I'm growing some tomato plants. I've read a few times that it helps to remove some of the buds on the plant - could anyone clarify what you are supposed to do please? And is doing this truelly worthwile, or just a myth? I happened to see on tv about farmers growing thousands of tomatoes in a big field. I doubt they do any bud nipping, but also they do not support the plants at all - is supporting the plants and trusses necessary? [[Special:Contributions/78.146.176.224|78.146.176.224]] ([[User talk:78.146.176.224|talk]]) 21:09, 7 August 2009 (UTC)
I'm growing some tomato plants. I've read a few times that it helps to remove some of the buds on the plant - could anyone clarify what you are supposed to do please? And is doing this truelly worthwile, or just a myth? I happened to see on tv about farmers growing thousands of tomatoes in a big field. I doubt they do any bud nipping, but also they do not support the plants at all - is supporting the plants and trusses necessary? [[Special:Contributions/78.146.176.224|78.146.176.224]] ([[User talk:78.146.176.224|talk]]) 21:09, 7 August 2009 (UTC)
:The process of removing the buds/side shoots of tomatoes is called "suckering" (at least that's what I learned it as). The thought is to remove growth that will never amount to much, and get the plant to put that energy into flowering and fruiting. The Wikipedia article isn't too applicable, but if you search the web for "suckering tomatoes" (or similar), you should get a number of sites which discuss it. The reason you stake/cadge tomatoes is to keep the fruit off the ground, and to allow it to dry out more thoroughly. Tomatoes are particularly susceptible to [[List of tomato diseases|diseases]] especially fungal ones, such as [[blossom end rot]], [[verticillium wilt]] and [[fusarium wilt]]. Commercial farmers don't prune or stake because it's very labor intensive, and labor is costly. It's cheaper/more efficient to just grow more plants, spray with fungicides, and hope for the best. The analysis is different with a backyard gardener, though. The labor expenditure is not as high with just half a dozen plants, and you'll get a much larger crop. -- [[Special:Contributions/76.201.158.47|76.201.158.47]] ([[User talk:76.201.158.47|talk]]) 14:57, 8 August 2009 (UTC)
== power leakage ==
== power leakage ==
Revision as of 14:57, 8 August 2009
Welcome to the science section of the Wikipedia reference desk.
The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.
I've heard that the DNA of humans diverged from that of clowns much more recently than with other primates. Is that the case? If so, around what time did human and clown DNA begin to diverge, and is it possible that a human/clown hybrid could ever be produced?--99.251.239.89 (talk) 00:11, 2 August 2009 (UTC)[reply]
My brother was a clown in the Ringling Bros. and Barnum & Bailey Circus for a while when he was in his 20’s, and now he has an office job and is more than half way through getting an MBA. So my brother appears to be some sort of clown/human hybrid. So hybridization definitely is possible. Red Act (talk) 01:18, 2 August 2009 (UTC)[reply]
My brother has produced an offspring, actually, with a fully-human female. It’s too early to tell the extent to which the offspring will exhibit clown vs. human phenotypes. Red Act (talk) 15:19, 2 August 2009 (UTC)[reply]
Guys, we have no idea about the sincerity of the original poster, but it's best practice not to start making joke answers until the question has been correctly answered. (See the Content and Tone guidelines). To the original poster - if there is any confusion at all, let's clear it up. Clowns are comic performers, but they are genetically human; there is no genetic divergence. Nimur (talk) 16:28, 2 August 2009 (UTC)[reply]
Sorry for my lack of humor, but if we all start clowning around on the Reference Desk, things will rapidly devolve from "helpful resource" into "another internet forum full of idiots." Nimur (talk) 16:29, 2 August 2009 (UTC)[reply]
I figured there was next to no chance that this question wasn't a joke question. To the original poster – if this question wasn't intended as a joke, my apologies for not taking your question seriously. Red Act (talk) 17:09, 2 August 2009 (UTC)[reply]
Reliable sources should be provided for the claimed humanity of clowns. They do not, in general look or act like most humans. More clowns fit in a small car, for instance, than would be possible for normal humans. Edison (talk) 00:46, 3 August 2009 (UTC)[reply]
Good point. I would also like to know where mimes fit in. Are they clown-human hybrids or a separate species altogether? How many mimes can fit in a tiny car? – ClockworkSoul02:34, 3 August 2009 (UTC)[reply]
I dunno - the tangled sentence structures used in the simple-english article make it quite a bit harder to understand than the regular english version! SteveBaker (talk) 00:57, 3 August 2009 (UTC)[reply]
Calculating size of projected image
How do I calculate the size of image a projector can project, given the distance from the projector to the screen, and the focal length and f-stop of the projector's lens? I have a projector with F = 2.41 - 2.66 and f = 18.17 mm - 21.81 mm. Can I calculate the projected image size from these numbers or do I need more information? (the projector in question is the Acer P1266) Thanks in advance! — QuantumEleven12:32, 2 August 2009 (UTC)[reply]
The f-stop does not affect the image size, only its brightness. To calculate the image size you need to know the source (a DLP chip I believe) size S. Then image size S' = S x F/f. Your projector has a zoom lens that can optionally increase S' to 1.2 S'. Note: in some modes the whole DLP chip may not be active. Cuddlyable3 (talk) 13:06, 2 August 2009 (UTC)[reply]
Ah-ha - thank you! The data sheet does not give a source size, but it gives a throw ratio, which, according to this, is the ratio of screen width to distance. They give a throw ratio of 1.6 to 1.9 (via a zoom lens, I presume), but they quote a screen size of 62" (1.58 m) at 2 m distance, which gives a throw ratio of 1.27. What am I missing? — QuantumEleven21:58, 2 August 2009 (UTC)[reply]
Seeking a ray-diagram of a toroidal lens
Cannot find one of these on the internet anywhere. If you put a toroidal lens up to your eye and looked through it, would you get a wide-angle field of view like a crude fish-eye lens? The only picture I could find of a toroidal lens is here http://www.isuzuglass.com/g_p.html78.147.244.14 (talk) 14:23, 2 August 2009 (UTC)[reply]
Do you mean a full toroid (geometry), or just part of one (a section)
In the first case the effect is like that of a cylindrical lens off axis - but rotated about the centre line of the eyes view direction.
In the section case the lens will distort images so that the aspect ratio is not preserved since the curvatures are different. (plus other distortions ie a point source will have a non-circular image of confusion)
I think the page that the OP linked to is a translation, and so uses an unfamiliar term for what is better known as a truncated f-theta lens. The name means that the displacement of the scanned beam is the product of f (the focal length) and theta (the deflection angle of the beam). I found a picture of one here, from Melles Griot, and it has some nice ray diagrams. Apparently, the view through a non-truncated (i.e. round) F-theta lens is like that through a fish-eye lens but with less distortion. The "toroidal" lens that the OP mentioned, though, is designed for one-dimensional scanning so would have a uselessly small aperture in one direction. You would just see a bright line, I guess. --Heron (talk) 18:57, 2 August 2009 (UTC)[reply]
Just to add a little bit more - the page (possibly translated) mentions that the "toroidal lenses" are... "It is used in the equipment such as a laser printer, a fax or a copier that incorporates a printing mechanism of a scanning laser beam." - in my experience such lenses have curvature in one direction, and infinite or very large curvature in the other - if the laser beam has finite width the large curvature aspect (at right angles to the scan) might be used to get a smaller laser spot (this is a guess) - and would be a good match for the description "toroidal".
I was assuming that when "fish eye" was mentioned it meant "very wide angle" rather than the type of distortion .. my apologies about that..83.100.250.79 (talk) 19:17, 2 August 2009 (UTC)[reply]
Oh, wait. I've just read an earlier post by the OP and realised that he is not looking for an f-theta lens. He has read the proximity fuse article and wants to know what the "toroidal lens" mentioned there looked like. I think that the lens mentioned in that article is unrelated to the Isuzu "toroidal lens" that the OP found on the web. The proximity fuse lens was, possibly, actually doughnut-shaped. There's not much point in speculating on what you would see by looking through one of those, since they weren't designed to create an image. --Heron (talk) 19:04, 2 August 2009 (UTC)[reply]
Actually I think a toroidal lens (two radii of curvature, not a donot) of the type used in scanners/laser printers - would work to capture a plane of light (roughly) - though maybe a concave version would be better. I can't see a optical donut shaped lens having any use..83.100.250.79 (talk) 19:23, 2 August 2009 (UTC)[reply]
The plot thickens. I've just found evidence that the proximity fuse lens was actually a Perspex ring that formed part of the nose cone of the missile. It was curved around the axis of the missile (obviously) to give it a 360° view, but it was also curved at right angles to that to focus the light onto an internal photocell. Thus it was almost doughnut shaped, and not the sort of thing you would want to look through. --Heron (talk) 19:56, 2 August 2009 (UTC)[reply]
I found that too, but couldn't make 100% sense of it - to me it would seem sensible to have a conical mirror in the middle of the torus reflecting light from the edges (perpendicular to flight) down onto a photocell - possibly that's what it means when it says "and to have the focal axis at any point around the lens lie on a conical surface" - possibly this type of lens could be used to make a 360degree angle lens - I think the image would be projected onto a disc (ie a circle with a circular hole in the middle) - so with the conical mirror - it might be possible to make a 'fisheye' type wide angle lens - 83.100.250.79 (talk) 20:10, 2 August 2009 (UTC)[reply]
To the original questioner - it seems to me that technically a toroidal lens should be convex, however using the same principles a similar type of lens could be made that was concave - speaking from experience I know that some laser printer lens of this type (the scanning lens) are concave, so maybe it doesn't matter if the lens is concave or convex for it to be called a toroidal lens (as long as the general principle of different curvatures remains) - coupling this with the info. given above it looks like a toroidal lens might (in principle) have a fish-eye like effect - though only in the way the image is distorted (rather than having the 180 degree view that people like me associate with fish-eye lenses) I'm assuming that the term 'fish-eye' includes at least some widening of view angle, as well as a particular type of edge distortion.
Its the shape of the lens in an optical proximity fuze that I'm curious about. I imagine that it would focus the light from 360 degrees onto a small disk-shaped photocell. Perhaps it is shaped like an invercone on a light meter. 89.242.100.18 (talk) 22:48, 2 August 2009 (UTC)[reply]
I think quite possibly you're right - though I'm not sure that the invercone uses exactly the same principle - it appears to be opaque and use light scattering inside a almost torus shaped thing - I don't know exactly how an invercone works though.83.100.250.79 (talk) 00:16, 3 August 2009 (UTC)[reply]
Some burglar alarms already use petoscopes as intrusion sensors. Those are usually installed in hallways where there's no room for someone to bypass the sensor's field of view -- the thief (inevitably) casts a shadow as he sneaks down the hallway, the shadow falls on the lens, the photo-cell senses the change in light intensity, the alarm sounds. A variation on this theme replaces the photo-cell with an infrared sensor that "sees" the thief's body heat and triggers the alarm. 98.234.126.251 (talk) 03:14, 6 August 2009 (UTC)[reply]
why so??/
the compression work "adiabatic reversible " is given by integration(vdp) why ? and why not as integration(pdv).please enlighten
Is it some textbook that you’re seeing the in? That does seem problematic. By the formula for integration by parts, those two integrals would be the same only if was the same before and after the process, which for an ideal gas, amounts to the temperature being the same before and after the process, which is not generally the case. Red Act (talk) 20:39, 2 August 2009 (UTC)[reply]
However, the article also says "However, P does not remain constant during an adiabatic process but instead changes along with V". In other words, taken on their own, both W=int(PdV) and W=int(VdP) are incorrect. --Phil Holmes (talk) 10:39, 4 August 2009 (UTC)[reply]
The correct equation is more clearly written as . At the point in the adiabatic process article where the integral is needed, it is already known that the pressure can be expressed purely as a function of volume, specifically, , where , and are constants. So there’s no point in showing the pressure as being a function of both volume and temperature. Red Act (talk) 13:45, 4 August 2009 (UTC)[reply]
Thanks for lot of discussions.let me say that i found the above stated question in a competetive examination file and both int(vdp) and int(pdv) are in option.please help now.
218.248.11.214 (talk) —Preceding undated comment added 16:20, 4 August 2009 (UTC).[reply]
OK, so it sounds like the real question is given that the work integral is one of or , how do you know which one of the two is correct?
I presume you’re familiar with work in terms of a force applied through a distance, i.e., ? You can kind of derive the correct work integral from that.
Suppose you have a piston of area in a cylinder full of gas, with the cylinder/piston system surrounded by a vacuum (it’s an idealized situation). Let be the length of the cylinder up to where the surface of the piston is. The pressure on the piston varies with , i.e., it’s a function . The pressure on the piston is force per area, so the total force on the piston is . As the piston moves, the work performed on (or by) the piston is . But is how much the volume of the gas changes when the piston is moved by , i.e., . So by considering the pressure to be a function of the volume instead of the distance , you can instead do the integral as .
The cylindricality of the container in the example above isn’t important. You can always think of the change in volume of a more general container as being equivalent to a series of adiabatic processes, in which one little piece of the container, with area , is moved by a distance . The force in that area is still , so the work done by that little movement is still , which is still . If you add together enough little changes in container shape that way using arbitrarily small little areas, you can get arbitrarily close to modeling any smooth change in container shape. Red Act (talk) 17:22, 4 August 2009 (UTC)[reply]
Lost in space during an EVA
What happens if during an EVA an astronaut floats off into space, beyond the reach of any mechanical arm? Is he or she doomed? It would be a horrible and drawn out way to go. Why do astronauts not seem to have safety lines connecting them to the airlock door so that they cannot spin off into space? 78.147.244.14 (talk) 15:16, 2 August 2009 (UTC)[reply]
I think they usually are tethered to the craft. You sometimes see them removing their tether and attaching it to a different bit as they move around. --Tango (talk) 15:54, 2 August 2009 (UTC)[reply]
Since the Challenger accident, NASA has done risk-reduction by tethering astronauts during all EVAs. They also eliminated the Manned Maneuvering Unit from EVAs. In the event of serious trouble, the Shuttle Orbiter can fly using the Reaction Control System thrusters for small jumps to pick up a stray object or astronaut. See the history section for the MMU, and the Space Shuttle Orbital Maneuvering System. The hardest part would be tracking the astronaut, whose RADAR cross section and thermal signature are both fairly small; visual contact is difficult because cameras and windows do not face in all directions - so once the astronaut is beyond a (very short) critical distance, the shuttle pilot will not know which direction to fly to recover him (even if that distance is within achievable range and is within safe orbit tolerances). Nimur (talk) 16:13, 2 August 2009 (UTC)[reply]
I don't think the voice radios have directional antennas suitable for location and range detection. (I don't think that functionality is usually needed, so they don't waste mass budget carrying up such equipment). By very nature of being omnidirectional, the voice radio antenanas (on the Orbiter) preclude tracking. It's possible that the shuttle carries a standard set of radio gear, though, and with a sufficiently smart engineer, a direction-finder can be rigged up; but I'm guessing that the Space Shuttle doesn't have that feature ready for use in a standard flight equipment setup.
This news article indicates that NASA is engineering a next-generation EVA radio - a digital, S-band packet system, which will be used for voice, data, and telemetry - but there's no indication of direction-finding capability. I'm looking for more technical briefs on the radios from official NASA sources. Nimur (talk) 19:29, 2 August 2009 (UTC)[reply]
Here is NASA's SBIR solicitation for digital EVA radios; if you have any ideas for how to build a low-power, directional antenna array, you can submit your business plan and research proposal... Nimur (talk) 19:31, 2 August 2009 (UTC)[reply]
I'd think some kind of flashing light Flashing astronaut locator from a bicycle shop would work as well as radio direction finding, unless the person has gone over the horizon. There's no pesky visual obstructions like hills up there. 67.117.147.249 (talk) 20:56, 2 August 2009 (UTC)[reply]
Of course - but it's a matter of range. How far away do you expect to be able to locate the lost astronaut? Also, as I mentioned above, the views are limited to where windows or cameras are mounted. Nimur (talk) 21:09, 2 August 2009 (UTC)[reply]
With a bicycle shop LED strobe, it should be possible to see the astronaut 10 miles away from the shuttle. It would take a long time to drift that far. As for which direction, the lost astronaut should be able to see the shuttle and say which direction he is from it, allowing the thrusters to be used to translate the shuttle to his location. Edison (talk) 00:41, 3 August 2009 (UTC)[reply]
The problem with things like flashlights is that they are very directional - the flashlight shines where you point it - but not much anywhere else. The same is true of the lights on the backs of bicycles. The hapless astronaut is highly likely to be spinning - so the odds of something bolted onto his suit being of any use is rather low. He might have it in his hand - but unless it is tethered to him, the odds are good that he won't.
The issue of the range of vision out of the spacecraft windows might not be such a big deal - the shuttle and space station both have robot arms that are covered with cameras that can be panned and zoomed - so it would be possible to slowly scan the region around the region he vanished from. The astronaut is likely to be in radio range for a LONG time - so whenever he can grab a view of the shuttle, he can say "I'm behind you at about 10-o-clock and above at about 3-o-clock and give everyone a good idea of which way to look.
I guess the biggest determining factor in the likelyhood of saving the astronaut is his speed. If he just missed a footing, the amount of velocity he'd pick up might be of the order of a few centimeters a second - every move the astronauts make on EVA is covered by at least a couple of cameras. It would take a LONG time for the eagle-eyed EVA watchers on earth to lose sight of him - and swivelling a camera in the direction he vanished out of sight in ought to allow them to get a decent fix on his speed and direction within at most a couple of minutes - by which time he's probably still somewhere in the vicinity of one of the shuttle's wingtips. The could aim the arm camera at him and read off the joint angles to get a very good fix on his direction. Once they have a good fix, it doesn't matter that they lose sight of him because his future trajectory is very predictable...and again, he'll be able to see the shuttle for much longer than they'll be able to see him - so he'll be able to say "you need to aim a bit to the left and a bit up". It would be dramatic - but far from certain death. SteveBaker (talk) 00:48, 3 August 2009 (UTC)[reply]
Astronauts are always tethered to the ISS (the last planned EVA from the Shuttle was during STS-125) during an EVA. But in the unlikely case somebody floats away untethered, a jetpack like device called SAFER is attached to the spacesuits. The astronaut deploys a hand controller from near the bottom of the backpack and can thrust himself towards the nearest structure. anonymous649402:07, 3 August 2009 (UTC)[reply]
I was under the impression that the 'SAFER' unit was only being used by the ISS personnel - due to the fact that the ISS could not be manouvered as the shuttle can in order to rescue someone in the event of a disaster. However, I presume the issue comes up when the shuttle is docked to the ISS too (undocking is presumably a time-consuming process)...and since that's pretty much all the shuttle will do from here on until it's scrapped - they may have switched over to using SAFER in all EVA activities. Also, while astronauts are generally supposed to be tethered at all times - there are times when they have to move the tether from one location to another when an accident could potentially occur. It's really unlikely though - the astronauts are well aware of the dangers and you can be pretty sure that their focus will be entirely on the job while they do those kinds of things. SteveBaker (talk) 14:04, 3 August 2009 (UTC)[reply]
If the limitations of joint mobility were not too great, a slowly spinning astronaut should be able to cancel all spin and orient himself in any chosen direction without the use of thrusters. The moves necessary are known to divers, gymnasts, and cats. A battery powered rotary tool might be used as a gyro to turn or to cancel spin. The station should be able to turn on external illuminants or strobes and be visible a l-o-n-g way off. A radar target would not add much mass to the EVA suit. NASA tested on the Shuttle a soccer ball sized robot which would be able to carry a rescue line to a drifting astronaut. A fisherman would be able to cast a strong lightweight line to a considerable distance in space; a "rescue line caster" should be able to target and fire a rescue line, perhaps with a large net at the end. In sci fi stories, spacemen might throw tools or valve off oxygen in the opposite direction to cancel motion and cause drift within range of a robotic arm. How would he acquire motion away from the ISS in the first place? Maybe he jumped off for some reason, and the tether broke or was not fastened. Maybe a pressurized pipe broke loose while he was in its way. Pipe whip can be an awesome propelling force if liquid shoots out an el at the broken end, until the attached end also breaks. Such an event could leave the drifting astronaut stunned and unable to help. Edison (talk) 19:05, 3 August 2009 (UTC)[reply]
Conservation of angular momentum assures us that the astronaut cannot use 'joint mobility' alone to stop the spin. Divers, gymnasts and cats can only do it because there is gravity and air resistance. In a weightless vacuum, he has to impart a spin in the opposite direction to something else...using an electric drill or something might work so long as it can be run continuously at very high RPM - when it slows down again as the battery expires, the astronaut would start to spin as the drill slows down - eventually ending up with PRECISELY the same amount of spin he had at the outset when the battery finally dies. You'd have to get the drill up to speed and then let go of it. Sadly, even that won't actually work because the electric drills and other power tools that astronauts are provided with have internal counter-rotating flywheels precisely so that they DON'T transfer angular momentum to the user. They also don't keep spinning indefinitely - they are programmed to do a specific number of rotations, delivering a closely specified amount of torque and then stop. So that's not likely to work as a means to stop yourself from spinning. You could cancel the spin by accurately tossing two masses in opposite directions...but the manual dexterity, timing and 'feel' for the amount of mass/speed required to do that seem daunting in a bulky space-suit...most likely, he'd end up making matters worse. SteveBaker (talk) 23:40, 3 August 2009 (UTC)[reply]
reduce CO2 by 89%: gross or net?
I read that world CO2 emissions need to be reduced by 89% to prevent unrecoverable disaster. Is this the figure for gross or net emissions? (Unless the rate of removal is expected to fall, the gross figure will of course be less intimidating.) NeonMerlin21:24, 2 August 2009 (UTC)[reply]
I got the figure from a university newspaper and don't have the original source or the details on what harm would and would not be averted. NeonMerlin22:09, 2 August 2009 (UTC)[reply]
It probably meant net emissions from human activity (i.e. something like CO2 emissions from fossil fuel burning plus deforestation plus cement production minus reforestation, etc.) Dragons flight (talk) 23:04, 2 August 2009 (UTC)[reply]
I don't understand your use of the terms "gross" and "net" in terms of CO2 emissions - these are economic terms relating to income taken before or after deductions. What 'deductions' are you thinking about here? I presume that the intended meaning in the article you read is that the annual tonnage of emissions must be 89% of what it is today...that meaning is pretty clear, although "unrecoverable disaster" is not and the number '89%' (why not '90%') seems suspiciously exact for such a fuzzy statement! But this isn't a percentage emission rate issue - the issue is of the total tonnage that's up there. It would take a much smaller cut performed today than the same cut taken in 20 years time.
The CO2 that we emit is likely to persist in the upper atmosphere for perhaps 10,000 years (Greenhouse_gas#Global_warming_potential). So the amount of CO2 we can safely add each year without ever reaching this mythical "point of no return" is 1/10,000th of the total CO2 amount required to hit the point of no return in any given year.
The problem is that we aren't sure where this point of no return is. There are things like the melting of the arctic ice which appear to have already passed the point of no return...as the ice melts, shiney white ice is replaced by dark green water - which absorbs more heat than the ice - which melts more ice. There is no return from that - but the consequences are not so very serious on the scale of potential disasters we expect. However, other systems like the Clathrate gun hypothesis have an unknown trigger point - but consequences that are probably "game over" kinds of event.
It's generally agreed that between 4 and 5 degC of temperature increase will put us past the point of no return - and that every 100ppm of CO2 we add will push the temperature up by around 1 degree. We've added 50ppm in the last 30 years - 25 ppm of which happened in the last 10 years. So if we merely held our emissions to the present level, we'd add 400ppm in 160 years - and that would probably push the global temperature up into the "point of no return". But if we made a 90% (or 89%!) cut in our emissions starting today, we'd still reach the point of no return in 1600 years - and remember that we have to emit at a rate that'll give us 10,000 years.
So the best guess estimate is that we have to cut emissions by about 98% to gain stability. Nobody believes that's possible - society and technology simply can't change that fast. Most authorities are working to give us 100 years of breathing space before we hit that 4 degree mark in the hope that technology (and our understanding) will improve over that time - and with a sizeable 'safety margin' because we know that we have a measure of uncertainty about some of the 'planet killer' effects like the Clathrate gun. But even a 2 or 3 degree rise is insanely bad - that's enough to annihilate an enormous number of major coastal cities, inundate valuable agricultural land, wipe out huge numbers of animal and plant species, etc, etc.
The sad fact is that there is no believable amount of change that will prevent all of the bad consequences...in a very real sense, we've left it too late. If the world had capped emissions at the 2000 levels at the first Kioto accord - we'd have twice as long to think about it. If people had listened 30 years ago and capped levels then - we'd have had many hundreds of years to deal with it. The best we can do at this late stage is to slow down the rate as fast as is reasonable, cross our fingers and hope that a technological miracle comes along before we hit too many of the irreversible barriers.
But with the three major contributors (US, China, India) still growing their outputs at a prodigious rate, with weak response from the US, polite words but almost zero actual action from China and a downright, blatant refusal to cooperate from India - we're in for a very rough ride. Politicians are used to reacting retrospectively to problems...when a couple of bridges collapse in the US, we rush out a program to check and reinforce our bridges...no amount of pleading about the height of the levees outside NewOrleans was effective - but after the city is flooded out, the politicians rush to spend money building them up. But the nature of the CO2 crisis is that if there is enough CO2 in the atmosphere to cause a disaster, then there is literally no action we can take to 'fix' it. It'll take 10,000 years for the planet to recover naturally no matter how much action the politicians take. We have to take action before anything really bad happens - not one day later!
You are oversimplifying. Carbon dioxide residence time is a complex issue because carbon dioxide emitted into the atmosphere will first mix into the oceans and biosphere on a short timescale (100 years), which reduces the remaining atmospheric burden ~70%. Further reductions occur as carbon dioxide in the ocean is converted to calcium carbonate minerals which has a geologically long time scale (100,000 years). (See: [2]) If one believes there is a magic number above which the atmosphere must not rise, then that initial dilution allows one to emit more carbon slowly than if you emit it all quickly. Also, one can maintain stable carbon dioxide concentrations in the 450-550 range while still having an appreciate emissions footprint even 300 years hence [3]. Eventually, those numbers need to trend towards zero, but we can envision emissions scenarios that give us hundreds of years to fully eliminate fossil fuels without truly running off the rails. Of course, even the optimistic scenarios depend on being able to cut ~50% this century (rather than growing by +200%, which seems to be the do nothing answer). Dragons flight (talk) 00:13, 3 August 2009 (UTC)[reply]
In Steve's defense, given the complexity of the subject - which science itself has not yet fully grasped - it would be difficult not to oversimplify at less than textbook length. 87.81.230.195 (talk) 04:31, 3 August 2009 (UTC)[reply]
May I also add that the first shots are being fired from the gun right now?[4] And there's also the permafrost gun, don't forget that one.[5][6][7] We just need tenths of a percent of the excess carbon stored in frozen soils to be released as methane and we don't have to worry about improving gas mileage, at least until the methane stabilizes to CO2 over the next few hundred years. We will have warm summers (and winters). And if the permafrost release triggers the ocean clathrate release, we might get the final answer quite soon, as in our great-grandchildren who don't happen to live in low-lying areas will know exactly how well we did. Franamax (talk) 09:05, 3 August 2009 (UTC)[reply]
If the gun is being fired, so far it is coming up blanks. Methane concentrations now are 30 ppb below the most conservative of the IPCC projections made circa 2000 (and 70 ppb below the most frightful ones). Existing climate simulations have been assuming that methane would increase significantly faster than has actually been observed. Yes, the possibility of methane feedback is a real concern, but with a half-life of only ~12 years and levels that remain inexplicably lower than expected, I think it would be premature to panic about this. Dragons flight (talk) 09:42, 3 August 2009 (UTC)[reply]
Firstly, the signs that some clathrate deposits might be melting are very recent - this may literally only have started during the last 9 months or so - and perhaps only in a small part of the oceans - and it might yet prove to be some other issue entirely. Secondly, while Methane has a fairly short half-life, it traps 70 times more heat than CO2 while it's there...so it has the scope to be a nasty problem that would happen quickly. The nature of the feedback would be to dump an enormous amount of methane into the upper atmosphere - which could produce a sudden and violent change in surface temperatures...far too fast for humans to adapt to. Admittedly, with a half-life of 12 years, the methane problem would abate within 25 to 50 years...but that's more than enough time to trigger all manner of other nasty problems. Also, when the methane disappears, it leaves behind both CO2 and water vapor - so when we say it's "gone" - that doesn't mean that the problem it left behind is over and done with. SteveBaker (talk) 13:49, 3 August 2009 (UTC)[reply]
Most of the clathrates are buried too deep to melt for at least a thousand years even under the most drastic global warming projections, and that's a scientific fact.98.234.126.251 (talk) 01:51, 4 August 2009 (UTC)[reply]
They're just reporters, how often do you think they get things right in matters of science? Besides, they're not even American reporters, they're European reporters -- so it's also likely that they have a vested interest in pushing for CO2 limits that will hinder America's economic growth so they could compete with us economically (which they can't otherwise). 98.234.126.251 (talk) 01:32, 5 August 2009 (UTC)[reply]
I strongly recommend that you actually read the articles Clathrate gun hypothesis and Methane clathrate -- they clearly state that most clathrates are buried very deep under the seabed and will not melt for at least a thousand years. While the Arctic clathrate deposits may melt sooner, they're only a very small portion of the total clathrate deposits -- so even if they do, they won't make a catastrophic impact on global warming. Here's the relevant quote (from Archer):
Most deposits of methane clathrate are in sediments too deep to respond rapidly, and modelling by Archer (2007) suggests the methane forcing should remain a minor component of the overall greenhouse effect.[10] Clathrate deposits destabilize from the deepest part of their stability zone, which is typically hundreds of metres below the seabed. A sustained increase in sea temperature will warm its way through the sediment eventually, and cause the deepest, most marginal clathrate to start to break down; but it will typically take of the order of a thousand years or more for the temperature signal to get through.[10]
Actually European countries are likely to suffer from CO2 limits just as much as the Americans, particularly when you consider the individual countries rather then the EU as a group which some people like to do. More significantly European journalists appear to have a better track record in recent times then American ones, considering how many American ones bought into the Iraq WMD bullshit which everyone else knew was bullshit. (I mean some of them even bought into the Saddam-Osama/al Qaeda bullshit which was absolutely ridiculous.) Besides that, I think you over-complicate journalists. Many journalists do a rather crap job, I agree, but most of them don't have such complicated conspiracy theory esq motives (the politicians and more ordinary public maybe) like the desire to 'hinder America's economic growth' or whatever but instead simply let their own biases and beliefs, lack of knowledge, lack of research etc get in the way. Besides it's not as if they're the only ones reporting on it. Fox News are hardly known for their support for "hindering America's economic growth". [8][9][10] are only not European. Of course, ultimately it's not so much the reporters, and particularly their nationalities that matter. It is the science. The only really thing the reports are good for is in summarising the science in a way ordinary people can understand. In this case, it may very well be that some or even many scientists still believe it is unlikely. But is this view changing? Is new evidence suggesting that the tradional view is wrong? How strong is the new evidence? How strong is the existing evidence? This I think is the key point Steve Baker was emphasising. I don't think he was suggesting that it's defininately the case the deposits are going to melt. P.S. On a somewhat related point, I would emphasise that until recently weren't even interested in tapping them for energy something which now is of great interest [11]. Indeed I think I've read some people suggest we should burn them as energy rather then let them melt. Nil Einne (talk) 10:31, 9 August 2009 (UTC)[reply]
OK, so dinosaurs roamed the earth for about 200 million years. First question is - why didn't they evolve to achieve intelligence like humans did in a much shorter period of time? Then I've been thinking about what would happen if SETI find aliens, or we become spacefarers and meet like-minded curious aliens, or they make their presence known because they have been waiting for us to achieve space travel... these aliens would presumedly come from far older civilizations and be far more 'advanced' than we are, given the age of the universe. Well, if dinosaurs did nothing for 200 million years, why is there a common presumption that aliens would have done any better? Sandman30s (talk) 23:16, 2 August 2009 (UTC)[reply]
Evolution isn't a straight line. You don't "evolve enough" over time and get some kind of prize (in this case, intelligence). It doesn't go towards any particular ends, and high, high-levels of intelligence, like humans have, are expensive and for most species unnecessary for their survival. You could easily say, humans have been around for awhile now, why haven't we evolved to achieve wings or giant horns on their heads? It's also worth recalling that though humans at at the top of the food pyramid now, we were quite scrawny and desperate for a good deal of known human history. While its true that in the long run, having lots of brains allows a species to become quite powerful, in the short term being able to adequately reproduce and protect your young is all that is really necessary, and there are plenty more direct ways to do that than having a gigantic frontal cortex.
