Wikipedia:Reference desk/Archives/Science/2007 January 25

=January 25=

Acid/base Indicators
What are acid/base indicators?
 * Would you be thinking of PH indicators? Yuser31415 (Editor review two!) 00:26, 25 January 2007 (UTC)

I think so, could you give examples.


 * If you click on the link Yuser31415 provided, you will find a list of no less than 27 indicators. —Preceding unsigned comment added by Chickenflicker (talk • contribs)


 * Yes, that article may be considered the litmus test for whether Wikipedia and the Ref Desk can provide useful answers. StuRat 09:07, 25 January 2007 (UTC)


 * Haha! − Twas Now ( talk • contribs • e-mail ) 09:19, 25 January 2007 (UTC)

What is the etymology of 'Pakicetid' ?
Hi all. I wasn't sure whether to put this in the language question section (etymology) or the science section (biology), so I put it in both. I am learning about the evolution of the whale, and I was wondering what Pakicetid means, in the latin or greek or whatever that it came from, as the article does not say. Much help appreciated ! Xhin 00:36, 25 January 2007 (UTC)
 * Well since it's based upon the words 'Pakistan' and 'cetacean', I would think your answer would lie with the origins of those words. Anchoress 00:39, 25 January 2007 (UTC)
 * Ah, thank you. I forgot it was found in Pakistan.

Nasal Drift Theory
As another followup to the evolution of whales topic (interesting stuff!), the article mentions something called "Nasal Drift Theory" but doing a wikipedia search only redirects back to the evolution of whales article. I was wondering if there's any evidence of nasal drift in anything other than cetaceans and whether it's an ongoing process that would cause the snout to drift even further in the future. Any other external links that would be helpful to the subject would be helpful.

Much help again appreciated ! Xhin 00:49, 25 January 2007 (UTC)


 * Evolution of cetaceans mentions nasal drift. | A ndonic O Talk · Sign Here 13:55, 25 January 2007 (UTC)

What happened to J. J. Sakurai?
I've been wondering for years (since reading Modern Quantum Mechanics) what happened to Sakurai. All sources that I have found merely say that he died suddenly while visiting CERN. Does anyone have any more information about this? I know it isn't really a Science question, but I expect that editors here would be more likely to know than anywhere else. --Philosophus T 01:04, 25 January 2007 (UTC)


 * I don't know the details of Sakurai's fate, but note that according to the article he wasn't really "visiting CERN" - he was a "visiting professor at CERN", which is a bit more permanent.  --bmk

Deleted Global Warming Graph
In September and October of 2006 Wikipedia showed a graph related to global warming and the hockey stick controversy. The graph portayed what was considered to be a reconstruction of surface temperatures before Mann's 1998 "hockey stick" graph. The graph was much more S shaped than the hockey stick shape. Is there any way I can find this graph again (or information about this graph) although it has been deleted from Wikipedia? -sk


 * On page 10. Not sure why it would be deleted since it's a government graph.  --Tbeatty 02:59, 25 January 2007 (UTC)


 * He's looking for an image which is no longer with the article which is not the "hockey stick" graph. My suggestion is to look through the archived versions of Hockey stick controversy, find a likely filename (if it has indeed been deleted), and then post it here. --24.147.86.187 03:01, 25 January 2007 (UTC)


 * IPCC reports and materials are not public domain. 128.32.95.83 03:18, 25 January 2007 (UTC)
 * Image:Temperature comparison.PNG was displayed in Global warming briefly. It is a copy of the one that is there now, only with more white space.  Is this what you were thinking? --TeaDrinker 07:05, 25 January 2007 (UTC)

physics help
"A 10g bullet is fired horizontally into a 300g wooden block initially at rest on a horizontal surface and becomes embedded in it. The coefficient of friction between the block and surface is (.55). The combined system slides 5.0m before stopping. With what speed did the bullet strike the block?"

I'm not asking for people to do this question for me. I'm just wondering if anyone can point me in the right direction, like an equation or something. Thanks in advance.


 * Conservation of momentum. It looks like the question isn't making any distinction between static and kinetic friction, so assume you should just treat the friction as kinetic.   -- mattb


 * Thanks but I can't find an equation fit to plug the numbers in


 * Having an equation does you no good if you don't know what it means. -- mattb


 * Could you explain it to me then?

Do your own homework and ask you teacher if you don't understand. The link given was adequate to solve the problem with only a basic knowledge of the physics behind it. Conservation of momentum. Deceleration. Coefficient of friction. Before and after mass. --Tbeatty 04:08, 25 January 2007 (UTC)


 * Harsh! You kind of need to work backwards in this problem to get the answer. Given the coefficient of friction, you will be able to work out the frictional force opposing the movement of the block (u = Ffriction/Fnormal). Thus, since you have the mass of the block-and-bullet, you can then work out the acceleration slowing the object down (from F = ma). So regarding the block-and-bullet combination, you have the acceleration, distance and final velocity (zero), and you want to find the initial velocity that it had. Use one of the one-dimensional motion equations. Once you find that, you can substitute this value into the conservation of momentum equation for an inelastic collision, as given on the page referred to above. Since you know the block was initially not moving, you can work out the speed of the bullet. --BenC7 06:39, 25 January 2007 (UTC)
 * (added a few references) bmk


 * I don't like the question: It seems to me we're missing some critical data necessary to provide an unambiguous answer. The question says a bullet is fired into a wooden block and becomes embedded in it. In other words, the bullet did an unknown amount of work blasting a hole into the wooden block (by crushing/pushing wood to the side), possibly distorting the bullet, etc. All that work is lost to the system and does not appear as impulse coupled into the wooden block. In other words, this is a very inelastic collision and I don't think we can make assumptions about the ratio of the energy spent machining the wood and the energy coupled to the wood as momentum.


 * But I suppose the teacher expects you to ignore that fine point :-(.


 * Atlant 12:54, 25 January 2007 (UTC)


 * Your assumption is correct. The verbiage seems typical of a high school level mechanics problem.  Also, I don't consider it harsh to try and make people think for themselves.  P.S. - Sure I can derive a plug-and-chug formula for the OP, but that doesn't make them think about the principles involved and in the end does them absolutely no service when they are tested on this knowledge.  You're welcome to provide whatever help you see fit, but I'd rather nudge a person towards an answer than give it to them. -- mattb


 * Physicists like to make simplifying assumptions to solve problems. There's the story of a physics professor who was asked to help with a problem of cows producing less milk than expected. He said he had a solution to the problem, and started by saying "First, I will assume a spherical cow...."Edison 19:06, 25 January 2007 (UTC)

Medicine and sneezes
Why does drinking cough medicine make people sneeze?


 * Probably because it has a relatively strong and volatile smell, so it might irritate the nose more than most things.--Shantavira 14:08, 25 January 2007 (UTC)

Energy density of a Supercapacitor...?
How many Farads per unit of volume or weight does a Supercapacitor need to have in order to equal or exceed the Energy density of Gasoline? -- 71.100.10.48 07:29, 25 January 2007 (UTC)
 * Just using the values from the Gasoline and Farad articles - remember not all gasoline is created equal! Regular Gasoline has 42.70 MegaJoules (MJ) per kg, and J=CV (J= Joules, C = Coulomb, V = Volt). So in a hypothetical 300 Volt system matching the energy in 1kg of regular gasoline, you would have 42700000/300 = 142 333.333 Coulombs of charge. And since F=C/V, 142333.333/300 = 474.444443. Thus you would need to be able to store approx. 474.4 Farads per kg of capacitor in a 300 Volt system to match the energy stored in 1kg of regular gasoline. As always it would be great if a real Physicist would check my calculations and method. :) --inksT 10:50, 25 January 2007 (UTC)


 * Even though not a real Physicist and did not sleep at a Holiday Inn last night I do seem to have this knack for putting equations into table form...

-- 71.100.10.48 12:49, 25 January 2007 (UTC)


 * However, as I mentioned above, you won't find an EDLC that can be operated at 300 V. 2.7 V is more typical, so you'll need something like 12 MF per kilogram to compete with gasoline (this isn't going to happen).  Also, the above calculations are off by a factor of 2.  The energy stored on a capacitor is
 * $$E_C = {1 \over 2} CV^2$$


 * If you notice on Maxwell technologies' site (an EDLC manufacturer), they cite one of their largest single-cell capacitors as having a maximum energy storage density of roughly 20.6 kJ/kg... More than three orders of magnitude below gasoline. If the energy storage capabilities of EDLCs were anywhere near that of fossil fuels, you'd probably see a lot more electric vehicles. -- mattb


 * Though, to be fair, you wouldn't need have an energy storage density nearly as high as gasoline to compete with the ICE drive train... Electrical motors are much more efficient than ICEs (if memory serves, about 80% compared to 20%), so even with conversion loss in the power inverter circuitry (which should be comparatively small), you can see that an electrical drive train should be much more efficient.  Still, you're going to at least be within the same order of magnitude to have comparable "fuel" weight.  Of course, here too you can usually get away with having a heavier capacitor bank.  Anyway, you can go on and on like this; there is a lot to be said about engineering an electrical (or hybrid) drive train that I'm not going to attempt to cover in a few sentences. -- mattb


 * Forget about energy density then and answer this: How many farads at 2.7 volts are required to equal the energy content of 1 gallon of gasoline? -- 71.100.10.48 17:15, 25 January 2007 (UTC)


 * I already gave you the energy density, just find the physical density (kg/gal) and do some multiplication. Just be careful about comparing the two figures; as I said the respective drive trains have varying efficiency so it's more useful to talk about usable energy output of the system than actual energy in the fuel. -- mattb
 * Where did you get the 12MF figure you used above? -- 71.100.10.48 20:56, 25 January 2007 (UTC)
 * or is this right...?

