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[
"Why don't (female) humans have estrous cycles like sheep and goats, and re-absorb their endometrium?"
] |
[
false
] | null |
[
"Here is a recent posting that is somewhat similar",
". I won't rephrase the top comment because it wasn't mine, but it's a pretty good answer for you."
] |
[
"ie. why do women have periods and not reabsorb period stuff internally like sheep and goats do"
] |
[
"And don't forget, pain is not necessarily a bad thing that evolution would aim to eliminate. Pain as a whole is net positive for the organism, but (non-severe, debilitating) menstrual pain probably doesn't have a selective pressure against it. "
] |
[
"Looking for info on how myelin affects reaction time."
] |
[
false
] | null |
[
"I'm not sure if anyone can give you practical advice for increasing reaction times, as it may constitute medical advice. When it comes to reaction times, most of the overhead comes from cognitive response, that is, how fast you can thick and act, rather than a nervous system lag. If I would give any advice, it would be to practice, and not worry about nerve action potential. :D ",
"As a side note, I searched some databases for academic papers regarding myelin and reaction times, and found no results. Myelin is the sheath surrounding the axon of a neuron. If you can find any sources discussing what you mentioned in your post, please post it! It might be an interesting read."
] |
[
"I'll answer where I can, your secondary question is referring to 'implicit' skill learning, be careful for depletion, your brain needs time to relax and it will struggle to learn associations when it's fatigued. Also, rewarding good behavior will always encourage it, even implicitly.",
"For your bonus question, a bonus answer! There was a study, I can't think of it's name right now, but it looked at individuals who smoked pot either while studying for a test, while taking a test, both, or neither, they found that individuals who did neither obviously scored highest, but that individuals who smoked while studying performed better when also high while taking the exam.",
"In terms of your primary question, myelin is fat, but more fat isn't going to help you, people like certain supplements for enhancing myelin but I'm not positive that there is enough scientific validity to offer evidence for that (after looking I didn't really find much in the literature). Even if it did add more myelin, there's no evidence that it would improve things, for example the brain kills off neurons after we're born to increase efficiency, it's fairly finely tuned."
] |
[
"I know things like how much Myelin your nerves have has some sort of effect regarding transmission speeds",
"The presence of myelin around a nerve does speed up transmission. Myelin is a coat of fatty white matter that wraps around the axon of the nerve—with occasional gaps called nodes of Ranvier (great band name)—which acts to speed up transmission. In fibres that are not myelinated, the electrical impulse (action potential) traveling down the nerve's axon moves in a continuous sweeping wave. Where myelin is present, the impulses jump from node of Ranvier to node of Ranvier. This means that the information travels much faster.",
"In terms of conduction speed, ",
"this old article",
" found the following:",
"These results therefore suggest that conduction velocity depends, in the first instance, upon myelin sheath thickness, fibres with a thick sheath conducting faster than fibres of similar, or even greater, diameter but with thinner sheaths.",
"But, while this may be true for individual neurons, these results may not be true for the brain as a whole. Using a method called diffusion anisotropy, this study found improved reaction to be associated with both increased and decreased white-matter (myelinated neural bodies). This suggests that increased presence of myelin may have different effects in different brain regions or at least for different cognitive functions.",
"Are there any specific nutrients, chemicals, vitamins, or other substances that can increase myelin",
"I've had a quick look, and I can't find anything in humans, and I don't think there is anything to find unless we start looking into disorders where neurons start to demyelinate, but this then comes with more caveats than I think would be useful here.",
"Even if we could increase the myelin sheath around your neurons, it is unlikely that it is the neural communication that is holding you back.",
"Are there any specific nutrients, chemicals, vitamins, or other substances that can increase… ",
"In terms of chemicals, ",
"dopamine",
" would be a good target in changing reaction time. But, this is somewhat impractical in people as we don't have easy access to our dopaminergic system the way we do in a rat (you can drip it straight into the brain if you like in the rat).",
"If we abandon the macro-level of the neuron and look at increasing reaction time, there are things that can be done. As others have commented, practicing a task in order to automate it is going to give you the biggest gains in reaction time. ",
"Yoga has also been reported",
" to lead to reductions in reaction time, but this study didn't have a control group so the change may be one that occurs without yoga, or as a result of something else related to the yoga practice (general relaxation, etc).",
"MY SECONDARY QUESTION:I know that when a specific hand-eye exercise is practiced repetitively, the nerve cells rearrange to optimize that function, I think. (Please tell me if I'm talking out of my ass at any point.)",
"What you're referring to here is plasticity. The brain is highly plastic and able to quickly and efficiently adapt to new environments and tasks as a result of learning or exposure. The plasticity of the brain comes in two forms: increased neural activity, and decreased neural activity in response to some stimuli (potentiation and depression, to be technical).",
"Other than simple practice, IS THERE ANY WAY to either speed up how fast these nerves rearrange, or prevent them from \"unarranging\" without practice?",
"The thing with plasticity is that it is not well understood. There are some known time of day effects (i.e., when the learning is done), and some simple genetic effects have been reported (associated with the BDNF gene, I believe), but other than this it is a bit of a mystery. It is possible to experimentally induce plasticity (depolarisation and hyperpolarisation), but this requires that you know the anatomical structure that subserves the function of interest, or that you have some way of identifying the anatomical region functionally (such as fMRI). Even then, it may not be possible to target the structure (if it is below the outer surface, or cortex, of the brain), and any effects are short-lived (less than an hour for most protocols).",
"As for preventing the neurons from \"unarranging\", the plasticity of the brain is a double-edged sword. In order to be able to quickly and easily learn new things, forgetting also needs to be quick and easy as well. Having said that, picking up a skill that was well practiced earlier is much easier than learning it anew (like riding a bicycle).",
"BONUS QUESTION: Some other players on my team are not straight-edge like me. A couple smoke cigarettes, another smokes marijuana constantly, and another needs to have a stiff drink in the morning to do anything right. Do these activities permanently affect the ability of brains cells to operate at peak natural efficiency? Or could they drop their bad habits and eventually be mentally \"perfect\" again?",
"Without going into the vast addiction literature, or trying to scratch the surface on what is known about the long-term neural effects of nicotine, marijuana and alcohol, here's some food for thought. Have you considered that perhaps your friends use smoking and drinking as a way to achieve \"perfect\" mental ability? People are very good at self-medicating in order to reduce certain symptoms. Shyness and hesitation in social settings might be alleviated with alcohol. Nicotine can help some people to relax, and others to focus their attention (interesting factoid, certain psychiatric populations—such as schizophrenia—have very high incidences of nicotine use, possibly because it helps to regulate symptoms).",
"As for the more general ideal of perfect mentality, not sure if there is such a thing."
] |
[
"If chemical elements like iron or uranium are created in hot and dense conditions (deep inside the stars or during supernova explosions), why weren't they created during the (post-)Big Bang era, when it was the hottest and the densest?"
] |
[
false
] | null |
[
"Hotter is not necessarily better for synthesizing heavy elements. As the temperature of the environment increases, the number and average energy of photons in the plasma increases, to the point where photodisintegration reactions will start to break nuclei apart at a rate similar to the rate at which they're produced.",
"Also, if you look at the processes which form the heaviest elements, the s- and r-processes, these start with some moderately heavy seed nuclei. During Big Bang nucleosynthesis (BBN), these seed nuclei weren't available. And there are certain bottleneck nuclides along the way which break apart very readily, and make it difficult to get past them.",
"So given the temperature and density conditions, as well as the initial abundances, Big Bang nucleosynthesis looked like ",
"this",
". As a function of time, it happened like ",
"this",
".",
"As a general trend, heavier nuclides had lower abundances at the end of BBN. By the time you get to isotopes of lithium and beryllium, the abundances relative to hydrogen are already minuscule. So you don't really have any chance of producing iron or uranium this way."
] |
[
"If you kept the conditions fixed for infinite time (which is of course very different than what happened in the Big Bang), the system would reach nuclear statistical equilibrium at whatever temperature it's at. At very high temperatures, the equilibrium favors free nucleons, while at low temperatures, it favors nuclides with the highest binding energies per nucleon (the stable isotopes of iron and nickel)."
] |
[
"Is time the limiting factor? Say if those conditions - which at some moment resembled star cores, right? - continued for a longer time, would iron be produced?"
] |
[
"Is gravity a theory? I've searched but haven't found a clear answer."
] |
[
false
] |
I understand a theory is an idea which can be tested and the same thing will happen. So, why isn't gravity a law, (assuming that it is a theory.)
|
[
"A law is something that describes what is happening.",
"\nA theory is something that explains why something is happening.",
"\nA law is not better than a theory. There are laws of gravitation and theories of gravitation."
] |
[
"I personally think it has to do with the time period in which the ",
" or ",
" were postulated. Back in the day things were labeled as law because they seemed to be just that. Now everything is just a theory because they're all successive approximations to reality. So basically it's just a label without any actual meaning...at least that's how I see it."
] |
[
"So, every law has a theory(or more than one)...",
"Thanks."
] |
[
"How fast does a photon reach the Milky Way from Andromeda in the time frame of the photon."
] |
[
false
] |
[deleted]
|
[
"Time doesn't advance in a photon's frame of reference, more or less. The Lorentz factor goes as \n1/sqrt(1-(v/c)",
" ), but since for a photon, v=c, weird stuff happens. Namely, for relativistically fast objects time slows down as observed from an outside reference frame. For a photon, the time slows all the way down to zero from our perspective. The problem with this is that there is now no way to change frames to the photon's perspective, since that would be like making the whole universe move at the speed of light while the photon is stationary, which can't happen.",
"Edit: (v/c)"
] |
[
"From the photons 'perspective' - the travel time is zero. From a photons 'perspective' it dies the moment it is created (I know... bummer right? Sucks to be a photon)."
] |
[
"The photon does not have a perspective or a time frame. One cannot parametrize the path of a photon with a proper time.",
"All it is is just a wriggle in the electromagnetic (EM) field. Somewhere in space the EM field is excited. This causes part of the field next to the excitation to get excited, and the original excited area calms down. Then this next part excites the part next to it, and so on. So this state of being excited is propagated through the EM field, and this state of being excited moves at the speed of light.",
"Massive ",
", such as particles with internal structure, astronauts, or stuff for which it even makes sense to talk about their perspective or personal ",
" - these all move at less than the speed of light.",
"Some signals, such as light, can move at exactly the speed of light, but not faster. This is the limit of how fast something can cause something else to happen. The excitation in one patch of space excites the next patch of space as fast as it can influence that next patch.",
"EDIT: spelling"
] |
[
"When riding a bike, why does the wind sound stop when you turn your head 90°?"
] |
[
false
] | null |
[
"Hello,",
"This would be more appropriate for ",
"/r/AskScienceDiscussion",
".",
"Best."
] |
[
"what? why? it's a science question, and the first thing in the sidebar is \"ask a science question\". the sub you linked appears to be about the scientist profession and meta discussion or discussion about recent developments in the field. this question is not related to any of these things, it's a pure science question about physics and acoustics."
] |
[
"Our ",
"guidelines",
" are a little bit more complicated than \"ask a science question\". ASD is not just for meta questions; this question belongs there."
] |
[
"Why did modern man's ancestors migrate to cold climates from warm ones?"
] |
[
false
] |
It is well established that modern human ancestors began in warm climates, and migrated over many centuries into colder climates. So, why did they leave warm, hospitable climates for colder, harsher climates in the first place?
|
[
"Before Europeans started re-discovering the world, humans (modern and archaic) had already established their presence almost everywhere (only a few exceptions - Antarctica, Falkland Islands, etc). Climate variation occurs gradually over space and it's likely that they didn't consciously/purposely seek out colder climates but instead happened to move into them while slowly adapting to the colder weather. On the other hand, humans also moved into much more humid areas of the world (SE Asia) and much more drier ones (Australia). There is a large volume of information regarding human migration. I've taken several courses on it, so PM me if you'd like to know more."
] |
[
"Any area can only support a limited amount of population, after that its starvation or migration. Plus natural disasters make people move. Repeat. In most places it gets cold just very little over distance so the migration is very gradually. "
] |
[
"Also, wars/fighting with other humans. Many mass human migrations have been driven by other humans displacing them with raiding/attacks. A great example of this is the Mongols displacing other asian steppe peoples, who displaced eastern europeans, who invaded western europe."
] |
[
"Did the first stars have planets?"
] |
[
false
] | null |
[
"This is not a bad assumption. You can't get complex structures with just hydrogen."
] |
[
"This is not a bad assumption. You can't get complex structures with just hydrogen."
] |
[
"That last one. Most of the heavier elements were formed in stars, so the very earliest stars would not have had rocky planets. They may have had planets that were mostly hydrogen though."
] |
[
"Why does the text on the bottle of C-Vitamin effervescent tablets say you shouldn't take more than maximum 1 per day?"
] |
[
false
] |
I just think it's a little strange... I mean, it's freaking vitamins. P,s I'm a Swede, had to look up the therm "effervescent tablets"... You may correct me if it's incorrect.
|
[
"I don't know, but Vitamin C is water soluble, so if you drink more than you can process you just pee it out."
] |
[
"Vitamin C is ascorbic acid. Too much of it can cause gas, nausea, diarrhea, heartburn, and possibly too frequent urination. So, pretty much stuff that you don't want to happen.",
" Forgot vomiting."
] |
[
"LD50 in rats is 12 g per kg per wikipedia. I dunno how the rats died, I can imagine their kidneys crapping out (diuresis->prerenal azotemia->rat funeral) or a toxic liver metabolite of some otherwise unseen secondary metabolic pathway, or end organ damage elsewise.",
"... work that way...\nwork what way?"
] |
[
"Is the Martian atmosphere too thin for a quadcopter drone to operate in conjunction with the rovers?"
] |
[
false
] |
Sorry if this is an incredible silly question. Considering the fact that Martian gravity is also a lot lower than that of Earth, it could negate the atmospheric density, but the calculations for that are a bit out of my depth.
|
[
"Not only is it possible, we're gonna do it. The upcoming Mars 2020 rover will include a small aerial scout that will work exactly as you describe.",
"https://www.jpl.nasa.gov/news/news.php?feature=7121",
"https://en.wikipedia.org/wiki/JPL_Mars_Helicopter_Scout",
"There have been proposals for Mars airplanes in the past, but since the 1970s we've believed that a helicopter was impossible due to the thin atmosphere. But only just recently did someone at JPL sit down and re-do the calculations and realize that it could actually work with modern drone technology."
] |
[
"Just as a minor elaboration, the Scout is a coaxial counterrotating dual rotor design instead of a quadrotor. Presumably because of fewer moving parts required."
] |
[
"The sea level density of Earth's atmosphere is 1.225 kg/m",
"The average density of Mars' atmosphere at its surface is 0.02 kg/m",
" (The surface pressure has a vast range on Mars, from 30 to 1155 pascals. Surface density therefore also varies widely , inversely with pressure.)",
"So at a typically landing site, a copter would need to generate lift in a medium 60X less dense than air against a gravitational force 34% as strong as on Earth. And there are size, weight, and power limitations. Seems like an quite an engineering challenge."
] |
[
"If you shine a light at an object, does it become heavier?"
] |
[
false
] |
[deleted]
|
[
"What p=m*v gives you is non-relativistic momentum. Mechanics gets a little wackier once you start moving close to the speed of light. Since a photon moves at the speed of light, we have to start using the relativistic versions of the equations.",
"The relativistic version of the momentum equation looks like:",
"p = m_0 * v\n ----------------\n sqrt(1-v^2/c^2)\n",
"where p is the momentum, m_0 is the rest mass, v is the velocity of the body, and c is the speed of light.",
"As you can see when you let the mass go to zero (because photons are massless) and v go to c, you get 0/0, which isn't helpful in this form, so we're not able to directly calculate the momentum this way.",
"However, using the general energy equation (Einstein's famous E=mc",
" ), we can make some substitutions and get total energy in terms of momentum and rest mass. This equation looks like:",
"E = mc",
" = sqrt( (p*c)",
" + (m_0 * c",
" )",
" ) ",
"(",
"Derivation.",
")",
"Now, in this case, letting m_0 go to zero leaves us with the equation E = pc. This can be arranged to give us p=E/c.",
"The planck relationship gives us energy in terms of the ",
"planck constant",
" and the frequency of the photon. This relationship is: E=hv, where h is the planck constant, and v is the frequency of the photon.",
"Making one last substitution in our equation, we get p = E/c = h*v/c. This shows that the momentum of the photon is directly proportional to its frequency, and is independent of mass.",
"Let me know if there's anything you want me to clarify!"
] |
[
"What p=m*v gives you is non-relativistic momentum. Mechanics gets a little wackier once you start moving close to the speed of light. Since a photon moves at the speed of light, we have to start using the relativistic versions of the equations.",
"The relativistic version of the momentum equation looks like:",
"p = m_0 * v\n ----------------\n sqrt(1-v^2/c^2)\n",
"where p is the momentum, m_0 is the rest mass, v is the velocity of the body, and c is the speed of light.",
"As you can see when you let the mass go to zero (because photons are massless) and v go to c, you get 0/0, which isn't helpful in this form, so we're not able to directly calculate the momentum this way.",
"However, using the general energy equation (Einstein's famous E=mc",
" ), we can make some substitutions and get total energy in terms of momentum and rest mass. This equation looks like:",
"E = mc",
" = sqrt( (p*c)",
" + (m_0 * c",
" )",
" ) ",
"(",
"Derivation.",
")",
"Now, in this case, letting m_0 go to zero leaves us with the equation E = pc. This can be arranged to give us p=E/c.",
"The planck relationship gives us energy in terms of the ",
"planck constant",
" and the frequency of the photon. This relationship is: E=hv, where h is the planck constant, and v is the frequency of the photon.",
"Making one last substitution in our equation, we get p = E/c = h*v/c. This shows that the momentum of the photon is directly proportional to its frequency, and is independent of mass.",
"Let me know if there's anything you want me to clarify!"
] |
[
"Light has energy and momentum, but no mass.",
"When ",
" an atom absorbs a photon, a few things happen. The largest effect is that the electron cloud undergoes a change to a new shape. The new shape of the electron cloud will be one in which the electrons are, on average, further away from the protons in the nucleus. This is a higher energy configuration since it takes energy to separate opposite charges. Thus, absorbing a photon causes an increase in energy of the atomic system because the photon carries energy.",
"Photons also carry linear and angular momentum, and can change the momentum of the atom. When an atom absorbs laser light, it recoils in the propagation direction of the laser beam. So-called \"Laguerre-Gauss\" modes of light have angular momentum, and can make an atom or molecule start to rotate.",
"But, again, while photons carry energy and momentum, they do not have mass.",
"It's true that energy and mass are related to one another; both cause distortions in spacetime. But that doesn't mean that everything with energy also has mass. So while you could say that an atom's increase in energy is ",
" to a small change in its mass, it would be incorrect to say that a photon has mass just because it has energy. A massive photon would necessarily have a rest mass, and could not travel at the speed of light.",
" Absorption of a photon by an atom increases the atom's energy, which may interpreted as an increase in the atom's effective mass but does not imply that photons have mass."
] |
[
"Is there an upper limit to the size of a black hole?"
] |
[
false
] |
A friend of mine made the claim that there was, and then proceeded to tell me some things that didn't make sense to me. He claimed that Hawking radiation limits the size of a black hole, but that doesn't sound right. Isn't Hawking radiation very slow?
|
[
"It sort of limits the size, but it actually sets a ",
" limit. Essentially, Hawking radiation increases its rate the smaller the black hole is. So it has almost no effect on very large black holes. It certainly does not set any upper limit. However, with very small black holes (think the mass of small mountains and downwards) it does actually cause them to radiate quite a significant amount of energy. When it comes to very very small black holes, the Hawking radiation is so rapid that the black hole very rapidly \"evaporates\", radiating all of its remaining mass.",
"TL;DR Hawking radiation sort of sets a lower limit, but not an upper limit, as it is faster the smaller the mass of the black hole."
] |
[
"Hawking radiation is very slow, and it's even slower for larger black holes. So no, there is no upper limit on a black hole except the limited amount of matter in the universe that you could throw into it to make it bigger."
