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[
"Does produce absorb pesticides directly or though water?"
] |
[
false
] |
So eating pesticides isn't good. I wash my stuff in baking soda usually to try to get off what I can. I'm curious however if plants absorb pesticides directly into their flesh? For example avocado... can you spray avocados with pesticides all you want and it will be safe to eat because you are removing the thick external cover? Or will the pesticide leach into the water, and then be absorbed by the plant, then eaten by you? Or does it perhaps get absorbed directly through the skin? Just curious!
|
[
"Most commonly used substances (in North America and most of the EU) are removed well enough by just water washing",
"This is not true. Washing will be ineffective against a large array of hydrophobic pesticides, or those that absorb deeply.",
"they're present in levels far lower than what is required to show any negative effects to an adult.",
"Premature to say. There's growing concern based on exposure assessments from produce consumption and epidemiological associations with various diseases.",
"regular old soap would be more useful than using baking soda to wash them ",
"Soaking in baking soda can in fact aid in pesticide removal from produce, and can be more effective than washing. Baking soda is particularly effective against organophosphorus pesticides."
] |
[
"Most commonly used substances (in North America and most of the EU) are removed well enough by just water washing",
"This is not true. Washing will be ineffective against a large array of hydrophobic pesticides, or those that absorb deeply.",
"they're present in levels far lower than what is required to show any negative effects to an adult.",
"Premature to say. There's growing concern based on exposure assessments from produce consumption and epidemiological associations with various diseases.",
"regular old soap would be more useful than using baking soda to wash them ",
"Soaking in baking soda can in fact aid in pesticide removal from produce, and can be more effective than washing. Baking soda is particularly effective against organophosphorus pesticides."
] |
[
"Thanks a lot for the info!"
] |
[
"How do astronomers share coordinates with each other?"
] |
[
false
] |
Let's say an astronomer notices something worth studying out there.... How do they tell other astronomers around the world, or just record exactly where they are looking at? For instance for coordinates on Earth they'd give a lat/long and that would always be the same place. But in space, everything is in motion and therefore relative to the observer. The earth is moving in space, and rotating as is whatever object is being studied. So on any given day, or even time, the object being studying is not going to be in the same 'relative' space as it was yesterday, etc.... So how are coordinates marked for collaboration or future study?
|
[
"The sky has a similar set of coordinates as the Earth - in fact, the coordinates have the same names: latitude and longitudes. You’re correct in that the sky appears to move above us as the Earth rotates, but we astronomers have solved this by specifying a point on the sky that we define as always having coordinates (0,0). So, from the point of view of someone on Earth, the (0,0) point moves as the sky apparently moves above us.",
"The choice of where we’ve decided (0,0) to be is somewhat arbitrary, but if you’re curious, it’s defined as the position of the Sun on the sky at the vernal equinox (around March 21st)."
] |
[
"We use something called ephimerides, which describe how much an object moves in longitude and latitude (Right Ascension and Declination) per day etc. In other words, they describe the trajectory of a moving celestial object. The vast majority of celestial objects don’t move appreciably on the sky from one year to the next, the exceptions being solar system objects (planets, comets, asteroids) and a handful of nearby stars."
] |
[
"thanks, very clear explanation... but followup ",
"The object we are studying might not move in the same repeatable orbitable pattern around our (0,0)... like say a comet or asteroid that is moving in a straight line out of any given orbit. So regardless of our \"0,0\" point - that will constantly be moving ... so a day or a week or a month later - how would that specific comet be addressed? ",
"Thanks!"
] |
[
"I have a few questions about embryonic development and nuclear transfer in cloning."
] |
[
false
] |
So, I know in nuclear transfer with an embryonic cell, the blastomeres of an embryo are separated and fused with enucleated eggs. These in turn are grown into embryos and implanted into surrogates. Does that mean the blastomeres are essentially just nuclei? I'm not sure what they consist of. I know the alternative is somatic cell nuclear transfer, but in that case it's just the nucleus of the cell being fused with the egg. Doesn't a blastomere have more content than just a nucleus? Also, at what point in development do embryonic cells differentiate? And are they innately programmed to differentiate a certain way or is that not determined until it happens? I know in embryo splitting the blastomeres have to be undifferentiated, but when those become their own embryos and cells start to specialize, would it matter what that blastomere was supposed to specialize as originally? Can it change that specialization if necessary now that it's part of a new embryo? I'm pretty new to this, so I'm not sure if these questions even make sense. But thanks to anyone who can help!
|
[
"Depends on what organism you are talking about (differentiation). I am assuming you are referring to mammals. The very first proto-differentiation would be the determination of the three germ layers (Ecto-, Endo- and mesoderm) which occurs ~3 weeks after fertilisation. ",
"Did you mean a more specific kind of differentiation? At the blastomere stage, they haven't begun to differentiate (which is usually dependent on molecular gradients originating from specific areas, like the \"node\" or nieuwkoop centre in mammals). They are still totipotent cells."
] |
[
"Blastomeres have undergone no differentiation events (As far as I know. Xenopus eggs undergo something called cortical rotation after fertilisation. It essentially creates a molecular gradient within the egg and specifies the formation/location of the inductive signal producing Spemanns Organiser). So blastomeric cells don't know what cells they are going to become. The blastomeric stage is composed of around 8 cells, which is too few a number to be usefully specified. ",
"These cells are totipotent and so can become any cell in the body. Differentiation of cells is based on conflicting chemical gradients, which in mammals comes from two signalling centres of the embryo: The node and the anterior visceral endoderm. ",
"This",
" section in wikipedia has some answers to differentiation. ",
"I hope this answer isn't too ramble-y. I guess the short answer is that, no, blastomere cells have not any differentiation event (or significant differentiation event) and as such are totipotent, in that they may become any type of cell within the embryo."
] |
[
"A blastomere is just a regular cell, morphologically as far as I am aware. I imagine in cloning they would specifically microinject the nucleus from the blastomere into the egg, or they would zap both with a jolt of electricity to fuse their membranes. The blastomere will be much smaller (~8 times in fact!) than the egg, and so it's contents (including nucleus) will spill into the eggs cytoplasm."
] |
[
"Can someone explain the difference between particles and virtual particles?"
] |
[
false
] |
Are they literally the same thing? If so, why are they virtual? Or is there some sort of meaningful difference between them? Or are they just never actually 'observed' quantum particles? That don't get a chance to define themselves? I've been confused on this. Side question, what do we mean when we say 'observe' in quantum mechanics. Is that really the same kind of observation we think of when we observe something on our own scale? How does a scientist actually 'observe' a particle, like I would 'observe' a cat. Am I asking the wrong questions?
|
[
"Virtual particles are created by vacuum fluctuations.",
"This isn't really true. Virtual particles are not real. Maybe we use virtual particles to represent quantum fluctuation of the vacuum, but you can not create a virtual particle, they are not real things."
] |
[
"Virtual particles are NOT REAL THINGS. They do not exist. They are calculational tools. They are things we use to help us break down the complicated interactions of fields into just the most important parts. That way we can compute only the important parts and get very close to the right answer.",
"You can not observe a virtual particles because they do not exist.",
"A charged particle influences the electromagnetic (photon) field around it. When it is near a different charged particle, the effect they have on the electromagnetic field around them causes them to attract or repel each other. This interaction is very complicated, because they don't just effect the electromagnetic field around them, but that effect causes an effect in ALL charged particle fields.",
"However rather than calculate the complicated interaction, we have a mathematical way of breaking down the interaction into parts, and only some of those parts need to be computed and the rest have a very small effect. The way of breaking the full calculation into parts is imagining something called a \"virtual particle.\" So instead of thinking of the complicated effect on the electromagnetic field, you imagine there is a \"virtual\" photon. Real photons are particular excitations of the electromagnetic field so this concept can be helpful. Doing so you can break it into \"one virtual photon\" and \"two virtual photons\" or \"two virtual photons and a virtual electron\" into a series of more and more complex virtual particles. If you compute the effect due to these virtual particles you can find you only need to compute a few of them to get the result to high accuracy and \"100 virtual photons\" is a tiny contribution and can be ignored.",
"However there are ZERO photons between the two charged particles. Instead the virtual photons are used to approximate the actual effect the charged particles have on the surrounding fields.",
"If you are not trying to calculate an interaction, with maths, it is not useful to think of virtual photons are a concept. IMO."
] |
[
"Well yes, but that's really about how we define real. For example is an electromagnetic field real or is it just how we describe the electromagnetic interaction by Maxwell's equations? Whether something is real or just a smart theoretical construct can be difficult to say. I find discussions like this insanely fascinating since they tell us how much we believe in the reality of what our theories tell us.",
"I also heard at a talk that you can change to a reference frame where virtual particles become real and vice versa, but I don't know enough to expand on it. "
] |
[
"What happens to the ectrons and protons in a neutron star?"
] |
[
false
] | null |
[
"The electrons merge with the protons to form neutrons, emitting a neutrino. This is known as electron capture, and also happens in less exciting scenarios like the decay of potassium-40 in bananas."
] |
[
"That's interesting. Do they emit enough neutrinos that having a banana at one of those subterranean neutrino labs could skew results?"
] |
[
"I don't think so. Much more neutrino flux from the sun."
] |
[
"How are the amount of calories in food determined?"
] |
[
false
] |
I assume they do a breakdown of the ingredients and go by how many calories are known to be in that ingredient, but how was it initially determined?
|
[
"An analysis of the item will determine the amounts of protein, carbohydrates, (both about 4 calories per gram) and fat (about 9 calories per gram.) If alcohol is present, that comes in at about 7 calories per gram. ",
"The rest is just math. "
] |
[
"It must be difficult to use this method for soup."
] |
[
"It must be difficult to use this method for soup."
] |
[
"How do GPS satellites cope with the millions of vehicles requesting their locations at once?"
] |
[
false
] |
I presume there are loads of GPS satellites that triangulate the position of vehicles with satnavs etc. but are there computers onboard these satellites and how do they relay all that information at once to the right vehicle?
|
[
"They don't. They simply beam their signal and the client does all the work "
] |
[
"The traffic is not peer to peer.\nVery much simplified it works like this:\nEssentially the satellites have super accurate clocks. They broadcast the current time and their ID with their radio. Like radio everyone with a receiver can listen to them. From ID and time you can calculate how far away they are. \n(Current Time -Time they broadcast) * speed of light = distance\nWith the distance and some complex math you can then calculate your position.",
"(edit: corrected mathematical brainfart)"
] |
[
"No, geometry is why you need signal from a few satellites. 1 satellite tells you that you're somewhere on a given circle (technically a sphere but there's a circle where that intersects with the Earth's surface), 2 narrows it down to two points (the circles from the two satellites intersect at 2 points), and 3 gives you 1 point. More can give you more precision, but you need at least 3 to be sure that you're even in the right city."
] |
[
"If sodium nitrate is known to cause DNA damage then why does everyone think it's OK for it to be used as a preservative in all our meat products?Are there not alternative preservatives?"
] |
[
false
] | null |
[
"It's a risk/reward scenario. Nitrates can potentially increase the risk of cancer - the degree to which the risk increases is not firmly known. However, nitrates are ",
" effective at inhibiting pathogen growth in high-pH foods like meat, especially considering their cost and ease of use. Much like sulfites, which can cause allergic reactions (in some cases fatal ones) in asthmatics yet are still used in winemaking and dried fruit, nitrates are still sitting on the 'useful' side of a risk/reward assessment. It's possible that that will change once we have a clearer picture of the risks."
] |
[
"According to the ",
"IARC",
":",
"Ingested nitrate or nitrite under conditions that result in endogenous nitrosation is ",
"(",
"source pdf",
" - lots of evidence there.)\ni.e. it probably can cause cancer when ingested with amino acids e.g. from meat. On the other hand alcohol is a ",
" proven carcinogen which people are just as happy to consume. I tend to lay off cured meat - ham etc. when I can. "
] |
[
"So is that information bullshit? I know it says a small percentage is converted but could it be significantly harmful to someone that includes meat in every meal?"
] |
[
"Do our brains create consciousness, or receive it? What's the hard evidence for each side, if any at all?"
] |
[
false
] | null |
[
"This would be a good question for ",
"/r/philosophy",
". If you sort by TOP it's probably been addressed"
] |
[
"The answer depends. How you define \"consciousness\" matters. If you include some kind of metaphysical, unscientific \"soul\" or \"will\" or something like that, then the answer to your question can only be metaphysical and unscientific, so you must be very careful and precise with your definitions to keep the answer in the realm of science.",
"Currently there is no generally recognized definition for what consciousness is, except for the very nonspecific definition found in dictionaries, which ultimately define consciousness as a synonym for awareness. If you go by that definition, then consciousness is almost certainly \"created\" (\"generated\" would be a better term, but \"arises consequentially\" might be best).",
"Since there is no direct and no reliable indirect way to measure awareness/consciousness (especially lacking an accepted, specific definition), there isn't much hard evidence for either side. To prove that consciousness is not created by the brain, one would have to demonstrate an influx of some tangible \"consciousness\" structure or quantity. No observations to date demonstrate this. On the other hand, to prove that consciousness arises consequentially due to the brain's structure, requires a testable and complete theory of the brain, which we don't yet have although we seem to get closer and closer as time goes on. Many observations support what theories we do have, but no such theory that I am aware of provides a definition for consciousness and explains how it arises."
] |
[
"If it's an emergent property, then it arises (i.e. it is generated/created) dynamically and is not merely some conserved thing which is received.",
"Either way I suspect that consciousness isn't simply a single property, but a complex collection of many coexisting properties."
] |
[
"Would deforming an open soft drink bottle to remove air space, before recapping, stop/slow it from going flat?"
] |
[
false
] |
I'm thinking the co2 wants to leech into the air space, if there is no air the co2 can't easily leave the soft drink?
|
[
"MAJOR EDIT 2! ",
"The great thing about Science, is that we can be wrong. Because I am very lazy, I did not read this carefully enough before posting. ",
"When, in the past, people have asked me this, they shown me deformed bottles, squeezed such that there is only about as much head space as there is when the bottle is new, ",
"or even less",
". This has usually been based on something they read on [the internet](",
"www.facebook.com",
"). Re-reading the title of this post (as it appears repeatedly in my inbox), I realize that isn't what ",
"/u/morgazmo99",
" was asking.",
"I am happy say, that if you squeezed ALL of the air out of the bottle (overflow it a little), so there is no \"air\" in the bottle AT ALL, then this will most definitely ",
" the release of CO2 from the liquid. Even just tiny little bit of air in the neck would be OK ",
"I'd go for fuller than this, to be safe, but even this should be OK",
". Additionally, keeping what small bottle atmosphere there is in the narrow (harder) neck only will ensure that the walls around are not flexible, so the head space won't expand much (ultimately, because water is relitvely non-compressible, it could still expand. Someone should do this experiment for me!). With a tight enough seal, you should be able to store your opened and partially consumed soft drink for a long period of time, weeks or even months maybe. This will again be dependent on how deformable your bottle is, temperature, and a bunch of other stuff.",
"Thanks in particular to ",
"/u/NewSwiss",
" for leading me onto a correct path (i.e. teaching me to read the question!).",
"For an explanation of why squeezing only some of the air out like ",
"this",
" or ",
"this",
" is not helpful, read my original reply below.",
"You can try this - experiments are fun! Report back to see if the explanation below holds true. Keep good notes & write it up. This is how science happens.",
"Unfortunately, what you will find is that the CO2 will still be released from the soft drink, which would then start to fill the bottle. It will probably start to \"pop\" back out to its original shape.",
"The amount that is dissolved is determined (in part) by ",
"Henry's Law",
", which has many interpretations, but essentially defines the equilibrium between dissolved gas concentrations and the (partial) pressure of those gasses in the atmosphere.",
"So when you buy a bottle of soft drink, it is super saturated, so that there is heaps of dissolved CO2 in both the head space and in the liquid, and it's bubbly. When you open it, pour some out, and re-seal it, the dissolved CO2 that's left equilibrates with the new (CO2-less) head space in the bottle. Eventually, if you open it too many times it will \"go flat\". Similarly, if you don't seal it properly, the CO2 in the head space escapes to your fridge, and more CO2 comes out of the soft drink to reach equilbrium.",
"So, in your scenario, you crush the top of the bottle so that there is hardly any head space - which at first glance seems to fix this. BUT, because the plastic is flexible, as more CO2 comes out of the soft drink to get to equilibrium, that headspace just expands (PV = nRT), and the pressure stays relatively constant until the bottle has \"reinflated\". So the soft drink loses MORE gas.",
"If you could keep the container in shape (in a vice, different plastics), then you might have some success.",
"TL;DR ... just drink the whole bottle!",
"EDITS: I see this has got some interest while I slept, so here are some answers to other questions:",
"\"I have done this heaps of times, and my bottles do not pop back out! You are a liar and a fraud\"\nExcellent! That means three things! (a) you have done the experiment just as I had imagined. YAY! (b) Your soft-drink bottle plastic is just a ",
" bit firmer than mine - perhaps your local bottle manufacturer makes them slightly thicker? (c) if b is not true, possibly you drink your soft drink faster than I do, and the bottle hasn't had a chance to re-expand?\nIF you are confident that your bottle will not expand, then by all means, this will work, as less heaspace means less CO2 needs to leave your liquid to get to equilibrium.",
"\"My plastic bottles are crappy like yours. Could I use velcro/rubber bands/clamps/a novel-space-deforming bottle to keep the headspace low?\" \nYes. You absolutely could. Or maybe your local bottles are better than mine? If you can maintain a low headspace, less CO2 will degas from the liquid to reach equilibrium.",
"\"What if I decant the left-over soft-drink into a smaller container?\"\nThe main problem here is that when you pour the drink, the agitation (and some other stuff) allows the super-saturated dissolved CO2 to seed bubbles, making your delicious, effervescent liquid. You would likely lose more in the transfer process than you would gain by having a smaller container.",
"\"What if I inject CO2/breathe in the cap/fill it with compressed air or remove all the air in the headspace using ",
"a fancy gadget I can buy online",
"?\"\nThis is really two questions, but the answer is that only the pressure of CO2 in the bottle is important. ",
"See partial pressures",
". So adding a different gas is irrelevent, and sucking all teh gas out is a terrible idea and makes it worse! (Aside: those pumps are designed to remove oxygen from (not bubbly) red wine, to slow down the oxidation of the wine into vinegar. They will have the side effect of decreasing the concentration of volatiles as well.)\nIf you could easily seal it with a little CO2 (i.e. exactly as it comes on the shelf), then that would do the trick perfectly. I am not aware of a product that does this. Simply squirting in some CO2 from and canister and then resealing won't do the trick, because it just comes out again.",
"BONUS - TEMPERATURE\nRight, nobody has asked this, but it's important. Temperature makes a big difference. At high temperature, gasses are less soluble in water. SO if you keep your bottle cold (not frozen), the equilibrium point is much lower! A bottle kept in the fridge, well-sealed will last the longest. This also applies to sparkling wines - keep them cold (anecdotally, I have kept open sparkling in the fridge about a day before it gets too flat for me to consider worthwhile, but that's obviously taste-dependent)"
] |
[
"No. In fact, quite the opposite. The bubbles are carbon dioxide gasses held in suspension in the soda by high pressures. As the pressure increases, more gas dissolves. Squeezing then capping the bottle puts negative pressure on the liquid, causing the gas to fall out of suspension faster. "
] |
[
"Fresh carbonated soda has about 4x its liquid volume in CO2, at about 25-30PSI (varies by temp) above standard air pressure in the headroom. The headroom is only necessary to prevent foaming over when it bubbles up when opened.",
"Any time it's opened, however much headroom is there immediately drops to the pressure of the air (~14.5PSI). Assuming it's recapped and left for long enough to reach an equilibrium or nearly so (maybe an hour or two?), pressure rebuilds in the headroom at the expense of whatever volume of soda is left. The equilibrium pressure does go down as CO2 concentration drops in the soda.",
"Basically means that when you open it, drink half, and recap once, you lose close to half the dissolved CO2 repressurizing once. You can get an exact answer with Henry's Law to figure out how much CO2 will come out of the soda and pressurize the headroom volume before equilibrium is reached for that particular temp.",
"If you were only to drink a little and recap, there's plenty of dissolved CO2 and not much headroom. Conversely, any time you recap with a minimal amount of soda and mostly empty headroom, it will go almost completely flat when it reaches equilibrium. Even if the remaining soda was fresh and fully carbonated when recapped."
] |
[
"Is there a strong likelihood that we will all die in the near future?"
] |
[
false
] |
[deleted]
|
[
"Don't listen to anyone here, it's all speculation, we have no idea."
] |
[
"Hmm a list: (Mostly questions, little answers.)",
"Greenhouse effect, main question is if it: 1) causes other biosphere breakdown 2) could it cause an iceage 3) where does land value in terms of food production decrease/increase? ",
" everything diplomatically/politically works out, and the overal value stays roughly the same, the shifts might go without significant human suffering. That is a big IF though.",
"Nuclear proliferation, it is inevitable that more countries will have nukes. This increases the chances of nuclear war. I doubt the nuclear winter scenario is as likely and significant as claimed:",
"The nuclear winter scenario predicts that the huge fires caused by nuclear explosions (particularly from burning urban areas) would loft massive amounts of dark smoke and aerosol particles from the fires into the upper troposphere / stratosphere.",
"Why don't forest fires do this? And why would it go so high?",
"So the threat of smaller nuclear wars seems to be mainly that of terrible contamination, and suffering around that, aswel as the direct effects, of course. Of course there is still the threat of a next cold war, and larger nuclear wars, or that with future technology, even small countries can build up large stockpiles.",
"Population growth. It makes all the scenarios harder to deal with, it becomes a problem when resources are truly stretched to their limits, or the production turns out 'borrowed'.",
"Disease.",
"Biotech and nanotech. The latter is inevitable unless defeater, and big question is when. Conservatively, ~80yrs estimating with Moores law, but it might well be sooner.(edit: but that is circuits, making it do other things could be difficult) The first is definitely in sight and is a watered down(quite literally) version(of nanotechnology) based on stuff we found evolved around us.(Though we're sure to find additions.) ",
"This could be solution to many problems. Both the use as weapon and the danger of them outperforming elements of the biosphere, are both a concern. The existing biosphere might have defenses against biotech, but i doubt it has against nanotech. There does seem to be a chance of grey goo. More likely specialized on certain materials, but (chitin)bad enough.",
"Nuclear fusion. Also a solution to many problems. Energy is still very cheap, but with fusion it could be even cheaper and with little side-effect. Fresh water anywhere near the sea would be a matter of making the facilities.",
"Spaceflight. Doesn't seem too likely getting into orbit will become easy enough to affect things down on earth much except for us being able to gather information up there. Once in orbit, gravity loss drops out, and given the 300 kg VASIMR can do 5N, and there is sure to be improvement in that, if we can get effectively in orbit it seems to me that we might be able to do a lot more. Probably need more energy to burn in spacecraft, though. Still, as i said, i doubt that spaceflight will help.",
"Edit: Possible effects of huge amounts of computing/neural net power? Very hard to see..",
"The main thing is that we need the better people in power, even if this power isn't quite right, there is a big difference between Obama and Bush. We can't have any more Bushes. Better power is power you can discuss with and which will listen/be criticized and revise their own view with that, as well as competence. And we do need activism and intelligence for things regardless. People seem to often waste activism on ideology, imo they should put it into (discussing how to)improving specific things. And develop ways/specific things to allow people and organizations to do things according to the ideology.(even if the organizations/people don't realize it) GNU is a good example in this."
