Wikipedia:Reference desk/Archives/Science/2010 November 9

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November 9

what animals can humans coproduce with?

since a donkey plus a horse can breed a mule, what animals can a human coproduce with, and what are the resulting animals called?

also, have most combinations been tried or is it possible a lot of viable (though, like the mule, possibly sterile) combinations simply were never tried yet? Thanks. 85.181.151.31 (talk) 00:08, 9 November 2010 (UTC)

Neanderthals. Count Iblis (talk) 00:14, 9 November 2010 (UTC)

Certainly as much an "animal" as homo sapiens sapiens, but still a human animal:

"Neanderthals are either classified as a subspecies (or race) of modern humans (Homo sapiens neanderthalensis) or as a separate human species (Homo neanderthalensis)."

according to the Neanderthal article.

There is, of course, no separate species today with which humans could co-produce, OP. I hope that resolves your interest in this question, but in case not I will put up the "{{RD-alert}}" tag. :| WikiDao ☯ (talk) 00:33, 9 November 2010 (UTC)

We do also have articles on the hypothetical humanzee and on parahuman. That's all I found in Category:Mammal hybrids, apart from the already mentioned Neanderthal admixture hypothesis. ---Sluzzelin talk 00:38, 9 November 2010 (UTC)

That's two corrections on assumptions-about-answerability-of-questions in a row, Sluzzelin – I promise I'll get with it by the third! :) WikiDao ☯ (talk) 00:45, 9 November 2010 (UTC)

It remains controversial whether or not Neanderthals could breed with anatomically modern humans (or more precisely whether genes were exchanged between the populations, which would require non-sterile offspring). Until a few years ago, most genetic studies suggested no genes were transferred from Neanderthals to humans, but in recent years the arguments have tended to support a limited amount of gene transfer. Dragons flight (talk) 01:16, 9 November 2010 (UTC)

Any information given in response to this question should be prefaced Do not try this at home . An aid to remember this warning is this extract from the article Origin of AIDS: ...the virus originated in populations of wild chimpanzees in West-Central Africa...scientists calculate that the jump from chimpanzee to human probably happened during the late 19th or early 20th century, a time of rapid urbanisation and colonisation in equatorial Africa. Cuddlyable3 (talk) 11:03, 9 November 2010 (UTC)

I think it's more likely that unsanitary butchering of apes (making Bushmeat) led to the chimp-human HIV crossover, rather than sexual contact. Monkey killing (I know, chimps aren't monkeys) is much more prevalent than Monkey fucking. Just saying. Buddy431 (talk) 20:24, 9 November 2010 (UTC)

I, the OP, (different IP now) was not thinking of sexual intercourse with 'em, but rather artificial insemination. Have they tried inseminating all the animals in zoos with human sperm to see if any give birth to viable young? Obviously I'm thinking of primates rather than dolphins and such. 84.153.236.235 (talk) 11:14, 9 November 2010 (UTC)

I'm not really much of a scientist/biologist, but aren't there a whole raft of laws to prevent people doing that sort of thing - It strikes me as something that would be seen as highly un-ethical, and likely quite illegal. Forgive my naivety if this is not the case Darigan (talk) 11:33, 9 November 2010 (UTC)

Did you read the linked article, humanzee? That also links to Ilya Ivanovich Ivanov (biologist) which may provide more details Nil Einne (talk) 13:34, 9 November 2010 (UTC)

