title list | over_18 list | post_content stringlengths 0 9.37k ⌀ | C1 list | C2 list | C3 list |
|---|---|---|---|---|---|
[
"Question about HIV/AIDS and its spread to the progeny of the affected individual."
] | [
false
] | [deleted] | [
"Having unprotected sex with someone who is infected with HIV is not a guarantee of transmission of HIV. As an example, we believe that unprotected receptive anal intercourse poses the highest risk of HIV transmission, and it is probably about 1.4% per act, on average (",
"source",
"). However, even this numb... | [
"If her mother never had HIV, there is no reason to suspect that she would have gotten it from her mother. ",
"As for her mother, she could either fit into the category of being immune to HIV, or more likely, didn't procreate much, and via luck of the draw, didn't become infected. You have to remember that it is ... | [
"And to put that in perspective if your GF's parents had unprotected anal intercourse once a week for a year the mom would only have a 50:50 chance of contracting HIV. "
] |
[
"When researchers say they have \"tested products on mice or rats with cancer,\" how do they give them cancer in a uniform fashion?"
] | [
false
] | [deleted] | [
"Often times this kind of research is done by implanting tumor cell lines into mice. These cell lines are cells taken from real tumors that are able to continually replenish themselves in tissue culture (for instance, HeLa cells). Then take a bunch of genetically identical mice, and implant these tumor cells into... | [
"Can confirm, this is precisely what I do in one of my research projects, and we inject a fixed volume of tumor cell solution at a fixed concentration of cells/mL directly into the vertebral body of athymic rats and monitor response to treatment."
] | [
"It's good to mention that what you described is a xenograft, meaning the cells you're injecting may not be derived from the mouse you're injecting them into."
] |
[
"So, instead off trying to mine asteroids, shouldn't we just build a moon base and mine meteorites?"
] | [
false
] | null | [
"When you say \"Moon base mining meteorites,\" you're saying \"Moon base mining the Moon.\" Which is certainly an idea, but it may not be all to great of an idea (or it might be a good idea... there's a lot that goes into that equation that I won't be able to touch on in this comment).",
"First, a bit of rocket s... | [
"But building a moon base has several benefits",
"No doubt. But that changes it from an apples-to-apples comparison to an apples-to-oranges comparison. Secondary benefits may be worth weighing, plus political goals and economic considerations. Unfortunately, that's impossible to answer without making large, unwar... | [
"But building a moon base has several benefits",
"No doubt. But that changes it from an apples-to-apples comparison to an apples-to-oranges comparison. Secondary benefits may be worth weighing, plus political goals and economic considerations. Unfortunately, that's impossible to answer without making large, unwar... |
[
"If two planets, similar in size and both with dense atmospheres, were to come close enough in their orbit that their atmospheres passed through each other, what would be the outcome?"
] | [
false
] | If the two planets in question are orbiting each other in a binary system with extremely low periapsis (several hundred kilometers or less), low enough that their atmospheres collided but their surfaces did not, what would happen? Would they just shed off gasses into the surrounding space? Would they create friction on... | [
"Check out the Wikipedia article on ",
"Roche limit",
"."
] | [
"So if two planets were to pass each other in such a fashion they would both simply be ripped apart by tidal forces? "
] | [
"Interesting question. The above answer on Roche Limits is correct; within a certain radius (governed by how strongly held together each planet is), the gravity from each would rip them both apart. This is why ",
"Saturn has rings",
" and why ",
"Comet ISON might not make it through",
" it's close interacti... |
[
"Do cats purr voluntarily or unvoluntarily?"
] | [
false
] | For example if we're petting a cat, does it purr voluntarily to tell us that its enjoying the attention, or is it more of a reaction, like when we laugh if tickled? | [
"They do purr in response to injury; the vibrational frequency of purring has actually been shown to promote healing , and not just in cats. That doesn’t answer the voluntary/reflexive question though. "
] | [
"As far as I know no one is certain about whether it's voluntary or in- or both (rare, but most animals have a few actions that can be either, like for us it is blinking and breathing). But you will sometimes see big cats, who structurally can't perform a true purr (they have differently structured voice boxes), wh... | [
"I've heard it's an involuntary reaction to stimuli. They are just as likely to purr as they're dying after getting hit by a car or something. I haven't fact-checked that and I heard it before the internet was a big thing so take it with a grain of salt. If you find out let me know."
] |
[
"Pleochroism vs Birefringence, same or different?"
] | [
false
] | TLDR: What's the difference? I learned a new word recently from the Skeptic's Guide to the Universe podcast; pleochroism. I am a lab tech in a hospital lab. We perform crystal exams on synovial fluid. In our procedures we call the crystals birefringent if, under polarized light, they display a different color when orie... | [
"MSU crystals (gout) are ",
", which can be observed (with no color changes) using crossed polarizers. If one additionally inserts a quarter-wave plate (which is made from a ",
" material) into the light path of the microscope, then you get the blue and yellow colors when you change the crystal orientation.",
... | [
"Pleochroism and birefringence are different and you're right, what you're describing is ",
"pleochroism",
" (i.e. a mineral crystal changes color when it is rotated on a microscope stage while being illuminated by plane polarized light). Birefringence, at least in the context of petrographic microscopy is a pr... | [
"That's because the terminology you've heard/seen (birefringence) is indeed the correct way to describe the optical properties of MSU crystals. MSU crystals are ",
" pleochroic. As I've noted in my ",
"earlier comment",
", the change in color that you observe in the gout assay is due to pleochroism in a com... |
[
"Will there ever be a \"glass\" stronger than sapphire or diamond?"
] | [
false
] | Currently the strongest screen in smartphones is sapphire (rumoured to come to iPhone 6). Will this be as strong as they can get? Is there a physical barrier reached? Is diamond viable as a "glass" material for phones? And how srtong would it really be? | [
"Your post is good in general but I have a few corrections to the terminology you use.",
"Polymer is not equivalent to glass. Although many polymers form glass phases most things which people think of as glass are not polymers. This includes window glass.",
"Regular glass is primarily oxygen and silicon ",
" ... | [
"I don't think this is true. Neither sapphire nor Gorilla glass are conducting."
] | [
"I don't think this is true. Neither sapphire nor Gorilla glass are conducting."
] |
[
"When riding a bicycle which will better reduce the likelihood of collision with motorists: blinking or solid lights?"
] | [
false
] | How do motorist perceive blinking or solid light sources differently? Would different time of day or weather conditions change the answer to this? Could the results be different depending on the density and speed of traffic? | [
"Blinking lights are mostly designed for day time use when the background is already quite bright. Blinking lights for night time use is more of a nuisance than anything for other drivers, as a solid, steady light is just as easy to recognize and much easier to judge distance, speed, and direction of travel.",
"... | [
"I'd say your best shot is to keep the solid light since it's the legal option, and to wear bright yellow reflective gear. It's easy for me to zone out and not pay too much notice to any tail lights, but the bright yellow reflective jackets/pants/shoes always grab my attention and put me on high alert."
] | [
"It's actually illegal to have the lights flashing they need to be solid",
"That varies by location. Where I live, both solid or flashing front white and red rear lights, or even just reflectors, are required for lawful night time riding on public streets, so long as they are visible from at least 500 ft."
] |
[
"Gizmodo claims that mass and weight are the same thing. Does this explanation make sense?"
] | [
false
] | Gizmodo posted a today with an explanation of why mass and weight are the same. TBH, the explanation made no sense to me. Can someone help explain this point of view please? | [
"They are not the same.",
"Mass is a measurement of how much matter is in an object.",
"Weight is a measurement of how hard gravity is pulling on that object. ",
"Your mass is the same wherever you are--on Earth, on the moon, floating in space--because the amount of stuff you're made of doesn't change. ",
"... | [
"Colloquial words and their scientific usage get muddled on a regular basis. Most scientists aren't overly pedantic on the topic in day-to-day life either. It is perfectly acceptable to say \"a proton weighs 940 MeV\" when the ",
" scientific terminology would be either \"a proton has a mass equivalent to 940 MeV... | [
"The Gizmodo article is just some vague nonsense, the ",
"Sixty Symbols",
" video is about how the \"mass\" of Newton's second law (behavior of inertia) and the \"mass\" of gravitation are one in the same, punctuated by the fact that bowling balls and feathers accelerate under gravitation identically.",
"Here... |
[
"How do services like Google Now, Siri and Cortana, recognize the words a Person is saying?"
] | [
false
] | null | [
"Baidu has now ditched some of the speech recognition techniques mentioned in this thread. They instead rely on an Artificial Neural Network that they call Deep Speech (",
"http://arxiv.org/abs/1412.5567",
").",
"This is an overview of the processing:",
"Generate spectrogram of the speech (this gives the st... | [
"It's really fascinating how quickly Deep Learning has been growing recently. I went to a talk last week given by Mike Houston on the different applications of deep learning (fantastic talk). He works at NVIDIA and does machine learning on GPU I believe. The sheer variety of uses was really impressive, and many of ... | [
"One of the reasons Google offered the free google voice system with voicemail text functionality was to test their voice to text reliability rate and find ways to improve it. At one point, part of the terms of agreement for using the service was that they would be able to anonymously compare the sound of the voice... |
[
"Muscle memory suddenly stopped working while solving Rubik's cube, Why?"
] | [
false
] | null | [
"We can't comment on personal anecdotes / isolated events without resorting to speculation which we always try to avoid."
] | [
"Means?"
] | [
"What?"
] |
[
"What do you think of this syllabus? I'm hoping to teach an intro QM course, and need your input. Anything I'm missing?"
] | [
false
] | null | [
"Comments from a physics grad student:",
"The pure classical stuff is probably not so useful. Fourier transforms certainly are, but I don't think discussing harmonics is really relevant for teaching QM.",
"H is commonly ",
" as T + U... this could be a pretty short discussion, depending on the target audience... | [
"Thanks, I appreciate the notes.",
"The hamiltonian thing is supposed to be a pretty short discussion.",
"I purposefully left dirac notation until after the solution of the infinite square well to try and use that simple example to try and create a more concrete understanding of what dirac notation represents."... | [
"Replying to you so you get the red-orange, but I'm basically seconding james. Your program sounds pretty much exactly like my university's syllabus on these topics, and I'm happy with it except for the Dirac notation stuff not having been first. We had to take a math class with the Dirac stuff which was terribly... |
[
"When feet are cold, why do they insist on sweating so much?"
] | [
false
] | What causes this paradoxical reaction? EDIT: Does the ventilation of your feet affect the amount of sweat? I notice my sweaty feet most when I'm barefoot at home, but maybe this is a related question worth asking too. (Based on the comments so far) | [
"That thread doesn't seem to have any scientific explanations -- I'm hoping this one will get some answers specific to feet as well as just armpits, and Hyperhidrosis.",
"EDIT: sorry, I did not see your explanation on the other thread. So does cold not enter into the cause at all?"