] |
[
"Thanks for that. "
] |
[
"Effect of house plants on air quality?"
] |
[
false
] |
I know we recently had a post about how many plants it would take to keep a person who alive, but does anyone know of any studies that show that average quantities of house plants have any measurable effect on home air quality?
|
[
"NASA studied this because they are interested of cleaning air in space stations. The answer is yes, they do improve air quality. ",
"Here is a list of plants and what they clean: ",
"http://www.colostate.edu/Depts/CoopExt/4DMG/Plants/clean.htm",
"Wolverton et al. ",
"\n",
"http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19860066312_1986066312.pdf",
"Wolverton, ",
"\n",
"http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930073077_1993073077.pdf"
] |
[
"I found a physorg article citing another study backing this up as well. ",
"news article",
"\n",
"source"
] |
[
"They tried an experiment with this as a part with the \"biosphere\" in AZ. They needed to fudge around a bit to keep it going."
] |
[
"Why does an infinite plane of charge have a constant Electrical Field?"
] |
[
false
] |
I'm learning electrostatics in Advanced Physics right now and was taught that the electrical force exerted on an object at any location in respect to an plane of charge is a constant, 4 pi k Q, regardless of distance. Why is this? On that note why can't you use this distance-ignoring factor and affect things faster than the speed of light? Does that make sense? After his lectures the vocabulary fades from memory a bit. Edit: All sorted out!
|
[
"I'm learning electrostatics in Advanced Physics right now and was taught that the electrical force exerted on an object at any location in respect to a plane of charge is a constant, 4 pi k Q, regardless of distance. Why is this?",
"This applies to an ",
" plane. For anything else, it's an approximation. For any plane not very very large, it's a very poor approximation for any distance that isn't very very small.",
"An example derivation is ",
"here",
". Is there a particular part that is confusing? I think it makes complete sense if you think of field lines trying to escape the plane, but since it's infinite the only way for them to go is continually outwards. This isn't physical, but only because the infinity in the question already made that true.",
"On that note why can't you use this distance-ignoring factor and affect things faster than the speed of light?",
"Well, first, the electromagnetic force is only transmitted ",
" the speed of light. Photons are even the mediating particle, and clearly have that speed limit. Also, your formula only applies to an infinite plane, which we obviously don't actually have."
] |
[
"Think about the field lines. Where else are they going to go?"
] |
[
"On that note why can't you use this distance-ignoring factor and affect things faster than the speed of light?",
"Well, you're learning electrostatics. That means that all the formulas for electric fields that you're using are technically only true when the objects are not moving, and were not moving in the past. The full electric field which you get from objects which are moving and accelerating around would be a lot more complicated, precisely because of the propagation delay due to the speed of light. However there are a lot of times when the electrostatic fields are very close to being correct- when the objects are all moving at much less than the speed of light, and the distances are all sufficiently small that they are established instantly for practical purposes."
] |
[
"Do these up and down changes in temperature effect mosquitoes and other bugs negatively or positively?"
] |
[
false
] | null |
[
"What temperature changes do you mean?"
] |
[
"Air temperature."
] |
[
"Daily? Seasonal?"
] |
[
"What tactics were used by humans to hunt mammoths?"
] |
[
false
] |
I hope this question isn't too speculative for . A confirms spears were used against Mammoths which got me wondering what were the tactics used during the hunt? How did humans take down such large animals? *How many humans had to be involved? *How many spears were needed to take down a Mammoth? *Were any other tools used, such a rope to tie down the animal? *Did hunters spear and let the animal bleed out? *What do we know based on current hunting techniques?
|
[
"Unfortunately, you're not going to find much on this topic aside from pure speculation. The evidence that humans actually even hunted mammoths isn't strong enough to be beyond question. What one archaeologist interprets as butchering marks on bones might be interpreted by another archaeologist as marks from trampling. Even when there is clear evidence of butchering, it's difficult to tell if the animal was hunted and killed or merely scavenged. Anyone who claims to know the details you seek is speculating wildly. ",
"That being said, we can draw some modern comparisons. For example, African elephants. How do people go about hunting these highly intelligent, fast, and aggressive animals without guns? There are some (crazy) people who actually hunt elephants with bows. It works. It's stupid and incredibly dangerous, but it's not certain suicide. If bows work, than atlatls (spear throwers) probably would have too. ",
"Stampeding mammoths off of cliffs in the fashion of a buffalo jump might also have worked, but elephants (and likely mammoths too) are a ",
" more intelligent than buffalo and might have been much harder to predict. Even humans stampede in the right circumstances, so intelligence does not confer absolute protection from this tactic. ",
"Persistence hunting might have worked on lone individuals. In this tactic, you chase an animal and rely on your endurance being greater than that of the animal (Surprisingly, humans are fantastic endurance runners). A group of humans could have chased a mammoth, perhaps throwing spears if it allows them to get too close. Over the course of several hours, the humans would keep the mammoth moving. Eventually it would overheat, tire and become easy to kill. Any wounds inflicted in the process would hasten the process, but the humans might prefer to avoid getting within spear-chucking range until the mammoth is very tired. Elephants are absolutely deadly when they charge, so getting close to a mammoth before it's very worn out might have been exceedingly dangerous. ",
"A popular trope in museums is to show a group of humans (sometimes neanderthals) taking out a mammoth with hand-held (not thrown) spears and an individual on a small cliff tossing a head-sized rock onto the mammoth from above. In reality, this would be ridiculously ineffective. The thrown rock would not have enough momentum to seriously injure the mammoth and the humans on the ground with sharp sticks have a high probability of being seriously injured or killed. We don't accept a high risk of death when traveling to the grocery store, so neither would our prehistoric ancestors accept such a high probability of death for securing dinner. However, you can imagine modifying this tactic slightly to be a lot more effective and far less dangerous. Imagine a much bigger cliff (too large to fit inside a museum). With sufficient height, thrown rocks would be deadly, even to a mammoth. Part of the team would attempt to herd the mammoths within rock-throwing range of this cliff while others wait in ambush. The hunters on the ground would likely not get close enough to confront the mammoths, likely relying on their scent, noise, etc. to drive the mammoths toward the ambush. ",
"This is all speculation, of course. "
] |
[
"What I know, from psychology and etology studies, is that humans tried to engage big animals, such as mammoths, when one of them were isolated from the group. They would have one put one human to distract it (probably a skinny, fast one), while the others, stronger and bigger, would throw spears at them and attack it's legs, trying to make it fall so they could group up and hit it in the head with stones and/or pieces of hard wood.",
"That's about what I know, not sure if it's 100% true, read it somewhere in a book about pre-historic hunting and farming."
] |
[
"Historically Native Americans would use the skins of other animals as camouflage to get close to buffalo, they would then all attack the bufflao by throwing spears and shooting arrows at it or chasing it off a cliff. It is likely that early humans used similar tactics to close the gap between them and the mammoth."
] |
[
"If the testicles are an external organ for sperm to survive (as they die in normal body temperatures), how do they survive once they are in the female body?"
] |
[
false
] | null |
[
"Sperm, like any other cells, have their optimal temperature in which they perform their task they are supposed to do. For spermatogenesis, the optimal temperature is 34ºC (that's why the testicles are a bit outside of the body), but for the end form (sperm), they move normally in higher body temperatures. \nWhat kills sperm in vagina and uterus is mostly different pH values and the time sperm needs to get to the oocyte since it doesn't have any energy sources once they get outside of the testicle. "
] |
[
"Yes! One interesting discovery is the idea that all mitochondria were once outside invaders that relied eventually ended up relying on its host to survive. The host kept the mitochondria around because of they produced energy. This theory of ",
"endosymbiosis",
" was proposed by ",
"Lynn Margulis",
", an evolutionary biologist who was laughed out of many rooms for her hypothesis. Coincidentally, she was also married to Carl Sagan. "
] |
[
"plus sperm mitochondria are spent by the time they inseminate the egg resulting in everyone's mitochondria being from their mother. This organelle has it's own DNA, mDNA, which has led to interesting discoveries."
] |
[
"How do you form long term memories? How can you form long term memories while studying?"
] |
[
false
] | null |
[
"The general consensus is that a memory causes connections between neurons in the medial temporal lobe of the brain to be altered more or less in real time. This process has been studied particularly well in the CA1 region of the hippocampus - a medial temporal lobe structure. The neurons there always have some levels of activity, or rate at which they generate short bursts of voltage called action potentials. The memory-induced synaptic plasticity causes new patterns of action potentials to reverberate in the medial temporal lobe. Over time, this reverberation causes the memory to be consolidated in nearby brain regions that cannot change as quickly, but are also more permanent and associative for other attributes of the memory. The consolidation process takes time, so one way to more effectively form long term memories while studying is to allow more time, total, to learn new material (I know, real helpful, huh). ",
"Here is an article by Alvarez and Squire summarizing some of these points. ",
"http://www.pnas.org/content/91/15/7041.full.pdf"
] |
[
"Thank you, great answer!"
] |
[
"From a psychology point of view, long term memory is the consolidation of memory from short term or working memory into a long term storage.",
"There are a few ways we do this. The most common is rehearsal. You simply rehearse whatever you want to memorize over and over, and this translates it into long term memory. This happens even when we don't intend it to (if we're looking for the same target over and over, we memorize the target object). Rehearsal isn't the only method, but it's pretty hard to store something in long term memory without it.",
"I'm assuming you're asking in the context of memorizing something you're studying for? There's a lot of answers for this, but some off the top of my head are using ",
"Mnemonics",
" or Generation (which means you generate your own material, such as writing your own notes instead of copying from the book/lecture or writing your own study questions). There's a lot of research on this I can link if you'd like, it's all fairly old though (this was an extremely hot topic at the start of the cognitive revolution in the 60s)."
] |
[
"Question about sedation dentistry"
] |
[
false
] | null |
[
"Hey there,\nIts normal to have a little pre sedation if you need it, and the dose and advice you were given is pretty common too, so dont worry about that being unusual - its not.",
"The chances of you waking up are absolutely incredibly minuscule. Seriously, usually its the opposite and the anesthetist is just sitting around impatiently for you to wake up afterwards.",
"I would say stop reading horror stories because you dont know who the writers are - they might be making it up, might have some hidden agenda, hate their rude doctor, or might just be confused on things etc.",
"Dont forget that people dont bother posting about the millions of uneventful, unremarkable operations that happen.",
"In the op, youll have an anesthetist next to you the whole time whose job it is( among others ) to make sure youve got enough sedation - he can spot if you need a top up long before you will ever come close to waking up. ",
"Talking to people after anesthetics, they remember nothing, not even their \"waking up\" at the end when you stop the anesthetic - even though they might be sitting talking to you and have tubes in their nose etc.",
"I actually have had 2 dental procedures personally under general anesthetic btw. totally fine. Freaked out a bit at the first one because I didnt know what to expect. - In hindsight their was no need to panic, but at the time, everything get blown out of proportion.",
"So big breath - close those windows, do something fun until your op, and good luck on Friday! get well soon!"
] |
[
"The chances of you waking up are absolutely incredibly minuscule. Seriously, usually its the opposite and the anesthetist is just sitting around impatiently for you to wake up afterwards.",
"I can't emphasise this enough. Anaesthetists are incredibly well trained to make sure you're sedated enough. They monitor your vital signs, blood pressure, levels of inhaled/exhaled gasses, etc. Especially if you're on an IV drip which is normally pumped, this means that everything is already set up and there's little chance of the anaesthetist just 'forgetting' about having to inject another dose (which is a pretty unlikely scenario anyway).",
"Benzodiazepines are commonly used perioperatively by anaesthetists because of their sedative, anti-anxiety and muscle relaxant properties. You shouldn't worry about being given Valium and then having an IV drip. It's perfectly normal to worry and be nervous, which is probably why you were given the valium to take before the procedure. It will help calm you down before you are put under.",
"If you're still worried, absolutely do not hesitate to speak to the anaesthetist before the procedure. That's what they're there for, and would be more than happy to answer any of your questions. This is routine stuff to them so they hear it often. ",
"Good luck and no doubt it will all go smoothly."
] |
[
"This is not my area, but your post is five hours old and you need some kind of reassurance. I apologize to the mods for the anecdote.",
"When I had my wisdom teeth taken out, the surgeon realized that they were going to be very difficult to remove. They prescribed a small amount of valium to be taken before surgery, then knocked me out for the surgery. In my VERY limited experience, this is not abnormal."
] |
[
"How do the waveforms generated by synthesizers (square, sine, triangle, etc.) compare to the waveforms of \"natural\" sounds and those of \"real\" instruments?"
] |
[
false
] |
I've been wondering this for awhile, and didn't have much luck with google. Some of the waves produced by synthesizers clearly do not occur in nature (I don't think anything natural sounds like a sawtooth wave) but what about, I don't know, sine waves? Every time I've seen an "example" sound wave it's looked like a sine wave, but then again it could be some other round-topped wave. Or, if not, what are the sound waves we hear from guitars, violins, or bird songs? Also, one secondary question: How is the waveform of guitars affected by distortion? Since modern-day distortion is usually extremely controlled and well-shaped, I'm assuming there's a bit more going on than just "making it louder until it distorts." I once heard that fuzz pedals start to "bend" the waveform of the guitar towards being a square wave as they're turned up, don't know if that's true or not, though. EDIT: Yeah, that is how fuzz pedals work.
|
[
"You're asking a few different questions here.",
"If you think of a wave as energy vibrating back and forth you have a constant compression/rarefaction cycle of the movement of the wave. A 'sine' wave is simply a mathematical construct to describe the position of the wave anywhere in this cycle of going back and forth. When you have start referring to tone generators in a synthesizer you're conflating both a simple tone(sine) with more complex waveforms(saw tooth, square).",
"The superposition principle is the idea that a complex waveform(saw, square waves) is merely a sum of many sine waves at the same time. When describing a square wave what we're looking at a fundamental tone frequency also sounding with only it's even harmonics; sine waves that are even multiples of the fundamental tone/frequency.",
"Conversely a triangle wave is a sum of a fundamental and it's odd harmonics; sawtooth is the fundamental tone and all of it's even and odd harmonics(integer multiples of the fundamental frequency). ",
"The sounds we hear from other sources(guitars, violins, birds) are all complex waveforms that have different emphasis on the fundamental and harmonics that make up all the partial tones of the complex result. ",
"Distortion: In an electrical amplification system you're taking a complex wave form(the plucking of the guitar string) and using the magnetic pickup as a transducer to change the energy of the vibrating string from mechanical to electrical. ",
"In the design of the amplifier circuit you have a known bandwidth of frequencies that the system will reproduce; all the frequencies that are important to the sound of an electric guitar.",
"Distortion: there are different ways to achieve distortion in an amplifier setup but the main effect going on is that nice periodic complex wave is being constricted and cutoff at both of it's peaks. Where the wave runs into this ceiling/floor new partial frequencies are created by the change in the waveform. ",
"This new partial frequencies can be pleasing to the ear or grating too; I'm sure you've heard an amplifier with a nasty sounding distortion before. In the case of a tube distortion circuit that tube is where the constriction of the signal occurs; how the tube constricts the signal is all a consideration of the design of the circuit. There are many different tubes that respond in different ways giving different distortion characteristics. ",
"Hope that was clear."
] |
[
"The waveforms commonly used in synthesizers weren't initially selected because of their musical quality. There were used because the circuitry to create them already existed. Sawtooth waves were used in televeision sets to sweep the electron beam across the front of the CRT and then rapidly return it to draw the next line. Square waves and pulses (narrow square waves) were used as sync signals in televisions as well as in many other types of electronics (range and bearing beacons in avionics for example). There aren't any acoustic instruments which produce these waveforms, but they can be filtered and combined to approximate the sounds of some acoustic instruments.",
"The most common method of producing distortion is to push a circuit past the maximum signal it can reproduce accurately. This chops the tops and bottoms off the waveform which adds harmonics, especially odd harmonics. While this is common, running a signal through any circuitry that has a non-linear dynamic response will produce distortion. Tubes, for example, tend to saturate before actually clipping the signal. This causes more rounded corners on the waveform than straight clipping does. The distortion has more even harmonics and is generally considered to be a \"sweeter\" sound.",
"In the early years of digital recording people complained that it did not sound as warm as analog recording. The warmth that people were missing was actually harmonic distortion from near-saturated tapes and circuitry. Nowadays there are digital audio processing plugins that reproduce the same sorts of saturation to \"warm up\" the sound."
] |
[
"The noise comes from when you clip off the peaks of the wave; if you were to zoom in very far on the wave form every ripple you see outside of a smooth line is essentially a new frequency being introduced into the complex waveform."
] |
[
"AskScience AMA Series: We are experts looking at connections between the gut microbiome and mental health. AUA!"
] |
[
false
] |
Is there a connection between what you eat and how you feel? A large body of research has demonstrated a strong association between the gut microbiome and mental health. Microbes have been associated with neurological disorders ranging from degenerative diseases (such as Alzheimer's, Parkinson's, ALS and dementia) to mental health disorders (like depression and anxiety) that are becoming all-too-prevalent in today's society. However, there is still much that we don't understand about how these relationships are established or maintained. Join us today at 2 PM ET (19 UT) for a discussion with experts on what is being called the "psychobiome", organized by the American Society for Microbiology (ASM). We'll discuss what we know about the relationships between microbes and hosts, how these relationships impact our behavior, moods and mental capacity, and what each of us can do to strengthen the health of our microbiomes, and, ultimately, improve our mental health. With us today are: Links: EDIT: We are done for the day, thank you all so much for your interest in our work!
|
[
"What effect do SSRI/SNRI medications have on the microbiome? How does the microbiome effect serotonin and other neurochemical production/uptake? Are there any correlations between inflammation and microbiome diversity? As somebody with Crohn's disease and depression I'm always desperate to understand the connection with my GI tract and mental health status."
] |
[
"My colleagues will reply after 2pm, but I suspect there will be lots of questions, so I will take some now. ",
"The answer is studies have not been done (but are badly needed) on the effect of these medications on the microbiome, nor on how the microbiome affects drug uptake and efficacy. I suspect drug companies are reluctant to fund these because if their products are influenced in a major way, they would have to go back and perform studies to then identify who would benefit the most and least from the drugs. ",
"Before that happens, we need to get to grips with what's really going on in the microbiome. Just sequencing DNA is not enough. Even showing what they produce is insufficient, albeit an advance. Nobody has the same microbiome yet most of us live okay. So there must be different organisms that take on similar tasks. I recently published a paper ",
"https://www.lidsen.com/journals/hg/hg-05-01-055",
" urging studies to be done to identify pairings, co-dependencies and how organisms associate with each other. I think this will get to the crux of the matter with how the organisms function, why some are associated with diseases like Crohn's, and how we design interventions. For example, disrupting some co-associations to alleviate bad outcomes or integrating a beneficial strain into an existing coaggregate to alleviate symptoms and signs of disease. ",
"I am not a physician and would not relay any medical advice on depression and disease. I will try to discuss if and how microbes might play a role in depression later. ",
"I hope that answers your question."
] |
[
"What sort of foods tend to have the strongest positive and negative effect on the gut microbiome, and in turn, mental health?",
"Slight tangent from that, is there a particular regional or cultural diet you've found that has a better overall impact on these two? Would be interesting to see if a particular area of the world happened to naturally \"win\" in this regard."
] |
[
"Why is the surgery room so cold? Is this so only to prevent surgeons and nurses from sweating too much, or is there also a reason for hygiene?"
] |
[
false
] | null |
[
"because the surgeons wear gowns, gloves, masks, and hats. Sometimes they have lead aprons on their body and neck to protect against radiation from x-rays. And there are bright, hot lights shining down on the patient that shine on the surgeons as well. These make the surgeons heat up and become uncomfortable."
] |
[
"This. Also, a lot of the equipment used in operating rooms can be temperature sensitive and can get pretty hot from running. So it’s also to maintain temperature in electronics."
] |
[
"Our operating room is set to between 68-72F primarily for staff comfort. Operating in a hot theatre is ",
" uncomfortable. Wearing lead vests and multiple levels of gowns and face protection gets hot very quickly. The last thing you want in an OR is surgeons sweating into the surgical site or passing out.",
"We do our best to keep the patient warm as well. General anesthesia is related to hypothermia and the cold room doesn't help. We use devices to help keep the patient warm and their temperature is routinely monitored to ensure that they don't get too cold. Hypothermia increases bleeding risk as well, so it's in our best interest to keep patients warm.",
"There is some evidence that cooler ORs are related to less microbial air colonies",
", with this study stating: \"Although the indoor temperature was not significantly related to the number of microbial colonies, the colony count significantly increased by 9.4 cfu/m3 with each additional 1 °C (p = 0.018)\""
] |
[
"Are there any other ways to relate Newtonian physics to Coulomb's laws, specifically Coulomb's constant, aside from special relativity?"
] |
[
false
] |
Even if just in theory, quantum or otherwise?
|
[
"special relativity does not depend on G (if by G you mean the gravitational constant). General relativity does say that space-time curvature is related to the stress-energy tensor through the gravitational constant and some other factors. But special relativity is constructed in 'flat' Minkowski space-time so there's no curvature, and no gravity.",
"Furthermore, general relativity doesn't take gravity as an assumption, but rather gravity is a ",
" from general relativity. Once you assume that the speed of light must be constant for all observers (and a couple other things about those observers and uniform or accelerated motion) gravity is a natural ",
". Even furthermore, the speed of light is only incidentally related to light and electromagnetism. More appropriately speaking it is the speed at which massless things must travel, and things with mass can never quite reach. Light is massless and thus travels at this universal speed limit."
] |
[
"If I'm to understand you correctly, you're saying the less mass something has, the more inherent it's velocity is to C? ",
"It's actually a binary thing. 0 mass implies velocity must equal c, no more no less, from any inertial reference frame. Non-zero mass implies speed must strictly be less than c from any inertial reference frame. Inertial reference frame just means from the perspective of some observer that is not being accelerated. ",
"That gravity as a force is more of a byproduct of the distribution of energy, than it is a natural force?",
"Forces don't exist. They're useful things we use to tell physics students younger than their second year of undergrad. What a force ",
" is the rate of change of momentum over time at some instant (F=dp/dt). But when you learn advanced classical mechanics you find much better ways of doing physics than forces called Lagrangian and Hamiltonian Mechanics. It's hard to exactly state how these work, especially because I'm not familiar with your background, and it seems like perhaps there are some basics you should become more familiar with before diving off the deep end. But the long and short of it is that whenever you work out the motion of an object without any forces on it in a curved space-time like what we calculate from general relativity, a ",
" term appears in the equation, even though we started without any forces acting on the object. So yes, in a sense, gravity is a by-product consequence of how mass and energy is distributed and not an invisible string pulling the earth toward the sun and the apples toward the earth. "
] |
[
"I'm not sure what you mean by connecting Newtonian Physics to Coulomb's law. What variable or constant do you wish to relate to Coulomb's constant?"
