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June 6

To charge a phone on a bicycle

Hi, is there any gadget I could get anywhere online (or preferably off) that will charge my phone while I pedal my bike? I remember bike odometers that hooked a little wheel to one of the tires (therefore, called "flywheels?") in order to spin the numbers. Could that same small wheel utilize the spinning of the tires to recharge my phone?

If so, where is a device that'll do exactly that? I would hope to find one before a long bike-ride. Thanks. --70.179.165.67 (talk) 04:29, 6 June 2011 (UTC)

Though someone smarter than I am on this matter will be able to give you the specifics, I recall that the amount of pedaling on a bike to produce any worthwhile amount of electricity makes the exercise impractical. So even if you were going to ride a marathon's length, there probably isn't a market for selling devices that charge cellphones this way, so you're out of luck unless you want to build your own contraption.--el Aprel (^facta-_facienda) 05:37, 6 June 2011 (UTC)

While the amount of electricity generated by a bicycle is low, and thus insufficient to heat, air condition, or light your home, or run a major appliance, it is sufficient for devices with minimal power requirements, like cell phones. However, the cell phone charger will need to be improved, as current chargers are rather inefficient (you can tell because they get hot). StuRat (talk) 05:59, 6 June 2011 (UTC)

Are you talking about the AC adapter? If so how old is your phone? All phones I've seen in the past 5 or so years, even very cheap ones come with SMPS power adapters (sometimes labelled as travel adapters). You can easily tell because of the weight (and to a lesser extent size and shape). Cheap electronics from China from eBay, DealExtreme etc also always come with (sometimes poorly made) SMPS. Various sources including our article say this has happened world wide, perhaps because of the decreasing cost of the electronics needed for an SMPS and the rising cost of iron (although the iron bit seems to have been removed from our article). Regulation or government pressure on power supply efficiency may have also played a part. Regardless, SMPS power adapter doesn't tend to get very hot. In any case it's a moot point since it's unlikely you're going to output 110 or 220V AC from your dynamo. Nil Einne (talk) 06:27, 6 June 2011 (UTC)

Yes, but inefficiency is possible with any charging system. And, unlike with the wall plug, there isn't much energy to spare in this setup, so efficiency would be key. StuRat (talk) 06:39, 6 June 2011 (UTC)

So? None of that relates to your original (generally false nowadays) claim about how inefficient current chargers are based apparently on some ancient phone with a linear/transformer based AC adapter. I suspect many dynamos output DC in the 4-12V range anyway since modern lighting systems tend to use that and ones with batteries often even use li-ion nowadays. And any slightly decent DC-DC adapter would generally be at least 50% efficient with something like 70-80% more likely and even 80-95% possible (at least from a more constant source, not sure how well they handle a more variable output you may get from a dynamo although again since dynamos for bikes tend to be targeted towards lighting systems it seems likely this is already something handled resonably well). The phone itself and the actually battery also has some loses but there's not much you can do about that.

Really you're approaching this from totally the wrong angle, sure the efficiency of the charging system and power adapter matters, but you don't seem to be considering the dynamo itself. For example [1] shows 60% but only for the best hub dynamos (which was where I found the link). 30% is more likely particularly for bottle dynamos and we're still talking about name brand dynamos. [2] from hub dynamos (where I found all the links) I think shows shows something similar. [3] ditto I think although you have to manually work it out. And this is at 15-20kmh, at high speeds you efficiency generally drops particularly in the crappier dynamos. Unless you plan to be charging your phone all the time, the 'daytime resistance' would likely matter (although on the flipside for a bottle dynamo you can just disengage it).

In other words, unless you're using a good hub dynamo like a Schmidt Original Nabendynamo, power loses in the DC conversion and charging are perhaps not your biggest concern. (Not saying they are not a concern but you obviously should be considering whether you want a better dynamo first.)

P.S. Worth remembering that given the 4.2V most li-ion batteries chargers or older mobile phones use and the 6V that our hub dynamo article and most of the refs above seem to say a typical dynamo for light systems outputs even a simple linear regulator just burning off the excess would achieve 70% efficiency. Of course nowadays phones are moving to microUSB for charging meaning they accept or require 5V so you get 83.3% with a linear regulator (the phone would have to do some conversion internally but it's likely most phones are fairly efficient).

Nil Einne (talk) 10:36, 6 June 2011 (UTC)

By "charging system", I meant to include the efficiency of the dynamo, as well. If this isn't the term you use, how do you collectively refer to it all ? StuRat (talk) 22:45, 7 June 2011 (UTC)

Many bicycle lights are powered by either rim or within-hub dynamos. You would need to build or commission a device that allowed this power source to charge or power a phone. This will increase the friction and thus effort needed to cycle. Fifelfoo (talk) 05:48, 6 June 2011 (UTC)

Another option might be regenerative braking, where you would pull more power from the wheel for charging purposes, but only when braking. This would be a big seller, if it worked. Obviously, such a system would provide more electricity in "stop and go" driving. One simple way to do this might be with the same dynamo, but where it had a user-operated switch to engage it or disengage (perhaps tied to the gear setting). This might work well in hilly areas, where excess speed could be bled off going downhill, but without the unwanted extra drag going uphill. StuRat (talk) 06:03, 6 June 2011 (UTC)

A simple search for 'bike dynamo phone charger' easily finds options both DIY and commercial [4] [5] [6] [7] [8] [9] [10]. So does 'bike phone charger' (mostly finding the Nokia device but also a few others) [11] [12] [13] [14] [15] [16] [17] [18] [19]. Other then specialist or biking companies evidentially Nokia and Motorola make devices too. Nil Einne (talk) 06:15, 6 June 2011 (UTC)

As an alternative, buy one of these traditional mobile phones (as opposed to these fancy new smartphones with large touchscreen), because they run much longer without recharging (despite that they typically have smaller batteries). – b_jonas 09:03, 6 June 2011 (UTC)

This answer is about as good as saying "Install Linux" when someone asks how to do something in Windows! APL (talk) 09:51, 6 June 2011 (UTC)

Another alternative would be simply to get yourself a solar charger..--Shantavira|^{feed me} 09:13, 6 June 2011 (UTC)

Unfortunately, Very few of those are worth the effort. In most cases you'd be better off economically and perhaps even ecologically just buying ones of those AA-to-phone adapters and popping in some AAs whenever you're away from line power. Problem is that solar panels with any sort of useful efficiency are very expensive, so the ones most of those "Solar battery chargers" use are pretty terrible. (Typically these devices are just rechargeable batteries that you charge from line-current, and the solar panel is mostly for show.)

You'll certainly never get enough juice from the sun with one of those devices to justify the cost, or the ecological impact of its own manufacture.

I've heard good things about the Voltaic backpacks, but even at it's theoretical peak output it's not as powerful as my phone charger. And you figure that unless you're pointing it right at the sun you won't get half that. (You don't normally keep your back to the sun while biking. You have to go where the roads go.) So it's still not really worth the effort unless you're honestly going to be away from line current for a while and for some reason can't carry AA batteries. APL (talk) 09:51, 6 June 2011 (UTC)

So, what would happen if you were to wire your bike lights dynamo to a spare car cigarette lighter socket (I think you can buy these from places like Halfords). You could then charge your phone from that using a car adapter/charger suitable for your phone? Astronaut (talk) 13:57, 6 June 2011 (UTC)

This is nitpicking, but the question says "on a bicycle", not "powered by pedalling a bicycle". When I go camping at music festivals I take a small 12V motorcycle battery and use that with the car cigarette socket charger to charge my phone. You could easily fit such a battery on a bike carrier rack - and charge the motorcycle battery up at home every few weeks. -- SGBailey (talk) 15:00, 6 June 2011 (UTC)

Earthquake tilting Earth axis

Originally asked over on the help desk [20] I've copied it here  Chzz  ►  12:14, 6 June 2011 (UTC)

I have been trying to find out more about the Earthquake in Japan. I read that it caused the earth to move 10 inches on it's axis. Is this true and are we tilted more or less on our axis. I have ask our TV stations abiut this and can't get an answer. I'm 71 years old and I took Astronomy Magizine for about 50 years but had to give it up because of my eyesight, it was just too hard to read. So if you can answer my question or tell me who to ask iI would appriciate it. (Redacted) — Preceding unsigned comment added by 75.221.228.71 (talk) 06:01, 5 June 2011 (UTC)

It was actually 10 cms. Please see our article on 2011 Tōhoku earthquake and tsunami.--Shantavira|^{feed me} 12:20, 6 June 2011 (UTC)

Hm, but in 2011 Tōhoku earthquake and tsunami#Geophysical impacts it says 25 cm (9.8 in), with this ref. And this one says 6.5".  Chzz  ►  12:28, 6 June 2011 (UTC)

Indeed this type of thing highlights the flaws with supposedly referenced information. The New York Times article that is supposedly a reference for the 10 cm figure in fact says "Dr. Gross said his calculations indicated a shift of 6.5 inches in where the figure axis intersects the surface of the planet". The other ref for that sentence gives the 10 cm figure. Regardless, all these articles are from fairly soon after the quake, but it seems that the closer the date of the article to the actual quake, the bigger the figure given, suggesting a bit of early sensationalism or hyberbole. Wonder if anyone can find a genuinely good source from a month or more after the quake that would likely be more reliable. --jjron (talk) 13:30, 6 June 2011 (UTC)

Also worth pointin out that the tilt didn't change. What changed was the position of the axis on earth's surface. Dauto (talk) 17:35, 6 June 2011 (UTC)

Is it more correct that the earth's surface changed relative to the axis? Getting back to the original issue though, it would really be useful to see this as a before/after two sets of axes on the same globe. Even if the actual number could be verified, it still isn't clear to me whether the earth tilted more/less, or the solid vs axis precessed a bit. Spheres have lots of "axis" directions. DMacks (talk) 18:27, 6 June 2011 (UTC)

Changing the tilt of the earth's axis would imply a change in angular momentum which is not possible without an external torque. Dauto (talk) 19:44, 6 June 2011 (UTC)

Cats can rotate themselves in mid-air with no externally applied torque (Falling cat problem). DMacks (talk) 22:43, 6 June 2011 (UTC)

Yes, and they do that by changing the position of their bodies around a rotation axis which remains fixed because of the already pointed out conservation of angular momentum, which is what I was pointing out. Dauto (talk) 15:39, 7 June 2011 (UTC)

I'm not so sure about that. Picture you have a rotating cylinder with heavy iron balls clamped to each of four sides, which are also attached by dangling chains. You spin up the cylinder and suddenly one of the balls gets loose and starts swinging around several feet from it. Well that cylinder is going to start rotating around a new axis. (Something similar can be done with an ultracentrifuge when one or more of the sample tubes break, but there the rotating mass changes) In this case, part of Japan moved down, and so the axis should be a little further "down" from that spot also. The angular momentum and thus the axis of rotation may be fixed, but only relative to the total rotation, not relative to the planet surface. Wnt (talk) 18:02, 7 June 2011 (UTC)

No it doesn't. The cylinder/ball assembly would continue to rotate around the same axis, since all you did was change the moment of inertia of the body. The ball swings out due to the lack of a centripetal force, and then air resistance begins applying an external torque due to a moved center of pressure. In this case, parts of Japan moved down, so the moment of inertia shrunk, producing a faster rate of rotation (similar to the often-used spinning ballerina) due to conservation of angular momentum. Titoxd^{(?!? - cool stuff)} 08:55, 10 June 2011 (UTC)

Hmmm, I wasn't clear there. I mean, the axis of rotation is fixed relative to the fixed stars, but it is not fixed relative to the Earth's surface. If a big enough chunk of crust around Japan drops by three feet, it's possible that the North Pole could move by a few inches. Wnt (talk) 17:20, 10 June 2011 (UTC)

So did it? How much? Sources seem to vary.  Chzz  ►  01:28, 11 June 2011 (UTC)

What are the materials of Polyethylene terephthalate

Does it come from Petroleum?--Inspector (talk) 12:55, 6 June 2011 (UTC)

Yes. If you read down to the Recycling section of the article you linked (and the information should perhaps appear more prominently), you will find the statement

". . . recycling back to the initial raw materials purified terephthalic acid (PTA) or dimethyl terephthalate (DMT) and ethylene glycol (EG) where the polymer structure is destroyed completely . . . ."

If you then read the articles about those ingredients, linking through where necessary to articles about their production, you will find that they derive from petroleum. {The poster formerly known as 87.81.230.195} 90.201.110.217 (talk) 13:14, 6 June 2011 (UTC)

Most PET is probably made from oil and/or natural gas, as are other thermoplastics, but as our polyethylene article notes, it is possible to make such materials from sugar cane and similar cultivated products. In addition, the level of recycling in PET is relatively high compared to other materials. AndyTheGrump (talk) 13:17, 6 June 2011 (UTC)

Checking on the PET article talk page, I see that PepsiCo are apparently working on making PET bottles solely from plant materials: [21]. How 'green' this actually is may be open to question though. AndyTheGrump (talk) 13:28, 6 June 2011 (UTC)

So, How many steps are there between petroleum and PET?--Inspector (talk) 13:41, 6 June 2011 (UTC)

[22] might be a good read. --Stone (talk) 21:12, 6 June 2011 (UTC)

Global Warming – Why Predominantly Negative Effects?

It seems that global warming produces predominantly negative climatic effects, i.e. ones that are inconvenient to humans. Why is this? Would a cooler climate make for milder weather? I find it hard to believe that we've found ourselves in such a climatic sweet-spot — especially when you consider that average temperature has been continuously drifting one way or another throughout history. I was also wondering if there is any geographic location that might actually benefit from global warming.

Thanks!

Alfonse Stompanato (talk) 14:59, 6 June 2011 (UTC)

We have not "found ourselves in such a climatic sweet spot" by accident, we have adapted to it. The climate has actually been remarkably stable for the last 10000 or so years - i.e. for the whole time of human civilisation. We have adapted our agriculture to work well with the combination of climate, soil, and seeds known to us. We have grown large populations where a reliable water supply is available year round by rivers that are buffered by glaciers fed by winter snow that melt in the summer. We build our cities on the current shoreline for both commerce and fishing. The primary problem is not that different global temperatures are inherently better or worse (though they may well be, depending on what criteria you use), the problem is that we experience changes to the status quo at record speeds. On a larger scale, the same applies not only to humans, but to whole ecosystems. Given enough time, both humans and ecosystems will be able to adapt to a new steady state. But we are a long way from reaching a new steady state, and the disruption will be predominantly negative, simply because our lifestyle is optimised to current conditions. There are some other concerns, primarily that a higher temperature means more energy in the climate system, which likely leads to more or stronger extreme weather events. As for benefits, we may be able to reliably use the Northern Sea Route or the Northwest Passage for shipping. --Stephan Schulz (talk) 15:25, 6 June 2011 (UTC)

(after ec)

To answer your last, "benefit" is a subjective term. No doubt the colder regions would benefit from being made warmer, if you're a human being who likes warm conditions. But if you're a capercaillie who has evolved to fit one particular niche, warmer conditions would spell the end for your species in that area. --TammyMoet (talk) 15:28, 6 June 2011 (UTC)

Another point is that we aren't necessarily in a "sweet spot". A few thousand years ago much of the Sahara desert was grassland, and in other parts of the world many areas supported people that are now flooded by rising sea level. Looie496 (talk) 16:09, 6 June 2011 (UTC)

The life around us now has evolved for the last couple of million years to live at about the current temperature or a bit lower as during the ice ages. Dmcq (talk) 16:57, 6 June 2011 (UTC)

I have to admit, I can't shake off the feeling that the Ice Ages that mark our current geologic era are in some way "pathological". If there is anything to the Gaia hypothesis then it would appear that Gaia noticed that the environment was constantly changing for some reason and decided to put some thought into how to dig up the old carbon and get it back out into the atmosphere... While I recognize, of course, that the very rapid warming caused by humans has harmful effects on the ecology, the world has been through such drastic changes quite a bit over the past few million years. So I'm thinking that while controlling carbon emissions is necessary, I wouldn't want to see atmospheric CO2 rolled back to 1600 or even to 1950. I think this position is implicit in climate plans that speak of partial (even 80%) reduction in CO2 emissions, but I haven't really seen the ideal endpoint seriously discussed. Wnt (talk) 21:42, 7 June 2011 (UTC)

See Holocene, Anthropocene, Holocene Climatic Optimum, Little Ice Age, Climate change and agriculture and current sea level rise. Several degrees Celcius of temperature rise would offset any benefits from CO₂ increases, while the greatest human benefits could be seen in previously subarctic areas that become arable land, but only after the permafrost problematicly melts. ~AH1 ^(discuss!) 17:07, 11 June 2011 (UTC)

Is it right that.. (Talking birds)

All bird kinds in the world, could imitate human Speech Just like the Parrots, Myna birds, and others do so?...

is it right that the only "barricade" from all other bird kinds to do so, is just Neural? (Their pro-Larynx Areas in their nervous system).

have i understand correct?

Best blessings. — Preceding unsigned comment added by 109.67.42.106 (talk) 15:35, 6 June 2011 (UTC)

No, not all birds. Only birds from three groups, the Myna and the relatives of the Parrots, the Crows are known to mimic human speech. These birds are relatively intelligent, and have vocal tracts capable of imitating speech. See talking birds μηδείς (talk) 15:51, 6 June 2011 (UTC)

The question is whether more birds than just these varieties have vocal tracts capable of imitating speech, even if the birds themselves don't actually do so. The article does not address that (or much else). --Mr.98 (talk) 16:29, 6 June 2011 (UTC)

I now understand that it's also because of this 3 groups of Birds - unique Larynxal Anatomy (off course, in addition to their neural capability).

Just to ensure i understand correct,

blessings 109.67.42.106 (talk) 17:00, 6 June 2011 (UTC)

Haven't you asked this already up there at #A_beatiful_question_about_Parrots_and_their_voice_producing_system..? – b_jonas 18:17, 6 June 2011 (UTC)

He'd better be careful, or he'll be charged with contributing to the deliquency of a Myna. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:43, 6 June 2011 (UTC)

Just for the record the adjective from larynx is usually laryngeal Richard Avery (talk) 07:14, 7 June 2011 (UTC)

Note also birds use a Syrinx (bird anatomy). Wnt (talk) 21:34, 7 June 2011 (UTC)

And all these years I've been saying "larynctive"! μηδείς (talk) 17:56, 8 June 2011 (UTC)

radiation from magnets

Since photons are the force carrier for electromagnetism, do magnets give of any form of radiation from the electromagnetic spectrum? Bugboy52.4 ¦ =-= 17:25, 6 June 2011 (UTC)

If you hold a magnet in your hand and make fast movements, it will radiate electromagnetic radiation, albeit it not very much. Count Iblis (talk) 17:38, 6 June 2011 (UTC)

(ec) A static magnetic field does not produce any radiation, but a changing magnetic field does -- this is a consequence of Faraday's law of induction. Looie496 (talk) 17:41, 6 June 2011 (UTC)

Is the frequency constant, or is does it change? Bugboy52.4 ¦ =-= 18:15, 6 June 2011 (UTC)

The frequency radiated will be the same frequency of the shaking movements you apply on the magnet. Dauto (talk) 19:39, 6 June 2011 (UTC)

That means 4.3 x 10^13 (43,000,000,000,000) vibrations per second for red light. μηδείς (talk) 20:05, 6 June 2011 (UTC)

So it is possible to emit light in the visible spectrum? Bugboy52.4 ¦ =-= 19:47, 6 June 2011 (UTC)

Not with your handheld magnet, your hand does not shake that fast. What you ahve here are virtual photons. Graeme Bartlett (talk) 20:52, 6 June 2011 (UTC)

I'm not sure what you mean. Radiated photons are real photons, regardless of frequency. -- BenRG (talk) 22:52, 6 June 2011 (UTC)

EM radiation from a rapidly vibrating permanent magnet should be indistinguishable from that generated by , say an Alexanderson alternator(early 20th century radio transmitter via rotating generator) or from a solid state radio transmitter coupled to an antenna. except for the difficulty of achieving physical vibration of a permanent magnet at frequencies beyond a few tens of Hz. Edison (talk) 02:31, 7 June 2011 (UTC)

(Edited to add) I had intended to say "10's of kilohertz," imagining a small permanent magnet bolted to a loudspeaker or an ultrasonic transducer. A permanent magnet could also be bolted to a vibrating rod or wire in tension, for instance, which could easily be tuned to vibrate at frequencies above the audible range, which would in fact be in the low frequency radio frequency range. A magnet held in the hand cold be vibrated manually at 5 Hz or so. This low frequency EM wave could certainly be picked up by a suitable nearby antenna or pickup coil. I've tried the experiment, and viewed the somewhat distorted waveform on an oscilloscope. I agree that the transmitted energy would be negligible. Remind me how EM waves work: would a rapidly vibrating magnet moving left and right produce a transverse electrical field moving up and down, both fields moving away from the origin? If I took an electrically charged object and caused it to vibrate left and right similarly, would it produce a transverse magnetic wave moving up and down? Surely electromagnetic waves are not restricted to electronic oscillators.Edison (talk) 05:16, 8 June 2011 (UTC)

Our piezoelectricity article talks about speed and size of deformation, but not general commentary on frequency limits to its oscillation. However, one of the noted applications mentions 100 kHz–1 MHz. Put a lightweight magnet on it, and you're well into the AM radio range. DMacks (talk) 03:15, 7 June 2011 (UTC)

With a handheld magnet, you can only move it at frequencies up to 10Hz. Radiation efficiency from this would be extremely low with less than picowatts of power transmitted as traveling electromagnetic radiation. Almost all the energy would be in the near field which would extend over 1000 km. This would be dissipated by electric currents flowing in the earth or the ionosphere and so just about nothing would escape into a radiowave far field. Even at the AM frequencies mentioned by DMacks, the antennas are dozens of meters high to get any significant power out. So a small vibrating magnet would still not do much. I am probably addressing Count Iblis q rather than bugboy52.40. For the original question the virtual photons answer still stands. The size of these photons is enormous, thousands of kilometers, so they are not like your normal particle! Graeme Bartlett (talk) 11:26, 7 June 2011 (UTC)

What? Radiated photons are always real, and photons are always point particles, and these photons are most certainly 'ordinary photons' in the sense that no other kind of photons exist. The wavelength of a photon is not a measure of it's physical size! — Preceding unsigned comment added by 129.67.37.190 (talk) 08:28, 8 June 2011 (UTC)

Yes, but I think Graeme's point is that an oscillating magnetic field which then leads to currents being induced should not be thought of as involving real photons. Suppose I have a magnet mounted on a spring that has an angular frequency of omega and next to it, I have a superconducting LC-circuit also with angular frequency of omega. Then both the spring and the LC-circuit have energy levels of

(n+1/2) hbar omega. The spring can jump to a lower energy eigenstate while the LC-circuit moves to a higher level. This process then doesn't involve excited states of the electromagnetic field (i.e. real photons). That process also can occur, but with much smaller probabilty. But in that case, most likely the spring would lose one quantum, while the photon simply moves away, it most likely won't interact with the coil to excite the LC-circuit. Count Iblis (talk) 16:14, 8 June 2011 (UTC)

Brightness of R136a1 when it goes hypernova

The article says it will have the luminosity of 100 typical supernovas. The brightness of supernova 1987A was magnitude +3, and its luminosity was about 1/10 of that of a typical supernova. So, does this mean that R136a1 when it explodes will become magnitude -4.5, making it barely visible at daytime? Count Iblis (talk) 17:44, 6 June 2011 (UTC)

They are about the same distance away from us, so yes. If those numbers are correct, then it would be about -4.5. --Tango (talk) 20:53, 6 June 2011 (UTC)

excited states / energy level diagram of nitrogen

If I look at the grotrian diagram of nitrogen in my book, I don't see a state 2²S_1/2, and the book says that it is not possible because of the Pauli principle. But if I assign the 3 valence electrons as follows, I don't see why this is wrong, where is my error:

• n₁=2, l₁=1, m_l1=-1, m_s1=1/2
• n₁=2, l₁=1, m_l1=0, m_s1=1/2
• n₁=2, l₁=1, m_l1=1, m_s1=-1/2

So the resulting atom should be S=1/2, L=0, J=1/2. ??

best thanks --helohe (talk) 21:01, 6 June 2011 (UTC)