The presumption about aliens is that if an alien had the capacity to reach us, they probably have much more advanced technology than us, because we don't really have any real prospects of being able to get across the vast, VAST distances of space in any reasonable amount of time. If something has managed to get over to us, it is probably more advanced than we are. --98.217.14.211 (talk) 23:23, 2 August 2009 (UTC)[reply]
There is some empirical evidence that dinosaurs were getting smarter (or more precisely that the relationship between brain mass and body mass was moving in a direction that favors intelligence in modern analogs). In general fish are less intelligent than reptiles, which are less intelligent than mammals, which are less intelligent than primates, etc. The evolutionary developments that led to human intelligence probably progressed through 100s of million of years, and not just the few million years of homonids. With respect to alien civilizations, I would also point out that a lot of the achievements of humanity are associated with the cultural preservation of knowledge and not intelligence per se. As species we biologically evolved almost not at all in the last millenia, but at the same time we have gone from the dark ages to space flight through the accumulation of knowledge. Regardless of their biological potential, an intelligent society with a million years of recorded history will almost certainly have accumulated far more knowledge than we have achieved in our few thousand years. Dragons flight (talk) 23:33, 2 August 2009 (UTC)[reply]
It is theorized that a great asset of modern humans has been grandparents. That of course necessitates life-spans long enough for 3 generations to be alive at once. The benefit of this is the knowledge that can be passed down from grandparents. Sounds quaint, but it is a scientific theory. You can read mention of it in this article. This is the relevant section:
"One more distinction between Neandertals and moderns deserves mention, one that could have enhanced modern survival in important ways. Research led by Rachel Caspari of Central Michigan University has shown that around 30,000 years ago, the number of modern humans who lived to be old enough to be grandparents began to skyrocket. Exactly what spurred this increase in longevity is uncertain, but the change had two key consequences. First, people had more reproductive years, thus increasing their fertility potential. Second, they had more time over which to acquire specialized knowledge and pass it on to the next generation—where to find drinking water in times of drought, for instance. “Long-term survivorship gives the potential for bigger social networks and greater knowledge stores,” Stringer comments. Among the shorter-lived Neandertals, in contrast, knowledge was more likely to disappear, he surmises."Bus stop (talk) 22:19, 4 August 2009 (UTC)[reply]
The comparison between Dinosaurs and Humans is false. Dinosaurs were (are if you include Birds) a Superorder successively divisible into 4 Sub-orders, numerous Families, many Genera and very many Species (see Taxonomic rank), whereas "Humans" is defined narrowly as a single Species (Homo sapiens) and most broadly as a mere Genus (Homo). A "fairer" comparison would be between Dinosaurs and Primates, the Order to which Humans ultimately belong. As Dragons Flight broadly said, the Primate Order is thought to have arisen as long as 85 million years ago, so one could say that it took the Primates at least 83 million years to evolve "intelligence" (depending on your definition of it): equally valid might be a comparison between Dinosaurs and Eutheria, the Infraclass of non-marsupial mammals to which Primates belong, which is at least 125 million years old.
Since evolution is not directed, but in large part contingent on varying external pressures, it says little to observe that one lineage acquired some new characteristic or notable improvement in one (such as intelligence), more "slowly" or "quickly" than another. In line with .211's observations, high intelligence didn't evolve in Dinosaurs over a long span because it wouldn't have been immediately advantageous in the prevailing conditions. It did so in Primates and in particular Humans because their conditions happened to favour it - this may have involved some low-probability coincidences in the preceding evolution of a series of traits (e.g. binocular vision, opposable thumbs, arboriality as a preconditioner for bipedalism, unusually complex social relationships) which, when combined, happened to make the evolution of intelligence more easy. 87.81.230.195 (talk) 00:57, 3 August 2009 (UTC)[reply]
I haven't got a good explanation for it but I recently read that becoming warm blooded was a necessary step in developing the brain beyond a certain point. So high intelligence in lizards is unlikely, even if the dinosaurs were not wiped out. Vespine (talk) 01:08, 3 August 2009 (UTC)[reply]
I believe there is evidence that at least some dinosaurs were warm-blooded (See this for a great summary of the arguments). Look at it this way: We know that birds are warm-blooded - and we're pretty sure that they appear to have evolved from feathery dinosaurs. Is it so unlikely that dinosaurs FIRST became warm-blooded THEN became birds rather than vice-versa? I'd argue that you need to be warm blooded in order to be able to fly (at least at the body size of birds) - hence things had to happen in that order. Ergo - there were almost certainly warm blooded dinosaurs. Either way, you can't rule out intelligence by ruling out warm-bloodedness because the latter is unproven. Furthermore - dinosaurs were not reptiles - relating what they could or couldn't do to modern lizards is simply not a valid thing to do. It's even possible that they DID become intelligent - at least to some degree - after all, there would be little or no evidence remaining of any kind of civilisation after all this time. We've only gained recognisable signs of civilisation in the last 5,000 or so years - we'd be very unlikely to spot signs of intelligence over such a small window.
As for the presumption that aliens would be intelligent...I don't think we do make that assumption. The most common argument that aliens must exist is the Drake equation. It contains a term fi that expresses the probability of life becoming intelligent. Plugging different numbers into fi gets you different probabilities that there are aliens out there who might be able to communicate with us. Most people have estimated that term at 1% - a few pessimists put it at 0.1% - some optimists put it at 100%. However, the total number of alien civilisations that are likely to be out there depends on so many unknown parameters that it's all just guesswork.
Steve: while your points about the likelihood of (some) dinosaurs' warm-bloodedness (though cold/warm-bloodedness is a rather crude and outmoded dichotomy) and the possibility of any evidence for dinosaur high intelligence being missed are valid, it is simply not true to say that "dinosaurs were not reptiles." Our Dinosaurs article's taxobox, for example, gives their classification as -
I agree with your point that modern-day reptiles are not fully representative of all that the Reptilia ever were and potentially could be, but bear in mind that, as well as "lizards," the rather impressive Crocodilia are also reptiles not too distantly related to Dinosauria, and that the majority of palaeontologist now interpret Birds as being, not merely "evolved from feathery dinosaurs," but actually to be dinosaurs, within the suborder Theropoda, though there is some dissent (some to the effect that instead, some dinosaurs are actually descended from birds) and many disagreements over the fine details. As is fairly well known, some birds such as Crows and Parrots can exhibit significantly high intelligence, to the extent of making and/or using tools and appearing to, not merely mimic, but actually to comprehend (and controversially, to rudimentarily use) human speech. 87.81.230.195 (talk) 04:24, 3 August 2009 (UTC)[reply]
Yep - I agree with all of that - I was somewhat oversimplifying for the sake of brevity. Indeed, the terms "warm blooded" and "cold blooded" are not completely explaining what's going on...however, the remark I was contradicting used those terms and I felt it better to reply in kind. Whether we call dinosaurs 'reptiles' and whether birds are indeed dinosaurs (and therefore 'reptiles'!) is mostly a matter of naming. The big prehistoric beasts that we think of as "dinosaurs" are certainly more closely related to birds than they are to lizards. Hence, there is no particular reason to assume that their metabolism resembles lizards more than they do birds. Hence (as I remarked before), the fact that lizards are not particularly intelligent does not prevent dinosaurs from being intelligent...and I agree that the relatively high intelligence of some birds leaves open the possibility of fairly intelligent dinosaurs. If you go with the idea that dinosaurs (or at least the therapods) are descended from birds - then the case may even more strongly be made. 13:07, 3 August 2009 (UTC)
Except that most dinosaurs had very small brains relative to their bodies. Only some of the most bird-like ones ("raptors" and the like) are comparable to (certain) modern birds and mammals in this respect. Not to the smartest birds and mammals either, as far as I remember (vaguely).--91.148.159.4 (talk) 19:40, 3 August 2009 (UTC)[reply]
But like the OP, .4, you're somewhat 'cherry picking' by implicitly comparing "most dinosaurs" (downplaying an alleged minority that were more intelligent) with the small minority of the mammals that have "intelligence like humans" in the OP's original phrase. Also, one cannot simply equate brain size (or better brain/body size ratio) with intelligence across Classes: the architecture and possibly more subtle workings of reptile/dinosaur/bird brains are different to those of mammalian brains, and studies of extant reptiles/birds suggest that a reptile with a given brain/body ratio is more intelligent (insofar as one can measure it) than one would expect in a mammal with the same ratio.
I think Steve and I are arguing somewhat past each other, but I can't agree that we should leave popular misconceptions exemplified by "The big prehistoric beasts that we think of as "dinosaurs" . . ." unchallenged. Bigger bones are preferentially preserved and easier to find, and big animals are disproportionally impressive, leading to sample bias and naive-observer bias, but in reality the majority of (Triassic/Jurassic/Cretaceous) dinosaurs in terms of both species and absolute numbers were probably smaller than, say, humans, and many (e.g. this) were tiny, just like a lot of their extant examples/descendants (e.g. this). In an encyclopaedic context we should surely endeavour to promote the more accurate picture? 87.81.230.195 (talk) 21:03, 3 August 2009 (UTC)[reply]
I'm not sure that's true. I recall reading a recent paper that argued that Mesozoic ecosystems were much simpler than modern ones, because niches normally filled by small animals today were often filled by large animals' offspring back then. The interrelations with vegetation were also less fine and less complex. Furthermore, not all dinosaurs were giants, but what appears to be the immense stupidity of their gigantic representatives surely somewhat discredits small and medium-size dinosaurs as well; the former would often evolve from the latter, too. To be a little crude here - we have elephants, they have sauropods. Finally, the claims about dinosaurs' brain/body ratio I remember did not, in fact, apply only to giants; few of the small and medium ones could actually compare to Troodon and Oviraptor. Even these, being the "brainiest", were close only to modern flightless birds such as ostriches (Martin, Introduction to the study of dinosaurs, p.243, p.262) (i.e. to some of the least intelligent modern birds), and may actually have been even worse than them, according to some [12].
As for the brain/body ratio - a citation of the studies you have in mind would be useful here (I'm afraid there's quite a shortage of similar studies, and I'd be surprised to find one). In the sources on dinosaurs that I've read, the brain-to-body ratio thing was accepted as a more or less adequate criterion, and I can't help but thinking that the differences you stress can't change things significantly, considering the immense differences in proportions we're talking about. I'm rather reluctant to believe that modern birds have managed to achieve a noticeably higher brain efficiency (intelligence-per-brain-size ratio) than mammals, but even if that were true, it may be connected to flight-related pressures on size and these certainly don't pertain to dinosaurs. Worse still, it would be much more surprising if the same thing were to hold true of the (non-avian, cold-blooded) reptiles we know; these are just plain primitive, very difficult to compare with any mammal at all, and I fail to see why mammals' brains would have become less efficient (in terms of size-to-intelligence ratio) than theirs. Yes, the crocodilians are impressive compared to other reptiles, but not really impressive compared to anything warm-blooded. --91.148.159.4 (talk) 21:32, 4 August 2009 (UTC)[reply]
The aim of evolution is survival and reproduction. From an evolutionary point of view, intelligence is of no particular value. Dinosaur intelligence might not have been their greatest asset -- again, from an evolutionary point of view. Bus stop (talk) 22:00, 4 August 2009 (UTC)[reply]
Sure. The whole issue is discussed because the initial asker was contemplating the possibility of sapient dinosaurs. And ultimately, because for some reason intelligence seems to be of some value from a human point of view.--91.148.159.4 (talk) 22:12, 4 August 2009 (UTC)[reply]
The question on crosswind landing above reminded me of a rough landing experience I had at SFO. It's been a while, but I believe the flight was a Boeing 767. We were arriving in windy conditions. At roughly 10 or 15 feet from touchdown, the plane tilted violently to the extent that the tip of one wing almost certainly was momentarily lower than the landing gear. The pilots recovered and we landing without further incident; however, if it had happened just a few moments later in the approach I easily could have envisioned the wing tip clipping the ground.
So, my question, how common are incidents like this? And, how bad would it have been if the wingtip really had made contact? It certainly made an impression on me at the time. Dragons flight (talk) 23:18, 2 August 2009 (UTC)[reply]
Well, if the wingtip touched the ground, the result would certainly be a major disaster - the plane would get a violent jerk in the direction of that wing and would probably cartwheel and break up. I have no idea how common it is for a wing to dip alarmingly low on approach - but I don't think there are many cases where it happened close enough to the ground to cause a crash. I don't know how you judge what happened - from the perspective of a passenger, even quite gentle manouvers seem rather violent...and you have no way to know how low that wingtip really dipped. Your estimate for the plane's altitude may also be 'off'. People tend to assume that the markings painted onto the runway are similar in width to road markings - but they are MUCH wider...that makes you think you're lower than you really are. If it's any comfort, aircraft have inherent stability when they get closer to the ground - there is a "ground effect" which increases the amount of lift under the wing the lower it gets to the ground. If one wing starts to dip low and the other raises up then the down-going wing will gain extra lift and the up-going wing will lose lift - that tends to level the plane out. The closer that low wing gets to the ground, the stronger this effect becomes. Even far from the ground, the fact that the wings on the plane have 'dihedral' gives it some degree of inherent roll stability...but ground effect is pretty powerful. SteveBaker (talk) 02:10, 3 August 2009 (UTC)[reply]
"Certainly" is too strong. See [13] - last year, an Airbus A320 hit the ground during a crosswind landing. The pilot managed to turn it into a touch-and-go landing, but the touch involved parts of the aircraft that should not really touch anything... --Stephan Schulz (talk) 02:48, 3 August 2009 (UTC)[reply]
Runways at SFO
Yes, it is possible I misjudged the height, but I don't think I would have done so by a large amount. SFO has an over water approach (image at right), and we had already reached the land/runway when this happened and were only moments away from landing. Dragons flight (talk) 03:24, 3 August 2009 (UTC)[reply]
I'd say too that it wouldn't necessarily be a disaster. Wings on large jets have a good degree of flex, so my first thought would be that the wing would "bounce". Especially so if it was a sideways roll as opposed to a "tilt-and-slew-down-and-to-the-side", which would tend to drive the wing into the ground. Now, as to Stephan's linked video clip, that's just plain crazy. I'd like to read the incident report on that one, as in, why did the pilot even make that approach? (And Df, I think there are FAA reports you can search to see if your own flight got listed as a near-miss type of incident). Franamax (talk) 08:08, 3 August 2009 (UTC)[reply]
That Hamburg incident in the video DID involve a wing strike, with slight damage to the winglet and leading edge. That means there would have to be an investigation. I've looked on the German aviation authority website and not been able to find a report. Perhaps at 16 months it is too soon. - KoolerStill (talk) 11:35, 3 August 2009 (UTC)[reply]
ID an integrated circuit (IC) manufacturer?
Hi, not really science, but I reckon the people best able to answer my question will be most likely to be watching this desk.
Can anyone here ID the logo of an IC manufacturer? Too hard to photograph, but the logo is a nice, distinctive italic capital T, with an additional stroke to make it also look like a capital F. An oblique 3/4 circle encloses the top of the logo The logo has a circle which cuts the upright of the T/F below the lower horizontal bar of the T/F. Incidentally the chip in question is an MC 34063.
--Polysylabic Pseudonym (talk) 23:36, 2 August 2009 (UTC)[reply]
Are you sure it isn't one of these?
These are the manufacturers of the MC34063, which is a switching voltage regulator. It sounds like you might be mis-interpreting the Texas Instruments logo as an "F" (it's really a map of Texas). Take a close look at this Texas Instruments SN7400 and see if it's the logo on your chip. Nimur (talk) 01:30, 3 August 2009 (UTC)[reply]
Definitely an italic capital T modified to make an F. No serifs. Is there a cheap knock-off manufacturer with initials TF? No hint of a texas map outline, no hint of an i -203.22.236.14 (talk) 02:00, 3 August 2009 (UTC)[reply]
There are literally a dozen companies that sell that part. "Fantastic Technologies"[14] are the only ones who have F & T as their initials...but I can't find pictures of any of their chips to see what they might stamp onto them. What kind of package is the chip in? That would help to narrow down the list of suppliers. SteveBaker (talk) 02:23, 3 August 2009 (UTC)[reply]
They resell, but do not manufacture, the MC34063. As you can see, they're vendors of an ON Semi version (and maybe a Motorola version - but I doubt that's a stocked part, since Motorola Semi is now Freescale, and they're not making this part). There really are only four manufacturers for this part. (One of the most important things to realize in hardware design is that "presence in the catalog" does not mean "part actually exists and you can order it"). Experience and a bit of "hunch" is necessary to sniff out a real part from a catalog-only part. Nimur (talk) 05:32, 3 August 2009 (UTC)[reply]
Great set of sites Nanonic! But can't find it there either. The logo looks a lot like the Fairchild logo, but with the top of the F extended to the left. --203.22.236.14 (talk) 04:10, 3 August 2009 (UTC)[reply]
acid strength versus pH versus acid ability (for strong acids)
Something that I don't quite get is the different behaviours of strong acids, since they all undergo complete dissociation. I have a salad of various conceptions. Why isn't there a lower bound on pH and pKa after complete dissociation?
I understand in some reactions, the acids form reactive intermediates after being protonated, and it is them and not the protons that carry out the reaction, especially in electrophilic substitution. I am not referring to this.
But take say, magic acid, and say I diluted magic acid to a pH of 1, and diluted a solution of hydrochloric acid to a pH of 1, and then added a hydrocarbon (or some other tough-to-protonate substance) -- would the magic acid behave similarly to the hydrochloric acid?
I do imagine that eventually among the strong acids the limiting factor becomes not the H+ concentration but the conjugate base which will "take away" the proton on substances that do not like to be protonated, even if the H+ concentration is very high -- because then the conjugate base concentration is very high too, and the conjugate base becomes a better proton acceptor than whatever is being protonated. Am I heading in the right direction here? John Riemann Soong (talk) 00:55, 3 August 2009 (UTC)[reply]
Actually, the better way to think of it is that strong acids are those whose pKa is higher than that of hydronium (H3O+). That means that, in all of the strong acid, hydronium has a higher "proton affinity" than does the acid, so the acid fully deprotonates. If you change the solvent to something that isn't water, for example pure acetic acid, then your list of "strong" acids would change to those that have a lower pKa than that of the "acetium" ion, and likewise for any given solvent. --Jayron3203:52, 3 August 2009 (UTC)[reply]
When you say "But take say, magic acid, and say I diluted.." do you mean in water, or in a totally inert solvent - the two situations are different - in water, as mentioned above the acid species is H3O+ .. so both act the same (since water is easily protonated by strong acids)
In an inert (non basic solvent) the pKa matters - so the magic acid and hydrochloric acid will have different aciditys - because H-Cl and H-magic still exist (they will have dissociated in water)
pH is the -log of the H+ concentration - so the more acid you add the lower the pH goes - there is a lower bound - determined by how concentrated an acid can be (I think about 20Molar is about the maximum)
Simialiar pKa is the -log of the dissociation constant - the more readily a compound dissociates the lower it goes - the dissociation constant is a ratio, and so can go from 0 to infinity (ie unbounded) In reality total dissociation is impossible, but the dissociation constant can get very very big.
"Complete dissociation" is an approximation - in practice it's 99.999% or more dissociation - so it can be treated as being total when measuring H+ concentrations.
You should at least read the first paragraph of pH and pKa linked above, or another source - to make sure you understand what pH and pKa are, and how they are measured (ie a logarthyms), and how they are different.
"I do imagine that eventually among the strong acids.." - no. You are describing deprotonation, ie the action of a base, not an acid. In general a strong acid makes a very stable base - eg HCl makes H+ and Cl-, Cl- is the base - it is not a good base - it is a very weak base, and is stable. The factor when comparing very strong acids (in pure form) is the stability of the conjugate base, and its lack of ability to accept a proton. Thus weaker conjugate bases are better.83.100.250.79 (talk) 11:24, 3 August 2009 (UTC)[reply]
If you're trying to protonate say an alkane, or benzene with different very strong acids both the pKa of the acid, and the pKa of the acid form of the alkane contribute to the extent of protonation.
eg if
Alkane + H+ >>> [AlkaneH]+ (equilibrium constant = A) .. how hard it is to protonate the alkane
and
Acid >>> conjugatebase- + H+ (equilibrium constant = B) .. how strong the acid is
Did you mean acids that are very strong because of the stability of the conjugate base - there are examples of this - a mixture of HF and PF5 is a very strong acid - not because HF is strong but because the anion PF6- is very very stable. ? Conversely there are very strong acids which the main reason for their strength can be considered to be in greater part the instability of the cation eg CH5+
Mmm, but pH (external H+ concentration) also dependent on acid strength ... if I diluted magic acid to a pH of 1, would it still be able to protonate alkanes, but just more slowly in diluted form? That is, if I didn't know the Ka of the strong acids, or what the acids were, in my solution nor their concentration, but I could measure the pH, would it all that would matter for most protonation reactions? (Again just looking purely at the protonation aspect: I'm ignoring reactions where the derivative products of the acids end up playing a role, e.g. with nitryl ions, sulfonation, etc.) John Riemann Soong (talk) 14:04, 4 August 2009 (UTC)[reply]
As per the answer by "Jayron" above - it depends on what you dilute it with - with water, or any weaker acid then the answer is no (the dilutant acts as a buffer)
If you are trying to protonate hexene, and the dilutant is hexane, then yes it will still work. (at 1Molar) (at very low concentrations the low concetration of acid will start to have a significant effect on the extent of protonation).
The limiting factor is the strongest base in the solution. eg if the solvent is Ether then the protonating strength of the solution is limited (approximately but effectively) to the protonating strength of the Et-OH+-Et cation.
To avoid confusion (in the answers) you need to say what the solvent will be when diluting. It's difficult to find a truly inert solvent for magic acid. (and some potential inert solvents may not work well because they are not polar enough to dissolve certain acids)83.100.250.79 (talk) 20:27, 4 August 2009 (UTC)[reply]
OH that makes sense now! In magic acid, dissociation doesn't really occur until the proton-SF6 complex meets with another molecule, and if I add magic acid to water or a solvent that can act like a base, I'll lose a lot of the protonation capability as heat because the formation of H3O+ will be strongly exothermic and H3O+ will turn out to be a much weaker acid than magic acid, no matter its concentration. It's all about the solvent. Thanks guys. John Riemann Soong (talk) 23:04, 4 August 2009 (UTC)[reply]
I'm pretty sure that once the food has passed out of the stomach into the intestines (i.e. past the pyloric valve) that it is pretty much only going out the back door... --Jayron3204:29, 3 August 2009 (UTC)[reply]
According to our article on Vomiting, the retroperistalsis starts at about the middle of the small intestine. Pyloric valve is relaxed, so it does not prevent the small intestine content from joining the vomitus. I did not know that, I am not a doctor (not an MD, that is; my PhD does not help here, it's in physics :) ; but I really hope our article is right. --Dr Dima (talk) 06:08, 3 August 2009 (UTC)[reply]
I have heard elsewhere that the intestine contents do not back up into the human stomach. ReverenceReference to a reliable source is called for. By the way, a physicist should start his answer to such a question be saying "http://www.physics.csbsju.edu/stats/WAPP2_cow.html] Assume a spherical stomach..."
Crash location on the Moon of Ranger 4 (April 26, 1962)
The article Ranger 4 gives three different sets of lunar coordinates for the crash site: “15°31'S 130°42'W” (infobox); “15.5°S 229.3°E” (paragraph 4, lifted from this page); and “15°30'S 130°42'W” (paragraph 5). The longitude of all three is equivalent, but the latitude in the infobox differs by one minute from the other two. The article List of artificial objects on the Moon gives a different location for the crash of Ranger 4: “12.9°S 129.1°W”. Since this location was on the far side of the moon, how did NASA even know where it was in 1962? Were they just estimating based on its trajectory at the time it was last sighted? See this source from NASA which gives a different longitude (229.5°E rather than 229.3°E), attributed to a statement by William Pickering. I would speculate that lunar orbiting missions in later years were able to pinpoint the location better, but if you read Wikipedia you only see different coordinates given with no indication of their source. Also there are three different formats for lunar coordinates used in the same article, which is unprofessional. —Mathew5000 (talk) 03:33, 3 August 2009 (UTC)[reply]
Well “15.5°S 229.3°E” is a rather unconventional way to express a longitude. One would normally either give a number in the range 0..180 followed by E or W (east or west) - or give a number in the range 0..360 without either an E or a W. So 229.3E is really (360-229.3)=130.7W - but that's in degrees. So 15.5°S 229.3°E is the same thing as 15°30'S 130°42'W so the error between the three sets of numbers in our main article is actually just one arc-minute in latitude. Since that's in the least significant digit, we're probably looking at different roundoff errors between numbers obtained from different sources...so the Ranger 4 article is actually pretty reasonably self-consistent (although one could wish they'd used the same representation in all three places in order to avoid confusion). However, 12.9S 129.1W is nowhere near there. It is of serious concern that these articles are not indicating their sources - because checking sources is the way we are supposed to be able to correct (or at least explain) these kinds of discrepancies. That's a serious matter that you should certainly take up with the authors of the article on the talk: page. SteveBaker (talk) 12:54, 3 August 2009 (UTC)[reply]
I elected to use NASA's coordinates from NSSDC ID: 1962-012A. They may have been guessing, but it's the most authoritative figure we've got. They most likely plotted the range and angle from the telemetry, and used ballistic curve fitting to arrive at the most likely impact point. The Lunar Reconnaissance Orbiter program is prioritizing imaging of landing and impact points for all human artifacts. As of June 22, 2012, Ranger 4 isn't yet on the list of imaged spacecraft. Cmholm (talk) 09:50, 20 June 2012 (UTC)[reply]
Of course! Carrots are great for a cake or a tzimmes. Other veggies can do great in desserts just as well. Here is an article in Gourmet on vegetable desserts. If you google for vegetable desserts, you'll find many others, too. Bon appetit! --Dr Dima (talk) 06:37, 3 August 2009 (UTC)[reply]
Cinnamon (bark), sugar (made either from tubers or stems), maple sugar (from sap), and the various syrups, treacles, and toffees that are made from sugar. -- Finlay McWalter • Talk01:18, 4 August 2009 (UTC)[reply]
Most of these responses seem to be assuming that vegetable just means plant. That's true at a very basic level, but I doubt it's what the OP was interested in, which (I surmise) referred to vegetables in the sense of "you should eat five (or whatever it is) servings of vegetables per day". The only answers that are responsive to that question are the ones about carrots and yams (sweet potatoes). oh, and I missed the pumpkins --Trovatore (talk) 03:24, 4 August 2009 (UTC)[reply]
Oh, and in this sense, pumpkins are definitely a "vegetable" and not a "fruit". Botanically, a fruit is anything that has seeds (more or less; I'm not a botanist), but culinarily, a fruit mostly has to be sweet (though it might also be sour enough that the dominant impression is sour rather than sweet). --Trovatore (talk) 03:55, 4 August 2009 (UTC)[reply]
Potato pancakes make the list, so do amaranth cookies. For a light summer desert try butterhead lettuce with a dressing made from sour cream, lemon juice and sugar. (Serve cool but not chilled.) Sweet corn counts which adds a whole list of things from cornflake crubles to pies to corn muffins etc. If you have friends in South Africa they could send you some gooseberry jam and you could try one of the countless cookie and cake recipes with jam filling. Arrowroot is listed in Root vegetable but seems to be missing from List of culinary vegetables. One can make all sorts of desserts from that. 71.236.26.74 (talk) 06:28, 4 August 2009 (UTC)[reply]
Corn is not a vegetable in the "eat five veggies a day" sense. It's a starch. Sweet potatoes are also a starch, of course, but they get counted because of their carotenoid content. --Trovatore (talk) 06:38, 4 August 2009 (UTC)[reply]
Well, I think so. For example if you have previously had a Caesarian section and are considering a natural childbirth they do a procedure called "trial of scar" which I imagine might be an assessment of exactly the risk of a scar bursting open. --BozMotalk12:08, 3 August 2009 (UTC)[reply]
Trial of scar isn't really a diagnostic test. It just means going ahead with a vaginal delivery, but keeping an eye out for signs of the old scar rupturing, and doing a Caesarean if any occur. --Sean14:36, 3 August 2009 (UTC)[reply]
Bleeding inside a space suit seems to have saved an astronaut's life. "..a suit was punctured in space. That incident was apparently caused by using the glove as a hammer to drive a balky pin. A 1/8" steel bar migrated out of the palm restraint and punctured the glove. In that one case, the steel bar and the astronaut's blood sealed the puncture;.." [1]Cuddlyable3 (talk) 09:50, 3 August 2009 (UTC)[reply]
I would think that a tapered rubber plug going from say 1/16 inch to 1/2 inch would be useful. Push it into the hole until the leak is minimized. A 6 mm hole in a glove was said above to give the astronaut 1/2 hole to get back inside a pressurized place. Even direct pressure from a finger should slow the leak. A plastic bag with a sticky seal tied tightly around the glove should also be a life saving measure. A wire could clamp it around the metal glove fitting, or the metal attachment of a boot, for that matter. Edison (talk) 18:51, 3 August 2009 (UTC)[reply]
Diamorphine pills
Do UK physicians prescribe diamorphine in pill form? I remember a chap at school who had what he purported were diamorphine pills, but now I imagine all diamorphine is delivered by needle. 82.111.24.28 (talk) 13:43, 3 August 2009 (UTC)
EDIT: I should add, I have no medical need for this information, am not asking for advice etc etc[reply]
Diamorphine is available orally. It is rarely used in the oral form. It has about twice the potency of morphine. However it is a pro-drug. Diamorphine's main benefit over morphine is its greater solubility in water, hence it is useful in minimizing the volume in a syringe driver. Axl¤[Talk]15:48, 4 August 2009 (UTC)[reply]
Since the human eyes is very sensitive, then what about if I'm in the blue light all the time, how come I still notice blue. When I'm in a green light all the time, the green light is still visible to me. What will happen if I'm in a room full of green light, would I still notice the green light. Would this be possible for a white object to look orangeish yellow, while pink object looking black? This never seems to happen in my lifetime. Since cherry color is at the front end of spectrum, violet is at the back end of spectrum, the fronter the spectrum, the color is easier to wash away?--69.229.108.245 (talk) 17:43, 3 August 2009 (UTC)[reply]
Your brain compensates, so if you look at something that you know should be white your brain will compensate for any colour in the ambient light so that it looks the "correct" colour. If you don't know what colour something is supposed to be you can easily get it wrong - try working out the colours of cars under sodium street lights. I don't think it makes any difference what end of the spectrum a colour is, the brain doesn't work in terms of wavelength, it works in terms of how much each of the three types of colour sensing cells in the retina (cone cells) is stimulated. --Tango (talk) 18:09, 3 August 2009 (UTC)[reply]
If your eyes are exposed to one color of light, afterwards things of that color will look very desaturated, and things of the complememtary color will have enhanced saturation. You say you "notice blue," but isn't it desaturated or less vivid compared to when you have not been exposed to light of the same color? Edison (talk) 18:46, 3 August 2009 (UTC)[reply]
Personal observation - back in the days when I used to spend long periods working at a monochrome computer monitor that displayed green letters on black, when looking out of the window for up to an hour or so afterwards I would see, for example, white cars as being pale magenta. Such chromatic adaptation effects (see under Color vision) can involve both a degree of photoreceptor fatigue (see under Complementary colour) and unconscious mental adjustment (see under Color constancy).