A sizeable proportion of farm boys have reportedly deposited sperm in various varieties of farm animals they had access to. Kinsey, pages 289-293, page 362 [1] in "Sexual behavior in the human male" said that 28% of farm boys (who ultimately went to college) had intercourse with animals. No offspring have been documented. Females also had intercourse with animal, per Kinsey: [2], with lower reported frequency, again without documented offspring. Few such farms have animals close to humans such as chimpanzees. Humans are said to be more closely related to chimps than lions and tigers are to each other, and they produce offspring commonly. If nothing else such data. despite laws against and moral repugnance of society toward such bestiality, make laughable the contentions of some scientists that intercourse would not have taken place between Neanderthals and "modern humans." Stating that no mad scientist would ever artificially (or via the old fashioned way) inseminate a chimp because it would be unethical or morally repugnant is also pretty silly, given that many scientists are happy to make new weapons of mass destruction, or to support industrial activities which harm humans or the environment. Current research is placing human tissues or genes in animals, such as placing human brain cells in mice [3](not sure if this is serious or a hoax) but also see The Times Online (2006): [4]. Despite the assertions of a (defeated) Tea Party Senate candidate, the mice did not have "fully functioning human brains," but they did have 1/1000 of their brains made of human brain cells[5]. Another estimate said that transgenic mice have been created with 1% human brain cells. [6], and reportedly have plans to create mice whose brains are 100% human brain cells [7]. If they created a Bonobo with 100% human brain cells, what would be its capabilities? I have seen no estimate of how many cells in which brain region would be required for an animal to have some human-type self consciousness, assuming that Bonobos or elephants do not already have some degree of such awareness. Attempts to fertilize chimps with human sperm, funded by a government in the early 20th century, are described in Humanzee. Now scientists can add human genes to animals, and presumably animal genes to humans, without insemination, through genetic manipulation. Present research uses the transgenic human-mouse model quite commonly. A discussion of possible future use of animal genes to improve human genetics is discussed in "Transgenics and evolutionary enhancement" section (pp 12-14) of a 2007 paper by Arthur Saniotis, "Recombinant nature: Transgenics and the emergence of hum-animals." [8] Edison (talk) 17:35, 9 November 2010 (UTC)

I think it's clear that the "Clyven" mouse with human intelligence is a hoax. If nothing else, the chat program that allows you to have a real-time textual conversation with a mouse should probably be tip-off. APL (talk) 17:15, 10 November 2010 (UTC)

Why doesn't cryonics just use a ton of insulation?

From my understanding, cryonics requires replacing the liquid nitrogen every week or so. Insulation decreases thermal conductivity exponentially with distance, so why not just use so much insulation that the temperature stays low until the singularity? — DanielLC 01:47, 9 November 2010 (UTC)

Thermal conductivity is linear in thickness not exponential. Dragons flight (talk) 02:37, 9 November 2010 (UTC)

And liquid nitrogen is cheap when compared to real estate! Physchim62 (talk) 03:56, 9 November 2010 (UTC)

As you increase the amount of insulation, you also increase the surface area over which you're gaining heat. For this reason, there is an optimal insulation thickness. (I don't have the book with me, but see Transport Phenomena by Bird, Stuart, and Lightfoot, I believe there's an example problem like this.) shoy (reactions) 13:03, 9 November 2010 (UTC) (Note: this only applies for cylinders such as pipes, which is what I assume the OP is talking about. --shoy (reactions) 14:07, 10 November 2010 (UTC))

Really? If I replace some volume of the environment (say, room-temperature air) around my system with anything — even something rather thermally conductive — I should be lowering the temperature at what was the outer surface because the outside of the new insulator will be at the air's temperature and the inside of the new insulator has to be colder. So then the gradients inside the original system must be smaller. (This doesn't apply, of course, if the new material establishes a good thermal connection to something at a higher temperature than what was previously the environment.) --Tardis (talk) 17:23, 9 November 2010 (UTC)

Heat flow may be linear, but the temperature profile is a natural log function (IIRC, at least for cylindrical systems), so at some point, you're causing a great increase in surface area for not that much difference in surface temperature. --shoy (reactions) 14:07, 10 November 2010 (UTC)

Do not believe it. Adding another layer of insulation to the existing set up is going to reduce the amount of heat flowing to the previous surface, and hence reduce the temperature of the previous surface. 92.15.3.20 (talk) 19:52, 11 November 2010 (UTC)

Do the math. Heat flow is proportional to the area times the temperature difference. Temperature difference changes O(ln r). Surface area changes O(r). shoy (reactions) 14:01, 12 November 2010 (UTC)

So you're saying that if you cover the surface of something cold with insulation, then that surface is going to get hotter? Surely the extra insulation outweighs any slight increase in surface area? Arent you also forgetting that the thing is likely to be surrounded by air anyway (which conducts heat with convection currents), so you are better off replacing the volume of air with the same volume of insulator? 92.28.248.229 (talk) 18:58, 12 November 2010 (UTC)

I'm not talking about the difference between no insulation and some insulation. I'm talking about the difference between some insulation and a lot of insulation. All of these statements are assuming heat loss by convection. shoy (reactions) 21:32, 12 November 2010 (UTC)

I was referring to adding another layer of insulation to something already insulated. I still don't believe it. You show some calculations and prove it. 92.28.248.229 (talk) 21:53, 12 November 2010 (UTC)