Wow. It's been many years since I studied this stuff myself, but there are ideas about Selection rules like the Laporte rule knocking around in my head, though I am not fully sure how to make it work for you. Remember that monatomic nitrogen is a radical, which may introduce some weird symmetry problems and degeneracies, akin to what you see in odd-electron molecules and ligand complexes, vis-a-vis the Jahn–Teller effect. I've forgotten most of this stuff, and how it works, but that may give you some leads... --Jayron32 05:48, 7 June 2011 (UTC)

Laporte rule might work but I still don't see it. Jahn–Teller effect seems a bit too advanced, as I'm currently only studying single atoms and this is for molecules. I guess I'm doing something wrong with the LS-coupling (Russell Saunders coupling scheme). But still thanks a lot for your answer :) --helohe (talk) 22:51, 8 June 2011 (UTC)

Desert basins

I was wondering what is distinguishable about desert basins which set them apart from deserts themselves. The article Kalahari Basin doesn't really help to explain what physical features separate it from the Kalahari itself.— Preceding unsigned comment added by Flaming Ferrari (talk • contribs) 21:08, 6 June 2011

I think the name Kalahari Basin refers to a drainage basin. The Kalahari Basin is an endorheic basin, which means that water flowing there does not reach the ocean. The same is true for the Great Basin in North America. In other contexts related to landforms, the word "basin" may mean something else; see Basin#Landforms. —Bkell (talk) 22:42, 6 June 2011 (UTC)

(Edit Conflict) So far as I understand it, there is no inherent connection between basins - large landform depressions of various sorts, and deserts - large areas with low precipitation: you can have either one without the other. However, if a basin happens to be in a desert, it's called a desert basin, and is likely to have certain features caused by the combination of shape and climate, namely seasonal water courses, salt lakes or salt flats (dried-up lakes), and perhaps subterranean water if the underlying geology is right. The Kalahari is a slightly different case in that the basin is larger than the desert, and the desert happens to be entirely contained within it; the Great Basin Desert in the USA is similar in this respect. Conversely, the Gobi Desert contains several basins. {The poster formerly known as 87.81.230.195} 90.201.110.217 (talk) 22:43, 6 June 2011 (UTC)

Well, as said in endorheic basin, they tend to be deserts because otherwise the water would break a channel flowing out. A desert is part of a system of classification of land that has a net moisture deficit. There's probably some slop here, I think, in that there are arid regions not classified as deserts that have a net moisture deficit, and lands with a net moisture deficit can still periodically overflow and erode a path to the ocean. Wnt (talk) 18:09, 7 June 2011 (UTC)

Not all desert endorheic basins are dry, however. The Caspian Depression is below sea level and has a huge inland sea. ~AH1 ^(discuss!) 17:01, 11 June 2011 (UTC)

Rotational physics

Hello all. This is a problem that I made up but can't solve :( Imagine an unevenly weighted barbell, say with 20 kg on one end and 10 kg on the other, dropped from an airplane. Intuitively I know that if it is allowed to fall for long enough, the heavier end will be pointed towards the ground. However how do I prove this? I know that I have to use torques but I'm not sure how. Thanks for any help. 72.128.95.0 (talk) 21:08, 6 June 2011 (UTC)

The center of mass will be approximately one third of the bar length away from the 20 kg object. This is where the weight of the entire barbell can be considered to be acting. As the speed of the barbell increases there will be a significant drag force acting on it. The drag on the 20 kg object will be greater than the drag on the 10 kg object, but probably not twice as much so the drag force will not act at the center of mass. As a result, there will be a torque on the barbell caused by the weight (acting downwards) and the drag (acting upwards) and the fact that the two forces are not acting at the same point. This torque will cause the barbell to rotate so that the end with the 20 kg object is pointing downwards, and the end with the 10 kg object is pointing upwards. Dolphin (t) 22:26, 6 June 2011 (UTC)

(ec) There is also an unstable equilibrium if the barbell is exactly vertically oriented, with the heavier weight on the upper side. You can formally solve for the stable orientations by construction torque as a function of rotation angles τ = τ(φ,θ), and solve for zeros of the torque function by setting its gradient equal to zero; and to determine stability, solve for the concavity of the function. Nimur (talk) 22:35, 6 June 2011 (UTC)

Here's a related question: I expect that when you drop it, there is liable to be a little bit of spin, which is going to cause it to rotate or oscillate as it falls (connected with the principle you've just stated), and eventually the heavier end will be pointing downward. My question is: If it were dropped lighter-end first, and with such machine-like precision that it had no spin, wouldn't the light end of it hit the ground first? ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:33, 6 June 2011 (UTC)

If it were dropped with the lighter-end first the weight and the drag would act through a common point so there would be no torque. However, this arrangement would be unstable and practical experience shows that even with machine-like precision, unstable arrangements don't persist for very long and they quickly move towards a more stable arrangement - in this case the barbell would invert and end up with the heavier end pointing downwards. Unstable arrangements can only be maintained with some sort of an active feedback control system - way beyond the scope of the simple barbell experiment. Dolphin (t) 22:40, 6 June 2011 (UTC)

Sure. The slightest variation in the air it's falling through would start it tumbling, I'm sure. I'm just talking theory. Yet another question: The barbell will oscillate and the heavier end will rotate to the downward. But it won't just stop there, right? It will kind of act like a pendulum, oscillating for some time, with less arc each time until it stabilizes. Right? ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:02, 7 June 2011 (UTC)

It is dangerous to rely on intuition for things like this. The answer actually depends on how the weights are shaped. If you use two disc weights, a 20 kg on one side and a 10 kg on the other, then drag will be relatively greater on the lighter side, and you will end up heavy-side downward. But suppose you use three equal disc weights of 10 kg, with two on one side and one on the other. In that case the drag forces will balance, at least at the start, and there will be no intrinsic tendency to spin. However if there is any initial instability, things can get very complicated. Looie496 (talk) 22:54, 6 June 2011 (UTC)

@Looie496: Please explain drag will be relatively greater on the lighter side. Dolphin (t) 23:04, 6 June 2011 (UTC)

The surface-area-to-mass ratio will be larger for the lighter side. Looie496 (talk) 23:18, 6 June 2011 (UTC)

I agree that the surface-area-to-mass ratio will be larger for the lighter side. The larger object has greater surface area than that of the smaller so I would say the drag on the 20 kg object will be greater than on the 10 kg object, but by a factor less than 2 for the reason you have given. The factor is less than 2 so a torque acts on the barbell to cause it to fall heavy-side down. If the factor was exactly 2 there would be no torque and the barbell would fall with the bar horizontal. (If the factor was greater than 2 the torque would cause the barbell to fall light-side down.) Dolphin (t) 23:53, 6 June 2011 (UTC)

Any equations we specify to estimate drag based on the geometry and mass distribution will be just that - estimates. As every high-school physics student knows, force due to air resistance is a very difficult parameter to quantify and model. But, for any specified model of air resistance, we can construct the equations of motion and estimate the dynamics of the object as it falls and tumbles. As I described above, one such approach is to seek the steady-state, where net torque is zero. This is not the only way we could model the dynamics; but it's simple and allows us to find a "preferred" orientation. In reality, with turbulence, velocity-dependent drag, and so on, the actual model should account for all kinds of higher-order effects. When I need more sophisticated models, I toss out the elementary physics and use MDATCOM for modeling airflow and estimating turbulence. Nimur (talk) 00:23, 7 June 2011 (UTC)

Why are you all saying that the drag depends on the mass? Drag depends on surface area, velocity and, in very complicated ways, shape and texture, but it shouldn't depend on mass. The resultant force will depend on the mass, since it's the sum of the weight and the drag, but those are two separate forces. If we assume the weights on either end are identical except for their mass, then the drag will be the same on both, so can be considered to act through the geometric centre. That is not the same as the centre of gravity, which will be nearer the heavier end, so you have a torque and the object rotates. It will eventually reach a stable equilibrium when the heavier weight is at the bottom (since then the drag acts along the length of the object, so goes through the centre of gravity) and stay there. How long it takes to get to that equilibrium will depend on how big the drag is compared to the mass and how far from the geometric centre the centre of gravity is. A barbell would take a while to reach equilibrium, while a piece of paper with a blob of blutac on one edge would reach it very quickly. --Tango (talk) 00:31, 7 June 2011 (UTC)

We are all making the obvious assumption that the objects on either end of the bar are made of the same material so have the same density. Therefore their volumes are directly proportional to their masses. Dolphin (t) 00:37, 7 June 2011 (UTC)

Yes. Now here's a different question: What if the two ends of the barbell were identical in size, but one was made of iron and one made of aluminum. Does "drag" still figure into it? ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:01, 7 June 2011 (UTC)

See Tango's answer just above that you're indenting from. The forces will act through the geometric center because the shapes are symmetric, but will not act through the center of mass because of the density difference. This creates torque that will eventually leave the heavier end at the bottom. — Lomn 12:19, 7 June 2011 (UTC)

Another way to approach this problem is to look at the location of the center of mass (where "weight" forces balance) versus the location of the center of pressure (where "drag" forces balance). The object will be stable when the center of pressure is behind the center of mass (which is why arrows have feathers--the feathers move the center of pressure backwards without appreciably affecting the center of mass). In essence, that's no different than what everyone else is saying, but I think it might be easier to visualize. Andrew Jameson (talk) 12:40, 7 June 2011 (UTC)

Surely at terminal velocity we are way above the critical reynolds number for steady flow, and the barbell will tumble as it sheds vortices. Supposing that the lyapunov exponents are greater than one (which for such a flow they almost certainly are) then there is simply nothing that can be known about the orientation of the system on impact, based on its orientation at release. — Preceding unsigned comment added by 129.67.37.190 (talk) 15:00, 7 June 2011 (UTC)

Ionic liquids

Why don't the intermolecular forces between the positive and negative ions crystallize them into a solid? --75.40.204.106 (talk) 23:13, 6 June 2011 (UTC)

Our fairly detailed article entitled "ionic liquid" says that it's just an ionic compound with a low melting point ("liquid at room temp" for example), not an intrinsically "liquid" chemical. DMacks (talk) 23:29, 6 June 2011 (UTC)

Sleep and endurance athletes

This 2007 NYTimes article explores why endurance athletes sleep so much. I tried searching the scientific literature about this, but came up empty. Although I'm a bit groggy from a workout this morning. Can someone explain why long, intense workouts seem to cause sleepiness (preferably cited to review articles)? Yet short workout seem to have the opposite effect? I looked at our sleep article, but was unimpressed. Thanks. -Atmoz (talk) 23:46, 6 June 2011 (UTC)

For short workouts, you get the benefit of the adrenaline, which wakes you up. For longer workouts, this wears off and fatigue starts to take it's place. This means that damage, like tiny tears in muscles and cracks in bones, builds up and needs to be repaired during sleep. StuRat (talk) 22:37, 7 June 2011 (UTC)

The short answer is that there isn't really much to add to the NYT article. (Gina Kolata is very good, and doesn't miss much.) The literature confirms that prolonged intense exercise leads to increased sleep (e.g., PMID 9140908), but doesn't explain why. It isn't that hard, of course, to come up with more or less plausible speculations. Looie496 (talk) 23:31, 7 June 2011 (UTC)

Thanks to you both. ...but doesn't explain why. It isn't that hard, of course, to come up with more or less plausible speculations. Yup. The most common I've seen is actually StuRat's example that sleep is needed to repair tissue. But why would you need to sleep for that and not just rest? What are the biological processes that occur during sleep that facilitate this healing? I don't expect the ref desk to answer that, because based on my searching the last couple days, it doesn't appear that anyone knows the answer, or everyone is satisfied with the plausible speculations. I guess I'll just have to be satisfied with that for now. :) -Atmoz (talk) 02:05, 8 June 2011 (UTC)

Well, there actually is some information about how sleep promotes recovery -- our article Sleep#Restoration summarizes the evidence. Basically the sleep state induces hormonal and immune system changes that don't happen during a simple resting state. What is not clearly understood is how tissue damage produces an increase in sleep -- which I saw as the question that was being asked. Looie496 (talk) 03:09, 8 June 2011 (UTC)

I was originally asking what causes that increase need for sleep. But the lack of answer got me to wondering why we need sleep and not just rest. It would seem from an evolutionary biology point of view that needing to sleep after strenuous exertion would be a disadvantage over those that could get the same restorative properties from simply resting. The sleep article has a paragraph that speculates on this, and actually cites doi:10.1016/0304-3940(91)90276-Y where arctic ground squirrels actually arouse from hibernation to sleep! -Atmoz (talk) 14:58, 8 June 2011 (UTC)

That's an interesting article! I always thought that since almost all animals need to sleep, this outcome of evolution must be someting universal, so the fundamental explanation needs to come from mathematics (optimization/game theory) and not biology. If you have machines competing with each other, then a machine that operates in a single mode in which it also repars itself is going to be outcompeted by machines that don't carry out repairs in a "normal mode" and switch to a specially designed "sleep mode" that is optimized for carrying out repairs. Count Iblis (talk) 15:28, 8 June 2011 (UTC)

In addition to the need to perform repairs, the spinning of the Earth also makes day and night, with light levels so different that plants and animals must be specialized for each. Thus, it makes sense for them to sleep (and thus perform repairs) during the period which they aren't adapted to handle. StuRat (talk) 17:57, 8 June 2011 (UTC)

Another issue here is the increased sleepiness after exercise. I think this is really due to not getting enough sleep generally. If you always sleep 8 hours or more then you don't feel more sleepy after exercise, not even if the night before you happened to get less sleep. But if you usually sleep 7 hours or less, then you may notice increased sleepiness after doing hard exercise, even if you happened to get 8 hours sleep the night before. Count Iblis (talk) 20:10, 8 June 2011 (UTC)

June 7

Bowel and bladder control with ALS

Can people with ALS usually detect a #1 or #2 coming on and, if so, do anything to hold it in? 76.27.175.80 (talk) 00:22, 7 June 2011 (UTC)

Did you read ALS? if you look at the end of the 'disease progression' section your question is answered, to some extent. Richard Avery (talk) 07:10, 7 June 2011 (UTC)

The original question was as follows:

Can people like name redacted usually detect a #1 or #2 coming on and, if so, do anything to hold it in?

I re-worded the question to the version you see above, out of respect for the person named. Dolphin (t) 12:59, 7 June 2011 (UTC)

Mechanism of rotating gas cloud round gravity center

question :how dos any interstellar gas cloud rotate round gravity field ?(replay by intering all dynamic and termodynamic and statistical physics factors)--[[

Special:Contributions/78.38.28.3|78.38.28.3]] (talk) 03:00, 7 June 2011 (UTC)—Preceding unsigned comment added by 78.38.28.3 (talk) 03:00, 7 June 2011

Why don't you create an account? Your questions often look like homework but for those who know you it is clear that they are not, and that you ask out of genuine interest. It would also make it easier to put some advice or help on your discussion page. And, when you sign your posts with ~~~~ the user name you had chosen would automatically appear and you don't have to do all this signing by hand each time. 93.132.188.46 (talk) 10:50, 7 June 2011 (UTC)

And it would not be as easy for others to put misuse to your questions, pretending it came from you. 93.132.188.46 (talk) 10:53, 7 June 2011 (UTC)

I have to apologize for my silly proposal. I thought for myself: why not create an account for myself? But I failed for every try because all user names I could think of are already in use or rejected because they are too similar to some already existing ones. 93.132.188.46 (talk) 20:22, 7 June 2011 (UTC)

many thanks of your guid I have account and this is my signature(I am online now)--Akbarmohammadzade (talk) 04:53, 8 June 2011 (UTC) (talk) 04:47, 8 June 2011 (UTC)

To get to the actual Q, the cloud likely has a tiny rotation inherited from larger galactic rotation, which in turn comes from galactic cluster eddies, ultimately going back to the Big Bang (although what caused the initial rotation right after the Big Bang is a mystery). As gravity pulls the gas in closer, it spins faster, due to the conservation of angular momentum. StuRat (talk) 20:42, 7 June 2011 (UTC)

I want to know can any gas cloud or nebula be able to have momentum of inerthia , and center of mass?--Akbarmohammadzade (talk) 04:56, 8 June 2011 (UTC)

Yes, a cloud of gas has both. StuRat (talk) 08:09, 8 June 2011 (UTC)

You may want to read star formation, protostar and molecular cloud. ~AH1 ^(discuss!) 16:35, 11 June 2011 (UTC)

grouping and cross-matching in blood bank

can plasma be used (instead of serum) for blood grouping and cross-matching in blood bank? — Preceding unsigned comment added by Goldenvikie (talk • contribs) 17:07, 7 June 2011 (UTC)

Yes. Blood anticoagulated with EDTA is often used. Details here. --NorwegianBlue ^talk 20:55, 7 June 2011 (UTC)

How healthful is this bread?

I want to buy low-sodium, low-sugar 100% whole wheat bread, but it doesn't seem to exist. For some reason this bread [23] is not labeled as 100% whole wheat. What's your verdict? (The link includes a list of ingredients as well as the Nutrition Facts. 66.108.223.179 (talk) 19:14, 7 June 2011 (UTC)

I'm surprised it can be sodium free, since I thought yeast needed some sodium to grow. That bread looks to be healthy, though. StuRat (talk) 20:34, 7 June 2011 (UTC)

Not at all: you can make bread without salt very easily: it rises quicker, but tastes blander. Less of a problem if you spread it with salted butter ;) The yeast don't need the salt: the salt actually slows the rising down, which is handy if the weather is warm, you don't have a cool enough spot, and you want a slow rise for taste or convenience's sake. You can only take that so far before the bread is inedible, which generally hits well before you risk killing the yeast completely. 86.163.0.72 (talk) 20:46, 7 June 2011 (UTC)

You all are talking about different things. The OP is asking about low-sodium, StuRat reads this as "sodium free" and 86.~ talks about salt, and it reads as if he is talking about additional table salt (NaCl) that was not already present in the wheat. 93.132.188.46 (talk) 21:25, 7 June 2011 (UTC)

No, I think StuRat is refering to the bread in the link which is listed as sodium free. Richard Avery (talk) 22:18, 7 June 2011 (UTC)

How would it be possible to make bread literally sodium free? Not adding salt and using distilled water would sure be necessary but still there would be the sodium from the wheat. Plants, like all living things (live as we known it), contain essential parts of sodium. 93.132.188.46 (talk) 22:31, 7 June 2011 (UTC)

Yes, I refer to the 0 mg of sodium listed under the "Nutrition" tab on the link. Perhaps it's a case of "rounding down", and it really has a small amount of sodium. I still think that yeast must require some sodium to grow, but perhaps the small amount already present in the wheat and water is sufficient, with no need for added sodium. StuRat (talk) 08:02, 8 June 2011 (UTC)

Or perhaps they used KCl instead of NaCl to salt the bread? I think it's rather unlikely, but... 67.169.177.176 (talk) 00:03, 11 June 2011 (UTC)

This bread is healthful and widely distributed. Their "Yoga Bread" is very good but so are their other breads. The company is called "The Baker". They make granola which isn't bad either, though I prefer udi's granola—also widely distributed. Bus stop (talk) 23:40, 7 June 2011 (UTC)

Physics Is Phun!

A curious thing happened today. I got up from my seat on the bus before it stopped moving and as the velocity decreased exponentially I felt that I were going to fall forward. I compensated by walking faster. Now my question is, was I really walking faster, or was it an illusion? What are the pertinent functions and how can I notate this action? Schyler (one language) 23:27, 7 June 2011 (UTC)

A very qualitative discussion: Let's imagine the bus was going a constant speed, say, 25 mph. While you're sitting on the bus, or even walking around on it, you won't feel like you're moving at all — basic Galilean invariance. When the bus starts to slow down, your body is still going 25 mph, but you are slowing down along with the bus. (If the bus slows down immediately, you'll fly through the window at 25 mph, because you didn't adjust to the speed of the bus.) If you're up and walking around, you're going to be potentially not slowing down at the same rate as the bus itself, and thus feel an acceleration (a falling feeling). The illusion is that when you walk forward, you feel like you're speeding up. You're not — the bus is slowing down, but your relative speed vs. the relative speed of the bus is probably faster than the bus (e.g. the bus is going 23 mph, but you're still going 25 mph). --Mr.98 (talk) 02:10, 8 June 2011 (UTC)

Yes, you were walking faster. When you are seated, friction is equal and opposite to the stopping force causing the bus to lose forward momentum. Therefore, when you stand up during this time, friction is drastically decreased, meaning the stopping force is also decreased for you compared to the bus. This difference in stopping force inturn results in a decreased deceleration for you, i.e. you lose forward momentum at a slower rate than the bus. Plasmic Physics (talk) 02:26, 8 June 2011 (UTC)

Friction has nothing to do with this. It is a question of relative acceleration, as Mr.98 explains, though it is also a matter of how you 'perceive' this. If you are standing still, and start to tip forward, you put a foot in front of you. If you are walking, and start to tip forward, you compensate by walking faster. Try standing still in the bus as it brakes - you will step backwards to avoid falling. Essentially, you are trying to keep the vector of forces generated by your weight (vertically downwards) and the deceleration of the bus (horizontally forwards) acting through your feet - you have to move them forward of your centre of gravity to avoid falling over. AndyTheGrump (talk) 02:35, 8 June 2011 (UTC)

Sorry, not friction, but torque. Plasmic Physics (talk) 07:23, 8 June 2011 (UTC)

Let us assume that the you can be represented by a rigid lever arm, where your center of mass acts as the axis of rotation. Obviously, the force is applied to the level arm at the point of contact between you and the bus. If you are seated, your center of mass will be lower down than when standing, thus the lever arm will be shorter. The applied force is the same whether you are seated or standing. Because torque is a measure of the lever arm distance multiplied by the (orthogonally) applied force, you will experience a greater torque when standing. This is an over simplification, since in reallity a person has many active axes of rotation i.e. skeletal joints, and is not rigid. The effect of the greater torque on a standing person means that they will be rotated around their center of mass, resulting in gravitational torque. Gravitational torque causes you to fall forward, this is a result of the first toque produced by the stopping force. You do not fall over when seated, because you are ellastic enough to absorb the lesser torque. Plasmic Physics (talk) 13:55, 8 June 2011 (UTC)

I should qualify my answer just to note that if you were walking forward at any particular speed, you might in fact be speeding up slightly, but the forces you feel are not due to you speeding up so much as the bus slowing down, and you not slowing down with it. (The reason your walking forward will not matter much is because the relative speeds of the bus are so much faster than your relative speed of walking — you're already going 25 mph, and at most your very brisk walking is going to be another 1 mph or so.) --Mr.98 (talk) 13:49, 8 June 2011 (UTC)

Brisk walking is 3-5 mph. Googlemeister (talk) 18:28, 8 June 2011 (UTC)

June 8

Red/white poppy flowers

Recently in south east england I saw some poppies in someone's garden where the petals were both red and white, with the two colours irregularly mixed together. Does anyone know the species and or variety please? They were undoubtedly cultivated garden flowers and not the wild ones. Thanks 92.29.122.28 (talk) 00:25, 8 June 2011 (UTC)

Interesting. I wonder if it's a chimera (plant). StuRat (talk) 07:58, 8 June 2011 (UTC)

Googling for variegated poppy leads to a few photos. Also Shirley Poppy might be relevant. AndrewWTaylor (talk) 10:37, 8 June 2011 (UTC)

Thanks. I have not been able to find any photos of what they looked like, except this http://1.bp.blogspot.com/_lk-o4M_gWu4/TU99gCr0wUI/AAAAAAAAB5c/53BhPQ0jQ1k/s1600/5RCARN.jpg They were not picotee either. There was not any pink (like Shirly poppies), they looked as if red and white paint had been put in a pot and just stirred once or twice only. 92.28.242.181 (talk) 13:49, 8 June 2011 (UTC)

With the greatest respect, are you certain they were poppies? Richard Avery (talk) 14:07, 8 June 2011 (UTC)

Yes. Some searching around the internet reveals that there are a large number of little-known varieties of garden poppies, but I havnt found what I saw yet. 92.28.242.181 (talk) 15:36, 8 June 2011 (UTC)

Perhaps what I saw was a clump of the "Danish Flag" variety, viewed from the side. 2.101.15.113 (talk) 11:30, 9 June 2011 (UTC)

Stomach and food poisoning

I thought that bacteria, apart from Heliobacter, could not survive being in the stomach. If that is true, then how do people catch food poisoning? 92.29.122.28 (talk) 00:29, 8 June 2011 (UTC)

(a) The stomach is a harsh environment for bacteria but it doesn't infallibly kill them. (b) However, lots of food poisoning comes from toxins created by bacteria rather than from ingesting live bacteria; for example botulism, usually. Looie496 (talk) 00:37, 8 June 2011 (UTC)

