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[
"Bones crushed and used for mortar. Can the DNA be found?"
] |
[
false
] | null |
[
"Hi tizzlenomics thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Archaeology biology"
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"/r/AskScience",
"For more information regarding this and similar issues, please see our ",
"guidelines.",
"/r/AskScience",
"/r/HomeworkHelp",
"guidelines.",
"/r/AskMath",
"/r/AskPhysics",
"/r/PhysicsHelp",
"/r/chemhelp",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"What is the biological advantage of blushing?"
] |
[
false
] |
When some people get embarrassed they turn red, causing them to blush more. Body, how are you helping me?
|
[
"I think ",
"this article",
" might have what you need. He explores various reasons for why we blush in different situations."
] |
[
"Now I only have a couple semesters of bio under my belt but it may be linked to getting a mate. Back when we first separated from our ape ancestor, the best male and females would mate. Now if you notice that when you are sick you lose color. So maybe if you blushed, then you would be perceived as being more healthy. And perhaps that is how blushing came to be."
] |
[
"I don't see any advantage mentioned."
] |
[
"How does propulsion work in space?"
] |
[
false
] |
[deleted]
|
[
"Imagine two ice skaters on an ice rink (imagine the ice is frictionless for simplicity's sake). When one pushes the other, they both move away from each other. If they have equal mass, they move away from each other at the same speed. This is conservation of momentum at work.",
"Now imagine one ice skater throws a baseball as hard as they can. The baseball is much smaller, but it's also going much faster when released. The skater will move in the opposite direction of the throw (but not very quickly). If the skater throws more baseballs, they will continue to accelerate backwards.",
"Now, turn the skater into a rocketship, the baseballs into exhaust out of a rocket engine, and the frictionless ice rink into the vacuum of space, and voila. The rocket 'throws' mass into space to move in the opposite direction of the throw; thrust is generated. Burning fuel is just a way of making gas expand very quickly, and the rocket focuses the direction of that expansion out the back using a nozzle.",
"P.S. You need a new teacher if they regard any on-topic question as 'dumb', and especially if they ignore a question outright. There is nothing that is worse for education than discouraging the asking of questions."
] |
[
"Imagine two ice skaters on an ice rink (imagine the ice is frictionless for simplicity's sake). When one pushes the other, they both move away from each other. If they have equal mass, they move away from each other at the same speed. This is conservation of momentum at work.",
"Now imagine one ice skater throws a baseball as hard as they can. The baseball is much smaller, but it's also going much faster when released. The skater will move in the opposite direction of the throw (but not very quickly). If the skater throws more baseballs, they will continue to accelerate backwards.",
"Now, turn the skater into a rocketship, the baseballs into exhaust out of a rocket engine, and the frictionless ice rink into the vacuum of space, and voila. The rocket 'throws' mass into space to move in the opposite direction of the throw; thrust is generated. Burning fuel is just a way of making gas expand very quickly, and the rocket focuses the direction of that expansion out the back using a nozzle.",
"P.S. You need a new teacher if they regard any on-topic question as 'dumb', and especially if they ignore a question outright. There is nothing that is worse for education than discouraging the asking of questions."
] |
[
"Conservation of momentum.\nBasically, a rocket (or ion engine) will shoot small particles at one end, at a high speed. This causes the body of the rocket to move a bit forward.\nDid you ever shoot a gun? It's pretty much like the recoil of the gun."
] |
[
"Why do flashing images cause seizures?"
] |
[
false
] |
[deleted]
|
[
"I'm hoping someone with better knowledge comes along, but here's my rough understanding:",
"First, if you haven't already, have a read of ",
"this",
", it explains what particular stimuli can trigger seizures in people with photo-sensitive epilepsy (PSE).\nThen have a read about ",
"epilepsy",
" in general.",
"After that, you'll know that in patients with PSE, cyclic, high contrast stimuli (flashing lights/images) seem to trigger the massive correlated activation of large parts of a person's brain (a seizure). ",
"Now the question is why? As usual we're not quite sure, but it seems that the brains of PSE patients get 'entrained' by these stimuli. That is if the rythm is right, the part of the brain that usually deals with these stimuli (usually visual centres) gets activated way more than normal. So much so that it will trigger a cascading out-of-control response that can then spread out into other brain areas. Essentially large groups of neurons are firing crazily much in a highly synchronised manner, completely disrupting normal brain function."
] |
[
"So you are saying that it is similar \nto a operating systems failure due to a \nrelatively unrestricted processing of a function or a \nmemory leak— i.e., how unrelated programs can crash \ndue to a single program heavily using available \nresources? "
] |
[
"No - what he is saying is that it is like ",
"soldiers marching in step over a bridge",
" making the bridge resonate in time with their steps."
] |
[
"What is the status on our ability to teleport objects/living organisms?"
] |
[
false
] |
Has it ever been done? Will it ever be possible?
|
[
"No it has never been done and no it will never be possible. I really wish that it weren't such a common thing in sci-fi, because it simply does not have any basis in scientific fact."
] |
[
"Can you expand on why it's not possible?"
] |
[
"Point teleportation is impossible because it breaks relativity. Even if it's constrained to be slower than the speed of light, the math of relativity just is destroyed on a fundamental level if worldlines are allowed to have step discontinuities.",
"Decomposition teleportation (where you get broken down and reassembled) is... well, not ",
" impossible I guess, but engineeringly impossible. You need the technology to make a perfect copy of the state of a human, the technology to transmit thaat copy with perfect fidelity over large distances, and the technology to construct a human from just raw materials and their state. None of these are things which we can reasonably expect to ever have.",
"I'm not aware of any other proposed forms of teleportation."
] |
[
"Does the 13.7 billion year age of our universe only apply in our frame of reference?"
] |
[
false
] |
I have often heard the age of our universe given as 13.7 billion years. However if time is relative to velocity and gravitational fields does this mean different parts of the universe have experienced different amounts of time since the big bang? Also if the earth is only 4.5 billion years old then what frame of reference is used before the earth formed? Does the figure just reflect how long someone in our frame of reference would have experienced if that frame of reference hadn't changed since the big bang?
|
[
"However if time is relative to velocity and gravitational fields does this mean different parts of the universe have experienced different amounts of time since the big bang?",
"Not different parts, but different observers, yes. The number of 13.7 billion years holds for so called comoving observers, observers who are at rest with the cosmic fluid. They see the cosmic microwave background radiation as isotropic.",
"We are actually not comoving observers, we move at 600km/s with respect to the CMB. That's why we see ",
"a large dipole in the CMB",
".",
"Also if the earth is only 4.5 billion years old then what frame of reference is used before the earth formed? ",
"Since we don't use the reference frame of the earth, this question should now be redundant."
] |
[
"It should be possible to put a number on that... let me see... ignoring the expansion of the Universe it's like .999998 times 13.7 billion years, so it's not significant."
] |
[
"I cannot answer this in full I believe you will want to read into the ",
"Hubble Constant",
" as it was a major breakthrough in being able to age the universe.",
"EDIT: Removed irrelevant information."
] |
[
"Why isnt geothermal energy not widely used?"
] |
[
false
] |
Since it can do the same thing nuclear reactors do and its basically free and has more energy potential why is it so under utilized?
|
[
"To start, my answer is going to focus on ",
"geothermal power",
", i.e., using geothermal energy to generate electricity, and ignore other uses of geothermal energy, like ",
"geothermal heating",
", since OP seems to mainly be interested in electricity generation (at least based on the relationship drawn to nuclear power). It's also important to note that depending on ",
"where you're considering",
", the premise of the question doesn't necessarily hold, e.g., in places like Iceland, the Philippines, El Salvador, and Kenya, geothermal power makes up a substantial component of their total power generation, but generally these are the exception rather than the rule.",
"As to why there is not wider global adoption of geothermal power, the closest to a single answer will be that it's not economically feasible in many places because of the background geology. Some of the geological considerations for what makes an area good or bad for geothermal power generation have been touched on in recent threads (e.g., ",
"this one",
"), but in short, in order for a geothermal power plant to be economically viable, there needs to be the expectation that the cost of building the plant can be recouped (plus a profit) by selling electricity over a reasonable lifetime of the plant. The cost of building a plant is intricately linked to how deep you have to drill to get to sufficiently hot rocks/fluids to generate power. Where these hot rocks are close to the surface, like in volcanically active areas like Iceland, plants are economically viable. In cold interior of continents, like the middle of North America, where you would need to drill much deeper to reach the same temperature, plants are not as economically viable. Thus, importantly, the idea that \"it's basically free\" does not consider that there are real, sometimes substantial, costs associated with accessing the hot rocks and fluids necessary to generate geothermal power.",
"Of course, the geology is not the only control, and there are important considerations like the type of plant in question some of which are viable with substantially lower subsurface temperatures, the ability to use preexisting boreholes as drilling is one of the most expensive aspects, technologies that improve the efficiency or longevity of plants, or simply the background cost of other power sources (i.e., an area where geothermal power might be too expensive now, might be a good option as the cost of other power generating mechanisms increase). That being said, as stated before, if you want something close to a simple answer, the geology and the local, shallow ",
"geothermal gradient",
" are good first order explanations as to why geothermal power has seen limited adoption in some places."
] |
[
"Only thing I’ll add to is existing bore holes rarely can be leveraged for anything other than data. Oil and Gas rely heavily on formation pressures or induced pressures to lift gas and liquids to surface. To pump fluid for purpose of geothermal a pump needs to be run down hole which usually means a much wider borehole is needed than the 4.5 inch production casing. (At least in my area)"
] |
[
"In addition to the other comments, it should be noted that geothermal sources can be quite toxic. ",
"The Hawaii one",
" has had continuous issues with hydrogen sulfide gas releases. It's a great source of energy, but not without its own dangers."
] |
[
"Are solar systems and galaxies fractal iterations of the atomic structure?"
] |
[
false
] |
[deleted]
|
[
"There are not really any similarities in how matter on small and large scales form structures.",
"As for some kind of golden ratio, even just for astronomical objects, there is such a large spread in planet, star, solar system and galaxy size that I don't believe any relationship exists."
] |
[
"Just a side note: the golden ratio isn't as important in Nature as you've heard. The spiral shapes of galaxies, hurricanes and mollusk shells are completely unrelated to the golden ratio and the golden spiral.",
"There are several types of spirals (archimedean, logarithmic, etc.), and different spirals of the same type can look very different. The \"golden spiral\" is just one particular version of a logarithmic spiral, and it is based on a nested square and rectangle construction that isn't expected to exist in Nature."
] |
[
"There are similarities, sure, but when you really get down to it, electrons aren't just little spheres rotating around a nucleus. They're more accurately described as wave functions, meaning their position isn't as well defined as a planet's. Also, the solar system (on a large scale) is pretty much held together entirely by one force (gravity). However, an atom's nucleus is held together by the strong nuclear force, and its electrons are bound due to the electromagnetic force. So, it's a fascinating similarity, but the analogy breaks down at a certain level."
] |
[
"How many fundamental physical fields are there?"
] |
[
false
] |
This question might be the result of my own misconceptions, but I know that there exists the Higgs field, and the electro-magnetic field (is this better phrased as the electroweak-magnetic field)? I'm wondering what other fields are there? Is there a gravity field? A strong field? Also, are all fields in physics Hilbert spaces?
|
[
"It's easy to forget one here or there, and to some extent it is arguable what is \"fundamental\" (I'm grouping fields that transform as a doublet as a single field but with multiple field components related by a symmetry, but some might describe them as two separate fields, same goes for left and right handed fields related by CPT symmetry... also I'm ignoring the fact that the SU(2) and SU(3) gauge fields have multiple degrees of freedom), but it might be simplest to say there are 19 fundamental fields in the Standard Model:",
"To answer your other questions:",
"The electromagnetic field is actually a mixture of the fundamental U(1) and SU(2) fields, which, after electroweak symmetry breaking (that's what the Higgs field is for), possesses U(1) symmetry. The remaining mixture of U(1) and SU(2) fields corresponds to the weak force. Since both the electromagnetic and weak forces are different components of the same thing (a combination of U(1) and SU(2) fields), together they are referred to as \"electroweak\" fields.",
"The \"strong force\" field is already included in the above list of fields. It is the SU(3) gauge field.",
"Above I gave the fundamental fields in the Standard Model, but it's true that there are other additional fields in nature. The gravitational field is one. There are also probably fields associated with dark matter (and anything else we haven't discovered yet).",
"Fields are not in Hilbert spaces. A Hilbert space is more relevant to quantum mechanics and to more subtle topics in quantum field theory. In quantum mechanics the states of a system are in Hilbert space. A quantum field is the application of quantum mechanics to a field. The state of a field can be defined by infinitely many states within a Hilbert space."
] |
[
"Although you could look at these fields as just particular instances of the first four fields at the top.",
"No that's just wrong. The gauge fields do not describe the fermions. "
] |
[
"Oh and about the \"sort of\", this paper is very readable:",
"http://philsci-archive.pitt.edu/2673/",
"Even just the introduction may answer your question better than I can."
] |
[
"Since pi is irrational, is there a point in pi's decimals where there are 1 billion subsequent threes?"
] |
[
false
] | null |
[
"Probably, but not just because it's irrational. For example, the ",
"Liouville constant",
" is irrational but has only 0's and 1's in its decimal expansion.",
"However, pi is strongly conjectured to be a ",
"normal number",
". If this is the case, you certainly can find a billion 3's in a row in its decimal expansion—in fact, you'd find this infinitely many times. Of course, the first occurrence would be ",
" deep, but it would be there."
] |
[
"The Borwein-Bailey-Plouff formula. But it doesn't work backwards."
] |
[
"If pi is a normal number, then yes. ",
"As existentialhero pointed out, that conjecture is not yet proven. If it's true, you'd still have to go really, really deep into pi to find that particular combination of numbers with any non-negligible probability."
] |
[
"How does fat move around the body? How does the body choose where the fat goes?"
] |
[
false
] |
[deleted]
|
[
"Fat is not very soluble in the mostly-water solution that is your blood, so it gets transported in soluble particles called lipoproteins. There isn't enough battery left on my laptop to type up an answer regarding the body's choice of where the fat goes, but this is mostly a cop-out because I'm much less well versed in \"why\" than in \"how.\""
] |
[
"When you absorb fat from your digestive system, it gets transported across the intestinal barrier first with the help of bile acids and some transporter proteins. Then it gets packaged into what are called Chylomicrons: these are just large \"Lipoprotein\" particles, with a large droplets of lipids surrounded by some protein markers which act as a kind of barcode for what the shipment contains. These chylomicrons then get dispatched through your lymphatic system.",
"Any cell that wants to take up these particles now just needs to look out for the barcode proteins that we talked about above. For chylomicrons its just liver and adipocytes and I think muscle cells. These cells take up these chylomicrons and process them further, the liver being the main center, where it can process it into different lipid types the body might want and dispatch it with a different barcode (And droplet size) that other cells can absorb now. The wikipedia section on this is extremely clear btw. ",
"http://en.wikipedia.org/wiki/Fatty_acid_metabolism#Digestion_and_transport"
] |
[
"Obligatory \"I didn't downvote you but...\"",
"We (the people who browse askscience, not we as in 'scientists') may not have a good idea of why fat is distributed the way it is, but we can surmise that your guess seems pretty unlikely. In the post-physeal-fusion human body, not much seems to be dependent on gravity. Not even the passage of food through the alimentary canal is gravity dependent. Why would fat deposition be so in humans? It seems exceedingly unlikely, which probably explains the downvotes. "
] |
[
"Why is Dyslexia being removed as a diagnosis?"
] |
[
false
] |
The latest version of DSM5 is changing dyslexia to specific learning difficulties, being dyslexic will still be mentioned within your diagnoses but it won't be your diagnosis. As quoted from there website Learning Disorder has been changed to Specific Learning Disorder and the previous types of Learning Disorder (Dyslexia, Dyscalculia, and Disorder of Written Expression) are no longer being recommended. The type of Learning Disorder will instead be specified as noted in the diagnosis. Can anyone tell me what motivated them to make this change and what effects it well have.
|
[
"\"Learning Disorder has been changed to Specific Learning Disorder\"",
"it's being absorbed by something else that is more descriptive. all dyslexia is not the same."
] |
[
"As someone who had a moderately unusual form of dyslexia as a child and had to deal with constant misunderstandings from teachers about how it might affect me, I just want to say that this change to the DSMS seems like a very good thing."
] |
[
"As someone who had a moderately unusual form of dyslexia as a child and had to deal with constant misunderstandings from teachers about how it might affect me, I just want to say that this change to the DSMS seems like a very good thing."
] |
[
"Why can't we make a camera that captures images that look the same as how we see them?"
] |
[
false
] |
[deleted]
|
[
"What you should be asking is, \"why can't we make a camera that captures images exactly how we see them and reproduce them in a medium which is visually indistinguishable from the original scene?\"",
"Designing a camera that captures information identical to the photoreceptor layer of your retina is simply a matter of engineering four sensors with the same sensitivity vs wavelength functions as your photoreceptors. This isn't perfectly accurate due to temporal effects, but suffices as a first approximation. Difficulty of engineering aside, this is perfectly feasible from a theoretical standpoint.",
"Reproduction, on the other hand, is a much more daunting task. Current display or printing methods rely on representing different perceptual hues, which are the result of activation levels for each of three different cones, as the weighted sum of three or more components, each of which has its own distinct spectral characteristics. Disregarding rods for the moment due to their relative absence in the fovea, the implication of this is that each has a single, 3-dimensional response vector which represents the activation of your different photoreceptors to that particular component. You might think that any three components with linearly independent response vectors would suffice to produce the full gamut of colors that we can observe, but this fails due to the fact that we cannot have negative coefficients when mixing. Because of the overlap of the wavelength response curves for different cones, it is very difficult to choose a limited number of components that can reproduce any photoreceptor response. For example, violet is impossible to reproduce in the RGB color space. Two solutions to this would be to either to design a technology capable of reproducing exact spectra in the visible range, or to use direct stimulation of photoreceptors, which would in effect give you the component bases [1, 0, 0], [0, 1, 0], and [0, 0, 1]."
] |
[
"The main reason why most cameras do not have the ability to capture images that look the same as what we see is that ",
"the human eye has a roughly logarithmic response function",
". This means that something that is 10 times brighter than a reference object might only ",
" ~ 2 times brighter to our eyes. This means that the human eye has a very wide ",
"\"dynamic range\"",
"Conversely, CMOS and CCD sensors have a much more ",
"linear response",
", meaning that something 10 times brighter will have 10 times the number of image \"counts\". If there was no limit to the number of image counts, then this would not be a problem: you could simply convolve your image with the response curve of the human eye and reproduce what the human eye sees. But in reality, most sensors are 16-bit, meaning there is an upper limit of 2",
" = 65536 counts per pixel. This may sound like a lot, but you also have the fact that the noise goes as the square root of the number of counts. This means that in practice you actually don't have very much dynamic range to work with, so you have to compromise by either taking a long exposure to bring out the faint part of a scene, or a short exposure to avoid saturating the bright part of a scene.",
"A way around this is to take both a short exposure and a long exposure, and combine them later, which is known as ",
"high-dynamic range imaging",
". You can achieve some fairly stunning images this way, but it must be done ",
" the images have been taken. A lot of newer cameras have features that allow you to \"take\" an HDR image automatically. ",
"TL;DR: The human eye sees logarithmically. Camera sensors are more linear. This means that you usually have to choose whether to pick out the bright part of a scene or the dark part. HDR imaging is a technique to circumvent this."
] |
[
"Any change away from RGB will have to introduce more primary colors, and in basically all display technologies that has a huge tradeoff in spatial resolution. It's only been in the past few years that any consumer products have included spatial resolution that's good enough to stop worrying about; adding another subpixel or two would set that back significantly."
] |
[
"How does polarized light work?"
] |
[
false
] |
[deleted]
|
[
"It's early in the morning, but I'll try. So, we have these abstract ideas that we call electric and magnetic fields. What do they do, and what causes them, you ask.",
"Magnetic fields cause moving charges particles to change direction. ",
"Electric fields are caused by charges (just sitting there) and by changing magnetic fields. ",
"Magnetic fields are caused by changing electric fields/moving charges.",
"So, that's the majority of of ",
"Maxwell's equations",
" and the Lorentz force law stated qualitatively, and it should be enough for us to proceed. Unfortunately, to really understand said equations you have to study some vector calculus.",
"Anyways, consider that a changing electric field causes a magnetic field, and a changing magnetic field causes an electric field. It turns out that when considering whether or not this can go on forever, Maxwell's equations yield something called the ",
"wave equation",
", which is a differential equation in which the solutions are of the form f(x-vt). If you think about (x-vt), that suggests when time increases, x has to increase proportionally to get the same value. This is something moving in space as time passes.",
"What happens is that as the electric field oscillates in the x direction, it causes a magnetic field to begin oscillating in the y direction, and these oscillations propagate in the z direction in time. Which is to say, though at one point there may be strong oscillations at Z=0 meters, shortly thereafter in time there will be strong oscillations induced at Z=1 meters, and the oscillations at Z=0 will be decreased.",
"So what is meant by the phase between the magnetic and electric fields? Well, when you boiled the Maxwell Equations down to the wave equation, it was clear that the electric and magnetic fields had to oscillate at the same frequency.",
"Edit: removed fail.",
"So, that's what we mean. The electric field is perpendicular to the magnetic field, and they're both perpendicular to the \"direction of propagation\" or traveling direction of the wave."
