Electrons can be "densely stored" in a superconducting wire coil and circulate as long as cyronic temperature is maintained. The Cooper Pairs (presumably) do "not knock" in to the coil. Could the same apply to positrons? If it did, positrons could be densly stored, allowing energy storage one hundred times more powerful than nuclear fusion, possibly allowing starship propulsion or anti-matter bombs. Switch off the cooling and the whole lot would annilhilate with total conversion of matter to energy. Some people have said I am irresponsible making this idea public, but making anti-matter is inefficient so only large states could do this. (Trevor Loughlin) — Preceding unsigned comment added by 91.224.27.227 (talk) 11:31, 14 June 2013 (UTC)[reply]

Wouldn't the superconductor also need to have antinuclei to conduct positrons? 139.193.214.10 (talk) 13:21, 14 June 2013 (UTC)[reply]

Funny post. The funniest part was "Some people have said I am irresponsible making this idea public". Dauto (talk) 18:21, 14 June 2013 (UTC)[reply]

In reality, positrons can be circulated in storage rings. The beams fly through a near-perfect vacuum, and are kept in position using magnetic fields. If you have a lot of positrons, you can do almost anything you like with them; but if you direct a beam of positrons into a wire - supercooled or not - the positrons will rapidly annihilate - because the mean free path is very short and the collision frequency is very high in condensed matter. Positrons are not easy to come by - so people who have access to them typically don't waste them - the particles are kept in ultra-high vacuums for as long as possible. Nimur (talk) 19:14, 14 June 2013 (UTC)[reply]

The best method we have yet discovered for producing positrons is a machine at Lawrence Livermore labs that is the size of a house and produces 10 billion (10¹⁰) positrons every 30 minutes by zapping a gold brick with a petawatt laser(!). Each positron (and each electron that you're going to annihilate it with to produce energy) weighs in at around 10^-30kg - so the results of 30 minutes production on this expensive machine is 10^-20kg of antimatter. E=mc² and c² is around 10¹⁷m/sec. So the amount of energy you get from an antimatter "explosion" produced by 30 minutes of work by this massive machine is somewhere near 2x10^-3 Joules - which is about 1/500th the energy produced if you drop an apple from a height of one meter. The energy stored in a AA battery is about five million times greater.

The energy it takes to fire the "Titan" laser in the positron creation machine is hundreds of Joules. So having a great way to store positrons isn't going to lead to amazingly powerful positron batteries or anything. SteveBaker (talk) 20:11, 14 June 2013 (UTC)[reply]

From the linked source: "... the electrons each break apart into a lower-energy electron and its anti-matter opposite, a positron.". This would violate charge conservation, so I think the source is not reliable. 95.112.240.62 (talk) 21:38, 14 June 2013 (UTC)[reply]

The "linked source" is a brief and general-purpose news summary - it's bound to "gloss over" minor details (like the laws of physics) - for the purposes of brevity. If you require scientifically-accurate descriptions of the laser phenomena that Steve mentioned, you might read the publications section at the Jupiter Laser Facility at Lawrence Livermore. It lists several published, peer-reviewed papers on the production and measurement of positrons in the laser laboratory. Nimur (talk) 22:48, 14 June 2013 (UTC)[reply]

I like to hijack the original question and reformulate it:

1. Can electrons really be "densely stored" effectively anywhere? Superconducting coil or not, electrons repulse each other due to the electrical charge.
2. Obviously, positrons would annihilate with electrons in normal matter. But if we would find some technical trick to strip the electrons off but still keep the nuclei in place and the positrons squeezed between them, wouldn't the positrons react with neutrons?

95.112.240.62 (talk) 19:41, 14 June 2013 (UTC)[reply]

I guess it depends what you consider "dense." There are a lot of electrons densely packed in ordinary, regular, condensed solid matter! I don't think you'll get denser packing of electrons-per-cubic-meter than what you'd find in a dense atomic lattice - like lead or uranium or a lump of any other other favorite heavy element. There's a few dozen moles of electrons per mole of uranium, or about a septillion electrons per cubic centimeter (plus or minus a few orders of magnitude).

For your second question - everything I've ever learned about positrons concerns either of two scenarios: (1) positrons, carefully isolated in an almost perfect vacuum (i.e., not interacting with any matter), for the purposes of some particle experiment; or (2) positron emission followed almost immediately (i.e., after a very short duration of travel-time) by a positron-electron collision event. For example, in medical imaging (PET), the positron is emitted and it exists just long enough to bump in to the first atom it encounters, annihilating one electron and releasing a bright shiny pair of easily-detectable photons.

I'm not familiar with any other type of positron absorption event. Though part of me wants to say that positron emission might be reversible, thinking along a symmetry argument, I've never heard of positron absorption by a nucleus. Nuclei absorb electrons, not positrons. So: probably the math doesn't work out - and positron emission is not reversible even in theory; but even it it's possible, it's so exotic an interaction as to be completely un-discussed in most of the experimental physics community; or maybe somebody else has spent more time studying experimental particle physics has some additional insight. Nimur (talk) 23:52, 14 June 2013 (UTC)[reply]

To add my own ignorant question to the mix: what controls the odds of electron-positron annihilation? I imagine that, given that an electron is "blurrier" than a proton, a positron ought to be localized to a region larger than a hydrogen atom, and likewise the electron it "orbits" just before annihilation. They're not point particles heading toward each other, right? Is there some period of time when they just sit there, one amidst the other, waiting for a probabilistic event to happen? And does that event depend on their parameters of motion - spin, angular momentum, velocity relative to one another, what kind of orbital they're in? Is it remotely conceivable to engineer an electron-positron material that somehow reduces the odds of annihilation by a measurable amount? Wnt (talk) 01:45, 15 June 2013 (UTC)[reply]

The electron and positron must collide - which is a well-defined event. The probability of the collision depends on the collisional cross-section of both particles, in turn which depends on the energy and momentum of the particles.

The way I would describe this: a collision between two particles is a purely deterministic thing. Particles have exact positions, and trajectories; we know when they hit each other. The part that's "probabilistic" - and here is where quantum mechanical stuff gets weird and your intuition may fail - is whether you even have two particles in the first place - and where those particles would be. In other words, if you have a given amount of energy, momentum, and a particular state of electric and magnetic fields, how probable is it that you observe those conditions in a particle-like way - that is, as a localization of the energy and the momentum and charge specifically in the form of an electron and a positron? The energy is there, the charge is there, and the fields are all there, but whether those constitute a pair of high-energy photons or equivalently whether the same fields, charge, energy, and momentum are localized as a pair of particles - is the probabilistic piece. Nimur (talk) 05:51, 15 June 2013 (UTC)[reply]

Hmmmm... I don't have the faintest sense how you calculate such a thing. But I suppose that simply classically, you could have some energy in an electron-positron pair, so that the two "orbit" each other (in a Bohr-ish model) and therefore don't collide. I don't know if there's a comparable "orbital" in a QM sense where the two likewise would fail to interact. What I'm wondering is... is there a chance that you could have a cloud of superconducting electrons in some simple material that are in a state such that a positron in some other specific state could be always near them, attracted by their charge, but never hit them, sort of like this hypothetical orbiting positron? Wnt (talk) 06:01, 15 June 2013 (UTC)[reply]

What you need is to make the transition between the intial state and a final state with one electron and one positron less (and two or more photons more) to be forbidden. But such a trnasition will always be possible. What you can have is that the annihilation between the electron and positron requiring 3 instead of 2 photons to be created. E.g. if you have positronium (bound state between elecxtron and positron) then the two spin 1/2's of the electron and positron can add up to a total spin 1 state (which can have a z-component of 1, 0 or -1) or it can have a total spin of zero. Then because the total spin of 2 photons will always be even the positronium with total spin 1 (which is called ortho-positronium) cannot decay into two photons, it has to decay into at least 3 photons. This causes the lifetime of ortho-positronium to be much larger than that of the spin 0 state (para-positronium). Count Iblis (talk) 12:46, 15 June 2013 (UTC)[reply]

I asked this question on July 16, 2011, and currently my area is again covered with cicadas. Are the ones of 2011 and the ones presently here different species? It certainly hasn't been 13 years since 2011. Peter Michner (talk) 15:30, 14 June 2013 (UTC)[reply]

OK, it looks like 2011 was Brood XIX and the ones I'm seeing now are Brood II. Peter Michner (talk) 15:41, 14 June 2013 (UTC)[reply]

Yep, you got it. Technically, you may also see a few of the Tibicen mixed in as well, but they have probably not emerged yet this year. SemanticMantis (talk) 15:53, 14 June 2013 (UTC)[reply]

Each brood may be made of several different species though. Rmhermen (talk) 17:03, 14 June 2013 (UTC)[reply]

If members of each brood can only mate within the brood, then I'd expect them to drift into different species eventually, so there must be a mechanism for interbreeding. Overlapping breeding periods is the obvious mechanism. I wonder, though, how the offspring of a cross-brood mating decide which brood they belong to. Is it always the mother or father ? StuRat (talk) 20:20, 14 June 2013 (UTC)[reply]

These questions are addressed at magicicada, and refs therein. Magicicada is a genus, comprising ~7 spp, and 13-year dormancy is dominant over 17-year cycles. SemanticMantis (talk) 21:09, 14 June 2013 (UTC)[reply]

Newton says that Gravity is a force which accelerates objects toward each other.

Let an apple is dropped from Pisa tower. T₁ is the striking time of earth and apple.

• Gravity force of earth on apple = F₁ = m₁g_e = m₁GM/R² where g_e=GM/ R² = gravitational accelaration of earth (say 9.8 m/s/s)
• Gravity force of apple on earth = F₂ = Mg_a = MG m₁/r₁² where g_a=Gm₁/ r₁² = gravitational accelaration of an apple

Where G= Gravitational constant, M= Mass of earth, m₁= Mass of an apple, R= Radius of earth, r₁=radius of apple

Although F₁ = F₂ but since earth can also be seen from apple and accelerate towards it with g_a , therefore, an apple look a lot to drop to the earth as compared to the falling of earth toward apple which is so minuscule to be perceived as g_e >>>> g_a.

Let a steel ball of radius 1 meter is dropped from Pisa tower. T₂ is the striking time of earth and ball.

• Gravity force of earth on ball = F₃ = m₂ g_e = m₂GM/ R₂ where g_e =GM/ R² = gravitational accelaration of earth (say 9.8 m/s/s)
• Gravity force of ball on earth = F₄ = Mg_b = MGm₂/r₂² where g_b=Gm₂/ r^₂2 = gravitational accelaration of apple

Where G= Gravitational constant, M= Mass of earth, m₂= Mass of ball, R= Radius of earth, r₂=radius of ball

Although F₃ = F₄ but since earth can also be seen from ball’s gravitational field and accelerate towards it with g_b, therefore, a ball look a lot to drop to the earth as compared to the falling of earth toward the ball which is so minuscule to be perceived as g_e >>>> g_b.

Since F₁ = F₂ ≠ F₃ = F₄ as g_b > g_a therefore T₂ < T₁ by definition but Galileo was first to demonstrate that in the absence of air, all things would truly fall with the same acceleration and 300 years later demonstrated this by the crew of Apollo-15 on the lunar surface (which has gravity & also lacks air) by dropping a hammer and a feather. So what would u think who is right?

• Galileo
• Newton or
• If Both then how

162.157.235.1 (talk) 23:02, 14 June 2013 (UTC)Eclectic Eccentric Kamikaze[reply]

My naive answer: Apollo_15#Lunar surface gives Galileo's theory as "all objects in a given gravity field fall at the same rate, regardless of mass". The ball, or apple, or feather, or hammer, contributes to the gravity field, although not much. Thus, both are right. (I think your fourth bullet point was meant to end with "ball", not "apple", by the way.)  Card Zero  (talk) 00:24, 15 June 2013 (UTC)[reply]

You're talking about forces, but you should be talking about accelerations if you are interested in times. Someguy1221 (talk) 00:42, 15 June 2013 (UTC)[reply]

The Earth cannot be treated as a rigid object here. When you drop an object, a shock wave travels through your body to your feet and then it moves into the Earth. Then as the object approaches the Earth, the gravitational force it exerts on the Earth increases, but this doesn't affect distant parts of the Earth at the same time. Finally, when the object hits the ground, you get another shock wave that travels into the Earth.