] |
[
"If the voltage id high enough, would electricity be able to arc in space?"
] |
[
false
] | null |
[
"What we see as an arc is the effect of molecules in the air being excited by the impact of electrons that are accelerated by the voltage. These excited molecules then fall back to a lower energy state and emit a photon. This is the light we see when there's an electric arc.",
"In space, without air, there's nothing to excite and emit photons. Instead, if you'd apply a voltage between two electrodes in space, you will have any free electrons (or electrons emitted by the negative electrode) being pulled towards the positive electrode. ",
"But that's it. There'll be no visible phenomenon and the electrons simply follow the electric field lines toward the positive electrode, instead of flowing through clearly defined thin channels as is the case with an electric arc in arc."
] |
[
"Of course, why wouldn't it?\nWith vacuum all around you, you'd be the best conductor around."
] |
[
"Once electrons escape the confines of the metal electrode, they just follow electric field lines. Between two charged parallel plates, the electric field is more or less constant and pointing in the direction of the negative plate, so electrons will be moving against the field lines (and accelerating according to Coulomb's law and Newton's 2nd law).",
"This is actually the simplest scenario for discharge. In air or other media, you would need to consider dielectric properties of the medium itself."
] |
[
"ARC - A nuclear fusion reactor from MIT smaller and cheaper than ITER - a year has passed and no one talk about it. Why?"
] |
[
false
] |
edit: The name of the reactor designed by MIT is SPARC. Video:
|
[
"The history of fusion, like it or not, are accounts of people saying \"my idea will work out great, I'm sure of it, if only I get enough money to scale it up!\" So far, whenever the money has been provided, it turns out that scaling it up is harder than they realized and creates new difficulties, and sometimes makes the original design totally unworkable as a reactor design.",
"Just because that's how it happened in the past doesn't mean it's doomed to always be that way. But there is a multi-decade history that has led the people who fund these things to be relatively conservative, because the history of this is that it is always harder than it looks on paper."
] |
[
"You can make a fusion reactor on your desktop. Fusion reactions are pretty easy to initiate, you just need to slam Deuterium and/or Tritium together at high speeds. But, to get a self-sustaining fusion reaction you need to confine a fusion plasma for long enough and at high enough densities and temperatures for the fusion energy to heat the plasma and cause further fusion reactions. And to make a power reactor you need to the total energy released by fusion to be much greater than the energy input it takes to confine the plasma and bring it up to fusion conditions. The figure of merit used to track progress in fusion reactions is the \"triple product\", the product of the plasma temperature, confinement time, and plasma density. This correlates very closely with the number of fusion reactions that will occur in the fusion plasma.",
"You can see a ",
"chart of this product and the progress of different fusion experiments over time here",
". One thing you'll note is that ARC (ARC-C specifically) is actually on this chart. And, disappointingly, it's not in a particularly remarkable location relative to other reactor experiments.",
"So, while the ARC design is interesting, it's not necessarily any more promising than other designs. Moreover, there just isn't a lot of money in fusion research these days, and most of what there is has been gobbled up by ITER. Without additional followup on their early research it's hard to say how much promise the ARC concept has relative to other fusion reactor designs."
] |
[
"But seeing how ITER is being continuously delayed, wouldn't be better if they could make smaller reactor in less time ",
"no you completely misunderstand the matter. we have been building small factors for decades! it's not better. we now want to build bigger. that's the whole point. yes it takes a lot of time but finding is extremely poor. iter costs 20 billion over several decades paid by 35 countries. just one of these 35 countries alone subsidises solar and wind with 30 billion every year. that's roughly a factor of 1000 in funding. Just be patient. ",
"and money as they said in the video? They said they can make them work(maybe) for short time using the new superconductors. Even if it's for short time they get some data in years and not decades. ",
"we now need realistic data from a device that is big enough to sustain a reaction and extract energy from that. you are comparing apples to pears. "
] |
[
"Has there ever been a pair of contradicting unsolved maths problems?"
] |
[
false
] |
i.e. A pair of unsolved conjectures such that proving one of them would automatically disprove the other.
|
[
"Yes. There are two conjectures by the famous mathematician(s) Hardy and Littlewood that contradict each other. ",
"The first is the ",
". This is a generalization of the Twin Prime Conjecture. The Twin Prime Conjecture states that there are infinitely many prime numbers p so that p+2 is also prime, ie there are infinitely many twin primes. One could ask a similar question about ",
"Cousin Primes",
", which is when both p and p+4 is prime. You could ask a similar question about ",
"Sexy Primes",
", which is when p and p+6 are prime. You could even ask this about ",
"Prime Triplets",
", which is when p,p+2,p+6 are all prime or p,p+4,p+6 are all prime (so p is either both sexy and twin or sexy and cousin). We can ask \"Are there infinitely many Cousin Primes, Sexy Primes, Prime Triplets?\", which is what the Twin Prime Conjecture asks about twin primes.",
"The k-tuple Conjecture is a very precise hypothesis that answers all these kinds of questions simultaneously. A \"Prime Constellation\" is a sequence of numbers a",
",a",
",...,a",
" so that p, p+a",
", p+a",
", p+a",
",..., p+a",
" are all prime. So a",
"=2 is the case for twin primes, a",
"=4 is the case for cousin primes, a",
"=6 is the case for sexy primes, a",
"=2, a",
"=6 is one case for Prime Triplets and a",
"=4, a",
"=6 is the other. Given a Prime Constellation, the Hardy-Littlewood k-tuple Conjecture gives us a very precise statement about how often we can expect the corresponding constellation to appear. If the constellation does not run into some basic problems, like how one of p,p+2,p+4 must be divisible by 3 (so that 3,5,7 is the only such constellation), then the k-tuple Conjecture predicts that the constellation appears infinitely many times.",
"The second is the aptly named ",
". It's a little simpler. If P(x) represents the number of primes numbers less than x, then they hypothesized (after much work and experimentation) that",
"To understand what this means, we can look at the y numbers 1,2,3,...,y, and then P(y) will be the number of primes in this sequence. If we then look at the y number x+1,x+2,x+3,...,x+y, then P(x+y)-P(x) will be the number of primes in ",
" sequences. These two sequences have the same length, and this conjecture says that there will ",
" be more primes in 1,2,3,...,y than there are in x+1,x+2,x+3,...,x+y. This follows what we know about how primes are distributed, since we know that primes generally spread themselves out as we go further along the number line.",
"These are both really nice conjectures that line up with our intuition about how the primes are distributed. But it was proved (",
"here",
", actually) that they contradict each other. It was shown that, assuming the k-tuple conjecture, that there exists a prime constellation of length 447 (so k=446) and an x so that the entire constellation fits between x and x+3159. This means that P(x+3159)-P(x) >= 447 whereas P(3156)=446, so we have P(x+3159)-P(x) > P(3159), which means that the Second Conjecture is false.",
"We generally think that it is the k-tuple Conjecture that is true, though we haven't proved it yet. It has many more important far-reaching implications and is generally more powerful and important than the Second Conjecture. So, since we strongly suspect that the k-tuple Conjecture is true and that the Second Conjecture is false. If we prove that either of them is true, then we automatically know that the other is false, thanks to this result."
] |
[
"/u/functor7",
"answer",
"Every even integer greater than 2 can be expressed as the sum of two primes.",
"Not every even integer greater than 2 can be expressed as the sum of two primes.",
"Point is, it's easy to construct one given the other. :-)"
] |
[
"No, they could both be false. The fact that both conjectures are inconsistent with each other only implies that they can't both be true."
] |
[
"Redshift and Conservation of Energy of the Photon"
] |
[
false
] |
So it's my understanding that light traveling from distant galaxies has its wavelength shifted due to the expansion of the universe. The energy of the photons is inversely proportional to the wavelength. So, if the photon wavelength increases, some of that photon energy is lost as it travels through the vacuum of space. Where does that energy go?
|
[
"From the reference frame of the star, the wavelength of the photon doesn't change at all (at least assuming constant velocity, which isn't entirely accurate because of \"Dark Energy\"), and from the reference frame of a stationary observer it also doesn't change. So the answer is that the energy doesn't go anywhere because the energy doesn't change, its just that the apparent energy changes depending on your reference frame."
] |
[
"I ",
"asked",
" the same question. ",
"The answer seemed to be along the lines of conservation of energy only applies in a closed system, and the expanding universe isn't considered a closed system."
] |
[
"In an expanding universe you don't have global conservation of energy."
] |
[
"When cold, why does covering oneself in a blanket produce the feeling of warmth instantly and not gradually?"
] |
[
false
] |
The title says it all. Shouldn't the body temperature increase gradually?
|
[
"It changes immediately because the feeling of cold is due to the rate of heat loss. Your body is still generating lots of heat you are just losing it too quickly to stay warm. A blanket immediately changes that dynamic and begin feeling warm almost right away. That isn't going to be the case if you are hypothermic and your core temperature has dropped significantly but you are simply 'cold' a good blanket warms you up quite fast."
] |
[
"Are you saying that we sense the rate of heat change and not the heat itself? That claim doesn't match reality. ",
"Or is it a combination of the two?"
] |
[
"No that isn't what I was saying. I was saying that your body is trying to keep up and can't so you feel cold. The cold you feel is generally due to your surface heat. "
] |
[
"What actually is balding?"
] |
[
false
] |
What is actually going on when hairlines start to recede and why do Humans bald in the first place? Do other creatures bald?
|
[
"Humans go bald when their hair follicles revert back to vellus hair, which is the hair that first grows on newborns and is also known as peach fuzz. Hair has three different stages, anagen (growth), catagen (when the follicle stops growing and begins to get pushed up) and telogen (resting phase). Balding occurs when certain transcription factors fail to activate and hairs in anagen stage prematurely enter the telogen phase, resulting in baldness. \nI learned all this in my Cell and Developmental course in college, so only know how it happens. Hope this is helpful!"
] |
[
"Makes sense, but why does it always start at the front and move its way back on men, and seem to thin out all over on women? "
] |
[
"I don't know if that is an accurate statement. Plenty on men develop a bald spot on the back of their head. I have also seen some men who the top of their head just gradually thins out relatively evenly. "
] |
[
"Hey science reddit! I know most of you are buy answering the elementary school class, but: What is the practicality of using piezoelectric generators in the infrastructure to offset electrical generation costs?"
] |
[
false
] | null |
[
"I work with piezoelectric transducers. The amount of power that they generate is incredibly small."
] |
[
"It's been tried for flooring, but the cost offset of the piezos is enough to offset electrical savings, in most cases. This hasn't stopped the development of a number of schemes that would integrate piezos into structures, but I haven't seen anything built beyond concept stages. "
] |
[
"Whoah. That's an idea I've never heard of before. Now, I'm not a civil engineer, but I don't think it would be terribly practical to replace say, even just flooring with these things. Materials used in piezo are very different from those we want to use in construction. "
] |
[
"Will there ever be a new eye color in humans?"
] |
[
false
] |
I know that at one point all humans had brown eyes, and blue and green popped up somewhere along the way as random mutations. How possible would it be for another similar mutation to take place again? What would be the most probable/realistic eye color? My guess was yellow, but I have no scientific evidence or reason to believe so.
|
[
"Here's a pretty handy ",
"chart",
" for the cause of various eye colours.",
"EDIT: Apart from the current causes, it would be unlikely different kind of pigment is produced to generate newer eye colours, unless we dabble in a little bit of genetic modification.",
"Also fun fact, Elizabeth Taylor had violet eyes, as well as double row of eyelashes. The mutation of the eyelashes is linked with heart problems which she suffered from."
] |
[
"I'm not an expert, but I've seen eye colours that came pretty close to being yellow. At the end of the day, colour is a subjective perception, perhaps yellow is poorly recognised because it may not come out too strongly."
] |
[
"Wow.",
"If I may ask, is your vision normal?"
] |
[
"I still don't understand why viruses aren't considered 'alive'."
] |
[
false
] |
Or are they? I've heard different things.
|
[
"There is not, at present, any ",
" evidence that \"alive\" and \"not alive\" are physically meaningful categories.",
"Look at it this way. Say I gave you a box of old books, and asked you to sort them into two piles: those that are \"cool\" and those that are \"uncool.\" Now, you're not just putting books in piles at random. You've got criteria to go by. While there might be ",
" ambiguity, in most cases most of your peers will agree on which books are cool and which are uncool. Unless one of your peers is Jeremy Clarkson, in which case he'll say that everything cool is uncool just to be prickly.",
"Perhaps you and I disagree, though, on an edge case. ",
" say. We both agree it's a stupendously important and influential work of literature, but … cool? Really? You say it's uncool despite its importance; I say it's cool ",
" of its importance and ",
" its inaccessibility.",
"So we sit down and work it out. We come up with a rigorous method of quantifying different aspects of \"bookiness,\" and agree on an objective means of determining whether a book is cool or not. (",
" is, by the way.)",
"But still, there's ambiguity in the details. We agree that books should be judged on their density of ideas, but we disagree about whether one particular book rates a seven-point-two or a seven-point-three on the idea-density scale. And so on.",
"Ultimately we're just going to have to make judgment calls. And that's okay, because we know we aren't talking about anything ",
" here. It's not like every book has some objective and intrinsic property of ",
" or ",
" Books are just books; they just exist. We ",
" the quality of being cool or not, because we want to sort them into piles based on that quality.",
"Whether something's alive or not is not ",
" an intrinsic property of that thing. It's possible that it's just a quality we ascribe so we can put things in piles.",
"Is a person alive? Clearly. Is a red blood cell alive? Okay, sure. Is a hemoglobin molecule alive? Errrr…",
"As to your specific question: viruses don't metabolize. So if your personal criteria for deciding whether something goes in the \"alive\" or \"unalive\" pile include metabolism, no."
] |
[
"The distinction between \"life\" and \"non-life\" at the fine level you're talking about isn't \"fuzzy\", as some people have said, rather it's ",
"."
] |
[
"You can say that they're viruses and prions, and that different people put them in different boxes.",
"To steal RRC's metaphor, you're asking \"Is ",
" definitively cool, definitely uncool, or definitively in-between-cool?\""
] |
[
"Does every solar system have an Oort cloud?"
] |
[
false
] | null |
[
"Well, given that we barely know anything about our own Oort cloud given how diffuse, distant, and dim it is, it's going to be a very long time before we can say anything definitive about other planetary systems.",
"However, it's extremely likely that any system that forms planets will have some leftover debris. Planet formation is not a perfectly efficient process, and there's always going to be little bits of rocky things (asteroids/comets) that get scattered out into very distant orbits that would make up an Oort cloud. Pretty much every planetary system is going to generate the debris required to build up an Oort cloud then.",
"That said, you have to remember that ~half of all stars in the universe are actually in binary or multiple star systems. Many of these binaries can be on very distant orbits (thousands+ AU), which means that the other star would have very little effect on the planet formation process inside of 100AU like our own solar system. The binary star ",
" disturb proto-Oort cloud objects though, and make their orbits unstable / act to constantly clear out any Oort cloud that tries to form.",
"I would imagine then that Oort clouds would be very different or not possible at all in planetary systems with a distant stellar companion. I can't recall any papers talking about this though, so maybe someone else can come along with sources and more concrete discussion."
] |
[
"What's known about Oort cloud basically amounts to \"wow, comets come through the solar system on all sorts of crazy trajectories, from basically every direction. Therefore, there must be a relatively large population of comet-like bodies in the outer solar system, more-or-less evenly distributed in every direction\". Only a tiny fraction of the objects in the Oort cloud have been observed, and those only as they're kicked into the inner solar system where we can see them (as comets)."
] |
[
"Correct. The Oort cloud isn't something well bordered. There is no exact inner and outer limit. It is basically just scattered debris."
] |
[
"Why is it that imaginary numbers show up frequently in electronic physics and not in particle physics?"
] |
[
false
] |
This came up in my calculus class today and my teacher had no clue. I figured might know. edit: By the responses I have gotten, I see that my calculus teacher was wrong.
|
[
"Imaginary numbers lie at the heart of the mathematical formalism of particle physics. The question doesn't have a good answer because its premise is false. What you predict in particle physics are probability amplitudes of a state being observed, which when multiplied by their conjugate give you the square of the probability of observing that state. It is the key fact that probability amplitudes are complex that allows the phenomena we observe to be possible."
] |
[
"Imaginary numbers do in fact show up quite frequently in particle physics (and indeed anything related to quantum mechanics). For example, the ",
"Schrödinger equation",
" contains the imaginary number i in its time-dependent formulation.",
"By \"particle physics\" did you mean something other than quantum mechanics?"
] |
[
"They also show up in the Dirac equation, spinors, and lots of Lie algebra stuff. "
] |
[
"Yet another relativity question"
] |
[
false
] |
I understand how your relative speed affects your observation of time. i.e. if you look at a clump of photons at speed A then those photons will hit your eyes at a particular rate, if you speed away from that clump (at speed A + nearly c) then those photons will hit your eyes at a much slower rate. The jump that I don't get is where people say "and the same is for the passage of time". I don't understand how this phenomenon affects clocks travelling at different speeds, how does your speed relative to light effect the mechanics of a clock? How does going on a space cruise effect aging? I just don't understand this. I've googled it and any explanation that I can understand seems to skip over this step. Can anyone help?
|
[
"if you look at a clump of photons at speed A ",
"Photons always ",
" travel ac ",
". You're confusing time dilation with the Doppler effect. Consider what would happen if you moved ",
" the photons. By your logic, time should speed up. This is now how time dilation works; an observer with a velocity relative to some object will ",
" observe time to ",
" for the object.",
"how does your speed relative to light effect the mechanics of a clock? ",
"The way space and time are observed to work when objects move relative to each other is a fundamental consequence of the geometry of our universe. It affects ",
" within it. There's nothing special about the mechanism of a clock, it's just something that exists in the universe. ",
"It's important to realise that time dilation only affects your observations of objects moving relative to you. You can hold a clock in your hand, jump into a spaceship and blast off at 0.9c relative to Earth; the clock would still move at the \"normal\" rate from your point of view, because the clock has zero velocity ",
". Observers on Earth, however, ",
" see it slow down."
] |
[
"One of Einstein's postulates were that the speed of light is always constant no matter which reference frame the observer is in (so no matter what speed objects are moving relative to the observer). So a constant speed of electromagnetic waves in a vacuum is necessary for all the time dilation business to be true, which we have confirmed experimentally. That postulate comes from Maxwell's equations, which are four equations describing electromagnetism. Substituting these equations into each other allows us to obtain a wave equation for an electromagnetic wave in a vacuum, and a wave equation gives the speed of the wave. For light in a vacuum this speed depends on the permeability and permittivity of free space only, and these are properties of the vacuum, so are the same in all reference frames.",
"For the first bit why not familiarise yourself with inertial reference frames and then look up Einstein's thought experiment for special relativity and work through the maths yourself, that might help."
] |
[
"Layman here but here is my take on it. I welcome corrections, \nof course.",
"The first rule is the speed of light is constant in all reference\nframes. Anytime the speed of light is measured, the same\nspeed is always the result.",
"Imagine a pulse of light bouncing between two mirrors, one on\nthe floor and one on the ceiling. The distance covered is the\nround trip, the distance between the floor and ceiling, twice.",
"Now imagine those mirrors on a spaceship moving from left\nto right. When you measure the distance the pulse of light\ntravels, it is the distance from the spaceship floor to ceiling\nand back again plus the distance left-to-right that the \nspaceship traveled in that time. ",
"People in the spaceship see light traveling only the distance \nbetween from floor to ceiling and back. People on the ground\nsee the greater distance that includes the sideways motion.\nBoth groups of people measure the speed of light to be the\nsame. A constant speed covering a longer distance takes\nmore time than that same speed covering a shorter distance.",
"Thus, compared to people on the spaceship, people on the \nground see the light taking a longer time to go from floor to\nceiling and back again. Compared to people on the ground, \nthe people on the spaceship see the light taking a shorter\ntime to go from floor to ceiling and back again. ",
"Note that the people on the spaceship would measure \nthe light bouncing on the ground as taking longer than\nit takes in the spaceship. Each set of observers measure\nthe other observers as having slower clocks. How can we \nmake sense of this?",
"The equation to transform times between the two reference\nframes is:",
"t* = ( t - v / c",
" * x_1 ) / Sqrt( 1 - v",
" / c",
" )",
"where t is time, v is velocity, c is the speed of light, and\nx_1 is the x coordinate in the other reference frame.",
"Notice that, because of the x coordinate in the numerator,\nthe further away the clock in motion is, the larger the \neffect on the\ntransformed result. This\nhas the effect of being an offset, like being in a different\ntime zone but continuously varying by x instead of jumping\nhour by hour as predefined boundaries are crossed.",
"The denominator, on the other hand, is a scaling factor\nand affects the rate of passage of time as measured\nbetween the two reference frames.",
"Say it a different way:\na clock in motion further away has a phase that puts it further\nin the past, measured\nfrom the ground, than a closer clock with the same motion\n(velocity) relative to the ground. Apparently, in some way,\nevery bit of spacetime between the motionless observer\nand the clock in motion \"adds a bit of \nbeing-further-behind-in-time\" to the\nmoving clock as seen\nby the motionless observers on the ground. (Flip that around,\nthe observers on the spaceship think they are motionless\nand the observers on the planet are flying by the spaceship.\nIt works both ways.)",
"The equation to convert an interval of time between \nreference frames is e.g.",
"t_2_b - t_1_b = ( t_2_a - t_1_a ) / Sqrt( 1 - v",
" /c",
" )",
"x doesn't appear in that equation, so distance\ndoesn't matter, but the interval is still scaled by\nthe denominator, so the greater the velocity, the\ngreater the scaling (i.e. stretching, or slowing down\nof time in the other reference frame).",
"A moving clock is being affected simultaneously by\nthe increasing phase difference as x increases,\ni.e. the numerator effect, and by the rate of passage of\ntime effect of the denominator.",
"A ground observer compares one moving spaceship clock\nwith a succession of clocks in the ground reference frame.\nThe further away the spaceship clock becomes from the\nground observer, the larger the phase difference between\nthe moving clock and each stationary clock being passed.\nThe phase difference is toward the past, so the moving\nclock appears slow.",
"Reversing the reference frames, i.e. considering the\nspaceship stationary while watching a planet whizzing by,\ngives exactly the same result. The moving clock appears\nslow.",
"Well, experts please jump in and correct the heck out of this\nI'll be glad to get it right, if I can learn to do it."
