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July 19

Image artifact of purplish and greenish/yellowish stripes

Take a look at this scan of the actress Shivani Ghai: http://thedressdiscerner.files.wordpress.com/2011/07/asiana-mag-inner.jpg. There are alternating diagonal purplish and greenish/yellowish stripes running across the image. What type of image artifact is this, and what causes it? —SeekingAnswers (reply) 01:41, 19 July 2012 (UTC)

It's a Moiré pattern, and luckily the article somewhat explains the cause, since I can't. Dpreview, who should know, say "If a scene contains areas with repetitive detail which exceeds the resolution of the camera (1), a wavy moiré pattern (2) can appear" and provide onwards links. --Tagishsimon (talk) 01:43, 19 July 2012 (UTC)

For a rigorous mathematical overview of moiré patterns, there are articles on aliasing and Nyquist rate. Nimur (talk) 02:30, 19 July 2012 (UTC)

But for a simple answer, it happens when the image is made of tiny dots, and the dot spacing for the image does not match the dot spacing for the scanner. Looie496 (talk) 17:37, 19 July 2012 (UTC)

To what extent are astronomical observations automated ?

For example, if one of our large telescopes is pointed at some spot in space, and there's a point of light there not in any previous observations, does a human have to spot it, or would it be spotted by software comparing with previous observations ? StuRat (talk) 03:47, 19 July 2012 (UTC)

It depends on what the goal of the observations is. There are projects that look for transient or variable objects (e.g. Supernova Cosmology Project, OGLE), and those apply automatic algorithms to their data to detect variability or "new" objects. In general, survey telescopes such as Large Synoptic Survey Telescope, that revisit the same part of the sky repeatedly, state the search for transient objects as one of their scientific goals and will run those algorithms on their data. On the other hand, data from "visitor telescopes" (like the Very Large Telescope) where astronomers propose observations for a specific scientific purpose are not routinely screened for transient objects (most of the time there will be no other observations of the same field of comparable quality), and it will be luck if an astronomer spots something they haven't looked for. --Wrongfilter (talk) 08:57, 19 July 2012 (UTC)

(ec) Astronomers usually agree to share their observations with the observatory where they make them. Many of the large observatories have standardized processing steps that they perform when they add new observations to their archive libraries. However, a new point of light isn't typically going to flag an image for review unless spectral characteristics are being measured and it doesn't look like something common such as a asteroid or artificial satellite. A missing object or significantly changed brightness in an expected point of light is another matter entirely, and is more likely to flag the observation for review. 75.166.200.250 (talk) 09:03, 19 July 2012 (UTC)

Considering that those new points of light could be a meteor headed for Earth or something else important, it's a shame they can be tracked from 1st discovery. You'd think they could be compared against an artificial satellite database to eliminate that possibility. StuRat (talk) 09:35, 19 July 2012 (UTC)

There are automated, specialized meteor-scanning telescopes plugged into computers. But not every telescope result is checked for meteors — the odds are super low and the number of false-positives would make such a system prohibitive, and many of them are not looking at the sky in ways that would even spot a meteor. I think you are underestimating the amount of astronomical data that is generated, as well. --Mr.98 (talk) 11:49, 19 July 2012 (UTC)

Is the amount of data collected from large telescopes just too large for all our computers to process ? If so, it sounds like we need to build up our computing capacity, maybe in the same way as SETI@home does (using volunteers' home computers). StuRat (talk) 18:34, 19 July 2012 (UTC)

Gluconeogenesis image review

Could someone please check commons:image:Gluconeogenesis_pathway.png please? The final product (top) purports to be glucose (in its pyran form), but is missing the methylol(?) group. This make me question if there are other mistakes in it. One of the previous steps is a furan ring with two methylol groups, so its unlikely the target is a pentose. TIA, CS Miller (talk) 05:39, 19 July 2012 (UTC)

What worries me most about it aren't structural errors, but what's the source of the sequence? 75.166.200.250 (talk) 21:08, 19 July 2012 (UTC)

Galactic wind-up problem

From our Milky Way article:

Another interesting aspect is the so-called "wind-up problem" of the spiral arms. If the inner parts of the arms rotate faster than the outer part, then the galaxy will wind up so much that the spiral structure will be thinned out. But this is not what is observed in spiral galaxies; instead, astronomers propose that the spiral pattern is a density wave emanating from the Galactic Center. This can be likened to a moving traffic jam on a highway—the cars are all moving, but there is always a region of slow-moving cars. This model also agrees with enhanced star formation in or near spiral arms; the compressional waves increase the density of molecular hydrogen and protostars form as a result.

So, how do these density waves manifest themselves ?

1) Do some arms fade away while other arms appear ?

2) Or is it that when they give the variable rotation speed of the inside and outside of the arms, what they really mean is the stars within the arms, but that, as new stars are created and old stars die, the actual location of the arms move relative to the stars, so that the arms really have constant rotation ?

Any clarification would be much appreciated. StuRat (talk) 06:55, 19 July 2012 (UTC)

The stars move at (roughly) constant speed (in km/s), the waves move at constant angular speed; their motion is essentially independent. Individual stars pass through the waves in the same way that water molecules pass through water waves (or the other way round - water molecules oscillate around a fixed position while the wave passes through). Unfortunately, we can only measure the motion of stars and gas clouds in galaxies, not the motion of the arms/density waves. --Wrongfilter (talk) 08:47, 19 July 2012 (UTC)

But the part I don't understand is how the stars and waves can move independently, if the waves are composed of stars. Are the stars inside a "crest" just pushed closer together as the wave passes ? Are the stars brighter while it passes ? StuRat (talk) 09:30, 19 July 2012 (UTC)

That's not specific to stars and galaxies at all, and a partial explanation is contained in Wrongfilter's reference to water waves. Generally speaking, when a wave propagates through a medium, it does not do so by moving all the medium with it, but by vibrating the medium. To take a more obvious example: vibrations move through the strings of a stringed instrument without the entire string moving. If I grab a loose garden hose and waggle one end, the entire hose can adopt a wave-shape without the end running away from me. So with water, the body of water doesn't move as a whole when the waves move - or the tide would come in vastly faster than it does. And with stars - although the forces holding them together are gravitational rather than electrostatic - the same principle applies.

(after ec) So, to answer your question - the stars don't get brighter, they get closer together. AlexTiefling (talk) 09:35, 19 July 2012 (UTC)

So, in that case, the wave must slow the stars at the leading edge and speed up the stars at the trailing edge, to force them closer together ? StuRat (talk) 09:38, 19 July 2012 (UTC)

FOLLOW_UP Q'S:

1) Why aren't pressure waves originating from the galactic core manifested as circular waves moving out from the core ? What gives them their spiral form ?

2) What happens to the pressure waves at the bar in barred-spiral galaxies, like the Milky Way ? StuRat (talk) 09:43, 19 July 2012 (UTC)

I really need to read up on this (it's not trivial), but I just point out that the waves in galactic discs are density waves, not pressure waves. The spiral pattern, i.e. the density pattern arises from the superposition of the stars' orbits, although the gravitational attraction also plays a role. It's a collective phenomenon in a non-collisional self-graviatating system, as is the bar. --Wrongfilter (talk) 10:55, 19 July 2012 (UTC)

Here's my casual explanation, no doubt wrong:

• Galaxies have a core, which contains sites where stars are formed, at least some of which for some reason then travel away from the core.
• They travel at different speeds, causing clusters. The clusters still move away from the core. This is like a series of small, non-stationary traffic jams.
• Galaxies rotate.
• Consider a long straight single-lane north-south road, with clusters of traffic on it. The traffic all emanates from a building in the middle point of the road, half going north, half going south. Rotate the entire road around this building, and the cars will form a spiral pattern (as the slower moving ones, and the ones stuck behind them, are left behind, falling off the rotating road, to form trails).

That analogy became increasing bizarre as I edited and improved it. Oh well. Hope it helped.  Card Zero  (talk) 12:41, 19 July 2012 (UTC)

Yeah, I'm pretty sure that is wrong. Stars orbit the centre - they tend to stay at a roughly constant distance. There will be some stars moving outwards or inwards (mostly due to close interactions with other stars), but I doubt there are enough of those for it to be a significant effect. I'm almost certain it won't be a large enough effect to cause the spiral arms. --Tango (talk) 16:36, 19 July 2012 (UTC)

• Let me give a pointer to density wave theory (already mentioned by Wrongfilter), which contains some animations that may be useful for getting an intuition for the process. Looie496 (talk) 17:34, 19 July 2012 (UTC)

Ooh, so rotated concentric ellipses cause the arms. How nice.  Card Zero  (talk) 17:43, 19 July 2012 (UTC)

Explanation of spiral galaxy arms.

Yes, that makes some sense, but can those spirals create more than 2 arms ? I'd like to create some animations of this illustration and one with multiple arms, if I can figure out how the multiple arms case works in this model. StuRat (talk) 18:29, 19 July 2012 (UTC)

Well, you can get that by superposing two (or more) independent waves. Dauto (talk) 19:06, 19 July 2012 (UTC)

Density wave theory is only a part of the set of theoretical explanations there are about galactic spirals; see Spiral galaxy#Origin of the spiral structure. In general, the dynamics of stars within galaxies is not as well understood as one might expect, with theory at times matching poorly with observation; see Galaxy rotation curve. Red Act (talk) 21:47, 19 July 2012 (UTC)

There is little discrepancy between theory and observations as far as galaxy rotation curve is concerned as long as that theory includes dark matter (which it should). Dauto (talk) 02:46, 20 July 2012 (UTC)

But dark matter fits solidly within the category of "not as well understood as one might expect". Without a clear-cut understanding of what exactly dark matter is, direct (as opposed to gravitational) evidence for its existence, or experimental evidence that would clearly rule out the alternative theories that compete with dark matter, dark matter currently isn't much more than a fudge factor that describes the discrepancy between observation and what the theoretical results would be without dark matter thrown in. That may well change if some good experimental evidence about dark matter starts coming in over the next decades, but at the moment, dark matter isn't a very satisfying explanation. Red Act (talk) 04:21, 20 July 2012 (UTC)

StuRat, perhaps you have figured it out already from the various links, but the density wave is principally a property of the galactic gas. We think of the interstellar medium as empty, but it is filled everywhere with diffuse gas. Though almost empty, waves can propagate through that gas provided that the waves are large enough (in this case on the scale of a whole galaxy). As the wave compresses the gas, that perturbation provides just enough impulse to trigger star formation in gas clouds that were already on the brink of collapsing. This means that the passage of the density wave is marked by a surge of young stars. It is those new stars, many bright and large, that make the spiral arms stand out visually. The stars, once formed, follow elliptical paths and are hardly affected by the density wave at all. However, many of the brightest stars are so big that they live short lives (only ten million years, for example), so they die out quickly compared to the travel time of the density wave. Hence the spaces far from the front of star formation appear darker. So yes, the arm positions (really a front of star formation) is moving relative to the actual stars. Dragons flight (talk) 19:23, 20 July 2012 (UTC)

OK, thanks all, but what actually generates the density waves ? StuRat (talk) 20:26, 20 July 2012 (UTC)

Li-ion current price per kWh

I was wondering how much rechargeable li-ion battery cost per kWh. To grab very rough estimate I gone ebay and searched for different types of li-ion batteries there. To my huge surprise, it seems that 18650 form factor cells are most cost effective... And 10 batteries 3800mAh each 3.7V cost $14.94 with free shipping...

My question, if advertised characteristics reflect real performance, that translates for 140.6 Wh for $14.95, or ~$107 per kWh. My calculations correct? Or have I made a mistake?

And second question, how likely that such lots(not only on ebay, but alibaba etc) reflect the cost of production of 1 kWh rechargeable li-ion battery selling for around $100 and still making profits? Or such batteries are left overs from bigger orders or even flawed cells that haven't passed quality control, and thus price of them do not really reflect cost of kWh...

Example ebay slot 70.49.169.86 (talk) 16:32, 19 July 2012 (UTC)

Um, don't ever trust mAh ratings from eBay. Given the price, you'd probably be lucky if the cells even have half the capacity [1]. I believe the real high end 18650 cells from Panasonic etc tend to be around 3100mAh [2] [3] [4]. From what I've read, cells with Xfire labels can vary from reclaimed battery pack cells to those that didn't make the grade for a battery pack. (You can get okay ones but you need to do a bit of research and ensure it's a supplier you can trust.) In any case, I wouldn't read too much in to the price, but it sounds like you should be more interested in the wholesale price anyway not the price from random eBay sellers who stick random labels on them. P.S. I'm pretty sure your calculation can at best be called simplified since you didn't take in to account the actual discharge curve for your cell which will depend on discharge current and to a smaller extent what voltage you stop at. Nil Einne (talk) 17:48, 19 July 2012 (UTC)

''it sounds like you should be more interested in the wholesale price anyway'' Yes, this is what I'm really interested to figure out. But not GM/Nissan/Ford claimed price of li-ion battery packs, but cheap modern li-ion chemistries produced out there(in China?) and wholesale price per kWh they are selling for... 70.49.169.86 (talk) 18:09, 19 July 2012 (UTC)

My point is the correlation between the price you pay retail for individual cells and the wholesale price is weak at best. Particularly in a case like this where the cheap retail options are of unknown heritage with random labels and the wholesale price will depend greatly on things like what sort of supplier you're willing to trust (given the way things can go wrong with li-ion cells, although of course one cheapish seller may give you total crap which blow up regularly, another selling at the same price may give you decent quality cells most of the time) and capacity (choosing the highest capacity cells is probably not the cheapest option), not to mention the typical stuff like quantity. Your best bet is probably looking at something like Alibaba or one of the other China B2B sites out there for the sort of quantity ranges you're thinking out, but you'd also have to have some idea of what you're looking at which to be honest it sounds like you don't. You can also try asking suppliers since they don't always bother to properly specify. Of course it does depend somewhat on what level you're actually looking at, I would guess at a low level range like 10000 cells a year you may get an okay idea from such sites, but if you're thinking of 100k a month, probably not. It's not that this info is super secret, it's just that it's not out there on some internet site because that's not how people who actually make the decisions are going to look for it. And navigating the China market can be difficult, if you don't much experience, given the variety of problems there is like unreliable suppliers. I don't really get the relevence of GM/Nissan/Ford as I didn't mention them, despite the recent interest in electric cars and the fact some of them now use li-ion cells, I'm pretty sure they still only make up a tiny percentage of the market. Nil Einne (talk) 04:44, 20 July 2012 (UTC)

First of all thank you Nil for pointing out that 3700 mAh was totally unrealistic to expect from 18650 cell. That helped me a lot:) Yes, correlation between retail and wholesale prices is hard to estimate precisely. But it still better then nothing and lowerest retail price would give some idea about wholesale price level... I have mentioned GM/Nissan cuz price of battery packs of Leaf and Volt has been published ($375 and $550 per kWh 'IIRC'). And that theoretically should help estimate wholesale price of batteries... But automotive packs are something different then what I'm looking for(at least the way GM define it). I have got a two question for you, Nil.

1) Wouldn't you think that LiFePO4 chemistry should be cheaper then bunch of 18650 cells with similar capacity?

2) Could you make an educated guess for me about a price of average capacity (2200 mAh?) 18650 cell. What would you consider cheap, but realistic and a good price for ~100k cells? Would you say that $1.50-$1.80 price range per cell is achievable? I know Tesla Motors was using hundred thirty one 18650 cells per kWh in their battery packs. So that translates into 7.6Wh per 18650 cell, should be a good estimate for price effective cell capacity I guess....

Thank you in advance, 70.49.169.86 (talk) 05:59, 20 July 2012 (UTC) PS. I have tried to use Alibaba even before I have asked question here, with very little luck. And really do not feel like approaching companies to get quotes...

energy drink

why we add salt,sugar in water to give energy to a person — Preceding unsigned comment added by 59.177.161.174 (talk) 17:08, 19 July 2012 (UTC)

Such drinks, like Gatorade, have three purposes:

• To provide a quick source of food energy, which comes from the sugar
• To rehydrate someone, due to sweating during exercise, this comes from the water
• Sweating also contains a lot of salt, which needs to be replaced. If you drink too much water and not enough salt, you can get Hyponatremia, so the salt is there to keep the electrolytes in the body at the right concentration.