] |
[
"It's early in the morning, but I'll try. So, we have these abstract ideas that we call electric and magnetic fields. What do they do, and what causes them, you ask.",
"Magnetic fields cause moving charges particles to change direction. ",
"Electric fields are caused by charges (just sitting there) and by changing magnetic fields. ",
"Magnetic fields are caused by changing electric fields/moving charges.",
"So, that's the majority of of ",
"Maxwell's equations",
" and the Lorentz force law stated qualitatively, and it should be enough for us to proceed. Unfortunately, to really understand said equations you have to study some vector calculus.",
"Anyways, consider that a changing electric field causes a magnetic field, and a changing magnetic field causes an electric field. It turns out that when considering whether or not this can go on forever, Maxwell's equations yield something called the ",
"wave equation",
", which is a differential equation in which the solutions are of the form f(x-vt). If you think about (x-vt), that suggests when time increases, x has to increase proportionally to get the same value. This is something moving in space as time passes.",
"What happens is that as the electric field oscillates in the x direction, it causes a magnetic field to begin oscillating in the y direction, and these oscillations propagate in the z direction in time. Which is to say, though at one point there may be strong oscillations at Z=0 meters, shortly thereafter in time there will be strong oscillations induced at Z=1 meters, and the oscillations at Z=0 will be decreased.",
"So what is meant by the phase between the magnetic and electric fields? Well, when you boiled the Maxwell Equations down to the wave equation, it was clear that the electric and magnetic fields had to oscillate at the same frequency.",
"Edit: removed fail.",
"So, that's what we mean. The electric field is perpendicular to the magnetic field, and they're both perpendicular to the \"direction of propagation\" or traveling direction of the wave."
] |
[
"Well, seems nobody's taken on optically active enantiomers directly, so I'll give it a shot. Instead of dealing with the somewhat-difficult math involved, I'm just going to go with an physical analogy here. But it does have some 'depth' to it:",
"Imagine you're drilling a hole in a flat wall made out of some ordinary stuff (say, plaster). The drill bit has its edges some way (clockwise/counterclockwise or 'right/left handed'), and the drill rotates accordingly. If you drill into the wall, it doesn't matter if you have a 'right-handed' drill bit with a 'right-handed' drill, or a 'left-handed' bit with the corresponding drill. Both drills will drill straight in. Why is that? ",
"Because the wall is flat, and the material in the wall is homogenous (or to be more specific 'isotropic', it's the same in all directions). So it doesn't put up any more resistance to one drill compared to the other. They just go straight in.",
"Now imagine a wall that's made up of a 'chiral' material. Say it's held together by some material that forms little clockwise or counterclockwise vortexes. (Maybe it's some knotted wood where the grain forms vortexes, for instance) Bottom line is the material is ",
" equal (on average) in all directions anymore. So when you drill into it, the drill bit will tend to veer off in one direction because the forces aren't equal in all directions anymore (unless of course you force the drill to keep straight), and the 'opposite' drill will tend to veer off in the opposite direction for the same reason. One is going 'with the grain' and the other 'against the grain'.",
"This is basically how optically active enantiomers work. They are mirror images of each other, and they're not geometrically equivalent in all directions. Circularly-polarized of light has a corresponding asymmetry. Which means that light with different polarizations will veer off differently when they encounter one or the other enantiomer.",
"But if you have a racemic mixture (50-50% mixture of both enantiomers), the two things will cancel out - much as if you had a wall made out of vortices that was a mixture of vortices going in one direction and the other. ",
"The (simplified) reason for why this is, is that light has a corresponding electrical field, and atoms/molecules are surrounded by charged electrons, which temporarily change their positions in response to that field (which in turn generates a new electrical field in response to that, which is how light diffracts) So, the response to the light depends on how the electrons are distributed in space (i.e. the molecular structure). If it's asymmetric in a way that mirrors this asymmetry of the light, the light will veer off in response. Just as a drill bit will veer off in response to something that's not symmetric around ",
" axis of rotation."
] |
[
"If Mars’ atmosphere is primarily Carbon Dioxide, why isn’t it succumbing to the green house effect that we’re trying to avoid on our planet (by limiting CO2)?"
] |
[
false
] | null |
[
"There ",
" a greenhouse on Mars caused by the predominantly CO2 atmosphere, but it's relatively small because the atmosphere is so thin. ",
"For the three planets that experience a significant greenhouse effect, the amount of warming is strongly a function of how thick the atmosphere is:",
"The expected global temperature of Mars from sunlight alone is -55",
" C, but the actual measured temperature -50",
" C. The greenhouse effect produces an additional 5",
" C of warming.",
"The expected global temperature of Earth from sunlight alone is -17",
" C, but the actual measured temperature 15",
" C. The greenhouse effect produces an additional 32",
" C of warming.",
"The expected global temperature of Venus from sunlight alone is -43",
" C, but the actual measured temperature 470",
" C. The greenhouse effect produces an additional 513",
" C of warming."
] |
[
"Excellent question!",
"While Venus is about 30% closer to the Sun - and should therefore receive about twice as much sunlight - it's also more than twice as reflective as Earth. It turns out our oceans are pretty dark and absorb most of the sunlight that hits them, while Venus' cloud tops reflect the majority of sunlight that they receive.",
"The net result is that Earth actually absorbs a bit more total sunlight than Venus does, raising its expected global temperature."
] |
[
"Why is the expected temperature for Venus from sunlight alone so much colder than the Earth? Is it the albedo difference? Is the value for the Earth taking into account the Earth's oceans?"
] |
[
"Do tall people have larger internal organs? If not, how do their bodies fill the extra space?"
] |
[
false
] | null |
[
"General surgeon here.",
"Larger people have larger organs in general for the reasons listed above, I’ve never read any studies on it, it’s just what I see at work. The cavities in your bodies adjust to the need for the organs IN MOST SITUATIONS.",
"Symptomatic Pectus excavatum is a good example of what happens when it doesn’t. ",
"And what happens when you have more space that needed? Well most spaces have atleast once size that is soft tissue that will decrease in size. But, for instance, in brain atrophy like in old dementia patients or alcoholics, the brain is actually a little “loose”, and can slosh more. Fluid will fill around it. You’re body never fills empty cavities with air, it’s always fluid if anything.",
"Here’s another example. In the abdomen sometimes we have to do really big surgeries like remove half the organs for a big cancer. At the end all we do is close the abdomen as normal. The the abdominal cavity will slowly shrink down some, all air will be absorbed (can take a month if open air, just a few days if laparoscopic). They may get a little extra fluid in their abdomen.",
"In terms of “making space”. People have lots of extra space inside them, especially in the abdomen. As people get fat, they can store so much fat inside their abdomen. So, so much. It can make my job very difficult.",
"Even on fat people, I’m talking like BMI of 60, I can still put around 3-4 liters of air in the abdomen to do laparoscopic surgery. The inside of their abdomen will expand with their need for space as long as the need for space happens slowly (over months, not over days. Google abdominal compartment syndrome’ for what happens if they need a lot of space over days).",
"Hope that makes sense. I added paragraphs out of order so hopefully didn’t repeat myself too much ",
"Edit: to the dude that says that air is also a liquid and I should use the word “fluid”.......get a life. Good lord "
] |
[
"Just because somebody is strictly tall doesn't necessarily mean they're volumetrically larger. I mean, you obviously have tall and lanky vs. short and stout.",
", there are physical factors that may directly affect organ size. The most obvious is the heart. In taller people, the hearts have to work harder to pump blood up to the heads, as well as bring blood back from the legs. This increased work load also \"works out\" the heart to increase its size, and is believed to produce extra stress on the heart, and may partially be responsible for ",
"lower life expectancy associated with height",
".",
"Of course, just because something \"makes sense\" doesn't mean that's the mechanism. I'm not certain if there has been controlled studies to see if we can alleviate only the \"height factor\" to see if there's a change in heart size, or if heart size and bone lengthening are attributable to a common factor (like growth hormone). It's likely both.",
"Edit: on the topic of empty space in a body - in the case of organ donation (e.g. kidney, partial liver, etc.), the viscera (the abdomen) is really soft and moveable, so other organs (mainly the GI) fills in the space. There are only a few places in the body where space is \"held\" open (mainly the ribcage and the skull), and those can be filled with different things depending on the pathology."
] |
[
"I know essentially nothing about congenital heart defects. They’re incredibly complex and only pediatric doctors deal with them, and only a small subset of them ",
"Edit: thought more about it. If she was part grinch, then her heart could have been up to 3x too small. Studies on this were done by the esteemed Dr. Seuss."
] |
[
"How do chemists assemble molecules in specific shapes?"
] |
[
false
] |
I was reading a Joe Schwartz book where he mentions the development of a molecule with 60 carbon atoms in the shape of a soccer ball. How do they do that?
|
[
"It's kind of like making snowflakes, they just self-assemble under the right conditions. For C60, you make soot, and the soot contains C60 along with other molecules. Then all you have to do ",
"is separate out the C60",
".",
"Here's a ",
"video of how to make buckyballs in your garage",
"."
] |
[
"In chemical synthesis, there are certain reactions that are known as sterioselective - that is, the reaction happens in a way that is selective to one specific shape over another. A lot of this has to do with the reagents you are selecting and how they interact in three dimentions. By selecting reactions and reagents that are favorable towards certain configurations over others, chemists can assemble molecules in specific shapes.",
"In terms of a 60C molecule in the chape of a soccer ball, I'm not a chemist and can't tell you the specific reactions involved, but I would assume it follows more or less the same process of sterioselectivity. Again a chemist would be able to give you more specifics, but this is just basically how synthesis works. "
] |
[
"Naw, we're not actually good enough at synthesis to produce them chemically. (although there's probably a lot of money in it if you can find a good way). By and large we just vaporize carbon with an electrical arc discharge, resulting in a plasma of free carbon atoms and molecular fragments, where a tiny amount will manage to randomly come together to form C60 (in decent amounts if the conditions are just right). Then we purify it out.",
"There are actually a lot of nifty theoretical compounds out there which we're pretty clueless on how to produce :) In this case, it's rather interesting to note that the theoretical prediction was pretty late (1970s), given that it's something which you could pretty much predict with a ball-and-stick chemistry model set and some imagination. "
] |
[
"How positive charges distribute on the surface of a sphere?"
] |
[
false
] |
I've been thinking about it and can't find a reasonable explanation. I can understand why it happens to negatively charged sphere, because the electrons CAN move. But if you remove the electrons from the sphere, how do electrons rearrange in the interior of the object?
|
[
"Empty valance electron spots are called \"holes\". They holes have an effective positive charge since they are the places where, with an electron, would have neutral charge. ",
"These holes can \"move\" in the sense that electrons can jump between valance band holes. When an electron moves from a full valance band to a hole location, the hole \"moves\" to the spot where the electron was. This is how positive charge redistributes itself.",
"So the answer to your question is that positive charges ALSO moves by the rearrangement of electrons. ",
"Not that current moving through a wire is generally defined to be positive moving charge, but physically it's really electrons moving in the opposite direction."
] |
[
"Yes, it's perfectly fine to model holes as positive particles that moves for most cases. ",
"Just like electrons they are trying to distribute themselves to minimize the electrostatic potential of the system, which happens to be done by placing them all on the surface with uniform spacing for a sphere."
] |
[
"But why is the arrangement - negative inside and positive outside? Can I conclude that the \"holes\" act just like a free \"positive electron\" and want to stack in the outer shell?"
] |
[
"Why does my microwave heat up the cup of coffee but not the air around it?"
] |
[
false
] |
I set the timer to five minutes and when I reach into the microwave, my coffee and cup are hot. But the inside of the microwave itself isn't overly warm. Why is that? Is it how electromagnetic waves travel through different mediums?
|
[
"The microwaves are tuned at a specific frequency to interact with water and other polar molecules. So all the energy is absorbed by the food, and a negligible amount is absorbed by the different components of air.",
"http://en.wikipedia.org/wiki/Dielectric_heating"
] |
[
"You linked to the right article, but your description is incorrect; ",
"there's nothing particularly special about 2.4 gigahertz",
":",
"It's a common misconception that the microwaves in a microwave oven excite a natural resonance in water. The frequency of a microwave oven is well below any natural resonance in an isolated water molecule, and in liquid water those resonances are so smeared out that they're barely noticeable anyway...",
"Instead of trying to interact through a natural resonance in water, a microwave oven just exposes the water molecules to the intense electromagnetic fields in strong, non-resonant microwaves. The frequency used in microwave ovens (2,450,000,000 cycles per second or 2.45 GHz) is a sensible but not unique choice. Waves of that frequency penetrate well into foods of reasonable size so that the heating is relatively uniform throughout the foods. Since leakage from these ovens makes the radio spectrum near 2.45 GHz unusable for communications, the frequency was chosen in part because it would not interfere with existing communication systems."
] |
[
"None that would taste good!",
"But in general, there are \"microwave safe\" containers that you can put in the microwave that won't get hot. I think you would need to have an absence (or at least a very low concentration) of polar molecules."
] |
[
"Why hasn't 'ugly' been bred out?"
] |
[
false
] |
Surely if more attractive people are more likely to produce offspring there should be a trend towards more attractive people.
|
[
"Genetics is complicated. The shape of your face (for instance) is determined by a rather complicated interplay between a lot of different genes, so the effect a particular gene has depends on all the other genes in your genome. ",
"Perhaps the same gene which gives your father a perfectly-shaped nose will, when combined with the genes which give your mother such perfectly-shaped ears, will wind up giving you an ugly chin. Of course it's be far more complicated than that, but the point is that there's no individual genes for \"pretty\" and \"ugly\", just a whole lot of ingredients that give varying levels of pretty and ugly in different genetic contexts."
] |
[
"To look at it socially, marriage for a long time wasn't based on attractiveness, but it was based on someone being a good provider/hunter for a future family, or possibly the marriage was arranged by family to help solidify business or social connections. ",
"Like Jorgesum said about the genetic factors, there's several social factors as well, and none of them take attractiveness into account. "
] |
[
"You're right, sexiness and beauty are all about sexual selection, which plays a big role in evolutionary processes. But:",
"Purifying selection",
" exerts weaker effects on the genes controlling phenotypes that are a result of recessive and complex traits as opposed to simple dominant traits. Beauty is undoubtedly a complex trait, and so is ugliness.",
"The traits aren't as impairing as you might think; ugly people have lots of babies. As far as I know, as many as beautiful people. So the selective pressure itself is probably unimpressive."
] |
[
"The Double Slit Experiment."
] |
[
false
] |
Hi everyone, I've recently been introduced to the double slit experiment, and I am really bothered by it's results. To me, it's perfectly acceptable that matter can exist in both wave and/or partical form. What I dislike, is the idea that it "chooses" to exist in partical form when it's being observed. It's impossible that matter can "choose" to be in partical form simply becasue it doesn't want humans to understand it. As a result of this, I honestly think that somehow the act of observing the electons are having a physical reaction that we don't yet understand. I was wondering if anyone agrees with me on this, or perhaps has some more information that can clear this up. To me, it sounds like magic, and I really want to get to the bottom of this. Please help?
|
[
"A good way to think of this is that it's not ",
" that behaves weirdly. Nature is not the one with the problem, ",
" are. We are so used to dealing with objects like waves and particles that we can not wrap our heads around things that behave as oddly as quantum objects. Remember, particles and waves are simply ",
" we use to describe behavior of quantum objects."
] |
[
"At first I had the same reaction to this result, however a college professor of mine helped to explain it a little better. First of all this is considered to be a quantum physics experiment, and as such it obeys very different rules than most other experiments. Most things in quantum physics are not determined through observation, but though probability. That means that if a particle has a high probability of being somewhere, we say that it is there. There is a lot of math behind this concept but we will take it for granted that it is true. Now lets apply this kind of thinking to the double slit experiment. ",
"Suppose we are observing which slit the electron or photon goes through. This means we are sure of where it went. There is 100% probability it went in one slit and 0% chance it went through the other since we saw which one it went through. Thus we can say that because of the high probability it only went through one slit. This is backed up experimentally when we measure the scattering pattern when the slits are observed, and see that you get a single hump (a particle like behavior).",
"Now lets suppose that nothing is observing the slits. We have no idea which once the particle went through. There is a 50% chance it went through one slit and a 50% chance it went through the other. By our new quantum way of thinking the higher probability is where the particle is, but these are the same. Thus we can say that the particle went through both slits. This is also backed up experimentally when we measure that there are multiple humps on the scattering pattern that match what we would expect if a wave passed through the slits and interfered with itself (wave like behavior).",
"So you see, it is not as if the particle is actively choosing what to be determined by if it is observed or not. But it is influenced by whether it is observed because the act of observation changes the particle's probability function (where it can be).",
"I hope this helps, and if you are interested in even more crazy and magic like experimental results, look up quantum entanglement."
] |
[
"We are capable of observing which slit it goes through without influencing the interference pattern, at least according to this recent paper: ",
"http://arstechnica.com/science/2012/05/disentangling-the-wave-particle-duality-in-the-double-slit-experiment/",
"I would love it if someone could explain the implications of this a bit more clearly though."
] |
[
"Could the moon be \"bumped\" out of orbit by a meteor strike and be sucked in by the Earth's gravity?"
] |
[
false
] |
I've always been intrigued by the fact that the moon orbits the Earth and doesn't get "sucked in" by the Earth's gravity despite the bombardment it receives from meteor strikes. I understand its centripetal force keeps it in a stable orbit, but could a sufficiently large meteor strike slow it down enough that it would fall out of orbit into Earth? Or would it just fall into a new orbit around Earth?
|
[
"This isn't quite right. It's not just some coincidence that the moon has exactly the correct velocity and radius of orbit to make the centrifugal force balance gravity. A better way of thinking about is to say that using fact that the moon is in a circular orbit, we can use the handy equation F=mv",
" /r to work out its radius or velocity from other known parameters (such as the strength of Earth's gravity).",
"A collision with a meteor could alter either the velocity or radius, causing the orbit to become unstable.",
"I agree that a collision will change the orbit, but it's not true that changing one of the parameters in mv",
" /r will cause the orbit to become unstable (unless by \"unstable\" you mean \"not circular\"). Changing one of the parameters ",
" mean that the moon spirals in towards Earth. All that will happen is that the moon will end up in some ",
" orbit, which may be circular, elliptic, parabolic, etc. This orbit could, in principle, intersect with the Earth, causing a collision. "
] |
[
"Because the moon is actually orbiting the sun. Well, obviously it orbits the earth as well, but if you calculate the gravitational force on the moon due to the earth and the sun, you'll find that the moon orbits the sun much more than it orbits the earth.",
"Whoa. What? That doesn't sound right. And Googling suggests it isn't right:",
"http://www.universetoday.com/20293/does-the-moon-orbit-the-sun/",
"\"Hey, here’s a question: does the Moon orbit the Sun? Of course not, it’s a silly question. Of course the Moon orbits the Earth.\"",
"http://blogs.discovermagazine.com/badastronomy/2008/09/29/the-moon-that-went-up-a-hill-but-came-down-a-planet/",
"\"Every now and again I get an email from someone who tries to tell me that the moon orbits the Sun more than it orbits the Earth.\"",
"\"Moreover, if you calculate the force of the Sun’s gravity on the Moon, you find it’s more than twice the force of Earth’s gravity on the Moon!\"",
"\"Turns out, it orbits the Earth, despite these claims. The above claims are true, but are not important in this argument.\""
] |
[
"Yes. There exists a quantity, centrifugal force (or is it centripetal?), that is equal to the velocity an object is moving squared divided by the radius at which it is orbiting. If this quantity equals the acceleration due to gravity, the satellite will have a stable orbit. A collision with a meteor could alter either the velocity or radius, causing the orbit to become unstable. The unstable orbit could result in the moon being slung out into space, or it crashing to earth."
] |
[
"Do high flying birds need less oxygen?"
] |
[
false
] |
Do high flying birds need less oxygen in their breaths, or do they take breaths when they are lower altitudes (like whales surfacing for air)?
|
[
"Birds have efficient lungs, they have air sacs connected to the lungs and oesophagus, when they breath their lungs and sacs get filled with oxygen and when they breath out the spent air in the lungs leaves and the sac air goes into the lungs giving them a double dose of oxygen."
] |
[
"Birds that fly at extreme altitudes (such as those that migrate over the Himalayas, have special adaptations that allow them to deal with the lower oxygen content at altitude. ",
"The ",
"bar-headed goose",
" has several mutations/adaptations that allow it to fly at altitudes in excess of 20,000’."
] |
[
"I just kept thinking about my vertebrates anatomy course in college. It was interesting learning that many dinosaurs like the T-Rex and other raptors had similar bone structure to modern birds, that their bones were hollow and had the same tubes in them that modern birds have."
] |
[
"Why is absorption of nutrients through the intestines safer than direct injection into the bloodstream?"
] |
[
false
] | null |
[
"Injection site = risk of blood infection, especially with nutrient-rich fluids as opposed to something like normal saline. Our intestines have natural ways to fight bacteria, like stomach acid. Also, the cells on the inside of the intestinal tract need nutrients too, often getting them directly from the food inside the intestinal tract."