Thanks, but news about the current E. coli food poisening scare in Germany suggests that the bacteria do infect people. 92.29.122.28 (talk) 00:39, 8 June 2011 (UTC)

Well yes, no one said otherwise Nil Einne (talk) 01:02, 8 June 2011 (UTC)

(e/c)There are many bacteria (including quite a lot of the more normal variants of E. coli) that routinely hang out in the gut. Once you get past the stomach it's quite habitable, and the stomach acid might kill 99.99% of the bacteria and still leave enough to establish an infection. EHEC inovlves an actual infection, so something has to survive, but it's more on the lines of toxicoinfection - the bacteria produces a toxin that causes the issue, the mass of bacteria isn't the problem. SDY (talk) 01:10, 8 June 2011 (UTC)

One method is endospores, which are the cellular equivalent of a bank vault. To quote the article, "Endospores can survive without nutrients. They are resistant to ultraviolet radiation, desiccation, high temperature, extreme freezing and chemical disinfectants. Common anti-bacterial agents that work by destroying vegetative cell walls do not affect endospores." Reputedly botulism endospores are killed by stomach acid,^[24] but Clostridium difficile (a diarrhea bug) is not.^[25] (But I don't get why people on Prilosec OTC don't get botulism from honey then...) Wnt (talk) 01:34, 8 June 2011 (UTC)

To the best of my knowledge, the stuff written above is correct, but a little bit beside the point of the question. Stomach acid is indeed a very harsh solution for anything to survive, which is why the dose makes the poison. A single E. coli has such little chance of making it through your stomach intact, that you might as well call it impossible, but if there are thousands or millions of bacteria present, even wiping out 99.999% might leave enough to start an infection. This is the nub of all food safety and food handling regulations: you can't completely eliminate the presence of germs, but by keeping food at a safe temperature, you can hopefully keep the bacterial load down to the point where normal human immuno-defences can do their part. Where you really run into trouble is where items not normally considered a potentially hazardous food get contaminated with something like E. coli, as in situations where untreated human or animal feces get into the irrigation system and essentially turn that tasty cucumber into a bomb filled with bacteria-laden water. Nobody worries about the temperature of a cucumber, you can't wash the bugs off, and few people routinely cook their cucumbers to a temperature high enough to kill of the germs (I'm using cucumber as an example here; it could be anything). Now you're ingesting thousands of bacteria, killing off 99% of them with your stomach acid and getting infected with the remainder. Matt Deres (talk) 14:05, 8 June 2011 (UTC)

Sorry, I didn't think about the EHEC outbreak when I wrote this. For E. coli, endospores are not an option; even so, it is said they can evolve resistance to stomach acid, and in fact, that the grain-fed diet of cows during "finishing" causes them to be much better at passing the consumer's stomach.^[26] I should say, though, that I don't really understand this argument - it implies that every strain of EHEC can evolve acid resistance or lose acid resistance over 5 days of feeding - yet the trait doesn't change while the bacterium is being tracked into a vegetable patch, picked, packed, shipped, and sitting on the supermarket shelf. But I suppose if any are resistant they stay in the vegetable population at some level... I don't know. But it's something of a political cause if you're interested. I should note, however, that sometimes I've gotten steaks produced in a more progressive way at a co-op store with a really strong "hay" taste, very much stronger than the mild flavor of venison, and I'm not sure grain feeding is all bad. Wnt (talk) 00:47, 9 June 2011 (UTC)

Gram-negative bacteria have a protective glycoprotein coating outside their cell walls, which makes them more resistant to extreme pH levels. -- An American ultranationalist 67.169.177.176 (talk) 23:58, 10 June 2011 (UTC)

Exercise and rest

If for example someone ran a marathon or half-marathon one day, how do sports coaches calculate how many days they should wait before doing the same thing again? I understand that it is possible to over-train. Thanks 92.29.122.28 (talk) 00:38, 8 June 2011 (UTC)

I believe these are mostly rules of thumb based on experience, not anything derived from science. Looie496 (talk) 01:10, 8 June 2011 (UTC)

Depends on the individual. For example, not many people could do this. -Atmoz (talk) 16:03, 8 June 2011 (UTC)

I vaguely recall hearing that the British army has changed its exercise/rest training schemes in recent years - does anyone know anything about that? Thanks 92.28.242.181 (talk) 13:51, 8 June 2011 (UTC)

But isn't that simply because the fitness of the general population in Britain has declined sharply? I've read that today's top 5% Cooper test scores for school children are below the average values recorded in the 1980s. Count Iblis (talk) 15:46, 8 June 2011 (UTC)

Really? I wonder if they changed the test or the way they scored it in the last 30 years because that would be quite the drop if true. Googlemeister (talk) 18:27, 8 June 2011 (UTC)

Are those tests taken by school children of approximately the same age? For example, I could imagine that in the 1980s most schoolchildren would take the test, whereas now many of the older children skip it with some excuses, so you only get results from the younger ones. – b_jonas 09:49, 9 June 2011 (UTC)

Yes, they compared children of the same age. I think this was mentioned a few years ago on BBC's Science in Action. Yesterday I tried to find some articles on this, but what I found was even more alarming. There is an Iranian study that measured fitness of young adults of about 22 years of age. Out of 250 males, the best result on the Cooper test was just 2300 meters. Now, 2300 meters is considered indicative of average fitness for someone of that age. In Britain, far more people are obese than in Iran, so you would expect even worse results. Count Iblis (talk) 15:12, 9 June 2011 (UTC)

I believe the army changed the length of the rest period - I do not remember the details. 92.24.128.171 (talk) 18:46, 8 June 2011 (UTC)

Presumably there are more then 100 countries with an "army" so we can't really help with the details. Googlemeister (talk) 14:42, 9 June 2011 (UTC)

Care to explain what you mean, or have you skipped the word "British" above? 92.24.129.68 (talk) 20:45, 9 June 2011 (UTC)

Animal Testing

The PETA article says that they "promote alternatives [to animal testing], including embryonic stem cell research and in vitro cell research". Would these be viable alternatives to animal testing? 65.92.5.252 (talk) 01:05, 8 June 2011 (UTC)

I think in general cell culture studies have a fairly poor reputation - different cell lines tend to do different things. In part that's because to this day people still fairly often use cell lines from tumors that have diverged greatly from the natural tissue they are supposed to represent - even having different karyotypes. I think that careful immortalization of cell lines with the smallest amount of genetic change possible might improve their usefulness a little.

That said, there's no substitute for the real animal - and the real animal is scarcely a substitute for the human. In vitro, dextran sulfate cures HIV. In vitro, immortality is easy, and gene therapy can target more than 90% of cells. There's not much you can do with pharmacokinetics and bioavailability in a tissue culture dish. And it makes poor practice for medical students learning surgery...

Of course, even animals can be a poor substitute for humans ... especially when studied by stupid people. See TGN1412, for example. That study would have been better off if they'd been allowed to go straight from the mouse to the human, because testing the human monoclonal antibody in a monkey made them think it had a low affinity ... when in fact there were a few 'minor' differences in the primate sequence. The results weren't pretty.

Much of this has more to do with "ethics", such as it is, than science. If we were serious about fighting disease - serious in the way that we've been about fighting wars - then we could line up a million test subjects, take every drug before it's ever entered the "pipeline", and test it on them flat out. Give the casualties medals, the survivors money and veteran health benefits, and jump medicine 15 years into the future - saving more lives than were lost. I don't know why that is only a noble thing to do when you're trying to kill people. Wnt (talk) 01:21, 8 June 2011 (UTC)

Not doing the basic research first would be ridiculous. The actual success rate for new chemical entities is dismal. The military equivalent would be like a human wave attack. Read up on WWI for how effective those are. For serious problems like HIV and malaria, it's not the lack of drugs that fails us, it's that the patients can't afford them, so mass suicide in the name of drug research isn't exactly justified. SDY (talk) 01:36, 8 June 2011 (UTC)

To be clear, I was not suggesting to try drugs before some rationale for activity had been devised. Nor trying them at once in large doses - rather, working up the dose gradually in a few subjects, like Sasha Shulgin's psychonauts. As for affordability, one aspect of a military-like campaign is that the drugs thus invented would be public property, and therefore quite inexpensive. Wnt (talk) 01:41, 8 June 2011 (UTC)

The way it's done currently is actually fairly sensible, though sometimes slow: they try and throw out the losers (the vast majority of candidates) in pre-clinical (mostly animal) testing, which is cheap compared to human testing because the standard of care is much lower (no one expects a $20,000 hospital stay for mice, except maybe PETA). Initial testing for things like genotoxicity (i.e. "is the drug mutagenic/carcinogenic?") are done in bacteria, which is dirt cheap (no one cares if you slaughter a million bacteria). Only 10-20% of drugs that enter clinical trials are approved, but most drugs don't make it to clinical trials at all, and approval isn't the final word on whether a drug is worth using. If the chances were higher, it might be worthwhile to go to human testing earlier, but the chances are really, really poor, and you'd just be throwing away people. PETA's point is that we're basically just throwing away animals with the same callous disregard. There are some ethical standards in animal testing, but they're mostly focused on easily avoided pain and suffering as well as ensuring the scientific validity of the study so that the deaths are not meaningless. As for "inexpensive" that a government pays for it doesn't make it free. SDY (talk) 07:03, 8 June 2011 (UTC)

With all forms of "intellectual property" there is a trade-off between the price and the number of copies sold. In the case of the newest pharmaceuticals, this is becoming rather absurd, with drugs routinely introduced that cost over $100,000 per patient, even though they are ordinary monoclonal antibodies any passable technician can make.

I don't deny the usefulness of screening in bacteria, cell culture and mice in many situations - it's more the bureaucratic requirement for a certain sequence of studies before a human test can be done. The primate studies bother me the most, but in general, once a compound has some promising indication, it would be nice to see if it can help those in great need. Instead companies are supposed to go through a gauntlet of intermediate tests, anteing up the venture capital ahead of time, paying the bureaucrats' salaries as they go, in the hope of a payout ten years later that depends more on marketing than medicine. There has to be a better way to do things. Wnt (talk) 08:05, 8 June 2011 (UTC)

If "any passable technician" can make them, why don't they? Also, the tests are there because the law demands it, and that obviously adds to the cost. But would you prefer the old (pre-regulation) way, where they just tested however they felt like doing it? ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:14, 8 June 2011 (UTC)

That would probably infringe on the patent and get the tech sued. Googlemeister (talk) 13:37, 8 June 2011 (UTC)

Sorry, I let myself get carried away here - this isn't really the place for a lengthy political debate, and I'm getting too far off topic. Wnt (talk) 13:46, 8 June 2011 (UTC)

Regardless, as you suggested in your first statement, using less-effective tests just for the sake of "political correctness" towards lab animals is not necessarily the best approach. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:05, 8 June 2011 (UTC)

Four wheel drive..... and two wheel drive

Hi. I know that four whell drive vehicle is more powerful then two drive vehicle . but which one consumes more fuel two wheel drive or four wheel drive.......... I have doubt because I think both carry equal weight so both should consume equal fuel. — Preceding unsigned comment added by 220.225.96.217 (talk) 05:48, 8 June 2011 (UTC)

Four wheel drive vehicle has at least one extra differential and a set of driving axles to wheels. Thes increases both weight and mechanicla losses (friction), so it will consume more fuel. -Yyy (talk) 06:52, 8 June 2011 (UTC)

Agreed. Also, 4-wheel drive vehicles are not inherently more powerful than 2WD. However, in order to be able to still move at a reasonable speed despite the increase in weight and friction, they do tend to put more powerful engines in 4WD vehicles. Such engines are often diesels and/or mated to transmission geared lower, though, meaning 4WD vehicles typically have more towing and climbing torque, but less horsepower, and therefore don't typically accelerate very quickly. StuRat (talk) 07:51, 8 June 2011 (UTC)

A king cobra question

I saw a TV show recently about a king cobra tracking project. One finding that apparently wasn't expected (although I'm not sure why) was that males sometimes kill pregnant females. Unfortunately, having an attention span of a puppy, I may have missed the bit where they explained how a king cobra can kill a king cobra. Seems puzzling given that they use their venom to kill other snakes. What does this mean ? King cobra venom is toxic to king cobras ? King cobras are only immune (I assume they are immune) to their own venom ? It wasn't the venom that killed the females ? I can't find anything in our article or in google. Thoughts ? Sean.hoyland - talk 08:12, 8 June 2011 (UTC)

Why do you assume they are immune to their own poison ? If it gets into their blood stream, it's probably toxic to them, too. But heck, bacteria from our saliva would do bad things if large quantities of it got into our blood, too. StuRat (talk) 10:17, 8 June 2011 (UTC)

For no good reason really other than an assumption that there will be a fairly large quantity of venom left in their mouth after biting prey and some of it could get in their bloodstream through mouth cuts etc. I didn't realise but the Snake_venom#Immunity articles mentions an Egyptian banded cobra that accidentally bit itself. Sean.hoyland - talk 11:22, 8 June 2011 (UTC)

That's an interesting writeup, and it raises a question. Apparently, it's possible for a human to become immune to snake venom by presumably small innoculations over time and somehow the body builds a defense for it. But apparently this does not hold for poisons such as arsenic or mercury. Is that because the venom is organic and those poisons are not? Also, in The Princess Bride there's a key sequence in which the hero has "spent five years building up an immunity" to a (fictional) poison that is supposedly the most potent in the world. Is that actually possible for any poison, or only (maybe) if the poison is organic? ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:09, 8 June 2011 (UTC)

I think it can work the other way too. I remember seeing something about a researcher who has been bitten by cobras a couple of times, survived because of antivenom but he's subsequently developed an allergy to the antivenom so that he now has the choice of dying from the next cobra bite or having a potentially lethal anaphylactic reaction to the antivenom. Marvelous. Sean.hoyland - talk 12:40, 8 June 2011 (UTC)

Sounds like he should take up a safer line of work, such as coal mining. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:43, 8 June 2011 (UTC)

People can build up an immunity to snake venom, just as they do to a virus, because it is an antigenic protein. While smaller chemical poisons might be bound as a hapten to some carrier protein to elicit an immune response (see cocaine vaccine), it would not readily occur naturally, and I haven't heard of it being done against an element. There are allergies against silver and nickel, and antibodies can be made against nickel-albumin.^{PMID 118843} I wouldn't rule out the possibility of an immune response to arsenic or mercury but most people would dismiss this out of hand. Also, the immune system can't actually destroy an element with reactive oxygen species; I'm not sure if secretory IgA in the gut would tend to exclude it from being absorbed. Wnt (talk) 13:55, 8 June 2011 (UTC)

That makes total sense. Those venoms are proteins that can be broken down into simple, and harmless, elements; whereas arsenic and mercury can't be. I was in the neighborhood anyway. Thank you for the explanation. :) The "iocane" powder discussed in Princess Bride is fictitious, but if it were a protein, it could be possible to develop an immunity. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:01, 8 June 2011 (UTC)

The process you're referring to is mithridatism. Our article is a little short, but provides an overview. Matt Deres (talk) 17:38, 8 June 2011 (UTC)

Most stable elements aren't toxic in every molecule they form, so it would be possible to render such elements harmless by supplying the reactants and conditions needed to change it into into a benign molecule. However, I don't think this is a common response. StuRat (talk) 17:47, 8 June 2011 (UTC)

I thought Wnt's was a good answer, but is it really just immunology that's involved? (The Poison article could probably explain better how the body deals with poison). WikiDao ☯ 18:15, 8 June 2011 (UTC)

For snake venom, yes - for chemicals, probably not (see cytochrome P450). There might be compensating mechanisms for individual elements - for example, cadmium poisoning damages the kidneys in such a way that cadmium is excreted much more quickly.^[27] Wnt (talk) 21:15, 8 June 2011 (UTC)

How to compound risk factors

Smoking or LDL triple my chances of a heart attack, hypertension or diabetes double it, sedentary lifestyle increases it 12%, and obesity increases it by 62%. What if someone has several of these factors?

If these were independent variables in a statistics problem, you could take 2 x 3 x 1.12 x 1.62 and have your answer. But it being biology, these factors might synergize and become more dangerous together, or only the worst may apply, or they might even cancel each other out (wouldn't bet on it) - you'd need a study on people with the exact combination of factors you have to really know for sure. Wnt (talk) 14:03, 8 June 2011 (UTC)

The cumulative effect could be less than 2x3x1.12x1.62, without them cancelling. It seems to me these things might increase the risk through the same mechanism, in which case they could just add less if you already have a problem. Grandiose (me, talk, contribs) 14:24, 8 June 2011 (UTC)

I suppose that would be 3 x 3 x 2 x 2 x 1.12 x 1.62, if the variables are independent. 2.139.12.164 (talk) 14:32, 8 June 2011 (UTC)

Well, the question said "Smoking or LDL", rather than "and". Grandiose (me, talk, contribs) 14:44, 8 June 2011 (UTC)

Hmmm, you also need to take into account how the risks of dying from other diseases are affected. If these risks are increased by larger factors, then the risk of dying from a heart attack may actualy go down. Count Iblis (talk) 15:34, 8 June 2011 (UTC)

You also need to define clearly what you mean by phrases such as "the chances of a heart attack", "triple it" and "increase it by x%", otherwise you could end up with absurdities such as having a 250% chance of a heart attack. AndrewWTaylor (talk)

Note that several of those factors may lead to one another. For example, a sedentary lifestyle may lead to obesity which then leads to hypertension. So, the risk of a sedentary lifestyle may be largely due to it already including the things it typically causes. Therefore, there's not as much need to include them again, as separate factors. StuRat (talk) 17:29, 8 June 2011 (UTC)

I believe you would calculate the probability of surviving all the risk factors. I forget the name this has. If for example you had a 10% (0.1p) chance per year of being run over by a bus, and a 20% (0.2p) chance per year of choking on ice-cream, then if these were entirely independent you would have a 0.9 X 0.8 chance of not undergoing either of these. The combined risk factor per year would be 1 - (0.9 x 0.8) = 0.28

You would have to know the baseline risk before you could re-calculate your overall increased risk. For example if your risk of dying by being struck by lightning per year was 0.0000000001p, then even a hundred-fold increase in the risk would be nothing to worry about. This sort of thing is often discussed in pop science books. 92.24.128.171 (talk) 18:21, 8 June 2011 (UTC)

"...if these were entirely independent". As noted above, this being biology, they probably aren't. --Carnildo (talk) 00:11, 9 June 2011 (UTC)

gold nuggets

If you were to pour melted gold into a large quantity of water, would you end up with gold nuggets? Googlemeister (talk) 16:27, 8 June 2011 (UTC)

More or less, yes. If you mean to ask if these can be distinguished from those dug up or found in a river, then yes, I'm sure they could. For one thing, the purity of gold is likely to be higher. Also, there may be steam bubbles included in the gold this way. StuRat (talk) 16:48, 8 June 2011 (UTC)

I think it's more likely that you will get one hell of an explosion, which will send tiny droplets of gold flying around. The melting point of gold is 1064°C. Looie496 (talk) 17:19, 8 June 2011 (UTC)

A glob of molten gold is still pretty dense and probably pretty viscous. You'd get a lot of steam and so forth if you dropped a couple of pounds of molten gold into eg. the ocean, but I'm guessing it would remain one big glob as it sank and cooled. WikiDao ☯ 17:35, 8 June 2011 (UTC)

See this article, Molybdomancy, and substitute gold for lead. μηδείς (talk) 18:10, 8 June 2011 (UTC)

In Jules Verne's The Chase of the Golden Meteor, they got a large explosion, but most of the gold was apparently not molten, only very hot. – b_jonas 09:29, 9 June 2011 (UTC)

"Granules" is probably the more common term for what you'd end up with. Examples: [28][29]. They are made by gold refineries for use by jewellers. If my memory serves me correctly (many years ago I used to work at the Perth Mint), they are actually made by pouring molten gold into water. It looks like the Mint's refinery still does make them. Mitch Ames (talk) 14:13, 9 June 2011 (UTC)

conservation at the amino acid level is evil

I would like to express that 'conservation at the amino acid level is good' but without using the word 'good' which I think is inappropriate (it's neither good nor bad; it's just a fact). Is there a word I can directly replace it with? --129.215.5.255 (talk) 17:55, 8 June 2011 (UTC)

Well, the obvious suggestion is 'conservation at the amino acid level is a fact'. I haven't the slightest idea what any of this means, though. Looie496 (talk) 18:30, 8 June 2011 (UTC)

The OP is possibly referring to a situasjon where a gene is undergoing synonymous mutations. --NorwegianBlue ^talk 20:45, 8 June 2011 (UTC)

Conservation at the amino acid level reflects stabilizing selection that preserves the amino acid sequence, which indicates the decreased relative fitness of individuals bearing genes with many other possible amino acid sequences in the region. It can be measured in terms of the ratio between synonymous mutations and non-synonymous mutations within the coding sequence. Wnt (talk) 21:23, 8 June 2011 (UTC)

I don't know much about this question in particular, but I do have experience in science writing. Rather than use 'good', which implies a value judgment, you could use 'beneficial', which does not (i.e. assuming there is some quantifiable benefit to the organism (in terms of fitness) that it receives from 'conservation at the amino acid level'. The idea is, good or bad may vary, but 'benefit to the organism' has the potential to be made into a rigorous statement about the science that does not reflect the writer's bias. Does that make sense? SemanticMantis (talk) 22:01, 8 June 2011 (UTC)

This is briefly discussed at Conserved_sequence#Conserved_protein_sequences_and_structures. I usually think of "conservation at the amino acid level" in terms of comparative genomics, where comparisons of orthologous genes are made between different species, not within an individual. Perhaps the OP is trying to figure out how to express the degree of amino acid conservation, as in "there is perfect conservation at the amino acid level" etc. --- Medical geneticist (talk) 22:58, 8 June 2011 (UTC)

Indeed, I'm talking about the degree of conservation. However, it's not perfect; it's just well conserved. I'm looking for an alternative word to 'good' which carries no connotation of benefit etc. 129.215.47.59 (talk) 00:03, 9 June 2011 (UTC)

A "high level of conservation"? I disagree with SemanticMantis's proposal of "beneficial" as being a valueless term...if I'm a pathogen or somehow else engaged in microbial cat&mouse, I might be selected-against if my amino acid sequences are consistent. DMacks (talk) 00:09, 9 June 2011 (UTC)

I only meant that saying that a feature is beneficial to an organism is better than saying that it is 'good'. I don't think statements/claims such as 'property X increases the fitness of a population' are invoking any particular values. Obviously things that benefit one organism could do so to the detriment of others. Anyway it's a bit moot since I missed the OP's intent :) SemanticMantis (talk) 02:33, 9 June 2011 (UTC)

I'd say that (in general) it is going to be a good idea to ask "Why is it good?". For example, we start with a statement "Breathing is good.". Now question "Why is breathing good?" might get an answer "Breathing is good because lack of it will result in death after several minutes [and prevention of death is good]." (yes, more than one answer is possible). Now this answer has one part that concerns Biology: "lack of [breathing] will result in death after several minutes". Thus one just has to write it down while leaving the part concerning Philosophy out. I guess the same process should work here too. --Martynas Patasius (talk) 20:48, 9 June 2011 (UTC)

There's nothing really wrong with using good in this context, except that the advice above by people who think good means beneficial rather than strong scares me. Well-conserved is perfectly cromulent--just be aware that well is the adverbial form of the adjective good. You could simply say the mutation rate is low, which will be more clear to non-experts. μηδείς (talk) 15:22, 10 June 2011 (UTC)

I apologize for scaring you ;) Please see the wiktionary definition of 'good' [30]. There is no mention of 'strong', but that may fall under definition 9.Effective. Note definitions 10.Favourable, and 11.Beneficial. Part of why there is confusion here is that 'good' can mean many different things depending on context. SemanticMantis (talk) 15:57, 10 June 2011 (UTC)

explanation about metallic solids

Metallic solids are usually described as "positive ions in a sea of electrons" but is there any more detailed explanation. the band theory is great for explaining energy levels and conductivity (and I understand it quite well).But I want to have a more "visualised" imagination of metallic solids. and besides I want to be able to fit the orbital models of atoms to the metalic solids(somehow like the way molecular orbitals are explained) so can you help me? thanks a lot--Irrational number (talk) 18:58, 8 June 2011 (UTC)

Conceptually this is easy to do with graphite, where the p orbitals form a single conductive layer of molecular orbital (which can be written in the resonance notation as having an odd charge anywhere in a vast network of conjugated double bonds). But as for metals, well, it's not my field. When I did a search just now, I found a fascinating-looking work a person self-published on the web.^[31] He comes across as a bit of a kook, but I can't tell if he's the kind of kook who came up with a neat way to look at metals the way you want, or just a kook. He's definitely dedicated to his efforts, one way or the other! Wnt (talk) 21:35, 8 June 2011 (UTC)

The molecular orbital model doesn't work with metals. If you think about, say, the molecular orbital theory explanation for a simple molecule, like O₂, the usual explanation is that the atomic orbitals of the two oxygen atoms merge and reorganize into a set of molecular orbitals shared by the molecule as a whole. A different set of molecular orbitals would be organized around a molecule like, say, ozone (O₃). These molecular orbitals have well defined structures and are localized into (relatively simple) geometry. Even for a complex network solid, like diamond, molecular orbitals can still explain things like the bonding angles and distances between the atoms. In metallic bonding, however, the orbitals are all "delocalized", such that they do not occupy a discrete geometry around the atoms themselves. In metallic bonding, the orbitals form a contiuum of orbitals rather than individually identifyable orbitals; the result is the "sea of electrons" model. The reason we use that model to describe metallic bonding is because its the only one that works. Any bonding model that uses discrete orbitals between atoms, in defined locations, sizes, and shapes simply doesn't work for metallic bonding. The article Metallic bond is fairly in depth, I recommend reading it for more details. --Jayron32 00:52, 9 June 2011 (UTC)

its true that the "sea of eletron" model works but I can't combine my understanding of the band theory with model, specially when its emphasized that the transition of one electron from one band to the other doesn't mean that it actually "moves" somewhere else. well, my question is what DOES happen--95.82.51.37 (talk) 20:12, 9 June 2011 (UTC)

When electrons promote from one orbital to another in, say, the Bohr model, they don't physically move either. An electron is not a discrete particle like a little ball. What it does when it gets more energy is that it enters a higher energy state. This is exactly the same whether you are dealing with, say, excitation from the n=1 to n=4 energy level in hydrogen OR whether you are dealing with promoting up into the conduction band in the metallic bond "band" model. The electron doesn't physically move, it jumps to a higher energy state. We draw pictures of this on a graph or little "ring" diagram to make it visually obvious, but the distances on the graph or little ring diagram don't represent physical distances, they represent energy. --Jayron32 00:57, 10 June 2011 (UTC)

how does diamond crystal look on the surface?

