of reaction - though it will obviously favour an equilibrium in one direction through the hole.

Is that the sort of calculations you were thinking of making.?83.100.250.79 (talk) 22:43, 31 August 2009 (UTC)

For diffusion of water molecules you need is the molecular size, though the diffusion will be affected by the interaction of the substance the material that contains the hole is made of with water. ie the hydrophobicity of the hole material.

You are looking for the minimum swept area for motion of a H2O molecule.

See Water (data page) - I would estimate somwhere between 10^-10 to 2x10^-10 meter for the minimum size (this is a hole that would only allow 1 molecule through at a time). This is assuming that the material is hydrophilic.

83.100.250.79 (talk) 21:55, 31 August 2009 (UTC)

You seem to be interpreting the Q in a completely different way than I did. I thought the Q was about what size hole would allow drops of water to drip thru, in which case the answer is likely in the millimeter to centimeter range, depending on the material. StuRat (talk) 00:06, 1 September 2009 (UTC)

There are going to be a couple of "knee point" diameters, at which the mass flux per unit-area will dramatically change. Between these "knee points", a continually decreasing diameter will result in slower fluid flow, probably along a rough 1/r^2 law; at the knee-points, this law will probably change. (I don't claim the following analysis to be complete or authoritative, but I think the proper methodology is to consider all the relevant physical effects that impede water flow, and start listing the characteristic length scales that they occur on). Starting with a large hole, the first impediment to flow will be the cavitation limit, which probably occurs around a few centimeters diameter, depending on the fluid head. Above this diameter, the water will exhibit laminar flow down the drain; below that limit, it will start to be predominantly turbulent (and spinning on its way). The next critical point, probably on the order of a few millimeters, is when the capillary action force is going to become critical - the adhesion of water to the wall orifice will approximately equal the force of gravity, and so the flow will be impaired (but not stopped). This rate will be highly dependent on the material the water is flowing through (as mentioned above, with hydrophilic and hydrophobic materials at the extrema). The next limits are going to be permeability limits, dictated by the porosity of the material. Now, the fluid will still flow, but it will do so in a slow, meandering style. This is the regime of reservoir engineering in the parlance of petroleum engineering (or aquifer/water engineering); it is an active area of research, as the presence of fluid inside a porous medium changes the medium's properties - the result is a very nonlinear fluid flow. Assuming a subsonic fluid, I think these are the primary physical scenarios which can occur; if, for some reason, the water is sufficiently pressurized or accelerated, it may also have a sonic-shock crossover, (again resulting in a nonlinear flow analysis). It should be noted that fluid mechanics is one of the most complicated areas of classical physics, and empirical observations often contradict theoretical predictions for even complex models; probably, the best way to get an answer suitable for your needs is to define the regime of interest and experimentally test a few conditions. Nimur (talk) 00:28, 1 September 2009 (UTC)

Masterful analysis Nimur. I recall doing a level-test on a low flowrate liquid distributor in a distillation column once, with 3 mm diameter drip points punched through 3 mm thick steel. I couldn't help but notice that there was no actual water flowing through the holes. As the manufacturer rep, this was a little awkward - but I was the only one in the column, hydrocarbon service has lower surface tension, we needed to complete the job, and it wasn't near as bad as the other liquid distributor which you could tell by eye would definitely overflow. Me keeps mouth shut - but you are absolutely right about boundary conditions where the expected equations break down. The flow regime determines the equations you use, and the knee points are critical. Oh yes, also the OP left out the liquid head/kinetic energy in defining the problem.Franamax (talk) 02:33, 2 September 2009 (UTC)

I can't help wondering if this condition is meant, in which any further increase in height causes the droplet to burst - ie the contact angle is "90 degrees" ? HappyUR (talk) 12:51, 1 September 2009 (UTC)

click to expand

Ok, imagine the hole is made in the material thickness value of which we can neglect. Will it be possible to express a hole diameter only in values of pressure of water, surface tension of water and contact angle?Renaldas Kanarskas (talk) 17:20, 2 September 2009 (UTC)

Cockroaches

Do they live in herds? If they do, how big are those herds? --Soppaluu (talk) 21:57, 31 August 2009 (UTC)

See Cockroach#Behavior for some information. In short, they aggregate into complex social groups and display emergent behavior. By the way, the collective noun for cockroaches is unlikely to be "herd"., According to List of collective nouns for fish, invertebrates, and plants (unsourced), it is an "intrusion of cockroaches", though various academic studies seem to prefer the term "group". As for the size of these groups, it seems to depend on resources available. According to Cockroaches: ecology, behavior, and natural history by William J. Bell, Louis Marcus Roth, Christine A. Nalepa, up to 100,000 have been observed in a single apartment (nice!), however in general most species live in much smaller groups: on average 2-8 adults and 5-8 nymphs. Rockpocket 22:28, 31 August 2009 (UTC)

Would New York City's subway be designed any differently now?

Sagittarian Milky Way (talk) 23:01, 31 August 2009 (UTC)

If someone were building a subway now, in a dense city like New York (and you wouldn't build a subway elsewhere) then the cut-and-cover method used to build the new york subway would probably antagonise too many people. The advent of tunnel boring machines makes a deeper bore a more affordable option than it was when the NY subway was built. Other than that, electric light rail is much the same world over, and new underground systems are built with mostly off-the-shelf components, and one is much like the others. -- Finlay McWalter • Talk 23:07, 31 August 2009 (UTC)

Also bear in mind that it grew organically (see History of the New York City Subway) , and that if starting from scratch now the designers would be able to optimise for current population and travel patterns.

Did you have a specific aspect of design you had in mind - there are many - architecture, route, technology used, track geometry, construction methods and materials, etc

Have you considered any of these or were wondering about a specific area?83.100.250.79 (talk) 23:37, 31 August 2009 (UTC)

Also please try to think a little for yourself, or at least show that you have attempted to consider some part of your own question.83.100.250.79 (talk) 23:38, 31 August 2009 (UTC)

I was thinking of locally specific, mostly routing, there's not much to be said in the ways of tech that's either not obvious (use fluorescent tunnel lighting), or didn't change) Unless you're a real subway buff, you won't be familiar with every line, so someone might notice something I haven't. Here's what I noticed: In Manhattan, there's a bias of service to the West Side. The D and the 4 run like 500 feet apart for miles in Bronx, a seeming lack of desire to go turn from Manhattan early to go into Queens. The 42 St Shuttle saves only one stop over the 7, the PATH and MTA duplicate service in Manhattan. Many PATH stations are very close to sea level. and their tunnels are below it (tropical cyclone storm surge + high tide + 21st century sea level rise). Queensboro Plaza and Queens Plaza not having transfers. A small stretch of Flatbush Avenue in Brooklyn with two lines whose stations seem to be avoiding each other. Incompatible car widths and platform clearances might prevent certain better routings. All because the system was built by 3 differant companies competing for riders. Sagittarian Milky Way (talk) 06:57, 1 September 2009 (UTC) edited 21:08, 2 September 2009 (UTC)

Routing is the most difficult of all the questions you could have asked :)

It would probably be easier to rebuild the entire city from scratch :)

One suggestion I'd make lightly is to have entirely parallel N/S tracks (under manhattan) turning east at S end (no crossing points) - with a series (about 6) of shorter high capacity crossing routes (again starting at the west end under manhattan) connecting 'at right angles' (topologically speaking) all the N/S tracks - this would have the effect of meaning that no subway journey would require more than 2 changes.

Where meaninful the e/w tracks could be extended east, and fanned out to form full length lines

Basically a grid system with dangling ends going into the subburbs.

It's not based on any knowldege of new york...83.100.250.79 (talk) 12:22, 1 September 2009 (UTC)

That's all my guess, and I am breaking my own rules by posting it, there's no reason I've got to suggest that it would be any better than any other sensible suggestion, OR, better than the current system that has grown and been modified 'organically'...83.100.250.79 (talk) 14:27, 1 September 2009 (UTC)

Novel idea. Like a street grid or Interstate made out of railroads. Somehow, I'm wondering if this would help the most unlucky station pairs and commutes at the expense of the city having slightly longer morning commutes on average (the time when people probably care most about shaving minutes) Because the current like for Midtown- and Downtown-favored glancing angle crossing and merging lines would be shorter than doing everything at right angles. Thankfully, the presence of Central Park allows some of the trunk lines to be peeled off in the current system without causing a shortage of lines in the Upper Central Side (as you can't annoy the commutes of people who don't exist) Sagittarian Milky Way (talk) 21:08, 2 September 2009 (UTC)

They would likely build it deeper down, as there's more stuff in the way at shallow depths now due to all the construction since then. StuRat (talk) 00:00, 1 September 2009 (UTC)

If you're interested specifically in how a new line would be constructed today see Second Avenue Subway. That doesn't say much about how the overall system would be designed if it were built today, but it provides some insight into things like construction methods. Rckrone (talk) 00:04, 1 September 2009 (UTC)

I don't know about the state of the NY subway now, but when I was there in 1996, I was negatively surprised by the construction quality, poor station layout, and state of the rolling stock. The noise was unbelievable compared to the more modern designs I was used to from e.g. Munich (essentially all remodeled for the 1976 Olympic games and kept reasonably up to date since). I think a new system would probably be somewhat deeper, more level along the tracks, and the stations designed more generously, and much higher (for improved lighting, better ventilation, and less claustrophobia). I also suspect new routes would be found to correspond to current and anticipated commuting patterns. Again, in Munich distances from the city center influence housing prices, but "distance" is not measured in meter or miles, but in minutes, usually walking to the next light rail station and riding into the city. As a result, housing prices essentially follow the star shaped layout of the light rail network. --Stephan Schulz (talk) 07:45, 1 September 2009 (UTC)

Claustrophobic, lol. It seems like a normal interior room to me. Now the huge barrel vaults (a la Washington Metro) seem grandiose and done for the sole purpose of showing off how much volume they can excavate! I suppose it could be cheaper than building all those columns? I never much noticed the noise much, but I see some conductors wearing earmuffs cause they stay there longer than the users. A rubber tyre metro would definately help the people living feet from the elevated tracks sleep much easier.

• I agree, stations like Times Square are way too complicated for what should essentially be a T-junction.
• There are many new cars now, but much the rolling stock was and is from the 60s. Sagittarian Milky Way (talk) 22:21, 2 September 2009 (UTC)

You may also be interested in the Jubilee Line and the major new addition to the London Underground it added quite recently. Some of the stations are very different to 'normal' London undeground stations. The line in the Paris Metro, France one of the lines is entirely automated. I can't remember which but there's basically no driver which makes for an enjoyable view from the front/back of the train. ny156uk (talk) 16:05, 1 September 2009 (UTC)

Ahh it's Paris Métro Line 14 apparently. ny156uk (talk) 16:08, 1 September 2009 (UTC)

• The most significant difference we can be certain of would be that the whole system would be wheelchair-accessible.
• As to technical changes, quite possibly the trains would use an AC power supply, as the technical advantages that DC had 100 years ago no longer exist. Very likely the trains would have either cab signaling or full automatic driving (with or without a human driver), rather than lineside signaling. Certainly there would be a greater ability to control and monitor the trains from a central location. A single width of train would be used for all lines rather than needing to have two separate fleets as now.

Different widths and lengths, that's caused by the competing companies. Stupid, isn't it? Sagittarian Milky Way (talk) 21:08, 2 September 2009 (UTC)

• Subway planners today tend to like to keep the operational patterns as simple as possible, so New York's many junctions where trains cross over from one line to another would be looked on with disfavor. Similarly, 4-track lines with express and local trains are rare in other cities: planners prefer to provide two separate lines instead. So some might argue for avoiding that design in a New York subway built from scratch; however, with the strong north-south traffic in the narrow island of Manhattan, they might find it worth doing there after all.

• New construction probably would not include the elevated sections over streets that are still common outside Manhattan today. (However, going underground adds cost, which leads to the point that any sensible speculation is conditional on the amount of money presumed to be available.) Similarly, we can expect that the airports would be served (if politics and funding permitted). Interchange stations would be planned as interchanges, without the awkward layouts you get when one line is built and another that was never thought of is added later.

• Finally, the system would never be given a prosaic name like "the subway"; there would have to be a political or marketing spin put on it, like "Metrorail" or "Metrolinx" or "The Alfred Beach Memorial - Michael Bloomberg City of New York Underground Transportation System".

--Anonymous, 20:28 UTC, September 1, 2009.

That's an uncannily accurate description of the RAV Line (oops, I mean the "Canada Line") opened a few weeks ago in Vancouver, including the Cambie Street switchover to cut-and-cover to save money, with the minor result of absolutely devasting the local mechants. Automation, central operation, airport access - all there. I do like the idea of express lines though. Is the existing NY metro quad-tracked? Franamax (talk) 02:56, 2 September 2009 (UTC)

In much of the system, it is. The 2 platforms are usually between the tracks in express stations. Sagittarian Milky Way (talk) 21:08, 2 September 2009 (UTC)

The provision of express trains on separate tracks is one of the most distinctive characteristics of the New York system. It generally isn't done over the full length of each line, but is done over the busiest section of many lines. On the outer portions often one 2-track branch feeds the express tracks and another feeds the local tracks. A few secondary lines are entirely 2-track. There are also a few lines with 3 tracks, allowing for express trains in the rush-hour direction only. --Anon, 03:55 UTC, September 2/009.

Some other details nobody has mentioned yet: First of all, the stations would prolly be built with vaulted ceilings, which would eliminate the need for columns (like many stations on the Washington DC subway). The ventilation system would incorporate air filters to remove car exhaust gases from the air before admitting it into the subway tunnels, and prolly some kind of air conditioning system as well. The tracks would be laid on concrete slabs to reduce maintenance expenses, with rubber pads under the rails to reduce noise. (Welded track might be a possibility too.) The trains would incorporate full rheostatic braking in addition to the normal air brakes. Finally, platform barrier gates might be a good option to prevent people from falling onto the tracks (which is a common type of accident on many subway systems). 98.234.126.251 (talk) 05:59, 2 September 2009 (UTC)

The newer cars (the ones that are brighter) use regenerative braking. It's amazing they didn't do that earlier, considering how much momentum they bleed. Sagittarian Milky Way (talk) 21:08, 2 September 2009 (UTC)

Also, train protection system and electronic track monitoring are recent inventions; earlier rail systems had more clumsy electric or mechanical monitoring, or none at all. Everything's digital now. Nimur (talk) 23:22, 3 September 2009 (UTC)

September 1

Mice Trap

Hi evry one .... i have abig problem with mice and i tried evry thing , but it just wont work , this creature is so clever .

so is an act of dispair i tried to make an electric trap ...

strik one : i take a phase from the source and connect it to a plate then connect the other side of the plate with the earth,then i put some cheese , nothing happened except he got hte cheese.

strike two: i connect a fan to the power then connect the plate to the nutral coming back from the fan , also no use .

strike three : i talked to afreind about the secound try and he said i had should connect the plate to the phase comming from the source to feed the fan because the power coming back wont be enuogh to kill the mice , so i did that and still nothing.

please what should i do , these mice are killing me , and i'am running out of cheese.

why these trys failed....--Mjaafreh2008 (talk) 06:11, 1 September 2009 (UTC)

Mice are fast, but not really that clever. Try some of the many types of traps listed at Mousetrap? If they don't work, its unlikely your Heath Robinsonesque trap will. Rockpocket 06:28, 1 September 2009 (UTC)

Get a cat or two. They'll keep the mice under control. Baseball Bugs ^{What's up, Doc?} carrots 08:54, 1 September 2009 (UTC)

I understood that you connected the phase to the plate and then the other side (same connection!) to the earth. Then how would you expect to cause a small electric shock for instance? It is already a short circuit to the earth, and no voltage drop will go across the rat or mouse. The same problem is done in the second step, where the neutral has almost 0 volts with the earth at all.--Email4mobile (talk) 09:02, 1 September 2009 (UTC)

I had a mouse and tried many method of getting rid of it (I even tried the Manuel Noriega method of playing deafening music). What ultimately worked for me was glue traps, and, as a bonus, they also trap insects. Unfortunately, they are exceedingly cruel, leading the mouse to rip off half of it's face in an attempt to escape. When I saw this I finished him off by drowning, which surprisingly only takes about 12 seconds for a mouse. StuRat (talk) 13:35, 1 September 2009 (UTC)

Mice are not clever, but they are cautious. This is what our pest control professional told me. Start with a regular mousetrap, and bait it but don't set it (peanut butter works well). Leave the trap there until there are signs of the bait having been eaten. Then rebait and set the trap. DJ Clayworth (talk) 14:41, 1 September 2009 (UTC)

Why try to reinvent the wheel? Victor sells an effective battery powered electronic mouse trap [34]. It uses a computerized circuit to detect the presence of the mouse with a low voltage resistance measurement circuit, then when a mouse is present, it applies pulses of several thousand volts several hundred times a second for several seconds. It signals with a flashing LED when the mouse has been killed. The mouse is not left struggling on a glue trap for days, and it is not likely to get away like with snap traps. Nor does it get a leg caught in a snap trap. 4 AA batteries are enough to serially kill 50 mice. Edison (talk) 16:26, 1 September 2009 (UTC)

hi guys .... can any one explain to me whats wrong with my circuts , for example the first try ... why did'nt the mice died he stand over a plate connect to the phase from aside and with the earth from the other side...if any one of us grap awire connected to the power source while his legs touching the ground he will died , is that right or what...? its not the mice problem only ... i need to understand why it does'nt work..?--Mjaafreh2008 (talk) 18:26, 1 September 2009 (UTC)

Dude! If you are serious?? If you are i think you are lucky you haven't fried yourself yet. Do NOT play with mains power, far out. I'm surprised no one has said this yet. You must be crazy. Trust me, that is NOT the best way to kill the mouse, it's the best way to kill yourself! And if you do manage to kill the mouse, you'll quite possibly also start a fire and burn your house down. Firstly and hopefully your house is fitted with a Residual-current device which maybe has already saved your life. If you don't then it's probably just lucky you aren't already dead. STOP immediately and find a purpose built mouse extermination solution. Vespine (talk) 02:09, 2 September 2009 (UTC)

I agree, there's no need to risk your life to dispatch a mouse. As for the glue-board method, there's no need for them to last for days, just check your traps a couple times a day. The mice also seem to start squeaking when so trapped, so they act as an alarm to alert you that the trap has worked. StuRat (talk) 15:45, 2 September 2009 (UTC)

I agree that the experimentation you are doing is likely to result in someone dead. What if a child finds it and picks up the wires? Or a pet? Or a janitor/cop/grandma? From your talk of hooking a fan into the circuit, it just sounds like you are not skilled enough to be working with mains voltage electricity. Please stop before you or someone else gets injured or killed. Your vaguely described circuit had no provision to make sure the mouse was touching phase and ground at the same time. Even if he were standing on the grounded part, his whiskers might vibrate and alert him of the presence of high voltage on the other part, or he might touch it tentatively and just get a painful shock, causing him to jump off. The commercial electronic trap as I said uses a low voltage, probably undetectable, to make a continuous resistance measurement to detect resistance below one megohm, then applies thousands of volts in a series of pulses for the kill. It is built so there is no quick escape, and it is built so it is unlikely someone would poke a finger inside and get injured. Edison (talk) 15:48, 2 September 2009 (UTC)

Strange calculations of C

Can you have a look at this website [35]; although it is discussing the speed of light in a sort of religion or philosophy. I tried hard to understand the calculations but because I lack for sophisticated knowledge in astronomy, I think someone here might understand them better. What I need to understand; are those calculations completely true and accurate? or is there some trick in the calculations?--Email4mobile (talk) 07:56, 1 September 2009 (UTC)

here is a quick link to the calculations [36].--Email4mobile (talk) 07:59, 1 September 2009 (UTC)

It looks like a big fudge to me. Cutting through the verbiage and hyperbole, here's what seem to be going on at that site:

1. A rather strained interpretation of a verse from the Quran that says "this affair travels to Him a distance in one day, at a measure of one thousand years of what you count" is used to create the claim that the distance travelled by light in one day is equal to the distance travelled by the Moon in 12,000 orbits around the Earth. First fudge: there are not exactly 12 lunar orbits in one year - even if you use the synodic period of the Moon, 29.5 days, the Moon goes through approximately 12.4 cycles of phases in one year. But if you calculate the distance that the Moon travels in 1,000 years you get about 1.24 light days, which is 24% greater than claimed - so the time period has been rounded down to 12,000 lunar cycles to reduce this error.
2. A calculation of how far the Moon travels in 12,000 synodic periods gives about 1.2 light days, so this is still a 20% error. Second fudge: to further reduce the size of this error, the site switches from synodic periods to the shorter sidereal period, 27.3 days. In 12,000 sidereal periods, the Moon travels about 1.11 light days - so still an 11% error.
3. There is then a very complicated argument that claims that if the gravitational influence of the Sun is removed (why ??) then the Moon's orbital speed and the Earth's speed of rotation (and hence the definition of "one day") would change by just enough to compensate for this 11% error. This looks like one big third fudge to me.

