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[
"How big can a black hole get?"
] |
[
false
] |
In terms of mass or the volume of the region inside it's event horizon.
|
[
"There is no physical upper limit, however, there are limits on how big one could realistically get given galactic evolution. That is likely in the billions of solar masses."
] |
[
"There's no theoretical limit. ",
"This",
" is the largest ever discovered, at 40 billion solar masses. That's really large. If put in the place of our sun, the event horizon would be 47 times further from the sun than Pluto.",
"The fact that this quasar is so far away (and therefore being observed at a the young age of just 1.6 billion years after the Big Bang) implies that by this point in the universe's life there could be far more massive black holes."
] |
[
"Theoretically, no. But in the real world (or universe I guess), yes. A black hole will continuously get larger as more mass gets pulled into it, but this will eventually stop. One reason for this would be that there simply just isn't any matter around it anymore, thus the black hole couldn't get any bigger. But let's say that there is for a second. It is possible that it could gain enough mass, and have enough matter around it, that as it gains mass, its gravity gets stronger and reaches further out, pulling more matter towards it, and then repeating this process over and over. One other way a black hole could get more mass is through darkmatter. Even if we don't see any more matter around the black hole, there could be large clouds of darkmatter with plenty of mass still feeding it. Hope this helps!"
] |
[
"Why is the three-body problem considered “unsolvable”?"
] |
[
false
] |
I just watched a that explains the and it states that the problem is unsolvable. But I don’t understand why. As I understand it we can run computer simulations that can show what happens with 3 bodies rotating around each other. But if we can simulate it why can’t it be solved for with a function?
|
[
"What is meant when we say that the 3-body problem is \"unsolvable\" really just means that there is no ",
" solution in terms of finite combinations of standard functions, like polynomials, exponents, trig functions, etc. This just means that there isn't a relatively simple expression where you could plug in any initial configuration of 3-bodies and get their trajectories.",
"What this does NOT means is that:",
"Solutions don't exist. There is a solution for every configuration, we just can't write them using our favorite functions. This is why we can model the 3-body problem with computers, which approximate these solutions",
"That ",
" 3-body problems are unsolvable. There are some configurations where we ",
" write the solution using our favorite functions. See ",
"here",
" for a list.",
"That we can't solve them with more complicated functions. For most situations, the 3-body problem can be solved using infinite power series. This vastly expands the number of functions we have access to and so it shouldn't be surprising that we can solve it there.",
"This notion of \"unsolvability\" is really down to our preference for what a \"solution\" looks like. Back in the olden-days, we could only compute ",
" functions really well and so we favored those functions which came to be known as ",
"Elementary Functions",
". But this is a very small sample of what functions can actually be and they are designed around our preferences, and so it makes sense that math/physics won't conform to such tight restrictions. There isn't really anything special about the 3-body problem, it just doesn't care about these restrictions. In fact, we should see the 2-body problem as having something special about ",
" which allows us to write solutions within these restrictions. And that special property is, likely, that 2-body motion takes place in a fixed plane which reduces the complexity of the problem to something elementary. ",
"So, in the end, the 2-body problem is \"special\" and \"mysterious\" because we can write it's solutions down using our favorite functions. The 3-body problem is typical in that there's nothing special about it that reduces its solutions to our preferential functions."
] |
[
"I think the issue is deeper than just that we want to write the solution in the specific form of using only elementary functions. The real problem is that the solution is chaotic, which is an inherent mathematical fact that has nothing to do with what functions we want to use. The reason why we want to solve with elementary functions in the first place is because they have very predictable behavior; for example, you can make long range predictions without much difficulty without increasingly large errors. We could introduce new functions (and people do, these are often taught under special functions), but other \"nice\" functions won't solve the problem, and the one that does solve the problem would be chaotic and hard to analyze. Ultimately, the main issue is that the general solutions to the 3-body problem is just too chaotic that it is resistance to analysis."
] |
[
"Chaotic is different from stochastic. Stochastic means there are randomness involved in the evolution of the state. 2-body and 3-body problems are deterministic, not stochastic. The state always evolve the same given the exact same initial condition.",
"But for 3-body problem, it's chaotic. If you don't have exact values for the initial condition, the error became exponentially large as time go by, so after a certain amount of time the state became essentially unpredictable (but there are special exceptions). If you do have exact values for initial condition, then you can make arbitrarily accurate prediction for arbitrary long period of time, but you will need to perform a lot more calculations compare to non-chaotic case to control this exponentially growing error (you always acquire error due to numerical imprecision). Chaotic implies a few properties. One is the butterfly effect, as I mentioned above. Another one is mixing: it's not merely that you can't predict precisely if time is long enough and you don't have the exact initial condition, you can't even make a vague estimate that carry any useful information at all.",
"Why is 2-body problem not chaotic? Essentially, it has too few variables compared to the amount of symmetry. It's known that if you have at most 2 free variables you can't be chaotic. A 2-body problem has 12 variables (position and velocity for each body), but standard physics 10 symmetries gives you 10 constant of motions (center of mass, linear momentum, angular momentum, energy) so the problem is reduced to 2 dimensions. Actually, there is a special 11th constant of motion specific to this problem: the LRL vector, but only its direction on the plane of motion matter, because the plane of motion and length is determined by angular momentum and energy, so the problem is reduced to just 1 dimension. 1 dimensional system is very easily solvable explicitly.",
"For 3-body problems, you start with 18 variables, but you only have the usual 10 symmetry. It's proven that there are no other algebraic constant of motions, so at most you can reduce this to an 8 dimensional problem using this technique. Actually showing that this problem is chaotic (and hence you really can't reduce further) is harder."
] |
[
"Why do pictures of bright lights/stars come out in the shape of a plus?"
] |
[
false
] |
For example, see how this picture of the stars doesn't show stars as a circle, but instead a plus? Same kinda thing for these Christmas lights image: Are those lines a byproduct of cameras? Or something strange about light?
|
[
"Those spikes are called ",
"diffraction spikes",
". They are caused by the light diffracting around the support arms that hold up the secondary mirror in the telescope. "
] |
[
"Yes, cameras can have this effect as well, although usually less pronounced because they lack the support struts that many large telescopes use on their secondary lens. We even see this effect through our eyes. If you look at stars or other bright spots, they often don't appear round. This is due to suture lines that occur in the lenses of our eyes causing a diffraction pattern (",
"http://www.ncbi.nlm.nih.gov/pubmed/9014354",
"). ",
"The shape of the diffraction is determined by the support structure. Different structures will cause different shapes. The four-strut structure gives the familiar \"plus-sign\" shape of stars in Hubble pictures. The shape is determined by the spacial Fourier transform of the aperture. ",
"edit: Even though cameras don't have support struts, they do use allow light through a small hole called an aperture. These can be circular, causing the light of a small dot (such as a star) to appear spread out. Frequently though, they approximate circles by using several \"blades\" that form hexagons, octagons, etc. The picture of the Christmas lights you linked is probably taken through a 6-bladed aperture, causing the diffraction spikes shown in the image. "
] |
[
"The shape of the pattern doesn't really depend on the brightness. Although it can be easier to see the pattern if the point is brighter than the area around it. What determines the pattern is the shape of the aperture the light went through.",
"Your eyes also do this, there are structures in the eye that cause diffraction patterns which is why stars appear star-shaped instead of perfectly point-like. ",
"https://www.youtube.com/watch?v=VVAKFJ8VVp4"
] |
[
"If I put my hand on a table, am I actually touching it?"
] |
[
false
] |
[deleted]
|
[
"I suppose it depends how you define touching."
] |
[
"Ultimately it's that push."
] |
[
"Ultimately it's that push."
] |
[
"Is sound affected by gravity?"
] |
[
false
] |
I'd assume since sound travels through air and other things which are affected by gravity, gravity must have some effect on the propagation of sound waves? Is there a measurable or even easily noticeable difference between a sound heard on Earth and one in a zero-gravity environment, or one played in an environment with more intense gravity?
|
[
"There is indirect influence. Atmosphere pressure gradient is caused by gravity. Speed of sound is faster in the higher altitudes. Wave which is entering a thiner medium can be relected. So you can hear distant sound as if they come from the sky. However there is also difraction which is not affected by pressure which makes similar effect.",
"Edit: Also seismic waves are sound as well, but relation between speed of sound and pressure is inverse in the solid medium. As you can see in ",
"this",
" image seismic waves are bend upwards."
] |
[
"Aparently dependence of speed of sound on hight in the Earth atmosphere is much more complicated than I thought. I take that back."
] |
[
"Aparently dependence of speed of sound on hight in the Earth atmosphere is much more complicated than I thought. I take that back."
] |
[
"Is there a unit to describe the speed that time passes?"
] |
[
false
] |
Such as the speed of time when at rest vs. moving near the speed of light or moving close to a large gravitational body?
|
[
"The unit of time is the second. A \"speed\" is defined as how a variable changes per unit time. Therefore, within a single reference frame, the \"speed of time\" would have units of seconds per second, which units cancel out to end up not being units. Furthermore, within a single reference frame, the speed of time is always 1 second per second, and therefore has a trivial, constant value in addition to being dimensionless. This is not very illuminating, but what it does show is that the concept of \"speed of time\" within a single, isolated reference time is not a very useful or meaningful concept.",
"But, we know that time can progress at different rates in different reference frames, therefore the concept of \"speed of time\" must have more significance in general. We can calculate the speed of time in one frame relative to another frame and then it will not be so trivial, because of relativistic time dilation. For instance, if we are at rest on the ground and measure the length of a second t' in some moving reference frame that is moving relative to the ground at speed v (i.e. we watch a clock tick that is moving with the moving reference frame), and then measure the length of a second t in our own ground frame, we find*:",
"t'/t = 1/(sqrt(1 - v",
" /c",
" ))",
"The part on the right is called the Lorentz factor, or the gamma factor. The ratio of time in one frame, to the time in another frame can be thought of as the relative speed of time. Therefore, the relative speed of time has the value of the Lorentz factor. This speed still just has units of seconds per seconds, which divides out to be no units. Therefore, whether talking about the single-frame speed of time (which is always one), or the relative speed of time (which is the Lorentz factor), the speed of time is always unitless. ",
"*To actually measure this equation, you need very accurate clocks and very high speeds.",
"UPDATE: Because this post has got a lot of hits, I'll summarize and respond to some of the comments below.",
"For brevity, I only mentioned relative-velocity time dilation. But gravity can ",
"also cause time dilation",
". ",
"Some people have argued that for a ratio of two variables that both have the same units (such as the speed of time), the ratio is \"dimensionles\" but not \"unitless\". This depends on how you use units. If you use a strictly standardized unit system only considering the main units, then such ratios do not have units. An example of this is the \"base units\" of the SI. If you use \"units\" more broadly to help you remember where such ratios come from, then such ratios do have units. An example of this is the \"derived units\" of the SI. In the SI, radians are derived units but not base units. Expressed in terms of base units, the radian has units of m/m which cancels out to unitless in base units.",
"The concepts, \"time is not real\" or \"time only exists in the human perception\" may make for some fun philosophizing, but do not real hold up in the realm of physics. Pulsars were periodically pusling in time long before humans came along to perceive time.",
"As far as we can currently tell, time is not quantized and there is no smallest increment of time. The Plank time is not a limit on how small an increment of time can get. This is a common misconception.",
"Relativistic effects such as time dilation are real and are independent of human perception. Machines can reproducibly measure relativistic effects without any humans being around. Einstein's famous quote about relativity being how time seems to go quicker when you are with a pretty girl was given as a joke. He was trying to be funny, and was not trying to actually describe the science of Relativity."
] |
[
"Well technically radians ",
" a \"false\" unit. There are a couple of different ways to approach measuring an angle measure in radians, however.",
"Degrees (obviously) are not bad but you have to include some measurement of size of the circle to know arc length, at least.",
"Meters are somewhat less useful since you end up going through the conversion to radians anyway, but technically correct. "
] |
[
"For some reason, I've spent a decent amount of time thinking about this curiosity, to.. well, to mostly no avail, but I guess I have a vaguely useful opinion on it. Since we're sharing...",
"Clearly something is going on when you have to hold on to 'radians' in all your calculations, even though they don't have a true unit on them. What is it? Well, start with: what is a unit?",
"There are only a few things that are truly fundamental in the system of metrics we use in physics - the dimensionless constants, like pi and e and the 'fine structure constant' (alpha ~= 1/137). No matter what coordinate system you place, and no matter how curvy and weird it is, you will always measure the same values for these constants, because all the units cancel out.",
"This is clearly far more fundamental than a distance being '1 meter' - you can trivially change to imperial units (gods..) and call it 3.28 feet. Or you can define 1 meter = 3.335*10",
" light seconds.",
"In relativity we go a bit further and say - hey everyone, wait a minute (...), meters and seconds are kind of measuring the same thing. Lorentz boosts are exactly the same as rotations in space, except that instead of the xy or yz planes you're rotating the xt and ty planes (with the caveat that the metric signature is -1 in that direction, aka hyperbolic, so you have to replace all your sin's with sinh's and cos's with cosh's. If you express your Lorentz factor in terms of 'rapidity' instead of 'velocity', in fact, you can literally just change the sines to hyperbolic sines in the rotation matrix, to translate to Lorentz boosts (or replace time with i * time. Whoa!)). So we define meters and seconds as actually being scaled versions of each other. Likewise Energy and Momentum, etc.",
"Next you wonder: okay, you're measuring seconds in seconds and meters in seconds. But what is a 'second'? I think that the answer is that all units are just ratios of something else. Someone, somewhere says - hey, let's define 'one second' by something that we could measure definitely, everywhere, since relativity says it's going to be hard to agree otherwise. Let's define it as 1 over (the time it takes a cesium atom to transition between two very-similar atomic states 9,192,631,770 times). That's not a unit anymore - it's a ratio. That says: if you don't know how long a second is, bust out a cesium atom, count some hyperfine transitions, and compare.",
"Similarly, 'how many meters is this?' is really 'how many multiples of a reference definition of 1 meter is this'? And that's something we can all agree upon (well, by comparing our definition of meters to our definition of seconds and then measuring cesium vibrations again).",
"All units, therefore, are defined as ratios. (makes you wonder what happens if the ratios don't commute in the QM sense - if you can't measure two at once.) And all constants that have units are, typically, conversion factors between different units. Because, fundamentally, the only thing we can trust once relativity and QM are in the picture is our ability to count events. So we base everything in counting - quantities, transitions between states, ratios of other units. Counting things always works, and ratios always work.",
"Similarly, unitless quantities are ratios between other things. If we wanted, we could get away from all units, and every value becomes a ratio of (counts of something thing) over (counts of some other thing). Hell, this would probably be pretty useful in some cases.",
"...",
"So what's a radian? It's something like a ratio between two orthogonal vectors, for some definition of orthogonal in whatever metric space we're in. Our coordinate systems can mess with that, so, radians are NOT constant across reference frames, sadly, but still - they don't have units but they are ratios between two different things that we're measuring. When our coordinate systems fudge the definition of orthogonal, that means we're defining one coordinate (such as x) as having different units (in terms of ratios with cesium atoms) than another (y, say). More precisely, radians aren't the raw ratio - the tangent function is. Radians are a computationally convenient way to store the tangent (y/x) as a single value: tan",
" (y/x).",
"This is also how it makes sense that the sine function can accept radians or degrees and seems to work on both, despite having a Taylor series that you've only ever seen defined one way (sin x = x - x",
" /3! +...). In fact, the unit of 'degrees' is a constant multiple (by 360/2pi) of the unit of 'radians', so all the x's in the Taylor series have to be divided by the same amount if you want to use it with degrees.",
"...",
"Edit: and I agree with the top poster about how t/t' isn't really a 'speed'. In light of my description above, I guess I would phrase that as: you can't define a coordinateless ratio of time to proper time because, well, the speed of time is intrinsically based on your reference frame. ",
"But you can definitely define a ratio of time to proper time given the reference frame, which we call the gamma factor (1/sqrt(1-v",
" / c",
" If you felt like calling non-proper time 'real time' or something, ",
" yes, you would have defined a unit for it. Since we're measuring both in seconds right now it's like we already did the step where we cancel our their units and express them as a raw ratio. And that ratio is.. \"counts of cesium transitions for me vs counts of cesium transitions for you\". :)",
"Actually, the ratio between t and t' is a WHOLE lot like the ratio between 'y' and 'x' that we use to define ratios. In fact, measuring angles in radians is precisely analogous to measuring (Lorentz) boosts in '",
"rapidity",
"', except that the boost is phi = tanh",
" (v) = tanh",
" (x/t) rather than theta = tan",
" (y/x).",
"This isn't quite the same as a ratio between t and t', but it's a ratio between t and <the part of your motion that is NOT along t, aka, your spatial motion>.",
"...",
"tldr: units aren't real. Everything is ratios between counts. When we hold on to units, we're holding on to ratios between counts. When we hold on to radians, we're holding on to (the inverse tangent of (a ratio between (counts of distances in two orthogonal directions)))."
] |
[
"Regarding the energy released during atomic fusion vs. atomic fission."
] |
[
false
] |
Since we know that: 1)Atomic fission releases less energy per mass than fusion (at least for the common fissile and fusion elements: Plutonium isotopes and Hydrogen isotopes.) 2)Fusion of heavier elements releases less and less energy per mass until iron, at which point it would begin requiring energy and is the beginning point for where fission releases energy. Would there ever be a point where an extremely heavy atom release more energy per mass during fission than hydrogen does during fusion (assuming that we could build idealized environments that kept these heavy elements stable until we allowed for fission,) or would the energy released per mass asymptotically approach that of hydrogen? Is the energy released purely a function of alpha/beta particles emitted? Or am I wrong in my assumptions altogether, and now the NSA is tracking me because they think I'm trying to build a bomb? Thanks for reading, any additional information is appreciated.
|
[
"Fusion releases more energy per nucleon than does fission because of the relative steepness of the two sides of ",
"this curve",
". Jumping from hydrogen to helium releases a colossal 7 MeV per nucleon, whereas the maximum you can gain from splitting e.g. ",
"U is about 1.5 MeV (if you were to split it right down to iron and nickel in one process).",
"The binding energy per nucleon decreases as elements get heavier but it's clear from the known elements in that graph that you would have to go up several orders of magnitude in atomic number before you got back to anywhere near hydrogen (i.e. zero). With such little binding energy per nucleon, the nucleus has very little energetic incentive to stick together in the first place and would take almost as much energy to form as it gave out in a fission event. To speculate about a technology that could keep such a weakly bound nucleus together is a bit too far-out for my tastes.",
"The energy released when a nuclear reaction takes place is based on the vertical difference between the reactants and products in that nuclear binding energy curve. The larger the jump you make, the more energy will be given out."
] |
[
"Free hydrogen nuclei (i.e. protons) have no binding energy and so occupy the zero position on that curve. Nucleons in a helium nucleus are in a bound state, which means they have less energy than the equivalent free nucleons. This makes intuitive sense, because the strong force is attractive - in order to separate the nucleons and return them to their free state, you have to add energy, so the binding energy is negative.",
"Because of this, when nucleons become more tightly bound, they must release some energy, which is where the energy for nuclear events comes from. Any reaction which moves a nucleus towards the peak of the binding energy curve will release energy because the nucleons are now bound more tightly than before."
] |
[
"Great reply, thanks. ",
"Somewhat related: I'm often confused by the right signs in binding energy. Since it's been over a decade since I looked into it, maybe you can help me out where the following reasoning goes wrong:",
"The binding energy of Helium is 7 MeV per nucleon. So, in order to create a Helium atom, you need to invest 7 MeV per nucleon (28 MeV). From that, my understanding is that, speaking simplified and not taking into account the several reaction steps, 28 MeV worth of mass of the original hydrogen atoms is converted to energy which is used as binding energy for the Helium atom. So how can the reaction release energy? Same with fission: you break up something with \"small\" binding energy and create elements with higher binding energy, why doesn't it cost energy?",
"Obviously there's a minus sign missing in my entire story that makes it correct again, but I can't explain that minus sign intuitively.."
] |
[
"Can stomach acid burn organs?"
] |
[
false
] | null |
[
"Normally, the cells in the lining of the stomach secrete a mucus that protects the stomach from damage from gastric acid. When your body moves your stomach contents (which contains substantial amounts of stomach acid) into your small intestine, your body pretty much immediately neutralizes it with alkaline secretions from the pancreas (EDIT: also from the gall bladder, as bile is also alkaline), because the intestines don’t have the same protective capacity as the cells in the stomach.",
"Other organs in the body lack this kind of protection/countermeasure system. Aspirational pneumonia is a great example (when gastric acid enters the lungs). Another much more common example is GERD (which results from gastric acid refluxing into the esophagus. And as has been mentioned, ulcers in the stomach and intestine result when these protective measures are compromised.",
"While the acid content of gastric juices is problematic, it’s not the only problem. Gastric juice also contains pepsin, which is a major player in the digestion of protein. Essentially, once protective measures are compromised (or if they were never present in the first place) you have damage from the acidity, but also you are literally digesting the proteins in your own tissue."
] |
[
"GERD can cause precancerous changes to the esophagus. It's called Barrett's esophagus or Barrett's syndrome, when normal esophageal cells are replaced with abnormal cells. I've had this and have been prescribed omeprazole for over 24 years, because my esophageal sphincter eroded."
] |
[
"Other reasons like getting stabbed?"
] |
[
"Why do sunsets contain every color except green?"
] |
[
false
] | null |
[
"This article",
" has a good explanation."
] |
[
"This says that the green and blue wavelengths get scattered by the atmosphere, but why does it only appear blue and not green?"
] |
[
"They do contain green sometimes, if the atmospheric conditions are correct."
] |
[
"Is it possible to eat just enough, to not have any waste?"
] |
[
false
] |
Urine and feces are our bodies' way of expelling parts of food that either cannot be digested or are just aren't digested. Given that, would it be possible to ingest exactly enough nutrients in exactly the right form, that our bodies would digest 100% of the material and we wouldn't have any waste whatsoever? Assuming that it is possible at all, is it further possible to do so using "normal" food?
|
[
"No, because feces is not just \"unused\" food, and for that matter is not at all \"unused\" food. Feces is roughly 30% bacteria. And the characteristic brown color is partially from \"dead\" red blood cells (not sure what percentage though). Urine on the other hand is bodily waste cleared out via the kidneys, and also includes certain components of broken down red blood cells (namely broken down heme). So even if someone stopped eating, they would still produce some of these waste products and would still need a means to excrete them."