Liquid nitrogen is like a dollar a litre.... we can generously assume that they have to replace 100 litres of liquid nitrogen per week. (depending on the machine, it may be as little as 10?) While $5200 / year sounds expensive to most people, it sounds like peanuts for whoever could afford the procedure to be cryonised. I mean...it's probably even less than medical insurance in America for the elderly! You're actually saving money! John Riemann Soong (talk) 23:42, 9 November 2010 (UTC)

desk chair

the arm of my chair tore open and the stuffing is exposed. the stuffing looks like a black tee shirt put thru a meat grinder. what kinda stuffing is this? —Preceding unsigned comment added by Kj650 (talk • contribs) 02:03, 9 November 2010 (UTC)

It may be exactly what it looks like. It's very common to recycle old textiles as stuffing. Ariel. (talk) 04:44, 9 November 2010 (UTC)

If I may again plug The Travels of a T-shirt in a Global Economy, there's a nice section about the used clothing market. Used T-shirts may be re-sold (if in pretty good condition), turned into rags (if in good condition, but with large tears), ground into stuffing, or even ground up and re-made into low-grade fabric. Buddy431 (talk) 20:19, 9 November 2010 (UTC)

wouldent cotton get moldy? —Preceding unsigned comment added by Kj650 (talk • contribs) 05:38, 9 November 2010 (UTC)

If it got wet, it could. If old shirts are used, they are likely treated with some sort of anti-bacterial/anti-microbial solution to keep them from getting mold simply from perspiration and skin oils. Dismas|^(talk) 05:40, 9 November 2010 (UTC)

You need moisture for mold to grow, so as long as it stays dry it won't mold. A single spill is not enough either, it would need to stay wet for about 2-3 days. Ariel. (talk) 06:22, 9 November 2010 (UTC)

what chemicals are they likely treated with? —Preceding unsigned comment added by Kj650 (talk • contribs) 01:38, 10 November 2010 (UTC)

Futon cotton is treated with boric acid, so that's probably a good guess for your chair. Ariel. (talk) 20:08, 11 November 2010 (UTC)

street lighting

metal halide lamps vs sodium vapour. —Preceding unsigned comment added by 59.161.130.15 (talk) 03:58, 9 November 2010 (UTC)

What about it and them? We have a Street light article that mentions and compares various technologies. DMacks (talk) 04:40, 9 November 2010 (UTC)

Inclined plane, Non-conservative forces help

A block of weight 8N is launched up a 30 degree inclined plane, of length 2 m by a spring, with spring constant 2 kN/m and a maximum compression .1 m. The average force on the block due to friction & air resistance, combined, has magnitude 2 N. Does the block reach the top of the incline? If so, how much kinetic energy does it have at the top; if not, how close to the top does it get?

Okay--so here's my approach, PE(initial)=PE(final) + KE (final) + Work(nonconservative)

the initial PE is (1/2)kx^2=10J, PE final=mgh=(8N)(2sin(30))=8J Work done by NC forces=(2N)(2m)=4J

Ergo: 10J=8J+[(1/2)mv^2]-4J 6J=KEfinal by those maths, it seems to me that it does reach the top, with 6J of KE at the top. Is my reasoning sound?24.63.107.0 (talk) 04:06, 9 November 2010 (UTC)

Why do you subtract the 4 J of energy dissipated due to friction? The dissipated energy must come from the initial 10 J, so 10 J = (potential energy 2 m up the plane) + kinetic energy + energy dissipated. Icek (talk) 14:40, 9 November 2010 (UTC)

ah! of course--in that case the KE at the top would be -2J so it clearly does not make it to the top, but rather only makes it up to the point when KE(final) = 0 solving there gives a height of (3/4)m. Dividing by sin(30) gives me the value on the slope it attains--1.5 m. Sound good?158.121.82.165 (talk) 20:43, 9 November 2010 (UTC)

Oldowan tools experiment

(I originally posted this at the Humanities desk, but maybe it ought to be here.) The author of this book review states, in passing, "Experiments have shown that Oldowan tools can be made using just the part of the brain that was available back in Homo habilis times." Is that true? What was the nature of these experiments? I can't find anything at the Oldowan article. LANTZY^TALK 06:31, 9 November 2010 (UTC)

This page says:

"Homo habilis is considered to be the first member of the genus homo because of two main reasons. First, their larger brain size, and second, the presence of tools indicates that the large brains were capable of more complex thought processes not seen in the Australopithecines."

