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[
"Is there any chance of getting an electric shock if you wear ear phones/buds in the rain? And if so, could said shock be damaging in any way?"
] |
[
false
] | null |
[
"The shocking answer is yes!",
"...sadly, in one case it has nothing to do with the rain, and in the other it has nothing to do with the earbuds.",
"Case 1: You're wearing your earphones out in the rain, and are doing any activity that builds static electricity. ",
"That static electricity could be delivered via your earbuds",
". Of course, this could also happen on a dry day, and with many static electricity generating activities, a dry environment will make it happen faster!",
"Could the shock be damaging? Not to you, but possibly to motherboard components that you touch!",
"Case 2: You're wearing your ear buds in the rain, and you get an electric shock from a lightning strike. Of course, the likelihood that wearing earbuds would impact how a lightning strike goes down ",
"is pretty out there",
". Sadly, ",
"when you win the lightning lottery",
" it's probably due to the fact that you're standing out in the rain in a high risk area, rather than the fact that you're bopping around to your tunes.",
"Could the shock be damaging? ",
"Yeah",
".",
"I know that you wanted neat stories about being zapped and fried by an iPod, and Apple even ",
"warns about using your iPod in the rain",
". But although there's a buzz of 'I heard that this happened', the level of energy discharged would be fairly low. It would have to be a perfect storm (damp skin that reduces resistance from the normal 100K to 200K Ohms to around 1K Ohms, exposed wiring, a faulty device, etc) to do real damage to a human being.",
"Edit 1: I can't believe I feel I have to say this but... DON'T TRY THIS AT HOME. As tempting as it would be to play junior Mythbuster, set up the worst case scenario, and see if you can get a fatal shock going... don't. Just don't."
] |
[
"Earphones usually operate in mV ranges. That's far lower than most other power sources we usually handle, like batteries.",
"You can take a 9V block battery and touch the poles simultaneously with your tongue and won't get more than a tingling sensation and a weird taste. If you get water into your earphones, the only thing that would probably happen is that you won't hear the music anymore."
] |
[
"Awesome thanks. As you guessed I was mainly thinking about the ear phone/your ear getting water in it and somehow conducting, hadn't considered these other scenarios. Really interesting.",
"It would have to be a perfect storm (damp skin that reduces resistance from the normal 100K to 200K Ohms to around 1K Ohms, exposed wiring, a faulty device, etc) to do real damage to a human being.",
"So in ",
" there could be a danger, but in real-world normal circumstances there's little to no risk?"
] |
[
"If you hold in poop does your intestine still absorb nutrients or does it just kind of sit there at the end of the line?"
] |
[
false
] | null |
[
"Its called ",
"encopresis",
". By the time you have conscious control, its more water being absorbed than anything else. If you refuse to poo, it gets harder and bigger so the next time you poo it hurts. Then, if you are a three year old, you repeat the process ad infinitum and drive me crazy. Don't do this. "
] |
[
"From ",
"Wikipedia",
"Food is no longer broken down at this stage of digestion. The colon absorbs vitamins which are created by the colonic bacteria - such as vitamin K (especially important as the daily ingestion of vitamin K is not normally enough to maintain adequate blood coagulation), vitamin B12, thiamine and riboflavin. It also compacts faeces, and stores fecal matter in the rectum until it can be discharged via the anus in defecation.",
"So yes, your large intestine does absorb vitamins and water, but once it compacts and is stored in the rectum, you gain nothing more from it except the urge to defecate."
] |
[
"impaction caused by constipation is really common and if it gets so bad you cannot remove it yourself, nurses can do it ",
"it's pretty common in obese and older people"
] |
[
"How can I weigh myself, at home, if I'm not able to stand on a scale?"
] |
[
false
] |
I am a wheelchair user, and unable to stand. Some hospitals have large scales, with a chair I can sit on, but that isn't an option at home, and I'd like to weigh myself regularly and accurately, which kneeling on the scale doesn't accomplish.
|
[
"can you pull yourself up by your arms? maybe get a hanging fish scale with a trapeze bar, and use that. ",
"Something like this"
] |
[
"I think this is the solution. Thanks!! "
] |
[
"Have two scales side by side that you can roll onto, and then add their displays."
] |
[
"What are some examples of different evolutionary adaptions among different populations of humans?"
] |
[
false
] |
Aside from Alcohol Dehydrogenase, Lactase never 'turning off', and melanin loss after the agricultural revolution I don't know of any changes in humanity that have been caused by environmental factors. Are there others?
|
[
"Melanin loss predated the agricultural revolution and is due to reduced solar intensity in temperate regions. Malaria resistance is a great example of an adaptation to a biotic factor; altitude adaptation (Tibet, Andes, etc) is a great example of adaptation to an abiotic factor."
] |
[
"Body size and stature.\nCentral African people living in the harsh heat of the tropics tend to be tall with long legs, with most of their body fat distributed in just a few places so they can radiate as much heat as possible. The native people of arctic Canada tend to be short and have body fat more evenly distributed around their bodies to conserve as much heat as possible. "
] |
[
"HIV immunity in some European populations ",
"as a consequence of negative selection by the black plaque",
".",
"Tay-Sachs desease",
" that either increases average intelligence in the population, or ",
"increases resistance to tuberculosis",
", or both. Implied selection in Ashkenazi Jews.",
"The ",
"eye shape usually associated with people of Asian descent",
" was traditionally linked to living in dusty steppe-like environments, but I am not sure there's any conclusive evidence here."
] |
[
"Assuming there is a part of the brain that creates the visuals we see when we think (and especially dream) is it within the realms of possibility that other people could, one day, see our thoughts?"
] |
[
false
] |
I'm not sure how well I phrased the question here but what I mean is, when I think (and obviously, more so when I dream), images are created. What I want to know is if, one day, it would be possible to somehow 'plug in' to this part of the brain and effectively stream thoughts for other people to see. I imagine this would be a holy grail of sorts for biologists, psychologists and etc. Imagine being able to see how other people and animals visualise the world.
|
[
"Apparently we already can (sort of). Not long ago this ",
"video",
" came out.",
"Here",
" is a related paper."
] |
[
"So you're unhelpful AND sarcastic? I bet you're a real hit with the ladies."
] |
[
"any source/elaboration you can give me on that?"
] |
[
"Why does riding a bike last so long in muscle memory?"
] |
[
false
] |
It's the archetypal phrase when it comes to long-term muscle memory: "It's like learning to ride a bike" What is it about bike riding that once it is learnt it is never completely unlearned? Is bicycling unique in this way or do all dextrous skills "stick" with us for life once we've become competent at them?
|
[
"Balance and praxis (learned sequences) are largely moderated in the cerebellum as they are learned, not in the muscles.",
"Like almost anything that you learn and rely on daily, the neural circuits for them are reinforced, strengthening them, so that even if you don't use them for a while, they remain accessible."
] |
[
"This would be interesting to experiment with and see if someone with amnesia and doesn't remember learning how to ride a bike, could still ride it."
] |
[
"This would be interesting to experiment with and see if someone with amnesia and doesn't remember learning how to ride a bike, could still ride it."
] |
[
"Are vitamins in cereal \"Sprayed On\"? Do you miss some of them if you don't drink the left-over milk?"
] |
[
false
] |
I grew up being told this, especially about sugar cereals - all the nutrients were "sprayed on" and would wash off into the milk, so unless you finished your milk you would get zero nutrition content. As an adult, I realize that there are some nutrients, such as fiber, where this is obviously not the case. I'm talking about the frequently-advertised "12 vitamins and minerals!" though. Are some of these only applied to the surface of the cereal and simultaneously water soluble? Alternative question: If the vitamins and minerals are not sprayed on, how are they added to the cereal?
|
[
"It depends on the cereal, really. Whole-grain cereals (including puffed grains such as Corn Pops) do in fact have any fortifying nutrients mixed into their coatings. Extruded cereals (Cheerios and the like, anything where the grains are reduced to dough before being shaped) usually have fortifications mixed into the dough during processing.",
"As for solubility, vitamins A, D, E, and K are all fat-soluble; all the rest are water-soluble. Unfortunately, the fat content in milk (excepting skim) is enough to wash these vitamins away as well.",
"So basically, your childhood admonitions were half-right. Mostly, though, I think it was just used as an excuse to get you to drink your milk."
] |
[
"I worked briefly in a kelloggs factory and i can confirm all the lines i worked on sprayed on their vitamins. A relatively small bottle, about 500ml, would cover several thousand boxes of cereal. It was sprayed on just after the cooking process. Don't really know much more than that (like if the vitamins come off in milk) sorry but i hope this helps!"
] |
[
"It depends on the cereal. Many of the \"kids\" cereals are ~49% sugar by weight - 49% so that they slip under the 50% threshold for the definition of \"candy\". Those cereals have few redeeming qualities because of the excess sugar.",
"But for whole grain cereals and those like Cheerios with relatively little added sugar, they're a good blend of protein and fiber which compares quite favorably to many other breakfast options - even without the added vitamins."
] |
[
"Why is a grossly over expanded nozzle more efficient than a slight over expansion?"
] |
[
false
] |
So I came across this when I was doing some gas dynamics research, and I am trying to remember back to my high speed aerodynamics class. A grossly overexpanded nozzle moves the oblique shocks at the exit into a normal shock that slowly moves into the nozzle, while a slight overexpansion has oblique shocks outside the nozzle. Is a grossly overexpanded more efficient because once that normal shock is within the nozzle, all flow pressure increases within the nozzle itself despite it separating from the nozzle wall? With a lot of shock patterns it seems like there is a normal shock some distance from the exterior of the nozzle, followed by a shock diamond pattern of obliques and expansion waves, but I would have thought that getting as close to ideal full expansion would reduce change in entropy and provide maximum thrust. I came across this claim that grossly over expanded was more efficient than slight over expansion (while not as efficient as ideal expansion) so I would just like some clarification on this.
|
[
"An overexpanded flow isn't optimal since it tends to be very unstable. It's generally more efficient at high altitudes where flow separation becomes less problematic. Unfortunately, ideal full expansion for a non-variable nozzle only occurs at a design point (vs a full altitude range), so engineers tend to \"pick their poison\" and use a combination of both types."
] |
[
"Why do they say that a grossly overexpanded flow is more efficient then a slightly overexpanded flow though? That's what I don't get because you'd think it would be the opposite. "
] |
[
"This reminds me of the main engines on the (now retired) Space Shuttles. They are often touted as the ",
"most efficient rocket engines ever made",
". It's interesting to note that this is not the case at take-off, but only much later at a much higher altitude, when they reach their design point.",
"Edit: Grammar."
] |
[
"Is there any discernible structure in the cosmic microwave background noise?"
] |
[
false
] | null |
[
"It would appear the CMB appears sufficiently random that it can be effectively used as a random number generator. That would suggest there's no discernable structure.",
"However, the CMB may not be entirely random, particularly with respect to anomalies like the ",
"CMB cold spot",
", though it's entirely possible it's just as random as the rest of the CMB."
] |
[
"There are some people who are trying to employ new techniques to find hidden structures in the CMB, see e.g. [1], where they use something called `Topological Data Analysis' (TDA).",
"[1]\n",
"https://arxiv.org/abs/1712.08159"
] |
[
"not sure I fully understand your question. could you clarify?",
"We do not see the CMB \"now\", we see it 3.8e5 years after the Big Bang (~1.4e10 years ago).",
" structures close by like a galaxy will cause gravitational lensing on it same as any other light wavelength but that's just a local effect (that I'm not even sure is significant enough for our instrumentation)"
] |
[
"Are there solid Planets as big or bigger than Jupiter?"
] |
[
false
] |
..or are all the really big planets gas giants?
|
[
"No rocky planets that large have ever been discovered.",
"Since exoplanet discovery is a relatively new phenomenon, it was previously assumed that exoplanets would follow the same general trends seen in the solar system, but the discovery of Kepler 10c in 2011 disproved that hypothesis. Kepler 10c, the largest rocky planet known to date, is 15-19 times the mass of Earth and about twice the radius. This planet is larger than rocky planets are predicted to be, but it's still quite a long way from approaching the mass or radius of Jupiter.",
"More reading follows:",
"http://rt.com/news/163232-rocky-super-earth-discovered/",
"http://en.wikipedia.org/wiki/Super-Earth",
"http://en.wikipedia.org/wiki/Kepler-10c",
"Edited for clarity."
] |
[
"is there any scientific reason that solid planets cant get that large?"
] |
[
"No, but just to clear something up: there's no precise definition for a gas giant vs. a terrestrial planet. It was thought that around 10-15 times the mass of Earth, a planet would accrete more atmosphere than what is considered \"rocky\" and be more of a Neptune-like planet- a gas giant with a rocky core. (You can see how blurry the line becomes.)",
"Of course, at hundreds of times that mass, the planet will have sufficient gravity to begin fusing hydrogen in its core, at which point it would be considered a brown dwarf.",
"So there's no hard limit, just constraints based on what we know about planet formation and how we expect the atmosphere to form, and a general concept that a planet dominated by atmosphere is a gas giant."
] |
[
"How does toothpaste affect the microbial flora of the mouth?"
] |
[
false
] |
Hi! I'm a microbial ecology M.Sc. candidate that works predominantly in soil. In soils, there is quite a bit of evidence that anthropogenic changes to the soil affect the microbial community and it seems (at least from what I read and work on) that this can sometimes severely limit the diversity of microbes to species and genera that are capable of withstanding the changes. For example fertilization can limit the ammonia oxidation community to a small subset of species that are capable of surviving at high ammonia concentrations and make better use of the substrate. The human microbiome is a pretty interesting subject to me even though my understanding of it is pretty limited. I've always wondered about toothpaste. I'm not sure what sorts of antibacterial properties it has and what exactly it's supposed to be doing to teeth... Does brushing your teeth 1 to 3 times a day cause the microbial community to shift towards species that can resist the perturbation? Could this practice cause us to have higher concentrations of bacteria that have negative effects on our health and hygiene (such as increasing the proportion of bacteria that cause bad breath or tooth decay)? It seems pretty amazing to me that we still follow a practice that has been around since before PCR and as far as I know, we kind of just accept it. Please enlighten me! Edit: As I watched the upvotes climb and the comments stay at 0, I thought about the similar scenario with soap. We wipe out most of the microbes every time we wash and let them colonize anew. I remember seeing some evidence that some bacteria metabolize odour-causing chemicals, but that by washing the "bugs" away, we end up stinking when we're no longer "clean". .
|
[
"Brushing just disrupts biofilms on your teeth basically. Streptococcus mutans and some other strains of strep live in your mouth and eat sucrose in your mouth to make glycan, which is a sticky extra cellular polymer that is water insoluble. This builds up, and sticks to your enamel. Normally this wouldn't be a big deal, but a lot of the bugs in the oral cavity that cause the most damage are anaerobic, and this polymer provides a safe place to live away from air in your mouth. Your saliva can't wash them away because the polymer is water insoluble. ",
"While the bacteria are stuck in this polymer, they are creating lactic acid, which drastically lowers the pH of the area right next to your tooth enamel, which can lead to demineralization. Simply brushing the area will break up the polymer and release the bacteria from the area so that you can spit them out before the acid builds up enough to damage your enamel. You're disrupting all bacteria, good and bad, but the bad bacteria are not necessarily growing faster or better than the good ones, they're just causing damage the longer they sit on your teeth. The good ones will be able to bounce back just fine (no one brushes well enough to get rid of a significant amount of bacteria anyways) so it's worth it to disrupt all the bugs and the sticky glycan polymer for the sake of your enamel. ",
"There are lots of other good reasons to brush too (fluoride, gum health, etc) but the biofilm is the reason I'm most familiar with. ",
"I work in an oral microbiology research lab, but I'm just an underling so if you want to read more about it from a more qualified person, look up papers about strep mutans, fusobacterium nucleatum, strep sanguis, and others. I'd link them but I'm on mobile. "
] |
[
"Thanks! That's super informative! I'm always amazed at learning about the parallels between microbial ecology and the human microbiome. I guess it's really no different from any other environment when you get right down to it.",
"I wonder whether there are any microbe-related ways to stimulate the growth of organisms that outcompete or eat ",
"."