Does that help? --Jayron32 17:25, 19 July 2012 (UTC)

For why they put salt in energy drinks, see water intoxication. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 17:33, 19 July 2012 (UTC)

Water intoxication and hyponatremia are basically two sides to the same coin. Not exactly, but they are very closely related conditions: if you have too much water, it also means you don't have enough sodium. If the two are in correct relative balance, your kidneys should be working efficiently enough to keep things working well; that is for a properly balanced solution with the right amount of salt, it is hard to over-consume it: you'll just tend to piss a lot more. If you don't get enough salt, you'll experience the symptoms of water intoxication/hyponatremia. Too much salt or not enough water leads to dehydration and Hypernatremia. --Jayron32 17:39, 19 July 2012 (UTC)

That's all correct, but my understanding is that there is also another factor: it is easier for the body to absorb fluids if they are approximately in osmotic balance with the bloodstream -- meaning that they have a comparable level of dissolved molecules, of whatever sort. Looie496 (talk) 18:00, 19 July 2012 (UTC)

The answers above are correct if you're talking about liquids consumed by professional athletes during strenuous training sessions. If you're talking about supermarket "energy drinks" consumed by non-athletes, the sugar and salt are there to make them taste good. -- BenRG (talk) 22:06, 19 July 2012 (UTC)

Yes, the answers above are for sports drinks, rather than energy drinks. Sports drinks are used by amateurs for the same reasons as professionals. Energy drinks are a completely separate market (do they usually contain salt? They're mostly caffeine and sugar, I think). --Tango (talk) 00:37, 20 July 2012 (UTC)

This may be an ultra-dumb question even for me, but one thing about Gatorade is that it tastes a lot better when you've been exercising strenuously than if you just take it like you would soda pop. So, does that have to do with a stressed body "craving" what Gatorade contains? ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:08, 20 July 2012 (UTC)

I don't know what is in Gatorade, but I do know you lose the ability to taste salt when severely dehydrated, which makes oral rehydration solution taste a lot better (it tastes like sugar water, rather than sugar and salt water). If Gatorade contains quite a lot of salt, then it could be the same effect. --Tango (talk) 06:04, 20 July 2012 (UTC)

That's exactly it: the salt. But it isn't that severe dehydration makes you unable to taste salt, it's that moderate loss of salt via sweating makes salt taste better than it usually does. Looie496 (talk) 06:39, 20 July 2012 (UTC)

I suspect that the real reason for companies adding anything to water, is so that they can convince people to buy it and thus take your money. Of course other companies manage to extract money from the consumers without even adding anything to the water. Mitch Ames (talk) 03:13, 21 July 2012 (UTC)

Earth and Jupiter

At what point would Earth have to be to Jupiter before it is sucked into its orbit? Reticuli88 (talk) 17:17, 19 July 2012 (UTC)

See Gravitational binding energy. If the kinetic energy of a body exceeds the gravitational energy holding it to another, it will be able to escape. If the kinetic energy of the object is less than the gravitational energy, it will eventually be "sucked in" to the other object. To answer your question meaningfully, which I take it to mean "how close must an Earth-sized object be to a Jupiter-sized object before it will be gravitationally bound to it" the answer is "it depends"; mostly on the relative motion of the two objects. The dynamics are very complex, and can't be answered without more information regarding the specific orientation and relative velocities of all objects involved. However, I wouldn't worry about it happening any day soon. The distance would be a LOT closer than they are now; Jupiter is 5 times as far from the Earth as the sun is at the closest it ever gets to the Earth, and it is only 0.001 times the mass of the Sun. Roughly speaking, that means that Jupiter should exert a gravitational influence over objects only 0.001 times as well as the Sun does, and the Earth falls well outside of that sphere. The earth does experience a tiny effect from Jupiter's gravity, but it isn't going to send us crashing into Jupiter. --Jayron32 17:35, 19 July 2012 (UTC)

Binding energy isn't really the best concept to look at. What you're really interested in is escape velocity. --Tango (talk) 00:39, 20 July 2012 (UTC)

See Hill sphere. manya (talk) 03:52, 20 July 2012 (UTC)

And also see Sphere of influence (astrodynamics). manya (talk) 03:56, 20 July 2012 (UTC)

Sorry, these links are not relevant to answer the question. manya (talk) 04:00, 20 July 2012 (UTC)

Cell Signalling in Development

Hello. Two-cell (comprised of P1 and AB) embryos were incubated either in a translation inhibitor or in a transcription inhibitor. The AB cells were then isolated, washed, and grown in culture. AB cells of embryos treated with the translation inhibitor produced only neurons and skin, while AB cells of embryos treated with the transcription inhibitor also produced muscle–their normal fate. The direction of signalling is from P1 to AB. Why would the signalling interaction at the two-cell stage most likely involve proteins? If proteins are the product of transcription and translation, wouldn't the P1 cells of embryos treated with transcription inhibitor not produce mRNA and, as a result, proteins? This would block the signalling pathway, right? Thanks in advance. --Mayfare (talk) 19:56, 19 July 2012 (UTC)

Because the two cells are adjacent. Low molecular weight hormonal signaling paths are unnecessary under those conditions. Yes to your second and third questions. 75.166.200.250 (talk) 20:46, 19 July 2012 (UTC)

In most organisms, transcription is marginal or completely absent for the first several rounds of cell division after fertilization. In Drosophila melanogaster, for instance, this stage lasts for ~2 hours and 12-14 rounds of cell division. Virtually every mRNA found in very early embryos has actually been produced maternally. And so the transcription inhibitors would have no effect because transcription isn't even on, or is nearly irrelevant if it is. Translation, on the other hand, is quite active, working from the maternally provided mRNA. Someguy1221 (talk) 22:14, 19 July 2012 (UTC)

Equivalent Animal Processing Power of Modern Computers

Out of some recent boredom, I have been reading up on the computer vs. human brain speed dealie. Though I knew that there is no easy way to measure and compare the two, I was interested in some of the (questionable?) methods used to approximate the processing speed of human brains and that they were considered to be vastly superior to current technologies. I was wondering, then: what animal's mental "processing power" is closest to the fastest computer processor available to consumers today? Have we even gotten past ant? Thanks, Sazea (talk) 19:57, 19 July 2012 (UTC)

Well, my opinion is somewhat heretical here, but since I have a Ph.D. in neuroscience I can present myself as enough of an expert to express it: I believe that the computational power of brains is way overstated, and that at a practical level a human brain has capabilities comparable to a powerful modern desktop PC -- except in terms of memory access bandwidth, where the brain really stands out. The thing that really makes brains superior, I believe, is the vast amount of information about the world they take in during the process of development. Looie496 (talk) 20:17, 19 July 2012 (UTC)

Aren't neurons arranged in more than 2 dimensions like computers are?--Canoe1967 (talk) 20:22, 19 July 2012 (UTC)

I'm not sure why you ask that, but there is no doubt that digital computers differ from brains in a variety of important ways. They differ so much that it is hard to find a basis for comparison. In my view, the only proper way to do it is to ask how powerful a computer would be needed to do the same tasks that the human brain can do -- for example, to pass the Total Turing test. I think it is likely that modern PCs, augmented by a few special chips, are powerful enough to do it -- that the real difficulty is in programming them, not in making computers that are strong enough. Looie496 (talk) 20:40, 19 July 2012 (UTC)

I just heard somewhere that they are thinking of biological memory to get some of the advantages of animal brain material and the configuration was one of them. I also remember that if we can make a wire small enough to connect we may try programming animal neuron groups.--Canoe1967 (talk) 21:22, 19 July 2012 (UTC)

Looie, what would be your estimation of the human memory access bandwidth? And yes, hard disks suck. Pitiful bandwidth. Sagittarian Milky Way (talk) 23:34, 19 July 2012 (UTC)

It's been quite some time since I worked through the calculation (calculating the rate at which information in the synaptic weight distribution generates information in the population firing pattern), but my recollection is that I could get a value on the order of 1 terabyte per second without making any assumptions that seemed unreasonable. Looie496 (talk) 03:04, 20 July 2012 (UTC)

Which even ultra high end GPUs are a while away from matching Comparison of AMD graphics processing units, Comparison of Nvidia graphics processing units. Nil Einne (talk) 04:35, 20 July 2012 (UTC)

I dunno, I see 264 GB/s and 2 x 192.256 GB/s for the desktop in those lists. What's the Moore's law for GPU bandwidth? That's only 2.6 times to 1 TB/s (wow, a TB/s, that's fast). Some people put 2 or 3 (4?) graphics cards in the same PC, right? We've already matched it on some PCs. With coolers for each card that can play top games at max settings on a 26, 36 inch or something screen that's like 4 HDTVs worth of pixels. There are supercomputers with 20 TB of RAM, they probably blow away human brains in terabytes/s. Sagittarian Milky Way (talk) 18:07, 20 July 2012 (UTC)

But it doesn't make any sense to multiply the bandwidth, because a single GPU only has whatever amount of bandwidth. Otherwise you might as well just talk about how we've matched it with a Beowulf cluster. You can see the history of GPU bandwidth in the articles. Nil Einne (talk) 17:02, 22 July 2012 (UTC)

Looie, what are your views on whether brains can even be considered computable. I have read penrose's thoughts on this, but for some reason have completely forgotten the gist of his argument. Perhaps it unsettled me. Egg Centric 17:55, 20 July 2012 (UTC)

I think it was that it's not (fully) computable due to quantum mechanics. I hope that's true, that's where free will comes from. Sagittarian Milky Way (talk) 18:10, 20 July 2012 (UTC)

Well I rather (personally) hope quantum mechanics explains my self-evident consciousness (as I define it) although I can't possibly see how it could. Free will I see no reason to belive in tbh. Egg Centric 21:35, 20 July 2012 (UTC)

Energy requirements for reverse osmosis

How much energy does it take to desalinate 10,000 cubic meters of seawater by reverse osmosis? 75.166.200.250 (talk) 20:38, 19 July 2012 (UTC)

You could try websites that sell them. They may have those specs. I assume the larger the more efficient.--Canoe1967 (talk) 21:24, 19 July 2012 (UTC)

Using numbers from http://urila.tripod.com/desalination.htm/ (for which I do not vouch), and assuming perfect efficiency, it comes to around 1000 kilowatt hours. Looie496 (talk) 21:55, 19 July 2012 (UTC)

You should buy one of these though, which I endorse. http://www.ansl.ca/candesal/article.html --Canoe1967 (talk) 23:40, 19 July 2012 (UTC)

"Mr. De Villiers says if CANDESAL can produce water for less than $1 a cubic metre, the technology has great potential. "If their business plan is right, then they're onto something really big," he says." --Canoe1967 (talk) 23:49, 19 July 2012 (UTC)

You can easily compute this from first principles. It follows from the change in the Gibbs energy. Suppose you have seawater with a concentration of n ions per unit volume in it. You take a volume V from this seawater, which will contain N = V n ions. The Gibbs energy of N ions in a volume V of water is approximately given as g = N k T Log[N/(V Z)] where Z is the single ion partition function. Then the initial state is the water of volume V with ions at concentration n, and the sea which has some huge volume V' with ions at concentration n. The Gibbs energy of the initial state is then

g1 = N k T Log[N/(V Z)] + M k T Log[M/(V'Z)]

We then remove all the ions from the water by dumping into the sea. The limit of N to zero of the first term is zero. The Gibbs energy is thus given by:

g2 = (M + N) k T Log{[M + N]/(V'Z)}

The maximum amount of work that can be extracted from this process is the drop in the Gibbs energy, g1 - g2. This will be negative, so it will require a minimum amount of work of g2 - g1 to get to the final state. We have:

g2 - g1 = (M + N) k T Log{[M + N]/(V'Z)} - N k T Log[N/(V Z)]

      -  M k T Log[M/(V'Z)]

We then want to take the limit of V' and M to infinity such that M/V' = n. We can simplify the first term:

(M + N) k T Log{[M + N]/(V'Z)} =

(M + N) k T Log(n/Z) + (M + N) k T Log(1 + N/M)

The first term of this cancels against the last two terms in the expression for g2-g1, we thus have:

g2 - g1 = (M + N) k T Log(1 + N/M)

For small x we have Log(1+x) = x - x^2/2 + ..., so the limit for M to infinity becomes:

g2 - g1 = N k T

Seawater contains 35 grams per liter of salt. Sodium chloride has a molecular weight of about 58.45 u, so 35 grams of salt contains 3.606*10^23 ions of sodium and 3.606*10^23 ions of chlorine. One liter of seawater thus contains 7.21*10^23 ions, 10^4 cubic metres contains 7.21*10^30 ions. If the temperature of seawater is 15°C, then g2-g1 = 2.87*10^10 Joules. Count Iblis (talk) 03:58, 20 July 2012 (UTC)

That's nearly 8 megawatt hours. I wonder why the discrepancy with the 1 MWh figure above. 75.166.200.250 (talk) 07:02, 20 July 2012 (UTC)

Looie probably forgot a factor of ten somewhere, the source he uses says "0.66 kcal / liter is the minimum energy required to desalination of one liter of seawater, regardless of the technology applied to the process.". If you use this then you get almost the same figure as I obtained (they use 33 g/L for the salt concentration and I took 35 g/L, if you correct for that, then the agreement become even better). Count Iblis (talk) 15:35, 20 July 2012 (UTC)

Neurodynamics of biomusicology

Hi. Recently, I became interested in the concept that some animals other than humans can "understand" music and appropriately respond to it. We all know that humans have a range of musical perception, interest and appreciation, and that other animals use music or music-like sounds as a form of communication. Also, there are videos on Internet of dog and cat dancing to music. Birds, on the other hand, use song that humans interpret as musical. Meanwhile, in the Chinese language there is a proverb that states "playing piano to an ox", suggesting perhaps that oxen do not understand music. In the extreme case, insect buzzing can also be music-like, but their brains are small. Finally, the clade of dinosauria may have used music[citation needed]. Dolphins and other cetaceans use human-understandble music, have the second-largest encephalization quotient in all of Animalia, and some evidence of human-cetacean communication is potentially documented. All of these are examples of anecdotal evidence. However, could there be an overlap between human and non-human music? More specifically:

• What brain structures and patterns allow for the comprehension of music?

Which lead to a more interesting question:

• Is there any corresponding resonance pattern between the types of music that a certain species "understands" and the more subconscious brainwave patterns such as delta, mu and theta?

Furthermore, this leads to an even more interesting question:

• What does this imply from an evolutionary psychology standpoint?