Which sort of makes it sound like the "experiments" may just have been the reasoning that they had 1) tools and 2) larger brains than other Homininae which did not have tools. There are some book references at that page, too. WikiDao ☯ (talk) 05:01, 10 November 2010 (UTC)

Although our own article indicates that reasoning may be a bit controversial:

"Whether H. habilis was the first hominid to master stone tool technology remains controversial, as Australopithecus garhi, dated to 2.6 million years ago, has been found along with stone tool implements at least 100,000 - 200,000 years older than H. habilis."

WikiDao ☯ (talk) 05:08, 10 November 2010 (UTC)

Thanks, Wikidao. I was thinking that maybe "experiments" was an overstatement. LANTZY^TALK 18:07, 11 November 2010 (UTC)

There's not that much you can say about how the brain was organized by looking at a skull. Even within modern humans, you can only go so far in predicting what skill will be handled where. (Brain mapping doesn't really cover this, but during brain surgery it is my impression that it is routine to stimulate different parts and try to figure out which are most important before deciding where to cut through to a tumor, because you really can't tell in advance. Though e.g. in neurolinguistics much can be mapped by fMRI and PETT - and where individual words appear isn't predictable, for example, though where a type of word is learned is somewhat predictable.[9] Also note that autistic people, which is a wide functional spectrum, have a different overall mapping within the brain than others. Considering these things and also bearing in mind that a few hundred thousand years is a very short period of time in evolution, I would not expect there to be any identifiable new anatomical structure in Homo sapiens, though the sizes and shapes of structures may be different — but unless we actually obtain full sequence data from the older species, synthesize it, and put it into zygotes, we'll never really know. And that's probably not going to happen until Indonesia has lots of money to spend on research, because as far as I know no other country in the world has quite their love for freaky spectacle. ;) Wnt (talk) 22:37, 12 November 2010 (UTC)

hydrogenated ketone

whats a hydrogenated ketone —Preceding unsigned comment added by Kj650 (talk • contribs) 08:28, 9 November 2010 (UTC)

Could have many meanings depending on context. Could be an alcohol (the result of hydrogenating a ketone), could be a ketone in an alkane structure (the result of hydrogenation of an alkene). DMacks (talk) 08:59, 9 November 2010 (UTC)

There are catalysts that will reduce ketones to alkanes with hydrogen, or any alcohol for that matter. (wait -- if you use a silane, does it still count as "hydrogenation"?) John Riemann Soong (talk) 22:06, 9 November 2010 (UTC)

Stereogram effect

While watching TV recently I saw an interesting effect whereby a photograph seemed to be stereoscopic, the camera moved away and to one side and the images in the photograph appeared to be separate and give a stereo effect. I can understand how a two eyed viewer achieves a stereo effect but this was with a (?)single lens camera. I have also seen the same thing with what appear to be paintings. What is this effect called and how is it achieved? Caesar's Daddy (talk) 09:06, 9 November 2010 (UTC)

For real scenes the effect is achieved by taking pictures simultaneously by a horizontal row of cameras. As the viewpoint moves sideways the display morphs from camera to camera giving the illusion of parallax that continually varies with viewing position. You may notice that the range of movement is seldom wide, because cameras are expensive.Cuddlyable3 (talk) 10:44, 9 November 2010 (UTC)

(EC) This is described somewhat in Stereoscopy#Wiggle stereoscopy, Stereopsis and Parallax Nil Einne (talk) 10:47, 9 November 2010 (UTC)

I have seen this type of effect where there are clearly no 'multiple cameras' or 'multiple images' available, such as in documentaries using historic photographs. I think this may be what Caesar's Daddy is talking about. I could duplicate this effect by using a program like Photoshop to cut out the foreground elements to separate them from the background, and then manipulate them separately to give the 3D effect. In so doing it would possibly help to enlarge the foreground elements in relation to the background and do some creative image cloning to fill in the holes left in the background - in these sort of images you'll notice they never pan too far across the image as that would expose the flaws in the background. The same effect could be used on a photo or a painting. Unfortunately I have no idea what they call it, or whether this is how they actually do it (as I say, I could duplicate the effect in this manner, but there may be some simpler automated technique; it may all be covered in one of the articles mentioned above, but I don't have time to look). --jjron (talk) 14:20, 9 November 2010 (UTC)