Gandalf61 (talk) 09:28, 1 September 2009 (UTC)

I guess the website refers to 1 lunar year, because for Arab, the year deal with is around 354 days not 365, and that's why the arguement confirmed, "...of what you count" in the Quran. The 3rd point you mentioned was the one I couldn't get along with and thus asked for some more information.--Email4mobile (talk) 09:58, 1 September 2009 (UTC)

Even if the site uses a lunar year, i.e. 12 synodic periods, as the definition of one year, then point 2, the switch from synodic periods to sidereal periods, is still a big fudge. 12 sidereal periods, or 327.6 days, is a completely arbitrary time period, unrelated to any definition of a lunar year. A lunar year is much closer to 13 sidereal periods than to 12. Gandalf61 (talk) 10:42, 1 September 2009 (UTC)

Thank you very much, Gandalf61 for clarification. I don't lime like to mix science and religion by all means. It was just a curiosity to do so. I am still wondering how they could play with values till they got a so precise light speed value.--Email4mobile (talk) 13:47, 1 September 2009 (UTC)

This is obviously bullshit. They cheated - rounded things off, used fudge factors, were suitably vague about details. If you are allowed to do that, you can come out with any answer you like. Hey have you noticed that PI is exactly equal to the square root of 10 minus the phase of the moon in radians on the day that the IPU (mhhbb) first ordered a pineapple and ham pizza? Ha! Proof! May the world quake at the passage of her dung! SteveBaker (talk) 20:31, 1 September 2009 (UTC)

Forgive me friends for my non-native English and typos. I'd like when discussing such tricky calculations to understand them better in order to argue. I sent the website author some further questions and then argued with him but he replied "My physics is perfect. Maybe the problem is with your ignorance." --Email4mobile (talk) 23:00, 3 September 2009 (UTC)

Pin tumbler lock

What are pin tumbler locks usually made of? Would aluminium make sense? It's for a video script we're writing. Anthrcer (click to talk to me) 12:51, 1 September 2009 (UTC)

Aluminum is soft, so that would be surprising. I'd guess steel. --Sean 14:20, 1 September 2009 (UTC)

No, not aluminum. I think brass is the most common material for the pins and plug, and steel the most common material for the casing. This page also lists die-cast zinc as an alternate possible material for the pins and plug, and brass as an alternate possible material for the casing. Red Act (talk) 14:50, 1 September 2009 (UTC)

I key my own locks. I have a box of pins precut to the normal sizes. They are all brass. I have seen silvery ones (zinc, I assume), but the set I purchased came in all brass. -- kainaw™ 18:27, 1 September 2009 (UTC)

perchlorate

I'm a bit puzzled by the hypervalency of this ion ... is it anything like the hypervalency of sulfur? Am I right in thinking that this feat of oxidising a halogen prolly wouldn't work as well with fluorine (seeing as it's period 2?). I also wonder how the oxygens protect the chlorine so well ... to me the oxygens still have reactive lone pairs, don't have complete double bonds (7 electrons among 4 oxygens!). Why is the system so stable? I mean, overall I guess with all these electronegative atoms the system is strongly electrophilic ... but I guess the actual negative charge of the ion repels most electron donors away? Also ... how do you get resonance in a tetravalent system? Perchlorate isn't planar...John Riemann Soong (talk) 13:00, 1 September 2009 (UTC)

How polar is the Cl-O bond anyway (MO-wise)? If the bonding orbital is closer to period 2 than period 3, I guess that would keep the bonding electrons well protected? What would be the attack mechanism for reducing this system? John Riemann Soong (talk) 13:09, 1 September 2009 (UTC)

ClO4- is 'made' exactly the same way as SO4- , in fact the two are isoelectronic, both are tetrahedral, both can be considered to be made by electron donor bonds from Cl/S to O atoms (6 electrons). (the O can be considered a lewis acid)

First row elements including fluorine don't do this - the electron lone pairs are there - but they are too low in energy to effectively bond with other neutral atoms (under usual conditions), the lone pairs can bond with positive ions such as R2O + H+ >> R2OH+

There's a obvious exception for N which is R3N + O >> R3NO (see Amine oxide)

These donor bonds are also known as "dative bonds" or "donor coordinate bonds" - they usually occur when a lewis acid bonds with a lewis base, in this case the lone pairs on chlorine can be formally thought of as a lewis base, and the oxygen atom (6 electrons) as the formal lewis acid. In all cases of 'donor bonds' one atom donates both electrons for bonding, rather than each donating/sharing one such as found when two H atoms bond. —Preceding unsigned comment added by 83.100.250.79 (talk) 14:16, 1 September 2009 (UTC)

The perchlorate system is kinetically stable because all atoms have their 'octets' filled - it's a perfectly legitimate structure , plus the tetrahedral symmetry will help a bit. Of course perchloraate is not thermodynamically stable at all.

Compared to ClO3- , ClO4- lacks a free lone pair on Cl - this reduces the number of ways it has to react, and contributes to it's higher kinetic stability.

You don't need planarity for resonance (this is a complex topic: sometimes you do - depends on the bond type)- the resonance (per bond) in this case includes :

Cl+-O-  <>  Cl:→O (donor bond) 

The Cl-O bond is expected to be polarised with negative charge on O

As for attach mechanism - as mentioned above Cl04- lacks attack mechanisms that other ClOn- species have, it also is non polar overal (due to symmetry) which doesn't help.

I don't know the mechanism of perchlorate reduction, though at a guess it would involve electron transfer to give an unstable Clorate(6) radical *when in acid solution - it would be the major difference in stabilities between the two chlorates that cause this reaction to have a high activation energy

ClO4- +2H+ +e- >>> H2O + Cl03· (radical)

(Note that the reduction of ClO3- to ClO2· results in a radical that can be stabilised by resonance onto a Cl lone pair

          O                O
          |                |
        O-Cl-O           O-Cl:          (the Cl-O bonds are donor bonds , not single bonds
          ·                ·                I can't find the correct symbol though...)
    
     ClO3 radical        ClO2 radical (can stabilise radical via resonance onto lone pair)

Cl03- , Cl02- , Cl0- all react much faster in general than ClO4- due to this effect (I think) —Preceding unsigned comment added by 83.100.250.79 (talk) 13:49, 1 September 2009 (UTC)

There's a possibilty that you might have noticed of stabilising the radical onto the oxygen

          O                O
          |                |
        O-Cl·            O-Cl:
          |                | 
          O                O·

The reason that this doesn't matter much is that second row elements are much better at stabilising radicals that first row (and so on for 3rd and 4th row..) - I general - moving down the periodic table the stability of non-standard molecular structures increases - due to various reasons..

So the stabilising effect of a Cl is much more than that of an O where radicals are concerned.

(Don't quote me on the reduction mechanism in an exam! I'm not sure what it is - that was a guess)83.100.250.79 (talk) 13:54, 1 September 2009 (UTC)

Wonderful as always. Thanks! Hmm, I am very curious now about possible attack mechanisms though. The thing I find interesting is that perchlorate is thermodynamically electron deficient (thermodynamically a strong oxidiser), but it carries a net negative charge, which would probably repel most electron donors away. Yet however, the pKa of perchloric acid is like -10, so I imagine H+ doesn't want to stay on perchlorate for very long! And of course, in explosives, you don't need the presence of magic acid (or sulfuric acid), do you? Or is that what some of the sulfur components in explosive mixtures are for? Is there an "attack mechanism" under high heat? Would it be as simple as high heat ripping the Cl-O bond apart? Given that both Cl and O are strongly electronegative, I don't think the bond energy would be very high, would it? What about polarisability? Would it be possible that at certain moments in time, one of the oxygens would become a bit bluer than the rest, leaving a small window for electron donation to occur or something to pull the oxygen off?

Say, something is burning and you have a hydrocarbon radical being formed or something (C-C bonds broken apart by high heat?) So I'm thinking something happens along the lines of thermal cracking... forming something like say, R2HC* to perform some sort of radical attack on the oxygen? John Riemann Soong (talk) 22:06, 1 September 2009 (UTC)

Also, what about the nature of the donor bonds? In perchlorate, the bonds are shown as a combination of solid and dotted lines ... but aren't there 8 bonding electrons (mostly being kept by the oxygens)? Do they have "double" donor bonds? I note compounds like chlorine pentafluoride or iodine heptafluoride ... in those cases the chlorine or iodine doesn't have a "full" shell! (Would iodine octofluoride be potentially possible? And why doesn't chlorine heptafluoride occur? Is it too small?) John Riemann Soong (talk) 22:18, 1 September 2009 (UTC)

ok first paragraph - mostly yes - sulphur is in gunpowder to burn - once the reaction gets started - above about 500C the compounds just fall apart into atoms - ending up with whatever is stable (usually oxides)

Yes combustion is mostly radicals (plus some ionised gas once it gets really hot) see Radical_(chemistry)#Combustion and Combustion#Reaction_mechanism the reaction

CH4 + O2 >>>> CH3· + HOO·

is an important one - the carbon radicals become more important when there is not enough O2 - and can polymerise to form soot.

Second paragraph (donor bonds often look like double bonds to a lot of people - but they aren't )

I tend to think of it as Cl- and 4 oxygen atoms - the Cl- has a full octet and four lone pairs, the oxygen atoms have only six electrons - and so need to get 2 to complete the octet.

As for the interhalogen compounds - there are difficult to explain - chlorine heptafluoride doesn't exist because chlorine is too small - 7 fluorines wouldn't fit (or be far too crowded to fit round a Cl atom)

Iodine octofluoride is unlikely at any temperature - maybe IF₈⁺ might exist - you'd need a very powerful fluorinating agent - and I imagine it would just oxidise any counter ion.

I think the problem with IF8 is this reaction

2 IF₈ >>> 2 IF₇ +F₂

Not only does it increase entropy, but is likely to exothermic as well - especially since the I-F bonds are going to be weaker than a standard I-F bond (too many electrons).83.100.250.79 (talk) 01:43, 2 September 2009 (UTC)

Okay I'm kind of confused because it seems to me that Cl and O are interacting in a kind of polar covalent bond (I mean otherwise water could easily solvate away the O) ... it's actually a single donor bond? In terms of MO theory, what's the exact nature of this bond and how do the bonding orbitals form? (The bonding orbitals are located closer to the oxygens, right?) John Riemann Soong (talk) 02:18, 2 September 2009 (UTC)

Does oxidisation get kinetically easier as valency increases from tetravalency? Perchlorate's bonding electrons are well shielded from attack ... but IF8's wouldn't? John Riemann Soong (talk) 02:19, 2 September 2009 (UTC)

Also, wouldn't it be IF8- ... an anion...? (I'm thinking IF7 + e- from an alkali metal + F radical). Or does the fact that the iodine is "crowded" provide an exception to the octet rule? (Too bad astatine isn't stable enough to see if we could get AtF8 ... damn you radioactivity.) John Riemann Soong (talk) 05:06, 2 September 2009 (UTC)

Donor bonds are covalent, and usually polar too. In ClO4- the electrons for bond can be considered to come from the Cl (if you are constructing the molecule from Cl- and 4 O atoms), they are shared between the Cl and O - so this means that the electrons have moved a bit from the Cl towards the O.

Does the reaction:

H3N: + BF3 >>>> H3N:→BF3

make sense - that's a donor bond too - the product can also be written as:

H3N+-B-F3

That's a covalent bond with a strong electric dipole in it.

The situation in ClO4- is similar - except Cl has a more complex set of molecular orbitals - in general any molecular orbitals that are close to both the two atoms will contribute to bonding.

The ease of oxidation depends on many things- mostly the big factor is the stability of the the intermediate, it depends a lot on what type of atom is being oxidised. I can't be more specific.

IF7 + an electron plus a fluoride radical would definately make IF7 plus F- , getting the F- to react is with IF7 is debateable - the F- is a lewis base - to react it needs a lewis acid to bond to. For IF7 to act as a lewis acid it would need to add two more electrons to it's already expanded 'octet'

I agree that IF₈^- is not a bad idea - it has certain properties going for it. It's difficult to show with hand waving arguments, or using calculations that it will not exist. What about

 IF8- >>>  IF6- + F2

Would the IF6- be more or less stable than IF8- ?

See also Xenon hexafluoride specifically the part about XeF²⁻
₈ which does exist - it's only one proton and 2 electrons more than IF8-, but otherwise identical.83.100.250.79 (talk) 10:56, 2 September 2009 (UTC)

IF8- and XeF8

Mmmh- according to this IF8- exists http://www.chemthes.com/rxn.php?side=RHS&entity=2542 however there's no reference at all, I'm not sure.

More reliably it seems that XeF8 might exist (which is isoelectronic with IF8- making it's existance very probable) -see http://www.google.co.uk/search?hl=en&q=Xenon+octafluoride+synthesised++sealed+tube&btnG=Search&meta= unfortunately I can't read the whole article.

It's interesting to note the decreasing bond strengths of XeF4 XeF6 as the number of F increases (see here "xenon+octafluoride"&source=bl&ots=NvqEqQNe_P&sig=TpJNiK2cW_6_fSFdgDqfM7LQ0Pk&hl=en&ei=plyeSqPuEsvt-QbUgO3aCw&sa=X&oi=book_result&ct=result&resnum=8#v=onepage&q=%22xenon%20octafluoride%22&f=false google book result)

This paper claims in a footnote [37] page 13 footnote 5, that XeF8 will be unstable to loss of fluorine atoms - but without reference to the calculations unfortunately.

If XeF8 exists then IF8- might exist - however I can't find cut and dried evidence for either. I'll ask a question to see if anyone else knows.83.100.250.79 (talk)

Hmmm, I just discovered xenon tetroxide.... it's tetrahedral with its bonding electrons well-shielded but now I wonder why the perchlorate ion isn't as explosive ... is it that the anionic nature of perchlorate stabilises the thermodynamically electron-deficient perchlorate somewhat? Or does the large size of xenon make it easier for oxygen to break off spontaneously? (And shouldn't they be resonating in the zrticle's Lewis structure?) John Riemann Soong (talk) 17:22, 2 September 2009 (UTC)

That's a good question - the isoelectronic species is (periodate) iodate(VII) IO₄^- which is stable as a salt and in solution just like perchlorate - the obvious answer is as you say - that the ionic bonding in the salt, or solvation energy of a the salt in solution gives enough addition stabilisation. I can't think of another reason for extra stability - though the difference in stabilities is vast.

It's worth noting that there are other compounds that are stable as salts or in solution, but attempts to make the free (covalent) acid (or the acid anhydride/acidic oxide) are generally met with failure.

An example of this is permanganate - potassium permangante though a strong oxidant is stable enough to be sold in chemists - it does decompose above ~230C (according to the article - I think this is right) but not explosively on it's own (usually) - however the free acid HMnO₄ is unknown as a pure compound, and the corresponding oxide Mn₂O₇ is dangerous above room temperature see Manganese heptaoxide and has a reputation to explode.

So thats a difference of over 180C in the decomposition temperature going from covalent substance to the ionic salt. I think the stabilisation from making an ionic salt must make a huge difference.83.100.250.79 (talk) 18:51, 2 September 2009 (UTC)

Almost forgot there's also Dichlorine heptoxide to compare with perchlorate as well - similar comparisons apply - perchlorate salts can be bought/transported etc fairly safely. The oxide is far to unstable to do the same.83.100.250.79 (talk) 19:13, 2 September 2009 (UTC)

And the XeO4 structure is problematic - I'd tend to write it as a donor bond, Xe:→O for each oxygen, as this sticks to the octet rule, Xe⁺-O^- is also valid (and also sticks to the octet rule) (the two forms are basically equivalent)

As it's drawn in the article it uses double bonds ie Xe=O , this is ok, but implies an extent of bonding that might not be there - ie the bond strength isn't that of a double bond : bond strength ~210kJ/mol , compare with ~220kJ/mol in XeF4 (expected to be single bonds) , though there will be some percentage of double bonding I personally don't think the extent is big enough to justify writing it as double bonds. (the comparison with XeF4 may not be the best one, but I couldn't find other data off hand).83.100.250.79 (talk) 19:39, 2 September 2009 (UTC)

MO wise, what's happening in a donor bond in perchlorate or XeO4? I guess I'm puzzled what happens here (my sense of chemistry totally breaks down). There's no pi system so that's why it's not a double bond, right? Would the donor bond be .... an sp3 orbital? Would the oxygens have 3 lone pairs each? Would most ab initio calculators be accurate if I used them in this situation? Ahhhh...John Riemann Soong (talk) 22:49, 2 September 2009 (UTC)

Re: ionisation -- I wasn't thinking solvation stabilisation so much more as the fact that both XeO4 and perchlorate are quite electron-poor systems and that perchlorate is an anion. John Riemann Soong (talk) 22:51, 2 September 2009 (UTC)

The orbitals are tricky, for O each O is in a triangularily symmetrical enviroment - therefor orbitals with triangular symmetry are sensible eg sp2 or sp3. In general the highest unoccuppied molecular orbitals will be the ones that do the bonding (provided they point in the right direcion - not a problem here) - so for O this will be the p orbitals - it could well be that most of the bonding comes from a pure p orbital, however since the lone pairs will want to repulse away from the Xe, probably sp3 is the best bet.

For Xe (as a donor) the highest occupied orbitals will be doing the bonding - I'm not sure - this could be some combination of the highest s, p or d orbtials. (see HOMO/LUMO for more details, as well as the Xenon page for its electron configuration)

Calcuations might help - I'm not sure how good they can be nowadays - with the increase in computing power to optimise molecular orbitals, years ago such calculations would have been impossible/useless.

As an aside if the possibility of pi bonding is considered it could be constructed like this:

- consider the hybridisation on O as p + 3 sp2 orbitals - if the p orbital forms the main bond to the Xenon (remember that Xe is spherically symmetrical so there are no problems with symmetry problems) - then the sp2 orbitals (at right angles to the p bond) can point between the other Oxygens - eg when looking down a Xe-O bond there would be a six pointed star - Oxygen/sp2orbtial/oxygen/sp2orbital/etc )

The other oxygens can do the same. Xe is a big atom so there should be some molecular orbital overlap (side on as in all pi systems) between the Xe orbitals and the sp2 orbitals.

So all the 4 O sp2 orbitals will be pointing (in sets of 3) to the points of a tetrahedron on the surface of Xe, this tetrahedron, and the tetrahedron of the molecule itself will be inverts of each other (ie consider the octahedron made up of 2 tetrahedra)

If this happens the that will be a spherical 'pi' system around the xenon, between the O atoms, (and made up of sp2 orbitals not the usual p (!)) - this is getting close to what starts to happen in clusters of metal atoms. However because Xe and O are electron rich both the bonding and antibonding orbitals will tend to be filled - this the 'pi' system, if it existed wouldn't contribute much to bonding, if at all... Yet another reason to expect sp3 on oxygen.83.100.250.79 (talk) 14:09, 3 September 2009 (UTC)

Surface tension image - comment

Surface tension this image

To me it looks like a huge paperclip on a blue cushion, with some drops of water added for effect - can anyone explain how it looks? 83.100.250.79 (talk) 13:21, 1 September 2009 (UTC)

It looks...like it looks--not sure what you're asking really. There is a blue glass surface covered with water and a paper clip floating on the water. DMacks (talk) 14:06, 1 September 2009 (UTC)

I think it's actually the rim of a drinking glass. It's a close-up photo. The uneven edges of the water and reflections (click the image for a closer look) mean it doesn't look like a cushion to me. AlmostReadytoFly (talk) 14:10, 1 September 2009 (UTC)

It looks more like a paperclip on the surface of a can of paint to me. Googlemeister (talk) 14:17, 1 September 2009 (UTC)

Maybe the skin on top of some blue paint? with a paper clip on, plus some water drops around the loops of the clip?83.100.250.79 (talk) 14:33, 1 September 2009 (UTC)

Ah yes, it actually is top lip of a blue drinking glass. DMacks (talk) 14:20, 1 September 2009 (UTC)

The glass sides are not blue, but the rim is, and the 'water' surface is exactly the same colour as the blue rim!!83.100.250.79 (talk) 14:29, 1 September 2009 (UTC)

Also look at the bottom (picture) two loops of the paperclip - there appears to be water droplets on the loops, on top of the "blue water" surface :)

83.100.250.79 (talk) 14:31, 1 September 2009 (UTC)

No, what you identify as droplets are the reflections I mentioned earlier. It's more obvious if you look at the full size image. What the reflection is of, I'm not certain. Something interesting on User:noodle snacks' ceiling, perhaps.