] | [
"You could be wrong, you could be right. But seeing as the warning below the text box states \"...layman speculation will be downvoted and removed\" I would suggest that is the reason for the downvotes."
] | [
"You could be wrong, you could be right. But seeing as the warning below the text box states \"...layman speculation will be downvoted and removed\" I would suggest that is the reason for the downvotes."
] |
[
"Breathing fumes of dry ice, bad for you?"
] | [
false
] | Dry Ice is frozen CO2: CO2 is toxic: Surely, if you had a big block of it in a room, you would feel these effects? Has anyone experienced this? Backstory: I was at a fancy restaurant and the waiter brings some dressing in a bubbling glass with what I assume was dry ice in there. My friend asks me if that would be d... | [
"A little bit of it, not that bad. But I once made the mistake of accidentally inhaling some really concentrated fumes, while bent over double trying to get some of the last chunks of the stuff out of a usually closed container. ",
" of blood out my nose in under a second. Do not try at home."
] | [
"I'm not intimately familiar with its mode of toxicity, just relaying a personal anecdote, but ",
"its MSDS",
" lists it as an exceptionally powerful vasodilator, which I suppose could be a cause (a quick google of \"vasodilation epistaxis\" seems to agree)."
] | [
"Why did you bleed?"
] |
[
"Can we use the AlphaFold database to invent new proteins based on the function we want?"
] | [
false
] | So AlphaFold released the predicted structures of 200 million naturally occurring proteins. Does this mean we can use this data to invent new protein structures that have different functionality? | [
"It is a helping step in the right direction, but not as transformational as one might hope. AlphaFold like many other folding prediction algorithms helps in the sequence to structure translation. In other words, given a specific peptide sequence, how will the 3-dimnesional shape of the protein look. It is a big st... | [
"I keep telling people that nano-technology isn't creating robots made of metal and electricity. It's more like biology."
] | [
"I keep telling people that nano-technology isn't creating robots made of metal and electricity. It's more like biology."
] |
[
"Can hadrons be coupled to each other by multiplet gluons?"
] | [
false
] | In other words, by gluons that aren't singlets, but gluons coupled with each other. | [
"Oh, by multiplet gluon, I meant ",
"http://en.wikipedia.org/wiki/Glueball",
" .",
"Wait, so are protons and neutrons connected by non-singlet gluons too? They're non-singlets of color, perhaps, but there are still 8 types of gluons (that can separately be considered as singlet gluons). "
] | [
"I think we're having a vocabulary issue. Singlet is a state that is composed of multiple particles where the total color charge is 0. It's the same as the |0,0> state for a two electron system (as opposed to the spin triplet |1,-1> ,|1,0> and |1,1>). A singlet gluon would be one that is a color-anticolor pair. ",
... | [
"Oh okay I see. Thanks! Yeah, I tend to think of \"pairs\" as \"multiplets\" - this may just be an artifact of thinking transferred over from a theoretical statistics course I just took."
] |
[
"If a Nazi regime and WWII had not happened in the 30's and 40's, would the U.S. have the capability, and desire, to focus on Rocketry as much as they did?"
] | [
false
] | null | [
"This would be more appropriate in ",
"/r/askhistorians"
] | [
"Thank you sir, I'll post there as well"
] | [
"I think I'll remove this post for being off topic for the main ",
"/r/askscience",
" sub.",
"As I said, I think it's more appropriate on ",
"/r/askhistorians",
", alternatively if you want to get a \"scientist's\" perspective try ",
"/r/asksciencediscussion",
" as that is intended for open-ended and ... |
[
"If we were to leave the Milky Way, would it be a shorter distance to go 'upwards/downwards' towards the edge or fly towards the outer rim?"
] | [
false
] | As far as I understand the properties of our solar system in the Milky Way, we are positioned in one of the outer arms in our disc/spiral-shaped galaxy. If we would have a device capable of leaving the galaxy would it be faster to go 'vertically' or 'horizontally'. Thanks! | [
"The thickness of the disk in which we are is roughly 2000 lightyears. The distance from our solar system to the outskirts of the disk is about 23 000 lightyears. So you would have to go in a vertical direction to leave the disk more quickly."
] | [
"The question kinda implies it's talking about the disc, because s/he's asking if we're close enough to the edge that it's quicker to go \"out\" than \"up\".",
"That said, we don't have a law for how we define a galaxy, but usually we use something like the radius at which the density of matter (including dark ma... | [
"Calculating the precise escape velocity is difficult because we can't calculate the Milky Way's mass precisely.",
"But once you get far enough from the Sun to discount its gravity, the escape velocity from the Milky Way is around 544km/s, plus or minus 10%.",
"See here for a related discussion - ",
"http://w... |
[
"Solar power + Hydrogen generator."
] | [
false
] | If a solar panel were placed in a system where some or all of the solar energy is used to separate the hydrogen from water during the day. Then at night combusting the hydrogen in the oxygen in some sort of piston generator or perhaps a turbine. How big would the system need to be to pump out 1000kwh per month? (just a... | [
"Your system is needlessly complicated. You are taking electricity and then using it to perform electrolysis, then using several steps before you are getting useful energy out.",
"There are many other ways to store the electrical energy - capacitors and batteries being two obvious examples. Burning hydrogen will... | [
"Use a ",
"battery developed for the purpose",
" as I stated above."
] | [
"But off grid though?"
] |
[
"Why do birds move their head back and forth while running on their feet?"
] | [
false
] | While watching them in the city I've always wondered why this happens. Can anyone give me insight? | [
"The same reason a dancer tries to look at the same place on a wall when pirouetting",
". ",
"Because the pigeon's vision is based on movement so much, it's easiest for them to see predators or prey when their head is sitting still. The way to do this while walking is to thrust their head forward, then hold it ... | [
"Look at your eyes in a mirror. Now rotate your head side to side. Your eyes will keep facing forward, not changing direction. The ability of keeping your eyes facing the same way, regardless of your head, keeps your vision becoming a blur. Birds do not have this intricate control of their eyes, forcing them to kee... | [
"Is that what's happening in ",
"this video",
"? (Took me a while to find the GIF version.)"
] |
[
"Are musical keys 'nature' or 'nurture'?"
] | [
false
] | Songs in certain keys sound sad, while others sound happy. Some chords sound gloomy, some chords sound exciting. Is this a result of conditioning through background scores of movies and such, or is it the same for everyone since birth? | [
"I researched this for a class in college. It's all nurture. Different cultures have different emotions tied to the same tones, there are different scales, not all have 8 notes. Even the notes in our contemporary music have changed over time, ie an A today is a slightly different frequency than it was during the bi... | [
"I'd argue both. As others have said, experience has a very large effect on the types of emotions attributed to certain keys. However, there is an inherent \"pleasantness\", also called ",
"consonance",
", to certain intervals like an octave or a major fifth that have to do with the physics of sound and how our... | [
"Well.... even proportions aren't constant. ",
"Okay, in general almost every society has a special place for some equivalent of the octave (notes whose frequencies are a 1:2 ratio) and a perfect fifth (notes whose frequencies are a 2:3 ratio) but that's about it. How they divide up scales between those ratios, h... |
[
"Why do great structures in our universe like rings of planets, accretion discs or galaxies have shape of discs?"
] | [
false
] | null | [
"http://www.reddit.com/r/sciencefaqs/comments/fui70/why_do_all_the_planets_in_our_solar_system_rotate/"
] | [
"Ok, but I mean why are for instance most of galaxies discs? Why rocks around planets form rings but not for example clouds?"
] | [
"Ok, but I mean why are for instance most of galaxies discs?",
"It's the same reason - conservation of angular momentum.",
"Why rocks around planets form rings but not for example clouds?",
"Because there are more than just momentum at work in the atmosphere.",
"Really, it's all addressed in that thread."
] |
[
"Why don't planes have multiple wings to generate more lift?"
] | [
false
] | Why do commercial aircraft utilize only one wing to generate lift? Would it not be easier to use two or more wings like bi-planes of the past? | [
"Actually most wings do that. At slow speeds (e.g. landing), flaps are extended that increase the wing area (and change the shape) for added lift at low speeds. As stated above they are not very efficient at high speeds (and actually give less lift). "
] | [
"A very few aircraft basically do that, by having variable wing geometry. They don't have ",
" wings, but their wings change shape relative to the wind. This adds lots of weight and mechanical complexity, and is generally not a good choice. The drawbacks outweigh the benefits."
] | [
"Firstly, commercial airplanes generate enough lift. They don't need more. ",
"Now the question becomes: Why they have one wide wing instead of two shorter wings so that the strength and thickness of individual wing can be smaller, reducing overall drag and weight? ",
"The problem with bi-planes is that the l... |
[
"What exactly is an electronvolt?"
] | [
false
] | I've been reading some of the material regarding the LHCs startup lately, and how it's going to be running 13TeV experiments. My question is, what exactly an electronvolt? How can I put it in context (in terms of volts, joules, whatever it's equivalent to). Also, I've heard it being used as a unit of weight for subatom... | [
"It's the energy gained by an electron passing through a one volt potential difference. It's equivalent to 1.6x10",
" Joules. When used as a unit of mass, it's implied that it's eV/c",
" , so an electron is 511,000 eV/c",
" ."
] | [
"Oh, some textbooks are good with that kind of thing. I just make them up as I need them. A good-sized apple weighs about a newton. The voltage needed to create a visible spark by rubbing your feet on the carpet and then coming close to a door knob is about 10,000 volts. A blowdryer or a microwave oven consume abou... | [
"I don't think the world correctly uses kg for weight, but it's just a misconception, and all our scales are calibrated to give the mass of an object, right? ",
"If I stand on a scale, I'm providing a force of say 600N on the scale, but the scale does an implicit division by 9.8 to yield the mass, which we incorr... |
[
"Doesn't the fact Quantum and Classic physics cant play nice prove we are living in a simulation?"
] | [
false
] | null | [
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"This question is based on fundamentally flawed premises. Please conduct some background research and revise your question if you wish to resubmit.",
"Plank length and plank time are not the minimum un... | [
"\"This world is pixelated\" - Leonard Susskind",
"So...."
] | [
"If you want to discuss the removal reason please do so in modmail."
] |
[
"If most of an atom's chemical properties are determined by its electrons, why do ions not behave like the element they share their electron number with?"
] | [
false
] | E.g., why does Fe not behave like cobalt and Fe not behave like manganese? | [
"Different numbers of protons/neutrons, different sizes, the charge itself. Many factors, really. To elaborate a bit, Fe+ has an extra proton than cobalt, meaning that the size of the electron cloud around the ion is shrunken relative to cobalt due to the increase in inner positive charge. Further, the charge of th... | [
"In short, because ions are charged. But this is a great question - in fact, if electron shells are the same, there is a great deal of similarity in behavior where the charge can be ignored. Two compounds with identical electronic structures are called ",
".",
"This causes CO (carbon monoxide) and the cyanide i... | [
"The answers thus far are generally or partially true.",
"In general, chemistry has everything to do with the interaction of an atoms electrons with the electrons of another. There are many rules/trends with these that are complicated and I won't go into detail about that.",
"The properties of an atom really ha... |
[
"What is the effect of distance on radiation induced ionization?"