] |
[
"When nutrients are absorbed into the blood stream in the intestines, that blood is then sent straight to the liver via the hepatic portal vein. This means that everything has a chance to get filtered by the liver before passing to the rest of the body. As a result, a significant amount of any toxins mixed in with the nutrients will never make it to more sensitive tissue.",
"If you instead inject the nutrients directly into the blood stream, this doesn't happen. The hepatic portal vein is rather deep in the abdomen and is never the site for an IV injection. All other veins instead will flow towards the heart and lungs before anything else. The blood is then mixed with all other blood in the body before being scattered throughout the body. While the liver can still filter out toxins from this blood, many of those toxins can reach sensitive tissue before ever touching the liver. Usually, this means chemicals affecting the brain in a way that the brain was never meant to handle.",
"If you could theoretically make a syringe of completely isolated nutrients that were perfectly balanced for the blood stream without any sort of contamination, it might be fine to inject into the blood stream. However, in most cases it is easier to just find a way of injecting less purified nutrients into the stomach."
] |
[
"Could be because the intenstine can prevent an over absorbtion of nutrients and it also filters out anything we don't want. Or it keeps a steady rate of absorption so that our body acclimate to the introduction of nutrients. Don't quote me by the way. It's just a thought."
] |
[
"Are the biological children of gay people more likely to be gay than the biological children of straight people?"
] |
[
false
] |
When I try searching for an answer, I get a bunch of results about whether gay couples can be good adoptive parents, or the affect of fraternal birth order on sexual orientation. This isn't what I'm looking for. Surely in societies where being gay is taboo, a significant number of gay men end up having biological children due to social pressure. I am curious if these children are more likely to be gay. If so, would this lead to a larger percentage of people being gay in societies where homosexuality is oppressed? That would be ironic. Any sources you could point me to would be awesome.
|
[
"There does seem to be a heritable component to homosexuality, but it is extremely elusive. Twin and family studies",
"[1]",
" have found that homosexuality runs in families. Genomic studies",
"[2]",
" suggest that homosexuality is a complex trait caused by many different genes, and the genes that cause male and female homosexuality are only semi-overlapping",
"[3]",
". Moreover, the impact that these genes have on sexuality is very subtle. Study #3 looked at the genomes of nearly ",
" people, and still could not find a single genetic variation that could confidently predict whether its donor was homosexual or not. ",
"The primary hypothesis for the \"cause\" of homosexuality appears to be hormone exposure during formative years (prenatal and early development). There are a lot of studies that claim this, and although none can draw causative links directly, the most convincing evidence IMO is that fetuses with CAH (congenital adrenal hyperplasia) are exposed to extremely high levels of testosterone in utero. Females with CAH go on to have higher rates of homosexuality",
"[4]",
". Again, this is not ",
" of homosexuality: just corollary. ",
"Broadly, it seems like homosexuality doesn't have any one specific cause, which makes sense because human sexuality is extremely diverse. It seems like homosexuality has a lot of contributing factors, some genetic, some environmental. Population-wide, children from families with homosexual members are probably more likely on average to become homosexual, but certainly not in a 1:1 \"sealed fate\" kind of way.",
"Not sure about your societal conclusion btw. Lots of gay people have biological children with their partners using sperm or egg donors depending on the situation. It's actually harder for gay couples to adopt in a lot of places."
] |
[
"Not exactly what you're looking for but it is still related to inheritability of sexual orientation. Fecundity in the maternal lineage is positively correlated to the increased likelihood of male offspring who are homosexual.",
"Basically, researchers found that in the families of homosexual men, the maternal aunts and mothers had increased number of female offspring compared to the maternal aunts and mothers of heterosexual men. They used female offspring instead of total offspring to control for fraternal birth order bias (which only affects male offspring).",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3515521/",
"Anyways, any putative genetic factor identified is thus inheritable and makes it more likely for homosexual individuals to have homosexual offspring (indirectly or directly e.g. can skip generations in the fecundity case as the factor is proposed to be X-linked)."
] |
[
"Not necessarily. \"Environmental factors\" when referring to genetic studies just means anything that isn't strictly genetic. This could be anything from what your mother ate while pregnant to the air quality where you grew up to whether or not you were bullied in elementary school. Not saying that any of those things are related to homosexuality, just examples. I don't believe there are any current studies that suggest certain cultures are more likely to beget homosexual individuals, especially considering that it would be difficult to control for genetic factors and the fact that different percentages of homosexual individuals will be closeted depending on how accepting their culture is."
] |
[
"If all humans died tomorrow, what traces of our civilization would be left in 10,000 years? 50,000? 100,000?"
] |
[
false
] |
[deleted]
|
[
"http://www.history.com/shows/life-after-people"
] |
[
"Read 'The World Without Us' by Alan Weisman.",
"Brief summary:",
"In The World Without Us, Alan Weisman offers an utterly original approach to questions of humanity's impact on the planet: he asks us to envision our Earth, without us.",
"In this far-reaching narrative, Weisman explains how our massive infrastructure would collapse and finally vanish without human presence; what of our everyday stuff may become immortalized as fossils; how copper pipes and wiring would be crushed into mere seams of reddish rock; why some of our earliest buildings might be the last architecture left; and how plastic, bronze sculpture, radio waves, and some man-made molecules may be our most lasting gifts to the universe."
] |
[
"The World Without Us has an excellent mouseover chart"
] |
[
"Does melatonin cause others to wake up at odd hours and have vivid dreams?"
] |
[
false
] |
I sometimes wake up on a strange schedule when I take melatonin to sleep and I also experience some of the strangest dreams I've had when I take melatonin. I am wondering if this is common and why it happens.
|
[
"I wake up at odd hours whether I take melatonin or not.",
"The main difference is that with melatonin, I can get back to sleep.",
"The vivid dreams are just a bonus."
] |
[
"I'm not sure, but I took 5 mg melatonin and a vitamin b6 supplement last night to catch up on sleep and I suddenly woke up after a long, intense, vivid dream thinking it was probably 5 o-clock in the morning, but it was only 11:30 pm. I couldn't even imagine what the rest of the night would be like after that."
] |
[
"It happens to me some nights I take it and then others I sleep like it's not a problem. Weird stuff man."
] |
[
"Why do dogs prefer to pee on vertical objects?"
] |
[
false
] | null |
[
"Animals navigate in much the same way that we do and use significant landmarks as waypoints and aids; like like boulders and tall trees. And in a modern context, lampposts and fire hydrants. ",
"Urination is used as a navigational aid, a literal breadcrumb trail when exploring new places, as well as for marking out territory or signalling presence, or just urinating. ",
"If you watch a dog on familiar territory after a heavy snowfall, their reaction can range from excitement to anger. Even though they know the territory well, all of the landmarks are \"gone\" as well as the scents, which results in a lot of confusion. "
] |
[
"To add to this, the reason it's on vertical surfaces is because that's nose height for other dogs, plus it's high enough that the wind catches it and spreads the scent even further.",
"Cats do this too, and there's also feces marking although that's done less often."
] |
[
"Other answers are true, but heres another take. The higher your pee is the higher your status. Even some female dogs will gcontort themselves or stand up so that theire pee gets deposited high up on a fencepost or tree or other object. If peeing high isn't possible, lots of dogs will pee on the ground and then use their rear claws to kick and fling the pee-dirt up into the air or onto a tall object. I can say for sure this is true for border collies and a high probability for other dogs.",
"TLDR: Height matters."
] |
[
"Why is Carbon and Water so fundamentally necessary for life? Couldn't an extraterrestrial lifeform be based on, let's say, silicium?"
] |
[
false
] |
[deleted]
|
[
"Water is important because it is a potent solvent and is liquid in a temperature range that is conducive to organic chemical reactions.",
"Carbon is important because it is fairly inert once in molecules so you can form many long complex molecules off the same more or less inert back bone. this has to do with the electron structure of carbon, so a chemist can expand on the specialness of carbon.",
"As for silicon based life, the short answer is no. the waste produce for most life is CO2 via cellular respiration this is a gas that can be easily dissolved into water. for silicon the waste product would be SO2 or sand/quartz and is very inert and highly stable. So the SO2 lockes down resources (like oxygene) much more than CO2 and as a solid is much more difficult to move around.",
"the long answer for silicon is maybe, but it would be at very high temperatures and be a bio chemistry very different, even on an mechanical basis (resembling more inorganic chemistry), than what we have on earth."
] |
[
"Silicon doesn't form homopolymers anywhere near as readily as carbon, which is another problem for complex life."
] |
[
"We KNOW for sure that life like ours exists and therefore CAN exist. There are zillions of other theoretical possibilities, but they're all just pure speculation. For now, it makes sense to stick with what we know is possible."
] |
[
"In Quantum Mechanics, how does the bound state of a negative delta potential relate to the first bound state of an infinite potential well?"
] |
[
false
] |
Hey guys, I'm getting a bit confused when it comes to delta potentials. I was wondering if someone could shed some light on why the bound state centres above a negative delta potential the same way that it centres within an infinite square well. Also perhaps, what would happen to the bound state when there are two closely neighbouring negative delta potentials. Thanks for your help!
|
[
"What do you mean by \"centers the same way\"?"
] |
[
"Does the potential really go to zero at a finite distance from the well in the second case? I'd think it would decay asymptotically to zero at infinity. The reason the wavefunction is 'centered' around the well is that the potential is symmetric on both sides of the well. The system in the first case is symmetric about x=0, so the wavefunction is 'centered' about that point.",
"The two wavefunctions aren't really the same though. There's a discontinuity in the derivative of the wavefuction in both cases, at points where the potential is a delta function, and that's about it.",
"Otherwise, it makes sense for the greatest probability of finding a particle to occur at places where the potential is relatively low. If you had mutiple negative delta function potentials, I imagine the wavefunction would have more peaks, like ",
"this.",
" (?)"
] |
[
"If you had mutiple negative delta function potentials, I imagine the wavefunction would have more peaks, like this.",
"Just gonna jump in here really quickly.",
"If you had multiple negative delta function potentials arranged ",
", then you would use Bloch's theorem for solving Schrodinger's equation for a crystal lattice.",
"Long story short, there are going to be areas where the wavefunction for a given momentum is going to be 0; in other words, there are ",
". And then you can get to the theory of semiconductors :-).",
"But in any case, ",
"you seem to be right about the appearance of the wavefunction in the presence of a Dirac Comb potential",
"."
] |
[
"Is there a universally used symbol to denote hours, days, weeks, months and years?"
] |
[
false
] |
For example, the way that "kilometre" is denoted as "km" I'm in university, and over the course of the last few years, I'm getting really frustrated by the (very small) inconvenience of writing these words in full. Some people use 500mg/52 to denote 500mg per week (as there are 52 weeks in a year), but I feel like using numbers in this fashion is just bad form. There must be a system for these things, right?
|
[
"ISO 8601",
" is an international standard for dates, times, durations and time intervals."
] |
[
"I suppose that the \"standard\" way would be h, d, w, and y (months is particularly problematic). In context, it's probably clear what you mean by this."
] |
[
"The only \"defined\" unit of time is the second, and you probably won't catch anyone using a decimal time system.",
"Ask others have stated, short units are pretty common and self-explanatory. When in doubt, you can always follow good practice in documentation and write it first in full, followed by the abbreviated version (e.g. \"500 milligrams per week (500 mg/wk)\"). Then you can use the abbreviated version from that point forward.",
"Note on style: there should be a space between the quantity and the unit."
] |
[
"If I look someone in the eyes in a mirror (or glass, foil, etc.), is he also looking me in the eyes back?"
] |
[
false
] | null |
[
"Yes"
] |
[
"Even if the foil is crinkled, or the glass is dirtied in a specific way? Basically, is there anyway for it to be untrue?"
] |
[
"Maybe I don't understand your example. If the person isn't looking at you (in the mirror), then no. "
] |
[
"Do photons and other massless particles interact with the higgs field? And if so why don't they gain mass?"
] |
[
false
] | null |
[
"No, they don't.",
"Nothing without mass interacts with the higgs field, which is why they can go up to the speed of light. If you do interact with the higgs field, you have mass, and are limited to speeds below the speed of light."
] |
[
"Nothing with mass interacts with the higgs field,",
"Just to clarify, this is a typo. It should be \"Nothing with",
" mass...\"."
] |
[
"Ah, yes it is... Thanks for pointing that out :P"
] |
[
"Does the Hoover Dam need the water from Lake Mead to stay structurally sound?"
] |
[
false
] |
I’ve been reading articles about how low the water level is in Lake Mead and it got me thinking about two things. Does the concrete that was used to build the dam rely at all on being continuously wet (i.e. is the concrete prone to crumbling prematurely when it’s dry for extended periods of time)? Since the dam was built to hold back tremendous pressure from the lake, now that the lake is so low is there concern that the dam could collapse into the lake because the water isn’t there to balance things out? The thing was built during the Great Depression and wasn’t sure, at the time, if they ever factored the lake ever drying up in their engineering plans.
|
[
"A few items of note. First, the concrete does not rely on being continuously wet. Once cured, water has little effect on concrete itself. Water, and especially repeated wet-dry cycles, can affect the reinforcement within concrete, but concrete itself is largely unaffected by water. However, Hoover Dam is largely built without reinforcement. It does have some small amount of reinforcement in it, but only a few areas such as the spillway actually rely on reinforcement for structural purposes.",
"Next, also consider that the dam itself is incredibly thick. Think about how a basement or cave remains at a constant temperature through the year. It takes a long time for changes to air temperature to work their way through the soil. And the same is true for moisture penetrating through concrete. It does happen, but it takes a long time and tends to average things out. So if low moisture levels could affect the concrete of the dam chemically, only decades-long swings in lake level would be relevant. ",
"Finally, do not worry about the dam collapsing if there is no water behind it. The dam was built not just to generate electricity, but to manage flooding on the Colorado. The designers planned that the water levels would wildly swing up and down. ",
"Structurally, a dam like Hoover is designed in such a way that the pressure from the water is resisted by the dam's raw weight. Lowering the water level simply reduces the component counteracting weight. At no point will any forces completely reverse direction. You could drain the entire lake and it would only reduce the loading on the dam.",
"Or, if you want to think of it a different way, we've already tested the dam in this condition! Think about how it was built. The river was first diverted around the dam site, and the dam was constructed on a dry riverbed. So when it was built, there was absolutely no water butting up against it. Furthermore, concrete only gains strength as it cures, so the concrete was slightly weaker when they started filling the lake than it is today."
] |
[
"Dam good answer. Thanks"
] |
[
"One interesting thing about Hoover Dam is that they had to install refrigeration equipment and actively cool the concrete. ",
"Without cooling, the interior of the dam would have reached about 140 degrees Fahrenheit (60 degrees Celsius) and taken 150 years to cool to ambient, during which time considerable thermal cracking would have taken place (pp. 20 - 22).",
" So they built a refrigeration plant, laid the concrete blocks in sections, and ran refrigerated water through pipes to remove the heat of reaction of the concrete curing."
] |
[
"Why are some fungal skin infections like tinea versicolor incurable/chronic?"
] |
[
false
] |
What causes the source of the infection to remain so that the condition can flare up again after treatment and remission? Why can’t we nuke the little fungi out of existence? Aren’t some fungal skin infections like tinea pedis (“athletes foot”) completely curable?
|
[
"Not a dermatologist but a vet tech and animals can also have chronic or one time fungal diseases that are highly analogous to ours in many cases, so although previous posters are correct that systemic anti fungal treatments can come with some hard core side effects, I don’t actually think that’s the reason for the difference in these diseases. ",
"Athlete’s foot (tinea pedis) is caused by one of a few different dermatophyte fungi. Like ringworm it is not supposed to be living on you and is highly contagious. So once you finally get rid of it, if you don’t reinfect yourself, you’re done. ",
"Tinea versicolor is an overgrowth of a Malassezia yeast that is a normal part of a healthy human skin biome. It’s not at all contagious, it only causes problems if conditions are right in that individual person to cause an out of balance overgrowth. So if the conditions recur (extreme heat and humidity, excessive sweatiness, immune system dysfunction from a different illness or medication side effect, antibiotics messing with the flora balance) well that organism is already everywhere on your body and everyone else’s body because it’s supposed to be there, it’s not an occasional infection like ringworm. The only way to cure it would be not to nuke the organism, but to stop the reason for the imbalance (move to a cold dry climate, successfully address the root causes of the immune disease, etc). ",
"Does that make sense?"
] |
[
"Fungi have been around long before us, and will be around long after haha.",
"Fungi are eukaryotic organisms just like we are, so things that kill fungi also tend to kill us (e.g. cycloheximide), making a chemical treatment rout somewhat challenging, and spore forming reproduction is exceptionally resilient."
] |
[
"There is a certain point as with chemo treatments for cancer, where you are pretty much poisoning the host along with the foreign infection/tumor you are trying to get rid of, pretty much just hoping you kill off the problem before the person. Some fungi are just that resilient. It's possible that you could essentially 'nuke' them, but you are risking similar and likely irreversible harm to the subject in question by doing so.",
"Of course medical advances are constant especially with nanotech starting to become somewhat viable, it's possible we'll be able to get around this problem eventually. It still exists for now though."
] |
[
"In biology, what is Hierarchical Assembly?"
] |
[
false
] |
I can't find a well versed explanation of this. Am I on the right track if I say... 1) The fewest building blocks in producing molecules is ideal 2) It provides quality control. Various noncovalent bonds that bind macro-molecules together prevent the wrong building blocks from attaching or prevent misfolding
|
[
"I'm also new to this idea, but after a little reading, this is what I got. Basically, if you want a complex structure to be self assembling from a mixed pool of the building blocks, you want smaller simpler self-assembly steps to be energetically preferable, and you work your way up, to prevent the complex structure from coalescing improperly. ",
"An example would be if you want to create a strongly bound bi-layer, with one layer of molecule A, and another with just molecule B. If ",
" had a strong affinity for ",
" you might end up with a bilayer, but the ",
"'s and ",
"'s wouldn't be segregated. A better way would be for ",
" to initially have a strong affinity for ",
", but once a single ",
" binds to a single ",
", each molecule has an affinity for others of it's type. That way you might have a bunch of ",
" pairs forming a bilayer segregating ",
"'s from ",
"'s. "
] |
[
"Thanks! I appreciate it!"
] |
[
"Do you mind explaining differential binding too? Is it just the various noncovalent bounds that holds macromolecules together, such as proteins"
] |
[
"What exactly makes inbreeding so bad?"
] |
[
false
] |
[deleted]
|
[
"Inbreeding itself is not such a bad thing. It's when inbreeding occurs in large populations where it becomes bad. You see, large populations have a lot of defective/bad alleles (forms of genes) that are mostly masked by good, dominant ones. When you start inbreeding, you end up having a higher chance of getting two copies of the defective allele - causing the defect to be expressed.",
"Smaller populations don't tend to experience this issue because any defective alleles are quickly weeded out by natural selection. There's a good case study/example of inbreeding depression in cheetahs: ",
"https://en.wikipedia.org/wiki/Cheetah#Genetics.2C_evolution.2C_and_classification"
] |
[
"On a small scale and timeframe, this is not that much of a problem. However, inheritable disorders become more apparant. Most notable, autosomal recessive disorders become more dominant in the blood line. Autosomal recessive disorders in short are disorders requiring two \"carriers\" of the disorder to mate. If one of the parent suffers or carries the disorder, and the other does not, the kid will be a carrier as well, but it will not manifest and, given enough time and some luck with having non-carrier partners, it will be eradicated over several generations.",
"Since this type of disorder requires two carriers, by reducing the diversity of the gene people (by inbreeding) these disorders are becoming more and more respresented in the population. So on a larger scale and timeframe, It reduces genetic diversity and lets these disorders spread out through the larger population. ",
"Most notable inbred disorders are autosomal recessive. And there are many real-life examples of how this affected families or small villages. Where I am from (Netherlands), there is a small fishing village nearby notorious for the incest which occured there in the past. There is an (autosomal recessive) disease there which manifested mainly amongst the local population there.",
"There is not really something wrong with inbreeding, save for it being weird and resulting in awkward family situations."
] |
[
"Relatives share too many of the same chromosones so the off spring often comes out with disabilities including things like cleft pallet cleft lip downs syndrome type mental disabilities and other problems.",
"Oh and its just straight freaky."
] |
[
"Can someone explain why this doesn't violate conservation of energy?"
] |
[
false
] |
[deleted]
|
[
"Key point: Quantum efficiency is not the same as energy efficiency.",
"Quantum efficiency=number of electrons you get out ÷ number of photons absorbed",
"Energy efficiency=amount of energy you get out ÷ amount of energy absorbed",
"In theory, this type of process means the solar cell absorbs one photon with a given energy \"E\" and creates two electrons, each with energy of 1/2 \"E\". Since the sum of the electron energies is not greater than the energy of the absorbed photon, energy is still conserved. (Note: The energy of a photon is determined by its wavelength, while the [kinetic]energy of an electron is determined by its velocity). "
] |
[
"well stated"
] |
[
"It isn't an energy efficiency. It is more of a mobile charge production efficiency. This efficiency being over 100% means that, on average, more than 1 electron is freed from it's parent atom per 1 photon entering the material. The actual energy efficiency is most likely a bit less than 100%. "
] |
[
"Where does uranium come from?"
