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[
"Could a nuclear waste repository be used as a large scale RTG (radioisotope thermoelectric generator)?"
] |
[
false
] |
Seems a shame to let all that toxic material go to waste.
|
[
"I don't see why not. Honestly I think it's just the fact that it generates such low grade waste heat (low heat generation per cubic foot) that it would be impractical and costly to harness the heat. It would be like getting a AA battery's worth of power from a metric ton of nuclear waste. "
] |
[
"Not really. The waste that goes into a long-term repository has already had time to \"cool\" off, i.e. the really super highly active material has all decayed away. That's why it can be put into a waste repository without active cooling like it would have when stored in a spent-fuel pool on site at a reactor.",
"Also, there's an issue of surface-area. The waste generates a lot of heat in the aggregate, but the heat per cubic meter isn't that high. For power generation, it's really heat ",
" that matters.",
"It also wouldn't be very safe. Practically speaking, you have to have some sort of working fluid to transfer the heat from the waste to your extractor (read: working fluid-> water; extractor-> steam turbine). Water flowing around waste defeats the idea of having a long-term storage solution.",
"Long story short, yes we could extract some electricity from it. It wouldn't be very practical, though. "
] |
[
"I'm only an armchair power engineer, but I don't think RTGs scale up very well... They're great for long term low power needs, but you get diminishing returns as they get bigger."
] |
[
"Does standing water help you fight bacteria?"
] |
[
false
] | null |
[
"If you have it, treat the water with a small quantity of ordinary household bleach, about 1ml per liter. Mix well and let it stand a while; 10 minutes or so. It's not perfect, especially for some of the nastier bugs; boiling or high quality filtration are better options by far. But bleach is better than nothing. ",
"For hand washing, ",
" dirty water is better than none, as most of what you're doing when you wash you hands is literally washing the bacteria away with the soap. But this depends ",
" on how contaminated the water is, and with what.",
"Also, the brown color may have more to do with particulates (flakes of metal from pipes, silt) than bacteria. If the pitcher of water sits, undisturbed, for a day or so, does it become more clear? Maybe with a layer of crap at the bottom?"
] |
[
"Boiling the water isn't an option? "
] |
[
"If you have a container that you know is reasonably sterile (perhaps rinsing a container with bleach and then washing it out several times very well with boiled water) you could store the boiled water and it would keep while sealed for a decent amount of time (depending how well it is sealed, how clean the container is initially, etc)."
] |
[
"How did the discovery of DNA affect the field of taxonomy? Were dozens of species 'wiped out' by discovery of identical genetic profiles?"
] |
[
false
] |
[deleted]
|
[
"There was reform to a large number of taxa, yes. For example the giant panda and the red panda are no longer considered to be closely related (giant pandas are bears, red pandas are closer to racoons or weasels). In some cases the genetics and the morphology had very different conclusions - bats, for example, were considered to have come from two distinct evolutionary origin points, but the genetic evidence indicates bats are monophyletic (had a single common bat ancestor); apparently this is still being debated, although I don't know much more than this.",
"As for species, genetics isn't the be-all of species boundaries. Usually reproductive isolation is the species marker for sexually reproducing organisms; polar bears and grizzly bears are perfectly capable of interbreeding genetically (and sometimes do), but are considered separate species because of morphology and habitat."
] |
[
"I can only comment on microbiology, but the actual discovery of DNA had little to no effect on taxonomy. It revolutionized the understanding of how traits are passed, how the cells work, etc, but classification needs a way to differentiate between the DNA strands. ",
"But to go further with your line of questions, DNA sequencing caused relatively large upheaval in the way bacteria were classified. Bacteria that were thought of being part of one group based on common methods (similar flagella, similar resource utilization, etc) were found to be completely different than the rest of the species in their genus. Others from multiple groups were found to be similar, so new groups were made to encompass them. Other groups were found to be offshoots of yet another group, so sub species were constructed. For instance, the Marburg virus, originally the sole virus in its genus, was found to probably be a strain of Ebola, so it's currently being considered for reclassification into that genus (ebolavirus) which will effectively kill its previous genus (marburgvirus). And don't say a damn word about the genus names...it's a million times easier to remember than some obscure Latin phrase that means something completely unrelated. ",
"To make things really fun, sometimes everyone said screw it and left it. E.coli subspecies only share about 20% of their genome, and as such should be bumped up from species to genus or higher, but to make things far less confusing for hospitals, the genus and species name have been left untouched. ",
"Many organisms new have a classical name and a current name due to the restructuring. It makes studying micro a pain since you have to always keep in mind when the source material was from. Luckily, most resources have been updated, so it's less of a problem now than in the past. ",
"You can check out Wikipedia which has a great explanation of the convoluted shit storm"
] |
[
"The bacterial flagella is really interesting to me because it's powered by the words smallest rotary motor. It's actually a modified atp synthase, an enzyme that uses the flow of protons to spin a molecular turbine, and uses that kinetic energy to create ATP. The bacterial flegallum uses the same structure, it creates a proton gradient and uses the flow of protons to spin the rotary motor attached to a corkscrew like flegallum. The smallest rotary motor in the world, the size of a few molecules."
] |
[
"How Does our Brain Identify the Direction a Sound is coming from?"
] |
[
false
] |
I've seen this topic touched on here, but not fully answered. I've noticed my 6 month old son being able to track the direction of our voices now (he now knows which shoulder to look over to find mommy entering the room while talking). How does our brain process the vector of the source of sounds?
|
[
"There are three main ways we can detect the direction of sound: 1) the difference in sound volume between the ears, 2) the difference in timing between ears, and 3) the difference in sound quality between the ears ",
"that comes from your head being in the way",
". This occurs because of the physical separation of your ears, the opposite directions they face, and the interference of our heads with the sound waves as they go from one ear to another. This means you can completely simulate the experience by recording sound using two microphones spaced similarly to the ears, ",
"try listening to this with headphones and closing your eyes",
", it gives an amazing illusion of auditory space!",
"In order for your brain to use information about the location in space for sound, it can create a lookup table of sorts for timing differences. In this case, when both ears get similar sound but the right ear receives the sound first, a certain group of cells will be active. On the other hand, another group of cells will be active if the left ear receives the sound first. This can be accomplished for example by the use of delay lines: the principle of this is the longer the cable, the more time it takes the signal to travel. Each ear gives information to neurons with a range of cable lengths that hook into an auditory processing center. Cells in this center may only be active when they receive input from both ears, but because the cable lengths vary, the timing of sound from each ear needs to be specific. For instance, a cell with a short delay line from the right ear but a long delay line from the left ear will only have simultaneous incoming signals if the sound first enters the left ear, and then enters the right ear after a delay. A Wikipedia article about this process ",
"can be found here",
". ",
"Now that the brain has a way of uniquely identifying sounds in space, the mechanisms for localizing sound rely on calibrating these sound differences between the ears with your other senses. For example, for your son to know which direction to look for a sound, he matches his experience of the sound “space” with visual space. Incredibly, this matching is arbitrary with respect to innate connections and instead is driven mainly by experience. For example, if you were to put ",
"prism goggles on your son to shift his vision",
", he would learn to adapt how he turned his head (even you could do this kind of learning as an adult!). ",
"A fantastic system we used to learn this (and the mechanisms of sound space processing in the brain) comes from ",
"owls!",
". Owls have very sensitive hearing to find prey, but one thing that makes them special is their ability to localize sound in 3D space, which humans are much less adept at. The reason for this is that their ears are located at ",
"different heights on their skull",
", so timing differences between the ears correlate not only with left/right, but also with up/down. "
] |
[
"sound waves don't arrive at both ears simultaneously",
"our brain (the auditory cortex) can use the timing differences to create location information. we do not have a full understanding of this process.",
"also, sound creates pressure waves which the brain also uses to assist and supplement the auditory information.",
"the auditory cortex processes these inputs and basically sends its \"result\" back to you using mechanisms that are not fully understood."
] |
[
"Thanks for this fantastic response. I had no idea HRTF existed, much less that our brains use it that much, and the simulation was a trip!"
] |
[
"how much degradation of signal strength occurs in outer space?"
] |
[
false
] |
My six month old wireless router barely reaches my front porch and yet we are able to communicate with Voyager 1 using technology developed over 30 years ago. Is that because there isn't any physical material between us and the Voyager probes? If there are issues with signal strength, what makes us so confident that we'd be able to listen to the signals from alien lifeforms far far away?
|
[
"Your router's antenna is pretty much non-directional, so signal strength falls off with the square of the distance. That is, the strength at two metres away from the router is a quarter of the strength at one metre away. You'll also suffer from walls in the way and interference from other devices.",
"However, you can use directional transmit and receive antennae to much reduce this problem. The simplest versions of these are just dish reflectors (think a satellite TV dish, etc). Used on the transmitter, a large portion of the energy emitted by the transmitter is converted into a beam which only diverges very slightly with distance. Used on the receiver, energy hitting the entire area of the dish is directed to the receiver, improving the signal strength there.",
"Communication with the Voyager probes uses communication dishes both to send and receive messages, meaning we can communicate over great distances with relatively little power usage.",
"Observations of objects which are not specifically transmitting to us rely only on a receiver dish - in other words, a telescope."
] |
[
"Well, remember a star or a galaxy is also non-directional and we can see those from mind-bogglingly large distances away with sufficiently powerful telescopes. Distance squared falloff doesn't make detection impossible by any means.",
"Also, note that the signals we're looking for will have much greater distance falloff than a message to Voyager, but we're looking with much larger, and therefore more sensitive, receiver dishes than Voyager mounts. Voyager has a dish with an area of 10.5 square metres; the Very Large Array has a total dish area of 13,000m",
" between its 27 telescopes. The Square Kilometre Array, currently in development, will have a total dish area of 1,000,000m",
" .",
"This isn't to say that an alien signal would necessarily be easy to spot - we really don't know how electromagnetically loud a planet might be for how long, which makes estimating this sort of thing hopeless - but it's not infeasible that we might pick something up."
] |
[
"Ah. Thank you, kind sir, for offering some clarity to the mysterious downvotes seemingly from nowhere. Do these clarifications rectify my statement's omissions?",
"Per the Inverse-Square Law:",
"the signal strength from ",
" radiation-emitting ",
" source is ",
" proportional to the square of the distance from the source."
] |
[
"Do spiral-galaxies slowly collapse?"
] |
[
false
] |
On the galaxy-scale, I understand that (for at least spiral-type galaxies) there is a super-massive black hole at the center around which is the highest density of stars and other cosmological bodies. Has it been determined whether, eventually, a galaxy will collapse as a result of the overwhelmingly strong gravitational forces of the black hole?
|
[
"There's no reason to believe that an entire galaxy would collapse or fall into a black hole. Just as the Earth orbits the Sun without falling into it, the arms of the galaxy orbit the galaxy center. These orbits are thought to be stable."
] |
[
"I see consistently the generalization that there is \"no friction\" in space, which is why the orbits appear to be completely unchanging, but I guess I find it difficult (perhaps impossible) to believe that there isn't at least a marginally small amount of friction which is slowing down, say, the earth's orbit an imperceptibly small amount."
] |
[
"And you're then suggesting that this friction would slow the orbits and cause the galaxy to be swallowed by the black hole?",
"There is tidal friction, but I think it could be shown that the angular momentum of the galaxy has far, far too much energy to be converted into tidal friction.",
"Also, I found ",
"this post",
" for you. Several good answers there."
] |
[
"Black holes exist, but the theory says we can never see something fall into it.... How do you reconcile both affirmations ?"
] |
[
false
] | null |
[
"Theory doesn't say that nothing crosses. It says that an observer outside the black hole will never see anything cross the horizon.",
"But the infalling object will see itself crossing the horizon and reaching the singularity in finite proper time."
] |
[
"Yes thats what i had understood. The theory says an observer outisde never sees anything cross.\nBut a distant observer present at the time of birth and growth of the black would have seen stars eaten by it, no ?\nI mean, he wouldnt have seen the black hole being born from nothing and grow without eating anything, would he ?",
"Thanks for your answer"
] |
[
"An outside observer can see things move toward the horizon, asymptotically slowing down and redshifting until it's not longer visible. But technically speaking, the infalling object will never reach a radial coordinate below the event horizon from the outside observer's point of view."
] |
[
"What necessities (food, air, fluids, etc..) would silicon based lifeforms need to sustain life?"
] |
[
false
] | null |
[
"This is pretty good background on it:",
"https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry#Silicon_biochemistry",
"The suggestions there, I think, aren't that it's necessarily impossible to imagine a silicon-based biochemistry, but that it's very difficult to imagine a planet where silicon-based life arises instead of carbon-based life. Even here, where silicon is much more abundant than carbon, it didn't go that way."
] |
[
"Keep in mind that the chances of silicon based life is a few million to a few googol times less likley by chance than carbon based life.",
"If there were silicon based life encountered it could occur naturally on Venus for example, but finding such life would be like winning the lottery due to carbon having far more opportunities for complexity through natural reactions. "
] |
[
"Berry interesting, thank you sir."
] |
[
"What does/could a mismatched Systolic/Diastolic pressure indicate?"
] |
[
false
] |
I noticed that the two numbers always seem to be given in pairs, and the numbers are typically AROUND a 3:2 relation. What does this mean is happening, and what does deviation from this ratio, say moving from 2:1 -> 1:2, suggest?
|
[
"If you subtract diastolic pressure from systolic pressure, you get what is called the ",
". So for example, if your BP is 120/80, then your pulse pressure would be 120 - 80 = 40.",
"There are many reasons for a narrowed or widened pulse pressure. For example, many elderly people have calcifications of their major arteries, including the aorta. This would lead to an elevated systolic blood pressure because the aorta is not as soft and compliant as it used to be, so it doesn't \"give\" as much during the heart's contraction. But this has little effect on the diastolic pressure. So this would lead to a typically elevated systolic, but normal diastolic pressure. In other words, a ",
".",
"Wikipedia has a pretty good article about this",
", with many other examples!"
] |
[
", If is ",
" higher than ",
", it suggests that somebody doesn't know how to read blood pressure, or that somehow physics has changed.",
"Systolic pressure is the pressure associated with the contraction of the ventricle, diastolic is associated with the filling (or dilation) of the ventricles. The systolic (top) number will always be higher than the diastolic (bottom) number"
] |
[
"Thanks, and the article was pretty great. Pulse pressure, who knew."
] |
[
"How does ammonium ion uptake into muscle promote mass gain?"
] |
[
false
] |
I'm learning about trenbolone and I saw this statement in the Wikipedia article about it, and I can't for the life of me figure out the mechanism of action.
|
[
"How deep do you want to go into it? It seems to act through Akt/mTorc to increase protein translation. Based on wiki looks like it also acts to increase transcription of androgenic hormone receptors, which could increase muscle sensitivity to circulating androgens."
] |
[
"That’s really what I’m interested in. Based on what I could find the only thing I could see is perhaps some signal cascade due to amino acid breakdown or possibly converting glutamate to glutamine for ammonium storage or maybe for anabolism of proteins."
] |
[
"From other cell types, it might directly phosphorylate/activate akt to kick the whole protein synthesis machinery into gear"
] |
[
"Can the existence of randomness be proven?"
] |
[
false
] |
[deleted]
|
[
"Two big topics you're bringing up are determinism (",
"https://en.wikipedia.org/wiki/Determinism",
" ) and time travel paradoxes (",
"https://en.wikipedia.org/wiki/Temporal_paradox",
" ).",
"It's impossible to experimentally disprove superdeterminism (",
"https://en.wikipedia.org/wiki/Superdeterminism",
" ), so you won't ever get scientifically conclusive proof that \"true randomness\" exists. At the same time, quantum mechanics strongly suggests that we won't ever be able to \"predict everything\" so we don't expect there will be compelling evidence for determinism either.",
"TLDR: We don't know whether things are 'truly random' and are very unlikely to ever find out."
] |
[
"I'm on my phone now, so I'll try my best. The experiments you are talking about are related to the famous Bell inequality. So the arguments go like this:",
"1) we have two entangled electrons. Entangled means that they have a special property that the outcome of measuring for instance the spin is correlated between the two. One possibility is preparing each electron pair (you will need to repeat the experiment many times) so that if you measure their spin in the z-direction (or just some direction), they will always yield opposite result. If one has spin \"up\", the other will have spin down, regardless of how far they are from each other! But from one pair to the next, it is impossible to predict which electron will have spin up.",
"2) Ok, so this sounds weird. What if there is some local hidden set of parameters that is useful in a more complete theory: they will suddenly remove all randomness of the experiment and it is then clear which electron will have spin up, and the other one down. ",
"3) let's be more general for a moment. If the electron pair is prepared so it has a 50% chance for spin up in the z-direction, it will yield different statistics if you measure along a vector pointing in x and z-direction. And we don't have to measure both electrons along the same vector. So our new experiment is measuring the spin of electron 1 along a vector a, and the spin of the other electron, 2, along a vector b.",
"4) Now that we have two vectors we measure spin of the electrons along, a and b, we can discuss the angle between the two vectors. We actually want to calculate the correlation between the outcome as a function of the angle between the vectors. Search on google images for \"bells inequality\" and you will see those graphs.",
"5) Assuming that there is a function predicting the outcome of the electron spins with the local hidden variable, H (this variable can be anything; a number, many numbers, your name, whatever). Using this assumption in the framework of quantum mechanics leads to a prediction that can be tested experimentally. This prediction turns out to be wrong which in turns means that some of the assumptions were wrong.",
"6) this could be the full quantum mechanics of course, it might be completely wrong. It is extremely successful though, so it is more probable that the assumption that there exists a function removing the uncertainty in the experiment, is wrong. We can then conclude that no such local hidden variable theory exists."
] |
[
"There are several interpretations of quantum mechanics that give different answers to this question, and we can't prove which is correct. Let's assume you can rewind time and observe what happens but you cannot affect the universe in the past in any way. Here is what three popular interpretations would predict:",
"In the Copenhagen Interpretation, quantum mechanics produces truly random results during a \"measurement\" of a system (i.e. the collapse of the wave function). So if you could rewind time events would happen differently. ",
"In Bohmian mechanics (aka the pilot wave theory), the universe is deterministic but you don't have enough information to predict the future. So if you rewind time and start again, everything will happen the same way.",
"In the Many Worlds Interpretation, the wave function evolves in a deterministic way (just like when we aren't taking measurements). However, our consciousness can only be aware of one set of outcomes from a measurement. This is often described as multiple parallel worlds being created by the measurement. In this case, if you rewind time you would get the same result for the universe as a whole, but some versions of you would think they were experiencing a different result. ",
"Again, there is no way to prove which of these is true, so we can't say for sure what would happen. ",
" SMBC recently explained these 3 interpretations in terms of ",
"cat justice",
"."
] |
[
"Why don't we out gas pollution to space?"
] |
[
false
] | null |
[
"We do not have the capacity to do that efficiently. Right now 1kg of cargo sent to low orbit cost about $10,000."
] |
[
"With heavier gases, such as CO2 and methane, would we need to get to LEO for it to escape our atmosphere?"
] |
[
"No you would need to get much higher, which would be even more expensive. If you had a way to capture such gases it would be way more cost effective to store them somewhere on earth or turn them into something else than sending them to space."
] |
[
"How does sunscreen protect my skin if it’s clear? It blocks UV— so if I were, say an insect that sees in the UV spectrum, would sunblocked skin look extra bright because UV is reflected, or extra dark because UV is absorbed?"
] |
[
false
] | null |
[
"This",
" is a cool video showing what our skin looks like under UV light recording, and at the end you can see what sunscreen looks like. Basically a black paste to the UV, preventing any from reaching your skin below. To answer your question, it absorbs UV not reflects"
] |
[
"Now I want a UV camera just to check if I have properly applied my sunscreen."
] |
[
"That’s cool. In the last few seconds, it shows the blonde girl who looks like her tooth is chipped under the UV camera, but looks unchipped in the normal light. I imagine that she had a tooth repaired at one point, and the resin used to fix the tooth absorbs UV. (Some dental resins use UV to cure them)."
] |
[
"Photons a massless particle with momentum?"
