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[
"Alternators convert kinetic energy into electrical energy, where does the energy go when the circuit is broken?"
] |
[
false
] |
An alternator in a car is connected to a battery charging system : the spinny motion, magnets and copper, charges the battery, and some noise and heat is generated. A cable between the alternator and battery is cut : the battery does not charge. What happens to this generated energy? It can't be noise/heat/light. Energy can't be created or destroyed so where does this kinetic energy go?
|
[
"I highly recommend playing with a pair of ",
"hand crank generator toys",
" and trying it yourself. If you do the answer becomes obvious.",
"Power is force times velocity, or in this case torque times rotation rate.",
", you have to work hard to get it to spin. ",
", almost no force is required so no power is transformed from mechanical to electrical form.",
"Why? If current runs through the generator’s coils, they create a magnetic force that pulls on the spinning rotor trying to slow it down. This is true whether the current was created by an outside source or the generator itself.",
"The toys I linked to above have a lot to teach about energy. You can hook them together so one acts as a motor and one as a generator, you can measure the efficiency of energy transformation, you can compare mechanical and thermal energy… they’re great."
] |
[
"It's probably clearer to say an alternator USES kinetic energy to ",
" generate electrical energy rather than converts. The kinetic energy is still there... the part that doesn't get converted to heat energy by friction, anyway. When the circuit is broken, the alternator stops generating electrical energy from the kinetic.",
"(Edit- to say generate instead of create.)"
] |
[
"Hate to break it to you, but energy can both be created and destroyed.",
"It's actually a quantity called the Stress-Energy-Momentum Psuedotensor (some times called the Landau-Lifshitz psuedotensor) that is conserved across the entire universe. For most intents and purposes, it's ",
" similar to \"energy\" as we think of it.",
"Energy, as in the quantity that Joules describe, is only invariant on flat spacetime. Spacetime is locally flat where we live, so this holds functionally true. But over vast distances, like between remote corners of the universe, or near gravitational anomalies such as black holes, this quantity is not conserved.",
"edit: Noether's theorem can be used to find a lot of symmetries (aka invariances) and is likely one of the most critical mathematical tools used by modern theoretical physics."
] |
[
"If we are able to take pictures of deep space (Hubble telescope or observatories), why can't we take videos? Would these provide new information?"
] |
[
false
] |
Even if it wouldn't provide useful information, I still think it would be very interesting if not eye-opening to see these stars and galaxies rotate and move.
|
[
"Most celestial objects are so large that they would appear basically motionless in any videos we might take. Galaxies, for example, can take hundreds of millions of years to complete a single rotation, and nebula can be light years across. ",
"There are some still frames taken long periods apart where we can see some movement",
", but realtime videos wouldn't be of much interest. There are some cool videos of Saturn stitched together from Cassini pictures on YouTube you might be interested in.",
"EDIT: ",
"Here's",
" one of the Cassini videos which I think's really cool. It was built from completely raw footage, and it's worth noting that the specs throughout are glitches stemming from being broadcasted through a billion miles of space.",
"EDIT 2: ",
"Here's",
" a video of Jupiter's cloud bands, as taken from Voyager 1. As the description notes, each second roughly corresponds to a Jovian day, so yeah, way too slow to watch in real time."
] |
[
"There are two issues with getting video of celestial objects. The first, which others here have addressed, is that the time scales that these things move on are so long that you would not see anything. ",
"The second is that these pictures are often not pictures in the sense we often use the word. Instead, they are composites or amalgamations of really long exposures. For example, in order to get the necessary amount of light, the Hubble Deep Field took something like ",
"40 hour",
" exposures at different wavelengths which were then reassembled. So a real time video would just be dark."
] |
[
"Yeah, important point. You need absurdly long exposures to take pictures of dim things like nebulas and galaxies. From our point of view when looking up, the Andromeda galaxy has a width of something like 8 full moons, but it's far too dim for our eyes to see. Most every deep space object is like this."
] |
[
"How do the millions of neurons, and multiple parts of our brain form a singular consciousness?"
] |
[
false
] | null |
[
"I think I can clarify: you are asking the answer to the ",
"binding problem",
" and whoever answers it is a nobel prize winner for ",
". "
] |
[
"Very interesting, thanks! I just hope this problem is solved before I die.",
"By the way, you accidentally a bracket. "
] |
[
"I hope they solve it too!"
] |
[
"Is it possible to create a sustainable, but completely isolated underground city?"
] |
[
false
] | null |
[
"Your question is fairly open-ended, so is likely more appropriate for ",
"/r/AskScienceDiscussion",
". But I'll suggest some possible issues and their resolutions:",
"Obviously, you need to get oxygen and remove carbon dioxide somehow. Happily, there are a number of compounds that appear in the Earth that are capable of doing this - you can extract oxygen from water and use something such as lime to scrub carbon dioxide. The problem is that this requires large amounts of power. You could mine for that, or similar compounds - or synthesize it from other minerals.",
"Water is readily available under the surface if you're in the right place. There are large underground lakes and aquifers that you could use.",
"Energy is easy to get in the right locations, since geothermal gives a virtually unlimited source - but unless you're near somewhere that actually has such a source (such as Iceland or the Ring of Fire), this would be more problematic. On the other hand, you could use a modern technology such as fission, or wait a few decades and use the hydrogen from water for fusion. Obviously, coal would also work if it's available.",
"Food could be made, since you've got water and energy. If you've got a large enough space and sufficient dirt, you should be able to set up a farm.",
"So the short version is that if you're in the right place and you get very lucky, then possibly yes (provided you're capable of mining or extracting some local resources). "
] |
[
"Well, that really depends on the tools you have available to you. If there's an underground water source and you have artificial solar lamps to grow crops and plants for oxygen then I would say yes. You would need some type of power source though. If the underground area was large enough and there was access to coal or some other power source I don't see why it would be impossible."
] |
[
"Unless you like the taste of worms, there's not a whole lot of food underground "
] |
[
"Why didn't incredibly condensed portions of the universe form black holes after the Big Bang?"
] |
[
false
] |
I've looked at similar posts on this subreddit asking why the whole universe didn't collapse into a black hole after the Big Bang and the most common answer was to not look at the universe as a whole because it was different then than it is now. If portions of the universe that were comprised of atoms were still within the range of the Schwarzschild Radius, then why didn't massive black holes form? I have an extremely limited knowledge of advanced physics, so please provide links for a layman like me.
|
[
"This shouldn't matter though, right? Energy vs solid matter doesn't matter in terms of a black hole, as mentioned in another post about matter/antimatter collisions inside a black hole. I was under the (possibly mistaken) impression that if the density needed for a black hole was present a black hole would exist, even if that matter was totally converted to pure energy. "
] |
[
"https://en.wikipedia.org/wiki/Primordial_black_hole"
] |
[
"If either of you could link sources to your information, that would really clear things up for me."
] |
[
"Is there any material that absorbs all sound waves like vantablack does for light?"
] |
[
false
] |
Are soundproofing materials even able to be as effective as vantablack? I know that sound deadening foams and stuff exists but from what I've had experience with they only muffle it at best.
|
[
"Vantablack works by having tiny nanoscale structures that the light bounces around inside. ",
"Here's a picture",
" of some Vantablack as seen through an electron microscope. You can see that it's made up of stacks of tiny tubes. Light enters the material and scatters repeatedly off the tubes. The actual tube material itself is not super-absorptive, but the repeated scattering ensures that almost all the light is absorbed in the end.",
"A similar principle is used for sound waves in the design of anechoic chambers. The walls are made of sound-absorbing foam shaped into very angular structures, ",
"like this",
". Although the material itself is no more absorptive than ordinary sound insulation, the sound waves repeatedly bounce between multiple absorbing surfaces as they impact the wall, and almost all the sound ends up absorbed."
] |
[
"A couple pieces of information to tag on this:",
"return waves to their source."
] |
[
"To be sure, vantablack is is incredible, however vantablack doesn't absorb 100% of light, it absorbs close to 100%, but not quite. it actually absorbs approximately 99.965% of light by bouncing the visible spectrum of electromagnetic radiation between the carbon nanotube arrays until eventually absorbed and thus creates heat.",
"Now let's look at the question shall we? Sorry for the tangent haha.",
"I cannot think of any microscopic material that absorbs as much acoustic waves, this is because of the size of acoustic waves vs electromagnetic waves in the visible spectrum. the visible spectrum is normally between 390 nm and 700 nm. 1 nm=0.000000001 meters. Acoustic waves meanwhile typically have a wavelength between 17 mm and 17m. As you can see audible wavelengths to the human ear have a FAR greater range than visible light. in fact it is well over 10,000,000,000 times a bigger range than the visible light spectrum.",
"Because of this a microscopic material can absorb sound but to get anywhere close to the amount of vantablack we need to look at a macroscopic scale, such as the room holding the world record. Created by Microsoft as seen at ",
"https://www.youtube.com/watch?v=Cyqc_4ixV80",
"\nthis room allows an ambient noise of -20.6 dB(A) while the brownian motion of air molecules(the sound that air molecules make by bouncing around and moving in a still environment) is at about -23 dB(A) The human ear can't hear anything usually below 0 dB(A) So as far as humans are concerned, that chamber produces absolute silence. If you are standing in that room and someone walks to the wall and talks to it, you would likely hear very very little if you are directly behind them a few meters away. ",
"As for a microscopic material that does this, we have no such thing mostly due to the size and range of acoustic waves.",
"Hope that helps."
] |
[
"Is there a numerical method to calculate the sine/cosine of a given number?"
] |
[
false
] |
Given a number x, is there an algorithm to calculate/approximate sin(x)? If so, could you explain how you arrive at this algorithm?
|
[
"If you have a not-shitty function, then when you zoom in enough onto a graph of a function, it'll look like a straight line. If we know a value of the function in this zoomed in space, then we can figure out the slope of this line and write it down. This is a ",
"Linear Approximation of the Graph",
". If you've taken Calculus, then the slope of this line is the derivative at a point.",
"For instance, if we're near x=0, then ",
"sin(x) is approximately equal to the line y=x",
".",
"But graphs have curves in them and lines don't, so this loses it's accuracy really quickly. Luckily, there is an easy type of function with a curve in it: Quadratic Polynomials. It turns out that, just as there is a line that approximates the graph, there is also a Quadratic that approximates the graph. But because Quadratics are more flexible, these approximations are better. ",
"For instance, if we're near x=0, then ",
"cos(x) is approximately equal to y=1-x",
"/2",
".",
"But why stop there? Quadratics can only turn in one direction, whereas something line sin(x) and cos(x) will change directions. So we can get ",
" approximations as well. These are degree three polynomials that approximate the function. ",
"For instance, if we're near x=0, then ",
"sin(x) is approximately equal to y=x-x",
"/6",
".",
"Again, there's no reason to stop. We can find polynomials that approximate sin(x) and cos(x) to an arbitrarily high degree. If we could go on forever, if we could compute an \"Infinite Degree Polynomial\", then we would actually find that this hypothetical infinite degree polynomial is equal to sin(x) everywhere. But, practically, we can't compute these, so we have to stop somewhere and just accept the approximated value. ",
"For instance, here are the first few approximations for ",
"Sin(x)",
" and ",
"Cos(x)",
". Note that as we increase the degree, the more the polynomial looks like sin or cos.",
"These kinds of objects are called ",
"Taylor Series",
" and if you can take derivatives of a function, then you can do this for that function. The idea of Taylor Series is that functions can be complicated and we may not be able to calculate them, but polynomials are easy and we can calculate values of polynomials, no problem. So why not try to find an infinite sequence of polynomials that will eventually infinitely approximate the function?",
"It should be mentioned that this is not how calculators calculate sin and cos, that's a more sophisticated method called the ",
"CORDIC Algorithm",
"."
] |
[
"If you have a not-shitty function",
"Going forward I will be using this terminology in formal correspondence. "
] |
[
"The actual series definition of the sine function is sin(x)=x-((x",
" )/3!)+((x",
" )/5!)-((x",
" )/7!)... (Continues in that pattern forever.)",
"Also Looks like ",
"this.",
"The series definition of the cosine function is cos(x)=1-((x",
" )/2!)+((x",
" )/4!)-((x",
" )/6!)... (Continues in that pattern forever.)",
"Also looks like ",
"this.",
"Most calculators only use so many terms to calculate the sine or cosine, but they end up being rather accurate approximations.",
"BTW, these definitions are calculated by the theory of Taylor Series, so if you want to learn more, ",
"here's the link.",
"EDIT: Fixed some formatting.",
"Edit #2: Added some images."
] |
[
"If energy neither can be created nor destroyed wouldn't that mean that the universe must be eternal and lack both a beginning and an end?"
] |
[
false
] |
[deleted]
|
[
"There's something called the zero-energy universe hypothesis. It postulates the net energy of the universe is zero, which means you can create one from essentially nothing. A beginning would be when \"nothing\" was split into positive energy (e.g., matter) and negative energy (e.g., gravity).",
"Currently it's assumed there really isn't an end. There will just be a point when the universe no longer has enough energy concentrated in one place to do anything interesting. The universe is expanding so the concentration of \"stuff\" is getting less and less dense."
] |
[
"Correct me if I'm wrong, but this is generally referred to as the \"heat-death\" of the universe? As in there are no interactions between particles and what-have-you to generate heat?"
] |
[
"Correct me if I'm wrong, but this is generally referred to as the \"heat-death\" of the universe?",
"Yep!"
] |
[
"What are some of the most interesting and pressing challenges still facing humankind?"
] |
[
false
] |
I have the opportunity for a full ride scholarship to any science, engineering, or math PhD program I can get into. During my undergrad years I was rather partial to probability theory/stochastic processes, but I'm not bound to it (although delving deeper into non-financial applications of it would probably pique my interest). What are some of the most interesting and pressing challenges facing humankind today that would be interesting to delve into? If you're passionate about your field or career please make a case for it here! What's the nature of the larger challenge you're trying to address? What attracts you to your field? What do you enjoy most about it on a daily basis? What do you dislike about it? What's the nature of your employment? Would you get into it with the benefit of hindsight? Thanks in advance!
|
[
"Eliminating or drastically slowing the human rate of aging may allow us individuals to stick around longer and help solve other problems, so that's a pretty good candidate to start with."
] |
[
"In my opinion, these are the most pressing challenges, and they are all related:",
"Energy, especially reliance on oil",
"Access to clean water",
"Family planning / overpopulation",
"Nuclear non-proliferation",
"EDIT: I don't work on any of these problems. I do medical research and epidemiology in the developing world."
] |
[
"How fast would we run out of room? I think another solution would be increasing the efficiency with which humans use their resources, allowing us to build more/better shelters and accommodate more humans. Although, I also think some sort of reasonable limit should be imposed on the number of children a person can sire."
] |
[
"EM waves can be generated from a perturbation of an Electric field. Does this mean that an electron wizzing about in the electron cloud emits light?"
] |
[
false
] | null |
[
"In the classical interpretation, yes. However this means that the atomic structure would be unstable, so clearly that is incorrect, it was realising this that lead to the understanding of quantum mechanics. We now understand that the electron is not in one specific place within the cloud, and therefore cannot be 'moving' in the classical sense. ",
"Energy also works differently in the quantum relm, the electron can only have set energy levels. The only way for it to emit a photon is to drop to a lower energy level, and the change in energy is released as a photon. "
] |
[
"What is a free electron density?"
] |
[
"The electron in the 'electron cloud' would not emit light autonomously. Cautioning that the idea of an 'electron cloud' isn't the most precise way to discuss electrons. The 'cloud' is just a practical way to visualize the idea that electrons are described by probability densities in space of where that electron might be. The 'cloud' describes every point in space where you MIGHT locate the electron. But it's not really a cloud in the precise way. ",
"Light will be emitted when an electron goes from a state of higher energy to one of lower energy--think of it as transitioning clouds (multiple clouds are required to describe multiple electronic states). The delta is the energy of the photon that is emitted. If by 'electron cloud' you mean an electron at a specific energy level (orbital, or what have you), then no, it wouldn't emit light because the electron isn't losing energy--it's always at the same energy level."
] |
[
"Once you locate a new asteroid and identify its trajectory, do you then have to keep revisiting it and confirming this data in case it was influenced by as-yet-undiscovered bodies?"
] |
[
false
] | null |
[
"Once you take a long enough observation of an asteroid to get an accurate measure of its trajectory, you know basically where it's going. There are no undiscovered bodies in the inner solar system strong enough to make very significant deflections to an asteroid's orbit. However, when we're doing things like predicting the location of an asteroid decades or centuries in the future (",
"we know of some that are going to come close to Earth in the coming decades",
"), you usually need to take observations at a later date to really precisely nail down the trajectory, since even a tiny fraction of a degree of measurement uncertainty can make a huge difference in space. "
] |
[
"Just to add a little personal experience to this:",
"I did this as an undergrad research project: Imaging asteroids with 'known' trajectories, determining their brightness and position with respect to the background star field, and submitting the coordinates to the ",
"Minor Planet Center",
" (which keeps databases of such things). If you think about how this works, the asteroids trajectories are determined only by observations of when someone has a telescope pointed at it, which is a tiny fraction of its orbit, and any uncertainty will propagate over time. So you need to revisit the object occasionally to add more data points, and even better that they're data points on a different night.",
"Nowadays there are large scale efforts to catalog asteroids and their orbits, like ",
"Catalina",
", ",
"Pan-STARRS",
", and the upcoming ",
"LSST",
"."
] |
[
"and even better that they're data points on a different night.",
"I do not know any statistics, but I am interested by your implication that there would actually be some use to taking multiple data points on the same night (even though, I assume, the object would not have made any meaningful motion). The implication being that you can improve your measurement of a stellar object, even one that is essentially fixed, by taking repeated measurements of it and -- um, averaging them or statistickizing them or something? "
] |
[
"As a black hole collapses, how does the resulting Hawking radiation affect its event horizon?"
] |
[
false
] | null |
[
"As Hawking radiation takes away mass from the black hole, the event horizon must necessarily decrease. As the event horizon decreases, the black hole gets hotter. As it gets hotter, it radiates more. Eventually the whole thing just evaporates away"
] |
[
"Heat death does not necessarily mean cold. It means everything is at the same temperature, so no work can be done by a thermodynamic process. Since almost ecerythng is a heat engine that requires a temperature gradient to function, that would be the end of most physical processes as we know them."
] |
[
"No those were raving lunatics or tabloid reporters.",
"Apparently it has created quark-gluon plasma, which is apparently the densest matter that is NOT a black hole.",
"http://news.nationalgeographic.com/news/2011/05/110524-densest-matter-created-lhc-alice-big-bang-space-science/"
] |
[
"Could you use carbon dating to find out how long a specific creature was alive?"
] |
[
false
] |
I know carbon dating can be used on fossils, but say a dead sea turtle washed up on shore. What would be an efficient way to find out how long it was living for?
|
[
"Carbon-14 dating is based on the premise that this radioactive isotope of carbon-12 is present as a specific portion of all the carbon present in living creatures. Once a creature dies, the carbon-14 content of its tissues is set and begins to convert to nitrogen-14 over thousands and thousands of years at a set rate. In other words, no. Radiocarbon dating is only useful for determining when something died."
] |
[
"carbon-14 content of its tissues is set and begins to convert to carbon-12 over thousands and thousands of years at a set rat",
"This is not correct. 14-carbon decays (by beta decay) to 14-nitrogen, not 12-carbon. However, SoBad is correct in saying you can only date the time since death."
] |
[
"With turtles and humans, you can always look at our skeletons and get a good idea of how old we were when we died. When scientists examine human remains, I know they look at our teeth for more accurate estimates."
] |
[
"Are different antibiotics better for specific tasks than others?"