] |
[
"Thanks for the response. I figured that he was wrong to claim that there was a limit. I imagine that there is a \"largest blackhole\" because of the finite age of the universe and the way that matter was distributed pretty evenly in the early universe. It seems like we would have crossed the Big Crunch off the list already if anyone found a theoretical limit to how large a black hole can possibly get as well."
] |
[
"Why can't humans create a food that contains everything the body needs?"
] |
[
false
] |
All the minerals, vitamins, proteins, etc. We can isolate these things, we know what they are and what we need -- obviously everybody's body is different, but we should be able to even personalize it a little bit or find a happy medium, shouldn't we?
|
[
"We have, according to some sources. A delicious pizza, containing 30% of an adult's recommended daily amount (RDA) of vitamins and minerals.",
"According to ",
"this article",
" \"The pizza has been developed by University of Glasgow scientist Mike Lean and entrepreneur Donnie Maclean and contains the proper proportions of calories, proteins, carbohydrates, fats, salts, sugar, fibre, vitamins and minerals that humans require for a balanced meal.\nTo create the healthy pizza, the scientists have added locally grown seaweed to the dough to cut down the sodium levels and provide vitamin B12 and iodine.\nThey also fortified the pizza with magnesium, potassium, folates and vitamin A, and added mixed red peppers to the sauce for extra vitamin C.\""
] |
[
"Because this happens: ",
"http://en.wikipedia.org/wiki/Nutraloaf"
] |
[
"There is still quite a disagreement about what a person ",
" to eat for a healthy lifestyle.",
"Some would argue no carb or low carb, some would argue low fat, some would want no sugar but also no sugar substitute, etc., etc. This doesn't even count people that actually have special dietary needs."
] |
[
"Are the lungs ever used as the delivery system for medication?"
] |
[
false
] |
I know about laughing gas and marijuana, but this seems like a quick and easy way to deliver drugs to the body. Why isn't it used more?
|
[
"It is used for many medications, the most common instance being inhalers or nebulizers for asthma or other breathing disorders."
] |
[
"1.1 - Any anaesthetic which is delivered through a mask - so yes, laughing gas would be included. ",
"1.2 - These are drugs which open up (widen) the airways, so yes, used to treat asthma and chronic lung problems like COPD and emphysema (often associated with smoking)",
"1.3 - These are drugs which open up (widen) the blood vessels, so they reduce blood pressure in the body. Amyl Nitrite is also known as 'poppers' and is a common club-drug.",
"1.4 - These are drugs which inhibit the parts of the immune system which cause inflammation and allergic reactions. They're used a lot to ease asthma symptoms and to help slow fibrotic lung diseases such as asbestosis or Farmer's Lung, etc. ",
"1.5 - These are used to fight infections, particularly lung infections. By inhaling them directly to the site of infection, it helps to reduce systemic side effects and first-pass metabolism (the drug goes straight to the place it's needed, rather than going all around the whole body first).",
"1.6 - These are substances that reduce the surface tension of the inside of the lung so that the membranes don't stick together and prevent the lung from inflating properly (think of a fresh balloon which inflates easily versus a balloon which is damp inside and sticks together). Premature babies often need extra surfactant put into their lungs because their bodies haven't produced it naturally yet and their lungs aren't able to inflate properly without it.",
"1.7 Aromatic ammonia is known as 'smelling salts' which are used to revive people who have fainted - they work by prompting the body to breather faster, increase heart rate and blood pressure so more oxygenated blood gets up to the brain.",
"Dornase Alfa is an enzyme which cuts long strands of DNA into smaller strands. It works specifically to break down DNA present in sticky mucous in patients with cystic fibrosis, so the mucous is less sticky and can be coughed up more easily so the patient can breathe more easily.",
"Inhaled insulin was suggested to treat diabetes, but isn't really used very commonly.",
"Methacholine is a drug which irritates the airways and can trigger them to constrict. It's used as part of a 'challenge' test where we give increasing doses of it to a patient to see at which point their lungs react. If a reaction is seen at a low dose, the patient may be diagnosed with 'hyperresponsive' airways (similar to asthma)",
"Nictotine is the active drug in cigarettes",
"Sodium Chloride is just table salt, and can be inhaled in a weak solution to try to soothe irritated airways and ease chronic cough. A bit similar to sitting in a sauna for a while, but with salty water."
] |
[
"Notably, nebulized gene transfer vectors can be administered to treat chronic respiratory conditions like cystic fibrosis. So even gene therapy can be essentially inhaled."
] |
[
"Where does the material for Earths new layers keep coming from every year?"
] |
[
false
] |
You always hear Archeologists say the deeper you go the father back. You can see photos of clearly defined layers, ect. Where does this new material keep coming from? Are there parts of the surface losing material every year? Is it all volcanic eruptions? Whats the deal?
|
[
"The primary mechanism by which material is recycled is the theory of plate tectonics as others have mentioned. More specific to the example you gave which is on a short time scale geologically the process of sedimentation is the means by which material is buried. Weathering and erosion especially the action of water cause the movement of material in tiny amounts at all times but the majority of material is moved in episodic events such as destabilisation due to earthquakes or large volumes of rain due to storms. Also extremely important is the decay of vegetation which provides additional material. All of the mass slowly accumulates over the area of interest and buries it. The layers are due to different processes dominating the accumulation of material or specific events. The new stuff is deposited on the top and so the old stuff must be at the bottom. There is plenty of material on the 'lifecycle' rocks that is governed by plate tectonics on the macro scale. here's a ",
"link",
" to some information and also another ",
"link",
" on how material is 'lost'."
] |
[
"This isn't relevant to archeology. Most sediment deposited on land comes from erosion of highlands."
] |
[
"The oceanic plates are subducting and being absorbed into the mantle. The new material is deposited mostly through volcanic fault lines, but also through volcanic eruptions. The continental plate tend to float on top of the oceanic plates, driving them under, much like in a convection oven."
] |
[
"Aren't all chemical reactions hypothetically reversible?"
] |
[
false
] |
Because all the original elements are still there, just paired differently. When we classify reversible reactions vs irreversible what we are basically saying is, types that can be easily reversed(straight forward) vs types that can't be easily reversed(but still hypothetical can be).
|
[
"Yes, but when considering \"degree of reversibility\" you look at Gibbs free energy, and it considers not only enthalpy (energy change from bond breakage/formation), but entropy as well. So for many reactions, while it is ",
" favourable for it to go one way, it is ",
" unfavourable in that direction.",
"So saying that all chemical reactions are hypothetically reversible is akin to saying it is ",
" for all air molecules in a room to be in one tiny corner, but statistically speaking it is so unlikely that it will not happen. You ",
" make a distinction and say it's hypothetically possible, but it's not useful to do so."
] |
[
"I guess what I meant was not naturally but artificially/forced.",
"Whenever you're doing that, you're simply manipulating the conditions such that the reaction ",
" likely, and that's reflected in the changes in ",
"Gibbs free energy",
".",
"For example, water doesn't \"naturally\" (here I just take you to mean room temperature and pressure) boil unless the temperature and pressure conditions are right. We apply heat until the phase change becomes spontaneous. So here's a good example of an entropically driven process."
] |
[
"It's hypothetically possible that the atoms of a cocktail party host's undergarments could simultaneously jump 1 foot to the left. Just improbable."
] |
[
"Why can the sun burn us on a hot summer day, but can barely be felt in the winter?"
] |
[
false
] | null |
[
"It's not the atmosphere. Even on planet lacking one season would still happen if it had axial tilt. It's because the flux is more spread out from being tilted. ",
"Near the equator at noon the intensity is I = I0×cos(0) = I0. The baseline intensity of solar radiation at earth's orbital distance.",
"At say 60 degrees off that, I = I0×cos(60) = 0.5×I0. Half the intensity gone just from the angle. 60 degrees off would be the 60th parallel (northern Canada) at the equinox, or the 37th (mid California) at the winter solstice. "
] |
[
"Because in winter the angle the sun strikes the earth spreads out the rays do less energy is being deposited per given area. In the summer when the sun is more directly overhead the rays of the sun are striking closer together, depositing more energy, which is of course heat."
] |
[
"That's just inaccurate. The temperature differences are due to the Earth's tilt, as during the summer your hemisphere is tilted towards the sun and during the winter it is tilted away. ",
", it's still ",
" being felt in the winter. If it disappeared, we would all freeze and die almost instantly. "
] |
[
"How far does electricity travel in water?"
] |
[
false
] |
I was just curious how far a current can flow in a body of water, I.e. if I went to a lake or a big pool and threw in a small voltage appliance, what radius will be affected?
|
[
"Depends on the strength of the household appliance (the higher the voltage the farther), but usually it will completely dissipate after roughly around 5 meters or so."
] |
[
"The snarky answer is... Not at all. Technically pure water does not conduct electricity, it is reliant on the dissolved ions to conduct electricity. So you would have to know the concentration of ions beforehand. I would expect electricity to travel farther in the oceans vs a freshwater lake."
] |
[
"Well, water does conduct a little bit. 2 water molecules can form a hydroxide anion and a hydronium cation. If I remember correctly the equilibrium constant (the ionic product of water) is about 10"
] |
[
"Why is the inlet for a hydroelectric dam always at the surface of the water?"
] |
[
false
] |
I've always wondered what the difference is between having the inlet on the surface of the water vs having it near the bottom. Whenever I see something about hydroelectric power they state the power comes from the potential energy of the water falling; how different is this from the weight of the column of water above a submerged inlet? Is it possibly for some other reason? I.e. problems with debris or fish? Obviously if it were too close to the bottom there would be problems with sediment. What happens during a drought and water levels drop unexpectedly low? If I'm way off on anything please blame documentarians. :) Thanks.
|
[
"Damn those documentaries!",
"The inlet is never on the surface (except in old fashion water wheels) but well submerged and forced through. ",
"Here is a picture",
".",
"The reason you are probably confused is because by falling they just ment giving up potential energy. Also all the water you see spilling over hydroelectric damns or running down a sluiceway to the side or whatever else, is usually just excess water overflow."
] |
[
"So then are ",
"these towers on Hoover Dam",
" just open the whole way down? What purpose do they serve in that case?",
"Seems like \"water falling\" is a horrible way to explain the way a dam works. The weight of millions of cubic feet of water makes more sense to me."
] |
[
"Those are penstock towers. Water doesn't 'fall' down them, because they are always full! So you are correct in thinking the pressure induced by the mass of the water is what drives the production of electricity."
] |
[
"Do compounds containing radioactive elements decay at the same rate as the elements half life?"
] |
[
false
] |
[deleted]
|
[
"As you can read ",
"here",
", nuclei decay with the same half-life pretty much regardless of context. In particular, being in one compound or another does not affect the half-life, as the scale of nuclear physics is vastly different from the scale of atomic and molecular physics. (Nuclear forces operate on scales of about 10",
" meters, while chemical bonds involve distances around 10",
" meters, that is, 100,000 times bigger.)"
] |
[
"Going off of that, how does decay affect the compounds of radioactive elements? Would something that undergoes alpha decay just release an alpha particle or would it cause the entire compound to collapse?"
] |
[
"MIght be easiest to take a look at ",
"this",
"."
] |
[
"How smooth is the surface of the earth?"
] |
[
false
] |
I once heard one of those "amazing facts" that if you scaled a billiard ball to the size of the earth, the earth would actually be more smooth (i.e. closer to a perfect sphere) than the billiard ball. In retrospect, that sounds like it would be extremely difficult to quantify, and the answer would just come down to you initial assumptions of the nature of the billiard ball. Is there any validity to that claim?
|
[
"[I've removed the comments, as they may not be accurate.] "
] |
[
"There's a ",
"relevant XCD followup",
" to the Bad Astronomy post. It says that the earth is much less smooth than a rough bowling ball (not billiard ball)."
] |
[
"This appears to be from a 2008 Bad Astronomy ",
"blog post",
", and is incorrect in both of its \"smoothness\" and \"roundness\" analyses.",
"In this case, it incorrectly interprets the WPA spec as \"having no pits or bumps\" (i.e., surface roughness), when even well-used billiard balls have nowhere near this rough of a surface. See these interesting magnified ",
"photos",
" of an actual ball, with surface peaks/valleys on the order of 20 microinches. At this scale, the Mariana Trench would be almost ",
" microinches deep.",
"In short, the Earth is nowhere near as smooth as a billiard ball."
] |
[
"Given the quantity of medications processed through a pharmacy, what sort of mass/dose of a particular medication could be collected from the counter tops in a given period of time?"
] |
[
false
] | null |
[
"Hello! I've removed your port as the wording is a bit confusing. If I understand it correctly, then it's not really a scientific question and isn't appropriate for ",
"/r/AskScience",
"."
] |
[
"Thanks for letting me know. I assumed as a statistics question it would be encompassed in the repertoire of askscience, the chemistry category was probably the wrong choice for it though.",
"The wording was definitely a bit confusing and open ended. Perhaps asksciencediscussion would be better suited for it."
] |
[
"Certainly. I wish you the best in rewording, sometimes putting our thoughts onto paper can be exceedingly difficult. :)"
] |
[
"Is there actually a disease where one would be required to drink blood (regularly)?"
] |
[
false
] |
There has been some in crime shows like CSI etc., I'm wondering if there's any real basis for them. To clarify: I'm not thinking about blood transfusions, but drinking/consuming the blood. Thanks!
|
[
"\"Blood is probably not going to fuel you're body very well.\"\nI'm not so sure about this. The masai are known to give a daily ration of bloody to pregnant women (and kids - I believe). Blood from healthy animals might contain valueable vitamins and minerals that we can absorb. ",
"<grammarpolice>\nAlso, it's 'your body'\n</grammarpolice>"
] |
[
"There is no condition where you would specifically need to ingest blood, rather than get a transfusion or take specific supplements. The only reason for needing to ingest blood would be iron deficiency, which is very common, but can be treated with iron supplements. Blood is high in iron due to its high concentration of hemoglobin. Drinking blood would alleviate iron deficiency. This is the reason a pregnant woman (who needs to produce more blood cells containing hemoglobin to support the pregnancy) would drink blood. Again, iron supplements would work just as well but might not be available in some cultures. "
] |
[
"No. I don't see in anyway someone would have to drink blood regularly.\nWhen you drink something it goes into your stomach which then breaks it down into something that the body can use for fuel. (Proteins, fats, iron, vitamins, etc)\nBlood is probably not going to fuel you're body very well."
] |
[
"Can your teeth be reattached after acci(dental) removal?"
] |
[
false
] |
I'm sure many of you have heard the advice to put a tooth in milk and get to the hospital as quickly as possible. I'm also skeptical that the milk actually does anything. I understand the association between milk, teeth, and calcium, but your teeth don't get the calcium straight out of the milk, do they?
|
[
"Yes, it's advisable to put the tooth in either milk, water, saline or saliva (you can place the tooth under your tongue) not because the tooth would get calcium or other minerals from they milk but because you need a storage medium to keep the cells of the tooth root alive so the tooth can become reattached to its socket. ",
"Water will probably damage the tooth cells because its osmolarity is lower than the one in the tooth cells and milk or saline are probably best because they have a fairly compatible osmolarity but lack the necessary substances to maintain the cell metabolism to a normal level. However, the root cells won't die immediately but they will be unable to replicate, lowering the chances of them reforming new cells after reattachment. ",
"Also, saliva is probably the worst because its osmolarity is very, very low plus its got all these bacteria in it, so not only will the cells already be dead by the time of replantation but the tooth socket will also become infected. "
] |
[
"I know this is possible from first hand experience, though it wasn't accidental. I had a tooth in my upper jaw removed (they actually had to split the tooth it was under first and then retrieve it) and then they reattached it to my lower jaw where it still is today.",
"If this fall under the anecdote-rule, feel free to remove it."
] |
[
"Can vouch for mouth storage. I knocked three of my front teeth out of their socket but they were still loosely attached at one end by some tissue, their wasn't an oral surgeon on call that night so they gave me some pain killers, packed my mouth stuff to hold the teeth in place, and had surgery the next morning to put them all back. 9 years later I still have all of those teeth."
] |
[
"Is someone trying to develop electric airplanes?"
] |
[
false
] |
[deleted]
|
[
"Unless there is an unprecedented breakthrough in battery technology, electric airplanes replacing regular commercial jets isn't something that's going to happen.",
"This is due to the fact that fossil fuels have a very high energy density compared to batteries. High end lithium ion batteries clock in at somewhere around the 1 MJ/kg, whereas jet fuel sits around 43 MJ/kg. Even considering the fact that electric engines may be more efficient, this is still a massive difference.",
"Fuel already makes up a very large part of the weight of an aircraft. The Airbus A320, a common short-haul craft can carry up to about 20,000 kg of fuel and has a maximum take off weight of about 68,000 kg. So fully loaded and fueled up, this aircraft already has about 30% of its weight in fuel. If you had to replace the fuel with batteries, the entire aircraft would be many times heavier (which would require more powerful engines and even more batteries to power them, making the thing even heavier).",
"So why not use solar panels? That sounds like a decent plan, after all, the Solar Impulse project already demonstrated an aircraft capable of circumnavigating the planet (in multiple stages) powered purely by solar energy.",
"But the answer is once again: Not enough energy for commercial purposes. The Solar Impulse aircraft had a wingspan comparable to that of the Airbus A380, the largest passenger plane ever built. But while the A380 can seat up to 800 people, the Solar Impulse craft had room for just 1 person. And while the A380 cruises at 900 km/h, the Solar Impulse had to settle for 90 km/h during the day and 60 km/h during the night.",
"And while the efficiency of solar panels will surely increase with time, this won't be nearly enough to cover the gap.",
"So right now, battery or solar powered electrical aircraft are simply not feasible as replacement for commercial jets. And this is not a matter of a few years of R&D, but a very fundamental gap between the amount of energy needed and the amount of energy we can get out of either solar panels or batteries. Fossil fuels are simply too good at what we use them for.",
"A more realistic approach may be found in the creation of artificial fuels. These fuels could be created in a way that extracts carbondioxide from the atmosphere and while upon burning them, the carbondioxide is released back into the atmosphere, the cycle is a whole would be CO2-neutral. However, producing artificial fuels is currently extremely inefficient and requires a large amount of energy. Once our land-based energy is provided exclusively by clean, renewable sources, we can look at funneling any surplus of clean energy into producing artificial fuels."
] |
[
"Great response, if I could just tack on a point that is worthwhile, that specific energy in terms of energy per mass must also be compared with its alternate, but equally important, conceptualization as energy per VOLUME. I bring it up because if you look at a chart like ",
"this",
" you can see that hydrogen as a fuel has a very higher energy / mass ratio, much higher than jet fuel (i.e. kerosene) which might make you think that hydrogen fueled planes with clean emissions are the way to go. However, you then see that for hydrogen, energy per ",
" is quite low and thus you need to make a very large plane (and all the extra metal and weight that goes with scaling up size) to carry fuel.",
"The nice thing about jet fuel and gasoline is that they're very competitive in BOTH volume and mass considerations."
] |
[
"The more I learn, the more it seems like the main problem with stopping climate change always comes down to producing enough clean energy for growing demand and storing it efficiently enough. I know a lot work is done trying to create better solutions for these problems but I feel like countries around the world should put more money into it before it's too late."
] |
[
"Could a plane (e.g. a fighter jet) fly through a traffic tunnel?"
] |
[
false
] |
Context: There are various videos from computer games, such as , where fighter jets fly through traffic tunnels. Of course the physics from video games don't always apply to reality, so I wonder if a similar stunt would be possible in real life. Could you fly a plane through a (sufficiently large) traffic tunnel, and if not, what would make it impossible?
|
[
"Is there a minimum of air that needs to be above a plane so that it can generate enough lift to fly? ",
"No. Wings actually start getting much more efficient as they get close to the ground - it's called \"ground effect\". ",
"I think your premise is possible, however the handling would probably change massively upon entering the tunnel, so without artificial stabilization it's unlikely that the pilot would be able to maintain control well enough to avoid a collision, even if the airplane was technically still flying well. "
] |
[
"It's more a matter of maintaining control over the aircraft with such a slim margin for error than a matter of simple physics. We also need to consider issues of complex airflow within the tunnel, including ventilation and thermal drafts, as well as the turbulence created by the aircraft.",
"Given that ",
"the current largest diameter tunnel stands at about 15.5 meters (or 50 feet 10 inches)",
", and most fighter jets have an approximate 40 foot wingspan, I know I wouldn't want to try anything more daring than a thread-the-needle type of exercise with a soft ring of cardboard and balsa wood in a fighter.",
"An ",
"ultralight aircraft",
" with smaller wingspan and slower airspeed might be more appropriate to a tunnel traversal attempt."