] |
[
"A simplified explanation: Enamel is made up of, among other things, the mineral hydroxyapatite. Acids from bacteria leech the OH (aka hydroxy) group from the enamel, which weakens the structure and makes it prone to cavitations.",
"Fluoride replaces the OH (aka hydroxy) group in hydroxyapatite to form fluoroapatite. Fluoroapatite is more resistant acid, which makes the teeth more resistant to decay."
] |
[
"Is there a reason why people \"look\" like their name?"
] |
[
false
] | null |
[
"It sounds like the question you are trying to ask is \"is there a correlation between names and physical appearance\" that's a different question from the title of your post. Please make a new post."
] |
[
"I don't think that's really what I'm asking because I don't think that's really true. Why would there be? Perhaps my description wasn't clear, what I mean to ask is whether science recognises this phenomenon of people believing that the physical appearance of others correlates with their name.",
"So not \"is there a correlation\" but \"why do people think there is a correlation\". Or even \"do people believe that there is a correlation\", since this might not be a recognised phenomenon. Do you get what I mean?"
] |
[
"So the last question you posted makes the most sense to me \"do people believe that there is a relationship between name and physical appearance\". Unfortunately, that phrasing isn't great because it sounds like you're polling the readers of this sub, and that's not what you mean. Maybe something like \"is there a belief shared by many people that there is a relationship between names and physical appearance\" "
] |
[
"When someone gets a transplant of an organ that they have two of, like a kidney, does the new organ have to come from the same side of the donor's body as the one it's replacing?"
] |
[
false
] |
I mean in a lung transplant I can understand why it would matter because a right lung in the left side of the body would be in the way of the heart, but what about kidneys?
|
[
"Doesn't matter. They don't even put a transplanted kidney anyplace near the original location, anyway, and usually don't remove the old kidneys either. See ",
"this image for a good example",
". ",
"Which side they transplant a kidney to depends really on the surgeon's preference or the recipient's anatomy, and not on what side the organ came from in the donor. [source: I am a kidney recipient]"
] |
[
"I've mentioned this in ",
"another transplant related thread",
" but something else to know is that when the transplant recipient receives a new kidney the original kidneys are usually left in place. It's often the case the ",
"kidney is not functioning in terms of filtering blood",
", but the tissue is otherwise fine. Unless the kidney is damaged/infected/cancerous, ",
"it's better to leave it in place."
] |
[
"I can only claim blindness. Somehow I missed the rest of the sentence after \"anyway.\" Sorry, didn't mean to repeat what you had already said."
] |
[
"How is heat transferred through the glass??"
] |
[
false
] |
[deleted]
|
[
"Some photons pass through glass and heat up what's on the other side.",
"Atoms with higher temperature hit the glass atoms and make them vibrate. The vibration spreads through the glass and then the atoms on the other side of the glass bounce off of the glass atoms and take some of the vibration energy away (heat up).",
"Look up ",
" on wiki."
] |
[
"It's both. Just like in the optical, the 'heat radiation' can pass through the glass. I had a quick Google and looked at a transmission diagram for silica and it is mostly transparent in the near-infrared (I think it's reasonable to consider the near-IR, I took a quick look at the sun's irradiance curve). Some of the energy also gets absorbed by the glass and then to the air on the other side (through vibrations) and that's the transfer by conduction. I think the transfer by radiation to whatever is on the other side is more prominent however."
] |
[
"So it's conduction not radiation?"
] |
[
"How come microwaving cooked chicken causes it to become rubbery?"
] |
[
false
] | null |
[
"Dehydration. You don't need a microwave for this. You can take almost any piece of chicken and put it in a pan on low for 40 minutes. Provided that you don't burn too much of it, try taking a bite and you'll find the same thing. The microwave tends to 'supercharge' the dehydration process causing even more moisture to exit from something than usual.",
"You can avoid this. Take your chicken and put it in a bowl with a teaspoon of water and cover it with something plastic. Do not use a plastic bowl for the chicken because most plastics react with the fats in foods and tend to melt a little where they come into contact with the food. NOW microwave it. It still won't be perfect but I think that you'll find it to be far more palatable."
] |
[
"Please delete this comment, as it is offensive and adds nothing to the conversation. Thank you."
] |
[
"Please delete this comment, as it is offensive and adds nothing to the conversation. Thank you."
] |
[
"Is it true that tasks requiring coordination of both hands ( driving, juggling, playing the piano ) can help with / train one's concentration?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"We do not debunk or vet theories or offer peer review on ",
"/r/AskScience",
". For more information regarding this and similar issues, please see our ",
"guidelines",
"You can find the basic answer with a google / wiki search. Please start there and come back with a more specific question.",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"Oh, I thought you guys could at least say what's the current state of scientific community. Controversial / mostly agree / disagree"
] |
[
"Sorry, but in general we cannot do bibliographic reviews. It's rare when a panelist has the time to do so or the question is very specific."
] |
[
"If you use a power tool in a vacuum, where does the extra energy that would usually be expelled as sound go?"
] |
[
false
] |
[deleted]
|
[
"Heat, mostly. Although even loud noises don't usually correspond to a lot of thermal energy. ",
"Power tools also tend to have fan bits to cool them, plus ordinary conduction/natural convection to the air. In a vacuum, where they can only lose heat through radiation, they'd be likely to overheat. (Which is an issue with satellites and such)"
] |
[
"I would think the tool would vibrate just a little bit more. The vibrating tool transfers a little bit of that energy into vibrating the air, which has a dampening effect on the vibrations of the tool."
] |
[
"The amount of thermal energy lost to radiation per unit of surface area is given by ",
"Stefan-Boltzmann's law",
", which simply states that it's proportional to the absolute temperature to the fourth power, with the proportionality constant depending on the material. ",
"Obviously increasing T would defeat the point. The material property (",
"emissivity",
") doesn't vary a whole lot between materials (same order-of-magnitude). Ideally it's 1, and for something that's colored black, it's often over 0.9. So the main thing you can do is increase the surface area (having heat fins), and have it made out of a material that conducts heat well, so it'll pull heat away from the satellite as quickly as it can radiate it away. "
] |
[
"Why doesn't Windows' 'estimated time remaining' ever work?"
] |
[
false
] | null |
[
"I believe it's more of a problem of the algorithm they used for calculating the remaining time. I also think they've re-done it for windows 8, it seems better. But anyways, from what I've experienced after years of watching the stupid/crazy file transfer bar, it probably goes something like:",
"start a running time;\ntake a larger time step: 1-10 seconds and measure the rate of transfer;\nevery second calculate how much time is left using measured data speed and current time;\nrepeat till finished;\n",
"which works great for consistent file transfers like downloads, not so great when the instantaneous speed isn't consistent (like in a hard drive with many different sized files). Also why when a transfer is stopped for some reason and windows doesn't realize it the time will slowly increase."
] |
[
"Windows (and all GUI's that I am aware) enumerates the file structure before the copy process: it knows the sizes and number of files and folders before it begins."
] |
[
"To give a specific example of this: way back in the IE4/5 days the algorithm that estimated the download rate and remaining time didn't start until several seconds ",
" the download started. This gave the algorithm the illusion that a lot of data had been downloaded in a very short period of time. Subsequent runs of the algorithm converged the deviation. To the end user it looked like their download started incredibly fast (several times their dial-up speed) only to taper off about half way through (depending on the size of the file)."
] |
[
"How do apps like Soundhound and Shazam work? Is there a database that matches songs or does it recognise far more than that?"
] |
[
false
] | null |
[
"They sort of explain it on their ",
"website",
".\nThey have a large database of audio-samples that is labeled (title, author, etc.). But you cant just directly compare your humming and singing with that database, you wouldnt find anything, because for that to happen your humming would already have to be in the database EXACLY as you hummed it. (And even then it is unlikely due to noise and audio compression.)",
"Instead, you apply machine learning (short ML). ML is essentially a combination of some smart math and brute force computation, that lets you extract \"useful\" information form your data (audio). Useful in quotation marks because that information helps you solve the problem of data matching, it usually does not help to give you an intuitive understanding of what's going on.",
"I'll run you through the basics of how you would set up this sort of ML problem. If you want to learn more you'll have to dig deeper, and be prepared to handle a bit of challenging math. (PM me in case)",
"First, you set up two databases, one containing the labeled music (title, author, etc.), the other containing recordings of people humming and singing which are also labeled with what songs those are supposed to be. To be effective, these databases have to be as large as possible. This is usually the most tedious and annoying part of ML.",
"Second, you define a model. A model is basically a (possibly complex) rule of computation a.k.a. an algorithm. The model takes the audio, which is just a long list of numbers and a set of parameters (also a list of numbers) and computes ",
" (another list of numbers). Coming up with a useful model is one of the key challenges in ML.",
"A model is deterministic, for a given combination of data and parameters you always get the same features. Those features will reveal characteristic information about the data (audio). E.g. BMP, rithm, tone, but also more complicated aspects, that often defy an intuitive understanding.",
"Third, you define a score or goal. You make pairs of hummings and songs and compute their features (from the model). If the humming and the song are supposed be the same (according to the database labels) and their features are very similar the scores goes up. If they are supposed to be different songs, and their features are similar, the score goes down.",
"Last, you tell a (super-)computer to play around with the parameters in your model in order to maximize the score.",
"Now if you have new humming from a user, you calculate its features and compare with the features of the database, to find possible matches (those with similar features).",
"Disclaimer: I know this is somewhat oversimplified and there are different approaches to this problem. But I didnt want to write a 10k+ words post.",
"TL;DR They have big databases of music and people humming and use some fancy math and massive computing power."
] |
[
"Shazam is explained in ",
"this paper",
" (see also ",
"here",
")",
"From the sample you send them, Shazam builds a list of numbers using an algorithm they developed, and compares it to the results of the same algorithm\napplied to a big database of songs. This representation is much more compact than the songs themselves, and is robust to quite a lot of perturbations (i.e. adding noise, using an equalizer, etc., won't change much the representation they used. There is a small risk that two different songs will have the same representation, but this is unlikely).",
"This representation is obtained by finding the peaks of the spectrogram of the excerpt. The spectrogram is the representation of the signal in function of time and frequency (a bit like a musical score). It is not invertible, this means that from this representation, you cannot recover the original signal.",
"Shazam does not really identify a song, but a sound. It does not identify from the sound itself the artist, the name of the song, etc, but only through comparison to a database. This means that it won't be able to identify a cover version of a song, if the cover version is not itself in their database."
] |
[
"Not a direct answer to your question, but as I guess the other answers will talk about complex and highly technical audio fingerprinting algorithms I thought I'd share one I thought was both ingenious and very easy to visualize.",
"Start the song and take the pitch of each note as it's being played. If it is the same frequency as the previous note then ignore it, if it's higher pitched then store a 1, otherwise store a 0. This converts a melody into a stream of bits, the first line of ",
"always look on the bright side of life",
" could be condensed to 010100000 (or the number 160 out of a possible 512). If you do the same thing to a different recording and the first 9 bits are 160 in decimal then you can be pretty sure it's that melody."
] |
[
"How did birds evolve wings?"
] |
[
false
] |
A summary of my understanding of evolution is that random mutations occur which lead to one animal being more likely to survive than the other, therefore passing on the mutated gene while the inferior gene dies out. So how did birds get wings? If I understand correctly it would have to be a very gradual change, lump -> stump -> bone -> wing etc.. Obviously nothing like that but it had to start off as something right? What possible survival benefit would a wing that's not a wing yet have? And when did it go from a flap to something that would be able to enable flight? Apologies for the poor wording, it's late here and I thought I'd ask this before I got to sleep to see if I get any interesting answers or if I've got it all horribly wrong. Thanks! P.S. is one of my favourite subreddits, thanks to everyone for taking the time to answer all these phenomenal questions! Some interesting answers here, thanks guys. I feel stupid that I didn't think of these myself.
|
[
"Ornithologist/herpetologist here, typing over breakfast, so please forgive typos etc.",
"Dinosaur scales, just like modern-day reptile scales, bird feathers, and bird and crocodile scutes (those tough scaley bits on bird legs, those big smooth bits on crocodile backs) are made from beta-keratin. Scientists have found that when you inhibit certain aspects of scute production in birds/reptiles within the egg, those hard, smooth scutes will \"unravel\" to some degree and form fluffy strings of beta-keratin with a central supporting structure-- down feathers.",
"Okay, so: zoom back in time to the mid-Jurassic, where some small therapods are doing their thing. Therapods are the fast predatory dinosaurs-- velociraptors, tyrannosaurus, etc. Some of them were quite small, down to the size of chickens.",
"Due to surface:volume ratios, smaller animals lose heat a lot faster than larger ones. This means that if you grow smaller, you have to find new ways to keep yourself warm enough to function. Mammals did this by developing the ability to generate their own heat, amphibians and most fish dealt with it by adapting the ability to operate at low temperatures, and eventually some small therapods were messed up in the egg and were born with those unravelled scales.",
"Feathers, even those early simple ones, are very good at keeping warmth in, as anyone who's ever snuggled down under a goosedown quilt can attest to. Their fluffliness traps pockets of warm air, while their larger combined surface area can soak up heat from the sun. Any small therapod with this adaptation had an edge over his non-fluffy compatriots.",
"So already we can see an advantage in feathers, even when not related to flight. Those small therapods mostly ate (frightningly) large insects, running on their hind legs and grasping their prey with their dexterous clawed hands (which were now on the end of feathered arms). Once they could stay warmer for larger, these little dudes could get a little more energetic. ",
"There are two hypotheses relating to what they did with those feathered arms:",
"The cursorial theory puts that these zippy little therapods ran after their prey as it flew just above the ground, chasing it down and grabbing it. As they spread their feathered arms, they were able to make leaps at their prey, their new feathers giving them a boost in the air for a short but useful moment. Think of pigeons flapping their wings as they jump up to a stair; not actually flying, but giving a boost to their jumping.",
"The arboreal theory puts that these therapods spent a lot of time climbing trees, and having feathered arms both A) helped them make jumping lunges at insects by letting them glide for short distances, much in the manner of the marsupial gliders today, and B) helped them survive falls when falling/leaping out of trees to avoid sudden predators.",
"Currently, the arboreal theory is most prominent, and there aren't too many supporters of the cursorial theory around.",
"Okay, so where we are at the moment: small running dinosaurs split their scales into fluffy feathers, got warmer, and were able to be more energetic and succeed more during hunting and escaping predators. How did these feathery dinosaurs turn into birds as we know them?",
"As their leaps became bigger and better, these proto-birds found themselves able to take advantage of a whole new range of flying insects, and the pressure was on them to fly even better and eat even more. They could do this by adapting in two important ways, which all birds today have been shaped by: these proto-birds had to both ",
" their weight and ",
" it. When it comes to flight, it's not good being lightweight if you're not streamlined, and it's not good being streamlined if you're heavy.",
"These adaptiations include: ",
"loss of external hands (except in one very special bird-- points if you know it); their clawed dinosaur hands were fused together into a lightweight hand-bone, and as their flight got better and they could snap prey from the air without their hands, those hands eventually lost all functionality together, becoming little more than a support strut for the primary (flying) feathers",
"replacing jaws and teeth, both of which require hefty bone, with the lightweight structure that is the beak",
"replacing the tail, a structure both heavy and non-centralised, with the ",
", that bump on their butts to which all the tail feathers attach (if you've ever roasted a chicken, you'll know it)",
"reducing the weight of their skeletons by replacing dense, solid bones with honeycombed ones, and by fusing other bones together (such as the ",
")",
"gaining streamlined feathers, the sort that zip together and allow air to flow over them neatly.",
"evolving certain adaptations for strong flight, such as the ",
" (wishbone) and keel bone, and the resulting muscles (the ",
" muscle team is a wonderful feat of engineering)",
"(There is some debate over whether other functional adaptations to flight (air sacs, being warm-blooded) were actually present in other dinosaurs prior to the evolution of feathered flight, so I won't cover them.)",
"Basically after a lot of selection for the lightest, most centralised flying dinosaurs, we had something that was pretty much a bird*. From there they were able to take advantage of the K/T extinction and radiate into the many different forms that we see today.",
"I think that covers it? If you have any other questions/requests for clarification, I'd be happy to answer them. Birds are neat!",
"*Note that this happened a lot of times-- there were several independent lineages of \"birds\" that all died out along with the dinosaurs, leaving the one sole lineage that we're familiar with."