Autostereograms (the "wallpaper effect") are fun. Could that be what you are asking about, OP? WikiDao ☯ (talk) 19:16, 9 November 2010 (UTC)

Jjron knows what I'm talking about, unfortunately he doesn't have the answer, Whaa, isn't that always the way. But, hey, thanks to Neil and Cuddly for your attention. No, WikiDao, autostereograms are something else, wonderful, but something else. Thanks. Caesar's Daddy (talk) 21:18, 9 November 2010 (UTC)

Those stereograms never work for me. But this is a nice stereo animation. Cuddlyable3 (talk) 09:47, 10 November 2010 (UTC)

Hollow-face illusion can give some surprising effects. Even an almost flat photograph (in reality a shallow negative relief) produces such an effect. Unfortunately, our article has no good visual samples. --Cookatoo.ergo.ZooM (talk) 21:57, 9 November 2010 (UTC)

Is it 3D pan and scan e.g. this kind of thing ? Sean.hoyland - talk 10:12, 10 November 2010 (UTC)

Sounds good to me - that's basically exactly what I was describing above, though I wouldn't have known how to do the video part in After Effects. So who's up for writing the 3D Pan and Scan article? :) --jjron (talk) 14:22, 10 November 2010 (UTC)

How do you compare grades?

If a candidate has an A in the course 101 and the second candidate has an A in the course 101 and a C in the course 202, the second would have lower grades, but more knowledge, wouldn't he? So, drawing the average doesn't seem always appropriate. How is this done in real life? How do you call this kind of mistake? (drawing the average when you shouldn't do it). Quest09 (talk) 13:13, 9 November 2010 (UTC)

GPA is known to be faulty. A common fix is to weight harder courses with an extra point. So, a B in a harder course is worth an A. That is how you end up with something like my high school GPA of 4.2 out of a 4.0 scale. In the end, it doesn't really matter. Nobody ever asks me what my high school GPA was. Nobody cares about my cum laude with my B.S. degree. I don't even have grades for my PhD. The degree is all that anyone cares about. -- kainaw™ 13:28, 9 November 2010 (UTC)

Nobody asks you what your GPA was because you have a higher degree. The same seems to be the case of your B.S. However, you'll still need a grade to get accepted at grad school, PhD program or whatever.--Quest09 (talk) 13:59, 9 November 2010 (UTC)

I was accepted to college with my score on the SAT and ACT. It had nothing to do with my GPA. I got into graduate school with my score on the GRE. They never asked about my GPA. -- kainaw™ 14:04, 9 November 2010 (UTC)

So, grades are still important (GRE is still a grade, isn't it?). (As a side note I have to say that the GRE is not as important as some folks - specially the institution which offers it - believe.)Quest09 (talk) 14:12, 9 November 2010 (UTC)

No, it's not accurate to equate a test score (which can be improved) with a final grade (which cannot). My own experience with college and grad school mirror's Kainaw's -- pointing to a nice GPA didn't hurt, but standardized test scores were useful. GPA was only relevant insofar as a minimum threshold needed to be met. — Lomn 14:57, 9 November 2010 (UTC)

Further, the initial question was about a discrepancy between getting an A in a 101 course and a C in a 202 course. There is only one SAT or GRE. So, the discrepancy isn't there. A score on the SAT is a score on the SAT. There is no score on an easy SAT being compared to a score on a hard SAT -- as long as you ignore that the SAT has been dummied down a tad over the years. -- kainaw™ 15:12, 9 November 2010 (UTC)

@Kainaw: I was not comparing the grade of an easy course with the grades of a difficult course. I was comparing someone with a good average (and less coursework) to someone with the some extra course (which pushes the grade down). It is like comparing $50 (average $50) with $50 + $10 (average $30). The second is definitely more, but the first has a higher average. Quest09 (talk) 16:58, 9 November 2010 (UTC)

Grades aren't even supposed to be a measure of how much knowledge a person has absorbed. It's closer to the truth to say that grades measure a student's capability to handle the material. I've forgotten nearly all of the facts about multi-variable calculus, and I've forgotten what grade I got, but if I were to look back and see that I got an A (and I knew that class wasn't too grade-inflated), I'd be confident that I could re-learn it and put it to use. Paul (Stansifer) 17:36, 9 November 2010 (UTC)

No matter how you phrase it, when it comes to college entrance exams, the students all take the same exam. So, you don't have a student taking more of an exam or less of an exam. It is one exam and one score per student. Technically, you can retake the exam and replace your old score. Still, it ends up being one exam considered with one score for that one exam per student. -- kainaw™ 18:27, 9 November 2010 (UTC)

