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[
"Are there any living organisms that can change the DNA of other organisms?"
] |
[
false
] |
You'll often see this in science fiction or horror, where an animal will bite/cut/wound/etc another, which will change their DNA and cause wacky things like superpowers (Spider-Man) or turn them into monsters (Prometheus). Obviously it wouldn't be this extreme, but is there any precedent of organisms changing the DNA of other organisms in real life? (Retroviruses can insert themselves into the genome of their host, but they're not really alive so I don't know if I'd count that)
|
[
"Well, if we're not counting viruses... there are parasitic bacteria like ",
" that infect plants, and inject a small piece of DNA (a plasmid) into their host plant's cells. This plasmid will integrate into the host's genome, and carries genes for things like growth hormones, that will trigger the formation of a gall — a kind of tailor-made tumor that the bacterium can live inside of.",
" has been widely used in genetic engineering because of this ability; just swap out its plasmid for some other DNA you want the plant to have, and it will do the engineering for you."
] |
[
"There are parasites that hijack their hosts - e.g. ",
"Apicomplexans",
" and ",
"Ophiocordyceps",
" - but not by changing the host's DNA. They change the DNA ",
", which means they can take over the protein-making machinery and have the host cells do their bidding.",
"Not quite an answer to your question, but I think zombie ants fits your monster/horror criteria"
] |
[
"To add to what has already been said, parasites can also change their host's behavior or physiology without messing with its DNA. To increase their own reproductive success, of course.",
"The ",
"lancet liver fluke",
" sends one of a group of sibling worms (so it makes sense genetically) to bore into an ant's brain. And the parasitized ant then tends to sit on top of grass blades, to be eaten by some grazer and maintaining the infection cycle.",
"Sacculina",
", a kind of parasitic barnacle, acts on the hormonal balance of its crab hosts.",
"So in a way nature has more imagination (in a metaphorical sense, of course) than Hollywood. 🤤"
] |
[
"Is Magnetism just a manifestation of relativistic phenomena?"
] |
[
false
] |
Does the magnetic field truly exist, or is it purely due to the contraction/dilation of lengths due to relativity? What about in the case of Electromagnetic waves? I know that in EM waves the electric and magnetic fields are always perpendicular, but I'm having trouble comprehending how a truly distinct magnetic field can exist.
|
[
"Well, the fact that electromagnetism doesn't really work without special relativity can be shown pretty easily (with modern hindsight). The definition of whether something is an effect of SR is whether it still exists at all in the limit c -> infinity. In electromagnetism, the vacuum permittivity and permeability are related by c",
" = 1/(epsilon x mu). So in the non-relativistic limit, either or both of those constants must be zero, and electromagnetism just doesn't work. So c must be finite. If the principle of relativity is true and your inertial frame doesn't matter, even to the laws of electromagnetism, then c must be the same in every reference frame. These assumptions lead you straight to special relativity. ",
"I wouldn't say that magnetic fields don't truly exist because it's a relativistic phenomenon, but rather that magnetic fields exist because relativity is true. An electrical field in one reference frame is a magnetic field in another (or vice-versa). Two observers do not agree on what fields there are. Moving charges give rise to magnetic fields, but whether a charge is moving or not depends on your inertial frame of reference. ",
"This",
" and ",
"this",
" may be good places to start for a more proper explanation."
] |
[
"This is not correct. It is not possible, in general, to eliminate the magnetic field by changing reference frames."
] |
[
"It is interesting, though, that ",
" you can get rid of a magnetic field, but you can ",
" get rid of an electric field. ",
"For example, a charged rod only produces an electric field in its rest frame, but produces an electric and magnetic field in a frame moving along its length. "
] |
[
"If the mass of an object was somehow zero would it be possible for it to travel at, or faster, than the speed of light?"
] |
[
false
] | null |
[
"i believe that particles with no invariant mass (such as photons) can only travel at the speed of light. there is no compelling evidence to suggest that there exist particles, massless or otherwise, that can travel faster than the speed of light."
] |
[
"I think theoretically it'd have to have ",
" mass to travel backwards through time, not negative mass."
] |
[
"It's \"theoretically\" possible by butting in imaginary values for the mass of particles in some Special relativity equations, but there's no experimental evidence that suggests that there are any particles with such properties. "
] |
[
"Are the divisions of sound frequencies into musical notes arbitrary or do they correspond to something in nature?"
] |
[
false
] | null |
[
"The frequency ratio between notes are what matters, not necessarily the absolute frequency. Specific ratios of frequencies sound nice to our ears, for example, two notes an octave apart have a frequency ratio of 2. A fifth has a frequency ratio of 4/3. Why these particular ratios sound nice has to do with superposition of sound waves and can get into some complex mathematics... so I can't give you a great explanation there, sorry."
] |
[
"Here is a longer explanation of the Pythagorean scale, where the whole musical scale is based on 3:2 ratios.",
"https://en.wikipedia.org/wiki/Pythagorean_tuning",
"This sort of tuning would work well on a simple instrument with limited range, but breaks down if you try to change key or shift up or down by more than a few octaves, as the maths gives the wrong result.",
"e.g go up 12 fifths should be the same as 7 octaves, but",
"1.5",
" =129",
"2",
" = 128",
"Therefore modern instruments tend to use an even tempered scale to avoid this problem."
] |
[
"They're not arbitrary. They're a pragmatic approximation of small integer frequency ratios. ",
"The \"pragmatic\" part is the equal division of the octave, which was done to make it easier to play in any key. ",
"12 notes per octave were chosen because it ",
"approximates the most consonant natural",
" frequency ratios, like 3:2 perfect fourth, 4:3 perfect fourth, etc.",
"These small integer frequency ratios are based in nature, since we usually produce sound using harmonic motion, which produces multiple tones at integer multiples of the root. When you play multiple such instruments in small integer frequency ratios, many of their harmonics align, and the ones that don't are far enough apart that they don't beat, so the combination tone remains smooth and sounds good to us. Harmony is actually fractal in nature, with increasingly dissonant intervals between each consonant interval.",
"Non-harmonic instruments are possible, too, like drumheads, vibrating bars, gongs, or bells, but we usually modify them to sound roughly harmonic anyway.",
"Some people make music using scales based on the natural ratios instead, which is called Just (\"natural\") Intonation: ",
"https://en.xen.wiki/w/Just_intonation",
" (And singers and some instrumentalists adjust to this without thinking about it.)"
] |
[
"How does the air inside of a tire (or other rotating body) behave? Are different zones of air pressure created throughout the tire, or does the air remain evenly spaced?"
] |
[
false
] | null |
[
"Because the rotation of the tire is slow compared to the speed of sound of the air in the tire, the pressure changes propagate much more rapidly than the tire is rotating. As a result, the distribution is essentially uniform throughout.",
"The inertial effects that ",
"/u/ninja_pigLP",
" mentioned are present in principle, but in practice do not have any significant effect."
] |
[
"As the tire spins, centrifugal force (caused by the outward inertia of the air in the tire) causes an increase in air pressure in the air farthest away from the center of the tire, wile causing a decrease in the air pressure closest to the center of the tire rotation. This is similar to how air pressure changes due to the force of gravity on earth.",
"Also, as the tire accelerates(spins faster/slower), the air in the tire does not immediately start spinning with the tire. It will slowly catch up to the rotation speed of the tire. So sometimes the air will be spinning while the tire is not, and vice/versa.",
"If you filled your tire up completely with water, It would basically behave the same air in the tire. This might be easier for you to visualize."
] |
[
"Apologies but could you give a more accurate formula for that? Im not familiar"
] |
[
"What exactly is dark matter? Is that what we would call the space in between our atoms? If not what do we call that?"
] |
[
false
] | null |
[
"We can tell how much stars and gas there is in galaxies by looking at their brightness. We can tell how heavy galaxies are by seeing the speed at which they orbit, and looking at the deflection of light through and around them. The amount of mass from the stars and gas is only about 10-20% of what is necessary to account for the measured masses. The rest, because we can't see it, we call dark matter.",
"We don't yet know what dark matter is made of, and there are several underground particle detector experiments trying to directly detect dark matter particles, and figure out what is and isn't possible.",
"edit: a common question that arises is how we know that it must be extra mass explaining the observations, and why it can't just be that our understanding of gravity is wrong. ",
"/u/adamsolomon",
" explains a bit ",
"here",
"."
] |
[
"No, because black holes are very localized sources of mass and dark matter is very diffuse. Even the supermassive black holes at the centers of galaxies only make up a small fraction of their mass, often less than a percent."
] |
[
"As the other comments here have discussed, dark matter is just a name given to matter that we don't see but that needs to be there for astrophysical observations to make sense. There are ",
" of observations that all point to a need for dark matter—that's an essay in itself, so I won't go there for now. Suffice it to say that most physicists believe that there is some kind of dark matter out there.",
"But to physicists, there's nothing fantastic about matter that we can't see. Remember, when you see something, you're actually ",
" reflected or emitted light. For something to reflect or emit light, it needs to interact with the electromagnetic field.",
"If some species of particle does not \"interact electromagnetically\", then it won't reflect any light and we won't see it! We already know of particles that don't interact electromagnetically—",
"neutrinos",
", for example. So we can imagine that there's some other kind of particle, harder to observe than neutrinos, that also doesn't interact electromagnetically.",
"But wait, you say. If there's a bunch of matter out there, shouldn't it be bumping into things? Why can't we see that happening? Well, almost all of the forces that come into play when two big objects bump into each other are electromagnetic in nature. If dark matter doesn't interact electromagnetically, it'll go right through other matter. This is true of neutrinos, too—this is why they're so hard to observe (or block).",
"There are other reasons to motivate this, but you can see why it makes sense for there to be dark matter that we can't see. So how do we know it's there at all? Gravity. Gravity couples to all energy, so even if they don't interact electromagnetically, dark matter particles should (and apparently do) interact gravitationally with other dark matter particles and with ordinary matter.",
"So what could dark matter actually be? There are a number of specific candidates that fit into our current theoretical framework. You might think, based on what I said before, that neutrinos would be a good bet—or at least a parsimonious guess. But we can rule out most neutrino-dark-matter models with other observations, so it's not looking too likely, at least with the neutrinos we know of.",
"One still-strong candidate for dark matter comes from the theory of ",
"supersymmetry",
" (SuSY). SuSY says that each of the particle species in our standard model has a symmetric partner—e.g., electron and selection, quark and squark… (Yes, \"squark\". I wish I could take credit for that name but I can't.) SuSY naturally gives rise to ",
"weakly interacting massive particles",
", which are great candidates for dark matter. The trouble is, SuSY is being tested bit by bit at the LHC, and we haven't found anything yet. ",
"Another candidate for dark matter is the ",
"axion",
". The axion is a hypothetical particle that was introduced from the solution to a very different problem, the ",
"strong CP problem",
". Without going into any detail, the great news is that if axions are real, we could solve two problems with one particle. That said, we've looked for axions almost everywhere they can be, and the recent BICEP2/Keck results just ",
"took out half",
" of the remaining parameter space. The good news is that we'll know pretty soon.",
"A third and ever-extant possibility is that this is some exotic particle we've never thought of, or any combination of candidates. I was at a talk recently where the speaker reminded the audience that parsimony, while one heck of a drug, isn't always real. To paraphrase what he said with much less flair:",
"\"Imagine a scientist made out of dark matter trying to explain the missing 20% of the matter in her universe. Somehow I doubt she would suddenly guess that it can be accounted for by a model with SU(3)×SU(2)×U(1) symmetry and three massive neutrinos and quark mixing given by the CKM matrix and…\"",
"The truth is that our 20% of the matter in the universe is reasonably complicated. While we obviously want to pursue the directions that are best motivated, there's no reason to be confident that the other 80% can be explained by a simple extension of our present theories."
] |
[
"Why is our galaxy relatively flat rather than a big cloud of stuff?"
] |
[
false
] | null |
[
"Galaxies ",
" sphere-like in shape. Here is a diagram of the ",
"dark matter halo",
" of a galaxy. Notice how the halo covers the flat normal matter of galaxy, making an ellipsoid shape. Considering that dark matter makes the vast majority of the matter in a galaxy, we can't just ignore it when we talk about the 'shape of the galaxy'.",
"So why is normal matter also not in a giant ball shape in a galaxy. Well it ",
" be. ",
"Elliptical galaxies",
" are galaxies in which the all the matter is in an ellipsoid shape. But in spiral galaxies, like ours, luminous matter is obviously in a flat disk. So what's the difference between these two types of galaxies? ",
"Gas. Dark matter does not collide with each other, but gas particles ",
". As gas particles can collide, they can lose their energy (kinetic to radiation), but angular momentum is a lot harder to lose. So the gas keeps spinning, but loses energy until it reaches the lowest energy configuration: a flat disk. Elliptical galaxies have less gas compared to spiral galaxies, and so they retain their ellipsoid shape.",
"Another intersting fact is that like dark matter, stars do not really collide with each other much. However, stars form ",
" the gas clouds of a galaxy, and so they also tend to form in the flat disk region. Which is why very old stars can be outside the galaxy's disk as they formed before the gas settled into a disk."
] |
[
"Great answer. Thank you. :)"
] |
[
"i'm pretty sure your description of how ellipticals form isn't quite right. ellipticals don't eventually settle down into spirals as you suggest. it's the other way around, ellipticals are thought to form through repeated mergers of different galaxies, for instance when 2 spirals merge most of the angular momentum eventually cancels out and most of the orbits become radial, giving you an elliptical galaxy.",
"and ellipticals have lower gas fractions than spirals not because they dont have enough gas to turn into spirals. ",
"ellipticals are much older and much bigger than most spirals because they've undergone many more mergers. as a result of being so old, they have lower gas mass fractions because much more of the gas has gone into star formation in the early universe in the giant first generation stars, and are how trapped in dwarfs, thats why they're much redder as well."
] |
[
"Could someone please explain how substances like activated carbon and aerogel can have a greater surface area than a basketball court in just 1.0 gram of material?"
] |
[
false
] |
This probably has a simple explanation, but I'm having a hard time wrapping my head around the geometry.
|
[
"The reason aerogels and mesoporous materials like activated carbon or silica have such high surface areas is because they have very very porous structures, with very very tiny holes, and trying to imagine such a small thing is where most people trip up. Instead of trying to imagine boreing tiny holes in a material, let us examine an analogous situation with the subdivision of a cube.",
"Imagine you have a cube of some arbitrary material with 1 cm sides. It has a surface area of 6 cm",
" Now imagine you sliced it into tenths through each of the x, y, and z axis, like you had a three-dimensional egg cutter. You would now have 1,000 smaller cubes, each with 1 mm sides. Each of those would in total have a surface area of 6 mm",
" but since you have 1,000 of them you have a total surface area of 6,000 mm",
" or 60 cm",
"Imagine you then that you slice each of those cubes in the same way. You will then have 1,000,000 0.1 mm cubes, and you will have a surfacea area of 60,000 cm",
" The size of the pores in a mesoporous material like a xerogel are orders of magnitude smaller than this, and as you can see already, the smaller you make the subdivisions in a material the larger the surface area becomes. This applies not only to cutting up cubes, but also punching out very tiny tunnels through the bulk of a material, as in mesoporous materials. The smaller the tunnels, the larger the surface area.",
"Anyhow... Divide those cubes up, and you will have 1,000,000,000 cubes with 0.01 mm sides (100 um), and your total surface area will be 60,000,000 cm",
" or 60,000 m",
"Divide those cubes up, and you will have 1,000,000,000,000 cubes with 0.001 mm sides (10 um), and your total surface area will be 60,000,000 m",
"Divide those cubes up, and you will have 1,000,000,000,000,000 cubes with 0.0001 mm sides (1 um), and your total surface area will be 60,000,000,000 m",
"Divide those cubes up, and you will have 1,000,000,000,000,000,000 cubes with 0.00001 mm sides (100 nm), and your total surface area will be 60,000,000,000,000 m",
"Divide those cubes up, and you will have 1,000,000,000,000,000,000,000 cubes with 0.000001 mm sides (10 nm), and your total surface area will be 60,000,000,000,000,000 m",
" This is the approximate size (approx. 10 nm) of the pores in many mesoporous materials. Now, you may ask, how do we relate dividing cubes back to the surface area of a real material? Well, take those sextillion cubes we had in the last step, and stick them back together. Instead of gluing their faces together though, glue their corners together. You will now have a material that has a phenomenally large surface area. How does this relate to real surface area though? Well, carbon has a density of approximately 2 gcm",
" depending on what allotrope you are talking about. This means that if our original 1 cm cube was made of carbon, it would have weighed 2 grams. This also means that the material which you just constructed also weighs 2 grams. It therefore has a surface area of 30,000,000,000,000,000 m",
" Now, this is obviously absurd. No material can possibly have a surface area this large, but what I hope this illustrates to you is that the smaller you make the features of a material, whether it be pores or the surfaces of cubes, the larger the surface area becomes. As you have probably already gleaned from Wikipedia, the surface areas of mesoporous materials usually range from about 100-2000 mg",
" whereas the surface area of a basketball court is 436.6 m",
" for an official NBA court."
] |
[
"I'm not sure about carbon or aerogel, but your lungs have a similar surface area. The lungs branch down in to the small alveoli. This allows for a huge amount of lung/air contact, which allows us to breath like we do. I'm guessing it's something similar."
] |
[
"Well done, thanks for the explanation!"
] |
[
"Anyone else feel like the Bill Nye saying he doesn't believe GMOs are a good idea but then publicly investigates and attempts to learn about them was like him saying, \"Science, this is how you do it.\"?"
] |
[
false
] | null |
[
"This post is better suited for ",
"/r/AskScienceDiscussion",
"."
] |
[
"Ok thanks, I'll transfer it "
] |
[
"This post is better suited for ",
"/r/AskScienceDiscussion",
"."
] |
[
"Why does a snow flake form on what appears to be a 2 dimensional plane?"
] |
[
false
] | null |
[
"Hey there, I'm an undergraduate gen physics major. This is really more of a physical chemistry question but seeing as its been 8 hours I'll try to help out. ",
"I was recently reading something saying that it has a lot to do with the specific atomic structure of the water molecules. Water is two hydrogens and a comparatively large and electronegative oxygen atom. This makes it polar, so when the body of water has little enough internal energy the atoms will slow down enough to sort of snap together magnetically in this very specific pattern. ",
"The fact that they are almost flat is just they way it works out with where and how the water molecules could possibly snap together. ",
"This is why ice expands and takes up more volume than water, because there is less energy so instead of sloshing around on top of each other, the molecules line up in this unique way and there is overall more space between them. If you've ever seen a video or witnessed a container of water that is in the liquid state and then some guy touches it and it freezes almost instantly. Those are the newly cooled molecules all snapping together magnetically. It's called supercooling a liquid. It's cool to watch if you haven't. Here's a link. ",
"http://m.youtube.com/watch?v=Fot3m7kyLn4",
"Nature is beautiful and it's amazing when you learn how the world around you really works. ",
"Hope this helped. "
] |
[
"No, there are a lot of different ways they can snap together on the atomic level. This is why every snow flake is so unique. "
] |
[
"Is this pertaining to water's \"bent\" molecular structure and that it's planar? (Err...not sure if the electron pairs on the oxygen make it planar or not...plz correct.)"
] |
[
"What computer programming language would one use to create a new programming language?"
] |
[
false
] | null |
[
"Before stating anything else, I should point out that programming languages are not inherently based on any implementation, in the sense that you can in principle come up with a programming language but never actually write a computer program to actually compile programs for it. Thus, until you actually decide to implement it, there's never a need for an initial programming language when creating the second.",
"When it comes to implementing a language, technically any ",
"Turing Complete",
" language will do. Examples include C++, C, Python, LISP, Assembly, Javascript, Haskell, PHP, LOLCODE, Java, Prolog, Brainfuck, BASIC, and most other programming languages you've heard of. Roughly speaking, Turing Completeness means that the language is powerful enough to allow you to make a full simulation of a computer. If you can fully simulate on a computer, then of course you can also simulate it running any program that can feasibly run on a real-life computer, including any programmable compiler for a programming language. Thus, at least in this very roundabout way, any Turing Complete programming language can be used to simulate any implementation of a programming language that would feasibly work on a computer, meaning that it can extract the compiled result from this simulation and hand it back to the user as its output.",
"In practice, most conceivable programming languages humans can actually intuitively break up into words/pieces (\"tokenize\") according to something understandable by ",
"regular expressions",
" and have a grammar of the \"",
"Deterministic Context-Free",
"\" variety, Thus, tools such as ",
"Lex",
" and ",
"Yacc",
" are commonly used to make a compiler for your language that first tokenizes the file (this part comes from Lex) and then parses the grammar and converts it into a program (this part comes from Yacc). While these work really well for projects where efficiency isn't 100% critical, most modern production-quality compilers are written in C-like languages to allow for finer control over low-level performance tweaks. ",
" My source on a lot of this last paragraph's information might be two to four decades outdated. I'd be happy to be corrected."
] |
[
"I have to say that compilers that are written in their own language just make me smile. Something about a system capable of producing itself is kind of magical and fun.",
"*I know its not magic. I am a programmer. I just like a little whimsy."
] |
[
"Agree. In general, most new language interpreters and compilers are written in C or C++ until they are mature enough to be efficient while self-hosting (compile themselves). This has been true for most of the major languages in use today. This is generally due to existing runtime libraries, speed and the penetration of C and C++ on most platforms."
] |
[
"Just finished the Chernobyl series on HBO. Could someone explain what positive and negative void coefficients are and why they exist? And what about a reactor design can make such a dramatic difference?"