] |
[
"Not a scientist, but there are animals that are gliders. They can't fly, but take advantage of increased skin spread to extend their leaping distance between trees.",
"http://en.wikipedia.org/wiki/Flying_squirrel",
"http://animals.nationalgeographic.com/animals/reptiles/flying-snake/"
] |
[
"You couldn't have explained it any better, thanks! "
] |
[
"What causes cell signal to seemingly go in and out, when both I and the tower are stationary?"
] |
[
false
] |
As I typed the title alone, I went from service, to no service, and back. What factors contribute to this behavior? To help narrow it down, I am indoors, in a public space.
|
[
"The dominant signal path between you and the cell tower is unlikely to be a direct line-of-sight one; there'll be multiple refractions around and reflections off of intervening objects. That path might be momentarily obstructed, for example by passing people in that public space (6' bags of salty water are great radio blockers), nice slab-sided vehicles out in the road, branches swaying in the wind, squalls on a rainy day - any number of factors. If your signal is marginal to start with any of these seemingly minor obstructions or changes to the environment could be the last straw.",
"I install building radio systems: I've seen comms disrupted significantly by installing a marine fish tank in the reception of a tower with a big atrium. Also, the big flappy doors in hospital corridors that are made of plastic with a core of chicken mesh make great mirrors for wi-fi signal and can cause ghost images of coverage to appear fleetingly across the building while the door is out of the closed position..."
] |
[
"Actually, my professor tried this experiment at a conference where they set up a wifi receiver and transmitter system in a lecture hall and then analyze the channel (all the reflections of all the people). They wanted to see if they could see the difference between a certain person being in the room or not (and have the rest remain constant). They discovered however that their system was so well designed that they could see people breathing by analyzing the channel characteristics. So yeah, it can get very messy!"
] |
[
"The detail is not there yet but medical applications are invented such as monitoring heart beat of patients in a room etc."
] |
[
"In the split second before someone is about to collide with another moving vehicle, would it be more beneficial for them to tighten their muscles, or relax them?"
] |
[
false
] |
Hypothetically, if someone is driving through an intersection in their vehicle and is wearing their seatbelt, and they are going anywhere from 30-60 MPH, and they see another vehicle run a red light, and it is going the same speed as they are, assuming there is no chance to stop or avoid the collision, would they have a lesser chance of being injured upon impact by tightening all of their muscles, or relaxing them? Or would it not make any difference?
|
[
"Drunk ",
" trauma victims have a higher rate of survival than their sober counterparts",
". It's possible that the alcohol-induced relaxation may help survivorship during that trauma, though as far as I'm aware, that idea is still speculative. ",
"In general, any structure with some \"breathing room\" can absorb force better without breaking (e.g., skyscrapers are designed to tilt 3-6 inches in the wind). This concept applies for bodies too, the more rigid a structure, the more brittle. In other words, you'd probably rather be a cooked noodle in a car accident then a raw one."
] |
[
"That sounds like some pretty heavy speculation on the part of the doctors. The relaxation theory makes sense, but it would seem that being ejected from the vehicle (regardless of muscle tension) would greatly increase your chances of harm from extraneous variables. Like having your body collide with a tree, wall, other vehicle, etc. "
] |
[
"That sounds like some pretty heavy speculation on the part of the doctors. The relaxation theory makes sense, but it would seem that being ejected from the vehicle (regardless of muscle tension) would greatly increase your chances of harm from extraneous variables. Like having your body collide with a tree, wall, other vehicle, etc. "
] |
[
"What evidence do we have that there wasn't any advanced civilization, like humans are currently, here on Earth some hundreds of millions of years ago?"
] |
[
false
] | null |
[
"There hasn't been any evidence found in support of it. And while absence of evidence is not evidence of absence, we have no reason to entertain any random claim since there are an infinite number of them. For example, if I say \"what evidence is there that unicorns don't exist and live at the bottom of active volcanoes?\" the burden of proof is really on me to provide some positive evidence in favor of this."
] |
[
"This is not a claim, it's a valid question. And it's not random, it's based on the evolution of species."
] |
[
"My answer was from a philosophy of science perspective: When we have a statement, or a hypothesis, or a theory, how do we test it to know that it is true? We either have some confirmatory evidence in support of it and then we might say that it is true as far as we know (something akin to inductive inference), or, as Karl Popper would argue, the statement/hypothesis/theory needs to be falsifiable and we can propose tests to try to falsify it. ",
"In this case, the hypothesis is \"there was an advanced human civilization millions of years ago\"",
"We have no evidence in favor of this hypothesis. We can try to make predictions based on this theory and see if they are borne out: if it were true, then we might expect to find X, Y, Z (I don't know what that would be, ancient metal structures? whatever you like), but we haven't. ",
"If one argues \"well any evidence of it existing would have been destroyed\" then Popper would say that the original claim is not a scientific theory because there is no way to falsify it. ",
"These ideas in philosophy of science extend to all statements, not specific to this one. You may be interested in checking this out: ",
"https://en.wikipedia.org/wiki/Falsifiability"
] |
[
"How fast does air get sucked into space?"
] |
[
false
] |
You see in movies when there is a hull breach or whatnot, air/object get sucked out of the hole extremely fast? How fast is it?
|
[
"Air molecules move QUICKLY. At 20°C, an average air molecule will probably move around 500 meters per second. When they bounce off something, they push off that thing, they impart some momentum. The force experienced by an area with a lot of air molecules bouncing off it is air-pressure. Normally, you'd have air molecules bouncing off either side of an object, and the net force imparted cancels out.",
"Air pressure in a spaceship would probably be around 1 atmosphere, which is 15 pounds per square inch of pressure. Now imagine you made a hole one square inch in size in your spaceship, and put say, say, a marble in the hole. That marble would feel 15 pounds of force pushing it out the hole... but because there's no air on the other side, nothing pushing back. And air molecules nearest the hole and coincidentally heading towards it would just fly out at 500m/s straight away. Others might take some bounces, but because they can't bounce off other air molecules that have already escaped, everything will tend to bounce towards the hole on average. Objects won't have that speed, because it takes a while to accelerate to it even at 15 pounds of force per square inch, and they'll be clear of the hole pretty quickly. How fast will depend on the object's size and mass. A ",
"1 m",
" hole with a 15 psi pressure difference yields 23000 pounds-force",
" which would in turn ",
"accelerate a 1 m",
" person at 1km/s",
" for a short time.",
". If we say that a person is 1 foot wide, they'll ",
"accelerate to about 25m/s",
" in the time that they're in the hole, (using the last of these ",
"kinematic equations",
".)",
"So how fast will all the air empty? It'll depend how much there is, but it might be quite tricky to calculate. Luckily others have done this in the past, ",
"here's an example",
". Their result for a 30m",
" cabin: ",
"We can see that a one square centimetre hole will reduce cabin pressure by 50% in 500 seconds (8.3 minutes). This value scales in inverse proportion to hole area. Thus a 10 sq cm hole will only take 50 seconds to halve the pressure, (...)",
"disclaimer: It's late, someone check my maths.",
"[edit] As Overunderrated says, this is not a complete picture and wantonly ignores fluid dynamics!",
"[edit 2] Well, it looks like this isn't quite the right answer, but I'll leave it up as an approximation until someone comes up with a better one."
] |
[
"Air flowing through a hole like this will always be choked, and limited to precisely the speed of sound through the hole, regardless of the pressure difference.",
"The link you provided is very wrong, because ignoring compressibility effects when you have density+pressure variations of this magnitude is wildly inappropriate.",
"... I've definitely answered this exact question here in the distant past."
] |
[
"This is the correct response. Air flowing through an orifice will max out at Mach 1. At that point, the flow rate is dependent only on the pressure within the chamber. The downstream pressure (vacuum) doesn't matter. The actual amount of time will depend on the size of the chamber, the pressure of the chamber and the size of the hole. ",
"http://en.wikipedia.org/wiki/Orifice_plate"
] |
[
"Is there a genetic code or mechanism that makes sure that our body grows uniformly?"
] |
[
false
] |
Like is there something that prevents our hands from growing significantly larger that the other or our bones from growing through our skin?
|
[
"Short answer: Yes.",
"Answering with a bit less factious cheek: the on/off switches for your genes are controlled by transcription factors. These are activated or inactivated by compounds they bind to. Binding is all about how well things fit against each other combined with how much of each is around. So if the transcription factor is made in one cell (and is stuck inside) and the binding partner is made by another cell (and can move freely to another cell) the activation of the transcription factor will be highest in the cells closest to the one making the binding partner and drop off as cells get further away. ",
"This is the basic principle that many of the body plan genes are controlled by. The combinations of genes that say \"keep making this bone longer\" are different for different genes and turn off at different times.",
"You can also have a cell make both the transcription factor and binding partner, but at some point it is told \"stop making the binding partner\" the cell keeps dividing so with each division the amount of binding partner decreases until there's not enough to keep the transcription factor activated. That's like having an internal countdown for gene activation.",
"There are lots of cool mechanisms and they all have to work together to make something as complicated as the human body",
"I highly recommend \"Life Unfolding\" by Jamie A. Davies for a more detailed explanation"
] |
[
"Yes, I was trying to cram a lot of information into a short answer.",
"Basically, cells are able to communicate to each other through signaling networks. These work at different levels of cell interaction. \"Cell-cell\" signaling is the term for two cells that are physically touching each other. \"Paracrine\" signaling is the term for when a cell makes a signaling molecule that diffuses away from it. That creates a zone around it that other cells can in the zone can sense and respond to. \"Endocrine\" or hormone signaling, is when that molecule can enter the blood stream and circulate to the entire body. There is also \"synaptic\" signaling, which is how nerves communicate with other nerves.",
"And yes, environmental factors play a role. You can think of it like, given your genes there is a range of heights you can be. Environmental factors can influence where on that range you actually end up.",
"For early development there are a lot of signals involved but one of the basic modes that is used a lot is based on a concentration gradient. Lets say a signaling molecule binds pretty tightly to a transcription factor, so that if they are both around at a ratio of 20 signaling molecules to 1 transcription factor (or higher), the signal goes through. Now imagine that the cell \"A\" that makes the signaling molecule can make it at a rate fast enough so that there are always 100 signaling molecules immediately next to that cell, and that number drops off by 10 every four cells you move away from it. Lets call another cell Cell \"B\" that is 34 cells away from cell \"A\"",
"The first 4 cells between cells A and B, will see between 100 and 90 signaling molecules, and will have the signal turned on",
"The next 4 cells (8 cells away now) will experience between 90 and 80 signaling molecules, and will have the signal turned on as well",
"We can keep going with the next 4 (12 cells away) will experience between 80 and 70 signaling molecules, and will have the signal turned on",
"At 16 cells we are down from 70 to 60, at 20 cells , we are down from 60 to 50, at 24 cells we get down to 40, at 28 cells we get down to 30 cells, at 32 we get down to 20 signaling molecules.",
"Here is the first time that we are exactly at the \"threshold\" for signaling. The signal is turned on all the way out to this region.",
"Between the next 4 cells the level will drop from 20 to 10, and the signaling molecule gets too diffuse to properly keep the signal on. By the time we get to our Cell B some 34 cells away from cell A the signal is around 15 molecules and we expect our signal to be shutting off this far out."
] |
[
"Thanks for your answer\nIt's a bit difficult to understand but after a few readings i could get, so there's something like a benchmark where the binding partners are present and the cells or the body as a whole grows until the cell's transcription factor reaches it and binds with it, right?",
"Does the binding partner also depend upon things like nutrition, exercise and other environmental factors? because we have seen basketball players who are really tall and it doesn't seem like it has been passed down by genes"
] |
[
"A question about how the velocity/acceleration of an object is affected by curvature in spacetime..."
] |
[
false
] |
[deleted]
|
[
"Best way to think of it is that general relativity dictates an equation of motion for the object, and from that equation of motion you can determine a potential that is similar to that of Newtonian gravity but with some corrections. The potential still goes primarily as 1/r, which yields stable elliptical orbits with speeds obeying Kepler's laws."
] |
[
"you always move through spacetime (with speed of light, actually). if your speed doesn't have any spatial components, you just move in direction of time. you cannot do anything to stop this. you can tilt the direction of your four-velocity vector in some of the spatial directions, so that the time component is smaller (because absolute value of the speed is always conserved) and hence cause dilatation of time, but you cannot stop time.",
"you can imagine two observers at equator, and say, that the curved surface of earth is like curved spacetime. you can calculate their shortest distance over surface of earth using metric. now their distance surely depends on the difference in longitude, but also on their latitude. if they maintain the same longitude, but will increase their latitude (i.e., they both go north with the same speed), you can see, that they will get closer and closer to each other... this is basically what's going on when two objects \"attract\" themselves gravitationally."
] |
[
"The curvature of spacetime is observed as a force on the object. A force is the same as an acceleration with a scaling factor of mass, therefore the curvature of spacetime accelerates the object.",
"In the case of your orbiting object, it is moving fastest when nearest the focus because this force is accelerating it in roughly that direction. Then, as it starts moving away again, the force is reducing its speed and slowing it back down."
] |
[
"How did the transition from egg-laying to live birth happen?"
] |
[
false
] |
I understand evolution is a very slow process. I can imagine a small node or protrusion slowly becoming a fin and a fin slowly becoming a limb, etc. But visually I have a hard time imagining what the "in-between" stages looked like between egg-laying animals and mammals that have live births. Did egg-laying animals slowly start keeping their eggs inside the body for longer periods, until eventually the babies finished developing inside the body? And the eggshells eventually stopped forming as they were no longer needed? Is an animal like the platypus related to this type of in-between stage?
|
[
"There are a lot of animals now that are basically the intermediate stage. They're live bearers like guppies, Platies, several types of snakes, sharks, flies... They're basically egg laying species that delay the egg laying step until after the eggs have hatched and then lay live young. This differs from true livebearers like mammals in that their young aren't really supplied with nutrients by the mother."
] |
[
"From the species alive today, we can guess how mammals transitioned from laying eggs to having a live birth. As you may know, echidnas and platypuses both lay eggs. The shell is more like a leather skin than a hard eggshell that you see when making your breakfast. The young will hatch early as there are not a lot of nutrients within the egg, the complete opposite of how modern fowl produce their young. The young would then feed on milk that seeps into the mother's pouch, as these animals lack nipples. You can imagine the next stage up would be live birth, nipple development or both, like the kangaroos.",
"\nKangaroos give birth to live young, but they are extremely underdeveloped, they are a few inches large and barely able to walk. Researchers think this occurs because kangaroos do not have placentas to protect the young from the mother's immune system. As a result, if they young stayed too long in the mother's uterus, it would die. Next, the need to crawl from the mother's birth canal to her pouch, where it will nurse for the rest of the baby's development. As you can imagine, the next stage would be to develop placentas. ",
"I am afraid this is all I know about the topic. I hope this helps!"
] |
[
"Evolution doesn’t necessarily HAVE to happen with gradual changes, there is a model called punctuated equilibrium that describes periods of not much change interspersed with periods of rapid change. ",
"https://en.m.wikipedia.org/wiki/Punctuated_equilibrium",
" ",
"I don’t know about egg laying/live birth atm, but if a single gene, for instance, happened to control it, and a mutation made it change drastically, that could be a means for evolution to happen without many in-between states."
] |
[
"What is the lowest possible orbit a satellite have on earth?"
