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[
"Why do clouds have flat bottoms? Why do they seem to just stop?"
] |
[
false
] |
When I look at clouds, cumulus to be exact, I notice that at the bottom, they appear to be flat. I just want to know why that is. I assumed that it had to do with the atmosphere but Im not sure.
|
[
"As air rises, warmed up by the ground, the temperature falls by adiabatic effect (fall in pressure) to an average rate of 0.65 C per 100 m of altitude. ",
"At 15 C (the average temperature worldwide) a cubic meter of air can contain 14 grams of water. No more. ",
"As the rising air cools down, it has less and less place for water vapour and soon the temperature reaches what is called the dew point, i.e. when the air is 100% saturated and cannot cools any further without condensing in droplets; the cloud. ",
"The base of the cumulus is flat because it is exactly the place where the air reaches the dew point. ",
"But once 'in the cloud' the air cools down at a lower rate because the condensation of water creates energy released as heat. Because of that, the air inside the cloud continues to rise until, eventually the temperature becomes even with the surrounding temperature and the convective rise stops. ",
"The reason the top of the cumulus is cauliflower shaped is that, each 'bump' is in fact the top of one cell of warm air that has been rising. ",
"Such cells, often called thermic cells are what glider pilots are looking for because they use it to circle in and climb. You will also see birds like seagulls and eagles taking those 'elevators' to gain altitude without effort."
] |
[
"When water evaporates, it rises since a water molecule is lighter than your average air molecule. It tends to rise together in large clumps. As it rises, air pressure drops, which brings the temperature down with it. At some point, the water vapor condenses into tiny droplets. Once this happens, it becomes visible as clouds. The flat bottom is where they get high enough for the water to condense."
] |
[
"a cubic meter of air can contain 14 grams of water",
"This is by calculating the Saturation Pressure of Water Vapor, which is a function of Temperature, then using this pressure you calculate Density of Water Vapor which is a function of Pressure and Temperature. At 15C it is actually closer to 13grams, I must have miss-typed but that is where I got those numbers from.",
"A simple google search will allow you to divulge more into \"",
"Vapour pressure of water",
"\" and due to the complexities of the formulas, ",
"there are tables made up that can be easily found as well"
] |
[
"Why does the smell of flatulence vary between people?"
] |
[
false
] |
I am sure that we've all noticed that not only does our own flatulence smell differently from other people's (probably because we've gotten used to that smell), but it even varies noticeably between different people. It varies between men and women and between fat and thin people. I can think of several potential reasons for this, including diet, different compositions of the chemicals in the intestines and stomach, but what is the factor that decides the smell of flatulence?
|
[
"Don't forget your flora! Personal experience: Never EVER be around when people working in worm labs release gas! The contaminations that grow in their cultures can apparently hop to places ;)"
] |
[
"The main factor is ",
"; but other factors include quantity (how much one eats), how long it sits in the digestive track, the amount of digestive enzymes one personally has, body temperature, how active one's parasympathetic nervous system is..."
] |
[
"Oh god, thanks for the heads up!"
] |
[
"What determines if a leaf can be eaten as green vegetable, such as in salads?"
] |
[
false
] | null |
[
"1: That it's not poisonous",
"2: That it tastes good",
"3: That it has a nice texture",
"4: That is has any nutritional value to us (although stuff like iceberg lettuce we eat just for pleasure)",
"There's a lot of vegetation around us that is safe to eat, but would taste awful and not feel nice to chew and swallow. You can eat pine needles but it would be an awful experience."
] |
[
"Oh man, iceberg lettuce has no value?"
] |
[
"Well not none, but a lot less than other types of lettuce or greens we eat"
] |
[
"If i had a stick that was 1 light year long, and at one end displaced it forward by say 1cm, wouldn't that displacement occur instantly at the end 1 light year away? Couldn't this be seen as information traveling faster than light?"
] |
[
false
] | null |
[
"No. Every material has a property called the \"",
"speed of sound",
"\", which is actually the speed that energy travels through that material.",
"When you push one end of the stick, the whole stick will ",
" move at once. You'll actually cause a ripple through the stick -- a compression wave -- and that compression wave will travel through the stick to the other end at that material's speed of sound. ",
"Edit: I should note that this is a great question, and because of that it's a very common thought experiment in undergraduate physics courses.",
"Edit 2: Why have you never seen this in real life? Because speed of sound is fast and the sticks that you're moving are small. But you can imagine this by pushing on a loose wobbly spring really fast -- one end of the spring will push in before the other end pops out, and you can watch the ripple move through the spring. Every material is basically a spring, with different stiffness and damping factors. "
] |
[
"that is an awesome question... can i assume that this \"speed of sound\" is dependent on the materials that that stick is made of? if so, could a material be made that would maximize this speed? if we had a super stick of some kind of space age alloy that allowed for a compression wave of say, .99c, would time dilation effects be present, and how would they manifest themselves??"
] |
[
"This is in the ",
"FAQ",
" btw."
] |
[
"If humans could invent a way to travel instantly to a far off galaxy(far enough that the light hasn't reached it yet(since the universe is still expanding, the light would theoretically never stop)), and we had a telescope powerful enough, could we see the beginning of the universe?"
] |
[
false
] | null |
[
"No need to travel, we can already see the beginning of the universe. Using radio astronomy, the ",
"Cosmic Microwave Background",
" is the after-image of the big bang itself. ",
"EDIT from the wiki:",
"When the universe was young, before the formation of stars and planets, it was smaller, much hotter, and filled with a uniform glow from its white-hot fog of hydrogen plasma. As the universe expanded, both the plasma and the radiation filling it grew cooler. When the universe cooled enough, protons and electrons could form neutral atoms. These atoms could no longer absorb the thermal radiation, and the universe became transparent instead of being an opaque fog. The photons that existed at that time have been propagating ever since, though growing fainter and less energetic, since exactly the same photons fill a larger and larger universe. This is the source for the alternate term relic radiation.",
" The discovery of the CMB was a landmark achievement because the Big Bang theory predicts that this fog should have existed at one point. And then we found visible (in the microwave wavelengths) evidence of it. "
] |
[
"the furthest you could see is ~13.7 billion light years in any direction, same as for earth.",
"Careful there. This is false due to the expansion of the universe. The observable universe has radius 45.7 billion light years. A long time ago, the distance between the Earth and the farthest thing in the observable universe was way, way smaller than it is now, and so in a fixed amount of time T, light traveled some fraction of that distance. But the universe expands, so as time goes on, light travels the same distance in T, but that distance becomes a smaller fraction of the total distance to us. ",
"So even though it takes light emitted ",
" more than 45 billion light years to reach us from some things, light emitted back just after the Big Bang would have taken much less time to reach us. This means that our observable universe is much bigger than the age of the universe times the speed of light."
] |
[
"Never having been this far away, any speculation is without proof, but what would happen, according to present theory, is that you would see a part of the universe that you can't see on earth.",
"Imagine that there is a bubble around each point in space that is expanding out at the speed of light - this is the visible universe at that point. This bubble has been expanding out from earth in the same way that it has been expanding out from Andromeda for instance, so in Andromeda, the furthest you could see is ~13.7 billion light years in any direction, same as for earth.",
"The same should be true for any galaxy outside our visible light bubble."
] |
[
"Does being exposed to confrontation/danger on a daily basis naturally increase testosterone levels?"
] |
[
false
] |
[deleted]
|
[
"Perhaps it's not the question you are really trying to ask, but the implication would be women and children who have lived with threatening partners or parents for large portions of their lives would then have extremely high levels of testosterone. Not sure that pans out. ",
"Testosterone isn't the stress hormone, cortisol is, and some studies indicated constantly elevated cortisol suppresses testosterone. Probably more of a balance between the two and whichever has control will determine whether you fight or fly."
] |
[
"I dunno about testosterone levels. ",
"Half of our troops come home with ptsd, which is the current name for an age old problem with leaving humans in stressful situations for too long. ",
"Stress eats at you like a disease. Too much, for too long, and it destroys your humanity. ",
"It could also be sleeps cycles, environmental, everyone reacts differently. ",
"TLDR: exposing yourself to danger on a daily basis will change you, probably not for the better."
] |
[
"Depends... Do the person ENJOY being exposed to this danger daily ? Does it stress him ? Does his support net assist him to overcome the stress ? ",
"A High stress enviroment is generally associated with a decrease in T Levels... BUT, (And here I will extrapolate) My guess is that if the person seeks that danger and enjoy the thrill of that danger their T Levels are usually already PRETTY high, and will not feel Stressed by the danger/confrontation and will probably boost/keep the T Levels. ",
"It would be intreseting to know the T Levels of returned soldiers, if their PTSD take-over because their T Levels dropped fast (lack of a support/hyping crew), and maybe if we return the soldiers and manage their stress level to be reduced gradually the PTSD effects will be lower or not..."
] |
[
"How do scientists know what the structure of receptors look like?"
] |
[
false
] |
For example, the structure of melanopsin... I see alot of 3d renders, but no actual photos. What tools and methods are used to determine what it looks like?
|
[
"There are three main methods:",
"1.) X ray crystallography is the original method used. It solves the 3d structure by shooting radiation at bonds and measuring what comes back to determine distance, angle etc. However, for something with a repeated structure like an ",
"alpha helix",
", you can know without this (just be looking at the constituent amino acids in that DNA sequence). It becomes more difficult for beta sheets and ",
" difficult for how proteins fold to form tertiary structures.",
"2.) Nuclear magnetic resonance spectroscopy (NMR) which is used for smaller proteins and intrinsically disordered proteins. Machines induce a magnetic field which is able to detect isotopes / molecules because different atomic nuclei resonate at specific frequencies that are detected by electromagnetic radiation receivers. ",
"Proteins are orders of magnitude larger than the small organic molecules discussed earlier in this article, but the basic NMR techniques and some NMR theory also applies. Because of the much higher number of atoms present in a protein molecule in comparison with a small organic compound, the basic 1D spectra become crowded with overlapping signals to an extent where direct spectral analysis becomes untenable. Therefore, multidimensional (2, 3 or 4D) experiments have been devised to deal with this problem. To facilitate these experiments, it is desirable to isotopically label the protein with 13C and 15N because the predominant naturally occurring isotope 12C is not NMR-active [...]",
"3.) Cryo-electron microscopy, where a sample is frozen and embedded in amorphous ice.",
"The resolution of X-ray crystallography is limited by crystal purity, and creating these samples is very time consuming, taking up to months or even years. Also, some proteins are hard to crystallize. Although sample preparation for Cryo-EM is still laborious, it does not have these issues as it observes the sample in its “native state”",
"",
"And then we use these data to inform models such as alpha fold and help gauge the accuracy of predictions, as other mentioned! We have to solve a ",
"distance geometry problem",
" as we know the distances between atoms by the patterns of frequencies in the case of NMR or by the diffraction pattern in the case of X-ray crystallography / cryo-EM. This last point I imagine is quite nuanced so I refrain from mentioning anything else before I say something completely wrong!.",
"Edit: added detail & to add cryo-EM (further reading: ",
"cryo-EM catching up",
" to Xray crystallography ",
"article",
", cryo-EM in drug discovery ",
"review",
"). ",
"Quotes are from wikipedia"
] |
[
"Whole lot of different ways really. These should be the more common ways as I was taught.",
"One key part is just isolating isolating a single protein from a soup of cell bits. Its's going to be some variant of chromatography which separates proteins into groups with different characteristics, like size, or degree of ionizstion. The term to look for is protein purification. There also preprocessing chemistry to isolate protein specifically from non-protien bits.",
"You also have to figure out what the protein actually does. That can happen by comparing protein distribution between mutated and normal cells.",
"Another part is determining the structure once you have enough protein to work with. X-Ray crystallography is one of the more well known ways and has been around for quite a while which works by taking your priorities proteins and processing them so that they group up into a crystal (all the proteins are oriented the same way). Then they hit it with x rays, and because of the crystal structure x rays are deflected the same way no matter which individual protein they hit. By recording the bounce angles the positions of individual atoms can be calculated.",
"Another way that works is by using chemical process to break apart the amino acids specific patterns of amino acids by stripping only specific amino acid in a series of steps. Then the strands of protein are separated via chromatography by size. And by knowing the patterns of the ends and sizes of the chunks you can piece together the whole protein sequence.",
"That doesn't actually give you the shape but with computer simulations you can determine how the protein folds up based on its sequence. And useful proteins only fold up one way so you don't get multiple answers for how the protein folds up."
] |
[
"This is a good general answer, but it doesn't really address OPs specific example of melanopsin, which as far as I can tell, has never had a crystal structure solved. This can happen if a protein is particularly difficult to isolate in a stable form, or if it doesn't like to crystallize in a uniform manner. In cases like this, you can make a model structure using computer simulations that compare the protein of interest to a related protein where the structure is already known. By comparing the sequences of the proteins and adjusting the parts where they differ appropriately, you can get a good guess at the original structure.",
"There are also computer algorithms such as ",
"AlphaFold",
" that attempt to predict the structure purely based on the sequence and knowing how proteins usually fold, but they're generally less accurate than if you work from a known starting point."
] |
[
"How do You Make KNO3 From Scratch?(AKA: Potassium Nitrate, or Niter)"
] |
[
false
] | null |
[
"Hello,",
"We can’t help you with this here.",
"Best."
] |
[
"Hello,",
"Why not? Is there not a chance that someone in the community knows about this?"
] |
[
"We don't offer assistance with personal projects.",
"Best."
] |
[
"An article I saw on r/physics today announced Fermilab's discovery of xi-sub-b, a baryon that had been predicted, but not previously observed. How exactly do the CDF/LHC and other particle detectors conclusively observe and determine the existence of a particle if it has never been observed before?"
] |
[
false
] |
edit: Another thing that confuses me is why a particle would appear in some instances of a collision, and not in others; from the article: " the Xi-sub-b was observed in 25 instances among almost 500 trillion proton-antiproton collisions." What occurred in those 25 instances that resulted in the detection of the Xi-sub-b? Was it present in the other collisions but simply not detected?
|
[
"It's likely a combination of both. ",
"When two particles collide the result is not deterministic. The slew of particles that result from the collision and the resulting decays is probabilistic. This is the nature of quantum mechanics. Though I don't know the details of the experiment, the creation of a Xi-sub-b is likely a very rare event because it's such heavy particle. On top of that, heavy particles decay extremely quickly into lighter particles, so it'd be hard to find it in the mess of particles. There's also a lot of noise that potentially hides it. The 25 instances are those that they're sure after much analysis are Xi-sub-b. "
] |
[
"As far as I know the particles that have been discovered have all been hypothesized to exist beforehand, so I assume they are looking for specific properties. What I don't get is how exactly these properties are observed. Another thing that confuses me is why a particle would appear in some instances of a collision, and not in others; from the article: \" the Xi-sub-b was observed in 25 instances among almost 500 trillion proton-antiproton collisions.\" What occurred in those 25 instances that resulted in the detection of the Xi-sub-b?"
] |
[
"I see, so yes that is a good question, as I said not a scientist. "
] |
[
"Are there \"degrees\" of color blindness? The optometrist always tells me I am red-green colorblind, but I've never experienced any practical deficiency."
] |
[
false
] |
[deleted]
|
[
"There are different varieties of colorblindness.",
"You most likely have deuteranomaly. This means that your green-vision cells are not quite what they should be and activate on frequencies closer to red than they should.",
"However, some people have deuteranopia, which is a complete lack of green-vision cells."
] |
[
"So...deuteranomaly is bad enough to fail all the tests, but not bad enough to actually see any effects in normal situations? Shouldn't the tests have been calibrated to distinguish this from deuteranopia? Or are there tests for that and I just never knew about them?"
] |
[
"Your vision appears normal to you, and it is unlikely that you would know that you were colorblind if it were not pointed out to you explicitly in the tests for colorblindness. This accounts for the phenomenon you are describing. "
] |
[
"Is there a layer of steam around Europa's core?"
] |
[
false
] |
My current understanding (based largely on wikipedia) is that Europa is mostly water. The crust, to an unknown depth, is solid ice, followed by a mantle layer of liquid water and a hot iron core. What would the transition from the water mantle to the iron core look like? Specifically would the heat of the core be enough to generate an insulating layer of steam (the Leidenfrost effect)?
|
[
"The internal structure of Europa is not well understood, but there is certainly not a layer of steam between the water and the iron core for a couple reasons. 1) Water vapor is less dense than liquid water, so it would rise above the liquid. 2) The physical state of the water depends on both temperature ",
" pressure. The core is likely hot, but the high pressure under the weight of the ocean forces the water molecules close enough so that it would be a liquid or solid at the base of the ocean. Another of Jupiter's moons, Ganymede, is thought to have ",
"Ice V",
" at the base of its ocean."
] |
[
"Europa is ",
"almost entirely a rocky planet",
", so it is unlikely that water from its oceans is being heated en masse by the inner core. You can see for yourself if you simply calculate Europa's density, which I find to be ~ 3000 kg/m",
" Since water is 1000 kg/m",
" this means that most of Europa cannot be water."
] |
[
"Thanks, this is the image I was missing."
] |
[
"What is oobleck and what does it mean for something to be non-newtonian?"
] |
[
false
] |
I keep on reading that it is a "non-newtonian" solid. What does non-newtonian mean exactly and how can we say that it is not liquid? Why does applying pressure to the corn starch and water mixture cause the liquid to harden? How is this able to act as it does on a molecular level? Sorry that my questions are all jumbled up. This thing is so bizzare to me.
|
[
"What does non-newtonian mean exactly",
": roll a ball along the floor. When you give 1 unit of \"push\", the ball rolls 1 unit of \"distance\"; 2 units of \"push\" = 2 units of distance; 3 = 3. etc. It's predictable according to Newtons laws of viscosity.",
": roll a ball along the floor. When you give 1 unit of \"push\", the ball rolls 1 unit; 2 units of \"push\" = 1.5 distance; 3 = 1.75 distance. 4 = 1.75 units. It's not predictable using only Newtons law of viscosity.",
"Molecular level lets talk about your blood and red blood cells.",
"RBC are shaped like discs. At very low \"push\" force they flow nicely and predictably. At very high \"push\" force the discs start to align to reduce resistance - they actually move faster than you would predict - the fluid gets ",
" with applied shear ",
". It's like hanging your hand out a car window - at low speed do whatever you want, at high speed the wind makes your hand tilt flat to the direction of travel.",
"Ooblek is the opposite. Push really hard and it thickens.",
"Ooblek contains little balls of starch floating in waters. You see flour with your eyes, but on a molecular levels its teeny tiny mini grains of rice all clumped together. These starch particles have really hairy arms and covered in static, maybe like velcro. At very slow speeds the particles can push past each other and the arms are relaxed. However, push it too hard/fast and the arms can't move fast enough, they get locked almost like a net/mesh and the starch particles effectively push back.",
"Imagine trying to walk through a busy crowd. Slowly, you can slip through the gaps. However, take a running start and you push into someone, who pushes someone else, who pushes back and overall you bounce off the crowd and you end up on your ass. We would say a busy crowd becomes ",
" with higher shear ",
" to the point it actually looks like a solid wall."
] |
[
"Ketchup. Ketchup gets more liquid when you hit it, which is why you have to thump the bottle sometimes to get it to come out. Materials that do this are called shear-thinning."
] |
[
"Hard impacts make it feel solid but once you let it sit for a min it turns to liquid. Non-newtonian refers to that fact that it doesnt follow Newton's law of viscosity. I.E. constant viscosity independant if stress. Non-newtonian fluids change viscosity under force to either more liquid or more solid."
] |
[
"A (most likely misunderstood) problem I can't get out of my head: regarding Heisenberg's uncertainty principle."
] |
[
false
] |
I may be wrong from the start here, but for this problem I've been treating the uncertainty of position of my small but massive particle (may as well be a proton) as a perfect mathematical sphere, whose centre is a measurement of position I made of the proton, i.e it is somewhere in the sphere but we'll be damned if we know where. Now for potentially false assumption two: If we were to accelerate the proton to a large percentage of the speed of light and continued to measure it's position while it orbitted around us, (I have been assuming) the uncertainty of the proton would contract in a Lorentz-like way, reducing the volume of the sphere to the observer. As (delta)position(delta)momentum>h/4pi; would the uncertainty of position increase as a reaction to the loss of volume of the imaginary sphere? That is assuming that everything that I've assumed is true. I am fairly sure that things just don't work like this, with any of the assumptions I've made. Hopefully you guys and gals can put my on the right track?
|
[
"when you boost into another frame the length goes like x-> x/g where g is the gamma factor and momentum goes as p-> g",
"p, the g's cancel. On a more fundamental note the product of a momentum and a velocity is called action (its actually more complicated than that, but we'll ignore that for now.) And unlike momentum and position, all observers agree on action so it is called an invariant. You can think of hbar=h/2pi as the minimum amount of action which is why the uncertainty on action is always greater than half the minimum amount of action."
] |
[
"Don't accelerate the proton: instead, consider the different observations of two observers of the proton. One observer observes from the rest frame of the proton; the other observer observes from a frame with a relative velocity which is a significant fraction of the speed of light. Also, as the relative velocity is happening only in one dimension, we might as well simplify to the one-dimensional case.",
"What does each observer say about the wavefunction of the proton? Due to Lorenz contraction, the moving observer will see a wavefunction which is much more \"concentrated,\" if you will, to a particular location. We are forced to conclude that the two observers will disagree, then, about the uncertainty in the position of the proton, and that the moving observer observes a ",
" position uncertainty.",
"The interesting question, then, is that of the ",
" uncertainty? To answer this, we Fourier transform from position space to momentum space. Since the moving observer saw a \"more concentrated\" position-space wavefunction, they will see a \"more spread-out\" momentum-space wavefunction. That is, we conclude that the observes see different momentum uncertainties, and that the moving observer sees the ",
" momentum uncertainty.",
"I haven't done the computation but I wouldn't be especially surprised to learn that both observes agree on the ",
" of the position and momentum uncertainties.",
"Edit: commas, minor grammar"
] |
[
"My intuition is that the uncertainty doesn't change. Seeing as the uncertainty isn't a physical thing, I'm not sure why it would be subject to Lorentz-contraction. I think possibly, to get a real answer, would require reconciling quantum mechanics with relativity...",
"It's been awhile since I've done any QM, but the HUP just says that product of the error in position and the error in momentum measurements is always larger than h-bar. So, thinking of the position of your particle as being somewhere in a perfect sphere is a bit erroneous. Really, what HUP tells us is that the more you know about where your particle is, the less you know about its momentum.",
"In your example, what this means is that knowing how fast the particle is going affects how well you know where the particle ",
"."
] |
[
"Why can there not be an n=0 mode on a waveguide?"
] |
[
false
] |
Take an elastic membrane for example. My physics notes say there has to be at least one oscillation in the x direction: why can it not be flat in the x direction, and a wave travelling down the z direction like normal?
|
[
"Shouldn't the excitation at the z=above,below boundaries be 0? Yet for a n=0 node, your membrane is flat along the x-direction. If it's both 0 at a point and constant, your wave won't be much of a wave. To be certain, I'd need more information as I don't even understand the diagram you just posted. Usually it's clear from the equations and the boundary conditions"
] |
[
"thanks, that made thinsg clear even if my question wasn't"
] |
[
"The question as you've asked it is a bit vague. Based on the linked picture I'm going to consider a rectangular (hollow?) waveguide. In this case you'll have indices m,n for x,y in cartesian coordinates. In the case of a TE waves it is entirely possibly for n=0 mode as long as m is non zero, ie TE_00 is not allowed (well, it kind of is but its really a TEM wave), but TE_10 is allowed. In a TM wave there can be no non-zero index and the lowest mode is TM_11. TEM wave can have all zero indices however not all waveguides will allow TEM waves to propagate, for example TEM waves cannot propagate in a hollow waveguide.",
"As for why this is true, by solving for the eigenvalues of your rectangular guide, (can be done using separation of variables) you get k_x =m pi/a and k_y=n pi/b where a, b are the side lengths of your waveguide. Putting your wavenumber, k, in terms of frequency (w) and the indices found from the separation of variables solution you'll get a term like ",
"k=sqrt((w/c)",
" - (pi",
" (m/a)",
" - (n/b)",
"so to get a real wavenumber we need ",
"w<c pi sqrt((m/a)",
" - (n/b)",
" ie there is a minimum cutoff frequency which is dependent on the mode numbers, so you must have non-zero modes.",
"See Griffiths EM section 9.5.2 for a much more indepth answer, and his problem 9.28 is very relevant."