-- 71.100.10.48 21:09, 25 January 2007 (UTC)


 * I'm not sure what the table is supposed to mean... I assume your calculations derive from some series/parallel capacitor bank. My 12 MF figure is simple, just re-arrange the equation I gave above for the energy on a capacitor, plug in 47.2 MJ for E, 2.7 V for V, and solve for C.  You should definitely heed Edison's comments below, though. -- mattb
 * I find capacitors lacking as a power source for vehicles and airplanes, not only because of the high cost and low energy density per volume or per weight, but also because of the rapid decrease in the voltage they supply as they are discharged. This presents a real challenge to design electronics which can accomodate the decreasing output voltage of the cap and keep sufficient voltage going to the motors. Batteries have a decrease of voltage, but it is not nearly so dramatic as for capacitors. Caps are great for rapid storage and release of comparatively small amounts energy through millions of cycles, and at high voltages, but less appealing for longer term discharge to power a device. Edison 19:13, 25 January 2007 (UTC)


 * How about this? and this? -- 71.100.10.48 05:03, 26 January 2007 (UTC)

Ice/physics question
Suppose I have a unventilated room in which I place a quantity of ice. How is the quantity of ice related to the subsequent temperature drop? I am not a physicist, so please explain and make any necessary assumptions, such as for simplicity, assume the room is at room temperature. I do not know whether the quantity of ice's cooling effect is dependent just on the volume or the surface area of the quantity of ice. Could a physicist or air conditioning specialist give me an equation of some kind, perhaps? Thanks.


 * There are two issues to address:


 * The ice must be warmed to the room's temp, which requires heat energy, which is subtracted from the rest of the room. Owing to the greater density of water, and the thus greater thermal capacity, changing the temp of a given volume of water requires considerably more heat energy than the same quantity of air.


 * The ice must also undergo a phase change, from ice to water. This also requires heat energy, even if the temp remained the same (0C or 32F).


 * It works out that the ice can cool quite a large volume of air considerably, for a long period of time, as long as the walls are well insulated. This is why the icebox, the predecessor of the refrigerator, worked.  A block of ice would be delivered and placed in the icebox, and would chill the air and contents until the next block of ice was delivered.  That's a bit before my time, but I believe they delivered ice once a day.  The total cooling is related only to the volume of ice, although the surface area would be important in determining how quickly the ice melts and lowers the temp of the room. StuRat 08:57, 25 January 2007 (UTC)

See the article on Refrigeration. -- 71.100.10.48 09:32, 25 January 2007 (UTC)


 * Assuming that the ice is colder than the room's initial temperature, the room will be cooled by three methods (in sequence):


 * Initially, the ice absorbs 1/2 calorie per gram per degree C change in the temperature of the ice as the ice warms up to the freezing point.
 * Then, as the ice melts, it absorbs 80 cal/gm as a result of its heat of fusion. The ice/water puddle remains at the freezing point until the last bit of ice melts.
 * Once the ice is fully melted, the water puddle that remains absorbs 1 cal/gm per degree C change in the temperature of the puddle until it reaches the (new) ambient temperature of the room.
 * Meanwhile, of course, the room is gaining or losing heat to the exterior world.


 * Atlant 13:07, 25 January 2007 (UTC)


 * Those are great answers. Thanks. To finish, I'm just curious how one would obtain a degree Celsius change from the calorie values you mentioned.


 * Atlant, did you mean to write "the ice absorbs 1/2 calorie per gram of ice per degree C as the ice warms up"? Similarly for the warming after melting. Skittle 15:55, 26 January 2007 (UTC)


 * Yes -- thank you. I'll edit that in. Please imagine the sound of my hand slapping my forehead.


 * Atlant 18:17, 26 January 2007 (UTC)


 * Per Sturat's comment about the icebox: The block of ice was delivered on demand. Each house or apartment had a square cardboard sign about 1 foot square. It have 3 symbols, for no ice, or 3 increasing quantities, which the iceman would carry up the stairs with icetongs. The symbol turned upwards told the iceman what to do and was clearly visible from the street. A block of ice might last 1, 2, or 3 days depending on how much was chipped off to put in drinks, how hot the kitchen was, how many times the icebox door was opened, and how much warm food was placed in the box. Food such as vegetables stayed fresh longer than in today's refrigerators, because the moisture did not migrate to the freezer compartment and get removed by the self defrost cycle. Someone had to be at home when the iceman cometh. Edison 04:43, 26 January 2007 (UTC)


 * How to work out the temperature of the room
 * Okay, this is how I would go about solving the problem (similar to Atlant, but with Joules rather than calories, and telling you how to do it).
 * There will be three stages to this. First the ice will warm up to freezing point, then it will melt, then it will warm to the same temperature as the room. All these stages will transfer heat from the room to the ice/water.
 * The information that you will need is:


 * 1) The Specific Heat Capacity of the ice, the water and the air in the room. This tells you how much energy is needed to raise the temperature of a specific amount of a substance, or how much is used in cooling it.
 * 2) The mass of ice used, and the mass of air in the room.
 * 3) The starting temperature of the ice and the room.
 * 4) The Latent heat of the ice melting.


 * The specific and latent heats can be found at the articles I linked to.


 * We will be using two equations. The first can be used to find out how much energy is involved in heating or cooling something.
 * Q = m c ΔT
 * In this equation, Q = Energy in joules (J), m = mass in g, c = specific heat capacity in J g−1 K−1 (joules per gram per Kelvin), and ΔT = change in temperature, in K (Kelvin), where a change in temperature in Kelvin is the same as a change in temperature in centigrade.


 * So, from this, you can work out how much heat energy goes into your ice to warm it up to melting point. You know the change in temperature (from your ice starting temperature to 0oC), you know the Specific heat capacity of ice (solid water) (2.114 J g−1 K−1), you know how much ice you have (in grams). So you plug these numbers in, times them together, and get a value for the amount of energy needed. Then you can use this to work out how much this has cooled your room.


 * According to our article, Density of air, at sea level and at 20 °C dry air has a density of approximately 1.2 kg/m3. So if you know the volume of your room, you can work out the mass of air in it by timesing the volume in cubic metres by 1.2: this will give you a mass in kg. As you remember, we're working in grams, so it would probably be best if you timesed the mass in kg by 1000, giving you grams. Now you rearrange the equation above to leave the ΔT alone, since this is what you want to work out for the room. You know the same amount of heat that went into the ice to warm it up had to come out of the room to cool it down. So your Q is what you worked out for the ice, your m is the mass of air in the room in grams, and your c comes from the Specific heat capacity article (1.012 J g−1 K−1). You work out the change in temperature by dividing Q by mc (mc meaning the mass and specific heat capacity timesed together). The temperature change you've just worked out is how much cooler your room will have got, so take it away from the starting room temperature.


 * Now you have a block of ice at 0oC in a room at a temperature you've just worked out. You now need to know how much energy the ice uses to melt. When it is melting, the ice won't be getting any warmer, but it will be cooling the room. This is because heat energy form the room is being used to break down some of the bonds in the ice to melt it. The equation we will need to work out how much energy the ice needs to melt is:
 * Q = m h
 * Where h is the Latent heat for melting ice, which that linked article tells us is 334 J/g. As you can see, because the ice isn't changing temperature, the energy required for melting only depends on how much we have. So you multiply the mass of ice in grams by the latent heat, and that gives you the energy required to melt the ice. Using that information, just like earlier, you can work out how much colder that makes the room. (using the first equation again, not this second equation!)


 * So now you have a puddle of water at 0oC in a room that you've worked out the temperature of. This is where it gets tricky. While the room is cooling, the water is warming up. The heat will continue to move from the air to the water as long as the water is colder than the air. The simplest way for you to work out what temperature they both end up at is by trial and error. First work out how much energy it takes to warm the puddle of water from 0 to 10oC. This is just like when you worked out how much energy was used to warm the ice, except now your change in temperature is 10 (10 minus 0), and the specific heat capacity that you will be using is the one for liquid water (4.1813 J g−1 K−1). Now work out how much cooler the room would be if it had that much less heat energy, just like you did with the warming ice. Now look at what temperature that would make the room. Is the room still warmer than the 10oC the water would be? If the room is colder than the water, try again but with the water only getting half as warm. If the room is warmer than the water, see how cool it would get if the water was warmed further, perhaps by 5oC. If you keep going with this process, you should eventually get to an answer with the water and the room at about the same temperature.


 * All this, of course, assumes that the room is perfectly insulated and sealed, and that the specific heat capacities don't change with temperature, but that seems reasonable enough for your purposes.


