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[
"How does drowning work?"
] |
[
false
] | null |
[
"I'm going to correct you here.",
"The urge to breath is based on our carbon dioxide levels not our oxygen levels. The urge to breat becomes great when we reach higher levels of carbon dioxide, while we still have sufficent oxygen to stay alive for a suprising ammount of time."
] |
[
"When people drown, do they eventually reach a point when they take a breath under water or is that biologically impossible?",
"There are two types of drowning.",
"http://answers.webmd.com/answers/1177901/what-happens-during-drowning",
"a. suffocation where the person doesn't get appreciable water in lungs",
"b. Actual drowning where water goes into lungs.",
"Humans can breathe liquids just fine. It's just that water in large quantities is not something lungs like. ",
"TIL Newer definitions don't make this distinction ( i remembered this from the 80s) ",
"As body function declines, the larynx may relax and allow water to enter the lungs. However, up to 20% of drowning victims have persistent spasm of the larynx, and no water is aspirated (this was formerly known as \"dry\" drowning)."
] |
[
"Hmm yeah that's interesting. Thanks for answer! I didn't think about it that it could go both ways."
] |
[
"What is Deja vu and how can it be explained?"
] |
[
false
] | null |
[
"The best explanation i have heard is roughly; It is by coincidence or fault in brain chemistry, that a pattern of neural pathways in the brain are activated which have been activated before at some point. The brain then tells you it is the same experience as before but because you know it isnt, you enter a brief state of confusion as the brain tries to figure out what is going on. ",
"Although it is aimed at a teenage audience, the recent rcib christmas lectures give a good grounding on how the brain works, i would definitely suggest a watch for a bit of understanding.\n",
"http://www.bbc.co.uk/programmes/b018l6vy"
] |
[
"Hi, I'm following this vsauce guy on youtube. He expains a lot in a good way!",
"http://www.youtube.com/watch?v=CSf8i8bHIns"
] |
[
"I'll check back later if your answer is the best because that's it what I was told also.",
"The brain has short-term memory and long-term memory and Deja Vu is really just a mix up between these two because it stored the \"new\" experience in the long-term memory and you are like: i've seen this before and are deeply convinced that it's true."
] |
[
"How do we know the indeterminacy principle is not illusory?"
] |
[
false
] |
With sub atomic particles "appearing and disappearing" or "disappearing then appearing else where" or "existing then not existing". Is it possible they simply move so fast that it appears to us there was no time between the particle moving from point 'A' to 'B'? So when we say that sub atomic particles do not occupy a definate space or time when perhaps our senses even our machines are simply not fine tuned enough to detect these particles "having a linear existence"? I feel perhaps I am missing a big piece of the puzzle and hoping someone might help clear this up for me, thanks
|
[
"So at its heart, this is the same question (or philosophically very similar to it) that Einstein was asking in the ",
"EPR Paradox",
": is quantum uncertainty (or indeterminacy) ",
" or is it just an artifact of the measuring problem? That is, even accepting that the limits on our perception of the information in question are hard-limited by QM, does one have to believe that the information ontologically does not exist in an ultimate, philosophical sense? Einstein really was unhappy with uncertainty — he believed the universe should, in theory, be knowable, even if only by some kind of omnipotent being. He had long debates with Niels Bohr about this very issue, and went to his grave believing that the Copenhagen interpretation of quantum mechanics just couldn't be right, that it just wasn't satisfying enough to be a final theory.",
"The EPR paradox was basically thought up to try and prove that the unknown information ",
" to be there, ",
", even if we couldn't possibly detect it. For a long time people thought maybe it was just a philosophical distinction, not an empirical difference. But John Bell ",
"actually figured out a way to test it empirically",
" in 1964, and since then ",
"many \"Bell tests\" have been run",
". The tests themselves, and their interpretation, are hard to explain without really getting into the nuts and bolts of it (and even then, I've found it difficult to explain them in a lay fashion that still made any sense), but the main interpretations of the results suggest that Einstein was wrong. The information just isn't there.",
"There are probably others who can explain the tests and their relevancy (assuming they are relevant, but they seem so to me) to your question, but the basic answer seems to be: actually, the indeterminacy, and the uncertainty, are ",
", not just artifacts of our inability to measure things or mathematical tools. "
] |
[
"Either you misunderstood my post, you misunderstand the Uncertainty Principle, or both.",
"The HUP is a fundamental and intrinsic fact of nature. It is independent of the mathematics we use to represent it.",
"I understand what you're trying to say. When we come up with a theory, we create a mathematical model to represent it, and these models aren't always correct/complete. ",
"In the case of the HUP, we know exactly what it is and how it works. It's not a question of measurement or technology. It's an intrinsic indeterminacy. If you think you can prove that it's wrong, be my guest."
] |
[
"The HUP is a consequence of the mathematics of QM. The mathematics of QM have not failed us yet, so assuming that the HUP is true is a reasonable assumption. Physicists everywhere assume the HUP is true all the time, and every experiment I've ever heard of has agreed with it.",
"I don't know if we'll ever have devices capable of measuring uncertainties at that scale, but I do know that there has never been a single piece of evidence suggesting that the HUP is not valid.",
"So at the end of the day, yes, maybe the HUP is an \"assumption.\" But that doesn't make it any less valid."
] |
[
"Why does the iron filings and bar magnets experiment result in the iron filings arranging themselves in neat lines when the magnetic field should be continuously distributed around the magnet?"
] |
[
false
] |
Like ?
|
[
"Because each tiny piece of iron becomes magnetized itself, and now you have a giant pile of tiny magnets that all attract and repel each other. The attraction and repulsion of the individual tiny magnets lead to spaced-out-lines pattern you see."
] |
[
"By that, if you dropped/buried a bar magnet in a bucket of iron filings would if form layered shells with gaps between them?"
] |
[
"If you did it in zero G, yes. On Earth, gravity will dominate over distances greater than a few mm/cm. ",
"This is basically the same thing as those ",
"desk toys",
" that have a jillion small metal bits and a strong magnet in the base. You can try building a tower out of the metal bits, but if you tower gets too high, it will topple over."
] |
[
"Can animals (ones capable of domestication) tell if you are male or female? Do they treat you differently/ acknowledge you accordingly depending on your gender?"
] |
[
false
] |
How about implications of homosexuality or transgenders? Do gay male animals treat male humans differently from heterosexual animals? What if the male humans are homosexual and the animal is not? And what if both are?
|
[
"I'm no homerun hitter but I'll step up to bat: The answer appears to be yes, at least with dogs.",
"Link: ",
"http://www.anthrozoology.org/pdf/anthrozoology.pdf",
"relevant bit starts on p. 136",
"Human gender had\nan effect on both dog barking, and eye orientation. Dogs showed a stronger decrease in barking and\ntendency to look towards the human whenever the subject was a women than a man, suggesting that\ndogs may be more defensively-aggressive towards men than women. There was no interaction\nbetween canine and human gender on the response of the dog towards the persons. This study\nindicated that both canine and human gender affect certain elements in the response of a dog towards\nthe presence of a human. The findings may have practical implications for the re-housing of dogs\nfrom rescue shelters"
] |
[
"How much of this could be due to how a male appears and projects himself onto others compared to females though? The sample size of 3 women and 3 men appears a bit small to totally account for this and could be a factor"
] |
[
"Related question:",
"Do dogs recognize and react to human age?"
] |
[
"How can any CD or DVD be re-writable?"
] |
[
false
] |
[deleted]
|
[
"Actually, that's not how ",
" CDs are created. Pressed, or manufactured, CDs do have microscopic indents in them, but writable and rewritable CDs and DVDs actually use a photosensitive dye- in the case of rewritable discs, a dye that can be reset back to its initial reflectivity."
] |
[
"It's actually based on the power level of the laser beam- it gets much more powerful to return the phase-change \"die\" to its original state. That's why rewritable discs have to be fully erased before being written to again- there's no guarantee that erasing one cell won't affect any others."
] |
[
"I assume there are two different frequencies of laser light, one that sets it and one that resets it? If not, how is it done?"
] |
[
"How are we so sure that there are no \"paranormal\" exceptions to natural laws?"
] |
[
false
] | null |
[
"If science deals with what can be replicated and controlled, and \"paranormal\" phenomena cannot be separated from the \"noise\" of random variables in the universe, how can one claim that \"paranormal\" phenomena exist?",
"Another way of asking: \nIs your friend suggesting that is impossible to replicate experiments that show evidence for \"paranormal\" phenomena? If so, and the phenomena cannot be replicated in any way, how can you show that the phenomena are actually happening? ",
"Also:\nWhat evidence ",
" there be for the existence of such things? Because if there was some kind of evidence, even if we ourselves cannot actually ",
" the thing to occur (that is, even if we cannot replicate the event ourselves), there would be some kind of pattern that science could decipher and use to predict the characteristics of future events. For example: when a high energy particle hits the atmosphere, it is not a human-driven process but we can still record data from the event. Using that data, we can correctly predict what will happen if another, similar particle hits the atmosphere, and we might even be able to extrapolate how other types of particles hitting the atmosphere might act. Is there any evidence at all for the \"paranormal\" events?",
"Finally, I don't think your friend understands the \"scientific\" use of the word \"law\". Scientists, especially physicists, like to use \"law\" to describe phenomenon that we have an overwhelmingly huge amount of evidence for. The \"law\" of gravity isn't some code written into the universe, it's a well described concept that shows how things with mass interact with other things with mass. If we find better equations than the ones we currently use (better = applicable in more situations or less incorrect in more situations) we will adopt the new equations, but the \"law\" of gravity still says basically the same thing. ",
"The notion of the \"laws\" of science not being absolute/without exception is, by the very nature of science, true. The \"laws\" are made by us, and will (hopefully) forever be updated to keep up with scientific progress, and even so there will almost certainly ",
" be various exceptions to the \"laws\". That truth can't be used to justify things for which there is no evidence, or for which there is evidence against. "
] |
[
"You can't prove something doesn't happen. What you can prove is that something happens, in a certain controlled situation. If someone claims to have some paranormal ability or tool to influence the world, it should be measurable. Science is forming an idea, describing an experiment to validate that idea, setting it up, measuring the results, and determining if the data supports the idea. Natural laws are just the set of behaviors that people have been able to set up experiments to accurately measure and describe.",
"There is no point in paranormal things that nobody can control, they would not help anyone. People who claim crystal energy or ESP are claiming that some paranormal object has real physical effects in the world. If they are able to control those physical effects, then an experiment can certainly be set up to measure the effects.",
"Presence of an observer and belief can be quantified. You can do an experiment with people who claim to believe in a certain result, and people who do not. All these variables can be controlled with enough diligence.",
"In the end, everyone wants to believe that there is an easy solution to our problems. If your friend really believes in crystal energy or homeopathy, invite them to put their money where there mouth is an do an experiment. Set up a double blind test with controls, and see if their crystal or sugar pill really makes a difference. With the resources of a normal person it is tough to do a test that will pass peer review, but you should at least be able to convince yourself and your friend if they agree.",
"If you want help designing a test feel free to ask."
] |
[
"Definitely related. The null hypothesis is often \"the observations are due to random chance\", and sufficient evidence can disprove this. If the evidence gathered does not disprove the null hypothesis to a sufficient confidence, that does not prove that the process happened by chance."
] |
[
"Is the earth still cooling from its formation? If so, does that mean eventually all tectonic activity will cease and our liquid mantle will solidify?"
] |
[
false
] | null |
[
"Yes, the earth is still cooling from formation, specifically heat generated by accretion and differentiation. A lot of the heat is actually due to radioactive decay of things like thorium-232, uranium-238, and potassium-40. A good discussion of the topic can be read over at ",
"Wikipedia",
". ",
"One thing to correct however: The earth's mantle is ",
" liquid. The outer core is liquid, but that's it. The mantle is solid, but warm enough to undergo ductile flow at a very slow rate. Again, ",
"Wikipedia",
" has a good discussion of the topic. "
] |
[
"The Earth is cooling at a rate of ~100C/billion years. So the sun is going to die and engulf the planet before we completely cool down (in around 5 billion years). ",
"Here's a press release from a Science article",
" that came out a few years ago that discusses how much heat the Earth still has."
] |
[
"That is mind blowing that the Sun will die before the Earth completely cools."
] |
[
"Why are dendrites 2-dimensional, rather than 3-dimensional?"
] |
[
false
] |
I'm studying dendrites formed by electrodeposition of zinc in an alkaline solution, but this could probably apply to dendrites formed in a binary alloy solidification process just as easily. Why do dendrites typically have a flat, tapering, 2-dimensional shape (leaf-like) rather than a conical, tapering, 3-dimensional shape (pine cone-like)? You'd expect the side-branches of the dendrite to grow in every direction where material is available, but instead they tend to grow only in a single 2-D plane.
|
[
"I'm a little confused by the human body flair added here so maybe I can't contribute. Alloy solidification that I am accustom to shows 3 dimensional dendrites. Dendrite formation is typically driven by chemistry, crystal structure, and temperature gradient. I deal with solidification of steel alloys."
] |
[
"Dendrites in the human body (that form synapses) are also 3-D, so the question is a little confusing."
] |
[
"I came here to answer a much simpler question (as implied by the flair)... I'll try to answer both...",
"\n",
"I assume you are referring to dendritic morphologies like this.",
"\nSolvated zinc ",
" tetrahedrally coordinated, but I cant say more without knowing the composition of the alkaline electrolyte solution. I can however say: Electrodeposition is regulated by ",
"diffusion limited aggregation",
"... a crystal cannot form unless the reactant touches the crystal. From what i could find (DOI:10.1021/la0611864) zinc crystals have preferential adsorption sites at the apical outgrowth edges. By default, this would mean that flat un-faceted faces are less likely to adsorb the zinc reactant for crystallization. The orientation of zinc ligands is also likely to play a role in the uniformity of this structure.\nThat's the best i can do for this topic. sorry.",
"\nDendrites ARE 3D in the brain... but they aren't easily imaged in the brain. So, the neurons are taken out the the brain and cultured in a dish for imaging. As a result, there is a common misconception that the brain works like a 2D circuit board with 2D dendrites."
] |
[
"Does gravity have any affect on rotation?"
] |
[
false
] |
It should not have one if gravity field is viewed as constant. But in space it might favor rotation in certain direction. Is there analogue of Newtons law for gravity for torgue? Sorry for improper English.
|
[
"Not in the Newtonian approximation, no. There are \"gravitomagnetic\" effects in ",
"general relativity",
", but they're extremely small.",
"http://en.wikipedia.org/wiki/Gravitomagnetism",
"http://en.wikipedia.org/wiki/Frame-dragging"
] |
[
"I should point out that tidal locking doesn't mean that the Moon has stopped rotating. It means that the Moon rotates at the rate of one revolution per Earth day."
] |
[
"If you're that close to a black hole, I'd imagine you've got a number of sufficiently urgent concerns that we can still call the frame-dragging effect relatively small."
] |
[
"As there are binary star systems, where two stars orbit each other, is it possible for a ternary star system to exist, i.e with 3 stars orbiting each other?"
] |
[
false
] | null |
[
"Yes, and the most stable form of a ternary system involves a binary system where a third star orbits the binary system, and is far enough away to where it could look at the binary system as a single gravitational object. If this is not the way the system is organized, one or more of the stars is likely to be flung out of the system"
] |
[
"To add, the closest star system to us, the Alpha Centauri system, is thought to be this. Alpha Centauri A and B orbit each other while Proxima Centauri orbits around the pair. Proxima Centauri is believed to be orbiting the pair every 500,000 or so years. ",
"Edit: changed orbital period"
] |
[
"The closest star to the Sun, ",
"Alpha Centauri",
", is actually three stars in this configuration. Alpha Centauri A and B orbit around each other, and Proxima Centauri, much smaller, orbits around the two. This actually makes Proxima Centauri the nearest star at the moment.",
"You can even get this in a more exotic scenario, such as the recently discovered ",
"pulsar triple system",
", where a pulsar and a white dwarf orbit each other, with another white dwarf orbiting around the both of them."
] |
[
"Are our gas planets in our solar system almost a perfect sphere/ellipsoid?"
] |
[
false
] |
Or are there "bumps" in the atmosphere?
|
[
"There are bumps and structures at the highest parts of the atmospheres of Jupiter and Saturn. I dont know much about them but you can think of the bumpyness of clouds when you look down on them from above on Earth and it is somewhat similar for gas giants. Just on a larger scale and different structures due to the dynamics of the flow.",
"The bumps are small in comparison to the whole planet which is approximately an ellipsoid (or oblate spheroid... which is not even perfect due to tidal forces)."
] |
[
"Even with their gravity field?"
] |
[
"Yes the fluid gets less dense as you get higher up so there is less mass to be affected by gravity. ",
"I cant find the picture anymore but there is at least 1 picture out there of the shadow cast by a cloud on Jupiter showing that there is depth. "
] |
[
"Do human women go \"into heat?\""
] |
[
false
] |
from Wikipedia " Recent research[1] suggests, however, that women tend to have more sexual thoughts and are far more prone to sexual activity right before ovulation (estrus)."
|
[
"One of the defining adaptations that gave rise to humans as we are now was the elimination of discrete periods of heat. A small peak in sexual interests is not going into heat, which is essentially turning on the female reproductive system.",
"May it be a small aspect of biology remaining from our heat-based ancestors? Sure, maybe. Is it going into heat? No."
] |
[
"Strippers earn more money when they are most fertile.",
"http://mindhacks.com/2007/10/04/strippers-earning-potential-affected-by-hormone-cycle/"
] |
[
". . .heat, which is essentially turning on the female reproductive system.",
"Being \"in heat\" is just a state of sexual responsiveness, timed to coincide with ovulation in order to maximize reproductive success. Some species may require copulation to initiate ovulation, but it does occur spontaneously in others. I haven't read the article cited in the OP, but if this response is triggered by the same hormones, I don't see how it would be any different. ",
"To be clear, though, menstrual and estrus cycles do differ in absorbing versus shedding the endometrium."
] |
[
"What are the long term effects of positive pressure ventilation as opposed to the normal negative pressure used to inflate the lungs?"
] |
[
false
] | null |
[
"Usually the most common physiological issue with long term use is ventilator dependency. People who have been on this type of therapy for a while often have to be weened off of the ventilator once they are healthy enough to survive without it to prevent acute respiratory distress and/or failure. The most common exogenous complication of both short and long term use is infection. No big surprise there. Beyond that, so long as the ventilator is properly maintained and used, the respiratory system should remain more or less fully functional (though I wouldn't expect to go run a marathon right after getting off long term ventilation)."
] |
[
"Another consequence to violating normal respiratory physiology is barotrauma, potentially leading to emhysematous changes in the lungs, fibrosis, and pneumothorax."
] |
[
"Infectious complications are primarily due to the bypass of physical immunologic barriers such as a the trachea and the coughing mechanism. A major problem with chronic infections is the development of resistant strains of bacteria."
] |
[
"Is Hawking still correct?"
] |
[
false
] |
In , Stephen Hawking wrote, “Now at first sight all this evidence that the universe looks the same whichever direction we look in might seem to suggest there is something special about our place in the universe. In particular, it might seem that if we observe all other galaxies to be moving away from us, then we must be at the center of the universe. There is, however, an alternate explanation: the universe might look the same in every direction as seen from any other galaxy too. This, as we have seen,was Friedmann's second assumption. We believe it on the grounds of modesty. It would be most remarkable if the universe looked the same in every direction around us, but not around other points in the universe!” ( 44-45). My question is this. Have we discovered something that would justify the belief that the universe has no center? Let me clarify my request. I'm not asking for explanations of the data that are merely with the idea that there is no center. I'm asking for evidence that has been discovered that can be explained (or explained) by believing that the universe has no center. I already infer from Hawking's statement that A) explanations of the data that are merely with the idea that there is no center already existed when he wrote his book, and B) no evidence existed at the time of his writing that could be explained (or explained) by believing that the universe has no center. Thanks. In an ideal world, I could have a source that directly addresses Hawking's statement and demonstrates how what he said is no longer the case, but I will be grateful for whatever assistance is on offer.
|
[
"Yes, Hawking is still correct. There is still no evidence either for or against the Copernican Principle. There ",
" models of cosmology that have a preferred center and which make the same predictions as a cosmology based on the Copernican Principle. We appeal to parsimony or some other sort of philosophy when we say that the Copernican Principle must be true.",
"For more details, you can read this response of mine: ",
"How Valid is the Theory of Geocentrism?",
"."
] |
[
"The LTB cosmology is one such example. ",
"(Also, by \"big bang cosmology\", you likely mean \"FLRW cosmology\". The LTB cosmology is also a big bang cosmology, but the time since the big bang is not the same throughout all of space. An FLRW cosmology is isotropic about all points in space; an LTB cosmology is isotropic about a single point in space.)"
] |
[
"No. It is quite easy to determine whether you are at the preferred center in the LTB cosmology. For instance, Hubble's Law would not be true; it would not be the case that all galaxies are redshifted and seem to be receding."
] |
[
"Are some cells more greedy than others? Do some cells use more resources than their benefit to the organism?"