] |
[
false
] |
After having a small problem recently, the doctor gave me an antibiotic that I had never heard of before. It got me wondering whether different antibiotics are more effective than others in different situations. Are there classes of antibiotics that are best for one task over another? How careful do doctors need to be about prescribing the correct antibiotic for a specific type of infection?
|
[
"I answered part of your question in a reply, but I felt it needed further clarification.",
"The answer to your first question is \"it depends\". Microbiologists/pharmacologists do studies in which certain antibiotics are used for certain types of infection/prophylaxis. ",
"We typically base therapy on what type of infection it is, where it is, what we think/know are the offending bacteria, the patient's current status (allergies, renal function, blood count, vitals, etc), what the antibiogram of the institution looks like, and what the culture/susceptibility tests show us (comparative to data from CLSI). Based on clinical condition, we would generally start a patient on broad-spectrum antibiotics and then narrow the spectrum as we get the culture and susceptibility tests back (in another words: make nice with your micro department). We also tend to follow guidelines from the Infectious Disease Society of America and Society of Infectious Disease Pharmacists - however, we tailor the guidelines to the patient's needs. ",
"Another example other than the one I used is something like a urinary tract infection. In terms of outpatient treatment, the patient could be given nitrofurantoin, ciprofloxain, or bactrim (note: there are other choices). The choice would be what the patient is allergic to, cost, ease of dosing, \"will the patient actually take it?\", does the patient have recurrent/treatment resistant UTI, \"is the patient symptomatic?\", colonization, and \"should we treat it?\". We wouldn't use certain antibiotics because certain ones don't cover the bacteria that you would \"normally\" see in a UTI (like aztreonam) or they're much too broad-spectrum (like meropenem)",
"Inpatient status, we could use IV antibiotics like ceftriaxone or ciprofloxacin. The same questions are asked, but the clinical picture would be a lot more complicated if they're in the hospital.",
"Physicians outside of the ED need to be quite careful about ordering certain antibiotics. In the ED, more broad-spectrum antibiotics are used due to emergence of the situation and unknown cultures and sensitivities. What we want to do is to clear up the infection, make sure that the patient physically looks better, make sure that the signs and symptoms are clear, and make sure that the patient makes it out of the hospital. What we don’t want to do is select the wrong antibiotic and treat the wrong infection. We also want to make sure that the patient tolerates the antibiotic and have the antibiotics managed so as to not harm the patient (kidney injury being a prominent one with antibiotics like vancomycin or your aminoglycosides). You can have infectious disease physicians consulted for difficult cases and can have infectious disease pharmacists consulted for antibiotic management. ",
"I know this is missing a lot of information, but it's a general background on what you can do in terms of antibiotics.",
"Edit: Crap...I forgot - pharmacokinetics/dynamics of certain antibiotics are used to dose and predict levels/concentrations."
] |
[
"Yep - different classes (as mentioned above) have different mechanisms of action and differ slightly per drug.",
"For example treatment for MRSA (broad generalization here, non-community acquired) - our lovely Gram positive nuke: vancomycin. Mechanistically, vancomycin will bind in the cell wall (specifically the d-ala-d-ala moiety) and inhibit cell wall synthesis.",
"On the other hand, we have linezolid, also used for treating MRSA: this mechanistically prevents translation of RNA, essentially disrupting protein synthesis.",
"And then we have daptomycin. It causes depolarization of the cell wall, disrupting DNA/RNA synthesis.",
"Also to clarify - certain antibiotics are bacteriostatic (inhibit growth), and some of them are bactericidal (kill). Then again, there are some that become bactericidal based on concentration used.",
"Edit: Sources for antimicrobial mechanisms are from memory/LexiComp."
] |
[
"There are many many classes and subclasses of bacteria. Some antibiotics are broad-spectrum and target most anything, others are narrow spectrum and target only specific families. Different antibiotics have different potencies and side-effect risks. Sometimes the choice of antibiotics is somewhat arbitrary, other times a very specific drug is warranted. It all depends on the situation.",
"Questions like this is what pharmacists are for (not to mention the prescribing doctor)"
] |
[
"Why can a sun-synchronous orbit only exist around an oblate body?"
] |
[
false
] | null |
[
"There are 2 special cases where the oblateness of the body can be ignored to meet the technical definition of a sun-synchronous orbit. A ",
"Lissajous Orbit",
" about ",
"L1",
" and ",
"L2"
] |
[
"The equatorial bulge causes inclined orbits to precess. When the satellite is overflying the equator, the gravitational force points exactly downwards; but when it's at the maximum latitude it can reach with its inclination, the bulge pulls perpendicularly to its velocity. It can be modeled ",
"like this",
", it's obviously oversimplified but not wrong. This causes precession.",
"Source for the above: ",
" by Donald D. Mueller and Jerry E. White, ISBN 0-486-60061-0.",
"Sun-synchronous orbits are just carefully calculated to make the precession rate match the length of the year. This way as the Earth moves along its orbit, the satellite's orbital plane rotates and compensates, pointing always to the Sun.",
"Edit: added source and linked a relevant image I found googling."
] |
[
"Why would the angle of the orbit need to precedes to maintain sun-synchronicity?"
] |
[
"If I were to somehow hover 300 feet in the air, could I be struck by lightning since I'm not grounded? Could it shock me? Could it kill me?"
] |
[
false
] |
[deleted]
|
[
"You can get struck by lightning in the air. Your body will be more electrically conductive than the surrounding air and thus electricity will take the path of least resistance through your body. Planes sometimes get struck by lightning in midair. ",
"You'd experience some sort of injury. Birds don't get electrocuted on wires because the path of least resistance for the electricity is to continue flowing along the wire, not up and through a bird. "
] |
[
"Airplanes also have a metal skin that is fairly conductive, shunting most of the current flow around the outside. This is not true for humans. "
] |
[
"Airplanes are being hit by lightning all the time. Just google \n'airplane' + 'lightning'. "
] |
[
"What causes the pain in your side when you run/jog? What exactly is it and can be done to prevent it from occurring?"
] |
[
false
] | null |
[
"A side stitch can be caused by a number of different things. The most likely cause is friction between the diaphragm and internal organs. It can also be caused by friction between organs within the abdominal cavity. Because the sensation of pain within the abdomen is referred to the exterior, sometimes in places that are not directly over the organ, it can be hard to determine the exact cause of abdominal pain. For instance, irritation of the diaphragm can present as pain along the lower border of the ribs, but it can also present as shoulder pain."
] |
[
"Check out the references for several suggestions to prevent it. ",
"http://en.wikipedia.org/wiki/Side_stitch"
] |
[
"That sounds like typical muscle pain from anaerobic exercise. I hardly think that's what side stitches are. Are your sides even working anaerobically when you run?"
] |
[
"Is it possible to attach a satellite to a comet or other traveling item in space to hitch a ride to somewhere in the galaxy?"
] |
[
false
] |
[deleted]
|
[
"If you can softly land your space probe on an object that is leaving the solar system, then you have already achieved enough speed to escape the solar system anyway, so the activity would be pointless."
] |
[
"Couldn't you put the satellite on an intercept trajectory at one of the 'slower' points of the comet's orbit, get captured by its gravity, land, then use it's velocity to catapult yourself out of the solar system?"
] |
[
"The gravity of basically any asteroid would be much too small to be used as a gravity assist. There are quite a few big objects in the solar system - like planets - that could achieve the same effect.",
"Remember - in space, you don't need to give it gas to keep going. You only need to get going and coast the rest of the distance."
] |
[
"In historical,natural climate change, what caused temperature to drop after a while? Will this happen again with human caused climate change?"
] |
[
false
] |
So historically, the earths climate has gone trough various cycles of hot periods and cold periods. I know that this time is different, but I was wondering what exactly caused the climate to cool again after a hot period? I know that there are 'breakaway' climate change triggers and was wondering how those were reserved in the ancient past.
|
[
"The norm during the last several million years have been periodic oscillations in climate between glacial and interglacial periods that are primarily dictated by changes in the amount of solar radiation. As a basic primer, this page from ",
"NOAA",
" does a good job in covering the major points. The short version is that the fluctuations in solar radiation are related to changes in various aspects of Earth's orbit, i.e. ",
"Milankovitch cyles",
". These periodic changes in orbital mechanics both change the total amount of solar radiation reaching Earth and the distribution of that solar radiation (in time and space, e.g. when does the northern hemisphere get the most solar radiation, etc), which lead to changes in climate. There are a lot of feedbacks that modify (some amplify and some damp) this underlying driver. In an unperturbed state, changes in concentration of CO2 are one of these feedbacks, i.e. the transition between glacial (cold) and interglacial (hot) periods are initiated by changes in solar radiation but are then are reinforced by changes in CO2. As highlighted by the NOAA page for example, a small amount of warming (caused by an increase in solar radiation) causes a release of CO2 from the ocean to the atmosphere, which causes more warming, etc. In the case of cooling, i.e. the transition from interglacial to glacial, again, the underlying driver is a decrease in incoming solar radiation (from changes in orbital dynamics), but this reinforced by various feedbacks, like storage of CO2 by the deep ocean as temperatures cooled and the ",
"ice-albedo feedback",
", i.e. cooling causes ice sheets to form, which reflect more sunlight, which causes more cooling, etc. In addition to the NOAA page, the wiki page on ",
"quaternary glaciations",
" provides a discussion of mechanisms that drive cooling.",
"In the modern, the input of CO2 (and other greenhouse gases) by human activity has swamped out a lot of these natural feedbacks (and the underlying orbital driver). Some work has suggested that without human influence we would expect the current interglacial period to be abnormally long and would not experience another glacial period for ",
"~50,000 years",
" (non-paywalled link through ",
"ResearchGate",
"). The argument here is again basically orbital mechanics, suggesting that several of the different cycles (as highlighted in the links on Milankovitch cycles) would interact to keep Earth warm for longer than normal. When the human CO2 contribution is added in, it's been suggested that the Earth will not experience ",
"another glacial period for 100,000 years",
", i.e. our modification of the climate either causes us to skip the next glacial or pushes it back another 50,000 years depending on your perspective. The implication here is that the various modifications we've made to the atmosphere have broken (or significantly modified) a lot of the feedbacks that would otherwise correct the climate back towards a more natural cycling."
] |
[
"The colloquial use of \"theory\" is actually a hypothesis.",
"When the word \"theory\" is used in a science context, it basically means a scientifically accepted model."
] |
[
"the oceans are a sink not a source for co2, Over geological time, most of the world's carbon (more than 90 percent) has settled into the ",
" *",
"https://earthobservatory.nasa.gov/features/OceanClimate/ocean-atmos_chem.php",
" The ",
" takes up ",
" through photosynthesis by plant-like organisms (phytoplankton), as well as by simple chemistry: ",
" dissolves in water ",
"https://earthobservatory.nasa.gov/features/OceanCarbon"
] |
[
"Every time I have a scratchy or sore throat, I am told to gargle salt water. Why?"
] |
[
false
] |
How does gargling salt water help your sore throat? Or does it even help?
|
[
"Believe it or not, this is actually a treatment commonly used for the great-great-grandaddy of all chest colds, cystic fibrosis. In CF, people get thick, sticky mucus because of a defect in their ability to secrete water into the airways. ",
"Normally, you secrete mucins (the proteins that make snot snotty) along with signals that tell the cells lining your airway to secrete enough water to dilute the mucins to a usable viscosity and elasticity. Think flour and water; add just enough water to the flour and you have a thin gruel. Not enough water and you have bread dough. People with CF, however, lack an important bit of the machinery of that whole process, so they don't push out enough water. As a result the mucus is much thicker and, like bread dough, is much harder to pour. ",
"One treatment is hypertonic saline; a high concentration sodium chloride solution that is put in an inhaler and breathed in as an aerosol. The aerosol particles sit on top of the mucus and this sets up an osmotic gradient that pulls water up from the epithelial cells to dilute the mucus. Bread dough becomes gruel again, for a short time.",
"Gargling salt water makes a poor-mans aerosol; bubbling air up through the water makes little salt water droplets that can float down into your airway. The osmotic gradient that forms when they land acts to pull water out into the airway. This water mixes with the mucus that may have solidifed somewhat around some irritant (be it bacterial, botanical, or whatever) and helps you flush it away."
] |
[
"Yes, this is a common remedy found in many cultures to soothe sore throats - it is also recommended after the removal of wisdom teeth as a way to help prevent infection and soothe pain in the area. ",
"The idea is that the salt creates a osmotic gradient. It draws the water out of the bacterial cells effectively killing them. It does not kill all the bacteria in your throat. Salt does have preserving properties and has been used in curing meats (preserving meats). \"Removal of water and addition of salt to meat creates a solute-rich environment where osmotic pressure draws water out of microorganisms, retarding their growth\" the idea is similar for your sore throat. Others suggest it soothes the tissue in your throat and improves blood flow to your inflamed tissues but I can't find primary sources for that. Not all sore throats are equal and some do require antibiotics, others may be caused by a virus but for this you need to consult your doctor",
"It also may be worth noting that ",
"saline solutions",
" are effectively just salt and water. \"Saline solutions are available in various formulations for different purposes\". It is used for a variety of purposes including:",
"\"Saline is also used in I.V. therapy, intravenously supplying extra water to a dehydrated patient or supplying the daily water and salt needs\"",
"\"Saline is often used to flush wounds and skin abrasions. Normal saline will not burn or sting when applied.\"",
"\"Rinsing contact lenses or in eye drop solutions\"",
"\"Often used to clean a new piercing\"",
"Disclaimer: You are not meant to swallow the salt-water mixture. "
] |
[
"Awesome! Thanks! My mother (I won't give away her age) is always telling me gargle salt water and I never believe her because she always says \"it's what my father told me to do.\" I guess I should trust her, since she is a doctor.."
] |
[
"Why exactly do we become tolerant to drugs?"
] |
[
false
] |
Is there any benefit in it? Any evolutionary advantage that has in some point of our history proved useful? I can't think of a reason why it'd be good to develop tolerance to any drug (in the broad sense of the word).
|
[
"Can you be a little more specific with what you mean by \"tolerance\"? For example, your body could be come \"tolerant\" to illicit drugs, requiring higher doses to achieve the same affect. Or your body could become \"tolerant\" to some antibiotic, requiring more or different drugs to treat an infection. Both might be considered examples of \"tolerance\", but they work by very different mechanisms."
] |
[
"In regards to biological tolerance, in short: bacteria can become resistant to antibiotics because they are adaptive and all cells are different. Likely, the bacteria that survived the first wave of antibiotics possess some gene to cause them to be immune. Since these resistant ones survive they replicate their beneficial genes.",
"In regards to chemical tolerance (such as with drug use), in short: Your body is ever-changing and very adaptive. Your body \"learns\" to react more quickly to changes of a certain chemical due to drug use."
] |
[
"This ability would have evolved millions of years before 'drugs', therapeutic or recreational, were invented. Basically drugs are toxins. So I'm taking tolerance to mean the ability to withstand more of a toxin (e.g. alcohol) when exposed to it many times. This happens because our liver produces more of the enzymes which break down a drug the more we are exposed to it. ",
"Out in the savannah it certainly would be a good thing to be less and less affected by a toxin you encountered. For example: you're super hungry, so your tribe eats a root that nobody has eaten before. You all get sick, but only some of you die. You're still really hungry so you're forced to eat it again, and some of the surviving tribe members get less sick than before. They keep eating it, while the others starve. Eventually it no longer makes the remaining tribe members sick. Congratulations! You just survived, where your peers who could not develop a resistance to the toxins in the root are dead of hunger/toxin. This is a potential evolutionary purpose of toxins.\nnote: I'm a pathology major and I also did a few anthropology subjects "
] |
[
"Inspired by Shitty Ask Science: How long *is* a year on the Sun?"
] |
[
false
] |
The sun isn't actually at the exact center of the solar system after all. It (like everything else) revolves around the common center of mass. How long does that take? A quick Google search gets me the galactic revolution period of the Sun, but not its "solar" period. Now that I think about it, is the earth's period actually 365.24 days, or is that affected by the sun's revolution?
|
[
"http://en.wikipedia.org/wiki/Barycentric_coordinates_(astronomy)",
"This is known as the solar system's barycenter and it is constantly in motion and dependent on what vectors all the planets and other masses in the solar system are pulling on the sun. "
] |
[
"Yeah, so there must an orbital mode at the same period as the year of each object in the solar system. This undoubedtly means that the sun's orbit around the barycenter is not ",
", which means it will not repeat the same pattern twice, and therefore there is no well-defined \"year\". ",
"Playing around with Celestia and comparing to the map in that wikipedia article, it seems that Jupiter and Saturn dominate the barycenter motion, which makes sense. The tight loop from 1945 to 1955 corresponds roughly to an orbit of Jupiter. Then Jupiter and Saturn happened to roughly align, so you get the big loop of 1955-1968. Then another small loop, then a big loop the next time they line up. You can see how this gets a bit chaotic."
] |
[
"I literally said that that is not what I'm looking for in the question."
] |
[
"Hypothetically: If our galaxy (all the planets and the sun) had somehow been shot across the universe, would we be able to tell?"
] |
[
false
] |
Referring to about blackholes. If I'm not mistaken theres one at our galaxy's center, what would happen if that was involved? I think I've gotten what I'm trying to ask across, help scientists of reddit. I should also say I meant to put the follow for the title. Would we be able to tell ?
|
[
"You must understand that galaxies are absolutely enormous. Any collision would take millions and millions of years to complete. We probably wouldn't notice anything significant here on earth.",
"If our galaxy was, in fact, suddenly moving in a different direction very quickly, we would begin to notice that local galaxies aren't in their correct positions. Based on how they look to us, we would be able to figure out where we are going and how fast. ",
"The Andromeda galaxy, M31, is ",
"heading towards us",
" at 301 km/s. We are eventually going to collide, but don't hold your breath! It won't happen for a very long time."
] |
[
"Gotcha, but let's expand on that real quick. Let's say we've been flying through space for a while and it got to the point that M31 is actually getting close. If different galaxy's blackholes were getting close to each others event horizon that would trigger massive acceleration of space-time in that area and would obviously stretch the space time, but let's say us humans were still alive, would we be able to witness the stretching of space/time with our bare eyes if we were close enough? (If that is hard to read, ELI5= If we threw a ball towards a black hole, would it visibly change/distort if near it?)"
] |
[
"You can see space-time stretching whenever you look at the sun.",
"If that doesn't explode your mind, then I don't know what will. But really, astronomers measured stars' positions near the sun during a solar eclipse and they noticed measurable differences in the stars' positions. This is because of the space-time stretching that comes from general relativity.",
"\"Normal\" people (not astronomers) would probably not notice anything significant. One exception might be that article you mention where the black holes come very close. That interaction might be visible to people on earth, but not in a space-time stretching sense, but in a \"it looks like there are 2 suns in the sky, and one of them is where the center of the galaxy is\".... Please note that I haven't done the math to see how bright this would be, but I'm fairly certain that if this happened to our galaxy, we would see at least SOME brightness from this black hole merger.",
"I urge you to look at the ",
"cool animations",
" on the wikipedia page about black holes. ",
"Especially this animation",
". Something like that would take many many years to happen, so it wouldn't be really noticeable by most. "
] |
[
"What are the ripples next to the atoms in the movie 'A boy and his atom'? (link in description)"
] |
[
false
] |
[deleted]
|
[
"The CO molecules are being placed on a copper crystal to make that movie. In a metal, the electrons are free to move around. So placing the CO molecule on the copper perturbs the electron density a bit and makes the periodic ripples. ",
"If you line up the CO atoms in a circle, you can get the ripples from each atom to add constructively. The same research team made a ",
"\"quantum corral\"",
" this way a while back."
] |
[
"IBM used a scanning tunnelling microsope to view the surface of their substrate making each frame of the film. The microscope detects current tunnelling of the free electrons from the substrate into the tip of the probe, so regions with more tunnelled current correspond to places where there is a localised charge (here, that's an atomic nucleus). That gives us atomic-level resolution, so we can \"see\" the individual atoms.",
"The ripples around the atoms are manifestations of the wave-like nature of everything at this level. The atom is localised in the place we see it most clearly, but its electromagnetic effects have stronger and weaker regions in the area surrounding it too. When there are lots of atoms close together, those ripples interfere with each other and create the straight-ish regions you can see too.",
"Where there are \"no\" atoms, you might be seeing effects of the underlying substrate. The clear atoms are protrusions from an otherwise very pure surface, but there is a regular periodic lattice of atoms one layer underneath which causes signals too. The microscope isn't \"focussed\" on that layer (the tip is too far away), though, so that periodic structure isn't very visible, except in regions where there's no stronger signal obscuring it."
] |
[
"That seems odd, couldn't you indefinitely keep adding concentric circles (like an onion) to produce a bigger and bigger electron density in the center?"
] |
[
"Why does a ball bounce higher the more air pressure it has?"
] |
[
false
] | null |
[
"Distortion of the material of the surface of the ball absorbs energy as it bends and rebounds. Higher pressure reduces the movement of the surface and allows more energy to go into the bounce.",
"There are additional gains depending on the material of the ball, for example if the material is somewhat elastic, then pre-stressing or pre-stretching the material keeps the tension forces closer to the impact area, which more efficiently converts the momentum."
] |
[
"Yes, it's friction internally, much like how car tires get hot while driving."
] |
[
"Where does the energy from elastic collision go? Heat?"