] |
[
false
] |
I made a post in askreddit trying to get an answer to this question but this seems like a better place, but I am trying to figure out where the naturally occurring elements with the higher atomic numbers like uranium come from. None of the processes I was reading about in wikipedia like proton capture or neutron capture seemed to reach the heavier elements found here on earth so am I misreading something or is there an undiscovered process that leads to their creation?
|
[
"Same place all the other heavy elements — everything heavier than iron — come from: supernovas.",
"Sometime in the distant past, before the Earth existed, there was a star. That star formed out of the primordial hydrogen (mostly) that precipitated out of the Big Bang. It burned for a while, and in the process fused light elements into heavier ones. Then it died, exploding and scattering its fusion products throughout a medium-sized region of space.",
"Later, another star formed from the stuff the first star left behind. Similarly, it lived and died and exploded, scattering its own fusion products through space.",
"Then the cloud left behind by those stellar processes, a cloud containing all the naturally occurring elements, collapsed under its own gravitation into little knots. One knot was quite massive and became the sun. Another knot was much tinier and became the Earth.",
"Some of the atoms that made up the Earth were uranium, forged out of lighter atoms in the supernovae that created the raw materials from which our solar system (and we) formed."
] |
[
"A little more detail... all elements heavier than Fe are formed by neutron capture and subsequent beta decay in stellar environments. In the s-process (",
"http://en.wikipedia.org/wiki/S-process",
"), beta decay rates exceed neutron capture rates; in the r-process (",
"http://en.wikipedia.org/wiki/R-process",
") neutron capture rates far exceed the rate of beta decay (supernova). Uranium is mainly formed by the r-process."
] |
[
"I do apologize. When I wrote that, I'd not long before come out of a solid hour of people telling me, over and over in different words, \"Wow, you're like totally blowing my mind, man, like woah.\" Idiot cannabis-headed kids get on my nerves like you wouldn't believe, and I brought some of that baggage with me when I responded to you.",
"I was out of line, and I'm sorry."
] |
[
"Concerning Mitochondrial Eve and Adam..."
] |
[
false
] |
[deleted]
|
[
"There was probably a major bottleneck due to a supervolcano eruption around 70 000 years ago. Look up the Lake Toba supervolcano. And yup, it could happen again. There are several of those around the world, including under Yellowstone Park :)",
"However, there's no need for a bottleneck to explain this at all. Because we each have 2 parents, 4 grandparents, etc, the number of ancestors doubles every generation you go back, and eventually you reach the point where almost everyone on that list is shared by a huge number of people. The math requires, more or less, that there will be people who are ancestral to all living humans. There are a lot of such \"Adams\" and \"Eves\"; the ones you mention are just the most recent ones."
] |
[
"It doesn't mean they failed to. It only means that none of them are likely around today. It's hard to make mathematical arguments on reddit, but ",
"here's a link",
" that explains the idea."
] |
[
"But even with such a terrible volcanic event I can't imagine how every other woman of her generation failed to produce their own family lines. To think all of humanity was essentially \"ground-down\" to one family at various points in history... "
] |
[
"Is there a type of star that emits only UVA light?"
] |
[
false
] |
Wondering if there is such a thing as a star that would essentially be a giant black light. From what I can find on Wikipedia, it would have to be a very hot star, meaning near the beginning or end of its lifecycle. Assuming such a star exists, could you reasonably expect an orbiting life-bearing planet be filled with fluorescent creatures and plants?
|
[
"Stars emit ",
"black-body radiation",
" corresponding with their temperature, which is essentially a distribution of frequencies (and colors) centered around a mean which is determined by their temperature. No matter how hot the star is, there is still going to be some portion of their spectrum emitting in the visible and infrared, and not only in UVA.",
"EDIT: I don't mean to say that stars only emit black-body radiation, but that they emit at least this in addition to their other radiative properties, so long as they aren't at thermal equilibrium with the surrounding space."
] |
[
"https://en.wikipedia.org/wiki/O-type_main_sequence_star",
"Not only UV, but mostly"
] |
[
"Yeah, that part was definitely more of a thought exercise than anything. I'm just trying to visualize what life on a planet orbiting a giant black light would look like... if it were to exist. ",
"Ultimately I'm just interested in knowing if there is a \"black light\" star. "
] |
[
"How fast could you theoretically travel in the vacuum of space with gravity being the accelerant. What if the gravitational force was everything in the universe clumped together?"
] |
[
false
] |
[deleted]
|
[
"your speed could get close to c. That's about as much as can be said."
] |
[
"I figured this would be the answer. I'm disappoint :*("
] |
[
"Correct me if Im wrong (which I often am) but isnt it possible for space to expand past c? This is my understanding of what would happen if space continues to expand at an accelerating rate. ",
"Wouldnt a gravitational force stretch space to a point to or past c? "
] |
[
"Does headphone use have an adverse affect on one's ability to hear?"
] |
[
false
] |
[deleted]
|
[
"Hearing damage comes from exposure to loud sounds; the louder the sound, the less exposure is needed to cause damage. But that's not the whole story.",
"The problem with headphones is that they don't give you the 'bodily experience' that live music or even full-range loudspeakers provide: only your ears get the soundwaves but the rest of the body is not being subject to the air pressure variations of the soundwaves (mainly bass), so there's a tendency to play louder on headphones than one would play on a regular stereo.",
"Another point to keep in mind: even if you keep your headphones at an apparently 'safe' level, the detrimental effect depends on the overall time spent under that volume; so while one hour of listening at 94dB(A) is considered the limit of daily exposure before hearing damage may occur, if you listen to eight hours at 85dB(A) the same level of damage happens.",
"A third point, and very important: our auditory system was not designed to be exposed to constant excitation round-the-clock, so even if you set the volume to a 'sedate' 76dB(A), if you spend the whole day with this kind of auditory stimuli you are bound on the long term to get stress, loss of attention, sleep disorders and other undesirable reactions of your body to this excessive input of sensory information. "
] |
[
"Why we like music? We like it because we make the music, and we make what we like to hear.",
"Music by itself does not destroy your hearing... listening to music loudly all day long will.",
"And 'loudly' depends of 'for how long'. Plenty of information is available on the web about sound exposure limits."
] |
[
"if our auditory is not designed for constant exposal music, why do we like it so much? To me, it seems dumb to make us love music when it basically destroys our hearing. or is this just one of those things where \"we developed faster than evolution could keep up\"?"
] |
[
"I don't understand \"Nuclear Radiation\". How does it work and what separates it from other forms of matter/elements in our world that seem to make it so much more dangerous?"
] |
[
false
] |
I understand that it's 'bad', is most closely related nuclear power plant meltdowns and atomic bombs. But I don't understand HOW it works. Are there different types of radiation? Is the radiation our phones give off the same exact thing, except at a much lower level? What is happening to our body when radiation gives us cancer? Why do we use radiation therapy to cure cancer when it also gives us cancer. It also seems a property of it is that you can't really stop it - it seems like putting up walls or barriers is not effective unless they are ridiculously thick, and even then it seems like we just do that because we don't really know what else to do and it's better than nothing Basically just looking for Nuclear Radiation 101 explanation.
|
[
"Regular matter is made of atoms. And every atom has a nucleus, made of protons and neutrons. Some nuclei are ",
", meaning that they decay. When a nucleus decays, it emits radiation.",
"There are different kinds of nuclear radiation. Some examples are alpha particles, beta particles, gamma rays, protons, neutrons, conversion electrons, fission fragments, clusters, and more. These are generally ",
" radiation, which means that the particles have enough energy to break chemical bonds or knock electrons out of atoms. This is the kind of radiation that can cause cancer. The radiation emitted by a phone or a WiFi router is ",
" ionizing.",
"What is happening to our body when radiation gives us cancer?",
"On a very basic level, ionizing radiation damages your DNA. This causes mutations which can lead to cancer.",
"Why do we use radiation therapy to cure cancer when it also gives us cancer.",
"Ionizing radiation can be used to kill cells. If you point your beam of radiation at cancerous cell, it will kill them. We have sophisticated techniques to specifically target the cancerous tissue with beams of radiation. The treatment kills cancerous tissue while delivering a much smaller dose to the surrounding healthy tissue.",
"It also seems a property of it is that you can't really stop it - it seems like putting up walls or barriers is not effective unless they are ridiculously thick, and even then it seems like we just do that because we don't really know what else to do and it's better than nothing",
"You can't stop radioactive nuclei from decaying, but you can certainly shield against radiation. Different types of radiation are easier to stop than others. For example, alpha particles are very easy to stop with a piece of paper, or even just a few inches of air. On the other hand, fast neutrons are much harder to stop."
] |
[
"a good way of explaining is by thinking of money. Say you have a dollar and it is unstable and randomly 25 cents breaks off and flies across the room. The dollar is now 75 cents and the 25 cents shot across the room and broke a window.",
"Same idea. If you have Uranium 238, 2 protons and 2 neutrons (exactly the same as Helium) can pop off and shoot across the room (through the wall, through you and your dog). You don't heve Uranium anymore, you have Thorium 234 and a Helium particle hurtling through your neighborhood."
] |
[
"Energy, momentum, angular momentum, etc. are all conserved during decays. If you add up these quantities for all the particles in the final state, they are the same as what they were before the decay."
] |
[
"Is the shape and general make-up of sperm identical, or at least similar, amongst all sperm producing animals?"
] |
[
false
] |
While watching a program on television documenting creepy sea creatures, they filmed a sea cucumber producing sperm in hopes of it finding eggs. I know the shape and make up of individual human sperm, I would assume it would be similar in chimpanzees (but maybe not?), but what about in animals such as sea cucumbers?
|
[
"Oh man, not even! For example, some species of fruit fly have sperm tat are multiple times longer than the fly itself. Some species have heterogeneous populations, some being incapable of fertilization but serving as 'blockers', some even being hunter killer sperm!",
"Check out Sperm Wars. It's a rad book. "
] |
[
"Not to mention all the crazy sex proteins that go ",
" with those sperm which can impart all kinds of behavioral effects!",
"I just found this great quote that puts the large sperm you mentioned into perspective:",
"Much of the research focused on the sperm of ",
"; an impressive six centimeters. The researchers explained that the female of the species had evolved to favor this long sperm because they developed long reproductive tracts in which longer sperm have the greatest chance at competitive fertilization success. \"The sperm of ",
" is 20 times longer than the male that produces it,\" says Bjork. \"To put that into perspective, if humans made sperm that long and you took a six-foot man and stood him on the goal line of a football field, his sperm would stretch out to the 40-yard line.\"",
"Here's the link to the full article."
] |
[
"Huge differences between mammalian species. Many kinds look different when you compare them via microscope. The craziest one I know off the top of my head is the echidna - individual sperm join together into a massive bundle of mega sperm\n",
"http://ichthyologist.tumblr.com/post/55037909532/echidna-sperm-bundles-the-echidna-tachyglossus",
"\nMale echidnas also have a 4 headed penis. Have fun with that google search. "
] |
[
"How can you determine the interference path of sound?"
] |
[
false
] |
[deleted]
|
[
"The interference pattern should be exactly the same as that for any wave phenomenon.",
"If you have two sources with spacing d with equal wavelength l, then sin (theta)= n.l/d for the angle theta of the nth minimum.",
"If you want to extrapolate this to 2 dimensions then you would have to take account of the azimuth angle too."
] |
[
"The mechanics of determining the interference condition is the same as for light. the only real difference is the wavelength and type of wave."
] |
[
"Are the formula the same as for the double-slit?"
] |
[
"When a meteor strikes the earth, are the pressures created upon impact great enough to compress any carbon present into diamonds?"
] |
[
false
] |
[deleted]
|
[
"Sure, there are examples from ",
"Finland",
". When there is an impact of a meteorite, there isn't just the impact pressure itself, but it creates a massive amount of heat. "
] |
[
"To add to this, any diamonds formed by an impact such as a meteor strike will be very small and of poor quality. A perfect diamond has a single crystal lattice structure through it's entirety - part of what makes it so beautiful is that it is literally a perfect arrangement of atoms which repeats indefinitely, and looks like this: ",
"Diamond Cubic",
".",
"Large and high quality diamonds are formed by consistent heat and pressure over very long periods of time, such that individual carbon atoms can click into this structure in the right spots, slowly growing the crystal larger and larger while maintaining it's lattice structure. Diamonds formed by a brief impact are very small, since they never have the time to form large, cohesive arrangements.",
"These kinds of diamonds can also be formed through the heat and pressure created by ",
"artificial explosions"
] |
[
"Nanodiamonds are commonly observed in impacts and can be used to document impact events even in the absence of a known crater. For example, ",
"Nanodiamonds in the Younger Dryas Boundary Sediment Layer",
"."
] |
[
"Are they any examples of 2-way predation in biology?"
] |
[
false
] |
What I mean is two species who both eat each other as part of their diet. I know there are examples where the prey can be a physical threat to the predator depending on the circumstance, but I've never heard of two species being both predator and prey to each other.
|
[
"Ooh, sure!",
"Intraguild predation",
" describes how predators sometimes kill and feed upon each other, usually when competing for shared prey items. The dynamic is often asymmetric, especially among adult animals, with one 'dominant' predator positioned at a higher trophic level, and another 'intermediate' predator, which usually loses out most of the time - think of coyotes and wolves; most often, the wolf gets coyote for dinner, but occasionally the coyotes triumph. ",
"Intraguild interactions are more symmetric when we take into account age- and size-associated effects however - i.e. many predators will commonly predate juveniles of other predators. Tigers and bears commonly prey on one another's young, whilst on the hypercompetitive African plains, it's no holds barred amongst lions, hyena, wild dogs, leopard and cheetah - all will opportunistally kill and consume juvenile members of the other species. For one, it's a decent meal, but more importantly it reduces competition for shared prey resources. ",
"In the aquatic realm, it's even more an 'anything goes' type situation. Most aquatic predators primarily select prey based on size (essentially anything that can fit inside their mouths), regardless of trophic level and even species. All planktivorous fish, for example, will regularly feed on any and all juvenile members of other, and even their own, species that they find in the water column.",
"So yes, intraguild predation is common, but usually only between adults and juveniles (unless the odds are otherwise disproportionately stacked; e.g. a pack of hyena against a lone lion) - and for good reason: it's far too risky predating on other mature adult predators, and there are no examples, as far as I'm aware, where two mature predator species ",
" prey on one another. Predators, through evolutionary time, essentially try to max out their offensive stats, whereas prey their defensive. When two fully primed predators are facing off, the chance of life-threatening injury, even if victorious, is therefore so high that evolution selects for behaviours that avoid such interactions. Better to prey on something a little less red in tooth and claw - you might have to deal with their defences, sure, and you'll be unsuccessful much of the time, but at least you won't be, like, eaten back. ",
"In short: predators rarely pick on something their own size, but regularly snack on one another if the balance is shifted in their favour, as when an adult comes across a juvenile. Between some species, it's usually to reduce competiton, with feeding a secondary objective; in others, it's the opposite. ",
" ",
" "
] |
[
"and there are no examples, as far as I'm aware, where two mature predator species ",
" prey on one another",
"It's not that regular even there, but there is ",
"the curious case",
" of Malgas Island, where lobsters eat sea snails (the normal order), and nearby Marcus Island, where sea snails eat lobsters. The large density of sea snails around Marcus Island means the occasional lobster that gets there is the prey.",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4448886/"
] |
[
"Oooh! That's really cool. Density-dependent inter-predator predation (oof, words) is a first for me, and kinda' seems the best example for what OP was looking for. Thanks for sharing!"
] |
[
"How is entanglement able to move faster than light?"
] |
[
false
] | null |
[
"Entanglement is just a fancy way of saying that two particles are correlated. To use a simple analogy, you take two coins, and you put them in two boxes in a way that one has to be heads, and one has to be tails. You move the boxes arbitrarily far apart, then you open one. It's tails, so you ",
" know that the other one must be heads.",
"So while your knowledge of the other coin \"moves\" faster than the speed of light, theres nothing really special about entanglement in that sense."
] |
[
"I don't think it demonstrates existence of higher dimensions, particularly since no-one has yet shown how it works or understood it. All we can do is show it occurs, not how."
] |
[
"It doesn't.",
"This is a very common misconception arising from the application of classical logic to quantum-mechanical systems. The logic goes like this: \"",
" and ",
" can each be either ",
" or ",
" but whenever ",
" is ",
" then ",
" must be ",
" and vice versa. Therefore, if I measure ",
" and find it to be ",
" then something must ",
" to ",
" to be ",
"Makes perfect sense in terms of classical logic. But it's complete bollocks in terms of quantum-mechanical logic.",
"Consider any pair of electrons. Ordinarily, each electron has its own state. If you measure the spin orientation of each electron individually, you'll find that it's either parallel or perpendicular to whatever axis you chose. If you call — purely arbitrarily — parallel ",
" and perpendicular ",
" then both electrons can be either ",
" or ",
" and there's no correlation between them. They're independent.",
"But when the particles become entangled, they become part of a system with a single state. They're no longer independent. They become like two sides of the same coin. The ",
" is either going to be ",
" or ",
" because those are the possible states of the system. It's never going to be ",
" or ",
" because those are not possible states of the system. (If you want to get technical, ",
" and ",
" are not eigenvectors of the spin operator.)",
"So to determine the state of the system, you need only measure the state of one part of it. If you measure the first electron and find it to be ",
" then you know the state of the system is ",
" If you measure it and find it to be ",
" then you know the state of the system is ",
" Because those are the only possible states in which the system can be found.",
"It's not that the two electrons are just off doing their own independent things and measuring one ",
" the other. That's not it at all. It's simply that you're able to observe the state of the system by looking at just a part of it. The relationship between the parts means that you can obtain sufficient information to describe the whole system by just looking at one part.",
"To put it in classical terms that, just to mix things up, do ",
" have anything to do with coins, imagine that you have two friends who've never met. Wherever you happen to be, there's a chance that you could run into one friend, both friends, or neither friend, because they're totally independent of each other.",
"But say those two friends start dating, and it goes poorly, and there's an ugly break-up. From then on, if you run into one of those two friends somewhere, you ",
" that you ",
" find the other friend there. Because they hate each other, and will never be in the same place at the same time. You know the state of the whole system by just looking at part of it, because you also know the ",
" between the parts of the system."
] |
[
"Why do airplanes fly at 30,000+ feet and not lower?"
] |
[
false
] |
[deleted]
|
[
"The air is less dense at altitude, allowing the aircraft to fly faster, and more efficiently.",
"You mention buildings, but I would suggest mountains too, although this is not the real answer."
] |
[
"When it comes to commercial aviation jet engines function better at higher altitudes where the air is colder and less dense. That allows companies to save in fuel $$. Also we live in the troposphere above that in the tropopause is the where the jet stream is with winds usually well about 50 knots and that saves time and money when it's a tailwind. Smaller planes for training and general aviation do fly much lower, but they're also much smaller so maybe you don't see them as much if you don't live by an airport."
] |
[
"Less resistance "
] |
[
"Can cells fuse togther, like mitosis in reverse?"
] |
[
false
] | null |
[
"For a \"typical\" cell, I would say no, they do not undergo fusion such that you have two cells in one(or any type of \"reverse mitosis\"). They can, however, transfer material by packaging material in vesicles and these vesicles can move into adjacent cells, which is kind of related to what you're asking."
] |
[
"Yes. There are many cells in our bodies that are known to \"fuse together\". This is described as ",
"syncitial",
". However, keep in mind two points:\n1) This is NOT equivalent to \"mitosis in reverse\". Many examples of fused cells retain the multiple nuclei of their uni-nucleate fore-bearers.\n2) The inciting cause, physiological mechanism, and functional reason for cellular fusion can be widely varied and different. Thus, it is important not to generalize too terribly with this idea, in my opinion at least.\nSome top-of-the-head examples:",
"Physiologically normal:",
"1) ",
"Osteoclasts",
" are present in the bones of all people, and are normally multinuleate. They form from multiple singly nucleated cells, called monocytes, fusing together. and function to microscopically break apart bone, releasing the dissolved calcium and phosphate from the bone into the bloodstream. They are thus useful in the body's regulation of blood calcium level. When blood calcium is low, osteoclasts are stimulated by parathyroid hormone to degrade/dissolve small portions of bone to release the bone's calcium into the blood.",
"2) All skeletal muscle in the body is composed of muscle fibers that are giant, elongated, multinucleated fibers formed from the fusion of individual cells. The reason for this, from what I know at least, is that for muscles to perform optimally, its best for individual cells to span the long distances of the muscle instead of having to just connect to other cells halfway along the length of the muscle. For example, say you are playing tug of war with two pieces of rope tied with a knot in the middle of the two teams. It is possible that the tension on the rope would break the knot apart, and this sort of rope would thus perform weaker than one long single piece of rope without a knot. Likewise, you'd rather have single, very long cells spanning the entire length of your bicep than for it to be \"knotted\" to another one halfway through. Cellular fusion into multinucleated muscle fibers accomplishes this. Here is ",
"picture of this",
".",
"3) One of the placental tissues is called the SYNCITIOtrophoblast, because it is tremendously multinucleated.",
"Normal inflammation-induced:",
"1) Most of the time when we're infected with a bacteria, we kill it off and that's the end of that. Sometimes, the bacteria might be so sturdy that it is virtually impossible to kill off entirely. Tuberculosis is an example of this. Once you have it, it is possible that you will always have it, and that's bad. In scenarios like this, your immune system reverts to a backup system, a plan B. If it can't kill the bug, it tries to wall it off in a cage of collagen and cells. This is called a ",
"granuloma",
". Often times, in granulomata, we see ",
"multinucleate giant cells",
". These are multinucleated cells formed from the fusion of macroPHAGes (cells that PHAGocytose things, i.e. cellularly eat them). Curiously, Mcrophages are the mature form of monocytes, the very same cells discussed above that can also differentiate and mature into normal osteoclasts of the bone. ",
"2) Same is true of HIV encephalopathy (if HIV gets to the brain it causes a multiucleated giant cell reaction) ",
"Aberrant inflammation-induced:",
"1) Mumps, measles, respiratory syncitial virus, and others all have an F-protein (F for fusion, no joke), and this causes abnormal syncitia. I ",
" this is something found in the Paramyxo family of viruses but you'd have to check that one out.",
"2) There are a good handful of other examples that I'd have to look up to be sure about, but some of the herpes viruses can cause syncitia.",
"Sorry, this is pretty long and by the last one my whisky was getting to me! Im done!"