] |
[
false
] | null |
[
"Getting some definitions out of the way, the ratio of the number of neutrons available for fission in one generation of the chain reaction to the number available in the previous generation is called k",
". This quantity determines the behavior of the fission chain reaction. If k",
" > 1, then the system is supercritical, and the neutron population will increase exponentially with time. If k",
" < 1, it's subcritical, and the neutron population decays exponentially with time. k",
" = 1 is a very special state called ",
", where the chain reaction perfectly sustains itself, and the neutron population stays constant.",
"Now, there's a quantity called ",
", which is just another way of representing k",
". It's defined as ρ = (k",
" - 1)/k",
".",
"So positive reactivity means k",
" > 1 and negative reactivity means k",
" < 1.",
"So clearly the k",
", or the reactivity is the parameter which determines whether the system is subcritical, critical, or supercritical, and it's very crucial that k",
" be as close to 1 as possible when the reactor is operating normally.",
"But basically any change you make inside the core can in principle affect the value of the reactivity, and people who design reactors need to understand exactly how so that they can compensate for or design away potentially dangerous reactivity excursions.",
"Writing the reactivity as a function of the various operational parameters of the reactor (temperature, void fraction, etc.), you can expand to first order in a Taylor series, and you find the linear response of the reactivity to small changes in each of its parameters.",
"Then the coefficient of that linear function is called the \"reactivity coefficient\". So if you're looking at how the reactivity changes as a function of temperature, you'd call it the \"temperature coefficient of reactivity\". Or for the void fraction, you'd call it the \"void coefficient of reactivity\".",
"And to study the stability of the system with respect to changes of that quantity, what's important is the sign of the coefficient. Negative coefficients are stable. That means that if you change the reactivity, it leads to a change in the quantity which tends to reduce the change in reactivity. This is a stable dynamical system. If the coefficient is positive, the opposite happens.",
"For example: temperature. Some reactors have negative temperature coefficients of reactivity. The physical explanation is that if you increase reactivity, you increase the rate of fission, and therefore the temperature. But higher temperature makes the core expand, and makes the fissile nuclei farther apart on average, and less likely for fission to occur. So the reactivity goes back down.",
"The void fraction is just the ratio of gas to liquid/solid, by volume. A positive void coefficient means that as voids begin to form in the core, reactivity increases, and that generally leads to ",
" void formation, and further increased reactivity. That's unstable. The RBMK reactors at Chernobyl had a positive void coefficient."
] |
[
"It’s very difficult to make ",
" of the coefficients of reactivity simultaneous negative. Usually it’s a tradeoff. Even if some are positive, but very small in magnitude, the system is technically unstable, but if the instabilities grow on timescales much longer than it takes for controls to take over, then the reactor can still be made safe. Of course, one would rather it to be “inherently safe” by designing away instabilities.",
"There are whole textbooks about reactor design, and how to make the various reactivity coefficients negative. I also remember a really nice table with different reactor designs and their various reactivity coefficients. I think that’s in one of Lamarsh’s textbooks, if you have access to those (they’re pretty well-known nuclear engineering books). Unfortunately, I don’t have it on hand right now."
] |
[
"Awesome, thank you! Is it know what about the RBMK design made the void coefficient positive vs. other reactors that had negative coefficients? Is it challenging to make it have a negative void coefficient and this is why the Soviet Engineers couldn't figure it out?"
] |
[
"Is there a way to measure pain objectively, instead of asking the victim to describe it?"
] |
[
false
] |
Inspired by : I think one of the problems that non-drug-seekers have with the "worst pain your can possibly imagine" concept is that they literally can't imagine worse because it's never happened to them. Everyone has a scale and everyone's scale probably goes to 10 where 10 is the worst thing that's ever happened to them. You can say "worse than dunking your feet in a hot deep fryer" and while I'm sure that would suck quite a bit, I can really only compare it to what's happened to me before.
|
[
"Here's something to read while you wait: ",
"http://en.wikipedia.org/wiki/Dolorimeter"
] |
[
"Well that's a complicated question because there are so many different types of pain that can be measured at several levels.",
"Thermal pain signalling differs from pressure pain which differs from painful itch. Its not only that our brain interprets these signals differently, its that they arise from different peripheral cell types and are relayed back through the spinal cord in different ways. ",
"To 'objectively measure pain' would require knowledge about all of the mechanisms of pain both peripherally and centrally, and we quite frankly don't know how all pain works at every level (afferent nerve, spinal tract, spinal modulation, central relay, central modulation, feedback (repeated process), emotional input, --------> conscious perception of pain)"
] |
[
"This",
" might be of interest."
] |
[
"How does the streetlamp stave off winter dormancy for part of this tree? Pic included in text (x-post from mildyinteresting)"
] |
[
false
] |
[deleted]
|
[
"That branch is actually still dormant; those leaves aren't functioning, the chlorophyll has already drained out of them. ",
"My guess is that it has something to with the abscission layer in those leaves, where the plant weakens special cells to allow the leaves to fall. Formation of this layer is thought to be controlled by plant hormones, especially auxin, production of which is influenced my light (this is the same hormone that causes plants to grow towards light). The increased light from the lamp was probably enough to cause the closest leaves to continue making auxin a little longer than the those on the rest of the tree, which has in turn delayed the formation of their abscission layers. "
] |
[
"There is some uncertainty as to the purpose of leaves changing color in the Autumn. Most agree that the yellow/orange/red tones of pigments called carotenoids (think ",
") are simply what is remaining after the green chlorophyll is broken down. In turn, as these pigments degrade, the last color you see is brown, from the structural elements of the leaf (e.g. cell walls). "
] |
[
"There is some uncertainty as to the purpose of leaves changing color in the Autumn. Most agree that the yellow/orange/red tones of pigments called carotenoids (think ",
") are simply what is remaining after the green chlorophyll is broken down. In turn, as these pigments degrade, the last color you see is brown, from the structural elements of the leaf (e.g. cell walls). "
] |
[
"Most animals seem to have an instinctive fighting style, what is ours?"
] |
[
false
] |
[deleted]
|
[
"Due to ",
"changes in Reddit's privacy policy",
", this comment has been overwritten by an open source script to protect this user's privacy. ",
"If you would like to do the same, add the browser extension ",
"GreaseMonkey",
" to Firefox and add ",
"this open source script",
". ",
"Then simply click on your username on Reddit, go to the comments tab, and hit the new OVERWRITE button at the top."
] |
[
"\"We\", as in modern man, did not exist before our tools. Our tool use stretches back ",
"far further",
". Additionally it is thought that early tool use originated, from the H. Habilis smashing bones to extract the marrow as they scavenged the plains. Thus, it is possible our tool use also predated our hunting so to ask what our \"natural\" attack without our tools is like asking what a tiger's attack is without claws or teeth. The question stems from a fundamental misunderstanding of what is currently understood from the fossil record and what is and what is not 'natural'. ",
"It's an interesting counterfactual discussion, perhaps, but totally useless from a scientific point of view. "
] |
[
"When the prey animal is lying in front of exhausted, they likely threw stones or beat it with clubs before they developed spears. Tool use ",
" our instinctive fighting style."
] |
[
"Does a person's circadian rhythm still \"work\" if they never see the sun? Even if they don't have an alarm clock?"
] |
[
false
] |
[deleted]
|
[
"The definition of a circadian rhythm is that it is inherent to the organism, meaning that it \"works\" independent of environment. ",
"For organisms, such as plants, fungi, insects, and vertebrates, the means through which they have an inherent cyclic rhythm may vary (for the organisms listed, I believe each evolved somewhat separately), but the end result is the same. ",
"If I were to stick you in a constantly dark or light room, you would start out sleeping and waking in the schedule of the time zone in which you live, but slowly you would break away from this schedule (assuming you are a normal, \"wildtype\" person) and begin to wake up according to an approximately 24.25 hour sleep/wake cycle.",
"It makes sense that this cycle would be inherent, as the earth's day/night cycle is ",
" 24.25 hours, rather, it is closer to 24 hours. ",
"Michel Siffre",
", a reporter, exemplifies this phenomenon:",
"In the 1960s, at the peak of the Space Race, scientists were curious how humans would handle traveling in space and living in fallout shelters. Could people cope with extreme isolation in a confined space? Without the Sun, what would our sleep cycles be like? Michel Siffre, a 23-year-old French geologist, decided to answer these Cold War questions by conducting an experiment on himself. For two months in 1962, Siffre lived in total isolation, buried 375 feet inside a subterranean glacier in the French-Italian Maritime Alps, with no clocks or daylight to mark time.",
"...But during his 63 days underground, he only dabbled in madness once. One day, Siffre started singing at the top of his lungs and dancing the twist in his black silk tights. Other than that, he behaved relatively normally.",
"When Siffre emerged on September 14, he thought it was August 20. His mind had lost track of time, but, oddly enough, his body had not. While in the cave, Siffre telephoned his research assistants every time he woke up, ate, and went to sleep. As it turns out, he’d unintentionally kept regular cycles of sleeping and waking. An average day for Siffre lasted a little more than 24 hours. ",
"Because many organisms have these circadian (and sometimes circa [\"around\"] other clocks: circaanual, circatidal, etc.) clocks, it suggests that having an internal clock is important to one's survival. ",
"As it turns out, chipmunks whose central \"boss\" clock has been destroyed are more likely to be eaten by predators, because they do not maintain the correct sleep/wake schedule. ",
"Circadian rhythms (and their associated clock[s]) control other things too. There is a clock in your fat which manipulates metabolic rate, along with the \"boss\" clock I mention in a previous paragraph (the \"boss\" clock is in your brain in a region called the \"suprachiasmatic nucleus\"). This means that you digest food more efficiently at certain times of day (spoiler: in the morning). ",
"And other parts of the body have clocks too, on a cellular level, which \"talk\" to the \"boss\" (suprachiasmatic nucleus) clock. As it turns out, the synthesis of certain proteins forms something called a \"feedback loop\" which regulates the length of one's clock. If these cellular clocks become dysregulated (out of synch when they form the \"boss\" clock), there is evidence that it can influence one's mood, such as with Seasonal Affective Disorder (SAD). Although it's sort of a \"chicken and the egg\" problem, some researchers think that a similar problem occurs with certain types of bipolar disorder. "
] |
[
"Can it be assumed that our circadian rhythm is linked to the earth's rotation? Had humankind evolved on a planet which had days that lasted several earth days, would our circadian rhythm also be drastically different?"
] |
[
"Yes, there is a central circadian clock - the suprachiasmatic nucleus, but every cell also has a circadian clock. This clock operates through expression of genes, including PER genes, which alter cellular activity. There's a continuous feedback between these proteins that are expressed and the system of gene expression. For example, if PER2 is expressed \"too much,\" this will be detected, and PER2 transcription will be stopped. This prevents shifts larger than about an hour per day."
] |
[
"What accounts for the difference in average human height between countries? i.e. Denmark, male avg = 6'0\", France = 5'9\""
] |
[
false
] |
I imagine there are many different factors; perhaps available nutrition, sunlight (do people, like plants, grow taller in an effort to get more sun?), culture, medicine, media influence, etc. Maybe elevation?
|
[
"Nutrition and genetics. "
] |
[
"Right, but I doubt there are many French marrying the Germans or Germans marrying the Dutch. Countries tend to stay within their own population."
] |
[
"The two tallest groups are Nordic and one of the tribes in Africa, I forgot which one. I think the Nordic is related to historical diet, while the African is related to heat dissipation and some other benefits.",
"An example of the role of nutrition is Japan, where over the past 100 or so years they have been growing by around 1\" per generation. Youngest are almost outgrowing some of their buildings. If you go to Europe, you will be struck by how short in stature they were 500 years ago when many of the castles were built. It is pretty neat. Europeans underwent the same changes as Japan back then, as protein became a larger portion of their diet and general nutrition was increased.",
"Another example are the Incas in the mountains of South America, after being isolated for thousands of years, they have become more squat and stout in stature, and the iron content of their blood is something like 10% more than average, all which helps a more efficient of transfer of oxygen in blood, a valuable trait when the air is so much thinner due to the high altitudes."
] |
[
"In nuclear pasta all the electrons merge with protons so what dictates nuclear pasta’s chemical properties? Please explain in simple terms because I am not an astrophysicist :)"
] |
[
false
] | null |
[
"Oh what a fun question!",
"So what you call 'chemical properties' I'm going to call 'material properties' since technically these aren't atoms, so there's no chemistry! Still, lots of your intuition from chemistry may hold. For example, what is the electrical conductivity of nuclear pasta? It depends on how electrons (and to an extent, the protons) can move through it! If the pasta has very regular shapes with very long range order then that makes for good conductivity, but disorder like twists and bends and 'defects' can scatter electrons and cause electric currents to dissipate energy to heat. It's a very good analogy with defects in a crystal, like where crystal planes are misaligned or an atom is out of place. ",
"Anyway, my most important point is that the physical/material properties ultimately depends on the microphysics, which can be influenced by the pasta geometry. ",
"Similar arguments can be made for lots of different properties - like thermal conductivity. How readily can particles bump into other particles to transfer that heat? Or neutrino opacity - can neutrinos pass through easily like light through glass, or does the regular spacing between the pasta line up in just right way to scatter the neutrinos similar to light in a slit experiment? And the elastic properties - the energy of attraction/repulsion between protons and neutrons is partially determined by their separation, so resistance from squishing and squeezing depends on the density of the matter and also the spacing and shape of the pasta phase."
] |
[
"Um... What's... What's nuclear pasta?"
] |
[
"Thank you very much! :)"
] |
[
"Statistically, what does it mean to go on a 'fishing expedition' with data?"
] |
[
false
] |
Is there a term for this? I believe it has something to do with having a large sample size, and measuring too many outcomes... Edit: I thought this was an easy one. I guess not...
|
[
"I have a nice example of this.",
"Take a look at ",
"this survey",
"\nAn insurance company collected data on 160,000 car accidents and then looked at how the star sign of the driver related to the risk of a crash. They found Geminis were the worst drivers, whilst Capricorns had the the lowest chance of causing accidents, and ranked all the other signs in order. The probability of this relationship occurring in the data by chance is around one in several hundred thousand. ",
"Well, how can this be true, because ",
"we all know astrology is crap",
", correct? Yet the astrologer who is writing about the survey is awfully excited as this seems to prove that there is something in it.",
"The answer is that analysis is the result of a fishing expedition. The insurance collects the data for other reasons, and only did the astrology analysis for a bit of PR. Most importantly, they did not collect and analyse the data with the hypothesis that Geminis would be the worst drivers, taurus the second, pisces third etc etc. They simply looked for any pattern at all, and this was the one that popped up. The chance of this particular pattern was very low, but the chance of seeing any pattern in the data is actually quite high - probably 70% or so. Had the pattern been different, then the astrologer in the article would have been going on about how of course aquarians are the worst drivers, etc.\nWhat should happen is that the data from fishing trips like this is taken as hypothesis generating. We say, well, we saw this particular pattern, so now we will analyse a new set of data and see if the exact same pattern is repeated.",
"Surprise, of course it isn't.",
"Fishing expeditions are when you analyse data looking for any pattern at all, not with a clear pre existing hypothesis. The nature of statistical analysis means that you will often see patterns if you do this, but taking them as anything other than hypothesis generating is a mistake, as they will often turn out to be just statistical noise."
] |
[
"Not sure I can explain it statistically, just think of your odds fishing, then think of you odds of catching a fish that's never been caught. If you go on your fishing expedition and catch something everybody else has caught, whatever but suppose you found that fish everybody has been trying to land. I guess you could also think of it by the size of fish you catch.",
"You go fishing at a lake to catch a fish, sometimes you catch fish, sometimes you catch nothing, sometimes you catch three-eyed fish.",
"You have a huge spreadsheet of data (the lake) and you go fishing in that spreadsheet in order to catch a fish (a pattern or trend in the data). Quite often you find nothing, but other times there may be a trend or pattern. Sometimes you find something that hasn't been discovered (three eyed fish) and you get some cool theory named after you.",
"Anyways that's just my guess/interpretation."
] |
[
"The idiom \"",
"fishing expedition",
"\":",
"a search for information without knowledge of whether such information exists. (This involves asking questions with no preconceived notion of what the answers might reveal.) ",
"I.e. in general, looking for something without knowing what you're looking for. The term is most often used in legal contexts, where you're not allowed to go on a 'fishing expedition' during the discovery phase of a lawsuit (which is when the parties demand documents/evidence from each other). Meaning you can't sue someone and ",
" use discovery to try to find evidence of wrongdoing. You have to first have evidence of ",
", after which you use discovery to get more support for your claims."
] |
[
"How can we know if higher dimensions exist?"
] |
[
false
] |
How can people possibly know that there are higher dimensions? Is there a sort of deductive process based on evident mathematical principles or is the general method more inductive, based on observations that seem to fit this idea? Furthermore, can the human mind even possibly comprehend a higher dimension? By higher dimension, I mean any dimension above 4, be it temporal, spacial, curled up, or otherwise altered.
|
[
"It's mathematical. Remember, a \"dimension\" is nothing more or less than a degree of freedom. The equations don't care if that degree of freedom is in position space or momentum space or in fact any abstract configuration space."
] |
[
"Here",
" is an experiment that is testing whether extra dimensions modify the strength of gravity at very short scales. They've concluded that an extra dimension must be smaller than 44 microns in size."
] |
[
"All equations."
] |
[
"Why/how are sulfonylureas, meglitinides and injectable insulin effective in the treatment of type 2 diabetes?"
] |
[
false
] |
In type 2 diabetes where the major problem is insulin resistance rather than an absolute inability of the pancreas to produce insulin as in type 1 diabetes, how do drugs such as sulfonylureas and meglitinides that act by simply increasing insulin secretion by pancreatic beta cells, and injectable insulin work in the treatment of T2DM? If the insulin is having a reduced effect because of the body's resistance to it, then how does simply increasing the levels of circulating insulin work?
|
[
"Sulfonylureas work to inhibit the opening of a certain potassium channel (the K_atp channel) which serves to depolarize the beta cell, releasing intracellular granules containing insulin. The depolarization opens voltage-gated Ca2+ channels which set the granule release process in motion. Meglitinides do the same, though they vary in the kinetics at which they bind and inhibit the channel.",
"It is important to note that T2DM isn't always just a consequence of the body's resistance to insulin, but can be due to beta cell dysfunction (low insulin levels). SubQ insulin works because the type 2 diabetic doesn't respond to normal levels of insulin in his/her bloodstream, so we augment it by adding more synthetic insulin. ",
"Source: 2nd year med student!"
] |
[
"The medicines don't work as well a person becomes more insulin resistant. ",
"As a person becomes glucose intolerant the person is started upon a biguanide like metformin which acts peripherally to reduce glucose levels (or inhibits hepatic glucose formation) or a slufonylurea that increases pancreatic insulin secretion.",
"As they become more insulin resistant the person needs to start insultin and then requires increasing dosages. They may ultimately be receiving 3-4 times the amount of insulin that a type I diabetic requires (Type I is a failure to produce insulin).",
"A person with type I diabetes may have glucose control on 30 units insulin daily, whereas a person with fairly resistant type II may be on over 120units daily. So you are broadly correct in wondering about the limitation of insulin in someone with increasing insulin resistance. But, at the moment, we just give more and more insulin to get the same effect. And we continue with the metformin in addition for its peripheral effect."
] |
[
"The idea behind a sulfonylurea is simple. You're right, the patient is insulin-resistant. But more insulin just gives a better response. ",
"I should also mention there is a shift from medications (like snfu's) which stimulate islet cells to other medications which dont cause the pancreas to effectively burn out more quickly. Exanitide and other GLP-1 agonists (and DPP-4 inhibitors, --gliptins) do function to increase insulin secretion, but additionally reduce glucagon levels from the liver effectively reducing glycogen mobilization via gluconeogenesis at night. ",
"Metformin is the gold standard because it doesnt \"burn out\" the pancreas nor does it cause hypoglycemia."
] |
[
"Do rockets suffer from aerodynamic drag caused by truncated tail?"
] |
[
false
] |
I don't know the right terminology so please let me explain. In car and airplane aerodynamics, engineers have to consider not only aerodynamics on the front-facing side of the vehicle, but also on the back side. The idea is to reduce turbulence and low pressure, which has the effect of "pulling the vehicle back". I imagine this by having a moving object creating a vacuum (low pressure) behind itself, which "sucks in" everything around, including the object itself. Better shapes of the object will allow more air to fill out the vacuum (low pressure) area quicker, which will induce lower "pulling" force on the object. Now the question is, what about rockets? If you look on , it clearly shows how the rocket body is simply "cut off", or flat, and then the engine nozzles stick out. In my mind such moving body has to create lots of low-pressure-pulling force in the area between the flat rocket bottom and the tips of the nozzles, especially at high speeds. Now obviously it cannot be perfectly aerodynamic as we may need some nozzle gimballing, or have the incoming air cool the nozzles down a bit, or simply vibrations prevent us covering up the engines/nozzles. But such a flat surface simply looks like a beginner's first attempt at rocket design (no offence :) ). Or is that simply ignored due to short time spent in the dense part of the atmosphere? EDIT: Because there's some confusion, I made a to explain. I am specifically talking about the area between the flat and the end of the nozzle. The red arrows on the picture depict turbulent air. The other rocket design does not suffer from this as there is no such empty space. Just look at the Saturn V tail as I linked before, it has the first design from my picture. I hope it's clear now. Also bear in mind I understand it is not always possible to engineer the second design, I mentioned that above, but it should be possible to do something in-between those two.
|
[
"The implication of the first statement is that the hot gasses in the plume are exerting a force on the rocket. They aren't, or at least whatever force is applied is inconsequential.",
"But they are exerting a force on the rocket. Conservation of momentum doesn't happen by magic; you can't have an acceleration without a force. The rocket is thrust forward by the exhaust pressure in the combustion chamber and nozzle.",
"You're right that once the gases leave the bell of the rocket motor, they're done. They exert force on the rocket ",
" leaving the bell."