] |
[
false
] |
[deleted]
|
[
"Yes, this is what happens in cancer. Essentially, through mutation and selection, cancer cells have lost their \"restraint\". They consume nutrients and grow in a way that benefits the cancer cells (temporarily) at great cost to the host body."
] |
[
"No, because the brain's use of energy is directly related to your most fundamental abilities to function."
] |
[
"Exactly, so the word \"greedy\" would not apply to the brain, although the brain does use a lot of energy."
] |
[
"Is there a term or specific rule sort surrounding the ‘shortened grammar’ often seen on signage?"
] |
[
false
] |
Many signs and labels use a sort of ‘shortened grammar’ in which certain words such as ‘the’ are omitted where their use should be obvious. I can think of a few common examples off the top of my head, although I have seen some signage where many more qualifying words are omitted: “Do Not Enter [the] Building”, “Employees must wash [their] hands before returning to work”, “Objects [seen] in [this] mirror are closer than they appear”, … Is there some term for this sort of shortening and/or a general understanding of when and where it tends to be used, the specific ‘rules’ followed surrounding what tends to be eligible for omission, etc.?
|
[
"The technical term for omission in linguistics is \"ellipsis\". The fact that utterances with ellipsis are understandable - i.e. that we can fill in the missing elements - informs us about how our brains process sentences, supporting the idea that language is parsed in abstract structures which exist independently of the specific words used.",
"You can look into X-bar Theory for one way of analyzing and graphically depicting syntax, though there are other frameworks. One important facet of the X-Bar framework though is that syntactic roles necessary for an utterance to be grammatical still \"exist\" in your mental representation of the sentence, regardless of whether a word filling that role was actually spoken or written. That seems like an odd and possibly unprovable claim, but it can be supported by showing how the omitted word or phrase still places constraints on how other elements the sentence can be changed without making the sentence ungrammatical. ",
"Outside of the context of signage, we use ellipsis in everyday speech. Consider the sentence \"John read fewer books than Mary\". The full sentence in our heads is \"John read fewer books than Mary (read books)\". We can also say \"John read fewer books than Mary read\", \"John read fewer books than Mary wrote\", or \"John read fewer books than Mary magazines\" - where just ",
" is omitted - but we can't say *\"John read fewer books than Mary books\". That is, if we are comparing numbers of books, we can omit both \"read\" and \"books\", or just \"books\", but not just \"read\" while keeping \"books\" - yet we can omit \"read\" if we are comparing the number of books to the number of magazines. (Also note that I could say \"comparing the number of books to (that of) magazines\" but not *\"comparing the number of books to of magazines\".) This shows us that there's some structure that exists in our heads when we parse and construct sentences, which determines what words and phrases can be omitted.",
"Edit: By the way, in case anyone's curious, the asterisks are not formatting errors. In linguistics, an asterisk before a word or sentence means that the following phrase is either unattested or ungrammatical. \"Unattested\" means never observed (within a particular linguistic community) and applies to ungrammatical sentences as well as reconstructed roots of parent languages. \"Ungrammatical\" means \"perceived as ill-formed by native speakers\" and does not refer to prescriptive rules (e.g. \"less books\" is grammatical in my native dialect but is \"wrong\" in the prestige register that I'm writing this comment in) or to nonsensical sentences (e.g. \"Colorless green ideas sleep furiously\")."
] |
[
"In some linguistic registers, rules for constructing valid utterances are more flexible. ",
"A ",
" is roughly the level of speech one uses in a given context. So before a court, a speaker may be exceptionally careful to sound precise, and a lawyer or expert may use a lot of legal jargon. But when drinking with friends, someone is more likely to say curse words, to use slang, and to phrase things in less restrictive ways. ",
"Written language has different registers too. For a sign, copula, articles, and other small words are commonly omitted for the sake of brevity. Sign readers rely on custom and context to interpret shorthand: \"Slow children at play\" is usually understood not to refer to \"slow children\" but an imperative (\"slow\") followed by why (\"children [could be] at play [in the neighborhood]\"). The sign doesn't need to explain the information added in brackets or otherwise disambiguate with punctuation. Instead, the sign trades explicit articulateness for brevity - a passerby seeing and quickly understanding the caution."
] |
[
"ASL drops and combines words, too.",
"ASL should be understood as its own language instead of a \"code\" for English. Besides the obvious vocabulary difference, grammar and constructs are significantly different. ",
"Native ASL and Deaf students often have really rudimentary written English skills, to the point of needing remedial classes and other supports. Many hearing students struggle with \"don't write how you talk\" too, to some degree, but native ASL writers tend to have more in common with ESL students. ",
"Especially entering undergrad math and engineering programs, it's not uncommon for their first year to have more language courses than technical ones. ",
"Not to pick at your post, it's just a fascinating subject."
] |
[
"In what sense is gene expression stochastic?"
] |
[
false
] |
I've heard many many times that gene expression is stochastic. What does this mean exactly? More to the point, is it just a statistical description of a process we don't know enough details about to describe more accurately, or is gene expression fundamentally stochastic (e.g. from quantum mechanical effect).
|
[
"All chemical processes are, to some extent, stochastic because they're all quantum mechanical. A better question to ask would be ",
" gene expression is \"truly\" stochastic; in other words, if you could \"rewind the tape\" on a cell and hit \"play\" again, so that every molecule has the same configuration as it did originally, how similar the expression profile would ultimately be."
] |
[
"I'm going to play a bit of devil's advocate here, just because I've been asking some people whom I trust on this topic, some that study gene expression for a living, and I've still been getting different answers.",
"(1) The paper you gave specifically says that they mean stochastic in the statistical sense (ie. not in the fundamental sense). In other words, they make no claim about the origins of the stochasticity, or why, exactly, they treat it as a random process.",
"(2) If gene expression is fundamentally stochastic, where would the stochasticity come from? To be more specific, I mean that flipping a coin is treated as a stochastic process, but it's not really. The fact that we treat it as stochastic has more to say about (a) what's a useful way to treat it, and (b) the lack of our knowledge on either the initial conditions or dynamics. In contrast, quantum mechanical systems will be fundamentally stochastic, by virtue of the dynamic equations they follow."
] |
[
"I'm going to play a bit of devil's advocate here, just because I've been asking some people whom I trust on this topic, some that study gene expression for a living, and I've still been getting different answers.",
"(1) The paper you gave specifically says that they mean stochastic in the statistical sense (ie. not in the fundamental sense). In other words, they make no claim about the origins of the stochasticity, or why, exactly, they treat it as a random process.",
"(2) If gene expression is fundamentally stochastic, where would the stochasticity come from? To be more specific, I mean that flipping a coin is treated as a stochastic process, but it's not really. The fact that we treat it as stochastic has more to say about (a) what's a useful way to treat it, and (b) the lack of our knowledge on either the initial conditions or dynamics. In contrast, quantum mechanical systems will be fundamentally stochastic, by virtue of the dynamic equations they follow."
] |
[
"What causes the intensely cold sensation when you drink water after you chew minty gum?"
] |
[
false
] |
I doubt the water actually gets physically colder, so why does it feel so brutally cold?
|
[
"Menthol",
" (found in mint plants) triggers the cold-sensitive receptors in the skin. It's sort of like the opposite of Capsaicin (found in chili peppers) which stimulates heat receptors."
] |
[
"Half true, just correcting the mechanism. Menthol alters the proteins that sense temperature in our mouth, effectively lowering the temperature that illicit a cold response. ",
"Good paper in Nature: Identification of a cold receptor reveals a\ngeneral role for TRP channels in thermosensation. "
] |
[
"Is there a reason that liquid causes the pain to magnify? Or is it simply because it spreads it throughout the mouth?"
] |
[
"How is memory related to intelligence?"
] |
[
false
] | null |
[
"Everything I'm going to write are only hypotheses so be careful, to be taken as a basis for reflection not as an answer.",
"The more elements a person is able to memorize, the more he will be able to do something new with these elements, to create, to modify, to bring out a new thought or a new way of solving problems with these elements.",
"In other words, memory is like a toolbox, the more different tools you have in the box, the more possible it becomes to solve complex problems if and only if you have something other than memory for making these tools interact together in a consistent way."
] |
[
"I would think that intelligence is the capability of doing things and invent interaction with unknown elements. Otherwise it's a memory thing."
] |
[
"Really not a thing you should be agreeing or disagreeing with unless you only asked the question to affirm some belief you had."
] |
[
"When civil engineers look at cracks in the walls of a building, how do they know if the structure has been compromised?"
] |
[
false
] |
[deleted]
|
[
"Most cracks you will see in a building come from small displacements in the structure which are probably not dangerous, but produce a mismatch with the rigid materials used for the walls. What is important here is not the crack itself but make sure that these displacements do not become too large and are not caused by some design or construction mistake.",
"Cracks on the main structure are a different problem. If you have a steel structure, you do not want cracks at all. In reinforced concrete structures, it will depend on where the crack appears.",
"Of course, every case needs to be studied in detail, and huge cracks are always unexpected, if not dangerous, but as a rule of thumb you can say that perpendicular cracks in beams are fine and perpendicular cracks in columns are bad. It is even common that cracks form in the perpendicular direction in beams. It means the steel inside the beam is sustaining the load, and not the concrete. However, if you have a pillar, you want the concrete to sustain the compression load, so you should not have cracks there. Parallel cracks should not appear because the load in that direction should be much lower, and would usually mean some construction failure.",
"Again, please take into account that this is an oversimplification. In case you are asking because you have seen cracks in your house or somewhere else, better get it checked by a professional."
] |
[
"The other thing that you look for is whether the crack is recent/old, or moving/changing.",
"As far as age of the crack, this is mostly something that you have to figure out through inspection (does it look fresh? is it filled with old paint? does the concrete look weathered? etc...).",
"To figure out whether it's growing or not is actually a little more interesting. The technique we've used on the foundation of one of the buildings at a historic site I help maintain is to put two globs of epoxy on either side of the crack, and glue on a piece of glass. If the crack moves, the glass will break. In our case, the glass has been up for two years now, through three freeze/thaw cycles, without breaking so we're pretty confident that the cracks are stable.",
"As a friend of mine who is a structural engineer once told me. 90% of your job as a structural engineer is to make sure that what you produce doesn't move."
] |
[
"Here's an article about different types of cracks in concrete: ",
"http://www.gsa.gov/portal/content/112806",
"They have to put together knowledge of the type/ location of crack, with their understanding of how the structure is loaded and what it is made of. A lot goes into it."
] |
[
"What is the ping to the Curiosity rover?"
] |
[
false
] |
I presume it must have one, considering that it also must have an IP address. Just curious (pun not intended)
|
[
"Between 9~42 minutes round trip, depending on the orbital positions of the Earth in relation to Mars. The Rover sends it's signals to one of 3 satellites in orbit around Mars, part of NASA's deep space network, which then relay the signals to NASA's ground stations on Earth. Any form of network address would be nothing more than one internally used by NASA. "
] |
[
"Not germane to the original question, but it's worth commenting that Curiosity does have the ability to send and receive directly from the Earth without going through one of the Martian orbiters. (I believe the instructions at the beginning of each sol were planned to be sent directly, though I don't know if that is still the protocol.)",
"Edit: Just verified that NASA plans call for instructions going straight from Earth to the rover at the beginning of each sol, but to use the Mars orbiters to relay data from rover back to Earth in ordinary operations. From ",
"this NASA document (PDF)",
":",
"Curiosity has the capability to communicate directly with earth via X-band links with the Deep space Network. this capability will be used routinely to deliver commands to the rover each morning on Mars.",
"Curiosity will return most information via UHF relay links ... [to] the Mars reconnaissance Orbiter and Mars Odyssey...While not planned for routine operational use during Curiosity’s surface mission, the European space Agency’s Mars express orbiter will be available as a backup communications relay asset"
] |
[
"Sorry if this is pedantic, but NASA's Deep Space Network antennas are all ground based and do not include anything in orbit around Mars. It is the DSN antennas that are used to talk to those satellite or to the rover directly."
] |
[
"Can all animals suffer from muscle atrophy?"
] |
[
false
] |
It seems like some animals can have very strong muscles which they rarely use, say like a crocodile's jaw. Does every animal need to exercise to preserve muscle mass, or do some not have to? Are there muscles in the human body that don't atrophy?
|
[
"Bears have been studied because their muscles don't atrophy over hibernation.",
"http://www.asbweb.org/conferences/2007/425.pdf",
"http://researchnews.wsu.edu/health/74.html"
] |
[
"Don't have an answer, but I'd like to add a question: How the hell does my cat maintain any muscle mass whatsoever, if the answer to the above question is \"yes\"?"
] |
[
"Walking to the litter box, walking to the food dish, eating and drinking food, walking to the couch, clawing at your face...plenty of movement if you ask me. "
] |
[
"What is the 'false positive' rate of coronavirus tests? Is this causing the stall of decline of cases in the UK, or is there another reason we are stuck at 5-6k per day?"
] |
[
false
] | null |
[
"There doesn't seem to be an exact statistic on this, but for most tests the false negative rate is much higher than the false positive rate. For saliva tests there is actually about a 40% false negative rate for asymptomatic people. This is the closes thing to a real source I could find:",
"\"The number of false positive and false negative results is not significant enough to affect the data on reported number of cases,\" said Dr. David Priest, Novant Health’s senior vice president and chief safety, quality and epidemiology officer. \"If anything, we are underestimating the number of cases out there.\""
] |
[
"The analytic performance of molecular tests (like PCR) is very close to 100% for this virus. In other words, if there is no virus RNA in a sample, less than 1% of the time the test will detect viral RNA.",
"The clinical performance is very difficult to test, and that's really what you're asking about. In other words, if a ",
" is not infected, what is the likelihood they will have a positive test. There is no \"gold standard\" test to compare results to, no way to 100% be able to diagnose or rule out Covid, and there are enough mild or asymptomatic people that we can't easily use clinical features to decide if someone was really positive.",
"But even early on in the pandemic, it was estimated that clinical specificity was ",
"very high",
". So the risk of false positive is very low. ",
"Testing in asymptomatic people without exposure is recommended against",
", so testing is primarily done in people who are already suspected of having been infected, raising the likelihood of a true positive even further. As for what is actually causing a plateau in the decrease of cases, it's likely spring - people wanting to be out and social again. March is part of coronavirus season anyway, and there are non-SARS CoVs going around right now in the US."
] |
[
"Or, it’s hard to get positives below 50,000/day when you’re doing over 1 million tests/day and not all PCR. Even with 99.5% specificity, you’d get over that. Clinical accuracy does not match the near 100% sensitivity and specificity on analytical samples."
] |
[
"When I eat something that is labeled 300 calories. Protien, Carb, or Fat--Does my body utilize 100% of those calories as energy/store it or is there wastage. And, would the calories be labeled differently if they were intended for an animal other than human."
] |
[
false
] | null |
[
"I'll only tackle your first question, since it hasn't been answered yet. There definitely is waste of energy at different times of metabolism. This doesn't mean your body is lazy or inefficient: waste is unavoidable. First of all, your feces are not \"calorie-free\", so your body only can consume part of the fuel you intake (from what I've read, we typically take at least half of it). Out of the food that is actually consumed, about 65% is used to just keep you alive, such as maintaining body temperature and keeping vital organs working. This is of course not a waste in itself, although the part that goes to digesting food (about 10% of all energy) can be considered unused since it's spent in fueling. There's also the fact that not all food is burnt for energy: much of it is used for structure (protein) or storage (fat, sugar). From a thermodynamics perspective, energy lost as heat can be considered a waste, but your body efficiently uses this heat to keep the body temperature at an ideal range for metabolism. However, when you start running and your muscles get hot from the work, so you need to sweat to keep the temperature low, then the heat can also be seen also lost energy. Also bear in mind that the cells in your body are not 100% efficient at using energy from food and respiration: there's always \"waste\" one way or the other at the molecular level. Finally, if you don't enjoy life, you can be said to be wasting 100% of the energy. "
] |
[
"Food calories are simply are not based on you or your metabolism (much), or any other human being, or animal. They come from lab measurements from over 100 years ago.\nConventional food energy is based on heats of combustion in a bomb calorimeter and corrections that take into consideration the efficiency of digestion and absorption and the production of urea and other substances in the urine. These were worked out in the late 19th century by the American chemist Wilbur Atwater."
] |
[
"That said, is there any measurable difference in the absorption efficiency between persons? So person A gets a full 100 calories from that piece of cheese but person B only gets 90?"
] |
[
"Is it possible to predict likely virus mutations in the wild by rapidly mutating the virus in a lab? (For example, predict the most likely future covid-19 variations.)"
] |
[
false
] | null |
[
"“Is it possible?” questions invite speculation and discussion, which are a poor fit for ",
"r/askscience",
". Questions based on discussion, speculation, or opinion are better suited for ",
"r/asksciencediscussion",
"."
] |
[
"“Is it possible?” questions invite speculation and discussion, which are a poor fit for ",
"r/askscience",
". Questions based on discussion, speculation, or opinion are better suited for ",
"r/asksciencediscussion",
"."
] |
[
"“Is it possible?” questions invite speculation and discussion, which are a poor fit for ",
"r/askscience",
". Questions based on discussion, speculation, or opinion are better suited for ",
"r/asksciencediscussion",
"."
] |
[
"Cardiac Question: In what manner is a 'rapid' or 'irregular' heartbeat dangerous?"
] |
[
false
] |
I was just thinking about this topic, and it seems that rapid (but regular) heartbeats from nutraceuticals is frowned upon and irregular heartbeats are frowned upon. In my field (dietetics) all 'heart' problems, and thus heart healthy foods, are just those that maintain circulation (reduce artherogenic build-up, regulate blood pressure, basically prevent a clot or thrombus from forming which would lead to a heart attack from disrupted blood circulation). What I'm wondering is whether arrhythmia is harmful, or whether just an irregular heartbeat. If one or neither of them is harmful, then where does the harm/risk come from? (Note: For people reading this, popping into the comments, and then jumping back up here in confusion. There has been some editing of text since it appeared I was 'seeking medical advice') Basically, is the danger associated with irregular heart beats inherent to the abnormally beating heart or is it merely the symptom of something else which actually possesses the harm?
|
[
"Thanks for the leads, will look into those two keywords."
] |
[
"There are two main ways that an irregular heart beat, or arrhythmia, occurs.\n1. Damage to the heart muscle (myocardial infarct, cardiomyopathy)\n2. Pathologic pathways of electrical conduction",
"The danger of cardiac arrest arises when the heart is beating with an arrhythmia (specifically ventricular tachycardia that degrades into ventricular fibrillation). Ventricular tachycardia is when the ventricles of the heart beat uncoupled from the beat of the atria for a minimum of 4 contractions. When this persists for over 60 seconds, the heart is in danger of entering ventricular fibrillation. Ventricular fibrillation is where the ventricle itself can't coordinate a contraction. This leads to not pumping enough blood to keep blood pressure high enough to support brain function or cardiac function.",
"The first mechanism of an irregular heart rhythm is pretty clear. There is not enough blood flow to a portion of the heart (blocked coronary artery), which infarcts (or kills) a portion of tissue. This tissue introduces an area of tissue that does not conduct the electrical signals of the heart. Normally, the heart tissue (myocardium) conducts electricity through an action potential. This is a transfer of ions that induces the next cell's action potential(depolarization). To get prepared for the next contraction, the ions will moved back to their original places(repolarization). Now back to our infarct. The tissue around the infarct will conduct around the infarct. For this to produce an arrhythmia, the cell that began the depolarization around the infarct must be repolarized. Now you have a self supporting cycle that will cause depolarization of nearby cells, rather than following the normal pathway.",
"The other way arrhytmias present is when there is a pathologic conduction pathway that is external to the normal conduction pathway. A good example of this is Wolff-Parkinson's-White syndrome. It is a conduction pathway that is a defect in the heart (congenital) where the contraction of the left atria induces contraction of the left ventricle before conduction down the normal pathway occurs. This will present on an EKG but usually is asymptomatic. Sometimes, it is only found when sudden cardiac arrest occurs in an otherwise healthy individual. Another one to look up is Brugada Syndrome."
] |
[
"SVT is ",
", tachycardia that occurs above the ventricles, either junctional or atrial in origin. Technically sinus tachycardia is an SVT, and sinus tach above 150 would be atrial tach, which can be difficult to distinguish from junctional tachycardia, hence the catch-all SVT.",
"SVT aren't as worrisome as VT, ventricular tachycardia, like gramercyriffs pointed out."
] |
[
"Regions in the brain?"