] |
[
"Wow thats really interesting. Thanks for the info man!"
] |
[
"Why is the clitoris on the outside of the vagina?"
] |
[
false
] |
If the only purpose of the clitoris is for pleasure, why has it evolved outside the vagina?
|
[
"You are thinking of this the wrong way. Evolution does not create traits with 'goals' in mind. The male and female genitourinary structures are embryologically ",
"derived from the same structures",
" and contain ",
"homologous anatomy",
". The clitoris is embryologically homologous to the glans of the penis, which explains its position. This is simply a remnant of embryology, much like why males have nipples."
] |
[
"Don't they urinate out the vagina too?",
"EDIT: I guess it sounded like a joke but it is true, technically. In pigs the vagina and urethra share a ",
"common urogenital passage",
" \nI remember this from A&P",
"EDIT 2: Wow, still getting downvotes? I hope you all never take an A&P class with fetal pig dissections..."
] |
[
"It's worth mentioning that some animals (pigs for instance) have the clitoris inside their vagina."
] |
[
"What keeps two solid objects composed of the same element from 'sticking together'?"
] |
[
false
] |
So I finally got around to watching the new Cosmos (which is pretty great by the way) and I got a little confused about the interactions of atoms and molecules. The show explains that atoms have this 'electron cloud' that keeps solid objects from really 'touching' each other. The example they used was a human finger going to touch a human face... They zoom in on the atoms and apparently some property of the atoms keeps the two objects from actually touching although we might think they are touching. What I don't understand is how the 'skin atoms' in the finger are able to 'touch' or be bound to themselves, but they are not allowed to 'touch' the other 'skin atoms' in the face. Why don't the finger and face just become one solid object when they get close enough? For a more clear example for a question: How come you can stack gold bars on top of each other without them becoming one single gold object? How do the atoms 'know' that they are part of one solid object versus another? Liquids and gases seem to have no problem mixing together, what is it about solid state objects that keeps their atoms from mixing? Hopefully I was clear enough!
|
[
"Great question! The first thing to note is that there are ",
" of substances and materials, and molecules in each of these stick to each other in different ways.",
"For instance, you have metals like gold and iron where atoms are bonded because their outer, most energetic electrons have become ",
"delocalized",
" and are free to move throughout the entire metal. The metal is then held together by the strong attraction between the positive nuclei and the negative \"sea\" of electrons. This does mean that if you were to push two masses of pure copper together, their sea of electrons would merge and they would become one. This is the principle behind ",
"cold welding",
", and also a theory behind how gold nuggets form.",
"On the other hand, this is clearly not how skin or organic material works. It wouldn't be good for our cells to stick to everything they come in contact with (imagine our blood clumping together), which is why cells have special molecules (like collagen) on their surfaces that specifically attach to other cells, also known as the ",
"extracellular matrix",
".",
"So yes, if you bump two pure gold bars together, ",
". (In reality, this doesn't happen because like ",
"/u/iorgfeflkd",
" explained, a layer of oxide usually forms on their surfaces and prevents bonding. As well, their surfaces are usually not perfectly flat, and the bonds formed at the few contact points are weak enough that you can separate them like nothing happened.) However, if you bump two skin cells together, ",
" unless there are the right proteins to hold them in place. Neither will it happen for plastics or other ",
"polymers",
" because of how they're held together."
] |
[
"Typically, metals have a thin layer of oxide on them that prevents them from bonding with other metals. For example, a bar of pure iron will develop a thin coat of rust pretty quickly. If you prepare to metals in a vacuum without an oxide layer, you can touch them and have ",
"cold welding",
"."
] |
[
"To add to this. In a vacuum deposition chamber, such as is used to apply thin coats of metals and construct semiconductor electronics, you don't have to do anything special to get the atoms you are spraying to stick to the substrate and become part of it. The bonding just happens naturally because the vacuum condition has gotten all the oxidation layers and impurities out of the way."
] |
[
"Why is radioactivity associated with glowing neon green? Does anything radioactive actually glow?"
] |
[
false
] |
Saw a post on the front page of regarding some green water "looking radioactive." What is the basis for that association?
|
[
"One of the first widespread applications of radium was luminescence - self-powered lighting. For instance, ",
"Radium Dials",
" or clock faces were popular, as they glowed in the dark. These materials convert the kinetic energy of radioactive decay (and subsequent ionization) into visible light. If you combine a radioactive source with the right phosphor, then electrons which were knocked away from their atoms will emit visible light when they fall back into an orbital. Zinc sulfide doped with copper was a common choice for the phosphor component in the early 1900's, which glows green. ",
"This was also one of the first times that the dangers of radiation became apparent. Many of the factory workers who painted these dials began to be diagnosed with cancers of the blood and bones at very young ages. ",
"edit: also note that Tritium is still used in this context today - ",
"link",
". ",
"edit2: There's an important distinction that needs to be made. The radiation itself doesn't glow. With the right materials, you can use radiation to produce visible light. In radioluminescence, a phosphor converts the energy of radiation into visible photons. If you had a small piece of tritium or radium sitting by itself, it would not glow. "
] |
[
"My preceptor had me read this about the \"radium girls\" when I was on a nuclear pharmacy rotation. ",
"http://www.damninteresting.com/undark-and-the-radium-girls/",
"Very interesting. "
] |
[
"Yeah, the Radium Girls is one of the first things you learn about whenever you study radiation protection. It was a real tragedy, but it lead to the creation of lots of good reforms. Their subsequent lawsuit established the right of a worker to sue for damages from corporations due to labor abuse. It helped kickstart the field of Health Physics. And it helped us understand the effects of ingestion of radionuclides."
] |
[
"How thick of a mattress would a person need to survive a fall at terminal velocity?"
] |
[
false
] |
What material would such a mattress be made of? Also what positional orientation would be best to land? Clarification: By surviving, I mean land reasonably comfortably.
|
[
"This is not quite enough to answer the question. The mistake is assuming constant deceleration. Initially, after hitting the mattress, you would have a deceleration of 0 (assuming a few things that I will get into shortly). The reaction of the mattress onto your body would increase linearly with its deformation (Hook's law). So, after falling 1 meter into the mattress you would have a deceleration of x and after 2 meters 2x. Think of how a mattress pushes back more, the more you deform it. This holds true as long as the deformation of the springs is within elastic limits, after a point it becomes nonlinear but we can avoid discussing the implications of nonlinearity here by designing a mattress that will do the job inside the elastic zone of the springs. ",
"To accurately calculate this we would also need to take into account the surface tension of the material that's covering the springs and the initial forces your body needs to exert to overcome the inertia of the springs (as you're coming in fast and the springs are stationary). ",
"Calculating the effects of surface tension and inertia would take extensive math so let's ignore them. ",
"I'll take the 40g deceleration figure as true and calculate assuming that. Calculations like these are usually done through kinetic/potential energy. Assuming 60m/s terminal velocity (terminal velocity actually varies quite a bit but let's assume a round number for the sake of simplicity), and a body mass of 80 kg, that's 80 * 60",
" / 2=144000 J of kinetic energy. The mattress needs to do the same amount of work along the path you take falling through it. Let's call your fall path through the mattress \"x\". So we need the mattress to do 144000 J of work along a path of x. Work is force over a path or F * x. Now we can calculate the force from the condition of maximal acceleration which is 40 * 9.81=392.4 m/s. F = m * a so F = 80*392.4=31392 N. Mind you, that's the maximum force the mattress is allowed to exert. Assuming like we did that this is all within the elastic zone of the springs, then the maximal force will be achieved for the maximal deformation, in other words at the moment you stop and have covered the path \"x\". As it will increase linearly in relation to x, the average force will be F / 2=15696 N. So going back to our energy equations, this means that the mattress needs to do 144000 J of work over a unknown path of x with an average force of 15696 N. Now we can calculate x and it's x=W / F / 2=144000 / 15696=9,17 m. Mind you, this is how far you will fall through the mattress, presumably you need even more space for the remaining contracted springs so we can round it up to 10 m.",
" 10 meters according to a simplistic calculation not taking into account higher order effects."
] |
[
"Let's say that the decceleration when hitting the mattress is a. Terminal velocity is 200 km/h. The time to deccelerate is then t=200km/h / a. Distance travelled is x=1/2 * a * t",
" = 1/2 * a * (200km/h / a)",
" = 1/2 * 200 km/h / a . From wikipedia, a brief 40 g acceleration seems to be just about survivable (I would guess that there is a significant chance of death already with this) when perpendicular to the spine, which is fine in this case. Putting in a=40 * 9.81 m/s",
" gives x=4 metres.",
"However note that four metres of ordinary mattresses would be no good. The springs need to be much less tight so that the decceleration initially isn't too hard. But if you engineer suitable springs, or some suitable spring-like material, and have four metres of it then that should be fine. A safety factor of some kind wouldn't hurt either."
] |
[
"Very thorough, thank you both."
] |
[
"How much of the earths surface can we see from the moon?"
] |
[
false
] | null |
[
"From the side of the moon that is facing us, one would see about half of the earth at any single point in time, or all of the earth over a period of time.",
"From the side of the moon that is not facing us, one would see none of the earth ever.",
"Asking \"How much of the earths surface can we see from the moon?\" is essentially the same as asking \"From where on the earth can you see the moon?\""
] |
[
"How would being an oblate sheroid make it possible to see more than 50%? You cant see more than 50% of a flat disc either.",
"Also I would assume that everything you said would be dwarfed by the fact thay Earth has an angular size of 2 degrees seen from a moon. Using basic geometry, this would mean we could see a maximum of ",
"50-((2/180)*50)= 49.5",
"49.5% of a perfectly round ball.",
"Edit: My formula works for 2D objects. I cant figure out the formula for 3D but as far as I know, it would result in sligthly less area seen."
] |
[
"The southern hemisphere of the earth is larger than the northern one (I will admit, that is not true of all oblate spheroids, but the one we are talking about is), which precludes there being an axis of symmetry other than through the poles.",
"You are modeling the earth as a perfect sphere, with a perfectly smooth surface. If I stick a pyramid on the surface of a sphere, it increases the surface area, and consequently increases the visible surface from angles which show the pyramid. It also means that from angles where the pyramid is obscured, I can now see a lower % of the surface than I could before, because there is more surface, yet I cannot see any more of it. ",
"There is more land mass in the northern hemisphere, and consequently the deformity from smooth is greater. The northern hemisphere is smaller, and more conical than the southern hemisphere. The result of these factors is that the visible surface area of the earth, from a viewpoint extended out from the North Pole, is greater than the surface area visible from a viewpoint extended out from the south pole."
] |
[
"When whole cities flood, does this mean the sewers are backing up into the streets or is there some sort of containment mechanism?"
] |
[
false
] |
My knowledge of sewers stems entirely from AHH Real Monsters, TMNT, and the fact that there are open drainage areas in the streets for rain overflow. I don't know how they've designed to differentiate between run off and waste once everything goes below street level, and in my brain if I can see the open run off holes in the street does this mean the sewage comes out those same holes when everything super floods?
|
[
"Modern sewer systems have 2 totally different systems, 1 for storms that empties into a lake or whatever and one for waste that goes to the shit plant. If something's going to overflow it's almost guaranteed to be storm. Old cities built combined systems years ago because street runoff was essentially sewage and they didn't treat it anyway. So there have been major overflows of combined systems and that's a huge health hazard obviously. Now, clearly when there's a flood, flood water's picking up whatever's on the ground so it's still contaminated, but it's not like human poo is coming out of the drains in the street."
] |
[
"There's no containment. Sometimes sewer water comes ",
"gushing out of manholes",
". "
] |
[
"Oh man. That is really good to know. Thank you for the answer! "
] |
[
"Smoke different from smell?"
] |
[
false
] |
The other day I heard that the smoke coming off of something (say a cigarette) is separate from the smell of the smoke. Meaning that the smoke molecules you see in the air are separate from the molecules that activate your smell. Is this true? I always thought the smell of the smoke the smoke itself. EDIT: Meant to ask a follow-up question If this is true, then can a room smell smokey if someone smokes in it (with well ventilation, of course) but not have any actual smoke in the air? So, for example, would the fire alarm go off if this would happen?
|
[
"Chances are that there are still smoke particles in the air, but they are too dispersed to be visible. Smoke detectors can be very sensitive so this could potentially still set off the alarm",
"EDIT: see ",
"this",
" for details"
] |
[
"The reason you smell smoke is because it contains various molecules that activate specific receptors in your nose. Our noses do not contain receptors for every molecule and if you do not have a receptor for a particular molecule, you will not be able to smell it. As a result, only a fraction of the molecules in smoke actually cause it to have a smell. Similarly, some of the molecules are visible whereas some aren't but there is no reason why a molecule can't be visible and odorous, or invisible and odourless.",
"Cigarette smoke contains such a wide range of chemicals that there will always be some molecules that you can smell and some that you can see. As for smoke alarms, they basically work by detecting tiny particulates in the air. The reason you can see smoke is because it contains tiny particles of soot (the actual gases are almost transparent). Therefore, if you can see smoke then it can also set off a smoke alarm"
] |
[
"That makes senes, thanks for the response. But what about if you ",
" see the smoke in the air but you do smell it? Does that mean there are smoke particles that could trigger the alarm?"
] |
[
"How do we know that dark matter isn't just ordinary matter our instruments can't detect?"
] |
[
false
] |
Most of the pop-sci explanations for dark matter that I've seen compare the light we detect from a galaxy with some observation of its mass: gravitational lensing, velocity, etc. There isn't enough light to explain the mass. But how do we know that this isn't just a limitation of our instruments? Is it possible that there is enough light, but that it's just too faint to detect?
|
[
"For example, we cannot rule out that the dark matter might be asteroid-mass black holes (e.g. figure 10 of ",
"this article",
"). Why couldn't it just be asteroids?",
"The main lines of evidence against such a possibility are related to the early universe. This is a time when the the universe was very hot. Asteroids could not exist in such an environment; they would dissociate into diffuse plasma like all the rest of the ordinary matter. In this context, all ordinary matter is equally detectable, in the sense that it has an equal impact on what we observe. But what do we observe?",
"1) The relative abundances of light elements throughout the universe. We understand nuclear physics and can predict the ratios of hydrogen, deuterium, helium, etc. that should have emerged from the Big Bang. What we find is largely consistent with ordinary matter comprising only 5% of the total energy density today. If the density of ordinary matter were higher, we should find less deuterium and more helium than we do. The first figure of ",
"this paper",
" (page 9) illustrates nicely how the primordial element abundances depend on how much ordinary matter there is.",
"2) Temperature variations in the cosmic microwave background. In the early universe, the ordinary matter and photons were tightly coupled, which led to such effects as pressure oscillations and sound waves. Dark matter, on the other hand, only interacted via gravity. This causes them to have very different effects on the evolution of temperature and density variations in the early universe, which manifest themselves to us in the cosmic microwave background. ",
"Here's an animation",
" of how changing the density of ordinary matter (\"baryons\") would alter the \"power spectrum\" of the cosmic microwave background temperature, which is something we have measured extremely precisely, e.g. ",
"the top panel of this figure",
"."
] |
[
"I think to restate this simply (with the caveat that simple == less correct) is that we do know it’s not things we can detect easily, like elements (hydrogen, helium, iron, etc). These things tend to clump together and do things like fall into stars where we can detect them by their emission lines. Which how we know things like the hydrogen/deuterium ratios of stars and galaxies. We know the mass is there through observation of galactic rotation. We just can’t see it. ",
"What’s left are largely things that are hard to detect. Like neutrinos. Or theoretical things like subsolar mass black holes or various WIMPs that are also really hard to detect. ",
"As to what dark matter is, there isn’t any definitive proof of one thing over another, though some things are more likely than others."
] |
[
"These things tend to clump together and do things like fall into stars where we can detect them by their emission lines.",
"I think that requires some additional assumptions. Dark matter indeed couldn't be gas, because we can detect gas on its own, and also gas would lose energy and fall into things (whereas dark matter does not). However, high-density low-brightness objects made of ordinary matter (like free-floating asteroids or planets) would behave just like dark matter and would be incredibly difficult to detect. Granted, it would not be easy to explain how they all formed.",
"But that's why I went to the very early-universe evidence for dark matter. Because irrespective of what form ordinary matter took in the late universe, it was all the same in the hot early universe."
] |
[
"What could I expect to find at the bottom of a sinkhole?"
] |
[
false
] | null |
[
"Depends on your location.",
"If you have a water-filled sinkhole in the countryside, then dove to the bottom of the debris cone, you'd find branches and trees, leaves, various small animals that fell in and limestone rocks. ",
"I've had the chance to get into a bell cavern formation where the locals had used it for a trash dump, but also a place where stolen vehicles wound up. To this day, I'm convinced the little blue hyundai has a body in the trunk. There were kaolin clay formations from just above the limestone surface, dead animals, various trees, and of course, the silt that deposited itself on the floor. ",
"No main access to the aquifer large enough for a human to pass through was found. There were several species of cave crayfish that were coming in from the aquifer to feed on the rich biota."
] |
[
"Here is a story about the original image. It is NOT a sinkhole. Rather, it is a \"piping feature\" which is very different, and far more dangerous. These sort of features are caused by the settling of lots and lots of volcanic rock or lava, over time. It turns out they are incredibly unstable to build on.",
"http://news.discovery.com/earth/dont-call-the-guatemala-sinkhole-a-sinkhole.htm"
] |
[
"Another question based on the picture in the original post. How come that the hole in the picture is circle shaped? I doubt it's a perfect circle, but it sure looks like one, it almost looks hand made."
] |
[
"Why do some songs sound \"sad\" or \"happy\" when we listen to them?"
] |
[
false
] | null |
[
"Happy and sad (and more) comes from the Amygdala. However, I don't know why major sounds happy or neutral and minor sounds sad.",
"I expect it has something to do with the tone when we speak or cry. And this is mimicked by the chords."
] |
[
"A major chord can be heard and processed through the brain smoothly because there is minimal tension between the notes. ",
"In a minor chord, the lowered fifth doesn't fit as perfectly. (This has something to do with differences in frequency and wavelength but that's a whole other story) That tension as a result mimics the feeling in your brain when you're sad or about to cry; there's just something out of place that brings your mood down."
] |
[
"This is not true. First of all, a minor triad consists of the first, third, and fifth scale degrees, it does not have a lowered fifth. are you referring to making a major chord minor? If thats the case then you would lower the third by a semitone to make it minor. A major or minor triad by itself will have no extensions or alterations that will cause dissonance or \"tension\" as you said. As for answering the question, there are many things in a piece besides the minor key that could cause it to sound sad. These things include timbre, slower tempo, instrumentation ect."
] |
[
"Black holes can expel jets of charged matter at relativistic speeds; do these jets provide thrust to the black hole?"
] |
[
false
] |
These 'astrophysical jets' are understood to be ionized matter. Should the incredibly powerful expulsion of this matter (thrown across thousands of parsecs at speeds up to .80c) not propel the expelling body in the opposite direction? Could not the supermassive black hole at the center of every galaxy be accelerating along the axis of the jet and dragging the galaxy with it? Are the galaxies all receding from us not due to expansion of space but because each galaxy has its own thrust?
|
[
"Well, first of all: yes. Black holes are still subject to conservation of momentum, so expelling something in one direction would accelerate it in the opposite direction. However, the jets are in opposite directions and so would cancel each other out. Also, the black hole could not drag the galaxy with it - the galaxy is a million times as massive as the black hole. Also, the recession of galaxies (all getting farther away from all, equally in all directions) cannot be explained by motion (which is separately detectable)."
] |
[
"On the other hand, that would require the black hole to be asymmetrical in some way and I don't know if that's even possible.",
"Jets are always at least slightly asymmetrical, and it's been my key area of work for 3 years now. In the Fanaroff-Riley classifications, hybrid sources (one jet is type FRI and the other is type FRII) are seen, although not commonly. The asymmetry between the two jets can be quite severe though even between jets of the same classification in terms of length and luminosity, and hence power. Some of this is undoubtedly the result of the local environment that the jets are expanding into ballistically, as a denser medium will increase entrainment of surrounding material into the jets and cause the collimation length to be shorter. "
] |
[
"On the other hand, that would require the black hole to be asymmetrical in some way and I don't know if that's even possible.",
"Jets are always at least slightly asymmetrical, and it's been my key area of work for 3 years now. In the Fanaroff-Riley classifications, hybrid sources (one jet is type FRI and the other is type FRII) are seen, although not commonly. The asymmetry between the two jets can be quite severe though even between jets of the same classification in terms of length and luminosity, and hence power. Some of this is undoubtedly the result of the local environment that the jets are expanding into ballistically, as a denser medium will increase entrainment of surrounding material into the jets and cause the collimation length to be shorter. "
] |
[
"What happens if VY Canis Majoris explodes?"
