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[
"What is up with Ron Hatch and his claims that GPS disproves the theory of relativity?"
] |
[
false
] |
I recently learned that some dude named Ron Hatch thinks GPS disproves relativity. I also learned that this Mr. Hatch is some sort of Big Shot as far as GPS is concerned. Can anyone with more experience with relativity give me a summary of what he's arguing for? And then tell me why he is (not assuming anything, but if I had to guess...) complitely wrong.
|
[
"I skimmed through the presentation you linked, it's basically a giant pile of trash and nonsense. To break down all of the errors in it would take someone versed in relativity several hours to walk through. Also I chucked at the end when he presents an alternative involving aether—Dude's a crackpot. ",
"Every physicist would sell their own mother if it gave them the chance to be the one to break relativity, but the ideas are beautiful, conceptually clean and most importantly verified by experiment six-ways to Sunday. ",
"I'd be happy to tackle any specific parts. The first thing that jumps out is his assertion that it must be the fundamental energy levels of the atoms which must be changing to account for gravitational redshift and not the frame change as light moves to a higher or lower potential and thus redshift or blueshift. There's a couple issues with this, ",
"The energy levels of an atom are absolutely dominated by electromagnetism, the modification due to gravity would be supremely tiny (and exactly zero if the atom was in freefall per the equivalence principle)",
"The ",
"Pound-Rebka experiment",
" famously measures gravitational redshift/blueshift using little more than the height of a building and some gamma sources in exact accordance to the prediction of GR.",
"Here's something to consider: He seems to bring up \"there is no energy increase as the signal falls\" while failing to realize that the time dilation he acknowledges is ",
" the blueshift he denies and both follow from the same contraction factor √(1-R/r) where R is the Schwarzschild radius of the Earth.",
"To demonstrate, consider your buddy on a GPS satellite with a clock and flashlight. Every second of his clock, he flashes the flashlight at you. From your point of view, you see the flashes appear at an interval slightly faster than one second: Congratulations, you've seen the essence of blueshift."
] |
[
"The accuracy of time in standard GPS receivers are high enough that they need to account for relativity. So in a way they are already measuring it every single seconds"
] |
[
"Thank you very much. I had barely any idea what he was talking about. I am very familiar with the effects of relativity (no idea of the maths, but a good idea on the basics and concepts), but still I was struggling to understand what his argument was. So basically he argues that relativity is false, but then comes up with problematic corrections to account for the relativistic effects that are missing from his theory? So no real way to do the measurement?"
] |
[
"How does Proteasomal degradation of TRAF6 happen in NF-kB signalling?"
] |
[
false
] |
I'm writing a literature review on NF-kB signalling in COPD, and in this pathway TRAF6 is targeted for proteasomal degradation although i can't seem to find how this happens, any ideas?
|
[
"I just saw this a few weeks ago on my RSS feed, SOCS2 and one of the MAP/TAK kinase",
" things. Complicated as hell but TL;DR....SOCS. ",
"I'll see if I can find it, I don't think I flagged it as something I wanted to keep, though. I usually get a headache around the third \"kinase\". ",
"Whaddya know....",
"there",
" it is. "
] |
[
"Sorry, but NF-kB is the classical example of Ubiquitin-independent post-translational modification."
] |
[
"No, I was just making a joke; sorry if that caused confusion. I only know of it going to three."
] |
[
"How can you \"perfectly\" sync two clocks? What is the smallest (acceptable) margin of error you can reasonably sync to?"
] |
[
false
] |
After the last week or so with the FTL neutrino discussion (which has admittedly been a ways beyond my grasp of physics) I have been thinking to myself: What is the closest you can sync two clocks to being? How do you go about doing this? How could you possibly test this? What kind of clocks can keep this kind of precision? Does gravitation / solar cycles / barometric pressure interfere with such precision clocks? This has interested me more than the discussion about the FTL neutrino to be honest, so any answers about this would be awesome. Thanks AskSci!
|
[
"Assuming that you synchronized two perfect clocks, and then carried one to another location, they wouldn't stay synchronized because of relativistic effects. Take it via car up a mountain and you have it in a different inertial frame, because the top of the mountain spins with the Earth faster than the bottom. The length of drift between the two may be so minor that it would take very fine measurements to detect.",
"The ",
"Hafele–Keating experiment",
" demonstrated this, using two airplanes and three clocks."
] |
[
"There's rather more to timing across ",
" networks than having accurate clocks at individual nodes; for more, see Leslie Lamport's "
] |
[
"You can't. One would assume that it would have to do with how distantly they were placed. Synchronizations using light rely on the two-way speed of light, as measuring the one-way has proved to be impossible, or in the least, contentious. David Malament and this awesome dude Reichenbach argued about it. ",
"Basically though it relies on not ",
" the one-way speed of light. I mean, it could be the same either way but it's impossible to tell. Then it gets into reference frames and far beyond my tired mind tonight.",
"Concepts of simultaneity is a fantastic book on the matter"
] |
[
"How does my immune system know not to kill my gut flora? Could diseases exploit this?"
] |
[
false
] |
I would imagine that an enormous repository of bacteria in the intestine would look a lot like a bacterial infection to an immune system. Also, given that my immune system kill my gut flora (by whatever mechanism that is), could harmful bacteria exploit this mechanism to prevent me from fighting off an infection?
|
[
"The gut, like our skin, mouth, nose etc is essentially outside the body. In the same way that bacteria on the surface of the skin does not elicit a full scale immune attack, the same is true of bacteria in the gut. That being said there is a specific immune system that operates at these surfaces, it doesnt work to remove any and all foreign cell as the immune system does within the body, instead it maintains tolerance to benign bacteria but still removes pathogenic bacteria. There is a brief description of mucosal immunity ",
"here",
". Of course, as with the immune system as a whole, proper immune function requires tolerance of our own cells or normal bacteria cells, while specifically attacking pathogenic cells, and pathogens of all sorts can evolve mechanisms to avoid the immune response. "
] |
[
"No, not really. Bacteria are opportunistic organisms. This means when the opportunity arises to attack us in any way. Usually by means of just getting more resources. They will do so. It just so happens that our bodies are good at keeping lots of random bacteria in our guts without letting them reach all the rest of our bodies.",
"There are a lot of bacteria that live inside of us that don't cause problems MOST of the time, but either through luck, someone being immunocompromised or some other factor involved, these mostly benign bacteria will \"attack\".",
"Our immune system will only fight off these attackers when they actually become a problem, or get somewhere they aren't supposed to be."
] |
[
"Also, colonization of the intestines happens as an infant, at the same time your immune system is developing. This includes producing regulatory T cells that are actually beneficial for the \"good\" bacteria. Your mother's secretory IgA in her breast milk is mainly responsible for assuring that bacterial colonization happens correctly. Once your immune system develops, your body produces secretory IgA to keep certain species from overpopulating. Specialized lymphoid tissues in the gut, Microfold Cells (M-cells), are really good at sampling antigen in the gut and responding whenever \"bad\" bacteria are present, and some pathogenic bacteria do actually take advantage of the M-cells and infect the tissue through that pathway."
] |
[
"In White Dwarfs, why does radius decrease as mass increases?"
] |
[
false
] |
I understand that it is electron pressure exerting a force to counter the force of gravity pushing in. What I don't understand is why this electron pressure does not increase directly with a mass increase. Why does gravity increase faster than the electron pressure?
|
[
"The pressure supporting a white dwarf is not the usual thermal pressure resulting from the random motions of electrons. In fact, white dwarfs are supported by electron degeneracy pressure, which is a quantum mechanical effect. Essentially, electrons must obey the Pauli exclusion principle -- the electrons don't like to be close together (even if they had no electrical charge, they would still tend to repulse each other). The magnitude of this pressure scales with density to some power between 4/3 and 5/3.",
"Being a little loose with the physics, you can think of it this way: if you want to have a larger mass white dwarf, you need more pressure. This means a higher density is needed, which means the white dwarf has to contract a little bit."
] |
[
"Thanks for the response! I still have one question though, if you double the mass, but keep the size the same, wouldn't that also double the density? So does that mean electron degeneracy pressure scales up by some factor less than 2 when density is doubled?"
] |
[
"Yes, that's correct."
] |
[
"Why do humans like music?"
] |
[
false
] |
[deleted]
|
[
"What in our brains makes us like music?",
"The short answer is, many distinct pleasure-related mechanisms are at play. ",
"Dopaminergic systems have been found to be related to music related expectations",
". Moreover, ",
"Oxytocin and its role to emotion and pleasure in music is being investigated by a team at ASU",
". Finally, ",
"David Huron posits that there may be a role for prolactin in why we find pleasure in sad music",
" (Sorry about the pop sci article; there is not yet an official study that has been published by Huron's team). ",
"Also consider brain facilities implicated in music: it requires auditory, spatiotemporal, motor, and visual systems. It is not a modularized activity. Contrast that with the thought that music is a ubiquitous phenomenon with considerable variability in its function, role, and importance for various cultures (for more on that see ",
"here",
" and ",
"here",
". ",
"It doesn't take too long before you realize that many peoples' notions for what are necessary and sufficient to be called 'music' are far too narrow. In fact, ",
"I'll argue that hearing (or audition) is not a necessary system to experience music",
".",
"What makes some songs better than others?",
"This is really dependent upon inter- and intra-related factors that deal with personal preference to cultural preferences. There is not one qualitative feature that is considered 'better.' I think what appeases the music cog/psych folks is the notion of what is 'preferred' depending on a context. Even then, the vast variability of what you're looking at here demands a monumental study with a sample size of billions. If you want a short answer: there is not one known feature or combination of features in a song that would make something 'better' than another feature. Until I see data for it, I'm going to stick with this answer.",
"Is there a model for the \"perfect\" song?",
"Simply, no. I think 'Why?\" is related to the answer I give above.",
"Why do humans like music?",
"I'll point to** NedDasty's** ",
"comment",
" which, points to my comment(s) from a previous thread involving the 'why' of music's ubiquitous experience in the human experience. A quick answer: we don't know just yet."
] |
[
" unscientific observation but I do find it a bit amusing that you keep referencing Jay Dowling's work. Please understand this is not a slight toward you or Jay as I admire his career and consider his work very important, especially in psychoacoustics/music perception and developmental music perception. I guess if you were to poll people for 'names in music cognition' they wouldn't be that high up. But I appreciate the citing of these researchers, the bottom two names are really names people ought to know.",
" to other readers I'll add other accessible literature that I am fond of: Ani Patel's ",
"Music, Language, and the Brain",
" and David Huron's ",
"Sweet Anticipation",
"**much needed clarity edits."
] |
[
"There is one music perception panelist hiding around these parts and they are the best resource.",
"However, I can at least point you in directions of specific authors/researchers and I am familiar with some of their work, but am not an expert on music cognition:",
"Dan Levitin",
"Barbara Tillman",
"Jay Dowling"
] |
[
"Newton's third law says that every action has an equal and opposition reaction. Do light sources experience a reaction force from emitting photons?"
] |
[
false
] | null |
[
"Yes."
] |
[
"Is that measurable? "
] |
[
"Yes",
"."
] |
[
"What is the normal radiation reading on Earth, what is it in space, and what is it on the Moon?"
] |
[
false
] |
And what sort of protection is needed to keep those radiation levels safe for humans?
|
[
"The radiation level on Earth is much lower than it is even in low earth orbit, because of the protection afforded by Earth's magnetic field and by the atmosphere.",
"Earth's magnetic field deflects solar wind particles away from the most populated areas to polar regions, where they create the very interesting and beautiful northern and southern auroral displays.",
"Sometimes, during times of high solar activity, airliners are kept out of the more efficient polar routes because of the high radiation levels there.",
"And the astronauts on the International Space Station must take precautions in the event of an increase in the solar flux -- a so-called \"solar storm\". The ISS orbit is high enough that the radiation levels can be much higher than on the surface.",
"And for the moon, the radiation levels are higher than low Earth orbit. The reason I am not giving specific figures is because the levels vary widely, depending on what part of the sun's 11-year cycle of periodic activity prevails, and specific solar events that sometimes create much higher radiation levels than usual."
] |
[
"This is all great information, but isn't quantitative. Anyone know the actual magnitudes?"
] |
[
"I avoided specific numbers because the values vary widely -- from tolerable for months at a stretch to lethal within 12 hours (in the event of a first-class solar storm while living on the moon)."
] |
[
"Could Iron eating bacteria survive on mars? If not what would be the limiting factor?"
] |
[
false
] | null |
[
"For an organism without a defined mouth or digestive system, it's convenient to say that they \"eat\" reducing compounds and \"breathe\" oxidizing compounds. That is, after all, what all life forms need in order to keep going. You perform reduction-oxidation reactions in your body between oxygen gas and sugar. Those iron bacteria you read about are eating iron(II) and ripping electrons out of it to form iron(III).",
"Iron oxide contains iron(III), which is pretty much as oxidized a state as you can get iron to form without whipping out the big guns. If an organism used iron oxide as a metabolic redox player, it would have to be an oxidizing agent (i.e., an electron acceptor to form Fe(II) or metallic iron). The problem here is that you would need a reducing agent to pair it up with. There aren't a whole lot of those on the surface of Mars; maybe some sulfides could be used as reducing agents as they are in oceanic thermal vents."
] |
[
"That's correct. Although, the final form of iron(III) doesn't necessarily have to be the oxide. That is how you usually find it, though."
] |
[
"That's correct. Although, the final form of iron(III) doesn't necessarily have to be the oxide. That is how you usually find it, though."
] |
[
"Brain in a vat"
] |
[
false
] |
Is anyone trying to do that? It doesn't seem impossible to me. We had more or less successfull attempts at isolating brains in the sixties, why doesn't anybody try for example the following: AFAIK we can also successfully simulate the input from both the retina and the cochlea, so it should be possible to supply an isolated brain with sensory information too. I think this would be fairly useful research in the long term as we would gain techniques that could be used for full-body prosthetics.
|
[
"Check out Solipsism. "
] |
[
"Yeah, that's what I was talking about. They work not because they are a perfect simulation of retinal circuitry, but because the brain is plastic enough to learn to use whatever signals they provide as an interpretable sensory source. Also, they don't simulate the input ",
" the retina/cochlea, they simulate the input ",
" the retina, which is a pretty significant difference."
] |
[
"I am getting confused wondering what you mean by your comment."
] |
[
"How does a relatively thin rotating shaft carry the weight of a helicopter when flying?"
] |
[
false
] | null |
[
"Your run-of-the-mill jack pole from Home Depot is typically rated somewhere around 20,000lbs.\nAnd that’s just hot rolled steel.",
"Ford awhile back ran an add using a 1/2” bolt to hang a truck from.",
"Steel is really really strong."
] |
[
"Steel is crazy strong. A single bolt, 1 inch in corss section, can easily support 30,000 lb. A large helicopter had a shaft cross section many times this. ",
"The weight of the helicopter is trivial compared to the tensile strength of the rotor shaft. The non-normal forces from vibrations are much more of a concern. AgAero gives an answer how these are adressed."
] |
[
"The mass of the blade itself plus the rotation speed give it a 'rotational stiffness' that keeps the coning angle relatively small. The weight is then supported by the flap hinge in the rotor hub assembly. ",
" I answered the wrong question. There's nothing remarkable about supporting the airframe by the rotor shaft. I was describing the strength of the blades."
] |
[
"Does your body burn more calories maintaining a stable temperature at 32F (0C) or 100F (38C)?"
] |
[
false
] | null |
[
"Considering that the human core temperature is 98.6 F, the body would have to work much harder, and burn more calories at 32 F than at 100 F, to maintain homeostasis. "
] |
[
"Furthermore, burning calories works against the goal of cooling the body down. While you would sweat, the body would attempt to avoid burning unneeded calories as they would tend to raise body temperature."
] |
[
"At 0C. It is well know that metabolic rate goes up at cold temperatures and that in places where cold last a long time like Antarctica, people develop some adaptation like increased thyroid activity with results in a higher basal metabolism. 38C is hot, but still inside the limits we can cope with, and regular mechanisms like sweating should be enough to control temperature."
] |
[
"Is EM radiation constantly being emitted by the AC wires in the walls of our homes?"
] |
[
false
] |
And if this is the case, does this mean even when we aren't using any power in our houses, our wires are constantly "bleeding" a certain amount energy on their own? I'm guessing it would be negligible anyway, but is there anyway to calculate how much power loss this is on average? And what would the wavelength of this EM radiation be? Also, is the EM radiation stronger near outlets as compared to the rest of the wiring?
|
[
"Yes. It has a frequency of 60 Hz (in North America) meaning it has a wavelength of about 5000 km. The total power is a tiny fraction of a watt.",
"They tried to capture some of the power on Mythbusters but found it to be unfeasible."
] |
[
"To calculate the amount of radiation you'd have to first calculate the gain of the antenna, i.e. the wiring. That depends on its geometry, so it's impossible to know for sure, but rest assured that to be a good radiator an antenna has to be at least a quarter wavelength, and with the wavelength of 60 Hz being thousands of miles, it's safe to say that the wires in your home make an incredibly poor antenna."
] |
[
"If the circuit isn't closed, there's no current running. So the answer is that no, there's essentially no radiation when there's nothing plugged in. There's probably a very tiny effect due to capacitance, as charge builds up on one side of the wire and then the other. When power is being drawn, though, radiation absolutely is emitted, at a frequency of 50 or 60 Hz, depending on where you live. As you suggest, though, it's a really tiny amount. ",
"Near outlets doesn't matter - it's the acceleration of the electrons over the entire length of the circuit that radiates."
] |
[
"I'm sort of confused about the sun and earth's position that causes seasons and day and night."
] |
[
false
] |
When we were in elementary school we learned that day and night and the seasons are caused by the sun moving around the earth and the earth spinning. But which is which, and can you explain it in layman's terms? I know it's a dumb question and that I should know it by now, especially since I aspire to becoming an astronomer, but I just get it mixed up, all the time. I really want to know it like I know the back of my hand. Also, can you elaborate on the phases of the moon? Like, waning gibbous, waxing crescent, and all those? They confuse me.
|
[
"helpful animation",
" of the earth around the sun",
"And, maybe ",
"this",
" will help about the moon",
"That last one is probably fairly misleading, but it shows part of the concept I think"
] |
[
"The moon is ",
"tidally locked",
" to the Earth. The name \"dark side\" is something of a misnomer, it should really be called the \"far side\" or something like that. We only ever see one side of the moon, and this side can be fully lit (full moon), completely dark (new moon), or anything in between. "
] |
[
"The moon spins. It also revolves around the earth. If these two rates happen to match, which is called tidal locking, then it spins exactly at the right speed for you to NOT see it, as you have guessed.",
"I understand this is hard to visualize, so I came up with an example you can try at home with a friend:",
"Take an orange or other round fruit and draw numbers on the equator in a circle, say 1 through 9. Stick a toothpick inside the number 1.",
"Now you are going to do 3 different experiments:",
"Experiment #1: Have your friend stand at arms length from you, stand still, and simply spin the fruit. You should see the toothpick turn and you should be able to read all the numbers as it turns in your friend's hand.",
"Experiment #2: Pick a wall in the room and have your friend point the toothpick in the fruit at it. Have your friend move around your body in a circle (you may turn however you like), but ",
". This means that the toothpick should always remain pointing at the wall. If you notice carefully, you can again see all the numbers on the fruit.",
"Experiment #3: Have your friend move around your body in a circle, as well as spin the fruit so that the toothpick is always pointing at you. You may turn as much as you like in the meantime. Now there will be numbers on the fruit you will never see. The fruit is tidally locked with you. The numbers you can't see are the \"dark side of the fruit\"."
] |
[
"Hello Reddit, If I placed an apple in a vacuum in outer space completely sealed off from anything. Would it rot?"