 * Let me know if this is all too confusing, or if you have a specific problem. Skittle 16:59, 26 January 2007 (UTC)


 * Allow me to check my progress for the first two parts of the problem.
 * Let $$m_\mathrm{ice} = 1000\ \mathrm{grams}\,$$ be the volume you mean 'mass'. Skittle 17:23, 27 January 2007 (UTC) of ice, so $$c_\mathrm{ice} = 2.114\ \mathrm{joules}\,\mathrm{grams}^{-1}\,\mathrm{kelvin}^{-1}$$ and assuming the freezer has the ice at -18 degrees Celsius, this means $$\Delta T_\mathrm{ice} = 18\ \mathrm{kelvin}$$.
 * Thus $$Q_\mathrm{ice} = m_\mathrm{ice} c_\mathrm{ice} \Delta T_\mathrm{ice} = 38052\ \mathrm{joules}$$.
 * Let $$D_\mathrm{air} = 1200\ \mathrm{grams}\,\mathrm{meters}^{-3}$$ be the density of air, and assume the room is five meters cubed in volume, so $$m_\mathrm{air} = 5^3\ \mathrm{meters}^3 \times D = 150000 \mathrm{grams}$$; then $$c_\mathrm{air} = 1.012\ \mathrm{joules}\,\mathrm{grams}^{-1}\,\mathrm{kelvin}^{-1}$$.
 * Thus $$\Delta T_\mathrm{air} = Q_\mathrm{ice}/(m_\mathrm{air} c_\mathrm{air}) = 0.250672\ \mathrm{kelvin}$$.
 * Let $$h = 334\ \mathrm{joules}\,\mathrm{grams}^{-1}$$, so $$Q_\mathrm{water} = m_\mathrm{ice} h$$.
 * Thus $$\Delta T_\mathrm{water} = Q_\mathrm{water}/(m_\mathrm{air} c_\mathrm{air}) = 2.20026\ \mathrm{kelvin}$$.
 * So far, now, $$\Delta T_\mathrm{total} = \Delta T_\mathrm{ice} + \Delta T_\mathrm{air} + \Delta T_\mathrm{water} = 20.457\ \mathrm{kelvin}$$.
 * Is this correct so far?


 * I'm seeing a bit of confusion, although your maths is mostly correct. Where I've marked, you mean the mass of ice, not the volume. Then, when you've written "assume the room is five meters cubed in volume" (that would be a very small room), what you've presumably meant is "assume the room is a cube with sides of 5 metres each", meaning it's 125 metres cubed in volume. But your maths there is fine. Where you've gone a bit wrong is right at the end.

$$\Delta T_\mathrm{total} = \Delta T_\mathrm{ice} + \Delta T_\mathrm{air} + \Delta T_\mathrm{water} = 20.457\ \mathrm{kelvin}$$.
 * Now, I don't know why you've tried to add these up. The change in temperature of the ice is how much the ice has warmed up. The two changes in temperature of the air are how much the air has cooled down. What you want to work out is the current temperature of the air in the room. So, you know the room has cooled by 0.250672 degrees, then it cooled by another 2.20026 degrees. That means the room has cooled by 2.45 degrees while the ice heated up by 18 degrees and then melted. So, if your room started at 25oC, it is now 22.55oC. Make sense? Skittle 17:23, 27 January 2007 (UTC)


 * Yes. Thanks :) Now I will have to figure out the third part of your explanation, which requires a bit of close attention. But what you have provided has been most helpful.

Economisers for steam bouilers
Any idea if we could remove the extra heat from the expanded steam coming out of the turbine by condensing it to water and return that heat to the water being boiled in the boiler would make it more efficient than it already is?
 * See Thermal power station. You can have combustion air preheaters, and boiler feedwater preheaters. --Zeizmic 12:49, 25 January 2007 (UTC)


 * They were doing this at power plants long before World War 1. Edison 04:35, 26 January 2007 (UTC)

Interglacials
I understand that in the past it was thought that interglacial periods were quite regular, lasting for 10,000 years each. Obviously it's been more than 10k years since the last ice age, and New Scientist magazine tells me (Histories: The ice age that never was, issue 2582, 15 December 2006): The planetary wobbles that periodically tip the world into ice ages are not identical, so some interglacial periods last longer than others. Good theoretical work now shows that the current one is likely to be unusually long. But they give no references for that statement (it appeared in one of their "Histories" sections where they never break up the story with references). I was wondering how long our current interglacial is expected to last - is "unusually long" 20k years? 100k? 15k?

--Psud 11:48, 25 January 2007 (UTC)


 * Actually, don't worry about this, I found the answer in Ice age - somewhere in the region 28k - 50k years.

--Psud 12:27, 25 January 2007 (UTC)


 * I wouldn't say they are regular, but there is an apparent pattern. X [' Mac Davis '] ( How's my driving? ) 14:26, 25 January 2007 (UTC)

Strange noise from a lightbulb
What's the mechanism where a soon-to-be-dead lightbulb generated a high-pitched sound? I heard a loud, steady high-pitched whine last night from a light bulb in my utility room. Some checking verified that the sound was definitely coming from the light bulb, and not from anything else in the room. Finally, when I turned the light switch off, the sound stopped. Then, when I turned the switch back on, the light failed to come on. It did not flash in the usual way a lightbulb makes a bright flash just before it burns out... it just did not turn on.

So clearly the lightbulb had suffered a failure, but was still able to generate light, and along with the light, a high pitched whine. I'm guessing the filament had separated, then just barely re-joined... and that had something to do with producing the noise. Maybe the 60hz. line frequency causing the filament to vibrate? Does that sound plausible? 71.112.10.12 13:32, 25 January 2007 (UTC)


 * I can't find anything scientific on this. There is a lot of material on filament vibration caused by cheap dimmers.  It's due to the 60 Hz AC being chopped up into square waves, and the filament picks up on this, like a guitar.  Near failure, I suspect that a filament starts chopping the AC, due to intermittent contact. --Zeizmic 14:43, 25 January 2007 (UTC)

Note that 60Hz would be a low pitched sound, not high pitched. I suspect some other type of oscillation was happening, like intermittent electrical contact with a part in the base. StuRat 16:54, 25 January 2007 (UTC)


 * Some of the light bulbs in my house whine, and I suspect it's because they're on a cheap dimmer, though I haven't verified this. (The presence or absence of a cheap dimmer, of course, has nothing to do with the bulb burning out right after the Original Poster noticed the whine.  That part I can't explain, although it might be a coincidence or a red herring.)  That dimmers can cause whine is confirmed in our dimmer article.


 * The whine from a cheap dimmer would be expected to be considerably higher than 60 Hz, because the whine is not due to the 60Hz base sinewave, it's due to the harmonics you get when the 60 Hz sinewave is chopped by the dimmer, and not adequately filtered. (All it takes to filter it is a choke, which is a cheap, low-tech component, but if you're a really cheap manufacturer...)


 * Here's what a basic dimmer does to a sine wave:


 * [[Image:Dimmer.gif]]


 * If you did a Fourier transform on this waveform, you'd find lots of high-frequency overtones resulting from the sharp corners where the sine wave is clipped off by the dimmer. —Steve Summit (talk) 03:38, 26 January 2007 (UTC)

Note that you may want to specify what type of lightbulb. There is a difference between incandescent light bulbs and fluorescent light bulbs. Fluorescents are known for making high pitched noises, especially when a cheap/poorly working ballast is used. -- 17:34, 25 January 2007 (UTC)


 * I'd say "light bulb" normally means incandescent; fluorescents are known by other terms. In any case, incandescent lamps do sometimes sing just before failing, in the manner the original poster describes.  And I once saw one fail explosively after doing it -- a piece of the filament punched right through the bulb and a glass fragment landed several feet away, apparently having been moving at around 10-15 mph.


 * Another failure mode you get sometimes is that the filament breaks and the broken ends fall together and make contact with a shorter path, so the bulb burns brighter than normal for a little while before it fails. I suggest that the singing effect happens when it doesn't make contact quite so solidly and the thermal expansion of the filament as it lights up causes it to break contact, and this repeats many times a second.  But that is only a guess. --Anonymous, January 25, 16:04 (UTC).


 * I've seen this "brighter burning" effect before, and I thought I must be caused by a shorted filament. Later I found out that this is an electric arc, and that incandescent bulbs are filled with Argon at low pressure.  Pure argon can support very long arcs at fairly low voltage, so if the filament broke in a bulb with pure argon, an electric arc would appear between the broken ends.  When this happens, the normal yellow/white emission appears much brighter, and colored blue-white.  Manufacturers try to eliminate this effect by mixing in a bit of nitrogen which poisons the "long arc" effect.  Note that the arc is fantastically hot, and if allowed to continue for long, it can pressurize the bulb and cause explosions.  So...  if the ends of the broken filament remained very close together, a small electric arc might persist until power was temporarily removed.  But I don't know why such an arc would make a noise.  Perhaps the nonlinear effects in the arc act as a Parametric oscillator/amplifer which amplifies any small motions of the broken filament and causes the filament to vibrate at a natural resonance.  Not only would the filament emit sound, but the arc itself might behave as a Plasma arc loudspeaker.  --Wjbeaty 01:58, 26 January 2007 (UTC)


 * Good catch- yes, it was an incandescent bulb (60W, 120VAC). It was installed base up, and did not seem to be operating any brighter than normal in the time it was making the sound.  As to the sound, it reminded me of when I was much younger, and could hear the high-pitched whine of a television flyback transformer.  71.113.114.81 00:09, 26 January 2007 (UTC)