I recently came across the above-linked articles, and they may be relevant in answering the question, as I knew nothing about this topic beforehand. Thanks. ~AH1 ^(discuss!) 22:40, 19 July 2012 (UTC)

Music appreciation is probably a learned social behavior. Please see PMID 22732561 (figures, tables, and supplementary material.) 75.166.200.250 (talk) 22:44, 19 July 2012 (UTC)

Let me just recommend the book Musicophilia by Oliver Sacks, if you want to know more. I haven't actually read it, by everything by Sacks is very readable. Looie496 (talk) 01:37, 20 July 2012 (UTC)

It is largely a collection of case histories, not a theoretical book. But yes, almost everything he writes is excellent, even his account of falling down a mountain. μηδείς (talk) 04:34, 20 July 2012 (UTC)

I was somewhat underwhelmed by it, I must say. I loved some of his early work (Awakenings was by far the best book I read in 1976, probably for the entire second half of the '70s), but Musicophilia didn't do it for me, and it received very mixed reviews. What I would recommend, though, is Robert Jourdain's book Music, the Brain and Ecstasy. -- ♬ Jack of Oz ♬ ^{[your turn]} 11:22, 20 July 2012 (UTC)

"Undertanding" music and enjoying it requires at fundamental level 3 things (1) a sense of timing, (2) a sense of pitch (ie frequency as it is called scientifically), and (3) able to sense and enjoy repetition. The are a number of subtleties, such as what pop music composers have called "ear grabber" notes (notes that are harmonically slightly out of place, or melody lines that sound exciting), but that's what it comes down to. A quite good explanation of music in terms of expliting these 3 aspects was published in a book on how to write pop songs by, of all people, Rolf Harris, about 40 years ago. You may be able to obtain a copy via your local library. Aspect (3) is of course short term memory. Aspect (2) is of general use to animals as it helps to recognise the sounds of prey and predators, and is vital to communication. Aspect (1) is of general use in communication and in understanding the behavior of prey and predators. The brain structures responsible for aspects 2 & 3 have not been pinned down precisely, but a multitude of texts have been published on it. Aspect 1 has until recently been pretty mysterious, however special "clock" neurons have been discovered through the brain. Scientific American and Scientific American Mind has carried articles about it in the last year or so. Given that enjoyment of music is based on such fundamental requirements of intelligence, it should not be a surprise that animals have some sense of music. Having said that, my experience in owning several dogs, from dumb breeds like spaniels, to highly intelligent breeds like german sheherds, is that our music is just noise to them. Wickwack124.178.34.188 (talk) 02:21, 20 July 2012 (UTC)

Medical Term

What is sphincter pharyngoplasty? Does it have anything to do with tonsils? Daonguyen95 (talk) 23:28, 19 July 2012 (UTC)

See Hypernasal speech#Sphincter pharyngoplasty. Red Act (talk) 23:38, 19 July 2012 (UTC)

July 20

Do different languages have different IUPAC names?

Well, sorry for asking this silly question, but I would like to know it. I mean are they comparable to scientific binomial nomenclature of living organisms. Vanischenu m^Talk 16:58, 20 July 2012 (UTC)

The naming rules are universal, however the words themselves are translated depending on the language. Please note this paper, PubMed Tombo7791 (talk) 17:13, 20 July 2012 (UTC)

Thank you so much! That link explained everything. (Did you notice that they thanked WMF in it?:) Vanischenum^Talk 04:10, 21 July 2012 (UTC)

Followup question
There is an Italian article with a different IUPAC name. I do not know why they have omitted the numbers. In our (en) article on it, it was me who put (replaced) the IUPAC name (ref from CHEBI).) So check on it would be helpful. Again thank you.Vanischenum^Talk 04:10, 21 July 2012 (UTC)

It is often omitted when there is no other possible arrangement. 1,1,2,2- is the only choice in this formula. (Unless I am missing something.) Rmhermen (talk) 04:53, 21 July 2012 (UTC)

Thank you! But I wonder why CHEBI has put it on to the IUPAC name. Can you please provide me a reliable IUPAC name source? The problem is, now I cannot trust any of those sites. Even PubChem provided me a false info (on a structure). So a reliable site which provides good IUPAC names. I want them to put as refs in articles. Thank you.Vanischenum^Talk 20:33, 21 July 2012 (UTC)

Freezing a liquid evaporating a part of it

Evaporating a liquid it is absorbing heat, but if you have just one liquid can you use it, evaporating a part of it, at a dissipator and freeze the same type of liquid in another closed chamber? Both parts are at the same temperature. OsmanRF34 (talk) 18:00, 20 July 2012 (UTC)

Yes, at different pressures. 75.166.200.250 (talk) 18:12, 20 July 2012 (UTC)

That's essentially how dry ice is made - they compress the CO2, so it becomes liquid, then release the pressure and some of it evaporates cooling the rest until it freezes (they aren't in separate chambers, though). --Tango (talk) 19:10, 20 July 2012 (UTC)

Yes. The difficulty is that, for most materials, the vapor pressure of the solid is very, very low, and the vapor pressure of the liquid falls quickly as you approach the freezing point. This means that evaporative cooling becomes less effective as you get close to freezing. 75.166 points out that you can get around this by manipulating the pressures in the two reservoirs, and Tango's example of dry ice works well because CO2 has substantial vapor pressure in the solid phase. This online Q&A [5] says that you can also freeze water in a single reservoir with a vacuum pump, and here's a video that does it: [6]. I believe it's not terribly efficient because of the low vapor pressure, but it's interesting to see that it can be done. --Amble (talk) 20:27, 20 July 2012 (UTC)

Liquid argon and liquid nitrogen also solidify if you pump on them. DMacks (talk) 07:57, 21 July 2012 (UTC)

Some substances though are impossible to solidify at room temperature with compression alone. Sagittarian Milky Way (talk) 18:26, 21 July 2012 (UTC)

Indeed they do. A video: [7] --Amble (talk) 23:22, 21 July 2012 (UTC)

I think liquid hydrogen and liquid helium is not made that way unlike warmer cryogenics. I don't know enough to tell if it be impossible if you did that many thousands or millions of atmospheres of pressure though. Sagittarian Milky Way (talk) 21:56, 24 July 2012 (UTC)

What would happen if a whale hit a deepwater petroleum pipe?

Maybe this could be figured out with the whale's mass, speed of swimming, tensile properties of the pipe and whale head compressive strength etc.? Generally mechanics and materials science. And what's the biggest species of whale in oil producing regions? (i.e. North Gulf of Mexico, North Sea, Persian Gulf etc.) Sagittarian Milky Way (talk) 18:22, 20 July 2012 (UTC)

A subsea blowout preventer would close the pipe, under ideal conditions. 79.148.233.179 (talk) 18:28, 20 July 2012 (UTC)

If you have access, you can check out this article "Hydrodynamics of a ship/whale collision" [8]. Which covers a lot of the physics involved. "whale collision" returns many hits on google scholar. But none on the first few pages have anything to do with stationary objects. The paper linked above seems to say that ships pose a special challenge for whales, which are normally rather good at avoiding smashing into things. A more realistic risk to pipelines might be large schools of fish, squid, or jellies. SemanticMantis (talk) 18:32, 20 July 2012 (UTC)

Whales are not bottom feeders.--Shantavira|^{feed me} 09:24, 21 July 2012 (UTC)

The risers I think they're called go up to sea level. And at least sperm whales dive very deep. Better not mess with their ability to use sonar, then. Sagittarian Milky Way (talk) 18:11, 21 July 2012 (UTC)

Thermoelectric materials

I was wondering what the best thermoelectric materials (not for measuring temperature, but rather for generating electricity) are that one would find in a normal household, or could easily and fairly inexpensively obtain at local stores? I know that there are far better out there, but I am not so optimistic about finding Bismuth chalcogenides laying around in the back room. The only other thing that I am concerned about is that they can be safely handled by an inexperienced experimenter. Thanks! Falconus^{p t c} 19:32, 20 July 2012 (UTC)

Solid state heat pumps are made from semiconductors. They are usually in modern CCD cameras, laser diodes, microprocessors, and the like, but I think you probably want to take the diodes out of something like a USB beverage cooler. 75.166.200.250 (talk) 22:10, 20 July 2012 (UTC)

Assuming you don't mean specifically manufacturered thermoelectric devices, such as the beer cooler mentioned by 75.166.200.250 (you did say materials), I don't think you will find anything much. A good thermolectric material combines a high barrier voltage with very low thermal conductivity. The Russians in the 1940's and 1950' made an extensive search for such a material - the best they could come up with is Bismuth Telluride, and even that isn't very good. Bismuth Telluride is what is used in beer coolers, but not because it is efficient, but because it means no moving parts and convenient to make in a size really too small for a compressor. There are two possibilities I can think of: Copper oxide (once used to make diodes), which you can easily make at home, and Russian "radio lamp" materials. I think copper oxide will be so poor you will only be able to measure temperature with it, and not generate usefull power. I will post the instructions for making a radio-lamp generator later, if & when I find the reference. Wickwack120.145.176.214 (talk) 01:43, 21 July 2012 (UTC)

Hmmm, alright thanks. I'll try some stuff and see what I can come up with. Falconus^{p t c} 00:45, 22 July 2012 (UTC)

See http://blog.modernmechanix.com/kerosene-lamp-powers-radio/. The radio's (a tube set) power requirements would be 1.5V at 300 mA and 90V at roughly 10 mA. The materials used in the thermocouples are quite ordinary metals, but I haven't found the reference I had in mind yet. Wickwack124.178.45.60 (talk) 15:22, 22 July 2012 (UTC)

What components of cigarettes keep weight down ?

First, I suppose I should ask if cigarette smokers weigh less, on average, than nonsmokers. If so, do we know why ? Is it the nicotine or the tar ? And what's the mechanism ? Is it that it retards the sense of smell, and thus the appetite ? StuRat (talk) 20:44, 20 July 2012 (UTC)

Nicotine is an appetite suppressant, probably because it's a stimulant.

thx1138 (talk) 20:46, 20 July 2012 (UTC)

Nicotine thx1138 (talk) 20:47, 20 July 2012 (UTC)

Thanks, is it ever prescribed as such ? Or is the additive nature of nicotine enough to prevent that use ? StuRat (talk) 21:00, 20 July 2012 (UTC)

I doubt it. There are plenty of other appetite suppressants you could use that don't have the same nasty side effects as nicotine. Appetite suppressants aren't usually prescribed at all, though - they just aren't that effective a way of losing weight (and they all have some kind of nasty side effects). I saw something in the news recently about the FDA approving a new appetite suppressant - it was newsworthy because its so rare. --Tango (talk) 21:20, 20 July 2012 (UTC)

What side effects does nicotine have other than addictiveness ? How are they worse than other appetite suppressant side effects ? StuRat (talk) 22:09, 20 July 2012 (UTC)

"First causing a release of glucose from the liver" ... so a cigarette is a way to access stored energy, instead of having a snack.  Card Zero  (talk) 21:16, 20 July 2012 (UTC)

I just wrote a long response full of unsourced speculation, then tried to find some sources and the first google hit was Cigarette smoking for weight loss (WP:WHAAOE!). It mostly contradicts what I had written, so I'll just leave you with the link! --Tango (talk) 21:20, 20 July 2012 (UTC)

Smoking also suppresses the sense of smell and thus the flavor of food. 75.166.200.250 (talk) 22:03, 20 July 2012 (UTC)

Smokers weigh less because they're lighter. Mitch Ames (talk) 03:20, 21 July 2012 (UTC)

One thing the article doesn't seem to discuss is that people who give up smoking usually put on weight. However, this seems to be (from my own observations) because they replace the habit of putting a cigarette in their mouth by putting food in their mouth, so they often suck sweets or generally eat more snacks. Maybe the idea that smokers are thinner is backwards logic from the observation that giving up smoking makes people put on weight. Richerman (talk) 09:45, 21 July 2012 (UTC)

July 21

Is is possible to be a sociopath in a narrow area?

we don't offer medical diagnoses, including psychaiatric
The following discussion has been closed. Please do not modify it.
I am certainly not a sociopath in any classical sense, indeed if anything I am fairly sure for various reasons that I have considerably more empathy than most people. However, what I just can't do is get offended by anything. I intellectually understand what offends other people (learned, I think, from trial and error) but have no visceral response at all. What's up with that? Egg Centric 00:41, 21 July 2012 (UTC) Addition: Sometimes I pretend to be offended just cause I have the sense I should be claiming to be, even though I'm not, and I still can't help but think that that is what everyone else is doing. Also sometimes I get angry with twats and express it as being offended, but only cause that seems to be socially acceptable thing to do, not cause I'm actually offended. Egg Centric 00:47, 21 July 2012 (UTC) Can't you get offended by anything, asshole? So, I can crack up a joke about your mommy (that whore) and you would laugh with me? 88.9.110.244 (talk) 00:54, 21 July 2012 (UTC) If it was funny Egg Centric 01:28, 21 July 2012 (UTC) Nah, you're probably just INFP. Some day, someone will cross a line that you didn't know was there, and you'll be surprised by your own reaction. --Amble (talk) 00:59, 21 July 2012 (UTC) Apart possibly from introversion, where I am probably an introvert in terms of intrinsic preference (in that I loves me some nerd time) but an extrovert by usual behaviour, I am basically the opposite on that scale, so I doubt it Egg Centric 01:35, 21 July 2012 (UTC) Interesting. Shows what you get for taking things like MBTI too seriously (bad guesses). --Amble (talk) 01:55, 21 July 2012 (UTC) Three unrelated points: A) As far as psychologists are concerned, there is only "sociopath" and "not a sociopath". While indeed you can fit some of the criteria and not others, there is no defined thing as "sociopath for some things but not others". B) That said, I have only known one other person who so adamantly insisted they never could not be offended. I later realized this insistence was a coping mechanism and they actually took offense quite easily, but hid it well; C) Are you sure that nothing offends you, or are you just talking about insults? Being able to be unbothered by someone's attempts to get a rise out of you makes you more enlightened than the average human being, in my opinion. What if it is something more extreme, like being formally and publicly accused of a wrongdoing you are not guilty of? Or something really extreme, like watching someone kill a baby? Truth be told, even if you could honestly say "not offended" to all of those, I would scream that you're a sociopath. Though if you want a formal diagnosis, you'll need to see a psychologist. Someguy1221 (talk) 01:00, 21 July 2012 (UTC) It may be that we are using different definitions of offended. Of course I would not want to watch someone kill, or even torment a baby. There would certainly be a visceral response. But I couldn't characterise that response as offence, it would be more like horror. I am not unable to be insulted either in principle, but it would just make me angry or irritated. I am talking more about say sexism, racism, or whatever. Egg Centric 01:28, 21 July 2012 (UTC) Still wouldn't call you a sociopath. You just sound like you subscribe to "don't give a fuck"ism, whether you know it or not. Someguy1221 (talk) 01:34, 21 July 2012 (UTC) You are not a sociopath. Sociopaths are narcissists, you are not. Check here: Sociopaths#Cleckley_checklist. Maybe you have reached enlightenment. 88.9.110.244 (talk) 01:52, 21 July 2012 (UTC) We should not be offering diagnoses of people's psyches. μηδείς (talk) 02:46, 21 July 2012 (UTC)

Effect of Electric or magnetic fields on crystallization

So I was thinking if we have a compound whose molecules have polar covalent bonds (imagine it's a simple one, a diatomic molecule) well,the favorable position for them when the compound is crystallized must be something like:

+ - + - + - + - + -

- + - + - + - + - +

But in the presence of an electric field, the favorable position is:

+ + + + + + + + + +

- - - - - - - - - -

(assuming the field is upward) This made me wonder does presence of electric fields or magnetic fields make the crystallization harder (like in this case, although I'm not sure because although the arrangement is unfavorable for crystallization, at least they're aligned in the same... strike?) or easier? Is it done? How effective/practical is it? Does it have any use? What, if so? — Preceding unsigned comment added by Irrational number (talk • contribs) 04:59, 21 July 2012 (UTC)

In an arbitrarily strong electric field, if you manage to get the second structure you show, the crystal has ceased to be a crystal. Although at the necessary field strength you'll also be stripping electrons off the atoms. Anyway, this does actually have applications in the "inverse piezoelectric effect". Basically, by applying an electric field to a crystal, you can cause a physical distortion in the crystal. This effect has been used variously to make buzzers, very-fine-tuned motion control systems, and experimentally in noise-cancellation systems. To find out more you'd best search on Google, as Wikipedia has precious little information on it. Someguy1221 (talk) 06:56, 21 July 2012 (UTC)

Actually, what I meant was that if the compound is initially in liquid phase, how is the kinetics and/or thermodynamics of crystallization affected by the field? could it crystallize at a lower/higher temperature? what about dipoles/ionic compounds in solutions? how are they affected, do they start crystallizing at different concentrations?(I think it will be less effective for ionic compounds I guess, since the separation of charges will be harder of course, but anyway)--Irrational number (talk) 08:13, 21 July 2012 (UTC)

...anyone?--Irrational number (talk) 23:41, 22 July 2012 (UTC)

How is this (the Poincaré recurrence theorem) consistent with the second law of thermodynamics?