] |
[
"Why do your clothes get unwrinkled in steam but your hair gets curly?"
] |
[
false
] |
I'm guessing it has something to do disulfide bonds and water molecules but that is as far as I got.
|
[
"You're on the right track.",
"What happens is that the amount of available water effects the interstrand hydrogen bonding, which is largely responsible for the wrinkles in clothes. The water binds to the cellulose (in cotton of course) or polymer chains (in synthetics) and breaks up the hydrogen bonds. ",
"So what's going on with hair then? Well, the curliness of your hair is determined by the disulfide bonds in the structure, but hydrogen bonding can modify this. If you get it moist (you really don't want to put steam on your head, it's a little to dangerous, I assume you mean humidity) again the water breaks up the hydrogen bonds and reverts it to the structure the disulfide bonds determined.",
"Here's the bit though: if your hair is naturally curly, it gets curly, but if it's naturally straight, it will straighten out. ",
"So you see, it's really the same thing going on in both. "
] |
[
"Amazing! Thanks!"
] |
[
"I just used \"The curliness of your hair is determined by the disulfide bonds in the structure\" as a fb update... what's wrong with me?"
] |
[
"What causes us to twitch and suddenly wake out of sleep?"
] |
[
false
] |
Does anyone know what causes us to suddenly twitch and move violently out of sleep? This happens to me most frequently during the early stages of sleep, and also most always when i'm falling asleep after MDMA use. I realize that might have two different answers, but i'm curious as to what they are.
|
[
"These are called \"hypnic jerks\" and are a form of myclonus. You mention MDMA. Drugs sold as MDMA usually have some affect on dopamine and seratonin, and these are thought to be involved in some hypnic jerks."
] |
[
"I thought it was \"myoclonic jerk\""
] |
[
"Well that about covers it then!",
"That's a brief intro to what it ",
" be. ",
"Given that you spend about a third of your life asleep, the dynamics of sleep should interest you. And just because your conscious mind is not driving the situation, you shouldn't be fooled into thinking that there's not a lot going on."
] |
[
"Dark-matter, expansion of the universe, Wimp and quantum mechanics"
] |
[
false
] |
So, I was reading this: From a earlier post today. My question is way off topic (in my eyes). With "80 per cent of the universe's matter must be dark" and "These WIMPs collide in space, annihilating and decaying into ordinary particles, including electrons and their antimatter counterparts, positrons." Does this imply that, in fact, the "Dark Universe" is shirking, to expand ours? And that "maybe" quantum mechanics is "part" of the interplay of the particles from "one" part of this "Dark Universe" (with our universe)? Like the "spooky action" called Quantum entanglement. Or am I being a Noob on my first post here?
|
[
"It's also important to stress that the notion that dark matter interacts via the weak force (hence, WIMPs) is a proposal that has by no means been confirmed. We know the vast majority dark matter doesn't interact via the strong or electromagnetic forces, and it is consistent with what we know that dark matter could interact via the weak force, but it is by no means certain. The AMS may provide this evidence, but we're not at that point yet."
] |
[
"First off, dark matter is in our universe, and isn't separated in any special way - it's actually mixed in quite happily with normal matter most of the time. Saying the universe is 80% DM, 20% normal matter is just like a cake which has 250g flour, 250g sugar and 3 eggs - they're all in there, but they're mixed together and not stuck in one part of it.",
"\"These WIMPs collide in space, annihilating and decaying into ordinary particles, including electrons and their antimatter counterparts, positrons.\"",
"That's actually a pretty misleading thing to say when discussing WIMPs (although not wrong) - the main point of WIMPs (Weakly Interacting Massive Particles) is that they spend most of their time ",
" doing any of those things (i.e. not interacting), hence why there can be so many of them around without being easily detectable, and not bumping into/bouncing off normal matter."
] |
[
"Indeed. It's not even certain that dark matter is a single kind of thing at all, it could be a combination of different particles. WIMPs are favored because they can be detected, even if it is difficult to do so. If dark matter isn't at least weakly interactive, we may not be able to ever directly detect it."
] |
[
"Why are cells (e.g brain cells) irreparably damaged so quickly when deprived of oxygen?"
] |
[
false
] | null |
[
"One of the things the other commenter didn’t mention is alternative metabolic pathways. When there’s no oxygen, your body will use other stuff to make energy, and that stuff can create byproducts that rapidly kill the cell. If a little gets created during normal function, the cell can clean it up. But no oxygen, no cleanup. ",
"Apoptosis (cell death) takes some time - minutes or even 10’s of minutes depending on the cell type because different cells work and live at different paces. Reactions slow down significantly as temperatures drop, which is why some people survive long periods of drowning at low temperatures."
] |
[
"A tourniquet stops the major flow of blood when there is a laceration, avulsion, amputation, etc.",
"But blood will still flow.",
"You've taped off a hole (the cut), you haven't turned off the pump (the heart).",
"So blood still makes it through via the smaller arterioles to feed oxygen to body parts.",
"Now, cells of the body can survive in this manner because they aren't doing any energy intensive tasks when the human is low on/lacking oxygen. In such an event, the brain sends signals to the body to cut off large energy drains so that the brain can use all that energy.",
"Why?",
"Because unlike the cells of the body, neurons need to be continuously maintained at a specific negative value. If it runs out of energy, then it can't maintain the negative value meaning no signals are sent to to other neurons, BUT even more important is that the cell dies because it can't maintain its function."
] |
[
"On the cellular level, cells require oxygen for cellular respiration in the mitochondria. No oxygen means no breakdown of glucose means no energy.",
"On a macro-level, being oxygen deprived means there's no oxygen being inhaled. Lungs can't oxygenate the blood. The heart can't pump oxygenated blood to the brain. No cellular respiration, no breakdown of glucose, no energy.",
"As to why the neurons die off more rapidly than say nephrons (kidney cells) when the human is oxygen deprived is because vascular connections to the brain from the heart are more direct than other connections. So the lack of oxygen takes slightly longer to get to parts further away. I mean we're taking seconds here but yeah still slower."
] |
[
"Schrödinger's cat: Is it beyond the limits of my understanding?"
] |
[
false
] |
I have read many sources and watched many discovery type shows, but somehow the concept of the cat being both alive and dead at the same time escapes me. I can understand that we don't know wether it is alive or dead until the box is opened, but how can we say it's both? Or is this going to take more brain cells than I have? EDIT: Thanks for the great responses, truly appreciated - I dont feel so 'inadequate' anymore
|
[
"That's sorta the point with the whole mind experiment. Schrödinger came up with it to show how inane quantum mechanics is when applied to bigger things. ",
"The truth is, particles are in a superposition of states until observed, then they collapse. You can't really understand that. That's just the way it is. It's not intuitive, but we evolved with a macroscopic brain, so of course it doesn't make much sense to us. "
] |
[
"Reminds me of the old joke about the mathematician...",
"A mathematician is sitting at his desk, thinking hard when his physicist friend comes up to him and asks what he is thinking about. The mathematician says he's thinking about a 23 dimensional space. The physicist looks confused and says 'how on earth can you visualise 23 dimensional space?'. The mathematician says 'what? It's easy! Just visualise n-dimensional space and then set n=23!\"",
"I'll get me coat..."
] |
[
"It's sort of a reductio ad absurdum, in that people don't have a problem with a photon being in two states at the same time, but when you make it a cat it just gets silly."
] |
[
"A doctor will clean an injection site before giving a shot - why doesn't a dentist need to do so before a numbing shot? Don't our mouths generally have more bacteria than our arm/leg skin?"
] |
[
false
] |
[deleted]
|
[
"The mouth is one of the main focuses of the immune system. Being an opening to the world, one that has to deal with decaying organic matter and whatever the hell is in the water. It has evolved different systems to keep infections in check. Saliva has a few different enzymes and proteins in it and is slightly acidic this kills many of the buggers trying to get in through a cut ( or puncture). Inflammation also plays a key part as you would notice if you've had a sore. Also saliva acts as a sort of bandage closing it off to other organisms, while healing faster due to the proteins in the saliva. This won't help with any major trauma but will if it's just a small wound. Compared to your arm which a low priority because it is a closed system, and only has the internal defense found everywhere in your system."
] |
[
"Please refer to the ",
"WHO paper",
" on best practices for injection. ",
"\"Although skin that is visibly soiled or dirty must be washed, swabbing the clean skin of a patient before giving an injection is unnecessary. Studies suggest that there is no increased risk of infection when injections were given in the absence of skin preparation (Table 3) (36,38,41–44). Bacteria from the skin flora might be introduced through skin piercing (41). However, most of these bacteria are non-pathogenic and the number introduced is\nlower than the minimal infectious dose for pus formation (45).\"",
"Swabbing of an injection site is done more for patient perception of safety than actual safety."
] |
[
"Evolution doesn't have a purpose, it simply responds to pressure. ",
"The pressure to protect a permanently open hole that foreign matter purposely and accidentally enter regularly is significantly more than protecting your arm. ",
"So if something is good enough, it's good enough. "
] |
[
"Is there \"dark matter\" nearby?"
] |
[
false
] |
Inspired by an posted in . First off...the article linked is about as unreliable as an article can be; the tagline of the website is "Mysteries, Phenomena, Paranormal, UFOs, Space and Science," and the article quotes the Daily Mail. By itself, it's entertainment at best. However, it raises a question in my mind...if a significant fraction of the mass in the universe is dark matter, shouldn't there be a significant amount of it realtively nearby? If so, is it something we could detect or study? If we can study it up close like that, what questions (if any) would that kind of study enable us to ask that we wouldn't be able to ask if it only existed far away? Dark matter has fascinated me for a while now, ever since I saw , but it's not something I really understand. I know we can only interact with it via gravity, and that there's a lot of it, but that's about it.
|
[
"There are 4 fundamental interactions around us, as we know. Although most of the matter we see interacts electromagnetically, there are some examples of fundamental particles that are actually uncharged, and thus almost invisible: the neutrinos. Neutrinos are literally everywhere and there is huge flux of these guys coming from the sun, but they only interact through the weak interaction (which is, surprisingly, really weak), and thus they are really hard to detect.",
"Dark matter particles are kinda like neutrinos, except that they are probably much heavier and we don't really know whether or not they interact through the weak interaction, only through gravity, or also with some other yet unknown forces. It's the WIMP (weak interacting massive particles) paradigm, if you want to check in more detail. ",
"The way we discovered neutrinos was through nuclear decay, by looking at the energy balance on the neutron decay into proton and seeing that \"something was missing\". We expect that if dark matter particles actually interact with the standard model particles in some way, we'll be able to see in some colider experiment or through astrophysical observations of ",
"gamma ray bursts",
". "
] |
[
"I'll add that there are additional attempts at direct detection on Earth. These experiments have detectors, and they wait for a dark matter particle to strike an atom in the detector and deposit some of its kinetic energy. There are no conclusive results yet, but they are really just getting started."
] |
[
"There's no escaping gravitation, when someone says \"only interacts through the weak force\" gravity is taken for granted."
] |
[
"AskScience, why does the shower curtain seem to be attracted to my body when I'm in the shower?"
] |
[
false
] |
I thought it might be in my head, but it very clearly isn't. I'm fairly certain the two are causally linked. Not only will an outstretched hand attract the curtain, but it will keep it there.
|
[
"When you shower, the hot steam rises and draws air from the bottom, which pulls the shower curtain towards you."
] |
[
"Hmm... How much spray from the shower are you getting when you are close to the curtain?\nYou'll notice that when you are sprayed by the shower directly, the curtain will rise less. However, if you are say, ducked out of way of the stream of the shower, the curtain will rise much more. "
] |
[
"Because ",
"this",
"Cold air rushes into your shower blowing the curtain into you.",
" Just read your actual post, not just your title. I literally have no idea why your curtain is attracted to you. If things get awkward maybe its time for a new curtain. Brutal I know, but the relationship is doomed from the get go..."
] |
[
"Can lahars happen in extremely cold climates?"
] |
[
false
] | null |
[
"Yes, lahars can be triggered in cold climates. Lahars are tephra (ash) laden mud/debris flows that occur on slopes and flanks of volcanic landscapes. How they are triggered is when rain water or snow/glacial melt occurs and undermines the slope. Even in colder climates, rain may occur and glacial melt is absolutely happening everywhere. The nice thing about lahars is they leave a good deal of evidence behind in the geologic record, so it is possible to go out to the field and construct a timeline of lahar events in the same area over time. Collect radiocarbon samples and you have a numerical age range for the events and the median age for each event provides a rough frequency of lahar events. Over time, slopes regain ash volumes due to subsequent eruptions.",
"For case studies, please refer to the following scientific articles:",
"Alaska lahars:",
"https://dggs.alaska.gov/webpubs/dggs/gr/text/gr053.pdf",
"Kamchatka, Russia lahars: ",
"https://link.springer.com/article/10.1007/s00445-016-1094-4",
"Iceland lahars:",
"https://www.researchgate.net/publication/275333068_Two_lahar_deposits_in_Iceland_The_Eyjafjallajokull_2010_deposit_and_the_Hekla-S_deposited_3900_years_ago_BP_A_comparative_study",
"Antarctica lahars:",
"https://www.nature.com/articles/s41598-017-16630-9"
] |
[
"Lahars form when pyroclastic material melts and/or mixes with snow and ice causing mass movement of material downslope. Often at very high speed and with lots of volume. ",
"Cold conditions are needed for the snow and ice, as is some sort of volcanic activity. Therefore they can occur in both high altitudes but also in cold climates as long as there is some volcanic activity to create the pyroclastic material."
] |
[
"Lahars happen much more often in cold climates because of snow and ice on the volcano as others have mentioned, but it should be said that there is such a thing as rainfall triggered volcanic mudflows of ash that's been on the ground already for a while (but sometimes very recently erupted). Those lahars have been some of the most deadly, in highly populated river valleys in the tropics. Volcano erupts in the dry sseason, everything's fine, then when the monsoon comes, there's a flash flood of what might as well be fresh wet concrete mixed with whole trees..."
] |
[
"Is \"same\" achievable in thermodynamics?"
] |
[
false
] |
What I mean is this. You have 2 objects at different temperatures: Object X is at 100 degrees, and Object Y is at 50 degrees. Slowly, you lower the temperature of X until it reaches 0 degrees, so that it is now colder than Y. Is it technically accurate to state that at one point in time, X and Y were the same temperature? I don't know why, exactly, but I've long had the idea that our understanding of quantum physics prevents this from being possible to an infinitesimal measurement. That at some instant J, object A will be hotter, and at the very next instant K, object B will be colder. What about if we talk about heat instead of temperature? Does that change the answer? TL;DR Are two objects ever exactly the same temperature?
|
[
"I've long had the idea that our understanding of quantum physics prevents this from being possible to an infinitesimal measurement.",
"I may be wrong, but it sounds a bit like you're restating the misconception that the uncertainty principle limits the accuracy of measurement, which it does not. A ",
" measurement may still be made to arbitrary accuracy. ",
"Now there's a lot of trickiness here. Temperature is a statistical/ensemble property, so you have a general problem with how to ascertain it with a single measurement, and the problem that any measurement comes with its own error, that measuring the temperature must change the internal energy to some extent, and all these issues that really apply equally both classically and quantum-mechanically.",
"To try to break this down into things I can attempt to answer without my head exploding, I'll try some related questions... First off, you need to remember that temperature is inherently related to entropy, so to say anything about temperature, you need a quantum-mechanical concept of entropy. Now, there's no problem extending classical thermodynamics to QM - in fact, there are multiple ways of doing it. (which is interesting)",
"Is temperature (or the energy of an ensemble) a continuous variable, quantum-mechanically? The answer to that is 'yes', because even in QM, you still always have some energetically-continuous (as far as we know) degrees of freedom in the system. E.g. the kinetic energy of free particles. ",
"Temperature is defined by how entropy changes with the total internal energy of the system. But the way I interpret that, is that it's really a measure of the internal energy. (Because, given complete knowledge of the available states of the system - the ",
"partition function",
" - you can calculate the entropy/enthalpy/temperature for any given amount of total energy, or the amount of internal energy corresponding to a given temperature. Provided of course that it's in thermal equilibrium. Otherwise the temperature isn't a very well-defined concept)",
"Now, quantum-mechanically, entropy (in ",
"von Neumann's definition",
") is a measure of the ",
" of the system. This is also a continuous variable, and multiple states can have the same entropy. So it's not quite like classical thermo, in that entropy and enthalpy do not fully characterize how occupations are distributed among the energetic states of the system. The 'true' description of the system would be in terms of the quantum-mechanical density matrix. ",
"Now, per the ",
"no-cloning theorem",
", you can't put two systems into the same quantum-mechanical state. (although theoretically, there's of course nothing stopping them from ",
" to be in the same state, however unlikely) In other words, you cannot measure one system's density matrix and create an identical system with the same density matrix. However, that does not stop you from setting up two systems with the same temperature/entropy, because there isn't a 1-to-1 correspondence between the two.",
"In other words, you could (somehow) measure the energetic states (of two identical ensembles, and nothing would ",
" prohibit the possibility of you getting the same result to arbitrary accuracy. Following that, you could let the systems sit in isolation for a while until they become ",
"cohererent",
" quantum-mechanically, which in the von Neumann picture is basically thermal equillibration, as it's a description of how the quantum entanglement (and thus entropy) of the system maximizes itself over time. The systems still won't (likely) be in identical quantum states, but they can still have the same quantum-mechanical entropy, and thus be at the same temperature. ",
"Which is what you'd expect, really. Since if you measured two identical, isolated, systems having the same energy at one point in time, it can't possibly be different in the future (without violating thermodynamics, and QM doesn't do that) On the other hand, per basic QM, the fact you measured the exact same temperature in the past, doesn't guarantee that you'll have the same correspondence in the future, as QM doesn't allow you to predict any ",
" measurement, either with a single system or two of them.",
"Not that there aren't points where QM and classical mech differs when it comes to thermodynamics. One key point is that a classical system at 0 K is entirely in a single state (and thus has zero entropy), whereas the same is not necessarily true of a quantum-mechanical system. And other interesting stuff also follows, like the ",
"recent result on 'negative' entropy",
". ",
"But the short of it is: Yes, things can essentially be at the same temperature in terms of quantum mechanics as they can in terms in classical thermodynamics. "
] |
[
"The reason I made the distinction between temperature and heat is that they are, actually, distinct (though interrelated) properties. You can get two objects that are both at the same temperature, but have very, very different heat. Similarly, one object can have less heat but a higher temperature than a second object."
] |
[
"The reason I made the distinction between temperature and heat is that they are, actually, distinct (though interrelated) properties. You can get two objects that are both at the same temperature, but have very, very different heat. Similarly, one object can have less heat but a higher temperature than a second object."
] |
[
"Does the gravitational constant change?"
] |
[
false
] |
Does the gravitational constant equal to 9.81 m/s² even apply if your outside of earths SOI? for example solar orbit or other planets
|
[
"That is the Earth's gravitational field at its surface, but it is not constant. It ",
"varies depending where you are on the Earth",
", and decreases as you go away from its surface. (it actually increases slightly as you go down towards the edge of the core)",
"The general formula for the gravitational field near a massive object is GM/r",
" where M is the mass of the object, r is your distance from its center of mass (the radius of the planet if you're on its surface), and G is the ",
" gravitational constant, also known as Newton's constant."
] |
[
"It's discussed in the physicsforums article I linked. The problem with your supposition is that it assumes the Earth is uniformly dense, but it isn't. The density density distribution is such that when you go down through the mantle, you're getting closer to the much higher density core, which has a bigger effect than the reduced enclosed mass above you."
] |
[
"No, but it's a coefficient in Einstein's equation relating spacetime curvature to energy density."
] |
[
"What happens to information that we delete off of our computers?"
] |
[
false
] | null |
[
"The system removes all references to it and marks it as over-writable. Think of it as a library card-catalog system - the card is removed, but the book is still on the shelf, and can be found if someone puts in the effort of looking for it.\nThe deleted data is treated the same as blank space and will be overwritten by any new file your OS chooses to put there.",
"This is how data recovery works, it works on the assumption that there is still enough of the deleted file left over to recover. This is why it's best to try data recovery ASAP after an item is deleted.",
"If you see an option to \"securely\" erase something, this means that instead of just marking the data as over-writable, the OS actually takes the time to erase all of the data.",
"Note that this is for spinning-disk hard drives, I'm not sure of how it works for SSD/flash drives."
] |
[
"Back in the DOS days, when you erased a file, it just over-wrote the first character of the file name with a ? ",
"This mean that the space allocated for the file was up for grabs.",
"The file and data was still there, it just didn't show up when you did a 'dir' command. Recovering erased files was pretty easy back then."
] |
[
"This is pretty much still the case. That's why certain \"undelete\" programs are able to work even after you empty your computer's trash."
] |
[
"Are the distant planets that we can \"see\" still even there? How do we know?"
] |
[
false
] |
I've been watching some docs and doc series about astronomy and my (for one) takeaway has been that the distant planets (as in another solar system) aren't really seen, it's the light that has reflected off of them that we see (much later in time). How do we know that those planets aren't just dust today (in that they haven't been smashed to bits by something (rogue planet? a la Melancholia lol) in the time it's taken for the light has become detected)? Also, I've come to see those powerful telescopes (Hubble, etc) as not so much viewing devices (like binoculars) but the closest thing we have to time machines (due to the extreme distance/time). Am I on the right track? If not, please illuminate. Thanks!
|
[
"We really can only detect exoplanets within our own galaxy, and only within a small chunk of our galaxy. The most distant exoplanet ever detected is less than 30,000 light years away, and most are far closer than that. So yes, we are seeing these things as they were thousands of years ago, but that's a very short amount of time on a geological or astrophysical timescale. ",
" some catastrophe has happened during that time, but most likely they haven't changed very much.",
"For ",
" physics, when we're looking at things billions of light years away, we are indeed receiving light from far in the past when the universe was younger and really quite different. This is a great tool because it means we can literally see the entire history of the universe - at least, until we're looking at such an early state that the universe filled with a thick opaque gas that we can't see through. I don't like the term \"time machine\" because I worry somebody will take that too literally, but we do indeed see very old light that has travelled for billions of years, which produces images of the universe as it was billions of years ago."
] |
[
"aren't really seen, it's the light that has reflected off of them that we see",
"That's true as well when you look at your hand in front of your face. You're seeing the light reflected off of your hand. And it takes time for the light to reach your eyes, so that by the time you see it, it's an image of your hand as it was in the past. There is nothing different about seeing planets from other solar systems. Only that it takes a lot longer time for the light to reach our eyes."
] |
[
"We do not, but we can safely assume they are still there, unless it's a supergiant star at its late stage. That means, despite extremely large distances spanning across thousands or tens of thousands light years those planets will be still there because the relative age of stars is far longer than the travel time fo light.",
"There could be some discrepancies in what we see and what's there, but so far, we don't have much evidence to make any conclusion."