] |
[
false
] |
In not a physicist but it seems that to have momentum you would need mass. Anyone mind explaining this?
|
[
"The other comments are correct, but to you they probably seem like variations on \"just accept that to have momentum you don't need mass\"; if you're asking the question in the first place your curiosity may not be satiated by such an answer.",
"So let's take a step back and look into why momentum and energy are such useful concepts. Historically, it was realized that the sum of momenta of a collection of particles would be conserved if there were no forces on the particles other than any forces the particles exerted on each other. This turned out to be a nice shortcut to solve a class of problems, where you could make some predictions without having to directly solve Newton's equations (which can sometimes get difficult). That is, the usefulness of the concept of momentum is that it is conserved in most situations -- it is the same value before and after some process. Furthermore it has an easily remembered definition in terms of mass and velocity, which I'm sure you know: total momentum = sum over each particle of (mass*velocity)",
"Furthermore, and crucially, you can prove that any solution to Newton's laws is \"Galilean-invariant\"; that is, if the momentum is conserved, it doesn't matter whether you stand still or move with a constant speed while making the measurement -- the initial and final value of the momentum will be the same. (Of course, this value will differ between the standing-still case and the moving case, but it will not change between the initial and final states.) This is really neat and allows quite some simplification in dealing with complex problems. Furthermore, the difference made by switching reference frames can again be expressed neatly in an easy equation -- if you know it in one frame, you can calculate it easily in another.",
"It turns out that Newton's laws are only approximations -- it still doesn't matter whether you are standing still or moving with a constant speed, and momentum and energy are still conserved, but this question is slightly harder to answer: \"if this is the momentum in given reference frame 1, what is it in given reference frame 2?\" But there's a well-defined mathematical prescription.",
"That's it for mechanics, the study of physical bodies like iron balls. But there's more to nature! Specifically, electromagnetic phenomena, such as light and radio waves. One of the first interesting things noted about electromagnetism was a rather weird phenomenon: accelerating charges automatically emit radiation. (In fact this is the mechanism used by cellphone towers: they send current up and down an antenna by applying a rapidly varying voltage; when the electrons oscillate in this fashion, they give off radiation because they are accelerating.) But if you've been following the discussion so far, you will immediately ask: \"where does the momentum of these electrons go when they continuously keep on changing speed and direction?\" You can at this point either throw up your hands in despair, and give up on conservation of momentum, or you can assign a momentum value to the emitted electromagnetic wave. Obviously the latter approach is more useful, because if this electromagnetic wave later collides with a particle (such as an electron in your cellphone antenna), it will impart a predictable amount of momentum to the cellphone electron and make it oscillate -- so we say that electromagnetic waves convey momentum and energy from one antenna to the other.",
"The final piece of the puzzle comes from Einstein's realization that electromagnetic radiation actually comes in bundles of single particles called photons. But if electromagnetic waves have energy and momentum, then so must the photons as well! In fact, we can make this more quantitative and precise, by giving an equation for how much energy and momentum is carried by a given photon. The usefulness of this concept is that if a photon is emitted by electron 1 and absorbed by electron 2, then electron 2 will receive a kick in momentum exactly equal to the amount lost by electron 1; if this value is ",
", then we say that the photon has conveyed momentum ",
" from electron 1 to electron 2, or, in other words, that the photon has momentum ",
". Using Einstein's idea we can actually express ",
" in terms of the wavelength of the emitted photon, and this idea holds up extremely well in all kinds of experiments.",
"Of course, as is usual in physics, there is another way entirely of looking at momenta and energies of all fundamental particles. It has to do with irreducible representations of the Lorentz group and is actually a rather beautiful way of making sense of many questions that you may have had while reading the above explanation, but it's too mathematically involved to be simplified in a short Reddit comment."
] |
[
"Momentum is a property of any particle which is moving, whether or not it has mass."
] |
[
"Just a random passer-by but awesome answer! Thanks for your detail!"
] |
[
"What are the risks of not replacing contact lenses as directed?"
] |
[
false
] | null |
[
"Risks?: serious infections which can lead to blindness.",
"Medical advice?: Listen to your damn doctor.",
"Do a cost-benefit analysis... save a few dollars on contacts vs. expensive medical bills and pain from eye infections with potential loss of sight. I know several people with this money saving attitude which led them to infections.",
"They do degrade in other ways beyond tears."
] |
[
"Just on top of this, there are different types of lenses. Daily change, weekly, monthly etc.... ",
"The difference is the design of the lense and how porous it is. Weekly/Monthly lenses let through much more oxygen to let your eyes 'breath' as opposed to Daily wear lenses which are quite solid. As the lenses get older, these pours get blocked up with the 'crap' from your eyes and theres less oxygen getting to your eye itself. "
] |
[
"The line is where it is. The FDA and contact manufacturer came up with a \nduration which they certify is safe within acceptable limits. Anyone giving you any other advice, especially someone who isn't a medical professional, could be held legally and financially responsible for any negative outcomes you or anyone else who reads it could encounter.",
"This post violates Reddit's terms of service and the rules of this subreddit.",
"Please delete it and refer any questions to the medical professional responsible for your care."
] |
[
"What % of power output is used to drive a Gas Turbines own compressor?"
] |
[
false
] |
For example, on an industrial gas turbine that produces 15MW/20000BHP in mechanical drive configuration (twin shaft). It's producing 15MW of shaft output. So from that we can deduce at 32% efficiency it will require 46.875 of fuel. How much energy is extracted from the expanding gases at the compressor turbines, to drive the compressor. I hope I made myself clear, any information would be great :).
|
[
"Approximatly 50% (it's a little less).\nSource: Son of Alstom engineer."
] |
[
"Here",
" is a Pressure volume diagram for a brayton (gas turbine) cycle. Pressure times volume is energy so integrating one of these lines gives you work. The energy required for to compress the air fuel mixture is the lower line, the energy done on the turbine is the upper line. The energy that can be extracted from the process is the area in the middle. It's not a quantitative answer but I hope it helps."
] |
[
"Company I work for bought out Alstom gas turbines in Lincoln. "
] |
[
"Question for upcoming art installation: What part of the visible spectrum does a regular CRT tv emit and can it be gelled/modified to support plant growth in a dark room?"
] |
[
false
] |
As the title implies, I'd like to take junk televisions and support new growth of a plant in a terrarium with them for a few weeks. The televisions would be in a dark room with old vhs footage of sunrises/nature scenes looping. Is this possible if all or part of the screens were gelled red or blue? does a full-spectrum gel exist? thanks!!
|
[
"A CRT's spectrum is fairly choppy in the red region. See ",
"here",
".",
"Compare this to the spectrum used by photosynthesis, ",
"here",
".",
"You can see that the blue may be well covered, but not the red. \"Gelling\" or filtering cannot add any frequencies to the spectrum, it can only subtract. A full-spectrum filter would imply filtering nothing...so it would be clear.",
"I would guess that you could keep plants alive, but not in optimal health."
] |
[
"It doesn't need to be well covered. Most of the red photons will have wavelengths that are well-absorbed."
] |
[
"http://en.wikipedia.org/wiki/File:Chlorophyll_ab_spectra2.PNG",
"There's the chlorophyll absorption spectrum. ",
"http://media.wiley.com/product_data/excerpt/24/35273140/3527314024.pdf",
"That has emission spectra for the phosphors used in CRT sets. ",
"Gelling can only reduce the light a plant receives, but it looks like the red and blue output light from a CRT set should be at good wavelengths for photosynthesis.",
"I have no idea if there will be enough light. Probably depends on the plant."
] |
[
"Does alcohol consumption provide any positive effects?"
] |
[
false
] |
Are there any short term or long term side effects of alcohol consumption which can be argued as being "good for you"?
|
[
"Yes. The benefits of moderate alcohol consumption are well studied and documented. ",
"Here",
" is an article on some of the benefits. That said, heavy consumption can damage the body."
] |
[
"There are a few, but they're mostly poorly understood and attributeable to parts of the drink other than the alcohol. Red wine has many of the same attributes as red grape juice, for example.",
"The one positive effect I do know though is that it prevents methanol poisoning. Your body can't handle methanol, but it can digest ethanol, and absorbs it preferentially. If someone drinks a bunch of methanol, getting them drunk will likely save their life."
] |
[
"Think of alcohol consumption and risks like a Nike swoosh. ",
"For men \n0 drinks and 2 drinks have equal long term Cardiovascular risks and benefits \nHowever those who drink 1 drink per day ( it can be wine, a shot of whisky, a beer, etc) showed a decreased risk than those who drank 0 or 2 drink. ",
"However after two drinks the risk goes up exponentially (the tail of the nike swoosh) ",
"Like everything moderation is key. Alcohol in small quantities is actually not that bad for us. "
] |
[
"Is there an upper limit to the highest possible bypass ratio of a turbofan engine?"
] |
[
false
] |
I am not an engineer and only have an rudimentary understanding of the physics behind the jet engine, especially for commercial airliners. Admittedly, much of the physics behind why a high bypass ratio for commercial airliners is fuel efficiency was quite counter-intuitive for me, I.e slower compressor speed and more air directed to bypass duct means more thrust. Theoretically, how far high up can the bypass ratio be reached and what new technologies can enable greater fuel savings and greater range for jet engines?
|
[
"Theoretically, no. Practically, there are many limits.",
"One quick example, as a fan becomes larger it would become a propeller. ",
"There are several limits to the overall diameter of both propellers and fans, in no particular order (it will be different for every airplane)\n- the structural integrity of the blade itself, to be strong enough not to break apart\n- the power of the core to adequately power the fan. As the bypass ratio increases the core becomes smaller relative to the fan and may not be able to provide the required power.\n- weight, as the bypass area grows, the weight of the engine increases. The heavier an aircraft gets the more fuel it burns, so there is a point where the benefit disappears"
] |
[
"Just latching on to this explanation to add: Another factor limiting the possible bypass ratio is the fan tip speed. The larger the outer diameter, the lower the possible RPM of the fan is before reaching Mach 1 at the tips and encountering problematic compressibility effects. This is currently addressed in (Ultra) High Bypass Ratio engines by implementing a gearbox between fan and the inner shaft, but that is also added complexity and weight, and has its limitations."
] |
[
"There is actually an example of this, the ",
"propfan",
". Also known as an ultra-high-bypass turbofan engine."
] |
[
"How large would a population need to be to insure that the species could grow without inbreeding?"
] |
[
false
] | null |
[
"The number, according to geneticists, comes to 160 people- 80 men and 80 women. This of course depends on the variance in genes, so these people would all need to be as distantly related as possible. While some animals are all genetically the same, humans need a pretty big gene pool to not turn out abnormally. ",
"In a colony started of only 2 people, inbreeding would create numerous health problems and likely lead to an extinction of the colonists after enough time. So remember kids: inbreeding bad, large gene pools good. \n",
"http://genetics.thetech.org/ask/ask113"
] |
[
"I have a curious question I'd like to piggy back off of this one with. If all but one woman were to vanish from Earth, leaving her with her choice of male mates, how likely is it that she and her offspring could repopulate the Earth with minimal negative side effects? If it helps the odds, let's say during her entire childbearing life she will produce nothing but females. "
] |
[
"How long before a 2 person colony dies off?"
] |
[
"Is it possible for an earth-like planet to have a ring around it?"
] |
[
false
] |
Or would the ring effect it?
|
[
"Yes, terrestrial planets can have rings."
] |
[
"Yes you do if you state that kind of fact.",
"The common theory about the theory of the moon is the giant impact hypothesis: A big body hit earth and the ejected material formed the moon.",
"But even if earth and moon formed out of the protoplanetary disk this does not imply the existence of a planetary ring unless you have evidence that the moon (or its material) used to be inside the roche limit."
] |
[
"Yes, just imagine breaking our moon into pebbles."
] |
[
"Brown Dwarfs?"
] |
[
false
] |
When a nebular starts to come together, the core of it starts to heat up due to friction. But if it does not have the required temperature to begin nuclear fusion it becomes a brown dwarf. My question is do brown dwarfs glow or let out light energy, and if so where does this energy come from, and will it run out of energy from producing light?
|
[
"More massive brown dwarfs can burn heavier elements than hydrogen, like deuterium or even lithium. Otherwise, most of their radiation comes from residual energy left over from gravitational contraction. Eventually, like an ember, they'll run out of energy, cool down and fade to black. But this process takes longer than the Universe has been around for."
] |
[
"Everything with a temperature above absolute zero gives out radiation. See the Wiki for ",
"black-body radiation",
" for a detailed explanation. But brown dwarfs, as explained in it's ",
"Wiki",
" give out extra radiation, the energy of which comes from gravitational contraction and radioactive decay. Yes, brown dwarfs will run out of this energy, but then again so will suns, stars and eventually, all astronomical objects."
] |
[
"So, all the stars will \"shut down\" after a while? Will new ones for or when the ones we have are done it's all done? What's the timeframe for this to happen?"
] |
[
"Are callouses made of living tissue?"
] |
[
false
] | null |
[
"Most of the skin on the outside of your body is made up of many generations of dead skin cells that have flattened and bonded together to make a thick disposable surface.",
"Callouses are just thicker parts of dead skin cells that make up your epidermis."
] |
[
"Why don't they go away?",
"They do, if there's no more need for them. Meaning, if you sand them down with a pumis stone, etc., they will just keep coming back thicker and thicker because the body will keep seeing a need for them as the skin keeps getting abraded away.",
"But if you gently rub in lotion at least once a day and otherwise take some care not to abrade that area, a callous will go away since there's no more need for it."
] |
[
"I just want to add that as a guitarist, my finger tips are always calloused. However, every now and then a fairly thick layer of callous will lossen up and peel off. They definitely remove themselves over time (usually in far less dramatic fashion) but also continue to build up at the same time - if they're caused by an activity you engage in constantly."
] |
[
"How much can you learn from someone's genome?"
] |
[
false
] |
I've heard you can learn id someone by looking at their DNA, but what else can you learn if you know what to look for?
|
[
"Well this is fun, we literally just covered this kind of stuff in my advanced molecular biology course.",
"Your genome will contain variation depending on genetics that has been passed down from your parents. You may be homozygous for 11 copies of a short-tandem repeat (STR, 2-3 'letters' repeated over and over again in the sequence) where I will be heterozygous for 13 and 8 copies. Your \"DNA fingerprint\" that the FBI uses involves these regions, when the areas that contain them are amplified by PCR, they show up as different lengths.",
"Furthermore, there are single-nucleotide-polymorphisms (SNPs) where you may have an A where I have a C (or C-A or T-G or T-A...you get the point). There are also \"indels\" - insersions or deletions relative to one genomre or another. These can serve as markers for disease or other traits, especially if they occur in protein coding genes. There are a very very large number of these variations, and I could predict (not even close to 100% certainty, though) some traits about you as well as heritable diseases you may carry. The debate on nature/nurture is how certain could I be given your genotype?",
"This database",
" is called Online Mendellian Inheritance in Man and catalogs diseases/traits and contains a ",
" of SNP and indel data about them. Doing some mining, you can find tables like ",
"these",
" that will list all known variants for a gene and link to more information about them. This example is the Von Willebrands Factor, mutations of which cause Von Willebrands Disease which is a mild bleeding disorder. I don't know your background, but this site contains a lot of very technical information.",
"You may have heard of ",
"23andMe",
" which is a commercial service that will assay your genome for specific markers as well.",
"EDIT: If your family has submitted their genomes to a database as well, we could ID them as well"
] |
[
"Sorry if I am misunderstanding what you said (I'm not very knowledgeable when it comes to science), but from what I can understand it sounds like you can predict what diseases may have been passed down to me from parents and grandparents, what diseases I might be prone to, and some traits I might have. What kind of traits? Would they all be health related?"
] |
[
"The relationship between genetic inheritance and environmental effects is one of the hottest topics in research right now.",
"Medicine related Pharmacogenomics looks at how your genes will predict your response to drugs. Understanding these links can help us predict allergies to medicine, how we'll you can metabolize drugs (would you need more or less of it) etc.",
"The links between personality and DNA is still being investigated, with many studies looking at identical twins who are separated at birth etc.",
"If you are interested like the first poster I recommend 23&Me for $99 you can do a spit test to get some of this information."
] |
[
"Why is that that \"flu season\" seems to be in the fall/winter months? Is the virus less communicable throughout the spring and summer?"
] |
[
false
] | null |
[
"It seems that the influenza virus survives longer in cold, dry temperatures. Dry air creates lighter mucus particles which travel farther in the air. ",
"https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.0030151"
] |
[
"Not an epidemiologist, but it's my understanding that it has more to do with human behavior. As the weather changes people spend more time indoors in closer contact with other people allowing the virus to spread."
] |
[
"fresh air",
"And I thought that general scientific knowledge is long past the Miasma theory.",
"https://en.wikipedia.org/wiki/Miasma_theory",
"\"Fresh air flow\" have nothing to do with it.",
"There are several factors why flu is in cold months, but not because of congregation.",
"We are protected by mucous membranes, typically in nose. These membranes can physically stop viruses entering inside our bodies. In cold dry environment, these membranes lose this function.",
"Another factor is that winter together with cold temperatures and so on is usually more demanding on organism than summer.",
"Another factor is seasonality of flu. Flu virus can mutate really fast, it has segmented DNA and different viruses can recombinate and create a new virus during coinfection. This happens typically in domesticated pigs or birds. However, domesticated animals are not source of viruses (reservoir), typical natural flu reservoir is bird population. And birds tend to migrate. Birds migrate during seasons.",
"I sidelined bit the speed of mutation. Naturally after infection, organism, if survived, will develop immunity or resistance against repeated infection. However, resistance might drop in time. Additionally, since virus mutate, it can change its form so it is being unrecognized by immune system, so even previous infection won't provide cross-immunity.",
"To sum it up, no need to come with miasma theory. Natural reservoir -- migrating birds, cold and dry environment -- decreased protective properties of organism and gained immunity and its decline could all explain this."
] |
[
"Why haven't we found any meteorites older than 4.5b years old?"
] |
[
false
] |
Isn't it possible for meteorites to come from interstellar space? Or even intergalactic space? Why aren't there any meteorites older than our solar system?
|
[
"It's possible, but the odds quite low. The solar system is generally believed to have ejected between 10 and 100 Earth masses in rocks during it's formation (there's a lot of uncertainty, but it's pretty reliable that something like this happened, since the same process forms the Oort Cloud.)",
"It was mostly in kilometer sized rocks, so there would've been ~ 10",
" of them. With 10",
" stars, figure 10",
" such rock/ice balls floating through the galaxy. The galaxy is something like 3x10",
" kilometers across, and maybe 10",
" kilometers high, call it 10",
" cubic kilometers. About one interstellar comet per 10",
" cubic kilometers, meaning each is surrounded by an area 10",
" kilometers across (about the distance from the Sun to Saturn). Finding the one interstellar comet in that volume (among the perhaps million such stellar comet/asteroids of that size in the same area) is very hard. ",
"Put another way, the Earth traces out tube about 7000 km in radius, and 60 kilometers long, every second. That's 10",
" cubic kilometers per second, or one impact from a kilometer sized interstellar comet every 10",
" seconds (which is about the age of the Earth). ",
"So probably once in the Earth's history, we've had a kilometer sized interstellar comet has hit us. This should scale like the size to the 2.5 power, so 300 100 m objects (every 10 million years). But a similar sized object from within the solar system hits us every 10 or 100 years.",
"The same ratio comes up - between a hundred thousand and a million solar meteorites for every interstellar meteorite. So if we took an age measurement of enough meteorites, we should find one that's interstellar. But that's a lot, a lot of tests, which aren't easy or automated. There just isn't enough labs, people, funding, or recovered meteorites. The chance is just too low."
] |
[
"Actually, no. Meteorites are mostly the remnants of the molecular cloud that formed our solar system. We can use them to determine the age of the solar system, about 4.6 billion years.",
"Small rocks like those that hit the Earth as meteorites can only form when a molecular cloud, like the one that made up the solar system, collapse under gravity. This can only happen if the cloud is very large, and thus it only happens around star forming regions. It therefore leads that all of the rocks that hit the Earth must have formed with the solar system. The chance that a rock can make it from another star all the way to us are ",
" slim."
] |
[
"This is great info, thanks for this. It seems like interest in meteorites is increasing, and the hobby of \"prospecting\" for them for cash as well. I, for one, hope one is found. I think it would be very exciting and the scientific value would be tremendous, I would imagine."
] |
[
"how effective, honestly, are surgical masks in the fight against airborne illnesses."