] |
[
"I was recently identified as a potential stem cell/marrow donor for someone, what makes me special?"
] |
[
false
] |
Several months ago I joined the Onematch stem cell and marrow network . They called me up and told me that I was a match for a sick person and asked me to take some additional blood samples to make sure. The patient is anonymous to me. I am curious why mine? Wouldn't a close relative be better? Is it based on Blood type? A-, B+ etc?
|
[
"Firstly, congratulations on being fortunate enough to be given the opportunity to save somebody's life!",
"The ABO and Rh blood types apply only to giving blood to somebody. They are less relevant in organ donation, and even less so in marrow donation.",
"The important in marrow donation is the HLA (Human Leukocyte Antigen - a kind of protein ALL cells have on their surface). These proteins have different patters from person to person and are recognized by white blood cells. In most marrow donations, the recipient is so sick that physicians have to eliminate all their original blood stem cells and completely replace it with the donor's. ",
"The immune system (and white blood cells in it) serves two functions:\n1.) It has to recognize your own organs as your own and not attack them. This is what happens when donated organs are \"rejected.\"\n2.) The one we know best, protect from foreign objects.",
"Because the patient already developed, all their organs have their specific HLA already. Their own white blood cells, before they got sick, were able to recognize the HLA on their own organs as \"safe\" and not attack. By the nature of a bone marrow transplant, they're replacing the patient's immune system with essentially your's. Your immune system, which is used to functioning inside your body, would recognize any organ with the wrong HLAs (e.g. the wrong recipient) as foreign and attack it.\nIn the recipient's case, this could cause a system-wide breakdown of all their organs just because a foreign immune system thought it was in the wrong place. If your HLAs are the same, your immune system is used to recognizing that HLA pattern, and will think the recipient's body is their own. Thus, they can live on with a healthy immune system.",
"They probably already tested a close relative, but it did not FULLY match - only probably partially. However, the relative's partial immune system will still not recognize some HLAs in the patient, and attack their organs respectively. The good thing is that, in the human population, there are only so many \"patterns\" circulating around. It could be that, by chance, you two shared very long lost ancestors (from prehistoric times, maybe) and, by chance, the HLA pattern reassembled itself into two independent people living at the same time."
] |
[
"Complete genetic chance. The HLA pattern is encoded in your DNA. You randomly inherited 1/2 of your pattern form your mother, and the other half from your father.\nInteresting note: Because distinct ethnic populations generally arise from a common ancestral group (i.e. all south asians arose from ancestral south asians, europeans from europeans, etc.) there is a good chance you have the same ethnic background as your recipient."
] |
[
"Wow! Thanks a lot for the very informative answer. So is it complete genetic chance, or has my specific actions in life changed HLA pattern to match?"
] |
[
"Why are there Hadley cells, Ferrel cells, and Polar cells? What causes the air to sink between cells?"
] |
[
false
] |
Ok, so all the videos about global air currents start with convection and imagine an Earth that was still warm at the equator but cold at the poles but did not rotate. This Earth would have one two big cells where air travels from the equator to the poles and vice versa ( ). I know the Coriolis Effect means that the air wouldn't travel in a straight line, but why aren't there still two big cells? What causes the air in the Hadley cell to sink? And why three cells per hemisphere?
|
[
"This should clear things up",
"",
"https://sites.google.com/site/moreapesfiles/home/documents/Atmospheric%20Circulation%20%26%20Climate%20slides.pdf?attredirects=0&d=1"
] |
[
"Some of the air has to sink if other air is rising, since the amount of air at each altitude is at equilibrium. So if you've got a band of uplift near the equator you've got to have an area of subsistence somewhere else.",
"I'm not sure about why there are three bands, but I suspect it has to do with Earth's specific size/geometry, since Jupiter (which is larger and has a different 'surface' structure) has eight bands per hemisphere. Compare ",
"high altitude circulations in Earth's atmosphere",
" with ",
"Jupiter's",
" and the two look rather similar."
] |
[
"As you rightly mentioned the coriolis effect acts to deflect moving air masses away from a latitudinal orientation like you might expect on a non-rotating body. The magnitude of this deflection is large enough that air masses eventually follow the longitudes or align E-W or W-E. The general dynamics of the coriolis force on these migrating air masses has allowed for the creation of the three cells you aforementioned. I believe that they sink because within their respective cells the northern most limb of the overturning circulation, in say Hadley, is colder relative to the it's southern most limb and hence creates a typical convection pattern of warm air rising at the Intertropical Convergence Zone and then typically cooling and subducting around 30N (sub-tropical high laititudes and it's interaction with the Ferrel Cell). ",
"The Ferrel Cell's migration of air mass is probably partly dictated by both the Polar cell's regime and the Hadley Cell's dynamics with each system complementing the same cell movement of the Ferrel. So for the Polar Cell the super cold, dense air masses flow at low altitude until the interaction with the Ferrel cell where upon it rises and retreats back to higher latitudes where it cools and the process repeats.",
"Hope this kind of made sense. ",
"I imagine if the Earth was rotating faster we'd see development of more atmospheric cells, perhaps these are already a thing on Jupiter etc? - a fleeting thought.",
"Also worthy to note is not to get too bogged down in simplistic overarching views of the atmosphere and oceans. In reality these systems are very stochastic in nature and the dynamics are wildly different to the popularly taught simplified \"sketches\" - such as the Hadley, Ferrel, Polar Cells or theromhaline ribbon etc etc. ",
""
] |
[
"Why are some insects attracted to bright lights, but others aren't?"
] |
[
false
] |
Wouldn't it be counter-productive to their survival by making themselves more visible when it gets dark? Also, why is this primarily something that some insects do, but not mammals or birds?
|
[
"They aren't \"attracted\" to the light. They use moonlight instinctively to navigate. Artificial lights mess with their guidance system, causing them to fly circles around the light or into it.",
"Mammals and birds don't use moonlight to navigate, as don't some insects.",
"It would be like if there was a big magnetic mountain that \"attracts\" hikers who navigate by compass and not ones who navigate by the stars."
] |
[
"Why are some insects attracted to bright lights, but others aren't?",
"Insects are actually attracted to the UV light, which we and presumably some other insects can't see.",
"Wouldn't it be counter-productive to their survival by making themselves more visible when it gets dark?",
"Not necessarily. How many nocturnal insect eaters use vision to hunt by? Most I can think of use other location methods. Even those that do would have very sensitive eyes and so bright lights would be even brighter.",
"Also, why is this primarily something insects do, but not mammals or birds?",
"Again, not being able to see the UV in an otherwise low UV environment."
] |
[
"Ok, and why are they attracted to UV light? And does a normal light bulb emmit lot of UV light? Thank you "
] |
[
"How far away are we from possibly creating a Dyson sphere (around the sun for example)?"
] |
[
false
] |
For those of you who do not know: So, when could such a structure ever be built, and how much would it cost?
|
[
"See ",
"http://en.wikipedia.org/wiki/Kardashev_scale",
"We're basically a Type I civilization, and most likely looking at several thousand years until we get to Type II, and the ability to construct a Dyson sphere. At that point, cost will probably (hopefully) be a concept of the past. "
] |
[
"If we assume it to be 1m thick and at the orbit of mercury (0.3au) then it will have a volume of ",
"2x10",
"m",
". The volume of Earth is 1/20 of that so there is actually a lot of leeway in saying we would basically need to convert all of the terrestrial bodies in our solar system into it.",
"This would require us to have colonized hundreds of star systems and a timeframe for that isn't really possible.",
"edit:",
"Just imagine the energy required to move a planet somewhere else."
] |
[
"Perhaps through a post-scarcity economy if you're into that sort of thinking. "
] |
[
"Why isn't ejaculation after penetration instantaneous?"
] |
[
false
] | null |
[
"The female body makes changes to the reproductive tract during sexual intercourse to maximize chances of conception, and these take time to occur. ",
"The male body also undergoes continuous changes during sexual intercourse, which ultimately lead to ejaculation.",
"Female",
" and ",
"male arousal",
", respectively"
] |
[
"And if the female has not warmed up and the male ejaculates, the chances of conception are lower. If one sex has to “warm up”, the other one must wait as well."
] |
[
"Everyone, can we please have a nice, mature, scientific discussion about this? Keep it factual, keep it mature, and keep up the citations. "
] |
[
"Can the static tension of tectonic plates be quantified, or how are predictions about future quakes made?"
] |
[
false
] | null |
[
"Can the static tension of tectonic plates be quantified?",
"So, the way we as geologists would discuss this would be in terms of measuring the magnitude and direction of stress(es) within the crust. There are a variety of ways we can directly measure stress, e.g., ",
"borehole breakouts",
", ",
"overcoring",
", etc., which we can then use to produce maps of stress like the ",
"World Stress Map",
". Ultimately though, while maps of stress are useful for some aspects of assessing earthquake hazard, we cannot directly apply these to \"predicting\" earthquake hazards as this would require knowing much more about the stress history (as opposed to short term measurements), how stress changes with depth, the amount of accumulated strain on individual faults, the strength of individual faults, along with a whole host of other properties. Stress maps and estimates are one part of what we can do to assess hazards though.",
"how are predictions about future quakes are made?",
"Here we want to be explicit about what we can and can't do and moreover what is implied by specific terms when used by professionals. Geologists, seismologists, and others who work on natural hazards often draw an important distinction between ",
" and ",
" This may seem pedantic, but these two terms imply very different things when being used by people like myself who works on natural hazards. Forecasts are hopefully partially intuitive from weather forecasting and we can use this to explore the implications of these two terms in this context. A weather ",
" would be something like, \"There is a 80% chance of rain today in this region\", whereas a weather ",
" would be \"There will be exactly 1 cm of rain, falling at a rate of 1 cm / hr, starting at exactly 4 pm at this precise location.\" I.e., for something to be a prediction implies certainty in time, location, and magnitude. Generally, we can forecast the weather, but we cannot predict it and the same is true for earthquakes. The reason we cannot predict earthquakes is much the same reason we cannot predict weather, i.e., incomplete data characterizing a non-linear dynamic (i.e., chaotic) system. The utility of the two are also the same, i.e., even though we can't predict the weather in a perfect sense, the forecast helps us plan (i.e., if you saw the forecast from above, you'd probably bring a rain coat or umbrella with you, etc.). If you want to read even more about why we can't ",
" earthquakes in the true sense of the word, ",
"this FAQ",
" goes into more detail.",
"For earthquakes, where do the forecasts from? Mixtures of basic mapping of fault locations and geometries, theoretical understanding of earthquake mechanics from both observations and modeling, a variety of geodetic measurements and measurements of stress (like from the first part), and records of earthquake histories from ",
"paleoseismology",
", historical seismology, and/or ",
"archaeoseismology",
". From all of these, we build assessments of how often particular faults have earthquakes, what the variability in style/size of those earthquakes are, time since the last event, and other various details we can glean from the geologic record. In the end, we end up with things largely similar to our weather forecast example, i.e., a probabilistic seismic hazard assessment, like the various ",
"ones for the US",
". These focus on different regions and consider different lengths of time (going back to the weather forecast analogy, largely equivalent to the difference between a daily forecast and the 10 day forecast, etc.). If you look at many of these, you'll see they are presented in a somewhat similar way to weather forecasts, i.e., the probability that a particular area will experience significant shaking in the relevant time frame covered by the map. Just like the weather forecast, while not a prediction, it provides a tool for us to assess risk and make preparations. I.e., much in the same way a forecast of sunny skies vs a chance of rain might determine your choice of clothes for the day, living in an area with a 20% chance of experiencing significant shaking in the next 10 years has very different implications than living in an area with a 1% chance of experiencing significant shaking in the next 10 years and you (and governments, etc) would/could/should respond accordingly."
] |
[
"Amazing explanation, thanks so much!"
] |
[
"Yeah, so, this is completely antithetical to everything I just laid out. I.e., you're effectively asking for a prediction after I just spent a significant amount of time trying to explain why these are not possible. PSHA maps for a given region are going to be the best bet for effectively background risk. As new events occur, these of course are updated as we consider whether a large event has increased or decreased risk in a certain place (e.g., through loading or unloading of related faults through ",
"Coulomb stress transfer",
", etc.) and as we learn more about an area (i.e., expanded paleoseismology records, faults are discovered through mapping, etc). Similarly, there will be specific short duration forecasts related to individual large earthquakes, i.e., ",
"aftershock forecasts",
". Beyond that, even within the area of the world I specifically focus on (and for which I understand the local geology and earthquake hazards reasonably well), there is no meaningful way for me, or anyone else, to make statements like what you're asking for. Anyone who does is either irresponsible or trying to sell you something.",
"As a relevant aside, for anyone musing on the potential benefits of true earthquake prediction in the sense outlined in my earlier answer (and sidestepping all of the reasons why we don't generally think it's possible), I would highly recommend this ",
"opinion piece",
" by Dave Petley (a geologist who works on quantifying natural hazards). The general thesis is that basically, unless predictions (as defined above) are 100% accurate (which they never could be, even in the rosiest view of our future capabilities), they are unlikely to improve outcomes anymore than forecasts (as defined above) and would likely actually have significant negative outcomes potentially making \"predictions\" worse than \"forecasts\", i.e., the risks associated with either false negatives or false positives are very large both in an economic and human life sense."
] |
[
"How can we differentiate so many simultaneous sounds?"
] |
[
false
] |
So I understand that sound waves are vibrations in a medium; for example, a drum sends a wave of energy through the air that eventually vibrates the air molecules next to my ear drum, which is then translated into a recognisable sound by my brain, as opposed to actual air molecules next to the drum being moved all the way over to me. But if I'm listening to a band and all the instruments are vibrating that same extremely limited number of air molecules inside my ear canal, how is it that I can differentiate which sound is which?
|
[
"Disclaimer: I know very little biology. I did a project in school that simulated a type of cochlear implant's performance and I know a fair bit about the psychosomatics of sound, but my medical terminology is poor. I may make mistakes.",
"The structure in the ear which detects sound is called the cochlea. It's located a bit behind the eardrum and is roughly the size and shape of a snail shell, which is where it gets it's name. If you unrolled it, it would be 28-38 mm long, depending on the person. A membrane (NB: not actually a membrane, but a fluid filled region between two mebranes) divides the cochlea down the spiral. Towards the big end of the spiral, the membrane is stiff and resonates only with higher frequencies. At the far end of the spiral, the membrane is looser and more flexible, and can only be affected by lower frequencies. Nerves in the membrane detect movement in a particular part of the spiral.",
"That's how the brain determines pitch. It doesn't hear one wave, it hears a very large (thousands) number of frequencies. This is very similar to a ",
"Fourier Transform",
", and is quite closely related. It allows the brain to discriminate tons of sounds at the same time. To the brain, sound almost looks more like a ",
"picture",
". ",
"There's also a lot of co-evolution going on in your example. The human ear/brain is most sensitive around the frequencies of human speech, and not coincidentally many instruments ",
"operate in that range as well",
". The brain has evolved a number of strategies for listening for certain sounds, cues, and blocking out noise. Even if we aren't exactly sure what methods it uses its very well developed to filter sounds."
] |
[
"To add to this, when multiple sounds are playing together in the same airspace, you still only end up with one waveform that is an aggregate of all of the sounds present. The cochlea basically untangles that single waveform into a series of individual frequencies and sends that data to your brain, which analyzes the signature and matches it against known sounds. With this method the brain can easily pick out individual sounds in a composite waveform.",
"The number of air molecules in your ear canal is enormous, in the hundreds of quintillions at very least, and that also doesn't matter.",
"The molecules are all moving back and forth roughly at the same time, what differentiates sounds is the period of oscillation, not which molecules are vibrating."
] |
[
"Neuroscientist here.. Actually, it's very different.",
"In terms of the signal itself (as opposed to its location), our vision is much more limited than our hearing. Imagine you could only hear three different frequencies, in the sense that you could detect the whole range, but they'd always sound like some mixture of those three frequencies. So supposing you could hear a middle A, C, and F, an A# would sound like a slightly quieter A with a tiny bit of C mixed in. It wouldn't sound like its own note.",
"That's how our vision functions, essentially.",
"As for your original question:",
"Part of it is localization. Your ears are actually pretty good at identifying where sounds came from. So sounds coming from one direction are judged more likely to be coming from the same source.",
"Part of it also is frequency separation: Because your cochlea provides pretty good frequency resolution, your brain can identify specific frequency mixtures that correspond to different sources. ",
"How do multiple frequency components of a signal get associated, when there is other sound? Probably part of it is identifying frequency components of the signal that stop and start together, and get louder and softer together, and so on. If a particular sound includes energy at 600 Hz and 540 Hz, then your brain will pick up on the fact that the 600 Hz and 540 Hz signals seem to change intensity etc. in lockstep."
] |
[
"Has anyone ever made a star chart not from Earth's perspective, Alpha Centauri A for example? How much would it differ from Earth's chart?"
] |
[
false
] | null |
[
"Yes. Here's one example:",
"http://www.astronexus.com/endeavour/chart",
"It starts at looking from Earth toward Orion. Replace \"Earth\" with \"Alpha Centauri\". As you might expect, the sky looks mostly the same, but a few of the nearby stars have moved. For example, Sirius is right next to Betelgeuse, and there is a first magnitude star in Cassiopeia: the Sun.",
"Also try ",
"Space Engine",
"."
] |
[
"Hadn't realized that Sirius is in Orion as seen from Alpha Centauri! Right next to Betelgeuse."
] |
[
"elite dangerous",
" does a great job too, and looks like it's based off the same data."
] |
[
"what is the optimum setting for efficiency on my storage gas water heater?"
] |
[
false
] | null |
[
"Lower temperature setting will always use less energy. Eventually you will run out so keeping the temp at the lowest setting you can without running out is best."
] |
[
"In terms of the shower... the temperature of the shower times the amount of water used is the only thing relevant. It doesn't matter if the temperature is achieved by all 40 degree water from the storage tank - or a mixture of cold water and 60 degree water - the same total energy is needed for heating.",
"Which doesn't take into account heat losses. The hotter you keep the water, the more heat will be lost from the tank and from pipes before the mixer (on taps or shower).",
"As such, it is best to keep the water at the lowest temperature to reduce (rate of) heat loss.",
"Volume may be an issue... if you need a lot of hot water in a short time... 80 litres times 60 degrees (mixed with cold water) represents a greater heat reserve to be called on than 80 litres (not mixed with cold water).",
"TL;DR If the tank and pipes were perfectly insulated, and the heating perfectly efficient - the temperature of storage doesn't matter. In this less than perfect world... the lowest useful temperature is the best option."
] |
[
"If the tank and pipes were perfectly insulated, and the heating perfectly efficient - the temperature of storage doesn't matter.",
"That's a very good point, I never thought about it in that way. I think that's why I have felt so confused about the question."
] |
[
"Is the DWave machine a quantum computer or not? And how can they market it as a quantum computer if what it does isn't clear?"
] |
[
false
] | null |
[
"It is a quantum computer in the sense that it, at least in principle, uses quantum mechanical effects to compute. ",
"It is not a quantum computer in the sense that even if the machine were expanded to have infinitely many qubits, it is not believed to be able, even in principle, to solve all problems that could be solved by a classical or quantum computer (it is not \"universal\").",
"More correctly, there is evidence that it indeed functions as a ",
"quantum annealer",
", which is its intended purpose. It runs one particular algorithm to find the lowest-energy state of a particular set of systems (specifically, the classical ",
"Ising model",
" with a large range of magnetic fields and couplings). If the problem you want to answer can be rewritten as finding the lowest energy state of the Ising model with a particular configuration, then you're fine. If it can't be written this way, then you're out of luck.",
"To my knowledge (I'm not fully current on this) nobody knows if all problems can be transformed into such a quantum annealing problem, but it is strongly believed not to be the case.",
"I should also mention that D-Wave's annealer does not always get the answer right. For certain problems it almost always gets the answer right, and for some it almost always gets the answer wrong.",
"Also, in its current implementation, D-Wave is slower than the best-optimized classical computer. It is, to my knowledge, unclear if it could be improved so as to be faster (I mean this in the asymptotic sense).",
"Sources: ",
"D-Wave's paper",
" and ",
"this paper",
". Sorry, these are paywalled."
] |
[
"Yes, it's a quantum computer",
"There is zero evidence for that. And even if there was, it still wouldn't be a quantum computer, it would rather be a dedicated solver for a class of problems that isn't even proven to be hard."
] |
[
"It is a quantum computer in the sense that it, at least in principle, uses quantum mechanical effects to compute. ",
"I strongly object. Consider a gas tank filled with oxygen gas. Oxygen molecules are quantum objects, and the gas in the box \"computes\" things like temperature and pressure of the tank. Does this make it a quantum computer? I don't think so.",
"So far, the D-wave machine has failed to provide ",
" evidence of quantum behavior at large scale. They (i) haven't demonstrated entanglement to be present in their system, (ii) haven't demonstrated a speedup over classical algorithms, and (iii) haven't provided even just signatures of behavior which can't easily be explained with some classical model."
] |
[
"Did not know that there had been so many Nuclear tests. Could they be partly responsble for climate change?"
] |
[
false
] |
Is a map/video showing the sheer number of nuclear detonations that have occured since the 40´s. But i have never heard much about the enviromental impacts they could have had on the planet.
|
[
"Most of those were below ground, and the above ground tests would have produced a slight cooling effect due to kicking up particulates."
] |
[
"The ",
"largest nuclear test ever",
" released about as much energy as the sun imparts on the earth every second. Considering the sun has been shining for about 2*10",
" seconds since the first nuclear detonation, its energy is much, much greater."
] |
[
"The total energy of the nuclear tests may not be significant compared to solar irradiation, but there could be other factors that contribute to global warming.",
"There are instances of erupting volcanoes that lead directly to global cooling",
"However, since exploding bombs do not kick up as much matter as volcanoes eject and since the tests were mostly underground, it's safe to say that nuclear tests haven't significantly affected our current weather patterns."
] |
[
"How do cells know to grow into organized structures?"
] |
[
false
] |
When an animal or even a plant is growing, certain cells will develop in different areas to perform different tasks. What governs the cells ability to know what type of cell it should be and where it is within the structure? How do cells organize themselves into complex structures like veins for example? I'm assuming its an emergent process governed by simple-ish rules. I would sort of like to simulate this behavior in a computer, but I think I'm overthinking the rules governing a cells awareness of its location within the structure. Anyone have any ideas about this?
|
[
"This is rather complex, and the exact \"how does a cell know\" is very difficult to specify, but is mostly mediated by gene expression. I'll do my best to explain, but someone more versed in morphology might do better. When a zygote begins to divide and forms a blastocyst, a process known as gastrulation occurs, where a gastrula is formed. The cells form themselves into layers, called germ layers. Vertebrates have 3 germ layers, while invertebrates commonly have 2 or in the case of sponges, 1. Each germ layer develops different body tissues:",
"Ectoderm: Outermost layer, itself consists of 3 layers. It forms the epidermis of skin and its derivatives like fingernails, the brain and nervous system, eyes, teeth and others.",
"Mesoderm: Forms muscle, bone, connective tissue, dermis, vascular tissue (blood and blood vessels), urogenital organs like kidneys and gonads, lymphatic system, and more.",
"Endoderm: Forms intestines, most internal organs.",
"Now the process of ",
" these differentiate is mediated by intracellular and extracellular processes.",
"Intracellular: This is mostly modification of DNA for gene expression. DNA with its histone proteins is known as chromatin. Chromatin is packed due to its histone complex. Ligter packed chromatin that is transcriptionally active is called euchromatin. By modifying chromatin, the cell affects gene expression by limiting accessibility to genes to transcription factors. This is primarily done by methylation of DNA or histone deacetylation. For an example, ",
"muscle cell differentiation",
" is partially mediated by muscle-promoting transcription factors like MyoD and MEF. These factors are thought to help recruit chromatin modifying factors, such as histone acetyltransferases and deacetylases.By doing this, the transcription factors control access to their target sites upstream of muscle differentiation genes.",
"Extracellular: These are environmental cues, small molecules, proteins, temperature and oxygen. These can originate from the outside environment or from other cells. Other cells interact by sending and receiving secreted proteins, also known as growth factors, morphogens, cytokines, or signaling molecules. When these signaling molecules are received, they trigger intercellular signaling cascades that basically cause semi-permanent changes in transcription or expression of genes. This is thought to be the major factor in cell differentiation in embryogenesis."