] |
[
"to answer question number two, the color begins as biliveridin, which is green, and is broken down by biliveridin reductase into bilirubin. which is yellow, this is the state in which it is passed through the urine. it is also passed through the liver to the small intestine as a component of bile and is converted into stercobilin in the colon, which is brown."
] |
[
"The best I remember is that it's by weight. Whether that is dry weight or wet weight, I no longer remember.",
"The broken down heme in urine is what makes urine yellow, and the heme comes from broken down red blood cells (it has another name at that point that starts with a u, but which I don't remember). What differentiates that from feces and makes it brown instead, I don't recall either. ",
"Ugh! Lots of 'not recalled', but perhaps my answers will provide you enough information that if you look it up, you'll be able to find it."
] |
[
"Theoretical question: Two identical planets that orbit each other ...."
] |
[
false
] | null |
[
"Well there is a lot of different answers here because much of what controls a solar system's orbit is defined by the mass of the planets and how fast they orbit the host star. Also, the moon's orbit is not perfectly stable, as it drifts slowly away from us over eons. So a number of scenarios could exist that satisfy your question."
] |
[
"The distance at which a stable orbit occurs depends on speed. The two planets could orbit each other closely if they were traveling very fast, and if they were moving relatively slowly they could orbit at a farther distance. The same idea applies to your two-planet system and the sun."
] |
[
"The distance at which a stable orbit occurs depends on speed. The two planets could orbit each other closely if they were traveling very fast, and if they were moving relatively slowly they could orbit at a farther distance. The same idea applies to your two-planet system and the sun."
] |
[
"Why do proteins evolve at different rates?"
] |
[
false
] | null |
[
"Imagine you have a short story - it's composed of letters written on a page. If you change a letter like \"e\" or \"a\", letters that are deeply involved in almost every word, you can end up with a garbled mess that's very difficult to read. If you change a letter like \"q\" or \"z\", then the story may still be quite readable.",
"In the same way, some proteins are more \"important\" than others in that they are more involved in the basic function of cell, rather than a specific function. For example, you would expect an ",
"RNA polymerase",
" gene to be more highly conserved than a protein involved in the regulation of the metabolism of a non-essential nutrient. The ones involved in basic cellular function are less tolerant to change because small inefficiencies propagate forward in every single cell at every single stage in the organism's life, and the effect becomes massively amplified. If the change is big enough, the organism simply doesn't survive.",
"From this concept, useful tools and follow-up concepts such as ",
"this one",
" can be developed."
] |
[
"This is a fundamental question in molecular evolution, and we do not have a complete answer yet. Nevertheless, it seems that there is a universal rule of thumb in protein evolution: \"Important\" proteins tend to evolve slowly. To explain what is meant by \"importance\", we should first define how the rate of a protein is calculated.",
"The rate at which a protein evolves indicates the rate at which a protein sequence (or the underlying nucleotide sequence) change over time. These changes correspond to mutations - base changes - in the sequence. Thus, if we want to compare the rate of evolution of two proteins, we need two things: (i) a reference point in time, (ii) a way to count changes. Standard approach in molecular evolution to determine a reference point in time is to choose an older sequence with reasonably good estimate of its age that our two proteins of interested are related by ancestry relationship. Once we have an anchor, then we can count the changes in the two proteins with respect to the older sequence. Comparing amount of changes over the same period of time (same reference point) tells us relative rate of evolution of these two proteins. ",
"What changes to count? Again this is an important issue and key to many fundamental concepts in molecular evolution. The changes or mutations can be classified into different types based on their effect. Canonically, we use two main types of mutations when calculating the rate of evolution in proteins. These are synonymous (silent) and non-synonymous (non-silent) changes. Synonymous changes are those mutations in protein sequence where the sequence preserves its identity and is not expected to show any change in its function. In contrast, non-synonymous changes alter the sequence identity, the protein sequence is no longer identical, and this change typically alter the protein function. Accordingly, non-synonymous changes are considered \"important\" changes, whereas synonymous changes are mere by-standers. ",
"Going back to the issue of \"importance\", we count number of \"important\" changes and use their excess or lack (for a given number of un-important changes) as an indicator of fast or slow evolution, respectively. That is, provided that there are, say, 5 unimportant changes in two proteins with respect to a shared ancestor protein sequence, if protein A has 10 important changes and protein B has 7 important changes, then we conclude that protein A evolves faster than protein B. However, somewhat paradoxically, protein B is deemed to be \"important\" because it has allowed fewer changes and therefore it is an important protein and must preserve its function. ",
"It is important to keep in mind that the rate of a protein evolution changes as the protein evolves. Some proteins may have evolved fast in the past, and evolve slowly now - or vice versa. Therefore, we need to be cautious about attributing importance simply based on function. There are a number of confounding factors that may bias our calculation of the changes. For example, not all parts of DNA or a protein for that matter is equal. Some parts may be prone to evolve faster due to its chemical nature, while other parts can be particularly stubborn to change. There are methods to account for these biases as much as possible, however, the point is that molecular nature of these machineries may affect rate of evolution in subtle ways. "
] |
[
"Cheers, i knew it was something along these lines I just couldn't word it right in my mind, thank you!"
] |
[
"Would the light of a populated planet be more apparent to us?"
] |
[
false
] | null |
[
"Hi EmoSensitivo thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Planetary"
] |
[
"Planetary"
] |
[
"Do thoughts have mass?"
] |
[
false
] | null |
[
"are you retarded?"
] |
[
"Please keep discussion civil. Name calling, insults, racism, sexism, etc. will not be tolerated."
] |
[
"http://www.reddit.com/r/breakingbad/comments/maaib/what_does_this_mean/c2zex57"
] |
[
"If a male/male set of identical twins had a pair of children with a female/female set of identical twins, would the children be identical? [xpost from askreddit, I wasn't familiar with categories, my apologies!]"
] |
[
false
] | null |
[
"The short answer is no, they'd probably look as similar as siblings, because while the genetic material of the parents is indeed the same, how it gets passed on is not. It is exactly the same as one couple having two children.",
"Remember that for each chromosome you have two copies, one from your mother and one from your father. If we're talking about a given chromosome in the child, there are four different possible combinations of that chromosome that child could have.",
"In text form, if we call dad's two copies of a chromosome D and d, and mom's M and m, a child could have DM, Dm, dM, and dm in equal possibilities of 1/4. So the odds of any two children have the same combination of the same chromosomes is the product: 4/16 (1/4). This would apply to each and every chromosome, because they sort independently.",
"To make matters more confusing, it is rather unlikely that any two children will have chromosomes with the exact same version of each gene on them, because as you make your sperm and eggs, the chromosomes do a little mixing. This is called ",
"chromosomal crossover",
"; a part of genetic recombination.",
"I hope that helps, let me know if I can be more clear."
] |
[
"In text form, if we call dad's two copies of a chromosome D and d, and mom's M and m, a child could have DM, Dm, dM, and dm in equal possibilities of 1/4. So the odds of any two children have the same combination of the same chromosomes is the product: 1/16. This would apply to each and every chromosome, because they sort independently.",
"The logic is correct here, but not the math. Specifically, there's a 1/16 chance of two children both having ",
", but there are 4 combinations, so it's a 4",
". Think about when you flip two coins. Each coin has a 1/2 chance of either side coming up, but the probability that the two coins come up the same is 1/2, not 1/4, as seen from the possible combinations, HH, HT, TH, TT, of which 2 out of 4 have the same result from each coin."
] |
[
"two coins",
"Sorry sorry, I stand corrected."
] |
[
"How do new species propagate?"
] |
[
false
] |
[deleted]
|
[
"Accessible explanation from PZ Myers' blog ",
"Pharyngula",
"."
] |
[
"jahutch2 hit it; 'species' is an artificial thing; we made it up to categorize something that's not really discrete. ",
"First, you have to keep in mind that there are several equally useful and accurate ",
"definitions",
" of \"species.\" To clear it up, let's take a hypothetical case study on fast forward.",
"You have a population of animals in a valley. They reproduce sexually. In one generation, and new trait shows up via random mutation that offers some advantage; say it has slightly longer legs so it can run faster. The individual that has this trait has an advantage, but it is not yet different enough to not be able to breed with the rest of the population. This trait increases in frequency; more animals have the longer leg trait.",
"A side effect of this is that these animals can get higher up out of the valley, so any animal with the longer leg trait hangs out a bit higher up the mountainside. One day, another new trait pops up; say flatter teeth to better grind up the plants that live on the slopes. This trait helps the long-legged guys on the slope, but not the guys in the valley. Frequency of flat teeth increases in the long legged guys, but not the regular legged guys. ",
"Add more and more of these; coloration to blend in with the rocks of the slope vs the grasses of the valley. Solid hooves to deal with soft ground vs cloven hooves to deal with the rocks. Thicker coats to deal with high winds, water-repellent coats to deal with the rains in the valley.",
"At each step, the populations are forced farther and farther apart. Eventually, they won't interbreed anymore because they just never meet (which fits one definition of species).Given even more time,they won't even be able to interbreed.",
"It all boils down to us taking a gradual, messy, and ill-defined process and trying to make it discrete and classified. It's useful in that it helps us make sense of things, but dividing organisms into species is a forced and artificial thing.",
"I hope that helps."
] |
[
"I've posted ",
"this article about human/chimpanzee divergence",
" several times, but never gotten an expert critique of it, so I'm not sure if it's true.",
"Basically the guy is saying that it's still possible for new species to mate successfully with their root species until one final mutation causes a break, I think."
] |
[
"What are the effects of masturbation on motivation, productivity and non sexual relationships?"
] |
[
false
] |
[deleted]
|
[
"I've found ",
"one paper",
" that links masturbation frequency with a reduction in almost all satisfaction measures. Nonetheless, this is the only study that I've been able to find doing a quick search so the results should be interpreted with caution because there could be some confounding factors. ",
"On the other hand. There is ",
"one study",
" that finds quite the opposite although only in women. Also, the results about masturbation of the first study were not replicated in a ",
"Chinese population",
". "
] |
[
"So they are linked, but which came first, the chicken or the egg? "
] |
[
"Good question. Unfortunately, determining causality is quite complicated. In my opinion, masturbation is not a causal factor in improving or decreasing motivation or non-sexual relationships. ",
"Nonetheless, having a good and active sexual life, with one or multiple partners, is very healthy and benefits multiple domains. I think the evidence is strong enough to support this. "
] |
[
"How many bits of data can a neuron or synapse hold?"
] |
[
false
] |
What's the per-neuron or per-synapse data / memory storage capacity of the human brain (on average)? I was reading the Wikipedia article on . It lists humans as having 86 billion neurons and 150 trillion synapses. If you can store 1 bit per synapse, that's only 150 terabits, or . That's not a lot. I also was reading about , a condition where people can remember massive amounts of information. Then, there's individuals with developmental disability like who can read a book, and remember everything he read. How is this possible? Even with an extremely efficient data compression algorithm, there's a limit to how much you can compress data. How much data is really stored per synapse (or per neuron)?
|
[
"The brain is a computer analogy is nice sometimes, but it doesn't work in many cases. Information isn't stored in a neuron or at synapses per se, and we're not certain exactly how information is stored in the brain at this point.",
"Best we can tell information recall happens as a product of simultaneous firing of neuron ensembles. So, for example, if 1000 neurons all fire at the same time we might get horse, if another 1000 neurons fire we might get eagle. Some number of neurons might overlap between the two animals, but not all. Things that are more similar have more overlap (the percent of the same group of neurons that fire for horse and eagle might be higher than horse and tree because horse and eagle are both animals).",
"With this type of setup, the end result is much more powerful than the sum of parts.",
" I did not have time to answer a lot of good comments last night, so I am attempting to give some answers to common ones here."
] |
[
"Exactly. In addition, there are many more cellular processes that affect neuronal signalling than just synapse location and strength.",
"The entire milieu of the metabolome of a given neuron at any given instant will be constantly changing, and will impact the response that neuron generates.",
"This means that ",
" that is itself capable of synthesizing and processing environmental stimuli, and producing different outputs based on the \"computations\" it does. Each individual computer then interacts with other computers via synapses.",
"Based on the various possible states the metabolome of an individual neuron could be in, an individual neuron can likely encode billions of bits of information. "
] |
[
"Neurons don't work like individual bits of a data in a hard drive. They basically work all of their memory from association. It's based on the concept of \"",
"\" and vice versa. It's best explained with an example. I'll use \"horse\" since another comment mentioned it. When you hear the word \"horse\" you probably have dozens of neurons all firing in recognition. They are each in different locations if your brain related to different aspects of memory. Example, let's say when you were a child you went to a petting zoo and saw a horse for the first time.",
"In the speech center if your brain, a cluster of neurons associated with the sound of the word \"horse\" light up. ",
"Somewhat nearby, other auditory neurons are hearing a horse whinny for the first time and they are all firing as they process the sound.",
"In your visual memory center, neurons associated with learning the basic image/shape of a horse will fire.",
"In the sensory part of your brain, neurons that are tasked with remembering the smell of that horse stable will light up",
"And so on. When you first encounter a horse, neurons in each of those parts of your brain (touch, sound, shape, etc) will all be firing. And since \"",
"\" a link gets formed between each group of neurons. Then in the future whenever any one individual neuron in that link gets activated, the entire chain fires up because, again, ",
"\". So when you are walking by a farm and hear a distant horse whinny, or catch the faintest smell of the stable, and your entire related nerve cluster of ",
" immediately fires and you know there's a horse over there.",
"It's a fairly effective and robust system of memory, but it doesn't translate well to bits on a hard drive. How many bits would your horse memory be? Is it just the X amount of neural connections between various memory neurons? Even that's not a good representation because some neurons have hundreds of connections and are triggered for various different memories. (For example the sound of a horse whinny might be triggered by neuronal clusters for memories about \"horse\" but also be used for recalling knowledge about \"generic animal sounds\") ",
"Trying to quantify exactly how much knowledge a brain holds is a nearly impossible task because some extremely simple \"memories\" are actually requiring tens of thousands of neural connections, while other single neural connections might account for a dozen different \"memories\". ",
"It would be like working with a hard drive where some bits are actually several megabytes of data, and other groups of millions of bits form only one kilobyte.",
" Brains store vast sums of experience in a fairly simplistic form that is effective, but it's a form of memory \"storage\" that is wildly inconsistent in regards to trying to quantify just how much actual data it contains. ",
"Any attempt at trying to compare a brain to a computer hard drive just breaks down because they are working with utterly different concepts of how data is stored. To use one last analogy, ",
"\". The answer is impossible to define."
] |
[
"Why does my accent shift from American to British/Irish/Australian?"
] |
[
false
] | null |
[
"Psychology"
] |
[
"Psychology"
] |
[
"We can't really comment on anecdotes / isolated incidents without resorting to speculation which we try to avoid."
] |
[
"What kind of meteor impact would it take to stop the Earth's rotation?"
] |
[
false
] |
I was inspired by a post of a related topic on this subreddit. I was curious how large the impact of a meteor opposing the rotation of the Earth would have to be to stop or dramatically slow Earth's rotation.
|
[
"First let's calculate the angular momentum of the Earth. ",
"L = I * (2*pi/T), where I is the moment of inertia and T is the Earth's rotational period.",
"I = (2/5)* (mass of Earth)*(Radius of Earth)",
"Then L = [(2/5)* (mass of Earth)",
"(2*pi/T) = 7.063 * 10",
" kg m",
" / s\nGreat.",
"Now, L= r x p, so lets find the linear momentum at the surface perpendicular to the direction of the radius.",
"Then p = L/r = 1.109*10",
" kg m/s\n(for simplicity assuming that it hits an \"edge\" of the Earth)",
"In order to avoid special relativity here we have to make this thing really massive (which then in turn may call in general relativity. But then again,this is pretty rough anyway), and in fact it would have to at least be on the order of 10",
" kg, which wolfram says is a mass equal to about 3/4 of Earth's oceans traveling at a speed of roughly 10",
" m/s",
"Again, this is very rough, but the point is, it's going to take a lot to instantaneously stop the Earth from rotating, and in fact a collision of this magnitude would do some serious damage to Earth's structure."
] |
[
"Buzzkiller: in collisions, planets act more like droplets of water than solid masses. ",
"Anything with enough energy to completely stop the Earth's rotation would turn the planet (and itself) into a very fine spray of hot magma."
] |
[
"An online figure puts the earths rotational kinetic energy at 2.138×1029 J, so a similar quantity of energy would have to be dumped into the system to counteract the spin. So a 100 billion tonne asteroid moving at 22% of the speed of light would about do it.",
"This is by no means an accurate calculation. But it gives you an order of magnitude estimate to see how absurdly huge and fast it would need to be."
] |
[
"[medicine] How does the body create an immune system that functions when one is born without a thymus but has parathyroid glands?"
] |
[
false
] |
I'm trying to learn about how the immune system functions, creates, and teaches immune system cells when one is born with no thymus. I've read all about how the immune system works when there is a thymus in play, but what about no thymus? I can't find anything online to explain this to me. Ps. I've read about no thymus/no parathyroid system (aka 'complete' DiGeorge) which requires a thymus transplant and I'm not looking for info about that at this time. Thanks! Pps. I also posted this question to
|
[
"Haven't got any sources as I'm on my phone but I'll clear up some things.",
"Firstly, the parathyroid has no role in the immune response - it is a gland attached laterally to each lobe of the thyroid and produces parathyroid hormone which stimulates bone breakdown and inhibits proximal tubule reabsorption of phosphate in the kidneys, in this way it works antagonistic ally to calcitonin to increase serum calcium levels and is the primary serum phosphate regulator.",
"Since you mentioned the parathyroid I'll also bring up that the thyroid is not the thymus, the thyroid and parathyroid are situated essentially over the top of the cricoid cartilage in the neck. The thymus on the other hand is parasternally (behind sternum in front of the heart). ",
"Now, let's talk about the thymus! The thymus is essential for T cell maturation. I'm going to assume at this point you have an understanding of T cells and B cells in the adaptive immune response and also understand about the innate immune response and it's subset of cells as well.. If not, just tell me and I'll explain that as best I can :) the important point to understand before I go any further though is that T cells help activate B cells and other parts of the immune system beyond the innate response.",
"So, normally at around 5 months into gestation the primary site for immature T cell production is the bone marrow. At this point they are functionally immature, can be identified by the surface molecule CD7 and travel to the thymus for further maturation and selection. ",
"The surface receptors expressed on T cells reflect their differing levels of maturity. In particular, CD4 and CD8 T cells make up the majority of our T cell response as helper and cytotoxic T cells respectively. Initially however immature cells in the thymus express no surface receptors and then are pushed towards CD3 and T cell receptor expression. ",
"The initial repsonse of T cell precusors in the thymus is to enlarge and proliferate rapidly and express an immature/pre T cell receptor and CD3 but do not express CD4 or CD8 and are thus called double negative T cells. Movement within the cortex of the thymus and expression of different surface receptors drives rearrangement of the pre T cell receptor DNA sequence which subsequently makes up the alpha and beta chains of the pre T cell receptor - it is this essentially random rearrangement process that forces T cell receptors to have a unique and very specific receptor chain that will only recognise specific sequences.",
"So what we have at this stage is an immature T cell with a pre T cell receptor that has undergone rearrangement and is expressed on the surface along with CD3. The successful rearrangement of the pre-TCR then drives the expression of both CD4 and CD8 receptors, thus making the cell we have now double positive. ",
"Double positive cells then are tested to see if they can recognise peptide-MHC complexes within the thymus so that they are positively selected as functional cells. The resulting T cells have the ability to recognise peptides presented to them by other parts of the immune system BUT these peptides can be either pathogenic or of self-derived nature.",
"To eliminate T cells that could potentially respond to self-antigen (I.e. Your own tissue) there is a negative selection process wherein recognition of a self-antigen drives apoptosis and cell death. All in all about 2% of double positive cells survive both selection processes.",
"Over this course of negative and positive selection a decision between CD4 and CD8 is made depending on which MHC complex the cell reacted most strongly with - MHC I for CD8 and MHC II for CD4.",
"After this whole long process we are eventually left with T cells that have a unique and infinite array of T cell receptors that are able to recognise peptide-MHC complexes but do not recognise or respond to self-antigen-MHC complexes. These T cells are further differentiated into helper or directly cytotoxic T cells (CD4 & CD8) by their surface receptors as a result of different binding capabilities to respective MHC conplexes.",
"That's a general run down of normal T cell maturation, now to talk about partial and complete DiGeorge/thymus aplasia.",
"In partial DiGeorge there is still some thymus available to function and run through this process, albeit it occurs more slowly and with less efficiency. In a normal neonate T cell numbers are peaked at birth and fall over the next 12 months. In partial DiGeorge they are low at birth and continue to rise in some cases upto adolescence (have references but can't link!). In this situation it appears that there is excess proliferation if existing T cells rather than thymic recovery. What this means is that while the T cell repsonse will be normal for antigens that have a recognisable peptide-MHC complex there is a limited pool of T cells to recognise different complexes. As such the specific response is limited (hopefully that makes sense).",
"There also exists the possibility of some B cell dysfunction and of an increased number of autoimmune reactions as there are limited specific T cell helper cells and limited T cell regulatory cells.",
"The resulting immunological response in partial DiGeorge is a spectrum ranging from immuno competent to completely deficient.",
"Now, for complete DiGeorge there is total absence or aplasia or the thymus. In this case there is no possibility for T cell maturation within the thymus, and while some extrathymic maturation occurs it is insignificant and neonates with complete DiGeorge are born with Severe Combined Immunodefiency (SCID). In this case if it is not recognised the disorder is fatal within the first year of life. Unfortunately I know very little about treatment so I can't help there! ",
"Sorry about the wall of text and the lack of references! Hope it helps :)",
"Edit: seems I completely misread the question and thought you wanted to know about DiGeorge! My bad. The topic you want to research is that of Severe Immunodeficiency or SCID. There are a number of ways it is brought about beyond thymic aplasia though invariably there is a failure of both T and B cells.",
"If SCID is not recognised it is largely fatal as there is no ability to form an adaptive immune response."