] | [
false
] | null | [
"There is no amount of closeness to a source of non-ionizing electromagnetic radiation that will make it ionizing. It’s just the frequency that matters, unless the source is so unbelievably bright, that it indirectly causes ionization due to heating."
] | [
"So lets say that we have two atoms isolated in space. One atom is at a certain temperature and is emitting radiation in all directions and some small fraction is intercepted by the other atom. The other atom is then reemitting the radiation at increasingly high frequencies as the two systems progress towards equil... | [
"The distance between them doesn’t change the energy of the photons they emit and absorb. Either the frequency of the photon is high enough to knock bound electrons out of the atoms, or not."
] |
[
"If an non-human mammal gave birth to their offspring while unconscious, will they still still recognize their offspring as their own or will they suffer a degree of disassociation similar to human mothers under similar situations?"
] | [
false
] | null | [
"I never knew that if a human gives birth unconscious there's a degree of disassociation. Could someone explain that?"
] | [
"General reasons for maternal unconsciousness",
"Extreme example",
" (coma)",
"Scientific perspective on impacts of common example",
" (C-section)"
] | [
"Most of what we know about this comes from research in sheep, due to the common practice of ",
"cross fostering",
" lambs. Scent is an important cue for mother-offspring recognition in many species (including ",
"humans",
" and ",
"non-mammals",
"). Developing a specific bond through scent does require... |
[
"Is it possible for a spaceship traveling around Earth to generate electricity?"
] | [
false
] | I am pretty sure that the Earth has "magnetic field lines," (or something like that) so can't a spaceship travelling across this field have the ability to generate power? | [
"Like this? ",
"http://en.wikipedia.org/wiki/Electrodynamic_tether"
] | [
"Yes, but the tether then acts as a brake, and the ship will fall from orbit. (Electric generators turn mechanical work into electromagnetic energy.)",
"The same tether can be operated as a motor to create thrust. Just pump a current through it (use solar panels or a nuke RTG.)"
] | [
"Yeah, or it would be more efficient to use fuel/oxidizer to run a small generator directly! :)"
] |
[
"Chemists: I ruined metal jewelry when I spilled iodine on it. Is there any way to remove the horrible tarnish?"
] | [
false
] | I accidentally dropped an open bottle of iodine on my jewelry - mostly sterling but also silverplated and some gold plated. The items seem ruined. The only thing I can think of is sanding/polishing the top layer off, but it won't work. Any ideas? | [
"Silver iodide is a pretty famous compound. It responds to light by breaking down to silver metal. For a long time this was how photographs were taken. ",
"Try putting your jewelry outside in full sun for a couple of hours. Burn it off. Dunking it in a tub of photographic fixer (sodium thiosulfate) should also wo... | [
"Are they like brown spots? I know brown iodine solution loses its color when added to sodium sulphite/hyposulfite solution. So soaking your jewelry in a small amount of said solution may do the trick. Take this only as a starting point and do your research however. Or wait till another comes and expands on this. I... | [
"Sounds like you formed some silver iodide. I know a regualr tarnish(silver sulfide) can be cleaned with ",
"Aluminum and vinegar.",
" You end of reducing the silver. It might work for you. I would have to look at a table of reduction potentials to know for sure"
] |
[
"What plastic does the ISS uses to store its food? I'm a student interested in food storage in space!"
] | [
false
] | [deleted] | [
"From the pamphlet, ",
"\"Space Food Packaging Facts\"",
":",
"Many of the foods used for the Shuttle and ISS\nare freeze dried and packaged into\nrehydratable containers. NASA packages both\nrehydratable and bite-sized foods in\nCombitherm-Paxx packaging materials made\nby Wolff Walsrode of Burr Ridge, Illin... | [
"What's the reasoning behind having five layers? And which one is the inside one?"
] | [
"Hey! What about the ethylene/acrylic_acid copolymer thermoplastic interlayers that keep the layers from delaminating?"
] |
[
"Caspian Sea: sea or lake?"
] | [
false
] | null | [
"The term 'sea' is kind of inconsistently used. ",
"Endorheic basins",
" like the Caspian Sea, Dead Sea, Aral Sea, Salton Sea, etc which have 'sea' in their common names, are all technically ",
"lakes",
" because they are internally drained and completely surrounded by land. Why the Caspian Sea is the Caspi... | [
"I can add an example of the opposite: The Baltic sea is called lake in Swedish (Östersjön, translation: Eastern lake)"
] | [
"Interesting. That is super confusing as (at least in a scientific sense) ‘lake’ has a clear definition and anything that was a part of the ocean would definitely not be a lake. This does highlight that some of this may also stem from different usages across different languages (eg in German, see = lake)."
] |
[
"What is the cause of a headache when travelling in a car/bus and reading on my phone/reading a book? Also getting a similar headache (not sure if related) when looking through a big magnifying glass for a longer time period or while listening to music with only one of my earbuds plugged in."
] | [
false
] | null | [
"Motion sickness for the car example. Not sure about the magnifying glass. When you read in a car, what your eyes see does not associate with what your inner ears are telling you about your current motion. This disparity causes the motion sickness."
] | [
"I'll address the magnifying glass issue;\nWhen you spend a substantial amount of time looking through the glass, your eyes are straining to bring as much of the light into focus as it can. this does cause strain on the eyes and can cause headaches. the same phenomenon happens if you were to wear a pair of glasses ... | [
"Exactly what I was thinking!"
] |
[
"Why do seasonal allergies only affect us for part of the year?"
] | [
false
] | As an example, a person may be fine for most of the year smelling flowers, prancing through fields, et cetera, but when allergy season rolls around, suddenly everything sets them off. Why wouldn't these things be a bother the rest of the year? | [
"Because the particular pollen, spore, whatever that the person is allergic to is only airborne during a specific time of year. ",
"If you are allergic to the pollen from Loblolly pine trees, you will have ",
" an allergic reaction during the few weeks that those pine trees drop their pollen. Once it's cleared ... | [
"Well what about pets?"
] | [
"I am not aware of any seasonal allergies associated with pets, but animals do shed fur at specific times of year, so that's possible as well."
] |
[
"I have a chemistry exam tomorrow, but I don't understand what moles are. Any help, Reddit?"
] | [
false
] | null | [
"This post was caught in the spam filter because it doesn't fit in this subreddit, try a place like ",
"/r/homeworkhelp",
" or ",
"/r/chemistry",
"."
] | [
"But it should fit in this subreddit because it's science. I'll move it now."
] | [
"You didn't ask a question about chemistry moles that science can answer, you just asked people to explain a scientific concept to you which is not what this subreddit is for. If you can form the question in a way that it is actually a question regarding chemistry moles, then it will be allowed."
] |
[
"Why does having a bigger particle accelerator help reach higher energy collisions? Can't we just spin around in a smaller one for longer?"
] | [
false
] | [deleted] | [
"The maximum momentum of the beam in a circular accelerator is set by the maximum main dipole magnetic field strength and the radius of curvature.",
"Magnetic field strengths are limited by technology, so in order to reach higher momenta, you need larger radii."
] | [
"This is the correct answer. But to also address about a point in the question (\"spin around for longer\"):",
"The way particle accelerators like the LHC operate is not that you constantly inject particles that are then accelerated over the course of the ring and then collide at one point where they have the nee... | [
"The acceleration segment of the LHC is really quite short - shorter than 100 m if I remember correctly. Less than 1% of the circumference. Accelerating the particles is easy, the LHC is purely limited by the magnets to keep the particles on track.",
"This is not always the case. LEP, the electron/positron accele... |
[
"How exactly does cancer work?"
] | [
false
] | I hear things like "cancer attacks" but I don't understand how a cell made incorrectly can do that. It's not like a virus who is programmed to attack body, so how and what does it do. | [
"Cancer is in large part a disorder of apoptosis (programmed cell death) and cell (growth) signalling. Cell lines which pick up mutations in their growth hormone responses or their duplication mechanisms are prone to grow out of control. However cells and tissues have a range of mechanisms and signals to prevent th... | [
"I think this is a already pretty good explanation! ",
"The \"attacking\" part OP asks about is merely a 'side effect' of the tumor. Bear in mind that it can have different ways to hurt the human body. It's big mass which gets in the way of the tissue's function is probable the most know. However a small tumor co... | [
"This is great. I wasn't sure how much extra detail I should go in to. In part because its not really my expertise but also because there are others with more knowledge will be better placed to answer more detailed questions."
] |
[
"Why do Squids have circular pupils, yet, other cephalopods such as Octopus and Cuttle fish have wavy or rectangular pupils?"
] | [
false
] | I'm not sure if squids are the only cephalopods with circular pupils, but, they are the only ones I know of that do. Why is it that other cephalopods have wavy or rectangular pupils, but, squids don't? | [
"Squids live in deep water. Big round eyes help them see in dim light. ",
"Cuttlefish live in shallow waters with variations of light: bright above, dark below. In dim light, the pupil is circular. In variegated light of shallow waters pupils are W-shaped. The horizontal aspect helps cuttlefish see toward the fro... | [
"A circular pupil is an ordinary sort of pupil, it's effective in getting an image even in dim light. So it's not surprising squid have one.",
"But weird octopus and cuttlefish pupils...they may actually help them see color. Chromatic aberration occurs when light passes through a lens. Different colors are foc... | [
"Eye evolution is fascinating. There are several pretty divergent evolutionary pathways to make an eye, so you have structures with a similar function but a pretty varied history. ",
"Wiki"
] |
[
"Chemists: how do you identify unknown chemicals?"
] | [
false
] | Hi Chemists, Everything you do is black magic to me. Say I present you with a challenge: I give you a beaker full of an unidentified compound dissolved in an unidentified solvent. Let's say it's an unknown complex organic molecule dissolved in some solvent. How would you go about identifying the compound? I'll give you... | [
"When you mention an \"unknown complex organic molecule,\" are you referring to the fact that it is unknown to us or that it is a never-before-seen molecule? If the former, then there are a variety of standard spectroscopic and physical/chemical tests, typically relying upon characteristic features in the spectra,... | [
"Modern structural determination revolves around 3 techniques: mass spectrometry, infrared spectroscopy, and nuclear magnetic resonance spectroscopy.",
"Mass spectrometry (MS) revolves around smashing the molecule up (using a variety of ionization sources) and determining the mass of the fragments. At the ",
",... | [
"This is only true for organic species (yes, the OP did say organic :)). For things like metals you'd need to use an ICP-MS (or AA). Also, the area under the curve part is only useful for quantification and not as important for identification (although we do need to know the peak to ID the compound). The key here i... |
[
"XKCD What If's \"Electron Moon\": how does this energy density make sense?"