] |
[
false
] |
Title says it all. The apple is sealed in a vacuum of a glass box so the apple can't interact with anything outside the box. What would happen to the apple?
|
[
"This is not entirely correct, bacteria are not the sole sources of spoiling. Each fruit contains ripening agents which change the chemical composition of the fruit with time. Some fruits, including apples, will continue to produce ripening agents such as ethylene after they have been picked.",
"I suppose it depends how spoiled the apple has to be for OP to consider it rotten. I think it would end up extremely squishy and acidic, but perhaps not the gaping-black-spot of bacterial growth."
] |
[
"Inedible FTFY"
] |
[
"Some of the bacteria on it will be just fine in a vacuum. Botulism and lactobacillus will grow as long as the temp and ph stay friendly. So it will rot."
] |
[
"How come inflation (of the universe) is accepted among scientists?"
] |
[
false
] |
So as far as I understand, inflation is a very, very, VERY fast expansion of the universe in a very short period of time after the big bang. It solves the problem of the smooth distribution of matter and energy in visible space. But isn't inflation just constructed around the problem, that we can't explain this phenomenon ? I also read that the background radiation can be "predicted" with the inflation model, but how can a model predict a seemingly random distribution so accurately ? I also have never heard of any explanation why inflation should happen. Is it based on quantum laws ?
|
[
"The important features of the Cosmic Microwave Background are not random, though. The CMB is remarkably relatively uniform, without strong large-scale features in it. That plus the seemingly uniform distribution of matter necessitate explanation.",
"You're right that inflation is constructed around the phenomenon. It's the easiest way we know of for explaining the phenomena, but maybe it's not right. Many theorists, both string and not string, are working on models where inflation is explained by some processes in quantum field theory and general relativity, and they are trying to generate predictions from these models. (If you search the arXiv database for ",
"\"inflaton\"",
", you'll see many of their papers, but I don't do research in this area and don't know much more.) Astrophysicists are also working on collecting more data on the CMB from the Planck telescope."
] |
[
"Some of our models of the inflation are based on some quantum fields, but the theory is relatively complicated and somewhat blurry on details (hypothetical \"inflatron fields\" and stuff like that)... just to touch the question about quantum model of inflation.",
"When we say, that \"the theory predicts CMB fluctuations accurately\", we don't mean, that we can reproduce the eact shape of the CMB fluctuations. It is just the statistical distribution of various quantities that you can calculate from it.",
"And yes, the inflation model is just workaround, in a way. The basic problem is, that if we look in two opposite directions as far as we can see, the universe, or more precisely temperature of the CMB (and hence of the universe) seams to be the same. Nobody could think about any other reason for this to be true, than that those parts of the universe must have been in contact with each other and the temperature differences distributed uniformly. But if it took the light entire age of our universe to travel from that two points (that are on opposite sides of the sky) to travel to us, then you cannot see from one of the points to the other. Light just didn't have time to go that far. And if not even the light didn't have time to go that far, then how could the temperature be distributed uniformly? The easy answer is, that they used to be very close in the beginning, and then the inflation happened.",
"But that's not the only reason for us to believe it. The universe is not only homogeneous and isotropic, but also flat (within precision of our measurements). There is also absolutely no reason for it to be ",
" flat. But locally (i.e., when you take small enough piece), even the most curved (hyper)surfaces are flat. And if entire observable universe used to be just very, very small piece of something bigger, that uniformly inflated, then it really should be flat.",
"So ",
" the inflation model is true, it is, in fact problem, why we even have ",
" inhomogeneities in our universe. And the answer is, that the primorodial inhomogeneities were the quantum fluctuations of vacuum, which were expanded (literally) to astronomical sizes, and today we can see them as large scale structure of the universe.",
"So you can see, that the inflation thery is very nice, and it explains lot of things. But it is still just a theory, that is quite difficult to test and the whole reason why everybody believes it is, that nobody could come up with anything better (there is just no need for better theory right now, with our level of knowledge)."
] |
[
"so basically galaxy clusters are blown up quantum fluctuations ? Does that even make mathematical sense ? Also, does that not directly contradict the fact that quantum fluctuations are always in a balance (e.g. the old antimatter-matter problem)"
] |
[
"Isn't Astatine the Rarest Naturally Forming Element on Earth?"
] |
[
false
] |
Pretty much what the description says, i've heard that Astatine is the rarest naturally forming mineral. Is that true? And if not then what is? And also, does that mean that Astatine is the rarest mineral in rock form like gold or diamond can be?
|
[
"Yes, that or Francium. Both are extremely short lived decay products of other isotopes. An atom decays into astatine, then the astatine quickly decays into something else. That's why there isn't much of it at any given time."
] |
[
"Well then does that mean that Astatine cannot be in a solid rock form? Like emerald, diamond, etc? It would just decay?"
] |
[
"Yeah it doesn't last long enough for that to happen."
] |
[
"If a person on the ISS stood on the outside and jumped off the surface away from the earth, would they keep floating off into space or would they be brought back to earth eventually by its gravitational field?"
] |
[
false
] |
I was curious because the moon, as far away as it is, is held in by the earth's gravity but because we are so much smaller I wasn't sure if it would be enough to pull us back. But I also thought that since the moon is so much further away than the ISS I wasn't sure if the sheer distance the body would have to travel would be enough for the minimal gravity to stop the body.
|
[
"With any reasonable jump you might/could take, you would still be orbiting earth close to the ISS (\nthe ISS is moving at +/- 7.600 m/s and the average human jump speed +/- 1.5 m/s). ",
"Assuming the ISS orbit is circular, your orbit would become a bit skewered/eliptoid after the jump. The apoapsis (the highest point in your orbit) would be a bit higher then the ISS orbit but the periapsis (lowest point in your orbit) would be about the same height or possible even a bit lower then the ISS. Your orbit would be ossilating between these 2 points with each orbit. However, since the ISS is in LEO (lower earth orbit), it is still moving through a very thin athmosphere. The ISS slows down because of this and occassionally needs to boost itself (by making itself move faster forwards, not upwards). If you would be regularly dipping below the ISS orbit level, you might actually increase you slowdown per orbit and thus causing yourself to fall down faster to earth.",
"So, if you want the most jumping-bang-for-your-buck, jump towards the direction the ISS is moving, parallel to the earth surface. "
] |
[
"This is a great answer. Just one minor correction: the speed of the ISS is ~ 7.6 km/s, not 7.6 m/s. Upshot being: your jump speed would be a ",
" fraction of your transverse speed due to being on top of the ISS. Therefore, the eccentricity of your orbit after the jump is still very, very close to zero."
] |
[
"You used both 7.600 and 1.5 though, you may want to change one to a comma for clarity"
] |
[
"I get it was big... but what banged?"
] |
[
false
] | null |
[
"I'd recommend reading this ",
"post",
" by robotrollcall. "
] |
[
"I can't write about it, but here's an old answer from the archives",
"http://www.reddit.com/r/askscience/comments/hsx2d/is_there_a_credible_explanation_for_how_the/c1y3gpq"
] |
[
"Thanks...",
"but I guess my question was... what was it that banged... I understand it was a singularity... but there has to be a action to induce a reaction... ",
"It's probably beyond comprehension... but I can't get around the idea that the big bang is not a zero-sum game... there's more."
] |
[
"If you could somehow inject light into a jar with a 100% reflective interior, would it ever get full?"
] |
[
false
] |
This is something I've wondered about for years. Imagine a jar where the interior is perfectly sealed and is 100% reflective. It does not absorb energy. Please ignore whether or not such a material would be possible, the question is more about the nature of light than the nature of reflective materials. Now imagine there is some way of getting light into this jar without opening it or screwing up its 100% reflective and sealed nature (again, forget about whether this would be possible). What would happen if you continued to pump light into it? Would it ever get "full"? What would happen if you put the jar on a shelf for 20 years and then opened it up in a dark room?
|
[
"Although this scenario isn't realistic I understand what you're getting at.",
"Light is a boson, meaning it doesn't block itself from being at a specific location. So, you could pump more and more light in without the photons interfering with each other.",
"However, if the energy density gets high enough, it could form a black hole. This is known as a kugelblitz."
] |
[
"Yeah but we're using a magical container."
] |
[
"Some pulsed lasers operate on a pretty similar principle. The laser cavity is typically 2 mirrors that bounce light back and forth through a gain medium. In a typical laser, one mirror is partially transmissive, and let's some of the light out one side.",
"If you want a laser with really strong, short pulses of light, you can do something called ",
" cavity dumping. With cavity dumping, one mirror is able to be switched from highly reflective to highly transmissive. You start out with both mirrors reflecting strongly and build up a whole bunch of light in the cavity. Then you switch the mirror and all that built up light dumps out in a short, intense pulse. ",
"Edit: Thanks to mdavenport for correcting my mistake"
] |
[
"If the Big Bang\\Big Crunch theory are correct, did time exist before the Big Bang and will it exist after the Big Crunch?"
] |
[
false
] | null |
[
"We don't know if that's even a reasonable question, for very specific reasons.",
"Let me set the current stage for you. Right now, we can observe lots of very distant objects and light from a long, long time ago (the cosmic microwave background, in particular). From these observations and a few assumptions about the universe, we can fit a model which tells us about how distances in the universe have changed over time. This model works extremely well. If we take this model at its face value and follow it back in time, it says that there was a time at which the universe occupied zero size.",
"The problem is this: as we trace the history of the universe backwards in time, before we get to that point of zero size, the universe must necessarily be hot enough and dense enough that both quantum mechanics and gravity become important. However, we don't know how to do quantum mechanics and gravity at the same time; there are people working on this, but there's no experimental evidence for a particular proposal yet. So what this means is that ",
". Maybe quantum gravity will allow us to answer your question, or maybe \"before the Big Bang\" will simply have no meaning. We'll see.",
"However, we can trust it to a time very, very close to that point. How close? If we take the model at face value, it's valid about 10",
" seconds after the Big Bang, and if we figure out inflation we'll probably be able to get it to the Planck time of about 10",
" seconds after the Big Bang. That's about 10 quadrillionths of a quadrillionth of a quadrillionth of a second!",
"I should also mention that current data suggests that there will not be a Big Crunch; instead, it seems that the universe will continue to expand forever. This is not yet certain though; we know the relevant number up to around a percent accuracy, but one percent change would move us from an always-expanding universe to a Big Crunch. However, if there is a Big Crunch the same problem will happen, in that the universe will get too dense and we'll need to understand quantum gravity to tell you what happens after a point."
] |
[
"I disagree",
"."
] |
[
"Mmmm...saying we don't know isn't really satisfactory.",
"But it is honest. It is placing the truth before comfort, which is why it is science and not religion."
] |
[
"Which (useful) information do we still get from the voyager probes?"
] |
[
false
] |
Because what could be "useful" for us in this empty space behind Pluto?
|
[
"Voyager 1 and Voyager 2 are currently studying the heliosheath (see ",
"Heliosphere",
"). Measuring the ",
"solar wind",
", plasma density and the density of energetic particles. This gives us information on how the heliosphere is built up, how big it is, where the termination shock is and what the interstellar medium surrounding us is made of."
] |
[
"They are using instruments specifically added for this purpose. The primary mission was to study Jupiter and Saturn (plus Uranus and Neptune for Voyager 2). Doing additional analysis of the heliosphere and the interstellar space is a secondary goal for which they added all the additional instruments - just in case Voyager 1/2 will make it all the way out there.",
"As far as i remember they are communicating with both probes on a daily basis via the Deep Space Network. The probes are still functional because they gain their energy from decaying radioactive material. These generators should last them until about 2025."
] |
[
"That is just too cool. Missions that long term give me hope for the future. I'm sure the space race being fresh in people's minds at the time helped, but still. "
] |
[
"Can generalized anxiety spread throughout a group of individuals?"
] |
[
false
] |
What brought up the question/ the parameters. My friends and I were all together tonight (4 of us). We were doing what we usually do, sitting around playing poker and listening to music, when everyone myself included got the urge to leave, so we go on a walk. I can tell one of my friends is getting distressed, so I suggest we get something to eat. While there I got the very eerie and intense feeling that someone was watching me. My one friend just seems outright depressed at this point. At the end if the night one if the other friends tells me that something just did not feel right at all that night, unrelated to my or the other friend's situation, as we didn't mention it to him. So, I was wondering if it was merely a coincidence, it if there is some psychological reason this may have happened. I would be intrigued to know. Thanks in advance
|
[
"Sure, and not just anxiety. Lots of emotional processing is heavily influenced by the affect of people around you, and if they have a negative affect or are predisposed to it then it's hardly surprising. It's also worth noting that a lot of affective/emotional processing happens below the level of conscious awareness, so it's quite possible for people to be \"feeding off each other's energy\" without being aware of it. This is super-simplified, and someone may well come along and flesh it out if they want, but short answer's yes."
] |
[
"Expanding a little more scientifically on this answer. There's many kinds of phenomena that can cause anxiety and similar feelings that are almost undetectable consciously. One example could be infra-sound.",
"These (and pretty much all) feelings between people are transmitted through mirror neurons. When you're watching someone shoot a basketball, or run from fear, mirror neurons fire in your brain that correspond to you doing that action, essentially simulating what you are observing (shooting a basketball, running and feeling fear). But mirror neurons can't tell that what they're simulating is coming externally, in other words, if you pick up on facial expressions and body language of your friend feeling anxious, mirror neurons will fire also subconsciously making you anxious. It's why we feel bad when we see someone frown or cry for example. This is essentially the mechanism of empathy - how and why we transmit emotions and feelings. "
] |
[
"They often are. Most personality disorders have mutually causal roots or at least influences in brain chemistry, structure (which is always changing even as an adult), and/or non-brain physiology. Almost by definition, if someone has cognitive struggles, there is something else going on too, and the perspective of cognitive issues being only based in cognition is a narrow view to a highly parallel issue due to how interrelated the mind and body are.",
"In fact, there are new treatment methods for TBI, PTSD, depression and other disorders, for example, that involve neurosteroid testing to determine what, chemically, is off baseline, and by how much. It also is testing for a broad range of these chemicals, so it's not just an approach of changing the levels of one neurotransmitter at a time. Those hormones are then supplemented with their natural precursors, or by more direct supplementation if necessary, to a high degree of effectiveness that's not seen with the older psychiatric paradigm of SSRIs plus psychotherapy. The cognitive approach still helps as well, but circling back to interrelation, the treatment is going to be most effective when it's addressed systemically. That means lifestyle improvements, on top of psychotherapy and targeted hormonal therapy.",
"Source: years of researching treatment resistant depression and anxiety for personal application. This particular method isn't something I've experienced or witnessed, all of this is just a paraphrasing of a 3 hour talk I've listened to by the doctor doing the treatment. The sensible mechanisms of diagnostic and treatment make it pretty convincing, as it expands more empirically on the current approach of guessing which neurotransmitters are deficient one at a time based upon reported symptoms.",
"The MD currently doing this is Dr. Mark Gordon. It's with focus to treating TBI, but in the talk he was mentioning how it works well on a range of mental disorders."
] |
[
"Does hot or cold water boil faster?"
] |
[
false
] |
Not sure what the right type of science is for this question but yeah title explains it. I heard that frozen things are best thawed with cold/room temp water because of blah blah blah science stuff. So does it work the same way with water?
|
[
"Cold water is a better idea for thawing because any heat is a bacteria problem—not because it thaws faster. It takes energy to heat water so starting with warm / hot will always be faster to boil or thaw things—anything else is a myth. Some people only cook by starting with cold water for other reasons such as cooking time standards based on how long boiling takes from cold water."
] |
[
"I use cold to boil because it's cleaner versus my occasionally cloudy hot water tank water."
] |
[
"Simple answer: no, cold water does not boil faster.",
"I haven't tested it, but from what I remember from my heat transfer course, rate of heat transfer between two objects is proportional to the difference between their temperatures. So, there's a chance that the temperature of cold water rises faster upto a certain level.\nFor example: if cold water is at 5°C and hot water is at 50°C, the temperature of the cold water may rise faster from 5 to 15 than that of the hot water from 50 to 60, as the heating flame is at the same temperature.\nBut, when the cold water reaches 50°C, it's temperature will rise at the same rate as that of the hot water.",
"Does that make sense? I'll explain more if you wish."
] |
[
"Since photons aren't elastic, the only way light can be reflected by a mirror is by being absorbed and re-emitted, if so, won't there be an extremely small delay for the electron shell to jump back down to it's unexcited state and re-emit the photon? Has anyone ever even measured this delay?"
] |
[
false
] | null |
[
"What do you mean by \"photons aren't elastic\"?"
] |
[
"Sorry, by that what I was trying to get across is that a photon can never change direction by \"bouncing\" off something, the are a straight vector. The only way they can change the direction they are traveling is if they are absorbed and re-emitted by some form of matter (and gravitational lensing too I guess)."
] |
[
"a photon can never change direction by \"bouncing\" off something",
"This is not true. Photons can scatter just like any other particle."
] |
[
"When a galaxy is born, what dictates it's rotation's direction?"
] |
[
false
] | null |
[
"Conservation of angular momentum. Nothing in the universe is stationary... everything has some form of movement. When the initial gas cloud collapses under gravity into a protogalactic disc, any rotation it had, no matter how miniscule, will be increased in speed. The common analogy is that of a ballet dancer pulling in their arms to increase their rotation speed."
] |
[
"A bit late, but found an interesting article somewhat related; ",
"https://phys.org/news/2020-06-patterns-spiral-galaxies-universe.amp"
] |
[
"True, but to actually answer the question, it will rotate in the direction it was rotating in before it was \"born\"."
] |
[
"How can I detect & measure infrasound at work/home?"
] |
[
false
] |
I suspect a fan in a particular room is resulting in infrasound (<20Hz) via sympathetic vibration, and perhaps unknowingly affecting people in the room. How can I investigate, assuming I have a decent mic (40Hz-20kHz) and a basic/free DAW (e.g. Audacity)?
|
[
"infrasound (<20Hz) ... decent mic (40Hz-20kHz)",
"... ?",
"I suspect you'd have to build your own mic if the one you have doesn't pick up the frequencies you want. I remember using headphones as mics, simply by plugging them in the other jack. Might work with bigger low freq. speakers as well, hoping that they can pick up those frequencies. The sensitivity will probably be bad, though, and I'm not sure whether the sound card even manages < 20 Hz.",
"What you'll also want is a software that can transform the incoming waveform into a frequency profile. Not sure whether Audacity does that, especially not \"on the fly\". (Google finds me for example ",
"this",
" and ",
"these",
".)",
"But if I may ask - what's your rationale for the hypothesis that it affects people?"
] |
[
"Here's the suggested link to ghost sightings: ",
"http://en.wikipedia.org/wiki/Infrasound#Suggested_relationship_to_ghost_sightings",
"On the microphone: A TLM mic is used for low frequency recordings, but its bottom end is around 20Hz. Also, most audio input for computers and other recording equipment is capacitively coupled to remove very low frequencies (usually below 20Hz, sometimes higher). ",
"In short, you're going to have to find dedicated infrasound equipment, or build your own. In theory, you could use a speaker (I'm thinking something like an 8-10\" cone speaker) as a microphone, amplify its output, and filter for frequencies below 30Hz or so. You're going to have to build it all end to end. Something like an Arduino might be able to handle it, along with a few op-amps to handle amplification and filtering. "
] |
[
"Your problem will come from the sound card in your computer. It is AC-coupled meaning that the input signals must pass through a series capacitor, effectively filtering out low frequencies (<20Hz).",
"I would build a mic like Antares42 suggests as well as your own amplifier circuit with a very large (very low freq) input capacitor. Then, record the amplified signal on a DC-coupled oscilloscope. (use this as an excuse to buy a USB oscilloscope) "
] |
[
"Why in a world so colorful have so many animals evolved to be colorblind?"
] |
[
false
] |
Obviously, color has been around since the beginning of time. It seems very strange to me that so many animals, especially hunters, have evolved to be colorblind. Wouldn't this be a significant disadvantage when trying to survive? Thanks Reddit!!
|
[
"I think you have this backwards. They did not evolve to be colorblind because evolution doesn't work that way. It's more like they didn't evolve to have color vision like most people have. If color vision did not provide an advantage for survival then those that did not have it would not be at a disadvantage and would not die off leaving only those with color vision."