] |
[
false
] |
Since we are a tiny molecule in front of it. What will happen to us if it goes super nova?
|
[
"Short answer? Essentially nothing, it's too far away.",
"VY Canis Majoris is a huge star, no doubt about it - it's more than a thousand times larger than the sun. But it's also ",
" far away - almost 4000 light years. (",
"http://arxiv.org/abs/1109.3036",
") A type II supernova has a visual magnitude of around -17. That's very bright, but it's so far away that from our point of view the apparent magnitude we'd see is closer to -6 or -7. For comparison, the full moon is about magnitude -12, so it would be more than a factor of 100 dimmer than the moon (more negative = brighter) and a few times brighter than Venus. In other words, it'd be pretty, and astronomers would be climbing on top of each other to be the first to observe it in detail, but it wouldn't be any threat to us."
] |
[
"But wont the radiation or other stuff reach us in 4000 light years?"
] |
[
"If it exploded 4000 years ago, we could see it explode today. We can only tell what it did 4000 years ago. If it exploded 3000 years ago, we won't know about it for another 1000 years."
] |
[
"Is going in a circle at the same pace turning at the same rate, still considered an inertial frame of reference?"
] |
[
false
] |
I had been given an experiment in which I held a ball tied to a string and walked in a circle at a constant pace. There was no acceleration. I was supposed to drop the ball after walking on the circle for 5 revolutions, then I would observe what happens to the ball and someone else who was stationary observes what happens to the ball. This all went fine until we had to do the discussion and we were given some questions. We had to identify if the 2 frames of reference were 'Inertial' or 'Non-inertial'.1 being the person moving in the circle and 2 being the stationary observer. Is the person moving in a circle at a constant speed in an inertial frame of reference or not? I have argued with my teacher quite a bit, and basically everywhere I have looked on the internet, this is made so stupidly complicated that I, a year 12 student can't understand. My teacher suggests he is but how is it inertial if the velocity is changing? Sorry if I am not looking at something obvious or any dumb mistakes, not the smartest guy out there :p
|
[
"Is the person moving in a circle at a constant speed in an inertial frame of reference or not?",
"A rotating reference frame is not inertial, even if the angular speed of the rotation is constant.",
"We had to identify if the 2 frames of reference were 'Inertial' or 'Non-inertial'.1 being the person moving in the circle and 2 being the stationary observer.",
"This is correct if you switch 1 and 2. The rest frame of the person moving in the circle is non-inertial, and the rest frame of the stationary observer is inertial."
] |
[
"Technically, velocity is a vector quantity, meaning it is comprised of magnitude (speed) and direction. Even though you’re moving in a circle at a constant SPEED, your direction is continuously changing. So say you’re circling in the XY plane. If you look only at the x-axis component of your motion, it oscillates back and forth, getting faster, then slower, then reversing. That’s acceleration and deceleration in the x axis, even though the overall speed never changes. Same thing happens in the y axis. "
] |
[
"Yes. The definition of inertial reference requires that the object be stationary or at a constant velocity along a linear path. Person 1 does not fit that description because his velocity (remember this includes direction) is always changing. "
] |
[
"Can someone explain what happens to the mind & body when it is suffering from anxiety ?"
] |
[
false
] | null |
[
"I answered this a while ago but here's my comment:",
"If you want to go with the neuroanatomy, then we shall start with the ",
"amygdala",
". This area is a group of nuclei that respond strongly to emotional / stress challenges. This area of the brain sends signals to the Lateral Hypothalamus and Paraventricular nucleus of the hypothalamus (PVN) will starts the activation of the HPA-axis: ",
"*The PVN will secrete vasopressin and corticotropin-releasing hormone (CRF) ",
"• CRF and vasopressin stimulate the release of ACTH from the pituitary gland",
"• ACTH will stimulate the adrenal cortices, which produce glucocorticoids (cortisol: stress hormones)",
"It's important to note that this is a simplified version of what is really going on. It is also negative feedback loop, so it will eventually after a certain amount of time, turn itself off. ",
"Additionally, the amygdala also has projections to other areas of the brain: Projections to the parabrachial nucleus of the pons causes an increase in respiration, and Projections to ventral tegmental area (VTA), locus coeruleus (LC), pedunculopontine nucleus (PPN), activate dopaminergic, adrenergic, and cholinergic neurons to increase arousal and vigilance. ",
"All of these projections and neurons releasing chemicals are part of the sympathetic nervous system, which is primarily responsible for fight or flight. It is responsible for dilating pupils, directing blood flow away from the gut and toward muscles, and more. Check out its wiki. "
] |
[
"I'm not so sure about the system turning completely off, but the stress response will definitely decrease over time. There are a couple of mechanisms that do this: ",
"1) They hypothalamus is composed of several subnuclei that can monitor what it is in the blood. Normally, the brain is \"blood exempt\" by the blood brain barrier, but certain parts of the brain (circumventricular organs) can sample chemicals from the blood. In this case, the subfornical organ can detect rising cortisol levels and this can inhibit the release of CRF and vasopressin. ",
"2) The frontal cortex sends out inhibitory projections to the amygdala and these neurons have glucocorticoud receptors (as well as a high density of CB1 receptors) that also contribute to the termination of the stress response. "
] |
[
"Personally, I try and stay away from the word \"wrong\" in neuroscience. The brain is extremely plastic (meaning it adapts very quickly to new situations). I truly believe that in things like anxiety disorders, it is the brain becoming hypersensitive because it was useful in the past (not evolutionary terms, talking about personal experience here). ",
"So no, I don't think there is something wrong with their brains, but I do think the changes that the particular brain underwent in the past to protect itself are to the point of being no longer useful or detrimental (a good example to think of here is PTSD). ",
"So what are the changes that happen?",
"Allostatis load (McEwen & Stellar 1993) is defined as the physiological consequences of chronic exposure to heightened neural response due to chronic stress / anxiety. Conditions that can lead to allostatic load include repeated stressors, failure to habituate to familiar stressors and failure to terminate the stress response (think PTSD)"
] |
[
"If dark matter can bend light does it mean that stars further away may appear to be in the wrong position?"
] |
[
false
] |
I've recently read an article where it explained that large clusters would bend light from stars and even galaxies. It did not get into specifics. I just assume that if light would get bent by large gravitational forces it would change direction, thus appearing to be in a different position in the universe than it actually is.
|
[
"Yes but only by a tiny amount."
] |
[
"Exactly, and that's one way we know that some type of dark matter exists. We know how deflected galaxies should be based on the mass we can see, but we measure a deflection much greater. Thus, there must be some mass that we can't see, some kind of \"dark matter\"."
] |
[
"Thank you. That is pretty much the answer I was looking for. "
] |
[
"Why do old helium balloons half-float"
] |
[
false
] |
I get that the amount of helium reduces but what is the actual reason that a healium balloon will float at say 1 foot off the ground after a certain amount of time. Is it something to do with air pressure/gravity vs the amount of helium left
|
[
"Look closely. Most balloons have a string attached. Initially it can easily support its weight and the weight of the string. As it looses helium it will reach the point where it can no longer support the entire string and it will drop until it is only lifting the amount of string it can bear. Thus as it continues to loose helium, it will be able to support less and less of the string and progressively come closer to the ground."
] |
[
"Tiny differences in temperature and pressure can cause a difference in density. \nThe balloon floats at a height where the air underneath it is more dense than the balloon and the air above it is less dense. "
] |
[
"Think about putting something at the bottom of a pool. Things don't float only a little bit and then stay there unless something funny is going on with the density of the water."
] |
[
"Why doesn't the phase velocity of light carry useful information?"
] |
[
false
] |
I've been looking around the internet and can't find a satisfactory answer. I was thinking about how dielectrics slow down the group velocity of light, but not the phase velocity, and then wondering if that would violate causality in some way. Apparently, the reason why it doesn't violate causality is because a pure sine wave doesn't carry any useful information because all it gives is a frequency. In the context of practical uses, it may not be very useful since there's no information about phase or amplitude, but in the context of photons however, it seems like there's enough information to know a lot. You know the energy using Planck's relationship E=hf, and you know the wavelength by the relationship c=lambdaf. What's missing?
|
[
"Imagine you have a light source (currently off) at one end of a medium and a detector at the other end. The medium is one light-second long. The group velocity of the frequency you're sending in this medium is 0.5 c, while the phase velocity is 2 c. After you turn on the source, the detector will start receiving light 2 seconds later because the wavefront moves at the group velocity. After that time, it would take a \"crest\" on your beam of light only half a second to travel across the medium, but any changes to the beam itself would take 2 seconds to get across. The fact that a crest has reached the detector is not information, a change in frequency or amplitude is."
] |
[
"Yes but the information is that the source is sending waves with that frequency to the detector. That information travels at the group velocity."
] |
[
"Photons are made up of a continuum of frequencies contained within an envelope, like ",
"this",
". The group velocity describes how fast the envelope propagates, and the phase velocity describes how fast the peaks within the envelope travels. In a dispersive medium, each frequency has a different phase velocity. If you want to measure the phase of a (short, strong, classical) pulse of light, you would measure the oscillating electric field, which requires overlap between the detector and the body of the pulse envelope, which will always move at v_g <= c.",
"Here is a loose analogy that might help. Suppose you have a giant TV screen that you project sinusoidally-varying black and white vertical bars on, sort of ",
"like this",
". You can move these bars across the screen arbitrarily fast (it's a TV screen, you can project whatever image you want for each frame), so you can have a \"phase velocity\" which exceeds c, but the bars themselves don't transmit information from one point to another on the screen. It's the same reason why moving a laser pointer in an arc can result in a dot moving across the surface of the moon faster than light without violating causality."
] |
[
"Are we able to observer and directly quantify any forms of magnetism outside of our galaxy?"
] |
[
false
] |
[deleted]
|
[
"Yes, magnetism is not unique to our galaxy. In fact all the light which we receive from other galaxies have a magnetic component to them. So if you ever see another galaxy in the sky the light hitting your retina has a magnetic field which initiated in another galaxy and your eye is quantifying it by its wavelength and the number of photons of that colour hitting your eye in that spot. "
] |
[
"Absolutely, black holes have some of the strongest magnetic fields in the universe. Large black holes have so much ionised material orbiting them so rapidly that it creates an enormous magnetic field. As far as forces go there are forces acting on everything everywhere all the time. Gravity is the major force that would be experienced near a black hole."
] |
[
"Absolutely, black holes have some of the strongest magnetic fields in the universe. Large black holes have so much ionised material orbiting them so rapidly that it creates an enormous magnetic field. As far as forces go there are forces acting on everything everywhere all the time. Gravity is the major force that would be experienced near a black hole."
] |
[
"How are protons and neutrons arranged within the nucleus?"
] |
[
false
] |
Are there different lattices as with atoms? Is there only a single stable configuration? How do additional neutrons (isotopes) affect the arrangement?
|
[
"Nucleons in a nucleus have a shell structure similar to that of electrons in an atom. For a given nuclide, there is at most one stable state, which is the ground state. Any excited state can decay to the ground state, and often the ground state can decay to a different nuclide."
] |
[
"The nucleon orbitals are probability distributions, just like the electronic ones."
] |
[
"Is that, again, a matter of probability, like the position of electrons? Is the mental model of sticky, little balls working when it comes to geometrical distribution?"
] |
[
"What is TV static and how does it come to be?"
] |
[
false
] | null |
[
"Most of it is ",
"noise",
" generated in the TV's tuner. TV's have automatic gain control circuits to be able to bring in weak stations or strong stations. In the absence of a signal, gain is at maximum, and so is amplifier noise. If an antenna is connected, terrestrial sources, the Sun, or Cosmic Background Radiation will add a small amount, but it won't change the display noticeably. "
] |
[
"I'd say that covers the basics. Without a TV station pumping a signal at a certain frequency, the radio signal is just a white noise mixture from all the faint earth sources as well as extra terrestrial sources. I've heard that some of the wave energy is actually the cosmic radiation background leftover from the big bang.",
"Anyway, the white noise is the analogue to random digital bits, on and off signals. So a TV randomly shows a black, white, or in between value at each pixel.",
"I'm not sure why there are not random colors, but color was encoded in a very narrow section of the transmission for PAL and NTSC, which might be a factor.",
"That might not be exactly accurate but hopefully describes it well enough."
] |
[
"I am pretty sure that tv (and radio) static is all the extraneous signals that are being picked up by your antenna. Lots of things make electromagnetic waves, which is what the antenna is designed to pick up, but they have no information, it is the em version of noise. This is where we get the term noise to signal ratio. ",
"I am sure I did a terrible job explaining this and I apologize, I woke up 3 minutes ago and only kinda know what it is when I'm awake."
] |
[
"How does a tempered glass screen for your smart phone pass the sense of touch to the sensors below?"
] |
[
false
] |
The title pretty much sums it up. I can guess that it would be through heat or possibly shadow but I can't say for sure. It probably isn't from pressure because the tempered glass seems very hard and therefore wouldn't flex much.
|
[
"I am currently working on a capacitive touch design right now, so I can take a stab at this.",
".",
"First you basically need a way to measure capacitance. There are several ways to do this, and every touch manufacturer has a variance on it. Essentially you apply a stimulus to the \"sense\" pad and then look at it's decay or response to get a base capacitance measurement. Generally there are 2 main kinds of base capacitance measurement, \"mutual\" and \"self\". Either way you are relying on the fact that this measurement is pretty consistent when there is nothing on the screen, that the glass is non-conductive so the fields can pass through it, and that your finger, which is conductive, will divert the electric field causing the measurement to change.",
".",
"Self capacitance",
" is essentially when you are measuring the capacitance of your floating sense pad to ground. The advantage here is you generally have a bit more signal, but the disadvantage is you essentially have 1 pin per pad.",
".",
"Mutual capacitance",
" is essentially when you are measuring the capacitance from one sensor to another. The disadvantage is you have a much smaller reference plane to measure capacitance to, which can be bad trying to measure through thicker pieces of glass/plastic. The advantage is you can multiplex the sensors. ",
"For instance, you could use 6 pins to measure 8 \"points\" by having 2 for the row and 4 for the column",
". Now you scan each row sensor with respect to each column sensor and you get 8 locations that are uniquely identifiable.",
".",
"I am going to preface this section by saying, I have never done an actual phone touch screen before, but I can speculate on a possible design based on things I am testing. Let assume we want to combine a mutual capacitance design with a touch screen, and my controller has 32 touch pins. I can combine this with an LCD, which I have glued down to prevent the air gap from changing my measurements. Since it is a rectangle, lets design my electrodes for say 18x14, using 32 pins giving me 252 zones behind my LCD. You would think you could only measure 252 points, but it turns out you get some leakage between the sense pads, so you you can get a proximity type measurement. You compare each pad's measurement with a nearby pad and you can better locate the location of a finger press.",
".",
"Sounds complicated right? Well luckily for a design engineer like me, the manufacturers of these sensing chips do most of the work for me. I can choose to dig into all of the sense values and run my own custom algorithms for finding fingers, or I can trust the built in libraries from the device manufacture. This means that if I followed their guidelines correctly I pretty much can get back a table of information that says there are fingers in X and Y positions and I am good to go.",
".",
"All images were linked from a ",
"Texas Instruments Technology design guide on their CapTIvate solution",
". You can thank TI for the lovely pictures, or read up on their guide for a more in depth detailing of their capacitive touch technology. I will note I have no affiliation with TI.",
" Some minor wording changes and a note, that I haven't actually done a Touch screen LCD on a phone, so I am speculating based on how I would design a phone touch screen from scratch"
] |
[
"Touch screens work on the electrical conductance of your finger. That's why if you use it with a wet finger and leave water on the screen, you will get strange behavior. You can use it with a cold piece of metal as well, as long as the surface area is big enough.",
"IIRC, there are many small areas of a clear, electrically conductive material (many different candidates, one source said indium tin oxide is most common) imprinted on the surface of the glass. When a conductive material makes contact, it disturbs the electric field in that area, and a touch is registered.",
"Edit: I'm describing what are apparently known as ",
"capacitive screens",
". Somewhat misleadingly, I think, \"resistive\" touch screens work by pressure, and the sensors are behind the actual display."
] |
[
"In capacitive touchscreens the electrically conductive layer is actually on the ",
" surface of the glass. When a conductive object, like a finger, is pressed against the outer surface of the glass the whole system - two conductors separated by an insulator - forms a capacitor (thus capacitive touchscreen). This change in electrical properties of the inner layer can be detected."
] |
[
"What is exactly meant by \"cementitious products\" formed in concrete?"
] |
[
false
] |
[deleted]
|
[
"\"Cement\", in the context of architecture and engineering, refers to Calcium oxide.",
"A bit more generally, cementitious particles could refer to calcium hydroxide, any one of multiple phases of calcium-silicate-hydrate (CSH) gel, or other phases. The chemical nature of cement is complicated. In this context, probably the products referred to are primarily CSH."
] |
[
"Cementitious Products are those products which contain cement. \"Cement\", in the context of architecture and engineering, refers to Calcium oxide. Examples of cementitious products include concrete, mortar, and terrazzo flooring."
] |
[
"Thank you!"
] |
[
"Please tell me major things that old physics books have misinformed me on."
] |
[
false
] |
I recently started reading , and a few years ago I read . They're both absolutely classic science texts from which I can/have learned a ton, but I also know there are some caveats in learning out-of-date information. Some of them I can catch from my own knowledge (Feynman said that we don't know the intermediate between DNA and protein; Asimov said that we don't have solid evidence smoking causes cancer and that freon is a natural wonder with no detrimental effects), but I know very little physics and incorrect facts in these fields I am likely to miss. Just curious, what are some big things that have changed, especially in physics (about which I know the least)? Thanks!
|
[
"The Feynman lectures took place in the early 1960s, and a lot of little things have been learned since then, but not too many big things.",
"The structure of protons and neutrons was just being discovered in this decade, which lead to quantum chromodynamics, the theory of quarks (partons according to Feynman) and their interactions. This makes up part of the ",
" which was formalised in the 1970s. We have since discovered that neutrinos have mass and oscillate between flavours.",
"The biggest discovery was perhaps in the 1990s, when we realized that the expansion of the universe is accelerating and that the cosmological constant/dark energy exists.",
"There are also lots of discoveries in condensed matter like high temperature superconductivity and fractional quantum hall states. Nanotechnology was basically the brainchild of Feynman and it's been moving along since then."
] |
[
"There is no such thing as relativistic mass. Things don't get more massive the faster they move relative to you. Applying the Lorentz transform to mass gives you back a number which looks like a mass and acts like a mass in your equations but which actually means absolutely nothing whatsoever.",
"That's not so much a change in accepted truth as it is a change in teaching methods. It was once fashionable to teach young students that you could apply the Lorentz transform to mass and get useful results back. But it was known since the 1910s that that's not true. So you might've been misinformed about that by what turned out to be bad teaching.",
"Also, black holes are absolutely nothing like what we thought they were like twenty years ago."
] |
[
"There are three yes."
] |
[
"Why do heavier elements (e.g. Lead) produce more secondaries when bombarded with radiation than lighter molecules (e.g. polyethylene)?"
] |
[
false
] | null |
[
"Secondary what? And bombarded with what kind of radiation? At what energy?"
] |
[
"Deep space radiation of heavy elements like lead is said to produce more \"secondary radiation\" than lighter shielding. The article I read wasn't overly technical and used a lot of analogies rather than direct explanation of mechanics."
] |
[
"They probably mean bremsstrahlung from charged particle radiation and possibly electromagnetic showers from high energy photons. Basically both of these processes become stronger with increasing atomic number of the target. That's what makes lead a good shield against certain types of radiation, but it also makes it susceptible to producing secondary radiation by the mechanisms I said above."
] |
[
"magnets have the ability to do work, and energy cannot be created or destroyed, so how are they able to do SO MUCH work (w=fxd) over their life?"
] |
[
false
] |
My guess is that its potential energy is tied to its electrons, NOT joules?
|
[
"Magnets create a magnetic field. Magnetic objects in this field have ",
" energy. The situation is similar to masses on earth. They gain potential energy when you lift them up. However, the earth itself (or the magnet) does not create the energy. No, its ",
" who does the work, by lifting them up."
] |
[
"When you \"make it into a magnet\" you certainly have to put a lot of energy in it. "
] |
[
"Ah ok, after you have done the work to separate them, and created the potential energy, this energy can be used to \"close the gap\" again. The total energy is always conserved. In principle, you could repeat such a process forever."
] |
[
"Can we just send prefabbed pieces for a Mars \"exiter\" ahead of a manned mission, assemble it once on Mars then return on it?"
] |
[
false
] |
I guess Im asking can we send easy to put together parts for some sort of launcher and supplies to Mars ahead of our manned mission. Send a rover to make sure its all intact and operational. Then a manned mission with something thats not designed to land and take off but just land safely (possibly bumpy). Assemble the new exiter and eat and rations and what not while building it that were also sent and when youre ready just launch out. Doable?
|
[
"You might want to consider the scales involved here. Lets look at MSL/Curiosity: The rover (ie final payload) weighted 900kg, and the rocket needed to get it to Mars weighted 334000kg. Based on that you'd need to use over 350 rockets to deliver the mass of one rocket to Mars. And that doesn't include any equipment needed to assemble or launch the rocket.",
"That back-of-the-envelope calculation didn't take to account that you probably wouldn't need as large rocket to return from Mars as you did to get there. And the scale of a manned mission would be almost an order of magnitude larger (eg. Saturn V which was used on Apollo missions weighted 2,800,000 kg), so that will affect estimates too.",
"If you were able to make fuel on Mars, that would make the idea far more feasible, considering that vast majority of the mass of rockets is fuel."
