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[
"Are carbon fiber implants in the body safe and feasible?"
] |
[
false
] |
I was talking to someone the other day and I said why not have carbon fiber implants in the body e.g. hip implant because carbon fiber is strong and low weight among other things (like resistant to high temperatures, etc..) The person I was talking to said that would be a terrible idea and dangerous? I assumed it had something to do with the metal on metal implants lately but what if you just had the implant made out of the carbon fiber and the other piece a bio-compatible plastic. Would the carbon fiber degrade and render the device useless and toxic? Why are carbon fiber implants in the body a terrible idea? Can it be done and if so, why aren't they more popular options?
|
[
"I'm sure if it was dangerous there would not be companies making them. ",
"Like this one"
] |
[
"Although by the look of the images on that website, they don't seem to show up on x-ray very well. Which for ongoing monitoring of implants, is Not A Great Thing.",
"Temperature resistance isn't particularly important (except for maybe the sterilisation process before implantation). Weight also isn't AFAIK that much of an issue. What is important is strength, inertness (inside the human body is more corrosive than seawater), and elasticity (bone has a natural amount of bendiness, it's nice for implants to have the same to lessen the risk of periprosthetic fractures). Similarly, a lot of plates and the like are slightly bent by the surgeons to better fit the patients' anatomy. Not sure if that's feasible with carbon fibre.",
"I'm not saying it's a bad idea, just there are a lot of issues, and CF implants will need to have some definite advantage over pre-existing devices before it gets much use. (Less complications, cheaper, whatever).",
"Disclaimer:- I'm not a doctor, and definitely not an ortho surgeon. Healthcare professional with an interest though."
] |
[
"Because companies never sell things that are dangerous."
] |
[
"Why when we stare at a negative image, then blink, do we see it in colour?"
] |
[
false
] |
Saw some on Reddit a few days ago, whereby if you stare at a spot on a negative image then blink/look at a white wall you can see it in colour.
|
[
"I am a computer vision PhD student, and I study human perception as part of my work.",
"What you are describing is a very interesting use of the ",
"afterimage",
".",
"Short, digestible explanation:",
"Your iris, cornea and lens act like a camera lens to project the image your eye is facing onto your ",
"retina",
", where a matrix of cone and rod cells analyze the incoming light for intensity and color. The color receptors, or ",
"cones",
", operate chemically and after a while get tired out and stop firing in response to the frequency of light you are looking at.",
"When you later shift to a white light (which contains light of all wavelengths), the tired cones offer a very weak response when compared to the fresh cones that were not responding before. The result is that you perceive a \"lack\" of the color that you were looking at before. If the initial image is a negative, your perception when looking at white light will be of the color of the developed photograph."
] |
[
"My understanding was that photopigment bleaching is only an indirect component of why you perceive afterimages. Rather, fatigue of opponent-process (parvo) ganglion cells (R+/G-, G+/R-, Y+/B-, Y-/B+) that receive their inputs from the cones and bipolar cells are what are responsible for the afterimage. ",
"EDIT: typo"
] |
[
"because your eyes get use to inputs (like the color of light) and slowly lose sensitivity to it. ",
"When you look away from the Negative image, the lowered sensitivity to the negative color produces the Illusion of a normal color image on a white wall"
] |
[
"Do common colds or flu strains leave permanent damage similar to what is being found with CoViD-19?"
] |
[
false
] |
This post has CoViD-19 in the title but is a question regarding the human body and how it handles common colds and flu strains which are commonly received and dealt with throughout a normal life. Is there any permanent damage caused, or is it simply temporary or none at all? Thanks! Edit: I had a feeling common colds and flu strains had long lasting effects, but the fact that I didn't realize it until I was reminded and clarified by you all is a very important distinction that this isn't something we think about often. I hope moving forward after CoViD-19, the dangers of simple common illnesses are brought to attention. Myocarditis is something that I have recently learned about and knowing how fatal it can be is something everyone should be aware about.
|
[
"Influenza can cause heart problems. Do you know what the most effective preventive treatment for a heart attack is? Influenza vaccination. ",
"There is a large body of observational and clinical trial evidence that shows that influenza vaccine protects against AMI. Estimates of the efficacy of influenza vaccine in preventing AMI range from 15% to 45%. This is a similar range of efficacy compared with the accepted routine coronary prevention measures such as smoking cessation (32–43%), statins (19–30%) and antihypertensive therapy (17–25%). ",
"—",
"Influenza vaccine as a coronary intervention for prevention of myocardial infarction",
"Influenza Vaccination Is Critical for Patients with Heart Disease",
"Flu Vaccination Linked to Lower Heart Attack Risk",
"Flu shot linked to lower heart attack, stroke risk",
"Flu Shot Helps Prevent Heart Attack"
] |
[
"There's a generally held strong suspicion that a lot of autoimmune chronic disease is cause by as yet unidentified viruses or bacteria - Most likely ones we're already aware of. There's a Nobel prize in finding the links.",
"For example there's a few big trials at the moment looking at the link between dementia and chronic coldsores (as opposed to primary herpes, which is harder to do big long term trials on) , and whether antivirals can protect against dementia - Would be big if true, particularly as the drugs are cheap.",
"Edit: To everyone in comments asking if their X infection could have caused Y. This is the internet, someone will come at you with a great anecdote or mechanism telling you that your Y is clearly caused by X. Don't give into the temptation to strongly agree, most autoimmune disorders have not been shown to have clear causes at this time. You're human, you want to see patterns in noise."
] |
[
"I was gonna make a pile but I'd like to just add on your your pile if that's okay.",
"Influenza vaccination reduces all-cause mortality in heart failure patients.",
"Significant association between respiratory infections, especially influenza, and acute myocardial infarction.",
"Of course, heart attacks cause heart failure quite directly."
] |
[
"Can multiple parallel procedures be simulated as a one?"
] |
[
false
] |
If you have an abstract system which runs a number procedures, naturally with possibility of being out of sync, is it possible to emulate the evolution of the whole as a single procedure. I just go idea that one could maybe encode the whole system as an evolution of one-dimensional string. Please grant any notable properties, pros and cons, of such way of structure if you know any.
|
[
"Whether you can do this in any meaningful way really depends on what you're trying to do. Yes, it's possible to ",
" multiple parallel processes, but in doing so you must pick one particular serialization out of many possible serializations. If by ",
" you mean \"explore the total range of possible behaviors\" then this is in general not possible.",
"One of the fundamental difficulties in parallel and concurrent programming is that parallel processes can generally execute at any rate relative to one another, and the programmer has very little control over the specific order of execution. For example, if you have two parallel threads executing functions A and B, then it's possible that function A executes first, and then function B executes second. It's also possible that B executes before A. Worse, it's possible that A and B execute concurrently, with different instructions from each function interleaving themselves, such as: half of A executes, then half of B executes, then a little more of A executes, then B finishes, then A finishes, etc.",
"In fact, there are an exponential number of possible parallel executions. Consider the following model: you have a processor and two parallel functions A and B. The processor executes one instruction at a time, and is allowed to choose which function it executes each cycle. Thus for cycle 1 it may choose to execute function A, for cycle 2 it executes function B, then cycle 3 it executes function B, then cycle 4 it executes function A again, etc. How many possible program execution traces are there? ",
"If the processor executes two cycles there are four possible traces:",
"If the processor executes for three cycles then there are eight possible execution traces:",
"If you follow the pattern, if the processor executes for N cycles then there are 2",
" possible execution traces. This grows exponentially, so for N=20 there are roughly a million execution traces, for N=30 there are roughly a billion execution traces, for N=40 there are roughly a trillion execution traces, etc. This behavior is confirmed analytically by observing that during each cycle the processor has two choices, and the decision at each cycle is independent of the cycle previous. ",
"Two things to note about the above situation. First, real processors don't generally switch between real processes at a rate of once per instruction, but it can still happen extremely frequently in real systems on the order of hundreds to thousands of times during a typical execution. Second, you'll notice we're not actually talking about parallel processing yet- here we just have a single processor switching between two concurrent processes. Parallel processing, predictably, just makes things worse and can lead to faster exponential growth in the number of possible execution traces. The conceptual model for true parallel procedures would be that you have two processors and three or more alternative functions, and each cycle both processors would have to pick which of the three functions they were going to execute. ",
"Now, back to serialization and emulation. It's very possible to serialize these asynchronous functions. All you have to do is to pick one specific execution trace and run it on a single processor, and that is your serialization. However, the total range of possible behaviors is only encompassed by all possible execution traces. In order to fully explore all possible behaviors you'd have to run all possible execution traces. Since the number of execution traces grows exponentially this is only possible for every small-scale situations.",
"In practice, rescheduling of processes onto processors happens about once per millisecond. My gut feeling is that it's probably possible to \"fully emulate\" all possible parallel behaviors for a time span of 5-20 milliseconds of execution, depending on how many processes and processors you're actually thinking about. Beyond that the number of possible execution histories is just too large. ",
"There are some parallel systems that support automatic serialization of a parallel program. For example, Cilk Plus is a parallel programming platform, and when you compile a Cilk Plus program you can ask the compiler to generate a serialization instead of a regular parallel program. What happens here is that the compiler essentially ignores all the calls to execute functions in parallel, and simply executes them immediately (in the main thread of execution) when the call to parallelize is encountered. This generates what you might call the \"depth first\" serialization of a parallel program. Other platforms such as OpenMP support serialization as well, but how exactly the serialization is generated is going to be platform-specific.",
"Now, there is work that has been done on what I'm calling \"explore all behaviors of a system\". What this comes down to is trying to prove assertions that limit the total possible behaviors of a system. There might be an exponential number of possible execution traces, but if you can prove that a number of execution traces are equivalent to one another then you can make statements like \"any one of these billion execution traces proves the validity of the entire class, so we only have to run one and it's like we had actually run all one billion of them\".",
"For example, a technique called ",
" analyzes a program to determine what conditions cause what parts of a program to execute. In parallel programming this might let you say that you have three parallel functions A, B, and C. But your symbolic analysis shows that either A and B can execute simultaneously, or B and C can execute simultaneously, but never A and C. The problem is still exponential, but that constraint means that you never have to consider any execution trace where A and C execute together. ",
"Another technique is called ",
", where the system is abstracted into a very precise formalization. Then you can feed your representation of the system into a ",
"boolean satisfiability solver",
" in order to make queries about the way the program executes. This allows you to discard execution traces that can't happen in practice. ",
"This is not my exact area of practice, but a quick Google search turns up this paper, which attempts to use both these techniques:\n",
"http://delivery.acm.org/10.1145/1350000/1348256/a10-siegel.pdf?ip=165.134.212.75&id=1348256&acc=ACTIVE%20SERVICE&key=B63ACEF81C6334F5%2EF8AA8898C57C2859%2E4D4702B0C3E38B35%2E4D4702B0C3E38B35&__acm__=1530314396_681229ecafcb45aa125fff9ed45f0a49",
"In this work, in case you're not able to read it, they apply some of these techniques to four small numerical parallel programs (~50 lines or so it would look like). The \"easy\" programs take about ten minutes to exhaustively check all behaviors, while the \"hard\" programs take a few hours.",
"The TL;DR is that this is possible in the small scale if you know what you're doing, but generally impossible for systems of any significant size or complexity. "
] |
[
"thanks! a simple-minded person could have just said the outcome, \"only in small scales\" but the massive explanation you granted is massive but even greater in meaning!",
"have a good day!"
] |
[
"Your question is one of the fundamental questions posed in ",
". In a distributed system, multiple processors execute tasks in parallel, and questions about their operations like the following need to be addressed:",
"There are sets of rules that, when all nodes in the system adhere to, answer this question. These sets of rules are called ",
". There is a variety of consistency models, some stricter than others, which define these rules and are applicable in a variety of situations / applications.",
"The stricter of all consistency models is called \"strict consistency\". Strict consistency is defined as:",
"Any read to a memory location x returns the value stored by the most (globally) recent write operation to x",
"The determination of most recent is unambiguous because of the assumption of a global clock. In reality, global clocks do not exist, and there is a limit on the propagation of information (the speed of light), therefore the strict consistency model is generally impossible to implement. There are less strict models however (see a survey ",
"here",
"), for which the answer to your question is yes."
] |
[
"Does polyoxymethylene block infrared radiation?"
] |
[
false
] |
Question came up today at work & seems to be ungoogleable.
|
[
"It will block infrared radiation the same way that small organic molecules do, certain frequencies will be blocked but it will likely be transparent to the majority of the IR spectrum. I can't find a specific plot for that polymer but it will likely look similar to ",
"dimethyl ether",
" as the primary bonds and orientations should be the same."
] |
[
"Here is a source for an ",
"FTIR spectrum",
".",
"It appears that Polyoxymethylene is \"translucent\" in the IR range, but I'm not sure exactly how one would interpret something like this. I guess we could say - it mostly doesn't block infrared radiation."
] |
[
"page 89. It is not translucent, it has several peaks."
] |
[
"So I just heard gravity is weaker than some other forces. What does that mean exactly?"
] |
[
false
] |
I'm watching a documentary on Netflix called Particle Fever. It's about the hadron collider and how it was built or the first time I turned on.. I'm not sure yet and I'm sorry my ignorance is shining through. I wish I knew that which I spoke of. But anyway. One of the scientists here was talking about asking the real questions. He listed a few things and then said "why is gravity weaker than other forces?"... What forces are stronger than gravity and has there been any progress in answering this since.. 2010 let's say.
|
[
"Don't mind me, just adding an additional detail that I think is helpful. :)",
"A simple test you can do to prove this to yourself: find a magnet and some paper clips. Use the magnet to pick up the paper clips. Clearly, you are overcoming the weight of the paper clips using the E&M force.",
"It's worth noting that when you use the magnet to pick up the paper clips and resist gravity's effects, you're resisting the ",
" net gravitational effect, with just a handheld magnet.",
"This should give the OP a clear idea of just ",
" weak gravity is compared to electromagnetism. It is ",
" weaker than all three of the other fundamental forces. The only reason we observe gravity at all is because gravitational effects are always attractive and have infinite range, whereas electromagnetic effects are both attractive and repulsive (and balance out almost exactly on large scales, despite its infinite range), while the weak and strong nuclear forces are limited to extremely short ranges (less than an atomic nucleus!) due to some particularly complicated details about those two forces."
] |
[
"That's a little unfair to gravity. ",
"I can't say I see how it is. I'm talking about directly comparing the size of the ",
"coupling constants",
", and the gravitational coupling constant is something like 10",
" times the strength of the electromagnetic coupling constant.",
"If the mass of the Earth were concentrated into an object the size of a fridge magnet then it would suck in the fridge, your house, and you more or less instantly through gravity alone.",
"This isn't exactly true, and it isn't a fair comparison either. The force of gravity is proportional to the mass involved, and the mass of the Earth would not change just because you compactified it. (As an example of this, it is well known that if you took the mass of the Sun and condensed it into a sphere roughly 3km in size, it would become a black hole ... but at 1 AU away, the Earth would still continue to revolve around it with essentially the same orbit.)",
"Also, this fails to account for the distance involved from the center of gravity. For a spherically-symmetric body with approximately uniform density, you can make accurate calculations by treating the Earth as an extended point mass where all of the mass is concentrated at its center. When you do this, you end up with the same -9.81/ms acceleration out at the Earth's radius. If you were to get closer in than one radius, sure, the gravitational force will be stronger since you are decreasing the distance, but to keep your comparison accurate, you'd still need to move out to one radius.",
"But let's say for a minute that sure, we condense it to a ball and we move the ball in much closer. Would gravity overpower the magnet? Yes. But then that is still not a fair comparison because you still are using the ",
" (a celestial body's worth) against just the ",
" (not even electric) charge of what would otherwise be a tiny mass made up of much fewer particles.",
"Bottom line: if you were to take a second condensed Earth, and give it a net electric charge equivalent to turning each particle in the extended Earth into an ion with an excess charge of e, and held the two at equal distance from a test particle, the electric force of ",
" condensed ion-Earth would be ",
" larger than the gravitational force of that first condensed Earth by about 10",
" orders of magnitude. Doing this is a much fairer comparison, because it allows you compare the contributions (gravitational versus electrical) from the same amount of matter.",
"Put another way, if you took two individual ions with identical charge e (so that they repel eachother), no matter what distance apart you put them away, they ",
" repel rather than attract eachother under their own gravitational influences -- regardless of which ions you choose, you could choose the heaviest known ions if you wanted -- and they would repel eachother much, much quicker, than two ",
" particles with the same masses would attract eachother due to gravity. The only way you could get gravity to dominate would be if those ions you chose happened to have such an enormous amount of mass that it would be equivalent to a celestial body's worth (which isn't fair, but that's what you're suggesting in your condensed Earth example -- you're just not giving the same treatment to the magnet that you are to the Earth)."
] |
[
"There are four fundamental forces: The two nuclear forces, electromagnetic force, and gravity.",
"When we say gravity is weak, it is in relation to those forces. Gravity is the weakest of the four. A simple test you can do to prove this to yourself: find a magnet and some paper clips. Use the magnet to pick up the paper clips. Clearly, you are overcoming the weight of the paper clips using the E&M force.",
"As for your last question, there are ideas that attempt to explain why gravity is (or maybe just appears) weak in comparison. For example, String Theory says that gravity only appears weak because it is folded into higher-order dimensions. However, no one has found evidence to fully support any one theory yet."
] |
[
"Do people with over-active immune conditions (like allergies, asthma, or IBD) actually have immune systems that fight off normal infections better, due to their hyper-vigilance?"
] |
[
false
] |
curious whether any clinical tests have been done. do they fight off colds and influenza any better for example?
|
[
"No. ",
"Your immune system is highly specific. Every lymphocyte white blood cell you have is specific for ONE thing. When a white blood cell is activated, and sees what it is specific for, it clones itself to make thousands of copies. Then the clone army attacks that one thing.",
"If you have an auto-immune disease, like type-I diabetes, you will have thousands of white blood cells specific for the Beta islets of the pancreas. They will only attack the pancreas. They will not be able to attack the flu or colds. ",
"Your body will still have a normal response against the flu, though. Just not an increased response. ",
"Does that help answer the question?"
] |
[
"How does this explanation jive with the ",
"hygine hypothesis",
" and ",
"helminthic therapy",
"?"
] |
[
"The immune system is far more complex than simply lymphocytes. Although lymphocyte specificity addresses the original question, there are other factors at work for the hygiene hypothesis and helminthic therapy, neither of which have been fully explained.",
"The TL;DR of both concepts is that they generally deal with or involve gut immunology, which is still rather poorly understood, although it's a topic of intense research. In that way, like many scientific frontiers, gut immunology has enough evidence to make it a plausible explanation without a large body of supporting mechanistic work.",
"That being said, the idea is that the gut is a privileged immune organ in which the normal immune system behaves differently because of environmental factors. This is how, for example, oral tolerance works: immune cells that react to certain common environmental or food allergens (which are not present in the thymus, where T lymphocytes develop) have their reactivity downregulated or reduced in the gut. My knowledge of that phenomenon is a few years out of date, so I'll refrain from offering any definitive mechanistic example and hope others can do so.",
"Similarly, there are some theories that say that our natural immune response to parasites, which is somewhat specialized outside of general responses to bacteria and viruses, is \"hijacked\" or somehow dysregulated by the modern first-world lack of parasitic infections. Because parasites have their own special responses outside or somewhat different than the \"canonical\" immune response, and there is some evidence that some of the cells involved in this response are also involved in various autoimmune reactions, there are some theories that this lack of \"parasitic immune education\" can lead to disruptions in normal function down the line."
] |
[
"If interaction with the Higg's Field is defined by mass, does an object with more mass therefore have more interaction with the Higg's Field?"
] |
[
false
] |
thanks!
|
[
"Yes. From page 5 of pdg.lbl.gov/2010/reviews/rpp2010-rev-higgs-boson.pdf",
"\"The SM Higgs couplings to fundamental fermions are proportional to the fermion masses, and the couplings to bosons are proportional to the squares of the boson masses.\""
] |
[
"Yes"
] |
[
"There are now even experimental results that support this relationship. I really happen to like ",
"this summary plot",
" which shows the coupling strength for fermions, or an equivalent quantity for bosons, as a function of the mass of the particle that couples to the Higgs."
] |
[
"What force caused the planets to start spinning about their axis?"
] |
[
false
] |
What caused the spin of the earth in the first place.
|
[
"Everything spins. Essentially because everything is not ",
" uniform, as it falls together, it doesn't fall straight \"toward\" the center. It falls, but misses passing through the center and shoots off into an orbit. This is true of stuff falling into place around the sun (forming planetary orbits) and stuff falling into a planet, forming it (forming planetary rotation). ",
"This is also why ",
" everything orbits in the same plane (a practically flat solar system), in the same direction, and generally, rotates in the same direction. (notable exceptions include Venus, which nearly doesn't rotate at all, and in fact does so \"backwards\" with a \"day\" longer than its year; and Uranus, which, for some reason, is tipped such that its pole lies almost in the same plane as its orbit)"
] |
[
"The moon does spin. It's period is ~28 days, the same length of time it takes to orbit us. If the moon didn't spin the same side ",
" always face us. ",
"Edit: We call such objects ",
". It's my understanding that space stations are largely the same as the moon in this regard but they maintain oreintation artificially with maneuvering thrusters and gyroscopes. "
] |
[
"satellites and the ISS have thrusters to carefully control the spin to make sure solar panels are in the correct place and docking with other vehicles."
] |
[
"Dark Matter Deniers: Is there room to doubt the existence of dark matter?"
] |
[
false
] |
[deleted]
|
[
"We have pretty good evidence of dark matter from a variety of sources. I could list them all, but I'd pretty much be copying from ",
"the wiki",
" anyway.",
"What we think we're looking for is a particle that only interacts weakly. We have an example of a particle that does that, in the neutrino (excepting certain extensions to the standard model that aren't relevant to this discussion). But we know that the neutrino is too light to form the \"dark matter halo\" structures we see in the galaxy. So we hope to find another only weakly interacting particle that is more massive than the neutrino. There's a lot of suspicion that it may be the 'Neutralino,' one of the supersymmetric partners to the family of photons and W and Z bosons. ",
"There are some other theories of gravity that attempt to explain ",
" of the phenomena that are attributed to dark matter, like the galactic rotation curves, but they usually don't explain as many phenomena as dark matter does. As physicists, there are many people pursuing these alternate routes, but until we find good evidence for them, the scientific consensus favors the dark matter hypothesis."