] |
[
"it's not the hot gasses in the plume pushing the rocket that makes it move. Rather it's the momentum of the hot gasses being ejected out the engines that causes the opposite momentum to be imparted to the rocket.",
"\"The hot gases push the rocket\" and \"the momentum of the hot gases being ejected causes the opposite momentum to be imparted to the rocket\" are entirely equivalent statements."
] |
[
"Two factors spring to mind.",
"Streamlined trailing edges are important to subsonic aerodynamics, but relatively unimportant in the supersonic regime. Check out the ",
"trailing edges of the X-15",
" There will be a shockwave originating at the corner of the trailing edge. Since aerodynamic disturbances cannot propogate forward of the shockwave, aerodynamics behind the trailing shock are effectively irrelevant.",
"As the rocket climbs air density decreases and correspondingly aerodynamic forces decrease. The point of ",
"maximum dynamic pressure",
" is passed within the first couple of minutes of launch, after which the impotance of aerodynamics decreases to zero."
] |
[
"Can we naturally exhaust our neurotransmitters?"
] |
[
false
] |
So as I know it serotonin and dopamine can be exhausted by certain drugs, and as a result we won't feel as good before they were all used up. The rate of the production also has something to do with this I believe. But say if we were to be naturally happy and social and being around someone we love (oxytocin?) all the time could we exhaust these stores and end up having a natural 'crash' where we don't feel as happy social or in love until these transmitters are restored? thanks in advance :) i'm very curious
|
[
"I can't really comment about the neuromodulators you mention, but there are other neurotransmitters that are used for the more basic excitatory/inhibitory communication between neurons such as glutamate and GABA. These transmitters can also deplete from synapses, or at least lower in their rate of release.",
"For example, there are special types of synapses called ",
"ribbon synapses",
" that are specialized for fast transmission. They are found in places like the retina and cochlea where fast release is important for accurate perception of light and sound, respectively. The ribbon itself is a special structure that assists in the packaging and release of neurotransmitter.",
"When a stimulus first turns on (e.g. light or sound), the already packaged vesicles (packets of neurotransmitter) are released, but this \"readily-releasable\" pool of vesicles quickly depletes. After this, the rate of neurotransmitter release is essentially the rate at which the ribbon synapse can repackage new vesicles.",
"So to answer your question, yes it's possible to for a synapse to exhaust it's supply of neurotransmitter, but that doesn't necessarily mean the rate of release is zero. The rate will depend on (among other things) whether the synapse can repackage new vesicles for sustained release."
] |
[
"Some tremors are caused by a central issue in the brain, rather than a peripheral issue with the muscles, but in general that type of depletion is thought to be quite common.",
"There were some very early studies done of muscle psychology that showed that you can continue to directly electrically stimulate muscle fibers for much longer than you can stimulate the associated nerves to produce muscle contractions. There is even a large number of training regiments that are designed to increase the capacity of your neurons to activate muscles rather than just focusing on muscle strength or endurance directly (I'm not qualified to say how useful those regiments are or if their gains are due to the mechanism the believe it to be). "
] |
[
"I've heard that similar mechanisms can explain fatigue in muscle tissue - that certain types of fatigues can occur where neurotransmitter depletion occurs before 'nutrient' (oxygen, glucose, etc) depletion occurs, causing muscle fiber activation to fail sooner than expected.",
"Do you know if such neurotransmitter depletion is possible? ",
"I've heard this as explanation for some types of muscle tremor, since, by my understanding, muscle activation occurs by activating groups of muscle fibers in a pulse train; the tremors occur because some groups fail to activate while others do, leading to a {fire, fire, fire, miss, fire, fire, fire, miss, ...} pattern, averaging out to tremor."
] |
[
"Why do I constantly get painful (and audible) electric shocks, and how can I stop it?"
] |
[
false
] | null |
[
"We can't comment on personal anecdotes / isolated incidents without resorting to speculation which we try to avoid."
] |
[
"OK. Can you suggest a sub to put this? I can't think of one that's quite right."
] |
[
"You could try ",
"/r/findareddit",
" for help in finding an appropriate sub"
] |
[
"Do beverages get \"flat\" quicker when in a plastic bottle, in comparison to a glass bottle?"
] |
[
false
] |
My workmate has a theory that this is the case. Any facts, theory or science behind it?
|
[
"Yes, they do. Plastic (soda bottles are usually made of ",
"PETE",
", which is much more permeable to CO2 and oxygen than glass is. Similarly, this is why you're unlikely to find wine in plastic bottles/bags unless it's intended for relatively rapid sale and consumption."
] |
[
"The CO2 and O2 will actually diffuse through the PET. It may be strange to think of diffusion happening in solids, but it does, just at a slower rate. Diffusion rates increase with increasing temperatures."
] |
[
"/u/Dpgg94",
" this diffusion is also why bottled water tastes bad after sitting out in the sun. The plastic isn't leeching into the water, rather the oxygen is diffusing out of it. ",
"See here\n",
"https://www.reddit.com/r/askscience/comments/1sdgna/why_does_water_that_has_been_sitting_for_a_while/"
] |
[
"Can left-coiled snails only mate left-coiled snails? And do snails have a gender?"
] |
[
false
] |
I have seen this post in : is this biologically possible?
|
[
"All but a few species of land snails are simultaneous hermaphrodites, male and female at the same time.",
"The whole body is asymmetrical, including the reproductive opening (which is on one side), so if the body orientation is flipped, things don’t line up right."
] |
[
"Most can inseminate themselves but they usually prefer to mate with partner if one is available."
] |
[
"The first part of your question has been well answered by others. The second part depends on what you mean by gender. In biology, we generally talk about animals' sex, based on their biology, which in most cases is either male or female.",
"In simultaneous hermaphrodites, individuals are both sexes at once. So the role they adopt in mating can be called their gender i.e. it's based on behaviour rather than anatomy or genes. Some snails will role reverse during a mating i.e. give and receive sperm. Others will choose one gender role, and this seems to depend on age and size.",
"Hermann PM, Genereux B, & Wildering WC (2009). Evidence for age-dependent mating strategies in the simultaneous hermaphrodite snail, Lymnaea stagnalis (L.). The Journal of experimental biology, 212 (19), 3164-73 PMID",
"DeWitt, T. J. (1996). Gender contests in a simultaneous hermaphrodite snail: a size-advantage model for behaviour. Animal Behaviour, 51(2), 345-351."
] |
[
"What is the speed of gravity?"
] |
[
false
] |
Annihilate a hunk of matter with an appropriate hunk of antimatter, leaving behind only energy. If you're paying attention, you will see the flash before you hear the explosion, assuming that you are performing this test in an atmosphere. (You're crazy if you are.) If you were carefuly monitoring the explosion with a device sensitive to discern the presence or non-presence of the gravitational pull of the mass of matter, would you notice the change in gravitational force before or after you saw the annihilation? Do gravity waves travel faster or slower than light?
|
[
"Some previous threads about this:",
"1",
"2",
"3",
"4"
] |
[
"c"
] |
[
"Thank you!"
] |
[
"Is it infinitely improbable to hit any random point on a sheet of paper?"
] |
[
false
] |
A sheet of paper has infinitely many points on it. When I take a needle, close my eyes and strike the paper at random, the probability of me hitting any random point is one in an infinite. What's wrong with this speculation?
|
[
"If a point is defined as being infinitely small, then your needle hits an infinite number of points when it touches the paper (since the tip of a needle is not infinitely small).",
"The main flaw in your reasoning is that you're trying to translate mathematical models into the real world, where things work slightly differently. For instance, the existence of the Planck length seems to indicate that trying to overlay the mathematical concept of \"an infinite number of points\" on top of a physical object is a meaningless exercise. According to Wikipedia:",
"According to the generalized uncertainty principle, the Planck length is in principle, within a factor of order unity, the shortest measurable length - and no improvements in measurement instruments could change that.",
"So in the real world, you have a finite probability of hitting the finite number of measurable points on a sheet of paper with the finite point of a needle. At the very least, we cannot construct (or even imagine) a physical object that can interact with only one \"point\" on another object."
] |
[
"You do have the issue of how big the paper and needle you are using with those parameters. Your paper could be infinitely small or big, as could your needle.",
"The moment you set a scale to it, you start dealing with real numbers and infinity cant really be used to describe it"
] |
[
"The probability of hitting a specific point is infinitely small (it may or may not be a zero depending on if we care about all that plank length malarkey). The probability of hitting any one of them is 1.",
"It's like the lottery. The probability that you (or a particular person) will win it is very small. The probability that someone, doesn't matter who, will win it is pretty big. "
] |
[
"Can a sane mind be turned schizophrenic?"
] |
[
false
] | null |
[
"Yes. About 1 in every 100 people. Kinda changes the way you view the world and the 'common person' you run into. "
] |
[
"But, just because you have the gene, doesn't mean you're schizophrenic. You need to the code (1%), and you need the trigger. Which, the trigger is different for everyone because it depends on how you personally deal with situations and perception. In most cases, it's triggered by traumatic stress or head trauma. In very rare cases, it can be triggered by just thinking about it. Schizophrenia is very strange, still even to the highest researchers in the field."
] |
[
"Follow up (more of a definition question): what is the state of mind called where you've truly convinced someone they're insane?"
] |
[
"Do all salts taste salty or just NaCl?"
] |
[
false
] | null |
[
"I'm sorry that people are downvoting you. I think people think you're trolling, but I had this very question back in the day, before I took chemistry. ",
"When you think of salt, you're thinking of table salt. Its chemical formula is NaCl -- one part sodium (Na), one part chlorine (Cl). ",
"In reality, there are lots of salts! If you live in a cold place, you'll know that they salt the roads. Perhaps you've used bath salts (or noticed the uproar regarding them about a year back). If you live by yourself, you may have had to buy salts for your water softener. These are all different salts other than the table salt you're used to.",
"In a more general, non-culinary sense, \"salt\" is used to refer to a compound that is ionically coupled (i.e. it has a anion and cation). As such, they can be comprised of a wide variety of materials other than the NaCl that you're used to. If you'd like to learn more about this, the wikipedia page for Salt is a good place to start. ",
"http://en.wikipedia.org/wiki/Salt_(chemistry)",
" . ",
"What Entropius was saying was that it is the sodium in NaCl that makes it taste salty. If your cation is something other than Na, then you might have a compound that is a \"salt,\" but tastes nothing like what you keep on your dining table."
] |
[
"Saltiness is a taste produced primarily by the presence of sodium ions. Other ions of the alkali metals group also taste salty, but the further from sodium the less salty the sensation is. The size of lithium and potassium ions most closely resemble those of sodium and thus the saltiness is most similar.",
"Basically, if your salt doesn't have sodium or something similar to sodium, it may not taste salty at all."
] |
[
"How can it be salt and not salty?"
] |
[
"Why do we always hear about early explorers spreading diseases to natives and never the other way around?"
] |
[
false
] | null |
[
"Repeat question"
] |
[
"Sure thing. I want to know why the early explorers who have been blamed for spreading diseases to the natives of countries they have visited, don't (or from what I've heard) pick up diseases from the natives themselves. ",
"Surely if both groups have been as isolated from each other then they must be as susceptible to different diseases, not just one group. "
] |
[
"These past questions may be able to help you:",
"http://www.reddit.com/r/askscience/search?q=disease+native&restrict_sr=on&sort=relevance&t=all",
"TL;DR version - population density and domestication of animals meaning the immune systems had different susceptibility to species-jumping diseases. "
] |
[
"Would a match be able to burn itself out in zero gravity?"
] |
[
false
] |
So if you lit a match in zero gravity, would it be able to burn itself out? Normally heat rises to move the carbon dioxide out of the way, but in zero gravity it would just form a bubble around the flame. Would there enough oxygen able to get in or would it just choke itself? What about a lighter, which is slightly different? Would it be able to sustain a flame in zero gravity?
|
[
"Sure, but the distribution of burning gas looks different (closer to a sphere). ",
"Here's",
" a video."
] |
[
"Here's what Google turned up.",
"http://www.youtube.com/watch?v=fuFftT6ZR4k&feature=youtube_gdata_player"
] |
[
"Yup, they have KClO3 in them thus the reaction can take place without oxygen."
] |
[
"Can something be waterpoof but not some other liquid proof?"
] |
[
false
] |
[deleted]
|
[
"Yes. Thin sheets of ",
"PDMS",
" are waterproof, but will let multiple organic solvent leech through.",
"In this case, it is really about the polymer being oily/hydrophobic/non-polar. So the water will not go through easily since it is such a strong polar molecule. But a non-polar solvent will find its way through the polymers backbone more easily."
] |
[
"Sure, easily. Nitrile gloves are waterproof and resistant to some common chemicals, but they're also permeable to a lot of solvents. Acetone is a very common organic solvent, and nitrile is at least semipermeable to acetone."
] |
[
"Yes, certainly. In one famous example, the highly toxic liquid ",
"dimethylmercury",
" can easily penetrate waterproof latex gloves, going right through them in seconds. ",
"This example was discovered when a scientist named ",
"Karen Wetterhahn",
" accidentally spilled a few drops of the liquid onto her intact glove during an experiment. Though nobody knew it at the time, that was enough to cause massive, irreversible poisoning. The tiny spill turned out to be fatal, even though it took nearly a year to kill her."
] |
[
"What exactly happens when you delete data from a computer? Where does the deleted data go? Is their residue from the deletion?"
] |
[
false
] | null |
[
"There are two parts to a file system: an index of the data, and the data itself. When you delete a file, you are removing the entry from the index, but the file stays right where it is until the space is needed for another file.",
"When you change a file (or the index itself), it overwrites the applicable portions. If it shortens the file, the parts at the end will probably stay what it was and the index will just mark it as being shorter."
] |
[
"When you empty your trash can, the system doesn't delete the data; instead, it just tells your hard drive that the data no longer exists, although it is still technically on your hard drive, allowing the system to overwrite those segments that previously contained the data.",
"With the proper equipment, one can recover that \"lost\" data, which is why governmental agencies do a thorough wipe of their used hard drives (Setting all the bits to either 0 or F), or sometimes just destroy the hard drive altogether."
] |
[
"Answering the question from a physical perspective...",
"\"Data\" isn't usually a physical substance. It is the interpretation of the state of an object. For different media (hard disks, flash drives, computer RAM) the state is stored in different ways.",
"For spinning platter hard disks, when we change (or delete) data, the alignment of the molecules/crystals on the disk is changed, changing the magnetic field slightly. The molecules/crystals of the disk don't really go anywhere, we simply change the way they are aligned. There is no physical residue from changes to a hard disk (although the realignment only targets the surface of the disk platter and below the surface, there may still be molecules/crystals aligned to previous states).",
"For Flash memory, when we change (or delete) data, the number of electrons accumulated in specific parts of the device are changed. Technically, if you were to set the entire contents of your Flash drive to zero, there would be fewer electrons trapped in the drive. The removed electrons travel out through the electricity circuit (although they don't travel very far and probably don't leave the Flash chip itself). You could say that these removed electrons are physical residue from the change.",
"In any case, the only measurable \"residue\" from any change is usually just heat. Realigning molecules warms up the material. Removed electrons get reabsorbed into circuitry elsewhere and heat that up. Almost everything that you do with electricity eventually ends up as heat."
] |
[
"How are the aluminum compounds in antiperspirants effective in blocking sweat production? What is unique about their acid/base properties that help them do this?"
] |
[
false
] |
- Aluminum chloride - Aluminum chlorohydrate - Aluminum hydroxybromide
|
[
"Aluminum salts form all kinds of gel-like hydrated precipitates in water -- the exact chemical composition depends on pH. In antiperspirants, the aluminum salts interact with moisture coming out of your sweat glands and create precipitates that block the ducts of those glands, preventing sweating. "
] |
[
"For very likely similar reasons, aluminum salts have notable antimicrobial properties and are pretty effective at killing any bacteria in the \"clogged\" areas.",
"Non-aluminum antiperspirants often have to add in another antimicrobial (triclosan, polyhexamethylene, etc.) as a substitute for exactly the reason you state. Well, plus the smell."
] |
[
"Why doesn't this cause a ton of pimples? It was my understanding that pimples and zits come from blocked sweat ducts in the skin."
] |
[
"Bacteriophage Reprogramming"
] |
[
false
] |
[deleted]
|
[
"Are you talking about ",
"phage therapy",
"?"
] |
[
"Possibly however this would increase the complexity of the phage far beyond its physical potential.\nPhage potential complexity can be measured by their size, and usually only come to about 50,000 base pairs, (Lambda phage only have about 48,000).\nFor more information on synthetic organisms the work of Craig Venter et.al. are essentially where the modern stuff starts."
] |
[
"Even if you could, there's no guarantee that an infected harmful bacterial cell would be any better for your body. For example, strep throat is caused by a viral infection. But the viral infection is of bacteria that live in your throat. These dying bacterial cells produce toxins that agitate the human tissue.",
"http://www.articlesbase.com/medicine-articles/bacteriophages-a-newly-discovered-cause-of-strep-throat-113429.html"
] |
[
"What are the chances meteorites hit satellites and space stations?"
] |
[
false
] |
Or on mars, with no atmosphere what are the odds a meteorite will hit the rover and destroy it? Is this risk something they consider? Or is it too rare to care about? Regarding satellites and space stations, surely taking damage from them isn't that rare!
|
[
"Let's look at the math. The surface of a sphere with the same radius the orbit of a satelite (I assume about r=7000km) is 4",
"r",
" so 6.15e8 km",
" = 6.15e14m",
" Assuming 10.000 satelites in orbit and one having a cross section of about 10m",
" we end up at an overall sattelite cross section of 100.000m",
" =1e5 m",
" so the chances are 1e5/(6.15 e14) = 1/6.15 e-9, so less than one in a billion. ",
"That's per meteorite entering the orbit of a satellite. ",
"Edit: Some additional thoughts. ",
"First, that assumes an infinitesimal asteroid. ",
"Second, an asteroid passing through earth orbit should penetrate the mentioned sphere twice. ",
"However, if a non-inifitesimal meteorite penetrates that sphere only once, we have bigger problems than a destroyed satellite."
] |
[
"A good start, next you need the frequency with which meteorites cross that orbital distance. Also, there exist asymmetries in meteorite frequency based on latitude and longitude. Micrometeorites HAVE hit satellites in the past and it is more common than you might think: ",
"http://blogs.smithsonianmag.com/smartnews/2013/06/how-do-you-shield-astronauts-and-satellites-from-deadly-micrometeorites/",
". The key is making sure your ship is properly shielded to survive the mission lifetime."
] |
[
"This maths is beyond me, but does this also assume that the meteorite will hit the orbital sphere directly? If it's at an acute angle it will have a greater chance of hitting something"
] |
[
"Why does a circular paper airplane fly so well?"
] |
[
false
] |
I have been searching for this for a while. A circular winged airplane (like ) works exceedingly well--fold one and throw it like a football if you don't believe me. Yet, i have no explanation for why it works so well. In principle, a circular wing should provide no net force in any direction, yet it clearly has a lift force. My other theory was that air funneled through the center should have a higher velocity and provide a lift force, but the plane stays aloft even without a positive pitch (I would also expect this to create a great deal of drag). So I pose to you, AskScience, why does a circular paper airplane fly so well?
|
[
"I think if a reddit search doesn't find it, it's fair game. Otherwise, reddit might as well abandon its own search and simply link to google."
] |
[
"No offense, but you mind giving us a hint on what you searched for to get to that thread via the search function? The title of that thread if \"Can someone please explain to me why this works so well?\" which is very vague. It doesn't mention the word \"circular\" or \"fly\" and it doesn't mention the word \"paper\" or \"Plane.\" I'm starting to believe the only way you found this thread is by looking through your own comment history."
] |
[
"Ok, I think I've got a reasonably plausible explanation. There are 2 important things in the design of a paper plane: Pitch Stability and Zero Lift Moment.",
"Pitch Stability first. A paper plane is basically a flat plate and flat plate aerofoils suffer from pretty horrendous pitching moments. To remain stable, the plane needs to be sufficiently nose heavy that the pitching force acts behind the centre of mass. Purely because it's stable, a plane can fly smoothly. It might smoothly veer sideways, or smoothly dive, but whatever it does will be reasonably smooth.",
"The next important thing is the Zero Lift Moment. For most paper planes you have a little bit of elevator flap at the back. This provides an upwards pitching moment when the plane is flying flat. The result of this is than instead of being pitch stable about 0 degrees, it's pitch stable about a small positive angle of attack. A flat plate with a small positive angle of attack provides lift, and you've got a working plane.",
"For a standard paper plane: All you need is to be pitch stable, with a small offset.",
"Now for our circular plane. Pitch stability is easy, all the weight is at the nose. But where does it get the offset from? How does it know to fly slightly upwards rather than in a smooth dive.",
"This is why it needs to spin. Because the nose is heavy, it would naturally fall forwards. But as it's spinning like a gyroscope, this forward tipping torque gets transformed into a small left (or right) rotation. Now it's flying at a tiny angle sideways, there's a torque restoring it to straight. Because its spinning this again gets transformed into a rotation upwards. The overall result is that what you should have a slight negative offset, but because its a gryoscope this ends up as a slight positive offset.",
"So to summarise for the circular plane: It's pitch stable like all good paper planes, and relies on gyroscopic effects to get a small pitch offset."