This is why, for example, one has to use different kinds of film for indoor and outdoor photography - pictures taken with outdoor film indoors under incandescent (tungsten) lights look astonishingly orange, even though to our acclimatised eyes such lighting seems quite "normal." Conversely, try out the effects of a "daylight bulb" (available from most arts/crafts supply stores) indoors at night. 87.81.230.195 (talk) 21:16, 3 August 2009 (UTC)[reply]
This effect is very noticeable if you ski with goggles. Ski goggles are typically tinted orange or yellow, and after taking them off the snow appears blue or purple. Rckrone (talk) 04:19, 4 August 2009 (UTC)[reply]
Because they know what various responses to the standard inkblots mean. They wouldn't know how to interpret responses to random ink plots. One of the things they look at is whether you come up with original responses or the same kind of responses as other people come up with, that certainly couldn't be done with random inkblots generated for each person. --Tango (talk) 18:16, 3 August 2009 (UTC)[reply]
(ec)Because there are set interpretations for subject responses. If there weren't, all the test would show was whether the subject had the same set of mental disorders as their psychiatrist. (insert usual caveats about Rorchach being untrustworthy and thus showing nothing of the sort). -- Finlay McWalter • Talk18:18, 3 August 2009 (UTC)[reply]
Well, yeah, but in most situations the patient doesn’t have some motive for fooling the psychologist. That would be about as useful as surreptitiously taking insulin before a glucose tolerance test, in order to trick the doctor into thinking you don’t have diabetes. Red Act (talk) 18:59, 3 August 2009 (UTC)[reply]
Well, it's a little more complicated than that. They are now quite easy to stumble upon online (and on Wikipedia) and a lot of psychologists are starting to wonder if the test is going to lose its use altogether for that reason. There was an article on this recently in the New York Times: A Rorschach Cheat Sheet on Wikipedia?. As for the motive to fool a psychologist, I think to assume total rationality in the realm of psychological or even medical practice on behalf of the patient is probably not totally correct. We all get a bit hung up about being diagnosed, I imagine. --98.217.14.211 (talk) 22:45, 3 August 2009 (UTC)[reply]
There has been a major change in the nature of this issue because the standard set of blots recently came out of copyright protection. That's why they recently ended up here on Wikipedia causing such an upset with the Physchologists. Check out this long argument about the ethics of Wikipedia doing that: Talk:Rorschach_test/images. SteveBaker (talk) 23:56, 3 August 2009 (UTC)[reply]
A psychologist who was trained on projective tests in the 1940's tole me that he could achieve the same results by having the examinee give his reactions to random cartoons, magazine illustrations or cereal box illustrations. This seems way to the mumbo~jumbo edge of science. Edison (talk) 01:32, 4 August 2009 (UTC)[reply]
Remember it's not just whether they can interpret them, but in many case whether they have the science (or whatever Edison wants to call it) to back it up. I'm pretty sure that the Rorschach blot tests have been extremely widely studied and there is an extensive amount of peer reviewed studies analysing the reliability of the interpretations. This is obviously not the case for random blots. Beyond the ethical reasons, I believe the Rorschach blots have (partially) formed the basis for a number of psychologists analyses of patients in court. Likely also in other legal settings, e.g. deciding whether to commit someone, ready they can safely be released etc. If you go to court, and say I gave these random blots and these are the results and this is what I think they mean and someone asks you why and you say, well it's what I think, your evidence is not going to have much weight. If you point to the countless studies to support you, your evidence will carry far more weight. Similarly, an opposing lawyer (or whatever), can get their expert to testify if they feel your conclusions aren't supported by the science. Nil Einne (talk) 13:10, 4 August 2009 (UTC)[reply]
Except that according to this Scientific American article from 2005: [15] the test is used in many situations, many of them in court evaluations, for which it has no proven effectiveness. 75.41.110.200 (talk) 13:46, 4 August 2009 (UTC)[reply]
Does use in court prove that a technique is scientifically valid? Several "expert testimony" types have been recently discredited for producing convictions of people later cleared by more exact DNA analysis. Those included matching of bites and hair, and footprints. A psychological test should be valid and reliable, and should have recent norms applicable to all the groups it is used on. The Rorshach has many failings documented in peer reviewed journals, as summarized in [16], which said the analysis criticized it for having norms based on small sample sizes, with norm groups that are not representative of the population, and which tend to classify normal people as having pathology. The studies also say that reliability is lacking: two different interpreters may score a session differently. The article says on the good side that the test may be useful for "schizophrenia, bipolar disorder, and borderline personality disorder," but doubts its validity for some other disorders. Edison (talk) 14:15, 4 August 2009 (UTC)[reply]
It would seem to me that this is more a failing of the legal system then anything else. If these tests have no proven reliability in a given situation or have even been proven unreliable, then that should have been challenged and disallowed in court. A key point here I think is returning to what I said, that this reliability and unreliability is well documented and I presume, known, therefore it should in theory be easy to challenge in court. This compares to some random test where there is little documentation and few scientific studies, which would be even more inappropriate to use in court. Nil Einne (talk) 10:21, 9 August 2009 (UTC)[reply]
History of science: from pseudoscience to empirical science
Not really. It's not that various types of science come from things that would now be called pseudoscience, it is that the entire concept of science came from the entire concept that is now called psuedoscience. Some pseudoscientific things could turn out to be right, but it would just be a coincidence. --Tango (talk) 18:12, 3 August 2009 (UTC)[reply]
It seems quite possible that future historians of science might look back on the beginnings of what by then is an established branch of science, and see that in the past it was considered pseudoscience. Things which might be called obvious hoaxes if presented now might really be just engineering challenges. But from this point, it it appears to run afoul of presently accepted scientific laws, and if it cannot be replicated in the labs of a skeptic, if it is not a robust phenomenon, then it is presently properly called pseudoscience. There might really be ways to "reading minds." Some glimmerings of that have been achieved with cortical evoked potentials recorded by scalp electrodes (the P300 potential), and by functional MRI. Cold fusion might be found practical. Messages or visits from extraterrestrials might occur. Levitation (they can do it magnetically with frogs in a lab) and "invisibility cloaking" (early steps toward it have been written up) might be practical on the human scale in the distant future. Edison (talk) 18:43, 3 August 2009 (UTC)[reply]
I don't think that affects the point that things like alchemy were a precursor (whether scientific or not) of more useful studies. Who knows, "cold fusion" research might eventually inspire something useful even though it almost certainly won't be limitless clean energy. Dragons flight (talk) 20:15, 3 August 2009 (UTC)[reply]
There is scientific research into cold fusion. It's fringe science for the most part, but it is science. It is certainly possible that something will come of it and it could well mean (near) limitless clean easily accessible energy. --Tango (talk) 20:33, 3 August 2009 (UTC)[reply]
An historian of science would tell you that historically speaking, what is "science" and "not science" has changed rather dramatically, and our modern definitions of "science" that people cling to (e.g. methodological rules, etc.) are often quite, quite recent. ("Falsifiability" didn't come into vogue as a demarcation criterion until the 1950s.) And most philosophers and historians are not at all content with the idea that such criteria can be applied historically or presently. (See demarcation problem.)
So yes, sure, things that are now considered "pseudoscience" could, depending on the circumstances, become the germ of something that is considered to be "real" science.
On the other hand, there is no reason to assume ahead of time that they will, and the fact of a few examples of things that did become important (alchemy, for example) does not actually prove anything about the likelihood of current pseudosciences becoming accepted as sciences. It is no more encouraging than the fact that some scientists were initially ridiculed but were later revered—the fact of it does not help you distinguish between the ones who were rightly ridiculed and those who are not (and a great deal of the scientists ridiculed deserved to be). One of my favorite Carl Sagan quotes: "But the fact that some geniuses were laughed at does not imply that all who are laughed at are geniuses. They laughed at Columbus, they laughed at Fulton, they laughed at the Wright Brothers. But they also laughed at Bozo the Clown." --98.217.14.211 (talk) 22:36, 3 August 2009 (UTC)[reply]
I'm going to agree that alchemy and astrology are not true precursors. The true ancestor of all modern science is the ascendance of secular knowledge and its codification. A process that started with the renaissance and just meandered its way across Europe. This codification dealt with almost all aspects of life but was arguably most transformative in how it dealt with natural phenomenon. This codification has been extended to all measurable phenomenon with remarkable results. Gentleman scholars such as Boyle had a need to create chemistry as we know it not to progress alchemy but to have a more complete secular explanation of the world. They were scientists first and chemists second, chemistry was just another part to understand. Chemistry in particular only developed after the scientific method (or process) had been successfully applied to number of other fields such as astronomy, physics, biology, and anatomy. I think chemistry is the youngest of the hard sciences (or "hard" natural philosophies). This isn't to say that early natural philosophers didn't use some of the "raw data" and "hints" they collected from alchemists or astronomers but they contextualized the data very differently. They had completely different motivations and interpretations. The early scientists really had to start data collection from scratch since maintaining a good reliable community record (a defining aspect of science) was part of the new codification system. Alchemy didn't evolved into chemistry, the practice of science spread to the transformation of matter and became known as chemistry.--OMCV (talk) 01:49, 4 August 2009 (UTC)[reply]
I just want to note that no professional historian of science today would agree with you. All have long since accepted that the line between "real" chemistry and alchemy is not only blurry, but impossible to distinguish. There is no methodological, epistemological, or quantitative criterion that you can use that successfully puts the "alchemists" on one side and the "chemists" on the other. Trying to say, "oh, well science developed, and got applied to alchemy" is even more incorrect from a historical standpoint. (There is no point in trying to go into strict historical details here, but if you want recommended reading on the topic, I'd be happy to send it along.)
Once question one might ask oneself is, what are the stakes in trying to draw that line, anyway? Is it because we want to say that bad science is always bad science and will always be? (Which is sort of obviously absurd, and certainly not epistemologically justified.) Or is it because we want to avoid having to give any credence to bad or pseudoscience today? (We don't really have to, even if the historical argument is as such, as I've emphasized.) --98.217.14.211 (talk) 01:58, 4 August 2009 (UTC)[reply]
That sounds rather post-modern to claim that things are too blurry to distinguish. From what I can understand a value for secular knowledge did emerge at some point and after a time dominated many cultures understanding of natural phenomenon. It was a cultural phenomenon that I would describe in evolutionary language whether or not that language is in vogue for historians. No doubt the edges blur just as the edges of "species" blur. I think alchemy would have gone on forever without any significant "progress" without the very significant introduction of a "methodology". In my view cross pollination form the other hard sciences. Like I said, Boyle and the The Sceptical Chymist seems to be a reasonable, if imperfect, place to draw the line for chemistry. But I am interested in the mainstream historic perspective, is it more consistent to follow disciplines according to its subject matter than it is to follow underlying practices and philosophies?--OMCV (talk) 02:19, 4 August 2009 (UTC)[reply]
Historians would say: you can't follow disciplines according to subject matter when the question of disciplinary lines themselves is a point of contention. (This whole debate is a subset of boundary work, in the parlance of sociologists of science.) You follow practices, philosophies, etc., but that's where things get the most mixed up, where you see that the "chemists" and the "alchemists" believe almost exactly the same things, do almost exactly the same experiments, and by modern standards, neither has the slightest claim to being more "accurate" or "progressive" than the other. Science textbooks (for obvious pedagogical reasons) emphasize the "modern" aspects of the chemists and emphasize the "pre-modern" aspects of the alchemists, but if you look at the whole of their practices you find that methodologically, philosophically, and certainly in terms of practice there is tremendous overlap. Historians have long since concluded (which you may take as you will) that trying to sort these out into even rough categories doesn't illuminate what people were doing at the time, and rather butchers any real account of how these people worked or what they cared about. The "popular" history of science is one that ignores (or marginalizes) the crazy moments and emphasizes the clever moments (Kepler is a perfect example of this). It makes for a good read, and encourages the modern scientist to feel superior in their position, but it doesn't actually represent the history of things accurately. --98.217.14.211 (talk) 15:29, 4 August 2009 (UTC)[reply]
You claim that the methods and goals of alchemist are indistinguishable yet I see big differences. Alchemists are known for their search for the transmutation, philosopher's stone, and a variety of other very ambitions methods to control the world. In contrast "chemists" choose much smaller problems their modest ambitions are rather boring compared to those of alchemists. Work like Jan Baptist van Helmont on conservation of mass and Boyle's work linking pressure and volume. This was a radical shift in the sort of questions asked concerning the transformation of matter. Some might argue that these models of the world had been proposed earlier (since they were). But that brings us to the second point these questions where now supported with empirical evidence instead of well written although idle speculation. Their was also the transition from secret experiments to public experiments. While "methodologically, philosophically, and certainly in terms of practice there is tremendous overlap" between the modern and pre-modern it doesn't make them indistinguishable. The use of this understanding and distinguishing modern form pre-modern is to teach people how to think like modern scientists, a student of science shouldn't try to create a philosopher's stone equivalent instead the student should look for fundamental questions, albeit a boring questions to the untrained, that can be answered with available resources. For most people subjects like photodiode, nuclear magnetic resonance, even high temperature superconductivity are extremely boring subjects until they are converted into a useful technology. Having the public understand that the technology pipeline begins with basic research where scientists tackle what appears to be boring and useless questions is very important for the health (ie funding) of the pipeline. As it is most people don't want to see money spent on research unless it is directly related to a tangible product that improves their lives (philosopher's stone). I agree that the cleaver stories are aggravating but most of my grips revolve around popular histories focus on theoreticians and devaluement of experimentalists and less prominent researchers. For every noble laureate their is a massive amount of grunt work that goes largely unacknowledged.--OMCV (talk) 22:39, 5 August 2009 (UTC)[reply]
Chemistry is a tough example; but in astronomy or physics, there are a few critical moments - like the publication of Principia or the church trial of Galileo - where one can definitely draw down the line and say, "in one corner, Modern Scientific Method, and in the other corner, outdated knowledge devoid of empirical basis". Specific instances and specific dates are more difficult in chemistry, but the adoption of atomic theory in the 18th century is a pretty crucial turning point. Nimur (talk) 02:23, 4 August 2009 (UTC)[reply]
Well, I don't want to spend all my time nit-picking here, but in one corner you've put a grand old alchemist (Newton) who was roundly criticized by scientists and philosophers in his day of violating basic, obvious tenants of science (e.g. postulating an occult force—Gravity), in the other you've rather dramatically simplified something that is considered by most scholars to be a specific political transaction rather than a broad philosophical transaction. Let me just say: the version of this you get from science textbooks and pop science is not, in fact, what historians believe at all, and they do not take this position just because they are namby-pamby postmodernists (many are not at all), but because careful study of it along historical lines (not presuming to find the conclusion that you expect) simply doesn't warrant it. --98.217.14.211 (talk) 15:29, 4 August 2009 (UTC)[reply]
I think the importance of drawing lines is so that as scientists we can successfully transmit our culture and its values. Values which including honesty and forthrightness. "Falsifiability" isn't the best example to give about the malleability of scientific philosophy over time since the ideas contained in the concept already existed in science in a variety of forms. Popper just codified the "concept" under a word, as Popper's fame diminishes so will the importance of the term "falsifiable". Nimur I think you are right that chemistry is hard but I think thats part of what makes its history interesting.--OMCV (talk) 02:36, 4 August 2009 (UTC)[reply]
Occam's Razor is a much more time-honored principle than falsifiability - it fills the same mental niche of allowing us not to have to concern ourselves with things that are just too crazy. The razor accords more flexibility in interpretation than falsifiability does - but on the downside, it's not as rigorous. The bottom line is the same though: There are a literal infinity of unproven and/or unprovable hypotheses (Russell's teapot, etc) - if we had to seriously consider them, our minds would be crippled by it.
Does this apple fall from the tree because the earth imposes a gravitational force on it - or is there an invisible purple unicorn from the planet Zaa'arg pulling it off the branch? Do I reject the latter argument because of the impossibility of proving that invisible purple unicorns exist (unfalsifyability) - or do I reject them because they introduce concepts like invisibility and the existance of unicorns which are unnecessary to our explanation? It doesn't really matter. The only way to proceed without being blindsided by that impossible number of useless ideas is to rigorously prune them.
Falsifiability and Occam's razor are vital and powerful tools for reasoning about the universe - almost as essential as the scientific method itself.
Pseudoscientific concepts always fail the razor - and often fail falsifiability too. We can falsify things like telepathy if the practitioner will submit to careful pre-agreed scientific study methods - and abide by the conclusions. However, it doesn't work like that. The tiny proportion of pseudo-science practitioners who actually agree to submit to these tests (eg James Randi Educational Foundation's million dollar prize) inevitably, fail to win. Mostly they just make up some lame excuse like "Well, my powers don't work when scientists study them." - which moves them firmly into the "unfalsifiable" category. Those who refuse to undergo these tests (despite the offer of a million dollars!) are already in the "unfalsifiable" category. But we could have avoided doing the experiment or offering the money at all just by invoking the razor...if telepathy worked, there would have to be a whole order of communications media that no experiment has yet revealed - the tissues of the brain would have to function in ways entirely differently than cellular biology would have us believe - we'd have to wonder why evolution has not given all of us use of this faculty. Since there is not a single experiment that points towards such things being true - the hypothesis that the practitioner is a lying, cheating bastard is far less complicated conclusion than it is to assunme that almost all of physics and biology is incorrect. Occam's razor really helps out under those circumstances - even though we know that it's not always right. SteveBaker (talk) 04:04, 4 August 2009 (UTC)[reply]
Lovely that you use the gravitational force as your pro-razor argument; you do realize that this was exactly the criticism that was made against Newton (postulation of new, invisible, "occult" forces) by his fellow philosopher-scientists in saying that what he was doing was not actually science? I bring this up only because what seems "most likely" (when one is not making a deliberate false dilemma, as in your unicorns) his historically contingent. When you've been taught that there are "forces" and one of them is named "gravity" and it is as obvious as night and day then you say, "oh, yes, that seems most plausible." When you've been taught something else, you tend to see things otherwise. Gravity is a wonderful example, in that the only way any of the larger gravitational schemes seem "most likely" is if you have built up a tremendous educational edifice beforehand. Saying that "no, it's not a force, it's a warping of space-time" certainly isn't compelling until you've already bought in to quite a few other concepts first. (And when you get into certain realms of science—e.g. quantum mechanics—Occam's Razor becomes something all the more queerer indeed. It is hard for me to see how it applies at all to my favorite experiment.) --98.217.14.211 (talk) 15:29, 4 August 2009 (UTC)[reply]
(Outdent) - Occam's Razor is not meant to suggest that the universe actually is simple - only that our scientific explanation of it should be as simple as possible. Both examples you cite - the introduction of a previously unknown force, and the treatment of a photon as a particle and a wave - are examples of how complicated the universe actually is. Scientific methodology demands that the introduction of these concepts be skeptically challenged (and as you say, they were). But in the face of overwhelming experimental evidence, and overwhelming observational data, there's no denying that some invisible force of gravity is exerting an effect - so Newton's peers had to accept a new addition to their conceptual world view. Regarding your assertions about historiography, I've got to respectfully disagree. As I mentioned earlier, I really think that an in-depth review of the writings of Newton or Galileo demonstrates that these guys were way ahead of their time, in terms of constructing logical ideas and testing them observationally. Short of a few "refresher" courses on modern differential equations and some computer science, Newton or Galileo would fit right in with a modern science team - because alchemist or not, these guys understood how to put aside their expectations and accept the data. But not only this - they proceeded to synthesize a new idea to explain the observations, still seeking as simple a method as possible. Galileo did not say that "The earth rotates the sun, therefore alien UFOs built the pyramids"; nor did Newton suggest an "invisible hand of God" pushing planets around.
I took a few history courses on the development of the scientific method, and I was stunned to see historians telling me how science works (when - sorry for my pejorative stereotypes here, but personal experience! - these guys hadn't even passed through the freshman courses in biology, physics, or chemistry. And yet, they professed to "understand" the scientific method "better" than us real scientists, because they'd analyzed it "in the writing of the era" and all this other "humanities" nonsense. At the end of it, though, they're obfuscating some key points. The famous dead white guys like Newton and Galileo earned their position in history because they were so pivotal in the development of the scientific method - which, and let me state this very plainly for the Humanities and Philosophy enthusiasts in the room - is not a fuzzy, vague concept that has evolved over the centuries. The scientific method is very simple. It can be phrased in a thousand different ways, but it is very simple:
Step 1: Think about something. ("Hypothesis")
Step 2. Find a way to test what you thought, by building an experiment or observing nature. ("Test")
Step 3: If you were right, great! If you were wrong, think again. ("Confirm or refute hypothesis")
Different philosophers of science emphasize different parts of this method - Popper's "falsifiability" has to do with the way that "step 1" needs to be phrased in order to make "step 2" feasible. All the rigorous reviews of experimental data collection that make up the bulk of 21st century science fall into the category of improving "step 2." And finally, this is the part that never seems to get across to people who don't actually study science - "Step 3" took a really long time for humans to get to. When Aristotle hypothesized that inertia did not exist (i.e. that the proverbial horse-cart will stop as soon as you disconnect the horse), he never bothered to test it - he never bothered to follow through on his implications and watch the real world. But then, 1500 years of looking at real world kinematics never inspired anyone to say, "wow, that is patently incorrect, and totally out of sync with what I see every single day." Newton's contributions to the mathematical description of physics were monumental - but equally important is that he challenged a millenia-old, incorrect theory. As 98. brought up, this was really part of an entire era of re-thinking old, broken ideas. But closing the feedback loop that is the Scientific Method - being willing to admit when an idea needs some re-work - is a huge leap forward in human comprehension of our universe. Once we got this stupidly simple three-step process down, it was trivially easy to start applying it to build up a body of scientific knowledge. (Philosophers and historians can debate about the fuzzy and vague borders of this body of knowledge, but they should lay off the "vagueness" of the scientific method). But this is why the period of time from ~ 1650 to ~ 1850 saw the explosion of accurate knowledge about physics, chemistry, biology, and engineering - because as soon as you are willing to check your work, it becomes possible to do things correctly. The more subtle parts, like advanced thermodynamics, subatomic physics, etc., took a long time to get right, because they're extraordinarily complicated compared to Newtonian physics - but we got those down pretty well, and we're now working on the even more subtle parts of science. Nimur (talk) 13:12, 5 August 2009 (UTC)[reply]
What is meant by 'any kind of pseudoscience'? Sometimes it is hard to distinguish between a science and pseudoscience. A good example for this thread would be neurolinguistic programming. I believe this started out as just some claims by the two guys who founded it, but now there is lots of research into the area. See: List of studies on Neuro-linguistic programming and NLP and science. Some of those studies show efficacy, but at what point do you classify NLP as science or pseudoscience? --Mark PEA (talk) 12:10, 4 August 2009 (UTC)[reply]
NLP doesn't fail either Falsifiability or Occam's Razor - so we can't simply hand-wave it away as pseudo-science. That doesn't mean that NLP is true - it just means that we can't dismiss it out of hand on those grounds. That suggests that we should probably do some serious experiments to test whether it's true or not. If it does turn out to work, we don't have to invent any new fundamental laws - all we're saying is that the brain is more complicated than we thought - which should come as no surprise to anyone who has considered such equally unlikely-sounding things as the placebo effect. However, if we do all of those investigations - and it turns out that NLP doesn't work - then if people continue to pursue it then we should probably label them as advocates of pseudo-science. SteveBaker (talk) 15:21, 5 August 2009 (UTC)[reply]
car brakes question
If someone was to wear their brake pads all the way down to metal, would it be possible to melt the remaining portion of the brakes, or will the friction of using the brakes not get hot enough for that? This is a hypothetical question, I advise that those who have worn brake pads and or damaged rotors get them replaced. Googlemeister (talk) 20:51, 3 August 2009 (UTC)[reply]
If you're braking metal to metal you can get some quite nasty consequences. Metal conducts heat very nicely so heat gets transferred from the discs to the brake calipers - that will wreck them in short order. You can also boil the brake fluid and wreck your entire brake hydraulic system. Exxolon (talk) 21:35, 3 August 2009 (UTC)[reply]
Yeah - the brakes can only get so hot before the brake fluid boils. Since the gasses that result are easily compressible, you lose all braking force and the brakes will release...in short...no brakes! Assuming you don't crash as a result, there would then be plenty of opportunity for the brakes to cool off - but they'll never recover full pressure after that...and there is a good chance you'd blow a brake hose or something along the way. You'd also gouge the disks (or drums) and disk brakes would probably warp too. SteveBaker (talk) 23:07, 3 August 2009 (UTC)[reply]
A bit of OR here: you don't need to wear the pads down to nothing, either. If the disks have been machined smooth once too often, they can heat up enough to boil the fluid, under sustained braking (eg down a steep hill, the last place you want to find yourself with no brakes).- KoolerStill (talk) 20:03, 5 August 2009 (UTC)[reply]
August 4
Bond Energy
Hello. Under which conditions (STP or SATP) is the bond energy of a single carbon-to-carbon bond 347 kJ mol-1? Thanks in advance. --Mayfare (talk) 00:54, 4 August 2009 (UTC)[reply]
Isn't it the other way round (1atm-101.325kPa) if A means 'atmospheric'.
I'm not sure that the acronym STP has a single defined value - it may depend on whether you are a chemist, physicist or other type of scientist.83.100.250.79 (talk) 20:16, 4 August 2009 (UTC)[reply]
STP stands for Standard Temperature and Pressure. SATP stands for Standard Ambient Temperature and Pressure. Sorry for being unclear in the first place. --Mayfare (talk) 18:35, 5 August 2009 (UTC)[reply]
Peter Pan Syndrome - refusing to heed written laws or just societal norms?
Reading the article in our link on the above, I was curious. When People refer to this, are they talking about people who refuse any type of restrictions, especially legal ones? Or, are they talking mostly cultural ones, not wanting to take the responsibilities that adults generally do.