] | [
false
] | Like many "What Ifs?", this one is really fascinating, but it ends right when things are getting interesting. The question concerns what would happen if the Earth were made entirely of protons and the moon were made entirely of electrons. Presumably the question was about charge attraction between the Earth and Moon. O... | [
"You gotta remember gravity is much much weaker the the other forces.",
"First, image if electrons were neutral for a second. The binding energy of the electron moon would just be the binding energy of the moon.",
"Now, imagine the electric repulsion of two electrons was equal to the amount they attracted to ea... | [
"According to the string theorist interviewed by the author, the amount of energy represented by our hypothetical electron moon would be equal to the mass/energy equivalence of the entire visible universe.",
"I guess I'm just boggled by that, and trying to understand it. How is that possible?",
"The raw strengt... | [
"Granted that gravity is very weak compared to all the other forces, all the same, it only takes a small amount of electric or magnetic charge for an object to exert forces that are comparable to the forces that humans can generate and experience every day.",
"Yeah, I guess it's hard to wrap your mind around just... |
[
"How do we know the composition and mass of some planets/stars ?"
] | [
false
] | null | [
"In terms of composition. We're looking at a technique called spectroscopy. Basically, for any chemical element (or larger structures like molecules but when you're talking about stars it's too hot for molecules), the electrons can only have specific energies. ",
"For each chemical the gaps between the available ... | [
"Is there a limit to the range, where we can use this method ?",
"The only case where distance really affects the usefulness of spectroscopy to identify composition is the resulting brightness of the object.",
"In order to do spectroscopy, you need to split up all the incoming light into its constituent colors,... | [
"There are characteristic emission lines, such as the Lyman alpha line that can be used to determine the Doppler shift."
] |
[
"Animals' organs (and how they differ from ours)"
] | [
false
] | How similar/dissimilar are the organs in an animal to ours? Do any (or, which) have more or less organs than us? At what point (as in size/evolutionary difference of the animal to us) does the set of organs in an animal become greatly different to ours? As a side question: how do insects and other invertebrates 'work' ... | [
"Depends on the animal! Each species is adapted to a particular habitat and behavioural pattern, meaning bodily function and structure will vary too! ",
"I don't know too much about biology, but I'm fairly certain that most mammals have similar major organs to humans. Apparently mammals all seem to have the corte... | [
"Here's one that I find interesting: Snakes only have 1 long, thin lung. The other \"lung\" has evolved into a little vestigial stump, much like how in humans the coccyx is a vestigial remnant of a tail. "
] | [
"Mammals, the group of animals to which humans belong, generally have similar organs and organ structures to humans. The less directly related to primates a given animal is, the more difference you will see between its anatomy and a human's. For example, when observing the digestive system of the cow, you'll find... |
[
"Why is kerosene/liquid oxygen still used as rocket fuel? Isn't it possible to harness nuclear fission as a means of reaching escape velocity?"
] | [
false
] | Just curious as to why rocket fuel technology doesn't seem to have changed much since the early days of the Space Race. Isn't there a better way to reach escape velocity? Having to use huge amounts of liquid fuel just to send a small crew of astronauts into space seems really inefficient. Can't we split an atom and ha... | [
"The principle behind rockets is really simple: things go out one end, your rocket goes the other way. ",
"This is what happens with rocket fuel, you burn it, which causes a high pressure so the gas is accelerated out the bottom of the rocket, which in turn pushes the rocket upwards. It is rather difficult to use... | [
"You're right that combustion is a terribly inefficient means of propulsion, whether solid or liquid fuel. There are many alternatives, but so far, none are viable.",
"Nuclear fission is a very promising option, but there are currently drawbacks to all such means. For instance, ion engines have specific impulse v... | [
"Generally speaking, the faster the gas exits the nozzle, the more propellant-efficient the rocket is. (This is the ",
", not to be confused with escape velocity).",
"If the rocket works by converting heat into kinetic energy then you want to reach a high temperature in the combustion chamber. You're right, ker... |
[
"What is the possibility of life on other planets that has evolved, but not to the level which we consider \"intelligent\"?"
] | [
false
] | Is there any reason to think that we got evolutionarily lucky in our intelligence? We seem to be a far ways apart from the rest of the animals on our planet. Is that a fluke? Or could there be other life that is vastly more intelligent than us? | [
"I think the answer to what you're asking for is the ",
"Drake Equation",
". Only without the f_i and f_c terms. And then the equation isn't the number of civilization which which communication is possible, but the number of planets that have developed life.",
"As for whether or not human are a fluke, we may ... | [
"Given the sheer vastness of the Universe, and the rate that such a variety of exoplanets are turning up lately, and that life on our own world was not \"intelligent\" for almost all of its history, I'd say it's damn near certain that life has arisen and come to dominate some other world, just as life dominates our... | [
"That's basically what I'm saying. Of course I'm nowhere near an expert in the field, so me saying that is as good as any random guy on teh street saying it."
] |
[
"What evolutionary advantage did feathers give to dinosaurs?"
] | [
false
] | [deleted] | [
"I think you might do better to ask \"what advantage did feathers give dinosaurs?\" Your question sound as if the environment can prompt a good physical change. That is not how evolution works. This modification results in the organism becoming more adapted to it's environment making it 1) more likely to survive to... | [
"We don't know, but I've read that they could have been selected for to provide warmth or for some sort of sexual selection."
] | [
"I once read that feathers are actually extremely kick ass, and that most land animals would benefit from obtaining feathers.",
"It seems like flight is a result of feathers rather than the other way around, since birds are entirely covered in feathers and only have specialized flying feathers in their wings and ... |
[
"If mars is cooler than earth, is it possible to mine deeper into mars and take advantage of a physical barrier to the sun’s radiation?"
] | [
false
] | null | [
"Yes. The fact that Mars is colder is irrelevant - you don't need to get that deep. Just a few meters underground will do.",
"Just to nitpick, solar radiation is the least of your concerns. During a storm the dose can be very high, probably even lethal, but particles won't penetrate very deep due to their relativ... | [
"Your answer got me thinking, ",
"Q1. Are Solar Panels Practical on the surface of Mars? I am worried about asteroids and overpowered radiation.",
"Q2. What are the risk factors of Tunnel Collapse in whatever material Mars is made from?",
"I am thinking about digging a big base underground to support humans a... | [
"Regarding radiation and meteors, solar panels on the surface are slightly safer than in orbit. If they work on satellites then they can work on Mars. An extra problem is dust accumulating on the panels. There are small dust devils on Mars that have a cleaning effect, but if you have humans, then they can go and cl... |
[
"Why exactly are mercury and lead poisonous?"
] | [
false
] | null | [
"Check out the respective Wikipedia pages on each of those metals - they contain a separate section on toxicity."
] | [
"Wikipedia tends to be a) incomprehensibly technical (to me, anyhow), or b) oversimplified. For example, I just looked at thallium's page, and it basically tells me that it is toxic and can cause cancer. Why? I'm not informed of that. "
] | [
"You can follow the link to ",
"thallium poisoning",
":",
"Part of the reason for thallium's high toxicity is that, when present in aqueous solution as the univalent thallium(I) ion (Tl+), it exhibits some similarities with essential alkali metal cations, particularly potassium (due to similar atomic radii). ... |
[
"Is ADHD over-diagnosed, and are stimulant medications over-prescribed?"
] | [
false
] | [deleted] | [
"There really isn't a way to answer your question with anything but anecdotes.",
"Rest assured that ADHD is a real thing with real impact on people's lives. Some doctors may overdiagnose, some may underdiagnose."
] | [
"I understand that most of the psychometric tests used in diagnosis of ADHD are actually to rule out other potential psychological or learning disorders. There is no diagnostic test specifically for ADHD, though people with the disorder do tend to have difficulties with working memory and (of course) executive func... | [
"I understand that most of the psychometric tests used in diagnosis of ADHD are actually to rule out other potential psychological or learning disorders. There is no diagnostic test specifically for ADHD, though people with the disorder do tend to have difficulties with working memory and (of course) executive func... |
[
"What food or edible item contains the most calories in one tablespoon (15ml)?"
] | [
false
] | null | [
"In terms of volume (i.e. mL) I can't find any data, but I can find the densities as well as the energy densities. Fat sits somewhere between 37-39 kJ/g, where the closest after that is alcohol sitting at 29 kJ/g, and then carbohydrates and proteins at 17 kJ/g.",
"Density of fatty acids or fat is approximately 0.... | [
"Pure ethanol."
] | [
"Well a supersaturated solution would have less energy per unit volume that pure sugar, sugar has 1,619 kJ of energy per hundred grams, and a teaspoon of sugar is 4 grams so the total energy would be 64.76kJ"
] |
[
"Why are particle accelerators called *-\"tron\" ?"
] | [
false
] | As asked in the title: were does the "-tron" comes from? E.g. Cyclotron, Synchrotron, Synchrocyclotron, Bevatron, Tevatron, Betatron etc. | [
"The etymological root of the -tron suffix is Greek - it is a suffix denoting an instrument; akin to Old English -thor, suffix denoting an instrument, Latin -trum. Source: ",
"http://www.merriam-webster.com/dictionary/-tron"
] | [
"The ancient greek name of amber was Electron. The first source of electricity has been observed by rubbing amber with wool, and noticing that it attracted small light objects by static electricity."
] | [
"True, but not quite relevant to this question."
] |
[
"Is there any evidence of human evolution within the timeframe of recorded history (i.e. the last few thousand years)?"
] | [
false
] | I think the question is pretty self explanatory, but I'll be a little more specific. It's easy to give examples of evolution when talking about other species, such as plants, dogs, bugs, etc; but are there examples of evolution within the human species that have occurred within the last few thousand years? Or even the ... | [
"As a species, we're getting taller.",
"Some individuals are totally immune to HIV.",
"The Tibetans have evolved a set of genes that let them cope at low-oxygen altitudes.",
"Changes don't always have to be \"positive\" (remember evolution is not purpose/goal-driven).",
"If your friend wants to see a human ... | [
"Lactose Tolerance. "
] | [
"Drift (non-selective) evolution has occurred a lot. Human vein patterns are a good example, as the common path of superficial veins has changed over the time period that anatomists have been studying them.",
"Height may not be a good one as it has a lot to do with diet."
] |
[
"Why are some berries poisonous? Isn't the purpose of a berry to be eaten and spread the seeds of the plant, thus making it pointless to deter consumption through poison?"
] | [
false
] | My current hypothesis is that they are only poisonous to certain species (such as mammals but not birds) in order to get maximum dispersion, but this is just a guess based on no evidence. | [
"Poisonous berries would take a while to kill you, in which time you would travel, fall over dead, and become fertilizer. Mission accomplished, right?"