] |
[
"If dark matter is defined to be gravitating, dynamical degrees of freedom that are independent of ordinary matter (i.e. known standard model constituents), then objects like the Bullet Cluster are convincing evidence for dark matter. Gravitational lensing clearly identifies sources of gravity that are dynamically independent of the observed baryonic matter in that cluster.",
"The only remaining uncertainty about dark matter is whether it is particle dark matter, or something really ugly like TeVeS (MOND). But any model that hopes to be consistent with the cosmic microwave background and objects like the Bullet Cluster inescapably must invoke dark matter."
] |
[
"One assumption, that there's a particle we haven't yet observed, explains an awful lot of data, including predictive power (like in the CMB spectrum matching predictions based on dark matter models we have from galaxies and clusters).",
"The other hand is that General Relativity, which has worked remarkably well over the years in explaining many types of data is really fundamentally broken. Many of the modifications to GR are, themselves \"Kludges.\" Additional scalar fields to the Tensor field, changing it to a double tensor field, introducing a decay term for the strength of the gravitational field, etc. ",
"The explanation that most scientists think most plausible is that there is a particle we haven't yet discovered. That's no huge surprise, we're just now in the process of discovering a particle that's been a part of particle physics theory for decades. And the particle we suspect to be \"dark matter\" also fits well with many \"beyond-the-standard-model\" predictions. Seriously, it just makes so many question marks and unknowns in science fit together so nicely that it seems like an assumption with an awful lot of explaining power.",
"If at the end of the day, there is no dark matter (evidence for it) then we will end up turning to how GR could be wrong, and so on and so forth. Time will tell. But for now, the scientific consensus is \"yes, there is dark matter.\""
] |
[
"What makes heat a more highly disordered form of energy than say potential energy?"
] |
[
false
] | null |
[
"This really comes from the defintion of heat. Heat is energy whose precise origins we aren't paying attention to. Have one billiard ball collide with another, and we'll talk about the energy transfer in terms of kinetic energy. Have two gases come in contact with each other, we'll talk about the energy transfer in terms of heat transfer. Microscopically, the heat transfer is just a bunch of atomic collisions, but instead we don't pay attention to those and instead lump the microscopic phenomena into the macroscopic one of heat transfer. The notion of disorder comes from our lumping together of various microscopic states into a macroscopic state, and thus our macroscopic description doesn't tell you everything you could in principle know about the system."
] |
[
"I always like thinking about statistical quantities in terms of their physical processes. ",
"Gas pressure, for example -- an average of the momentum transfer from individual particles colliding with the surface at various angles and speeds, producing a net effect. I think it helps to break these things down to understand how equations like PV = nRT make intuitive sense."
] |
[
"This is an explain it like I'm 5 approach:",
"Heat can go many directions, potential is defined to go into one."
] |
[
"Do electrons actually move through a conductor?"
] |
[
false
] |
I've been watching some physics videos, and most of the time electricity/current is represented as particles (electrons?) moving through a conductor, like copper. However, I've recently "learned" that electrons barely move in conductors, it's only the electromagnetic waves that move significantly. Close to the speed of light I believe. As an example, in one of these videos capacitors were represented as two plates close together. It was explained that a higher concentration of negatively charged particles would be forced into one plate, causing the second plate to fill up with positively charged particles in response. I believe a similar phenomenon occurs to some degree in many electromagnetic components, like coils for example. I guess the root of my question is, how do these two concepts reconcile? Moving particles vs moving waves? A battery might be an example as well. More electrons on one pole, less on the other. If only the waves move through a circuit between the two, why would they ever lose their electric field/voltage?
|
[
"Electrons always undergo thermal motion, so they're moving about randomly quite fast, but when no current is flowing the thermal motion all cancels out; the mean electron speed is on the order of kilometres per second (at room temperature) but the mean ",
" is zero.",
"When a current is flowing this means the electrons tend to drift in one direction so their average velocity is non-zero, this is known as the ",
" and is generally on the order of micrometres per second.",
"The signal velocity however is typically close to the speed of light."
] |
[
"The simple answer: Electricity is energy. An electron is just one particle. Electricity can travel at near the speed of light. I've read that the electrons themselves actually only move at about an inch in five minutes. \nHere's how that works. Imagine a long tube full of ping-pong balls. Push insert a ball in one end and another ball will pop out the other end almost instantly. The individual balls only moved an inch or so but the energy of the push traveled down the tube almost instantly."
] |
[
"so the electron is just a vessel for electric energy? Kind of like buoys in an ocean?"
] |
[
"Any books suggestions to start out on understanding physics?"
] |
[
false
] | null |
[
"It depends on whether you want to actually learn physics or read a collection of interesting facts."
] |
[
"It is a little old, but I always liked \"A Brief History of Time\" by Stephen Hawking."
] |
[
"I was going to suggest this same book. Great read."
] |
[
"How Can I Support Stem Cell Research?"
] |
[
false
] |
[deleted]
|
[
"EDUCATION EDUCATION EDUCATION!!!",
"Honestly, I'm sure any and all of us scientists on here could write out a million things, but it all comes down to educating the general populous.",
"General info on stem cells:\n-The embryonic stem cells are harvested at the stage where they are called 'blastocysts' at and around 5 days after fertilization. They contain two types of cells: an inner cell mass(the actual stem cells that turn into the embryo), and a trophoblast (which turns into the placenta/fetal membrane).\n-50% of blastocysts fail to implant ANYWAYS. A ton of people's collective jaw tends to drop at that one.\n-A blastocyst isn't even an embryo. It is literally a glob of cells one stage up from a morula. The way my med-school embryo professor explained it was the best: \"it is a product of fertilization without any differentiation that would lend it to be more human than a sloughed off skin cell.\""
] |
[
"I have read articles about how judges extend or deny stem cell research phases, congress banning or passing bills pertaining to stem cells, Obama lifting the stem cell research ban, etc.. At the risk of showing my own ignorance; what affect does the general populous have on stem cell research?",
"What are the issues that hold up research? The main controversy I've come across is based upon religious beliefs. I would be very interested to hear any additional reasons why people feel stem cells/regenerative medicine should not implemented. ",
"Do you know of any organizations currently in place which are working to support stem cell research? ",
"And, do stem cells fall under the full scope of regenerative medicine or do stem cells overlap into regenerative medicine as well as being included in any other purposes? "
] |
[
"The issue that the public has comes to funding. The NIH, NSF, and other federally funded organizations have to follow strict rules when it comes to giving grant money out. When the \"stem cell ban\" was in place, you could not use ANYTHING procured with federal funds for embryonic stem cell research. That included things like computers, refrigerators, incubators, microscopes, you name it.",
"Obviously, this didn't stop stem cell research in any way, shape, or form. Induced pluripotent stem cells became the bigger thing during that time (since they were not affected by the ban). However, FoxJohnson up there brings up the best point in the fight to allow federal funding to extend to stem cell research. Education of the masses will allow them to understand that, as was previously stated, that blastocysts are little more than a glob of cells.",
"The things that hold back stem cell research now are the same things that hold back research in other fields--not enough knowledge, and limited practical application. Stem cells are ",
" capable of doing amazing things therapeutically, we just don't know how to use them effectively yet. Once a major breakthrough occurs using stem cells, most of the resistance will likely dissolve.",
"Stem cells do fall under the regenerative medicine label almost entirely. This isn't to say that their only use will be in regenerative medicine--one of the major goals with stem cells is to see if they can be used to create ",
" models, of sorts, of human organs other systems. However, that type of research also falls under the regenerative medicine label, as the term is very broad.",
"Organizations that support stem cell research include the Christopher Reeve Foundation, American Cancer Society, WiCell, and numerous others."
] |
[
"could you orbit a planet with much higher gravity at an altitude to give you earth like gravity?"
] |
[
false
] |
Ok, so I'm not sure if this is even a correct premise, but if gravity decreases in intensity as distance away from its source increases. Would it be possible to have a space station orbit a planet at a set distance to simulate earth like gravity?
|
[
"When something is in orbit, that means that it is in freefall, and thus the experience of living inside the space station would be that of weightlessness.",
"It's true that the gravitational force drops as 1/(distance to planetary center)",
", so at a suitable altitude, yes, the gravitational force would be comparable to the surface gravity of the Earth. However, you'd have to be at that altitude and not be in free fall (say at the top of a really tall mountain or building -- leaving engineering considerations aside). In such a situation, if the planet is rotating, you'd have to pay attention to rotational effects (\"centrifugal force\") as well to figure out the correct altitude."
] |
[
"Absolutely. This is depicted wonderfully in the very science-accurate movie 2001."
] |
[
"Off topic, but could a donut-shaped space station rotate at a rate such that the centrifugal force would pull you outward so as to simulate gravity?"
] |
[
"Atomic Theory"
] |
[
false
] |
This is a rather simple question compared to many on here. I am in a high school science class. We briefly touched on chemistry but most of the course is focused elsewhere. We were taught the Bohr Model of the atom. It was explained that the Bohr model is not a perfect way to represent the atom but it works fairly well for a high school course. I would like to know how the actual atomic model compares to the Bohr model. I know I could read Wikipedia but I have difficulty understanding their science articles due to my small scientific knowledge.
|
[
"Here's what the various electron orbitals actually look like",
". As you can see, every orbital is described by a set of ",
"three numbers: l, m, and n.",
" The shape of the orbital comes about from solving the wavefunction for those parameters. They take on all those different kind of shapes because electron interaction is much more complex than the Bohr model allows, because electrons act as waves and when two waves interact you get constructive and destructive interference, which forms the shapes.",
"Note that these shapes don't represent actual physical shapes. They represent areas of probability. You can't really say that an electron is in a certain place, you can only describe the shape formed when you add up all the possible places that it might be."
] |
[
"It will be difficult to describe the exact details, but here are some important basics:",
"The Bohr model of the atom describes electrons as discrete particles that revolve around the nucleus in different orbits.",
"What current atomic theory states is that electrons are not discrete particles you can see orbiting around a set path, but rather a negatively charged particle/wave that most often occupies a bubble of probability around the nucleus. You can never exactly know where the electron is, but each electron has a certain energy level that allows us to mathematically describe regions where electrons are most likely to be found.",
"These are atomic orbitals. They have many different shapes, but only describe the space that electrons are most likely to lie. Different electrons occupy different orbitals.",
"Summary: The most important difference is the realization that in atoms, electrons exhibit more wave-like properties. As such, you can never be sure where they are or what they look likely, and they don't follow any defined path. They do still \"orbit\" the nucleus, but in atomic orbitals, which are just functions that describes the space that electrons are most likely to occupy. Electrons of different energy levels occupy different orbitals. "
] |
[
"The next level up is sometimes called the orbital model. It assumes that the attraction between the electron and the nucleus is the same as between two bulk charges particles.",
"It gives the probabilities of finding an electron in various states, and you can calculate the difference in energies of these days, which give you information about the spectrum, which you can measure to confirm.",
"The next level up goes one step deeper and doesn't assume that attraction between the nucleus and electron."
] |
[
"How did we get a picture of the milky way (if we did)?"
] |
[
false
] |
I feel like I should know this, but I don't. If we are inside the milky way and haven't sent and telescopes outside of it, how did we get a picture of it? I understand that we can find out how it should look like and our location on it. Do we actually have a picture of it or is it some sort of interpretation? Or is it a stitching of pictures from different directions?
|
[
"Past",
" - ",
"/r/asksci",
" - ",
"threads",
" - on this precise question, fyi."
] |
[
"We don't have a picture of it. It's all extrapolation based on the limited amount we can actually see, and what we observe of other galaxies. There's even debate about whether it's a spiral galaxy or a barred spiral galaxy. The ",
"Wiki article",
" contains several sources for recent studies which show that we don't really know much about some significant properties of the overall shape."
] |
[
"Well we have one where you see it from the side, just as you would see it if you looked up at night where there isn't a city nearby. The ones from the front are either other galaxies or CG."
] |
[
"How do scientists across the world accurately repeat experiments that use very fine weight measurements when the force of gravity isn't consistent across Earth?"
] |
[
false
] | null |
[
"For the majority of experiments, the variations of the Gravitational Field are small enough that any affect on the results are minimal, and quite often not relevant.",
"If the experiment relies on a more accurate measurement of the force of gravity then any weights are re-weighed extensively and for very important experiments a local value of g can be calculated.",
"Often though, more relevant errors come from other sources which can contribute a lot more heavily to inaccuracies of results."
] |
[
"The one that instantly comes to mind is Millikan's Oil Drop experiment. Trying to repeat those results and achieving a suitably accurate result would require measurement of the local gravitational field strength."
] |
[
"A common approach is to use torsional balances, which test the attraction/repulsion between two or more objects in a plane perpendicular to the Earth's gravity. This is how Cavendish measured Newton's gravitational constant, and how micro gravity research is still often pursued."
] |
[
"Why are stirling engines not used instead of passive heat exchangers?"
] |
[
false
] |
A stirling engine is likely the simplest of all engines. It runs by simply vibrating a piston from a hot side to a cold side. In doing so, it helps cool the hot side (the heat has to go somewhere). The piston is usually connected to a rotary output shaft. That rotor could either generate electricity or spin a fan aimed at the area to be cooled (heat exchanged). Even if you don't care about the electricity generated or extra work possible, and there's rarely a good reason not to care, you should care about the extra cooling power. Heat exchangers are useful for PCs and solar cells, but another application is in engines, especially closed system engines such as steam engines. You (I) want to cool the steam as much as possible after the work phase so that you reduce the pressure as much as possible and the less possible is pushing back against new hot steam doing work, but you still want to keep the steam and route it to the head of the cycle because its much more efficient than starting with room temperature water and heating that. Are stirling engines an outright bad idea for the purpose, or just too complicated to bother with?
|
[
"Are you considering cost and reliability?"
] |
[
"Well, a heat sink is a hunk of metal. Hard to get more reliable than that."
] |
[
"can someone elaborate on this? whats so special about sterling engines that makes them expensive and unreliable?"
] |
[
"Is it possible to know the charge of a black hole?"
] |
[
false
] |
With the event horizon "hiding" all the information about the singularity inside, how is it possible that we can know the charge of a black hole? The charge information is conveyed via the electromagnetic field, but as I understand it no light can escape from the event horizon?
|
[
"The charge is something you can define and measure outside. It doesn't matter what is \"inside\". As the black hole forms the field is already there, and infalling charges can change the charge - and all you need to describe this is the region outside."
] |
[
"It doesn't have to propagate past the event horizon. The charge was there when the mass collapsed, or it was outside later and fell in. Nothing that happened beyond the event horizon matters for the description of a black hole."
] |
[
"I might have a misunderstanding of electromagnetics then, how does the electric field propagate through space if it can't propagate past the event horizon? Does the electric field just stay static after the black hole forms, and the field from infalling matter as well? "
] |
[
"Evolution: how can new species arise?"
] |
[
false
] |
I work in the field of theoretical computer science; I study and love to think about complex systems. In my opinion populations and the theory of evolution fall right into this field and are the most interesting application of the theory of complex systems. However, there is just one thing I can't wrap my head around: how do new species develop? As far as I understand, there is no universally accepted definition of the notion of species. The simplest (and maybe incorrect) definition is that two organisms belong to one species if they are capable of interbreeding and producing fertile offspring (see ). So the first question is whether "being capable of interbreeding and producing fertile offspring" is a (i) sharp yes-no kind of property or whether it is a (ii) somehow gradual, i.e., probabilistic. I thought about this question and dismissed answer (ii). Why? Simply because this renders the notion "species" useless. Consider this example: suppose there is a population of 1000 animals. Lets call them animal 1 to animal 1000. Assume that the probability that animals i and i+1 can interbreed is 99%. Moreover, let's say that the probability that animals 1 and 1000 can interbreed is 0.1%. In general lets say that the probability that animals i and j can interbreed is small if i and j are far apart and is high if i and j are close. In this scenario it is clear that animals 1 and 1000 do not belong to the same species. But: there is no meaningful way to partition the 1000 animals into species. I know, this scenario is constructed but supposing answer (ii) there might be populations of organisms in nature that resemble my example. So I speculate that answer (i) is correct: I guess that this has something to do with the structure of the genes and the chromosome (is that correct?). For instance, humans and chimps cannot interbreed because humans have 23 and chimps have 24 chromosomes. Hence, during the evolution of apes and humans from a common ancestor there was definitely a first human having 23 chromosomes (supposing that the common ancestor had 24 chromosomes). So considering these sharp boundaries there was always a first organism of a new species. This organism was not able to interbreed with any other organism in its population; hence, there was no offspring and, hence, actually no new species! there was another organism in this very population at this generation having the same mutation. In other words: our first ancestor having 23 chromosomes had to find another human having 23 chromosomes during his life. I guess that such common mutations of a male and a female in the same population at the same generation are so unlikely that the development of new species are very very rare events. So maybe both answers (i) and (ii) are correct. However, for some species only answer (i) applies, e.g., if a new species developed from an ancestral species having a different number of chromosomes (this happened again and again during the last billion of years). Then there was no gradual but a rather abrupt change and definitely no way that the first organism of the new species could interbreed with any other organism within its population. Whatever I read about evolution, I have the impression that the literature on evolution avoids to discuss this, in my opinion, obvious problem. : answered all my questions. It seems that I had a misunderstanding of the word "species". The article explains that the (absolute) term "species" should be avoided and be replaced by the (relative) term "infertible", which makes much more sense.
|
[
"You're on the right track but let's make a model to examine a key point - a species will generally be able to mate with it's parent's generation, it's grandparent's generation, going back several generations. There will never be a scenario where its like \"Oh my offspring is genetically isolated from me, hope someone else has a similar offspring to start a new species with him\". ",
"Lets assume sexual reproduction (asexual organisms may speciate rather quickly but this isn't where you're confused so we can skip it) and lets assume that some genetic difference is guaranteed with each generation (with mutation and recombination this is a reasonable assumption).",
"OK so we've got our ancestral population at t=0. They have genetically different children which exist at t=1, genetically different grandchildren which exist at t=2 etc. Note we don't really care about time passage, just genetic difference. ",
"So our ancestral population is affected by some environmental changes, maybe some cultural changes, maybe one part of it is isolated geographically from the other part, whatever happens, not everyone breeds with the exact same success rate. ",
"For simplicity, we'll first say that one strategy works best. The genes of the offspring thus drift towards maximizing that strategy, and by t=40, we've got some real specialists on our hands. So we're 40 generations / steps / mutations / whatever away from t0 ancestors. We'll say this is sufficient so that a t40 individual cannot mate with a t0 individual. Bam. New species. ",
"Note that the \"new species\" designation requires those (in this case) 40 steps. t40 can still breed with it's parental generation, t39, and then t38, and so on. It can probably mate poorly with t=3, t=2, and t=1 as well (maybe lots of miscarriages, or maybe behaviour differences prevent mating from happening... but it still might happen rarely). But at t0 (compared to t40) the difference is insurmountable. ",
"So that's how one species becomes another species in a simplified model. What about one species becoming two species? ",
"Go back to ancestor population at t0. Now they get isolated into two pockets - maybe one herd migrates, maybe a stream separates them, maybe they have two body types and predators hunt each type differently - whatever they're somewhat different but two general strategies are leading to survival. ",
"We now have two t=1 generations - t1a and t1b, who are probably almost identical, they can mate with each other all they want. t2a and t2b can mate as well, but they're drifting apart (maybe geographically, maybe behaviourally, physiologically, anythingly). At some point they can no longer mate. Bam. Two new species. ",
"It may be that our \"b\" strain of organisms didn't change that much from their ancestor - maybe t58b can mate with t0 - in this case it's still the same species as its ancestors. That said, t58a cannot - it can mate with ancestors going back all the way to t1a, but not t0, so its a new species from t0. ",
"If you extrapolate the principles from our model, you'll notice that if t=58 cannot mate with t=0, then that's a new species ",
". t57 and t0 are same species, t25 and t0 are same species, it took (in this case) 58 changes to mess up mating sufficiently. Cool. ",
"But what about t_minus_1 (t0's parents)?? t=58 definitely can't mate with it because it can't even mate with t0, which it is more similar to. What about t_minus_2 (our original ancestor's grandparents) ?? Can't mate with t58 either, of course, but can it mate with t57 (who is a little bit closer to it's grandparents going back ~60 generations) ?? Can t_minus_2 mate with t56 (an interval of 58 generations - this was sufficient to separate t0 and t58...) ??",
"This is why \"species\" is a cloudy term - we kind of arbitrarily set where it happens. The process isn't ignored, however, and several illustrative examples exist. ",
"Take a look at ",
", where species exist in a geographic ring. Its like a clock face where each number is slightly different from the previous, as a result of migration and evolution. Species at 1 o'clock can mate with 2, 2 can mate with 1 and 3, 3 can mate with 2 and 4, 4 can mate with 3 and 5 etc. so they can all mix with their neighbours as the organisms speciate. When the string of speciating organisms winds around (geographically) and the species at 12 is exposed to the original species at 1, 12 cannot mate with 1. ",
"A cool real-life example of exactly your question! :) "
] |
[
"First of all, this is a very good and interesting question. The subject is not, at least in my opinion, ignored nor avoided in the field but of course these type of questions do not receive as much grants and attention as do research focused on cancer and such which might be why it may seem as an ignored set of questions.",
"As far as I understand, there is no universally accepted definition of the notion of species. The simplest (and maybe incorrect) definition is that two organisms belong to one species if they are capable of interbreeding and producing fertile offspring (see wikipedia).",
"It is indeed not a very good definition for species. To being with the reasons why two organisms can or can not produce fertile offspring are many and the ability to produce fertile offspring is infact gradual due to this. It is good to remember that several different types of hybrids exist, some are fertile, in some one of the sexes is fertile the other sterile, cases where most offspring are sterile to all offspring being sterile. A few examples on that, in the case of mules, there are some reports on fertile female mules. The same has been noted for lion-tiger crosses. Domestic cats bred with wild cats produce in general fertile female offspring which is also true for mixing bisons and cows. ",
"Moving on to mechanisms that may lead to inability (more or less stern) to produce fertile offspring. Simply behavioral traits can prevent mating even if it would be physiologically possible for members of two species to give rise to fertile organisms. In this case the members of two groups (or species, if you will) do not recognize each others sexual clues (mating rituals for instance) or each other as prospective partners. \nOne example regarding fruit flies comes to mind. Drosophila ananassae and D. pallidosa are twin species and it has been shown (in laboratory conditions) that they indeed can produce fertile offspring they rarely do so in nature. The reason seems to be that females from both species prefer males of their own while males court females from both species. If I recall correctly, they even identified a genetic component responsible for this. A similar situation has been described between wolves and coyotes, where male wolves occasionally mate with female coyotes but the opposite has not been observed.",
"Sometimes mating is prevented by size and shape differences in genitalia or just the physical size of an animal as whole. In some cases it is possible that m ",
"Incompatibility can also rise on cell level, the sperm and egg simply do not fuse. For instance, due to the glyocprotein membrane surrounding the oocyte and can prevent cross-breeding between members of different species. Also, incompatibility on genome level (chromosome number and structure) is important (to a wrying degree, note that humans can produce offspring with extra chromosomes but lack of one chromosome is less well-tolerated) . ",
"I have to unfortunately get back to work, but unless someone brings up chromosomes & genome duplications I'll continue later with an edit."