What brought this up was a monarch - Ludwig II of Bavaria whom I had heard elsewhere might been like this (I hesitate to use 'suffered" since it's not an actual diagnosis), because of the fantasy world in which he often seemed to live. Although, I imagine just "living in a fantasy world" isn't the only criteria, it certainly seems to be part of it. Or, does the term generally refer to someone a little more dangerous or odious than just someone "living in a fantasy world"?209.244.30.221 (talk) 01:08, 4 August 2009 (UTC)[reply]
In a social setting (i. e. not a medical one), I have only ever heard this term used to describe men who never seemed to be interested in taking on adult responsibility. (Please note that I am not suggesting that this only happens to males, but simply that "Peter Pan" is usually applied only to males.) I have never heard the use to mean anything illegal or odious, unless the idea of perpetual childhood is an odious one. Usually it is women making the complaint, and it is a complaint. // BL \\ (talk) 01:36, 4 August 2009 (UTC)[reply]
As our article says - this is a "pop-psych" term - it's not a proper medical term with a hard definition. So what do people mean when they use it? Well, it's just some vague concept that an adult behaves like a kid. Different people are bound to use the word in different ways. SteveBaker (talk) 03:30, 4 August 2009 (UTC)[reply]
Old refrigerators making more ice
I have an old refrigerator and it makes more ice as when it was new. Now it needs to be defrosted at regular intervals. Why? Wouldn't it be much more logical if it made less ice as it gets older?--80.58.205.37 (talk) 11:01, 4 August 2009 (UTC)[reply]
I agree, maybe the gasket in the door is old, so outside air leaks in and carries moisture with it. It could also be that different stuff give off different amonunts of moisture (if your fridge held two sixpacks of beer a few years ago and today it holds vegetables, home made baby food and leftovers you will probably see some difference in the amounts of ice). Also if you open the door more often you let more air in.Sjö (talk) 11:10, 4 August 2009 (UTC)[reply]
Yep - your refrigerator is still getting cold enough to freeze the moisture out of the air. Usually, what happens is that the air inside the fridge is first cooled to the point where it can't hold so much water. That causes the water to condense onto the cold surfaces - just like the windows on your car fogging up when it's cold outside. The water droplets that end up on the freezer compartment then freeze into ice. However, if all was well, there would now be no more water in the air inside the fridge and no more ice would form. But if the door seal leaks (especially if it's towards the bottom of the door) then the cold/dry air (being denser) will slowly flow out of the fridge to be replaced by moist/warm air from outside. The warm air carries with it more moisture into the fridge and the cycle repeats, gradually building up the ice. Replacing the door seal should stop that and will save you money too. Failing that (as others have suggested) it would have to mean some change in life-style...perhaps different foods being stored, open containers of liquids - increased opening of the door - or perhaps a new family member who doesn't shut the fridge door firmly enough or soon enough. I suppose it's also possible that you have the thing dialled down to a colder setting than before, or that the thermostat has gone wonky...but that doesn't explain where the water to form the ice is coming from...so I'm still betting that the door seal is failing to keep the thing airtight. You should consider changing the seal though - it's a real waste of electricity. But at least you know that your old fridge is still capable of keeping things properly cool! SteveBaker (talk) 12:06, 4 August 2009 (UTC)[reply]
To check the door seal, use a piece of ribbon. Close the door on it and see if it can be pulled out freely. Check several places around the door, including the hinged side. —Preceding unsigned comment added by 98.21.108.4 (talk) 13:48, 5 August 2009 (UTC)[reply]
P.S. Instead of a ribbon, a narrow strip of paper would be better. This has the stiffness to allow it to be inserted easily in the sides of the door. —Preceding unsigned comment added by 98.21.106.176 (talk) 13:22, 6 August 2009 (UTC)[reply]
No - you don't insert the paper into the closed door - you open the door, place the ribbon/paper against the seal, then close the door and see how hard it is to pull it back out again. If there is a significant gap in the seal, the ribbon/paper will come out easily. It's gonna be hard to find a problem that way though. I'd get one of those electronic temperature probes and just look for cold spots on the outside of the seal when the door has been closed for an hour or two. Personally - I wouldn't bother - if the problem is all that serious, it's going to be a defective seal for 100% sure...so just replace it already! SteveBaker (talk) 13:46, 6 August 2009 (UTC)[reply]
does the acidity of aromatic rings, alkenes (or even alkanes) contribute to petroleum formation?
So, the pKa of an alkane is like 60, and that of alkene around 45, .... but that means a proton still comes off occasionally. That starts to make me think ... if I say stored a pure olefin (or maybe benzene) in a glass jar for 1000 years, would I eventually see some signs of chemical reactions (maybe on the ppm scale ... if someone was alive to run the jar through NMR later?). I'm thinking carbon-carbon bonds would be formed in this way ... well, let's say we had liquified 1-butene or something, ever so often, the boltzmann distribution apparently gives a lucky butene molecule enough energy to lose a proton ... a proton which then proceeds to readily protonate some other butene .... which makes it a cation, which then finds the anion, forming a C-C bond. (Well, it doesn't have to find the original molecule that lost the proton, the original anion would probably have pulled a proton off some other molecule later on, creating a new anion....)
Yeah, it probably would occur very very slowly ... but then it occurs to me, that would probably happen in an oil bed under high heat and pressure, given enough time (like 50 million years). I'm using a pure olefin as a purely hypothetical thought experiment of course (to allow ease of detection of new products), since I assume in peat or whatever you have a wide collection of organic olefins. Or is the breakage and reformation of C-C bonds (homolytically or hemolytically) under high heat and pressure the more predominant process? John Riemann Soong (talk) 11:42, 4 August 2009 (UTC)[reply]
I don't know the answer, but Petroleum#Formation and Catagenesis (geology) say that C-C bonds are formed by living organisms, which die and become kerogen. Kerogen subsequently undergoes thermal decomposition to hydrocarbons.
No mention of acid-base reactions. The pKa values of alkanes and alkenes are very approximate and in any case depend on the solvent they're in.
The loss of a proton, or H radical could contribute to petroleum formation, as will all conceivable chemical processes including dehydration, other eliminations, pericyclic additions rearrangements and eliminations etc.83.100.250.79 (talk) 14:28, 4 August 2009 (UTC)[reply]
By the way peat etc is predominately polysaccharides/cellulose (and lignin) and one of the major reactions to get hydrocarbon is loss of Oxygen (possible as water), additionally the carbon skeleton of 'peat' is not the same as oil/coal so C-C bond changes must be a major factor, along with C-H and C-OH bond changes. (It's heterolytic cleavage not hemolytic)83.100.250.79 (talk) 16:41, 4 August 2009 (UTC)[reply]
Wow that lignin seems to have some ring strain ... I mean, I like how two substituents on a benzene ring can later "join up" later on.... and just how does it react that it fuses multiple aromatic rings together? That's amazing. John Riemann Soong (talk) 18:15, 4 August 2009 (UTC)[reply]
The contrast between the two structures is interesting... looking at the disulfide and nitrogen linkages in the coal structure, it's pretty clear that protein is a major precursor, while lignin is essentially purely carbohydrate, which is what you would expect from collulose-like matter. Hmm... I wonder how common these patterns are among the compounds. – ClockworkSoul01:55, 5 August 2009 (UTC)[reply]
ok Lignin is not pure carbohydrate at all (it's not a cellulose)- carbohydrate has not bezene rings/polyphenols (there are good structures of carbohydrates at cellulose)
As for the N's and S's in coal - I would guess that they do derive from proteins - but possibly by decomposition (eg anaerobic bacteria action to give H2S, or NH3), though it could equally be by direct interaction of proteins and other plant matter. This article suggest that both methods may contribute [17] - (though don't take that as fact)
I'm no sure the disulfide linkages in coal mean anything about it coming from "protein". Given the sort of chemical changes that occur between the living tissue and the fossil fuels, there really should not be any recognizable biomolecules there, and any "evidence" of such biomolecules should merely be the chemical equivalent of "convergent evolution". If there is sulfur and carbon present in the mix, then disulfide linkages are likely to form regardless of the source of the sulfur and carbon. I would say that it is impossible to consider that the disulfide linkages found in protein (via cystein) would remain unchanged through the harsh conditions that created coal from decayed biological material. --Jayron3202:56, 6 August 2009 (UTC)[reply]
"ok Lignin is not pure carbohydrate at all (it's not a cellulose)- carbohydrate has not bezene rings/polyphenols (there are good structures of carbohydrates at cellulose)" -- Benzene rings, polyphenols and other aromatic-type compounds in coal (lignite, whatever have you) form by thermal dehydration / dehydrogenation of carbohydrate units in lignin and cellulose (that's pretty obvious, when you think about it). FWiW 98.234.126.251 (talk) 06:02, 6 August 2009 (UTC)[reply]
Yeah, I know that, what I'm saying is that cellulose is also subject to thermal dehydration/dehydrogenation to form polyphenolic and polyaromatic compounds. (In any case, wood contains more cellulose than lignin.) 98.234.126.251 (talk) 23:04, 6 August 2009 (UTC)[reply]
Interstellar travel
In the far future, when travel to distant stars is possible or even common, will it be easier/faster to travel along the comparatively crowded arms of the galaxy or along the emptier spaces in between?
Maintaining a constant speed while travelling from one location to another requires no energy if no other forces act upon a body, so it should be equally easy for both (though travelleing intergalactically would take considerably longer). However, the common theme in sci-fi is that to travel faster than light you need to maintain something (a warp field, a subspace bubble, etc) which is a constant drain on energy. So going somewhere closer would be easier. I'm not sure exactly how crowded the arms of our galaxy are, but if I recall correctly, you could travel in a straight line to a nearby star without expecting to hit anything along the way.
Assuming real-world (non warp magic) physics, which way you'd go depends greatly on the technology of your spaceship and its drive system. The advantage of the space between arms is that there's a bit less debris - once you're travelling at relativistic velocities then impacting even a modest sized particle can be damaging, forcing you to have quite a robustly constructed spaceship (this assuming that there really is less matter between the arms than in them). The advantage of being in the arm is that if you rely on there being free matter (e.g. if your ship is propelled by something like a Bussard ramjet) then you'll have more to chew on in the arms. But really we're so far from being able to to anything like this, that the engineering details are really anybody's guess (it'd be like arguing with Da Vinci about whether his hang-glider thing would be better than his helicopter thing; you don't know until you build one). -- Finlay McWalter • Talk13:48, 4 August 2009 (UTC)[reply]
How much variation is there in density between the arms and the 'gaps' (in the plane, at a given distance from the core)? I've gotten the impression that the bright 'arms' are merely where a pressure wave passed recently, creating young bright stars. —Tamfang (talk) 02:09, 11 August 2009 (UTC)[reply]
I was thinking more in terms of the effect of gravity, similar to how current space probes and such like are sent close to certain planets on their way somewhere else, helping them go faster. Though I suppose not crashing into things would also be useful. 88.108.8.64 (talk) 14:09, 4 August 2009 (UTC)[reply]
The stars are probably too far apart for you to gravity assist in a useful fashion. A gravity assist will not get you faster then light, and if you have to travel 5 years to get to the star to do the gravity assist that will increase your speed by 10%, is that really worth it? Googlemeister (talk) 14:23, 4 August 2009 (UTC)[reply]
I just want to point out, since it is assumed but not addressed directly in the comments above, that most people here have been answering in a way that assumes faster-than-light is probably the only way to do this efficiently. There are slower-than-light approaches but they require a ship that takes decades and decades if not centuries to get from point A to point B (which, even if it really is possible for humans to do that—which I'm not convinced—cannot certainly be a "common" activity). This is because the vastness of the universe is, well, VAST. The distances are HUGE. If we cannot travel faster-than-light, there is little likelihood of any kind of Star Trek future for us. Even traveling at the speed of light is pretty slow on intergalactic scales, compared to the span of human lives (or, worse, the span of human attentions). --98.217.14.211 (talk) 15:10, 4 August 2009 (UTC)[reply]
Relativity can (mostly) fix the timespan issue for the passengers, though. If you posit a spaceship that can withstand debris at relativistic speeds (a Bussard ramjet above is a good starting point), then you don't need a multi-generational ship even if Earthbound observers note a multi-generational journey. This still prohibits a Star Trek-type future, but not a humans-in-space future. Poul Anderson's Starfarers is a good treatment of the subject. — Lomn15:25, 4 August 2009 (UTC)[reply]
It depends how far you are going to travel, obviously, and whether you want to have any kind of communication with Earth (which is basically prohibited in any useful way). Even with relativity, I find it unlikely that you could get many humans to sign up for 20 years on a ship. It's not Star Trek; you're going to read all the books you have pretty quickly, have all the conversations you can have pretty quickly, and the stars are going to get a bit dull. Even a five year trip would be quite disruptive in the course of one's life, if nothing was happening on it (it would be one thing if you were traveling around the world, a different port every night... but in space it's a lot more monotonous). (As you may be able to tell, I am quite pessimistic about space travel without the possibility of FTL. I tend to think that those who push most strongly for it are just being escapist.) --98.217.14.211 (talk) 18:00, 4 August 2009 (UTC)[reply]
So no chance then of any particular route across the galaxy being much better for long distance transit? I was hoping for some sort of trans-galactic path with lots of starships running back and forth through it.88.108.8.64 (talk) 17:16, 4 August 2009 (UTC)[reply]
Not without faster than light technology. If you have that, well, that changes things, but since we don't know what that truly would look like (since there is not the slightest indication that it is possible), it's hard to say. --98.217.14.211 (talk) 18:00, 4 August 2009 (UTC)[reply]
Certain routes may well turn out to be better than others, but I can't see lots of starships covering interstellar distances without faster-than-light travel. You don't start journeys that are going to last years very frequently. I would be surprised if craft passed other craft more than a handful of times during their journey. --Tango (talk) 20:57, 4 August 2009 (UTC)[reply]
I've talked about this many times before - so I'll keep the explanation short. There IS a way...at least in theory. You have to transfer your brain into a computer...build a computer that can replicate in great detail the precise functioning of every neuron every chemical pathway. This concept doesn't violate any fundamental laws - and many people believe it will be possible in the not too distant future. You arrange that your entire psyche - everything that makes you be "you" is in the machine - and then you destroy your physical body. OK - now you can put your brain into a computer on board a very slow spaceship - and adjust the clock rate of the computer such that the computer program that is your brain runs very slowly (You could install Windows Vista, for example!)...you will be "thinking" very slowly. For you, inside the computer, time can now be speeded up and (to some degree) slowed down at will. So - off you go on your million year (thousand lightyear) trip - and it seems to you like it only took half an hour maybe...if you see something interesting along the way - you can temporarily speed up the clock on your computer...spend as long as you want observing whatever it is...and then slow the clock down again to 'fast forwards' over the boring parts. So long as we can make spacecraft that are reliable enough - speed is a relatively insignificant barrier for "humans" (gotta use the quotes to keep everyone happy!) to colonise the entire galaxy. When you get where you're going, you put your brain/computer into a realistic humaniod robot and you can carry on with life more or less as usual. Of course, for very long trips, you have the problem that the place you saw through the telescope (which is already a very out of date view) will have changed considerably by the time you get there. But it's not an impossible prospect. If the spacecraft you're using is unreliable - you can send out a spacecraft with an 'empty' computer. When it gets where it's going, it can send you a speed-of-light radio message to say it's OK - then you can send your brain software as a digital data stream back to the computer. In effect, you can travel at the speed of light...so long as there is a suitable computer at the other end. But for you, it would seem just like instantaneous teleportation. Your robotic self climbs into the booth - you dial up some far distant star that humanoid robots have already been to - you push the button and in literally zero time (for YOU), you can step out in an identical robotic body at the other end. Of course the actual elapsed time would be vast...but maybe you don't care about that. SteveBaker (talk) 22:26, 4 August 2009 (UTC)[reply]
You don't really need any special computer technology to do this, as Lomn pointed out. Travelling in a ship at very near light speed, time goes by much slower for the passengers than for an observer on Earth. For example if you had a ship that could accelerate to 0.9999995c relative to its initial frame in a relatively short time period, you could travel 1000 light years from Earth and only experience 1 year passing. Of course if you made the return trip, everyone you knew on Earth would be long dead. Rckrone (talk) 00:45, 5 August 2009 (UTC)[reply]
While there are no theoretical problems with near-light speed travel, there are several engineering problems that we are nowhere near solving (some means of propulsion and a way of surviving hitting interstellar dust particles at such high speeds being the main ones). Steve's idea may be more achievable. We have ever improving computer systems, it probably won't be long before they are powerful enough to simulate the human brain, we just need a better understanding of how the human brain works. Personally, I think we should just be content with travelling to nearby stars, where less exotic means of transport would suffice (travelling at 0.1c there are several stars within a lifetime's travel of us and at those speeds relativistic effects aren't too serious - you need to account for them in your calculations, but you don't need to worry too much). --Tango (talk) 01:07, 5 August 2009 (UTC)[reply]
But, but...but...I want my instantaneous (to me) interstellar transporter! I want to teleport to some planet orbitting Proxima Centauri - spend a few days looking at the sights - then teleport back again. Sadly, I'll need 8 years off work in order to do it...but it would certainly be worth the trip! SteveBaker (talk) 01:20, 5 August 2009 (UTC)[reply]
You're a computer graphics expert - make a virtual Proxima Centauri. What is the difference between a real you observing a virtual star and a virtual you observing a real star? They seem equally good to me, except the former is far easier and doesn't require 8 years off work. --Tango (talk) 02:02, 5 August 2009 (UTC)[reply]
I don't think a nomadic group on the Silk Road is a very good comparison to interstellar travel. You could walk the entire silk road in about 1 year, and while it isn't a stroll through Paris, there is a whole lot more to see on the way then on a 20 year trip through space with nothing in it. Googlemeister (talk) 12:56, 5 August 2009 (UTC)[reply]
Plus, with any kind of realistic technology, you can't even get out of the solar system in 20 years. People who signed up for 20 years on board ship would get shore leave every six months or so. The guys on the spaceship can't even look out of the window and see anything interesting. SteveBaker (talk) 15:05, 5 August 2009 (UTC)[reply]
Plenty of realistic technologies can get out of the solar system in under 20 years. They don't exist yet, but they are perfectly realistic. Laser beam propulsion is probably the most likely to happen. I wouldn't be surprised if an unmanned flyby probe is sent to the Alpha Centauri system within my lifetime (it might not get there within my lifetime, though...). --Tango (talk) 20:45, 5 August 2009 (UTC)[reply]
I sure wouldn't want to sign up on a laser-beam-propelled spaceship (or indeed on any spaceship without a self-contained propulsion system) -- there's always a serious risk that by the time you get to where you're going, the laser-beam apparatus would have been de-funded for financial / political reasons and you got no way to get back home again. 98.234.126.251 (talk) 02:24, 6 August 2009 (UTC)[reply]
I think manned interstellar travel, at least at first, would be a one way trip anyway. While you can get to nearby stars in a lifetime at, say, 0.1c, you can't get back again (and if it is a generation ship you would probably be planning to establish a colony which could build its own beam emitter for any return journeys). More of an issue with beamed propulsion is deceleration at the other end. You can do that using a mirror to reflect the beam back at the front of your craft, but only if they turn the beam on at the right time. You could decelerate a little using a conventional solar sail (almost like parachuting into the new star system), but probably not from near-relativistic speeds. That's why the probe I think might be launched in my lifetime would be a flyby, it would be too difficult to slow it down so it could be captured. --Tango (talk) 02:51, 6 August 2009 (UTC)[reply]
The Migration Period lasted for centuries, and I don't mean to imply that permanent nomadism does not exist, but I doubt that anyone ever planned a definite route to take more than a few years. "We'll cross the Bering Strait, then our grandchildren will reach Vancouver Island, and their great-grandchildren will drink margaritas in Cancún" – nope. —Tamfang (talk) 02:09, 11 August 2009 (UTC)[reply]
This generation might not like to sign up .... but lifestyles can change, and culture can adapt. Would you really want to be a pioneer and own a log cabin out in the middle of nowhere, where you might not see town for another 30 years? Perhaps occasionally (as you're being flung forwards), you could get out of the ship and stretch (well, as long as you somehow maintained velocity with the ship). John Riemann Soong (talk) 02:30, 6 August 2009 (UTC)[reply]
If I were planning a long interstellar voyage, especially if it were a generation ship, I would send about 3 ships at once. It would allow those on one ship to evacuate to the others in an emergency (perhaps not permanently, but for a couple of days while life support was repaired - what you do if it turns out to be irreparable, I'm not sure...). It would also help reduce the feeling of isolation since you wouldn't be alone in the interstellar void, you would be part of a formation and could travel between the ships. --Tango (talk) 02:51, 6 August 2009 (UTC)[reply]
I'm curious -- can you perform gravity assists (not necessarily stars -- perhaps large Kupier Belt objects, etc.) for minor trajectory corrections for a fleet of ships of different masses while keeping them altogether? I know at a certain distance away from the object, their gravitational accelerations are all going to be the same, but their kinetic energies won't be. John Riemann Soong (talk) 05:21, 6 August 2009 (UTC)[reply]
"Would you really want to be a pioneer and own a log cabin out in the middle of nowhere, where you might not see town for another 30 years? Perhaps occasionally (as you're being flung forwards), you could get out of the ship and stretch (well, as long as you somehow maintained velocity with the ship)." -- That's not the issue that I was talking about. The problem specific to a laser-beam propelled ship is that it's dependent on an external laser installation inside the Solar System to propel it to its destination and back again (similar to, say, a cable car being dependent on a lineside winch to propel it forward). Now, it's a given that the journey will take many, many years, during which time the laser installation will have to be maintained by us Earthlings at considerable expense so it could generate the laser beam again to propel the ship back to the Solar System on its return journey. Well, during that time it's very likely that some cost-cutting politician will come along and say, "Why are we spending all that money maintaining that laser installation that ain't doing nothing? Let's cut it from the budget and save some cash" -- and if that happens, the astronauts on that spaceship will be stranded in some galaxy far far away with no way to get back home. As for "this generation might not like to sign up", etc., etc. -- well, for one thing I might sign up if they paid me enough for it, but ONLY IF THE SHIP GOT ITS OWN PROPULSION ENGINE ON BOARD!!!98.234.126.251 (talk) 03:03, 6 August 2009 (UTC)[reply]
I don't think John was replying to you. A reply is usually indented one tab more than what it is replying to, not indenting at all usually means it is a general reply to everything that has gone above or a completely new point. I've moved your reply to the bottom and undone the change you made to the indentation of my reply - people don't alter other people's comments and keep comments at the same level in chronological order. --Tango (talk) 04:00, 6 August 2009 (UTC)[reply]
For a ship going at a substantial fraction of 'c', the time dilation effects would mean that more time was passing on earth than on-board the ship. But even without that - over a period of decades, there are wars, natural disasters, all kinds of things that could stop that laser from working. But in any case, to be practical, the laser would have to be set up in it's own solar orbit with gigantic solar panels providing the power source for it. We're not talking about a small laser here. To transmit enough power to push a spacecraft along at a reasonable acceleration, we're talking about a laser that would look MUCH brighter than the sun at the distance of the earth's orbit with a beam diameter of a couple of kilometers to cover the large solar sail that the spacecraft would need in order to be able to keep it cool enough. Out in interstellar space, this thing is by far the brightest thing in the sky even when you're lightyears away from it. The laser would have to be pretty reliable because going out to fix it would be costly - and focussing it would require lenses out at the orbit of Mars or so because even lasers diverge by a tiny amount - and over lightyears, that dilutes it's power to a massive extent. Aiming the thing would be an interesting trick too...if the spacecraft ever somehow drifted out of the beam, it might have an impossible task finding it again and given the years it would take a radio message to return to earth to ask what happened to the laser...the mission would be in DEEP touble if that ever happened. SteveBaker (talk) 13:43, 6 August 2009 (UTC)[reply]
Indeed, using a laser here to decelerate a craft to be captured by another star or to accelerate it back towards Earth would be very difficult. For a flyby it's relatively easy, though, there is no need to keep beaming when it is lightyears away. Just propelling it for the first couple of years would probably be enough. Some back of the edit form calculations: To accelerate a 1 tonne probe to 0.1c requires (ignoring relativity) 4.5x1017J. If we do that over 2 years that requires a power of 7GW. At Earth's distance from the Sun (I would put the laser at Sun-Earth L4 or L5) solar power generates 1.4kW/m2. Therefore we need solar panels 5 km2 in area. That's big, but it's not impossible. --Tango (talk) 22:29, 6 August 2009 (UTC)[reply]
That seems to be assuming that the energy of an absorbed or reflected photon all turns into kinetic energy of the probe. I don't think you get within orders of magnitude of that. If you reflect the photon, most of its energy is carried away in the reflection; if you absorb it, it mostly just heats up the probe. Try doing it with momentum instead of energy. --Trovatore (talk) 22:40, 6 August 2009 (UTC)[reply]
The scarce resource is energy. Momentum is just a technicality based on the details of the design, which I don't have. It is also a more difficult calculation - the momentum transfer is going to vary over time as the relative velocities change, with energy you can just compare the initial state and the final state. I was assuming 100% efficiency, which is obviously unrealistic, but I was hoping it would get the right order of magnitude. I'll go and look it up... --Tango (talk) 23:37, 6 August 2009 (UTC)[reply]
You could use more of the energy if, say, you used it to power an ion drive, accelerating a propellant backwards at high velocity. The fraction of it you're going to get when you just bounce the photon backwards is tiny. 100% is not just unrealistic, it's wrong by orders of magnitude.
You might get a bit more of the energy once the craft is already moving at relativistic speeds. Then the photon is redshifted when you reflect it. Maybe you get to keep some of the difference between the incoming and outgoing photon; not really sure about that. This is a billiard-ball physics question, but it has to be done relativistically, which obviously makes it a bit more difficult. --Trovatore (talk) 23:42, 6 August 2009 (UTC)[reply]
Using the beam purely for power is an option, but it means you have to carry whatever you are going to use as exhaust. Even with the kind of exhaust velocities you get with an ion drive that's still a massive inefficiency on the scale we're talking about. If the photon being redshifted helped you could just start with a longer wavelength laser. I'm talking about speeds of around 0.1c, relativity isn't a big concern. If we only want orders of magnitude, Newtonian physics will suffice. --Tango (talk) 23:58, 6 August 2009 (UTC)[reply]
I sense that you're still missing the point, which is a pretty simple point and you're going to groan once you see it. The energy analysis that you've done is completely bogus. When you have a mirror sitting in space, and a photon of energy E hits it, does the mirror's kinetic energy increase by anything remotely close to E. No. The reflected photon has energy almost exactly E, and that's where almost all the energy goes.
Alternatively, you can absorb the photon, but in that case you get even less impulse, which should be obvious -- the photon's incoming momentum was E/c; if you reflect it, the impulse you get is the difference between that and the outgoing momentum −E/c, namely 2E/c. Whereas if you just eat the photon, the impulse you get is only E/c. So absorbing the photon is only half as good as reflecting it. --Trovatore (talk) 00:33, 7 August 2009 (UTC)[reply]
Yeah, I got that point after your last message. I've been trying to come up with a loophole to get me out of it. It all comes down to wavelengths - the reflected photon will be slightly redshifted and that is where the energy comes from. What determines how much it gets redshifted by? If you could redshift it enough you could get a large proportion of the energy. As we said, it is collisions of billiard balls. If we assume perfect reflection with no absorption then it is a perfectly elastic collision. If I can remember my A-level mechanics lessons [snip]. Ok. I can't remember by A-level mechanics lessons! I've just spent ages on it and can't get a useful answer. It seems, though, that you get a greater proportion of the energy if you use low energy photons, but I don't think the limit is 100% efficiency and I can't work out what it actually is (it seems to be dependant on the mass of the spacecraft, although I'm not sure in what way). Could someone else have a go at the maths? Also, can someone explain how the hell I just got a First Class MMath degree when I apparently can't do maths? Thanks! --Tango (talk) 03:12, 7 August 2009 (UTC)[reply]
Let's see. Using momentum instead of energy, 2E/c=mv, and plugging in the numbers gives 4.5*10^18 J: exactly 10 times the amount that Tango calculated. As for the redshift, a ship moving at 0.1c sees the laser photons coming in at approx. E(1-v/c); it reflects the photons, and Earth sees the reflected photons at E(1-v/c)^2. For v=0.1c, and considering the other uncertainties involved, we can simply forget about the redshifts and treat the photons as if they were reflecting off a stationary mirror. --Bowlhover (talk) 22:31, 7 August 2009 (UTC)[reply]
No, we can't. You can't assume the thing you are propelling is stationary, that's never going to work! There must be a flaw in your calculation somewhere - since the craft starts off stationary that would mean it gets zero energy per photon, it would never go anywhere. --Tango (talk) 00:22, 8 August 2009 (UTC)[reply]
The redshift can't be ignored for accurate computation, not even if you want a second significant figure, but for order-of-magnitude analysis (using momentum rather than energy) it can.
It's true to first order that the kinetic energy is not increasing at the start of the trip. K.E. is (1/2)mv^2, so the first derivative is mv(dv/dt), that is mva, where a is the acceleration. The acceleration actually diminishes as the craft speeds up, because it's reflecting redshifted photons which don't carry as much momentum -- but the rate of increase of K.E. goes up. --Trovatore (talk) 00:30, 8 August 2009 (UTC)[reply]
True, but I wasn't trying to determine the acceleration, I was trying to determine the efficiency. That is, of the energy that goes into sending the laser how much is used to accelerate the craft. That is all down to redshift. --Tango (talk) 17:24, 8 August 2009 (UTC)[reply]
It's interesting that Tango comes up with the number 4.5x1017J...that's almost exactly the number some OP quoted in a thread below for the energy produced by a decent-sized nuclear weapon. A 100 Megaton nuke (appropriately applied) would theoretically provide 4.2x1017J - enough energy to put that 1 ton capsule into an 0.1 c trajectory. 50 Megaton hydrogen bombs are certainly buildable with 1960's technology...perhaps the Project Orion approach is the right one after all? If we're talking about "Brain in a computer" transportation systems - or robotic probes of a more conventional kind...maybe that's a better way. SteveBaker (talk) 01:29, 7 August 2009 (UTC)[reply]
It's a possible idea. You do, however, want to accelerate the ship without blowing it up. You would need lots of small nukes, not one big one. --Tango (talk) 03:12, 7 August 2009 (UTC)[reply]
Wait - everyone is getting confused. Project Orion was the seemingly crazy idea to build a spacecraft with a gigantic, heavy "pusher plate" at the back, then a bunch of huge shock absorbers and springs - and the payload/crew-quarters at the front. The idea was to toss small nuclear bombs out of the back of the machine and to explode them against the pusher plate. Project Daedalus was to use a continuous controlled fusion reaction - akin to the ideas use in experimental fusion power generators. Daedalus is technologically exceedingly difficult - we know that controlling and confining fusion reactions is really difficult. Orion seems absolutely crazy...totally insane...but when you crunch the numbers, it's quite do-able, even with present day technology. Well...do-able, IF you had the launch facility to get all of the thousands of tons of material needed for the pusher plate and shock absorbers up into earth orbit - and the political will to violate every nuclear and orbital weapons treaty ever to be signed!! Realistically, you'd have to construct it from lunar materials out in orbit around the moon because that's the only reasonable way to get all of that tonnage of 'stuff' up there. Orion-style spacecraft are much beloved by science fiction writers simply because they just about the only hope of reaching a significant fraction of 'c' with believable technology. SteveBaker (talk) 18:31, 7 August 2009 (UTC)[reply]
It might be better to build it out in the asteroid belt. Lots of resources out there and not even the Moon's gravity to contend with. Of course, a space elevator would make it all much easier. --Tango (talk) 19:27, 7 August 2009 (UTC)[reply]
I'll plug the book Interstellar Migration and the Human Experience, edited by Ben R. Finney & Eric M. Jones (U.Calif.Press 1985). —Tamfang (talk) 02:09, 11 August 2009 (UTC)[reply]
Birch tree with golden bark??
There is a tree groing at my workplace that I cannot identify for the life of me. It is definitvely not native to where I live and is intriguing to say the least. It cunningly resembles a birch tree and has a similar peeling type of bark. However, the bark isn't with or gray, it's golden-brown. The leafs also do not seem to be that of a birch. Anyone know what it could be? I'm going to try to attach photos later on too. It has been bugging me all summer long!! Veronika Stolbikova (talk) 15:53, 4 August 2009 (UTC)[reply]
I haven't actually noticed this myself. I imagine it is just parts of the nuts rubbing against each other, or your teeth, and the "squeak" has just something to do with the surface of the nut. --98.217.14.211 (talk) 23:12, 4 August 2009 (UTC)[reply]
I see often in science fiction shows that people are exposed to space for maybe 5 seconds or so without spacesuits. In reality, how long would a person stay alive when exposed to space, and what would the effects be of a 5 second exposure (assuming they're "beamed up" to their spaceship almost immediately after exposure)? —Preceding unsigned comment added by 82.43.91.27 (talk) 16:05, 4 August 2009 (UTC)[reply]
in my basics i've learned that independent variable is marked in x axis and the dependent variable in y axis.in refrigeration i learned about T-s and P-H plots where entropy(S) and enthalpy(H) are in x axis.kindly explain me how it is made.