] |
[
false
] |
I've been reading up on neuroanatomy and I'm trying to get the regions straight but I've been having difficulty because of the terminology and whats a part of what and where and so on, I guess my questions are: I suppose that sums it up, I've looked through a lot but can't seem to make sense as to what is part of what, whats where in relation to everything, and what is within what else or... everything. I figured it would be worth a shot to see if there were any kind souls out in the interwebz who would lend just a moment to clarify any of it.
|
[
"Your question pretty much hits on why understanding brain anatomy is so difficult--regions are both distinct and not distinct, and many regions contain further subdivisions within them. For example, the cortex is thought to house the conscious thought and processing of the brain (language, planning, attention, motor movement, etc. etc. etc.) and there are sub regions within it (e.g., the prefrontal cortex or the occipital region). As you descend further into the interior of the brain, you get 'lower' functions. ",
"You have systems such as the 'limbic system' which is composed of various neural anatomy like the amygdala. Amygdala is a nuclei primarily associated with processing high-emotion memories. ",
"And then you've got big chunk parts, like the cerebellum, which is involved with processes such as coordination and balance.",
"Online brain atlases can be invaluable resources for understanding and learning the various regions and functions of the brain. I cannot remember the site that got me through behavioral neurobiology, but I found a link to this one: ",
"http://human.brain-map.org/",
", which is a whole library of composed images and charts of the brain. Happy learning :) ",
"edit: sorry for few examples... if I got more detailed, I would be here for an hour. There are MANY different regions. All I can say is identifying them all on MRIs is not fun. ",
"second edit: alright, I lied, it is fun for me, but that's because I'm a hopeless neuro-nerd."
] |
[
"Depends on what you mean by region. Broadmann areas are defined by the structure and organisation of their cells. Another way of looking at it is by considering cortical and subcortical structures such as the thalamus, cerebellum, basal ganglia etc... some structures are within other structures, for example, the thalamus is made up of many smaller structures such as thalamic reticular nuclei etc. Google and wikipedia will get you far on this. "
] |
[
"Thank you! I'm perusing this as we speak. Or type. And the examples are fine, I just need something to get me started on it and good resources, which I now have.",
"And you're not alone in the neuro-nerd category, I hope to be joining your ranks quite soon. I've already majorly geeked out in most other various neuroscience categories, now I just gotta get the anatomy down and I vill have ze basics! Then on to world domination...",
"Edit: I'm downloading a mouse's brain as we speak. So... questionably... exciting."
] |
[
"Could someone explain the relationship between spacetime and gravity?"
] |
[
false
] |
My initial understanding was that gravity somehow bent spacetime, but I'm not entirely sure how or what that even really means :P
|
[
"We know from relativity that how one measures lengths and times is, well... relative. Special relativity, the easy case, tells us these measures are related to relative velocity. But what happens when my velocity ",
" is different than my velocity ",
". I have a change in measure with respect to my previous measurement. ",
"I mean, I'm moving, right? So over time, I occupy a new position in space. So for each of these locations in space and time, ",
" I'm measuring space and time keeps changing. ",
"Well when we take all those measures of space-and-time and how they change with location, we can most easily describe it as a ",
" of space-and-time. (To be more specific, we need to start using non-Euclidean geometries to describe space-time. Geometries where parallel lines maybe converge or diverge.)",
"Now let's step back a second to the principles of special relativity. Einstein notes in special relativity, he ",
" that no local experiment can distinguish between rest and motion. When you wake up at a train station and you look out the window and see a train passing you by... are you moving or is that other train moving? And if there were no windows, how would you ever know at all?",
"Now suppose you are in an elevator car, a \"vertical\" train if you will. You find yourself floating around in the elevator car. But we know if the elevator car was in free fall, you'd be floating around inside of it. And we know that if the elevator car was in \"deep\" space away from any other mass, you'd also be floating. Similarly, if you're standing on the floor of the car, is it \"at rest\" on the \"ground\" of a planet, or does it have a rocket firing exactly 1g of thrust somewhere again in \"deep space\"? ",
"Einstein asserts again, No local experiment* can distinguish between deep space and free-fall. (* though due to the size of planets, there can be secondary effects unrelated to what we're talking about that could distinguish. But we're ignoring those, since they're a different question, much like looking outside a window would answer your question too)",
" So if gravitation is indistinguishable acceleration, and acceleration is best described using ",
", then ",
". Specifically, Einstein discovers the ",
"Einstein Field Equations",
" that say \"thing representing how space is curved\" is equal to \"thing representing mass and energy and momentum and other stuff\" (the ",
"Stress-Energy Tensor",
".)",
"So, now we have some massive body curving space... what happens nearby? Well we take a body, a \"test mass\" that we'll simply assume doesn't change space-time itself. And we give it some initial location and motion. But ",
". Well as it moves a bit forward, it moves to a location where how one measures \"forward in time\" and how one measures \"forward in space\" change slightly from where it just was. The result means that to conserve its momentum, it turns a little bit. Remember it doesn't feel any forces. It just... must change direction (as observed from some outside observer) in order to keep going \"straight\" through this curved space.",
"More specifically, we can mathematically describe all of this using more complicated mathematics than Newton did, called a Lagrangian, or a Hamiltonian. We place a free-body (feeling no forces) particle in motion in curved space time. But now our derivatives (rates of change) of space and time start producing terms that describe how space and time change with respect to location in space and time. ",
"What's amazingly remarkable is that ",
". Remember we haven't put a force on the particle. Just passed it through curved space-time, where an \"inertial\" path no longer looks \"straight.\" ",
", it looks like.",
"\"But wait!\" you say, \"When I stand still at rest on the ground and throw a ball... it certainly looks like gravity pulls that ball back down.\" ",
"Well let's look at ",
"this famous xkcd",
". He speaks of \"coordinate transformations.\" What that means is that from my \"god's eye\" perspective, while you're in a car making a sharp turn... there's no force \"pushing\" you against the outside door. There's no \"centrifugal\" force. Your body wants to go in a straight line, but the car door wants to turn, being pulled by the rest of the car. From my outside perspective, you're the one pushing the door. But from inside the car, you feel a centrifugal force. What's the deal?",
"Well again, let's go back to our basic relativity, special relativity. We said rest was indistinguishable from uniform motion, right? We call such observers, ones that are at rest or in uniform motion, \"Inertial Frames of Reference.\" They're observers for which inertia is a good way of describing the world. Objects at rest stay at rest, objects in motion stay in motion. ",
"But there are non-inertial frames of reference too. A non-inertial frame of reference is one that's being accelerated. You can always tell if you're being accelerated (or by point 2, that you're near some massive body). When your car is turning, you're inside of it, being accelerated, so you're in a non-inertial frame of reference. The centrifugal force that comes from this frame of reference is a ",
" force. It's a force that doesn't exist in inertial frames, but a force that makes doing physics in a non-inertial reference frame easier. If you toss a ball in your sharply turning car, that ball will act (from your perspective) as if there's a force pushing it towards the center of the turn, just like the door pushing you. It's a fictitious force, since that outside observer will just see the ball travelling in a straight, inertial line (ignoring gravitation for the moment, we're about to get there).",
"So now we come to you standing still on the ground. And hopefully there are enough hints to see where I'm going with this. You're not being \"accelerated\" in the conventional sense. But you're not in an inertial reference frame because you're not free-falling towards the center of the mass. You're being ",
" upwards by all the ground beneath you, all the same as a rocket would be ",
" you upwards in our conventional way of thinking of acceleration. So since your reference frame is non-inertial... guess what fictitious force now exists to describe physics around you? gravitation. All the basic Newtonian ballistics and stuff works because there's this fictitious force from your reference frame that ",
" it's a standard kind of force. ",
" Gravitation, as seen from a point stationary with respect to the center of mass of an object, appears as a ",
" force, and is useful as such in standard kinds of gravitational equations."
] |
[
"The best book on this is Hartle's ",
". Simple title, brilliant book. You'll need to pick up a little bit of how Lagrangian and Hamiltonian formulations of physics work, but I think those are fairly straightforward concepts if you have a decent background in differential equations. Plus it has great pictures that a webforum just isn't suited for. See if you can get a copy through a library, or a used textbook sale.",
"That being said, what you'll find is that suppose your test particle is \"at rest\" near a body. The way that body has curved space and time means that the ",
" of that particle is \"pointed\" toward the body. So it falls inward toward the body. ",
"Interestingly enough, though it's rarely taught because it's not precisely useful, you can reformulate Newtonian gravitation entirely in terms of a space-time curvature. I forget exactly the details, but you end up with terms that talk about rates of change of space over time (derivatives of space wrt time) and rates of change of time over space (derivatives of time wrt space), but you lack the rates of change of space over space (derivatives of measures of length over various directions from a point) that exist in the GR solution. Bleh. Suffice it to say, you can recreate Newtonian gravitation by ",
" just pointing the future of a particle toward the planet some. But GR is the better description of reality. "
] |
[
"This is a poor description because it still implies gravitation. I mean what's pulling \"down\" on the sheet, what's pulling objects towards \"lower\" parts of the sheet? You could just as easily represent a gravitational field (in the Newtonian sense) by this rubber sheet analogy and come up with the same result. It doesn't say anything really about GR."
] |
[
"How do we reach temperatures such as 3500 degrees Celsius?"
] |
[
false
] |
I was on the topic of tungsten for an irrelevant project, and wikipedia said that its melting point was 3422 degrees Celsius, and an even higher boiling temperature of 5555 degrees Celsius. What sort of process is required to reach such a temperature? Or are those numbers just based on predictions?
|
[
"Acetylene oxygene welding or cutting goes up to 3500 degrees, abd it is a commonly available tool. Plasma cutting achieves temperatures of up to 25000 degrees. Lasers can also be used for achieving very high temperatures.\nThese are only some ways of achieving high temps, and i think induction heating can too. Can't libk any sources from the phone atm."
] |
[
"We can reach temperatures far hotter than that.",
"The fusion core ITER for example will operate at 150 000 000 K.",
"Just for reference: this is 30 000 times hotter than the surface of the sun. ",
"You can visit ITER's website in order to get some insight in the process.",
"Source"
] |
[
"In addition to the heating methods that other people have mentioned, you can also play games with the pressure of the system to adjust the temperature. If the system has a fixed volume, then you can increase the pressure to proportionally increase the temperature."
] |
[
"Why does flies seems to like to buzz around/on our faces?"
] |
[
false
] |
From the point of view that flying around out face will get us irritated and more incline to kill the little bugger, why does they keep doing so? Plus, why are they sometimes really fascinated by our facial cavities (ears, nose and eyes)? maybe these aren't the cases for all flies, but a lot of the kinds I meet fit those profiles..
|
[
"Confirmation bias, you don't notice the other ones..."
] |
[
"Could be earwax and the oily layer on top of they eye"
] |
[
"sounds good, but what about other places like ears and eyes?"
] |
[
"Do non-PID Controllers Exist?"
] |
[
false
] |
It seems an odd question; whichever design method I use, I invariably get a PID controller, possibly with some filtering. My question, then, is why we must keep using the acronym PID and not just say 'controller'? Edit: is this something to do with it? I'm not sure I know what's going on exactly...
|
[
"Yes.",
"The most basic kind of controller is a ",
"bang-bang controller",
", of which a common example is the thermostat used in homes. There are also proportional and proportional-derivative controllers, which are like PID controllers, but lacking the integral and derivative parts, or just the integral part."
] |
[
"From a letter to the editor in ",
" Magazine (Dec 2013):",
"\"As an engineer, I hope that someday very soon, we abandon Proportional + Integral + Derivative (PID) control algorithms altogether. Instead, I hope that we embrace a slight modification of PID that produces stunning improvements in performance: faster response times with zero overshoot.",
"A PID system integrates a signal that it has just differentiated. We get remarkably better performance by simply feeding back a second but different proportional signal downstream of the integrator. My old professor Dick Phelan called this Pseudo Derivative Feedback, or PDF. It's as though there was differentiator there, but without any of the noise introduced by differentiating a noisy feedback signal such as one gets from a real-world transducer in a vibration environment.\"",
"-Bill Nye, (yes, the science guy)",
"So to answer your question, yes, non-PID controllers do exist."
] |
[
"Yes.",
"Feed forward controllers use a physical model of the system to predict the next state, and apply a force based on this prediction. This allows control system to handle non-linear forces like sliding friction. It is most useful if the physical system has predictable or easily measurable properties.",
"Sliding mode is a non-linear control scheme that provide attempts to move a system along a state plane. I implemented one in school but have never seen one in industry thus far."
] |
[
"How come chocolate milk expires several weeks after regular milk?"
] |
[
false
] |
I just bought a carton and it doesn't expire until August 18th, whereas the regular milk all expired by the 27th of June. I understand this isn't a very scientific analysis.
|
[
"Chocolate milk, with that much of a shelf life, would be produced using ",
"UHT milk"
] |
[
"Do you know whether or not they were produced on the same day?"
] |
[
"No, which is why I was saying it's not a very scientific analysis. I did look through all of the milk for expiration dates though and the latest the regular milk expired was the 27th and the earliest the chocolate milk expired was August 18th."
] |
[
"Can overweight people survive longer without food?"
] |
[
false
] |
I'm not biologist, but I am wondering about this. Can the fat be used as an emergency "food" supply, or does malnutrition mean that starvation occurs at the same rate.
|
[
"Yes, there is a famous example of an obese guy fasted who for over a year under medical supervision and lost most of his bodyweight. ",
"Abstract here"
] |
[
"Yes they can, however they can soon run into vitamin deficiencies and other micronutrients that arent stored in fat. There was recently a story of a doctor who essentially helped a morbidly obese man (400+ lbs) lose a HUGE deal of weight by essentially starving him of all food, while providing vitamins and other essential nutrients. He went 382 days without food while under medical survellience. "
] |
[
"Actually not super recent. The fast itself was conducted in the 60's and the ",
"case study",
" published in the 70's."
] |
[
"Where do hermit crab’s shells come from?"
] |
[
false
] |
I’ve heard a few times that when a hermit crab gets too big for its shell it just finds a bigger one and transfers. Where do the shells come from in the first place?
|
[
"They will often times kill and eat- or even just discard- a snail to steal its shell.",
"I've witnessed this several times in my reef tank.",
"One time, i put a golf ball sized Tiger Nassarius snail that cost me $19 into my tank. I'd had it in quarantine for 3 months, it checked out disease free so I moved it to my display. It took 3 minutes before a blue legged hermit crab 1/3rd the size dragged the snail out, stole the shell. My fungia plate coral then ate the snail. It was the size of my pinky finger."
] |
[
"They come from snails...",
"They don't wait until they are too big, they change the shell whenever they find a better one.",
"Shells also get reused by other hermit crabs. If a big hermit crab finds a larger and better shell, a bunch of smaller hermit crabs can upgrade to larger shells."
] |
[
"Yes. I agree with this. Hermit Crabs are home scavengers. You can google images of them making homes out of anything. The doll heads are the creepiest homes, imo. It was also a big trend to keep them as pets in the 70s. Not sure if that’s still a thing."
] |
[
"How or could a small consistent charge of electricity affect the way cells communicate?"
] |
[
false
] | null |
[
"Can you clarify your question further? Are you talking about neurons and neurotransmission? Also, what did you have in mind for a small consistent charge? 5mV? 10mV, 20mV? "
] |
[
"there are ion-pumps that work very hard to maintain the cell's resting membrane potential at ~-40mV. any change to this that you could cause (say by using a voltage clamp) could significantly alter a cells ability to send an action potential in one of two ways:",
"1) if it was made more positive (depolarized closer to 0mV) then the cell would have a higher probability of firing an action potential. This could lead to things like epilepsy where there is too much excitation in the brain causing a cascade of electrical activity due to the balance being thrown off.",
"2) if it was made more negative (hyperpolarizng) then it would be LESS likely for a cell to fire an action potential and you would get things reminiscent of the effects of drugs such as benzodiazepines which potentiate the action of GABA (inhibitory neurotransmitter) which caues chloride anions to enter the cell hyperpolarizing the membrane.",
"In reality, if this was done to a whole bunch of cells for a long period of time the organism would probably be able to restore homeostasis by up regulating the sodium potassium pump that maintains the -40mV membrane potential to begin with (it would just consume more energy to do so)"
] |
[
"Thinking around 10mV-20mV \nSo exactly what I’m asking is how would it affect the receptors around the body and mind. Would the constant charge of electricity adjust the way we process things in real-world in any way beneficial? Considering that the human body it’s self produces electricity what would happen if we just in general added a small sum of electricity course through our body?"
] |
[
"Why do teenagers and children seem less affected by COVID than other age groups?"
] |
[
false
] |
Not trying to turn this into a should they get vaccinated argument. During the height of lockdown there was this argument that children and teenagers weren't coming down with those symptoms and getting as sick as adults. Shouldn't their immune systems be weaker since they haven't been exposed to as many things as a healthy adult would?
|
[
"I couldn't find a particularly detailed answer on this question, but childrens' bodies deal with a COVID infection differently to adults for a number of reasons. I can't answer the question with *specific* reference to COVID, but I can talk about some differences between kids and adults that are likely part of the answer.",
"For a start, children aren't old enough to have developed a number of the comorbidities that make adult COVID deadly - in particular, the riskiest ones like hypertension, Type 2 Diabetes, cardiovascular disease, and so on. That doesn't fully explain the difference, since some well children become extremely unwell due to COVID, and some unwell children do just fine.",
"Another difference is that your immune system changes over the normal course of your lifespan. It's really common for children to produce rapid, very high fevers in response to relatively minor infections, and non-specific febrile illness is quite a common diagnosis among children who attend emergency departments even pre-COVID. These differences are in part anatomical - kids have large thymuses, which atrophy slowly over the course of your life and end up tiny in the elderly - and in part physiological, as the child's immune system becomes exposed to more stuff over the course of your life.",
"Kids do sometimes become really unwell from COVID, though, and a major source of mortality and mobidity from the disease is a newly recognised condition called Multisystem Inflammatory Syndrome in Children (MIS-C). It's characterised by a severe inflammatory response to COVID, and developing this condition markedly increases a child's risk of death.",
"For some really good, detailed information about paediatric COVID I highly recommend the excellent health professional-focused evidence summary at ",
"Don't Forget The Bubbles",
"."
] |
[
"Yeah, they say it's rare. But I've been getting at least 2 MIS-C cases a week in children as young as 6 months. Just had a 3 year old die of a heart attack due to it"
] |
[
"Multisystem Inflammatory Syndrome in Children (MIS-C)",
"Is this a new condition that has come to light with the pandemic? Does it potentially affect their lives beyond the effects of COVID-19? Why did it take until COVID to identify this condition?"
] |
[
"what makes 'drinking' tap water safer than the stuff you wash your hands with?"
] |
[
false
] |
I've always wondered how places with drinking water taps (usually bars and clubs) can differentiate between the different water used. is there actually a purifier or a better kind of piping that does make the water safer to drink, or is it just a way to have one sink that peopel crowd around for tap water?
|
[
"There is only one source of water, and unless you are in a third world country or drinking from a well, it is safe to drink. It depends on the business but some may have extra filtration on the faucets intended for drinking water. Usually these filters only effect the taste, since again, the water coming from the mains is safe to drink. "
] |
[
"I think they also have extra aeration devices; water that is colder and has more dissolved oxygen typically tastes better. "
] |
[
"In older systems, the non-drinking water is stored for a time in ",
"header tank",
", which is in an unknown condition, sometimes with a poorly fitting/no lid... Whereas the drinking water tap comes directly off the mains supply."
] |
[
"How do radio signals work?"
] |
[
false
] |
I'm writing my final in a creative lit class - and I won't bore you with self-advertising or such - but why I want to know how they work is because in the story, there are a group of people who teleport by attaching themselves to radio signals. Another main question I want to ask is how do signals drop, or what causes a signal to drop?
|
[
"They work by oscillating electric and magnetic fields reinforcing each other leading to propagation (more detail in appendix A). I guess in your story what would be possible is for the people to convert to signals which then latch onto carrier waves. This is exactly how you receive the songs while driving in your car. The FM signal frequency, say 88.9 MHz is the carrier frequency which has the song's signal latched on to it in the form of varying the frequency slightly.",
"How do signals drop?\nDrop as in get cut off abruptly?\nIf so, it could be because of some sort of obstruction in the path of this carrier signal. Say a metal sheet which completely bounces the signal away (like in an elevator) or some dielectric material that is very lossy and kills of the signal's strength greatly (like when u drive into a tunnel...although I think in the tunnel there is some bouncing back phenomenon too)",
"Drop as in gradually fade away..like on a road trip where your FM stations becomes more and more static filled and you can't rock out to your favorite metal band anymore?\nIf so, this happens because the field intensity of the carrier signal falls as 1/r2. And your instruments need a certain minimum signal strength to be able to properly decode the sounds of the song (I keep saying song but it could be voice or anything). This is denoted by a term called SNR and the further you go away from the signal's point of origin, the lower your SNR will get. Below a certain SNR you only get static.",
"I know this is bit of a hodge-podge answer. Hope it helps!",
"Appendix A: The essential answer to your question is the combination of Faradays Lawr and Maxwell-Ampere Law. What Faradays Law says is that a time varying magnetic field (H) will induce an electrical field (E). What Maxwell-Ampere's Law says is that a time varying electric field will induce a magnetic field. Now put these two together, the varying H field will induce an E-field (which also turns out to be time varying due to the sinusoidal nature of the H-field) and this time varying E-field will reinforce and reinduce the original H field. Thus, the varying E and H fields will support each other and this leads to propagation of the EM waves without the requirement of a medium."