] |
[
"Do lenses work for radio signals or X-rays? Do antennas work for visible light? They are both part of the electromagnetic spectrum..."
] |
[
false
] |
I assume that you have an antenna for visible light, or that you have a lens for non-visible parts of the EM spectrum, but they would be need constructed differently. Why, though? I have wondered about this for a while. Why would an optical lens not work for a radio signal or X-ray?
|
[
"Lenses do work for x-rays, but there are many problems. ",
"This paper",
" outlines them. The TL;DR is that the refractive index for x-rays is very very close to 1 for all materials, so it is hard to build a refractive lens that has any effect. Also, in the higher energy regime, the particle effects of photons start to dominate, so you begin to see more photoelectric absorption and incoherent scattering.",
"Diffraction is possible with x-rays using materials like HOPG. ",
"This paper",
" describes some of the possibilities. In my opinion though, this is more useful for selecting a single energy of x-ray from a broad beam (known as \"monochromatization\") than as a lens.",
"For the \"antenna\" part of your question, remember that an antenna is roughly the same size as the wavelength of the EM radiation in question. A single electron is an \"antenna\" of x-rays, much like the cones and rods in your eye are \"antennas\" of visible light.",
"Hopefully someone that knows more about radio waves can answer that part. All I know is that a radio wave lens would need to be very large (again, on the order of the size of the wavelength)."
] |
[
"Radio frequency waves can be, and are, passed through lenses quite frequently. They aren't always geometrically similar to lenses for optical light, although their functions are the same - see ",
"rotman lens,",
" which is generally fabricated as a parallel plate structure with a dielectric inside. Propagation through it is likely quasi-TEM rather than TEM. ",
"A very clever professor once inspired our class to pretty much invent a microwave lens by asking a very clever question: ",
"As you make a horn antenna flare out larger and larger, waves entering the outer parts of the aperture accumulate more phase on their way to the feed point than do waves entering the center. This results in reduction of directivity and introduction of ripples to the radiation pattern. How do you fix this? An easy and effective solution is to load the horn with a dielectric lens, which counters this phase distribution across the aperture face such that the waves all sum together in phase at the feed. ",
"Here is an example."
] |
[
"I work with synchrotron radiation (5keV-120keV x-rays). For higher energies beyond about 25ish keV, compound refractive lenses are at times a viable option depending on the required numerical aperture, focal points, acceptable divergence, and acceptable energy spread. One way to fabricate them is to create parabolic (or elliptical or circular or cylindrical) 2D or 3D voids in a low Z material, namely beryllium, and viola - a working x-ray lens. ",
"For low to moderate energy x-rays (500 eV - 25ish keV), the losses through refractive lenses make them terribly inefficient. Focusing is generally done via curved mirrors or bent diffractive optics. "
] |
[
"How does voluntary movement happen?"
] |
[
false
] |
Being a medical student (graduating in 1 year), I feel really embarassed to ask this question. I have neurology exam in 1 week and I have learned all about the pyramidal and extrapyramidal tract, alpha-gamma coactivation, motor control etc. But still I haven't been able to answer the question : where does this process originate? Where does the first action potential occur, and mainly - HOW? ; given the fact that action potential is a merely a response to an adequate stimulus. What is this stimulus, then? A thought? Are there then "thought receptors" ? I know this sounds ridiculous, but the more I think about it, the more puzzled I feel.
|
[
"As far as I know, the answer to your question about 'what is the original stimulus' (the thought about moving) is unknown and goes into the 'do we really have free will' and 'neural correlates of consciousness' territory. You might like to look into Libet's experiments: ",
"http://en.wikipedia.org/wiki/Benjamin_Libet",
"The brain is more than a series of action potentials - that would probably be a reflex arc. There are no thought receptors, and the origins of thoughts are not well understood. You can look at pathways and connections in the brain - such as areas of the prefrontal cortex, primary motor cortex and then move it down to the midbrain to basal ganglia.",
"What you may be interested in looking up is the 'Direct pathway of movement' and Indirect pathway of movement' as they deal with the execution of voluntary movement. Understanding these helps you to understand conditions such as Parkinson's (direct p/w disorder) and Huntington's (indirect p/w disorder).",
"Information can be found in any good neurology textbook which deals with the basal ganglia. A quick google and this looks okay on a skim read: ",
"http://www.ncbi.nlm.nih.gov/books/NBK10847/",
"You shouldn't at all be embarrassed to ask such a question. You seem to be thinking about it and questioning it instead of trying to memorize pathways and tracts for your exam. "
] |
[
"Voluntary movement is a complex beast of an issue and is best thought of a combination and cooperation of several different areas of the brain. I feel as though trying to simplify the whole process into a single inciting event does it an injustice. That being said, I'm sure you are already reading up on this but I wouldn't neglect the role of the primary motor cortex (betz cells), thalamus, peremptory cortex, anterior horn cells in the spinal cord, and the motor unit. ",
"From a previous med student to another, don't worry if you don't understand it all now, it takes a while for this all to sink in and make sense. I'm only now getting the grasp of a lot of these more complex processes as I put it into practice. Good luck on your exams, and hope this helps!"
] |
[
"Think about what you're asking here. What would a satisfactory answer look like? You've already said stimulus response doesn't quite say what you're looking for. If you're looking for a scientific explanation of the illusion of free will/consciousness you're going to have some interesting answers but little consensus."
] |
[
"Why is the speed of light a whole number?"
] |
[
false
] |
I would expect it to be 299,792,458.625976 or something similar but instead it is a nice whole number
|
[
"The meter is defined such that light speed is exactly that many meters per second. It was changed that way in 1983. An earlier measurement ",
"from 1972",
" puts it at 299792462 +/- 18 m/s."
] |
[
"It was close enough to a whole number that they slightly changed the definition of a meter in order to make the speed of light a whole number."
] |
[
"In plank units its not just a whole number, its 1 ",
":)",
"Sorry your question already got answered so I just threw in something new :P"
] |
[
"When we increase the temperature of a system, the atoms in that system vibrate more. Do they increase in frequency or amplitude? or both?"
] |
[
false
] |
I've just been reading 'The laws of thermodynamics' by Peter Atkins. In the book he says at some point "Temperature.. is just a parameter that summarizes the relative populations of energy levels in a system at equilibrium." And "Each speed corresponds to a certain kinetic energy, and so the Boltzmann distribution can be used to express, through the distribution of molecules over their possible translational energy states, their distribution of speeds, and to relate that distribution of speeds to the temperature." Now i've heard before that when the temperature increases we say that the atoms are vibrating more. Is this increase in vibration an increase in the frequency of vibration or amplitude? or both? Is this increase in vibration due to electrons occupying higher ? What causes the vibration? (might be more of a philosophical question than a scientific one) and how does this relate to the 'speed' as described above? Does he mean the speed of vibrations, or the forward speed of the atoms?
|
[
"Yes, increasingly high energy states of all sorts get populated as the temperature increases.",
"Electrons interact with each other and with nuclei. A change of vibrational state can change the orbitals themselves as well as excite electrons to higher ones. And electronic energy can be transferred to vibrational energy. Translational energy can excite electrons as well, if two atoms collide at sufficient velocity. ",
"Why ",
" the electrons be able to change their kinetic energy if the nuclei suddenly change position or velocity? These things interact, and therefore it's part of the thermal equilibrium."
] |
[
"Vibrational amplitude isn't really a thing on the molecular scale. A molecule either vibrates or it doesn't. There is obviously some limit to the displacement in a bond when vibration occurs, but there's not a hard length value that the bond stretches to every time.",
"When you make a system hotter, what happens is that the Boltzmann distribution shifts to a higher average with a larger spread. From a molecular standpoint, this means that more molecules are excited to those higher frequency vibrational states (I suppose you could call this amplitude).",
"Very simply, vibration occurs because it's another way for a molecule to be. It also doesn't take much energy to vibrate a molecule, so it happens all the time at room temperature."
] |
[
"Re: #4, Atkins is talking about the distribution over translational energy states, so speed refers to rate of travel.",
"Re: #2, just like increasing the temperature alters the distribution over possible translational energy states (i.e., adding energy makes it so that some molecules can move faster, and the average of all molecules is moving faster), it increases the distribution over possible rotational and vibrational energy states also. Adding enough energy can alter the distribution over electronic energy states, too. A diagram that shows schematically the relationship between these energy states is ",
"here",
"."
] |
[
"Does normal metabolic function eventually return to formerly obese individuals that underwent major weight loss?"
] |
[
false
] |
Most articles I've read on the matter estimate that between 80-95% of individuals that achieve major weight loss regain most or all of the weight down the road, typically within a couple years. Many people, in fact, will become heavier than they were originally. It seems that more and more articles are released every week discussing the seemingly "irreversible" metabolic impact of being obese and remaining obese for an extended period of time. That got me wondering, if the duration of obesity likely impacts long-term (potentially life-long) metabolic function, could the inverse be true as well? Could there be a critical period of time that a formerly obese person must maintain their weight loss before their normal metabolic function recovers or will they always have "obesity in remission?" Does anyone know of any long-term studies that address this question? EDIT (17:30): It just occurred to me, many people that lose large amounts of fat tend to lose a significant amount of lean muscle mass as well. I wonder if this may explain some or most of the loss in metabolism observed in some studies or if that's just a gross oversimplification
|
[
"Part of the problem is the adipose cells. When you become overweight your adipose stem cells proliferate. If you lose weight the cells essentially deflate, but they are still there secreting hormones affecting metabolism. They are also waiting to fill back up if you fall off the wagon. Adipose cells can stick around for 8ish years, so it can take awhile. It isn’t clear if everything goes back to normal over time, but I hypothesize after about a decade of discipline you’ll be back in business."
] |
[
"You're getting a lot of answers that belong in ",
"r/confidentlyincorrect",
"The real answer is that we have some theories and a paltry amount of data that isn't of particularly high quality. Human metabolism and weight is stupendously difficult to study. Anyone who claims to know exactly when and how metabolism changes in relation to weight loss is wrong.",
"In regards to your specific question: Few weight loss trials survey participants beyond 6 months. For those that do, the vast majority of patients regain most of the weight they've lost by two years post intervention. ",
"So patients that DO lose weight long term are pretty rare, making them inherently difficult to study. Are their results generalizable, or were they just a specific subset to begin with? ",
"This question you're asking is a really important one, but it's a bit of an indictment against the current state of knowledge that it's not answerable."
] |
[
"Unfortunately, all of the answers you've received so far are variations on the folk wisdom that a person must only make a long term lifestyle change and then they will lose weight. And that is because, to the best of my knowledge, there are no long-term studies addressing your question. ",
"In fact, to the best of my knowledge, there are no long-term studies demonstrating participants maintaining enough weight loss for them to no longer be considered obese ",
". ",
"Most studies show very modest weight loss. For example, in ",
"this meta-analysis",
" purporting to show that weight loss is maintainable, shows a mean weight loss at 6 months at 5-9% of body weight, and at 12 months it's already down to 3-6%. ",
"This older meta-analysis",
" is more positive but still shows 3-6% body weight reduction at the 5 year follow-up mark. For perspective, a 300 lb person losing 3-9% of their body weight has lost between 9 and 27 pounds and is still comfortably fat.",
"There are ",
"some studies based on the National Weight Control Registry",
", which consists of people who were able to lose a lot of weight and maintain it for at least 5 years, and these people tend to be very active and eat lower-calorie diets. Groups like this are useful as researchers can use them to generate hypotheses for how to maintain weight loss. But to my knowledge, research has not shown that the methods the people in this registry claim they used to lose weight are successful when applied in controlled studies. This means we can't yet say, based on this group, that any particular behavior or intervention results in long-term weight-loss maintenance. It could easily be that some other factor, be it genetics or just damn luck, is what allows these folks to maintain their weight loss while the vast majority of people do not."
] |
[
"Is there a freezing point where meat can be effectively sterilized from bacteria as it is when cooked?"
] |
[
false
] |
Is there a freezing point (or method) that meat can be subjected to that can kill off possible contaminates without compromising its nutritional value? Is heat the only way to prepare possibly tainted food safely?
|
[
"Freezing doesn't sterilize food. You can store bacterial colonies in -80 deg C freezers for years and they come out okay. You can also flash freeze bacteria using LN2 to create something similar to 'dippin dots' which will preserve them. Some sort of media might be used, but I think the general concept holds. Freezing slows them down, but doesn't sterilize.",
"Food can be preserved many ways, by salting it, irradiating it, heating it, exposure to acids or bases (think pickling), or fermenting it to create alcohol. Also if food is super rotten cooking it may not help you at all, if something toxic has already been produced by bacteria.",
"edit: my source is a close friend who works in the bacterial cultures industry."
] |
[
"You can store bacterial colonies in -80 deg C freezers for years and they come out okay",
"True, but to be fair, they need to be stored in glycerol to disrupt ice crystal formation. Storing them in growth media alone at -80 deg C would probably lyse most cells, but do correct me if I'm wrong."
] |
[
"Conveniently, -40ºC and -40ºF are the same temperature."
] |
[
"how much do Genetics play a role in muscle building and endurance?"
] |
[
false
] |
do genes determine things like amount of fast twitch muscle fibers vs. slow twitch? things like that?
|
[
"Genes also control your ",
"endogenous",
" hormone levels (testosterone, androgens, etc) which are critical for building muscle mass and strength."
] |
[
"Genes also control your ",
"endogenous",
" hormone levels (testosterone, androgens, etc) which are critical for building muscle mass and strength."
] |
[
"genetically engineered \"super cows\"",
"They're called ",
"Belgian Blue Cattle",
" and it's not genetic engineering, just selecting for a mutation."
] |
[
"Is daytime darker on Mars since it is further than the sun? How does atmosphere affect the brightness of a planet?"
] |
[
false
] |
[deleted]
|
[
"Mars is about 60% further from the Sun than Earth, so by the inverse square law it gets about (1.6)",
" = 39% as much solar radiation per square metre.",
"That's appreciably darker, even considering the atmospheric effects on Earth.",
"Atmosphere reflects some of the incoming light from the Sun, and sometimes (clouds) blocks it. This is not as big a factor as Mars's distance."
] |
[
"Here's something interesting. Even on Pluto, billions of miles away, it's not as dark as you might think. ",
"This calculator",
" takes your location and tells you what time of day it will be as bright as Pluto - just after sunset for me, 6:12 PM today. So yes, it will be darker on Mars than on earth, but due to the huge dynamic range of human vision, it would still seem very bright. "
] |
[
"A cloudy day has <25% of the light of a sunny day, so it is a bigger factor.",
"Basically, mars looks like it's cloudy all the time during daytime."
] |
[
"What would happen if we nuked a hurricane?"
] |
[
false
] |
[deleted]
|
[
"Funny you should ask this. It gets asked so often NOAA (the National Oceanographic and Atmosphere Administration) actually made a response you can read ",
"HERE",
".",
"The short answer, nothing. The amount of energy a fully developed storm has is magnitudes more than the amount of energy a nuclear bomb could release. For comparison, a hurricane can release energy at a rate of around 5x10",
" watts. That's 50,000,000,000,000 Joules per SECOND. ",
"The energy released is equivalent to having a 10 megaton nuclear bomb released every 20 minutes. ",
"In addition, only about 10% of energy from any heating device like a hurricane or nuclear bomb goes into wind generation - the rest is radiated heat (infrared heat and other heat releasing mechanisms). ",
"So a nuclear bomb would do very little to actually affect the winds. Also note, most hurricanes are a hundred miles or more wide. A nuclear bomb's blast is maybe two or three miles across, a mere fraction of a percent of the entire hurricane's footprint. ",
"It'd be like poking a bear with a sewing needle. You might get its attention, but it won't stop the bear. ",
"Plus, nuclear bombs would release radioactive fallout that would get spread by the winds and just make the hurricane radioactive - like a huge, radioactive super villain."
] |
[
"Now what if one were to drop several thousand spiders into this giant radioactive hurricane?"
] |
[
"Perhaps we could also dump tonnes of sedative into the storm to keep the spiders nice and docile.",
"And who knows, maybe we could increase the amount of...electricity? "
] |
[
"How does the mRNA-1273 vaccine that Moderna is testing work (or is expected to)?"
] |
[
false
] | null |
[
"In general, mRNAs are translated into proteins. For an mRNA vaccine, some mRNAs that match target viral mRNAs are injected, which causes your cellular machinery to translate them into the viral proteins. These are not functional viruses but rather are disassembled parts of the virus that the body can recognize. Your immune system learns to recognize these proteins and create antibodies to target them. Then, if the actual virus enters the body, your immune system recognizes the proteins on it and attacks it with antibodies."
] |
[
"No, sorry for the confusion. The things that your body makes are the ",
", which are parts of the virus. The thing that’s injected (the mRNAs) are copied from the virus’s genetic code. Your body reads the injected mRNAs like a blueprint and then starts constructing viral proteins.",
"Edit: ",
"viral mRNA copied -> mRNAs injected -> human body translates mRNAs into viral proteins -> immune system creates antibodies to viral proteins -> real virus arrives and is recognized/attacked"
] |
[
"You only need to know the genetic code (sequence) of the virus. Once you have that you don't need any viruses.\nYou can then just synthesize mRNA based on the sequence that you already know.\nModerna then packages this synthesized mRNA into nanoparticles and injects them into a patient. \nOnce injected the nanoparticles will be taken up by cells (probably hepatocytes). Inside the cell the mRNA will be released and used by the cell to produce viral proteins. These viral proteins are not dangerous as they cannot produce a real virus. Nonetheless, the immune system will recognize the produced viral protein as foreign and initiate an immune response against it, leading to the generation of antibodies etc.. Now you have immune cells and antibodies in your body that can recognize the real virus and kill it before it does much harm, making you immune."
] |
[
"We have been measuring the age of earth by looking at the layers of ground, how do we know there aren't any older evidence underneath the thick snow of North pole? Or the deepest ocean floor that human has yet to discover?"
] |
[
false
] |
We have been measuring the age of earth by looking at the layers of ground, how do we know there aren't any older evidence underneath the thick snow of North pole? Or the deepest ocean floor that human has yet to discover? Or even unknown creatures that lived before the dinosaurs.. Edit: I don't mean literally looking at the ground alone, what I meant was looking at the stuff/rocks that is from underneath the ground. Since anything from that long ago probably got buried for a very long time..
|
[
"Lets start by having a look at the ages of material we ",
" observed.",
"The first blunt observation we have is that the age range of geological materials is much narrower for oceanic rocks than it is for continental rocks. The oldest oceanic crust is about 340 Ma old, in the eastern Med basin; most oceanic crust is quite a bit younger. This makes sense because we observe that oceanic crust is preferentially destroyed by subduction (look up a ",
"primer on plate tectonics",
" for an overview).",
"The oldest continental crust we've found so far is 3.8 Ga old, in the eastern part of the Canadian Shield",
" - that's ... pretty old. But the age of that oldest rock is complex and layered. The 3.8 Ga age is an U-Pb age of crystallisation, the age at which the magma solidified into a rock (it was a volcanic rock). But the very same sample was dated using another method (Nd/Sm geochronology). This yielded an age of 4.38 Ga - the meaning of this second age is different from, and complementary to, the first one. What this Sm/Nd age indicates is the time at which the volume of magma which ended up in that rock was extracted from the Earths mantle.",
"That 4.38 Ga age is extremely interesting, because we have also been estimating the age of the earth by dating meteorites, which we believe to be leftover material from the building of the Solar System. And the age of formation of most meteorites (4.5 Ga) is getting pretty close to that of the oldest dated event on Earth (4.38 Ga). Those specific rocks, located in the Nuvvuagittuq Greenstone Belt, were found about ten years ago; we might find older material still in the years to come. But we expect the age of older materials to be somewhere within that range of 4.38 to 4.5 Ga.",
"So ... back to your initial question:",
"We have been measuring the age of earth by looking at the layers of ground, how do we know there aren't any older evidence underneath the thick snow of North pole?",
"Well, we don't. And that's why people like me and my colleagues keep studying northern rocks. Although it is worth pointing out ",
"the North Pole is in the Arctic ocean",
", and not above a continent. But the rocks of the Arctic seafloor are under study, as are the rocks of the surrounding landmasses.",
"Or the deepest ocean floor that human has yet to discover?",
"As I mentionned earlier, oceanic rocks tend to be destroyed much faster than continental ones. They are still being studied of course, and any abnormally old rocks in the oceanic crust which might be found will certainly be the object of intense scrutiny.",
"Or even unknown creatures that lived before the dinosaurs..",
"You're in luck there. The dinosaurs lived from about 230 Ma ago to 65 Ma ago, but the fossils of complex life forms are quite abundant and diversified in the preceeding time period starting around 541 Ma ago. During this earlier period in the history of life, critters started off in the oceans and eventually colonized the land. New species and genera are identified and described every year by paleontologists. You may want to have a look at the following references, and look up trilobites, anomalocarids, crinoids, orthocone cephalopods, graptolites and brachiopods, for starters:",
"https://en.wikipedia.org/wiki/Paleozoic#Periods_of_the_Paleozoic_Era",
"http://www.fossils-facts-and-finds.com/paleozoic_era.html",
"http://www.ck12.org/biology/Life-During-the-Paleozoic/lesson/Life-During-the-Paleozoic-BIO/",
"http://www.ucmp.berkeley.edu/paleozoic/paleozoiclife.html"
] |
[
"Or even unknown creatures that lived before the dinosaurs..",
"Other users can handle the geology question, but for this I'd like to point out that ",
"Dinosaurs only showed up fairly recently on the time frame of the history of the entire Earth,",
" and we have discovered countless animals that predate them by millions of years. We are constantly making new discoveries about early life on Earth, including this very year, discoveries showing that life began ",
" of years ago. However, the fossils from billions of years ago are all basically just microscopic remnants of little microscopic single-celled organisms. Still plenty of complex animal life before dinosaurs though, lots of ",
"weird sharks",
", ",
"giant bugs",
" and ",
"monster fish",
" and things. Always more to discover.",
"You'll definitely be interested in ",
"this wikipedia page, the Timeline of the evolutionary history of life",
"!"
] |
[
"A million years is a Mega annum (Ma)",
"A billion years is a Giga annum (Ga)"
] |
[
"If we only drank water every three days, how much would we have to drink?"
] |
[
false
] | null |
[
"This question depends on so many things. What kind of activities are you engaging in each day? Are you eating food that contains water at the same time? Average temperature of your surroundings? How much does this hypothetical person weigh/gender/age/metabolism?"
] |
[
"Wow, I can't believe I didn't think about those things to add them in, thanks, I'll edit."
] |
[
"How about if we assume an \"African bushman\" lifestyle? Surely our species had to survive for a while without water 50,000 years ago."
] |
[
"Is it possible for a star to orbit a rocky body?"