At the full size, you can also see part of the paperclip underwater, without there being any join from water to "cushion". AlmostReadytoFly (talk) 14:45, 1 September 2009 (UTC)

this other variant makes it more clear what is going on. The "cushion" effect is just how the light is hitting the glass on the other side of the water. -98.217.14.211 (talk) 14:31, 1 September 2009 (UTC)

I'm very suspicious - where is the ref desk fraud squad when you need them?83.100.250.79 (talk) 14:36, 1 September 2009 (UTC)

Right. The whole point is that surface tension does make something of a cushion effect, or a fabric layer rather--the water bulges up out of the glass like a muffin and the paper clip depresses the surface a little still on it without actually falling completely into the water. You could always email the photographer and ask him the details. DMacks (talk) 14:39, 1 September 2009 (UTC)

I assume that the inside of the cup is blue. And the reflections are of the scaffolding used to hold up a set of professional photography lights. ... But what's causing the hard edge between the reflecting portions of the fluid and the blurry (See-through?) portions of the fluid. Are those bubbles?

This is an amazing photograph. Anyone can balance a paperclip on water and get that "Cushion" effect, but to photograph it so dramatically takes a lot of skill and effort. APL (talk) 15:05, 1 September 2009 (UTC)

That picture looks pretty realistic to me. I don't think it's a fraud. Dauto (talk) 16:24, 1 September 2009 (UTC)

You can do this right now. The trick is to slowly place the paperclip on the water so that it doesn't break the surface tension. Generally, the easiest way to do this is to bend a second paperclip into an "L" shape (just pull the middle portion out at a 90 degree angle to the outer portion). Use this "L" to very slowly lower the other paperclip into the water. The paperclip will float gently off and look exactly like the above picture. --Jayron32 16:55, 1 September 2009 (UTC)

But it doesn't look like that image - it looks like this (see), the image doesn't look right for a blue glass either - it looks like the liquid is blue - see the striations in pigmentation on the surface (to the left of the paper clip, starting about the middle of the paper clip going roughly horizontally left) - looks like paint to me?83.100.250.79 (talk) 17:08, 1 September 2009 (UTC)

As I said before, if you look at the full size image, you can also see part of the paperclip underwater, without there being any join from water to "cushion" (or paint). If it were paint, that wouldn't work. AlmostReadytoFly (talk) 20:26, 1 September 2009 (UTC)

Why is there a total absence of refraction or reflection effects except at the loops of the paperclip? 83.100.250.79 (talk) 20:42, 1 September 2009 (UTC)

Most of the surface is actually a reflection from the main light source per below. Noodle snacks (talk) 03:09, 2 September 2009 (UTC)

If you are just concerned about the coloration of the water, any number of lighting effects could lead to that; it could just be a result of the type of room lighting, camera flash, or an artifact of the way the camera recorded the image which could result in such coloration. I see nothing in the color of the water that makes me to believe it isn't water. --Jayron32 20:47, 1 September 2009 (UTC)

The rough lighting behind the shot

Speaking here as the photographer. Per the caption in Surface tension the water is in a blue glass. I have updated the file caption to reflect this as well. The explanation for the appearance can come purely from the lighting used. The water facing in the right direction (including flat) is reflecting the light source, a white umbrella. Other parts of the surface are letting the light through from below the surface. That light is blue due to a tinted glass. The reflections that User:AlmostReadytoFly refers to are the silver support arms of the umbrella. I've thrown some bits and pieces on to the kitchen table and took a shot of it all, giving you some idea what is going on, though things haven't been put together very carefully or in exactly the same way. And yes, my poor old radio trigger is on it's last legs, held together with glue and duct tape. I feel that this method is initially a little less clear, but it does let you see the shape of the surface very well. I will add a link to the lighting demonstration in the file caption to help clarify this. --Noodle snacks (talk) 03:08, 2 September 2009 (UTC)

Oh, as far as Surface tension goes, it wouldn't matter if the fluid was paint. Surface tension is a property of many liquids. Noodle snacks (talk) 03:20, 2 September 2009 (UTC)

Thanks for coming and explaining - (I still can't persuade my eyes to see it right) - I suppose the 'flat' or 'silk' effect on the surface of the water comes from the surface of the special reflecting umbrella then.83.100.250.79 (talk) 11:39, 2 September 2009 (UTC)

Chemistry

Can Hafnium be mistaken for Thorium 232 during gamma spectrum testing —Preceding unsigned comment added by Radioactiveman6552 (talk • contribs) 14:25, 1 September 2009 (UTC)

Optical beam combiner?

I am working on a DIY project that involves mixing the output from an array of red, green, and blue LEDs to create a single color. Is there some sort of way to easily mix the light output from the different LEDs besides putting some sort of diffuse, semi-opaque sheet of material in front of them? Could I use lenses or mirrors to achieve the same effect? Thanks so much. Ilikefood (talk) 15:48, 1 September 2009 (UTC)

EDIT: Sorry, forgot to mention, the LEDs will be red, green, and blue Luxeon Rebel Stars from http://luxeonstar.com/ , arranged in a hexagonal grid. Ilikefood (talk) 15:52, 1 September 2009 (UTC)

You can buy a beam splitter, and run it "in reverse"; but you're going to lose significant energy to reflections, so it will suffer from brightness problems. Also, these tend to be expensive, and large compared to an LED. I think a diffuse surface will be better suited to a small hobby project. Thin tissue paper will work. Nimur (talk) 16:00, 1 September 2009 (UTC)

Are there any materials that are a bit more durable than tissue paper, but will diffuse the light about the same without losing too much brightness? (Like some sort of readily-available plastics?) Ilikefood (talk) 16:10, 1 September 2009 (UTC)

Sure - you can search for frosted glass, or frosted acrylic / frosted plexiglass, which are available from suppliers. (If you search your phone book for "acrylic", you will probably find some light-industrial suppliers in your area); or you can mail-order frosted acrylic or frosted plexiglass via the internet. Various thickness are available; depending on your needs, these may be suitable. Nimur (talk) 18:30, 1 September 2009 (UTC)

It seems like in theory a prism could be used to line up the images of the 3 LEDs. There might be practical problems with that. I don't really know. Rckrone (talk) 16:43, 1 September 2009 (UTC)

How about a lens with a really bad spherical aberration? Would that work as well as the tissue paper method? Ilikefood (talk) 16:47, 1 September 2009 (UTC)

Why should we bleed when blood pressure is lesser than atmospheric pressure?

The atmospheric pressure is 790mmHg and our blood pressure measures 120/80mmHg. Blood being a fluid is supposed to flow from high pressure to low pressure. Then we are not supposed to bleed when cut, on the contrary air must rush in to cause embolism. I am quiet convinced that my understanding went wrong somewhere or does it mean that the blood pressure measured is 120/80 mmHg above atmospheric pressure(since the atm pressure acts on the blood pressure cuff too), if yes why should'nt we say 910/870 mmHg? please help me out.Neduncheralathan (talk) 16:31, 1 September 2009 (UTC)

Blood pressure is the pressure exerted on the walls of the blood vessels. Think of a balloon if it makes it easier. Just sitting there, uninflated, there is some air inside. That air is exerting the same pressure on the inside of the balloon as air on the outside of the balloon. If I say that I put 10 pounds of air in a balloon, I mean that there is 10 more pounds of pressure inside than outside. Blood pressure is the same. There is 120mmHg more pressure inside than outside. As for why don't add atmospheric pressure to it... It doesn't matter. I brought the following up earlier and some others felt the need to say it was completely wrong. We don't need to know our exact blood pressure. We need to know our blood pressure relative to everyone else. When we say "below 140/90 is controlled blood pressure", we mean that those who get a reading of below 140/90 on a blood pressure measuring machine have a blood pressure that does not pose a high risk for heart attack or stroke. If the machine used letters instead of numbers, we would measure a lot of people and, perhaps, discover that anyone with a blood pressure letter below J was not at high risk of heart attack or stroke. The numbers don't have nearly the importance as the comparison of values among the population. -- kainaw™ 16:46, 1 September 2009 (UTC)

(edit conflict with above reply) Blood pressure is always the measurement above the current atmospheric pressure. Average atmosheric pressure is defined by international standards to be 760 mmHg (see Standard conditions for temperature and pressure) not 790. But this is a defined standard; not an actual measurement of current atmospheric pressure, which could vary up or down considerably from that average. However, since the blood pressure cuff is currently under that same atmospheric pressure, it is measuring relative to that, not to some hypothetical vacuum state. --Jayron32 16:50, 1 September 2009 (UTC)

Such readings, BTW, are called gauge pressure, as opposed to absolute pressure. See Pressure measurement#Absolute, gauge and differential pressures - zero reference. Your car's tire pressure is also an example of gauge pressure—a flat tire at "0 psi" contains air at the ambient atmospheric pressure, not a vacuum. -- Coneslayer (talk) 17:01, 1 September 2009 (UTC)

(more ec and weird interleaving) The idea of relative (gauge) pressure is right-on here. As to what that's used instead of absolute, it's certainly more convenient to set up a mercury manometer for a pressure range 0–250 mmHg (only has to be 25 cm tall) than 750–1000 mmHg (need a meter height and 4x as much Hg) and probably easier to set up/fill an open-ended manometer than a closed-ended one. I wonder if it really does matter more what the relative pressure is than the absolute because people are kinda squishy: have to overcome the crush of the atmospheric pressure to keep vessels open? DMacks (talk) 17:06, 1 September 2009 (UTC)

Some of the blood pressure is probably overcoming the "crush" of the atmosphere, but not all of it, which makes the attempt to define the absolute blood pressure by addition to be an incorrect method. Most of the pressure in our vessels comes from the integrity of those vessels themselves; if we put our bodies in an absolute vacuum, and measured the blood pressure by the standard method, we would not find a pressure of 800+mmHg. I would anticipate the pressure to be higher than 120/80, but not that much. --Jayron32 20:44, 1 September 2009 (UTC)

What's the closest human equivalent to what a bird feels when going through a heavy moult?

Any suggestions? When my parrots and parakeets have their big moults, it's clear from their body language and demenour that they're feeling like crap. Apart from the obvious all-over itching and possible pain from the pinfeathers coming in, it also seems to suck the energy and playfulness right out of them. I'm just trying to imagine what it might feel like. --84.69.205.30 (talk) 16:44, 1 September 2009 (UTC)

Have you had the flu? Because when I had it, I felt a general lousiness. Vranak (talk) 01:15, 2 September 2009 (UTC)

I have no idea since no one here can definitively state exactly how the bird feels. Maybe a rash would be similar. Just multiply it across your entire body. Googlemeister (talk) 13:43, 2 September 2009 (UTC)

How about if you have an all-over sunburn and your skin starts to peel ? That has the same combo of pain and itchyness, I would think. StuRat (talk) 15:39, 2 September 2009 (UTC)

Combine that with the sensation of teething, perhaps? It's also the case (AFAIK) that whilst still growing in, a bird's feathers have sensation in them - and will bleed heavily if damaged. I can't think of anything that humans experience that could compare to that. The long, thick wing and tail feathers must be hell. --Kurt Shaped Box (talk) 05:30, 3 September 2009 (UTC)

Astronomy: Stray Stars?

Are there thought to be any stars that exist, at least for a time, independent of any galaxies? If so, wouldn't they then inexorably fall into orbit around one galaxy or another, and wouldn't they then to cease to be stray stars?68.166.245.91 (talk) 16:52, 1 September 2009 (UTC)

• Yes, they exist, but no, they will not necessarily be captured by a galaxy within their lifetimes. Stars don't live forever, and galaxies are far apart. -- Coneslayer (talk) 17:04, 1 September 2009 (UTC)

• There are certainly stray stars outside of galaxies - at least those that have been ejected from their original host galaxy via gravitational interaction. Google for intergalactic stars for some hits. Hubble has found some, see [38], and ESO caught one on the run [39]. And while they would, of course, always be gravitationally attracted to some galaxies (well, actually to all in the visible universe), there is no automatism that would ensure that a star would become gravitationally bound to another galaxy - that would require a n-body interaction so that the star could shed some of its kinetic energy. --Stephan Schulz (talk) 17:06, 1 September 2009 (UTC)

If such a star fell into a galaxy it would travel so fast through it, that it would probably come out the other side in a few dozen million years in a hyperbolic orbit. Graeme Bartlett (talk) 22:21, 1 September 2009 (UTC)

It might even fly faster, gravitational slingshot. Sagittarian Milky Way (talk) 22:50, 2 September 2009 (UTC)

Electromagnet Vs Headphones

When an active (recieveing message/phonecall etc) mobile phone is near to a speaker or a set of headphones, it creates an intermittant buzzing sound, and disrupts the sound being produced by the speaker. I've come to understand that this comes from the amplifier in the the speaker picking up the much higher mobile phone frequencies and translating them into frequencies the speaker can produce.

My question is whether an electromagnet can create the same phenominon or disrupt the speakers/headphones in a similarly effective way. How strong would that electromagnet have to be, and what sort of design would it require?

When I last put this question to someone, the answer was that it was theoretically possible, however, it would require excitation of the electromagnet to about a few kHz. This answer didn't make much sense to me, as my studies of electromagnets did not extend to them having their own frequencies, unless this answer refers to a pulsing field? The same answer also said that mobile phones are entirely incapable of interfering with speakers, so I am less than inclined to think of it as overly authoriative.

Thank you for any light or theory you can shed on this query80.46.18.68 (talk) 17:54, 1 September 2009 (UTC)

The suggestion is to drive the electromagnet with an alternating source current at an audible frequency (in the kilohertz range). This will probably send out some interference and couple to the speaker or amplifier; but kilohertz wave propagation isn't very easy to achieve. Alternatively, you can try to hit an RF frequency and hope to mix back down to audio range via the audio amplifier; this is what causes the buzzing interference you hear when a cellular phone is sitting near a HiFi amplifier. Nimur (talk) 18:52, 1 September 2009 (UTC)

An electromagnet is generally driven with a DC electrical signal - the magnet turns on - it stays on. The might produce a momentary click when turned your earphones (if they are magnetic ones) - but otherwise not. However, if you drive the coil with an AC signal - it will emit electromagnetic waves at that frequency (and probably harmonics of that frequency too)...and if it's a frequency that's disruptive to the headphones - you may get a horrible noise. It's not always the amplifier that picks up this stuff - sometimes it's the cable, which may happen to be a nice exact multiple or submultiple of the wavelength of the radio frequency stuff. Often it's more a matter of luck whether something is screwed up or not. Also, with a cellphone, there are a lot of other frequencies involved - the cellphone may output a bluetooth or WiFi signal when it gets a call. The internal electronics of the phone will be waking up - so you'll see the clock frequency of the microprocessor - and of the sound generator that drives the ringer. There are all sorts of other frequencies involved that could be causing the interference. I have a set of wireless headphones at home that go nuts if there is a microwave oven turned on...either in my own home OR in my next-door neighbors house! SteveBaker (talk) 20:11, 1 September 2009 (UTC)

What psychological aliment or psychosis does this person have?

A guy enters a new relationship with a female. They agree to be exclusive with one another. However, he starts to snoop through her things: cell phone, social pages, photographs, etc. He finds some evidence of the female's past relationships. So he begins to get very jealous and angry and demands that she erase the evidence. She states that what he did was an invasion of privacy and she doesn't have to address him in this state of mind. Then he calls her foul names and starts drinking alcohol. What sort of psychological aliments/psychosis does the male have? --Reticuli88 (talk) 19:59, 1 September 2009 (UTC)

FYI - this plot comes from a fictional short story I wrote for English. I wanted to sound 'professional' by trying to diagnose with something even if it is fake. Thought someone could throw me some bones. --Reticuli88 (talk) 20:10, 1 September 2009 (UTC)

Something along the lines of a person who asks us to diagnose a medical condition when the top of the page clearly states that we will not do so. -- kainaw™ 20:02, 1 September 2009 (UTC)

Even hypothetical ones? Is this medical? --Reticuli88 (talk) 20:05, 1 September 2009 (UTC)

Diagnosing a hypothetical person is diagnosing. We won't do it. -- kainaw™ 20:08, 1 September 2009 (UTC)

Firstly, it's entirely impossible to diagnose mental problems from third-party reports over the internet, even if one were a psychiatrist (and even if psychiatrists had a much better track-record of diagnosing things than they really do). And secondly don't mistake being a jerk for a mental illness. -- Finlay McWalter • Talk 20:04, 1 September 2009 (UTC)

This question falls solidly into the category of request for medical/psychiatric diagnosis (even if it is "hypothetical"). It is an explicit request for diagnosis.

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Please see the article Wikipedia:Medical disclaimer for more information.

Nimur (talk) 20:10, 1 September 2009 (UTC)

If it is in a work of fiction, you could just make up some rare condition and say your character has it. It is pretend, so accuracy is not required. Googlemeister (talk) 20:22, 1 September 2009 (UTC)

Unfortunately, jealousy is not that rare a condition. In this case, it's whatever the medical term is for "control freak". Baseball Bugs ^{What's up, Doc?} carrots 20:45, 1 September 2009 (UTC)

It's called being paranoid, an alcoholic, and a shitty boyfriend. No special diagnosis. ~ Amory (user • talk • contribs) 20:51, 1 September 2009 (UTC)

The internet is full of sites where you enter symptoms and it tells you possible diseases. Google for one and enter "paranoia, aggression" and pick one of the conditions it comes up with that you like the look of. Or just go with my colleague's suggestion above and say he's a jerk. --Tango (talk) 21:34, 1 September 2009 (UTC)

How about trying things the other way around. Read up on psychiatric conditions. If you just start with psychiatry and/or mental disorder you can probably read and follow links until you find a condition that seems "interesting" to write about. Do more research about that condition. Then construct your character and story to fit a condition that you are now knowledgeable about. No internet diagnosis needed, just some background research. The really good authors do insane amounts of research on their subjects, even for works of fiction. --- Medical geneticist (talk) 21:40, 1 September 2009 (UTC)

Your character's kinda flat. I agree with the idea of reversing your search -- pick a few conditions, give them a twist and write your character from there. John Riemann Soong (talk) 00:45, 2 September 2009 (UTC)

And if you need more inspiration, pick a few symptoms, look them up to find a suitable disease/condition - then read about the other, more obscure symptoms and pick some of the more weird ones. If that's not enough to make your character what you want, you could look up the treatments for this condition - some of them are bound to be drugs with even nastier side-effects - so you can have your character stuck between the symptoms of the disease and the symptoms of the side-effects of the cure...the character might even be able to swing back and forth between these symptoms when (for example) the plot causes him to lose his medication or attempt to overdose on the stuff. If you want, you could find two diseases with a similar set of symptoms and have the poor schmuck get mis-diagnosed so he gets the symptoms of one disease and the side-effects of the ineffectual cure for some other disease. (It's a hard life being a character in this kind of novel!) SteveBaker (talk) 01:05, 2 September 2009 (UTC)

A rather similar type of behaviour is described in the novel Before She Met Me by Julian Barnes. AndrewWTaylor (talk) 13:48, 2 September 2009 (UTC)

cause of death

What gets put on the death certificate as the cause of death when the person was executed by lethal injection in the US? It obviously would not be ruled accidental, and they probably could not call it homicide or suicide. Googlemeister (talk) 20:17, 1 September 2009 (UTC)

Timothy McVeigh's says "lethal injection". -- Finlay McWalter • Talk 20:26, 1 September 2009 (UTC)

Manny Babbitt's said "homicide", which is a perfectly valid and non-judgemental use of the word homicide - as that article says, not all homicides are crimes. -- Finlay McWalter • Talk 20:29, 1 September 2009 (UTC)

Homicide is not a synonym for murder. Homicide includes legal killings such as justifiable self-defense and, yes, executions. --Anonymous, 20:40 UTC, September 1, 2009.

And possible accidental overdoses of anesthetics applied to pop singing stars. Baseball Bugs ^{What's up, Doc?} carrots 20:42, 1 September 2009 (UTC)

In England and Wales (when we had the death penalty) it was "execution of a sentence of death" according to Coroner#Verdict. --Tango (talk) 21:39, 1 September 2009 (UTC)

That was the Coroner's verdict: the death certificate went into more details - according to this page Ruth Ellis's gave the cause of death as "Injuries to the central nervous system consequent upon judicial hanging." AndrewWTaylor (talk) 08:18, 2 September 2009 (UTC)

European Space Agency's Bernard Foing

I've created an article for Bernard Foing who was the Principle Project Scientist for the SMART-1 mission to the Moon. I'm trying to figure out what exactly his current job title at ESA is. I originally wrote "Bernard Foing is Chief Scientist and Senior Research Coordinator at the European Space Agency (ESA)" but now I'm wondering if this is one job title or two? Either way, is he at this/these position(s) for ESA as a whole or for the Research and Scientific Support Department? Can anyone help on this? The sources I've used for the article aren't 100% clear. Thanks! A Quest For Knowledge (talk) 20:26, 1 September 2009 (UTC) 20:24, 1 September 2009 (UTC)

Here's his page from Ecole Polytechnique Federale de Lausanne. What more information do you need? Nimur (talk) 20:46, 1 September 2009 (UTC)

And this source[40] describes him as "Chief Scientist and Senior Research Coordinator". (I only created the article a few days ago and it's already #10 on Google's search results. If any false information gets spread because of the article, it's my fault. I'm just trying to be accurate.) A Quest For Knowledge (talk) 22:31, 1 September 2009 (UTC)

Read WP:BLP. This is a very serious issue, and it's a topic that has a lot of Wikipedia policy to help guide your article. Tread carefully and be sure to cite reputable information sources. Nimur (talk) 23:36, 1 September 2009 (UTC)

I've changed the article to say "scientist" until I can get some clarification. A Quest For Knowledge (talk) 04:09, 2 September 2009 (UTC)

Does the gravitational constant implicitly include 4 pi?