One can still argue that the total momentum of the Earth should clearly increase as the object approaches its surface due to conservation of momentum, but even this statement is not without problems. This is because the Earth's total momentum is not a precisely defined quantity, according to quantum mechanics an object of mass M in a thermal bath at temperature T will have a typical spread of its momentum of order sqrt(M k T). For the Earth, taking T to be room temperature, this is of the same order as the momentum of the ball. This means that the probability that the Earth's center of mass state changes during the fall is close to zero (this is why you can observe interference phenomena, a photon taking one path or another, bouncing off different mirrors doesn't cause the state of the mirrors to be different in the two different paths despite conservation of momentum, due to the finite spread in the momentum of the mirrors and other macroscopic objects). Count Iblis (talk) 01:00, 15 June 2013 (UTC)[reply]

The shockwave Iblis mentions starts at the point of contact between the Earth and body, and moves upward from the feet to the head, while travelling downward from the sole of the foot into the earth. μηδείς (talk) 01:05, 15 June 2013 (UTC)[reply]

First off, your distinction between R and r1/r2 is wrong. The appropriate distance to use is the distance between the center of masses - which is the same for the apple acting on the earth and the earth acting on the apple. For the earth, a few dozen meters more or less doesn't make much of a distance in scale when compared to the radius of the earth, so we typically don't care about the distinction. However, the difference between the gravitational field (from the apple) on the surface of an apple versus an earth radius away is substantially different, so you need to be careful to use the center-of-mass to center-of-mass distance there. So gravity force of apple on earth = F₂ = Mg_a = MG m₁/R² where g_a=Gm₁/R² = gravitational acceleration of an apple at the distance of the radius of the earth. More to your point, you're trying to apply Newtonian mechanics to an non-inertial reference frame. Because the earth is so massive, the distinction between taking the earth as a reference frame and an inertial reference frame is negligible. This *isn't* valid when you're using the apple/ball as a reference frame. The deviations there become significant. To properly treat the system with the (accelerating) apple/ball as the fixed reference frame you need to add in fictitious forces, which makes your third law assumptions invalid. (You can't assume g_a and g_b keep a constant value once things start moving, changing your assumptions about how accelerations lead to times.) -- 205.175.124.30 (talk) 02:03, 15 June 2013 (UTC) Correction:[reply]

When earth is seen from a ball:

Also r1=r2=R (approximately) for on center distances.

Sorry about the mistake that I did in copy and past — Preceding unsigned comment added by 74.200.19.65 (talk) 06:28, 16 June 2013 (UTC)[reply]

Recently many movies have alien ship crashing to earth and the scientists always says this: After our spectrometry analysis we find out that this object element does not exist in our periodic table. My question is, is that possible? Can the alien have finally find the mythical island of stability? Or they shouldn't need that at all because they probably have the tech to make force field? — Preceding unsigned comment added by 118.136.5.235 (talk) 02:23, 15 June 2013 (UTC)[reply]

I think you've answered your own question. Bearing mind that creators of fiction can do whatever they want in their stories, the island of stability could be this, I suppose. Mingmingla (talk) 02:44, 15 June 2013 (UTC)[reply]

Unobtainium may be an interesting read for the OP. --Jayron32 02:54, 15 June 2013 (UTC)[reply]

Wouldn't the spectral data from new, super heavy elements be recognizable as such? I mean, especially if it's ICP-MS...the software wouldn't be able to identify the element, but the charge to mass ratio should just tell you straight off which element it is, even if we never knew that it existed before. 202.155.85.18 (talk) 03:15, 15 June 2013 (UTC)[reply]

Since this is fiction, Clarke's third law bears reading and understanding in relation to this. --Jayron32 03:31, 15 June 2013 (UTC)[reply]

Things past Element 173 are said not to exist, and I doubt the mass spec leaves room in its detector for them. :) It is entirely conceivable that if you're staring at a lump of Element 3501, you'll be seeing some physics you never guessed at. :) Wnt (talk) 04:04, 15 June 2013 (UTC)[reply]

Actually, there is no theoretical limit preventing elements from going past #173. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 14:10, 15 June 2013 (UTC)[reply]

Mass spec can certainly detect things of rather large mass, MALDI can get mass spec of proteins and DNA whose mass runs in the tens of thousands of daltons or more. --Jayron32 04:17, 15 June 2013 (UTC)[reply]

I may well be wrong here, but MALDI uses a fairly special time-of-flight mass spectrometry with a large mass range. I would assume that if you have some instrument where you vaporize a bit of metal to see what elements are in it, that you'd be using maybe a sector instrument or a quadrupole mass analyzer with (perhaps) a far more restricted range? I'll admit though, I'm out of my expertise entirely where that's concerned. Wnt (talk) 05:52, 15 June 2013 (UTC)[reply]

MALDI is going to several thousands of u. If you assume a island of stability there you should go for a ToF instrument as you suggest. For me this looks a little bit strange to assume that but if gravity takes over the stabilisation there might be a chemical element very similar to a neutron star. This is a little bit larger than what a ToF can handle.--Stone (talk) 06:10, 15 June 2013 (UTC)[reply]

• I don't think we can totally rule out the possibility of making exotic atoms out of subatomic particles that go beyond the usual protons, neutrons, and electrons. We don't know any way to make anything exotic that is stable, but I don't think we can absolutely prove that it is impossible. Looie496 (talk) 15:25, 15 June 2013 (UTC)[reply]

Right. The way the periodic table is set up, anything composed of protons, electrons and neutrons would be on it, even if you'd have to extend it for things with lots of protons. However, there are a number of exotic atoms which don't fit the proton+electon(+neutron) model of normal atoms, and as such "would not exist in our periodic table". All the ones we know about (and all the ones we've theorized to exist) are unstable - often rapidly so, so even if you were able to get a sizable chunk of it, it would rapidly disapper. (So unfortunately no super-strong ship hulls, etc.) - That said, when exotic atoms are used in fiction, they're always a plot device. TV Tropes calls it Applied Phlebotinum - it's just a way to pretend to explain off unrealistic or exotic effects: "Why doesn't the blaster melt in lava? It's made of unobtainium - now let's get back to shooting things." -- 71.35.105.42 (talk) 18:59, 15 June 2013 (UTC)[reply]

That's certainly true - "unobtainium" is a way out for lazy authors. But although we're reasonably sure that we know about all of the stable elements - and we've mapped the properties of all of their stable isotopes - we haven't explored all of the compounds that can be made from them - and even more significant, we're just scratching the surface of what can be made from nano-structures and smart materials. We can be pretty sure that there isn't a metal that would withstand our most powerful weapons in thicknesses still light enough to build a spaceship hull from. But we certainly don't know whether there isn't some kind of clever material that could heal up puncture holes or ablate to dissipate energy. It's almost certain that there are no magical new elements - but it's just as certain that a sufficiently advanced civilization could find some means to combine them in ways we've never imagined to produce magical-seeming materials. You only have to look at the strides that material science had made in the last few decades to realize that we've got a long way to go yet.

SteveBaker (talk) 20:29, 15 June 2013 (UTC)[reply]

Strange matter and the stranglets made from it are a "possible" way to get elements that are not in the table. Dauto (talk) 23:06, 15 June 2013 (UTC)[reply]

I vote for hypertungsten. Plasmic Physics (talk) 23:36, 15 June 2013 (UTC)[reply]

See also here Count Iblis (talk) 00:20, 16 June 2013 (UTC)[reply]

Let we speculate a bit now: What properties will the strange matter/hypernucleus/island of stability matter have? Maybe they are sufficiently dense to make its own gravity field that can mess up with projectiles? Maybe because of there is so many atoms between that they become strong? Its just an spaceship why do they need strange stuff while our normal mundane titanium is enough? If they are going FTL a force field would be better because it will make it lighter 118.136.5.235 (talk) 00:27, 16 June 2013 (UTC)[reply]

Strange matter could be more stable than ordinary matter. Iron is then not the most stable nucleus, it is then only meta-stable with an astronomically large lifetime. But strange matter could catalize the transition of ordinary matter to strange matter. So, a piece of strange matter hirtting the Earth could destroy the Earth in a gigantic nuclear explosion where all the matter in the Earth is converted to strange matter. Count Iblis (talk) 01:14, 16 June 2013 (UTC)[reply]

I never understood why strangelets during an early hot epoch of the Big Bang wouldn't have taken everything over then. Wnt (talk) 01:44, 16 June 2013 (UTC)[reply]

Look at a science book published every 5 years back for a few decades and you'll see we are constantly adding new elements and there surely are many more combinations of neutrons protons and electrons that form elements we not only have not included on the periodic table but that might just not exist on earth. Further we always discover elements way before we add them to the PT. My2¢ — Preceding unsigned comment added by 108.212.70.237 (talk) 04:40, 16 June 2013 (UTC)[reply]

No - that's absolutely not true.

The elements are numbered according to the number of protons they have. We know most of what it's possible to know about every single one of them from Hydrogen (1 proton) to somewhere up elements in the mid 110 range - so no new elements in that range are possible - even in principle. You're correct in saying that new elements are added every few years - but none of them with more protons than Einsteinium (element number 99 - discovered in 1952) is stable with a half life over a year - they all decay into something more mundane after a few days - so you can't build starships out of them. Not one element that has been discovered since 1952 has a half-life longer than a year...and there are no gaps in our table of the elements up to well over element 110 so no new discoveries of stable elements is now likely.

The plot over on the right here is a graph of number of neutrons versus number of protons. The color and height of each column shows how stable each combination is. The dark brown columns are "stable" elements that would exist for more than a year or two. The red ones are stable for days to weeks and all of the other colors represent things that decay within hours to milliseconds. So only the brown combinations are useful for making physical objects. Viewed as a landscape, there is that island off to the top-right of the table. This is the hypothical "island of stability" - a bunch of elements that have yet to be discovered that might be stable. If any "unobtainium" starship hulls are to be found, they'd have to be made up of elements in that part of the table. Sadly, even the peak of that island is a red column...and that means that those very heavy elements are unlikely to be stable for more than hours to days. Only a very few "fringe" scientists believe that the peak on that island will be tall enough for elements found in that region to be stable for more than a few days...and nobody who knows what they're talking about believes that there will be other islands of stability in the further realms of that chart.

Altering the number of neutrons does generate new isotopes - and some of those are moderately stable - but because the majority of the chemistry of atoms comes from the number of electrons (which equals the number of protons), these isotopes are unlikely to have much in the way of interesting properties - and, again, they are likely to be much less stable than the form of the element that we already know.

Summary: Our current knowledge strongly suggests that the 99 elements up to Einsteinium (along with a handful of isotopes of each of them) are the only ones that will ever be sufficiently stable to be useful - and we know of every single one of them in wonderful detail. There are no "new elements" or "new isotopes" that could possibly be used to make a starship hull.