] |
[
"Thank you for your reply. Is there a minimum of air that needs to be above a plane so that it can generate enough lift to fly? I would have thought that a plane in a tunnel would push a lot of air below it and the lower pressure above the plane would inevitably suck it towards the ceiling."
] |
[
"Why doesn't general relativity rule out the existence of gravitons?"
] |
[
false
] | null |
[
"GR is a completely classical theory. It makes no attempt to even describe quantum effects, so it can’t rule them out."
] |
[
"what would the next breakthrough need to be in for there to be another paradigm shift like quantum mechanics?",
"My guess is that we'd need to see something profoundly wrong with quantum mechanics. But it's been tested so precisely in so many ways, I'm not expecting this anytime soon.",
"I've heard stuff about string theory but it all seems very mathematical and theoretical to me.",
"Yes, string theory is an attempt to quantize gravity (among other things). There are already stringent constraints in place in that string theory has to postdict everything we've ever observed in every experiment so far. But unfortunately, the ",
"dictions it makes and where we'd expect to see deviations from currently-accepted theory is at much higher energies than anything we'll be able to probe experimentally for the foreseeable future."
] |
[
"I see. Thank you for taking the time to respond!"
] |
[
"Has sea water always been salty? And how did it all become salty? Shouldnt there be areas where the sea does not have salt? Why is it all salty?"
] |
[
false
] |
Also, is water on comets salty or is this just unique to planet Earth?
|
[
"The seas get salty as minerals (mostly NaCl salt) are dissolved in rain run-off from the land or picked up in glaciers and carried to the ocean. Once in the ocean, the salts dissolve into the water and stay there until life forms absorb it or it precipitates out (but minerals in ocean water haven't reached a concentration high enough to start precipitating out). ",
"When the salt minerals get to the ocean, the water evaporates out but the salts stay entrained in the ocean. This concentrates salt in ocean water over time. This means the oceans are getting saltier over time.",
"Other than rain run-off, the oceans get salty from dissolving rocks along shore lines and newly formed volcanic ridges.",
"The oceans have likely started relatively low salinity, but got salty soon after they started forming. They increase in saltiness over time and will continue to do so until the salts reach their saturation levels. I don't know how close they are to doing this, though.",
"There are areas that are less salty, but not many. The Amazon River spews so much fresh water into the ocean that for almost 200 miles out to sea a sailor could drink fresh water at the surface. ",
"Submarines have to account for various salinity levels because there are local variations based on currents, rivers, glaciers, and other even winds. Salinity raises the density of water and a submarine will feel 'heavier' in freshwater since it displaces less 'weight' in fresh water. ",
"Salt diffuses quite quickly in water and current keep the ocean pretty uniformly mixed on the whole. Remember, there are giant currents that wrap around the oceans like conveyor belts and those conveyor belts carry salt minerals from the surface to the bottom, from the north to the south, and from the east to the west. It's a really good way to mix everything up... but unlike James Bond, it's stirred, not shaken (sorry, couldn't resist).",
"Water on comets could be either salty or fresh. It's likely to be fresher because comets are cold and don't have the same processes (like rivers and evaporation) that concentrate salt into a specific spot. ",
"However, anywhere there is landmass/rocks and liquid water with currents, it's likely to have salty oceans. Europa (the moon of Jupiter) probably has a very salty liquid ocean under it's ice blanket. ",
":D Cheers!",
"EDIT: Source: I'm an Ex-submarine sailor and had to worry about driving the sub around in low salinity areas (we adjusted internal ballast by pumping water on or off to maintain neutral buoyancy)."
] |
[
"Good answer just one correction: The oceans are not getting saltier with time, in fact ocean salinity has been fairly stable for billions of years. ",
"While evaporation does lead to a higher local salinity that loss is balanced out by freshwater entering the oceans as rainfall or via rivers and streams. Salt is also lost in the formation of evaporite deposits (e.g. the Messinian salinity crisis), pore water burial, hydrothermal alteration of basalt, and filtering through hydrothermal vents.",
"Salinity of the oceans always varies depending on where you are as well as the current climatic/tectonic regime. Still, the salinity of the oceans has been reasonably stable over Earth's history."
] |
[
"That actually all makes a lot of sense. I thought the Navy taught us that the oceans get saltier with time, but then again the guys that taught me that were engineers by trade, not oceanographers or geologists :) ",
"Thanks for the fix"
] |
[
"DRACO (a potential cure for most viruses) will it really work?"
] |
[
false
] |
Do yo guys have any interesting thoughts? I did my research and even read the AMA that was done 8 months ago. I understand that funding is the biggest problem but why wouldn't any multi-millionaire or billionaire try to fund him? not even one?!?
|
[
"Funding is straightforward. This requires lots of funding. It's novel research, unproven, it may not generate any clinically useful medicines. Success in the lab and in a mouse model far from guarantees clinical success. Also it looks to me like Rider wants to retain control over his work and attract funding. And lastly, as you would have seen in his AMA, there are many practical hurdles yet to be overcome."
] |
[
"We don't currently have a population problem, we have a food and shelter distribution problem. The earth could support a whole lot more humans than it is, if we could get our heads out of our asses."
] |
[
"In one of my grad school classes we had a relatively long discussion about DRACO research. We came to the consensus that it's sketchy research. There are very few studies based on it. What published research there is had sketchy experimental design. It's too experimental to be funded and required further studies. There are concerns about efficacy and safety. Also the media caught on to it very early and played it off as a \"magic bullet.\" "
] |
[
"How do orbitals move inside an atom?"
] |
[
false
] |
This may seem like a stupid question because the root word is "orbit" but I have heard that they don't actually orbit the nucleus and do something else entirely. Can a science-savvy reddit user guide me on the correct path?
|
[
"unfortunately the planetary model of the atom breaks down quite a bit when you try to look at the elementary particles that compose matter, however all models are inherently flawed by virtue of being models, but are approximations that help us understand the subject based on the scientific consensus at the time. the most correct model of the atom we have so far is the \"electron cloud\" model, this is like the planetary model of the atom with the electrons in certain groups of electrons in certain places around the atom at certain times. Now the electron cloud model has the added benefit of adjusting for quantum effects that make directly observing an electron rather difficult, what this model does is give a ",
" of where an electron will be at certain points in different orbitals (orbitals stuck around for this model) with four distinct shapes of orbital possible: S orbital, P orbital, D orbitals, and F orbitals (each with different orientations about the x, y, and z axes). the higher an element is on the periodic table the fewer number and types of orbitals are present\nafter you start getting to the transition metals, electron placement in the orbitals gets more complicated, with some orbitals getting filling priority as opposed to other orbitals some times and not in other times. i hope this helps make things it a little more clear on just how complicated it gets when you get this far down with regards to matter\nEdit: changed \"priority to filling\" to \"filling priority\" to make it sound nicer"
] |
[
"Thank you for your answer. I really want to get into chemistry so this is very helpful information. You have indeed guided me. (:"
] |
[
"Under quantum physics, electrons have properties of waves. It's less like a planet orbiting a star and more like a sound wave in acoustic cavity. Or if you want something you can actually see, kind of like ",
"sound waves on a square plate",
", but three-dimensional and spherical. The different orbitals are just different modes of vibration."
] |
[
"what would happen if NASA's vehicle assembly building was filled halfway with water?"
] |
[
false
] | null |
[
"Earth Sciences"
] |
[
"Earth Sciences"
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"It is hypothetical or speculative in nature. We do not allow hypothetical questions because questions that cannot be confidently answered with any available data often invite non-scientific speculation. For more information regarding this and similar issues, please see our ",
"guidelines.",
"A good home for this question is our sister subreddit ",
"/r/AskScienceDiscussion",
" because of its open-ended or speculative nature. Please feel free to repost there!",
"Please see our ",
"guidelines.",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"How does black iron oxide form on hand forged iron, and why is it better at preventing deterioration than rust?"
] |
[
false
] |
Another amateur blacksmith question. I'm my case, I've only begun to set up the smithy, gathering beautiful handmade tools. Some are well over a century old, without a trace of corrosion. They've been kept indoors, but they are only protected by the black oxide, not paint, zinc, chrome, or oil. I understand that firescale forms in the heat of the forge, the smith controls the thickness by scraping it off with a steel brush. But what is this black iron oxide that seems so much more favorable than red rust? Is it a different chemical compound, or a different oxidation state of iron? I know that traditional wrought iron develops a silicate layer, but this is mild steel.
|
[
"If the oxide is black it is most likely magnetite Fe3O4. Two processes come to mind, ",
"blackening",
" or ",
"bluing",
". I'd think blackening would be the simpler process for these tools.",
"Magnetite is not as porous as the red rust Fe2O3 which gives it the better corrosion resistance."
] |
[
"I think it is quite similar to blackening, but it forms without chemical dipping by prolonged working at high tempratures. I have heard of smiths dipping hot steel in oil to protect the oxide better."
] |
[
"I'm going to disagree with Unnat and BCC, as I don't think blacksmiths had the means to make Fe3O4.",
"I think more likely, the oxidation resistance is due to carburization of the iron during the heating process. Back in \"the days of the blacksmith,\" their forges were powered by wood and/or coal. The temperature of the fire would be enhanced by the liberal use of a large set of bellows by the blacksmith.",
"During forging, the blacksmith would heat the material in this carbon-rich fire, hammer, and repeat, working a significant amount of solid-solution carbon into the material. The blacksmith would then quench the part, transforming the casing of the part to hard martensite. GreenStrong is correct, sometimes materials are quenched in oil, which is a common way of case hardening iron/steel (you can do it at home with motor oil).",
"Carburization is, in fact, one method of increasing corrosion resistance. You can read more about carburizing on the wikipedia.",
"Edit: Now that I've read more about how easy it is to create Fe3O4 on cast iron pans, it's quite possible I'm wrong. I'll leave the comment as it is, however."
] |
[
"Given their long lifespans, do turtles or bowhead whales get dementia?"
] |
[
false
] |
[deleted]
|
[
"This is a really cool question.",
"There seems to be an absence of research supporting the idea that these animals experience recognizable dementia; for example, this Society for Neuroscience conference abstract seems to suggest that new neurons continue to be born in turtle brains throughout the entire lifespan (",
"http://eurekamag.com/research/035/470/035470297.php#close",
") and dolphins, another large-brained and long-lived animal, retain social memories for decades, or up to 75-100% of their average lifespan (",
"http://rspb.royalsocietypublishing.org/content/280/1768/20131726?utm_source=HEADS-UP+9+-+15+AUG+2013&utm_campaign=SMC+Heads-Up&utm_medium=socialshare",
"). Both of these are measures that are associated with cognitive and neuronal health.",
"However, these results don't definitively say that dementia never occurs in these or similar species, and neither one examines dementia directly.",
"One thing that future research in this area might help clarify, is what are the evolutionary factors that promote dementia and disorders that involve dementia. I would expect dementia to be like cancer; risk does go up with age, but there are also selection pressures and the physiological mechanisms they act upon that can change that level of risk. One reason I think bees are so interesting, for example, is that they actually show better learning and memory and more brain growth late in their lifespans, because that's when they perform the most learning-intensive behaviors, like foraging for food. Studying those organisms that are long-lived but don't experience dementia, if they are out there, could help us find ways to preserve brain health in older humans."
] |
[
"I tend to take issue with the idea of separating disease from 'natural consequences of ageing.'",
"Cancer is the most obvious example, since the typical mechanism (compounding mutations to DNA which collectively promote growth while preventing inhibitory processes from taking effect) is largely a 'natural consequence of ageing' - the longer you live the more oxidising agents and cosmic rays will zap your genes and the more likely you are to develop cancer. This doesn't preclude other causes, such as CMV and the other oncoviruses, but even if it did it still remains a distinction without a point.",
"The fact that something happens naturally as we age (e.g loss of cilia in the cochlea, loss of taste buds, degeneration of the cornea, loss of skin elasticity) is not in and of itself a useful fact, our interest is in ",
" it happens as we age, and what we can do to prevent or reverse it."
] |
[
"Stupid question, but is there any evidence that the forms of dementia that we commonly associate with 'aging' are a natural consequence of aging, even with humans?",
"Certainly it could be the case (might even have been proven) but just naively it seems like it didn't \"become an issue\" until everyone started living so long, which primarily occurred after the advent of medicine (and to a certain extent the industrial revolution). Not sure how exactly you \"clean your sample\" to control for the possibility of environmental factors like heavy metals (lead, mercury, etc...) or even conceivably prion diseases (post hospitals).",
"Written history only goes back so far but even if you go back to the beginning you're seeing them taking things known to cause dementia as a form of medicine. Cinnabar (asia) for sure but even sodium nitrate (egypt) has been linked strongly with issues like these."
] |
[
"Against a background of auditory noise, why is it much easier to pick out a drumbeat than to pick out isolated or stochastic sounds? Are we specifically sensitive to frequencies of signals, rather than just signals themselves?"
] |
[
false
] |
This has been something I have been wondering about for a while. The same observation applies to a blinking light against a colorful or noisy backdrop. Is there some scientific basis to this?
|
[
"You may be mixing up the term ",
" with ",
"."
] |
[
"It takes an incredible amount of energy for our brain to interptret the information our senses give us, and it is more efficient for it to focus on \"important\" things than it would be to focus on everything. In nature, \"important\" refers generally to either human faces, voices, etc., or \"things that are different.\" Drumbeats are easy to hear because, unlike the rest of the music, they are very sharp, atonal sounds. "
] |
[
"Not necessarily. While the brain is very good at picking up patterns, it is also very good at picking up things that don't fit a pattern. If there are a bunch of people in a room playing random stuff on drumsets, it will be easier to single out the one guy playing an actual beat, but if there a bunch of people playing beats, it will be easier to single out the one guy randomly hitting things. It depends on what you mean by \"noise.\""
] |
[
"How does music effect the brain?"
] |
[
false
] |
I am doing a project on how music effect's the brain and stumbled upon the theory of The Mozart Effect. My question is how exactly does the playing of classical music increase spatial reasoning? Is it a certain beat and frequency that stimulates certain parts of the brain? If so do certain genres of music effect people in different ways?
|
[
"Thanks this is what i was looking for! My last question was not as important as the rest of it. But basically I was wondering if the theory of the Mozart effect working on a person varies from who it is on rather than the music itself. For example a Mozart song temporarily increases the spatial reasoning of person X but not person Y. However when both subjected to a different kind of music such as rock, person Y gains temporarily increased spatial reasoning and not person X.",
"That was what I was wondering before you answered but on my understanding from your reply it seems like that song itself based on the 11 different elements would play a larger factor in possibly increasing spatial reasoning tasks.",
"Again, Thanks for your reply!"
] |
[
"I'm pretty sure the Motzart Effect is a theory at best to be honest, but I may be wrong. We try to separate out brain functions into lower and higher order processes, and spatial reasoning certainly falls in the higher category, which is a process we understand much less clearly than the lower level sensory processing of music. Your asking a fairly broad question but I'll try to answer you as best I can.",
"Basically, there's thought to be 11 elements of music processing: Pitch, consonance, loudness, timbre, reverberation, tempo, rhythm, meter, melody, contour, key. So there's alot to consider in any single piece of music alone and many different genres will still have similar parts of some of these elements within their songs. So, in general, listening to music helps with auditory pattern recognition but this doesn't necessarily mean that particular genres enhance different abilities I don't believe. You just become accustomed to those patterns typically seen in the genre.",
"Music is first processed in the primary auditory cortex (A1), before shipping it's signal off through 4 different pathways each with their own process to contribute to the experience of listening to music. For instance: ",
"A1-----> limbic system (emotional processing of music), ",
"A1-------> Insula (emotional recognition of music), ",
"A1---->Planum Temporale (secondary auditory analysis of pitch, timbre, interval, melody, rhythm and location), ",
"A1------>Heschel's Gyrus (HG) (processing pitch interval and melody).",
"Keep in mind, this is an oversimplification of how those processes work, they still incorporate many other regions to grant the functions I've said they provide, but that's a basic overview.",
"Every song has components of the 11 elements, and so it's always the same regions processing these elements, but they are being activated in different ways depending on the music you listen to. I don't completely buy into classical music increasing spatial reasoning to any obvious degree, however, over time your brain becomes more in tune with these elements being presented in music, and as a result you come to understand and process their elements faster and more efficiently. Which does suggest a degree of improvement in music ability, and pattern recognition, but like anything if you subject yourself to a phenomena frequently enough, you become better at discerning the nature of it. So this isn't revelatory with music.",
"For instance, people with absolute pitch (the ability to name an isolated note when hearing it) have a high degree of dorsolateral prefrontal activity when hearing single tones compared to people with relative pitch (the ability to only name a note if it is referenced with another note). The running theory is that people with absolute pitch have more refined categories of memory for each note, that don't require them to reference another note specifically to tell you what it is. the DLPFC in this case was thought to be contributing to working memory processes attempting to retrieve the memory of a note. ",
"If so do certain genres of music effect people in different ways?",
"I don't really know what you mean by effect people in different ways besides what I had mentioned. In what ways do you mean? Anyway, I hope this helps, if not maybe someone else can drop some knowledge on you!"
] |
[
"Ahh I see what you're saying. Well, if you control for length of time listened and type between person X and Y, there's still a variety of factors that come into play such as attention allocation to the music, history of musical influences in the family, genetics, intelligence, etc, there's alot that could impact differences spatial reasoning. Some people are more naturally gifted at picking apart these patterns I suppose. ",
"I mean Person Y may show improvement if they listen to a different type of music simply because they prefer that genre and listening to the music itself is a more enjoyable process compared to Person X and classical, who knows! The deeper you go the more confused you can get. "
] |
[
"When Betelgeuse goes nova, why will the neutrinos arrive first, before photons?"
] |
[
false
] |
Since both travel at the speed of light, one would naively expect them to arrive simultaneously. do the processes which produce then occur at different times, or does something about traveling through interstellar space "slow down" the photons? EDIT: Duh, neutrinos are massless particles that travel at the speed of light. Still fast enough & with enough of a head start to stay ahead of the photons over 600 light years though.
|
[
"do the processes which produce then occur at different times,",
"Yes, this is the answer.",
"There are layers in a star that are opaque to photons, but are still nearly transparent to neutrinos. (",
"https://snews.bnl.gov/popsci/neutrino.html",
") So it's possible to detect neutrinos from the star's core in the early stages of the supernova, but there's no optical signal until the supernova starts to affect the visible layers of the star."
] |
[
"or does something about traveling through interstellar space \"slow down\" the photons? ",
"Traveling through the star slows down the photons.",
"\nStar goes supernova. The center of the star (which is actually what starts going) makes photons and neutrinos at the same time.",
"\nThe neutrinos more or less don't interact, so they exit the star at the speed of light.",
"\nThe photons interact pretty readily, they do that within the star and get reabsorbed.",
"\nEventually the effect of the supernova starts to noticeably affect the outer parts of the star, but this takes a while."
] |
[
"Ethan Siegel has a good article on just this!",
"This Is What We'll See When Betelgeuse Really Does Go Supernova",
"Bascially the supernova collapse is on the order of seconds, but the light takes a month to reach its maximum output.",
"More than 90% of the energy exits in neutrinos within the first seconds."
] |
[
"Is there a formal name in psychology/psychiatry for the inability to correctly judge the logical relationship of one event or thing to another?"
] |
[
false
] |
I have some friends that seem to seize upon the weirdest tangential things while when they critically examine an event or circumstance. It really seems like a bizarre inability to filter data for relevance. Instead of being able to assess the relevance of an event or data they seem almost unable to gauge its relevance, which then forces them to construct a scenario to accommodate all of those irrelevant facts under one bizarre theory. Please forgive me if my description isn't very clear, but it's very difficult to verbalize.
|
[
"It sounds like you are describing a ",
"logical fallacy",
". I don't think it is specific to any mental disorder, since everyone is prone to use them from time to time."