Widener (talk) 08:37, 21 July 2012 (UTC)

How is it inconsistent with it? Poincaré recurrence theorem is related to Ergodic hypothesis which basically states that all possible states are equally probable (a priori), while the second law (within statistical mechanics framework) states that the number of available states increases with entropy, making the higher entropy a more likely outcome. Dauto (talk) 13:53, 21 July 2012 (UTC)

I do not know your example, but the second law a little outdated and has problems.thanks water nosfim . — Preceding unsigned comment added by 81.218.91.170 (talk) 13:57, 21 July 2012 (UTC)

The 2nd law presents some difficulties of interpretation, but that's our problem, not the law's problem. The law itself is considered correct (no problems) and up to date (not outdated). Dauto (talk) 14:05, 21 July 2012 (UTC)

Considered to some people, depending on your points of view,And how you doing statistics , thanks water — Preceding unsigned comment added by 81.218.91.170 (talk) 14:26, 21 July 2012 (UTC)

Here are some articles related to that question: H-theorem, Loschmidt's paradox, Fluctuation theorem, Arrow of time. Dauto (talk) 14:02, 21 July 2012 (UTC)

The Poincaré theorem applies to a system in equilibrium. The second law only makes meaningful statements about systems that are not in equilibrium. Looie496 (talk) 15:46, 21 July 2012 (UTC)

There is only a contradiction within classical thermodynamics where you take the second law as a basic postulate. As Dauto points out, there is no problem with statistical mechanics as the second law is formulated in a probabilistic way there. It can be shown that large fluctuation to lower entropy states are most likely going to happen via a sequence of small steps which under time reversal is just how the system would relax back to the higher entropy state starting from the lower entropy state, see this article. Here they give an example of how a piano will most likely re-appear out of thin air. Count Iblis (talk) 16:22, 21 July 2012 (UTC)

Interesting paper, thanks for the link, Count Iblis. A nitpick: the authors assume that "a series of consecutive statistically unlikely events, rather than one instantaneous very unlikely event" is more probable. But, this depends on the specifics of each event - it is not a generally true statement. For any specific case, we'd have to specify what the events are, and calculate their probabilities, in order to determine which case is more unlikely. Nimur (talk) 17:13, 21 July 2012 (UTC)

Thank you for your responses. In particular, I was interested to know how the Poincaré recurrence theorem was consistent with the heat death of the universe (a consequence of the second law of thermodynamics). Widener (talk) 18:18, 21 July 2012 (UTC)

Homo Erectus (et al) Extinction?

What are the theories as to the disappearance of stable populations of tool using, fire making hominids like H. Erectus, ergaster, etc. And why doesn't it mention those theories on the wikipedia article for them? I'm not sure I buy that H. Sapiens showed up and were just so awesome that they hunted down and out-competed every last pocket of them from the entire planet. Surely there are more cogent theories than that. --68.190.114.51 (talk) 09:36, 21 July 2012 (UTC)

For H. ergaster see Homo ergaster#Origin and extinction. Otherwise Neanderthal extinction hypotheses#Interbreeding. These species may also have simply evolved over time into other forms of Homo (before H. sapiens existed). See also human evolution and Human evolutionary genetics. And possibly Archaic human admixture with modern Homo sapiens
• If there are any other encyclopaedic theories, with reliable sources, you (68.190.114.51) are free to add them.
So possibly Interbreeding. They genetically became part of ... us, Homo sapiens (Wikipedia editorailis) (man who edits Wikipidia) ;-). - 220 of ^Borg 10:23, 21 July 2012 (UTC)

Specific to H. Neanderthal, climate change may have been a factor: "Climate Change Killed Neandertals, Study Says," National Geographic News, or maybe it was Volcanism? "Volcanoes Killed Off Neanderthals, Study Suggests", again, National Geographic . - 220 of ^Borg 10:34, 21 July 2012 (UTC)

One species only has to be ever so slightly better suited to it's environment than another to replace it. Consider the introduction of various placental mammals to Australia, which threatened to wipe out the native marsupials, with only massive culling by humans able to prevent this from happening. StuRat (talk) 22:49, 21 July 2012 (UTC)

In that case Extinction particularly Species#Causes may make enlightening reading. Unfortunately it only makes passing mention of extinction relating to Homo, and then relating only to Homo sapiens. One interesting point made is "A typical species becomes extinct within 10 million years of its first appearance ..." according to A Mathematical Model for Mass Extinction.Cornell University.- 220 of ^Borg 07:17, 22 July 2012 (UTC)

Does this physicist literally want to go back in time to save his dad?

I vaguely remember hearing Ronald Mallett talk to NPR talk show host Terry Gross about what first got him interested in time travel (the death of his father) and from what I remember, despite his intelligence, I got the impression that he actually still harbored the idea of going back in time, finding his dad, and saving him. From our article: "In 2006 Mallett declared that time travel into the past would be possible within the 21st century and possibly within less than a decade."

Can anyone confirm if it's the case that this man literally thinks he will one day engage in some fantastical journey through time to save his dad? Peter Michner (talk) 14:06, 21 July 2012 (UTC)

I seem to recall that at the end of the interview/story that Mallett concluded that he wouldn't be able to go back to any time prior to the building of the machine? But my understanding was yes, he was invested in the idea of creating a literal time machine. --Mr.98 (talk) 16:12, 21 July 2012 (UTC)

I heard an interview with the same person (I don't recall the name, but I'm fairly certain it was the same guy) on a certain radio show some time ago. I do recall him stating that the death of his father was what motivated him to research time travel. He also pointed out, though, that (by some complicated physicist reasoning that I don't particularly recall) he believes only time travel to the near future is possible, and that neither he nor anyone else will ever be able to travel backward in time. Citation needed on that one, though. Evanh2008 ^{(talk|contribs)} 03:43, 22 July 2012 (UTC)

How is steam weighed?

The article for New York City steam system says "Roughly 30 billion lbs (just under 13.64 megatons) of steam flow through the system every year". How is steam weighed? Dismas|^(talk) 14:30, 21 July 2012 (UTC)

By conservation of mass, the amount of steam out is equal to the quantity of water in. You may also find steam quality interesting: for a specific sample of steam, it is possible to derive the percentage that is gaseous water and the percentage that is liquid water in suspension, because that affects thermodynamic and other properties. For a given pressure and temperature, "wet" steam is less energy-dense, and therefore less efficient for engineering purposes (e.g., produces less mechanical work) than dry steam. Nimur (talk) 14:58, 21 July 2012 (UTC)

That makes sense. Thanks! Dismas|^(talk) 15:02, 21 July 2012 (UTC)

missing sub-topic under either Buprenorphine or Substance Abuse on "Methods of detxiing off of Long Term Buprenophine Maintenance"

This information is going to be more and more needed as the tidlewave of Opiate users are switched from Methadone to High Dose Buprenorphine, not for detox, but years of maintainence. The missing topic is very specific and almost impossible to find anywhere except on Scholorpedia where they have an article on this. The missing information or sub-title is "METHODS OF DETOX FROM YEARS OF HIGH DOSE BUPRENORPHINE USAGE"? Even with 18 years of pharmacology experience I've had, and even the so called "Certified MD's" who prescribe it don't even know. My MD said when I told him that I need to get off as I can no longer afford to take them said, "oh, just take a half every other day" which is ludicrous when your on 16 to 24 mgs a day. I've been on it over 5 years and big money is being made due to the forementioned MD's don't take insurance and the new sublingual filmtabs cost $510.00 US dollars at CVS the number 1 retail Pharmacy in the US for a ONE MONTH SUPPLY ! Also besides that issue, under buprenorphine, the new film tabs that have come out at the aforementioned price needs adding, and also the Patent on 'Subutex" but not Suboxone has expired, and with a coupon I get the generic Subutex for only $182.00 which is a cost savings of 328.00 dollars. If you show your MD the proof, and you've always been clean on your urine tests, a compassionate MD will Prescribe the genric for you which works really well. Just sharing some new info. Utilize, research, or trash whatever you want. Sincerely, A WIKIPEDIA FANATIC (I JUST LOVE THIS SITE SO THATS WHY I'm trying to help.) — Preceding unsigned comment added by 70.119.99.213 (talk) 19:10, 21 July 2012 (UTC)

Or you could just move to a country with a civilised (or semi-civilised) health system. 16mg of buprenoprhine a day costs me £21 a quarter, and if I were on benefits or poor then it would be entirely free. Anyway, what's the question? Egg Centric 19:13, 21 July 2012 (UTC)

It sounds like you found the info you need, and don't have a Q for us, so I'll mark this resolved. StuRat (talk) 19:14, 21 July 2012 (UTC)

Resolved

When people comment on information they think is missing from our articles, we should direct them to the article's talk page (Talk:Buprenoprphine in this case). Raising a point on the Reference Desk is unlikely to lead to any improvement in the article -- it happens sometimes, but not often. The personal anecdote doesn't have much value for that purpose, but pointing out things that are missing is one of the primary purposes of a talk page. Looie496 (talk) 00:03, 22 July 2012 (UTC)

Micro-stuttering and perceived frame rate

According to this Tom's Hardware article, the effect of micro-stuttering on the perceived frame rate is more severe at lower nominal frame rates -- that is, the perceived frame rate goes down faster than in inverse proportion to the longest delays between successive frames. Is there anything in the psychological literature that confirms and quantifies such an effect? NeonMerlin 22:26, 21 July 2012 (UTC)

If the frame rate is slower to begin with, then you are more likely to notice discontinuities in it. http://jn.physiology.org/content/103/1/230.long maybe? 75.166.200.250 (talk) 05:00, 22 July 2012 (UTC)

Will-o'-the-wisp

Is there a scientific explanation for why will-o'-the-wisp marsh gas lights move away as the observer approaches? I don't understand why it wouldn't be possible to walk right up to the marshlight and watch it burning from close by. 174.88.8.149 (talk) 23:35, 21 July 2012 (UTC)

Is that even true? Can you point to a reputable source that says so? Looie496 (talk) 02:30, 22 July 2012 (UTC)

That is what it says in the article here. I am asking you for sources. If I could find them on my own I wouldn't have to ask here. 174.88.8.149 (talk) 03:20, 22 July 2012 (UTC)

The article says specifically that the will-o'-the-wisp "is said to recede if approached". I'm guessing that it's "said" to do this in the same way Bloody Mary is "said to appear in a mirror when her name is called multiple times". In other words, such claims are nonsense. I don't blame you for inquiring further, though. Evanh2008 ^{(talk|contribs)} 03:25, 22 July 2012 (UTC)

Will-o'-the-wisps are anecdotal and thus are not always the same phenomena. And actually they have been observed up close. There's a very interesting article by the late 19th century British scientist Charles Tomlinson regarding them (see Charles Tomlinson (1893). A. Cowper Ranyard (ed.). "On Certain Low-Lying Meteors" (PDF). Knowledge: An Illustrated Magazine of Science. Simply Worded—Exactly Described. 16 (New Series, Vol. III). Witherby & Co.: 46–48., note: "meteor" is an archaic scientific term for atmospheric phenomena). In the article, he recounts a Major Blesson from Berlin who made observations on ignes fatui in marshlands in a forest in Neumark, Germany. By day the water in the marshland was visibly bubbling with gases rising to the surface. By night, bluish-purple flames are seen at the surface. Here's an account of a closer inspection of the flames:

On visiting the spot at night, the sensitive flames retired as the major advanced; but on standing quite still, they returned, and he tried to light a piece of paper at them, but the current of air produced by his breath kept them at too great a distance. On turning away his head, and screening his breath, he succeeded in setting fire to the paper. He was also able to extinguish the flame by driving it before him to a part of the ground where no gas was produced; then applying a flame to the place whence the gas issued, a kind of explosion was heard over eight or nine square feet of the marsh; a red light was seen, which faded to a blue flame about three feet high, and this continued to burn with an unsteady motion. As the morning dawned the flames became pale, and they seemed to approach nearer and nearer to the earth, until at last they faded from sight.

So one explanation (if it is swamp gas) is that the gas disperses easily on nearby movement. Blesson apparently repeated similar experiments in other marshlands. Succeeding in actually creating ignes fatui on a couple of occasions by firing rockets over marshlands. Here's another account by a reader's letter from a certain Charles Nielsen of Hartlepool of a similar phenomenon again caused by ignited methane:

Three miles north of here there is a small deep dam, which serves as a reservoir to supply the railway company with water for their locomotives, and on which I, with a few friends have skated, whenever it has been sufficiently strongly covered with ice, for many winters past. It has been our custom to take a borer with us and make a small hole on the centre of the ice, through which a stream of CH₄ issues and which we ignite by applying a lighted match, when a pale blue flame, rising occasionally to a height of three feet, appears; in bright sunshine this becomes practically invisible, but it is undeniably very hot.

Modern science of course explains it now as phosphine igniting on contact with oxygen and touching off nearby methane gases (see Roels, 2001). But to underline the fact that ignes fatui are usually various phenomena, here's a starkly different recounting by a certain Richard Taylor (also from reader's letters in reply to Tomlinson), while out camping on a rainy night in New Zealand:

No sooner, however, had the men fallen asleep, and the fires began to die away, than a light was observed, like the moon shining through a chink. There was no moon, and the night was very dark. On a closer examination the object appeared as a globe of pale light attached to the point of a palm leaf which hung from the roof. Another ball of light was now seen, attached to the wet sleeve of a shirt hung up to dry. "The air appeared to be charged with these luminous vapours, for while regarding the two in the shed a series of them floated past at an elevation of about a yard from the ground." These and similar phenomena, which are evidently electrical, the author endeavours to trace to the remains of the highly resinous Kauri pines which abound in the place.

His account, in contrast, seem to be the far more mysterious phenomenon known as ball lightning. And that in contrast seem to have no problems being approached, as evidenced by accounts where people or animals are actually injured or killed on contact with them.

And lastly ignes fatui, like UFO sightings, can be anything from legitimate unknown natural phenomena (see F. St-Laurent, 2000 for example of a description of strange lights after the 1988-1989 earthquakes in Saguenay, Quebec), hoaxes, hallucinations, or caused by other more mundane things. A swarm of fireflies mistaken for an ignis fatuus will fly away when approached. Or more hilariously, it may simply be other people carrying lanterns or torches through fog, who upon seeing each others' lights promptly flee from each other in terror. :D -- OBSIDIAN†SOUL 03:47, 22 July 2012 (UTC)

I'm partial to the fireflies. Excellent answer! The article needs a {{cn}} tag on the statement in question. 75.166.200.250 (talk) 05:12, 22 July 2012 (UTC)

I think we can expand the article with the above (at least Tomlinson's account). I'll try to insert it under the Scientific explanation section.-- OBSIDIAN†SOUL 05:44, 22 July 2012 (UTC)

I linkified the title. StuRat (talk) 06:05, 22 July 2012 (UTC)

The type which moves as approached suggests some form of optical illusion to me, like a rainbow or mirage, which also move or disappear as approached. The gas explanation could work, too, though, especially since many flammable gases can only ignite within a narrow range of percentages of gas and oxygen, and any nearby movement would tend to change that. StuRat (talk) 06:09, 22 July 2012 (UTC)

Alright, I've significantly expanded the scientific explanations section of the Will-o'-the-wisp article, including earlier experiments by Volta, Priestley, Saint-Lazare, and Blesson. Feel free to copyedit (or expand further) if necessary. -- OBSIDIAN†SOUL 07:32, 22 July 2012 (UTC)

Oh, and I also found an online copy of Blesson's original paper. It's definitely worth a read.-- OBSIDIAN†SOUL 07:37, 22 July 2012 (UTC)

Wow!! That is the best answer I have ever received here and that you fixed the article is amazing. Thank you!! 174.88.8.149 (talk) 13:11, 22 July 2012 (UTC)

yw :) -- OBSIDIAN†SOUL 14:37, 22 July 2012 (UTC)

Has the Altair spacecraft been cancelled?