] |
[
"Yes for sexual reproduction it would always be somewhat gradual - keep in mind different organisms have vastly different reproductive rates so \"gradual\" can still seem pretty quick to us. ",
"Species ",
" probabilistic in that you're categorizing something based on a man-made label. In truth, all organisms are just a giant pool of interweaving nucleic acid and the concept of \"individuality\" is even an approximation.",
"As for the development of different chromosome numbers, I'll have to look it up. Intuitively, I think it should be OK as the human chromosome is just a fusion of two ape chromosomes, so ultimately you're getting a very similar genetic contributions. Chromosomal abnormalities in present day humans often prevent reproduction though not always. Stay tuned, I'll poll some guys who work in evolutionary bio."
] |
[
"AskScience AMA Series: We're Experts Studying COVID-19 In Deer and Other Wildlife. AUA!"
] |
[
false
] |
In the past two years, dozens of animal species have been found to be infected with the SARS-CoV-2 virus. Of these, only two types of animals were found to be infected in the wild: mink and white-tailed deer. These findings have serious implications for managing (and ultimately ending) the COVID-19 pandemic. Join us today at 2 PM ET for a discussion, organized by the American Society for Microbiology (ASM), about our work to identify, diagnose and treat COVID-19 infections in wildlife. We'll discuss your questions about animal disease reservoirs, the potential for additional SARS-CoV-2 variants, and what our research (and the work of others) tells us about the role of wildlife in the COVID-19 pandemic, as well as future pandemics. We are laboratory researchers, veterinarians, and evolutionary biologists. Ask us anything! With us today are: Links:
|
[
"You mentioned “ending” Covid-19. Do you really think it’s possible to bring the pandemic to an end? How?"
] |
[
"All pandemics technically end, even the Great Influenza (Spanish Flu) of 1918 that killed 20-50 million people. That flu virus wasn't destroyed, it continued to circulate and cause annual winter flu epidemics that killed smaller numbers of people. But technically the pandemic ended by ~1920 when it stopped causing massive waves at random times of the year and settled into a typical seasonal pattern. Eventually SARS-CoV-2 is expected to do the same, recurring annually in a seasonal pattern that is more predictable"
] |
[
"Is it a threat to the animal populations or only a concern as a reservoir for new infections of humans?"
] |
[
"When the topic of our existence comes up in conversation, I always say that humans exist only for about 200.000 years. How is this determined? What drew the line between humans and whatever it was called before that?"
] |
[
false
] |
Stupid question, but I really never had any idea how to explain it when someone asked.
|
[
"Are you asking what precipitated the evolution of H. sapiens? The big picture answer is a combination of sexual, natural and social selective pressures. I can go over these in a bit but I have to get to a meeting. Moreover, many behavioural and physical trends for traits that we see in the Homo genus continued to be exaggerated as time went on. e.g. brain size continued to increase. ",
"If you want to know exactly how we define where species lines are drawn it can get pretty messy when we are talking about fossils. Perhaps ",
"this explanation",
" of macro and micro evolution will help you. At what point did an ancestral Homo species (perhaps H. heidelbergensis as has been suggested) become H. sapiens? We don't know the exact date for this, there probably isn't one. But at some point enough differences accumulated in the behavioural and physical repertoire that the descendants were no longer like its ancestors...and voila a new species. ",
"I might also recommend a book called ",
"\"How Humans Evolved\"",
" by Boyd and Silk. "
] |
[
"It's not a stupid question at all! The issue of when \"we\" as a species began is one that is subject to debate and interpretation even in the anthropological community. ",
"The 200 000 years ago date comes from ",
"this",
" site called Omo Kibish in Ethiopia where an \"anatomically modern\" cranium was found. This skull has a number of the hallmarks of Homo sapiens cranial morphology like a small brow ridge and such which serve to differentiate it from \"archaic Homo sapiens\" like H. erectus and Neanderthals. ",
"Now the problem with this is we don't know if the Omo human was ",
" modern. There's no archaeological evidence that anatomically modern humans that old were doing things like burying their dead with symbolic offerings and making markings on caves like we know H sapiens were doing by around 60 000 years ago. ",
"Hope this helps!"
] |
[
"But the question is not about that.\nDuring what transition in history did a species evolve to something we call homo sapiens?"
] |
[
"Are there animals which are allergic to humans?"
] |
[
false
] | null |
[
"I'm not an expert in veterinary medicine. However, the study below cites research indicating that some dogs can indeed show an allergic response to human dander (skin, hair, other cells shed from the body). (Sorry, tried to link in text but the parentheses in the url was screwing up the formatting.)",
"http://www.vh.ntu.edu.tw/tasam/jvcs/JVCS2009.2(2)/JVCS2009.2(2).31.pdf",
"EDIT: ",
"Here is another study directly assessing human dander as allergens.",
" "
] |
[
"You can use the backslash prior to the parenthesis to escape it. So instead of JVCS2009.2(2), you'd type JVCS2009.(2\\).",
"Link"
] |
[
"unless i'm misunderstanding you, people are not allergic to cat's hair, they are allergic to proteins in their saliva, urine, and dander.",
"source",
"additionally, long haired cats are less likely to trigger an allergic reaction because their long fur holds the protein causing allergen closer to their skin rather than releasing it into the environment.",
"according to ",
"this",
" link, a light-colored long-haired female cat should be the least allergenic cat."
] |
[
"If mass increases with energy, then shouldn't subatomic particles have almost infinite mass? Then why doesn't the inertial property of the particle increase and its motion stopped?"
] |
[
false
] | null |
[
"Mass does not increase with energy. The concept of \"relativistic mass\" has largely been discarded because in order to get the math to work, you have to define relativistic mass so narrowly that it does not really act like a mass anymore, and leads to confusion as evidenced by your question. An object that that travels at a high speed has its kinetic energy increase faster with higher speeds than that predicted by classical physics. In the limit that an object approaches the speed of light, its kinetic energy becomes infinite. Its mass stays the same."
] |
[
"Yes, there is a concept called relativistic mass, in which the mass of an object increases with its velocity. Quantitatively, you'd have mR = gamma * m0, where m0 is the rest mass of the particle, and gamma is the Lorentz factor. In the case of subatomic particles at accelerator energies, they would have very high relativistic mass.",
"Why doesn't the inertial property of the particle increase and its motion stopped",
"Because intertia doesn't stop the particle. It only makes it harder to accelerate. One way of thinking of it is that the particle gets heavier and heavier, as it approaches the speed of light, and so it requires more and more energy to speed up. To actually reach the speed of light, you'd need to put in an infinite amount of energy. That's why a particle with m0 greater than zero can never reach the speed of light.",
"On the other hand, since massless particles remain massless in any reference frame, they can reach the speed of light with zero energy input!"
] |
[
"The other answers here are correct—but I want to add that subatomic particles don't necessarily have much energy at all. For instance, your run-of-the-mill electron has very little energy beyond its mass-energy. Subatomic particles that we shoot through particle accelerators ",
" have a lot of energy, and their inertia is significantly increased. But—as ",
"/u/yablebab",
" explains—this does not mean that they stop moving.",
"I also want to add an example that might be more in line with what you're thinking. Most of the mass in the matter you regularly interact with comes from protons and neutrons, and protons and neutrons are made of quarks. But if you add the masses of the quarks in a proton, you get a number that's about a hundred times smaller than the mass of a proton. This is because the energy of interaction between the quarks is very large—and that's what accounts for the difference.",
"There are a lot of subtle details in the relationship between energy and mass. Feel free to ask whatever questions come to mind!"
] |
[
"Does the sun rotate?"
] |
[
false
] |
If so, how long does a "solar day" (i.e. one solar rotation) last?
|
[
"Yes. It doesn't rotate rigidly, it rotates in about 25 days at the equator and 35 at the poles.",
"https://upload.wikimedia.org/wikipedia/commons/1/11/Sun_turn.gif"
] |
[
"Short, sweet, to the point.",
"If you want to watch it rotate, you can track sunspots as they move across the face of the sun over the course of a couple weeks. You can project the sun onto a sheet of paper with some binoculars, or use a pinhole camera, or any of the tricks that get passed around every time there's a solar eclipse. A piece of welder's glass 14 will also let you observe the sun without eye damage. ",
"http://ircamera.as.arizona.edu/NatSci102/NatSci102/movies/sunturn.gif"
] |
[
"The sun rotates about its axis with a period of about 25 Earth days (at its equator).",
"http://en.wikipedia.org/wiki/Solar_rotation"
] |
[
"Difference between a black hole and infinite potential (e.g. coulombic) when considering Hawking radiation"
] |
[
false
] |
Hi. Material scientist here so I'm not big on cosmology. As I understand, hawking radiation can occur whenever we have an event boundary - for exaple sound waves moving through a fluid which is flowing faster than the speed of sound is the classic example. Can someone tell me the difference between this and, say, some sort of charge boundary with charges unable to make their way through. Why does this not count as an analogue black hole? I hope this is clear, thanks in advance!
|
[
"I'm a cosmologist but not big on material science, so there you go :) My impression is that for any (finite) Coulombic potential, there are charges which can escape, and an infinite potential isn't really physical. A black hole (or a black hole analogue, like they make in condensed matter systems that trap sound waves) relies on the fact that nothing can move faster than light, so it's actually physically impossible to escape. But maybe I'm misunderstanding your question."
] |
[
"If I have some sort of region which has infinite coulombic potential (of finite range)",
"I have no idea how you would make such a thing, or how it would make any sense physically.",
"Remember, black holes ",
" have infinite gravitational potential anywhere except (classically) the singularity at the very center. The extended region outside it where nothing can escape ",
" have a finite potential, but it's still large enough that any particle travelling at or below the speed of light can't escape."
] |
[
"The singularity in the Coulomb potential isn't very physical ",
" I don't think there's any problem with it quantum-mechanically though, since it doesn't lead to any unphysical results for any observables. Unless you consider a cusp in the wave-function to be unphysical. "
] |
[
"Are there objects in our eyes that our brains block out?"
] |
[
false
] |
I can see floaters when I look at a bright light, but there must be a whole mess of stuff in there!
|
[
"Do you mean foreign objects, like dust? If so, I think our eyes do a pretty good job of removing stuff like that. Here's what wikipedia has to say about floaters: ",
"http://en.wikipedia.org/wiki/Floater",
"As for our optic nerve, it does indeed give us a \"blind spot\" in our field of vision. Want to know something cool? Look at a cross section of a cephalopod eye (like an octopus or squid) compared with a mammal eye. They're functionally very similar, but morphologically very different. The placement of the optic nerve and its analog in cephalopods (called the optic ganglion) are different--cephalopods don't have a blind spot. Even though it's a digression from your question, it's sort of relevant and I've always found this particular instance of convergent evolution very interesting."
] |
[
"Floaters and blood vessels exist in our eyes."
] |
[
"optic nerve"
] |
[
"Can light, be it wave or particle, ever be motionless? or do they have to have some speed at all times?"
] |
[
false
] | null |
[
"A full and precise explanation would require more math than is appropriate here. However, the short answer is no. A photon (which is massless) cannot stand still; it must always travel at c as a consequence of relativity. In fact, the existence of a massless particle at all is a consequence of relativity, so it should be no surprise that we need relativity to deal with it.",
"However, this discussion really only holds in vacuum. In matter, we can have many photons that interfere with each other in such a way that it ",
" that light is moving slower than c, an effect known as index of refraction. The index of refraction of a material can be (in principal) arbitrarily large, so light in the material can travel arbitrarily slowly.",
"Moreover, if you take two mirrors and put a photon between them, then the photon bounces back and forth. The effect is a standing wave which does not propagate through space. You can sort of think of this as a photon standing still, but probably a better way of thinking about it is as a superposition of photons traveling in opposite directions. It's worth noting that this phenomenon is as exotic as it sounds: it happens in a microwave, water waves in a bathtub, etc."
] |
[
"Thing is, a \"photon has no rest mass\" or mass of any kind, when mass is 0, acceleration is infinite for any sort of force that you can apply to it (also read the * if you haven't by now). So, if you have a particle of mass zero, the second you flick it, it zooms off at infinite (or in a limited frame of reference, speed of light***) speed.",
"This is is a Newtonian explanation and is not why massless particles travel at the speed of light. According to your explanation, it's perfectly possible for light to be stationary until it is nudged into moving at the speed of light, and that is just not the case.",
"EDIT:",
"If someone has a good explanation for why the speed of light is A) a limit and B) the speed of light, I'd love to have it.",
"This gets asked a lot here and on ",
"/r/explainlikeimfive",
" - a quick search on either should give you the answers you're after."
] |
[
"It should also be noted that speed of light is a really important feature of this universe, it's something derived directly from the properties of space-time. It's not just some arbitrary stick in the mud somewhere."
] |
[
"Why is there supersonic wind on Neptune and how do we know about it?"
] |
[
false
] | null |
[
"They measured the movement of observed clouds from a voyager satellite. Why is being debated? Strong planetary rotation, internal heat fluxes, active thermodynamics associated with the hydrologic cycle, and a shallow atmosphere are all important factors."
] |
[
"So I can only suppose they're talking about the speeds of the wind relative to each other.",
"Nope, we measure wind speeds on giant planets relative to the rotation rate of the magnetic field. That's also a good estimate of how quickly most of the interior is rotating, too, since that's where the magnetic field is generated. The interior is much closer to rotating like a solid body than the differential rotation of the weather layer on these planets."
] |
[
"Correct, all the magnetic field rotation measurements came from Voyager 2's flyby. Neptune's magnetic field is ",
"highly inclined",
" relative to its rotation axis, producing a very clear signal - unlike Saturn, where the magnetic field is perfectly aligned with the rotation rate and we have to come up with other interesting ways of measuring the internal rotation rate.",
"Prior to Voyager 2's flyby in 1989, you're right, it was much more difficult to estimate Neptune's rotation rate, let alone wind speeds. That was also pre-adaptive optics, so even in the best telescopes of the day, Neptune looked like barely more than a star.",
"The ",
"best estimates",
" came with photometric methods. In essence, you accept that you can only observe Neptune as a point source, but assume that there are bright atmospheric features that rotate with the planet. You should see a regular cycle of that point source's brightness as the bright, unresolvable features cross into and out of view over the limb of the planet; the time period to complete one cycle should be the planet's rotation period.",
"There were also spectroscopic methods; looking at the planet as a point source, spectral lines should be a combination of wind moving toward you along the sunrise limb and wind moving away from you at the sunset limb as the planet rotates. In a spectroscope, that should appear as doppler-shifted wings on each emission line.",
"That said, these are hard measurements to make and the data can be pretty rough. There was still disagreement between methods up to a few hours prior to Voyager 2."
] |
[
"How are my eyes changing to a completely different colour as I grow older?"
] |
[
false
] |
I was born with dark brown, almost black eyes. When I was about 16 I started to notice small flecks of green at the bottom of my eyes. Now at almost 25 my eyes are nearly completely green. My father, who now has grey eyes, told me he had the same thing happen to him as he grew older. He said that he went from dark brown, to green, to grey by about age forty. How is this happening? And does it have any eye health implications?
|
[
"This image",
" has best explanation that I've found ",
"I don't work on the anatomical or genetic side of vision, but my ",
" rudimentary understanding is that the amount of melanin can change with age. ",
"Your father probably has a differently structured stroma, so his eyes became gray. Maybe an anatomist can explain whether the stroma can change over time too."
] |
[
"Thanks for the link. It's nice to know a little about whats going on :)"
] |
[
"Nope no meds. Though I may ask my parental units if I took anything as a child that would have that effect."
] |
[
"If we were to build a bridge perfectly straight from the north pole, how long could we walk on for?"
] |
[
false
] |
Assuming we could build a bridge, or walkway similar to the one in this , (infinite flight aside), how might we expect to experience walking the length of it? How would we be affected?
|
[
"OP asked about the ",
" of walking the length of the bridge, so here goes:",
", you would be on a causeway 40 feet tall, high enough that a fall would cause serious injury. The slope would be so mild that you wouldn't notice it.",
", you would be as high as the ",
"Burj Khalifa",
", the tallest structure in the world. You would be walking up a gentle 2.2% grade (1.3°).",
", you would be entering what mountaineers call the ",
"death zone",
", where unaided respiration is no longer possible. You're walking up a 5.1% grade (2.8°), the same slope as ",
"steepest standard railroad line in the US",
".",
", you are 7.5 miles off the ground, the cruising altitude of a 787. There's 20% as much oxygen as at sea level. This is the coldest part of the atmosphere: -70 °F, though ",
"it would be colder if you'd built at the equator",
". And it gets worse. Since you're walking up a 1:12 slope, your bridge is no longer legally ",
"wheelchair accessible",
".",
", you're 13 miles high and the atmospheric pressure has dropped 95%, from 15 psi to 0.7 psi. Break out your high-altitude cooking directions: water boils at 90 °F, lower than body temperature. Get the sunscreen too – that faint smell of Geraniums means you're passing above the ",
"ozone layer",
". It's a balmy 40 below.",
" you're ",
"officially in space",
", 100 km up. If you'd sped the bridge project up, you could have won the ",
"Ansari X-Prize",
" pretty easily (well, not ",
". Driving at this altitude is obviously impossible - no air to burn. The Tesla electric car has less than 300 miles of range. A small car would need about 60 gallons of gas to drive this far, plus 60 gallons of liquid oxygen. Still, that's easier than building the bridge). You're walking (or driving) up a 25% grade (14°), and gravity is 97% what it was at the surface.",
"You have to go ",
" to be at the orbital altitude of the international space station - 250 miles up. If you were smart you built your bridge toward Russia, so you're still inside the ",
"Van Allen radiation belt",
" that protects you from cosmic rays. However the tradeoff is that you're within the ",
"high-energy electron belt",
". You're being bombarded with electrons at 10-100 million volts, so your hair will stand on end constantly. You're walking up a 51% grade (27°), which is about the ",
"optimal ergonomic slope for stairs",
". Gravity is 89% what it was on the surface, so if you weighed 160 lbs, you now weigh only 145 lbs. If you fell now, you'd land somewhere in Russia instead of the ocean",
", you're at the end of the bridge, one Earth radius from where you started. The grade is of course 100% (45°), you're 1640 miles up, and if you built toward Russia you're now near the border between China and Kazakhstan. Gravity is exactly half what it was on the surface, but your centrifugal force due to Earth's rotation still contributes only a negligible amount - reducing gravity by about 0.001 G. You would need a bridge over 5x as long, 22,000 miles, to bring you near ",
"geostationary orbit",
"."
] |
[
"You fall straight down, not sideways as in the drawing. Down in our case is toward the center of the earth, so you'd fall at at roughly 45 degree angle to your bridge (if you were able to build it out that far).",
"This also gives you some insight about how gravity pulls on your bridge. At the pole, you'd feel gravity pulling you in the same direction as the normal face of the bridge. As you went out onto the bridge, the angle between \"down\" (the direction gravity pulls you) and the normal face of the bridge would increase. Effectively, you'd be climbing uphill. Once you get farther out (on the order of earth radii), the gravitational force would noticeably be weaker since you're getting farther from the planet. Then you'd start to feel some of the forces due to the bridge spinning with the planet. Once this force balances with gravity, you'd be in geostationary orbit. After this point, if you were to jump off the bridge, you'd end up in a highly elliptical orbit. Go even farther on the bridge and you could break free of earth's gravity.",
"Of course, all this assumes a magical bridge that would be able to support itself and not bend as the planet whipped it about."
] |
[
"You would experience such a walk as going up a ramp that became steeper and steeper. Draw a line between any point on the ramp and the center of the earth and you can see how steep the ramp would seem at that point."
] |
[
"What exactly does a sex change entail?"