] |
[
"Cognitive dissonance refers to anxiety or discomfort by trying to consolidate competing thoughts. It's a symptom of a thought state, not really a type of reasoning-->although it can lead to some pretty interesting mental gymnastics."
] |
[
"I'm sorry this is so specific to you. It is hardly a scientific question though beyond the obvious he was told x=y and he is x so he does y. Reaching out to people beyond this view will be painful. I wish I could help. Just know that you knowing the truth is a step in the correct direction and even if it hurts you you are helping people in the future.",
"Sorry."
] |
[
"Could someone explain what happens in this video? (And whether it is accurate)"
] |
[
false
] |
At 3:00 of this video.
|
[
"You mean when they drop the object into the assembly, and everything flashes blue for a second?",
"What's happening is that they have an assembly containing some fissile material. The object that they drop into it contains more fissile material.",
"When the object enters the assembly, the addition of the extra fissile material quickly increases the neutron-induced fission reaction rate inside the assembly. But it does ",
" increase enough to go critical.",
"So what you see is a quick jump in the reactivity of the assembly, followed by a fast die-off with time called a \"fizzle\".",
"For a movie, the physics of it and the approximate timescale seem plausible.",
"As for the blue glow, that's supposed to represent Cherenkov radiation. It's light, with the frequency distribution peaking somewhere in the blue-UV range, which is emitted when charged particles move faster than c/n through a medium with index of refraction n. In this case, you've got fast electrons which penetrate out of the assembly, which can produce Cherenkov radiation.",
"I don't really have a sense for how accurate the video is in terms of the brightness of the Cherenkov radiation. Luckily, I've never been standing near a critical assembly like this when it's been made to fizzle or go critical, so I don't know how much Cherenkov radiation would be visible, if any."
] |
[
"This is exactly what happen in a gun-type weapon, except the assembly would go supercritical with a real weapon.",
"I don’t know why he’s not looking towards it. It might be a joke, because when you’re standing that close to an unshielded assmebly, you’re getting a huge dose. Whether or not you look directly at it makes little difference. It could be a joke about the naivety of the people working on nuclear weapons at the time."
] |
[
"Thank you very much for the clarifications! I appreciate it."
] |
[
"I know that GPS systems have a resolution of a few meters. Is there any way to bring this resolution down to the cm? Any available commercial solution?"
] |
[
false
] |
Maybe an algorithm that takes different measurements and makes another estimation can improve the system.
|
[
"Plenty of ",
"GNSS",
" (the more generic term for GPS, GPS is the US system, but there are several constellations of satellites, e.g. GLONASS, Galileo, and BeiDou) systems already have cm scale accuracy. There are a couple of different strategies for achieving higher accuracy. In general, having receivers that are able to track more satellites (e.g. receiving signals from several or all of the satellite constellations mentioned above) will help improve accuracy, but the best results come from using some source of 'corrections' to apply to a receivers measured position to account for errors, e.g. distortions of the signal(s) from atmospheric effects. These corrections usually rely on a stationary receiver measuring its position very frequently (several times a second) for a while (this can be a permanent station averaging over years, or a station that's running for a few hours). If you have a roving receiver that can receive these corrections, it can update its position based on this information to improve the accuracy. There are a variety of ",
"differential GNSS systems",
", where there are networks of stationary receivers with known positions broadcasting corrections. Another strategy (and usually actually better in terms of accuracy, depending on the distance of your rover from a DGPS station) are ",
"RTK",
" systems where you set up two receivers, a base station that averages its position over the duration of a survey, and a rover that is measuring the positions of interest and correcting those positions based on the distance from the base and the position of the base (the accuracy of which generally increases the longer it sits in a single place). Recently, there has also the been the proliferation of satellite correction services, i.e. the ability for a single receiver to receive GNSS signals but also corrections from separate satellite constellations broadcasting real-time corrections, so that you don't have to have two receivers (with real time communication) or be plugged into a local DGPS network, though the accuracy is generally lower than most DGPS solutions and definitely lower than an RTK setup, e.g. ",
"the Atlas service",
". These are all systems that are commercially available, but not exactly cheap. A GNSS receiver that can receive signals from multiple constellations and get corrections from a local DGPS network will usually run you a few thousand dollars (there are some out there for less than 1K). A good RTK setup will set you back few tens of thousands of dollars (just bought one for my lab that's sort of middle of the road to high end that was ~50K). ",
"Caveat: I'm a GNSS user who cares about high positional accuracy, but am not a good source of technical details, so I'm sure others can contribute more relevant details."
] |
[
"Accuracy refers to the difference of the mean location reported by the receiver and the true location of the measured position as determined by an independent method, which is generally what we care about more (and ultimately what the OP was asking about). Precision is referring to the narrowness of the range of repeated measurements from a given receiver. As you move up in quality of receiver, both the precision and accuracy will improve, but the corrections as discussed in the original comment are what's improving the accuracy by significant amounts. You can be using a $20k GPS receiver and the precision may be quite good, but if it is not receiving corrections from some source (or itself is not sitting motionless for several hours) the accuracy will likely be on par (or at least not so much better to legitimize the cost) with a standard handheld GPS."
] |
[
"New GPS satellites are beginning to broadcast a second civilian navigation signal, L2C, which will have improved accuracy and, because two frequencies will be broadcast from each satellite, will allow receivers to factor out errors like those induced from the ionosphere. Slated for full deployment by 2021.",
"There are layers of broadcasted GPS signals which can allow for higher access - P code and soon M code - but the encryption algorithms are reserved for military use."
] |
[
"Can you see stars during the day?"
] |
[
false
] | null |
[
"Sometimes. We don't really know what you saw in particular though"
] |
[
"The question is, is that a star that is typically visible during the day?"
] |
[
"Oh. In that case I recommend posting such a specific question to an astronomy or stargazing sub"
] |
[
"Relativistic length contraction: a nuclear bomb that explodes or not depending on observer?"
] |
[
false
] |
[deleted]
|
[
"Criticality depends on the geometry of the material, and the Uranium wouldn't look like a sphere to an observer moving relative to it. It would appear denser but flatter, like a pancake.",
"You can think about it in terms of what happens to individual fission neutrons. Critical mass is reached when the neutrons emitted by a single fission event generate more than one additional fission. Something like 2.5 neutrons are emitted on average per fission, so if the cross section for absorption of a neutron is higher than 1/2.5, the material is supercritical. Every observer will always agree all events, which means that if it were possible to observe the Uranium on a subatomic scale then every observer would agree on which neutrons escape the material and which neutrons generate further fissions. They will just disagree on the geometry of the situation. The observer at rest relative to the Uranium will observe a normal-density sphere of such a size that the average neutron will have just under a 1/2.5 chance of inducing another fission before it escapes the material. The observer in motion relative to the Uranium will observe a higher-density but deformed sphere of such a shape that the average neutron will have just under a 1/2.5 chance of inducing another fission before it escapes the material."
] |
[
"In a reference frame where the uranium moves at relativistic speed the critical mass will be different, and the calculation will be so complicated that the answer is \"consider the rest frame of the uranium\".",
"All observers agree on whether there is a nuclear explosion or not, of course."
] |
[
"Why should it stay the same? The usual calculation if something is critical or not assumes the uranium nuclei are at rest (or at least with negligible motion), the decays are isotropic and so on - all these things are no longer true for the observer who moves relative to the uranium."
] |
[
"Were days longer thousands/millions of years ago?"
] |
[
false
] |
A friend of mine has just told me that in the past (thousands, millions of years) the days of the Earth were longer than 24 hours. Does this have any scientific backing behind it? (Also, I know days are not exactly 24 hours long, but it is rounded for simplicity).
|
[
"Your friend has it backwards. Days used to be as short as ~6 hours or so back when the Earth had just formed, and have since lengthened. ",
"Here",
" is a random paper I dug up that shows in Table 2 on p10 (i.e. the third page of the document) how day length has increased with time."
] |
[
"Per ",
"wikipedia",
":",
"About 320 million years ago there were 400 days in the year."
] |
[
"But has the absolute length of the year changed at all in that time?"
] |
[
"How did scientists know the first astronauts’ spacesuits would withstand the pressure differences in space and fully protect the astronauts inside?"
] |
[
false
] | null |
[
"They built vacuum chambers on Earth large enough for people to fit inside. That way they could test the suits, with people inside them, in a hard vacuum before they actually sent anyone to space. If something went wrong during one of the tests the could open the door to the chamber and instantly repressurize it."
] |
[
"It’s not just opening a door. They did have one persons pressure suit fail in a test and he actually passed out before they could get to him, he said he could fell the saliva in his tongue evaporate before he lost consciousness. I don’t remember his name though."
] |
[
"Jim le Blanc, 1966",
"http://www.spacesafetymagazine.com/aerospace-engineering/space-suit-design/early-spacesuit-vacuum-test-wrong/",
"https://www.spaceanswers.com/space-exploration/incredible-footage-of-a-nasa-test-subject-being-exposed-to-a-space-like-vacuum/",
"It is the only well-documented case of a human exposed to a strong vacuum. While the crew of ",
"Soyuz 11",
" experienced vacuum as well they died and we don't know what exactly happened to them."
] |
[
"How close are asteroids and Kuiper belt objects to each other?"
] |
[
false
] |
I'm just trying to get a sense of the distribution. So what's the mean and median distance, and about how close would the average closest encounter be on any given orbit? This can be limited to objects of a certain minimum size, if that helps.
|
[
"That tells me how far they are away from Earth, but not how far the components are from each other. The first graph on the Kuiper belt page is actually what sparked my question."
] |
[
"econleech, I don't think you're answering the OP's question. I think the question is whether the space density of Kuiper Belt Objects (KBO's) is high enough that they have close encounters during single orbits. If that's the question, then the answer is no.",
"The best number I can find is from ",
"this paper",
". Figure 2 shows a plot of the angular number density as a function of the size of KBO's. For 1 km sized objects, there are about 5 per square degree. Assuming a distance r=50 AU, dividing this angular density by r",
" gives a space density of about 10",
" km",
" . Taking the cube root of this to get a typical separation gives around 10",
" km, much larger than the roughly 1 km size of the KBO. "
] |
[
"From wiki:",
"http://en.wikipedia.org/wiki/Kuiper_belt",
"http://en.wikipedia.org/wiki/Asteroid_belt",
"Kuiper belt goes from 30 to 50 AU from the Sun, and the asteroid belt is between Mars and Jupiter, so between 1.5 to 5.2 AU from the Sun."
] |
[
"As a preventive measure: can someone donate blood and store it for his own surgical procedures in the future?"
] |
[
false
] |
A relative of mine needed surgery and we were asked to donate blood for him. Which in turn led me to wonder about this topic. Is is possible? For example, someone that should not donate blood because he or she has a certain disease: could this person store blood for him/herself?
|
[
"Yes, this is known as ",
"autologous blood donation",
", and ",
"is usually done before (up to about a month) operations",
". ",
"They should also be done no sooner than 3d prior to surgery, to give the body sufficient time to recover.",
"(You can also use this technique for non-medical uses - ",
"blood doping",
".)"
] |
[
"This is accurate, and I will add on a bit. Whole blood donation can be done once every 56 days, platelets can be done twice a week, and plasma is about the same. These are all used for different treatments, and red blood cells are used most often for replacement of fluid volume, as platelets and plasma regenerate quickly.",
"If you were to consider donating as a preventative measure for an accident, this would be close to impossible. Red blood cells have a shelf life of 42 days, and most accidents that require blood transfusion will need at the very minimum 8 units of blood. Severe cases (car crashes, etc.) can require up to 50 units.",
"Not a scientist, I just work at a blood bank."
] |
[
"Yes. Interesting fact - ",
"the President of the US has a supply of his own blood in the Presidential limousine in case of emergencies",
"."
] |
[
"What was the diet of early man before the discovery of fire and how soon after did man start \"cooking\"?"
] |
[
false
] | null |
[
"You only need to look at our ancestor's teeth and general size to determine what our diet most likely would have been. Homo habilis being the most recent hominid that didn't use fire, their dental structure and damage shows a diet of tough plants. Their small size indicates it wasn't all foliage, as a diet only in grasses and leaves would make them much larger. Like gorillas, animals need a large gut to breakdown plant fiber. Most likely a diet of high calorie fruits, nuts, roots, and the occasional meats was the norm along with the much more available rough greens.",
"Regarding when did homonids start cooking, it's unknown. However we do know the affects it had. Eating cooked protein greatly increased their physical size as well as promote an increase in myelin protein growth. This was the key factor for the increase in homonid intelligence. Animal protein has Neu5Gc, a Sialic acid that the human body normally rejects. By cooking meat, this protein is broken down, allowing the body to use the amino acids to create Neu5Ac. An important Sialic acid for neuronal growth. Neu5Ac also is the key factor in preventing simian malaria and other diseases. This is where the unknown knowns issues occur. Did malaria create Neu5Ac to start the increase of human intelligence, or did cooking meats create Neu5Ac that helped fight off malaria. No one knows. (it always made me laugh that it is possible that mosquitoes created modern man)"
] |
[
"No. Dogs create Neu5Gc. They are not carries of Neu5Ac. Dogs will always create it from eating proteins of any kind, cooked or raw. Chimps would be a good candidate for dietary study though. They carry both, but the Neu5Ac is much lower in their cells. It would have to be a multi-generational study of course.",
"Neu5Ac and Neu5Gc is an absolutely fascinating subject to study. We can trace it back to the creation of the homo genus, possible reasons humans have cancer(Neu5Gc is in all cancer cells), find cures for malaria and influenza, create supplements to increase myelin protein during infancy. So many avenues to venture into.",
"Here's a fun fact. Human breast milk is high in Neu5Ac. Formulas do not. Think about that before you decide to formula feed your child from the start."
] |
[
"Regarding when did homonids start cooking, it's unknown.",
"It doesn't suggest an absolute timescale, but this information is interesting:",
"Great apes prefer cooked food to raw",
" (NCBI)",
"I would expect that among fire-using humans cooking was \"discovered\" independently many, many times... every time someone dropped food into the fire by accident, in fact. And that once it was discovered, it caught on immediately, literally that day, because it was very easy to do and produced a more palatable meal."
] |
[
"Is there a reason for the order of the English alphabet? Where/when was its earliest appearance in its current form?"
] |
[
false
] | null |
[
"They have a gif that gives brief insight on the alphabet: ",
"http://i.imgur.com/5b3bI.gif",
" "
] |
[
"The English alphabet derives heavily from Latin, which itself borrowed from Greek - but it's mutated over the years.",
"http://en.wikipedia.org/wiki/History_of_the_alphabet",
"(This is actually a science question in multiple fields. Linguistics, archeology, ",
" err I meant anthropology, more.)"
] |
[
"I think you would really love this documentary ",
"the adventure of english",
". ",
"\"...the biography of English as if it were a living being, covering the history of the language from its modest beginnings around 500 AD as a minor Germanic dialect to its rise as a truly established global language. In the television series, Bragg explains the origins and spelling of many words based on the times in which they were introduced into the growing language that would eventually become modern English.\""
] |
[
"Does our vision deteriorate while we sleep?"
] |
[
false
] |
Staring something at an unchanging distance for long periods of time is detrimental to our eyesight, as with a computer screen - but when our eyes are closed, aren't we just staring at our eyelids? Or do our eyes start functioning differently? Also, when we experience REM sleep, does the lens react to our dreams as it would to something we'd see in real life? I came up with the ridiculous speculation that a dream's purpose is to stop our eyesight from going bad. So many questions, but so little knowledge! Help me out, asksience :)
|
[
"While there likely it's a definitive answer to this, eyes are just receptive organ, the brain puts everything together and presents them in dreams. ",
"The reason why computer screens ",
" be bad for your eyesight is the bright lights being stared at constantly, but I'm not absolutely certain on that one. "
] |
[
"I don't think it's detrimental, since your eyes aren't attempting to focus on the inside of your eyelid. There's no muscles being used, so you can't strain anything."
] |
[
"Staring something at an unchanging distance for long periods of time is detrimental to our eyesight",
"...is it? I thought that this was debunked/no longer applicable since we don't really use CRT monitors anymore. Could someone confirm or deny this?"
] |
[
"How long without opiates would it take to start going through withdrawal if you're addicted?"
] |
[
false
] |
I take them kind of regularly with a few days off every now and then and have never noticed any withdrawal symptoms and don't feel addicted. I've been taking them for about 3 years now. Just curious how long it would take before you start going through terrible withdrawal, which I guess is sweating, vomiting, flu-like symptoms, etc.
|
[
"I'm going to go ahead and say the obvious, because it needs to be said.",
"Stop now.",
"I watched a love one destroy herself with opiates. The only thing worse than her dragging me through her addiction by stealing my shit, lying to me, taking advantage of me, and playing venomous guilt games with me was the fact that I knew it was so much worse for her, and that the sweet and loving person I fell in love with was dead.",
"Please stop. They'll turn you into a monster. If you can still take a few days off, it's not too late. Don't wait til you hit rock-bottom."
] |
[
"Pain Management physician here, it depends on the half life of the specific drug. It also varies from person to person, I've had people on high doses of potent opioids go cold turkey with almost no withdrawals. I've had patients on hydrocodone have terrible withdrawals. If you can provide more details, I am willing to give completely unbiased information.",
"Also, consider a medically supervised detox such as a suboxone or methadone program."
] |
[
"If you were experiencing withdrawal symptoms, you would probably start to feel crappy and anxious within hours of your last dose. By the next day, you would begin the crazy sweating and feeling a maddening restlessness that will not stop.",
"Honestly, if you can skip days, you should probably think about managing your pain in another way. It is a ",
" slippery slope for those with chronic pain to descend in to physical dependence (or even addiction). I assure you, no one is immune - it can happen to anyone.",
"Edit: Removed improper assumption."
] |
[
"Does the perceived gravitational force of an object increase as it approaches the speed of light? If so, can a hypothetical spacecraft approach the speed of light without having the gravity of the universe tear it apart as the gravitational force approaches infinity?"
] |
[
false
] |
I've tried asking this before, but it didn't get much attention. My curiosity hasn't diminished, so I apologize ahead of time for bringing this up repeatedly. I was criticized last time for my misinformation of general relativity, so I'd first like to ask whether one of the relativistic distortions that occur when you observe and object approach the speed of light from a stationary reference frame is a perceived increase in mass. I remember learning that gravitational force exerted by an object increases near the speed of light, but everyone insisted that that wasn't the case. A confirmation would be greatly appreciated. Lastly, if the gravitational fields of an object accelerating closer to the speed of light relative to a stationary reference frame approach infinity, would the gravitational distortion of every object in the universe coupled with Lorentz Contractions in the direction of travel tear a ship apart?
|
[
"It is my understanding, yes",
" a particle's kinetic energy, and therefore relativistic mass, does contribute to its gravity. However, ",
"a particle cannot go fast enough to turn into a black hole",
" ",
"Your question regarding whether accelerations result in a ship tearing itself apart ",
"has been discussed at length for some time",
" and is related to the question of whether Lorentz contractions act on space itself or are physical stresses in objects in space. And it seems ",
"affirmative",
" that the stresses exist. But this doesn't require gravitational stresses from any other external objects. ",
"You're also asking if the apparent mass increase of nearby objects you see when you are traveling very fast will tear you apart? I do not know."
