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December 14

Does the electrical conductivity of graphite increase as temperature increases(for some lower temperature)?

Just saw such statement in some physics questions--Inspector (talk) 01:08, 14 December 2012 (UTC)[reply]

Yes. The temperature coefficient of resistivity of graphite is negative.[1] Red Act (talk) 02:49, 14 December 2012 (UTC)[reply]

Is the temperature coefficient always constant until the change of state?--Inspector (talk) 05:19, 14 December 2012 (UTC)[reply]

No. The temperature coefficient increases with increasing temperature, and becomes positive when the temperature is above about 400 to 600°C.[2] Red Act (talk) 05:47, 14 December 2012 (UTC)[reply]

a feature used in heathkits and such to soft start the power supply. Gzuckier (talk) 21:23, 14 December 2012 (UTC)[reply]

I think that Gzuckier is thinking of the old non-encapsulated type of inrush current limitter (http://en.wikipedia.org/wiki/Inrush_current_limiter), very common in the larger types of tube-type consumer electronics, stereo amplifiers, TV sets, and the like. These were not graphite but they were black and sintered so they looked like graphite to the uninformed. They were a black rod, generally about 25 to 35 mm long with a connecting wire alloyed to each end. Graphite does not change its resistance sufficiently for this application. Inrush current limitters of this type were made from a metal oxide ceramic. Keit 124.178.56.108 (talk) 03:00, 15 December 2012 (UTC)[reply]

Thanks. Still, is graphite a better conductor than those metals at higher temperatures? Also, how does the conductivity of steel containing carbon and other alloys differ from the pure metals?--Inspector (talk) 01:31, 16 December 2012 (UTC)[reply]

The electrical conductivity of reasonably pure metals can be modelled approximately by a straight line passing throgh absolute zero and having a positive slope of around 0.39 % of the 293 K (20 C) value per K. The actual line is not straight, it is slightly curved, but in practical engineering it is generally sufficient to assume it is straight, and improve the accuracy by using a different notional value of absolute zero temperature.

For commercial high purity copper, the slope is 0.00393, the notional zero point is 38.7 K, and the 293 K resistivity is 1.724 x 10^-8 Ω.m

For commercial high purity iron, the slope is 0.0059, the notional zero point is 35 K and the 293 resistivity is 9.71 x 10^-8 Ω.m

From these values, you can calculate the resistivity of iron and copper, compare it with the resistivity of graphite given by the data cited by RedAct.

When other elements are alloyed with the main consituent (copper, iron, etc), the curve can depart seriously from a straight line. For instance the alloy manganin has virtually a zero temperature coeficient at human comfort temperatures. The situation with carbon steel, cast iron, etc, is complex, as the carbon may be interstitial with iron crystals, or be chemically combined in several ways. In general, the presence of carbon and other elements, whether interstitial or chemically combined, causes a significant increase in resistivity. For instance, a typical resistivity of mild steel is around 12 to 13 x 10^-8 Ω.m at 20 C. Keit 120.145.76.197 (talk) 04:33, 16 December 2012 (UTC)[reply]

Bloating or concussion?

A few days ago, I caught a mouse in a sticky trap, so like the previous three mice that I caught, I took it outside and dropped a concrete block on it to kill it quickly; since I live in the woods, I just left it in hopes that something would come along and eat it. Two days later, I noticed that the block had landed only on the head, which was flattened by the impact (except for the eyes, which were protruding somewhat), but the rest of the body was substantially larger than it had been. I live at 39°N, so everything was covered with frost. Given winter weather, is bloat possible, or is it more likely that the sudden blow from the concrete somehow forced blood and other parts into the rest of the body, making it swell? Reading the page that I linked in the previous sentence, I'm questioning whether bloat can happen in the winter, since so much of the process depends on gasses and fluids that behave differently in temperatures below 0°C. I've since disposed of it (put mouse and trap together into a zip-lock bag and threw them away in a public trash can), so I can only answer questions based on my memory. Nyttend (talk) 02:04, 14 December 2012 (UTC)[reply]