The final question doesn't seem to have been touched on. I don't know if there's a formal name for it (see informal fallacy), but it would seem to depend a lot on specifics. In some cases, it would be almost like comparing apples to oranges; in others, it would be close to fallacy of distribution, a lot is contingent on how similar the two courses are and how different the marks are. Some would argue that getting a very poor grade in course 202 would mean that the breadth of knowledge gained was probably not significant and the poorer average is entirely deserved (hence the reason most educational institutions have a cut-off date where a class can be dropped without "earning" the poor grade). 64.235.97.146 (talk) 20:14, 9 November 2010 (UTC)

This is precisely why you are always asked for a transcript. The GPA alone only tells you almost nothing. Any college, graduate program, etc asks for a transcript. The problem you propose really doesn't exist in the real world. The Masked Booby (talk) 00:33, 10 November 2010 (UTC)

And once the college (or whatever) get the transcript, how do they compare the grades? This does not change the situation. I was asking exactly what happens when you have the grades and you don't exactly the same values. I suppose that in the case of an undergraduate program, it will be easy to compare. But what about employers or graduate programs or PhD programs? Quest09 (talk) 17:22, 10 November 2010 (UTC)

In the real world, you actually don't have this problem. A college or any other educational institution ask you for specific grades and compare them to other specific grades, no matter what they are. Employers, who could have some interest in comparing all your grades, no matter how asymetric with other candidate they might be, normally don't ask for transcripts and do not compare grades. In an ideal situation, I would compare the best grade of candidate A with the best of candidate B and see the rest as a bonus. Mr.K. (talk) 17:29, 10 November 2010 (UTC)

Where is Steve Baker???

This discussion has been moved to WP:RDTK#Discussion moved from Science Desk.

Plasma pressure : FACT / FICTION

hi guys

I know this sounds stupid but I have wondered for a while, In fiction plasma weapons / bolts etc exert physical force on things, knock them backwards etc, (e.g sorcers apprentice) would this actually happen with superheated plasma or is this pure fiction.

Thanks —Preceding unsigned comment added by 81.154.151.222 (talk) 14:40, 9 November 2010 (UTC)

Much like mundane bullets sending people flying backwards, it's fiction. A rough guideline from Newton's 3rd Law of Motion: if it doesn't send the firer flying backwards, it can't send the target flying either. — Lomn 14:52, 9 November 2010 (UTC)

(Excepting rockets and/or explosives projectiles, of course.) APL (talk) 15:28, 9 November 2010 (UTC)

So the physics behind the PEP (pulsed energy projectile) wouldnt work? thats supposed to knock people over?

—Preceding unsigned comment added by 81.154.151.222 (talk) 14:40, 9 November 2010 (UTC)

That's different. Pulsed Energy Projectile is basically a laser that causes an explosion (of plasma) at its target. That explosion at the target would send things flying in all directions. In its method of action, it is more analogous to a grenade than a bullet. The weapon itself doesn't exert much force, but the effect it creates can exert a large force. Dragons flight (talk) 15:32, 9 November 2010 (UTC)

Pulsed Energy Projectile claims that it produces an explosion that knocks people over, which is distinct from a projectile that knocks people over via transfer of momentum. Grenades are the mundane example: the user, obviously, does not suffer the effects of the explosion when he throws a grenade. Additionally, the "knocks people over" thing isn't really cited at all -- I'd guess, based on a quick overview, that the effect isn't so much "physical force knocks you down" as it is "shock, surprise, and pain incite you to fall down" -- two very different things. — Lomn 15:34, 9 November 2010 (UTC)

Consider reading our article stopping power, particularly the knockback section. Back in July, we had this discussion about plasma weapons, and I compared a hypothetical plasma weapon to a conventional flame-thrower. In reality, a plasma weapon has few or no advantages over conventional armaments. Nimur (talk) 16:25, 9 November 2010 (UTC)

The citations for that article aren't done right, but the sources listed in the "Sources" section say "The resulting shock wave will knock you to the floor"[10] and "The weapon … could literally knock rioters off their feet"[11] The grenade analogy doesn't work well in terms of conservation of energy or conservation of momentum. A grenade carries potential energy that's converted to kinetic energy at its destination, so the kinetic energy produced by the grenade isn't felt as kickback by whoever threw the grenade. But the PEP is basically just a laser. Only light comes out of the laser. There's nothing coming out of the laser that has any potential energy. Every bit of kinetic energy experienced at the destination ultimately comes from the kinetic energy of the light coming out of the laser. Ditto for momentum. Red Act (talk) 16:58, 9 November 2010 (UTC)