] |
[
"Thats a good point. Well could we use the ion propulsion systems for the larger pieces to slowly get there to help with the weight and then send a separate payload of just fuel using the same thing. I dont know just spitballing here. Then once its there send the rover to give it a look over to make sure nothing broken. ",
"I guess for some of this to work some or most of the building process would have to be automated to minimize the time it took us to get off mars, which poses more weight though. Eh obviously its a tough problem top people have been working on forever and Im not about to figure it out in a reddit post."
] |
[
"The ",
"Mars One mission",
" intends to do this to send over their materials, rather than as an \"exit\" strategy - but they include the rover!",
"(I have heard it mooted as an \"exit\" strategy before, though I don't know if that was mission-specific)"
] |
[
"Does fiber simply speed up our digestive system, or do our bodies want to expel fiber quickly?"
] |
[
false
] | null |
[
"Fiber acts as a bulking agent, and as mentioned by HonorAmongSteves, it carries water, creating a rather substantial mass that moves through one's digestive tract. Peristaltic movements by the colon and eventually defecation are stimulated by stretch receptors present in the wall of the colon. Due to the increased bulk in the colon, stretch receptors are activated, passage is expedited, leading to a faster mouth to anus transit. "
] |
[
"Let me translate it into layman language:",
"Fibers are bulky.",
"Without the fibers, your guts think there's nothing there, and they get lazy. With the fibers, all that bulk tells your guts \"hey, there's stuff in here, get busy\" - and they do."
] |
[
"Your body can't break down fiber, and it holds water as it moves through your bowels, making it easy to eliminate compared to denser or drier stuff. "
] |
[
"How would Superman's cape actually behave if he was flying in space?"
] |
[
false
] | null |
[
"If Superman is \"flying\" in space, we can remove two of the effects that usually act on a cape: gravity and aerodynamic effects. We're left with the forces on the part of the cape attached to Superman's neck, which will generally follow his flight, and internal friction forces in the material which will eventually damp out any oscillations in the cape, dissipating that energy as heat.",
"So, let's assume he's going to accelerate in one direction and then just coast. As he accelerates, the same magical force also causes the top part of the cape to accelerate in the same fashion, and the rest of the material will follow suit as the fabric is pulled taut. This will introduce some crazy, unpredictable motions in the cape, but due to the aforementioned internal friction, this motion will be damped out somewhat quickly. Now, we have a cape that is extending straight behind its attachment at the neck with no flapping or movement, much in the same way that a short piece of string held up in the air will swing and oscillate but eventually come to rest along a vertical line.",
"But this isn't the end of the story, if we assume he's going to stop accelerating at some point. When he does, the force on the neck of the cape stops, and, assuming the cape has some stretch to it, the energy stored in those little \"springs\" in the material will be released, pulling the material back in the direction in which it was previously being tensioned. This motion will be damped out again, but not before the cape has become more or less rumpled up along Superman's back depending on how springy its material is. Then, it holds that shape until he decides to accelerate again (in any direction).",
"In the end, Superman just kinda looks like crap, with a rumpled cape that isn't streaming behind him as expected."
] |
[
"Outstanding. Many thanks. "
] |
[
"It would wave more than it would in an atmosphere as the only resistive force would be from the spring effect in the individual fibers of the cape."
] |
[
"Any tips/protocols on making your own recombinant ligase?"
] |
[
false
] |
I'd like to clone the T4 DNA Ligase gene. Then I'd like to purify T4 DNA Ligase. Has anyone attempted this on their own before?
|
[
"Amplify the mRNA using PCR. Insert that into a vector apt for protein expression. Transform some E.coli and select your single colony cultures. Sequence the vector for confirmation of insert. Check a lysate for protein expression using a western or something. Let those bad boys grow like there's no tomorrow. Lyse the bacteria and purify them with one of several different techniques (protein G beads + anti-T4Ligase antibody, you can electrophoretically purify it, etc, google these). Run a test ligation with your resultant product to confirm functionality. Find an optimal storage condition (lyophilized, -20, -80, LN2, etc).",
"Question 1: Why do you want to do this instead of buying it? It's comparatively cheap. ",
"Question 2: Why did your mentor/boss not tell you how to do this?"
] |
[
"I've got access to T4 DNA, so I plan on just PCRing it up with His-tags and then cloning it. Antibodies kinda defeats the purpose. His-tagging seems like the easiest way to do it.",
"I was hoping I might be able to find a protocol, though. I've all I got so far is some papers from the 80s."
] |
[
"Are you allowed to use kits? Check Qiagen if so. ",
"Google has never failed me for some protocols. "
] |
[
"Why do canaries show symptoms of poisonous gas before humans do, in the context of canaries in coal mines?"
] |
[
false
] |
In elementary school, I was told by the teacher that canaries have smaller lungs than humans, making them more susceptible to poisonous gas but that answer never sat well with me because smaller lungs should take in less total poison dose. Also birds are smaller than humans so the poison concentration should be fairly similar on a per weight basis. The only way I could see the bird showing symptoms first is if it has a disproportionately increased respiratory and metabolic demands compared to humans, resulting in faster accumulation of poisonous gas or that poisonous gas of equivalent dose is more potent towards canaries than to humans?
|
[
"Canaries, like other birds, are good early detectors of carbon monoxide because they’re vulnerable to airborne poisons, Inglis-Arkell writes. Because they need such immense quantities of oxygen to enable them to fly and fly to heights that would make people altitude sick, their anatomy allows them to get a dose of oxygen when they inhale and another when they exhale, by holding air in extra sacs, he writes. Relative to mice or other easily transportable animals that could have been carried in by the miners, they get a double dose of air and any poisons the air might contain, so miners would get an earlier warning. (Source: ",
"https://www.smithsonianmag.com/smart-news/story-real-canary-coal-mine-180961570/",
")"
] |
[
"Bird have respiratory systems that are way more efficient than ours. They need tons of oxygen to power flight so they have a unidirectional flow of air, while we have bidirectional. We inhale fresh air, gas exchange takes place, and then we breathe out, repeat. Birds have lungs and air sacs. The air comes in, and it kind of gets stored in air sacs, passes through the lungs, where gas exchange happens, and then into more air sacs and out. It happens on a loop, there’s a nice gif on ",
"this page at the bottom.",
"Because there is no in-and-out, it’s continuous, bird lungs are able to extract more oxygen from the air. However, this also means they extract more of everything else. This is what makes them so much more sensitive to air pollutants than us. It’s also why you should never cook with Teflon pans if you have birds. The gases given off by Teflon as it heats are toxic and can kill birds."
] |
[
"Slightly off topic, but if like me you used to feel sorry for the canaries, a lot of them were kept in resuscitator cages like the one shown at ",
"this link,",
" (sorry i don't know how to embed the picture)"
] |
[
"Do stimulants (like Adderall and Ritalin) really have a different effect on \"ADHD brains\" as opposed to \"normal\" brains?"
] |
[
false
] |
[deleted]
|
[
"Everyone's brain is structurally different - this is the reason that we are all unique. ",
"Stimulants like amphetamine and methylphenidate work by increasing the levels of the neurotransmitters dopamine and norepinepherine (although the mechanisms in which they do so vary slightly).",
"ADHD disorders are associated with lower levels of metabolic activity in certain areas in the brain, notably the prefrontal cortex (PFC). The PFC is involved with what are known as executive functions: planning, thinking, motivation, etc. Dopamine and norepinepherine are both involved with learning, memory, reward, etc. and also generally act as excitatory agents (although this is a pretty gross oversimplification) and can increase the metabolic rate.",
"By increasing the levels of these neurotransmitters in the brain, you increase the levels of these transmitters in the prefrontal cortices. At the proper dosage, the levels of these neurotransmitters are primarily raised in the PFC as opposed to other areas like the striatum and the nucleus accumbens (which deal with reward and addiction). At higher doses - ie: those that one would take to get high from these compounds - these areas begin to become more and more affected by the drugs.",
"source: i am a neuroscience student"
] |
[
"Aderrall at least, once in the bloodstream, stimulates the production of norepinephrine and dopamine, both of which are associated with attention. It also stops these hormones from being absorbed quickly, so that the effects of increased focus last longer. The reason it would affect a non-ADHD person so well is that they are able to focus and keep concentration at a relatively \"normal\" level, so this extra surge of hormones will get them feeling even more focussed and concentrated. You have to remember that Adderall is made of amphetamine salts, which give, in layman terms, a \"speed\" effect. Essentially, it increases the activity of the central nervous system.",
"Ritalin also acts as norepinephrine and dopamine reuptake inhibitor, meaning that once those hormones are released, the body won't absorb them back readily because the neurotransmitters are saturated with Ritalin (correct this if I'm wrong, been a while since I studied this). Ritalin does not increase the amount of norepinephrine and dopamine, unlike amphetamines, rather it increases the general firing rate of neurons, and the signal to noise ratio in the neurons, which indirectly causes more dopamine to be released, and it is thought that this increases attention, and decreases distractibility."
] |
[
"Although it hasn't been 100% scientifically proven, those with ADD and ADHD typically have lower functioning prefrontal cortexes. Stimulants, such as Ritalin, increase the functioning in this area. Video games have also been shown to stimulate this area which is why people with ADD and ADHD can typically focus very well on them when they can't with other tasks. I'd go further into it, but I'm on my phone. I hope this helped answer your question. "
] |
[
"What are the major disasters we'd see if bees really disappeared?"
] |
[
false
] |
I've heard all this: "Oh no, bees are disappearing!!!! Help them everyone but I haven't yet heard a good reason for why it's such a big deal. I have a feeling it has something to do with pollination but I'm not very informed.
|
[
"Yes, you're correct, it's all about pollination. Without bees to pollinate plants, we'll lose a lot of food products that have been staples of human life for millennia. Take a look at this ",
"list of plants that bees pollinate",
" and imagine the ones listed as 3 or 4 on the pollination impact scale no longer existing in sufficient quantity to feed any significant human population. On top of massive food shortages, there would be a mass reduction of flowers and other inedible plants that depend on bees for pollination.",
"TL:DR There wouldn't be as much to eat, the world would be a lot uglier, and there wouldn't be any pumpkins on Halloween."
] |
[
"Yes, but it would require incredible amounts of time and money. The production would be significantly reduced, and the cost of food that had to be hand pollinated would skyrocket to the point of being unaffordable to most people. The cost of hand pollinating, for example, apples to keep current production levels would be ",
"876,538,125 USD",
", and that's figured at the federal minimum wage of $7.25. If we end up raising minimum wage to $15, it would cost about $1.8 billion ",
" to keep apple production at current level. You can imagine what that will do to the price of apples.",
"Edit: And this doesn't solve the flower problem. Unless massive armies of volunteers spend all their time hand pollinating wildflowers, if the bee population dramatically decreases, so will the world's flowers."
] |
[
"Radiolab did an episode where they discussed this exact thing and according to the farm in China, hand pollination actually resulted in greater yields considering you got near 100% pollination as opposed to a mismatched 75% or so that bees tend to have. Write up on it by Robert -> ",
"http://www.radiolab.org/story/how-important-bee__kw/",
" and a link to the episode -> ",
"http://www.radiolab.org/story/what-dollar-value-nature/"
] |
[
"If wealth was distributed evenly amongst all of Earth's population, how well-off would each person be?"
] |
[
false
] |
Assuming productivity remained the same.
|
[
"Total global wealth is ",
"currently pegged at $231 trillion (pdf)",
", so that's $33,000 per person. Global GDP is around $70 trillion, which makes for $10,000 annual income per person.",
"According to the Credit Suisse report, global wealth is expected to increase to $345 trillion in four years, which will be about $47,000 per person."
] |
[
"True. I wasn't figuring property, but yeah it would be worse if people didn't get to keep the stuff they already had. It would become a free for all if all things were equal. "
] |
[
"Is that 345 trillion nominal dollars, or real dollars?"
] |
[
"Do humans have the ability to \"sense\" when someone is behind them or staring at them or is it usually just a lucky guess?"
] |
[
false
] |
I've always wondered... You'll be sitting somewhere like the library, then suddenly you look up and turn around and catch someone looking at you, or simply standing behind you. Can we naturally sense when someone's behind us or next to us or does it just depend on the situation? EDIT: I suck... "I've always wondered," not "I've always wondering."
|
[
"Obviously you can't tell what someone else's eyes are doing (the difference between them looking at you and not looking at you). This is a great opportunity to consider bias! When you look around and no one is looking at you, that doesn't stand out in your brain. But when you \"feel watched\", look around, and someone IS watching you - think how amazing that is! You have superpowers! Your perception is paranormally good! This gets remembered.",
"So due to bias, you have a tendency to have noticed all the times you \"felt watched\" and WERE, and a tendency not to notice/remember the times you weren't, thus you end up with a vague sense that you can somehow tell."
] |
[
"Try it yourself, ask someone to stand behind you and see if you can tell when he looks at you and when he looks away."
] |
[
"I like this kind of answer because it encourages testing the world around us to find out, rather than asking someone else."
] |
[
"Do Animals have Blood Groups like humans?"
] |
[
false
] | null |
[
"human blood types (ABO) are present in other primates. The other great Apes have very similar blood to ours. not much research has been done on this for a lot of reasons (for one human blood is much easier to get than gorilla blood). It is probably possible to transfuse ape blood to an acceptable donor (accounting for blood type). There may be some issues with other blood products or other markers (antigens like ABO) on ape red blood cells. ",
"most other animals have different shaped or sized blood cells, or have different chemical properties like hemoglobin concentration that make them incompatible with human bodily functions. ",
"some research has been done into pigs since they have similar blood cell size and composition as humans. The pigs would probably have to be genetically modified to produce viable blood for humans though, and again, it’s easy enough to get human blood nowadays anyway."
] |
[
"Blood groups in humans typically describe features of the cell surface antigens on our red blood cells. These antigens can be sugars or proteins or a mixture of proteins with sugars bonded to them. The ABO designation is controlled by which version of an n-glycan sugar is sticking out of your red blood cells. But there are many other blood classification groups types Rhesus positive and negative being one well known one, which is a gylcosylated protein. Related primates have a similar system sugars and proteins on their blood cells perhaps these might adaptable for use in humans (or vice versa). But the reality is that the immune system is very sensitive and and any non-trivial change in the related proteins would ensure that you can't swap these out.",
"When you start looking further afield to other red blooded mammals you find they also have blood groups but they aren't a consequence of the same proteins and sugars. Obviously domesticated animals are best studied. Dogs have 2 major blood types; DEA1 and DEA2. Cats have a system of A, B and A/B. But when you look closer the proteins and sugars involved are quite different to primates. Blood between any of these animals would not be compatible at all."
] |
[
"The blood of the marine lugworm ",
" contains a type of hemoglobin that is a more efficient O2 carrier than the human hemoglobin, and there has been a lot of research on the potential of this hemoglobin as a therapeutic agent. This would not be a blood transfusion, though, just hemoglobin. ",
"Here is a reference",
" if you are interested."
] |
[
"What happens to neutron stars, pulsars, and other super dense objects after they've spent their energy? Can their material be reabsorbed into new stars, solar systems, or galaxies?"
] |
[
false
] |
Considering how dense objects like neutron stars are, what happens to them after they die? Are they broken apart, exploded, absorbed into new objects, or something else?
|
[
"What do you mean by \"spent their energy\"? Neutron stars are already fragments of stars that have spent their fuel (for nuclear fusion) and then exploded in supernovas. As such, neutron stars are just really tightly packed blobs of neutrons (and other matter). These bodies don't need an input of energy in order not to collapse, that is taken care of by the Pauli Exclusion Principle, through the ",
"degeneracy pressure",
". So to answer your question, on \"short\" timescales of a million years, neutron stars will simply get colder as they radiate away heat. On really, really, really long timescales ",
"the physics get murkier",
" and we can't really say anything for sure at this point. One possibility is that all nucleons will slowly decay, leaving behind an empty and cold universe."
] |
[
"/u/totitiganiisuntgunoi",
" described what we know (and don't know) about neutron stars pretty well.",
"We also have a pretty good idea of what will happen to White Dwarfs over time; like neutron stars they don't require fuel to resist collapse. Electron degeneracy pressure holds them up against gravity (whereas neutron degeneracy pressure holds up neutron stars). White dwarfs also don't generate energy, which is why they're considered remnants or dead stars, but they do radiate the thermal energy that the start out with and very slowly cool. As it cools, it emits less and less light, and what light it does emit is predominantly at longer and longer wavelengths, and eventually - to a human eye, anyway, it would be dark. We call such hypothetical stellar remnants black dwarf stars (hypothetical because it's estimated that it would take about one quadrillion years for this to happen, about 100,000 times longer than the age of the universe, so we will never be able to see one).",
"On even longer timescales than that, as ",
"/u/totitiganiisuntgunoi",
" also mentioned for neutron stars, electrons and protons might decay but we don't really know what to expect from that. ",
"It is unlikely that much material in these stellar remnants will ever be reabsorbed into new stars. They are held together very strongly by gravity, so with the exception of jets from neutron stars and the occasional nova or supernova of a white dwarf, pretty much all of their \"stuff\" will be held onto indefinitely until long after new stars have stopped forming."
] |
[
"Thank you for the answer.",
"Always!",
"Does the mass and gravity of these super-dense objects slow them down relative to other objects in the galaxy they are a part of?",
"Yes, time passes measurably more slowly on these stars compared to almost anywhere else in the galaxy. ",
"Would the galaxy they were born in ever leave them behind?",
"Regardless of time dilation around these stars, they are still gravitationally bound to the galaxy*. When we say that time is slower in one place than on another, it means something very specific. Imagine you're an immortal alien looking at our galaxy from outside, and you observe a neutron star. Over millions of years, you'll observe that neutron star interact with its stellar neighbors gravitationally, being pushed and pulled - and pushing and pulling them - and over the course of a couple hundred million years you'll see it make a full orbit around the galaxy. Time dilation at the neutron star itself doesn't affect any of that! ",
"If I'm interpreting your question right, it sounds like you're suggesting that because time is slowed near the stars, so their velocity will slow down and they'll be left behind as the rest of the galaxy wanders away in whatever direction its going. But the speed of the neutron star isn't affected by time dilation like that. ",
"For example, imagine I have two stars with equal mass: one a compact neutron star and one a normal star a few times heavier than the sun. Now imagine I apply an equal force on each star for the same amount of time ",
" (like our alien from before). Since the stars are the same mass, and the impulse on each star is the same, then acceleration and therefore final speed of the stars must also be the same!",
"I hope that helps; it's not very straightforward. The TL;DR is that time dilation merely affects how quickly time progresses for clocks/observers within the gravitational influence of the object, it does not affect how that object interacts with others."
] |
[
"How close do atoms in a given space have to be in order for sound to be able to travel across them?"
] |
[
false
] |
I've learned that there's no sound in space, because there are none (or very few) atoms, whereas sound moves just fine through our atmosphere. So where's the line drawn? How many atoms are needed for sound to travel and how close must they be?
|
[
"The is no distinct line. The average distance between atoms in a gas (ideal gas really, but it's the same at the low-pressure limit) is inversely proportional to the pressure. ",
"So what you're asking is the same thing as what the lowest pressure is, at which you can have sound. But sound is a propagating ",
" in the pressure",
". Clearly, the fluctuation in the pressure (i.e. the amplitude of the sound wave, or simply 'volume' of the sound) can't be larger than the absolute pressure, since the pressure cannot go below zero. The less matter you have to make waves in, the smaller the waves can be. ",
"So sound doesn't 'stop' at any point, a single atom bouncing off something could be counted as part of a sound wave, but it's certainly not a very ",
" sound. So it doesn't stop, it just gets quieter."
] |
[
"Well, no, not really. But atoms/molecules are moving about, the Cosmic background temperature is about 3 K. And there is a point at which the forces will be negligible compared to the average velocities. That is, they're moving much faster than the required 'escape velocity'. For a pair of non-charged, ordinary sized molecules (not macromolecules, that is), that'd occur pretty quickly, at a range of a few nanometers."
] |
[
"Is there a certain point at which the pressure is sow low, and thus the distance between particles large enough so that they don't interact witch each other any more?"
] |
[
"On a molecular level, is there a gradual transition between phases of matter, or is more like a lightswitch? For instance, are the molecules in melting ice switching from solid configuration directly to liquid configuration, or is more of a gradual transition process?"
] |
[
false
] |
I guess an analogy would be two different light switches. Where one is the on off type, and the other the dimmable type. The light can be on or off in both cases, but in the latter there is a gradual transition from on to off. I hope this makes sense. : Thanks for all the answers! posted by user in I think best illustrates my question. At one end there is a clear geometric structure (solid). At the other end there are "free flowing" molecules (liquid). But in between there seem to be molecules with 2 bonds, some with 1 bond, some with no bonds. What I am asking is, does there exist a state where a volume of water molecules can exist where there are only groups of three molecules bonded together, and swimming in a sea of other similarly bonded molecules? Like 1-1-1 with 1-1-1 with 1-1-1. Or a volume containing only a soup of two bonded molecules? Like 1-1 and 1-1 and 1-1. Or four? 1-1-1-1 and 1-1-1-1 and 1-1-1-1. Or some combination that does not form a complete solid, but is also not pieces of a solid floating in a liquid. A state where not all are bonded in such a way to form a solid and not separate enough to form a liquid. I use water as an example but wonder this for most substances.
|
[
"Somebody correct me if I'm wrong, but the molecules themselves don't have \"states\" so to speak. They just kinda do their thing. If, say, in ice, enough energy gets into a single molecule that it begin to drift, you wouldn't necessarily consider it liquid, only when they are all moving relative to each other. Basically what I'm trying to say is that it isn't a switch because each molecule behaves individually.",
"I'm not certain on this, nor did I do extensive research, this is just what I understand of it."