] |
[
false
] |
Would it be possible for a mass that can sustain fusion orbit a rocky body given the mass of the rocky body would need to be greater?
|
[
"Technically, one body doesn't orbit another; they both orbit their common center of mass. But for a planet orbiting a star, this center is basically at the position of the star.",
"Whether a body will undergo fusion or not is dependent on its mass. If it gets big enough, it becomes a star.",
"Basically, no rocky body could have a mass that even slightly approaches that of a star. The gas giant Jupiter has a solid core, but the bulk of its mass is gas, and it is a long way short of being a star. ",
"It would be possible for a white dwarf and a companion star to orbit each other, but a white dwarf is not 'rocky'. The center of mass would be somewhere in between them, and it probably would not look like the star was orbiting the dwarf.",
"So the short answer is no. Sorry ..."
] |
[
"No there couldn't, stars attain fusion due to their mass, so if something weighs enough for a star to orbit it because it is heavier then that object will also be undergoing fusion, in other words it will be a star. "
] |
[
"No there couldn't, stars attain fusion due to their mass, so if something weighs enough for a star to orbit it because it is heavier then that object will also be undergoing fusion, in other words it will be a star. "
] |
[
"Is there a hormonal difference with people who live in consistently cold climates compared to people in warm climates?"
] |
[
false
] |
It seems like (just an example) eskimos compared to natives in the tropics have extremely different body structures; even though it could be simple an evolutional difference. I am just wondering if their bodies have different homeostatic levels of hormones.
|
[
"Based on day-night cycles, there is absolutely a difference.",
"http://www.ncbi.nlm.nih.gov/pubmed/7982827",
"Additionally, vitamin D from sun exposure can affect metabolism, bone growth, mood disorders and a number of other things potentially blamed on \"hormones\"."
] |
[
"what about person who has moved from warm climates to severe cold climates? how do they get ill affected and what remedies can be done to counter these changes? "
] |
[
"Simple and even folk remedies are often effective enough, in my understanding. Drinking vitamin D milk or using tanning beds can help, as can artificial lighting to prevent Seasonal Affective Disorder. All-in-all, humans are very adaptable and the changes will be readily made in time.",
"http://www.mayoclinic.com/health/seasonal-affective-disorder/DS00195"
] |
[
"Is the threat of a nuclear EMP attack as serious as they say?"
] |
[
false
] |
I understand that a nuclear explosion puts off an Electro Magnetic Pulse that radiates around it and can negatively effect (if not disable) surrounding electronic devices. Though my impression was that once the EMP was past, you could just just restart your computer or turn back on your tv with the consequences that you might have to replace a few fuses. However, I then started hearing US National Security Experts talk about how a single bomb, detonated a couple hundred km up, would create an EMP that could cripple virtually the entire country for years. "An electromagnetic pulse (EMP) attack on the American homeland, said one of the distinguished scientists who testified at the hearing, is one of only a few ways that the United States could be defeated by its enemies – terrorist or otherwise," wrote Sen. Kyl "And it is probably the easiest. A single Scud missile, carrying a single nuclear weapon, detonated at the appropriate altitude, would interact with the Earth's atmosphere, producing an electromagnetic pulse radiating down to the surface at the speed of light. Depending on the location and size of the blast, the effect would be to knock out already stressed power grids and other electrical systems across much or even all of the continental United States, for months if not years." From this and other sources, I get that they are implying that all ROM chips, SSDs, unshielded storage, etc would be wiped. Thus all bits of machinery and electronic equipment that runs our everyday lives would "forget" how to do their jobs and virtually all technology (including cars) would be useless until they were repaired (had their ROMs replace/reflashed) - thus not just a simple 'restart'. I'm a bit of a skeptic, so I question it when someone who's authority comes from worrying people with threats of attack, tell me about the potential damage of an attack. Can anyone give me an accurate scientific understanding of just how devastating such an EMP attack really would be to our lives? EDIT: Found but I only understand about half of it.
|
[
"EMPs don't erase ROMs. They physically destroy chips. The parts would have to be outright replaced, not reprogrammed."
] |
[
"Ok, so all personal computers, cell phones, ... basically anything more sophisticated than a toaster will be useless until you replace the ROMs in them?",
"Any insight into the radius of such an effect?",
"I've heard it said that one exploded over Kansas would affect the entire continental US. Does \"affect\" mean \"All devices in the country would be broken\" or \"If you live outside of Kansas and the surrounding 6 states, your power would go out for awhile.\" or something in between?"
] |
[
"First, the devices would be useless period; we would have to outright replace all damaged circuits.",
"As for the affected radius, I don't know. But wikipedia mentions that Starfish Prime damaged electronics ~1,300km away."
] |
[
"What properties of matter dictate it's malleability/ductility?"
] |
[
false
] |
I had assumed it would correlate to density, but after some preliminary research it apparently isn't that simple.
|
[
"The properties of metals (and of most solids) are determined by the material's ",
"crystal structure",
". The effects of crystal structure can be expressed in both macroscopic and microscopic terms. ",
"On a macroscopic scale (what makes this beam/girder/bar) ductile/malleable: the macro properties depend on how the crystal grains (of which any metal is composed of) are formed and arranged. Operations such as tempering, annealing, and hardening of metals are simply modifications of the metal's grain structure. Large grains tend to make metals more malleable. ",
"On a micro scale: the symmetry and density of the crystal structure determine malleability (and the other properties) of materials. So your density guess is a tad accurate. Densely packed crystal structures with high degrees of crystal symmetry tend to be more malleable and conductive (e.g. metals). Low symmetry low density crystals tend to be brittle and inusulators (e.g. minerals). ",
"Here are a couple of other resources. Cheers:",
"Metal Crystalline Structures",
"Metal Grain",
"."
] |
[
"Turbine and Simon seem to have pretty much nailed metals but I think it's worth mentioning that there are materials that, for a few different reasons, defy that type of analysis. ",
"Within the category of \"crystalline\" materials, there is variation in the type of bonding, which is heavily dictated by electron structure. Metallically bonded crystals obey very strongly the rules Turbine stated. Ionically and covalently bonded structures go a little bit wonky.",
"Metallic bonding is basically non-directional whereas ionic and covalent are highly directional. As such, ionic and covalent crystals tend to be hard and brittle, even with a relatively dense and ordered structure. It's been a while since I did much on ceramics so I'd love to see a ceramics panelist take on the intricacies of mechanical properties of non-metals.",
"There are also solids that fall somewhat outside the category of \"crystalline.\" A vast majority of polymers are at least partially amorphous (that is, have no long range order). Polymers are very difficult to classify and quantify and have an incredible degree of variety in properties. It seems risky to go into a full description of polymers for fear of jumping off the deep end but to answer your question as succinctly as possible: Imagine a box of uncooked spaghetti. It's rigid and stiff like a bundle of sticks. You really can't stretch it; all you can do is just break it. Now imagine cooking the spaghetti. Get it as soft as possible. You can stretch it and you can break it and if you give it time, it will flow like a really gooey liquid. That's the spectrum of polymers. Really gooey flowy liquid-type stuff to super stiff stops-bullets-type stuff. And actually, that's a not so terrible approximation of their structure. Except imagine that all those spaghetti are different length, and some of them have mini-spaghetti branching off, and some strands are glued to other strands, and sometimes you have a mixture of uncooked and cooked strands all mixed together."
] |
[
"To add to Turbine_Heart, the malleability and ductility also have to do with microscopic imperfections in the crystal structure called \"dislocations\". Visually this look like snakes or cracks. Dislocations form when ever there is relative movement between nodes in the crystal structure like in fast cooling of a hot metal, or bending. When dislocations form they \"travel\" through the crystal and are impeded by different imperfections in the material such as other dislocations, grain boundaries, or interstitial materials (such as ",
"metal matrix composites",
". When ever the movement of a dislocation is impeded, the material becomes less ductile.",
"A good example of this is a perfectly ",
"annealed",
" 1\" diameter bar of copper. The annealing process allows all of the dislocations to travel, meet up and annihilate each other resulting in a much more ductile material. You can easily bend it by hand which generates many, many dislocations in it's structure. These dislocations then make it very difficult or impossible to bend the copper bar back by hand."
] |
[
"What exactly happens when you hit the Ulnar Nerve (aka Funny Bone)?"
] |
[
false
] |
Hey Reddit, I was wondering if you could help me out with this one. I know how a nerve is stimulated, and how action potentials are propagated down nerves to send signals, but what I don't understand is why when you hit your "Funny Bone" it only sends those signals one way (towards the hand, where the nerve continues/innervates). My main question is: Does anyone know why this pain doesn't shoot up the arm and towards the body? I can't find it in any textbooks, I can only find why it shoots down the arm/towards the hand. If you're pinching that ulnar nerve, why wouldn't it cause pain up AND down, or even just more localized than sending the signal down? Thanks Reddit!
|
[
"When the ulnar nerve is hit with force in the elbow region, most of the nerves that are passing through that point are stimulated. This means that the nerve sends a signal to the brain, which is interpreted as pain/dysaesthesia in the region the ulnar nerve innervates. \nThis is why you feel part of your hand tingling. Not because the nerve sends signals to the hand, but because it sends signals to the brain. Nothing happens to the hand, it is just your brain misinterpreting phantom signals from the ulnar nerve."
] |
[
"You would be correct, I didnt see your post before I answered. I could have saved some time and just given you my upvote hahah."
] |
[
"When your elbow is bent, the ulnar nerve gets trapped between the bone and your skin. When you whang your bent elbow on something (this is extremely technical), it triggers action potentials in the axons (nerve fibers) that are compressed.",
"There are two types of axons in your ulnar nerve: ",
" (from the skin) axons and ",
" (to the muscle) axons. Cutaneous axons transmit sensation from your skin to your spine. When you whang a cutaneous axon it causes ",
"paresthesia",
", which is doctor for \"tingling\" -- this is the primary sensation you're describing in your question. When a cutaneous axon is triggered by whang, it makes your brain think that something weird happened in the part of your body that the cutaneous axon originates. In contrast, motor axons transmit orders from your spine to your muscles. When you whang a motor axon it causes ",
"fasciculation",
", which is doctor for \"twitch\".",
"Ok, so let's get back to your question. ",
" We know that the tingling is caused by cutaneous axons. All the cutaneous axons that pass through your elbow are (probably, who the fuck knows) coming from your hand/forearm. It would be just silly for a patch of skin on your shoulder to send an axon down to your elbow only to go back to the spine. Thus, when you whang your elbow, you only feel tingling in your hand and forearm.",
"We can also ask another question. ",
" ",
"This paper",
" (which is a ludicrously thorough study on the funny bone and the source of much of this post) found that the motor axons actually seem to have a higher mechanostimulation threshold.",
"I hope that answers your question!"
] |
[
"Do people retain information better depending on the color of light source they're under?"
] |
[
false
] |
I'm not sure if that's a dumb question or not.
|
[
"It's worth noting that Osram is an enormous (the biggest?) lighting manufacturer and has a large incentive to create markets for new speciality lighting systems. "
] |
[
"I don't think that's dumb at all, rather interesting, but complicated question!",
"There's ",
"that",
", a study of the effect of \"biological lighting\" on students, so that's close-ish to what you ask..."
] |
[
"Certain people?? With certain unique conditions? Possibly. Edit: synesthesia can give color unique effects on perception.",
"It's important to clarify the question here. If your asking if different conditions such as the color of light or colors in general can effect mood and mind then.... Yes...",
"It is believed that cool color tones and skin tones are soothing, which is why they are used in psychiatric facilities. ",
"Now the optimal retention of information can be achieved by thinking of stress on a bell curve. If you are incredibly stressed, you will not retain information as reliably, if you are sedated or very relaxed, you can see the same effect. You want to be stressed, but not too stressed, between reading a book and going for a jog...",
"So my answer is this, if you are a very mellow or relaxed person, consider painting your office/work space a bright, hot color! If you are a stress case, use a cool color! ",
"I personally require extra stimulus when I work. A little background noise can go a long way! "
] |
[
"What is the scientific definition of odourless?"
] |
[
false
] |
I recently had an inconclusive discussion about the nature of odour, and the question came up; is 'odourless' based on whether a human/known animal can smell it, or is it actually a chemical property which makes a compound odourless to every possible lifeform?
|
[
"Visible light spectrum/infared and how animal can or cant. I suppose you could use the same way of thinking a \"smell\" spectrum?"
] |
[
"Odor or smell is not a real property of anything. It is based on our perception. ",
"Our noses contain receptors that can bind certain chemicals that causes our brains to perceive a \"smell\". Different chemicals that bind in different combinations to these receptors causes different smells to be perceived by our brain. If there is a certain chemical that cannot bind to any of our limited receptors in our nose then it is considered odorless. "
] |
[
"I dont think a \"smell\" spectrum might work. we can measure light objectively but i havent heard of an instrument to measure odor. you can measure the concentration of known smelly compounds, but besides expirience there is no way to tell if comp A stinks worse if comp B is also present and so on.",
"Also the human sense of smelling is far less universally equal then seeing. i for one cant smell hydrogen cyanide, which can be dangerous for a chemist."
] |
[
"Can someone explain how DNA/RNA microarray imaging works using laser excitation? How does one go from a hybridized cRNA transcript to an intensity value?"
] |
[
false
] |
Basically, I understand the principles behind hybridization of transcripts to microarray probes, but how does the imaging machine excite the fluorescence and correlate such a dense sample set to intensity values for expression analysis?
|
[
"This question might be better suited for ",
"/r/askscitech"
] |
[
"Get cDNA, label with fluorescent dye, hybridize. Excite array with usually blue light, take a picture through a green filter and magnifying lens with a CCD camera. Camera converts light signal as a function of position to intensity values for you."
] |
[
"The probes are labeled with fluorescent dyes, i.e. molecules that emit a certain wavelength of light when stimulated with a different wavelength of light. The intensity of the emission, which ought to correspond to the amount of probe that hybridized, is measured with a camera.",
"I'm not sure what you're asking beyond that, and I don't think I can answer in a greater level of detail, but if I may take a slight tangent, you should know that microarrays are on the way out (already long gone in many places), replaced by high-throughput sequencing for basically all the applications they could do plus a lot more they couldn't."
] |
[
"Why do photons always move at the same speed?"
] |
[
false
] | null |
[
"Special relativity says that a particle with zero mass must always move at c."
] |
[
"It does answer his question, because it tells OP what to look for. This is how scientific articles work. It would not be reasonable to describe the entire underlying theory for your work in a publication, the article would become way too long. Instead, you have several dozen references to other articles that your work is based upon, and only explain what is necessary in your own words."
] |
[
"It does answer his question, because it tells OP what to look for. This is how scientific articles work. It would not be reasonable to describe the entire underlying theory for your work in a publication, the article would become way too long. Instead, you have several dozen references to other articles that your work is based upon, and only explain what is necessary in your own words."
] |
[
"Why can't we harvest energy from lightning?"
] |
[
false
] | null |
[
"We can, we just can't store enough of it to be meaningful.",
"Lightning is a huge amount of energy over a very very short period of time.",
"We can capture some of it, but we don't have the battery capacity to store it, or a battery capable of being charged that fast without melting",
"Catching the energy is fairly simple, lightning rods do it all the time, storing it is impossible given current tech."
] |
[
"True, but I sorta figured that he was asking why we didn't use lightning as a source of power."
] |
[
"Imagine the infrastructure you would need to capture a lightning bolt and put it on the grid. First, you would need some kind of a tower capable of carrying thousands of amps of current. This would feed into a huge capacitor bank with a few gigajoules of capacity at hundreds of millions of volts. Based on my calcs, it looks like the best option would be something like the General Atomics 3330CMX2205 high voltage capacitor (",
"https://en.wikipedia.org/wiki/Power-to-weight_ratio",
"). Even with the insane power-to-weight of 6.8MW/kg, absorbing the ~5 terawatts in a lightning bolt would require about 700 tons of capacitors!!! You would then need to have high-voltage power electronics to convert this electrical energy to a more useful voltage. Admittedly, it would be simpler to use the energy to heat something and then generate electricity from steam, but it would be considerably less efficient. Either way, it's a lot of expense and effort to harvest a few lightning strikes each year, which would equate to the energy in only a few hundred litres of petrol. TL;DR lightning is awesome, but forget about using it for much"
] |
[
"Do we know much about the limits of human physical achievement with supplemental oxygen?"
] |
[
false
] |
My friend and I were out for a 10 mile run today, and we started talking about what would happen if you took a champion runner (any aerobic distance) and had them run the same race with supplemental oxygen. How fast could they go? If pure or highly enriched oxygen were available, what would be the limitation on their speed? Could a human run a 10k race or marathon at the same speed as a sprinter?
|
[
"In general, oxygen will help slightly but there are many factors involved in such athleticism. For a 10k race, your metabolism changes drastically throughout the course of such exercise. First you will burn through your ATP stores. Second you will begin to use glycogen, and third fat. This is a limiting factor as these methods of energy use require more oxygen and are generally not as \"fast\" as burning sugars. So - this is your energy that you will use to run. You will need oxygen to \"burn\" this energy and turn it into useful ATP.",
"Oxygen delivery to tissues is generally limited by ",
" to the lungs and subsequently the tissues.",
"I am going to assume you know some anatomy here, I don't feel like explaining that. In pulmonary capillaries hemoglobin is oxygenated essentially to it's full carrying capacity within .25 seconds at sea level barometric pressure of 760 torr and 21% O2 content (Amazing isn't it!). Considering hemoglobin accounts for the vast majority of oxygen carrying capacity in the blood, this is vital to life that oxygen delivery is \"Perfusion limited\" instead of \"diffisuion limited\" in the lungs.",
"Basically, supplemental oxygen will slightly increase the amount of oxygen delivered to tissues, but an increase in cardiac output in the form of faster beating with higher volumes will help you deliver more oxygen.",
"OK now that we have discussed both of those ideas, athletes are pushing both their metabolism and cardiovascular systems pretty hard during a run such as a 10k or marathon. Supplemental O2 will not help nearly as much as a healthier heart and better metabolism - under normal circumstances.",
"If you are still wondering why this is, feel free to contact me.",
"Source: Medical physiology class, medical biochemistry class"
] |
[
"My lab has done research in which we provide supplemental oxygen to elite and amateur endurance athletes at a level that would mimic 17,000 ft below sea level. The improvements were equivocal or marginal at best. Oxygen delivery isn't the main limiter of human performance. In fit people it's not an especially significant limiter even. The best guess we have for the marginal improvements we did see are that it's a neurological effect. The same reason supplemental oxygen makes you euphoric, it's a mild stimulant."
] |
[
"When I was taking a scuba class I had an old fart of an instructor, and one time he was talking about diving in his younger days and how after a night of heavy drinking, him and his buddies would simply take a few huffs out of an O2 cylinder and their hangovers would almost immediately be alleviated...given that breathing pure oxygen won't significantly increase the carrying capacity of hemoglobin, how else can this be explained?"
] |
[
"Why can't fusion happen with elements heavier than iron?"
] |
[
false
] |
[deleted]
|
[
"That’s not a true statement, you can pretty much fuse anything with anything. However the Q-values for fusion reactions of two heavy nuclei tend to be negative, so the reactions are endothermic. So that makes these heavy ion fusion reactions undesirable for applications where you want to use the reactions to release energy.",
"The reason why people specifically mention iron is that the binding energy per nucleon curve for near-stable nuclei peaks around the stable isotopes of nickel and iron. ",
"However I’ll warn that the common claim that “fusion up to iron and fission down to iron release energy” is oversimplified."
] |
[
"Unfortunately, most of what you’ll find on the internet just reinforces the oversimplified statement that I mentioned. Rather than trying to fit all of the behavior of reaction Q-values into a soundbyte, I’d recommend just playing around with Q-value calculators like ",
"this",
". You can use that for arbitrary nuclear reactions (at least ones where the masses of all involved particles are known). If you play around with it, you can find some “fission” reactions for nuclides lighter than the stable iron/nickel isotopes with positive Q-values, and same for “fusion” reactions with nuclides heavier."
] |
[
"That’s interesting. Do you have any web sources that explain this further?"
] |
[
"How are orbiting objects not accelerating due to gravity?"
] |
[
false
] |
We constantly describe orbits as falling, but going so fast horizontally, that you miss the planet. When you fall you accelerate towards, but satellites in a perfect circular orbit are traveling at a constant speed.
|
[
"You're simultaneously asked two questions, let's address the first.",
"We constantly describe orbits as falling, but going so fast horizontally, that you miss the planet. When you fall you accelerate towards, but satellites in a perfect circular orbit are traveling at a constant speed.",
"Acceleration doesn't necessarily mean you change speed, it acceleration manifests if you change speed and/or direction. In a perfectly circular orbit, you are undergoing centripetal acceleration and only changing direction.",
"The second question is a little deeper. Arguably, any object following a geodesic (free trajectory) in general relativity is by definition ",
" accelerating. This includes free falling objects and orbits—where tidal forces are insignificant. Well how can that be? Does an apple not accelerate towards the ground when you drop it?",
"We can nicely wrap all gravitational acceleration as curvature, therefore the \"proper acceleration\" of a falling apple is ",
"! It's just following a straight line, inertial free fall. To the apple, it feels weightless and under no force. Here's a neat video explaining this:",
"\n",
"https://youtu.be/jlTVIMOix3I",
" "
] |
[
"Acceleration is a change in velocity, not speed. Velocity is a vector quantity (i.e. it has both a direction and a magnitude) and so the change can either be in the magnitude (a change in speed) or the direction. Unfortunately, we don't have a separate word for the vector acceleration, so that fact that you associate acceleration with a changing speed (scalar 'acceleration') makes this less intuitive.",
"Only force in the same direction as the movement will change the speed; however, in the case of the orbiting satellite, the force and velocity are always at right angles, so only the direction changes."
] |
[
"If you are changing direction constantly, like in an orbit, you are accelerating as velocity also has a directional component, and acceleration is change in velocity. ",
"This is why you can simulate gravity by being a rotating structure around a spaceship, as depicted in many movies (2001, Interstellar, and others). People in the rotating structure are \"orbiting\" and the constant change in direction produces a feeling of acceleration which in turns simulates the feeling of gravity. "
] |
[
"Is there any advantage to using anti-bacterial dish detergent over the regular (presumably non-anti-bacterial) detergent?"
] |
[
false
] |
With respect to both washing dishes and washing hands. Would the regular detergent do the job just as well? Is the anti-bacterial tag just a gimmick?
|
[
"In most cases, not really. The main antibiotic ingredient in these antibiotic soaps is triclosan, which is a really good antibiotic, just not one which we can take (its not very bioavailable). These detergents will kill more bacteria than standard detergents, in fact 2% triclosan washes are standard procedure in hospitals to combat Methacillin resistent Staphalococcus aureus (MRSA - a pretty nasty infection if you get it), but its just overkill in most home settings.",
"http://www.ncbi.nlm.nih.gov/pubmed/7677266",
"http://en.wikipedia.org/wiki/Triclosan#cite_note-44",
"So yes, it can be helpful but its not really necessary at home, MRSA isn't really likely and most germs get washed off anyway. Its just put in because its cheap, it \"feels\" healthier to the public, and it will cause no real harm. Some mention that there could be cross-resistance developed with other antibiotics, but there's no real evidence for that, the mechanism of action of triclosan and say most antibiotics taken for infections are sufficiently different.",
"http://www.ncbi.nlm.nih.gov/pubmed/15273108"
] |
[
"it \"feels\" healthier to the public",
"This is certainly why I buy it. Thanks for the info! Very helpful."