 * I do not believe that arcing has any role whatsoever in a filament emitting a tone. During one cycle, the filament heats up and cool off twice, so it might be a multiple of 120 Hz. They are basically long helixs of tungsten, like  a tiny Slinky, so they could vibrate at a multiple of the exciting frequency, due to the expansion and contraction twice per cycle. I believe lower wattage filaments have less thermal inertia and might be more subject to the heating/brightness variation during the cycle, since they take longer to become dark when turned off.   It would be interesting to do high speed photography of one to see what its vibration mode was. When the "Mazda" or tungsten filament was introduced in the early 20th century, people learned that they could sometimes weld an open filament back together by flicking the bulb gently (do not try this at home under any circumstances, especially without eye protection and adult supervision). I repaired a burned out expensive decorator bulb this way and it worked for another year. Carbon filaments did not have this capability. If light bulbs are supplied with Direct Current they hardly ever whine or even grumble. I have some ancient carbon filament bulbs, and I have never heard them hum or whine even on AC. Edison 04:32, 26 January 2007 (UTC)


 * Great discussion, thanks for all the comments! I attempted to open the light bulb (er, smash it) and examine the filament.  I was as careful as I could be (and wore eye protection) but the filament separated from the lead-in wires and so I couldn't really see any evidence of a break that had welded back together (and it was a frosted globe, so I couldn't see inside without ope- smashing it). 71.112.114.63 18:00, 26 January 2007 (UTC)


 * The tungsten spiral is usually supported by wires. Depending on the manufacturer's preference and the wattage, there might be a support midway of the filament or 2 supports each about 1/3 of the way. Like any other vibrating string, these may create nodes and antinodes and greatly influence the predominant frequencies of vibration. I believe I have noticed the bulbs singing more when the current is from an electronic dimmer. I expecet that different brands of bulb might differ in their susceptibility to this. It can certainly be annoying. Edison 18:04, 26 January 2007 (UTC)

Ah... the filament was supported by three rigid wires, each one having a loop that encircled the filament. The bulb was on an switched circuit with no dimmer. I do have a couple circuits on dimmers- one has an incandescent bulb that has never made a sound, and the other is a dimmer built in to a halogen floor lamp... it makes a noticeable buzz that grows louder the more the dimmer is turned down to dim the light. 71.112.114.63 23:58, 26 January 2007 (UTC)

Appeal to restart the improvement process at physics
As you might know, there has been a slow article improvement process ongoing for the last few months at Talk:Physics/wip. One of the tasks understaken was a "vote" on several proposed leads for physics at Talk:Physics/wip/leadvote. However, the process has ground down to a halt. We need input and possibly a moderator to assist us.--Filll 15:30, 25 January 2007 (UTC)


 * Have you contacted the Mediation Cabal or WP:AMA? | A ndonic O Talk · Sign Here 15:42, 25 January 2007 (UTC)

First Time in Outer Space
I am assuming that in the next ten years or so, there will be regular civilian flights into our Earth's orbit. My question is what does the average human being have to look forward to on their first trip? i.e. nausea, etc

Hello,

Thanks, for your question. The answer for your question i found on a different website... this was a message from a DJ in Pack 791 to Commander Altman. If you would like to know more about space flight and what they do in space please visit this site... Click here to learn more!

From: D.J. Lake, Virginia Beach, Va., Age: 8 To: Commander Scott Altman

Question: I'm a Cub Scout with Pack 791, Den 8. Tonight, we are doing a sleepover at the Air & Space Museum in Hampton, Va. My question is what does it feel like being in space, and how would you describe the takeoff? Someday I hope to become a pilot to fly jets.

Altman: Well, DJ, it's a very interesting feeling floating in space, here on the flight deck, as we are working outside. In some ways, it makes working a lot easier -- we can move heavy equipment really easily. But on the other hand, you don't have your feet on the ground. It would be like moving into your house without being able to walk. You have to use one hand to balance yourself and the other hand to hold onto the equipment and another hand to translate. You find you run out of hands sometimes.

But we love being up here. It's beautiful looking back at the Earth. Takeoff was an incredible experience as clouds lit off and we just exploded into the sky. It was really a tremendous feeling of acceleration. I give you all the best, hope you become a jet pilot someday. I loved flying jets my whole career, and then onto the shuttle. So good luck to DJ.

This message was contributed by: Jdswebservice 16:47, 25 January 2007 (UTC)jdswebservice

I was thinking in terms of physical changes to the body. What does the average human being (with no flight or space training) should anticipate?


 * Possibly strong g-forces should definitely be anticipated. Its an interesting feeling weighing half-a-ton for a few seconds, can also be a bit painful.  As you described as well, nausea due to weightlessness can also be a factor. Cyraan 18:01, 25 January 2007 (UTC)


 * See space sickness. --Robert Merkel 01:43, 26 January 2007 (UTC)

Oceanography and Marine Biology
What is the average salary for a marine biologist who actually goes into the water with animals? What is the salary for Oceanograhpers that go into the water and take pictures of animals? I know it`s not really a science question, but since it was about science I put it here. I really need to know. I am hoping to pursue a career in one.


 * The real answer should be, choose because you want to do it, not because it pays. --Wirbelwind ヴィルヴェルヴィント (talk) 01:28, 26 January 2007 (UTC)


 * This webpage provides some info for the USA. Rockpock  e  t  07:01, 26 January 2007 (UTC)

Energy density of compressed air...?
If 20 bar = 290.075475 pounds per square inch and compressed air has an energy density at 20 bar of 270 KJ/Kg and a lead acid battery an energy density of only 72-90KJ/Kg why compressed air is not used in place of a battery to store energy in a vehicle? -- 71.100.10.48 17:34, 25 January 2007 (UTC)
 * You need to compare the density of compressed air and a battery - the compressed air is less dense and takes up a lot of volume.83.100.254.239 17:42, 25 January 2007 (UTC)


 * If you look at this webpage about halfway down (dated June 9th I think) it has some coherent arguments as to why it isn't all that simple.--Neo 17:44, 25 January 2007 (UTC)

Vehicles powered by compressed air have been built. Paris had a whole fleet of compressed-air streetcars (trams) that operated with reasonable success from 1894 to 1917 1914. Their storage cylinders totaled 95 cubic feet and held 530 pounds (weight) of air at 80 atmospheres. Conventional cylinders as on steam locomotives were used to drive the wheels, but the air first had to be heated using a small fire so they wouldn't freeze up as it cooled on expanding. The trouble was that the vehicles had limited range: recharging stations had to be established at the ends of each route, and I think some long routes needed an intermediate recharging point too. Compressed-air locomotives were also used at one time in industries such as mining where a compressed-air supply was already provided for other purposes and the distances to be traveled were short.

--Anonymous, January 25, 2007, 18:16 (UTC), corrected 20:05.


 * It is my understanding that a compressed air vehicle would be quite practical if it weren't for the unavoidable safety issue - if a compressed air car crashed, it would almost invariably weaken the air tank and explode violently. But I don't have any sources for that.    --bmk


 * The figure for energy density of compressed air may be omitting the tank in which it is stored and the valve, gauge, tubing needed to control it. A better comparison would decrease the energy density to reflect this. I have used compressed gases at far higher pressure, and I suspect the energy density (and the explosion hazard) gets higher at higher pressure.See Compressed air energy storage. I have seen the energy of compressed air used to start utility peakers, which are basically aircraft jet engines. A blackstart peaker unit (intended to be the first 20 megawatt generator started after a total grid blackout) had a compressed air tank which stored enough energy to spin it up to speed 3 times without electricity. High pressure compressed air also works nicely to operate high voltage circuit breaker mechanism. In both cases, noisy as hell. Even 30 years ago, researchers built hybrid cars which used compressed air and hydraulic fluid to start the gasoline engine and to store energy from regenerative braking.  Energy stored in compressed air can be released or stored far more rapidly than can the total energy stored in a battery.  So functionally, compressed air is an energy storage device which can be used interchangably with batteries in many applications, especially when the system must absorb or release energy rapidly. For other possible non-fuel and non-battery energy storage systems, see also Flywheel energy storage and Superconducting magnetic energy storage. For those who are nostalgic for bygone days, there is always the winding and unwinding of a spring.Edison 19:43, 25 January 2007 (UTC)

Global Warming
Assuming one degree fa. increase in global temperature, how much additional plant growth would result, and as a result of this increase how much more CO2 would be converted to oxygen by photosyntheses? Wouldn't such an increase decrease levels of CO2 and over time reverse global warming?Bovinus 17:43, 25 January 2007 (UTC)Bovinus


 * We really don't know. Any guesses out there are almost less than guesses. The climate is a complicated thing. It seems likely that there would be more plants, converting more CO2 into O2, however the textbook definition of how the carbon cycle works is not that easy and there are many more factors to include. An excellent discussion on this is found here. X [' Mac Davis '] ( How's my driving? ) 23:41, 25 January 2007 (UTC)

While some areas now covered with snow may become fertile, other areas now fertile may become desert. Thus, it's not clear that more plants would grow. StuRat 09:39, 26 January 2007 (UTC)

Magnetic Resonance Imaging
In trying to understand how MRI's work, I discovered that the wikipedia article on the subject is a bit dense. I would like to try and rewrite the physics aspects of the article so that it might be a bit more accessible to non-physicists. But, I still don't understand the physics myself. I posted the following message to the MRI talk page, but it doesn't seem to get much traffic. The following is a disection of Wikipedia's mri article section called 'Principal'. Any and all feedback greatly appreciated:

Medical MRI most frequently relies on the relaxation properties of excited hydrogen nuclei in water and lipids. Does the MRI work only with hydrogen atoms? Does it work only with hydrogen atoms in water and lipids? Are there any hydrogen atoms in a human (or other things commonly scanned) which are not contained in water or lipids? (i.e., could this be changed to state simply it relies on relaxation properties of hydrogen nuclei (or perhaps any nuclei with net non-zero spin)?