] |
[
"why \"Steam\" is the driving force of most of the power plants for more than 150 years? Does no other fluid has capability to replace it?"
] |
[
false
] | null |
[
"Don't underestimate the benefit of it being cheap, clean, readily available and well understood. Another fluid would have to have significant technical advantages over it before making the switch would be worthwhile. "
] |
[
"Fuel and heat energy is the driving force. Steam or whatever medium used is just a method of transferring that heat. Water has the highest latent heat value (stores most heat energy) of its kind. There are \"closed circuit\" gas turbines that use air as a working fluid."
] |
[
"This is the answer. Water has a huge specific heat capacity (the amount of energy required to increase its temperature - second only to ammonia) as well as a huge latent heat values (the energy required to change its state between solid/liquid/gas).",
"Superheated steam is therefore a great medium to transfer energy from one system to another."
] |
[
"Why do hamsters become flat when extremely relaxed? Does this occur in other rodents as well?"
] |
[
false
] | null |
[
"Similar to how your cat can flatten out when laying on its back, or stomach. The arms and legs splay out and that brings all the associated fur and skin with them. Gravity does the rest.",
"This question can be broken down into a few more complicated questions requiring more specific answers. But they can be generalized:"
] |
[
"Wow! Thank you for taking the time to type such a long and detailed answer!",
"What would happen if the human shoulder is structured like that of rodents'? Would it be more prone to injuries such as sprains? Why didn't we evolve that way?",
"Once again thank you so much! I learn something new every day."
] |
[
"We would likely not be able to do much of the stuff we do now, weight bearing. It works for a small quadruped to have a shoulder that is basically suspended within muscles and having no bony joints, because the relative strain on the should is so much less. The largest mammal without a clavicle is a whale, and it doesn't have a mobile shoulder at all; the strain on the shoulder is much less."
] |
[
"What study is this?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"listed in our wiki!",
"You can find the basic answer with a google / wiki search. Please start there and come back with a more specific question.",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"Try ",
"/r/AskScienceDiscussion",
" perhaps?"
] |
[
"Which sub would be appropriate? ",
"The last one seems most appropriate, but isn't it just for physical objects? ",
"I already posted in tip of my tongue, but I thought this sub would be more knowledgeable about this sort of thing. "
] |
[
"Why does Euler's sum of powers conjecture hold for the case where k=3 but not when k=4 or k=5? Does it hold true for k=6?"
] |
[
false
] |
From what I understand, the Conjecture itself was disproved in 1966 by finding a counterexample where 27 + 84 + 110 + 133 = 144 (case where k=5). It was also proven that there are infinite solutions for k=4 (1986, Noam Elkies). The smallest example for k=4 is 95800 + 217519 + 414560 = 422481 A few questions: 1) Which branch of mathematics specializes in understanding the relationships of this question? 2) Why is it not possible for k=3, but possible for 4 and 5? 3) Are there infinite solutions for k=5? 4) Is there any theorem that attempts to find what values of k are possible and which are not. If k can be 4 and 5, is it most likely k can be >= 6?
|
[
"OP probably meant solutions for a,b,c,d,e which have no common divisor."
] |
[
"1.) Number Theory, in particular ",
"Diophantine Equations",
" and ",
"Algebraic Geometry",
". (Sometimes called ",
"Diophantine Geometry",
")",
"2.) The case k=3 is equivalent to Fermat's Last Theorem when the power is 3. So why does Fermat's Last Theorem hold for this particular case? This actually has to do with the arithmetic of a slightly larger collection of numbers called the ",
"Eisenstein Integers",
". These are the normal integers, but we're allows to use a \"Cube Root of 1\", that is a number w, not equal to 1, so that w",
"=1. Usually, w=e",
". This is a slightly larger number system and it has it's own arithmetic and primes. It turns out that if there is an integer solution to x",
"+y",
"=z",
", then you can show that there is a prime in the Eisenstein Integers that divides z an infinite number of times. Which is obviously nonsense. ",
"Why is it possible for k=4 & 5? For k=4, some interesting things happen. The counterexample is derived from the arithmetic of an even larger object than the Eisenstein Integers: ",
"Elliptic Curves",
". Through careful manipulation, we can relate the k=4 equation a",
"+b",
"+c",
"=d",
" to the equation of an elliptic curve. Given a solution to the equation of the associated Elliptic Curve, we can find a new solution to the k=4 case. Now, we can define a kind of addition on Elliptic Curves, as just a way to combine two points into a new one. So if we can find one solution, we can add it to itself to get a new solution and we can keep on adding to get infinitely many solutions. ",
"It should be noted that the proof of Fermat's Last Theorem is based in properties of Elliptic Curves.",
"The k=5 case was done by brute force on a computer, so there is no hidden arithmetic object yet. My guess is that there is an object associated to this case and the arithmetic of this object determines the solutions. But there are a lot of algebraic objects that we can do arithmetic with, Eisenstein Integers would be a dimension 1 flat object, Elliptic Curves would be a dimension 1 object with more complicated geometry ( they're kind of like a torus), so there are many more dimensions and geometries to explore for possible candidates. But it is hard, for sure. ",
"3.) There could or there could not be infinitely many solutions to the k=5 case. It all depends on the arithmetic of the associated object. Some points in Elliptic Curves are cyclic, they start to repeat themselves after you add it to itself too many times, in this case there would only be finitely many solutions. As far as I can tell, we got lucky in the k=4 case. ",
"4.) I think that we know way too little to make a conjecture about which k the conjecture would be true for. It seems reasonable to say that it is false for all k>3, but the only reason we would say it is because we have counterexamples for ",
"k=4,5,7,8",
". But many were obtained by computer, so we don't really have a great understanding of the arithmetic machinery governing these equations. Maybe it is true for all multiples of 3? Maybe it just becomes true after k=423987? Who knows? We need to look under the hood with much better tools in order to figure it out."
] |
[
"To follow up, I'm assuming people have used computer time to try and find a case for k=6. I'm assuming that computers today could brute force testing of very high values. ",
"If someone discovered a case where k=6 has a solution, would it be interesting enough to get noticed? Would it have any further application?"
] |
[
"In most models of the solar system, the planets are all show on the same flat plane - are they?"
] |
[
false
] |
to be more specific, we see that the planets all seem to be on a roughly flat slope going out from the sun in a straight line. My question is, are any of the planets 'above' or 'below' earth relative to our position and the sun? Most documentaries about the solar system seem to reinforce this, but I'm not sure if this is done for cinematography or that's really the way it is. Related to this, wouldn't various objects (comets, etc) have altered some of these paths to a greater extent over the millions/billions of years our solar system has existed? (I'll apologize if this question has been asked, or seems ... dumb :) )
|
[
"There is a reason for this - when planets form there is usually a larger structure influencing the patterns. For instance, the dust planes of most proto systems we've seen tend to follow the Milky Way plane. I am not sure if we have seen this happen in other galaxies yet (they are kinda far...) - but it figures to follow the pattern.",
"As the dust in the galaxy has this flat shape and the dust in the young solar systems have the same shape - the planets tend to form within the shape of the dust. You get an alignment.",
"This is also why most things rotate and revolve in the same direction. The general motion of the system of the Milky Way is one direction (not sure if clockwise or counter). The star follows that, the dust follows it, the forming planets follow it, etc etc."
] |
[
"Conservation of angular momentum writ large."
] |
[
"They are almost all co-planar, the highest inclination is from Mercury, at ~7 degrees. All the inclinations of the planets are listed here: ",
"http://en.wikipedia.org/wiki/Orbital_inclination",
"Most objects like comets are too small to alter the paths of planets significantly."
] |
[
"I have a HUGE maple tree in my backyard. It towers over our three story house. What measurements/data would I need for someone to give me a good guess about it's age?"
] |
[
false
] |
It makes delicious maple syrup too!
|
[
"I'm not a scientist but I can answer this.",
"Find someone with a friend/relative who works in the forestry industry/education/government etc and borrow their core sampler.",
"You basically drill a core sample from the center of the tree and count the rings. If the tree is really big, you might not be able to do it this way. :/"
] |
[
"Cool, thanks!",
"Edit: Wait, I'm in askscience, right?"
] |
[
"Cool, thanks!",
"Edit: Wait, I'm in askscience, right?"
] |
[
"What do the dot product/the tensor product of two vectors represent geometrically?"
] |
[
false
] |
So the cross product isn't too hard to understand conceptually, since there's an actual geometric representation for what it is (if a x b = c, then c is perpendicular to a and b and has a magnitude equal to the area of the parallelogram made by a and b (E: that goes in the direction according to the right-hand rule)). But what about the dot/tensor product? I know how to do them, but what exactly do they represent geometrically?
|
[
"The dot product of ",
" and ",
" is |",
"||",
"|cos(θ), where θ is the angle between ",
" and ",
".",
"The tensor product of ",
" and ",
" is a bit more complicated. This is also called the outer product of ",
" and ",
". If we represent ",
" as a column vector, then the outer product ",
" ⊗ ",
" is the matrix ",
". Note that (",
" ⊗ ",
")",
" = (",
")",
", which is just a multiple of the fixed vector ",
". Hence ",
" ⊗ ",
" is a rank-1 linear mapping from ",
" to ",
", which means the image is one-dimensional. Its image is just the span of the vector ",
", i.e., the line through the origin containing the vector ",
". So ",
" ⊗ ",
" is a projection (although it is not necessarily an orthogonal projection). The transformation ",
" ⊗ ",
" generally projects a vector ",
" onto the line spanned by ",
" and then multiplies it by some scalar (that depends on ",
").",
"Also, for the cross product, your description is not enough to uniquely define the cross product since there are two possible vectors with the two properties you have described. You must also declare that the direction of ",
" x ",
" is determined by the right-hand rule. This means that if ",
" and ",
" are linearly independent, then the ordered basis (",
", ",
", ",
" x ",
") is right-handed, i.e., the determinant of the matrix whose columns are ",
", ",
", and ",
" x ",
" is positive."
] |
[
"Short answer for dot products is: how close they are to pointing in the same direction.",
"Dot product will be zero if two vectors are perpendicular (orthogonal), increasingly positive if the vectors are going in the same direction, and increasingly negative if they are pointing in opposite directions.",
"If you use unit vectors (with length equal to one), the max on a dot product will be one if the vectors point in the exact same direction and the minimum will be negative one if they point in exact opposite directions. That makes finding the angle between them pretty easy: it's the arccosine of the dot product.",
"(if you use vectors bigger than one, their size will factor into the dot product as well, and you can get really big outcomes from large vectors, then not be able to arccos them because domain.)"
] |
[
"The dot product of A and B is the length of A times the amount of B that points in A's direction, or vice versa."
] |
[
"If clouds and fog are essentially the same thing, then why doesn't fog produce spontaneous thunder and lightning?"
] |
[
false
] | null |
[
"Difference in potential is what allows electricity to flow, fog essentially is at the same potential as the ground it covers. Any difference it might generate quickly dissipates to ground, in the case of clouds they are very high and to bridge the difference over an air gap they can build quite a charge before it can dissipate. ",
"http://www.weatherquestions.com/What_causes_lightning.htm"
] |
[
"Fog is a type of cloud, but most clouds do not produce lightning.",
"For a cloud to produce lighting, the component droplets of the cloud have to acquire electric charges and to accumulate with similarly charged droplets. This only happens in tall clouds, i.e. \"thunderclouds\" or \"cumulonimbus\", both because of need for space to separate the charged particles to create the potential difference as well as because droplets acquire charges as a result of colliding with other droplets, which happens more in a deeper cloud with more vertical wind.",
"Clouds at any altitude are composed of water droplets which are suspended in the air and are not grounded. Lighting is in fact frequent at high altitudes because of the physical proximity of the ground to the charged cloud base in comparison to lower lying areas.",
"P.S. I know my tag is misspelled."
] |
[
"Due to the altitude of fog, the charge that accumulates in the low laying cloud is constantly grounded and never builds up to the point in which lightning could occur. "
] |
[
"How does waste water testing identify specific viruses based on protein fragments, especially after hours or days of degradation?"
] |
[
false
] |
I'm having a very hard time establishing exactly what technology is used for waste water testing for viral fragments, most fact sheets just say things like The samples are analysed for viral fragments Which while perfectly fine as a public service announcement, leaves me craving a jucier explanation. What tests are actually performed and how accurate are they? Is the same technology used elsewhere or for other reasons? (eg: could it detect proteins that could, for example, indicate areas with relatively good or poor nutrition?)
|
[
"It's a PCR test. The actual magic of a PCR test is the PCR part isn't actually the test. The PCR part is a trick we found where you can take basically anything, Mix it with some chemicals and free DNA bits and then heat and cool it a bunch and you'll end up with a billion copies of every single bit of DNA that was in the thing in a big bucket. ",
"Then you do the actual test, which is thinking of a sequence of DNA you are sure is only in the thing you are looking for then you make a chemical that can stick to that sequence and react and you make a jar of that. Then you pour the jar into the bucket and if it turns red then it found the DNA and if it didn't the DNA wasn't there. ",
"It's really extremely accurate, it can fail for sure, but the steps it failed you KNOW it failed, if you don't end up with a bucket of DNA then you did it wrong and have to try again, if the reaction happens then you know it really stuck to that specific sequence of DNA, and you know that there was some of that creature in it, and since it multiply the DNA a bajillion times you know it'll find it even if there was only a teeny tiny amount."
] |
[
"That is true for a pure sample, in a lab, under controlled conditions, and perfect reaction efficiency. Real world samples invariably have contaminants, PCR inhibitors, and other \"muck\" that can reduce DNA extraction yield, purification, and PCR amplification efficiency, which make it difficult to amplify a single copy of a DNA target. And it may not be that it doesn't amplify anything, it could be (and is most likely) that DNA targets DO amplify, but the time (aka number of PCR cycles) it takes to generate enough copies to be \"detected\" indicates that the viral titer is too low to be of concern."
] |
[
"I’m not sure you are giving a good description of PCR generally or accurately describing how you test for the fragment you want. You take your DNA sample and add specific single stranded DNA sequences, called primers, which flank the regions you want to amplify. DNA requires these primers to synthesize a new strand complementary to the old strand, and DNA replication only goes in one direction on a strand, so in theory only stuff between the sequences you provide will be amplified. Then you make sure that the chunk of DNA you made is the right size and sequence it if you want to be super sure. Amplifying ALL the DNA/RNA in a sample is rarely done for this specific reason."
] |
[
"Just because two animals have similar features like scorpions and spiders having eight legs does it mean that they came for the same or related ancestors that evolved differently?"
] |
[
false
] | null |
[
"In the case of spiders and scorpions, they came from the same ancestor, they're both arachnids.",
"But that's not true for every animal that looks like another animal. Two completely different species can evolve the same features in convergent evolution."
] |
[
"All life came from the same ancestors if you follow it back enough, but convergent evolution is a thing. For example, birds and mammals evolved to be warm-blooded independently. Scorpions and spiders are not an example of that though. All arachnids have eight legs."
] |
[
"If animals share phenotypical similarities (these can be obvious like number of legs, or less obvious like chemical composition of bodily fluids, etc.), there are two possibilities: either 1) the animals evolved from a common ancestor that had this trait, or 2) the animals \"convergently\" evolved this trait because the environment made it beneficial.",
"With spiders and scorpions, they evolved from a common ancestor that also had eight legs.",
"With another example, like birds and bats, although they evolved from a common ancestor (like all life), this ancestor did not have wings. They separately evolved flight and wings to adapt to similar environmental pressures. "
] |
[
"[Physics] How is momentum conserved if I throw a ball up in the air?"
] |
[
false
] | null |
[
"There is a net external force acting on the ball."
] |
[
"Thanks for the answer. While this may seem trivial to someone of your expertise, can you please give some detail as to why this matters? Does conservation of momentum not apply with external forces? I don't remember this being a highlight of the idea when it was taught to me in high school and college, but it makes enough sense. Just curious for more detail."
] |
[
"The momentum of an object is not conserved if there is a net external force acting on it.",
" = d",
"/dt. If ",
" is not zero, the momentum of the object will change with time."
] |
[
"Why does tomato sauce stain plastic so effectively?"
] |
[
false
] |
After arduously scrubbing my child's plate with little success, I find myself wondering what is in tomato sauce that so quickly and effectively stains plastic items such as plastic storage containers? Is it a chemical compound in tomatoes? Or something added to the sauce?
|
[
"Specifically it is a non polar molecule called lycopene that is causing the stains. The plastic is porous and it enters the pores and diffuses through the container. To help prevent this you can rub the container down with a little butter before dumping the sauce in."
] |
[
"Thank you, kind internet stranger!"
] |
[
"The plastic isn't porous in the sense that it has pits or cavities. The lycopene is very non-polar, as is the plastic. The lycopene simply dissolves into plastic from the water-based tomato sauce.",
"Sticking the plastic in the sun for a while will bleach the lycopene and at least make it not look orange/red anymore."
] |
[
"Why do humans have long hair?"
] |
[
false
] |
I think I read somewhere that humans are the only apes capable of growing hair as long as the hair on our scalps. The trait seems to be rare in the animal kingdom at large. Is there some evolutionary advantage to it, or is it just a fluke of sexual selection?
|
[
"Hmm.. some animals do have long hair on their \"heads\". ",
"Like horses and lions and other animals with manes."
] |
[
"I am not an anthropologist, but this is what I found from reading ",
"Wikipedia's article on \"Long hair\"",
":",
"Anthropologists speculate that the functional significance of long head hair may be adornment, a by-product of secondary natural selection once other androgenic/somatic hair (body hair) had largely been lost. Another possibility is that long head hair is a result of Fisherian runaway sexual selection, where long lustrous hair is a visible marker for a healthy individual. For some groups or individuals, however, short hair is the selected trait.",
"So, if Wikipedia is correct (and it could very well not be; let's wait for the anthropology panelists to step in), then your guess is correct that long hair is a result of sexual selection."
] |
[
"Well, orangutans may have quite long hair, too: ",
"http://images.mylot.com/userImages/images/postphotos/2078254.jpg"
] |
[
"Question regarding band gap values of Germanium"
] |
[
false
] |
Alright scientists, I have a question that I haven't been able to make any headway solving. I've read academic papers, looked through books, asked class mates and I can't come up with anything. I am given two curves of the absorption coefficient (cm vs the photon energy (eV). These two curves consist of a sample at two different temperatures. I have been tasked with finding the values of the direct band gap, the indirect band gap, and the phonon energy participating in the indirect transition. I have no idea what I'm doing and would really appreciate help. I realize this is an extremely specific question, but I need it for the paper I'm trying to finish.
|
[
"This will not answer your question, but you may find it informative nonetheless."
] |
[
"Abrupt changes in the absorption coefficient will signal a transition, such as the band gap. "
] |
[
"A plot of the data would be good, but I expect based on your description that there will be a small increase in the absorption at one photon energy and then later a much larger one. That would indicate the locations of the indirect and direct band gaps respectively.",
"As for temperature, you could try and do some fitting via this\n",
"https://ecee.colorado.edu/~bart/book/eband5.htm"
] |
[
"A rod more than a lightyear long?"
] |
[
false
] |
[deleted]
|
[
"This question has been asked before. Please use the reddit search function to see if your question has been asked previously. Have a read through some of those answers, and if you still have any questions, feel free to ask them here. ",
"The following 2 results with similar intent to your question was obtained by searching the term \"light year\":",
"If you are holding on to one end of a taunt, light-year long nanotube and give it a tug, how long would it take your friend at the other end to feel the tug? One year? More? Less?",
"Say you had a tube full of marbles 1 light year long?"
] |
[
"Not an expert here however found this in ",
"r/sciencefaqs",
" ",
"http://www.reddit.com/r/sciencefaqs/comments/fj1qd/if_i_had_an_infinitely_stiff_rod_could_i_push_and/"
] |
[
"Over in ",
"r/scienceFAQs",
":\n",
"http://www.reddit.com/r/sciencefaqs/comments/fj1qd/if_i_had_an_infinitely_stiff_rod_could_i_push_and/"
] |
[
"Where does the additional mass come from during a beta-plus decay when a neutron is formed?"