Sorry, I wasn't clear: the sources themselves are remarkably poor with regard to "knock to the floor". There's actual discussion about the pain aspect of the weapon. There's nothing but a throwaway line about knockdown. — Lomn 23:29, 9 November 2010 (UTC)

I'm stuck on the same thing Red Act - only photons are coming out of a laser, so the total momentum imparted should be small (non-zero, but small). On the other hand, suppose the thermal energy from the laser activates a chemical reaction at the target, liberating some chemical potential energy that is already down-range. In the extreme case, imagine using a laser to heat a balloon full of hydrogen until ignition. The laser provides a tiny "pilot light" activation energy, the majority of the energy and momentum will be liberated by the secondary action. The limiting factor would then be the types of chemical reactions that can be triggered by laser-heating. Nimur (talk) 17:08, 9 November 2010 (UTC)

I have no idea what the specifications of the laser system are, but to see how this might work, consider the following. A 500 J laser pulse at 1000 nm would have 2.5×10²¹ photons and a impulse of 1.6×10⁻⁶ m kg / s (i.e. the same momentum change as a 1 N force applied for 1.6 microseconds). However, if you could somehow dump all 500 J into 1 cm³ of water in a microsecond, you'd flash it to 200 C steam. Using the ideal gas approximation, that steam would then have a overpressure of 2000 atmospheres causing it to "explode" and delivering a force to it's immediate surroundings of ~25 kN during the ~50 microseconds before it dissipates. In this example, the impulse of the laser was thus amplified ~1 million times as a result of using the energy to boil water. This is a purely physical change and doesn't rely on any potential energy being in the target. Obviously the PEP is trying to do something like this, but presumably without blowing up chunks of flesh (if they want it to be non-lethal anyway). Dragons flight (talk) 17:38, 9 November 2010 (UTC)

500 J isn't enough to do that. The heat of vaporization of water is 40.65 kJ/mol, of which R(373 K)=3.1 kJ/mol is the $p\Delta V$ part of the enthalpy change (taking $\Delta V=V-V_{0}=1.7{\text{ L}}-{\text{cm}}^{3}\approx V$). One cm³ (or gram) of water is 55.5 mmol, so you need 2084 J just to vaporize that much water in place, never mind heat it to 100 °C or from there to 200 °C. (That actual heating, from 20 °C, takes 487 J; perhaps that's what you calculated?) But your point stands: just up it to 5 kJ and you still have an amplification of ≥10⁵. --Tardis (talk) 19:37, 9 November 2010 (UTC)

Eh, I originally did the calculation for 5 MJ. I then realized the result was too enormous and tried to scale it down to something more reasonable. Apparently, I loss track of some factor in the process. Oh well. The basic point is correct though, the pressure created by a rapid phase change can lead to a much bigger impulse than the photons in the laser do directly. Dragons flight (talk) 19:48, 9 November 2010 (UTC)

It is is usually not the dominant source of the pressuse, see e.g. here:

The force that compresses and accelerates the fusion fuel inward is provided solely by the ablation pressure. The other two possible sources of pressure - plasma pressure (pressure generated by the thermal motion of the plasma confined between the casing and the fuel capsule) and radiation pressure (pressure generated by thermal X-ray photons) do not directly influence the process.

Count Iblis (talk) 00:29, 10 November 2010 (UTC)

Condensing top for cooking pot

I was cooking "Steel cut Irish Oatmeal" which requires (per the recipe on the can) keeping it at a simmer for 30 minutes. It tended to dry out and scorch, even on low heat. If I covered the pot, it tended to boil up and spill out. I tried putting an oversized Pyrex glass lid over the pot, with the convex side projecting down, and with some cool water in the concave side above, like a reflux condensor. The goal was to let the oatmeal and water simmer, while condensing the water which evaporated or boiled off and letting it drip back into the pot. Through the glass I could see a steady stream of large drops returning to the pan, while the water above the lid heated up only minimally. The knob hanging down distributed the condensed water rather than it all falling in a small pool in the center of the oatmeal. It functioned great, and the result was good. A normal metal saucepan cover might condense some of the vapor, but it tends to heat up and then steam escapes. A pressure cooker is unusable, since a food like steel cut oats can clog the relief vent resulting in overpressure and overtemperature, and possible a blowout. So is such water-cooled condensing saucepan top a commercial product, and if not why not? All I could find was a domed lid with a small depression in the center, apparently not water cooled [12]. Edison (talk) 17:04, 9 November 2010 (UTC)