] |
[
"There's no single answer across the whole body.",
"In some cases, such as during brain and spinal cord development, there are proteins produced from one side of a structure that can diffuse across the structure, and cells can \"read\" these gradients to determine what position they occupy. In the developing cerebral cortex, for example, the early identity of areas is determined by four overlapping gradients from the front, back, and sides of the developing cortex. Using these four gradients, a cell can determine its precise position within the developing brain. (See ",
"here",
"; unfortunately paywalled)"
] |
[
"So this is actually a pretty complicated process, which the ",
"Wiki",
" can give you a brief idea of.",
"To generalize though, there are two broad modes of interaction that can help determine cell fate, specifically external and external signalling. External signals can include things like ",
"Matrix Stiffness",
", or how \"hard\" the surface the cell is growing on, which can act as a que for cells. These external factors can also include molecular interactions, where chemical factors signal cell differentiation. ",
"Additionally, cells have internal signals that can determine cell fate, for instance small molecules inherited from the mother cell, called cytoplasmic determinants, playing an important role.",
"Additionally, cell determination is a ",
"stochastic process",
", meaning that there is some level of inherent randomness to the whole process, with cells actually specifically ",
"utilize this random behavior",
" to respond uniquely to their environment. ",
"This is really just the tip of the iceberg though, as the categories are very broad. Also, I would note that this is not an entirely closed question, as there is strong evidence to support that even things like ",
"electrical signals",
" between cells can play a role in cell's behavior, however these electrical interactions have not yet been fully detailed."
] |
[
"Will the current ebola outbreak in Africa be a threat to Africa's primates?"
] |
[
false
] |
In the past Gorilla's have been threatened and died to ebola viruses . How much of a threat is the current strand to the Gorilla (and other primate) population and is there anything that is done to quarantine endangered animals susceptible to these kinds of outbreaks?
|
[
"Interesting question, experts still aren't certain which species are hosts, although they believe the fruit bat may be a major player in the spreading of the virus, as to this strain, it's hard to say, no large animals have been reported dead from this recent outbreak, this strain of Ebola In particular doesn't seem to be as an efficient killer as past strains, which had a 90% fatality rate, this current one is closer to 55%. Also, contact of large primates with humans is rare, which makes them an unlikely candidate to either receive the virus through cross-species infection, and to be a likely cause for hosting the virus and thus spreading it to humans! I hope this helped."
] |
[
"Since the fruit bats may be the biggest offenders in spreading the disease, does this mean that ebola likes a sugary host? "
] |
[
"The short answer to that would be no, or not likely, I could be wrong but I've never read any journal on correlation between sugar and ebola homeostasis and or/survival benefits. The fruit bats fill a niche where they are likely to pick up the disease, it's worth noting that bats, are merely carriers of the disease, they do not die from it, so they can spread the virus for almost their entire life span, meaning vast population of the bats are infectious, it's not so much that their diets contain maybe more sugar than a lot of organisms, it's just that they're ",
". When a host of a virus dies, so does the virus, and so in the fruit bats case, evolution has played a role where the virus, through natural selection has become prevalent in this species. Other known cross species infections have been known to occur via canines and pigs too. "
] |
[
"At this point in time, are we able to simulate nuclear bomb tests by a computer with similar accuracy to a real life test? If so, are these test done as frequently as in the Cold War?"
] |
[
false
] | null |
[
"So the \"holy grail\" of nuclear simulation is to go from the subatomic scale all the way up to the macroscopic. That's like 15 orders of magnitude of distance from the femtometer to meter scale (even more so if you blow the nuke up!), with a ridiculous number of interactions that come into play, and huge amounts of turbulence and complicated instabilities that happen when you are talking about the temperatures and pressures in a nuclear weapon (in which neutrons can act like a solid and solid metals can act like gases). ",
"While supercomputing efforts of this sort did begin during the Cold War, they were accelerated in the post-Cold War when nuclear testing stopped. High-performance simulation is considered a major part of the \"stockpile stewardship\" program of the United States, allowing it to do a lot of simulation and prediction without actually blowing anything up. It does this not only from \"first-principles\" physics simulations, but also by incorporating \"codes\" derived from actual nuclear tests to bridge over the difference between theory and reality (some of these tweaks are amusingly called \"knobs,\" even though they are code-based). ",
"The exactly capacities of these are not disclosed, though the reports that have been released imply that they can simulate quite a lot of different types of things they might want to know about, ranging from \"what happens if we change this material in a weapon\" to \"what happens if we drop this weapon\" to \"what happens if we set this weapon off.\" Of course not all of this information needs to be done entirely by simulation; the US also does zero-yield (subcritical) nuclear testing, as well as hydrodynamics tests, as well as uses instruments like the National Ignition Facility (a massive laser fusion installation) to get information of relevance to these simulations.",
"I think the question that you'd want to ask is not \"can you simulate a nuclear test,\" but \"to what degree of accuracy and confidence can do you do so.\" Because you and I can simulate (very poorly) a nuclear test using just our own laptops, if we are willing to have a significant amount of error in our calculations. (The first computer codes for simulating things like processes inside an implosion bomb, or fusion burn, were developed in the 1950s.) What differentiates the professional simulations from the amateur ones are the amount of fidelity, incorporation of test data, and confidence in the models. But this is exactly the sort of thing that is not easy for the people who make these simulations to publicly talk about. ",
"Separately, I would just point out that there is a social component to the question of accuracy and confidence. We can't easily \"check\" these codes, except by using past data — which has its limits. When you use such codes to develop new innovations, how much confidence can one have in them, without testing? There's no absolute way to answer this question, and at different times and places, this kind of uncertainty has been wielded to different ends. (The fact that the US has only ",
" tested a fully \"mated\" weapons system is a similar sort of location for uncertainty, if you want to look for it.) ",
"But we can say that considerable effort and resources have been expended on this, and that probably more has been expended on this in the post-Cold War than in the Cold War. But it isn't the same thing as doing a nuclear test in the Cold War; the nuclear tests in the Cold War were experiments of different sorts, whereas a simulation is something a bit different."
] |
[
"I mean a system in which you've got a live warhead on a live missile. There was only one of those — the Frigate Bird test."
] |
[
"It's not a stupid question. The degree of confidence you require is not a technical answer, it's a question of values and strategy. Some countries have tended to want a ",
" of confidence that they know what would happen in the event of a nuclear war — the US is historically sort of obsessed with this, and desires extremely low chances of failure, to the degree that it redundantly targets in a way that produces overkill (because if you think there is a 20% chance of any given target not getting destroyed, then you can get your destruction chance up there by just aiming more missiles at it). The Soviet Union/Russia tend to be more tolerant of the chance of some failure, knowing the whole thing is still likely to be bad enough to \"do the job.\" What's the right approach? There's no technical answer here — it comes down to what you're willing to tolerate, to spend, to improve-upon. ",
"For countries without large arsenals, like North Korea, there is anxiety that their enemy nations might not believe that their nukes would work. If that was the case, then their deterrent effect would be decreased if not eliminated. This doesn't require microscopic interactions to know, but doubt (whether external or internal to a country) can very hard to dispel! ",
"Fears that \"maybe our nukes won't work\" are why the US tested a full-system submarine-launched missile in the 1960s, with a nuke onboard — a very dangerous exercise. Even after they did it, there were people who said, \"well, you showed us that ",
" of them works... to know the whole system would work, we'd need more tests...\" You can see how this ultimately can be impossible to resolve if a given party is intent on being a skeptic."
] |
[
"If I eat two days' worth of calories, then the next day eat nothing, what are the effects on my body?"
] |
[
false
] |
Lets say I eat 5000 calories one day, then I fast the next day and eat nothing. How does that compare to eating 2500 calories each day? Is it any worse on my body/health? Thinking about things in the food like carbohydrates, salt, fat, etc - do they absorb at different rates? I wonder if a lot at once is better/worse than a moderate amount twice.
|
[
"OP specifically mentioned a two day experiment and wanting to know what happens. This is neither unhealthy nor the beginning of a Binge eating disorder outbreak. And using the word starving for not eating one day makes it worse. ",
"A healthy body will be able to store vitamins, minerals, etc for more than a day (I am thinking weeks but I haven't verified storage capacity for every essential nutrient). So nothing will really happen. You may be hungry the 2nd but that is about it. "
] |
[
"OP specifically mentioned a two day experiment and wanting to know what happens. This is neither unhealthy nor the beginning of a Binge eating disorder outbreak. And using the word starving for not eating one day makes it worse. ",
"A healthy body will be able to store vitamins, minerals, etc for more than a day (I am thinking weeks but I haven't verified storage capacity for every essential nutrient). So nothing will really happen. You may be hungry the 2nd but that is about it. "
] |
[
"No source here, just regurgitating information from a human nutrition course. It takes months to years to develop vitamin deficiency assuming a specifically nutrient-void diet, depending on the vitamin of course. "
] |
[
"How can you estimate the temperature of an arc discharge in air generated through high-frequency AC?"
] |
[
false
] |
Hi everyone. I'm wondering if it is possible or if there are methods to estimate the temperature of a plasma generated from an high-frequency arc discharge in air, like arcs generated from an arc lighter. Would it be dependant on the frequency, the distance between the electrodes or other things? The closest thing I found is related to the concept of electron temperature, but I haven't found any clear way to compute it. Thanks for your help and have a nice day! Edit: it would be in order to build an arc furnace capable of reaching temperatures up to 2100°C, to melt corundum
|
[
"An important thing to consider in these types of plasmas is exactly what you mean by \"temperature.\" A plasma includes, at the very least, very light electrons and heavy ions. These populations do not exchange energy with each other very easily so they are often at very different temperatures. In most low temperature plasma physics, we are interested in the temperature of the electrons (Te) rather than the ion temperature. ",
"Measuring the emission spectrum would only give you the ion temperature. (and you have to be careful since it is certainly not a black body.) To measure the electron temperature, you would want to use a double or triple Langmuir probe or some other form of energy analyzer.",
"As for estimating from theory: In partially ionized plasmas (plasmas where there is a significant population of neutral atoms that haven't been ionized) your electron temperature is generally limited to a few eV and your ion temperature is not much above room temp. If you add more energy (turn up the voltage etc.) you will actually not make it much hotter but instead increase the density (by ionizing more neutral atoms). This is because, if The electron temperature were to increase, you would have exponentially more electrons with enough energy to cause ionization (these energies are generally in the 10s of eV). The ionization collisions cool the electron population and increase the plasma density. ",
"If you want to make a more concrete estimate, you'd have to look into the cross sections for ionization collisions and estimate where equilibrium would occur. But it is going to be a complicated process and there are a lot of effects I've left off like non-thermal populations, e.g. the energy in the bulk electron motion due to the accelerating voltage."
] |
[
"The simplest way is to look at the emission spectrum and compare it to ",
"black body radiation",
"At lower temperatures you can tell the temperature by just finding the right colour on something like ",
"this chart",
". Arcs are generally hot enough that you'd struggle to tell the difference in colour, even if your monitor is calibrated to represent the colours accurately, but ",
"this chart",
" probably includes the right range..."
] |
[
"For a somewhat less simple but more quantitative option, you can make a papercraft spectrophotometer (usually based on a CD as a diffraction grating). Some versions are designed to attach to a phone, in order to record the results.",
"Example",
"."
] |
[
"Does counting \"one-one thousand, two-one thousand...\" after seeing a flash of lightning until you hear thunder actually give you a good estimate how far away you are from the flash?"
] |
[
false
] | null |
[
"Sound travels 1 mile in 4.7 seconds (or about 1 km in 2.9 seconds). We can round them up to 5 seconds and 3 seconds, responsively. If your counting of \"one-one thousand, two-one thousand...\" is a good approximation of a second (and that's why we add the extra \"one thousand\"; to force a pause in our speech of roughly the right amount of time), then you can take the number that you count up to, and divide by 5 to get the distance in miles, and divide by 3 to get it in km. ",
"Your results will vary based on how closely your counting matches up with actual seconds, your reaction time (how soon after you see lightning do you start counting, and how soon after you hear thunder do you stop), and I suppose also on weather conditions, which will have some negligible impact on the speed of sound. And of course, our rounding will introduce some error as well."
] |
[
"Follow up question: Why does a thunder clap last longer than a lightning flash??"
] |
[
"My first thought was \"Doesn't the vertical distance of the lightning matter?\"",
"Then, I realized something profound - the fact that lightning stretches from the ground to the sky completely explains why the sound of a thunderbolt persists over a few seconds, rather than being an instantaneous CLAP. The sound of the thunder emanating from a few kilometers above ground would take longer to reach our ear, which would totally account for why the sound is smeared over time."
] |
[
"[META] Bots and AI tools on r/askscience"
] |
[
false
] |
Over the past few days we have seen a surge of accounts using bots/AI tools to answer questions on . We would like to remind you that the goal of is to be able to provide high quality and in depth answers to scientific questions. Using tools like GPT-3 chat not only do not provide the kind of quality that we ask for but they are often straight up wrong. As with all bots on this subreddit any account using those tools on will be and banned.
|
[
"Usually the comment will restate the question, for example if you ask \"is water wet?\" the comment will contain \"Researchers say that water is wet because...\". The comment also often doesn't really answer the question or contain any actual information. ",
"Those bots are also often posting way too much, too fast and on too many topics to be an actual human.",
"Obviously this is not foolproof but so far we have not had any false positives on bans."
] |
[
"I had no idea that this was happening. Are there any post characteristics that we can keep an eye out for that would point to an account using these tools?"
] |
[
"Ai is ruining every sub. Low effort ai art also constantly floods fan Reddits."
] |
[
"What would happen on the outside of a spinning spacecraft?"
] |
[
false
] |
I understand the physics of centripetal force creating a sense of gravity (inside of a spinning spacecraft, for instance) but I could never figure out what would happen to a person standing on the outside of the craft.
|
[
"Take a single point attached to the outside edge of the object, as if you were following it in time. Now, at any instant it will have a given velocity that is tangent to its rotation. For example, if the spacecraft is circular the velocity would be tangent to the ship. The centripetal force causes this point to accelerate in a manner that continuously changes the velocity so it remains tangent to the rotation. Now in the first case you discuss, being inside the vessel, the centripetal force would be acting on you just as it is the point attached to the outside of the ship. Thus, you would accelerate in the same manner.",
"Now, imagine the part of the ship you are standing on that is exerting the force on you to cause the acceleration disappears. At that instant, you are going to continue with the velocity you were at in that instant of time, with no acceleration. This is the same concept as it would be if you were on the outside of the ship with no barriers to force you to turn with the ship.",
"TL;DR: You would blast off the ship. Pun most definitely intended."
] |
[
"You could have them wear magnetic space boots to keep them held on!"
] |
[
"That sounds very very bad. Well, there goes an entire chapter from my short story. No spacewalks on generation ships, apparently."
] |
[
"When you lose a pound, how does it get out of you?"
] |
[
false
] | null |
[
"Mostly through your breath, the remainder through urine."
] |
[
"A lot of that is water weight, the permanent weight loss is almost all through your breathe (CO2). "
] |
[
"A lot of that is water weight, the permanent weight loss is almost all through your breathe (CO2). "
] |
[
"Do negatively charged phospholipids affect the resting membrane potential of a cell?"
] |
[
false
] | null |
[
"We're getting right to the edge of my knowledge here, as surface charge is a pretty esoteric area these days. But my understanding is essentially: no, but it depends. Specifically, if you think of the resting membrane potential as something that is the property of an entire cell, e.g. this cell is at -70 mV, then the surface charge of the membrane has essentially no bearing on this. However, if we zoom right up to the membrane, then we see that surface charges have a big influence, but it only occurs on a very small spatial scale.",
"Specifically, the negative charges that exist on about a quarter of the membrane lipids, of course, have a large influence on the electric field in the peri-membrane area. So at the actual surface of the membrane, the electrical potential is 50 mV less than the bulk fluid. However, this effect falls of very rapidly, and within a handful of nanometers the potential is equivalent to the rest of the cytoplasm/extracellular fluid."
] |
[
"Well when it comes to Neuroscience textbooks, the go to should be \"principles of neural science\" by Kandell Schwartz and Jessel. \"Ion channels of excitable membranes\" probably has a chapter or two of use. But one that will get to this level of depth? I'm not sure. I would reckon most text books will stick to \"potassium goes out, membrane potential goes down\"."
] |
[
"Well when it comes to Neuroscience textbooks, the go to should be \"principles of neural science\" by Kandell Schwartz and Jessel. \"Ion channels of excitable membranes\" probably has a chapter or two of use. But one that will get to this level of depth? I'm not sure. I would reckon most text books will stick to \"potassium goes out, membrane potential goes down\"."
] |
[
"What is infrasound, and how was it used to estimate the size of the Russian asteroid?"
] |
[
false
] |
How useful was any of the other evidence accumulated (videos and damage reports) in estimating the size?
|
[
"Infrasound is just a word used to describe very low frequency sound waves (below 20 Hz). They propagate just like normal sound waves, but carry further because atmospheric losses increase with frequency. As a result, you can measure these waves very far away with great accuracy, with the right equipment.",
"Because the waves carry so far, infrasound measurements are used as part of a network of sensors, including seismic and satellite data, to enforce the nuclear test ban. Since they have done a lot of tests and measurements, they can estimate the size of an explosion based purely on the sound energy received. Since explosion size is based on kinetic energy, and assuming you can estimate the velocity, you can back out the mass. Using the mass and composition, you can find the average diameter.",
"That said, I don't have hard data or a report on the methods for the estimate, but this is my educated guess as an acoustician."
] |
[
"Infrasound are low frequency sound waves (20 Hz and under). At this range they can penetrate further through the Earth so are often used for stuff like earthquake monitoring.",
"As to how specifically it was used for the meteor strike, I do not know."
] |
[
"Could this or could this not be used with the right amount of sensors to monitor any combustion reaction of a certain size within the atmosphere?"
] |
[
"What do \"tangent,\" the trigonometric function, and \"tangent\" the line that intersects a circle at one point, have to do with each other?"
] |
[
false
] |
Also, how do a secant in trig and a secant on a circle have to do with each other? I am doing trigonometry in school right now and I was wondering what the relationship between the two were.
|
[
"The tangent is the length you get when you project an angle onto the tangent line in a specific way. Here's a drawing of the tangent:\n",
"http://upload.wikimedia.org/wikipedia/commons/c/c7/Tangent-unit-circle.svg",
"If you have a secant of length 1 on a circle, and you draw the diameter at one of the end points of the secant, then the diameter of the circle will be the secant of the angle the diameter forms with the circle. I'll see if I can find a drawing.",
"Edit: Apparently this is the history.",
"from: ",
"http://mathforum.org/library/drmath/view/52578.html",
"\n\"... \nSECANT comes from the Latin SECANS, the present participle of SECARE, \"to \ncut.\" In other words, it means \"cutting.\" It was originally applied to \nthe line segment OB in the figure - the line that cuts off the \ntangent. The ratio of the secant OB to the radius OA is the SECANT of \nangle AOB. ...\""
] |
[
"The inverse tangent function maps slope (derivatives) to angles. The slope of a tangent line is (the limit of) d",
"/d",
" = ",
"'(",
"). The angle this line makes with the horizontal axis is arctan d",
"/d",
" = arctan ",
"'(",
").",
"The secant represents ",
"this length",
". I don't think it has such a deep connection to secants of the unit circle. Maybe it's so simple that both names stem from the latin root ",
" (to cut).",
"Edit: Thanks Swiss person."
] |
[
"This small collection of gifs helps make trigonometry more intuitive, at least to me. The last one is most relevant to your question, but I find them all useful.",
"http://www.businessinsider.com/7-gifs-trigonometry-sine-cosine-2013-5",
"EDIT: ",
"Imgur",
" link instead."
] |
[
"Are neurons in the brain simply put just complex multi-function logic gates, or does their function go much deeper than that?"
] |
[
false
] | null |
[
"Good question.",
"It is certainly very tempting to conclude that neurons, generally, yes. But of course, you need to extend the metaphor, as a neuron doesn't just have two inputs, it (usually) has thousands (though numerous classes on have 1-4). And of course, it isn't just any two inputs (usually speaking again) so it's like a massive \"AND\" gate and the \"AND\" is when a certain percentage of the inputs are active, not all of them...",
"And then you need to put in a few inputs capable of shutting down output, kind of like putting an inverter running into an AND gate, but of course it isn't a simple any gate.",
"And then it appears that in certain neurons, areas that are close together form individual computation units, e.g. you have one AND gate (though like I said before, with 100s of inputs and a threshold) and then it's output connects into a hub, with lots of others of the AND gates, and this hub is a giant OR gate.",
"And then you get to a point where you realize you've bastardized the original metaphor to such a degree you should kind of just stop."
] |
[
"Depends on exactly what you mean by input. It also depends hugely on the cell type in question. I just published a paper showing that in a particular cell type, all input, no mater where it comes from in the cell, is the same size once it gets to the cell body. So, so long as you exclude inhibition, you should be able to measure the spiking rate, and a few properties of the cell, and have a good idea how many input signals (EPSPs) it received.",
"However, there are other cells types where some inputs are much smaller than others. Hence you could never tell whether it received one big one, or 5 smaller ones. Combined with non-linearities, it'd be impossible.",
"But if you wanted to know exactly which cells provided the input, rather than just knowing how many there had been, that would be extremely difficult in nearly all cell types."
] |
[
"Neurons certainly aren't literally a gate. But then, neither are any physical logic gates. They are only logic gates if used correctly. Or put more generally, there are certain regions within the parameter space that the abstraction of the circuit to a logic gate is legitimate. It could very well be the case that a ",
" statement could be made about neurons (but more like the linear combination + activation function as shown in the diagram).",
"It is certainly possibly to simulate the behaviour of even a very complex, non-linear neuron very accurately. And by and large there is no non-deterministic behaviour. THAT SAID, there is certainly space for large amounts of behaviour which is practically non-deterministic. That is to say, ion channels opening and closing, neurotransmitters binding and unbinding is very 'Brownian'. Could true quantum uncertainty come into play? Certainly, though to what extent, I honestly don't know, but I have no issue with the notion that they do to some extent effect the behavior of the brain over a long enough time course. But on a practical angle, if we knew the state over every neuron at t = 0, we could not predict the behaviour of every neuron at some arbitrarily distant time point, because of the 'brownian' effects of ion channel opening/close... ligand binding/unbinding. And this source of \"noise\" almost certainly outweights and noise due to quantum sources."
] |
[
"You shoot a bullet out of the back of a jet. Does the bullet fall flat?"
] |
[
false
] |
If I'm standing on the tail of a jet facing its trail and fire a bullet, from my point of view it will travel at normal bullet speed away from me, right? To someone on the ground, would the bullet appear to fall flat? This makes the assumption that jet speed = bullet speed.
|
[
"Yes. ",
"Video of experiment."
] |
[
"Yes, basically that is exactly what would happen."