] |
[
false
] |
It just seems that there can't really be a breathable material that would trap germs significantly. And even if it did, aren't there already billions of pathogens floating in the air? And a mask really doesn't seem like it would make a notable difference. And I do realize that this is a stupid question, but I couldn't find the answer anywhere. AND I REALIZE THAT I HAVE STARTED FOUR SENTENCES WITH "AND" I'M NOT AN ENGLISH MAJOR!!!!!!
|
[
"Different masks are rated differently, based on how much particulate matter in the air they let through on inhalation.",
"A typical surgical mask is not designed to protect the wearer from the environment, but the environment from the wearer; it has poor fit around the edges, and its main purpose is to trap exhaled matter, not to filter inhaled matter.",
"A respirator, which can come in the form of a fitted mask, is designed to protect the wearer from the environment; typical respirators are rated N90, N95, and N99, depending on whether they filter 90%, 95%, and 99% of particulate contaminants. (There are even higher ratings.)",
"Respirators are breathable, but with noticeable difficulty, and have to be worn properly to maintain fit around the face to ensure most inhaled air passes through the respirator filter.",
"So, the answer is approximately this:\n * If many people wear surgical masks, then they ",
" effective against airborne diseases, because they will reduce transmission from the infected mask-wearers.\n * If only a few people wear surgical masks, then they ",
" effective against airborne diseases, as they will not substantially decrease transmission from non-mask-wearers nor will they substantially decrease transmission to mask-wearers. \n * If people wear respirators, then they ",
" effective against airborne diseases, as they will reduce transmission to and from wearers. However, respirators are a giant hassle to wear for a significant amount of time.",
"I work in EMS and I get annually fitted for an N95 respirator, to make sure I can safely enter contaminated spaces. We routinely put surgical masks on all coughing and sneezing patients."
] |
[
"Ok so what about the chinese that are using them for the thick smog. How is that effective? "
] |
[
"I work in a hospital and by the time that they usually suspect that a patient may have something which could be airborne, we'll usually have spent quite a bit of time with that patient, breathing the same air as them. Usually the first we know is when we have to start gowning up and the masks appear outside the door. For suspected cases of active tb we get the 'duck bill' masks which have a built-in filter - these were also used during the swine-flu scare and we had to be trained in how to put them on. For cases when we are just waiting to have something ruled out, we usually get the simple surgical masks. After 9 years of working in hospitals I have yet to contract tb or swine flu, although I have caught norovirus which I wouldn't wish on my enemies and which is a nasty, airborne virus. On that occasion a patient on the other side of the ward from where I was attending to another patient vomited - that bug ripped through the ward within 12 hours! "
] |
[
"Are the mobility of heavy metals (all) always higher under reduced conditions?"
] |
[
false
] | null |
[
"The solubility of metals depends heavily on what they are complexed with. For example, halide complexes of HMs tend to be highly soluble, whereas oxides tend to be insoluble. In these cases the oxidation state has little correlation with the solubility. These are both examples of metals in positive oxidation states, however. If you reduce a metal further you often form a colloidal dispersion of metal particles, which are not technically soluble but can be highly mobile. Reducing further to negative oxidation states is not worth worrying about, because it practically never happens."
] |
[
"You'll need to clarify your question a bit.",
"By mobility do you mean diffusion? And I assume by reduced conditions you're referencing the oxidation state.",
"Smaller, lighter, and hotter materials diffuse faster. The temperature should be referenced with respect to the melting point of the material."
] |
[
"Sorry about the confusion, I mean solubility of the material in water, or mobility if you factor in the flow of water."
] |
[
"How do scientists make sure that the light they are getting is from that particular heavenly body and not a nearby star, like the Sun?"
] |
[
false
] |
Did not know how to word it in google
|
[
"This question is extremely broad. Your question will most likely be interpreted as:",
"\"How do Astronomers get spectra of specific objects when there are other objects nearby?\" ",
"The answer to that is, we just block out the other light. Here's an example of an SDSS plate that takes a bunch of spectra from one \"Image\". Keep in mind SDSS is a specific survey, but plates are relatively common in the Astronomy world. I'm just using SDSS plates as an example. There's a few other methods, but this one is the most obvious and a very commonly used one. ",
"SDSS plate visualization",
"Actual sdss plate",
"Basically SDSS people know exactly where each object is, and hook up a bunch of fiber optic cables to the back of each hole in the plate. Then you can take 100 spectra in one image because you're only getting the light from one object in each cable. This is just a large scale use of this method. ",
"Also keep in mind that spectra for different objects are vastly different. ",
"spectra of O-type star",
"spectra of M-type star",
"spectra of super-massive-distant quasar object",
"So it's pretty hard to mistake what exactly you're looking at if you've got spectra. If you have a field of stars they're usually separated enough to isolate their light, and their spectra are unique enough to clearly distinguish them. Galaxies are equally unique, as are any other of the objects in the sky. If you have a spectra of a galaxy it's pretty clear when a star shows up in it because of the giant peak of light, usually at specific wavelengths for specific elements that are emitting in that spectra. ",
"\"When taking images of objects in space, how do you tell that you have the right object?\" ",
"Scales are pretty vastly different. ",
"This isn't a spectra, just a color filter. The Stars in this image are all the bright points of light with little crosses. There are a lot of methods to pretty easily filter out unwanted light from stars in the way.",
" If you're trying to take images or spectra of galaxies, you'll notice at one point your data is super bright and screwed up. You can either ignore it or filter it out. To filter it out you can take a lot of images from all the unwanted stuff, images of the wanted stuff, subtract the two, and you're left with the wanted stuff. ",
"edit:\nWhen you have a star field and you're attempting to take images through a filter, ",
"look at this post"
] |
[
"I'd like to add that fiber optic cables operate as a sort of filter themselves. ",
"Fiber optic cables work thanks to a phenomenon called \"Total internal reflection\": light cannot travel from a material with a higher index of refraction into another one with a lower index when encountering their interface (surface of separation between the two materials) at angles greater than the so-called critical angle (which depends on the indexes). ",
"Choosing the proper materials, one can obtain very high critical angles (close to 90 degrees): this means that only the light arriving into the fibers with a direction which is almost parallel to the fibers can be reflected along them (and so transported to the detector). ",
"This is a simple method that can be used to select light arriving exactly from the direction of the object one wants to observe, and to avoid any form of contamination (\"stray light\")."
] |
[
"To prevent confusion from overlapping light sources and scattering they analyze pictures from different locations and because the stars are at a different distance they will appear at a slightly different angle. They can then triangulate the image data to see the exact distance. ",
"I've worked as an astronomer for 10 years, and I'm not exactly sure what you mean here. If by \"analyze pictures from different locations\" you're talking about something like a ",
"parallax measurement",
", that's definitely ",
" done regularly for images of crowded star fields - that's a much more specialized kind of observation that's usually only done by spacecraft these days. For your typical crowded star field observation, you almost never have resources or the precision to do that.",
"Instead, what's usually done for images of crowded fields is an analysis using a ",
"point spread function",
". Almost every star is so far away that it should ideally appear as a point...but because of the nature of diffraction-limited optics, it will instead produce a very specific pattern on an image - generally that of an ",
"Airy disk",
" - that depends on the aperture size and optical layout of the telescope.",
"This is then used for doing ",
"aperture photometry",
". You measure the total amount of light coming in with successively larger circles around the object you're measuring. By knowing how light spreads out in the telescope from a point-like object using your point spread function, you can determine how much of the light comes from the object you're measuring, how much light comes in from nearby objects, and how much light comes in from the background sky."
] |
[
"Is gas spent driving uphill offset by going back down?"
] |
[
false
] |
On my way to work everyday I have to drive up a big hill, and on the way back home I obviously drive back down the hill. If the hill never existed and the distance was flat, would the gas spent be the same? Of course it wouldn't be spot on but is it close?
|
[
"A lot of the gravitational potential you have at the top is transferred into heat (friction) and sound as you come down the hill, so you won't break even."
] |
[
"Well if its a frictionless slope, you and your car are screwed going up and down."
] |
[
"If we assume that you are trying to maintain a constant speed, then no, they will not be close. You must spend excess gasoline with respect to your drivetrain's overall effeciency to comensate for the potential energy gain of driving up the hill. Once you peak and start back down, you must use your brake to prevent excess speeds. The braking represents converting the potential energy you invested as gas to get up the hill into heat from friction on your brakes. This is a non-conservative force and therefor you get very little energy back from going down hill. ",
"If you coasted all the way down, you would still get dramatically higher losses as your drag will increase drastically wiht the highed speeds going down the hill."
] |
[
"How are nutrition facts on every food item specifically calculated? Are any assumptions made in the process?"
] |
[
false
] | null |
[
"This always puzzled me. A wooden chair would have a certain amount of calories, but they are not accessible via digestion. Does this phenomenon happen with food? I don't see why it shouldn't."
] |
[
"There is stuff in our food that burns and I assume shows up on the calorie count that we can't process (like fiber), so there is a discrepancy."
] |
[
"Sure, but if we are interested in nutrition info, we don't care about the calories we can't get and the method of burning in a calorimeter doesn't take it into account."
] |
[
"why do bugs die upside down?"
] |
[
false
] |
Like roaches, when you kill them, they flip over. Why?
|
[
"Spiders move by applying hydraulic pressure to extend their legs. When they die the pressure reduces and their legs curl up beneath them. The dead spider is top heavy due to the body being above the legs, and the curled legs form a curved bottom. Such a structure will naturally roll over onto the spider's back. ",
"I'm not sure if the same applies for insects or other bugs."
] |
[
"What organ allows a spider to move it's legs so quickly and accurately? And what does it use as it's hydraulic fluid? "
] |
[
"Spiders, like us, have a hard skeleton moved by muscles. The difference is that their skeleton is on the outside - that's why it's called an exoskeleton. They also have hydraulic movement, which we don't. So the movement of spiders (and most arthropods) is a combination of both muscle-skeletal interaction, and hydraulic pressure. The fluid, which is analogous to blood, is called haemolymph. It circulates freely throughout the spider's internal body cavity. "
] |
[
"Why are there no thunderstorms in the winter?"
] |
[
false
] |
Not really winter for everybody, but I live in a colder area of the country where it is typically below freezing and I don't think I ever remember hearing thunder or seeing lightning in the winter time. Why is this?
|
[
"Nevermind, did a little research and found the answer!",
"In case you're curious like me:",
"It is a matter of humidity. The cold weather\nthat allows snow means the air is not humid\nenough to allow an electric current to travel\n(along the water vapor in the air) over the differently\ncharged clouds and sky. People who say temp are\nsort of right, but it is the low temp that leads to the low\nhumidity that causes the \"problem\".",
"Feel free to agree or provide any more insight!"
] |
[
"It is entirely possible to have a thunderstorm in the winter. ",
"There's even a Wikipedia article on it."
] |
[
"I've been in at least two thundersnows before, in Kansas. Mightta been three, cain't 'member."
] |
[
"If we extracted all excess CO2 from the atmosphere, how large would the pile be?"
] |
[
false
] |
Assuming we had a way to extract all the carbon emissions causing climate change from the air, how large a pile of carbon would we have? Where would we store it all?
|
[
"Using what method? Different methods of sequestration exist, leaving different end products and this different volumes. ",
"Let's break out a napkin and run some rough numbers. \nLet's assume we have boundless energy, and could somehow extract the carbon and form it into diamonds of pure carbon.",
"We're starting with roughly 250 billion tons of CO2 in the atmosphere from anthropogenic sources in modern times. ",
"By atomic weight, that puts the carbon part of co2 at about 68 billion tons. ",
"The density of diamond is about 3.5 metric tons per cubic meter. ",
"So 68 / 3.5 = about 19 billion cubic meters of diamond. ",
"Many of my numbers were pretty rounded. It's unclear if all my sources that referenced tons were metric ton or not. So I wouldn't count this as particularly accurate, it gives some sense. Continuing with the rough estimates, that's about 540 Empire State Buildings made of solid diamond. ",
"This is kind of the floor of your question. Creating diamonds from the carbon would be very energy intensive, but would be denser than existing sequestration methods that usually leave the carbon not in a pure form but instead in a compound of some sort. If we could keep it as plain amorphous carbon but can't do diamond, you can roughly double these numbers. ",
"Anyone who would like to do more accurate math, feel free to rip these numbers apart. ",
"TLDR; very roughly 19 billion cubic meters of diamond or 540 Solid Diamond Empire State Buildings. "
] |
[
"19 billion cubic meters is so hard to relate to. 19 cubic kilometers is much easier. Thanks for the work, though. :)"
] |
[
"Wow! That's a lot of diamond. Thank you for the response."
] |
[
"Do we know of covid-19 reservoirs in wild animals yet?"
] |
[
false
] |
Knowing that Denmark had to cull their mink population because they contracted covid-19 and knowing the role of wild bird populations with regards to influenza, what do we know of similar wild animal populations that could play an important role as virus reservoirs for covid-19 in the next couple of years? Thank you very much!
|
[
"Well, the virus probably originated in bats, so those bat populations probably still harbor the wild-type of the virus and/or its close relatives. ",
"Also this coronavirus is demonstrably capable of jumping between species, so it should not come as a big surprise if the virus spills over from humans into other animal species, and we should be actively monitoring for such events."
] |
[
"The virus is most likely a zoonotic disease, and other coronaviruses have been shown to infect various animal populations. Sometimes it's a deadly infection (therefore less likely to function as a reservoir species) and sometimes they aren't as severely affected. My understanding of the mink culling is that they were transmitting it to each other and getting a fair bit of viral evolution, therefore it was a dangerous variable they'd rather pay to take care of (cull).",
"On Coronaviruses, this paper from 04 looked at how they behave in various animal populations:",
"There is concern about possible transmission of SARS CoV to rodents or domestic cats (as proven experimentally) with perpetuation of the disease in these species. In livestock and poultry, CoVs are recognised causes of enteric and respiratory infections that are often fatal in young animals. Although the emergence of SARS surprised the medical community, veterinary coronavirologists had previously isolated CoVs from wildlife and documented their interspecies transmission to livestock.\n",
"Source",
"So TL:DR it's probably best to avoid frenching any marmots for the time being. And in the future. Generally, really."
] |
[
"We're way past this point. The reservoirs are humans. Just like we never could eradicate the flu or the common cold. Experts predict it will remain circulating, hopefully less deadly over time. The culling probably had more to do with slow the spread of disease in the short-term."
] |
[
"Why does it take so long for radioactive material to decay?"
] |
[
false
] | null |
[
"All things being equal, the more energy a decay releases the faster the decay happens. This is because in quantum mechanics the more ways an event can happen the more likely it is to happen quickly, and if there is more energy to distribute among the decay particles then there is more ways to distribute it. Enrico Fermi developed the quantum mechanical theory behind this, so it's called \"Fermi's Golden Rule\".",
"So radioactive isotopes have lifetimes that vary over huge spans depending on (among other things) how much energy is released in the decay. Some have very little energy to release, so have very long lifetimes."
] |
[
"It doesn't, necessarily. Nuclear decays have half-lives ranging from zeptoseconds to hundreds of billions of years. Some species decay very quickly."
] |
[
"Additionally, some decays are strongly suppressed because the vast majority of possible decay channels can be forbidden by other conservation laws, like conservation of angular momentum."
] |
[
"What evidence do we have that suggests the universe is infinite?"
] |
[
false
] |
I cannot find a concise article or report on Google which describes the whole of our current evidence supporting the now mainstream view that the universe is infinite. Can someone help me out here?
|
[
"It is believed that we live in a freidmann universe. This is a universe theory that forwards 3 possibilitys: a closed universe, an open universe and a flat universe. A closed universe's shape would be similar to that of a sphere, all space connected. An open universe is shaped like a saddle, and a flat universe is flat, with a total of 0 net energy. The first 2 universe shape theories disrupt Pythagoras theorem, which is that all angles inside a triangle must equal 180 degrees. So if the universe is curved in anyway, which it is in the open and closed models, then the angles would not equal 180 degrees, and so the flat universe is the preffered model. ",
"Freidmann also came up with formula\n to his theory that a flat universe is infinitely large.",
"The argument against an infinite universe and so a flat universe are because we are measuring Triangle's angles in such a small space, it is possible that that the internal angles are very slightly more or less than 180. These differences would be extremely small, and we would only be able to clearly see if a triangle's angles are more or less than 180 degrees by making one over a huge space in the universe.",
"The full explanation why a flat universe is infinite is very long. So if you care to read more on it here is a link explaining why a flat universe is infinite by simplifying and solving freidmann's formula: ",
"http://physics.stackexchange.com/questions/123674/why-does-a-flat-universe-imply-an-infinite-universe",
"Hopefully I explained it relatively clearly, ask if you have any questions"
] |
[
"Sorry to confuse you with the flat like \"paper\". When we mean a flat universe we mean that the geometry of the universe is such that parallel lines will never cross, the angles in a triangle will always add up to 180 degress, and the corners of cubes will always make right angles. We call this kind of geometry Euclidean geometry.",
"To answer your second question no one is sure but there are a few theories on what is at the edge of the universe shown here: ",
"http://en.m.wikipedia.org/wiki/Ultimate_fate_of_the_universe",
" \nUnder the \"Theories about the end of the universe\" sub heading."
] |
[
"There's no way to know, since we can only see as far as light has traveled. We know the \"observable universe\" to be finite, but again, that is bounded by physics. Any theories regarding an infinite universe are conjecture, because from our point of view the light from some parts of the universe hasn't had enough time to get here."
] |
[
"Can we create mass from energy? Or is it impractical?"
] |
[
false
] |
I know we're well accomplished at releasing energy from mass - been doing it since Trinity - but does science ever go the other way? Have humans ever created mass from energy?
|
[
"This is what happens in particle accelerators: particles with a lot of kinetic energy collide and produce particles with mass, at the cost of that kinetic energy."
] |
[
"You could say that mass is a ",
" of energy, and the \"classical\" view of mass is just energy bundled together into a bound, stable state (as opposed to, say, kinetic energy). So the question that you're probably asking is, can humans create ",
" (or other stable forms) from raw energy.",
"The physics that gets in the way is certain conservation laws. We all know that mass/energy must be conserved, and momentum must be conserved, all of that. There are also other properties that must be conserved. For example, electric charge. You can't create net new electric charges, but you can create canceling positive and negative charges from from nothing.",
"There are also other qualities that must be conserved, which sort of resemble electric charge but for the other fundamental forces (strong & weak nuclear forces) rather than electromagnetism. Primary among these are the ",
" and the ",
". Protons and Neutrons have positive Baryon Numbers, while Electrons have positive Lepton numbers. ",
"It is possible to form stable objects from raw energy, so long as all of these forces are conserved. Since raw energy has 0 for these values, normal matter has positive values for several quantities that must be conserved, then you must also create stable forms with negative values so that everything balances out. And you know what that means, right? Sure you do--Antimatter~! :D",
"Humans have successfully turned raw energy into matter/antimatter pairs. Antihydrogen has actually been contained for several minutes at a time."
] |
[
"Well, there's a certain amount of energy before. There's the mass of the two protons (remember E=mc",
" ), as well as the kinetic energy of the particles. Then they collide, the kinetic energy is reduced, and a bunch of particles shoot out. They all have mass, and that mass as well as their kinetic energy adds up to the total energy from before the collision."
] |
[
"Do animals (humans in particular) have pre-built in beliefs?"
] |
[
false
] | null |
[
"I see. I wouldn't call these beliefs. I would rephrase the question as \"is there an instinctual fear response to spoders\" for example. ",
"There is some evidence for differential responses to snakes and spiders in 6-month old infants (",
"Hoehl et al. 2017",
". However, whether this is a fear response or not is not clear and it's important to note that they were comparing responses to two images and saying there was a difference. It's possible you'll see similar differences between two other images neither of which is \"scary\". LoBue and Adolph (",
"2019",
") offer a review and critique of such studies and argue that the evidence isn't so strong that there is such an instinctual fear.",
"Moral judgment in very young infants (e.g. < 1yr) is almost impossible to test, but there is plenty of work in slightly older infants. There is some evidence for innate sense of morality especially around fairness, cooperation, reciprocity, and retribution (see ",
"Hamlin 2013",
" <- pdf! for a review). These kinds of behaviors (especially around fairness) are also observed in non-human animals.",
"Innate knowledge is a separate question and we need to be careful about what we mean by \"knowledge\". Liz Spelke has been arguing for a while that we have multiple \"core knowledge\" systems that help us learn about things like objects, numbers, and maybe social interactions (see, e.g. ",
"Kinzler and Spelke 2007",
" <- pdf!), but these are more properly thought of as innate scaffoldings that allow us to learn certain things about the world as opposed to specific \"knowledge\"."