] |
[
"Some clarification is needed here. Do you mean colorblind in the colloquial sense which typically refers to dichromats, or do you mean truly colorblind (monochromats)? ",
"If you mean the former, the wiki on dichromacy says that most mammals are dichromats. Main exceptions are old world primates and the females of some new world primates. And maybe some marsupials.",
"Birds can have four or five different kinds of photoreceptors and can be sensitive to light in the UV spectrum. Reptiles and amphibians ditto. ",
"If you meant monochromats, wiki says that pinnipeds (seals, walrus etc.) are monochromats and I believe that whales are too.",
"Fish and insects have weird eyes and it varies a lot. Bees are trichromatic I think.",
"TL; DR. I don't think it's hunter-prey specific; depends more on the environment. "
] |
[
"Well you cannot see IR but you can certainly perceive it as heat."
] |
[
"Help with non-Newtonian fluids?"
] |
[
false
] |
I understand the basic concept of why a suspension like corn starch and water absorbs and disperses the pressure of impact, but is there a physics equation to express this?
|
[
"I suggest that you start reading about ",
"rheology",
"; see 'Deborah number' and 'Reynolds number'. In theory, the Navier-Stokes equations describe fluid flow for any system, but the solutions to the NS equations have not necessarily been found yet."
] |
[
"Navier-Stokes equations are directly derived from Newton's second law: F = ma. As such, I don't believe non-newtonian flows are governed by Navier-Stokes. But as you say, perhaps there is some way to modify the stress tensor to represent non-newtonian forces, but no one has found that solution yet."
] |
[
"Yeah, you're correct. The stress tensor in Navier-Stokes / Cauchy needs to be suitably modified for non-Newtonian fluids, but that's a very complex problem which I don't believe has been solved yet."
] |
[
"Was it common for healthcare professionals, undertakers, etc to catch influenza from handling bodies in the 1918 Flu epidemic?"
] |
[
false
] | null |
[
"Yeah, those temporary morgues that some cities brought in because of Covid wouldn’t have been an option in 1918, obviously. And with the much higher death rates, pre-refrigeration, it must have been a horrid mess to deal with all those bodies."
] |
[
"Yeah, those temporary morgues that some cities brought in because of Covid wouldn’t have been an option in 1918, obviously. And with the much higher death rates, pre-refrigeration, it must have been a horrid mess to deal with all those bodies."
] |
[
"Nurses definitely got it. One of the things that slowed down the response to the pandemic in 1918 was the fact that the people who were working hardest on treatment and trying to develop vaccines kept getting sick",
"As for handling the dead, probably not, as a respiratory virus it's just not that dangerous when the patient isn't breathing."
] |
[
"At what point does classical/Newtonian mechanics 'break down'?"
] |
[
false
] |
I'm aware that classical mechanics is an approximation and therefore not exactly correct. However, I'd like to know the speed at which relativistic effects start becoming noticeable. 50% of .c? 75% of .c? Thanks in advance
|
[
"It depends how accurately you can measure things. A good measure of the relativistic effects is the ",
"Lorentz factor",
".",
"If you can measure differences of 10%, then relativistic effects become noticeable at about 50% of c. ",
"If you can measure differences of one part in 1000 (0.1%), then relativistic effects become noticeable at about 5% of c."
] |
[
"In addition to relativistic effects, you also observe non-Newtonian mechanics when the de Broglie wavelength of a quantum is of a significant size, and there is enough coherence to witness non-classicality. It's hard to be comprehensive about this (since the quantum/classical divide is actually a rather contentious issue) but generally expect low-temperature physics to be rather non-Newtonian. High temperature physics is usually only non-Newtonian if it involves relativistic speeds."
] |
[
"Thanks! So what I think you're saying is that relativistic effects are always present, but only become noticeable if you measure to a greater number of significant figures. Is that right? How about if there is no motion in relation to the frame of the photon (in other words, if the moving object is completely still) - do you still get relativistic effects? Or perhaps the concept of 'no motion in relation to the frame of the photon' is flawed?"
] |
[
"How do night vision goggles work?"
] |
[
false
] | null |
[
"They take in ambient light and amplify it typically into monochromatic (usually green) image that is updated live. Essentially its a camera that goes through a brightness filter and amplifies the existing light. So if you have ever had a very dark image that appears black but you crank up the brightness to show whats really there? Its basically that. "
] |
[
"You can find the answer with a simple google search / on wiki."
] |
[
"Watch this ",
"video",
" and this ",
"video",
". They both explain it well."
] |
[
"How are seedless fruit plants' seeds obtained?"
] |
[
false
] |
[deleted]
|
[
"Many seedless varieties are triploids (3n*). These are created by crossing a standard diploid (2n) plant with a 4n plant, which produces 3n seeds that can be planted normally. When the triploid plant tries to reproduce sexually, meiosis produces nonviable gametes, and the seed won't develop. This is why, in \"seedless\" watermelon, for example, you will see small, white, soft/undeveloped seeds.",
"Some plants produce fruit even when they haven't been fertilized, and being seedless is just a result of that.",
"Further reading:\nStenospermocarpy:\n",
"https://en.m.wikipedia.org/wiki/Stenospermocarpy",
"\nParthenocarpy:\n",
"https://en.m.wikipedia.org/wiki/Parthenocarpy",
"*n = the number of copies of each chromosome. \n(Edited for clarity)"
] |
[
"Your \"PS\" pretty much describes the plant \"cloning\" process. You can also hermaphrodize a single branch and use that to pollinate a single plant for seeds."
] |
[
"Also, all plants produced by vegetative propagation (one type of which is described in the P.S. above) are going to be genetic clones of the parent plant. It is a normal survival strategy for many plant species, whether humans get involved or not."
] |
[
"How do these new Dyson fans work?"
] |
[
false
] |
I saw these recently on TV and they said to go on their website to see how it works but it doesn't really say anything is the website edit: i watched the video but didn't help much
|
[
"http://en.wikipedia.org/wiki/Bladeless_fan#Coand.C4.83_effect",
"hope this helps."
] |
[
"There's actually a real fan inside of it that just blows jets of air out of the circle. "
] |
[
"perfect. thank you."
] |
[
"If computer power increased 1000x fold in performance per watt and per dollar, what cool things would computers be able to do?"
] |
[
false
] | null |
[
"Hello,",
"This would be more appropriate for ",
"/r/AskScienceDiscussion",
".",
"Best."
] |
[
"Because there is no clear answer?"
] |
[
"It's an open-ended question."
] |
[
"If the half-life of Uranium-238 is 4.5 billion years, how do we know it's half-life without having been around for that long?"
] |
[
false
] | null |
[
"For something with a long half life like uranium-238, the method usually followed is you measure the activity and divide by the number of atoms. Essentially the half life =.693*Number of atoms/Activity. So if you have a known quantity of U-238, you would just have to measure how often it decays to get the value for the half life. ",
"Trying to use the normal method of seeing count rates change would not work since the difference in activity is extremely small during a short time period (days/weeks/years) compared to its half life."
] |
[
"See:",
"\n",
"http://www.reddit.com/r/askscience/comments/onfp1/how_do_we_know_that_the_half_life_of_a_certain/",
"\n",
"http://www.reddit.com/r/askscience/comments/14p1uh/how_do_we_know_that_uranium238_has_a_half_life_of/",
"\n",
"http://www.reddit.com/r/askscience/comments/k4wmx/how_do_we_observe_the_halflife_for_particles_that/"
] |
[
"For something that long-lived you won't actually get a measurable decrease in any reasonable timescale. You have to take the derivative, which leads to tauneutrino9's method above."
] |
[
"Would being underwater help survive a nuclear bomb?"
] |
[
false
] |
[deleted]
|
[
"Assuming you survive the initial blast and the water shields you from any ionizing radiation associated with the explosion and you surface as soon as the pressure wave passes you, you have quite a bit of time to escape the fallout. Fallout is literally irradiated debris lifted into the altmosphere that falls from the sky. It will take a while for this to happen. There is no way this occurs fast enough to \"destroy your lungs\" in a couple of breaths. In fact, while taking a couple of breaths of air containing significant fallout will certainly increase your cancer risk in the long term, there is no way it will \"destroy your lungs\" as rapidly as you are implying. ",
"Edit: I missed a word"
] |
[
"No. Fallout 3 is not a documentary. The radioactive pollution caused by nuclear bombs is vastly overstated in popular culture. The amount of radioactive material produced by a nuclear blast is fairly small, and it is distributed across a very large area. It is enough to produce a statistically significant cancer risk, but it is not an immediate danger to anyone who isn't extremely close to the center of a ground burst (but still miraculously survived). At 10km distance from the centre, radioactive fallout would only be a long-term concern, unless it's an enhanced radiation weapon or dirty bomb."
] |
[
"If it was a powerful airburst, in a clear cloudless sky, the thermal radiation from the initial burst, expanding at the speed of light, could give you severe burns before you realize anything unusual was afoot. If you were looking in the wrong direction at the wrong time, you're also blind now. ",
"A modest weapon – 100kt – isn't going to do much blast damage at 10 km. So if the prompt thermal radiation didn't get you, you might not even need the pool to evade the pressure wave. And if you're upwind of the blast, you may not have to worry about fallout.",
"A 1 or 2Mt airburst is a different story. A 10km, you're probably toast regardless. The thermal radiation will spontaneously ignite suseptible materials out to 10km and beyond. Blast effects will be harder to survive as well."
] |
[
"During a heart transplant, when does the heart start beating again?"
] |
[
false
] |
I was watching a movie (I think it was John Q...meh) and someone had to get a heart transplant. At the end of the procedure before closing the chest cavity the surgeon gave the heart a gentle tap with two fingers causing it to start beating again. Are there any surgeons out there who can shed a bit of light on this? Is that really how they start the heart beating again after a transplant or is it a move involved process? If that's all it takes what keeps it from starting to beat mid procedure?
|
[
"I did the anesthesia for a heart transplant recipient a few weeks ago.",
"The heart comes from the donor chilled on ice, in a cardioplegia solution to inhibit activity. The patient is anesthetized, chest is opened, and the patient is placed on a heart-lung bypass machine. Moderate hypothermia to about 28 C is instituted. Old heart out, new heart in, warm up. The donor heart starts beating on its own with warming - if it starts too soon, it can be cooled with cold fluid, and cardioplegia solution can be readministered. ",
"In some cases, the rhythm is not normal and requires electric cardioversion. A gentle tap isn't going to do it. Generally, the new heart also requires infusions of drugs to promote contractility and adequate rate. It's pretty common to place a wire for electric pacing of the heart as well. Unlike the old heart, the transplant is not attached to the autonomic nerves that control rate and contractility. Air is sucked out of the heart, I stick an ultrasound probe in the esophagus to confirm that the air is gone, then we turn off the heart-lung machine and let the new heart do its thing.",
"Piece of cake - after all, it's not like it's brain surgery :D"
] |
[
"Yes, cardiac cells have their own intrinsic rhythm (the sinus node being the primary source, if functioning), and with warmth it starts beating. A cold heart shouldn't beat, but it might fibrillate some, which is undesirable as any cellular activity prior to attaining blood supply increases the risk of injury."
] |
[
"Does it start just by virtue of being warmed up? Would a frozen heart beat on it's own for a while outside the body or is it getting electrical signal from the body or from the blood pushed thru the bypass machine or something?"
] |
[
"If a space shuttle accelerates in space, what stops it from accelerating with no friction acting on it ?"
] |
[
false
] |
I am aware that every action has an equal and opposite reaction, but if a ship was to say sling shot round the moon using its gravity, why doesn't the ship just keep on accelerating to infinite speeds?
|
[
"when you stop applying a force you stop accelerating. that's newton's law. force free motion is uniform motion (no acceleration), not accelerated motion. ",
"if you want to keep accelerating you need to add thrust (or for instance use gravitational attraction) "
] |
[
"It will get arbitrarily close to c but never reach it."
] |
[
"Well a slingshot maneuver will not allow the ship to accelerate indefinitely (at least not meaningfully). You get one quick boost while near the planet, but once you're further away you essentially just coast unless you get close enough to some other gravitational body.",
"But anyway propulsion mechanism aside, there is nothing stopping you from accelerating indefinitely. If you strap some drive on your ship which can provide constant proper acceleration for eternity, you'll just continue to accelerate forever, no problem. But you'll still never reach nor exceed the speed of light.",
"Your proper acceleration (acceleration in a momentarily comoving inertial frame) will remain constant forever, but your acceleration relative to a stationary inertial observer will asymptotically approach zero, and your speed will asymptotically approach c."
] |
[
"My grandma takes nitroglycerin pills for her heart. I was led to believe that nitroglycerin is incredibly explosive. Why hasn't this been an issue for her?"
] |
[
false
] | null |
[
"Nitroglycerin in tablet form is stabilized inside of a water-soluble polymer called povidone. It is also fairly disperse in that one pill contains less than a milligram of nitroglycerin, meaning you wouldn't be able to get it to explode if you wanted to. ",
"The largest problem is that the active ingredient decomposes over time, which is somewhat prevented by the povidone, but it won't last forever."
] |
[
"More to the function Nitroglycerin is a vasodilator, meaning it causes your blood vessels to dilate and as such can increase blood flow to the cardiac muscles which is especially useful when used as an intervention to a Myocardial infarction (literally translates to death of the heart muscle, more commonly known as a heart attack) ",
"It is often prescribed for individuals with a history of cardiac issues or circulation issues and is incredibly useful to avoid angina (pain in chest due to hypoxia ((a lack of oxygen to the tissues)) of the cardiac muscles) turning into a full blown MI (death of said muscles). I use nitroglycerin quite regularly in my field, as a side note never handle the pills with bare hands as nitroglycerin is incredibly easily absorbed, you will know if you absorbed some accidentally by the massive headache caused from blood rushing to your brain! (also a common thing people say in the field is that they are allergic to nitro because they get a terrible headache after taking it, which in reality is a side effect not an adverse reaction, pro tip for new EMT's and medics it is impossible to be allergic to nitroglycerin, shove that pill under their tongue if they need it a headache is better than death of the cardiac tissues) "
] |
[
"Thank you!"
] |
[
"How do smart phones track battery percentage?"
] |
[
false
] |
One thing I've always wondered about is, how do smart phones with, say, Li-Ion batteries track their remaining life and report them to the operating system as a percentage level. I should imagine it would have something to do with the current millivolt level of the battery, but seeing as to how sensitive those electronics are, it seems unlikely to me to expect a large enough deviation from the standard volt level of the battery, without disrupting the actual workings of the device, so that you could establish, for example, 3923 - 3925 mV is 10% battery. I'm sorry if this has already been answered or if this isn't the correct subreddit for this question.
|
[
"Generally in the case of smart phones, manufactures typically rely on a coulomb counter embedded within the device to measure the SoC.",
"Coulomb based measurement would be determined by measuring the current flowing from the device/battery, which in tun would be subtracted against the reference battery capacity to provide a percentage of battery life remaining. ",
"I would be more than happy to explain further if you would like additional details. "
] |
[
"You have part of the answer. The open circuit voltage off a voltaic cell is proportional to its state of charge. (The more it is charged, the higher the voltage). However, this by itself is not enough to estimate the charge level of a battery. Drawing current from a battery can mask the actual open circuit voltage as series resistance of cell depresses this voltage. ",
"Another approach would be to estimate the number of electrons that are flowing into and out of the battery. This is usually done by measuring the current flowing into and out of the battery, and integrating with respect to time. Note however, that this tends to be unstable: the longer you integrate, the less accurate your SoC estimate. ",
"The smartest chargers tend to combine these two approaches using a Kalman filter, or one of its nonstationary extensions. This is a technique that combines all the sources of information about a system along with a model in order to estimate both state variables and their error covariances. "
] |
[
"Thank you for your answer. :)\nIt would be great, if you could elaborate a bit more on the topic, especially as to how does this measurement work exactly. \nAlso, do devices generate a statistical model for a more accurate battery measurement, based on some sort of a discharge history?"
] |
[
"How do \"warm-blooded\" mammals *actually* make that warmth?"
] |
[
false
] |
So I know warm blooded (apparently that term is going out of fashion, but anyway) animals keep warm by converting food into energy. But, how exactly is this done? What is the process that "heats" up the blood? What is it that cold-blooded animals aren't doing inside that means they need external heat?
|
[
"The dissipation of the proton motive force through uncoupling proteins in the mitochondrial membranes. This is like poking a hole in a dam--the protons pour \"uselessly\" through the membrane, not generating ATP, and the free energy of the gradient is released as heat. "
] |
[
"The difference between warm blooded and cold blooded animals is not really the temperature of the blood, but how it is regulated. Cold-blooded animals simply let themselves enter an equilibrium, or close to equilibrium temperature with the surroundings. ",
"Warm blooded animals instead regulate their temperature in various ways. You may have noticed that when you get warm you start to sweat, your blood vessels expand, and you feel hot, causing you to take off clothing to cool down. Conversely, when we get cold we stop sweating , our body hair may rise, blood vessels contract, and we may even start to shiver ( the energy expended by the muscles turn into heat, warming us). ",
"The consequence is that the body temperature of a cold blooded animal can vary considerably depending on the temperature of the surroundings. Warm blooded animals instead tend to have a fairly narrow temperature range, which in humans is close to 37C. ",
"Now, as for your question. While cold blooded animals can tolerate a wide variety of temperatures, this ability is limited. If they go too cold, they will die. Since their bodies frequently lack the ability to retain and produce heat as efficiently as warm blooded animals, they compensate for this by seeking out natural heat sources, such as sunlight or fires. "
] |
[
"I took a physical anthropology class about the development of primates and humans and one of the things that was instrumental in humans' survival was the ability to sweat. As I recall, our ability to sweat came about around the time we lost our body hair. Having more skin and therefore more surface to sweat through gave us an advantage over haired mammals who could only let off heat by panting or through their ears. As a result, humans were (and are) able to run much further and for longer than animals. Although animals are faster, they can't go for as long in the hot sun because they can't sweat as much to cool themselves down. To this day, certain tribes in Africa use this advantage to hunt. They go out when the sun is hottest during the day, and chase a group of animals for hours, keeping them moving until exhaustion and heat render them unable to move. The hunters can easily kill them from there (Just checked on Wiki, it's called ",
"persistence hunting",
"). ",
"As a funny/gross sidenote, anthropologists were able to figure out when humans lost most of their hair based on when lice split into two species-- pubic lice and headlice! "
] |
[
"If a pool is on a ship and the ship is in rough waters, how do the waves in the pool mimic the waves that are hitting the ship if at all?"
] |
[
false
] | null |
[
"The size and frequency of waves on the ocean are determined mostly by wind speed and fetch (how long the waves are exposed to the wind in the same direction). ",
"The size and speed of waves in the pool would be determined by the depth of the pool. the size by the amount of the ships pitch (or roll as the case may be).",
"The most likely scenario is that the ships pitching will not be aligned at all with the available frequencies for a standing wave of the pool shape/depth.",
"As the ship pitched, from the perspective of the water in the pool, the walls and floor moved up and then back down, causing a sloshing. Yes this would (to a small extent) dampen the pitch and roll of the ship.",
"The speed of the wave across the pool will be much faster than the time between pitches of the ship",
"Since the frequencies will be quite different, each large sloshing wave will bounce back and forth slowly decreasing in amplitude until the next sloshing event.",
"Depending on the height of the pool walls above the water line, for a given (constant) pitch of the ship, a certain amount of water will slosh out onto the deck and then the remainder will slosh back and forth at the speed of the wave based on pool depth until the next pitch and it starts again."
] |
[
"Interesting. Related question: If the pool was closed off at the top with a strong rigid cover with an airgap at the top, would the whole thing act as a sort of tuned (or untunned) mass dampener for the ship against ocean waves?"
] |
[
"Like Ballast Tanks? "
] |
[
"What is the cause of axial tilt of Earth?"