] |
[
"You'd also be hurt by the acceleration. In the video, the ball is going from rest to 60mph in a split second. Think of how bad you would be hurt if you went from 60 to 0 in that amount of time. It would be like crashing into a brick wall."
] |
[
"What is happening on a circuitry level when I turn the brightness up or down on my phone?"
] |
[
false
] | null |
[
"For LCD screens the LED backlight is set to a lower PWM duty cycle. Instead of being on 100% of the time, it'll flash on and off, spending some time off (more time off = darker). ",
"LEDs are funny; you can technically control their brightness by controlling the voltage/current, but tiny changes in electricity can lead to large, very obvious changes in brightness. On top of that individual LEDs will have different response curves and will look very different brightnesses at a give voltage/current. The fundamental problem is that LEDs really only want to be on or off. If you put them all to on, the differences in brightness are much harder to see. If you toggle them on and off fast enough, the flicker is totally undetectable. They turn on/off thousands of times per second. This method is totally digital so it also requires no external circuitry, like a digital->analog converter would. It lets you control brightness incredibly well. ",
"OLED screens and simliar just change their own PWM."
] |
[
"It’s not the frequency which is changed, it’s the duty cycle (i.e. how long it is on and off during each period)"
] |
[
"Assuming your display is LED based, the brightness adjustment is most likely a pulse width modulated(PWM) signal. A PWM (in this context) is a square wave that changes in frequency. If the frequency is fast enough it is effectively always on; if slow enough it is effectively off. LED dimmer often use PWM to introduce a flicker into the output of the LED. The greater the flicker, the dimmer the LED as it spends more time off. ",
"The adjustment input on LED screen modules apply the PWM flicker to all the LEDs in the screen. "
] |
[
"Does the rule preventing homosexuals from donating blood make any sense?"
] |
[
false
] |
Many countries ban homosexuals from donating blood, presumably due to AIDS, but does that rule actually save more lives than the ones that would have been saved if homosexuals were allowed to donate? or is that rule in place due to homophobia?
|
[
"Yes, it does, from an administrative perspective. ",
"The numbers can be googled, but I'll limit myself to describing the principle. The target is having less then x% chance of a disease being transmitted through blood donations, say one in 100k. You know the incidence of the diseases you're interested in is higher in the general population, maybe one in 20k. So you need ways of decreasing it.",
"Among many other ways of accomplishing it is to take easily distinguishable subgroups from the general population and look at their statistics. There is at least one source that mentions about 50% of new HIV infections as occurring by same-sex sexual contact. If the percentage of homosexuals in the general population is about 10%, you can eliminate those 10% and get from an incidence of 20k to 30-40k. That's a deal well worth making.",
"Of course, there are other ways to get to the desired result, but in the end it goes to efficiency. If by giving up 10% of blood donations you can half your screening costs, then if would be illogical not to do it. It's not homophobia, it's simply good management."
] |
[
"The rule is in place to save lives, because gay men are at a higer risk of getting HIV, and since gay men make up a rather small amount of the population, it is safer and easier to just exclude them from donating blood.",
"http://www.thebody.com/content/art13321.html",
"\nThis article is okay, search for \"What to Do About Gay Men\" for the tl:dr.",
"Also, ",
"http://www.guardian.co.uk/world/2011/sep/08/gay-ban-blood-donation-lifted",
" gay men again allowed to donate, because screenings got more effective. This is if they have not had sex with another man in 12 months (same category as prostitutes and people who has slept with prostitutes). "
] |
[
"Please check out the ",
"window period.",
"It is possible to be infected with a disease, yet test negative even with our 'superior screening'."
] |
[
"Why is there such a high rate of leukemia for children?"
] |
[
false
] |
I've read a statistic that says one third of cancers for kids below the age of 14 are leukemias. Why is that so and why does this rate change when you grow up?
|
[
"Children have a very low rate of all cancers, including leukemia: most cancers are caused by accumulated damage from lifelong exposures (e.g. smoking, obesity, sunlight) and children haven't yet racked up much exposure. However, it's not as clear what causes most leukemias, and it doesn't seem to be mostly exposure-driven, so the age effect is not so strong."
] |
[
"Yes. ",
"Leukemias are most common in middle age: see here: ",
"https://seer.cancer.gov/statfacts/html/images/age_distribution/Age_Dist_New_Cases_Site_086_Sex_0.png",
"Unfortunate that they don't have a population-corrected graph: I suspect the rate rises throughout adulthood, but the population also shrinks.",
"But there is a second peak in childhood, which presumably reflects genetic causes."
] |
[
"I think the genetic causes are mostly due to chromosomal translocations that can occur during embryonic development. So children can be born with a predisposition to leukemia. Since translocations are common in leukemias (blood cancers) and sarcomas (cancers of connective tissues), but not as common in carcinomas (cancers of epithelial origin), then leukemia and sarcoma are relatively common in children, despite the fact they are not old enough to have accumulated years of genetic damage."
] |
[
"Why is the brain split into two?"
] |
[
false
] |
So why is the brain split into two sides instead of being a singular mass of tissue? I understand that separate parts operate different cognitive and behavioral functions. What I want to know is why we actually have two visible physical hemispheres rather than being a single mass.
|
[
"Well, ultimately it is a product of our bilaterality and need for specification, the wiki on lateralization is pretty awesome:",
"http://en.m.wikipedia.org/wiki/Lateralization_of_brain_function",
"The two hemispheres are something that Pre-dates us for quite a bit:",
"http://www.scientificamerican.com/article.cfm?id=evolutionary-origins-of-your-right-and-left-brain",
"If you are still curious there is a really cool nature podcast that explains what happens when your brain looses the side to side connection (so when you have a fully effective split-brain).",
"http://www.nature.com/news/the-split-brain-a-tale-of-two-halves-1.10213"
] |
[
"And adding to this: the brain's computation occurs in the surface of the brain, which is heavily wrinkled to maximize the neuron count. The fact this structure is chosen rather than some other is probably an evolutionary accident, but since surface area is important, we have this wrinkled organ."
] |
[
"Well no. The sphere has the lowest possible surface area for a given volume. If you accept as a given that surface area is important for brain, then the smooth, spherical brain would be the worst possible choice for a given volume."
] |
[
"What caused dinosaur evolution to lead from larger terrestrial animals (dinosaurs) to smaller flying ones (birds)?"
] |
[
false
] | null |
[
"The stuff about atmospheric oxygen is bullshit. We all read that in Jurassic Park, but it's simply not true. Dinosaurs appeared in the Triassic and became dominant in the Jurassic, but the atmospheric oxygen was actually LOWER then than it is today. See ",
"this graph",
", where you can see that the peak was during the Carboniferous period, before the Permian-Triassic extinction event that started the Mesozoic era. It's pretty clear that the dinosaurs appeared at the ",
" of oxygen levels over the past several hundred million years, and those levels have in fact been climbing since then."
] |
[
"Thanks, I didn't know this"
] |
[
"One notable feature is the extinction event which ended the Cretaceous period, and all non avian dinosaurs. Theorized to be an asteroid event, the suspected resultant obscuring of sunlight would have led to a decline in photosynthesis, and thus a major collapse in food chains which would seriously afflict large animals that require far more food to sustain themselves.",
"However, while dinosaurs were prevalent, there were both large and small dinosaurs."
] |
[
"How do reflective surfaces (like a mirror) differ physically from non-reflective surfaces? What makes them reflect light?"
] |
[
false
] | null |
[
"Reflective surfaces are generally smooth on their surfaces and this allows light rays to reflect at mostly the same angles (uniform reflection). When the reflection of light is uniform, and when they enter your eyes, your brain is able to form back the image as it perceives light rays to be straight. \nOn the other hand, non-reflective surfaces are usually rough or have uneven surface. (Even paper have uneven surface seen microscopically, hence it is non-reflective) The roughness causes scattered reflection, where light rays are reflected at all the different angles. Hence, only minimal amount of light rays from the object can enter your eyes and even if so, they are in different angles. Therefore, the 'image' is diffused and scattered, causing no image to be formed. "
] |
[
"So virtually anything could be a mirror if you had the means to smooth it out?"
] |
[
"If you rearrange the structure at that level, is it still the same thing?",
"If you went through a paper shredder, would you still be you?"
] |
[
"When I'm driving steadily up a hill, what's going on in my car's engine?"
] |
[
false
] |
Let me see if I can be more specific. My car is an automatic, 4-cylinder, gasoline model, and a bit under-powered. When I approach a large hill, I begin pressing more on the gas pedal to open up the throttle. If I do this slowly, I am able to pretty much maintain steady speed up the hill without causing the car to downshift, which would cause the RPMs to increase. I can keep the RPM needle steady while pushing the pedal down quite far while going up a significant hill. What I'm wondering is, if I depress the pedal like this and the car doesn't decide to downshift, is the engine burning more gas even though the rev counter doesn't change?
|
[
"if I depress the pedal like this and the car doesn't decide to downshift, is the engine burning more gas even though the rev counter doesn't change?",
"An engine's fuel consumption doesn't depend solely on engine speed. So if you're asking if your car burns more fuel when going up the hill than on a flat, the answer is yes. You can increase the load and throttle, and end up with the same engine speed."
] |
[
"Yes. The car's engine time specific fuel consumption is the product of only two things, the speed of the engine in RPMs, and the amount of fuel injected per cycle. By depressing the pedal you are doing 2 things (when the car does not downshift), first it opens the throttle a adjustable plate that covers the air intake to the engine. This causes the engine to be able to more easily pull in air, reducing the vacuum behind the throttle body. This causes more oxygen to flow into the cylinders. At the same time the car will add more fuel to each injection cycle, by increasing the length that a solenoid is open. This is to keep the ratio of fuel to air about the same. (This is very complex and it will actually enrich the mixture as you apply the gas more).",
"\nSo what is happening in your case is that the RPM is not increasing, however the amount of fuel per cycle IS increasing and this causes a greater expenditure of fuel per mile, and an increase in torque.",
"When the car downshift the RPMs go up AND the fuel per cycle may go up or down. In general downshifting will cause a greater amount of fuel to be used when going up hill, but this may not always be the case depending on the electronics controlling the car."
] |
[
"When you go up a hill the road load increases (kW) To maintain speed the engine output must increase. This takes more energy, I.e., fuel. The transmission and drive ratio mechanically link the engine speed to wheel speed. So when the road load kW increase the engine torque must increase, since engine speed is fixed by the drive ratio. More engine torque requires more fuel, which is supplied by pedal demand. If the engine cannot produce sufficient torque (tongue times engine speed = power in kW= road load) then the transmission downshifts to change the ratio of engine speed so that a lower engine torque can be used to generate the same power to meet the road load (power = forgive x engine speed). Downshifting and or increasing engine fueling enabling sufficient engine power for the road load demand."
] |
[
"If everyone frequently washed their hands how much would the spread of disease be stopped?"
] |
[
false
] |
[deleted]
|
[
"umm... Source? (for pretty much the whole thing.)",
"For example this statement",
"antimicrobials will selectively breed microbes to resist them, until you get nasty, nasty shit like MRSA becoming more and more common",
"Is false. Bacteria such as MRSA came from the incorrect usage of antibiotics, not from washing hands."
] |
[
"If everyone washed their hands very regularly, before and after every meal, and didn't touch their face without having washed their hands first, would disease still spread as much from person to person?",
"http://www.sciencedirect.com/science/article/pii/S0140673605669127",
"Here is just one study that suggests 50% less illness as a result of more frequent hand washing.",
"Pretty much all studies on the subject have found a lower incidents of disease when a person frequently washes their hands. I don't think that infectious diseases would be stopped because there are several different ways for pathogens to be transmitted.",
"It would, however, significantly decrease the number of incidents of disease."
] |
[
"http://en.wikipedia.org/wiki/Anthroposophical_medicine",
"Anthroposophical medicine is a complementary approach to medicine[1] that integrates the theories and practices of modern medicine[2] with homeopathic medicines, physical and artistic therapies and biographical counseling.[3] The medical approach has its foundation in a spiritual-scientific understanding of the human being[4] that regards human wellness and illness as biographical events connected to the body,[mind] and spirit of the individual.",
"I'm sorry but that is not a scientific source."
] |
[
"Why are cats able to develop on their own but people are not?"
] |
[
false
] |
Taking into account the feral child case ( ), where a child was deprived from human interaction for thirteen years, and once freed was incapable of ever catching up to where a normal 13 year old would be with speech, or even however old she is now. Also, she was incapable to walk normally from what I've learned (had a more animal approach to walking). But when you see cats they all have the same abilities of "talking" which I guess would be a meow? Why is this? I guess an obvious answer would be that they are with their mothers for a little while when they are first born, but later in life when they live on their own they pick up the same habits as a wild cat or any cat that lives with a family for at least a little while. I guess this could be interchangeable throughout the different species of animals. Tagging this psychology because I don't know what else it'd be
|
[
"Humans are a highly ",
"altricial",
" species. \"Altricial, meaning \"requiring nourishment\", refers to a pattern of growth and development in organisms which are incapable of moving around on their own soon after hatching or being born\". The amount of energy, time and knowledge gained required to be able to live on ones own varies between species. In some species, as soon as the young are born they are able to do everything that the adult can, some are even born sexually mature. These species are highly ",
"precocial",
". So that there is a spectrum, and humans are at one extreme where our infants require a lot of time and energy investment to grow in order to be able to function on their own. ",
"In terms of language aquision there is thought to be a ",
"critical period",
" in humans (and other social species) where if they are deprived of conspecifics they will fail to develop the full repertoire of sounds made by that species. \"In general, a critical period is a limited time in which an event can occur, usually to result in some kind of transformation. In developmental psychology and developmental biology, a critical period is a phase in the life span during which an organism has heightened sensitivity to exogenous stimuli that are compulsory for the development of a particular skill. If the organism does not receive the appropriate stimulus during this \"critical period\", it may be difficult, ultimately less successful, or even impossible, to develop some functions later in life\". Which basically explains that certain behaviours, knowledge or skills are very difficult or impossible to learn later in life because there is a \"critical period\" in which they must be learned in order for them to be mastered. The same concept has been applied to language acquisition. The idea states that after some time, once the growing stage is mostly over and the brain is more or less fully formed, it becomes very difficult for people to learn language. The age old adage \"You can't teach an old dog new tricks\" applies here. We have seen the same applied to other animals, like birds, who cannot learn to sing the songs of their species if they are not exposed to them when they are young. They may learn the songs partially, but compared to others who have been exposed to the songs at younger ages their songs come out all wrong. It may be harder for them to find mates, or retain a territory. ",
"As you can imagine it is very difficult to get appropriate ethics clearance on experiments which deal with depriving animals of certain stimuli. A series of very inhumane experiments took place where they deprived newborn ",
"rhesus monkeys",
" of their mothers and instead replaced them with either wire mothers or cloth mothers. Those infants without mothers failed to develop and thrive despite being provided all the necessary nutrients etc. As a consequence these infants suffered severe physiological, emotional and social issues. \"Confirming the existence of a critical period for a particular ability requires evidence that there is a point after which the associated behavior is no longer correlated with age and ability stays at the same level. Those who are exposed to the stimuli after the critical period should perform significantly worse than those who were exposed to the same stimuli at the appropriate time. Some experimental research into critical periods has involved depriving animals of stimuli at different stages of development while other studies have looked at children deprived of certain experiences due to illness (such as temporary blindness), or social isolation (such as feral children). Many of the studies investigating a critical period for language acquisition have focused on deaf children of hearing parents.\" "
] |
[
"You assume talking and walking upright is innate. Or is it culture?",
"(I'll let the actual social scientists take over from here.)",
"As an aside: cats meow to communicate with humans, not each other. See: ",
"http://en.m.wikipedia.org/wiki/Cat_communication"
] |
[
"You assume talking and walking upright is innate. Or is it culture?",
"That's an interesting one. It's innate for humans to talk and walk upright given a normal environment. But a part of a normal environment is having other humans around, and so, eg, what language you wind up speaking is culturally determined. ",
"It's kind of like asking if children growing taller is innate or due to food. It's innate for a child to grow taller, but it also isn't going to happen without food."
] |
[
"How does being blind at birth affect someone's sexuality?"
] |
[
false
] | null |
[
"I am legally blind (with a guide dog) and I'm studying psychology at a university. Unfortunately I don't think there's much research on this topic, but I've read some books about disability and sexuality and I think the other stimuli from someone (voice, the way their body feels, personality) is what attracts most blind people. I have some partial vision so my experience may not be the same as someone else's. I do not think it's possible, or recommended, to try and change someone's attraction to one gender over another. It's not just the appearance of someone's gender that can be attractive, blind people still understand the IDEA of what is male or female and can most likely determine their sexuality that way. Even if you were willing to fiddle around with chemicals/hormones people still are what they are, that being heterosexual, homosexual, bi, etc., so no, I don't think you can trick a blind person into feeling a certain type of attraction. ",
"For me, I am most attracted by the way someone's body feels. This may seem like a difficult way to determine if you like someone, but remember, I have some partial vision, so I can make out someone's shape/build. For a totally blind person they would probably rely on voice and personality in the beginning, but I'm sure tactile info would also play a large role. Smell is also really important. If I like the way someone smells that means a lot. Honestly though, appearance is important even to blind people. My friends will tell me if a guy is cute or not and I know other blind people who have friends that do the same thing. That probably seems ridiculous but it does happen."
] |
[
"From Dick Swaab's ",
" (We Are Our Brain), page 89:",
"Even though it is said often that development after birth is influential to sexual orientation, the evidence is absent. Children that grow up with two mother or fathers do not have higher odds of being homosexual themselves. ",
"Page 88:",
"Twin and family research show that sexual orientation is 50% genetic, but it is unknown which genes are responsible. The other 50% derives from the development in the womb. Girls with higher testosteron levels in the womb have higher odds of being homosexual, and the chance of homosexuality with boys rises with the number of boys that came before them. Stress during pregnancy also increases the odds of homosexuality, through the influence of the mother's cortisol on the hormones of the child. ",
"This at least shows that you can't trick blind people into being attracted at a specific gender. ",
"I don't know much about the other factors in attractiveness. "
] |
[
"At risk of sounding crude and without much scientific basis... He can still TOUCH. He can still envision what a body looks like. Men and Women have different personalities, vocal traits, scents. The, uh, physical sensations of more intimate interactions would vary as well. There are more ways gender exists beyond SEEING. "
] |
[
"How many of an average human's genes are mutations?"
] |
[
false
] |
How many of our genes are not simply reshuffled from previous generations in whatever form was expressed in one of our parents? I suppose this would be something like average mutation rate per b.p. x average length b.p. length of genes x number of genes in genome, or is there something I'm missing?
|
[
"As arumbar points out, the human mutation rate is now estimated at around 1.1*10",
" mutations per base pair per generation. There are ~ 6 billion bases in a human genome, so that yields about 66 new mutations in every individual. Approximately 1.5% of the genome is coding sequence, so under the assumption that these mutations are distributed entirely at random (which is not an entirely air tight assumption, as we suspect that there may be some variation in mutation rate across the genome), then you're looking at about 1 genic point mutation per person per generation.",
"However, non-genic sequence is not useless. In fact, a large fraction of it is known to be involved in regulating gene expression, or non-coding RNAs, which likely have very important roles in the cell, but which we don't necessarily understand all that well. So it's not only the mutations in coding genes that matter.",
"Note that I'm only talking about point mutations (i.e. a single DNA base changes from a C to an A, or something like that). There are also going to be insertions, deletions and other rearrangements (and these are often responsible for certain genetic diseases), although I'm not aware of good estimates on rates of these sorts of mutations."
] |
[
"This paper",
" cites the mutation rate at ~1.1e-8 per bp per generation. Beyond that, it gets muddled because you don't know how the mutations are distributed (eg clustered in a few genes or distributed across many), and what types of mutations they are (eg silent vs missense vs nonsense)."
] |
[
"Thanks, but that's not what I was asking. My post title may not have been clear enough, but I think I clarified it in the body. How many new mutations are produced in an average individual?"
] |
[
"What's my brain doing? I've done this my entire life, it's involuntary, and I've never met anyone else who does it. (X-post from askreddit)"
] |
[
false
] | null |
[
"\"Medical advice is always off-topic and inappropriate. Please consult with a doctor regarding issues of health. Please do not ask for, listen to, or offer diagnoses, treatment advice, or personal medical opinions.\" ",
"Per Rule #4 in sidebar."
] |
[
"Not sure he's seeking medical advice. If you were to actually read the post and watch the video, you would see that whatever is happening does not negatively affect his quality of life."
] |
[
"I did both. I love being loosey-goosey with this rule, but the place where he says \"My plan is to see a Neurologist, assuming my insurance would make it affordable. But hey, maybe one of you knows what's up.\" Shows pretty clearly the intention is to get medical advice. He addresses his question to \"Neurology buffs hanging around.\""
] |
[
"How well do we really understand hieroglyphics?"
] |
[
false
] |
Are there older languages we understand better?
|
[
"There are still some graphemes that we don't know either what they do/mean and/or what sounds they might have represented. However, the vast majority of known graphemes across the recorded history of Egyptian's development are known to us. And we understand how they were used systematically. Namely, we know that they represented strings of consonents of length 1-3 with vowel phones becoming represented at a later stage as individual letters, along with the use of determinatives which had no pronunciation but were written after lexemes to differentiate them from homonyms, and we know of the use of various ideographs that were used in combination with all of the above rebically. ",
"There are no older examples of language that we know of that are attested, which is to say Egyptian was the first language in the world to have been written down (linguistically) as far as we're currently aware of. I'm speaking of the ",
"bone and clay tags found in the U-J tomb in Abydos",
" from ~5400 years ago. See ",
"Mattessich 2002",
" for more detail. I've answered your second question in the way that I have, because it involves a fallacy. Languages are not provably older than one another. They develop concurrently, and so all existent languages are theoretically equally as old as all other contemporaneous languages so long as language did not develop multiple times, which is something we can't currently prove or disprove. "
] |
[
"We have comparative evidence from (the descendant language) Coptic (older descriptions, when it was still alive, and its current ecclesiastical form), from related languages like Hebrew and Arabic and from reconstructions of their ancestors (cousins to Egyptian), and from renderings of Egyptian names/words in the scripts of contemporary languages."
] |
[
"But the answer to the question, isn't \"we don't know.\" The question doesn't make sense because it misunderstands how languages work on a fundamental level and therefore doesn't make sense as a question. "
] |
[
"What are the stains in my glasses when I look at the computer screen through them with sunglasses?"
] |
[
false
] |
When I look at the screen through my regular eyeglasses and sunglasses lens combined, I find out that there are stains in my regular lenses. What are they and are they harmful to my sight? Photos:
|
[
"Oh oh this is so exciting!!! This relates directly to my area of specialty!",
"First of all: they are not stains, and they are not harmful to your sight.",
"So light has a property known as ",
"polarization.",
" The following metaphor isn't perfect, but its good enough for now. The basic premise of it is this: You can think of light traveling through space like a wave rippling through a pond. The height of the wave tells you how strong the electric field of the light is. The electric field is what gives light the ability to slosh electrons around in matter, which is why pigments have color. The higher the wave, the brighter the light. (Incidentally, in this metaphor, the space between ripples tells you what color the light is, but it's not relevant for the rest of the explanation.) EDIT: In this metaphor, the direction of polarization for a ripple propagating through a pond would be vertical.",
"In general, any beam of light will have some polarization. Imagine a beam of light striking you directly in the eye. For the purposes of our discussion, the three options are horizontal, vertical and unpolarized (like the sun). You can think of unpolarized light as being a mixture of horizontal and vertical. Because of the way they are designed, modern computer monitors (like LCDs) emit polarized light. In your case, the direction of polarized light is the same as the direction you are holding your sunglasses. If you rotate the sunglasses 90 degrees, I'll bet you won't be able to see your monitor.",
"A polarizer is a type of light filter which prevents light which does not share its orientation from passing through. This allows you to take an unpolarized source and convert it to polarized light, though there are some losses involved since you're essentially throwing away the other light. This is how sunglasses work. Sunglasses are just polarizers. This is how they prevent glare from surfaces, for example. Light reflected off surfaces (like a lake) will tend to be horizontally oriented, so a vertically polarized pair of sunglasses can filter out the glare.",
"So, what's going on with your glasses? Because of the way they are manufactured, the material in your glasses has a certain amount of stress in it. You can also see this in your frame, which also appears \"stained.\" This stress is a normal part of the manufacturing process, and when taken to an extreme is why tempered glass can occasionally ",
"spontaneously shatter.",
" The result of this stress is that your glasses treat light which is horizontally and vertically polarized differently, which has the net effect of being able to rotate the polarization of the light coming from your monitor. Because the polarization has rotated, when you pass the light from your monitor which has traveled through your glasses through a your sunglasses (a polarizer), your sunglasses filter out the part of the light which has been rotated to have the opposite orientation.",
"The reason you don't see this effect in sunlight, or using room lights, is because those are (generally) unpolarized light sources, so the glasses by themselves are just rotating unpolarized light, which is still unpolarized."