] |
[
"What do you mean by beliefs? Can you give an example?",
"Birdsong is not a belief..."
] |
[
"For example: Killing people is bad. Spiders are scary.",
"Doesn’t it base itself on beliefs? It is knowledge to say the least and every knowledge is also a belief."
] |
[
"How does the hydraulic ram water pump work and why does it not violate conservation of energy?"
] |
[
false
] |
[deleted]
|
[
"In hydrostatics where the water velocity is zero or small pressure will be equal in the whole system and the maximum height of water will be the same in the whole system.",
"Looking at the water ram it takes a moving stream of water and suddenly stops it by closing the waste valve. This sudden stop mean the pressure increases to stop the water from flowing and this pressure opens the valve into the compression chamber with the air that then seals itself, and the air pressure then manages to force water up through the higher pipe.",
"The key is the energy taken from the water's motion to pressurize the tank. A large volume of water at low pressure is manipulated to create a smaller volume at higher pressure. ",
"If you tried to loop the device it would return a continually smaller fraction of water up the hill after each cycle."
] |
[
"Also even if you ignore the kinetic energy component of the description (which is important to its operation) you still should be able to work out a potential energy balance. In this case, you start with a pool of water at a middle elevation and end up with some water at a higher elevation and some water at a much lower elevation that went through the waste valve.",
"In this way it's no different than taking two weights at the same height and using one to lift the other. If you had a pulley system you could take a 5kg weight and a 1kg at 10 meters and then drop the 5kg weight down to zero while lifting the 1kg weight 50 meters in the air."
] |
[
"This is a great explanation. Dynamics are not necessary to explain the gravitational potential energy before the pumping and after. "
] |
[
"Reading the 'fan theories' thread from a few days ago made me wonder, is there any truth to the idea of heavily traumatized or comatose people inventing alternate realities to \"cope\" with their state?"
] |
[
false
] |
Many of the theories were based around the idea of someone being traumatized by an initial event, with an extremely intricate and complicated reality invented within the mind of the individual to cope with that trauma. Is there any scientific evidence of the human brain actually inventing extremely intricate realities to cope with trauma? EDIT: Sweet responses guys thanks.
|
[
"Well, that is one of the ideas behind ",
"Dissociative Identity Disorder",
" (formerly called multiple personality disorder). Another interesting dissociative disorder (dissociation simply means a split from reality) is dissociative fugue. In this condition, the sufferer will leave their current situation, often to another state or city and start a new life for a period of time. When that period is over, they'll have no recollection of what they did in that time and then go back to their old life. It's a very mysterious disorder but the idea seems to be the same as DID, when there is significant enough trauma, the brain can alter reality in a way that makes the experience manageable.",
"Read more about dissociative disorders ",
"here",
"Edit: To be clear, most of the \"fan theories\" in that thread would probably have been Dissociative Identity Disorder, not Dissociative Fugue. I probably got a bit carried away explaining that because it's so fascinating and most people have heard of DID. "
] |
[
"Paul Bloom of Yale has posted his introduction to psychology lectures on iTunes and YouTube. They are fascinating. The section on psychopathology covers dissociative fugue if you're interested. It's been a while since I watched them, but I believe he mentioned that there was some doubt as to whether this was a \"real\" disorder, or if people just said \"Fuck it\" and then made up an excuse later.",
"Seems like it would be rather hard to study since it's supposed to be extremely rare and such people aren't generally found until the episode is over."
] |
[
"Paul Bloom of Yale has posted his introduction to psychology lectures on iTunes and YouTube. They are fascinating. The section on psychopathology covers dissociative fugue if you're interested. It's been a while since I watched them, but I believe he mentioned that there was some doubt as to whether this was a \"real\" disorder, or if people just said \"Fuck it\" and then made up an excuse later.",
"Seems like it would be rather hard to study since it's supposed to be extremely rare and such people aren't generally found until the episode is over."
] |
[
"Questions you have or recommend I ask for select MIT Brain and Cognitive Sciences Researchers/Professors?"
] |
[
false
] |
I wasn't sure if this would be the proper category for this post, but I figured I would get the most feedback from this subreddit of prestigious repute. I will have personal access to the following 6 individuals for the next week thanks to a "Research Topics in Neuroscience" mini-course I'm taking: If anyone has any questions they would like answered by these individuals, please post them here and I will record them and ask them - returning here with the answers or creating a new post if necessary by volume. Also, what kind of questions do you think I should ask, being a relatively new neuroscience student, since I want to get the most out of this experience. One of the questions I'm being sure to ask each professor is whether or not their lab currently has openings for undergraduate research position (I have promising results so far.)
|
[
"For all:",
"Brain imaging system ",
" is becoming more and more refined. How do you imagine future advances affecting your studies? Will you be able to pinpoint more precisely the group of neurons responsible for your specific brain function? (hint: the answer may be difficult as the number of neurons involved in a process can be quite .... large)",
"in the future, the \"story\" of in synaptic chemistry will continue to become more and more ",
". How will this affect your understanding of how your process works? Do different regions of the brain have different neurotransmitter usage patterns?",
"For BOB:",
"How well defined is the group of neurons in \"synchrony\" and what influences the \"shape\" of this group? What stops all neurons from joining in on the fun?",
"How does neurotransmitter imbalance affect the ability of neuron groups to form \"ad hoc networks\" when needed?",
"For JIM:",
"What would cause someone to create more \"false positives\" in facial recognition than a \"normal\" person?",
"Does the neural process of object/face recognition use the same resources as \"active\" contemplation or imagination? (Don't make a joke about thinking about purple elephants)",
"For PETER:",
"Here is his paper",
".",
"How do advances in understanding the AOS contribute to our ability to develop \"replacement\" retinas? (Bio or electronic, either would be awesome)",
"How would genomics contribute to your ability progress in this field? Do specific genes that control the function of the AOS even exist? What would you like to see?",
"For EARL:",
"Relevant TEDtalk",
"For MRIGANKA:",
"(I'd ask him questions about psychoactive substances <_<, particularly the difference between them )",
"(I'd also ask about how \"specific circuits\" might \"communicate\" with other regions of the brain, like the motor cortex. Especially so if done during an \"unconscious\" process)",
"For MICHALE:",
"How do nootropics affect ... well any aspect of his work, really.",
"Ahem ... long term vs short term.",
"NOTE: I am not a neuroscientist."
] |
[
"For your own career planning, you might want to ask them how they got into the field (what drew them, what paths they took getting into it). You'll probably get a lot of stories and it'll help you figure out if it's an area you really want to pursue."
] |
[
"I've just got one for all of them. I'm curious as to whether they have any interest in altered states of consciousness (meditation, dissociation, psychedelic experiences), and if they have any ideas about whether or not they can contribute to our understanding of human cognition and intelligence in general. "
] |
[
"Why did our immune systems evolve so that we need our meat cooked? (please read description)"
] |
[
false
] |
My question, as stated above is, why do we need our meat cooked? I know it is because we need to get rid of the bacteria, but every other carnivore or omnivore does not need their meat cooked. So why does ours? Why would our immune system evolve so that we need meat to be cooked? Why would it need that extra step to be taken when it is unnecessary?
|
[
"We do not need to eat our meat cooked.",
"Does it kill bacteria? Yes. But that is an added benefit.",
"If you were to eat raw meat straight of the bone right after it was killed, as animal carnivores do, you would not need to worry about bacteria. Bacteria only move in and set up shop and multiply after hours and days.",
"The advantages of coking is that you can eat meat after several days, instead of only several hours.",
"In addition, cooking makes things more easily digestible, at least at the front end (mechanichal digestion - chewing)."
] |
[
"I never even thought about how they eat their prey directly after they kill it so no bacteria is on it. Also about how it simply an added benefit to make it more easily digestible. Thanks for answering and giving me a very complete and straight forward answer."
] |
[
"Not to mention the fact that animals DO get sick if they eat a sick animal. That's one of the many reasons wild animals don't live as long."
] |
[
"How did scientists figure out that coal came from plants?"
] |
[
false
] | null |
[
"There are lots of grades of coal, and one of the lightest, lignite, is full of plant residues. Cook and squeeze lignite and you get shinier, more homogeneous coals: anthracite. Peat is a clear precursor of lignite and you can see peat forming from plant residues. The huge amount fo coal formed in the Carboniferous period is thought to be due to plans involving lignin, a phenolic hard compound, well before bacteria nd fungi were able biochemically to devour it."
] |
[
"Sometimes there’s fossil scale trees and stuff in it. So it’s clearly made of plants.",
"That’s not the full answer (because paleontology is my autistic special interest, not my job) but I just wanted to chime in if no one else did"
] |
[
"Kind of... there's fossil trees in other rocks too, but those rocks didn't come from plants. And we find animal fossils in coal too (just in case someone is curious: no, coal is not made from dinosaurs either). But like you I'm struggling to find a good explanation of how we know.",
"https://theconversation.com/coals-formation-is-a-window-on-an-ancient-world-54333",
"https://www.abc.net.au/science/articles/2013/02/18/3691317.htm"
] |
[
"Would the radioactive spike shown in those trees from ad 774* (let's not get into dates being wrong or right) could that radiation have any significant effect on genetic data?"
] |
[
false
] |
kind of like a nuclear fallout. If so, how much?
|
[
"No. You're looking at a small percentage increase in a naturally occurring carbon isotope (about 1 part per trillion of all carbon). You could only detect that difference by very careful analysis be mass spectrometry, using carefully prepared samples. Waving a geiger counter near it is not going to show anything, and it's waaaaay below the dose levels needed for measurable cellular damage.",
"Incidentally, the reason they were interested in the tree rings in particular is that the dating is done by counting the tree rings. These carbon isotopes are not being used for radiometric dating (which I assumed is what you inferred from your date confidence comment)"
] |
[
"You are right that the actual C-14 spike would have no measurable impact on life, but whatever generated that spike may have. C-14 is made when radiation impacts the upper atmosphere. If there were some large event that caused C-14 concentrations to spike (like a nearby gamma ray burst), it may have been enough radiation to lead to measurable effects on the ground. But that all depends on what made the spike, which as far as I know we have no answer to."
] |
[
"Yes, I guess I took the question a bit literally.",
"Anyway, the most popular explanation (something which has to close enough to inject high altitude radiation but leave no presently visible trace) seems to be solar flare activity, which would be entirely buffered by the atmosphere. Interesting piece ",
"here in New Scientist",
" which quotes a contemporaneous report of what sound like extreme auroral activity "
] |
[
"How come modern computers still use floating point arithmetic instead of having hardware supported rational numbers?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"flawed premises",
"Could you elaborate, please?"
] |
[
"There are multiple issues:",
"If you have a more specific question, please clarify it with some relevant bibliography, then feel free to resubmit."
] |
[
"Do NSAIDs reduce healing times?"
] |
[
false
] |
Just curious here. I recently posted a similar question to and got a wide variety of mutually contradictory answers. Is swelling at an injury site an undesirable response by the body, or is it like a fever where it serves a beneficial purpose?
|
[
"I'm pretty sure an immunologist will come along (or I'll summon one), but here's my take that I feel is accurate from my studies:",
"Inflammation is caused by your body trying to clean up the mess from an injury. If there's tissue destruction or blood vessel damage, debris from that injury is going to sit around inside your body until the clean up crew shows up. Here's a summary of what happens:",
"Tissue injury releases histamines or other chemicals that cause dilation of blood vessels so there is more blood flow to the area.",
"Blood vessels become more permeable in the area of injury / infection so plasma leaks out of the blood vessel and into the tissues causing swelling and pain.",
"Different types of white blood cells show up at the site and start to clear out the bad stuff through phagocytosis",
"The clotting process is activated to stop any bleeding",
"So in the scheme of things reducing swelling changes how this whole process works. Now here's the thing, the studies out there really don't conclude much other than the use of NSAIDs should be conservative because they absolutely can interfere with healing. However, no studies really show just how much they interefere. Soft tissue injuries definitely seem to be affected, as do bone injuries. ",
"So my two cents here is that if you have a pretty nasty sprain or something more than a little bump, don't use them. Rely on ice to control swelling. If you have serious bruising, don't use them as they interfere with blood clotting and your bruise is only going to get nastier. Obviously in severe cases like brain injury swelling must be controlled but they don't use NSAIDs in those cases either."
] |
[
"NSAIDs are not so effective that they stop the entire inflammatory process, but instead they are another tool that will control it. If the inflammation gets to be too severe, then the swelling itself will cause issues with the healing process and can possibly lead to large amounts of swelling becoming permanent. I recommend to those I treat that following minor acute injuries such as things more than a little bump take NSAIDs. This will not be the same for all people, and I am not suggesting that all people should blindly take them. As with all medications, consult your physician before taking any of them.",
"Also, only certain NSAIDs interfere with blood clotting, Asprin being the worst about it because it thins the blood. Naproxen (Aleve) for example does not thin the blood but uses other mechanisms to slow the inflammation process; ",
"this article",
" points to NSAIDs working on \"suppression of a nociceptive process, presumably prostaglandin formation, rather than a generalized anti-inflammatory effect.\" to control the inflammation and pain. ",
"This being said, use of Steroidal anti-inflammatories is usually limited with acute injuries, but for most chronic type injuries the steroidals are very effective."
] |
[
"I agree with your statement 100%. The main issue is there is no conclusive answer to this because there are too many studies out there that contradict each other. ",
"Also, ",
"this article",
" shows that naproxen does affect the clotting process by inhibiting the formation of thromboxane A2 which is essential for platelet function.",
"I also have anecdotal (!) proof of clotting interference. I have a severe vitamin K deficiency and already bruise easily. If I take naproxen I invariably end up with bruises from things like crossing my legs.",
"Not saying you're wrong, I'm just saying. "
] |
[
"Should I recharge a half-full battery?"
] |
[
false
] |
Specially a lithium-ion one that we find in electronic devices. I got a new Nexus 7, and I might only use 20% of the battery in a day. Should I be recharging at night?
|
[
"Theoretically, Every battery has some degree of memory. Thus, you should always charge it fully, and always let the battery totally die before you charge it.",
"This is plain wrong. Lithium-ion batteries ",
"have no memory",
". In fact, ",
"full discharge of Li-ion batteries hurt battery life",
"."
] |
[
"The thing is, when the battery has reached 100% charge, the charging stops and no more heat is accumulated."
] |
[
"Lithium-ion batteries are a bit different than the ones most people grew up with and require a different set of guidelines for use and care.",
"First off, storing a lithium battery at full charge reduces it's life, so leaving it on a charger 24/7 is a bad idea for overall life.",
"Secondly, they have no memory (unlike the NiCd batteries) so topping off a battery after running it down 20% isn't a bad thing. Cycling the battery continually to death and then fully charging it is bad for it's life cycle as well.",
"Both are about as equally bad. Running a lithium ion battery down near its cutoff voltage IS bad for it, but many phones have their cut off above the 'oh crap this is going to hurt' level for the batteries so it's not as harmful as a complete discharge.",
"Both ways increase the overall resistance in the cells. Since Voltage = Amperage * Resistance, with a constant range of voltage this means reduced amperage, and by extension reduced amp hours (battery capacity)."
] |
[
"Do photons ever accelerate?"
] |
[
false
] | null |
[
"They can ",
" to accelerate, as their path, as seen by a distant observer, curves around massive objects. Similarly, if you watch a light signal pass a massive object, measure the distance it appeared to travel and the time it took to complete the trip, you'll find that it took longer than if it had traveled at c the whole way.",
"But these are both observer effects, arising from the fact that a person watching an event uses her own coördinates to measure distance and time. ",
" a photon will always be seen to be traveling in a straight line at c."
] |
[
"The apparent slowing down of light in a medium is a consequence of absorption and re-emission of photons as they pass through. Any single photon is ",
" traveling at c."
] |
[
"Its velocity is constant, but acceleration is a vector quantity, not a scalar",
"Velocity is a vector quantity as well. I think you're thinking of speed.",
"Changing direction at constant velocity is acceleration according to everything that I remember from physics. ",
"Again, speed. Also, everything you remember about physics was developed in the Newtonian approximation.",
"Can you please explain how a change in direction at constant velocity is not acceleration",
"A gravitational orbit isn't really \"changing direction\" in the context of general relativity. Specifically, when we say something has constant velocity we ",
" it's traveling along a \"straight line\" at a \"constant speed\". The generalization of this statement to curved spaces is the statement that \"it's path through spacetime is a geodesic\". Now, in the Newtonian approximation or in flat spacetime, this ",
" following a straight line at a given speed as measured in some inertial reference frame. Now we have acceleration, which in those cases corresponds to \"changing direction or speed\". The generalization of ",
" to curved spacetime is \"having a path through spacetime that's ",
" a geodesic\".",
"And that's the context in which a gravitational orbit is not acceleration. Objects in free-fall, whether that's just radial free-fall or orbital free-fall, ",
" following geodesics. This is why when someone on the ISS holds something out at arms reach and let's go that object just stays there: there are no forces acting on it that would cause it to accelerate. On the other hand, for those of us being held at a fixed distance by Earth's surface, there's the ",
" force that occurs because we're ",
" following a geodesic. We let go of an object, so it's no longer accelerating with us. It then follows an inertial path while we accelerate away from it, until it's intercepted by something that ",
" accelerating (Earth's surface again).",
"even if it is a special case for near-luminal velocities.",
"Who said anything about \"near-luminal velocities\"? I'm talking about any gravitational orbit, regardless of the orbital speed."
] |
[
"Why is it so easy for us to remember and describe images and sounds but so difficult to retain smells and scents?"
] |
[
false
] |
For example I was walking through an area of my local park and caught a wiff off something. I instantly remembered the smell (though I wasn't sure what it was) and then couldn't remember or mentally recreate the smell when I left that area.
|
[
"And a side quetion to this one, why are smells the most powerful reminders for something, like you remember a beautiful situation from smelling freshly cut grass, just because the lawn was freshly cut on that day? Sorry if I'm not doing the best job at explaining my question."
] |
[
"The prevailing idea is that smell evokes emotion and memory strongly because of the olfactory system's location relative to the amygdala. The amygdala can crudely be looked at as the emotion and partially memory area of the brain (it is a particular type of memory more related to emotion and survival instincts than fact memorizing).",
"The neural inputs of smell go from the olfactory epithelium in your nose through the ascending nerve and many of them end up in the olfactory tubercle. The tubercle is not only extremely close to the amygdala, but also has direct connections to it. If I remember correctly, no other sense has this quality. Many believe that such a direct connection between smell and the emotion/memory portion of the brain is what evokes such responses to smell."
] |
[
"You can definitely train it, yeah. It's what you do when tasting wine. For an 'outsider' it might sound like gibberish or just people making stuff up to sound sophisticated (and probably it is a lot of times), but if you know your salt you would know what somebody is talking about. Say you would have two sommeliers blind taste two wines, and one describes both wines to the other. The other one would know which wine was which 9 out of 10 times, easily."
] |
[
"Is a global earthquake possible?"
] |
[
false
] |
With all this May 21st nonsense going around it made me wonder if a global earthquake is even possible, and if it is how could it happen?
|
[
"if you are talking about complete destruction from an earthquake, then no its not possible.\nEarthquakes generally happen at techtonic fault boundries. if you look at a map of the worlds techtonic plates you will see that in a grand time scale, the plates on one side of the world will interact with the plates on the other side of the world. this is called continental drift in a simple explination. but as far as an global earthquake, no"
] |
[
"Not unless it is a VERY big impact. I suspect that impactor would have to be something Moon-sized or bigger. If you want to experiment with different types/sizes of impactors, this ",
"Impact Calculator",
" might be of interest."
] |
[
"Yeah, thats my understanding as well. The only thing I could think that would be even plausible would be some kinda disturbance with the earths core. But I have no clue how or even if that could happen."
] |
[
"Could we easily spread life to another planet by sending a capsule filled with bacteria?"
] |
[
false
] |
In a recent post today, it said that rocks containing earth bacteria had flown to other planets outside our solar system from the the meteor strike 65 million years ago. Could we potentially do this ourselves by launching a big capsule filled with bacteria towards places like Gliese 581, Europa, and Enceladus, and actually start the process of life on another planet? We should have the resources and ability to correctly calculate where to shoot the capsule to make sure it hits the target, and then just release the bacteria once it reaches the planet. I realize that if we did this, they wouldn't reach their destination until long after we are dead but I think it would be worth a shot.
|
[
"When you contaminate Mars with Earth bacteria, then any further research on extraterrestrial life on that planet will stop being valid. "
] |
[
"We could easily send them there. The problem would be getting them to survive there and reproduce. What would they use for an energy source, is there liquid water there (all organisms on earth require liquid water for life), could they live alone instead of in a web of organisms like almost all organisms on earth do, these and many others are the difficult questions and hurdles."