] |
[
false
] |
Earth's axis is tilted by an angle of ~23.4° What is the cause of this tilt? I read that it is caused by a collision with a dwarf planet during early history of the solar system resulting in the tilt and formation of Moon as well. But that theory doesn't seems to be proved. What other explanations are there?
|
[
"I do not think that there needs to be a cause for the tilt of the earth's axis. The angle of axis of rotation could simply be the resultant of the inertia of the mass as it coalesced due to gravity during the earth's formation.",
"There is a theory that the moon is a result of a relatively large collision, which could have changed the tilt of axis of rotation.",
"All the planets have a tilt to their axis of rotation, thus the earth is not unique. "
] |
[
"They vary wildly in their tilt. ",
"Anywhere from 0 deg to 177 degrees.",
"Not all of them have tilts."
] |
[
"Yeah. So collision is the explanation?"
] |
[
"Yosemite super volcano. Hype or fact?"
] |
[
false
] |
How big of a threat is it? The stories sound like sensational hype but where is the nugget of truth?
|
[
"If Yellowstone were to have a full super-eruption, it would be reasonably catastrophic. It has smaller eruptions relatively more frequently (about 80 known since the last super-eruption), and those wouldn't be nearly as devastating.",
"But that's just one side of a threat - any threat assessment has to include the chance something will happen. And it is very, very unlikely Yellowstone will have a super-eruption anytime soon. There are no signs of imminent super-eruption, and it is observed very closely by volcanologists.",
"I've seen varying estimates from my volcanologist friends, but most agree the earliest we should reasonably expect a super-eruption to occur is at least tens of thousands of years into the future. Many sensational sites/people, ",
"like this one",
", will claim \"we're overdue\" by pointing at the time between the last few eruptions; but if anything the opposite is true. The previous two eruptions occurred ~.66 million years apart. The time span before that was ~.8 million years. It's been .64 million years since the previous eruption, so just looking at that data we would expect another 20,000 to 150,000 years before the next eruption. The USGS very roughly estimates this at about 0.000014% chance of eruption each year. Much more realistically, that just isn't near enough data points to predict when the next eruption will occur with any confidence. So if a site claims we are overdue, it's a huge red flag.",
"Back to the worst-case-scenario - a full Yellowstone eruption would be quite a bit stronger than anything humans have seen in recorded history - but not amazingly so. The 1815 Tambora eruption was about 1/20th as powerful as the last Yellowstone super-eruption. That's a big difference (and the Tambora eruption did impact climate and crop harvests) but it's not doomsday big. A large region of the western US would be impacted, and global climate would take years to decades to recover. The social impacts of that are difficult to predict, but it could put dangerous amounts of strain on struggling regions, especially in regards to food production. ",
"But life on Earth has seen many super-volcano eruptions, and not one of them is associated with one of the massive extinction events (Basalt Flows, another type of magma eruption, are). As a reference, humans were around for the Mt. Toba super-volcano eruption about 70,000 years ago, and while many think it may have put a great deal of strain on our species (how much is debatable), it was also several times larger than the last Yellowstone eruption 640,000 years ago. If you weren't a geologist you would have a hard time ever noticing the Mt. Toba eruption occurred at all, ",
"even if you were standing right where it happened",
". Lake Taupo, another supervolcano, erupted about 26,000 years ago and was also stronger than the last Yellowstone super-eruption. But again, the possible social impacts of such an eruption are difficult to predict - it would definitely be bad for a great many people."
] |
[
"USGS predictions for the path of the blast are pretty grim for food production in the US. We're talking major food production shortages worldwide, immediately upon eruption. Good thing it's not likely to erupt soon."
] |
[
"Do you think/know that the 1815 Tambora eruption would have been bigger, smaller or roughly the same size as the theorised dark age eruption that cause extreme weather events and civilisation collapse - ",
"http://en.wikipedia.org/wiki/Extreme_weather_events_of_535%E2%80%93536"
] |
[
"Humans cannot survive with only water from cellular respiration. Can bacterias survive in a environment with no water without producing endospore? If so, why can't humans?"
] |
[
false
] |
[deleted]
|
[
"Bacteria can generally only survive in dry environments by producing spores (or otherwise reducing metabolic activity). That's the reason why dry foods keep pretty much indefinitely. The low water activity prevents active multiplication of microbes."
] |
[
"Desiccation is hard on cells - proteins can denature and the cell membrane can rupture. But there are ",
"many ways to survive it",
" for bacteria, not just through spore formation. E. coli can survive some drying, and ",
"genetic engineering",
" shows that the survival rates can be boosted substantially without spore formation. As a rule, though, desiccated cells have essentially no metabolism, so they are in a state of suspended animation in a sense.",
"Now, why can't human cells do the same? Mainly because they don't need to, and haven't evolved the mechanisms for it. In general it requires some extra work for a cell to be ready for extreme environment changes. Bacteria rarely have a choice - a single celled organism will experience huge swings in temperature, hydration, and nutrient levels because of its small size. But human cells get to live in the climate-controlled environment of our bodies, and therefore have few mechanisms to deal with extreme stress. Even a temporary depletion of oxygen will cause many neurons to die, for instance.",
"Desiccation resistance isn't limited to bacteria. Other extremophiles can survive desiccation, even animals like the ",
"tardigrade",
". Although the process of desiccation imposes stress on a cell, once a cell is desiccated it is essentially isolated from oxidative damage (no water to carry reactive oxygen around) and can survive for long periods. But a cell built to survive desiccation needs to spend energy building the molecules that will prevent it from dying, and there isn't much reason for our cells to bother."
] |
[
"Bacteria are generally a lot less complex than an entire human organism. We've got a lot of stuff going on inside us, while a bacteria generally has very specific structure/function. This very specific function can be something like being able to resist drought without necessarily containing an endospore."
] |
[
"In herbivores, cellulose digestion is facilitated by symbiotic bacteria in the gut. Would it be possible to transplant herbivore gut microbiota to a carnivore's or omnivore's gut to allow them to digest plant material?"
] |
[
false
] | null |
[
"They tend to have multiple stomachs and specialized organs, so it's unlikely that our digestive tract would benifit from a transplant."
] |
[
"I’m no expert on the matter but I think the digestive tract on herbivores is specifically suited to house these bacteria and hold the cellulose, I don’t think it’s a fast process. I’m going to do some research and edit add what I find. Neat idea though if humans could survive on wood."
] |
[
"Humans already have some gut microbiota that express cellulase and can digest cellulose.",
"See for example",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1432575/",
"https://academic.oup.com/femsec/article/74/1/205/2680467",
"It's not clear how much energy we gain from this microbial interaction though. Probably not a huge amount."
] |
[
"A somewhat naive question: How comes there is an \"absolute zero\" temperature, and, if it's possible to answer that, why is it exactly the temperature it is?"
] |
[
false
] |
In other terms perhaps: What's so special about "absolute zero" that makes it, well, absolute and "zero" (in Kelvin of course)?
|
[
"So temperature is basically a measure of how much thermal energy some hunk of matter contains. You can add as much thermal energy to said matter as you want, and it might change around a bit, but you keep on adding that energy like it's nobody's business. Get that matter nice and hot. When it comes to cooling that matter down, there isn't an infinite amount of thermal energy you can remove. The more you remove, the colder the matter gets, until the matter has almost zero thermal energy and some crazy shit happens. If you were to somehow remove ALL of the thermal energy from that matter, there would be ",
" thermal energy units in that matter, and you absolutely can't take any more out of it!",
"The reason why absolute zero is expressed as 0 degrees in kelvin is that when some matter has no thermal energy, it can't get any colder, so it makes sense to start at zero. Also, it helps make math easier when doing chemistry work. Hope that helps!"
] |
[
"Perhaps s/he should have labeled it an oversimplification that demonstrates the point."
] |
[
"So temperature is basically a measure of how much thermal energy some hunk of matter contains.",
"Not quite. Temperature is often proportional to the amount of energy a substance contains, such as for ideal gases, but it is defined as one over the rate at which the entropy of a substance will increase as you add energy. Thus, taking energy out of a hot substance doesn't decrease the entropy very much, while putting energy into a cold substance causes the entropy to increase a lot. This is why energy flows from hot things to cold things, it results in a net increase in entropy.",
"Interestingly, it is actually possible for a substance to have negative temperature. However, a substance with negative temperature will not be colder than absolute zero, but will actually be hotter than anything with positive temperature. This is because removing energy from a substance with negative temperature actually increases the entropy."
] |
[
"Are there any types of cancer that live on after the host organism has died?"
] |
[
false
] | null |
[
"HeLa cells are cancerous cervical cells from Henrietta Lacks, and given a nutrient base, grow on.",
"And this guy died from cancer he contracted from his tapeworm. Not exactly the scenario you ask about but it certainly opens up interesting (frightening) possibilities.\n",
"https://www.iflscience.com/health-and-medicine/parasitic-worms-cancer-cells-caused-tumors-hiv-positive-man/"
] |
[
"I would say no. Cancer still needs a food/energy source since it’s pretty much living cells that have gone haywire, so it’s still your body but slightly off. The energy would need to be delivered in a way that would ensure the cancer cell’s growth, which would be the same as or very similar to normal human cells. Unless you’re culturing cancerous cells on specialized media that contains all essential nutrients and a “food source” for its survival, it would die off with the host. ",
"Disclaimer: I’m not a professional but I am a science grad student. "
] |
[
"DFTD in Tasmanian devils and CTVT in dogs are transmissible cancers, which have been propagated to hundreds of hosts since their original host died. There are also examples of humans getting cancer from transplant recipients, or fetuses getting cancer from their mothers. ",
"If you are thinking of a cancer continuing to live inside a dead body, no that is not possible anymore than having say your liver cells live on for months after you have died, all cells need oxygen/nutrition to survive, and have no way to obtain that outside the body or in a dead body without outside intervention. "
] |
[
"Normally in the body fluids and minerals in those fluids flow from areas of high concentration to low concentration. However the kidneys are able to remove minerals/toxins from your blood and concentrate them into urine which is much more concentrated. How does it do this?"
] |
[
false
] | null |
[
"The nephron is a microscopic “unit” of the kidney that controls this. It’s essentially a series a tubes set up in a way to allow only some solutes to pass out - effectively concentrating it. These “concentrating” parts are not permeable to water, so you only pump out certain ions. How does it seemingly work against a gradient? By using energy elsewhere to build a temporary gradient of another ion (not found in high concentrations in fluid used to build gradient, so you don’t have to work against another gradient), and using ",
" gradient to pump that solutes to very high concentrations. ",
"Then the kidney uses that very high concentration to then draw out water elsewhere, which forms the concentrated urine. In some desert animals, they have very long nephrons that are able to build up a much more concentrated gradient, and therefore concentrate their urine that much more.",
"Of note, kidney is a pretty energy-intensive organ, needing to build up that high concentration gradient and all. That’s why kidneys are easily injured during critical ICU-level illness (and you see a lot of people on dialysis after long hospital stays)."
] |
[
"Along with the other explanations here, I'd like to add that there's a very clever arrangement of blood vessels around the nephron which forms a countercurrent multiplier for the concentration of the solute. The nephron tube also changes along its length, being permeable to different substances.",
"This video is a wonderfully concise explanation of the countercurrent multiplier in the kidneys: ",
"https://youtu.be/XbI8eY-BeXY"
] |
[
"So in the case where the hyperosmotic zone stops being hyperosmotic, can the nephron re-establish the hyperosmotic state if given time? And what if the region were to somehow turn hypotonic instead?"
] |
[
"How much Cobalt-60 has been produced by nuclear power programs in the world?"
] |
[
false
] |
I have heard that as little as .1 grams per square mile (correct me if I'm wrong) is lethal to anyone in that square mile. That being said, does anyone have information on any studies that have tried to determine how much cobalt 60 has been produced by humans either by nuclear power programs or, if it is generated this way, by nuclear weapons production? I realize that the lethal dose is dependant on how acute the exposure is and whether it is ingested or not, among other factors, since I work in nuclear power. I was just curious what the impact of nuclear programs on generating Co-60 has been throughout the course of history. Edit: Grammar
|
[
"Co-60 isn't very prevalent in spent fuel, which makes the total amount hard to quantify (since the composition of spent fuel is so well known/controlled). Fission yield is basically zero below about 80 atomic mass.",
"As a side note, 200 KCi is about 175g of Co-60, and a new gamma knife unit has around 6 KCi total activity."
] |
[
"Lots of radioisotopes are lethal in certain conditions--not just Co-60. Anything that emits a gamma > 1MeV could really do you in if you sat around long enough. This is why don't purposely scatter them around.",
"I dont know about the rest of the world, but the US gets its Co-60 from the Advanced Test Reactor in Idaho Falls. The produce 200KCi a year of it a year. Keep in mind that this is mainly used for ",
" purposes---such as the gamma knife technique.",
"Source: ",
"http://www.inl.gov/technicalpublications/Documents/3374760.pdf",
"I don't know how much Co-60 is generated as fission products in a nuclear reactor."
] |
[
"Yes, as I mentioned before, Co-60 is a gamma emitter:\n",
"http://www.nndc.bnl.gov/chart/decaysearchdirect.jsp?nuc=60CO&unc=nds",
"The spectrum is here:\n",
"http://upload.wikimedia.org/wikipedia/commons/8/88/60Co_gamma_spectrum_energy.png",
"Pretty energetic gammas, above 1 MeV.",
"I doubt the Manhattan project was producing Co-60, when nuclear reactors didn't exist.",
"You are correct that after 26 years you can basically neglect the source. Find the amounts produced around the world for the past 26 years and you'd get a great estimate if you put in the decays."
] |
[
"How close are we to the event horizon of the black hole in the center of the Milky Way?"
] |
[
false
] |
Do we have any idea?
|
[
"the black hole at the center of the milky way is absolutely tiny compared to the whole galaxy. So it's pretty much the same as our distance from the center of the galaxy."
] |
[
"Ahh, okay. I've heard people refer to it as a supermassive black hole so I had no idea how big it actually was. Thanks!"
] |
[
"The event horizon of a black hole is equal to the Schwarzschild radius, which is ",
"2.95km per solar mass.",
" The mass of the object at the center of the Milky Way is around 4.3 million solar masses. So the event horizon extends about 12.7 million km from the center. That's about 18 times the radius of our Sun, which is really, really big for a black hole, but still tiny on the grand scheme of things. An object with radius 12.7M km would fit well inside the orbit of Mercury and is far smaller than the radius of the largest known stars. "
] |
[
"Why do oil slicks have a rainbow shimmer when it's wet outside?"
] |
[
false
] |
Is there a reason why they shimmer a rainbow shine?
|
[
"Simply put, the spectrum is caused by different thicknesses of oil.",
"When light hits the top surface of the oil, some of it is reflected, and some passes through. When some light that passed through hits the bottom surface of the oil, some more is reflected. The result of this is two different reflections on top of each other - this is called superposition.",
"Sometimes, depending on the thickness of the oil, the wavelengths of the two reflections don't line up properly (they are out of phase). This can have the effect of making the light stronger or cancelling it out completely, depending on the difference between the waves.",
"Different colours of light have different wavelengths, so the thickness of oil that makes the light stronger or weaker varies for each colour. As the thickness of oil changes across the puddle, you get each colour being made stronger and weaker in turn, creating a spectrum.",
"This is also true for most other things that do this, such as soap bubbles",
"This Wikipedia article has some helpful diagrams"
] |
[
"It is dependent upon angle of view as well - an oil patch of uniform thickness will still exhibit ",
"iridescence",
", since the light will travel through different lengths of oil at different angles. So I wouldn't say it's caused solely by different thickness of oil."
] |
[
"Just to add some equations, check this ",
"link",
", you can calculate the thickness of the film from the color."
] |
[
"Is it credible that people who are naturally thin despite leading unhealthy lifestyles are so because their bodies tell them they're no longer hungry sooner when eating?"
] |
[
false
] |
[deleted]
|
[
"This is grossly oversimplified, but will provide you with some starting points for your own research:",
"Leptin is a hormone that helps tell your body to feel satiated. It is produced in fat cells and in the stomach. Relatively few humans suffer from congenital leptin deficiency, and I dare to say that if you have this, you probably know it already ",
"[1]",
". Overweight people (more fat cells) produce more leptin than thin people; it is a way for the fat cells to tell the brain that there is a higher level of energy storages from fat. Again, few overweight people were born with mutations in the leptin receptor and are unable to respond to their elevated levels of leptin ",
"[2]",
". Just because most overweight people don't have a mutation doesn't mean they are responding fully to the leptin; however, I am ignorant of whether there is conclusive proof that leptin dysregulation generally ",
" overweight (similar to how insulin insensitivity follows overweight) versus whether leptin dysregulation generally occurs on its own and ",
" overweight. Many other factors influence hunger/satiety including ghrelin; neuropeptide Y; and blood levels of glucose and amino acids. This is a complex regulatory system and cannot be simplified past a certain point. "
] |
[
"A thin person has a smaller stomach than an overweight person, since eating a lot of food stretches it. That's part of the reason why they feel full on less food. Being on a diet for a while or fasting shrinks it again though.",
"http://www.ncbi.nlm.nih.gov/pubmed/8561056?itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum&ordinalpos=1"
] |
[
"In addition to thecrusha's comment, and recognizing there are likely hundreds of factors that contribute to this phenomenon, recent research by Ruth Ley at Cornell has shown that the composition of human gut flora (bacteria living in the intestines) may have an enormous effect on weight. Her research showed that people vary greatly in the copy number of the gene for amylase, the enzyme that breaks down carbohydrates. Blood lines that come from places where agriculture was used earlier tend to have more copies of the gene (which in this case, translates to more enzyme) broke down more carbs, making them bioavailable for uptake in the intestines, leaving less food for bacteria. Members of this group tended to have statistically significantly higher BMIs. People with fewer copies of the gene (note: with a sample size of around 300, number of copies ranged from 2-24!) left more carbohydrate to be used by the bacteria, which in turn produced short-chain fatty acids, a product that the body extracts much less energy from. Members of this group had statistically significantly lower BMIs. Thus, the genotype of the human led to the composition of the gut flora, which in turn yielded a human phenotype (BMI). That may be a major contributing factor to BMIs that contradict lifestyle: genes determining how much energy we can actually extract from the food we eat!"
] |
[
"Why does a space shuttle do a quarter turn 15-30 seconds into launch? Why not just launch it with that orientation rather than turning?"
] |
[
false
] | null |
[
"Excellent question!",
"The roll program is executed around T+12 to orient the shuttle into a heads down attitude to reduce structural loading, gain downrange velocity, and provide a easier abort maneuver setup.",
"The roll program is a combined roll, yaw and pitch maneuver. I think your question is mainly about the roll and yaw portions of the maneuver. The pitch maneuver brings the nose around with the belly up, points it downrange and gives the trajectory that arc shape.",
"So, why does the shuttle need to roll and yaw? Because the launch pad has a fixed orientation, but the shuttle orbits at various inclinations (angle relative to the equator) depending on the mission. A typical inclination of 28 degrees takes advantage of the earth's rotation for lifting heavy payloads. Space station missions are flown at a 52 degree inclination. So, since the pad is fixed, the roll program is necessary to orient the shuttle to the correct orbital inclination.",
"So, why didn't they just pick the most likely inclination and orient the launch pad accordingly; thereby only needing to execute the pitch portion of the program for most missions? This is the answer I didn't know and had to dig for. Apparently the launch pads are leftovers from the Apollo program and the access tower and support structures are oriented as they were for the Saturn V rockets. Also, the shuttle straddles two leftover flame trenches, one for the boosters and one for the main engines, which also dictate the shuttle's launch orientation.",
"Edit: Fixed the time of the roll program."
] |
[
"Because the orientation it needs will be different with each launch, but it can only sit on the launch pad one way. If you watch the video Enkaybee posted, notice the Shuttle rolls just before it pitches (starts leaning over on its \"back\")---the angle it rolls to determines its heading as it flies away from Cape Canaveral. Ultimately, that heading determines which orbit it flies into. In the video, it's going to rendezvous with the International Space Station, so it has to launch into a matching orbit.",
"Exactly which angle it'll take to do that depends on the time of the launch, down to almost the second. A different launch window means a different roll angle. A different destination orbit (visiting the Hubble telescope, say) means a different roll angle."