So I was reading the article on the article of the Altair lander. It is stated that Project Constellation was cancelled, except for the Orion spacecraft and the Altair lander. While Orion is still in development, the tense used in the Altair article implies it was cancelled, despite the article stating that it hasn't. Also, I saw other articles saying that Altair is indeed cancelled. Once and for all, has it been cancelled or not? Narutolovehinata5 ^tccsdnew 23:36, 21 July 2012 (UTC)

My understanding is that Orion is still going, but isn't actually projected to be sent to the moon. Thus, Altair would become slightly superfluous to the project. It's probably cancelled, but I'm not sure I can find a source that supports that. It's really amazing how little coverage Orion is getting nowadays; the whole project is probably NASA's best kept secret. Evanh2008 ^{(talk|contribs)} 01:08, 22 July 2012 (UTC)

Space.com specifically talks of Altair in the past perfect tense ("would have" gone to the moon, etc.). However, I haven't been able to find any specific sources on its cancellation. It probably was scrapped at the same time as Ares and the rest of Constellation. Evanh2008 ^{(talk|contribs)} 03:37, 22 July 2012 (UTC)

Yes, the current US government manned spaceflight plans are to take the Orion CEV to asteroids. There's nothing even vaguely useful on the Moon or any other planet or moon short of Titan. In contrast, at least 5% of asteroids are expected to be rich in ice and dry ice cores, along with metals in similar proportion to those in the Earth's crust. Asteroids are also the only cost effective source of radiation shielding needed for viable manned space stations beyond Low Earth Orbit. Those asteroid resources are much more accessible for space utilization than anything in Earth's gravity well or on the Moon or any other planet or moon (not counting skimming hydrocarbons from Titan, which isn't really practical until the asteroids are harnessed, and isn't really necessary until deployment of a fleet of replenishable-propellant construction robots which may be likely to skim from Titan if asteroid fluids aren't practical.) 75.166.200.250 (talk) 03:50, 22 July 2012 (UTC)

Actually, there is water on the Moon, which is helpful if you're interested in producing oxygen via electrolysis, either for breathing or for fuel purposes. Producing these things in a low-G environment is extremely useful for reducing fuel costs during lift-off. Helium is also present in significant quantities and has a few more uses than just birthday parties. The Moon is also rich in silicon dioxide and numerous other materials that would be quite useful for establishing a permanent presence in space. It's also only three days away, whereas the asteroids take a significantly longer period of time and a greater amount of fuel to access. To sum it up, there are all kinds of reasons that the Moon is a better target for space exploration than the asteroids at present, including a few that I didn't mention. Titanian hydrocarbons are promising, of course, but are a long way off right now. Evanh2008 ^{(talk|contribs)} 03:58, 22 July 2012 (UTC)

I'm pretty sure that asteroid water is orders of magnitude more accessible than lunar water, both on a time and energy basis per liter. Of course there are a lot of unknowns, but just going by mean estimates, many of the asteroids are old comets likely still composed of more than 20% water under a rocky crust, if comet 103P/Hartley is typical. There is only one way to find out. I'm not a fan of lunar or martian colonies for their own sake, and would much rather have a shielded space station to establish a permanent presence in deep space because of the extent to which it would show how interstellar sleeper ships might be feasible. I am in favor of terraforming Mars, but prior to establishing a colony there, and that is likely to take many hundreds of years. 75.166.200.250 (talk) 04:24, 22 July 2012 (UTC)

I hear you on the interstellar stuff and on terraforming, and I sort of look at lunar colonies as a means to those ends. The problem with Apollo was that once it was finished, it was over and the US had no real incentive to go back. Once you begin actually colonizing the moon and exploiting its natural resources, you do have an incentive to be present on a continual basis. Starting strong in the local neighborhood and branching out from there seems to be the best path possible to me. The asteroids can and should be part of that, of course, but lunar colonisation is more conducive to deep space travel than most people realize, simply because you can manufacture things there and launch them at a far lower cost than you ever could on Earth. Lagrange point space stations, for example. You may be right about asteroid water, though. I'd have to do more reading to be certain on that point. Evanh2008 ^{(talk|contribs)} 04:29, 22 July 2012 (UTC)

Gold and non-gold pendants together?

I've been wanting to buy a pendant from Shapeways, but I'm unsure of which material to select. I normally wear a necklace with five other charms. The charms and necklace are gold, but I can't say what percentage gold they are. I've worn this necklace nearly every day for five years, and I haven't noticed any wearing down of material / corrosion / what have you. The current state is durable for the foreseeable future.

It's adding another, dissimilar pendant that has me a little worried. Would adding a steel or silver pendant adversely affect the other pendants? What if the new pendant is only gold-plated? Will the gold plating last under such conditions? These are the materials that Shapeways offers, though the only ones available to use on the pendant are the top row, steel (with its finishes), and silver. The last thing I would want is for anything to damage anything else. Thanks for your help.--The Ninth Bright Shiner 23:42, 21 July 2012 (UTC)

What type of damage do you mean ? If you mean scratching the gold, then you want to avoid anything much harder than gold. Silver isn't too hard, compared with the most common gold alloys, but steel is, so I'd avoid that. You should also space the charms far enough apart that they don't strike each other while you wear it (but of course they still can when you take it off). If you meant damage due to galvanic action, I don't think that would be a concern with any of these materials, I'd be more worried with copper, brass, bronze, and aluminum.

As far as gold plating goes, yes, it will wear off eventually, starting at the corners. How long it lasts depends on thickness and usage. StuRat (talk) 23:50, 21 July 2012 (UTC)

Hmm. The charms are constantly in contact with each other; there isn't really any spacing between them. I wouldn't want to replace or discard worn-down gold plating. Add to that I don't really want a mismatched charm on the necklace... it looks like I won't be purchasing that pendant, at least with my current plans in mind. :( Thanks for the info!--The Ninth Bright Shiner 04:27, 22 July 2012 (UTC)

You're welcome. Can't you get new charms made the same way as the old ones ? A jeweler can tell you what percentage of gold is in your current charms. StuRat (talk) 06:12, 22 July 2012 (UTC)

I doubt I could get this new charm made like the old ones. The closest I could get from Shapeways, the manufacturer, is steel plated with gold. Can you take any old charm to a jeweler and have a similar one made in a new material? Unlike some products from Shapeways, this charm isn't terribly complex...--The Ninth Bright Shiner 17:42, 23 July 2012 (UTC)

Production of chemical fertilisers

This question was asked at talk:fertilizer, so I've moved it here. SmartSE (talk) 23:49, 21 July 2012 (UTC)

This article lacks information on how chemical fertilzers are made. It would be nice if someone knowledgable on the subject would elaborate this subject. I have heard that chemcical ferilizers are derived from crude oil. If that is the case I can not see that using it would violate organic principles since crude oil is the waste of feces of ancient animals. 2602:306:C518:62C0:290F:5E4E:7E60:2AD6 (talk) 19:43, 21 July 2012 (UTC)

That strikes me as a reasonable comment to have on an article's talk page, given that it directly relates to the content of the article. Looie496 (talk) 23:57, 21 July 2012 (UTC)

There is a wide variety. Some are synthetic, but most such as potash or fixed nitrogen, potassium, and nutrient compounds are merely refined from minerals, animal waste and byproducts, or sewage. Ammonium nitrate is mostly synthetic these days. 75.166.200.250 (talk) 05:06, 22 July 2012 (UTC)

Actually oil isn't the feces of organisms, it's the bodies of various once-living organisms (mainly plankton and algae): see Petroleum#Formation. --Colapeninsula (talk) 16:08, 22 July 2012 (UTC)

July 22

Short-term memory fading

If someone demonstrates bad short-term memory recall are there ways of improving their memory or is it a case of once its gone its gone? -- role^player 00:10, 22 July 2012 (UTC)

That's sort of a confused question. The term "short-term memory" actually comprises a number of different types of memory, with different properties. For some of them, there are ways of improving memory. However, improving memory doesn't generally mean gaining the ability to bring it back after it's gone, it means developing the ability to keep it from going away. Looie496 (talk) 00:55, 22 July 2012 (UTC)

I asked the question after reading the article short-term memory. There is nothing there about improving memory, which is why I asked. Sorry it's confusing, I thought it was a fairly simple question. -- role^player 01:03, 22 July 2012 (UTC)

Psychology books and my experience show that "rehearsal," or repetition of the entities in short term memory, aid in preserving therm far better than passively "trying to remember" them. .Show the subject a long telephone number or license plate. If the subject thinks about nothing, then the briefly presented information fades from memory in a few seconds. If the subject is given an interfering task ("Count backward by threes from 97") the fading is much faster. Now let the subject keep repeating the license plate or 10 digit number until permitted to write it , type it, or say it. The recall is amazingly better. Beyond that, there are special mnemonic techniques which would allow a person to absorb and recall masses of information. Edison (talk) 01:26, 22 July 2012 (UTC)

(ec) Ah, I've never looked at that article. The ideas it covers are actually a bit antiquated, dating back to cognitive psychology of the 1960s and 1970s. As I understand it, most people who study memory nowadays don't think that a distinct "short term memory" in that sense really exists. Anyway, the article does briefly mention the two things that are most useful in improving that sort of memory: chunking (meaning forming high-level concepts for complex clusters of information), and rehearsal (meaning focusing attention on the material you want to remember, and repeating it to yourself. Looie496 (talk) 01:27, 22 July 2012 (UTC)

It's pretty funny to read about "antiquated cognitve psychology of the 1970's" and that "short term memory doesn't exist." One memory technique is to learn a rhyme: "One is a bun, two is a shoe, three is a tree, four is is a door, five is a hive, six is sticks, seven is heaven, eight is a gate, nine is a lion, ten is a hen." It should take only a couple of repetitions and repetition trials to learn this perfectly. Then if one has to memorize ten concrete objects in order, each can be quickly associated with the noun at that position in the rhyme, by forming a vivid image of the key and the thing to be remembered. If the second thing is "honey," it is easy to remember a shoe full of honey. I. A teacher I knew had 26 such mnemonic links, one for each letter of the alphabet: "A is ape, b is bee, c is cat..." etc and could hear and recall 26 arbitrarily chosen things in a room in order. If numbers are to be remembered, there is a system for substituting consonants for digits, then remembering a concrete object for each number. One mnemonist could hear and recall 500 arbitrary three digit numbers thus. Edison (talk) 02:11, 22 July 2012 (UTC)

I didn't mean to say that there is no such thing as short term memory, just that the properties discussed in that article do not distinguish one particular type of memory that can be clearly separated from other types of memory. Looie496 (talk) 02:27, 22 July 2012 (UTC)

Alcohol and various psychotropic drugs like valium and ambien as well as marijuana and narcotics like oxycontin interfere with short term memory. Not taking them will help if taking them is a problem. One of the major benefits of marijuana is that every time you watch a movie high is the first time. μηδείς (talk) 03:32, 22 July 2012 (UTC)

Context is important to this question. Specifically the age of the person. If the individual is younger and previously fit with a good short term memory then there will be a range of causes that will different from those of a person aged, say 70+years. Whether the ability to recall recent events can be improved will depend to some extent on the cause. Some kinds of organic brain disease will cause this phenomenon, and although it may be delayed a little by therapeutic intervention its progress will be inevitable. Short term memory impairment caused by vascular shortcomings in the brain may require different therapeutic strategies and the outcome will be varied, depending on the medical abilty to resolve the circulatory problems. Some forms of new growth in certain parts of the brain may cause short term memory problems and again the ability of the medical intervention will have much influence on the final resolution of the memory difficulty. Taking psychotropic drugs can impair concentration and thus short term memory, in this group can be included many illegal mind-altering substances. If the memory is unrecallable after a short time it is possible in some circumstances to prompt a recall with clues but generally the further back an unrecalled memory slips the more difficult it will be to permanently 'imprint' it and recall it. Richard Avery (talk) 08:03, 22 July 2012 (UTC)

I have something of short term memory problem. Sometimes when people ask me what I did that morning, I have to say I can't remember, but ask me in ten years time, as my long term memory is excellent. Myles325a (talk) 08:31, 22 July 2012 (UTC)

Personally I have found marijuana only effects my memory about a fortnight to a month after stopping taking it, if I have taken a reasonably sizeable amount. Get a lot of "tip of my tongue" type stuff for a week or two. Egg Centric 16:27, 22 July 2012 (UTC)

Surprised to learn taking marijuana effects one's memory. Although there may be a difference between elephants and aardvarks. μηδείς (talk) 03:35, 23 July 2012 (UTC)

3rd order gas phase reactions - pressure limit

In elementary 3rd order reactions of the type A + B + M → AB + M and A + A + M → A₂ + M, where M is some other low affinity or inert atom or molecule, it appears from various chemistry texts that the reaction rate for any given concentration/partial pressure of A & B, increases in linear proportion to the concentration of M, up to a certain limit (the pseudo 2nd order region), which is independent of what M is. Below this limit, the rate is proportional to [A]²[M] or [A][B][M] and depends on what M is. In other words, if you plot the reaction rate against [M] for various M, you get a family of curves with more or less parallel upward slopes merging into a common horizontal line after a certain concentration [M].

What, in simple words, determines this limit? The textbooks I have don't say. The only thing I could think of is that it occurs where the concentration [M] is so high that the probability of an A+B+M or A+A+M collision is about the same as an A+A or A+B collision. But that does not seem likely, and in any case increasing the concentration of A and B would then re-eastablish a 3rd order relationship - so that cannot be it.

Second question: What happens if the concentration of A or B is increased to the same [M]-limit value, with low [M]? Does the reaction rate become 2nd order involving the concentration of M, ie [A][M] or [B][M]?

Ratbone124.182.180.91 (talk) 12:06, 22 July 2012 (UTC)

Effective power of a satellite dish turned into a solar cooker

Greetings,

If a satellite dish identical to this one is covered in standard Aluminium foil and placed in a region where the mean insolation is about 200 W/m², what would be the effective power of the resulting solar cooker? I've calculated the theoretical power expected myself, but I'm sure there are more practical bounds on the resulting power than I've taken into account. I would also be happy to hear estimates about the time it would take to boil about five litres of water with such a solar cooker, assuming that their initial temperature is about 30°C. Many thanks, ליאור • Lior (talk) 15:16, 22 July 2012 (UTC)

The dish appears to be about 4 m in diamter. Therefore the area = Πr² = 12 m² approx. So the collecting power is 12 x 200 = 2400 W = 2400 J/s. The thermal capcity of water is 4182 J/l.K and the latent heat of vaporisation at 1 Bar is 2260 kJ/l. So the required heat is [4182 x (100-30) + 2260,000] x 5 = 2,552,740 J. So the converted dish could in theory boil 5 l of water in 2,552,740/2400 seconds = 1064 seconds, ie about 18 minutes. This should be multiplied by the reflection factor of the aluminium, which can be very high, nearly unity, or very low, <<1, depnding on how well it is pollished. Your figure for insolation is very low. Most locations will be closer to 1kW/m2 if the dish is pointed correctly. On the other hand, the performance may be degraded if the dish is not made to track the sun as it moves across the sky. This problem can be largley eliminated if the hated surface is made wide enough so that the focussed hot spot allways falls on part of it. Ratbone120.145.152.248 (talk) 15:54, 22 July 2012 (UTC)

The "hated surface" ? StuRat (talk) 19:12, 22 July 2012 (UTC)

Stu, if you keep squawking about my typing, I'm gonna crawl right up your internet connection and heat you with an oxy torch. Ratbone124.182.137.103 (talk) 03:10, 23 July 2012 (UTC)

Not complaining, I just can't tell what you meant. (You had 7 other typos, which I didn't mention, since I can figure those out on my own.) StuRat (talk) 03:39, 23 July 2012 (UTC)

Note that this 18 minute figure doesn't consider that the water will be radiating heat back out and cooling due to evaporation. The hotter it gets, the more cooling there will be. So, it will take longer to boil than that, or may only boil once much of it evaporates so the heat is concentrated on a smaller volume, or may never boil at all. StuRat (talk) 19:16, 22 July 2012 (UTC)