] |
[
"Probably not \"easily\". If it is a lifeless planet then there is probably a reason for that. Conditions aren't very suitable for life. If there is life on the planet then the introduced life, unadapted to its new surroundings, is unlikely to be able to compete for resources against the other well adapted lifeforms.",
"If the conditions on the planet are well known then with effort it may be possible to genetically engineer an organism to survive those conditions and ",
" send it. But all of the planets in our system have extreme conditions even by our extremophile standards. The mean temp on Mars is -63 C and the psychrophiles on this planet can only grow at temperatures around -15 C. Issues like temperature, acidity, access to free water, and exposure to radiation all pose problems for life on other planets. It isn't that life might not be possible on these planets but that the organization of such lifeforms might need to be so radically different from ours to exist in those conditions that modifying life from earth could be prohibitively difficult."
] |
[
"How to use Schrodinger’s equation to find the probability of an electron at certain place in electron cloud ?"
] |
[
false
] | null |
[
"The solutions to the Schrodinger equation in coordinate space give you the spatial wavefunctions for the electrons. The squared modulus of the wavefunction is the probability density.",
"You now have a continuous probability density function for where the particle would be found if its position were measured.",
"If you evaluate the probability of finding the particle at any single point, it’s zero. Since you have a continuous PDF, you can only assign meaningful probabilities to ",
" on the support of the PDF. ",
"So you can define a probability that the electron exists between x",
" and x",
", for example.",
"For that, you just integrate the PDF between x",
" and x",
"."
] |
[
"I'm not really sure how to answer this, since it's really the kind of thing that if you don't know the answer then you probably won't be able to make heads or tails of the answer. ",
"However, assuming you do have the requisite background in the necessary math, the time-independent Schrodinger equation is an eigensystem. If the Hamiltonian operator is expressed in a position basis then the eigenvectors of the time-independent Schroedinger equation are possible states (i.e. wavefunctions) in position space. Wavefunctions are amplitudes so their square at a given point is a probability ",
".",
"EDIT: Even at a point, it's still a density."
] |
[
"No their square is a probability density, their square AT A POINT is a probability, which, of course since position is continuous, will be zero unless you integrate over some finite volume."
] |
[
"Windows 10 says pins are safer than passwords how can this be when passwords have more combinations?"
] |
[
false
] | null |
[
"Pins aren't to increase the security of your machine, they are to increase the security of your microsoft account. ",
"Pins are for logging into the particular machine/account combination, and passwords CAN be for this, but also can be (and what microsofts wants) be multiplatform/cloud based (microsoft account) wide.",
"Therefore, using your microsoft account to log into the computer creates a point of vulnerability for something much larger than just that computer. If that password is compromised, a person has access to all of your platforms, and a vast amount of data.",
"If your pin is compromised, they only have access to that one computer, and perhaps your one drive. ",
"There are also procedure issues. Because people want to log on convienently, they may make easy password. But because microsoft accounts are online and always vulnerable, AND worthwhile targets, it should never have a simple password. Pins relieve this conflict, and so increase security of microsoft accounts this way as well.",
"EDIT: Reading some posts made me realize that a lot of people missed a basic feature of the PIN. The login PIN is only enterable by someone who is physically present. ",
"The PIN, like biometrics (the other login feature added to win10) requires the operator to be physically in possession of the device, and manually interface with it. So, brute forcing your PIN is a slow and bloody fingers affair, and the PIN can complement other features like a security camera. So, the PIN is highly secure by design.",
"by that same note if you make it so that only your PIN, and not your microsoft account, worked to logon to the machine, then switching to a PIN would make your machine more secure. But, as it stands, if your microsoft account is compromised, then the attacker can access your machine without knowing your PIN. This, coupled with the PIN being technically (though not meaningfully,) easier to guess manually, is why your PIN does not increase the security of the machine. PINs increase the security of your microsoft account, which, defacto, increases the security of the machine.",
"If you want no exposure to microsoft account vulnerability, I believe you have to setup the PC with only a locally stored login. That local only login/password would be more secure than a PIN.",
"IF you hear of someone logging in with a PIN remotely, then PINs become a huge liability until patched, and you should immediately disable it. no human enterable number is going to be secure against a brute force attack."
] |
[
"This needs to be at the top. The PIN is only for the computer, and is bound to the computer alone.",
"You can log into a Windows 10 machine with your Microsoft account and associated password. Once you've authenticated yourself, you can then set up a PIN on the device to log into your MS account on that computer (any time you log into a new device with your MS account, device info is reported back to MS, so they know which devices are which, and what PINs are associated with each device and account). Now, you no longer need to use your password to get into that device. You only need the PIN, just like with a smartphone. However, your PIN won't get you access into your account via web browser or via any other Windows device. ",
" If someone gets your PIN, they've only compromised one device - not your entire account.",
"Essentially, Microsoft is enabling you to use your laptop or desktop the same way you would a Windows Phone (or an iPhone, or an Android). You can use a PIN to unlock the device, but a password is still used with your MS account (Apple account/Google account, etc.), in order to access your email, OneDrive, the app store, etc. from any other location. It's another layer of protection. The PIN isn't intended to replace your account password for anything other than unlocking the device."
] |
[
"It's a marketing thing, in reality the average user of Windows 10 when prompted to set a PIN will end up using their credit or debit card PIN. Not good for your bank security.",
"A well chosen classic password will always be stronger than a 4 digit PIN."
] |
[
"What exactly is it about alcohols that make them liquid at room temperature?"
] |
[
false
] |
If you have etOH at standard conditions, you have a liquid. If you remove the hydroxyl group, you have ethane, which is a gas. Is it the alcohol group which causes the chemical to be a liquid at standard conditions? Are there any other rational behind it?
|
[
"Hydrogen bonds. Same thing that makes water a liquid at room temperature makes alcohols liquid. "
] |
[
"Alcohols all contain the OH-group, with the oxygen being partially negatively charged and the hydrogen being partially positively charged. Inside the liquid (as well as in the solid/gas) phase, the positive hydrogen interact with negatively charged oxygen on neighbouring molecules. This interaction is attractive and thus helps hold the liquid together and is commonly referred to as a ",
"hydrogen bond",
". This type of interaction also explains why water is a liquid at ambient conditions where as H2S, which does not form hydrogen bonds, is a gas even though it is structurally similar."
] |
[
"The -OH or hydroxyl group that all alcohols have is what makes them a liquid at room temperature. There is a significant difference in electronegativity between H and O, so oxygen tends to hold the electrons shared between it and H much closer to the O atom. As a result the H atom has a somewhat positive charge to it and the O becomes somewhat negatively charged. So one molecules positive hydrogen and another's negative oxygen will be electrically attracted to each other, and as this happens with every molecule of alcohol, all the molecules are fairly close together. That's what a liquid is. A bunch of molecules with enough attraction between each other that they are very close, unlike a gas where there is usually tons of space between particles, but not so much attraction that the forces held them together in an unmoving rigid structure, as that would be a solid."
] |
[
"What experiment am I thinking of?"
] |
[
false
] | null |
[
"Mercury(II) thiocyanate AKA Pharoah's Serpent?",
"http://www.youtube.com/watch?v=yN9pioJWTk0"
] |
[
"Yea, that's the stuff! My thanks, friend."
] |
[
"You are probably thinking of burning of ",
"Mercury(II) Thiocyanide ",
"."
] |
[
"What makes water such a good solvent?"
] |
[
false
] |
What is it about water that means so many different substances dissolve in it? EDIT: Wow, I didn't expect so many answers! Thank you for taking the time to explain it to me (and maybe others)!
|
[
"It has to do with polarity. The small water molecules have different electrical charges at each end which means that other polar molecules can dissolve in it.",
"Apolar molecules, like oil, cannot dissolve in water but will dissolve in other apolar liquids like gasoline. Apolar molecules do not have different electrical charges at each end. ",
"This is why oil and water don't mix. "
] |
[
"It's not just about polarity. It's also about hydrogen bonding and hydration shells, as well as the two lone pairs that are so free to generate hydrogen bonds. Think, for example, about the hexagonal structure of ice and how it could fit molecules or ions in there. That kind of happens with the hydration shell of water. Think, too, about the way aquaporins fit water!"
] |
[
"Rule #1 of solution chemistry: Like dissolves Like.",
"You can group substances into roughly three major categories:",
"Nonpolar substances have a uniform charge distribution. This means that the electrons that make up their bonds do not tend to clump up in any particular areas. Oily substances are basically nonpolar. This includes hydrocarbons such as methane, octane, vegetable oil, and beeswax. ",
" of these substances dissolve well in water. Some small molecules might get trapped in ice, but that's a different discussion.",
"Polar compounds like water have a charge separation. This is caused by the constituent elements having a different affinity for electrons. So in water, the oxygen \"pulls harder\" on the electrons, which clumps up negative charge around the oxygen end of the molecule. Hydrogen is left behind as a slightly positive end of the molecule. The geometry (bent in the case of water) of the molecule also affects this overall polarity. Sugar, on a \"functional group\" view, is basically just water-like sections attached to a backbone. These are called hydroxyl groups, they are found in many compounds in biological systems, and they confer an easy solubility in water.",
"Ionic compounds like table salt have so much charge separation that they can actually dissociate into their constituent ions when dissolved in water. Water's polarity actually causes it to surround an ion, so each Na",
" is surrounded by the negative oxygen-ends of a group of water. Each Cl",
" is surrounded by the positive hydrogen-ends of a group of water.",
"To answer your question, it's because so many substances that we're interested in, usually biologically-important substances like proteins, sugars, and salts, are similar enough to water (polar and/or ionic) that they dissolve well. There is an equally large group of nonpolar substances that do ",
" dissolve in water, however, so don't just drill into your head that \"water dissolves everything\"... it very much does not dissolve oil unless you help it with soap."
] |
[
"Considering that the sand dunes in deserts move like water in slow-motion, would it be possible to calculate it's motion through Navier-Stokes Equation?"
] |
[
false
] | null |
[
"Granular flows are similar to fluid flow but cannot be modeled solely by the Navier-Stokes equation. Specifically the viscosity term is different because for sand the inter-particle interactions are are governed by friction and collision. A pile of sand can have a stable configuration with a sloped surface (which a fluid cannot). If the slope is increased, a critical value is reached, friction is overcome and then there is sudden movement of sand down the slope.",
"Work is being done, however, to unite the fields: ",
"Unifying Liquid and Granular Flow",
". Also see ",
"NASA: City-swallowing Sand Dunes",
" regarding saltation and jumping grains."
] |
[
"Probably not what a fluid dynamicist would call turbulence but certainly the potential for chaotic regimes."
] |
[
"Do granular flows exhibit turbulence?"
] |
[
"Do fungi have immune systems?"
] |
[
false
] | null |
[
"Fungi use a system of protein receptors which can identify foreign matter in a manner similar to plants and animals.",
"\"A class of cytosolic Nucleotide Oligomerization Domain (NOD)-like receptors, or NLRs, contribute to this recognition and discrimination process in plants and animals [2,3]. Less is known about how fungi monitor their interactions with their biotic environments. ",
"Here, we summarize evidence indicating that fungi have similar NLR proteins and may use similar mechanisms to recognize and respond to heterospecific nonself; we outline similarities and differences with their plant and animal counterparts, and we propose future directions elucidating aspects of fungal immune systems.\"",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5658179/"
] |
[
"\"Heterospecific nonself\". I'm going to casually insert that into conversation today."
] |
[
"They won't have anything like the vertebrate adaptive immune system, but they do have a variety of immune defenses. They can use ",
"RNA silencing",
" to control viral infections, and of course fungi are famous for producing antimicrobial compounds to fight off bacteria...most notably penicillin. Many of those may be fighting competitors more than pathogens though."
] |
[
"4 Physics Questions"
] |
[
false
] |
1) It seems strange to me that at a fundamental level physicists don't explain a mechanism behind relativity. Is this just not widely discussed? Are there proposed mechanisms, but the even the question of a mechanism is too abstract to pin down any real ideas? Is relativity only an effect of the geometry of the universe itself? 2) I am reading about Bell's non-locality inequality. My book does a poor job in explaining what this means in regards to actual phenomena. What does non-locality mean to a single particle. How can things be connected in this non-local universe. Isn't quantum entanglement an example non-locality? 3) I've read that no information can be "sent" superluminally through entangled systems. Couldn't the act of collapsing the probability wave function of one particle and hence its partner, be information in and of itself? For example, when I choose to measure my particle, it signals to the observer of the second particle that I have done so. Doesn't this qualify as information? 4) This last one was inspired by Shavera's specialty of "experimental strong force physics". Can you do any experimental work on strong force interactions with any tools besides accelerators? What unsolved problems can you work on without "a bigger accelerator". Could you tell me a bit more about what you are working on? I apologize for not breaking these up into separate posts. Any input would be greatly appreciated. Cheers.
|
[
"Geometry. It all stems from the very special relationship that time and space have together. Let's take a simple case. If you want to know the distance between two points in 2 space dimensions, you take sqrt(x",
" +y",
" ) where x is the distance in one space, and y is the distance in the other. But if you want to find the distance between two points in one space and one time dimension, the distance is sqrt(x",
" - t",
" ). That minus sign gives rise to what we call a hyperbolic geometry, and all of special relativity comes out of that. General relativity involves more complicated things than \"just\" a minus sign, but that's how you take the next step as it were.",
"And 3. really, the mistake most people make with entanglement is that you're not measuring ",
" a particle, you're measuring a ",
" of particles. And that measurement always requires at least one step that is light speed or slower. ",
"Here's",
" a pretty good thread in which we discuss it in greater detail.",
"I'm not sure of any non-accelerator effects. Well, aside from what we learned about atomic nuclei when we studied them in the mid 20th century. The \"residual\" strong force interaction between protons and neutrons; like the Van der Waals force in chemistry, it's like a little bit of the strong force \"leaks\" out of the interactions holding the proton or neutron itself together, and that leakage holds the whole thing in a nucleus. This can be modeled with a Yukawa potential and pi meson mediating particles.",
"But I'd wager that there really isn't much you can do without an accelerator. There's just ",
" much energy in such a tiny volume that the only way to get a look inside is to accelerate particles to extremely high energies and probe the structure. You can do this with electrons on protons and see things like charge distribution that neglects the strong force; or proton on proton which is dominated by quark-quark, quark-gluon, and gluon-gluon interactions.",
"A bit more as to what I'm specifically working on, well at the moment I'm doing \"heavy flavour tagging of jets.\" See, as a quark comes out of whatever it's in, it necessarily creates a lot of quarks and gluons with it. Well these can often decay and whatnot into a big spray of particles that come out of the collision we call a jet. I'm working on techniques to help identify when the quark that created the jet was a charm or beauty quark. Then hopefully we'll be able to use that knowledge to say something about a few different things in our collider. For instance, it's thought that beauty quarks may not lose as much energy in the quark-gluon plasma; so, if I can say that these jets are likely to be beauty jets, then we can compare those against other types and make a measurement that says some stuff about the quark-gluon plasma environment."
] |
[
"1) You're going to have to define \"at a fundamental level\" for me. The way that fundamental physics works is that you observe some phenomena, you make up a theory that explains the structure of the phenomena consistently, and then you check that your theory predicts everything you observe.",
"General relativity is a self-consistent theory that can explain almost everything we see in space. It readily reduces down to our familiar Galilean relativity and Newtonian gravity at slow speeds and weak gravity. ",
"Perhaps/likely there is another theory, readily visible at higher energies or higher distances, that reduces down to general relativity in some limit. But we do not know it yet. Even if we did, though, you would be asking the same question of what the mechanism behind the higher theory is.",
"So, we're just explorers in science, pushing out from our familiar confines of normal human speeds, energies, and distances, out into the unknown that lies beyond the frontier of human experience. And we create models that bring together what we see in a consistent fashion. But perhaps there is always something that lies beyond our knowledge, for now... perhaps there will always be something, or perhaps we'll reach the end at some point and have a theory of everything.",
"2) I'm not an expert with respect to Bell's inequalities, so I'll leave this for someone else. I have a response, but I'm not so sure it's right. Sorry!",
"3) There's no signal. Let's say you were given an entangled particle, while some other guy very very far away (we'll call him Joe) is given the other one. When you measure the particle, you can either find it in state |1> or state |2>, with equal probability. Because they're entangled, you and Joe would measure the particles to be in the same state.",
"However, if you had no communication with Joe, you'd still measure the particle in |1> and |2> with equal probability. Only after you and Joe communicate can you compare notes and see that the particles were indeed entangled. You can't even tell when or whether or not he measured his particle at all, until you ask him.",
"And communication+asking does not occur at superluminal speeds. No information is transfered.",
"4) I can't think of any way to probe the strong force with anything but accelerators. The energy that is required to penetrate the structure of the proton, for example, is ridic. You need more than a ",
"GeV",
", which is just about 10",
" Joules, but compressed into a really small point (10",
" m or so). The binding energy of protons, neutrons, and other nucleons is somewhere on the order of 100 GeV.",
"Shavera's work on ",
"quark-gluon plasmas",
" and stuff at ",
"RHIC",
" is in the a-few-GeVs-per-nucleon range, I believe. The ",
"ALICE",
" experiment at the ",
"LHC",
" deals with nuclei in the a-few-TeVs-per-nucleon range, so about a thousand times more energetic than RHIC. (Sorry, shavera.)",
"Without a bigger accelerator than that... there's not that much else you can do in experimental strong force physics. You don't see much unexplained phenomena at lower energies, since we've already spent so many decades figuring out explanations/self-consistent theories. However, there are also many experiments that aim at generating a lot of data at lower energies, for precision measurements and very slight effects. But they're not really strong force experiments. (See ",
"MINOS",
", ",
"BaBar",
", ",
"IceCube",
", ",
"CDMS",
", etc.)",
"What am I working on? I'm a theorist, so I don't do the experimental stuff, but I sort of work at the interface between theory and experiment. ",
"Supersymmetry",
" is one thing we're looking for at the LHC, and I'm involved in thinking up and fleshing out tests for supersymmetry at the LHC and future particle colliders."
] |
[
"Curses! You beat me to this by 17 minutes. I was typing for a long time."
] |
[
"Could any biologists help me with this question about penguins?"
] |
[
false
] | null |
[
"Hi Al_Rapee thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Biology"
] |
[
"‘Biology’"
] |
[
"Do dogs really learn words? Or do they just learn tone of voice?"
] |
[
false
] | null |
[
"Very interesting: ",
"Nova did a documentary on dogs recently, I can't recall if that clip was from this episode or from on of those nova science now episodes.",
"http://www.pbs.org/wgbh/nova/nature/dogs-decoded.html"
] |
[
"Very interesting: ",
"Nova did a documentary on dogs recently, I can't recall if that clip was from this episode or from on of those nova science now episodes.",
"http://www.pbs.org/wgbh/nova/nature/dogs-decoded.html"
] |
[
"Very interesting: ",
"Nova did a documentary on dogs recently, I can't recall if that clip was from this episode or from on of those nova science now episodes.",
"http://www.pbs.org/wgbh/nova/nature/dogs-decoded.html"
] |
[
"Where did the moon come from?"
] |
[
false
] |
I've heard two theories. One is that the moon accreted along with the earth during the formation of the solar system. The second is that a Mars sized object collided with the proto-Earth and ejected enough material into orbit that eventually coalesced into the moon. I seem to remember a recent article that says the moon has been determined to have an Earth-like iron core, which would suggest the moon accreted along with the Earth. But the moon also has a pretty low density, which would seem to be indicative of being formed from the upper layers of the Earth. What do scientists think?
|
[
"It is pretty much accepted that a Mars sized object hit the Earth at a glancing blow. ",
"Wikipedia"
] |
[
"Yes yes, internet meme, blah blah blah. But it's actually a good question and it deserves a serious answer. And yes, I agree that it's pretty much accepted nowadays that the Moon was formed from a collision in the early solar system. ",
"(Also, internet memes these days suck. In my day we would have said that the moon was a ridiculous liberal myth. )"
] |
[
"Yes yes, internet meme, blah blah blah. But it's actually a good question and it deserves a serious answer. And yes, I agree that it's pretty much accepted nowadays that the Moon was formed from a collision in the early solar system. ",
"(Also, internet memes these days suck. In my day we would have said that the moon was a ridiculous liberal myth. )"
] |
[
"How long are acidic/spicy things like Orange Water or Enchilada Sauce safe to eat in the fridge?"