] |
[
"I agree with you on the anti-rejection/immunosupressant medication side of things, the point I was trying to make is that previously (and in the case of the 'Bubble Boy') the bone marrow donation was unmatched - i.e. there was no screening process - and assumed to be best fit as it was from a close relative. This is nowhere near the process used today and the immunosupression required is nowhere near as rigorous as it once was.",
"Anyway, if we look at David Vetter's case in particular it's now known that the cause of his SCID was an X-linked mutation on the IL2-ry gene which is integral in the formation of IL-2 and IL-7 receptors (amongst others). Importantly, and the cause of much confusion initially, he still had normal-ish populations of B cells though they weren't activated or differentiated. This was further complicated by the discovery of random X chromosome inactivation in B cells, but eventually led to the realisation that despite random X chromosome inactivation the receptors on the B cells were non-functioning in all B cells. Eventually it was discovered that T cells required the IL-7 receptor for their initial maturation, while B cells required it for activation and differentiation - thus without it a patient was left with no mature T cells but a mature, naive population of B cells unable to be activated or differentiate.",
"The discovery of this as a single gene mutation brought on what was the first successful curative gene therapy in medical history wherein the use of a retrovirus re-inserted a functioning version of the defunct X-chromosome which then resulted in proper IL-7 receptor formation and subsequently T and NK cell differentiation and proliferation. The seminal paper on the therapy is available ",
"here",
" and a good summary of the difficulties faced in discovering the cause for and the treatment for X-linked SCID is available ",
"here",
".",
"Edit: I'm also unsure about what point you were trying to make about page 18."
] |
[
"Wow. Thank you so much for this incredible and detailed reply. It's extremely appreciated. I am also grateful you took the time to type all of that out on your cell phone. ",
"Because I know very little about this I assumed that the parathyroid had something to do with the immune function because someone classified as 'complete DiGeorge' has no thymus and no parathyroid (at least from what I could tell from the internet)",
"I really enjoy learning and believe that the more information I have about things related. To my babe, the better I am able to care for my child. A nice bonus is that I've always found medicine and the sciences extremely interesting and at one point in my life wanted to be a paediatrician. But then I realized i would be working with very sick children and didn't feel like I had the emotional capacity for it. And then I ironically had an unwell child. ",
"Thank you for explaining this all to me. It's been frustrating for me as a parent of a child with this syndrome with no Pediatric immunologist serving our provincial population. From what I gather, if my child has CD4/8 cells, then that means she does indeed had some thymus tissue somewhere in her body like I originally assumed. ",
"I'm also so happy to understand a bit more about what makes the immune system different in someone with this syndrome and it also gives me hope that her cell count will improve more as she ages. ",
"We just had an unfortunate incidence with this virus. In the ER she presented with only low sats. No fever or increase in white cells. Because of that, an infection (due to aspiration) in the lungs was missed and we ended up with a sick little one very quickly. Healthy at breakfast, in the observation unit on 4L by suppertime. I did tell the ER physician about the syndrome and the absent thymus at birth and they later tracked me down to apologize and request at future ER visits to use the words, \"she does not mount a proper immune system response\". ",
"This has happened before and when the doctor told me it's because she had absolutely no thymus tissue anywhere in her body it confused me and I couldn't make sense of how she had T cells without the gland. When I asked the doctor, the doc said it was because her lymphatic system took over. ",
"I now know that's wrong and I super appreciate your reply. I would happily read and devour any other information you might have to offer!",
"Ps. I just read your edits! I'm glad you misread the question because the answer you gave is great! I put the blurb in about complete DiGeorge because I know it produces zero T cells and thymus transplant is a promising looking treatment. I was 100% looking to understand how a person with DiGeorge with an absent thymus could possibly produce T cells. ",
"Pps. A boy that was from not too far from us recently passed at the age of two from complete DiGeorge after a failed thymus transplant. He was not treated with immunosuppressants prior to the transplant (I think) as part of the study. "
] |
[
"Why don't all phones, computers, etc, have a coating on the important electronic circuitry and other components for waterproofing?"
] |
[
false
] |
I know coatings are out there. I have even seen some posts on reddit. Is it a cost or heat problem? It seems a thin spray would not be expensive and I can't imagine a microthin layer being that much of an insulator. This would have saved my last two phones (RIP).
|
[
"Those phone cases aren't air tight, the electronics inside can still shed heat to the air within the case.",
"Also, your sim card and battery need electrical contacts. ",
"Another possibly issue is the heat damaging the coating."
] |
[
"Heat exchange is the primary reason I originally thought this would not work, but would a super thin coating really be that great of an insulator?",
"My big concern there is surface area. Even a very thin coating could fill in spaces between components where air circulation would occur.",
"I could see gaskets getting ripped, yes, but as I said before, Olympus does this with cameras and it works great. But would it short something or hurt the phone if it is just the battery port?",
"I don't know how big a deal it would be, but gaskets can fail from being dirty. The summer before last I was working with a particle accelerator and one day we had trouble pumping down the target chamber after putting in a target. It just wouldn't drop below 900 mPa. After a few hours scratching our heads I discovered a single one of my beard hairs was lying across the O ring.",
"One inseparable piece? Do you mean to coat it? What about a spray coating that could do any individual piece or pieces after the electronics were assembled?",
"You'd need exposed electrical contacts for that. Water could cause short circuits between them.",
"Waterproofing electronics is absolutely is something we can do now, but the engineering concerns are considerably tougher than you have assumed."
] |
[
"Cooling issues mostly. There's also the problem of servicing or reconfiguring such electronics."
] |
[
"Is it possible for nuclear fuel to accidentally reach criticality?"
] |
[
false
] |
[deleted]
|
[
"Ah, well that's far simpler. For that, any explosion or fire, following physical damage to the fuel bundle, will spread radioactive dust over a wide area. The higher the cloud (vertically), the more widespread the damage. Note: Only spent/used fuel bundles are dangerous. Virgin fuel is more or less safe, even if physically destroyed. Don't get me wrong, if someone lit a virgin fuel bundle on fire it'd still be a major news event and lots of shitstorms would occur, but the ONLY radioactive thing in virgin fuel is U-235, and there's only ~3% of it by mass...virgin fuel is safe enough to handle with (gloved) hands.",
"Spent fuel however, remains dangerous for decades after it comes out of the reactor."
] |
[
"Ah, well that's far simpler. For that, any explosion or fire, following physical damage to the fuel bundle, will spread radioactive dust over a wide area. The higher the cloud (vertically), the more widespread the damage. Note: Only spent/used fuel bundles are dangerous. Virgin fuel is more or less safe, even if physically destroyed. Don't get me wrong, if someone lit a virgin fuel bundle on fire it'd still be a major news event and lots of shitstorms would occur, but the ONLY radioactive thing in virgin fuel is U-235, and there's only ~3% of it by mass...virgin fuel is safe enough to handle with (gloved) hands.",
"Spent fuel however, remains dangerous for decades after it comes out of the reactor."
] |
[
"PWR / BWR fuel bundles (they are basically the same) can go critical if physically damaged ",
" in the presence of water (ie: submerged). The catch is, normally when they are physically damaged, they do so by melting, which boils all the water off, so...what breaks them that isn't heat?"
] |
[
"So I just finished book that deals with epigenetics..."
] |
[
false
] |
How real is it? Is there anyone who can point me to some articles and papers either supporting it or denying it? The book I finished is called . Just trying to get some context, thanks! EDIT: Here's a link to the wikipedia page for epigenetics EDIT2: Sorry was in a hurry before. The author does site all of his sources, and is very good about that, but he did seem to refer to the same few studies a lot, not that it's a bad thing at all, I just noticed that. Also, I just wanted to make sure it was still respected by the community, as all of those studies were down roughly ten years ago. I wasn't sure if it survived scrutiny these past few years. The book basically uses epigenetics as a basis for an argument that we are actually hardly genetic creatures, that it is actually a complex interplay between our genes and environment, that they are both changing each other. In the sense that people can't just say "oh it's his good genes", lots of it actually comes from upbringing and personal drive in the individual.
|
[
"Not familiar with the book. Does it not have references to scientific papers? (if it doesn't, yikes.)",
"Epigenetics is real. The most famous example of epigenetic influence on phenotype is probably ",
"Angelman syndrome",
" verses ",
"Prader-Willi",
": The same genetic problem, depending on whether it came from the mom or dad, causes a different disorder.",
"To give you a sense of how much literature there is on epigenetics, \na ",
"PubMed",
" search for \"epigenetic\" results in 18968 scientific papers.",
"Based on the title of the book, I'm assuming the author tries to relate epigenetics to intelligence, or some such. Ignore the rest of this post if I'm off-base.",
"~~~~~~~~~~~",
"To give you a sense of how much literature there is to link intelligence to epigenetics, a ",
"PubMed",
" search for \"epigenetic, intelligence\" results in 35 scientific papers. Most of those results seem off-topic, too. Epigenetics might be linked with inter-individual differences in intelligence (in the normal population)... but that's certainly not what epigenetics is famous for.",
".",
"I did find one paper linking the two, ",
"\"Human Intelligence and Polymorphisms in the DNA Methyltransferase Genes Involved in Epigenetic Marking\"",
". The first sentence of the abstract is",
"Epigenetic mechanisms have been implicated in syndromes associated with mental impairment but little is known about the role of epigenetics in determining the normal variation in human intelligence.",
"So be wary of bold claims that the two are strongly related.",
".",
"Seriously, that book should have references for exactly this reason: A reader that wants to know more, or wants to see the support for the author's claims, shouldn't have to ask the internet."
] |
[
"Nature affects nurture, nurture affects nature. Sorry for being touchy but I have a peeve with \"vs.\" Genetic effects influence things like maternal care, home environment, and internal biochemistry (through influences on food and drug choice, for example). Environments can completely determine the direction of a biochemical effect (e.g. pro-longevity gene in a warmer environment, same gene causes earlier mortality a cooler environment). Not saying that you didn't know that, just had to type it out. Also in agreement with everything else everyone is saying, of course."
] |
[
"Well, I don't know that book, but it sounds very pop-sciencey. Epigenetics is a real field of good and valid scientific research. What ",
" about epigenetics were you interested in?"
] |
[
"What distance do your eyes move in a given day?"
] |
[
false
] |
If your pupil moves from one corner of your eye to the other, although it is rotating, the pupil probably covers around 1cm? I was wondering what the average distance your eye moves over the course of a day?
|
[
"I'm sorry to hear that. I'm also sorry to hear that it has made you so sour."
] |
[
"I wouldn't be surprised if it were miles. I have a program that tracks how far in miles I move my cursor everyday, it's usually well over a mile."
] |
[
"What program is this? I would live to try it."
] |
[
"What's the role of imaginary numbers in electronics and circuits?"
] |
[
false
] |
I just don't get how the square root of -1 can be so relevant in these areas.
|
[
"I'm going to disagree with ",
"/u/fishify",
" for a bit because I think it's more fundamental than simplifying computation. That's sort of a trick of phasor analysis, but the reason that works has to do with more complex (heh) things. ",
"Circuits behave according to a set of linear differential equations. If you take a peek at the equations for voltage across a capacitor or current through an inductor, you'll see they behave according to the integral and derivative of the current and voltage across/through those components. So when you do your good ol' fashioned mesh and nodal analysis of a circuit with inductors and capacitors, you don't get neat algebraic systems of equations. You get a linear system of differential equations. ",
"The solutions to those differential equations are contain the set of complex exponentials, or Ae",
" ",
" ",
" where A is the amplitiude, j is the sqrt(-1), w is radial frequency, and phi is a phase offset. ",
"According to Euler's identity, complex exponentials are really sine and cosine functions. Here's a good proof",
"e",
" = cos(w) + jsin(w)",
"e",
" = cos(w) - jsin(w)",
"e",
" + e",
" = cos(w) + j sin(w) + cos(w) - jsin(w)",
"e",
" + e",
" = 2cos(w)",
"cos(w) = (e",
" + e",
" )/2",
"That proof is a short way of convincing you that sine and cosine functions are linear combinations of complex exponentials. When you see that linear combinations of complex exponentials are solutions to circuits differential equations, you'll see that means that the behavior of circuits has to do with linear combinations of sine and cosine functions. ",
"Which makes sense. Fourier tells us that things that vibrate, oscillate, etc can be described as summations (or integrals, as is more correct) of sine and cosine. Euler tells us sine and cosine are equivalent to complex exponentials. Ergo, because we have circuits that vibrate and oscillate, we're dealing with sine and cosine, and because we're dealing with sine and cosine, we're dealing with complex numbers. "
] |
[
"It's for calculational simplicity. If you are dealing with sinusoidal signals, you can represent these more easily using complex numbers. Since e",
" =cos(a)+i sin(a), anything you can do with sines and cosines you can do instead with complex exponentials. But exponentials are simpler: the derivative is an exponential again (as opposed to sines and cosines turning into each other under differentiation), you can introduce phase shifts by multiplying by e",
", etc.",
"In addition, thanks to Fourier analysis, any signal can be written as a sum of sines and cosines, and so as a sum of complex exponentials, and so the importance of complex exponentials goes beyond the case of pure sinusoids."
] |
[
"You do not have to have complex numbers to do sines and cosines. What complex numbers allow us to do is to collapse multiple equations into 1 due to the orthogonality of the sine and cosine functions. Note that in your examples the sines and cosines go with either the real or the imaginary part and not both."
] |
[
"Why is the dibromonation reaction of 2,3-dimethyl-1-pentene stereospecific?"
] |
[
false
] | null |
[
"It's a matter of ",
"assymetric induction",
". Essentially the existing chiral feature (the methyl group labelled) will affect which face of the c=c bond will be attacked. "
] |
[
"You are correct about the mechanism. I want you to draw out each of the possibilities that you could get in forming the bromonium ion intermediate. In one instance, the bromine will have no steric interference with the isobutyl group and in the other, there is severe steric strain. The latter will be formed slower, so it will result in less product formed. "
] |
[
"so would I be correct in concluding that the stereoisomer on the left would be more readily formed?"
] |
[
"Are we hampered in understanding by the languages we use?"
] |
[
false
] |
This is prompted by the post about deaf people thinking in sign language. I remembered reading that some cultures have very limited systems of counting, so I wondered if it was possible that our languages could be ruling out the possibility of us grasping some concepts.
|
[
"To add on to this: in addition to English, I speak a language where there is a separate word for large spoons and small spoons (that is more present in the vernacular than the words teaspoons and tablespoons are in English), but no such distinction for different sized forks. I noticed that the kitchen drawers of speakers of said language overwhelmingly use two of the four slots for spoons, whereas native English speakers are about 50/50 spoons vs forks when a distinction is made (some group based on size instead, mixing small forks with small spoons). ",
"Is such a thing a known phenomenon? Is there a list of similar situations where perhaps language changes our positions without us noticing?"
] |
[
"Linguistic determinism is dead in the water, but research on linguistic relativity is alive and well, mainly at the Language and Cognition research group at the Max Planck Institute for Psycholinguistics in Nijmegen, and in the cogsci department at UC San Diego, but there are also plenty of others."
] |
[
"I'm no linguist, but you might find interest in the ",
"Sapir–Whorf hypothesis",
".",
"As a piggyback to your question, I'm interested if there are any hypotheses or evidence that ",
" has any impact on conceptualization, not just limits imposed by a spectrum of verbs and nouns."
] |
[
"Where does there energy in the Earths core come from?"
] |
[
false
] |
Was just thinking about how almost all life on earth has is energy provided by the Sun, but the sun never reaches the core of the planet, so where does all this energy in the center come from? There's so much energy there (seen by volcanoes, earthquakes, tectonic shifts etc). Where is this energy actually from? Is it all stored energy from the formation of the planet? What does this energy deplete, will we ever 'run out' of energy from the core of the planet and no longer have events like earthquakes?
|
[
"In my astronomy class last semester we talked about this. The Earth's core is heated(at least partially) from the differentiation of materials in the mantle and core. Differentiation is when the heavier and denser materials, like iron and nickel, move towards the center of mass(the core) and heat the surrounding material as it is pulled inward by gravity. This process is how planets like Jupiter produce more energy than they receive from the Sun. Plus the decay of radioactive material in the earth gives off heat as well. ",
"Also, the atmosphere of a planet can contribute to its heating or cooling. Mars, for example, had little to no atmosphere to trap in the heat radiated from the surface. (It may have lost it after several powerful meteorite impacts) It may have suffered from reverse greenhouse effect where the cooler it gets, less water is evaporated and remains on the surface, trapping any excess CO2 in the bodies of water, which allows more heat to escape and makes it even cooler. ",
"\"We\" will never run out of this energy, but some Human-like creature in the distant future may have that happen to them. That is if the Earth isn't destroyed by an asteroid or some other unforeseen event. ",
"The Moon is currently geologically dead and no longer has volcanoes or tectonic activity, but it used to. Those dark areas of the Moon's surface are actually 3 billion year old lava flows."
] |
[
"The core's rotation, and the rotation of the planet itself, is an artifact of the angular momentum of the protoplanetary material carried as it formed our planet. Imagine a big, swirling cloud of elements, falling in slowly as gravity takes over. Because all that dust and debris is moving, it conserves it's angular momentum. So as it falls inwards, it moves faster and rotates. Eventually our planet will \"run down\" and becomes tidally locked to the sun, but we still have plenty of rotation left. "
] |
[
"Well it's mainly do to gravity. See since earths hot firery formation the heat has been kept in its core. Tidal friction is a big factor in keeping the earth warm but it's not enough. Plus the moon is inching away from earth so our days will also be longer. I digress, it's really just the compression of the mass of earth keeping it warm. Volcanos and plate tectonics are really earths pimples and flaky skin for a metaphor. Earth got all its energy in its creation, slowly like all things it loses that energy just simply do to thermodynamics."
] |
[
"What happens when the universe expands too far?"
] |
[
false
] |
If the universe is continuously expanding and taking into the conservation of mass, would the universe eventually freeze because the distribution of all energy and mass is spread too far?
|
[
"Yes. The alternative is that the universe won't continue expanding forever, which a few physicists believe."
] |
[
"It doesn't have to expand into anything. \"Expanding\" in this context just means \"the distance between two points increases with time\"; there's no need for something outside the universe to hold it."
] |
[
"What does \"around our universe\" mean? \"Around\" is a weird word in this context, because there's no direction you can go that's into or out of the universe."
] |
[
"What would \"The Suns\" on a binary system look like from the surface of a planet?"
] |
[
false
] |
If such a planet exists, is there any mechanical understanding of how a planet might orbit the stars? would there be two days or one drawn out one? Seasons? Is there a size limitation or minimum on orbiting bodies?
|
[
"Depends on how luminous the stars are and the distance between them. It's also important to know the orbital configuration. The stars can orbit each other very closely with the planet orbiting both stars further out. Or a planet could orbit a star, while a companion star orbits further out. ",
"In the first case, the planet would simply orbit both stars like a single one. The stars would have to be very close to each other or the planet would have to be far enough away from the, so the orbital disruption are small enough. ",
"In such a system, an observer would see a \"double-sun\", that's wandering over the sky each day, rather than a single sun. The observer would also see both disk orbiting arounfd each other, obscuring each other from time to time, if the planetary orbit is properly alligned to the orbit of the stars. ",
"In the second scenario the planet would orbit its main star just like we orbit the sun. The second star would have to be far enough away to not disturb the orbit. Since even the smallest stars are extremely massive compared to planets (75 ",
" jovian masses at the very minimum), they would have to be in a distance where they not strongly influence the weather or climate, but still are extremely bright to the human eye. ",
"As the planet orbits its main star, the background of stars is chaging over one \"year\". The second star would therefore be a day star at one time and half a year later it would be a midnight star, similar on how the planets in our solar system are culminating at midnight while they are on opposition. Roughly half a year later they are in conjunction with the sun and culminate at noon.",
"In such a scenario wouldn't be a change between day and night, but some weird twilight, at least if the second star has a significant luminosity. ",
"If you had two stars similar to the sun, the second star would still be several hundreds to thousands times brighter than the full moon on earth if you place it somewhere between Uranus and Neptune. This would be bright enough to do everyday stuff like reading, working outside or strolling around, but wouldn't influence the temperature or clamite to a noticeable amount. Its basically like sunset would last the whole night. "
] |
[
"Just a quick correction:",
"...even the smallest stars are extremely massive compared to planets (75 solar masses at the very minimum)...",
"Don't you mean 75 ",
" masses or something smaller? Since, by definition, stars would have to be able to be just one solar mass (and smaller)...",
"Otherwise, very informative!"
] |
[
"Aye, it's 75 jovian masses, not solar masses. Thanks for the correction!"
] |
[
"I have a question about planetary gravity."
] |
[
false
] |
I was wondering: If there were a planet physically smaller than Earth, but with a core sufficiently dense enough to compensate, could you end up with the same gravitational pull as Earth? Or a larger planet with a very light core? Is that how that works? Thanks.
|
[
"The acceleration of gravity is related directly to mass and inversely to the square of the radius, so as long as m/r",
" is the same, the gravity will be the same."
] |
[
"To expand on that, if you write mass in terms of density ϱ, then as long as ϱr is the same, the gravity will be the same. If you double the radius, you need to halve the density.",
"EDIT: This is assuming constant density throughout the planet. It gets a bit complicated otherwise. Also, we are referring to the gravity at the ",
" of the planet."
] |
[
"Right, just to expand a little more...If the surface gravity is the same on a much smaller planet..the volume of space around the planet that could house orbiting satellites would be much smaller. ",
"For example, the earth's radius is 6,000km, and the gravity is about 10m/s",
" . This means at 12,000km, the gravity would only be 2.5 m/s",
" (twice the radius, a quarter of the force). For a new earth, say half the radius of earth...about 3,000km. The same 12,000km radius (or 9,000 feet above the surface) would yield an acceleration of less than 1 m/s",
" . (A four times the radius, one sixteenth of the force). ",
"That, of course, is an extremely long winded way of saying 'the acceleration due to gravity decays much faster for a small earth'."