] |
[
"Mmm.... it contributes to the ",
" in so far as momentum is a part of the stress-energy tensor, but I can't be so certain that would produce Newtonian-gravitation like effects.",
"It's far better, IMO, to avoid the \"relativistic mass\" concept entirely, and only define mass to be the Lorentz-Invariant scalar magnitude of the energy momentum 4 vector. "
] |
[
"Ah, so in this case, a curvature field alters the way one handles the derivatives in a Lagrangian. Not only are you taking derivatives of spatial position of some object with respect to time, but now you must take spatial derivatives with respect to space, and time derivatives with respect to space, and so on. So if we begin with a free-body Lagrangian (ie no forces/potentials) and work out its physical behaviour, we can ",
", from the way the derivatives are handled, a gravitational potential like term appears in the equation. This is why it is often discussed as to whether gravity is even a force or not, as it's an apparent term derived from a free-body Lagrangian in curved-space time. ",
", we only have certain solutions of spacetime that provide terms like classical Newtonian gravitation. When you consider the GR solution of the large scale structure of the universe, it's dominated by the notion that space expands as a function of time. That's nothing at all like Newtonian gravitation. ",
"Furthermore, if we take the naive application of Special Relativity, we'd assume that gravitation always points to the time-retarded position of the barycenter of the orbit (ie points to where the sun was 8 minutes ago, rather than where it is right now). But Newtonian gravitation is instantaneous and points to where a body is right now. And it can be further shown that if gravitation was truly time delayed, then orbits would be unstable. Well ",
"this work by Carlip",
" (given more simply ",
"here",
") demonstrates that it is the momentum of the sun, and the momentum term in the stress energy tensor that actually shifts the \"focus\" of gravitation from where the sun ",
" to the time extrapolated position of where the sun ",
" 8 minutes from 8 minutes ago (ie right now). ",
"So, while I can't at all have claimed to ",
" the above question, it would seem to me that the variations arising from motion would likely not produce a substantial change in gravitation.",
"Caveat: Carlip's claim holds because terms cancel out through (v/c)",
" , and that since v<<c, these aberrations are negligible. Perhaps at the higher speeds mentioned in OP, the negligibility drops out, and some other effects hold/dominate. I don't rightfully know the answer to either of these questions."
] |
[
"Why don't sealed terrariums explode?"
] |
[
false
] |
Is it balanced so perfectly that the oxygen released by the plants is utilised by microorganisms that in turn provide carbon dioxide and nitrogen/waste, which feeds the plants and the cycle restarts? I'd just imagine there being some offset that causes gas accumulation eventually causing the glass jar to explode. Especially when the animals within, snails and such, piggybacking on the plants I introduce, begin to breed? Similarly to when I did sauerkraut that one time and didn't provide a release valve 😅 How can these jars stay sealed for years with no mishap it's amazing!
|
[
"In order for the pressure to build up, you need something that is solid or liquid to be converted into a gas. In your sauerkraut case the bacteria doing the fermenting broke down your cabbage (solid/liquid) and released part of it as a gas.",
"In most ecosystems (the terrarium in this case) things are broken down and turned into gasses, but then other organisms will work in the opposite direction and turn those gasses back into solids. When a plant is doing photosynthesis, it is using power from the sun to take the carbon on CO2 and turn it into glucose (sugar), which is taking gas out of the terrarium and turning it into a solid (sort of). Other organisms will take nitrogen (N2) out of the air and turn it into something usable (often ammonia), which is then released again as big molecules break down. The balance of all of this is very important, and when things get out of flux it can have negative impacts. Sometimes runoff from farms can put too much (solid) nitrogen into an ecosystem and cause algal blooms that kill everything off.",
"Luckily ecosystems evolve in such a way that things are often kept at sort of a balance. If you have an ecosystem with too much oxygen in the air then organisms that can use that oxygen will flourish and naturally reduce it. So when you make a healthy terrarium you often are getting all of those balancing components. It is possible to create the sauerkraut situation though, if you don't have places for your water to drain and move through you can cause bacteria similar to the ones fermenting your cabbage to build up quickly, and then will create excess pressure, though there is less food available so it might not explode."
] |
[
"It's true that the net photosynthesis reaction consumes CO2 and produces O2, but I just want to add here that the O2 released from plants undergoing photosynthesis actually comes from water, not CO2. This was discovered using radio-labeled water IIRC."
] |
[
"Photosynthesis does not create oxygen, it simply strips the carbon off of two oxygen atoms and lets them go free. So while the original molecule looks like O-C-O (carbon dioxide) the molecule released after photosynthesis will look like O-O (atmospheric oxygen), converting some of the mass that was a gas into a solid. ",
"Respiration (burning fuel for energy) will later take one of those carbons and attach it to two oxygens to get some energy out of the reaction, hence our cycle.",
"edit- I feel like I should also point out that how the actual chemical composition of a gas impacts how it will behave in regards to pressure is very complicated (you will need a physical chemist for that question). So while the total mass of the molecule goes down how it interacts might change. I don't think it would change much, but I do not know for certain. The important idea is that it cycles between different states of matter in a healthy ecosystem."
] |
[
"How is it that I can have a different blood type to my biological parents."
] |
[
false
] |
I just recently found out my blood type again (after continuous forgetting of it) and found that my parents either have a different RH or alternate blood type to me. It baffles me because from what little I know about blood type is simply that blood types are picky about what blood types can be introduced into the body via blood transfusion. I would think if this is the case, then surely I would just inherit blood type like one does hair colour etc, through the strongest gene and what not... That being said, what would then happen if both parents were the same blood type and their offspring was born with a different blood type all together? Is that even possible and why? I'm sorry if this question is profusely discussed on the internet, but I not only cannot seem to find the right wording for searching it, but was also hoping someone could explain in laymen's terms for me. Thank you in advance for any assistance offered.
|
[
"This is an oversimplification, but should work for most cases. Your ",
" - which genes you have - determines your ",
" - what antibodies your blood has on it. There are three possible gene types - A, B, and O - and you get one from each parent. Thus, your genotype could be OO, OA, OB, AA, AB, or BB. Type O is ",
", while A and B are ",
". This means that O will only express itself if there is no-one else around - i.e., the genotype is OO. If you have OA (or AA), then you will have type A blood. If you have OB or BB, you will have type B blood, and if you have AB, you'll have AB blood.",
"Imagine that both of your parents are OA - therefore, they both have type A blood. When they did the dirty and made you, there are four possible genotype combinations you could have inherited from them:",
"If you work out all the possible combinations and example, the only way you're ",
" to have the same blood type as your parents is if both of your parents are type O. (Even then, as I've said, I've oversimplified by ignoring rhesus type and some other possible blood types.)"
] |
[
"Your dad is probably O+. You inherited the dominant allele for a positive Rh factor from him, and the dominant allele for the A protein from your mom. "
] |
[
"What's your blood type? What is your parents' blood type? With this information we can give you some specific examples of how this happens."
] |
[
"Why is the delta++ baryon less stable than the proton, when the up quark is more stable than the down quark?"
] |
[
false
] |
In other words, why does uuu -> uud (+ pi ) when udd -> uud (+ e + antineutrino)?
|
[
"Because it is not as simple as \"up quarks are more stable than down quark\" or \"up quarks always tend to decay to down quarks\".\nIt always depends on the quantum mechanical (well, quantum field theoretical) details of each single bound state and the possibilities of their decay.",
"Just as another example: a delta+ baryon and a proton consist of the same quark ingredients and still behave wildly differently. In that specific case it's because of the spins alignment of the quarks within the bound state."
] |
[
"Because the delta++ baryon has a lot more energy. A baryon can have two identical quarks in the ground state (opposite spins), but not more than two. One of the up quarks in the delta++ baryon therefore needs to be in an excited state, which makes it more energetic than a proton + a pi meson."
] |
[
"This makes a lot of sense, thank you!"
] |
[
"Is chemical rocket exhaust usually a plasma?"
] |
[
false
] | null |
[
"It is a very weakly ionized plasma. I don't have sources right now but it's probably much less than 1% ionized. For comparison a \"real\" plasma rocket usually has more than 70% ionization of the exhaust (depends quite a bit on the tech)."
] |
[
"The exhaust typically reaches around 3000 k, which is much too low to form a plasma",
"The exhaust ion temperature in most plasma thruster is much lower than 3000 K. In Hall thrusters it is in the neighborhood of 1000 K. "
] |
[
"The exhaust typically reaches around 3000 k, which is much too low to form a plasma",
"The exhaust ion temperature in most plasma thruster is much lower than 3000 K. In Hall thrusters it is in the neighborhood of 1000 K. "
] |
[
"Why are tritium and deuterium suitable for nuclear fusion? Why not use hydrogen?"
] |
[
false
] | null |
[
"Deuterium and tritium ",
" hydrogen. Hydrogen (any of its isotopes) is ideal because it’s got the lowest possible Coulomb barrier (proportional to Z",
"Z",
").",
"However “fusion” of hydrogen-1 with hydrogen-1 into deuterium has an extremely small cross section, because it involves the weak force. This works in stars because there’s just a huge amount of material, but the cross section is way too small for this reaction to be useful in a terrestrial reactor.",
"But DD and DT have more or less the same Coulomb barrier as hydrogen-1 on hydrogen-1, much higher cross sections, and they’re very exothermic. So much better-suited for this application, you just have to amass a bunch of deuterium and tritium."
] |
[
"It is difficult to overstate just how incredibly inefficient proton–proton fusion (ie. fusion of ”normal” hydrogen nuclei) is. The often used comparison is that every cubic meter of the sun’s core produces approximately as much power as a decaying compost pile. This is fortunate for us, because otherwise Sun-like stars would burn out much faster, likely giving complex life too little time to evolve."
] |
[
"The lifetime of the Sun doesn't depend that critically on fusion cross sections because the conditions are self-regulating. If the cross section were larger the Sun would be stabilized at a lower temperature/pressure in the core, but with a similar power density and with similar conditions outside."
] |
[
"Why can my dog easily differentiate between the barking of a dog on T.V. and a legitimate dog?"
] |
[
false
] |
[deleted]
|
[
"The dogs bark heard on TV will have been recorded, digitally stored (most likely, that or on tape) and then re-emitted by your TV. Each of these steps will have distorted the bark in some way, your TV especially is likely to have done so as the sound system will be designed for humans who hear sounds in the frequency range of 20Hz-20kHz while dogs can hear at much higher frequencies (20Hz-40kHz, which is why you cannot hear a high frequency dog whistle but they can) so a large part of the recorded bark will be lost to your dog (assuming the speakers are limited/optimised to the human hearing range).",
"Edit: I may be wrong on the frequency range cutting out part of the dogs bark as apparently they are over a lower range more similar to human hearing than I thought they were."
] |
[
"Audio Engineer here:",
"A little off, but I remember watching a video of an octopus seeing its reflection on a mirror and responding to it as a threat, then on a SD Television and he would not recognize the image as true for the definition of the octopus eye is so high that they could see all the little pixels and therefore not see it as real, but when shown in a HD set, the octopus would see the image and respond to it like it was a mirror.",
"Similar case with the dog.",
"Using a Lab microphone and an uncompressed 192 or 96Khz recording run through a very high end set of speakers (rated accordingly) is set to provide different results.",
"EDIT: Found the article about Octopus and HDTV ",
"http://jeb.biologists.org/content/213/7/i.2.full",
"Edit2: Remember Victor's Logo? A dog listening to his masters voice trough a Victrola (",
"http://upload.wikimedia.org/wikipedia/commons/7/75/VictorTalkingLogo.jpg",
") "
] |
[
"I know we're all talking science here and all, but we're overlooking the fact that a lot of commercials and narrative tv/film, don't use actual dog sounds. ACTORS are often brought in for ADR to record a more specific sounding barks and animal noises.",
"So a lot of times you're seeing a dog and HEARING an actor bark. And you're dog is like: \"what's up with this actor guy barking?\" and ignores it.",
"Here's one such actor: ",
"http://www.lycos.com/info/frank-welker.html"
] |
[
"A dumb question on water"
] |
[
false
] |
[deleted]
|
[
"http://en.wikipedia.org/wiki/Water_cycle"
] |
[
"If you drink water, you will sweat, urinate, breath it out etc... If you cook with water, you will eat some, most will evaporate.",
"Anything else?"
] |
[
"Urine is mostly water. Water is not lost inside the human body. What goes in will eventually go out.",
"Anything you flush down the toilet is processed and dumped back into environment. "
] |
[
"In terms of anatomy, why are some voices husky and some smooth?"
] |
[
false
] | null |
[
"If you mean husky as in rough (a long-term smoker's voice would be an extreme example of this), the answer is that there are asymmetries along the edges of the vocal cords. So when the vocal cords adduct, the mucosal wave that kind of vibrates between the cords is off and the sound comes out rougher. This kind of asymmetry could be caused by something like a little bit of swelling after a long night of talking in a loud place, by a benign pathology like a polyp or nodules, or by something like a tumor. I've heard from a colleague about one of her clients who is an actress--she spends a few minutes screaming each night before bed to keep her rough voice (not recommended). ",
"If you mean husky as in breathy (think Marilyn Monroe's voice), the breathiness comes from the vocal cords not achieving full adduction during phonation. This can be physiological if there is some kind of structural or neurological deficit but this is something we also have the ability to control ourselves. ",
"Source--I'm a speech pathologist"
] |
[
"It has to do with your vocal cords. ",
"This link",
" (Warning, sort of gross) is a video of a camera recording someone's vocal cords while they talk and sing. The white area in the middle is the vocal cords. They're very easy to damage in the long run, through things like excessive yelling or singing. When they get damaged, the voice becomes more husky or scratchy, and it can be hard to reverse the damage. People with smooth voices generally have healthier vocal cords."
] |
[
"Does your voice develop unfazed by certain habits during your teens? Does it develop better with healthy choices? If so, what are they?"
] |
[
"Heat via flame is more efficient than putting an electrical step in the middle--how about light?"
] |
[
false
] |
If heating a house directly with gas is more efficient than heating it with gas-generated electricity via incandesent light, is your house with gas flame also more efficient than lighting it with light bulbs? Or does a flame put out much more of its energy in the form of movement rather than photons?
|
[
"No. The term for what you're talking about is efficacy. It's the amount of visible light energy output for a given amount of total energy consumed (the difference is convective hat or nonvisible light such as infrared). ",
"The frequency of light emitted from a blackbody increases based on temperature, following something called Wein's Displacement law. There's a wide distribution of frequencies, but Wein gives you the most prevalent one (the peak of the spectral distribution).",
"For the temperature of a gas fire, the peak is way in the infrared, and the efficacy is low. ",
"For an incandescent bulb, the filament is much hotter, making the efficacy higher, more than compensating for the less overall efficiency.",
"For instance, giving a ballpark estimate of efficiency, gas is burned at a powerplant for 250w. The steam turbine and generator is able to get 125w of electricity from it. Transmission losses take up another 25w, and you're left with 100w. An incandescent lightbulb has an efficacy of about 10-20 lumens per watt (absolute theoretical maximum is 683 lm/w, high powered LEDs can get up to around 100 lumens/watt, CCFLs in the 50lm/w neighborhood), and you're left with maybe 1500 lumens of visible light. The majority of the energy consumed by the bulb is emitted as heat or nonvisible light.",
"If you burn the same 250w right at home, the efficacy is far lower. You get less visible light, but far more heat and nonvisible light."
] |
[
"Wikipedia has a table under \"luminous efficacy\" showing what I wrote. 14-24 lm/w for incandescent, but only 0.3-2 lm/w for a flame. So it's far less efficient to burn a unit of gas for lighting purposes only than it is to burn a unit of gas to generate electricity and run an incandescent light bulb. Flourescents are 50-80 lm/w, even more efficient. ",
"Th difference with heating your house is that you're only interested in heat, and it's more efficient to convert 100% of the gas energy to heat in your home than to convert 50% to electricity in a power plant then conveert 100% of electricity to heat in your home."
] |
[
"Btw the difference in efficiency of heating is because there's a mechanical step in the process, where heat is used to turn a turbine that makes electric current. Work is lost to heat while turning the turbine blades, and also when the turning coils make current. When you burn the gas in your house, almost all of the heat goes to heating the house, there's no worry about efficiency because instead of losing work to heat, you want the heat. ",
"Burning things to make light isn't as efficient because most of the emitted light is invisible infrared and it ends up heating the house anyway."
] |
[
"Why do thinly sliced meats taste different from thicker cuts?"
] |
[
false
] |
[deleted]
|
[
"Thinner meat requires less chewing. When you don't chew as long, less saliva is in your mouth, which is less water. The quantity of water can dilute the taste of the meat.",
"The sides of the meat may be more rough on thicker meat, which affects the texture. That goes the same if you use different sharpness of knives to cut the meat, which would affect the whole layer.",
"Aeration of the thinner meat may also make a difference, at first, when the thinly sliced meats are not fully chewed.",
"You used a chemistry flair, but if no one else responds, at least you can look up why there are changes in why we taste food differently with these qualities. Since I don't know the answers right now."
] |
[
"Also, the middle cooks less than the outside, and the thicker the meat, the bigger the difference. That's why everyone should buy thick cut bacon. "
] |
[
"Thinly sliced meats also have a different texture than a chunk of meat. There is a \"taste\" lab down the hall that studies gustation (sense of taste). Most people who work in the field will tell you that texture is a large part of the taste that you experience, as well as the actual chemical makeup of the food. How taste signals are transduced by taste cells and processed by the brain are actually not that well understood. We know a lot of the players, but we still don't understand how it all fits together nearly as well as other sensory systems such as the visual system.",
"Source: I am a graduate student in a lab studying sensory neurons. I am actually sitting next to someone who is researching just how taste signals are transduced for L-amino acids.",
"*Edit: spelling"
] |
[
"Will the volume of a bubble change while rising from depth in the ocean?"
] |
[
false
] |
So I was thinking about this last night. Let's say we have some mass of air that is released at 100,000 feet (depth doesn't really matter for my question) below the surface of the ocean. Will the volume of the bubble increase as it rises since temp will increase and pressure decrease? If so, is this something that is able to be calculated?
|
[
"10 m of water is about 1atm of pressure. Using round numbers, 30,000 m depth has pressure of about 3000 ATM.",
"So your bubble will be about 3000 larger by volume (cube root of that or about 12 times larger in diameter.)",
"The change due to temperature is small compared to pressure."
] |
[
"Depending on the gas in the bubble, your intuition is generally correct: increasing temperature will generally increase volume, decreasing pressure will generally increase volume, and decreasing gravitational potential energy will even contribute (though not much).",
"It's not likely to remain a single bubble though. "
] |
[
"Yes, in most cases it would.",
"Pressure at the bottom of the ocean is quite extreme and would crush the average human very easily. So as most gases are compressible, it would be squeezed into a smaller volume the further down you went.",
"It would also be very cold at those depths, meaning the gas would also rise in temperate as it rose to the surface and be much colder at high depths of water.",
"Gas expands as it gets hotter.",
"The lowering of the pressure around it as it came to the surface, as well as the increased temperate would cause the volume of gas to expand no doubt.",
"Though it would probably turn into more than one bubble as it expanded."
] |
[
"What is the ultimate fate of rocket fuel that is expended in the vacuum of space?"
] |
[
false
] |
[deleted]
|
[
"but it is possible that if ejected at exactly the right velocity and angle that the gas could orbit the earth",
"For spacecraft in LEO (Space shuttle, comms satellites and their launch vehicles, ISS payload vehicles, etc) I'd wager that most of their exhaust gases stay in Earth's Hill Sphere."
] |
[
"I was very surprised by this so I looked it up. Sure enough ",
"propellant speeds",
" are around 5km/s while ",
"earth's escape velocity",
" is around 11km/s so pretty much all exhaust gases orbit or fall back to earth. ",
"EDIT: grammar"
] |
[
"Rockets in space move by ejecting mass (gas usually, but a large supply of toasters would be equally valid as space rocket fuel) into space. The gas follows more or less the same laws of gravity as any other material. It will however, diffuse into space over time, but it is possible that if ejected at exactly the right velocity and angle, that the gas could orbit the earth. This is highly unlikely though, and if there is any gas in this particular scenario, it would be very little of it."
] |
[
"Everyone at work is scaring me into taking a flu shot. What are the actual benefits of getting a flu shot?"
] |
[
false
] |
The title says it all. I've gotten flu shots back in college, but I only remember getting sick shortly after. I've skipped the flu shot since then and have made it out of every winter perfectly fine. However, my work is giving away free flu shots and I want an educated perspective on them. Are there actual benefits to getting a flu shot?
|
[
"It is a tricky subject, as the benefits are often not as obvious as simply not getting sick. First off, the shot itself carries little risk. You may be a little sore the next day and might feel a little ill. The actual flu is much worse.",
"But think about the bigger picture, the public health responsibility. Are you ever around children? Old people? People that maybe can't get a flu shot or are still susceptible despite getting a flu shot? Well when you get a shot you also prevent spreading it to them, and while the flu might just make you feel sick, it can kill them.",
"So there are benefits, some potentially huge and with very little risk to you. ",
"Edit: Disclaimer and wording"
] |
[
"You are less likely to catch the flu.",
"It is still possible if you catch a strain not covered by the immunization, but they try to design the shot to cover the expected strains each year so it should significantly decreases the likelihood."