] |
[
"Follow up question: Why are you using sunglasses to look at your computer monitor?"
] |
[
"Minor thing: sunglasses aren't universally polarized sunglasses. Plenty of sunglasses, especially cheap ones, are simply dark-tinted lenses without any polarization."
] |
[
"What is the largest a sun could possibly be?"
] |
[
false
] |
How large could a star physically be without collapsing upon its own weight? How large could one be with natural processes? What is the largest star we know?
|
[
"http://en.wikipedia.org/wiki/List_of_largest_known_stars",
"\"There are theoretical reasons for expecting that no stars in our galaxy are larger than approximately 1,500 times the sun, based on evolutionary models and the Hayashi instability zone.\"",
"\"UY Scuti is a red supergiant star in the Scutum constellation. It is one of the largest known stars by radius at 1,708 ± 192 solar radii,\"",
"http://en.wikipedia.org/wiki/UY_Scuti",
"Note that this is about largest stars, not ",
"heaviest stars",
"."
] |
[
"That is only for volume and the temperature assumption is only true for stars that have exited the main sequence. The opposite is true when a star is on the main sequence. The heaviest a star can be is thought to be ~300 solar masses. This is called the Eddington limit. The reason why stars can't be larger is not because they would collapse, but because they would blow themselves apart. In very large stars, the heat at the center from the pressure drives fusion so quickly that the solar wind blows off the outer layers of the star at an astonishing rate. The pressure at the center of even the largest stars is too small to violate the Pauli-Exclusion principle, forming a black hole. When the star exits the main sequence, after just a few million years, and eventually turns its core into iron, all fusion stops and this is when the star collapses due to the lack of the pressure from the fusion to counteract gravity. The material falls inwards and collides with the core fast enough to produce a black hole from the pressure, causing a hypernova and gamma ray burst. The largest stars often blow themselves apart before ever reaching this stage, leaving a radioactive cloud of gas as the only remnants of the star. "
] |
[
"The largest star that we know of (and that we have accurately measured the size of) is VY Canis Majoris, which is approximately 2000x the size of the sun. Put it in our solar system and it would extend past the orbit of Saturn.",
"As to the biggest possible, I'm not sure. I've seen a source that says that about 2500x the size of the sun is the limit for a red supergiant. The bigger they are, the cooler they are. I don't know, but I assume the problem is that if they get any bigger they'd be unable to sustain fusion."
] |
[
"What is Anaphylaxis and how does Epinephrine reduce the impact of an episode?"
] |
[
false
] |
I understand the why we have EpiPens, but I'd like to know the how it works too.
|
[
"Anaphylaxis is basically a very severe allergic reaction characterized by one or more of the following:",
"a very itchy rash, typically in the form of hives",
"vomiting",
"swollen tongue, throat, lips, eyes, or all of the above (also known as angioedema)",
"low blood pressure due to vasodilation",
"shortness of breath, stridor, or wheezing due to bronchoconstriction",
"a weak, rapid pulse",
"It typically presents within minutes of exposure but can occur up to 30 minutes after exposure. I've also read about instances happening up to 72 hours after exposure to the allergen, but this is very uncommon).",
"Epinepherine is a bronchodilator and vasoconstrictor. It opens up the airways, so it counteracts the constriction of the bronchi, this treats the symptoms of shortness of breath, wheezing, and stridor. It also constricts blood vessels, helping treat the low blood pressure. Epinepherine has a plasma half-life of about 2-3 minutes, but when given in a muscle it lasts a bit longer, but I don't remember how much longer. Its buying you time to get your ass to the hospital so we can finish treating the allergic reaction. The main things that are going to treat anaphylaxis are benadryl, pepcid, and prednisolone (no, not prednisone). As soon as an EpiPen is used its imperative to get to the hospital, both to treat the allergic reaction and to monitor cardiac activity as Epi can cause arrhythmias. Typically we keep a patient in the ER for about 4-6 hours, if symptoms subside and don't rebound in that time period, they're usually discharged home with instructions to come back to the ER if they have symptoms again or follow up with their PCP/allergist."
] |
[
"The two previous answers are very good, I'd just like to add on a little bit of information. All of the symptoms that come with an anaphylactic reaction are due to the release in the blood stream of substances (chemical mediators) from some specific cells : mast cells or basophils. Epinephrine or adrenaline here in good ol' Europe (same molecule, different name) has a lot of interesting effects, but it isn't the only molecule to dilate the bronchi, or to constrict vessels. However, it seems that it also stops the release of these chemical mediators from mast cells, which makes it the drug of choice for anaphylactic reactions. That way it not only treats the symptoms but also the root cause. \nBtw, just to confuse you even further or maybe clarify things, anaphylactic reactions can be either allergic : your body has an overpowered reaction to something you're allergic and already sensitised to, in which case it is called anaphylactic reaction. Or it can have the same degranulation of mast cells, same symptoms, but for non allergic reasons (some medication, for instance, can cause allergic like reactions without there being an allergy in the physiological sense). We call those anaphylactoid reactions. Symptoms and treatment are the same though.",
"\n(My credentials : nurse anesthetist, where we work with two very anaphylaxis inducing groups of products : antibiotics and paralytics!) \nThis is a good, accessible article that goes in to a bit more detail : ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC286326/"
] |
[
"To add to this, people with true anaphylaxis will need more than one EpiPen shot and the ER will likely give more epinephrine before they mess with any of those other drugs. Some people even require intravenous infusions of epinephrine. As the previous answer stated, epinephrine keeps the airways open and the blood pressure up. It should be emphasized that it is the most important drug out of all of those mentioned, it is truly the one that will save a life. If you see someone starting to have trouble breathing after exposure to a possible trigger, getting them to swallow some Benadryl and hoping for the best is not enough, they need epinephrine."
] |
[
"Could we create gravity waves by spinning a massive 'rod' in space at high speed?"
] |
[
false
] |
Because it would not be spherical like everything else in the universe it's 'spot mass' would change drastically, thus the gravity would fluctuate while the systems forces could remain in equilibrium.
|
[
"Yes and no. In theory, any accelerated mass will radiate gravitational waves, but in practice, only the most energetic sources of gravitational waves (like supernovae and colliding black holes) will produce a signal that could ever be detectable. ",
"Additionally, even if your rod is very long and very fast and very massive, you'll eventually hit the limit where the centrifugal forces from the acceleration will destroy the rod. Basically, it'll get ripped apart, with the ends snapping off because the rotational forces will exceed the breaking stress. "
] |
[
"Moving a charged particle \"up and down\" causes EM radiation.",
"Moving a particle with mass \"up and down\" cases gravitational radiation.",
"Whether or not we could be able to detect this infintesimal fluctuation in space-time is another story."
] |
[
"In theory, any accelerated mass will radiate gravitational waves",
"That is not the theory. Accelerating mass can be in a non-radiating condition. A spinning star will not generate gravitational waves if it has symmetry about the axis of rotation, and it very nearly does.",
"The spinning rod could be in a radiating condition depending on the axis about which it rotates. There is one axis which a cylindrical rod has rotational symmetry. If it is rotating about some axis other than this one, the answer is \"yes\"."
] |
[
"Effectively, how are nuclear weapons regulated? I remember reading (on here somewhere) that Uranium 238 isn't regulated, but rather the technology of making it into 235 is. Is this true, and how is this achieved?"
] |
[
false
] | null |
[
"Separating U-238 and U-235 is a difficult process. The issue is that you want U-235, but that is only 0.7% of naturally occurring uranium. Being isotopes of the same element with only a ~1% weight difference makes traditional chemical separatations not feasible. ",
"So, what do you do? A few things. ",
"You do not need 100% pure U-235, you just need to enrich it (increase the fraction of U-235 relative to U-238). For nuclear power generation, ~20% U-235 will do it. For nuclear weapons, you need about 85% U-235 ",
"Physical separatations based on weight is possible. ",
"You can chemically change the uranium to increase the feasibility of separatations based on weight, but this still doesn’t allow for chemical separatations. ",
"During the Second World War, the Manhattan Project needed highly enriched uranium. The technology at the time was limited, and this had never been done before. The solution was to separate using mass spectrometry. Mass spec. allowed for individual atoms of U-235 and U-238 to be separated but took a ",
" time and ",
" of mass spectrometers. ",
"You have a problem though, uranium is a solid. Solids don’t work with this method. So, you have to using fluorine gas (nasty) to make gaseous uranium hexafluoride (UF6). UF6 has an even smaller weight difference but is workable. By allowing gases to diffuse across a barrier (which will start the separatation based on thermodynamics), and then feeding the higher U-235 concentration of UF6 into a mass spec., US and UK scientists were about to get ~84% pure U-235, with the balance being U-238. This was enough to sustain fission and allowed for the atomic bomb based on uranium, which was one of two in WWII, the other being based on Plutonium-239. ",
"Now, we must leave the technology of the 1940s behind, and look to the present. Now, instead of hundreds of mass spectrometers, we use hundreds of ultracentrifuges. Remember the Iran deal, where centrifugation was a sticking point? That is because these centrifuges are central to producing weapons grade uranium. ",
"Again, using UF6, a series of centrifugation steps are taken. The lighter U-235 species stays towards the center, which U-238 is pushed to the sides. Doing this repeatedly, and taking various fractions and retuning them to the beginning and centrifuging again, allows for the production of highly enriched, weapons grade, uranium. ",
"Therefore, the premise of your question is generally correct. Rankin is abundant and nearly impossible to control. I could buy some uranium online now if I wanted to. However, enriched uranium is strictly controlled, as are the methods of doing so, as it is much easier to control the methodology than the base uranium metal and uranium compounds (such as uranium oxides). "
] |
[
"Uranium-238 and uranium-235 are really hard to separate. They are both uranium, and have identical chemical properties, and the difference in physical properties is minuscule. Therefore, you need very complicated technology to separate them.",
"You don't make it into 235, it does not work that way. But, you can irradiate U-238 with neutrons in a nuclear reactor and obtain plutonium-239. However, you also obtain plutonium-240 and still need to separate them using the same technology; if you skip this step, your plutonium bomb will be a dirty fizzler, not a proper nuke."
] |
[
"Just as a clarification: the Calutrons of WWII were one one of the three methods of enrichment used during the Manhattan Project. Thermal diffusion and gaseous diffusion stages were all used before electromagnetic. After the war, the gaseous diffusion plant was made to operate without any additional stages, and could enrich all the way up to +90% on its own. ",
"Raw uranium is indeed somewhat controlled (there are limits to how much you could buy online; over a certain amount you need a permit in the USA), though it is also true that many states have access to ores within their borders. "
] |
[
"What are the actual differences in breathing at high altitude, what makes it hard, is it simply less oxygen?"
] |
[
false
] |
Is it that simple or are there other factors at play?
|
[
"I think there are 2 main things at play here:",
"We breathe by creating pressure differentials, so the pressure of our surroundings (Ps) determines how much total air flows in to our lungs. During inspiration, inspiratory muscles contract to expand the chest wall, which ultimately decreases the pressure in our alveoli (Pa). Air flows in from our surroundings until Pa increases up to Ps. At higher altitudes, Ps is lower, and the amount of air we breathe with every breath is therefore less.",
"As you mentioned, less oxygen. Although the composition of air is quite uniform, simply having less total pressure means less oxygen in general. For instance, 21% of air is oxygen, so at sea level (P air = 760mmHg), we would expect 760 *21% = ~160mmHg of oxygen. But on top of a mountain where P air = 380mmHg, there would only be 80mmHg of oxygen."
] |
[
"As a pilot all I know is that it is not less oxygen. It is the reduced pressure that no longer allows the oxygen to pass the membrane in your lungs and then onto your blood cells. The concentration of atmospheric gasses is nearly uniform throughout most altitudes; it is only a reduction in pressure at higher altitudes that causes hypoxia. "
] |
[
"Some back-of-the-envelope calculations using generally accepted figures. ",
"Starting at sea level:",
"\nAir is always around 21% oxygen at all altitudes. The average person moves about 6 litres of air through their lungs every minute at rest. Exhaled air has around 15% oxygen content. So let's say that, in these conditions, humans extract roughly 25% of the oxygen from the air. So the amount of oxygen moved from the air to the blood, per minute, at sea level should be:",
"\n6000 mL * 0.21 * 0.25 = 315 mL O2 / minute",
"\nAt rest humans require approximately 250 mL oxygen per minute (VO2). 315 is more than 250 so there's no problem here.",
"At the top of Mt Everest:",
"\nAtmospheric pressure is 1/3 of sea level. The percentage oxygen is the same, but ",
"the inspired partial pressure of oxygen is only around 30% of the amount at sea level",
". Hence:",
"\n315 * 0.3 = 95 mL / min.",
"\nNow there's an obvious deficit between the amount of oxygen being extracted and the oxygen that is required. The body has methods of detecting falling oxygen levels in the blood and compensates through several mechanisms (including increasing the rate of breathing). It should be clear that when doing something strenuous like climbing a mountain the oxygen consumption of the body (VO2) rises greatly, but the maximum amount of oxygen that can be extracted from the air is reduced at altitude, impairing performance. ",
"Some other factors such as diffusion limits and pulmonary vasoconstriction also may have a part to play but the most significant factor is simply that there is much less oxygen at altitude."
] |
[
"What is the biggest limiting factor keeping videogames from looking photorealistic?"
] |
[
false
] |
recent post on got me thinking about why even some of the most impressive combinations of hardware and painstakingly developed player modifications still seem to mostly fall short of looking realistic. The screenshots are very impressive, yet something about them makes me think, had someone handed me a printout of one of them, I would probably recognize them as computer generated rather than a photo. I can't put my finger on it, but I was wondering if science has identified that limiting factor.
|
[
"The short answer is, as you might imagine, \"software and hardware aren't there yet.\" But a more detailed answer would be that 1) we haven't yet developed efficient (real-time) algorithms for reproducing a lot of what we see in the real world in a 1:1 way, 2) even if we had those algorithms today our hardware would be unlikely to be able to handle them, and 3) it's really, REALLY hard from a design standpoint to \"make something more realistic\" just out of nowhere.",
"Now, there are some exciting things going on: everyone knows that hardware is improving rapidly, so that won't/can't be a limiting factor forever. But what many don't realize is that there are huge strides being made in areas like rendering and AI that make games far more \"real\" to the player. If you haven't looked into hardware tessellation, for example, I'd check that out post-haste.",
"Lastly, there's this issue of \"The Uncanny Valley\". Put a mostly-realistic zombie, or mutant, or attack dog or whatever in front of a player and they'll react appropriately, but put a not-quite-perfect human before them and the player will emotionally disconnect. The brain tells you, \"This isn't a real person, you shouldn't feel a connection.\"--and you won't without great storytelling. The point at which we can NOT have that happen, the moment we can climb out of the Uncanny Valley--THAT will be a magical moment for games."
] |
[
"In the past, one of the things that we could scale up to make things look realistic most easily was the total number of polygons in a scene; every year, as videocards got faster, we could draw more and more polygons to the scene concurrently. This made all the shapes that we see look smoother and smoother, but it didn't really make the scene look more photorealistic.",
"Lighting, shadows, and reflections are the current area that we're trying to expand into. We've been coming up with a lot of different algorithms for making satisfying looking lighting and shadows, but because it's currently a tradeoff between \"satisfying\" and \"computationally feasible\". We have a lot of different lighting shaders that do those things (",
"http://en.wikipedia.org/wiki/Cube_mapping",
" , ",
"http://en.wikipedia.org/wiki/Normal_mapping",
" , ",
"http://en.wikipedia.org/wiki/Radiosity_%28computer_graphics%29",
" , etc, etc) but a lot of those will not approach a level of photorealism in a reasonable amount of time. ",
"Real time raytracing could be used to make things look more realistic, but in order to make things look more photorealistic, you have to do more iterations per frame. From a time complexity theoretic point of view, this is pretty complex and it will be a long time before hardware will be able to do this quickly (if ever). I'm sure that you'd agree that this is pretty realistic looking: ",
"http://en.wikipedia.org/wiki/File:Recursive_raytrace_of_a_sphere.png",
"Note too that videogame art assets have to be made by hand; and videogame developers cut corners when they feel that they can get away with it because the player won't notice. An example was last night when I was replaying through Bad Company 2 -- trees aren't two dimensional billboards, but BC2 likes to pretend they are. Billboarding is common and a lot of the unrealism comes from the fact that videogames are an economic process, and if a company can get away with doing something unrealistic, they will. "
] |
[
"One of the fundamental areas of research and study in computer science is the study of data structures - how data is organized and represented in an abstract sense by the computer. When I say \"abstract sense\", I mean it as in \"I know that character strings are all in the computer as zeroes and ones, but let me treat them like they're regular strings of words and letters\". ",
"There are lots of data structures. There's one called a queue, which is exactly what it sounds like - the first piece of data that enters a queue is the first thing that leaves. A stack is also one of those intuitive names - like stacks of paper, data that enters last gets pulled off first. One of the abstract models for data is called a tree - and the name is apt here, too. Technically, a tree is an acyclic graph that is completely connected (which means nothing to you but let me explain). ",
"Imagine an actual tree. It has leaves and branches. All of the leaves are connected to branches - there are none floating out in space. All of the leaves have just one branch that they connect to, in other words, there are no leaves with two branches leading to the same leaf. None of this is surprising. The fact that no leaves are floating in midair means that the tree is connected, and the fact that no leaves have multiple branches means that it's acyclic (without any cycles)",
"Now pretend that the leaves were \"nodes\" (or vertices, they mean the same thing) and the branches were edges. (This analogy is imperfect because the part where the branches actually split should also be a node, but whatever. Here's a picture of an actual tree so you can see what I mean. ",
"http://en.wikipedia.org/wiki/File:Binary_search_tree.svg",
")",
"So there are many different types of trees, and trees are really convenient in computer science because they speed up a lot of things that would take much longer if done in a naïve way. The link I just gave you was a \"binary search tree\" - the beauty of such a data structure is that you can find a data value much much more quickly than if you had to actually check every element manually to see if its there. (Trust me, I'm getting to the point soon). Like I said, there are lots of different kinds.",
"One of the kinds is called an octree. This is a data structure where each node (or data point) can have eight children, and those eight children can have eight children, and so on. Here's another picture of a tree, this time it illustrates the octree that I'm talking about. (",
"http://en.wikipedia.org/wiki/File:Octree2.svg",
"). It's a recursive data structure; you can keep subdividing and subdividing and adding more complexity. ",
"Octrees are used all the time in video games because it's possible to efficiently cut down how much processing is used by only drawing stuff that the video game camera would actually be able to see. The open source video game engine Cube 2: Sauerbraten uses octrees to represent all of its world terrain and geometry (albeit using ordinary meshes other than the octree).",
"Even though the video didn't outright say this (and they've tried to hide it so as to appear more important), these guys are using voxels in what's called a \"Sparse Voxel Octree\". Voxels are just particles, \"sparse\" means that compared to the potential size of the octree there aren't a lot of data points, and I just told you about octrees. ",
"Yes, it is true that you can use SVOs to represent 3d data with high precision and have that precision scale up and scale down depending on what the game camera can see, just like I described earlier. However, the tree is not as flexible as using traditional polygons because deforming them screws up the data structure that was used to represent the points. Yes, you can rotate and scale the SVOs, but actual deformation (changing the shape of the thing dynamically) is totally infeasible. You'll notice that the video shows no animation.",
"Further, you'll note that the video shows very few unique objects. They have the same (extremely detailed) object all repeated over and over again all facing the same direction. It is easy to tell a computer to do the exact same thing many times and that doesn't incur a significant memory cost. However, if you were to have a ",
" \"island\" like the one that they have, you would have to pull in a vast amount of data because you couldn't just repeat the same thing over and over. If you have billions of unique voxels that you need to pull in, that incurs a memory cost of billions of bytes. That's gigabytes. Clearly you couldn't have a way of having an arbitrary amount of unique data without also incurring an arbitrary memory cost. ",
"So their demo shows that SVOs (which they didn't invent and have been done many times before) are really good at displaying a small number of unique things with high detail, but they're impossible to animate. As it turns out, that wasn't a problem the industry was desperately trying to solve. SVOs might be useful for terrain, but regardless of what the video tells you most people don't spend their time looking at the minutiae of terrain, which is why 3d modellers skimp on those art assets. SVOs would be 100 percent useless for character models, which is where a lot of people direct their attention. ",
"SVOs could never (and I mean never) act as a complete replacement for polygons. At best, they could act as a supplement in certain limited circumstances, which is where ID Tech 6 is going. ",
"Now in truth I could've given you two links to the stuff that debunks this video, but I felt it was worth my time to put the whole idea into context by giving some background. I hope you took the time to read this comment. ",
"Here's some other stuff:\n",
"http://www.reddit.com/r/gaming/comments/j6sr1/a_simple_and_efficient_explanation_of_the/",
"\n",
"http://www.reddit.com/r/gaming/comments/bbg9c/unlimited_detail_the_end_of_poligon_based/c0lxc1e"
] |
[
"Controlled hunting programs keep species from going extinct? Is this a valid statement?"
] |
[
false
] |
I see this argument lately (specifically, in defense of the ). Is this valid? Have there been studies to defend/refute this line of reasoning? Sorry if this the wrong place to post.
|
[
"This claim is potentially true depending on the relevant facts. Normally, the ideal case would be that zero individuals of an endangered species are killed by humans. But perhaps the national parks (and countries) where the species lives are not able to provide the necessary resources to prevent poaching.",
"If a private hunting reserve is able to generate funds by allowing some individuals to be hunted for a fee, and these funds allow the preserve to have enough resources to provide adequate security, and the kill rate is less than the reproduction rate, you might have a situation where controlled hunting is a net gain for the population. "
] |
[
"This is basically a communism work \"in theory\" situation "
] |
[
"For this to be effective you really need to meet a few requirements:",
"You need to have a very good understanding of the population dynamics of the species and their life history. I.E. how many individuals there are in each age-sex class, how long it takes individuals to mature, how many individuals typically survive to adulthood, how large and continuous populations are, how easily individuals move between populations, how genetically diverse your populations are. To gain this information you need field biologists studying the species. To get field biologists you need adiquate funding. ",
"The ability for you to enforce controlled hunting practices. The ability for you to control poachers. For this you typically need a strong parks system, not what we call \"paper parks\". This typically means having people as 'rangers' who patrol the protected area. Those who enforce the law once illegal poachers have been caught. Having strong laws which discourage illegal hunting. e.g. A 100$ fine probably won't deter a poacher. But a fine equal or greater than the black market value of the animal may."
] |
[
"What factors lower the tide in this video by 12 meters? Why is it lowered so briefly?"