How about a laboratory-grade condenser? Surely some of those have the form-factor you're looking for. I've seen some intricate coiled tube systems - their intent is usually to maximize the rate of heat-removal; but in your application, that would be simultaneous with maximizing the quantity of collected (and re-precipitated) water. Nimur (talk) 17:21, 9 November 2010 (UTC)

Those all seem like overkill, and generally would not deposit the condensate back into the saucepan as well as an inverted glass lid from Corningwear pan did. The regular metal lid from the saucepan would also work inverted and with some cooling water in it, but it was interesting to see the condensation in action. Edison (talk) 18:13, 9 November 2010 (UTC)

As to why this product (may) not exist. Many cooks experiencing similar problems would be happy to use some combination of these techniques rather than buying a special reflux condenser lid. 1 turn temperature down, 2 add a small amount of liquid, 3 use slightly larger vessel, or 3 only partially cover with existing lids. (perhaps your range is lacking on fine control at the low end?) Interesting idea though, I'll try it next time I have an opportunity :) SemanticMantis (talk) 19:37, 9 November 2010 (UTC)

A condenser seems necessary only if the evaporated material contains something precious, something you need to retain in order to preserve the character of the food you're cooking. That's obviously the case for a whisky still (where the evaporate is a key element of the final product). But in the case of oatmeal, or a casserole, is there anything really precious in that evaporate. If there isn't, then SemanticMantis' suggestion of simply adding more virgin water is sufficient (your condenser would merely save you work. and that only until you have to clean it). I guess the test is to manually collect the condensate (say by periodically lifting the lid and pouring it off into a glass, and the rest of the time keeping a bag of ice on the lid to keep it cool). Once that's done and the collected condensate has been left to cool you can taste it. If it's sufficiently strong, and sufficiently different from the mass of the food, such that adding it back in would noticeably improve the food, then a condensing pan would be a valuable addition. I'm guessing that, for most recipes, it won't - that it'll either taste (weakly) like the food, or like nothing at all. -- Finlay McWalter ☻ Talk 20:26, 9 November 2010 (UTC)

Identify this bush

• 
  The bush
• 
  Up close on some leaves and a berry like thing.

What type of bush is this shown in these pictures? I took the pictures today at my house in Kansas, and in the picture the bush is displaying it's autumn colors.
P.S. I apologize for the relatively poor quality of the images, but my normal camera is out of commission, forcing me to take the images on my cell phone.

Thanks in advance, Ks0stm ^(T•C•G) 23:06, 9 November 2010 (UTC)

Some sort of Euonymus, perhaps Euonymus alatus? It's rather hard to tell from the pictures. Deor (talk) 01:30, 10 November 2010 (UTC)

It's definitely Euonymus alatus. There is one of those right outside my house. J.delanoy^gabs_adds 03:49, 10 November 2010 (UTC)

Explanation behind a cosmic ray exhibit

An exhibit on cosmic rays at the Pacific Science Center.

Could someone please explain the science behind this exhibit better than the informational text seen in the picture did? I don't really get how cosmic rays are visible in the cloud chamber. The little tracks they make in the chamber can be seen in the picture where I highlighted them on the image's page at Commons. They appear in person as little yellowish white streaks in the blackish cloudy material. How do the cosmic rays form these little streaks?

Thanks in advance, Ks0stm ^(T•C•G) 23:16, 9 November 2010 (UTC)

Cloud chamber should help. 75.41.110.200 (talk) 23:27, 9 November 2010 (UTC)

Yes, you're seeing secondary effects caused by high-energy particles - it's not possible to see the particles themselves. This is sort of like lightning - you never see the "electricity", you see the air that the electricity has flowed through. In the case of lightning, the air has been super-heated and glows because of a combination of ionization and incandescence. In the case of a cloud-chamber, a supersaturated solution has formed a precipitate because an ionized trail has created nucleation sites in the wake of a high-energy particle. Nimur (talk) 01:42, 10 November 2010 (UTC)