SCI-hunter (talk) —Preceding undated comment added 16:32, 4 August 2009 (UTC).[reply]
I’m not sure I understand what the confusion is. The convention when plotting a function is to show the dependant variable vertically, and the independent variable horizontally. A function y=f(x), where y is a function of x, is plotted with y (the dependant variable) vertically, and x (the independent variable) horizontally. In a T-s plot, T is a function of s, so T (the dependant variable) is vertical, and s (the independent variable) is horizontal. In a p-h plot, p is a function of h, so p (the dependant variable) is vertical, and h (the independent variable) is horizontal. Does that help at all? Red Act (talk) 18:05, 4 August 2009 (UTC)[reply]
The above explanation is not exactly correct. Even in the simplest thermodynamic applications there will be functions of more than one variable. For instance, the ideal gas law PV=nRT can be used to obtain a relationship bewtween pressure, temperature and density for some gas, therefore one of them can be taken as a function of the other two. That means that there isn't a unique relationship between temperature and entropy that could be used to plot the temperature as a function of the entropy. More information needs to be specifyed. You could, for instance, specify what kind of thermodynamic process is being used. It could be isothermic, isobaric, isocoric, adiabatic, some other kind, or a combination of these. A carnot cycle, for instance, is given as a sequence of four different thermodynamic processes (Isothermic expansion, Adiabatic expansion, Isotermic contraction, Adiabatic contraction) which show up on a T-s plot as a rectangle, not as a function. Dauto (talk) 19:44, 4 August 2009 (UTC)[reply]
Ah. I had looked at Fig. 25.10 here, and the T-s plot and p-h plot look very much like the plots of two functions. However, reading further, I see that those two plots are actually phase diagrams, which are a different beast. The 2D phase diagrams section of that article might be a helpful read. Red Act (talk) 20:06, 4 August 2009 (UTC)[reply]
thanks a lot for the discussions on above topic.let me clear my doubt is that how could entropy become the independent variable(in case of T-S plot).we never change entropy for a system.what we usually do is to vary the temperature of a system and that causes a change in entropy of the system.
SCI-hunter (talk) —Preceding undated comment added 22:34, 4 August 2009 (UTC).[reply]
No, what you do is transfer/take heat or compress/expand the system and, that way, change both the entropy and the temperature. The distinction between dependent and independent variables is often quite arbitrary since many of the functions that show up in practice can be inverted. In the T-s diagram, though, that doesn't really matter since you are not actually plotting a function. As I said, what you are doing is plotting the path taken by the system through the T-s space as some kind of thermodynamic process is being performed. Dauto (talk) 23:13, 4 August 2009 (UTC)[reply]
Keep in mind that x-independent/y-dependent convention is only that - a convention. There's no reason to have it that way, except that that's what everyone always does, and anyone looking at your graph will initially expect that's the way it's set up. As mentioned, there isn't a clear dependent/independent distinction in thermodynamics, so the first researchers set up the graphs the way that they thought looked best or made the most sense in context. (For example, the plots could have been made by a theoretician who thinks of the entropy as the core concept, and the measured temperature is simply a derived result of the intrinsic entropy of the system.) Others repeated that same sort of display in other contexts, and that then became the convention used for those graphs. Now everyone sets up T-S and P-H plots that way because that's how researchers expect the plots to be set up. By doing so their not necessarily claiming that one variable is dependent and one is independent, they're just showing the relation between the two in the conventional fashion. -- 128.104.112.100 (talk) 17:37, 5 August 2009 (UTC)[reply]
Moldy Bones
What would be the best way to wash this green, smelly stuff that I think might be a kind of mold off of some (real, animal) bones (which I think are for a comparitive collection)? I tried scrubbing with a wet toothbrush (per boss' suggestion), but that didn't really work. 138.192.58.227 (talk) 17:04, 4 August 2009 (UTC)[reply]
Like all good bosses would say "try scrubbing harder"
Alternatively why not search for "bone cleaning" - I think you need to get all the organic matter out of the bone to stop it going green/smelling.83.100.250.79 (talk) 18:13, 4 August 2009 (UTC)[reply]
Somewhere I read about preserving bone for bone handled knives. You have to remove all the marrow. Prolonged soaking in ammonia solution can remove the fat and protein. Caustic soda in water could do this dissolving too but is more hazardous and needs more cleanup, it will leave the mineral component behind. Graeme Bartlett (talk) 22:48, 4 August 2009 (UTC)[reply]
On prolonged boiling I would imagine caustic soda to attack the bone (it would), though it is good at defattting. Has anyone tried using washing powder - maybe a biological washing powder?83.100.250.79 (talk) 22:57, 4 August 2009 (UTC)[reply]
Per National Public Radio (U.S), museums use maggots to clean bones of small animals. Books on 19th century medicine say that a doctor might take human bones and put them in a wire mesh cage submerges in a pond for a year, so the small fish etc would clean them. Edison (talk) 03:00, 5 August 2009 (UTC)[reply]
A classic way to get clean bones is to use ants. At least one friend of mine has, on several occasions, taken a small dead animal and buried it in an ant hill for a couple of weeks or so. They pick the skeleton clean. This time-lapse video of ants eating a dead gecko demonstrates this ability fairly well. -- Captain Disdain (talk) 10:16, 5 August 2009 (UTC)[reply]
Most natural history museums use dermestid beetles to clean bone samples. They do an extremely thorough job, but controlling the process can be tricky simply because of how thorough they are. You likely wouldn't want them chewing your carpet away, for example. I don't know how readily ants or maggots would eat mold; I don't know if the dermestids even do that, but that's where I'd put my money. Matt Deres (talk) 16:22, 5 August 2009 (UTC)[reply]
The ants in the video not only clean the bones, but the disarticulate the skeleton and carry away some of the bones. The gecko is left in a Napoleon condition. ("bone-apart") Edison (talk) 17:18, 5 August 2009 (UTC)[reply]
electrical grounding
My son has just asked a good question (at least I thought so, with my limited scientific knowledge). I explained to him why birds don't get electrocuted while standing on an electrical wire - because the bird is not grounded and does not complete an electrical circuit. So he asked - what happens if we touch a live (exposed) wire inside an aeroplane - are we 'grounded' (earthed) or not - will we get electrocuted? Hmm! Sandman30s (talk) 19:28, 4 August 2009 (UTC)[reply]
It's all about forming a circuit, rather than grounding per se - if a (very) big bird managed to put one foot on one overhead wire, and another foot on another wire then it would get zzzapped.
The same applies in a plane or anywhere - if you make a circuit you get 'it'.
However if you touch a live wire which has the 'ground' connection also connected to the ground (ie the soil) the you can form the electrical circuit without touching two wires - the circuit being through the wire, through you, and the through the earth (soil) to the grounded connection.83.100.250.79 (talk) 19:37, 4 August 2009 (UTC)[reply]
I think the key concept here is that electrical grounding isn't "are you touching the ground?" but "are you touching something at a different voltage?" (still an approximation). Birds are OK not because they're sitting up high but because they don't provide an interesting electrical path. Even assuming an uninsulated power line, electricity will continue to flow through a short highly-conductive wire than through a long poorly-conducting bird. Since the endpoints (and end voltages) are the same, there's no reason for electricity to flow through the bird. On an airplane, though, there's a complete electrical circuit. The power supplies in the airplane are at 28 volts or 400 volts or whatever they happen to be, relative to 0 volts as defined by the plane itself. If you're touching the plane (and you are, you're in a seat or in the aisle or what have you), you're grounded, and subject to shock. You may also be interested in a past discussion of birds here or at the Straight Dope. — Lomn19:42, 4 August 2009 (UTC)[reply]
Note also that the usual procedure for jump starting an automobile involves connecting the positive terminals of the batteries and then connecting the negative terminal of the charged battery to some metallic portion of the vehicle with the dead battery. This is called "connecting to ground" even though an automobile is actually insulated from the earth by its rubber tires. Deor (talk) 20:36, 4 August 2009 (UTC)[reply]
Your explanation of why the bird doesn't get zapped isn't correct anyway - the correct answer is actually that the bird DOES get zapped - but not by enough to bother it. The electricity has two paths it can take - the short path down an inch or so of copper wire - or the longer path: up one leg of the bird, past it's "naughty bits" and back down the other leg. The amount of current that flows down each path is inversely proportional to the resistance. Since nice thick copper wire has very little resistance - and birds have (relatively) high resistance, a huge amount of current flows down the wire - and very little of it flows through the bird. BUT that amount isn't zero! The bird is indeed being very slightly electrocuted...but the current flow, even with a soaking wet bird on a very high voltage wire is so slight that it doesn't seem to harm them. SteveBaker (talk) 22:07, 4 August 2009 (UTC)[reply]
Here's a question for you SteveBaker (without going to any reference materials!): If the line were suddenly cut so that one foot of the bird was on one side, the other foot on the other side, would the bird get electrocuted? 82.234.207.120 (talk) 23:49, 4 August 2009 (UTC)[reply]
If cutting the wire caused the two sides of the copper wire to reach different voltages, then the bird would be zapped. The crucial bit is that voltage loss along a conducting wire is "negligibly small" - so when the bird stands with two feet only inches apart on the wire, there's a small voltage drop across the bird. As Steve and others mentioned, the bird has a high resistance, so the small voltage yields an even smaller current (V = IR, or Ohm's Law). Cutting the wire could cause the two parts of the wire to reach different voltages - one half is still attached to the power source, while the other is loaded to ground (via the electric delivery network - but it might take a few seconds to decay that energy out through the grid - it's hard to say in the purely hypothetical case). But if the bird continued to stand on the two wire parts, its feet are now at very different voltages - and it will get zapped. Nimur (talk) 00:32, 5 August 2009 (UTC)[reply]
Yep. If the wire was cleanly cut - then the electricity still has two paths to choose from...through the bird - or through an inch of air. Air is a pretty good insulator - and birds are mostly salty water - which conducts electricity reasonably well (but not as well as copper wire) so the bird represents a lower resistance path than the air - so the current goes that way and the bird is undoubtedly zapped. If the process of cutting the wire allowed a spark to be produced between the ends of the wire, the air would be ionized - ionized air has a much lower resistance than regular air...so perhaps the the bird stands a better chance in that case...but I'm pretty sure the heat from the spark would still fry the poor thing. SteveBaker (talk) 01:09, 5 August 2009 (UTC)[reply]
Correct. Birds do get electrocuted by creating a complete circuit. Usually it is by touching one wing to a power source and another to ground. When I lived in the Mojave, the power poles were being redesigned because the birds there were getting zapped far too often. -- kainaw™00:14, 5 August 2009 (UTC)[reply]
On power poles here, the lines are far enough apart so that birds' wings do not touch two wires. But occasionally a big bat will make that mistake, and be electocuted. Because their feet are designed to lock them upside down automatically when they are asleep, you can sometimes see electrocuted ones hanging on a wire, dead as a doornail. Bolshy birds like Currawongs will amuse themselves all day attacking this 'interloper' who should have been at home during the day. Myles325a (talk) 01:25, 5 August 2009 (UTC)[reply]
If a power line is at a sufficiently high voltage, a bird touching it even with a single foot would get a painful and perhaps dangerous jolt, even without being grounded or without touching a wire at a different voltage. The bird acts as a capacitor, and alternating current can flow through a capacitor. Higher voltage means more current. Birds will sit on power lines of 4 thousand or maybe 12 thousand volts, but I have not seen one sitting on a 69 thousand or 138 thousand volt conductor. Edison (talk) 02:57, 5 August 2009 (UTC)[reply]
Thanks for all the answers. Steve, when I google 'bird on electric wire grounding', there are lots of answers that agree with my explanation about the bird needing to be grounded, although there are just as many that talk about the potential difference/voltage between its legs. Some argue that the grounding explanation is more correct. Surely there is some compromise between these different opinions? Sandman30s (talk) 07:59, 5 August 2009 (UTC)[reply]
The potential difference between two spots an inch apart on a power line will be negligible. Take the full rated current of the conductor, multiply it by the resistance of one inch, and you have the voltage. A 4kv conductor might be bare #1/0 copper, with .105 ohms per thousand feet. One inch would be resistance of .00000875 ohm. At 300 amperes of load current, the voltage would be .0026 volts. At 1000 amps, which would overload the circuit, the voltage would still only be .009 volt across the birds feet 1 inch apart. The conductor would literally be too hot to stand on, and on its way to burning down, before it electrocuted the bird just due to the potential difference between two spots 1 inch apart. Edison (talk) 14:28, 5 August 2009 (UTC)[reply]
The "grounding" explanation is an over-simplification - and that vague and fuzzy thinking explains why you were confused about touching wires inside airplanes. Suppose there were two power lines strung parallel to each other. One is at 10,000 volts and the other one isn't quite adjusted correctly so it's at 10,100 volts. If the bird puts one foot on each wire, it'll get a 100 volt jolt and die without ever being within 50 feet of "ground". It's a matter of "potential difference" and relative resistance. If the difference between the voltages at the bird's left and right foot are sufficiently different, it dies - if not, it doesn't - irrespective of this fuzzy concept of "ground". The potential difference between 10,000 volts and "ground" is 10,000 volts - so of course the bird gets zapped if it has one foot on the ground and the other on the wire. But if you had your electricity transmission lines made out of (say) plastic instead of copper - then the bird would get zapped just standing on the plastic wire because the resistance through its body and the resistance through the plastic would be almost the same - roughly half the current would travel through the bird and it would die.
The concept of "ground" is mostly a notational matter for electrical engineers. When you talk about "grounding" a wire in a car for example - you're attaching it to the bodywork - which is typically attached to the negative side of the battery. But on some older british cars (like my '63 Mini), they opted for "Positive ground" - so the positive side of the battery is connected to the body and all of the electrical systems run on -12 volts supplied from the '-' terminal of the battery.
However, when you step out of either kind of car so that your feet are "grounded" by touching the ground - you can still get a brief but painful 'zap' (a 'static shock') from touching the door handles because the "ground" of the car isn't the same voltage as the "ground" of the planet earth. There is really no such thing as an absolute zero of voltage to use as a reference. In a sense, the bird on the 10,000 volt wire isn't getting zapped because as far as it is concerned, "ground" is the wire it's standing on.
In telecommunications and some computer applications, you have to talk about "signal ground" and "frame ground" and treat them separately because again, it's just a notational convenience. Check out (for example) RS232#Pinouts - where you'll see a "Common ground" and a "Protective ground". Note the comment there: "Use of a common ground is one weakness of RS-232: if the two devices are far enough apart or on separate power systems, the ground will degrade between them and communications will fail, which is a difficult condition to trace.". SteveBaker (talk) 14:55, 5 August 2009 (UTC)[reply]
Further... If you've worked with high-end audio equipment, you know that ground is not ground. If you assume ground is ground and connect all your equipment to the closest ground, you will get a hum on your speakers. That is because ground in one area is not necessarily the same potential as ground in another area. You need to ensure that all your equipment is using the same ground to remove difference in potential. -- kainaw™15:12, 5 August 2009 (UTC)[reply]
Grounding of communication lines or control wires is indeed a confusing subject. Sometimes the ground braids are only connected to earth ground at one end of the line, to avoid ground current travelling over the braid and having a "ground loop." Edison (talk) 17:14, 5 August 2009 (UTC)[reply]
Speaking of trams... I thought that the engineer could lower the pantograph from the cab without having to jump out of the tram. Is that not so? 98.234.126.251 (talk) 04:56, 6 August 2009 (UTC)[reply]
You can look it up in the USDA's nutrient database - there it says that it contains 5.8% monounsaturated fatty acids and all of this is 18:1 fatty acids (most likely all of that is oleic acid); and 1.8% polyunsaturated fatty acids and all of this is 18:2 (most likely linoleic acid) - so it seems likely that there is 1.8% omega-6 fatty acids and 0.0% omega-3 fatty acids. Icek (talk) 17:11, 9 August 2009 (UTC)[reply]
I've just been watching the film 'Knowing'. Is it possible that a solar flare would burn up the earth to such an extent as detailed in the film. When I say possible, I am referring to the likelihood of it occuring, rather that the damage caused by such a large-scale event. --russ (talk) —Preceding undated comment added 00:18, 5 August 2009 (UTC).[reply]
"Solar flare" is a pop-science term for a coronal mass ejection (it can also mean the less-severe, closed-loop solar prominence and some related phenomena). Gross quantities of solar ejecta are unlikely to ever reach Earth's orbital radius in any significant way. (Read: no giant flameballs will reach us). However, the density and flux of charged particles will increase; and an electromagnetic effect is common; these effects can significantly harm objects in space near Earth. It is very important to understand that solar wind is a charged plasma - as such, it is "deflected" (rather, trapped in cyclotron resonance) by Earth's magnetic field - and the result is the Van Allen belts. During periods of high solar activity, these regions increase in size, energy, and particle content. Also, it's worth noting that 2007-2009 has been "the quietest Solar Minimum ever"[18] - so if there were going to be a catastrophic solar flare (or even any medium-large ones), it would be really unlikely timing. Nimur (talk) 00:36, 5 August 2009 (UTC)[reply]
I also have not seen the movie, but the book Death from the Skies has a chapter on the actual threat posed by CMEs. I don't have it in front of me, but here's what I recall: the most likely result of a severe CME directed at Earth is rendering satellites inoperative. More severe CMEs could potentially cause widespread damage to the power grid. A particularly severe CME in 2003 was the most violent flare recorded in modern times: it is described here, but there's a good chance you had no idea that anything happened. CMEs are common, and obviously we get smacked by them from time to time. No CME will incinerate the world as in Inconstant Moon; that more properly describes the sun going nova (story claims notwithstanding). We have no reason to expect the sun to go nova. In about one billion years, the sun's energy output will have risen enough (10%) to render Earth uninhabitable; in about five billion years, it will become a red giant. See our article on the sun for details. — Lomn13:13, 5 August 2009 (UTC)[reply]
Steel yourself for this question
When I was a youngster, my family watched too much TV, as evidenced by the fact that we even watched crap shows like That's Incredible! and Real People. Anyway, it was on one of those shows (or similar) that I saw a segment about this dude that could (briefly) touch molten steel with his bare hand. I believe he worked in a steel mill or something of the sort. Anyway, they showed him on camera, quickly flicking his fingers across the liquid metal, flinging globs of steel. I don't think it was a video trick (though I was very young at the time). Does anyone remember the name of that guy or how he did what he did? Firewalking works because ash is actually a poor conductor of heat, but the same is definitely not true of iron/steel! Matt Deres (talk) 00:24, 5 August 2009 (UTC)[reply]
I've never seen it done with steel - but I've seen people stick their hands up to the wrists in molten lead - which is probably just as bad. The trick with molten lead is to have your hand be wet - as the water flashes to steam, it insulates your hand from the heat of the metal. It's still insanely hot - and you can't hold your hand there for more than a second or so...but if you know what you're doing it's possible. However, iron melts at 1,370 degC and lead at only 320 degC - that's a very different matter! So I'm frankly a little skeptical about the steel thing - but perhaps if your memory is imperfect, it could have been some lower melting point metal than steel. I certainly don't recommend experimenting! This is an incredibly dangerous thing to try. SteveBaker (talk) 01:01, 5 August 2009 (UTC)[reply]
Is there a physical chemist in the room? Does liquid metal have the same thermal conductivity properties as solid metal? If you don't have the same delocalised electrons as you do in a metallic lattice (I'm not sure if you do or not) then the conductivity would be much lower and it would be far easier to touch molten metal than you would expect based on solid metal. --Tango (talk) 01:28, 5 August 2009 (UTC)[reply]
76.21.37.87 here (with a new IP address); while I'm a petroleum chemist, not a physical chemist, I'm pretty sure that molten metal has the same delocalized electrons as solid metal, so there's no reason for thermal conductivity to be much lower -- if anything, it'll prob'ly be higher. Besides, with molten metal you also got convection adding to the heat transfer, so you got a lot more of the heat going from the metal to your hand! My advice is, DON'T TRY THIS AT HOME!!!98.234.126.251 (talk) 01:59, 5 August 2009 (UTC)[reply]
I read a book by a 19th century magician, perhaps Robert Houdin, who asserted that molten metal would roll of the hands as described here. At the time I suspected it was a ploy by him to get his rivals to burn their hands to smoking cinders so he would get all the bookings for magic shows. DO NOT ATTEMPT ANYTHING REMOTELY LIKE WHAT IS DESCRIBED. Edison (talk) 02:52, 5 August 2009 (UTC)[reply]
It was actually demonstrated on Time Warp (TV series) very recently (I think the episode title is "Hot Stuff and Cold Steel") - the guy gets his hand soaking wet - then calmly dunks it up to the wrist in molten lead - and pulls it back out again within about a second. I've heard of this being done by many people in many situations - it certainly works (although it's obviously dangerous). This is a very different thing than (say) a blob of molten metal landing on you (where the speed of it's arrival could cause it to penetrate the layer of water - or which might allow the steam to escape around the sides. The demonstration is very specific and precise details matter. The guy who did it said that it does hurt quite a bit - and he has what looks like a severe sun-tan on his skin afterwards. SteveBaker (talk) 14:17, 5 August 2009 (UTC)[reply]
I think it's a little funny that everyone feels so important to add "don't try this at home!!!" As though, you know, we all have molten iron (at 1300 degrees C) around the house :) 82.234.207.120 (talk) 09:04, 5 August 2009 (UTC)[reply]
Of course don't try it. But molten metal touches skin often by accident. (i) When soldering connections in electronics, excess solder may fall on the hand i.e. tin/lead at about 200 °C. (ii) When welding, molten steel may fall on an unprotected part of the body i.e. steel at 1400 °C or more. I can report that (i) hurts and leaves a burn. (ii) hasn't happened to me yet. Cuddlyable3 (talk) 09:26, 5 August 2009 (UTC)[reply]
To this day I do not understand how it happened, but once when I was around 15 I was near my uncle while he was welding a steel fence post together. I was supposed to paint over the welds after they cooled. However, after the third one a bit of molten steel flew nearly 15 feet and hit me on the arm. I felt like I had been shot (and yes, I know what that feels like as well, but thats a different story). Considering the molten steel flew a good distance, thus cooling quite a bit, I would say that unless the guys nerves where dead he probably wouldn't be able to touch the molten steel without at least showing some sign of pain.DrewSmithWhat I've done10:16, 5 August 2009 (UTC)[reply]
We can speculate on how it happened: molten metal dripped from the weld point onto a surface which was either wet, or painted. The heat of the metal vaporized the water or paint, which provided sufficient impetus to launch it in your direction. We'll not, owever interested, speculate on the shooting ;) --Tagishsimon(talk)13:03, 5 August 2009 (UTC)[reply]
There is no question that in general, molten metal will burn your skin. The particular trick that's being described here requires an extremely special set of circumstances for it to work. SteveBaker (talk) 14:17, 5 August 2009 (UTC)[reply]
As Steve noted, it's been a long time since I saw the piece (~quarter century). Any details I might recall are obviously susceptible to imagination, etc. My recollection is that the metal was lighter than that, more yellow-ish than orange. Steve also mentioned getting the hands wet before performing the stunt. Upon seeing that comment, I do recall the guy dipping his hands in a barrel of water. I had assumed or conflated the idea that he was dipping them in water afterwards, but it very well could have been beforehand; my memory is just not that clear on it. Is the TV show scene ringing any bells for anyone? If I could determine the guy's name, it might help me research it. And don't worry folks, I've taken both AAA batteries out of my Acme U-Smelt-It just to prevent curiosity from getting the better of me. Sheesh! :-P Matt Deres (talk) 16:38, 5 August 2009 (UTC)[reply]
It's not just the heat- but the density of the molten steel - assuming he could flick it without being burnt, it would (I imagine) be like flicking a concrete bollard - sorry for my unbelieviness.
Hmm. On the one hand, it seems that the stunt is much more likely to be done with lead than with iron or steel (assuming it wasn't a literal "trick"). On the other hand, I have a very low resolution video in my memory banks of a guy playing with yellowish orange molten metal, flicking small globs of it with the tips of his fingers. The more I consider it, the less likely that seems. Unfortunately that makes me all the more curious about the original stunt. Did I assume it was steel because it was shiny and metallic and then over the years alter my memory to make it appear as I now know molten steel to be like? Or was it someone actually playing with molten steel? Or was it an actual trick in the normal sense? Matt Deres (talk) 23:41, 5 August 2009 (UTC)[reply]
"My recollection is that the metal was lighter than that, more yellow-ish than orange." -- In that case, it could not have been molten steel: at the temperatures required to melt iron, the metal is hot enough to glow a brilliant white that hurts your eyes just to look at it. It could've been copper, or maybe manganese, but not iron. 98.234.126.251 (talk) 02:41, 6 August 2009 (UTC)[reply]
As someone said earlier (though its somehow been ignored) this is probably through the Leidenfrost effect. If you pour a drop of water on a really hot stove the bottom of the water drop will boil immediately and you will have some water vapor between the drop of water and the stove, insulating the water drop. If you put water on your hand and dip it in the metal it will insulate your hand temporarily. It's easy to demonstrate. Take a normal hot plate (the one's at my school worked fine and they're old) and heat it up for a while. Then pour a drop of water on it. If it's hot enough the water will skittle across the plate, like it's bouncing. It's really cool you should try it. 66.133.202.209 (talk) 04:01, 6 August 2009 (UTC)[reply]
Yes, obviously...but the question is: for how long? Evidently (from the dunking your hand into molten lead demonstrations) - it provides enough insulation to allow you to withstand 400 degC temperatures for a second or two with only slight damage (the guy said it felt like sunburn). The effect isn't going to last much longer than a second or two anyway because there isn't a continually replenished supply of water - and in any case, the steam itself is hot enough to do you some pretty severe damage. It's not impossible that this trick would work with steel or copper...but we only have actual evidence of it being done at much lower temperatures using lead. It might be (for example) that because molten steel isn't a dense as molten lead, that the steam layer would be at lower pressure in the case of steel - that would provide a larger volume of protection than in the case of lead - and that might be enough to allow you to survive the much higher temperatures. It's a tough thing to guesstimate - so I wouldn't completely rule out the possibility of doing the trick with molten steel - but my gut feel is that it wouldn't work. However, gut feels are not science. SteveBaker (talk) 13:24, 6 August 2009 (UTC)[reply]
Catching flu twice
Is it possible that someone suffering from the current swine flu pandemic strain could fall ill twice? Should one fall ill once, would the immunity gained from combatting it be sufficient to prevent them from falling ill a second time? --russ (talk) —Preceding undated comment added 00:25, 5 August 2009 (UTC).[reply]
It might be possible...or at least it might seem to be so. The problem is that identifying the flu strain is pretty tough - the symptoms of H1N1 are pretty similar to 'normal' flu strains - it's possible that the first dose someone got wasn't swine flu at all and they'd just been misdiagnosed - it's also possible that the virus is mutating and mixing with other flu strains - and that too could result in a "new" Swine flu which even people who recovered from the original strain might not have immunity to. So it would be risky to assume that you had immunity. On the other hand, it's believed that people over the age of 52 may have some degree of immunity left over from the 1958 Asian flu - so it's certainly possible that someone who had it once before is now immune. SteveBaker (talk) 00:53, 5 August 2009 (UTC)[reply]
There are lots of different strains of 'flu and catching one often gives partial immunity to others. There are strains of H1N1 that are endemic in human populations and have been since long before the recent "swine flu" came on the scene. If at some point in your life you have caught one of those strains (which isn't unlikely, especially for someone in their 50s or older than has had plenty of time to be exposed to various strains of flu), that could well mean you won't get as seriously ill if you now catch swine flu. You shouldn't be able to catch exactly the same strain twice and if you catch a slightly mutated strain you'll still have partial immunity. If you do get flu twice in quick succession, chances are it was a completely different strain. Now, all that aside, there is one important thing to remember - it's just the flu, the cure is bedrest, simple as that (unless you are in a vulnerable group). If in doubt, ask a doctor (or a call centre worker who did a 2 hour course on how to read a script and is now qualified to dispense prescription drugs to people that don't need them). --Tango (talk) 01:19, 5 August 2009 (UTC)[reply]
Help identify this aquatic creature
Help identify me!
We received this inquiry via e-mail. The image was donated to us, but part of the stipulation was that we help identify what it is. So please, go at it! It looks like a green sand dollar, only it has long legs (maybe like a sea star), photo was taken at Bali, at Nusa Dua beach. Thanks. Please send me a note on my talk page if you think you know the answer. -Andrew c[talk]04:46, 5 August 2009 (UTC)[reply]
We observe that this is empirically the case, and set up a mathematical framework based on that assumption. To date, everything which we define as a force tends to obey this mathematical rule, so there's no reason to assume it's invalid. On the deep subatomic scales, more precise definitions of force are necessary (usually a more complex set of physics, like Hamiltonian mechanics is used - where forces are defined as a gradient of a potential field. In the case of certain nuclear interactions, a potential field cannot be defined, so the simple linearly adding forces are probably not applicable to the deep sub-nuclear scale, where really strange quantum physics applies. Nimur (talk) 05:21, 5 August 2009 (UTC)[reply]
According to Thermal Conductivity, the thickness of a material has an influence on thermal conductivity; k. I modelled the equation in Excel using the formula:
k = Q/t * 1/A * x/T as stated in Thermal Conductivity. However, when everything else is constant, increasing the thickness (x) causes an increase in the thermal conductivity and a decrease in thermal resistivity (the reciprocal of k). This seems counter intuitive - I would have thought increasing the thickness of a particular material would cause a decrease in the thermal conductivity as the distance between the source of heat and the colder area would be greater.