] |
[
"What are possible solutions to the issues that GMOs (in agriculture) present? [more ?s inside]"
] |
[
false
] |
Can GMOs feed the world? Does it matter if it can or can't? Potential Environmental Risk: -Gene flow -The emergence of resistant pest and weeds What can be done in regards to GMOs and consumer confusion? If a GMO product isn't labeled how can one know whether or not there are consequences to the consumption of GMOs? Is this even a valid question? Is it true that GMOs can create allergies, toxins, new diseases, and nutritional problems? How valid are the claims this is making?
|
[
"What about Golden Rice II a 70gram serving provides a daily requirement of vitamine A. It is licensed for humanitarian use.\nWhat about animals engineered to produce certain drugs in their milk, between a few animals can be produced the worlds supply of a drug needed to treat emphysema which used to cost per patient $40,000 dollars per year but now is much reduced because now only the animals need to be maintained."
] |
[
"At the risk of getting downvoted into oblivion, i'd like to offer what should be perceveid as an ",
"Today's commercial GMO's are a load of rubbish i cannot even begin to describe the amorality and bullshit-laden top of. That is: Leaving all the science behind for a moment, and honestly there isn't much \"real\" science involved with commercial GMO's, the whole class of product can be summarized as: \"Let's make food production a monopoly and bind farming industry to our products FOREVER MWAHAHAHA.\" Yea i can't be bothered to be more serious atm. Sadly that's pretty much accurate. Oh no doubt there is some research being made into actually beneficial GMO's but that's independent and equally badly funded as just about every other independent biology research project. The big money is behind such marketing monstrosities as Monsanto(tm) RoundUp(tm) Ready(c). As a result that's what ordinary folk are talking about when refering to \"GMO's\" and quite frankly those products geared solely towards control and domination of the food market through patents on natural genes and soil-poisining mechanisms through tolerant, infertile, copyrighted crop can ",
" for all i care.\nWhew. Sorry for the rant =p"
] |
[
"Oh i don't doubt it. Who developed these, how are they licensed, and who is selling them at what profit margin to whom?",
"Never said \"GM is evil\", but i did say \"the people that deal in GMO's are evil\"*",
"*: for an implied realistic definition of \"evil\""
] |
[
"Questions about how they're keeping the Fukushima nuclear cores cool."
] |
[
false
] |
I've been keeping up on Fukushima and know the basics, but I was reading and am confused as to why they need 400 additional tons of water a day to cool the core. I get that they need a lot of water to keep the core(s) cool. My question is why they aren't using some kind of closed loop system, incorporating some kind of cooler, which would be more efficient and alleviate (at least in part) the storage issue. Does the water reach some sort of radioactivity saturation point? Is there no pumping equipment that can operate in that environment? Is there something I'm missing? I'm hoping someone can explain this to me. Obviously they cannot sustain this method indefinitely, and hopefully there are some bright people working on a better solution.
|
[
"The other response here is a poor response that not only doesn't answer the question, but also places judgment on a particular reactor design based on opinion. ",
"The cooling system involves injection through the core spray, feedwater, or coolan injection lines. The water trickles down through the remains of the reactor into the containment drywell where it cools the ejected core debris. Then it is drawn into a cleanup and cooling system and reinjected to the reactor. ",
"As for why they are adding water, we do not know. One possibility is that they do not have sufficient cleanup capacity, and are storing water until it is cleaned up. The reason you would do this is to limit dose rates on site and in the reactor building. But this is just speculation on my part."
] |
[
"Around 5-6 months after the event they reached cold shutdown. This means that the average water temperature is below 200 degrees, so there should be no boiling and consequentially no steam. Unless there's something we don't know (but that's just speculation)"
] |
[
"As for why they are adding water, we do not know.",
"Hmmm. If they're adding water as a result of loss to the system (in the form of steam, maybe?)...that is an awful lot of loss, but it wouldn't explain why they are still needing to store so much water.",
"Thank you for your answer."
] |
[
"How would inserting a floating balloon into the atmosphere of a planet from space be technically different from landing a craft on the rocky surface of a planet from space?"
] |
[
false
] |
So I know there are a some important technical differences between landing a craft on Earth (which has a moderate atmosphere) versus landing a craft on Mars (which has a thin atmosphere). If my understanding is correct, the thinner atmosphere of Mars poses particular challenges because it's not thick enough to make use of air braking, but it is thick enough to cause frictional heating. I've also heard that landing a craft on Venus is damn near impossible because the heat, pressure and chemical composition of the atmosphere at ground-level basically melts any craft we might send to its surface. And I've read briefly about proposed missions to Venus that involve floating a lighter-than-atmosphere vessel in the upper layers of the venereal atmosphere, where the heat and pressure and causticness of that atmosphere won't be so severe. But how would we go about inserting a balloon-like craft from orbit into the upper atmosphere of Venus?
|
[
"Edit: I realized I wrote something that looks more like an ",
"/r/AskHistorians",
" answer than a ",
"/r/askscience",
" one. But at this point I have put too much work on it. I hope it answers some of your questions anyway.",
"\"We\" have already done it! And by we I mean the Soviet Union. Technical data on how exactly is was done are a bit hard to come by but the history of the program is fairly well documented. During the 60's, 70's and 80's the USSR launched a whole series of probe to Venus under the Venera program. I love this program because it's an awesome example of planetary explorations with big unknown, silly mistakes and awesome results. Moreover it's relatively unknown by people who are not space geeks so it always great to see the reactions when you tell people we actually have pictures from the surface of Venus!",
"After several failed attempts at reaching Venus with a functional probe the Soviet union managed to get Venera 3 to Venus. They got there 4 years after the American Mariner 2 mission. However unlike the Mariner 2 flyby the plan was to enter the atmosphere and parachute down as far as possible while collecting data. Venera 3 atmospheric probes failed pretty much right away but the dead probe became the first man made object to touch the ground of another planet. Venera 4 (1967) probes worked for a while but got crushed as it descended. The hot and high pressure atmosphere of Venus was already known at the time. There was also the possibility that seas or lakes covering Venus, so the lander part of the spacecraft was made to be able to float. After an entry at about 11 km/s and reaching 11000C on it's exterior the probe deployed a breaking chute (at around 300 m/s) and a main parachute. However scientist didn't realize how hellish the conditions were and Venera 4 was only built to withstand 25 atmospheres instead of the 90 present at the surface. Coincidentally this was measured literally the next by flyby of the American Mariner 5 probe. ",
"They did not have the time to modify their spacecraft to survive those unexpected conditions before the next launch opportunity. Venera 5 and 6 were launched and had similar mission profiles at Venera 4. They both got crushed tens of kilometers above the surface but confirmed that there was enough light going through the clouds to be able to take pictures.",
"From this point onward the objective became to softly land on Venus and actually transmit data from the surface. Venera 7 was launched and pretty much had for only objective to survive the pressure and hellish temperature while still transmitting some data. It was designed to withstand 540C and 180 bars for 90 minutes. The parachute was also made smaller to reach the ground faster. It would serve as reconnaissance for future mission. On December 1970, after a hard landing it became the first functioning probe ever landed on any planet. In the same year the Soviet also had broken the record for the longest manned mission in space, the first robotic sample return and the first rover on another body.",
"In 72 Venera 8 was launched. It was based on the 7th but with the safety factors taken down a notch now that the conditions were better known and with more science. They confirmed earlier measurements and saw that the light level though the cloud was about the same as dusk on Earth.",
"Up to this point it's also worth noting that the USSR had kept secret that nearly half the probes sent to Venus never managed to leave earth orbit. Those were usually renamed and not counted as part of the official Venera program. After 1975 they did not suffer anymore launch failure.",
"After all those missions the Soviet program decided to design a whole new spacecraft family, much bigger and more capable. Venera 9 and 10 were around 5 tons, and designed to have an orbiter part get into orbit while releasing the lander. The lander part was encapsulated into fairly spherical heat shield that separated once air resistance had slowed down the craft enough. They once again chose to use very small parachutes to get to the surface faster and even cut them 50 km above the ground. It used the antenna as an airbrake in the thick Venusian atmosphere. Venera 9 landed on October 22, 1975. It had two 180 degrees camera, one of the camera cover didn't release but it managed to take ",
"this picture",
" (",
"here it is corrected",
")of the surface of Venus. This was the first ever picture from the surface of another planet. Venera 10 landed on the 25th and took another very different (for geologists) ",
"picture",
".",
"At this point the American landed on Mars with the Viking mission and decided to get into the Venus game. They packed 3 small conical entry probes and one larger 73 cm diameter spherical one on PIONEER VENUS 2. The bigger one got quite a shock as it slowed from 11.5 km/s down to 200 m/s in 35s. It slowly drifted down under parachutes for one and a half hour before crashing into Venus. The smaller ones did not have parachute but only crashed at 35 km/h as they were slowed down by the very dense Venusian atmosphere. One of them survived for more than a hour after the crash!",
"The next Soviet missions, Venera 11 and 12 arrived in 75 and both carried color camera but once again the lens cap didn't eject and they got no pictures. Finally in 82 Venera 13 and 14 landed and got ",
"color",
" ",
"panoramic pictures",
" of the surface. However Venera 14 ejected the lens cap under the arm that was supposed to test how hard the ground was...",
"Venera 15 and 16 were radar mapping missions and did not carry landers. ",
"As early as 1967 balloon missions to the clouds of Venus were suggested. In 1984 the Vega 1 and 2 were launched. Their mission was to drop their payload on Venus and then continue on to the Halley comet which was in a favorable spot. After atmospheric entry the probes deployed a parachute at around 55 km altitude and the balloon separated from the lander. One kilometer lower helium gas was pumped into a 3.5 m diameter teflon coated balloon. Special paints was used on the electronics to prevent chemical attack by the sulfuric acid clouds. Vega 1 dropped its balloon on the night side in fear of it bursting in daylight. No camera were installed for this reason. Sadly the lander part of Vega 1 malfunctioned and started its drill program 15 km above the surface. The balloon covered 11,000 km in 45 hours. Vega 2 worked pretty much flawlessly.",
"Those were sadly the last missions to land/fly on Venus.",
"Most of this is based on the \"The Soviets and Venus\" series of article by Larry Klaes published in the journal of the Astronomical Society of the Atlantic"
] |
[
"Very nice. Thanks for the post. "
] |
[
"Astounding... can't believe I didn't know about these missions and pictures. Thank you so muchfor sharing!"
] |
[
"How much warning would we have before a solar flare?"
] |
[
false
] |
Would the lapse between solar flare going off and its effects hitting earth but more or less than the ~8 minutes it would take to get here? Just curious considering how catastrophic for electronics it would be. Follow up question, in that interval between us knowing there would be a flare and the flare's effects hitting the earth, would there be any way to protect the basic electronics? How would the effects be different for a large, medium or small flare?
|
[
"Solar flares doesn't travel towards earth at the speed of light. Solar flares consists of particles with mass, and according to the wikipedia article, they reach earth within one or two days. The SOHO satellite can spot flares and warn earth, so we'll know within a day or two that a flare is about to hit earth.",
"The consequences of a flare depends on your location. Countries close to the poles will suffer the worst. Large currents are induced in transformers and other power line components, destroying them. The best solution is to ground all equipment when a storm is about to arrive."
] |
[
"Well, we certainly couldn't know about it in less than 8 minutes. If the light from the flare was the dangerous part, we would see the flare at the same time it hit us. But the X- and UV radiation produced just causes temporary radio interference and possibly increased atmospheric drag on low-earth orbit satellites.",
"The charged particles from the flare are what we need to worry about, and they travel more slowly. We typically have a day or two between observing the flare, and the arrival of the storm, but sometimes the warning time can be less than an hour.",
"Large solar storms can push down the protective magnetic field around the Earth, and damage satellites that would otherwise be protected."
] |
[
"We're pretty well protected here on the surface, by the atmosphere and magnetosphere. My understanding is that a very large flare which might happen less than once per century may take down part of our power grid, and maybe expose people on high-altitude aircraft to enough radiation to cause minor, temporary health effects. ",
"Generally, though, to be harmed by a flare, you have to be outside of Earth's magnetosphere. The Apollo astronauts, for example, could have died if they were unlucky enough to be up at the wrong time.",
"I don't have any idea how often a flare powerful enough to harm people on the ground might happen, or whether that ever happens at all."
] |
[
"What happens to a tumor once the person dies? Assuming nothing is done to the body."
] |
[
false
] | null |
[
"Just like any other cell in the body, it stops receiving oxygen/nutrients and dies. This process is ",
"necrosis",
".",
"One interesting side note is that, due to the malformed vasculature of most tumors, there are generally regions of a large tumor that do not receive any blood. So often times a tumor will be composed in a large part by necrotic tissue. This is why sometimes patients with advanced cancer have a very powerful odor.",
"edit: I'm not sure that necrosis is the 100% correct term, since it is generally used to mean \"cell death while the organism itself is alive.\" If you want to know more of the specific processes, you can look into decomposition.",
"The takeaway is that nothing particularly special is known to occur in tumors. It is all the same processes that occur in normal tissue."
] |
[
"More accurate than or as accurate as?"
] |
[
"Well for very internal tumors, it doesn't. Generally you might experience this in a tumor that has broken through the skin, like a very advanced breast cancer. Another possibility is for the odor to be present in the breath of a lung cancer patient. ",
"Second interesting side note: Studies have been done to diagnose lung cancer by having ",
"dogs sniff the breath of patients",
". "
] |
[
"Statistics Question!"
] |
[
false
] |
In recent front-page article it talks about the . My question is what difference is there between their method and just taking the average of the samples and doubling it to find the maximum? You know that the average is going to be half the maximum since the numbers are sequential. And just as the accuracy of their method increases with the number of samples, the sample average should approach the true average as the number of samples increases. So I know their method must be better (I haven't even had a stats class yet), so I'm just wondering why, and is there a way to plot the accuracy as it increases with the number of samples for the two different methods in order to visualize it?
|
[
"Think about it this way. Suppose you sampled serial numbers 1,2,3,4, 100. The average is 22, double that is 44, but you know that there must be at least 100 tanks. This is an extreme case that almost never happens, but there are lots of inextreme cases that are off a little bit. You can also get off the other way, by sampling 96,97,98,99,100.",
"On average, taking the average gives you the right answer, but it increases the ",
"variance",
" (how far off you are likely to be) of your guess over just looking at the last one. The last one is more robust than the mean -- it varies less across samples. I believe in this case that the maximum is a ",
"sufficient statistic",
", but can't prove it."
] |
[
"Both methods would \"work\". The sampling distribution of means will approach the population mean with sufficiently large samples (n>20). The MVUE is a better estimator over all samples, as other have said. So you'll get a closer estimate with MVUE than with the mean doubling method nearly every time. ",
"Take a look at the sampling distribution of these methods",
" (e.g. all possible combinations of a population of N=30, with a sample size of n=7). ",
"Code :",
"\n import pylab\n import itertools",
"mvue=[]\nmean=[]\nn=7\ntanks=range(30)\n\n#generate all samples of sample size n\ncombinations=itertools.combinations(tanks,n)\n\n#don't loop if you want speed\nfor i in combinations: \n s=sum(i) \n m=max(i)\n k=float(len(i))#insures floating point division\n mean.append((s/k)*2.)\n mvue.append(m+(m/k)-1)\n\n\npylab.subplot(211)\npylab.hist(mean)\npylab.title('mean method dist. n=%i,N=%i'%(n,len(tanks)))\npylab.xlim(0, 2*len(tanks))\n\npylab.subplot(212)\npylab.hist(mvue)\npylab.title('MVUE method dist. n=%i,N=%i'%(n,len(tanks)))\npylab.xlim(0, 2*len(tanks))\npylab.savefig('meanVmvue.png')\npylab.show()\n"
] |
[
"is there a way to plot the accuracy as it increases with the number of samples for the two different methods in order to visualize it?",
"Further searching finds ",
"http://en.wikipedia.org/wiki/Uniform_distribution_%28discrete%29",
" which gives the variance of the estimate-from-maximum method as being (N-k)(N+1) / k(k+2). The variance of the estimate-from-mean (allowing duplicates) will be (N",
" - 1) / 3 k. These are the same for k = 1, as it is the same procedure there, but as k increases, using the maximum does a factor of k better. (Standard deviation, the square root of variance, is more intuitive though usually more mathematically difficult, so \"square root of k better\" might be a better description)"
] |
[
"Neurologically speaking, what makes a child's brain better at learning new skills and languages than that of an adult?"
] |
[
false
] | null |
[
"Lack of myeline around axons makes new synapsis easier to form, and our cerebral axons get myeline coats from age 25 or so onwards.",
"A very young child also has quite a bit more neurons than will have as an adult, and those will make a massive ammount of synapsis. Most of those will end up being pruned.",
"Our species retains brain plasticity well into adulthood, but we lose a bit of it."
] |
[
"A child doesn’t really lose his neurons. It’s rather that the connections between the neurons (synapses) change. For example the number of synapses can decrease if the child doesn’t use a particular part of his brain."
] |
[
"Becoming adult, how does a child \"lose\" his/her neurons?"
] |
[
"If the universe is expanding, does that mean that space between particles in my cells is expanding too?"
] |
[
false
] |
The way universe expansion has been explained to me is that every point in the universe is moving away from each other. Does that mean that we expand as well (although staying the same size relative to the universe).
|
[
"The metric expansion of the universe only occurs on the inter-galaxy-group scale. Within a galaxy, space is not expanding. It's not just that it is expanding such a small amount that we don't notice. Space inside a galaxy is not expanding at all. "
] |
[
"Not exactly. This is a popular explanation but it is misleading. Rather, spacetime is only expansive away from matter. Metric expansion is simply the cost of having empty spacetime. At the sub-galactic-group level, spacetime is curved such that objects are attracted to each other, and beyond this level, spacetime is expanding. The key here is that gravitational attraction is really just a curved spacetime. To say that gravity locally overcomes the expansion of the universe is to say that the curvature of spacetime overcomes the expansion of spacetime, which does not really make sense. More accurately, gravitational attraction is spacetime acts in the presence of matter, and metric expansion is how spacetime acts in the absence of matter. The ",
"FAQ",
" on this is helpful."
] |
[
"Space itself is expanding, but particles can hold onto each other with chemical/electric bonds, gravity, magnetism, etc. These forces are strong enough to make sure you don't drift apart. Gravity is strong enough to keep entire galaxies together, the expansion of space is only really noticable between them."
] |
[
"Why is Ebola so successful this time around?"
] |
[
false
] |
Ebola has appeared many times, killing less than 100 people each time, and then it is gone. Why is it killing so many more people today? Is this a new strain with better propagation characteristics? What has changed?
|
[
"Africa has changed, not Ebola. There are now more than a billion people in Africa, in the 80's, less than half that. With more people packed into bigger cities and more people pushing out into the rural areas, and with faster transportation between the bush and the cities, it was only a matter of time before Ebola got out of a small isolated community and into a major population center. That's what happened this time, and that's why the epidemic is killing more people. It's reaching more people."
] |
[
"\"The virus amassed 50 mutations during its first month, the researchers found. They say there is no sign that any of these mutations have contributed to the unprecedented size of the outbreak by changing the characteristics of the Ebola virus — for instance, its ability to spread from person to person or to kill infected patients. But others are eager to examine these questions.\"",
"The article you linked says the opposite of what you are saying. Just because something has mutations doesn't mean it has any phenotypic result."
] |
[
"Well, obviously it's mutating some, but all viruses constantly mutate. That's not really relevant. Fundamentally, it's behaving in exactly the same way it always has. It's just in large cities rather than small isolated villages. If you were to take a sample of ebola from an earlier outbreak and release it into the places it spread to this time around, the exact same result would have occured"
] |
[
"Is a measurement of Planck time arbitrary in time?"
] |
[
false
] |
Does a measurement of Planck time have to occur during a discrete period/cycle (i.e. clock cycle), or can it be measured during any arbitrary period along an infinite timeline? And if time is not infinite, does this then impose a universe "clock cycle"?
|
[
"The Planck time is far too short to be measured with any existing technology. However, there is often a misconception about the importance of Planck units. They are not universal pixel sizes, they are just units constructed from physical constants.",
"https://www.physicsforums.com/insights/hand-wavy-discussion-planck-length/"
] |
[
"Could universal pixel sizes exist?"
] |
[
"Aw c'mon. Speculate here. What if you're right?"
] |
[
"How are drug classes grouped or chosen?"
] |
[
false
] |
[deleted]
|
[
"You can group them by any of those categories to be honest. SSRI's are all selective serotonin reuptake inhibitors, meaning they all have relatively similar affects on the brain/neurotransmitters. PPI's and NSAIDs are also grouped by effect. You can also classify by structure like TCA's. TCA's are all tricyclic amines that have quite a wide variety of processes that they affect differently and to different extents so they are harder to classify by effect and moreso by structure. You can also classify them by the diseases they treat, examples are the DMARDs. They are disease modifying anti rheumatoid drugs (I believe, mighta got a word mixed up in there) and they are a few diff types of drugs that are supposed to help prevent progression (not just symptoms) of arthritis and similar type diseases. Does that help and/or make some sense?"
] |
[
"It help a little but it seems like it's not as clear cut as I had thought. What brought this up is I'm a pharm tech and we had a dr order flurbiprofen (I'd never seen it before). I assumed it was an nsaid (and was right) just based on the -profen suffix. I was just wondering if all the -azoles, -azolams, etc. all had similar makeups or effects and that's what made them a drug class."
] |
[
"I worked as a pharm tech for 3 years so yeah I get ya. A lot of them are named similarly so you can guess like that (ketoprofen too etc). And yes there are many other classes that have similar names but not all of them are, so be careful. Fluconazole and itraconazole are \"azoles\" but metronidazole isn't. So yes, it is very very complicated haha."
] |
[
"Doctors, If a HIV positive person lived out the rest of their life in a sterile bubble without medication, what would they experience?"