] |
[
"Breeding super bugs? Really all dish soap and very hot water works to kill bacteria and by thoughly cleaning, then drying your dishes you make them less habitable for bacteria to grow, but as soon as you touch the dishes with your hand you are reintroducing bacteria. Everything you eat, or use to eat is covered with bacteria. Your mouth and gut are even more so. There are more bacteria living in you than there are cells that make you. Don't worry too much about it."
] |
[
"What is there in between neurons?"
] |
[
false
] |
I was sitting in today's Histology course and realized that although I have this idea iin my head that neurons are apart, I don't know what is the medium in between neurons. I noticed on an electron microscopy image that they seem to be relatively tightly packed. (axodendritic and axo-axonic synapses were being explained). I suppose it depends on what type of neurons we're talking about but perhaps some of you can offer some explanation, perhaps this is a stupid question to ask but still it hasn't been explained to us and I can only offer guesses.
|
[
"You might be thinking of a ",
"chemical synapse",
". The space between two neurons making a synapse is called the ",
", and is filled with ",
"extracellular fluid",
". Mostly water, but with plasma and ions and other stuff in solution."
] |
[
"Mostly ",
"glial cells",
" (which are \"support\" cells for neurons) and blood vessels"
] |
[
"It will vary a little depending on which part of the nervous system. For example, gray matter contain the neuronal cell bodies in the brain, and it has what is referred to as neuropil between them. This is a broad term for glial cells, and a dense network of axons and dendrites. Particularly the axons and dendrites are difficult to distinguish unless a special stain is used. Interestingly enough, glial cells make up the majority of the nervous system, and which glial cells surround the neurons differs between the CNS and PNS. ",
"Myelin with also be something between neurons, but it is coming from glial cells (oligodendrocytes in the CNS and neurolemmocytes/Schwann cells in the PNS). ",
"Also, I did a little searching, and apparently there is also a ground substance present in the CNS. It is a neutral mucopolysaccharide sunstance that stains magenta with the periodic acid schiff stain. ",
"Link to the abstract.",
"Edited for grammar.."
] |
[
"So what's the big deal with genetically modified food or GMOs? Why are people against it?"
] |
[
false
] |
[deleted]
|
[
"One sensible fear is that a non-invasive species might be transformed into an invasive species. For example, if you were to engineer a species of corn that contains natural insecticides, that might turn out to be a survival advantage. That species of corn might end up thriving in places where corn doesn't normally thrive, and it might drive out the plants that normally live in that area. That, in turn, might kill some of the insects in that area. These are the sorts of risks that are always associated with invasive species - that they might permanently and irreversibly alter an ecosystem.",
"Of course, corn may already be so heavily domesticated that there's no chance of it surviving in the wild, even with a genetic survival advantage.",
"Genetic modification is different from modifying an organism by breeding it, because breeding is unlikely to make an organism more fit for its original environment. It may be more fit for living among humans, but not for its original environment. So breeding is unlikely to turn an already-existing species invasive."
] |
[
"As is elaborated in some of the other comments, GM crops could fundamentally change some ecosystems, which can be very carefully balanced. If GM crops are unregulated (politically, biologically, economically, or something else), they may begin to change the ecosystem and corrupt that balance, having adverse effects in unpredicted ways."
] |
[
"That's more to do with the fact that genetically engineered seed is also hybrid seed. Hybrid seed does not produce seed that is suitable for replanting (it can be replanted, it just produces progeny that aren't as good). Farmers decided, back in the 1930's or so, that buying new hybrid seed every year was better than saving their own, because not only do they not have to clean their own seed, but the hybrid seed was superior, and the companies that bred them (being specialized in that sort of thing) could continuously produce better lines. That's the main reason why farmers don't save seed. There is also the contracts, yes, but even without those saving seed wouldn't work too well. The terminator trait would actually not be as bad as its made out to be for this reason, and it would have the benefit of preventing complaints about cross pollination.",
"I don't think you can say they are worse for farmers. Like hybrid seed before it, farmers willingly choose to grow GE seed because ti benefits them. That's why they grow so much of it for varieties that are GE. Heck, in the case of corn, they grow more of the GE variety than they should. Farmers are supposed to plant a refuge area (an portion of their field that is not GE which, to make a long story short, prevents resistant pests from emerging), however, because some have not planted the refuge area like they should and decided to grow more GE crops than they were supposed to, we did get resistant pests. That doesn't really sound like something the farmers consider unfavorable.",
"You are correct in that those are reason as to why people oppose genetic engineering, I'm just saying they are bad reasons that probably would not be so prevalent if more people understood the topic a little better."
] |
[
"what would it take to build walking talking intelligent synthetic life?"
] |
[
false
] |
I realize we are a while away from such a thing. But its been bugging me for a while, so I figured I'd ask. Are there groups or people seriously discussing such things?
|
[
"Are there groups or people seriously discussing such things?",
"Yes. Quite a lot of us, actually :)",
"what would it take to build walking talking intelligent synthetic life",
"Whoa, whoa. There are like three questions here you need to separate:",
"walking",
"Better robotics. See research on bipedal robots: some that come to mind are those by Boston Dynamics, Honda's Asimo, etc.",
"talking",
"Speech synthesis is already pretty good. But to actually understand and generate intelligent speech, we need the next thing:",
"intelligent",
"If we knew how to do this, we would have it by now :). There are a set of problems called ",
"AI-complete",
", which many researchers believe are all we need: If any of those problems are solved, we can (relatively) easily achieve artificial human-level intelligence."
] |
[
"Are there groups or people seriously discussing such things?\n",
"Yes. Quite a lot of us, actually",
"where?",
"I realized I asked a lot, I just find it rather fascinating. now to be a bit clearer, I think you think I was referring to computer AI exclusively. But I was wondering more so about synthetic biology or cultured neural networks(think roborat) standpoint.",
"thanks for the input, it was really informative."
] |
[
"That's similar to asking the meaning of life and why as humans we have the will to live.\nOther than electrical signals and chemical changes in the brain responding to cognitive functions, it is impossible to say why we do what we do.\nWe have the programs in place for a robot to walk, respond to it's surroundings as in detect a wall or object etc, we have \"AI\" which can write letters and essays, even recognise and create images through a program as I recall reading a post about.\nBut for something synthetic to be self aware and thinks for it's self which I'm guessing you mean, no one will ever know I believe. \nThe prospect of AI appears to be less hopeful than 20 years ago."
] |
[
"What is happening at cellular and tissue levels in “muscle knots”?"
] |
[
false
] | null |
[
"At the neuromuscular junction between motor neurons and muscle tissue, the motor neurons release a chemical called acetylcholine which triggers the muscle tissue to contract. When the motor neuron is damaged or recieves abnormal signals (e.g. from a nerve being pinched) it releases more acetylcholine than usual which causes the muscle cells near the junction to clench without releasing, forming a contraction knot known as a trigger point. A cluster of these contractions is called a trigger point complex and forms what we think of as a muscle knot.",
"Here's a fascinating video explaining this from the perspective of treating trigger points with dry needling:",
"https://www.youtube.com/watch?v=xrFF7n29XOU",
"edit: here's a paper that nicely summarizes the topic and goes into detail about the concept of different kinds of \"locus\" within the trigger point complex that correlate to symptoms of tenderness:",
"https://www.mcgill.ca/anesthesia/files/anesthesia/wk_3c_myofascial_trigger_points.pdf"
] |
[
"Jumping on board with some simple links:\n",
"https://en.m.wikipedia.org/wiki/Myofascial_trigger_point",
" \nWiki also has some paper links. Pubmed also has a lot with simple keywords such as 'trigger point theory'.",
"I'd also like to point out that trigger point theory is very common among healthcare practitioners but is just that, a theory. Here is one criticism article I found with a quick pubmed search ",
"https://www.ncbi.nlm.nih.gov/m/pubmed/25477053/",
"It's a great basis for physical therapy. Stretching, massage, and dry needling can work well but oftentimes the muscle with the active trigger point actually needs to be strengthened in order to prevent getting \"knotted\" again."
] |
[
"I work in Physical Therapy and work with Trigger Points. I just want to second the statement that the muscle with the Trigger Point does actually need to be stretched (gently) and strengthened in its proper biomechanical position to help prevent it from occurring again. ",
"For example, if one has a Trigger Point in the Upper Trapezius muscle and has a forward head, forward shoulder (slouched) posture, all the stretching, therapy, and strengthening in the world is not going to prevent that TP from coming back because the muscle is under an increased work load. Correcting the basis of the problem, in this case, the alignment issue, and looking deeper to find the cause of the mal-alignment (habit, weakness, tightness in anterior chest muscles, etc) is key in preventing the TP from returning."
] |
[
"Does a manual car save more gas going down a hill in neutral or in gear?"
] |
[
false
] |
I've argued this with friends before, many people say putting the car in neutral while going down a hill saves gas. So the parameters of the question: Is it more gas efficient to go down the slope in neutral or in gear? Is the answer different if the slope is considerably more steep (can accelerate your care if it were in neutral?)
|
[
"Definitely in gear. Fuel would be needed to keep the engine idling while in neutral, whereas momentum will keep the engine spinning while it's in gear. The car will sense that there is no load on the engine and cut fuel off."
] |
[
"Thanks so I think we can summarize it as follows. If you are going down hill at constant speed in neutral, then switch to gear, if after switching the car is going",
"(this can be seen by analyzing what happens in each case, or simply by noting conservation of energy)"
] |
[
"This is actually incorrect, regardless of the car design.",
"The question is worded such that the hill's steepness keeps the car at the same speed, whether it's in neutral or in gear. This means that even if the car stops delivery of fuel when it senses engine braking, that would not be applicable here, because the way that cars sense engine braking is by comparing the engine speed to the throttle position - if the TPS is at 0% but the speed is a specified level beyond idle, then engine-brake mode is activated. In this case, the car would never detect engine braking.",
"So the answer is that both scenarios are equally fuel-efficient. For a steeper hill, the fuel consumption may be higher or be zero, depending on the car.",
"The problem here is that Reddit read the question, thought to it's collective self, \"I've heard this question before - the answer is that cars use more fuel in neutral,\" and then answered/voted accordingly. However, in the context of the question, this is not the case."
] |
[
"Do water droplets reach a uniform volume before gravity overcomes adhesion and the drop drips?"
] |
[
false
] |
I know that rain droplets can vary in size, but what about water dripping off of a surface? The drops seem much closer in size.
|
[
"No. The oscillations of the water left on the surface will affect the size and time of the next drip. In this way successive drops are causally linked. The time between drips will follow a repeating pattern with an increasingly long period. Eventually the period on the drip pattern will tend to infinity and the drips will no longer follow a repeating cycle. The system breaks into chaos. The dripping faucet experiment was the foundation of chaos theory and strange attractors."
] |
[
"Mind blown. Is there a maximum volume of a drop of water? "
] |
[
"Droplet size is a way to measure surface tension of a liquid. Using a syringe and water, you can cause a droplet to grow on the end of the needle until gravity overcomes the adhesive force and causes it to fall. In that case, if the water is all the same the droplets would be the same size, and the system can be simplified into a force balance physics problem. Not quite the situation you were talking about but still interesting."
] |
[
"Why aren't we using more Heliostats/Power Towers?"
] |
[
false
] |
They seem like a really cool/powerful invention. The mirrors adjusting for the sun would draw a bit of energy, of course, but the focusing of the light should more than make up for it.
|
[
"More expensive per unit energy than fossil fuels."
] |
[
"I think that article stated that a new nuclear plant is $2-3/W, and that the costs for coal plants have been \"similarly unstable\" -- not necessarily similar. Many of the stated reasons that coal and nuclear plants have been getting more expensive probably apply to solar plants as well.",
"When you see an \"11 MW\" solar plant, that doesn't mean you can get 11MW 24/7 out of it. PS10 produces about ",
"24.3 GW hr / year",
", or 2.8MW. That puts the cost at more like $1.70/W.",
"edit: Also, as you pointed out, you don't get to choose when the solar plant provides this power. Wikipedia states that power storage at the plant is achieved using pressurized steam, and can effectively store power for ~1 hr. Molten salt, according to the ",
"PS10 article",
", is only a ",
" method for power storage. Right now, long-term power \"storage\" comes from using other power plants to make up the difference when the sun is obscured."
] |
[
"Because it's cheaper (for now) to just burn more coal, oil or gas. It also needs a lot of land and, of course, a lot of sun."
] |
[
"How can a human survive a 300 degree temperature change?"
] |
[
false
] |
, there is an activity called the 300 club in which people go from a sauna to swimming in Antarctica. The body undergoes a 300 F temperature change. How is this possible without getting hypothermia or going into shock? I assume there is some internal homeostatic effect that is going on that will protect the body for a certain amount of time. The wiki says that alcohol aids in this, but I thought that warmth from alcohol was a placebo? Basically I'm wondering how it's possible!
|
[
"The human body thermoregulates and it does this extremely well. A 300 degree temperature change in the external environment, especially for a very brief period of time will hardly effect the bodies core temperature. Let's say you set your oven to 300 degrees and briefly stick your head inside, yes it's hot, no your head won't instantly heat to 300 degrees. As long as core temp remains at at an acceptable temperature and the body doesn't inter hyperthermia or hypothermia then this temeprature change would be easily survivable. "
] |
[
"To expound, in a really simplistic way. Buy a 6 pack of soda at room temperature. Throw it in the freezer for 5 minutes - take it out and drink it.",
"It will be barely colder than room temp. And soda doesn't have many homeostatic mechanisms for thermoregulation like the human body."
] |
[
"They actually go from a 200F sauna to a -100F outdoor temperature (not swimming, which would be only 32F or a bit lower if the ocean is freezing).",
"In either case, however, you go hypothermic fairly rapidly. If you jump into a sub-freezing ocean -- I've done it -- you only have one thought, and that's GET OUT NOW! Water conducts away heat extremely fast. People doing the 300 club have to wear shoes or they'll get frost bite, that thermal conduction thing again."
] |
[
"Do blind people experience a circadian rhythm?"
] |
[
false
] |
Or is there a different cycle responsible for helping manage daily fucntions?
|
[
"I've been totally blind since about the age of 5.",
"When I was about 11 I participated in a sleep study in Oregon about this, measuring the levels of melatonin via saliva samples.",
"I guess it was considered very rare to be able to wake up with the sun totally blind but I was apparently doing it.",
"As I got older though, past puberty, this ability went away unfortunately....",
"Many blind people suffer from sleep problems do to this lack of a proper sleep cycle, and also the common headaches resulting from ambient light that plague many of those who are still partially sighted.",
"Their is now medication for it under the name HETLIOZ® (tasimelteon) but it's very expensive."
] |
[
"\"Most blind people with no perception of light, however, experience continual circadian desynchrony through a failure of light information to reach the hypothalamic circadian clock, resulting in cyclical episodes of poor sleep and daytime dysfunction.\"",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3202494/"
] |
[
"Follow up question: If a blind person set an alarm and went to sleep and woke up at the same time everyday would they develop a natural circadian rhythm? If so, without the alarm after two weeks would they experience disymetry again in their sleeping patterns?"
] |
[
"Does potential energy \"count\" as energy?"
] |
[
false
] |
To clarify, if I were to lift say, a few kilograms of matter a kilometer up, and then combine it with anti-matter, would it release more energy than if I were to combine it on the ground?
|
[
"I somehow miss your sub-question, and I gave an answer. I will keep some of what I wrote there, maybe you will like it.",
"Maybe you didn't realize it, but gravitational energy is also consider/named potential energy. Why? because it has the potential to generate a force (gravitational force in this case) if you put an object in a gravitational field, it will be attracted to the effective force generated from all the gravitational potential in there. ",
"Why is it so intriguing?, well it has point out that if you count this potential energy into the evolution of the universe, we could reach a total amount of 0 energy at the beginning. And that is outstanding. Because it means that the Universe was created from nothing.",
"Edit: Read DocSmile answer"
] |
[
"Somewhat related to your question: Did you know that a compressed spring becomes heavier by e=mc",
" "
] |
[
"Yeah, it's the sub-question that I am curious about.",
"So when the potential energy of something goes up, e.g. Going up a mountain, does it's mass go up?"
] |
[
"Is it harmful to live close or under high-voltage power lines?"
] |
[
false
] |
Is it harmful to one's health in any way at all to live near them? I'm talking about the one's that are high in the air not the residential one's that you can climb with a ladder.
|
[
"\"I've talked to one of my professors who did a proof in class which showed that it isn't possible for the transmission lines to affect you.\"",
"Without reproducing his reasoning, that's a rather hollow statement."
] |
[
"This is a single study I found, submitted to BMJ, I'm not at my home institution so I couldn't read the whole thing but i'll leave it here.\n",
"http://www.bmj.com/content/330/7503/1290.abstract",
"This study did find a 1.69 factor increase in lukemia of those living within 200m of a high voltage power line.\nHopefully more people can weigh in as well."
] |
[
"From the cited abstract:",
"There is no accepted biological mechanism to explain the epidemiological results; indeed, the relation may be due to chance or confounding.",
"http://www.who.int/mediacentre/factsheets/fs322/en/",
"From the factsheet:",
"However, the epidemiological evidence is weakened by methodological problems, such as potential selection bias. In addition, there are no accepted biophysical mechanisms that would suggest that low-level exposures are involved in cancer development. Thus, if there were any effects from exposures to these low-level fields, it would have to be through a biological mechanism that is as yet unknown. Additionally, animal studies have been largely negative. Thus, on balance, the evidence related to childhood leukaemia is not strong enough to be considered causal."
] |
[
"How do carrion birds and other scavengers keep from getting sick?"
] |
[
false
] |
Doesn't decaying meat have all kinds of nasty things in it that make animals sick?
|
[
"Typically they have extremely low pH in their stomach acids which is enough to kill off pathogens which would be harmful to humans.",
"Carrion feeders like Vultures have stomach pHs of around 1-2 (",
"Houston and Cooper 1975",
"). More standard carnivores like lions also have pH around 1 in their stomachs, whereas a human's is up near 3/4."
] |
[
"As BillTheDoor says, low pH stomach acids is there main defence. As an added defence, most carrion birds are bald (that's what gives them that evil look) so they can stick their heads inside a carcass and not get a bunch of nasty stuff trapped in their head feathers.",
"Most animals that eat raw prey have pretty strong stomach acids. Humans lost that after we started cooking our food. That's why we have to be so much more careful about eating meat. "
] |
[
"It's a natural adaptations to their diets, they produce stomach acids with a lower pH than non-carnivores. ",
"Stomach ulcers are actually caused by a bacterial pathogen, Heliobacter pylori. So I don't believe the different pH would have any impact on ulceration rates."
] |
[
"How do sensory neurons exactly communicate? (contrary to motor)"
] |
[
false
] |
Effector(motor) neurons send neurotransmitters, like acetylcholine which is absorbed by muscles inducing the sacroplasmic reticulum to release calcium which exposes actin binding sites for the myocin heads to bind and crawl up (using ATP.)--> contracting muscles. But how do sensory neurons instigate one and other? What neurotransmitter do they use? How does the chemical reaction work backwards from the source to the brain? I couldn't find much information about sensory neurotransmitters. Would greatly appreciate if someone could point me in the rigth direction. I fear, could there be several different neurotransmitters specific to heat/pressure/oldfactory, etc. protien complex sensors?
|
[
"In addition to efferent motor neurons, there are afferent sensory neurons. There are a number of different types, but for the sake of simplicity, we'll just assume they all work the same. The sensory system has less to do with what neurotransmitter, and more to do with what stimuli the neuron responds to. There are inhibitory neurotransmitters (GABA, Glycine), and excitatory neurotransmitters (glutamate). This can be thought of as an on/off switch of sorts. So if a particular neuron can detect a stimulus, then it will fire. If not, it will do nothing. There are many different receptors - light, pressure, vibration, etc. - and if they are stimulated, they lead to release of an on or off neurotransmitter."
] |
[
"I understand. Would you happen to know what neurotransmitters are specific to sensory only? Not inhibitory but exciting neurotransmitters. Also, im under the impression that the neurotransmitters aren't specific to which receptor initiates a stimulus. Your indication \"more to do with what stimuli the neuron responds to \" suggests it's all in the wiring of afferent neurons and less of the \"type of switch\" they respond to. Thank for your reply!"
] |
[
"Far and away the most common neurotransmitter for sensory neurons is glutamate. Almost all neurons with far-reaching projections (think, from your toe to your brain stem) work via glutamate. Motor neurons work via acetylcholine (ACh). They dump ACh onto muscles across the neuromuscular junction, causing them to depolarize and contract."
] |
[
"To what extent is the saying 'You are what you eat' true? How much of me is molecularly rearranged chocolate milk?"
] |
[
false
] |
I'm mostly looking for a qualitative answer, but if numbers help, let's say 150 lb person who eats a 2500 calorie diet, 500 of which come from chocolate milk.
|
[
"Ok, let's break down what's in the chocolate milk, shall we?",
"Water: most of the water we take in makes it out unchanged, or if it is incorporated, is kicked out soon thereafter.",
"Carboyhydrates: broken down and metabolized for energy. The carbon leaves in your breath as carbon dioxide, the oxygen and water are combined into water, see above.",
"Fats: Mostly metabolized for energy, either instantly or for storage. Depending on your body fat, could linger for years. Some essential fatty acids are incorporated into your bodily tissues, but these are relatively minor by mass.",
"Protein: Mostly kept. Broken down into amino acids and used to build bodily proteins. Eventually degrade and are flushed out, but likely to stay in your body for years.",
"Calcium and Phosphorus: If you're still growing, these are likely to end up as bone mass. If not, they will be retained to a much lower (though nonzero) degree.",
"Vitamins: Retained if you are deficient. If they vitamins are present in excess, they will be excreted.",
"Milk is only about 3.5% protein, and 3.5% fat, so the bulk of the calories in chocolate milk are coming from the carbohydrates, which as described are broken down and excreted. So qualitatively, the answer to 'how much of me is chocolate milk' is 'not very much'."
] |
[
"Thank you!",
"I'd never made the connection between carbon in carbohydrates and carbon dioxide when we exhale. That's cool. ",
"It seems like your answer kind of approaches the chocolate milk as a one-time intake. But what if it's a consistent flow that reaches a 'steady state' presence in my body. Old chocolate milk carbs get burned and replaced by new chocolate milk carbs. Does that change your answer much? "
] |
[
"Food intake is discrete, yes. We eat a meal, it's consumed for energy. That energy is used and the excess is stored as either fat or glycogen, and once the initial meal has been digested, those reserves are tapped to continue metabolism between meals.",
"If you were somehow managing a steady-state intake of food, I don't know that human metabolism would handle that properly; we're really meant for a feeding-fasting cycle."