] |
[
false
] | null |
[
"This is probably a particularly low tide. It's worth remembering that the tides are not entirely due to the moon (explanations given to Bill O'Reilly to the contrary) and in fact the sun's tides are about half as strong as the moon's. When the two tides are in sync, they constructively interfere, leading to what are known as spring tides. When they are out of sync, you get a neap tide where there is very little variation.",
"Particularly strong tides happen when the solar and lunar tides are in sync at the same time the moon reaches perigee (the moon's orbit is eccentric, so sometimes it's closer to the earth than other times)."
] |
[
"All well and good but that was John Hurt, not David Attenborough.",
"Source: ",
"http://en.wikipedia.org/wiki/Human_Planet",
"\nSource: ",
"http://www.imdb.com/title/tt1806234/"
] |
[
"c'mon, please not in a science sub-reddit. Let's not pollute, mmkay?"
] |
[
"Do our bodies have much empty space inside?"
] |
[
false
] |
The reason I'm asking is this image (NSFL, leg with a cut in it, from ): It looks like there's a lot of empty space inside...in my head that makes little sense, I thought everything is very closely aligned. What's the deal here?
|
[
"Very little, outside the body cavity (and not a lot, there, really). That gap is actually a result of the opposite being true: there is enough pressure against the skin from all the stuff filling its insides, that when it is opened, it gapes."
] |
[
"Actually, in your friend's case, the flesh has been pulled apart for finding and removing any foreign objects (shards of glass inside the body are extremely dangerous), so it \"seems\" like there is empty space there. The doctors will press the flesh together, and will stitch it up afterwards.",
"If you open up a body (lets assume all the free fluids have magically evaporated, but the body is not \"dry\" per-se), you will find that just below the skin, the muscles start. Below the muscles, there are the organs. below them, the skeleton.",
"Every little thing in our bodies is tightly packed together. if it wasnt so, you'd hear or feel your innards sloshing about (gross!), kinda like when you drink something on an empty stomach(in the morning, or when really hungry), and if you move around fast, you can feel the liquid splashing about in your stomach."
] |
[
"that space is an artifact of the plasticizing process. Those spaces aren't there in life."
] |
[
"What is the minimum size necessary for an object to cause planetary destruction while moving at the speed of light?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"/r/estimation",
"/r/theydidthemath",
"guidelines",
"/r/askscience",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"Thanks! Sorry about that!"
] |
[
"Thanks! Sorry about that!"
] |
[
"What was the world like before life?"
] |
[
false
] |
I am doing some amateur research on the origins of life, and am fascinated by the extent to which organisms effect their surroundings. I find it hard to imagine a world without trees or grass or micro-organisms. How different would the composition of the atmosphere or seas for example, be without the influence of living organisms?
|
[
"Indeed, life does have a significant impact on Earth and its evolution through time. The presence of oxygen, amount of CO2 etc.",
"The earth before life is pretty hard to constrain with actual data as we don't have many rocks that are that old that give definitive evidence for the presence or absence of life. The Isua rocks of Greenland (3.8 billion years old) have evidence for a biologically mediated carbon cycle on the basis of stable carbon isotopes (cellular enzymes partition isotopes, more on this if you want). ",
"Prior to 3.8 there were periods of heavy bombardment (asteroids and comets) that may have limited early life or could have provided the necessary molecules to get life started, as mentioned by stonerphysicist. We don't have a good handle on how, or if, plate tectonics worked. Plate tectonics is one of the primary regulators of the chemical composition of the Earth's surface and ultimately regulates the availability of nutrients for life (phosphorus, iron, molybdenum, sulfur).",
"Atmospheric composition is obviously different. No oxygen. Not necessarily more nitrogen by mass, but a higher fraction. Higher CO2 (no life to make organic carbon and bury CO2). ",
"The oceans were anoxic and iron (Fe2+) rich but not necessarily saltier. The minerals that make up the salinity in the ocean are ultimately soluble and weathered from rocks regardless of the presence of plants. The Fe would have been derived from the weathering of rocks or from hydrothermal vents. ",
"Early in Earth's history is is also unknown whether there was an ocean as we know it. Some think that most of the water was brought to earth by comets and arrived in the late heavy bombardment or that it was mostly in the mantle and had to be 'degassed'",
"Interesting question...I can do some digging around if you have more specific questions."
] |
[
"If I read the original question correctly, it's more about what the Earth would look like today if life had never taken hold here than it is about what primordial Earth was like.",
"That means plate tectonics would still be a factor, and there would be an ocean regardless of whether it was built by comet bombardment or mantle degassing. It also means we can ignore differences in solar output, day length, and tides.",
"I found your comment regarding the saltiness of the oceans interesting - I really would have thought that biomass is locking up a fair amount of what would otherwise have run off into the oceans, leading to a slightly higher level of salts in the waters of a life-free Earth."
] |
[
"ilovemud",
"\"So, what do you do?\"",
"\n\"I study mud.\"",
"\n\"Oh! Um... how about them Red Sox, huh?\"",
"\n\"No no, mud's really very interesting! Let me explain...\"",
"\n\"I just remembered I have to return a library book, gotta run!\""
] |
[
"Can someone put \"pair production\" into layman's terms for me?"
] |
[
false
] |
Specifically as it relates to the modern supporters of the Expanding Earth hypothesis. Since the guy who came up with the hypothesis (Neal Adams) is a comic book writer and not a scientist, I'm quick to dismiss it, but alas I am no scientist myself so I cannot find the grounds to do so.
|
[
"So e=mc",
" right. Mass is energy.",
"You probably know that certain things are conserved. Energy is conserved, momentum is conserved, and charge is conserved.",
"An electron or positron has 511,000 electron-volts of energy, or 511 keV. The pair of them has 1,022,000 electron-volts of energy, or 1.022 MeV.",
"If you were to provide this much energy, you could theoretically create an electron-positron pair, so long as you conserved momentum and charge. Charge is already dealt with: an electron and positron cancel each other out.",
"As for momentum, well if you have a big heavy thing nearby to absorb a little bit of momentum, you can deal with that problem too.",
"So when a photon of high enough energy (at least 1.022 MeV) passes close to the vicinity of a nucleus (a big heavy thing), you can create an electron and positron.",
"I'm not familiar with the expanding earth hypothesis, but I noticed that people have suggested pair production as a means of mass creation (high energy photons create electron-positron pairs). Pair production does create mass out of energy. ",
"I'm dubious as to the magnitude of this effect in Earth, as electrons and positrons aren't very heavy, and will annihilate each other (matter-antimatter reaction) to create two 511 keV photons."
] |
[
"\"4-momentum\" is conserved, mass isn't. That's why nuclear power plants work. Mass is a form of energy - it's just the energy that a particle has when it's in rest. "
] |
[
"That's not really the main reason nuclear power works. It's just binding energy. It's really the same principle as chemical energy. When we burn coal we convert chemical binding energy into thermal energy through a chemical reaction. When we do nuclear fusion, we convert nuclear binding energy into thermal energy through a nuclear reaction.",
"The only difference is that nuclear binding energies are big enough that you can actually measure the mass difference. It's the same basic thing happening, it's just a difference of scale."
] |
[
"What is the difference between neurons in different parts of the brain?"
] |
[
false
] |
If different parts of the brain perform different processes(visual,motor, somatic etc.) what is the difference between neurons in different parts of the brain? somehow i made too much of the word "different", still it makes sense :) edit: thank you all for your answers, it was interesting to see the brain from a deeper perspective. @PKThundr7, i was just thinking one day about the brains and thought that in different parts of the brain neurons should be somehow different and i wanted to check if it's true. sorry that i didn't reply earlier, i just forgot that i posted this question here until now that i checked again my reddit overview of activity.
|
[
"Good question.",
"I'm going to take a slightly different tack to the others, and say this, highly controversial statement:",
"There is no fundamental difference between different brain cells in different regions of the brain.\n",
"Already, some of the more educated readers will be outraged, and any neuroscientists reading this will be trying to track me down in order to end my life. But hear me out.",
"Firstly, I am not suggesting that all neurons are identical. This is plainly not the case, neurons vary between the tiny cerebellar granule cells, to massive corticospinal layer V pyramidal cells. Cells so small the the opening of a single ion channel has a noticeable effect, to ones so large that it requires 100s of input neurons to make it spike. However, even given that, they have more in common that they have in difference. Indeed, I would go so far as to say that most of their differences are their to make them MORE similar, that is to say that because they exist in slightly different niches (say, dealing with 1000 inputs, rather than 10), they need to change some of their properties in order to, in the end, achieve the same function.",
"What is that function? What is the point of a neuron? Well I would say on a second to second time scale, a neuron is there to perform a simple equation, that looks basically like this:",
" IF (INPUT > THRESHOLD) THEN SPIKE\n",
"There are small numbers of neurons that do not perform this calculation, but the vast vast majority does. The difference is where that threshold is. Of course, there are slight caveats, some neurons prefer if all the inputs happen on one part of the cell, other neurons want them spread out. But basic logic still applies.",
"So what does this have to do with your question? Ultimately, that the visual, auditory, and somatosensory cortices are doing very very similar things. They are wired up in very similar fashions, and have very similar cells. The big difference in the input they receive. As we look at areas that are wired in increasingly different patterns, like the periform cortex, and onto the hippocampus, till we get to completely different regions like the basal ganglia, we still see neurons performing the same function as explained above. What changes is the way they are wired up. That, is what I believe is the fundamental difference between areas, not the cells that make them up, but they way the neurons are wired together, and the inputs and outputs the circuit has.",
"[Just so I don't get lynched - Obviously, there are significant differences between neuronal types. However, I think there is very strong evidence that most of those differences (be they in intrinsic properties, or in synaptic properties) are their to overcome cable issues caused by physical properties (pyramidal cells are prime examples). The basic input output function I have used is highly simplified, but fundamentally captures the essence of neuronal function]"
] |
[
"/u/NeuroBill",
" is right, but so are the other two responders so far. What you need to do is clarify your question. What level of analysis do you care to measure? If you only care about the output of a neuron (action potentials) then ",
"/u/NeuroBill",
"'s analysis is spot on. A neuron is a neuron, they receive inputs, they integrate those inputs, and they relay action potentials. The main difference between different parts at this level of the brain is wiring, where those neurons are receiving information from (is it from pain fibers? from touch fibers?) and where they are connected to. That's why this level of analysis is called Systems Neuroscience. Yet I am not totally satisfied with this answer. As my tag suggests I am interested in studying what on a cellular and molecular level makes neurons distinct from other neurons. ",
"Let me give you an analogy. Think of a city. In any given city there are people. For the purposes of this analogy people = neurons and the city = the brain. All these people perform different jobs, right? Construction worker, doctor, barista, librarian, waiter, etc. What makes these people different? After all, they are all people and at a \"systems\" level we are all the same. We eat, we drink, we sleep and we communicate with each other. So all these people are the same and it is who they talk to (customer or foreman) and what they output (coffee or buildings) that largely distinguishes them. Yet some people are better baristas because they have an expertise making coffee over people who are experts at building stuff. Builders may be stronger and better with object transformation whereas baristas may have better memories for orders and names and work faster under pressure (ha, espresso pun).",
"In the same way neurons are specialized for the tasks they perform. For example neurons that synthesize dopamine contain a special set of enzymes so make dopamine, package dopamine into vesicles and release dopamine throughout the brain. Some neurons in the retina are specialized with particular receptors and ion channels that allows them to release neurotransmitter when they ",
" receiving excitatory information from the neurons talking to them, opposite from classical neurotransmission. There are neurons in the auditory system that have to maintain very precise spike fidelity and so have particular ion channels to make sure they can fire action potentials with incredible precision and speed. Some neurons fire continuously like a pacemaker, some are silent until they integrate proper input that leads to an action potential.",
"So while it's true that a neuron is a neuron, not all neurons are the same and I think the most interesting differences are not at the network level but rather at the cellular and molecular level. However, this does reveal my bias toward my research and what I find fascinating. Systems neuroscience is of course interesting and extremely important to study and understand, especially given the recent push in this direction with Obama's Brain Initiative."
] |
[
"Well! There are a lot of phenotypic differences when you look at neurons in different areas of the brain and body. A lot of the really cool work showing gross phenotypic differences was done over a hundred years ago by a dude named Santiago Ramon y Cajal. His adapted a guy named Golgi's method of staining to make really nice pictures of individual neurons. Here, for example, is a Cajal drawing of a pyramidal neuron, like one you could find in the prefrontal cortex. ",
"http://theperceptionalist.files.wordpress.com/2011/09/cajal1.jpg",
"Here, on the other hand, is a Cajal drawing of a Purkinje Neuron, like one you could find in the cerebellum. ",
"http://38.media.tumblr.com/tumblr_m337nn2xyE1qb6etto1_500.png",
"They are obviously very different looking! There are also many molecular differences between different neuronal types: Some produce GABA (generally inhibitory), some produce Glutamate (generally excitatory) . Some neurons make connections with thousands of other neurons, some with just a single other neuron. If you think of your brain as an exquisitely complicated computer, the different parts of your brain handle different jobs through stereotypical connections that they make within their local neighborhood and at long distance, as well as through having very specialized phenotypic and molecular signatures. I know this probably raises more questions for you than it answers, but the brain is really complicated! There's simply no easy way to put it without invoking a lot of black boxes. Hope this is interesting to you!"
] |
[
"If planes are pressurized why do we have our ears popping?"
] |
[
false
] |
I mean, there is supposed to be a constant pressure in the plane and the pressure is supposed to be independant of the outside pressure, so why do we have our ears popping when the plane is gaining altitude?
|
[
"Aircraft ",
" maintain constant ground level pressure in their cabins. They’re required by law to maintain a ",
" pressure, which is equivalent to the pressure at an altitude of 8,000 feet. So when a plane takes off, the pressure in the cabin falls until it reaches the minimum required by law, and then remains at that level for the duration of the flight. When it lands, the pressure increases until it matches ground level. So your ears may pop on take-off and landing.",
"The reason is cost. A pressurized cabin must hold in high pressure air at cruising altitude, and the greater the pressure differential between the inside and outside, the stronger the cabin must be. Strength requires more material, adding weight and reducing fuel efficiency. At sea level, the pressure is 14.7 psi, while at 8,000 feet the pressure is 10.9 psi, for a difference of 3.8 psi. So if the cabin maintained sea level pressure, it would need to withstand an extra 3.8 pounds for every square inch of surface area, making it heavier.",
"The FAA determined that 8,000 feet is a good compromise that the vast majority of people find comfortable. Even if you’re sick, it won’t kill you unless you have something like pneumothorax, in which case you shouldn’t be flying anyway. So they settled on that number. But the majority of aircraft manufacturers do better. The Boeing 767 maintains at least 6,900 feet of pressure, the Airbus A380 averages around 6,100 feet, while the Boeing 747-400 won’t let it drop below 5,200 feet. So your subjective impression of ear popping may vary based on which plane you’re in. It’ll also vary depending on where you take off or land. If you’re taking off from sea level, the drop from zero to 8,000 feet is substantial, and you’re going to feel it. If you take off from Denver, you’re already at 5,200 feet, so you may feel no change at all, or a very small change.",
"There are business jets that can maintain sea level pressure all the way, like the Emivest SJ30. They don’t care as much about per-seat passenger costs, so they’re willing to spend a little extra on reinforcing the cabin for passenger comfort. But big commercial airliners are designed with compromises between comfort and cost, and not having sea level pressure is one of those compromises."
] |
[
"Plane cabins don't typically pressurize to sea level (or wherever you are starting from) but can range anywhere from that to up to a cabin pressure equivalent to 8000 ft of elevation (according to the FAA at least). As you climb the pressure will gradually decrease from your starting pressure to whatever the cabin pressure is set at and you may feel the change in your ears."
] |
[
"Remember that commercial jets typically fly above 30,000 feet anyway, so yes, they can actively increase the air pressure in the cabin. Typically they bring in air compressed by the engines' turbines."
] |
[
"How does Google know my location even when I am using a laptop or a device with no GPS?"
] |
[
false
] |
I have been wondering everytime I open my browser with location services enabled, it knows my location with a high accuracy. How does it manage that? I know my IP address plays a part but, I am sure you cannot just know exactly where I am using my IP address.Thanks in advance ya'll. EDIT: Thanks a lot to everyone who replied. Much appreciated.
|
[
"IP addresses can be used for a rudimentary location fix, but they're typically rather inaccurate (limited to the general region at best).",
"Much better location data can be obtained by analyzing which WiFi networks your device is able to see. Google has a database of WiFi networks and their physical location (send forth a Streetview car with a GPS and WiFi monitor and store the results). So by comparing the networks you can see to this database, it's possible to get a reasonable estimate of your location."
] |
[
"If there isn't much to work with, then location accuracy will falter obviously.",
"Note that not broadcasting SSIDs doesn't really do anything, because even if you have set your router to hide the SSID, it's still broadcast in different ways. Hiding SSIDs only keeps out the most casual of listeners."
] |
[
"Two ways: WiFi networks and IP Geolocation.",
"Google keeps an absolutely massive database of known WiFi networks and their corresponding MAC address.",
"If you have WiFi on, your phone will be able to see a pretty unique set of wireless access points and their signal strengths. Since the effective broadcast area of a WiFi network is a couple hundred feet at best (and usually much less), Google can use this list of visible WiFi networks to pretty accurately predict where you are within a few hundred feet.",
"This is why your phone will tell you that turning on WiFi will improve location accuracy. Apple does the same thing.",
"There are companies that provide this as a service (not going to name any of them here but I've used a few). Basically, they maintain a IP address to physical location database. This method is not at all accurate for many things, such as geo-based games, mapping, GPS, etc... But it will usually be accurate to within a city or two. It can get weird sometimes if you're using a VPN, or your cell carrier is routing traffic to some trunk like hundreds of miles away. But it's usually pretty accurate for things like home cable-based internet or other static, wired connections."
] |
[
"How would/does microgravity affect the function of an induction motor?"
] |
[
false
] |
How does/would microgravity affect the function of an induction motor? If the stator was not anchored to anything would part of it's torque be transfer to itself resulting in the stator spinning counter directionally to the rotor and decreased rotational speed for the rotor relative to the initial position of the stator? For another example on Earth a motor spins it's rotor clockwise at 1rpm, would and attempt to run this motor in microgravity result in the rotor spinning clockwise at .5rpm and stator spinning counterclockwise at .5rpm? How does the mass of rotor and stator play into this? Basically in space will the stator stay?
|
[
"It would mostly not affect it. In a running motor, the electromagnetic forces dominate, and do not depend on gravity. ",
"The momentum of the motor would of course have to go somewhere. If you start a motor with a stator that is free to rotate, the stator will of course start to rotate. This could be demonstrated by mounting the motor on a rotating disk here on earth.",
"The speed of each part would depend on the inertia of those parts. "
] |
[
"At first I thought there would be no effect, maybe reduced wear on bearings, but then I saw that it might not be anchored. Yes, if it were not restrained, the rotor and stator would take off in opposite rotations. Power lines might twist, or a battery might be involved. Rotation speeds would depend on the rotational inertia of the stator and rotor, and any torque which might resist rotation of the rotor. . . . and any speed limits on the motor. "
] |
[
"It depends on the mass of the parts. Think about using an electric screwdriver in a space ship. The screw is much smaller than the person holding the screwdriver, so the screw will spin freely while the person remains stationary. But once the screw is fully home and has become part of the ship, suddenly it becomes the mass of the whole space ship against the mass of the person, and providing the screwdriver motor is strong enough, the screw will stay put and the person will (gradually) start rotating.",
"If the rotor and stator have identical masses then yes, they will both push against each other and rotate at equal speeds in opposite directions. If one has more mass than the other (i.e. it would weigh more on Earth) then it will rotate slower. And if one of the parts had a huge amount of mass - say it was anchored to a whole planet - then it would move such a small amount that it would appear to be completely stationary.",
"And of course, if you had a sensor on the stator measuring the RPM then it would show the same reading regardless of the scenario."
] |
[
"What's in the way of creating a natural-sounding voice that doesn't rely on pre-recorded words?"
] |
[
false
] |
In other words, when I get directions from a navigation device or the announcer on public transport there's usually either a pre-recorded message (e.g. "examplestreet") or a combination of an established set of words, such as "head" "right" "next" "turn", resulting in a rather jarred sentence. I realized there's a lot to a voice and humans are great at noticing even the slightest mistakes, but considering how incredibly great we got at rendering facial expressions and the astonishing sound design in various media I couldn't yet figure out what's keeping us from creating such thing. I also have no clue wether this is the correct flair, sorry.
|
[
"It's really important to note that this Yamaha synth was hardly new, and was in fact built on the better part of a century of research. Formant synthesis underlay basically every kind of early speech synthesis, although the inventors of the earliest goes didn't exactly understand what they were doing. But people had talking machines in the late 30s and early 40s, like ",
"pattern playback",
", where spectrograms were hand-drawn onto a roll of paper to be converted into a speech signal, or ",
"the voder",
", where specially trained keyboardists produced synthetic speech in real time with about 15 keys. Given the recording and playback capabilities of the time, the speech was quite natural-sounding, and when put side-by-side with natural speech it can be hard to distinguish them (see item #4 ",
"here",
").",
"That said, there are a lot of ",
" problems that stand in the way of generating natural-sounding speech parametrically. I wrote about some of them ",
"here",
"."
] |
[
"If a big part of it is computational cost, does that mean it's possible to naturally generate a synthetic voice, but not in real time? Like even though it only takes a couple seconds to say \"Hello, nice to meet you.\" that you could generate a naturally sounding voice clip of that phrase in a few hours? Assuming of course that all the necessary context was understood as well?"
] |
[
"If a big part of it is computational cost, does that mean it's possible to naturally generate a synthetic voice, but not in real time? Like even though it only takes a couple seconds to say \"Hello, nice to meet you.\" that you could generate a naturally sounding voice clip of that phrase in a few hours? Assuming of course that all the necessary context was understood as well?"
] |
[
"Why does water all freeze at once at 32 Fahrenheit (0 Celsius) instead of gradually getting thicker/harder as it cooled?"
] |
[
false
] | null |
[
"Because of symmetry breaking. Phase transition is not a process, but a state for few molecules. Molecules attract each other pretty much like weak fridge magnets. Let's pretend the molecules are like these weak magnets, in a glass box being shaken vigorously. They attract each other, but as soon as they can bind themselves to one another they hit the wall or another molecule, splitting them apart again. That's the liquid state. If you, however, shake the glass box less and less(decreasing energy, thus temperature) the molecules will stop hitting themselves so hard, and eventuallyl giving the chance for the molecules to start binding themselves together and stay that way, giving form to the solid state. That's why you see water crystals in freezing water, it's nothing more than conglomerates of molecules that were given the chance to bind together and stay that way. The point that they start binding together is given the name \"freezing point, 42F. ",
" Hope it helps"
] |
[
"Precisely. as we increase the temperature, molecules have more kinetic energy and can more easily break free of the forces holding them together. EDIT: more heat = more kinetic energy."
] |
[
"The ",
" water has no in-between \"thicker/harder\" state is because of its simple molecular structure. You're probably considering an analogy between other substances like sugar perhaps, which can change its viscosity depending on its temperature. However such materials have more complex molecules, with opportunities to form chains and to tangle up. Water molecules simply don't have that option. And so they either stick together via their intermolecular forces, as in water, or they snap into a crystal structure via covalent bonds, as in ice. ",
"The definition of a phase transition relies on this ",
" kind of state: Phase transitions require a discontinuous change in properties, given a continuous change in surrounding conditions (like temperature or pressure). This discontinuity means that if a substance does ",
" go from liquid to solid (like glass) then it technically never changes phase. Water is special for a number of reasons, but ultimately this sudden transition in phase has to do with the limited distinct arrangements it can be in, due in part to its molecular simplicity."