There are two other problems with the calculation. First, there is the factor of 5 between the 200W/m² and the more realistic 1000W/m² around noon time. Secondly, I would interpret "to boil 5l of water" as "to bring 5l of water to a boil", not "to boil it away". So the latent heat of vaporisation does not really come in. With these assumption, an ideal 4m dish can bring 5l of water to a boil in about 25 seconds under optimal conditions - much more plausible, given how fast e.g. a 2kW electric kettle will bring 2l to a boil. --Stephan Schulz (talk) 20:44, 22 July 2012 (UTC)

You are correct, he will have meant "bring to boil" - my error. Ratbone124.182.137.103 (talk) 03:10, 23 July 2012 (UTC)

Note that aluminum foil will reflect in all directions, so you won't get anywhere near 100% pointing at the water. Also note that you'd need to rig a system to suspend the water where the cone of the satellite dish was, and hold it there, without spilling, as the dish is moved to track the Sun. You also need a way to add and retrieve the water, since, at that radius, you won't be able to reach it directly. StuRat (talk) 19:12, 22 July 2012 (UTC)

Not necessarily Stu. You can polish aluminium to a mirror finish, and it will then act as a mirror for infra-red as well. You don't need to have the dish moving to track the sun. As the cook time is only minutes, it is sufficient to make the heat surface large enough so that the focused heat always falls on it even as it moves across, as I said. This trick is sometimes done in radio communications - or the actual antenna nominally at the focal point is moved instead of moving the whole dish. Ratbone124.182.137.103 (talk) 03:10, 23 July 2012 (UTC)

Polished aluminum would be much better, yes, but we are talking about aluminum foil here, wrinkles and all. I recommended against trying to track the Sun further down. However, to have it work at a wide range of positions of the Sun, like at the Arecibo Observatory, you need a spherical reflector, not the parabolic reflector of a satellite dish. StuRat (talk) 03:29, 23 July 2012 (UTC)

We should also ask why you want to boil the water. Is this to sterilize it ? If so, I suggest a continuous distillation system where water flows in, boils, the steam condenses, and the condensate runs off as sterile water. Ideally you would add dye to the water to make it absorb the light, but, if you don't want to do this, a dark bottomed, clear topped container will work, although not quite as well. You will need to periodically dump the water left in the container, as it will build up salt and other minerals otherwise. StuRat (talk) 19:25, 22 July 2012 (UTC)

The application is, basically, cooking in a remote village with no regular electricity. Clean water are generally available, but a clean energy source for cooking could be of use. Let's say that an Aluminum foil reflects about 80% of the incoming radiation back to the focal point. To what extent will this figure drop due to the fact that it is not applied tightly to the surface of the dish? That is, there will surely be some wrinkles that will scatter light away to other directions, rather than to the focal point. How significant will the effect of these wrinkles be, assuming that we're just manually gluing the aluminum foil to the dish? ליאור • Lior (talk) 20:16, 22 July 2012 (UTC)

I would not be too concerned about conforming exactly to the parabolic shape - reasonable care will be fine, as you don't need (nor is it desirable) to bring the focussed energy to a pin point. You only need a rougfh focus that brings nearly all the refelcted energy to the surface area of the container to be heated. Ratbone124.182.137.103 (talk) 03:10, 23 July 2012 (UTC)

Besides, this figure suggests that an average insolation of ~200 W/m² is rather typical at ground level. Is it wrong? ליאור • Lior (talk) 20:20, 22 July 2012 (UTC)

That is averaged over 24 hours. Your cooker will not cook anything at night, but will be much better at noon. --Stephan Schulz (talk) 20:32, 22 July 2012 (UTC)

I take it by "cooking" you mean food which requires cooking to be made safe to eat, like meat. I assume such food would be opaque to light, so a clear glass container, with lid, should work. I think you'll do better to cut it into small pieces first, so the heat will penetrate better. Try to minimize the amount of added water, as that will require more heat. As a practical matter, repositioning such a satellite dish as the Sun moves might be quite difficult, so you might do best to position it pointing straight up (or aimed a bit to the south, if north of the tropics, or a bit north, if south of the tropics). Cook most the food when the Sun is highest in the sky. You could possibly cook reduced quantities in the morning and afternoon, so long as no shadows fall on the satellite dish. The satellite dish will need a drain hole at the bottom.

Placing and retrieving the dish will still be difficult. You'll need something like a pizza paddle, and the grill on which the dish is placed will need a backstop to prevent the paddle from pushing the container off the grill. The weight of the food and container will be critical here, as the torque created by trying to lift a heavy load at the end of the paddle could cause you to drop it. It might also be necessary to cut an access point into the edge of the satellite dish, to enable you to get closer to the center when placing and retrieving the food.

Also note that children must be warned not to play inside the dish, when the Sun is up, as they could be burnt or blinded. Something else you should consider is that aluminum foil isn't very durable, and will likely be torn to shreds in a storm, and the expense of replacing it after every storm might be considerable. Some type of cover, or just flipping the satellite dish over when a storm approaches, might prevent such damage.

How to support the grill is another concern. Setting it on the inside of a rounded satellite dish would make it rather unsteady. You would either need to cut holes in the satellite dish for the legs to poke through to the ground, or have a system where there's a frame which extends beyond the edges of the satellite dish and down to the ground, but this might be rather heavy, making it difficult to flip the satellite dish prior to a storm.

To minimize wrinkles, the aluminum foil should be cut into thin strips, as they will more closely conform to the parabolic shape than wide sheets. I'd expect that placing the strips circularly would require less overlap than placing them radially. Also, have you considered just painting the inside of the dish with a reflective coating ? Or perhaps it's already reflective enough ? Try placing a thermometer at the focal point to see how hot it gets when pointed at the Sun. StuRat (talk) 20:47, 22 July 2012 (UTC)

Given the above calculations, you can afford quite some wrinkles. Check solar cooker to see some examples of practical designs. If you live in an area with plausible weather conditions, the average size of the collecting area is more like 1-2m². With 12m², you should be able to do with some reduced efficiency for added convenience and ease of construction. There is, e.g. no need to point the dish exactly at the sun - you can keep it at an angle that will result in the focal point not being over the dish, making access to the pot much easier. --Stephan Schulz (talk) 21:22, 22 July 2012 (UTC)

Did anyone bother to mention that a disk that shape focuses the reflected beams on the antenna propped up in front of the it, not on the surface of the dish or any water it would actually hold, due to its (it's if you are StuRat) shape, were it tilted against gravity? I mean, really, folks. μηδείς (talk) 03:26, 23 July 2012 (UTC)

When I was at school in the 1960's, we were taught that it's is the correct form when saying something like "It's going to rain today" - the apostophe signifies the missing letter from it is. The other valid form is its' - the correct form for writing "The dog wants to go for a walk and has fetched its' leash." - here the apostrophe signifies belonging - the leash belongs to the dog (similar use to "The handbag is Susan's.") The apostrophe is placed after the s in its' to distinguish it from it is. We were taught that there is no correct use of its (no aprostrophe) - however it has crept into wide use as school teaching is not to the standard it once was. Ratbone124.182.2.119 (talk) 06:52, 23 July 2012 (UTC)

I have an almost identical anecdote, except I was taught that its' is never a word and the correct form of the possessive pronoun is its (no apostrophe). I guess the standard of school teaching was never really that great to begin with. 203.27.72.5 (talk) 07:56, 23 July 2012 (UTC)

You geolocate to the same country as I (Australia), so it can't be regional differences. But you didn't give the decade you were at school. In a number of ways standards have slipped over the years. I noticed that when I went to uni 11 years after finishing school at Year 9 - kids in the same classes who had just finished Year 12 didn't know things that I did know. Ratbone124.182.2.119 (talk) 08:18, 23 July 2012 (UTC)

I did, when I said "note that you'd need to rig a system to suspend the water where the cone of the satellite dish was". StuRat (talk) 03:33, 23 July 2012 (UTC)

Is that thingy indeed called a cone? μηδείς (talk) 18:01, 23 July 2012 (UTC)

Water

Has anybody ever attempted to estimate how many cubic metres of water are on the earth? For instance, if the earth's crust fragmented and all of the water poured into the mantle, would it affect the internal temperature of the earth?

The mantle is already saturated with water, dissolved in the rock. What we see on the surface is merely the excess. The crust is already fractured all over the place. Looie496 (talk) 16:03, 22 July 2012 (UTC)

According to our Wikipedia article on water, the collective mass of water found on, under, and over the surface of Earth is approximately 1,338,000,000 km3 (321,000,000 mi3). This is a mass of 1.34 x 10¹⁸ kg. Since the mass of the Earth in total is estimated at 5.97 x 10²⁴ kg, water accounts for only 0.000 02% of the total, and thus can be assumed, if it were to be somehow absorbed, to make no significant effect of the Earth's internal temperature on a thermal capacity basis. However water has a big effect on surface temperature by moderating climate and by evaporation into clouds, providing a greenhouse effect. Ratbone120.145.152.248 (talk) 16:06, 22 July 2012 (UTC)

As Looie wrote, most of the water on Earth is dissolved in the magma in the Earth's interior anyway. When the solar system just formed, there were many proto planets that collided with each other to form the present day planets. Water at the distance we are from the Sun is not stable, it will evaporate. The problem is then to explain where the water on Earth could have come from. It is now believed that some of the proto-planets that gave rise to Earth came from the outer solar system. Jupiter formed quite rapidly and it caused perturbations in the orbits of the proto planets. Some proto plantes from the outer solar system containing a lot of ice moved to the inner solar system.

The water from the proto planets ended up in the interior of the planets. This water is dissolved in the magma. Slowly this water percolated to the surface giving rise to oceans. The vast majority of all the water on Earth may thus still be in the Earth's interior. If all the water in all the Earth's oceans were removed, the oceans would slowly refill with water from the Earth's interior. Count Iblis (talk) 16:17, 22 July 2012 (UTC)

Confusion on proportional sign

I am unable to understand meaning of proportion in physics. One says x ∝ y and then writes x = ky, where k is the constant of proportionality. But what does this 'constant of proportionality' means. As in case of force, we write F ∝ ma, then we write F = kma and putting value of k = 1; we write for another time that F = ma. I am confused what is the reason behind using k. I could not understand what is the use of writing '∝'. In gravitation, we write F ∝ m₁m₂/r². Then, we write F = Gm₁m₂/r², where 'G' is constant. In the case of force, 'k' was removed but in this case 'G' itself became a part of the equation. Why is this so? What does ∝ sign mean? I am a student of 9th standard, so, don't use high level language. Please, explain me in easy language with suitable example. --Sunny Singh 16:07, 22 July 2012 (UTC) — Preceding unsigned comment added by Sunnysinghthebaba (talk • contribs)

The convention is to write ∝ to signify that we suspect its proportional (ie varies in step), but we don't know, or haven't yet proved, what the multipying constant is.

As you have realised, the constant is not always 1 (unity). Usually in physics, we use logical reasoning to first prove the required result is directly proportional to something, proportional to the square root of something, or whatever, and then reason out or measure what the actual constant is. For example, we might suspect that the longer we heat water the hotter it will get, and the greater the heat the hotter it will get. We would state it as T ∝ Q x T / m where T is the temperature (K), Q is the heat (W/s), m is the mass (kg) and T is the time duration (seconds). We could then conduct a series of experiments, measuring these four quantities accurately. We would then find that dividing the quantity on the left, T, byt the bit on the right, Q x T / m, always gives 0.2391, i.e., our data will fit T = 0.2391 Q T / m. So now we know the constant of proportionality is in this case 0.2391, and is ALWAYS 0.2391, so we can write T = k Q T / M (where k = 0.2391).

We could suspect that water flowing in a pipe is F ∝ AP/L where L is length, F is flow rate (L/s), P is pressure (Pa), and A is the cross section area of the pipe (cm2). We could then do some experiemntal measurements. If we did, we would find the flow does indeed increase with pressure, but the multiplying factor is not constant, it varies. So, in this case we can't write F = kAP/L. We would then need to ponder it further - perhaps try a square root or an exponent somewhere.

In the SI (System Internationale), the common standard of measuring units, the units (meters, kilograms, etc) have been chosen so that the constant is in fact equal to 1 as much as possible, or if not a simple integer or pi, but often it isn't either.

Ratbone120.145.152.248 (talk) 16:13, 22 July 2012 (UTC)

Where did you see "F ∝ ma"? I think it makes no sense, for the reason you gave. -- BenRG (talk) 20:37, 22 July 2012 (UTC)

It makes more sense to say, "F ∝ a" where the constant of proportionality is the mass m. This equation is valid for most conventional non-relativistic problems. Nimur (talk) 20:50, 22 July 2012 (UTC)

Isn't that proportionality valid for relativistic problems also? 203.27.72.5 (talk) 07:31, 23 July 2012 (UTC)

Yes. But I assume Nimur was implicitly referring to rest mass, which, for non-relativistic problems is (very nearly) equal to total mass. --Stephan Schulz (talk) 07:38, 23 July 2012 (UTC)

And that is how Newton originally stated it in his second law. I don't know if he knew that the constant of proportionality was mass (he must have had a general idea that it was - it's fairly obvious from every day experience) but he didn't mention it in his statement of the law. He just stated the proportionality. --Tango (talk) 21:30, 22 July 2012 (UTC)

F = kma where k = 1 and is dimensionless is just as valid. In a different system of units (not SI), k might not be equal to 1, though an arkward system of unit it may be. However, in SI, other formulae of similar form k is not 1, but a numeric value with dimensions, as with the water heating example I gave. Ratbone124.182.137.103 (talk) 02:55, 23 July 2012 (UTC)

Why has this kid got fecal matter in his or her armpit?

If you review the article at Constipation then the very first image (i.e. in the info box) at least according to the caption has fecal matter more or less in the armpit of the child. Now presumably the caption is wrong so I plan to change it but thought I should check here, after all I'm not exactly used to X rays and may be making a stupid mistake, so... Egg Centric 16:24, 22 July 2012 (UTC)

Its not in the armpits - notice it is at the position of the lowest ribs. Small children have comparitively small chests relative to their abdomen. So the poo has accumulated at the top corner of the large intestine (ie where it does a right angle turn). Ratbone120.145.152.248 (talk) 16:33, 22 July 2012 (UTC)

Does this child have a freakishly tall abdomen? Egg Centric 21:04, 22 July 2012 (UTC)

No. You seem to be reading the X-ray wrong. Their shoulders are well off the top and the bottom of their ribs are right where they should be. StuRat (talk) 22:00, 22 July 2012 (UTC)

You're right. I've found a few x-rays of complete skeletons and counted the verterbrae. It's very peculiar to me though how small the hip turns out to be. Just on the offchance is this likely an example of systematic "delusion" or is it something idiosyncratic to how I perceived the body? Egg Centric 23:36, 22 July 2012 (UTC)

What you probably mean is how small the hip bones are. The actual hips are larger, since they have muscle, fat, and skin on top. Skeletons, by their nature, always seem "skinny". StuRat (talk) 00:36, 23 July 2012 (UTC)

Working of rockets

Can you explain me on which principle rockets work and how? --Sunny Singh 16:51, 22 July 2012 (UTC) — Preceding unsigned comment added by Sunnysinghthebaba (talk • contribs)

See rocket. Looie496 (talk) 17:31, 22 July 2012 (UTC)

If that article doesn't answer all your questions, please ask us specific questions about the propellants, aerodynamics, guidance systems, etc. StuRat (talk) 19:05, 22 July 2012 (UTC)

Rocket flight *in vacuum* is often quoted as an example of Newton's third law, which is a consequence of conservation of momentum. Low mass propellant goes in one direction at high speed; more massive rocket goes in the opposite direction at lower speed. Gandalf61 (talk) 15:22, 23 July 2012 (UTC)

What do butterflies eat?

butterfly is herbivorous or carnivorous i like to know? — Preceding unsigned comment added by 1.187.13.34 (talk) 17:21, 22 July 2012 (UTC)

Herbivorous, if they eat at all. Looie496 (talk) 17:31, 22 July 2012 (UTC)

Most adult butterflies sip flower nectar, but other imbibe fluids from sap flowers on trees, rotting fruits, bird droppings, or animal dung. OsmanRF34 (talk) —Preceding undated comment added 17:52, 22 July 2012 (UTC)

They are not all exclusively herbivorous at all stages of their life cycle. For example, see Lycaenidae and particularly Miletinae. - Karenjc 19:08, 22 July 2012 (UTC)

Like Karenjc mentions, some lepidopterans are not herbivorous as larvae, some are predators, parasites, and scavengers. But these are very few in number - only about 200 species of lepidopterans are exclusively predatory or parasitic. Aside from the lycaenids, members of the families Epipyropidae and Cyclotornidae, for example, are unique among lepidopterans in that their larvae are parasites of other insects (primarily leafhoppers and cicadas).