It might have been just ice, which takes up something on order of 10% more volume than the equivalent mass of water. StuRat (talk) 04:05, 14 December 2012 (UTC)[reply]

Yeah, I wouldn't expect it to bloat in that kind of temperature. Something as big as a human or bear might (depending on the environmental temperature), but a mouse wouldn't have enough residual body heat to allow for much of anything to happen. Any chance that it was simply, well, fluffy? I could see a traumatic death causing the fur to stand on end. Likewise, I could see post-mortem muscle relaxation allowing the breeze to muss the fur as well. Matt Deres (talk) 22:33, 14 December 2012 (UTC)[reply]

Are there any non-sterile hybrids?

Are all hybrids sterile? The hybrid article uses words like "very often sterile" and "normally sterile" which sounds like there are some rare non-sterile corner-cases. Dncsky (talk) 03:49, 14 December 2012 (UTC)[reply]

Some ligers aren't sterile. --Jayron32 03:52, 14 December 2012 (UTC)[reply]

I don't think sterility is the norm at all. For instance, our article gamebird hybrids says "Domestic fowl can be crossed, and produce fertile offspring, with Silver Pheasants, Red Junglefowl and Green Junglefowl." Most wild teal species can also produce viable hybrid offspring. Note that the hybrid article opens with eight subtly different concepts, so there is bound to be plenty of variation in viability, depending on what is crossed, and how closely related they are. My guess is that sterility is probably more likely when the parents are more taxonomically distant. See also bird hybrid, which suggests "successful hybrid" as a search term for fertile hybrids. SemanticMantis (talk) 04:04, 14 December 2012 (UTC)[reply]

At least one Wholphin is fertile. There are two species of Caenorhabditis that can produce fertile hybrids (Sp. 9 and briggsae). But you're dealing with statistics, regardless. Take the case in caeno I just mentioned: The hybrid offspring (F1 hybrids) are almost all fertile, but have half as many offspring as their full-blooded parents (P1). Those offspring (F2 hybrids) are sterile more than half the time, and the fertile ones have very few offspring, giving a population fertility something like 1% that of the P1 fertility. You sometimes have to dig into the original literature to parse what is meant by "mostly sterile". It could mean that most of the hybrids are sterile, or the hybrids have very few live offspring, or both. And just because the hybrid is fertile does not mean its children are fertile. Someguy1221 (talk) 04:13, 14 December 2012 (UTC)[reply]

Thanks, guys! Dncsky (talk) 04:41, 14 December 2012 (UTC)[reply]

Resolved

At the root of this issue is that a "hybrid" is defined as the cross-breeding of two different "species". The problem being that the definition of what is or is not a distinct species is very fuzzy. That being the case, we can no more decide for sure whether some animal is a true "hybrid" than we can whether its parents were from different species. So the issue isn't always in defining whether or not hybrids can be fertile - but whether a cross-bred animal or plant is a true hybrid at all. SteveBaker (talk) 13:56, 14 December 2012 (UTC)[reply]

That's precisely why I asked the question. If there is a hybrid out there with a 100% non-sterility rate, then wouldn't it imply that the two parent species, along with the hybrid, are in fact one specie? But since there's no such case out there this doesn't happen. Dncsky (talk) 20:20, 14 December 2012 (UTC)[reply]

Those cases do exist. Some you never hear about because scientists correct themselves before much has been written. Dolichorhabditis carpathica (which was actually not even in the right genus) has a 100% hybrid fertility rate in crossbreeding with Oscheius tipulae, but that was caught before any formal papers were published. Not every taxonomist is so lucky. The two major categories of domestic cattle, Bos taurus (aka the cow) and Bos indicus (aka the zebu) were long considered separate species descended from Bos primigenius (the auroch). However, taurus and indicus actually make fertile hybrids quite easily, and most would now consider taurus and indicus to be separate subspecies of primigenius. But old habits die hard, so they are still often referred to as if they were different species. Someguy1221 (talk) 00:33, 15 December 2012 (UTC)[reply]