] |
[
"I can't remember the last time I had the flu, but this is why I get the vaccine anyway."
] |
[
"What does yawning do, and why does the body feel the need to do it?"
] |
[
false
] |
And why is it "contagious" or is that just a myth? I've tried to find the answer, but there hasn't really seemed to be an accepted answer, e.g that yawning is a social signal.
|
[
"There is such a thing as contagious yawning. And not just with people... dogs and chimps, too. In fact, dogs yawn when they see a human yawn. Interesting stuff.",
"http://blogs.scientificamerican.com/thoughtful-animal/2012/05/17/contagious-yawning-evidence-of-empathy/"
] |
[
"That is, as far as my knowledge reaches, wrong. It is some sort oft urban myth. Your brain actually lacking oxygen would compensate via increased breathing frequency, not a single inefficent breath. \nThen why do we yawn?\nI prefer some social explanation. The \"contagious-yawning\"-pattern is seen in many mammals. For example, dogs yawn when they somehow want to reduce stress. Another dog sees it, joins in on yawing and they both know that there is no need to piss each other off. \nAs to why we yawn when we are tired i can only speculate; \nmaybe the concept yawn--> relax works just as well the other way round."
] |
[
"That is, as far as my knowledge reaches, wrong. It is some sort oft urban myth. Your brain actually lacking oxygen would compensate via increased breathing frequency, not a single inefficent breath. \nThen why do we yawn?\nI prefer some social explanation. The \"contagious-yawning\"-pattern is seen in many mammals. For example, dogs yawn when they somehow want to reduce stress. Another dog sees it, joins in on yawing and they both know that there is no need to piss each other off. \nAs to why we yawn when we are tired i can only speculate; \nmaybe the concept yawn--> relax works just as well the other way round."
] |
[
"How do thermophiles survive temperatures that would quickly cook animal tissue?"
] |
[
false
] | null |
[
"I found a website that has several different adaptations thermophiles have:",
"https://bitesizebio.com/2169/the-secrets-of-thermophile-survival-part-i/",
"Basically it boils down to having extra-tough proteins that can withstand the higher temperatures without denaturing. The flipside is though, that some of these tougher proteins are only viable at higher temperatures.",
"If the temperature drops too far the protein essentially freezes and the organism is ... going to have a bad day."
] |
[
"Wow, thanks for the answer. \nI didn’t know that they required high heats. I’d assume those types must mainly live in hot springs and ocean vents in that case "
] |
[
"Correct! In fact, the metabolic processes of many thermophilic microbes depends on inorganic compounds found only in harsh environments such as deep sea vents. This is a reason why it is beneficial for the microorganism to be able to thrive in these locations! The diversity of microbial growth is awesome. "
] |
[
"Does it feel cold in space?"
] |
[
false
] |
I get the impression that space is desperately cold (for instance, I believe spacesuits have heating coils), but I don't really see why this would be. Granted, space is pretty empty. But precisely because of that, you can't conduct heat away into space as there aren't many molecules to pass energy on to by direct contact, and I suspect radiated heat loss would be pretty slow. If you weren't wearing a spacesuit your fluids would evaporate, but this is a Boyle's law thing and relates to the low pressure, and so the evaporation process wouldn't reduce your average temperature in the way it does at normal pressure. So does space really chill you, and why? (P.S. I suspect space is actually quite hot in terms of average kinetic energy of particles, but of course that doesn't really matter)
|
[
"http://www.reddit.com/r/sciencefaqs/comments/hd4ib/what_happens_to_a_human_body_in_vacuumhow/"
] |
[
"Not mentioned in that thread, but a fun fact: the space suits they used on the moon had active cooling because the day side is a 400° F dry sauna."
] |
[
"The fact that molecules with heat energy are leaving the body doesn't affect the average temperature of the body, does it?",
"Yeah that's how evaporative cooling works. The situation with the arm is very cut and dry (pun intended). Assuming the arm is the same temperature and density as your body, your body's average temperature will not go down. With the water, there are a lot of differences. Water has a high heat capacity so it is going to be removing more heat from you per mass. This will lower your body's average temperature. Second, there is a heat associated with evaporation and boiling (all phase changes) called enthalpy of evaporation. That heat is removed by the evaporating molecules anyway, and for water it is particularly high. Third, it will happen very fast but is not instantaneous. An astronaut who got trapped in a vacuum during training said the last thing he remembered was the boiling away of his saliva. This happened in like 15 seconds. While it happens the water is evaporating and lowing its own temperature very quickly, which is going to draw heat from the body at a fast pace. What would really happen according to tests run on animals is the evaporation would result in a thin layer of frost building up on the parts of your body that were moist. ",
"The cold that you will feel will actually mostly come from your body radiating heat. Your body puts out 1000W of energy as thermal radiation. On earth it gets back like 900W from the thermal radiation of everything around you and the rest from food, but in space that is going to be a straight loss of heat."
] |
[
"Europa in our lifetime"
] |
[
false
] |
Some of my friends and I were discussing wether we thought we would land a probe on Europa to explore the oceans in our lifetime. I am only 25 and the general consensus was NO. I was hoping we would, what are your thoughts on this and why? P.S. This is my first post on here. Much respect to the community!
|
[
"There's a couple of issues here.",
"The main one being that we don't really have the technology to drill through potentially kilometres of ice and retain communications with the surface.",
"There are advances being made in sterile (and non-contaminating) ice drilling techniques in the subglacial antarctic lakes, but we're not there yet, and the tech doesn't easily apply to a space context.",
"The other problem is communications. Given the power/mass constraints and the requirements for heat it would be difficult to communicate with an orbiter above. The only real way would be a submersible tethered to a lander that communicates with an orbiter. And that makes for a big, complex mission. Plus there's the fact that Europa is in possibly the worst radiation environment in the solar system and anything orbiting it won't last very long. ",
"All of this means it's going to be a big investment of time, expertise and money to get a mission like that going. So unfortunately, it's pretty doubtful."
] |
[
"Thanks, that makes perfect sense"
] |
[
"I don't know much on this topic, but ",
"this article",
" at least speaks for a possible orbiting probe in the near future."
] |
[
"What makes Norovirus so contagious compared to other infections?"
] |
[
false
] |
I'm from the United Kingdom where "Winter Vomiting Bug" better known as Norovirus, is making big headlines and is spreading rather rapidly, and closing down hospital wards and generally making christmas miserable for some people. My question is: What makes this virus such a problem, when other infections generally prevented by sanitation aren't found in the civilised world(cholera, dysentry)? A follow up question is what is causing the recent rise in prevalence? Is it easily evolving to counter modern cleaning products through a natural(natural?) selection process? Or is there something different at work here?
|
[
"First off, norovirus is not airborne. It's a super tricky pathogen to control because 1. As already stated, it is incredibly environmentally stable; most detergents won't kill it, hand santitizer doesn't kill it. 2. The infectious dose for this virus is super low (it only take a few viral particles to establish an infection) 3. The forceful vomiting and watery diarrhea common with this virus mean that the virus ends up everywhere, which is problematic especially because of point no. 1. 4. You really don't get any long term immunity from infection, so you can get it more than once and every outbreak has a fresh pool of susceptibles. "
] |
[
"That's actually poorly understood, but it seems that climate (cold dry weather is associated with outbreaks) characteristics of the virus, and human behavior all play a role. ",
"http://onlinelibrary.wiley.com/doi/10.1111/j.1469-0691.2009.02846.x/full"
] |
[
"Why do outbreaks occur during winter? Those factors seem like they'd be equal year-round."
] |
[
"Population genetics: will acceptance of homosexuality lead to a decrease in the amount of gay genes in the population?"
] |
[
false
] | null |
[
"Right, it's probable that if being gay is genetic, that the pattern of dominance is complex, controlled by multiple genes and possibly environmental factors.",
"But even if this is the case wouldn't the argument still hold? Assuming there is some threshold that needs to be passed for an individual to express the \"gay phenotype\", and thus that there is a certain percentage of recessive, unexpressed gay genes in any genetic population, won't gay people who reproduce will still pass on more gay genes to their offspring than straight people?"
] |
[
"I would point out the being gay doesn't preclude reproduction. Surrogate mothers and sperm donors make it possible for any couple (in theory) to have a child that is biologically related to at least one partner."
] |
[
"Now I’m getting a bit more speculative (perhaps too speculative for ",
"r/askscience",
", but I can’t help it, I’ve been thinking about this all day). ",
"The presence of “gay genes” seems almost counterintuitive, since being gay by definition makes an individual less inclined to reproduce in the traditional sense. Obviously in today’s world we have egg donors and in vitro fertilization, allowing gay people to reproduce without having sex with someone of the opposite sex, but I imagine due to the cost of these technologies that this is a such a small subset of total reproductive acts as to be nearly insignificant.",
"We might assume that gay genes would naturally diminish their presence in human populations, by having a phenotype that expresses itself, among other ways, in the nonreproduction of the individuals who carry the genes. Yet presumably gay genes have always persisted in the human population; indeed they seem to appear in animal populations as well.",
"Let’s assume then that it’s beneficial for a population to have a certain percentage of gay individuals. ( For example, nonreproductive adults are able to contribute to the population while using a minimal amount of resources since they never have kids, and kids sap resources, and thus might be important for maintaining an optimal fertility rate. Gay people, for whatever reason, also seem to function significantly in the transmission of culture in a lot of populations.)",
"If it is indeed the case that the population “wants” to keep a certain amount of gay genes floating around, is it possible that the social pressure not to be gay has the genetic function of increasing the number of gay genes in the population, by forcing gays into reproductive roles? Or is that not a good scientific way to think about it?",
"Edit: added some detail to a sentence to make my point better"
] |
[
"The two hot leads in a 250 volt electrical circuits are said to be \"180° out of phase with each other\", but 480v systems are 120° out of phase. How does the 120° phase get turned into 180°?"
] |
[
false
] |
I recently wired an outlet for a welder that was 250v. From some basic YouTube videos, I understand that industrial applications of electricity often use 480v. If 480v is made in three phases, 120° from each other, how is 250v with exactly opposite phases made for houses?
|
[
"It goes back to the transformer feeding the house. They are weird single phase, centred tapped transformers. The primary voltage side of the transformer is fed with a single utility feeder. The secondary side coil is centre tapped, and that centre tap is the neutral. The two legs are connected to top and bottom of the winding, making one +120V and one -120V, or 120V 180 degrees out of phase."
] |
[
"Three phase is delivered to the \"industrial\" user facilities with three high voltage lines. Where it three phase step down transformers are used to drop the voltage to 120 V per phase at 60 degrees. Using phase notation, if you add the two vectors of 120<0 and 120<60 there is a square root of 3 multiplier on the 120 giving you 208V.",
"For home use one of those lines goes into a transformer with a center tapped output which provides 120 to ground on each output. When you measure between the two outputs of a center tapped transformer you get the sum of the voltages.",
"If a home shop wants 3 phase power they need either an motor generator set to make 3 phase power or a three phase inverter which is electronic in nature."
] |
[
"The short answer is that it doesn't. ",
"The 240v split phase system that powers your house is not derived from a 3 phase system. ",
"So they aren't pulling two legs off of a three phase system and shifting the phases to be 180° apart. Your split phase residential power isn't coming from 3 phase power in the first place."
] |
[
"Questions on antimatter"
] |
[
false
] |
Why does antihelium core have a negative charge? What spins around and balances out the charge on antimatter? Positrons? Why are there no stable anti-elements between helium and lithium? This kind of surprises me as I had thought that anti-matter was just like regular matter but with a different core charge. My questions are based off of this article: Antihelium is the heaviest breed of antimatter created by scientists, with each particle is roughly 10 million billion times lighter than a grain of sand. The next heaviest that is stable is antilithium,
|
[
"Why does antihelium core have a negative charge?",
"Antimatter is just normal matter with the opposite charge. In normal helium nuclei there are 2 protons (each with positive charge) and a some neutrons (charge zero). So, in antihelium we have two antiprotons (some negative charge), and some still-neutral neutrons (minus zero is zero). So the overall charge of the antihelium nucleus is negative. ",
"What spins around and balances out the charge on antimatter? Positrons?",
"Yep.",
"Why are there no stable anti-elements between helium and lithium? This kind of surprises me as I had thought that anti-matter was just like regular matter but with a different core charge.",
"There are no stable normal elements between helium and lithium. They are next to each other in the periodic table; helium has 2 protons and lithium has 3. ",
"*",
" I dislike my own use of \"normal\" to mean non-antimatter, but I don't know what else to call it. There's nothing exotic about antimatter, it's just not what our part of the universe is generally made of. There could be whole anti-stars, anti-planets and anti-aliens out there, who would just call it \"matter\". Using \"matter\" to mean \"non-antimatter\" often leads to confusion because people often interpret \"matter\" to include antimatter.",
" numbers, see AgentME's reply."
] |
[
"The physical difference is that they have opposite charge, just like a normal proton and a normal electron have opposite charge. Charge is just a fundamental property of particles. ",
"The existence of antiparticles was first predicted by the fact that if you try to describe an electron in a way which takes into account both quantum mechanics and special relativity, you get the ",
"Dirac equation",
". This equation predicts the existence of antiparticles because, basically, the square root of a number is ",
" positive or negative (i.e. the square root of 9 is +3 ",
" -3). One of these solutions represents a particle, the other an antiparticle."
] |
[
"That's how they're defined."
] |
[
"What is the probability of 2 snowflakes being the same"
] |
[
false
] | null |
[
"Depends on what you define as \"the same\" snowflake (the same or merely looks the same). And how large your minimum snowflake needs to be before you consider it. The smallest ice crystals can easily be alike. For large complex snowflakes there are more possible shape configurations than atoms in the universe.",
"Basically, there is no fixed formula, but if you consider complex snowflakes (the beautiful ones) the probability of two identical snowflakes is essentially zero. So close to zero, that it is unlikely that any two complex snow crystals that have ever existed on earth have looked completely alike.",
"http://www.its.caltech.edu/~atomic/snowcrystals/alike/alike.htm"
] |
[
"Couldn't the same be said about finger prints? "
] |
[
"Yes, BUT:",
"For prints we usually do not look under a microscope to identify all features but look at what is reproduced if you smudge your dirty fingers onto a surface. Furthermore, on that level the variation is much less random than for snowflakes.",
"This reduces the number dramatically. Galton, the pioneer of fingerprints is often cited with a chance of ~1/64billion for two prints to match, but today this is deemed to be an overestimate. But even the low probability is comparably far from zero when you consider that 7 billion people are living today..."
] |
[
"Why didn't the outpouring of matter from the Big Bang immediately collapse into a bunch of black holes all over the universe?"
] |
[
false
] |
I'm aware that there's no specific point at which the Big Bang occurred, and that it happened everywhere at once. What I'm a little fuzzy on is whether this means a bunch of matter just randomly pops into existence instantly and explosively, and if so why these explosions were able to overcome what must have been the immense gravitational forces of whatever pre universal container the matter was in.
|
[
"One reason massive Blackholes didn't form immediately following the Big Bang was due to the equal distribution of matter in the universe at the time. ",
"If all matter is simultaneously pulling at all other matter, then the effective gravitational force is canceled out and mass never collates. "
] |
[
"Early inflation happened incredibly rapidly, too fast for gravity to have time to pull matter together. In 10",
" seconds, the volume of the universe increased by a factor of at least 10",
" which is enough to expand a length of nanometers to light-years.",
"But while all the universe didn't collapse into a black hole, one possible explanation for dark matter is that some black holes may have formed in the early universe and remain, unseen, throughout the universe today."
] |
[
"Does that mean that cosmic inflation made material move faster than c?",
"Materials didn't move any faster than normal, it was the empty space between materials that rapidly expanded."
] |
[
"When walking, why do people swing their arms opposite to their feet? (eg: left foot forward, right arm forward)"
] |
[
false
] |
I was walking around the city and noticed that when people take a step, they swing the opposite arm to the foot stepping. It seems to be involuntary, I caught myself doing it too without thought. Why does this happen?
|
[
"It's part of the way our muscles are structured. Having one arm forward and the opposing leg back causes a twist in the torso and hips. The whole set-up causes a chain of muscles to lengthen from shoulder to opposing thigh-- muscles which \"slingshot\" the body back into the opposite posture with minimal energetic effort. It's a way for the human body to walk with less energy!"
] |
[
"In addition to the human physiology answers here, you can also look at this question in terms of evolution. Why completely redesign a system if you don't need to do so? Our wormy ancestors were ",
"contracting alternating segments of their body for locomotion",
" a long, long time ago. "
] |
[
"Many animals have same-side movements, where humans are strictly alternating. Some animals have even more dynamic movements depending on their speed/gait. And perhaps some are much more hoppy due to the lack of the necessary physiology to make alternating gait efficient, like in many birds. (Wondering about kangaroo physiology now)",
"I think looking at the evolution of bipeds from quadrupeds provides some physiological links, but some of them are still confusing. Like how the functions of the illiopsoas came about in bipeds. "
] |
[
"How large would a levee able to be before outside water pressure becomes too great?"
] |
[
false
] |
image came up on my news feed this morning, and it got me thinking about just how large it would be possible to have the levee before the pressure of the water became too great and they collapse? Would it be possible to end up with something akin to an open cast mine and have a massive hole below sea level surrounded by giant levees?
|
[
"The question you're asking depends on too many things to be accurately answered I believe.",
"Strength of build materials, levee height, soil properties, water height, external eroding forces, depth before bedrock, available resources (including cash), etc."
] |
[
"Water pressure is due to gravity. ",
"27.7 inches of water increases the pressure by 1 psi. You start at 14.7 psi because the atmosphere is at that pressure. ",
"So the pressure a levee has to withstand is a function of water depth vs material strength. At some point a mound of dirt can no longer withstand the pressure at the bottom and it fails."
] |
[
"This is more of a civil engineering question. The answer depends on what counts as a levee. Does it need to have dirt walls, or can they be concrete?"
] |
[
"My doctor says that chemotherapy works by specifically targeting rapidly-dividing cells, which is how it works to fight cancer and also why it has the side effects that it does. But how does it “know” which cells are rapidly dividing? And how rapidly is “rapidly”?"
] |
[
false
] | null |
[
"Chemotherapy drugs gain their selectivity for cancer cells by a variety of mechanisms. For those that target rapidly dividing cells, the drug molecule generally interferes with a process involved in cell division. Especially the earlier chemotherapy drugs like cisplatin do this by reacting chemically with DNA and causing crosslinks. If these crosslinks are bad enough, the cell will not be able to divide and will “commit suicide” (apoptosis) and die. These drugs tend to have nasty side effects because they are chemically reactive and therefore react with all cells’ DNA to some degree, according to their rate of division. Other drugs known as intercalators fit between the base pairs in DNA and create a similar disruption to replication. Another class of drugs includes taxol and binds to the microtubules that form during cell division, again causing apoptosis or failure to divide.",
"As for how rapid is “rapid”, I would say there’s no hard cutoff and most of these drugs will interfere with most cells’ division to some degree, on a spectrum proportional to the cells rate of division. There is probably some research on cell division rates and chemotherapy to put numbers to this, but I’m on my phone right now... Hope this answers some of your question at least.",
"Edit: Also might be interesting to note that ",
"the first chemotherapy drug was literally a chemical weapon",
" that worked by cross linking DNA"
] |
[
"During mitosis, DNA strands replicate and must be physically pulled apart by strands of microtubules so that one copy of the DNA will end up in each of the 2 daughter cells. Without microtubules being able to form. The Two strands of DNA will be stuck together forever and Mitosis stops dead in it's track."