SteveBaker (talk) 14:25, 16 June 2013 (UTC)[reply]

The problem with that is that nobody has ever managed to make isotopes with lots and lots of neutrons - nothing to make them out of - so when you look at the tables, the cutoff of what is known is at the most stable point known. See Isotopes of livermorium, Isotopes of flerovium, etc. Wnt (talk) 18:30, 16 June 2013 (UTC)[reply]

Now that would be just totally ignoring my suggestion. Plasmic Physics (talk) 11:30, 17 June 2013 (UTC)[reply]

That is like LHC doomsday scenario so creepy because a single strange matter could destroy entire Earth... so if we have those how do we contain it? 118.136.5.235 (talk) 10:38, 16 June 2013 (UTC)[reply]

You can't, strange matter is electrically neutral. Only gravity can keep it at bay, and last time I checked, we can't artificially cause gravity. Plasmic Physics (talk) 11:05, 16 June 2013 (UTC)[reply]

What type of bot provides the most clearance? machine, high strength, rib, spline? — Preceding unsigned comment added by 67.101.160.118 (talk) 02:37, 15 June 2013 (UTC)[reply]

Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know. And if I may add a personal comment, this is the type of "learn the answer by rote without understanding the subject" question that Feynman so robustly decries in Surely You're Joking, Mr. Feynman!. Our articles Screw and Bolted joint may be useful. Tevildo (talk) 17:37, 15 June 2013 (UTC)[reply]

Can anyone recommend a good location, centered on Camden and Gloucester Counties, NJ, for me to look for cicadas this weekend? I missed them in 1996, and only found one molting in 1979. Thanks! μηδείς (talk) 03:10, 15 June 2013 (UTC)[reply]

No personal experience, but these maps [1], [2] are fairly reliable, from what I can tell. If you are interested, many people also enjoy eating them: [3]. SemanticMantis (talk) 04:05, 15 June 2013 (UTC)[reply]

The maps are cool, but the dots range up to covering areas of hundreds of square miles. I would really need a source that says "spotted in Cooper River Park" or something like that to be helpful. Thanks. μηδείς (talk) 19:00, 15 June 2013 (UTC)[reply]

This map depends on reports from the public, so it's not likely to be complete; but the closest locations to your area of interest that it currently shows are Franklinville and Pittsgrove. (Note that it shows only the 500 most recent reports, so there may have been earlier reports from the area.) Deor (talk) 09:41, 16 June 2013 (UTC)[reply]

My understanding of the process of reverse osmosis is that it is essentially molecular level filtering, where the solution is pumped through a membrane that allows the solvent molecules through, while excluding dissolved ions and molecules that are too large to pass through. If I understand the process correctly, then it seems that fluoride, with its small radius, should pass through a membrane more easily than water, so RO should be ineffective for its removal. The Wikipedia article on RO seems to say that only molecules are able to pass the membrane, and ions are always rejected irrespective of size, but it doesn't say that clearly, or explain why that would be the case. A Google search shows many commercial sources that say RO units are effective for home removal of fluoride from drinking water [4], [5], [6]. I also found this opinion that isn't obviously commercial and claims to be from a PhD [7]. But there are some sources that agree with my reasoning that it is ineffective [8]. So if RO is effective, what the flaw in my reasoning? 202.155.85.18 (talk) 03:11, 15 June 2013 (UTC)[reply]

Your most obvious mistake is the assumption that the fluoride ion can somehow pass through the membrane while leaving its positively charged counterion behind -- an impossible situation in the absence of a strong electric field such as is used in electrolysis. So even if the RO membrane doesn't block the fluoride ion itself (and I don't see why it shouldn't), it could easily block the fluoride ion indirectly by blocking the counterions (sodium, potassium, etc.) Also, even though the fluoride ion is small, its high electronegativity means that it's much more likely to form ion pairs (which would be too big to pass through the membrane), and also to stick to the membrane itself. These are just 2 reasons why RO can remove fluoride from the water -- I'm sure there are others, but these are the first two I can think of. 24.23.196.85 (talk) 03:51, 15 June 2013 (UTC)[reply]

According to ionic radius, the ionic radius of Na⁺ is only 116pm compared to 119pm for F^-. Oxygen as a neutral atom is 73pm and water's bond length is 95pm according to water (data page), so if you negate the contribution of the hydrogen, the width is minimum width of a water molecule is 130pm at its equilibrium bond length and angle (this is using the trig to work out the minimum distance between one hydrgogen and the axis formed by a line running from the oxygen to the other hydrogen, and adding that value to half the neutral oxygen atom's radius). Even if the NaF is present as an ionic pair, the two can orient themselves along the axis of the membranes hole's and pass through with the minimum width of the largest ion. So, again, as I see it, NaF can pass through a membrane hole with a minimum width of 119pm whereas water requires a minimum width of 130pm. This same analysis results in the conclusion that Cl-, Br-, K+ and I- are all removed from the solution by RO, which I know from experience to be the case. 202.155.85.18 (talk) 04:23, 15 June 2013 (UTC) Oooops...I was conflating radius and diameter. The water's minimum width is 166pm whereas F- is 238pm. 182.6.227.104 (talk) 05:50, 15 June 2013 (UTC)[reply]

A different perspective on 24.23.196.85's view above. While I don't believe strongly dissociating ionic solutions can be characterized as forming ion pairs (in that the counterion is anywhere nearby), each ion has a strongly polarized cloud of solute molecules around it that in a sense displaces the charge of the ion towards the outside of the cloud. If a flouride ion were to fit into a the channels of a membrane, and the membrane material were not as readily polarized as the solute (and water is exceptional amongst most materials in this regard), stripping most of this cloud to allow it through would be energetically unfavourable. Ions with their polarized clouds of water molecules, therefore, will behave like much larger "balls" that will not fit into the small channels of the membrane – it should have the effect of an effective repulsive force that keeps the ion itself at a distance from the membrane surface. — Quondum 17:38, 15 June 2013 (UTC)[reply]

Very true for all ions in aqueous solutions; but in addition, in the case of the fluoride ion specifically (and unlike most other ions), ion-pair formation is also significant. (BTW, can you please explain what is a "flouride" ion -- is it an ionized form of flour?) 24.23.196.85 (talk) 18:59, 15 June 2013 (UTC)[reply]

Point taken about my misspelling – I'll watch for that particular case in future. My explanation is not applicable to ion pairs, though a dipole variant of the argument may apply to extremely polar molecules (though I would not expect a species such as biflouride to be polar). — Quondum 12:57, 16 June 2013 (UTC)[reply]

If female sex hormones are estrogen and progesterone which are produced by the ovaries, could a celibate adult female have her ovaries removed to end her natural occasional desire for sex? What noticeable changes would this have on her mind and body? And I read today that women have a small amount of testosterone as well - can a woman have that removed? — Preceding unsigned comment added by 174.65.51.113 (talk) 16:15, 15 June 2013 (UTC)[reply]

Yes, removing a woman's ovaries would end her desire for sex -- but it will also have some VERY noticeable changes on her mind and body (like the effects of menopause, but MUCH more severe -- see Oophorectomy#Risks and adverse effects). 24.23.196.85 (talk) 19:12, 15 June 2013 (UTC)[reply]

I can't find any backup for the contention that it ends a woman's desire for sex, but rather that there is an increased risk that it will. (See the abstract of the article referenced in the linked section above.) And it is not so much the loss of estrogen and progesterone -unless I am misreading the report- as it is the reduction in testosterone. Bielle (talk) 19:23, 15 June 2013 (UTC)[reply]

Libido isn't just moderated by the obvious female hormones. There is some evidence that hypothyroidism also affects libido. I really wouldn't recommend thyroid removal as a means of managing the female sex drive! --TammyMoet (talk) 10:22, 16 June 2013 (UTC)[reply]

Did you doubt it? We have an article (or at least a section of an article) about that. Oophorectomy#Adverse effect on sexuality. Thincat (talk) 11:20, 16 June 2013 (UTC)[reply]

"as a means of managing the female sex drive"? While we can comment on the possible effects of oophorectomy, we most certainly cannot comment on it as a means of managing anything, and it does not appear that we have any material on that subject. The OP's original question does carry with it an implication of inquiring about it as a means rather than its effects, which pretty much puts it out of line of permissibility for this page as being a request for medical advice. BTW, the bald statement that "removing a woman's ovaries would end her desire for sex" is not even correct, even though there is apparently a correlation. — Quondum 18:17, 16 June 2013 (UTC)[reply]

History tells us that celibate orders came up with far more restrained methods of managing sex drive, such as the use of lettuce opium,^[9] common rue and various other reputed anaphrodisiacs. The level of evidence for such things varies, but surgical methods would need to prove not merely some possibility of effectiveness, but superiority to herbal approaches. (There is also a question here that science can't answer, namely whether religious orders would view such methods as "cheating" rather than fighting an inner jihad against what they perceive to be sinful temptations) Wnt (talk) 19:17, 16 June 2013 (UTC)[reply]

Not just a reference desk question but an article issue. At the help desk, here, a user asked for help fixing the display of {{chembox}} in calcium acetate, which was displaying an error upon his change from listing the melting point in it from 160 °C to 400 °C. I fixed the template error, but then seeing such a radical difference in the information, went to check myself, and the sources seemed to verify the earlier number. I thus changed it back to 160 °C and added a source I found. I don't have access to the paper the user had cited when he made his change. He has followed-up. I am posting below the conversation to this point, and hope that someone here with a chemistry background can speak authoritatively on this issue, where I certainly cannot.--Fuhghettaboutit (talk) 16:56, 15 June 2013 (UTC)[reply]

---

(Originally posted at help desk)

Hi Fuhghettaboutit. Thanks for solving the formatting problem. I would be grateful if you could confirm that you read the paper I cited before your latest edit. The TGA curve and Results and Discussion section showed 400°C, and the XRD data supported this. I also have several other published papers that give this figure. Please could you provide a TGA curve, or some other actual data (ie not just a number), that proves that calcium acetate melts at 160°C - I have not been able to find this data on the net. I was curious, so actually heated calcium acetate in the lab, but all that happened at 160°C was that it lost the water of hydration and became calcium acetate anhydrous. TIA Taikobeat (talk) 14:50, 15 June 2013 (UTC)[reply]

Taikobeat - I'm sure you know far more than I do about chemistry. I only know that the article previously said 160, and after fixing the chembox display, I went to look at what sources say because 400 °C and 160 °C are so radically different—it's not like you were correcting a rounding error to something more precise. So upon looking I found that everything seemed to confirm the original number. I accordingly added what appears to me to be a very reliable source ([10]) upon reverting back to 160.

Now I note that this and other sources qualify "melting" to decomposition to acetone and CaCO₃ I don't precisely understand that distinction. Are they using "melting" loosely; that we are not talking about a change from the solid to liquid state but that "melting" is used as a term of art in chemistry to denote the decomposition point into another substances, even if there is no state shift? I don't know. I certainly can't argue from a knowledge standpoint with you on this topic and have no stake but to keep the encyclopedia proper. But on Wikipedia we follow the sources. Since you cite a source (which I don't have access to), I think it's best at this point to turn to people who actually know this stuff. Let me go post to the science section of the reference desk, laying out the issue, so that people with a background can hopefully comment.--Fuhghettaboutit (talk) 16:39, 15 June 2013 (UTC)[reply]

---

I see values in the mid-100s from various refs based on MSDS, NIOSH, etc. and much higher values from some journal articles. The journal articles suggest several origins of confusion in figuring out the "right" value. First, various hydrate salts loses water at mid-100s, which is technically decomposition of the chemical...if the chemical is the hydrate rather than the anhydrous form. It's the anhydrous form that decomposes to form the carbonate via loss acetone. But there appear to be two different crystalline forms: one seems to be described as one O from each acetate binding to the Ca2+ ion, whereas the other specifically has two acetates each binding by both oxygens (chelation). I have no idea which (or both) of these would decompose how and at what T. DMacks (talk) 19:13, 15 June 2013 (UTC)[reply]

I think this] is the article used to reference 400 °C. So far as I can see it is publicly available. Thincat (talk) 19:25, 15 June 2013 (UTC)[reply]

Thincat, Yes, Bilton (2012) is the open access article I linked to as a reference. Perhaps the best solution is to expand the information included to make the entry easier to understand. The information currently displayed is incorrect as decomposition to CaCO₃ + acetone occurs at 400°C. Taikobeat (talk) 11:06, 16 June 2013 (UTC)[reply]

I'm not qualified to express an opinion on the temperature. However yesterday, when looking into the matter, I found a fascinating discussion about completely different chemicals but along similar lines. see Talk:Cyclohexanone#Cyclohexanone melting point. Thincat (talk) 12:10, 16 June 2013 (UTC)[reply]