] |
[
"2 questions.",
"If traveling away from a signal source in a car, is the doppler effect negligible? ",
"Furthermore, how come the frequencies aren't more precise? For instance why do we use 95.5 instead of 95.52831?"
] |
[
"Doppler effect: Yes, because it depends on your speed as a fraction of that of light. "
] |
[
"Could a small star orbit a really large planet?"
] |
[
false
] |
Last weeks question about a moon having a moon got me thinking. Is it possible for a star to orbit a planet? I'm assuming that most suns are the largest object in their system, but are all of them like this? Also on the same note, could a small star orbit a larger star?
|
[
"It would be extremely difficult for it to happen. First, everything orbits a common barycenter, so the sun does orbit depending on the earth's location (and this produces the wobbles we use to detect planets outside of our solar system).",
"Anyways, a star is simply a large chunk of matter undergoing fusion, that is it is so large that the gravity increases the pressure to the point that fusion starts, the star then heats up until it's density is low enough that the fusion is a steady state thing. A planet is a large lump of matter that is not fusing (and most definitions say it must orbit a star, but I'll ignore that). Anyways, to say a star is orbiting a planet, then you're saying a planet is bigger than a star, and that would be next to impossible because that that size you would expect the planet to start fusing and turn into a star. I suppose if it was all iron or some heavy metal that wouldn't happen, but due to the ways planets form you would expect the planet that large to become a star.",
"Now the new planet-star can burn out, become a brown drawrf, and then a star can orbit that, which If it was cool enough might look like a planet."
] |
[
"Theoretically it's not impossible, if you had a planet that is made up of elements that don't fuse (elements heavier than iron) it could be larger than a star and not become a star. But the chances such a planet forming naturally are immensely small.\nBut then again, the universe is really big, so it might exist."
] |
[
"Stars absolutely orbit each other in whats known as a binary star system and they're awesome. William Herschel first discovered them. A star, however, cannot orbit a planet because of the way stars and planets are formed. The star comes first and then makes the planets from leftover nearby materials and can only form smaller bodies. If somehow a planet got to be bigger than the star, it would mean that the star would have to get bigger than it. You should read and look at images of binary star systems. I think theres one in the crab nebula thats pretty amazing."
] |
[
"How can you lose horsepower in a car?"
] |
[
false
] | null |
[
"Hi lukdboss thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Physics"
] |
[
"‘physics’"
] |
[
"In theory would it be possible to keep blood \"alive\" with the right kind of equipment?"
] |
[
false
] |
I don't mean freezing it. I was thinking about how blood is a cell in our bodies but its independent (in a way) of other bodily structures, if that makes sense. Could a machine be created that could supply blood with whatever it needs to keep it alive? Does blood have a finite lifespan once its created? Does it need oxygen and/or "food" to live. At what point does blood "die"? Sorry thats more than one question.
|
[
"The main cellular component of blood is the red blood cell, which if I understand your question correctly is what you would want to keep alive. These cells are responsible for gas exchange, i.e. bringing oxygen to tissue and bringing carbon dioxide to the lung. There are many other components to blood as well.",
"First, red blood cells (RBCs) in the body DO have a finite functioning period, roughly 120 days. The main problem is that RBC does not have nucleus (where DNA is stored) and therefore has no ability to create new structural/functional proteins. It is not so much a problem of supplying the RBCs energy (which could easily be done with a tissue culture medium) as it is their lack of ability to repair themselves structurally.",
"When RBCs have grown old enough, they are filtered out of the blood, mainly via the spleen. Each RBC must squeeze through capillaries single file in what is essentially a structural stress test. Those that are starting to wear down don't quite make it through and are filtered out. The process is more complicated than this but that is the overview."
] |
[
"\"Blood banks store freshly donated blood for up to six weeks before it is considered outdated and thrown away. But some recent studies suggest that people who receive transfusions of blood older than two or three weeks may suffer adverse effects.\"\n",
"Studies Question Shelf Life Of Donor Blood"
] |
[
"But they could be kept alive outside the body?! That's cool."
] |
[
"If you split a crystal and pushed the two pieces together would the lattice snap back into place?"
] |
[
false
] |
I'm sure it would require some energy and the particular symmetry would have an effect. Assuming no contamination .
|
[
"Whenever you split a crystal in the real world, the surface atoms will have dangling bonds, which is a ",
" high energy state. It will immediately find some way to lower that energy state, by either forming extra bonds with neighboring atoms, which creates an irregular crystal structure in the outer couple atoms, or by bonding with something else (eg. oxygen from the air). So because the structure is always modified in some way after the cleave, being able to put it back the way it was is unfathomably unlikely. Cold welding can happen (generally only in a vacuum), but it doesn't mean that the crystal has returned to the way it was before like nothing happened. It just means that enough bonds have formed between the two halves to make a solid connection."
] |
[
"That is called ",
"cold welding",
" and happens with pristine crystal surfaces. In principle it can happen with a broken crystal (before an oxide layer forms), but my intuition tells me you'd have to get the alignment juuuust right."
] |
[
"That is very interesting. Is the problem with dangling bonds always present or are there some crystal arrangements (cubic, tetrahedral etc., I'm not very familiar with the terminology) that can be cleaved cleanly in any or some planes?",
"This question is highly speculative, but I'm interested to know if it is theoretically possible, assuming all necessary perfection."
] |
[
"Why do different materials sound different?"
] |
[
false
] |
Since sound is just a bunch of oscillations in pressure, shouldn't two different materials with the same mass and surface area create very similar pressure oscillations - and therefore similar sounds? Obviously though, if you drop a rock and piece of metal you get two very different sounds.
|
[
"Imagine the sound that a square sheet of steel makes when you tap it with a fork. ",
". When you tap it with the fork you create a little deformation right at the spot the fork hit. Steel has some decent elasticity, some springiness and stiffness to it, so if you were to zoom in with a microscope, you'd see something akin to throwing a rock into a pond: a circular wave emanating out from the point the fork hit. That wave propagates outwards, wobbling the material as it goes, hits the edges of the steel plate, bounces back, and then the reflection of the wave from the edge interacts with the original wave on the return trip. This wave is wobbling the steel plate all along, and the steel plate wobbles the air, the air wobbles our ear drums, and we hear the sound of the steel plate being pinged with a fork.",
"Now imagine the same steel plate except it's made of plastic. You tap it with your fork. What sound does it make? Probably a dull ",
" or ",
". Picture this material, zoomed in with a microscope as the fork hits. The plastic is not nearly as stiff as the steel, so the wave that emanates out from the tap site is nowhere near as impressive. It dies out much more quickly. Not only is the plastic less springy, it's also more damped (more absorption of the wave), and the wave itself moves slower through the material because of its lower density and speed of sound. Maybe by the time the wave gets to the edge of the plastic plate, it has already died down and there's no real reflection. The wave ends up not interacting with itself on the way back. It doesn't create the harmonics or the overtones that the self-interacting reflection did in the steel case. Again, the plastic plate wobbles, and that wobbles the air, and that wobbles your ear, but the way it wobbled was totally different because of the material the plate was made of and the manner in which the wave traveled through the plate. The sound is duller, deader, and shorter because the wave never got to generate harmonics from the reflections, and the wave itself dies out much more quickly.",
"Shape, size, material, stiffness, damping, viscosity, temperature, and speed of sound through the material, and a number of other factors affect acoustics. "
] |
[
"Materials have different properties, densities, and atomic compositions. Since the atoms they are composed of have different masses, they oscillate differently, which causes the oscillations to have different frequencies, which produce different sounds. "
] |
[
"This. This wiki page has a good visualization and more info on this matter. ",
"https://en.m.wikipedia.org/wiki/Phonon"
] |
[
"What factors determine whether something (event, occurrence, experience, etc) makes it into our memory?"
] |
[
false
] |
We obviously don't remember everything. There's got to be some system of separating the wheat from the chaff. So what determines what makes the cut and gains admittance to our cranial repository?
|
[
"There are probably multiple mechanisms and we don't understand them all yet, however one mechanism is fairly well understood. ",
"We generally remember experiences that cause strong emotional reactions: earthquake, car accidents, deaths, etc. This works through stress hormones. Particular emotional reactions lead to the release of hormones from the adrenal gland. These hormones enhance memory consolidation.",
"For more details check this article\n",
"https://www.ncbi.nlm.nih.gov/books/NBK3907/"
] |
[
"In simplest terms, it's determined by how important a certain event is.",
"Your mind holds everything that you see in short term memory - these memories, like the face of someone you don't know, could last anywhere from 20 seconds to a minute. After that, your short-term memory starts to taper, and you'll start forgetting details. It's one reason why bystanders in a crime scene are typically unreliable in small numbers.",
"It's also during this stage that the mind determines what's most important, so it can commit some of these memories to your long-term memory. Once this happens, you can store it and access it at any time during a later date.",
"During those 20-60 seconds, your mind determines what's most important, and what isn't (based on experience, moral values, opinion, etc), and that commits it to memory.",
"For instance - your first year in elementary school. You don't remember all the details - it was long lost as a kid. But, you know the classroom, and you know the feel of the room. That room, since you've experienced it for a year in your life, has been committed into long-term memory, simply because it was a significant portion of your life. I haven't gotten into details about why all of this happens on a biological scale, but that's the information that I know from my Psychology class, when we discussed memory stages.",
"EDIT: If you like things like this, watch Brain Games when you get the chance. They give good insight and explanation into things that some people might not understand - like how many memories we can store in a short time, why humans aren't aware of their environment, and other things!"
] |
[
"Does that mean if I make a drug that mixes epinephrine (or cortisol) and some kind of \"emotion enhancer\", I've created a memory enhancement drug?"
] |
[
"Why does opening both the window and the door make a room so much colder than just opening the window?"
] |
[
false
] |
Whenever I just open the window in my room, there is a slight breeze, and not much more. If I also open the door, the room gets significantly colder, as if there were some kind of vacuum effect. It probably has something to do with equilibrium, but can someone clarify why this happens?
|
[
"I don't know how your room is set up but I'm guessing it's just a matter of airflow. If you have a door open as well it is easier for air to flow through the room to cool it rather than just trying to enter / exit through the window and mix. "
] |
[
"It is sort of like an issue of pressure. If you only have a window open if air blows in it doesn't have anywhere to go really other than compress. If you have the door open also it can sweep through cooling more effectively. "
] |
[
"it doesn't have anywhere to go really other than compress",
"Well, it probably flows in the room through the lower half of the window and out of it through the higher half. But still, less efficient than opening a door too."
] |
[
"Why can't we synthesize Antibodies to treat Viruses?"
] |
[
false
] |
I don't know a ton about biology and chemistry seeing how I am studying physics. Why can't we take blood from a patient who successfully generated antibodies for a virus, isolate those antibodies, synthesize replicas and use them to treat new patients?
|
[
"Making a complete antibody is quite complex, even in today's time. For pharmaceutical companies it is usually much easier to look into other ways to vaccinate, like with dead viruses to make the appropriate immune response. It may still be relatively complex to do it, especially with viruses that mutate fast (like for flu), but it is always better if the body makes an immune response itself.",
"This is because antibodies are just one part of the immune response. They help other immune cells to detect a virus when it is not inside a cell or help them clump them up for destruction by other cells. Another important part of the immune response though is to treat cells that have been infected. There are special immune cells, called T-Cells that engage independent from the antibody producing cells (B-Cells), these cells develop a receptor on their surface in a similar way as the antibody-producing cells make antibodies, but as I said, independent, so if you have an antibody that you inject to a person, the T-Cells of this person still lack the right receptor to engage the virus you are trying to vaccinate from.",
"One of the T-Cells functions is to destroy infected cells in a controlled manner so that the infection does not spread any further. This is important as if the cell dies by itself while being infected, which is actually the result of many viral infections, it undergoes a process called nekrosis, rupture of the cell. All contents are spilled in the surrounding area, including newly produced viral particles that can infect more cells. T-Cells induce a control cell-death, apoptosis, which essentially leads to self-digestion of the cell and all its contents.",
"Hm, not sure if I forgot something, maybe others can add up on this.",
"edit: realized some more points. Antibodies are not stable indefinitely, so while it may help short term they have to be reproduced. If your body makes them itself, the cells will continue producing antibody, if you administer them from outside your body will not pick them up and produce them.\nAlso, recognition of pathogens by the immune system will lead to long term immunity by storing the information in a sort of memory. Once the infection has died down, most immune cells with the specificity against the pathogen will die off, but some turn into memory cells which will get activated to launch the same immune response once again should the same pathogen turn up again. You would miss this part as well if you would just give antibodies."
] |
[
"There are many problems with your suggestion's details, but in the big picture it's not only possible to do this, but routine. ",
"The way it's actually done as a rule is to immunize mice with the agent, under controlled conditions; when the mouse has made antibodies (which are functionally the same as a human would make -- but see below) the cells making the antibodies are isolated and made immortal so they produce vast amounts of the antibody of interest. These are monoclonal antibodies, which earned a Nobel in 1984 but now are pretty much trivial. ",
"If you're going to use the antibodies in humans, there are some issues with having mouse sequences as part of the antibody, so you'd just clone them, swap out the mouse part with human sequences, and then produce the cloned antibody however you like. Again, pretty much routine.",
"There are quite a few examples of this, with the one most in the news these days being the ZMapp treatment for Ebola, in which exactly this process was followed.",
"ZMapp also illustrates a couple problems with the approach. Antibodies are complex things and need to be made in cells -- they can't be chemically synthesized (or at least not efficiently). That means that making them is relatively slow and cumbersome compared to many drugs. ",
"There are other reasons to prefer conventional drugs over antibodies. Antibodies are also hard to deliver efficiently. They're large proteins, which means they don't necessarily get to the site they're needed quickly and efficiently. Large protein drugs have other issues, like storage and so on, but that's not a giant concern. And antibodies are generally less effective than you might think, as single treatments for viruses. ",
"Back to the specifics of your question, there's really no point in taking antibodies from a recovered patient for this, you can get more effective antibodies -- with no risk of carrying along blood-borne pathogens -- by immunizing mice.",
"And you don't want the antibodies themselves. You want the cells that make the antibodies, since you can much more easily sequence and characterize the nucleic acids that encode the proteins, than the proteins themselves.",
"It's not particularly easy to isolate the B cells that make the antibodies you want, but it's becoming much more routine all the time. ",
"If you do have recovered patients, and you're kind of desperate, you can try just transferring serum from one to a new patient. That transfers the antibodies in bulk, even without you needing to identify the ones of interest. There are obvious problems there -- transfer of blood-borne pathogens, for example, and the need to do some cross-typing. This is being done with Ebola, once again, and you may have heard the the patient who died (Duncan) was not a safe match to receive serum from the first doctor who recovered, though he (the doctor) has repeatedly donated for other patents .",
"But you can also see that transferring the serum isn't a large-scale solution. One recovered patient can't treat all that many new patients (it's also not 100% clear that this actually does any good, in the case of Ebola). ",
"Anyway, bottom line, the concept is good and has been done for 20-30 years already, but also has major disadvantages compared to conventional treatments. "
] |
[
"That was one of the most thorough answers ever. Thanks. That explained quite a bit"
] |
[
"How are we utilizing quantum mechanics in the pursuit of technology?"
] |
[
false
] |
I think my question is more basic than it sounds. I understand HOW we use it, entanglement, superposition, etc. What I'm wondering is how we even get there! Atoms themselves are so incredibly small; how do we go about manipulating electrons and fundamental particles? What kind of equipment or technology is necessary?
|
[
"One way to include quantum mechanical effects in otherwise bulk materials is to include very thin layers of another material. ",
"If you were to heat a bit of material in a vacuum chamber to the point where it beings to sublime, atoms from that material fly off and may stick to whatever they hit. If you do that briefly, you get a very thin layer of the source material on some target. If you do it for a long time, you get a bulk material, perhaps a crystal. By varying the material being evaporated, as well as the time and temperature, you can vary the structure that you are growing. This is MBE: ",
"Molecular Beam Epitaxy",
". You can also chemically deposit materials, for example in ",
"Metalorganic vapour phase epitaxy",
", and there are other ways.",
"The structure is also dependent on what you're growing on, and you may get anything from clean layers (quantum wells) to patterns or random distributions of quantum dots. These in turn affect what the next layer will look like, and so on. Depending on the material being evaporated and the shape of the crystalline arrangement of the substrate, you may be able to grow homogeneous thin quantum wells, or patterns of quantum dots, or even quantum wires. ",
"Another, entirely different way of introducing quantum effects is with ",
"electon-beam lithography",
", by which you use beams of electrons to draw shapes on electrosensitive chemicals on the surface of samples, which changes the solubility of the resist. You can then wash away either the exposed or the non-exposed bits, and you're left with a mask with features as small as 10nm, which is well in the quantum domain, features that can then be etched or otherwise processed into actual target structures."
] |
[
"I do research in spectroscopy, particularly electronic/laser spectroscopy. The laser alone represents some amazing advances in quantum mechanics that allowed us to construct it in the first place. The system I study are semiconductor nanocrystals, often referred to as quantum dots (QDs).",
"QDs are remarkable materials with electronics properties that depend largely (but not solely) on their size. They're great candidates for LEDs, solar cells, and are in fact used in some current generation Sony/Samsung TVs.",
"The reason they're called \"quantum dots\" is because they exhibit a phenomenon known as quantum confinement. In essence, this means that the wavefunctions of their electrons (and holes) are (in terms of size) on the same order as the size of the entire molecule. The effect of this is that they show (near) discrete emission spectra. Some more \"purely\" quantum applications of these things are generating entangled photon pairs, and random number generation. I could go on for hours about this, and if you're really interested feel free to PM me.",
"EDIT: I noticed ",
"/u/viscence",
" mentioned quantum dots made by molecular beam epitaxy, and while these exhibit all the same properties, are harder to process and actually apply, as opposed to colloidal quantum dots, which are synthesized in solution and can be cast/dropped/placed onto a variety of different substrates."
] |
[
"Photonic quantum information devices are probably the easiest. For polarization-entanglement you can use ",
"spontaneous parametric down-conversion",
" in a nonlinear crystal. It is not very complicated and merely requires a strong laser to pump the crystal and a suitable crystal plus a bunch of generic optics. Then of course you also need single photon detection, if you actually want to measure something. Depending on the frequency of the photons effective detection is not very hard. You can use for example single-photon avalanche diodes, so essentially semiconductor-based photomultipliers. For other wavelengths you will need superconducting nanowire detectors for reasonable efficiency which work at temperatures of less than a Kelvin and therefore ask for a lot of additional infrastructure. ",
"For qubits that are encoded into atoms things are more complicated. There are two approaches to confine a single atom and play around with its internal state: Using ions and using neutral atoms. The first is easier in several aspects. The ions can be confined very strongly in electric fields in so called ",
"Paul traps",
". For placing them you just 'spray' the ions, turn on the trap and look if you catched something by chance. The largest part of an ion lab is filled with setups for laser preparation: You need to drive many different transitions with high fidelity, which means you need very narrow band lasers at very specific frequencies. This is achieved with frequency conversion in non-linear processes and different laser-locking techniques. So the necessary infrastructure includes high finesse optical resonators, a bunch nonlinear crystals for frequency conversion, the electronics for your trapping potential and also a vacuum pump since the ions are stored in vacuum. For neutral atoms things are pretty similar except that they cannot be confined with an electrical field. Therefore you use for example the AC stark effect to trap them with lasers. Because the confinement is much weaker the atoms need to be very cool in order to stay in the trap. ",
"There are also many other implementations and tools, for example defects in crystals or Josephson junctions, each with different advantages and disadvantages and difficulties in the implementation."
] |
[
"When I stretch a piece of red plastic wrap over the end of a flashlight and turn it on, what is really happening to the light?"
] |
[
false
] | null |
[
"The \"white\" light coming from your flashlight is leaving the bulb and traveling towards the red plastic. White light is of course all colors of light traveling together. ",
"When this white light hits the red plastic, the part of the light that is red continues through, but all of the other colors of the rainbow are blocked and absorbed into the plastic."