And another example is the Beefalo, a fertile breed that is a 'hybrid' between bison bison and bos taurus. Note that these animals lack a binomial classification, because they don't fit in the system. - Lindert (talk) 10:01, 15 December 2012 (UTC)[reply]

The beefalo is a curious one because it's not simple to define the fertility of a bos/bison hybrid. Crossing a bison male with a bos female doesn't produce anything, just as you'd hope from an interspecies cross. Doing the cross in the other direction gives you slightly fertile females and sterile males, but not a self-sustaining hybrid population. The initial beefalo breeders generated a new set of hybrids for each generation, but it was later found you could outcross the hybrids to one of the original species and get an uneven mix of DNA. And its the uneven mixes that have proved to be self-sustaining hybrids. So, yeah, it doesn't classify well. Bos and Bison really seem to be at the edge of reproductive isolation. Someguy1221 (talk) 10:58, 15 December 2012 (UTC)[reply]

Also see this listing of macaw hybrids. There are loads. Some of them are fertile. Some are even intergeneric hybrids. --Kurt Shaped Box (talk) 14:19, 14 December 2012 (UTC)[reply]

Thirty-odd years ago I saw an article somewhere or other about a second-generation cross of gibbon and siamang. Experts were amazed because their chromosomes are grossly different. —Tamfang (talk) 10:58, 26 June 2013 (UTC)[reply]

There is no science issue here. This is nothing but a word game.

The word "species" is defined by the idea that organisms from one species cannot produce fertile offspring with those from any another species - but they can produce offspring with members of the other sub-species within their own specie. So if two organisms can produce a fertile hybrid, then (by the definition of the word "species"), they must be sub-species of the same specie - and that means that (by the definition of the word "hybrid"), the offspring wasn't a hybrid at all. Ergo, if a "hybrid" is fertile then technically, it isn't a hybrid! This has nothing whatever to do with science - it's all about the definitions of words in the English language. The problems arise because our notion that there are distinct species at all is a fuzzy, messy, ill-defined, poorly-implemented one. We know that dogs and butterflies are definitely from different species and black horses and white horses are definitely from the same species...but whether a bison is or is not a taurus is a fuzzy taxanomic mess. That's not because there is some fundamental fact of nature that's weird or difficult, it's because some taxonomists continue to insist on using this word "species" without a testable, bright-line definition for what they're talking about. Worse still, you can get real-world situations with three or more kinds of organism (call them 'A', 'B' and 'C') where organisms of type A cannot successfully inter-breed with type C (so by definition, they are different "species") but A can happily breed with B and B can breed with with C. So now:

A is the same species as B.
B is the same species as C.
A is not the same species as C ?!?

Is this a paradox? No! What's going on is easy to understand - there is no paradox in nature, the science is easy to understand. It's entirely a man-made mess of a linguistic nature. SteveBaker (talk) 15:16, 17 December 2012 (UTC)[reply]

Alexander Siddigs eye color

look at his picture, do you think it's a result of Co-dominant alleles of Blue and brown eyes?, does dark-brown allele + Light-blue allele equals yellowy-green eyes? thanks ! 109.64.147.11 (talk) 14:25, 14 December 2012 (UTC)[reply]

Yellowy-green eyes are called "hazel" colored eyes. The Wikipedia article on eye color has a lot of information on the biology and genetics of eye color, but it is not a simple or facile thing as you are described above. --Jayron32 14:47, 14 December 2012 (UTC)[reply]

Quantum theory, constructivism, and postmodernism

I'm looking for a Wikipedia article I remember reading a few weeks ago that pretty much said in a sentence that "Many quantum theorists believe in social constructivism/are social constructivists" (in the meaning of radical constructivism), due to the belief in the inexistence of any objective reality on behalf of certain interpretations of quantum theory because of quantum effects and theorems such as Observer effect (physics), consciousness causes collapse, and quantum mind, where everything is really in constant superposition of all possible outcomes, and it's only the human mind and cognition that can perceive only a single outcome at a time (the "collapse" of the waveform of all possible outcomes into a single reality within the human mind). AFAIK, it was a pretty short article, maybe something to do/in the vicinity of Schrödinger's cat and Wigner's friend.