] |
[
false
] |
If a satellite moves fast enough, would it be possible to orbit at 100 feet? 10 feet? 1 foot?
|
[
"Ignoring the presence of the atmosphere, a satellite can orbit at any height above the surface (ignoring the presence of mountains, etc.). Including the atmosphere, orbiting close to the ground would result in you no longer having a satellite pretty damn quickly. "
] |
[
"Assuming atmosphere, the lowest a satellite can orbit without beginning to experience significant decay is 160 km. Atmospheric drag is high enough to cause break up around 80 km, so technically a satellite with an engine to counter decay could dip below 160 km. ",
"https://en.m.wikipedia.org/wiki/Low_Earth_orbit",
" "
] |
[
"Theoretically yes, as the difference in gravitational pull is minimal. If you assumed the earth were a smooth sphere then almost any any distance is feasible if you go fast enough, although how close you could get before you'd have to go past the speed of light I don't know"
] |
[
"Why do I only seem to hear about “upper” respiratory infections but never “lower” ones? Is there such a thing?"
] |
[
false
] |
Also, if they are a thing, what would a “lower” respiratory infection be in relation to an “upper” respiratory infection
|
[
"Its more a matter of language than that there aren’t lower respiratory tract infections - you just know them as pneumonia, acute bronchitis and tuberculosis for instance. Upper respiratory tract infections are generally more common, so you hear about them more often, and more diverse (anything from colds, sinusitis to sore throat and tonsillitis). They are also generally less dangerous and only require treatment of the symptoms, usually using the same spectrum of medications, making the umbrella term of URTI medically relevant. Lower respiratory tract infections are less common, more dangerous and require different treatments, which focus on both the symptoms and actually eradicating the infection itself. It is therefore medically necessary for them to have their own names.",
"Edit: to answer the second part of you question - the upper respiratory tract includes the mouth, nose, sinuses, throat and trachea. The lower respiratory tract includes the lungs and bronchial tubes."
] |
[
"Upper respiratory infections are very common. Colds and Flu's are common upper respiratory infections. They happen primarily in your mouth, nose, throat area.",
"Bronchitis is when the infection reaches the bronchial tubes. Pneumonia is when it reaches the lungs. They just don't call it a lower respiratory infection because it's more exact on where it is."
] |
[
"While upper respiratory infection are most common... one can not get one while traveling through the south. one can still get an upper respiratory infection in the north. ",
"With out treatment, an upper or lower respiratory infection could spread to become a sideways infection. Most cases are self limiting but there have been recent reports of upside down respiratory infections so watch out."
] |
[
"If you placed a combination of molten metal inside a centrifuge that is inside a furnace, would the metals separate in the same way as it does when placing blood in a centrifuge. Heavier metals going to the bottom and lighter to the top?"
] |
[
false
] | null |
[
"Metals are atom sized. Gravity has nearly no effect atoms because they are so small. The only force moving the atoms is going to be heat.",
"This is not a good explanation. Take oil and water- the oil floating on top of the water is due to gravity. Oil and water may be molecules, but I know there are metal atoms that have much larger masses than water molecules (I don't have any idea off the top of my head what the mass of molecules in cooking oil is).",
"And we DO use centrifuges (and other things) to separate out vaporized metals. That's how we enrich uranium.",
"You may be right that in a lot of cases using a centrifuge won't work, but your explanation for why that is true is not good enough. The metals being inseparable due to forming an alloy is a very different phenomena from \"gravity doesn't effect atoms because they are too small\"."
] |
[
"Phase diagrams are almost universally simplifications, and typically don't account for non-hydrostatic/anisotropic stress states. Just wait for Thermo 102 ;-)!",
"Edit: More to the point, liquid (or solid) solutions don't rule out chemical concentration gradients, especially at non-equilibrium conditions. "
] |
[
"I'll defer to someone with more specific expertise, but here's my take:",
"In the case of blood separation, you're dealing with relatively large solid particles suspended (not dissolved) in a fluid. In the case of different liquid metals mixed together, it would depend on whether the metals are miscible (soluble in one another), or not. In the case that the metals are miscible a concentration gradient of the different metals would likely form due to differences in the mass of the molecules, but you would only get a sharp separation with immiscible metals. Solubility/miscibility are also a function of pressure and temperature. ",
"tl;dr: You could probably generate at least concentration gradient; would depend on which metals and what conditions. ",
"Edit: language for clarity. "
] |
[
"Would it be better to neutralize an acid spill with a weak base or a strong base?"
] |
[
false
] | null |
[
"How you neutralize depends on the acid. If you spilled concentrated sulfuric acid, you're best off avoiding water and using something like solid calcium carbonate. If it's hydrochloric acid, you should dilute before attempting neutralization because HCl produces vapors when it heats up. If you spill something like hydrofluoric or perchloric acid, you run.",
"Either way, you will produce less heat if you neutralize with a weak base instead of a strong base."
] |
[
"What makes HCl a weaker acid than HF?",
"HF is the weaker acid. (pKa 3.2 vs -6.5 for HCl) ",
"But HF is toxic. The F",
" combines with Ca",
" to nearly insoluble CaF2 but the body needs its calcium. ",
"Additionally the lower acidity means that more hydrofloric acid exists as non-dissociated hydrogen fluoride. So over any concentrated hydroflouric acid spill you will have a cloud of highly toxic HF. ",
"HCl is the stronger acid and therefore better soluble in water and not as toxic. So less gas over a spill and that HCl is easily filtered out in the nose (if not too concentrated). That stings in the nose but saves the lungs. ",
"HCl should be handled with care too. But its at least an order of magnitude less problematic than HF. ",
"They both have the same amount of H+ so what difference does the Cl or F make? ",
"F is smaller so the negative charge of F",
" is distributed over less volume and therby less stablized. "
] |
[
"The acidity is determinded by the equilibrium.",
"HF <-> H",
" + F",
"and",
"HCl <-> H",
" + Cl",
" respectively.",
"H",
" has always the same energy. But when I say F",
" is less stable (with respect to HF) than Cl",
" (with respect to HCl) then the first equilibrium is more on the left side and less free H",
" is in solution.",
"So yes the acidity is determined by the concentration of H",
" but the concentration of H",
" is determined by the stability of the remaining part."
] |
[
"AskScience AMA Series: I was NASA's first \"Mars Czar\" and I consulted on the sci-fi adventure film THE SPACE BETWEEN US. Let's talk about interplanetary space travel and Mars colonization... AMA!"
] |
[
false
] |
Hi, I'm Scott Hubbard and I'm an adjunct professor at Stanford University in the department of aeronautics and astronautics and was at NASA for 20 years, where I was the Director of the Ames Research Center and was appointed NASA's first "Mars Czar." I was brought on board to consult on the film , to help advise on the story's scientific accuracy. The film features many exciting elements of space exploration, including interplanetary travel, Mars colonization and questions about the effects of Mars' gravity on a developing human in a story about the first human born on the red planet. Let's chat! Scott will be around starting at 2 PM PT (5 PM ET, 22 UT). EDIT: Scott thanks you for all of the questions!
|
[
"Do you think there are compelling reasons to eventually build large scale settlements on Mars, or will human presence there be limited, like on Antarctica?",
"If you think colonization is realistic what do you think will motivate a large number of people to move to Mars?"
] |
[
"Some people say that this desire to live on Mars is to ensure the survival of the human race, if and when a large scale extinction event occurs here on Earth. That's a valid reason. We've evolved, with the rest of the world, to pine for the maintenance of our own genetic line. Putting human beings on the face of another planet is a veiled extension of our basic goal in life.",
"I think it's more our need to explore that hurls is towards the red planet, the insatiable curiosity of mankind. Sure, it'd be cool, but it would also answer the question of 'Can we?' that seems to drive most every innovation. ",
"We've conquered our own environment, living relatively comfortable lives in places too hot and too cold. We've seen the deepest of depths on our home planet, the tip of it's highest peak, and most of what sits in between. For the curious, for the bold, and for the sake of having done so, Mars is next.",
"I think eventually you'll change your tune. When we land on Mars' surface, and you're watching ~225 million kilometers away, on Earth, in your home with your loved ones beside you, any feeling of 'Why' should slip away. I say now that in that moment, it will be obvious for everyone watching that this was something we were meant to do."
] |
[
"Some people say that this desire to live on Mars is to ensure the survival of the human race, if and when a large scale extinction event occurs here on Earth. That's a valid reason. We've evolved, with the rest of the world, to pine for the maintenance of our own genetic line. Putting human beings on the face of another planet is a veiled extension of our basic goal in life.",
"I think it's more our need to explore that hurls is towards the red planet, the insatiable curiosity of mankind. Sure, it'd be cool, but it would also answer the question of 'Can we?' that seems to drive most every innovation. ",
"We've conquered our own environment, living relatively comfortable lives in places too hot and too cold. We've seen the deepest of depths on our home planet, the tip of it's highest peak, and most of what sits in between. For the curious, for the bold, and for the sake of having done so, Mars is next.",
"I think eventually you'll change your tune. When we land on Mars' surface, and you're watching ~225 million kilometers away, on Earth, in your home with your loved ones beside you, any feeling of 'Why' should slip away. I say now that in that moment, it will be obvious for everyone watching that this was something we were meant to do."
] |
[
"General relativity question"
] |
[
false
] |
From my understanding, planets are imbedded in time space as it expands, so the planet is moving with space time as well as through space time. But what about the point where space time and the planet actually meet, does space time continue through the planet, or stop at the surface of the planet? I thought perhaps space time exists between the atoms of earth. But if that is so, what about where space time meets the surface of the atom?
|
[
"http://en.wikipedia.org/wiki/Spacetime",
"\n\"In physics, spacetime (or space-time, space time, space-time continuum) is any mathematical model that combines space and time into a single continuum. [...] By combining space and time into a single manifold, physicists have significantly simplified a large number of physical theories, as well as described in a more uniform way the workings of the universe at both the supergalactic and subatomic levels.\"",
"-It's a helpful abstract for dealing with relativistic physics. Not always useful when interpreted literally."
] |
[
"So you're saying that the fabric of space time is not a literal thing and is used to help understand theories "
] |
[
"That's my understanding, but I'm no physicist. Light slows and even changes direction when it passes large celestial systems, creating a gravitational lense. ",
"http://en.wikipedia.org/wiki/Gravitational_lens"
] |
[
"Why does a clock gain time?"
] |
[
false
] | null |
[
"Clocks tend to work by having some sort of oscillating natural phenomenon. The clock counts the oscillations and thus makes the time. However, the oscillations are not exactly in sync with real time as they don't tend to be that fast and so the clock loses time."
] |
[
"Thank you for your response!\nBut in this day and age, isn't there a better way to keep time?\nOr is it just not cost effective? "
] |
[
"There is, and it's called an internet connection."
] |
[
"How much lava is there on earth?"
] |
[
false
] |
My son’s actual question (the relevance of which we may ignore for now) was if there was more water or more lava on earth. I have read estimates on the amount of water, but it seems to be an interesting, uncommon question how much lava there is on (in) our planet. (I guess this would be a question for Randall Munroe..) PS: Hope I got the right flair. Please tell me otherwise.
|
[
"In terms an actual number on the total amount of magma (liquid rock not erupted) and lava (liquid rock erupted) that exists at a particular time, it's going to be very hard to quantify with any accuracy. ",
" To go beyond that general statement, let's do some estimations. For the sake of these comparison, let's just consider the ocean in terms of a volume water to compare against and we'll use a value of ",
"1.335 x 10",
" km",
". ",
" Now, in terms of lava + magma, the important things to realize are (1) that eruption / melting rates are going to be quite variable on short time-scales so it's easiest to consider long-term averages (e.g., average rates per year reflecting averages of > 1 million years) and (2) there is going to be a pretty wide range of residence times (i.e., how long it persists) in terms of magma, but extremely short residence times in terms of lava, i.e., nothing stays as lava for very long as it will tend to solidify into rock quickly. ",
"The closest I could find to global rates or volumes of lava or magma are the estimates in ",
"White et al., 2006",
". Here, they assemble a variety of data to come up with average volumetric eruption rates for different types of volcanic systems (i.e., the average amount of lava produced in a given system per year) and the \"intrusive:extrusive\", or I:E, ratio, i.e., an estimate of the volume of magma under the surface that exists for a given volume of lava erupting at the surface. Two important points we can take away from their Figure 2 are that for a given type of system (e.g., continental arcs) there are a wide range of eruption rates and that there is even larger variability between types of systems, with some on average having relatively low eruption rates (e.g., continental hotspots with an average of ~10",
" km",
"/yr) and some with much higher rates (e.g., flood basalts with an average of 1 km",
"/yr). We can also see a good amount of variability in the I:E, ranging from 1:1 to 10:1. They suggest an average of ~5:1 for a global I:E. ",
"Now, the important thing from above is that these are average rates so to get at total volume at a particular time, we would need to extrapolate over the total number of a particular types of volcanic systems to get at a total global estimated volume of magma + lava. That becomes a challenge in of itself, cause then we need to start thinking about the number of eruptions per year of different types of systems and which ones we need to consider (e.g. at least in the modern, we can totally ignore some of these, like flood basalts as there are no active flood basalt provinces today and there haven't been for at least 10 million years). To get at the main point though, let's just consider the rates from ",
"mid-ocean ridges",
", the largest volcanic system on Earth. Looking at the estimates of eruption rates from White et al, there is a decent variability from 1x10",
" km",
"/yr to 9.6x10",
" km",
"/yr (though only a few examples that they include). These represent the rates based on average volumes erupted over 1 million years over 100 km of ridge length. If we do a little dimensional analysis and extrapolate these rates over the total length of the mid-ocean ridge system (~80,000 km) we can calculate estimated total eruption rates of 7.7 km",
"/yr to 0.8 km",
"/yr using the high and low average rates respectively. Those are just the lava eruption rates, so if we apply the I:E ratio, first using the 5:1 average, this implies total (lava + magma) volumes of 46.1 km",
"/yr to 4.8 km",
"/yr. Given that generally the White et al synthesis suggests higher I:E ratios for mid-ocean ridge systems closer to ~10:1, using this would bump it up to 84.5 km",
"/yr to 8.8 km",
"/yr. These could be thought of as kind of rough averages of the total static volume of liquid rock at mid-ocean ridges at a given time as (1) the lava doesn't stay lava for very long, becoming oceanic crust and (2) we would expect the magma volumes feeding the lava to remain roughly constant. Even at the low end, these almost certainly represent over estimates as well because magma/lava production rates vary a lot over the mid-ocean ridge and in some places, these are very low (e.g., at ultra-slow spreading ridges - ",
"Dick et al., 2003",
"). ",
"Obviously, for a complete assessment, we would want to try to estimate other systems besides the mid-ocean ridges, but given that mid-ocean ridges represent a major component of the volcanic output of the planet and this ends up representing a comically small volume of magma + lava compared to the global ocean, even using the extremely high end (i.e., ~6x10",
" % of the ocean volume), it's safe to say there is a lot more water than melted rock on average. Even if we consider the total volume of extremely large volcanic deposits like the ",
"Deccan Traps",
" and assumed their entire volume (1x10",
" km",
") was lava at the same time (which it never was, flood basalts erupt over hundreds of thousands to millions of years) and applied a conservative 5:1 to I:E ratio, this hypothetical total volume of lava + magma would still only reflect ~0.5% of the total ocean volume.",
" the first thing to realize is that the vast majority of the mantle is solid, but small portions of the ",
"asthenosphere",
" maybe liquid. This melt likely exists as thin coatings along grain boundaries and there are a wide range of estimates of the percentages of melt, but usually hovering around 1-7% (e.g., ",
"Hammond & Humphreys, 2000",
"). If we again do some simple estimations and calculate the volume of the asthenosphere and apply a range of partial melt percentages, we can then get an estimate of total amounts of magma in the asthenosphere. In reality, things get very messy, very quickly, because (1) the depth of the lithopshere-asthenopshere boundary is likely quite variable and probably not a sharp boundary (e.g., ",
"Rychert & Shearer, 2009",
", ",
"Eaton et al., 2009",
", ",
"Hamza & Viera, 2012",
"), (2) the thickness of the asthenosphere is unclear (e.g., ",
"Fjeldskaar, 1994",
", ",
"Morgan et al., 2013",
"), (3) the partial melt percentage is unclear (see Hammond & Humphreys, etc), and (4) the extent to which the same fraction of partial melt exists throughout the total (uncertain) volume of the asthenosphere is also unclear. For our purposes, we'll take a rough guess at a lithosphere-asthenosphere boundary of ~100 km depth and a thickness of the asthenosphere of 150 km. With those two (and assuming a spherical Earth with a radius of 6378 km) we can calculate a volume of asthenosphere (~7.25 x 10",
" km",
"). Then the critical question becomes what's the appropriate amount of partial melt to consider. If we assume partial melt exists at a fixed percentage throughout our total estimated volume of asthenosphere, we can get at total estimated volumes of melt distributed throughout the asthenosphere of between 7.25 x 10",
" km",
" (for 1% partial melt) to 7.25 x 10",
" km",
" (for 10% partial melt). Turning back to our ocean volume, those two numbers reflect around 50% (i.e., there would be about 1/2 as much melt in the asthenosphere as there is water in the ocean) to upwards of 500% (i.e., there would be 5x more melt in the asthenosphere than water in the ocean) comparing the estimated volumes of melt to ocean water. What this really tells us is that the error bars are large on these estimates, but that assuming our ridiculously simplified averages are approximately right, the volumes of magma vs water are largely in the same order of magnitude.",
" from the kind of back of the envelope estimations, we can say with some confidence that there is definitely a lot more water at the surface of the Earth than there is melted rock at the surface or in the shallow crust. When we start considering partial melt in the asthenospheric mantle, the volumes start to become more similar, but a lot hinges on the exact values used (which we know vary a lot and have large uncertainties). This also of course neglects water that may exist in hydrated phases within the crust and mantle, the latter of which could represent a significant volume of water (e.g., ",
"Fei et al., 2017",
")."