] |
[
"You got it a bit backwards. Grass, just like most other things with green chlorophyll in it absorbs most of the light in the visible spectrum. Its absorption minimum is around 550 nm, which gets reflected. That reflected light looks green to our eyes.",
"Now, if you take a photo of the grass and print it on a standard CMYK printer, then the similar green colour will be generated differently. Your eyes will perceive the overlapping cyan and yellow pigments on paper as green. "
] |
[
"You got it a bit backwards. Grass, just like most other things with green chlorophyll in it absorbs most of the light in the visible spectrum. Its absorption minimum is around 550 nm, which gets reflected. That reflected light looks green to our eyes.",
"Now, if you take a photo of the grass and print it on a standard CMYK printer, then the similar green colour will be generated differently. Your eyes will perceive the overlapping cyan and yellow pigments on paper as green. "
] |
[
"As an enveloped virus, why can COVID-19 survive on surfaces for so long? From my understanding enveloped viruses must stay wet to remain infectious and are sensitive to environmental changes"
] |
[
false
] | null |
[
"Not to flip the question back to you, but what do you define as \"for so long\"?",
"Non-enveloped viruses, such as norovirus, can survive on surfaces for weeks, if not months. In contrast, enveloped viruses survive for hours (days depending on type of surface). Comparing the two, enveloped viruses such as COVID-19 do not really survive that long compared to their counterparts.",
"I feel that it is also important to emphasize that just because COVID-19 can be detected on a surface does not mean COVID-19 is unaffected by the surface. A study out of NEJM (a leading medical research journal) found that on plastic, only 10% of virus of what the researchers deposited could still be found 8 hours later. That being said, virus could still be detected up until 72 hours later. Survival of virus does not mean virus is thriving.",
"Sources:",
"Norovirus longevity - ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7091010/",
"NEJM on SARS-CoV - ",
"https://www.nejm.org/doi/full/10.1056/NEJMc2004973"
] |
[
"Also - that a virus DNA has been detected on some surface doesn't mean that the virus is actually \"alive\" (as much as a virus can be considered being alive), viable and capable of causing an infection. ",
"Many of the studies, especially the ones with the large number of hours/days for the coronavirus that have been so much bandied around at the start of the Covid-19 pandemics, did not actually evaluate this. They were testing for the presence of the viral DNA - which could be a viable virus as well as just \"viral debris\" from the disintegrating viral particles incapable of causing serious harm anymore. ",
"The tests used (e.g. the PCR method) don't permit to determine this and at the same time they are sufficiently sensitive to pick up even traces of already \"dead\" virus.",
"So these numbers need to be considered in the light of that."
] |
[
"It only survived that long in optimal perfect conditions. And the longer it’s there, the fewer there are. If someone says it survives 72 hours, that doesn’t mean 100% of it survives that long, that’s when the last remnants die off. Friction and environmental changes do effect how much of the virus is still alive very much"
] |
[
"Reddit do you have any examples of bias within science?"
] |
[
false
] | null |
[
"This might be an interesting example of bias that was eventually overcome."
] |
[
"Thank you"
] |
[
"There's plenty of bias in science. It's actually harder to find an example where bias ",
" exist in some form or another. The point is that the process (repeated peer review and duplication) is designed to minimize the ",
" of bias. That's the beauty of the scientific method - it can succeed in a relatively unbiased way even if the participants are biased."
] |
[
"Do COVID-19 vaccines prevent Long COVID?"
] |
[
false
] |
There have been reports that COVID-19 can for some leave lasting damage to organs (heart, lungs, brain), even among people who only had minor symptoms during the infection. Since some of the vaccines, notably the one developed by Oxford-AstraZeneca, report ok-ish efficacy in preventing symptomatic COVID-19, but very high efficacy in preventing severe COVID-19, I'm also interested in how does this vaccine fare in comparison to the ones that have higher reported efficacy against symptomatic COVID-19. So, to phrase that as a question:
|
[
"I wouldn't confuse 90 plus percent efficacy with only okay results. The bottom line is the vaccines, even after only the first dose, drastically reduce your likelihood of getting covid-19 of any type, long, asymptomatic, death, etc.",
"The data are very clear that the vaccines are highly effective and highly safe."
] |
[
"Long covid is just a term for the side effects of residual damage from the virus and resulting inflammation. This could be damage to the lining around the heart, lung damage that reduces lung capacity, neurological damage, or damage from blood clots. In extreme cases, people have even had limbs amputated. ",
"Long term damage from a illness is not a new phenomenon. People have gone deaf from Measles and lost kidneys due to strep infections. Covid-19 is just another virus. Considering that the vaccine prevents most illness and even more severe illness, it definitely reduces the odds of developing \"long covid\"."
] |
[
"Long covid is just a term for the side effects of residual damage from the virus and resulting inflammation. This could be damage to the lining around the heart, lung damage that reduces lung capacity, neurological damage, or damage from blood clots. In extreme cases, people have even had limbs amputated. ",
"Long term damage from a illness is not a new phenomenon. People have gone deaf from Measles and lost kidneys due to strep infections. Covid-19 is just another virus. Considering that the vaccine prevents most illness and even more severe illness, it definitely reduces the odds of developing \"long covid\"."
] |
[
"Most star systems are binary. Is Jupiter a sun that never 'ignited'?"
] |
[
false
] |
In 2001 or the sequel (or both) Jupiter gets turned into a sun. Was Jupiter just a sun that didn't have enough mas to fire up?
|
[
"I'm not sure if there's any more recent research, but at least as of about 2006, astronomers had concluded that, in fact, most stars are singletons, not binary or higher. You can see articles on this ",
"here",
" and ",
"here",
". The studies showed that while most bright stars were in multiple star systems, there are lots of dim stars that are singletons, which tip the overall balance the other way.",
"As for Jupiter: It's not really close in size at all to being a star. It would have to have been about 80 times bigger for fusion to start and for it to have become a star."
] |
[
"The radius could easily stay the same, just as it could shrink or expand. ",
"Mass is not always correlated with radius. Keep in mind that black holes are collapsed stars. These entities are single points with densities approaching infinity. Similarly, you can have red giants that are overall less dense than the Sun if you consider their overall volume. "
] |
[
"Just to add: \"bigger\" here means more massive. Jupiter actually has a very similar radius (if not a slightly larger one) to a brown dwarf tens of times more massive than it."
] |
[
"Does the spin of a ball reverse upon hitting a wall?"
] |
[
false
] |
I play racquetball once in a while, and came up with this question. If I give the ball a spin, will it continue to spin the same way on its way back or will it spin differently? Thanks!
|
[
"Not necessarily. On a frictionless ball this would be true, but in the real world you can get a ball to change its spin when you bounce it. ",
"Basically, rubber balls have both friction and elasticity. When a bouncing ball hits the ground, it compresses and acts as a spring. Some energy goes into the ball and is then released, making the ball travel in the opposite direction. ",
"Normally, we think of elasticity as being through the centre of the ball (causing it to bounce), but the ball is elastic in all directions. If a ball is spinning, friction also plays a role - the bottom of the ball sticks to the surface, while the rest of the ball's inertia makes the ball deform. When ",
" energy is released, it acts parallel to the surface the ball was on before, and in the opposite direction of the previous spin. ",
"This picture may help you visualize things - think of the red lines as leaf springs."
] |
[
"This is dependent on the materials used and the friction between the two. In a perfect bounce. All kinetic energy is converted into elastic potential energy as the ball hits the surface, then is reconverted back into kinetic energy. Now if a ball's spinning, those mechanics come into play, albeit a little differently. Lets say we have perfect lateral friction, meaning the ball can go up and down, that's it. Upon hitting the ground, both the kinetic energy from the drop, and the energy from the spin, kind of twisting the ball. When it leaves the ground, it will be traveling in the opposite direction (up) and spinning the opposite way. Friction isn't always perfect though, and there are multiple variables in play such as the initial friction, the force and speed of the spin, ect. Think of a pool ball when you apply english. It goes in the same direction as it would originally, but as soon as the spin slows enough, and friction overcomes the momentum, it will start spinning in the opposite direction. This can also be seen with the old hoola hoop game, if that's a better reference. As far as racquetball goes, the spin is ",
" dependent on the angle at which the ball hits. While it's compressing and uncompressing while against the wall, it is essentially rolling, so the spin is the same direction as it hit the wall as. However, this may change the angle the ball leaves the wall at if there is spin applied to it beforehand (heavy backspin, and the ball will drop after hitting the wall, but depending on what angle it hits the wall it, will also play a factor in it's spin direction. "
] |
[
"It depends on the angle at which it hits the wall. That said, I'm curious as well for the case of a head on collision.",
"And even for a head on collision, it is going to depend on the properties of the ball. If the ball weren't elastic in any way, certainly no. But racquetballs are not perfectly ridgid, which makes this problem an experimental one certainly. Why don't you test it?"
] |
[
"Energy: What exactly is it? How would you describe it physically?"
] |
[
false
] |
How would you physically describe different types of energy e.g. Energy produced from respiration in body cells, energy in EM(Electo-Magnetic) waves? How does energy made from respiration enable you to make your muscles work? Thank you for any answers.
|
[
"Energy: What exactly is it?",
"It's a (usually) conserved quantity that can be calculated from measurements on a system, and becuase it is conserved, it can be used to calculate/predict new measurements when the system changes or interacts with another system. This makes it very useful to know! The same is true for other similarly conserved quantities, such as momentum. Because it is conserved, we can construct equations relating different quantities/systems.",
"If you are looking for a technical definition ... the ",
" fundamental definition we have for energy is: energy is the conserved quantity associated with ",
"; meaning, the fact that the laws of physics don't change over time, leads to the quantity we call energy being conserved. This is proven mathematically through ",
"Noether's theorem",
".",
"How would you describe it physically?",
"Well, you wouldn't really. Energy has no \"form\" or \"substance\" of its own -- rather, energy is a ",
" associated with systems.",
"It would be equally difficult to describe \"velocity\" physically. Velocity doesn't really have a physical, tangible existance, it is just a property that systems have; they can be moving quickly or slowly in various directions, or they can be stationary. Likewise, systems can have large or small energies and in various forms.",
"How would you physically describe different types of energy e.g. Energy produced from respiration in body cells, energy in EM(Electo-Magnetic) waves?",
"You can only describe energy insofar as you can describe systems which possess energy, and the way they interact. Energy in EM waves is just a property that each photon carries with it, and which is transferred to another system upon interaction with the photon. Energy produced from respiration in body cells is transferred through the interactions of the body's systems with oxygen molecules in the air. And so on ...",
"How does energy made from respiration enable you to make your muscles work?",
"It's just a big, long, (often complicated and poorly understood) chain of interactions which transfer energy from one system to the next. From the air, to your lungs, to your blood, to your muscles, and so on. You can get into much deeper levels of detail, but the deeper you go, the more you realize you're just describing the other informational aspects of the system itself, and not only its energy. Yet, that is why the quantity of energy is useful to know, because we can calculate some of those other informational aspects ",
" the energy, if we know how the system behaves.",
"Hope that helps!"
] |
[
"There really isn't a satisfying definition without understanding advanced classical mechanics. Until then, you have circular definitions like \"energy is the capacity to do work.\"",
"Energy is something that is conserved when a system doesn't change if you move it forward or backwards in time. This comes from something called Noether's theorem, which is a concept that relates conservation to symmetry."
] |
[
"Etymology is not the same as definition though. Atoms are sliceable."
] |
[
"Why can we see so far into the past?"
] |
[
false
] |
Why can we see so far back into the past? This has always puzzled me. If we are expanding then I would think any light emitted long ago must have already passed the earth. Since we are now able to see roughly 12 billion years ago, I am obviously missing something. My Google and Reddit searches have failed me. There are lots of answers for how far back, but I have found none for why.
|
[
"I think you may be confused about what the expanding universe actually looks like.",
"If by an \"expanding universe\" you picture a bunch of stuff moving away from each other, then indeed you would imagine that there would be some sphere around 13 billion light years in radius, and at the edge would be the first photons from the big bang, behind that would be the next-fastest-moving stuff, 12 billion years old, and behind that the 11 billion year-old matter, etc.",
"But that is ",
" what the expansion of the universe looks like. The expansion of the universe is not the expansion of \"stuff\" in space. It's the expansion of space itself. A second after the big bang, the universe was ",
" infinite, and somewhat uniformly filled (very densely) with stuff. Because the universe was infinite then (as it is today), there were objects way back then which were ",
" separated by 13 billion light years, or 100 trillion light years. Some of those objects are objects we'll probably never see. The universe continued to expand, but not because objects were moving with respect to each other; ",
" was expanding (and still does today). This is why the cosmic microwave background radiation (essentially left-over radiation from the big bang) is still uniformly filling the universe everywhere, instead of expanding outward along the surface of some sphere 13 billion light years in radius. The big bang didn't happen at a single point in space, it happened at ",
" points in space; indeed, it may have been the creation of space itself.",
"(For those who would like to point out that it is not actually known whether space is infinite, or whether it's a sphere, or a torus, or some other shape, it's true that we don't know that for sure, but it doesn't change the most important point that the big bang occurred at all points in space)"
] |
[
"Fun fact: The term \"Big Bang\" was actually coined ",
" by someone who was mocking the idea. The name stuck. Though \"Horrendous Space Kablooie\" has been rising in popularity in recent years.",
"In fact, it was neither big, nor a bang."
] |
[
"light we see that is 13 billion years old came from a source 13 billion light years away.",
"This is not true. Read up about the expansion of space."
] |
[
"Why isn't it possible to create a monopolar magnet by just creating a ball of stick magnets with all the same pole pointing inwards/outwards?"
] |
[
false
] |
Wouldn't that create a magnet which has the same pole on all sides? For illustration i tried to make a paint sketch: Why would the magnetic field created by those two be different? Wouldn't both magnetic fields just radiate straight outwards?
|
[
"Maxwell's equations, specifically div(",
") = 0, say this is not possible. In fact, the magnetic field of the (ideal) configuration that you propose would just cancel entirely and be ",
" everywhere. (If ",
" is spherically symmetric, then ",
" = B(r)",
" and the flux across a sphere of radius ",
" is 4πR",
"(R). This is equal to the integral of div(",
") in region enclosed by the sphere. But since div(",
") = 0, we find 4πR",
"(R) = 0 for all ",
". Hence ",
" is identically ",
".)"
] |
[
"It won't work. Individual magnets would have field lines between them. Even if you could make a hollow sphere which was radially magnetized, you can't create a monopole. The fields of magnets on opposite sides cancel each other. There is no field inside or out. ",
"Source"
] |
[
"The \"SN\" magnets on the left side would also have an effect on the field on the right side, cancelling the \"NS\" magnets there, and vice versa. Same for all other regions. As result you only get small irregular fields from the not perfectly symmetric arrangement of magnets.",
"An analogy with electric charges: if you put a small negatively charged sphere in a larger positively charged sphere and the sum of charges is zero, the electric field outside is exactly zero. You would have an electric field between the spheres, but here the analogy breaks down because actual magnets are not two monopoles at a distance."
] |
[
"Why doesn't the speed affect the amount of work done by friction?"
] |
[
false
] | null |
[
"My confusion comes from believing the an increasing velocity would increase the distance traveled by the box thus increasing work done. Can someone explain to me why this isn't true?",
"That's only true if the initial velocity is >0 and F_f>F_g (kinetic friction is causing the box to slow down), in which case if you go from initial time to the time the box stops moving. It may well be the case that friction is slowing acceleration but the box is still accelerating down the slope, or that the force due to kinetic friction is the same as that due to gravity.",
"After posting I found a source saying that increased velocity leads to decreases contact between the two surfaces due to \"microjumps\". Unless someone explains otherwise I'm going to assume the increased distance and decreased contact cancel each other out.",
"Maybe, but this isn't what the MCAT test is talking about, it's using first year physics model of having a 'kinetic' coefficient of friction, which isn't velocity dependent (even though in reality it is). Microjumps have nothing to do with your problem. Stuff like this belongs in ",
"/r/learnmath",
" ",
"/r/cheatatmathhomework",
" or another homework/study help subreddit, not ",
"/r/askscience"
] |
[
"It would travel farther if the force due to friction was greater than the force due to gravity, and hence it stopped moving eventually. There's two other possible cases where the object continues to travel indefinitely."
] |
[
"It would travel farther if the force due to friction was greater than the force due to gravity, and hence it stopped moving eventually. There's two other possible cases where the object continues to travel indefinitely."
] |
[
"What happens to the lungs after death?"
] |
[
false
] |
Do bodies really exhale like on TV? Can you die with a full breath inside your lungs? If you can die with air inside, how long does the remaining air last? Does your diaphragm need to move to empty the lungs? Edit: Thanks to everyone who answered! Follow up question(s): what happens when someone dies of smoke inhalation? Is the residual air in their lungs clean or does the nature of this type of death mean it’s all smoke? Is there visible remaining smoke or do the lung cells absorb it?
|
[
"I will give you an example from my experience as a nurse. When turning/moving a person who has recently died, yes you can hear them exhale. Maybe the movement changes the pressure in the chest or abdomen. Let me just tell you that the first time I heard it I freaked out a tiny bit."
] |
[
"Worked as a mortician for a few years during my apprenticeship as a carpenter (in small villages in Germany usually the carpenter doubles as mortician) and the first time moving a dead person was pretty upsetting.",
"If you lift the body on both ends it bends in the abdomen area which compresses the lungs and forces the body to exhale. Sometimes you can hear a muffled “haaaaaaa”. Even more if you set the person upright to dress for the funeral. Haunting for the first few times…",
"edit: joiner seems to be the better fitting translation for “Schreiner” or “Tischler” ",
"Carpenter are more the ones working in construction and building wooden roof etc."
] |
[
"Does it make a sound like a sigh or is it just a rush of air?"
] |
[
"Why isnt space super bright even though The Earth is bright."
] |
[
false
] | null |
[
"Astronomy"
] |
[
"Astronomy"
] |
[
"Things appear bright because photons are entering our eye (after bouncing off of something or straight from the source). There is (practically) nothing in space, so it is black. When we look at sun, photona emitted from the sun hit our eyes and we see light. Photons bouncing around in our atmosphere eventually reach our eyes making the sky appear light."
] |
[
"Can plants get \"cancer\"?"
] |
[
false
] |
They are made out of cells and exposed to UV rays nearly all the time. So why shouldn't the UV rays ionize their cell nucleus and corrupt the DNA?
|
[
"Any complex multicellular organism can be suseptible to defects in cell proliferation causing individual cells or groups of cells to develop abnormally. In animals, these defects lead to tumour formation and cancer and plants develop tumours too which can be detrimental to how they function or develop. One crucial difference between plant and animal tumours is that, unlike many animal cells, plant cells are incapable of moving as they are fixed in a cell wall matrix. As such, the 'cancer' in plants is not able to spread to other parts of the organism and rarely kills.",
"So why do plants develops tumours? You asked in your question whether exposure to UV light could be a cause, but as far as I can find this is not the case. A vast majority of tumours developed by plants are caused by pathogens - specialised viruses and bacteria that invade plant cells and cause defects. One of the most common plant tumours are called ",
"Crown Galls",
" which develop in the plant stems and are caused by a specific soil bacteria. Similarly, certain fungal diseases can also lead to the development of tumour like growths.",
"Certain plant varieties are also suspect to spontaneous tumour formation due to genetic disorders, particularly hybrid plants. Tobacco plants, for example, are one of the most suseptible to this and hybrid can be so over-run with tumours that flower and seed development is severely comporised. ",
"Reference: ",
"Doonan & Sablowski (2010) Walls around tumours — why plants do not develop cancer, "
] |
[
"A side note: tumors on trees are also known as \"burls\", and the wood that comprises them is called burlwood. Because tumors are basically unregulated growth, they generally have a ",
"very irregular grain",
", which actually makes it superior to normal wood for certain purposes. For example, burlwood is far better suited for applications in which it must be bent; normal wood tends to split along the grain when bent too far in the wrong direction, while burlwood doesn't actually have any straight lines in its grain, making it far less susceptible to splitting.",
"Oh, and it's also used for aesthetic reasons; its unusual grain pattern just plain looks cool."
] |
[
"I always imagine DNA as being a \"code\" which says \"put the next cell here, the next here, etc.\"",
"It's more like a complex network of interconnected chemical mechanisms running independently in each cell. There isn't a \"next cell wall here\" overseer imposing high-level order so much as there are many self-regulated cellular processes acting on local information, such as \"this cell sees local concentrations A, B, C of signal molecules X, Y, Z, so the cell should produce protein G now\". The structures that result are an emergent phenomenon. \"Put the next cell here\" is an outside, abstract perspective - the cells have no such luxury. It's just cells interacting locally - none of them have the 10,000 foot view. And yet their regulation mechanisms interact in such a way to produce coherent larger-order structure. It's really pretty amazing.",
"I don't know much specifically about structure formation in plants, but ",
"here is a wiki page",
" that explains how chemical concentration gradients help form structure in fruit fly embryonic development. All information about structure formation comes down to where certain chemicals are present and in what concentration, and the structure forms as an emergent result of the cells responding to and interacting through those chemicals.",
"Here is a high-resolution video of a fruit fly embryo developing",
", and ",
"here is a ~30m lecture",
" on structure formation in fruit fly embryonic development. The discussion of bicoid protein starting at about 15:00 is especially relevant - the gradient of bicoid in the early embryo is what determines which end will become the head.",
"Anything that alters these cell feedback and signaling mechanisms can drastically alter larger structures. There's a specific presentation I wanted to find, but I can't find it online - I saw it in person. I'll just introduce the main concept:",
"If a sheet of undifferentiated stem cells differentiates such that there are evenly spaced cells of type A with the spaces filled by type B, this is regulated through concentration gradients of signaling molecules. At one edge of the sheet (determined by some earlier chemical process) the cells will begin to produce molecule X with a weak positive feedback loop, such that seeing local concentrations of X causes higher production of X. Once one cell reaches a critical concentration of X, it triggers the beginning of a sudden differentiation to type A, and the production of large amounts of signalling molecule Y which then leaves the cell. This produces a chemical gradient of Y that diffuses past and into the surrounding cells, and strongly ",
" production of X in those cells and causes differentiation into type B. But it only diffuses so far before the concentration of Y is too low to suppress production of X, and at that distance away a cell is able to reach a critical level of X and become another type A cell. In this way you end up with a regular lattice of type A cells among a sheet of type B cells. What determined how far the type A cells should be spaced? The diffusion length and resulting concentration gradients of signalling molecule Y as produced by the earlier A cells! Nowhere in the DNA was the explicit high-level instruction \"OK, now put another type A cell over there\". It's all in terms of interconnected chemical mechanisms that are promoting or suppressing each other, and the way these chemicals diffuse through (or are actively transported between) neighboring cells.",
"(This last paragraph was a rough sketch of a presentation I saw on cell differentiation in the development of fruit fly eyes, where this type of regular lattice is present in the early cell differentiation)",
"Now imagine what happens if there is a mutation in the cell that divided to form a portion of the sheet, and it has a defective gene for signalling protein Y, producing nonfunctional Y* instead. The first few mutant cells become type A, but they don't produce the inhibitor Y, and so their neighbors become type A too. That patch of the sheet will have too many type A's with maybe a few type B's irregularly scattered through them, since the protein Y* isn't functional in causing neighbors to become type B instead. ",
"Or maybe alternatively there's a mutant variant Y+ that is ",
" effective, either because it diffuses more easily or is more directly inhibitive, resulting in the type A cells being spaced too far apart, with too many type B cells between. You'd get a similar result from having a mutation in the regulation mechanism causing an overproduction of Y, even if the gene for Y itself is normal."