] |
[
false
] |
From the understanding that HIV only weakens the immune system and AIDS is all the diseases you get as a result of not being able to kill easy to kill viruses, what would happen if a still healthy HIV person lived in a sterile bubble for the rest of their life and was never again exposed to viruses. What other problems might they have if any?
|
[
"They could still end up succumbing to the infectious agents already in their body waiting to reemerge. Most people end up getting exposed to a variety of viruses that remain latent and don't cause much of a problem: ",
"CMV",
", ",
"EBV",
", herpes, ",
"HPV",
", HHV-8, etc. With AIDS, you can get reactivation or progression of disease that would not have happened otherwise. This could present as a disseminated infection that could affect their brain or heart, or it could result in cancers such as Kaposi Sarcoma, lymphoma, or cervical cancer among other things. Certain yeasts and bacteria can similarly lie dormant until they get a chance to attack. "
] |
[
"Thanks! I couldn't sleep last night and this was one of those middle of the night \"what ifs\" that came into my mind."
] |
[
"Bacterial cells outnumber your cells 10-1 in the body, so there would definitely be an infection from a bacteria getting somewhere it should and would normally just be phagocytize. "
] |
[
"If we were to theoretically point the James Webb Space Telescope straight towards Earth, how magnified of an image will we be able to see?"
] |
[
false
] | null |
[
"So, this wouldn't actually be doable - Earth is too bright and too hot etc - but JWST has a resolution of about 0.1 arcseconds, where an arcsecond is 1/3600th of a degree, and at its distance (1.5 million km), that comes out to a resolution of a bit under a kilometre. So JWST's resolution would be enough to make a more than 10,000x10,000 pixel resolution image of Earth, if it were possible for it to image the Earth. That might be lower resolution than you'd think, but JWST really is very far away, many times further than any astronaut has ever travelled from Earth."
] |
[
"That might be lower resolution than you'd think, but JWST really is very far away, many times further than any astronaut has ever travelled from Earth.",
"This is a really important point. If you look at reconnaissance satellites (and wave, because they're looking at you!) then they're in much closer orbits. The U.S. KH-11 series of satellites typically have a perigee of around 300 km: one five-thousandth the distance to the JWST.",
"So if you put the JWST in low Earth orbit, that same angular resolution would amount to resolving features about 20 centimeters across."
] |
[
"Also, pointing at the Earth would also point it nearly directly at the Sun - which would destroy it almost immediately."
] |
[
"What would need to happen in order for it to be called the LAW of evolution?"
] |
[
false
] |
There's laws of motion, gravity, and thermodynamics (and I'm sure others), what other laws are there, and what does it take to become a ?
|
[
"There's nothing weak about the word theory. For instance, quantum field theory is the most accurate description of nature that we have.",
"As for laws and theorems in physics:",
"*Bell's theorem",
"*Newton's law of gravity, laws of motion, law of heating and cooling",
"*Kirkchoff's laws",
"*Kepler's laws",
"*Laws of thermodynamics",
"Are a few"
] |
[
"'Laws of Science' on Wikipedia",
"Theories are models. 'The world is like this'. Laws are fundamental rules that always apply (in the specified circumstances) and are distilled into statements of fact. Natural selection could perhaps be formulated into a law, or set of laws, but evolution is not a simple proposition."
] |
[
"I don't think laws and theories are really the same thing. ",
"Theories are conceptual frameworks that suggests at a mechanistic explanation at how something happens, while laws seem to tend to be concise statement of a specific, accurate observation. ",
"For instance, Newton's law of gravitation is just a specific equation relating the strength of a gravitational force to the masses and distance of the objects, while the theory of gravitation encompasses things like general relativity and how gravity works and what it affects.",
"I could be wrong, but that's what I always interpreted laws as. In any case, there are hardly any laws in biology since few things are ever concise and simple and almost nothing is ever absolute. "
] |
[
"Why doesn't the brain filter out Tinnitus?"
] |
[
false
] |
I know that the brain filters out inputs after being present for too long (thus if you don't move your eyes AT ALL the room starts to fade to black). So why doesn't the brain filter out Tinnitus? It's there all the time.
|
[
"This is not my field of expertise (otolaryngology), though, in 2014 a ",
"comprehensive review and clinical guidelines",
" were published in ",
".",
"It includes, amongst many other notable portions on the pathology, the current understanding of the disease, the treatment options, and further avenues of exploration and clinical management of patients with the disease.",
"They classify Primary and Secondary tinitus as follows:",
"Primary tinnitus is used to describe tinnitus that is idiopathic and may or may not be associated with SNHL ",
". Although there is currently no cure for primary tinnitus, a wide range of therapies has been used and studied in attempts to provide symptomatic relief. These therapies include education and counseling, auditory therapies that include hearing aids and specific forms of sound therapy, cognitive behavioral therapy (CBT), medications, dietary changes and supplements, acupuncture, and transcranial magnetic stimulation (TMS).",
"Secondary tinnitus is tinnitus that is associated with a specific underlying cause (other than SNHL) or an identifiable organic condition. It is a symptom of a range of auditory and nonauditory system disorders that include simple cerumen impaction of the external auditory canal, middle ear diseases such as otosclerosis or Eustachian tube dysfunction, cochlear abnormalities such as Ménière’s disease, and auditory nerve pathology such as VS. Nonauditory system disorders that can cause tinnitus include vascular anomalies, myoclonus, and intracranial hypertension. Management of secondary tinnitus is targeted toward identification and treatment of the specific underlying condition and is not the focus of this guideline.",
"The paper is rather technical in looking into clinician practice and epidemiology, but it does give a very thorough breakdown of tinnitus as a physical malady. Understanding the specific pathology of the patient allows for more effective treatment. Unfortunately, this has the effect of splitting tinnitus into many subgroups of categories, though it may be a good place for OP to start to understand why this is a more difficult question to answer than he might've anticipated."
] |
[
"The acoustic reflex, which decreases sound transmission to the inner ear, is dysfunctional. This makes loud sounds which previously weren't too loud become significantly louder and reach a persons uncomfortable level. ",
"https://en.m.wikipedia.org/wiki/Acoustic_reflex"
] |
[
"The acoustic reflex, which decreases sound transmission to the inner ear, is dysfunctional. This makes loud sounds which previously weren't too loud become significantly louder and reach a persons uncomfortable level. ",
"https://en.m.wikipedia.org/wiki/Acoustic_reflex"
] |
[
"What happens to the earth/soil beneath large cities over time?"
] |
[
false
] |
[deleted]
|
[
"It really really depends on the type of geologic environment you're building on. In NYC, it's mostly alluvial, so the foundations of the buildings go very very deep, whereas in Finland, you can build a highrise just on almost the open ground because the bedrock is on the surface. ",
"Buildings are no where near heavy enough to cause any kind of geologic phenomena (earthquakes) if that is what you are concerned about. "
] |
[
"This is probably an exception, but the city of Venice is sinking partially due to the weight of the buildings on the soft water-logged ground.",
"You can watch about it on Nova's ",
"The Sinking City of Venice",
". I linked to the time where I think they explain it but I can't verify it as I have no sound on this computer. I highly recommend watching the whole documentary when you get the chance."
] |
[
"This is very hard for me to answer since it pulls on a couple years worth of soil science classes and requires such sweeping generalities. I will try to be very brief.",
"Chances are that what's underneath buildings is not soil; it's either fill or dirt. Soil is a highly complex and alive combination of physical, chemical, and biological systems. Fill is a construction material and dirt is simply what's beneath your feet; it holds little value or function. All three are the same thing except for their function and value.",
"Fill in cities is likely compacted to prevent buildings from settling (sinking into the ground). As a result, water will not enter the fill as much as it would a natural soil. Without the water, the amount of soil biota will be very limited as will be the amount of organic matter. The water that does enter the fill will be contaminated with pollutants dependent on where it is occurring. For example, it'd be a very safe guess that underneath a gas/petrol station you would find ",
"BTEX",
" contamination. Under a dry cleaning business there's a good chance you could find ",
"TCE",
" contamination. All of these contaminants tend to be fairly conservative, meaning that they travel through the soil unimpeded. All of these contaminants also dissolve poorly in water so, depending on their density, may sit above or below the water in an aquifer. Soluble contaminants are much harder to talk about in a general fashion. Without knowing any of those four, it is hard to say whether a specific metal would move downward or if it would become deposited in a certain soil layer, or adsorb to a specific soil mineral. (And even then, ",
"some particles",
" are the right size to travel underground.) Soil and water pH and pe have very significant affects on what actually happens on the chemical level.",
"That all said, I can probably make one accurate sweeping generalization: It's very different!"
] |
[
"Can someone give a detailed explanation on how the touchscreen cellphone works in laymen's term?"
] |
[
false
] |
[deleted]
|
[
"This explanation is not correct because it implies you have to touch a capacitive touch screen, this is not the case.",
"The two main types of touch screens used in phones are capacitive and resistive. In both cases there are a grid of sensors.",
"In the capacitive case as you bring your body closer to the object you will change the capacitance, this occurs because there is always a cross capacitance between any two objects. There are many ways to measure a change in a capacitance: bridge method, lock-in based phase methods, RC time methods, resonance methods...",
"A typical low cost capacitive button, its design and how it works is considered here:",
"http://www.ti.com/lit/an/slaa379/slaa379.pdf",
"The touch screen is simply an array of these, multiplexed in a cleaver way.",
"Resistive touch screens are also a clever multiplexing of a single button. A resistive switch simply passes current when connected.",
"In a typical resistive touch screen there are two grids with a small space. Pressing connects one grid to the other at a point. One grid is passing a current and the other is detecting a voltage. Lets press at an XY position. First X will pass the current. If the press is right in the middle of the screen the voltage the Y layer detects is half the supply voltage, if it is at the bottom it is 0 and if it is at the top it is the full supply voltage. The distance and voltage detected are linearly related. To read out the X position you simply reverse the roles."
] |
[
"http://computer.howstuffworks.com/question716.htm"
] |
[
"There are also IR-based touchscreens, which use a grid of infrared transmitters aimed across the screen at infrared receivers. When something (finger, stylus, link sausage) blocks a horizontally and a vertically aimed set of beams, the intersection is easily calculated.",
"I believe that one of the new Kindles is using this technology."
] |
[
"Antarctic Research - I was looking at a map of US research stations and had questions about placement."
] |
[
false
] |
[deleted]
|
[
"I spent some time at McMurdo. Part of the reason that we use that area today is heritage. It was first chosen not for science purpose, but pure exploration. It is the furthest south you can go on the water, and hence provides the closest access to get to the south pole. Even now if something is going overland to the pole it goes through Mcmurdo. Because of this, infrastructure was added, and because there was infastructure it enables science and it snowballed from there. So, it's not so much that the best science is on that side, but the most resources for the US are there."
] |
[
"I don't do antarctic research, but I work with people who do. The geographical significance of McMurdo is due to how you get to the continent. Flights leave Christchurch, NZ provided the weather is favorable, and weather conditions can keep travelers laid-up for weeks at a stretch waiting for a window. It's not easy, and definitely not safe, to take unfamiliar flight-paths into and out of the continent, and it restricts your available choices for where to put a station. ",
"A lot of the stations on the interior of the continent are automated, taking weather measurements. There are also some ice-drilling stations for taking cores for paleoclimate data."
] |
[
"oh, and the belt of sites is temporary science sites. All the permanent stations are on the second map you linked. I'm not sure what they all studied, I think the big 'X' is just core sample sites, but if you zoom in on the first map with all the red dots and go just to the left and down from mcmurdo that was my field site. It was a multi-disciplinary project mixing geology and ecology. "
] |
[
"Why biofuel? isn't it just burning what amounts to man made fossil fuel? how much better is it for the environment if at all?"
] |
[
false
] |
I saw on but they used the term biocrude, making me think this is something similar to crude oil. What is the difference? What are the byproducts? how are those byproducts different from petroleum
|
[
"If a biofuel requires no fossil fuels to produce, it's better because it doesn't introduce new carbon into the system. This is the problem with fossil fuels: when burned, the carbon they introduce into the system is new carbon, in the sense that it has been sequestered and kept out of the system, and now it is being reintroduced.",
"In other words, biofuels take carbon out of the air and then put it back, while fossil fuels take carbon out if the ground and increase the amount of carbon in circulation. Thus biofuels have no effect on the amount of CO2, while fossil fuels increase the amount of CO2 in the atmosphere. "
] |
[
"FYI the term is \"carbon neutral.\""
] |
[
"And by saving fossil hydrocarbons, we can later use them for useful stuff like plastics and medicines instead of just burning them."
] |
[
"Why are anti-particles shown as going backwards in time in Feynman diagrams?"
] |
[
false
] |
Are they really going back in time, and if so would this explain the lack of antimatter, due to the anti particles essentially creating an identical universe, just going back in time, relative to us?
|
[
"Really, it's just a way of determining which quantities in your perturbation series are negative. It's mathematical notation only - it doesn't mean particles are actually traveling backwards through time.",
"That being said, it is a necessary mathematical convention to preserve causality. Particles traveling a certain direction in time are indistinguishable from their anti-particles traveling the opposite direction in time, and this causes the probability amplitude over spacelike intervals to exactly cancel, giving zero probability of a particle taking a \"faster than light\" path."
] |
[
"It doesn't ",
" mean particles are actually traveling backwards through time. That they really are is a perfectly valid interpretation."
] |
[
"It really should be stressed that feynman diagrams are not a description of what is physically happening at all. It is a way of representing a single term of an infinite expansion. It happens that in many cases the first term in overwhelmingly dominant, but NEVER a physical system does \"single virtual particle exchange.\" It is just a method of approximating what is really going on."
] |
[
"I don't quite understand Gamma decay. How does an atom emitting a gamma ray cause it to gain a proton?"
] |
[
false
] | null |
[
"This is not the case. The emission of a gamma ray (photon) does not occur until after a process of beta decay (or alpha decay, or electron capture) leaves a new nucleus (with more or less protons or neutrons) in an excited state. The new nucleus in an excited state will then decay into a lower energy state by emitting a photon (much like electrons in atoms do). Since this decay occurs in about 10",
" seconds, it is nearly simultaneous with the beta decay event, but not quite. ",
"For example",
"http://en.wikipedia.org/wiki/File:Cobalt-60_Decay_Scheme.svg",
"Cobalt-60 decays to Ni-60 by beta decay, but the Ni-60 is initially in an excited state, and subsequently undergoes 2 emissions of gamma rays before reaching a stable state. (.12% of the time the beta decay leaves the Ni nucleus in the lower energy excited state, so only one gamma ray is emitted.)"
] |
[
"A photon is a packet of energy. The nucleus had extra energy, spat out that extra energy as a photon, and now the nucleus has less energy."
] |
[
"This is a common misconception. Except in a handful of contrived cases, there is no such thing as pure \"gamma decay.\" What you have is ",
" decay, which leaves the nucleus in an excited state. This excited state decays via gamma emission, and so you can call this \"beta decay with associated gamma decay.\" So beta decay is what causes the constituents of the nucleus to change."
] |
[
"Why wasn't the grand canyon uniformly eroded?"
] |
[
false
] |
[deleted]
|
[
"The grand canyon was carved out over a long time and spans a large area. Many things could have fallen in the stream, altering the speed and rate of erosion. There might be some answers from the geological side too but I'm unsure of it."
] |
[
"Fractals! In general, it's a consequence of the scale-invariance phenomenon in Complex Systems found throughout nature: patterns created by nonlinear effects, rather than hidden patterns in the ground being eroded. \"Grand canyons\" of very similar structure can form in drainage ditches on the scale of meters ",
"or even mm",
", rather than kilometers. Find material on ",
"fractal watershed, etc.",
" The faster the water flow, the more rapid the erosion, and the deeper/narrower the eroded channel, the faster is the water flow. So, we have a sort of runaway positive feedback effect, but because of sensitivity to initial conditions, this creates two-dimensional fractal patterns across the landscape, rather than just uniform erosion with no channels forming.",
"Also, see material on ",
"grand canyon strata types",
"Do you have example photos? Rather than the above fractal effects, perhaps you're seeing a thick soil/sand layer above bedrock. If so, then rains would constantly erode the soil/sand layer into a gentle slope near the canyon edge, while river-flow would carve away the rock to form the canyon below."
] |
[
"It's all about the rocks. Simply put, not all rocks are the same. Some are harder than others. The classic canyon shape that we see today comes from these different types of rocks eroding at different rates. Hard rocks typically form cliffs, soft rocks form slopes. At GC there hard and soft layers mixed together (ie, hard, soft, soft, hard, soft, hard, etc) - this creates the classic stair step shape we see.",
"The river itself is mostly working to cut straight down, but the walls of the canyon are constantly being eroded back from the river. If you were to look at a cross-section of the canyon (make a \"V\" with your hands) with the river at the bottom and the rims on either side, you might expect it to be pretty symmetrical (remember the V you made?). What you would actually find is that the North Rim is (on average) much farther from the river shore than the South Rim (take that V with your hands and now slide the heel of your palm up to where your fingers meet your palm on the opposite hand - and keep the tips of your fingers level with each other on both hands). This is due to the fact that the North Rim receives much, much more precipitation than the South Rim. The summer monsoon rains, the freeze/thaw cycle, and spring snow melt are working to erode or pull the North Rim away at a much faster rate than the South Rim.",
"The walls of GC have been shaped by this erosion much more so than by the Colorado River. The river was never 10 miles wide (GC's average width) and so is not responsible for shaping it's wall. It is really only working to cut straight down through the bedrock. It's the canyon walls eroding away from the riverbank, and the differing rates of erosion in different types of rocks that gives us the splendid view we can enjoy today.",
"*Edited for readability/simplicity"
] |
[
"How does bee hair or trichome work?"
] |
[
false
] |
[deleted]
|
[
"I'm not familiar with the term trichome, where did you see it? I do not recall seeing it regularly in bee literature.",
"The hair on bees is typically branched unlike the hairs on other hymenoptera (ants, wasps). This is one of the distinguishing features of bees. The hair attracts pollen, and other dust like substances by gathering a slight charge while the bee flies. The pollen is seen to jump from the negatively charged flower to the positively charged bee. Most pollen is gathered by brushing up against the anthers of a flower but particles can be picked up in flight. This leads to other substances being brought back and mixed in to the pollen stores. Different bees have different methods of collecting the pollen for transport. Honey bees have a basket on their rear leg and groom the pollen into it. Megachilidae are solitary bees and collect the pollen on their undersides.",
"The ability to collect other substances in flight leads to one of the major sources of complaints about neonicitinoids. They are insecticides often used to cover seeds. If planted improperly that planting generates a lot of dust which bees flying through and can pick up because of the electric charge. The bees return to the hive, clean all the pollen/dust off themselves and mix the toxic substances into the pollen which is food for the larva.",
"I have seen pollen (both pollinator carried and wind borne), plastics, and pesticides all mentioned as picked up. Basically they could pick up anything of small enough size."
] |
[
"I am sure someone has but I don't have a direct source for it. It is commonly known that flying bees generate a positive charge, collisions with minute particles in the air strip electrons. ",
"There has recent been work showing that [bees sense](http:/dx.doi.org/10.1126/science.1230883) a negative charge and go to those flowers more than neutral and positively charged ones. Since most articles on the subject refer to work done in the 60's on the charge the bee develops look at the references of that article."
] |
[
"Thank you I thought I was never going to figure this out. I thought or rather assumed bees had trichomes which help collect pollen as they land on the flower. So thanks for clearing that up. I am mostly interested in the collection of the pollen, when you say \"slight charge\" what do you mean by that? Has anyone tried measuring it before? If that is even a thing. Many thanks! "
] |
[
"Q: Why do clouds lump together, rather that spread out evenly across the sky?"
] |
[
false
] |
Sometimes when the sky is clear you might see one solitary cloud moving across the sky. Why don't they spread out until the vapor is more evenly distributed? Is it because the water molecules are "attracted" to each other?
|
[
"Clouds do not stick together at all. Clouds are formed by micron sized droplets of water. They appear to stick together because the temperature-humidity characteristics of the atmosphere in the locality of the cloud is right for the droplets (cloud) to form. ####This is totally copy/pasted."
] |
[
"There's no attraction involved, per se. However, once formed, a cloud tends to maintain a local environment of high humidity, which reduces evaporation. ",
"Also, water vapor does not evenly spread out rapidly, it is concentrated and moved around by atmospheric motions. ",
"So once a cloud forms, as long as it maintains a sufficient temperature and humidity, it will persist. Once enough dry air gets entrained into the cloud or if it rapidly warms up, then the cloud will start to dissipate."
] |
[
"Don't think of clouds as physical objects in the sky. A cloud is simply a patch of air where conditions are right to condense water. A cloud does not necessarily have more water in it than the air around it, it's just that the water in a cloud is visible."
] |
[
"What makes the velocity of a charged particle, the direction of the magnetic field, and the direction of the force felt by the particle all perpendicular to each other?"