] |
[
"How did scientists figure out how many electrons/protons/neutrons are in each element?"
] |
[
false
] |
I've often wondered how scientists have figured out how each element is composed. You can't see electrons as far as I know, so how do you go about measuring them? Weight? Charge before and after? Some other method?? The reason I ask is because I have always taken the atomic theory at face value, and while I don't doubt it's veracity, I am puzzled as to how we came about it in the first place. Thanks guys!
|
[
"The charge of an electron was figured out by ",
"Milliken's oil drop experiment",
" (even though it was still slightly off - but amazing nonetheless). In short, he sprayed droplets of oil in an electric field and measured how fast they dropped. From there he can calculate how much charge was contained in the drop, and ultimately he found that the charge was some multiple of a constant - the charge of an electron.",
"Prior to that, the mass to charge ratio was discovered by ",
"J. J. Thomson",
". He deflected electrons with magnetic and electric fields, and from the angles at which it was deflected he can calculate the mass to charge ratio.",
"For the rest of the history, I highly recommend ",
"this series",
". That's the link to the first episode. There are three in total, but I can't seem to find them. It's widely available in torrents though."
] |
[
"Chemistry has a fascinating history of scientists figuring out pretty complex natural puzzles with very scant information.",
"Early chemists mostly used weight to determine the results of reactions. From this, they observed that quantities reacted in simple ratios -- for example, Hydrogen+Oxygen -> Water always involved a certain weight ratio of hydrogen:oxygen (in this case, 1:8). At this point, some very simple and inaccurate theories of atomic weight came about (for example, assuming an oxygen atom was 8 times the weight of a hydrogen atom, when actually it's ~16 times). ",
"Further refinement came with knowledge of gas laws: that a gas with twice the number of particles would take up twice the volume at the same temperature (edit: and pressure). This then gave early chemists two pieces of information: ratios of weights, and ratios of number of particles. From this and lots of experimenting, they gradually came up with a list of the relative masses of the fundamental atomic elements: if hydrogen (the lightest) is 1, helium is 4x that, etc. ",
"Turns out if you arrange the elements in increasing order of their masses, they have \"periodic\" similarities with each other. If you put similar elements in columns, you get the periodic table. The relative mass of each element versus hydrogen is the total number of protons+neutrons in its nucleus (approximately).",
"After the discovery of the electron and proton, theories began to take hold as to how electron and proton charge figure in to each element. Quantum theory finally produced a robust prediction of the different \"orbits\" that electrons could be in, and therefore explained why the periodic table has the structure it does (I'm a little fuzzy on the actual timeline here).",
"http://science.jrank.org/pages/634/Atomic-Weight-History.html",
"\n",
"http://en.wikipedia.org/wiki/History_of_chemistry#From_alchemy_to_chemistry"
] |
[
"I'd say so! An error of 1% is damn impressive. I knew the oil drop experiment was precise, never realized he practically nailed the bulls eye. "
] |
[
"AskScience: What would the universe be like if the if the speed of light was 1 m/s?"
] |
[
false
] |
I know there would be a major delay in seeing objects, but what else would this change? Also, would everything appear brighter since light would be "more compact"? Instead of m/s (since pjfoster and xnihil0zer0 pointed out a meter is defined by the speed of light) how about we pretend we use a unit that would remain the same regardless of the speed of light. How about 1 yard/second. Just a clarification, I am saying that c=1 yard/second
|
[
"Special Relativity Simulator",
" on Youtube. It is a simulation of what you would see if the speed of light were 1 m/s."
] |
[
"Further question to this--when you talk about being able to run a letter faster than the information down a wire--wouldn't the \"new\" speed of light still be the \"universal speed limit\"? As in, wouldn't it still be the fastest thing in the universe?"
] |
[
"Further question to this--when you talk about being able to run a letter faster than the information down a wire--wouldn't the \"new\" speed of light still be the \"universal speed limit\"? As in, wouldn't it still be the fastest thing in the universe?"
] |
[
"What are actin and myosin made of?"
] |
[
false
] |
I was curious after reading this article from what exact amino acids are actin and Myocin made of? If there are a lot of amino acids involved, are there specific amino acids I could take that are used to convert into the needed actin sequence? For example taking glutamate supplements would be good for repairing muscle tissue because it can be converted into (let's say) glycine? Original article here! THX!
|
[
"Here is the sequence for the human beta actin protein:",
"MDDDIAALVVDNGSGMCKAGFAGDDAPRAVFPSIVGRPRHQGVMVGMGQKD\nSYVGDEAQSKRGILTLKYPIEHGIVTNWDDMEKIWHHTFYNELRVAPEEHPVLL\nTEAPLNPKANREKMTQIMFETFNTPAMYVAIQAVLSLYASGRTTGIVMDSGDGV\nTHTVPIYEGYALPHAILRLDLAGRDLTDYLMKILTERGYSFTTTAEREIVRDIKEKL\nCYVALDFEQEMATAASSSSLEKSYELPDGQVITIGNERFRCPEALFQPSFLGMES\nCGIHETTFNSIMKCDVDIRKDLYANTVLSGGTTMYPGIADRMQKEITALAPSTM\nKIKIIAPPERKYSVWIGGSILASLSTFQQMWISKQEYDESGPSIVHRKCF\n",
"This is using the single letter code for the amino acids that you can look up ",
"here",
", where glycine is G. In general, you can find any sequence of known proteins with some time by going to the ",
"National Center for Biotechnology Information",
" website (one of the biggest repositories of biotech info) and looking up the protein you are interested in. Try to also name the organism as we have many proteins in different organisms by the same name that might have different sequences.",
"On to your actual question. As you can see for actin, and really for a vast majority of proteins except those that have very unique structural characteristics or super special domains, all the amino acids are used. In general some amino acids are preferred over others, but all are needed in roughly similar quantities. More importantly, however, is that your body has biochemical pathways to convert from one type of amino acid to another, and from other types of biomolecules such as DNA and sugars to amino acids. So eating a specific amino acid will not necessarily make it more efficient to build muscle. Why do supplements use glycine as the amino acid of choice? Because its the cheapest.",
"So just make sure to have enough of the essential amino acids in your diet, since your body can't synthesize those, and get the rest of your protein nutrients from other protein sources, doesn't really matter which."
] |
[
"Since your question seems to revolve around the effect of amino acid supplementation on muscle tissue repair or muscle building, I will address that question, as opposed to just giving you the sequences for the proteins or mRNA etc...which are not particularly useful in answering your question.",
"Here is the short answer...No, loading up on amino acids (in excess of what is needed for normal daily function), will not necessarily provide an increased generation of actin or myosin filaments. They are made of many different amino acids. ",
"There is some evidence from clinical populations that certain amino acids (e.g., arginine, histidine, lysine, methionine, ornithine, and phenylalanine) may stimulate the release of growth hormone, insulin, and/or glucocorticoids and thereby promote anabolic processes. However, there is little evidence that supplementation of these amino acids provides ergogenic benefit for athletes.",
"Branched-chain amino acids and glutamine have been hypothesized to affect central fatigue and exercise-induced immune suppression, but their ergogenic value during prolonged exercise is equivocal at present. ",
"Most studies indicate that creatine supplementation may be an effective and safe means to enhance intermittent high-intensity exercise performance as well as training adaptations. Of the nutrients evaluated, creatine appears to have the greatest ergogenic potential for athletes involved in intense training.",
"Hydroxymethylbutyrate supplementation has been reported to reduce catabolism and promote greater gains in strength and fat-free mass in untrained individuals initiating training. Limited data are available on the effects of HMB supplementation on training adaptations in athletes.",
"Here is more detail...on the supplementation of the amino acids mentioned above and their effect on muscle mass and muscle building. ",
"There is little evidence that supplementation of Anabolic Amino Acids (e.g., arginine,histidine, lysine, methionine, ornithine, and phenylalanine), during training significantly affects body composition, strength, and/or muscle hypertrophy. Consequently, the effects of amino acid supplementation on growth-hormone release and training adaptations are as yet unclear.",
"Researchers have expended a considerable amount of effort on evaluating the effects of supplementation of branched-chain amino acids (e.g. leucine, isoleucine, and valine) on physiological and psychological responses to exercise. There are two primary hypotheses regarding the ergogenic value of supplementation with these amino acids.",
"First, BCAA supplementation has been reported to decrease exercise-induced protein degradation and/or muscle enzyme release (an indicator of muscle damage) possibly by promoting an anti-catabolic hormonal profile.",
"Theoretically, BCAA supplementation during intense training may help minimize protein degradation and thereby lead to greater gains in fat-free mass. Although several studies support this hypothesis,additional research is necessary to determine the long-term effects of BCAA supplementation during training on markers of catabolism, body composition, and strength.",
"Second, the availability of BCAA during exercise has been theorized to contribute to central fatigue. During endurance exercise, BCAAs are taken up by the muscles rather than the liver in order to contribute to oxidative metabolism. The source of BCAAs for muscular oxidative metabolism during exercise is the plasma BCAA pool, which is replenished through the catabolism of whole body proteins during endurance exercise. However, the oxidation of BCAAs in the muscle during prolonged exercise may exceed the catabolic capacity to increase BCAA availability, so plasma BCAA concentration may decline during prolonged endurance exercise.",
"Some researches have suggested glutamine supplementation as a strategy to promote muscle growth. They based the suggestion on animal and human studies of the effect of glutamine on protein synthesis, cell volume, and glycogen synthesis. Glutamine is also an important fuel for white blood cells,so reductions in blood glutamine concentration following intense exercise may contribute to immune suppression in overtrained athletes.",
"Preliminary studies indicate that supplementation with branched-chain amino acids (4 to 16 g) and/or glutamine (4 to 12 g)can prevent the decline or even increase glutamine concentration during exercise. In theory these changes in glutamine concentration could have beneficial effects on protein synthesis and immune function. However, in the few studies of increased glutamine availability, there was little or no effect on performance or immune status. It is also unclear whether long-term supplementation of glutamine affects protein synthesis, body composition, or the incidence of upper respiratory-tract infections during training.",
"Creatine is a naturally occurring amino acid derived from the amino acids glycine, arginine, and methionine. Most creatine is stored in skeletal muscle, primarily asphosphocreatine; the rest is found in the heart, brain, and testes. The daily requirement of creatine is approximately 2 to 3g; half is obtained from the diet, primarily from meat and fish,while the remainder is synthesized. Creatine supplementation has been proposed as a means to \"load\" muscle with creatine and phosphocreatine (PCr). In theory,an increased store of creatine or phosphocreatine would improve the ability to produce energy during high intensity exercise as well as improve the speed of recovery from high-intensity exercise.",
"A number of studies have been conducted to determine the effects of creatine supplementation on muscle concentrations and performance. Creatine supplementation (20 g per day or 0.3 g per kg body mass perday for 4 to 7 days) has been reported to increase intramuscular creatine and phosphocreatine content by 10 to 30%. There is also evidence that creatine supplementation enhances the rate of PCr resynthesis following intense exercise. Most studies indicate that short-term creatine supplementation increases total body mass, work performed during multiple sets of maximal effort muscle contractions, and single and/or repetitive sprint capacity. In addition,long-term creatine supplementation during training has been reported to promote greater gains in strength, fat-free mass, and sprint performance. However, it should be noted that not all studies report ergogenic benefit and that caffeine has been reported to counteract the potential ergogenic value of creatine supplementation. Although more research is needed, creatine supplementation appears to be a safe and effective nutritional strategy to enhance high intensity exercise performance and improve training adaptations.",
"The leucine metabolite hydroxymethylbutyrate (more exactly the calcium salt of b-hydroxy-b-methylbutyric acid) has recently become a popular dietary supplement purported to promote gains in fat-free mass and strength during resistance training. The rationale is that leucine and its metabolite a-ketoisocaproate (KIC) appear to inhibit protein degradation, and this anti-proteolytic effect may be mediated by HMB. Animal studies indicate that approximately 5% of oxidized leucine is converted to HMB via KIC . The addition of HMB to dietary feed improved colostral milk fat and growth of sows, tended to improve the carcass quality of steers, and decreased markers of catabolism during training in horses. Supplementing with leucine and/or HMB may therefore inhibit protein degradation during periods associated with increased proteolysis, such as resistance training.",
"Although much of the available literature on HMB supplementation in humans is preliminary in nature, several recently published articles and abstracts support this hypothesis. Leucine infusion appears to decrease protein degradation in humans. HMB supplementation during 3 to 8 weeks of training has been reported to promote significantly greater gains of at-free mass and strength in untrained men and women initiating resistance training. In some instances these gains were associated with signs of significantly less muscle damage (efflux of muscle enzymes and urinary 3-methylhistidine excretion). Although these findings suggest that HMB supplementation during training may enhance training adaptations in untrained individuals initiating training, it is less clear whether HMB supplementation reduces markers of catabolism or promotes greater gains in fat-free mass and strength during resistance training in well-trained athletes. Indeed, there are several reports of no significant effects of HMB supplementation (3 to 6 g per day) in well-trained athletes."
] |
[
"Muscles are composed of more than just those two proteins. so loading up on the amino acids for actin and myosin would be as effective as loading up on beta-carotene for the end purpose of improving your eyesight. It will help you maintain and grow but it's not going to supercharge your body."
] |
[
"When the \"temperature\" of the CMB is described as being 2.7K, is this describing the blackbody spectra or some other statistical mechanics way of measuring temperature?"
] |
[
false
] |
I've found contradictory information on this point when trying to research it before. I'd always assumed that 2.7K referred to the apparent blackbody radiation spectra of the big bang afterglow, but redshifted due to the expansion of space. However, I read a comment on another thread a while ago that made the claim that 2.7K was some statistical mechanical measure of the temperature of the resulting . I never did take a statmech class, so I'm a bit clueless on that part of it. Are the two even related? Which does the 2.7K figure relate to?
|
[
"Blackbody."
] |
[
"Those two are the same thing. Same distribution, same physical idea. Photons are emitted from a perfect absorber (so that the emission spectrum is independent of any incident spectrum), and the emitted photons are in thermal equilibrium with that absorber.",
"Another way to think of them being the same is that a blackbody spectrum is the same spectrum as a gas of photons trapped inside a container whose boundaries are perfectly absorbing (so you're thinking about the \"interior\" of the blackbody)."
] |
[
"It fits the black body radiation very well. "
] |
[
"How does gravity affect fire? Theoretically if we were to artificially increase or decrease gravity would it affect a flame?"
] |
[
false
] | null |
[
" The higher the gravity, the more 'teardrop' shaped a flame will be, and the less gravity, the more spherical.",
" To answer your question with a picture, check this out - ",
"the candle on the left is on earth, but the one on right is in space.",
" Since there isn't a preferred direction (on earth is given by the direction of gravity), the flame in space remains spherically symmetric and the heat diffuses away radially. On the earth, the hot air can rise, which produces the familiar flame shape. ",
"This isn't a property of air, or even a property of temperature, it's a property of ",
" I mentioned a 'preferred direction' in the last paragraph because in an accelerated frame (like the earth under normal gravity, or in a car that's stepping on the gas), there is pressure gradient. Stuff at the bottom gets the stuff on top of it pressing down on it. The result of this pressure gradient is a force that tends to sort materials by their relative densities- the densest things go to the bottom, and the less dense things go to the top. This force has a name- the buoyant force, and it's the reason why oil floats on water, or why hot air (which is less dense than cold air) rises. ",
"In space, you're in freefall, so this pressure gradient doesn't form. The result is that things don't 'sort' themselves in space in the same way they do on earth. If you increase gravity, the bouyant force increase, so I imagine that the flame becomes more strongly teardropped because hot air which is less dense will more quickly diffuse upwards. If you decrease gravity then you decrease the bouyant force, so your flame will become more spherical.",
"On a completely unrelated note, if you want to do an experiment about how fluids behave in weightless situations, you don't actually have to go to space, you just have to get one of those salad dressings that has oil and vinegar and water that you have to shake up before using. If you shake it, it will always sort itself so that the oil is on top. If you take it on a roller coaster that has a long vertical drop, and shake it up at the top, the oil and water won't actually settle back out while you're in free fall, but right when you hit the bottom you'll experience a strong decelerating force, and the salad dressing will settle very suddenly - faster than it otherwise would if you were just standing around. I've actually done this experiment, and it is wicked cool. If you could do this experiment with a candle, without having it getting blown out (perhaps by keeping it in a sealed container) you should be able to see the flame do a dance between tear drop shaped, to sphere, back to tear drop shaped. "
] |
[
"I went to youtube and searched \"space fire\".",
"Here is the video of the picture you linked. ",
"New Form of Fire Seen Aboard the Space Station",
"And here is another video result: ",
"Fire In Space - It's Not What You Know\n",
"And here is an article from space.com which pretty much says everything OP said. ",
"Fire Burns Differently in Space, Space Station Experiment Shows"
] |
[
"right when you hit the bottom you'll experience a strong decelerating force, and the salad dressing will settle very suddenly - faster than it otherwise would if you were just standing around",
"I'm a bit short on roller coasters at the moment. Couldn't you reproduce just this by swinging the bottle around on the end of a rope?"
] |
[
"Why do cleaning/washing products only claim to kill 99.9% of germs?"
] |
[
false
] |
Why can they not claim to kill 100%? Are there some bacteria that are resistant to these products or is it just for legal reasons?
|
[
"This is actually a statistics issue, not a legal issue. In order to make the claim that something is a disinfectant (i.e., it actually kills germs), you have to run tests and gather data. Numerical data is always reported in terms of confidence intervals and significance, which means you always have some variability. So, the 99.9 is really an artifact of the number crunching."
] |
[
"In the same line, it's also too expensive to prove that you killed 100% of them. "
] |
[
"http://www.reddit.com/r/askscience/comments/n29fi/when_a_soap_says_it_will_kill_999_of_germs_what/",
"\n",
"http://www.reddit.com/r/askscience/comments/mtoqi/what_is_the_01_of_germs_that_my_soap_cant_kill/",
"\n",
"http://www.reddit.com/r/askscience/comments/kyhr1/kills_999_of_germs_so_why_hasnt_the_surviving_1/",
"\n",
"http://www.reddit.com/r/askscience/comments/ix2m6/my_bottle_of_bleach_claims_to_kill_999_of_all/",
"etc"
] |
[
"How is a Honey Bee's sting evolutionarily advantageous if it dies after using it?"
] |
[
false
] | null |
[
"It's less about the survival of the individual honeybee and more about the survival of the colony. If a small number of bees attack an intruder and fend that intruder off, then the colony survives even though a small number of individuals died defending it. There's really no selective pressure to produce more robust and stronger individuals because that would make each single bee more energy dependant and that would be less economical to have a colony of strong bees that have an exponentially higher calorie demand opposed to a bunch of weaker,more energy efficient bees that suffer a few casualties while defending the hive"
] |
[
"Because only the queen and the drones reproduce. The death of the worker does not reduce the reproductive success of the bees that reproduce. In fact the death of the drone can prolong the life of the reproducing bees in the hive, and hence their reproductive success, by discouraging attacks on the hive. "
] |
[
"I think for yourself you may find the wikipedia entry on ",
"eusociality",
" interesting. \"Eusocial animals have appeared paradoxical to many theorists of the field of evolution, including W. D. Hamilton: if adaptive evolution unfolds by differential survival of individuals, how can individuals incapable of passing on their genes possibly evolve and persist? Since they do not breed, we ought to expect any genes causing this condition to be highly unlikely to persist in the population. In Origin of Species (first edition, Ch. 8), Darwin called this behavior the \"one special difficulty, which at first appeared to me insuperable, and actually fatal to my theory.\" Darwin anticipated that a possible resolution to the paradox might lie in the close family relationship, but specific theories (e.g. kin selection or inclusive fitness) had to wait for the discovery of the mechanisms for genetic inheritance.\" The article goes into further detail into how eusocial animals have evolved. Basically, even though the worker dies it is so closely related to the queen (who does all the reproduction) that anything the worker does to improve the survival or reproductive success of the colony ultimately enhances its own fitness indirectly. For more on this see ",
"kin selection",
" and \"Inclusive Fitness\".",
"For yourself or others the following may also be informative. The public often lumps all bees and wasps together however they are very different.",
"European Honeybees",
": The female workers have a barbed stinger and when they sting you they do die (the barbed stingers are only found on the worker bees). Female queens also have stingers, but these are not barbed so they could sting you more then once. \"It is presumed that this complex apparatus (the stinger/venom sac), including the barbs on the sting, evolved specifically in response to predation by vertebrates, as the barbs do not usually function and the sting apparatus does not detach unless the sting is embedded in fleshy tissue. While the sting can also penetrate the flexible exoskeletal joints in appendages of other insects\"...it does not detach, so the honeybee worker does not die. Honeybees are not native to North America, they are colonial nesters that we use to pollinate our crops. When you hear people talking about colony collapse disorder or disappearing bees, they are usually talking about honeybees. ",
"Wild bees, like ",
"bumblebees",
" lack a barbed stinger so they can sting you more then once with no lethal effect to themselves. Both queens and workers have stingers. Bumblebess and other wild bees (e.g. leaf cutter bees, orchard mason bees, carpenter bees etc.) are semi-colonial or solitary nesters. As a result they are not as defensive/aggressive as honeybees. Not all wild bees have stingers that can sting, e.g. ",
"the stingless bees",
". Bumblebees and other wild bees are native to North America and are important pollinators for local wild flowers. If you have a backyard you can attract helpful wild bees by setting up bee nest boxes. Wild bees are subject to a number of negative impacts due to human activity, including habitat loss and insecticide/pesticide use. Wild bee populations are in decline in some areas and this is cause for concern as bees are good indicators of the health of the local environment.",
"In general, a ",
"\"wasp\"",
" is an all encompassing word used by the public to incorrectly describe anything that resembles a bee. I.E. \"wasp\" and \"bee\" are used interchangeably, despite the fact that they are categorized very differently by entomologists. In any case, most people when they use the word \"wasp\" are typically referring to a ",
"yellow jacket",
" which also has a barbed stinger although they are capable of stinging more then once if the barb is cleanly removed. True wasps can either be colonial or solitary nesters. Not all wasps are aggressive and most wasps are parasitic with other insects. "
] |
[
"What causes a blister to hurt soo much when popped?"