] |
[
"The answers presented thus far are excellent descriptions of how we can target cancer cells due to the cells' ",
" properties. Drug delivery has been a hot topic in chemotherapy research for at least 15-20 years. The idea is simple - we can't stop the drug from damaging healthy cells it's exposed to, so how about we try to release the drug at the tumour. ",
"Most traditional chemotherapy agents are injected IV. They destroy the cancer cells, but at the cost of exposing potentially every other healthy cell in the body to chemotherapy. If we released the drug right next to the tumour, you would get the same effect on the cancer cells, with less healthy cells exposed.",
"We can target cancer cells based on the properties of cells collectively as tumours. Like all other cells, cancer cells need a blood supply, both to supply nutrients and oxygen, and to remove metabolic waste. This is normally regulated by Vascular Endothelial Growth Factor (VEGF). When VEGF is overexpressed by a cancer, it lays down lots of new blood vessels (which is a key step in some tumours becoming malignant). These vessels differ from those of healthy cells - they have lots of large 'holes' (interrupted endothelium, better known as fenestrations) in their sides. ",
"Blood vessels supply the interstitial fluid - the fluid that surrounds cells. But that fluid needs to drain somewhere. This is normally performed by lymphatic fluid, but as you might have guessed, this is also malformed in tumours.",
"So you have leaky blood vessels into the tumour, and poor drainage out of the tumour. A molecule that is just the right size will be small enough to fit through the fenestrations of the blood vessel, whilst large enough to not be easily drained into lymphatic vessels. It would be stuck in the tumour. This is known as enhanced permeation and retention (EPR) and is exploitable. PEGylated doxorubicin (i.e. an anticancer agent, doxorubicin, surrounded by a nanoscopic plastic mesh) is an example of one product designed with this in mind. It ",
" the tumour - it gets there if the circulation allows, and does not actively seek it out. ",
"This article provides ",
" more information on the EPR effect",
".",
"The EPR effect is not without its limitations. Despite improving accumulation of the drug at the tumour, there are still significant amounts of drug leaked in healthy tissue. Furthermore, the thick, dense matrix surrounding cancer cells may prevent these larger molecules from actually reaching the cancer cells. ",
"Read more on the limitations of passive targeting via EPR here",
". There are other passive targeting methods, such as exploiting the temperature difference of tumours, but this post is already long enough.",
" is when the drug molecule 'seeks out' the tumour. I am stuck behind paywalls so unfortunately cannot source many of the articles I would like to for this. I've already added a lot here so maybe someone else would like to carry on with that exciting topic?",
"[1] ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4219254/",
"\n[2] ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3833679/"
] |
[
"If a bullet was fired towards earth from the ISS, would it burn up?"
] |
[
false
] |
Inspired by from TIL
|
[
"First the question of whether it's going to make it to the atmosphere at all or just end up orbiting Earth.",
"A muzzle velocity of 400 m/s, which at a quick glance of Wikipedia seems to be around hand gun figures but I'm no gun expert, aimed directly down from a circular orbit with altitude of 400 km, would bring the bullet down to about 60 km altitude at the other side of the planet. 60 km is around what the shuttle was aiming for for re-entry. But since the bullet has a much bigger mass to surface area ratio, it might not be enough to bring it down in one pass. So it may do a few more orbits before properly re-entering. (Edit: See below, the mass to surface area actually seems to be roughly the same. So it might re-enter immediately, or it might not.)",
"A muzzle velocity of 300 m/s would only drop the perigee altitude to about 150 km which is still fairly high. So the bullet definitely wouldn't re-enter in a while though atmospheric drag would eventually slow it down enough.",
"A bullet fired from a modern rifle, with muzzle velocity closer to 1000 m/s, would definitely re-enter in less than an orbit.",
"The re-entry speed in any case is around 8 km/s. For an object that small, I'm pretty sure it would completely \"burn\" during the re-entry."
] |
[
"A smaller mass to surface area ratio would predict a greater acceleration due to drag. Your answer seems to assume the opposite. This logic should predict that it requires fewer passes to be arrested by aerobraking compared to larger reentry modules."
] |
[
"The bullet will be slowed by atmospheric drag more than the shuttle. The drag force is 1/2 rho v",
" C_d A. Between the bullet and the shuttle rho, v, and C_d are all the same as far as we care. The drag force to mass ratio will then determine acceleration as F=ma, so a=F/m. The value of a is then 1/2 rho v",
" C_d A / m. We can divide the bullet's acceleration by the reentry module's acceleration, a_bullet / a_spaceship = (A_bullet / m_bullet) / (A_spaceship / m_spaceship) = (A_bullet/A_spaceship) * (m_spaceship/m_bullet)",
"From this, we note that the mass ratio is much larger than the area ratio. That means that the acceleration of the bullet will be much greater. This is by a_bullet/a_spaceship = (R_bullet",
" * (R_spaceship",
" = R_spaceship / R_bullet. The radius of the spaceship is greater so the acceleration of the bullet is greater. The bullet will burn up in the atmosphere much much faster."
] |
[
"Why does coffee make you have to poop?"
] |
[
false
] | null |
[
"Caffeine is an analog for cAMP (cyclic Adenosine Monophosphate). cAMP is a common signaling molecule in cells. Caffeine binds to the protein that cuts cAMP so it is free to accumulate to higher concentrations. In intestinal cells it serves to activate them, which in turn triggers more fluid being dumped into the intestinal cavity. This in turn facilitates bowel movements.",
"As a side note, cholera toxin works in a similar way. ",
"http://en.wikipedia.org/wiki/Cholera_toxin"
] |
[
"If this is the case, then why do sodas with caffeine not cause increased bowel movements like coffee?"
] |
[
"Best I found is ",
"this abstract",
" that says a study showed caffeine decreases intestinal transit time (how long it takes for stuff to move through the digestive system). It does this in part by causing the small intestine to switch from absorbing fluid to secreting it. So in other words, caffeine causes the intestine to move more fluids into their lumen, moving more material along toward, you know... the toilet bowl.That is, if I'm interpreting the abstract correctly.",
"I'm pretty sure caffeine also increases intestinal peristalsis (the wave-like muscular contractions that move stuff through the intestines), but I didn't see a study to back that up."
] |
[
"What would happen if a geneticist were to Hybridize and Inbreed the Green Fluorescent Protien (GFP) with a desired gene? Could you see the exact areas where your desired gene affected? Is this even possible?"
] |
[
false
] |
Taking high school Biology, liking genetics. Was wondering. I've probably used a million terms incorrectly already. :P Pre-thanks for anyone's input.
|
[
"This is common practice in many fields of biology (molecular, cellular, neuro, biochemistry ect).",
"The molecular tools for doing this are well established. We can physically attach GFP to just about any protein creating a fusion protein. If done properly this fusion protein acts like the original protein (cellular location, expression, function) but also fluoresces green. The result is that yes, we are able to see the cellular location of proteins that we fuse with GFP. "
] |
[
"What you're asking about is a very common technique (though the wording of your question is way off). I've done it myself. I've made strains of fruit flies that express a protein I'm interested in physically fused to GFP.",
"I do this by taking a plasmid - a circular piece of DNA - that has been designed to easily integrate into the fly genome. Using molecular tools, I cut and paste in the gene for GFP and the gene for my protein, so that together they make one new gene. I can then inject the plasmid into fly embryos and screen for flies that have integrated my new hybrid gene into their germline.",
"Now I can take ovaries out of the flies, plop them under a fluorescent scope, and see exactly where my protein is being expressed.",
"(That was a very quick overview of about a year's worth of work there)"
] |
[
"What you're interested in is where a gene - or rather, its products (proteins) - are being expressed. This can be accomplished with techniques such as ",
"immunohistochemistry",
".",
"And yes, hybridization and inbreeding are separate, unrelated concepts from what you're describing. Not to worry though, genetics is a huge field. There's plenty to learn."
] |
[
"How much do we understand about the actual mechanics of ion channels/pumps?"
] |
[
false
] |
[deleted]
|
[
"While it is difficult to watch an ion channel function in real time, we have lots of structural snapshots from experimental methods such as electron microscopy and X-ray diffraction. For example the five-lobed channel in your image is the well studied acetylcholine receptor. ",
"Here",
" is a detailed molecular structure such a channel. For some ion channels and pumps we have structures of multiple states. So we can intrerpolate between open and closed structures, for example. Plus there are MANY experiments that map certain functions to specific parts of the protein sequence. ",
"Most channels open and close by movement of the large parts (lobes) in relation to one another. Since the channel opening is usually very narrow even in the open state, it takes little movement to close it.",
"How can we be sure? Well we may have some of the details wrong, and the models are just hypothetical, but the current models of ion channel function are supported by and are consistent with a huge amount of data from many researchers in many fields. That is the hallmark of a \"hypothesis\" that is widely accepted because it is almost certainly correct, like evolution."
] |
[
"There are quite a few molecular dynamics simulations of ion channels. It is sometimes difficult to know if the details they reveal are correct or simply artifacts of the simulation. Anyway, ",
"here",
" is a flashy one of the acetylcholine receptor."
] |
[
"Recent developments in combined SECM-SICM probes have allowed for realtime mapping of the topography and activity of surfaces and ion channels. They may not be as structurally accurate as other methods but are much cheaper to run and can be run over the course of an experiment to measure a change which can be rather useful. I'll link an appropriate journal when I have access to a computer, I'm currently on my phone mid lecture actually covering this right now.",
"Edit: ",
"Link to relevant Journal from PNAS"
] |
[
"Why is pH measured on a logarithmic scale?"
] |
[
false
] |
Did we assign acids' and bases' pH to the log scale or do they naturally follow the log scale?
|
[
"pH is defined as the -log(concentration of H+). So its kind of one in the same. We decided to use the log scale because of the large ranges of concentrations that we would be dealing with."
] |
[
"As Tigerlealc said, it's basically just to make the numbers easier. The range can be absolutely huge, so as with a lot of things which have a large range (many, many orders of magnitude), we use a log scale to represent and compare them more easily."
] |
[
"Mathematically, pH is the negative logarithm of the activity of the (solvated) hydronium ion, more often expressed as the measure of the hydronium ion concentration.[2]",
"Initially, probes were used to pH measure H+ activity, and the Nernst equation was used. pH was a simplified term used to represent part of this equation. "
] |
[
"If someone lost a significant portion of their brain due to injury that left the separated part relatively intact, is it possible that the separated part would still think for a short time?"
] |
[
false
] | null |
[
"Your scenario is unneccessary to explore this question, but we don't know the answer. Read up on split-brain.",
"http://www.reddit.com/r/askscience/search?q=split+brain+&restrict_sr=on&sort=relevance",
"http://en.wikipedia.org/wiki/Split-brain"
] |
[
"I was thinking less \"single hemisphere' and more \"significant portion of the brain removed without paying mind to keeping structures intact\"."
] |
[
"Oh, I think I get what you're asking. I can't fathom an injury that would cause the scenario you're talking about and not result in massive trauma that would confound the answer, so how about this hypothetical: Let's say a surgeon removes a chunk of the brain (not intentionally resecting any specific structures), would that chunk continue to \"think\" even for a brief second or minute? Is that what you're asking? That's tough to answer because there is no real medical definition of \"thinking\". Would the brain tissue continue to \"function\" (i.e., chemicals would be released, there would be electrical impulses)? It's possible it would, but only briefly."
] |
[
"How does acclimatization work? How can painfully hot water be fine after a few minutes? What happens when you get used to a bad smell?"
] |
[
false
] | null |
[
"Densensitization. I can't find a perfect one for heat, but the same thing applies for cold as well.",
"http://i.imgur.com/bfbGG.jpg",
"In this image scientists are applying menthol to a cold activated ion channel. Activation of the ion channel is what tells your neuron it is cold. When the channel as active, the current gets more negative (i.e. goes down the page). See how when menthol is applied for a long time, the current returns back to the baseline level? Furthermore, see when they apply the menthol a second time, the peak current is less? That is desensitization. The same thing happens with hot activated ion channels. And hence when you get the same stimulus (hot) a second time, you don't perceive it as as hot.",
"Oderant receptors are the same. They desensitize too. Here is a trace (b) showing an odour being applied twice in a row.",
"http://i.imgur.com/aMZTU.gif",
"There is probably desensitzation going on further down the pathway (i.e. in the brain, rather than at the sensory neurons), but the first step is very important."
] |
[
"So pain is the signal that you're doing something bad to your body; when you get desensitized, does that mean you're hurting yourself but not realising it, or the pain signal was wrong in the first place?"
] |
[
"Well.... I'm too anally retentive to agree with the first statement. Pain is not a neural signal. The neural signal may cause pain, but pain is something you experience in your mind. It is not something that exists in the physical word.",
"But I get what you're saying, the neural signal is what leads to you experiencing pain. And when those pain sensing neurons become desensitized, you experience less pain.",
"As to whether there was damage or not, in this case would depend on the exact temperature of the water. Certainly, there can be temperatures where you would experience pain but that after desensitization, there would be no pain. And this temperature is not enough to cause damage.",
"I am not sure if there are temperatures high enough to cause cellular damage but that you could desensitize to given the right circumstances. My suspicion is just."
] |
[
"Can ancient DNA be extracted?"
] |
[
false
] |
I posted this in askreddit which is apparently the wrong subreddit. So here goes. Sort of inspired by the 100 million year old spider & wasp on the front page yesterday that was encased in amber I started to wonder. Could any sort of DNA be extracted from this a-la Jurassic Park? I know cloning or recreating is waaaay far fetched but could any of the DNA still be in tact? Does this work just like fossilization or does the amber have a preservative property that would keep things like DNA in tact? If not is there any way we could extract ancient DNA otherwise?
|
[
"The short answer is, probably not. The long answer is:",
"DNA can suffer many different types of damage, it can fragment (imagine taking your favourite book and cutting it up into sections that are just a few characters long, it would not be possible to reassemble that book -- even if you had started with 100 copies and had overlapping fragments) and it can under go chemical changes that alter the chemical structure of the DNA itself. This link talks generally about DNA damage: ",
"http://en.wikipedia.org/wiki/DNA_repair",
". ",
"These problems make it hard to use the normal enzymes we use every-day to manipulate DNA (note: I assume you mean \"extract the DNA and do something with it\", like eventually clone it or sequence it) and thus makes the DNA sort of useless. This is compounded by the fact that the guts of all animals contain enzymes that specifically break down nucleic acids for digestion. Relatedly, here's a story about ",
"mammoth dna",
" -- note this DNA is several orders of magnitude younger than any dinosaur DNA, and they still found it too damaged to do anything with.",
"That said... DNA damage is a stochastic (random) event. Theoretically, if you had enough DNA samples, sooner or later one would probably have enough intact DNA to get a good sequence off of. In fact, every sample probably has ",
" intact DNA in some short stretch, but getting at those few molecules is tricky. So, if you had...I don't know, 10,000 samples of DNA, say, all from the same, or a small subset of dinosaurs, and you could easily remove the contaminating mosquito DNA, then you could maybe sequence a dinosaur.",
"Oddly enough, if we had the full genomic sequence of a dinosaur, it would not be too far fetched to clone it using the DNA of birds/reptiles/dinosaur cousins as a starting point and just making the changes needed to make something more \"dinosaur like\". To be sure, it'd be a huge effort, but I think it would be technically possible with current know-how."
] |
[
"Discovery News reported that scientists have discovered 419 million year old DNA \"intact inside ancient salt deposits\". ",
"Link",
" !",
"Amber would preserve DNA for the same reason it preserves the body of the ancient mosquitoes. Once it solidifies, it's a strong, solid environmental barrier. Because DNA can survive intact for millions of years, and because amber can preserve ancient bodies, yes -- it is likely you can extract, and sequence, DNA from an ancient body encased in amber. Unfortunately, most things don't die due to some once-in-a-life-time amber accident! But amber is an ideal way to go, DNA preservation-wise.",
"If there is only a small amount of DNA that is preserved, PCR can be used to amplify DNA. This technique creates many identical copies of the genes. From there on, and with further techniques, it may be possible to clone a simple organism. Believe it or not, it's not too far-fetched. The most difficult part of cloning would be making sure the clone is healthy, that is, without a developmental disorder.",
"For example, Lucy the cloned sheep died young. ",
"Link"
] |
[
"I would like to see them clone an ancient spider."
] |
[
"How many calories, or how much of my food goes to being energy for bacteria reproduction rather than powering me physically?"
] |
[
false
] |
With as much bacteria that is in our feces, and the pure amount that are in our bodies, how much energy does it take to keep up this microcosm within us?
|
[
"I probably should point out that the relationship between our body and bacteria isn't always competitive as the question may imply. Not all the energy from the food can be absorbed by us, so the bacteria are often breaking down out waste product and sometimes releasing nutrients that we can then absorb. The rumen of ruminant animals is a more advanced example of this symbiotic relationship."
] |
[
"You know, citations...stuff like that, this is ask science not ",
"/r/askreddit",
". ",
"I have no idea if you're serious or just joking, but even if serious...this gives us nothing of scientific value. Please read the link next to the one beneath \"answers to questions\". "
] |
[
"You know, citations...stuff like that, this is ask science not ",
"/r/askreddit",
". ",
"I have no idea if you're serious or just joking, but even if serious...this gives us nothing of scientific value. Please read the link next to the one beneath \"answers to questions\". "
] |
[
"Can someone please explain to me Long branch attraction with regards to parsimony analysis?"
] |
[
false
] |
From what I've read I think It involves..... Since there are only 4 nucleotides its very likely that during evolution, separate taxa will have evolved, independently, the same nucleotide for a particular site, and will be grouped because of it? Is that right?
|
[
"You have the gist of it. In the Maximum Parsimony method of phylogenetic reconstruction, one searches for the tree requiring the fewest evolutionary events to explain the observed data (assuming irreversible changes in the character state tree) in a non-parametric statistical framework. LBA occurs when there is a high frequency of parallel changes causing sequences to arrive at the same character state by accelerated rates of evolutionary change. ",
"If you'd like to see the math, check out ",
"Felsenstein",
"'s 1978 article \"Cases in which Parsimony or Compatibility Methods Will be Positively Misleading\". ",
"Bergsten",
" did an excellent review of testing for and dealing with LBA."
] |
[
"Okay, Quality. Lovely Concise explanation. Cheers man. ",
"Are there any real world phenotypical examples of this or is it all based at nucleotide level?"
] |
[
"To be honest, I haven't followed morphology-based cladistics, so I can't give you an example of when LBA led to problems in an analysis. However, the math should hold if one were to count morphological changes as evolutionary events. "
] |
[
"Where does the 70% of water in the human body go when it dies? Is the amount of water on earth steadily increasing as more humans die?"
] |
[
false
] | null |
[
"Mass is conserved. The amount of water on earth has been roughly the same for the last billion years. When an organism dies, the water inside diffuses to areas of lower water concentration. This is carried out by biological or thermal processes (i.e. into the bacteria/plants/animals which decompose the body, or into the atmosphere as water vapor)."
] |
[
"Hi Thelittlefungi thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Planetary sigh"
] |
[
"Why is the melting point change between Na and Mg large but from Mg to Al small?"
] |
[
false
] |
Been searching on Google for quite sometime but I haven't been able to find the answer. As an addition to the above question, the change in melting points between Mg and Al is small but the change in boiling points between the two is large. Why is that?
|
[
"The melting point of a chemical is fundamentally bound to how well it packs together in a solid state. For things in their elemental state, you want to look at their crystal structure to determine how tightly they pack together. For boiling point, you are looking at how well the chemicals interact with each other in solution. For this, we look at how surface effects of each individual molecule or atom will interact with one of its kind. These are the so called Van der Waals interactions."
] |
[
"The proton and electron difference between Na and Mg is the same for Mg and Al. Since all these elements are metallically bonded, why doesn't the melting point change equally?"
] |
[
"Like I said, melting point is dependent on how things pack together as a solid. Take butter and olive oil. They are both long chain hydrocarbon compounds but butter has few double bonds and olive oil has more double bond (This is the difference between unsaturated and saturated fatty acids). The lack of double bonds in butter allows it to coil into a ball and many of the balls pack together tightly. Olive oil cannot do this due to the double bonds and will not pack tightly together. This is why butter is solid at room temperature whereas olive oil is a liquid. The same holds true for the elements, how well they pack together with themselves will determine the melting point. So, you need to look at how well Na will pack with itself vs. how well Mg will pack with itself. "
] |
[
"Why are the leaves at the end of the branches the last to fall?"