] |
[
"The earth's mantle is mostly soft hot rock, so let's go with the earth's outer core. That's liquid.",
"170,391,230,000 cubic kilometers.",
"Estimated water on earth is 1,400,000,000 cubic km So, there's about 121 times as much magma in the earth as water."
] |
[
"The Earth’s core isn’t what we would call magma though. It does not solidify into rock, it is never erupted and it has no material interaction with the mantle."
] |
[
"Is there such a thing as a perfect hermetic seal and/or a material which is completely impermeable? If not, is such a thing even theoretically possible?"
] |
[
false
] |
Basically, what I am asking is if there is anything which can perfectly contain fluids, in particular hydrogen and helium, without any leakage. As I understand it, even metal flasks have trouble with this, due to the hydrogen seaping through. Moreover, this seems to especially be a problem with helium since it is monoatomic unllike the diatomic hydrogen, coupled with how inert it is. EDIT: As I suspected, the answer is no. That being said, what is the closest we can get to "perfect?"
|
[
"\"Perfect\" is a tricky word. No container is going to give you zero losses over an indefinite period of time (if nothing else your container will eventually evaporate). As a practical matter, you have to define acceptable losses per unit time."
] |
[
"What is the best one could do? What material has the lowest reported permeability to hydrogen/helium?"
] |
[
"I'm sorry, I don't know."
] |
[
"Quick question about the ionosphere and radio waves."
] |
[
false
] |
So, I live in Northwestern Ohio, and I was working today at my delivery job. So obviously, for entertainment, I'm listening to my radio. I have it turned to 88.7, which is an alternative rock station based in Detroit. And as I'm listening, it starts to fade out, and I hear, clear as day, a completely different station coming in. Right in the middle of the promo for the station, actually. All I hear is "...Southwestern Florida's 88.7..." then it faded out, and back to 88.7 based in Detroit. So I'm wondering if maybe the radio waves from the Florida based station may have bounced off the ionosphere, and in some kind of crazy geometrical coincidence, ended up hitting the Earth again right where my car was? Or maybe someone could have just been boosting the signal somehow? TL;DR: Is it possible for radio waves to be bounced off of the ionosphere, and be heard clearly a thousand miles away by using a simple antenna?
|
[
"I've never heard of it in the FM frequencies (but neither have I looked). But I know for sure that plenty of people use this for AM and Shortwave radio communication. Radio waves do bounce off of the nighttime ionosphere and can travel vast distances from this reflection."
] |
[
"This is certainly possible. Searching for long-distance propagated TV and FM signals is a common pastime in the amateur radio community, which wikipedia refers to as ",
"TV DX",
". The mechanism's of propagation over long distances are generally more complex than just 'bounced of the ionosphere', though.",
"The other effect which might cause this issue you heard is completely unrelated. Many modern radio receivers have auto-tuning features which can occasionally cause them to switch stations if the one they are 'locked on' to fades out for some reason. I don't know anything about the FM radio setup in the US, but are you sure that Florida station isn't broadcast in your area on a close-by frequency band?"
] |
[
"Somebody could have been streaming internet radio on a smartphone and using a small FM transmitter to listen to it on their car stereo."
] |
[
"Are the martian landscapes we see in photographs uncharacteristically flat and smooth for Mars in order to make it easier for the rovers? Are there typical, dramatically steeper/rockier landscapes that we haven't seen yet from the ground because the rovers can't go there?"
] |
[
false
] |
Are we only seeing photos of the martian "great plains" because our rovers couldn't handle the martian "Rocky Mountains".
|
[
"We see where the rovers can go. Mars is a very tricky planet to land on: it has a very dusty atmosphere where particles impact heat shields, but it also doesn't have enough atmosphere to decelerate a probe to a safe landing. Since parachutes are not enough, the last part of the descent is usually performed on retrorockets. Recent missions have been mostly successful, but there were lots of landing failures in the '1970s.",
"In order to make it relatively safe, the landing site is chosen at a low elevation, where you have more time to decelerate with atmospheric drag. This automatically excludes any kind of \"rocky mountains\". Flat terrains also have a lower probability of exhibiting large boulders; some landers (e.g. Curiosity) could avoid them but would have failed if they were too close to each other, others (like Spirit/Opportunity) were just unable to avoid obstacles as they went bouncing around.",
"The rovers wouldn't be able to drive on a very bad terrain, and they would even not be able to land at a very steep angle. (They are calculated to land on a slightly non-horizontal terrain, but excessive values are impossible to deal with). Moreover, every spacecraft is specifically designed for the environment it will have to operate in (in fact the \"mission phases\" are defined by the different environments the spacecraft will traverse from launch and transit to decommissioning). Excessively harsh environments are usually avoided because designing for them would add a lot of mass and complexity to the system, boosting the cost to the stars and increasing the probability of failure.",
"This may sometimes conflict with the scientific interest of exploring a particular site. You have to get down to a compromise if you want a successful mission.",
"That said, we do have ",
"images of the harsh terrains on Mars",
" taken by the rovers."
] |
[
"Mars mission planning is always a conflict between the scientists, who want to go to \"cool\" places, and the engineers, who want a nice safe flat spot to land on. (That's not fair, the engineers want to go cool places too, but they know the risks.)",
"Over the years, as we've gotten better at recon and landing, there's been a shift toward \"riskier\" landing sites with more mountains. Just compare the photos from the ",
"first Mars landing",
" to the ",
"most recent one",
"."
] |
[
"Thanks. I'm just starting to really appreciate that landing once or twice on a planet isn't close to exploring all it has to offer. I look forward to future missions and seeing many as-yet unseen wonders of Mars. PS: Your second photo is now my desktop"
] |
[
"Is dark energy/matter created by the expansion of the universe? Does this violate conservation of energy if it does?"
] |
[
false
] | null |
[
"Dark energy has a constant energy density. If the volume of a region gets larger by expansion, the total dark energy inside obviously increases. This clearly violates conservation of energy, but energy is not conserved in cosmology, so no problem.",
"Dark matter is actually much more down to earth and acts like normal baryonic matter. The mass of dark matter in a region is conserved. As a region of space expands, since the total amount must stay the same, dark matter gets diluted, just like normal matter does."
] |
[
"A better way to phrase it is that general relativity does not have a well defined, global \"total energy\" so conservation of energy doesn't really apply to a cosmological scale. ",
"General relativity does require ",
" conservation of energy, so any reaction happening at any point will obey energy conservation. "
] |
[
"The first law of thermodynamics ",
" conservation of energy. This is a tragically common misconception. In cosmology, the law of thermodynamics are true, energy conservation is not."
] |
[
"Phd about fungal alpha carbonic anhydrase!"
] |
[
false
] |
[deleted]
|
[
"The function of carbonic acid anhydrase is pretty simple, as the reaction barely needs catalyzing to begin with (just H2CO3 <--> H2O+CO2 has a barrier of ~20 kcal/mol in water). In this case, it's likely little more than the zinc ion acting as a Lewis acid. ",
"If you want to see a change, I suppose the obvious suggestion would be to get rid of the zinc, or substitute it with a different metal by some other means. Point is, you wouldn't necessarily expect zero \"activity\" even without the enzyme."
] |
[
"I'm not familiar with fungi, specifically, but I've flanked it with bacteria and mice. In both of those, the first question would be \"Did we really get it?\"",
"1) It sounds stupid but....are you sure you got the gene? Run a Southern, not just PCR, to see if the gene is ",
" gone.",
"2) Is the transcript ",
" gone? Run RTPCR/Northerns to see.",
"3) Is the protein ",
" gone? Western blot.",
"4) Is the function really gone (that is, is there maybe an analog?) Check for activity. CA activity should be easy to assay for.",
"After you've confirmed you do have a true functional and genetic knockout, look in the literature for the role of CA in your species; when is it turned on? Pick 4 or 5 of the biggest change conditions and hit your mutant. I'm sure you knocked it out for a reason; just keep in mind that even if the unexpected happens, it doesn't mean it's a bad thing. You may have just discovered something new."
] |
[
"You are absolutely correct. A friend of mine was given a transgenic ",
", which was supposed to have only one gene of an operon knocked out...it tuned out that the entire operon was gone, as well as any chance of publishing during her master's program. ",
"I would certainly determine the status of the \"knocked out\" gene before proceeding. Additionally, you can never completely discount contamination. Go ahead and clone the inoculum and test several colonies for CA expression."
] |
[
"Why do human beings have such distinguishable facial features?"
] |
[
false
] |
We could identify each other just by examining our faces from 7 billion other people in the world, why doesn't this apply to any (most) other species?
|
[
"It's not that our features are inherently recognizable, it's that our brains have evolved to recognize our features."
] |
[
"We are 'wired' to specifically recognize and differentiate human facial features and expressions. If you were a Baboon, you would be able to recognize specific features of other Baboons very well, but not humans. Basically, most animals are tuned to be able to recognize specific features of their species (sounds, colors, features, etc.) but not other species since they aren't necessary to their (reproductive) survival."
] |
[
"Also, you are very capable of training yourself to recognize the minor differences in animals. Cattle and sheep herders can often recognize every individual in their flock, while to the untrained eye they all look the same. Those who do long term studies on social animals (primates, elephants, dolphins, whales...) can recognize or have database systems where hundreds of individuals are catalogued and named. In primate studies its not uncommon for a researcher to be able to identify 90+ individuals based off of facial markings (length and colour of fur, size and shape of nose, size and shape of eyes, birthmarks, moles, sun spots, scars, missing fingers...)"
] |
[
"What does \"structure of lowest energy\" mean?"
] |
[
false
] |
How come: low surface area => low energy? see 10 seconds of the video linked below
|
[
"Imagine molecules being bonded as people holding hands and trying to make a shape. If you cover a lot of surface, people will have to stretch and this is very tiring. On the opposite, if you squish everyone together people will be crushed and this is very tiring as well.",
"There is a shape that all those people will take that is optimal for everyone. When you take people as an example, they're standing on the ground so it's in 2 dimensions, and they usually make a circle. They could make a square, but then the people at the corners will have to be in a weird position. In a circle, everyone has more or less the same positions, and everyone feels fine.",
"If you take molecules, let's say from a soapy solution, they're in 3D and they usually form a nice bubble, which is the 3D equivalent of a 2D circle. But if you give them constraints, like a metal canvas on which they have to form, they can create weird shapes like tessaracts. That's because it's the shape that will be less \"tiring\" for all the molecules forming the bubble."
] |
[
"Surfaces can always be considered as defects. The specific reasons for this vary whether you are looking at a solid, like a metal or crystal; a liquid; or more complex matter, as the bubbles in your example.",
"In solids, atoms at the surface have a higher energy because they have a non-ideal bonding configuration in comparison to the atoms in the bulk (because they are only bound inwards to atoms in the bulk). The energy associated with the surface is called surface energy and is equal to the work required to create that surface.",
"For liquids the phenomenom is similar. Individual atoms or molecules have a greater attraction to one another (cohesion) than to molecules in the air (adhesion). For liquids this results in surface tension, which acts as an inward force at the surface.",
"(Surface energy and surface tension are equivalent. The first has units of energy per are and the second of force per length, which however have both dimension of kg/s",
" and can therefore be converted to each other. Surface energy however is more general, while surface tension is almost ecxlusively used for liquids.)",
"In more complex matter, as in the examples of bubbles, a combination of these forces and some more can result in the higher energy of the surface compared to the bulk. In bubbles for example you will have additional forces resulting from the hydrophobicity/hydrophilicity of the amphiphiles making up the bubble.",
"In any case, the system in question tries to minimize its total energy by minimizing its surface area if the associated energy barriors to do so are low enough. This depends ond the specific material, the temperature, pressure, etc."
] |
[
"How come: low surface area => low energy?",
"You mentioned that with certain constraints they make weird shapes, so does that mean that this isn't always true?"
] |
[
"Does fitness (or lack thereof) affect immune function? (IOW, do out-of-shape people get sick more?)"
] |
[
false
] |
Having a debate with someone on the matter and I didn't recall seeing any evidence one way or the other on the matter.
|
[
"There are several lines of evidence to suggest that physically fitter people have stronger immune systems compared to people lacking fitness; however, as with all immunology, nothing is straightforward!",
"This study found that people with a high level of self-reported fitness experienced fewer colds (46% fewer) than those with a lower level of fitness",
". This is a finding supported by a number of studies.",
"Fitness results in reduced levels of markers of inflammation in many studies",
"; some of this is related to the reduction of obesity in fitter people (in obesity, fat tissue releases these inflammatory markers) yet even when people are matched by their fat mass, fitness still carries anti-inflammatory benefits",
"Bearing in the mind the above long term benefits of general fitness increases, \"over-reaching\" during periods of intensive physical exercise actually suppresses the immune system in the short term (3-24hr).",
"Runners of long-distance events suffer increased risk of infection immediately post-race",
"Immune cell function may be temporarily decreased post-acute exercise"
] |
[
"Sorry, the increased infection rate is for upper respiratory tract infections (URTI, colds and the like), which rather rules out foot injury. I should have mentioned! ",
"These studies are far from conclusive, due to inherent errors in self-reporting both URTI frequency and perceived fitness. Non-fit/strong immune people such as yourself do seem to be the outliers, but this data is drawn from large populations where natural variations even themselves out, as you said."
] |
[
"I saw a cool seminar on this about 5 years ago by Monika Fleshner (UC Boulder). She studies aerobic exercise in rats. The running (on the running wheel) releases endorphins. The endorphins impact neural activity in the hypothalamus that causes the release of noradrenaline in the spleen (sympathetic effect). The release of noradrenaline boosts immune function by releasing immune cells. ",
"Now, how does fitness play into it? Well, the sympathetic pathway is desensitized by the exercise. Then, when any other stressor comes along, the pathway stays within its dynamic range. If an \"out of range\" stressor comes along, the spleen will max out, and then there is a recovery phase with no immune cell release. So, people who are fit will be less likely to max out this pathway and undergo a period of significant susceptibility. ",
"Of course, fit people can still overdo it - just like marathon runners getting sick after races as noted by pairyhenis. I thought this was really cool, and I asked Monika what happens to this pathway if you give the rats naltrexone or naloxone (opiate blockers). She replied \"They don't run\". "
] |
[
"Do human females produce pheromones during ovulation to attract males?"