The covalent bonds cannot simply go on for ever. I thought about it and I reached the answer "hexagonal with single bonds" is it correct?(probably not)--Irrational number (talk) 19:04, 8 June 2011 (UTC)

I don't believe it. I went to look this up, and according to Wikipedia, there's a whole nother kind of carbon called Lonsdaleite with a hexagonal matrix, which is harder than diamond in one plane but much softer in practice. You learn something new every day here! In general the structure of a face of diamond should depend on how it is cut, and of course whether the diamond has been exposed to hydrogen to form CH3s at the edge. There are lots of papers about the diamond (111) plane during vapor deposition of diamond, modeling the addition of atoms to the structure, but I can't read them here, and they don't give away any secrets in their abstracts. Wnt (talk) 21:43, 8 June 2011 (UTC)

The covalent network in a diamond is generally terminated with hydrogen atoms at the surfaces. The article and section Material_properties_of_diamond#Hardness_and_crystal_structure mentions this briefly; you can also substitute the hydrogens for other terminators under extreme conditions; its possible to replace the hydrogens with hydroxyl groups instead, which changes the surface properties of the diamond. --Jayron32 00:41, 9 June 2011 (UTC)

Which way around is the Moon in the sky?

In regard to my earlier question, surely the Moon cannot always seem to be the same way around in the sky regardless of where you are on the Earth and how you look at it? Because otherwise, "north" and "south" would be fundamental laws of physics and not just something we humans arbitrarily assigned one way out of a possible two ways. What does the Moon's orientation in the sky depend on? JIP | Talk 19:15, 8 June 2011 (UTC)

It is true, the moon is not always in the exact same orientation in the sky, but it is pretty close; the moon is tidally locked with the earth, so the same side is always facing us when we look up at it (this isn't entirely true, see Libration, but it is essentially true). If you stand on an astronomical body and designate one pole as "North" (as we have done with the Moon, it is in the same direction as Earth's north pole), then it follows that if you face "North" on the surface of said body, the direction directly to your left will be "West". Since the moon is essentially oriented the same way in the sky (except for minor changes from the aforementioned librations and variations in your viewing latitude on Earth), if you are looking up and facing North, then "West" on the moon will be to your RIGHT, since you are standing upside-down relative to the Moon's surface.

Sorry if I'm repeating stuff that has already been said, but I haven't read the whole thread above. Hope I have given a sufficient answer. -RunningOnBrains^(talk) 20:03, 8 June 2011 (UTC)

I'm not sure I understood your answer fully, or you understood my question fully. I will try to phrase my question more specifically. Suppose we define "north" on the Moon as the direction that the pole facing the same way as the Earth's North Pole (near Scandinavia, not near Australia) is facing. Is it possible to look at the Moon in one place on the Earth and see north pointing up (away from the horizon) and look at in another place on the Earth and see north pointing down (towards the horizon)? Does this depend on the place or the orientation, or both? (After edit conflict: It looks like Tango below has answered my question. I have never been in the southern hemisphere.) JIP | Talk 20:11, 8 June 2011 (UTC)

The simple answer is usually to think about the most extreme cases: If you are standing on Earth's North Pole, you will see the Moon's North Pole pointing up, whereas if you stood on Earth's South Pole you would see the Moon's North Pole pointing down. The tilt of the Moon relative to Earth's horizon is a simple function of latitude (again, roughly, ignoring minor factors). -RunningOnBrains^(talk) 00:21, 9 June 2011 (UTC)

It depends on your latitude. The most obvious example of this is comparing a crescent moon viewed from, say, London with it viewed from near the equator. Near the equator, the crescent moon looks like it is lying down. Viewed from Sydney, on the other hand, it would look upside-down compared to the moon Londoners are used to. --Tango (talk) 20:06, 8 June 2011 (UTC)

Compare these two photos: A, taken in Florida (about 25 degrees north) with B, taken in Sydney (about 33 degrees south). [Use this atlas if you need more guidance] Compare the position of Tycho, the light area with the prominent radiating ejecta. In A Tycho is at about 7 o'clock; in B Tycho is way up at about 2 o'clock. -- Finlay McWalter ☻ Talk 21:55, 8 June 2011 (UTC)

Our conception of "east" and "west" are also different between the Earth and the celestial coordinates. ~AH1 ^(discuss!) 15:41, 11 June 2011 (UTC)

Solder

I've got the garden variety solder that is sold a Radio Shack for electronics. Would this solder be appropriate for soldering a connection that will carry 2.5A 120V?

Yes, it will work. However if you are going to solder steel (which is likely for those values), you are going to need to use a special acid flux in order to get the solder to stick to it. The flux in the core of garden variety solder only works properly for silver, gold, and tin. Copper also requires a special flux, but a different one. This is important -- you can cause a lot of trouble for yourself by not using the right flux. Looie496 (talk) 21:37, 8 June 2011 (UTC)

Misinformation alert with respect to the previous post. Why would anyone use steel to conduct 2.5 amps? Copper commonly conducts orders of magnitude more current than that in power conductors. Rosin core solder is commonly used for copper connections. Traditional rosin core electronics solder was a mixture of tin and lead, with rosin as a flux to prevent oxidation of the solder copper. The claim that "garden variety solder only works properly for silver, gold and tin" is nonsense. I agree that the proper flux is important. Rosin core is for electronics, acid core is for plumbing. Edison (talk) 04:23, 9 June 2011 (UTC)

My assumption was that if you are dealing with 120 V, you are probably trying to solder wires to wires or wires to posts of some sort. Wires are usually made of copper or steel; posts can be made of anything. Looie496 (talk) 07:01, 9 June 2011 (UTC)

The voltage 120V is lethal and you must take proper precautions, preferably with advice from someone experienced. The article Solder tells you much more than you probably need to know. Look closely at the illustrated solder joint of a red wire to a circuit board because all the joints show proper "wetting" of the underlying metal by the molten solder. Solder wire for electronics typically has flux in core(s) in the wire. "Ersin Multicore" is a common brand that will wet well to copper or previously tinned copper wires (but soldering aluminium is difficult). Some usual advice is to apply the solder to the parts being soldered, not directly to the soldering iron. Gain some experience in making bad "dry" solder joints caused by too low iron temperature, or parts moved while the solder cooled, to recognize the kind of joint to avoid. Another rule is that solder alone must not hold the parts together mechanically. Cuddlyable3 (talk) 22:36, 8 June 2011 (UTC)

Regulations vary with region, but in general it is not advisable to make high-voltage, high current connections with solder because a high current could melt the solder leaving a loose high-voltage wire. Use a compression fixing instead for safety and to keep within regulations. I have no idea what garden solder is, but I would have thought that any solder sold by Radio Shack would have a flux designed for copper, definitely not silver or gold! In the UK, 240v wiring is almost always copper, but I don't know if this is true for 120v wire in the USA. Dbfirs 07:22, 9 June 2011 (UTC)

Garden variety solder just means typical or common solder. Googlemeister (talk) 14:26, 9 June 2011 (UTC)

wikt:garden variety DMacks (talk) 21:35, 9 June 2011 (UTC)

Yes, I was only pretending to misunderstand, but plumbers and silversmiths would have different gardens! Dbfirs 09:20, 11 June 2011 (UTC)

Also, for connecting wires for that voltage, you usually want to use Screw terminals instead of soldering. The disadvantage of soldering is that sometimes all the current has to flow through the solder alloy, which has too high a resistance and so will overheat, which can cause the soldering to break at best, and a fire at worst. – b_jonas 09:17, 9 June 2011 (UTC) (Ps. ah, apparently User:Dbfirs has already said this above. Sorry. – b_jonas 09:18, 9 June 2011 (UTC))

That's OK, you said it more clearly, though I was intending to include other Electrical connectors that are sometimes also used. Dbfirs 09:25, 11 June 2011 (UTC)

Soldering instructions I've seen in Heathkit manuals and the like emphasized making a solid mechanical connection before soldering. I agree that there are other good means for high voltage/high current connections. There are crimp connectors which cannot loosen in the way screw terminals do. But a proper solder connection makes a stable low resistance connection. Here is a reference to a book on soldering which says typically the solder joints add little resistance to an electronic assembly. A solder joint can fail if the load cycles up and down while there is mechanical strain on the joint. Edison (talk) 18:34, 9 June 2011 (UTC)

The given current and voltage values 2.5A and 120V are conditions that affect the cross-sectional area of the conductors to be joined, and the insulation needed around the conductors respectively. They have practically nothing to do with the suitability of the solder. Cuddlyable3 (talk) 21:28, 9 June 2011 (UTC)

True, but they do affect the decision about whether solder on its own makes an appropriate choice. Dbfirs 09:31, 11 June 2011 (UTC)

Thank you everyone! In case you are interested, I'm swapping out a broken panel mounted Variac. One of the connecting wires appears to be steel and one is copper (this equipment is quite old). ike9898 (talk) 16:44, 10 June 2011 (UTC)

anaphyalactic shock

Is the inability to breathe the only thing that would cause anaphyalactic shock to kill a person? For instance, if a person was in a hospital and had one of those breathing machines hooked up so that their airway stayed open, is there something else that would kill them? Googlemeister (talk) 21:13, 8 June 2011 (UTC)

Anaphylaxis#Anaphylactic shock says it also causes a drop in blood pressure. That could kill you too. --Tango (talk) 21:51, 8 June 2011 (UTC)

The "signs and symptoms" part of that same section also lists a couple of other options. Even with an open airway, aspiration of vomit could kill a person, and myocardial infarction would also pose a danger. 98.94.135.184 (talk) 22:21, 8 June 2011 (UTC)

nuclear power reactor

What is the smallest nuclear power reactor on a naval vessel (a nuclear wessel as it were) and what does the reactor weigh? Googlemeister (talk) 21:17, 8 June 2011 (UTC)

You may also be interested in nuclear power used in space satellites, such as Systems for Nuclear Auxiliary Power. 92.28.247.193 (talk) 23:36, 8 June 2011 (UTC)

NR-1 Deep Submergence Craft was the smallest nuclear submarine that I know of, but our article gives no details of the reactor. -- 110.49.249.59 (talk) 23:56, 8 June 2011 (UTC)

Note that our article Nuclear marine propulsion states The smallest nuclear submarines to date are the 2,700 tonne French Rubis class submarine attack submarines. and makes no mention of the long serving but never officially named or commissioned NR-1. Rubis class submarines are powered by the 48MW K48 PWR, but we lack an article on the K48 reactor. -- 110.49.249.59 (talk) 00:08, 9 June 2011 (UTC)

Also note that our article List of United States Naval reactors lists:

• NR-1 reactor

• one-of-a-kind reactor built for the U.S. Navy research submarine NR-1

but the link is to the article on the sub itself.

Haze Gray's entry on NR-1 states that it was "initially constructed to evaluate small nuclear power plants", but again, there is no details of the reactor beyond stating that, "most of the hull [was] consumed by the reactor". So, the best answer I can give to the OP's question of "what does the reactor weigh?" is "under 400 tons", and even if details of NR-1 reactor were available, the answer would vary considerably on whether the weight of just the fully fueled reactor vessel was given, or if the weight included the entire plant, including the pumps, steam generator, turbine, control stations, shielding, structural substrate, etc. For the latter case, I suspect that you are talking about 100 - 200 tons. For the former case, I haven't been able to find weights of other naval nuclear reactor cores to form a basis for comparison. -- 110.49.249.59 (talk) 00:45, 9 June 2011 (UTC)

Just to clear things up, there is a difference between an nuclear battery and a nuclear reactor. Plasmic Physics (talk) 07:18, 9 June 2011 (UTC)

Not sure if this is of use to you, but we do have an article on List of small nuclear reactor designs. --Mr.98 (talk) 13:44, 9 June 2011 (UTC)

"The design of an idiot"

G'day mates :) </offensive Aussi impersonation> I was watching an interview with noted biologist Richard Dawkins, and it quoted him as saying that the design of the eye, with the nerve "wiring" on the outside of the photoreceptors, can be traced evolutionarily, but if it were just to be created directly from scratch, as by a designer or engineer, to put them on the outside would be "the design of an idiot". This piqued my curiosity: Are there any other examples of features, human or otherwise, whose construction makes sense if understood from an historical and evolutionary perspective, but which make no sense if thought of as created suddenly and from scratch? Thanks. 72.128.95.0 (talk) 23:40, 8 June 2011 (UTC)

Oh Lord, there are vast numbers of examples. Microsoft Windows and English Common law, to pick two at random. Our article on the Argument from poor design gives a number of examples from evolutionary biology. Looie496 (talk) 23:55, 8 June 2011 (UTC)

Not to mention the appendix. Why would God design us specifically with a useless flap in our intestines that gets easily infected? If He wanted to smite someone, I could think of other, more efficient ways.-RunningOnBrains^(talk) 00:24, 9 June 2011 (UTC)

Someone once remarked (somewhat famously) of the platypus that it looked as though it was cobbled together from spare parts. --Jayron32 00:34, 9 June 2011 (UTC)

And the old joke that a camel looks like "a horse designed by a committee". (Keep in mind that Genesis says, "Let us make man in our image." That would be the Elohim Committee.) ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:46, 10 June 2011 (UTC)

Are you thinking of The Last Continent? Hans Adler 07:35, 10 June 2011 (UTC)

Two specific examples I like are the food pipe and wind pipe being the same thing, leading to thousands of people choking to death every year merely by eating. The second is Recurrent_laryngeal_nerve#Evidence_of_evolution. Vespine (talk) 01:21, 10 June 2011 (UTC) sorry was not logged in. 00:46, 9 June 2011 (UTC)

If you've ever had your nose so clogged up that you couldn't breathe but through your mouth, you wouldn't say that. Two large holes, one to breathe through, and one to eat and drink with, would be a waste of space. – b_jonas 09:08, 9 June 2011 (UTC)

Au contraire, lots of animals have evolved mutually exclusive breathing and eating systems. See gills and spiracles. --Jayron32 00:52, 10 June 2011 (UTC)

You don't need God as an excuse for an "idiot design". Where I live there are many buildings that have gas (methane gas) heating. It is implemented where once the coal stove was. The coal stove was fed in the evening and had solid, heat storing stones about it, so it could store the heat until morning, when it would be fed again. With gas, that heat storing and thus heat shielding oven is just an idiotic design. When you turn on the stove at full power, most of the heat goes up the chimney. At the time the gas heating was to replace the coal oven, gas was cheap and no one bothered for a few extra pence up the chimney. So at that time it was not at all idiotic to do it that way instead of bulldozing down the house and rebuild it completely. If you think about it, you will find plenty of examples like that in completely different context. 5BYv8cUJ (talk) 01:07, 9 June 2011 (UTC)

I think you've misunderstood what Dawkins was saying. He's saying that the fact that biology is full of "idiot design" probably implies that the structures you see are evolutionary in nature rather than divinely engineered. (Or you end up in the uncomfortable position of saying that God designed it, but was a bad designer. Which neither Dawkins nor the Intelligent Design people he is arguing against support.) --Mr.98 (talk) 01:14, 9 June 2011 (UTC)

Note that "evolution" isn't limited to biological evolution. Many other things evolve, such as cities. And, just like biological evolution, the results are often sub-optimal, compared to if the city had been well planned from the start. Thus, we can get a series of road grids which are at different angles and/or with different spacing within one city (those were probably separate towns when the grids originated). StuRat (talk) 01:36, 9 June 2011 (UTC)

Reverting to biological structures, an excellent example is the Recurrent laryngeal nerve which, because of gradual evolutionary morphological changes from a common fish ancestor in which it followed a straight-line path, makes an "unnecessary" diversion of many inches in humans and around 15 feet in the giraffe. This topic was well explored in Series 1, Episode 4 of the documentary series Inside Nature's Giants, if you can get access to it. {The poster formerly known as 87.81.230.195} 90.201.110.36 (talk) 09:58, 9 June 2011 (UTC)

The Vas deferens loops around the pubic bone instead of taking the direct route. 2.101.15.113 (talk) 13:04, 9 June 2011 (UTC)

If I were God I wouldn't have put the points of maximum pleasure so close to the points of waste disposal. Caesar's Daddy (talk) 13:44, 9 June 2011 (UTC)

The absence of wheels which could have been a more efficient way for land animals to move around than legs. Cuddlyable3 (talk) 21:16, 9 June 2011 (UTC)

Wheels would make stairs a bit tricky though ;-) Alansplodge (talk) 18:18, 10 June 2011 (UTC)

Having humans being able to re-grow lost body parts would have been useful, instead of only allowing animals like the salamander that privelidge. 92.24.185.180 (talk) 21:31, 9 June 2011 (UTC)

Another interesting subject I discovered recently is Genetic sexual attraction which also can not be explained if the human race were created, but makes perfect sense if we evolved. Vespine (talk) 06:12, 10 June 2011 (UTC)

Belief in God and belief in evolution are not mutually exclusive. It depends on whether you consider God to be merely a "creator" or also a "tinkerer". On the other hand, there is this cogent comment in Love and Death: "I wouldn't say that God is evil. I think the worst you can say about Him is that He's an underachiever." ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:48, 10 June 2011 (UTC)

June 9

Small flows of water

My fairly small garden pond loses considerable volumes of water to evaporation in summer, but using a watering can to refill it disturbs the sediment and plant roots in an unsatisfactory way. Ideally the water would flow in very gently, perhaps even drip by drip, but I don't want to be standing holding a watering can for a couple of hours to achieve this. One solution I am thinking about, involves having a second container that can be topped up with water manually - perhaps a bucket or barrel sitting by the side of the pond, with a lid that can be closed after refilling to prevent clogging up with dead leaves or other garden detritus. The idea would be for the water to then flow through a pipe connected near the bottom of the container, and drip into the pond. So I'm talking about something gravity-driven, and in terms of scale of water-flow, imagine a dripping tap. This raises several practical questions:

1. How thin should the internal diameter of the pipe be to ensure there is a flow, but to minimise the volumetric flow rate? Japanese water features seem to produce a surprising flow even through a tube of bamboo. But if we get down to the couple-of-millimetres scale, there must be considerable risk of the tube clogging, and presumably at some point it just stops flowing at all.
2. What's the trick to getting the water to drip out (or just barely trickle out), rather than flow out? I'm guessing the idea is to have some sort of narrower cap fitting over the end of the tube?
3. Bearing in mind this is a gravity-fed contraption, are there restrictions on e.g. the length of the pipe, or the angle it need to run at? I suspect that a longer thinner pipe may need to be put at a steeper angle to ensure flow. The length of pipe I am thinking about is in the 10 to 30 cm region. It's Question Time (talk) 00:37, 9 June 2011 (UTC)

Since this is all quite empirical, I'm thinking you're best off with a stopcock or plug valve or an adjustable clamp on a piece of rubber tubing. To prevent annoying clogs, I think your tube should generally be wide open except for one key point. Wnt (talk) 00:52, 9 June 2011 (UTC)

An adjustable set-up makes sense - if it's set to produce nothing more than drips, does that have any impact on the length of tube that can be sustained, or the angle it needs to lie at? (It seems intuitive that a continuous flow can "push" further/harder.) It's Question Time (talk) 01:03, 9 June 2011 (UTC)

Wouldn't a simple soaker hose do the trick ? (That's a flat garden hose with many small holes in it and a cap at the end [32].) Curl the soaker hose around the perimeter of the pond, and adjust the water pressure at the tap down to a level where it drips out of the many holes slowly. Having so many tiny holes makes it unlikely they will all get clogged. StuRat (talk) 01:08, 9 June 2011 (UTC)

Also, a caution, having standing water on your property, like you described, can allow mosquitos to breed there, unless chemicals are added to prevent that. StuRat (talk) 01:14, 9 June 2011 (UTC)

The water container would have a lid on it, and should drain near-enough completely within a couple of hours at most, so it shouldn't act like a water-trough. Mosquitos already come to the pond to breed, although most of the larvae just get predated! The flat soaker is an alternative; would it work if connected to a standing water source? (The solutions on sale seem to be several metres long which is excessive for my needs, although the site you linked to has the interesting review snapshot "Cons: Inefficient (3), Leaks (3)" which suggests not everyone gets the point! I wonder if it's possible to rig one up from other materials) It's Question Time (talk) 01:25, 9 June 2011 (UTC)

I would just use a short length of old hose pipe and drill many tiny holes with the smallest drill bit I could find (and stop the free end). The hose could be fixed above the bottom of the pond to avoid disturbing the sediment, and fed by gravity from your container a foot or two above pond level. If the container empties after an hour or so, then there will be no problem with insects breeding there. The rate of flow will be roughly proportional to the difference in height between the surface of the water in the container and the surface of the water in the pond. Dbfirs 07:08, 9 June 2011 (UTC)

Once the container is nearly empty, there will very little pressure in the tube. Does that mean there's a minimum size of hole that water would be able to drip through? I'm imagining there will be surface forces that would make the water cling to the hole, so that some pressure is needed to force the water through (the same reason, I presume, that flat soakers nneed to be connected to a faucet with at least a little pressure) and that intuitively a smaller hole produces a greater contact force per volume of water. It's Question Time (talk) 12:38, 9 June 2011 (UTC)

Why not just use a watering can rose. Its what I used when I had a pond.--Aspro (talk) 11:52, 9 June 2011 (UTC)

I think StuRat/Dbfirs may be on to something with the soaker hose, which is more fault tolerant than a pipe with a single pinch point.