We all know that the force due to gravity is:

$F_{g}=G{\frac {m_{1}m_{2}}{r^{2}}}$

where the m's are mass, r is distance, and G is the gravitational constant.

It is clear that the force due to gravity attenuates as the distance between the objects squared, and I was wondering if since this is the case, it is similar to something like brightness where as the spherical shell around an object of constant luminosity enlarges, the brightness diminishes as the surface area of that spherical shell ($4\pi r^{2}$). I won't be surprised if someone who knows something about gravity says that this is a totally bogus comparison, but assuming it isn't, then I would think that:

$F_{g}=a{\frac {m_{1}m_{2}}{4\pi r^{2}}}$

where a is a constant, and therefore

$G={\frac {a}{4\pi }}$

So does the gravitational constant implicitly include a 4 pi? Awickert (talk) 20:53, 1 September 2009 (UTC)

Sure, but unlike the electrical analog, (Coulomb's constant has a meaningful physical interpretation $k={\frac {1}{4\pi \epsilon _{0}}}$, where ε₀ is a relevant physical constant), your rearrangement of constants does not seem to have any practical purpose. In your construction, you introduced a new parameter, a, and as far as I know, this has no useful meaning (except that it is G * 4π). Nimur (talk) 21:00, 1 September 2009 (UTC)

Right, it's totally trivial, but I was going for something more like whether gravity's decay with distance is fundamentally based on spherical shells. Awickert (talk) 21:07, 1 September 2009 (UTC)

Which constants do and do not include factors of pi is entirely convention. We choose definitions which lead to the key formulae being as simple as possible, although there is some disagreement over which formulae should be considered key. The current conventions are pretty entrenched, though, so I doubt they will change. --Tango (talk) 21:16, 1 September 2009 (UTC)

(EC) Sorry, I didn't elaborate enough. The above electromagnetic counterpart, Coulomb's force law, can be derived via a 3D Stoke's integral transformation (what you're calling "spherical shells" are, in general, surface integral solutions). But in the case of gravitation, at least as far as I am aware, there is no counterpart that can be converted to a surface-integral. So, it makes no physical sense to represent the constants in a form which elucidate that relationship. Nimur (talk) 21:19, 1 September 2009 (UTC)

I'm not sure exactly where they come from (I did see and understand the derivation once, but I've forgotten it!), but there are pi's in the Friedmann equations, alongside a G. It has been proposed that G should be redefined to be 8piG to make that formula simpler. --Tango (talk) 21:28, 1 September 2009 (UTC)

The factor of 4π is always there in more modern statements of the law of gravity like Poisson's law (∇²Φ = 4πGρ), the GR field equations (G_μν = 8πGT_μν), and the Einstein-Hilbert action ($\textstyle \int {\tfrac {R}{16\pi G}}\,dV$), and, as Awickert says, you can make a good case that it ought to have been in the 1/r² law too. I think there's no question that 4πG is more physically relevant than G. By historical accident we ended up with the "wrong" gravitational constant, and the "wrong" Planck's constant too (h instead of the more important ħ). I don't understand the distinction you (Nimur) are trying to make between the electrical and gravitational force laws. The mathematics is essentially the same. -- BenRG (talk) 21:32, 1 September 2009 (UTC)

The mathematics are virtually the same, but the physics are totally different. Is there a gravitational dielectric constant? We can represent gravity in whatever equational form we like, but unless those equations correspond to useful physics, it's not worth redefining our constants to make those equations prettier. Nimur (talk) 21:36, 1 September 2009 (UTC)

Come on Nimur, I think BenRG gave you three examples where the factor 4piG does correspond to physically useful quantities (Poisson's Law, Einstein's Field Equations, and Einstein-Hilbet action) and you yourself gave us a fourth one (Stokes theorem). Dauto (talk) 23:08, 1 September 2009 (UTC)

Thanks, Ben, that's what I was looking for. Sorry, Nimur, but whether or not it is "worth it" is outside of what I was trying to ask (as I tried to get across above); thanks for the comments but I am wandering in "what-makes-math-pretty land". My question was more "is the 1/r² relationship due to the 'dilution' of that force over a larger and larger area as one moves further away, with the result that for a point mass, that force should be diluted across a spherical shell". But I am pretty sure that once I look at those equations that Ben mentioned my question will be answered; thanks. Awickert (talk) 02:27, 2 September 2009 (UTC)

Sorry - years of stodgy engineering have worn my appreciation for "pretty equations" away. I just want four decimal places and no more than a cubic polynomical fit. For everything. If it's worse than that, I'll take a data table.  : ) Nimur (talk) 03:09, 2 September 2009 (UTC)

It's all right. I work with field data. Slap it on log-log, fit a power law, and hope for the best. (Well, I usually try to do better, but sometimes there is nothing else I can do!) :) Awickert (talk) 06:03, 2 September 2009 (UTC)

(outdent) After doing some research, the answer seems to be yes; Newton wanted to make his statements as simple as possible, and the fact that the Poisson expression includes the 4 pi seems really to be to compensate for the fact that G incorporates a 4 pi in the denominator. Awickert (talk) 17:09, 3 September 2009 (UTC)

Density

The Sulfuric acid page states that its density is 1.84 g/cm³. Is it possible to calculate the density of a .1M solution, or would I need to measure it physically? Nadando (talk) 23:19, 1 September 2009 (UTC)

The densities of solutions are usually very complicated, because volumes of solvent and solute do not add linearly. If you find an equation for calculating the density at 0.1M, it is probably an empirical formula; your safest bet is to measure it yourself or consult a chemistry reference table. Nimur (talk) 23:39, 1 September 2009 (UTC)

If this is homework at a stage below college, it's possible that they're assuming linear addition and simply wanting you to understand dimensional analysis. If that's the case, consider whether you know how to convert grams of sulfuric acid to moles of sulfuric acid, and whether this helps you get to the density of a dilution of sulfuric acid in water. If indeed this is homework, we won't do it for you, but let us know where you're stuck and we'll try to help you go in the right direction. --Scray (talk) 23:45, 1 September 2009 (UTC)

No, nothing like that, I was just curious. Nadando (talk) 23:48, 1 September 2009 (UTC)

I see that Wolfram seems to know, although the calculations probably being simplified, like Nimur said. Nadando (talk) 00:02, 2 September 2009 (UTC)

Wolfram is wrong, as ever.

0.1M Sulphuric acid is ~0.2% sulphuric acid by moles, or 0.2 x 98/18 by weight which is ~1.1% by weight - water has a density of 1. So 0.1M sulphuric acid will be 99% water - and hence will have a density very close to 1g/cc (within 1%). Any simple calculations you could make might get a slight better figure - but not meaningfully - you'd have to measure the density to get a density figure better than 1% error (even that is not easy without proper measuring equipment).

The answer is 1g/cc within 1% error.83.100.250.79 (talk) 01:06, 2 September 2009 (UTC)

See here for a table - 1.0049g/cc [41]83.100.250.79 (talk) 01:20, 2 September 2009 (UTC)

You might want to go straight to the original source for that number, which was the CRC Handbook of Chemistry & Physics. This is a handy reference, and your school or library probably has a copy or ten floating around. Nimur (talk) 05:57, 3 September 2009 (UTC)

Buying a telescope.

I'm not really sure if this is the sort of thing that would be appropriate here, but if this doesn't fall within the scope of the rules for posting on the science reference desk, then feel free to delete my post.

I'm getting interested in astronomy and especially with astro-photography, but I have very underpowered equipment because I have limited monetary resources. I have a cheap $80 Wal-Mart telescope I was given for Christmas when I was 12 (you know...the kind that makes you buy it using impressive pictures of galaxies and nebulae on the box, but you actually get better magnification from a pair of binoculars). I also have a pair of binoculars my father gave me. I can see the moon and a few nebulae pretty well with the binoculars, but the telescope is so difficult to align perfectly, that I almost never use it unless I want to take photographs through it, but the results are never anything to write home about.

So I've been researching about buying good entry-level quality telescopes. It turns out that good telescopes for this purpose are extremely expensive and out of my price range. E-bay seems to have better prices on used telescopes, but I want to make sure I'm getting a good beginners telescope which good enough optics to keep me from getting bored with it and the unfamiliar technical specifications for these products confuse a newbie like me.

So my question is: what sort of specifications should I look for in a telescope to meet my needs? Price is a major factor, but I will probably end up getting a used one from E-bay (if I can find one) and that will reduce the price a lot. Also, if there are any websites or primers on the internet for beginners like me, I would greatly appreciate links to such sites. Thanks for your time. 63.245.144.68 (talk) 23:51, 1 September 2009 (UTC)

Your first choice is the type of telescope, e.g.:

• Refracting telescope
• Schmidt-Cassegrain telescope
• Newtonian telescope

These are the most common commercial distinctions. They each have various characteristics. You might read Sky and Telescope Magazine, which is a sort of good place to get your bearings and learn some terminology. Many of their back-issues are available online, and they have a beginners' guide and a How To Choose A Telescope tutorial. Nimur (talk) 00:04, 2 September 2009 (UTC)

IMHO astro photography and "budget" are mutually exclusive. Sorry, it is an expensive hobby full stop. I've been to several astro camps and there are very few people who have cheap gear who do successful astro photography. They generally fall into a couple of categories, either you stick to wide field and maybe moon photos, or you are extremely dedicated and patient and willing to learn A LOT about the tricks like squeezing resolution out of specially modified web cams; home building accurate tracking stands and stacking and processing images. Don't underestimate how patient and dedicated you have to be, it takes years of learning to get any good at it. I've probably come across 3 such individuals while countless have tried and given up because they weren't satisfied with the speed of their progress. It is really not something you can pick up and be good at. On the other hand, 95% of the photos you see from amateurs are taken with gear adding up to thousands of dollars. I think $3k or $4k is a starting point. Even then that's not a guarantee, there's still lots to learn, you see just as many rubbish pictures from people with expensive equipment too. I own a nice 12" Dobson scope, cost me $1.5k, not including a few accessories, I went for viewing aperture because I knew my budget wouldn't stretch to astro photography and I wanted a telescope I could enjoy actually looking through. Dobson = cheap for big aparture, but no good for photos (wihtout complicated and/or expensive accessories). A great forum is iceinspace.com it's australian based but has members all over the world. It has very good amateur photographers there which you can learn a lot from. Vespine (talk) 01:51, 2 September 2009 (UTC)

I endorse the idea of getting an issue of Sky and Telescope or Astronomy Magazine. You will see tons of ads for real astronomic scopes. More than that, you will probably find a listing for an astronomy club somewhere near you. Talking direcrly to the members will allow you to ask detailed questions beyond what the ref desk can provide. Additionally, some members may be getting ready to upgrade themselves and looking to sell their old scopes at a good price to you. B00P (talk) 01:45, 2 September 2009 (UTC)

But yes! Don't let me put you off! Most astro clubs have a "guest" night, you'd be silly not to look up a club near you and give them a visit. Just be aware that a high percentage of astro club members are total hopeless gear junkies so even though they are certain their advice is the best advice you can get, you should still indapendantly weigh up your own options. Vespine (talk) 01:59, 2 September 2009 (UTC)

Yeah. I'd second the $3-4,000 benchmark as a good "introductory" level. It only goes up from there... Nimur (talk) 03:05, 2 September 2009 (UTC)

Bear in mind that some Astronomical Clubs and Societies also own (or have regular access to) observatories, telescopes and other gear, which as a member (and with supervision/after training) you would be able to use. If like me you've had a somewhat nomadic home life and/or live in a light-polluted location and/or have limited personal funds, precluding a decent home-based astronomical setup, this can be a way to obtain the use of otherwise unobtainably expensive and/or large equipment, as well as advice and help from more experienced members. 87.81.230.195 (talk) 12:55, 3 September 2009 (UTC)

When you're choosing a new telescope, make sure you don't fall for the magnification (power) trap! Magnification is not important; a decent aperture is! For example, if you see an advertisement for "500 POWER!" on a 3-inch scope, ignore it. The field of view will be so small that even if you do happen to find anything, it'll be dim and move out of the field in a few seconds, and it'll be too shaky to add any photographic equipment. I own a $150 CAN reflecting (Newtonian) telescope (it was at reduced price; regular price $250) and a regular digital camera (price varies on this one, SLRs are usually better but not the type I used because I can easily hold this one). By using different eyepieces (you have to have those to change the magnification), a reasonally stable mount (this includes the tripod AND the ground condition; pavement is better than soil), and simply holding the camera up to the eyepiece, the most I've managed to take are some decent pictures of the moon and some blurry photos of Venus and Saturn, too blurry to find any detail but possible to identify the shape (cresent of Venus, thin rings of Saturn). Having some photographic filters also helps, in case the object is too bright, some details need to be shown, or even to compensate for light pollution (a lunar filter, an extra eyepiece, and a barlow lens cost me $50). Please be aware that some fainter objects require longer exposure times, and some of the pictures I've taken required several seconds of exposure, which means that you need a steady automatic or manual tracking system (an Equatorial mount helps), and a way to hold the camera steady (which may require a special camera adapter). The amateur photos of deep-sky objects (which I haven't managed to produce with my setup) that you see in magazines and on boxes of department store telescopes (that's the other thing–AVOID department store telescopes!) are usually taken on exposures of several hours (you'd need a very stable tracking system and equipment costing thousands of dollars, and excellent sky transparency conditions, or good seeing for planets), or alternatively hundreds of several-minute exposure photos stacked together using image processing software (which is sometimes free). There's also the option of CCD cameras, USB connections, and computer software to guide the telescope and control the camera's shutter (so you don't have to be outside while the astrophotos are being taken), ranging from a few hundred to several thousand dollars). Some telescopes also have automated GoTo mount controls and even GPS, so you can find a specific target with the push of a button (again ranging from a few hundred to several thousand dollars). If you have a low budget, I suggest sticking to simple lunar and some planetary images. Of course, there's also the option of piggyback mounting (my telescope has this option), where the camera can be attached on top of the telescope (thus pointing in the same direction), and can be used to take pictures of the constellations, the moon, the Milky Way (limited to locations with low light pollution) and conjunctions, and the trails of bright satellites like the International Space Station (requiring an exposure time of perhaps 15 seconds to a minute. There's also the option of recording star trails (okay, that's the wrong link, but the image shows star trails) while on piggyback, which requires exposures of several minutes to several hours (and again, low light pollution). For close-up photos using this technique, you need a good telephoto lens. And yes, star parties and observatories are good places to learn more about astrophotography and amateur astronomy in general, and there are some good books and online sources as well. Good luck! ~AH1^(TCU) 16:58, 3 September 2009 (UTC)

September 2

pot handle gives off vapors at high heat

Smells kinda like ammonia. One time (in a dorm kitchen), I was lacking a large enough baking pan, so I stuck a frying pan in the oven with my baked goods in it ... well then it started emitting a strange smell (I was running at about 350-400 F). The funny thing though is that the handle didn't appear to be melting, but I could tell the funny smell (reminded me of burning rubber) was coming from the handle. (must be a ppb detection thing...) Now this time, I made the mistake of switching the wrong burner on, so the burner just below the handle (but not below the pot) turned on for a good 10-20 minutes (I didn't notice until I checked on what I thought should have been boiling food). This time, it smells even stronger -- before I didn't notice its similarity to ammonia, but now I do. (I could tell it was quite hot -- I tried to take hold of the handle with a wet towel and the water became instant steam even after touching it several times.) However, I've tried sticking other pots in other ovens with no problem ... (namely pots with teflon-texture handles) .... does anyone know what sort of handles do this and what the reaction is? John Riemann Soong (talk) 00:14, 2 September 2009 (UTC)

Well, it might be Outgassing - or it might be that the substance making up the handle has a boiling point that's lower than it's melting point so when it gets hot, it goes straight from a solid to a gas (like dry ice turns into gaseous CO2 without ever being a liquid, for example) - or it might be that it's somehow decomposing and giving off reaction products as it does so without actually burning per-se - or it might be that the handle is not made of a single chemical - but a mixture - and one of the chemicals is burning/boiling and the other is not. There are a lot of possibilities here! Pot handles are obviously made to be pretty good insulators with a high specific heat capacity - so they take a long time to get hot - but once they are hot, it takes a lot to cool them off again. But we'll see if some of the resident chemists can't come up with a more specific explanation. SteveBaker (talk) 00:56, 2 September 2009 (UTC)

Possibly melamine . I'm fairly certain the 'teflon' feel handles are either nylon, polypropylene, or maybe ABS or similar - all thermoplastics - they'll melt over 200C (over 400F?) More expensive pans may use much more heat resistant plastics.

If it's melamine prolonged heat will cause it to slowly disintegrate - it tends to lose its strength and eventually disintegrates under any real force or pressure. Here's a link to prove some pans do use melamine [[42]] - it's usually recognisable because it's quite a shiny or glassy plastic as produced (vaguely lacquer like)

On the other hand it might be something completely different.83.100.250.79 (talk) 01:17, 2 September 2009 (UTC)

Thanks! I think melamine is the thing you're describing. It's glossy, kinda light and feels plasticy. Reminds me of the kind of plastics some hard bowls are made out of. Why would it release ammonia gas though? John Riemann Soong (talk) 01:33, 2 September 2009 (UTC)

Also, the handle was still very much intact. In fact, it looked quite identical in strength and feel ... except for temperature and smell of course. Would it be releasing trapped ammonia that couldn't quite be completely removed during manufacture? John Riemann Soong (talk) 01:36, 2 September 2009 (UTC)

I'm not sure - I think the resin may be decomposing a bit - half an hour in the oven probably isn't enough to substantially weaken a big bit of plastic.83.100.250.79 (talk) 02:04, 2 September 2009 (UTC)

Yep - remember, 1 mole of an ideal gas is 22 liters. If it's really ammonia that you're smelling then 17 grams is all it takes to make 22 liters - and you can smell ammonia when there is only a TINY amount of the stuff mixed into the air of a room. Ammonia is really smelly stuff - I'd be surprised if the handle lost even a tenth of a gram of mass in order to fill the room with a pretty powerful stink - a tenth of a gram is about what ten grains of sand weigh...you wouldn't notice so little material lost from the handle.

salty tastes and Cl- and Na+ ions

I came across some chlorine-containing compounds (can't remember if Cl was ionically bonded or not, but I guess the idea is that Cl- gets released) that supposedly tasted very salty, even though there was no sodium in them. This interests me ... because I thought that the salty taste would come purely from sodium cations. On the other hand, seeing as Na+ is already used for the action potential perhaps taste receptors want to use Cl- instead? If I ate a whole bunch of say, sodium acetate (yes I know it's mildly toxic), versus a whole bunch of some other chloride salt, which would taste saltier? (After normalising for moles of Cl- and Na+?) Do Na+ and Cl- have a synergistic effect? John Riemann Soong (talk) 00:48, 2 September 2009 (UTC)

I think one of the compounds that I encountered was potassium chloride. So is Cl- mainly responsible for salty taste? John Riemann Soong (talk) 00:53, 2 September 2009 (UTC)

It's the Na+ or K+ not the Cl-. See taste#Saltiness for more information. I don't know if Cl- has any enhancing effect or is just an inert counterion in this effect. DMacks (talk) 01:25, 2 September 2009 (UTC)

I can confirm that KCl tastes salty, but somewhat less so than NaCl, having tasted both sylvite and halite back in my geology days. The content of Taste#Saltiness looks plausible to me. Deor (talk) 21:48, 2 September 2009 (UTC)

Hmm yes I did read that but apparently google tells me that presence of chlorides in water (without any alkali cations) can result in a salty taste for some people ... and I also looked at this http://www.newton.dep.anl.gov/askasci/gen06/gen06166.htm. Which is more important -- the Na+ or the Cl-? John Riemann Soong (talk) 01:31, 2 September 2009 (UTC)

This is interesting - I think the Cl- is responsible for the some of the taste - the strong bitterness.

The Na is more subtle - though I think it has a saltly taste. You can test this with sodium hydrogen carbonate which is relatively non toxic (in small amounts). Sodium hydroxide has little bitterness at all - but is perceptably saltly in a vaguely 'meaty' way - don't try this at home - sodium hydroxide can burn skin , tongue etc.

There are lots of relatively safe sodium compounds you can try - the citrate, tartrate, and of course monosodium glutamate all should give a good idea of what Na+ actually tastes like.