] |
[
"Are there any historical or current examples of cultures in which it is common or acceptable for \"settled\", unrelated* families of equal social status to share housing**"
] |
[
false
] |
*By "unrelated" I mean they do not consider the other families they share housing with to be their kin ** By "share housing" I mean share rooms to do at least 2 of these 3: sleep, cook, or do laundry. Please only include examples where the families shareing the housing are of equal social status. Please exclude examples such as these: people of the same tribe sharing housing in the manner mentioned or families sharing housing where, say, a noble family shares its house with its servants who are commoners or a family that ownes slaves living in the same house as their slaves. Also, please exclude things like religious or socialist communes or perhaps more generlly communes accociated with widely recognized recent (i.e. in the last 200 years) historical movements (e.g. social movements commonly associated with religious or ideaological movements). I don't have much of a background in anthropology, archeology, or history. I took one course at a community college in anthropology and one at the same place in history, so I'm sorry if my question seems vague or ignorant.
|
[
"You might have more luck asking in ",
"/r/AskHistorians"
] |
[
"Kommunalkas",
" were a very common form of living in the former USSR. A lot of it was a function of economic necessity / lack of other options, but they were considered normal and acceptable. Most people who lived in them had a desire to move into more private residences but I imagine that a lot of modern-day apartment dwellers aspire to live in single family homes as well. ",
"Not sure if this counts since you were asking for the exclusion of socialist communes, but this wasn't merely a small group of ideologues -- it was a large fraction of a large nation. "
] |
[
"Yes there are examples of this. Domestic residence patterns vary highly from culture to culture. An example that springs immediately to mind are the apartment compounds at Teotihuacan. These were large, multi-room compounds that had shared public spaces and courtyards. Some were likely composed only of extended families, but many were large enough to accommodate multiple families. Currently, the archaeological data seems to indicate that these functioned similar to the Aztec ",
" (the Aztecs lived in the same area but 500 years later). Like calpolli, these were economically specialized communities - so one apartment compound might be making pottery and another would make jewelry. If we can extend the calpolli analogy further, we could say that they probably owned the land on which they lived communally.",
"I also wanted to point out that you said to exclude people of the same tribe. I assume this is because that qualifies as family. These days most people think \"tribe\" is a fairly meaningless word, but when anthropologists do use it it's typically a political unit not a kinship unit. So you can have multiple, unrelated families that are part of the same \"tribe.\"",
"Also, since you said to include current examples, there's the obvious case of modern college students moving into dorms or apartments with roommates. That is a cultural pattern that fits the description you provided - and one many of us are likely to be more familiar with."
] |
[
"Why would this crab rip off its own claw?"
] |
[
false
] |
[deleted]
|
[
"It is probably injured. Crabs can regenerate their limbs, so it will grow back.\n",
"Here is a video of a crab amputing his claw after getting in a fight with boobies"
] |
[
"Does this show that the crab has foresight, or are they just reacting to stimuli? Does the crab think \"my claw is damaged, I'll rip it off and grow a new one later.\" Or does it simply feel pain in it's claw and rip it off, without realizing it will regenerate and regardless of the extent of the damage?"
] |
[
"Unfortunately, I don't think that is an answerable question. We don't really have access to what a crab is thinking."
] |
[
"If I were in a helicopter above a city when an earthquake hit, what would it look like was happening?"
] |
[
false
] |
Since you wouldn't be able to feel the shaking, would you be able to see the ground moving around, or would it just look like buildings are falling down for no reason?
|
[
"I think we're still misunderstanding each other, but perhaps the fault is mine. I think OP was asking what the ground would look like. I.e. would it be undulating, pulsating, bouncing up and down... I think the helicopter is just there to provide a stable viewing platform not affected by the ground's motion. But like I said, I could be wrong."
] |
[
"The question was, though, what would it look like? Not, what would happen to the helicopter."
] |
[
"http://science.howstuffworks.com/nature/natural-disasters/fly-over-earthquake.htm",
"This says that you likely wouldn't feel it and you wouldn't hear it above a certain altitude (at least not over the sound of the engine). I've flown helicopters and fixed wings before, but Askscience does not like personal anecdotes so I can't really use em.",
"Helicopters operate by pushing themselves off of the air. The movement of the air by an earthquake is negligible so you won't feel anything. However if you were to hover low enough to push off of the ground (about 4 meters give or take on a small heli like the R66), you would definitely feel the movement of the ground translating into the helicopter. ",
"edit: I suppose if the earthquake were to open up cracks in the Earth or move about debris in an insane way (San Andreas movie level) you would suffer from heavy turbulence from the differences in air temperature.",
"edit2: you can think of it like operating a helicopter over a boat. If you fly high enough so that you are only pushing off of the air, you won't feel a thing but you can still see the ocean oscillating. If you hover low enough that you are pushing off of the boat, you will feel the ocean's movement slightly."
] |
[
"Quick question for Sulfuric acid."
] |
[
false
] |
What materiels wont Sulfuric Acid melt through? We are making a science project in school, and cant seem to find an answer anywhere. Reddit you are my last hope.
|
[
"Depending on my concentration, I can be kept in various types of glass/plastic containers.",
"Lead and Tungsten are ",
"resistant to me."
] |
[
"As mentioned, sulfuric is commonly stored in glass, lead, or plastic. ",
"Glass however, is unmachinable, unweldable, and brittle. It also has poor thermal conductivity and a slew of other properties that are undesirable for large scales. Plastic and lead have a low melting point. Tungsten is unweldable and unmachinable. It might be obvious now that there have to be other things that allow industry to perform in high temperature large scale conditions.",
"For normal temperatures, in commercial concentrations, sulfuric can be stored in good old carbon steel and stainless steel, provided that its passivating layer isn't removed, and that exposure to air is minimal.",
"There exist exotic alloys which can work too. I suggest taking a look at Haynes International's line of corrosion resistant alloys:\n",
"http://www.haynesintl.com/cralloys.htm",
"These alloys will corrode minimally as well as operate over a wide range of temperatures. You better believe they are expensive. ",
"Alloy G-30 seems like it corrodes only 1 mm a year in 99% sulfuric at 140 C, which is incredible.",
"Another good exotic alloy company is Special Metals. I'm not as familiar with them, but they list their corrosion resistant alloys in this document:\n",
"http://www.specialmetals.com/documents/Corrosion%20Resistant%20Alloys.pdf",
"As you can see, there exist a wide variety of materials that can do the job. It then becomes an engineering challenge to determine the purpose, the price, and the factor of safety."
] |
[
"When in doubt, PTFE (polytetrafluoroethylene aka Teflon): ",
"http://www.vp-scientific.com/Chemical_Resistance_Chart.htm",
"This pertains to storage. ",
"Zero's post is quite good regarding the sulfuric acid in industry. Due to environmental disposal problems, most companies have either switched to solid acid catalysts or have considered switching."
] |
[
"Why are we looking for exoplanets?"
] |
[
false
] |
We can't live on them considering the distance alone, so what are the current goals in the exoplanet search? Just to learn about the universe?
|
[
"Being able to get a better handle on number, location, size, and make-up of expolanets is fundamental for a number of reasons. It gives us a much better idea of how common other life might be in the universe. It gives us perspective on how 'special' the Earth is. It allows us to better understand solar system formation processes. And, perhaps most importantly of all, we find out something we didn't know before."
] |
[
"Because it's interesting."
] |
[
"I think it's worth pointing out that science doesn't like the idea of special cases. So far, life on Earth seems like a special case - we haven't found life anywhere else. So we're looking for life anywhere we can find it. Currently, we're looking for evidence of life on Europa and other moons in the outer part of the solar system, but it's thought that any life we find there will be pretty small and pretty simple - for complexity and size (it's thought) you need lots of oxygen and lots of energy.",
"Now if we count all of the possible planetary bodies in the solar system that might contain life, you get quite a small number, < 10. That's a pretty poor sample set. We're looking for exoplanets to allow us increase the size of the sample set. The more planets we see, the more we can figure out just how rare life is. We've really only begun to scratch the surface of this exciting field. I was reading from a textbook last night that was updated in 2011, and noted that it would already be out of date by the time that it got into our hands.",
"Anyway, the endgame here is to search for life. We're looking to constrain the variables of the ",
"Drake equation",
". And we're searching for life that looks like life as we know it because we don't know what else to look for. Exoplanets may harbour life, and whether or not they do will have profound implications for us here on this warm, wet rock."
] |
[
"What's the difference between Special Relativity and the Lorentz transformations?"
] |
[
false
] |
Einstein is famous for special relativity, but the Lorentz equations that it uses predate his theory and was developed by Lorentz apparently to explain the same phenomena. What's the difference?
|
[
"He came up with a consistent framework for kinematics and electrodynamics that made use of the mathematical tools developed by Lorentz. A decade later he formulated a theory of gravity that was consistent with the principle of relativity."
] |
[
"He does, the symmetry is named after him."
] |
[
"The Lorentz transformations are an integral part of SR. They are how you transform between different inertial reference frames."
] |
[
"Can our DNA be used to guess at our fingerprints?"
] |
[
false
] |
Or vice versa? Are the patterns on our hands and feet are result of specific alleles in our genes, or are they a result of our environment instead of our DNA?
|
[
"Not much is known about the specifics, but enough is known to answer your question. ",
"We know that there is a genetic component to fingerprint formation. For instance, a mutation to the regulatory gene SMARCAD1 can yield adermatoglyphia--a rare condition that results in no fingerprints forming. ",
"We also know that environmental factors must be at play in the womb, as identical twins do not have identical fingerprints."
] |
[
"Usually much more similar compared to non-twins, but still quite distinguishable. ",
"This study",
" measures \"Minutiae matching between twin–nontwin scores a 3, whereas matching between twins scores matching score of 38 -- both on a scale of 0–999.\" "
] |
[
"Are the patterns on our hands and feet are result of specific alleles in our genes, or are they a result of our environment instead of our DNA?",
"A little of both. Twins have similar fingerprints, which shows there is a genetic component, but they are definitely different, due to local, random events during fetal development."
] |
[
"Has the total number of organisms on earth at a given time increased, decreased, or remained generally static over the last 500 or so years (more recent history)"
] |
[
false
] | null |
[
"Are you including prokaryotes (i.e. bacteria and archaea)? If so, the number is so large as to be more or less incomprehensible.",
"There are something like 10",
" bacterial cells (each one being considered an individual organism) in your body alone (also interesting to note: that's ten times as many of \"your\" cells as there are in your body), meaning that the population of bacteria that live directly on or in human bodies on planet Earth is about 7*10",
" .",
"That's only those associated with humans.",
"Anyways, I don't really have an answer to this question. Just wanted to point out how damn many microbes there are on this planet."
] |
[
"Yeah, I guess I didn't really complete my thought there.",
"I guess my point was that when dealing with numbers that large, I'd be skeptical as to whether we can even take a reasonable guess.",
"ninja edit: excluding microbes might get us a better chance at coming up with an answer, but I'm not the person who has it."
] |
[
"I'm not looking for specifics so much as I am a general trend in their change.",
" Ok, for the purpose of fulfilling the intent of the question, lets disregard single-celled organisms."
] |
[
"How dangerous are lead glazes, really?"
] |
[
false
] |
This question is specifically about glazes on ceramic mugs. Is there a stable way manufacturers can use lead glazes that doesn't lead to leaching of the Pb into liquids? What factors influence leaching?
|
[
"The factors that influence leaching are a combination of the relative solubility of lead in the glaze versus liquids in contact, and kinetics.",
"Relative solubility tells you how lead would be distributed between the glaze and the liquid if the liquid were left in contact for a very long period of time. However, it is possible to develop systems that will trap ions or molecules. One example is polymer networks that can be synthesized with pore sizes too small for a protein to squeeze through, with the protein trapped inside until the polymer network degrades or swells. Another example is a set of molecules known as chelators that can bind with coordination sites on metal ions. These could be used to trap something like lead inside of a material.",
"Judging from a public health advisory (",
"http://www.dhs.wisconsin.gov/lead/doc/Porcelain%20and%20Ceramic2.pdf",
"), leaching rates vary. It is almost certainly possible to develop lead-containing products that would be of minimal health risk, but why would you want to?"
] |
[
"They actually leach out very quickly, I have seen Secondary Ion Mass Spec data from crystal decanters and there is a lead depletion zone on the surface. I believe pH has a big affect on the solubility of lead compounds so acidic foods and lead glazes would pry be bad.",
"If you were alive before the 80s when leaded gas was common you already have been exposed to more lead than you can imagine, little more wont kill you right away"
] |
[
"They actually leach out very quickly ... a lead depletion zone on the surface.",
"Does that mean that after rinsing/soaking them (with acid?) enough, they'd become pretty safe since the surface lead had all leached out?"
] |
[
"Aside from height, did homo sapiens look significantly different in the distant past?"
] |
[
false
] |
As I understand it, modern humans have been around for about 150,000 years. Did we look significantly different then? What about 10,000, 1,000, or even 500 years ago?
|
[
"As I understand it, modern humans have been around for about 150,000 years. Did we look significantly different then?",
"This doesn't have a simple answer",
".",
"One identifiable group from about 160,000 years ago was ",
"Homo sapiens idaltu",
"Some images of what Homo sapiens idaltu might have looked like",
"."
] |
[
"Keep in mind that the pictures are somewhat guessy recreations of what they looked like. Sure we know where all the face muscles go but there is a certain amount of artistic freedom taken in this type of recreation.",
"Another thing is their facial features may have looked as modern as the recreations show but the skulls themselves are a bit more robust which may be obvious if looking at an idaltu in real life. We are really good at picking out tiny differences in faces and bodies."
] |
[
"I see. From those pics, I bet I wouldn't look twice at a homo sapiens idaltu if I saw one. Looks like a modern human to me. Thanks for the answer."
] |
[
"What's the limiting factor in making bipedal robots?"
] |
[
false
] |
After the somewhat recent DARPA robotics challenge, its pretty clear that we have a very long way to go before we get to machines like the police robots seen in chappie and the like. My question is, what's stopping us? I'm referring mostly to the problem of balance/walking. I understand that this is certainly not a simple problem, but I would think that current accelerometers have a high enough polling rate and servos are fast enough that this wouldn't be an issue anymore. When it can get reading from sensors 100s of times per second and react with minute changes, wouldn't balancing and running be possible with good programming?
|
[
"If you just need it to move on an infinite plane, it would be easy. Walking up stairs and over obstacles is more complicated than just walking normally and trying to balance. And if the robot can't walk up stairs and over obstacles, wheels would be better."
] |
[
"The CMU robot seemed to be a hybrid: mostly bipedal, but occasionally used four legs. And the legs had treads, too. "
] |
[
"But that's just it, I would understand it being considerably more difficult on uneven terrain, but it seems like even on a flat plan, it hasn't been done yet. A brief Google search brought me to examples like this ",
"https://m.youtube.com/watch?v=gBA-9PelR5E",
"And this ",
"https://m.youtube.com/watch?v=lPEg83vF_Tw",
"Which are certainly impressive, but they don't appear to have completely freedom movement. They can probably only walk/run in a straight line/circle."
] |
[
"Which part of the body has the highest Pain Threshold?"
] |
[
false
] | null |
[
"Your back and thighs have the lowest density of pain fibers. The skin on your back, especially between your shoulder blades is much thicker compared to your thighs, so the pain receptors are less likely to be activated.",
"It really depends on what you mean by pain threshold. Each of the nerves is going to have roughly the same threshold, just the amount of nerves being activated is going to be different."
] |
[
"Any location where you build up a high density of dead epithelium on the surface and low nerve induction. The back of the elbows could be argued."
] |
[
"Thanks guys! I'llbe sure to include this in my research! You guys helped a lot!"
] |
[
"Do Chloroplast also get dna from the maternal line."
] |
[
false
] | null |
[
"In terms of sexual reproduction, I think maternal chloroplast inheritance is more common than paternal chloroplast inheritance (at least in what's been studied so far), but it is definitely not the rule. There are several organisms that show near exclusive paternal chloroplast inheritance and some that show a mix of maternal and paternal inheritance.",
"1"
] |
[
"How are chloroplasts in pollen? Or do plants do it differently than human cells that inherit the actual mitochondria from the mother and ovum cell?"
] |
[
"Chloroplasts are plastids specialized for photosynthesis. There are a lot of other forms of plastids (chromoplasts that make flowers colorful, amyloplasts that store starch in potato tubers, elaioplasts, etc.) All of these plastids have the plastome, not just chloroplasts. Pollen stores a lot of the energy it needs in the form of starch in amyloplasts. So while plastids usually come from the female gametophyte (in angiosperms), the male gametophyte also has plastids. ",
"http://en.wikipedia.org/wiki/Plastid"
] |
[
"Do simple carbs release more insulin than complex carbs per carb consumed?"
] |
[
false
] |
I was discussing with a friend who studies this and he was saying that it all matters about the area under the curve. Simple carbs spike insulin to a peak but wear off quickly whereas complex carbs raise it to a steady level for a longer period but the insulin release is the same. Is this correct?
|
[
"Your friend is correct. The islet cells in the pancreas (that secrete insulin) use ATP as their marker for how much glucose is floating about (glucose is of course broken down and used to produce ATP)-- the pertinent ion channel is called Kir6.2 and we have drugs for diabetes that target their co-receptor to stimulate insulin release. They're called sulphonylureas (examples include glibenclimide and gliclazide). The same amount of ATP will trigger the same amount of insulin released. The difference is in how long it takes for sugars to be 'converted' to ATP. The process is much longer for complex carbohydrates, which have to be broken down to their constituent sugars first."
] |
[
"There are many factors that influence insulin resistance e.g. just being south Asian puts you at risk. The manner in which different carbohydrates do is controversial- lots of conflicting studies. Dietary studies are inherently difficult. However, losing weight does seem to reduce insulin sensitivity, thought to be due to the resultant loss of visceral fat around the pancreas. The controversy lies in knowing what diet plan is best for doing that (e.g. low-carb/high-fat or vice versa). At the end of the day though, to lose weight, energy out must be greater than energy in. Balanced 'mediterranean' diets have the most evidence behind them and are reccomended by NICE.",
"As for insulin spikes, they are known to cause inflammation to the vessels, thereby increasing cardiovascular risk. Lower, more prolonged insulin release is better for you."
] |
[
"Great response. In regards to the complex carbs, even though the same insulin is released, does that longer process help dissuade insulin sensitivity when compared to the spike from simple carbs? Or does it not have an impact at all?"
] |
[
"Why are so many types of \"special\" functions orthogonal to each other?"
] |
[
false
] |
[deleted]
|
[
"Well... orthogonal functions are useful right? And functions that are dense, i.e. functions that can be used to approximate other functions are also useful, right? The most useful thing is therefore functions that are dense ",
" pairwise orthogonal.",
"The good thing is: Give me a dense set of functions and a definition of orthogonality - a scalar product, in other words - and I give you a set of ortogonal dense functions! And I can do that by the Gram-Schmidt algorithm.",
"For example, give me an especially simple set of dense functions - polynomials, and an especially simple sense of orthogonolity, namely the L²-sense on [-1,1]. I know that 1, x, x², x³ etc. are a basis of the polynomials, let me apply Gram-Schmidt, and out come the Legendre-Polynomials! ",
"Give me the same dense set, but a different sense of orthogonality - L² with weight function (1-x²)",
" - let me apply Gram-Schmidt, and out come the Chebyshev-Polynomials!",
"In other words, they are \"special\" because they are orthogonal, and \"discovering\" them is sort of a natural process, simply because orthogonal functions are so useful.",
"Please realize that you could also use a different basis to represent your wave-functions in! You could write your wave functions as the linear combination of your favourite set of functions. Only, doing calculations becomes much harder if you do so."
] |
[
"We can forget about the QM, but we can't forget the abstract vector space stuff. It all works for physics ",
" we work in these spaces (a consequence of superposition).",
"Maybe I'm just not making the connection between the abstract linear algebra and the more concrete differential equations.",
"It all boils down to the fact that differential operators are linear. Differential operators ",
" operators on some abstract vector space. If you have any (nice enough) differential operator on some function space, and that function space has an inner product, then we are 100% guaranteed that it will have orthogonal eigenfunctions. If you look at all of these special functions, Bessel, Spherical, Chebychev, you'll see that there is always a corresponding differential equation that these satisfy. These differential equations are the original context in which the special functions became special. It is a consequence of the fact that they are solutions to some eigenvalue problem that they are orthogonal. ",
"If you have a non-linear differential equation, we are no longer guaranteed that this will orthogonality process will happen. Linearity of differential operators is at the heart of all this."
] |
[
"We can forget about the QM, but we can't forget the abstract vector space stuff. It all works for physics ",
" we work in these spaces (a consequence of superposition).",
"Maybe I'm just not making the connection between the abstract linear algebra and the more concrete differential equations.",
"It all boils down to the fact that differential operators are linear. Differential operators ",
" operators on some abstract vector space. If you have any (nice enough) differential operator on some function space, and that function space has an inner product, then we are 100% guaranteed that it will have orthogonal eigenfunctions. If you look at all of these special functions, Bessel, Spherical, Chebychev, you'll see that there is always a corresponding differential equation that these satisfy. These differential equations are the original context in which the special functions became special. It is a consequence of the fact that they are solutions to some eigenvalue problem that they are orthogonal. ",
"If you have a non-linear differential equation, we are no longer guaranteed that this will orthogonality process will happen. Linearity of differential operators is at the heart of all this."
] |
[
"Does electric stimulation actually build muscle?"
] |
[
false
] |
In "Return of the Dragon" a movie based on Bruce Lee's life, he uses them. I have tried looking for other evidence that it actually stimulates the muscle in a similar way to exercising, but there seems to be none on it. Couldn't constantly exposing your body to electric current cause other problems as well? I also wanted input from actual experts, not broscience, that is why I posted to /askscience
|
[
"http://www.reddit.com/r/askscience/comments/k28kg/why_cant_i_build_muscle_by_electrically_shocking/"
] |
[
"Unless I'm terribly confused, you shock your muscle and ",
" means your body is still doing some work. But as I recall from discussing this with some physical therapists and athletic trainers and a couple exercise physiologist (I run in some weird circles, believe it or not) part of the problem is that it doesn't push your myofibers to the level of performance, and there's no increase in heart rate to accommodate the relative increase in need for oxygen and whatnot, which results in limited potential for gain. But, having gotten stim many times myself, I can tell you them make a sore muscle feel a hell of a lot better after 20 minutes or so.",
"Oh, and a lot of athletes do use it, just not the way Bruce Lee did in the movie. More for use on sore muscles, less to make your core muscles look good."
] |
[
"Thanks. I tried searching but it did not show up. Looking at that thread though still leaves the same question unanswered: why is Ems so rarely used? "
] |
[
"My mom is convinced cancer is contagious. Obviously it's not, but she wants the \"opinion\" of medical students/doctors, not a lowly premed such as myself. Would you mind debunking this?"
] |
[
false
] | null |
[
"Couldn't you just get a note from a doctor, if you're premed and working at a clinic it shouldn't be terribly hard to find an MD"
] |
[
"I won't start for a couple weeks. It's more of a spur of the moment debate that I'd like to settle before I fly back out to school."
] |
[
"Cancer is an out of control cellular growth that develops out of environmental or genetic reasons on a cellular based level. Someone sneezing on you will not make your cells begin to grow without necessity. It's not like one can high five prostate cancer into yours. It's much more complex than that and if her thoughts are otherwise perhaps she wouldn't mind finding the cure for those with actual cases of cancer they didn't get from a bathroom hand rail."
] |
[
"Is it normal for metastudies to discard vast majority of considered individual studies?"
] |
[
false
] |
I was browsing through a list of studies on beneficial effects of alcohol, and ran across . Abstract states that Of 4235 studies reviewed for eligibility, quality, and data extraction, 84 were included in the final analysis. That's less than 2% of the studies, which seems surprisingly small. Is that normal? Also, am I correct in assuming that with such small fraction, even a slight change of study selection criteria may substantially affect results?
|
[
"Yes. Typically, the authors will specify some search criteria for finding all studies that could possibly be related to the issue at hand. Then they will select from those studies ones that fit certain criteria. The initial search criteria may be overly broad, to ensure that no studies are missed.",
"Fig. 1 in the paper you linked goes over this (",
"direct link",
"). For example, 4005 of the 4235 studies identified by keyword literature search did not report on alcohol intake and cardiovascular disease outcomes, or did not contain original data."