] |
[
"Does the force of ejaculation influence the probability of impregnation, or is this only determined by the swimming speed of individual sperm cells?"
] |
[
true
] | null |
[
"Right, I see that most folks have decent answers but were kinda 'half-answers'. I'm hoping to provide some simple, complete and conclusive answer considering I just did a thesis on this.",
"Here's the first part of the answer: ",
"The second part of answer, we'll explore what exactly determines probability of impregnation. I've included some proper scientific terms just so in case you come across these terms while reading around, you'll have a rough idea what scientists are talking about.",
"We must all bear in mind will be that sperm literally 'go through hell' in order to meet the egg. I remember an ",
"experiment",
" done by my professor way back in 1990s where they asked women who were about to have their womb removed, to be inseminated either with partner's or donor sperm, let the sperm swim for a day, and then performed surgery to remove the womb and then check how many sperm cells made it to the fallopian tubes. Fertilisation usually occurs in the fallopian tube. Considering that a normal ejaculate roughly contains at least 20 million sperm (usually in the order of 40-60 million for most people), it was found that a median of ~260 (range 79 to 1300+) made it to the tubes and had a ",
". That's some serious competition and some harsh drop out rates.",
"The main factors that affect impregnation, from a sperm point of view, would be:",
"Only when the sperm possesses all these capabilities then will it have a chance to be considered at fertilisation.",
"Increasingly folks have realised that there's another checkpoint that the sperm must bypass to trigger fertilisation:",
"So it's really quite an arduous journey a sperm cell has to make within the female reproductive tract, making all of us miracles of nature.",
"edit: formatting, edit2: fact checking",
"edit3: someone rightfully pointed out that i didn't really explain why ejaculation velocity ",
" matter. I've copied the comment into this post for easier reading.",
"Apologies if I failed to provide any direct answer.",
"Ejaculation velocity does not matter at all, due to presence of a mucus plug at cervix. No matter how strong the force of ejaculation (and it's really not that strong - another poster in this thread has cited the source), the cervical mucus plug is the mechanical barrier that all sperm must overcome. Sperm cells can reach here earlier or later, but if they do not acquire hyperactivated motility to violently wiggle their way through, they are stuck there. The mucus plug is constantly replenished, so the earlier sperms can't really kamikazi for their later teammates.",
"Currently, fertility doctors are toying with the idea of physiological intracytoplasmic sperm injection (PICSI) in order to select the best sperm. Traditionally, sperm selected for ICSI just need to swim properly, look normal, and become hyperactivated when triggered with some chemical. PICSI introduces an additional step where sperm are challenged to swim up some gel which has a similar density/composition as cervical mucus plug. Only the ones that survives this ordeal would be considered.",
"Hopefully that answers the question!"
] |
[
"I got so desensitised to semen/sperm after the thesis that i found wearing gloves to handle donor sperm too much of a hassle.",
"That old wives tale, as you rightly put it, is an old wives tale.",
"We tell the women who receive embryos or intrauterine inseminations to just do whatever they like and move however they want. ",
"Although, if you are someone who loves the view, no one's gonna stop you from asking your partner to stay in that position with elevated legs :P"
] |
[
"Seems like they are an assortment of potential research topics here that could garner an Ig Nobel Prize. ",
"https://www.improbable.com/ig/"
] |
[
"Why when you chop an ant's head off, both, its head and torso keep moving separately for a while, but when something similar happens to a mammal, it immediately dies?"
] |
[
false
] |
[deleted]
|
[
"Newborn mice continue to move for up to about 30 seconds after they have been decapitated. If you squeeze a paw on the body after they have been decapitated, the body will respond similarly to how it does before it was decapitated. The movements are all likely just reflexes.",
"Source: working in a bio lab doing brain research for 6 years and have decapitated a fair number of newborn mice.",
"So I think the issue isn't insect vs mammal, it's conscious movement vs reflex movement; you still have reflexes even if your head's cut off, at least for a little bit of time."
] |
[
"It turns out, most insects have nerve-groupings in their bodies that can control limited functions. I cut the head off a wasp once by accident and I noticed it could still walk, beat it's wings, etc. It couldn't fly, that's a higher level function that needs a brain to control it. So, it's kind of like the nerve reflexes firing off as it dies. Although, it might be able to do this for a while because it probably won't die until it starves or dies from dehydration, which could take days. Mammals don't do this because almost all of our nerve reflexes are controlled by our brains, and we don't have those specialized nerve groupings like they do."
] |
[
"It has a lot to do with the structure of the nervous system as well as the means of providing oxygen to the nervous system. Insects are invertebrates and have no central nervous system; it is distributed throughout the body. All mammals have a central nervous system which includes a spinal column and the brain (of course). Also, mammals provide oxygen, which is required for neuron function, to the brain via the cardiovascular system (lungs, heart, arteries, etc; all centered in the torso) while insects absorb oxygen through pores in their exoskeletons which are distributed all over their bodies. This means that removing the head of an insect has little effect on the ability of the rest of the body, and of the head, to function. Conversely, the removal of the head of a mammal separates the brain from it's oxygen supply and the rest of the body from its control center, essentially halting communication between the two(note: some bodily functions will continue for a short while after decapitation, such as the beating of the heart).",
"a little clarification: arthropoda (insects) ",
"http://en.wikipedia.org/wiki/Arthropoda",
" mammalia (mammals) http://en.wikipedia.org/wiki/Mammalia\n"
] |
[
"Two Part: 1st - Which produces more carbon - car or bicycle rider - and what is the difference in the carbon that is emitted and possible impact to global warming? 2nd - What has the highest impact of road stress/damage (weight, contact area, total force applied to road, points of contact, speeds)?"
] |
[
false
] |
This got me thinking (for a TL:DR, there's a congressman who argues that cyclists are causing more impact on the environment due to their increased CO2 output and are damaging the roads and should be taxed proportionally). First, is there any real difference on the carbon emissions between the car and the human riding a bicycle (quantity/quality/impact to environment etc.)? 2nd, for the road stress, I found one descibing damage with extra axles of vehicles, but not sure if this is even useable for a comparison between a car and a bike rider. Things I thought could possibly impact would be weight, contact area, total force applied, # of points of contact, speeds. Back of the envelope calc for total force applied to the road shows that a bicycle rider applies more force: 250 lb rider/bike with ~4in2 (1 inch x 1 inch x 2 tires) of contact = 62.5 psi 4000 lb car with ~144 in2 (6 inch x 6 inch x 4 tires) = 27.8 psi I could see the congressman arguing that the increased force applied does more damage. I found one article talking about excessive truck weight having a larger impact than cars. I don't want this to turn into anything political (whether or not there should be a tax), but just wanted to figure out if there's any truth to the increased CO2 emissions statement and then what type of damage a bicycle causes to roads compared to cars.
|
[
"First, is there any real difference on the carbon emissions between the car and the human riding a bicycle (quantity/quality/impact to environment etc.)? ",
"Without trying to be condescending... how is this even a question?",
"Assuming a male ride, bicycle rider + bike + gear is going to weigh around 200-250 pounds or so. A car + passenger + fuel, closer to 3,500 for a small car, 4,000 for a medium sized car. The amount of energy necessary to move a car the same distance as a bike is going to be an order of magnitude greater. No matter the carbon-based fuel source, there is quite simply no way for the car to be releasing less carbon back into the atmosphere than the bicycle rider.",
"To put this in perspective, it takes me 1 \"hamburger\" to travel 30 miles on my bike. That's about a gallon of gas for a car, ",
"or, according to this link",
", 14 pounds of CO2. According to ",
"this",
" link, that's about 7 times the total CO2 output of a human from a ",
" of breathing. Me upping my O2 intake for the hour it takes me to bike 30 miles is not making up the difference any time soon.",
"Making the argument that the total carbon footprint of a bike is worse than a car make no sense on any scale. Fuel costs are lower by an order of magnitude because energy needs are lower by an order of magnitude (and then some, as speeds increase). Production costs of the bike and the associated carbon footprint of manufacturing, lower by at ",
" an order of magnitude (my bike: 28 pounds of metal and rubber) relative to the car.",
"Back of the envelope calc for total force applied to the road shows that a bicycle rider applies more force:",
"250 lb rider/bike with ~4in2 (1 inch x 1 inch x 2 tires) of contact = 62.5 psi 4000 lb car with ~144 in2 (6 inch x 6 inch x 4 tires) = 27.8 psi",
"I could see the congressman arguing that the increased force applied does more damage. I found one article talking about excessive truck weight having a larger impact than cars.",
"This is also kind of wonky. You are measuring the normal force, not actual applied sheering force to the surface of the road. You are in effect saying that the road is damaged by a stationary bike or a car. But it's not. A road is damaged by the force applied to the road by the tires of the bike or car from: acceleration, deceleration, and calculable rolling resistance. The latter will be about the same, in some senses. The value of first two? How many 30 foot burnouts do you see a cyclist doing from a stop light? How often do road bikes power slide during an emergency stop? How often does a road bike have to emergency stop from 60 mph? How about 40?",
"And that's the stuff that actually damages a road. Not just ",
" on the road, but actual friction between the tires and the surface of the road during movement. Torque applied by the car's drive wheels is going to be much higher, rolling resistance is going to be much greater, heat generated much more significant, and the force applied from a sliding car much greater, all because the size and speed and momentum of the vehicle is commensurately higher.",
"The question you're asking here is superficially interesting but when you actually look into it, it's a bit absurd. The forces needed to move and stop a car are so beyond the performance profile of a bicycle.",
" Math done in links not verified by me, and could be wrong, in which case, I will revisit this post, but I don't have time to double check it.",
": Units, oh god, the units. Pounds and kilograms! Fixed a minor detail."
] |
[
"One minor correction: \"pounds of pressure\" is an inaccurate term. You're probably thinking of PSI, or \"pounds per square inch\"."
] |
[
"One minor correction: \"pounds of pressure\" is an inaccurate term. You're probably thinking of PSI, or \"pounds per square inch\"."
] |
[
"Is the digestive system's time to absorb energy dependent on the amount of new food pushing previous food through the system, or is the timeframe relatively constant?"
] |
[
false
] |
For example, take 4000 calories worth of donuts. If they're consumed and immediately followed by a low calorie high bulk 'meal' of indigestible fiber, would the donut meal be less absorbed compared to if the donuts were eaten and followed by a period of fasting?
|
[
"Average calories of a Doughnut: ~250",
"Are you saying that eating 16 doughnuts is an implausible act for 1 person over the course of a day? ",
"High cal diets for body builders can range as far as 16,000cal/day consumption. That 4000cal doughnut binge would then only account for 1/4 of daily intake. ",
"You came in here and posted about how you don't like the question. That wasn't helpful."
] |
[
"There would be very little difference.",
"The digestive system does not work in a perfect linear fashion.",
"Food goes in, and is mixed together with other food in the stomach/intestine.",
"The digestive system would extract close to the maximum amount of energy in both cases."
] |
[
"IIRC, sympathetic and parasympathetic system activity would make a difference. Basically, if you are stressed out (distress OR eustress - your brain doesn't know the difference really), your body shuts down digestion. ",
"The body also takes different amounts of time to digest different types of foods like proteins, fats, fruit, etc. Different sources of energy will metabolize at different rates depending on activity. "
] |
[
"Do bird's nests get reused?"
] |
[
false
] | null |
[
"Yes they do, I could walk outside and take a picture of a Kookaburra nest which is made of mud. It's halfway up a gum tree on the edge of our property. It's been there for at least three years and probably longer. Not sure if they use it every day or just for nesting etc"
] |
[
"Some birds, like blue jays, will go so far as to kick out eggs in nests and take them over.",
"So to answer your question, yes, but often times, they won't be useful after the migratory season because they would have not been maintained and would have decayed during that time."
] |
[
"Bald eagles re-use their nests. They can get huge as they keep building and sometimes the tree breaks from the weight.",
"I live near the Mississippi and this gas station owner hated this pair of bald eagles that built a nest in a tree next to the station. It was popular for everyone who drove by it but this guy was having none of it and cut it down."
] |
[
"Why do particles decay?"
] |
[
false
] |
Also what is the difference between "radioactive" decay and say the way carbon decays (I'm thinking of they way archeologists date their digs).
|
[
"There are two competing forces in the nuclei of an atom 1) The Coulomb force (electromagnetism) which pushes protons apart and 2) the nuclear force (strong interaction) which pulls neutrons and protons together. In some atom configurations one force is stronger causing the atom to be unstable and decay. ",
"Radioactive decay is decay where the decay product is ionizing, i.e. when it carries enough energy to knock electrons of other atoms and thus ionize them. There are 4 types of radioactive decay: ",
"Alpha decay: Ejects alpha particles consisting of 2 protons and 2 neutrons. ",
"Beta- decay: A neutron is converted to a proton and a free electron is emitted.",
"Beta+ decay: A proton is converted to a neutron and a free positron is emitted (the antiparticle of the electron).",
"Gamma decay: Excess energy is emitted as high energy photons.",
"Carbon dating is possible due to radioactive decay. A carbon-14 atom is a carbon atom with two extra neutrons, making it unstable. The particle undergoes beta- decay, converting a neutron into a proton thus becoming nitrogen + a free electron. ",
"A substance can be radioactive but not dangerous. XKCD has a nice chart for scale: ",
"http://xkcd.com/radiation/",
"Other links where one can read more:",
"http://en.wikipedia.org/wiki/Radioactive_decay",
"\n",
"http://en.wikipedia.org/wiki/Ionizing_radiation",
"\n",
"http://en.wikipedia.org/wiki/Nuclear_force",
"\n",
"http://en.wikipedia.org/wiki/Coulomb%27s_law#Electrostatic_approximation",
"\n",
"http://en.wikipedia.org/wiki/Radiocarbon_dating"
] |
[
"Curiosity sated!! Thank you."
] |
[
"Follow-up question to your great answer: What would make one force stronger than the other in unstable atoms? Also, decay caused by a stronger Coulomb force makes sense to me, as a repulsive force, but how does having a stronger nuclear force than Coulomb force lead to decay? Wouldn't that just cause the protons and neutrons to fuse?"
] |
[
"Why is the thruster on the X-37B off center?"
] |
[
false
] | null |
[
"If the outside of the craft is symmetrical then it is likely that I the weight on the inside is not evenly distributed. A craft that is heavier on the right becomes harder to \"push\" on the right and will then turn in that direction. Applying more force on the right than the left side (an off center rocket) will counteract this effect and the craft will fly straight. Where to place the rocket depends mostly on the center of mass (COM) and probably some significant part on aerodynamics of the unbalanced craft. "
] |
[
"The thruster you see is only useful in space (it's a glider in the atmosphere), where the aerodynamics of the ship really don't matter, only the mass of the machine, the center of the ship when you take in mass is right over that point no doubt."
] |
[
"But if the COM is off-centre the aerodynamics will also have to compensate for this, right? This would imply that the internals were arrange prior to the design of the airframe. This doesn't seem like an optimal way to go about designing an aircraft, so there must be a good reason. Is it designed for a specific highly asymmetric payload? Is it designed to glide down in a spiral?"
] |
[
"Can we digitize smells yet?"
] |
[
false
] | null |
[
"It doesn't quite work the same way. Your visual and auditory senses work by interpreting waves of energy. Energy is something we know how to create, or transfer rather. However smell is not quite the same. Smell works by receptors in your nose picking up on the presence of molecules. If we were to artificially recreate smell we would need the ability to create matter, or at least transform matter. This is a problem that as of yet, is \"impossible\"."
] |
[
"very true indeed. I guess i figured with the idea of recording the \"play back\" option would be implied. But i do see that I've made a mistake."
] |
[
"I think you answered without reading the rest of his question. His intentions were about \"detecting\" smells, not creating them."
] |
[
"Would nuclear fusion reactors have a more destructive explosion than a nuclear fission reactor or is it the other way around?"
] |
[
false
] | null |
[
"Fusion reactors are much less prone to explosion than fission reactors. And neither can undergo a ",
" explosion. When fission reactors have exploded in the past, it has been due to chemical combustion reactions and/or buildup or large gas pressures in confined spaces."
] |
[
"So fusion reactors can not explode no matter what?"
] |
[
"Other than some kind of issue with the cryogenics, that's correct. The plasma can't explode."
] |
[
"What do we know about what exists beyond the observable universe?"
] |
[
false
] |
I apologize for the wording of this question(or if it's been asked before), and realize it might be confusing, so I'll try to explain... From what I know, the observable universe is defined as all that we can possibly see from around us, due to the distance light has traveled since the spawn of our universe, with us in the center of this. I haven't been able to find much about what we can figure out about what is beyond this light horizon. I read an article some time ago, talking about how we can somewhat study what's beyond the observable universe. In the article, it talked about studying things near the edge of what we can see, and comparing how we assume things such as gravitational forces should affect them, compared to what is actually happening. From this, they were able to hypothesize that something had to be exerting a force from beyond what we can see, in order to cause such an effect. My question, I suppose, is what do we know, or can assume, about what is beyond our observable universe? What can we theorize based on indirect observation?
|
[
"I read an article some time ago, talking about how we can somewhat study what's beyond the observable universe. In the article, it talked about studying things near the edge of what we can see, and comparing how we assume things such as gravitational forces should affect them, compared to what is actually happening. From this, they were able to hypothesize that something had to be exerting a force from beyond what we can see, in order to cause such an effect.",
"Yep. What the article is referring to is often called the ",
"dark flow",
", where certain galaxy clusters appear to have a small trend of movement not easily explainable through normal Big Bang cosmology only, suggesting the presence of a gravitational source lying outside the observable universe.",
"what do we know, or can assume, about what is beyond our observable universe? What can we theorize based on indirect observation?",
"Mainly, only that the rest of the unobservable universe is ",
"homogenous and isotropic",
", just like the observable universe appears to be."
] |
[
"By analyzing CMBR, the topology of the Universe has been fairly well determined to be flat (i.e. no lines which start off as parallel will ever diverge or intersect). This also means that the Universe would be infinite. Furthermore the Universe that we can see is extremely isotropic and homogenous, in other words it looks the same everywhere.",
"Although it is impossible to say for certain what is beyond the observable Universe for the reasons that you mention, all signs point to it continuing on pretty much the same."
] |
[
"Yes, gravitational waves are theorized to travel at the speed of light in general relativity, which means if an event occurs that changes the gravity of a thing (such as a supernova), you won't see any changes until the gravitational waves propagate out to you."
] |
[
"Can anyone help identify this object? We think it is a model of a 5 dimensional cube, but we have no clue of the usage!"