And, of course, whether the thermal resistance (or conductance) of the material increases or decreases depends whether the direction of heat flow is alomg the direction of increased thickness or at right angles to it. Dbfirs01:47, 7 August 2009 (UTC)[reply]
Transverse Processes
Hi everyone I am a little confused about where transverse processes are located on a human vertebrae. The article on transverse processes states: (Hope its ok for me to copy and paste this) 'The transverse or costal processes of a vertebra, two in number, project one at either side from the point where the lamina joins the pedicle, between the superior and inferior articular processes.' Take a look at Grays picture of a cervical vertebrae in the article. I don't know if its just me but I think the Grays picture and the description don't match! The transverse processes don't project at either side from the point where the lamina joins the pedicle. The point where the lamina joins the pedicle is where the articular processes are. I would say that the transverse processes are posterior to the pedicle. This is just a subjective speculation. Can someone else offer an input? Thanks in advance to anyone who helps RichYPE (talk) 12:54, 5 August 2009 (UTC)[reply]
I agree that the description does not easily match a cervical vertebra but a cervical vertebra is significantly different from a thoracic vertebra where the description does seem to tally quite well. I guess it is not easy to describe transverse processes on vertebrae without qualifying which type of vertebra you are describing. 86.4.181.14 (talk) 13:34, 5 August 2009 (UTC)[reply]
Last's anatomy shows the cervical vertebrae with the "true" transverse processes projecting forwards (anteriorly) from the posterior end of the pedicle. The "anterior" part of the transverse process is described as the anterior/costal bar. The transverse processes of the cervical vertebrae are, if anything, anterior to the pedicles. However you shouldn't be too worked up about this. It's only important if you're going to become a spinal surgeon. Axl ¤ [Talk]17:55, 5 August 2009 (UTC)[reply]
PiCCO cardiac monitoring
I am looking for information for an essay regarding PiCCO cardiac monitoring.
I am also looking for the following information for the same essay:
(i) What does 'stroke volume variation" tell us? Especially a value of 15% , and a value of 9%?
(ii) normal valyues for extra vascular lung water. I have fgound articles about this but no 'normal' reference figures, or information about what a value of 7ml/kg or 5ml/kg would indicate.....
(iii) Intrathoracic blood volume (ITBV). Again, I have found articles about this but no 'normal' reference figures, or information about what a value of 820ml/m2 or900ml/m2 would indicate.....
I would be very grateful for any information that may help me. I would love to be able to complate this essay this week if at all possible.....
The sun seems to have an 11 year sunspot cycle. While we probably have not been able to directly observe sunspots on other stars it seems unlikely that our star would be unique to have sunspots. Would other stars also have an 11 year cycle? Would a red giant have sunspots? Googlemeister (talk) 14:16, 5 August 2009 (UTC)[reply]
Astronomers may have detected a brightness change in a star, but I doubt they have actually "observed" a sunspot by creating an image of a star showing a spot on the disc of the star, like we have long been able to make images of sunspots. "Detect" or "measure the effect of" might be more accurate than "observe." Edison (talk) 17:08, 5 August 2009 (UTC)[reply]
The above statement that starspots have been observed is idiomatic in observational astronomy—see the lede of that article for the general sense of what is considered "observation". If they meant to say that they directly formed a picture of the star with spots on it, like we do for the sun, they would have said that they "imaged" or "directly imaged" the starspots. See, for example, this press release concerning the first direct imaging of extrasolar planets. -- Coneslayer (talk) 17:21, 5 August 2009 (UTC)[reply]
what kind of metal does a knife have to be in order for it to be so sharp, that a gently falling piece paper with easily cut in two in the air? Or, does this metal even exist? --Reticuli88 (talk) 19:26, 5 August 2009 (UTC)[reply]
I would think that a lot of different metals could be sharpened to the point where they would do that, but I guess what you're asking is for one that would hold that edge for a useful period of time. For that I think you'd need as hard a steel as possible, which means a high carbon content and perhaps some more exotic things like nickel or chromium thrown in, especially if you don't want it to rust (see stainless steel). TastyCakes (talk) 19:33, 5 August 2009 (UTC)[reply]
I'm not sure it has too much to do with the sharpness of the knife anyway. When the paper hits the blade, there are perhaps three possibilities:
The paper is cut.
The paper stops moving and rests on the knife.
The paper spins off to one side and continues to fall.
Which of these happens depends on the forces involved. In the case (1), it takes a certain amount of energy for the bonds holding the paper together to be broken. If that energy is greater than the kinetic energy of the falling paper - then the paper will simply stop moving (2) or spin off to the side (3). I don't think it matters (beyond a certain point) how sharp the knife is. Here is a thought experiment for you. A GIGANTIC piece of paper that's 100 feet wide by 100 feet tall comes hurtling out of the sky, landing edge-on onto a 6" wide concrete beam. Obviously - the weight of the paper is huge - and it'll tear in half as it falls past our super-amazingly-blunt concrete "knife". On the other hand, if you dropped a sheet of copier paper onto a 6" concrete beam - there is no way it'll tear. So there is a relationship between the kinetic energy of the falling paper and the sharpness of the knife that is not easy to explain.
Now imagine a large blob of jello falling onto a knife blade - you can imagine it hitting the blade and the blade penetrating a couple of inches - then stopping with the jello balanced on the blade with a couple of inches deep cut on the underside. What happens in that thought-experiment is that the Jello is initially moving quite fast - it has lots of kinetic energy - and that's enough for the knife to start breaking the bonds and cutting into it. However, the act of doing that cutting absorbs some of the kinetic energy - so the Jello slows down a bit. Now it has insufficient kinetic energy for the knife to cut any deeper and everything stops.
With the paper, we could imagine a small cut occurring just at the edge of the paper - then it rolling to one side and falling off...that's when there is just enough kinetic energy to get the cut started - but not enough to go all the way through the sheet.
If you did the experiment in a vacuum - the paper could fall much faster - and I'd expect it to have enough kinetic energy to let the knife cut all the way through it. But the terminal velocity of a sheet of paper is just pathetically low - so there is no way for it to fall fast enough to impart enough energy to make a decent cut.
Well, if the knife is sharp enough, you only ever need to break one bond at a time - this effect is why a knife works better at cutting than a brick. --Stephan Schulz (talk) 21:06, 5 August 2009 (UTC)[reply]
That's the key thing. The energy involved is the same regardless of the sharpness of the blade, the difference is whether that energy goes into breaking bonds or stopping/deflecting the paper. A standard way to test the sharpness of a blade is to try and cut paper with it. A sharp blade should be able to cut paper by just sliding the blade over the edge of the paper with minimal weight behind it. If you do that with a blunt knife the paper just bends. It has everything to do with the sharpness of the blade and very little to do with energy (there is a minimum amount of energy required to cut the paper, but that is very small indeed). --Tango (talk) 03:10, 6 August 2009 (UTC)[reply]
But that's the problem. That "minimal amount of energy" is still larger than a normal-sized sheet of paper falling at it's terminal velocity. Hence, you can't drop a sheet of paper onto a knife and have it be cut in two because there isn't enough kinetic energy present to break enough bonds to make a noticable depth of cut. But no matter how sharp the knife - the energy required to break bonds is the same - and each bond that's broken consumes more of that kinetic energy. It slows the paper down to the point where no more bonds can be broken - even with a one-atom-thick blade. For a large, fast-moving sheet of paper to move past a brick (to pick a canonically blunt object) - only TWO bonds at a time have to be broken - one on either side of the brick...and even those won't have to be broken simultaneously. I really don't think it much matters about the knife. As for your "knife sharpness test" - it's completely bogus. I can poke an unsharpened pencil through a sheet of paper - and using enough force, make a jagged tear through it. It's simply a matter of the amount of force and energy in the system. I don't think a sheet of 8"x11" paper, falling at it's terminal velocity has anything like enough energy to break the bonds of more than maybe a quarter inch length of cut. That being the case, it doesn't matter a damn how sharp the knife is. On the other hand - if the paper has enough kinetic energy (eg if you dropped it from enough height in a vacuum) - then a brick could cut it in half almost as easily as a super-sharp knife. SteveBaker (talk) 13:16, 6 August 2009 (UTC)[reply]
The test is not bogus, it's a standard test that I have used plenty of times. As I said, you apply minimal force, you just stroke the blade along the edge of the paper. I think we've interpreting the OP's question differently, though - I'm imagining the blade moving and slicing the paper as it falls like the proverbial samurai slicing a handkerchief in an intimidating manner. --Tango (talk) 22:39, 6 August 2009 (UTC)[reply]
There is no answer to this question, without knowing particular details. How large is the paper? How stiff is the paper? What is its shear strength? Is there an atmosphere through which it falls (as pointed out by SteveBaker)? At what angle does it encounter the knife? Is it's weight equally distributed on either side of the blade? And only finally, how sharp is the knife? Even after knowing all these details it may take empirical tests, because the calculations are probably beyond those applicable to already known experiences. It is possible to stack the odds in favor of achieving a nice sliced in half rectangle of paper. That I think may be possible. Strength of materials seems to be an article that may have applicability here. Bus stop (talk) 15:04, 7 August 2009 (UTC)[reply]
Gravity and Mass
I understand that objects of differing mass will accelerate toward the ground at the same velocity, i.e. a ping pong ball and a metal ball bearing (excluding aerodynamics)
This can be shown in NASA's vimit comet, when the aeroplane will drop at the same rate as its passengers giving the illusion of zero gravity.
What I can't understand is why planets of different mass have different gravitational pulls. I.e. Jupiter would pull us toward it with much greater force than Earth due to it's greater mass!
Does this mean that there is a correlation between mass and gravity? Is it simply the case that the difference between the ping pong ball and the heavier metal ball bearing is insignificant in comparison to the mass of the planet earth.
Does the origin of the gravitational force come from within the particles or the forces that hold them together? Can it be associated with the possitive and negative charge?
From Stuart McPhee86.174.230.38 (talk) 22:41, 5 August 2009 (UTC)[reply]
This is an easy mistake to make. The thing to get straight is this: a ping pong ball heads towards earth at an acceleration of roughly 9.8 meters per second per second. This is not relative (at least in Newtonian mechanics); it is indisputable fact that it is the ping pong ball that is accelerating towards the earth, not the earth towards the ping pong ball. The earth is also accelerating towards the ping pong ball, but it is doing so by a much tinier amount, so we only perceive the acceleration of the ping pong ball.
However, suppose we increase the mass of the ping pong ball. Let's replace it with a small planet (but we still want to keep it at the same distance from the center of the earth). The new planet's acceleration towards the earth is still about 9.8 m/s2, but the earth's acceleration towards the new planet has increased significantly, to the point that we can actually perceive and measure it.
The earth's acceleration towards an object based on that object's gravity is directly proportional to its mass. For example, if the new "planet" has a mass equal to one tenth of that of earth, then earth will accelerate towards the new planet at a rate of .98 m/s2 (one tenth of the new planet's acceleration towards earth).
Similarly, if earth's mass were increased, then the acceleration at which objects fall towards the earth would also increase proportionately. However, the earth's still imperceptible accelerations toward falling objects would remain unchanged (assuming the same distances from the centers of mass are unchanged), since its accelerations toward ping pong balls depends only on the mass of the ping pong ball and the distance between their centers of mass.
You probably don't have the background to understand the equations involved, but here they are for reference. That is, those are the equations Newton formulated over 300 years ago; they have been replaced nowadays by general relativity, which is significantly more complicated. --COVIZAPIBETEFOKY (talk) 23:14, 5 August 2009 (UTC)[reply]
To bring that back to your example about Jupiter, the thing to realize is this: Jupiter's acceleration towards earth is exactly the same as that of a hammer if we replace Jupiter with that hammer. It is earth's acceleration towards Jupiter or the hammer that changes in these two scenarios. --COVIZAPIBETEFOKY (talk) 23:28, 5 August 2009 (UTC)[reply]
the above answer is pure semantics. The simple answer is: everything attracts everything. (The exception is things that have no mass). And you guess the key already; you say: "Does this mean that there is a correlation between mass and gravity?" YES. Gravity is proportional to mass and inversely proportional to distance. Just remember: everything attracts everything (but the farther away from each other the things, the weaker the attraction). Then you'll be all set. 82.234.207.120 (talk) 01:26, 6 August 2009 (UTC)[reply]
I'm not sure how you came to the conclusion that my answer was "pure semantics", but maybe I should clarify the key point in my answer, since I did kind of ramble a bit. Your answer doesn't really seem to address the main question being asked, which was: why should Jupiter have a stronger pull on the earth than earth has on everything else? The error in this 86.174.230.38's train of thought comes from thinking about the acceleration between two bodies, rather than the acceleration of one body due to another. The former is a sum of two instances of the latter (ie. the ping pong ball accelerating due to the earth's gravitational pull and the earth accelerating due to the ping pong ball's gravitational pull), and it is important to distinguish between those two separate accelerations.
Failure to make that distinction can lead to the conclusion that the earth-ping pong ball system should behave identically to the earth-Jupiter system: just increase the mass of the ping pong ball to that of Jupter. The acceleration "between the two bodies" (remember, this is the wrong way to think about it) remains unchanged. Clearly, the earth-ping pong ball system should behave identically to the earth-Jupiter system, at least as far as gravity is concerned. The problem here is that we didn't make the important distinction between the acceleration of one body and that of the other.
The key detail is that mass appears in two places in the relevant calculations. It appears in the formula for gravitational force, and it appears in F=ma. The reasons hammers and feathers fall at the same rate is because that mass cancels out. However, only the mass of the object we are measuring the acceleration of cancels out, the mass of the other object doesn't cancel out (since it doesn't appear in F=ma, since that is only concerned with the object in question and the force, not the source of that force) so it still has an effect. (That gravitational mass and inertial mass are equal is far from trivial and has been the subject of much discussion.) --Tango (talk) 02:57, 6 August 2009 (UTC)[reply]
August 6
can ethers act like alcohols in acid-catalyzed addition?
My lecturer never really seemed to cover this (or I must have forgotten) and a quick google search isn't helping. Basically I'm wondering since ethers also have lone pairs to donate, whether they can interact with carbocations ...
So let's say we have an (R2)+ carbocation after the addition of H+ to a C=C alkene bond, and a R1-O-R1 ether, and say R1 was a shorter alkyl chain than R2. Shouldn't a R2-(O+)-(R1)_2 intermediate develop, with the resulting ejection of one of the alkyl groups? I'm basically wondering if you can exchange alkyl groups in an ether this way. Shouldn't the lone pairs on an ether oxygen be even more reactive than an HOH or ROH, since the ether oxygen will have more electron density. I know alkyl groups aren't that labile, so would that just make it kinetically unfavourable to form the ether cation?
I assume one of the difficulties is that acids don't like to dissolve into ethers -- and since the ether doesn't have an H group, it can't "return" the H+, so H+ is getting consumed....and I suppose nature would prefer to have H+ ions than R+ ions? But to address the first problem, we could choose a mixture of methylene chloride and ether to try to solvate the acid, and choose a strong acid whose conjugate base makes a poor nucleophile... (magic acid?). John Riemann Soong (talk) 02:15, 6 August 2009 (UTC)[reply]
Alkyl groups are not great leaving groups in these sorts of reactions. And the lone pairs are LESS reactive on the ether, because the long alkyl chain acts as a "soft" electron sink, basically giving the electrons a place to disipate to, making them less concentrated on the oxygen. This is in contrast to the "hard" hydrogen, which cannot absorb extra electron density. These two effects (poor leaving group + less electron density around oxygen) probably make the reaction unlikely to happen to a great extent. --Jayron3202:30, 6 August 2009 (UTC)[reply]
That's not quite right - the lone pairs on ethers are less reactive maybe due to steric effect - but they have a greater ability to stabilise a cation compare to water when R=alkyl,benzyl, ethenyl etc..83.100.250.79 (talk) 13:04, 6 August 2009 (UTC)[reply]
Well yes, but carbocations aren't too great either -- would that in fact prevent the H+ from attacking the alkene? (As in, the intermediate will convert back to the alkene + H+ before an ether would attach?)
Why is that ether oxygen lone pairs are less reactive? Because alcohol oxygens are still reactive (the reaction proceeds merrily), and I note the pKa of an alcohol is higher than that of water ... and the pKa of a tert alcohol tends to be highest. My interpretation of this is that the electron-donating effects of the alkyl chain were greater than any electron-withdrawing effects -- that is, the alkyl chain destablised the lone pair conjugate base. John Riemann Soong (talk) 03:16, 6 August 2009 (UTC)[reply]
Carbocation formation is different cause there ain't nothing being actually ejected from the molecule in this case (i.e. no C-C or C-O bonds being broken, as they would be in your scenario). It's the strength of the bonds to be broken that accounts for the reaction not happening. FWiW 98.234.126.251 (talk) 03:25, 6 August 2009 (UTC)[reply]
So what would happen after the acid addition step? Would we have a "stabilised" carbocation solvated in solution? (Assuming the acid's conjugate base is a very poor nucleophile, e.g. SbF6-.) After we evaporate the ether and the methylene chloride off, would I get a strange crystalline salt of alkyl carbocations and SbF6- anions? (Granted, it would probably be hygroscopic and quite reactive to water, but it would be interesting....) John Riemann Soong (talk) 05:03, 6 August 2009 (UTC)[reply]
I think what will really happen is the anions would add to the carbocations forming a neutral covalent compound. Or if not, then the carbocations will instantly react with any moisture available (even the moisture in the air, no matter how slight) and form a sec / tert alcohol and regenerate the acid (and prob'ly give off a whole bunch of noxious vapors and maybe splatter the reaction mixture all over the place cause this final step is very exothermic). FWiW 98.234.126.251 (talk) 05:50, 6 August 2009 (UTC)[reply]
Mmmm, but diborane is extremely reactive with water as well, and yet we can still observe it meaningfully without too much hassle. And one could just view it in dehumidified air... John Riemann Soong (talk) 06:27, 6 August 2009 (UTC)[reply]
You said you formed the carbocation by protonation of an alkene. That's essentially an equilibrium process--loss of H+ adjacent to a carbocation forms an alkene as the standard E1 reaction mechanism. On the other hand, reaction of carbocation(-like species) and ethers is known, and leads to alkylation of the ether as you suggest (an O+ compound). These compounds can be isolated in some cases, for example, triethyloxonium tetrafluoroborate. DMacks (talk) 05:58, 6 August 2009 (UTC)[reply]
It attatchs at the ether oxygen, and the resultant compound may or may not be stable, depending on what exactly it is, and the temperature, and other factors.83.100.250.79 (talk) 13:45, 6 August 2009 (UTC)[reply]
Well, I see several scenarios: the ether is alkylated and doesn't eject any of the alkyl groups, and forms a stable cation, assuming again that the conjugate base of the acid used is a poor nucleophile; an alkyl group is eventually ejected (would the ether oxygen prefer to retain the longer-chain, and if so, could we exchange alkyl groups on an ether this way?); though much less labile than H+, the alkyl groups act somewhat like H+, being constantly exchanged; the ether doesn't react, leaving just the carbocation (the strange salt described above); the ether doesn't react and the carbocation isn't stabilised enough to keep the H+; so the equilibrium favours the reactants and most of the alkene is left unreacted. John Riemann Soong (talk) 06:27, 6 August 2009 (UTC)[reply]
Assuming you have produced a carbocation, it will and can react with an ether - but you need to consider steric effects, which will tend to hinder their production in general.
Compounds R1R2R3O+ are called oxonium ions. eg the triethyl oxonium ion mentioned above, which can actually be bought as the tetrafluoroborate in solution (needs to be kept cold)
Yes you can/could exchange alkyl groups this way. As you expect the reaction will tend to favour the most stable carbocation being ejected (all other things being equal)
Wouldn't the protonated ether then protonate the alkene? Or would the H+ prefer to stick with the oxygen? I mean H3O+ protonates alkenes in the classic acid addition of water setup... John Riemann Soong (talk) 13:17, 6 August 2009 (UTC)[reply]
Yes, I was assuming you wanted pure solutions of carbocation - the reaction will still work.
By the way did you know that one of the common reactions of ethers is acid catalysed decomposition - eg
How important is the consumption of H+? I guess it's not acid-catalysed addition anymore, is it, since H+ is being consumed? What determines whether the oxonium ion is stable or not? And even if alkyl exchange occurs, we'll still get an interesting crystalline species once we evaporate off the solvents... John Riemann Soong (talk) 13:15, 6 August 2009 (UTC)[reply]
The same things that stabilise carbocations, stabilise oxonium ions.
The concentration of H+ (from which the concentration of C+ derives via H+ addition to alkenes) will affect the rate of reaction. But it's not catalytic if oxonium cations are the product - since H+ is used up.
The oxonium cation will be the product if the ether oxygen is the strongest base in the system - most oxonium cations will be stable at low enough temperatures - at high enough temperatures - decomposition occurs.
It's probably worth noting that ethers can interact (form bonds) with a wide variety of lewis acids such as BF3to form Diethyl ether boron trifluoride adduct (aka Boron trifluoride etherate), and in general can act as ligands (as lone pair donors) or lewis bases with a wide variety of compounds (not just carbocations, and H+) 83.100.250.79 (talk) 14:53, 6 August 2009 (UTC)[reply]
Interesting -- normally I assume high temperature favours carbocation formation .... but I guess this principle applies only as long as we want the carbocation to be an intermediate? I assume this is the same for oxonium too. Re: oxonium stabilisation: I suppose we can't do anything about trying out allylic-ish oxonium cations, since the pi bonds are going to be attacked. And if oxonium stability is analogous to carbocation stability, I guess actually alkylated ethers are more stable than H3O+?
This makes me very interested now -- well, if tri-alkyl oxonium cations are more stable than say, a protonated alcohol or a protonated ether, why don't most textbooks mention ethers as something you could play around with during acid addition? I assume the ether would be a very good competitor for the cation compared to other nucleophiles. Is the fact that H+ might not be returned, potentially making a reaction scheme infeasible?
Also, so many different possibilities -- I'm trying to work them out. I guess a useful reaction might be mixing a straight-chain alkene, an ether with tertiary alkyl groups and the strong acid with a poor nucleophile conjugate base; the ether solvent binds to the carbocation and expels one tertiary alkyl group. So if we run the reaction at high enough temperatures, this favours both the decomposition of oxonium and the alkyl group into a new ether and a new alkene...but then it occurs that some of the ether molecules might react twice with the protonated alkene -- I guess it depends on just how much alkene is there compared to ether, isn't it? (And what would be a general principle of separating two different ethers? I assume that if tert groups are being ejected in favour of primary groups, the boiling point of our products will be higher and we can evaporate off the original solvent -- but that's one case.)
To me, I'm seeing this as a game of which type of cation is more stable -- protonated ether, tri-alkyl oxonium, or the alkyl carbocation. What if we had straight chain alkenes and ethers? I assume in general the longer-chain primary carbocation would be more stable? And now I realise that tertiary carbocations are more likely to be ejected, but primary carbocations are more likely to convert back into alkenes. Aaaahh, so many different considerations! John Riemann Soong (talk) 11:43, 7 August 2009 (UTC)[reply]
Why is the Mandelbrot Set so complicated?
Infinitely complicated in a way that is awesome, distressing, beautiful, fearful, samey, completely obsessed and obsessive, suggestive of an infinitely talented but hermetically sealed divine lunatic of a geometer. Pray answer me in such a way as this. Suppose that I had asked: “Master, why is this river so quiet and this other river so wild and noisy.” And the Master replied: “Grasshopper, the first river has little water and flows over land only slightly tilted so it runs slowly and quietly, but this other river runs over steep ground with many rocks and crevasses, and there is much water so it is churned up as it runs, and thus the noise and the spectacle.” You see, Grasshopper can understand that. And I am such a one as that Grasshopper. I am Termite. And I would appreciate you answering me in just such a way as the Master answered Grasshopper. Why is the Mandelbrot Set so complex, and why is a triangle so simple? Myles325a (talk) 05:50, 6 August 2009 (UTC)[reply]
I don't think the mathematicians are going to help you. You may get an answer there - but I'd bet good money that you'd be unable to understand it. This is a case of observer bias. The fact is that if the Mandelbrot set wasn't all of the things you describe, nobody would have given it a second glance. There are an infinite number of mathematical objects - and only the interesting ones are ever investigated or written about. The Mandelbrot set (and it's close relatives) is well known BECAUSE it's complicated. The triangle is known because it's useful. Anything significantly simpler than the Mandelbrot set is simply too boring to have made it into your stream of thought. There are many other things that are as complex as the Mandelbrot set (a Julia set, a Sierpinski sponge, or a Koch snowflake for example) - but somehow we don't see them as beautiful - so most people never hear about them. Check out List of fractals by Hausdorff dimension for lots more examples. SteveBaker (talk) 13:04, 6 August 2009 (UTC)[reply]
Triangles are one of the abstractions of Euclidean geometry that Buckminster Fuller pointed out cannot exist[21]. The Mandelbrot set reveals the form in 2-D of an iterative oscillation that actually exists, in the same way that prime numbers actually exist. Triangles are useful for designing things and bracing them, while the other two are more intriguing than useful. No one promised that reality would not be complicated. Cuddlyable3 (talk) 20:56, 6 August 2009 (UTC)[reply]
Huh? Triangles and prime numbers are both ideal objects; I don't see any basis for saying one really exists and not the other. Of course triangles are completed infinite totalities, and it's possible that finite ideal objects exist but infinite ones don't. But empirically this doesn't seem to be a very productive assumption to make. --Trovatore (talk) 21:01, 6 August 2009 (UTC)[reply]
I consider the Julia set to be more beautiful than the Mandelbrot set. I have some home-gener:ated prints produced on a BBC Archimedes computer many years ago. Most of the set is not particularly inspiring, but I spent many hours looking for the beautiful bits. I think the same is true to some extent of Mandelbrot: we are shown just the attractive bits. Dbfirs01:59, 7 August 2009 (UTC)[reply]
Yes, do ask at the mathematics desk. But the Mandelbrot set is complicated because of the phenomenon of sensitive dependence on initial conditions (SDIC). If you're really a grasshopper, then among your insect relations you have probably encountered a few butterflies, so you can understand the butterfly effect, another example of SDIC. A triangle is simple because moving from one point to another in one operation doesn't have SDIC. If you start from a slightly different place, you end at a slightly different place, and there you are. The SDIC in the Mandelbrot set comes from the repeated iteration of the squaring function, like in the butterfly effect it comes from evolving the chaotic system for a long period of time. Points in the Mandelbrot set can behave much differently from very nearby points under the iteration, because of the SDIC. The exact pattern of differences is the complexity that you see. 70.90.174.101 (talk) 07:09, 7 August 2009 (UTC)[reply]
Biology has its own version of such sets, in even more abstract form. Deuterostome gestation arguably follows a fractal pattern (radial cleavage) -- one cell's signals ends up determining the positions of other new cells, but the conditions for such patterns must all be stored within a single zygote cell. Mysterious, because there are no such things as "arm genes" or "elephant trunk genes" -- just a whole lot of signalling genes cooperating together to encourage division in the right direction and arrest division in the wrong direction (over and over). What's especially fascinating is how did such a gestation pattern evolve? Some dynamic patterns you might be interested in might include Conway's Game of Life. John Riemann Soong (talk) 08:35, 7 August 2009 (UTC)[reply]
amper-current and relativity
hello, this is a passage from article and i can't understand it,the context is that scientists didn't want to deal with theories that they couldn't measure.
"One can see an analogous sort of indeterminateness at the basis of A. Einstein's (1952, p. 37) complaint against pre-relativistic mechanics and electrodynamics. His criticism was that they lead "to asymmetries which do not appear to be inherent in the phenomena." Whether one assigns an absolute velocity of zero to a conductor and a non-zero velocity to a magnet, or vice versa, the measurable result (current) is the same. Hence, the absolute velocity is indeterminate: "The phenomena . . . possess no properties corresponding to the idea of absolute rest," as Einstein put it. Interpreted a la Glymour, the point is not the naive one that absolute velocity is not measurable-that would be alright-but that it cannot even be computed from measured quantities via any seriously proposed (let alone well-tested) hypotheses.
why does Einstein says there is no symmetry? why it is not the same to rotate object around another which stand still and then swap the rolls? why can't we measure current according to the text? if so, what is ammeter??
"why does Einstein says there is no symmetry?"
He means that Maxwell's equations are not invariant under the Galilean transformation. In simple terms : In Einsteins time, people thought they could transform from a "stationary" frame of reference to a moving frame of reference simply by adding velocities. The equations describing electromagnetism change when you do this. In reality, the observed phenomena stay the same for both observers. It is this observation that eventually led to the discovery of the Lorentz transformation, which does have the required symmetry : the Maxwell equations are invariant under the Lorentz transformation.
http://en.wikipedia.org/wiki/Maxwell%27s_equations
I'm not really too sure what you're asking, but to give you I think a suitable analogy, take the Earth-Sun system. If they were stationary relative to one-another, the Earth would be sucked into the Sun. And there is a suitable rotating reference frame in which they are stationary relative to one another, but even in this frame the Earth is not sucked into the Sun. This is an asymmetry; the laws of physics do depend on your frame of reference. Incidentally, even in Special Relativity, acceleration is still absolute, it's only in General relativity that there are no inertial frames. I'm not too sure if I've addressed your clearly, so please post again if I haven't.--Leon (talk) 10:51, 6 August 2009 (UTC)[reply]
There was an asymmetry in the physical theories of the time that did not correspond to any asymmetry in the real world (the phenomenon). We can measure current, but the theory at the time seemed to do a bad job of explaining why, and Einstein was criticizing it for that.
I would advise against reading this article, whatever it is, because it looks like bad philosophy. It seems to imply that "absolute velocity is not measurable" is different from "absolute velocity [...] cannot [...] be computed from measured quantities"—which is nonsense and certainly not something that Einstein believed—and it implies that "absolute velocity is not measurable" is an obviously true statement a priori; see Section 16–1 of the Feynman Lectures on Physics for a response to that. -- BenRG (talk) 11:17, 6 August 2009 (UTC)[reply]
thank you all. i can't understand why when you swaping the objects the result shuold be a-symmetric. why the frame of reference imoprtant when i (the observer) don't move and one time i take the counducter rotate it around the magent and the other time, the smae places but the magnet is rotating. each object was one time static and the second time mobile - soo it should'nt change the current result. it is the way you look at that, one can say both pbjects moving but one is faster (the frame reference is earth). if we will think about a person seeing a child throw an apple on a moving train (a magnet make electron move) is the equivalent for the child to see the man outside throwing an apple. [not connected to the fact the apple will move slower for the an outside) - i really hope i didn't make it much to confusing
the speed of light is absolut, so there is an absolute speed or not?
about the article itself is michael r. garder - realism and instrumentalism in 19th century atomism
if i may,the lorentz transformation article is complicated, is there intuative explantion?
Einstein was pointing out a problem : in reality, the result is symmetric. Science in Einstein's time suggested it should be asymmetric.
The Maxwell equations allow you to calculate the speed of light without specifying an observer who measures this speed. In classical mechanics on the other hand, all calculated speeds are relative to a (usually implicitly specified) observer : if you calculate the speed of an apple that falls from a tree, your result will be relative to an observer who saw the apple at rest in the tree.
Thus, consider a light in a train with speed v. According to the Maxwell equations, an observer in the station sees the light moving with a speed c. According to gallilean relativity, an observer in the train will see the light moving with a speed c-v, but according to the Maxwell equations, he will also see it moving with a speed c. This is a problem! In reality, both observers will observe the light moving with speed c, but that is not what Einstein's contemporaries thought.