] |
[
false
] |
I've been reading up a bit on the basics of radioactivity, but there's something I just don't understand. When a nucleus undergoes beta-plus decay and converts a proton to a neutron while emitting a positron and electron neutrino, it seems to mysteriously gain mass as neutrons are slightly heavier than protons, but where does this additional mass come from? Does the process of changing one of the up quarks to a down quark somehow increase the particle's mass, or are there other forces at work here?
|
[
"Yes, that's right -- actually I had a discussion about this exact topic with a flaired nuclear physicist on this sub a while back, where he explained that it is never correct to think about the constituents of nuclei in a decay process; it is only correct to think about the parent and daughter nuclei as whole systems. Thus, beta+ decay ",
" \"a proton decaying into a neutron and emitting an antielectron and a neutrino,\" rather beta+ decay properly is \"a parent nucleus decaying into a daughter nucleus and emitting an antielectron and a neutrino.\"",
"Fun fact: the proton actually gets its name from being the nucleus of the most common hydrogen isotope. There are three \"long-lived\" (I use that phrase loosely) isotopes of hydrogen. You probably know the names of the heavier isotopes: deuterium and tritium, which have one neutron and two neutrons in their nuclei, respectively. But you may be unfamiliar with the name of the isotope that has zero neutrons in its nucleus -- that isotope, the most common one, is called protium. And just as the nucleus of a deuterium atom is called a deuteron, and the nucleus of a tritium atom is called a triton ... the name for the nucleus of a protium atom is called a proton. :)"
] |
[
"In a beta-plus decay, it’s the nucleus as a whole that’s decaying. Even though the mass of a free neutron is higher than the mass of a free proton, the Q-value for beta-plus decay of a nucleus with A > 1 can still be positive."
] |
[
"Where does the additional mass come from during a beta-plus decay when a neutron is formed?",
"It is already present in the initial state of the nucleus that is decaying.",
"Does the process of changing one of the up quarks to a down quark somehow increase the particle's mass, or are there other forces at work here?",
"Neither of those is the case. Perhaps an analogy would be useful here. Suppose you have a 1L glass of water (this represents our parent nucleus, which is decaying), and you need to fill three other glasses -- one for the daughter nucleus (900 mL), one for the antielectron (50 mL), and one for the neutrino (10 mL). Since energy (the water) is conserved, it must be the same between the initial state and final state, so you can fill all three glasses and still have an extra 40 mL remaining (the corresponding extra energy goes into the kinetic energy of the decay products).",
"It's still true, of course, that a neutron is heavier than a proton -- in our analogy, this is a bit like saying that a 500 mL glass you have to fill holds more water than a 450 mL glass, which is certainly true. But you aren't starting with only 450 mL in your initial glass -- you're starting with the full 1L representing the energy content of the entire nucleus. You have more to work with than just the one proton.",
"Hope that helps clarify!"
] |
[
"How does a population experience an increase in genetic diversity?"
] |
[
false
] |
Is it only mutations? How would a bottleneck population such as Native Americans increase their genetic diversity without interbreeding with some other population? My question is general, it does not necessarily pertain to race or Homo sapiens but any population.
|
[
"Either mutation or mingling with other populations"
] |
[
"Yeah, it's either going to be via mutation or via introgression of new alleles from outside populations. If the population fails to admix with any outside populations, then it will recover to an equilibrium level of diversity in time, and will thus continue to become more genetically distant from other populations (Europeans, Africans, etc.) as they accumulate their own independent mutations. If they do admix with an outside populations, however, their diversity will increase because the outside population is likely to contain genetic diversity that they lack. The distinctions between these two populations will begin to blur, however, if interbreeding continues, as they'll become more and more genetically similar."
] |
[
"So would it be wrong to conclude that as a general principle, that younger species will have less genetic diversity than there evolutionary ancestors?"
] |
[
"Do gravitational waves have frequencies?"
] |
[
false
] |
I feel like the obvious answer is they do, but I don't know the answer. And if so, what determines their frequencies? Mass? How noticeable are these frequencies, and what would the frequency of a gravitational wave from the sun be compared to the black hole collision that LIGO observed?
|
[
"Not only do they have frequencies, but the range of frequencies LIGO detects are partly within the limits of human hearing.",
"So you can listen to ",
"natural-pitch black hole merging noises.",
" ",
"The frequency they produce is related to how fast the holes are orbiting eachother. As they spiral towards eachother and shed energy as gravitational waves, they orbit faster and the frequency goes up. So if you adjust the pitch they sort of make slide whistle noises."
] |
[
"Yes, they do. Gravitational waves in free space obey the same kind of dispersion relation that electromagnetic waves do: ω(",
") = |",
"|c."
] |
[
"Wow listening to a black hole sounds like someone making something up, that’s amazing!"
] |
[
"Has there ever been an estimate on how many planets there could possible be with the existence of Life?"
] |
[
false
] | null |
[
"A very simplistic but easy estimate can be made with the ",
"Drake equation",
".",
"The problem is that the values of things such as the fraction of planets that develop life and the fraction of life‐bearing planets that develop ",
" life are unknown and perhaps unknowable.",
"Here’s ",
"Wolfram|Alpha’s interpretation",
", with interactive coefficients."
] |
[
"And ",
"here's",
" xkcd's interpretation. The Drake equation is worse than simplistic. It's ",
" worse than meaningless, it's actually ",
". "
] |
[
"Stuff like ",
"The Drake equation consists of a large number of probabilities multiplied together. Since each factor is guaranteed to be somewhere between 0 and 1, the result is also guaranteed to be a reasonable-looking number between 0 and 1. ",
", making the result worse than useless."
] |
[
"Why are morphogens not capable of growing back lost parts of our bodies, without the risk of developing cancer?"
] |
[
false
] |
My question is why did our bodies develop in this way? Why didn't our body find a way to use morphogens to it's advantage in order to restructure or repair/grow back completely missing limbs? Why wouldn't morphogens be able to start or stop working only when needed, in order to not work continually - leading to cancer? So I guess my question would also be why did our body develop this way. Or rather, why did it NOT develop a way to grow back missing limbs instead of just being able to repair wounds or broken bones? PS: If anything I said in here is wrong, please do correct me as I'm not too knowledgeable on the subject.
|
[
"Evolution doesn’t routinely do luxuries. Can your current form and life-processes keep you alive in your current environment long enough to breed the next generation? Yes? Then you are “successful enough”. Rinse, repeat, refine through those generations.\nIf the need to regrow limbs and organs was the only thing keeping a species successful enough to continue surviving “better”, then it would either happen or the species would go extinct. You gotta keep throwing mutations at the wall and see what sticks."
] |
[
"Evolution is adaptability to an enviroment. We humans do not need to regenerate body parts (although some organs can regenerate) since we are not constantly getting amputeed or hunted by predators. The body of a living being necessitate conditions to modify, so maybe, if we were at the same conditions of prehistorical humans, we will be able to have such features, but since we don't, we don't.",
"Sorry for bad english!"
] |
[
"We have stem cells, which are totipotent and have the capability to become whatever the body needs. We are not capable of naturally regrowing body parts, but thanks to them we can work out new improvements and help everyone!"
] |
[
"Why isn't the Universe condensing, or at least decelerating, with the constant gradual pull of gravity?"
] |
[
false
] | null |
[
"One of the interesting things about the way the general theory of relativity extended our understanding of gravity is that gravity (i.e., the curvature of spacetime) need not be attractive. That is, the curvature can be such that the trajectories of objects through spacetime diverge rather than converge. When we model spacetime in the vicinity of a massive object, we find that you get an attractive effect that is very closely approximated by Newton's gravity. But this attractive effect drops off quickly with distance, and it turns out that the repulsive effect doesn't. As a result, at very large distances the repulsive effect dominates and you get expansion."
] |
[
"Well, it's actually speeding up. Which really isn't what one would expect. So, this is where dark energy enters into the equation. Hopefully in the coming years we'll get a better idea of the nature of what dark energy is. What this dark energy actually IS is still a debated question."
] |
[
"In the general theory of relativity, gravity is identified with the curvature of spacetime. In the absence of curvature, if you have two objects that start out at rest relative to one another they will remain at rest with respect to one another. That is, neither object will see the other object move as time goes by. If you think of that in terms of the trajectories through spacetime, what we're saying is that if two trajectories start out parallel, they will remain parallel.",
"Now, when spacetime becomes curved, that may not remain true. For example, consider the case where one of your objects has mass. In the reference frame of that object, it's always stationary, so it's trajectory through spacetime is just a straight line \"into the future\". Now, let's say there's a second object that starts out at rest relative to this one. Then the curvature of spacetime caused by the presence of the first object will cause the second object's trajectory through spacetime to bend toward the first object. The trajectories start out parallel, but then, as time passes, the second object's trajectory gets closer and closer to the first object's trajectory, and it does so at an increasing rate. To an observer on the first object, it will look as though the second object is accelerating toward the first object in a manner that is very nearly that predicted by Newtonian physics.",
"That's the \"classical\" attractive effect of gravity: the curvature of spacetime is such that initially parallel trajectories tend toward one another. In three-dimensions, it's possible for this curvature to result in orbits, where the separation between the two trajectories stays the same (or varies only a bit), while the angular positions change.",
"Now, that's not the only way spacetime can be curved. It's ",
" possible for the curvature to be such that as time passes the distance between two objects ",
". That is, gravity is a repulsive effect. This happens when there's something called a 'nonzero cosmological constant'. The value of that constant determines the scale at which this repulsive effect dominates any attractive effect caused by the relative masses of objects.",
"Now we look at our universe and we notice that at large scales objects tend to be moving apart. We call whatever is causing this expansion 'dark energy'. It turns out that the rate at which objects are separating is just what we'd expect for a nonzero cosmological constant, which is our current leading explanation for dark energy."
] |
[
"AskScience AMA: I’m Professor Brian Hare, a pioneer of canine cognition research, here to discuss the inner workings of a dog’s brain, including how they see the world and the cognitive skills that influence your dog's personality and behavior. AMA!"
] |
[
false
] |
Hi Reddit! I’m , and I’m here to talk about canine cognition and how ordinary and extraordinary dog behaviors reveal the role of cognition in the rich mental lives of dogs. The scientific community has made huge strides in our understanding of dogs’ cognitive abilities – I’m excited to share some of the latest and most fascinating – and sometimes surprising – discoveries with you. Did you know, for example, that some dogs can learn words like human infants? Or some dogs can detect cancer? What makes dogs so successful at winning our hearts? A bit more about me: I’m an associate professor at Duke University where I founded and direct the , which is the first center in the U.S. dedicated to studying how dogs think and feel. Our work is being used to improve training techniques, inform ideas about canine cognitive health and identify the best service and bomb detecting dogs. I helped reveal the love and bond mechanism between humans and dogs. Based on this research, I co-founded , an online tool featuring fun, science-based games that anyone with a dog can use to better understand how their dog thinks compared to other dogs. Let’s talk about the amazing things dogs can do and why – Ask Me Anything! For background: Please learn more about me in or check me out in the new podcast series by Purina Pro Plan on iTunes and Google Play to learn more about dog cognition. This AMA is being facilitated as part of a partnership between Dognition and Purina Pro Plan BRIGHT MIND, a breakthrough innovation for dogs that provides brain-supporting nutrition for cognitive health.
|
[
"So sorry for your loss and what a fascinating observation. I would love to say there's an experiment or systematic study to cite for this one, but there is not. Scientist have written papers about other animals - like primates - that they interpret as grieving the loss of their offspring. That said dogs showing behaviors that can be interpreted as 'grief' is something that has been recorded throughout the ages. The best one I know of is of Napoleon Bonaparte. At the end of a battle in Italy, Napoleon came across a dog sitting beside the body of a fallen soldier, licking his hand. Later, during Napoleon’s final years in exile, he would write;\n‘This soldier, I realized, must have had friends at home and in his regiment; yet he lay there deserted by all except his dog… I had looked on, unmoved, at battles which decided the future of nations. Tearless, I had given orders which brought death to thousands. Yet, here I was… moved to tears. And by what? By the grief of one dog.’"
] |
[
"I am laughing right now. YES! Your dog knows how much you love them! I sort of spoke about this in one of the earlier answers, but dogs have hijacked the human oxytocin bonding pathway that is normally reserved for our actual babies. When you stare at your dog, both your oxytocin levels go up, same as if you pet them and play with them. It makes you both feel good and reinforces your bonding. Does your dog ever stare at you for no reason? They are just hugging you with your eyes. If you want to read more about it, I wrote this article here: ",
"http://www.livescience.com/40065-dog-kisses-are-more-than-just-slobber.html"
] |
[
"Do dogs recognize other breeds of dogs (e.g. a chihuahua seeing a husky) as being one of \"them\", or do they see other types of dogs as separate species altogether?"
] |
[
"Why can't doctors fuse the two halves of a bone back together after a fracture instead of letting the body do it?"
] |
[
false
] | null |
[
"Bones need to tolerate a high degree of stress and large forces. We could glue bone fragments together or graft with mashed up bone but it won't be strong enough. To get sufficient strength for weight bearing we use metal rods, plates, and screws.",
"There may be a product that can join bones but I don't know of one that would provide enough strength to join a weight bearing bone and would be non toxic and affordable. "
] |
[
"Can you clarify what you mean by fuse? When a break occurs the fracture needs to be reduced and immobilized. For the bone to grow back together the two ends have to be in close proximity and not have any motion relative to each other. If either requirement is not met, you have nonunion of the bone which might require surgery. ",
"There are biologic and mechanical therapies to help prevent nonunion. Casting and open reduction with internal fixation (ORIF) are mechanical methods to bring bones to alignment and keep them that way. Recombinant human bone morphogenetic protein-2 (rhBMP-2) is also used in some spinal surgeries where the rates of nonunion are high. As with any medical therapy, there are possible side effects, which are being studied at labs around the world. "
] |
[
"Vertebroplasty",
" is really for stress fractures, but it's kind of doing that: joining the bones across a fracture with a kind of glue. My mother had this done on her back and was pain free immediately. Before, she couldn't even tolerate riding in a car."
] |
[
"What would happen to oil if it didn't get extracted?"
] |
[
false
] |
If it were to remain dormant, what would become of the crude oil we humans extract?
|
[
"Really depends on where it is. If it is in a basin that is still subsiding, eventually the heat will cook it into a graphite like substance. Many times there are ",
"natural oil seeps",
" where the oil finds a way to the surface like in offshore California or in the Black Sea. ",
"In geologically 'inactive' areas like the west Siberian Basin, it will stay there until all of the light volatiles have left and will then end up with this sticky substance like what the tar sands are in Alberta. ",
"So, it really depends on the geologic area and how close to the surface the hydrocarbon trap is. "
] |
[
"Not to derail this good question too much, but tar sand extraction is directly causing a lot of habitat loss & trace amounts of heavy metals in the areas where digging occurs, is being swept away by rain & entering rivers, which fish & local people are becoming poisoned. Such a shame. I can't totally say oil is completely bad, because other than fuels, we make a lot of useful products. Tar sands are a really awful way of obtaining hydrocarbons. "
] |
[
"Sure, you can find the wiki article ",
"here",
" if you're interested in reading it. Basically it's just a highly viscous bitumen that is mixed in to some loose sand. The reason it is not seen as the best way to get oil is because you have to dig the sand out (you can't pump it), take the sand to a refining place, throw a whole lot of chemicals and water at it (349 million cubic metres per annum in Canada alone) in order to extract the oil from the sand, and then you have to send the oil out for conventional processing. It's very energy and resource intensive, not to mention a really horrible extraction method. "
] |
[
"What makes certain metal ions suitable for use in biological systems?"
] |
[
false
] |
I was recently asked the fairly simple question of "Why is the calcium ion so important in Biology?", however it got me thinking - why are some ions used preferentially over others? What is it about Ca that makes it more suitable for signalling transients over Mg ? In an action potential why are sodium ions outside and potassium inside? Obviously it all comes down to 'it evolved this way', but can anyone offer a more compelling reason as to why these ions might have been 'selected' for these roles? Thanks
|
[
"Abundance and chemical properties determine which elements we use.",
"Abundance isn't just for metal ions and so the explanation will be generalized. If you look at what elements living things use, you'll see that the most common elements used are also the most abundant elements in the universe. Because there's so much of these elements around, life is more likely to \"generate\" out of these elements. Life will also evolve to use common elements because that makes growth easier.",
"Chemical properties also matter in ion systems and coordinate chemistry. You'll find that free metal ions in living things are usually light alkali or alkali earth metals. They are good at staying as a solution in water and are able to carry electrical charges easily since they are not heavy. For example, two of the lightest ions sodium and potassium are used for cell gradients. Other transition metal ions are also used because they can have lots of different oxidation states and can thus react with proteins to form useful \"chemical-mechanical\" complexes. For example, iron (also super common due to terminal fusion) in hemoglobin will change oxidation state if bound to oxygen and change the shape of the whole molecule to absorb more oxygen.",
"You may wonder why lithium, helium, and silicon aren't used. Lithium is relatively rare due to how stars do fusion, and is also hard to come by since it reacts so easily with oxygen. Helium is a noble gas and doesn't react with anything, and is rare on earth since most of it floated into space. Some organisms use silicon, but it is so different from carbon and so similar to carbon at the same time that accidentally using it with carbon basically breaks some things.",
"Tl;dr: Metal ions that are easy to find on earth are used because its easy to find and use them. Metal ions that do useful things like act as electricity carriers are used because they provided an advantage to organisms. Some elements don't follow the rules due to specific properties or because they aren't found on Earth much."
] |
[
"Thank you for the detailed reply! I understood most of the biological points you made (I'm currently a biochem undergrad) but was hoping you could elaborate on some of the chemistry:",
"What do you mean by the akali metals being good at staying in solution? Is that because they don't form many insoluble precipitates or something else? Why does their lightness allow them to hold charge more easily? Is there any specific reason that potassium is 'inside' and sodium 'outside', or why magnesium isn't used in signalling over calcium?",
"Also why aren't aluminium, titanium and manganese used more prevalently considering their abundance? Is there any reason some organisms use haemocyanin with copper over haemoglobin, despite copper being much less common?",
"I realise that's an absolute mountain of questions, if you could answer any that would be great! "
] |
[
"I love answering these questions; there's just so much stuff to know and to ask!",
"Yeah, alkali metals don't form precipitates since they are much more stable in solution. ",
"Lightness means that a light element will have a higher charge to mass ratio. This effectively means there is a high electrical force(or energy) per unit mass and they can move faster than an ion of equal charge but heavier mass.",
"I think the sodium/potassium polarity is pretty much arbitrary and could work the other way around. There might be some advantage since sodium moves faster than potassium.",
"Magnesium precipitates too easily while calcium can be dissolved in high concentration. Lots of magnesium uses though, such as as ions in chlorophyll.",
"Aluminum is very unavailable because the oxide is highly stable (it's sapphire).",
"Manganese and titanium are fairly common in enzymes, but I don't think that their simple compounds are very useful for non-catalytic functions. Might even be harmful due to the oxidative stress their oxides create.",
"Hemocyanin (wikipedia) - \"Species using hemocyanin for oxygen transportation include crustaceans living in cold environments with low oxygen pressure. Under these circumstances hemoglobin oxygen transportation is less efficient than hemocyanin oxygen transportation.\" There's no reason that an enzyme with copper will be evolved inferior to hemoglobin; might just be chance."
] |
[
"What would a nuclear detonation on the surface of the Earth look like from the ISS or similar orbiting platform?"
] |
[
false
] |
[deleted]
|
[
"Okay. The ISS orbits between 200 and 250 miles high. A 20 megaton bomb will produce a fireball ",
"about 2 miles in diameter",
". It will cause a \"conflagration\" ",
"40 miles in diameter",
".",
"What would this look like from 200 miles away? Here's a place to start: imagine driving down the interstate and passing a \"1 mile to exit\" sign. What does the exit sign look like at that distance? You can definitely see it, you can't read it, but you can tell it's there. You could make out its shape. If it was lit up, you would sure as hell notice it then. An interstate exit sign is probably 15 feet high. 15 feet at 1 mile distance is 3000 feet at 200 miles distance. So ",
" produced by the explosion would be 3 times the apparent size of the sign that we're talking about. The destruction would extend for another 20 times that distance. I think that would be pretty noticeable.",
"Here's a picture taken from the ISS.",
" If you look at Christchurch, NZ in Gmaps you can see where this is. View the picture full size and find the river that makes a downward-facing number 3 (it's at 10 o'clock from the astronaut whose face you can see). That number 3 is about 10-12 miles high. I think the picture was taken with a relatively short lens (look how much perspective you can see in the parallel lines of the space station).",
"Conclusion: you can see lots of stuff from 200 miles away. Nuclear explosions are big. "
] |
[
"Also. Here's a graph of ",
"mushroom cloud dimensions.",
" The left axis is thousands of feet, the bottom axis is megatons. So go back to that ISS photo and imagine a mushroom cloud 20 miles high and 60 miles in diameter..."