] |
[
false
] |
I am just curious as to exactly what it means to have a sex change operation. Do converted genitals function as they would normally? Seeing as how you are still genetically XX or XY (for the most part), to what extent could someone actually change genders?
|
[
"There is no such thing as \"a sex change\" surgery. There are many different genital surgeries, and many trans people do not get any at all.",
"Trans women, a.k.a male-to-female transsexuals: The most common genital surgery is orchiectomy. (castration) This will greatly reduce testosterone levels in the body and is often acceptable for correction of the sex marker on the birth certificate. Vaginoplasty (done in conjuction with labiaplasty and orchiectomy) is usually what people think of when they think of transgender and surgery. (It's referred to commonly as SRS - Sexual Reassignment Surgery.) The most common technique is penile inversion, which involves using part of the glans penis (the head) to make a clitoris, the skin of the shaft to make a vagina, and part of the scrotum to make labia. Depth varies depending on the donor tissue, and the neo-vagina obviously terminates in a dead end and not a cervix. The prostate always remains in place. The majority of women who've had this particular surgery are able to have an orgasm. Many or most require lubrication for sexual penetration.",
"Other common surgeries for trans women include FFS (Facial Feminization Surgery and breast augmentation.",
"Trans men, a.k.a. female-to-male transsexuals: relatively few trans men get any kind of genital surgery. Chest reconstruction (bilateral mastectomy) is the most common surgery for trans men, and is usually enough to correct the birth certificate sex marker. There are two radically different types of genital surgery for trans men. The saying is: \"sensation and looks - pick one.\" More common is metoidioplasty, which mostly involves altering the position of the clitoris, which has already grown significantly due to the testosterone most trans men take. The resulting penis is still relatively small and probably not large enough for penetration, yet will be able to provide orgasms. The less common and much more expensive surgery for trans men is phalloplasty. This usually involves using a skin graft from the forearm to construct a neo-penis. The urethra can be lengthened using skin from the labia minora in a later surgery. Another optional surgery involves the insertion of a device to make erections possible. Most of the phalloplasty surgeries have a relatively high complication rate. Most trans men with phalloplasties are not able to orgasm from penetration, although the clitoris remains in place at the base of the neo-penis. Either of these surgeries may be done at the same time as a hysterectomy, oophorectomy (removal of the ovaries), vaginectomy, and scrotoplasty.",
"That was probably more information that you're interested. For reference, few trans people refer to \"getting a sex change.\" A trans woman who says \"I got surgery\" with no qualifiers is probably referring to SRS. A trans man will typically refer to top surgery (chest reconstruction) or bottom surgery (any combination of the genital surgeries for trans men I listed)",
"Keep in mind than few of these surgeries are anything a person can just \"go get,\" unlike most other plastic surgery. Most surgeons require one year living as the target gender, time on hormones, and letter(s) from psychologists/psychiatrists \"permitting\" the patient to receive the surgery. Hormone replacement therapy (HRT) is what affects many secondary sex characteristics. A trans woman on HRT(most commonly estrogen and a testosterone blocker) will usually see a reduction in body hair, fat migration in the body and face, smoother skin, muscle shrinkage, and the growth of breasts. Trans men on HRT(always testosterone) will usually see body and face hair growth, fat redistribution in the body and face, muscle growth, an enlarged clitoris, and a lowered voice. Secondary sex characteristics not affected by HRT include the voice for trans women and breasts for trans men.",
"On a less scientific note, please avoid asking trans people about their genitals and what surgeries they have and haven't had. Most trans people consider that one of the most ignorant and/or offensive questions asked by cis (Latin for not-trans) people, since it's the reduction of an individual to what's between their legs. Also, surgery is only one potential part of transition - taking hormones and living as their target gender are probably more significant parts of transition. After all, when you meet a stranger, you don't do an underwear check before you put someone in a gender category in your head.",
"Finally, trans people are not trying to change their gender. They are trying to change their body to better fit their gender. A simple way of thinking of sex and gender is that gender is more in the brain (probably partly biological) and sex is more about the body.",
"Source: I'm a trans woman who comments frequently in ",
"r/asktransgender",
"."
] |
[
"I've had several friends who have undergone this, I'll share my gained knowledge...",
"They make you live as the opposite sex for at minimum one year before allowing any operation. During this time you dress, act, speak, and use the appropriate changing/bathroom areas as your desired sex. You take the appropriate hormones to help ready your body for surgery. This is to make sure you are making the rich decision, after all, there's no \"going back\", is there?",
"My friends both got facial plastic surgery first, giving the. The desired look of the opposite sex, making it easier to get by in the world dressed the way they wanted. My most recent friends' surgeries were placed over a 5year period and she just finished with I about 6mo ago. She now has a vagina, boobies, and no penis. She is legally married to another woman, as she was legally a male at the time of the marriage."
] |
[
"The penis gets removed, the head is whittled down into a clitoris, and the balls are removed. They take the leftover flappy bits and try to make them look like a vagina, but t doesn't. Depth of the new \"vagina\" averages around 5 inches, and lubrication is always needed, as fake vaginas cannot self-lubricate."
] |
[
"If the planets in our solar system are formed from basically the same gas and mineral debris compressed over time, why are they so different from each other?"
] |
[
false
] |
My basic understanding is that gas, space rocks, asteroids, planetoids, etc. attracted to and trapped in the orbit of the sun eventually grew larger and larger until their own gravitational pull compressed themselves into planets. If this is close to correct, why are the planets so vastly different? The best analogy for my thinking is that if you have a palette of hundreds of different colors of paint, and mix them together, you get relatively the same brownish mess, why aren't all of the planets the same when the material is mixed at random?
|
[
"Because the mixing of the material wasn't totally random-- there was a pretty significant influence on how it was sorted. Also, the planets, particularly the outer ones, did not necessarily form in their current orbits. Most of the outer ones likely migrated outward.",
"Let's assume, for the sake of argument, that we start with a homogeneous disk of gas and dust, with roughly the same composition as the Sun: ~98% hydrogen and helium and then ~2% everything else, with a lot of carbon/nitrogen/oxygen. ",
"Now, what happens to this disk when you have a star at the center? The innermost part of the disk is subject to powerful heating and solar wind, which preferentially blows away the lighter elements and prevents the formation of many chemicals. This leaves behind denser things like heavier atoms and especially dust grains. Radiation pressure, much like ordinary wind, will blow away low-density objects faster than it will blow away high-density objects. So within the first few AU, much of the hydrogen and helium is gone and you're left with mostly heavier elements and dust (which is usually carbon-based or silica). ",
"Farther out, the solar wind is less strong, so the hydrogen and helium mostly stick around. Planets like Jupiter and Saturn have compositions not too dissimilar from the Sun-- hydrogen and helium and a pinch of everything else. Keep in mind that while they're called gas giants, they do actually have rocky cores which are more massive than the Earth. ",
"The outermost two planets, Uranus and Neptune, are sometimes known as \"ice giants\". This is because while ~97% of their atmospheres are still comprised of hydrogen and helium, they also have significant abundances of methane as well as a bit of water and ammonia, and it's cold enough that the water and ammonia form ices. These chemicals are H",
"O, CH",
", and NH",
", so basically it's a situation where hydrogen bonds onto most of the available heavier elements, and there's very little heat or radiation so they don't dissociate.",
"The Kuiper Belt is ",
"thought to have originated much closer to the Sun",
", but early in the Solar System's history many of the large planets were migrating around due to their mutual gravitational effects, and this disturbed the orbits of many smaller rocky and icy bodies, flinging them outward."
] |
[
"Your planetary formation explanation doesn't mention the \"snow line\", which is really key to the resulting difference between inner rocky planets and outer gas planets. Somewhere around 3 AU and beyond, it's cold enough that water can exist as ice instead of just gaseous water vapor (note that you can't make liquid water in the vacuum of space).",
"This threshold is important, because the general rule of thumb is that for a forming planet to start accreting hydrogen from the solar nebula to make a gas giant, the proto-planetary core needs to have at least ~5 Earth-masses of material. It's much easier to reach that mass when you can make your core out of rock and ice instead of just rock alone.",
"The outermost two planets, Uranus and Neptune, are sometimes known as \"ice giants\". This is because while ~97% of their atmospheres are still comprised of hydrogen and helium, they also have significant abundances of methane as well as a bit of water and ammonia",
"More than just ",
" - by total planet mass, they're mostly water and ammonia ice. Beneath the predominately hydrogen/helium atmosphere exists a massive slushy ionic ocean mantle of water/ammonia ice...that's why they're called ice giants."
] |
[
"You're right, I was talking about the atmospheric composition when I should have been talking about the overall composition."
] |
[
"How do we know the age of the sun?"
] |
[
false
] |
My mom asked me this question and while I think I have a decent understanding of astronomy and astrophysics, I don't know the answer. Googling was unhelpful (it told me the age, and vague hand-waving about how stars are formed, but not a real answer). I guess that we just know what stage of the star's lifecycle the sun is in, but that raises another question: how do we know how long each stage of a star's lifecycle is? We can see millions of them in their own parts of the lifecycle, but how do stitch that information together into a coherent timeline?
|
[
"We can measure the sun's mass, energy output, and chemical composition.",
"On earth, we can measure the mass of various atomic nuclei, the energy output of various fusion processes, and the age of the oldest rocks.",
"Put this all together, and we can start making some reasonable guesses and set upper and lower bounds. ",
"For example, we know if a star with the sun's mass and energy output were more than about 10 billion years old, it would have burned up its nuclear fuel by now.",
"Similar, if the sun were less than a billion years, it wouldn't have had time to create the helium, carbon, and oxygen we can see in its chemical makeup.",
"So with a few facts and solid assumptions, we built theories that say the sun is between 1 and 10 billion years. It also makes predictions about what other stars will be like, so we can test its validity. With more observations, we can built better theories, tighten those upper and lower bounds until we have a really good estimate: 4.5 billion years.",
"Unfortunately, it took a lot of different theories to get here. There is no easy, one sentence, \"the sun is 4.5 billion years old because...\" answer you can give your mother."
] |
[
"Recent article",
" which goes a bit deeper, with lots of relevant references."
] |
[
"Wikipedia is your friend. From the ",
"article",
"Solar formation is dated in two ways: the Sun's current main sequence age, determined using computer models of stellar evolution and nucleocosmochronology, is thought to be about 4.57 billion years.[86] This is in close accord with the radiometric date of the oldest Solar System material, at 4.567 billion years ago.[87][88]"
] |
[
"Why is it that carbonized wood (charcoal) is used for it's heat instead of plain wood? Shouldn't it contain less energy since it was \"burned\" off?"
] |
[
false
] | null |
[
"The energy used to get rid of all the water and excess hydrocarbons from wood is quite large. Charcoal isn't actually ",
" already, in that it is done in a low oxygen environment (incomplete combustion).",
"What you're left with is far more efficient because burning off all of those waters and hydrocarbons means you only have to do the final bit of combustion, getting water and carbon dioxide from the more complex molecules. Incidentally this releases a lot of energy.",
"If you were to do this pre burning of the wood in a normal environment you'd just be left with useless ash and cinders. It's a little decieving to say that charcoal is already just pure carbon."
] |
[
"To make charcoal, you take a piece of wood and you break up many of the chemical bonds. This releases energy, true, but it also puts the remaining energy into a much more easy-to-release form.",
"It's analogous to the reason you don't want to put one gigantic salt crystal in your soup. You're rather have it broken down into a powder. It will make your soup salty faster if it's broken down into tiny easy-to-dissolve pieces.",
"In charcoal, the wood molecules are broken down into smaller pieces so they will burn faster, and thus give a hotter flame."
] |
[
"Interesting! Thanks!"
] |
[
"Is there such a thing as an \"anti-scent\"? That is a scent that is close to the opposite of a scent that can somehow cause the effect of cancelling out, or lowering the original scent?"
] |
[
false
] |
also: is there a link to a list of scents that are the natural offsetting "anti-scents" to the original? Thanks
|
[
"There are odor antagonists, which can keep you from smelling a certain class of molecules. However, the antagonist itself is usually odorless, or smells pretty similar to the odor which it is \"cancelling out\".",
"http://chemse.oxfordjournals.org/content/34/7/625.short"
] |
[
"Are you interested in the human nose, or just volatile chemicals in general? There are things that can 'mask' an odor by out-competing and binding with a series of receptors on the nose, but they don't 'get rid' of the chemical in the air - they change our perception of it."
] |
[
"I'd like to figure out the best way to mask the smell of linseed oil "
] |
[
"How do you predict the outcome of a covalent bond?"
] |
[
false
] |
Sorry if this is a bad question. How is it that you can get SO2, SO3 and SO4? Why don't they just share the atoms among just SO? And how come the charge doesn't change among them?
|
[
"Charge does change among them.",
"Sulfate (SO4) carries a -2 formal charge",
"Sulfur trioxide (SO3) carries a formal charge of 0.",
"Sulfite (SO3 as well) carries a -2 charge",
"Sulfur dioxide (SO2) carries no charge.",
"We get the different sulfur compounds due to the reagents involved in production. "
] |
[
"Why do SO3 and SO4 have the same charge? And can you give an example of reagents that would affect the compound? Why wouldn't the compound want to end up as SO3 or SO2 which both have a charge of 0? And how do they have the same charge if one possesses an additional atom?"
] |
[
"I am going into grade 12 chemistry very soon and am recalling how I never learned about this in grade 11 chemistry. When I would ask my teacher she would say \"It's not on the exam, so don't worry about it!\"."
] |
[
"Does wearing sunblock every day leave you naturally unprotected and dependent on the sun screen?"
] |
[
false
] | null |
[
"Unfortunately, you seem know just ",
"enough about this to be dangerous",
".",
"Without question being paler increases the damage the sun does to you. However, the difference is miniscule compared to the protection provided by the sun block in the first place, which is UV opaque, unlike your skin.",
"So, no she is not 'too dependent' on sunscreen. She just lost her tan."
] |
[
"However, the difference is miniscule compared to the protection provided by the sun block in the first place, which is UV opaque, unlike your skin.",
"Indeed. Also, it should be pointed out that tanning, ie. the production and redistribution of melanin by your skin, only happens in response to UV damage. So you're slightly increasing your resistance to UV damage... by deliberately exposing yourself to UV damage."
] |
[
"You don't get very much vitamin D from being in the sun, roughly 10-30 minutes is really all you need after that the returns are greatly diminished or aren't even there, as at a point the uv rays destroy the excess vitamin d, and the risk of skin damage [cancer] outweighs the benefit. Also you can get Vitamin D from food or supplements and as far as I'm aware you get most of your vitamin D from food in most cases.",
"Source"
] |
[
"Novel Mathematical Proofs: Are they discovered or invented?"
] |
[
false
] | null |
[
"The question of whether mathematics is discovered or invented is a deep philosophical issue about which is there is not consensus (realists and Platonists take the former view, intutionists and constructivists the latter).",
"To get a sense the range of thinking on this matter see",
"http://en.wikipedia.org/wiki/Philosophy_of_mathematics",
"or",
"http://plato.stanford.edu/entries/philosophy-mathematics/"
] |
[
"This is really more of a philosophy question. I suggest you take it to ",
"/r/askphilosophy",
" or maybe ",
"/r/philosophy",
"."
] |
[
"As most proofs of a certain thing are equavilent end merely expressed differently, it is hard to say something new is invented when somebody figures out the relationship between various things. For example, the golden ratio was always there before the discovery, as well as Maxwell's equations. The matematical proofs were also equally valid and in effect before and after discovery. If something was proven possible, it was obviously possible before being proven so. ",
"It is not really like putting things together in new ways, it is more like experimenting with what is there and finding out new things. But that new engine weren't there before."
] |
[
"\"There's a chemical reaction. It was a powerful singular thrust to the neck.\" -Sleepy Hollow"
] |
[
false
] | null |
[
"The film bears very little similarity to the original short story, IIRC the whole forensics element is entirely new. It was most likely artistic licence on the side of the filmmakers. "
] |
[
"Thanks for this, I've never had the pleasure of reading the original tale. I've added this to the OP."
] |
[
"Where's the link?"
] |
[
"What makes a deep-sea fish able to live in that immeasurably high pressure, where a submarine would be tore apart?"
] |
[
false
] |
I've been searching for an answer on Wikipedia, but the only thing that I found is that they adapt. I'm really curious about how they adapt in organs and stuff, and what differentiates them from a normal fish.
|
[
"They consist mainly of water, which is almost incompressible and is also the medium of the environment of these fish. So they do not experience any pressure gradient at all.\nA submarine, on the other hand, is filled with air which can easily be compressed by a factor of 100 at these depths. So you have to build a shell to keep the internal pressure at atmospheric level -> very high pressure gradient to the outside!"
] |
[
"Something similar is called a ",
". This has a small air-filled crew cabin, which needs to withstand the incredible pressures, supported by a float filled with petrol. Petrol is less dense than water so provides buoyancy, and the float is not crushed because it's liquid both inside and out."
] |
[
"So let’s just make a submarine of water - right?"
] |
[
"How come that rail tracks can be weld together and they don't bend when the temperature changes?"
] |
[
false
] |
I saw a documentary (not sure what was its name) about building a railroad in Spain. It was a high-speed rail (Madrid to Barcelona I think). They were using very long rails (250m I think) and they alwasy welded them together. Sidenote: If we have a metal rod, it expands when temperature changes, right? It expands to all directions, but since there's a lot of atoms in its length, we can actually see/measure it. (I hope I'm right here) The change between min/max average temperatures in Madrid is about 30°C. Even if it was build in the "middle" of this range, shouldn't the track bent somewhere when it's too hot (and the metal is exposed to sun)? As a bonus it's used by high-speed trains. Why the trains won't derail? Is the structure holding the tracks so strong it won't allow the metal to expand? Or is the expansion so minor it's not noticeable? Note: This is physics/train engineering question, I hope it's OK to put it in this subreddit.
|
[
"http://en.wikipedia.org/wiki/Breather_switch"
] |
[
"The track structure itself resists the stresses from temperature change. The stress is transferred to from the rail to the tie through anchors or elastic fasteners, then from the tie to the ballast that it is embedded in, and to the subgrade.",
"When laying the rail, it is heated to the desired Neutral Temperature (DNT) for the property which is chosen by the expected temperature range of the region (typically around 95-105 deg F) which is the temperature at which the rail is in neither compression nor tension.",
"Below that temperature the rail is in tension and at risk for a pull-apart, and above that temperature the rail is in compression and at risk of a track buckle.",
"I teach a annual course on standards for track construction and maintenance, and we spend a good portion of time on the forces involved in continuous welded rail (CWR). Additionally, the FRA (Federal Railroad Administration) here in the US requires a three day course on CWR for any roadway workers that construct maintain of inspect welded rail. If you are really interested, you may be able to find some of that course material on the web. I unfortunately cannot share our materials."
] |
[
"Interesting stuff. The regional rail network in Victoria, Australia (VLine) runs a fast rail system where trains reach speeds of up to 160 km/h (100 m/h). These services started running about 5 years ago on newly built/upgraded sections of track.",
"Since launch they have introduced ",
"hot weather speed restrictions",
" on days hotter than 36C (97F). This means services often slow to a crawl (half their usual top speed or less) and is attributed to the tracks bending due to the heat.",
"Given your experience does this sound reasonable, assuming the new track was constructed using international best practice for fast rail?"
] |
[
"Why does stuff in the Universe like to rotate?"
] |
[
false
] |
Everything out there spins. From galaxies all the way down to quarks. I read "the solar system condensed and started to spin..." Why does everything like to spin? And for a bonus question; does stuff always spin the same direction? I mean, except for cases where a planet gets knocked sideways, etc.
|
[
"Imagine you have a massive cloud of dust. The odds of the total angular momentum of this cloud being exactly zero is negligibly small. This means the cloud is rotating very very slowly with a defined direction. Now consider what gravity does to the cloud. It will cause the cloud to collapse in on itself. As the cloud collapses, the angular momentum is conserved, but the size decreases. This means the rotation rate must increase significantly. Now you have a smaller cloud rotation more quickly. Stars and planets can form from this cloud, with higher likelihood that these stars and planets have a rotation vector in the direction of the cloud's rotation vector than other directions. Our solar system is a great example of this. The sun is rotating, and the planets are orbiting and rotating with very similar vectors, with only a few exceptions. This is because they all formed from the same cloud of rotating dust that collapsed on itself."
] |
[
"That explains the macro scale, but what about particles? Obviously they're different phenomena, but why does an electron or quark ",
" have a spin?"
] |
[
"I'm not sure if I can get to the ",
" of this question, but I can maybe offer some insight. Electron spin is kind of a misnomer. It is not the electron actually spinning. It is simply an amount of angular momentum that the electron must have (and happens to be quantized). Why must the electron have this spin? The best answer I can give is that the electron is a Fermion. For total spin S, the allowed spin states are -S,-S+1,...,S-1,S. For half integer spin states, for example S=1/2, the allowed states are -1/2 and 1/2, and not 0. For Bosons, with integer total spin, say S=1, the allowed spin states are -1, 0, and 1, so a Boson is allowed to have no angular momentum. Just to be clear, an electron can be in a quantum state that has no angular momentum (where if you measured the same electron a bunch of times in the same conditions, the average angular momentum you measure is 0), but that state is a superposition of s=-1/2 or s=1/2. For any one measurement you would always measure -1/2 and 1/2, with equal probability. All of this is a result of symmetry arguments in quantum mechanics. Fermions have antisymmetric wavefunctions, which means if you take 2 electrons and exchange their places, the overall wavefunction gets a minus sign. Bosons have symmetric wavefunctions, meaning the wavefunction is unchanged if you exchanged 2 Bosons. I can't explain ",
" electrons are Fermions, but you can show that if you have Fermions, their allowed spin states do not include s=0."
] |
[
"Does a person suffering from amnesia retain the personality traits formed from/during the experiences they can no longer remember?"