] | [
"To extend ... if a particular species often travels into an unfavorable environment between eating the berries and defecating the seeds, then it will be advantageous for the plant to become unpalatable, inedible or poisonous to that species. That way, fewer berries are wasted on a worthless carrier and the plant c... | [
"You are correct, poisonous berries are typically not poisonous to all species. Some birds eat yew, which is quite toxic, and the capsaicin hot peppers does not effect birds"
] |
[
"Is it possible for the brain to permanently lose ability to regulate circadian rhythms via the day night cycle?"
] | [
false
] | null | [
"Yes, via damage to the suprachiasmatic nucleus (SCN), which receives input from a special subset of light-sensitive cells in the eye and uses that input (among other cues) to keep its internal \"clock\" aligned with the day/night cycle. ",
"Animals with lesions to the SCN will still engage in sleep and other cyc... | [
"is it possible to reverse the rhythm in these animals?"
] | [
"Bizarrely, yes. ",
"There have been experiments in which the SCN of one animal has been transplanted to another, resulting in the recipient acquiring the circadian rhythm of the donor. ",
"This would not, of course, work with most brain structures."
] |
[
"Why, when exposed to high radiation, you die a week or a month later and not immediately? What happen in the body?"
] | [
false
] | [deleted] | [
"I'm on mobile so I'm hoping someone will link some sources for me. When dosed with high amounts of radiation, DNA gets irreparably damaged, and the cells go apoptotic/necrotic. Instead of having normal cell division and turnover, there are no cells left to divide, and you rot slowly from the inside out."
] | [
"Actually, with enough radiation you do die immediately.",
"Anyway, what it does is it cooks you. And your internal organs being quite resilient, will keep you going as long as possible - it all depends on how much you recieved. ",
"And a little may be enough to knock some electrons off of your DNA creating a m... | [
"The health effects of radiation are dependant on the quantity of dose absorbed, and the period of time over which it is absorbed.",
"If the dose is absorbed in large quantities very quickly, you could die from organ failure. Beyond acute effects (cell death), radiation really just increases chances of cancer due... |
[
"Galaxies are said to mostly have black holes in the center. Have we observed any without them? And if so what object is center that has the mass needed to form one without being a black hole?"
] | [
false
] | It seems to me nothing would have the mass to form a galaxy without being a black hole. My google-fu isn't bringing up any known galaxies that have something such as a hypergiant in the center. | [
"It seems to me nothing would have the mass to form a galaxy without being a black hole.",
"Galaxy formation isn't exactly about one very massive object capturing other objects into orbit around it. So galaxy formation without a black hole would from that perspective be possible.",
"In the same way, the individ... | [
"Only a little over a trillion times the mass of our planet. Basically negligible."
] | [
"Only a little over a trillion times the mass of our planet. Basically negligible."
] |
[
"Yesterday I captured a (female) mouse that was on my apartment. Today, when I checked on her, she had aborted. What kind of abortive natural abortive mechanisms animals have?"
] | [
false
] | I'm curious if this was an abortive mechanism or just a consequence of bad health. I'm unaware if animals can abort "by will" under certain situations. Although the simplest explanation I can come up with is that it got pretty nervous, affected its health and provoked the abortion. EDIT: Just in case, my roommate and I... | [
"I work with rats, and often have to breed them. Too much stress or too little nutrition will cause them to abort their pregnancies which is true of just about any species. Can they \"will\" it to happen? Probably not, but most animals, especially those that typically fall into \"prey\" categories are pretty tightl... | [
"Stress-induced abortion has been studied quite a lot in mice and rats due to interest in stress's role in human miscarriages. First off - a pregnant mouse, or almost any oregnant mammal really, must have high progesterone at all times or the uterus will almost immediately shed the placenta. Bear in mind here that ... | [
"Correct, but this generally occurs before implantation, and over the course of two prolactin surges wherein the female is exposed to the urine of a novel male. Females are separated as early as possible from males, and not exposed to any other males, immediately after breeding for this very reason.",
"I would no... |
[
"If the Higgs field gives mass to matter, and the mass of matter curves spacetime, and said curvature is the basis of gravity; does this imply that the Higgs field causes gravity?"
] | [
false
] | null | [
"Here the distinction between two types of mass becomes important. There’s inertial mass, which is the m in Newton’s F=ma. It takes effort to make something with nonzero inertial mass move. In contrast, something with zero inertial mass, such as photons, must always move at the speed of light. We know that electron... | [
"No.",
"Coupling to the Higgs field is not the only way that particles get mass. For example, any hadron, where the majority of its mass comes from strong interactions rather than the bare masses of the constituent particles.",
"And furthermore, mass is not the only source of gravity. Things like mass, energy, ... | [
"Took years of maths and physics training for me to begin to understand this stuff, but I'll try to summarise."
] |
[
"How does black tea have more caffeine than green tea, when they come from the same plant?"
] | [
false
] | I know that oxidation plays a role to make it taste and look different. But does that play into the caffeine content too? | [
"Black tea and green tea are both made from the leaves of the Camellia sinensis plant, but they are processed differently. Black tea is made from leaves that are fully oxidized, which gives it its dark color and strong flavor. Green tea is made from leaves that are steamed or pan-fried to stop the oxidation process... | [
"two black teas from the same region might have totally different caffeine levels. a green tea may have the exact same caffeine as a black tea, black tea having more caffeine is just a myth, albeit a half decent generalization, but that's not because of something inherent but rather due to advertising companies wan... | [
"When I looked into tea compositions for caffeine and theanine, the best study I found suggested teas have similar caffeine contents, but they vary in ratio of theanine to caffeine. Green tea is richer in theanine with respect to caffeine, 2:1 caffeine to theanine in green tea and 3:1 in black tea. Red, white, and ... |
[
"How does evolution account for things like an enjoyment of music and art? How did these pleasures first come about?"
] | [
false
] | null | [
"Any answer to this question is inherently speculative, but I've read it argued that these phenomena are basically a \"side-effect\" of the development of language. E.g. That the way the brain changed to process language made these other more \"frivolous\" activities possible. \nSo the capability to enjoy music and... | [
"There is also sexual selection. Humans have been shaping stones for a really long time, some examples of which don't have wear indicative of tool use. Sure that one dude has a sick sabertooth tooth, but you made a stone wedge out of obsidian and she never saw anything like that before.",
"Tor Nørretranders, in... | [
"You are making a fallacy that says all our aspects are required to survive. A lot of the stuff our genes carry is simply dead weight that we can survive with, as long as it doesn't kill us/keep us from reproducing."
] |
[
"When a battery loses its energy as it sits in the drawer, where does that energy go?"
] | [
false
] | null | [
"The answer to \"where does that energy go\"? is almost always ",
", and batteries are no different. ",
"The potential energy in a battery is \"locked up\" in chemical bonds. An unused battery undergoes self-discharge, which is an internal chemical reaction that breaks these bonds, releasing the energy in the... | [
"It turns into heat. This is actually a process used to estimate the lifetime of battery chemistries- microcalorimetry. ",
"This excellent lecture",
" by Jeff Dahn (probably the most famous battery researcher, now working at Tesla motors) talks a bit about how his group used microcalorimetry to measure the pa... | [
"A bit late, but I'm kinda curious. So if you had a battery with much higher discharge rate, after you stop charging it could eventually just melt? Also, do we have any mechanisms or devices that use this ?"
] |
[
"Does something exist which is not made out of energy in a form or another?"
] | [
false
] | Since E=mc2 means that it is possible to convert matter into energy and vice versa, is there anything which is not made out of energy? Is space itself made out of energy? | [
"Never stop. I don't."
] | [
"Space itself has vacuum energy, according to current models of cosmology. In these models, the vacuum energy is actually quite large."
] | [
"So could one say that space itself is made out of energy? Or is it just that space contains energy?",
"That's up to you. The vacuum itself makes a healthy contribution to the expansion of the universe. The ",
"First Friedmann Equation - the last equation in this section",
" separates radiation, matter, cur... |
[
"How does fire spread?"
] | [
false
] | null | [
"An ignition source initiates combustion of a flammable mixture of fuel and oxidizer. This reaction is exothermic, and given that the fire is spreading by the premise of your question, enough heat is released by the oxidation of the fuel to heat nearby fuel to a temperature at which it ignites in contact with the o... | [
"It depends on what's burning. In a campfire, for example, the wood is the fuel and the oxygen in the air is the oxidizer. In a candle, the wax is the fuel and again the oxygen in the air is the oxidizer."
] | [
"Thank you. Which is the fuel and which is the oXidizer?"
] |
[
"Questions about the Acid Dissociation Constant"
] | [
false
] | I understand pKa values in water in terms of determining which molecules will deprotonate which other molecules, but for extreme values, I can't wrap my head around the definition. For example, methane has a pKa of ~50. Does this really mean that the ratio [CH3-] [H+] / [CH4] in water is 10 ? This would mean something ... | [
"pKA Values beyond the H3O",
" and the OH",
" ions (The strongest acids or based that can exist in water) work a little differently. From water's stand point the only thing you can infer from those values is that if you place one of those compounds into water it will immediately and completely give/accept it... | [
"One thing to be aware of is that equilibtium constants, and thus pK",
", can be calculated from \\Delta G of the reaction, so we don't have to measure concentrations to talk about pK",
". This doesn't really solve the problem, though, as \\Delta G",
" of ions in water is not easy to come by if not by some f... | [
"When dealing with the pKa values for very weak acids/bases, the solvent used to determine these quantities is not water, but a weaker acid or base than water, respectively. By changing the solvent, one can achieve a higher concentration of the conjugate species. In water, the very strong conjugate acid/bases would... |
[
"Evolution as a bodily response to environmental pressures?"
] | [
false
] | Involuntarily of course. Is it possible that another pathway for evolution is the response from the body to environmental pressures (aside from random mutation and gene exchange etc.)? After learning about Hox genes, I began to wonder if the body somehow 'knew' that it was no longer competing as well for resources, or ... | [
"No, only populations evolve. Individuals adapt, and if they can't, they aren't selected for. There's no evidence for anything that \"increase\" mutation rate in individuals who aren't competing effectively for scarce resources.",
"Where did you get the idea that it's pretty rare to find transitional forms? Sure,... | [
"Your post is very well thought out and has many key points... therefore I am going to reply point by point.",
"Only populations evolve. Yes I agree, I mean, that is the definition of evolution: changes in allele frequencies in a population over time. However, I was just wondering what drives this evolution.",
... | [
"What drives evolution is random mutations in an organisms DNA, and how that mutation causes the organism to respond to the environment. If the mutation is advantageous, then the organism will be more likely to reproduce and survive, therefore being more likely to pass on its genetic code. ",
"Environmental facto... |
[
"I've lived in Los Angeles my whole life and seen everything from historic El Niño rains, to historic droughts. But before me for 8,000 years, the Tongva people lived in what is now Southern California. What was the climate like for them, compared to the climate is for me now?"