] |
[
"Sources:\n",
"http://stason.org/TULARC/science-engineering/space/53-Why-does-the-shuttle-roll-just-after-liftoff.html",
"\n",
"http://www.satobs.org/shuttle.html"
] |
[
"If atoms are 99.99999...% empty space, how do we see anything?"
] |
[
false
] | null |
[
"Atoms are ",
" 99.99999...% empty space. This is a misconception propagated by elementary education and is based on a model of the atom (the Rutherford model) that was shown 100 years ago to be false. Electrons in an atom are not solid little balls that orbit the nucleus like planets orbit the sun, with a vast chasm of empty space between the electron and the nucleus. Rather, electrons in an atom are smeared out into wavefunction clouds ",
". These clouds (often called \"orbitals\") are not formed simply because a solid little electron is traveling too fast for us to pinpoint it, nor is it formed because we simply don't know where to look to find the solid little election. The cloud ",
" the electron. Electrons are quantum particles, and as such, they are complex beasts that act somewhat like waves (clouds) and somewhat like particles. In a stable atom left to itself, the electrons act mostly like waves. Therefore, the electrons in an atom literally spread out in the wave state to fill the atom, and there is no empty space. But this concept has little to do with why we can see objects made out of atoms.",
"Humans see objects by detecting the visible light that comes from the object. Visible light (red to violet) has a wavelength that is a thousand times larger than an atom. Therefore, when visible light hits an object made of many atoms (e.g. a metal spoon), it is not really interacting with one isolated atom at a time. Light is interacting with many atoms at once. Furthermore, when atoms bond into a solid structure, they don't act like independent atoms anymore. The atoms bond into an integrated structure, and the outer electrons smear out into waves that stretch over many atoms. So when you have sunlight reflect off of your metal spoon and into your eye, allowing you to see the spoon, there is not really a stream of photon particles, each individually interacting with different, separate atoms. Rather, you have photons spread out over the size of many atoms, interacting with electrons spread out over many atoms. You aren't really seeing atoms when you look at an object. You are looking at the bonding lattice of the atoms. That is why carbon can be black when arranged into a graphite lattice and clear when arranged in a diamond lattice.",
"What is this interaction? It is the electromagnetic interaction. Light is a fluctuation in the electromagnetic field, and electrons carry electric charge. Because of their electric charge, electrons can destroy, create, and redirect photons. As far as visible light and everyday objects are concerned, its the outer electrons that are each spread out over many atoms that mostly allow us to see objects."
] |
[
"This is incredibly wrong. Glass electrons are in no way \"held onto more tightly\" nor is absorption and reflection in any way related to \"taking away an electron\", this is called ionization. ",
"The way that electrons behave in a solid is quite complicated and dictated by what is called quantum mechanics but in a nutshell the way electrons in a system behaves means that there are only certain \"energy jumps\" an electron can make. What dictates these allowed jumps is called the BAND STRUCTURE of a material (though strictly speaking glass is an amorphous solid and doesn't have a band structure).",
"The frequency, or colour, of light determines how much energy each light packet ( a photon) is carrying. A material will only absorb a packet of light if that packet of energy corresponds to a possible allowed energy jump. There is a certain energy range associated with visible light, light we can see. If something, like glass, is transparent then ALL IT MEANS is that there are no allowed jumps in the energy range of visible light. There will be jumps at higher and lower energies as you say.",
"To drive the point home, the allowed energy jumps are not related to \"how tightly\" an atom hold electrons, in fact it is usually the valence electrons, which are often delocalized, which are responsible for the optical properties of the material",
"EDIT: Just to carry things a little further, if transparency WAS related to the strength of which an electron is held than transparency would go up as you move to the right and to the top in the periodic table and would be directly related to the ionization energy (the energy needed to strip an atom of an electron). This is quite false."
] |
[
"This is incredibly wrong. Glass electrons are in no way \"held onto more tightly\" nor is absorption and reflection in any way related to \"taking away an electron\", this is called ionization. ",
"The way that electrons behave in a solid is quite complicated and dictated by what is called quantum mechanics but in a nutshell the way electrons in a system behaves means that there are only certain \"energy jumps\" an electron can make. What dictates these allowed jumps is called the BAND STRUCTURE of a material (though strictly speaking glass is an amorphous solid and doesn't have a band structure).",
"The frequency, or colour, of light determines how much energy each light packet ( a photon) is carrying. A material will only absorb a packet of light if that packet of energy corresponds to a possible allowed energy jump. There is a certain energy range associated with visible light, light we can see. If something, like glass, is transparent then ALL IT MEANS is that there are no allowed jumps in the energy range of visible light. There will be jumps at higher and lower energies as you say.",
"To drive the point home, the allowed energy jumps are not related to \"how tightly\" an atom hold electrons, in fact it is usually the valence electrons, which are often delocalized, which are responsible for the optical properties of the material",
"EDIT: Just to carry things a little further, if transparency WAS related to the strength of which an electron is held than transparency would go up as you move to the right and to the top in the periodic table and would be directly related to the ionization energy (the energy needed to strip an atom of an electron). This is quite false."
] |
[
"Where is the antigen presented with adeonviral vaccines?"
] |
[
false
] |
I understand that the virus carries the gene of the specific antigen (e.g. SARS-CoV-2 S protein). But upon entering the body where is this expressed? If the viral vector infects a cell, and expresses it in the host, would not this trigger an immune response against the antigen AND the host cell as well? What host cells do these viral vectors infect, anyhow? Or are they presented on the virion surface only? Thank you.
|
[
"I’ll try to answer your questions sequentially:\nIt’s not just adenovirus vaccines, but for any infection (viral or bacterial) essentially any nucleated cell is able to present antigens to the immune system. \nCells that are directly infected by viruses will ultimately utilize MHC class 1 proteins to present antigens to CD8+ T Cells (Also known as Killer T cells). CD8+ T cells directly kill the infected cell, so yes the immune response kills infected self-cells to hopefully prevent the spread! But there is also another option. Viruses/bacteria that are intercepted by phagocytes like Dendritic Cells or Macrophages get presented as MHC class 2 proteins. These proteins present antigens to CD4+ T cells, which are the “helper T cells” that ultimately “help” B cells create antibodies. MHC2 proteins are specific to these phagocytic cells only. \nThe ultimate goal with vaccines is to inject either an inactivated virus (killed) or attenuated virus (alive but without the virulent factors) so that they cannot “infect” cells, but instead are easily picked up by those phagocytes to ultimately begin that MHC2:CD4+ cascade to create antibodies with B cells. \nViruses will infect any cell in which they can enter. There is no one specific tissue that they prefer, to them meat is meat. \nIf you can understand all of this, you will pass the immunology they teach in medical school. ",
"Side note: Since you mentioned adenovirus, I am obligated to tell you to look up Jesse Gelsinger."
] |
[
"If any cells can present the antigens, can the immune system accidentally think that cell is a pathogen and attack it?"
] |
[
"Not usually. In the healthy population, immune cells should not attack healthy cells that are not presenting antigens. Through the development of B and T cells, there are processes that take place which will destroy (negative selection) any type of immune cell that erroneously binds to self without a foreign antigen. Buuuuuut it is possible if a person has an autoimmune disease like APECED (Autoimmune Polyendocrinopathy Candidiasis Ectodermal Dystrophy) in which their T-cells regularly attack their own cells due to a mutation in the Autoimmune Regulator (AIRE) gene. These people make T cells, but they do not make a functioning protein that is responsible for directing the negative selection of self-binding immune cells. And unfortunately, those who have this disease are usually very young kids and they do not live very long.",
"Edit: forgot the 2nd E in APECED."
] |
[
"Does our moon have a name in common english?"
] |
[
false
] |
Saturn's moons all have names, what is ours?
|
[
"The proper English name for the moon is \"the Moon\". (",
"source",
"). \"Luna\" is sometimes used in literature, and is the name of the Roman goddess that was the personified moon to the Romans."
] |
[
"Well, I think the Moon as an object is actually a natural satellite, and the Sun is a star. So when we refer to ",
" Sun and Moon, we call them by their names. When we call other things suns and moons, we're actually using those names as eponyms. ",
"Think about it like asking for a Kleenex rather than a tissue, or making a xerox rather than a photocopy. "
] |
[
"Sol Invictus (lit. \"unconquered Sun\") was a specific sun deity whose cult was popular in the Roman Empire, it wasn't the everyday name for the object.",
"The English name for the earth is just Earth or the Earth. Terra and Gaia are sometimes used poetically or figuratively but aren't the actual name."
] |
[
"On a cellular level, what is a memory and how are they stored/accessed in the brain?"
] |
[
false
] |
[deleted]
|
[
"You won't get a concrete answer. From a pragmatic materialist perspective, yes there is some sort of physical structure that lends itself to memory storage within the neural networks in the brain. The problem is we have very little understanding of how this process works."
] |
[
"This isn't necessarily true. The knowledge might still be there in a dead brain (at least until it rots), but we would have no way of knowing. "
] |
[
"What's crazy about this is that it's not like we can surgically extract knowledge from a dead person...so all our memories are in ram ALL THE TIME.",
"Aside from the fact that your train of logic there doesn't really make sense: It's no more accurate to think of the memory of the brain as RAM than it is to think of it as an SSD or HDD. ",
"I suspect you meant to bring up the topic of ",
"volatility",
" but even then that just doesn't make sense to bring into the conversation since dead nervous tissue would clearly lose all function. ",
"So, the lyrics to that song you haven't heard in decades but you can suddenly remember them JUST as you need them to keep singing along... yeah that's actually been somewhere in your head for every waking/sleeping moment of your life for all those years. ",
"Well... obviously? What was the other option? Telepathy? I may be giving out a hostile vibe but come on.. what are you even saying. "
] |
[
"AskScience AMA Series: Happy World Octopus Day! I'm a marine biologist who raised a day octopus in my home for a PBS Nature documentary called \"Octopus: Making Contact.\" Ask me anything!"
] |
[
false
] |
Hi, I'm , a professor of marine biology at Alaska Pacific University. I've studied octopuses for more than 20 years and recently raised a day octopus in my living room for a documentary. The octopus was named Heidi, and she came to recognize me and my daughter and would play with toys and display other remarkable signs of intelligence. I also caught her changing colors while sleeping, you may have seen . If you haven't yet watched "Octopus: Making Contact," you can stream it at (US viewers only) It also aired on the BBC under the title " ." I'll see you all at 12 noon ET (16 UT), ask me anything!
|
[
"As far as I understand with regard to animal intelligence, certain species of gorillas have been taught sign languages, and dogs can understand vocal commands such as \"sit\", recognise their own name, or even know that pointing is indicating a direction.",
"How much communication is possible with an octopus? Can they learn what is meant by certain human body languages/expressions/sounds? Do they have the capacity to learn how to communicate certain things to us, and how would they go about this? For example, in the way a dog can be trained to communicate it wants to go out."
] |
[
"I know that octopuses live relatively short lives, but are highly intelligent. At what age do they develop an “adult” level of intelligence? Do they go through recognizable cognitive development stages analogous to human cognitive development? Do they keep getting “smarter” or do they plateau?"
] |
[
"Congratulations! Not every diver gets an octo high-five of approval.",
"At the sites I visit in Australia (Octopolis and Octlantis), we often see that behavior between octopuses - they 'high five' each other, or reach out to (almost) touch arms in passing."
] |
[
"Is the area of a Mandelbrot set infinite?"
] |
[
false
] | null |
[
"Since it is contained within a circle of radius 2, it does not have infinite area, its area is less than 4pi. More precisely, it has area about ",
"1.507"
] |
[
"The boundary of the Mandelbrot set is not very straightforward",
"This is one of the most wonderfully understated phrases I've come across in the realm of mathematics"
] |
[
"Now a more interesting question: is its ",
" infinite?"
] |
[
"Why can't we move our toes as easily as our fingers?"
] |
[
false
] |
[deleted]
|
[
"There is a number of reasons, not the least of which is the lack of an opposable digit. The thumb has significant special muscles (the thenar group) to aid in movements like opposition/adduction.",
"On a deeper level though you are probably asking why don't we have the similar feeling of fine control over our feet as our hands?",
"The answer for this is in our brains. The motor cortex is divided up into regions specific to body parts, and the hand region is huge.... It makes up maybe 25% of the motor control volume. See ",
"here",
".",
"The evolutionary pressure for this should be obvious, on the ground feet are not useful in the same way as hands."
] |
[
"Could some of this be down to practice? If a young child practised using their toes as we do with our hands, could they get much more dexterous?"
] |
[
"I've seen videos of people that lost their hands, which forced them to use their feet for everything. THey got really good at it."
] |
[
"If you continued accelerating in space at a constant 10m/s, would you eventually reach the speed of light, or even exceed it?"
] |
[
false
] | null |
[
"No matter how high your acceleration is, and or how long you accelerate for, you'll never reach c."
] |
[
"Why would that be? "
] |
[
"It's a consequence of relativity. There's many ways to see it, the simplest is that you'd need infinite energy to accelerate a massive object to c."
] |
[
"I know this is just semantics, but why are the organisms in our digestive tracts called 'gut flora' and not 'fauna'? Are all microorganisms considered flora?"
] |
[
false
] |
[deleted]
|
[
"Tradition. It is technically incorrect to call them microflora, but they have been calling them that a long time. A lot of people now are just referring to the microorganisms in your gut as microbiota, which is technically inclusive of microfauna and microflora.(although there is no microflora in your gut)"
] |
[
"Fauna only refers to animal life. The microbes in the digestive tract are not of the Animal kingdom. Flora usually refers to the plant kingdom but bacteria are usually referred to as bacterial flora. It really is just tradition. "
] |
[
"All known life is classified into six kingdoms currently. Most bacteria and microbes (not including viruses) are classified as Kingdom Bacteria. ",
"http://en.wikipedia.org/wiki/Kingdom_(biology)"
] |
[
"Aeronautic experts of Reddit, how _slow_ can a plane go before simply falling down?"
] |
[
false
] | null |
[
"The speed an aircraft needs to be going to start airborne can be found using the equation V = sqrt(2 * M / CL * rho * A) where M is the weight of the plane, CL is the coefficient of lift, rho is the air density, and A is the wing area. A 737-300 has a wing area of 105m",
" , a maximum coefficient of lift of ~2.2, and a maximum takeoff mass of 68,000kg (666.4kN). At sea level air density is roughly 1.2kg/m",
" Using the equation above we can see that a fully loaded 737 flying at sea level will maintain altitude at an airspeed of 69m/s (250km/h). At an altitude of 10km the air density drops to .41kg/m",
" and the plane must fly at 118m/s (427km/h). ",
"This results need to be taken with a grain of salt as the airfoil is designed to work specific Reynolds numbers above or below which the coefficient of lift can vary significantly.",
"The equation I gave earlier indicates what factors affect a plane's minimum speed. A very slow plane would feature a very large wing with a high lift coefficient and lightweight construction. This can be seen in the video that CatastropheJohn posted, although in that scenario the pilot was aided by a strong headwind. This means that air was passing over the wing very quickly relative to how the plane was passing over the ground.",
"A detailed and thorough but fairly easy to understand explanation of aircraft aerodynamics is available ",
"here"
] |
[
"If you research STOL (Short Take Off & Landing) your mind will be blown. Try this YT video for starters: ",
"17 foot takeoff, 10 foot landing",
"I am not an expert, just an admirer."
] |
[
"The clip of the Claus' flying their super cubs shows just what can be accomplished with ordinary technology so long as the payload is very small. The flow of air from the prop over the wing, plus the headwind is more than sufficient to get off the deck in ground effect. ",
"There are clips of STOL military aircraft nearly as impressive and those are seriously heavy machines. Look up C-17 stuff",
"BTW those guys are AWESOME. if you are jaded about flying just go to Ultima Thule and they'll show you how to have fun with little airplanes in BIG mountains. Amazing skills and a backyard second to none. "
] |
[
"Why are some metals stronger than others?"
] |
[
false
] |
[deleted]
|
[
"Why are some metals shiny, why are some magnetic etc etc. ",
"It's all about the atomic properties, in what kind of structure do they bond?\n",
"http://www.learneasy.info/MDME/focus/materials/enmat/LECTURES/Lecture-04/webpages/crystals_files/h12_27.jpg",
"and how strong are the bonds between the individual atoms?\n",
"https://en.wikipedia.org/wiki/Electron_configuration"
] |
[
"As stated it depends on electron structure and bonds BUT almost everything in our daily life depends on them so its not a good explanation. One higher level is crystal structures, the arrangement of the atoms effect their properties. If the structure is FCC or HCP the metal maybe more ductile. However the real thing that determines the strength of engineering metals is alloying.",
"What alloying does is complicated but I will talk about some aspects of it. First some background: as mentioned metals have crystal structures, think about perfect arrangement of atoms everywhere. Now we want to deform it. All deformation in metals happen in shear mode, meaning that one layer of metal atoms slip on another. But slipping trillions of atoms at once is quite impossible. So what happens is a defect occurs in the crystal structure. Its called a \"dislocation\". Its hard to describe with words so better look it up. When a metal deforms whats happening is billions of these dislocation gliding in the metal, deforming it one row at a time. ",
"Why are alloys strong but pure metals aren't? Because there is not much to stop these dislocations from gliding. But when you add carbon to steel in right amounts, carbon atoms segragate at dislocations and make it hard to move. But not impossible to move. That would make the alloy brittle. Or in some aluminum alloys, copper and aluminum form one atom thick plates that are very small in other directions too that impede the motion of dislocations. Or alloy may change the crystal structure and make it hard for dislocations to move. ",
"The perfect crystal is arranged in regions, one formation ends and another starts in grains. Think of soldiers in perfect formation but in another region the rows stand at 15 degrees to the other region. (arbitrary number) In the boundary between them atoms are not perfectly aligned so this irregular regions makes dislocation glide hard. As the grain size of metal shrinks, the graind boundry area increases and makes metal stronger. The extreme edge is amorphous metals with nearly no long range crystal order.",
"Also in some alloys like steel, hard intermetallic compounds may form in various forms (lamellar in some steels) and again make dislocation glide harder."
] |
[
"Other folks are focusing on bonding, but there are many possible reasons one metal might be stronger than another:",
"As noted, the bonding between the metal atoms may be weaker. This will generally be correlated with a lower melting temperature (think soft lead vs. harder, more refractory metals such as nickel) and often a lower stiffness. Here, we're changing the base metal.",
"Or we can replace one refractory metal with another with a different crystal structure. Here, it's useful to note that ductile materials generally fail by dislocations (1-D defects) sliding through the crystal, carrying plastic deformation (i.e., permanent slip or shear). Dislocations generally move ",
"more easily",
" through face-centered-cubic crystal structures such as gold and copper (soft metals, right?) than through, say, iron (body-centered cubic) or zinc (hexagonal close packed).",
"Or we can keep the base metal and its crystal structure and nucleate ",
"precipitates",
" of another compound within the interior. Precipitates force dislocations to cut through another material, which impedes their motion for several reasons.",
"Or we can keep the base metal, crystal structure, and phase and add impurities that ",
"strain the crystal",
". These impurities interact with the strain field of the dislocations, impeding their motion and thus adding strength.",
"Or we can keep the base metal, crystal structure, phase, and purity and change the grain structure, adding grain boundaries that also ",
"resist dislocation motion",
".",
"Or we can keep the base metal, crystal structure, phase, purity and grain structure and ",
"add more dislocations",
", which tangle and present a further impediment to permanent deformation. In a classic classroom example, my tiny advisor would bend a thick copper rod and hand it to the strongest-looking student, who found the rod impossible to straighten. The rod had been annealed before class, increasing the grain size and essentially cleaning out the existing dislocations. Upon bending, untold numbers of dislocations formed at the atomic scale within the rod, strengthening it substantially.",
"The reason this area has been explored so thoroughly is the tremendous need our society has for cheap, light, refractory, STRONG materials (with various other preferred material properties). This is just a very brief overview, and ",
"other strengthening mechanisms certainly exist",
"; one could spend an entire research career investigating some flavor of steel alloys, for example, or the preparation of very strong amorphous metals that lack grain boundaries entirely."