] |
[
false
] | null |
[
"The most fascinating thing is, women have evolved to attract males from a distance as well (ie. when they're not close enough for them to be able to smell naturally released pheromones).",
"For example, at a bar or night club, more women are likely to be wearing perfume, but there are hints men can pick up subconsciously from a distance that make certain women appear more attractive than others (ie, the ones closer to ovulation/ovulating vs the ones not ovulating).",
"During ovulation, women naturally have higher libido levels; therefore their behaviour becomes more 'flirtatious': playing with hair, displaying their wrists or walking with a bit more flair round the 'behind' (reminiscent of feline 'presenting' behaviour). ",
"The hormones released also help to give a more natural glow (sign of youth) and the lips a slightly darker tone (lips that are dark pink or red are considered more attractive as they make a connection with the labia majora-hence the popularity of red lipsticks!). ",
"Finally, during ovulation, women's waists tend to shrink marginally (seriously, not kidding) which brings a woman's waist to hip ratio closer to 70% (this has been for thousands of years considered the optimum waist to hip ratio to indicate a woman's capacity for child bearing). There has also been a correlation between temporal proximity to ovulation and amount of female skin displayed (closer to ovulation=less clothing:-)",
"It may not be obvious, but these signals are picked up on some unconscious level. Due to the sophistication of our society and the fact that we have started seriously frowning upon our natural odours (unlike even 100 years ago), we are constantly evolving new ways to maximize our reproductive capacities.",
"More of that in the works of David Buss and ",
" by Jared Diamond. Enjoy!"
] |
[
"This looks like an interesting starting point:",
"http://pss.sagepub.com/content/21/2/276"
] |
[
"Nope:",
"http://www.slate.com/articles/double_x/doublex/2011/08/the_scent_of_a_woman.html"
] |
[
"If there are 10x as many micro-organisms on you as there are cells in your body, do they make up most of your weight?"
] |
[
false
] | null |
[
"They make up about 1-2 kg of your weight. Don't forget that the most abundant type microorganism of your body, the bacteria, are only a fraction of a size of a single eukaryotic cell (they're about as large as mitochondria), and only weigh a tiny fraction of an eukaryotic cell as well. Even though the number of bacteria popularizing your body is huge, they don't actually add a lot of weight."
] |
[
"It's also worth noting that a portion of a human's mass stems from non-living matter. Bones, teeth, etc all contribute to our mass, though they aren't included in the 'self cells' vs 'non-self cells' question."
] |
[
"You mean the mineral component of bones and teeth in the extracellular matrix though, right? Because bones and teeth are absolutely built from and incorporate living tissue with an active metabolism that is capable of proliferation + differentiation, apoptosis and regeneration."
] |
[
"If we could dig a hole deep enough that the heat was enough to convert water to steam, could we produce an endless supply of power by harnessing that steam?"
] |
[
false
] |
I'm making a couple of assumptions in my question - namely that we can move water to the hole in a steady consistent fashion and that we can build a steam turbine at the hole or close enough to the production of steam to be useful. I don't know if the water would eventually cool down the heat source. I just think about underwater magma and how that seems to continuously flow.
|
[
"Yes, you're describing ",
"geothermal power",
", which has been around for over 100 years, though didn't start to be used on industrial scales until around 1960. The main issue with geothermal is the cost of getting a plant up and running as it requires drilling (which is always expensive). These in many ways are identical to drilling for oil or water, but here we're talking about drilling a 'geothermal reservoir' instead of an oil or water reservoir. The economics behave similarly as well, a geothermal reservoir is viable if you generate enough power over some period of time to recoup the amount of money spent developing the plant. This will depend on the local geology and the type of plant. Heat increases as you move deeper into the crust everywhere (i.e. the ",
"geothermal gradient",
"), but in some cases there are localized heat sources closer to the surface of the earth (usually through some sort of magmatic activity) that means you don't have to drill as far to heat up water, this is a geothermal reservoir. This is also why the majority of geothermal plants are in areas with some amount of volcanic activity (so the western US, Iceland, New Zealand, etc). As the technology improves, (e.g. ",
"Binary Cycle",
" stations), it's becoming possible to build geothermal plants in places that are not as volcanically active because you don't need to heat up the water as much. You're still looking for a geothermal reservoir of some point, so some area where it's hotter closer to the surface than in surrounding regions, but it doesn't have to be as hot as some of the early plants."
] |
[
"As long as the earths core produces heat, there will be a supply of energy. You pouring water there is neglible to the temperature.",
"Earths core is powered mainly by radioactive isotopes with half lifes ranging from 1billion to 14 billion years. So very slowly the energy supply is dimishing, but remember that its already likely thay after 5billion years the Sun will eat Earth."
] |
[
"Geothermal energy is limited in the same way as solar energy. It's not literally infinite, but it comes out at the same rate whether or not we use it (the amount of Earth's interior heat that's lost through the surface is much more than human energy usage, but it absolutely pales in comparison to the amount of solar radiation at the surface)",
"The main source of heat is probably radioactive decay of minerals, either in the crust right under you (radioactive minerals are very strongly concentrated in the crust) or distributed thinly around the mantle. If you have a passive geothermal system for your house, it's possible that most of that heat is from sunlight, but otherwise it's radioactive decay. It's a misconception that gets taught in a lot of intro geology classes, but heat flow from the core isn't all that important.",
"So there's a finite amount of power (that is, energy per time) that you can extract, but using geothermal energy doesn't make the radioactive decay go any faster and it won't run out for billions of years.",
"You \"can\" drill geothermal wells anywhere, since deep stuff is always hotter than the surface, but it's not guaranteed that the well will generate more power than it takes to pump the water around. Locations are pretty limited for actual useful geothermal energy."
] |
[
"Is GP120 found anywhere besides the exterior of an HIV molecule? If yes, where? If no, what traits of the HIV molecule prevent the development of an effective GP120 inhibitor?"
] |
[
false
] | null |
[
"gp120 can also be found in SIV (simian immunodeficiency virus), and it can also be shed from the HIV surface. I do not know the difference/similarity between gp120 of different viruses.",
"gp120 is hard to inhibit because it contains multiple variable regions. Constant regions that are required for binding are covered by glycosyl chains and also variable loops (V1-5). These variable loops are flexible and can move out of the way when binding to CD4 / chemokine receptors. The variable property of the surface protein makes it difficult for the immune system to adapt to.",
"If you would like more information, this article is a very interesting read regarding the antigenic structure of gp120. ",
"http://www.nature.com/nature/journal/v393/n6686/full/393705a0.html"
] |
[
"My basic understanding is that the nature of the protein makes it difficult for immunoglobulins to attach/bind to. There has been moderate amount of research into producing such antibodies that are able to accomplish this, with mixed results. As far as why its particular structure or electrostatic properties keep antibodies from performing their function, I'm not versed on the literature."
] |
[
"Thanks for the link and the answer; it was a better description than my teacher could give "
] |
[
"How dense does air get in the compressor of a jet engine?"
] |
[
false
] |
How dense does air get in the compression and propulsion stage of a jet engine? Is there a way to conceptualize how incredibly dense this is in simple terms?
|
[
"For an isentropic (idealized) compressor, the density change is equal to the pressure change raised to the power of 1/gamma (1/1.4 for air). So a (high end) compressor ratio of 40:1 will give a density ratio of 14:1.",
"At sea level, you're looking at 1.2 kg/m",
" ambient density, so it'd be compressed to ~17 kg/m",
" Less than half that at cruising altitude.",
"I wouldn't really characterize that as \"incredibly dense\". That's about 1 pound per cubic foot."
] |
[
"The density of air at 1 atm is 1.204 kg/m3. So the max pressure of air in the GE90 should be 50.568 kg/m3. This is about 1/20th as dense as water.",
"kg/m",
" has units of density, not pressure. Compressor ratios of 42:1 doesn't mean the density of air increases 42 times, it means the pressure has increased 42 times. It does increase the density, but not by 42 times."
] |
[
"viscosity?"
] |
[
"Determining the path c(t) of a particles using it's starting position+velocity?"
] |
[
false
] |
This has been bothering me for some time now: Say you have a particle in a (static-)field (e.g. an electron in an electric field, or a small asteroid near the sun) If you know it's starting position and it's velocity wouldn't that be enough to analytically determine the path c(t) of the vector as the classical laws/mathematics are deterministic? [i.e. Let P(t) be the location of an abstract particle at time 't', given a starting position P(0) and a starting velocity P'(0) as well as a Vector-field E(P) and the fact that P''(t) = E( P(t) ) is it possible to determine P(t) analytically?] I tried to solve it/find the answer myself but so far I haven't gotten any further then a handful of very specific 1-D cases. Most people I've asked (undergraduates like myself and 1 or 2 professors) seem to think it's unsolvable, is it? Can it be shown mathematically? edit: I proof-read it twice, but not the title, particle* and its* ...
|
[
"You're asking if differential equations have solutions? They do, as long as the function E is not too pathological. See ",
"the Picard–Lindelöf theorem",
".",
"You're asking if we can write those solutions as \"nice\" expressions? That can't even be done for integrals. See ",
"Liouville's theorem",
"."
] |
[
"Yes and no.",
"The acceleration of the particle depends on its position and the position of the other particles around it. This results in the formula for position usually being expressed as a differential equation. We can approximate it with varying degrees of success, but an explicit solution for position is not always known to exist. One such example is the three-body problem; solving the orbit of three particles subject to gravity. There is no known closed form solution, but we can numerically approximate it."
] |
[
"The 3-body problem is sort of similar to what I'm trying to determine but not exactly. For the 3-body problem you have 3 particles and they all interact, but in my situation there is 1 particle and the field in which it moves is independent of the particle itself.",
"\nI saw on the wiki page for the 3-body-problem that it has been shown that there there exists an analytic solution to the n-body problem, I'll look into that after my exams; perhaps I can tweak the proof for my case."
] |
[
"Is it possible that matter and antimatter were produced in equal quantities and that our abundance of matter where we are is just due to a slightly uneven distribution of matter/antimatter production during the Big Bang?"
] |
[
false
] |
Apparently the cosmic microwave background has slight density variations, which have been attributed to quantum fluctuations way back nearly 14 billion years ago. Could our abundance of matter be due to similar circumstances? I'm imagining it something like this: When the universe was undergoing the Big Bang, many regions produced matter and antimatter, most of which annihilates. However, some areas had slightly more matter, such as our region, and perhaps other regions have a slight abundance of antimatter. To observers in that sector, though, I'll bet that they would just call it matter. So, is this realistic? I'm not familiar with theories regarding the origin of our abundance of matter. My hypothesis posits that there are many regions of our cosmos ( and I mean the whole cosmos, not just the observable universe) that are pretty blank due to even amounts of matter and antimatter in the beginning, and other regions where matter or antimatter takes dominance. Only in regions of slight abundance could structures form and observers evolve. And when I say region, I mean a huge region, bigger than our visible universe.
|
[
"Could our abundance of matter be due to similar circumstances? I'm imagining it something like this: When the universe was undergoing the Big Bang, many regions produced matter and antimatter, most of which annihilates. However, some areas had slightly more matter, such as our region, and perhaps other regions have a slight abundance of antimatter.",
"This is possible, but with a caveat: The size of our \"pocket\" of matter would need to be on a scale larger than the observable universe.",
"If there were large regions of antimatter in our observable universe, the boundary where the antimatter would come into contact with matter would emit radiation that could be calculated and detected. However, the observational absence of this radiation suggests that there is no abundance of antimatter in the observational universe.",
"So, if there ",
" parts of the universe which are primarily made of antimatter, we'll likely never be able to demonstrate that they exist. It's a hypothesis that can't really be tested."
] |
[
"It's not an abundance of matter, it's only a small fraction of matter over anti-matter"
] |
[
"Why did this get down-voted. The imbalance is around like 1%... seems pretty small.",
"http://science.slashdot.org/story/10/05/18/0034227/matter-antimatter-bias-seen-in-fermilab-collisions",
"Love me some Reddit where people get negative karma for being right... "
] |
[
"Question about instantaneous transfer of forces."
] |
[
false
] |
[deleted]
|
[
"The signal transfers through the balls at roughly the speed of sound in the metal. Because they are so much smaller than the distance sound can travel through metal in a second, it appears instantaneous. If you had a bunch of balloons filled with jello in the same configuration, it wouldn't seem so instantaneous."
] |
[
"That's pretty good reasoning from balls to a rigid body. The force is going to be transferred from one side to the other by a compression wave, and the speed of that wave is determined by sqrt((bulk modulus)/(density)). So a wave would travel through an infinitely stiff object infinitely fast, and would have an instantaneous transfer of force.",
"I've never seen a perfectly rigid body, but they show up in the theory of mechanics a lot because they're easy to deal with. Ever since Newton's law of Gravitation, people have been skeptical that some of the laws of physics seemed to act instantaneously, it's just that no one could really say ",
" exactly was wrong. The observation that the speed of light is finite, and the same in all reference frames finally allowed Einstein to put a finger on what was wrong with the rigid bodies in Classical Mechanics."
] |
[
"The force would be transferred instantaneously ",
"rigid***. In reality, there is no such thing as a truly rigid object. Matter simply doesn't work that way.",
"When the balls collide they deform. If the forces in the collision are really high (hitting them with a sledgehammer) they will deform inelastically- the deformations will be permanent. If the forces are small, the deformations are essentially elastic- like compressing a spring and allowing it to stretch back to its original shape.",
"It does take time for this compression to happen. The force propagates through each ball as a pressure wave. Perhaps that sounds familiar? That's because it's basically sound. Sound is nothing more than a pressure wave with a frequency inside the range that our ears can pick up. It's the same thing as ",
"dropping a pebble in water",
" or the ",
"movement of earth in an earthquake",
". Sound (pressure waves) moves through ",
"different materials at different speeds",
", depending on the nature of the material.",
"Of course on the scale of the desk toy it seems instantaneous. Unfortunately this is not the case, and you would notice on a larger scale."
] |
[
"Why doesn't the strong force make atomic fusion easier?"
] |
[
false
] |
If the strong nuclear force is such a strong attractive force that increases with distance between hadrons (to a point at least), why does it take so much energy to combine nuclei instead of them getting close and fusing together by themselves?
|
[
"The forces between quarks increase with distance (really the potential is approximately linear with distance, so the \"force\" stays constant).",
"But the forces between ",
" do not increase with distance. This is called the \"residual strong force\", or simply \"nuclear force\". The nuclear force is generally attractive at low energies, and very short-ranged (a few femtometers). It's also spin- and isospin-dependent, but that's unimportant for our purposes.",
"The nuclear force is exactly why fusion happens in the first place. But since the nuclear force has such a short range, any two nuclei which you're trying to fuse will have to overcome a repulsive barrier (Coulomb and centrifugal) in order to do so. (The only time there is no barrier to overcome is for a neutron with zero orbital angular momentum.)"
] |
[
"I see, I didn't realize that the coulomb forces were that strong, but I suppose they do interact over a much larger distance. In that case could we not bombard a nucleus with neutrons that would then beta decay into protons and give off energy? Or am I misunderstanding the neutron decay?"
] |
[
"In that case could we not bombard a nucleus with neutrons that would then beta decay into protons and give off energy?",
"Sure, you can do that. This happens in some astrophysical situations; it's how many of the heavier elements are produced in nature."
] |
[
"How do greenhouse gases 'trap' heat?"