] |
[
false
] |
I've got some spicy Enchilada sauce with a pretty darn acidic PH, that's literally 6 months sitting in the fridge, as well as some orange water (4 slices of a large orange, pre-washed and scrubbed with soap, and then added to about a pint of water and has been sitting in my fridge for two weeks. Is the acidity of such things, combined with refrigeration enough? What kind of bacterium can grow, or will grow in an acidic and cold environment and how long before I throw these things out?
|
[
"DOH! I meant 'eat FROM the fridge.' That was such an epic failure, given that this ",
"/r/askscience",
". Forgive me, oh dogs of grammar.",
"Also some clarification: The orange itself is washed before slicing, no washing of the slices themselves, that would be just rather odd."
] |
[
"As a general rule, if it smells fine, looks fine, and tastes fine, it's probably fine. There aren't any stealth spoilage bacteria that creep into things the minute they hit their expiration date, so you don't need to worry about suddenly dying.",
"From personal experience, chili pepper sauces will pretty much never spoil, just dry out - I use the same container of chipotle peppers in my fridge for at least a year with no ill effects. Spicy food is a natural antimicrobial, and became popular in human history because it was a great way of keeping food safe. ",
"The orange water isn't a great media for bacterial growth, but a fungus could hang out on top of it without too many problems. If you see mold floating in it, it's probably gone bad."
] |
[
"As a general rule, if it smells fine, looks fine, and tastes fine, it's probably fine.",
"True, but botulism is a very important exception. It doesn't like acid, though."
] |
[
"Idle Speculation on a Geoengineering Question"
] |
[
false
] |
Forgive the speculative nature of this question. I imagine this is wholly implausible; mostly I'm asking because I'd like to learn more about how modern lasers transmit information through the atmosphere, how railgun technology has advanced in recent years, and whether it could serve as a viable satellite launching technology (and if so, how). Thanks to anybody who responds. ~Koala EDIT: The original link got lost somehow, so here it is again
|
[
"Rail guns only require the projectile to be conductive, the magnetic field is generated by the current passing through the object."
] |
[
"Lasers are subject to atmospheric distortion.\nRailgun technology has increased as much as capacitor technology - they are dependent on the capacitors for the high voltages required. The US Navy is the largest researcher."
] |
[
"Launching with lasers is described in ",
"The Millenial Project",
", an interesting book on terraforming. The author suggests initially accelerating ships like a railgun and launching them out of Mt. Kilimanjaro. Then, many large microwave lasers would ablate a large block of ice under the space vessel without hitting the rest of the vessel. The water molecules would shoot of the rocket at high velocity. ",
"This would be efficient because the high KE given to the water molecules would be carried from the ground via the lasers, and no conventional hydrogen fuel would be lifted by the \"rocket.\" "
] |
[
"When the first nuclear submarine, the Nautilus passed under the North pole in 1958, how did they know there is enough room for it between the sea floor and the bottom of the ice?"
] |
[
false
] |
It was occasionally a close call, so did the Captain of the sub knew in advance the gap's size and that the sub has enough space? Edit: After learning more about the Poles, the correct answer is that there is no continental shelf under the North Pole and the Arctic sea's depth is 4.2 km there. The ice is only about 2 meters thick so there is plenty of room. Due to global warming during the summer months, it is occasionally iceless now. But getting there is another issue. The Nautilus had to give up its approach once because in the Bering Sea the ice's thickness was 18 meters and the sea floor was too high up due to a ridge, thus it didn't have enough room. The second US submarine (USS Skate) reaching the North Pole breached the surface by breaking through the ice.
|
[
"They had been using sonar both active and passive on submarines for a long time. They can hear how far it is from the bottom and the ice sheet. It was also definitely not the first venture of a sub under ice. Just further and longer than they have gone before."
] |
[
"Sounding below the ice have been taken all across the artic. Even then they had a decent idea of the topography. It has long been known that the artic was an archipelago."
] |
[
"How did they know it was feasible at all?",
"Do we actually know that they knew for sure that it was possible? It seems to me that one of the reasons you might send a sub under the North Pole is to find out if it's possible to move subs around down there. After all, exploration is often less about what you know and more about what you don't know.",
"I mean it's not like they would have ",
" to know it was possible before going to take a look."
] |
[
"What triggers Apoptosis in the human body?"
] |
[
false
] |
What makes certain cells kill themselves in Apoptosis while other types continue to reproduce? If its a chemical trigger can we reproduce it artificially to target specific cells such as cancer?
|
[
"I'll just quote the introduction of my thesis proposal.",
"Apoptosis is a highly conserved function by which individual cells can initiate and control the process of their own demise. An essential process throughout multi-cellular organisms everywhere, apoptosis is critical for the timely destruction of damaged cells before necrosis sets in. Many factors can lead to the triggering of apoptosis, which takes place through one of two pathways: intrinsic or extrinsic (see Fig. 1). Extrinsic apoptosis requires the production or presence of factors external to the cell which bind to death receptor proteins in the membrane, triggering a cascade of proteolytic enzymes and DNases to destroy the cell in an orderly fashion (Mehlen and Bredesen 2004). Intrinsic apoptosis relies upon the failure of the individual cell's homeostasis, often resulting from irreparable DNA damage or various types of oxidative stress (Reed 1997, Green and Reed 1998). Both pathways yield the same results: cytosolic shrinkage, fragmentation of the nucleus and subsequent condensation of the chromatin. Apoptotic cells eventually disintegrate and are consumed by phagocytes (Kroemer et al. 2007).",
"The extrinsic apoptosis pathway is mediated by proteins expressed on the cell surface which all belong to the Tumor Necrosis Factor (TNF) superfamily (Bhardwaj and Aggarwal 2003). Upon binding the appropriate ligand on the death domain of the receptor protein, signal transduction and adaptor recruitment occurs, forming a complex of TNF, the adaptor protein FADD, and Caspases 8 and 10. Ligands consist of TNF, Fas ligand, and TNF-related apoptosis-inducing ligand (TRAIL), which bind to TNFR, Fas, and various isoforms of DR, respectively. TRAIL is a highly conserved gene product of 299 amino acids which has been cloned out of humans, mice, chickens, and fish (Chang et al. 2006) The promoter region of the TRAIL gene in Zebrafish has been found to contain many transcription factor binding sites for lymphoid-specific transcription factors, as well as p53 (Chang et al. 2006). Given this, and the finding that Zebrafish TRAIL is constitutively expressed in most tissues, suggests that it may share a similar role with Human TRAIL in the apoptosis pathway. This pathway consists of TRAIL binding DR4 or 5, which causes the recruitment of FADD. FADD recruits pro-caspase-8 and -10 to form a death-induced signaling complex (DISC). The pro-caspases are catalytically cleaved and activated to destroy the cell. FasL and its receptor, Fas, constitute another method of apoptosis induction. Proteolytic cleavage of FasL, a membrane protein, yields a soluble domain which will bind to Fas, another membrane-bound receptor (Schulte et al. 2007). FasL is expressed primarily on T-cells. Binding of FasL to Fas on cells expressing the protein receptor leads to initiation of apoptosis, which can be assumed to be homologous to the pathway exhibited in humans (Griffith and Ferguson, 1997). TNFR has two isoforms, but only TNFR1 has a death domain (Bhardwaj and Aggarwal 2003). Its ligand, TNF, mediates apoptosis as well as other physiological responses such as inflammation and cell proliferation. Little is understood of the interaction between TNFR and its ligand in fish, but preliminary studies in Japanese flounder and Zebrafish have identified and characterized these genes (Park et al. 2003, Eimon et al. 2006).",
"The intrinsic pathway is controlled by the Bcl-2 gene family, having members of either pro- or anti-apoptotic properties. Protein products of these genes contain a few important domains, called Bcl-2 Homology Domains (BHD) 1 through 4 (Borner 2003). Anti-apoptotic members typically have 3-4 of these domains involved in their function, while pro-apoptotic members may have only one (BHD3), or several. BHD1-3 of anti-apoptotic proteins form a hydrophobic groove for the binding and sequestering of apoptotic cascade proteins and caspase activators, also constituting a site where pro-apoptotic proteins can bind and competitively inhibit this protective function (Puthalakath and Strasser 2002). BHD3 of pro-apoptotic members, instead of forming a groove, is exposed via a conformational change or post-translational modification (Sattler 1997). This allows it to bind to and inhibit the function of the hydrophobic groove in anti-apoptotic Bcl-2 members. Multi-domain proapoptosis proteins will sometimes bind to the membrane with their hydrophobic site, occluding the site from further interaction or binding to some other inhibitory molecule until activated. Activation depends on the cellular environment, be it transcription of p53 due to DNA damage, death receptor ligation from the extrinsic pathway, or other indicators of failing cell integrity. Ultimately, interaction of proapoptosis BH3-only members with anti-apoptotic members near mitochondria, as well as BH3-only protein-mediated conformational changes of multi-domain proapoptosis members, cause the formation of pores in the outer membrane of mitochondria. The resulting expelled contents act as death signalers or catalytic activators of caspase, causing cell death, termed \"mitochondrial membrane permeabilization\" (MMP) (Skommer et al. 2007, Antignani and Youle 2006)."
] |
[
"All cells follow a predetermined growth and reproduction cycle, and there are certain chemical triggers that the cell recognizes at 3 points during the cell cycle, if a cell is damaged it will tell will not allow itself to build some of the proteins crucial for mitosis. Some stop reproducing, others stop functioning and are recycled."
] |
[
"Some. It gets complicated. The main pathway for apoptosis involves a series of enzymes called caspases, and these are activated by (among other things) calcium. So large influxes of calcium can cause apoptosis. In the brain during prolonged seizures, for instance, neurons may die because of energy failure (in which case they undergo necrosis) or may go through calcium-induced apoptosis as a result of excessive calcium flux from NMDA and other receptors.",
"CD8+ T cells (cytotoxic T cells) can also induce apoptosis in infected cells or cancerous cells, first by binding to the cell and and recognizing foreign antigen bound to the MHC, and then by secreting enzymes and chemicals which perforate the cell membrane and activate the caspase system.",
"During development, populations of cells may be programmed to die to, for instance, shape fingers out of a stub of a hand. This is guided by ",
"developmental signalling molecules",
".",
"Just a few examples."
] |
[
"Is it actually possible to \"inhale\" a disease from somebody who is infected?"
] |
[
false
] |
For example, TB or Tuberculosis... can you get TB from inhaling the air around a person who is infected?
|
[
"You don't get diseases from air, you get diseases from inhaling viruses or bacteria that are ",
".",
"Any \"air borne\" disease can become suspended in air and can be transmitted by inhaling air that contains that particle. ",
"Some examples include the common cold, flu, and yes, TB."
] |
[
"There is a subtle difference in transmission between TB and the cold or flu. TB is truly airborne which means it can hang out in the air for a long time, like dust. The infectious aerosol can remain in the air even after the patient is long gone, and can even travel on air currents to other places. The cold and flu viruses have a \"droplet\" transmission which means they are passed in tiny droplets of body fluids that come from sneezing talking etc. But droplets settle out of the air relatively quickly. So to get the flu from the air, you'd have to be in close proximity to an infected person who is talking or otherwise creating tiny infectious droplets. "
] |
[
"Yes, definitely. I did not think the difference was substantial enough to explain the difference. "
] |
[
"What's the relationship between sharpness and hardness? Could a sharp enough blade cut through steel a la Snow Crash?"
] |
[
false
] |
In Snow Crash, Raven would use blades a molecule thick at their edge to cut through material far harder than the blades were made of--say obsidian cutting through steel. Is such a thing possible? More to the point: what, if any, is the relationship between hardness and sharpness in determining if something gets cut or not?
|
[
"How sharp a material is will define how neat the cut will be, but beyond that has very little bearing on deciding what cuts what.",
"Hardness is the variable you're looking for if you're trying to decide if something will cut something else. Simply put, hardness is a measure of how much force a material can take before it begins to plastically deform. ",
"Hence, if you push two materials against one another, they will exert an equal and opposite force/pressure upon one another and the one that is less hard will \"give\" first, and be cut by the other, more hard material.",
"And that's really it in a nutshell. There are of course extreme cases of exception. These occur when the two materials are drastically different in dimension from one another.",
"One extreme case is that one material is much larger than another, such as say, steel cutting into a huge block of aluminium. If the aluminium block is too large, or the cutting area is not sufficiently cooled, then the build up of heat combined with the local deformation of aluminium (which increases it's hardness) could result in dulling the steel blade.",
"One of the other extreme cases, as you mentioned, is where a materials is extremely thin. Having a thin piece of metal does two things to it's properties. Firstly, the thinness means that the macrostructural properties will be affected. (For example, a pencil is harder to snap the shorter it is), and secondly if you reduce the thinness to the microscopic level then you increase the effect of imperfections in the lattice on the overall properties of the material.",
"PS: The ",
"Mohs scale",
" is a easy, albeit slightly simplified way of tackling the problem."
] |
[
"No, such a thing is not possible with current materials. Raven's blades were a molecule thick at the edge, but they didn't cut through steel. Read the book again, they cut through things like human flesh and bullet proof vests. That's not really surprising, though, as steel knives will also cut through kevlar without trauma plates. "
] |
[
"Just throwing out ideas;",
"Maybe the better question involves edge geometry instead of just sharpness. Just throwing out ideas here, but it seems intuitive that a Raven style blade would allow for more shearing (as opposed to ploughing) at the cut. Furthermore, at the microscopic level where the contact actually occurs, we're just looking at a stress concentration at the edge. With a molecule thickness, that's an extremely small cross sectional area (on the order of 10",
" meters) for the force to be applied over. "
] |
[
"Is it easier to get food poisoning when on a course of Antibiotics or more difficult?"
] |
[
false
] |
If I was on a course of Antibiotics would their presence in my body help fight of the bugs of bad water or fish? Or would my lack of gut bacteria due to being on antibiotics help the germs flourish in an open game?
|
[
"Classic food poisoning is not actually caused by infection, rather the symptoms of food poisoning are typically due to the ingestion of bacterial toxins that are present in the environment. So in these cases, antibiotics won't do anything because no infection is necessary to cause the illness. Classic food poisoning is associated with meats, canned goods, refrigerated foods and the like. These produce the symptoms you are probably familiar with like intense vomiting and nausea and potentially diarrhea.",
"Actual infection from food is slightly different, although sometimes this is called food poisoning as well. Some infections that might fall under this category are salmonella and campylobacter. However, the symptoms of these infections are typically restricted to diarrhea and fever, without significant vomiting. These infections could potentially be blunted by prior antibiotic use; however, it has to be an antibiotic that the pathogen is susceptible to.",
"Now, you mention bad water or fish. Illness from drinking bad freshwater typically are due to either pre-formed bacterial toxins (as above) or protozoal infections, neither of which are affected by bacterial antibiotics. Protozoa are eukaryotic and bacterial antibiotics work exclusively on prokaryotes. Another common water-borne illness is salmonella, but besides that, actual bacterial infections from freshwater are uncommon. Illness from contaminated seafood is similar, although there are additional parasitic infection to worry about, which again are not affected by bacterial antibiotics. There is one bacterial infection from seafood that is worth mentioning: Vibrio vulnificus. This can be contracted from fish and shell fish and lead to the typical symptoms of food poisoning as well as even potential sepsis. Prior antibiotics might stave off this infection; however, again, it has to be the right antibiotics.",
"One last comment: even if you are exposed to a gastrointestinal bacteria that is susceptible to whatever antibiotic you are using, it might be enough to prevent that infection. If the group of bacteria first entering your system are immediately presented with an obstacle like antibiotics, it may actually select for the few most hardy bacteria that are part of that group. Those could go on to cause an infection that is actually worse because the bacteria are more resistant to antibiotics. That is why it is always best to hit any infection with a regimen most likely to get rid of the pathogen in a single course. "
] |
[
"This is just too broad of a question for a specific answer. For one thing, \"food poisoning\" refers to an incredibly varied set of situations. ",
"Mycotoxins are produced by fungi that grow in stored food, and can cause serious illness even though the fungi themselves do not survive the cooking/digestion process and don't infect humans.",
"Under the right conditions, several bacteria can produce exotoxins that also cause illness without an actual active infection - some can even survive subsequent reheating. ",
"Viruses, protozoa, flatworms and nematodes are also potential causes of foodborne illness, and would be unaffected by antibiotics. The most common cause of \"food-poisoning\" is actually a virus - norovirus - commonly referred to as the stomach flu.",
"In the case of a bacteria that causes illness through a true infection, it's conceivable that they might more easily gain a foothold due to antibiotics induced changes in your gut flora. At the same time, many bacteria that cause foodborne illnesses are very susceptible to antibiotics themselves, and so may never be able to cause a noticeable infection. I know this answer sucks, but it just ",
" on the specific bacteria and a lot of other variables... there's really no definite answer. "
] |
[
"I have to clarify one part of your answer there. While you are correct in saying that often people are made sick by bacterial toxins it looks to me like you're saying that those toxins are just hanging out in the environment and a person can become sick just by say drinking a glass of water with the toxin in it. This isn't really the case. Let's take a classical example, ",
". ",
" is a potent human pathogen which causes the disease Cholera, a severe case yes, but a food or water-borne pathogen none-the-less. This bacterium does not produce the toxin responsible for the disease in the environment. This virulence factor is expressed due to the activation of receptors that recognize signals that the bacterium has invaded the human gut, (namely the absence of Sodium). This is the case with many secreted toxins (and other virulence factors). Those genes aren't expressed all the time. ",
"Here",
" is an interesting site I came across giving a lot of good information on different bacterial pathogens and their methods of virulence. "
] |
[
"Step Function Symbol"
] |
[
false
] |
Picture: Our lecturer has awful handwriting, his notes are one of the reasons our year is going to fail (see above link for example). In the above link, the symbol outside the brackets for unit step function is unknown. Literally 200 students have no idea what symbol it is meant to be. All we know is that its something to do with the unit step function! Please can you help decipher what that symbol is sci?
|
[
"Sometimes it is marked as \"1\"",
"Seriously? That's the worst abuse of notation I've ever seen, and there are a ",
" of abuses out there."
] |
[
"The last one is probably a delta function, which is the \"derivative\" of the step function. The step function is usually represented by a H in physics, but I guess he meant a 1"
] |
[
"I would email him if you are too worried about it. But given the context of the other functions I would say its probably the Heaviside function, especially if he told you the derivative of the 'uknown function' gave you a \"dirac impulse.\""
] |
[
"Is quantum phenomena the only example of a truly stochastic system?"
] |
[
false
] |
It seems to me that, at a macro level, if there is enough information about a system, that it can be entirely deterministic. I am aware of the "Hidden Variables" conjecture, and that it is countered by Uncertainty and Quantum Mechanics. My lab mates have cited Entropic systems as a macro-level system, but I (maybe falsely) see that as deterministic (apart from the quantum effects within the system). So a rephrasing of my question is: If the output of all quantum phenomenon in a system is somehow known ahead of time, can every system be determined from a starting state?
|
[
"So a rephrasing of my question is: If the output of all quantum phenomenon in a system is somehow known ahead of time, can every system be determined from a starting state?",
"Yes. ",
"Let's say you assume the MWI of quantum mechanics, which insist the schrodinger equation is universal. The schrodinger equation describes change of a physical system as completely deterministic. There is no information loss here. Knowing a system at any point in time will tell you the system at any other point in time. No matter how complex. There is no room for randomness.",
"Of course, we might still use probabilities to describe systems because it's impossible to know the exact state of the system. "
] |
[
"I'm sure there are examples of larger thermal systems that behave truly stochastically but these are two that immediately come to mind.",
"You cannot get true randomness if the underlying physics is deterministic. I'm not familiar with your area, but if you're using a classical description that contains true randomness, that randomness does in fact originate from quantum mechanics. There is no randomness in classical physics. "
] |
[
"In many classical problems, an ",
" small change in the initial conditions of a system can result in a totally different outcome over time. The word \"infinitesimal\" is not to be taken lightly. No matter how well you define your initial conditions, it is always the case that subtle differences in those conditions, far below your theoretical ability to measure them, will give rise to totally different outcomes, i.e. stochastic behavior. ",
"The issue of \"below your ability to measure\" need not be about Quantum Mechanical Uncertainty. For example, in the n-body problem of gravitation. The point being, stochastic behavior starts in physical systems long before we need to go to a quantum mechanical origin.",
"EDIT: Just read about ",
"Chaos, where the deterministic nature of these systems does not make them predictable",
"."