When the object to be imaged is placed in a powerful, uniform magnetic field, the spins of atomic nuclei with a resulting non-zero spin have to arrange in a particular manner with the applied magnetic field according to quantum mechanics. Hydrogen atoms (= protons) have a simple spin 1/2 and therefore align either parallel or antiparallel to the magnetic field. My understanding of spin is a little rusty; "with resulting non-zero spin" - what does the word 'resulting' mean here? The spin is created as a result of applying the magentic field? Any given proton may obtain either spin 0, 1/2 or -1/2? Is the direction of alignment (parallel/antiparallel) arbitrary or a result of some other property of the proton which will precisely determine the direction (+ or - spin)?

Common magnetic field strengths range from 0.3 to 3 T, although field strengths as high as 9.4 T are used in research scanners and research instruments for animals or only small test tubes range as high as 20 T. Commercial suppliers are investing in 7 T platforms. For comparison, the Earth's magnetic field averages around 50 μT, less than 1/100,000 times the field strength of a typical MRI. Is this paragraph appropriate/needed in the principal section?

The spin polarization determines the basic MRI signal strength. For protons, it refers to the population difference of the two energy states that are associated with the parallel and antiparallel alignment of the proton spins in the magnetic field and governed Boltzmann's statistics. Is this saying that spin polarization is the integral difference in protons in one state versus the other? So, if I have 500,001 protons that are parallel and 500,000 protons that are antiparallel then my spin polarization is 1? What is Boltzmann's statistics and what does that have to do with the calculation of spin polarization? What is the cause for the descrepancy; is it arbitrary or is it a result of some fundemental property of protons?

In a 1.5 T magnetic field (at room temperature) this difference refers to only about one in a million nuclei since the thermal energy far exceeds the energy difference between the parallel and antiparallel states. Yet the vast quantity of nuclei in a small volume sum to produce a detectable change in field. The thermal energy causes protons to switch between parallel and antiparallel? (which seems to argue that the state is arbitrary) If the selection of parallel and antiparallel is arbitrary than each "small volume" would statistically cancel out each other "small volume" (since that would not be helpful; seems to argue that the selection isnt arbitrary and must favor either parallel or antiparallel statistically.  If so, why?)  '...detectable change in magnetic field...'?

Most basic explanations of MRI will say that the nuclei align parallel or anti-parallel with the static magnetic field though, because of quantum mechanical reasons, the individual nuclei are actually set off at an angle from the direction of the static magnetic field. The bulk collection of nuclei can be partitioned into a set whose sum spin are aligned parallel and a set whose sum spin are anti-parallel. This is describing the heisenberg effect? Each proton could never be precisely in a specific alignment, but simply has a probablity cloud of alignments which is centered along the magnetic field? If thats the case then there is a certain probablity that a given proton is precisely aligned with the magnetic field and the probablity cloud is statistically parallel with the magnetic field? Can be partitioned theoretically or is partitioned in practice during the scan?

The magnetic dipole moment of the nuclei then precesses around the axial field. While the proportion is nearly equal, slightly more are oriented at the low energy angle. The frequency with which the dipole moments precess is called the Larmor frequency. Ok, starting to get really lost... Is this saying that similar to -- electron orbitals around a nuclei--, the proton's axis has multiple quantized "orbitals" which effect the probablity cloud of its angle of incidence with the magnetic field? Ok, all my previous theories start to breakdown when adding that the proton precesses at a specific rate. And the angle of incidence with the magnetic field is a function of energy level. Perhaps the higher level orbitals are donuts centered around the magnetic field which allows for a specific frequency, but then it seems that the 0 level orbital should still have no frequency (and should still include the magnetic axis itself). ...the proportion is nearly equal... Proportion of 0 level to 1 level? Why would it be nearly equal? Why are the protons in the level 1 state at all? Aren't there states above level 1? Larmor frequency is specific to the level 1 state or all states precess at the same frequency?

The tissue is then briefly exposed to pulses of electromagnetic energy (RF pulses) in a plane perpendicular to the magnetic field, causing some of the magnetically aligned hydrogen nuclei to assume a temporary non-aligned high-energy state. Or in other words, the steady-state equilibrium established in the static magnetic field becomes perturbed and the population difference of the two energy levels is altered. The frequency of the pulses is governed by the Larmor equation to match the required energy difference between the two spin states. Is the EM applied from a single direction or radially? The EM waves hit the protons and move them from level 0 to level 1? How are the states measured; photons created when the proton relaxes and released in a random direction as opposed to the original direction of the source beam? What does that information tell one about the material being scanned? What is really being measured; proportion of hyrdrogen atoms at every given location? Different regions are detected by measuring intensity of photons detected bouncing randomly? I have no idea how far off from reality I am at this point, but if that's the case how does measurement work in 3D?

Anyway, I'm sure I'll have more questions and if this goes well I'd like to try and tackle the k-space section also. Aepryus 18:02, 25 January 2007 (UTC)


 * Hmm - that's a lot of questions. MRI is a pretty involved topic, and I don't think you'll get far without reading a lot of more basic material that makes up the technique.  I'll try to answer some of the questions and reference you to pages that you could read to understand nuclear magnetic resonance better.  First of all, as you can see from the MRI article, there are many different variations on MRI technology which are used to image different aspects of a sample, but I'll go over the basics.  The first article you should read is quantum spin, which should clear up many of your question.  You could also take a look at a somewhat poor article on spin 1/2, and at another poor article on the Bloch sphere, which is an essential theoretical tool for understanding NMR.  Speaking of which, Nuclear Magnetic Resonance is the basic theory, and the article is decent - you should read the "Theory of nuclear magnetic resonance" section.
 * Ok. Here's the basic idea.  Protons are spin 1/2 particles, meaning they are a two state quantum system.  That is, you can find only two orthogonal eigenstates, and the proton will be in some superposition of the two eigenstates.  For instance, $$ /sqrt{2} (|z+>+|z->)$$ is an equal superposition of the eigenstate in the positive z direction and the negative z direction in the basis of the z-direction eigenstates, and $$ |x+> $$ represents a proton only in the x+ direction eigenstate.  The idea behind the Bloch sphere representation is that any superposition of eigenstates can be represented by a vector in space which represents the direction of the magnetic moment of the spin (each spin produces a magnetic field like a little bar magnet).  In the absence of an external magnetic field, your choice of basis is arbitrary - there is no eigenstate with more energy than any other eigenstate.  However, when you apply a magnetic field (say, in the z direction), the z+ eigenstate gains a higher energy than the z- eigenstate.  It is the peculiar property of a 2-state quantum system that when it is put in a superposition of the energy eigenstates, it precesses.  I am amazed that we don't have an article on spin precession - perhaps I'll write one.  In the Bloch sphere geometrical representation, that means if you point the spin off axis, it will spin about the magnetic field axis at the larmor frequency.  Now:  the idea behind NMR.  If you have a bunch of these proton spins in a magnetic field, then you zap them with a circularly polarized RF pulse at the larmor frequency, then an interesting thing happens.  Imagine a small magnetic field component (the RF pulse) rotating with the precessing spins at the larmor frequency.  The spin sees a small constant magnetic field perpendicular to it (the RF field in it's rotating frame), and precesses about it.  The result is a spiral down the Bloch sphere which, depending on the duration of the RF pulse, can put the spin at any latitude on the sphere.  Once the spin is precessing at a nonzero angle to the z-axis, it acts like a little antenna, and can be detected by placing an induction coil around the sample.  Thus, you can zap the sample, then detect a response.
 * How do you use this for imaging? That is another very long story, and you'll have to do some reading before you'll understand the fourier space idea.    -bmk

Mesotherapy is it safe?
Does anyone know anything about Mesotherapy? Is it safe? What is in the injections? Does it really reduce cellulite? It is done in South America all the time, and some people really swear by it. 72.153.91.215 18:05, 25 January 2007 (UTC)Tawney


 * We've got an article in mesotherapy which states that there are a variety of chemicals used in the injections but ultimately surmises that mesotherapy probably doesn't even work. Sorry. --Seans Potato Business 18:19, 25 January 2007 (UTC)

Commercial vs Academic Scientific Research
I'm writing a letter for my university application (MSc) which must include a statement of my career plans. All I really know is that I want to contribute to research in the field of gene therapy (development of certain molecular tools and vectors interest me). I expect that a PhD would be the next logical move after an MSc, perhaps at the same university to which I'm writing this letter. After that, how do I know if I want to stay in academic or go to commercial research? Should I even care? My limited understanding is that academic researchers are under pressure to churn out lots of little journal articles whilst a company is more likely to undertake a very large project with the ultimate goal of a viable product. How often do companies even publish results? Just enough to elicit some interest? I imagine their main greedy scheme is to keep all the information to themselves :) --Seans Potato Business 18:12, 25 January 2007 (UTC)
 * Academic research vs. industry research is a decision that many of us scientists wrestle with...Here's a short list of things I've found typify the situation, at least in the US of A:
 * Academic PROS: greater freedom to pursue research paths, often higher job satisfaction, college towns
 * Academic CONS: less pay, always looking for new funding--grant-writing takes up a lot of time for lab heads, at the whims of national/state/department funding patterns
 * Industry PROS: much more money, more like a 40-hr week job (academics often work well beyond 40/wk), directly working on clinical applications
 * Industry CONS: you research what the company says to, limited publications, "big business" feel, more limited jobsite locations
 * Also, you should weigh your interest in teaching, university administative work vs. climbing up in a more business-like environment. It's important to weigh intellectual freedom vs. your earnings. One thing to consider: you can always try a post-doctoral research position in industry and feel out whether you like it better than academia. -- Scientizzle 21:13, 25 January 2007 (UTC)