] |
[
false
] |
I've noticed that all the deciduous trees have lost all their leaves. But the ones that have a few leaves left have all their leaves at the very end of the branches, near the top usually.
|
[
"I'm an arborist and googahgee has it right. In the fall the tree emits enzymes that break down the cellulose at the leaf/stem junction, causing it to eventually fall off. That's the simple version and the older a leaf is, the better prepared they will be when fall arrives. The younger leaves at the tips of branches haven't had time to set up these changes. They're at an immature stage in development and are still using the tree's growth hormones to get larger. The extra growth hormones tend to get in the way of the cellulose eating enzymes so leaf drop is delayed until the environment gets too severe and everything gets shut down. If they are really immature leaves they might not even fall off but shrivel up and die still attached."
] |
[
"Well, the reason leaves fall is because their circulation is cut off by a layer of cork, as in the winter there isn't much sun. The leaves at the top or at the ends of branches are part of new growths. They would need to mature a bit before automatically being able to shut the leaves with cork. To be honest, I am no professional, and may be wrong, but this is honestly the only explanation I have, and it is logical. I think..."
] |
[
"In cases like this, it is best to do a quick search to confirm your intuition before posting. After all, it helps solidify your knowledge (or dispel wrong thoughts) and avoids the risk of posting wrong information.",
"As the sidebar says:",
"Please keep discussion:"
] |
[
"Questions about planet in the orbit of multiple stars and brown dwarf stars."
] |
[
false
] |
Im trying to figure this out for a story i plan to write. What would happen to a planet in the orbit of four stars in a cross shape with the planet in the middle. The stars in question are brown dwarves.
|
[
"Conflicting information. In physics, an orbit is the gravitationally curved path of an object around a point in space. The planet being in the middle of the four stars suggests the stars are orbiting the planet instead, which gravitationally is not logical. I would suggest not mentioning any kind of orbit, but rather the four stars being locked as they are, while the planet is somehow exactly in the middle of them with equal pull from each star."
] |
[
"It would be endless day. The stars would have to be far enough away from the planet to not cause it to burn up, too. ",
"From Wiki: When still young, up to a billion years (a gigayear) old, brown dwarfs can have temperatures and luminosities similar to some stars."
] |
[
"If a planet had endless night (no sun or other light source) it would be required to have a hot core. Preferably a molten core so that it would also provide some kind of magnetic field protecting it from whatever radiation was present.",
"\nIf this was for human habitation it would most likely require a water source. It would also require a reasonably thick atmosphere with a high O2 component. As for life on this kind of planet; you could perhaps have some sort of simple life or life such as that found around thermal vents in deep sea trenches."
] |
[
"If time and space are parts of the same thing, is there equivalency in their measurement? In a 4-dimensional graph with axes X/Y/Z/T, can we say that \"1 foot of distance along axis X equals 5.3 seconds of movement along axis T\"?"
] |
[
false
] |
In a 3-dimensional space, "distances" can be easily equated between axes. If I show you a ruler lying on a table, you can easily imagine that same distance vertically. "Five miles along a road" vs "five miles above sea level" is a simple thing for people to understand. You're moving along a different axis in space, but the distances are the same and easily calculated and compared. Can the same be said for spacetime? Does "1 foot" of distance have a temporal equivalent, along a fourth-dimensional axis? Is there a Fahrenheit/Celsius conversion equivalent, wherein "1 cm = 1.394 seconds" or something similar?
|
[
"You need a velocity to convert between distance and time. So the most common units are chosen are those in which ",
" = 1. So 1 second is comparable to 1 light-second of distance."
] |
[
"But (it seems to me) that's a different thing, drawing a connection between two different systems of measurement. Like saying \"one gallon of milk costs $5\" and therefore \"my rent is 300 gallons of milk per month.\" It's understandable to the listener because you've established a conversion standard, but there isn't actually any connection between your rent and any quantity of milk. The connection is invented for purposes of discussion. Similarly, you can say \"I'm moving at 10 miles per hour\" and thus \"my destination is 1 hour away\", but that's establishing a conversion between two systems of measurement.",
"As I understand it, according to the \"spacetime\" concept, space and time are ",
" the same thing. Not just equivalent or related, but manifestations of the exact same property of the universe. Which, to me, means they ought to be subject to the same units of measurement, right? Everyone intuitively knows that a given distance within 3 dimensional space can be measured on any axis and remain the same, e.g. \"5 feet forward\" vs \"5 feet up\", a shift from the 2nd dimension to the 3rd but requiring no conversion beyond the axis change. ",
"So if space and time are the same thing, shouldn't there be a similar possibility there? \"5 feet up\" vs \"5 feet ago\", a shift from the 3rd dimension to the 4th? A simple change in axis from vertical to temporal, similarly requiring no conversion?",
"Put another way: if all 4 axes of space and time are the same, why can we measure the first three in \"inches\" but not the fourth? How can space and time be the same thing, if they cannot be measured using the same units?"
] |
[
"Units are never a problem in physics, you can always just choose a set of units where your speed of choice, e.g. the speed of light c, is 1. Then, any measurement of time is a measurement of distance, because you have to multiply or divide by 1 for conversion. There is nothing deep at all about units, it is all just convention. For example, I'm European, so I don't measure my spatial axes by feet or inches.",
"Not all 4 dimensions of spacetime are the same though, there is a reason we say spacetime has (3+1) (or (1+3)) dimensions.",
"First, let's go over basic geometry. Suppose you have two points in (euclidean) space. You can shift the origin of your coordinate system, and rotate your axes, but the distance (dr",
" = dx",
" + dy",
" + dz",
" between any two points remains invariant.",
"Now let us go to spacetime. You can manipulate space as before, you can move the zero on your time axis, and you can 'boost' to a coordinate frame moving at constant velocity (slower than light).",
"In special relativity, the invariant property of two events is their 'spacetime interval', defined as ds",
" = dr",
" - c",
" (or sometimes with opposite sign). Note that writing 'ds",
" is an abusive notation, since the number 'ds",
" can be negative.",
"If ds",
" = 0, the interval is light-like: the two events can be connected by a light-ray. The time-order of the two events is well-defined, i.e. one is in the future of the other.",
"If ds",
" < 0, the interval is time-like: there are reference frames in which the events occur at the same spatial coordinates and are separated in time by sqrt(-ds",
" The time-order is again unique.",
"If ds",
" > 0, the interval is spacelike: there is a set of reference frames in which the two events occur simultaneously at a spatial separation of sqrt(ds",
" (In other reference frames, either event can occur before or after the other.)",
"As you can see the time and space axes are distinguished by the sign with which they appear in the invariant. Similar to how rotating spatial axes works, boosting your reference frame rotates time and space axes by a 'hyperbolic rotation'. However, your time axis can never become a spatial axis, and vice versa. You cannot just 'change axis from vertical to temporal'."
] |
[
"What is the extremely high pitched noise I hear from old televisions, that most of my friends can not?"
] |
[
false
] | null |
[
"There is a component in old style Cathode Ray Tube (CRT) based TVs known as a ",
" that provides the necessary \"signal\"",
" to move an electron beam from the back of the TV tube to a horizontal location on the front of the display, where it will hit a phosphor to light u that part of the display. It typically has no/very low output when on the left side of the screen, and is at full output at the right side of the screen. This \"ramp up\" is generally linear, and occurs quite quickly in order to draw a single line on the display (it takes about 3.33ms on an NTSC based TV, and 40ms on a PAL or SECAM based TV). This is repeated for every line.",
"On an NTSC TV, this means we do this \"ramp up\" for 525 vertical lines. At 30 lines per second, the flyback transformer is operating at 15 750Hz (likewise, on a PAL/SECAM TV that uses 625 lines at 25fps, the flyback transformer frequency runs at 15 625Hz). As the process generates a small amount of sound at this frequency, this is the \"whine\" you hear from old CRT TVs.",
"As to why you can hear it and your friends can't, 15Khz is considered to be around the top end of normal adult human hearing; your ears are simply more sensitive to this frequency than that of your friends.",
" -- In reality, this is an electromagnet that is generating a magnetic wave."
] |
[
"If you want to be really pedantic, for NTSC the flyback happens 59.94 times per second. It's interlaced video, running at 29.97 frames/second, resulting in 59.94 fields per second."
] |
[
"This nswer is correct, however you said 30 lines per second where it should have been 30 frames per second."
] |
[
"Why is a successful drug trial in mice an indicator of possible human trial success? Or: are mice and humans really that similar?"
] |
[
false
] |
Some talk about drug trials in the male oral contraception thread got me thinking about this. Intuitively, it seems like the biological mechanisms of a mouse would be vastly different than those of a human, but they must be somewhat similar if they are used for drug development. In what ways are we actually similar? Are there any realms of pharmacology where mice are too dissimilar for productive drug development?
|
[
"a successful drug trial in mice is \"suggestive\" of possible success. more than anything, it is an initial proof-of-concept. it is not a direct indicator for success in humans.",
"mice are widely used in experimentation because they are compartively cheap and because there are many disease models that can be studied in mice that can't be studied in other animal models. knock-out mice, knock-in mice, induced autoimmunity, induced arthritis, induced asthma, viral challenge, bacterial challenge etc etc. mice give us an INITIAL model to look at how a drug or vaccine MIGHT work.",
"generally once a drug or vaccine shows some promise in mice it will progress to a more rigorous model, such as non-human primates. but unfortunately even the non-human primate model isn't always totally informative. i personally have seen compounds work WONDERFULLY in guinea pigs, ferrets and non-human primates and then be completely disappointing in humans.",
"TL;DR - mice are used as a first step very commonly because there are a number of well-established disease models in mice. but they dont strictly inform human clinical trials"
] |
[
"In all honestly I don't think those studies exist. What you are talking about would be something of a \"hybrid\" study between public health/epi and laboratory pharm/bio. Generally the public health folks dont care about animal work and the basic folks dont look to collaborate with the public health/epi. ",
"I could be wrong, that study might exist somewhere. If it does and you find it, I would love to read it. But realistically I don't see that type of study being feasible for the issues i mentioned above and because there are so many variables involved it might be nearly impossible to isolate them to account for similarities or differences in study outcomes in mice vs humans. ",
"Mice are used because the models systems bare some similarity to human disease. i.e. \"i can induce arthritis in the mouse model, and it is driven by immune responses in this model. we know that rheumatoid arthritis in humans is based on immune responses, so in that way the models are similar. if i can impact the immune-driven arthritis in the mouse, that might suggest that there is a possibility of impacting rheumatoid arthritis in humans through a similar treatment\""
] |
[
"I'm curious, but I have to think that studies have probably been done that tell us just HOW likely (statistically) various animal models are to be able to predict the outcome in eventual human trials and treatments. Are you aware of these studies and can point me to them? Well, the actual studies would probably be dry, but to a source that would summarize the information from reliable studies, such as a good summary article or meta-study?"
] |
[
"How does a strep test work? And how can it be accurate in such a short amount of time?"
] |
[
false
] | null |
[
"The rapid strep test is an immunoassay (it tests for the reaction of antibodies specific for group A streptococcus bacteria and their antigens). The swab sample is placed into conditions which allow the antibody to either bind to antigen (if present) and then react in a visible way, or not bind and be washed away. The \"accuracy\" of this sort of test is quantified as sensitivity (aka: how likely is it that the antigen is present and the test is able to detect it) - there are a few types of strep test, but this can be in the 90+% range for most ones use today. Sensitivity is mostly limited by how well the test agent (the antibody) can bind to the test subject (the strep antigens). The main factor which limits this is the rate of bacterial evolution: the test needs to detect as many versions (aka mutants) of the bacterium as possible, but the bacterium is under neutral/positive selective pressure to change its antigens, so it is very diverse. The more specific the test gets to bacterial antigens, the less sensitive it is to changes in those antigens, so the more likely it is to miss bacteria that have mutated but are still causing disease."
] |
[
"Additionally, they usually swab you twice, once is for the rapid test, the other is retained for culture pending a negative result.",
"So to confirm a negative can take a couple days, but if it is group A strep and rapid test positive, they don't bother sending the specimen to culture."
] |
[
"Adding on the answer to the second part: our body's immune system responds pretty fast. If you arent exposed to the antigen (but have been before), antibodies are present only in miniscule quantities such that it won't turn up positive in the immunoassay. But if you are currently infected by strep, antibody production as a secondary immune response begins almost immediately and is present in much greater quantities that it'll test positive."
] |
[
"Why is alpha decay always in the form of helium-4? Why does the particle never break apart into larger particles, like lithium?"
] |
[
false
] |
Is it to do with the amount of electrons on the outer shell? Because that would make sense as to why it's always helium. Just curious.
|
[
"Alpha decay is ",
" to be the emission of a ",
"He nucleus.",
"But the alternative kind of decay you're describing ",
" exist. It's called ",
". It's when a nucleus decays by emitting some cluster of particle larger than an alpha particle. It's sort of in between alpha decay and spontaneous fission.",
"Cluster decays are rare, because alpha particles are extremely tightly-bound. It's so energetically it's very favorable for a heavy nucleus to proceed toward lighter masses by emitting alpha particles.",
"There is also the fact that these kinds of decays proceed via quantum tunneling. It's generally easier for an alpha particle to tunnel out of a heavy nucleus than it would be for a ",
"C cluster, for example."
] |
[
"That's not an easy question to answer. Some of the best studied cases are the cluster emissions in thorium-232 and uranium-234 isotopes, see, e.g. ",
"E J du Toit, S M Wyngaardt and S M Perez, Cluster decay of 234U and 232Th by the emission of neon isotopes",
" (and refs therein) where the heaviest observed emitted clusters are 24-Ne and 26-Ne."
] |
[
"Basically, any sub-nucleus can be emitted in a nuclear decay, but the emission of a He-4 nucleus is so common it has its own name. Alpha particles turn out to be extremely tightly bound, if you look at the ",
"nuclear binding energy curve",
" you'll notice there's a sharp spike around He-4. That means there are lots of conditions where emission of an alpha particle is favorable.",
"Also, He-4's high binding energy causes some weird quirks in fusion reactions and stellar evolution. Binding two He-4 nuclei together is something they really don't want to do, the resulting nucleus (Be-8) is massively unstable with an extremely short half-life. But if the conditions for fusion are intense enough the few Be-8s around at any given time can be fused into C-12, which is stable. This is called the \"triple alpha process\" because it involves the fusion of three alpha particles together within a timeframe of attoseconds."
] |
[
"Has selective breeding and genetic modification of fruits changed their nutritional content and flavor in the past few decades? If so, how?"
] |
[
false
] |
I am particularly interested in the changes to the tomato. My subjective opinion is that other fruits and vegetables have improved their flavour vis a vis to tomatoes. For example store bought blueberries thirty years ago were tasteless with a woody texture compared to wild blueberries. But today store bought blueberries are large and flavourful.
|
[
"The answer is yes. ",
"Breeding, other types of genetic modification, and cultivation practices have changed many fruits and veggies in the last few decades, but there are sooo many different varieties even for tomatoes, it's impossible to give a general answer as to how. "
] |
[
"The bananas we eat today are ",
"Cavendish Bananas",
". We used to eat ",
"Gros Michel",
" bananas, but ",
"Panama Disease",
" caused growers to switch over."
] |
[
"the effect on rats is enough to keep me away",
"Which effects? The flawed Seralini study?"
] |
[
"Are there any island to be discovered yet? I mean, has the surface of the ocean been checked at all for more spots of land?"
] |
[
false
] | null |
[
"Yes. The only new land is that which will be formed when undersea volcanoes breach the surface. For example, ",
"el Hierro in the Canary Islands",
"."
] |
[
"Forgot about melting of the ice caps. <sigh>"
] |
[
"May I add another process: isostatic rebound in circumpolar areas, which is constantly redrawing the map up there. New islands all over the place."
] |
[
"Is there any fundamental difference if you switch signs in the minkowski metric?"
] |
[
false
] |
If you change: to Does anything really change, or is this just a choice of coordinate systems? Thanks.
|
[
"None whatsoever. It's not even a choice of coordinate systems; it's purely a convention. It has no more significance than whether you choose to write your equations in pencil or pen.",
"Now that said, once you've chosen a convention you have to stick to it. For example, in the ",
" sign convention — i.e., the ",
" — timelike intervals are negative. So the proper time infinitesimal element has to have a minus sign under the radical in order to keep everything real. (Or you could just use an absolute value on the inner product, but that's the coward's way out.) If you chose the ",
" convention, you'd have no minus sign in the proper time element, but you would have one in the proper distance element.",
"So long story short, there is zero significance to the choice of sign convention, but if you start with one you have to stick with it, just as you wouldn't start out calling velocity ",
" and change it to ",
" midway through an exercise for no good reason.",
"(Though if you put the time component ",
" in your quadratic forms, you're a bastard who deserves to be publicly flogged. Just saying.)"
] |
[
"Amen. So it is written, so let it be done."
] |
[
"Noooooooooo. p",
" = m",
" , dammit."
] |
[
"How are membrane proteins, e.g. receptors, ion channels, oriented in the correct direction? Has it ever been observed for them to be \"upside down\" and what might cause this if so?"
] |
[
false
] |
Was thinking about the N- and C- terminals of GPCRs and got to wondering how they actually get oriented so the ligand binding domain is faced to the outside and the portion that interacts with G proteins, arrestins etc is faced towards the cytosol.
|
[
"Many have exactly seven trans-membrane domains (membrane crossing parts). So, by their very nature, they end up with certain parts outside and certain parts inside based on how they are loaded N-first into Golgi body membranes that are transported to the surface as vesicles. These proteins have a 'signal sequence' usually built right into their protein sequence at or very near the N-end that direct the proper direction.",
"Based on studies of activities inside and outside the cell, my guess is that this rarely ends up backwards. Again, it is based on how all the many parts of the process work together. If one thing fails, the likely result in nothing ending up on the cell surface."
] |
[
"Expanding on what ",
"/u/Sunfest",
" said, transmembrane proteins contain ",
"topogenic sequences",
", that are required to orient them properly. Among other functions, these sequences are N-terminal signal anchors that are recognized by the ",
"signal recognition particle (SRP)",
" and direct free ribosomes to dock on SRP receptors adjacent to ER translocons and extrude the nascently synthesized protein into the lumen, where they are then cleaved by signal peptidase. Hydrophobic topogenic sequences (usually in the middle of the protein) function to arrest extrusion and promote lateral transfer into the bilayer of the ER membrane -- if you mutate these residues to charged amino acids the protein will be released into the ER. In other words these sequences function as both stop-transfer and membrane anchor sequences. Some proteins are do not contain membrane anchors and are instead C-terminally conjugated to ",
"GPI anchors",
" post-translationally. ",
"Importantly, the orientation that the protein acquires during this extrusion step is the same orientation it will have if and when it is trafficked elsewhere; for plasma membrane receptors, for example, cytosolic domains remain cytosolic, lumenal domains become extracellular. If you visualize a transmembrane protein with these endo- and ecto-domains embedded in the ER and imagine its budding through the Golgi and the fusion of a vesicle containing it with the PM, it's easy to see why this orientation would be preserved. "
] |
[
"Also the conditions inside the Golgi are different to those in the cytoplasm. A lot of receptors require 'activation' between synthesis and function. The conditions can be something in the lines of allowing cleavage of inactivation motifs etc etc. If a receptor did turn out upside down then it wouldn't function, would be recognized and digested. Bear in mind that every proteins process is slightly different so there are so many technical answers. "
] |
[
"Why does the smell of a skunk disappear after a day when sprayed on the road but the smell stays for days on clothes and your body no matter how much you clean?"
] |
[
false
] |
I'll go running and pass by a skunk corpse that smells very strongly of skunk. However the smell disappears usually within a day. However the smell of skunk is clearly not easily taken out of clothes. Why is this?
|
[
"Yup. Its actually healthier than a dryer anyway (so I hear, but I'm not sure on the science behind this one) because the UV light from the sun kills bacteria."
] |
[
"You forgot \"and in the coat of your dog for years, everytime it rains.\" Now that I'd like a scientific explanation to!"
] |
[
"First of all the fibers of clothing trap the smell causing chemicals better than road does. Also the road is outdoors, making easier for the chemicals to be dispersed through diffusion and the elements. Diffusion happens faster outdoors than indoors because, every simply stated, there is more outdoors than indoors; so it becomes a bigger gradient and forces the chemicals to dispel faster."
] |
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