] |
[
"Yea, let the scientist pop in on this :P"
] |
[
"How large would a telescope have to be to be able to see the closest known exoplanet, in decent detail?"
] |
[
false
] | null |
[
"Yes it would."
] |
[
"We do exoplanet discovery and we use an 8.2 meter mirror. Currently we either infer the exoplanet (based on techniques such as dimming of the host star, etc) - or directly image it (only for the closest and largest exoplanets, but only about a pixels worth).",
"New instruments coming online will give us much better resolution.",
"However, TMT is being built - and it will have a 30 meter mirror (segmented). That should be able to directly resolve close exoplanets for much more direct spectrographic data (still super tiny, but potentially more pixels for more detail).",
"We're still not talking surface detail.",
"And again, these would be only for the closest and largest exoplanets... ones not likely to support life."
] |
[
"Would a moon-based telescope give a better image due to a lack of atmosphere?"
] |
[
"Various cultures eat cow brains on a regular basis. Is this not dangerous? Why isn't there a high rate of BSE in these cultures?"
] |
[
false
] |
maybe I'm just ignorant? But I thought eating brains was a dangerous thing to do and carried the risk of contracting certain types of diseases Like bovine spongiform encephalitis? yet these cultures don't seem to have a high rate of that disease. Re: . Beef brains and veal (juvenile beef) or calf's brains are used in the cuisines of France; Italy; Spain; El Salvador; Mexico, etc. where they are called sesos in Spanish and are eaten in tacos and quesadillas; Pakistan, where they are known in Urdu as Maghaz; Portugal; Indonesia; and in the United States, especially in St. Louis, Missouri, and the Ohio River valley.
|
[
"Eating brains does run a higher risk than eating muscle or other organs, but that risk is still very low. If you read about the epidemiology of Creutzfeldt–Jakob disease (CJD), the most common prion disease, the incidence was 1 in 1,000,000 from 1979 to 1994 and 5 in 1,000,000,000 in those under the age of 30 in the US. With that said, CJD is is thought to have a 20-50 year incubation period which could explain why it's so rare in young people. I think more supportive (or contradictory) evidence of this will start appearing in the 2000-2040 time frame (20-50 years after) the UK 80s-90s outbreak and those that ate that tainted beef.",
"Testing for BSE in cattle and discarding those that have the disease helps protect those that eat cattle organs (particularly the brain). ",
"TLDR: It's all about statistical probability and the risk of a prion disease infection is very low."
] |
[
"Tougher for the prions to transmit from cows to humans, however, cultures like the \"Fore\" in Papua New Guinea experienced much higher rates of prion-related diseases, ",
"Kuru",
", because they used to consume the body and brains of their deceased. Ironically, they only would participate in this ritual if the deceased looked healthy upon their death, and Kuru had a side effect of 'marbling' muscle making it more appetizing--only leading to the continuing spread of the disease. ",
"Source--wrote a research paper on Kuru and CJD for a physio class"
] |
[
"Any relation to whether or not the cattle herds in question ate cow products? I was under the impression that part of the problem in the US was that cows were being fed (among other detritus) ground-up cow leftovers."
] |
[
"Why do we measure precipitation in inches? It seems primitive to me."
] |
[
false
] | null |
[
"Why is it primitive? Do you suggest centimeters then?"
] |
[
"At the very least I would suggest changing to metric measurement, but I was meaning the way that it is measured, as it is currently how much rain/snow falls in one particular spot. Possibilities I could think of were perhaps the amount of time that the rain fell, or some kind of measurement based on the size of the cloud that it fell from. "
] |
[
"Wouldn't you rather want to know how much rain fell?",
"Instead of how long it fell for or how big the clouds are (which doesn't tell you anything too conclusive about the amount of rain in it either).",
"I'd rather know how much rain fell yesterday, than how long it rained for -- especially when the rate of rainfall fluctuates over time.",
"In any case, it really is a matter of convention. I guess meteorologists just think that amount-of-rain is more useful as something to record than duration-of-rain or size-of-cloud ... or anything else, for that matter. Not that they aren't allowed to record all of that and everything else. But when they put out their reports/try to make conclusions...",
"edit: it might be worth noting that when they say \"inches\", they don't mean they measure one infinitessimally small spot and see how many inches are caught. Rather, it's collected over an arbitrary area. The larger the area, the more it represents the \"average\" inches of rain per spot of the rainfall."
] |
[
"How high bats can fly? Is the maximum altitude comparable to birds one?"
] |
[
false
] | null |
[
"https://en.wikipedia.org/wiki/R%C3%BCppell%27s_vulture",
"\n11km, can check prays from above",
"Bats",
"\nno real need of altitude except for migratory purposes, but the Plecotus auritus found near the Himalaya was seen up to 3.3km.",
"Also, just found bats got the record of horizontal speed (160km/h instead of 120km/h for birds), neat."
] |
[
"Numbers are impressive, especially those 11+km, where weather conditions are so deadly. Thanks!",
"Worth to notice that at 160km/h bats may be faster than cheetah :-)"
] |
[
"Hold-on, That might be a mistake",
"https://www.newscientist.com/article/2112044-speedy-bat-flies-at-160kmh-smashing-bird-speed-record/",
"\nsays",
"The fastest bird on record for level flight is the common swift (Apus apus), which reaches around 112 km/h.",
"But ",
"https://en.wikipedia.org/wiki/Fastest_animals#cite_note-:Pigeon-13",
"says",
"[race homing] Pigeons have been clocked flying 92.5 mph (148.9 km/h) ",
" speed on a 400-mile (640 km) race.",
"Edit: same here ",
"https://www.popularmechanics.com/science/animals/a23848/bat-100-mph/"
] |
[
"How do you calculate the average sum of dice rolls when a \"drop the lowest roll\" mechanic is used?"
] |
[
false
] |
In various tabletop role-playing games, game designers will often use a system to set character statistics that is some derivation of "roll an x-sided die y-times, drop the lowest z rolls, and sum up the results." The most common example of this is rolling a 6-sided dice 4 times and dropping the lowest result. Now, calculating the average sum of 3 six-sided dice rolls is simple and intuitive, yielding a result of 10.5, but when adding a 4th and dropping the lowest result, the average comes out to a (seemingly) strange irrational number of ~12.22. There are other derivations of this problem that yield other seemingly random irrational values, and while I can get to the result by writing out all the combinations and summing up the probabilities, is there a way to write this problem out algebraically?
|
[
"Suppose we roll a die ",
" times and label the results as X",
", X",
", ..., X",
" and let ",
" denote the minimum roll. Then the sum of the best N-1 rolls is",
"S = X",
" + X",
" + .... + X",
" - M",
"Expectation is linear and all of the X",
"'s have expected value (d+1)/2 where d is the number of sides of the die. (This assumes that the values of the die are 1, 2, 3, ...., d.) So then the expected value of the best N-1 rolls is",
"E(S) = N(d+1)/2 - E(M)",
"It's then just a matter of finding the expected value of the minimum. For a random variable with a continuous probability density, this is a standard exercise and not too difficult. For a probability density that is not continuous, the calculation is bit more subtle.",
"You can do this via \"brute force\" by considering the possible values of M and with what probabilities they occur. For instance:",
"Then you can calculate the expected value of ",
" by summing m",
"P(M = m",
") over ",
".",
"d",
"E(M) = 1*[d",
" - (d-1)",
"] + 2*[(d-1)",
" - (d-2)",
"] + 3*[(d-2)",
" - (d-3)",
"] + ... + d[1",
" - 0",
"]",
"The sum on the right simplifies quite a lot and we end up with:",
"E(M) = (1",
" + 2",
" + 3",
" + ... + d",
")/d",
"So putting this all together we find the following result. If we roll ",
" fair ",
"-sided dice with face values 1, 2, ..., d, then the expected value of the sum of the rolls with the lowest roll dropped is....",
"E(S) = N(d+1)/2 - (1",
" + 2",
" + 3",
" + ... + d",
")/d",
"For N = 4 and d = 6 (rolling a 6-sided die 4 times and keeping the best 3 rolls), we get",
"E(S) = 15869/1296 = 12.2446",
" You can also use the result that if X is a random variable that takes on only non-negative integer values, then E(X) = Σ",
"P(X ≥ j). In this case, P(M ≥ j) = (d-j)",
"/d",
" for j = 0, 1, 2, ..., d; and P(M ≥ j) = 0 otherwise. So we have",
"E(M) = d",
"/d",
" + (d-1)",
"/d",
" + (d-2)",
"/d",
" + ... + 1",
"/d",
"and we just recover the same result as before.",
"As an interesting side exercise, if these rolls were really, say, uniformly distributed on the interval [0, 1], then this calculating is much easier. For that case, the ",
" rolls would, on average, all distribute themselves at equally spaced intervals in [0, 1]. So if there were only 2 rolls, they would, on average, divide the interval into [0, 1/3], [1/3, 2/3], and [2/3, 1]. So the min and max would have expected values of 1/3 and 2/3, respectively.",
"In general, the minimum of N rolls would have expected value 1/(N+1). The next highest roll would have expected value 2/(N+1), and so on. The maximum would have expected value N/(N+1).",
"Now you ",
" recover this result from the discrete case as a suitable limit with d --> ∞. First, normalize the rolls to take on the ",
" values 1/d, 2/d, 3/d, ..., 1. So the rolls are discrete and uniform and all have values in the interval [0, 1]. Then the expected value of M is just the same formula as above, but divided by ",
".",
"E(M) = (1",
" + 2",
" + 3",
" + ... + d",
")/(d",
")",
"Now take the limit of this expression as d --> ∞. But be careful! Not only do the terms depend on ",
", so does the ",
" of terms. In fact, this is just a Riemann sum which approximates the integral of f(x) = x",
" on the interval [0, 1]. Thus as d --> ∞, the limit is just the value of that integral, which is.... 1/(N+1). That is just the expected value of the minimum of ",
" rolls for a ",
" uniform random variable!"
] |
[
"The formula for E(M) (the expected value of the minimum roll) is given above. Just put N = 2 and d = 20. It's about 7.2."
] |
[
"This is a perfect response and exactly what I was looking for. Thanks!"
] |
[
"How is it that you can compress TBs of data into small easy to move zip files? Shouldn't the data take up the same amount of memory all the time?"
] |
[
false
] |
I don't get how you can make data take up less space even though it is the same amount of information.
|
[
"Imagine you had a file which consisted of a 4TB long string of \"1s\". You could compress that file into the following line:",
"\"This file consists of a 4TB long string of 1s\"",
"Basically compressing a 4TB file into something under 50bytes.",
"It's a silly example, of course, but the idea is that compression algorithms look for repetitions and redundancies to do their magic - and a lot of other sophisticated stuff too of course."
] |
[
"Compression assigns shorter outputs to more probable inputs. Lets say my input was something like AAABCABAABA. I would assign A- 1 B- 10 and C-100, thus the sequence would be compressed as",
"1 1 1 10 101 1 10 1 1 10 1,",
"which is 16 bits long. If you were to going to use a naive binary scheme where each letter was represented with the same length string (such as A- 00, B-01, C-10), it would require 22 bits. If you were to represent the number in ternary, and then convert the entire number to binary it would require 18 bits. ",
"More probable sequences are more heavily compressed. Zip files simply do this in a clever way. "
] |
[
"More probable sequences are more heavily compressed.",
"And the corollary is that a truly random data stream cannot be compressed in this way. Compression algorithms take data with redundant data and turn them into shorter sequences of more random data, which is why you cannot zip a zip file repeatedly to make it arbitrarily small."
] |
[
"How did the elements form after the big bang?"
] |
[
false
] | null |
[
"Stars. All elements heavier than helium (some lithium ?) are formed inside stars and released into the universe during nova's. Elements up to iron release energy when they fuse, and this help drive the stellar engine. Elements heavier than iron are formed during supernovae."
] |
[
"It's hydrogen, not helium and the 'pressure' bringing it together is gravity. How does hydrogen form ? It's the simplest element there is. One proton and one electron. It was formed during the big bang. "
] |
[
"As the universe cooled",
"Just to note, the net energy of the universe is always the same. The fact that the universe expanded is why we say \"the universe cooled\"."
] |
[
"Can someone explain this sentence? \"[Gravity] is just the differential rate of time between high places and low places.\""
] |
[
false
] |
[deleted]
|
[
"It's a not-necessarily-wrong but also highly unorthodox way of describing gravity. You might say that objects \"want\" to be in places where time runs slower, so if an object is in one place, and right next door is a place with a slower time rate, it will tend there, the way a ball on a hill \"wants\" to be in lower rather than higher places, so it falls to the lowest place available.",
"I don't know how enlightening that is, personally. An equivalent, but hopefully more insightful, way of saying the same thing is that gravity is what happens when spacetime is ",
". Think of the surface of a sphere, which is a curved space. You know how there are no straight lines on the sphere? It's the same thing in curved spacetime. Particles naturally, due essentially to inertia, want to travel in straight lines, but when spacetime is curved they can only travel on the next best thing - ",
", or paths of least distance from point A to point B. (In spacetime, \"point\" really means \"event,\" so point A and point B have a time A and time B as well.) Particles following geodesics through curved spacetime look ",
" as if they're being pulled by a gravitational force, because massive objects curve spacetime strongly around them."
] |
[
"This is a very odd way to think about it, and without further explanation I think the author is being misleading to a layman. (and trying to sound fancy to get more books sold)",
"So in GR objects follow ",
"geodesics",
", which is a generalization of a straight line in a flat space. (shortest 'distance' between two points). But remember GR is four dimensional (ct,x,y,z), so what we see in 3-space is just a projection of the path in 4-space (and therefore might not seem like the shortest path). So the time change is a part of the total 'distance' change that must be included to find the 'shortest path'."
] |
[
"You might say that objects \"want\" to be in places where time runs slower, so if an object is in one place, and right next door is a place with a slower time rate, it will tend there, the way a ball on a hill \"wants\" to be in lower rather than higher places, so it falls to the lowest place available.",
"It seems to me that the author was trying to draw an analogy with indices of refraction. Light changes direction when it encounters a medium in which it travels more slowly, and similar effects hold for other kinds of waves. I think the author is saying that the bending of geodesics is accounted for by the same effect when it's produced by time dilation as opposed to interaction with a medium. I don't have the necessary background in physics to say if this description is correct or not."
] |
[
"How is hairgrowth regulated?"
] |
[
false
] |
How come your body hair stops growing at a certain length, but after shaving it grows again?
|
[
"Pubic hair sheds after about 5 months, I believe. If you cut it to half length, it'll just keep growing until it's destined to fall off."
] |
[
"This is actually pretty interesting. ",
"You see, each hair follicle follows it's own schedule. Put simply, it's either in a growing stage, or a resting stage. So, when you cut your hair, some of the hair you cut is still 'growing', and so grows back when you shave.",
"It seems like it stops growing at a certain length sometimes because the hair that is the longest has reached the rest stage."
] |
[
"I don't really get this. My assumption is that e.g. pubic hair grows to a specific length and then it stops growing. Is this even correct?",
"Now if I cut all that hair to half length, wouldn't it grow again to its specific lenghth? How does it know that it was cut?"
] |
[
"If your looking through the window of a spaceship traveling at near light speed as a stationary observer what do you see?"
] |
[
false
] |
You are a stationary observer with a very powerful telescope. There is a spaceship traveling at near light speed. You point your telescope at the window. To you does it appear that the people in the spaceship are moving in slow motion?
|
[
"look compressed along the axis of movement",
"Nope, see ",
"Terrell rotation",
"."
] |
[
"Yes, they would look like they are moving in slow motion as they ARE moving in slow motion. However, if you are looking from inside the ship at someone outside, they would be the ones moving in slow motion. ",
"The people in the ship would also look compressed along the axis of movement of the ship, making for a comedic view of them. "
] |
[
"Thanks for that. I was simplifying (perhaps over-simplifying) the optical effects of relativistic motion due to the OP having seemingly basic understanding of the subject.",
"The effects that contradict the statement regarding optical compression are only apparent when the object is viewed parallel to its movement axis (where rotation and elongation is observed due to the finite speed of light). When viewed perpendicularly, the object is viewed as compressed as a whole and rotating."
] |
[
"Do taller people die younger?"
] |
[
false
] |
This has only just occurred to me. I don't think I've ever seen a really tall person who's about 85+ years old, and it certainly seems that all the people who manage to get to 100 are typically very very small. I know that people "shrink" as they age but I cant imagine a 6"2 skeleton inside any of the elderly people I've seen. Is it truly the case that taller people generally die younger? If it is, why? I know this is a fairly morbid question but I'm just curious.
|
[
"Yes.",
" There are a couple of reasons for this. One is that tall people's hearts have to work harder to circulate blood, which will wear them out more over time. Another reason is that tall people have a larger number of cells than short people, which will lead to a statistically increased risk of cancer. "
] |
[
"There probably is an association between being tall and earlier death. One recent paper (",
"Shorter men live longer: association of height with longevity and FOXO3 genotype in American men of Japanese ancestry.",
") found a relative risk of 1.006 per cm of height, which is a very small though statistically significant effect. ",
"Note, though, that other studies have found the reverse, and hypothesized that being tall is an indicator of having better nutrition and better health during childhood, which in turn should lead to longer lifespan. This paper argues that studies that did find that had various statistical issues, particularly that they didn't track the same group of people over very long periods but used different age cohorts instead. They argue that you need to track thousands of people, preferably a fairly homogenous group (in this case, men of Japanese ancestry) for many decades to pick up on the statistical signature. ",
"In particular, the effect doesn't kick in until people are already quite old:",
"We compared survival curves between participants who were 165 cm or taller in height, those who were 158 cm or shorter, and those whose height was between 158 cm and 165 cm. ",
" Survival curves in the follow-up for these three groups of people differed significantly between age 80 and 95 years ...",
"(My emphasis) ",
"Consistent with the taller-people-had-healthier childhoods hypothesis, they found that even though taller men tended to die younger, they also tended to be healthier in old age - less risk of dementia, stronger grip strength, etc. ",
"The mortality effect was driven mainly by cancer, and one hypothesis is that because taller people have more growth factors they may be more prone to cancer. Another is that it's linked, at the genetic level, to the calorie reduction model of longevity. ",
"The mortality effect is so small, and there are so many complicating effects, that it's not something any one person will be able to notice individually -- that is, your observation that old people seem to be smaller is almost certainly due to confirmation bias and confounding effects (for example, on average people are getting taller, so older people were smaller on average). "
] |
[
"tall people have a larger number of cells than short people, which will lead to a statistically increased risk of cancer.",
"By the same reasoning, whales shouldn't exist. This is known as Peto's paradox."
] |
[
"Could a person have two different sets of DNA due to early mutations?"
] |
[
false
] |
Please excuse my bad non scientific english, english is not my native language: Okay so as far as I know mutations can occur when cells are creating copies of themselfs. Now lets imagine an early fetus that has it's cells dividing and there is a mutation in one of the cells that changes its DNA. This cell keeps on replicating itself with a different DNA than the other cells (which of course keep on replicating aswell). Could a child end up with two sets of DNA? Or is this not possible at all because I got something wrong? Would one DNA prevail over the other? My first AskScience post so let me take a minute to thank all the scientists here on reddit for sharing your knowledge with us!
|
[
"Not to nitpick, but are you sure? ",
"A chimera or chimaera is a single organism (usually an animal) that is composed of two or more different populations of genetically distinct cells that ",
"(My emphasis added.)",
"The cells in the OP didn't originate from different zygotes... "
] |
[
"Your body does, in fact, have many \"different sets of DNA\" although phrasing it that way makes things sound exciting than they actually are. Most of the differences we're talking about are very tiny (for example a change to a single one out of the 6 billion bases of DNA that make up your genome) and will have no effect. And each of these \"different sets of DNA\" will be possessed by only a fairly small number of cells.",
"This type of mutation is called a \"somatic mutation\" (a mutation of the body) as opposed to a \"germline mutation\" is inherited from a parent and will be present in all of a person's cells.",
"Like I said, they do occur but the particular scenario that you seem to be imagining where the somatic mutation is present in a large part of the persons body will be very very rare. The reason for this is simple: like you say, it would have to occur early in development when there are relatively few cells. Fewer cells means fewer chances for mutation."
] |
[
"Thanks for the answer!"
] |
[
"Could our universe be a 4 dimensional shape?"