] |
[
false
] |
Why is it a cross product?
|
[
"I can think of at least two ways to answer this question. On the one hand, almost all fundamental \"why\" questions are meaningless: eventually the answer is \"because that's how it is\". In this case, we can say in a rather anti-climactic and probably unsatisfactory way that the magnetic force is proportional to ",
" x ",
" because that's what experiment shows.",
" Math to follow. Some familiarity with special relativity is required.",
"On the other hand, there is perhaps a slightly more satisfying answer. Forget about electromagnetism entirely for now. What is one of the simplest field theories that is consistent with special relativity? That is, we want to come up with a Lorentz-invariant field theory with no regard for whether there are natural phenomena described by it. Start with the following two assumptions:",
"The force associated to the field is ",
". This means that the force preserves the rest mass of a particle or system of particles. (A force that is not pure is called ",
" because of the analogy of heating a system of particles, like a steel ball. The total momentum of the ball does not change, but its rest mass increases as it is heated.) Pure forces are exactly those forces that are orthogonal to the proper velocity.",
"The force associated to the field is proportional to ",
", the scalar particle charge associated to the field.",
"Okay, so what could the force law possibly look like? A 3-force law independent of the velocity of the particle is ruled out immediately because it is not Lorentz-invariant. A 4-force law independent of the velocity of the particle can be Lorentz-invariant, but it cannot be pure (violating our first assumption). There are several choices to make at this point, hence several \"simple\" field theories we may come up with based only on our two assumptions. One such choice is a 4-force law that depends ",
" on the velocity of the particle. Hence the force can be written in the form",
" = ",
"The field associated to this force law is ",
". Because we have assumed the charge ",
" is a scalar, the field ",
" must be a tensor to make the force law Lorentz invariant. If we impose the condition that the force be pure, we find that the field ",
" must be ",
". That is,",
" = -",
"The field ",
" can be determined experimentally with test charges. That's about half of our field theory. The other half consists of ",
", which are differential equations that tell us how the field is affected by the charge distribution. We don't really care about those right now since the original question is about why the magnetic force has a cross product.",
"Since the field is antisymmetric, it takes the following form (in, say, a Cartesian coordinate system):",
"[ 0 -E_x -E_y -E_z\n E_x 0 -B_z B_y\n E_y B_z 0 -B_x\n E_z -B_y B_x 0 ]\n",
"That is, we identify the time-components of the field as the components of some 3-vector field ",
", and we identify the spatial components of the field as the components of some 3-vector field ",
".",
"(Of course, we could have made different identifications. We could have placed the minus signs on the other component in each anti-symmetric pair. We also could have labeled the spatial components with different xyz-indices. Those choices are actually completely arbitrary, as long as the field is anti-symmetric. However, there are some good ",
" reasons for making these choices. Given any 3x3 antisymmetric matrix ",
", there exists a 3-vector ",
" such that the matrix ",
" represents the linear operator that maps the vector ",
" to the vector ",
" x ",
". Our choice of identification of the 3-vector field ",
" is so that ",
" is this vector ",
", associated to the lower 3x3 antisymmetric matrix of spatial components of our field ",
".)",
"Okay, now look back at the force law",
" = ",
"The spatial components are the components of the 3-force ",
" = (F",
", F",
", F",
"). With our identification of the components of the field tensor ",
", the spatial components of the force law take the form",
" = q(",
"+",
" x ",
")",
"where ",
" = (u",
", u",
", u",
") is the 3-velocity associated to the 4-velocity of the particle. Voila! (The time component of the force law is ",
" = -q",
" · ",
", which essentially tells you how the force increases the energy of the particle.)",
"All that is left mathematically is to derive the ",
" and all that is left physically is to determine whether our simple field theory actually corresponds to anything in the real world. It does, obviously. We have partially reconstructed Maxwell's theory of electromagnetism. Note that we only used four simple assumptions: (1) the field theory is Lorentz-invariant, (2) the associated force is pure, (3) the electric charge is a scalar, and (4) the associated force depends linearly on the particle's velocity. The first three assumptions are very natural to impose on ",
" field theory in special relativity. The only major choice we really had to make was assumption (4). If we had made a different choice, we would come up with some other field theory that may or may not be physically realized.",
"It's debatable whether that satisfactorily answers the original question. All that I have really done is shown that there is a set of very natural and mild assumptions we can impose on a field theory in special relativity that allows us to mathematically reconstruct the Lorentz force law of classical electromagnetism. The cross product associated with the magnetic field is ultimately a result of the antisymmetry of the electromagnetic field tensor, which itself is ultimately a result of our assumption that the force is pure.",
"This response does not answer the question of why this field theory is physically realized at all. It could very well have been the case that this field theory is just a fun mathematical toy model and has no relation to the actual world. Relativity cannot answer that question, and I doubt any other physical theory can either. Perhaps a more advanced theory like the Standard Model or a quantum theory of gravity can answer that question, but that is almost certainly not the case. Sometimes there just is no reason, and we should not expect there to be an answer to every \"why\" question anyway. Why is Lorentz invariance a symmetry of our universe? Because it is."
] |
[
"This is probably the same thing ",
"/u/Midtek",
" said, but I'm going to try to say it with fewer words.",
"We can observe charged particles. We can observe the forces they exert each other when they move. But the magnetic field is entirely our own invention. It's a mathematical model we use to predict how a moving charged particle will be affected when its near another current or a ferromagnetic object.",
"Defining the magnetic field to be perpendicular to the motion of the particle that created it, and perpendicular to the force on the particle it's influencing, and connecting them together with the cross product is just the simplest representation that preserves all the information about what direction a force will act on a particle with which kind of motion, and accurately predicts the behavior we see in the real world."
] |
[
"Like u/ midtec said, the key is lorentz invariance. A magnetic field can be viewed as an electric field the appears in a moving reference frame.",
"Tak the example of two stationary charges q1 and q2 at positions (0,0,0) and (x1, y1, 0) respectively in a reference frame (R2). The electric force on q2 is F2=(q1*q2/(r2",
"))(x2,y2,0) where r=(x2)",
"+(y2)",
". ",
"Now suppose frame R1 moves at constant speed v in the x direction (1,0,0) with respect to frame R2. Now the two frames are relatable via the Lorentz transformation. ",
"Skipping a long derivation we find that the electric force measured in frame R1, F1= [(gamma)(q1q2/(r1",
")](x1,x2,0) - [(gamma)(v/c)",
"(q1q2/(r1",
")](0,1,0). Note that here r1=((gamma)*x1)",
" +(y1)",
". ",
"This is consistent with our understanding of electromagnetism. We just applied Quolombs law and special relativity and derived the expression for force on a moving charge F = q( E + (v x B)).",
"Notice that in frame 1 there is an additional term in the expression for force that's in the y direction. We correctly guess that the term on the right is equal to the cross product of the velocity (v(1,0,0)) with the vector [(gamma)(v/c",
")(q1/r1",
")](0,0,1). This vector is our magnetic field."
] |
[
"The planet Mercury is actually just a core?"
] |
[
false
] |
Is it true the planet Mercury is simply a core of a former planet? Is there any research going into what happened to the rest of the planet? Like did the rest of the planet.. the surface exists before it got close to the sun or was it melted away by it? Edit: sorry I have been having notification issues on reddit. Thanks everyone, wiki would be the last place I go form science info but I guess it worked out this time along with your comments
|
[
"you should edit the wikipedia page if you think the text is misleading"
] |
[
"Mercury's core has a higher iron content than that of any other major planet in the Solar System, and several theories have been proposed to explain this. The most widely accepted theory is that Mercury originally had a metal-silicate ratio similar to common chondrite meteorites, thought to be typical of the Solar System's rocky matter, and a mass approximately 2.25 times its current mass.[25] However, early in the Solar System’s history, Mercury may have been struck by a planetesimal of approximately 1/6 that mass and several hundred kilometers across.[25] The impact would have stripped away much of the original crust and mantle, leaving the core behind as a relatively major component.[25] A similar process, known as the giant impact hypothesis, has been proposed to explain the formation of Earth’s Moon.[25]",
"from wiki.",
" I usually hate to just redirect people, but it explains it really well."
] |
[
"Actually not a higher Fe content... a larger core relative to the size of the planet. The Wikipedia wording is misleading. I don't know of any theories which postulate that the inner planets started as gas giants. In order to make a gas giant you probably need to be far enough from the Sun that ices can form to help bulk up the planet's core and make gas accretion possible..."
] |
[
"Do overweight people have extra amount of nerves and pain receptors distributed around their body?"
] |
[
false
] |
[deleted]
|
[
"Yes - ",
"https://www.quora.com/Do-obese-people-have-more-touch-receptors-than-non-overweight-people-Or-are-people-who-are-obese-less-sensitive-due-to-their-touch-receptors-being-spread-out-over-their-bodies-increased-skin-surface-area",
"Basically the skin is an organ and is continuously remodeling itself. This includes generating more nerves to “conform to the sensory profile of a particular area”."
] |
[
"If your skin would shrink accordingly, yes. Since it doesn't and your cells won't get more dense: No. "
] |
[
"So theoretically, if you were to become obese and then rapidly lose weight, would you have a significantly higher density of nerves? "
] |
[
"Mandelbrot sets, Julia sets and fractals in general."
] |
[
false
] |
Periodically, I come back to the world of fractals and remind myself that I still do not fully grasp their implications. I've watched documentaries, played with Java applets and read articles on the subject; however, I still only see it as an infinitely complex shape and not so much a fascinating, mathematical construct (if you could even call it that). I need help grasping the math behind these fractals, the reason for even discovering them and why they're so important. The Madelbrot set has, after all, been referred to as "the fingerprint of God." Whatever that may mean.
|
[
"Consider asking this in ",
"/r/math",
", a little better fit.",
"There are many different kinds of fractals, with different math behind them, but as a rule, fractals are more interesting than they are important. ",
"If there is one important thing they show, it is how very chaotic behavior can arise from seemingly simple systems. This could lead to insights into other complex systems, like fluid dynamics or economics.",
"The Mandelbrot set is pretty straight forward: ",
"Start with a complex number c and the series Z(0) = 0; Z(n) = Z(n - 1)",
" + c",
"c is in the Madelbrot set M if Z does not diverge.",
"For c = 1, Z = {0, 1, 2, 5, 26, 729, ...}, diverges, not in M",
"For c = (-1/2 + i/2), Z = {0, (-1/2 + i/2), -1/2, (-1/4 + i/2), (-11/16 + i/4, ...} does not diverge, is in M",
"So, you just run through all the points in the complex plain, and see which ones are in M. If you are extra clever, you count how many iterations it takes to converge below a certain threshold, and paint each point a different color. "
] |
[
"One significant aspect of fractals sets is that it's difficult to tell whether a particular point ",
" or ",
" part of it, along the frilly edges. If it takes 7 billion iterations to determine that a point falls out of the set, that really tells you nothing about any given nearby points. Move over 0.0000000007 units, and it may take 70 billion iterations, or 7 thousand iterations, or it may very well ",
" to the set and not fall out even if you keep on calculating until the heat death of the universe (but even then, it might still not have belonged to the set in the limit). ",
"What you can take away from that is a lesson in chaos theory: the tiniest change in parameters can have consequences which far outshine the scope of the change, in a way which is intrinsically difficult to predict."
] |
[
"The key feature of a fractal is a self repeating pattern. You look at it as a whole, then zoom in on one part, and it looks as it did when you were zoomed out. "
] |
[
"Is there any research on the percentage of depressive outpatients that complain of loss of cognitive function(and of which type) even after their illness remission?"
] |
[
false
] |
[deleted]
|
[
"I don't have a reference off hand for you, but it is important to note that loss of grey matter is not the only cause of cognitive complaints.",
"Residual rumination, worry, and sleep disturbance (",
"which is common after remission of depression",
") can all contribute to cognitive inefficiency. A continued tendency to view oneself negatively or to catastrophize can also lead a person to focus on normal cognitive errors and extrapolate that they must have cognitive problems."
] |
[
"Predominantly insomnia symptoms - difficulty initiating and maintaining sleep. This is in contrast to older views that insomnia could be secondary to (caused by) depression. A considerable amount of research has now shown that insomnia can have an independent clinical course, and so merits focused treatment, particularly CBT-I, which is a specialized form of CBT that is now ",
"recommended by the American College of Physicians",
" as ",
" first line treatment for all adults with chronic insomnia",
"Other comorbid sleep disorders such as obstructive sleep apnea would be expected to be unchanged by remission of depression. Obstructive sleep apnea frequently co-occurs with depression but has a very different pathophysiology and requires very different treatment. The gold standard for treating obstructive sleep apnea is CPAP."
] |
[
"Predominantly insomnia symptoms - difficulty initiating and maintaining sleep. This is in contrast to older views that insomnia could be secondary to (caused by) depression. A considerable amount of research has now shown that insomnia can have an independent clinical course, and so merits focused treatment, particularly CBT-I, which is a specialized form of CBT that is now ",
"recommended by the American College of Physicians",
" as ",
" first line treatment for all adults with chronic insomnia",
"Other comorbid sleep disorders such as obstructive sleep apnea would be expected to be unchanged by remission of depression. Obstructive sleep apnea frequently co-occurs with depression but has a very different pathophysiology and requires very different treatment. The gold standard for treating obstructive sleep apnea is CPAP."
] |
[
"Does the act of boiling actually help cook foods (e.g. potatoes), or do you get the same results with really hot (99C) water?"
] |
[
false
] | null |
[
"Boiling is simply the hottest water temperature you can achieve under given atmospheric conditions. Typically, when cooking food by submerging it in a non-oil liquid, there is no danger of burning the food, so the highest available temperature is preferred because it will yield the shortest cooking time.",
"This is why most boiled food products, such as pastas, have ",
" instructions, which are usually as simple as \"boil an extra few minutes.\" The lower atmospheric pressure experienced at higher altitudes means water boils at lower temperatures, so you need to cook it longer.",
"Another way to look at your question involves pressure cookers. The whole point of a pressure cooker is to increase the pressure of a system in order to increase the boiling point of water. That is, to make liquid water hotter without necessarily boiling. The benefit of this is mostly a decrease in cooking time.",
"TLDR: it is the temperature that matters, not the actual phase change from liquid to gas."
] |
[
"I agree with all of this, but I thought I'd just throw in my 2c as a biologist. Let's think for a second about what \"cooking\" actually is: It's the denaturation of proteins and lysis of cells in your food. We cook food for various reasons, but high on that list is to kill the bacteria, and also to make the food easier to get energy from. Anyway, ",
"there are many ways to denature a protein",
". You can heat it up. You can put it in acid. You can use enzymes to do it. Notably, all of these methods are indeed ways to \"cook\" food. The fish dish ",
"ceviche",
" is cooked by the acid in the lime juice that it sits in. Meat tenderizers like the ones found in ",
"papaya",
" denature proteins enzymatically. ",
"So back to your question: 99c will denature proteins almost identically to 100c. Bringing the water to a boil, may however, create steam inside of cells, forcing them to lyse. This will have a much weaker effect on what you consider \"cooking\" than the temperature will, but could make a small difference, particularly in plant cells that are resistant to lysis because of their tough cell walls. "
] |
[
"And this is exactly why it is more nutritionally beneficial to steam your vegetables than to boil them: when the cells do lyse, all of the contents get distributed among the boiling water solution, and thus not in the cooked vegetable food you finally eat. Steamed veggies, on the other hand, may also have lysed cells, but the surrounding water vapor is much less efficient at leeching the contents out than was the liquid.",
"Follow-up question for you: defining \"cooking\" as denaturation of proteins and lysis of cells works well for many foods, but would you argue that it applies directly to something like pasta? Or the other end of that same spectrum: bread? How about legumes?"
] |
[
"Froze a bottle of gatorade, turned to ice, left gatorade out at room temperature, melted back to liquid form but with a significantly higher amount of water (i.e. it was watery). Why?"
] |
[
false
] | null |
[
"What would happen is that the water would freeze out; if you freeze salt water, you get ice- not salty ice, but ice. As the Gatorade froze, the solutes (the sugars, etc.) would be the last to freeze. As it re-melted, the ice would float on top, and the sugar and other components would sink to the bottom. As more of the ice melted, it would result in sugars at the bottom, and more water-y towards the top."
] |
[
"Did you do this with the bottle cap on or off?"
] |
[
"On sir."
] |
[
"Do black holes obey conservation of mass-energy when it grows/evaporates?"
] |
[
false
] |
[deleted]
|
[
"Energy is still conserved when considering black holes. The energy taken away by hawking radiating equals the energy the black hole looses. Incidentally this radiation equals what you would expect if you treat a black hole as a black body and were to calculate its black body radiation. A black hole is then a very hot ideal black body. ",
"There are other circumstances where energy is not conserved, but this isn't one of them because the homogeneity with respect to time of the Hamiltonian and Lagrangian is preserved. To break energy conservation you must consider very long time scales, where the universe has undergone appreciable expansion violating the homogeneous assumption."
] |
[
"So, as this layman understands it, inside a black hole is a veritable \"no man's land\" of physics, where laws break down.",
"Not really. It's just that unless you happen to be falling into a black hole yourself, the event horizon is a solid, impenetrable boundary which nothing ever crosses. And if you ",
" falling in yourself, you certainly can't ever share any observations you make. So the interior of a black hole is a place that doesn't exist except to observers who can never tell anyone about it, so nothing we imagine about it can ever be confirmed or refuted. But the models we have are entirely consistent and there's no good reason to question them.",
"If we tabulate all the energy/mass that goes into the black hole from creation to dissipation (lets say Y), will the amount of hawking radiation it emits from when it was created till when it completely dissipates = X + Y?",
"Yes.",
"If not, and the black hole gives physics the middle finger by causing a net change in the universe's mass/energy after it's gone…",
"Well, first of all remember that conversation of mass-energy isn't actually a conservation law. It's an ",
" conservation law in low-energy interactions. Conservation of energy is more rigorously defined, but that's not an actual conservation law either. It's apparent only locally.",
"That said, the more interesting question is whether ",
" is conserved across black-hole interactions. In this context, \"information\" is a catch-all term for all the conserved charges: electric charge, angular momentum, basically everything we have an exact conservation law for.",
"This question went unresolved for many years, only really coming to a conclusion recently. The answer is best understood by thinking of black holes not as astronomical objects or ",
" in any real sense, but as extraordinarily slow scattering processes. When a photon approaches an atomic nucleus, it undergoes a scattering process and has a chance of coming out the other side as a particle-antiparticle pair, or a photon of a lower energy, or whatever. That scattering process is ",
" near instantaneous; it happens over a very, very brief time interval. Black-hole scattering happens exactly the same way — in that stuff that interacts with one scatters, and has a chance of coming out the other side in a variety of different forms — but it takes place over ",
" When a bit of information falls toward a black hole — a little charge, a little spin, whatever — it might be a trillion years before it comes back out again. But apart from that, it's essentially the same as any other scattering process.",
"In technical terms, you can in principle write a single unitary S-matrix that describes the evolution of a particle across a black-hole interaction. In less technical terms, what goes out is determined entirely by what goes in."
] |
[
"No-hair is false."
] |
[
"Why is there \"more\" land above the equator?"
] |
[
false
] |
As the question asks, why is there "more" land above the equator? I put more into quotes because I don't know if Antarctica equals out off of the North's land mass.
|
[
"You're not the first person to ask this question... ",
"The notion of Terra Australis (The Great Southern Continent) was introduced by Aristotle. His ideas were later expanded by Ptolemy (1st century AD), who believed .. that the lands of the Northern Hemisphere should be balanced by land in the south."
] |
[
"To put dinosaurs into perspective, more time passed between Stegosaurus and Tyrannosaurs than between Tyrannosaurus and human. In fact there was 10 million more years between Stegosaurus and Tyrannosaurus than Tyrannosaurus and human."
] |
[
"The reason it's arbitrary is because the of continental drift. We're considering a very particular time in the billions of years of Earth's existence, during which land mass has evolved enormously. It just doesn't make sense to ask why at some seemly unimportant time more land mass exists in a particular hemisphere. ",
"Of relevant interest, the ",
"land hemisphere",
" is the hemisphere with the maximal land area, which according to Wikipedia contains just under 7/8 of the total land area. "
] |
[
"How could natural selection bring about the evolution of wings?"
] |
[
false
] |
All aspects that require flight, such as wings, feathers, and low body mass seem like evolutionary disadvantages up until flight is possible. Why would creatures such as chickens, or the predecessors to flying birds, evolve these features if they didn't immediately present an advantage?
|
[
"Excellent link on the evolution of flight in birds by justanotherusername_",
"However, winged flight evolved independently at least 4 times (I wont argue the case of instances of gliding such as flying snakes and sugar gliders...) in the following lineages:",
"Birds (duh...)",
"Pterosaurs",
"Mammals (bats)",
"Insects",
"In the case of insects, one of Natures greatest success stories, it seems wings may have first evolved as thermal regulators in very small insects, and that they may later have given an advantage through scaled growth towards gliding, and parachuting and that sort of thing... (See: ",
"http://jgking.web.unc.edu/files/2012/06/KingsolverKoehl.Evolution.1985.pdf",
").."
] |
[
"Indeed - a key concept in the evolution of new and powerfull capacities is \"pre-adaptation\" (which is often mistakenly taken to imply the directed evolution of features in view of future benefit, which it isn't). Evolution doesn't work on a vacuum, it need to work on structures and variation. Thus a little nubbin on the back of a collembola-sized bug gives an advantage as a heat radiating/capting surface ans will be actively selected for. Later on, a slight increase in size makes it a neat parachute and adds something to that lineages bag of tricks, exposing that trait to a new set of selective pressures.",
"Same for birds: The apparition of feathered forelimbs was one possible pre-adaptation which could have (and did) lead to flight; but at first is gave other advantages in nesting, signaling and in running.",
"As to the pterosaurs and bats (and perhaps others), other evolutionary pathways must have been sollicited. What stands out is that there has been more than one pathway to winged flight."
] |
[
"excellent point that insects first may have evolved wings for purposes other than flight. it is theorized that birds early ancestors, (think ovoraptor, bipedal, with feathered forelimbs) the feathers wouldn't be useful for flight just yet, but they were awesome at keeping a nest of eggs warm. the further development of this feathered forelimb may have been selected for by hunting or fleeing; those specimens with the ability to make extra course corrections mid-step would be better hunters and evade predators more successfully. ",
"eventually the aerodynamic use of the forelimb developed to the extent that high jumps and short flights were possible. the more successful creatures were the highest jumpers and longest flights, leading eventually to fully functional flight. ",
"so even though the early feathered forelimb was not useful for flight, is was advantageous for brooding a nest, and incidentally it also had useful aerodynamic uses."
] |
[
"Is it true that the effects of caffeine in (black) tea are inversely proportional to the brewing time?"