• For another point of view, consider why it is that you want to spend resources to keep the pond full all summer. What is your goal? Have you ever seen what happens when no water is added? Depending on where you live and how the pond was formed, it may just be a natural Ephemeral pool, which will attract a unique blend of flora and fauna. You also may be able to decrease evaporation by installing shading trees, or even water lilies. SemanticMantis (talk) 14:14, 9 June 2011 (UTC)

The pond is artificial (and indeed is already shaded). But the point is a good one! Unfortunately without topping up the surface level drops very rapidly into the pre-formed shell, and it gets more difficult e.g. for frogs to to get in and out. It's also less aesthetically attractive that way. It's Question Time (talk) 18:32, 9 June 2011 (UTC)

I was going to say a capped hose with pin pricks, but I see someone beat me to it. μηδείς (talk) 15:30, 10 June 2011 (UTC)

Although they said using a small drill bit ;) Will that make a difference? It strikes me that when the container has nearly drained) the difference between water surfaces will be < 10 cm then the pressure will be very low and I wonder if pin-holes will actually hold the water in. It's Question Time (talk) 21:57, 10 June 2011 (UTC)

Pinholes will quickly become blocked with bacteria and algae, so I recommend drilling holes of at least a millimetre (larger would be OK because the flow will be slow for many holes and low header). If all the holes are under the surface of the pond, and the header container is designed to drain completely, then there will be no water above pond level for most of the time, and the container and upper hose will dry out, mainly preventing growth of clogging agents. Using an opaque hose rather than a transparent one will also reduce growth of any "nasties". Dbfirs 09:42, 11 June 2011 (UTC)

Gauss's Law for Electric Fields

Brushing up on my E&M, I just realized the one of Maxwell's equations, Gauss's law for electric fields has the permittivity of free space. My questions is that is this law true in any kind of a medium or only in a vacuum? If I want to use this law in some other medium like water for example, do I need to change the constant? Thanks!-Looking for Wisdom and Insight! (talk) 02:40, 9 June 2011 (UTC)

Only vacuum. To apply to other dielectrics, one must multiply εo by the relative permittivity (εr) of the dielectric to get the effective permittivity of the medium.--78.148.131.253 (talk) 13:48, 9 June 2011 (UTC)

So the law is still valid in any medium as long as the value of the constant is appropriately changed? Another question I have, for magnetic fields there are diamagnets (which lower the strength of an externally applied magnetic field) and paramagnets (which increase the strength of an externally applied magnetic field). Comparing that with electric fields, I only know of dielectrics which weaken an externally applied electric field. Is there a paramagnetic analogue for electric fields? Have any experiments/research been done on this? What about gravitational fields? Any such matter which will strength or weaken an externally applied gravitational field?-Looking for Wisdom and Insight! (talk) 01:21, 10 June 2011 (UTC)

I would say so. The appropriate substitution for a magnet when considering an electric field would be an electret wouldnt it, rather than somwthing with different relative permittivity ?--78.150.235.218 (talk) 12:52, 10 June 2011 (UTC)

Second coming of Christ & research support

I am M.J.Varghese, the chief commender of LOVE (Liberation Organisation of Virtual Energy). LOVE is for doing charitable works in the name LOVE of Charity. Our supream commander is father God, who create, exist and controlling this nature. 2000 years ago, Jesus said that love each other because God is love. After 2000 years, I am saying that love everybody, then you get love because love is God.

Dear sir, I am contacting you to clear one of my doubts that is: there is BC that is before Christ, it means before the birth of Christ; and AD (after Christ), it means after the death of Christ. If so, the life time of Jesus is not accounted - 2000 AD is 2000 years after his death. If he come back by birth, he should born approximateky 33 years before 2000 AD, becasue then 2000 years after his birth is completed.

None of the incarnations or the prophets comes directly from heaven, and all of them born in between us. Hence, the second coming Jesus may be in between us, am I right?

Thanking you. With regards, M.J.V, C.C, LOVE.

I am exposing three ideas, want urgent research, I have no facility for research.

First one is: tender-coconut is the remedy to HIV, because HIV attacks our w.b.c., tender-coconut-water increases our w.b.c. rapidly, and the increased w.b.c. overlaps HIV. Hence, HIV cannot split up and attacks out w.b.c - thus, AIDS cannot forms. HIV happens like the seed thrown in to the cactus (the parable said by Jesus).

The second one is: water is a good fuel because it consist hydrogen and oxygen - by electrolysis, we can split water in to hydrogen and oxygen. This hydrogen burns in an engine chamber, we will get power to run a motor engine.

The third one is: the definition, location, and stages of mind. The modern medicine cannot define, locate, say about the stages of mind, but here I am saying about it. Mind consist of three main parts like a computer:

• Brain like monitor
• Heart like a CPU
• Kidney like keyboard

There is seven stages for the mind:

• Excited stage – positive in x-axis
• Depressed stage – negative in x-axis
• Doing rights only - positive in y-axis
• Doing evils only - negative in y-axis
• sexually excited - positive in z–axis
• sexually depressed - negative in z-axis
• absolute stability - it is only for God

Do need full research and inform me the progress.

Thanking you

M.J VARGHESE, C.C, LOVE — Preceding unsigned comment added by 117.206.58.137 (talk) 04:41, 9 June 2011 (UTC)

A.D. doesn't stand for "after death". It stands for Anno Domini, which is a Latin phrase meaning "in the year of our lord". There is no 33-year gap between the B.C. years and the A.D. years; indeed, there isn't even a year 0. 1 A.D. is the year immediately following 1 B.C. Red Act (talk) 05:04, 9 June 2011 (UTC)

Water isn't a fuel. Sure, you can electrolyze water into hydrogen and oxygen, and then burn the hydrogen. But the electrolysis requires energy in the form of electrical energy, that's actually somewhat more than the energy gained by burning the hydrogen, due to some heat loss in the process. So electrolyzing water and then burning the hydrogen results in a net loss of usable energy. Red Act (talk) 05:16, 9 June 2011 (UTC)

It isn't possible to do research into your idea that there are seven "stages for the mind", because that isn't a falsifiable hypothesis. I.e., without so much as a definition of what exactly a "stage of the mind" consists of, there is no experiment which can determine whether the number of "stages" the mind has is 7 or 42 or 666. Red Act (talk) 05:35, 9 June 2011 (UTC)

Although of course this is all fundamentally bizarre, the idea actually has something in common with the Big Five model of personality, except with three factors instead of five (and different ones, of course). Looie496 (talk) 06:54, 9 June 2011 (UTC)

(edit conflict)If you can prove that "tender-coconut is the remedy to HIV", then you deserve a Nobel Prize and you will probably become very rich. Unfortunately, others have not been able to find a remedy. Jesus never mentioned a cactus, by the way. In your "stages for the mind", why restrict yourself to three dimensions. The human mind is much more complex, with many more "axes". Dbfirs 06:57, 9 June 2011 (UTC)

Looie, I think you have something there! The axes of "extraversion" and "conscientiousness" would seem to fall pretty close to the energy/depression and good/evil stages he describes. I don't see from the article which of the Big Five axes is given credit for, shall we say, "Weiner games", but surely one of them must be.

It seemed like the tender coconut thing was too original for this person to have devised, and it is so - there's stuff about tender coconut water or coconut oil curing HIV all over Google. Looking back to see where the fire started I get PMID 11365012 "interviews and anecdotal reports": "The third interview reveals a patient's success at dropping HIV viral load and increasing CD4 counts using Naltrexone and NK911 and supplementing with coconut oil, garlic, and raw goat's milk." (1998, Posit Health News) Another article PMID 11366549 from that source talks about "transfer factor" as a prophylaxis for hepatitis, which somehow tied into coconut oil. Then PMID 12349090 (1999, Reprowatch) is an abstract about a trial that was going to be started in the Philippines about coconut milk and "monolaurin, a coconut oil byproduct". Then nothing, at least in NCBI. Another 2007 article PMID 20161889 talks about coconut being used in African traditional medicine for HIV. My guess is that there was some kind of flash in the pan about HIV and coconuts around the time of that Philippines trial, but it must not have come to anything.

I should say that I do hold traditional and herbal medicine in fairly high regard; I believe that likely half, or at least a third, of the treatments described by Dioscorides or extant in Chinese traditional medicine are somewhat effective, and of those only about half have been studied scientifically to this day. But traditional medicine for a new disease is a dicey business, and traditional medicine was never much good with diseases that take a long time to worsen or get better - things like lead and Aristolochia were used in traditional medicine on several continents, because only the short-term effect was apparent. With HIV, the alternative medicine is unfortunately all a matter of hoping for luck despite a lack of published success, whereas conventional treatments have with much difficulty evolved to the point of saving lives. Wnt (talk) 07:35, 9 June 2011 (UTC)

This is total gibberish. I'm finding it hard to tell if it's trolling, or just very weird. Zzubnik (talk) 10:43, 9 June 2011 (UTC)

Too weird to be trolling. HiLo48 (talk) 10:47, 9 June 2011 (UTC)

Cacti are native to the New World, so I don't think Jesus would have encountered them unless you adhere to Mormon beliefs. Googlemeister (talk) 14:18, 9 June 2011 (UTC)

Indeed. "Kidney like keyboard" should make our actual trolls hang their heads in shame. --Sean 15:41, 9 June 2011 (UTC)

The OP posted the same message here. The organisation of which the OP is chief commender(?) is unknown to Google. The OP should not be using the Ref. Desk as a soapbox for a bizarre collection of claims. Cuddlyable3 (talk) 21:05, 9 June 2011 (UTC)

Note that the OP's final comment "commends" responders here, "Do need full research and inform me the progress." I wonder what he thinks of the progress made so far? :) ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:41, 10 June 2011 (UTC)

This clip http://www.youtube.com/watch?v=TpicfnfcEiM is appropriate on many levels. μηδείς (talk) 15:32, 10 June 2011 (UTC)

See wp:NOT a RESEARCH LAB ;) - 220.101 talk^\Contribs 12:51, 11 June 2011 (UTC)

Can you explain what w.b.c. is supposed to mean? Also, many small electrical devices run on water, for example a water-activated battery, this thing, this thing, some other recent inventions worldwide], and another program I've encountered discussing a German company powering about a volt of energy from just a drop of water. For the Latin phrase you discussed, see Deus Caritas Est. ~AH1 ^(discuss!) 15:31, 11 June 2011 (UTC)

Could you please explain what "a volt of energy" is? (sounds German to me) 5BYv8cUJ (talk) 18:51, 11 June 2011 (UTC)

The volt is a fairly common electrical term. StuRat (talk) 19:00, 11 June 2011 (UTC)

But so what is "a volt of energy" ??? 5BYv8cUJ (talk) 19:14, 11 June 2011 (UTC)

Err, I meant a volt of potential difference in the context of a battery. Energy is measured in joules and in Coulombs for charge. ~AH1 ^(discuss!) 20:15, 11 June 2011 (UTC)

So why did they need a complete drop for *that*? And what was the effective energy output? I can make 2000 volts with a silk tie. 5BYv8cUJ (talk) 20:24, 11 June 2011 (UTC)

re w.b.c., I think the OP means White blood cell. - 220.101 talk^\Contribs 18:06, 11 June 2011 (UTC)

Oh, I was about to think it meant Westboro Baptist. ~AH1 ^(discuss!) 20:15, 11 June 2011 (UTC)

The coconut cure should be easy enough to test, so why not set up your own trials and see how many people with AIDS it cures ? As for using water as fuel, while it does require more energy to split it than you get back when you burn it, this still might make sense if you have a large source of electricity and want to produce oxygen and hydrogen gas as more portable sources of energy, such as for a car. There might be more efficient means of producing hydrogen alone, though (a car normally just uses atmospheric oxygen). Therefore, splitting water only makes sense if you have some use for the excess oxygen produced. StuRat (talk) 18:44, 11 June 2011 (UTC)

Bootstrapping differential Manchester encoding

Is the first "transition" of a differential Manchester encoding signal the first time it deviates from its initial level or the first time it returns to that initial level? 76.254.22.47 (talk) 06:03, 9 June 2011 (UTC)

Or are signals from both possibilities generally tracked and chosen from after a sufficient number of samples to discern between have been observed? Can some kind of bit parity, start or stop bits make that easy? 76.254.22.47 (talk) 22:54, 9 June 2011 (UTC)

Infinity and superconductivity

Hello.

I've been told the concept of "infinity" is essential to explaining superconductivity. Why is that so?

Thanks! Leptictidium (mt) 06:24, 9 June 2011 (UTC)

We have an article that is essential preliminary reading - see Infinity#Physics. Dolphin (t) 07:39, 9 June 2011 (UTC)

After reading this, I've come to the conclusion that infinity cannot exist in the physical universe, that it's just a mathematical construct. Is that true? --Leptictidium (mt) 10:23, 9 June 2011 (UTC)

There are those who think that, but I think they're wrong, at least depending on what you mean by "cannot". For example it is consistent with all known observations that the physical universe itself is infinite (contains infinite volume, infinitely many particles).

A superconductor, according to theory as I understand it, has infinite conductivity, which simply means that a current passing through it does not dissipate any energy whatsoever to resistance (it can still lose energy by interaction with external electromagnetic fields). Whether that constitutes an infinite measurable quantity seems to be a question of definition. --Trovatore (talk) 10:35, 9 June 2011 (UTC)

Does that mean the universe has always been infinite? If so, how does that fit in with claims that the universe was infinitely dense just before the Big Bang? Thanks for your answers. --Leptictidium (mt) 10:45, 9 June 2011 (UTC)

My understanding is that, if the universe is infinite, then it always has been. But there are subtleties I've never completely come to terms with. You should ask User:BenRG, who seems to know about these things. --Trovatore (talk) 10:50, 9 June 2011 (UTC)

As a rule of thumb, when a physicist says "infinite" they mean "finite but much larger than the typical values in my problem". A mathematician, of course, knows that there are an infinite number of different infinities. Gandalf61 (talk) 11:02, 9 June 2011 (UTC)

However that is not what a physicist means by "the conductivity of a superconductor is infinite". According to theory, the conductivity of a superconductor is literally infinite. --Trovatore (talk) 11:07, 9 June 2011 (UTC)

(Which simply means that its resistivity is exactly zero.) --Trovatore (talk) 11:08, 9 June 2011 (UTC)

Well, yes, according to theory. But to what extent can this prediction be experimentally verified ? How can you experimentally tell the difference between exactly zero resistivity and a very, very small resistivity ? Sometime when a physicist says "zero", they mean "smaller than I can measure". Gandalf61 (talk) 12:32, 9 June 2011 (UTC)

If we assume the theory to be correct (because it is based on quantum mechanics and the approximations made are not relevant for this issue, otherwise the theory would not have been accepted as the explanation for superconductivity), then you can see that zero resistance arises in the limit of zero frequency. As long as the current has finite frequency components, the resistance is not exactly zero.

If you take a non-superconducting loop, and then move a magnet near it, there will then be a nonzero magnetic flux through the loop. If you then cool the loop so that it becomes superconducting, then you get a current if you move the magnet away from the loop. This is because the superconductor will keep the flux through the loop the same. This persistent current through the loop is then very stable, but according to the theory, it will slowly decay. The system is clearly not in the ground state and it can make transitions to lower energy eigenstates. But the time scales involved here are astronomical. Count Iblis (talk) 14:57, 9 June 2011 (UTC)

I am not completely up-to-date on this, but I don't really think your remarks about frequency are correct. I think what you mean is that the impedance is nonzero when there are finite frequency components. But impedance is not resistance. It does allow there to be a potential difference across the ends of the superconductor, but it does not allow any energy to be lost to thermal processes, which is the definition of resistance. --Trovatore (talk) 19:34, 9 June 2011 (UTC)

The real part of the impedance of any object at finite frequencies will be strictly larger than zero. If you have non-steady currents, you get all sorts of dissipative processes e.g. due to changing magnetic fields inducing currents elsewhere. So, if you have an LC-circuit and the current oscillates at some frequency, the current will die down on quite small time scales, nothing like the astronomically large time scales for superconducting rings carrying DC currents. I think that at a frequency of 1 kHz, the best superconducting coils have a quality factor of just 10^6 or so. The current will thus dissipate on a time scale of a few hours at that frequency. Count Iblis (talk) 02:15, 10 June 2011 (UTC)

Hmm, is it fair to attribute dissipation due to currents in nearby objects to resistance in the superconductor? It's a bookkeeping question, maybe, more than a physics one strictly speaking. --Trovatore (talk) 03:40, 10 June 2011 (UTC)

I think there are also other processes involving only the superconducting object. I think that the dominant source of the losses are due to processes in the surface layer of a superconductor. Electromagnetic fields penetrate a small distance into the superconductor, the perfect screening only happens some finite distance into the superconductor. An oscillating supercurrent will give rise to an oscillating electric field in the surface layer. There, the supercurrents are not effective in screening this out 100%, so this leaves room for charges there to oscillate with that electric field, causing dissipation. Count Iblis (talk) 15:13, 10 June 2011 (UTC)

Ah, but aren't you then saying that the surface layer is not in fact superconducting? So there is resistance, but it's not in the superconducting part of the object. Or no? I'm certainly no expert on superconductivity. --Trovatore (talk) 20:30, 10 June 2011 (UTC)

Yes, you could say that. I studied this quite a long time ago, so I don't know all the details. But it should be clear that in any material there are always degrees of freedom that are able to dissipate energy. What happens in a superconductor that carries a DC current is that all these processes are 100% frustrated. The supercurrent nullifies any potential difference, so there is nothing left for the dissipative processes to do. You can also say that putting a resistance of zero parallel to a resistance of R > 0 makes the net resistance zero. When you have a non-steady current, things are completely different. You can now excite all sorts of processes that were perfectly frozen in the DC case. Count Iblis (talk) 16:30, 11 June 2011 (UTC)

The statement that conductivity is infinite simply means that resistance is zero. No actual positive infinity is implied, or could be. μηδείς (talk) 20:40, 9 June 2011 (UTC)

Not sure what you mean by that. The conductivity is by definition the reciprocal of the resistivity; if the resistivity is zero, then the conductivity is infinite (in the Riemann sphere sense, say, although the more relevant structure is really the interval [0,+∞]). Your second sentence has the feel of an ideological rejection of infinity. --Trovatore (talk) 21:14, 9 June 2011 (UTC)

I think the statement that conductivity is infinite means that the resistance is theoretically zero, and is in practice too small to measure. No-one has yet provided experimental evidence that the resistance of an actual superconductor is exactly zero, and the theroetical models seem to make various simplifying assumptions (see spherical cow). Gandalf61 (talk) 06:10, 10 June 2011 (UTC)

"All observations are theory laden". See confirmational holism. --Trovatore (talk) 07:30, 10 June 2011 (UTC)

Conductivity is a potential, and is not the same as what is actually conducted. Any actual current will be finite, but it may meet zero resistance. Again, no actual infinity is involved. Of course conductivity is defined as the reciprocal of resistance. We might arbitrarily define the term "applelessness" as the reciprocal of the number of apples one has in one's lunch bag. But it would be absurd to pretend that saying someone with no apples in his bag has infinite applessness proves the existence of real infinities. Actual concrete existents are always finite because they are what they are, and no more (or no less), while infinities are not concrete entities, but are relative abstractions. μηδείς (talk) 15:46, 10 June 2011 (UTC)

Do you imagine that the numbers used to quantify, say, current, are less abstract than infinities? Take a current of 2 Amperes, and point out to me the 2 in that.

The somewhat valid point that you have here is that conductivity is defined as a ratio of things that we find intuitively more basic. It has that in common with intensive properties generally (although conductivity is an intensive property itself, that isn't really the issue here, because its intensiveness comes from the fact that it has area in the denominator, and we're not concerned with zero area). For example, density is an intensive property, and point particles may have infinite density (if they're truly point particles, that is).

However there may also exist concrete extensive infinities, as I alluded to above; the physical universe itself may well be infinite, and contain, for example, infinitely many baryons. --Trovatore (talk) 20:10, 10 June 2011 (UTC)

Both integers and the various concepts of infinity are abstractions, but the concept of infinity exists at a higher level of abstraction than do the counting numbers. Numbers are abstractionss and infinity is an abstraction form abstractions. Concrete realities, however, are not abstractions. Any real act of conduction or any real entity or charge or substance is a real existent. Any concepts we use such as the reciprocal of zero which deal in infinities are based on abstracted concepts of relationships. If, for example, we were to talk about the conductivity of water through a hose we could imagine that none of the pressure of the water entering the hose was converted into heat and that the water exiting the hose did so with zero loss of pressure. Only from those concrete relative terms could we manipulate the math and speak in terms of the infinite conductivity of the hose, but that would be like the infinite applelessness of the empty lunch bag, a derived formal infinity, not a real concrete infinity.

As for infinite baryons, the notion is not coherent. It would amount to saying that there is no actual number of baryons in the Universe, because whatever the actual number of baryons were, there would have to be even more. If the unioverse were infinite we couldn't even make a mathematical statement about it in any relation to any known object since the equation would be undefined, like dividing by zero. The standard theory of the universe is a finite closed but unbounded system having existed for some finite duartion, apparently a hyper(^x)sphere some 13,500+ million years in radius. There is no physical evidence of an infinite universe. Any such notion is incomplete or incoherent or at some point undefined. All very mysterious, but not infinite. μηδείς (talk) 02:00, 11 June 2011 (UTC)

If the curvature of the universe is negative, then the most natural simple model is not a finite 3-sphere, but rather a pseudosphere I think it's called, which would have infinite volume, and therefore (assuming constant density) infinitely many baryons. That's a very simple-minded analysis and as I say there are some subtleties I'm not extremely solid on; for more details ask User:BenRG.

There is nothing incoherent about the notion of infinitely many baryons (please, not "infinite baryons"; no one is suggesting that any individual baryon is infinite). Your remarks on that meaning that there would "not be any particular number of them" seem to come from a pre-Georg Cantor understanding of mathematics. --Trovatore (talk) 02:09, 11 June 2011 (UTC)

I hope I didn't say finite three sphere, did I? The negative curvature of spacetime is usually taken to mean that it is not gravitationally closed in the future, not that currently existing space is infinite, of which there is no evidence. And yes, I am familiar with the formal notion of commensurable and non-commensurable infinities, but there is no evidence of the actual existence of a concrete infinity of baryons, hence nothing to refute. μηδείς (talk) 17:55, 11 June 2011 (UTC)

No, I believe your second sentence is not true. If the curvature is negative (I think we're talking about the curvature of space, not spacetime, but I'm a little fuzzy on that point) then the most natural models do in fact have infinite extent in space. If that is the case, then the principle of uniformity would suggest that the number of baryons is infinite, and that would in fact constitute evidence (albeit somewhat indirect) that a concrete infinity of baryons exists. --Trovatore (talk) 19:43, 11 June 2011 (UTC)

Coulomb's Law

I can show that Coulomb's Law + superposition implies $\nabla \cdot \mathbf {E} ={\frac {\rho }{\epsilon _{0}}}$ and $\nabla \times \mathbf {E} =\mathbf {0}$. I want to go the other way and derive Coulomb's law and superposition from the vector identities. I know from Gauss' Law that Gauss' Law implies Coulomb's law if we assume that the electric field is radial. Can the assumption be justified from $\nabla \times \mathbf {E} =\mathbf {0}$? And how does superposition emerge? Nevermind, that's easy to show. Thanks. 65.92.5.252 (talk) 07:36, 9 June 2011 (UTC)

Well $\mathbf {F} ={\frac {\mathbf {E} }{q_{1}}}$ and $\int dV{\rho }=q_{2}$ if you take the limit as V is small you will get the point charge used in Coulomb's Law. I think you are ontrack with Gauss's law which would apply when $\nabla \times \mathbf {E} =\mathbf {0}$.

Gauss' Law should apply whether or not the electric field is curl-free. My trouble is that I can't use curl E = 0 to show that E is radial and symmetric, which would be enough to prove Coulomb's Law. 65.92.5.252 (talk) 21:54, 9 June 2011 (UTC)

Well the next step is to use $\nabla \cdot$ in spherical coordinates.