I don't see any advantage in burning and inhaling the resulting smoke, I wonder why people don't administer the drug through a more efficient way. Specially if you are taking a scarce drug, you don't want to partially waste it. Is there any regulated drug that was ever smoked? I know that some are inhaled, but that's a different scenario, more efficient. OsmanRF34 (talk) 18:43, 15 June 2013 (UTC)[reply]

Smoking gives direct access of the drug to the bloodstream, similar to injection, which is even more unpleasant to most people, and snorting. The point in smoking is not to burn the active ingredient, but to volatilize it. That's the benefit of such things as e-cigarettes. μηδείς (talk) 18:57, 15 June 2013 (UTC)[reply]

Indeed, that's the benefit of e-cigarettes, pipes, bongs or whatever you got. But why would any one smoke a plain cigarette, given that it's either a highly taxed legal substance or a expensive due scarcity illegal substance? Lots of the substance gets lost through this inefficient way. OsmanRF34 (talk) 19:06, 15 June 2013 (UTC)[reply]

Smoking was never about efficiency. There was probably originally an element of "proving your bravery" by having something on fire in your mouth. Later on it became a "mark of sophistication" since only the wealthy could afford tobacco. Then it became "a sign of rebellion", especially after it was found to be unhealthy. So, various social aspects explain smoking, more than delivering nicotine efficiently. Indeed, trying to get people to quit smoking by giving them nicotine patches or gum isn't all that successful, precisely because the social aspects are lacking with such a delivery system: "What do you say we go out on the balcony and chew some nicotine gum together ?". :-) StuRat (talk) 19:39, 15 June 2013 (UTC)[reply]

Also, smoking not only volatilizes the drug, but in some cases also partly ionizes it, thus increasing its solubility and making it easier for it to diffuse into the bloodstream. 24.23.196.85 (talk) 19:04, 15 June 2013 (UTC)[reply]

• Smoking is rarely used with prescribed drugs because it is very difficult to precisely control the dose. For nicotine that doesn't matter so much, and consuming nicotine by mouth is not a good option, because in the stomach it causes nausea and vomiting. In fact if you consume poison and need to make yourself vomit quickly, eating a cigarette is one of the standard suggestions for how to make it happen. Looie496 (talk) 23:57, 15 June 2013 (UTC)[reply]

  Well, not only that but there are huge numbers of nasty side-effects from all of the other ingredients present in the smoke. But there are other "drugs" that are volatilized and inhaled - I well recall as a child having to lean over a bowl of hot water with a towel over my head to allow me to inhale some kind of menthol-based decongestant (although I suspect that the high humidity levels that resulted did most of the work!). Transdermal_patch#Vapour_Patch describes a device that releases vapors to treat various conditions. SteveBaker (talk) 13:34, 16 June 2013 (UTC)[reply]

Whether combustion or vaporization (or both) occurs, the lung alveoli are a huge absorption surface, and they provide a rapid delivery to the rest of the body, and in the case of psychoactive drugs, the brain. It also avoids first pass metabolism that occurs in ingested drugs. IV injection is similar, although different. Shadowjams (talk) 00:54, 17 June 2013 (UTC)[reply]

Is it feasible to make homemade high explosives from creosote, or are the necessary separations/purifications simply not worth the effort? Has anyone actually made high explosives from creosote (I'm asking about the French Resistance, in particular)? DISCLAIMER: I'm NOT trying to blow anything up, so please don't give me any recipes, I don't CARE about the recipes -- all I want to know is, is it feasible in practice, and has it been done in real life, either in the French Resistance or elsewhere? (For the record, I'm asking because I've read in Nancy Wake's biography that she was trained to make explosives from "everyday ingredients", and it seems to me that creosote would be particularly suitable for this purpose -- and also, because I'm writing a military thriller about the French Resistance where one of the good guys works as a chimney sweep, and another as a pharmacist, which suggests how they can collaborate on making explosives.) 24.23.196.85 (talk) 19:35, 15 June 2013 (UTC)[reply]

One comment: Creosote stinks. That makes it less than ideal for secret use, as a French resistance member trying to bicycle past some Nazi guards with a basket full of the stuff would give the show away. StuRat (talk) 19:43, 15 June 2013 (UTC)[reply]

I know it does (I've worked with the stuff personally) -- but, if the person bicycling past the guards with the stuff has a legitimate reason for having it with him, wouldn't that make the odor a moot point? 24.23.196.85 (talk) 19:46, 15 June 2013 (UTC)[reply]

And, just so we're clear, I wasn't envisioning the Maquis demolitionists nitrating raw creosote (which would in any case be very dangerous due to the risk of runaway side reactions, etc.), but rather, separating it into its individual components by distillation, liquid-liquid extraction, etc., to make picric acid, TNT and other suchlike compounds. 24.23.196.85 (talk) 20:06, 15 June 2013 (UTC)[reply]

My understanding is that high explosives generally have lots of loosely bound nitrate groups. Looking at our article for the composition of a typical creosote, I can't see even a single nitrogen atom in there. So it doesn't seem likely to me. It would probably be relatively easy to get stuff that would burn like gasoline, but I doubt you'll be able to get something that makes a bang. Looie496 (talk) 20:12, 15 June 2013 (UTC)[reply]

Creosote consists of about 20% cresols. These can be converted to toluene, which can be used to produce TNT, a high explosive. The other chemicals used in the process are easily acquired. As for "homemade", not exactly. Making significant quantities of high explosives requires considerable expertise and a good facility. However, the resistance movement had access to these and it is entirely feasible that they covertly produced high explosives from creosote. Whether they actually did so is another matter.

More likely is using creosote in improvised low explosives and incendiary devices. Creosote lends itself well to such purposes, as do most flammable fluids. Dominus Vobisdu (talk) 20:29, 15 June 2013 (UTC)[reply]

Also, as I suspected, creosote has been used to make high explosives, including before the war: [[11]]. It's a cheap and easily available source of raw material. Dominus Vobisdu (talk) 20:39, 15 June 2013 (UTC)[reply]

I can't help but think of Mr Creosote now. -- Jack of Oz ^[Talk] 20:59, 15 June 2013 (UTC)[reply]

• Why do you want to know this 24.23.196.85 ? One can even make explosives form oxidants in denture cleaners mixed with any suitable fuel. Why, oh why, do you think your life will be enriched by this information? And to have the answer posted 'here' so that others can see and maybe miss use the chemical technology? I am aware that I can be accused of being paternalistic here, but if you don't already know then you need not to know. --Aspro (talk) 22:34, 15 June 2013 (UTC)[reply]

• Aspro, read the OP's post more carefully. The answer to your question is there. HiLo48 (talk) 23:50, 15 June 2013 (UTC)[reply]

Indeed, our OP has a long and interesting history of asking the weirdest questions in the process of writing this book. It's quite clear that no ulterior motive is present here. This is a shining example of why the Reference desk does not have a rule about not giving out information about dangerous activities such as making high explosives. SteveBaker (talk) 13:28, 16 June 2013 (UTC)[reply]

You're missing the point! OK, so 24.23.196.85 is researching for a book. Have you ever noticed the artist licence taken by Hollywood films? You could go through the footage of similar scenarios frame by frame and try to duplicate it and it wont work. There is also creatures commonly referred to as teenagers. Now you may have come into this world for all I know, equipped with false dentures, hearing aid, wrinkly skin and knowing all the irregular Latin verbs already. Some teenagers don't have your advantage. You say: Reference desk does not have a rule about not giving out information. I also agree with that but would you agree that with that freedom comes responsibility. One of my flatmates told me how as a school kid he badly got the back of his hand burnt trying to make gunpowder. He was woefully ill informed about the correct process. Now lets get back to 24.23.196.85 question. Yes, creosote would be a suitable fuel and in occupied France probable more obtainable than paraffin (kerosine). Yet, creosote is far from a pure hydrocarbon. It is a complex mixture. Why does that matter you might well ask. Well, mixing fuel with an oxidiser can be a risky process. Pure paraffin mixed with say con nitric will just sit there … unless you introduces a suitable catalyst. Then it reacts. It may not exploded but the reaction is so quick that one hasn’t the time to take one or two steps back until its finished. The heat pulse is such, that one cloths can just spontaneously ignite in an instant. Now, I have never attempted to make an explosive with creosote and I'm pretty sure that posters here haven't but I do know that it is a dirty chemical. It may well react whilst mixing in the oxidant (ie it contains it own catalysts). So back to the OP question and to help him with his book. “Is it feasible to make homemade high explosives from creosote”. My gut reaction is that creosote mixed with any oxidant won't make a good high explosive, it will be too unstable and the Nazi's will laugh themselves silly that all the French Resistance can do is blow themselves up. However, a low explosive mix of creosote with a booster (to achieve true detonation throughout the charge) could well have all the neighbours with in earshot asking c'est quoi ce bordel que c'était? So finally, to 24.23.196.85. Use your artistic licence to the full, be vague in the details (after all its fiction and only a small percentage will relize that like all Holywood films it too cantains a lot of nonsence ) and good luck with your book.--Aspro (talk) 22:15, 16 June 2013 (UTC)[reply]

AND Don't forget to add in the intro that Wikipedia aided (hindered ?) you in your research.--Aspro (talk) 22:23, 16 June 2013 (UTC)[reply]

Whilst uploading this reply, someone was looking over my shoulder and asked (as teenagers do) what is a “# ¿ @%** booster”? So for completeness -please also see:Explosive booster. --Aspro (talk) 22:37, 16 June 2013 (UTC)[reply]

Creosote is not easily available anywhere in the European Union, due to its carcinogenic properties. Sale to the public was banned on 30 April 2003 and use was prohibited from 30 June 2003. It can only be used commercially with a special licence. [12] Alansplodge (talk) 16:23, 16 June 2013 (UTC)[reply]

We're talking about WWII. Read the original post. Dominus Vobisdu (talk) 16:38, 16 June 2013 (UTC)[reply]

Oops! Alansplodge (talk) 17:42, 16 June 2013 (UTC)[reply]

Hmmm, something smells fishy there. "Creosote and coal tar creosote are complex mixtures of coal tar derivatives..." But the article says there is also a wood tar creosote. Did somebody manage to get wood tar banned as coal tar for financial advantage? (From [13] it kind of sounds like it ... wonder who has the patent?) Wnt (talk) 18:24, 16 June 2013 (UTC)[reply]

Creosote itself is sticky enough to be an acceptable substitute for napalm, it would probably make a fairly good molotov cocktail filler if petrol or diesel was hard to obtain or too valuable as a vehicle fuel - a likely sitution in the "Resistance v. le Boche" scenario. Roger (Dodger67) (talk) 16:47, 16 June 2013 (UTC)[reply]

By the time that the French resistance were able to truly take offensive action, there was so little of anything available, that any inflammable liquid served the purpose. Used engine oil (sump oil) (remember Nazi aircraft had around ten gallon sumps and the ground crew were not against earning a little on the side by selling the wast oil off), this stuff only needs a little petroleum sprite and alcohol added to make it into a incendiary grenade. It would be interesting to get the input from an member of the French Resistance as to what measure he-himself had to go in-order to to singe the Nazi's hair. All my antidotes are second hand.--Aspro (talk) 23:10, 16 June 2013 (UTC)[reply]

Creosote to explosive the safe way: Wood tar creosote -> liquid-liquid extraction or fractional distillation -> get cresol -> distill cresol with zinc dust to get toulene -> I have no idea what to do with it, search it yourself but toulene can be used to make bioplastics or TNT — Preceding unsigned comment added by 118.136.5.235 (talk) 02:18, 17 June 2013 (UTC)[reply]

The obvious next question is whether that chemical pathway would have been known to a civilian chemist in France during WWII...also whether you could have performed those steps with easily available equipment and in a manner that would not attract a lot of attention (eg, Does it produce nasty smells? Is the equipment sufficiently compact that you could run it out of someone's basement?). SteveBaker (talk) 13:21, 17 June 2013 (UTC)[reply]

The reason why this discussion has been foundering is that the OP is actually asking a Humanities question (did anyone ever USE creosote as an explosive) but the people here are more oriented to explain how, which the OP isn't even looking for. I'd suggest re-asking over there. Wnt (talk) 17:09, 17 June 2013 (UTC)[reply]

(un-indent) Thanks for the replies! And no, the discussion has NOT been "foundering" the way I see it -- in fact, I see a lot of useful info here. So, let me answer you one by one:

-DV and Dodger: Yes, creosote can in fact be used as a thickener for Molotov cocktails (along with some other chemicals to make it self-ignite on impact) -- in fact, that sounds like a good use for the heavier hydrocarbons left over as still residue after the cresols and toluene have been distilled off! I'll have Francois (the pharmacist) make use of this in the "Sub Pens at St. Nazaire" chapter (which I will start writing shortly).