Furthermore, I'm looking for sources for that statement, examples where quantum theorists explicitely refer to constructivist/constructionist ideas and theories in philosophy, and how vice versa radical contructionists/constructivists and especially postmodernist philosophers refer to the natural science of quantum theory in order to justify their complete abolishment of objective reality (other than moderate constructivists/constructionists who do believe in an objective reality and it's only our malleable perception of it that's socially and culturally constructed/shaped/influenced). Postmodern philosophers for instance go so far as to deny any reality, history, society, or social conditions beyond human language. It's my impression that to a degree, certain philosophers and certain factions of quantum theorists are circularly covering each other's backs here.

And I'm also looking for sources on the affinity between quantum mysticism and the tendency of some postmodernist philosophers to flirt with irrationalism, mystic (often far-eastern, as Buddhism and Hinduism) religions, and occultism. Two examples that may come to mind would be Foucault's (if you're willing to count him as a central father figure to many postmodernists) glorification of the Iranian mullahs, and Butler's appraisal of Hamas as "part of the global emancipative left". --87.151.21.55 (talk) 20:28, 14 December 2012 (UTC)[reply]

Sounds like you were reading the Sokal hoax. μηδείς (talk) 20:39, 14 December 2012 (UTC)[reply]

That was my thought as well. Looie496 (talk) 20:53, 14 December 2012 (UTC)[reply]

I'm not sure whether Sokal and the article science wars are really what I'm looking for, as they're lumping postmodernism together with the Frankfurt School, whereas it was Frankfurt School thinker Theodor W. Adorno who authored fundamental critiques against the very mindset later found also in this kind of postmodernism in his 1951 Theses against Occultism and the 1952-'53 essay collection The Stars Down To Earth: And Other Essays on the Irrational Culture. I'd say Sokal & Bricmont are to Adorno's Theses against Occultism what the modern notion of "political correctness" (that has become a mere empty rhetorical slur) often is to Herbert Marcuse's repressive tolerance: The modern conservative appropriation of an originally progressive idea.

And as said, the Wikipedia article I remember reading was rather short and positive/neutral on quantum theory, no denouncement such as Sokal. Within the explanation of some quantum theorems relating to experiment, measurement, and observer, it was mentioned only in passing that "Many quantum theorists believe in social constructivism/are social constructivists", to help explain their concept of reality only existing within/being caused by the observer's mind. --87.151.21.55 (talk) 21:03, 14 December 2012 (UTC)[reply]

Proof of life on other planets

What are the chances of sufficient evidence of "alternative life beings" from another planet being found by the end of the decade that is significant enough that the President of the USA makes a speech confirming we are not alone? 86.130.165.225 (talk) 23:08, 14 December 2012 (UTC)[reply]

Pretty low. We aren't returning samples from many new places now, so even if they are out there, we're not likely to find them. Assuming you will settle for a fossilized bacterium or virus, perhaps one of our Mars probes might snap a pic and send that back, but this probably isn't sufficient proof for a Presidential speech, since we already had the Mars meteorite which at first look appeared to bear signs of life, and any bacteria we find might also be a result of contamination from the probe. StuRat (talk) 23:15, 14 December 2012 (UTC)[reply]