$\nabla \cdot \mathbf {E} ={\frac {1}{r^{2}}}{\partial \over \partial r}\left(r^{2}E_{r}\right)+{\frac {1}{r\sin \theta }}{\partial \over \partial \theta }\left(\sin \theta E_{\theta }\right)+{\frac {1}{r\sin \theta }}{\partial E_{\varphi } \over \partial \varphi },$

This can then be simplified by assuming no variation with theta or phi, leaving $\nabla \cdot \mathbf {E} ={\frac {1}{r^{2}}}{\partial \over \partial r}\left(r^{2}E_{r}\right)$, which ends up with r^-1. The force will be proportional to derivative of E over r, yielding a r^-2 proportionality. Graeme Bartlett (talk) 13:16, 10 June 2011 (UTC)

Adrenaline sensing anti-perspirant/deodorant

Advertisers are such liars but they shouldn't go completely off the reservation in claims. I just acquired a stick of Degree "Adrenaline series" anti-perspirant/deodorant, which claims on its label that it "is designed to respond to increases in adrenaline..." Sounds like total bullshit to me. Is this possible?--Fuhghettaboutit (talk) 13:31, 9 June 2011 (UTC)

Phew, what's that smell Richard Avery (talk) 13:37, 9 June 2011 (UTC)

I would assume that it "responds" to increased moisture. The antiperspirant ingredients (generally aluminum compounds) can be encapsulated or otherwise designed to have low availability until wetted. Adrenalin (epinephrine) in the blood triggers increased secretion from sweat glands, so by a somewhat indirect route, they're not flat-out lying to say that their product responses to adrenaline. On the other hand, it's definitely not an adrenaline-specific response, and I'm not sure that the basic mechanism of action (sweating dissolves more antiperspirant ingredients, increasing their effect) is particularly novel or unique to this product. TenOfAllTrades(talk) 14:00, 9 June 2011 (UTC)

Just saying they designed it to do X doesn't mean they are competent designers. For example, would you deny that tinfoil hat creators have designed the hats to block mental transmissions? Of course they have. That doesn't mean such things exist or work, though. 20:37, 9 June 2011 (UTC)

Ah, so it's like all those “dermatologically tested” cosmetics. – b_jonas 14:55, 10 June 2011 (UTC)

science

how science and technology affect one life — Preceding unsigned comment added by 112.198.250.3 (talk) 14:58, 9 June 2011 (UTC)

Compare society as it exists today with how the bushmen live, which is similar to how our ancestors lived in Africa 150,000 years ago. Count Iblis (talk) 15:15, 9 June 2011 (UTC)

Hunter-gatherers use technology too. AndyTheGrump (talk) 15:22, 9 June 2011 (UTC)

Even Chimpanzees use technology of their own devising. --Jayron32 19:46, 9 June 2011 (UTC)

And don't forget my personal favourite, the new caledonian crows. See also Technology#Other_animal_species. SemanticMantis (talk) 20:13, 9 June 2011 (UTC)

That's pretty dismissive of Bushmen. They have the bow & arrow, after all. I would recommend looking at the hypocrite anti-tech bomber Ted Kaczynksi instead. μηδείς (talk) 20:33, 9 June 2011 (UTC)

The question is about technology and science, i think it's pretty safe to say that so far we are the only species to employ science, and methodologically only fairly recently. I think this sounds like a homework question. Vespine (talk) 04:25, 10 June 2011 (UTC)

Earmarking Human Infants at Birth

I asked my mom about this Earmarking of mine, had it ever since I can remember. She told me I was born that way. I don't buy it. By the laws of science I tell you. I like to imagine I was a Genetically Modified Baby, created in joint-venture of the U.S. Government and IBM Labratories in Silicon Valley. Project: OLD NAZI FILE. The Project was scrapped and all test subjects terminated. I was the one that got away. I'm in Hollywood now, watching too many movies. I figure the reality of this marking probably not as cool as all that. Note, if thought leads towards marking a twin, I was born by C-section at 11 lbs, rules out the twin possiblity, unless my moms an elephant. She's not. I did much online research on this, found nothing. Anything known in the Wikiworld? For conversation, possibilities. Cheers, --i am the kwisatz haderach (talk) 16:08, 9 June 2011 (UTC)

Sorry but do you actually have a question for the reference desk? This isn't the place for medical advice, to have a conversation or for rambling ideas on your birth. (But hint: the Nazi's were before the role of DNA in carrying hereditary information was even clear; it's difficult to be sure but from the photo it looks like you were born before Flavr Savr; when what your suggesting is wackier then an episode of Fringe (TV series) you've perhaps gone too far; and if you're really the only one that got away posting on a highly public forum about it probably isn't a good idea) Nil Einne (talk) 17:12, 9 June 2011 (UTC)

So what am I supposed to be looking at on your lug'ole, that lumpy bit that is horizontally level (in the photo) with your tragus? Richard Avery (talk) 17:36, 9 June 2011 (UTC)

Instead of the non-serious tone I took to bastardize Hollywood productions, maybe amend question for OBJECTIVE Science. Click on image, where face meets top of ear, little hole. Fact: It is a Piercing. Question: Possible reasons on piercing an infant? --i am the kwisatz haderach (talk) 19:48, 9 June 2011 (UTC)

It certainly does not look like a congenital condition. Maybe mommy did something at some point, but doesn't want to confess? μηδείς (talk) 20:31, 9 June 2011 (UTC) I mistook you to be speaking about what looks like a mark from a stapler across your lobe--that would wscare me more than your vestigial extra gill hole.μηδείς (talk) 15:52, 10 June 2011 (UTC)

It looks like a freckle in that pic. But from your description, that could be the result of a routine medical test. I have something like that from the tine test administered on my shoulder (although it's 6 indentations, in my case). StuRat (talk) 20:37, 9 June 2011 (UTC)

It could easily just be the scar left from a pimple or boil. 92.24.129.68 (talk) 20:56, 9 June 2011 (UTC)

My son was born with a similar tiny hole on his ear and the doctor referred to it as a "preauricular dimple". Try googling that term or "preauricular pit" and see if the descriptions that you find match what you have. — Preceding unsigned comment added by 148.177.1.210 (talk) 21:04, 9 June 2011 (UTC)

(ec)Are you saying that hole goes all the way through? (Have you tried an earring in it?) Otherwise, to me it looks like a very small thing indeed, something like a dimple at most. (You should also examine the photo carefully in dimples of Venus for purely academic interest) Now your ear lobe looks unfamiliar to me - I expect them to be smoother - and somewhat reminds me of various paranoia about ear lobe creases and risk of heart disease.^[33] But, yours doesn't look like the ones I saw in the pictures, which were more diagonal and seemed less cartilage-y, so probably not. None of this should be taken in any way remotely as medical advice, as it is all purely speculation about natural physical diversity.

P.S. thanks 148.177 for getting the goods while I was too busy spouting off! Wnt (talk) 21:17, 9 June 2011 (UTC)

No, does not go all the way through. This 'Preauricular' thingy, very strange indeed, genetically that is. I also have a Pectus_excavatum to boot. Cheers, --i am the kwisatz haderach (talk) 21:33, 9 June 2011 (UTC)

Odd, there are actually nine different genes on OMIM in which both "preauricular" and "pectus excavatum" are mentioned.[34] You might find it interesting to go through the list and see if any have other effects that are familiar to you. (Remember, for every extreme case in which people have diagnosable genetic diseases, there are many others in which people simply tend a little in that direction as part of the healthy natural diversity of the human species). Wnt (talk) 21:39, 9 June 2011 (UTC)

We are definitely straying way too far into the field of medical diagnosis here, let's rein it in and call this question answered. If the "kwisatz" is concerned about a genetic disorder, he or she should see a doctor. --- Medical geneticist (talk) 22:22, 9 June 2011 (UTC)

As I said, we are dealing with normal, natural variation. This person is not sick; therefore this is not medicine. Wnt (talk) 22:37, 9 June 2011 (UTC)

You have no way of knowing that, and it is inappropriate for us to speculate. --- Medical geneticist (talk) 22:55, 9 June 2011 (UTC)

I'd say it was pretty natural, had it since birth, never had any infections, cysts, inflamations. Just a superficial skin marking. --i am the kwisatz haderach (talk) 19:58, 10 June 2011 (UTC)

There is an article on Preauricular sinus and cysts. --- Medical geneticist (talk) 21:19, 9 June 2011 (UTC)

And you'll find out more than you ever wanted to know at http://www.youtube.com/watch?v=M-aUukFk-tY (a presentation by a surgeon who deals with what happens in the worst case scenario). Wnt (talk) 21:34, 9 June 2011 (UTC)

To address the conspiracy question expressed by the OP (not even that unusual - from the forums it sounds like there are a lot of people with strange explanations about these pits; in any case I would wonder if some environmental factor influenced development), and because some people with them notice a smelly keratin-containing fluid coming out on a routine basis, I went hunting for "ear" in Dioscorides' Materia Medica (Osbaldeston's translation). There are very many sections describing ear treatments for purulence or sores, but his section on myrrh said that "rubbed on the ear externally it alleviates long-enduring discharges". Since this is the only section specifying externally I wonder if indeed this is a description of such pits from ancient times, but alas, it's just too vague to tell. There doesn't seem to be much sign that current herbalists do this, so I can't even argue by tradition. I feel like there ought to be some way to wring a clear mention of this out of ancient literature, but I haven't hit on it yet. Wnt (talk) 23:12, 9 June 2011 (UTC)

Not on humans, but the old Bible story of Jacob marking the healthy of Laban's flock, then making a deal to take only the Spotted and Striped. --i am the kwisatz haderach (talk) 23:41, 9 June 2011 (UTC)

Now that's a weird story. "Strength" is inherited, but coat color results from parents mating in front of willow branches with stripes?^[35] Wnt (talk) 00:04, 10 June 2011 (UTC)

I guess the only way I would believe is if like 148.177, I actually saw a baby coming out of a womb with this Preauricular Dimple. Seems more like an Earmarking, a Branding when the Nurses/Doctors take the baby to the side tray to clean and wrap before handing back to the mother. Because its close to the Sinus there are complications with infections later. This seems like better logic. I'm not a geneticist, so I could be wrong (more than likely). If the theme of my questioning is earmarking a baby then it isn't about diagnosable genetic diseases. For hard science, best answered by 148.177/Wnt/Medical geneticist. A co-worker brought up Satanists like in Roman Polanski's horror 'Rosemary's Baby'. I like that answer, but also far fetched. --i am the kwisatz haderach (talk) 23:41, 9 June 2011 (UTC)

It sounds like you're actually looking for imaginative explanations. On the Medhelp forum^[36] I read people who thought they'd been poked with the amniocentesis needle, or the holes were from being grasped with obstetrical forceps during delivery, or their parents had pierced their ears as a baby, or that they were "ghost holes"/"spirit holes" with some kind of psychic significance. Wnt (talk) 23:52, 9 June 2011 (UTC)

I still would like to see a birth and check for it being genetic (odds not in favor), maybe talk to an OB that's seen one right out the womb. In regards to marked humans, I've seen foreigners with the Smallpox Vaccination scar on upper arm. Leaves a pretty big mark in comparison to my marking. That could be from the actual vaccine. I am looking for both scientific and imaginative explanations. The more the merrier. Thanks much y'all. This is a lot to work with from just googling EARMARKING HUMAN INFANTS. --i am the kwisatz haderach (talk) 20:11, 10 June 2011 (UTC)

Safety on stairs

Running downstairs or only using every second stair is clearly more dangerous than walking and using every stair. But if someone is doing this dangerous thing, how much safer is the activity IF they grip the handrail? (Let's say a hypothetical "average person".)

My hunch is that using the handrail does not make it very much safer because a) a person can't maintain a good grip on the handrail when they have to "regrip" quickly due to running and b) most people are not strong enough to maintain a grip on it if their feet go out from under them (or they lose their balance in some other way.) Thanks, CBHA (talk) 18:45, 9 June 2011 (UTC)

Ask yourself what it would even mean to say "using the handrail is 12% safer". Now imagine what kind of data it would take to support that claim. I'll be surprised if anyone can give us a quantified answer, but who knows what kinds of data e.g. OSHA might have... SemanticMantis (talk) 19:45, 9 June 2011 (UTC)

Now if only we still did medical experiments on prisoners..... Wnt (talk) 21:01, 9 June 2011 (UTC)

Thank you. I understand that pinning this down to "X percent safer" would be very difficult or impossible. I was just thinking of three or four levels. For example, "trying to use a handrail while running downstairs"

- a) "makes it considerably safer",

- b) "makes it a bit safer",

- c) "does not make it safer" or

- d) "makes it more dangerous because it takes the runner's attention off the stairs".

Given the varied backgrounds of Reference Desk editors, I look forward to hearing from some with experience in running downstairs. ;o) Perhaps there are some movie stuntpeople answering questions here.

CBHA (talk) 21:32, 9 June 2011 (UTC)

Well, as somebody who at a younger age frequently used to run down stairs or take them two or three at a time, my opinion is that using a handrail is safer because it makes it easier to get your feet to land where you want them too. Also it steadies you on the landing. I don't think it has much value for saving yourself once you start to fall. Looie496 (talk) 00:19, 10 June 2011 (UTC)

Unrelated fun fact : In college I discovered that by jumping forwards, catching the handrails like they were parallel bars, and sort of flinging myself downwards, I could go down entire flights of stairs without touching a single step except the landings. In this manner I could go down 15 floors much faster than the elevators. I guess you need long arms to do this. Great for making up lost time when I was late for class. However, I can't make any claims as to how safe this was. Probably not very. APL (talk) 07:04, 10 June 2011 (UTC)

"most people are not strong enough to maintain a grip on it if their feet go out from under them". Is this really the case? I know there was a recent news story about most children not being able to hang from the monkey bars any more, but have our arms and hands really withered this much? I don't think of myself as especially strong (I couldn't go hand-over-hand on the monkey bars anymore), but I'm also someone who used to fall down the stairs a lot, and still have occasional 'incidents'. I find it is much safer to hold the handrail because a) it steadies you if you start to fall b) you can hold tightly and stop yourself pitching down the whole flight c) even if your grip is not strong enough to hold you there, it jerks you back so that you fall backwards and slide down the stairs, which still hurts but less severely than going head first or tumbling d) if you slip, you don't tend to slide as far if you have even an imperfect grip on the banister. 86.161.212.100 (talk) 14:16, 10 June 2011 (UTC)

I agree with the post above. Having a hand on the rail (not necessarily a grip) means that you can quickly grip the rail if you start to fall. It's pretty common to start to fall on stairs and to grab the rail and either prevent the fall or improve how you land.--Srleffler (talk) 17:05, 10 June 2011 (UTC)

"Cotton intended for food use"

The article Flavr Savr includes mention of "cotton intended for food use". Can someone tell me how cotton is put to use as food? Thanks, CBHA (talk) 18:56, 9 June 2011 (UTC)

Cottonseed oil -- Finlay McWalter ☻ Talk 18:58, 9 June 2011 (UTC)

There's been a few projects that attempt to genetically modify cotton so that the seeds can be used as human food. Ordinary cotton seeds have a substance on the seed coat that prevents them from being a useful food source. Here is a relevant link, which was the first google hit for /cotton seed food/ [37]. SemanticMantis (talk) 19:41, 9 June 2011 (UTC)

See Milo_Minderbinder#The_Syndicate for a humorous attempt at feeding cotton to people. --Jayron32 19:44, 9 June 2011 (UTC)

Jokes aside, cotton seeds contain gossypol, which is poisonous. Though presumably, if you somehow remove all traces of it, you might then use the detoxified cotton seeds for food. 67.169.177.176 (talk) 23:35, 10 June 2011 (UTC)

I don't know if that's the intended meaning here, but a frequent use of cotton yarn in cooking is dressing up and binding fowl, or roasts, or roulades. --Stephan Schulz (talk) 16:09, 11 June 2011 (UTC)

Electron spin

Why did they decide to give the two electron spins the values ±1/2 rather than ±1? --75.40.204.106 (talk) 20:33, 9 June 2011 (UTC)

Because there are two types of particles, fermions and bosons where the values of the spin are either 1/2 integer (fermions) or whole integer (bosons). Furthermore, they have unique properties regarding how each class of particles obeys certain physical laws, such as the Pauli exclusion principle. The mathematics of 1/2 integer and whole integer spins are covered by such topics as Fermi–Dirac statistics and Bose–Einstein statistics. But basically, the answer is that 1/2 spin particles like electrons have a spin which is half of the magnitude of whole integer spin particles, like photons or the Higgs particle. --Jayron32 20:45, 9 June 2011 (UTC)

I think the way to look at it is that Planck's constant relates the energy of light to its frequency. The "reduced Planck's constant" (h/2pi) is the "fundamental unit of angular momentum". Note this 2pi is the difference between radians and full cycles. Now if an electron wants to go from +1/2 to -1/2, it changes by emitting or absorbing a photon, and the reduced Planck's constant is the angular momentum of that photon. There is no particle that changes from 0 to +1/2 or +1/2 to 1 (unless I'm terribly wrong about something). That's because there are no half photons with half angular momentum. So there's no call to create a unit h/4pi and present that as a fundamental unit so leptons are odd and bosons are even - it would just make a sometimes confusing system much worse. Wnt (talk) 21:00, 9 June 2011 (UTC)

Not sure about changing, but it is possible for fermionic matter to form bosonic matter. mesons are bosons composed of two quarks, which are fermions. Likewise the Bose–Einstein condensate has bosonic properties (it violates the Pauli principle, for example) despite being otherwised composed of normal atoms (composed of fermionic protons, neutrons, and electrons). I do not, however, know of any process whereby fermionic matter can be created by multiple bosons. In other words, you can additively create whole integer spins out of even numbers of half-integer particles, but there is no way to get a half integer spin with nothing but whole integer spin particles. --Jayron32 00:49, 10 June 2011 (UTC)

Still, the OP raises the question if there is anything more intuitive about the current scheme of assigning integer and half integer spins to bosons and fermions respectively versus assigning them even and odd spins, or is it just a historical accident such as the choice of positive and negative charges? -- 110.49.241.141 (talk) 21:25, 10 June 2011 (UTC)

I'm pretty sure that is completely arbitrary; you could do all the math with odd/even spin numbers, and just do the math with spin/2 and get all the same results. It's probably one of those things where the standard is abitrary, but has to exist as a standard, i.e. someone had to pick SOME standard, so they chose halves and wholes instead of odds and evens, for no reason in particular other than preference. --Jayron32 00:36, 11 June 2011 (UTC)

The spin quantum number, s, is related to the physical angular momentum via $L=\hbar {\sqrt {s(s+1)}}$. That $\hbar$ is generally introduced first from the energy relationships in quantum mechanics, but is also ubiquitous in momentum problems as well. You can't really change either L or $\hbar$ (aside from redefining the units on both) without screwing up lots of relationships between classical and quantum mechanics. What one could do is define $s'=2s$, such that $L={\hbar \over 2}{\sqrt {s'(s'+2)}}$, and other similar relationships. I don't see anything wrong with that other than that it adds an arbitrary 1/2 or 2 everywhere. Personally, I suspect that equations of the form $L=\hbar {\sqrt {s(s+1)}}$, with s taking integer or half-integer values was simply preferred due to an economy of notation, i.e. it felt more "natural". Dragons flight (talk) 01:23, 11 June 2011 (UTC)

color perception different in each eye

I've always had a slight difference in color perception between my eyes. I know this is not uncommon, but I only have anecdotal evidence - other people confirming they too have the same experience. I would like to find something written by a medical authority (journal article, book, something!) that confirms this, and might provide some explanation. Thanks, Kingturtle = (talk) 20:43, 9 June 2011 (UTC)

Unfortunately no refs were uncovered last time this was discussed Wikipedia:Reference desk/Archives/Science/2010 December 19#Unusual Vision? but perhaps it is still of interest Nil Einne (talk) 20:56, 9 June 2011 (UTC)

In the extreme case, there are reports of unilateral colorblindness: PNAS article (PDF). The subject of that paper had normal color vision in one eye, and deuteranopia in the other.

The previous Ref Desk discussion touched on a much more likely explanation for most cases of differential perception of color: transient changes in sensory adaptation, blood flow, and pigment bleaching. TenOfAllTrades(talk) 23:09, 9 June 2011 (UTC)

Amongst astronomers, particularly amateurs today and professionals in former times when visual as opposed to photographic & digital observations are/were more common (and describing the exact visually perceived colours of stars was thought interesting and/or useful - see Stellar classification), it was a commonplace that most observers' two eyes differed detectably, and sometimes obviously, in their colour perceptions, just as they usually do in various other parameters of focus and abberation.

One factor affecting this is that as the eyes' lenses age, they absorb relatively more at the blue end of the spectrum, and an individual's two eyes sometimes show the effects of age differentially (resulting partly from differential light exposure if he/she has favoured one over the other at the eyepiece). This becomes very obvious if he/she develops cataracts and has one lens removed or replaced (with compensation provided by an external spectacle or internal plastic lens) before the other (as is usual for obvious reasons) - the contrast between the gradually changed eye and the suddenly restored one is very noticeable, as was once described to me by the eminent amateur astronomer Commander Henry Hatfield following such an operation.

In addition to the lenses, presumably the colour absorbtions in the cornea, aqueous and vitreous humours of each eye might also differ slightly. {The poster formerly known as 87.81.230.195} 90.201.110.206 (talk) 14:22, 10 June 2011 (UTC)

Since the colour is transient, the tints between eyes may "switch". ~AH1 ^(discuss!) 15:10, 11 June 2011 (UTC)

My vision seems tinted blue in my left eye and orange in my right. I wonder if this has a benefit for distinguishing similar shades? When I took the standard vision plate test as part of a lab experiment in Biology 102 I (the only one out of some 30 students) received a perfect score, which the proctor complained was statistically impossible. I always wondered if it was my eyes or if I guessed well.μηδείς (talk) 18:02, 11 June 2011 (UTC)

Good cholesterol

What foods have good cholesterol but no bad cholesterol? --75.40.204.106 (talk) 20:56, 9 June 2011 (UTC)

When people talk about "good cholesterol" and "bad cholesterol", they usually are referring to HDL and LDL, respectively. These actually aren't different cholesterols (all cholesterol is the same chemical compound), but rather different cholesterol-carrying complexes in your bloodstream. Because HDL and LDL are really only found in blood, it doesn't make sense to talk about food having "good cholesterol" or "bad cholesterol". (Animal derived foods/fats do have cholesterol in them, but not as HDL or LDL.) Different foods, however, will have different effects on your HDL vs. LDL levels. High-density lipoprotein#Diet and lifestyle mentions eating omega-3 fatty acids and soluble fiber, and avoiding trans fatty acids as some dietary ways of increasing your HDL levels. Other places have other recommendations - if you are specifically concerned about your HDL levels, your best bet is to talk to a dietitian or doctor. -- 174.31.219.218 (talk) 23:04, 9 June 2011 (UTC)

Specific articles you might find interesting which are related to this topic are Monounsaturated fat and Olive oil. Vespine (talk) 04:20, 10 June 2011 (UTC)

Just one possibly applicable example: Avacado#Nutritional value. ~AH1 ^(discuss!) 15:08, 11 June 2011 (UTC)

June 10

Avian body odour?