] |
[
"Well, sort of. If we take water for instance, when it freezes, it does crystallize forming a hexagonal geometry. It's not just a jumble of molecules.",
"So yeah, I get what you're saying about them not having \"states\" but solid and liquid water definitely have different arrangements of their molecules"
] |
[
"As always, it depends.",
"Phase transitions can be defined in term of some order parameter. It might be something obvious like temperature but can equally be something more obscure. Phase transitions with a discontinuity in energy vs order parameter are called first order transitions and are very much one-or-the-other and involve latent heat. Phase transitions with a no discontinuity in free energy vs. order parameter but with a discontinuity in its first derivative are second-order transitions and are continuous/gradual transitions. If you take a look at a classic pressure-temperature phase diagram, the transitions across lines of coexistence are first order."
] |
[
"Why don't LEDs \"run out\" of electron-hole pairs during recombination?"
] |
[
false
] |
We learned recently in class about how recombination in LEDs turns an electron-hole pair into light energy, but doesn't this deplete LEDs eventually?
|
[
"I think this comment is missing the point. Thermal excitation alone is not enough to power an LED. Otherwise, you would have a perpetual-motion / free-energy device on your hands (a magical LED that outputs light using nothing but ambient thermal energy!).",
" ",
" carriers are injected into the p and n regions from their respective contacts. This current is supplied by an external circuit. When an LED is forward-biased by such an external circuit, the concentration of conduction electrons in the n region and the concentration of holes in the p region are forced ",
" their thermal equilibrium levels. This causes excess recombination in the depletion region, which results in photon emission."
] |
[
"I think this comment is missing the point. Thermal excitation alone is not enough to power an LED. Otherwise, you would have a perpetual-motion / free-energy device on your hands (a magical LED that outputs light using nothing but ambient thermal energy!).",
" ",
" carriers are injected into the p and n regions from their respective contacts. This current is supplied by an external circuit. When an LED is forward-biased by such an external circuit, the concentration of conduction electrons in the n region and the concentration of holes in the p region are forced ",
" their thermal equilibrium levels. This causes excess recombination in the depletion region, which results in photon emission."
] |
[
"In a conducting LED holes are created in the p-type material and migrate towards the junction. The electrons freed in creating holes become the current flowing round the circuit which eventually flows into the n-type material where they recombine with holes.",
"Every extra free electron created results in an extra hole to be filled.",
"As long as you have voltage across the LED and a current flowing you won't run out of holes or electrons. ",
"If the current stops then the electrons fall into the holes near the junction until the junction is depleted. Then the LED goes out. "
] |
[
"What has more possible building combinations- 50 2x4 lego bricks or 100 2x2 lego bricks?"
] |
[
false
] | null |
[
"I don't think that's entirely true. Picture three 2x4 bricks connected in a straight line, two below and one on top. This is going to be an elevated piece, supported at each end. Try to do the same with your 2x2 blocks and it would be several separate pieces, you'd have to modify the design. I do think 100 2x2s is a bigger set, but you can't use them to reproduce the 2x4s potential set exactly."
] |
[
"If \"building combinations\" is defined so that only the overall shape matters (and assuming all the bricks have glue on their sides so they can join horizontally), then this analysis is pretty much correct, but if it depends on the individual bricks as well, then consider the following: a 4×4 square has only one decomposition into 2×2 bricks, but two decompositions into 2×4 bricks."
] |
[
"I'm not sure we should assume the blocks can be joined at their side, since the question specifies lego bricks, and they can only be joined top and bottom.",
"So, if we take that view, that we're only interested in structures that can be made by joining bricks together, then we know:\n- There are 3 different ways you can connect 2x2 blocks together. the low number of options is because the bricks are symmetrical, and only have 4 contact points\n- I count 14 different ways to attach 2 * 2x4 bricks together to create different resulting shapes",
"In this example, I propose that 50 2x4 bricks has more combinations because 14",
" > 3"
] |
[
"What is the fastest known object with mass?"
] |
[
false
] |
So as far as I know a massless object must move at the speed of light, but what is the fastest known object that has mass?
|
[
"If you mean relative to us, we have studies suggesting the existence of high energy cosmic rays, composed mostly of protons, that are slamming towards our atmosphere at approximately 99.9999999999999999999% of the speed of light.",
"It seems they are accelerated to such speeds with the help of a black hole. Some of the matter pulled is \"swallowed\", while the other is ejected at speeds very close to the light.",
"Edit: For people asking the source, ",
"http://www.space.com/694-blazing-speed-fastest-stuff-universe.html"
] |
[
"at approximately 99.9999999999999999999%",
"Are all those 9's ",
"significant",
" or are they hyperbole?",
": Added link to clarify my use of the word \"significant\" per \\u\\RepostThatShit's comment ",
"here"
] |
[
"They're significant. When you're dealing with (special) relativity 'gamma' is the all important quantity. The difference each 9 makes is definitely noticeable. Its like comparing the energies of the tevetron particle collider and the large hadron collider. Its just another decimal point closer to c."
] |
[
"Where does the swelling volume come from when you get injured?"
] |
[
false
] |
When you get injured, from where does all that extra volume originate? Is there a maximum volume increase that you can get from swelling?
|
[
"I think what you're talking about is inflammation around an injury, correct? If so, this is due to the inflammation response of your immune system. There are a lot of things going on when you are injured. First, you might notice that the area around the injury becomes reddened; this is due to increased blood flow to the area. Second, if you've cut your skin, there's a good chance that some bacteria has entered your body. This bacteria is recognized by the immune system and is marked for destruction. Third, a special type of cell, mast cell, is attracted to the site of injury. Mast cells contain intracellular granules, which will release two chemicals (histamine and heparin). ",
"Histamine is what we're interested in here: histamine increases the vascular permeability of the surrounding blood vessels. In a sense, the cells lining the blood vessels shrink and the vessel becomes leaky. This new permeability allows more white blood cells and blood plasma to enter the site. This influx of material causes the swelling you see around the injury.",
"I hope this clears things up!"
] |
[
"In simplest terms, the swelling is part of what causes the pain. In order for you to properly use that body part again, aka be able to go through full range of motion, the swelling would have to be reduced or gotten rid of completely."
] |
[
"Could you by any chance also explain the reason many efforts immediately after an injury focus on reducing swelling? I was under the impression that the swelling prevents further injury from movement. "
] |
[
"How did ancient people preserve their food?"
] |
[
false
] |
I buy fruit and vegetables from my local farmer's market, and often find them turning moldy within 3-4 days of my purchase. If I am storing them in the height of preservation technology (the refrigerator) how did ancient people preserve their crops through the winter? I really hope the answer isn't "They weren't picky about mold."
|
[
"There are lots of ways you can do it. Refrigeration is in the \"Make the food inhospitable for microbes\" department, and this is a reasonable and long-practiced habit. In fact, the Romans were among the cultures to use refrigeration pits long before the mechanical refrigerator came along. Pliny talks about Romans keeping ice for their drinks.",
"Far easier than refrigeration is drying or curing - picture jerky or salt cod. This is very easy, and cheaper than preserving fresh food with imported ice or stored snow.",
"Another widely-used method of preservation is fermentation. The famous Roman condiment ",
" is a fermented fish sauce. Incidentally, Worcestershire sauce is the modern version of garum.",
"If you wanted to save your fruits or veggies in the pre-industrial world, you could dry them, pickle them, or ferment them into drinks. If you're in the industrial but pre-refrigeration world, then canning is a good bet.",
"Sugar is also a preservative - it's why jams and jellies are called 'preserves'.",
"Sometimes people would bury their food - IIRC sauerkraut used to be buried.",
"To make the extremely long story of preservation short, people didn't sit around eating purely rotten food... usually."
] |
[
"how did ancient people preserve their crops through the winter?",
"In one sense, they didn't. Cheese, yogurt, yeast bread, and alcohols (esp wine, beer, mead, or cider) are all basically just controlled spoiling of foods, and the edible \"mold\" (actually bacteria) displaces harmful stuff, so it stays edible even though it is, by one definition, \"going bad.\" ",
"In addition to controlled fermentation, though: canning, pickling, smoking, salting, dehydrating, sun-drying, candying, and storing in oil are all old technologies for preserving food.",
"And, of course, when you get right down to it, \"they weren't picky about mold\" probably did play some part as well."
] |
[
"You insulate it with dirt, sawdust, and plant matter. In other words, you bury it. There are still ice pits behind old houses you can fall into if you're not careful.",
"Keep in mind that the Alps are in what's now northern Italy."
] |
[
"Can the kind of DNA lesion that causes melanomas also damage germ line cells (in a way that damaged DNA is passed forward) if similarly exposed to UV radiation?"
] |
[
false
] |
[deleted]
|
[
"Sure can! I want to point out though, there's not one kind of lesion that causes melanoma (you can induce melanoma the same way you induce any other cancer); it just so happens that skin is heavily exposed to UV light, so UV lesions are the most common.",
"If you exposed germ cells to UV, they would acquire the same DNA damage and if the damage wasn't repaired it would be passed on through the germ line."
] |
[
"Yes and no - There's a lot of speculation that this is the source of many cancers, where dividing cells (they're often referred to as cancer stem cells) undergo damage, which then spread the mutation to other cells. This is somewhat contentious because there are indications that sometimes you can cause mutations in an already divided cell that then gains stem cell like properties. It's pretty hard to differentiate between the two cases, really. And there's no guarantee that only one of those is valid, either.",
"In the case of UV damage, basically you're talking about creating errors in the DNA sequence that are difficult to interpret. There are enzymes that constantly search the DNA for these specific types of mistake (dimerized bases, mainly) and repair them. Because these mistakes are simply read incorrectly if they're not fixed, they lead to mistakes when the DNA is copied. For most non-dividing cells, that's really not an issue unless you happen to create a major monster, such as a cell that suddenly produces the wrong type of signal that influences other cells. The cell would simply be a little different than the others, but would carry out it's job happily.",
"However, if you are unlucky, and the cell starts doing something funny, or suddenly thinks it's job is now to replicate, instead of placidly sit on your surface protecting you, you start to get into trouble. Worse still, the more times a cell divides, the more errors you can start getting. And, if those errors start to occur in the machinery that repairs the errors, then you're really in trouble because the mutations start to get out of hand.",
"To come back to the question about germ line cells, yes, you could do exactly the same thing to them. If you were to expose the germ line cells to the same radiation, they'll react in the exact same way. Fortunately, we don't see that happening because most germ cells are not exposed to UV radiation. However, chemical exposures DO get to the germ line cells. Smoking, pesticides, etc etc. Many of those are able to get into the blood stream, and they do cause mutations in germ line cells.",
"However, it's worth pointing out that on average, we now know each child inherits about 300 snp mutations that their parents didn't start out with, so it's not like we don't expect to see \"de novo\" variations at all - you just don't want to start passing on chemically induced errors. At this stage, it starts to get into reproductive biology, which is gender specific, so I'll answer more questions, but otherwise end the answer here.",
"Edit: typos."
] |
[
"Ok, try to answer those one at a time:",
"In modern humans, does UV penetrate to the gonads?: not really. Check out this illustration: ",
"http://library.med.utah.edu/kw/derm/pages/meet_2.htm",
"Basically, the skin does a very good job of stopping UV light. By the time you get to the testes, just about all of the UV should have been absorbed. ",
"As for causing infertility, no, that's not a likely outcome. Infertility generally requires something that happens to all of the cells that are dividing to produce sperm, while UV radiation can only hit one cell at a time. Thus, you'd have to expose your gonads to a WHOLE LOT of UV to kill off all the progenitor cells. Infertility would probably require a chemical or surgical intervention, and UV isn't a reasonably effective way to do that.",
"Cell phones in pants pockets doesn't really have much science backing up any direct effect on cells, so I'm going to more or less dismiss that one. Kind of like letting your cells hang out near magnets - It doesn't seem to do much that we can demonstrate. The vast majority of cells don't have any of interaction with magnetic fields. There may be some, but I wouldn't expect reproductive cells to be one of them. (There's some evidence that dogs are sensitive to magnetic fields, but even that would require specific brain cells, not sperm cells.)",
"Anyhow, Yes, you can have tetratogenicity solely from lesions - but lesions is a wide field - and the issue is always more of where the lesions are, rather than how many. Put a lesion in the RB gene, and your odds of getting cancer soar dramatically. Put a thousand lesions into the genome randomly, and it's unlikely anything will happen. ",
"Each cell has over 3 billion bases in each of two copies of the genome it caries. One lesion is probably going to fall into the >98% of the genome that is structural, non coding, non-regulatory and otherwise non-essential. (Note, I didn't say non-functional). Only if you manage to hit somewhere in the remaining 2% that includes genes, regulatory regions or actively transcribed regions will you have a shot at causing a noticeable effect on the cell - and only a small fraction of those effects will be teratogenic.",
"Hope that's clear."
] |
[
"Why do squealing-scraping sounds like nails on a chalkboard and forks across a ceramic plate irritate us/our ears so much, even if they're not that loud?"
] |
[
false
] | null |
[
"This sounds like a Just-So story to be honest. What evidence is there that nails on a blackboard sounds like a human baby cry? Frequencies are not the only component of sound, and anyway a huge number of natural sounds fall into the human speech frequency range. Yet there are not the same response to these ambient sounds",
"Furthermore, is there any evidence that the response of people to nails-on-blackboard is similar to their response to a baby crying? ",
"Because the nails-response superficially seems to be qualitatively different - involving a sort of involuntary shudder and intense, acute discomfort, rather than being merely bothersome."
] |
[
"By all means, if you find fault with my explanation please feel free to offer an alternative. If you read my response, you'll see at no point do I compare nails on a blackboard to a human baby cry. That would be silly. Ignoring the issue of baby cry/nails on blackboard;",
"The human brain processes sounds of different frequencies differentially, and preferentially in favour of high pitched noises;\nStorace, Higgins & Read (2011) ",
".",
"Evolutionary psychologists suggest that preference evolved because it gave an individual greater chance of survival and successful reproduction - because they would more likely respond to the cries of a baby, or a shriek of fear, warning or pain - these noises being of a high pitch. ",
"If I can clarify this further for you, let me know."
] |
[
"Our ears are attuned to certain frequencies (more generally, the range of frequencies that human voices cover) meaning we 'hear' those sounds louder than others.\nEvolutionary psychologists suggest especially high pitched noises elicit a greater response because they sound like the noises we make under distress - for example a baby crying or a screech of pain. We have adapted a greater response to such noises because doing so means we have a greater chance of caring successfully for our young, and ensuring our own survival. "
] |
[
"What is the biological reasoning behind the frustration that you can feel in the middle of your chest?"
] |
[
false
] |
Why do we feel it only at the chest? Does some sort of acid build up?
|
[
"Stress releases epinephrine increasing heart rate and constricting blood vessels, norepinephrine activating the amygdala and increasing heart rate, and cortisol which will increases stomach acid and blood pressure. It is likely you feel it most in the chest because the heart and esophagus are under increased load and have nerves bundled together."
] |
[
"This is something I've always wondered as well. Strong feelings of things like frustration, shame, embarrassment and regret all seem to make something in my chest feel ignited. Negative emotions can sometimes feel physically painful when they are strong enough. I'd love to learn more about the science behind things like this. Any good books out there for the uneducated?"
] |
[
"Can we suppose this is the origin of the former belief that the heart was the seat of the emotions?"
] |
[
"Light Speed travel and Invisibility?"
] |
[
false
] |
Could an object traveling at faster than light (I know its impossible but for this question lets assume it isnt) conceivably be invisible to the naked eye? Since the eye requires light to register images would an object traveling faster than light not give off color and hence not be observable?
|
[
"Imagine a jet fighter. It travels faster than the speed of sound, but that does not make it inaudible. Regardless of the consequences of time travel and infinite energy requirements, an FTL object with mass would encounter normal matter in its path and collide with massive consequences, which would certainly be visible."
] |
[
"I know its impossible ",
"Then there is no need for asking, right? From the guidelines for askscience:",
"Avoid hypothetical questions that require speculation. ",
"Examples of violation: ",
"“What do we see when we go faster than light speed?” ",
"Asking for impossible things can never be answered scentifically accurate. Where do things fall at the edge of the flat earth disk? What's more northern than the north pole? Any answer to those questions is wrong, because they are based on wrong assumptions. A pseudo scientific answer would be just as (in)correct as telling you'd be seeing blue and red unicorns flying all over the place when traveling faster than light."
] |
[
"Cherenkov Radiation",
" is relevant here. It is the light equivalent of a sonic boom.",
"You cannot go faster than the speed of light in a vacuum, but it is possible to go faster than light in a dielectric (where light slows down because of interactions with the atoms and electrons).",
"While I cannot really speculate ",
" to go faster than light in a vacuum, if you did so in such a manner that you still interacted with normal space (as in, no weird star trek space bubble funny business) then presumably you would create Cherenkov Radiation."
] |
[
"Antibiotics kill a wide range of bacteria, which is needlessly destructive to the human microbiome. Is there an effective alternative that only kills specified bacteria?"
] |
[
false
] |
If not, is there any research being conducted to create such a therapy?
|
[
"Antibiotics do have some selectivity. As shown ",
"here",
", antibiotics have what we call a spectrum of activity (tetracyclines being the broadest one). Having a wide range isn't necessarily a bad thing, because bacteria are very diverse. While we can associate a pathology with a specific bacteria, it can have different strains. Some strains of bacteria will provoke bigger symptoms, because they produce an additional protein or such. So having something too specific mean you just reduce the number of cases in which it can be used.",
"That being said, there are alternatives. Well, at least one which I'm aware of. ",
"Phage therapy",
" consists in using a bacteriophage to destroy a specific bacteria. Bacteriophage are viruses that infect bacteria, and they can be very selective, invading only a specific strain of a certain bacteria. So some people have been thinking about developping this (since 1923 !).",
"There is also the advantage of evolution. As bacteria develop resistances, viruses adapt to counter them. One can easily see the dangers of developing super-viruses, though... "
] |
[
"It is not actually used in healthcare anywhere. As far as I remember, the discovery of antibiotics interfered with the research in phage therapy, because it was seen as useless at that time.\nNowadays, with the increasing problems with antibiotic resistance, it looks like an interesting alternative again, so there is more research activity in that field."
] |
[
"In the past there has been work with bacteriophages to eliminate unwanted bacteria called ",
"phage therapy",
". Bacteriophages are viruses which infect only a select number of bacteria and could consequently leave the human microbiome unharmed. There is current research into using phage therapy to eliminate salmonella infections if you were interested in learning more. ",
"Link"
] |
[
"What do we know about Long-Covid (i.e. people who haven't had any measurable damage but feel like something is wrong in their body)?"
] |
[
false
] | null |
[
"There is a lot of noise out there on what causes long covid and almost no medical consensus, however, there are a lot of theories, and the truth likely lies in one or more of them. ",
"Firstly it's important to note that long covid is not defined aetiologically but symptomatically and circumstantially. It is a diagnosis if individuals present persistent flu-like symptoms(and neurological symptoms) for several months after covid infection. This means that long covid may not necessarily have one origin, but potentially numerous origins. It is also important to note that long covid may not be new. It mirrors an existing condition called chronic fatigue syndrome(CFS)/ myalgic encephalitis(ME). CFS/ME is also a symptomatic diagnosis and tends to be one of exclusion(doctors rule out other possibilities/'measureable damage'). The existing evidence points to several potential aetiologies for long covid and these have a lot of overlap with CFS/ME research.",
"These are the one's I am aware of: ",
"his article",
"This study",
"This article",
"esearch pape",
"n oxford s",
"https://www.imperial.ac.uk/news/218933/new-national-study-long-term-impacts-lung/#:~:text=Many%20recovering%20COVID%2D19%20patients,immune%20system's%20reaction%20to%20it.)",
"metabolic trap",
"methylation disorders",
"Evidence points to the efficacy of CBT",
"Read this to see critique",
"There are literally hundreds of other hypotheses for long covid and even more if you consider it as necessarily part of ME/CFS. I hope I have highlighted the main ones which have achieved the most research recently."
] |
[
"This article ",
" discusses how Covid tends to lead to a significant increase in autoantibodies (antibodies that recognize human proteins). That could potentially lead to an autoimmune response over a long period of time that could lead to long Covid."
] |
[
"I'm a dysautonomia awareness advocate and participating in research on POTS (a form of dysautonomia). Viruses have long been known to trigger Dysautonomia, and it seems that COVID is triggering POTS at very high right. Pre-print studies show that 5-8 percent of people who have had COVİD still have POTS symptoms after 6 months -- we simply don't know if it will be a life-long condition. \nThis article is from July, which is a bit out of date, but it's a good representative and from Nature so the research is really excellent. \n",
"https://www.nature.com/articles/s41598-021-93546-5",
"More recent research has noted that though men are more likely to die of COVID, women are much more prone to be disabled by post-covid dysautonomia. We are not ready for the fact millions of women will not be able to work or care for their families ever again."
] |
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