Personally I associate the description 'salty' with the bitter effect of NaCl, though I believe that the body actually responds to the Na+ (in terms of needing rehydration/remineralisation) rather than the Cl- - in this sense it's the Na+ in salt that is attractive as a taste (instinctively), and not the Cl-83.100.250.79 (talk) 02:00, 2 September 2009 (UTC)

It's probably very conditional on what you actually consider a salty taste.83.100.250.79 (talk) 02:06, 2 September 2009 (UTC)

I've seen iodated salt (which is sodium iodide) being marketed and used as a NaCL substitute, so the salty taste must presumably come from the sodium ions? Zunaid 10:03, 2 September 2009 (UTC)

I think iodate salt contains 99% NaCl, pure NaI would be far too expensive for food use, amongst other things.83.100.250.79 (talk) 10:30, 2 September 2009 (UTC)

iodised salt was the blue linked article, you don't need that much iodine to eat pure NaI. Graeme Bartlett (talk) 11:12, 2 September 2009 (UTC)

Our article says "Two ounces of potassium iodate, costing about USD$1.15". I don't know how that price compares to sodium iodide but if the price is half, that's still US$0.625 for 2 ounces or ~56.7g according to Google. Presuming it's double the price, that's US$2.30. And that's the cost price. While not unusable for food, it's definitely expensive Nil Einne (talk) 20:19, 2 September 2009 (UTC)

~£200 per kilo for the standard NaI stuff[43] , (I can get a kilo of food grade NaCl for £0.26 !) - still not out of the range of things to buy for food - provided it's delicious... LD50 >1g/kg [44] page 5. I'm sure it would do some serious damage long before the lethal does was reached, best not to try it

Anyone know what iodide tastes like (no new original research please)83.100.250.79 (talk) 21:21, 2 September 2009 (UTC)

For KIO3 it's ~£100/kg [45] - that's from Aldrich which isn't cheap - but a long way off the new york times figure of ~$20/kg - it pays to but in bulk obviously :)

83.100.250.79 (talk) 21:29, 2 September 2009 (UTC)

Just to clarify - over 1mg/day of iodide in can cause chronic toxicity [46] 83.100.250.79 (talk) 21:47, 2 September 2009 (UTC)

anions of -2 charge and higher

Isn't there sort of an inherent kinetic difficulty to making such anions, due to their tendency to self-decompose (and donating electrons to an already formally negative system?) Or does solvation solve (no pun intended) some of these issues? In particular I'm thinking the synthesis of ATP. How do you covalently bind two anions together (via esterification) ... I assume it's kind of hard to perform a nucleophilic attack (even if you're aided by an enzyme) on an anionic center... John Riemann Soong (talk) 04:18, 2 September 2009 (UTC)

I think in a aquous solution the anions negative charges become shielded by water molecules around them. Dauto (talk) 05:10, 2 September 2009 (UTC)

But when the ATP is synthesised by ATP synthase, I imagine that solvation significantly decreases as hundreds of amino acids displace the space where water molecules once were ... (although maybe some of the amino acids might be electropositive and compensate for the lostsolvation). Is it the positive charges that would be located on some of the amino acids? John Riemann Soong (talk) 05:21, 2 September 2009 (UTC)

Sure, water solvation decreases, but the characteristics of the amino acids surrounding the ADP > ATP reaction site makes up for it. Nucleophilic attack in such a situation would be virtually impossible if the molecule were simply in aqueous solution. The enzyme does not simply aid the nucleophilic attack, it is the essential component that allows the reaction to take place. The Seeker 4 Talk 13:56, 3 September 2009 (UTC)

Ions in solution do not repel each-other at a distance, and not at all like classical charged particles. Charges at that scale simply do not work like that; You cannot get real assessments of electro-negativities just from formal charges. Real methods are more complicated (e.g. Mulliken population analysis, and a lot of other related work by Mulliken). --Pykk (talk) 05:17, 2 September 2009 (UTC)

I suppose in solution far away ... they do not. (That is, kinetic energy + solvation allows anions to become reasonably close to each other.) But when you get separation distances of 100-150 pm or smaller... you prolly approach the level of bound quantum mechanical states with bond breaking and bond forming, electron density and whatnot, and I imagine that electron repulsion becomes very important. John Riemann Soong (talk) 05:21, 2 September 2009 (UTC)

Solved Problems in Gauss law & Columbs law

i am an engineering student i need many solved answers in Gauss law & Columbs lawmy branch is Electronics&Telecommunication

You may find the article "Gauss's law" helpful. Axl ¤ [Talk] 07:46, 2 September 2009 (UTC)

Here's one [47] Try searching the same site for coulomb questions.

The best way to find these seems to be to search for "gauss law exam question" or "coulomb law exam question"83.100.250.79 (talk) 09:20, 2 September 2009 (UTC)

Xenon octafluoride and isoelectronic species

It came up Wikipedia:Reference_desk/Science#perchlorate about the possibility of the existence of IF₈^- - I found only one unreference example on the web, and the existence of XeF₈ is also uncertain - one russian journal may have a claim to it's synthesis - but I can't read it..[48] (at least according to the results of this google search http://www.google.co.uk/search?hl=en&q=Xenon+octafluoride+synthesised++sealed+tube&btnG=Search&meta= ) Other sources give good reasons why XeF8 would not exist..

Does anyone know about the more recent discovery of either of these, maybe someone already has access to the journal above, or a big library. Thanks.83.100.250.79 (talk) 12:17, 2 September 2009 (UTC)

for octafluoroiodate there is [49]. Dictionary of inorganic compounds, Volume 7 By Jane Elizabeth Macintyre on page 503 gives it a mention too on Google books (CsIF₈ NO₂IF₈(this one does not mention XeF₈). Graeme Bartlett (talk) 07:52, 3 September 2009 (UTC)

Thanks!83.100.250.79 (talk) 10:19, 3 September 2009 (UTC)

Lap Tops and Cell Phones in the next 5 years

Will laptops and cellphones merge in the next 5 years? If so, how do you think it will?--Reticuli88 (talk) 12:59, 2 September 2009 (UTC)

Maybe, but once people start getting arthritis in their fingers and especially their thumbs due to all the texting on those tiny keyboards, that might trigger a backlash. Baseball Bugs ^{What's up, Doc?} carrots 13:12, 2 September 2009 (UTC)

There is evidence that cell-phones will continue to become more and more like laptops (see iPhone and all the other various Smartphones already in market) but they are unlikely to replace laptops as they offer and realstically service quite separate functions. The lack of a Full size keyboard is a factor that makes it difficult to perform large-document Word Processing and Spreadsheet work on a mobile phone, and even with a Tablet PC with the best word-recognition software it's still going to be slower to work than anybody who types quickly (unless a form of shorthand becomes popular to increase that speed). Similarly we have seen in the past few years (with the major uptake of wireless networking) that more and more homes are purchasing laptops in place of their old desktop PC. These laptops are not used for their 'portability' in the way that business-laptops are. They are likely to be moved from room-to-room in a house, not from location to location. As a result I would expect this market to focus on features and design more than ultra-portability and battery life/robustness.

Personally I don't envisage carrying a phone the size of a laptop and I have no desire to work on a laptop the size of a phone. That said my wants and that of the general market will be largely different - I don't doubt that the huge success of the iPhone, Blackberry etc. will all increase the amount that mobiles start to perform laptop functions, but I don't see one leading to the demise of the other - just yet more integration of cross-product features/functionality. 194.221.133.226 (talk) 14:28, 2 September 2009 (UTC)

Maybe a full sized keyboard is answerable by a thin plastic keyboard that can be rolled up into a compact form. Bus stop (talk) 14:44, 2 September 2009 (UTC)

The tiny keyboard is one limitation on cell phones or even PDAs. Another is the tiny display. I suppose I could watch my streaming Netflix videos on a cell-phone, but I can't see a postage-stamp-sized picture like that being in any way comparable to one viewed on a full-sized screen. There may be some solutions to these issues, like a pair of high-def virtual reality glasses to display the images and a projection keyboard (but that, or the roll-up keyboard, would still lack the tactile feedback you get from a full keyboard). Given that these issues need to be resolved first, I'd say it will be decades before stand-alone computers begin to be phased out, if ever. StuRat (talk) 14:55, 2 September 2009 (UTC)

We can't predict whether they will converge. However, I will point out that netbooks can already connect to mobile networks. Use Skype (commonly installed as default) and a headset, and you're pretty much there already. AlmostReadytoFly (talk) 15:38, 2 September 2009 (UTC)

It would actually be trivial to install bluetooth-compatable cell phone circuitry into a laptop case and then you could use a bluetooth earpiece, and viola; you have it. I am not certain if anyone has done this, but you could certainly easily build a full-sized laptop with full cellphone capabilities; you would need to actually have your laptop nearby to use the cell phone functions, but it is very feasible... --Jayron32 21:31, 2 September 2009 (UTC)

It's likely they will continue to occupy separate though similar niches for some time. I do imagine that things like iPhones are close to being a bridge; you could imagine having a phone/hard drive that could be plugged into a full-sized keyboard and monitor at a base station, or something like that. With enough base stations in the world you could just carry your computer around with you. But that's an infrastructure thing, not a technology thing (the technology is there, there just aren't base stations all over the place). --98.217.14.211 (talk) 22:55, 2 September 2009 (UTC)

Actually, the technology would require no base stations. If you are looking for a cell-phone sized object with laptop computing capabilities, two pieces of paper would do fine; a white one which acts as a backscreen for a projector, and one with a keyboard layout for you to type on. There is already prototype technology out there to read body movements by camera and detect them; the next generation video game consoles may even incorporate this for true "controlerless" video games. Apply the same technology to your fingers, and it can, by camera, "read" what you are typing in space. A keyboard layout on a piece of paper would be all you would need to type; it wouldn't even need any communication to the cell phone since the camera would be tracking your typing. The basic technology could for such a device could probably be in place in the next decade or so; but I have no idea when a market-ready version may be ready... 20 years? --Jayron32 02:52, 3 September 2009 (UTC)

I think they can (and therefore will) merge. There are three technologies that will allow this to happen:

1. Tiny video projectors. These have already been demonstrated at cell-phone scales - they allow you to project the display onto any handy white-ish surface - such as a sheet of paper - the wall...whatever. This removes the constraint of the laptop screen size - and indeed allows you to project (albeit dimly, initially) at maybe 10' away to make a huge screen.
2. A second video projector could be used to project a picture of a keyboard - or a touch-screen or some other 'virtual' user interface onto another surface - your desktop, say.
3. A stereo camera could double as a keyboard/mouse/touch-screen interface by focussing onto the projected keyboard picture and observing where you tap your fingers. I've seen that very thing demonstrated several years ago - so that's definitely do-able. Since the keyboard is entirely "soft" - it no physical parts whatever, it can adapt to the task you want to do - flipping from a QWERTY keyboard for entering text to an old-fashioned rotary phone dial for dialling numbers - to a touch-screen - to...whatever. Tilt sensors and other gadgets would doubtless permit even weirder interfaces "beyond QWERTY".

The result could be even be much SMALLER than a present cellphone since it would not require any keyboard at all - just one "on/off" button - and no display surface whatever. The two video projectors and the camera could be fitted into a box perhaps an inch on a side - if you can squeeze the battery in that little space. It would use a bluetooth headset interface to avoid the need for a speaker or microphone. If small enough, it could perhaps even be made to clip onto a headset arrangement and project graphics directly into your eyes - using it's camera to aim and stabilize the image. This "heads up" display approach would obviate the need to find a flat surface to display onto. The stereo camera could perhaps even allow you to do simple data entry using something like sign-language when no physical surface is around to conveniently project a keyboard interface.

In the end, I think the battery is the limiting factor.

SteveBaker (talk) 03:17, 3 September 2009 (UTC)

You can get projected keyboards today. They're impossible to type on. If computers are going to ditch physical interfaces like you describe, we're going to have to radically reconsider how we enter textual data. APL (talk) 14:14, 3 September 2009 (UTC)

The crappy ones that don't work well use a single camera. You need a stereo camera to do a good job of it. The one I tried (which was a stereo device) worked - in that it could figure out where I put my finger onto the "key" - the thing that bothered me was that the keys (obviously) don't move - and that made it quite uncomfortable because your fingertips keep hitting this hard, unyeilding surface. However, I think that's something you could get used to. SteveBaker (talk) 18:17, 3 September 2009 (UTC)

The state of the art 2014 cel phone could have the power of an earlier laptop. Typing may become as obsolete as the telegraph key. The input could be by voice, with a greater accuracy than today. Semantic analysis rather than phoneme matching would help vastly. If a bigger display is needed or is a large keyboard is to be used, a fold up/rollup electric paper display could be used, or it could wirelessly couple to a keyboard, screen or printer. It is easier to have one high powered cel phone and couple it to peripherals than to carry a laptop everywhere. A docking station could be a plug-in base which charges the battery while coupling it to printer, keyboard and big screen. It could be the GPS which gives you driving directions as well as directions while you're hiking. Edison (talk) 19:14, 3 September 2009 (UTC)

What's the black stuff in my apple juice bottle?

I waited too long to recycle it. To clean it for recycling would require me to stick my hand in the bottle, but the opening is too small. How else can I get rid of the stuff?Vchimpanzee · talk · contributions · 18:14, 2 September 2009 (UTC)

Pour some boiling water in the bottle, add a squirt of washing up liquid (or a sprinkling of a bio washing powder). Put the top on and shake vigorously. Leave for a while, empty liquid out, rinse under cold tap. --TammyMoet (talk) 18:30, 2 September 2009 (UTC)

That sounds like a lot of resources for recycling one bottle. Just rinse it and recycle it. I'm sure the company has ways of cleaning the bottle that are not so wasteful of resources. 86.4.181.14 (talk) 19:08, 2 September 2009 (UTC)

Boiling water I haven't tried. Soap didn't work. The truth is they'll never know I did it. But there sure are a lot of these bottles now, and they're disgusting.Vchimpanzee · talk · contributions · 19:24, 2 September 2009 (UTC)

If the bottle is actually recycled, it will probably be first shredded and then incinerated, so any mildew will be irrelevant carbon contaminant in the final material. Such contaminants are inevitable, and I suspect your mildewy residue is a negligible contributor to the total contaminant. See Plastic recycling. Nimur (talk) 21:27, 2 September 2009 (UTC)

Usually incineration refers to the process of complete (or near complete) combustion. Plastic which is incinerated wouldn't usually be called "recycled", as it couldn't be re-used as plastic. I'm not overly familiar with the plastic recycling process, but I believe that plastic recycling usually employs melting rather than incineration; although I think there are some places which are looking into pyrolysis and syngas-based proceedures to repurpose waste plastics, however, I doubt those would technically be classed as recycling. -- 128.104.112.102 (talk) 22:35, 2 September 2009 (UTC)

Poor choice of word on my part. I didn't intend to imply anything other than melting. In any case, the residues and impurities will be melted or burned, too. Nimur (talk) 05:30, 3 September 2009 (UTC)

The trick with cleaning out any bottle is to, as TammyMoet says, put in a little soap, some (but not much) water, and to shake vigorously. I've never seen any dirt that could really withstand that kind of treatment. If it is more than that, just throw it out, it's not worth it. --98.217.14.211 (talk) 22:52, 2 September 2009 (UTC)

Well, I guess we need some more information. First, is it a glass or a plastic bottle? Secondly, is it a one-way or a returnable bottle? About the only case I would worry about the dirt is if you directly want to reuse the bottle for something. If it goes back to any commercial recycling company or bottler, they will bombard it with enough heat and chemicals to make it safe enough. --Stephan Schulz (talk) 23:14, 2 September 2009 (UTC)

Can you believe that, in all the many years of Wikipedia, with all the many articles about the intimate affairs of non-canonical Pokemons, that yet we do not have an article about (or a picture of) the humble bottle brush, a simple tubular cleaning brush with stiff tines radiating from a flexible wire rod, suitable for inserting into tight voids such as bottles, and sold in shops near wherever a man has a strange bottle calculus that proves unamenable to soap and bleach and just letting it sit there for a day with hot water in it? -- Finlay McWalter • Talk 23:04, 2 September 2009 (UTC)

The brush article on its own is a bit of a car-crash :( --Tagishsimon (talk) 23:35, 2 September 2009 (UTC)

... and if you don't have a bottle-brush, rice, or even sand, shaken vigorously with some water inside the bottle will remove any deposit. Dbfirs 00:26, 3 September 2009 (UTC)

There doesn't seem much potential for expansion beyond a dictionary entry, and it's already in wiktionary. AlmostReadytoFly (talk) 07:12, 3 September 2009 (UTC)

I suppose that the history of the bottle brush, it's construction, who invented it, different types, etc. could be covered in a WP article, if someone had the inclination to do some research. I've got no idea as to how easy it would be to find any of that stuff out - but I'd imagine that there are at least a few people out there who would be interested in reading about that sort of thing... --Kurt Shaped Box (talk) 07:19, 3 September 2009 (UTC)

I think I'd be dismayed if such a reliable source exists. It sounds worse than Lucky Jim's decision to write a paper so boring and obscure that no peer-reviewer would contradict it. AlmostReadytoFly (talk) 08:41, 3 September 2009 (UTC)

Well, I've now managed to discover that bottle brushes existed prior to 1892, as Anton Zolper's patent on an improved model demonstrates... --Kurt Shaped Box (talk) 09:16, 3 September 2009 (UTC)

This is part of a general problem that I'd sort of like to know as well. I know that in some cases recycling dirty stuff is worse than throwing it away (never recycle greasy pizza boxes, for example — you could ruin a whole batch of pulp). But there are lots of corner cases where I don't know the answer. We don't recycle broken glass because of the danger to the workers, but what about the tops to cat-food cans, which have sharp edges? How much water is it worth to get rid of the last bit of peanut butter in a glass container? That sort of thing. --Trovatore (talk) 07:38, 3 September 2009 (UTC)

Our recycling company here in Australia said don't wash bottles, they don't mind the dirt. They don't mind pizza boxes. Graeme Bartlett (talk) 07:46, 3 September 2009 (UTC)

Rigidity

It seems no matter how strong the material, when you create a long thin rod of it and hold it in the middle then the ends will sag. Is there some equation to determine how much the ends will deviate from the center assuming you know some properties of the material and the length and diameter of the rod?

And is there some super material (maybe carbon nanotubes?) that will remain perfectly rigid? TheFutureAwaits (talk) 21:44, 2 September 2009 (UTC)

They wont sag outside a gravitational fields. Nothing is infinitely rigid. The formula escapes me ATM —Preceding unsigned comment added by 79.75.114.6 (talk) 22:02, 2 September 2009 (UTC)

Would it have anything to do with a strain-stress relationship? (Could it be related to a linear coefficient?) John Riemann Soong (talk) 23:41, 2 September 2009 (UTC)

Isn't it like an upside-down three-point compression/tension relationship? DRosenbach ^{(Talk | Contribs)} 05:11, 3 September 2009 (UTC)

If you are holding two ends of the rod, the equation is the Catenary equation, often given (as in our article), by:

$y=a\,\cosh \left({x \over a}\right)={a \over 2}\,\left(e^{x/a}+e^{-x/a}\right)$

We have a whole section on this. The constant a can be expanded in terms of all the relevant physical parameters - material properties, force of gravity, etc. In this case of a very rigid material, like a short metal rod, the constants in this formulation might be problematic; other formulations can be found which are more suitable approximations for specific material properties. The equation can also be generalized in many ways to deal with (for example) a non-horizontal suspension.

Alternatively, since you asked about suspension from a single point, (holding the rod in the middle), you can model the effect as two symmetric cantilevers; the result is a similar equation but with one free end; constants will again depend on the material properties and force of gravity, etc. Displacement, y, of a cantilever, can often be expressed as a growing exponential:

$y=-Ae^{\frac {x}{\alpha }}$

but this formulation will have obvious physical limitations for sufficiently long cantilevers (i.e. they will snap before they displace by arbitrarily large amounts!) The derivation of this expression is often given in an ordinary differential equation textbook as a "trivial example" of a physical modeling problem in one dimension. Nimur (talk) 06:12, 3 September 2009 (UTC)

See Euler–Bernoulli beam equation. Red Act (talk) 06:31, 3 September 2009 (UTC)

A fairly common question here is "if you had a perfectly rigid rod one light year in length, couldn't you communicate faster than the speed of light by tapping it?", and the answer is yes, but the problem is that nothing can be infinitely rigid. --Sean 14:16, 3 September 2009 (UTC)

impact force from braking

(Relocated from the Miscellaneous Desk. --Anon, 23:00 UTC, Sept. 2/009.)