Is it a noted fact that birds tend to have little or no body odour? Just something that occurred to me today while my friend's really stinky dog was running around the room in front of me - while accumulations of bird poop do smell bad, I'm yet to encounter a bird that in itself, has an obvious scent. --Kurt Shaped Box (talk) 00:47, 10 June 2011 (UTC)

Feathers don't work very well if they get dirty so birds spend a lot of time preening and keeping themselves clean. Conversly, some dogs seem to take pleasure from rolling around in the foulest substance that can be found. Vespine (talk) 01:10, 10 June 2011 (UTC)

Could the fact that birds lack sweat glands be a significant/more significant factor? I mean, odour-producing bacteria grows in sweat, doesn't it? I know that it's also said that (IIRC) most birds have a poor sense of smell too, so odour-for-the-purposes-of-identification/scent marking would seem to me to be a rather unnecessary. --Kurt Shaped Box (talk) 01:17, 10 June 2011 (UTC)

Yes, but dogs don't sweat either. StuRat (talk) 03:39, 10 June 2011 (UTC)

Dogs don't sweat? Hmmm. Never owned a dog, but I could swear that I've known other people's dogs that've been all sweaty after going for a run (might be wrong). --Kurt Shaped Box (talk) 10:52, 10 June 2011 (UTC)

Overheated dogs have been known to jump into puddles or other water, so a hot, wet dog might be mistaken for a sweaty one. StuRat (talk) 17:35, 11 June 2011 (UTC)

Knowing nothing about this topic, I did a Google search for "odorous birds", and the top hit is a National Geographic article titled BO Attracting Predators to Birds, whose first sentence is "New Zealand's native-bird BO is so pungent, it's alerting predators to the birds' presence, ongoing research shows". The remainder of the article contains some useful information about bird body odor as well. Looie496 (talk) 02:33, 10 June 2011 (UTC)

Doing a casual google also suggests that some birds have fairly highly developed sense of smell, but most do not. So it's not a class wide feature (or more specifically 'lack of' in this case). Vespine (talk) 04:15, 10 June 2011 (UTC)

From what I've smelled of the parrots I've been close to (not that I've been deliberately going around sniffing parrots, mind), they do have a very faint, oily scent. I'd actually theorized that this may be the smell of the preen oil/wax. FWIW, Caiques are supposed to have a distinctive scent, as mentioned in the article. --Kurt Shaped Box (talk) 10:52, 10 June 2011 (UTC)

Penguins have a terrible odour. I couldn't stand being near to them for a long time. But then again those are not "normal" birds. --helohe (talk) 22:30, 10 June 2011 (UTC)

It seems to me that their odor comes from the fish they eat, not from the birds themselves. 67.169.177.176 (talk) 23:30, 10 June 2011 (UTC)

Yeah, is it the penguins themselves that stink - or the accumulated penguin crap, penguin vomit and half-eaten fish in the general area? --Kurt Shaped Box (talk) 00:13, 11 June 2011 (UTC)

Hijacking a ride on a comet

Antoine de Saint-Exupéry aside, has any fiction or pie-in-the-sky proposal ever proposed "hijacking" a comet to use as a generation ship? Presumably the comet's orbit could be changed to eventually leave the solar system instead of continuing, which would mean you'd already be moving at a very healthy clip on top of a big stash of reaction mass and/or in-situ resource utilization raw material. SDY (talk) 01:01, 10 June 2011 (UTC)

I don't know about comets (might be difficult to keep them frozen with livable environment inside), but asteroids have been proposed, to the point where "hollowed asteroid generation ship" pops up as an autocomplete option on Google if you start typing "hollowed as...". There was even a Star Trek (original series) episode with it as a key plot point: For the World Is Hollow and I Have Touched the Sky. -- 174.31.219.218 (talk) 02:48, 10 June 2011 (UTC)

Hollowed asteroid generation ships are a common science fiction theme; see for example Greg Bear's Eon. Hollow comets are little bit harder to come by (there seems to be a certain psychological reluctance to use ice as a building material, even though it would stay quite comfortably frozen on the long journey between the stars). Nevertheless, David Brin offers us Heart of the Comet. Those examples are novels; I strongly suspect that you'll find quite a few examples if you delve into the world of short fiction. (Isaac Asimov's novella The Martian Way introduced the use of chunks of ice from Saturn's rings as cubic-mile-scale spacecraft (but didn't broach the subject of generation ships). TenOfAllTrades(talk) 03:32, 10 June 2011 (UTC)

With out current technology it wouldn't make much sense, as it would take more energy to move that extra mass around, and to catch up to a comet and land on it in the first place, without any corresponding benefit. However, my fave design for an interstellar ship is a massive linear accelerator/nuclear reactor combo (or maybe anti-matter reactor) that clamps onto an asteroid, and hollows it out for material to fling out at the speed of light, while using the asteroid as a shield in the front. StuRat (talk) 03:37, 10 June 2011 (UTC)

Another science fiction example is Jules Verne's Hector Servadac. – b_jonas 14:37, 10 June 2011 (UTC)

Let's not forget that many comets follow a hyperbolic trajectory that takes them out of the Solar System on their own.^[38] While it is unlikely indeed, it is possible to imagine spotting a comet on its way into the Solar System, plotting out a trajectory that comes close to Earth, and seeing that it will go near a planet you want to colonize in a bazillion years or less. So you round up a bunch of idiots astronauts and convince them to take a few tiny, fast ships with just a few basic essentials, confident that they can live off the water and carbon dioxide and other goodies locked away in the cold, dark core of the comet for countless generations before sallying out to claim some barren rock a few parsecs over. (Better bring a lot of mirror foil to concentrate that starlight...) Wnt (talk) 17:12, 10 June 2011 (UTC)

It's obviously still unrealistic, but the only realistic proposals so far in space travel are to extremely local things like the moon or the inner planets, so that it's not immediately feasible isn't surprising. Regardless, my original question was answered. SDY (talk) 17:50, 10 June 2011 (UTC)

You might be interested in the Project Orion (nuclear propulsion). 5BYv8cUJ (talk) 20:14, 10 June 2011 (UTC)

Do pigs have orgasms that last for thirty minutes?

Somebody told me that pigs have orgasms that last for thirty minutes, but I can't find any evidence supporting it. I've already checked the pages about pigs, orgasms, and animal sexual behavior. Additionally, if this is true, is it true for both sexes? — Preceding unsigned comment added by Undercooked (talk • contribs) 04:03, 10 June 2011 (UTC)

Sounds like nonsense to me, and there is an awful lot of nonsense out there. I suggest you ask them to support their claim. Why would you prefer to believe something that someone told you than trust your own researches?--Shantavira|^{feed me} 07:19, 10 June 2011 (UTC)

Simple: No. More details: It's an Internet meme. [39]. Gryllida 09:47, 10 June 2011 (UTC)

This google book page has some details, but I haven't been able to find a scholarly source on the subject.Smallman12q (talk) 11:11, 10 June 2011 (UTC)

A pig told me that it feels like flying. Cuddlyable3 (talk) 22:44, 10 June 2011 (UTC)

Same weight or not?

if 300ml water in liquid state has a weight of say 1 kg, would it have the same weight in solid state(i mean after freezing)? — Preceding unsigned comment added by 175.110.91.49 (talk) 08:44, 10 June 2011 (UTC)

• Yes, it would have same mass. But ice would have different density than water, which means a volume change (water grows, most other substances usually shrink). Please see Crystallization#Process. --Gryllida 09:16, 10 June 2011 (UTC)

(edit conflict) The simple answer is yes, assuming that (1) by "weight" you mean "mass"; (2) the substance you are calling "water" has a density more than 3 times that of ordinary water; (3) we can neglect any small changes in mass due to release or absorbtion of dissolved gases etc; (4) we can neglect the really really small changes in mass due loss of thermal energy. Basically, mass stays the same, but volume and density will change. Gandalf61 (talk) 09:20, 10 June 2011 (UTC)

I'd have to disagree with the first two posters, just on an everyday level, as ice has a lot "heavier" feel to it, from being solid. --188.29.60.182 (talk) 09:35, 10 June 2011 (UTC)

This means: "If you take ice and water of same volume, ice would feel heavier". This is not right for the reason: 1) Unlike other solids, ice is less dense than its liquid state (water). (See Properties of water#Density of water and ice). I have to note that this statement is unrelated to freezing a piece of water in isolated environment and having its mass save due to the law of conservation of mass, which the question is about. :) --Gryllida 09:41, 10 June 2011 (UTC)

"Feels solid" (maybe mentally related to things that are hard and therefore large and/or massive?) and "feels heavier" are separate issues. If you are trying to compare "how heavy" (the question), take a bucket-full of each. Gandalf61 makes an interesting point #2 I'd like to emphasize: though the poster might just be making up numbers for this example, 300 mL of water would actually weigh approximately 300 g and 1 kg of water would be approximately 1000 mL at normal earth conditions. DMacks (talk) 09:53, 10 June 2011 (UTC)

To make things clear: I'll rephrase the question. It can be interpreted in two different manners (I used the first one). --Gryllida 10:04, 10 June 2011 (UTC)

1. "Does water get heavier when it freezes?" --The answer is "no" (see here). --Gryllida 10:04, 10 June 2011 (UTC)

2. "Is a solid of given volume heavier than liquid?" --The answer is "yes" for everything almost everything [updated per reply -Gryllida 13:27, 10 June 2011 (UTC)] other than water (see here). --Gryllida 10:04, 10 June 2011 (UTC)

Not everything other than water. Properties of water#Density of water and ice lists some other examples of substances that expand when they freeze. Red Act (talk) 11:41, 10 June 2011 (UTC)

Thanks, -Gryllida 13:27, 10 June 2011 (UTC)

300ml of water weighs 300g. When frozen into ice, it would weigh the same. 92.24.176.232 (talk) 12:41, 10 June 2011 (UTC)

Yes. It would merely occupy more than 300ml in volume. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:24, 10 June 2011 (UTC)

Right! -Gryllida 13:27, 10 June 2011 (UTC)

The change in volume is an important point to consider, given the distinction between weight and mass. The ice and the liquid water would have essentially the same mass; the state change doesn't affect the amount or type of matter present, and the relativistic effects (associated with different amounts of internal energy) are negligibly small for any reasonable purpose I could imagine.

Whether or not they are the same weight depends on one's definitions, however. If one defines 'weight' to be solely the attractive gravitational force between the ice/water and the earth, then they will have the same weight. If one defines 'weight' as the net apparent force between the water/ice and the earth, then under sensitive measurement conditions the two states will actually show slightly different weights. This latter 'operational' definition represents how most balances and scales tend to work in real life. To consider an extreme example, think about what happens if you tie a helium-filled party balloon to the pan of a balance. Even though we all know the balloon has real mass, it will show up as having a negative weight. The net force exerted by the balloon on the scale is upwards, because the balloon displaces more than its own mass in air: buoyancy.

While this effect is usually only obvious when weighing objects that are comparable in density to (or lighter than) air, it actually comes into play for all objects being weighed in atmosphere. In round numbers, the density of air at sea level is on the order of 1 gram per liter, so 1 kg of liquid water will displace about 1 gram of air. The density of ordinary ice is about ten percent less than that of liquid water; a kilogram of frozen water will displaces about ten percent more air (an extra 0.1 g). This extra volume means extra buoyancy, which means that the measured, apparent weight will be reduced by about one part in ten thousand. That doesn't sound like a lot – it's too small a shift to pick up on a bathroom or kitchen scale, for instance – but it's readily detectable using a good analytical balance (of the sort you'd find in any reasonably-equipped chemical laboratory). That said, buoyancy due to air is something that only has to be explicitly accounted for when making extremely precise measurements of weight. TenOfAllTrades(talk) 14:35, 10 June 2011 (UTC)

Hence the ice would have the same mass as the water, but would weigh slightly less, right? If you take two equal-weight buckets, each containing 300ml of water, as well as plenty of room at the top to expand, you could freeze one of them, and although the one containing ice would weigh measurably less, merely carrying them they should "feel" the same weight. Right? ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:42, 10 June 2011 (UTC)

Because the heat of fusion of water is 337 kJ/kg, and the weight of a joule is 11.1 femtograms, a 1 kg block of ice should be 37.2 nanograms lighter than the corresponding amount of water at the same temperature. Additionally, if we suppose that the 1000 cc of water begins as a 1 decimeter cube, and if we constrain the sides and force it to go only upward when freezing, then because ice is 0.9167 the density of water, the center of gravity of the ice will be 4.54% (0.454 cm) higher than that of the water. Since the Earth is 6371 km in radius, at sea level this increases the distance to the center of the Earth by a ratio of 7.13 x 10^-11 - which should decrease the weight by twice as much (i.e. (1 + that) squared), or 142.6 nanograms. In total then (for that shape and manner of freezing) that's 0.18 micrograms - almost a weighable difference! B) Wnt (talk) 16:54, 10 June 2011 (UTC)

You need the change in internal energy here, not the enthalpy; the latent heat is the heat needed to melt ice, which is less than the internal energy change in this case, because you get some energy "free of charge" due to the volume decreasing and the atmosphere performing work on the water. Count Iblis (talk) 18:29, 10 June 2011 (UTC)

If 300ml of water weighed 1 kg then it wouldn't be water on planet Earth. Here the heaviest water we know about is only 10.6% denser than ordinary water. If you freeze heavy water you get heavy ice that actually sinks in ordinary water. I suppose one could make an alloy of ordinary and heavy ice that has exactly the same density as ordinary water (and I think they could coexist at slightly above 0 deg. C.). Cuddlyable3 (talk) 22:34, 10 June 2011 (UTC)

There seems to be a general confusion in several posts here (including the original poster) between mass and weight. 300ml of water has a mass of approximately 300g anywhere in the universe; on Earth it has a weight of approximately 3 Newtons. Gandalf61 (talk) 02:42, 11 June 2011 (UTC)

Following Wnt, if 300 g (or 1000 g) of water gave up energy and froze, consider the mass equivalent of the energy lost, by the formula E=MC² Would this energy loss make the ice have less mass than the water? Granted, no practical measuring device could measure the difference. But theoretically is the ice less massive than the water? I've heard that a car accelerated from zero to 100 km/hr gains a tiny amount of mass, and that a wound up clock gains a tiny amount of mass. Does this energy-mass equivalence extend to freezing/thawing? Edison (talk) 04:10, 11 June 2011 (UTC)

Yes, and there is a very simple way to see this. The center of mass of an object at rest on which no external forces act, cannot change. If you assume that this is always true, then considering a situation where a pulse of light is exchanged between two parts of the object, leads to the conclusion that the transfer of energy was accompanied by a transfer of mass. If there were to exist another hypothetical process in which energy is transferred without a change of mass, the relation E = M c^2 would not be valid; you would be able to transfer arbitrary large amounts of mass from an object of mass M without affecting its internal energy, you could make that mass negative while makig the mass of another object arbitrary large. Count Iblis (talk) 15:46, 11 June 2011 (UTC)

Electric signal

Hi i need what will be output waves form if the input signal were standard test signals(sine, step, square, ramp, triangle,) to the passive components resistor, capacitor and inductor separately and two combined in series and parallel then three combined in series and parallel actually what happens when these combinations are energized with these signals and how they respond (pictures preferred) — Preceding unsigned comment added by Kanniyappan (talk • contribs) 14:45, 10 June 2011 (UTC)

This appears to be homework, but it is hard to tell what level. At the most basic level, a resistor reduces the amplitude of any wave in the direction of 0V (a big enough resistor and you'll pretty much have just 0V). A capacitor allows AC signals to pass, but inhibits DC signals. An inductor allows DC signals to pass, but inhibits AC signals. I know, the idea of a DC "signal" is silly. But, if you are in a higher level, you will be discussing how current and voltage relate to one another as they go through a capacitor/inductor. I was taught "ELI the ICE man" in the Marines. E (voltage) in an L (inductor) precedes I (current). I (current) in a C (capacitor) precedes E (voltage). -- kainaw™ 15:02, 10 June 2011 (UTC)

See RC circuit, RL circuit, LC circuit, RCL circuit.--CookerSock (talk) 18:28, 10 June 2011 (UTC)

Your list of test signals starts with a sinewave, which has a single frequency. The other signals are actually just sets of sinewaves added together. See the article Fourier series. A Resistor is not frequency-sensitive and it passes a current according to Ohm's law. To tackle your circuit questions you need some AC theory. In fact your question looks much like the syllabus of an AC electronics course. This article gives a general introduction: Network analysis (electrical circuits). Cuddlyable3 (talk) 22:12, 10 June 2011 (UTC)

thnx for ur reply these are known by myself what makes me confusion is using resistor and capacitor in parallel when voltage taken across resistor it both act as filter and spike signal generator so that how this is possible — Preceding unsigned comment added by Kanniyappan (talk • contribs) 03:32, 11 June 2011 (UTC)

See RC circuit. Cuddlyable3 (talk) 15:33, 11 June 2011 (UTC)

Question about prisms

Hello. I am a costumer who has been given a very specific request by a client, and I wanted to verify that the client's idea is going to work before I go to the trouble of making the thing.

The client wants a large prism on her costume that will throw rainbows all over the stage. Client's idea is to mount the prism (like a precious stone) on her costume with a mirror backing, on the assumption that light will pass into the prism, bounce off the mirror, and come back out of the prism as rainbows. I was unsure whether rainbows would be created and thrown about the stage without the light being able to pass all the way through the prism and out the other side. So I thought that I'd better try to find a physicist to explain whether this will work or not before I build the thing.

Any assistance would be deeply appreciated. Thanks greatly in advance! Heather (talk) 15:27, 10 June 2011 (UTC)

Light has to pass through a prism in order to bend the light. If it is reflected back by a mirror, any bending will be unbent on the reverse trip. Light would have to pass through the prism and then hit a mirror on the side and not come back through to cause a rainbow. And this will cause just one rainbow per prism, not throw them all over the place. Unless your client is actually wearing little lamps on her body, any such effect is going to be minor and overwhelmed by the amount of white light stage illumination she will need. She'd be better of with a reflective costume of some sort and an experienced lightman with colored lights. μηδείς (talk) 16:07, 10 June 2011 (UTC)

Anyone who has tinkered with a prism knows that getting good rainbows can be problematic. Though with a mirror-backed prism it seemed easier to me. I wonder if you could do better using a diffraction grating, perhaps concealed as the "mirror" in the prism. But still you're up against the solid wall that the light coming out of the prism is no more than what goes in, so if you have a spotlight on her and one little jewel reflecting, it's going to be washed out. If you had the sophistication to use a video camera and image recognition to lock onto the prism and send a 1-inch wide beam straight at it all the time no matter how fetchingly it jigged and danced ... (which I think really could be done with off the shelf technology, but maybe not your shelf or mine!) ... then you'd have something. Wnt (talk) 17:00, 10 June 2011 (UTC)

In my opinion, it would be cheaper and easier to use a color-changing LED kit. I've seen color changing LED keychains for around $5. With those, you can get a lot of colors glowing. Keep in mind that with a prism or LED (or anything similar), you will not a rainbow arcing through the air. You will get an array of colors on the floor of the stage, which the audience most likely will not be able to see. You can use smoke to keep the color around the performer but that won't work well. The smoke will appear to glow and make it very difficult to see the performer. -- kainaw™ 17:54, 10 June 2011 (UTC)

I can only see this working if she wears the prism on the top of her head and has a strong spotlight shining at it from behind? Exxolon (talk) 18:02, 10 June 2011 (UTC)

Which will of course, make her look like a person wearing a prism on top of her head. μηδείς (talk) 18:12, 10 June 2011 (UTC)

A mirror ball hat under various coloured spotlights could do. Add Sequins for effect.Cuddlyable3 (talk) 21:55, 10 June 2011 (UTC)

Perhaps it would be better for her to wear a costume with lots of small diffraction gratings sewn in. Or perhaps use diamonds or something -- those can act as prisms without needing any mirror backing. Just my non-expert opinion. -- An American ultranationalist 67.169.177.176 (talk) 23:25, 10 June 2011 (UTC)

On second thought, she could wear a costume that has some kind of small glass prisms (such as rhinestones, etc.) sewn in; their shape could cause them to act as Porro prisms and redirect the light back toward the audience by total internal reflection at the same time as refracting/dispersing it. Her original idea (with the mirror backing) simply will not work. -- An American ultranationalist 67.169.177.176 (talk) 03:23, 11 June 2011 (UTC)

Suggestion: To stick with the prism idea, how about it she has several prisms on her head, with a vertical light between them, and a mirror on the top, like the 3 prisms show here (top view, with mirror removed):

         /\
        /  \
       /    \
      /\    /\
     /  \ °/  \
    /    \/    \

If an electric cord wouldn't work, then a battery pack would be needed to power the light. This light could be either fluorescent or incandescent. The latter requires more energy and creates more heat, but might also make better rainbows. No other light source should be used on stage, as that would wash out the rainbows created. Unless, that is, you want to create additional rainbow light sources to supplement the prisms. StuRat (talk) 08:56, 11 June 2011 (UTC)

Your client may be thinking about the diffraction effect of diamonds, which is supposedly similar to prisms. ~AH1 ^(discuss!) 15:02, 11 June 2011 (UTC)

Throwing rainbows wouldn't work that way unless you're using magic. – b_jonas 18:46, 11 June 2011 (UTC)

Re; Electro Mechanical Spectrum

I have a question: Isn’t it about time the geniuses (et al) call the electromagnetic spectrum what it really is; the ENERGY SPECTRUM? J Hoelz, P.E. Ret (c/q thermo) — Preceding unsigned comment added by 173.69.175.253 (talk) 19:27, 10 June 2011 (UTC)

Er, let me think about it--- NO--CookerSock (talk) 20:18, 10 June 2011 (UTC)

The place on a spectrum doesn't tell you the energy of light. You'd need both a measure of intensity and frequency to determine the overall level of energy in a beam of light. Your idea seems half baked. i kan reed (talk) 20:33, 10 June 2011 (UTC)

The only reason the geniusses of the World haven't done this already is that we can't deduce whether you mean electromechanical or electromagnetic. Cuddlyable3 (talk) 21:43, 10 June 2011 (UTC)

Are you sure it isn't the fault of et al? Nil Einne (talk) 23:07, 10 June 2011 (UTC)

Light has energy, it isn't energy. Plasmic Physics (talk) 08:18, 11 June 2011 (UTC)

The only thing correlating energy and frequency is the fact that photons of shorter wavelengths, higher frequencies generally have greater energy and vice versa. However this breaks down when you start discussing non-photon non-spectrum particles such as beta particles and some cosmic rays. ~AH1 ^(discuss!) 14:59, 11 June 2011 (UTC)

Isotopes

Is there any difference between atoms with the same number of protons and neutrons in the nuclei but with those nucleons arranged differently in the nucleus? --75.40.204.106 (talk) 19:50, 10 June 2011 (UTC)

Yes. See, nuclear isomers. While alternate nuclear configurations are possible, the atom will seeks out the lowest energy nuclear configuration and typically reach it within a nanosecond. As a result such configuration differences only occur very briefly and only under very specific circumstances. They won't generally be observed in everyday experience. Dragons flight (talk) 20:21, 10 June 2011 (UTC)

Electron diffraction

The article says that electrons can be diffracted, but how can a single electron be diffracted? --75.40.204.106 (talk) 21:13, 10 June 2011 (UTC)

Wave–particle duality is not easy to imagine, but apparently it's how things work on that scale. APL (talk) 21:52, 10 June 2011 (UTC)

So if a single electron is diffracted into two (or more) parts, what are the resulting parts? Are they both electrons? Doesn't that violate conservation of mass? --75.40.204.106 (talk) 22:04, 10 June 2011 (UTC)

The two blobs are the probability of finding the single electron in either spot. Every atom heavier than Beryllium has split blobs. Hcobb (talk) 22:08, 10 June 2011 (UTC)

It is one electron that goes through both slits. At the receiving screen you will find that each electron arrives at a single unique position, but the distribution of the arrival positions over many electrons is not uniform, and has peaks and valleys caused by the wave-like properties of the electron interfering with itself. Quantum mechanics isn't known for being very intuitive. Dragons flight (talk) 22:54, 10 June 2011 (UTC)

(EC) You can try reading the later parts of Double-slit experiment (look for discussions of single photon or one by one or one photon) and if you're really interested Englert–Greenberger duality relation. These are primarily about photons (although the first article does mention when the first one electron at a time experiment was performed) but I'm pretty sure it's the same for electrons. Nil Einne (talk) 23:01, 10 June 2011 (UTC)

Electron diffraction occurs in the dual-slit experiment (interference pattern) even when electrons are fired and arrive at the detector one-at-a-time. You can model this pattern as a probability distribution of finding any arbitrary individual electron at any point in the diffraction pattern; the deal with wave-particle duality is that the particles, in bulk, obey statistics that give the same results as the wave properties would. Thus, its not that an individual particle behaves as a wave, its that in bulk particles behave as waves, and they do so whether emited in bulk or emitted individually. If you look at discussions at articles like Wave function you see it is full of statistical language, that's because the core of wave-partile duality is probability... --Jayron32 00:27, 11 June 2011 (UTC)

Echolocation in cats?

If you have a housecat or watch them stalk birds, then you're probably familiar with the teeth chattering behavior they engage in when they spot a bird. Looking at the popular literature to find out why they do this, I found this site which summarizes the concept.[40] Chattering in cats is considered a "frustrated hunter reflex", usually seen when a cat can't get to a bird and/or the cats way of preparing to bite the bird. Has anyone ruled out animal echolocation as an alternative explanation? Viriditas (talk) 22:19, 10 June 2011 (UTC)

An interesting idea, but a little implausible, I'd think. Cats are basically ground-level hunters, and picking up the echo of prey against the background clutter would be difficult. I'm sure they use their excellent directional hearing to hunt, but passively. Any noise loud enough to produce an echo may alert the prey. For bats, this isn't really a problem, as an insect in free flight has nowhere to hide, but a cat stalking a bird isn't going to have much success. There may be technical difficulties as well, to do with the relative size of the prey and the signal wavelength - but I'll leave that to someone else to clarify... AndyTheGrump (talk) 03:08, 11 June 2011 (UTC)

Apparently, echolocation is used by smaller ground mammals. The last two times my cat has done this, he has had a view of the bird above or below him. Indoors, he was looking down at it from about four meters; outdoors, the bird was about the same distance above him on a small hill. Intuitively I got the sense he was trying to measure the distance to the bird before he could pounce, but that's just my own idea; I have no such evidence. I'm also curious how my cat was generating the chattering and clicking sound, and I wonder if there is a way to record and analyze it. Viriditas (talk) 07:44, 11 June 2011 (UTC)

The only terrestrial mammals our article mentions are shrews and tenrects Animal echolocation#Shrews and tenrecs. For shrews according to both that article and Shrews#Echolocation they only use it to "investigate their habitat rather than additionally to pinpoint food". The article includes a quote:

Except for large and thus strongly reflecting objects, such as a big stone or tree trunk, they will probably not be able to disentangle echo scenes, but rather derive information on habitat type from the overall call reverberations. This might be comparable to human hearing whether one calls into a beech forest or into a reverberant wine cellar.[9]

In other words, it's only used to give broad based info and doesn't give precise location and distance information of small objects.