] |
[
false
] |
I've heard several times already that if you brew black tea longer, it's not going to have as much effect on you (or that if you want to get a biggest "kick" out of your tea you should brew it quicker not longer). Google couldn't seem to find anything "serious" on the subject. page for tea says that tannins released by black tea prevent the quick absorption of caffeine by "trapping" it, and releasing it gradually over the digestion time. Since caffeine is seemingly released quicker than tannins during the brewing, a tea that is brewed a short amount of time would have little tannins but still most of the cafeine in it. Which would explain the aforementioned claims I've heard. However the source for this is Pierre Dukan, creator of the Dukan Diet. He's a "medical doctor & nutritionist" ( ) but seems controversial. Looking for studies (in English) on this effect (tannins preventing absorption of caffeine) I found nothing but a few websites mentioning the same effect, without sources (and no chemistry/medical/nutritional credentials that I could find) such as: Thank you to anybody who can shed some light on this.
|
[
"I had always assumed that the caffeine was destroyed by the heat of roasting, not that it sublimed out. ",
"Also, it seems strange: Coffee-roasters stand in front of open-top coffee roasters - you'd think that they'd inhale the caffeine, and adsorb it through the lungs and airways?",
"Oh, and about the tea - black tea may also be made from buds and young leaves - it's a matter of grading, sorting and quality. Most buds are used for green tea, though - but it's not an innate quality of the buds, that make the tea green, but rather a matter of manufacture process (no fermentation, for one)"
] |
[
"http://jat.oxfordjournals.org/content/32/8/702.full.pdf"
] |
[
"There's obviously going to be more raw caffeine in a tea brewed longer than one brewed shorter, but I think your idea of tannins interfering with bioavailability is spot on. Sorry for the shitty reference, you're right about the lack of serious articles on the subject, but ",
"this",
" experiment uses tannic acid to precipitate caffeine out of several solutions to try to show the difference between normal and decaffeinated tea. It seems reasonable that overbrewing your tea can increase the tannin load (making the tea taste bitter and gross) which will reduce the solubility and subsequent absorption of caffeine in the gut."
] |
[
"If we could rearrange all the atoms(protons, electrons-all that jazz) on earth into denser elements, would gravity stay the same?"
] |
[
false
] | null |
[
"Nope. If the earth becomes denser, the gravity at the surface GM/R",
" is now using a smaller R, so becomes higher. Measuring mass and radius of exoplanets lets you not only determine surface gravity, but also tells you a lot about what materials make up the exoplanet based on the density. Is it mostly ice? Rock? Iron? Gas? We can learn a surprisingly large amount from transit data. "
] |
[
"However, gravity at the same distance from the center (where the old surface was) would stay the same."
] |
[
"Yes, just like for black holes, there's no extra pull, it's just that you can now get closer to the same mass."
] |
[
"Sexual reproduction - Why?"
] |
[
false
] |
Why do we have various species including plants perform sexual reproduction? Isn't asexual reproduction more efficient? What advantage would sexual reproduction have over say splitting or budding?
|
[
"Well, in asexual reproduction, if one plant has a gene that gives it sharper thorns and another has a gene that gives it stronger roots, that's all there will ever be. If their descendants survive, there will be plants with sharp thorns and plants with strong roots, but no plants with both. And whichever one gives the bigger advantage will ultimately force the other into extinction entirely.",
"On the other hand, if these plants were capable of sexual reproduction, the two could theoretically breed together and get a single descendant with sharper thorns ",
" stronger roots. Which would then have an advantage over the asexual plants, who are incapable of having both."
] |
[
"Sexual reproduction allows variations in genetics, which can provide important advantages to the species. ",
"For instance, in a Reef Aquarium, most corals multiply by budding or splitting. If a disease is introduced that effects a species multiplying in such a manner, there is no diversity from one of said coral to the next so if one isn't immune, none are immune. "
] |
[
"Sexual reproduction has a distinct advantage due to the opportunity to acquire new (and potentially better) genes. New genetic material can also replace damaged genetic material and restore a healthy genome."
] |
[
"Why can I hear the bass from music playing far away but not the high frequencies?"
] |
[
false
] | null |
[
"Bass is low frequency, so it has longer wavelength, so the sound wave is more likely to propagate around obstructions instead of being reflected or absorbed by them. "
] |
[
"This is also the reason that foghorns have a low frequency (or pitch)."
] |
[
"not entirely. That's a lot more to do with the ionosphere being reflective of that band of frequencies. "
] |
[
"AskScience AMA Series: We're Chris Joyce, a science correspondent for NPR, and Rebecca Davis, a senior producer with NPR's science desk. Ask us anything about plastic pollution!"
] |
[
false
] |
We've been taking a . Global plastic production has grown to 420 million tons in 2015, and some plastics will last for centuries or even longer. NPR most recently published a story looking at for the plastic waste from their products and who've been campaigning to ban plastic bags. ready to go at 1 PM (ET, 17 UT)! Follow and or the on Twitter, and ask us anything!
|
[
"We will never replace the concept of plastic (lets use a better term, consumer polymers. Plastics are a fuzzy lay term for thermoplastic elastomers, a technical term for certain polymers). However we are trying, with some success, to make consumer polymers that mimic the properties of the nondegradable polymers that are widely used today out of degradable or more recyclable feedstocks.",
"Its an immense technological challenge. The big 3 consumer polymers (polyethylene, polypropylene and PET) have been intensely studied and optimized for decades. They are about as cheap as anything can be, their material properties are very reliable, their production is scaled all the way up, and they are easily obtained from oil.",
"It takes, frankly, a lot of energy and technology to convert them back into feed stock monomers. More than it takes to just make more from oil.",
"Cleaning up may take a life time :(. I was in Bali last year and saw so much plastic waste while snorkeling, it was heartbreaking.",
"We can do it though! The expertise, ingenuity, and technology do or will exist to fix all this, we need more money and willpower.",
"Source: I'm a polymer chemist. "
] |
[
"What alternatives to plastics can be mass produced on the scale plastics are produced? Can plastics be reverted into a previous compound more suitable to ethical standards? And what strides are being made to clean up plastic pollution? "
] |
[
"Hi. One shouldn't burn plastics at all. That can release toxins into the environment. If you have recycling at all just follow your local recycling guidelines. Don't put anything you aren't sure can be recycled into recycling because it creates contamination and reduces the possibility that other recyclable plastics can actually be recycled. If you aren't sure that something can be recycled, put it in the trash. Yes it will end up in a landfill but that's considered the least offensive of the options. "
] |
[
"What are some areas of science that can still be added to by a hobby scientist a la Sir Isaac Newton?"
] |
[
false
] |
If someone had a strong scientific/ technical background but wanted to pursue research as a hobby rather than strictly a profession as the "gentleman scientists" of yore did. I know of the DIYBIO movement, etc. If you were going to attempt to contribute some meaningful scientific knowledge to the world, what area of science/technology would you immerse yourself in purely for enjoyment? What skill sets would you want to develop?
|
[
"The area a single hobbyist is most likely to contribute to (IMO) is anything computational.",
"It seems limiting, but you can work in almost any field via computing. You can work on computational physics problems, simulate chemical reactions, model infectious disease, analyze the human genome, mine behavioral data using search engines, etc.",
"The beautiful thing about computing is that computers are dirt cheap and there are an unbelievable amount of resources for programmers, for free, on the internet."
] |
[
"Keeping a natural history journal is something a layman can do easily. It can contribute to baseline data of an area. Ecologists look back at these journals to figure out what has changed in an ecosystem among other things. Once you know a place well enough you can determine whether a certain species is invasive, dwindling, or even a whole new species. It can also lead to a better understanding of animal behaviors. People often do this with birds, but I think bird people are weird and miss out on a lot of stuff. Look up Joseph Grinnell and don't let his OCD deter you."
] |
[
"Anything that can be done with computers!",
"Let me tell you what all you can do with just a desktop PC that I could think of in 5 minutes (any of which I'd love to do if I can squeeze more time off my unorganized life):",
"You can run simulations to fold proteins (few Tesla GPUs and small simulations are easy; this requires a lot of biophysics and other subjects' knowledge though, stuff that I barely know the basics of)",
"You can do sequence analyses to test hypotheses about regulatory mechanisms, find new ones people didnt know about, try to find needles in the haystack genomic data people produce. You can look into how sequence evolve, etc. At least one Nature/Science paper every month makes significant insights but would have been done purely on computers. Doesn't mean its easy, but its not out of anybody's league because of lack of facilities.",
"Anthropology: Try to analyze data thats out there in the internets to figure out interesting behavior patterns",
"All you need to start though is extensive knowledge and a killer idea :)"
] |
[
"Dopamine surges in the brain cause down regulation of dopamine receptors. Is this always true, regardless of what caused the surge? (Drugs vs. natural rewards like orgasm, food, ect)"
] |
[
false
] |
Can overstimulation caused by abusing natural rewards be equally as "damaging" as the same amount of over stimulation caused a drug/drugs?
|
[
"Well, there are couple things to consider.",
"1) Amphetamines can lead to increased synaptic dopamine (DA). Theoretically, this increase in DA levels should produce more DA receptor activation, and a function of that would be increased DA receptor desensitization. A common compensatory mechanism to said desensitization is to upregulate the expression of the desensitized receptors, in this case, DA receptors.",
"2) Different receptor types, even within the same family, can have competing effects. For instance, in some cases, D1-like receptors (D1 and D5), and D2- like receptors (D2, D3, and D4) can produce competing downstream effects that can mask the effects produced by one of the receptor types (1). This is a phenomenon that is observed in a few receptor classes, but most notably (at least to me), the serotonin system. These competing effects could produce some sort of functional antagonism in the presence of amphetamine that would be behaviorally similar to that of receptor desensitization.",
"Those are the two thoughts that predominantly pop into my head. Full disclosure, my specialization is not in dopamine pharmacology, but I had to study the DA system for my graduate work. That's a fancy way of saying, I don't have definitive answer to your question, but if I had to make an educated assessment, it would be upon evaluation on the two points I mentioned above. That being said, in some way, yes, it is to deal with the excess dopamine, but not in the sense that there is too much dopamine, so there needs to be more receptors to handle the DA. Most likely, it is a response to a decrease in available sensitive DA receptors. Anyway, I hope that answers your question!",
"(1) ",
"http://www.sciencedirect.com/science/article/pii/S0166223607000690",
"Edit: spelling",
"Edit: Added a small point in part 2."
] |
[
"As an educated guess I would say yes. Similarly to the way that viewing pornography frequently for an extended period of time can decrease the brain's \"value\" for actual sexual intercourse. I wouldn't expect it to be anywhere near as drastic as drug use can be. In example, MDMA. The substance itself acts on the brain by producing a large surge of serotonin release, which is then passed over serotonin receptors. But frequent use of the substance, without recovery periods, can severely damage and degrade serotonin receptors, a condition known as \"serotonin syndrome\".",
"But, if abused, the brain's \"reward response\", a release of dopamine, the brain will value the stimuli less gradually over time and produce a reduced response. That is just my understanding of it, however."
] |
[
"a condition known as \"serotonin syndrome\".",
"No. That's not what serotonin syndrome is. SS in an acute excess of serotonin, which causes symptoms ranging from anxiety to seizures. ",
"https://en.m.wikipedia.org/wiki/Serotonin_syndrome"
] |
[
"Why is cuisine from hot places, spicy?"
] |
[
false
] |
I have observed that the food in all Hot places around the world tends to be much spicer than the cooler areas. Be it Mexico & central Americas, Sub-saharan Africa, or India, the food eaten is usually spicy and lot of chilies are usually used. If you name any spicy food, it is a good bet that it comes from the equatorial regions. This is in direct contrast to the bland food eaten in cold climates. Is this just because the spice & chilly plants grow in hot regions, or is there any other benefit to eating spicy food in hot climates?
|
[
"There are a couple of reasons\n1. cover taste\n2. antibacteria\n3. natural availability",
"Many spices have Antibacterial qualities. As you can read from the link\n",
"http://www.news.cornell.edu/chronicle/98/3.5.98/spices.html",
"Also, just FYI, many spices (cummin, curry, black pepper) have been shown to have some anti-cancer qualities but this is an asside since it has not been known until recently."
] |
[
"They don't just cover up the spoilage, some spices have antimicrobial properties and actually prevent it."
] |
[
"lay person - hot temperatures mean more food spoilage, more spices are used to cover that up. "
] |
[
"How long after eating a peanut butter sandwich must I wait before I kiss someone with a peanut allergy?"
] |
[
false
] |
Let's say I eat a peanut butter sandwich at noon and go out later that night and meet a girl who tells me she's got a peanut allergy. I say: "oh that sucks" and then we start making out at midnight. 12 hours enough time? What if I brush my teeth and rinse with mouthwash beforehand? If I was dating a person with a peanut allergy does that mean I would have to avoid peanuts too?
|
[
"Is letting go of peanuts so hard? ",
"Seriously though it depends. Try to be as clean as possible and go ahead once, (with precautions like meds on the side of course) and see what happens. Then decide yourself..",
"But letting go is simpler right?"
] |
[
"There is an unknown variable in this, so it's difficult to answer.\nHow severe is this peanut allergy? Are they going to die or just get a rash?",
"If I was dating a person with a peanut allergy does that mean I would have to avoid peanuts too?",
"You should obviously be more selective of when you consume peanuts, but the moral thing would be to stop to avoid harming your SO."
] |
[
"My gf in high school was allergic to peanuts. One of the more severe allergies. One time someone in 1st period ate some peanut butter crackers and got some crumbs on a desk. When fifth period came around, she entered the room and her throat started itching and closing up.",
"Needless to say, I once kissed her 5 or 6 hours after eating a pb&j and she was affected. :("
] |
[
"What are the distinctions between antisocial personality disorder and psychopathy and sociopathy?"
] |
[
false
] | null |
[
"Psychopathy is an outdated term. It was replaced by antisocial personality disorder in the DSM III. Sociopathy is the layman's term for antisocial personality disorder.",
"They are all the same."
] |
[
"Work Cited ",
"Bergman, M (Producer), & De Palma, B. (Director). (1983) ",
" [Motion picture]. United States: Universal Pictures. ",
"Drake, J., et al. (Producers), & Harron, M. (Director). (2000) ",
" [Motion picture]. United States: Lions Gate Films"
] |
[
"What do you base that classification on?"
] |
[
"How long does it take to measure the physical effects of age? Conversely, how soon could it be conclusively determined that someone is not aging?"
] |
[
false
] | null |
[
"The question becomes \"at what scale\"?",
"Physically, it's my understanding that the length of telomeres during mitosis can be seen to reduce during subsequent replications, which would allow one to measure the physical effect of age, in a cell, as soon as that cell divides a second time. Conversely, you could also conclusively determine that cell is not aging if there is no reduction in the length of telomeres between mitotic cycles. Given the replication rates of some cells, such as epithelial cells in the stomach, you could potentially determine whether or not someone is aging in about 24 hours (the average rate of replication in those cells)."
] |
[
"I would say theoretically you are correct. But our methods of detecting subtle changes in Telomere length have limits and the difference between the two measurements would likely be within error. ",
"Now, I have no idea on a time scale, what those limits are to detect \"aging,\" but I would have to say greater than 24hrs. "
] |
[
"Hi feo_sucio thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"There's a lot of pseudoscience in the fitness community, so anyone know of studies which show what kinds of exercises lead to the most strength gain?"
] |
[
false
] |
[deleted]
|
[
"Isn't that a fitness community that apparently has a lot of pseudoscience?"
] |
[
"Eh I'm inclined to agree with OP and PillsInButt that anything fitness related is plagued with pseudoscience. It is really truly difficult to know what's out there with scientific evidence. ",
"r/fitness",
" is a nice community and they may have a lot of anecdotal experience, but what does the data really say. Same of ",
"r/loseit",
" or the other dieting reddits."
] |
[
"You've been here for 1.5 years?!",
"You should check out ",
"/r/conspiracy",
", ",
"/r/health",
", etc. for more accurate information that's free from pseudoscience and anecdotal evidence."
] |
[
"If, as suspected, the earth was hit by Theia early in its creation, why don’t we have a ring of debris around us like Saturn?"
] |
[
false
] | null |
[
"Because Saturn has multiple moons that actually keep its rings in a (roughly) stable orbit. The inner moons actually speed falling particles up and keeps them from falling into the planets atmosphere while the outer moons slow objects down and keep them from escaping the planets gravity.",
"That’s really simplified.",
"The earth on the other hand, didn’t, (as far as we know), have anything that would produce a similar process."
] |
[
"Agreed, nothing atomic is happening. Then again, nothing atomic is happening during the actual impact either. The same amount of potential energy is converted to kinetic energy whether it's a dust cloud or meteor, as long as it's the same amount of mass. So sure, spectacular meteor shower, but still boiling oceans (EDIT: depending on the total mass of the ring system anyway; I'm assuming it'd be as significant as a planet killer asteroid)."
] |
[
"Agreed, nothing atomic is happening. Then again, nothing atomic is happening during the actual impact either. The same amount of potential energy is converted to kinetic energy whether it's a dust cloud or meteor, as long as it's the same amount of mass. So sure, spectacular meteor shower, but still boiling oceans (EDIT: depending on the total mass of the ring system anyway; I'm assuming it'd be as significant as a planet killer asteroid)."
] |
[
"Why do skydivers have a greater terminal velocity when wearing lead weight belts?"
] |
[
false
] |
My brother and I have to wear lead to keep up with heavier people. Does this agree with Galileo's findings?
|
[
"For a quadratic drag force, your terminal velocity is proportional to the square root of your weight. If everything else is the same, an object with a higher mass will have a higher terminal velocity."
] |
[
"The acceleration due to gravity is independent of mass and is not affected by the lead weights.",
"What is affected is drag. Loosely speaking, the drag when falling depends on the shape of the object that is falling. Your shape does not change significantly with the lead belt, but your mass does, and the result is that drag becomes less important relative to gravity. For similar reasons you will find that a sheet of paper falls more slowly than the same sheet of paper crumpled up into a ball.",
"What Galileo found is that when drag is ",
" important, the acceleration of a falling object is independent of mass. This is because, as stated above, the acceleration due to gravity is (to a very good approximation) independent of mass.",
"Edit: a helpful Redditor suggested the correct term to use here would be \"drag\" instead of friction. Original edited for clarity."
] |
[
"A quadratic drag force takes the form of ",
" = - cv",
".",
"It has magnitude cv",
", and direction opposite to the velocity of the object.",
"c is a constant that depends on the medium and the object. You can roughly expect c to be linear in the cross-sectional area of the object.",
"To find the terminal velocity for a vertically falling object, you set the drag force equal and opposite to the gravitational force:",
"mg = cv",
", so",
"v",
" = sqrt(mg/c).",
"If c is proportional to the cross sectional area A, then v",
" is proportional to sqrt(m/A)."
] |
[
"Why are snowflakes flat? Why not something with more depth?"
] |
[
false
] | null |
[
"Under the conditions where snow crystals grow, the growth is fastest in regions where the crystals are sharp",
". So basically, the rate at which the crystal gets thicker is much lower than the rate at which it spreads out in it's major plane."
] |
[
"If you look into the work of Wilson A. Bentley, you'll see that he discovered, through photography, that they do in fact form much more complicated shapes such as columns and pyramids. Kind of hard to find the pictures, but if you look enough they're there."
] |
[
"This is ultimately the answer I was looking for, thanks. "
] |
[
"Can anyone explain the anthropological basis of grinding grain to produce a flour?"
] |
[
false
] |
[deleted]
|
[
"I think the question is ",
" they discovered this. Waking up one day and saying \"Eureka! We will get more nutrition this way!\" seems unlikely, but something allowed cultures that were not in contact with each other to come up with the same concept. ",
"I'm curious on this one as well myself."
] |
[
"I think that people will commonly try grinding any foodstuff that's tough or difficult to chew, and they often decide that continuing to do so is a good idea. "
] |
[
"Well remember that ancient grains like teosinte the original corn was very hard almost rock hard So prehistoric people had to grind them down to get inside. "
] |
[
"In which direction is the universe expanding? Is the universe expanded the same in all directions?"
] |
[
false
] |
If the Big Bang theory is right, wouldn't the universe have some kind of 'center' it 'errupted' from? Shouldn't we see celestial objects move in a certain direction? It would seem really contra intuitive for everything to move away from earth in the same manner, like it would be the center of the universe.
|
[
"If the Big Bang theory is right, wouldn't the universe have some kind of 'center' it 'errupted' from?",
"No, although this is a very common misconception. The Big Bang wasn't an explosion, and the subsequent expansion isn't like debris spreading out from a central point.",
"A better picture to have in your head is something like a very large fruit loaf that's in the oven. As the cake bakes, it rises causing all the raisins to spread out further from each other. From the perspective of any one raisin, all the other fruit appears to be moving away, but that doesn't mean the raisin is at the centre of the cake."
] |
[
"The expansion appears to be homogeneous (the same at all locations) and isotropic (the same in all directions), as described by the ",
"FLRW metric",
"."
] |
[
"When you are thinking about The Big Bang, you shouldn’t think about objects moving through space because of some “explosion”. Instead, it is space itself that is expanding.",
"Imagine a deflated balloon. If you draw a bunch of dots on the surface and then start to blow air into the balloon, what happens? Each dot appears to move away from every other dot. No matter which dot you pick, it appears to be at the center of the “explosion” since every other dot is moving away from it. The rubber of the balloon is like the spacetime in our universe (except it’s 2-dimensional). It is the fabric on which all things exist that expands and thus we appear to be at “the center” no matter our location in the universe.",
"This is, of course, a simple example of how one should consider the expansion of the universe and doesn’t demonstrate all the complexities. But it is a good starting point to gain some kind of intuition."
] |
[
"When an object is burnt completely what happens to all the atoms, electrons and protons that are there in it?"
] |
[
false
] | null |
[
"I'll define burning as oxidation. If something is completely burned, it is completely oxidized. All of the molecules break apart and form oxides. The carbon becomes carbon dioxide, hydrogen becomes water, etc. Under incomplete oxidation (insufficient oxygen, low temperatires), you will see carbon monoxide and soot (various carbon particles)."
] |
[
"Nothing really happens to them other than being combined in different compounds.",
"If something burns completely away, it's not gone. It's all been converted to gasses or smoke which is blown away. ",
"Which is why I think it's kind of funny, for example on a sci fi movie, if someone is vaporized they just kinda disappear. But what they should do is you'd have massive plumes of smoke billowing off them, probably depositing 100 kg of ash and oils on everything in the area. If it was gas it would be a big explosion, or a pretty significant wind blowing from them."
] |
[
"Yep, what DarkMatter wrote is correct; burning is simply a chemical reaction, not a nuclear reaction as the OP seems to be asking, so all the atoms, electrons, neutrons, and protons are there in the combustion products. Much of the burnt fuel is converted to gases and vapors, so it might appear that some matter is lost through burning, though that is an illusion since much of the combustion products have escaped."