] |
[
false
] |
In the same way that we thought the earth was flat even though it's a sphere, could the universe that we perceive as 3 dimensional exist in 4 dimensional space?
|
[
"Technically we ",
" perceive it as 4-dimensional, with time being the fourth dimension. However, IIRC it is widely thought to be at least** a 4-dimensional shape. But we will never be able to perceive it as such because we live in a 3-dimensional (4 with time) world. The book ",
" does a great job ",
"explaining",
" why we can't \"see\" the fourth dimension. Also, imagine you are an ant on a very tiny branch. You can only move forward and backward (2-dimensional). Now imagine that this branch grows a lot thicker, and you can now go forward, backward, and around the branch (3-dimesional). Finally, imagine an iguana comes onto this branch. You can go forward, backward, and around, while the iguana can only go forward and backward.",
"On another note, every point in space is the center of the universe. The center is everywhere, because it expands in every direction, even ones we may not be able to see. One potential idea is that the universe may expand into itself. And that would be 4-dimensional. ",
"I love questions like these, I hope I could help! ",
"**According to String Theory, it could have as many as 10 or 11 dimensions.",
"Also, nobody ever really thought the Earth was flat. "
] |
[
"Currently it looks like space is flat and don't have curvature, or it's very small. Space can be infinite or not. ",
"http://map.gsfc.nasa.gov/universe/uni_shape.html"
] |
[
"Currently it looks like space is flat and don't have curvature, or it's very small. Space can be infinite or not. ",
"http://map.gsfc.nasa.gov/universe/uni_shape.html"
] |
[
"Why are most amino acids found in the L configuration and most sugars in the D?"
] |
[
false
] |
My biochem prof briefly stated that they fit together well because they're opposite configurations, but said she didn't have time to get into it because it's only a 5 week course instead of 17. Is there a reason that it's this way and not flipped so that AAs are in D and carbs in L? Is there something fundamentally unstable about a D amino acid that they just pass over in orgo? Because as far as I know, the only difference in reactivity between the chiral molecules should be reaction with polarizing light. Or is this just a random chance thing with the universe, or something that we just don't know the answer to?
|
[
"This is a huge unresolved question (sorry, couldn't resist a little chirality humor there). It has major implications for origin-of-life studies, but despite a great deal of research over the decades, there's no definitive answer. Various mechanisms have been proposed for those two optical series to have been slightly favored over their enantiomers (effects of polarized light and other electromagnetic explanations, for example) but all of these are very subtle and their importance hasn't yet been proven.",
"And many of these explanations come down to \"random chance, but there was more of this kind around to start with because of subtle effect X\". I don't think that any of the explanations based on reactivity or mechanisms hold up, including the one that your professor gave you (which I'd never heard before).",
"It's a safe bet that the arguing over these will probably never end until we have more than an N of 1 for protein/carbohydrate life. And probably not even then!"
] |
[
"That is one of the big mysteries in chemistry. Until we find life on other planets, we won't know if luck or some deeper reason is responsible. ",
"One possibility is polarized light. Light in interstellar space is circularly polarized, so this might have an effect on enhancing or destroying one orientation over the other. Another possibility is a small (and this is very small which I don't believe has been measured) energy difference between different chiral molecules because of parity violation due to the weak interaction. I personally don't give much to this one, but it has been mentioned."
] |
[
"There's no difference in stability or reactivity. The main reason is evolutionary - things get re-used both substances being re-use metabolically but also genes getting \"re-used\" evolutionarily. So there's a benefit if we all use the same stuff, which we do to a much higher extent than just chirality - we all use the same DNA code (with a few exceptions), the same 20 amino acids for making proteins (again with a few exceptions), the same phospholipids for making cell membranes, and so on. ",
"Since there's no significant difference one would expect it to be equally likely for life to evolve to use one as the other. But precisely because there's no real advantage in having both around but a significant benefit to everyone using the same thing, you wouldn't really expect it to be stable at 50-50 but rather veer off randomly to stable equilibria at 100% of one or the other form. Most think which of L or D you use is random chance, but the fact that nature wound up 'picking' one is not so random. ",
"I suspect your teacher was being a bit glib; I've never heard that there'd be any connection with amino acid and sugar conformations, and I don't really see how they'd fit together better. The important thing if you want to be stereoselective is that you only have one isomer around. If you had a racemic mixture of amino acids, you could end up with a racemic mixture of enzymes with mirrored binding sites that'd work to produce a racemic mixture of products and so on. But as long as you use a single isomer your binding site can be specific for either isomer regardless of which AAs are used to make it, as long as your'e only using one isomer of the AAs. ",
"It's still interesting to consider what might've ended up pushing things in one direction or the other though. There are natural processes that can separate isomers, such as crystallization. (separating tartaric acid crystals was how Pasteur discovered chirality in the first place) The ",
"current hypothesis",
" is that RNA came about before DNA and proteins, so we likely reached homochirality with RNA before that of either AAs, sugars etc came into play."
] |
[
"Ok, Scientists, Could engineers [et al] make a lead-shielded mechanical suit that could let a workers work on the Fukushima reactors? [Fukushima #2 blasting 73 SIEVERTS / hr]"
] |
[
false
] |
Just heard that Fukushima #2 is not a good place for a tea party, with the area just above the cooling water giving a healthy 73 Sieverts / Hr [that's Sieverts, NOT ] Someone has made a mechanical suit that lets a human lift lots of weight.. to wit So could you make a bigger, lead-armored suit that would let workers get in there to...um... do... something?
|
[
"Why must it be a suit? A suit designed to track movements and give tactile responses could be used to control an unmanned vehicle with robot arms attached. We're at the point where it's so precise, we can perform surgery with it."
] |
[
"Good point.. I'm hearing that this environment is too radiactive even for FUCKING ROBOTS to operate without extensive shielding... the radiation interfering with the electronics. I am interested to know how much lead would be needed to keep a person safe, or at least kind of safe for a while, in this kind of environment ",
"Seems like an intractable situation on that blasted coastline. "
] |
[
"I'm not the one that asked the question and I wasn't saying the title was at its most optimized and semantically-correct state (Jeez, who argues about this kind of stuff, really...)",
"I was just saying, it should be easy to understand what he was wanting to know (you understood just fine if you're able to suggest a better title) and that your first answer didn't even address the question whatsoever."
] |
[
"How do integral membrane proteins get associated within the membrane?"
] |
[
false
] |
Integral membrane proteins are tightly associated within the cells membrane but how do they get associated in the first place? Are there special chaperones that do this in the beginning of the cells life cycle? What are he stages between protein synthesis and membrane association?
|
[
"Many integral membrane proteins are transmembrane proteins (proteins that go through the lipid bilayer and have exposed parts on either side of the membrane).",
"Transmembrane proteins are inserted into the membrane as they are translated at the ER (",
"diagram",
"). For these proteins synthesis and membrane insertion occur at the same time.",
"Other membrane associated proteins may bind to the membrane after synthesis by a variety of means. Some proteins are modified with lipid groups (",
"wikipedia",
"), the lipid group is embedded in the membrane and the protein is covalently attached to the lipid.",
"Other proteins may have a ",
"hydrophobic loop",
" or ",
"amphipathic alpha helix",
" (both are often associated with membrane curvature) that can insert into the membrane."
] |
[
"Well, there's a chemical reason, and there's a mechanical reason that integral membrane proteins end up in the membrane.",
"First, the chemical reason: it all has to do with entropic favorability that integral membrane proteins want to be in the membrane in the first place. They have hydrophilic and hydrophobic regions, and remember that like dissolves like, no matter if it's in your body, or if it's in a test tube. The hydrophobic regions will associate with other hydrophobic regions (i.e. the fatty acid tails of the membrane) and the hydrophilic regions will associate with the molecules that can stabilize their partial charges and their full charges (i.e. water and the other hydrophilic regions), so this differential association will inevitably occur.",
"Now, mechanically, it's a little bit more complicated to explain. To answer the question about special chaperones, not really. Not during the beginning of life cycles, at least. There are chaperones, but they occur later. Remember from the cell theory that all existing cells came from other cells. Basically, when a cell divides and gives rise to progeny, its plasma membrane gets divided as well. Theoretically, you would expect about half of every type of membrane protein in the original cell to be found in each of the progeny cells, and indeed, in cells where there is no organization of where you'd find specific proteins, that is what we see. However, there are certain cells that have differential expression of membrane proteins depending on where you look. A good example of these cells would be the epithelial cells lining the renal ducts in your nephrons (where reabsorption, etc. take place). In cells like these, sometimes (but not always) cell division tries to account for this differential expression by dividing in an orientation that will still evenly (or almost evenly) distribute the proteins in the membrane.",
"Regardless of whether or not the cell division gives each progeny cell about the same amount of membrane protein, the stages between protein synthesis and membrane association are as follows (in most cases, at least):",
"1) mRNA transcription of a pre-mRNA transcript occurs in the nucleus. This mRNA strand can NOT yet be translated, as it has factors that aid in its departure from the nucleus.\n2) the pre-mRNA leaves the nucleus and enters the cytoplasm, where the factors that allow it to leave the nucleus are snipped off by various factors in the cytoplasm. These factors are cool, but they aren't really important to this explanation, so I'll let you look them up.\n3) The mRNA (which is now ready to be translated) associates with an unoccupied ribosome (the smaller portion of the ribosome, to be exact)\n4) Here, at about the same time, a special \"tag\" if you will on the mRNA coding for the membrane-destined protein causes the small portion of the ribosome to associate with the rough ER, and a large portion of the ribosome associates with the mRNA. Now, translation is ready to begin.\n5) Translation happens. Again, a very interesting mechanism causes translation to occur, but I'll leave that to you to look up. The important point here is that the protein product is fed into the rough ER as it is translated.\n6) Translation finishes, the mRNA and the ribosome dissociate, and the pre-protein is all happy inside of the rough ER.\n7) The pre-protein travels from the ER to the Golgi Apparatus, where it is chemically modified in various ways into a form that is more similar to its final, ready-for-insertion form\n8) Something triggers exocytosis of vesicles originating in the Golgi that happen to contain your pre-protein (or protein, it depends). In many cases in humans, this trigger is a MASSIVE influx of calcium ions into the cell's cytoplasm, but it depends.\n9) In some cases, during this exocytosis, other proteins are allowed into the vesicle and they change the structure of your pre-protein so in can insert into the membrane.\n10) The membranes of the vesicle and the plasma membrane fuse, and voila, you have a membrane-bound protein.",
"Now, there are some points to this process that I've left out (such as chaperonins, specialized proteins that will promote the folding of proteins so that they assume the correct three dimensional shape faster), and I trust other people will point them out, but here's the point: If a protein has the properties of having hydrophobic and hydrophilic regions in a certain three-dimensional conformation, and the cell appropriately promotes the assumption of this three-dimensional conformation, the protein will associate with the plasma membrane naturally. This is because of entropy. While you decrease the entropy of the hydrophobic molecules by having them associate, you greatly increase the number of available microstates to the water that doesn't have to dissolve (or try to dissolve, at least) such a large surface area. Processes like these, where the free energy is negative (here it's negative due to the huge entropic favorability), will occur on their own.",
"I hope I answered at least some of the questions you posed for you, and please let me know if you'd like clarification on anything."
] |
[
"Are there special chaperones that do this....",
"I believe you're looking for the ",
"translocon",
", at least for a number of cases IIRC."
] |
[
"What distinguishes wasabi (or any other horseradish) and hot peppers (such as tabasco) from each other in terms of their heat when we eat them?"
] |
[
false
] |
[deleted]
|
[
"Radish and peppers have different type of molecules that cause you to experience a hot sensation. Peppers contain the compound capsiacin which will directly bind to subset of temperature sensors and activate them. Rasishes on the other hand, generate allyl isothiocyanates as their \"hot\" compound. These two compounds will bind a different set of receptors causing you to percieve the heat differently. The difference in heat location (tongue versuses nose) could be due to a number of possibilities that may, such as differing receptor expression (more receptors that respond to isothiocyanates are in the nose), differential sensitivity between receptors, differential volatility between capsaicin and allyl isothiocyanates (so the allyl's are more likely to just get into the nasal cavity). "
] |
[
"Here are a couple previous threads on the subject:",
"Why do foods like wasabi, horseradish, and mustard make a person's sinuses burn? What is happening exactly to cause the sensation?",
"Why is the burn felt from eating a hot pepper different than that felt from eating horseraddish or wasabi?",
"Can someone explain the inexplicable phenomena that happens when one takes a spoonful of wasabi paste?"
] |
[
"Spiciness as we know it is a function of the amount of a molecule called capsaicin. Spicier foods have a higher concentration of capsaicin. This is quantified (albeit in an incredibly subjective way) by the ",
"Scoville Scale",
". The Scoville number of a food indicates the dilution factor necessary to make no spice detectable by a panel of 5 tasters. ",
"On a neural level, capsaicin activates pain neurons by activating an ion channel called TRPV1 and resulting in action potentials in pain neurons."
] |
[
"How is the original amount of C14 in a fossil determined?"
] |
[
false
] |
When it comes to carbon dating, I understand how the age of a fossil can be determined with the necessary information, being how much C14 is in the current fossil, how fast that C14 deteriorates, and the original amount of C14 in the animal. My question is how the original amount of C14 is determined? Looked everywhere I could and couldn't find an answer, so thank you for any replies.
|
[
"It's not the absolute amount of C",
" that matters, but the ratio of C",
" to C",
" in the sample. The atmospheric ratio is held more or less constant by the creation of C",
" from Nitrogen, but once stored inside a body, it will decay to ",
" N",
". The longer it has been since the body breathed or ingested, the more C",
" will have turned into ",
" N",
"."
] |
[
"To add to this, the \"more or less constant\" originally threw off carbon dating a bit since it has not been perfectly constant. A calibration curve was created to correct for this using, among other things, dendrochronology from bristlecone pines. Bristlecones can live thousands of years (oldest currently alive is about 4800 years old) and by carbon dating their tree rings it was possible to reconstruct the exact atmospheric C12/C14 ratios over time for more precise dating."
] |
[
"That's only a problem for dating plants that grew after there was a lot of nuclear testing. 1950 is considered the cutoff point. But for example wood from a tree cut down in 1610, we can still carbon date that, it's not affected by the later nuclear testing."
] |
[
"How do scientists \"figure out\" the chemical structure of things?"
] |
[
false
] |
How do we know water is made up of molecules with 2 hydrogen and 1 oxygen atom? How do we know the chemical structure of dextrose or propane or hexane?
|
[
"Ugh experimentalist....time to get a theorist in here to clean this up. ",
"Ok so the OP was asking how do we know there are two hydrogen and 1 oxygen atoms. While your answers aren't wrong, they aren't really answering enough. ",
"Yes in modern day we have techniques like NMR, IR, UV/VIS, etc to figure out structure, but for a long time we didn't have those (In fact only up until the last century did we have them while our understand of chemical structures goes much further back) and actually it was our idea of what the structure of molecules which resulted in those techniques!",
"In the early days the first task was discovering which compounds were elements (or fundamental units) and which ones were mixtures. There were criteria for proving something was an element, but I won't go into much detail here since that is a topic all its own. Once they began sorting the elements out they could then determine what compounds were made up of by how they reacted.",
"For instance with hydrogen it was observed that when you combusted it with oxygen the reaction would form water (In fact the name hydrogen means water-generator). Since hydrogen was an element and oxygen was an element it could be concluded that water was made up of hydrogen and oxygen. They could figure out the empirical formula H2O by carefully performing experiments to determine the mass ratio and as a result the mole ratio of H/O in water.",
"The same could be done for organic compounds where you can burn them and figure out the ratio of carbon, oxygen, hydrogen, etc. by the ratio of the products of its combustion (CO2 and H2O). From that you can determine things like Methane's formula was CH4, Ethane is C2H6, etc.",
"Essentially before the fancy equipment we have now structures were determined from chemical reactivity and products. If you know the fragments and/or the building blocks you can know what the compound was made of.",
"The actual shape of the molecules was a whole different problem and actually many of the structures they came up with was incorrect, but they were working with very few tools to actually determine the shape. ",
"Now a days we can use techniques that were mentioned to investigate larger more complex structures. We can take simple compounds and obtain a spectrum and figure out how certain functional groups behave. For instance we can take Infrared Spectrums of molecules containing Ketone functional groups and figure out how the Ketone group absorbs light. So if you were to take a spectrum of Acetone, Butanone, etc. You might notice there is a strong absorption toward light at 1700 cm-1. Since this is found on ketone containing compounds, but not simple chain hydrocarbons (IE We see it on Acetone which is a three carbon chain with the oxygen, but not Propane which is just a three carbon chain) we can show that the peak we observe is associated with that functional group and now we can use that information to look at other compounds and determine what functional groups are contained.",
"Science in general is \"Take what we know and figure out how to use it to determine what we don't know\""
] |
[
"So I will comment on the structure.",
"The two experimental gold standards for this are microwave spectroscopy and xray crystalography (other spectroscopic techniques exist but they are far less accurate).",
"In MW spectroscopy the spectrum is determined by 3 rotational constants that are inversely perportinal to the mass distribution of the molecule. If we substitute the atoms in the molecule (or with natural abundance) with isotopes we get a different spectrum and different constants but the same structure. There are then mathematical equations (Kraitchman) to solve the positions of the atoms to ~0.001As accuracy. This is generally used for small molecules (<20 heavy atoms) and is difficult for metal containing species.",
"Larger systems typically use xray. Here a crystal or a powder is put in front of a beam of xrays. These xrays scatter off the nuclei of atoms and the angles are measured. This gives the position of the atoms in the crystals and thus a molecular structure. The downside is that structures change when they are in crystals vs liquid vs gas.",
"Another notable method is NMR. This technique is best used for large biological samples where crystals cause problems. Here various atom substitutions are made and the NMR spectra are recorded. The spectra then give information on the chemical environment of the atoms and allow the user to deduce the final structure. The downside is the data is extremely complicated and there are fairly reasonable errors.",
"The final method is really theoretical ab initio methods. Here you can calculate the structure very accurately using quantum mechanics and various harmonic forcefields. The main disadvantage is beyond \"small\" molecules it becomes extremely computationally intensive so many assumptions have to be made for biological systems leading to large errors.",
"People are obviously going to mention AFM and STM but they are extremely limited in what they can measure and are popularized from their images rather then real abilities."
] |
[
"I've rarely heard of many chemists using Microwave Spectroscopy regularly. And I know a lot of chemists who avoid using XRD for as long as they can. ",
"I'd say NMR (Nuclear Magnetic Resonance) and Mass Spectrometry are your main techniques. Both methods don't require much work up and give you quite a bit of data.",
"NMR can tell you what different kinds of H, C, N, P, F, anything with an odd number of protons or neutrons, you have. This normally tends to be ",
"H and ",
"C NMR due to the abundance of the elements, and the fact that most chemistry involves at least some of each. ",
"H NMR for small molecules takes less than 10 minutes to run so it is an extremely useful technique.",
"Mass spec gives you a mass/charge ratio of what's in your chemical. As an example, if you've got H",
"O",
" (Hydronium Ion), it will have a mass charge ratio of 3/1 = 3. Often you also break up the elements at weak bonds which helps you identify common functional groups. ",
"Another good one is Elemental Analysis, in which chemicals are burnt and then relative amounts of different gases are measured and can be used to calculate the amount of Nitrogens, Carbons, Hydrogens, Oxygens and Sulfurs.",
"I guess the key to it all is that we normally know roughly what we're looking for, so we can pick the techniques best for us to look at."
] |
[
"Is it true that our eye needs to focus light for us to use it effectively, but our body doesn’t focus touch sensations, and yet we can still use our sense of touch effectively?"
] |
[
false
] | null |
[
"Some focus is needed, yes, but doesn't have to be perfect. Near and farsighted people can still see things even without their classes (although very blurry). You have different kinds of touch receptors, some are sensitive to more localized sensations (like pinpricks) and are more closely spaced (like on your fingertips) than others (like for stretching/pressure; ones on your elbow or back)."
] |
[
"But is there any sense in which your body \"focuses\" touch sensations like the eye focuses incoming light?"
] |
[
"No"
] |
[
"Since the outer layer of our skin is essentially dead cells, why isn't our skin a more attractive target for decomposing bacteria?"
] |
[
false
] |
Why wouldn't our outer skin normally rot?
|
[
"We have a protective layer of bacteria which prevents pathogenic bacteria that rot us from growing and our skin is quite acidic and low in moisture anyway which makes it hostile to invaders. The bacteria that live on us survive on compounds in sweat and oils."