] |
[
false
] |
I read today, "...Some of them can trap more heat than CO2. A molecule of methane produces more than 20 times the warming of molecule of CO2..." It lead me to wonder what's the physical property of such molecules which makes them 'trap' heat. Is there a combustion reaction with CH4 which releases energy? If that was the case how come CO2 also heats up? I know CO2 won't combine with more O2 for combustion. Or is it thermal diffusivity of the molecule?
|
[
"The relevant property of the gas is its absorption spectrum.",
"The Earth continuously radiates heat out into space, keeping it in thermal equilibrium with the incoming energy from the Sun. The amount of energy radiated away and the wavelength of it depend on the temperature of the Earth. This radiation is called thermal radiation.",
"The Earth, and all other objects with a temperature in the range that we consider everyday temperatures, primarily emit thermal radiation in the infrared part of the spectrum (sidenote: This is why we often associate infrared radiation with heat, even though visible light is more energetic. Second sidenote: when an item becomes so hot that it glows, this means that it has started to emit thermal radiation in the visible part of the spectrum).",
"As it turns out, carbondioxide and other greenhouse gases absorb some amount of infrared radiation. Shortly after absorbing this radiation, it is emitted again, but while the thermal radiation from the Earth is headed outwards into space, the reemitted radiation will have a random new direction. So a large part of it is directed back to Earth.",
"Because of this, part of the thermal radiation the Earth emits doesn't make it out into space. That means that the Earth warms up, which causes it to emit more thermal radiation, until a new balance is reached between the incoming energy from the Sun and the outgoing energy of the thermal radiation that makes it into space.",
"(Third sidenote: since the Sun is much hotter than the Earth, the thermal radiation from the Sun is primarily in the visible part of the spectrum. Our atmosphere is far more transparent to sunlight than it is to our own thermal radiation)",
"Finally, the difference between various greenhouse gases is related to the amount of radiation they absorb and this depends on the absorption spectrum of the gas. There are some other factors that play a role, such as the longevity of a certain substance in our atmosphere (something that leaves our atmosphere relatively quickly will have less of an impact than something that sticks around for a long time)."
] |
[
"And here's a wikipedia page, with the actual math used to compare greenhouse gases, and some practical examples:",
"https://en.wikipedia.org/wiki/Global_warming_potential"
] |
[
"molecules are atoms connected by bonds, but these bonds are not rigid but springy. Infrared radiation is absorbed by chemical bonds and the energy is converted into vibrational energy, making these springy bonds vibrate. ",
"Different bonds absorb different wavelengths of infrared, so absorb different amounts of energy per bond. ",
"A carbon-hydrogen single bond (like in methane) absorbs more energy than a carbon-oxygen double bond (like in carbon dioxide) and just as these bonds can absorb energy, they can release it as the same infrared wavelength it absorbed which is how the greenhouse effect works, atmospheric gases are constantly absorbing and releasing infrared energy."
] |
[
"Does the atmosphere have tides?"
] |
[
false
] |
It’s my understanding that the moon causes sea levels to rise and settle as it’s gravity pulls water towards it. Does it do a similar thing with the air surrounding earth? Does the atmospheric boundary fluctuate as the moon orbits?
|
[
"Yes - the atmosphere has tides, but they are predominantly thermally driven. Consider if the Earth was stationary, and you suddenly turn on the sun. A portion of the atmosphere would heat up and expand, creating a pressure wave which would propagate around the Earth at a speed proportional to √h, where h is the column height of the atmosphere. If the Earth is spinning at about the same speed that the pressure waves are traveling, you can build up a large resonant effect which can result in a large mass excess around 45 degrees from the sun (see this ",
"Figure",
"). This can create competing tidal torques which can completely cancel out the lunar tidal acceleration, and this effect may have been responsible for maintaining a ",
"constant day length of about 21 hours",
" for about a billion years during the Precambrian era."
] |
[
"Good question, the answer is yes. Atmospheric tides have been studied for centuries. There are a lot of papers written about them, google scholar is a great resource for these. Atmospheric boundary layers fluctuations are influenced by the moon but solar forcing via heating, turbulence, and an assortment of waves cause much greater fluctuations."
] |
[
"the speed of sound is the propagation speed of vibrations of audible frequencies in air, and is actually different for each frequency. If your wavelength is comparable to the height of the medium, different physics (",
"Lamb waves",
") is needed to accurately describe the propagation"
] |
[
"How circular is our moon’s orbit, and do any moons have very stretched orbits or are they all usually circular?"
] |
[
false
] | null |
[
"It has an ",
"eccentricity",
" of 0.055, the farthest and closest point differ by ~10%. The gas giants have some very eccentric moons, most likely captured from asteroids passing by. ",
"Jupiter LXVII",
" with an eccentricity of 0.5569 is an example, its closest and farthest point differ by a factor of about 3."
] |
[
"Short answer: orbiting for a long enough time could make an orbit stable. Same thing happened with the moons rotation, and it became tidal locked, which means only one side faces us. (One rotation every orbit makes it look like its not rotating)"
] |
[
"I'm actually surprised there is no answer to this yet...",
"Orbits are not circular. They follow a path called an ellipse which is something like a circle, but it has two centers. In shape is close to what most people call an oval. In any given orbit, the larger object will sit at one of the two foci of the smaller object's elliptical path.",
"To your question, ellipses have a measurement called eccentricity which can be used to determine how round the ellipse is. The smaller its eccentricity is, the closer it is to being a circle. (Also, the closer the two foci are, the more circular it is, but \"close\" is a relative term, especially when talking about objects in space.) So all orbits are stretched, but they can be stretched to different degrees. For example, most planets are close to being circular, but if you do an image search for Halley's Comet Orbit you can see that Halley has a very stretched out orbit around the sun.",
"Honestly, my math and astrophysics is pretty rusty so thats the best answer I can give without doing more research. Jupiter and Saturn both have lots of moons, so if you wanted to look for a moon with a stretched orbit, thats probably where I would start looking. Nereid, a moon of Neptune, supposedly has one of the most eccentric orbits of any known satellite, so that might be starting place. Looking up Irregular Moon on Wikipedia might also interest you."
] |
[
"Straight To The Gut: Why When Some People Put On Weight It Appears To Gravitate To A Certain Body Part IE. <Butt,Gut> Is There A Scientific Answer To This"
] |
[
false
] |
When we gain weight are some people more prone to gaining weight in specific areas? Shouldn't it spread proportionally throughout everyone? Before someone else says it, an example of this would be a girl gaining an extra few pounds but instead of going to her stomach it appears to show up on her butt, or a guy gaining a few pounds and instead of going to his butt it goes to his gut, thanks AskScience!
|
[
"There is a fairly clear association with the distribution of fat and circulating sex hormone levels. Unfortunately, while there are pieces of the puzzle being worked out, I don't think anyone can say for certain why men gain weight in their gut, while women gain it on their arms/thighs/butt. It's related to testosterone and estrogen, but it's a complicated interplay of factors going on."
] |
[
"Thanks!! Though if anyone else has further info, I'd love to hear it."
] |
[
"I kinda have a question to add on to it, if anyone answers. ",
"I've heard that stress can promote fat being stored in the abdomen. A woman gains 40 pounds, but was always very stressed and most of the weight went to her abdomen. Say if she were to lose the weight, and gain it again minus the high stress levels, would the fat distribution favor her thighs, hips, etc. instead of her middle?"
] |
[
"How does GABA(a) presynaptic depolarization lead to inhibition of transmitter release?"
] |
[
false
] |
[deleted]
|
[
"Yes, the classic/textbook view of GABAa effects is about anion currents and hyperpolarization (as this review affirms in its introduction).",
"The place you refer to in the review is specifically addressing axo-axonic connections to primary afferents—sensory nerve fibers traveling in the spinal cord toward their first synapse.",
"The review is wrestling with the same question you're posing. It may help to suspend your notions of how GABAa receptors classically work and follow the evidence and arguments carefully.",
"A somewhat newer review of just primary afferent depolarization is ",
"here",
"."
] |
[
"In case it helps, here's one important thing to understand about ionic currents:",
"A given ion type does not always do the same thing. Opening sodium channels does not always depolarize a cell, opening potassium channels does not always polarize a cell.",
"In actuality, opening channels for a particular ion species ",
" You could think of the reversal potential as an ion's \"preferred\" potential. Sodium's reversal potential is strongly positive, potassium's is negative. ",
"Chloride's reversal potential is often close to the resting potential, so that sometimes opening Cl- channels doesn't change the membrane potential much, or might even depolarize it a bit. ",
", if cl- channels are open at the same time that depolarization is occurring, those cl- channels provide a means to counteract the depolarization. ",
"So under some circumstances, opening Cl- channels may depolarize the membrane, but at the same time make it harder for the membrane to get any ",
" depolarized, because anytime the membrane gets more depolarized, it causes more Cl- to enter the cell. This is what the article you referred to is talking about when they say \"shunting of excitatory currents\".",
"Now, this may not necessarily explain the phenomena they're talking about, but it should hopefully help explain why everything's not as simple as depolarization = excitation."
] |
[
"Thank you so much. I will give it a read. '",
"It may help to suspend your notions of how GABAa receptors classically work and follow the evidence and arguments carefully.",
"Hahah. yeah. That is a skill I really need to work on."
] |
[
"Is it possible that creatures very similar to those currently extint come to exist again in a very distant future? (through evolution)"
] |
[
false
] | null |
[
"It depends what you mean by \"very similar\", but I believe you will find the answer you seek in the concept of convergent evolution. This is what happens when different unrelated organisms converge upon the same solution to the set of problems which is a given way of life.",
"There are numerous examples, but a classic one is the overall shape and structure of dolphins and Ichthyosaurs. Dolphins are modern and need no introduction. ",
"Ichthyosaurs were swimming reptiles",
" which emerged in the Triassic and bit the bullet in the Cretaceous. Both faced the same problem: how to adapt a land-dwelling vertebrate to the ecological niche of a marine predator. And both developed similar features in response to the demands of that life strategy, and converged on the same solution developed by other lineages which shared that lifestyle [swordfish & tuna for instance]: ",
"a long, hydrodynamically tapered & powerfully muscled body,",
"limbs were redesigned as flippers and contributed to maneuverability,",
"the mouth became long and narrow on a narrow triangular skull with rows of pointed teeth well suited to gripping slippery fish,",
"the tail became finned and a powerful motive organ capable of sustained speed and sprinting,",
"Ichthyosaurs became viviparous and capable of delivering their young without leaving the sea to lay eggs on the shore – dolphins started viviparous and were sort of pre-adapted in this regard.",
"However, there are other subsidiary problems on which Ichthyosaurs and Dolphins developed different solutions. The problem of locating prey for instance. Dolphins went the way of sonar and modified their skull and brains accordingly, while Ichthyosaurs located their prey by sight and developed the largest eyes in relation to body size of any vertebrate. Then there was breathing – dolphins migrated their nostril into a fused blowhole on the top of their skull, while Ichthyosaurs migrated their nostrils to the sides of their head in a pre-ocular position.",
"So, to come back to your question, convergent evolution has allowed lineages as unrelated as mammals and reptiles to converge on a roughly similar body plan in order to adapt to a similar ecological role. Ichtyosaurs dissapeared 65 Ma ago, while dolphins and other toothed cetaceans didn't really emerge in a form we'd recognize today before ",
"about 34 Ma ago",
". If you saw both side by side, you would not confuse one with the other, but you would recognise a series of similar traits. In that sense, you could argue that dolphins are recently evolved creatures similar to an extinct lineage. And there is indeed nothing precluding other lineages from such convergent evolution in the future, say for instance some other lineage of mammals such as rats (for arguments sake).",
"EDIT: Gold? Why thank you! Enjoy this reconstruction of a ",
"pod of Ichtyosaurs",
" in return!"
] |
[
"Thank you for that great answer"
] |
[
"Yes, I agree this is a good answer. Additionally, there is the idea that \"nature abhors a vacuum\". In ecology, the concept is that a vacant ",
"ecological niche",
" will not stay empty for a long time."
] |
[
"If the core of the earth is 5,700K, the earth is constantly bombarded by tons of energy by the sun, and heat doesn't dissipate well in space, why is the surface a moderate 298K after 4.5 billion years?"
] |
[
false
] |
I was thinking about geothermal energy and hit this question.
|
[
"I'm on mobile and just woke up so I can't do the energy balance equation for you, but the thermal energy generated within the planet and the energy received are balanced with outgoing energy in the form of e&m radiation. Heat can definitely be dissipated effectively in vacuum, but only through radiation (convection/conduction are negligible). ",
"Edit: I should add that the planet radiates most strongly in the infrared wavelengths. This can be shown with a quick lookup of black body radiation, and the direct correlation between temperature and maximum emitted wavelength."
] |
[
"making the equilibrium of this heat flow occur at higher temperatures, when the earth gives off even more infrared radiation.",
"Well, sort of.",
"The Earth is trying to emit exactly as much radiation as it receives from the Sun to maintain planetary energy balance. If it's prevented from emitting this much because of infrared absorption features in the spectrum, the planet will heat up to emit in shorter wavelengths. However, the total amount of radiation emitted by a warm greenhouse-gas-filled atmosphere will be exactly the same as that emitted by a cool greenhouse-gas-less atmosphere - and in both cases, the emitted radiation will equal the amount of incoming sunlight."
] |
[
"It sounds like you're saying a warm planet with greenhouse gas is a stable equilibrium, as is a cooler planet with less greenhouse gas.",
"Yes, but my point is that they will both emit the exact same amount of radiation. The warm planet ",
" emit more than the cold planet if both are in equilibrium.",
"Heat is also generated by nuclear reactions in the Earth's core, the sun is not the only source of heat.",
"That's completely negligible. The incoming solar radiation at the top of the atmosphere is 1370 watts per square meter. The amount of heat coming from internal geothermal processes is roughly 0.09 watts per square meter, more than 10,000 times less."
] |
[
"Why is it that all Marine Turtles have flippers, and all freshwater turtles have feet that work on both land and water?"
] |
[
false
] |
I know that there are exceptions to this rule, like how Fly River and Soft-shell turtles basically have flippers, and Diamond Backed Terrapins lives in brackish areas. However, it does seem to be the general rule. There’s plenty of costal areas where the terrapin body type would work, and plenty of large lakes and rivers where turtles with flippers could survive.
|
[
"During winter months, the flippers wouldnt allow freshwater turtles to dig proper holes to hibernate. In marine turtles, there able to swim to warmer waters during the winter months and therefore need the flippers to swim long distances."
] |
[
"I was just about to start spotlighting the pig-nosed turtle when I saw that you are already aware of it. I think the answer to your question has less to do with whether flippers on a terrapin ",
" benefit them and more to do with ",
" it would benefit them.",
"Sea turtles are specifically adapted to a marine environment in all aspects of their life cycle save one: reproduction. They appear quite capable of overcoming this limitation with their flippers, as they've been successful for a very long time (until now, but that's not exactly their fault).",
"Most freshwater turtles are much more reliant on terrestrial environments for a good portion of their metabolism and behavior. Retaining the ability to interact with terrestrial environments allows them access to terrestrial food sources, which they do exploit, as well as giving them a leg up - ha - in behaviors like basking, which are quite important for most freshwater turtles. An exception here are snapping turtles, which are specially able to remain submerged indefinitely, and do not require basking to maintain their metabolism. So then why don't snapping turtles have flippers?",
"The simple answer really seems to be that having flippers, or more specifically possessing traits that might lead to the development of flippers in later generations, doesn't appear to present any benefit to freshwater turtles. Emydid turtles for example, of which your diamondback terrapin is a member, are capable of great agility and speed in the water with their webbed claws, so flippers wouldn't necessarily present much of an advantage. Snapping turtles don't typically move their bodies quickly through the water, so have no pressure to become faster swimmers. Clearly, as the pig-nosed turtle shows us, developing flippers can be a fine strategy for freshwater turtles, but the rarity with which this occurred suggests that in the face of other environmental factors, and if I were to speculate I would say most importantly competition with other turtles, flippers don't present an advantage in environments that are heavily dependent on terrestrial resources and spaces.",
"I got curious about how the pig-nosed turtle regulates its body temperature and found ",
"a 2005 study by Christy-Louise Davies",
" that explores the topic. I also looked up thermoregulation in marine turtles and found a ",
"thesis written on leatherback thermoregulation",
", which is maintained by specific behaviors intended to preserve or disperse body heat. Without these adaptations, marine turtles and the pig-nosed turtle would not be able to spend nearly all their time submerged underwater and would be required to bask as do most other turtles.",
"So then why don't other turtles evolve adaptations to do the same? Likely because they haven't been put under any ecological pressures that are limiting their ability to thermoregulate through basking, and thus have no reason to explore alternative strategies. Evolution is a totally random process and the majority of freshwater turtles are doing well enough with their claws.",
"TL;DR pig-nosed and marine turtles, those with flippers, have very specific metabolic and behavioral adaptations that allow them to stay underwater almost indefinitely while thermoregulating. Other turtles don't have those adaptations and don't really have any reason to develop them, as they have been remarkably successful in many different environments with the adaptations they already possess."