] |
[
"Why do some beer bellies feel firm if they're caused by extra fat? Why aren't they soft and squishy like fatty tissue in other areas of the body?"
] |
[
false
] |
Okay, so odd question, I know. But sometimes when a man gets a beer belly, it can feel kind of firm, like the belly of a pregnant woman. I searched a little online for why, but all I could find were "causes of beer bellies" which, is obviously extra calories leading to extra fat. What I want to know is why the beer bellies are firm instead of feeling soft and squishy like other fat. So why is that?
|
[
"This is not specifically down to excess fat as a result of calories in alcohol, but down to the difference between subcutaneous ('soft') fat and visceral fat, which is fat stored deeper in the body, which also feels firmer.",
"For reasons mostly down to genetics, some people divert excess calories to visceral fat, while others produce mostly subcutaneous fat. This is largely responsible for the difference in 'feel'."
] |
[
"So when I hug a guy with a big, firm beer belly, am I feeling his abs? If so, is the fat behind the abs? Or, I guess a better question- How much deeper is \"deep?\"",
"Is the visceral fat stored between the organs? Would it eventually run out of room in there and go more toward the surface? I can't imagine muscle being all that... Uh, flexible with space.",
"Is there a difference between the textures of visceral fat and subcutaneous fat if say, a mortician were to hold a pound of each?",
"I'm super curious about this because it's something I have literally never thought about until yesterday."
] |
[
"You're very welcome! Check out ",
"this colorized MRI",
" that shows visceral adiposity and subcutaneous fat storage in two women who are the same height (one normal weight/thin, one morbidly obese). The black represents air so the weird black things you see on the left image are her intestines that have been moved around because they are being crowded out by the visceral fat."
] |
[
"Why do small birds hop and not walk to move around?"
] |
[
false
] |
I walked past 4-5 small birds today and they just hopped away, then started taking steps as they ate things off the ground.
|
[
"I believe it's actually a very efficient way to move around, using less energy to cover the same distance.",
"Another example of this type of movement would be the astronauts hoping around on the moon. I seem to recall one of them commenting how efficient it was to move around that way."
] |
[
"I am pretty sure someone with bird knowledge will expand but I read in a book that's their fear instinct kicking in. By hopping they are ready to fly away at moment notice since they spring themselves before taking off."
] |
[
"I assume this is the reasoning behind small mammals hopping also? Rabbits, kangaroo mice, etc."
] |
[
"Are there non-primates that live to see their grand-young? If so, do they recognize them as such?"
] |
[
false
] | null |
[
"Elephants and orcas both live in matrilineal societies often headed by a grandmother, orangutans are another species that even though they do not live in tight groups you often see multiple generations in over lapping territories. We think that there are multiple ways of identification include scent and other bio markers along with sound, most animals communicate far more then we previously believed. "
] |
[
"Elephants live that long, as do some turtle species. Elephants probably would as their society is dominated by very close nit family bonds. Herds are mostly either matriarchal or bachelor groups, and the matriarchal ones are usually run by the eldest female, so she would more than likely live to see her grand-offspring. I cannot speak for the turtles on such matters... "
] |
[
"Turtles wouldn't recognize their offspring regardless of whether or not they can recognize individuals because they're not around to watch them hatch."
] |
[
"Can people who have a cochlear implant tell which direction sound is coming from?"
] |
[
false
] | null |
[
"Hi dangerevans007 thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Medicine"
] |
[
"Medicine"
] |
[
"Physics mistake with the rotating body of Rama - does nearing the outside of the cylinder increase centripetal acceleration, even while not in contact?"
] |
[
false
] | null |
[
"My impression reading the book was that the atmosphere inside the cylinder would push him around and give him the lateral acceleration needed to create the centripetal acceleration."
] |
[
"But would the air really be swirling? I'd figure it would be turbulent around structures, but otherwise wouldn't be rotating uniformly."
] |
[
"I realize now that my answer is laymen speculation which is forbidden in askscience, but over time any gas inside the rotating cylinder would begin to rotate at the rate of the cylinder due to friction."
] |
[
"How did fish wind up in lakes that are far inland or in high altitude areas?"
] |
[
false
] |
If I had to guess, then I imagine they are remnants of when the oceans were in that particular location but I would like clarification on this.
|
[
"If the fish were from when the area was covered by oceans then they would be unique species, having evolved from old salt water species. That's almost never the case with lakes.",
"Rather, the answer is much simpler. Lakes often have streams or rivers connecting them elsewhere, and so fish migrate along those routes. Even in cases where a lake doesn't have a connecting stream today it may have had one in the very recent past (years or decades) due to local flooding. Since flooding is fairly common on the scale of centuries just about everywhere, most lakes have been connected to other lakes and rivers at some time in their past."
] |
[
"I read on here that fish eggs can be carried inadvertently by birds."
] |
[
"I won't speak for all alpine lakes but in Yosemite NP in th US, the park authorities used big bombers left over from WW2. To increase the \"value\" of the lakes, they basically bombed them with fish. I was a ranger there but ill update this with a more legitimate source once I'm off my phone.",
"edit: info ",
"http://www.yosemite.ca.us/library/guardians_of_the_yosemite/fish.html"
] |
[
"What is the deal with solar energy?"
] |
[
false
] |
I hear every week about a breakthrough in solar be it using some kind of bacteria or nano-material or what not. I've also read that solar efficiency is doubling every year and is only a few doublings away from out-competing fossils. Basically it just sounds a bit too good to be true and my sensationalist-senses are tingling. So I thought I'd turn to you knowledgeable people of askscience! What the deal with solar? What do all these new "breakthroughs" mean for solar? Has any of them produced commercially viable improvements yet? How does the efficiency compare to fossils today? How was it say 5 years ago? What does the development of solar realistically look like? I know you can't tell the future but, educated guesses? What promising research projects are going on today? What is needed to allow solar to compete with fossils?
|
[
"Not every development that works in the lab works in the field. Not every concept is capable of working on a commercial scale.",
"Most of these 'breakthroughs' are news releases to publicize academic research, which in turn 1) promotes the academic research facility (in order to secure more funding, improve the name of the institution in rankings which are largely a beauty pageant anyway, and get better students) and 2) find a commercial partner to take it from concept to product.",
"Columbia",
"Some of these developments- a very few- will come to fruition. There will be patent battles, and inasmuch as energy costs are a race to the bottom (in contrast to pharma and biotech), the field is self-selecting in a cutthroat fashion.",
"How does the efficiency compare to fossils today?",
"Efficiency doesn't matter that much, really. It's cost-effectiveness that matters. ",
"Here",
" is an excellent chart from NREL. If you're going to cover your rooftop, you're worried more about the cost; if you're going to launch a satellite that runs on solar cells, you're going to worry about reliability and efficiency."
] |
[
"Most of these 'breakthroughs' are news releases to publicize academic research, which in turn 1) promotes the academic research facility (in order to secure more funding, improve the name of the institution in rankings which are largely a beauty pageant anyway, and get better students)",
"I believe the term is \"academic masturbation\".",
"As for OP, I'll try my best:",
"What do all these new \"breakthroughs\" mean for solar? Has any of them produced commercially viable improvements yet?",
"Right now - not much. It's mostly academic masturbation to see who can get the highest efficiency cells. As far as commercial feasibility or mass production ability, not much progress has been made. The high efficiency cells (called mulit-junction) are expensive as fuck and hard to produce. The most practical, economical stuff (dye sensitized, QD, amorphous, organic) is not efficient right now. ",
"How does the efficiency compare to fossils today? How was it say 5 years ago?",
"For your ",
"run of the mill polycrystalline Chinese mass produced crap",
", when all is said and done you can get around 10% optical efficiency and $1.00 per Watt (with all the extra hardware, installation, time, etc.) Compared to ",
"30-60% energy efficiency for coal/gas power plants",
" and $0.20 per kwh. Make of that data what you will. But compared to 5 years ago, solar power is getting cheaper and more efficient, whereas conventional power is pretty much fully optimized and is not getting much better. ",
"What does the development of solar realistically look like? I know you can't tell the future but, educated guesses? What promising research projects are going on today? What is needed to allow solar to compete with fossils?",
"The trend will likely continue. So long as there are no new nuclear power plants coming on line, there will be a steadily increasing demand for electricity which will be satisfied by a blend of technologies. One of them will be solar. The question of whether this means personal photovoltaic panels or large solar thermal concentrator plants remains to be seen. IMO the most promising research is in the field of thin film solar cells. In theory these cells could be transparent so you could have the windows of office buildings generating part or all of the building's power while at the same time blocking and absorbing the IR and UV light outside of the visible spectrum. Solar panels are already a viable competitor to fossil fuels, all that remains is time and research funding to push them over the edge. Within the next 20 years, and likely within the next 15, solar will surpass fossil fuels in terms of efficiency. "
] |
[
"What do all these new \"breakthroughs\" mean for solar? Has any of them produced commercially viable improvements yet?",
"Industry tends to lag behind academic research by something like 10 years. Everything in use now was first discovered in a research lab. That said, the biggest push towards cheaper and higher efficiency devices today is the fact that the market expanded enough so that there are very cheap sources of solar grade silicon wafers.",
"How does the efficiency compare to fossils today? How was it say 5 years ago?",
"I don't understand this question. Are you asking to compare the efficiency of PV to coal/gas power plants? That is a completely meaningless comparison. If this is in fact the question, I can explain why. ",
"What does the development of solar realistically look like? I know you can't tell the future but, educated guesses? What promising research projects are going on today? What is needed to allow solar to compete with fossils?",
"Solar modules fell in cost from 85 cents per watt in 2011 to about 50 cents per watt in 2012/2013. At this price, solar is approaching cost competitiveness in a lot of places (depending on how you factor in interest rates, rises in energy prices, etc.). The prices will continue to drop - this is all that is needed to continue to expand interest and usage.",
"I think one technology to keep an eye on is epitaxial liftoff, currently in use by ",
"Alta Devices",
". It allows the use of high quality materials (better materials than silicon) in a cost effective manner by pealing off very thin films. "
] |
[
"How did the Ice Age support huge animals such as Mammoths and other giant versions of today's animals?"
] |
[
false
] |
The cold would likely hinder plant growth and thus limit food resources available to herbivore species, which carnivores also need to survive. How were such animals anle to live in that time?
|
[
"Remember that evolution and the occurrence of a natural ice age work over very long periods of time. The plants and the animals had a chance to evolve with the changing climate.",
"The land was also differently distributed because of plate tectonics.",
"Next there's the fact that we experience cold currently because of reduced sunlight, but during an ice age many of the cold areas still got a full day's sun in summer, it was just colder because of the climate.",
"So the plants that were growing would be well adapted to cold while still getting the necessary light to grow. there was the same amount of sunlight in the tropics and subtropics and so could support delivering the same amount of energy for the production of sugar and photosynthesis. The plants just needed to have protections against the lower temperatures. They would look more scrub like and be more likely to have narrow leaves and needles and that sort of thing. But the potential to grow and produce sugar were not strictly reduced by conditions we would think of as winterish today. Today we only get to winterish conditions when we get to the highest and lowest latitudes comparably.",
"Also it's possible that there were fewer clouds and more bright sun all things considered.",
"So more land was covered with ice but that doesn't necessarily mean that the ice-free areas were that much colder. The average temperature was lower. But some climates probably got quite warm. and many of the cooler climates were still probably quite capable of growing abundant plant life.",
"So the animals might have been selected for slower metabolism, or better heat conservation. The plants would be selected for colder air but still ample sunlight.",
"So there isn't one specific answer, and we don't have the actual genetic material to test, but it's a matter of using the energy you get not thinking of the temperature. As long as it gets warm enough for liquid water sometimes, and as long as there's enough sunlight, there's going to be plants and animals in proportion to the amount of available energy.",
"After all the ocean is actually fairly barren all things considered, particularly the deep ocean far from the shore, but it supports giant whales."
] |
[
"This is a great answer and I agree with pretty much all of your points apart from one:",
"The land was also differently distributed because of plate tectonics.",
"This factor is actually completely negligible on the timescale of the Quaternary ice age, which is only the last 2.5 million years or so. Plate tectonics modifying the arrangement of the continents operates on the order of tens of millions to hundreds of millions of years. ",
"To show what I mean, ",
"here is a reconstruction of the global map at the last glacial maximum",
". There would have almost certainly been the shape of coastlines and other finer points of inland morphology that were quite different than today, but the actual position of the continents was practically identical, differing by a few hundred metres relative to eachother is all. The reason why you see the reconstructed coastlines of countries as extending further out to sea than the modern day outline (in yellow) on that map because all the ice locked up at the poles meant a much lower global mean sea-level, exposing more of the continental shelves. ",
"Oh and this bit: ",
"Today we only get to winterish conditions when we get to the highest and lowest latitudes comparably.",
"I guess you just meant higher latitudes here. Lower latitudes are centred on the equator. The highest latitudes are the North and South Poles."
] |
[
"A large animal a a smaller surface area to mass ratio than a smaller animal. It helps to retain heat."
] |
[
"The faster you go the slower time goes relative to Earth; what happens when you go much slower than how fast Earth is traveling and is there an actual zero velocity relative to the Universe?"
] |
[
false
] |
I apologize if this is a stupid question but I've been wondering it for quite some time. Everyone always compares speeds to Earth and considers it as the point of zero. However we're actually traveling through our solar system which is traveling through the galaxy, galaxy clusters, etc., so the rate at which we perceive time is different than zero. Is there a way to get out of the influence of galaxies, superclusters, etc., to the point where you are traveling almost zero (or should I say traveling at the speed the universe is accelerating?)? How much would time speed up? Is there a maximum and is there a point where you could be going zero relative to the universe? Or do I just not understand relativity whatsoever? Thanks.
|
[
"There is no absolute frame of reference, therefore there is no \"zero speed\".",
"The time dilation you're referring to applies to two frames of reference. If you are moving very fast relative to me, I would observe you as travelling through time slowly, while you would observe the same for me."
] |
[
"So if I'm moving fast I still would see the person moving slow as moving slow through time, not fast? That's odd... ",
"I guess I worded my question wrong. Let me are if this makes any sense: there's a point at which time can reverse itself, or faster than light speed. Is there a relativistic speed that makes time to by insanely fast, almost instantaneous? "
] |
[
"if you were traveling at .999c then time for you would travel \"normally\" but if you stepped out of your spaceship, time would have traveled \"insanely fast\". i don't want to do the math, so here is a very rough estimate: if you traveled that fast for what seemed like 1 second, then the world outside would have experienced around a day's worth of time. the conversion factor is around 100,000 for that speed, i think. so for every second you exist at that speed, the rest of the world experiences 100,000 seconds of existence. is this what you are asking?"
] |
[
"If all galaxies in the universe are flying away from each other (red-shift, right?), how is also true that the galaxy Andromeda is on a collision course with us?"
] |
[
false
] |
As I understand it, everything in the universe is moving away from each other. We know this because of the red-shift in galaxies far away, and galaxies that are furthest away have the most red-shift - meaning the universe is expanding at an expanding rate. But I also understand that we are on a collision course with Andromeda. How is this possible?
|
[
"The expansion is most evident on extremely large scales. At smaller scales, it's practically undetectable. Everyday objects have EM interactions that utterly overwhelm the expansion. The planets aren't moving away from each other or the sun because they are ",
", so aren't affected by the expansion. Similarly, the sun is gravitationally bound to our galaxy, and the galaxy is gravitationally bound to nearby galaxies, like Andromeda. ",
"However, most of the galaxies we can observe are not, in fact, gravitationally bound to our galaxy, and are far more distant. The further up in scale you go, the more obvious expansion becomes. When you get to the scale of galactic superclusters, which are not gravitationally bound to one another, you see the expansion takes over and becomes dominant. "
] |
[
"The space between galaxies is expending, therefore some galaxies move apart, while other galaxies, that are close together, are attracted though gravity and will merge."
] |
[
"While the universe overall is expanding, that doesn't account for every single part of the universe. Think about it like a big, expanding, crowded asteroid field; if you look at the asteroid field as a whole it's expanding, but it's so densely packed with asteroids that the odds are pretty significant a few of those asteroids will bump into each other along the way."
] |
[
"Is there any way to make oneself dream less often?"
] |
[
false
] | null |
[
"Ever since I started smoking weed, I rarely have dreams. It seems to take a few days of sobriety for dreams to return."
] |
[
"You can learn to control them - that way you won't be able to get enough. The first evidence of lucid dreaming was produced in the late 1970s by British parapsychologist Keith Hearne. A volunteer named Alan Worsley used eye movements to signal the onset of lucidity, which were recorded by a polysomnograph machine.",
"The first peer-reviewed article was published by Stephen LaBerge at Stanford University, who had independently developed a similar technique as part of his doctoral dissertation. During the 1980s, further scientific evidence to confirm the existence of lucid dreaming was produced as lucid dreamers were able to demonstrate to researchers that they were consciously aware of being in a dream state, primarily using eye movement signals.",
"I am working an app that records my eye movements during sleep and plays a song when it detects that I am dreaming. I can sometimes hear the songs in my dreams and act on that knowledge - by flying, for example. And I post the raw logs along with a printout of the most interesting minute to LSDBase every other day."
] |
[
"If you feel like you're dreaming too much, there is a good chance you aren't going into the deeper sleep cycles and there are factors preventing you from reaching deeper sleeping states. Generally either too much light in the bedroom or your health and hormones are out-of-wack."
] |
[
"Where do photons go? [elaboration in the text]"
] |
[
false
] | null |
[
"They are absorbed by the walls and objects in the room."
] |
[
"Absorbed how? Where do they go once they're in the wall?"
] |
[
"https://en.m.wikipedia.org/wiki/Absorption_(electromagnetic_radiation)"
] |
[
"How long would it take to get to Mars if you accelerated at 1G til half way there, swivelled around and then decellerated at 1G the rest of the way?"
] |
[
false
] |
The idea being you experience earth-like gravity for the journey. Also - what would your top speed be?
|
[
"Are you sure this doesn't belong in ",
"/r/homeworkhelp",
"??",
"The Earth and Mars are 2.629×10",
" kilometers apart at their closest. 1g=9.8m/s/s. So half the distance is 1.315×10",
" kilometers. d = 0.5",
"t",
"Answer is ",
"11 days",
"I forgot to divide by acceleration as others pointed out. Actual time would be 3 days 18 hours..."
] |
[
"Cheers",
"I haven't been in high school for over 15 years and wasn't smart enough to do the math back then either!"
] |
[
"Fun fact: the top speed would be about 0.5% the speed of light."
] |
[
"How do candles work?"
] |
[
false
] |
I know the wax is burning, but why is a wick necessary and why doesn't all the wax catch on fire?
|
[
"Liquid wax doesn't burn in a candle, vaporized wax does."
] |
[
"The burning of the wax is a chemical combustion reaction, in which the wax hydrocarbon reacts with oxygen in the air to form water and carbon dioxide. There is an optimum ratio of oxygen to wax which can be determined from the balanced chemical equations. \"Wax\" typically is not a single pure compound, but a mixture of several hydrocarbons, so showing a balanced reaction here may not be all that useful. What is important is that waxes contain a lot of carbon atoms, and thus require a lot of oxygen to burn. A system in which the entire candle catches on fire is certainly possible, but would require either a) a lot more available oxygen, or b) a lot more energy driving the reaction (by that I mean: a lot more energy than the heat energy released by the candle flame)",
"The wick serves a couple of purposes then. The first is that it restricts the fuel entering the flame, thus altering the ratio of wax to oxygen to that which is more favorable for combustion. The second is that it acts as the fuel delivery system: some of the energy released in the combustion reaction is reabsorbed during the following consecutive combustion reactions, however most of it is released as heat energy. Some of that heat energy is absorbed by the wax in nearby proximity to the flame, which melts from a solid phase to a liquid phase. As the liquid wax at the top of the wick ",
" vaporizes, more liquid wax is drawn up into the wick via capillary action, itself now available for combustion."
] |
[
"Good point! As the liquid wax is drawn up through the wick nearer to the ongoing combustion reaction, some of that released heat energy is again absorbed to drive one more phase change, from liquid wax to vapor. This helps to explain why the wick, itself, does not burn (or burns very slowly) as the candle burns: the combustion reaction of wax and oxygen takes place in the vapor phase, while the wick remains in the solid phase."
] |
[
"Are we able to harness the power of waterfalls and is the output enough to make it a viable source of renewable energy?"
] |
[
false
] |
[deleted]
|
[
"That's essentially what hydroelectric power is, except in most cases the \"waterfalls\" are artificial."
] |
[
"Have you looking to the power station at Niagara Falls? Have a look at the (overview on Wikipedia)[",
"http://en.wikipedia.org/wiki/Niagara_Falls#Power",
"]. ",
"Hopefully more people will chime in on this one. I know there are other hydroelectric plants positioned on waterfalls."
] |
[
"Snoqualmie Falls, in Snoqualmie, WA generates power by having a cavity ~ 100m below the top of the falls and behind the falls themselves where water falls through the turbines. ",
"Here's a few images of the cavity during renovation work"
] |
[
"If lightning struck a pool of pure water with someone submerged in it would they survive?"
] |
[
false
] |
I know that pure water does not conduct electricity because it does not dissociate into ions, but would that insulate someone from the lightning?
|
[
"Water actually autoiionizes. Water dissociates into H+ and OH- spontaneously, albeit to a small extent: ",
"http://en.wikipedia.org/wiki/Self-ionization_of_water",
"This is enough to carry a current through the water. "
] |
[
"Pure water has a resistivity of 182 Kohms per meter which while high is not much compared to the power of a lighting strike. ",
"Assuming you are half a meter under the water you would experience at least 32 amps. About 0.3 amps are fatal btw."
] |
[
"It's worth noting that 0.3 amps ",
" can kill you. The body has a high resistance already that will lower the effective current, and the path the current will take might not pass directly through the heart. This is why most people struck by lightning survive the event. The electricity will enter through their arm for example, and leave through their foot. It will give them some nasty burns, but not kill them. Grabbing power lines with the electricity going from one arm to the other would be much more dangerous."
] |
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