] |
[
"Probably, skin bacteria are adapted to our skin conditions and fight off any interlopers and, in general, other skin bacteria- they're quite antagonistic.",
"Skin cells falling off wouldn't kill bacteria, the acidic conditions and competition from other bacteria stops invading bacteria colonizing you. Symbiotic bacteria and some disease bacteria are very capable of living on your skin despite skin falling off."
] |
[
"so, sort of a co-evolved/symbiotic relationship?\nalso, could it have anything to do with the fact that the dead cells are constantly falling off?"
] |
[
"How did we get the high resolution photos of the bright spots on Ceres?"
] |
[
false
] | null |
[
"The Dawn spacecraft, which went there."
] |
[
"As ",
"u/rantonels",
" points out, it is from the Dawn spacecraft (a discovery class NASA mission operated by JPL/UCLA). The specific instrument in question on Dawn that took those pictures is the Framing Camera, an instrument from the German institution DLR. Dawn also has a visibile and near-infrared spectrometer and a gamma-ray and neutron detector (which are from Italian and USA institutions, respectively)."
] |
[
"lol"
] |
[
"Do liquid form medications actually work faster than tablets?"
] |
[
false
] |
I see this in advertisements and packaging a lot, the claim that liquid form medicines (such as pain relief or cold medication liqui-gels, etc) are "fast acting", taking effect quicker than regular tablet formulations. Is there any truth to this?
|
[
"This question is surprisingly complicated.",
"Different routes of administration can result in different Tmax, which is the time to maximum concentration in plasma. I've seen a suspension formulation that beat a tablet, a gelcap that beat a liquid formulation, and a fast-acting tablet beat a liquid formulation. The bottom line is that route of administration can affect Tmax, but the effect can't be stated categorically as there are many types of formulations that are \"liquid\" or \"tablet\".",
"Liquid formulations are usually developed for administration to children, patients with trouble swallowing pills (such as after a stroke), or the elderly who have higher incidence of dry mouth.",
"So, the answer is that it's probably true for the drug they're advertising, but the effect difference or time to maximum plasma concentration might be marginal, and the term \"fast-acting\" doesn't necessarily hold for all liquid formulations.",
"Edit: ",
"Here's an example",
" of a gelcap beating a liquid."
] |
[
"Pharmacology PhD student here (finally, my time to shine!).",
"The short answer is, it depends on the medication. For a slow-release capsule, clearly it takes longer for all the medicine to get on board. But it's designed this way, because you have to take fewer pills throughout the day to get a steady state of medication. For the classic asprin tablet, or something that is simply medication compounded in dissolvable pill form (ie, no coating/layering/time-release mechanism), it dissolves in your stomach acid almost instantaneously. Liquid formulation would have no advantage as far as being in solution more quickly.",
"However, like everything else, the real answer is \"its complicated\" because the goal is not to get the compound in solution quickly, it's to have it absorbed into the blood stream quickly. This is where it really depends on the medication. The most important characteristics for the absorption of a small compound which passes into the blood stream by passive diffusion (ie, there's no protein transporter that causes it to be taken up from the gut), is by and large molecule ",
" (small molecules can slip in between cells into the blood stream whereas large molecules have to go through cells), ",
" (how \"non-polar\" the compound is, because lipophilic molecules can cross cell membranes more easily than polar molecules), and ",
" (which determines at what part of the gut the compound can be absorbed). Of these three, formulation can really only help with pH. Acidic compounds are absorbed in the small intestine and basic compounds are absorbed in the large intestine, which is why some medications are given as suppositories. By coating a tablet with a buffered compound, you can change the local pH in the area of the gut you want absorption in (early or late). You can't really do this with a liquid that you're swallowing. As far as the alcohol goes, this is more about the chemical characteristics of certain compounds which lead them to dissolve more easily in alcohol than in aqueous solution. In this case, alcohol-containing liquid is generally the most effective formulation.",
"Liquid vs. pill of the same drug isn't going to make a large difference with just a few exceptions. Liquid formulations can allow absorption in the upper GI tract (mouth and throat), but if you're swallowing it quickly, it likely doesn't have time to happen. Some people just don't like swallowing pills. The fastest way to get any medication into the blood stream quickly is IV, but clearly most people wouldn't be comfortable shooting up asprin whenever they get a headache.",
"Note that these are all for systemic effects. If you want a localized effect (ie, anesthesia for a sore throat), then liquid wins because it's already in solution. Also, for CNS drugs, the limiting step is often crossing the blood-brain barrier rather than absorption, but that's a whole 'nother post."
] |
[
"Can for example cold medicine react with other parts of the body which aren't interesting for recovery?",
"If I'm understanding you right, then the answer is yes. An example: ",
"pseudoephedrine",
" (Sudafed).",
"Pseudoephedrine is a sympathetic agonist (meaning it \"turns on\" the alpha and beta nerves of the ",
"sympathetic nervous system",
"), so while part of its effect is to dry up your sinuses, it also carries side effects like tremors, heart rate above 100 beats per minute, and increased blood pressure. This isn't usually a problem for healthy people, but for someone with hypertension or heart disease, it can lead to exacerbation, stroke, dysrhythmia, and possibly death.",
"This leads into the pharmacology principle of selectivity: The ideal drug has an effect that we want, on the part we want, without effecting anything we don't want (aka, side effects). Sudafed has an effect that we want (constrictions blood vessels in the nose and sinuses to clear up congestion), but it isn't selective for just the nose/sinuses, thus, it causes increased heart rate and blood pressure. An example of a drug with good selectivity is ",
"penicillin",
", which binds to ",
"penicillin-binding proteins",
" that only exist on bacterial cell walls (we, being eukaryotic, don't have cell walls)."
] |
[
"Why and how is it that the O blood type is recessive and yet O is the most common blood type?"
] |
[
false
] | null |
[
"So the percentages are 38% type O+ to 34% A+, so it's not ridiculously more common. Positive is also more common than negative. Some of these changes likely have to do with maternal incompatibilities making + more favorable. There have also been studies that type O is at lower risk of heart disease and certain cancers, so some benefit there. So if it was selected for by survival being greater and for those benefits before we even knew what blood types were, then it wouldn't matter if it was recessive or dominant. The same is true for polydactyly which is dominant. Just because it's dominant doesn't mean it was selected for so we aren't all walking around with 6 fingers on each hand"
] |
[
"Recessive doesn't have to mean \"bad\", although \"bad\" recessive alleles are widely known. There's little adaptive pressure on ABO blood types, at least prior to the invention of blood transfusions. I am unsure if ABO blood types have ",
" function.",
"In genetics, blood types are called I for \"isoagglutinogen\" (thanks Wikipedia for the long name, and this simply refers to blood antigens sparking an immune response), and I recall they were called i, IA, and IB (O, A, and B).",
"Type O antigens are \"missing a piece\" and so lack a binding site and do not provoke an immune response. (Wikipedia says they lack an enzyme to modify the antigen.) This causes no clear harm, and the only clearly notable effect is people with type O blood (no type A and no type B antigens) will launch an immune response to type A and type B antigens since their immune systems will not recognize those antigens. This should only come up in a botched blood transfusion.",
"Because there is \"no harm\" there should be \"no\" selective pressure. In practice there seems to be some slight differences (more resistant to some diseases, perhaps less resistant to some diseases) but the effect seems to be fairly minimal.",
"Blood is a liquid tissue, and it's fortunate it provokes so few immune responses, compared to a liver transplant, skin transplant, etc. There are lots of blood types, as a matter of fact, but only ABO and Rh +/- normally provoke an immune response. (Another commonly studied blood type, MN, doesn't.)"
] |
[
"Those numbers change depending on what population you look at. Geographically or ethnically, the numbers can change. These days, it's not going to be some huge difference though. O is the older type, but A & B showed up a long time ago from a human perspective."
] |
[
"Is time divided up into discrete quanta? Is time \"quantized\"?"
] |
[
false
] | null |
[
"No this is just wrong. It is not known if time is discrete but if it is then the units are much smaller than a Planck time. A Planck time is the scale at which quantum events happen, and a discrete unit would have to be much smaller than that"
] |
[
"This is not what the Planck scale is.",
"It's simply the scale at which our current models don't yield meaningful values anymore and we'd need Full Quantum Gravity to provide an accurate description of these kinds of interactions..."
] |
[
"This is not what the Planck scale is.",
"It's simply the scale at which our current models don't yield meaningful values anymore and we'd need Full Quantum Gravity to provide an accurate description of these kinds of interactions..."
] |
[
"Why can't neural cells divide while other somatic cells can?"
] |
[
false
] |
I know basic biology, and, as far as I can understand, neural cells, such as brain cells and spine cells, can't divide and regrow once they are destroyed. This is why people with spinal damage are permanently crippled. Why is this? Are there restriction proteins stopping the division process? if so, which ones? Is there a lack of a certain protein necessary or are there proteins that stop cell division from occurring? Is it something else? I apologize ahead of time for any grammar or spelling mistakes. I have never been that good at English.
|
[
"Surprisingly, we now know that neurons can both repair themselves (neuroregeneration) and divide (neurogenesis), but only to a small extent and in limited contexts. Otherwise, they are termed \"postmitotic\" and are in the G-zero phase of the cell cycle. It's believed this is a result of how specialized they are. "
] |
[
"They are post-mitotic and enter Go, as stated below. Think about it. Neurons have made connections to other cells in the brain and while some of these connections can be altered or strengthened over time (google \"cells that fire together wire together), it wouldn't make sense for a neuron to divide. It would have to sever all connections and split into 2 cells and alter the existing framework in place.",
"\nNeurons do send out axonal projections after injury in the spinal cord and peripheral nervous system, but often these projections may not be long enough or are improperly guided. Equally likely is that these projections get impeded by the formation of scar tissue (fibrosis) that quickly assembles at the injury site. A lot of spinal cord injury research attempts to tackle these problems by reducing fibrosis as well as using substrates to guide axons to proper endpoints.\nAs mentioned below as well, there are a few sites in the brain that contain neural stem cells that can give rise to new neurons. Off the top of my head I believe these are the subventricular zone of the hippocampus and the olfactory bulb"
] |
[
"Could you explain the contexts in which they can multiply?\nOr, can you provide the names of any articles that cover neural regeneration?"
] |
[
"Do water droplets oscillate naturally and, if so, what amplitude and frequency do they oscillate at?"
] |
[
false
] |
So I have had an idea for a while now that I have recently started to explore properly and I am having trouble distilling the information out there into the information that I need. Since we have such a good variety of experts then maybe someone already knows what I need. Suppose you have a droplet of water or other aerosol, if unperturbed it should sit as a sphere with the pressure and surface tension in balance. If it is then perturbed it will oscillate I assume in shapes according to spherical harmonics. I know that if you have a charged droplet (e.g. Millikans oil drops) then you can by the application of an alternating electric field. However, if no driving force is present do they still oscillate? As in imagine you sprayed some perfume and as it hangs in the air are the droplets oscillating or still? In terms of a single droplet, if they do oscillate then at what frequency do they oscillate? Is there a preferred mode(s) from an arbitrary perturbation (in terms of power spectrum)? Does that mode have a set frequency? Lastly, what are the typical amplitudes of any oscillations? I assume there must be a limit where the droplet would become droplets but are they deforming in terms of radius by 1% 10% 100%? Any help (or useful discussion) would be greatly appreciated!
|
[
"A while back I came across ",
"this paper",
", which seems close to your question. These guys (dia)magnetically levitated water drops of different sizes in a solenoid and looked at the vibrations as a function of the size. For example, for a drop about 6mm in diameter, the vibrations were on the order of 0-100Hz.",
"They even measured the ",
"power spectrum",
" and compared the results to numerical calculations for that potential (by applying the ",
"Rayleigh method",
" to an elastic continuum model of the droplet), finding a decent match between the two. Even though this situation is not quite identical to having free droplets, the paper claims that the trapping only shifted the vibration energies by ~1Hz.",
"edit: formatting and a brief description of the expected shift in frequencies caused by the trapping"
] |
[
"Wonderful, exactly the kind of stuff I was hoping for. ",
"They seem to be concerned with the effects of the trap on changing the frequencies but this is the knife needed to wedge open the literature seam I think.",
"edit for your edit: Yeah, seems reasonable. The question of amplitude remains, which I knew was going to be the hard part I guess. It is also further complicated by the conversion from amplitude of these oscillations to the thing I want is equally spotty."
] |
[
"Something that is sort of opposite this is a gas bubble in a liquid. The competing external pressure of the fluid and internal pressure of the bubble cause harmonic oscillations. These oscillate at what's called the Minnaert frequency, which is associated with the sound made by babbling brooks. The angular frequency squared is inversely proportional to bubble radius, with a prefactor of roughly thrice the ratio of gas pressure to fluid density (with corrections for surface tension, compressibility, etc).",
"Here",
" is the historical source; nowadays one of the main applications is in ultrasound contrast bubbles."
] |
[
"Why do firearms (especially fully automatic firearms) recoil upwards, instead of just recoiling directly backwards in the opposite direction of the bullet? Additionally, why do they recoil up instead of sideways or down?"
] |
[
false
] | null |
[
"Recoil pushes the gun backward towards the shooter, but the barrel is usually off-center compared to the handle and weight of the gun.",
"Your hand, holding the handle of the gun and looped into the trigger, creates a pivot point, which pulls the gun around, pointing upward.",
"If the gun barrel were somehow below the pivot point, it would recoil downward."
] |
[
"Older rifles",
" had the sights right on top of the barrel, which to fit to the shoulder required the stock to bend downwards. This of course ended up creating a torque and pushing the barrel upwards. ",
"Modern rifles",
" have the sights above the barrel so the stock goes directly back into the shoulder to try and lessen this effect. As a result, the recoil goes more towards a backwards kick and less to a torque raising the barrel. "
] |
[
"Yes, I have noticed in high speed movies of guns like a semi automatic pistol, the gun doesn't kick much until the slide travels backward and hits the stop. Then the gun flips upward. So the spring is absorbing the recoil, until it can't."
] |
[
"Why do some things burn and others don't?"
] |
[
false
] | null |
[
"Things that burn have a chemical structure that allows their molecules to form simpler, energy-stable molecules in a chain reaction that is started when heat energy is added. ",
"The heat provides the energy for the more complex molecules to form less complex ones. When they change, the new forms requires less energy to hold together. The extra energy is released as heat and light. The heat causes the same reaction in remaining complex molecules. This happens until the fuel (complex molecules) is exhausted.",
"Normally when we think of burning, we mean combustion. So, usually the more complex molecules are hydrocarbons and the less complex molecules are carbon dioxide and water, with residual ash and smoke being released due to incomplete conversion. Also, O2 is a part of the process."
] |
[
"\"Complex\" might not be the best adjective. Take for instance hydrogen, or pure metals, which can be very energetic fuels. Oh, and carbon. Come to think of it, I wonder if silicon burns well."
] |
[
"O2 isn't the only oxidizer that can propagate a combustion reaction. The oxidizer just has to have a higher electronegativity than the substance it is oxidizing so it can win the 'battle' for the electrons. F2 can also be used to propagate a reaction when O2 is not present or isn't capable of oxidizing a substance."
] |
[
"What universal constants are in the range of size/time which humans can relate to?"
] |
[
false
] |
Most are far too huge (speed of light) or far too small (size of even the longest non-chain molecule) The only one I can think of is the few dozen half lives between Carbon 15 (2.449 seconds) and Nickle 63 (a hair over 100 years). This isn't very helpful for me, as a half life is by definition an average of a random event, rather than a reliable clock or meterstick.
|
[
"I always found it fascinating that a Planck unit of energy is about the same as a tank of gasoline.",
"There's also the ",
"barn-megaparsec",
"; a barn is a unit of nuclear cross-section and multiplying that area by one megaparsec produces a unit of volume equal to about 2/3 of a teaspoon."
] |
[
"I'd just like to point out that the barn-megaparsec is ",
" a physical constant in the sense of Planck's constant or the speed of light."
] |
[
"You must choose which units you work with, because the choice of units scales the universal constants. As a (boring) example, take the atomic units (",
"http://en.wikipedia.org/wiki/Atomic_units",
"), they are chosen so that\nelectron mass = electron charge, hbar, coloumbs constant = 1.",
"But assuming you want to use SI units, there aren't any fundamental constants being around unity (which basically is what we can relate to). You can see a few listed here",
"http://en.wikipedia.org/wiki/Physical_constant"
] |
[
"WiFi signals are electromagnetic radiation, which are photons. How do they travel through walls?"
] |
[
false
] |
As above. Where am I confused? Edit: thanks everyone!
|
[
"ELI5: Walls are see-through in a color we can't see."
] |
[
"Photons are absorbed by different materials depending on their energy (proportional to the frequency of the electromagnetic wave that they represent). The reason for this is that when a photon is absorbed by an atom, its entire energy must be absorbed by an electron, which \"jumps\" up to a higher energy level inside the atom. Electrons in different atoms are restricted to certain energy levels, which means they can only absorb certain photons, because the electrons can't absorb just a bit of the energy of a high-energy photon, nor can they absorb a lot of low-energy photons and add them up to create enough energy to make the jump. ",
"The light that we see is of a fairly high frequency in comparison to the electromagnetic signals that WiFi uses (radio waves). It happens to be of the right energy* to be absorbed by the materials that we regularly encounter. Radio waves, however, have too low a frequency (and therefore energy) to be absorbed by those same atoms, so they just go straight through. Photons are not charged particles so they don't interact with the atom in any other way. ",
"There are still some effects that can disturb the propagation of radio waves though (hence the radio signal sometimes becoming \"static\" when you drive under a bridge for example) - these are due in various ways to the wave properties of the radiation. More info on that ",
"here",
". ",
"EDIT: *Well, actually, it's more correct to say that we evolved in such a way that our eyes detect that particular frequency, rather than \"It happens to be the case\".",
"\nEDIT2: clarity/expansion"
] |
[
"Yeah - that's how UV sunglasses work. They're opaque to UV but let visible wavelengths through."
] |
[
"If You Can Smell the Odor of something, Are You Breathing in Microscopic Particles of that Substance?"
] |
[
false
] | null |
[
"Yes, although when we say \"the smell of this thing\" we may be referring to a different microscopic particle which is associated with that thing's presence.",
"For example, the smell of rain is not tiny particles of rain, but rather ",
"geosmin",
", which \"occurs in the air when rain falls after a dry spell of weather or when soil is disturbed.\""
] |
[
"And the smell of feces is mostly due to gasses that do not constitute \"poop\" in a literal sense."
] |
[
"But more to the point here. When you smell poo you are smelling the gases emitted by poo. You are not inhaling microscopic bits of poo. I may be wrong but I think that was the real question/concern."
] |
[
"Scientists created a “radioactive powered diamond battery” that can last up to 28,000 years. What is actually going on here?"
] |
[
false
] | null |
[
"Link to the article in question",
"This battery is basically similar to the ",
"radioisotope thermoelectric generators",
" used in space probes: radioactive material decays, which produces heat, which is converted to electricity.",
"The researches here have found a way to make such a battery quite small, durable and (as far as I can tell) working with relatively \"harmless\" radioactive material."
] |
[
"It's also old news and the specific power output is really low.",
"https://phys.org/news/2016-11-diamond-age-power-nuclear-batteries.html",
"https://theness.com/neurologicablog/index.php/nuclear-diamond-batteries/"
] |
[
"https://theness.com/neurologicablog/index.php/nuclear-diamond-batteries/",
"Nice read. Quoting it:",
"Even with low power density, we could theoretically fill a warehouse-sized building with millions of NDBs and hook them up to the electrical grid. This would provide steady power for thousands of years.",
"Probably it will all come down to cost-effectiveness.",
". Clearly, you won’t be powering a cell phone, let alone a car, with such a power density. So what is this company talking about? While I have yet to see an interview or report that says so explicitly – ",
". This actually makes perfect sense, and is a great idea. So the chemical battery provides the power density and the output to power the device, and the embedded NDB slowly recharges the battery. The company claims – “",
".” This sounds like a claim that needs to be verified, and seems to be out of proportion to the typical power density of such devices.",
"But I agree",
"I am always skeptical of claims that a technology can be “scaled up”",
"So where is this research in 2021? Who bought it? Who invested on it?"