Although I found lots of calculators and charts for hitting a barrier at various speeds what I am looking for is a calculator or chart that will show the force generated by dropping from one speed to another above zero. In other words if you slam on the brakes in a Volvo at 70 MPH and let off the breaks when your speed hits 30 MPH how much force is generated and is it enough to crash the passenger's head into the windshield? -- Taxa (talk) 18:46, 2 September 2009 (UTC)

Force = mass * acceleration. Acceleration = change in speed / time. So, if you drop 40 miles per hour in speed, it doesn't matter whether the drop is from 70 to 30 or from 50 to 10 or from 40 to 0; its the same acceleration. What needs to be known to do the calculation that you have NOT indicated is the time involved in the slow down. Does it take 10 seconds? 1 second? 0.1 seconds? That is a necessary part of any force calculation. --Jayron32 21:14, 2 September 2009 (UTC)

What you want is the Impulse. Impulse = Force * change in time = mass * change in velocity. That means that we're missing both the time interval and mass of the vehicle in order to calculate the force. ~ Amory (user • talk • contribs) 22:25, 2 September 2009 (UTC)

The force on the vehicle is irrelevant; the question is about the force on its occupants or their body parts, which depends on their own mass. In fact for this sort of thing one usually just uses the acceleration directly: a human in such-and-such a type of restraint can withstand such-and-such an amount of acceleration. Impulse is also irrelevant to the question. But as Jayron said, the time to decelerate is extremely relevant and we weren't given that. However, one would not expect the brakes of a vehicle to provide enough acceleration to smash someone's head into a vehicle unless they were unconscious as well as unrestrained. --Anonymous, 22:55 UTC, September 2/009.

Okay, lets say I'm decelerating at 15 feet per second per second so that it takes 4 seconds to go from 60 MPH to 0 MPH. At 15 FPS then an unrestrained passenger will travel 3 feet in 1/3 second. So what would the impact be (or force) of their head traveling 3 feet in 1/3 second and striking the windshield? In pounds per square inch and with an initial 2 square inches hitting the windshield how much pressure will be generated and would that be enough to cause them to die? -- Taxa (talk) 06:29, 3 September 2009 (UTC)

First of all, you're confusing your units, 60 MPH is 88FPS so an acceleration of 15FPS per second will take closer to 6 seconds to reach 0. When the car decelerates, the passenger is going to continue traveling at 60 MPH(ignoring friction) while the car's speed slowly decreases. So the speed at which the passenger hits the windshield is more complicated than you're making it, but if my back of the envelope calculation is correct the passenger will hit the windshield traveling at 0.6FPS, not enough to be deadly. The amount of force is way way more complicated, it depends on the mass of the person and how much time it takes them to stop when they hit the windshield. -- Mad031683 (talk) 17:08, 3 September 2009 (UTC)

I really think that body mass can be mostly ignored. It's acceleration that's the most important. When a sumo wrestler trips or bumps his head against the doorway I think the net pressure (measured as pain) is roughly the same as when normal people trip or bang heads against doorways. The whole body accelerates, but not all of the body mass is sent against the window. And the human body isn't a rigid object, either... John Riemann Soong (talk) 07:05, 3 September 2009 (UTC)

Two things you've not mentioned are the safety belts and the passenger's location. Is the passenger in the front seat or the back? Is the safety belt fastened; and if so, how strong is it? Nyttend (talk) 00:40, 4 September 2009 (UTC)

No safety belts and passenger in front seat probably crying with head head facing down in hands. Then wham. -- Taxa (talk) 01:30, 4 September 2009 (UTC)

calculating the BPs and MPs of pure perchloric acid

Has this been found out? Google is being really annoying and keeps returning me all these 60-70% solution results. I mean, I imagine measuring the BP or MP of 100% perchloric acid would be dangerous ... but it's something you could do behind a blast screen or with a glovebox. It forms a negative azeotrope with water, right? Could we do various extrapolative techniques? What's the dipole moment of perchloric acid compared to sulfuric acid? (I can't find this easily...) Should we expect that perchloric acid's anhydrous BP be lower or higher than water's? John Riemann Soong (talk) 23:34, 2 September 2009 (UTC)

I can't find the data either.

The way to find the boiling point would be to find the boiling points at low pressures (lower boiling points) - because it seems certain that perchloric acid will decompose before it boils at atmospheric pressure.

The situation may be complicated by this equilibrium [50]

3 HClO4  <<<>>> Cl2O7 + H3O+ClO4-

Basically the anhydrous acid is unstable with respect to the monohydrate and the oxide (the oxide has a low boiling point)

If you know the boiling point at two temperatures (of the heat of vapourisation and one boiling point) - you can use a formula to extrapolate (fairly well) the boiling point at another pressure. There's an equation in Boiling point / Clausius–Clapeyron relation

As a guess the boiling point of the pure acid would be greater than water , just by its mass. Compare anhydrous nitric acid - which has one H for hydrogen bonding, and a lot of oxygens which boils at 83C, I'd expected anhydrous perchloric acid to boil at a higher temperature - maybe 110-120C???

I can't find any dipole moment data (probably because of the difficulties with working with it), it should be similar to sulphuric acid in the overal scheme of things.83.100.250.79 (talk) 10:16, 3 September 2009 (UTC)

Anhydrous perchloric acid appears to be quoted as freezing at -112C http://www.google.co.uk/search?hl=en&q=melting+point+anhydrous+perchloric+acid&start=10&sa=N

Heres one data point for the BP

pure anhydrous compound can be prepared by vacuum distillation as a colorless liquid, which freezes at -112C and boils at 16C at 2.4 kPa (18 mm Hg) without decomposition[51]

Staring at black and gray object for a looong time without blinking

Will desaturation happen if I stare at black and gray object for a day without blinking. Will white surface look differnt color if i look at black and gray stuff for 24 hours? Will whole color system change? Will I not notice black and gray stuff?--69.226.35.110 (talk) 23:51, 2 September 2009 (UTC)

You can't possibly stare at anything for more than a minute or two before you'll reflexively blink. But even in that short period of staring at some colored object, turn away and look at a contrasting surface, and you'll likely see an afterimage of some kind. Baseball Bugs ^{What's up, Doc?} carrots 00:51, 3 September 2009 (UTC)

A basic "Training Drill 0" exercise done by scientologists is to stare without blinking for many minutes, reputedly hours. If you dare blink your watcher calls "Flunk!" and you have to start again. I managed about 5 minutes. Cuddlyable3 (talk) 06:36, 3 September 2009 (UTC)

(ec) IANAD nor an eyesight specialist but, in order: No, No (not for very long), No, Yes. ~ Amory (user • talk • contribs) 00:54, 3 September 2009 (UTC)

You may want to read Color vision and Adaptation (eye). The adaptation processes in the eyes proper happen on the time-scales of milliseconds, seconds, or minutes. Changes on a longer time scale mostly happen on later stages of visual processing, that is, in the brain. Looking at a gray-scale object engages neither the retinal nor the cortical mechanisms of color adaptation or color constancy, so gray stays gray. However, looking at a stationary object and not shifting the gaze (not even by a few arc-minutes) for a sufficiently long time will make the object "invisible" to your brain, even though its image is still captured by the retina; see Stabilized images. This requires a sophisticated setup, though. Simply looking at an object for very long won't make it invisible for you, as your eyes keep moving (head movements, microsaccades, drift, etc...) even as you try to maintain fixation at a certain point. On the other hand, staring at a complete darkness for too long (days or more) will eventually cause your visual cortex to ramp up its gain, trying to pick up the whatever weak signal that may be reaching the retinas. This will result in magnification of the "electric noise" (spontaneous activity) of the retinas and the visual thalamus, and may lead to an effect called "Prisoner's cinema". --Dr Dima (talk) 01:33, 3 September 2009 (UTC)

Well, I don't know about 24 hours - but you've personally stayed in a dark room for 8 to 10 hours with your eyes shut almost every day of your life. Did you notice yourself being unable to see black objects after you woke up? No? I didn't think so. SteveBaker (talk) 12:00, 3 September 2009 (UTC)

Moon to survive without earth

Will sun becomes a giant in 5.5 billion years. if Earth gets swallow up is this possilbe Moon will survive. If moon is moving away from earth, then is this possible for moon to become a planet? moon will just be superheat though--69.226.35.110 (talk) 23:53, 2 September 2009 (UTC)

Sun#Life cycle says that it is likely the Earth will indeed be swallowed by the expanding Sun, so the Moon will likely follow, especially as it is often closer to the Sun than Earth. And yes, it will be superheated. The odds of it becoming a planet are extremely unlikely, but theoretically possible if all the perfect massive interactions happened, presumably with asteroids altering its orbit. ~ Amory (user • talk • contribs) 00:46, 3 September 2009 (UTC)

Not quite, if the earth were swallowed up by the sun, the moon would be too. When the earth is swallowed up it does not cease to exert a large gravitiational force on the moon, and so the moon would be unable to escape without some kind of colossal intervention from an outside body. Elocute (talk) 10:32, 3 September 2009 (UTC)

When the Sun turns into a red giant it will be extremely thinly spread out, so planets that end up inside it won't be instantly destroyed. There will be lots of drag on the Moon as it orbits the Earth so it will pretty soon end up crashing into the Earth. While the Moon is moving further away from the Earth it is doing so very slowly, it won't be a significant distance further away by the time the Sun dies. --Tango (talk) 18:37, 3 September 2009 (UTC)

September 3

replacement of secondary alcohol (in benzyl position) with H

I suppose the use of hydride and the use acid catalyst don't go together? Is there anyway of protonating an OH group, having it leave, making a secondary benzyl carbocation, and then have hydride take up the spot? I think the issue is that it's kind of difficult to have functioning acid and hydride in the same solution. (And I don't mean that acid and hydride, har har...) Would it be feasible to replace the OH with a halogen, extract the product out of acidic solution, and then put it in basic solution where hydride would perform a nucleophilic attack on the halogenated carbon? John Riemann Soong (talk) 04:34, 3 September 2009 (UTC)

Try this on for size. Oxidize the alcohol to the ketone using PCC and then reduce the ketone to the alkane using the Wolff–Kishner reduction (aka Hydrazine reduction). Working with raw "hydrides" is kinda messy (like, they ignite in air), and reducing alcohols directly, even with "harsh" reducing agents like Lithium aluminum hydride, doesn't usually work so well. --Jayron32 04:46, 3 September 2009 (UTC)

Are there any complications to oxidisation/reduction if the alcohol is in benzyl position? (Also my pen and paper problem set doesn't give me good marks for excellent yield lol ... I just need a theoretical mechanism...). Carbocation formation as a mechanism first came to mind because of it. John Riemann Soong (talk) 05:21, 3 September 2009 (UTC)

I don't believe so. The benzylic position generally tends to improve reactivity of nearly ALL reactions at that site since the benzylic position will stablize cation/anion/radical formation via conjugation. I am not aware of any particular reaction being LESS favorable at the benzylic position. I am pretty certain PCC will oxidize ANY secondary alcohol to a ketone, and Hydrazine/Hydroxide will reduce ANY ketone to the hydrocarbon. You may want to double check your textbook on these, but any introductory organic text should have both PCC oxidation and Wolff-Kishner reduction mechanisms in them. --Jayron32 05:28, 3 September 2009 (UTC)

Oh I was wondering about possible side reactions that would take place at the benzylic position, since it's as you say, more reactive. I mean, if you convert the alcohol into a ketone, you're going to get a pi system interaction with the benzene ring. (But I guess this will make the carbonyl group more nucleophilic?) John Riemann Soong (talk) 05:38, 3 September 2009 (UTC)

"a hydride [...] to pull off the halogen, with another hydride coming in" doesn't make chemical sense: anion attacking halogen seems electrostatically unlikely, and I can't think of a way to make "BnCl + 2H– → BnH + ???" a good balanced reaction. Once you have halide attached, you just displace it SN2 with hydride. Or else you would need something that attracts chloride to pull it off and so an SN1 (a cation not anion, since you want to pull off chloride in order to have a carbocation for hydride to attack). Chloride is already a good leaving group, so you don't need to activate it further (unlike hydroxide, which you correctly observe needs to be protonated to become a good leaving group). Simple alkali-metal hydrides aren't often used as H- nucleophiles for SNx reactions (more often Group-3 complexes like NaBH₄). I think there are both solubility and mechanistic reasons, can't remember what specifically is important for this case.

There are actually ways to get hydride donors in a lewis-acidic environment. Hypophosphorus acid is one such, and it (alone or with additional strong acid in solution) may be sufficient to allow you to protonate and then SNx your alcohol. There are other direct ways to accomplish this change too. The major chemicals for the direct transformation are regulated because this reaction is how to make speed (conversely, your local meth-dealer might know some clever ways to do it and/or suppliers for the chemicals). DMacks (talk) 04:55, 3 September 2009 (UTC)

Re: the hydride pulling off the halogen -- that was a total brain fart on my part (as you see in the history where my edit summary was 'remove silliness').

Hahahaha, I just realised meth synthesis relies on displacement of a benzyl secondary -OH too ... lol what a coincidence. (I'm just trying to do a problem set.) John Riemann Soong (talk) 05:03, 3 September 2009 (UTC)

It sounds like you are thinking of converting the OH into a good leaving group eg

R-OH + CF3COCl >>> R-O-C(O)CF3

If not continue reading after the indent

The trifluoroacetic ester is a good leaving group, and can be displaced by nucleophiles - including potentially "H-" equiavlents, unfortunately the ester group is also susceptable to nucleophilic attack. I think there is a synthetic method that involves a process like this for converting R-OH to R-H - but it's obscure, involving specific leaving group, and "H-" donor, and currently I can't remember it.

There's some examples here http://www.organic-chemistry.org/synthesis/C1H/deoxygenations.shtm

The first example using a thioester is actually a radical reaction, so doesn't count.

The chlorodiphenylsilane reduction is much nearer to a Sn2 reaction - probably via a cyclic intermediate.

Ah here it is - convert the alcohol to the toluylmethanesulphonate, then reduce with LiAlH4 [52] also [53]

See 4-Toluenesulfonyl chloride the reaction is also mentioned in that page too.

The benzyl group should just speed up the reaction (excluding steric effects) - for Benzyl alcohol I don't imagine any side reactions, for others such as 1phenyl butan-1-ol there's the possibility of elimination as a side reaction to make a styrene83.100.250.79 (talk) 11:48, 3 September 2009 (UTC)

The "via a halogen" method is also good - but usually done like this - convert the alcohol to the halogen, then metallate eg use lithium metal to make the Benzyl Lithium compound, the just add water , or another H+ source to get the alkane.

Ph-CH2-OH >>> Ph-CH2-Cl use thionyl chloride or something else
Ph-CH2-Cl >>> Ph-CH2-Li use lithium
Ph-CH2-Li >>> Ph-CH2-H add water

83.100.250.79 (talk) 11:55, 3 September 2009 (UTC)

Note there are quite a few different ways to reduce halo compounds to alkanes, including direct 'hydride' reduction.. The link below gives many examples pages 1 onwards.

Ahh! Here is exactly what you where asking for! (in addition to the one already given by DMacks)[54] Page 13, scheme 15, bottom example -- note here that NaBH4 is used becuase even though it can act as a hydride donor, it is quite stable to mild acid (?) (well more than most - I'm slight dubious about that without more info., but the other examples in the text are good). There's a lot more examples in the text.83.100.250.79 (talk) 12:26, 3 September 2009 (UTC)

how is -COOH formation oxidisation?

This aspect of COOH formation always seems to be glossed over ... but I don't really get how it's "oxidisation". I can totally see how increasing unsaturation (via elimination or oxidising an alcohol into an aldehyde) is oxidisation, because the organic compound actually sees electrons exit its system. But I don't see how RCOOH is any more electron deficient compared to R(C=O)H.

Plus, when I look at the thermodynamics of alcohol metabolism in the body, I see that aldehyde formation is moderately endothermic (e.g. ethanol to acetaldehyde), but the conversion of aldehyde into -COOH is quite exothermic . John Riemann Soong (talk) 05:31, 3 September 2009 (UTC)

It's just the "formal oxidation state" that increases - obvious the carbon stays as a 4 bonded atom.

If you consider RCHO + 'O' >>> RCOOH

It's clear that oxygen has been added - hence oxidation, though in fact the O has just been inserted into the C-H bond. The molecule has been oxidised, but the carbon atom hasn't really changed it's oxidation state.

83.100.250.79 (talk) 09:05, 3 September 2009 (UTC)

Ah, wikipedia has an article - see Oxidation number versus Oxidation state (note that Hydrogens at considered to have oxidation +1 , not -1 ; when in organic compounds)83.100.250.79 (talk) 14:17, 3 September 2009 (UTC)

Organic redox reaction does explain it quite well. --Jayron32 20:23, 3 September 2009 (UTC)

pressure distribution , how amount and area of effect works

Hi guys

Ok I have been puzzling on this for a while so can someone answer me this. I know from watching a show called mythbusters that even the most high powered rifles cannot knock a person backwards by force alone. The question I have therefore is this. If you add up the amount of kinetic energy, or simply the amount of pressure I can produce with my hands when I push someone, this would not be very much compared to a bullet, put simply if you could focus all the kinetic energy of my body to one point the size of a bullet, it would not penetrate steel or shatter concrete. A bullet however can do this. My question is how come if less kinetic energy is transferred to the object that I push does it move further backwards than when It is struck with a bullet. I.E I can push someone over but a high powered bullet cannot. Does the area of my hands, much wider than the surace of a bullet have anything to do with it. I know weight comes into it as well, Im talking pure pressure, I could produce about 50 psi at best, while bullets can produce thousands of psi. How does this work?

Thanks guys —Preceding unsigned comment added by 79.68.243.180 (talk) 09:37, 3 September 2009 (UTC)

Force and energy are NOT the same thing. Someone owes me a dollar - because it's a Wikipedia Ref Desk rule the I get a dollar every time someone confuses the two! Kinetic energy is calculated as energy = mass x velocity²/ 2. Velocity squared means that when you double the speed that something is moving, you quadruple the amount of energy it can deliver. When you gently poke someone in the chest with your finger - it's moving at maybe 0.1 meters per second. Even a really crappy pistol can propel a bullet at maybe 400 meters per second - 4000 times as fast - and if the bullet weighs about the same as your finger, that's 16 million times as much kinetic energy...OUCH!! However, the force of the recoil for the shooter and the force applied to the victim is calculated by force=mass x acceleration. Which means that the forces involved don't depend on the speed - but the rate at which the bullet speeds up or slows down. For the victim, that means that the distance the bullet travels through their body - which determines the time it takes to come to a complete stop - and that determines the force it applies while it's slowing down. Of course with a really high powered weapon, the bullet may go in one side of the body and out the other without stopping or even slowing down by very much - which reduces the force it applies still more!

So that's why the bullet produces immense amounts of kinetic energy (which can do you a whole lot of no good) - but not enough force to knock you backwards 10 feet like in the movies. Newton's laws tell us that every action has an equal and opposite reaction - so the force of the recoil felt by the shooter is equal to the force felt by the victim (minus a bit due to air resistance). However, in a rifle, that force is spread out over many square inches by the big, fat stock of the rifle - where the victim feels the same force - but has all of it applied at the teeny-tiny tip of the bullet. Hence the pressure that the victim feels is much more than the shooter - which is why the bullet ends up embedded in some vital organ while the shooter doesn't have the recoil blow his shoulder off. SteveBaker (talk) 11:55, 3 September 2009 (UTC)

So would they get knocked back 10 feet if they had a bulletproof vest on, which quickly decelerated the bullet? Googlemeister (talk) 13:13, 3 September 2009 (UTC)

We should be considering momentum here to determine the speed with which someone is knocked back. If the bullet is stopped by the vest then mass times velocity of the bullet will be equal to the mass of the person times the speed at which they start to move backwards. Because the person is many times the mass of the bullet, their speed will be low, but if the person is caught off-balance, they may well stagger backwards. A marginally greater momentum is given to the gun (and the person firing it), but this is only a problem if one is holding the gun lightly, or balancing on one leg to fire. Dbfirs 15:21, 3 September 2009 (UTC)

Also, if the person was running for cover and shot near the center of mass while his feet are in the air, it might cause his path to veer slightly. Sagittarian Milky Way (talk) 17:11, 3 September 2009 (UTC)

bus bar

what is the use of bus bar atGSS?Satyendra singh sihoria (talk) 10:39, 3 September 2009 (UTC)

Busbar may help you; you'll need to explain what you mean by GSS if you need a more specific answer. -- Finlay McWalter • Talk 10:41, 3 September 2009 (UTC)

Attachment of dental crowns

Dental crowns are attached to the root of the tooth by a metal post being put into a hole drilled into the root. How is this post kept firmly attached to the root, particularly when newly made, and for upper teeth? What stops it falling out? Thanks. 78.146.78.240 (talk) 10:43, 3 September 2009 (UTC)

According to post and core, the post is either smooth-sided and held in place only by cement, or is serrated or threaded to engage with the remaining tooth root. The X-ray images on that page show a variety of post designs. Gandalf61 (talk) 11:39, 3 September 2009 (UTC)

Prosthetic crowns are cemented to teeth that exhibit decay or are fractured to an extent that does not allow a filling (intracoronal restoration) to be placed -- thus, the restoration must be placed around the remaining tooth structure, and is referred to as an extracoronal restoration. Crowns are routinely cemented to the underlying tooth structure with a number of various types of dental cements. When there is not enough remaining tooth structure to provide adequate physical retention for a prosthetic crown (although cement is used, a crown placed onto a tooth that does not provide adequate physical retention, e.g. overtaper, will not remain there predictably), a core build-up is necessary to compensate for the missing internal tooth structure. If there is not enough tooth structure to retain a core build-up, the core build-up can be built around a post that has been cemented into the coronal portion of of a root canal that has had a portion of it's root canal filling (after root canal therapy has been completed) removed. While the core build-up is often a resin-based composite material which bonds to the tooth structure, the post and crowns are affixed with cements like zinc oxide phosphate (ZOP), flowable resin-based cements and other similar materials. Upper teeth have root canals for housing posts just the same as lower teeth, and without proper cementation, a lower tooth will not remain in position any more predictably long-term because of chewing forces, sticky foods and the tongue -- gravity will have very little effect on displacing upper crowns and allowing lower crowns to remain. DRosenbach ^{(Talk | Contribs)} 03:42, 4 September 2009 (UTC)

Why do ruins end up buried under soil?