] | [
false
] | [deleted] | [
"Firstly, it is important to understand how climate works in response to the local landscape. Geologically speaking, 8,000 years is hardly anytime. Because of this, the landscape was not effected by any new landforms such as mountains which’s have a drastic effect on climate. ",
"Next, global weather patterns ... | [
"I think there are some tongva museums in the area ",
". Perhaps with some guides available that can answer that question, and others you don't know you have yet. ",
"I know this isn't a typical answer, but native folklore about conditions is a viable source of evidence, and given OPs location, I think it's a... | [
"Here's something that might intrest you. ",
"https://research.noaa.gov/article/ArtMID/587/ArticleID/2560/Old-weather-%E2%80%9Ctime-machine%E2%80%9D-opens-a-treasure-trove-for-researchers",
"This could help you figure out that regions weather patterns before the asphalt and smog set in.",
"As for the questio... |
[
"How does the concept of time work in relation to places that are light years away?"
] | [
false
] | Say, for example, 50 lightyears away there's an alien race. Are they living in time the same way as us. If you could travel 50 lightyears in one second; would they be living in time the same way as us (e.g. second by second) (n.b. this one may sound a bit elementary but it messes with my mind that species so far away c... | [
"Yes unless they're moving really fast relative to us or are near a collapsed star."
] | [
"When we say 'light year', we mean 'the distance light will travel in one year', which is a very, very long way. So the light you would see in your telescope would have departed from the aliens 50 years ago--you're seeing what they're up to 50 years ago (and vise versa)."
] | [
"If we sent an astronaut there at 0.9999c (c is the speed of light), then we'd be constantly seeing images of them (although horribly redshifted) while they are traveling. The moment they got there would be roughly 50 years from our frame. However, that image is also delayed by exactly their distance from you div... |
[
"Why do aerosols cans all use flammable gas as the propellant? Why not use an inert gas/normal air?"
] | [
false
] | null | [
"Aerosol propellant needs to have specific properties. It needs to be liquid at room temperature at about 15psi. If you wanted to use normal air or nitrogen, you’d have to either cool it down to far below room temperature, or raise the pressure super high, which would require a pressure vessel instead of a can. Tha... | [
"Aerosol cans used to use CFCs. They were perfect - liquefy under pressure as needed, non-flammable, non-toxic, inert. Turned out they destroy the ozone layer.",
"So that's why they all use butane now.",
"Aerosol cream uses nitrous oxide. I'm not sure why that isn't used in other things?"
] | [
"You can even buy refillable \"air in a can\" bottles, and they provide ludicrously small amounts of air-squirting for their size, compared to the liquid-based ones. I have one, even starting at 6 bar it's disappointing. The Air Zound bike horns work the same way, but because you don't hold it in your hand you can ... |
[
"To what extent do you think that birds have evolved to recognise windows over the past 200 years?"
] | [
false
] | null | [
"An insufficient extent."
] | [
"They pass the knowledge down generation by generation through song.",
"No, they don't. And I'm not citing that for obvious reasons. "
] | [
"To the same extent that the recognized not to fly into trees. Windows aren't perfectly transparent, so it can be fairly easy to discern a window, even at a distance. "
] |
[
"Is the water ice present in the solar system the same as ice on earth, just much colder, or is it in a different phase?"
] | [
false
] | I suppose I should specify I'm asking about the ice on the surface of icy bodies, or rather ice that isn't buried and under pressure. So, for example, is the ice on the surface of Europa or Enceladus the same as the water ice on Earth? What about cometary ice, is that the same? I've read a few times about "ice as hard ... | [
"The short answer is that they aren't quite sure. Depending on the formation mechanism they have different predictions for which of the ice phases it might be in, not all of which are kinetically accessible. It turns out that theres a good chance that depending on how the water got there, rather than being crystall... | [
"it might be amorphous based on some spectroscopy they've done.",
"I'm writing a paper on this very topic. ",
"Ignoring all other variables (eg: impurities) then amorphous ice forms at temperatures below ~100 K, if the temperature is above 100 K crystalline ice will form.",
"Edit: ",
"here is a paper on thi... | [
"I've read a few times about \"ice as hard as rock\" ",
"Just to get you started:",
"http://en.wikipedia.org/wiki/Ice#Phases",
"Ice can have many different crystal structures depending on T / P. Not sure how mechanical properties change w/ crystal structure."
] |
[
"Is there more efficient ways to gather hydrogen from water? And are there any theoretical ways we havent tried/cant try yet?"
] | [
false
] | Also, what is the most efficient way to gather large amounts of hydrogen? | [
"Extracting hydrogen from water will never be very efficient due to the thermodynamics. Water is essentially \"burned\" hydrogen and you may have an idea how much energy that process releases, to get it to go backwards you need to put in at least that much energy back in. That being said we might be able to devel... | [
"Well we have cheap ways that produce less clean hydrogen like using super hot water vapor on coal or heavy oil producing CO2 and hydrogen Gass this also creates SO2 wich kills platinum catalysts you could use but it is super cheap. You can also use superhot water vapor on iron this is also cheap and cleaner but yo... | [
"Energetically speaking this method is extremely expensive. The amount of heat and energy you put in to the water is excessive and most of that energy is lost as heat/formation of byproducts instead of producing the desired H2 gas. A selective catalyst that could be MUCH more energetically efficient as it wouldn'... |
[
"If we upgraded Hubble with modern tech/optics, how much better would it get?"
] | [
false
] | Or would it just make more sense to start from scratch and throw a new telescope out there? | [
"Isn't JWST basically impossible to upgrade because it'll be so far away?"
] | [
"Yea there's no way we're upgrading that, it's going to be at the ",
"L2 Lagrange Point",
", which is almost 4 times as far away as the Moon (image ",
"here",
")."
] | [
"That is the plan, the James Webb Space Telescope is about six times the size of Hubble and should go up in about three years."
] |
[
"How exactly does radiation \"stick\" to objects and living things?"
] | [
false
] | How can ionizing radiation stick to things? Radiation is not matter. It is invisible, you cannot "touch" it or hold it. And yet, apparently you CAN wash it off, at least to a certain degree. What gives? Stranger still, is the fact that objects which have been contaminated, somehow "lose" radiation stuck to them over ti... | [
"I can't really answer your question, but just wanted to clarify your 'radiation is not matter' statement.",
"3 of the 5 major types of radiation are in fact matter. Alpha, beta and neutron radiation are all particles of matter. Only Gamma and X-Rays are an electromagnetic wave.",
"As others have said, often... | [
"Radiation doesn't stay around for more than a millisecond.",
"Radioactive material can stick to things and keep producing radiation. You want to avoid getting radioactive material on you or your clothes, and washing it off is effective: The material will still produce radiation but now it doesn't do that on your... | [
"As others have pointed out, \"radiation\" is the energy \"radiated\" away from something. It could be electromagnetic radiation (radiowaves, microwaves, visible light, X-rays, gamma rays, etc.), or it could be particles (alpha or beta particles).",
"When we talk about washing off radioactive contamination we me... |
[
"How long does it take a person to build muscle in a gym? AND RELATED QUESTIONS"
] | [
false
] | In addition, does using protein supplements such as powders and shakes actually help build muscle? Are there any negative side effects of using them? Is there any truth that shorter reps more weight versus longer reps less weight will relate to muscle growth and tone respectively? | [
"It's impossible to generalize how long it takes a person to build muscle by weight lifting. It completely depends on the type of workout, their diet and other individual factors.",
"Supplementing protein powder may help building muscle, but only if you don't ingest enough protein in your regular diet. The protei... | [
"A similar question was asked a few weeks back regarding many reps with light weights compared to few reps with heavy weights. It seemed like we have a somewhat decent understanding to how lifting heavy weights make us stronger, but we're not entirely sure ",
" high repetitions with lighter weights make our muscl... | [
"yeah see if you can...i really didn't get a good answer to any of my questions here... all layman answers no bio/chem explanations."
] |
[
"If gravity is the disortion of spacetime, does centrifugal force apply to planets orbiting a star?"
] | [
false
] | I've been reading many questions and wonderful explanations about the relativistic and quantum based nature of the universe, and I could grasp most things by reading comments, scientific articles and wikipedia. I must say though I'm pretty much a layman in this field, being a 2nd year programmer student on the universi... | [
"In difficult enough physics problems it doesn't make sense anymore to talk about force. Pretty much anything involving general relativity meets that criterion. If you were to calculate the force from gravity, it would indeed point towards the centre of the system. But you can solve the entire problem without menti... | [
"It is centripetal force that points inward. Centrifugal force points outward from a system and arises from our linear momentum resisting circular motion. Also it is fake and is a result of using non-inertial reference frames to describe rotating bodies, and is generally a result of the normal force or some other n... | [
"You're technically dealing with linear movements, yes, but not in any useful sense. You can't say that it's moving linearly therefore there are no tangential forces; the curvature of spacetime is what ",
" gravitational force. If you're going to consider the forces on a planet, you have to consider the forces pr... |
[
"How is it that the math of a certain theory (like general relativity) can yield conclusions that are known to be physically impossible? Does this imply that the theory/math of that theory is incomplete in some way or could be improved upon?"
] | [
false
] | It just seems odd to me that a theory could be considered completely consistent with reality, when some of its equations can lead to things that we know aren't possible. I've read on this subreddit that there are solutions to general relativity that are known to have no physical significance (worm holes and such). I th... | [
"You have three apples. I take away five. How many apples are you left with?"
] | [
"Newtonian physics will tell you that what happens if two unicorns collide elastically. However this does not imply that unicorns ",
"."
] | [
"Newtonian physics will tell you that what happens if two unicorns collide elastically. However this does not imply that unicorns ",
"."
] |
[
"How does pressure (e.g. in the earth's mantle) generate heat?"
] | [
false
] | Does this require movement of mass, so you get friction, or is there another mechanism? | [
"There are kind of two separate (not really related) questions in here. There is (1) a question about basic physics/chemistry with regards to how changes in pressure relate to changes in temperature (which I'm not going to try to answer, because I'll just get something wrong and have angry people messaging me all d... | [
"The previous poster gave a good explanation on the impact of radioactive decay on the Earth's internal temperature. I'll add some on the internal temperature driven by pressure off the top of my head. ",
"The earth, like all planets and stars, is held together by gravity which has assembled the large ball of mat... | [
"Thank you so much. This is really enlightening - I had no clue that so much of the heat was due to nuclear decay."
] |
[
"How is message tampering discovered in the E91 quantum key distribution protocol?"
] | [
false
] | The E91 protocol roughly proceeds as follows. There is some central device (perhaps a satellite) which distributes pairs of anti-correlated entangled photons to Alice and Bob. These photons can either be vertically or horizontally polarized. When Alice or Bob receive their photon they measure that photon with respect t... | [
"Alice's measurement ",
" collapse the wave function, but for the bits that Alice and Bob care about (the ones where they measured along the same axis), it collapses the wave function into eigenstates that they will both be measuring for, i.e. if Alice makes a measurement, the wave function collapses into an eige... | [
"What you're describing sounds very similar to BB84's (another QKD protocol) method of detecting tampering.",
"In BB84 Alice sends a photon to Bob prepared in one of two bases previously agreed upon, with the polarization in that base dictating the bit value (e.g. the horizontal-linear base might be used, and 0 d... | [
"Ah, apologies, I misread the question... It seems that there is a lot of math that goes into it, and to be honest, I think it will not make a whole lot of sense unless you sit down and do the math yourself. At a basic level though, I would think that it is a similar concept. Alice and Bob will always be under the ... |
[
"How is a behavior passed down through generations?"