-SteveBaker: Thanks for helping me make my intentions clear! As I've already said in a previous discussion (that one was about the effects of EMP), I would NEVER seriously consider blowing up my own countrymen for ANY reason (true, I might want to blow up some others, but I wouldn't need to make my own explosives for that, given that those nations are at war with my country). (And in any case, if I was up to anything, I wouldn't be asking this on Wikipedia from my own personal computer -- I'd just get ahold of a copy of the "Terrorist's Handbook" (or is it the "Anarchist's Cookbook"?) ) So yes, in a word, this IS for book research ONLY (as evidenced by the "No Recipes" disclaimer in my original comment) -- and if Homeland Security wants to make sure, they're welcome to look, I got nothing to hide and will even let them see my manuscript if they ask for it.

-Aspro: Thanks for the technical info in your comment, but I find it VERY hypocritical of you to screech about teenagers "miss using (sic) the chemical technology" when in fact the relevant Wikipedia articles THEMSELVES have some quite detailed info about how to make guncotton, nitroglycerine, TNT, Molotov cocktails, thermite mixture and a whole bunch of other high explosives (believe me, I checked -- see for yourself if you want to know!) So if someone wants to misuse this knowledge, it's ALREADY out here on Wikipedia, REGARDLESS of my question! Also, regarding the nitration process itself: You said that "Pure paraffin mixed with say con nitric will just sit there … unless you introduces a suitable catalyst. Then it reacts." Well, I already know that you DON'T premix the organic material with the nitric acid and then introduce the catalyst (not unless you're competing for a Darwin Award, anyway) -- you FIRST mix the acid with the liquid catalyst (I know what the catalyst is, but I won't say here -- but anyone who's taken college-level o-chem would know this without me telling them, or otherwise they can just look it up in the relevant Wikipedia articles), and THEN add the organic material, SLOWLY, with CAREFUL STIRRING, and in some cases in an ice bath for cooling. And also, I'm well aware that "[creosote] may well react whilst mixing in the oxidant (ie it contains it own catalysts)" -- that's exactly what I meant when I said that nitrating raw creosote would be "very dangerous due to the risk of runaway side reactions", and this is precisely the reason why I specifically said that they WON'T be nitrating raw creosote, but instead will separate it into its individual components and nitrate THOSE. (And one final comment: Yes, I know exactly what is an explosive booster, as well as what is a "f*&%ing booster" ;-) .)

-118 IP: Yes, I'm aware of the pathway you mentioned for making "toulene" (sic) from creosote (as well as how to convert the "toulene" to TNT by aromatic nitration, which I won't describe in detail either here or in my novel, for obvious reasons). And for the record, this reaction was well known since the late 19th century, so it's very plausible that a French chemist in the 1940s would be aware of it.

-And finally, regarding SteveBaker's last comment: As I just said, this reaction was well known in the 1940s; as for the necessary equipment, it depends on the quantity to be manufactured, but for small quantities (up to a few pounds per batch), ordinary lab glassware would suffice (or even improvised equipment, provided that it's made of suitably acid/base-resistant material). And as far as attracting attention: The equipment CAN be made compact enough to fit in a basement (for small quantities of explosives, anyway), but the process WILL produce nasty smells -- so in order to conceal this activity, ALL who live in the house upstairs will have to be sworn to secrecy.

24.23.196.85 (talk) 21:41, 17 June 2013 (UTC)[reply]

Its toluene herp derp and anyway it is theoretically possible to hide the smell at that time, which is to make an improvised fume hood out of the fireplace chimney and for optional extra protection if they really want to dedicate the chimney to making that stuff put some charcoal inside it to absorb the smell and put a fan on top of it. Well no one in the house will recognize that that is creosote smell because it is coming from the usual place it come from and the authorities wouldn't suspect a secret lab because they probably will think ohh that is a normal fireplace chimney, alright nothing wrong here 118.136.5.235 (talk) 23:19, 17 June 2013 (UTC)[reply]

Thanks for the idea! Yes, this would be a feasible option; however, in my case, I'll have the homeowners be willing to put up with the occasional smells from the basement, and to keep the explosives-making activities of the Maquis team a secret. After all, they want to help drive the Nazis out of France, and this small sacrifice would be well worth it, wouldn't it? 24.23.196.85 (talk) 23:41, 17 June 2013 (UTC)[reply]

Heh, when I suggested that improvised hood I was thinking more of small but dangerous amounts of chlorine gas. Distilling flammable liquids and using a wood-burning stove for draw might be pushing your luck too far. :) But then again... for Maquis safety was definitely a rare luxury, and it certainly adds a little dramatic question when you're never quite sure if it will reach an explosive mixture. Wnt (talk) 01:28, 18 June 2013 (UTC)[reply]

It would strain credulity that anyone who had the requisite expertise to synthesize high explosives would be stupid enough to do it in an occupied residential building. The risk of mishap is pretty high, and they wouldn't want to put innocent lives at risk. Even if it doesn't blow up, your still talking about some pretty nasty chemicals, including phenol and toluene, that you definitely don't want to expose anyone to. Getting rid of the waste products is going to be a major problem, too. These aren't things you can just dump down the sink.

Making high explosives isn't kitchen chemistry like making Molotov cocktails. The French resistance would most probably convert a remote and isolated barn or abandoned industrial building into a properly equipped facility. The French resistance would have had contacts who could supply the equipment and chemicals. Dominus Vobisdu (talk) 01:59, 18 June 2013 (UTC)[reply]

Thanks! I'll reconsider the basement -- maybe they could convert a horse stable into their explosives lab, or something (which would also keep the smell from becoming an annoyance to the homeowners). But then, there's another difficulty -- how can they rig up a vacuum pump for creosote distillation and for "getting the red out" (an essential precaution to keep them from blowing themselves up during the nitrating process) if they don't have running water? 24.23.196.85 (talk) 06:29, 18 June 2013 (UTC)[reply]

Dealing with phenol and toluene doesn't seem like that big a deal. Yeah, sure, if you get phenol on your hand and you don't wash it off you get a big nasty (but oddly painless, for some people, it seems) blister. Toluene is technically not that good for you but back then I don't think people knew nor cared. I mean, those were the days when the maids scrubbed the floors with carbon tetrachloride! You don't want your Maquis to seem like shrinking violets. As for disposal, it's called a pit. Preferably an outhouse. The Nazis are welcome to search through it all they want. :) Yeah, I know, I know, it's not really so funny because they had the local citizens for that... Wnt (talk) 07:43, 18 June 2013 (UTC)[reply]

They'll have running water. It's a trivial thing to set up a proper water and power supply when converting the barn. Just so that you understand, the resulting facility is going to be pretty sophisticated and rather high tech. It's definitely not going to be a slapdash effort, like the tunnels in Hogan's Heroes, nor you local meth lab, nor even your college chem lab. Even a facilty for "small scale" production is going to be much larger scale than you imagine for it to be worth the undertaking and investment. The smallest feasible operation would be still be a very professional industrial setup, requiring at least a few professional industrial chemists, and a few professional engineers, as well. It would be a VERY BIG project for the Resistance, requiring the coordination of dozens of members and contacts.

It's far beyond the capabilities of a handful of non-specialists, like your two blokes, one of whom is a "pharmacist". If that's all you have to work with, forget about high explosives altogether and stick with improvised incendiary devices like molotov coctails. If your two blokes really needed high explosives on small amounts, it would be far, far easier simply to steal them from the Germans than to attempt to manufacture them themselves. And a lot less risky. Dominus Vobisdu (talk) 08:13, 18 June 2013 (UTC)[reply]

For someone that says you cannot pour this chemical down the sink, who cares? This is a warfare situation and no one thinks about enviromental stuff now. For the vacuum distillation part, the vacuum pump could be a steam ejector outputting into a radiator that outputs to a open ended pipe under water. For the still part, it could be like your normal moonshine still with all the leak sealed to seperate the cresol from creosote, and run the cresol vapor into a zinc bed to convert it directly into toluene and condense it.

But there is still a question: How do you get enough wood tar creosote? It is more feasible to make a fertilizer explosive in my mind 118.136.5.235 (talk) 07:40, 19 June 2013 (UTC)[reply]

• Explosives for demolitions (civil or military) come on two forms: those for steel and those for masonry. Destroying masonry requires large quantities of cheap explosives, set carefully into place beforehand by digging holes and tamping them into place with soil or rubble on top. A vast bulk effect "shoves" the masonry out of the way. It's a lot of work, for a lot of people, for a lot of time. There's a lot of materiel to bring, and a lot of work to do on-site. Even for an occupying army, this is hard work. Many bridges were built with demolition chambers pre-formed during construction to simplify this work. On the other hand, cheap low-velocity explosives like TNT (cheapish) or ammonium nitrate can be used.

Destroying steelwork is rather easier (assuming good supplies, but a well-guarded target), whether this is high value equipment (factories, electricity distribution, railways, trucks) or just the girders of a steel bridge. A high-speed shock wave is used to cut the steel. This is generated by explosives with a high Vdet, such as plastic explosives. Inertia at these high velocities is such that tamping is less essential (although charge placement is even more so) and a small package of explosives can be placed, tied or held magnetically in place and left uncovered. The explosives used are complex, expensive, but are required in smaller quantities.

In the French Resistance context, the obvious implications of all this are that they went after the high-value steel targets, using small quantities of high-quality plastic explosives, supplied by the Allies. These could be put in place by small teams, working quickly and quietly. Masonry targets were either ignored, or marked as targets for air bombing. The French Resistance was well-supplied by RAF air drops, including explosives, and shortage of demolition explosives (AFAIK) just wasn't a problem. They had neither the need, nor the capacity to start making their own. The SOE training for "home made" is almost entirely about incendiaries, not blast. It's also notable that the ordnance consumed by infiltrating demolition teams (whether the Resistance or Popski's Private Army) much favoured plastic explosives over the TNT that was the stock in trade of mainstream Engineers performing battlefield demolitions. Andy Dingley (talk) 10:06, 19 June 2013 (UTC)[reply]

In our aquatic ape hypothesis article is the claim that "humans also have a considerable amount of control over their breathing, which is an involuntary reflex for most terrestrial mammals.[21][27]" I can't access either of the two references, so how do scientists know whether other animals can consciously control their breathing? It's not as if we can talk to a dog and ask him to hold his breath. --50.125.164.7 (talk) 07:07, 16 June 2013 (UTC)[reply]

The sentence you quote doesn't imply that other animals cannot consciously control their breathing. It's an "involuntary reflex" for humans too. Many terrestrial mammals (including dogs as well as the numerous aquatic mammals) are excellent swimmers, which requires control of the beathing.--Shantavira|^{feed me} 07:45, 16 June 2013 (UTC)[reply]

I think the study specifically refers holding one's breath, to enable submersion. Plasmic Physics (talk) 08:00, 16 June 2013 (UTC)[reply]

Even so, I know of diving dogs. Plasmic Physics (talk) 08:00, 16 June 2013 (UTC)[reply]

A few points. It might be partly an involuntary reflex for humans, but not entirely. If I'm in a pool and I know I'm going to put my face in the water, I will consciously hold my breath. Some dog's certainly do it too. But the real marine mammals such as seals, whales and dolphins have a bigger advantage. They can close their nostrils. Kinda wish I could do that. HiLo48 (talk) 08:25, 16 June 2013 (UTC)[reply]

@HiLo48 buy yourself a noseclip. Roger (Dodger67) (talk) 11:05, 16 June 2013 (UTC)[reply]

To parallel what a seal can do I'd need one with telepathic controls. HiLo48 (talk) 12:09, 16 June 2013 (UTC)[reply]

I can close my nose if I inhale hard and quick enough. Of course, inhaling hard underwater isn't smart. An electronic remote controlled noseclip would work nearly as well, I suppose, and more easily than telepathy. InedibleHulk (talk) 21:42, June 16, 2013 (UTC)

Just because animals like dogs can swim, doesn't mean that they have conscious control of breathing - it could just be an involuntary reflex to the face getting wet. Our Mammalian diving reflex article says this explicitly: "Every animal's diving reflex is triggered specifically by cold water contacting the face – water that is warmer than 21 °C (70 °F) does not cause the reflex, and neither does submersion of body parts other than the face. Also, the reflex is always exhibited more dramatically, and thus can grant longer survival, in young individuals." - and our Primitive_reflexes#Swimming_reflex article says that human infants can swim from birth using only reflexive behaviors...and Reflex#Human_reflexes says that the diving reflex is present in all humans.