] |
[
false
] |
When I compare it to a cut that goes much deeper than a blister, the cut doesn't have much pain compared to it. What causes it pain and why does it get easily infected?
|
[
"Please read what I wrote, I see you have just skimmed it. \n\"When I compare it to a cut that goes much deeper than a blister\""
] |
[
"This answer still applies. Do a quick calculation of surface area of the cut vs a blister. ",
"For a cut, the surface area can be something like 1 inch long X .25 inches deep X 2 because the cut has two sides= .5 square inches. ",
"For a blister, its surface area could have a radius of .5 inches, so its area would be pi X .5",
" X 2 sides= 1.6 square inches for a blister the same size as a cut, even though the cut is very deep. ",
"To equal the same surface area, a 1 inch cut would need to be .75 inches deep, which is almost the width of your thumb. A cut that goes .25 inches is already a serious one, so tripling that would be a huge wound. ",
"This also has to do with a much higher density of sensory nerves on the surface of your skin that decrease with depth, so cuts aren't crossing the same number of nerves that a blister does. "
] |
[
"Ok, I guess it's not 100X bigger, but a cut still has less surface area and nerve density"
] |
[
"Why can't we rotate antibiotics?"
] |
[
false
] | null |
[
"Hi inkoDe thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'"
] |
[
"You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'"
] |
[
"Why do bubbles in my water bottle stick to the sides?"
] |
[
false
] |
I was waiting to enter my calc 3 lecture one day and started to wonder why all the bubbles in my water bottle did not just float to the top. - sorry for the poor picture, this is my water bottle I know that water can have gases dissolved and as the water warms these gases for bubbles but why do they stay there? I knew from the fluids chapter in my physics class that the pressure below the bubble, so it should rise. The fact that they don't led me to two possibilities: Are either of these correct? Why does the bubble not move?
|
[
"The surface tension of water is a high energy state, so to create surface area on water, it requires energy. Having part of the bubble's surface made up by the inside of the bottle requires less energy than the whole bubble being surrounded by water, so it stays because that is the lowest energy / entropy state."
] |
[
"The bubble is, at that point, in a state of force balance. There is a buoyant force created by the pressure difference you mention, however, there are drag forces of the bubble against the water, and against the wall which balance it (shear).",
"In static situations this force is dominant. When even small flow velocities are incurred the momentum of the higher density fluid dominates and you get a net motion of the droplet that is effectively the same as the bulk fluid. This is why that bubble moves to the top of the container when a small net motion is introduced (also because it is pulled away from the wall and bouyancy can provide enough force to overcome the drag forces previously acting against the wall).",
"Computational simulation has had a fair amount of success with this type of problem using homogenous models. This is a summary of several mathematical approaches with various strengths and weaknesses for the interfacial drag between the two fluids, and the bubble against the wall can often be resolved with the viscosity (possibly a limited slip model if a high knudsen number). The Grace Drag model is a commonly used approximation.",
"http://www.arc.vt.edu/ansys_help/cfx_thry/i1304903.html"
] |
[
"Great explanation, thank you! "
] |
[
"Is there a difference in reading comprehension when reading an ebook vs. traditional print?"
] |
[
false
] | null |
[
"It was an interesting read, but it feels a lot like an op-ed piece that is on a mission to prove the writer's bias as being correct rather than just letting facts tell the story.",
"It goes on - at great length - to point out that reading a book is generally more efficient than reading on a LCD or CRT screen - usually by using one of the worst formats possible for on-screen presentation (pdf) to compare it against. One study mentioned gets two different groups to search for specific information in both formats, but specifically disallows everything that makes the electronic variant the superior choice for searching.",
"It mentions, but completely glosses over e-ink, and tries to downplay the efforts to simulate a book-like experience (in a \"why bother when we already have books?\" vein) on an electronic device without really exploring whether or not the efforts are paying off, or talking about the many benefits that come with electronic methods. It also dedicates a fair amount of time to point out that the studies don't produce consistent results, but continues to act as if the science only points one way."
] |
[
"It was an interesting read, but it feels a lot like an op-ed piece that is on a mission to prove the writer's bias as being correct rather than just letting facts tell the story.",
"It goes on - at great length - to point out that reading a book is generally more efficient than reading on a LCD or CRT screen - usually by using one of the worst formats possible for on-screen presentation (pdf) to compare it against. One study mentioned gets two different groups to search for specific information in both formats, but specifically disallows everything that makes the electronic variant the superior choice for searching.",
"It mentions, but completely glosses over e-ink, and tries to downplay the efforts to simulate a book-like experience (in a \"why bother when we already have books?\" vein) on an electronic device without really exploring whether or not the efforts are paying off, or talking about the many benefits that come with electronic methods. It also dedicates a fair amount of time to point out that the studies don't produce consistent results, but continues to act as if the science only points one way."
] |
[
"I simply don't remember as much from a book that was read on a device that can easily browse Reddit, check work emails or play Angry Birds in an instant. ",
"How do you play Angry Birds on a e-ink device?"
] |
[
"Is watching TV in the dark bad for your eyes?"
] |
[
false
] |
[deleted]
|
[
"I like have a TV light on. It's a very low watt lamp behind the TV that casts a little light onto the wall. It makes for less contrast between the bright light from the TV and the otherwise dark room.",
"Also: ",
"http://www.sciencedaily.com/releases/2006/04/060425015643.htm"
] |
[
"So is it bad to watch movies in theaters as well?"
] |
[
"I'd like an answer to that too, but reading the article quoted above...",
"visual discomfort is caused by the ",
" in luminance between the television screen and the room’s dark background",
"Since the screen in a theater is so large itself (guessing it covers more than 3/4th of my visual space - in comparison to a television screen which covers only about, what 1/5th?), theater screen shouldn't have that large ",
" in luminance, right? And so, by this logic, would it be rather more beneficial to watch large television/computer screen in the dark up close rather than far off?"
] |
[
"How does the perception of spice scale?"
] |
[
false
] |
With the YouTube show , the host and guest eat increasingly spicier wings as the interview goes on. Why does it seem that the 100k-300k Scoville range hits much harder than the 1m-2m Scoville range?
|
[
"The flagship chemical in hot peppers is called Capsaicin, which basically works by tricking your brain into thinking your mouth is on fire.",
"No, seriously.",
"your tongue and mouth are covered with a chemical receptor called the Transient Receptor Cation Channel V1 abbreviated as TRPV1. The purpose of this organic molecule is to measure dangerous levels of heat. They're the same Proteins (along with generic nociceptors) that activate when you drink your coffee before it cools. You may observe people reacting to spicy food, and overly hot (temperature-wise) food in the same manner, such as panting or drinking cold water etc.",
"Just like any chemical receptor on your body, TRPV1 when exposed to a continuous stimuli, in this case being the capsaicin in the pepper sauce, exhibits a phenomenon called Desensitization. This is your brain's way of \"bookmarking\" the response until it ceases, preventing new, potentially dangerous stimuli from being overlooked by the same receptors.",
"In the case of Hot Ones (I'm a big fan of that show by the way) the guest's relatively nonchalant response to the hotter sauces is due to the brain desensitizing itself from the capsaicin from the first few sauces. If the guests waited about 15 minutes for the desensitization from the first sauces in the brain to diminish, the hotter sauces would cause a much more exciting reaction from the guests."
] |
[
"This may not completely answer your question, but one thing to point out is that Scoville was originally based on how far you could dilute a spicy food and still detect it. For example, 100 Scoville meant that you could detect it in a 100:1 dilution, while 100,000 meant you could detect it when diluted by a 100,000:1."
] |
[
"Do you know of any desensitization curves for TRPV1? Where is the point of diminishing return for higher Scoville?"
] |
[
"In Carbon Dating, why hasn't all the Carbon-14 decayed over the millenia?"
] |
[
false
] |
I understand how carbon dating works, but I'm wondering how there are any carbon-14 to test when it has a half life of 5700 years. Wouldn't it have all decayed over millions of years?
|
[
"This is covered pretty well in ",
"http://en.wikipedia.org/wiki/Carbon-14",
". Basically carbon-14 is produced in the upper atmosphere and absorbed by living creatures (by respiration). When the creature dies, it no longer absorbs carbon-14, so you can use that for a while to date when it died."
] |
[
"Carbon-14 dating doesn't work to date objects from millions of years ago, as you have rightly concluded. You can use it back to around ",
"50,000 to 100,000 years",
".",
"There are other decay processes that can be used for earlier times. You can read about some of them ",
"here",
" and ",
"here",
".",
"Edit: As ",
"/u/walexj",
" points out, OP may have intended a different question, which ",
"/u/pobody",
" has answered. Maybe OP can tell us which question was intended."
] |
[
"I think the OP is more concerned with where any 'new' C14 comes from."
] |
[
"How small and detailed could we make a Fresnel lens?"
] |
[
false
] |
Seeing them in the wild, you either look at it from a distance or they're quite grainy, I know they're cheap. So, probably the image might look slightly like the way insect-vision is portrayed in movies, segmented like, but if we can make the tiny tiny little mirrors and sensors in DLP projectors and smartphone camera sensors, (I don't know if the features are smaller on phone cams or pro 16k cams or what) is there any way, expensive and convoluted it may be, to manufacture a super small scale fresnel lens that would provide a clear picture. I understand this would likely never be profitable in a smartphone or anything but I just love the idea of a telescope that's much wider than it is long, or a pair of binoculars that's scarcely thicker than some thick glasses. In case you can't tell I don't know how optics work.. I flaired it for Engineers because I suppose that's closest? Rather than physics? I also just imagined a microtelescope could be made using a DLP mirror module as the collecting mirror with a little sensor in front of it, the uses however, escape me, aside from proof of concept or just messing about.
|
[
"In an ordinary Fresnel lens, the step changes in thickness are not especially damaging to their performance; you can mostly ignore them. But as the steps get closer together, they start to really matter. You end up in a regime where the device would be considered a diffractive optical element (DOE).",
"The steps should have a height that depends on the wavelength, and on the angle of incidence. A \"blazed grating\" is an example of a diffractive element that has a simple sawtooth pattern. The main use of such a device is to disperse different wavelengths into different directions, and to do so with a high efficiency into one direction in particular.",
"DOEs are very useful devices, and they can be cheaply manufactured. You heat up a soft material, and you press a hard stamp into it - that's a form of nanoimprint lithography (NIL). It's not out of the question to find a DOE in a consumer product. (For example, many credit cards have a plastic hologram.)",
"Unfortunately there is a catch to making a diffractive lens: the exact shape of the DOE has to be tuned to the wavelength of interest. A DOE that efficiently focusses one wavelength to a tiny point, will be unlikely to focus another wavelength to the same point. So that's a challenge to using them in a colour camera."
] |
[
"The main advantage of the Fresnel lens is that the lens itself is much thinner and lighter than an equivalent normal lens. But small lenses are already lightweight so there is very little to gain from switching to a Fresnel lens.",
"A Fresnel lens does not automatically make the whole optical system shorter. A camera lens with a Fresnel lens element may be somewhat shorter than a conventional lens because a Fresnel lens is acting like a much thicker lens than what's in a conventional lens. But it doesn't magically flatten it to a pancake."
] |
[
"As your gradations approach the wavelength of the light you're dealing with, your efficiency falls off a cliff. I'd guess 10-100x wavelength is the theoretical lower limit? It's not going to really make a clear picture for the camera though, these lenses are mostly used to focus the flash."
] |
[
"How do power plants, on a national grid level, figure how much electricity to generate?"
] |
[
false
] |
The amount is dynamic based on consumption. I may or may not turn on the AC for instance. How do the plants ramp up or ramp down production that is so closely tied to consumption in real time?
|
[
"One of the parameters that can keep the energy net in check is the kinetic energy of the generators. When more energy is being used than there's been produced, the generators will start spinning slower, feeding their lost kinetic energy into the net. This wikipedia page has some nice information: ",
"https://en.wikipedia.org/wiki/Automatic_Generation_Control",
"Control systems at the power plants make sure more fuel is fed to get the frequency back up."
] |
[
"Well, among other things, they can try to predict peaks and valleys in the usage, and lower production in times of the day or year where people would be too hot for a heater and too cold for an AC. They make that prediction based on past usage, demographic changes, temperature variations, even data on unemployment rates (higher unemployment means more people at home during the hottest parts of the day).",
"It's all very complex.",
"Occasionally, they underestimate need, or worse demand skyrockets out of proportion. This leads to blackouts and brownouts.",
"As for your individual desire to turn on your AC, that in itself is a tiny fraction of the overall usage and rarely makes a difference."
] |
[
"Think of it this way. At any given time there could be any number of drivers using a certain road. Yet oddly there generally is a consistent flow of traffic. Adjust it for the time of day you could make a pretty good guess at the rate of cars. ",
"It's the same with power. You might think what if everyone plugs in at the same time! Same thing with cars. If everyone drove at the same time bad things happen. Like rush hour. But in general that doesn't happen too often. It can though. But power stations and plants generally have some wiggle room."
] |
[
"[Physics] If the universe is expanding, that must mean that space is being created. If space is being created, then is time also being created? If so, what does that even mean exactly?"
] |
[
false
] | null |
[
"that must mean that space is being created.",
"Why must it mean that?",
"If space is being created, then is time also being created?",
"I'm not sure of the link you are trying to establish here. Whether or not the future and past really exist is a philosophical question."
] |
[
"Space can't exist without time right? If the universe is expanding, that means space is being created, right? And if space is being created, wouldn't that mean that time is being created?"
] |
[
"Within the current paradigm of physics these are not well posed statements or questions. ",
"Space can't exist without time right? ",
"In the same sense that left \"can't exist\" without up, i.e. they happen to both exist but there is no reason they had to.",
"If the universe is expanding, that means space is being created, right?",
"How do you define space being created? The expansion of the universe is analogous to a map with a scale which depends on time, you don't need more paper.",
"And if space is being created, wouldn't that mean that time is being created?",
"Again I'm not sure this has any real defined meaning. There is a philosophical, not scientific (at least at the moment), question of the nature of time. As a philosophy layman I can only tell you what wikipedia does so here are the links to the first three points of view I found: ",
"presentism",
", ",
"eternalism",
" and ",
"growing-block-ism"
] |
[
"How do we still have radioactive particles on earth despite the short length of their half lives and the relatively long time they have been on earth?"
] |
[
false
] |
For example carbon 14 has a half life of 5,730 years, that means that since the earth was created, there have been about 69,800 half lives. Surely that is enough to ensure pretty much negligable amounts of carbon on earth. According to wikipedia, 1-1.5 per 10 cabon atoms are carbon 13 or 14. So if this is the case for something with a half life as long as carbon 14, then how the hell are their still radioactive elements/isotopes on earth with lower half lives? How do we still pick up trace, but still appreciable, amounts of radioactive elements/isotopes on earth? Is it correct to assume that no new radioactive particles are being produced on/in earth? and that they have all been produced in space/stars? Or are these trace amount replenished naturally on earth somehow? I recognize that the math checks out, and that we should still be picking up at least some traces of them. But if you were to look at it from the perspective of a individual Cesium or Phosphorus-32 atoms it seems so unlikely that they just happen to survive so many potential opportunities to just decay and get entirely wiped out on earth. I get that radioactive decay is asymptotic, and that theoretically there should always be SOME of these molecules left, but in the real world this seems improbable. Are there other factors I'm missing?
|
[
"Yes, carbon-14 is constantly being produced on Earth, for example by nuclear reactions in the atmosphere caused by cosmic rays."
] |
[
"Radioactive materials with short half-life are produced naturally on earth through:",
"Radionuclides which have a short half-life and are not found in decay chains of longer-lived isotopes are, indeed, not found naturally on earth, except in tiny trace amounts; for example, pretty much any isotope of Technetium"
] |
[
"Which is why it's useful for dating. C14 (in CO2) is produced in the atmosphere, then captured by plants and turned into larger carbon molecules, which then potentially get eaten. Once the carbon is out of the atmosphere, no new C14 is produced and it'll eventually all decay, so you can measure how long ago the carbon was absorbed by a plant."
] |
[
"Does the mass of an object affect the intensity of the sonic boom that it creates when traveling at mach speeds?"
] |
[
false
] |
I am a tour guide at a museum in New York City with several prominent supersonic planes. Several days ago two of my fellow tour guides got into an argument about the effect an objects mass has on the intensity of the sonic boom that it creates. One believed that two objects with the same external shape would create different sounds as they passed the sound barrier if their mass was different, and the other believed that they would make the same sound. So, if there were two Concordes flying at the same mach speed, say 1.5 times the speed of sound, one loaded with passengers and cargo, the other empty, would the heavier Concorde make a louder "boom?" Also, there was some confusion in the debate between mass and weight, these two concepts are different, but does it make a difference in this context?
|
[
"The only factors that matter for the creation of shock waves in atmospheric flight are outer geometric profile (size, shape), orientation of that geometry relative to the free stream, airspeed, and air temperature."
] |
[
"Yes, I agree. Mass (or density) of object does not matter. What only matters is the outer geometry of an object. ",
"In OP's example - two identical Concorde planes, only differing in total mass, the sonic boom will be the same in both cases."
] |
[
"Gross wieght definatly has an effect on the shock wave as seen in this paper published by NASA ",
"http://www.nasa.gov/centers/dryden/pdf/88387main_H-2068.pdf",
" "
] |
[
"If an electric motor is supplied power but restricted in turning (like holding back a ceiling fan) what is happening which would cause it to 'burn up'?"
] |
[
false
] | null |
[
"When a motor is turning, that rotation generates a voltage, a 'back EMF', that acts against the flow of current. It is this voltage, not the resistance of the coils, that restricts the amount of power the motor draws. And as this is an impedance, it doesn't generate heat. The power - the current in the motor pushing against this voltage - is what turns the motor.",
"When the rotor is locked, there is no back EMF to impede the flow of current through the motor. All the electricity flowing through the motor is converted to heat by the resistance of the windings. This quickly overheats the wiring, melting insulation, creating shorts, reducing the resistance and further increasing the current, until some wiring melts and blows."
] |
[
"An impedance it's just a complex resistance so it's false to say it doesn't make heat, it can and in a motor it does. But the back emf limits the current and hence power and hence heat. As speed slows back emf drops, impedance drops, current rises, power rises, heat rises.",
"You don't have to stop a motor to lower the impedance either, any load on the motor will slow it which reduces back emf and increase current power and heat. My electric lawnmower overheats for example if I get to aggressive with the tall grass.",
"Compounding the issue is the fact that most motors are air cooled and the slower they turn the less effective the cooling becomes."
] |
[
"I second this post. Over my years of attending scrapheap challenges at the university where we make robots out of printers, this story is not only consistent with the theory but also with the practice. Motors that can't turn can draw much larger currents than when they do. The explanation offered here is also in harmony with that."
] |
[
"How do scientists know what specific genes to put/insert in GMOs?"
] |
[
false
] |
Since there are a lot of genetically modified organisms, how do scientists know what type of gene or what specific gene to put/insert in GMOs to obtain the best produce?
|
[
"You have to work backwards from what the desired phenotype is, what protein(s) are responsible for that phenotype, what genes are responsible for creating those proteins. ",
"Mapping the genome of many organisms has been a goal for many years after we conquered sequencing."
] |
[
"By observing the gene's effects in its native organism? Geneticists aren't making genes from scratch. At most they are modifying what nature has already created, and then introducing them into their organism of interest. Then they would still observe their modified organisms throughout their lifespan to ensure it has the intended effect."
] |
[
"A lot of times GMOs are just crossbred plants that exhibit exceptional toughness, high yield, resistance to parasites, etc. Basically if this plant grows up to better than other plants through one way or another it will be used to crossbreed. ",
"For instance if this berry bush has higher than average fruit yield while this other berry bush has sweeter fruit than average then the gardener will cross pollinate these plants and grow the seeds in hope of getting a plant that has the the fruit yield of the first one with the sweetness of the other one. They grow many plants from this crossbreed to find the plant with both traits then they either clone that plant or use it to grow plants with those traits."
] |
[
"Is the longest Neuron in the human body visible to the naked eye?"