It's strange, should be simple, but I just can't work it out. Where does the soil come from that buries anything lying around for long enough? Are the continents getting thicker?

Adambrowne666 (talk) 10:56, 3 September 2009 (UTC)

(EC with Steve below) Mostly it's just localised redistribution of material. I think the four main mechanisms involved are:

1. Dust and other small soil particles are blown on to the ruins by the wind, and build up significantly over long periods. In areas subject to sandstorms and similar phenomena, the periods may not be so long. Think how often one has to sweep a path clean.
2. Plants (which are mostly made of molecules extracted from the atmosphere) grow on, up through, and over the ruins, trapping more windborne dust/soil, and themselves die and decay on top of them forming a mulchy component - this can build up surprisingly quickly (you should see my neglected patio!).
3. Earthworms churn up the underlying and surrounding soil causing more solid objects to sink into it, as Charles Darwin famously observed. Other larger burrowing creatures can contribute to this effect.
4. People may build on top of the ruins using less durable materials and later abandon the site, allowing those overlying structures themselves to decay into soil components.

Hopefully a trained archaeologist will quantify, correct and expand on this initial stab. 87.81.230.195 (talk) 11:46, 3 September 2009 (UTC)

Simplistically: When there is erosion due to wind, rain, rivers, ice-sheets & glaciers, dirt gets eroded from one place - and deposited someplace else. Hence, by the law of averages, you might expect about half of ancient ruins to be eroded to nothing and the other half to be buried in the resulting dirt - which protects them from erosion. Obviously the ones that were eroded away are never found - so pretty much the only ruins we ever find are the ones that were buried. However, it's likely that the nature of erosion processes is to transport material from high peaks and dump them into lower valleys (well, mostly) - and because people like to build their homes close to water sources - that may well result in there being more ancient habitation in valleys than there on mountain-tops...so I guess, statistically, more ruins get buried than are eroded away. The continents don't get thicker - just smoother - the mountains get lower and the valleys higher. But on geological timescales (too long to concern the preservation of human-constructed ruins), mountain ranges are pushed up by the buckling and colliding of continental plates and are also raised by volcanoes - and the ancient, smoothed-off, eroded land is subducted away to be recycled in the earth's core - or gouged out by rivers and glaciers. So there are two sets of processes - the plate techtonics and vulcanism make the world rougher and erosion mostly makes it smoother. SteveBaker (talk) 11:28, 3 September 2009 (UTC)

The Straight Dope did an interesting article about this : How Come Archaeological Ruins are Always Underground. APL (talk) 13:18, 3 September 2009 (UTC)

We also have an article on subsidence, which is the geological term for changes of the ground surface. In many cases, the entire ground level is actually lowering, and new material is being replaced on top. In some cases, the rate of subsidence can be measured in inches or feet per century; this effect alone may account for some archaeological sites being buried. Nimur (talk) 16:15, 3 September 2009 (UTC)

What do stock traders do?

Is it just a gamble, no matter what, or are there people able to predict the movements of the stock market?--Quest09 (talk) 11:44, 3 September 2009 (UTC)

See fundamental analysis, and the slightly pseudoscientific technical analysis. --Mark PEA (talk) 12:15, 3 September 2009 (UTC)

I'll take a loot at these two links above. However, I consider the technical analysis not better than astrology and the fundamental analysis very suspicious. --81.35.253.86 (talk) 17:50, 3 September 2009 (UTC)

Fundamental analysis isn't suspicious. You analyse the company and work out how much it is worth, divide that by the number of shares and you get what the share price should be. If that is higher than the current price, you buy, if it is lower, you sell. It is perfectly logical. The problem is that everyone else can do the same analysis and reach the same conclusions so there won't generally be much of a difference between the current price and the calculated price. This is known as the efficient market hypothesis. The only way to reliably make money on the stock market is by breaking one of the assumptions in that hypothesis - the most obvious way to do that is to get hold of information other traders don't have (either by having better contacts or by interpreting the same data better). If you can do that, you can make money. Technical analysis, on the other hand, is complete nonsense - it only works because of self-fulfilling prophecies (all the technical analysts see a certain pattern and think the price will go up, they then buy and that pushes the price up). --Tango (talk) 18:45, 3 September 2009 (UTC)

Well that's if you want to speculate -- you basically are driven to look at undervalued shares and buy them. After all, to sell them to someone, there must be some value in the shares. In an IPO, shares are sold, giving capital to the company in return for some cut of future profit (voting rights, whatever). The company uses the IPO money, expands, and pays investors back (e.g. in the form of dividends). As the company grows the share price rises, because the company's profits will probably increase. If you're a speculative trader, you prolly don't want to hold on to the stock for too long, simply because when you buy stock you're tying up capital in that stock (think opportunity cost). Theoretically, the idea is to find rough diamonds, and stocks create an incentive to fund their expansion. (But such funding only occurs during an IPO of course -- the rest of the trading afterwards is what the investors do with their "reward".)

The game is also slightly different for private stocks or funds, etc. There's this firm that looks like it has a promising business plan, and it seeks investors to give it capital. In return, it promises you a cut of future profits. Except in an IPO, this aspect of the game doesn't exist for public stock. John Riemann Soong (talk) 19:09, 3 September 2009 (UTC)

"Mass" of colour

As a partially red-green colourblind person reading Color blindness, I was surprised to see the following line in that article's section "Design implications of color blindness":

“ Thirdly, for some color blind people, color can only be distinguished if there is a sufficient "mass" of color: thin lines might appear black while a thicker line of the same color can be perceived as having color. ”

I've often experienced this, finding it harder to distinguish the colour of a line one pixel wide than a line ten pixels wide. For you who can see normally — is it generally equally easy to distinguish the colours of small and large amounts of colour? I've always assumed that it would be harder for smaller amounts for anyone, simply because less colour is present. Nyttend (talk) 13:24, 3 September 2009 (UTC)

Pretty much just as easy. If something is relatively far away, and the sizes are out of proportion (TONS of blue and a little green) then maybe, but not really. The only time it actually ever sort of happens (for me, anyway) is when there are very similar colors - light gray text on a large, off-white background from far away can look fuzzy. I think a bigger issue is that when there are lots of colors together it can be hard for some to focus on individual colors rather than an amalgam, but it is still quite discernable. ~ Amory (user • talk • contribs) 14:01, 3 September 2009 (UTC)

In my experience, if an object is in the center of my vision, (ie: I'm looking right at it) I can distinguish the color down to very small sizes. Almost, but not quite, down to the visual threshold. Certainly identifying the color of a single bad pixel on a monitor at a reasonable desk-sitting distance is no problem at all. APL (talk) 14:40, 3 September 2009 (UTC)

I think distinguishing between similar colours is easier for everyone where there is a large expanse of each, but small areas will be more of a problem for those whose receptor cones are less efficient at distinguishing. Dbfirs 14:52, 3 September 2009 (UTC)

Same color illusion is worth a look for how even 'normal colour sight' (?) people's eyes get confused. 194.221.133.226 (talk) 15:37, 3 September 2009 (UTC)

That's a different phenomenon, though -- it depends on higher level processing. The basic and universal fact is that the color pathway has lower resolution than the contrast pathway -- the brain combines information from the two to make "guesses" about color. You can see this in action in the "Just GREY" illusion here, for example. Looie496 (talk) 16:36, 3 September 2009 (UTC)

The density of rods and cones in the eye is the issue here. There are about 90 million rods and 6 million cones in a "normal" eye. The rods are denser around the edges of the eye - but even in the center of our visual field there are about 6 times as many rods as cones. Since rods are responsible for monochromatic 'brightness' detection and the cones do color - you can readily see that very small features lose their color because there isn't sufficient spatial resolution of cone cells. Hence the observation that our article makes is true of normal people as well as colorblind people. In SOME kinds of colorblindness there are even fewer cones than usual - because (perhaps) all of the green-detecting cones are missing - that would make the effect more pronounced - but that's not true of all kinds of colorblindness. SteveBaker (talk) 18:12, 3 September 2009 (UTC)

Your input is quite helpful. Part of the reason I was surprised is the contrast between blue and black in my sight — while I see blue (and yellow) without problem, if I go into Microsoft Word and change the colour of a comma or a single letter from black to blue, I don't generally notice it at first glance; I need to pay attention or change the colour of other letters to notice it. Nyttend (talk) 21:58, 3 September 2009 (UTC)

I think I would have difficulty noticing a blue comma in black text depending on the shade of blue and I don't have any form of color blindness. For example the wikipedia link color is very noticable, but the visited link color is less so. For an entire word it stands out reasonably well, but if it were a single letter I might miss it if I weren't specifically looking out for it. Rckrone (talk) 00:20, 4 September 2009 (UTC)

earth without moon

If the moon were to magically disappear, what would the impact to the earth be? Would there be a mass extinction? Googlemeister (talk) 14:53, 3 September 2009 (UTC)

See Wikipedia:Reference desk/Archives/Science/2009 January 29#Earth without a moon. There's some really good talk there, and not just the obvious stuff about tides. ~ Amory (user • talk • contribs) 15:16, 3 September 2009 (UTC)

Interesting. So it would seem unlikely that there would be a mass extinction? Googlemeister (talk) 15:40, 3 September 2009 (UTC)

Depends. You are asking for scientific predictions of outcomes in a fundamentally unscientific scenario. Maybe the magical disappearance of the moon creates huge flocks of flying pigs which blot out the sun and trigger a new ice age. Who can tell ? Once you postulate magic then all bets are off. Gandalf61 (talk) 15:57, 3 September 2009 (UTC)

"Once you postulate magic then all bets are off." Coming from an account named after Gandalf. ~ Amory (user • talk • contribs) 17:27, 3 September 2009 (UTC)

Hmmm....are all bets off for Maxwell's demon? 204.2.252.254 (talk) 17:46, 3 September 2009 (UTC)

A mass extinction of what? People? I don't really see why species not directly influenced by the moon (that depend on the tides, for example) would be affected, especially not immediately. Whether life would have evolved in a similar manner had the moon never existed is another matter... TastyCakes (talk) 16:02, 3 September 2009 (UTC) TastyCakes (talk) 16:00, 3 September 2009 (UTC)

You may be interested in the following documentary: The Universe - The Day the Moon Was Gone. A Quest For Knowledge (talk) 16:58, 3 September 2009 (UTC)

The complete elimination of lunacy? Edison (talk) 19:06, 3 September 2009 (UTC)

Werewolf movies would make a lot less sense to future generations. Googlemeister (talk) 19:49, 3 September 2009 (UTC)

According to Tides#Forces, the Sun has 46% of the effect on tides as the Moon does. As such, the tides would always be about as strong as they usually are at their lowest. Also, the poles are always at low tide, so weaker tide would mean more water there, and less everywhere else. I suspect all this would have drastic consequences on plants that live on the coast. I may be wrong, though. — DanielLC 00:28, 4 September 2009 (UTC)

Tin Pan Alley would be stumped to come up with romantic songs rhyming "croon," "June", and ????? Businessmen currently seek to tear down the physical block of New York City which was "Tin Pan Alley" for comercial development. Seems a common theme.Edison (talk) 04:01, 4 September 2009 (UTC)

CO2e emissions

Hi. What are the carbon emissions produced by a 12-hour commercial flight? Assume a Boeing 777, travelling at typical speed for a continental flight, using regular fuel. Calculate the CO2 emissions produced, in addition to the equivalent GHG warming potential of any other greenhouse gases resulting from fuel combustion and on-air energy usage. Preferable units include pounds, kilograms, and metric tonnes. Total emissions for the flight are preferred to emissions per passenger, although that's fine too if calculateable. This is not homework. Also, how much net CO2 might one square metre of tropical rainforest remove in its lifetime, assuming current climate conditions and current CO2 concentrations for the entire lifetime of the square metre, and assuming a lifetime of 40 years? Thanks. ~AH1^(TCU) 15:54, 3 September 2009 (UTC)

This looks a lot like a homework problem. We're not supposed to solve those. Looie496 (talk) 16:23, 3 September 2009 (UTC)

(ec) Just thought I would point out that fuel consumption on an aircraft is extremely non-linear. So, if anybody is planning to calculate "average fuel consumption" and multiply by flight duration... reconsider? It would be better to find an actual end-to-end fuel consumption estimate for a 12-hour flight on a 777 and use that as a baseline for estimation. Nimur (talk) 16:24, 3 September 2009 (UTC)

I highly doubt it is a HW question because of the level of complexity. To be honest there is absolutely no way to give a good answer with the supplied information. first, there is something like 6 different variants of the 777, each would have a different fuel consumption profile. Second, weather conditions will be a huge factor for this flight, especially whether the flight will be against the wind or with the wind, and what speed of wind do we have. Also, we need to know how loaded the plane is. Do we have a full load of fuel and passengers, or is the flight half full? Even this information was known, the resulting calculations would be quite substantial. Probably not something you could spit out in 5 minutes. As to the rain forest part, there is still some question as to whether rainforest scrubs CO2 at all since the carbon just renters the atmosphere when the plants die and decay. Googlemeister (talk) 16:31, 3 September 2009 (UTC)

Thanks, but I already indicated that "This is not homework". I will now bold the relavent sentence in my question. Also, is any calculus required to solve such a problem? ~AH1^(TCU) 17:22, 3 September 2009 (UTC)

Such claims are ignored because homework-askers have been known to lie. Sorry. Comet Tuttle (talk) 19:42, 3 September 2009 (UTC)

I didn't disbelieve it, I just failed to see it -- sorry. Looie496 (talk) 20:57, 3 September 2009 (UTC)

Google is your friend. A five second search turned up a bunch of links. This says saving one kilo of fuel saves 3.16 kilos of CO₂. This says a 747 uses about 36,000 gallons of fuel on a 10-hour flight (approx. 1 gallon per second or 5 per mile) so by simple calculation using the density found at Jet fuel, that flight would produce around 383,000kg of CO₂. Also, here's a a link to calculate the emissions for any flight. ~ Amory (user • talk • contribs) 17:40, 3 September 2009 (UTC)

Personally I'm more concerned about the massive consumption of fuel than the emission of CO2. John Riemann Soong (talk) 18:47, 3 September 2009 (UTC)

That, of course, is the full plane, which isn't THAT bad when you consider that it's moving 250 people at 5 times the speed of highway cars at 0.2 mpg. --antilived^{T | C | G} 04:27, 4 September 2009 (UTC)

Ants inside me

What would happen if an ant crawled up my nose or into my ear while I was sleeping? Would it find conditions favorable to stay awhile? Would it get lost? Would it be able to reach my brain or lungs? —Preceding unsigned comment added by 75.36.223.130 (talk) 16:29, 3 September 2009 (UTC)

Unless it was going to make its own tunnel, it could not get to your brain. It would also have a hard time getting to your lungs because it would trigger the coughing reflex. Googlemeister (talk) 16:33, 3 September 2009 (UTC)

While following up on a dubious claim in an article a while ago, I came across this very real and very reputable report from the Royal Society of Medicine, Doctor, there are maggots in my nose. Gross. The article also cites some case studies of other insect species infestations. The most common are fly larvae; and most of the medical techniques known to human-doctors are attributed to prior research from agriculture, livestock, and veterinary procedures. Nimur (talk) 16:49, 3 September 2009 (UTC)

And let's not forget about the earwig. Baseball Bugs ^{What's up, Doc?} carrots 17:49, 3 September 2009 (UTC)

But, earwigs don't really do that. APL (talk) 18:33, 3 September 2009 (UTC)

Involuntary Ingestion of an Airborne Diptera Specimen by the Geriatric Female: Incidental Report and Treatment Methodology Cuddlyable3 (talk) 18:46, 3 September 2009 (UTC)

Without looking, I'm guessing that's a report about an old lady who then swallowed an arachnid that wiggled and wriggled and tickled inside her. And so on. :) Baseball Bugs ^{What's up, Doc?} carrots 20:59, 3 September 2009 (UTC)

Technically, she swallowed the spider to catch the fly. I presume she will die.Quietmarc (talk) 02:11, 4 September 2009 (UTC)

In addition, According to the report, she took the further absurd step of consuming live avian fauna in an attempt to eliminate the aforementioned arachnid. It is predicted that this will be fatal. APL (talk) 02:42, 4 September 2009 (UTC)

Perhaps. ~ Amory (user • talk • contribs) 02:50, 4 September 2009 (UTC)

As an emergency measure, non-morbid feline ingestion may be indicated. 87.81.230.195 (talk) 02:55, 4 September 2009 (UTC)

nucleus volume

Does the volume of the nucleus of an atom grown in proportion to the volume of multiple cubes or in proportion to the volume of an expanded sphere? In other words does the volume increase in proportion to adding marbles to a bag or in proportion to blowing up a balloon? -- Taxa (talk) 16:38, 3 September 2009 (UTC)

Neither. The characteristic radius of a nucleus can be defined in many ways, but the collisional radius is a very complicated parameter. See nuclear cross section for a quick introduction. In general, a quantum mechanical treatment is necessary to define this parameter. Nimur (talk) 16:43, 3 September 2009 (UTC)

Where would the actual radius plot on this diagram? -- Taxa (talk) 17:03, 3 September 2009 (UTC)

Our Nuclear size article uses an expanding-sphere model. DMacks (talk) 17:32, 3 September 2009 (UTC)

Okay I see that - density remains the same for all atoms - hence a solid and not a homogeneous sphere. -- Taxa (talk) 21:32, 3 September 2009 (UTC)

Sorry my earlier post was so brief; I didn't explain thoroughly enough. Nucleons are sufficiently small that they behave quantum mechanically. This has many important implications for things like the definition of their size. Because we can't actually measure the nucleus directly, we instead estimate its size by bombarding it with a beam of particles, and statistically determining how many of those particles "bounced off" - thus determinining a collision cross section. However, and this is very critical - the collision cross section of an atomic nucleus depends on how we set up the experiment. That is, changing the incident energy, or the spin, or polarity, or any other quantum characteristic of the incident beam, changes the size of the nucleus that is measured. See here for an example of nucleus-particle resonance. So, it's not really possible to tell you the "volume" or the "length" of the atomic nucleus, let alone how it scales with proton-number; because it doesn't scale in any classical sense. Instead, every nucleus has its own characteristic cross-section profile and interacts uniquely with various incident particles. One of the simplest models, as documented in Atomic nucleus#Nuclear models, approximates the trend as a power law, r ≈ Z^1/3 (Z=atomic number), or the similar r ≈ A^1/3 (A=atomic mass); but these are very bad approximations. This entire chapter from the source I linked earlier, may be helpful for conceptual understanding (though it is written for a reasonably high level physics background, you can probably parse through it anyway - it's surprisingly light reading!): Nuclear Cross Sections and Neutron Flux, from the Department of Energy handbook on Reactor Theory. (Also available at the DOE Standards website. Nimur (talk) 18:00, 3 September 2009 (UTC)

Note that for a cube, a sphere, or any other 3D shape scaled proportionally, any length measurement scales in proportion to the cube root of the volume. Asking whether something scales more like a cube or like a sphere isn't really meaningful since they both scale the same. Rckrone (talk) 19:12, 3 September 2009 (UTC)

My reference to the cube root of a cube and the radius of a sphere may be confusing because of the difference in the reference I am making. The reason for referencing a cube is that a cube can approximate the space between the spheres (I lost my equation for this. It was in my bag of marbles) Anyway if you stack a bunch of blocks (small cubes) so that they make a large cube and take the cube root of the large cube and divide by 2 then you have something to compare with the radius of a sphere formed by a bunch of marbles in a bag of marbles where there are spaces between the marbles. One would think this sphere would have a larger radius that a sphere based on the absence of spaces between marbles (nucleons) which should be the smaller spheres that would compose the bigger one - the atom. I'm just wondering whether the neutrons and protons retain their spherical shape when part of a nucleus like a bag of marbles or if they meld and loose their shape and "liquefy" so to speak and become indistinguishable inside the nucleus as individual nucleons. Is it a bag of marbles or a water balloon? -- Taxa (talk) 21:09, 3 September 2009 (UTC)