] | [
false
] | null | [
"You may be underestimating the ability of your dog to respond to positive reinforcement; you never had to purposefully, deliberately \"teach\" him, but showing approval through body language allows them to learn, through experience, that this behavior is wanted and rewarded. Dogs are amazingly ",
"attuned to hum... | [
"There’s a reason it’s called a retriever though. They have been specifically bred to enhance one specific trait that’s a part of the (at least partially) instinctive ancestral hunting pattern, in this case the catching of prey and bringing it to pups.",
"Other parts of the wolf hunting behavior have been selecte... | [
"because smaller dogs were selected for things other than that behavior"
] |
[
"If my speed is 100 km/h and my destination is 100 km away and then I move 90 km/h if it's 90 km away. 80 km/h if it's 80 km away. Keep on slowing to match the distance. When will I arrive?"
] | [
false
] | null | [
"Never. You can think of it like this, since you're constantly changing your speed, your destination is constantly 1 hour away. If it is one hour away, then you can't be there, so you can never get there.",
"More precisely, if v is your current speed, and d is the distance from your destination, then d/v is the t... | [
"If you get within 0.5 nm (in ~200K years) you'll probably just get sucked the final distance by intermolecular forces, so you have that to look forward to."
] | [
"By my calculation, getting to within 0.5 nm will take about 32.925 hours.",
"Here's the script I used, which you can run in your browser's console.",
"(function() {\n var d = 100000; // Initial distance in meters\n var s = d/60/60; // Initial speed in meters per second.\n var targetDistance = 0.000000... |
[
"With a manual transmission, does coasting down hill in neutral actually save more gas than coasting in gear?"
] | [
false
] | [deleted] | [
"When you push down the clutch the engine will use gas to keep up the idle rpm. When in gear, you can use the energy of going downhill to do that and you won't spend gas."
] | [
"This is a fantastic question, there is a very long hill (mile or so) near my house and my car gives real time estimates on gas mileage.",
"I shall return with data.",
"Edit: alright, just finished my laps. My car is a new 2012 Jetta TDI. It was about 3.4 miles around, and I did six laps for each of the driving... | [
"Right, but your still injecting fuel fuel into the cylinder when coasting. The fact that your in or out of neutral has zero Bering on the TPS and what the vehicle base idle is. "
] |
[
"Is there a good scientific theory about how ancient civilizations cut and measured stone so precisely?"
] | [
false
] | There are approximately 180275901823057760 videos on YouTube that make claims about ancient civilizations using stone cutting techniques that are even more advanced than the ones we use today - especially when they're talking about the Pyramids (Meso-American, Egyptian and even Chinese). Some go as far as to say that h... | [
"The most satisfying explanation is the copper saw and fine sand combination. The grit from the sand assisted the metal saw in cutting blocks of granite and marble. The saw used was similar to the two-man felling saw used by lumberjacks. Sand was spread ahead of the saw blade as it was worked. Copper and bronze wer... | [
"From the dim recesses of poorly attended college level history courses, I seem to remember that the postulation of \"advanced help\" is a bit of left-over racism from when 19th and 20th c. explorers who were awed by the \"native\" workmanship they saw, especially in the more southerly parts of Egypt."
] | [
"Cool, thanks for the explanation. So the answer to the big question is - no, serious scientists questioning the existence of some inexplicable tool at work in creating these structures?"
] |
[
"Is it more efficient to boil cold tap water or to wait for hot water to start running out of the tap and then boil that?"
] | [
false
] | So I imagine the two competitors here are the efficiency of my gas stove vs. the efficiency of my hot water boiler? Maybe they're not that different (both run on gas) - if so, is there a cost difference? If they're the same, the obvious loss of efficiency comes from the cold water I waste while waiting for hot water to... | [
"Regardless of efficiency, it is safer to take cold water and boil it. Hot water allows for more things to be dissolved in it, and depending on your pipes, you could be increasing intake of unwanted substances."
] | [
"I shit you not, I did this experiment when I was younger to dispel the old wive's tale about cold water somehow boiling faster than warm.",
"\n.",
"\nResult: ",
".",
"\n.",
"\nI repeated the experiment at least 3 times with identical masses of cold and hot tap water on the same stove temperature, and boi... | [
"Having drained; refilled; then reused many water heating tanks mostly with CPVC pipe I am amazed at the accumulated rust in the bottoms of tanks. Coming from the tanks themselves is my assumption. I would never drink from my hot water tap but I definitely use my cold water as my main source of drinking water.",
... |
[
"Endurance sports e.g distance running - differences between women and men"
] | [
false
] | Womens' distance running times are dropping fast. I have heard some say that with advances in training, technique and technology (in which men currently have a slight advantage due to womens sport being less well developed until recently) they may one day equal or better mens' times for distance running due to differen... | [
" Ok so after finding my presentation and material, I think it would be a bit lengthy to rewrite, and it's very difficult to shorten it since this is one of those \"big picture\" kinda arguments. I'll try to keep this short and simple, but accurate based on the material I found. If anyone knows better than I, or se... | [
"I'd love to hear the differences/advantages/disadvantages of barefoot vs shoe running."
] | [
"For me:",
"Shoes hurt my back and knees and are hassle. Barefoot running (with thin soles in case of glass) doesn't hurt anything but is calf and hamstring pain to re-learn. You need to be competent with your body to avoid hurting yourself since you have to unlearn a whole adult life's muscle memory (caution: me... |
[
"Is it possible for a material to redshift light passing through it?"
] | [
false
] | A blueshift would also be interesting, but it seems like you would get conservation of energy issues. | [
"There are, in fact, materials which can halve the wavelength of light (effectively a blue-shift, although not quite in the doppler sense) passing through them - they do this by absorbing two photons, then emitting one. Green laser pointers often make use of this effect, among other things. This page has more detai... | [
"Second Harmonic Generation, or the frequency doubling effect is extraordinarily inefficient. You will not find a currently known material which can do this well enough to convert enough light that your eyes can detect it. It is done with lasers because you can pass the light through the upconverting crystal many... | [
"If by \"light\" you mean \"photons,\" then any material will do this to x-rays or gamma rays. Once you get above 1 keV or so, the effects of inelastic scattering between photons and electrons becomes noticeable, and as these photons travel through a material they will lose energy to these scattering collisions. ... |
[
"How would a Nuke behave on the moon?"
] | [
false
] | Well...I guess the title says everything... How would it look like? How would the moon after that look like? What would happen to the tides? | [
"What would happen to the tides?",
"The tides would stay exactly the same. One nuclear weapon would do ",
" to the moon. ",
"The Hiroshima bomb let out about ",
"63 TJ (terajoules) of energy.",
" The largest nuclear bombs in the US let out about 60,000 TJ of eenrgy. ",
"That's 60 x 10",
" Joules.",
... | [
"They'll put out exactly the same amount of energy, but it can be in a different form. More radiation, less shockwave."
] | [
"Blinding. Literally. You would go blind.",
"The process that goes on in hydrogen bombs is the same process that goes on in the sun: fusion. And it releases a lot of the same products, namely lots of radiation. ",
"So, just look at the sun. That's what a nuclear bomb in space would look like (for a few moments)... |
[
"Blackbody radiation: only visible and IR, or also radio waves?"
] | [
false
] | All of the textbooks make it clear that there is an upper limit to the energy of blackbody radiation (i.e. UV catastrophe). But, why do hot objects (e.g. your stove) not emit micro- or radio waves? The peak is probably in the red region (at least when it's glowing red-hot). Does the black body radiation curve have a lo... | [
"No, they emit at all wavelengths, albeit at very low intensity at very high and very low wavelengths (relative to the peak). Your interpretation of the UV catastrophe is wrong. The UV catastrophe is that when using the wrong law of black body radiation (the Rayleigh-Jeans law, which they didn't know was wrong at t... | [
"Easiest way to think about it is that light will interact with matter that is roughly the same size it the wavelength of the light.",
"X-rays are smaller than atoms so they go straight through. Radio waves are larger than walls so they go straight through.",
"Visible light interacts with the electrons in the a... | [
"Awesome, something in my field finally.",
"Black bodies emit at all longer wavelengths but the flux becomes increasingly small with longer and longer wavelengths. Using a black body source in spectroscopy becomes almost impossible under ~100 cm-1 (wavenumbers = longer than 100 micrometres).",
"This, along with... |
[
"What is global wrench tectonic theory? Does it discard plate tectonics?"
] | [
false
] | I posted this in AskReddit and they directed me here. I hope someone can help me find more information. I am in a master's program for math and science education. In my biology class we are discussing evolution and some students are quite resistant to accepting the theory of evolution, often citing "the significant vul... | [
"I'm not an expert on geology. But my psychoceramic sensor goes off because:",
"In addition:",
"Index of Creationist Claims"
] | [
"I don't know of any geologists (in academic, mining, oil industry, etc.), who believe that the theory of plate tectonics is wrong. There is just too much evidence supporting it, including things like actual measurements of plate movement using GPS. As noted by adoarns, there is no reason to link plate tectonics an... | [
"The thing about evolution-deniers is: they can only get to you if you buy in to the gimmick. The gimmick is that there's some small chance they have special knowledge and everything you know from your science education is wrong. You can't lie awake wondering if that's true. Because it's not. If their special ideas... |
[
"For what purpose was radioactive minerals mined in the 18th, 19th and the early 20th century, before nuclear programs existed?"
] | [
false
] | null | [
"Some of them glowed in the dark. Radium was used for watch dials, for instance. The workers who made them died inexplicably early..."
] | [
"To be extra precise, radium provided stimulation to a zinc sulfide phosphor, which produced light. Radium by itself doesn't glow, but the combination does. "
] | [
"Prior to use for their ",
" properties, some of the minerals had commercial uses due to their ",
" properties. For example uranium oxide was used in ",
"ceramic glazes",
" and ",
"uranium glass",
"."
] |
[
"What is quantum confinement?"
] | [
false
] | I know it has something to do with light but that is about it. | [
": Quantum confinement is increase in apparent band gap of a nanoparticle due to the confinement of the exciton to a space smaller than its Bohr radius.",
"\n",
" - Ignore this section if you know what a bandgap is.",
"\nThe band gap of a material is a physical property commonly attributed to semiconductors. ... | [
"Is there a method of upper limiting the conduction band with a 2nd valence band to prevent a photon with frequency greater than some arbirtary value from producing an exciton?"