] |
[
"How does a catalyst affect activation energy?"
] |
[
false
] |
I have seen diagrams of catalysts which hold molecules in place so that they are in the correct orientation for reactions to occur but my textbook says that they provide a alternative route which lowers activation energy. Does that mean orientation is factored into activation energy or are they separate things? If so how do catalysts reduce activation energy? Does it do with the way they deform the electron shells of a molecule?
|
[
"As an example, for a reaction with one intermediate state the activation energy is the energy required to reach that state. A catalyst changes the intermediate state in a way that the energy required to reach it is reduced.",
"A simplified (and not necessarily correct) view of the oxidation of hydrogen on a Pt surface is a more specific example. The bond dissociation energy of both H2 and O2 are lower when undertaken on a Pt surface. Or in other words, the intermediate state, where the atoms are fully dissociated/ separated, has a lower energy when the individual atoms are bonded to the Pt surface. This makes sense. Making bonds always lowers the energy of the system - the surface bonds 'stabilise' the individual atoms and make it a more favourable reaction route than gas phase dissociation.",
"This has no affect on the total energy change of the reaction however, because we are still going from gas phase H2+O2 to gas phase H2O regardless of reaction route. ",
".",
"Other factors also play roles. In the ends it's also highly catalyst dependent."
] |
[
"I'll try and give a biochemical perspective, as catalysis is fundamental to biology. The activation energy of a reaction refers to the energy needed by a given chemical species to reach its reactive state. Typically, this energy is used to overcome some kind of steric hindrance. (As you suggested, the electrons in the outer atoms of a molecule can prevent other reacting species from getting too close) In biology, many catalysts function simply by \"holding\" the reactive molecule in its transition state. By stabilizing the transition state in this way, these catalysts can \"bypass\" large activation energies. ",
"But this leads to a common misunderstanding. ",
". So instead of needing a lot of energy to get to a highly energetic transition state before the reaction can proceed, a molecule can have its transition state stabilized by a catalyst, offering a reaction route that requires less energy to overcome steric hindrance. Importantly, ",
".",
"There are also more complicated catalysts that bind multiple molecules at once or actually perform the chemical reaction, but I think that is beyond the scope of your question. Hope this helps."
] |
[
"Don't worry about kinetic energy for the moment. The potential energy associated with the bonds is what we care about.",
"Breaking these bonds requires energy. In some cases, less energy is required to break bonds when the molecule is 'bonded' (to differing amounts) to a surface. H2 dissociation on Pt is an example.",
"Since, in our simple case, the activation energy is the energy required to break the H2 bond, the reaction undertaken on the Pt surface will require less energy.",
"Now, this means that more of our molecules will have or be above the required energy (in this case vibrational energy and not kinetic because bond dissociation is associated with high energy vibrational modes) to dissociate. This is because the distribution of molecules at different energies is spread out - they all don't have the same energy.",
"In the end, more of our molecules will be in the transition state and so our rate has increased."
] |
[
"Are there lifeforms with translative joints ?"
] |
[
false
] |
So I noticed that every joint in the human body is based on a rotation, the only difference between them being the number of liberties (for example : elbow and knee : 1, neck and ankles : 3). I've thought about pretty much every living species I could think of, and all of those which have joints have, I think, rotative joints. I have also noticed that a wheel component is hardly possible because there needs to be a permanent link between the different parts of the body in order for body fluids to circulate, and a free wheel would involve torsion, which is bad. But for translative body parts, this does not seem to be an obstacle. I would provide schemes if I could because it's kinda difficult to explain. I hope at least some of you are understanding it the way I mean it. So, does it exist on Earth ? PS : sorry for the sloppy English, if there is some. EDIT : a friend of mine pointed that cats have retractile claws, which makes them having translative joints. Now I wonder if there is a species with translative limbs.
|
[
"Would you consider that a joint? That is the mechanism of the molecular motors (related to ATP synthase motors), but it isn't really a joint like those of an animal's arms and legs."
] |
[
"Yes there are, a sperm's tail can rotate clockwise and counterclockwise without a stop ",
"http://en.m.wikipedia.org/wiki/Flagellum#section_1"
] |
[
"You're right, but I was thinking about something macroscopic."
] |
[
"How did monkeys get to the new world?"
] |
[
false
] |
How did monkeys get from Africa to South America? I'm actually writing a research paper on it and two theories I have found are the drifting theory in which a giant tree brought them across the ocean, or the Antartica theory which has been pretty discredited. I need sources to for my bibliography so if anyone has links of legitimate scientific studies done on either studies or any other ones I would greatly appreciate it. It seems the drifting theory is the most supported but it seems kind of crazy to me that a giant tree full of hundreds of monkeys blew over the ocean millions of years ago.
|
[
"AFAIK, the raft of vegetation is the best (only?) theory out there. Even though the Atlantic Ocean was narrower about 40 m.y. ago (around 1000 miles at the narrowest), it seems a remarkable journey."
] |
[
"You want aliens just watch the history channel. But rafting is the going theory. Here's an article (the bit about rafting is down toward the bottom, and mentions some other groups thought to have rafted) ",
"http://blogs.scientificamerican.com/tetrapod-zoology/2011/10/05/hoatzins-in-africa/"
] |
[
"Thank you. It sure is remarkable, when it was explained to me I was like, \"You really expect me to believe that?\" But that is the best hypothesis out there. Still searching for articles that support electromagnetic anomalies or even better... ALIENS! "
] |
[
"Why does the shower curtain get 'sucked' inwards when you turn the shower on?"
] |
[
false
] |
Edit - thanks for the answers everyone! I still find myself curious, there's been lots of different principles given as answers...
|
[
"A minature sideways huricane",
"http://www.scientificamerican.com/article/why-does-the-shower-curta/"
] |
[
"Because the water flow is also dragging air along with it, creating an air current. If you remember your physics class, or if you've ever studied how airplane wings work, you'll be familiar with the concept at work here. ",
"To put it in simple terms, air that is moving quickly has a lower pressure than air that is moving slowly. By turning on the shower, you just created an air current, increasing the velocity of the air inside the shower, thereby creating a low pressure zone.",
"The air outside the shower is still sitting relatively still, therefore it is a high pressure zone. The shower curtain is pushed on one side by a high pressure zone, and because the opposite side of the curtain does not have a high pressure zone to counteract it, it moves as it is pushed.",
"Let me know if my explanation was not clear in any way! "
] |
[
"While that is a contributing factor, the same phenomenon can be observed when cold water is used."
] |
[
"Does temperature affect cellular signal?"
] |
[
false
] |
[deleted]
|
[
"It shouldn't be a significant factor. I believe that this battery depletion is due to some other effect. Not temperature related impact on the reception."
] |
[
"Temperature does affect the resistivity of conductors but that doesn't usually impact signal processing and transmission because the information flow is not proportional to the charge flow but rather information flow. "
] |
[
"Temperature does affect the resistivity of conductors but that doesn't usually impact signal processing and transmission because the information flow is not proportional to the charge flow but rather information flow. "
] |
[
"Is there a sweet spot on any of the gas giants where we could float something like a blimp?"
] |
[
false
] |
If so, could there be the possibility of a maned mission some day that does just that (other than first testing the idea with a probe)?
|
[
"Kind of relevant xkcd"
] |
[
"So this idea has been explored somewhat extensively. ",
"This PDF",
" gives a decent insight into some preliminary mission planning for an aerobot that could be used on Jupiter.",
"Technically speaking, a \"blimp\" itself would never work on Jupiter. Blimps work on the principle that you maintain buoyancy by containing a gas that is lighter than the surrounding atmosphere. The problem is that on Jupiter, the atmosphere is mostly hydrogen...and there's no gas lighter than hydrogen!",
"With that said, though, a Montgolfiere-style hot air balloon - the kind where you heat up the contained gases to maintain buoyancy - would actually work, and folks have been starting to propose such a missions. Now, maintaining an internal flame to heat the balloon contents (as we do for hot air balloons here on Earth) would be very difficult. Flame requires free oxygen, which doesn't exist in Jupiter's atmosphere, so you'd have to bring your own oxygen for combustion...and that would likely add a lot of weight. ",
"However, you can design a balloon filled with some of Jupiter's own atmosphere, has a top surface that absorbs sunlight (but doesn't emit infrared energy back out to space) as well as a bottom surface that absorbs infrared energy escaping from the deep interior of the planet. As the Sun appeared each day to warm the balloon, it would rise in the atmosphere for 5 hours, then descend at night for another 5 hours. If properly designed, such a balloon could last months.",
": A blimp wouldn't work. Blimps use lighter-than-air gases to float, but Jupiter's \"air\" is made of mostly hydrogen, and there's no lighter gas. A hot air balloon could work, though."
] |
[
"So, uh, scientist who actually studies Jupiter's atmosphere here...",
"Atmospheric pressure is about 10 bars at the start of what we consider Jupiter's atmosphere",
"That should read ~1 bar, not 10. Earth's pressure at sea level is 101.3 kilopascal, and 1 bar is defined as 100 kilopascal. Based on our best estimates from spectroscopic retrievals, that's an altitude either right at or below the ammonia cloud tops.",
"If you avoid any areas with 150 m/s winds or whatever, of course.",
"This probably wouldn't be a problem for any regular-sized blimp. The east-west jet streams on Jupiter are relatively wide, and don't meander like the jet streams here on Earth. So long as the entire atmosphere surrounding you is traveling uniformly 150 m/s, there would be no problem. It's only when there's considerable shear that you'd notice a bumpy ride."
] |
[
"Is there a nearby neutron star / pulsar associated with the supernova that created the heavy elements found on Earth?"
] |
[
false
] |
We know that all of the elements on the periodic table with an atomic number greater than iron are created from supernovae events. Therefore, much (if not all?) of the matter in our solar system is made up of material left over from a supernova in our cosmic past. We also know that neutron stars are the stellar cores left over after the gravitational collapse of a star during a supernova event. Does this imply there is a neutron star somewhere in our cosmic neighborhood associated with the supernova that generated all of the heavy elements found in on Earth? If so, have we identified the location of this neutron star?
|
[
"So anything greater than about 8x the mass of the sun will explode in a supernova. This means that the remnant can be either a black hole or a neutron star. (Though Neutron stars are way way way cooler.)",
"The seeding of the milky way to produce metals did not come from just one supernova. It came from many supernova that seeded the galaxy with metals that the sun and the planets formed from.",
"Also, a supernova imparts a large kick to the remnant. So even if there was one that was more chiefly responsible, it almost certainly got a huge kick that would make it very hard to identify as being once associated with the birthplace of the sun."
] |
[
"Also, a supernova imparts a large kick to the remnant.",
"Just to chip in on this...neutron stars are kicked randomly out at a few hundred kilometers per second from an exploding supernova. The solar system is about 5 billion years old, so the neutron star could have gone a couple million light years in this time. This isn't enough velocity to escape the Milky Way, so it isn't ",
" that far away, as the space crow flies, but the point is that if there were a supernova strongly associated with our solar system's formation, whatever compact object it produced is far enough away that there's no obvious association with us."
] |
[
"Does this imply there is a neutron star somewhere in our cosmic neighborhood associated with the supernova that generated all of the heavy elements found in on Earth? If so, have we identified the location of this neutron star?",
"The solar system is about 4.5 billion years old, and it takes about 230 million years to orbit the galaxy. That is, the solar system has orbited about 20 times. It is very unlikely that any stars have remained nearby after so many orbits, unless the Sun is a member of a bound multi-star system. There is no evidence for this."
] |
[
"Does hot water flow faster than cold water?"
] |
[
false
] |
[deleted]
|
[
"It can flow marginally faster while remaining laminar(smooth) rather than turbulent. This is defined by the Reynolds number and is proportional to density and viscosity which both reduce with higher temperature. Lower Reynolds is less turbulence. Water is liquid over a narrow range of temperature though. "
] |
[
"The viscocity of water varies by about a factor of 3 between room temp and boiling point. "
] |
[
"The thermal particle motion you are referring to is random, there are just as many particles moving \"forward\" as there are \"backward\", so the net effect is zero.",
"Two potential effects on flow due to temperature are:",
"If the flow is driven by a constant pressure difference (eg, water flowing down a hill or pumped using a centrifugal type pump), the viscosity of the water will decrease with increasing temperature which reduces the friction between the water and the pipe walls, which will allow for a slightly faster flow rate as compared to the cold water.",
"If the flow is driven by a constant volumetric flux (a progressive cavity pump, for instance), then the velocity of the flow will not be effected by temperature, however since the density of the water decreases slightly with increasing temperature, the mass flow rate of water will be a bit lower than it is for cold fluid (you will still pump 5 litres per minute, but those 5 litres will weigh a bit less, so there are less water molecules being transported per unit time.) Incidentally, this is why gas pumps in some places have a label like this: ",
"http://2.bp.blogspot.com/-N_XZEdSRygE/VGlxDkFkKUI/AAAAAAAA0yk/uDdtXoOfgnI/s1600/3-14-expansion-.003.png"
] |
[
"What does a black hole look like?"
] |
[
false
] | null |
[
"Like a black circle which lenses background light around itself. Probably something a bit like ",
"this artist's rendition",
". That's assuming it's just a black hole with no accretion disk.",
"The event horizon of a black hole describes a spherical shape in space."
] |
[
"Think of the gravitational field of a star or planet. In the same way, a black hole's gravitational field is spherical. conservation of momentum tends to form the accretion disk into a flat shape, though."
] |
[
"Okay, it makes sense now! and that's a really cool picture. Thanks! "
] |
[
"Do other species have cultures?"
] |
[
false
] |
Humans have a wide variety of cultures in different areas. Do other widespread species have similar cultural variation? I've heard examples of a certain group of predators developing a hunting technique that other groups don't use, but how far does this go? Which other animals present wide variation within the species like this?
|
[
"Many cetaceans (whales and dolphins) have been demonstrated to have cultural differences in behavior. This can include hunting and foraging behavior, communication, and social interaction.",
"Groups of the same species in different regions often have widely varying behaviors. For example, Killer whales (",
") in the Pacific northwest are split into a number of different pods, some of which are called \"resident\" and others of which are \"transients\". The resident pods eat only salmon and have distinct dialects that they use to communicate with other individuals in their pods. They also have much smaller home ranges than the transient pods. Transient whales have much more varied diets, which include fish, invertebrates, and marine mammals. They travel much more widely than the residents, and very rarely, if ever, interbreed with other pods.",
"This is the only system with which I am familiar enough to explain at length, but I know that similar dynamics exist in other species. \"Culture\" is likely a result of high intelligence in social animals. We can surmise that other social, highly intelligent species also exhibit variation between distinct groups. Examples of this may include other primates, elephants, cetaceans, and other large predators."
] |
[
"Chimpanzees have many well documented forms of culture. Most of it comes from differences in tool use or communication. Chimpanzee populations that are isolated from one another tend to develop cultural differences. They learn the techniques from others within the group",
"http://www.sciencedaily.com/releases/2009/10/091022122321.htm"
] |
[
"http://www.youtube.com/watch?v=bXQAgzfwuNQ",
"This is just one example of species having idea sharing!"
] |
[
"How are HELA cells immortal?"
] |
[
false
] | null |
[
"This answer is incorrect.",
"The end replication problem that you describe applies to (as the name strongly suggests), replication, not transcription (the process you describe) and especially not translation (which does not involve DNA at all). As well, RNA polymerases ",
" attach to single-stranded DNA. Primase, which adds RNA primers, is an RNA polymerase which adds the RNA primers in order for DNA polymerase (the enzyme that cannot bind single-stranded DNA) to bind.",
"I'm also a bit lost by what you said towards the end. Did you imply that telomerase functions to cut off telomere fragments? Because that is also incorrect. Telomerase adds nucleotide repeats to the ends of DNA, ",
" the telomeres. Telomeres naturally get shorter as a result of the end replication problem, which eventually causes cells to stop replicating. Cancer ",
" telomerase activity, it does not lose it. By gaining telomerase activity, it can continuously extend telomeres to ensure that they never become short enough to trigger senescence."
] |
[
"This answer is incorrect.",
"The end replication problem that you describe applies to (as the name strongly suggests), replication, not transcription (the process you describe) and especially not translation (which does not involve DNA at all). As well, RNA polymerases ",
" attach to single-stranded DNA. Primase, which adds RNA primers, is an RNA polymerase which adds the RNA primers in order for DNA polymerase (the enzyme that cannot bind single-stranded DNA) to bind.",
"I'm also a bit lost by what you said towards the end. Did you imply that telomerase functions to cut off telomere fragments? Because that is also incorrect. Telomerase adds nucleotide repeats to the ends of DNA, ",
" the telomeres. Telomeres naturally get shorter as a result of the end replication problem, which eventually causes cells to stop replicating. Cancer ",
" telomerase activity, it does not lose it. By gaining telomerase activity, it can continuously extend telomeres to ensure that they never become short enough to trigger senescence."
] |
[
"They are cancer cells. Cancer cells generally are immortal. But obviously, that doesn't really answer the question.",
"Cancer cells obtain immortality in the sense that they no longer have any limits to how many times they can replicate themselves, thus growing continuously (and why we can harvest enough cells for virtually any application all across the world from one woman's tumour). The predominant theory as to why they are capable of this is through the gain of telomerase expression. At this point, you may be thinking \"LOLWUT?\"",
"There's a bit of an inherent flaw in the way linear DNA strands like yours or mine get replicated. DNA polymerase, which generates the new strand, cannot grab onto the single-stranded template it's supposed to function on. So another enzyme called Primase, which ",
" do this grabs on and adds some RNA to the place where replication starts. The DNA/RNA double-stranded structure can bind DNA polymerase, which will then translate the rest of the strand. For replication origins within a strand, when the primer is removed, another polymerase from a different direction will synthesize the empty bit of single-stranded DNA where the primer used to be. However, at the end, there is no other direction, and no other polymerase to come and synthesize that extra bit of your DNA. So cells have extensions beyond the regular genome called telomeres, that are specifically designed to gradually shorten due to this end replication issue. When they do, the cell is signalled to stop replicating, reaching a state called ",
". So you may ask, why don't we have something that can add to this single-strand so our cells never get old and die?",
"And it turns out that we do! Telomerase is an enzyme typically expressed in rapidly dividing cells so that they can do exactly that; rapidly divide. And it's useful for things like hair and your gut, but not so much for things like your brain, prostate, or cervix. And here's the kicker. ",
" What makes them different is changes in expression. They all work with the same information, but used differently. You can sort of think of cancer cells as those cells that got into information they weren't supposed to access. And in the case of immortality, this information is telomerase expression. Without those shortening telomeres, there's nothing keeping the cells from growing and growing and replicating and replicating. And they still go on to this day. In fact, HeLa cells have a nasty tendency to get into cell stocks that you weren't expecting them to get into. It's kind of a nuisance...."
] |
[
"A question about relativity..."
] |
[
false
] |
I understand that all observers measure the speed of light as a constant, no matter how fast they travel, and that time slows down to ensure that you don't match or exceed the speed of light, but why does time dilation only affect one of the moving objects. If we had somebody get on a spaceship from earth, travel at 0.5c for a while and then come back, they would've measured less elapsed time than the people on earth. But why is that, if, instead of portraying the spaceship as traveling 0.5c away from earth, we could also view the same situation as one where both the earth and the ship are traveling 0.25c away from each other. So my question is, how can we calculate absolute time dilation if all motion is relative?
|
[
" isn't relative, and you have to accelerate to come back. That's the deciding factor."