 * That's a great list. I'd also add that many tenure academic professor-ships offer a six-month/one-year paid sabbatical every 5+ years.  --Cody.Pope 01:46, 26 January 2007 (UTC)


 * Adding to that list - academic scientists have a wonderful chance to travel and work internationally. Industry slightly less so. Rockpock  e  t  05:11, 26 January 2007 (UTC)
 * Those are great additions. Tenure is definitely a good thing to have. Also, a Ph.D. isn't as necessary to have a comfortable, successful career in industry, but no doctorate will severely limit academic research options to basically high-level tech positions. -- Scientizzle 18:37, 26 January 2007 (UTC)

One more important point: universities are often reluctant to spend money on doctoral students that openly seem willing to dump academia as soon as they get a degree. It's a subtle bias, but it's there. It costs a lot of money to keep a Ph.D. student around for 5-6 years (since they usually pay the student a stipend + tuition & benefits), and there's a general institutional idealism that wishes to see that investment repaid within the same system--later academic work as post-docs & faculty. (As for master's degrees, I'm not sure what the opinions are there, but since MS students often pay their own way, there's probably less of that idealism...) Whether you're sure or unsure of your future desires, it's probably pragmatic to emphasize any interest in academic research you hold over industry goals. -- Scientizzle 18:48, 26 January 2007 (UTC)

Determining the therapeutic index of a drug
How do I find the therapeutic index of a specific drug? I understand that it is the ratio of the LD50 to the ED50, but I can't find those numbers for specific drugs on the FDA website. Thanks,

-- Creidieki 18:12, 25 January 2007 (UTC)


 * A Physicians' Desk Reference will give you that information. Your library or local bookstore conglomerate will have one (I believe the current edition is the 61st). tucker/ rekcut 22:42, 25 January 2007 (UTC)

Future Human Evolution
In your most scientific opinion, considering that all environmental, technological and social surroundings remain relatively the same as today, what would a human being look like say in 1000 years? 5000 years? 20,000 years?


 * People may be increasingly designed rather than their genome left to chance as now. So far we have varied from our ancestors due to random variation and natural selection, and have changed slightly (skin color, for instance) in the last several millenia, and more dramatically over the last tens of thousands of years. So the question is, what sorts of people will be designed in 1,000 years? Consider what people look for when they select egg donors. A race of tall blue eyed blond haired handsome men and beautiful women genius athletes? Small people to work in miniature cubicles? Invincible warriors? Hobbits? Elves? Giants? Furry people? Human-animal hybrids like mermaids and centaurs? "People" who can live on Titan and drink methane? Cyborgs with electronic internals? Robots with wet human brains? Robots with silicon emulating human brains? "People" with DNA designed for purposes we have not imagined and with less similarity to ours that ours to a mouse? Edison 19:23, 25 January 2007 (UTC)


 * I'd have to go with the Elves suggestion. When I look at 'good-looking' people (models, celebrities etc) from 30 and 40 years ago, they don't strike me as being terribly attractive. Even the 'beautiful people' from 10 years ago can't hold a candle to contemporary average-looking models, in my mind anyway. I'd expect there to be a lot more 6-foot plus, golden-haired, slim, smiling happy people in 50 years, nevermind 5000. Vranak


 * The terms "beautiful" and "attractive" are very subjective. I could be just fashion or maybe some other change to our preferences  (undercover marketing or conspiracy theories anyone?) that most of us find the models described above the most attractive. I personally like the style of the earlier decades more. --V. Szabolcs 11:15, 28 January 2007 (UTC)


 * I think it's important to realise that natural evolution will likely slow down to a halt. In the west at least, people no longer die before reproduction age in any great number. So it seems to me that selection pressure has largely dissapeared. If we don't go the route of genetic engineering, I reckon future humans will be less healthy, with more genetic diseases, and lower fertility than ever. :Theresa Knott | Taste the Korn 19:49, 25 January 2007 (UTC)


 * You are forgetting, of course, sexual selection − Twas Now ( talk • contribs • e-mail ) 20:39, 25 January 2007 (UTC)
 * Sexual selection only works if attractive people have more babies than unattractive ones. I'm not sure if that is actually the case. Theresa Knott | Taste the Korn 10:57, 26 January 2007 (UTC)


 * The only trend I've seen reported is that poverty and a lack of education increases the number of children. Unless it can be shown that poor/uneducated people are not attractive, then I doubt there's much correlation between attractiveness and the number of offspring. --Kainaw (talk) 11:00, 26 January 2007 (UTC)

So if in your answer above, that means that humans could be shorter with ugly features. etc?


 * I once read a paper about this topic (I forgot where, but I'm sure I did) and it said that the current evolutionary trend will result, within the next millennium or two, in two "categories" of humans: very tall, smart humans (the giants) and very short, stupid humans (the elves). I am very sorry if this is offensive to anyone, but this is really what the paper said. I also think Theresa knott's got it right about natural evolution slowing down to a halt. Humans are no longer subject to the same Darwinian forces that were at work 10,000 years ago. A person with diabetes today can live long, (not that I'm saying he/she shouldn't) have children, and quite possible transmit his or her existing genetic predisposition to the disease to his/her progeny, which is the exact opposite of evolutionary natural selection, in which people with disadvantageous phenotypes die out because they cannot reproduce and transmit their phenotype. &mdash;  Lestat deLioncour t  13:00, 26 January 2007 (UTC)


 * So the paper you read was a little like The Time Machine? | A ndonic O</b> Talk · Sign Here 13:05, 26 January 2007 (UTC)


 * I wouldn't really know :). I haven't read the book before. &mdash;  Lestat deLioncour t  16:38, 26 January 2007 (UTC)


 * I remember that paper coming out. All the papers enjoyed reporting it, because they got to illustrate it with pictures of eloi and morlock from The Time Machine. Skittle 17:25, 26 January 2007 (UTC)


 * As I heard from a molecular biology professor researching chaperones, if mankind continues it's behavior, we will genetically degrade and possibly die out in a few centuries, as natural selection has nearly stopped, and for various other reasons.
 * So should we either stop all social care and charity, letting natural selection and evolution do its work, or should we further develop genetic engineering to a point it could compensate for the ill-effects of our society? By standing in the middle, we could soon face extinction, and not because of some doomsday event, pollution, global warming, etc., but solely by genetic degradation. --V. Szabolcs 00:07, 27 January 2007 (UTC)
 * How likely is it that we'll stay as we are (socially) for an evolutionarily significant length of time? Sensibilities and the conditions we live in will change before too long, and some driving force will be applied. Anyway, surely this only really matters is useful genes are being selected against? If it's just a matter of no selection right now, if it becomes a significant effect (which I doubt), selection will start again in one form or another. Plus, for how much of mankind is it true that natural selection has become insignificant? If one country 'degrades', there are many others available to restock them. Skittle 17:06, 27 January 2007 (UTC)

Nickel's anti-corrosive properties
I've read that nickel is frequently used in alloys to create resistance against corrosion. Could nickel stand up against something as corrosive as liquid gallium?


 * IIRC, Nickel is very resistant against oxidation. That's not to say that that it is chemically inert, though.  Oxidation isn't the only kind of corrosion. -- mattb

Gallium is corrosive by alloying? So any metal that alloys with gallium would be corroded? But nickel and many other metals have a surface oxide film that would tend to prevent wetting and hence prevent corrosion by alloying. My guess is yes - but that would be at say 350K at 1000K the situation may be different. I'm interested as to why you say 'something as corrosive as liquid gallium' I've never thought of it as a corrosive thing before.87.102.5.92 17:38, 26 January 2007 (UTC)


 * No. Gallium does attack most metals, however, so it can easily contaminate samples on contact.  -- mattb

What type of plastic do I need?
I have been looking constantly for the trype of platic that I need. What I am looking for is the type is ruber/plastic that can be heated at someones house in hot water and be molded to anything, such as the type of plastic that is used in making athletic mouth gaurds.

Also, I would like to ask for advise on anyother types of plastic, rubber, foam... that a person could make their own mold or indentation, and have it harden up after the user makes their indentation. I ahve e-mailed many plastic companies but many just reply that they do not work with that specific type of plastic/ rubber, so any advise or answers would be a ton of help!!

Thanks for your time, Simon


 * http://www.newton.dep.anl.gov/askasci/chem00/chem00038.htm -- 71.100.10.48 00:25, 26 January 2007 (UTC)

Thanks for the advise, but what about more along the lines of a rubber or a foam. I know that some rubbers can be heated in warm or boiling water, formed while hot and them if you cool the rubber it wil hold form. Where would I get some of that type of material, or any ideas on this part??