] |
[
"How much current does my CPU use?"
] |
[
false
] |
I wanted to calculate how much current my CPU uses just because I was curious. To do this, I just used the equation P = VI. My CPU runs at 1.15V, and has a TDP(average power) of 115W. So, according to the equation, the CPU runs at ~100 amps. But, this didn't seem correct because North American outlets have a max current of 15amps. What is going on here?
|
[
"For a theoretical ideal transformer, yes. Conservation of energy implies that what goes in, must come out. Since power is the product of current and voltage (again, in an idealized situation), any decrease in voltage in the transformer will cause an increase in current.",
"In reality, transformers aren't perfect and there are various losses of energy along the way. Modern power supplies often come with the \"80+\" certification (in a variety of flavours), which means that under specific circumstances, the power supply has an efficiency of at least 80%. But the rest is simply lost in the form of heat (which is why some power supplies have a cooling fan).",
"Furthermore, a computer PSU transforms alternating current to direct current, which makes the story more complicated since many of the simple laws like power equals voltage times current need a correction factor when alternating current is in play."
] |
[
"Between your wall socket and the CPU, the electricity goes through several transformers. Initially (in the US), your wall socket will provide you with a voltage of 110 V. This means that the electrons making up the current have a rather high energy. Your CPU doesn't like such energetic electrons, so it needs a series of transformers in between. In this case, the power supply unit (PSU) of your computer transforms the 110 V input into 12 V output (and other channels). In order for the PSU to provide the same amount of power on the output side as it receives on the input side, it has to generate a higher current on the output side.",
"So if it takes 1 A of current at 110 V as input (110 W power), the output that runs at 12 V will have a current of 9.17 A (assuming no losses in the PSU, in reality the output current will be somewhat lower).",
"Your motherboard also contains components to regulate voltage. They take the 12 V coming from the PSU and transform it into a lower voltage in order to be usable by the PSU. But in order to do that while keeping most of the power, the current of the output signal has to be increased again.",
"So while your CPU may be running on a ~100 A current, this current only runs through your CPU, to and from the transformer circuitry on the motherboard. This 100 A current never comes close to your power outlet."
] |
[
"Can I ask a follow-up? ",
"It's been a while since I've done any power supply work, but I recall a relationship between stepping down the voltage and a step up in the current. Like, 120V/1A steps to 12V/10A. Dropping one by a factor of 10 results in a factor of 10 rise in the other (ideal). ",
"Am I remembering that incorrectly? "
] |
[
"What Mechanism Produces Black Body Radiation?"
] |
[
false
] |
I have spent about a half hour trying to google this, and I always get the same page often titled "How is black body radiation produced?" that keeps on telling me what black body radiation does after it's radiated. I learned long ago about the basic equations used to describe the phenomenon or how to calculate the spectral lines, and I'm very familiar with how a spectrum with a graph on it looks. None of these answer my question. So Reddit please save me. is black body radiation actually produced on the quantum level? What mechanism takes place to generate the actual photon and what parts of the atom are involved, what are the specific quantum interactions, and which specific Fermions and Bosons are doing what in what way? What energies are involved? I realize this will have at least 3 different answers depending on the phase of the material, and that there is quite a bit of cross over with thermal radiation. Bonus: How do monatomic gases emit black body radiation in rare cases?
|
[
"For any object above absolute zero temperature, the component particles will have an energy distribution in which at least some of the particles are sitting above their lowest possible energy state (i.e. the Bose-Einstein distribution for bosons, and the Fermi-Dirac distribution for fermions). This means that some particles always have a possibility of transferring to a lower energy state, releasing a photon at a specific wavelength corresponding to the energy transition. At the same rate, other particles are thermally excited into higher energy states maintaining a constant energy distribution if the object is in thermal equilibrium. The resulting spectrum of emitted photons is dependent on the energy distribution which is a function of temperature and gives us ",
"Plank's Law",
" and black body radiation."
] |
[
"You only get discrete energy levels when you are talking about single atoms or molecules. Once you have a body consisting of more than a few atoms the electron orbitals overlap and you get a series of continuous energy bands. An \"ideal\" black body is said to be an \"ideal emitter,\" that is we assume that the distribution of states is continuous and uniform. In a real object of course this is not often the case and some state transitions may be preferable to others. This results in extra absorption or emission at certain frequencies and is the phenomenon responsible for ",
"spectral lines",
", which can be used by scientists to determine the composition of the body."
] |
[
"Sure, but the question is how do you get that kind of distribution? If we look at the most basic level, photon energies should only correspond to discrete energy transitions. So how do the wavelengths \"smear out\" like that?"
] |
[
"Does lotion actually \"protect\" your skin in any way?"
] |
[
false
] |
I've only ever used body lotion to make my skin non-ashy and soft, though some advertisements seem to push their lotion as some kind of therapeutic treatment. On that note, is there anything wrong with having dry skin in the first place?
|
[
"The active ingredient in most non-medicinal, non-sunscreen skin lotions is lanolin.\n",
"http://en.wikipedia.org/wiki/Lanolin",
"There is a ",
" amount of evidence that applying lanolin does help minor skin wounds heal somewhat faster. It is not well known how that occurs--if there is some chemical action upon the wound itself, or if the lanolin just keeps the skin more supple which prevents tearing the wound open as much. ",
"You can buy pure anhydrous lanolin online; there are sellers on eBay. The smell is rather,,, animal-like. But it does work well as a skin softener. It softens your skin better than petroleum jelly does. It doesn't leave your skin greasy like petroleum jelly does, but it does leave your skin \"waxy\". "
] |
[
"Very dry skin does break and crack. This isn't a problem for most young, healthy people, but it is a problem for some. For instance, in medical care, people are expected to wash their hands on the order of a hundred times a day, and that leads to some really really dry hands that crack and open. That hurts, and leads to increased risk of infection, and of course looks bad.",
"This is an easy thing to experiment with yourself-- just wash your hands every time you open a door for a week or so, without using lotion, then try it again for another week while using lotion.",
"In addition to protecting against dry skin, lotion protects against overly wet skin. Moisturized skin isn't really moist in terms of water-- it's moist in terms of oil. That blocks the passage of water through the skin, which protects against maceration. This is something that gets important when you're talking about people with fragile skin and/or problems like incontinence.",
"Commercials overstate the therapeutic value of lotions, though."
] |
[
"Does lotion actually \"protect\" your skin in any way? ",
"It really depends on what you mean by 'lotion' and 'protect'. Sunscreen lotion for example protects your skin from damaging ultra violet radiation but I don't know if you consider that a lotion. Calamine lotion is an antipiretic which helps with itching and prevents you from further irritating your skin by scratching but I don't know if you qualify that as \"protect\".",
"is there anything wrong with having dry skin in the first place?",
"Wrong isn't a very scientific term unless determining the validity of something. Having dry skin is often a symptom of an underlying problem and in itself can be painful and irritating if that answers your question."
] |
[
"This video is getting up voted in r/videos, but I'm pretty sure it's inaccurate and misleading in parts. Can someone confirm? (link in comment)"
] |
[
false
] |
Specifically when discussing a black hole's effect on time, as well as the center of the universe. A second opinion would be great as I'm not 100% on this myself.
|
[
"It's all pretty accurate. There are just a few slight technicalities that aren't quite correct. The only one that really stood out to me was when he talked about traveling ",
" the speed of light. What he described was traveling ",
" the speed of light (relative to the stuff around you). Nothing that has mass can travel at the speed of light. Equivalently, nothing that can travel less than the speed of light can be accelerated up to the speed of light. And there is no speed of light reference frame, so the question, \"What would it look like to travel ",
" the speed of light?\" is meaningless."
] |
[
"Actually this is pretty much all correct.",
"Gravitational Time Dilation",
"\n",
"Centre of the Universe",
" - This site actually has the same little toy he uses in the video to show how every point can see itself as the centre. See ",
"here",
" for a more complete explanation."
] |
[
"You're right to distrust infinities. Physicists don't really like them either. General relativity predicts that anything compressed to smaller than its Schwartzchild radius will collapse into a singularity, so a lot of physicists think the GR picture is incomplete. They consider this prediction to be a breakdown of the theory. This doesn't mean GR is wrong. GR is still very accurate in many other contexts (including the exterior of black holes). It just means that we need new physics to fully describe the interior of black holes. We don't know yet what that new physics is.",
"One could argue that since we can never actually observe a black hole singularity, this isn't a problem. All observable properties of black holes don't involve infinities, but I find this argument unsatisfying and I think many other physicists do as well."
] |
[
"[Mathematics] Why are we unable to express the antiderivatives of some functions e.g. (e^x)/x?"
] |
[
false
] |
I mean shouldn't we have developed some technique by now to express these functions since we can numerically solve them?
|
[
"Usually we want to write out antiderivatives as functions we know (e",
" , ln(x), x, sin(x), arcsin(x), etc.) as well as their sums, products, compositions, and other simple operations (where we only look for finite sums). The problem is that for some functions that is impossible, and I don't mean really hard, I mean that the resultant function is not expressible in such a form. You have to do numerics, or series expansions, or some other way to express the solution. ",
"In some cases we define new functions as being some integral or the solution to some equation (for example Bessel functions are solutions to Bessel's differential equation). If the closed form expression of that integral is somehow very important to you you can always defined blarg(x) = integral of e",
" /x dx and go on from there"
] |
[
"There is a theorem by Liouville showing that you can have functions without integrals that are a closed-form expression of elementary functions: ",
"https://en.wikipedia.org/wiki/Liouville%27s_theorem_(differential_algebra)",
"You are absolutely right that it relates to the unsolvability of the quintic, which is why the field of research that studies it is called \"differential Galois theory\": ",
"https://en.wikipedia.org/wiki/Differential_Galois_theory",
" (Galois theory having originally having applications in solvability for polynomials).",
"As for general theorems, I don't know the literature, I do know what someone in my department's logic group told me about them: the theorems are hard, and it's hard to come up with a good definition of an \"elementary function\"."
] |
[
"We can express it. It's Ei(x). What we can't do is express it in terms of a finite composition of elementary functions. It's (most likely) not that we don't know how. It's just that there is no finite composition of elementary functions that have that as a derivative. Sort of like there's no natural number that has zero as a successor."
] |
[
"Can large man-made structures be used as radio transmitters/antenna?"
] |
[
false
] |
[deleted]
|
[
"As long as they're conductive, sure. But they won't work well.",
"The first issue is that antennas only really work well for signals with about the same wavelength as their electrical size. Large structures will only really work well for very low frequencies. You need a ",
" of current to transmit low frequencies well. ",
"The other issue is that these buildings just aren't designed as antennas. They will be full of impedance mismatches, and you won't get power distributed uniformly through the structure. A lot of the signal will probably reflect back into the signal generator. Given the amount of current you'd need to drive a bridge as an antenna, for example, this will cause some damage."
] |
[
"It'll work if the structure is designed for it because then it's basically a really large antenna that doubles as a building. But you can't take an existing structure and expect it to work as a good antenna."
] |
[
"What if it were shaped to focus the signal to a receiver. Like could we use the Superdome to do Radio Astronomy if we add a collector at the 50 yard line?"
] |
[
"In quantum computing they talk about using atoms and molecules etc. to store information. Can these be of any element?"
] |
[
false
] |
For example, can one use a helium atom or boron atom or whatever to store the information on? Or am I completely missing the point here? My understanding of quantum theory is remedial at best, but this is one thing that I haven't been able to understand (among many other things concerning quantum theory).
|
[
"You certainly could, but you probably don't want to. I'll try to explain. Quantum computing uses the fact that quantum states can be superimposed. The most famous example of this idea is Young's double slit experiment. You've probably heard of it? Shine a light through two slits, and they will form an interference pattern on a screen. Which that isn't too odd, because waves interfere, and light acts like a wave. But only shoot one photon at a time, same pattern appears on the screen. (This is a really short explanation, I'm assuming you're familiar, if not check out ",
"this article",
" The reason the single photons still show an interference pattern is because of superposition. The photon's wavefunction becomes part \"passed through slit 1\" and part \"passed though slit 2.\" You'll hear a lot of people say \"the photon passed through both slits\" which isn't exactly true, but not a horrible layman explanation. ",
"Ok, so now we talked about superposition. That's how quantum computing works. You place some particle into a superposition, so that it is in a very complicated state, thus carrying more than 1 bit of information. The classic example is using a series of mirrors that have a 50% reflective probability, and then shining a photon into this system. It will go into a complicated superposition of \"reflected and not reflected\" according to how many mirrors you have. Then this single bit (1 photon) carries a lot more than 1 bit of information. ",
"In theory, quantum computers are easy, and we have actually developed many quantum algorithms and we're just waiting on the quantum computers to catch up. The problem is, particles only are in a superposition state until they interact with another particle. When that interaction takes place, the superposition collapses. This is why normally quantum computers try to use simple particles. The more complicated the particle, the more likely that it will interact, either with itself or something else. When that interaction happens, the quantum computation pre-maturely ends. ",
"So in theory yes, any particle could be used, because any particle could be put into a superposition. But normally scientists use simple particles to try to avoid wavefunction collapse. This is also the most modern part of quantum computing, attempting to find an acceptable ",
"qubit",
": stable arrangements which do not easily collapse. "
] |
[
"No. While I agree that you could argue that a \"bit\" is conceptual object, as a piece of information, it inarguably has very physical basis: a transistor. The physical properties of the transistor store the information (via where most of the electrons are located).\nA qubit is conceptual in the exact same sense, and it is also physical in the exact same sense. The information is stored in the quantum state of a physical atom."
] |
[
"No. While I agree that you could argue that a \"bit\" is conceptual object, as a piece of information, it inarguably has very physical basis: a transistor. The physical properties of the transistor store the information (via where most of the electrons are located).\nA qubit is conceptual in the exact same sense, and it is also physical in the exact same sense. The information is stored in the quantum state of a physical atom."
] |
[
"Where does your mind/memories go when you’re blacked out drunk?"
] |
[
false
] |
Are there subconscious ways to get these memories back? What actually happens to them? Or is it like a recording device that just stops and you’ll never see them again?
|
[
"It's long ",
"been demonstrated",
" that alcohol suppresses long-term potentiation in the hippocampus, one of the crucial areas for memory formation. ",
"Memory requires protein synthesis among an engram of neurons in order to be properly 'stored'. Alcohol prevents this from occuring. ",
"So in the context of your example, the recording is stopped in the long-term memory area.",
"If a friend describes what happened when you were in that state it is possible that you believe you are recovering the true memory but instead may be forming a false memory of the event. This is a widely acknowledged phenomenon (see Elizabeth Loftus)."
] |
[
"to add to that, the physiology is basically that in order to form these memories you need glutamate to react to its receptors. When you're really drunk, the ethanol binds to glutamate receptors and prevents glutamate from eliciting a typical response, that being allowing an influx of sodium and later calcium ions into the neuron (which after enough repetition and added stimulation would, under normal circumstances, alter gene expression to produce more of these receptors and cause what is known as long term potentiation), so the signal is not induced to a strong enough degree as to cause the epigenetic change which would in turn create a long term memory.",
"That is in part what also causes the euphoria like feeling when you're drunk, because glutamate's effect is enhanced by dopamine (part of the reward feedback, the feel good molecule makes memories of successful actions become a memory easier), but since the effect of glutamate is blocked, the dopaminergic neurons around try to compensate the lack of response by producing more dopamine, which basically in this case adds nothing in the memory formation department, so all you get is temporary happiness"
] |
[
"They are in the short term memory (as you can see when someone absolutely smashed will be very stubborn about some things \"lets go to Dan!\") but they dont go to long term memory. So you can function in a moment but you wont remember it the next day. The same way we dont remember the moment we fall asleep."
] |
[
"Does hand sanitizer work? Is it as good as washing your hands?"
] |
[
false
] |
[deleted]
|
[
"To some degree. They often contain an antiseptic like triclosan, and bacteria can become resistant to that. However, they're almost always alcohol-based, and alcohol is the microbial equivalent of a flamethrower. Stuff is going to die, and resistance doesn't matter much."
] |
[
"Related: if it is indeed antibacterial, doesn't it increase the risk of breeding multiresistant bacteria?"
] |
[
"Your intuition (which is incorrect) doesn't count as scientific evidence and is inappropriate in the askscience subreddit. "
] |
[
"Can a civilization exist within the event horizon of a black hole?"
] |
[
false
] |
I'm picturing a civilization that wants to escape from some enemy and buries their cities directly under the event horizon where they can live in peace forever. If the black hole is massive enough, tidal forces wouldn't be a problem, correct? Could they maintain their orbit?
|
[
"No. By the clock of people falling into the black hole, it takes less than a few hours (and often a second or less) to fall into the singularity. That's unavoidable. If they fired their rocket engines to try to slow their decent, they'd only arrive at the singularity faster. ",
"They would die from spaghettification (torn apart by tidal forces) well before that, but they definitely couldn't hang out there \"forever\""
] |
[
"No. Once inside the event horizon, everything inevitably heads towards the center. The event horizon can be thought of as the point of no return, and interior to this shell all paths forward in time go inwards."
] |
[
"not really. How do you have particle interactions when ",
" paths point towards the center of the black hole? (referring to abiogenesis at least) As for the big bang, I'm under the firm impression that the answer is no, but I'm not well enough versed on the explanation to give it here."
] |
[
"What did I do wrong in this Schwarzschild radius equation?"
] |
[
false
] | null |
[
"G has units m",
"/(kg s",
")",
"That's all"
] |
[
"Oh that easy... much thanks stranger"
] |
[
"More than welcome :)"
] |
[
"Can someone please provide a scientific argument why the intro to \"Idiocracy\" will not come true... I'm worried"
] |
[
false
] | null |
[
"Selection for/against intelligence takes thousands of years - supposedly you could take a human from 50,000 years ago and train him to be a fighter pilot. In the end we're all pretty much genetically the same. I've seen some of the most intelligent, hardworking people come out of the \"trailer park\" background shown in that video, and seen the most incompetent people come from \"educated\" families. I know several brilliant research scientists born in 3rd world countries. There are so many humans and genes are shuffled so much that it's really hard to say which way we're heading. There may be limits to what a brain is capable of achieving, regardless of background, and we may be there. Or the genes from the trailer park family may contribute to some grand combination of humanity that leads us to the next stage in evolution. ",
"Intelligence is also nurture, meaning food, vitamins, proper education, technology, the ability of farmers to support education so I don't have to look far for my next meal (and can instead focus on learning), lack of constant war, and much more. I like to imagine there were farmers 1500 years ago as intelligent as Einstein, but they just didn't have the tools or opportunity. It's sad really when you think about how many Einsteins we've probably lost.",
"I guess I don't have a concrete answer, but we're all really the same, regardless of education or outside appearances, and the differences you see are so minor and get shuffled so much that it's hard for much change in our intelligence level to really occur. You're talking about hundreds of thousands of years and generations. Humanity as a whole will likely continue to have selective pressure towards intelligence, or else we will die off. We have some big problems facing us (food, diseases, asteroids) that will require well-educated individuals to overcome. "
] |
[
"I believe the examples you point out have nothing to do with evolutionary effects upon intelligence. The widespread propagation of certain concepts, such as evolution and heliocentrism, was mainly due to advancements in science and economy that enabled more people to be educated. The only reason \"intelligence\" is moving forward is because of the push towards universal education. I do think that a situation such as the one presented in Idiocracy could occur in a short period of time (less than 1,000 years) if the emphasis on education were lost. Intelligence is mostly a nurture thing, not nature. ",
"Here's an example: ",
"If a poor family that doesn't put an emphasis on education has many children, those children are likely to be less educated than the children of a small family which stresses the importance of education. As a result, the majority of the new offspring will lack education, and it is likely that they won't put any emphasis on education (possibly due to financial reasons) while also having large families. If this process continues, it's pretty easy to see how a system similar to the one in Idiocracy could arise. While intelligence is not being biologically inherited, it is being passed on indirectly due to socio-economic situations. I'm not saying it will happen, but it is possible. Because of the emphasis we place on education in modern society, I seriously doubt anything of the sort will occur in the near future."