Moreover, dogs can easily be observed to inhale sharply before barking - and barking certainly appears to be a conscious decision because you can train a dog to bark on command. You could argue, perhaps, that they make a conscious decision to bark - and that the necessity of taking a breath first is still an involuntary matter - but if you get into the realms of "in order to perform some conscious act, the involuntary systems must first intervene" - then it becomes hard to decide what is truly a conscious act and what isn't - even in humans.

Worse still, it all becomes a fuzzy line anyway. There is no sharp line between the conscious and the involuntary reflex: I decide (consciously) that I wish to walk across the room - but I don't consciously consider how to shift my balance and move my feet to do that. So walking has become as subconscious as breathing.

But what about driving to work? I don't consciously think about how to move my feet to operate clutch and gas pedals when shifting gears - I don't think I consciously consider when to shift gears either. I certainly haven't "evolved" to develop special brain circuits for driving a car - and at one time, back when I was learning to drive, this was an entirely conscious activity. So what I choose to have conscious control over - and when - is a learned behavior and being in the right gear for my car to operate optimally can now occur at a subconscious level. When I was teaching my son to drive stick-shift, I found myself unable to explain the precise sequence of pedal actions when shifting gears without first watching myself do it!

Sure, conscious behavior *can* take over those things - but mostly, my conscious mind can be thinking about something entirely different while my subconscious takes control of the mundane tasks.

The aquatic ape hypothesis is widely regarded as a load of hogwash - so the things it claims do not have to be rationalized! SteveBaker (talk) 13:20, 16 June 2013 (UTC)[reply]

• Note that the sentence quoted by the OP doesn't use the word "conscious" -- for good reason, it's really irrelevant in this context. The practical issue is simply whether various animals are capable of holding their breath, that is, inhibiting breathing while closing off their air passages. Whether they can do it in response to instructions is not relevant to their ability to dive. Looie496 (talk) 13:38, 16 June 2013 (UTC)[reply]

The article may not make this clear - but the original aquatic ape hypothesis uses this "conscious control of breathing" idea to explain all sorts of things - such as our ability to talk. We needed to evolve to swim in order to switch to a fish-based diet, we needed conscious control of breathing in order to do that, we were better able to develop speech with conscious breath control. But that's really nonsense on several levels - firstly that conscious control of breathing is necessary for swimming (it's not - the mammalian dive reflex provides a means to do that reflexively) or that mammals in general don't have this conscious control ability (watch a dog barking to realize that they do). SteveBaker (talk) 00:43, 17 June 2013 (UTC)[reply]

Actually I'm quite fond of the aquatic ape idea in a weaker form. The Okavango Delta is part of an ancient lake in a region with dramatic yearly climate change. Part of the year it is dry desert, part of the year it is a vast area of waist-deep flooding. Chacma Baboons learned to stand upright there. Lechwe antelope developed elongated feet (like ours?). Every year there are massive fires that leave behind cooked meat, for those clever enough to avoid them. The place seems like the mold that humanity could have been stamped from, and part of that is dealing with life largely in the water for part of the year. Wnt (talk) 01:25, 18 June 2013 (UTC)[reply]

in a direct current circuit that is initiated by a plasma field why does the circuit preform its normal circuit path ,but also operate on a one wire system in the off position and when operating in the one wire off position the batterys in the d c circuit seem to recharge themselves the question is ,are the characteristics of the diode changing or is the a reversal of polarity happening in the battery cell material itself causing this unusual characteristic 50.93.30.1 (talk) 18:46, 16 June 2013 (UTC) or are both conditions of the circuit changing .50.93.30.1 (talk) 19:11, 16 June 2013 (UTC)[reply]

I'm not sure I understand your question, but I think by "electron spin" in the question title, you're not actually referring to the quantum mechanical spin of an electron, but rather an apparent reversal of the flow of electrons within the circuit in question. If I'm understanding you correctly, I think you're asking why the battery appears to become somewhat recharged when you switch off the normal flow of current in a circuit containing a battery and a gas-filled tube acting as a diode. There wouldn't actually be a reversed current flow in such a circumstance, since no current flows around an open circuit. Rather, I think what you are seeing is the voltage recovery effect that some types of batteries have, in which the battery appears to regain a bit of its charge when the battery goes for a little while without a current being drawn from it. The effect is most pronounced after drawing a large current from the battery, as would be the case if you're discharging the battery through a forward-biased diode without using a resistor to limit the current. I unfortunately can't seem to find a Wikipedia article discussing the recovery effect in batteries, but you can read an excerpt from a book that briefly mentions the effect if you click on this link and scroll down a bit to the section entitled "Battery Peculiarities: Voltage Recovery". Red Act (talk) 02:31, 17 June 2013 (UTC)[reply]

QBold text — Preceding unsigned comment added by 68.115.48.41 (talk) 22:28, 16 June 2013 (UTC)[reply]

Mainly the axial tilt of Earth which during a year changes the time from sunrise to sunset when you are not on the Equator. See more at Season#Causes and effects. PrimeHunter (talk) 22:39, 16 June 2013 (UTC)[reply]

The angle of the sun to the ground makes a huge difference to how much heat it provides. That's why it's hotter at the equator than at the north and south poles - and why the middle latitudes are somewhere between those extremes. At the equator, the sun is almost vertically overhead around noon - but when you're closer to the poles, it scarcely rises above the horizon. The seasonal variation is caused by the fact that the earth's axis of rotation is tilted. So at some times of year, the northern hemisphere is tilted towards the sun during the day and the southern hemisphere is tilted away. That makes for summer in June/July/August in the northern hemisphere when those are the winter months in the south. Six months later...in December/January/February, the earth has moved around to the opposite side of it's orbit and the positions are reversed making it winter in the north and summer in the south. That axial tilt simply makes the sun be higher or lower in the sky depending on the time of year - which accounts for the temperature variation. Some seasons are rainier or drier than others SteveBaker (talk) 00:37, 17 June 2013 (UTC)[reply]

I suddenly wondered why the difference between nosecone shapes on passenger and fighter jets - the article says the simple cone is easier to construct, but hints that it isn't very aerodynamically efficient - seems odd, since companies that makes fighter jets have money to burn... Is it possible they use the simple cone because it looks more badass? The friendly ellipse or whatever it is of passenger jets is certainly less weaponish in appearance... Adambrowne666 (talk) 22:44, 16 June 2013 (UTC)[reply]

I don't see any fighter aircraft with true "cones" (ie simple, circular cross-section, straight-sided) - they all seem to have curved sides to some degree. The optimum shape is a symmetrical "volume of revolution" - and the exact shape depends on the speeds that the aircraft is expected to travel and whether top speed or best fuel economy is the goal. Nose cone design goes into this in incredible detail. That said, not all aircraft have optimal drag coefficient as a goal - some have to accommodate equipment such as cameras and radar gear in there - others have to be stealthy and have a minimal radar profile. There are dozens, perhaps hundreds of variables determining the best shape, so it should be no surprise that there is a wide variety of shapes out there. However, I'm very sure that "looking badass" isn't one of them - and "ease of construction" is an unlikely goal compared to all of the other things (such as engines and instrumentation) that cost so much to manufacture. SteveBaker (talk) 23:28, 16 June 2013 (UTC)[reply]

I don't think the article suggest this. The shape may deviate from the ideal in order that is protects the avionics but the reasons are never to make the aircraft look badass. It is not the 'look' of a fighter aircraft that makes it effective but its actual in combat effectiveness. Consider the Fairey Swordfish. Saw service in during WWII and it was a biplane. Yet, it could spoil your whole day if it dropped its load on you.--Aspro (talk) 23:31, 16 June 2013 (UTC)[reply]

@Aspro: from the article: A very common nose cone shape is a simple cone. This shape is often chosen for its ease of manufacture, and is also often (mis)chosen for its drag characteristics. - but I was assuming the fighter jet nosecone is a simple cone, which SteveBaker points out it isn't.Adambrowne666 (talk) 23:36, 16 June 2013 (UTC)[reply]

The fundamental reason for different shapes is the intended operating speed. Airliners operate at subsonic speeds, where a 'blunt ellipse' is the optimum shape, whereas jet fighters are designed for transonic and supersonic speeds, where a more pointed shape is better. AndyTheGrump (talk) 23:40, 16 June 2013 (UTC)[reply]

Thanks, Andy - yes, that makes sense - I thought I was onto something - some semiotic reason for the pointy tip on fighters... Adambrowne666 (talk) 23:55, 16 June 2013 (UTC)[reply]

“This shape is often chosen for its ease of manufacture” A defence contractor usually gets a contract based on development cost plus 20% profit. “Ease of manufacture” doesn’t come into it at all. If it is technically feasible they will push to incorporate it. Flight duration and max speed is a very important parameter. The tax payer then pays for it. So it is shaped... however the aircraft designers (defense contractors) think it should be shaped. Passenger aircraft (with exception of Concord) are sub or transonic. So they don't benefit from these type of cones. Don't believe everything you read on Wikipedia. Take it from me, I know some of the editors that contribute!--Aspro (talk) 02:22, 17 June 2013 (UTC)[reply]

The whole "to make them look more badass" idea is probably upside down. They only look like noses of planes which are known to be badass. If the planes which featured this kind of nose had not been successful, we wouldn't associate their shape with speed, nor any other kind of badassitude (is that a word???) - ¡Ouch! (^{hurt me} / _{more pain}) 10:19, 17 June 2013 (UTC)[reply]

If it's not a word, it SHOULD be! How does one nominate a word for "Best New Word of the Year"? 24.23.196.85 (talk) 20:06, 17 June 2013 (UTC)[reply]

It's not even the best I can think of. I should go ahead and post some on my user page - unless a WP: rule says I cannot do that. Then my talk page will have to do. - ¡Ouch! (^{hurt me} / _{more pain}) 07:06, 18 June 2013 (UTC)[reply]

The technology concealed within will often lead to some rather odd shapes. I believe that the Hawker Siddeley Harrier GR3 had a forward looking infrared sensor, while others have air-to-air radar scanners. Alansplodge (talk) 12:53, 17 June 2013 (UTC)[reply]

Our F-106 and F-4 fighters also had FLIR sensors installed along with the normal air-intercept radar, but that didn't influence the shape of their nosecones in any significant way. 24.23.196.85 (talk) 20:09, 17 June 2013 (UTC)[reply]

You can find all sorts of weird nose cones out there - the F117 nose...erm..."wedge" for example is an aerodynamic disaster area - but it keeps the aircraft stealthy - and that's what matters most. Curved surfaces are a very bad thing for keeping a low radar cross-section, and nose cones are amongst the worst offenders. SteveBaker (talk) 13:14, 17 June 2013 (UTC)[reply]

Hello

I had a question about Near Infra Red Spectroscopy. If we were conducting the measurements on a powder sample, is there any potential for the electrosatic forces within the powder to affect the readings in anyway?