] |
[
false
] | null |
[
"Wow, no comments still...",
"It really depends on what types of traits you mean. H.M. (Henry Molaison) is the best studied case of amnesia, though he had both retrograde amnesia (memory loss), and complete anterograde amnesia (cannot make new memories).",
"After a surgery, he lost certain memories of his past, and most of the last few years before the surgery. More noticeable was his inability to remember anything past short term working memory.\nHe was kept in an institution until he passed, where he would take part in experiments and studies.",
"H.M. Would not remember you if you walked into his room, introduced yourself, left for 15 minutes, and return. If you played chess with him, he did not improve day to day. If you taught him history or writing, he would not learn. However, a skill game like darts he could improve on. He would excuse his skill as beginners luck. As per personality or more long term changes, he got very sad and spend several days going to church after being told his mother had passed away the first time, not knowing why. He still got sad when he has to be told this, but it was less intense, and less impactful. I'm not 100% sure, but I think I remember him having a similar response to his own reflection, where repeated experiences dulled the emotional response.",
"This is for one person, who had a specific surgery, so theres no way to say this is the case for other patients. However, the takeaways I picked up were that: ",
"His emotional structures were intact. I think this because he was able to have a persistent emotional reaction over several days, including sleep where he was unconscious, and unable to hold onto the event.",
"His muscle control and cerebellar timing can still learn, and is unaffected by the memory loss.",
"Source: Went to college for cognitive science. Had a class on disorders, and covered H.M. in it along with K.C. (Kent Cochrane)"
] |
[
"Just read up on him and this last bit I read was very interesting.",
"\"Near the end of his life, Molaison regularly filled in crossword puzzles. He was able to fill in answers to clues that referred to pre-1953 knowledge. For post-1953 information he was able to modify old memories with new information. For instance, he could add a memory about Jonas Salk by modifying his memory of polio.\"",
"Do you have any insight into what was going on in that context?",
"Edit - I find it very interesting and I believe it displays how complex the system that forms and retains memories is. He couldn't remember new information but was somehow able to modify old ones to remember new information. I think it also displays how it's possible for someone to believe their own lie or version of an event happening so much that they themselves believe their lie or version to be truth. Maybe they are using the same \"ability\" without realizing it. "
] |
[
"I had a small stroke several years ago and I've noticed this phenomenon with my own memory. Things I learned before the stroke came back fairly easily but trying to learn a new skill is much more difficult. Once I could concentrate reliably again, I picked up the crafts I'd abandoned in the order in which I'd previously learned them. Knitting was too hard until I started crocheting and somehow unlocked access to my muscle memory for all things with sticks and strings. ",
"I had trouble making change one day until I was able to relate it to a previous experience and now I can do it in my head again although I prefer to use a calculator just to be safe. ",
"It's crazy what I'm able to do again and at the same time, struggle with other things. Data recovery on a damaged hard drive is a crap shoot. "
] |
[
"What is the probability of shuffling a random deck of cards into new deck order?"
] |
[
false
] |
Also, how long would it take for this to occur?
|
[
"Without jokers, the probability is 1 in 52! or 1 in about 8.07 x 10",
" . And, if I mathed correctly, it would take about 5.59 x 10",
" shuffles for that to occur on average."
] |
[
"For those not familiar with the notation, that's 52 factorial he's talking about (he's not just super pumped to tell you the odds are 1 in 52)."
] |
[
"Persi Diaconis -- professional mathematician and magician and MacArthur recipient -- and collaborators have provided a rigorous mathematical analysis of shuffling. You can read about the various results ",
"here",
", which includes reference to the ",
"1992 paper (PDF)",
" with Dave Bayer proving the 7 shuffle result.",
"The Wikipedia page on ",
"Diaconis",
" has a nice summary of some of the results, such as this:",
"Diaconis is often cited for the simplified proposition that it takes seven shuffles to randomize a deck. More precisely, Diaconis showed that it takes 5 shuffles before the total variation distance of a 52-card deck begins to drop significantly from the maximum value of 1.0, and 7 shuffles before it drops below 0.5 very quickly (a threshold phenomenon), after which it is reduced by a factor of 2 every shuffle.",
"By the way, if you repeatedly execute ",
" (cut the 52-card deck exactly in half, and riffle so that the cards from your left and right hand literally alternate, one at a time from each side), you will get back to your starting order after 8 such perfect shuffles."
] |
[
"Why do prion diseases have 100% mortality rate?"
] |
[
false
] | null |
[
"Prions are simply misshapen proteins that have a rather unique ability to change their counterpart normal proteins around them into more misshapen variants. Because they were normal proteins there is no immune response against them so they are allowed to just sit there eventually turning your brain into Swiss cheese and ultimately killing you."
] |
[
"Nope, it is extremely rare though."
] |
[
"Nope, it is extremely rare though."
] |
[
"What would happen if you were shot with a single, non-radioactive atom?"
] |
[
false
] |
Let's say there's a gun that fires atoms at bullet speed, what kind of effect, if any, would the atom have on the body?
|
[
"Virtually nothing, your body is bombarded by atoms and particles traveling far faster than that on a daily basis and very little damage is ever done. This is a much bigger concern in outer space where astronauts don't have Earth's atmosphere and magnetic field to shield them from cosmic rays, which can eventually do damage to DNA or cells. That type of damage can take months or years of bombardment by countless numbers of particles. "
] |
[
"The Ivory Soap of velocities.",
"I think OP might have been wondering whether the atom would interact with the body, or just pass through it. "
] |
[
"Indeed, some of them as fast as ",
"99.99999999999999999999951% the speed of light"
] |
[
"Does exercising help my brain function?"
] |
[
false
] | null |
[
"Yes. I read a book called Brain Rules which talked about how, compared to those in a sedentary life style, those who have 30 minutes of aerobic exercise 3x a week had significant increases in reaction time, executive function, and mathematical thinking. I think mathematical thinking was double in the aerobic group but I don't know what sort of mathematical thinking this was. An important part of the study(s) was that they took sedentary people and had them start exercising and their scores increased to those of the active people."
] |
[
"These effects exist for all age groups, and effects are limited to executive function. Minimal impacts are found, for example, on verbal fluency. But you nailed it - 3x/week, 30 minutes, high but sustainable heart rate throughout. ",
"As to WHY these effects exist, the answer requires some speculation. A connection has been made with the release of BDNF - a neurotrophic factor. More broadly thinking, delivery of metabolic nutrients to neurons may be limiting cognition throughout life, so training the cardiovascular system will enhance its health - which in turn limits brain executive function. Again, all some speculation. What is not speculative is that it works, and works well, in study after study after study."
] |
[
"I'm confused about what executive function is."
] |
[
"If the human body were to be struck by a very small object (say a needle or something smaller) shot out of a rail gun and traveling at a huge velocity, would this object transfer all of its energy and rip the body apart or would it just blast straight through and leave a pin sized hole?"
] |
[
false
] |
How does energy transfer based on the size of the object? If it were to shoot clean through and not hit any major arteries or organs, could one survive this impact?
|
[
"If the needle is very small (in cross section) but built to deform on contact then it could distribute more energy. This problem is an actual science - weapons designers want to either maim or kill (depending on the application) as many enemy as possible for a minimum \"investment\" of mass/propellant. Tanks can carry anti personnel rounds that approximate to a \"big shotgun round\" for attacking groups without armor. Bombs or shells can have ",
"flechettes",
" to injure people - say for use over infantry in trenches.",
"With respect to bullets the word used is \"lethality\" and you start to depart science somewhat - how do you compare the human effects of a fragmenting bullet to one that expands on impact.",
"With respect to your example, people survive getting shot through with bullets so yes, getting hit by a high velocity, stiff, short needle that entered and exited \"clean through\" the person might not only survive but if (say) no arteries, organs, bones etc. were hit then the bleeding might even stop from clotting.",
"Not a human victim but my mechanical engineering school was investigating very high pressures (5000 times atmospheric) in a small container. The sensors were pin like metal tubes about the size of your pinky, passing through the pressure wall. One worked its way out and the resulting projectile went through five floors of a building leaving pinholes before embedding itself in a roof timber. Their \"fix\" was to greatly lengthen the sensor tubes so they would buckle on impact."
] |
[
"I don't know. I think they fixed it such that the \"needle\" wouldn't skewer anyone again (I think it passed through an office and chair, but it was late at night.) They had already anticipated the vessel rupturing (it was in a bunker in the basement) but had expected shrapnel/disintegration rather than a single really fast dart."
] |
[
"I don't think they were being crazy reckless. The pressure vessel was about the size of a coke can. When under pressure it was at night (empty building) and in a big room with nobody near it - control was from far away. It's not anticipating that mode of failure that caught them out. ",
"That said, they could have killed someone... five floors above them."
] |
[
"Does the Higgs Boson give mass to itself?"
] |
[
false
] |
Does the Higgs boson interact with the Higgs field so give itself mass? Would this be similar to the behavior of gluons that (as far as I understand it) add to the strong color charges nearby themselves?
|
[
"higgs boson : higgs field",
"photon : electromagnetic field",
"electron : electron field",
"(and so forth)"
] |
[
"we'll see is the best answer I can say. It depends on if/what the Higgs boson ends up looking like."
] |
[
"The Higgs boson is not about gravity at all. Or at least only very indirectly so. We know particles have mass. We would like to know ",
" they have mass. The leading idea is that they couple to a Higgs field, and that ineraction gives rise to mass behaviour. In order to prove it's right, you have to show that the Higgs field exists, and so you need to find the Higgs Boson, the excitation of that field."
] |
[
"Space Suit Manufacturing"
] |
[
false
] |
What keeps us from making space suits that are more compact and mobile? edit: I do already know some of the general reasons. So, I am really looking for more in depth explanations on why we are not able to solve the problem of suit pressure decreasing mobility.
|
[
"Current \"production\" space suits are flexible human-shaped air bladders. They work by holding in air, providing a constant-pressure environment for the human to exist. They also have to have several layers: protection for the bladder from dust, micrometeorites, and wear-and-tear; insulation to prevent excessive loss of heat; and active cooling using a working fluid (to replace open air convective cooling). The last two systems are there because it's easier to regulate the cooling with a working fluid and a thermostat than to try to adjust radiative cooling from each square inch of the suit.",
"The multiple layers make for bulky outerwear even in the absence of the pressure function -- imagine going outside dressed head-to-toe in Kevlar outerwear, a down jacket, a mesh of water tubes, and a \"body sock\" to prevent all that from chafing, plus diapers and a bulky backpack of course. ",
"There are some groups working on an elastic suit that holds pressure by clinging tightly to the body, rather than holding a preset (but flexible) shape. But the insulation and thermoregulation functions are likely to bulk it up too before it ever sees space."
] |
[
"Atmospheric pressure on mars is only about 0.08 PSI. The pressure difference between inside the suit and outside the suit on mars would be almost exactly the same as being in space."
] |
[
"This guy",
" developed a suit for use on mars. The ",
"mars atmosphere",
" is about the same pressure as 115,000 ft above Earth, about the height of the ",
"Red Bull Jump",
". ",
"Here is the suit",
" that Felix wore."
] |
[
"Can anyone please explain what appears to be a boundary layer over the wing from my flight last night?"
] |
[
false
] |
I was a passenger last night in an A320 at 34,000 ft when I looked out at the wing only to see a weird, light-bending boundary layer (I think). I had to blink a few times to make sure I wasn't just seeing things. This thin strand (sometimes three closely-spaced strands) bounced back and forth with turbulence. I leaned back to look out the window behind me and I couldn't see it. It could only be seen from dead on. It persisted for tens of minutes. I can only guess it was a layer between air masses of differing pressure? I've flown jets for a few years now but no one has ever mentioned being able to see such phenomena. Thank you for your help!
|
[
"You're seeing a local shock wave - even though the plane is not traveling faster than the speed of sound, at certain spots over the top of the wing, the local airspeed is faster than the speed of sound. A shock boundary is a local 'jump' or discontinuity in pressure and density, which refracts the light differently than the surrounding air. See here: ",
"http://en.wikipedia.org/wiki/Supercritical_airfoil",
"See here for some pics of this effect over the fuselage of an F-18. Note, the F-18 is NOT supersonic:\n",
"http://home.comcast.net/~bzee1b/Fleetwk08/Blues_F18/Blues_F18.html",
"This one in particular: ",
"http://home.comcast.net/~bzee1b/Fleetwk08/Blues_F18/DSZ_2345.jpg",
"Edit: Actually, this one is the coolest (tails, fuselage, cockpit bubble): ",
"http://home.comcast.net/%7Ebzee1b/Fleetwk08/Blues_F18/DSZ_2346.jpg",
"I don't know how to add my technical skill 'label', but I am an aero engineer."
] |
[
"Air flowing over the wing decreases in pressure. As it decreases in pressure, water vapor condenses out of the air, forming a cloud like the one you saw. ",
"Here",
"'s a more extreme example."
] |
[
"That is caused by the shock, when the fluid is locally accelerated to Mach > 1. As the pressure decreases when the fluid is accelerated, the air-density also decreases and influences the refraction index..."
] |
[
"What kingdom or domain of life are viruses in, and what differentiates them specifically from other single-cell organisms like bacteria?"
] |
[
false
] |
I was doing some reading for fun on this and I can't find them anywhere in the Taxonomy wikipedia( page
|
[
"The list your looking at details cellular life, the 3 domains don't include Viruses, on account of them not being cellular life. ",
"I belive there are people that want to add 4th domain to account for \"non-cellular\" life such as virus. ",
"https://en.m.wikipedia.org/wiki/Virus_classification",
"the biggest difference is that that viruses aren't alive in the way you're probably thinking of \"living things\""
] |
[
"So does fire, by many of the common definitions of life. Coming up with a ",
"scientific definition of life",
" has been a bit of struggle and ongoing debate. Most textbooks these days will give you a list of characteristics that living things have, such as reproduction and metabolism, a list that neither viruses nor fire can completely check off."
] |
[
"Looks like this one is mostly handled, but for a little bit of added clarification about viruses not being cellular life- What a cell is has a distinct definition in Biology. Cells have either a membrane or wall, and contain a nucleus and a number of organelles. Viruses are simply DNA/RNA wrapped in a protein envelope (called a capsid).",
"For this reason, they are very much unlike anything defined as life (Prokaryotic or Eukaryotic). Also for this reason, they are entirely unable to consume anything or reproduce on their own (as has been outlined by other posters). There are some parasites that may fit the criteria of not eating or not being able to reproduce without their host, but those parasites have cells and cellular machinery. Viruses are truly different. ",
"Viruses can not \"die\" in the same way that cellular life can die because there are no cell functions that cease in the same manner as cellular life.",
"It's important to note though, that this is simply a biological definition and this does not mean that viruses cannot be destroyed or do not deteriorate on their own. their protein envelopes can be (fairly easily) destroyed. If this happens they are \"dead\" as far as any layperson may be concerned."
] |
[
"What is the difference between a good and an outstanding music instrument?"
] |
[
false
] |
For example, can we say that a superb violin produces a different spectrum than an ordinary one?
|
[
"As a French Horn player, I can try to explain this as it is for brass instruments.",
"It is predominantly down to a few things: the quality of the metal it is made from, the valves, the connections between the pipes and the flare.",
"Firstly, the metal is made from. If you took a lump of doorhandle, melted it down and made a gong out of it, it would sound rather dull. This is because doorhandle metal is not able to resonate. However, nickel silver, which is what most horns are made from, is able to resonate much more easily. This means the sound made is much clearer.",
"Secondly, the valves. Most horns made nowadays are called double horns (which means they are able to alternate between two different pitches by pushing down a lever). They also incorporate rotary valves, which turn to allow air through different pipes, which changes the pitch. The valve which changes the pitch of the instrument (the fourth valve) can allow air to travel two ways- for simplicity, forwards and backwards. Most poor quality horns have the air travelling in one direction for one pitch, and another direction for the other, as it is much cheaper and easier to make. Professional horns incorporate the Merriwether system, which makes air travel the same direction around the fourth valve. This minimises interruption from the rotor inside the valve as it turns, giving a nicer quality of sound, since the air does not have to change direction through the valve.",
"Thirdly, the connections between the pipes. The air in an instrument travels from mouthpiece (where you stick your face) to the flare (where the sound comes out). Between these are various slides which can be pulled out and pushed in to slightly adjust the pitch is the air is flowing through the slide. To make the valves stay in, one tube is slightly smaller than the other on the inside, so it fits in snugly. However, if the air hits this ridge, less air is travelling in the right direction, and this interrupts the player. Most professional instruments have the air going 'down' from the ridge, as opposed to hitting it. This makes a clearer sound.",
"Finally, the flare. When the air leaves the flare, it is bouncing all over the place as it leaves. This is what gives horns such a resonant sound- its ability to resonate. As said before, if it is made with a crappy metal, then this will not resonate as well. Most poor quality horns have a flare which was just a piece of metal which was cut and attached. Most professional horns have flares which can take up to two weeks to hammer into shape by hand. They are made each time using various maths based stuff to resonate perfectly.",
"However, the key thing in all of this is a player. A professional horn player could probably take a crappy horn and play a beautiful concerto and most would think their horn was also exquisitely made. However, you couldn't give an inexperienced player a professional horn and expect them to be at the same quality. A lot of time, it is the instrumentalist who is outstanding, and not the instrument."
] |
[
"For science, set up some really sensitive microphones around a room, and have a simple machine that does the \"Sound making action.\" If you switch out the instruments, you'll be able to hear the differences and even observe the wave forms using some cool software. The difference between a shitty instrument and a professional one is audible to just about anyone - but I doubt many people could tell good from superb. It'd be a whole different experiment to blindfold people and have them listen to good/superb - then see if they could identify which was which accurately. Again you'd have to use a machine to produce the sound, because a performer might play differently if he/she thinks she's playing a superb instrument."
] |
[
"Record a note then load it into MATLAB. Use the FFT function to examine the harmonics. Then, overlay the harmonics for both crappy and good instruments. That'd be cool."
] |
[
"Could you stop a tornado with a large explosion?"
] |
[
false
] | null |
[
"In theory you could, but it's a terrible idea for just about every reason imagineable",
"."
] |
[
"Here's the answer for a scaled up version: ",
"http://www.aoml.noaa.gov/hrd/tcfaq/C5c.html"
] |
[
"How about some fluids-informed speculation? It's possible to stop a vertical vortex either by injecting dense material into the updraft, or also by disrupting the circular flow in the \"wall\" near the core, which eliminates the centrifugal action and radial pressure distribution in a small region, essentially \"poking a hole\" in the barrier which preserves the low-pressure core. Could an explosion accomplish the latter? Yet any small, brief disruption would probably \"heal\" rapidly, and the tornado continue as before. So we'd have to produce a disruption which in extent was a fair percentage of the central tornado diameter, and of duration long enough to inject outside air sufficient to eliminate the low central pressure.",
"Even with no numbers attached to the above, I strongly doubt that an explosion could do any such thing. The effects are too brief: explosions are wave-generating \"AC\" or transients, while a tornado is \"DC\" with constant flows only changing over many tens of seconds at least. Worse, the explosion produces heated air which would ",
" the tornado, not damp it.",
"Another problem: very large tornados are composed of several \"suction centers:\" essentially a group of tornados dancing around a common center. Disrupting one of these tornados doesn't necessarily damp out the pattern as a whole.",
"Destructive tornados are known to lose power when traveling over water. PURE speculation: to stop a tornado, let it suck up many tons of liquid nitrogen! (Let the Experiment be Made!)",
"PS",
"In pre-internet times, \"Tornado Videos\" had an excellent set of VHS tapes on early tornado research and much footage of tornados, including miniature wind-tunnel models of giant multi-center tornados. Are they still around?"
] |
[
"Why do humans have many specialized cells, rather than one cell that can perform many functions?"
] |
[
false
] | null |
[
"By specializing the cells they can perform better- for example the thin alveoli cells can absorb oxygen and co2 faster than the thick skin cells of your foot which resist trauma from collision.",
"This improved performance grants organisms a major advantage."
] |
[
"That's the answer I was looking for, thanks!"
] |
[
"It's part of our evolutionary history.\nIn the beginning there were single cellular organisms. Then some formed colonies which could as a group achieve something that each individual cell couldn't. Then some of these colonies organised in a way that assigned different functions to these identical members. Thus multicellular life was born. Then some of these colonies begain to have different cells which were better suited for each task. Some didn't. We belong to the former group of multicell life"
] |
[
"Origins of Life"
] |
[
false
] |
How could life on earth have originated without oxygen being present in the atmosphere?
|
[
"Most all early life was anaerobes, which do not need oxygen and instead can release it as a byproduct. In fact oxygen would have been quite toxic to early life on Earth. There are still many anaerobes in existance today, in fact inside your gut right now are billions of them"
] |
[
"Methane contains no oxygen. The oxygen comes from nitrite who reacts with methane."
] |
[
"Thanks for the correction. I was in a rush unfortunately."
] |
[
"Since your liver regenerates, can you remove and freeze a chunk of your healthy liver at a young age, and then use it as a backup to regrow your liver later in life after it's been damaged?"
] |
[
false
] |
[deleted]
|
[
"Theoretically, but the real problem is that it’s very difficult to avoid damaging living tissues in the freezing process to the point where it’s unusable. Unless you have access to decent quantities of liquid nitrogen and a suitable storage environment, such as a large industrial dewar, ice crystals will inevitably form within the protein cells, bursting them and rendering your liver into a useless mess. ",
"You may have heard about tissues, organs, and even entire cadavers (such as Walt Disney’s head) being stored long-term in cryopreservation conditions (generally -196°C, which neutralises enzymatic and other chemical processes) in the hope that one day, the technology and expertise will exist to return them to life. There are all kinds of complications though, such as the necessity for introducing cryoprotectants to protect against intracellular crystal formation. There are also solution effects - as ice forms, solutes remain suspended in the non-frozen portion and thus dramatically increase in concentration, which can make even simple salts and sugars highly toxic. ",
"The sad truth is that it’s ",
" that any of these frozen tissues will ever be viable, for the fact that it’s near impossible to get and keep them at such low temperatures without damage. ",
"A better way would be to combine your liver with water and sliced onion. Bring to a boil, reduce heat to low, and cover. Simmer for about 20 minutes, or until liver is cooked and tender. Remove from heat, drain, and discard onions. Also remove and discard any hard portions of the liver.",
"Place cooked livers in a blender or food processor, and process until smooth. Add chopped onion, sherry, butter or margarine, salt, black pepper, and mace; pulse to blend. With hands lightly greased, form pate mixture into a mound, and place on a serving platter. Chill for 1 hour before serving."
] |
[
"While pate is chilling, take 500g fava beans (fresh, shelled) and boil for 5 min. Immediately remove and place in ice water bath to cool. Once cooled, sauté beans in equal parts butter and olive oil for 7 minutes, until tender. Salt and pepper to taste. Best served with a nice Chianti."