] |
[
"Given how difficult it is to get off our own planet, how would we go about bringing a team of people back from the surface of mars"
] |
[
false
] |
I realise that Earth's gravity is greater than that of mars but I assume it would still take a lot of fuel to get back off the martian surface. Would we send fuel ahead of the landing party or use ice from the surface to create fuel down there? It's been a slow day at work and my mind has started wandering to things like this. ** edit. Just realised I forgot the question mark in the title. Oops
|
[
"There are a lot of plans to this effect. ",
"Some use multiple launches to land multiple objects on mars, including habitation modules, fuel, a rocket to get back, etc. ",
"Some want to send a small factory to mars which will produce the fuel necessary. ",
"Some don't want it to be a two way trip at all. It just depends on how you're planning on setting up the mission. "
] |
[
"Just off the back of this, would it not be more practical to build a kind of mini ISS in orbit around mars instead of going straight to the surface? Surely we could learn a huge amount about the planet from orbit and shipping supplies to a station is much easier and carries less risk to the payload? Could we then use unmanned probes to collect rock/soil samples and fire those back into orbit for collection and study?"
] |
[
"We don't need to send people to mars to study mars. That can be done with robots. ",
"We send people to mars as the first steps of colonization, the first steps at sending humans to permanently inhabit more than one world. It won't be an overnight process to colonize. It'll be long and difficult. But simply put: there's no reason to send ",
" when machines can do more science per dollar spent. "
] |
[
"There has been an increase in electric car sales. How do we dispose of their batteries, once their lifespan ends? And would disposing batteries release less pollutants compared to gas engines?"
] |
[
false
] | null |
[
"Lithium-ion batteries used in electric cars get worn out when they can only retain about 80% of their charge. That being said these batteries are still perfectly good for other applications like backing up solar or wind power. So these batteries are first repurposed once they can no longer be used for electric cars.",
"After that these batteries are recyclable when they go end of life as well. Recycling of Li-I is still a new process and is under development. In the years to come we will get as good at recycling these batteries as we are at recycling lead acid batteries. An example of existing technology to recycle Li-I batteries is below:",
"Eventually discharging supersaturates lithium cobalt oxide, leading to the production of lithium oxide. Li",
" + e",
" + LiCoO2 -> Li2O + CoO",
"A potential recycling process would take the degraded particles from the cathodes, pressurize them in a hot alkaline & lithium salt solution, then heat them. The result would product particles to make new cathodes. ",
"More options for recycling are listed ",
"in this study.",
" "
] |
[
"Batteries would have to be properly disposed of and not dumped in a site, improperly disposed batteries could mix with rain water and release toxic chemicals into the soil and contaminate any nearby lakes or rivers making it more devastating than gas engines... "
] |
[
"Thanks! That’s a very informative answer!"
] |
[
"As global temperatures increase, will cloud cover also increase and buffer temperature increases?"
] |
[
false
] |
If surface temperatures are hotter, there should be more evaporation leading to more cloud cover with a higher albedo. Will this buffer temperature rise, or am I missing something?
|
[
"Hello! We discourage addressing yourself as a source. A source should be external corroboration that independently verifies your statements. You being a graduate student in itself does not constitute a source."
] |
[
"Hello! We discourage addressing yourself as a source. A source should be external corroboration that independently verifies your statements. You being a graduate student in itself does not constitute a source."
] |
[
"It is entirely possible that clouds will be able to partially offset increasing surface temperatures, but the net effect that clouds will have has yet to be determined.",
"It's ",
", but there is mounting evidence that it is not true; in fact, clouds likely constitute a small, but ",
" feedback to warming. For instance, ",
"Dessler et al, 2010",
" analyzed a decade of CERES data and showed that any negative cloud feedback was fundamentally inconsistent with observations. Because we do not have long-term satellite observations of clouds (really, you can't trust much beyond the mid-1990's for this sort of calculation), other work has been done to indirectly ascertain cloud feedbacks, such as looking at meteorological parameters; work towards this angle, such as ",
"Trenberth and Fasullo, 2012",
", suggest that the total or equilibrium climate sensitivity is likely high, regardless of whatever the sign of the small-magnitude cloud feedback.",
"One simply can no longer hold out for hope that cloud feedbacks will counteract anthropogenic warming. These feedbacks are ",
" small, and the most of the evidence suggest that they're slightly positive to boot."
] |
[
"Is the universe still growing?"
] |
[
false
] |
Apologies if this question has been asked before. I googled some other posts but they didn't seem to address this question directly or in a way I could understand. I vaguely recall someone somewhere making a comment that the universe itself is expanding and not simply that the distances between galaxies are increasing. I know this is attributed to the period of inflation but is this still believed to be happening today in some measure? If so, is there any empirical evidence for this or is it purely conjecture?
|
[
"Yes, ",
"the universe is still expanding",
". Hubble was built to answer the question of whether the universe is expanding or contracting, and how fast. It's evidence showed that the universe is expanding. In fact, the rate of expansion is ",
", so it is expanding faster and faster. How and why this is happening is unknown, but we call the unknown force behind it ",
"Dark Energy",
". Very recently, ",
"new results from Hubble showed that it is expanding even faster than we thought!"
] |
[
"Both evidence and theory suggest that the universe will never slow down in its rate of expansion. The \"still growing?\" question seems to assume the universe is growing from a smaller place to a larger, and this is not the case - it's not expanding INTO anything. Google \"universe big rip\" and check the Wikipedia article."
] |
[
"In fact, the rate of expansion is increasing, so it is expanding faster and faster.",
"So it's unknown whether or not it will slow down?"
] |
[
"Why does an oil/soap film look colored due to interference when everyday light is not coherent?"
] |
[
false
] | null |
[
"All light has some degree of coherence, even sunlight. One way to view coherence is to see when you split one beam into 2, how much of a difference in the optical path they would have and still interfere. Now the bigger that difference the bigger the coherence length. Coherence also depends on the spectrum:\n Lc = c/(n(f1-f2)) \nWhere Lc is the coherence length, c - speed of light, n - refractive index and f1,f2 are the different frequencies. Now this is aproximation for the case when f1 is near to f2, but you can still see the dependance. There is an article on coherence length of black-body radiation (",
"http://iopscience.iop.org/article/10.1088/0143-0807/19/3/006/meta",
"), unfortunately it's behind a paywall, but I can tell you that they have found a dependence of coherent length and the black-body's temperature:\nLcT = 3.6 mm K , now in the sun's case that roughly translates to T~6000 k, and Lc = 3.6/6000 mm = 0.6 um = 600 nm.\nSo what I'm trying to say is that sunlight has some degree of coherence, in the case of oil/soap films it's actually enough to cause interference.\nYou might be interested to read ",
"http://soapbubble.wikia.com/wiki/Color_and_Film_Thickness",
" , where they have a great picture which shows you the color for the various thicknesses of the film. You might notice that After around 500 - 600 nm the contrast between color greatly falls of, which I believe agrees well with the theoretical model that predicts the suns coherence length to be around 600 nm."
] |
[
"Oh thank you! That is certainly very interesting! I learned something new today thanks!",
"What about the light from artificial sources like tubelights in our home etc? Do they have that much coherence lenght? "
] |
[
"Here",
" you can read the article without paywall. I think its message is slightly different. Unfiltered sunlight has a coherence length of 600 nm which is about equal to the wavelength of yellow light, so it is hardly coherent. However, the photoreceptors in the eye (cone cells) contain filters with a narrow bandwidth of about 100 THz, which increases the coherence length of the detected light fivefold to about 3 μm. So, due to the narrow color filter of our cone cells, we are able to see colored fringes up to fifth order. Color photography, which employs three color channels with human-like filters, is able to see the same number of fringes. ",
"(Almost no fringes are visible when the eye is using its rod cells, or when black-and-white photography is used, obviously.)"
] |
[
"Can we do anything interesting with the weak force?"
] |
[
false
] |
We are pretty good at harnessing electromagnetism to do useful things. Can we make the weak force do anything interesting or useful? I don't mean wait around to see randomly occurring beta decays, I mean set up a weak field to harness the force in some way.
|
[
"There have been proposals to use neutrinos for communicating through the Earth or with submarines."
] |
[
"Don't underestimate the power of beta decays. Voyager 1 and 2 spacecrafts that explored the solar system and now interstellar space are powered indirectly by weak force. They put around 13kg of plutonium. The weak force interaction makes beta decay happen and this generates a lot of heat which is then converted to 470W of electricity with ",
"RTG",
". This is needed because going away from the sun means you don't have enough sunlight to generate power thru the solar panel array.",
"It has been 39 years since launch, 17 light-hours away in pitch darkness, and weak force still generates enough power to run the spacecraft instruments. It's incredible that a man made object is so far away from man that it takes 17 hours for light from earth to reach it. Yet, it's still being controlled by man and still sending scientific data back home, all thanks to the weak force."
] |
[
"I've met someone who worked on neutrino detector to \"spy\" nuclear power plant (for example in Iran). The conclusion of her Ph.D work was that it's feasible but only very close to the detector meaning that (again for example the Iranians) could just build nuclear weapons 100 meters away. ",
" : Clarified the unit"
] |
[
"How will the end of the universe be different from before the big bang? Will there be a discernible flow of time?"
] |
[
false
] |
[deleted]
|
[
"Nobody can answer this question because nobody knows anything about \"before the Big Bang\". In fact, it's generally accepted that the universe itself was created in the Big Bang, so asking \"What was the universe like beforehand?\" doesn't have any meaning.",
"That being said, one possible scenario for the end of the universe, called \"The Big Freeze\", has the expansion of the universe spreading the energy content so thinly that there will be no energy left in any usable state (meaning the universe is unable to do work). In that sense, there will be no discernible flow of time. However, this scenario doesn't come to pass for something on the order of 10",
" years from now, so it's highly speculative."
] |
[
"Not really. Heat death may be a more precise definition, but they describe the same fate of the universe.",
"The heat death of the universe is a final state in which there is no thermodynamic free energy with which to perform any work, which is a very specific state. The Big Freeze more generally refers to the eternal expansion of the universe pulling everything apart until all is cold and dark and nothing is happening."
] |
[
"Just because something would happen a long time from now doesn't make it speculative. Rather, our incomplete knowledge of the physics involved in the universe, make it speculative. An alternative to the big freeze is the Big Crunch, the opposite, in which gravity wins out, and everything gets pulled together into one big mass - to be fair, the most popular theory is the freeze, and now with the latest readings on the Higgs boson suggesting less likelihood of a multiverse, the universe might be a cold lonely place. "
] |
[
"Can a superconductor get trapped in it's own magnetic field?"
] |
[
false
] | null |
[
"But a superconductor is subject to the meissner effect."
] |
[
"No, because the magnetic field has no affect on the object itself"
] |
[
"You might first consider why ",
"this contraption",
" doesn't work. It's not an entirely trivial issue despite the joke nature of it. A self-suspended solenoid isn't very different than that."
] |
[
"What's the difference between Crigler-Najjar syndrome and Gilbert syndrome?"
] |
[
false
] |
I've read much about them, and all I know is they are the same: same mutation (2q31.1), same damaged protein (UDP-glucuronosyltransferase), same symptoms, same inheritance (autosomic recessive); what's the difference?
|
[
"Gilbert's Syndrome is a defect where the enzyme is still functional, but in a lower proportion. Thus, bilirubin will not accumulate unless under minor physiologic stress (that includes drinking, lack of sleep and so...) and neonates will not be usually affected. \nIn Type I Crigler-Najjar syndrome the enzyme is completely absent, so Indirect Bb will accumulate since birth and can cross to the brain. Therefore, it is lethal to the newborn unless treated promptly. The neurologic prognosis is still very bad, however. \nCrigler-Najjar II consists of reduced enzyme activity as well, but to a greater extent than Gilbert's (there may be some overlap) and can be present in the neonate. It will respond very well to medical treatment."
] |
[
"Thank you so much, you are smarter than the internet. Only thing I could find is that bilirrubin concentrations are 100 fold higher in the Crigler-Najjar. Now it all makes sense."
] |
[
"You're very welcome!"
] |
[
"Water Pressure"
] |
[
false
] |
I was reading on deep sea creatures withstanding high water pressures, and a question came to me. If I were to take a vessel to a certain depth and seal it at that depth, would the water pressure in that vessel stay the same, or would it change when brought to the surface? Of course, this is all assuming some ideal vessel that doesn't expand or contract. Here is a to help explain my question.
|
[
"Water doesn't compress all that much, so the amount that it has to expand to change from 10 atm to 1 atm is miniscule.",
"So, if you had a perfectly rigid vessel to keep the water in, it would still be at 10 ATM when you brought it back to the surface, and wouldn't equalize to 1 ATM until you opened it. When you do open it, the water will expand slightly, and nothing all that exciting would happen."
] |
[
"If you vessel had a valve on it that you then opened at sea level it would spew out water like nobody's business.",
"Water is pretty incompressible.",
"With a non-replenishing container, it would only take a small volume of water to escape to equalize the pressure. "
] |
[
"The pressure in the vessel would remain the same at whatever level you sealed it at. If you took the vessel to 1000ft below sea level and filled it up the pressure would be about 445psi. In comparison the air pressure at sea level is about 14.7 psi. If you then brought this vessel back up to sea level the pressure inside would still remain at 445 psi. This is because your vessel has no way to equalize to the air pressure now surrounding it. If you vessel had a valve on it that you then opened at sea level it would spew out water like nobody's business. ",
"So in reference to your painting the answer would be 10 atm inside the vessel."
] |
[
"Are emotions innate or learned ?"
] |
[
false
] |
I thought emotions were developed at a very early age (first months/ year) by one's first life experiences and interactions. But say I'm a young baby and every time I clap my hands, it makes my mom smile. Then I might associate that action to a 'good' or 'funny' thing, but how am I so sure that the smile = a good thing ? It would be equally possible that my mom smiling and laughing was an expression of her anger towards me !
|
[
"Paul Ekman and Wallace Friesen demonstrated that there are universally understood facial expressions which transcend cultural knowledge. In one experiment they went to Papua New Guinea and showed Fore tribesmen photographs of people making faces of happiness, fear, anger, disgust, sadness and surprise. Despite 1000+ years of separation from any other civilization, these tribesmen were able to recognize the correct emotion to go with a picture far above the rate of chance. This was but one of many trips they made to many different cultures to try this experiment but one with the tightest controls on cross-cultural influences because of the separation this culture had with all others. ",
"Here",
" is one of their widely cited 1987 journal articles on the subject. ",
"Here",
" is some early work on the subject, a paper by Ekman on universal emotions from 1970. Finally, ",
"here",
" is Ekman writing a chapter in a textbook on the subject in 1999. "
] |
[
"Ekman's work is highly controversial and oft-criticized, so this is really only a small part of a much larger answer. Indeed, to fully answer this question, you'd have to address not only Ekman's views, but also those of LeDoux, Barrett, Russell, Panksepp, Izard, and so on. To suggest that emotions are definitely universal is not a claim you can really make."
] |
[
"PhD student in psych who studies emotions here.",
"Paul Ekman had some studies that showed what appeared to be innateness (as cited in another answer), but recent work by Lisa Feldman Barrett has (imho) cast doubt on innateness hypotheses (and basic emotion views in general). ",
"Here",
" is a 2014 Emotion paper that shows a lack of innateness in a remote tribe.",
"One of the more difficult problems in the study of emotion is simply coming up with a good definition of what an emotion is in the first place. For example another paper by Barrett questions whether ",
"emotions of natural kinds",
" or if there are even \"basic\" emotions as Ekman proposed.",
"If you want a better explanation of the flaws in Ekman's work, ",
"here",
" is an article by James Russell. ",
"None of that answers your question. In my opinion the only honest answer is that we don't know yet and it is still being debated."
] |
[
"Is there a theoretical ceiling to the human ability to learn?"
] |
[
false
] | null |
[
"I dunno, it seems like we've reached a point where our intelligence is so vastly greater than any potential competing species that there's really not much selection pressure in favor of even more powerful brains. "
] |
[
"Certainly. One of the major anthropological findings we see in human evolution is that, over time, the size of the cranial cavity increased vastly.",
"It is therefore likely that future humans will be able to grasp even more complicated concepts than we could ever hope to. Who's to say that any alien races we encounter wouldn't be vastly more evolved on a physiological/anatomical level than us, giving them greater mental abilities?"
] |
[
"It also ignores our growing ability for self-guided evolution."
] |
[
"What determines how our voices sound?"
] |
[
false
] |
I mean, I understand genes must play a role, but how? How can a husky voiced mother and a gruffy voiced dad have five adult daughters with high pitched voices? Why do I sound different from my sisters? How do we all get our unique sounding voices and rarely sound like anyone else?
|
[
"Voice is a factor of a few things. First is the larynx, or \"voice-box\" (your adam's apple). Inside the larynx are two flaps of tissue attached to small muscles--the vocal folds or vocal chords. The muscles and cartilage in the larynx puts the chords under various amounts of tension, and when air passes over them, they vibrate and made sound (sort of like how a guitar string makes sound when it vibrates). The size, shape, and position in the neck of the larynx will affect the pitch of the sound created. \nIf someone has a larger larynx and longer vocal chords, they will tend to have a deeper voice. Inversely, a smaller larynx and thus shorter chords results in a higher pitched voice. That's why a child's voice is usually higher than that of an adult-their larynx is smaller.",
"After that, we have to account for the rest of the head. Your nasal passages and to a lesser extent your sinuses serve as resonating chambers, and the position of your tongue in your mouth will further affect the sound being produced, as will the precise size and shape of your mouth.",
"source: human gross anatomy and a sister in audiology"
] |
[
"To add, take a look at ",
"this video.",
" You can see how much the resonance in the vocal tract changes the sound coming from your vocal cords. "
] |
[
"It has to do with the way sound resonates from the air being passed through your vocal folds in the larynx, the movement of your mouth and tongue, and even the sinuses within your skull. This ",
"video",
" is very explanatory."
] |
[
"Can you effectively cool your house using evaporation?"
] |
[
false
] |
Evaporation of water, being an endothermic process, cools the area around it. What I want to know is can this process be used as a cheap way to cool your house? Specifically, I would like to know if this process would be plausible in an apartment, and if so, what equipment would I need to get?
|
[
"Yes, in certain areas (you need low humidity ambient air). It's called a swamp cooler."
] |
[
"Yes, but as nalc said it is most effective in dry areas because more evaporation means cooler AND a good thing to mention is you also have to consider humidity. If you have constant evaporation you better either have some way to get the humidity out or keep dry air coming in.",
"Evaporative cooling"
] |
[
"thats how we lived in Death Valley in 1960s"
] |
[
"Could a nuclear powered Ships be feasible?"
] |
[
false
] | null |
[
"Yes there are several nuclear aricraft carriers and even nuclear ice breakers across the world. They do not have smokestacks because they use pumped seawater as cooling."
] |
[
"I'm asking this because I'm doing a writing thingy so pardon me if this question is absolutely inane buuuuuuuuuuuuut",
"If there was a smokestack, would it have any benefits? Or would it be mostly cosmetic, and thus if damaged by lighting strike or something would the boat still be safe to function?"
] |
[
"Well you don't need one so you don't put one on. But if you had one it would just be useless weight and it being damaged shouldn't affect the way the ship work too much."
] |
[
"Is there any evidence space actually curves in the presence of gravity and isn't just a field effect like magnetism?"
] |
[
false
] |
If space is empty how can nothing curve? Do they actually mean a fabric like the aether curving?
|
[
"\"ancient and medieval thinking, not modern science\"",
"\nIt was a legitimate theory proposed and investigated by founders of modern science - Newton, Huygens, Fresnel, Young... There is nothing unscientific about having a theory that turns out to be wrong."
] |
[
"To play the devil's advocate, the \"curvature of the space-time\" is a very abstract concept. Claiming that the space itself curves has a very specific meaning that cannot be extrapolated intuitively.",
"We describe how particles move by putting them on top of a \"background geometry\" and calculating the shortest paths between two points. Gravitation changes this background over which they propagate, and this we can actually show, accepting given general relativity as the \"right theory\" for gravity. But one can also understand this \"curvature of the background metric\" as just lots of interactions. ",
"EDIT: Yes, we can understand gravity as a field effect just like EM. There are some technical problems, but up to linear level, things are exactly the same. The problem is that gravitational charge is actually energy, or in big lingo, the \"stress-energy-tensor\". The EM fields do not carry charge, so there isn't a \"self-feeding\", while in gravity, the gravitational field itself has energy, so gravity creates more gravity, which makes the theory infinitely more complicated to be described in the same language as EM. But it can be done, and as long as the energies are low, gravity is just like a complicated EM."
] |
[
"That was ancient and medieval thinking, not modern science.",
"The aether was well within the tradition of modern physics. The Michelson-Morley experiment which put it to rest was done by the head of the American Chemical Society and a Nobel-winning physicist. It was no phlogiston or medieval music of the spheres."
] |
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