 * Have you considered using clay, instead ? It has many of the properties you desire, although you need to fire it to make it permanent. StuRat 08:40, 26 January 2007 (UTC)


 * What about Fimo or some other brand of similar properties. It's a plasticy modelling clay that comes in a variety of colours. You warm it in your hands, mould it as you choose, then bake it hard in an oven. Skittle 15:19, 26 January 2007 (UTC)

When I injured my hand last year I had a splint made of the material that you are speaking of. Perhaps medical suppliers can help you? Theresa Knott | Taste the Korn 15:45, 26 January 2007 (UTC)

photographic memory
what would happen to a person who have a photographic memory when he/she develop Alzheimer Disease? Dragonfire 734 22:58, 25 January 2007 (UTC)


 * Probably the same thing as a normal person with Alzheimers, but I don't have a source on this. --Wirbelwind ヴィルヴェルヴィント (talk) 01:25, 26 January 2007 (UTC)


 * Yes, you could expect the same negative developments as in all Alzheimer's patients; flashes of recognition and the occasional ability to focus, superimposed on steadily fading mental capacities.  StuRat 08:33, 26 January 2007 (UTC)

Light from the Sun
How long does it take for light from the sun to reach the earth? There are bets going on what the answer is. Thanks :-) Kittykat700 23:45, 25 January 2007 (UTC)


 * The speed of light in vacuum is 186,000 miles per second. The distance from the Sun to the Earth varies, but is somewhere around 93,000,000 miles. Divide the second number by the first and you get 500 seconds or 8.3 minutes. Interestingly, the photons generated by fusion inside the Sun actually take much longer just to reach the Sun's surface because they get absorbed and re-emitted (almost always in a different direction) many times. They zigzag around and finally get out in an average estimated time of between 17,000 and 50,000,000 million years Clarityfiend 23:54, 25 January 2007 (UTC)


 * To clarify on Clarityfiend (how fitting): 8.31 minutes is equal to 8 minutes and 18.6 seconds. − Twas Now ( talk • contribs • e-mail ) 03:18, 26 January 2007 (UTC)


 * So who won the bet? ;-) | <b style="font-family:Papyrus; color:black; font-size:x-small;">A</b> ndonic <b style="font-family:Papyrus; color:black; font-size:x-small;">O</b> Talk · Sign Here 13:06, 26 January 2007 (UTC)


 * Clarity, is the 'million' as your second-to-last word, meant to be there? If so, that's a very big number! 86.139.237.132 15:12, 26 January 2007 (UTC)


 * Oops. Clarityfiend 19:01, 26 January 2007 (UTC)


 * If you want to be very exact, the time varies between 8 minutes 27.34332 seconds at perihelion and 8 minutes 10.5554 seconds at aphelion. Earth is very close to its perihelion right now; the one-way light time is only 8 minutes 11.34 seconds, according to NASA's HORIZONS system.  --Bowlhover 01:22, 27 January 2007 (UTC)

Physical appearance of ovarian cyst
Can anyone provide me with a visual description of an ovarian cyst, complete with details of its fine structure? Thanks Adambrowne666 23:47, 25 January 2007 (UTC)


 * Check out Wikipedia's article on ovarian cyst and this Google image search. − Twas Now ( talk • contribs • e-mail ) 03:15, 26 January 2007 (UTC)


 * That's great, thanks, Twas - I was also hoping for a firsthand description from an anatomist or surgeon - I realise it might be a vain hope... Adambrowne666 22:31, 26 January 2007 (UTC)

Transfat now, sugar later...?
If the government can regulate the use of transfat in the making of donuts now will it also be able to eliminate pure sugar coatings on donuts in the future? -- 71.100.10.48 00:19, 26 January 2007 (UTC)


 * Probably not, because there are much safer alternatives to trans-fat-based shortening, but few alternatives to sugar. In addition, the dangers of trans fats in the food supply are more significant than those of sugar. Frankg 00:25, 26 January 2007 (UTC)


 * Whether they *can* ban it is more of a legal/political question than a scientific one. I'm no lawyer, but if you're referring to the NYC ban, I don't think there is any legal barriers. Note that it was the city which did the ban, not the FDA. Local municipalities have quite a bit of jurisdiction on what they can permit/ban -- they don't even need to have a "safety" rationale. For example, Chicago banned foie gras, for animal welfare reasons (not human health reasons). Now as to whether they would actually do it, I agree with Frankg - The trans fat used is an artificially made product (produced by partial hydrogenation), and can be substituted for by natural fats, either unsaturated fats or saturated fats. White sugar, although highly refined, is natural, and does not have an equivalent substitute for all recipes. (Artificial sweeteners, although they are able to substitute in sweet taste, do not have the same physical properties that sucrose does.) -- 23:55, 26 January 2007 (UTC)

Nuclear bombs in a vacuum
For some reason I was thinking about the film from a few years ago (I think it was Deep Impact) where nuclear bombs were detonated on an asteroid in an attempt to blow it up and prevent impact with earth.

It only occurred to me today however to wonder whether a nuclear bomb would in reality actually detonate in the vacuum of space, and if so whether the effect would be as it would be when exploded in earth's atmosphere? Thryduulf 01:02, 26 January 2007 (UTC)


 * Yes, it would detonate. Most chemical explosives already have their oxidiser mixed in with them, so (modulo temperature constraints, which could be engineered away with enough care) it wouldn't be difficult to make a spaceworthy nuclear trigger.  Once the supercritical mass was assembled the presence of an atmosphere (which is a mere will-o-the-wisp compared to the extraordinary temperatures and pressures achieved in a nuclear detonation) makes essentially no difference to the bomb itself.


 * The effects would be very different, however; the thermal and blast effects would largely disappear because there is nothing to transmit them; conversely, the radiation would be much more lethal out to a considerably greater distance because of the lack of an atmosphere to absorb it. While it's nearly 50 years old, as I understand it the explanation in this Congressional report is about right.  An effect not mentioned is what setting off a bomb in orbit might do to the ionosphere; see electromagnetic pulse for a good discussion. --Robert Merkel 01:25, 26 January 2007 (UTC)


 * In open space you wouldn't get the fireball effects due to heating of the atmosphere, but if we're talking about exploding the bomb adjacent to an asteroid, that's another story. The asteroid or a chunk of it would be evaporated just as solid things next to a nuclear blast on the Earth are evaporated, due to direct heating by radiation, and this would form a fireball. However, it wouldn't be constrained by surrounding atmosphere, so it would disperse more rapidly and without forming a shock wave. I think. I'm no expert on this. --Anonymous, January 26, 2007, 02:24 (UTC).


 * Yes, you're right, though I certainly don't know enough physics to guess the exact physical effects. But you would certainly cause a blast if you exploded a nuclear weapon right next to a solid object.  --Robert Merkel 02:52, 26 January 2007 (UTC)


 * See also Project Orion (nuclear propulsion). --Arcadian 06:54, 26 January 2007 (UTC)


 * Also, I have seen simulations that the U.S. national labs have done on detonating megaton-range weapons inside asteroids — they seem to think it will break them apart pretty nicely. (this is the simulation I refer to). --24.147.86.187 14:01, 26 January 2007 (UTC)

You would expect to see a spherical plasma shell which would rapidly cool in space, or a roughly hemispherical plasma shell in a vacuum against a large body, assuming the large body remains intact. StuRat 08:27, 26 January 2007 (UTC)


 * You get other visual effects too, such as if a large amount of charged particles decides to zip this way or that. See high altitude nuclear explosions for some images. --24.147.86.187 13:59, 26 January 2007 (UTC)

Different species of humans
Are there any reputable scientist that consider different races of humans different species? I realize this is controversial and would be met by much condemnation, but lets say we ignore what anyone says and speak strickly scientifically: Yellow Labrador and Black Labrador dogs are considered different species, and it seems to me that they are MUCH more similar in physical appearance than lets say, a Russian person, a Chinese person, and an Ethiopian. There are countless other examples of animals that are catagorized as different species that apear to be more closely related than the different kinds of humans out there, so why do we clump all humans into Homo Sapien?


 * Subspecies? --Kurt Shaped Box 00:56, 26 January 2007 (UTC)


 * But, Yellow Labradors and Black Labradors are not considered different species, or even different subspecies. They are all Canis lupus familiaris. The basic criterion of a species is that members can interbreed to produce fertile offspring. (See our article on Species for more details). That's the case for all the different kinds of humans we know. So referring to different subgroups of humans as different species wouldn't just be controversial, it would be wrong according to the definition of "species." FreplySpang 01:26, 26 January 2007 (UTC)


 * I'd also add that some scientists don't even consider Neanderthals a separate species of human. --Cody.Pope 01:49, 26 January 2007 (UTC)


 * Yellow Labrador and Black Labrador are different breeds not different species.Johntex\talk 04:27, 26 January 2007 (UTC)


 * I'm sorry but that's absolutely incorrect. Not only are all lab colours the same breed, but as it says in the frappin' labrador retriever article, they often occur in the same litter. It's like saying that people with black hair are a different 'breed' from blond(e)s. Anchoress 05:47, 26 January 2007 (UTC)


 * OK, Geez. I was mistaken.  No need for the pseudo-profanity.  Take a chill pill, OK? Johntex\talk 05:58, 26 January 2007 (UTC)


 * Oops I thought I was being funny. Sorry to have offended you. Forgive me? Anchoress 06:07, 26 January 2007 (UTC)