] |
[
"No, but they have done somewhat related things with frozen ovaries. It’s still experimental and early days, but they’ve removed and frozen sections of ovaries, then reimplanted them later and they’ve worked. I think they’ve tried sewing them to an existing ovary, but also they’ve implanted them in the arm. They’re not regenerating tissue like with livers, they’re just reinvigorating frozen tissue."
] |
[
"Boundary Conditions of EM field Around a Solenoid in Cylindrial Coordinates"
] |
[
false
] |
My first askscience question! How exciting! I am having trouble with some EM field simulations and I think my problem is my boundary condition assumption. I am simulating a solenoid with several cylindrical layers of dielectric material inside and outside of it. I am trying to get some numerical solutions to this thing's flux linkage with some exterior conductors. My geometries are all cylindrically symmetric. I have modelled a system where the wire thickness is much smaller than the radius, and so I am approximating B as being exclusively in z, and E as being exclusively in phi. I don't want to get into too much detail with what this is for/about, because I have a specific question which I think is already complicated enough. I am essentially solving for bessel/hankel functions as a function of radius for the phasor values of the fields across a series of boundaries. The equations are continuous across all boundaries, BUT, not at the solenoid, (as it is the driver). In my simulation, the solenoid is just treated as a cylindrical shell of zero thickness, (actually it has a thickness but nothing happens inside that thickness), with the following boundary conditions at the boundary of the solenoid coil itself: B_inner(z) - B_outer(z) = B_BOOST_COIL(z) B_BOOST_COIL(z) =difference between interior and exterior of solenoid only system in a vaccum as calculated w/ biot-savart law E_in(z) = E_out(z) I am making the assumption that the mag field , (the boosting effect of the solenoid), is the same as a solenoid in a vaccum. This is simply (interior - exterior) magnetic field at the boundaries of the solenoid as calculated with Biot savart in the magnetostatic formulation. I did think I needed to use a retarded time derivation as the driving frequency's wavelength is significantly larger than the entire system I am concerned with. Would there be any caveats here? I can't seem to think of any. If anyone has a better suggestion for the mag field, I'd love to hear it. My larger concern is with that electric field BC. My reasoning behind it is that the internal and external electric field will be effectively the same because the skin effect will push most of the current density to the outside of the wire. , in hindsight, that is certainly a decent approximation for a straight wire, but here we have a solenoid. I feel like the effect of the self inductance will introduce additional opposing eddy currents on the interior of the solenoid mostly. Won't this turn the current density "donut" into more of a squashed donut? Like a donut that got punched in the side? I'm not sure how to go about quantitatively evaluating that. If anyone has any advice/links to papers/textbook chapters that would be much appreciated. Thanks.
|
[
"Do you have access to Jackson's E&M textbook? I think he discusses similar problems in all their gory detail."
] |
[
"Yep. If you don't have it, it shouldn't be hard to find in a library or used (or...in pdf form...somewhere on the internet...).",
"It's the standard physics graduate student E&M textbook...so there's lots of them around."
] |
[
"this?"
] |
[
"Why are semiconductors used in photovoltaic cells instead of conductors?"
] |
[
false
] |
Actually, not only in PV cells, but in almost all electronical devices. How come?
|
[
"Going a little further - electrons can flow through conductors easily, but can only flow through semiconductors under certain circumstances. These circumstances (voltage, electric field, etc.) can be indirectly adjusted in the semiconductor to optimize it for particular applications - by altering the structure of the semiconductor and its distribution/type of charge.",
"What this means is that whenever you need a circuit element that can change its behavior, you need a semiconductor. Electronic switches, logic gates, amplifiers - these ",
" exist without semiconductors. (Vacuum tubes aside....)",
"For a solar cell, semiconductors are necessary because we only want the electricity to flow one way. The photovoltaic cell is actually very much like a diode in structure - due to its nature, it's very easy for electrons to flow in one direction, but difficult for them to move in the opposite direction. Somewhere down the line from the solar cell, there's a battery of some sort. If the entire system was composed of conductors, then the battery would be discharging through the solar cell when it wasn't charging. ...but the diode-like nature of the solar cell prevents this from happening."
] |
[
"There are two energy bands you need to worry about, the valence band and, at a higher energy, the conduction band.",
"See ",
"here",
". Semi-conductors are useful because the band gap is non-zero (the valence and conduction bands do not overlap) but small enough for electrons to move from one to the other when you want them to.",
"Basically, the electrical properties of the material depend strongly on how many electrons move up to the conduction band. In a semi-conductor, you can control this. This is fundamentally useful for electronic devices."
] |
[
"Thank you!"
] |
[
"Are Rubbing Alcohol & Hydrogen Peroxide actually bad for cuts? [MIC]"
] |
[
false
] |
1) Doesn't rubbing alcohol make the blood thinner which actually causes you to bleed out more? Is rubbing alcohol actually a good disinfectant at all? Is it bad for cuts? 2) Wouldn't Hydrogen Peroxide be bad for cuts as it actually eats away at good and bad tissue? In the time that your tissue recovers from Hydrogen Peroxide, couldn't you pick up an infection? Is it bad for cuts?
|
[
"Normal saline is really only good for irrigation, it isn't considered antibacterial."
] |
[
"Most of the dressings I've done consisted of clean bandages and normal saline, no antibiotic component. "
] |
[
"Normal saline works just fine for most wounds and it doesn't hurt or irritate it. "
] |
[
"If our moon causes our tides, and considering the size, wouldn't moons around a planet the size of Jupiter have tides that would flood entire continents?"
] |
[
false
] |
Pretty self explanatory... I know there is no moons like earth with liquid water on the surface around Jupiter, but theoretically the tides would be enormous, right?
|
[
"(not my field of expertise) The moons of Jupiter have huge tidal forces. For instance take Io, it's the closest large satelite of Jupiter and it's tidal forces are so extreme that they heat the core of the moon, causing volcanos with plumes hundreds of kilometers high!",
"http://en.wikipedia.org/wiki/Io_(moon)#Tidal_heating",
"(I remembered all of this from Arthur C Clarke's 2010)"
] |
[
"Fuck. That is pretty much the definition of 'awesome'."
] |
[
"I'd say ",
"carbon dioxide at 460",
" C and 90 atmospheres of pressure",
" is pretty hellish."
] |
[
"Could we recreate the pyramids?"
] |
[
false
] | null |
[
"Hello,",
"Open-ended questions are more appropriate for ",
"/r/AskScienceDiscussion",
".",
"Cheers."
] |
[
"Thank you for your reply but, sorry, it is physically impossible to find good answers and scientific discussion in ",
"r/AskScienceDiscussion"
] |
[
"Well your question has been removed from ",
"/r/AskScience",
", so it needs to be posted elsewhere. You can choose to post it to AskScienceDiscussion or not.",
"Cheers."
] |
[
"If a helicopter were to ascend in a perpendicular line, hover, and then descend in a perpendicular line, would it be able to eventually deviate from its original launch point when it lands, due solely to the Earth's rotation?"
] |
[
false
] |
That is, could a helicopter "defy" or "counter" the effects of the momentum of Earth's rotation simply by hovering, and if so, approximately how long would it have to hover for? Fuel is not a factor. Somebody posed a similar question, which I was unable to locate, on Reddit a while back and it had little to no followup discussion. One of the responses was that the helicopter would not be able to avoid the Earth's rotation because it took off from Earth and was therefore spinning in conjunction with Earth and was not inert. That is, it was subject to the Earth's momentum. My theory is that if it hovers for a long enough time period, it will in fact be able to eventually "shed" the momentum/effect of the Earth's rotation. Thanks!
|
[
"No, probably not. As the helicopter goes up, hovers, and then descends, it will always be stationary w.r.t. the surrounding air. The thing is, the air itself is ALSO rotating along with the earth. If this weren't the case, we would always have a pretty stiff breeze, because the earth would be rotating, but the atmosphere would not be.",
"does this make sense?"
] |
[
"You could do something like that, but you would need a rocket, not a helicopter.",
"The helicopter pushes against the atmosphere around it, which is also circling the earth at great speed. You'd have to break free of the atmosphere before you could use the earth's rotation to your advantage. And the cost of doing so is pretty great, I doubt you would be any better off than flying there directly."
] |
[
"The air at the equator on a calm day is going 1000 miles per hour. \"Staying still\" would require going through that air at that speed. No helicopter can achieve such an airspeed."
] |
[
"Why feature of sound causes words or instruments to sound so different."
] |
[
false
] |
Why do sounds not all sound like this: I understand frequency determines pitch and amplitude determines loudness. What changes the 'timbre' of a sound eg. a clarinet vs a flute. How do we distinguish different words? What physical feature of sound waves determine the sounds of the different vowels for instance? Why do all sounds not sound analogue (by this I mean what you would hear on a synthesiser, or in the video previously posted?) Thanks in advance! Edit: I think between you guys you explain it very well. It look's like I will spend the rest of my afternoon reading, not a bad thing at all! Cheers
|
[
"With instruments, they have a harmonic structure. That is, there is the bass note, lets say A which is 440, and then that value times various integers, so 880, 1320, 1760 and so on. Those integer values are called harmonics. A musical note can be defined as a sound that has harmonic structure of those integer values. The human ear can process 7 harmonics at a time, meaning that if you started out with a hundred harmonics, then slowly took out one at a time, you could get down to 7 before any change would be heard. The tonal difference of any musical instrument, comes from the shape of these 7 tones. If graphed in a bar graph, the graph would appear to slope downward, with higher harmonics not being as loud. "
] |
[
"One of Vihart's awesome videos covers this ",
"here",
". Be warned, if you haven't encountered her videos before be prepared to waste the next few hours."
] |
[
"She is fantastic. Thank you"
] |
[
"I don't know if this is a question of politics rather than science, but why is NASA spending so long developing the Ares V to be a HLV? Why can't they just pull the Saturn V out of retirement if they'll both cost similarly?"
] |
[
false
] | null |
[
"I can't speak to the first question, but ",
"this",
" essay describes several of the challenges in restarting production of the Saturn V's engines, and why a new rocket would have to be developed to use them. The answer is not simply that the plans for the Saturn V were destroyed, as is widely reported on the Web."
] |
[
"To piggyback - very little, if any of the physical production facilities exist. Machining parts like this requires machine tools that are often specific to the job. Those aren't going to be left taking up valuable floor space in a production plant."
] |
[
"Wouldn't it cost more to develop a whole new rocket though? Why not just bite the bullet and rebuild it all?"
] |
[
"Is there any significant difference between cars that drive on different sides of the road? Are their blueprints just a mirror image of each other or are there some challenges to overcome for each side?"
] |
[
false
] |
[deleted]
|
[
"Don't forget about the brake booster, master cylinder, and pedal. With that comes new plumbing for the brake lines. There is also the clutch pedal and routing for that system if the vehicle is a manual. If the vehicle has a floor pedal instead of hand brake, that whole system needs to be redone and rerouted. There is also the accelerator and it's whole system. Then there is the rerouting of all the parts that used to be on the right hand side that are moved to make room for the new parts moved to the right side. All the electronics on the steering wheel and column, and much more.",
"I won't go into it all, but there are a lot of packaging issues that need to be worked out. To answer the OP's question, no, it is not simply mirrored. The entire vehicle is repackaged with RHD in mind while keeping everything else that doesn't need to change the same. Many things simply cannot just be switched sides without adding a ton more cost. You want to keep the number of unique items to a minimum, and if the entire vehicle is mirrored you would have a ton more unique body stampings along with difficulty assembling things that would switch sides (stock would have to be on both sides of the line, some machines would have to work for both sides of the line, workers would have to know 2 different jobs, etc).",
"There is a ton more I am not getting into, but lets just say it's pretty complex especially when you add in the federal regulations that are different in the countries with RHD and a whole host of other issues. It's not simple at all, and costs a lot of money.",
"Source: I am an automotive engineer that worked in automotive braking systems so I dealt with changes in RHD and LHD often."
] |
[
"Nope only the dash, steering column, windshield wipers, and headlight adjustments flipped. It's not too uncommon to find cars in the US converted to RHD. Some people buy the front half of a car known as a clip, usually imported from japan, and would swap out the parts. The steering column is the only thing that requires any modification as you have to cut a hole in the firewall. Though I wouldn't ever recommend driving a RHD car on LHD roads as it is very impractical. One such instance is driving on a two lane road and you want to pass a slower car, you have to switch lanes before you can even see if a car is coming in the opposite direction."
] |
[
"You are not wrong, I just want to point out some cars are made with RHD/LHD swapping in mind. For example, late model RX7. The Jspec is LHD, but to swap it only requires the RHD dashboard and a small kit of parts (including longer brake lines/accelerator cables). It's easily done. I've done it. ",
"I have a feeling, but I'm not sure, that a lot of Asian cars are like that. "
] |
[
"How does the shape of a hyperbolic cooling tower (like those in nuclear plants) help evaporate water/remove heat?"
] |
[
false
] | null |
[
"The hyperbolic shape itself does not help the cooling of a power plant. ",
"What makes the cooling successful is the height of the tower: by \"protecting\" the warm and moist air further up, it will maintain an updraft inside the tower.",
"The hyperbolic shape is just to have a stronger structure to deal with the high winds you get by increasing altitude..",
"Edit: If you are curious, the updraft is caused by pressure difference between inside/outside the tower. Big cooling towers have holes at the bottom, where ambiant air can rush in. Since hot moist air is less dense than the cool ambient air, it will tend to rise. This rise is then directed directly upwards by the tower.",
"If there was no tower, the moist air would rise, but with enough warm air exhaust, you could reach a stagnation point where the moist air just doesn't really move away much, hampering your cooling. Higher towers are necessary for big enough power plants, as they prevent the mixing of the rising up air with the cooler air around."
] |
[
"Also the Hyperboloid shape is used in construction of cooling towers because the hyperboloid is what's called a double-ruled surface, which means every point on the surface is the intersection of two lines that are also on the surface. This means hyperboloid constructions are strong and can be cheaply built using only straight beams."
] |
[
"By moist, I mean water vapour, not water droplets. If we talk about gases, any gas molecule can approximated to have the same volume (it's true to quite a few digits of precision). 99% of air is made of Nitrogen and Oxygen, but these two elements usually binds to themselves, making a dinitrogen or dioxygen molecule. Look up the periodic table, you see that two nitrogen (or oxygen) is actually heavier than two hydrogen and one oxygen (water). Therefore, vapour (gaseous water) would technically rise. Truth is, the mass difference is usually not important enough: due to turbulences, a parcel* of air will be uniformly mixed for the most part. The \"moistest\" air will have a 3%-5% water content (in mass). Temperature is usually a much more important factor in such cases.",
"The exhaust of power plants will usually be ",
" warm. Warm air can dilute much more water vapour than cold air. As it rises and cools, the maximal amount of vapour that can be stored will diminish. This will \"force out\" some gaseous vapour into liquid form (small water droplets, usually sticking to aerosols in suspension). This is very much like a cloud. While clouds are \"technically\" heavier than ambient air, the mass difference is (again) so little that it doesn't really matter (which is why clouds don't fall). This is also why cooling tower seem to spit out clouds.",
"*A parcel of air is a \"bunch\" of gas molecules. A parcel can change in volume, temperature, but a given parcel retains the same mass.",
"Edit: changed 78% to 99% because I can't math."
] |
[
"How exactly do electromagnetic waves carry data through the air?"
] |
[
false
] |
I've been under the impression that radios signals are turned on and off rapidly to represent 1's and 0's. Am I correct or is data transmitted somehow else entirely? Edit: To clarify, I'm talking about all wireless technologies, such as wifi and Bluetooth.
|
[
"I tend to disagree that AM is turning the signal on and off. The whole carrying thing deserves a better explanation than that.",
"OP should check this video which explains it quite simply and makes a great base to understanding it better: ",
"http://www.youtube.com/watch?v=4Qgg_upU_5s"
] |
[
"802.11ac",
" uses up to 256-QAM. ",
"802.11n",
" uses up to 64-QAM.",
"QAM",
" uses a combination of shifting amplitude and phase to transmit information. The AM part might be a familiar concept to many, but ",
"PSK",
" (Phase-shift Keying) might not be. To see a breakdown of just the phase shift portion, look at BPSK and ",
"QPSK",
".",
"Edit: An example of a 64-QAM constellation grid can be seen ",
"here",
". I mirrored the image from ",
"this site",
". A line drawn from the center to any point has both a length and an angle--a combination of those two is the agreed-upon 'key'.",
"The animated ",
"16-QAM gif",
" shows the concept."
] |
[
"Turning the signal on or off (or more precisely varying the amplitude) is called amplitude modulation (AM) and is one way to transmit data. A more common way for high data rates is frequency modulation (FM), where the frequency of the signal is shifted a fraction of a carrier frequency. E.g. in WiFi the main signal is 2.4 GHz, and the signal will modulate a few MHz around that carrier. "
] |
[
"What differences would there be in a planet with a different water-to-land ratio from Earth?"
] |
[
false
] |
Everyone knows that the Earth is composed of 70% water and 30% land. Let's say that there exists somewhere a planet absolutely identical to Earth in its size, distance from its star, its geological makeup, etc, except that it is composed of 30% land and 70% water. Or say, an equal 50-50 ratio. What changes, ecological or otherwise, would there be?
|
[
"This is a really good question. ",
"There would be quite a lot of differences. For starters, the oceans act as something of a temperature buffer, so with more land you would see more extreme seasonal and diurnal temperature fluctuations. With more or larger land bodies you will get more extreme daytime heating, which will lead to more upwelling air, which will likely result in more wind.",
"Increased land mass is likely to result in larger continents, and from our climate history we know that large continents are usually associated with large internal desert areas. This would likely be worsened, as you have less sea surface to provide evaporation.",
"Sedimentation is an interesting one. Assuming that more land means more erosion, you increase the sediment flux into the oceans, which increases nutrient levels. That leads to higher marine biomass potential. So although you reduce the ocean size, you basically make them more fertile.",
"There's a lot of esoteric effects which are dependant on the exact structure of this extra landmass - is it all large continents, or many smaller micro-continents. For example, ocean circulation, species distribution, biodiversity, climate belt development, migration barriers, distribution of volcanism, mantle processes and subducting slab interaction, tidal ranges, seaonal weather patterns.... I could go on."
] |
[
"Wouldn't a lack of water also result in fewer/weaker storms since there is less water vapor available?"
] |
[
"Possibly, yes, although more land suggests there's a chance for more forests, which are excellent at putting large amounts of water vapour out."
] |
[
"Is kinetic energy/ mass relative?"
] |
[
false
] |
Motion is relative. Velocity makes an impression on spacetime in the same manner as mass does. Is that impression relative, depending on who's measuring it? Or is it measured relative to a stationary spacetime standard? Does this make mass relative? Tl;dr: How do I relate?
|
[
"Mass is invariant, kinetic energy depends on the reference frame. \"Velocity makes an impression on spacetime in the same manner as mass does.\" isn't a meaningful statement."
] |
[
"Yeah, it makes more sense just to consider momentum p=γmv, where the mass is invariant, rather than demand p=mv where m changes."
] |
[
"Yeah, it makes more sense just to consider momentum p=γmv, where the mass is invariant, rather than demand p=mv where m changes."
] |
[
"How does passing genes/traits to offspring work?"
] |
[
false
] |
[deleted]
|
[
"There are different kinds of traits. Mendelian traits refer to the simplest ones where its only 1 gene that affects the trait. For example lactose intolerance can be a mendelian trait because a protein is expressed and active if you arent intolerant and isnt expressed well/inactive when you are intolerant.",
"However most traits arent controlled by a single trait. Its a complex mix of many traits working together to lead to the actual phenotype (trait).",
"Height is a great example of this. You dont have binary options with height where its either moms height or dads height. There are many many genes that affect height and the interesting combo of getting some of moms and some of dads genes that affect height is what gives you your actual height (to be fair other variables affect height too like nutrition but the point still stands). ",
"The vast majority of traits are complex traits where its a mix of different genes. Now some genes are more important for a given phenotype and so some traits may appear to be more moms or more dads often, but again combos make things different.",
"Things can get way more complicated though as genes can go through recombination which means you can get minor variants of your parents original gene. Another way to make heredity more complicated is that some genes are dominant and recessive, which is the binary examples ive talked about, but some genes can be codominant and semidominant. ",
"Basically lots of genes affect a given traits in different ways.",
"Lmk if you've got more questions!"
] |
[
"Not the original poster but is semidominant another term for incomplete dominance or are they different things? It’s just that I’ve never heard of semidominance before."
] |
[
"Theyre the same thing! Just another name. Now there is a difference between those 2 synonyms and codominance. Incomplege dominance its a blending of the 2 alleles while codominance its weirder where one is dominant in one part of the tissues and the other is dominant in another. A good example is how you can get weirdly striped or patterned colored flowers"
] |
[
"Why is it, that the smaller of a particle we want to detect, the larger of a detector we must build?"
] |
[
false
] |
[deleted]
|
[
"All of these very small particles are held together by very strong forces. In order to find smaller particles, we have to bash them together at very high speeds in order to break those forces and see what things are made of. It's not the ",
" that's large, it's the particle accelerator. We use electromagnetic force to zip things around giant racetracks until they're going nearly the speed of light. Then, when they bash into something else the forces involved are strong enough to break up very small particles into the things they are made of. "
] |
[
"Also, not all of the particles are small. The Higgs Boson is about as heavy as an Iodine atom, massing as much as around 125 protons and/or neutrons."
] |
[
"All particles are \"epiphenomena\" (a secondary effect or byproduct that arises from but does not causally influence a process) of excitation of fields. It's the higgs field which gives fermions their mass. Not the particle. It takes a lot of energy to excite this field into a particle hence the higgs bosons high mass."
] |
[
"Are we born with bacterias in our stomach or do they develop afterwards?"
] |
[
false
] | null |
[
"Until quite recently it was assumed that the interior of a developing fetal gut was sterile. However, there are now multiple lines of evidence to suggest that initial colonization of the gut by microbes occurs before birth. How the bacteria cross the placental barrier and how it is absorbed by the fetus is not completely understood. It may be that the microbe crosses the placenta into the fetal bloodstream or it passes into the amniotic fluid and is ingested by the fetus orally. ",
"See ",
"this",
" article for an easy to approach review."