] |
[
"Tons of grad students. :)"
] |
[
"Yes and No",
"1- A good meta-analysis allowing good conclusion needs good material like prospective randomized studies without bias and with a sufficient number of patients included, which are not the majority of the studies.",
"2- The selection criteria is defined before the inclusion of the studies in the meta-analysis, thus the change of the selection criteria will require to go again through the list of studies to select the more relevant and not \"change the results\" because the studies selected with the previous criteria won't be relevant anymore.",
"I hope this helps.",
"You can check out the PRISMA statement which offers good guidelines on how to do a meta-analysis.\n",
"http://www.prisma-statement.org"
] |
[
"Can you siphon air?"
] |
[
false
] |
I understand you could siphon a dense gas, but could someone siphon air on earth?
|
[
"Siphoning water works because water has suface tension, not because of a difference in atmospheric pressure. There was an experiment in 2014 by Dr Hughes that showed siphoning in a hyperbaric chamber. Since air doesn't have intermolecular adhesion that siphonable liquids do you couldn't \"siphon\" it."
] |
[
"I was wondering this myself... I would think at a column of enough air would be buoyant enough to overcome the pressure of water, and thus rise to the surface, creating a negative amount of pressure behind it...",
"But like Anonymous_scientist pointed out, water works by surface tension, if air rises, it could be displaced by water instead of air.",
"But I'm wondering if there's a type of porous material or certain size of pore whereby air can be transferred in one or both directions, but not water.",
"If you had a pore which could only let air pass and not water, and a column of air beneath it which had enough buoyancy to overcome the water pressure and resistance of the pores, wouldn't that establish the siphoning effect?"
] |
[
"Siphoning requires something above the fluid pushing down on it. You can't siphon water on the moon. It only works because of air pushing on it. You could siphon air if you stuck something lighter, like hydrogen or helium, on top of it."
] |
[
"Do passing asteroids have an effect on for example the tides?"
] |
[
false
] |
Seeing as how a relatively big asteroid passed earth at "only" 200.000km last Sunday I wondered if passing asteroids (or other things) affect the tides.
|
[
"What's interesting about gravity is that it has an infinite range, which is not true for the other 3 forces (strong, weak nuclear and magnetism). Because of this, you could say that every atom of matter in the universe has an effect on the tides of our oceans, this includes you! You walking around has an effect on tides, that's pretty crazy.",
"A better question is \"do passing asteroids have a perceptible effect on the tides\" and the answer to that is leaning very heavily to the no side. The moon weighs 1.2% of the entire earth which is still like a bajillion tonnes (or something) so its affect on the oceans is quite great. Asteroids usually have a mass in the few thousands of tonnes, which is like a speck of dust compared to the moon, the gravitational affect of this is negligible."
] |
[
"What makes you think electromagnetism has a limited range?"
] |
[
"(not OP) It has infinite range, but it is so strong that all macroscopic objects tend to be close to neutral, typically leading to very small electromagnetic forces over long distances."
] |
[
"Is there estimated upper limit for mass of a star before becoming a black hole? Is mass the only determining factor for if a star becomes a black hole or not, or what are the other factors?"
] |
[
false
] |
[deleted]
|
[
"http://en.wikipedia.org/wiki/Chandrasekhar_limit"
] |
[
"When discussing whether or not a star will become a black hole the only thing considered in most discussions is the mass of the black hole. In fact, the initial mass of a star pretty much determines that star's entire lifetime of evolution. However, there is one major assumption that we use in these discussions: when the star is formed it is formed out of primarily hydrogen, with measurable amounts of helium and all other elements (during formation, not throughout lifetime) are trace. This is a very valid assumption for the stage of universal development we're currently in- however in the future this will not be the case. At that point, the composition of the star will play a role in its development as well. "
] |
[
"I believe that is the symbol for the sun, and should be read as 0.1 solar masses."
] |
[
"What does it mean for a coordinate to be timelike?"
] |
[
false
] |
In the wikipedia article about Schwarzschild black holes, it says : For r < rs the Schwarzschild radial coordinate r becomes timelike and the time coordinate t becomes spacelike. What does it mean for a coordinate to be "timelike" ? Does it just mean that an object must move forwards in that coordinate?
|
[
"It's referring to the sign that that coordinate gets in the metric.",
"For example, in the Minkowski metric in the (-+++) convention, the metric is ",
"ds",
" = -c",
"dt",
" + dx",
" + dy",
" + dz",
".",
"The dx, dy, and dz terms are all positive, while the dt term is negative. So t is a timelike coordinate while x, y, and z are spacelike coordinates.",
"The Schwarzschild metric is",
"ds",
" = -(1 - 2M/r)dt",
" + (1 - 2M/r)",
"dr",
" + r",
"dΩ",
",",
"where I've used Ω as a shorthand for the angular part containing the two spherical angles.",
"Focus on the t and r terms. For r > 2M (the Schwarzschild radius), (1 - 2M/r) > 0, so the dt term is overall negative and the dr term is overall positive. That's the normal case, just like in Minkowski. The t coordinate is timelike and the r coordinate is spacelike.",
"But for r < 2M, (1 - 2M/r) < 0, and the signs flip. The Schwarzschild coordinate t becomes spacelike and the Schwarzschild r becomes timelike. Some people say that this means that \"space and time are switching places\" at the event horizon, but a more correct explanation is just that you chose bad coordinates. t looks like time and r looks like the radial coordinate from your typical spherical coordinates, but that's not quite true. This set of coordinates has a coordinate singularity at r = 2M. There are other sets of coordinates which behave perfectly fine at the horizon, so this bad behavior is just an artifact of the choice of coordinates."
] |
[
"There are lots, one example is ",
"Kruskal-Szekeres coordinates",
"."
] |
[
"Well then you’ve missed one of the major points of general relativity, coordinate invariance. There’s nothing special about a set of coordinates, they’re just labels for points in spacetime. You can choose to label the points in your spacetime however you want, and it should not affect any physics. As a corollary, coordinate singularities are not physical, they just reflect the fact that your set of coordinates fails to work at certain points.",
"But anyway, a specific example of a set of coordinates for a Schwarzschild black hole that works fine at the horizon is Kruskal-Szekeres coordinates."
] |
[
"Can you demonstrate why cycling through a one-time-pad encryption key that's shorter than the message is not secure?"
] |
[
false
] |
I wrote a in python, to try to better understand one-time pad encryption. (Warning: Does not work with python 2.x, use Python 3). The program works as follows: Though it's obvious in the first example why cycling through an encryption key shorter than the message to be encrypted is not secure, it's not so obvious in the second example. Could you explain what would be the approach to decipher the message in the second example? : Updated sample code to work with unicode.
|
[
"The reason the standard one-time pad is perfectly secure is that regardless of the message, the distribution over ciphertexts is always identical. Once you recycle your key, this is no longer true. For example, (working over a binary alphabet of 0 and 1), if your key is 3 bits long, then no matter what, if your message is 3 bits long, each of the 8 different 3-bit strings is the ciphertext with probability 1/8.",
"On the other hand, suppose your message is 6 bits long. Then the distribution of ciphertexts for the message 000000 is different from the distribution of ciphertexts for the message 000111. In the first case, your ciphertext is the same 3-bit string repeateed twice. In the second, the second 3-bit string is the bitwise negation of the first 3-bit string. ",
" You have in fact pretty much realized this I think, based on your first example.",
"This is the theoretical background. \"Security\" in the cryptographic sense is generally defined along these lines -- you should not be able to distinguish between the encryptions of two different strings of equal length. You should check for yourself that if you don't know the key, you can never tell the difference between these encryptions in the one-time pad.",
"Naturally, you might ask \"this is a bit contrived, what about in real world terms?\" Well, if your message is much longer than your key (as it will be in some applications -- keys may be 2048 bits long, 256 8-bit ASCII characters), then you are vulnerable to statistical analysis on the ciphertext. It is well-known that letters do not occur with equal probability in English or any common language. You simply need a key length (or a few guesses at it) and now you can separate the ciphertext into the letters encrypted by the first letter of the key, the second letter, and so on. Now you can basically use some average distribution of letters in english to figure out not only the original message but the encryption key.",
"So in fact this pretty broad requirement in cryptography that security is taken to be the indistinguishability of ciphertexts is not that contrived after all.",
"In fact, most cryptography is under a definition of security where algorithms have to be efficient (that is, they run in polynomial time). The one-time pad in fact has information-theoretic security -- no algorithm, regardless of its running time, can defeat the one-time pad."
] |
[
"Let's assume the attacker knows the length of your secret key and aligns your message like so",
"short key\n---------\nThis a lo\nng messag\ne and sho\nuld be so\nmehow dec\nipherable\n",
"He knows \"s\" combined with first column (\"T\",\"n\",\"e\",\"u\",\"m\",\"i\"), \"h\" combined with second column etc. This is too little, but if your message was slightly longer, the most common combination in any column would probably be combination of whatever the letter in your code is (here \"s\") with space or a common English letter (\"e\", \"a\" etc.). So you look at frequencies of encoded characters in any particular column and make a guess that those correspond to space. Once you get the guess right, you know the character in the secret key and you get the whole column for free. Once you have several columns, it snowballs: if you see \"Th_s\" you can guess _ is \"i\" and then the whole third column collapses.",
"But there's no need of breaking it completely. It's enough to know this schema allows to extract nontrivial information about the plaintext to reject it."
] |
[
"By repeating a shorter key, it becomes a Vigenère cipher rather than a one-time pad. The Vigenère cipher is vulnerable to frequency analysis. Assuming the plaintext is in a natural language, then the frequency of letters for writing in each language is well known. For English, we expect an index of coincidence of about 1.47. For your plaintext the value is about 1.5, which is right on target.",
"By encrypting the text, you somewhat hide the expected frequency of letters in the message. However, if a repeating key is used, we can use trial and error to guess the key size, break the message up into chunks of text of the guessed key size, and then perform frequency analysis of the chunks.",
"Since the cipher is simple, it will not hide the underlying letter frequency, as long as the chunks of text correspond to the key size.",
"When we try a key size that gives an index of coincidence close to the expected language, e.g 1.47 for English, then we have likely guessed the key size or a multiple of the key size.",
"Once the key size is determined, then a brute force attack can be used on the chunks of text of the given key size to determine the key.",
"References:",
"http://en.wikipedia.org/wiki/Vigen%C3%A8re_cipher",
"http://en.wikipedia.org/wiki/Index_of_coincidence",
"http://en.wikipedia.org/wiki/Frequency_analysis",
"Note that your longer example is too short to illustrate these techniques, but for that short of a message you might as well use a one-time pad anyway.",
"EDIT: For the curious, the cipher text must be arranged as a matrix where the row length is the guessed key size, and the number of rows depends on the length of the key and the length of the text. Short plaintext won't give us many rows if the key size is close to the text size. The index of coincidence must be calculated for each COLUMN, because we have to assume that each letter of the key is different, and therefore each column of the matrix is encoded using the same letter of the key. And so we need enough rows in the matrix to get a good index of coincidence for each column."
] |
[
"How do hand sanitizers work? (in chemistry terms)"
] |
[
false
] | null |
[
"It's not really like soap and water. But has some of the same end results.",
"Saponification yields polar molecules capable of micellars formation which results in dirt and microbes being surrounded and washed away while polar molecules can also break apart phospholipid membranes and cause cellular damage.",
"Alcohols generally have two covalent bonds that contribute to polarization, which means they can also be very disruptive to a phospholipid membrane but because it is an organic solvent, it easily dissolves many other organic substances, is soluble in water because of its polarity, and can aggressively crenate microbes and cause lysis.",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3175087/",
"https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Supplemental_Modules_(Organic_Chemistry)/Alcohols/Reactivity_of_Alcohols",
"Also look up protein denaturation."
] |
[
"I'd also suspect some of it has to do with diffusion of water. The concentration of alcohol exterior being high (60% or greater) means a good amount enters the pathogen as well. This allows it to act on both the exterior and interior of the cell. ",
"Additionally, I'd like to add there is some variation between effectiveness with different alcohols. ",
", IPA tends to be slightly more bactericidal than ethanol, but ethanol is ",
" slightly more virucidal. ",
"CDC page",
"As for staying healthy, soap, water, and thorough scrubbing is generally the most effective."
] |
[
"Crenation lysis and protein denaturation.",
"Among other disruptive effects. I'm not sure it readily traverses the envelope or membrane though, you don't hear much about that."
] |
[
"Could I make liquor from a chocolate bar or candy?"
] |
[
false
] |
Ok, so I've heard that if you let a Twinkie ferment for a while you end up with a pretty nasty liquor, I'm not sure if that's a myth or not. I know that alcohol is made from distilling fermented sugars so theoretically, if I had a still, could I know make alcohol from a chocolate bar or candy?
|
[
"So long as you have clean containers and equipment, essentially any sugary item that is mixed with water or is liquid already and not too saturated with sugar, can be mixed with yeast to initiate safe fermentation. You could also begin fermentation in unclean containers, but you risk letting other fungi or bacteria take over your yeast culture or contaminating your culture with something else that might prevent a successful culture.",
"I don't recommend using candy for fermentation. A friend of mine has experimented with this and the results are disgusting. There is definitely alcohol in the resulting product though.",
"If you have a still, anything you ferment successfully can be turned into liquor.",
"edit: Removed some information to attempt brevity."
] |
[
"I wonder how many chocolate bars I would need to fill a 20L bucket and what it would yield",
"This is a crazy path to go down. I'll outline why and answer your question.",
"I'll assume you want as much alcohol as possible to begin with to make distilling faster and more productive, and I'll assume you're using only chocolate bars to provide food for the yeast. This would normally land you at around 19% alcohol because as I understand it, yeast doesn't perform well and eventually dies in a more alcoholic environment. Hence the reason we use stills to concentrate alcohol. Unfortunately, this would require far too many chocolate bars (Over 30 of them) per volume of water and I personally wouldn't want to attempt fermenting what resulted, so we'll aim for a still not so modest 10%.",
"To accomplish this you will need ",
" .9 Kg of sugar for every 4.5 liters of water in your container, as per the standard hydrometer tables.",
"On lindt.com, the 70% cocoa chocolate bar",
" is 26.66% sugar. This poses a significant issue; nearly three quarters of what we're using for our sugar source is a solid that will not be digested by yeast and will be difficult to separate and discard. A clarifying solution may help us, as will repeated racking and then distilling, but it will be an issue.",
"But oh well, we'll do it anyway. For a 4.5 liter batch, we're going to need 34.02 (Let's go with 34) Lindt Excellence 70% cocoa chocolate bars to get enough sugar (900 grams) in order to obtain 10% alcohol. Since the bars are 100 grams, this means we'll have about 2.5 Kg of ",
" materials in our fermenter. That's a lot of stuff. It's a lot of cocoa, cocoa butter, the odd bit of trace nuts, soy lecithin and milk.",
"If you're not discouraged yet, you'll be disappointed that your ~3400 grams of chocolate bars mixed with 4.5 L of water is actually leaning towards being more of a soup than a potential alcoholic beverage. But it will ferment.",
"If a clarifying solution and then racking helped, you'd eventually have a liquid that was suitable for distilling without being disgustingly messy. If you're confused as to how I worked all of this out, I'll outline the math, but if you're familiar with brewing I think you'll understand.",
"Ultimately, you want to use a bit of chocolate and a lot of water and sugar. Filling a recipe with chocolate bars is not a good idea. With fruit you can easily separate solids in the end, so adding such a low sugar to solids ratio is okay... Plus most of the sugar is added in the form of nearly pure refined sugar. The material in chocolate bars on the other hand will give you the equivalent of chocolate milk in water form. A lot of the solids will remain suspended.",
"Perhaps I've taken you too literally. Regardless, I highly recommend using pure forms of the ingredients you want from chocolate bars such as cocoa, sugar and vanilla. The rest of what you'll get from a bar is not suitable for fermenting.",
"I've seen some terrible mold because we didn't fill the buckets enough.",
"This has nothing to do with how full your containers are. Mould occurred because you weren't sanitary enough and/or your buckets aren't actually sealed from contaminants in the air.",
"they're usually packed to the brim and sealed airtight.",
"You want the release of CO",
" to be possible during primary and secondary fermentation. Fresh air exchange is not wanted, but a relatively tight lid with some gaps for air will allow CO",
" to leave without letting fresh air enter. If you don't let some air through, the container will almost definitely explode. Be careful. Also be careful of leaving enough room for vigorous fermentation - Sometimes you can get several inches of yeast and gas bubbles on the surface. That stuff will poor out of your bucket, forced out by the production of gas and more bubbles, once it reaches the top.",
".",
" A fine standard for this experiment, but 65% is better. Clicking the ingredients on their website isn't working so I've chosen to go with 70% which does work. 65% is the most sugar you can get in a non-milk chocolate bar as far as I know. Unfortunately, that 5% difference will not make this recipe a good idea."
] |
[
"Good beers get their distinctive taste from the yeast and i assume wines as well (i don't know much about wine.) Brewing stores have many types of yeast and it is impotent to use the correct yeast for the style of beer you are brewing. I think that the taste from the yeast is less important for distilled spirits but I don't know if it would be possible. Yeast is so cheap and scales up to large batch sizes i can' imagine how your method would cheaper."
] |
[
"Is Fuzzy Logic used in science, and more specifically in Quantum Mechanics?"
] |
[
false
] |
So I am self studying Fuzzy Sets from . Chapter 1 concludes with a discussion on paradigm shifts, and how fuzzy logic is a new paradigm that will change science considerably. The book was written in 1995 though. So did scientists adopt this new paradigm, and more specifically did this new paradigm make its way to quantum mechanics?
|
[
"I've never seen fuzzy logic used in quantum. Quantum mechanics is a probabilistic theory, sure, but we still work within well-defined sets (i.e., a normed vector space). It sounds like fuzzy logic works with a different sort of set.",
"It's possible that this is because our language about quantum mechanics is based on observable operators, and when you make an observation in quantum mechanics, the result of that corresponds to a classical truth value - it either is in the state you are measuring, or it's not. We can describe the probability of it being in that state ",
" we measure it, but ",
" the measurement is made, it was ",
" in whatever state was measured.",
"It's like flipping a coin - while it's in the air, there's a 50% probability of it landing heads up. But after it lands, it's either ",
" heads or ",
" heads.",
"From the sound of it, fuzzy logic doesn't really help there.",
"However, I think fuzzy logic ",
" used to make things like control circuits and artificial intelligence."
] |
[
"It appears that there are some relations between fuzzy logic and quantum logic. I know near nothing about fuzzy logic, so I cannot give a very knowledgable answer to the question, but I did find a ",
"paper",
" that discusses exactly this topic."
] |
[
"Of course fuzzy logic is used in science. Computer science.",
"As for how or if it is related to QM, well, first understand that people who know about QM probably don't know much about quantum computing or fuzzy logic/computer science, and vice versa. So each person who is the expert in each field will probably say \"oh, no, my field is nothing like that other thing which sounds similar but is actually very different because of some superfluous terminology.\"",
"Now, is fuzzy logic ",
" in QM? I don't think so. Are there some similarities between fuzzy logic and probability theory(and by extension, QM)? Sure: ",
"http://sipi.usc.edu/~kosko/Fuzziness_Vs_Probability.pdf",
"Mainly they are both probabilistic theories. But there are differences also. Probability theory pretty much determines the likelihood of something happening or not. Fuzzy logic determines the degree or severety of which that 'something' will happen, given it does happen."
] |
[
"What causes the black halos around bright objects in some 1950s television programs, such as the those around the participants of this game show?"
] |
[
false
] | null |
[
"It appears to be an artifact of the imagine capture technology.",
"http://en.wikipedia.org/wiki/Video_camera_tube#Dark_halo",
" "
] |
[
"Observe more carefully. For instance, when Dali paints on the board moments later, there are large, dark halos around the white paint."
] |
[
"I want to mention that shows in the '50 were so much more entertaining than today.",
"The TV cameras back then were an exact mirror image of a CRT (Cathodic Ray Tube). The light hit the photosensitive glass panel, and generated a positive charge while an electron beam scanned the surface of the glass. The black halo, I guess, is caused by either the camera trying to compensate for the bright face over-saturation, or is an artifact of a localized high positive charge on the glass in the bright areas which leaves the adjacent areas positive charge poor, thus darker. ",
"More about this:",
"http://en.wikipedia.org/wiki/Video_camera_tube#Image_orthicon",
"An image orthicon camera can take television pictures by candlelight because of the more ordered light-sensitive area and the presence of an electron multiplier at the base of the tube, which operated as a high-efficiency amplifier. It also has a logarithmic light sensitivity curve similar to the human eye. "
] |
[
"Why don't refineries reclaim their flare's energy to heat water or the distillation stack?"
] |
[
false
] | null |
[
"I worked at a refinery. And we did use hot exhaust from the refining process to fire a steam plant that powered a ",
" 10MW co-generation plant that mostly powered the refinery with a small amount of sell-back to the power company.",
"\nBut that hot exhaust was a continuous part of the ongoing process, not temporary like a flare would be.",
"\nAs you may know, refineries are just big giant chemistry sets.",
"\nOne process feeds another process feeds another process and so on.",
"\nIf some part of the process fails, bad stuff can happen, vessels get over filled, or over pressurized, or under filled and under pressurized, or flammable and poisonous product gets spilled. The hard part about this is : a refinery + co-generation can't just start up and shut down with the push of a button. It takes days, sometimes weeks to do a proper start-up and days to do a shut down.",
"\nSo, what you have, for safety and efficiency, are those emergency flare stacks at various points in the process so that in the event of an \"upset\" in the process, the production flow has somewhere to go wile the process is either being fixed or shut down.",
"\nThe burn-off is so the material does not collect anywhere and form an explosive air/gas mixture.",
"\nYou can tell if a plant process is \"upset\" if you see flares when you drive by.",
"\nIt means something aint right up in there.",
"\nFlares are supposed to be temporary in nature so there is no economic benefit to build co-generation for them."
] |
[
"Most modern refineries already use flare gas compressors to win back their base load flaring. This way, you don't have a flame in a normal operating scenario. The compressed gas will then be reused. Only in case of an emergency, you depressurize to the flare, and then you can see a flame. Because of this intermittancy, and the fact that you only use the flare in emergencies, it won't be useful to win back that heat."
] |
[
"Yes. It was small. I guess. The turbine was in a 4 story building with the top half of the unit on the 3rd floor and the bottom half in the ceiling of the 2nd floor, and the plumbing on 1st and 2nd floor.",
"\nIt ran at 60 cycles a second = (60 x 60) = RPM and sat on \"gas bearings\" which I think was really just an injected steam cushion of some sort.",
"\nA very nifty piece."
] |
[
"I want to string together about 300ft of power cables. Googling around tells me that this is a bad idea, but doesn't explain why. What happens when you (a) join to extension cords together, and (b) run very long distances?"
] |
[
false
] |
I'm trying to power my laptop about 300 feet from the nearest outlet. I'm curious for the reasoning behind all the warnings against daisy chaining cables.
|
[
"There are ",
"online calculators",
" that tell you the needed wire gauge for a given amp draw and circuit length. Assuming a 60 watt power consumption from your laptop you would need a 14 gauge cord. ",
"The problem is this assumes one continuous cord. If you are chaining cords together you will get additional resistance from the plugs themselves. This is harder to calculate because the condition of the plugs degrades with age and wear and tear. "
] |
[
"You could try ",
"/r/AskElectronics",
" for advice on what to do"
] |
[
"You are wrong. If the cables are the same thickness and material resistance is constant per unit length or cable and the heat will be dissipated easily by said cable length. The issue is overall resistance will drop the voltage. Or if the cables become coiled they could create induction and heat up."
] |
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