] | [
"I don't think there is, but I could be wrong. The diagrams I linked above were simplified band diagrams with straight lines as the top and bottom of the valence and conduction bands. In reality, the band structures are a bit more complex. Examples of ",
"GaN",
" and ",
"Si",
" band diagrams. Due to this co... |
[
"Engineers of AskScience! What would you say is the most powerful machine that mankind has ever created?"
] | [
false
] | Of course powerful is probably a relative term, but perhaps this could spark some interesting debate? | [
"In terms of sheer physical power it was ",
"Tsar Bomba",
". I can't find the figures off hand but its been estimated that in the tiny fraction of a second as it detonated its power output was around 1% that of the ",
".",
" If you want something that ",
" destroy itself in the process try the ",
"Z-mac... | [
"The computer."
] | [
"Half a nanosecond."
] |
[
"How efficient is gravitational potential energy compared to chemical storage?"
] | [
false
] | Could you get comparable energy density to a lead acid battery from lifting a block of dense material with an electric motor, and lowering it when you wanted to generate current? | [
"Lifting a block of dense material won't get you very far, because you have to go really high to match the energy density of conventional power storage. Quick example, a 12 V car battery with 50 amp-hours of energy stores a total of 12 V * 50 A-h * 3600 s/h = 2.16 MJ. (1 J = 1 A*V * 1 s)",
"If you lifted a 1000 ... | [
"Ok, clearly this depends on many factors, but to get a sense of the orders of magnitude, lets make this simple : ",
"How much gasoline would it take to generate about the same amount of energy as can be generated from water behind the hoover dam (100m height)? (Ignore all inefficiencies)",
"Answer : For every... | [
"It really depends on the scale you're talking about - both in terms of power rating - how quickly energy can be delivered by the storage system, and total capacity, or how long the system must deliver the rated power. There are lots of ",
"charts",
" around the web that show which type is best suited for a gi... |
[
"Does Air Emit Blackbody Radiation?"
] | [
false
] | I'm kind of embarrassed I'm asking this question - I know that rule #1 of thermo (all thermo rules are rule #1 -- they're almost never violated) is that all matter emits blackbody radiation. But maybe I'm wrong about that rule. But what I wonder about is how we make those IR temperature sensors work if the air around ... | [
"Air emits blackbody radiation, and the blackbody rule only fails when a system is maintained in a non-equilibrium state, such as in a gas discharge tube or flame. For an IR sensor, this does not present a problem, at least ideally, because at equilibrium the air radiates the same simple, featureless blackbody spe... | [
"Yes, but for small distances in air, the air is transparent, otherwise the IR thermometer wouldn't work except when in contact with the object being measured.",
"Try using a thermal camera. They \"see\" the same thing as silicon-based IR thermometers. Look at the air above a hot electric stove ",
"or simila... | [
"Nice question :)\nAir does indeed emit blackbody radiation, but remember that, just like visible light, the wavelength (or colour) is not the only property measurable - you also have ",
". And since air has a very small mass density, it doesn't emit enough light of a given wavelength to distort the measurement o... |
[
"Do quasars exist right now (since looking far into deep space means looking back in time)?"
] | [
false
] | Quasars came into existence within 1 billion years after the Big Bang. The heyday of quasars was a long time ago. The peak of quasars corresponds to redshifts of z = 2 to 3, which is approximately 11 billion years ago (or 2 to 3 billion years after the Big Bang). They were thousands of times more active than they are n... | [
"We do need to be clear on what we mean by \"now\". There are two potential sources of confusion here - one physical, and one semantic.",
"In terms of physics, there is no universal \"now\" - different objects experience time at different rates, and events that are simultaneous from one perspective may not be sim... | [
"Stars will stop forming at around 100 trillion years into the universe. If we scale that down to 100 years, the current universe is on January 5th of the first year, at around 2:30 am. If I am doing my math right humans showed up on earth about 6 seconds ago on this scale"
] | [
"Stars will stop forming at around 100 trillion years into the universe. If we scale that down to 100 years, the current universe is on January 5th of the first year, at around 2:30 am. If I am doing my math right humans showed up on earth about 6 seconds ago on this scale"
] |
[
"Is frosting an emulsion?"
] | [
false
] | Is it also considered a colloid or is it too thick to be considered a colloid? | [
"I'm not sure what goes into frosting, so I can't say, but emulsions are a subset of colloid, so if it's an emulsion, it's a colloid."
] | [
"All emulsions are colloids, it's the former term that's the more specific one for the case when both phases are liquid. ",
"Apart from that, it really depends on the frosting. I mean, some frostings are essentially just sugar and water, giving it a single phase of liquid or glassy kind of consistency. (Edit: Cou... | [
"I'm thinking of standard buttercream frosting. I don't imagine there would be too much difference between American and French buttercream in terms of make up.",
"I am not looking at fondants and glazes. Just the sort of thing you would probably find on a cupcake in the grocery store.",
"What specific charact... |
[
"How can you calculate sea level rise from a given melt rate of glaciers?"
] | [
false
] | My professor told me that glaciers are currently releasing 400 Gigatonnes/year of melt water into the ocean and this results in roughly a 1 mm/year rise in sea level. How do they know this? What's the calculation used for that, given how much water there is? | [
"One doesn't need to get immersed in spherical geometry to calculate this. 400 Gigatonne = 400 *10",
" kg. Density of water is 1000 kg/m",
" (to first order) so the 400 Gigatonne works out to 400 *10",
" m",
" of volume. If you spread that evenly over the surface of the ocean (3.61 x10",
" m",
" ), y... | [
"Well it can't be that hard to work out. The water would form a spherical 'shell' of water in the areas of the earth that are covered in water.",
"Volume of a sphere = (4/3)pi *r",
" \nImagine there are two concentric spheres of water, one with unknown radius, and the other with radius defined by current sea le... | [
"I hate to ask, but could you run through your steps?"
] |
[
"As a nurse reflecting on climate change"
] | [
false
] | Two questions: 1. We live with our internal chemistry within a narrow pH range: from 7.35 to 7.45. CO2 is acidic. With CO2 levels at historic highs in the air we breathe, how does this affect our acid/base balance? 2. With historic glaciers disappearing, does the addition of so much freshwater to our oceans change ... | [
"I can answer #1 for you as my PhD thesis project is on a carbonic anhydrase enzyme.",
"Our body's pH is maintained by a family of enzymes called ",
"Carbonic anhydrases",
" which uses the bicarbonate buffer system (CO2 + H2O <--> HCO3- + H+) to buffer pH. ",
"If the number of protons(H+) goes up, the equil... | [
"The pH thing affects sea life much more than humans -- lots of sea creatures have a planktonic phase where they depend on the pH being a fairly narrow range. Humans probably won't notice it directly.",
"Overall changes to ocean salinity are going to be small, though you will see big localized changes where the ... | [
"Carbonic acid in the water (basically dissolved CO2) also prevents corals, shellfish, etc. from growing shells and other hard materials due to the low pH."
] |
[
"How do penguins know that their baby is dead when the egg freezes?"
] | [
false
] | From watching penguin documentaries, when the penguin parents trade the egg between each other, the egg will sometimes fall from their clutches and land on the ice. At this point they will chase after the egg and try to reclaim it, but after a short while will give them up as lost. Do the penguins have some way of kno... | [
"I couldn't find any information about this, but I do know that due to the almost and below freezing temperatures cause the eggs if dropped to freeze in about a minute or less. I do infer that the penguins can sense the heat from an egg that is an average of 77-84 degrees."
] | [
"The bell was not in the casket after it was buried, there was a rope attached to the bell at the surface."
] | [
"I'm sure they've been wrong before, either way. Assumed it was dead when it was alive, and assumed it was alive when it was dead.",
"We used to put bells in caskets to prevent this. I'm sure they've had their errs."
] |
[
"Am I missing something about cardiality and well-order?"
] | [
false
] | Since every set S admits a well-order, and this implies both the existence of a minimum in the set and of "consecutive" elements (the consecutive element of some X defined by min{y in S : y>X}), why does this not allow for a way making every set countable? Take the real numbers R. They admit a well-order. A certain num... | [
"Or is it just that you might never be able to get to certain numbers?",
"Essentially, yes.",
"Let's consider a simpler example so you can see why the well-ordering cannot be used to create a one-to-one correspondence with the natural numbers, even for countable sets. Suppose the set ",
" is well-ordered. Thu... | [
"It is true that the well-ordering theorem and the axiom of choice (AC) are equivalent statements. It is also true that AC is independent of the other ZF axioms, and so we have the freedom to choose whether to add AC or its negation to our list of axioms.",
"There is much mathematical philosophy written about the... | [
"I said with AC the range is not always countable, but I was struggling to find a canonical definition of \"recursive function\". If you say the domain is N then obviously the range is countable. But it's possible to define functions recursively whose domain is not N, and such functions arise in the proof of the we... |
[
"Why does the flu virus continually mutate (requiring us to get new vaccines each year), but other viral diseases (such as chickenpox) do not?"
] | [
false
] | We seem to always need new influenza vaccines because of the continual emergence of new strains of the virus. But, for example, we get chickenpox once in our lives and then it never seems to occur again. Why does this virus not mutate into a new strain our bodies are unaware of? EDIT: Hey thanks guys, these are great a... | [
"Influenza, like many other fast mutating viruses (common cold, stomach viruses, anything you can get year after year) is an RNA based virus. RNA is like DNA, except it only has one strand, not two strands like the DNA double helix. This one stranded structure is less stable and makes the virus more prone to mutati... | [
"Many viruses have evolved mechanisms allowing them to evolve quickly. For influenza A specifically, there are two main reasons it can rapidly change. ",
"First, the viral genome is RNA-based and encodes an RNA-dependent RNA ploymerase to replicate said genome. These enzymes are much more error-prone when comp... | [
"There are many reasons, and I don't want to reiterate things said above, so here's another reason.",
"Many of the HxNy flus (H1N1, or bird flu, for example) are so virrulant, that a host could be infected with two strains at once. If two viruses infect the same cell, and reverse transcription (copying the viral ... |
[
"Why do space ships have to enter the atmosphere at such great speeds?"
] | [
false
] | Why couldn't a ship just slowly enter the atmosphere and not build up heat? Would it be like a bit of dust trying to enter a soap bubble. Quick enough and it will break through. Too slow and it gets stuck on the surface? | [
"it takes a ridiculous amount of fuel to slow down in space. Much better for air resistance to do it for you."
] | [
"If the shuttle were to slow down to zero relative to the earth could they enter without burning up?",
"Yes, but then it wouldn't be the Shuttle, it would have to be some other spacecraft that carried almost as much fuel into orbit as it needed to get there in the first place. This would completely change the des... | [
"aerospace engineering student here, putting off some homework so sorry about the long answer. TLDR: if you hit the atmosphere, you slow down relative to the ground (lower your orbit) and fall toward earth. if you speed up, you fall away from earth (increase the size of your orbit) and move slower relative to the g... |
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