] |
[
"It's important to note that there's still very good evidence that significant colonization also occurs during birth, such that babies born via C-section have different gut bacteria than babies born vaginally.",
"So, a newborn's gut bacterial community is presumably a mix between what it was exposed to in the placenta plus what it was exposed to on it's way out. The relative importance of each exposure has yet to be experimentally determined."
] |
[
"The link between maternal microbiome and offspring allergies would undoubtedly be a difficult one to make, but it is entirely possible. ",
"this",
" article describes how high fat diets in macaques can alter the fetal microbiome."
] |
[
"If light travelled at the speed of sound, would we be able to see light \"echo\" ?"
] |
[
false
] |
If instead of travelling at 300 000 m/s (sorry for those of you who don't use the metric system) it travelled at the speed of light (+- 350 m/s so 1000 km/h), how would it affect our vision system? Could we see light travelling over long distances? Could we see "echo" in a mirror room?
|
[
"We already see light \"echo\" at its current speed. We just aren't able to perceive the time separation between the signal (a light-bulb turning on) and its echo (the reflection of the light bulb off a mirror). If the speed of light were much slower you would be able to tell the difference between a light-bulb turned on in a mirror room and the reflection of the light-bulb in a mirror. You'd experience two distinct flashes of light."
] |
[
"You wouldn't be able to see light moving around the room and towards you, because that light hasn't reached your eyes yet... your eyes can only respond to light that hits them, not light that's some distance away.",
"The effect would be, from your point of view, that things would light up much later than you'd expect them to."
] |
[
"I actually just read ",
"this article",
" today. Scientists have created a camera that takes pictures at a trillion frames per second. It gives you a good idea of what the world would look like if the speed of light were much slower."
] |
[
"If a chihuahua gets impregnated by a great dane, what keeps the puppies from growing too large inside of her? Is the female gene for size dominant over the male's?"
] |
[
false
] |
[deleted]
|
[
"Vet here - It's actually somewhat common for small breed dogs to have fetuses that are too large and cause considerable problems. This is especially true when there is only one fetus, and the body puts all of its resources into the one, making it too large. These puppies usually cannot be delivered naturally, and require c-sections. \nI have not seen someone try to inseminate a large breed dog into a small breed (as this breeding could not happen naturally), but I don't believe there would be mechanisms for \"keeping the puppies from growing too large\". I would be surprised if they'd be viable puppies in the first place, but if they were, there would certainly be numerous complications in delivery, if not pregnancy. "
] |
[
"This may not be helpful at all, since the topic at hand is dogs, but here we go: In equines if you breed a large male and a small female, the mare (female) has various mechanisms to limit the growth of the fetus within her. Effectively, the fetus will grow to fit whatever space it can achieve - the bun will fit the oven. When performing embroyo-transfer, a mare of large capacity (often a draft mare) is often used as a recipient in order to grow the foal (baby) as large as it can get before birth. ",
"Sadly I have no idea if the same mechanism exists in dogs, considering that their uterus is designed to carry a litter of puppies, not just one (or occasionally two) offspring like in equines. ",
"Please pardon my parenthetical terminology explanations; not everybody knows these farm-animal words. "
] |
[
"A chihuahua male can still impregnate a great dane female. ",
"There are actually quite a few instances in canines and other animals where a male of breed 1 impregnating a female of breed 2 will fail, while a male of breed 2 impregnating a female of breed 1 will succeed. ",
"A lot of factors come into play, like size, gestation period, etc."
] |
[
"Why does water put out fire, if water is hydrogen and oxygen?"
] |
[
false
] | null |
[
"They're not just mixed, they're bonded. The flammability of hydrogen and oxygen is due to the energy given out when the two elements bond together to form water. If they're already water, that energy has already given out, and is unavailable. Water puts out fire because it stops fresh, available oxygen from reaching the fire."
] |
[
"Why can't I burn the ashes in my fireplace, if they're made of logs and oxygen? If logs and oxygen are flammable, how come when mixed they become fire retardant?",
"Why can't I burn the exhaust from my car, if it's made of gasoline and oxygen?",
"Why can't I burn [anything that has already been burned], if..."
] |
[
"Also, water needs a lot of energy to be heated up. If you put water on a fire, water pumps this energy out of the fire."
] |
[
"Ages 1 to 4 are very important for brain development but yet most people can't recall anything from that time period. Why don't we remember our earliest memories?"
] |
[
false
] |
I know the brain is rewiring a lot of neurological pathways to determine the most effective route, but what stops us from remembering our early years?
|
[
"It’s not that we forget our earliest years, it’s that we don’t form memories in the first place. The term for this is infantile “amnesia”, but this is not actually a form of amnesia — that would require forgetting. As infants grow into toddlers, their brains grow fantastically quickly. So much so, that any pathways that are deemed unimportant/weak are “pruned”. Pruning is the technical term actually. By age three, pruning calms down to the point where toddlers can start forming the memories they’ll remember for possibly the rest of their lives. However, usually the very earliest memories are traumatic or notable in some way. Pruning continues for some time into childhood. Maybe age 4. ",
"Edit: this has gotten more traction than I anticipated, and I have to clarify: when I say “we don’t form memories in the first place” what I’m saying is that we form memories that we will NOT be able to RECALL after our brains grow and pruning occurs. Toddlers can remember things, but, as we’ve all experienced, they forget an exceptional amount of their day-to-day experiences. As another user pointed out, toddlers actually are learning a metric ton of stuff (motor, language, etc.). ",
"Edit 2: another user pointed out that it is the delayed development of the hippocampus (learning/memory/encoding center) that contributes to infantile amnesia. "
] |
[
"One of my degrees is child development, and this is a great answer. Simple so anyone can understand and still spot on. "
] |
[
"What you are taking about is autobiographical memory. Infants easily form other types of memories, including procedural memory (eg learning to walk), and semantic memory (learning what things are). Infantile amnesia is limited to autobiographical memories. There are lots of ideas as to why this is. One is a lack of self awareness - the child hasn't yet learned that they are an individual and that there are other individuals. The second is language development. Autobiographical memory is often descriptive, eg. \"I went to the store \". Encoding this memory may rely on language skills that have not yet developed. These are all related to the underlying neurophysiological development."
] |
[
"Why is dineutron unstable?"
] |
[
false
] |
Edit to explain my question in more detail: Well I guess I should be more detailed in my question and that's my fault. Is there any theory that predicts why deuterium is stable but not dineutron? Is there some mathematical explanation from the strong force that explains why dineutron decays, and for that matter why free neutrons are unstable? Or is it just an empirically observed fact with out backing from theory?
|
[
"Yes, modern atomic theory can explain this quite nicely.",
"Deuterium is a proton and neutron forming the nucleus. Why is this stable? Why doesn't the neutron decay and just pop off?",
"Well to fully explain this you need to know about binding energy or packing fraction. Nuclear fusion as seen in stars is a process which liberates energy, it has to be otherwise we wouldn't be alive.",
"Where does this energy come from? Well when hydrogen fuses (over several steps) to form He-4 the mass of the He-4 is actually less than if you add up the masses of the individual free particles. (E=mc",
" )",
"One atom of deuterium is actually only ~99.88% of the mass of one proton + one neutron. Actually you end up with a difference of 1.7130 MeV/c",
" in mass or roughly 3.4 electrons (coincidence) worth of mass difference.",
"For decay to happen, the resulting product of 2 protons would have to be lower in energy than the original state. As He-2 can't exist, you essentially can't decay uphill. H-2 is a stable happy isotope."
] |
[
"Well I guess I should be more detailed in my question and that's my fault. Is there any theory that predicts why deuterium is stable but not dineutron? Is there some mathematical explanation from the strong force that explains why dineutron decays, and for that matter why free neutrons are unstable? Or is it just an empirically observed fact with out backing from theory?"
] |
[
"This paper",
" places the binding energy between two neutrons to be around 70 keV. This is woefully smaller in magnitude than the change in energy done through beta decay.",
"However, this is about as good as I could find. A couple papers list binding energies of dineutron at ~3 MeV hypothetically in the early moments of the big bang where the magnitude of the strong force might have been larger.",
"Oddly enough, a binding energy of ~3 MeV would place it right at the boarder between the liberation due to double beta decay.",
"However, even then, why wouldn't our hypothetical dineutron single beta decay transmuting the material to deuterium?",
"Paper of primordial dineutrons",
"EDIT: This paper places the binding energy of dineutrons as 210 keV",
"EDIT: Original paper which the paper in my first paragraph cites, claims they may exist, but only in the presence of nuclei rich atoms and may partake in reactions",
"EDIT: This paper claims the existance of 0.3 MeV bound a dineutron present in Li-11, but only as a three body problem."
] |
[
"What natural things cause wildfires, besides lightning and volcanoes and meteorite impacts?"
] |
[
false
] |
Before people started using fire, what caused wildfires besides the 3 mentioned above? Also, any guestimates of how frequent each cause was or how much burned due to each of these?
|
[
"In at least ",
"one rare instance,",
" a landslide uncovered shale with high concentrations of pyrite. Oxidation of the pyrite generated enough heat to cause low-grade coal to burn.",
"American Geophysical Union",
" notes on the landslide.",
"Highly recommended on the subject: ",
"Tending Fire,",
" by Pyne."
] |
[
"Also, large piles of decaying vegetation can combust from the heat of their own decomposition. This is why it's unsafe to fill a barn with bales of moist hay."
] |
[
"Except for the ones you have already given, one that would come to my mind is hot weather. If you have really hot and dry weather, parts of some plants like pines and equivalent trees which contain terpenes and aromatic oils can inflame themselves, when they are hot and dry enough. Another way can be oil and gas sources which can also inflame themselves when hot or under high pressure. ",
"But i have no idea in which frequence any of them could occur. It certainly has to do with climatic and geographic circumstances. You won't have much thunderstorms in a desert and no pine woods at the equator. "
] |
[
"How exactly did the initial Chicago Pile nuclear reaction work?"
] |
[
false
] |
It seems, from my reading of the , that upon removing the control rods, the uranium atoms started absorbing the free neutrons and fissioning. How then, did they keep the pile from going supercritical (just the rods?), how did they determine the energy was being released, and where did the released energy end up? Also, how did they not totally irradiate themselves? If anyone has a better explanation, I'd be appreciative.
|
[
"I'm going to talk about reactors in general here.",
"When the control rods are inserted, they absorb the majority of the neutrons and cause the reactor to be subcritical (non-self-sustaining).",
"When you remove the control rods, less neutrons are absorbed, and the number of neutrons detected in the reactor increases. We call this \"Sub-Critical Multiplication\". The reactor is not yet self-sustaining, however because neutrons aren't getting absorbed as often, more neutrons will be in the reactor. By plotting the detected neutron counts as you increase sub-critical multiplication, an estimation of the critical position can be made. This allows you to have a good idea of when the reactor will go critical.",
"Criticality in a nuclear reactor is identified when you have three things. First, neutron count rate is increasing. Second, the time it takes for the count rate to double is constant. Third, no control rod motion is in effect. When all three of those are observed the reactor is slightly super-critical, or increasing count rate. Super-critical is not bad, and all large power reactors go supercritical for around 20-30 minutes during startup to reach heating power.",
"As the neutron count rate increases, the number of fissions occurring also increases. More fissions means more heat. At low power levels, even small amounts of heat being added to the core will cause its temperature to rise. Any increase in fuel temperature will result in a reduction in fissions occurring due to the doppler effect (also known as the Fuel Temperature Coefficient). ",
"So the sequence of events here. The core goes slightly super-critical. The neutron count rate increases exponentially. The fuel starts to heat up a little bit. The increase in heating results in the fuel doing a poorer job at absorbing neutrons. The core passively returns to exactly critical, at a higher power level.",
"You can determine energy is being released using thermocouples. You also know energy is being released based on the neutron counts. If your neutron counts are below 1 million, you probably don't have enough energy for it to be noticible. When you get to a neutron flux around 10",
" you will definitely be seeing noticeable heating effects.",
"Now the next few parts are my guess:",
"Where did the energy end up. Likely it was removed through heat radiative emission and conduction. There was likely airflow paths through the core providing a natural convection heat removal method as well. Heat was transferred to the surroundings.",
"How weren't they irradiated? ",
" low power levels and very low quantities of fission products. The radiation emitted by a reactor is proportional to the power level and directly related to the amount of waste products the reactor has inside of its fuel. Because they were doing primarily low power testing, the radiation fields involved were very low.",
"I hope this helps.",
"edit: There was no shielding. Just low power levels/low fission product concentrations."
] |
[
"In a power reactor, prompt critical is avoided by design conditions. It's not impossible though. For example, during control rod ejection/drop events it is possible to have localized prompt criticality leading to the destruction of a small section of nuclear fuel. This is a postulated event however, and usually requires multiple failures and/or human errors to occur. ",
"Generally, in a power reactor, due to the large delayed neutron fraction and the reactivity coefficients in the core, you are either going to get some type of flux/rate automatic scram well before a prompt condition or you are going to have natural effects like heating or boiling prevent prompt criticality. If you somehow got to that condition in a light water reactor, all the water around the fuel would flash to steam, resulting in a loss of moderation and shutting the reactor down (also likely damaging the vessel leading to a LOCA). ",
"Another important thing to note, is that prompt critical isn't some discrete cutoff spot in the core's reactivity profile. A lot of operations training states that once your core's reactivitiy reaches the delayed neutron fraction, you are prompt, and the core will rapidly destroy itself. However that is based off of the period equation which uses an estimation which is only valid for reactivities near k = 1, and is not valid at conditions where prompt critical could occur. Instead, the reactor period equation begins to exhibit an ever increasing rate of change as you get closer to prompt critical, which provides much needed time for your neutron monitoring systems to detect the condition and trip the reactor.",
"NukeFacts",
" covers this topic in pretty good detail. Any derivation of the reactor period equation would also show that an assumption is made where a natural log term is being set equal to reactivity for reactivities near 0 (k near 1)."
] |
[
"There was actually no radiation shielding at all, CP-1 ran at 1/2 watt max power. "
] |
[
"What would happen if you touched lava?"
] |
[
false
] |
It seems like a obvious answer, but would your arm be incinerated? Or would you be killed instantly? But the kind of lava that would be found just after an eruption. EDIT: Thanks for the awesome replies, and the interesting facts about lava!
|
[
"Aloha from the Big Island of Hawaii...",
"My house is only 15 miles from the active flow and we play with lava and cook in lava (I've posted on this in the past).",
"We use special kevlar/glass gloves (labsafety.com) that allow us to directly contact lava for about 20 to 30 seconds. This lets us do cool things like pick lava up off the ground (a surface flow can actually be lifted like thick taffy). Another really fun thing is to find a 'firehose' (this is a breakout where the lava is fluid enough to flow like water from a hose) and let the lava fall through our hands and fingers.",
"Again, you can only handle this for about 20 to 30 seconds before the heat breaches the gloves.",
"An active flow can be walked on as long as the surface of the flow has stopped moving for about 10 minutes (even if the underside is still liquid). At this point the surface is around 600 to 800 F (we always are equipped with pyrometers). You can't physically walk over anything hotter than that because your body won't let you.",
"You can make lots of great things with lava. We take kitchen whisks and spin them in the lava to make a big blob - fun for the tourists. Cooking in lava involves wrapping a chicken or pork loin in banana or Ti leaves (about 10 layers) and then covering it with lava (leave a steam hole) and let it sit for 45 minutes then crack it open with a shovel.",
"I've been at the bench (where lava enters the ocean) during a bench collapse (where several unstable acres of new land collapses in seconds into the ocean) and have had lava shoot up over me and some fall on my jacket. Unless the lava is VERY fluid (which is fairly rare) it tends to bounce off things. In this case it hit my jacket, left a nice burn mark but bounced off.",
"In a similar way - tourists are always surprised when they throw a rock onto an active surface flow that the rock simply bounces on the surface - again, it is more like taffy than water.",
"Here are some pics...",
"Me pulling a aircraft cable out of a skylight (a hole in the ground with magma pouring in a lava tube below): ",
"http://i.imgur.com/gKL9Q.jpg",
"Kitchen whisk with lava (you can also see the glove we are using): ",
"http://i.imgur.com/jivoD.jpg",
"My gloved hand after I just picked up some lava - some is stuck to my thumb: ",
"http://i.imgur.com/vlbCP.jpg",
"Preparing pork loin for cooking in lava: ",
"http://i.imgur.com/L5y2W.jpg",
"Getting shovel full of lava: ",
"http://i.imgur.com/XTaMJ.jpg",
"Letting a tourist get a thrill covering the pork loin with the lava: ",
"http://i.imgur.com/70a3D.jpg",
"TL;DR: Playing with lava fun... don't touch with bare skin!"
] |
[
"Actually it is not 'cool' in terms of the lava temperature. In the photo where I am pulling the aircraft cable out of the lava tube - that tube was about 40 ft deep and 2/3 full of magma roaring like a liquid river. We are trying to get a sample from the tube (very hard to do). In that case the magma was over 2000 F.",
"In the pictures with the shovel - again, that is LIQUID Lava - that is well over 1500 F. Same as with the whisk. In order to get the lava onto the whisk it has to be a fairly liquid flow - we generally look for a breakout and poke a stick or shovel into it to get the liquid lava to pour back to the surface - at that point it is fairly liquid and can be 'whisked'. Once we remove it from the lava it takes the rock on the whisk about 45 minutes to cool to the point where you can touch it.",
"Even in the one with my gloved hand with the lava stuck on it. If you look at the ground to the left you can see where I had pulled the lava up off the ground and it is settling back down - that lava was over 1000F.",
"The only lava that is 'cooler' is lava that has hardened for at least 10 minutes on the surface. Anything below that is at least 1000 F or higher.",
"We carry pyrometers and IR goggles when we do the lava field - this lets us map out the heat and find tubes, etc. We are specifically looking for the hottest and most liquid lava we can find.",
"The maximum temperature for Magma is around 2500 F."
] |
[
"Awesome reply.",
"Though I do feel compelled to add in a \"don't try this at home, kiddies\" for those who might ever encounter lava in the wild. Your lava is very cool -- barely glowing, and about to solidify. Lava can be a lot hotter, and a lot more unpredictable, and is best avoided unless you really know what you're doing.",
"OK, safety lecture over. Have fun playing with lava!"
] |
[
"Does photon decay ?"
] |
[
false
] |
Hi, I was wondering recently if photon decay. Usually, structures are able to decay (such as molecule, atom, protons, etc...). More the structure hold energy faster is the decay process (again typically with heavy atoms) and can stabilise (iron-55 ?). So a heavy photon (very short wave lenght, high frequency and then high energy) could it decay into two other photons ?
|
[
"As far as we know, they do not decay, nor does anything without mass.",
" they do decay, by having a very small mass (experiments show it must be below 10",
" kg if it exists) and decaying into the lightest neutrino (which would have to have a smaller mass in this scenario), they would have to have a lifetime of around three years in their rest frame to be consistent with the thermal spectrum of the cosmic microwave background, but because they are going so fast this would be dilated to like a quadrillion years."
] |
[
"I'm on my phone but look up j. heeck 'how stable is the photon'"
] |
[
"Do you have a link to any papers on this? I'm interested in reading about the limits imposed by the CMB thermal spectrum."
] |
[
"There are notes between B and C or C and C#, right?"
] |
[
false
] | null |
[
"Not in the chromatic scale, no. The chromatic scale is what you find on all pianos and guitars, for example.",
"However, notes between them can be played, for example by bending on a guitar. The resulting notes are dissonant with the other notes in the scale though."
] |
[
"There is an infinite number of notes between B and C, and C and C#. However, if you want to get technical I guess there'd be as much divisions between two chromatic notes as there are divisions of the Plank's length. So for example, between B1 (61.74 Hz; wavelength of 5,5884 m.) and C2 (65.41 Hz; wavelength of 5,2747 m.), there would be about 1.94x10",
" different notes. However, how many notes you would be able to tell apart is a different story. It is said that we can notice a 3% difference in pitches of around 100 Hz, while we can tell apart two notes differing from only 0.5% at around 2 000 Hz (reference : ",
"http://www.indiana.edu/~emusic/acoustics/pitch.htm",
" ). "
] |
[
"432 tuning",
" is a chromatic scale that uses frequencies between the normal 440 chromatic scale. ",
"Here is a paper",
" talking about non-harmonic wind chimes. Also, there are ",
"enharmonic music scales",
"."
] |
[
"Can someone please explain the criticisms of the Myers/Briggs personality test?"
] |
[
false
] |
[deleted]
|
[
"The test is not accepted at all. It's popular in the business world and I'd say we keep it there. ",
"There's no scientist that would take that test seriously. It was developed by people with limited understanding of psychology, based on theories founded on absolutely no proof. ",
"Furthermore there isn't any scientific foundation for the test. There are other personality tests which are accepted and based on actual research. ",
"However, for the purpose of HR-management or getting to know someone in the business world, it's probably a decent method. Because you still answer some questions and of course it will tell something about you.",
"\nYou shouldn't however draw conclusions from it. For example: ''O we really need a ESTJ type for our ''program developer'' position, and sorry, you're a ESFJ so you're clearly incompatible with our business.''"
] |
[
"A key observation I have from taking the test online several times is that the questions may reflect temporary mood or life situation, rather than actual personality. For example, questions such as:",
"I have always been a notably extroverted person. But at my stage of life, long past the \"partying years\", with a family and other outside-work commitments, I'd much rather read a book than be the Social Queen in a new office. It doesn't mean I'm suddenly introverted - ",
" - just that my preferences have changed. ",
"Preferences=/=personality. It doesn't mean I can't be assertive and outgoing in the workplace, dazzlingly sociable and communicative at a networking function, or confident and happy to make a presentation to a few hundred people. Or that I'm not very happy to attend and socialise at select social events.",
"Another issue is that it involves false dichotomies. For example:",
"This ",
". If I have a tried and tested method for a routine task, that's efficient and reliable, I'll almost certainly use it. If it's a new task, and I can perceive a way to complete it that seems better than the one suggested, I'll experiment.",
"Here's one that's really absurd:",
"I imagine this is trying to detect a \"shy wallflower\" versus \"The Life & Soul of the Party\". The reality is that I often steer myself near to the side of a room so I'm nearest to the buffet, and I often drag the people I'm with along with me so we can all feast while we chat ;)"
] |
[
"It's about as effective as a Buzzfeed quiz or knowing your Hogwarts house. Sure, maybe it tells you something useful about yourself based on your responses to the questions...but it's not exactly reliable.",
"If you re-take the test later on, there's a good chance you'll get a different result. And it isn't clear that the test result has any predictive value in terms of...anything. (How well you'll do at certain jobs, whether you'd be a good leader, how well you do in relationships, etc)."