As Stu alluded to, the fact is that we're just not really looking in many places at present. Luckily the current site of the bulk of our efforts in this regard is a pretty good candidate, as the solar system goes, and the search for signs of life is likely to continue to be a major focus for all exploratory missions on Mars for a long time to come. However, the scenario you describe is not necessarily probable in the event of a discovery anyway. It is very likely that evidence for the case of pre-existent life on Mars will be built slowly; if such life did exist, then many indicators in the martian soil will begin to suggest their presence or prior influence, very likely some time before the first organism or remnant of an organism is confirmed. If this happens, and a certain combinations of physical qualities in the soil seems to add up to a compelling degree, then sooner or later some prominent voices will begin to make the argument that it's significant proof. But the matter will be certain to be hotly debated from the outset and will undoubtedly become a source of immense discussion, both within scholarship and in general culture. The point of which being that thing are unlikely to unfold all in one rush and not likely to be revealed and settled in one statement by a single politician, no matter how prominent his position, as it's well outside his sole domain. If there ever were a major announcement by the president on the matter, I would expect it to come well after the debate had started, officially announcing some position on the matter. Unless it's the type of life that has lasers -- then the president might very well be the first person you hear about it from. Assuming you don't listen to late night talk radio, in which case you've been getting "warnings" about the impending invasions for some time. Myself, I just want to go on the record here as saying I for one welcome our new benevolent overlords. All hail Zrag! Snow (talk) 01:12, 15 December 2012 (UTC)[reply]

A planet with a large amount of oxygen or another gas out of expected equilibrium will be strongly indicative of biological activity driving its production. Planetary atmospheres can be analyzed using spectrophotometry (we may have a more relevant article than that one) in principle, and its how we know the makeup of the atmospheres of the planetary bodies in our solar system. Someone else might know our capabilities regarding other planetary systems. μηδείς (talk) 02:03, 15 December 2012 (UTC)[reply]

There's a great body of work speculating on which star systems feature qualities that make them more likely candidates to include planets that could host life, but there's really zero chance of confirming the possibility remotely. Bear in mind that, despite being a presumed ubiquitous feature of the cosmological model for centuries, it has only been in recent decades that we could even confirm the existence of extra-solar planets by observing the minute influences they have on the behaviour of their host star. Needless to say, observing these tiny effects -- tiny in the relative sense of the mass of the planet and the star -- over such vast distances is a complicated affair in it's own right; getting a refined enough understanding of the physical nature of a planet so as to confirm life there is, for the time being, well outside our capabilities. Barring something like a transmission or other attempt at communication made by another intelligent species of course, and there are challenges to these reaching us as well. Snow (talk) 04:37, 15 December 2012 (UTC)[reply]

In my view the best candidates for life are Europa, which has oceans of liquid water beneath an ice crust, and Titan, which has lakes and rivers of liquid ethane and methane. Mars is a bleak place in comparison. Looie496 (talk) 03:44, 15 December 2012 (UTC)[reply]

My money's on Earth, then Europa, then Mars, then the Moon. Shadowjams (talk) 04:37, 15 December 2012 (UTC)[reply]

Well, I said Mars was a decent candidate as the solar system goes, not the only one. I'm aware of the cases made for more exotic life on Europa (and other Jovian moons) and Titan, but the truth of the matter is that there's a fair deal of speculation for all of the candidates. Mars, however, is the only one which we can directly scrutinize in terms of the chemical and other physical tests which are most useful to us in this search. And Mars may be bleak now, but it's believed that it once had a very different atmospheric make-up and liquid water on its surface and at that time it would certainly share a lot more in terms of general physical properties (mass, rotation, atmospheric composition and pressure, orbits in terms of both size and the central body, rotation rate, and many other) with the only planet we know for a fact to have hosted life -- Earth -- during its life-bearing history than any other candidate in the solar system. Personally I believe if life is found within the Solar system outside of Earth, my money would be on the smoking gun being found first on Mars. Snow (talk) 05:05, 15 December 2012 (UTC)[reply]

I don't understand your "zero chance remotely" comment, Snow. Do you think we could never detect the oxygen (or other gas not in equilibrium) atmosphere of a distant planet? The notion that scant, "anaerobic", microbial life on another planet would be hard to detect is one thing. Denying aliens could ever detect and interpret our planet's atmosphere is another. μηδείς (talk) 17:45, 15 December 2012 (UTC)[reply]