] |
[
false
] |
The longest neuron in the human body, according to my AP Biology class, is 1 meter long and runs down the leg(s). Would it be possible to see it without any aid, or is it still too small to be seen? Would someone be able to feel it if it was draped across their hand?
|
[
"You’re thinking of neurons of the sciatic nerve, which runs from your toes to your spinal column. The nerve itself is visible to the naked eye as it is quite large. At mid thigh the nerve contains approximately 27,000 axons. However, a single axon (while the size may vary) is approximately 1-20um in diameter, simply too small to see with the naked eye. If you wanted to visualize a single axon with the naked eye your best bet is the Giant Squid Axon, which can reach a diameter of 1mm. ",
"https://www.ncbi.nlm.nih.gov/m/pubmed/3706794/"
] |
[
"The giant squid axon is the structure we have used as a basis to study computational neuroscience as we could attach probes to it. "
] |
[
"There are some very famous electrophysiology studies done on the giant squid axon by Hodgkin and Huxley (amongst others). "
] |
[
"Do the tidal forces of the moon affect clouds?"
] |
[
false
] |
Do the tidal forces of the moon affect clouds, or any other types of fluid bodies on earth? If so, how come the ocean’s tides are the only effect we (humans) are generally aware of or concerned about?
|
[
"There are \"atmospheric tides\", and they cause atmospheric pressure to vary very slightly over the course of the day. The height of the atmospheric tide is about a meter, meaning the pressure change is similar to what you'd experience climbing a 1-meter-tall hill. Totally not noticeable. That's actually similar to the height of the ocean tides, but the consequences of moving the whole ",
" up and down by a meter are a lot more obvious.",
"https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2014GL060818"
] |
[
"Note that these are gravitational atmospheric tides. There are also thermal atmospheric tides (still a tide!), which are typically just called atmospheric tides. They come about as a result of heat from the sun expanding the atmosphere and hence changing the distribution of mass of the atmosphere. The thermal tide typically opposes the gravitational tide (and hence can prevent tidal locking, e.g. Venus)."
] |
[
"The Moon has gravity--just like Earth, but it's weaker (because it has less mass and it's farther away). The Moon's gravity affects every single thing on Earth--even the planet, itself. We really notice the tides, because they can be easily measured (unlike, say, clouds), because they can be obviously seen with the naked eye, and because they are extremely important to anyone living on the water.",
"So, yes, the Moon's gravity affects clouds. We don't think or talk much about it, because it's generally irrelevant, to us. Who's going to notice, if some clouds move a little bit due to gravity, when they're already moving due to wind?"
] |
[
"It's blazing hot in your room. You open the window and put a fan in it. Do you blow the hot air out? Or blow the cold air in?"
] |
[
false
] | null |
[
"Mine Ventilation Student- Personally, I would say bring the cold air in, it cools you down faster and more directly. If you were to implement an exhausting system it would be best to open another window to ensure steady state air movement."
] |
[
"Summary of top five voted answers so far:",
"All agree to open a second window."
] |
[
"you want the fan to be directly against your window. not just somewhere in the middle, and you want it blowing into your room. ",
"like this horrific drawing illustrates"
] |
[
"In alternating current (AC) devices, does the same electrons do all the work as they are just getting pushed back and forth?"
] |
[
false
] | null |
[
"TL;DR (Sure, sorta. But it doesn't really matter.)",
"The answer to this question can be a bit complicated. I will do my best to cover the major points from a relatively broad scope and hopefully someone else can help elaborate if necessary.",
"In AC circuits it is quite conceivable to have a zero net change in electron flow through a cross-sectional area of a conductor over time.",
"It may be helpful to note that we measure current in ",
"Amperes",
". Amperes are a measure of the electric charge passing through a cross-sectional area of conductor per unit of time. We measure this electrical charge in ",
"Coulombs",
", with a Coulomb representing the charge of a very large (but constant) number of electrons. ",
"Electric current",
" is the flow of ",
"electric charge",
" through an object. ",
"Electrons",
", along with things like ions, are electrical ",
"charge carriers",
".",
"In that regard, the mean position of electrons in a conductor is largely irrelevant.",
"Another tidbit that can often add to the confusion is flow notation. Way back in the day when electricity was first \"discovered\" the assumption was that the charge flowed from positive to negative. This is commonly referred to as Conventional Flow Notation. Fast forward a bit to when we have the tools to actually determine which direction the electrons are flowing and it turns out those old guys got it a little backwards. We call this ",
" Electron Flow Notation.",
"As it turns out, it doesn't really matter which one you use. The math works fine both ways, so long as you are consistent.",
"In truth, we are still learning a lot about electrons. New discoveries in the field of quantum mechanics have shown a lot of our conventional notions about the nature of electricity to be inaccurate or insufficient to describe the reality of the situation. What this means is that it is quite possible that in the not too terribly distant future, answers like mine here may be laughably inaccurate.",
"Hope that helps, if only slightly!"
] |
[
"When you get right down to it the electrons aren't small balls moving through an even fluid, but wavefunctions in a highly disordered semi-crystalline grid. What you're saying will be true on average, but the picture for an individual electron is horribly complicated."
] |
[
"I'm a soon to be EE, (51 more days!) but I know nothing about AC, they just don't teach that at my school! I just figured that if for example, the input signal is sin wave then at intervals of 2*PI is the same electron in pretty much the same spot, it was just pushed forward and backwards again. ",
"EDIT: Thanks for the awesome reply though! "
] |
[
"Does the human brain consume more energy depending on what kind of task someone is performing? Such as digging a hole, playing chess, reading a research paper, daydreaming etc."
] |
[
false
] | null |
[
"Not really. The brain's metabolic requirements are very stable across time, regardless of activity. The notion of \"thinking hard\" is somewhat misleading in this respect. Although the distribution of energy consumption across the brain does vary based on the cognitive tasks in which people are engaged (making techniques like fMRI possible), these shifts correspond to relatively small changes in overall activity. ",
"With regard to tasks that seem cognitively demanding (like playing chess or reading a research paper) - while these tasks do typically involve greater activity in the frontoparietal network, engagement in them actually typically corresponds to deactivation in another set of brain regions known as the default network. Conversely, the default network becomes usually more active while we are daydreaming or thinking about people. Thus many activations are offset by reciprocal deactivations. Moreover many regions - such as those involved visual or auditory perception - are usually pretty active regardless of task. Even when we're sleeping, the brain remains quite active - probably in the service of memory consolidation."
] |
[
"Different mental activities can affect the energy consumption outside the brain. Performing demanding mental activities than one does not specially like causes stress and stress increases metabolism (sweating, faster heartbeat, tensions in the body). ",
"https://www.scientificamerican.com/article.cfm?id=thinking-hard-calories"
] |
[
"Good overview!"
] |
[
"Metacognition in animals: where does science stand on that?"
] |
[
false
] |
[deleted]
|
[
"There is some of this work being done at a lab in Columbia University, looking at metacognition in monkeys. They have several studies that claim to have evidence that monkeys possess metacognition. I've actually attended a few of the talks given by these people.",
"I don't know if I fully agree that this is definitive evidence of metacognition, but it's not my field so I am by no means an expert on the topic. If I remember correctly, they only demonstrate it using 2 pretty spectacular monkeys that they've been training for years and years and years.",
"http://www.columbia.edu/cu/psychology/primatecognitionlab/References/KornellSonTerrace2007.pdf",
"Hope that's what you were looking for."
] |
[
"What is metacognition?"
] |
[
"A few studies have suggested that bees may possess some degree of metacognition, ",
"example",
".\nI'm not an expert though, so maybe this is full of baloney."
] |
[
"Liquid water is above the melting point of ice. If I put boiling water in a bowl made of ice the sides melt. If I put boiling rock in a bowl made of rock (crater or caldera) why don't the sides melt?"
] |
[
false
] | null |
[
"They do, just not as drastically as the ice. There are a few reasons for this. ",
"It takes a lot more heat to turn solid rock into liquid rock than it takes to turn solid water into liquid water. The temperature difference between solid water and liquid water is a lot smaller than the temperature difference between solid rock and liquid rock. Assuming things are happening in a room at room temperature, the liquid rock has to transfer a lot more heat to the solid rock in order to make it liquid than the liquid water has to transfer to the solid water to make it liquid water.",
"Adding to this is he object's ability to transfer heat. Water transfers heat to water a lot more readily than rock transfers heat to rock. It will take the two forms of rock longer to reach equilibrium than it will the water. ",
"In addition, both things are losing their heat to the (presumably room temperature) air. While the liquid water more readily transfers heat to the air, the liquid rock is a lot hotter than the liquid water and so is giving off a lot more heat more rapidly. In addition, air more readily absorbs heat than rock, and so the liquid rock will lose more heat to the air than to the solid rock. Conversely, water absorbs heat from water more readily than air.",
"All of these things combined are the reason that far less rock melts than ice melts."
] |
[
"One nitpicky thing...when you see lava bubbling in a lava lake its not truly boiling. That's escaping gas bubbles percolating out...its more correctly effervescing like a giant bowl of face melting Dr Pepper. Pure quartz, for reference, boils at 2230 C (4050 F). Hottest lavas erupt right around 1200 C.",
"But anyway, magma often does melt the rocks it comes into contact with underground. The melting and incorporation of crustal rocks is hugely important in igneous geochemistry. If you put lava into a rock bowl, it will melt some of the rock before the lava in contact with the sides begins to solidify. There are also some really complicated dynamics going on here as lava isn't just one chemical compound. Different minerals will begin to solidify at different temperatures, and the first solidifying ones have higher melting temperatures so you'd end up with a rind of high-melting point crystals and a now slightly cooler magma.",
"These chemical changes, the poor conductivity of rock to heat (as ",
"/u/JohnQK",
" hinted at) and the fact that the mass of the rock \"bowl\" (i.e. the volcano) usually far outweighs the lava, means that you won't really see much melting going on on the sides of a lava lake."
] |
[
"It takes a lot more heat to turn solid rock into liquid rock than it takes to turn solid water into liquid water. The temperature difference between solid water and liquid water is a lot smaller than the temperature difference between solid rock and liquid rock. Assuming things are happening in a room at room temperature, the liquid rock has to transfer a lot more heat to the solid rock in order to make it liquid than the liquid water has to transfer to the solid water to make it liquid water.",
"I'm not sure this part is really true, though. Water's latent heat of vaporization is 334 Joules/gram, right on par with most of the silicates."
] |
[
"What is the lethality of Drosophila Tra gene loss?"
] |
[
false
] | null |
[
"If ",
"this",
" is the gene that you're interested in, it seems that a loss of function for this gene may cause sterility and courtship behavioral defects, but the flies are still viable. (See the \"Summary of Allele Phenotypes\" tab)",
"EDIT: ",
"This",
" page details the specific alleles (some with loss-of-function) and links to their specific phenotypes.",
"EDIT 2: Drosophila questions? FlyBase to the rescue! Really, though, if you're working on a test, than any gene ontology databases (like ",
"this",
"), KEGG, BLAST (NCBI), Ensembl, and other gene-oriented databases are invaluable. Start building a repertoire of them and it'll pay off nicely."
] |
[
"Wow, I honestly did not think I would get any sort of response, and certainly didn't imagine somebody providing links, advice, and multiple edits to make sure the question was answered! I'm doing independent study of C.Elegans next semester, and it looks like using those databases for extra gene info would save me incredible amounts of time. "
] |
[
"Oh, man, independent research is awesome -- that's going to open your eyes to the intricacies of science. It's pretty amazing.",
"And, on your point, the gene databases which have cropped up over the past few years are incredible. There are a variety of them for every purpose imaginable -- different species types, different forms of analysis, time-point expression data, you name it. There are even pretty obscure ones like ",
"Stanford's database of expression profile information for yeast during diauxic shift",
". In short, if it is, there is a database for it.",
"As far as tips go: 1) Start with papers that are related to your topic. These usually include a wealth of information, including methodology that you can adopt (and, if you're unaware, most university libraries allow access to journal articles and databases, so start there). 2) Once you get into the nitty-gritty -- like analyzing RNA seq or microarray data, if you're looking at expression profiles -- databases are your friend. 3) If you know of any bioinformaticians, befriend them! They're pretty good at parsing through datasets and finding what you need."
] |
[
"My son, a fledgling evil genius wants to know what is the deadliest substance known to man. In case he has the chance to hold a city ransom by contaminating the water supply."
] |
[
false
] | null |
[
"They say \"the solution to pollution is dilution\" so as far as my knowledge goes no small amount of substance could do that unless it was a self-replicating virus or bacteria. ",
"If you wanted to go the most evil route I thing heavy metal poisoning is right up there. Heavy metal poisoning is terrible because the victims do not notice it at fist and the effects last for decades. The victims would slowly succumb to dementia and depression with no way to identify the source until they inevitably die. This scenario has haunted my memory ever since I did a case study on the Camelford incident. \n",
"http://en.wikipedia.org/wiki/Camelford_water_pollution_incident"
] |
[
"Here is a list of LD50 for various substances. Its measured in mg/kg. So that means if you give a bunch of people this many mg for each kg of their body weights 50% will die. ",
"From this it can be seen that giving a person (~70kg) 6.3 L of water would kill. Your son might not need anything, just making people drink. ",
"Looking at the bottom, Botox will do apparently. 1 ng/kg will kill 50% of people. A person drink 2 L a day so lets say 35 ng/L will do fine. That means if you could get 10g, probably about a vile, you could poison 285,714,285 L of water. Looking at new yorks daily water consumption of 5,299,576,800 L, you could poison about 5% of the cities 9 million people to LD50 levels. That's 485,213 people poisoned and half that dead with a vile. That good enough for him? "
] |
[
"Thanks for the info. I know it will spark a conversation about self replicating viruses. He will think that is really cool."
] |
[
"Why metals are crystalline and not amorphous?"
] |
[
false
] |
Gibbs free energy equation : G = H - TS, H: Enthalpy T: absolute temperature S: Entropy, Since an amorphous structure has more entropy than a crystalline structure, which should reduce the Gibbs free energy, so why most solids exist in a crystalline state and not amorphous ?
|
[
"Better, dG = dH - TdS. Now, for the TdS term to be dominating, it needs to be larger than dH. In crystallization, entropy is lost and dS is negative, so -TdS is positive. Meanwhile, dH is always negative for crystallization: the system releases energy when the atoms are locked into the right place, because it's energetically better than a less optimal orientation. So, dH and -TdS work in opposite directions. dG can be negative - i.e. the reaction is spontaneous - if -dH is bigger than -TdS, i.e the enthalpy trumps the entropy gain.",
"When we have a situation where enthalpy differences are very small, in this case indeed it happens so that entropy dominates, and fractal or amorphous shapes are produced."
] |
[
"It is hard (read: nearly impossible) to vitrify pure metals due to very rapid configuration to the crystalline state- all bulk metals, when solid, will be crystalline. Funky things can occur at the atomic scale, however. ",
"Alloy systems with very deep eutectics can be turned into metallic glasses, however, with no crystalline structure. From a melt, with the right composition (enough such that partitionless solidification is not possible) and high enough cooling rate, the viscocity of the metal reaches around 10",
" poise (someone correct me if I am wrong) and the system can no longer reconfigure to the crystalline state, remaining amorphous at room temperature. ",
"As for properties, the lack of grain boundaries allow for higher wear and corrosion resistance than traditional alloys. They have usually higher strength and hardness, but are less tough, as well. ",
"Here is a general overview of BMG mechanical properties: ",
"http://www.sciencedirect.com/science/article/pii/S0079642510000277"
] |
[
"ΔG = ΔH -TΔS",
"Since the influence of entropy is ",
" many things adopt a lower-entropy configuration at lower temperature if doing so is more enthalpically favorable than entropically unfavorable (i.e. ΔH<-TΔS). But at high temperatures, -TΔS dominates and they melt (or undergo a phase transition to a more disordered structure).",
"So why is ΔH<0? A chemist (like me!) would tell you that it's because metal atoms brought into close proximity experience bonding interactions (covalent, metallic, other, the exact nature doesn't matter for this discussion), whose formation is favorable (ΔH<0). For most metals, the optimal arrangement of atoms, energetically speaking (i.e. most negative ΔH of crystallization) is simply to maximize these interactions by putting the atoms in a ",
"close-packed lattice",
" where every atom has the maximum number of interactions with neighbors. It just happens that this close-packing arrangement is nice and ordered, so it's crystalline."
] |
[
"The earth is often referred in it's ancient state has having been very hot, and it had to cool down before life developed. Why was it hot to begin with?"
] |
[
false
] |
Was it the impact of all the debris that made up the earth in the first place? Or the gravitational forces between lumps of earth trying to force themselves closer together?
|
[
"http://www.youtube.com/watch?v=IO45ZiGql8E",
"thats a pretty cool video that explains a little about it"
] |
[
"Yes, there is a actually a small liquid core in the moon that hasn't solidified (we just found this out earlier this year!), but smaller bodies cool off faster than larger bodies since they have more surface area per unit volume. "
] |
[
"This is horribly wrong. The Earth and Sun were both formed by gravity... but that in no way makes the Earth a former sun (or star)."
] |
[
"What limits the specific impulse of an ion engine?"
] |
[
false
] |
[deleted]
|
[
"It depends on the technology you are considering. Gridded ion thrusters (probably what you were thinking about) are limited by the potential difference you can apply to the grids. Ignoring the engineering issues that come with high voltage power supplies in space, the ion current between the electrode is limited by the space charge effect (Child–Langmuir Law)",
"The issue is different with Hall effect thrusters. I actually work on those. I can detail more tonight when I get out of work."
] |
[
"To answer your last question:",
"The specific impulse for a rocket is roughly the speed of the exhaust of the rocket, and is ",
" proportional to the amount of energy that must be spent to accelerate the rocket to a given speed. Thus higher specific impulses are very fuel efficient, but very energy ",
".",
"As an analogous situation, suppose you are in a rolling chair and want to push yourself across the room. The low-specific-impulse option would be to push off against your desk or some other heavy object; the high-specific-impulse option would be to get a bag of baseballs and throw them as fast as you can in the other direction. Clearly it would be exhausting to use the baseballs, but the total mass (\"fuel\") you push would be much less.",
"One easy way to get extremely high specific impulse is just to point a flashlight out the back of your spacecraft. This is essentially the highest possible specific impulse, since your \"propellant\" is travelling at the speed of light.",
"Picking the best specific impulse for a spaceship is a balance of concerns, where at one extreme you need too much fuel, and at the other extreme you need too much power - in the form of giant solar panels, or a massive amount of radioactive plutonium, etc."
] |
[
"Picking the best specific impulse for a spaceship is a balance of concerns, where at one extreme you need too much fuel, and at the other extreme you need too much power",
"Yeah that's what I guessed.",
"Interesting perspective with the flashlight, I never thought of a flashlight as having a specific impulse. This leads to solar sails if you want the sun to be the power source."
] |
[
"Would it be possible for a huge body of free flowing liquid to exist in space (but not in planetary form)?"
] |
[
false
] |
[deleted]
|
[
"It would boil (because the partial pressure of the water would be larger than the ambient pressure), then it would freeze into ice (because boiling takes energy, and because the ambient temperature is low), and then it would sublimate into gas (because ice still has a vapor pressure)."
] |
[
"The solid-liquid spectrum is a continuum, not a binary distinction. Asphalt at room temperature or below is far on the solid side for practical purposes. It's not going to bubble and boil in space. It's going to sit there, evaporating hydrocarbons very slowly, for a very long time."
] |
[
"The solid-liquid spectrum is a continuum, not a binary distinction. Asphalt at room temperature or below is far on the solid side for practical purposes. It's not going to bubble and boil in space. It's going to sit there, evaporating hydrocarbons very slowly, for a very long time."
] |
[
"Is it true that even several hours after heavy alcohol consumption, one can \"sweat out\" alcohol"
] |
[
false
] |
I drank around 10-11 drinks of beer and whiskey ending at around 2am. I arrived at work at 230 pm the next day, showered, teeth flossed, brushed, had eaten, plenty of water was drank, but my boss insisted that he could smell alcohol on me. he claimed I was "sweating it out" Is there any possibility of this?
|
[
"Alcohol lost due to sweat is virtually nothing. It's mostly a myth. Nothing significantly decreases BAC other than waiting."
] |
[
"It's more likely that he smelled alcohol expelled in your breath."
] |
[
"This is just my personal anecdotal experience but you can totally smell it on someone the next day if they have been drinking really heavily. I don't know if they are actually \"sweating it out\" though."
] |
[
"What would happen to a water bottle in space?"
] |
[
false
] |
[deleted]
|
[
"Whether the bottle of air, or the bottle of water, would pop would be entirely dependent on the strength of the bottle. ",
"The water wouldn't boil as long as the bottle remained intact, and the water itself under normal temperatures. While the bottle is intact, the water isn't subject to the vacuum of space. "
] |
[
"is that not a little...chicken and the egg? does the water not push on the inside of the bottle at all?"
] |
[
"Of course the water pushes on the sides of the bottle, but if the bottle doesn't break, the water can't be exposed to vacuum. ",
"The strength of the bottle is an important factor, the major factor. "
] |
[
"How close are pro drummers to the actual beat?"
] |
[
false
] |
Like within milliseconds? Closer?
|
[
"Tens of milliseconds. See ",
"this article",
" in which the author has plotted the drummer tempo differences for some popular tracks."
] |
[
"That's true; depending on the genre, playing a little ahead of or behind the beat is a skill that a talented drummer utilizes. But to have that skill you need the ability to play the beat nearly perfectly before you have the skill to play around with it, so OPs question could still be asked by asking such a drummer to play at straight-forward as possible."
] |
[
"In most songs, a good drummer would try to add some emotion and emphasis by purposefully not hitting every beat to within a millisecond. That's why a good drummer sounds so much better than a drum machine, I guess."
] |
[
"So how much lithium can we ultimately recover and use?"