To summarise, if you mean: a) what is the exact size of a nucleus and how does it grow with the addition of a nucleon, your question is unasnwerable per Nimur. Nucleon sizes cant be measured as they are defined by probability densitys and so depends on the critical probability you define as 'the edge' of the nucleus. b) how does it scale with the addition of a nucleon your question is pretty much meaningless per Rckrone. In that with all n dimensional shapes a 1-dimensional measurement scales with respect to the nth root of the nD-volume. 92.19.128.192 (talk) 19:26, 3 September 2009 (UTC)

Finally don't forget binding energy. Adding nucleons will add volume (let's take a theoretical definition like a 95% probability density cutoff with a bombardment by a particle with a characteristic energy, used for all measurements), but I suspect how volume increases or decreases also depends on whether binding energy per nucleon increases/decreases or not. John Riemann Soong (talk) 19:38, 3 September 2009 (UTC)

Sounds like you favor the marble model. -- Taxa (talk) 21:35, 3 September 2009 (UTC)

Instead of speculating about marbles, or guessing about which model is favored, you might consider reading the sources I linked, or the relevant articles at atomic nucleus. Unfortunately, modern physics is not very intuitive; it really needs to be learned by studying the basic formulations of quantum mechanics. These maths weren't invented for the fun of it - they're the accepted models because the observations we have of nuclear size contradict intuition, and require a more complicated branch of physics to model their behavior. You can replicate these observations, but the machinery and equipment necessary is sort of expensive, making it hard to do in your backyard laboratory - but they've been independently confirmed hundreds of times. Quantum mechanics is hard, and weird, but you can understand it if you just try carefully. But speculation about incorrect intuitive ideas is not a substitute for studying prior experimental evidence and theory. This is not meant to be harsh or mean - I'm just trying to help you get on the right track to really understanding the problem - it sounds like you're stuck on formulating a visual model of the size of the nucleus, but that will not help you correctly understand the real physical behavior. Nimur (talk) 22:22, 3 September 2009 (UTC)

Okay, then you seem to favor the solid or balloon model. I'm not trying to be mean or harsh either but only to understand which concept is correct. While I do not have a backyard lab I do have intuition and the ability to conduct a thought experiment and have basic calculator skills to explore the idea I find most intriguing, which is the idea that the nucleus is like, if not identical, to the electron quantum shells in which an applicable equation such volume of a sphere is based upon integer values (see graph above) similar, if not identical, to integer wavelengths for the orbital shells of the electron around the nucleus. -- Taxa (talk) 00:20, 4 September 2009 (UTC)

No, it's not a solid or a balloon. It's an atomic nucleus, and it behaves like atomic nuclei. The best model is the quantum mechanical description of the cross-sectional radius, which is not a measure of a volume. Nimur (talk) 03:56, 4 September 2009 (UTC)

Animals and birds fear of humans

Apart from domesticated animals, only a few such as penguins in the antartic do not seem afraid of humans. In the case of penguins I suppose it is because they usually never meet any humans. Why are other animals and birds afraid of humans? Is it encoded into their genes? Or is it learnt from parental behaviour?

Learning it from their parents is problematic - since in remote places, neither the parent or the offspring may have seen a human before, so how do they learn the behaviour? 78.146.3.82 (talk) 20:30, 3 September 2009 (UTC)

Or in the case of some animals, like most amphibians, their parents were not around to teach them anything. Googlemeister (talk) 20:50, 3 September 2009 (UTC)

Running from humans, or anything large, is good instinctive behavior. Those who didn't run probably got trampled or eaten, thus quashing the "too dumb to run" gene. Unfortunately for the dodo, they didn't have time for natural selection to weed out the dopes, and apparently did not breed as prolifically as penguins... although climate might figure into it also. Los conquistadores probably didn't spend all that much time poking around Antarctica. Baseball Bugs ^{What's up, Doc?} carrots 20:57, 3 September 2009 (UTC)

I'm thinking about people filming wild animals in Africa from cars - the animals ought to be afaraid of the cars, but are not. 78.146.3.82 (talk) 21:19, 3 September 2009 (UTC)

They might be used to it, or of comparable size. Think of it: If you were a rhino, what would you be afraid of? (Aside from possible extinction). Baseball Bugs ^{What's up, Doc?} carrots 22:28, 3 September 2009 (UTC)

Some animals do have neural circuits the encode innate fear. For example, laboratory mice that have spent their entire lives in a sealed room and never encountered a predator, show fear responses to the smell of cats. It is unknown exactly how this works, but it is thought that some cat smells act as kairomones to mice. This does appear to be specific (they don't show the same response to all animal odors), which would suggest there is some genetic code the tells mice to be afraid of cats.

Other animals show natural caution towards all other animals, irrespective of whether they are dangerous or not. If you are at the bottom of the food chain and only eat plants for example, then it makes evolutionary sense to avoid pretty much every other animal, as they can only do you harm.

The animals that are unafraid of humans are usually those that have little experience of natural predation in their environment. If you have evolved to have no reason to avoid other animals, then you will not show fearful behaviour towards them. Sadly for animals such as the dodo, this can be catastrophic when a predator is introduced. Rockpocket 22:34, 3 September 2009 (UTC)

Finally, animals are extremely good at learning. Innate and learned responses are highly integrative, and the latter can over-rule the former (this is the reason some predators and their prey become "friends"). Rockpocket 22:34, 3 September 2009 (UTC)

Radiation from a curvy line on a 2D plane

This relates to a question I asked on the Maths Desk. http://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Mathematics#Weighted_sum_of_distance_from_a_curvy_line What is the right way to estimate the radiation at X,Y from a curvy line (which could be radiating heat, light, or sound etc)? You could treat the line as a series of points, and estimate the intensity of radiation at X,Y by summing (the magnitude of the radiation at the line divided by the distance squared) from each point on the curvy line. But the problem with this is, the more points on the line you use, then the greater is the resulting sum, up to an infinate amount, which is absurd. 78.146.3.82 (talk) 21:02, 3 September 2009 (UTC)

It appears that your question was answered immediately at the Math desk. You integrate, and most radiation follows the inverse square law. Our article on integrals explains why this does not lead to a solution of infinity. — Lomn 21:28, 3 September 2009 (UTC)

Ah, but a point is infinitesimal, so the radiation it emits is infinitesimal. If you add together an infinite number of infinitesimal values you can get a finite result. (Roughly speaking, anyway.) This is exactly the kind of problem integrals are for. --Tango (talk) 21:29, 3 September 2009 (UTC)

I'll try to make it a simple dectiption - say the line is 10 long, and you have 10 points , then you sum the values for ten points. Now say the line is 10 long, and you have 100 points now you sum the hundred points time 0.1. (since each of the hundred new samples is 1/10th the size of the original ten samples) - and so on

Now say the line is 10 long and you have 1000000 points, again you take 1000000 samples each multiplied by 1/100000 - thus the sum doesn't become infinite but converges to a really good estimate.

83.100.250.79 (talk) 22:23, 3 September 2009 (UTC)

Humane way to remove paper wasp nest from a tree.

There is a huge beautiful paper wasp nest in my parent's tree near the entrance of the driveway. Their neighbors were giving them advice on how to get rid of it but I thought it seemed barbaric. I tried to explain to my 'rents that wasps are like nature's pest control. Are there laws in certain US states about getting rid of wasps or other insect nests on your property? Is there a humane way to remove or transplant a wasps' nest? Is the venom of a wasp any stronger/weaker than a bee's? --Reticuli88 (talk) 21:23, 3 September 2009 (UTC)

See Schmidt Sting Pain Index for a partial answer to your last question. A bigger issue perhaps is that there's always a risk that someone would be allergic to the wasp sting. The risk may be no greater then with bees but it is obviously there. Perhaps the greatest issue however is that while it's unclear from your description, it sounds like the location of your wasp nest means it could easily be disturbed. If the nest is disturbed, the wasps could attack en masse and this could be bad to the person who disturbed the nest, or anyone in the vicinity. In terms of your 'nature's pest control' comment, have you tried to identifying what kind of wasp you're referring to? The US has atleast one but I'm guessing several invasive paper wasp species [55]. As with most invasive species, these tend to have a far more negative effect on 'nature' then positive as they did not co-evolve to fill a ecological niche and instead may outcompete native fauna (particularly wasps in this case) and may lack natural predators and so end up distrupting the ecological balance. While the US situation isn't as bad as in NZ (where all social wasps are invasive and the small size and long history and other issues means the balance tends to be far more delicate/sensitive) it might be wise to find out precisely what it is you are defending before you argue it's an essential part of nature. Just to be clear, I'm not saying that means it's justified to kill them that's an ethical issue the RD can't answer. Nil Einne (talk) 22:13, 3 September 2009 (UTC)

This is really a case of asking for advice rather than asking a factual question, and the bottom line is that it's not a good idea to mess with bees unless you know what your doing. In other words, call your Orkin man, or perhaps a beekeeper you might find in your yellow pages. Baseball Bugs ^{What's up, Doc?} carrots 22:27, 3 September 2009 (UTC)

Or spray the wasps' nest with a suitable wasp spray (like Ortho Wasp Killer), it kills wasps within a few seconds (and also scares away any wasps that return to the nest). Just make sure not to get any of that stuff in your face. 146.74.230.104 (talk) 22:50, 3 September 2009 (UTC)

I've had great luck with plain distilled vinegar. Not only will it shoo off the wasps but eventually will cause the paper nest to fall to the ground, which the wasps tend to abandon not yet having learned the squadron replacement technique of how to grab hold of several corners in unison and fly the thing back into place while the others try to remove the vinegar and cement the thing back in place. -- Taxa (talk) 23:50, 3 September 2009 (UTC)

Special sprays are made for killing wasps. Some have a foaming quality which prevents them flying around after sprayed, and can hit them from many feet away. Some believe that spraying them at night when they aree home is better than during the day when they are out foraging. I have no qualms about killing a nest of wasps on my property, having experienced their unprovoked stings. Edison (talk) 00:01, 4 September 2009 (UTC)

Paper wasps definitely aren't protected in the USA; otherwise companies such as Orkin wouldn't be able to advertise that they're able to get rid of the things. Nyttend (talk) 00:37, 4 September 2009 (UTC)

I used to have a paper-wasp problem under my wooden porch; I used to use a commericial wasp-spray to kill the wasps and nests one at a time as I came across them. They would come back several times per season. Then I got fed up (got attacked while mowing the lawn under the porch one day. Not fun!) and sprayed the entire underside of the porch with that spray. Like two cans worth, just doused the wood. That was 4 years ago, and every once in a while I see a wasp or two, but never a paper wasp, and haven't seen so much as the start of nest. So the spray can not only kill live wasps, but per my experience, it can also prevent the start of new nests. The most humane way of dealing with wasps is to stop them from coming around so you don't have to kill them at all. --Jayron32 03:22, 4 September 2009 (UTC)

Wolves afraid of red flags/objects?

Yet another wildlife-related question for today (from your "friend" 98.234 posting from a library): I've lived in Russia for some time (as some of you may have figured out by now; this is also part of the reason why I hate anything that even smacks of Marxism, but that's another matter entirely). Well anyway, in Russia they often have problems with large packs of wolves pulling down cattle in the winter (and also with rabid wolves attacking people, so I'm told), so in the winter their hunters often hunt down and exterminate entire packs of wolves (well, from what I hear, not as much as before, now that they're having their "green revolution"). Anyway: what they often do, according to what I've heard, is to cordon off an area around a wolves' lair with red bunting (lots of little red flags strung on a rope), and then (reportedly) the wolves can't run away cause they're scared of the red bunting, so they won't cross the line even if it's a choice between crossing the line or getting shot. Do any of you know if it's true, and if so, what possible explanations could there be for it? (My wild-ass guess on this would be that maybe the wolves mistake them red flags for fire, so they're scared of getting burned.) Thanks in advance! 146.74.230.104 (talk) 22:43, 3 September 2009 (UTC)

Wolves and dogs colour vision can't distinguish between red and green (dichromacy), so they're can't tell the difference between red bunting and green bunting. While they might be terrified of bunting in general (who isn't) but not because it's red. -- Finlay McWalter • Talk 22:51, 3 September 2009 (UTC)

It's much more likely that the flags smell of humans, and the wolves are justifiably apprehensive about contact with poeple. -- Finlay McWalter • Talk 22:53, 3 September 2009 (UTC)

ratio of brain size to body size

Is there a list showing what animal has the largest brain and nervous system compared to its overall body size? -- Taxa (talk) 23:44, 3 September 2009 (UTC)

I haven't seen such a list. It's sort of a tricky question, because the overall general relationship is that within a group of similar organisms, brain size tends to increase in proportion to the 2/3 power of body size. This means that small animals tend to have the highest brain-to-body volume ratio. The highest I know of is for the hummingbird, where the brain weight is about 1/12 of the body, see this web page. Most neuroscientists place more importance on the so-called encephalization quotient, which is roughly speaking the ratio of actual brain size to the "expected" brain size for a given body size. Perhaps not surprisingly, the species with highest EQ is homo sapiens. Looie496 (talk) 00:08, 4 September 2009 (UTC)

September 4

Containment of Rust

In principle, if I cover something metal that already shows a degree of rust with a clear sealant, will that clear sealant stop the rust from progessing? (I have a sculpture that has an element that is wrought-iron bulrushes. I am stripping the sculpture of old paint that has started to crack, and am scouring off the rust. However, I like the look of the rusted bulrush heads and would like to leave them as they are. I don't want them to rust further.) If the answer is no, is there any other way of stopping the rust at just this point? If the answer is yes, what type of clear sealant would be recommended? The sculpture sits outdoors in the Canadian climate all year round and is in direct sun. Everything else on the sculpture I am painting with a Tremclad primer and then a rustproofing paint for the top coat. Thanks // BL \\ (talk) 00:49, 4 September 2009 (UTC)

"Canadian climate"? Where in Canada? It's a huge place. Rusting is heavily dependent on local humidity, which is different throughout the country. --✶♏‭ݣ 02:16, 4 September 2009 (UTC)

Southern Ontario, in a wetlands valley area, but not on a lake or near salt water. // BL \\ (talk) 03:19, 4 September 2009 (UTC)

Here we use stop-rust-converter, which is phosphoric acid. It turns the rust a grey colour though. Graeme Bartlett (talk) 03:24, 4 September 2009 (UTC)

Toxicity of lead(II) nitrate

Is lead(II) nitrate toxic enough that skin exposure to a single small drop of its solution, washed off after only 1 or 2 seconds, will cause fatal poisoning? --75.40.206.92 (talk) 00:53, 4 September 2009 (UTC)

Probably not lethal, per the compound's MSDS, if there's no cut, etc, and it's pure skin contact. However, we do not offer, and are not qualified to offer, medical advice, and it is advisable to seek proper advice from a doctor asap. Tim Song (talk) 01:03, 4 September 2009 (UTC)

How soon after exposure do the symptoms typically appear? I couldn't find that in the article you linked to. Also, the solution was 1 molar, if that matters.--75.40.206.92 (talk) 01:12, 4 September 2009 (UTC)

These are medical questions that we are not qualified to, and will not, answer. Please seek medical advice from a medical professional. Tim Song (talk) 01:22, 4 September 2009 (UTC)

This is verging perilously close to seeking medical advice, which we can't give here. If you were handling the substance, you should have first read its Material Safety Data Sheet. If you don't have access to that, you can link to it here:[56]

You will note that in the section relevant to skin exposure, it instructs you to seek medical advice (it means face-to-face, from a qualified Medic, although it doesn't explicitly state that). Unless your question was indeed purely hypothetical, please do so. (Addendum: I swear those earlier answers weren't there when I posted mine.) 87.81.230.195 (talk) 02:41, 4 September 2009 (UTC)

No. It wasn't. The guy was probably dissatisfied w/ my response, so he rewrote the question & removed the response. Then you responded; then someone else undid the rewrite/removal. Hence the mess. Tim Song (talk) 03:10, 4 September 2009 (UTC)

green leaf mulch - metabalism of decay?

I have a truckload of mulch which is part mulched branches and about half mulched green leaves. It rained a little and I noticed vapor coming off the pile. When I dug beneith the surface I was shocked to find a large amount of heat coming from the pile. Is the heat due to continued metabolism of the leaves? I can not imagine they have had time to start the process of decay sufficient to produce as much heat as is coming off the pile and besides they are still green. -- Taxa (talk) 01:18, 4 September 2009 (UTC)

• How long has it been there? I found this in Composting: "If the pile is built in a short period, and has a good mix of materials (C:N) and a coarse structure, with about 50% moisture ("like a squeezed out sponge"), the temperature should rise within days to as high as 60 °C (140 °F)." Looks like decay can begin pretty quickly. You might also check Decomposition. Makeemlighter (talk) 04:00, 4 September 2009 (UTC)

Mustard stains turn pink?

So being the slob I am, I just got mustard all over my grey track pants. I went to the bathroom and sprayed a variety of household cleaners on my pants -- I figured I didn't care much if they had bleach stains; I just didn't want them to be yellow. Something even weirder happened: The mustard stains turned pink when I sprayed them with a particular foaming cleaner (containing, among other things, ammonium chloride). What's going on? --✶♏‭ݣ 02:10, 4 September 2009 (UTC)

Most yellow mustard contains tumeric as a coloration agent (it gives it its bright yellow color). Tumeric is also a good acid-base indicator, in that it turns a brilliant vermillion in the presence of a strong base. Usually, there is enough acid (vinegar) in the mustard to keep the tumeric in its yellow form; but if you overwhelm the acid with enough soap, it will turn a bright red. My guess is that the ammonium chloride is of a high enough pH to turn the tumeric red. --Jayron32 03:16, 4 September 2009 (UTC)

The only problem is that ammonium chloride solution is acidic. And per this, you need a pretty strong base to turn it red. However, per Curcumin, if your cleaner contains borates, that can cause the formation of a red compound. Tim Song (talk) 03:53, 4 September 2009 (UTC)

Yes, in particular, borax (sodium borate) is widely used in detergents. Does that foaming cleanser happen to contain borax, by any chance? Red Act (talk) 04:12, 4 September 2009 (UTC)

two neutrons

Suppose I shoot two neutrons out of two neutron cannons at the same time and speed so that they traveled almost parallel but get closer and closer becasue of the slight angle of the cannons. As the neutrons got closer and closer what will they do when they touch? -- Taxa (talk) 02:20, 4 September 2009 (UTC)

Neutronium and Dineutron cover your topic if you would like to take read. Graeme Bartlett (talk) 03:21, 4 September 2009 (UTC)

Neutrons do not repel each other with the electrostatic force, but they do repel each other according to the Pauli exclusion principle. As above, the only relevant way to describe their collisional interaction is quantum-mechanically. Nimur (talk) 03:59, 4 September 2009 (UTC)

Since neither of the above directly answer your question, I'll try. I believe the answer is that, depending on random quantum details, there are various possibilities. They either glide right through each other, bounce off each other, or briefly stick together and then keep going their separate ways. 24.174.30.146 (talk) 04:48, 4 September 2009 (UTC)

Born with feet the wrong way round?

My uncle on my mother's side was born with his feet facing completely the wrong way round, along with webbed toes. He also suffers from some minor mental handicaps, though my family suspect this is the result of the extensive and painful treatment he had to undergo to reverse the position of his feet.

I've searched everywhere and can find no reference to this disorder - my main question is; what is it, and is it hereditary in any way (e.g. is there any chance my or my sister's children could suffer the same fate)? — Preceding unsigned comment added by 94.195.129.212 (talk • contribs)

The best person to answer such a question is a physician. We can't advise whether the condition you described is hereditary. It sounds like your description is not quite correct, either; there are a wide variety of possible physical aberrations which might be close to what you have described, such as club foot, but "feet facing completely the wrong way round" sounds like an implausible scenario. Again, you should ask a physician about this, since we can't diagnose what the actual condition was. Nimur (talk) 04:00, 4 September 2009 (UTC)

It does happen.[57] Red Act (talk) 04:15, 4 September 2009 (UTC)

It's not implausible at all. The genes that control development operate in a hierarchical way, and there are many cases of mutation of a high-level laterality-controlling gene leading to things of that sort. A quick scan of Pubmed didn't show any easily findable descriptions of a syndrome, though. Looie496 (talk) 04:20, 4 September 2009 (UTC)

Well, I understand if it's something you can't comment on. I'm not looking to sue wikipedia over some hysterical self-diagnosis though - I just wanted to know if those symptoms are similar to any kind of recognised disorder, and if they are, whether that same disorder can be passed along.