Einstein (and Lorentz) discovered that you must not only transform velocities, but also lengths and durations, when calculating what a moving observer sees. This is known as the Lorentz transform.
The above example involves the speed of light. Light is an electromagnetic phenomenon, and comparable examples can be found for other electromagnetic phenomena, including moving magnets.
---
If you read the whole paragraph (the first one) in Einstein's paper it is clear what he meant by the asymmetries. The problem is that theory of the day gave a different physical explanation for what happened when you had a moving magnet and a stationary coil, and when you had a moving coil and a stationary magnet (this is a problem relating to a unipolar dynamo, if one is interested). Einstein says that this is silly and means something is fundamentally wrong: you can't distinguish between the two if you don't believe in absolute rest (which he doesn't). It's an introduction to a general attack on the theoretical framework of the day (a clever one, but not necessarily a convincing one in its time, more of a logical attack than an empirical attack), and gives some indication of Einstein's characteristic style in attacking problems (Machian, axiomatic, concerned with basic concepts and definitions, not specific experimental results). Asymmetries are a huge deal to Einstein—he says if you can't possibly distinguish between two different states, then you shouldn't have a separate set of physical explanations (or physics) for them. It's a philosophical critique, though one that led him to some rather fruitful revisions of the theories. The specific criticism is something of a throwaway introduction—here's one of many things that indicate something is wrong, so let me try and rework this from the ground up without assuming the existence of concepts (e.g. absolute rest) that we can't measure. --98.217.14.211 (talk) 16:39, 6 August 2009 (UTC)[reply]
thank you very much, that is very intersting, why the physicists at that time thought those are completly different phenomena? can you give me a link please to those different explanations? —Preceding unsigned comment added by מני111 (talk • contribs) 22:38, 6 August 2009 (UTC)[reply]
Click the link—he discusses it. It isn't very interesting in and of itself. I don't remember the details of it, but it's basically that in both cases you get an electric current. One explanation was used to say that this came from some sort of interaction with an electric field. The other said there was an electromotive force involved. These are two rather different types of answers and Einstein said, "you can't have both of them." this (from "Electric Dynamos" on) gives a good discussion of the technical aspects of what Einstein was talking about. --98.217.14.211 (talk) 14:12, 7 August 2009 (UTC)[reply]
An article on BBC News Science page says there is methane being produced on Mars it says this could be geological in origin or biological, Geological would be Active volcano not heard of this before on Mars 1.is there known active Volcanoes? or by a process of Serpentinisation - which is a process involving water. 2.is water in suffcient quantity to produce this effect would it need to be free flowing or in a solid form Ice maybe? and last but not least Biological activity which i assume they mean life in some form? —Preceding unsigned comment added by Chromagnum (talk • contribs) 07:30, 6 August 2009 (UTC)[reply]
How can I connect my Ipod to my Sony (maybe Panasonic) Hi Fi? It has a usb port on the front, but when I put my Ipod, or a flsh drive in there it says Unsupport In fact what can I plug into this port to make it work. I have put about 3 months worth of music on my Ipod, but some times I want to listen to music through proper speakers, eg a party. Any help in this would be greatly appreciated. Thank you. ~~Zionist —Preceding unsigned comment added by 62.172.58.82 (talk) 06:58, 6 August 2009 (UTC)[reply]
I don't know about your specific hi-fi, but I would connect the two via audio cable. On the back of your Hi-fi there is likely an auxilliary input (probably an RCA connector, but check). You can buy a cable that plugs into the headphone jack on your iPod at one end and into the auxilliary input on your Hifi on the other. That way, your Hifi is acting as speakers for your iPod. — QuantumEleven08:39, 6 August 2009 (UTC)[reply]
Your Ipod doesn't support the USB mass storage device class (MSC) interface the way that a pen drive or some other mp3 players do. You have to get an ipod docking adapter that connects to the docking socket on the bottom of the ipod, or else use an analog audio cable as Dismas suggested. There are also lots of boom boxes with dedicated ipod ports these days. 70.90.174.101 (talk) 07:18, 7 August 2009 (UTC)[reply]
Another option is to buy a transmitter for your iPod which will transmit what your iPod is playing over an FM radio frequency, and tune your hi-fi to this. These are predominantly used in cars without iPod inputs to the stereo, but I have used mine with my home stereo and it works fine. --jjron (talk) 08:34, 7 August 2009 (UTC)[reply]
But the solution suggested by QuantumEleven above is by far the simplest and cheapest. The connector (with a 3.5 mm stereo jack at one end and two phono plugs at the other end) costs only a few dollars/pounds, and most amplifier phono inputs are happy with an earphone output, though you can add an impedance matching circuit if you are concerned about highest quality of sound. The next cheapest is the tape adaptor (a mock cassette tape at one end and a 3.5 mm stereo jack at the other end). Dbfirs19:33, 7 August 2009 (UTC)[reply]
Fast poison
I've recently read a novel (Joe_Abercrombie-Best Served Cold) in which one of the characters poisons a number of his victims via fast acting poisons. Specifically;
Using a needle/pin dipped in a vial of poison to prick his victim.
Brushing a solution of poison onto books/metal and allowing the victim to touch the poison.
My questions;
Assuming that the pin prick allows direct transfer to the blood, do such poisons exist that work fast at such a small dosage (the amount that would be left after the pin is pushed through the skin)?
Do fast acting poisons exist that could be transmitted by touch?
Lastly, how many of these would be available to medieval level technology?
There was that case of Georgi Markov - a Bulgarian dissident working for the BBC who was killed in London by a soviet agent using a poison-tipped umbrella. I know that sounds like the plot of a James Bond movie...but it's true. The poison use in that case was Ricin. The lethal dose is 500 micrograms...which could certainly be administered with a pinprick. The stuff is found in the beans of the Castor Oil plant - it's easy to extract and separate - so I presume it would have been possible to make it in medieval times. (Oh - but that's no good - you wanted "Fast acting". Markov died 3 days later.) SteveBaker (talk) 12:36, 6 August 2009 (UTC)[reply]
These are are excellent examples of injected poisons. As for touch, the only thing I can think of off the top of my head is some variation of organophosphatenerve agent, like sarin or VX, which will soak right through the skin. Most of the really nasty ones, though, are also pretty volatile since they were designed to be employed as gas weapons. – ClockworkSoul17:55, 6 August 2009 (UTC)[reply]
This fits number 1, but not so much for 2 and 3. From our article on Suicide pill, The Central Intelligence Agency began experimenting with saxitoxin, an extremely powerful neurotoxin during the 1950s. It was rumored that they issued a tiny, saxitoxin-impregnated needle (hidden inside a fake silver dollar) to each American U-2 pilot, with instructions to stab themselves with it if shot down over the USSR.. Vespine (talk) 23:11, 6 August 2009 (UTC)[reply]
Maaan -- from the article it sounds like that's one of those things where you're completely conscious, but can't breathe. I wouldn't do it. I'd take my chances with the Reds. --Trovatore (talk) 23:27, 6 August 2009 (UTC)[reply]
A pin dipped in cyanide would work pretty quick too. As for medieval stuff -- well, Black widow venom might be a good candidate (better even than snake venom, which is not that fast-acting at any rate). FWiW 98.234.126.251 (talk) 23:17, 6 August 2009 (UTC)[reply]
I have found the figure 4.184×1017 J for a potential nuclear weapon yield, and 17500 Joules to fry an egg. I can't, however, find or understand any figures on the dissipation of energy per unit of distance from ground zero. Does anyone have these figures? I want to work out how far from a nuclear blast I need to be to fry an egg, my cooker is broken. SGGHping!11:52, 6 August 2009 (UTC)[reply]
Not sure, but you need to make sure you can actually touch it afterward. :-) I'd suggest using the rule of thumb Johnny Carson suggested once for turkeys, and extrapolate down for eggs. He noted that if you heat your oven to 10,000 degrees, you can cook your turkey in 2 seconds - but you won't be able to touch it for six years. :-)Somebody or his brother (talk) 12:05, 6 August 2009 (UTC)[reply]
That would be: 4x1017J, not 4.184x1017J...anyway: The big question here is how the energy dissipates over distance - and that's a real tough one because we don't know what's between you and the bomb. We also don't know what percentage of that energy is heat, radiation, the pressure wave, etc. But we also don't know what percentage of the energy impinging on the surface of the egg will be absorbed by it and turned into heat...an egg isn't like a 3" thick slab of solid lead...it doesn't stop all of the energy passing through it. Furthermore, it's very likely that if you throw enough radiant energy at an egg to cook it - but you do it all within a couple of milliseconds - then it's pretty safe to assume that a lot of that energy would actually go into splattering the egg all over surrounding landscape rather than cooking it. In short, I think the error bars on this thought experiment are so huge that the answer could be incorrect by several orders of magnitude.
In other words, we might calculate the answer at 1 mile - when in fact it's something like 100 yards or perhaps 10 miles. Bottom line - we don't know. SteveBaker (talk) 12:31, 6 August 2009 (UTC)[reply]
If I recall correctly, there are places in the world where you can cook an egg just by dropping it on a rock. Probably somewhere with a lot of geothermal energy. Iceland? Jeremy Clarkson did it. Vimescarrot (talk) 18:23, 6 August 2009 (UTC)[reply]
From accounts of the effects on people and structures at the Hiroshima and Nagasaki bombings, along with U.S. tests, it should be possible to determine what distance from a blast of what magnitude would produce the desired effect. If your skillet is too close, the blast effect would scramble the egg and send it flying. But farther from ground zero the thermal effects might provide enough heat energy to do the trick, without excessive radiation or blast. Edison (talk) 18:43, 6 August 2009 (UTC)[reply]
According to the article Effects of nuclear explosions, the thermal radiation would be enough to cause second-degree burns (and also to fry an egg) at about 3.2 kilometers from ground zero for a 20-kiloton bomb detonated at 1800 feet. Unfortunately, at that range the blast wave would be powerful enough to splatter the egg all over the place and also send the pan flying through the air at Mach speed. Also, the thermal radiation will have the effect of cooking the OP's skin, not just the egg, and it will hurt like you wouldn't believe. "Prompt" radiation will be negligible at that range, but radioactive fallout could be a concern if the nuclear explosion is upwind of the frying pan. FWiW 98.234.126.251 (talk) 00:18, 7 August 2009 (UTC)[reply]
Ah, but the radiation travels at the speed of light whereas the blast wave is only somewhat faster than ordinary sound. I'm not sure exactly how much faster, but supposing it is at Mach 1.1, say, what you need to do is cook the egg for 8 seconds and then you have 1 second to cover the pan. --Anonymous, 01:28 UTC, August 7, 2009.
Supersonic flight tends to heat up the skin of aircraft fairly well. When Concorde was fliying, it would be at 100C on the outside surface of the aircraft. Fry the egg on that. Googlemeister (talk) 13:34, 7 August 2009 (UTC)[reply]
Please clarify the question:
1) Which egg?
2) Can the egg be still inside the bird ?
3) Is it a requirement that the OP survive to eat the egg ? 4) Is this method of frying to be used regularly until the OP's cooker can be fixed ? Cuddlyable3 (talk) 20:20, 6 August 2009 (UTC)[reply]
You forgot point 4. Will the egg be radioactive enough to kill you if you eat it. Maybe not the egg, but I bet the pan would be pretty nasty to be around. Googlemeister (talk) 20:36, 6 August 2009 (UTC)[reply]
Mmmm... probably not. Thermal radiation extends much further than the ionizing radiation does in most scenarios (neutron bombs excepted). Mildly radioactive eggs will probably not kill you. Trivia: During Operation Teapot, they did test the effects of nuclear tests on varying types of food products, including beer. Radioactive beer apparently is somewhat stale tasting but definitely potable. --98.217.14.211 (talk) 01:20, 7 August 2009 (UTC)[reply]
The U.S. also exposed live pigs to nuclear blasts (in lieu of U.S. servicemen) at close enough distances to produce 1st, 2nd and 3rd degree thermal burns. So you could have ham or bacon with your hypothetical eggs. Wear oven mitt or welding gloves, and hold the skillet out the window for a few seconds until the ham and eggs are cooked to taste, then bring in and cover before the blast wave and fallout arrive. Edison (talk) 05:30, 7 August 2009 (UTC)[reply]
From Tsipis, K. "Arsenal" c. 1983 App. D: (brokenly translated by me to an ASCII approximation of the math):
Energy of a nuclear explosion = 4.2x10E15 joule / megaton
Neutron flux in rads = 5x10E13 * (Y/R**2)*exp(-R*rho/780)
Y is yield in megatons henceforth, rho is density of air = 1.1 g/l, exp is the natural logarithmthe exponent of Euler's number, the inverse of the natural logarithm oops, I meant what a calculator does when you push the e**x key!, R is distance in feet (bear with me, the guy was writing for an American audience)
And neutron flux and the forthcoming peak overpressure are important. Presumably you will be persuading someone else to hold the frypan out there, preferably swinging the pan face on into the blast at just the right time, otherwise I don't think the egg will get properly cooked. You don't want the egg to be overdone on one edge, right?
Thermal radiation for an airburst is Q = 1.8X10E3*(Y/R**2)*t
Q is cal/cm**2, R is in km, t is the transmission factor through the atmosphere, ~= 0.8 at 1km
Groundburst, use 1.15 instead of 1.8
And the big question which sunk my ship is whether these are "big" calories or "little" calories. Comments later.
Also from Tsipis: there are two thermal pulses, the "prompt" pulse is 0.1% of the total energy before the fireball becomes opaque (the double-flash) and the following emission when the fireball has cooled enough, for a 1-megaton device this lasts about 10 sec and emits approx. 1/3 of the total energy.
Airblast, as in peak overpressure: P-naught = 3300*(Y/R**3) + 192 * (Y/R**3)**-2
P-naught is in psi, R is in "kilofeet"
Again, this will be important for whoever you persuaded to cook your eggs. The peak overpressure at your location will determine whether their arm gets blown off. (Or whether the tank gets pushed away)
So I've calculated so far that by analogy to my stove burner, you could cook a good egg at 4.5 km distance from a 500 kiloton detonation, or 0.9 km from a 20 kiloton Hiroshima-style egg cooker. I need to look at those peak overpressures though, to find out if 1 psi overpressure exceeds the sonic velocity needed to push that tank off of the frypan. :) Franamax (talk) 05:01, 8 August 2009 (UTC)[reply]
In a literal sense, no, because a (typical) Julia set has complexity (lack of smoothness) on every scale, whereas the complexity of natural objects is limited ultimately by the size of atoms and molecules. However, it is possible to use Julia sets and other fractals to model or approximate natural objects - see fractal landscape for an example. Gandalf61 (talk) 13:04, 6 August 2009 (UTC)[reply]
Idealised, perfect, fractals are impossible in the real world - but things like clouds, landscapes, trees, coastlines, (broccoli!)...those are all fractal to a point...they can't be fractal down to the smallest scales of atoms because the laws of nature are very different down at those sizes. Coastlines can't be fractal above the scale of a continent because the earth isn't flat. Clouds can't be fractal on scales larger than a few miles because the weather patterns that form them aren't fractal - and around the size of a single water droplet, the cloud is dominated by the 'new' force of surface tension that's not relevant when it's hundreds of feet across. But within the range of a couple of inches to a mile or so, clouds are pretty decent fractals. You can even calculate things like their "fractal dimension".
So if, for example, you measure the angle between the trunk of a tree and the first two main branches - you'll find that the angles are pretty much the same as between the main branches and the secondary branches, and between the secondary branches and the tertiary branches - and so on down to the smallest twigs. The ratio of the diameter of the trunk and that of the main branches follows a similar rule. One consequence of this is that if you cut a main branch off of a tree and stick it upright into the ground...it looks more or less like a little tree. This 'self-similarity' is the same kind of thing you're seeing in the mathematical fractals like the Mandelbrot and Julia sets - and it's at the heart of fractal mathematics. It's interesting to note that humans find both natural and mathematical fractals beautiful. We've evolved to enjoy things like mountainscapes, trees and clouds - and that's probably at the heart of the reason that we enjoy mathematical fractals. SteveBaker (talk) 13:59, 6 August 2009 (UTC)[reply]
Yeah - indeed, I find it very hard to believe that anyone actually eats broccoli without being forced to by their moms. We need references for any claim that someone actually does that! SteveBaker (talk) 00:31, 7 August 2009 (UTC)[reply]
Just steam them a little so then soften up! Or put them in the oven with a little bit of olive oil and something slightly spicy. Mother will be soooo happy with you. --98.217.14.211 (talk) 01:09, 7 August 2009 (UTC)[reply]
It would be time related. At the moment of pouring the concentration would be high, but the toxin will start to diffuse away, and some time later, depending on the speed of the wave and tide actions, the concentration will fall below a "no effect level". Ronhjones (Talk)18:56, 6 August 2009 (UTC)[reply]
Probably not too big - no more than a thousand feet I'd say. A cup is 236 cm3, and that in a cubic kilometer of water is a concentration of 2 × 10-13 by volume. Botulinum toxin has a toxicity of 1 ng/kg, but only when administered intravenously. Its effect would dissipate quite rapidly. On the other hand, if you spill a tanker full of oil into the sea, the entire area can be quite severely affected, not least because oil floats on the surface. Dcoetzee19:40, 6 August 2009 (UTC)[reply]
The effects in order of increasing radius (dilution) would be: (i) kills everything, (ii) kills some things and paralyses others, (iii) paralyses some things only, (iv) temporarily hides wrinkles on a mermaid, (v) does nothing and can't be detected, and (vi) can be marketed as a homeopathic remedy for literally anything. Cuddlyable3 (talk) 19:58, 6 August 2009 (UTC)[reply]
I've heard that one as "The solution to pollution is dilution." More rhyming makes Mother Nature smile while we poison her. DMacks (talk) 22:20, 6 August 2009 (UTC)[reply]
Diluting a toxin until it has negligible effect has more basis in scientific reason than the concept of "mother nature". This is not to suggest that I enjoy polluting lakes, rivers, or oceans - but a thorough, unbiased analysis is necessary to determine if a particular action is environmentally harmful, or merely "repugnant". Nimur (talk) 23:44, 6 August 2009 (UTC)[reply]
Of note is that we (in which "we" can mean I think any of the five "nuclear weapons states," among others) have, in fact, dumped tons and tons of radioactive wastes into deep sea trenches. The idea here is that the buffer of the ocean would generally keep it in one place and if it got spread out a bit, no harm, no foul (unless you are some sort of deep sea creature who is unfortunate enough to live near it). --98.217.14.211 (talk) 01:05, 7 August 2009 (UTC)[reply]
I specified who I meant. The US, the USSR, the UK, France—all of them did ocean dumping of radioactive wastes. Look it up! (I don't know about China, but I would be surprised if they didn't.) --98.217.14.211 (talk) 13:07, 7 August 2009 (UTC)[reply]
I'm absolutely sure the USSR and China did the most radioactive dumping of all (easy enough for them, cause they don't let anyone know what they're doing); France and the US did some "dumping" of radioactives (mainly through atmospheric nuclear weapons testing), but not nearly as much. I don't think the UK did any, though -- why don't you look it up? 98.234.126.251 (talk) 22:25, 7 August 2009 (UTC)[reply]
Only 200 kg? The Soviets used to dump nuclear waste in the Arctic Ocean by the shipload. BTW, the claim in the Sellafield article that you're referring to has a "citation needed" tag. FWiW 98.234.126.251 (talk) 22:41, 7 August 2009 (UTC)[reply]
There is a significant difference between "nuclear waste" - which can be things as (relatively) harmless as the disposable paper coveralls used by workers in nuclear power plants...and "plutonium". The lethality of plutonium is not just due to the radioactivity - but it's also poisonous in a conventional sense...however, a lot depends on how big the chunks were that they dumped - what it was encased in - and (especially) what mix of isotopes it contained. If it were Plutonium 241 - encased in a good amount of lead and concrete and in small chunks, then after 50 years, there would only be 1/16th as much of the stuff as they dumped - most of it having decayed to something less lethal. SteveBaker (talk) 22:55, 7 August 2009 (UTC)[reply]
By "nuclear waste", I specifically meant high-level nuclear waste, like plutonium, fission products, etc. As for what the Soviets used to dump in the ocean: they used to dump many tons of spent nuclear fuel, which is even worse than plutonium. 98.234.126.251 (talk) 23:12, 7 August 2009 (UTC)[reply]
Yes, absolutelly, and that contribution will also have to be included in the Einstein's field equations which will feed back as a gravity source. That's the main reason why Einstein's field equations are not linear. Dauto (talk) 21:49, 6 August 2009 (UTC)[reply]
Gravitational waves do not contribute to the stress-energy tensor. In weak-field gravity they clearly carry energy, as seen in PSR B1913+16, so doesn't express conservation of energy even though it looks like it ought to. As Red Act said, you can define a "pseudotensor" that includes gravitational energy, but that breaks general covariance. In general spacetimes it's far from clear what energy even is. See this Physics FAQ entry and also §19.4 of MTW ("Mass and Angular Momentum of a Closed Universe"). -- BenRG (talk) 04:47, 7 August 2009 (UTC)[reply]
Jumping Americans cause earthquake in China
Is this possible or just a myth? If most of the population of the USA co-ordinated jumping in the air at the same time, would this cause an earthquake in China? Or vice-versa - jumping Chinese cause an earthquake in the US? 92.26.30.9 (talk) 21:21, 6 August 2009 (UTC)[reply]
Seems to me I read this in one of Cecil Adams books, or antoher like that. the short answer - it is a myth. If 300 million people exert enough force, coming down at the same time, and each is an average of a little over 100 pounds, that's only 30 billion pounds of force, and when cmopared witht he mass of the earth (not sure the exact number, but I'm sure more than what, 30 million tons?) it wouldn't be nearly enough. it's like saying "what's the effect if a few thousand people tried to push a WW II battleship." You also have the problem of the cushioning of the erth's crust, too.Somebody or his brother (talk) 21:57, 6 August 2009 (UTC)[reply]
There would also be the counteracting force of the gravitational pull of the 30,000 airborne people just above the surface of the planet Earth. That too should probably be factored into any total calculation. Bus stop (talk) 22:10, 6 August 2009 (UTC)[reply]
It certainly isn't going to throw "earth of its axis". Jumping or not the centre of gravity of "earth+humans" stays the same. 1 human (75kg) jumping to 0.5m high against gravity at 10m/s^2 has an energy of 375J. If 1.000.000.000 people do that its 375GJ or about 80t TNT. The Hiroshima bomb was about 15000t TNT. There was no earthquake in the USA after that. I always thought it is more interesting if by coordinated repeated jumping you could somehow trigger some resonance frequency of the earth/earth's crust. But I would guess the calculation above suggests that the energies involved are far too small - apart from the considerable synchronization problem195.128.250.173 (talk) 22:41, 6 August 2009 (UTC)[reply]
The part of this that most people forget is that the total momentum of the earth/people system never changes as they all jump. So when they push off - they make the earth move a little bit in one direction - but the force of gravity pulling them back down again accelerates the earth towards them. When they land, all of those forces exactly cancel out and the earth is exactly where it was before they jumped. That's not to say that there wouldn't be some vibration and such - but you can't knock the earth out of orbit that way. SteveBaker (talk) 01:33, 7 August 2009 (UTC)[reply]
If they have any effect at all, your jumping Americans are probably more likely to trigger an earthquake along the San Andreas fault (but only because it is going to happen soon anyway). Dbfirs02:07, 7 August 2009 (UTC)[reply]
Ah. but what if Nikola Tesla had determined the sequencing and used radio to direct the repeated jumping, so as to establish a resonance which focussed the reflected disturbance at a particular spot in China? The amplitude of motion of the earth there should be huge. Edison (talk) 05:24, 7 August 2009 (UTC)[reply]
Tesla was a clever guy - but he was also, in many ways a typical clueless nut-job! This is annoying because many of the full-time nut-jobs out there latch on to every word he said and insist that it must all be true (I'm not putting User:Edison into that category of course!). In truth, maybe 10% of the things Tesla worked on were sheer first-class brilliance - the other 90% were WAY out in la-la-land. His theories on resonance mostly fall into the 90% category. He extrapolated his small scale experiments into gigantic thought-experiments without really thinking about what he was saying - and came up with some ridiculous claims as a result. The Mythbusters attacked some of those in one of their shows - and while the results they had were somewhat surprising, they all fell FAR short of Tesla's claims. Notably, his ideas about resonance...that if a system oscillates - and you add just a tiny bit of energy into each oscillation at just the right moment - then the energy and the size of the oscillation will build up without limit until the object disintigrates. Sure, there are some kinds of resonance that can destroy things in impressive ways...opera singers breaking wine glasses, the spectacular failure of the Tacoma Narrows Bridge (1940), etc. But unaccountably (for such a smart guy) he completely failed to realise that if the amount of mechanical energy the system dissipates due to internal friction, heating, etc during the course of one oscillation exceeds the amount of energy you are adding with each oscillation - then the amount of oscillation won't increase at all. And that's why your idea fails...sure, all of the people jump - and the earth oscillates a little bit. However, the planet is so big that all of the energy from that jumping has been absorbed LONG before it's time to jump again...so no resonance will build up. SteveBaker (talk) 18:01, 7 August 2009 (UTC)[reply]
Indeed I wonder if this idea is based in part on the myth that China is exactly on the oppposite side of the planet of the US (common in cartoons for example). This isn't true, that's the Indian Ocean [23][24]Nil Einne (talk) 09:25, 7 August 2009 (UTC)[reply]
It's quite impressive how little of the inhabited land surface of the Earth has an antipodal point that's also on land and inhabited.
I'm interesting in finding out if some sunglasses and a camera filter that I have are actually doing a good job of blocking UV light. Is there any easy or cheap way to measure the amount blocked? Any way to tell if cheap sunglasses are actually helping or just hurting or to see if my UV camera filter is doing anything put protecting the lens? Tobyc75 (talk) 02:38, 7 August 2009 (UTC)[reply]
Sunglasses in some countries are standards tested and rated, see Sunglasses#Standards, but may depend where you live, and don't know how you'd do this yourself if you live somewhere where they're not. In general, in Australia, the rule of thumb is don't buy them if they're so cheap as not to be standards approved. Re the camera what are you actually wanting the UV filter to do? Try the identical shot with and without the filter on and compare the photos down to a pixel level - but many people (myself included) chiefly use the UV filter to protect the lens itself rather than for any real effect. See UV filter and Photographic_filter#Clear_and_ultraviolet. --jjron (talk) 03:10, 7 August 2009 (UTC)[reply]
I bought a Hoya Super HMC UV filter for a camera lens, and inside the package was a paper card with a specially treated dot. The dot changes color when exposed to UV light. Outdoors in sunlight, the dot would change color, and when I put the filter in front of it, it would go back to white. I don't know what the dot was made of, or its wavelength response, or sensitivity, or anything else that would make it a quantitative test. -- Coneslayer (talk) 12:42, 7 August 2009 (UTC)[reply]
A fluorescent thing would help - but only proves that a narrow band of uv is being blocked/transmitted in general. A better solution would be a photodiode (light meter) and a filter that you know only allows uv (but not visible)83.100.250.79 (talk) 13:00, 7 August 2009 (UTC)[reply]
I don't know that it matters to you - but I recently got a new set of eye glasses - specifically for driving. I asked about photochromic lenses (the kind that change color) and asked if they were able to block UV efficiently. I was surprised to hear that pretty much all normal eye glasses sold through mainstream opticians in the US now have UV-protective coatings as a matter of course...even the glasses that are completely clear! So you don't even need tinted glass - a completely clear lens can be an efficient UV blocker if it has the right coatings. SteveBaker (talk) 17:46, 7 August 2009 (UTC)[reply]
In fact you often don't even need coatings - CR-39 which is (probably) the most popular lens material blocks almost all uv itself. It's quite difficult to get a glass or plastic lens that doesn't cut out practically all uv.83.100.250.79 (talk) 23:24, 7 August 2009 (UTC)[reply]
UV filters are essential for outdoor photography using film, since film is more sensitive to UV than to visible light, and even the near-opacity of glass to UV isn't enough. Digital cameras are the other way around: they're more sensitive to visible than to UV, and the glass that makes up the lenses is sufficient to filter out the rest. --Carnildo (talk) 23:00, 7 August 2009 (UTC)[reply]
Thanks for the responses. Re: the sunglasses, I was actually interested in whether the cheap children's sunglasses did more harm than good, and I'm in the US, so I'm not sure if I've seen any government testing stickers on them. I'd guess that, yes the cheap ones most likely are pretty bad. As for the camera filter, I mostly just use it to protect the lens. It's on a DSLR and I can't see any difference between with and without the filter. Tobyc75 (talk) 23:19, 7 August 2009 (UTC)[reply]
As I mentioned above in response to SteveBaker - most optical materials block uv anyway, so your uv filter is probably only protecting the lens (which is a good thing anyway). Don't know about sunglasses - you're probably right. 83.100.250.79 (talk) 23:43, 7 August 2009 (UTC)[reply]
The trouble with sunglasses is that the darkened lenses fool people into looking at brighter objects without squinting and the reduction in visible light causes your irises to open wider to allow in more light. So if the sunglasses aren't really good a blocking UV, the result is much more UV entering the eye than would normally be the case if you weren't wearing them. However, at least in Europe, those kinds of sunglasses are supposedly banned. SteveBaker (talk) 03:05, 8 August 2009 (UTC)[reply]
Bike gearing
This came up in a discussion about motorbike gearing, but probably easier to ask in the context of bicycle gearing and in a simplified form.
Consider a multi-speed bike with typical front and rear gears, and for convenience express the ratios as FR:RR. Now lets take two gear ratios, say 28 teeth front and 14 teeth on the rear, i.e., 28:14, and 48 front & 24 rear, i.e., 48:24. Mathematically both these ratios simplify to 2:1, which is the easy bit.
For a perhaps less 'artificial' or simplistic example consider ratios of 38:16 and 48:20, which come out to 2.38 & 2.40, which again is mathematically essentially the same.
The question is that while these ratios are basically the same mathematically, physically is there a difference between changing the gearing on the 'bigger' chainring or the 'smaller' chainring, i.e., would these gear ratios require say an identical amount of energy to push them?