] |
[
"So my question is, how can we calculate absolute time dilation if all motion is relative?",
"The thing you calculate in this theoretical scenario is called the \"proper time\" along the trajectories of the two observers. The most convenient way to do this is to pick a single inertial reference frame in which to perform the calculation. That word \"inertial\" is important. It basically means \"unaccelerated\", and you have to be sure that you're working in an inertial reference frame or you calculation can go all wonky. Now, there are ",
" inertial reference frames of interest here. The one corresponding to the person on Earth, the one corresponding to the outbound traveler, and the one corresponding to the inbound traveler. Note that those last two really are distinct; in order to get from the outbound frame to the inbound frame our traveler had to accelerate, and that means it ",
" inertial reference frame.",
"I've drawn up three spacetime diagrams for you to see this. The rules for such a diagram are these:",
"Here",
" is the scenario as seen from Earth's reference frame (Earth is green and the ship is red). Notice Earth is stationary so it's represented by a vertical line. The ship returns after four-hours in this reference frame. I've drawn the ship as moving at 3/5 the speed of light to make my life easier. How much time passes for the ship? We do that in two pieces. For the outbound flight, Earth sees it flying away for two hours at 3/5 the speed of light. So the time passed is 2 and the distance traveled is 6/5. Then the \"length of the line\" is 1.6 according to the rule give above. The same applies on the inbound trip, so the total length is 3.2. The ship experiences 3.2 hours while Earth experiences four.",
"Now ",
"here",
" is the same scenario in the outbound frame. If you do the same sort of calculations, you find again that between the ship leaving and returning, four hours pass on Earth. The outbound journey takes 1.6 hours as measured on the ship, and then another 1.6 for the return, so the ship clock reads 3.2 hours at the moment of return.",
"Finally, ",
"here",
" is the same scenario as seen in the ",
" reference frame. Once again, the Earth line has a \"length\" of four while the total length of the red line is 3.2."
] |
[
"Wow, thanks a lot. If everybody explained things this well I wouldn't have had to ask the question in the first place."
] |
[
"Are there any benefits from eating sugar?"
] |
[
false
] |
[deleted]
|
[
"Sugar's not harmful if you don't overdo it, but it wouldn't hurt to leave it out altogether. You get plenty of sugars in almost all the food you eat, unless you only eat whale blubber. Even proteins can be converted into sugar by your body if the need arises."
] |
[
"Glucose in particular is extremely important to the function of the human body. ",
"Hypglycemia",
", or low blood sugar, is a condition that wreaks all sorts of havoc on normal brain function. Fortunately, as mutatron said, most everything you eat can be used as a glucose source by the body, so you don't necessarily need to eat sugar itself. Many athletes, particularly endurance athletes, take glucose supplements to provide energy to the body during grueling workouts."
] |
[
"Sugar is not harmful if used in moderation, but this can be said about everything. In excess it can be converted to fats for storage. So if you take in more than you use, you'll get fat. Also, excess sugar floating around in your blood can cause damage (the same damage that results from diabetes).\nGlucose is not essential, like certain amino acids and fatty acids, because your body can create it through a process called gluconeogenesis. Your body will simply use proteins to create the sugar it needs. "
] |
[
"In string theory, if strings are 1-dimensional, how do they vibrate in more than 1 dimension? E.g. If a piece of paper (defined by dimensions ,y) was truly 2 dimensional, could you bend it along the z-axis?"
] |
[
false
] |
typo: ...(defined by dimensions x,y)...
|
[
"They vibrate in the dimensions orthogonal to its length, called transverse dimensions.",
"They can because they are elastic! Paper is not analogous because it's not elastic."
] |
[
"No, the string is vibrating in the transverse dimensions. The string is ",
" a background spacetime and moves in it. It's really like a normal guitar string.",
"Now for the advanced part: the curvature of spacetime has actually an equivalent (dual is the best word) description in terms of virtual gravitons. But gravitons are nothing else than particular modes of the strings. So actually that background is built by the strings themselves."
] |
[
"No, the string is vibrating in the transverse dimensions. The string is ",
" a background spacetime and moves in it. It's really like a normal guitar string.",
"Now for the advanced part: the curvature of spacetime has actually an equivalent (dual is the best word) description in terms of virtual gravitons. But gravitons are nothing else than particular modes of the strings. So actually that background is built by the strings themselves."
] |
[
"What causes shivers when you pee sometimes?"
] |
[
false
] |
[deleted]
|
[
"Ahhh the good 'ol pee shakes, or, rather \"Post-Micturition Convulsion Syndrome\". This is completely unknown cause but is thought to be part of a sympathetic reflex of your sacral portion of the spinal cord to the pedundle nerve during micturition. "
] |
[
"what about poop shivers?"
] |
[
"I was always told it means that a bunny ran over your (future) grave"
] |
[
"If this graph from NASA is used to show that global warming is occurring, what was going on before 1940?"
] |
[
false
] | null |
[
"The line in the middle of the chart is the average temperature during this time period. Because the temperature has been increasing, this is above what the old average would have been. The average looks like it would have been around -0.25 C, with regular yearly fluctuations occurring throughout."
] |
[
"I'm not sure what you're asking. Can you elaborate on your question or explain what has you confused? Also, can you link us to where this graph is from?"
] |
[
"Warming was still occurring prior to 1940, but to show increases in temperature, we subtract a time period in question relative to another time period, which is usually 30 years. ",
"For example, the recent release of the ",
"National Climate Assessment",
" will usually use a base period of 1980-2010. Temperature is averaged over this time period, then subtracted from, say, some time period in the future. So, the negative temperature anomalies you see in that NASA graphic is because the base period was warmer than temperatures back then.",
"Hopefully that makes sense."
] |
[
"Can you recommend a good book that explains an area of complicated science in layman's terms?"
] |
[
false
] | null |
[
"Oh, hey, also do a search in AskScience (make sure the checkbox is checked) for \"books\". There are quite a few threads there that did get some traffic before we became despots. "
] |
[
"We are going to do a little special on this topic soon, so stay tuned!"
] |
[
"Haha did you remove my post from public view? I was wondering why I couldn't see it on the \"new\" thread. And how will I know when you do the special/where to find it?"
] |
[
"Electro-Convulsive Therapy - how does it work?"
] |
[
false
] |
[deleted]
|
[
"I will assume you mean ECT for the treatment of severe major depressive disorder. As far as I am aware this is the primary indication in the modern age.",
"The short answer is nobody really knows. ",
"Here",
" is a PDF of an overview of proposed mechanisms of action. (It's fairly technical.)",
"The goal of ECT is to induce a generalized seizure. It is only considered to be effective when seizures can be induced. Clearly it induces changes, some long-lasting, in the transmission of neural signals. Exactly how that helps with psychiatric disease is still debated."
] |
[
"There was research published about ECT just this week. ",
"1",
", ",
"2",
"."
] |
[
"I not familiar with the details but what I do know is its overdramatrized in films. Those \"shocks\" are very short, like a defibrillator. Exposure to current through the brain for any period of time can be very lethal, keep in mind. As for how it works, as I understand it puts the patient into a small seizure and is believed that it allows the brain to \"reboot\"."
] |
[
"How was the first computer OS created without another OS to create it on?"
] |
[
false
] | null |
[
"The first computers didn't have operating systems, they just had dedicated programs that performed specific functions or would have programs and data loaded using punch cards. These were written manually.",
"Predating operating systems were assemblers and compilers that allowed for simple programming languages. Eventually, these tools were used to create operating systems. With the current complexity of operating systems and software, it can be hard to imagine writing an entire operating system in something as low-level as assembly languages (languages in which each command corresponds to a single processor function), but the first operating systems were much simpler than the current ones.",
"Edit: typo"
] |
[
"This is like asking how a house knows how to stand upright when you put nails in 2x4s and build a frame...",
"A processor is a processor because we designed an electrical circuit to respond to stimuli in a given way. If I tell it to load 23 in the A register it puts 23 in the register because that's what the circuit was designed to do.",
"It's not like the processor was designed before the instruction set or bus interface was designed and it \"learned it\" they were all designed in unison."
] |
[
"At its core, a CPU is just a complex circuit that when given certain inputs produces some output or performs some action. At the lowest level, there is memory that stores instructions for the processor, encoded as ones and zeros, that tell it to perform some operation. ",
"One such simple operation is to move data from an address in the system memory (RAM) to the memory in the CPU where you can manipulate it. Another operation might be to add two values in the CPU memory together and store it somewhere else. How the CPU does those specifically requires more in-depth discussion of the CPU hardware, but the simpler examples aren't as complex as you might think.",
"Anyways, a program is really just a list of those instructions that the processor goes through one by one. Combining many of those instructions allows complex programs to be made. Along the way, people decided that it was easiest to write these assembly instructions in more human readable ways, like \"ld [CPU address], [RAM address]\" to load some data into the CPU. ",
"Later, people created programs to interpret this assembly language called assemblers. These were often written ",
". Of course, they were first transcribed to the machine-readable binary by hand, but once that work was done, they could just use a program to do it for them.",
"So to answer your question, programming languages were planned out long before they had any implementation, and then interpreters (assemblers and compilers) were written in already existing languages, or if none existed at the time, raw machine code (1s and 0s)."
] |
[
"In the electromagnetic spectrum, what do you get at frequencies higher than gamma rays?"
] |
[
false
] |
What is the result of electromagnetic radiation at a frequency greater than that of gamma rays? It seems that as the frequency increases, it interacts more strongly with matter. Does this continue?
|
[
"What is the result of electromagnetic radiation at a frequency greater than that of gamma rays?",
"In proton-proton collisions many neutral pions are produced which predominately decay into high energy photons. At LHC energies, these photons can range into the 100 GeV range. As far as I know, these are just called photons or perhaps more informally 'gammas'.",
"It seems that as the frequency increases, it interacts more strongly with matter. Does this continue?",
"At very high energies, the dominant interaction mechanism is electron-positron pair production, where the photon will exchange momentum with some particle in the material and then convert into the e+/e- pair. Those e+ and e- particles will radiate off more photons which will convert into more pairs and so forth, forming what is called an electromagnetic shower. ",
"Higher energy photons result in more energetic showers, but for dense materials like lead the penetration depth of the shower does not depend strongly on energy in the 1-100 GeV range."
] |
[
"Indeed.",
"Also, very high energy photons tend to \"leak out\" their energy as they travel through the universe:",
"http://en.wikipedia.org/wiki/GZK_cutoff"
] |
[
"They turn into e+/e- pretty quickly assuming that they are in some dense material like lead (on the order of centimeters), but otherwise they can travel a long distance before 'converting'. Conservation of energy-momentum prevents them from converting without exchanging momentum with a nearby charged particle. ",
"I think that the reason for no special name is that by the time people started producing GeV energy scale photons, it was known unambiguously that they are in fact photons, and not just some new mysterious invisible rays."
] |
[
"Could an orb of photons orbit a massive enough object?"
] |
[
false
] |
If you had a massive ball of photons traveling at the speed of light at the proper trajectory could they orbit a massive enough object? I'm assuming that this object would have to have more mass/be dense enough to surpass any known black hole. I would also guess that the ball of photons would be invisible since none of the photons would be reaching our eyes/telescopes, but that's not the point. Is it theoretically possible?
|
[
"A massive ball of photons doesn't really make sense, but for individual photons it is called the ",
"photon sphere",
"."
] |
[
"Every black hole has a region around it where photons are trapped in orbit."
] |
[
"Similar"
] |
[
"Why are men better than women at chess at the elite levels?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"statistically",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"Thank you for getting back to me but that does not seem to cover why men are better at the elite levels. "
] |
[
"Thank you for getting back to me but that does not seem to cover why men are better at the elite levels.",
"Please direct your objections to the authors. Thanks."
] |
[
"Why is it that some dyes, like that used in laundry detergents, do not stain [white] clothes and can actually do the opposite, clean them?"
] |
[
false
] |
The question popped in to my head as I poured a popular detergent in to my washer containing white clothes and I noticed how dark blue the detergent was, completely opaque, and I found it odd that it cleans as opposed to leaving a dreadful blue splatter all over my clothes.
|
[
"I work in textiles so I can answer this question:",
"When you are using a detergent, especially for whites, the blue color most likely comes from the optical brighteners that are in the detergent.",
"Modern detergents have a number of active agents. They have surfactants such as SLS (same as your shampoo or liquid soap) as well as enzymes \"clean\" the fabric. There are fragrances to make the fabric smell better. Water softening agents to allow better soaping to happen, anti-foaming agent to make sure there is minimum sud which can overflow from the machine. Fabric softeners to improve the feel of the fabric and other things as required. ",
"Optical brighteners basically help the white look brighter and more brilliant by absorbing UV radiation and re-emitting it as violet/blue light. The slight blue tint gives white a much brighter feel. This is why, if you have ever been under a \"black light\" (Uv light) you will see that your white clothes will shine brilliantly. That is due to the optical brighteners that are used in the dyeing process of whites as well as some detergents."
] |
[
"Hey I have a related question you might be able to help me with!",
"What are some good anti-foaming agent for SLS? It was a problem I came across at work last year and I did't have time to track down a good answer, only a few generic lists of anti-foamers to try."
] |
[
"I actually don't. We did a bit of anti-foaming stuff for the mining industry back when I was in uni but I wont be much help. Perhaps look at what they have in dishwasher liquid vs the regular dishwashing soap. "
] |
[
"With solar sails being so thin, how do they avoid being punctured by tiny space debris?"
] |
[
false
] | null |
[
"Answered for the Planetary Society's LightSail project at ",
"http://sail.planetary.org/faq.html",
". Their sails use rip-stop construction so that a pinhole doesn't develop into a large-scale tear, and they can accept several localized holes without losing mission effectiveness."
] |
[
"To add to this, protecting the sails from debris would not be feasible. ",
"This is what happens when something gets hit by space debris"
] |
[
"I'm pretty sure there is always a chance of a space pebble killing everyone."
] |
[
"What type of wire should I use for high-T petrological experiments?"
] |
[
false
] | null |
[
"Not the right sub. Maybe try ",
"/r/labrats",
" or ",
"/r/askchemistry",
" or another more specialized sub"
] |
[
"Thanks, I've tried both of your suggestions. Could you explain why this isn't right for AskScience? I don't see anything in the guidelines that could disqualify this. \"Chemistry\" is definitely too broad of a flair for such a question, but I don't see anything better suited, such as \"Materials Science\"."
] |
[
"This sub isn't the right forum for project or research help. There are other, more specialized subs that might be more appropriate."
] |
[
"Spherical universe and relativity"
] |
[
false
] |
Although my understanding is that measurements are pointing towards the universe being flat, how would the "paradoxes" of relativity (both watches going slower than the other, both twins being older than each other) work out if the universe were shaped like a sphere or other closed object? The other person wouldn't have to accelerate in order to return to the original spot, since if she just kept going in the same direction she would return.
|
[
"Not really, no. In this context, we have to talk about ",
" trajectories, not merely spacelike trajectories.",
"In a Minkowski universe, there is, at most, exactly one inertial trajectory between any pair of events. An inertial trajectory is, in practical terms, any one along which no acceleration will be measured by an accelerometer moving along that trajectory. Just as on a piece of paper there is exactly one straight light that connects two points, there's ",
" exactly one inertial trajectory connecting two events. (There may be none.)",
"The inertial trajectory between events will always be the trajectory of greatest proper time. That is to say, a clock moving along that trajectory will measure more elapsed proper time between those two events than a clock moving along any ",
" trajectory that connects the two events.",
"So there's your so-called \"twin paradox.\" In Minkowski space, the inertial observer is the one who'll \"end up older,\" while all other observers who move through the two events will \"be younger.\"",
"But if you take the \"in Minkowski space\" constraint out of it, the \"exactly one inertial trajectory\" part goes away. For example, consider the phenomenon of gravitational lensing. Light propagating through space from a single point can follow ",
" different inertial trajectories around a massive body. If the object is not rotating, the two trajectories both maximize proper time. No paradox is introduced by this; the kinematics are such that observers moving along each of the two trajectories — one to the \"left\" of the massive body and one to the \"right\" — will both move along trajectories of maximal proper time. It is exactly as if they moved along the same trajectory. Nothing interesting there.",
"That's how your counterfactual \"spherical universe\" thing is resolved. In that case, there are infinite inertial trajectories that connect each pair of events. Any observer moving along any of them would, purely hypothetically, measure the same elapsed proper time between the two events.",
"But remember: We're talking about ",
" here. If you imagine an astronaut standing on the Earth — that is to say, at rest in the Earth's rest frame — then boarding a magical rocketship and flying off in some other direction, you're not talking about an inertial trajectory any more. The astronaut has to accelerate, which means the equivalence principle no longer applies, so the symmetry of the system is broken. The astronaut will measure less elapsed proper time ",
" she turns around and comes back, or \"circumnavigates the universe,\" as it were."
] |
[
"Have a look at this ",
"old post",
"\nIt should answer most of your questions."
] |
[
"I read most of the ",
"paper",
" linked in one of the comments, and so to make sure I understand correctly: The twin paradox doesn't directly translate from \"go somewhere, come back\" to \"go around the universe\" because the paths are not really the same; the second path \"goes around\" and therefore can't be transformed into the first path. For the same reason, homeboy's and merry-go-round's paths are not comparable either.",
"Is that about right? "
] |
[
"What is the long term effect of human growth hormone?"
] |
[
false
] |
[deleted]
|
[
"There was a lot of buzz about it that basically amounted to nothing. In people not deficient (the majority), all it really does is increase lean muscle mass and decrease fat content without any increase in strength. This is interpreted as increased water content in the muscles. So I suppose it'll make you look a little better, but it's basically a veneer. As far as side effects go, it can exacerbate diabetes, cause joint problems, and heart problems like hypertension. It's quite expensive if I recall (like 5 figures a year), so it's really not worth it unless you're deficient. ",
"www.ncbi.nlm.nih.gov/pubmed/17227934",
"That guy's body has a lot more to do with good diet, intense exercise, and probably the testosterone to a much lesser degree (which has its own side effects). If you are eating right and exercising regularly, you'll feel and look better for longer. Exercise releases endorphins that probably explain why it lowers rates of depression, for one. There's no magic bullet to combat aging...it takes perseverance and hard work.",
"Edit: One thing that's occuring to me is that I've never seen a study that compared resistance training w/ placebo to resistance training w/ GH/Testosterone. Most studies just give men the drugs and measure their response (and probably the men exercise according to their usual routines). It seems possible that GH/T could perhaps give more ability to grow without causing much growth on their own.\nNevermind.\n ",
"www.ncbi.nlm.nih.gov/pubmed/9920193"
] |
[
"What about people who are deficient?",
"When I was a kid I took growth hormone shots, but stopped taking them when I was about 17. In college I was a summer camp counselor, and by coincidence, one of my campers took HGH. I spoke to his mother when she came to pick him up and she said that he would be taking the shots for the rest of his life. I remember that there was research into the effects of HGH on adults just about the time I was getting ready to go off the stuff."
] |
[
"\"",
"Acromegaly",
" \n is a syndrome that results when the anterior pituitary gland produces excess growth hormone (GH) after epiphyseal plate closure at puberty\"",
"This wikipedia article explains the long term side effects of too much GH, especially after the growth plates in many bones have fused. Although, I couldn't find any of the same side effects with synthetic HGH. So with that, I have my own question: What is the difference between synthetic HGH and pituitary produced GH? Or is it just a matter of EXCESS GH that produces these side effects?"
] |
[
"What is the science behind acne, and how do products work?"
] |
[
false
] |
[deleted]
|
[
"There's actually a lot of research going on regarding acne, due to the high prevalence in society (something like 80% between 12-24yo). The disease process starts with an abnormal proliferation of the keratinocytes (skin cells) that line the top of a hair follicle. This results in blockage of the follicle, as well as the sebaceous gland that drains into it. Androgen stimulation during puberty results in increased sebum production from those glands, which further exacerbates the problem. This blocked follicle tends towards bacterial overgrowth of Propionibacterium acnes, which produces enzymes that hydrolyze the lipids in sebum into free fatty acids, which contributes to inflammation. The P acnes bacterium itself also induces an inflammatory response. This inflammation can then result in rupture of the follicle.",
"A whitehead is simply the swollen follicle (called a comedone). Once it gets exposed to air, the fat oxidizes and turns black, turning it into a blackhead (open comedone). Continued inflammation leads to a papule and then pustule, as well as the formation of acne sinus tracts. ",
"Treatment generally involves a combination of comedolytics (commonly retinoids), antibacterial agents (commonly benzoyl peroxide or systemics like tetracycline), and hormonal therapy (OCPs or spironolactone). "
] |
[
"Are you able to provide any sources? I'd like to learn more."
] |
[
"Resource from another redditor; fairly comprehensive. ",
"Link"
] |
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