Many thanks

114.77.39.141 (talk) 12:44, 17 June 2013 (UTC)[reply]

Yes - in science, almost everything has some effect on almost everything else. I would not consider the presence of an electrostatic field to be a primary contributor to the infrared spectrum for most materials. But, it is detectable - at least in some materials, with some very specialized equipment. For example, a near-field optical microscope can detect Raman scattering, and the spectrum of the Raman-scattered light may be affected by an applied electric field. In fact, I know of a specific professor who specializes in this sort of thing, and you can read his publications-list; and here is Electric field gradient effects in Raman spectroscopy (Physics Review Letters, 2000). I don't think powdered substrates are very good candidates for an NSOM microscope experiment; but in principle, the application of an electric field does have a small and measurable effect on the scattering spectrum. For most cases, in ordinary spectroscopy using ordinary equipment, the DC electric field has no significant effect on the infrared spectrum of a sample. Nimur (talk) 17:41, 17 June 2013 (UTC)[reply]

There was a line in the "Jurassic Park" film that said that dinosaurs could change their gender, or even have offspring by themselves when in a time of need. Just to confirm it: that was a huge artistic license, and in the real world dinosaur's reproduction did not work that way, right? Cambalachero (talk) 14:28, 17 June 2013 (UTC)[reply]

Did they claim that the dinosaurs of old did that? I don't recall them saying it. What I do recall is them saying that the dinosaurs in Jurassic Park had that trait because the bits of DNA that were missing from the archeological samples were replaced from frogs who do, in the present day, show this ability in times of need. Dismas|^(talk) 14:35, 17 June 2013 (UTC)[reply]

Of course there's much artistic license there, but it does not seem impossible. Our knowledge about dinosaurs is limited, but the process you describe, which is called Parthenogenesis has been observed in some modern-day reptiles (I'm talking about having offspring by themselves, not changing their gender). - Lindert (talk) 14:37, 17 June 2013 (UTC)[reply]

(EC) Well, we can't really be sure if dinosaurs could change sex or not. As I recall, the book had some "rationale" for this plot device. The idea was the partial genomes recovered were supplemented with frog DNA. And it is true that some frogs (and fishes, and a few other things) can change their sex, even after sexual maturity. The common example of this is the Common Reed Frog, you can find other examples by googling things like /frog fish sex change/. I don't think the book or movie had the dinos selfing, but I could be mistaken. Lastly, not to nitpick too much, but recall that gender is a social identity in humans (and perhaps a few other social animals), while sex is the biological concept. SemanticMantis (talk) 14:38, 17 June 2013 (UTC)[reply]

Temperature-dependent sex determination occurs in reptiles but not birds. It would probably be hard to figure out if it happens dinosaurs, which are generally agreed to occupy the "space" between reptiles and birds. Roger (Dodger67) (talk) 17:23, 17 June 2013 (UTC)[reply]

More specifically, dinosaurs lie between birds and crocodilians, not the much more distant lizards and turtle. Crocodilian eggs are known to beinfluenced in sex by external temperature, but I am unaware of sex change in adults. That usually occurs in species where the female is the larger sex (if the one large female is removed from a group of smaller males, the largest male will turn female), but this is not the case in crocodilians. μηδείς (talk) 18:16, 17 June 2013 (UTC)[reply]

Put another way, birds are dinosaurs, a subgroup of the theropods :) SemanticMantis (talk) 18:32, 17 June 2013 (UTC)[reply]

Yes, but all that proves is that some branches of the dinosaurs can't/couldn't do it. We still don't know whether some could. Actually, birds can kinda/sorta change sex. This article and others indicate that about one in 10,000 female birds will spontaneously change into males towards the end of their lives. Female chickens will grow rooster tails, start crowing and become quite defensive about males trying to muscle in on their hareem. However, they don't completely finish the job - they may change plumage and behavior and in most outward ways appear to be male - but they don't grow primary sexual organs to match - so they can't reproduce as males. There is no particular reason to assume that dinosaurs were unable to do that - so perhaps they did. However, that doesn't fit with the plot point in Jurassic park which was that somehow the dino's were breeding even though they'd all been created as females...so we're left with some very dubious handwaving about frog DNA, yadda, yadda, yadda. SteveBaker (talk) 18:47, 17 June 2013 (UTC)[reply]

As I recall, the book made it pretty clear that the sex change was an accident based on the frog DNA, and unexpected by the experimenters. As for real life, I would speculate pretty confidently (uh-oh...) that we can't know, because we're still short on dino sequence, and a fossil is a snapshot, not a video. (One of the beautiful things about biology is that certain speculations like this that are logically foolproof are often wrong) Wnt (talk) 23:27, 17 June 2013 (UTC)[reply]

If dinosaurs fit between crocodilians and birds in a taxonomic sense, then why would you repair their fragmented DNA with frog DNA? Why not use bird or reptile DNA? 39.214.54.44 (talk) 04:41, 18 June 2013 (UTC)[reply]

Good question! A crocodile's DNA would be a particularly good match in this case -- MUCH better than frog DNA! But I guess they needed some kind of plausible explanation for the dinosaurs breeding despite being all of the same sex (a similar kind of handwaving used for the movie "Godzilla", as far as I remember...) 24.23.196.85 (talk) 06:19, 18 June 2013 (UTC)[reply]

Pardon my ignorance, but if missing DNA portions are filled with that of another species, how do you still get a dinosaur, as opposed to some other, exotic creature? ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:49, 18 June 2013 (UTC)[reply]

Some species of algae make a large amount of PUFA. This leads me to ask the question of, why? What are the functions of PUFA for single celled organisms? As I get it, one of the reasons is to maintain membrane fluidity under a variety of temperature and salinity conditions. But, why do different algal species make chains of varying lengths? For instance, some make C20:5 others C22:6. What's the added advantage of an extra double bond? Especially considering that these organisms tend to inhabit the same ecological space (thus enviromental effects are the same). If anyone has any ideas, or can refer me to papers published on the subject, I'd be eternaly grateful. 137.224.252.10 (talk) 14:53, 17 June 2013 (UTC)[reply]

As I've commented recently, it is hard to say "why" evolution does something. But I should point out that every organism has a cell membrane, made up of phosopholipids, typically 16-20 carbons long according to the article (which sounds right). Even in humans, which you would think would do more to regulate such things internally, polyunsaturated fatty acids incorporate into membranes and change their mechanical properties concerning "rafts" of lipid-modified proteins, cholesterol etc. [14] If you can name the species you have in mind it would be easier to try to research further about the specific system, but tracking exactly why two extra carbons are used by one rather than the other can't be easy, and might even be chance. Wnt (talk) 17:01, 17 June 2013 (UTC)[reply]

The article Race (biology) is kind of incomplete. I still want to know how do biologists put into words the difference between humans who belong to what's socially considered different races. I understand that the socially relevant definition might be biologically inaccurate, but how do you express that? OsmanRF34 (talk) 17:04, 17 June 2013 (UTC)[reply]

Existing human races aren't different enough for scientists to consider them subspecies, which would lead to terms like Homo sapiens causcasicus. Individual traits which are considered racially salient include the cephalic index, objective descriptions of human skin color, eye color, and human hair. There are other traits like Steatopygia and the epicanthic fold, blood types, limb length, tooth shape, lactose tolerance, and many other things that can vary along with what is perceived as race. μηδείς (talk) 17:38, 17 June 2013 (UTC)[reply]

The problem is that many of these indicators vary more within a "race" than between races. That is the source of the statement that "race has no biological basis in humans". --Stephan Schulz (talk)

Right, your quote is a good answer to Osman's final question. It's not that the social notion of race is biologically inaccurate, it's that it is biologically unfounded, or perhaps ill-defined. SemanticMantis (talk) 18:36, 17 June 2013 (UTC)[reply]

That's a rather facile and unhelpful, but typical denial. Something like "naive social notions of race are rarely rigorously defined or helpful biologically" would be much more accurate. The desire to remove the term race from all scientific discussion is a political one, not a scientific one. μηδείς (talk) 19:01, 17 June 2013 (UTC)[reply]

I agree with μηδείς. Unless you believe that skin color varies more within a race (defining by a society) than between races, you have to admit that there is something biological there, and that some societies consider these differences to group people. It's not all chaos when it comes to the social identity. OsmanRF34 (talk) 22:44, 17 June 2013 (UTC)[reply]

The problem even with this trait is you are referring to, skin colour, is that if you go solely by it you will often be highly mislead. Someome with dark skin could easily be more closely related to someone with light skin. This shouldn't exactly be a surprise. A chimpanzee (either species) is far more closely related to a a human than a New World monkey even though both the monkey and chimpanzee have a lot more fur. And Opossums are quite distantly related to primates despite some having shared features like opposable thumbs and a prehensile tail. Nil Einne (talk) 00:17, 18 June 2013 (UTC)[reply]

To be fair to Stephan, if you define the traditional three old-world races, then compare Saami people and Tamil people, you are going to find a far greater difference in skin color than you will betweeen any various populations of Sub-Saharan blacks. But that is taking a very specific and limited definition of race as if it were the only way that four-letter word beginning with arr could be used. Obviously it is quite reasonable to talk about the racial differences between Madagascans and Tanganyikans, or between Ainu and Japanese, as opposed to the linguistic or religious differences between such peoples. Arguing that the word has no use, or that there are no scientific correlates for some of the word's various senses, is simple sophistry. μηδείς (talk) 01:16, 18 June 2013 (UTC)[reply]

• Biologists usually talk about differences in terms of ancestor groups and geographical regions. For example a paper might refer to people of sub-Saharan African descent, or people of Polynesian descent, etc. Looie496 (talk) 18:39, 17 June 2013 (UTC)[reply]

• There are biological terms for groups of a species which vary by less than those of two subspecies. There's a population, a breed (as in cats or dogs), and a color phase, to start. Those seem closer to what we call "race", in humans. Of course, it's complicated because there's so much interbreeding between historically distinct populations in humans. So, we're all "mixed breeds", if you want to put it in those terms. StuRat (talk) 19:46, 17 June 2013 (UTC)[reply]
  • Presumably the races arose due to lengthy isolations of groups from each other in prehistoric times. With that isolation having been significantly compromised in relatively recent times, and with more and more cross-race children being produced, the notion of race is getting increasingly murkier. We've got a ways to go, though. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:42, 17 June 2013 (UTC)[reply]

• See Haplogroup. The way people have been classifying race is sort of like a dog pound that gets lots of French poodles and chihuahuas. Something is either a French poodle, a chihuahua, or "sort of like one or the other". Or, of course, it could be Spanish-speaking, in which case it is opted out of the classification scheme entirely.  ;) Though what's sort of clear is that by and large, genetic variation beyond a certain point is called "black". Wnt (talk) 20:03, 17 June 2013 (UTC)[reply]

Spanish-speaking chihuahuas? I didn't know they really existed! 24.23.196.85 (talk) 20:15, 17 June 2013 (UTC)[reply]

Were you expecting it to speak Norwegian, perhaps, hmmm? Bielle (talk) 01:22, 18 June 2013 (UTC)[reply]

Is momentum something that applies and is conserved in all dimensions? So if I push something back in time, I can be accelerated through time? Or is that nonsense? --92.19.68.88 (talk) 23:20, 17 June 2013 (UTC)[reply]

First of all, there's no way to "push something back in time" -- this would in itself violate the laws of physics. 24.23.196.85 (talk) 23:37, 17 June 2013 (UTC)[reply]

I don't understand. Could a mass A travelling through time at a greater rate than another mass B, collide elastically with mass B and transfer some of its energy, increasing the rate of passage through time of B? Or do those laws apply specifically to three dimensions of which time is not one? --92.19.68.88 (talk) 23:48, 17 June 2013 (UTC)[reply]

You can interpet a particle moving back in time as its anti-particle moving forward in time. So, pushing an electron to move back in time is equivalent to that electron getting annihilated by a positron that it collides with. Two photons will be created, you do obviously have conservation of energy and momentum in the conventional sense. Count Iblis (talk) 23:54, 17 June 2013 (UTC)[reply]

If the OP would be so kind as to define acceleration "through time..." we might possibly answer the question. Acceleration is the rate of change of the change of position per unit of time. (In other words, the second derivative of position with respect to time). Is the question supposing to ask about the rate of change in the change in time per unit time? That quantity makes very little physical sense, whether it is expressed in plain English or expressed mathematically. Things don't travel through time; they change with respect to time. In other words, the latter part of the OP's question is nonsense. Nimur (talk) 00:18, 18 June 2013 (UTC)[reply]

Are we moving along a time dimension like a cart moves along a track in, say, x dimension? Or is that nonsense again? 92.19.68.88 (talk) 00:48, 18 June 2013 (UTC)[reply]

Obviously we are not moving along time in a cart! So the direct answer to your question is "NO!" But your question can be answered with a little bit more substance, albeit with a lot of abstraction - if you're willing to think a little bit abstractly.