 * All forgiven, thank you! Sorry if I was touchy, I guess I don't like being wrong. :-)  Johntex\talk 06:20, 26 January 2007 (UTC)

At best, races of humans might be analogous to color phases in other animals (I knew you were going to ask this question, so wrote that article a few days ago, just for you). StuRat 08:12, 26 January 2007 (UTC)
 * @Johntex Cheers, thanks! @StuRat YOU ROCK! Neat article. Anchoress 05:47, 27 January 2007 (UTC)
 * For speciation to occur, you need an isolation for about a million years. While human races have only been separated from each other for about 25K years. {Y chromosomal adam is tentatively dated to about 60K BP}. We can say that had we continued to live in isolation for about 900K years more, we would have been different species of humans. See for example Bonobos and common Chimpanzee. They separated about a million years ago from their common ancestor.nids(&#9794;) 08:35, 26 January 2007 (UTC)


 * Just a note, speciation can happen under all kinds of time frames. For example, while not true "specitation," reproductive isolation has been induced in fruit flies in only a few generations, or about 6months-10 years (depending on the study) of lab breeding.  Other examples of speciation in the wild have take far less than a million years (see Vidua for example).  Also, it is interesting to note that if you do consider Neanderthals a separate species that speciation event may have take far less time than a million years. --Cody.Pope 16:05, 26 January 2007 (UTC)


 * Yep, depending on your definition of species you can have almost instant speciation (in the case of polyploids), and there were on the order of 400 species (per lake) derived from a common ancestor in a few thousand years in many of the African Great Lakes haplochromine cichlids. Guettarda 16:14, 26 January 2007 (UTC)

There are cretainly genetic differences between different races (particularly in gene expression), but even the most conservative speciation definitions aren't met by the subtle variations between populations--there seems to be no problem with interbreeding, for example, between the several major ethnic groups. I think human groups are generally considered simply separate populations of the same species with variable interbreeding and migration patterns. They're definitely not separate species. -- Scientizzle 19:02, 26 January 2007 (UTC)

Applied kinesiology
My friend is a practitioner of Applied kinesiology. I have always been extremely skeptical of this kind of medicine, or therapy, as things such as 'energy lines' just don't exist as far science is concerned. To me, it's always just been a bunch of mumbo-jumbo - especially the parts about energy meridians and the notion that they can be affected by as little as eye contact, things like that. However, having been made the subject of some 'tests' by my friend several times, it seems at least some of the stuff he claims is true works, whether it's because of these energy lines, or something less fanciful. What's going on when he weakens by arm or leg, ostensibly by a glance or a stroke of my stomach? The power of suggestion? How come it works every time? There's a whole bunch of other stuff far more wacky than that, too. By placing a vial of some substance (I can't recall what at the moment) next to my head, he was able to stretch my leg a full foot further out than it had previously been able to. Now, to me, and even to him, that sounds like something that should be categorically impossible...and yet, it seems to work. As an aside, he's not intentionally trying to trick me. He sincerely believes this stuff works. Can anyone shed some light on this? 121.73.21.141 03:12, 26 January 2007 (UTC)


 * Well, it works according to their methods, so there's no reason to think it's false.


 * Read up on the Placebo effect. 75.138.84.159 05:02, 26 January 2007 (UTC)


 * There is a forum at the James_Randi_Educational_Foundation website - I am sure there are Wikipedians who are good at debunking pseudoscience, but I would consider them to be the experts!--inksT 06:05, 26 January 2007 (UTC)


 * First of all, if what your friend says sounds like mumbo-jumbo, nevermind the words, just observe the results. He's just trying to explain what he does; the words aren't that important. Second, this applied kineseology sounds a lot like reiki. You might find that article makes a more convincing case, with words that don't challenge your understanding of science. Vranak

I know a chiropractor who does "kinesiology", and I agree that it's pure BS. In particular, all the methods he uses to evaluate whether it's working seem to be intentionally subjective. For example, he will push down on your hands before and after a "treatment", claiming that he is applying equal force both times. Before, he knocks me over, and afterwards he can't supposedly budge me at all. Now why, exactly, would he choose such a subjective method when he could just have had me hold up the same weight before and after ? I can only think of one reason. He also used the length of the legs trick. Depending on how he holds my legs up; the right, left, or neither can look longer, at all depends on the angle. To get the actual length, you should look at X-rays and take precise measurements. StuRat 08:06, 26 January 2007 (UTC)


 * There are quite a few references on the net to Ideomotor action.The article How People Are Fooled by Ideomotor Action gives a good discussion of the honest self-deception and sincere mistakes involved. --Seejyb 13:06, 26 January 2007 (UTC)


 * This reminds me of this April Fool's joke: In 1976, British astronomer Sir Patrick Moore told listeners of BBC Radio 2 that unique alignment of two planets would result in an upward gravitational pull making people lighter at precisely 9:47 a.m. that day. He invited his audience to jump in the air and experience "a strange floating sensation." Dozens of listeners phoned in to say the experiment had worked.

Superconducting magnetic energy storage...?
My understanding is that when the coil is energized it "freezes" the magnetic field which does not collapse after the current is turned off until the temperature is raised and allows the field to collapse. Is this a correct understanding or not? -- 71.100.10.48 05:12, 26 January 2007 (UTC)


 * The energized coil is a closed loop of wire with current running through it. There is no energy loss here because the low temperature has reduced the electrical resistance of the coil to zero. A moving current produces a magnetic field, but the field isn't "frozen" in a thermal sense. Current can be added or removed, perhaps by intercepting it (break the loop and attach the ends to something) or by interactions with the magnetic field (since current induces magnetism and vice versa). The electrical storage loop is something like storing a motor's rotational energy in a flywheel with a perfectly lubricated (zero friction) axle...the superconductivity is a bit like the lubrication for the electrical storage. DMacks 07:51, 26 January 2007 (UTC)


 * So the field does not collapse after the current is turned off because the ends of the coil are connected together instead of to the supply? -- 71.100.10.48 10:45, 26 January 2007 (UTC)


 * Correct. DMacks 20:20, 26 January 2007 (UTC)


 * Then maybe this would explain the state of the Universe prior to the Big Bang in that if the entire Universe was at a temperature below that of superconductivity regardless of the small amount of space it occupied and then gained enough temperature to reach or exceed superconductivity or acquired some other parameter that would amount to the same thing then... but then no and I guess this has already been considered. -- 71.100.10.48 20:32, 26 January 2007 (UTC)

What is the appropriate device for viewing terrestrial objects at high magnification
I would like to know what the best design for viewing a mountain in significant detail aprox. 150miles away from my house. Its from my house so portability is not important. However it is still important that the image not be inverted and that distortion is kept to a minimum?

is it a spotting scope? is it a special type of telescope? are there eyepieces that can flip an inverted image without signifigant degredation of quality?

Thanks   Beckboyanch 06:47, 26 January 2007 (UTC)


 * Yes it is indeed a spotting scope although any refracting telescope will do. Generally a refracting telescope will be more expensive then a comparable quality spotting scope, because the optics are optimised to transmit very low levels of light. Binoculars are of course your other option, they are more versitile then a scope but won't offer as much magnification, if that's what you are after. At over 15 or 20x magnification a stable tripod is a must. Vespine 07:38, 26 January 2007 (UTC)
 * And yes, there are optical arrangements to turn an image through 180 degrees. Any degradation would be negligible. See --inksT 10:25, 26 January 2007 (UTC)

Could Japan really sink in our lifetime?
So, it is alleged that in the future, tectonic plates will pull Japan under the ocean. Is there anything, any hard evidence to truly back this up? Besides, instead of the 338.54 days that the tectonic plates would take to pull Japan down in the movie, how long would it really take? Also, how do we know for sure that the tectonic plates won't instead push up and cause Japan to have more land reclaimed from the sea? --70.179.170.119 06:55, 26 January 2007 (UTC)


 * The rocks that make up continental crust are usually less dense than the rocks that make up oceanic crust, so usually when oceanic crust collides with continental crust, the oceanic crust slides under continental crust in subduction. This is what happens near Japan right now. Japan rests at the edge of the Eurasian Plate. To the east of Japan is the Japan Trench, where the old and dense Pacific Plate subducts under it. To the south is the Ryukyu Trench, where the Philippine Plate subducts under it.
 * There is a term for the reverse, obduction (where oceanic crust goes over continental crust); but I've never heard of it and even if it exists it's very rare. Even if the plate that continental crust goes on is somehow obducted, the rocks and stuff will probably be scraped up by the other plate because of their low density.
 * As to the timescale, these things takes millions of years. --Spoon! 07:22, 26 January 2007 (UTC)
 * Just an addition to Spoon!s excellent reply - obducted oceanic crust often results in ophiolites above sea level, and good examples can be found in Northern California, Cyprus, Oman, and many other places. But just as Spoon! says, the relative low density of the continental crust upon which the oceanic crust is pushed keeps the whole mass relatively high standing, often even above sea level. Japan consists of mixed rocks that are mostly closer to continental densities than oceanic, so even after millions of years, much of what is now Japan will still be above sea level.  Cheers Geologyguy 22:34, 26 January 2007 (UTC)

I'm just reading a special BSSA journal on the 2004 Sumatra earthquake. The amazing thing is that everyone argued that this could not happen, since all the subduction segments were rupturing separately. So I could see a big one like this for Japan. But in that earthquake, some places went down and some went up! --Zeizmic 13:01, 26 January 2007 (UTC)