In terms of adult lepidopterans, some species may feed (technically they drink) on carcasses of animals. This is an extension of a behavior known as mud-puddling, necessary for obtaining salts important for their metabolism that they do not receive from nectar (if they feed on nectar at all). This also explains why butterflies may sometimes land on humans (they're attracted to sweat). In extreme cases, some moths in the family Noctuidae, Pyralidae, Geometridae, Notodontidae, Thyatiridae, and Sphingidae actually drink tears (sometimes exclusively) of large animals including humans. They do this by either crawling over the edges of the eyes or hovering over the eyes with their probosces extended. Some species deliberately irritate the eyes by poking at it with their probosces or with their feet, a behavior that has been linked to keratoconjunctivitis in cows. In one species from Madagascar (which does not have many large animals), they instead drink the tears of sleeping birds by piercing the eyelids, and doing it in such a way as to not awaken them. And lastly, some members of the noctuid genus Calyptra are known as vampire moths because they drink the blood of animals (including humans) by piercing their skin. As far as I know though, no adult butterflies are actively blood or tear-drinkers.-- OBSIDIAN†SOUL 20:07, 22 July 2012 (UTC)

See calyptra (moth) (that other link points to a part of a plant). StuRat (talk) 21:57, 22 July 2012 (UTC)

Abovementioned corpse eating butterzombies: http://www.youtube.com/watch?v=ApWAs9P0Sh8 μηδείς (talk) 21:02, 22 July 2012 (UTC)

Objectum sexuality and orgasms without physical stimulation

let's at least sign this if we're going to address it further
The following discussion has been closed. Please do not modify it.
I was just reading this article, which is about on my level both intellectualy and puriently, and I was interested whether she actually is likely to have had a proper orgasm without stimulating herself at all physically (I assume for the moment that Ms. Liberty neither resisted nor reciprocated). An additional question incidentally - I hope none of us would class this as rape. Yet the only justification that I have heard for non-abusive bestiality being illegal is that the animals cannot consent. Well, neither did the statue here. Does that pretty much destory that justifaction? In fact I suppose one could be a bit more down to earth and compare two examples: a vibrator, or a dog licking up peanut butter strategically placed. Any sensible differentiation between the two? Actually tehre are so many questions here that it may be daft having it at the reference desk, but I will post it and see if anyone is interested. Otherwise, it's going to a message board! 21:39, 22 July 2012 (UTC) Personal opinion here: First, when you suggest that looking at a statue has the same legal implication as humans having sex with animals, I have to think you are verging on trolling. As for the vibrator and the dog comparison, to the best my knowledge, there has never been a Society for the Prevention of Cruelty to Inanimate Objects. That part is just silly. I'm not just talking about looking at it. I'm talking about have physical contact with it, which a lot of them do. And when I refer to sex with animals, I am not talking about all kinds of potential intercourse with animals (e.g. mr hands or worse) - I am talking particularly about the kind in which the animal is going about its business and so far as we can tell has no knowledge about it being a sexual activity (such as my peanut butter eample) Egg Centric 23:24, 22 July 2012 (UTC) Looking for cite; believed to be factual: Your first question is answerable: yes, both men and women can have orgasms with touching anything on their bodies at all. There is a whole website about it, though I didn't stop to read any of it. It is taught in seminars on sexual technique, and is sometimes used as a way to learn to control premature ejaculation in men. (I'm looking for a cite.) Bielle (talk) 22:10, 22 July 2012 (UTC) Yes. At the very least, I would remind the OP that animals are not things. [9] SemanticMantis (talk) 23:24, 22 July 2012 (UTC) Of course animals are not things. Not being funny, but I genuinely value my two dogs above 99% of individual human beings (which is not the same as saying I would kill 99% of humans to make them live - this isn't a trolley problem - it's more to do with me not having met 99% of humanity... actually I cannot see how anyone who feels different can have a pet as otherwise they would send the pet food money to charity). I think that Haidt has something to say about this, something about morality coming from personal relationships. Nevertheless, in a hypothetical situation where I were a bestialist (what is the correct term for that?) I would see no problem with the peanut butter situation I described. Well I accutally wouldn't because I wouldn't give my dogs peanut butter either but I'm being a bit silly here focussing on problems with scenarios... must repeat... DON'T FIGHT THE HYPOTHETICAL, EGG... Egg Centric 23:30, 22 July 2012 (UTC) Golly, I have a lot to learn to learn! Egg Centric 23:24, 22 July 2012 (UTC)

heat wave

Just thinking - Could the Japan Tsunami and resulting change in the tilt of the earth be a cause of the heat wave in the USA? — Preceding unsigned comment added by Bobant28 (talk • contribs) 21:47, 22 July 2012 (UTC)

Unlikely. The tilt of the Earth changed by a tiny amount, while the jet streams which drive weather patterns move by hundreds of miles. StuRat (talk) 21:50, 22 July 2012 (UTC)

[10] Count Iblis (talk) 03:29, 23 July 2012 (UTC)

Ah, Excellent, that clears it up. No arguing with that!!!!! Richard Avery (talk) 07:19, 23 July 2012 (UTC)

Indeed. Very illuminating... --Tango (talk) 11:44, 23 July 2012 (UTC)

Firstly, the change in the axial tilt was caused by the earthquake, not the tsumani. The tsumani was also caused by the earthquake. Secondly, as StuRat mentions, the change in the tilt was tiny ("between 10 cm (4 in) and 25 cm (10 in)" according to 2011 Tōhoku earthquake and tsunami). There is no way a change of a few centimetres coult have measurable climatic effects. Also, there is no reason to be looking for a cause of this heat wave. Heat waves happen. They've always happened and they will always happen. It's just part of normal weather. --Tango (talk) 11:44, 23 July 2012 (UTC)

Please may we have a share of your heatwave? So far this summer, we've had almost constant cloud cover and lots of rain where I live! Dbfirs 12:52, 23 July 2012 (UTC)

Added reference DOI not linking and same reference showing multiple times.

Hello,

I edited the pages on "polymerase chain reaction" and "Real-time polymerase chain reaction" to update them. When I added the reference, the DOI didn't come through as a link after the reference. Also, multiple instances of the reference are showing as different numbers in the reference list.

I know you get a million of noobs like me not doing something simple, but I can't find help in the archives. — Preceding unsigned comment added by Wine Weed (talk • contribs) 23:11, 22 July 2012 (UTC)

You wanted {{doi|... instead of {{doi:... per {{doi}}, and see WP:NAMEDREFS. 75.166.200.250 (talk) 01:47, 23 July 2012 (UTC)

July 23

Can our scientific knowledge be understood any other way than it is?

okay, so I was watching a video of Hank Green in which he basically talks to aliens, introducing earth. Now one thing is that he used the radius of Hydrogen atom as a unit for human body's height. Now since the real hydrogen atom doesn't really have a definite radius, and the radius we define is not very fundamental in a universal sense (I mean sure it's a constant in the whole universe, but there's no reason for ANY sentient being to define a radius that way, correct me if I'm wrong) that may not be a good unit. Then I thought what if they don't have a notion of atom? I mean in molecules, the thing we call atom doesn't exist anymore (maybe only nuclei and electrons "distributed" around them, but not atoms in the way we think about it) so why would they have a notion of atoms?(that's my first question)

Now a deeper question. Given a different "science history", can they come up with theories in physics and chemistry that are self-consistent and correct, and logically equivalent to ours, but look totally different, theories that for example do not have a notion of wave or particle, or even mass? In other words, if their theory is correct , does it have to include the notions and definitions that we have? can our understanding of science be shown, or understood, any other way?

Also, does having an advanced technology require the same kind of knowledge that we have? like do they have to know what an atom is in order to make a space ship? or satellite? or any other of our inventions?--Irrational number (talk) 00:00, 23 July 2012 (UTC)

On that last point, it does seem to be entirely possible to develop advanced technology by trial and error alone, without any understanding of the underlying concepts. For example, some current medications work despite us not knowing the mechanism by which they work. And many technologies were developed before the theory. For example, I believe projectile weapons were in use long before physics of projectile motion were fully understood. There may be a few areas of technology which can't be arrived at by trial-and-error, though, like nuclear weapons. Nuclear power, on the other hand, might be possible, say if people noticed some perpetually warm rocks, used them to heat their home, but then all got sick, except those who stored them under a pile of normal rocks, so then people would start doing that, and maybe learn how to refine the rocks so they get hotter, and learn that putting them in a pool generates steam, etc. In another example, Thomas Edison didn't seem to have any theory that told him which filament would be best in a light bulb, he just tried everything he could think of until he found tungsten carbonized bamboo.

It's also possible to have a theory that's fundamentally wrong, but that nonetheless is useful. For example, during the black plague, many thought it was caused by "bad air". This is wrong, in that it was transmitted by fleas of rats. However, to avoid foul smelling air, you would implement sanitation measures, such as burning or burying corpses and trash, and this would eventually reduce the rat population, and hence the disease. Of course, there are other things they did, like using perfume, which were useless against the disease. More generally, contagion theory was developed before microscopes allowed us to actually see that the contagions were microorganisms, and they even determined which diseases were airborne, waterborne, etc. . StuRat (talk) 00:19, 23 July 2012 (UTC)

There are both superficial and deep answers to these questions. At the heart of it, you're asking whether our understanding of reality is based in an objective world picture or is a essentially linked to our language and culture. Philosophers and scientists have been arguing over this for literally thousands of years. Applying it to the question of extraterrestrials doesn't necessarily prove it one way or the other (commensurability is possible through shared culture, for example), but is a related question.

The right answer to this question is that there is no simple, obvious answer to this question. A fun book which explores this question in some depth, and actually spends quite a good amount of time playing with the philosophy of it, is Neal Stephenson's Anathem. --Mr.98 (talk) 00:56, 23 July 2012 (UTC)

It's a darn good question. Although there's plenty of our mathematics, physics, and chemistry that feels pretty utterly fundamental (and might therefore be equally comprehensible to an alien), I suspect there's also plenty that's somewhat artificial, and wrapped up in our scientific tradition, and might be amenable to alternatively systematic explanation based on completely different principles.

You're right, measuring distances by atomic radii is lame. But I've never heard of anyone doing that -- the more usual "fundamental" length units are wavelengths of various oscillators (krypton-86 emission, spin-flip transition of hydrogen, etc.).

I always thought the Pioneer plaques did a pretty good job of communicating using "fundamental" constants. —Steve Summit (talk) 01:44, 23 July 2012 (UTC)

P.S. StuRat: Edison didn't find tungsten; that came later.

Thanks, I corrected it. StuRat (talk) 03:03, 23 July 2012 (UTC)

H2 has an average width between the nuclei at a given temperature. μηδείς (talk) 01:58, 23 July 2012 (UTC)

Edison, the example quoted by StuRat, is a good example in a way he may not have appreciated. Edison famously tried an immense variety of materials for possible use in incandescent lights, before finally settling on one (carbonised bamboo if I remember correctly) that worked acceptably well for long enough. If he had a good theoretical knowlege of both materials and the requirements for a lamp filament, then (a) he could have got there much more quickly, and (b) he might have realised that the best material would be a metal (because its electrical resistance is self regulating), and not some form of carbon/graphite (which to an experimeter looks good becaues of its higher electrical resistance).

An even better example with Edison was his lab experiments aimed at discovering why his lamps didn't last long. He put an extra electrode in the bulb not in contact and notice a current never the less flowed. But because he was not a physicist he completely missed the importance of this discovery (the fundamental basis of electronics).

A different sort of example: Rudolf Diesel relaised that vastly better engine eficiency was possible than was then obtained from internal combustion engines, which had until then been designed on experience. Efficiencies of 15% of so were common, but Diesel thought he could do as well as 50% or more, and set about achieving it, based on sound theoretical knowlege of thermodynamics gained in his career in early refrigeration techniques. His theory was not quite right, never-the-less, with only 2 prototypes he achieved an efficiency of ~37%, and was able to immediately correct his theory.

So it seems that while it may be possible to have advanced technology with only practice of the art, and not a good theorrectical undertsanding, but advancement with good theory is much more probable.

It should aslo be realised, that the natural reaction to something not working well, or not working as expected is "Let's try and figure out why" - which inevitably leads to good theory, except where the theory is exceptionally difficult.

Note that there are two kinds of boffin - Scientists, who seek to understand what has been discovered, and Engineers, who seek to apply the scientist's understanding to design things we need. In different words, there is analysis (why is it so) and synthesis (let's make it so) - both analysis and synthesis depend on good theory. In nearly all fields, good analysis and good synthesis vastly outperforms mere practice of art. An example: By practice of the art and successive refinement, and limitted theory, AM radio was taken from a novelty to practaical home entertainemnt in the 1920's. But Armstrong's excellent theorectical knowlege produced a breakthrough in sound quality in one step - FM radio. That's the key - Good theoretical knowlege enables breakthough progress & technology change, without it, you mostly get only incremental improvement.

Ratbone124.182.137.103 (talk) 02:19, 23 July 2012 (UTC)

You may find some answers in the philosophy of science, specifically in the philosophy of science related to linguistics. Fifelfoo (talk) 02:47, 23 July 2012 (UTC)

No one has mentioned Bohr radius yet. Also the article on Model-dependent realism might be interesting. Vespine (talk) 03:25, 23 July 2012 (UTC)

Pseudo-freezer

I was at a motel last week and there was one of these mini-fridges in the room. Inside, there was a freezer-like compartment, but it was not completely sealed off from the larger refrigerator compartment. How is it that putting something into the freezer pseudo-compartment can reliably and consistently freeze while the things just inches away do not? DRosenbach ^{(Talk | Contribs)} 01:53, 23 July 2012 (UTC)

Direct conduction of heat. If you were planning on staying long enough that it would matter, you could rent a freezer. Most college students don't have that problem. μηδείς (talk) 01:55, 23 July 2012 (UTC)

Those things don't work all that well anyhow. If you put stuff inches away from the freezing compartment it can easily freeze too. Looie496 (talk) 02:09, 23 July 2012 (UTC)

Your complaint seems to be that they work too well. How in the world do you get things that near the freezer coil anyway unless the entire compartment is full, Looie? μηδείς (talk) 03:06, 23 July 2012 (UTC)

It's a thermal gradient thing. The piece of metal that forms the freezer compartment is the cooling element for the entire refrigerator. Since the inside of the freezer compartment is small, you can think of the cold getting "concentrated" there and making it that much colder. On the other side (the outside of the freezer compartment, the inside of the rest of the fridge) there's much more space (and much more outside surface area for heat to leak in), so the little piece of cold metal can't keep that larger volume frozen, and doesn't. (It's actually sort of a clever design, if you like minimalist kludges.) —Steve Summit (talk) 02:31, 23 July 2012 (UTC)

I have a full size fridge like that in my house, manufactured by Phillips Australia (known in the USA as Magnavox I think). It actually works very well, but not quite as efficient as a more traditional design. (I've had it for over 25 years). The cooling by the refrigeration machinery is only applied to the freezer compartment. Cold air from the not quite fully enclosed freezer compartment (-12 C) then flows downward to the meat box, which tends to be about 6 to 8 C. From the meat box the air flows downward to the general area, which tends to be about 10 to 12 C, ideal for bread and vegies. Air relatively warmed in the general area then flows by convection up the back into the freezer compartment again to be re-cooled. Critical to the success of this system is the small gaps in the freezer box and the meat box that the air "leaks" thru. In fact the manufacturer provided 2 temperature controls - a thermostat to adjust the freezer temperature, and a slide to vary the meat box air leakage to set the main compartment temperature. Ratbone124.182.137.103 (talk) 02:33, 23 July 2012 (UTC)

The equilibrium temperature for any volume will be where the total amount of heat coming in equals the total amount of heat going out. In the general fridge section, a fair amount of heat is going in, coming from the large outside surface area. A fair amount is also going out, being removed by the refrigeration coils around the freezer section. So, you get a cool, but not frozen, fridge. Inside the freezer compartment, much less heat is going in, since it needs to go thru that small surface area of freezing metal to get inside, but just as much heat is being taken out by the refrigeration coils, so it's much colder inside.