] |
[
false
] |
I am talking about object. It is currently placed at Delft University of Technology in the Netherlands. There has been a post on there website about it and they aren't sure what its exact properties are. This post draw my attention as a student and I thought that might know what it is. This 'cube' was use from 1950 ~ 1980 as a demonstration in electrical engineering classes. On this sphere there are small grooves. These grooves represent the five-dimensional cube. It has 32 corners indicated with 32 holes. 31 holes all have their own letter and number combinations and the last, 32nd, hole is just for the stick it sits on. The numbers run from 0 ~ 15 colored with red and from 1 ~ 15 in black. Al the corners are connected with a wire. There has been one reply on the post the university made and this only tell us it has been used to symbolize 5 bit signals. Also it tells that you should be able to figure out how to pick 5 bit signals under certain contraints. (this hasn't been verified yet) There isn't any more information available to us, so hopefully you could fill me in here. I hope there is someone out here, who can help explain how they used this object in the classes and how it helps to imagine 5 bit signals. Edit: as RickRussellTX pointed out. Not all the corners are connected by the wire. Some aren't connected, I am not sure why they choose this layout or if it's possible to arrange the wire in a different way. Edit 2: Thanks for the big input ! You have helped a lot! For now I think we can say that it is a model of a hypercube, that represents a model of some computer architecture (for example processors, servers of any form of memory). There hasn't been any further updates from the university yet, whenever they give out more information I will post an update!
|
[
"The same way you drav a 3-dimensional cube on 2-dimensional paper. Aspects will be lost, but it is not a useless representation.",
"EDIT: Hey guys. You are not supposed to downvote this guy. Question, AND WRONG ANSWERS that encourage good discussion should not be downvoted. Go read it yourself: ",
"http://www.reddit.com/help/faqs/AskScience",
"Actually, I will just quote it for you and save you the trouble:",
"Please do not downvote answers/comments you disagree with or are wrong. Downvote answers/comments that are off-topic or distracting from the conversation. Wrong answers can have great discussions and educational opportunities that expand on the OP's question, and it's best if everyone can see them. ",
"EDIT2: That's better :)"
] |
[
"I'm not exactly sure how you can represent 5 dimensions with a 3 dimensional object. On another note, to even call this a cube is rather odd."
] |
[
"It's simply a map of the connections between the vertexes. When you draw a cube on paper, you put down 8 vertices (2",
" ), 12 edges. Each vertex has 3 connections.",
"To represent a 5-dimensional object, you would write down 32 vertices (2",
" ), each with 5 connections to other vertices. There would be 80 edges."
] |
[
"Rocket Science - How Exactly Does Thrust Work?"
] |
[
false
] |
Question about Rocket Science I’m probably doing a presentation on rockets for kids, using balloons as an analogy. Anyways, I began to wonder what the exact action-reaction is that causes the rocket to move. For instance, when I jump, I’m pushing against the ground. But what is the rocket fuel ‘pushing against’? Many sites I’ve seen just seem to say “well, something goes this way so something must go that way” but don’t really explain it. Others have asked how rockets work in space since there’s ‘no air for the rocket to push against’. This implies it’s pushing against whatever is directly outside the exhaust pipe. Which in space would be almost nothing. I was wondering if the thrust might also (or primarily) be from the gas that’s pushing against the rocket itself. That is, if the gas explodes in the middle, some amount of that gas will shoot in every direction. Some “upwards” against the ship, and some “downward” right out the exhaust hole. Might the thrust be from “upward” gas? All help is appreciated. So, any ideas?
|
[
"The easiest way of conceptualizing how a rocket engine works is by imagining you are wearing ice skates and standing on ice, while holding a few bricks. If you throw a brick away from you really hard, you will start moving backwards.",
"Now imagine you have billions of bricks, and you're shooting them out with, well, a rocket launcher. That's essentially how a rocket works!"
] |
[
"Thanks for the response! I did find this a bit confusing though, for similar reasons. i.e. why does throwing the brick move the person back. but I guess the person is pushing on the brick when throwing it, and the brick is 'pushing back' before it exits the person's hands. ",
"either way, very much appreciated, thanks =)"
] |
[
"Alright, here's an explanation that relates more to the underlying physical principles: at the core of the brick-throwing idea lies the conservation of momentum. For our purposes, momentum is simply mass times velocity. According to the momentum conservation principle, the momentum of a system must remain constant. Therefore, when you throw a brick away from you, the mass of the brick multiplied with the speed you throw it at ",
" equal your mass multiplied with the speed you move backwards at. Since the mass of a brick is much lower than the mass of a person, this means that when you throw a brick at some speed V, you will move backwards at a speed that's only a fraction of V. The product of mass times velocity must be the same for both the person and the brick. Does this make sense?"
] |
[
"Researchers were able to speed light up to 30c. How is this consistent with special relativity?"
] |
[
false
] |
From : [The authors] demonstrated they could speed a pulse of light up to 30 times the speed of light, slow it down to half the speed of light, and also make the pulse travel backward. I realize that the speed of light is dependent on the material it travels through, but my understanding is that nothing can ever go faster than c. How can this be reconciled with the statement in the article? Alternatively, have I misunderstood something? Or is the statement incorrect?
|
[
"You can manipulate the properties of the medium to change the group velocity from c to something less than c (“slow light”), something greater than c (“fast light”), or basically zero (“stopped light”).",
"This article is about increasing the group velocity above c, so fast light.",
"But this doesn’t cause any problems with relativity, because the ",
" (the speed at which information is transmitted by the wave) is still limited by c."
] |
[
"Well \"light is moving faster\" doesn't have a well-defined meaning, as there are multiple different ways that you could define the \"speed\" of the wave. And furthermore, each of those measures of speed is in principle frequency-dependent, and a pulse of light is never purely monochromatic. So different components of the wave travel at different speeds. The group velocity is just the derivative of the frequency with respect to the wavenumber. In a non-dissipative medium, this coincides with the signal velocity, which is the speed that actually must remain less than or equal to c, or else you have a causality violation.",
"But in general, the group and signal velocities don't have to be the same. And you can play games with the medium to make the group velocity do funny things, including take on values much slower than c, or even faster than c.",
"So while you can make dw/dk > c for some range of frequencies in the medium, the time delay that it would take you to send a message using this pulse is still limited by the L/c, where L is whatever distance you're trying to send the message over."
] |
[
"Why would that be the case? If light is moving faster, surely the pulses could be interpreted faster as well? I'm just a curious layman."
] |
[
"Are there any phages for viruses like there are for bacteria? (i.e. bacteriophages)"
] |
[
false
] |
I was wondering if there are any phages for viruses like there are for bacteria? Is there a way to create phages to kill viruses as a form of vaccine?
|
[
"The closest thing to this would be a ",
"virophage",
", but virophages require coinfection by their host virus; that is, they secondarily infect the cell already infected by their viral target, at which point their activity inhibits the activity of the initial infectious agent. Virophages couldn't simply infect their host viruses, since viruses do not have metabolic capability, and are thus unable to perform certain tasks like protein and nucleic acid synthesis, both of which are necessary for creation of new viruses."
] |
[
"It's highly unlikely (maybe even impossible) for a viral phage to exist. Viruses reproduce by taking advantage of the host cell's ability to create proteins. A virus doesn't have the capability to produce its own proteins, so a virus that infects another virus wouldn't be doing much, except giving that virus its genetic material. It could happen, but there would be no evolutionary advantage to infect a secondary host in order to infect the primary host. "
] |
[
"Thank you for humoring me with this!"
] |
[
"Do volcanic islands preserve fossils in the same way as sedimentary rocks? If not, how do paleontologists reconstruct the evolutionary history of organisms on volcanic islands?"
] |
[
false
] |
To be more specific, are there well understood evolutionary histories of the animals native to the Hawaiian Islands or Iceland, for example?
|
[
"Yes they (can) do, because volcanic islands can host depositional environments for sedimentary rocks. Just because an island has a volcanic origin does not mean that sedimentary rocks are unable to form. Many volcanic islands in the tropics will host carbonate reefs that record fragments of the island's palaeontological history. Even terrestrial life can be recorded. Although volcanically active islands are not particularly good at preserving sedimentary rocks because (as with all topographically prominent features on the Earth's surface) they tend to be erosional rather than depositional, some depositional environments may remain such as river channels, lakes, and dunes. Volcaniclastic deposits such as ignimbrites and other mass flow deposits may also preserve a palaeontological record.",
"I'll illustrate this with a few examples. If you look at a ",
"geological map of Bermuda",
", you'll see that the entire surface is made of sedimentary rock. But Bermuda is actually a volcanic island - the carbonate rocks (and associated dunes) that make up the modern island were actually originally formed as a large platform on top of an ancient volcano that once rose over 2km above the sea surface. Another example is ",
"Madeira",
", which was geologically active more recently than Bermuda and is in waters too cold for coral reefs. Nevertheless, even Madeira preserves sedimentary rocks in the form of some ancient carbonates (which have since been uplifted to over a kilometre above sea level). There are also occasional fluvial deposits that can be found intercalated with the volcanic deposits that dominate the island's geology."
] |
[
"I really appreciated the word \"volcaniclastic\". I hope to use it soon.",
"Thanks"
] |
[
"Geology has a lot of good words. Carbonate classification schemes allow you to create some wonderful terms such as biooopelintrasparite (which would be a carbonate rock with skeletal grains, a kind of carbonate grain called an ooid, grains of carbonate mud, and fragments of local rock that have been washed in, all bound together with crystalline calcitic cement)."
] |
[
"What is the exact time on the solstice at which the North Pole is pointed most directly away from the Sun / the Earth is furthest from the Sun?"
] |
[
false
] | null |
[
"Winter ",
"solstice",
" this year is December 21st, 11:12 am, UTC.",
"Earth is ",
"furthest from the Sun",
" on 3rd of July. Don't have the time of day for that but I'm sure you could find it somewhere if you really want to."
] |
[
"...and that seasons have to do with the angle of solar energy through the atmosphere, not with orbital distance from the sun."
] |
[
"It is a myth.",
" The urban legend says you can do it on an equinox, but actually, you can balance an egg on its tip any time of year. The earths gravity doesn't alter depending on it's tilt. :/",
"Although, technically it ",
" true. You ",
" balance an egg on it's tip on the solstice. just nothing exclusive about it. :)"
] |
[
"What happens when I jump inside a space centrifuge?"
] |
[
false
] |
Let's say it's a fairly low-acceleration centrifuge, so I'll be able to jump quite 'high'. I preserve angular momentum and velocity, but where do I land?
|
[
"You would land most likely face first due to the rotation of the floor around your body as it floats during the jump. If you jump straight up head pointed at the center of rotation, your body still maintains its angular momentum and will travel along with the floor. This sounds fun though."
] |
[
"Due to conservation of angular momentum, a jump(reduction in radius) would result in an increase in velocity. So it would seem like you rush ahead of the floors rotation. Similar if you dropped something, it would be swept backwards relative to the floors rotation.",
"This effect would no doubt make any vertical movements somewhat difficult. Even when just standing up you would have to correct for it."
] |
[
"If the radius of the centrifuge is large (I'm imagining something like an ",
"O'neill cylinder",
"), so that you don't cross the axis of rotation, it's fairly simple.",
"You will experience an acceleration a = 2v X Ω, where v is your speed jumping up (remember this is negative because you are jumping inwards), X is the vector cross product and Ω the rotation speed of the centrifuge.",
"The direction of this is in the direction the surface is moving(forward, if you will).",
"This makes sense; if you face forward, then jump in, you retain the velocity of the rim, take a shorter path because the radius is smaller, and you will land ahead of where you were."
] |
[
"Would each of my sperm result in a different baby? How different?"
] |
[
false
] |
I'm assuming each of the little sperm is different in some way but they're all mine, so varied versions of my code?
|
[
"due to genetic recombination its actually even higher than that."
] |
[
"and with mutation, it's even higher. "
] |
[
"1 / (0.5^23) = 8 388 608\n",
"8.3 million different combinations"
] |
[
"Do extremely loud sounds (150 decibels) at frequencies beyond human hearing (21kHz or 10Hz) still cause hearing damage or loss?"
] |
[
false
] |
[deleted]
|
[
"Yes. Ultrasonic sounds (above 20kHz) can cause some hearing damage but only from a prolonged exposure. At lower subsonic frequencies can cause your eyballs to vibrate making it difficult to see or focus. With rising amplitude sounds become more dangerous regardless of frequency. Above around 200 db sounds can cause fatal haemorrhaging and rupture of some tissues inside the lungs. Above that you have more of a blast wave. It becomes closer to being comparable to getting hit by a truck. When you pump energy into the wave the frequency doesn't really matter, it still hurts."
] |
[
"Above around 200 db sounds can cause fatal haemorrhaging and rupture of some tissues inside the lungs",
"Before that point, at around 195dB 'sound' ceases to function as a typical wave and turns into a shockwave."
] |
[
"The limit before you clip the waveform due to drawing vacuum \non the lower peak and it becomes more of a shock front is ~194dB"
] |
[
"Do photons and quarks interact?"
] |
[
false
] |
I was thinking about atoms, and it occurred to me that the electron cloud is essentially shields the nucleus from photons. I wondered, though, what if the atom had no electrons, perhaps just a proton. Would there by any interaction between a photon and the quarks, or would they not affect each other no matter how closely they passed by?
|
[
"A good rule of thumb (and by that, I mean, the rule itself) is that photons can directly interact with anything that has an electric charge. "
] |
[
"Yes they do.",
"A stylized picture of the Feynman diagram"
] |
[
"Thanks! Quantum mechanics never fails to surprise."
] |
[
"Are there any elements in the earths crust which are anomalously abundant?"
] |
[
false
] |
Speaking of the types of planets which are similar to earth, is there more or less gold, for example than there should be according to our current models of how a planet forms? ****Could there be a planet out there with abnormally high deposits of a certain mineral or element? I know there’s asteroids out there that contain a lot of a certain element and we’ve been considering(?) harvesting them.
|
[
"The planet is not homogeneous in terms of element distribution now even though we believe that it was, mostly, at the time of formation, so in a sense, a lot of elements are \"anomalously abundant\" in the earth crust. We even have a term for one class of scuh elements, the Large Ion Lithophile elements, which basically says \"the atom is huge so the element has trouble fitting into crystals under high pressure, because high pressure favors small spaces for elements, so small elements tend to stay and large ones go into the liquid and migrate to low pressure zones (the lithosphere)\". Potassium and Uranium are classic examples of LILEs."
] |
[
"Last I heard, phosphorus seems to be a lot more abundant on Earth (or in the solar system in general) than anywhere else we've looked. Since it's an element pretty essential to life, it may be one of the main reason we have life here but can't see it anywhere else.",
"Edit: Isaac Arthur to the rescue ",
"https://www.youtube.com/watch?v=oPU9jeQbTOU"
] |
[
"Uranium's an interesting one because pop culture tells us that it's only found as glowing green crystals in remote caves in the desert, when in actuality it's somewhere around forty times more abundant than Silver in Earth's crust; somewhere around the same order of magnitude as Tin and Tungsten. The exact figure depends on ",
"whose list you look at",
", but the overall gist is that there are a lot more ",
"/r/Radioactive_Rocks",
" out there than the layperson tends to expect. Especially since Uranium and its compounds are generally extremely dense and you'd expect them to have mostly migrated ",
", if not for the geochemical flim-flammery referenced above by ",
"/u/Busterwasmycat",
"."
] |
[
"Do astronauts on extended missions ever develop illnesses/head colds while on the job?"
] |
[
false
] | null |
[
"Head colds actually significantly impacted Apollo 7, the first manned Apollo launch. All three astronauts developed head colds during the course of the 11-day mission. They became snappish and irritable, and refused a number of orders from the ground. The blame for this \"mutiny in space\" is mostly placed on mission commander Wally Schirra. One of the original Mercury 7, he was NASA's most senior astronaut and the only person to fly in all three manned rocket programs: Mercury, Gemini, and Apollo. When he began refusing to cooperate, his two crewmates followed his lead. Experiments outside the scope of testing the new capsule were scrapped, one of those \"live from space\" TV interviews was refused, and the entire mission took on an air of stubborn negativity. Everything came to a peak before re-entry: the astronauts were supposed to put their helmets on, in case of depressurization. But the astronauts, with head colds and fearing burst eardrums, wanted to be able to pinch their noses to equalize their sinus pressure as they landed. They ended up disobeying a direct order to put their helmets on, and Schirra basically told the flight director to go to hell.",
"None of the three astronauts flew again: Schirra retired, while the two younger astronauts kept their jobs but were permanently grounded. Schirra actually used the experience to star in commercials for a cold remedy.",
"For later missions, I'm unaware if illness has ever significantly affected performance. However, there have been recorded infections: at least 29 according to ",
"this article from 2012",
". These can potentially be serious, as zero gravity is a terrible place to get sick. For reasons we don't really understand, the immune system is significantly weakened in zero-g, while pathogens are strengthened. And the aerosol cloud from a sneeze doesn't drift to the ground like it does on Earth - it just flies outward, to land on and stick to all the instrument panels and such. Infection control in space is serious business."
] |
[
"Chris Hadfield's book ",
" talks about the medical isolation Astronauts undergo before heading to space.",
"This article",
" states that 10 days before launch, they're screened for illness and cleared for quarantine if good. Quarantine lasts a week to allow latent symptoms to surface. ",
"So it's still possible to get sick, but NASA and the Russian Space Agency try to minimize this risk."
] |
[
"Pathogens can't come from no where, so if no one going to space had any pathogens on them, and the equipment didn't either they could not become sick from infection, while in space.",
"That said this will never happen, because that level of sterilization would almost defiantly kill the astronauts, if we assume it is possible. "
] |
[
"What is exactly phantom limb pain?"
] |
[
false
] |
A little background : I'm an amputee for 11 years, and I can still sense my left leg like it was there. I want to know what causes that? Is my brain screwing with me? Is there any solution? Because sometimes, especially when there's too much humidity in the air, the pain becomes a bitch. I'm sorry if this isn't the right place to ask this. If so, please point me in the right direction.
|
[
"I am not going to pretend that I have any accolades that give me the authority to speak scientifically about this. However, there is a facinating Ted Talk about this that you may find informative, and not linking it here would be a travesty. If you skip forward to about nine minutes in, that's when he really hits on the phantom limb syndrome. (I do recommend watching the whole thing though. This is by far and away my favourite Ted Talk.)",
"The Link."
] |
[
"Awesome! Will check the link at home, for some reason it doesn't load very well on my phone. Thanks, man."
] |
[
"I think you can get your answer from the wiki page as far as what it is...I'll assume it covers the fact that we have created a \"map\" in our brain about where out body parts are, so just because our body doesn't have it anymore doesn't mean our brain understands it isn't there.",
"What I think is the more important part of your question is probably the \"how to get rid of the pain\" part.I'm a (super) amateur and I'm sure people can give you better information but I hope to get the general idea across even if it isn't 100% accurate. Your body has a mirror neuron system which makes it so that you can \"feel\" in your brain when other people are in pain (think of the \"owww\" you feel or say when you see someone stub their toe). The only reason you do not literally feel this pain in your toe (depending on how psychosomatic you are) is because the nerve endings in your toe tell you it hasn't happened. Well, when you have a phantom limb, your mind can use literal mirrors to create the same kind of effect; you see your opposite arm in the mirror and massage it, tense and relax it, until it feels calm. There's no message from your own nerves that this is not actually calming, so the pain can go away. ",
"Anywho, one type of therapy is called the \"mirror box\" which was created by VS Ramachandran. I think this is a decent exposition of the ideas and how to construct your own ",
"mirror box",
" which has had great effect in therapy. ",
"Good luck! "
] |
[
"How does your body know when someone is behind you?"
] |
[
false
] |
People call it the "sixth sense" but how does it actually work? Why does your body get that tingling feeling when someone is behind you? My hypothesis is that the pressure in the room changes just enough for your ear to pick up on it. How does it really work? Edit: It's a hypothesis, not a theory
|
[
"In a quiet environment your sense of hearing is better than you think. If you stand near a wall, and lean in closer to it with your eyes closed, you can easily pick up audible, \"ambient\" sounds that will tell you fairly accurately how close you are to the wall. We're not bats, but we have a limited ability for passive echo-location... ",
"One of my fave Richard Feynman stories is how we also underestimate our sense of smell -- he had a colleague hold a book in his hand for a minute or so, before putting it back into the bookcase. Feynman could pick the book out by smell alone... "
] |
[
"We're not bats, but we have a limited ability for passive echo-location...",
"backing up this statement"
] |
[
"It's pretty clear that he didn't think it was paranormal. "
] |
[
"I need help understanding infinity and 0"
] |
[
false
] |
[deleted]
|
[
"This is true for any two numbers. You can always describe an asymptotic curve that approaches a limiting value but never reaches it.",
"Infinity is a different concept altogether. There can't be any infinite integer because you can always still perform operations on it. If that number exists and is X, what is X + 8, or X",
" ? "
] |
[
"Here's some information on Limits",
". This might help to understand the concept of 0 and/or infinity."
] |
[
"Thinking in terms of something like distance, I do not see how both 0 and infinity and exist at the same time.",
"It's important to note that ",
"infinity is not a real number",
" -- infinity only exists in nature as a ",
" (and really, it represents an absence of limit more than anything else). It is not possible to measure or even define an actually infinite distance -- the only thing that can be said is that one may be able to forever travel in a direction without reaching a boundary, but if one were to do so, the distance would always remain finite. To put it in another way, infinity is not an actual quantity.",
"Zero on the other hand, is a real number, and can be found in nature as both an actual quantity and a limit, and distances of zero can be measured/defined.",
"It gets small forever but never really reaches one. If this is so, how can 0 exist?",
"Because now you are speaking about ",
"infinitesimals",
", which like infinity, are also not real numbers and cannot be measured in nature. Infinitesimals can be thought of as the reciprocal of infinity if you treat infinity as a number, but to treat both as numbers is to extend the real numbers into another number system such as the ",
"hyperreal numbers",
", but such a number system is not real (and such numbers as infinities and infinitesimals cannot be found in nature).",
"doesn't the existence of 0 in it's self disprove the existence of infinity?",
"No -- why would the existance of any number disprove the existance of any other number or limit?",
"Also, if all numbers by themselves are finite, how can infinity exist?",
"It doesn't except as notation for limits, where it denotes the absence thereof.",
"If 0 is the representation of nothing",
"As harbo pointed out, it isn't -- zero is something, it is an element that exists in the set of real numbers. \"Nothing,\" by contrast, would better be thought of as the empty set {}.",
"how do we know there isn't a number that is a representation of a finite everything?",
"I don't think I quite understand your meaning, but no real number represents anything other than its own quantity -- that is to say, no real number (a single element in the set of real numbers) represents the entire set of real numbers."