] |
[
"Here's how I see it. Some of this is supported, some isn't.",
"Because it confuses poverty and intelligence. Poor people do breed more, but poor people are not stupid. Usually poor people are poor because their parents are poor. Making a between group comparison is unfair. Making a within group comparison on the other hand, makes sense. Within groups we find the people who are breeding are those that are charismatic, have money, and have traits that indicate stability. Does your poor catholic half cousin twice removed have twelve kids? Yes, but he is also probably a pillar of the community, has a stable job, a house, and a wife. Another note is, religious people, like poor people, are not stupid by default. Making this assumption is silly.",
"The second major point is intelligence is not all that genetic. (or rather we don't know how genetic it is) In middle class families they might cite that it is 50 percent heritable, but that is ONLY in a limited very specific context. To say that this incredibly complex trait is somehow being selected for or against, is difficult or impossible to say in current society. It is also worth noting, people below a 50 IQ(which is a terrible measure) aren't reproducing much. As AmericanChE and bobzor said below, other factors are much more important. ",
"Also AmericanChE is absolutely right in his assessment, education/nutrition/etc is really pushing us forward much more rapidly than a rate than evolution could ever work out, the curve is moving forward.",
"Tl;Dr The movie relies on classist assumptions combined with a loose understanding of evolution. The growth of education/nutrition/lack of wars well outpaces any almost impossible to perceive genetic shift in 500 or 50000 years."
] |
[
"Has \"Feeling the future\" been debunked?"
] |
[
false
] |
Daryl Bem's paper on precognition made a lot of news when it was published last fall. Is anyone taking it seriously and/or trying to replicate the experiments?
|
[
"Yes",
", it has. ",
"And no, nobody takes that stuff seriously. Per Google Scholar, only other articles citing it as of yet besides that critique are from non-reputable woo journals such as the now-defunct Journal of Cosmology."
] |
[
"Yes. Replication attempted and failed."
] |
[
"At least ",
"one replication has been attempted",
", and it failed to show any statistically significant results whatsoever.",
"As far as I know, the consensus is that Bem's results were due to a ",
"fundamental misunderstanding of statistics",
". [PDF] (See also: ",
"this recent XKCD comic",
".)"
] |
[
"Are the skeletal formulas of chemicals depicted on Wikipedia accurate? I'm in desperate need of your help /r/askscience!"
] |
[
false
] |
I'm working on a digital painting for a friend that incorporates the skeletal formulas of Seratonin, Dopamine, and Acetylcholine. I plan on getting it printed and framed to give to her as a gift but I would hate to display anything improperly since she's studying bio and chem and such and error would stick out like a sore thumb to her. I'm not a science buff by any means and am wary of wikipedia. Can I trust the pictures of skeletal formulas that are posted there? Anything I should bare in mind when making this digital painting? I want it to be as accurate as it is aesthetically pleasing and I can't ask her about it without raising suspicion. Please help! Thank you in advance!
|
[
"Yes, Wikipedia is accurate in chemical formulae and structures."
] |
[
"Thank you so much!"
] |
[
"For these three examples, yes it is (I just checked :).",
"For 99% of them I would say, but there are bound to be a small percentage that are wrong, due to errors in the sources used.",
"As a minor point, the methyl groups on acetylcholine might be better if they were explicit and not implicit. What I mean by explicit is having \"N-CH3\" and not just a line coming out of the N. It's a little clearer for terminal groups like this. edit : Oh, and the \"NH\" in the Seratonin ring could look better as \"N-H\".",
"Another aesthetic choice is whether the 6-membered rings in Seratonin and Dopamine should have circles in the middle or not. Sometimes images like this:",
"http://en.wikipedia.org/wiki/File:Benzene_circle.svg",
"are used to indicate that the double bonds are delocalised (spread out) around the ring."
] |
[
"Why is it that, on long highway drives, sometimes a patch of road ahead seems to take on a mirror-like quality, but this shiny mirror effect disappears once I get closer to the patch?"
] |
[
false
] |
Hi, I did a quick search and it doesn't seem like this question's been asked before. I just finished a 7 hour drive in the northeastern U.S. and I noticed that at some points in the road (especially when going down a big hill) that patches of the road farther up would start to reflect the cars up ahead or seem to shine. Sometimes you see this effect in movies where they film a road in the desert. I was just wondering what this is, I'm guessing that maybe it has to do with the physical makeup of the asphalt and the effect of the sun shining on it, however I'd appreciate a more specific answer. I've been reading askscience for a while now, there's a lot of interesting topics on here. This is my first question. Thanks!
|
[
"This called a highway mirage and basically a fata morgana.",
"The road is hot and so is the air close to the road, and it is a lot hotter than the air a couple meters above the street, so you have a temperature gradient. The diffraction index of air depends on the temperature, and just like a light ray has a \"kink\" when going from air into water, it is also bent here. But it is bent smoothly due to the smooth transition from a higher to a lower diffraction index. So the light ray reflected from a car roof is bent in such a way that it hits your eye from an angle, making it look like it came from under the car, effectively creating a mirror image. That's why the street looks like it is wet or something. When you come closer, the temperature gradient is not strong enough for the light ray to bend all the way.",
"This picture",
" should clear it up a little."
] |
[
"The road heats the air above it. The temperature gradient causes light to bend (like a prism), and light from above the road is bent as though it were coming from the road. This creates the illusion of reflection."
] |
[
"It's called a mirage. [Wikipedi](",
"www.wikipedia.org/wiki/Mirage",
") has a good article about them. "
] |
[
"Do electrons travel through spherical nodes or do they just appear in the next ring?"
] |
[
false
] |
My chemistry teacher was taking about spherical nodes in an atom and how they are certain places where electrons just don't go. But to jump to the next shell, don't they have travel through the node?or do they literally teleport from one shell to the next?
|
[
"This is a really neat question! Let me address it in two ways, first let's consider the hydrogen atom which only has one electron. Here is ",
"what the probability densities look like",
". Interestingly enough you can see those \"nodes\" where the electron cannot be found. To see them explicitly, let's only plot the ",
"radial probability distribution",
" (r = distance from proton). Explicitly you can see these nodes where the probability distribution goes to zero on the graph.",
" ",
"Fundamentally, this is a great mystery. Our best explanation is that quantum objects such as electrons do not have true classical trajectories (a distinct position and momentum). You cannot follow an electron as it moves around in the same way you could with a thrown baseball. We say the electron behaves quantum mechanically which has aspects of both waves and particles, but is truly neither itself. All we know is there is a chance of finding the electron on either side of the node, but never on the node itself and we can never \"catch\" the electron in the act of crossing the node because electrons do not have trajectories so it doesn't make sense that the electron has to cross it.",
"The second aspect of your question is how electrons jump from one orbital to another like when the atom absorbs or emits a photon. Again there is no precise trajectory. You might then ask does the wave function \"morph\" from one orbital to another. Even this isn't so clear cut as transition itself behaves quantum mechanically as a probability."
] |
[
"That means that our intuition that even the smallest particles behave like small solid ball that follow deterministic trajectories, i.e. follow Newtons law of motion, does not work anymore.",
"But we do have an understanding of how the particles then behave - quantum mechanics describes this. But this of course depends on what \"understanding\" really means: We have a mathematical theory that can be used to predict measurements and observations, but is it other than a theory? Can we put \"meaning\" to the mathematical entities and find a deeper description? Maybe, maybe not... There has been made many attempts at interpreting quantum mechanics that there is a whole ",
"wikipedia article about it",
", but it is hard if not impossible to scientifically prove that one interpretation is better than the other. Thus we might just drop the whole interpretation and the search for an intuitive meaning and just use the theory as a tool for prediction - a.k.a. ",
"\"shut up and calculate\"",
"tl;dr: Our classical Newton mechanics break down our understanding is still fine, in that we have theory that can be used for predictions."
] |
[
"A fascinating and clear explanation. Does this mean that our concepts for understanding things break down or are no longer any use at this level of 'fineness'?"
] |
[
"Would clothes dry faster in a cold, dry climate or a hot, humid climate?"
] |
[
false
] |
I know that in a cold dry climate the air is less saturated with water but being cold has less capacity to hold moisture and vice-versa for a hot humid climate. This is ignoring other factors, such as wind and seasonal weather patterns, etc.
|
[
"It is not possible to answer without more specific information. In general, the rate of evaporation is proportional to two factors:",
"A) wind speed: the faster the wind blows, the more quickly the micro-layer of air against the clothes is swept away and replaced by drier air. ",
"B) The difference between the actual humidity of the air and the saturation humidity. Here's a ",
"graph of saturation humidity as a function of temperature",
". You can see that at equilibrium, warmer air is capable of holding quite a bit more water vapor than cold air - but it's not a linear function. What is important for evaporation is how much much moisture is already in the surrounding air. If the air is already saturated with water vapor for it's given temperature, you're not going to get any evaporation. The rate of evaporation is going to be proportional to the 'saturation deficit' of the air. If the air is really dry than you get lots of evaporation. ",
"The difference between how much water an air parcel can hold and it's dew point can also be expressed as ",
"relative humidity",
". If the relative humidity is 100% the air is already saturated and clothes will dry slow. If your Hot, Humid climate is always near 100% humidity than clothes dry slow and it is likely that the clothes would dry more quickly in cold,dry case. But warm air with a relatively humidity of 90% (which still feels very muggy) can potentially hold more additional water than cold cold air with 50% humidity. Because the non-linearity of the dew point, an exact answer really depends on the specific humidity numbers and relative temperatures.",
"And you can't really think about the problem without also considering the wind. Without some air movement, even a dry climate will dry the clothes slowly because the air immediately surrounding the clothes becomes saturated as the water evaporates. You need at least some air movement to sweep away this saturated air and replace it with the lower humidity air."
] |
[
"ASD certified technician (I dry buildings) confirming. ",
"I live in a cold, dry climate. We use heat exchangers to, basically, warm up the cold, dry air outside and vent a building that has suffered a water damage. Air movement, though, is extremely important. As a material dries there is a layer of 100% RH sitting just above it. Without air movement, no more drying occurs. "
] |
[
"Depends where you live. If your air is generally low in humidity, airflow alone is effective. However, if you live in a muggy climate, you need the heat. Heating the air is a very effective way to lower its relative humidity. If you heat a parcel of air, the total amount of water vapor in the air stays the same, but you ",
"drastically increase it's saturation value",
" (the total amount of moisture the air could hold) so you end up decreasing it's relative humidity and make it more efficient for drying clothes."
] |
[
"Is there a scientific reason they ask you not to use flash on your camera when taking photos centuries old interiors or artifacts?"
] |
[
false
] | null |
[
"The concern is that the brief-but-intense light may damage artworks and artifacts.",
"The spectrum of flashlamp light is typically bluer than indoor illumination in galleries, and xenon flashlamps also emit a certain amount of ultraviolet (though this is very nearly always filtered out from camera flashes.)",
"In practice, this seems to be more of a precautionary-principle measure, than anything supported by data. A study back in 1995 looked at this issue and found the effect of flash on pigments was essentially negligible. I can't locate the original paper's text, but ",
"here's a report discussing its findings",
".",
"That said, regardless of any effect on the artworks there's still one very good reason that flash photograph is - and should forever remain - banned in most galleries. It's ",
". People trying to look at art don't want random, intermittent, blindingly bright flashes of light interrupting their viewing experience, or burning little purple afterimages onto their retinas."
] |
[
"That's certainly a possibility.",
"Additionally, the old-style flashbulbs were a potential source of hot shrapnel. While the glass bulbs were typically plastic-coated to contain failures, I can certainly see a museum curator saying \"",
" ",
" ",
"\""
] |
[
"I wonder if the old magnesium flashes were capable of more damage, like unfiltered UV? And it's just been carried over without really being questioned? Although not being annoying seems reason enough, so maybe that's irrelevant."
] |
[
"Is there any evidence to show if humans developed cognitively as a response to not developing our 5 senses as well as other animals did, or vice versa?"
] |
[
false
] |
In other words, did we(humans) get smart because we didn't see/hear/smell as well as other animals did? Or did our intelligence allowed us to stop relying on just our senses to survive?
|
[
"It's true, we can see better (in some ways) than many animals, but we are significantly less advanced in many ways. Most of our advantages (dexterous fingers, good color vision, tall stance and long reaching arms) play into our intelligence. ie all of those things would be useless if we weren't intelligent. We aren't very fast or agile or strong. We don't have natural defences such as sharp teeth, claws, spikes, thick fur, poison, or threatening colors. As op said, our senses are not up to par with many other animals. Really the only sense we are any good at is color vision. We don't even have almost any instinctual abilities - we learn everything rediculously slowly. So op's question stands, did we become intelligent to counter the poor hand we were dealt by evolution, or did we get lucky with the intelligence and stop relying on our other advantages?"
] |
[
"Humans aren't too fast, but we are exceptional distance runners. That, combined with good color vision, did play very well into the particular hunting style we used to use. And evolution doesn't deal \"poor hands.\" A species either adapts pretty well to the particular type of life it leads, or it dies out. No species gets stuck being sub-optimal for long periods of time. There are a lot of animals that are faster and have natural defenses like big teeth and claws. But just because we don't have that doesn't mean we're inferior. Your problem is you're trying to compare humans to other animals on their terms. We don't have giant teeth and claws like lions because we don't live like lions. Any group of humans who did, for whatever reason, start to develop large teeth and claws and begin to modify their hunting style to match would actually likely be at a huge disadvantage because now they're directly competing with another species that has spent millions of years evolving to that lifestyle."
] |
[
"I think you are missunderstanding my post, and I admit it is a little badly explained. What I meant is that the particular niche that we fill is the intelligent one, and our abilities aren't very useful without the intelligence compared to the other animals we would have to compete with for food. So the question is, did our intelligence enable us to enter that niche, or were we doomed die out as you say and managed to develop on intelligence side in order to prevent that?"
] |
[
"Is copper conductive in gas form?"
] |
[
false
] |
If you had copper gas contained in a vacuum, could it conduct electricity and if so would it glow like neon? What color?
|
[
"Not in gas form, but as plasma it can. (Same goes for neon)",
"Lamps using sodium (pure yellow) and mercury (bluish white) metal vapor are the most common kind of electric lights these days, they're used in fluorescent lights and street lights.",
"There's usually some argon in there, which initially gets ionized to a plasma and then heats up the metal, which also starts to excite/ionize and glow.",
"Copper lamps aren't made often or used for much except as somewhat obsolete light sources for chemical analysis. The light from the copper is greenish."
] |
[
"You are correct that Cu gas won't be conductive, however you have a lot of errors in your answer.",
"1) Cu and all pure metals are crystalline. Cu has a ",
"face centered cubic crystal structure",
". Metals are not like a pudding, they are very ordered, however the electrons are delocalized and have high mobility.",
"2) I think by crystalline you meant ionic bonding, such as salt NaCl. Ionic solids are generally bad conductors, but the better explanation is because the ions are localized and cannot move. Salt is a great conductor in the molten state.",
"3) Covalent bonded solids can also be crystalline (diamond, graphite) or amorphous (window glass). The conductivity will depend completely on the type of bonding. For example ",
"diamond",
" is crystalline and the carbon atoms are SP3-hybridized so they each make 4 strong covalent bonds with other carbon atoms. ",
"graphite",
" is also crystalline with the (Hexagonal dihexagonal)[",
"http://webmineral.com/crystal/Hexagonal-DihexagonalDipyramidal.shtml#.VapODovDrwM",
"] crystal structure. It however is SP2 hybridized and is a good conductor because of electron delocalization in each carbon layer. "
] |
[
"Yes, in both cases it is caused by excited electrons falling back down into lower-energy states, so you should get the same spectrum from a copper flame or a copper gas discharge lamp. The only difference is the method of excitation, chemical reactions in the flame, and electric current in the lamp."
] |
[
"Is there a fixed amount of water on Earth?"
] |
[
false
] |
I'm a thousand years out of school, but have it in my head that water doesn't ever really go away...it just changes form: evaporating to vapor, freezing to ice, or existing as liquid. So is there a finite, unchanging amount of H2O, or does the molecule ever break down, and new H2O is created from elements? And if the latter is the case, what dictates that creation, and what regulates how much is created? And are those FORMER oxygen and hydrogen atoms, freed from their duties in water, then free to become part of other molecules? (head hurts now)
|
[
"I'm inclined to respectfully disagree. It's not a vast amount, but there is \"atmospheric escape\" of hydrogen one of the components of water. There are geological processes bring water up through igneous rock formation. You could state we have an initial amount of the elements of water from the start of planet formation but continually are decreasing our supply of the hydrogen components. Some of it is reincorporated into the earth through subduction of oceanic crust. In addition there is the water cycle that also re-incorporates vapor back into water.",
"Meteorites would not bring in a significant amount of ice H2O except for massive ones that only have about 50-100 confirmed impact sites over massive lengths of time.",
"All that said we won't be running out of water for a very very long time. Now whether that water is potable or not is another question.",
"--edit\nstill new to reddit and may have replied to the wrong comment - sorry if that is the case."
] |
[
"I'm inclined to respectfully disagree. It's not a vast amount, but there is \"atmospheric escape\" of hydrogen one of the components of water. There are geological processes bring water up through igneous rock formation. You could state we have an initial amount of the elements of water from the start of planet formation but continually are decreasing our supply of the hydrogen components. Some of it is reincorporated into the earth through subduction of oceanic crust. In addition there is the water cycle that also re-incorporates vapor back into water.",
"Meteorites would not bring in a significant amount of ice H2O except for massive ones that only have about 50-100 confirmed impact sites over massive lengths of time.",
"All that said we won't be running out of water for a very very long time. Now whether that water is potable or not is another question.",
"--edit\nstill new to reddit and may have replied to the wrong comment - sorry if that is the case."
] |
[
"No, but the amount doesn't really change by a significant amount, given the amount of water in the Earth. The matter and atoms remain the same, but there are reactions that change it. Eg: ",
"Photosynthesis: 2n CO2 + 2n H2O + photons -> 2(CH2O)n + 2n O2",
"Hydrocarbon combustion: CH4 + 2O2 -> CO2 + 2H2O",
"EDIT: \nSource: Took formulas from the respective wiki articles"
] |
[
"How come Apollo astronauts took 3 days to get to the Moon, when it only takes SpaceX a few hours to get 1/4 of the way there?"
] |
[
false
] |
According to , SpaceX carried Thaicom 6 to geostationary orbit in a matter of hours. How come it took so long for Apollo to get to the Moon, and will it take that long again for future manned missions? I would have thought that less exposure to radiation on a quicker journey would be more ideal? *Thanks for all of the great answers!
|
[
"For that matter, New horizons is taking advantage of this for the trip to Pluto as well. If it was trying to get into Plutonian orbit, it'd have to be going much slower at the target destination, and it would've taken probably 80 years to get to Pluto, not 9 years. Instead, it's just doing a flyby."
] |
[
"For that matter, New horizons is taking advantage of this for the trip to Pluto as well. If it was trying to get into Plutonian orbit, it'd have to be going much slower at the target destination, and it would've taken probably 80 years to get to Pluto, not 9 years. Instead, it's just doing a flyby."
] |
[
"Excellently described here",
"The Tyranny of the Rocket Equation",
".",
"To wit: every extra pound of payload you have to bring with you requires more fuel. Every extra pound of fuel you bring requires more fuel as well. The only thing saving it from recursing indefinitely is that the fuel does at least get used up, causing the total weight to drop."
] |
[
"How do computers keep track of time?"