For an analogy, think of heating your house in winter. You could close and seal all the vents (I'm assuming a forced air system) in every room but one small room, in which case that room would get hot, and the rest of the house would barely be warmer than outside, even if you had all the doors open. StuRat (talk) 03:14, 23 July 2012 (UTC)

Passive smoking locked

Can someone explain why the description of passive smoking is locked? It appears to be provided by an entirely driven special interest [an advertisement for smoking patches] with many factual extensions and outright inaccuracies with many evidence links dead. The IARC report much to the contrary of what is written demonstrated also much to the embarrassment of the World Health Organization who financed it, in the press of the day; displayed no significant risk to non smoking spouses, even among those who worked and lived with smokers, In fact the effects to children seemed to demonstrate a curative effect. The much larger Enstrom and Kobot study a few years later demonstrated that the risks of second hand smoke are largely overstated. Continuing with the risk to children and cognitive losses, anyone who actually read the made for media research claims and followed up with an evaluation of the data, saw that the author was led more by agenda than her acknowledgement of the facts observed. You see the data actually showed a lowered risk pattern which was inversely proportional with most exposures, so the media report stated that they "could not find a level where no losses were observed" while those with no exposures, had the highest level of losses by far. There are far to many inaccuracies and outright untruths stated in the WIKI article none more abhorrent than the "causal link to SIDS" claimed to be found in the 2006 surgeon Generals report. While no such statement exists in the report, it was claimed in the news release purchased by an obviously financially conflicted special interest group, prior to the report's actual publication. Locking an article as controversial as passive smoking, which is more a religious belief as a product of paid promotion, than any connection to legitimate science. This brings a deficit of credibility in the entirety of what is provided by WIKI to the public, as a work of the public or any community beyond the 1% who are profiting billions every year by misleading advertising and the existing ad agency ability to flow their purchased spin to the front pages without restriction. WIKI should work harder to protect itself as distinct, from the traditional and bottom line oriented "mainstream" sources of information. — Preceding unsigned comment added by 64.56.250.14 (talk) 02:25, 23 July 2012 (UTC)

The article is pretty one-sided; I see what you mean. I wouldn't call it a stellar example of Wikipedia's neutrality principles.

It is "semi-protected", not completely locked. This is (unfortunately) the norm for more and more of Wikipedia's controversial articles. Any established (registered) editor can edit the article -- register an account and you can, too. Others can request changes on the article's talk page.

This reference desk isn't really the right place to discuss editorial issues with articles. Bringing up your concerns on the talk page would certainly be a good first step. If you get lots of pushback there (as I fear you might, if the article has indeed been "taken over" by special interests), you can consult Wikipedia:Dispute resolution for lots of resources on resolving disputes. In this case, if you don't get anywhere on the talk page, posting a notice at Wikipedia:Neutral point of view/Noticeboard might be in order. —Steve Summit (talk) 02:39, 23 July 2012 (UTC), updated 02:49, 23 July 2012 (UTC)

Semi protection is applied when there is a lot of drive-by vandalism or contentious edits by anonymous editors. The purpose is to make sure all edits are constructive and according to consensus. Non anonymous users who refuse to discuss issues get blocked. The locking is no indication of the articles current quality. Make your suggestions for the article on the talk page. Even better, if you have a rewrite, put it in a new section on the bottom of the talk page. Good luck!Staticd (talk) 13:24, 23 July 2012 (UTC)

Will science come to an end?

Will we eventually discover everything discoverable and learn everything learnable? Or will there always be more to discover and learn, no matter how much we discover and learn? -----150.203.114.14 (talk) 06:13, 23 July 2012 (UTC)

From my experience as a working scientist, the more I learn, the more new questions I have. It's like the border of an unknown country - if I start an expedition into the wilderness, I may discover something new - but I also extend the length of the border into the unknown. Of course I don't know if the "continent of knowledge" is infinite, but it sure looks like it. BTW, what makes me realise how far we have come is teaching - it draws me back from the perpetual half-ignorance in my research onto a well-established map, and makes me realise how big the mapped area has become. --Stephan Schulz (talk) 06:46, 23 July 2012 (UTC)

Asked and answered. 203.27.72.5 (talk) 07:08, 23 July 2012 (UTC)

At first thought I want to say that there are an infinite number of things to know, so we can always learn more. However, their could be limits. String theory, for example, may never be testable, which makes it as much a philosophy as science, with each person choosing their own version, according to their beliefs. So, that may put a limit on delving into the super small. On the large scale, once we've fully explored the observable universe (admittedly that may take a year or two), that may put an end on that large scale exploration. StuRat (talk) 08:33, 23 July 2012 (UTC)

There may also be theoretical limits to the total amount of information in the Universe[11]. This would mean that the "continent" of all there is to know is finite, but of course this would exceed our capacity to hold knowledge by many orders of magnitude. -- Q Chris (talk) 08:41, 23 July 2012 (UTC)

My understanding of science, from history and philosophy of science, is that science is a human practice dependent upon small group power relations and classed power relations. As there are no plans to sustain human culture beyond the information death of the universe (as currently expected), science will end with the end of the universe, or with the end of human and post-human cultures, or with the abandonment of the cultural construct of "science" in favour of other (almost certainly) instrumentalist understandings of material reality. For example, "technologism" could conceivably replace science in our lifetime. This is in contrast to the unlikely abandonment of material instrumentality altogether. Fifelfoo (talk) 08:49, 23 July 2012 (UTC)

Gesundheit! --Stephan Schulz (talk) 08:51, 23 July 2012 (UTC)

Read more HPS Steve. This stuff came out in the late 1960s as a result of pursuing pre-structuralist arguments in science itself. Most of it is hardly even influenced at its commencement by Marxism. See Feyerabend for the debate. Fifelfoo (talk) 08:59, 23 July 2012 (UTC)

Based on previous millennia of human history, scientific knowledge, even just pretty basic stuff, may be lost and may need to be rediscovered. Adam Bishop (talk) 08:58, 23 July 2012 (UTC)

It seems unlikely. It is somewhat of a cliché, but nonetheless true, that the more we discover, the more we realize how much we do not know. In the grand scale of the universe, humanity devotes precious little time and precious little resources to knowledge generation. I would not expect us to exhaust that knowledge within the limited lifetime of our species.

This entirely avoids the question of whether you could write down "reality" in an unmediated way, given infinite time and resources. This is a much stickier philosophical question, with a great many disagreeing answers, and depends on whether we, as conscious beings, can actually have unmediated access to the fundamental nature of reality. People have been arguing over this for thousands of years. --Mr.98 (talk) 13:30, 23 July 2012 (UTC)

• We may eventually discover a complete set of basic laws of physics. But there is no limit on the phenomena that can result from complexity. Looie496 (talk) 16:14, 23 July 2012 (UTC)

Sulfonamide antibiotics

I remember reading somewhere that before the first Sulfonamide antibiotics were discovered, people used to just swallow sulfur and it was just as effective. Is this true? --Wrk678 (talk) 08:56, 23 July 2012 (UTC)

Sulfur was used medically as a tonic and laxative. I doubt that it was effective as an antibiotic. -- Q Chris (talk) 09:54, 23 July 2012 (UTC)

How does the seat push when a pilot ejects?

F-16 ejection seat in action

I was just reading about the American pilot who ejected out of his crashing F-16 in Japan recently and I was trying to picture in slow motion in my mind the process of the cockpit opening and the pilot's seat rising up both without him hitting the windshield and quickly enough so that the forward-moving pilot, who is moving very fast, is not pushed back into the opened windshield by the no-doubt great amount of wind force on him. Does the ejection mechanism provide some forward boost in addition to vertical to counter wind immediately experienced that would tend to push him into the windshield before he got the 3'-5' clearance needed to clear the windshield and the presumably still-powered jet safely rushes ahead below him as the wind continues to drag down his forward speed? 20.137.18.53 (talk) 12:04, 23 July 2012 (UTC)

There's quite a bit of information in our Ejection seat article. —Steve Summit (talk) 12:32, 23 July 2012 (UTC)

The short version, though: bear in mind that the canopy is subject to the same factors (initial speed, drag, etc) as the pilot, and as it probably has higher surface area and lower mass, will be dragged aft of the plane more rapidly than the pilot. Note also that we have a picture of a pilot ejecting from an F-16 that nicely illustrates this. Alternate options include ejecting through the canopy (with reinforcements above the pilot's head to break through the glass) or, in a handful of cases, ejecting out the bottom of the plane (obviously less useful at low altitude). — Lomn 13:46, 23 July 2012 (UTC)

The initial impulse of a fighter jet seat tends to be backwards, so allow the pilot's legs to clear the instrument panel under which they normally rest (ref). That's done by a system sometimes called the "ejection cartridge" or "ejection gun". That's just enough to get the seat out of the cockpit. Then the problem is, as you say, to clear the airframe. The high drag of the seat is one issue, but a bigger is the consideration that the aircraft may be pitching or yawing wildly, and may be compromised in some other way. So your assumption about airflow is valid in level flight, but so many ejections happen in other circumstances (spiral banking, pitch-up stalling, uncontrolled diving, etc.) that the seat has to conservatively cope with all kinds of unpleasant and unpredictable scenarios. So the gas generator (which is how aeronautical engineers spell "bomb") they use to blast the pilot clear of the aircraft's environment is massive (this gives mass of 3.73 kg for a Russian fighter seat design), burning for only about 0.1 seconds (ref). That's enough force to throw pilot, suit, seat, and parachutes one to 200 ft in the air (ref)(ref) (and given that's a subsonic trainer, the system for a supersonic aircraft is surely more powerful still). Modern seats have attitude control (cf the howstuffworks ref and this). But the key point is the astonishing vigor of that explosive ejection - the ejector seat article cites 12-14g for western designs, with older Soviet designs yielding an astonishing 22g. Those are car-crash-like forces, more than enough to tear the tattered pilot away from the aircraft and its environs. The onrush of air is injurious, and tends to wrench the pilots knees violently apart - if they weren't restrained the pilot would sustain serious hip injuries. -- Finlay McWalterჷTalk 14:11, 23 July 2012 (UTC)

Excellently detailed explanation. Anecdotally, the force of the ejection is particularly problematic for the human spine. Apparently at some point in history (and possibly still the case), U.S. fighter pilots were only "allowed" two ejections because of the potential cumulative spine damage - after you ejected twice, your career as a fighter pilot was over. --Demiurge1000 (talk) 14:21, 23 July 2012 (UTC)

This paper says that between 30% and 70% of ejectees sustain vertebral fracture. At least anecdotally there's some evidence that ejection makes the pilot slightly shorter, due to the trauma to the intervertebral discs. I can only imagine that being ejected from a tumbling aircraft must feel like being an Action Man in the grip of an angry toddler. -- Finlay McWalterჷTalk 14:33, 23 July 2012 (UTC)

A ejection seat isn't an amusement-park ride; it's an option of last resort, when a combat pilot believes he should be safer outside his aircraft than inside. That means that his aircraft is probably in bad shape: not only damaged, but unable to land safely. When compared to almost certain fiery death, an ejection seat need not set a high bar for comfort or safety... as long as it's "mostly" better than exploding. Even this Air Force Fact Sheet bluntly says it... "Not all emergency situations are escapable, but ejection seats greatly enhance a pilot's chances of getting out of most of them." Nimur (talk) 15:32, 23 July 2012 (UTC)

Indeed. Ejecting is hazardous even from a stationary aircraft - broken limbs are common, and I believe an accidental ejection from a stationary BAe Hawk on the ground recently killed a pilot. The pilot who ejected from a hovering Harrier jump jet at an air show off the Essex coast a few years ago, broke his ankle after landing on the remains of his aircraft. --Demiurge1000 (talk) 16:12, 23 July 2012 (UTC)

In the 1960's era F111 fighter-bomber, the entire crew compartment was designed to be blasted away from the airframe in emergencies, as they considered it was not possible to eject and survive from an aircraft going at Mach 2.5 at low altitudes, and probably any altitude. Ratbone121.215.33.69 (talk) 15:51, 23 July 2012 (UTC)

The F-111, like most fast aircraft of its era, was not capable of Mach 2.5 at low altitudes - its maximum speed (in level flight) at sea level was less than half that. --Demiurge1000 (talk) 16:12, 23 July 2012 (UTC)

a puzzling biophysical relationship

While processing my data, I found that the instantaneous curvature of the 2D plane-constrained trajectory of a fruit fly is positively correlated with the inverse hyperbolic cosecant of its instantaneous speed (r=~0.7) Such a relationship is the best fit I've found (among logarithmic, inverse square, etc.) and gives a very convincing straight line correlation in the scatterplot. I have no idea why. Does anybody have an ideas? I don't know how to interpret this relationship.

This is regardless of whether they are on cocaine or not. (Yes, I work in a cocaine behavioural lab.) 128.143.1.64 (talk) 12:42, 23 July 2012 (UTC)

It seems that the logical place to start would be to find prior research that correlates instantaneous curvature and instantaneous speed for other test subjects under other conditions. What techniques and methodologies did they use? What correlations have been found to exist by previous researchers? What causative factors explain those correlations? It's very easy to crunch a lot of numbers, but if you don't have any motivating reason to assert a cause, detecting a correlation might be totally useless (even if it is very strong). Even worse, the calculation may be incorrect, due to some detail of your process that you overlooked. (Is there a geometric relationship between radius of curvature, and instantaneous velocity, possibly amplified by your data collection methodology? Can you test for such an effect in your algorithm by feeding it a synthetic or randomized data-set, as a control experiment?) Nimur (talk) 15:13, 23 July 2012 (UTC)

Curvature on a plane is abs(yx' - x"y') / speed^3. If I multiply the curvature set by speed^3, I get a weaker line (correlation r=0.55) and a lot more scatter. 76.104.28.221 (talk) 19:26, 23 July 2012 (UTC)

Why doesn't the fruit fly operate in 3-dimensions of aerial flight? Did God made that individual incorrectly? Bus stop (talk) 15:24, 23 July 2012 (UTC)

Actually the experiment involves hundreds of fruit flies, "a" is just rhetorical. The arena is 3x4 inches long but only ~1.5mm in height. 76.104.28.221 (talk) 19:17, 23 July 2012 (UTC)

It might be worth looking at what happens if you use the radius of curvature as your variable rather than the curvature itself -- that's what most of the literature does, and it gets you away from the singularity at zero, which can really distort your numerics. Most of the literature looks for power law relationships when examining curvature-velocity relationships. Looie496 (talk) 16:10, 23 July 2012 (UTC)

SYSTEMIC LUPUS ERYTHROMATOSUS

CAN MENTAL STRESS CAUSE SLE NEPHRITIS — Preceding unsigned comment added by 115.242.37.13 (talk) 13:08, 23 July 2012 (UTC)

After looking at several medical sites including Merck Medical and Systemic lupus erythmatosis I have found no reference to stress as a causative factor. The disease itself is thought to be possibly genetic in origin. It is a long duration disease with periods of remission punctuated by flare-ups of signs and symptoms. The flare-ups are caused by clear physical agents like strong sunlight, infection or surgery, among others. Richard Avery (talk) 13:28, 23 July 2012 (UTC)