Echolocation in tenrecs isn't described but as they have poor eyesight it seems likely it's similar to shrews. In other words, echolocation in these animals doesn't seem particularly relevant to the suggested ability of cats to use it to locate or sense the distance of prey. If there are other small mammals with a comparative sense of echolocation to what you suggest in cats, this isn't described. The closest thing is perhaps the learnt human skill Human echolocation.

Nil Einne (talk) 13:13, 11 June 2011 (UTC)

Partially based on [41], some non RS suggest domestic cat chattering is actually a form of mimicry [42]. Of course demonstrating why an animal shows a behaviour is usually fairly difficult. Purring seems to be better studied but is still poorly understood. About how the sound is produced, I believe it may be a combination of vocal chords, lips and teeth, see [43] for example. Nil Einne (talk) 14:03, 11 June 2011 (UTC)

I think they want to "shout" because they see something exciting, but know they can't or will give away their position, and this results in partially suppressed sounds. Compare this to when they dream, but the partial paralysis of sleep makes them move just a little bit. Evolutionarily, I suppose that the suppression in both cases continued to grow stronger as long as doing so increased their chances of survival. However, once it became "good enough", such that further suppression wouldn't increase their survival chances, no further strengthening of this suppression response occurred. StuRat (talk) 08:29, 11 June 2011 (UTC)

Cats chattering at a bird and a

fly (videos). Cuddlyable3 (talk) 15:25, 11 June 2011 (UTC)

I'm surprised a fly is exciting enough for this response. StuRat (talk) 17:26, 11 June 2011 (UTC)

Bookbinding question

What kind of glue is best for binding the spine of a hardcover book? 67.169.177.176 (talk) 23:17, 10 June 2011 (UTC)

I would suggest you find a local art supply store and ask for an acid free or "archival" quality glue. Dismas|^(talk) 02:41, 11 June 2011 (UTC)

PVA glue was recommended to me one for archival stuff, as it does not stain the paper or migrate, and it can be removed readily if needed. Graeme Bartlett (talk) 03:02, 11 June 2011 (UTC)

Thanks for the tip, everyone! 67.169.177.176 (talk) 03:16, 11 June 2011 (UTC)

Binding paste with PVA is good. 76.254.22.47 (talk) 03:21, 11 June 2011 (UTC)

June 11

Eye muscles

So I'm having surgery in two months on my eyes. The surgery is to correct a rather villainous Strabismus that has become noticeable lately (both for myself, damn double vision, and those around me). Apparently my doctor is going to basically detach and reattach muscles attached near the front of the eye that control the ability to see inward. I'm curious, what muscle or muscles are those exactly? Sir William Matthew Flinders Petrie | Say Shalom! 01:26, 11 June 2011 (UTC)

It looks like you are talking about the medial rectus muscle. Looie496 (talk) 02:46, 11 June 2011 (UTC)

Hmmm, looks like it. I guess that wee bugger is going to be moved in each eye. Thanks! =D Sir William Matthew Flinders Petrie | Say Shalom! 04:41, 11 June 2011 (UTC)

The klein bottle as a musical instrument

I'm thinking of an object similar to this made of glass or metal, but more elongated, turn it upside-down, and putting holes or tabs on any of the surfaces so that they could be directly fingered or remotely adjusted (think trumpet valves), and using the entire device similar to a saxophone or like a pan flute. What's the timbre? ~AH1 ^(discuss!) 14:45, 11 June 2011 (UTC)

Hi. What would a klein bottle sound like as a musical instrument, considering that a mouthpiece is attached to the open end, while holes on any part of the surface that can be fingered either directly or using valves adjust its pitch? Thanks. ~AH1 ^(discuss!) 02:16, 11 June 2011 (UTC)

I don't see how you could use a klein bottle as a horn or similar instrument. There's nowhere for the air to go once you blow into it. I suppose you could use it like a jug though. In which case, it would depend on the interior dimensions of the bottle. More space = deeper tone. Dismas|^(talk) 02:40, 11 June 2011 (UTC)

A Klein bottle is a topological entity. The musical characteristics of a container depend on its resonances, which are essentially independent of its topology. So, the question doesn't really have an answer. (Also it's impossible to embed a genuine Klein bottle in 3D Euclidean space, but that's another issue.) Looie496 (talk) 02:53, 11 June 2011 (UTC)

You don't have to be able to blow through something to use it as a musical instrument, you can blow across it, as a closed tube, eg a pan flute. Mitch Ames (talk) 03:09, 11 June 2011 (UTC)

I thought I said that. Dismas|^(talk) 04:33, 11 June 2011 (UTC)

Something like this. Cuddlyable3 (talk) 15:05, 11 June 2011 (UTC)

Navigation in space

Can someone please direct me to an article that discusses how a space craft is navigated between planets, and between galaxies? I can find a number of Wikipedia entries on space travel, orbital dynamics, etc, but nothing that explains how a space craft can recognise where it is in relation to (say) Earth, what direction it is travelling, and what course corrections it needs to make in order to arrive at where it's destination will be when it gets there, be it another planet or another galaxy.58.174.69.136 (talk) 06:31, 11 June 2011 (UTC)

Have a look at Inertial guidance system#Guidance in Human spaceflight. Dolphin (t) 06:36, 11 June 2011 (UTC)

Also note that intergalactic travel is really not realistic because of the incredibly large distances. Dauto (talk) 06:59, 11 June 2011 (UTC)

Dawn sun tracker is the pink rectangle on top, seven others are on each other corner

All space crafts I know of use a Star tracker and a sun tracker. A light sensor looks for the sun which is very easy, for example the Dawn (spacecraft) has a sensor at every corner. The Camera system makes an image of the stars and compares the image with stored maps. With this information it is clear where you are and the where you go is easy to know, because you always go on a straight line (plus gravity) if you do nothing, which is the case most of the time. --Stone (talk) 11:10, 11 June 2011 (UTC)

How about interstellar travel, or when you lose sight of the sun? Plasmic Physics (talk) 12:57, 11 June 2011 (UTC)

X-ray pulsar-based navigation -- Finlay McWalter ☻ Talk 13:04, 11 June 2011 (UTC)

Just for clarity - no human-built space probe built to date has ever needed a guidance system for interstellar travel. So far, only a couple of our space probes have ever left the vicinity of our Sun; and it's fair to say that they are unguided spacecraft at this time. For example, Voyager II is widely regarded to have transmitted the solar magnetopause and is by some definition now "interstellar" - but the craft has not made an orbital trajectory correction in something like a decade or two. Currently, we here on Earth know where Voyager II is because we track it from Earth using powerful, specialized RADAR (Deep Space Network) - but up there, Voyager II probably doesn't know exactly where it is. It's guidance systems aren't designed for this phase of its lifetime. Its limited computer programs and guidance were intended to control its planetary flyby stages, not post-heliopause navigation. All that the spacecraft is currently aware of are a few readings from a few still-functional scientific instruments. It may still have attitude awareness, but probably has essentially no positional awareness. Nimur (talk) 17:42, 11 June 2011 (UTC)

Note, everything mentioned so far is for working out what direction the spacecraft is pointing in. You also need to know where you are, but that isn't too difficult. You can just see what direction the radio signals from the spacecraft are coming from and how long they take to get to the Earth (or a relay craft if one is being used). --Tango (talk) 17:36, 11 June 2011 (UTC)

Ah yes, in case it hasn't been explicitly pointed out, you need both orientation and position to navigate. We have an article on Attitude control system. We also have several relevant articles on position control: station keeping, orbital maneuvering, reaction control system, and so on. Here's a chapter from a NASA JPL introductory course on spacecraft dynamics: hosted at the USAF AWC. Nimur (talk) 17:49, 11 June 2011 (UTC)

Infinite vs. infinite

Hello.

If I apply an infinite force to a stationary infinite mass, which of the following will happen?

A) The mass will be accelerated by the force; or

B) The mass will remain completely stationary.

Thanks. Leptictidium (mt) 07:29, 11 June 2011 (UTC)

Your question is entirely hypothetical because an infinite mass does not exist, and an infinite force also does not exist. Science does not concern itself with things that are known not to exist.

To understand the concepts of mass and force, see Newton's laws of motion. Dolphin (t) 07:37, 11 June 2011 (UTC)

It is often claimed that the universe has an infinite amount of mass. Hence, according to these claims, the mass of the universe is infinite.--Leptictidium (mt) 07:43, 11 June 2011 (UTC)

The universe may have infinite mass, but it's hardly a rigid object. Supposing you had a way of applying infinite force, where exactly would you hook it up to? --Trovatore (talk) 08:04, 11 June 2011 (UTC)

I was actually thinking of the Big Bang. If the universe indeed had an infinite mass, it would've taken an infinite force to initiate its expansion, wouldn't it?--Leptictidium (mt) 08:10, 11 June 2011 (UTC)

So I have to admit I don't understand the Big Bang in detail, but I don't think you can apply notions like "force" to it in exactly the same way you do in the current era. Those things get confusing when you start talking about things on the scale of universal expansion. At the time of the Big Bang, everything is on the scale of universal expansion. So for example I have only the vaguest notion of what might have caused inflation (cosmology); maybe there's more information at that article. --Trovatore (talk) 08:47, 11 June 2011 (UTC)

You say it is often claimed that the universe has an infinite amount of mass but you haven't commented on who makes that claim. It isn't a scientist or a mathematician. The mass of the universe is extremely large - so large that we have no way of assigning a number to it, or knowing exactly how large it is, but this does not make it infinite. Most of the universe is empty space and if the mass of the universe was to be infinite all that empty space, all of it, would have to be filled with mass and both the empty space and the mass would have to be increasing continuously. Clearly that isn't the situation so it is incorrect to apply the mathematical concept of infinite to the universe. Dolphin (t) 08:14, 11 June 2011 (UTC)

Hmm? No, that's not so. If the universe has infinite volume, then it can have arbitrarily small positive density and still have infinite mass. --Trovatore (talk) 08:36, 11 June 2011 (UTC)

Thanks for your answer, Dolphin. I actually knew everything you're telling me, but forum members at Physics Forums made me doubt by saying that the volume of the universe is simply more infinite than its mass. From what you're telling me, the forum members' claim is plain gibberish. Leptictidium (mt) 08:20, 11 June 2011 (UTC)

No, Dolphin is simply wrong. Whether the universe is finite or infinite is not known. --Trovatore (talk) 08:40, 11 June 2011 (UTC)

I apologize to Dolphin for my tone in the above. I allowed myself to get upset. --Trovatore (talk) 19:37, 11 June 2011 (UTC)

Physics Forums works by arguments from authority, don't trust a word they are saying on face value. I'm not saying that they are wrong, but they still managed to ban me indefinitely last year, simply because they could not stand that I would very, very occasionally contradict what the "mentors" were saying. What they do is very effective at keeping cranks out, but over time the forum has become similar to Libya under Gaddafi's rule. Count Iblis (talk) 16:51, 11 June 2011 (UTC)

This sounds like the Irresistible force paradox. The article may help. Mitch Ames (talk) 09:24, 11 June 2011 (UTC)

Hmm, I think that article could use work. For example, we learn from it that [i]f there exists an irresistible force, it follows logically that there cannot be any such thing as an immovable object, and vice versa. But is that really so? Why can't there exist both an irresistible force and an immovable object, but for some reason the force cannot be applied to the object? For example, maybe the force is attached to an unstoppable object that happens to be moving away from the immovable object. The article doesn't seem to be well-sourced; I'm sure someone willing to put in the work could find a more in-depth analysis somewhere. --Trovatore (talk) 09:31, 11 June 2011 (UTC)

Better sources are always appreciated, but I believe the issue is one of definitions. What do you mean by "immovable object"? Usually you mean "an object that nothing (if it tried) could move". What do you mean by "irresistible force"? Usually "a force which will move anything (if it were applied to it)". So if the "irresistible force" is applied to the "immovable object", and the latter moves, it really wasn't an "immovable object". Conversely, if it *doesn't* move, then it really wasn't an "irresistible force". The only way around that is to alter the definitions (e.g. by dropping the implication of the parenthetical elements). But then you're talking about something different, and would need to be clear what exactly you meant by "irresistible" and "immovable". ("I once knew a dog which danced professional ballet" is surprising until you're told by "a dog", the person means their ex-boyfriend.)

Likewise, the original poster's question hinges on how they come by (the definition of) their infinities. In physics, "what happens when I combine two infinities" is usually referred to a "renormalization", which can yield sensible results, but which depends on where the infinities are from and how they're combined. For example, with a = F/m, we could have $F=\lim _{d\to \infty }d+3$ and $m=\lim _{d\to \infty }d^{2}+5d+6$, which would give one answer (no acceleration), or we could have $F=\lim _{d\to \infty }27d+5$ and $m=\lim _{d\to \infty }45d+2$, which would give another (a finite, non-zero acceleration). -- 174.31.219.218 (talk) 16:03, 11 June 2011 (UTC)

The premise of this question fails, since the mass of the universe is not infinite. --Phil Holmes (talk) 12:35, 11 June 2011 (UTC)

Slight correction, the mass of the Observable universe is not infinite. The entire universe seems to be much larger and so could easily have an infinite extent, infinite mass and an infinite number of flame wars. Hcobb (talk) 16:59, 11 June 2011 (UTC)

The only example I could think of was the creation of multiverse. Mass-energy equivalence might also generate mass from the energy required for the metric expansion of the universe, but any question about the relative position of the Universe is nonsensical. ~AH1 ^(discuss!) 14:41, 11 June 2011 (UTC)

Low earth orbit

I'm studying physics on a very basic level with a book and without a teacher, and now there is a line of reasoning in my book that I don't understand. The book says, summarized:

"A projectile thrown horizontally will in the first second fall a vertical distance of 5 meters below the straight-line path it would have taken without gravity. The curvature of the Earth is such that its surface drops a vertical distance of nearly 5 meters for every 8000 meters tangent to its surface. Thus, a stone thrown fast enough to go a horizontal distance of 8000 meters during the 1 second it takes to fall 5 meters, will orbit Earth. So we see that the orbital speed for close orbit about Earth is 8000 m/s."

Now, I understand how this would work during the first second. But what happens with the acceleration of gravity??? Because during the 2nd second a projectile thrown horizontally will fall 15 meter. How come the projectile keeps orbiting and doesn't crash during the 2nd second??? Lova Falk talk 08:21, 11 June 2011 (UTC)

I'm too lazy to do the numbers, but from the principle, in the second second, the 8000m line segment has a slight angle with respect to the first. With respect to the second, the first one goes "upward" and the and gravity bends it down for the next segment to be tangential again. Note that in this picture the circular orbit is approximated by straight line segments. To get good results, the approximation would use ever more but shorter segments. 5BYv8cUJ (talk) 09:49, 11 June 2011 (UTC)

I did a quick sketch (at right, click to zoom) of the situation. The black curve is a segment of a circle and represents the surface of the earth. The gray line is a horizontal tangent at height equal to zero units. What one finds is that the surface of the circle locally approximates a parabolic curve; at time t=1 it has bent away from the horizontal tangent by 1 unit of vertical height; at time t=2 there is a separation of 4 units of height, at t=3 the distance between the tangent and the circle is roughly 9 units. In other words, the rate at which the surface of the earth moves away from the horizontal tangent increases with o distance from the starting point.

What this sketch doesn't account for is the fact that the direction of gravitational acceleration changes as our hypothetical orbiting object changes with time. (Having a constant direction for 'down' is fine when one deals with objects travelling well below orbital speed – a ball tossed in the air really does follow a parabolic path from start to finish – but it doesn't work at all for paths that approach the size of the planet.) From the sketch, it's plain to see that at later time points the gravitational force being exerted won't be straight towards the bottom of the picture. At each point in time, there is a new 'down'; this is what bends the path of the orbiting object into a circle instead of a parabola. TenOfAllTrades(talk) 14:22, 11 June 2011 (UTC)

(edit conflict) Picture the projectile being far above the Earth's surface, travelling fast enough to maintain a roughly circular orbit, rather than either crashing toward the Earth or flying off into space. At this velocity, the object will experience centripetal acceleration, such that the orbit will follow the curvature of Earth, where every 8 km of forward motion experiences 5 metres of motion toward the Earth's core. Assume also that a hypothetical straight-line velocity, ie. one tangential to a circular orbit with a given radius distance from Earth's core from the object's position, will experience no accelerational "tugging" effect toward the Earth. Conversely, such an object with no forward motion will fall toward the Earth in full gravitational acceleration (9.8 m/s²), given negligeable air resistance. Thus, in low earth orbit, the Earth's acceleration is largely applied unto the object's forward motion, keeping its trajectory the same distance to the Earth's core, which in fact does not accelerate the object, but keeps it at constant velocity. In other words, there are vector components of acceleration (down and forward), but along the projectile's velocity there is no +/- acceleration. Hope this helps. ~AH1 ^(discuss!) 14:37, 11 June 2011 (UTC)

The key point here is that acceleration is a change in velocity, not just a change in speed. Velocity, and thus by extension acceleration, is a vector, not a scalar, so it has a direction as well as a magnitude. In a constant orbit, even though you're not experiencing a change in speed, you *are* experiencing a change in velocity, as the direction of movement changes. Gravity, acting as a centripetal force, causes an acceleration which rotates the velocity vector, but doesn't change its magnitude. -- 174.31.219.218 (talk) 15:21, 11 June 2011 (UTC)

Another way to explain this problem: the book is trying to explain a change in height for each second. But, as you intuitively know, the projectile isn't falling all that distance during one single instant - it's falling continously. To really describe the height, and velocity, of the projectile as it flies it's trajectory, we must use a little bit more sophisticated physics - that is, the mathematics must handle the height and velocity as continuous functions of time. Ultimately, this is the the most basic and fundamental application of simple calculus - and it is this problem that forced Isaac Newton to formulate the kinematics of falling objects using calculus. Basically, the book is describing a Riemann sum to approximate height at the end of each second, while in fact height changes continuously during each second. When we treat the function continuously, the math is actually easier to compute (even though a more complex process is being conceptually described). So we simply write that velocity is the first derivative of height, and (here is the most important contribution that Newton made to simple kinematics) ... Acceleration is the second derivative of height ... and acceleration is due to gravity only. You know this when we phrase it as "F = m a" but we are now going to write it as "the height at any time is equal to the integral of velocity, and the velocity is equal to the integral of the acceleration of gravity.". Now, because we're near Earth's surface, gravity is almost constant, so the height is a simple parabola. But in your more sophisticated "orbital cannon" case, the problem becomes more complicated - force due to gravity is changing with position - so we have to compute a more challenging integral! Saving you the complexity of that slightly more difficult Calculus problem, you can accept that the solution to that math problem is a conic section - it can be a parabola, a hyperbola, or an ellipse. If the trajectory intersects with the surface of the planet, the object falls back and hits the Earth. If not, the object becomes orbital, and either stays bound to the Earth or reaches escape velocity and never returns. Our article on orbit illustrates each of those cases. If you want to solve this math for yourself, you can - the simple two-body problem walks you through a standard solution. As you add more complicated effects, like perturbations in the gravity field due to the Moon, Sun, Jupiter, or the imperfect/not-quite-spherical Earth, you must solve a very difficult orbital dynamics math problem, usually with the help of a powerful computer. Nimur (talk) 17:27, 11 June 2011 (UTC)

I get it now. Thank you all so very much!! Lova Falk talk 17:55, 11 June 2011 (UTC)

Plasticisers and incineration

Some unscrupulous food producers in Taiwan have been adding plasticisers to food. Some of the plasticisers include Di-isodecyl phthalate, DIDP; Di-(2-ethylhexyl) phthalate, DEHP; Di-n-octyl phthalate, DNOP; Di-isononyl phthalate, DINP; Di-n-butyl phthalate, DBP; Butyl benzyl phthalate, BBP. The government responds by burning al the contaminated products in incinerators.[44] Is this a good way to destroy the products? Would the plasticisers escape in the air and pollute the environment? F (talk) 09:50, 11 June 2011 (UTC)

That depends on the temperature. But I think the main purpose is destroying the food, so no one will eat it. I don't think that low quantities of such stuff are dangerous unless you eat it. From the names they look like organic molecules (in the sense of organic chemistry) and will be decomposed by nature (UV-radiation, weathering, micro-organisms), just as the many toxins produced by a large number of poisonous plants. 5BYv8cUJ (talk) 10:37, 11 June 2011 (UTC)

See phthalate#Health effects. The effects often depend on mode of entry into the body. ~AH1 ^(discuss!) 14:03, 11 June 2011 (UTC)

Principles of Quantum Mechanics

Wikipedia says ( Postulates of quantum mechanics) the Ket-Vectors were elements of some Hilbert space, wheras Dirac (The Principles of Quantum Mechanics, 4th edition, page 40) says "The space of bra and ket vectors when the vectors are restricted to be of finite length and to have finite scalar products is called by mathematicians a Hilbert space. The bra and ket vectors that we now use form a more general space than a Hilbert space." To resolve that contradiction I assume that some later development has put all of Diracs intuitive integration and the need for infinity as a number (with all its ensuing troubles and inconsistencies) into a solidly defined mathematical framework that turned out to really be a proper Hilbert space. The question is now: where can I find this solid definition? 5BYv8cUJ (talk) 10:26, 11 June 2011 (UTC)

Not infinity as a number per se, but the theory of distributions had yet to be set up. One could then use that re-define the Hilbert space you need in quantum mechanics when you want to work in an infinite volume. You then get the Rigged Hilbert space. Note that you don't actually need to know about this to do computations in quantum mechanics. Count Iblis (talk) 15:12, 11 June 2011 (UTC)

I remember a talk long ago when someone stated that students of mathematics can't do computation. For example, they cannot compute the inverse of a matrix, whereas students of physics can. Someone answered, yes, that's true. But, on the other hand, students of physics can compute the inverse for any matrix.

Having told this anecdote I hope you understand what I have in mind if the following looks like nitpicking or trolling. Dirac thinks he needs vector lengths and scalar products to be allowed to be infinite, and vector lengths and scalar products should result to give numbers (elements of a commutative field), because otherwise all the theorems for vector spaces (and basic computation, too) would have to be prooven again. Every try to do computations with infinity leads to a hell of trouble, the least of which is me proving that zero equals one, using only the contradicting assumptions. Now your link to the rigged Hilbert space doesn't give me the mental breakthrough. Just for any one simple example from quantum mechanics, how exactly would that H and that $\Phi$ really be defined? 5BYv8cUJ (talk) 16:15, 11 June 2011 (UTC)

History of airline lavatories

Did the early airline aircraft (e.g. 1920s) have toilets/lavatories, at least on longer flights?--68.175.35.188 (talk) 18:45, 11 June 2011 (UTC)

The world's first aircraft designed to carry multiple passengers in commercial service was the Russian Sikorsky Ilya Muromets (first flight 1913). "The Ilya Muromets was first conceived and built as a luxurious aircraft. For the first time in aviation history, it had an insulated passenger saloon, comfortable wicker chairs, a bedroom, a lounge and even the first airborne toilet.". The Ford Trimotor was the first big US airliner; "The early cabins were filled with wicker chairs, a luggage compartment and a toilet." If Americans airliners had 3 engines, we Brits could have 4 - the Handley Page HP 42 of 1928 featured "toilets and galleys. Stewards were attending to the passengers serving full meals in-flight; a first by Imperial Airways." Alansplodge (talk) 19:26, 11 June 2011 (UTC)

Orbital docking

I am in orbit round a planet and am a few hundred meters behind my command module at the same altitude. I need to dock with the command module. What combinstion of forward and reverse thrust should I use? (Not home work-- just interested).--78.150.233.171 (talk) 19:45, 11 June 2011 (UTC)

Is the Pythagorean scale universally pleasing?

Pythagoras said that musical strings of lengths in simple ratios (1 through 4) will produce "pleasing" sounds. Are only people in Western cultures (beginning with the Greeks) pleased by such sounds, or do all people people find the sounds pleasing? 82.31.133.165 (talk) 20:29, 11 June 2011 (UTC)