] |
[
false
] |
[deleted]
|
[
"Somewhere in your computer there's an oscillator circuit, which produces a clock signal at a fairly accurate and specific frequency. This might be 32768 Hz, allowing it to be divided by 2",
" to produce a clock tick every 1 second. ",
"In olden times, we used to be asked to tell the computer the wall clock time every time we powered up a PC. Then later a battery was added to most PCs to allow the oscillator to keep running and keep track of time even when the rest of the PC was shut off. Nowadays, most PCs will just get the time from a server on the internet (using some clever tricks to account for the delay in sending the time through the network) occasionally to keep their clocks synchronized with the rest of the world."
] |
[
"Even PC's probably still have a battery to maintain the clock and CMOS settings. But the clock might not be very accurate (since less accurate oscillators can be cheaper) so there's still a reason to update from the internet occasionally."
] |
[
"If you're talking about a modern computer (anything made within the last 20 years), they all have a quartz clock inside them. Without internet access they will all keep time to within a few seconds per day. Desktops and laptops have a tiny watch battery to keep it running, cell phones might just use a super capacitor instead of a battery to keep it running when you switch batteries (not too sure, but I know they don't have a second battery)."
] |
[
"Does the human body prioritize the healing of different wounds by severity?"
] |
[
false
] |
Say you were in a severe accident and you suffer several serious injuries. Would your body invest more resources in healing the most life threatening wound first? Thanks!
|
[
"Nope, Your body systems tend to work independent of each other. The cells around each wound have no idea that there is damage elsewhere in the body, they just each do their thing."
] |
[
"Wounds closer to the heart tend to be healed faster anyway as the blood supply to them is much greater than to extremities like the foot. That's why you get issues with diabetics who need foot amputations due to lack of blood supply in their legs. "
] |
[
"Could there be an effect similiar to hypothermia, so that blood circulation is restricted to the core, and therefore wounds closer to the core are healed quicker, while blood loss through the extremeties is reduced?"
] |
[
"By what mechanism does Energy become Matter?"
] |
[
false
] |
I know that technically the answer to this question is "pair production". I'm hoping for a somewhat deeper answer. Does anyone know why matter spontaneously appears when the local energy density gets high enough? Is there a way to somehow prevent matter from forming in high energy density areas? Or is it all simply treated as a "black box" right now?
|
[
"From the viewpoint of quantum field theory, all energy has to be in some form, i.e. the excitations of some field, it cannot be \"just energy\". For example, I could have light, or excitations of the photon field, or electrons, which are excitations of the electron field. Some excitations are massive, some are not.",
"Maybe you can say something a little deeper about special relativity itself. For any system of particles, E",
" = m",
" c",
" + p",
" c",
" , where E is the total energy of all particles in a system, p is the total momentum, m is the total mass, and c is the speed of light. So if you have a system comprising two photons moving towards one another, the system will have some nonzero mass. You can calculate this total mass by adding up the energies and momentum vectors of the photons in the above equation. If that total mass is more than twice that of an electron, the photons can pair produce if they collide.",
"You could also imagine something like a beach ball with a perfectly reflecting interior. If I put photons in the beach ball, they will just bounce around inside. According to Einstein's equation, the system of the beach ball and photons will have more energy than just the beach ball, and if the total momentum is zero, then it must have more mass. So if you had this special beach ball, and then filled it with a lot of light, its mass would increase and it would be harder to push it around."
] |
[
"Just hijacking this to ask a question which is bugging me.. is a positive weak charge on a w boson (W",
" equivalent to a positive charge on a positron? Is the difference simply the mass of the carrier, and the force essentially the same? Or does the spontaneous symmetry breaking split two forces which aren't equivalent but would be indistinguishable except for the mass of their carriers, which makes one extremely short range and the other longer range? ",
"If you get a chance to answer, thanks :)"
] |
[
"The W+ boson has a standard electric charge of +1, which is exactly the same as the positron. The mass is of course much greater.",
"It also has a weak isospin number of +1. This is a completely different number. For example, a down quark has electric charge -1/3, and weak isospin -1/2. It can absorb a W+ and become an up quark with electric charge +2/3 and weak isospin +1/2. Both numbers are conserved.",
"Not sure if there was some confusion, but the photon described as the \"carrier\" of the electromagnetic interaction, and the positron is influenced by it as it has an electric charge.",
"Or does the spontaneous symmetry breaking split two forces which aren't equivalent but would be indistinguishable except for the mass of their carriers, which makes one extremely short range and the other longer range?",
"Kinda sorta yes :) Before symmetry breaking, there are two interactions, one mediated by the B",
" boson, and another mediated by the W",
" , W",
" , and W",
" bosons. These are all massless and therefore effectively long range. They all get scrambled together by spontaneous symmetry breaking to form the W",
" , Z",
" , and photon, all with the peculiar charge and mass values."
] |
[
"Will patients in a clinical mRNA HIV vaccine trial show up as HIV positive in testing?"
] |
[
false
] | null |
[
"There is a potential risk they test positive on antibody tests (depending on the antigen being produced by the vaccine). But the more accurate test for HIV is similar to what we use for COVID, nucleic acid testing, or PCR for those of us with some molecular biology experience. They will only test positive with PCR if the test targets a sequence contained by the vaccine, and only for the few days the mRNA will remain for, since all RNAs inevitably degrade."
] |
[
"I'll add a bit to the previous answer. I work in a COVID lab inside a hospital, but know more about the process of HIV testing in hospital settings. There are a lot of rapid antibody tests (take less than 30 minutes) that we use for something called the \"needlestick protocol\". We use a rapid test as a screening measure. This test is fairly accurate, but isn't 100% reliable. One thing the previous response got wrong is how hospitals test for HIV. The standard method is called an immunoassay. I won't bore you with details, but the patient's serum tested for the presence of HIV antibodies through the addition of an antibody directed at HIV antibodies. Then something else is added (usually a secondary antibody that produces a color when attached to the first antibody). The specimen is washed several times and the color is measured. If color is detected the assay is positive for the presence of HIV antibodies. The specimen is then sent for confirmation testing by looking for certain pieces of the HIV virus. This is generally where PCR comes into the equation. If you have access to real time PCR, you can also quantify the virus in the specimen and produce a HIV viral load (which is monitored through treatment to access when drug changes are required)."
] |
[
"Further question:",
"Isn't that what happened with the covid vaxx that was being developed in aus, they used some HIV proteins but it was then causing those HIV antibodies to be produced, making the HIV tests flag as positive or something? Do I have that right."
] |
[
"Can animals that are typically skittish in the wild be bred in captivity to not mind human interaction?"
] |
[
false
] |
Shrimp, fish, what have you. And I mean through generations of breeding, the animal's line loses its tendency to flee. Thanks!
|
[
"Absolutely! This is actually a pretty common practice in animal research with things like mice. If you breed a generation of mice, and then pick the ones that have a natural tendancy for being more tame than their litter mates and continue to breed them, you have a higher likelihood, assuming the tameness is a partly genetic feature, to then have tame offspring. So then you do the same thing over and over and over again and your likelihood of having tame offspring gets really really high.",
"If you work in an animal research facility (mice in my case), you might work with different strains of mice, all of which have different phenotypes that they have been bread for. For example, c57-black6 mice are known for being particularly skittish and aggressive, but other strains tend to be calmer and more amiable to handling by humans.",
"This strategy gets applied to a lot of behavioral research, actually. There are lines of mice/rats/etc that are bred for traits like high anxiety or high alcohol consumption, and all that was done to generate these animals is selective breeding over many many generations.",
"We've actually known this for quite a while. Here is a really old genetics article regarding breeding tameness/wildness in mice.",
"http://www.genetics.org/content/17/3/296.full.pdf"
] |
[
"There was a project in the USSR that dealt with this very question using ",
"selective breeding of foxes",
". it seems that the primary difference is that the domesticated variety has less adrenaline production so a milder fight-or-flight response."
] |
[
"This can happen in a generation or so which individual families of animals. Antelope are a good example of this. They are extremely flighty, but hand raised antelope are much more manageable and their offspring even more so. I don't know of any truly domesticated antelope but there are plenty of tame ones that will eat out of your hand."
] |
[
"Really interested in getting a degree in biology, but not sure about it. Any advice?"
] |
[
false
] | null |
[
"i LOVE biology. I'm continuing my education so I never went looking for a job with just the BSc but my friends didn't have much problem, and if you go for your MSc it opens up even more doors. ",
"Most people think biology is the \"easy\" science. My degree has been a lot of sleepless nights and lack of eating. I know a lot of people who ended up dropping out. Make sure your very committed and love learning before doing a 4yr program. If you are to learn anything though, biology is super useful for daily life. I do not regret a single moment I put into my degree. ",
"What you do on a daily basis will depend on the field of biology you choose. Being an ecologist is a lot different from a neuroscientist. It would be best to pick a specific field in biology, then ask what they do on a daily basis.",
"I have no information about Marine biology. Maybe another redditor will be able to answer that one. Either way, best of luck with your choice! "
] |
[
"See that's the thing, I have noooooo idea what I'd want to specialize in. There's so many things to choose from!\nI'm actually glad that it takes a lot of work to stay in school. That means I'll actually be engaged. I dont like getting bored of my studies but with biology there's so much to learn and discover. \nThanks for the tips:)"
] |
[
"I went into school wanting to study general biology. I fell in love with cellular & molecular biology. It completely changed how I think of life"
] |
[
"How is mimicry in plant reproduction successful?"
] |
[
false
] |
In my ecology class we learned that some plants will use mimicry to get pollinators to visit them because they look like other plants, yet they offer no reward (nectar). In order for mimicry to be successful, there must be fewer mimics than the plants they are mimicking. My question is this: If these plants are using mimicry to bring pollinators to them, how do they ensure that the pollinators go to other mimics instead of the plants they are mimicking?
|
[
"Lets say you have bumblebee as a pollinator, this bumblebee will visit a few thousand (varies a lot) flowers a day. If they have no preference between the mimic or the original they will obviously visit both and not only the originals in one of the many following visits. "
] |
[
"It is more like a random picking (from the pollinator). The amount of energy needed to pick exclusively the plants with rewards and not the mimickers would be greater than just doing a random selection and take the losses when they do not get the correct plant. The competition between organisms is what drives evolution, so your point is right. The mimickers have to be fewer than the original plants otherwise both the pollinator and the original plant would be driven out of the ecosystem. "
] |
[
" Deceiving flowers reach an equilibrium point within a population of flowers where there are enough flowers to keep the trait reproducing, but not too much to avoid getting considered by pollinators as not-worthy flowers to scavenge.",
"Phenomenons like this are studied under the ",
"game theory approach",
". So, to understand more this problem, I will explain some things about game theory.",
"Game theory states that any endeavor with different payoffs and participants can be viewed as \"a game\", with rules and strategies. The most fundamental scenario is explained in the \"Prisoner's Dilemma\", which derives in the \"Nash Equilibrium\". Here's a video showing & explaining ",
"how Prisoner's dilemma works",
" ",
" The outcome of your decision is influenced by the decisions of other participants in the game.",
"~",
"Pollinators, have a certain target ingrained in their instinct. Maybe you pollinator is ",
" by the colours and patterns of their female counterpart. Plants can take advantage of this",
"2",
" Plant A has trustworthy flowers, plant B has lying flowers. Let's make up an scenario:",
"~",
"In this scenario, at the beginning there's a 1/100 chance to visit the lying flower. In a single interaction event pollinators aren't very likely to visit the lying flower. However, the deceiving plant reproduces a little more. So, in the next generation, we have 95 trustworthy flowers and 5 lying flowers. The chance to visit a lying flower changed from 1/100 to 1/20 (simplification of 5/100).",
"From their previous experience, pollinators trust the flowers, so they decide to visit again. Let's assume in this second interaction event, some pollinators stumble with lying flowers. They \"feel betrayed\" because they didn't get the reward, so they decide to don't visit the flowers in the next event. Again, the lyings plants took advantage and spent less energy to reproduce. In the next generation we have 80 trustworthy flowers and 20 lyings flowers. The chance to visit a lying flower has changed from 1/20 to 1/4 (simplification of 20/100). Here's where it gets interesting.",
"Now that the chance of stumbling with a lying flower is 1 out of 4 encounters, pollinators stumble with liars more frequently, changing their behaviour. They are going to be more picky about visiting a flower, thus, reducing the total number of visits. This means there will be less pollination events. Overall, flowers were visited less than in previous events, this decreases the number of lying plants since they depend on visits. In the next generation we have 90 trustworthy flowers and 10 lying flowers. The chance has gone from 1/4 to 1/10 (simplification of 10/100).",
"~",
"This process goes on and on and on and on. But with more factors. New pollinators come, therefore, they don't know about the liars. Pollinators do need to eat, so, it's a must to go an visit flowers, they can't afford stop visiting at all. At a certain moment in time, the frequency of liars won't change too much in comparison to previous generations. This is the point of equilibrium: If more liars arise, the pollinators will stop visiting, decimating the population overall; if there are less liars, they will increase their frequency. In both cases, the frequency of liars reaches an equilibrium point."
] |
[
"Do viruses have a preferred location in the genome of a host organism to splice themselves in?"
] |
[
false
] |
My understanding is that retroviruses & viruses actually get spiced into the genome of their host. Is this true or do they function more like plasmids? If they do in fact splice themselves in, Are there any studies which demonstrate that virus will target a specific spot within the genome or do they just splice in wherever they can?
|
[
"Introduction of a virus into a host cell can take either of two pathways. In the lytic pathway the virus genome is incorporated into the host cell, but it is not incorporated into the host cell genome. So in the lytic pathway the viral DNA or RNA behaves similarly to a plasmid, but only in the sense that it is separate from the main genome of the cell. The lysogenic pathway involves the incorporation of the viral genome into the host genome. This does occur at specific sites, and the process is aided by proteins present in the host organism and proteins included in the virus prior to its introduction into the cell. Overall viruses are extremely selective in the organisms they infect, and I believe they are very selective in the sites they splice themselves into in general. For example, bacteriophage lambda is lysogenic, and splices its genome into a very specific site in E coli. ",
"Also an interesting side note, some bacteria contain DNA that was once part of a virus, so it's possible that viruses have contributed to the evolution/genetic variation of some organisms. "
] |
[
"Yes, retroviruses do splice themselves into the host genome. They are (+) sense, single stranded RNA viruses which, upon entry, use a reverse transcriptase and after several steps, creates a double stranded DNA version of their genome known as proviral DNA. A viral protein called integrase does some fancy cutting which allows the viral DNA to insert itself into the host DNA. Host DNA polymerases then come and repair the spot where the viral DNA was inserted, and just like that, the virus will now replicate with the host cell.",
"To answer your question about genome location, a quote from Fundamentals of Molecular Virology, \"Integration sites appear to be distributed randomly over the host genome.\""
] |
[
"I don't believe it is as specific as a single nucleotide, but there are specific sites that consist of a handful of nucleotides. "
] |
[
"What type of calorimeter should I use to measure solid things?"
] |
[
false
] |
Such as bread or Cheezits. Thank you!
|
[
"Sounds like you need to use a bomb calorimeter."
] |
[
"What kind of measurement are you making?"
] |
[
"We are looking to measure the caloric content of things, so I suppose calories? I'm terribly inept at science, sorry."
] |
[
"Is there truth to the claim that manual cars get better MPG than automatics?"
] |
[
false
] |
[deleted]
|
[
"In addition to gear optimization, automatic transmissions have torque converters while manual transmissions do not. The coupling efficiency of a torque converter is worse than a clutch, so automatic cars are losing energy to the torque converter. There have been a few cars with locking torque converters, however the extra fuel efficiency was deemed not worth the added complexity.",
"http://en.wikipedia.org/wiki/Torque_converter#Efficiency_and_torque_multiplication"
] |
[
"Also, manual and automatic versions of the same car often have different numbers of gears (e.g., the option of 5-speed manual or 4-speed automatic is common). So even if, with equivalent gear ratios etc, the auto and manual would have equivalent fuel efficiency, such a configuration usually is not an option on most cars."
] |
[
"From that same article:",
"In the late 1970s lock-up clutches started to reappear in response to demands for improved fuel economy, and are now nearly universal in automotive applications.",
"My crummy 90s chevy lumina had a torque converter clutch, so it can't be that rare..."
] |
[
"If I am to the point where I am happily intoxicated will drinking one beer an hour keep me there?"
] |
[
false
] |
I have heard that your body is able to "get rid of" about a beer an hour or something like that. So I was just wondering if I was at a comfortable stage of drunkenness, if i could just drink a beer an hour and create sort of a plateau effect. Edit: may not belong in ask science but i feel that i have the mental capacity to understand the scientific side of this. Edit 2: Didn't really edit anything but I did just sort of realize that i could have went to askreddit instead of askscience, so my bad.
|
[
"The body eliminates alcohol in what's called pseudo-zero order kinetics - meaning basically the elimination rate is constant, regardless of alcohol level. While elimination rates differ from person to person - and this depends on body mass, fat content, sex, race, and tolerance - a crude approximation is one standard drink per hour. This translates to roughly one bottle of beer, one glass of wine, or one shot. ",
"Therefore, yes you can ",
" maintain the level of intoxication by drinking one beer an hour."
] |
[
"Brewing science guy here, weighing in.",
"Regardless of the type of alchol it is (beer, wine, liquor), it is going to contain differing amounts of ethanol, methanol, and phenol.",
"When the body begins processing and breaking down the alcohol, it begins with ethanol and then follows with the others. Ethanol is, basically, the \"good stuff.\" When you get a hangover the morning after drinking, it is because your body has already broken down all the ethanol and is now trying to break down all the methanol and phenol.",
"This is why \"hair of the dog\" works. When you drink more the next day while you have a hangover, your body stops breaking down the methanol and phenol and starts breaking down ethanol again. This gives you the chance to expel more of the bad stuff through other means, like urination. You are still going to be hung over, its effects will just be lessened.",
"Drinking a beer an hour, your body is eventually going to process all of the ethanol and start breaking down the methanol and phenol, making you feel bad.",
"How and when this occurs is subjective to not only the person, but also in relation to the type and quality of alcohol you are drinking. As a general rule, the more expensive the alcohol, the higher quality products and process used to make it, which in turn means more ethanol and less methanol and phenol. This also means that if you use cheap and poorly made alcohol for your hair of the dog drink, you could be making things worse in the long run.",
"Are you going to be drinking quality beer during your beer-an-hour endeavour? If so, it may work, but if you start to feel bad, now you know why."
] |
[
"I'll suggest ",
"mouse party",
".",
"With regards to intoxication versus concentration, it's a very subjective effect, and highly variable amongst individuals. The only thing I can tell you for sure is that impairment is in a continuum, and may start at a blood alcohol level much lower than the legal limits - as low as 0.02 % in some people."
] |
[
"When my guitar is out of tune, the strings are always in a too high pitch. Intuitively, it feels like it should be the other way since they would loosen. What's going on?"
] |
[
false
] | null |
[
"The coefficient of thermal expansion of the (steel or bronze) strings is higher than that of the wooden neck of the guitar (along the grain). After you've been playing the guitar for a few minutes, both strings and wood will have warmed up due to you touching them.",
"If the thermal expansion of each material were equal (along the string axis), then the guitar would stay in tune quite well. Instead, as it warms, the strings expand more than the wooden neck, causing some tension to be lost. This lowers the pitch of the strings.",
"If you tune your guitar perfectly in this warm state, when it cools, the strings will be tuned too high.",
"TL;DR: Don't check your guitar's tuning until you've been playing it for 5 minutes."
] |
[
"If the thermal expansion of each material were equal (along the string axis), then the guitar would stay in tune quite well. ",
"would your intonation remain correct? "
] |
[
"It won't change much. I'm pretty sure the strings experience a larger change in temperature than the neck, due to their smaller mass and higher thermal conductivity.",
"The fret placement (as a fraction of vibrating length of the string) is dominated by the expansion of the neck, which will be very slight. Additionally, the neck only makes up perhaps 3/4 the length of the string."
] |
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