] |
[
"What is your preferred method of plasmid mutagenesis?"
] |
[
false
] |
[deleted]
|
[
"What organism?",
"I've had some success with the Agilent/Stratagene Quickchange II kit, but I'm guessing you've tried that already. ",
"Where is the SNV located? Do you need to stitch two fragments together to make your construct? Ones in the middle become a pain and, in such cases, I've had luck with some PCR in stages, building away from the central bit with a couple PCRs, with \"adapters\" added in between by 3-4 cycles in a short PCR simply to get primers on, then gel purify again. Or, stitching fragments together. I know it seems entirely roundabout, but sometimes it's just necessary to try something outlandish to get the materials you need just to run the experiment! I wouldn't start here, though.",
"If you're familiar with the protocol, I suppose you could put the sequence in with a lambda Red recombination, but you'd likely need to do it twice, once with a Kan marker, once with a Cm marker. This could get around the problem by moving the primers to a new place.",
"Can you just beat the hell out of the plasmid and select for your mutation somehow? If so, try hydoxylamine.",
"Is it possible the mutation causes lethality in your transformed cells?",
"I also imagine you've gone through the PCR primer checklist (this is 90% of my problems with PCR). If you've not - 1) Make sure the 3' end of your primers are purines, 2) Check the Tm of your primers, try to get them to about 55C, 3) Shoot for a 50% GC concent, 4) Make sure you're not doing to make primer-dimers"
] |
[
"Used to do PCR fragment assembly or quickchange.",
"Lately, switched to gBLOCKS from IDT and Gibson Assembly (NEB or make your own mix). Highly recommended."
] |
[
"Not at all! Askscience has tons of high quality scientific questions, they're just not as nuanced and technical and thus do not warrant such esoteric vocabulary."
] |
[
"Is it possible to make eye-glasses that are hydrophobic?"
] |
[
false
] |
Inspired by walking with glasses in the rain, I was wondering if there is a way to make glasses that would allow rainwater to slide off (without the use of some spray). If not, why? Can hydrophobic glass, if that's a thing, be shaped into a lens while maintaining it's hydrophobic-nature?
|
[
"It is very possible to chemically treat glass to modify the surface chemistry and make it even more ",
" hydrophobic. An oxidized glass surface has many -OH groups exposed which can be bonded with other chemicals to create a hydrophobic surface. Note that this is a chemical bond, and is distinct from the addition of a spray coating, which would just be the addition of a mechanical layer. Silanes are commonly used to increase the hydrophobic nature of glass, and you can check out the details in this comprehensive paper: ",
"http://www.gelest.com/goods/pdf/Library/advances/HydrophobicityHydrophilicityandSilanes.pdf",
"Basically, hydrophobicity is measured by the contact angle the water makes with the surface. The higher the contact angle, the more hydrophobic. Based on that paper, silane treatments can increase the contact angle of water to 115 degrees from normal soda-lime glass at 15 degrees. The theoretical maximum for a smooth surface is 120 degrees, but superhydrophobic surfaces can be created by modifying the surface geometry (wenzel and cassie states) and contact angles of over 150 degrees can be achieved.",
"Both of these surface modifications would be destroyed by further shaping the lens, or anything else that would damage the surface (eg scratches). You would have to apply them as the last step.",
"source: nanotechnology student, surface chemistry is fun"
] |
[
"Is there some way to make lenses that are fingerprintphobic? Cause that's what I really need."
] |
[
"Yes and no. Fingerprints are mainly just oil, and the governing physics are the same as for water. You can make an olephobic (oil repelling) surface a number of different ways, but I'm assuming you want to stick to your previous condition of a chemical surface treatment. The contact angle is a function of the difference in surface tension between the two materials. Water actually has a very high surface tension due to the all the hydrogen bonds, while oil is much lower. Thus it will be much harder to make a surface that repels oil than one that repels water. The surface modification techniques are still applicable because they rely on different physics (look up the lotus effect). "
] |
[
"Over the course of a half-life, what happens to the decomposed(/decomposing) part of the substance?"
] |
[
false
] |
For example, let's assume that the 2nd half life had just occured. So now 3/4 of the original substance is gone. What happened to that 3/4th portion? Where did it go? And how does it reform into something else?
|
[
"The substance is not \"gone\" so much as transformed. I presume your are primarily referring to radioactive decay; in radioactive decay its not that 1/2 the substance is gone, it just means you have 1/2 as many of that nuclei as you started with. There are many types of decay, but a common one is beta-minus wherein a neutron transmutes into a proton and ejects an electron from the nucleus.",
"When a sample of a nuclei (say 100 carbon-14 nuclei) undergoes one half life, your new sample will (statistically averaged) have 50 carbon-14 nuclei, and 50 nitrogen-14 nuclei. You will also have released some energy as gamma radiation.",
"The decay products don't have to \"reform into something else\" because the process by which the parent decays is the same process that produces the decay product."
] |
[
"But what exactly happens with the decayed product? Does it just hover throughout the subatomic world without a bond for the rest of the universe (or at least when all bonds finally break)?"
] |
[
"I'm not sure I understand your question. The decay products are still atoms, just like the parents and will behave however the new chemical element would behave. Lets continue with the carbon-14 example and assume a C-14 atom is part of a CO2 molecule. When the C-14 atom decays, it becomes a N-14 atom. So the CO2 molecule becomes a NO2 molecule. ",
"However, when the C-14 nuclei decays to N-14, it has a bunch of energy to let off (through gamma radiation) but that energy could result in breaking up the molecule, in which case the N and 2 Os do whatever free atoms do. I suppose the 2 Os would probably bond and then the free N would float around and find something to react with (my area of knowledge is the nucleus not the chemical interactions, so I can't really say for certain)."
] |
[
"Why is Raman scattering such a low probability event?"
] |
[
false
] |
In the optics lab that I work as an undergraduate in, we have a Raman setup, and I was told by the graduate students that Raman scattering typically has a probability of occurring of something like one photon in millions or maybe even billions of photons. I understand the process of how Raman scattering works in terms of what happens once a photon does get scattered: Stokes and Anti-stokes creation or annihilation of a phonon in the material and then ejection of a lower or higher energy photon, and then how the vibrational modes depend on degrees of freedom. What I don't understand are the conditions for Raman scattering to occur in the first place.
|
[
"The classical answer is that if you Taylor expand the polarizability of a molecule w.r.t. the nuclear coordinates, the lowest order term is the polarizability that controls the strength of Rayleigh scattering, while the next leading order term controls Raman scattering. This next leading order term is slope of polarizability and coordinates, multiplied by the change in nuclear coordinates. This second factor is usually small (hence Born-Oppenheimer approximation usually works), and the slope isn't going to compensate that, so Raman scattering is suppressed that way.",
"The hand-waving answer to this is that when a photon scatters elastically (Rayleigh), all you're doing is exciting the system to some virtual state, and then letting it relax pretty much instantaneously back to the original state. Comparatively, when it scatters inelastically (Raman), the phonon event has to happen at pretty much the same time as the relaxation, which is improbable (also if the system had significantly many phonon generation events, you probably would have started in a different vibrational state). You're essentially asking the system to do more things in Raman scattering."
] |
[
"\"exciting the system to some virtual state, and then letting it relax pretty much instantaneously back to the original state.\"",
"\"the phonon event has to happen at pretty much the same time as the relaxation, which is improbable\"",
"Can you elaborate on how those are different? I'm having trouble understanding because they seem quite similar to me."
] |
[
"In both cases, you're exciting the system to an unstable energy state. When it Rayleigh scatters, it just returns to its original state. When it Raman scatters, the system needs to generate a phonon mode to absorb the correct energy from the photon. This generation is essentially governed by temperature (stochastic), but it also has to occur within the small decay period of the unstable state, so it rarely happens that they match up."
] |
[
"Why don't all colleges have a distributed computing platform?"
] |
[
false
] |
Why don't all colleges give their students an option to install a distributed computing client on their computer? It could be a requirement of using the campus network or be an opt-out program. Is it too hard to make such a client? Is there too little benefit to the professors who would have access to it?
|
[
"A large bureaucracy that doesn't understand computers, for one."
] |
[
"My friend, I go to a small university. We have exactly 2 tech people, both of whom are ridiculously incompetent. We're lucky we can print over the network."
] |
[
"not every problem is necessarily well solved by distributed computing. It's largely for taking giant data sets, breaking it up into chunks and having users analyze the data. Or a parameter space that can be used to generate data and then analyze that data.",
"Then you also have to rewrite your code to work with whatever client....",
"Or you can just piggyback onto BOINC and anyone anywhere can contribute, including those same students you're talking about.",
"I just don't see the point of a school-based system, maybe you could elaborate on what the benefits would be?"
] |
[
"Is crying a learned response? For example, if every time a small child fell, and you laughed instead of coddled them, would they laugh every time they got hurt?"
] |
[
false
] | null |
[
"The act of crying is not a learned behavior. How to deal with a situation is kind of, according to:\n",
"http://www.sciencedirect.com.proxy1.athensams.net/science/article/pii/016363839190052T",
" and ",
"http://onlinelibrary.wiley.com.proxy1.athensams.net/doi/10.1111/j.1467-7687.2004.00344.x/abstract;jsessionid=ED0244B9DAB1B9ACCD60E111771AF886.f03t03",
"\nchildren takes cues from others. So in your examples if the child fell and you laughed he will think he should laugh (the laugh itself is not learned but the fact that he should laugh is) in the same way if you coddle the child he will think that he should act hurt and so cry.",
"Edit: Did not realize the link is behind a paywall. Here is the screen shot of the abstract:",
"\nFirst paper ",
"http://i.imgur.com/vbOdNbt.jpg",
"\nSecond Paper ",
"http://i.imgur.com/6iA4qfF.jpg"
] |
[
"(Differences between personalities aside) - If you always panic and overreact when a child falls, they will indeed learn to react the same way to that situation and grab for attention. If you act calmly, they will learn to react the same. If you laugh, they will most likely laugh for the small bumps and falls (and will still cry when they really hurt).",
"That does not mean that crying itself is learned. They will cry when they really need to, as that is a natural reaction to certain types of distress. The threshold for this is different for everyone and primarily biological, with examples as the falling down reaction attenuating it though environmental factors.",
"Crying is not learned - Learning how to react to certain situations are.",
"EDITED - For clarification."
] |
[
"I wouldn't think it would extend that far. Some cultures smile when they are nervous/scared, but they aren't actually happy"
] |
[
"Dogs, cats, horses, cows and other animals that sometimes have white stripes down their face/nose: Is this an example of common ancestry or convergent evolution? What's the advantage here? Camouflage? Attraction? Seems like an oddly specific reoccurring mammal trait."
] |
[
false
] |
[deleted]
|
[
"The white strips you're talking about are just coloration patterns, and the animals you mentioned as examples are all domesticated, which would mean that it's not evolution at work here, rather artificial selection and I can't think of any wild animals with that specific marking. So there's no real selective advantage, except perhaps that they're interesting to look at so we bred them more often. "
] |
[
"I think it's important to mention that evolution does not equal natural selection. Natural selection is an agent of evolution as it artificial selection. The only real difference between the two is that the selective pressure in artificial selection is being provided by humans. I think your last sentence is perfect in that the interesting character serves as what is selected. The shift in allele frequency that produces the commonality of the white stripe(evolution) is a byproduct of natural selection. "
] |
[
"Thanks for answering. It didn't occur to me that the commonality is mankind. I forgot about guinea pigs, too. This brings up new thoughts... like how intentional this trait is (and if intentional, why?), or if that's just what will happen to mammals if you breed to get the tuxedo look, or if this a curious side-effect of domestication. I remember reading about foxes being bred for passivity that unintentionally developed dog-like fur patterns; I wonder if the white nose showed up to the party."
] |
[
"[physics] Becuase it's possible to \"mimic\" a 3-d image on a 2-d surface, would it be possible to make a 3-d object that \"mimics\" what a fourth dimensional object would look like?"
] |
[
false
] | null |
[
"http://en.wikipedia.org/wiki/Tesseract"
] |
[
"http://en.wikipedia.org/wiki/Tesseract"
] |
[
"I don't have the answer, but I just wanted to say this is a splendid question."
] |
[
"If you had enhanced strength by using a powered exoskeleton, could an average person fly by flapping man-made wings? How big would they have to be?"
] |
[
false
] |
, but let's say you make one around 40 pounds. Approximately how much weight/force would you be carrying/pushing with the necessary wing size?
|
[
"Well, the objective would be recreational enjoyment. We already have jetpacks, but some might want the fun of bird-like flight. ",
"Would the wings need to be around the size of the average hang glider? And can you move in multiple directions with a servomotor?"
] |
[
"Well, the objective would be recreational enjoyment. We already have jetpacks, but some might want the fun of bird-like flight. ",
"Would the wings need to be around the size of the average hang glider? And can you move in multiple directions with a servomotor?"
] |
[
"Couldn't you just make wings big enough to carry the weight?"
] |
[
"Does Plan B prevent implantation or not? If not, why isn’t there an emergency contraceptive that does?"
] |
[
false
] |
The FDA says that Plan B however almost says it simply delays ovulation. I have also heard from my own OBGYNs that Plan B only works before ovulation. If Plan B isn’t effective at preventing implantation, why isn’t there an alternative that is? Is it a physiological issue or is no one simply interested in developing a drug with that effect?
|
[
"The closest alternative to anti-implantation is anti-fertilization, via copper IUD aka Paraguard.",
"Plan B is simply produces a transient surge of progesterone in your body in order to delay/prevent ovulation. If you take the pill AFTER you've ovulated, then there's nothing the pill can do. If you take Plan B several days before your normal ovulation window, then it works better. If you take Plan B closer to your ovulation window, then you may or may not delay it long enough. ",
"After ovulation, your body is already prepping the uterus for implantation so the only way to prevent implantation is to block fertilization. You would have to use a copper IUD for that. The copper IUD is directly toxic to sperm and can be used up to 120 hours after barrier-less sex. In fact, copper IUDs have the highest efficacy of all emergency use contraceptives.",
"It is generally preferred to stop fertilization than to stop implantation because if you prevent implantation, then the fertilized zygote is just gonna implant elsewhere and cause an ectopic pregnancy."
] |
[
"Studies show for a fact that levonorgestrel will usually delay or prevent ovulation. Studies also show that the it ",
" interfere with fertilization and implantation in some cases. ",
"Unlike mifepristone (R-486) it does not cause the rejection of an implanted embryo.",
"The ",
" actions have not been extensively studied, likely because of the fact that the primary action makes it harder to get to the later stages. It is also possible that there would be even more push back against the drug if it was proven to actively interfere with fertilization or implantation."
] |
[
"That's actually pretty cool. It's a lot easier for conservative jurisdictions to regulate Plan B or medication than to regulate metals like copper. I'm AMAB (she/her) and don't know much about IUDs but I'm curious how viable it would be to make a comparable spermicidal copper instrument at home from common copper metal or metal salts?"
] |
[
"Why does cold temperatures dry clothes?"
] |
[
false
] |
In a rainy day, if I leave wet clothes in a bedroom with a heater, they will dry. And if I leave wet clothes in a bedroom with cold air conditioning it will dry. Why?
|
[
"Important part is the that liquid water will always just spontaneously evaporate with speed depending on a number of factors like: temperature, humidity of the air, and airflow over the surface.",
"An AC lowers the air temperature, slowing down evaporation, but also lowers humidity, speeding up evaporation. AC also creates a draft in the room, speeding up evaporation.",
"Once you get to freezing temperatures the water will solidify and no longer evaporate."
] |
[
"Once you get to freezing temperatures the water will solidify and no longer evaporate.",
"It can actually be surprisingly effective to dry clothes on a freezing but sunny day. Some of the water will freeze, but the ice will then sublimate away."
] |
[
"Once you get to freezing temperatures the water will solidify and no longer evaporate.",
"You still have molecules entering the gas phase, the rate just keeps going down."
] |
[
"Is it possible to walk from the southest of South America to the southest of South Africa?"
] |
[
false
] | null |
[
"So in the 1980's especially it was possible to walk over an ice bridge in the Bering Strait, but for the last two years the ice there and elsewhere (e.g. between Russia and Canada via the north pole) has been more sparse, inconsistent, and shifting. It certainly used to be possible, but I'm not sure if it is this year or last year."
] |
[
"Earth Sciences"
] |
[
"Earth Sciences"
] |
[
"What's actually going on inside your stomach when you feel \"butterflies\"?"
] |
[
false
] | null |
[
"This is a fairly common question on ",
"/r/askscience",
". Here's a list of previous threads on the subject:",
"Why do we sometimes feel emotion in our stomachs (e.g \"butterflies\" and \"that sinking feeling\")?",
"What's happening when one gets \"butterflies?\"",
"What causes the \"butterfly\" gut sensation one gets during a sharp drop on a roller-coaster, car, or the like?",
"What happens when you get \"butterflies\" in your stomach?",
"When people get \"butterflies\" in their stomach, what is actually going on? And why does it only happen when they're nervous?",
"What is the feeling someone gets in the gut when nervous or excited we call \"butterflies\"? ",
"What makes the feeling of \"butterflies in my stomach\"?",
"What causes the \"butterflies\" in your stomach when you are nervous about something?",
"What is actually happening when I have \"butterflies in my stomach\"? ",
"What causes the \"butterflies\" feeling in your stomach, And what is it?"
] |
[
"The answer you're looking for is in one or more of those posts. I listed all of them to give you an idea of the regularity of this question."
] |
[
"You're linking me to another post where you wrote that exact same thing but with no resolved answer. Looking at the post before you link me to it would be helpful. "
] |
[
"How does r/askscience regard scientists in the public eye and how science presents itself to the public? (ie Dawkins, deGrasse Tyson, Hawkings, Harris, etc.)"
] |
[
false
] |
There seems to be two ways the public scientist engages non-scinence communities or the general public. One, as passing along the findings of science such as Sagan's PBS series "Cosmos" or Hawking's "A Brief History..." Second, as an agent of social/cultural change such as science backed Atheism or Harris's newer book "The Moral Landscape: How Science Can Determine Human Values." I'm looking at this from the stance of the public as I am not a scientist, but these figures are my way into the scientific world. (I imagine like many redditors and others curious about such things) So how do the other scientists, the ones that are unheard from, regard this breed? Does Hawking overstep cosmology because of his public popularity? Is Dawkins giving science, biology, and zoology a bad name because of his engagement with religion? I'm not necessarily asking about if the information is accurate, unless it is the case or pertinent to the discussion, or about individual people but rather... tl,dr: are field/lab scientists embarrassed by their field's public representatives? (apologies for breaking OP etiquette, xpost , ) Edit: Making Hawkings Hawking
|
[
"First of all, it's Hawking. No ",
".",
"Second of all - and I say this with all respect due Neil Tyson - I always shake my head when I see his name right next to Stephen Hawking's.",
"No scientist will look down upon science education and communication, as long as it's well done and doesn't communicate mistruths. It's a very important part of science.",
"But a scientist's greatest respect comes for achievements in the field. Neil Tyson, while an excellent communicator, hasn't made a tremendous impact in research. He's more or less a full-time educator, and that's great. But a scientist's respect for him should pale in comparison to their respect for Stephen Hawking, not because A Brief History of Time is better than The Pluto Files, but because Hawking has helped revolutionize our understanding of general relativity and black holes, and has generally been one of the major figures in 20th century physics."
] |
[
"What adamsolomon said. However, I'd also like to add an important point.",
"We are embarassed when scientists start speaking about things way outside their field or without justification. This seems to happen not infrequently to famous particle theorists/astrophysicists in their old age. For example, recent \"works\" or statements by Hawking, Susskind, and Penrose are embarassing not just because they can't really be backed up by science, but also because they are ripe fodder for journalists who understand nothing but love a sensational statement."
] |
[
"Tyson is one of the most important figures in science today. Why? Because he's a great educator, and makes the average person understand the value of science. Most scientists do a pretty piss-poor job of outreach,and I'd argue that that's okay, as long as people like Tyson are picking up the slack. If our culture loses respect for science, though, then you can kiss science funding goodbye. More importantly, I'd argue that a society that doesn't value science and reason will quickly fall apart.",
"So no, he's not among the greats in terms of scientific contribution, but he's certainly among those who have contributed the most to the enterprise of science in recent years."
] |
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