] |
[
false
] |
I am wondering about all the new trends of electrical vehicles, phones, laptops, rechargeable toothbrushes, R/C Toys all using some sort of Lithium-ion or similar chemistry in their power systems. Won't we hit "peak lithium" rather fast?
|
[
"I'll just quote from a report done by Argonne National Lab on the availability of materials used in Li-ion batteries. You can check out the full report at ",
"http://www.transportation.anl.gov/pdfs/B/583.PDF",
"\"In the case of materials for lithium‐ion batteries, it appears that even an aggressive program of vehicles\nwith electric drive can be supported for decades with known supplies\""
] |
[
"I'm glad you said \"peak lithium\", instead of saying \"run out\".",
"All to often people disregard the effect of supply on price and therefore on demand."
] |
[
"Well there are the proven reserves:\n",
"http://en.wikipedia.org/wiki/Lithium#Terrestrial",
"It all depends on economics. The amount of extractable lithium is entirely dependent on the market price. At low prices, only the most concentrated sources are viable. At high prices, very dilute sources are viable. ",
"You will never \"run out\" of lithium. If the price goes high enough, you could even tap the 230 billion tons of the stuff that is dissolved in seawater. "
] |
[
"Why do Australians have the highest per capita CO2 emissions?"
] |
[
false
] |
[deleted]
|
[
"That's probably the main factors I would imagine. No source on anything so take it with a grain of salt - I'm sure others have better information / experience.",
"Source - am Australian, some environmental science experience. "
] |
[
"Would our large agricultural industry also ramp up emissions?"
] |
[
"False: The plants are going to be eaten by humans or animals that turn them into CO2 again so at best this would be CO2 neutral - but since you use machinery running on fossil fuels you are adding CO2, not removing. If your farm runs 100 % on renewables and you plant trees that stand forever or bury them deep in the ground you will be removing CO2."
] |
[
"Why do we create igM antibodies first?"
] |
[
false
] |
My understanding is when a t cell activates a b cell it goes into germinal center and goes through class switching. Shouldn't we start off with igG antibodies first?
|
[
"The first heavy chain exon in the gene's locus is for the μ heavy chain, which is for IgM. The second is δ - IgM and IgD are the first immunoglobulin classes produced by naive B cells. Class switching is primarily deletional, so the exons for μ, δ, etc heavy chains are actually spliced out, so γ-1, α (or whatever heavy chain exon) is read instead.",
"The Wikipedia article actually has a good ",
"visual",
" for this."
] |
[
"IgM is the first antibody to be produced in response to infection since it does not require ‘isotype switching’ to another antibody class. These early IgM antibodies are produced before B cells have undergone somatic hypermutation. However, it is only synthesized as long as antigen remains present because there are no memory cells for IgM. As a B-cell surface immunoglobulin, IgM exists as a monomer and functions as a receptor for antigens",
"Murine studies suggest that IgM plays an important role in innate defense against infection, allowing time for the initiation of antigen-specific B cell response; it also enhances antigen-specific B cell responses through its ability to fix complement and thereby co-stimulate B cell activation through complement receptor 2 (CD21). IgM is mainly found in the blood and, to a lesser extent, the lymph due to its large structure. The pentameric structure of IgM makes it especially effective in activating the complement system. Infection of the bloodstream has serious consequences unless it is controlled quickly, and the rapid production of IgM and its efficient activation of the complement system are important in controlling such infections."
] |
[
"u/mystir",
" answered it down to the biochemistry components beautifully. To take this further, take a look at a condition called hyper IgM syndrome. These patients lack the ability to class switch antibodies so ONLY have IgMs."
] |
[
"Why is earths gravity so similar to saturn (relative to other planets) when its only a fraction of the size, when the gravity on mars is close to a third of earths when its so much closer in size?"
] |
[
false
] | null |
[
"Because gravity is a function of mass over radius squared, so whilst Saturn is much more massive, it is also much larger, so the surface gravity is the same.",
"\nBecause the Gas Giants have very dense cores, but very sparse, thick gas layers, at the surface you are far away from most of the mass.",
"\nWith Mars, it's a similarly rocky and dense body to Earth, but smaller. Mars' radius is 0.5 Earth radii, but its mass (since M=4/3πr",
"ρ(density)) is only ~0.1 Earth masses."
] |
[
"Indeed so, but acknowledging that the mass is there but far away was easier for me to explain than saying that planets may as well be eggshells with point masses at their centres."
] |
[
"Assuming approximately spherical symmetry",
"Actually, this assumption doesn't work well for Saturn, because it's the most oblate of all the planets.",
"Its polar and equatorial radius are different enough that Saturn's polar \"surface\" gravity is 12.1 m/s",
", while its equatorial surface gravity is only 8.96 m/s",
"."
] |
[
"How does visual stimuli get stored in genes and subsequently expressed in the brain? (For example, the innate fear of spiders, &/or possible sexual stimuli.)"
] |
[
false
] |
I'm talking about things like innate fear of spiders: This only seems possible if the brain has "preprogrammed software." Its seems like an image of a spider (or a visual form) has to exist in the mind at birth. It sounds like a memory has gotten passed down from a previous generation. But that is a Lamarckian idea which is generally debunked. How does a gene encode a visual stimuli? Let's say memory cannot be passed down. This would mean there are genes that produce innate fear in random visual stimuli, and the spider-looking-stimuli so happened to get evolutionary selected? i) That seems statistically unlikely. ii) It seems to imply that we would have a storage of innate fears for other random stimuli. We do not have such a storage. I am also curious if sexual visual stimuli is innate (and expressed at puberty.) I am also curious how the brain determines what defining characteristic of a vision is the necessary threshold to trigger fear or desire.
|
[
"This is a super complicated question since visual stimuli are processed at many levels from the retina to cortex and beyond. I doubt that sexual visual stimuli are innate in humans, but don't think this is known one way or the other. Fearful stimuli are more likely to be genetically encoded via the connectivity and sensitivity of different types of visual cells because there is a more pressing need to know what is dangerous the very first time you encounter it. It's not clear how/to what extent this is true in humans since we are obviously very limited in what experiments we can perform.",
"However, in mice it is well established that certain predator-like stimuli (rapidly expanding overhead dots and to a lesser extent steadily 'sweeping' overhead dots) cause innate freezing and flight responses. ",
"This",
" is probably the best paper written so far on this topic if you want to really get some details on how this computation is performed. The gist is that an ancient brain area called the superior colliculus is sensitive to certain patterns of visual stimuli—in this case, a dark expanding edge—and through its connections to the periaqueductal grey (a motor area) and the amygdala (a fear/memory area) it triggers a flight or freezing response when activated.",
"This has also been described in great detail in locusts if you are interested more in the details of how the computation is performed at a cellular level rather than a circuit level. ",
"Here",
"."
] |
[
"I don't see how sexual visual stimuli could be learned. When straight boys hit puberty, they are attracted to women IRL and on pictures. The attraction is strong and immediate. It hits them before they have sex- so there is no reward mechanism involved. "
] |
[
"In animal models I would define innate behaviors as naive responses to stimuli that an animal has never encountered before. Let me know if you disagree with that and we can discuss. In humans, it's hard to say whether any behavior is innate because so much information is communicated from parents, friends, media etc explicitly and implicitly in a totally uncontrolled way. If you're asking whether sexual visual stimuli evoke an innate response at puberty, id say it's actually impossible to answer since nobody who gets to that point lives in a vacuum — they have preconceived notions based on their experience up to that point which can't be separated from what we would call innate factors in animals. The human aspect of this isn't my area of expertise though, and I think the distinction between innate and learned behaviors is very much subject to interpretation especially in humans."
] |
[
"What's your thoughts on Emergy Medicine (EM) and its use in the East?"
] |
[
false
] | null |
[
"I was recently given this ",
"article",
" and as I am skeptical of EM, I decided to try and review it. I was advised that the East uses primarily medicine of this nature, and I would love to know a comparative analysis (if that statement is even true).",
"Honestly, it seems like it's overstepping, equating Quantum physics to our body functions, but I don't know enough to refute. Another thing I noticed was that a great deal of the references/citations making claims were from holistic/integrative medicine sources- followed by a definition which would come from what I would consider a more reputable source. It gives the illusion of an impartial study. ",
"I am bias and I acknowledge that. I want to make sure I know and I can refute these claims reasonably. It's hard to refute acupuncture and touch therapies when its presented in a study like this.",
"Are there glaring lies from those more well versed?"
] |
[
"Hi Headshothero thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Medicine"
] |
[
"In the time we've been watching the moon and keeping track of its appearance, have we seen new craters being added to its surface? Aka have we witnessed any collisions?"
] |
[
false
] | null |
[
"Yup, there are new craters that show up on the lunar reconnaissance orbiter images that did not show before. Here's a NASA link on one example: ",
"https://sservi.nasa.gov/articles/new-impact-crater-on-the-moon/"
] |
[
"Here is a video of an impact in 2019.",
"https://www.newscientist.com/article/2191526-a-meteorite-hit-the-moon-during-mondays-total-lunar-eclipse/",
" ",
"The reddit thread.",
"https://www.reddit.com/r/space/comments/ai79zy/possible_meteor_impact_on_moon_during_the_eclipse/"
] |
[
"Nice! Thanks for the article!"
] |
[
"When you stub your toes, why does it take a second for the pain to fully hit you?"
] |
[
false
] |
Maybe this is just me, but whenever I stub my toes (like I just did- ow!) it takes about one second for the pain to fully hit me. It comes like a wave. Why is this?
|
[
"I do know that a similar experience is putting a foot into a hot bath. It takes a second or so to realise that the water's too hot. I always thought that this is to do with the speed at which the nerves can transmit the sensation to the brain."
] |
[
"Im definitely not an expert in this matter but in my experience, when that happens to me, my feet tend to be really cold. So lack of bloodflow to the feet may make the pain receptors slower or less receptive. The impulse to the brain and back to the foot is the same as any bodypart. When touching or jabbing your foot with something sharp your foot you dont feel a delay. These special instances of delay most likely are a result of delayed integration at the site of the receptor or possibly in the CNS. But the distance traveled and speed of the afferent/efferent \"connecting\" nerve is most likely not related."
] |
[
"This is probably not true. If he had stepped on something sharp, the pain would have been immediate. It might have to do with the type of injury - blunt trauma that doesn't break the skin. Can't really offer an answer but I think we can rule out that it has to do with distance from the CNS."
] |
[
"Why are calculations that are fed through a graphics processor completed so much faster then when run through a CPU?"
] |
[
false
] |
Not completely sure, but I think Sanford's Folding at Home completes basic computations, predictions, and calculations by using the computer's graphics processor instead of the more typical mathematics that occurs within the computers cpu. I get that it runs faster, but I'm not sure why a gpu would be so much faster for completing the computation if the cpu's the normal base. Better put, if the tech on the gpu is better and faster, why don't cpu's use it for everything else they do for computations.
|
[
"CPUs are more general-purpose. GPUs are more specialized, and they specialize in putting out a massive number of calculations under proper circumstances. The \"proper circumstances\" is the key phrase there. The key thing that a GPU brings is parallelization. It's not that GPUs are faster at doing a single calculation, it's that GPUs can do 50 identical calculations faster than a CPU can do 50 identical calculations.",
"If you just want a single number multiplied by 4.3, the GPU probably isn't the best way to achieve that. But, if you want one enormous block of memory all multiplied by 4.3, yeah, fire up the GPU."
] |
[
"GPUs do less complicated things, and do a ",
" of them. They're useful for graphics because if you need to do something for each pixel, you likely only have a few multiplications and additions but you have a ton of pixels. And, importantly, the computation for each one is unrelated to the others, so they can be calculated independently. A CPU would have to devote time to each pixel and do them one after the other in a \"serial\" way, but the GPU does many of them at once in parallel. ",
"The reason GPUs aren't used for everything is that some problems do not lend themselves to parallelism. If each step in your calculation relies on the answer to the previous step, there's no way you can do all of them at once. ",
"tl;dr GPUs don't do one thing faster, they do ",
" of one thing. "
] |
[
"That's exactly what I fucking said.",
"(1) No, it's not, it's the ",
" of what you said. I began the sentence with \"can't\" to indicate that what you said is ",
" the case. Here's a rephrasing for you, to make the meaning clearer: It is not the case that GPUs can complete some operations faster than CPUs because we don't know whether P=NC.",
"(2) I would appreciate it if you didn't take out your anger by swearing at me -- I'm only explaining why your answer was downvoted. Thanks in advance.",
"Except if we knew P = NC, we could force a construction out of the proof which will allow us to use GPU-like structures for sequential operations at only polylog blowup in FLOP count.",
"Again, this doesn't answer the question. The question is why GPUs can perform some computations faster than CPUs. It's a question about what ",
", not what ",
".",
"Practice is just applied theory. We could have easily had the same argument before we knew NP = PCP(log n, O(1)), but now even PCP-based programming languages are being developed and deployed for practical use in verified computation.",
"This is all irrelevant to answering the question that was asked."
] |
[
"To what extent does temperature influence coefficient of friction between two materials?"
] |
[
false
] |
EDIT: let's assume that the two materials are not nearing a phase change
|
[
"Anywhere from none to a lot.",
"This question is very vague, so it can't really be answered with any specificity. However, suffice it to say that there are cases where temperature wouldn't change the coefficient of friction, and there are cases where it would significantly change it.",
"Note that in all the cases I can think of, the temperature change doesn't influence the friction directly, but rather it influences the general behavior/properties of the material, which in turn influences the friction.",
"A few examples:",
"Between two pieces of metal, where neither is near a state change, and have fairly stable mechanical properties, temperature will have a near-zero effect on friction.",
"Between a tire and pavement, the temperature of both/either can very significantly change the coefficient of friction. This is because the mechanical properties of both, but especially the rubber tire, have a great dependence on temperature (softness, strength, etc)."
] |
[
"This is a super interesting question.",
"Friction is a macroscopic manifestation of repulsion between valence electrons in two materials. Like charges repel, so when the microscopically jagged edges of two materials pass by one another, the repulsion slows them down. What interesting, though, is that we know that the electrical properties of metals change as a function of temperature. This suggests that in other materials, the properties of electrons may also change with temperature.",
"I could make an intuitive physical argument that goes either way. When it's colder perhaps the electron cloud is just ever so slightly smaller. And maybe, because most things shrinks as they get colder, the surface irregularities that cause friction smooth out as they shrink. That would mean uniformly less friction with cool temperatures.",
"Alternatively, if the electron cloud got larger with high temperature, it would also be less dense on a time-averaged basis. This would mean that perhaps a material, when heated, would have a lower coefficient of friction. (And I don't mean just the electron cloud as a function of distance from the nucleus, but the nuclei will move more at higher thermal energies so the electron cloud itself is a little bit of a smear around the jiggling nucleus.)",
"Either way, I suspect the answer is incredibly difficult and may not be generalizable. Feynman famously tried to study friction from first principles and declared it could not be done. I'm much dumber, but I'm smart enough to know that if Feynman can't hack it then I can't either."
] |
[
"Hi!",
"I am agreeing with you that the question is very interesting and hard to study, but in recent times a lot has been done to understand friction on the atomic scale.",
"First, you are incorrect in your interpretation of friction as a result of repulsion between valence electrons. The opposite is true! You need to make and break bonds to get a net frictional force. And if two materials come together the generally are going to have an attractive interaction anyhow. (There are of course some exceptions, but these will have extremely low friction!) In your example with the microscopically jagged edges, the repulsion you feel while climbing a hill in the effective potential would be countered by the propulsion while sliding down the opposite side. If the two bodies are not commensurate the net force in all directions would, by the theory of ",
"structural superlubricity",
", even be zero theoretically!",
"You might want to check out ",
"this paper",
" and the references therein to learn about energy dissipation in very simple sliding systems.",
"Also your arguments about the electron clouds and their change with temperature are invalid. The electronic temperature at the Fermi level is HUGE compared to room temperature and the smearing due to temperature is generally small at ~300K. On the atomic scale, the effect of ionic movement is key for friction and usually lowers the barriers and thus the friction coefficient. The electronic structure on the other hand is pretty much the same for 0 and ~300K.",
"To come back to OPs original question, I have one aspect to add to ",
"u/mtnclimbingta",
"'s answer which covers the macroscopic part well in my opinion: On the atomic scale there has recently been an interesting development regarding lubrication by temperature. I fear the ",
"paper",
" is behind a paywall, but you might find it somewhere on the net for free also... In short, thermo-assisted random movement of a tip can lead to ultra low friction on the atomic scale."
] |
[
"Why does bad eyesight transfer into mirrors?"
] |
[
false
] | null |
[
"Focual distance for objects seen in a mirror is distance from eye to mirror + distance from mirror to object. If you are seeing an object that is 10 ft behind you in a mirror, it is as if the object is actually 10 ft in front your in terms of how your eyes are focusing."
] |
[
"Thanks for the reply, didn't realize that's how mirrors worked. I assumed they would reflect a perfect image and my eyes then only have the eye to morrow distance to see."
] |
[
"Here",
" is a helpful illustration"
] |
[
"If a significant period of time passes since an individual had last used a muscle, can that individual literally forget how to move that muscle?"
] |
[
false
] | null |
[
"when i read the question i was thinking of something like raising one eyebrow. you would still use that muscle enough so it doesnt suffer from atrophy, but you might forget how to individually control that muscle."
] |
[
"Not sure there is a way to know. A muscle will atrophy beyond use before enough time passed to 'forget'.\nI remember seeing this guy on a show a few years back, maybe this will answer your questions.\n",
"http://www.odditycentral.com/pics/indian-sadhu-has-kept-his-right-hand-up-for-the-last-38-years.html"
] |
[
"Probably not. Basic use of single and related groups of muscles is hardwired in motor cortex. You have anatomical regions of your motor cortex devoted to specific sets of muscles; the function of those regions is to control those muscles. However, like Calyber said, though you may not forget how to use an unused muscle, your ability to actually execute what you want to do will depend upon whether the muscle has degraded as well as the intactness of all the connections between motor cortex and motor neurons innervating the muscle"
] |
[
"Why doesn't plants seem to have an age limit?"
] |
[
false
] |
I have the impression that plants have no built-in age limit like humans and many animals. If perfect conditions persist indefinitely, it looks like plants can also live indefinitely. I am primarily thinking of trees, but I've read about herbaceous plants that can re-sprout annually, apparently without limits. In humans I've been told that telomeres partly determine the life-span. They reduce in length every cell division, and when worn away, genetic material deteriorate from the edges of the chromosomes. Does plant chromosomes have telomeres? How is genetic material preserved in plants for such long time periods? Does the age of (viable) seeds determine life-span of plants? Some seeds may stay viable for decades and longer, are there any notable differences between two individuals of a species who have sprouted from very differently aged seeds?
|
[
"I wouldn't say all plants are \"absent of organs\" as spermatophytes do have what are analogous to reproductive organs, but you're correct that a lack of major organs is a big factor.",
"Basically, plants have way fewer types of tissue than most animals do, and one of the other big causes of aging is our bodies doing things to prevent oncogenesis (ie, telomere shortening). I don't actually know whether telomerase is present in plants or not, I'd have to check, but part of why cancer is so dangerous in complex animals is because of how many different highly specialized tissues we have. Even a slight alteration in the behavior of those tissues could be catastrophic, depending on the importance of the organ it occurs in.",
"Plants have three main types of tissue: vascular, dermal, and ground. Vascular and dermal tissue are exactly what they sound like, and they're also exceedingly simple compared to ground tissue. Ground tissue is basically all the tissue that isn't vascular or dermal, and it's where the majority of metabolic processes occur, most notably photosynthesis. While plants do occasionally have tumor-like growths (often caused be infection or infestation), they don't tend to happen without an outside factor, and when they do, it mainly affects dermal tissue.",
"I don't really know why this is; I'm guessing the presence of a cell wall is a factor? But because of this plants don't really need the same pre-programmed aging that we do. Plants do still age, and deteriorate with age, but it's not a matter of self-preservation the way it is with humans. If we were to remove our innate aging factors, we'd eventually become giant balls of cancer (due to things like oxidative stress, radiation exposure, and spontaneous mutations) so in part, human aging is a way to prevent that. Plants don't have that kind of need."
] |
[
"You can look at it in terms of a probability. The probability that an event will cause the death of some animal is pretty high, since they have to move around, predation results in death, their systems are more complicated and have more points of failure, they require more energy to power locomotion and brains which means they’re more susceptible to death from scarcity, etc. ",
"Since the probability of death is rather low for some plants, they tend to live very long lives in the right conditions. But keep in mind, that’s mostly survivorship bias and can play fast and loose with the concept of “organism” and “alive.” Plenty of plants die before their seedling can sprout."
] |
[
"I've got no idea what everyone else in the thread is talking about. Plants age slowly because they don't age at all on the cellular level. When they get old and die it's because they get big and gnarled and can no longer sustain themselves properly but their cells are just as young as ever. If you take the newest growth shoot of a 4,500 year old and near death bristlecone pine and let it root, it will go another 4,500 years no problem if conditions are right. ",
"It's not a matter of probability at all. If you take a human and care for his every need, he'll live to be somewhere between 80 and 110 most likely. If you do that with any kind of plant that can put down new roots by itself you'll be there literally forever because it's not gonna die."
] |
[
"How do we know that the Ice on other planets consists of H2O?"