In physics, we use very precise terminology. This helps us avoid logical errors or semantic ambiguity.

Matter has position. We say something has moved when its position changes: displacement. Let's say we have an object with a measurable position. In classical physics, we define this type of object to be a particle - just a thing with a position. If we measure a starting position (on the x-axis, for example), and a final position, we have a displacement - let's call it Δx for a displacement along the x-axis. If we know when we took the starting measurement, and when we took the final measurement, we also have a change in time: let's call it Δt. The average velocity is therefore, by definition, Δx/Δt. We can talk about the particle moving on the x axis during the experiment time. We can say that the object was at a position x₁ at time t₁. Equivalently, we can use time as a generalized coordinate and describe a position ( x₁, t₁) - but this is just a different way of describing the same event.

When we describe motion in this way, we are conducting the science of kinematics - the pure mathematical relationships of motion. When we attribute these motions to observable physical law, we are progressing to the science of dynamics - the study of physical motion.

In kinematics, we can easily consider time as just another coordinate, but when we study dynamics - in any of its forms, including the modern style relativistic mechanics, we find equations of motion where the dependence on time is not symmetric with respect to the dependence on position. One very trivial example of this is a simple case of energy conservation. We find that in many cases, potential energy and kinetic energy are interchangeable, but the dynamics of the real world show us that the dependence on position is a first-order effect; and the dependence on time is a second-order effect. We call this coupled first- and second- order time-space relationship Hooke's law and we use it to describe simple harmonic oscillation, one of the simplest and most fundamental physical descriptions of motion. (Some people use this to model the behavior of a "spring").

So: we can use mathematical abstraction to describe displacement in space, and displacement in time, using the same language; but when we study even the most simple cases, we quickly find that time- and space- do not behave in the same way. Dynamical systems almost always exhibit different properties - rates of change, stability, and so on - with respect to time and with respect to position. Nimur (talk) 01:12, 18 June 2013 (UTC)[reply]

Nimur's very excellent and easy to understand explanation is the inherent reasoning behind Minkowski space, which is the four-dimensional space created to do the geometric calculations behind special relativity. The four dimensions in Minkowski space are not identical. Three are "space-like" dimensions, which behave like space, and one is a "time-like" dimension, which behaves as time does. Space and time are all different dimensions, but they do not behave the same way, and cannot be treated equivalently, so one's "motion in time" is not equivalent to one's "motion in space" and one cannot discuss the two concepts as though they were interchangeable. --Jayron32 12:12, 18 June 2013 (UTC)[reply]

Yipes. The OP has asked a reasonable question, but the answers confuse and miss the point. An object does not have a position in space or time without specifying a slice through spacetime (e.g. "now"): it has a world-line through spacetime, and acceleration is a change in angle of this worldline: a curve in spacetime. Objects do not travel through spacetime. Energy–momentum is conserved in all four dimensions. — Quondum 01:50, 18 June 2013 (UTC)[reply]

Last week, the term "now" referred to last week; today it refers to today. Presumably if that change were to happen more quickly, it would be an example of the kind of thing the OP is talking about.  Card Zero  (talk) 01:53, 18 June 2013 (UTC)[reply]

Isn't that a bit like saying if a metre were longer, things'd be further apart? If by "that change" and "quickly" you are referring to some concept of movement through time in terms of elapsed time, you're confusing things. By "now" I simply meant a given instant in time as perceived by some observer. — Quondum 02:20, 18 June 2013 (UTC)[reply]

• This is a sort of have-your-cake-and-eat-it-too question. There is no meaning in the idea of changing your rate of travel through time. You always go through time at a rate of exactly one second per second. Looie496 (talk) 05:08, 18 June 2013 (UTC)[reply]
  • unless you speed up. --Jayron32 12:12, 18 June 2013 (UTC)[reply]

According to Noether's theorem the consevration of (linear) momentum arises from (or is, at least, intimately connected to) the invariance of physical laws under arbitrary translations in space. The equivalent conservation law that arises from invariance under translations in time is conservation of energy. Gandalf61 (talk) 13:09, 18 June 2013 (UTC)[reply]

Are there any known examples of heterozygous genetic traits subject to assortative mating, but for which homozygotes prefer heterozygous mates and vice-versa? (This would be equivalent to the same allele coding a disassortative recessive trait and an assortative dominant trait. The reason I ask is that if autism-spectrum disorders were partly the result of a partially dominant trait, then people "square enough for the peg and round enough for the hole" would more often become partners and parents of those that needed them, as I have anecdotal evidence to suggest.) NeonMerlin 03:25, 18 June 2013 (UTC)[reply]

I have no answer here, only the observation that the same thought had occurred to me. I think the 'square enough/round enough' phenomenon you're describing is what's known as the 'broader autism phenotype'. If anyone can supply some genetics insight here, I'd be fascinated. Thanks! AlexTiefling (talk) 11:37, 18 June 2013 (UTC)[reply]

Given samples of two sources/instruments/voices performing/speaking the same piece in identical fashion is it possible to workout a transform between the two so that given new samples of one, we could transform it into a decent approx. of the other? For example, given a violin and an acoustic guitar playing various scales at various rates, could we generate an algorithm to map violin pieces to guitar pieces? What about for voices and speaking (This is my primary interest, but the situation is interesting in general)? Finally, what about less specific cases, for example: changing a male voice into a "female" voice (not a specific one, just removing male characteristics and adding feminine ones); or, with music, changing a string instrument to a brass version of it? I'd be interested in any information pertaining to this, including info on what characterizes one source from another (and the science/mathematics of it). Thank you for any help:-)Phoenixia1177 (talk) 04:52, 18 June 2013 (UTC)[reply]

what do i do? i can't figure it out and ain't got no money. it rattles upon slow acceleration and is a light vibrator noise coming from my right rear wheel. — Preceding unsigned comment added by 108.212.70.237 (talk) 05:38, 18 June 2013 (UTC)[reply]

I'm not a mechanic, but my personal opinion is that your wheels need to be balanced. Lucky for you, this can be done pretty easily and inexpensively at most tire shops. (BTW, if you "ain't got no money", perhaps you might consider selling your luxury BMW and buying a more affordable car to make ends meet?) 24.23.196.85 (talk) 06:13, 18 June 2013 (UTC)[reply]

Hmmm.. A 2001 740i could have been purchased for as low as $5000 if in poor condition and with no maintenance logs, even though it is a top line luxury vehicle. Sometimes young guys buy these before realising that a car costs a lot more to own than the purchase price, so the question could be genuine. Check the driveline: Check each universal joint. These rwd cars have a split prop shaft like trucks and some GM cars. Check the prop shaft carrier/bearing underneath the center of the car. When the resient mounting fails you get just the symptoms you describe. If the carrier and bearing are ok and the universal joints are ok, check things like engine mounts and suspension components. Note that if engine is misfiring one cylinder this can combine with other problems to cause rattles during mild acceleration. Also note that if te car has been correctly serviced by properly certified mechanics since new, all these faults are just about impossible. — Preceding unsigned comment added by 124.182.43.219 (talk) 10:20, 18 June 2013 (UTC)[reply]

Introduction:

James Hansen's book, "Storms of My Grandchildren" make it clear that our understanding of Ice Ages, which has come about from a combination of Milankovitch Theory with much hard work by geologists on coring and complex analyses of those cores, is at the centre of our understanding of what is likely to happen to us as Global Warming picks up pace.

Unfortunately, even though I am a climate physicist of 40 years experience, engaged on writing a popular book on this subject, I cannot yet say I understand Milankovitch theory as described in this article (or any other popular books on the subject) well enough to write a simple but authoritative account of it for my readers.

I am not blaming the authors of the article at all for this -- it is genuinely a brute of a subject for anyone to get one's head around, and I have learned a lot from what they say.

My question:

Could the Reference Desk kindly get me into email contact with the authors of the article? In particular, with whoever provided the box, found on the right side of the first page of this article? Whoever the person is who came up with this box, it's clearly got nearly all of what I need to understand. I would like to email back and forth with him/her to explain what I am trying to do, and to work out some wording that satisfies both me and that person as a description of the physical things that govern the summer warming of icecaps. What's already there is very good. However, my purpose is to explain the observational history of the past few centuries that led to these astrophysical results, and this is the area where I most need the advice of the authors of the article. (Ivars Peterson's "Newton's Clock: Chaos in the Solar System", Freeman and Co 1993, unfortunately just misses giving what I need). 06:45, 18 June 2013 (UTC)~ — Preceding unsigned comment added by Neergtrish (talk • contribs)

Hi. Firstly, it's probably worth pointing out that almost all Wikipedia articles are collaborative efforts, so it's unlikely that there is a single 'author' of the article, which seems to be what you're looking for. Nevertheless, if you want to find out who has contributed to the article, simply click 'View History' at the top of the article and you will be able to see all the changes made throughout its history.

As for the image in the top right, this was added on 3rd June 2009 by Incredio. If you wish to contact them, the best way would be through their talk page. Some editors allow others to email them through Wikipedia's EmailUser, but Incredio has not enabled this, so on-Wiki communication is the only way.

Alternatively, since this is the reference desk, we may be able to help. If you post the questions you have about the article, maybe we can find some sources to aid your understanding. - Cucumber Mike (talk) 07:55, 18 June 2013 (UTC)[reply]

These two photos were taken just a few days ago in Vermont. I'm guessing that it's a common snapping turtle. It was a bit aggravated by me being as close as I was and I didn't want to bother it too much. What was it likely doing? Would the other two, for lack of a better word, divots in the soil next to the road in the foreground of the second image have been dug out by the turtle? Was she(?) laying eggs? There wasn't a large body of water near by. She was scratching at the dirt when I found her. Thanks, Dismas|^(talk) 07:11, 18 June 2013 (UTC)[reply]

Yes, laying eggs I think. They live is small streams, don't they ? So you might not know there's one nearby. Since turtles don't exactly travel long distances on land, I'd expect the stream it came from to be quite close (maybe even a drainage culvert). They don't seem to understand the danger of roads, either, unfortunately. StuRat (talk) 07:31, 18 June 2013 (UTC)[reply]

Thanks!76.218.104.120 (talk) 11:28, 18 June 2013 (UTC)[reply]

Yes. Like all elementary particles, neutrinos have mass/energy - therefore their paths are affected by gravity, and therefore they undergo gravitational lensing. Gandalf61 (talk) 11:36, 18 June 2013 (UTC)[reply]

I don't have a background in particle physics, but I have been doing some reading. I recently picked up on some ideas brought up with Imaginary time and the complex plane. So is it possible to project an imaginary axis on a 3D, maybe as (x,y,z,i), n-dimensional Euclidean space? I could only assume this logic could be used to explain occurrences such as particle-wave duality. In a similar way this little diagram (http://commons.wikimedia.org/wiki/File:Dualite.jpg) shows how what we may see as 2 separate figures may in fact be the same because we fail to see a superfluous axis of space. Bugboy52.4 ¦ =-= 13:51, 18 June 2013 (UTC)[reply]