Well I'm not saying that we couldn't one day directly observe (as opposed to intuit) the chemical composition of an extrasolar planet's atmosphere, just that at present it's well outside our capabilities and is likely to remain so for some time, given the scales and limitations involved. And even if we did have the capability to detect oxygen in the atmosphere of another planet it would be a far cry from proof of life; oxygen is one of the most common elements in the universe and we can expect it to be found in large amounts in any number of planets that don't necessarily support life. All of that being said, I wasn't completely dismissing the notion that an extremely advanced species could detect us; it's impossible to make that assessment without having an understanding of their hypothetical capabilities, which would involve speculation on technologies currently outside our understanding. However, I will say that there are complications to that process that I can't imagine being easy to overcome even assuming such an advanced intelligent species. And that's assuming an initial proximity to us which involves the nearby stellar neighborhood and the closest extrasolar sapient species could very well be much farther away than that, we just have no way of knowing at present time. Snow (talk) 21:29, 15 December 2012 (UTC)[reply]

It's not oxygen, per see, which is rare, but rather O₂. Oxygen is quite reactive, and doesn't normally stay in it's diatomic form for long. Thus, it's presence in large quantities is a good indication that plants are producing it. However, there may very well be other life forms which don't produce (or use) diatomic oxygen, so it's absence certainly isn't proof that a planet is barren. StuRat (talk) 21:42, 15 December 2012 (UTC)[reply]

I didn't think it was necessary to get so specific, but in just about any case in our solar system a planetary body with more than 1% O2 (not just atomic oxygen) would be well out of equilibrium on a geological scale. You'd have to have some sort of mechanism like life or oxygen factories to be driving it out of equilibrium. Knowledge of the other gasses present would allow scientists to make such a judgment. I doubt, StuRat, that you are saying sensing an atmosphere like ours would indicate anything other than the presence of life. μηδείς (talk) 01:48, 16 December 2012 (UTC)[reply]

I don't believe any known process other than life could create a planet with a 19% O₂ atmosphere, but there's always the possibility of an unknown process. StuRat (talk) 19:10, 16 December 2012 (UTC)[reply]

There's almost certainly a multitude of planets out there with basically the same relative ratios of atmospheric gases as Earth whether life exists outside of Earth or not. There are a lot of chemical processes that go into the formation and evolution of planetary bodies. I can't claim to have done an exhaustive investigation of every element found in abundance on this planet, but just considering the major elements that make up our atmosphere, nothing stands out to me as impossible to explain on another planet by any other means but the presence of life, regardless of the amount found. Even the presence of Oxygen is not a smoking gun; many terrestrial planets have large amount of oxygen trapped within them or bound into compounds on their surface, either of which can be freed by normal geological processes. While its true that the stereochemistry of Oxygen means it would not remain unbound for long under many atmospheric conditions, its not utterly implausible that you'd find it in the atmosphere of a planet without an organic source. It would absolutely be a very encouraging sign, no doubt, but I just have a hard time believing it would be accepted as complete confirmation. Admittedly though, I'm no exogeologist. Snow (talk) 12:12, 16 December 2012 (UTC)[reply]

Yes, we can imagine some very strange circumstances where a rocky planet might be so enriched in oxygen, and so lacking in other elements that could reduce it, that free O2 would be in high levels. (Read P. A. Cox's The Elements: Their Origin, Abundance, and Distribution on the unlikelihood of this.) But scientists would immediately be able to tell from the other gases in the atmosphere whether this was an equilibrium or disequilibrium state. Without life, all the O2 on the earth would combine to form carbon dioxide, rust, and various compounds with sulphur and nitrogen and so forth. Even if it weren't absorbed by the land and ocean, lightning strikes would eventually convert all the oxygen in the air to compounds with nitrogen. An atmosphere in an unstable-over-geological-time disequilibrium atmosphere would quickly point to a process causing it. μηδείς (talk) 19:57, 16 December 2012 (UTC)[reply]