] |
[
"Had the chemistry or production of gasoline changed enough over the decades that gasoline from 1945 would not work in a modern car (new from 1945, not very old gas)?"
] |
[
false
] | null |
[
"Actually, much of the gasoline between 1920 and 1945 was leaded, meaning it included a compound called tetraethyl lead to boost octane performance.",
"Modern cars can not handle leaded gasoline and will die or foul up in response to it. Only in aviation fuel is the compound even legal anymore, and only some middle eastern countries even use leaded gas in their cars.",
"Even if your car was old enough to use leaded gas, it is phased out because of the toxicity on the human body, increasing lead levels and leading to an increase in crime rates and health problems."
] |
[
"In fact, the old gas pumps would not work in a modern car. During the transition from leaded gas to unleaded, when both were sold, the unleaded nozzles were made smaller as was the opening on the car. This prevented leaded gas from being put into an unleaded car. "
] |
[
"Leaded gas lasted well into the 1970's, maybe even 1980's.",
"\nUnleaded gas was introduced in 1974, and for a long time gas stations sold both unleaded and leaded."
] |
[
"How do you optimize a rocket or space vehicle liftoff?"
] |
[
false
] |
I was thinking about the problem of lifting a space craft from the earth's surface to space and for some reason only just now realized that there's an optimization problem here (I think) and I'm curious what the model looks like for this and how it's performed. Suppose I want to lift a mass to an orbit of some altitude, I can compute what energy the system has to have once it's in orbit; what's the best way to generate that? Suppose you launch with low power; then you spend more time in a higher gravitational field which means you're counteracting gravity for a longer period of time. I assume that minimizing the integral over time of the force of gravity on the vehicle would save you fuel, which saves weight which saves you fuel... (I assume this converges) Suppose you launch with very high power; you accelerate quickly out of the gravitational force but then air resistance becomes an issue and with too much velocity any additional increase in velocity requires O(x^3) power. At some point it's not efficient to add more power because you'll need a lot more fuel. In both of these cases the higher you are the lower those forces are; so maybe a launch system which has a lot more power early and cuts the power later is useful (SRBs are useful here). Now, if you build a rocket or launch system with more engines you incur more weight that you're trying to move, also bad. Along with this is the weight of the fuel which goes down over time. The more fuel you have also starts to incur more non-usable weight for the fuel tanks. I presume that the effects of wind resistance and gravity create non-linearities in the system since the forces acting at time t are functions of altitude. Is there a model that's used to get started and then iterated on once certain discrete parameters are figured in (that is, you can't add 0.5 engines)? Edit: I’m familiar with both KSP and the rocket equation. The problem of designing the system seems like a optimizing a function described by a non-linear differential equation which I assume probably doesn’t have an analytical solution. I’m curious about what things get modeled and which don’t and how this is actually done in practice.
|
[
"A lot of simulations. There is essentially nothing that only has advantages or disadvantages, so you need to consider tons of options.",
"If you have a given rocket design and a fixed mission: Launch at full power - this is a very wasteful part of the flight and you want to gain speed as soon as possible. Acceleration will (almost) always be low because the rocket is still full of propellant. Tilt a bit to the side and follow an approximate ",
"gravity turn",
". Throttle down before reaching the maximum aerodynamic pressure if needed for safety. Typically this is only a pretty short period.",
"Some more things to consider, in addition to what you mentioned:"
] |
[
"A faster ascent does take less energy - not because the gravity is stronger at lower altitude (the difference is pretty minor) but because the rocket spends more time fighting gravity. Think about the extreme case where the rocket is barely moving up - it will use up all fuel before it gets to any meaningful altitude. It's kind of like walking up a downward escalator - you have to expend energy just to stay in one place, and it's actually easier to run up quickly. Once you're at the top (in orbit), you can stay there without using any energy. ",
"But there are limits on how quickly a rocket can accelerate, such as:"
] |
[
"Rockets launch at full power. The effect of air resistance comes into play for some, more fragile rockets which cannot withstand maximum frontal forces, so there is a point during ascend (maxQ), when engines are temporarily dialed back to reduce acceleration.",
"A few seconds later, the max power is restored in less dense atmosphere.",
"Why the let-off is stepped rather than gradual is a mystery to me, perhaps some optimization is available. Also relevant the path of the rocket - the more vertically it launches, the faster it clears the atmosphere, but then longer takes to gain lateral orbital speed."
] |
[
"Is there higher background radiation directly under the Aurora?"
] |
[
false
] |
If i'm not mistaken, earth's magnetic field deflect charged particles, and pushes them to the poles, creating the Auroras. Also if i'm not wrong, the background radiation can vary really highly from place to place, because it's affected by many variants. But is there any increase in the background radiation, if you stand right under the northern lights or the cosmic radiation level stay consistent?
|
[
"I actually just looked this up because of another recent post.\nThe short and skinny is that the aurora borealis ",
" be harmful to you but the rarity of such events is so low as to not be a concern.\nYour more immediate concern would be experiencing artic circle weather and temperatures."
] |
[
"From the ground, one generally cannot measure radiation from a geomagnetic storm above background levels. There's sufficient atmosphere to act as very effective shielding, even at the poles.",
"At altitude, however, you can receive a decent dose. A trans-polar flight (for example, New York to Shanghai) during a large geomagnetic storm is roughly equal to a few chest x-rays. Full PDF from the FAA showing dosage at a variety of altitudes and latitudes available ",
"here",
"."
] |
[
"VERY interesting! Thank you!"
] |
[
"How did/does a classical model of light (i.e., as waves) reconcile \"interference\" with Conservation of Energy?"
] |
[
false
] |
I understand that an interference pattern created by light doesn't violate Conservation of Energy because the overall intensity is the same as if there were not bands. But how can this be explained with a wave model as the dark bands (where waves "cancel" each other) would seem to say the energy from each wave just disappears at those spots? (Whereas in Quantum Mechanics, I assume you would say the photons just don't hit those spots, but all photons do hit somewhere. Which is also quite odd but at least consistent with energy conservation.)
|
[
"Whenever there is an interference pattern like this, where there are dark bands- there will also be extra bright bands. This is why the overall intensity stays the same. So, with interference, the bright parts are brighter than they would be without the interference. ",
"On a fun side note- this is different from how something like noise cancelling headphones work. It's not like the sound is minimized in your ears and then somewhere else the sound is really loud. Instead, noise cancelling headphones raise the DC value (the non oscillating part). Since sound waves are pressure waves, with NC headphones, there aren't \"waves\" anymore, instead just the air pressure without oscillation is raised. This is why NC headphones can make you feel \"stuffy.\""
] |
[
"The second part sounds wrong. A membrane driver as in headphones can't generate a \"DC pressure\".\nThe reason why NC headphones are not \"amplifying\" any sound outside the headphones is that the part where noise would be increased is simply inside the headphones (basically on the other side of the driver)"
] |
[
"I don't know deeply about nc headphones, but if it truly does cancel the incoming wave, it makes sense to me. The energy has to go somewhere, intuitively it would be randomly into temperature. Which basically is just an increase in the pressure (DC pressure). That being said, it should be a small increase, the energy in the sound I think is much less than the thermal energy of air. I wouldn't think we would be able to perceive it."
] |
[
"Question regarding Quantum entanglement"
] |
[
false
] |
I'm trying to get a grasp on the following scenario: Consider replacing our Sun with spaceship equally massive. There are two entangled particles, one on the Spaceship, one on the Earth. Say we are to measure spin of these particles. The Spaceship is set up so that If clockwise spin is measured, It will move to a different location at a relativistic speed so that Earth's orbit is significantly altered. If counterclockwise spin is measured, then Spaceship stays put. Spaceship is fully automatic (assume no room for error) and time of measurement is predetermined. My question is the following: If we measure counterclockwise spin on Earth (so we are sure that the Spaceship has moved), would we observe change in the Earth's orbit immediately after measurement or we would have to wait the usual 8 minutes for It to change? It seems to me that If we can have information on position of the Spaceship "immediately" so should nature. Thank you for explanation in advance.
|
[
"Let's change up your question a little bit. ",
"Assume we have a sun-sized spaceship which replaced the sun, and it was simply pre-determined that on \"March 13th, noon Greenwhich time, the space ship was going to move.\" Would you expect to feel the effects immediately or after 8 minutes? The correct answer is that since gravity propagates at the speed of light, you would feel the effect in 8 minutes. ",
"Now, with your scenario. You measure counterclockwise on Earth- you know what is going to happen on the spaceship. So you can say \"well, we're about to feel something in 8 minutes!\" but you still don't feel anything until then. ",
"So, you might be thinking \"information has traveled instantaneously\" but it really hasn't. While analogies of \"two balls, one red and one blue. I pick one and put it in a box and give it to you. I take the other one with me, we look at what ball we have at a predetermined time\" do not fully capture the details of quantum entanglement, for your scenario it truly is identical. The principle at play here is artificially delaying your choice is not the same as instantaneous information transfer. "
] |
[
"Here's the thing: unless I'm greatly misunderstanding you, the entanglement is actually irrelevant to your question. Imagine that instead of having two entangled particles with opposite spins, you have two sealed envelopes, one with a piece of paper in it that says \"clockwise\" and the other with a similar piece of paper that says \"counterclockwise.\" Shuffle them and send one to the spaceship and keep the other on Earth, and then at the predetermined time each party opens their envelope and uses the result written in it as you described. No entanglement is involved, but do you see how the situation is still essentially the same?",
"In any case, you would still have to wait 8 minutes to observe any changes on Earth. It doesn't matter that you know in advance what's going to happen. Sure, nature knows that the ship is going to move, but that doesn't mean that it magically transports the change in the gravitational field from the Sun to the Earth faster than it would get there otherwise."
] |
[
"So basically, I was trying to argue, that If I know something will happen, It will happen immediately. What a waste of space I am. Thank you for the answer though."
] |
[
"Is hypnotism a legitimate practice/is there any evidence?"
] |
[
false
] |
Does hypnotism hold up in double-blind studies, etc.? I personally have a hard time believing that the power of suggestion could be as strong of an influence as it's often made out to be.
|
[
"There are a number of studies looking at hypnotism as a psychosocial intervention to reduce pain, with somewhat varying results. ",
"J Vasc Interv Radiol. 2008",
"Procedural hypnosis including empathic attention reduces pain, anxiety, and medication use. Conversely, empathic approaches which provide an external focus of attention and do not enhance patients’ self-coping can result in more adverse events. ",
"J Clin Oncol. 2012 (meta-analysis, not specific to hypnosis)",
"Psychosocial interventions had medium-size effects on both pain severity and interference. ",
"Cochrane Database Syst Rev. 2012 (meta-analysis)",
"There is insufficient evidence to make judgements on whether or not hypnosis, biofeedback, sterile water injection, aromatherapy, TENS, or parenteral opioids are more effective than placebo or other interventions for pain management in labour. "
] |
[
"Everything I've read about studies on hypnosis all mention how difficult it is to perform a proper experiment due to the fact that hypnosis requires the patient to understand that they are being hypnotized and be willing to accept suggestions. And since that makes double-blind testing impossible, I guess it bothers me that a near fool proof method can't be used. A stubborn skeptical patient wouldn't be open enough to allow hypnosis and if you only selected test subjects that would be open to it, couldn't that suggest they already have a bias towards its validity and behave in a way to lend credibility towards it?"
] |
[
"Everything I've read about studies on hypnosis all mention how difficult it is to perform a proper experiment due to the fact that hypnosis requires the patient to understand that they are being hypnotized and be willing to accept suggestions. And since that makes double-blind testing impossible, I guess it bothers me that a near fool proof method can't be used. A stubborn skeptical patient wouldn't be open enough to allow hypnosis and if you only selected test subjects that would be open to it, couldn't that suggest they already have a bias towards its validity and behave in a way to lend credibility towards it?"
] |
[
"How fast does dawn travel across land?"
] |
[
false
] |
How quickly does light travel across land as the sun rises? Or the reverse, how quickly does night "fall" across land? Is it possible to literally chase it using any existing form of human transportation?
|
[
"Circumference of the Earth is about 40,000 km. It spins around once every 24 hours. ",
"At the equator the speed of dawn is 40,000 km / 24 hrs = 1667 km/h, or about 1036 mph. ",
"At the geographical poles, this speed approaches zero. "
] |
[
"And certain planes can easily travel faster than that. Also for the OP, the technical term for the night/day line of a planetary body is \"terminator.\""
] |
[
"It depends on your latitude. Slowly at the poles, quickly at the equator. This is because it has to move all the way around the width of the earth at the equator, but a shorter distance at the poles. Rockets can definitely go faster than this speed at the equator."
] |
[
"Would a gun fire in space? And if so, would the bullet travel forever?"
] |
[
false
] |
[deleted]
|
[
"Actually, gunpowder, like rocket fuel, contains an oxidizer. As long as the firing mechanism works, the gun will fire. I dont know about the oils or the metals, but assuming that everything else is in working order, the gun will fire."
] |
[
"Gunpowder, like rocket fuel, contains a nitrate based oxidizer built in. Assuming that the mechanism of the firearm will function in the cold of space, it will fire, and the bullet will go until it collides with something else."
] |
[
"It should. I'm not entirely sure if the firing mechanism in the bullet would work, but I'm, fairly certain it would.",
"The bullet would get launched out of the gun at it's usual fire speed, and the gun would go off in the opposite direction at some fraction of the bullet's speed dependent on the ratio of the masses. I.E",
"(mass of bullet / mass of gun) (velocity of bullet) = velocity of gun ",
"Both would travel until they struck something. And would gradually slow as they hit interstellar dust. Over an absolute IMMENSITY of time, given absolutely no interstellar dust, the bullet may stop due to collisions with quantum fluctuations in the vacuum."
] |
[
"Would a persons feeling towards a drug inhibit it’s ability to work, like a nocebo?"
] |
[
false
] |
Does a medicine or tablet. E.g. panadol, have a lesser effect on a person if they are sceptical about it. even though the drug works would the effect be felt less by the body depending on the persons feelings toward either the person who administered it or the drug itself. Also if this has been studied what would the name of the effect be or would it just be referred to as nocebo
|
[
"There was a research in Germany by a medical university where they looked at 31 empirical studies and found out that not only the nocebo effect exists (and it's called like that), but it's also causing an ethical dilemma for all the doctors and nurses. ",
"Why? Because if they inform patients as to the potential risks and negative side effects of a given treatment, the patients may believe they'll experience those harmful results and it could be a self-fulfilling prophecy, but if they don't tell it to their patients, they might get sued for malpractice for violating informed-consent laws."
] |
[
"Nocebo causes \"harm\" though, it doesn't refer to the drug simply becoming ineffective."
] |
[
"Because nocebo does not mean \"no effect\" like OP asked, but comes from \"nocere\", to harm.",
"I'm not saying your info was incorrect, I just wanted to clarify where the term comes from. Because the question was whether positive effects can be nullified, which has nothing to do with the (factual) nocebo-effect."
] |
[
"After prolonged exposure to SSRIs do the effects on the brain remain once the administration stops?"
] |
[
false
] |
To me more specific, by effects I don't mean positive behaviors that a patient might have acquired while in a non-depressive period. I mean actual alterations from the substances the SSRI pills have. From what I know, SSRI's have been linked with an increase in neurogenesis, and since neurogenesis itself seems to be a factor in depressive disorders, are there any reasons to believe that the brain might keep up the neurogenesis "positive rate" after the administration of SSRI have stopped? Or does the brain revert to its pre-SSRI state when it comes to creating new neurons and therefore be prone to mental disorders again?
|
[
"Agree with above comment. Some are shown to have a better long term outcome but the research is very very limited. The idea behind that thought is that once we can chemically alleviate our depression, we start doing things that make us happy like working out, having hobbies etc which in turn also helps alleviate depression and can be continued without medication. Some people (like me) will probably take an SSRI their whole life, and some might not"
] |
[
"For major depression, we don't have good evidence for ongoing benefit beyond the period when the drug is taken, as contrasted with cognitive-behavioral therapy and similar treatments which do see sustained benefit well after the course of therapy is done. Exactly how that correlates to whatever's happening at a cellular-molecular level is unclear. "
] |
[
"Could that mean that a person taking SSRI's can, along with cognitive-behavioral therapy or just by having their symptoms of depression alleviated, have certain (possibly new?) pathways in their brain reinforced after a long exposure to both these treatments? Kind of like creating new habits, e.g. having a different response to stress, a different regulation of their mood, etc? "
] |
[
"How would quantum computers change the field of cryptography?"
] |
[
false
] |
I know most modern encryption relies very heavily on factorization and that quantum computation would severely shorten the time necessary to solve factorization problems. If quantum computation is realized, what methods will likely replace factorization in encryption algorithms? Also,
|
[
"RSA would break. AES256 will remain strong. There are other public key cryptos that would still work."
] |
[
"You can't make that kind of comparison. It's fundementally a new model of computing. "
] |
[
"There's always ",
"quantum key distribution.",
" and one time pads. These would be completely unbreakable (unless our understanding of quantum mechanics is wrong), and interception of the key would be extremely difficult or impossible to do without detection.",
"The question, of course, is whether a practical system can be built along these lines. Considering the immense benefits, it's probably safe to say that a lot of government money is looking into it right now."
] |
[
"Would a Roman be able to digest today's food? How about a caveman?"
] |
[
false
] |
Or going even farther back, would Lucy have been able to digest the stuff we eat today?
|
[
"I don't see any reason why they wouldn't, the genetic varieties of plants have changed quite a bit but the fundamental nutrients are the same. It would be like us eating food in a foreign country, you can easily get a tummy ache but you won't starve. ",
"The bigger problem would be the pathogens and any bacteria in the food, as the diseases have changed dramatically over the centuries. Fatal infections are very possible and diarrhea is all but guaranteed. ",
"And the term \"caveman\" doesn't really apply to the majority of our ancestors, living in caves is mostly what Neanderthals did, and it is not yet clear how closely related we are to them. Neanderthals had a very different diet from our traditional ancestors, but apparently we are both of the same species. They ate much more meat than we do, up to 80% of their diet in some cases! "
] |
[
"Even chimps (and rats, for that matter) can eat human food. Actually the human digestive system doesn't look all that different from that of most other primates that don't eat a specialized diet."
] |
[
"Of course rats (and many other animals common to areas with large human populations) are heavily adapted to survive on nutrients available in a human-heavy environment. So, in a funny way, it makes more sense for rats and roaches to eat like us than for chimps."
] |
[
"Could our solar system ever move into a large area of dust?"
] |
[
false
] |
If so would it superheat our planet from all the particles burning up in our atmosphere?
|
[
"Even \"high density\" areas of space are very low density. There's no way it would be enough to noticeably affect our temperature or environment. Also keep in mind that these \"dust\" particles are much less massive than the dust we're used to - I think most of them have less than a thousand atoms."
] |
[
"I suppose our solar system could indeed move into a large area of dust. However even the most dense nebulae are still not particularly dense with particle densities of at max ",
"10",
" particles per cubic centimeter",
". Compare that to the 10",
" particles per cubic centimeter that the air we breathe consists of. Now I don't know if that would actually burn up our atmosphere, i don't think so, but I can't tell you with certainty. "
] |
[
"No, even if it was a million times more opaque we would be fine - the dimming effect with regular interstellar gas/dust is still small enough to hardly effect light coming from many stars, even ones millions of times farther from us than the Sun is. Even in the densest of nebulae you can still see through tens of billions of kilometers of space - the reason many are opaque is because they are several light years thick (one light year is about nine trillion kilometers or five trillion miles if I remember correctly)."
] |
[
"Does exposing yourself to cold climate regularly make you more tolerant/less likely to become ill due to it?"
] |
[
false
] |
I caught a friend of mine riding his bike with nothing but a t-shirt and shorts on while it was snowing. He's a pretty smart guy and a premed student who knows his stuff. His reason was that he wanted to build tolerance for cold weather so he wouldn't be so effected by it. I called bullshit, but would like to know from someone with more knowledge on the matter.
|
[
"This is true, but the key word there is regular. On a biological scale, an hour a day of exposure is not enough for the body to use the resources to make more fat. Making fat deposits is costly to a person on a regular diet, so the body won't do it unless it's necessary. When you go to your cabin and you are living and sleeping in the colder temperature, that is regular, almost constant exposure. It's the same as your body not ditching the fat it stores if you ride in your heated car for an hour a day despite spending more time in the cold."
] |
[
"It seems that one can acquire cold-resistance through repeated exposure.",
"From an ",
"article",
" entitled ",
" (Harrod et al, 2002):",
"It has long been known that humans and nonhumans acquire tolerance to environmental stressors that challenge the thermoregulatory system. In particular, tolerance to the hypothermic effects of cold stimuli has been examined extensively. In general, these studies demonstrate that while an initial cold exposure induces hypothermia (i.e., lower body temperature), repeated exposure to the same cold stimulus results in progressively less decline in body temperature.",
"In this article, they measured the activity of rats after exposure to cold. Rats who were exposed to cold every day acted exhibited normal activity (similar to noncooled rats) while rats cooled only once right where much less active."
] |
[
"I didn't read the whole thread but seems relevant. It's about people growing up in cold climate.",
"http://www.reddit.com/r/askscience/comments/11erzc/when_someone_grows_up_in_a_cold_weather_climate/"
] |
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