] |
[
"Is it possible to boost the speed of sound up to the speed of light?"
] |
[
false
] | null |
[
"There is reason to believe that the fast any sound can get is ",
"57% the speed of light",
", but this isn't rigorously proven. It may be faster in extreme environments like the cores of neutron stars."
] |
[
"You’re in a photon gas right now. Photon gases are everywhere, they’re not particularly “extreme”."
] |
[
"What if the ligth is slowed down by some means? Can sound travel faster than the ligth it is using as a medium?"
] |
[
"The vehicles used in the cleanup after the Chernobyl disaster (1986) are still too radioactive to be around safely. Is this beacuse the metal in the cars has become ionized, or is there radioactive material embedded in them?"
] |
[
false
] | null |
[
"After the Tokaimura nuclear accident, where several Japanese nuclear workers were exposed to neutron radiation because of a criticality accident (a nuclear chain reaction), scientists were able to estimate the dose each worker received by examining the 5 yen coins in their pockets, the neutron radiation created some radioactive Zinc-65 in the coins.",
"Tokaimura accident: Neutron dose estimates from 5-yen coins"
] |
[
"Do you know which material in the vehicles have been activated? Are there any radioactive isotopes of iron? Or would it be trace metals that have become activated?"
] |
[
"Do you know which material in the vehicles have been activated? Are there any radioactive isotopes of iron? Or would it be trace metals that have become activated?"
] |
[
"AskScience AMA Series: I am /u/CosmoSounder and I study the processes inside supernovae. Ask Me Anything!"
] |
[
false
] |
Hi everyone. I do theoretical and computational work on supernova neutrino oscillations and nucleosynthesis. I have worked with trying to predict the neutrino output of a star undergoing the early stages of supernova, and am currently working on a project that will examine the feedback process between neutrino oscillation and nucleosynthesis in supernovae. I should be available between 12-2 EDT (17-19 UTC). AMA!
|
[
"Hi ",
"/u/CosmoSounder",
", thank you for doing this AMA. I am about to start my undergraduate degree in astrophysics and am completely obsessed with the field and especially the physics of stars.",
"I recently asked a question on AskScience that didn't gather much interest and was wondering if you could maybe give a little insight? My question is on Thorne-Zytkow objects - a supermassive red/blue giant that has swallowed up a neutron star into it's core. Does the neutron core have any effect on the normal lifespan of said star, could it produce an outward pressure that would keep the parent star 'alive' past what should have been it's end?",
"I was also under the impression that the window of mass in which a neutron star can exist is quite small (within 1 solar mass?), so wouldn't the neutron star accrete matter from the parent star and by doing so push it over the TOV limit, therefore rendering these objects an effective impossibility?"
] |
[
"So this is actually outside of my area of research, I actually don't really know anything about Thorne-Zytkow objects, so everything that follows is pure conjecture based off what I know of neutron stars, Giants, etc. ",
"The neutron star core will almost certainly affect the remining life span of the Giant. It'll be a small change though since a red/blue giant is already a late phase in a star's life, after it has exhausted core hydrogen burning. The neutron star surface temperature is much hotter than the cores of a typical giant so you're going to see increased fusion at the border and rarer kinds of fusion events. The effect of this will most likely ",
" the remaining life of the giant rather than extend it. ",
"As for the range of masses of neutron stars, this is actually still a matter of research but it appears that neutron stars can exist anywhere from ~1 - ~2.5 Solar masses (I don't recall exact numbers) and can even go higher than this if it is maximally rotating. So depending on the status of the neutron star in the core and how much pressure it feels from the giant envelope above it it could be stable for a while, but eventually you will get a situation where the nuclear ash (byproducts of whatever fusion reaction is happening in the layer above the neutron star) will push the neutron star over the max mass it can support and it will collapse into a black hole. This doesn't make them impossible, it just means we know what the end result of such an object would be. "
] |
[
"So if you look at the table of the ",
"standard model",
" you'll see that there are three different \"flavors\" of neutrino, electron, muon, and tau. We also know that there are three neutrino masses, and since physicists are creative we call them mass 1, 2, and 3. The problem is that the mass states don't line up with the flavor states. ",
"To give you a reference for this, most people have at least heard of Heisenberg's uncertainty principal, that the more precisely you know ",
" something is, the less precisely you know how fast it's moving, and vice versa. It is fundamentally impossible to know both where an electron is and what it's momentum is. It's just a law of nature. ",
"The same thing is going on with the neutrinos. No neutrino has both a definite mass and a definite flavor. This gets more interesting because when neutrinos interact with matter, they do so according to their flavor state (e, mu, or tau), but when they move through space, they do so according to their mass state (1,2,3). So in the Sun the fusion reactions create electron type neutrinos, but each one is a mix of mass 1,2, and 3. As they propogate through space toward earth, their relative mixture of 1,2, and 3 remains constant, but this means their flavor becomes a super position of all three, meaning each neutrino has a probability of becoming e, mu or tau at any point in time later. When they reach earth and go through one of our detectors it forces the neutrino back into a definite flavor (making it choose e, mu, or tau) and returning it to having a mixture of all three masses. ",
"This is important in my field, because when we introduce matter the neutrinos propogate differently. Since their interactions are based off their flavor, but propogation on mass, propogating through matter will change the way the neutrinos oscillate based upon the properties of the matter around it. By studying the neutrinos that escape a star we can learn a lot about what is happening inside the star where we can't see because the light is trapped by the high densities. "
] |
[
"In North America, periodical cicadas (magicicada) have life cycles of either 13 or 17 years, depending on their brood. What is the significance that both of these numbers are prime?"
] |
[
false
] |
And why are there no magicicada broods or other cicada subspecies on 7, 11, or 19 year cycles (those also being primes), or are there?
|
[
"Because they're prime (actually, relatively prime is enough, but primes are relatively prime to everything but their multiples), the length of time between double-emergence years (which is the least common multiple of their cycle lengths) is maximized. For example, with 13-year and 17-year cicadas, you only have a double emergence once every 13*17=221 years.",
"I'm in no position to talk about the biology of why the other primes aren't used."
] |
[
"More importantly, a prey-type of creature having a prime-number life cycle would not sync up with many other organisms' life cycles.",
"If a cicada had a life cycle of 12 years, it may have been threatened by a predators with life cycles of 2, 3, 4, 6 and 12 years. Imagine a predator with a life cycle of 4 years. In year 2000, the cicada and predator hatch, and the predators have a good catch. In 2004 and 2008, the predators have to make do with other prey. In 2012, the predators and cicadas hatch together, and the predators have a good catch. This happens again in 2024 and 2036.",
"If the cicada's life cycle extended to 13 years, they will be less vulnerable to predation (until a predator with identical life cycle appears)."
] |
[
"It isn't totally known. However, most of the current guesses (based a lot on mathematical modeling) suggest that having a prime life cycle that is also relatively long helps (1) prevent predators from being able to sync their life cycles with yours and (2) prevent inter-brood competition.",
"Here's a good paper:",
"http://www.esajournals.org/doi/pdf/10.1890/04-1615"
] |
[
"Why are viruses that result in a global pandemic so rare?"
] |
[
false
] |
[deleted]
|
[
"A pandemic usually requires a virus that can infect human which is new and distinct enough that there is not pre-existing immunity, but well adapted enough to spread quickly and has the right characteristics to escape containment. As for why it's \"so rare\", I'd point to the last one. We ",
" have an influenza pandemic in 2009, but we were lucky that it was not as severe as predicted. We also have had many recent close calls with several viruses that would have been far worse had they had a longer lapse from exposure to symptom onset or other characteristics to escape containment: namely Ebola, SARS, and MERS off the top of my head. We have a current HIV pandemic as well, and several influenza strains are cooking."
] |
[
"Sure, but SARS onset was sooner after exposure and most importantly typically started with a clear fever. You are correct though that we got lucky, but it wasn't exactly a fluke die off. If it didn't have that clear fever right away it might have been a much more terrifying situation."
] |
[
"“Emergent Infectious Diseases” occur about once a year, but most of them don’t reach pandemic-level. ",
"The reason we don’t have more pandemics is because they need to be in a sweet spot of circumstances, particularly in reference to their symptomology. If the symptoms are too slight the disease may be difficult to spread (easily spreadable diseases often spread by coughing, sneezing, vomiting...). Diseases like the flu spread this way, but they also dissipate quickly so it just gets chalked up as “flu season” instead of a pandemic.",
"On the other hand, if the symptoms are too severe then people will stay home. If the symptoms are EXTREMELY severe, it might even kill the host before the disease can spread.",
"Additionally, the disease needs to start in the correct location. High population density areas allow for rapid spreading. If the disease begins in a rural area it may simply die out before it has a chance to spread. ",
"Finally the disease itself must be hearty. The SARS outbreak was very similar in many ways to recent events, but the disease itself just wasn’t genetically strong enough to withstand our immune system. We didn’t handle things well in that case; we just got lucky. As other have stated, this can be related to the uniqueness of the disease, i.e. whether we already have similar antibodies. This is why many of the major disease outbreaks are what we call “zoonotic” meaning that they mutated to affect humans from some other species."
] |
[
"If a human were to have a blood transfusion with a blood type that was not their own, what would happen?"
] |
[
false
] | null |
[
"serious medical problems.",
"This is more what I was interested in. Could you please elaborate?"
] |
[
"Because of the way the body recognizes the proteins on the erythrocytes (red blood cells), it depends. A simplified way of looking at it is purely using blood types. ",
"Let's say person 1 has type AB blood. That means their blood cells have protein A and protein B on them. If you were to give them blood without those proteins in it, person 1's body wouldn't see anything amiss, as there are no recognizable foreign pathogens.",
"Person 2, on the other hand, has type O blood. that means their blood cells lack proteins A and B. If we give them blood that is their own type, nothing happens. But if we give them blood with proteins A, B, or both A and B, their body raises its defenses, because it sees these strange new contaminants that it has never dealt with before. So the body attacks anything with these new proteins A and B, \"rejecting\" the transfusion and causing some serious medical problems.",
"A similar thing happens with Rh- people receiving Rh+ blood.",
"That is why people with blood type AB+ are known as universal receivers, and people with O- blood are called universal donors."
] |
[
"Your body just completely goes into attack mode. Your antibodies would bind the red blood cells from the transfusion and these would be destroyed by your immune system. This is called an acute hemolytic transfusion reaction. This is accompanied by low blood pressure and fever, due to the activated immune response. Jaundice can also occur because the liver now has to process and metabolize all the hemoglobin that is now floating in your blood because the red blood cells have been destroyed."
] |
[
"Is looking through a mirror same as looking at a distance for eye health ?"
] |
[
false
] | null |
[
"Focal distance in a mirror is eye to mirror + mirror to object"
] |
[
"so say if distance to relax your eyes is 6 m and you look at yourself in a mirror which is 6m away that will relax your eye ?"
] |
[
"No, that would be 12m. 6m is to focus on the surface on the mirror. Your reflection is \"behind\" the mirror"
] |
[
"Why are the evolutionary advantages of being a snake? (having no limbs, lack of eyelids/external ears, etc.)"
] |
[
false
] |
I know a little about reptiles and amphibians from my earlier days of studying them out of interest, but from what I understand they are hard to place in the evolutionary tree, are often excluded when talking about reptilian ancestors, and hardly ever seem to come up in discussions about evolution unless you are specifically studying them. Are they "newer" than lizards, amphibians, and such? edit: Sorry I meant "what" in the title
|
[
"Large amounts of genetic data have consistently placed snakes as the sister group to the group composed of Anguimorpha (monitor lizards, Gila monsters, and their relatives) and Iguania (iguanas, chameleons, and their relatives), as in ",
"this study",
", which is one of the best studies of higher-level squamate relationships to date.",
"In a phylogenetic context, snakes are lizards, because snakes are nested within the lizard clade (known as Squamata) such that some \"lizards\" are more closely related to snakes than to other \"lizards\" (e.g., monitor lizards are more closely related to snakes than they are to skinks or geckos). In this sense, the snake clade is certainly younger than the group that contains all lizards because this group also contains snakes. The snake clade is also younger than the overall amphibian clade.",
"As ",
"/u/atomfullerene",
" mentioned, there are many squamate groups that have lost their limbs but are not snakes, such as lineages of legless geckos and legless skinks. Limb loss often evolves in burrowing lineages, as limbs are a hindrance when moving through tunnels underground. Terrestrial lineages that live in grassy habitats also sometimes evolve limbless forms, and these limbless lizards use a type of movement referred to as \"grass swimming\" to rapidly move through the grass. Evidence suggests that snakes fall into the first group and lost their limbs in response to evolutionary pressures associated with a burrowing lifestyle."
] |
[
"oh wow, I was obviously misinformed then. Thanks for all the info, I'm going to check out that study"
] |
[
"To be fair, most of the relevant genetic work on deep-level squamate relationships has occurred within the last 10 years or so. Before these studies, relationships among the major clades of squamates were estimated based on morphology (primarily skeletal characters), and snakes were problematic in many of these analyses because convergence in the body form of snakes and other legless squamates distorted relationships."
] |
[
"If my goal is to witness as much sunlight as possible In a 24 hour period on the winter solstice, would I achieve this by going towards the equator or by traveling west?"
] |
[
false
] |
Assume that you start in New York, and you can only travel in speeds allowable by a car - say 100 mph. Additionally, is the optimal route actually some combination of west and south due to the curvature of the earth?
|
[
"At the solstice, the ",
"formula",
" for the number of hours of sunlight is:",
"(24/pi)*acos(tan(x*pi/180)*tan(23*pi/180))",
"Where x is your latitude. Since New York is at about 41 N, that means it gets about 9.1 hours of daylight. If you started moving south at the crack of dawn at 100 mph, you could go 910 miles which would translate to 13 degrees latitude. Hopefully you are in a boat since this puts you in the middle of the ocean. There, the length of the day would be 10.3 hours, and you get half of this gain (because the dawn was earlier here too). So 36 minutes of extra sunlight.",
"Driving west is easier. In 9 hours you would travel the same 910 miles, but this moves you by 17.5 degrees in longitude (a circle at constant latitude is smaller than the circumference of the earth). That gains you 1.16 hours, or about 70 minutes. So, driving west wins.",
"You could get a little farther if you kept on driving while the sun was up, but if you want to be that precise you can play with the equations some more. Also, there would be some optimal angle between south and west that would get you slightly more sunlight than going straight west.",
" ",
"Go West, young man!"
] |
[
"The winter solstice for NY is the summer solstice for Antarctica."
] |
[
"I haven't done any calculation. I am just trying to visualize it. ",
"To achieve what you are asking you basically want to flee faster as possible from the \"shade\" of the night incoming towards you (try to imagine the light/night cicle on a 3D earth).",
"The best flee ruote is traveling perpendicular to the curve of the shade and its direction will then vary over time.",
"It is a SW ruote and the more you travel S the more you want to correct it towards W.",
"Could be wrong but this is what i \"see\""
] |
[
"Is the deep ocean floor littered with the bones of fish and mammals which have died over the years?"
] |
[
false
] |
[deleted]
|
[
"Do bones dissolve in the ocean, or do they sink to the bottom and stay there until something covers them up?",
"A bit of all of the above. Critters of all kinds die in the ocean, and their dead remains drift to the ocean floor. The descent to the bottom takes time and is usually measured in days, which gives bacteria and scavengers time to scoop up at least some of that organic matter on the way down. This scavenging and decomp usually proceeds at much faster pace than simple direct dissolution of organic remains, so it is the effect of these metabolic processes which dominates.",
"But some of the stuff makes it to the bottom. Once there what happens depends on the sedimentation rate. If the sedimentation rate is low, those organic debris will remain at, or close to, the surface and be eaten up by either bacteria or benthic scavengers. Some debris such as whale carcasses remains on the bottom for quite some time, and they have their own unique suite of scavengers which take a go at their remains over the several months it takes to gnaw away at them, ",
"supporting a unique ecology in the process",
". ",
"But large stuff such as whale falls are the exception, and most of the debris is small to middling size and the overwhelming majority of it is phytoplankton. If the sediment rate is high enough, this plancton will be sequestred in the bottom mud and cut off from oxic environments. It may then be buried until it reaches such depths where it may chemically evolve towards the oil window, and eventually generate hydrocarbons.",
"This leaves the middling stuff, fish hash and like that. This may have a different overall composition from fine grained phyto-planctonic dominated assemblages: amongst other things, it would be richer in phosphates because of a comparatively larger proportion of arthropod shells and fish bones. In suitable environments such as zones of upwelling, biological productivity may be high enough that the downward flux of fish debris leads to the accumulation of phosphate-rich sediments, ",
"which may if the setting and chemistry are right become phosphorite deposits",
"."
] |
[
"Phenomenal answer"
] |
[
"Marble involves a completely different process, at most marginally related to the pelagic sedimentation I glossed over in the comment above.",
"What you need for the formation of marble is carbonate rocks. There are all kinds; some form in deep water environment and others not. Most are sedimentary, but a few are igneous or even related to chemical replacement (metasomatism) near deep fault zones. You have to keep in mind that carbonate rocks are extremely variable in texture and composition, especially when you keep track of impure carbonates (mixture of carbonates and siliciclastic material in variable proportions) - these will make our life complicated later on.",
"So, you start with carbonates, and just like any other oceanic sediment, you bury them, and keep burying them until they reach such depths as the mineral assemblage becomes unstable. At that point, the mineral assemblage re-equilibrates through chemical reactions which will bring it to a new, stable, composition of minerals. And as the rock keeps going deeper and deeper, it will progressively re-equilibrate to newer and weirder mineral assemblages. (Note: marbles can also form at shallower depths, say a few km, in the vicinity of magmatic intrusions in a context of contact metamorphism - woo hoo! even more variability).",
"All of these mineral assemblages are loosely termed ",
"\"Marble\", or \"Calc-silicate rocks\"",
". ",
"Their mineralogy is complex",
" (especially in the case of those impure carbonates we mentionned earlier), and will vary depending on the maximum pressure and temperature conditions which will have been reached. Strictly speaking, marbles are metamorphic rocks with more than 95% carbonate minerals (Usually a mixture of calcite and dolomite). But that 5% can be screwed up. When you get into the impure marbles and assorted calc-silicates, the mineralogy can be very diverse and include such minerals as talc, wollastonite, tremolite and diopside, as well as any from a long list of others. Also worth mentionning, I'm pretty sure when you are thinking \"Marble\", you are envisioning ",
"ornamental stones such as \"Carrara marble\"",
" or some other high quality ornamental stone. You would thus probably not recognise most marbles as such \"in the wild\", since most do not reach \"ornamental stone\" quality. They can be a very variable bunch of rocks in terms of overall texture, grain size and color."
] |
[
"How come Delta has been able to crowd out other strains of Covid inmost countries?"
] |
[
false
] |
Alpha used to be dominant in UK and now it's almost nonexistent there. Is that just due to delta's sheer transmissibility. I would think, since alpha is also quite transmissible it would still somewhat keep a foothold in most countries.
|
[
"The real population dynamics are pretty complex, but it really all comes back to the nature of exponential growth. If two variants have the same generation time, that is, the same time between a person initially becoming exposed and then becoming infectious and then either recovering or dying, even a relatively small difference in transmissibility will show up after a few generations. ",
"If each new Delta variant infection generates three additional infections, compared to two and a half for Alpha, there will be 10 times as many Delta infections as Alpha infections after only about 13 generations: (3 / 2.5)",
" = 10 => X = 13 if we round the answer up to the nearest integer. And if generation time for both is a week, that means new cases will be 90% Delta in 13 weeks after Delta begins spreading. It's not that the alpha variant is not still spreading. It is. It's just that the Delta variant is spreading faster. In this toy model, without the existence of the Delta variant, at the end of those 13 weeks you would have had only the Alpha cases and none of the Delta cases. In other words, you now have 11 times as many cases as you would have.",
"Like I said, this is a toy model that doesn't accurately reflect the full dynamics. Exponential growth can't go on forever, and it doesn't -- we see waves as people react to rising infections. And there's no guarantee that any two variants will have the same generation time. But hopefully it does help demonstrate how you can perceive that one variant is crowding out the other when you would observe that behavior whether it was or not."
] |
[
"To answer your question, I went to do a quick googling to find information about the transmissibility of Alpha and Delta variants. And it seems that the Delta variant is about 50% more contagious than the Alpha variant according to ",
"The Washington Post",
".",
"Furthermore, according to ",
"CDC",
", Delta variant also can have breakthrough cases even after the person have taken their vaccination. Though, people who opt to get vaccinated who were infected with the Delta variant seems to not cause as severe illness compared to those who are not vaccinated.",
"*",
"-> "
] |
[
"The missing piece may be either of",
"Once you recover from Delta, you have cross-immunity against Alpha, so the rapid spread of Delta leaves Alpha with few potential victims. Alpha may, so to speak, starve to death. (Not that viruses can starve, or indeed eat.)",
"If you are protecting yourself well enough to prevent Delta, you are even better protected against Alpha."
] |
[
"When swinging a baseball bat, tennis racquet, golf club, etc. why is \"follow through\" so crucial?"
] |
[
false
] |
Once that spit-second of contact has been made with the ball, why should any further motion (or lack thereof) make any difference at all?
|
[
"It did not go well."
] |
[
"At the risk of sounding like a layman, I would tend to think that if you don't follow through and decide to stop at the point of impact, your body is going to start working to reduce your motion before you actually end up hitting the ball.",
"Thus, energy that could have gone into the ball is being squandered on an unnecessary and early stop. "
] |
[
"He didn't aim for the comment, he aimed at an imaginary spot below the comment."
] |
[
"Have their been any vaccines that were and still are safe for adults but not for children?"
] |
[
false
] |
With the current wait for the covid vaccines to get approved for children, has there ever been a vaccine that was and still is approved for adults but not for children? Or even where the adult dosage would be dangerous if given to children?
|
[
"There are two main concerns with giving vaccines to children:",
"Firstly whether the dose needs to be adjusted, either up or down to maximize immune response while minimizing side effects.",
"Secondly whether there are any new or unique safety issues with the vaccine in children. Children are not just \"smaller adults\". In some respects their bodies work very differently than adults.",
"There are many vaccines that are only approved for adults, but usually this is because they've only been studied in adults. Running clinical trials in children is ethically challenging and expensive."
] |
[
"The smallpox vaccine which used a live virus was not safe for infants under 1 year old. ",
"https://www.ph.ucla.edu/epi/bioter/smallpoxvacriskyeyes.html",
" (Article from 2003).",
"COVID vaccines are quite different from this, though."
] |
[
"To expand on this, out of curiosity, what are some aspects in where their bodies work differently?"
] |
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