] |
[
false
] |
Watching another run of the mill "Colonize Mars" videos and I heard what I've heard hundreds of times before about there being ice underneath the surface. I remember hearing the same about there being ice on the Moon and even Pluto. I never thought about it before, but how are we sure the frozen liquid we've found is H2O and will be useful in colonization or terraforming? Aren't there many other kinds of frozen liquids this could be?
|
[
"In many cases it's not H20,but other liquids.",
"It is really just a deduction based on:",
"- What liquids we know are easily formed from chemical reactions or base elements, there are not that many.",
"- What the temperature is on the planet",
"- What temperature those common liquids and elements freeze at.",
"",
"Water is the most likely solid to meet all those criteria on Mars.",
"",
"If you get hotter, like Venus or Mercury you start looking at metals (usually solid on Earth) that melt and become liquid, if you start getting colder, further out in the solar system you start getting gases (usually gas on Earth) that start becoming liquid."
] |
[
"I learned about this at the Greenwich Observatory. Fascinating, yet very simple. They use a special light filter, a spectrometer. Each element has a unique signature that is detected by the filter. Here is some information about it. \n",
"http://www.scholastic.com/browse/subarticle.jsp?id=2498",
" \nAnd here \n",
"http://curious.astro.cornell.edu/physics/56-our-solar-system/planets-and-dwarf-planets/general-questions/199-how-do-we-know-what-other-planets-and-stars-galaxies-etc-are-made-of-intermediate"
] |
[
"Yes, of course there can be other liquids too. Wasn't it on Titan where we found liquid Methane?",
"\nAnyhow; the answer to the \"real\" question has two components. First one is probing. If we send a probe to a planet/moon and this probe finds ice, that turns out to be water ice, then of course we know that there is ice. Another component (however, I am unsure about the) would be e.g. IR-spectroscopy. If we e.g. find that the atmosphere of the planet absorbs the characteristic wavelengts for H2O, we know that is there too."
] |
[
"Why is mercury-vapor used instead of non-harmful noble gases in lamps?"
] |
[
false
] |
Why not use gases like Helium, Neon, or Argon in lamps? Instead of mercury-vapor, which is hazardous.
|
[
" mercury just happens to have atomic characteristics that make it useful for producing visible light at high efficiency, and it is superior to other elements to the point that we use it despite the possible dangers. ",
" in a ",
"gas discharge lamp",
", you pass electrical current through an ionized gas (plasma). This excites electrons in the plasma atoms to a higher energy state, and when they fall back down to a lower energy state they give off photons of light. ",
"Different atoms have different energy states for their electrons, and as such produce photons of various energies characteristic to the type of atom. Mercury happens to produce intense ultraviolet light (along with some visible light), and the UV light can be converted into other colors of light by applying a fluorescent coating. The combination produces visible light with good efficiency at reasonable power levels. ",
"As an example of other technology, ",
"xenon arc lamps",
" are also used, and (at high power levels) can produce very bright light that is actually a closer approximation of natural sunlight than fluorescent lamps. However, they are less efficient. ",
"Metal halide lamps",
" use mercury vapor plus metal halide vapor to add in other spectral lines. They are effectively a combination mercury-vapor and sodium-vapor bulb, as the most common metal halide is sodium iodide. Note that these two are both \"high-intensity discharge\" lamps, with an electrical arc running between electrodes inside the lamp. They tend to operate at higher power levels, making them less useful for residential lighting. The metal halide lamps also have to (literally) warm up to their full light output, as the metal halide takes some time to heat up and vaporize - not good for residential lighting where they might be turned off and on regularly. Some of them actually cannot be re-lit after being turned off (intentionally or due to interruption of power) without being allowed to cool down for several minutes first. Metal halide lamps have similar efficiency to fluorescent lamps, and are growing more common in large-scale lighting applications where their drawbacks are less relevant and their high power, high ",
"color rendering index",
", and high efficiency are useful. ",
"Low-pressure sodium vapor lamps",
" are some of the most efficient light sources in existence and use no mercury, but the nearly monochromatic yellow light they produce almost completely destroys the ability to recognize colors, resulting in them being considered unacceptable for most indoor lighting applications. "
] |
[
"Uh ... good question. This ",
"EPA site",
" states that there is such a thing as \"low-mercury\" fluorescents, which leach so little mercury when disposed of normally that they are not regulated as hazardous waste. They still contain mercury, just less of it, along with other chemicals to encourage the mercury to remain in chemical forms that are insoluble in water. ",
"Second reference from GE",
". ",
"It appears that there is no such thing as a genuinely mercury-free fluorescent bulb (",
"1",
",",
"2",
"), although other lighting technologies like LEDs can of course be made without mercury. "
] |
[
"Mercury vapor gives off uv light which is the right wavelength to excite the phosphor coating on the inside of fluorescent tubes. None of the noble gasses emit a white light which is comfortable to the eye. "
] |
[
"If you could download the schematics of every part of a car, could you make a functional car with a 3d printer?"
] |
[
false
] |
[deleted]
|
[
"http://gizmodo.com/5678476/the-worlds-first-3d+printed-car-actually-works"
] |
[
"I'm not sure I'd take a Fast Company press release too seriously -- it's pretty much an advertising site aimed at venture investors. I note that their web site doesn't repeat any of these claims about 3-D printing.",
"With that said, it would certainly be possible to 3-D print a range of exterior and interior parts. But I don't think that epoxy resins are quite ready to be drivetrain components or engine blocks."
] |
[
"but to make something like an engine block would be difficult",
"Use a metal printer then (yes they do exist), or CNC the engine block from a solid piece using a 5 axis CNC machine. Not a printer since it's not an additive process... but it gets the job done."
] |
[
"Why does bad eyesight persist in humans?"
] |
[
false
] |
Why does bad eyesight persist among humans despite evolution or natural selection? Seems like it would have beared strongly on survival and reproduction of our ancestors and the trait would have been removed.
|
[
"Well, for most people, the onset of bad eyesight doesn't occur until middle/late age. The evolutionary pressure against it only lasts until after prime breeding age. ",
"\"Evolution doesn't care about organisms, it only cares about genes.\"* Thus, if you can pass your genes on before problems develop, there's no real selective pressure against it.",
"*These words have most likely been used by many people before me, and I don't claim explicit ownership of them. Regardless, the point is true."
] |
[
"Here is an article on just that in the ",
"New York Times: The Sun is the Best Optometrist",
"Some quotes:",
"in the early 1970s, 25 percent of Americans were nearsighted; three decades later, the rate had risen to 42 percent, and similar increases have occurred around the world.",
"In this case, the rapid increase in nearsightedness appears to be due to a characteristic of modern life: more and more time spent indoors under artificial lights.",
"Researchers suspect that bright outdoor light helps children’s developing eyes maintain the correct distance between the lens and the retina — which keeps vision in focus. Dim indoor lighting doesn’t seem to provide the same kind of feedback. As a result, when children spend too many hours inside, their eyes fail to grow correctly and the distance between the lens and retina becomes too long, causing far-away objects to look blurry.",
"Full citations and article linked above.",
"Edit: Here is a copy of the ",
"article",
" not hidden behind paywall if you can't access the NYTimes."
] |
[
"I'm not a biologist, but it seems to me that the eye is a pretty complex work of evolution, and should we have imperfections in other parts of the body (we all do), that it's pretty likely the eye may not develop PERFECTLY also.",
"As far as survival goes, the ability to see vs. the ability to read tiny print on a page are two very different things."
] |
[
"Does the procession of Earth's axis have any effect on the climate?"
] |
[
false
] | null |
[
"The precession of the Earth's rotation axis is one of several factors that enter into the ",
"Milankovitch cycle",
"."
] |
[
"Perihelion (closest approach to the Sun) tends to occur during winter in the northern hemisphere, while aphelion (greatest distance from the Sun) occurs during summer in the Northern hemisphere.",
"The Earth's ",
"next perihelion",
" is January 2, and the next aphelion is July 5."
] |
[
"Wow, only one answer but it's a good one. Thanks!",
"Bonus question edit: Do you know if we are currently in perihelion or aphelion?"
] |
[
"How do you cool things to extreme low temperatures +1-2K?"
] |
[
false
] | null |
[
"For anything below liquid helium temperature, generally laser cooling is used. There are many different mechanisms for exactly what physical properties are used. The general principle is that you shine photons at very specific frequencies, so that the material is more likely, on average, to give momentum to the photon rather than remove momentum from it."
] |
[
"Cooling things to extreme low temperatures is a very long, tedious process, but shockingly enough, 1-2k is not really \"extreme(ly) low.\" If you have just a nice bucket of liquid helium, that helium is around 3.5k, then using a \"simple\" ",
"Evaporative cooler",
" you can actually cool something down to .3K, no lasers required. (Evaporative cooling is basically just allowing the higher energetic helium to evaporate away, leaving only the lower energy (thus lower temp) helium around)",
"Now, if you want to get into the \"extreme low\" range (below .3k) then laser cooler, as described by fizzix, is the way to go. "
] |
[
"Yes, that is about the best we can do. Our instruments like to be around 4K to 10K depending on the instrument.",
"Of course, we are doing this at 13,796 ft - which helps quite a bit."
] |
[
"Why do things like saliva or melted cheese pull into strings when you try to separate them?"
] |
[
false
] | null |
[
"Saliva \"pulls into strings\" due to water's property of ",
"cohesion",
" (saliva is over 99% water), as well as the mucus content in the <1% non-water part. Miscellaneous proteins also composing the admixture may increase saliva's \"stringy\" properties.",
"Melted cheese \"pulls into strings\" due to its material properties at the given temperature. At high(er than room) temperatures, cheese melts from a solid to liquid. As it melts, it doesn't turn straight into a soupy mess; moreover, it becomes a thick, ",
" fluid as it transitions from a solid. Viscosity is a quantity that describes a fluid's resistance to flow. Since it had a high viscosity after the phase change, it had a high \"resistance to flow,\" causing the \"pulling\" phenomenon."
] |
[
"The cohesion of molecules of pure water cannot resist the adhesion forces between the water mass and the object touching it. The mucus content of saliva adds to that cohesion and causes the \"stringy\" effect."
] |
[
"Saliva \"pulls into strings\" due to water's property of cohesion",
"If it was due to that, water would also behave similarly, and it obviously doesn't."
] |
[
"Does Eating Healthier Disproportionately Affect People of Low Income?"
] |
[
false
] |
Hello folks. I always hear that eating vegetables is better for the body and that we should eat more of them. However from an economic standpoint, is it actually feasible for people with a limited income or people that are struggling economically to purchase healthier foods like fruits and vegetables over unhealthier processed foods like easily prepared mash potatoes or fast and ready mac and cheese? I'd like to hear people's thoughts on this as I have been trying to research whether eating healthy is actually feasible economically.
|
[
"It is possible, but increasingly difficult as you go lower down the levels of economic stratification. Not only is price an issue, but in low income areas, it is common to find ",
" These are areas where there is limited or no access to healthy food at all. Think of a slum with only a corner store and MacDonalds. Even if you had the money to afford healthy food, you may need to travel significant distances to even find it. This requires access to transportation which is already an issue for the economically deprived.",
"The second part of this is education. Understanding what to eat and how to actually prepare it requires education. In low income areas where education systems may be weak or non functional, you have to wonder where people can learn these things. ",
"There are other issues such as eating habits that may be ingrained into a family or community culture.",
"This is a decent article from the guardian that explains things pretty well with a few inconsequential inaccuracies.",
"https://www.theguardian.com/commentisfree/2015/nov/29/kis-junk-food-dont-blame-parents"
] |
[
"I would add that prep time is also an issue the further down the economic line you go"
] |
[
"The guardian piece puts it well. They describe it along the lines of: a project that is described as a hobby or stress reliever in the affluent becomes another time consuming stressor in the poor."
] |
[
"Does the centripetal force of Earth's rotation make you lighter at the equator than at the poles?"
] |
[
false
] |
I was bored at work one day and thought of this. My buddy who has an engineering degree worked some math on the back of a paper plate (sadly misplaced now) and told me that the average person will indeed be a few pounds lighter (depends how much you weigh in the first place) at the equator as centripetal force combats gravity somewhat. Thought I would see if his conclusion holds up to scrutiny by the larger community.
|
[
"and told me that the average person will indeed be a few pounds lighter (depends how much you weigh in the first place) at the equator ",
"Actually, the difference in a measured weight between the north or south pole and the equator, arising both from ceptripetal force and the earth's oblateness, ",
"is about 0.5%",
"So a 150-pound person would weigh 3/4 of a pound less at the equator than at the poles."
] |
[
"It is true that due to the centri",
" force, in the frame of reference rotating with the Earth you will in fact be a little bit lighter at the equator. In an inertial reference frame, some of your gravitational attraction to the Earth is being used as a centri",
" force to keep you rotating with it. "
] |
[
"Neil Tyson has answered this very question in many of his talks, which you can find on youtube, and yes, you are lighter at the equator than at the poles. He mentioned hypothetically, you could speed up the rotation of the earth and make it so that people at the equator would essentially be weightless. But people at the poles wouldn't feel a difference."
] |
[
"What happens when there are two, different dominant alleles in the genotype?"
] |
[
false
] |
[deleted]
|
[
"The short answer: It's likely co-dominance. ",
"I'm not a geneticist, but I know enough to try to answer your question. I will also try not to over generalize this question because the genetic mechanisms at play are not always as simple as one just being dominant over the recessive (such as functional gene vs defective gene) and it really varies depending on where and how you look at the phenotype. There are many biochemical processes that are at play with gene function and expression. But let's look at your specific example. ",
"The simplest way to address the question of whether or not a gene is dominant is to just look at the overall phenotype. Not from the molecular point of view but just at the big picture. What happens when D",
" and D",
" are expressed? Since they are both dominant, then they have some phenotypic activity on the heterozygote individual. If they are expressed in equal amounts, and don't affect each other, we are likely to have a co-dominant phenotype. The general classic example of this would be your blood type. ",
"However, if in the presence of one allele \"affects\" the other allele, we could get varying levels of expression of D",
" and D",
" proteins. This could lead to a phenotype that is an intermediate between the parental strains. This is more in line with incomplete dominance. ",
"So in both cases, we see different phenotypes than the parental strains. But the main difference comes down to if you can see an intermediate, like getting a pink flower from mixing white and red, we say it is ",
". In the case of ",
", we look to see we observe both phenotypes. This would be like getting splotches of both red or white on the flower. ",
"Hope this helps you!"
] |
[
"It depends, say you have a white mouse and a black mouse with both color traits being dominant. If the offspring are grey, then you have incomplete dominance, which is characterized by a blending of the traits. If you wound up with a spotted black and white mouse, then it would be codominance."
] |
[
"None of these answers really answer the question very well. It's more useful to think of ",
" or ",
" as being dominant or recessive rather than individual alleles or genes. An allele is a variant of a gene that produces a protein. You can have different alleles at different loci within that gene that cause different amino acids to be added to the polypeptide, which then alters the shape of the polypeptide, and therefore alters its function in some way. Downstream interactions can be massively complex or relatively simple, and ultimately, the only way to tell whether or not a gene is dominant to another is to look at its phenotype. This could be as simple as seeing a white, pink or red flower, or as complex as realizing that one protein product from an allele complexes with two other proteins in a way that inhibits the product of the other allele (through any number of mechanisms) which would then appear dominant, though it depends on many other gene products to be this way. ",
"Long story short, look at the traits, not the genes when thinking about dominance. "
] |
[
"Do my brother and I share the same genes?"
] |
[
false
] |
I guess I am not yet clear about DNA and genes. My brother and I clearly must not share the same genes because we are different people. Then, this must mean that every sperm/egg's DNA/gene (?) content is unique. If that is the case, then when someone performs a DNA test, what are they getting?
|
[
"You have received half your father's genes and half of your mother's genes.\nIt's the same for your brother, but with different halves.",
"In the end, it is highly improbable that you received exactly the same genes or totally different ones. In average, two brothers share 50% of their genes."
] |
[
"Genes are the bulk of the \"data\" stored on the DNA. There are other important elements that are called non-coding, because they are typically not ultimately translated into proteins. However, they play important roles in the regulation of gene transcription, for example.",
"All humans share an almost identical set of genes, where a gene is a transcriptional unit that encodes a protein with a specific function. The phenotypical differences among humans can be explained by the alleles discussed elsewhere in this thread. They are essentially small variations on the same gene but do not typically change the function of the encoded protein dramatically. In other words, two alleles of the same gene are much more similar to each other than any two genes.",
"In addition to the phenotypically evident genetic differences, our DNA also differ by so-called silent mutations. These are changes in the actual DNA sequence that do not result in changes of the encoded protein. This is a consequence of the redundant nature of the genetic code where a combination of 3 nucleic acids on the DNA encode one of 20 amino acids in a protein sequence. Since there are 4 different nucleotides, there are actually 64 different codons (combinations of 3 nucleotides that encode a single amino acid). Only three of those do not code for any of the 20 amino acids but \"are used\" to terminate the translation of an mRNA transcript of a gene.",
"When people compare the similarity of species, they often use percentage numbers based on the identity or similarity of protein sequences in those two species. For example, when you read that humans are 97% identical in their genes to chimpanzees, what it really means is that the sequences of two homologous proteins (two proteins with the same function in two different species) in humans and chimpanzees are, on average, 97% identical. Between two humans, that figure is much closer to 100% but only identical twins share 100% of their protein sequences. For everyone else, especially when it comes to identity of the DNA sequences, the numbers are much smaller.",
"TL;DR: The number of differences in the DNA of two humans are significant but smaller in number than the differences between a human and an ape, for example. The number of differences in the proteins of two humans are significantly smaller than the number of differences in the DNA of those individuals."
] |
[
"The three responses you have so far are correct to some extent but may also be a bit confusing. All three leave out the reason why some of your genes aren't even the same as any of the genes your parents have.",
"To answer your question more directly: your brother and you share about 50% of your genes. About half of your genes come from your father and the other half come from your mother. Your selection of genes that you received from dad is made up from a different set of genes than the set of genes your brother received from dad. The same is true for the genes that you received from your mother.",
"Genes are located on your chromosomes, which are essentially very long pieces of DNA rolled up and twisted around special proteins in the nucleus of each cell in your body. You have 23 pairs of homologous chromosomes, meaning you have a duplicate copy of each chromosome. These copies are not exact duplicates as you received one copy from your mother and one from your father. With human males, there is the exception of the X and Y chromosomes, which are not homologous and for which you only have one copy. As pointed out below, if you are a boy you and your brother both received a copy of the same Y chromosome that your father has plus one of the X chromosomes from your mother. There is a less than 50% chance that the X chromosome you received is identical to the one your brother received.",
"During the maturation of the female egg and the male sperm (germ cell differentiation), the 46 chromosomes (23 pairs) are divided up into two sets of chromosomes (one copy of each of the 23 different chromosomes) per cell in a process called meiosis. During meiosis, each of the homologous chromosomes may exchange pieces of DNA with its counter part in a process called chromosomal crossover. This leads to a genetic recombination of genes and each of the resulting 23 chromosomes (22 in the male germ cell as X and Y chromosomes do not recombine) is no longer completely identical to any one of your father's or mother's chromosomes.",
"The combination of the male sperm and the female egg during fertilization results again in a complete set of 23 pairs of chromosomes. Each embryo now has two copies of each gene, one from your mother's egg and one from your father's sperm. If these are slightly different variants of the same gene, they are called alleles. If you have two different alleles of a gene, you have a heterozygote set. If the two copies are identical, it is called a homozygote set. Typically, only one of the copies of each gene is used by the body.",
"There are many different ways to check for maternity (probably less common), paternity, or the origin of a DNA sample, for example. In most cases, DNA \"fingerprints\" are compared with each other providing a statistical measure of the chance that two samples are related or identical with each other. You would, for example look at a set of markers for specific and frequently occurring alleles of several genes in each sample. You can then calculate the likelyhoods of whether the samples came from the same individual, related individuals, or completely unrelated individuals. In paternity tests of boys, you can simply compare pieces of the Y chromosomes of a putative father and his putative child. There should be an exact match. Likewise, for maternity tests, you can compare the DNA from the mitochondria of two individuals. Mitochondria are cellular organelles that have their own small set of genes. They are only passed on from the mother to her children.",
"TL;DR: A little less than half of your genes are likely to be the same as your brother's. DNA fingerprinting is a statistical measure of the relatedness of two DNA samples."
] |
[
"Why do power plants need cooling towers?"
] |
[
false
] |
Why does the steam after going through turbines and then condensers needs to be cooled by cooling towers? Wouldn't it be more efficient to pump hot water into the boiler to generate steam? My preliminary research shows, there are such systems as closed circuit that does not use cooling towers. I would think this was the obvious choice. What then, would be the advantage behind the design with cooling towers and open circuit water system.
|
[
"There are two different things going on here. All “heat engines”, and a power station is one, need to dump waste heat in order to be efficient. That might be done by ",
"a conspicuous cooling tower, or some other way",
", but it's always done somehow. As the wiki articles says, if the power station has access to abundant cooling water that can be more efficient and cheaper than the alternatives.",
"The working steam coming out of the turbine is condensed partly to create low pressure on the outlet side of the turbine which makes it work more efficiently. But that's also a useful place to extract the waste heat. In all cases (so far as I know) of electrical power generation from steam the condensate from that process is exactly the feedwater to the boiler, in a closed cycle—what you see coming out of the cooling tower is not the working steam, it is vapour from the cooling water (or ambient air). ",
"EDIT: typos"
] |
[
"It's cooling the steam that has already been through the turbine to convert it back to water. The water has a MUCH smaller volume than the steam and is easier to pump back into the boiler."
] |
[
"Yeah, but the Carnot cycle describes a perfect heat engine, doesn't it? "
] |
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