I'm thinking in terms of effects due to torque, angular velocity or momentum due to the different sized rings, or other relevant things. Anyone with better knowledge of this than me... Thanks in advance. --jjron (talk) 02:58, 7 August 2009 (UTC)[reply]
Torque (rotational force) depends on radius. What is the relationship between number of teeth and the circumference of the gear? What is the relationship between circumference and radius? Based on those answers, you can determine if tooth-ratio is equivalent to torque-ratio. Once you've figured it out yourself, you can check with our gear ratio article for more information. DMacks (talk) 03:24, 7 August 2009 (UTC)[reply]
Yes, you are right. what matters here is the ratio so, as you pointed out, 28:14 and 48:24 will lead to essentially the same torque, assuming that other factors such as friction can be considered negligible. Dauto (talk) 04:36, 7 August 2009 (UTC)[reply]
Near the end of the summer I was given my first real design job: a machine that would make a continuous curve out of a set of points--one point coming in every fifteen seconds--from a new invention developed in England for tracking airplanes, called "radar." It was the first time I had ever done any mechanical designing, so I was a little bit frightened.
I went over to one of the other guys and said, "You're a mechanical engineer; I don't know how to do any mechanical engineering, and I just got this job.
"There's nothin' to it," he said. "Look, I'll show you. There's two rules you need to know to design these machines. First, the friction in every bearing is so-and-so much, and in every gear junction, so-and-so much. From that, you can figure out how much force you need to drive the thing. Second, when you have a gear ratio, say 2 to 1, and you are wondering whether you should make it 10 to 5 or 24 to 12 or 48 to 24, here's how to decide: You look in the Boston Gear Catalogue, and select those gears that are in the middle of the list. The ones at the high end have so many teeth they're hard to make. If they could make gears with even finer teeth, they'd have made the list go even higher. The gears at the low end of the list have so few teeth they break easy. So the best design uses gears from the middle of the list."
I had a lot of fun designing that machine. By simply selecting the gears from the middle of the list and adding up the little torques with the two numbers he gave me, I could be a mechanical engineer!
And the parts in the middle of the spec range are most likely to be available on short turnaround. As I mentioned above, there's a difference between "it's in the catalog" and "you can order it and receive it in a reasonable time". This is what's mean by the "OTS" in "COTS." Nimur (talk) 17:21, 7 August 2009 (UTC)[reply]
Naturally, if we neglect friction, the torque onto the pedals of a bicycle needed to drive it forward with a specified force is dependent on just the gear ratio. However, the torque is transferred to tension in the chain and that is inversely proportional to the radius of a gear. Hence, to save the chain it's best to use preferably large cogwheels, as then both the tension and the bending of the chain are minimum.—Pt(T)02:39, 8 August 2009 (UTC)[reply]
The actual diameters also matter if you're dealing with shifting Derailleur gears. This shift is a change of absolute radius and chain-slack on one gear, not a ratio between two gears, but the goal is a shift of relative ratio. That means if the gear has a large radius, a relatively large change is needed to accomplish a shift of ratio. That is, if you are doing a ratio shift 3:1→2:1, changing gears 30:10→20:10 is a change of 10 whereas 60:20→40:20 is a change of 20. WP:OR says derailleurs and chains are more susceptible to jamming with very large changes. Also, the derailleur needs to take up all the slack, so the larger the change, the larger the derailleur cage needs to be. At the other extreme (small gears), a small change in radius represents a more significant change in ratio, so they need to be manufactured more accurately and precisely. DMacks (talk) 05:09, 8 August 2009 (UTC)[reply]
going 30:10 to 20:10, you're changing by 10,
conservation of momentum and heat
Does a system gain momentum when it absorbs blackbody radiation, or when it emits it? Thus even though photons are massless, are they potentially carriers of momentum? (This was never covered in AP Physics really...) John Riemann Soong (talk) 08:41, 7 August 2009 (UTC)[reply]
Yes, photons carry momentum (despite their rest mass being exactely zero, the classical formula p=m*v does not hold here). Yes, systems absorbing or emitting electromagnetic radiation in a non-uniform way will gain or lose momentum.
Doesn't this mean the Earth is actually gaining and losing momentum just through radiation alone...? Or is it assumed that global net radiation flux (Rnet?) is zero? John Riemann Soong (talk) 11:12, 7 August 2009 (UTC)[reply]
It's pretty close to zero, yes. If it were not, it's difficult to see how the Earth could remain habitable over millions of years. Although photons don't have rest mass, they do carry energy. The formula gives the relationship between these quantities, where is momentum.--Leon (talk) 11:27, 7 August 2009 (UTC)[reply]
Well, I mean, does Rnet account for photosynthesis? So all those plant sugars and fossil fuels ... are actually carriers of momentum? It's strange cuz in high school (AP Physics C) they always told me, that excepting tiny particles colliding with the Earth, or asteroids, that as far as momentum was concerned, we could treat Earth as a closed system, with no mention of light as a bearer of momentum.
Momentum ain't energy! Momentum isn't really "stored" perse, and whilst the momentum of the Earth would be changed by this, the momentum of the Earth--bomb system would be constant. But you would be converting energy from one form to another. --Leon (talk) 12:31, 7 August 2009 (UTC)[reply]
I also remember solving a few problems about conservation of momentum on a system composed of bound protons and neutrons...(yeah a nucleus). The nucleus underwent nuclear decay, ejecting various daughter nuclei. Since the original nucleus was at rest to begin with, we used this condition to solve for the velocities and masses of some of the daughter nuclei (being given the mass of the original nucleus and the masses and velocities of some of the other nuclei, etc.). Thankfully, the problem was in 2D ... I don't think I could have done it in 3 dimensions without some serious linear algebra. Anyway, I'm wondering whether the methodology is necessarily valid, since 1) gamma radiation is likely to be emitted nonuniformly 2) since fission energy is being converted into kinetic energy, why should the total momentum of the system be still zero? John Riemann Soong (talk) 12:02, 7 August 2009 (UTC)[reply]
It's a law of physics that momentum is always conserved. However, kinetic energy needn't be. If bombs are detonated as you describe, the kinetic energy of component parts is increased, but the momentum isn't. Remember, momentum is a vector quantity and if you add up those vectors the result doesn't change. Kinetic energy is scalar, and is proportional to v squared not v. --Leon (talk) 12:31, 7 August 2009 (UTC)[reply]
Wait a minute - if light is converted to stored energy through photosynthesis there's no impulse (change of momentum) on the body (tree/plant) it acts on - if there was then the energy would be dissapated as kinetic energy - but it's not - it's stored as chemical energy. - a momentum change would need the light to be reflected.
No, a momentum change does not need light to be reflected. Though a certain amount of reflection does occur, incidentally. And there is some impulse on the plant! --Leon (talk) 12:31, 7 August 2009 (UTC)[reply]
(edit conflict)The force on the earth due to light reflection is ~ 50 mega newtons (assuming intensity of 920W/m2 [[25]], albedo of 30%, radius of earth = 3x106m , p=E/c , F=dp/dt )83.100.250.79 (talk) 12:29, 7 August 2009 (UTC)[reply]
Hmm, but now take billions of years of cyanobacteria and fossil fuel formation ... also I ask about photosynthesis because it's basically a sort of energy sink, allowing Earth to reach thermal equilibrium while actually stockpiling energy. Thus even if no reflection occurs, the system of Earth's atoms has arguably gained momentum, hasn't it? Also, I assume things like angular momentum, axial tilt, and other planetary parameters could be more sensitive? (Though still not very sensitive to anything man-made ... but I am wondering about variation over long periods of years, after accounting for things like tidal lock effects and such.) John Riemann Soong (talk) 12:45, 7 August 2009 (UTC)[reply]
Not really momentum - they have gained energy. If you say convert carbon dioxide and water into sugar (increase in energy) there's no real increase in classical momentum.83.100.250.79 (talk) 12:57, 7 August 2009 (UTC)[reply]
Indeed, the earth absorbs more momentum by reflecting and/or absorbing photons on the dayside than is radiated away by thermal radiation on the nightside. The photons exert a tiny net force away from the sun. Gravity exerts a force towards the sun. The net effect is a tiny decrease of the force keeping the earth in its orbit, as if the sun were slightly less massive than it actually is. For orbiting dust particles and solar sails, the radiation pressure is comparable to or larger than the gravitational force due to the sun, and the orbits of these things are significantly different from purely gravitational orbits.
Bullets fired in the air returning to ground
When live bullets are fired into the air (9 gun salute e.g.) are the falling bullets just as deadly as usual, or do they burn up or something? Are blanks used in these kind of displays? —Stanstaple (talk) 17:45, 7 August 2009 (UTC)[reply]
It depends on the trajectory of the bullets. If fired at an angle, the bullets can maintain their spin and lethality -- there are many documented cases. If fired strictly vertically, the bullets lose their spin and fall at a much slower speed. The MythBusters covered this in some detail a few years back. As for whether blanks are used in x-gun salutes: it depends on who's doing it. — Lomn17:52, 7 August 2009 (UTC)[reply]
Depends how massive the bullets are. If you use cannon, you might want blanks. If you're dealing with a lighter object like a bullet, you should be familiar with the concept of terminal velocity because of air resistance. Bulkier objects tend to have a larger mass / surface area ratio (due to geometric trends). John Riemann Soong (talk) 17:53, 7 August 2009 (UTC)[reply]
Of course! For some reason i'd never figured in the effects of wind resistance- Firing a bullet into the air would be akin to droping the bullet from the apex- makes sense when you think about it- thanks again. —Preceding unsigned comment added by Stanstaple (talk • contribs) 18:59, 7 August 2009 (UTC)[reply]
Not quite. If you read the article careful enough, it all depends on whether the bullet keeps its spin or not. If it does, just the terminal velocity after the fall can be fatal. If, however, it starts tumbling on the way down, it will fall to earth harmlessly. Seems whether it will tumble or not is very hard to predict.195.128.250.139 (talk) 21:18, 7 August 2009 (UTC)[reply]
I like the "Bullets are not greeting cards. Celebrate without firearms" slogan from Macedonia. I wonder - are the people who fire off their guns in joy the same kind of people who shoot their TV set when their football team loses, or shoot their monitor when their PC crashes? --Kurt Shaped Box (talk) 23:00, 7 August 2009 (UTC)[reply]
No, no, no! Be VERY careful how you answer this question. Shooting a gun into the air is lethally dangerous - period. Unless you shoot it pretty much exactly vertically - it will have considerably more velocity when it finally comes to earth than if you dropped it from the maximum height it achieves. You can imagine the horizontal and vertical velocities of the bullet as entirely separate things. If you shoot a bullet horizontally (eg if there was no gravity) then only air resistance slows it down - and not by very much...the bullet is (predictably) lethal. When you fire it vertically, it travels to the apex, gradually slowing down because of gravity and wind resistance - and then stops - and falls back to earth with gravity accellerating it and air resistance slowing it down. Because of the air resistance, the bullet is travelling more slowly when it hits the ground than when you fired it. The terminal velocity of a spinning bullet is pretty fast - because they are fairly aerodynamic - and quite heavy for their cross-sectional area...but when the bullet is fired vertically, it slows to a stop and has to flip over...it loses the spin that keeps it stable in flight - and one the way back down again it's tumbling randomly - which introduces a lot more drag and slows it down quite a bit. A bullet that fell back on you would hurt quite a bit - but it wouldn't kill you. Mythbusters found them buried in a couple of inches of dirt. But what gets complicated (and VERY dangerous) is when you fire the bullet at an angle - not quite vertical. The horizontal component of the motion isn't slowed down by gravity at all - and that allows the bullet to keep its spin - so as it goes over the top of the arc, it stays nicely pointed into the airflow - wind resistance hardly slows it down at all and it remains completely lethal - exactly as lethal as if you'd fired it in a straight line over the same total distance. The precise angle at which the spin of the bullet turns into a tumble and it becomes much safer is unknown and would certainly depend on the initial muzzle velocity, the precise shape of the bullet and a whole bunch of aerodynamic complications. However, it is very safe to say that if you fire a bullet into the air - you could quite easily kill someone. There are PLENTY of well-documented cases of innocent people who have been killed and injured by stray bullets at celebrations where people shoot guns into the air. Please don't let anyone convince you otherwise...most of them are oversimplifying a complicated aerodynamic situation. They simply don't understand what's going on in enough detail to explain the problem - so they claim to "know" that it's safe - which it patent nonsense given the number of documented cases of people dying.
Shooting blanks is obviously safer - but even so, there have been people killed by blank rounds too - blank rounds are far from "safe".
Paradoxically, if you were going to fire off your AK-47 in celebration of <whatever>, aiming it straight up in the air would seem like one of the most stupid things that anyone could possibly do... --Kurt Shaped Box (talk) 22:56, 7 August 2009 (UTC)[reply]
Yep - ironically, perfectly vertically is the safest...(well, safest for humanity in general...perhaps not safest for you personally!) But that requires much more faith in aerodynamics than most people have! The Mythbusters tried quite hard to fire their guns perfectly vertically - but the bullets still landed hundreds of feet away. SteveBaker (talk) 02:59, 8 August 2009 (UTC)[reply]
Space-filling models software
Hello, I am looking for free software that allows me to generate atomic and molecular space-filling models. Do you know of any? Thank you. Leptictidium (mt) 20:33, 7 August 2009 (UTC)[reply]
I'm growing some tomato plants. I've read a few times that it helps to remove some of the buds on the plant - could anyone clarify what you are supposed to do please? And is doing this truelly worthwile, or just a myth? I happened to see on tv about farmers growing thousands of tomatoes in a big field. I doubt they do any bud nipping, but also they do not support the plants at all - is supporting the plants and trusses necessary? 78.146.176.224 (talk) 21:09, 7 August 2009 (UTC)[reply]
The process of removing the buds/side shoots of tomatoes is called "suckering" (at least that's what I learned it as). The thought is to remove growth that will never amount to much, and get the plant to put that energy into flowering and fruiting. The Wikipedia article isn't too applicable, but if you search the web for "suckering tomatoes" (or similar), you should get a number of sites which discuss it. The reason you stake/cadge tomatoes is to keep the fruit off the ground, and to allow it to dry out more thoroughly. Tomatoes are particularly susceptible to diseases especially fungal ones, such as blossom end rot, verticillium wilt and fusarium wilt. Commercial farmers don't prune or stake because it's very labor intensive, and labor is costly. It's cheaper/more efficient to just grow more plants, spray with fungicides, and hope for the best. The analysis is different with a backyard gardener, though. The labor expenditure is not as high with just half a dozen plants, and you'll get a much larger crop. -- 76.201.158.47 (talk) 14:57, 8 August 2009 (UTC)[reply]
power leakage
Is it true that power leaks away when, for example, a phone charger is left plugged in without the phone? How does this happen? How much energy is wasted? --Halcatalyst (talk) 22:10, 7 August 2009 (UTC)[reply]
Even the best phone chargers waste some energy - even if they are not connected to anything - they're mostly better than 90% efficient, and probably waste even less when not charging.
Well, the power doesn't "leak" out of the end of the wire...that's a common fallacy. (If it did, every power socket in your house without something plugged into it would be "leaking" too!) However, because a charger is a transformer - which has a coil of wire on the wall-socket side of things, there could be a VERY tiny amount of current consumed - which would appear as a small amount of heat being emitted by the charger. But unless the charger has an LED on it that's lit up to show that it's plugged in - I think the amount of energy wasted is very small indeed. If you are looking for places where electricity is being uselessly consumed, consider things like TV sets which can be "turned on" with a remote. Anything that can be turned on and off with a remote has to have some circuitry running in order to detect the signal coming from the remote. So when you turn off your TV/DVD/Satellitebox/etc - it's not REALLY being turned off - it's just turning off most of it's functions and hopefully saving energy. However, nothing short of unplugging such devices will truly get them "turned off" completely. SteveBaker (talk) 22:24, 7 August 2009 (UTC)[reply]
I've heard wall warts (transformers) tend to take significant amounts of energy even if nothings plugged in. I think the good ones have a way of telling if something is plugged in, and disconnect the circuit nothing is. I know from experience that I have at least one wall wart that tends to get warm if you leave it plugged in, even if the device it's connected to is off. — DanielLC04:16, 8 August 2009 (UTC)[reply]
Cecil Adams did a column on this here. He found the the idea that wall-warts wasted huge amounts of energy was mostly a myth. APL (talk) 04:47, 8 August 2009 (UTC)[reply]
Surgery recovery time
Suppose someone has had surgery for eye injuries due to a shotgun backfire (see the science ref desk archives section "Shotgun backfiring"), and also for multiple bone fractures and lacerations due to being mauled by a bear. How long must the patient stay in one place before he can be evacuated by plane? Also, how likely is he to have complications that would require follow-up surgery? (No, this ain't no medical advice, it's for my story again.) Thanks in advance! 98.234.126.251 (talk) 22:59, 7 August 2009 (UTC)[reply]
Too many unknowns to make a definitive decision. The main fulcrum of the decision to move the patient would be the need for improved care against the possibility of damage caused by the evacuation. Helicopters are frequently used to move seriously injured individuals. What sort of plane had you in mind? A small single engined plane that did not ascend to altitude would OK for early evacuation. IMHO. 86.4.181.14 (talk) 07:24, 8 August 2009 (UTC)[reply]
The plane I had in mind was that same Queen Air that had to land in a 15-knot crosswind (see the section "Crosswind landing"), but the pilot knows that there's a surgery patient on board, so she flies low and does her level best to avoid any turbulence. What I wanted to know is, how soon before it's safe to even move the patient? Assume that he had to have (1) the splinters taken out of the scleras and corneas of both his eyes, (2) small tears in both irises repaired, (3) blood drained from inside both eyeballs, (4) a SMALL part of the vitreous humor taken out to remove dried blood, (5) compound-comminuted fractures in both forearms cleaned, aligned, and fixed in position, (6) simple fractures of the ribs repaired, and (7) lacerations sutured on face and body. (Quite a list, huh?) 98.234.126.251 (talk) 10:13, 8 August 2009 (UTC)[reply]
That bear must have been fairly close to a largish city, for that level of surgical help to be available to your victim. So why does he have to be moved? If it happens in the back of nowhere, then he'd just have pressure bandages applied to stop bleeding, splints applied to stop the bones moving (possibly those inflatable splints carried by ambulances) and then he'd be evacuated to a place with a large enough hospital to do the actual surgery.
Once he's had the surgery he could be safely moved immediately, by road or air transport, as long as his IV drips go with him. It would be no different than being wheeled through 2 hospital buildings to get from the operating theatre to his ward. But if he had the full surgery close to where the incident happened, why move him?
If moving him is a necessary part of the story, you either need a compelling non-medical reason for moving him, or he'd only be able to get basic first-aid at the scene and need evacuation to be able to get the surgery.- KoolerStill (talk) 14:28, 8 August 2009 (UTC)[reply]
How can I tell if a martial arts school is crap?
I know to avoid the ones that guarantee that you'll become a black belt in n years (as long as you keep paying every month), or don't actually do any real full-contact sparring against a resisting opponent, tell you that they'll teach you to be able to beat up six guys at once - every time, or claim ninja movie rubbish like that they have 'ancient secret high-level techniques' that will allow you to kill people with one punch, or levitate/teleport/become invisible using chi magic, or throw fireballs, or move fast enough to catch bullets, etc.
But what else should I look out for, as a newb, before I sign up for training that might be generally poor and ineffective? Sorry if this is in the wrong place, but I think that MA is a sort of science. Wasn't exactly sure where to put my Q. --84.69.218.212 (talk) 23:25, 7 August 2009 (UTC)[reply]
It's not really a 'science' in the usual sense of what questions are posted here, but here goes: Word of mouth is wonderful for things such as these, similarly if you can find more about local tournaments then you'll maybe find which 'schools' teach the top performers in your area (a-la Karate Kid). Perhaps find a few local ones and ask if they'd let you come and watch in on a session - most will be receptive if they know you're seriously considering joining. ny156uk (talk) 23:35, 7 August 2009 (UTC)[reply]
Well, as a karate brown belt, I'd say that you should seek out a martial arts school that first puts an emphasis on teaching the right moves so that you do them right every time, and then, once you learn the techniques, incorporate them into one-on-one full-contact sparring with your fellow students. It's also highly desirable that the instructor should take the time to personally demonstrate the martial arts techniques to the students, and explain or demonstrate what (if anything) they're doing wrong. It's also generally (but not always) true that small MA schools offer better quality training than bigger ones. And last but not least, if within a reasonable amount of time (say a year or so) you don't see your technique improving in perceptible terms, then you should consider changing your MA school. There might be other considerations too, but I can't think of them off the top of my head. 98.234.126.251 (talk) 23:44, 7 August 2009 (UTC)[reply]
Why not invite the instructors to a no holds barred fighting competition? The winner will be the best fighter and likely the best instructor. Marcus Greene (talk) 23:49, 7 August 2009 (UTC)[reply]
I find your second statement unlikely. Many people who are good at something are not great teachers. Many great teachers are not the best at their subject. While I'm primarily thinking of academic teachers here, I don't see why this won't apply to martial arts as well. Indeed if we consider sports, the best coaches were often not the best players, and the best players often fail as coaches. Of course a more significant fact is that I don't see any evidence the OP is particularly interested in learning no hold barred fighting and most importantly, unless you happen to have a large amount of money, the chance you a prospective student will convince many instructors to get involved in such a thing is slim Nil Einne (talk) 09:43, 8 August 2009 (UTC)[reply]
I recently saw a TV programme where a scientist said that he had seen a woman's body who had been buried in a lead lined coffin for 200 year and yet he could still tell that her eyes were blue. Is that level of preservation really possible? Would the body have had to been subject to some other preservation? In the same programme they exhumed Mark Sykes and were able to obtain lung tissue after 90 year (even though his lead coffin was split) so I guess it is not impossible that sure amazing preservation can take place. This article on Snopes suggest that an air tight container wouldn't preserve a body very well, without other preservation techniques being used. If somebody eye colour was preserved for 200 years, I would have thought that they would be in pretty good shape for at least the first few years. Are Snopes wrong? Would lead preserve a body better than an air tight casket made of another material? Bury me in a Y shaped coffin (talk) 23:36, 7 August 2009 (UTC)[reply]
Is the mind software or hardware?
I have been wondering whether if the electrical activity in the brain stopped just for a split second and was then restored, would your "mind" still be there? (I imagine that "mind" is a concept that is a can of worms, but basically would all of your memory and mental faculties be in tact). I guess that it is a bit like a PC, in that if you turn it off and then back on, the hardware is still there and so is the data on the hard drive, but any running software is gone. So is the mind software or hardware? Has anybody ever recovered from a complete cessation of electrical activity in the brain? Bury me in a Y shaped coffin (talk) 23:46, 7 August 2009 (UTC)[reply]
I think the important question here is how is memory physically stored in the brain? Is it some chemical or electrical state that needs to be actively maintained like RAM, is it more physical changes in the ways the neurons behave like hard disk storage, or is it physical changes in the way the neurons are linked together like chip architecture. I have no expertise in neuroscience, but I think the answer is first that it's not all that well understood, and second it's probably a combination of a lot of these things. There seems to be a fair bit of information on Wikipedia about this stuff although I'm not really sure where a good place to start is. The memory article talks about the different kinds of memory. I think it's safe to assume that sensory memory (which lasts less than half a second) is probably not facilitated by any permanent physical changes in the brain. Meanwhile neuroplasticity talks about how the brain can over time rewire itself in response to experiences. Rckrone (talk) 00:45, 8 August 2009 (UTC)[reply]
It would take a library to address all of the issues you brought up so let's grimace and push those aside. I think the core of what you're asking is "are pathways hard-coded in physical structures, or are they volatile?" It's a tough question. The brain isn't a digital circuit, it's chemical. Neurotransmitters metabolize, unused enzymes build up or break down.. The problem is, brains don't just stop working for a split second. The chemicals that are there are ionized and produce current.. how do you plan to neutralize them? Are they just going to disappear? Well they're critical to the functioning of the brain.. you might as well have asked whether a bullet ripped through your skull for just a split second would cause permanent damage. .froth. (talk) 01:41, 8 August 2009 (UTC)[reply]
Electroconvulsive therapy rather thoroughly disrupts normal brain functioning for a fraction of a second, which is fairly similar to what you are asking. There is a lot of electrical activity going on in that case, unlike none as in your question, but the electrical activity that’s going on during that instant is a far cry from what would normally be happening in the brain. The immediate short-term effects of electroconvulsive therapy are confusion and loss of short-term memory, but the confusion goes away, and long-term memories are largely retained. Red Act (talk) 02:39, 8 August 2009 (UTC)[reply]
As best we understand it (which is not great), long term memory is in 'hardware' - hard connections that grow between neurons. Short term memory is 'software' - electrical signals circulating around the brain that holds the information until neural connections can fill in and make the memory "permenant". This is kinda backed up by the fact that people who have accidents and lose consciousness often lose all memory of the incident - presumably because the software short term memory disappears (just like losing RAM memory in your computer if you turn it off). SteveBaker (talk) 02:50, 8 August 2009 (UTC)[reply]
Try mind, electroencephalogram, coma, and brain death. When awake, the brain always has electrical activity, there's no such thing as electrical activity stopping for a "split second." During anesthesia, loss of consciousness can be associated with a flatline on EEG (though this may be more reflective of the limited sensitivity of EEG as opposed to actual complete electrical inactivity). When brought back to consciousness, the "mind" is unaltered. Complete loss of electrical activity on EEG is sometimes used as a criteria for determining brain death. The brain death article references the case of a man who was declared "brain dead" but later recovered. The references cited in the article indicate that he had no cerebral metabolism on positron emission tomography scan shortly after an injury, though this is not quite the same thing as declaring that there is no electrical activity. He apparently remembers hearing the doctors say that he was dead, so presumably his short term memory (and therefore electrical activity) were working normally. As a hand-waving answer to your questions, it seems as though the brain structures (hardware) are what enable the mind (software) to run and that memories can be written to short-term RAM (as with SteveBaker's analogy) or long-term ROM to be accessed by the mind when needed. --- Medical geneticist (talk) 03:22, 8 August 2009 (UTC)[reply]
It's a fungal infection. Probably it starts as a tiny dot at the center - as it spreads outwards, the damage it does is being repaired by the victims' body - so you wind up with a circular infected area with a smaller circular healed area in the middle. But that's just a guess...I don't know for sure. SteveBaker (talk) 02:38, 8 August 2009 (UTC)[reply]
Suppose there is Negative Matter. Assume we have a negative positron at position p. When it moves to another position, say k, subluminally external observers may interpret this as an electron moving back in time. Is this counted as superluminal travel? Also, this travel into the past does not violate casualty because the information is sent from future to the present, which affects the future. The Successor of Physics04:18, 8 August 2009 (UTC)[reply]
Antimatter moves through normal space in the normal way. It does not travel back in time.
There is no such thing as a "negative positron".
I don't understand how moving a "negative positron" from one place to the other would be the same as moving an electron back in time.
If information was sent from the future to the present it would absolutely violate causality as we understand it.
You might be trying to describe Tachyons. Keep in mind that Tachyons are a hypothetical construct. There is no theoretical or experimental evidence of their existence. APL (talk) 05:29, 8 August 2009 (UTC)[reply]
I think the OP might be talking about Feynman's idea of anti-particles being thought of as their regular counterparts traveling backward through time. It's important to stress that this is just an interpretation used to help intuitively understand what's happening. A given particle exists at various point in time-space, but it's not really meaningful to say that a particle is traveling in one direction along that path or the other. There's also no violation to causality. If we assume determinism in both directions, then the state of the universe at one time determines both the state immediately before and immediately after. The direction of causation is which ever direction we choose to look at things from, so it's not really meaningful to say that in this case events in the future are causing events in the past. It's just a matter of perspective. Rckrone (talk) 05:53, 8 August 2009 (UTC)[reply]
slow cooking of pork -- where does all the fat go?
A lot of recipes say the fat "melts" after a long slow roast (or a braising) ... and sure enough, the huge chunk of fat on the pork slowly seems to dissolve; if I'm braising the liquid becomes quite oily. What happens to the fat? Is it broken down into smaller fatty acids (and maybe some of it gets oxidised into CO2 and water?). I also note that we generally use acidic liquids like tomato sauce, fruit juice, beer, or some liquid with a bit of vinegar tossed into it ... does some sort of acid-catalysed elimination reaction occur? John Riemann Soong (talk) 10:35, 8 August 2009 (UTC)[reply]
If you're heating triglycerides (i.e. fat) in an acidic aqueous solution, the fat is hydrolysed to glycerin and free fatty acids (the glycerin is fully water-soluble, the fatty acids only partly water-soluble); however, oxidation to CO2 and H2O does not take place. 98.234.126.251 (talk) 10:52, 8 August 2009 (UTC)[reply]
Animal fats are just solid oils. (Or rather, edible oils are simply liquid fats). You said it yourself - the braising liquid becomes oily. No quotation marks needed, the fat literally is melting, and is being added to the drippings. If you poured off the liquid and separated out the oil, not only would it solidify when it cooled, but it would probably be equivalent in volume/weight to the fat lost from the roast. One caveat to this would be that some of the fat may be emulsified into the water portion. I seriously doubt that a significant portion of the fat has been converted to fatty acids, as free fatty acids are, well, soap. (Your bath bar possibly lists sodium tallowate as an ingredient - that's saponified (hydrolyzed) beef fat.) A small amount of free fatty acids as well as mono- and diglycerides may form, which would help to emulsify the fats, but if a significant amount of free fatty acids were formed, your roasts would taste "soapy". -- 76.201.158.47 (talk) 14:36, 8 August 2009 (UTC)[reply]
Light as a feather, stiff as a board
There is a fairly common "party trick" where somebody sits in a chair and a small group of people lift the chair and the person, using only one finger each (alternatively the lifters put their fingers under the subjects armpits and knees). I have found some discussions about how it works (it seems that it is called "light as a feather, stiff as a board" by some) but no definitive answers as to how it works. It seems to me that it is likely the case that the combined lifting force of the lifters is simply sufficient when the weight is shared between them (even though that seems counter-intuitive). Is it that, or is something else involved, or maybe is it really a "trick" with the lifted individual or one or more of the lifters in on the trick and somehow "cheating"? There is a Wikipedia article on the game, but it seems pretty vague, I am hoping that there is, in fact, a recognised scientific explanation for it. Bury me in a Y shaped coffin (talk) 10:57, 8 August 2009 (UTC)[reply]
We have an article Light as a feather, stiff as a board on that, it doesn't seem to suggest it is anything special - just that a number of people can easily lift a person and so the 'effort' is a trick of the mind (though it has a 'dubious' statement around it). ny156uk (talk)
Pushing things out of earth orbit
Would it be possible for an astronaut on the International Space Station to easily shove some garbage in the optimal direction so that it fell to earth and got burnt up? Or in reality is this not possible? If something was pushed towards earth, then as there is virtually no friction in space it should keep on going to earth, at least it would seem that way when viewed from the Space Station. 84.13.197.233 (talk) 14:55, 8 August 2009 (UTC)[reply]