] |
[
"But wouldn’t turtles that live in warm areas not need to worry about digging down to brumate, or needing flippers to migrate?"
] |
[
"Why does motion of electrons cause magnetism?"
] |
[
false
] |
I am familiar with the classical concept, but I am wondering, how does relativity fit into this. What is the reference point for the magnetic field to "know" it is moving in relation-to. Is a magnetic field, merely a cause of a quantum of energy change at the wave-level, like a ripple in a pond?
|
[
"This is an argument that relies on two principles from special relativity.",
"Let's say we have an infinitely wire with stationary positive charges and moving negative charges from our frame of reference. (Could be protons and electrons if you want.) Also, this wire happens to have a balanced, net-zero charge in this frame of reference.",
"Here is a small section of it.",
"+ + + + + + + + +\n- - - - - - - - - ⇒ (negative charges are moving to the right)\n",
"Let's say there's also a negative charge that happens to be floating next to the wire, moving to the right.",
" - ⇒\n",
"At this point, the charges are balanced so the single - charge has no reason to feel any force, at least from any electrostatic force.",
"Now let's redo this situation from the frame of reference of the negative charges. Remember that this wire is infinitely long.",
"+ + + + + + + + + + + + + ⇐ (positive charges are moving to the left)\n- - - - - - -\n\n -\n",
"Suddenly this - charge \"sees\" a whole lot more + charges in the wire. It's now feeling a whole bunch of force pulling it into the wire. But you can't have zero force in one frame of reference and non-zero force in another. This is a paradox.",
"As it turns out, you can calculate the force that the - charge should get in the first frame, and the amount of force happens to be the exact amount we expect from magnetism. The solution to our paradox is that the - charge does receive this force in the first frame from magnetism. Magnetic and electrical forces are just two sides of the same coin, since by simply changing the frame of reference, we can choose to calculate the dynamics of the system based on either one."
] |
[
"Electric and magnetic fields are two different manifestations of the same thing.",
"Imagine I'm standing still and you're moving at some velocity, while holding some charged object.",
"You're not moving relative to the charged object, so all you see is an electric field.",
"I ",
" moving relative to the charged object, so I see an electric field and a magnetic field. Part of what you see as an electric field looks like a magnetic field to me.",
"And we're ",
" correct."
] |
[
"Suddenly this - charge \"sees\" a whole lot more + charges in the wire",
"Huh? I don't follow. Why does the negative charge suddenly 'see' more + charges?"
] |
[
"How does traveling faster than light violate the principle of causality?"
] |
[
false
] | null |
[
"Thanks much for this comment. That's a good explanation and helps a great deal. ",
"However, I still don't get how that violates causality. Instead, that seems more like the perceiver (i.e., the one reacting to the cause) being tipped off to the cause before the perceiver can perceive the cause. To put it another way, in that explanation, the cause still happens in time before the effect; but the perceiver learns of the cause before he/she has the opportunity to perceive it. ",
"Here's an example. Suppose there's a plot to kill me. Suppose further that the plot is put into motion and the conspirators on on their way to my house to kill me. I haven't yet perceived this \"cause\" -- the plot -- but fortunately a friends calls me to warn of the plot. Thus I leave my house and manage to escape death without ever having perceived the plot first hand. ",
"In this hypo, the plot is the cause and my escape is the effect. My escape does not violate the principle of causality, yet I think this is no different than your (admittedly very lucid and clear) explanation. In your explanation, just like in my hypo, the cause would occur in time before the effect even though the perceiver -- the effect -- would not perceive the cause before acting. This would not logically violate causality. ",
"I am positive that I am completely wrong about all this and that you're correct. I am probably just misunderstanding some principle that renders my argument false. But I can't figure out where I'm wrong. ",
"Again, thanks for all the help. This is very intriguing!"
] |
[
"Special relativity tells us that if two non-accelerating observers are moving relative to each other, they will obtain different results for when and where things occur.",
"Now we apply the rules of special relativity to something traveling faster than the speed of light. So suppose there is an object that travels faster than the speed of light according to one observer. Then there will be other observers (moving, by the way, at speeds less than the speed of light) who will see that object as traveling backwards in time.",
"Since, according to the principles of special relativity, the laws of physics are the same for all non-accelerating observers, if things can travel backwards in time relative to one observer, things can travel backwards in time relative to any observer (though it may be different things for different observers).",
"And if things can travel backwards in time, we have a problem with causality: Imagine I flip a switch that send out a particle that goes backwards in time, and let's say when that particle arrives, it flips another switch that turns off a light. That would mean that I could do something on 10 November 2012 whose effect would be a light switching off on 5 November 2012. In other words, we would have the effect preceding the cause.",
"This is how having things able to travel faster than the speed of light leads to problems for causality."
] |
[
"Wouldn't the ships frame also crash into the door because the operator didn't open it, regardless of perspective"
] |
[
"Why do mosquitos not spread HIV and other blood-sharing diseases?"
] |
[
false
] |
I have nothing...Maybe a toxin that kills it?
|
[
"Well, some insects can spread certain specific blood born diseases. ",
"Malaria",
" is spread this way as is ",
"Yellow fever",
". The problem is that if a pathogen hasn't specifically evolved to survive or reproduce in a specific host, survival is highly unlikely. In the case of say HIV, the virus itself has a short lifespan is fairly unstable so even if it were picked up by a mosquito, the virus would likely die before it got to anywhere. "
] |
[
"Well, we are completely different species. It isn't something particularly special about mosquitoes that makes them immune, they just do not provide the natural habitat that HIV requires. "
] |
[
"Mosquitos apparently don't ingest enough HIV particles/virions to cause infection to a host. But this is largely irrelevant because for HIV+ blood to travel from a mosquito's stomach to your bloodstream it would have to somehow get into the mossie's salivary glands first, assuming it can survive the harsh environment of the stomach.",
"\nThis is because a mosquito's eating needle doesn't regurgitate past meals, only sucks bloods from new hosts. The only thing it excretes is saliva, from a separate gland. "
] |
[
"How much angular momentum does blood flowing through the aortic arch have?"
] |
[
false
] |
I am not sure if I am thinking about it right but it seems as though the fact that the blood arcs from front to back changing its flow direction by 180 degrees means there would be a significant amount of angular momentum in the system. I don't well understand how angular momentum works in fluids, but my question arose because I was envisioning the aortic arch as acting a bit like a gyroscope, with weird things happening during sideways rotation. Would there be some resistance to torquing the arch?
|
[
"I don't have numbers in front of me, but determing the volume of the aortic arch, determine peak flow, find mass of the blood in the aortic arch at this time, determine velocity, and you should be able to calculate angular momentum and any resulting gyroscopic forces. ",
"i would wager that the pressure differential between the heart and the rest of the body is more than enough to overcome any forces imparted by movement. That said, a person's movement certainly has some effect on blood pressure throughout the body, an easy example being when you stand up too fast. "
] |
[
"L = r m v. ",
"r = radius of turn\nm = mass\nv = [tangential] velocity",
"I would imagine the mass of blood flowing through the arch to be very low (comparable to the rest of the body), so not a very high angular momentum.",
"[edited: clarification]"
] |
[
"to be a bit more precise ",
" is actually the components of the velocity perpendicular to the length ",
"."
] |
[
"Uncertainty principle - why is the ability to measure the location and movement simultaneously a violation of the laws of physics instead of insufficiently advanced measuring tools?"
] |
[
false
] |
[deleted]
|
[
"An ELI5 explanation would be that the uncertainty principle is a statement about the structure of waves. Position uncertainty basically corresponds to how spread-out a wave is, and momentum uncertainty corresponds to how spread-out the wave's frequency spectrum is. These two things are inversely related to each other.",
"It may be helpful to consider the two extreme cases. On one hand, you can have a sine wave that repeats infinitely in both directions. That has the maximum possible spread, but contains only a single frequency. On the other hand, you can have a spike at one point, which has the minimum possible spread, but contains ",
" frequencies. This should at least make it seem plausible that the spread in position space and the spread in frequency space are inversely related, though of course you need to get into some math to actually prove it."
] |
[
"The uncertainty principle (UP) is not a statement about measurement. It is a mathematical consequence of the foundations of QM.",
"Consider a wave function ψ, which is an element of some abstract separable Hilbert space and which contains within it all information needed to describe a particle or system of particles. (Let's stick to one dimension to make the typing a bit less cumbersome.) There are several ways to express ψ. For instance, ψ may be given as a function ψ = ψ",
"(x,t), in which case we may interpret |ψ",
"|",
" as a probability density for the position x. But we can also give ψ as a function ψ = ψ",
"(p,t), in which case we may interpret |ψ",
"|",
" as a probability density for the momentum p.",
"Note that ψ is some fixed element, and we are considering two representations of it, ψ",
" and ψ",
". A natural question is: is there a relationship between ψ",
" and ψ",
"? It turns out that, yes, there is a natural correspondence between the two representations. Indeed, they are simply scaled Fourier transforms of each other.",
"The UP now follows immediately from general functional analysis. Given any square-integrable function f(x,t), we can define its mean in the usual way. The mean of f (label it M) is just the integral of xf(x,t) over the x-domain. The variance of f is then the integral of (x-M)",
"f(x,t) over the x-domain. Give the x-variance the label S",
". We can define the p-variance similarly. The function f has a Fourier transform g. The variance of g we can label S",
". Now if the integral of f is normalized to be equal to 1, then the integral of g is also 1 (this follows from Plancherel's theorem). It then turns out that the product S",
"S",
" has some lower bound, depending on the exact scaling of the Fourier transform used. In QM, we have S",
"S",
" > h/2, where h is the reduced Planck constant. Equality holds if and only if the wave function is a so-called Gaussian. (The exact proof in QM is not exactly how I have written it because I have not made exactly clear what the correspondence is between a wavefunction, its Fourier transform, its mean, and its variance. Needless to say, it doesn't take much more math to make this clear, but it's just not necessary here.) Also, just for reference, the quantity S",
" is also called the \"standard deviation\".",
"Note that the quantities S",
" and S",
" give a measure of the \"spread\" of the respective functions about the mean. If the function has a tall, narrow spike centered at the mean, then the variance is small. What the UP then says is that a function and its Fourier transform cannot both simultaneously have very small variance. Given the spread in the position space (real space), there is a limit to how spread out the function can be in momentum space (Fourier space). In particular, there is no wavefunction which has both a single position and a single momentum. (By \"single position\" or \"single momentum\", we mean an eigenvalue of the appropriate operator.)",
"So the UP is not fundamentally a statement of our ability to measure various observables. It is a purely mathematical statement about the spread of a wavefunction in two equivalent representations. The statement does then imply something physical about our inability to measure both position and momentum exactly simultaneously. But do not be tempted into thinking that the UP can be derived from physical principles. You will often read about how the UP follows from or is related to the so-called ",
", which itself describes how we cannot make a measurement without changing the system itself. That is, we cannot make a measurement without changing some other measurement. I suspect that there will even be comments in this thread that attempt to explain the UP in that manner. But it is an incorrect characterization of the UP.",
": The UP is technically a statement about the standard deviation. I originally defined the variance, and then wrote the UP incorrectly. I have corrected this typo."
] |
[
"The uncertainty principle is not fundamentally a statement about measurement, though that's one of the consequences. It's a statement about the possible physical states of a system in quantum mechanics. For position and momentum, for example, there simply are no states that have both a perfectly well-defined position and a perfectly well-defined momentum."
] |
[
"About how many water molecules are in an average size water droplet?"
] |
[
false
] |
[deleted]
|
[
"As ",
"/r/ahhwell",
" said, one drop of water is about 1/20th of a milliliter. This is called one ",
"metric drop",
".",
"If you look at the bottom of that very page, the number of water molecules would be 1.671*10",
"."
] |
[
"Given that a water/rain droplet has a large variance (",
"see here",
"), I'm going to assume ~1 mL. Given that the density of water is 0.99997 g/mL, this corresponds to 0.99997 g of water. Since the molecular weight of ",
"water",
" is 18.01528 g/mol, this corresponds to 0.0555068 mol of water. Now, to convert to number of water molecules, you need to use Avogadro's number (",
"6.02214129×10",
" molecules/mol",
"), which gives the number of molecules for one mole of a compound (An explanation of the mole unit ",
"here",
"). This means that there are ",
" in one drop of water.\nHope this helps."
] |
[
"I'm going to assume ~1 mL. ",
"Your size for a water drop is a bit off here. As your link says, they can vary a bit, but they don't ever get to this big a size (a cube with sidelenght 10mm would be 1mL, while the largest recorded raindrop had 8,8mm diameter according to ",
"Wikipedia",
"). ",
"A water drop is closer to around 1/20mL. So weight of the drop, and number of molecules should be adjusted accordingly.",
"Edit: this 1/20mL waterdrop is what you'd expect if you have a leaky faucet or something like that. I don't know the sizes of the drops in something like a light rain, but they can probably be quite a bit smaller."
] |
[
"Does this simple experiment cause problems for gravity?"
] |
[
false
] | null |
[
"Can you elaborate? The same would apply for something like a boomerang. How do they experience gravity? ",
"Is this not the same equation used for the Earth? Only the center of mass is the core because of its shape"
] |
[
"Can you elaborate? The same would apply for something like a boomerang. How do they experience gravity? ",
"Is this not the same equation used for the Earth? Only the center of mass is the core because of its shape"
] |
[
"I’m confused here. I was taught throughout physics every single item is applying a gravitation force to me, but they are small compared to Earths. Except, if you have a radius of near zero, it would overwhelm every other gravity force. How do these things experience gravity?"
] |
[
"Chimps and Humans have around 98% same DNA. In order to know this we would have to know the 2% difference. Why can't we take the 2% difference from Humans and put it in the Chimps?"
] |
[
false
] |
Scientists say that we have similar DNA to Chimps. In order to know that we have similarities we would have to know the differences. Since we know the differences, why can't we take them and put the in the Chimps to try to produce a transitional-man made Homosapian. I am simply trying to understand some questions I have towards these understandings; please no harsh answers, I know this may be a very dumb question.
|
[
"You'd have to make millions of little individual changes and we don't have the technology to do that. You can't just take the part that humans have and chimps are missing and stick it on the end of the chimp genome.",
"There are parts that chimps have that humans don't so you'd have to remove stuff as well as add stuff.",
"The differences between humans and chimps are not just in DNA sequences but also DNA regulation, so even if you gave a chimp a bunch of human versions of genes, those genes would be regulated differently.",
"Humans have 23 chromosomes while chimps have 24, so the organization of the genomes is different, as well as the sequence."
] |
[
"Because it's ",
" a coincidence. Humans and chimps sharing a lot of the same DNA is ",
" what you'd expect to see if humans and chimps are related–combined with a lot of other smoking guns of common descent, like fossil lineages linking us."
] |
[
"Well in the grand scheme of things our DNA isn't ",
" dissimilar to chimps, but even small changes can have huge effects."
] |
[
"How accurate is this saying and why does it work? \"red sky in the morning, sailer heed warning. Red sky at night sailors delight\""
] |
[
false
] | null |
[
"It seems to be true within limits but of course very limited compared to modern techniques. to quote from ",
"this website",
"\"When the western sky is especially clear, there is often a red sunset. That's because as the sun sets, its light shines through much more of the lower atmosphere, which contains dust, salt, smoke and pollution. These particles scatter away some of the shorter wavelengths of light (the violets and blues), leaving only the longer wavelengths (the oranges and reds.) If an area of high air pressure is present, the air sinks. This sinking air holds air contaminants near the earth, making the sunset even redder than usual. This would be the “red sky at night.” In the middle latitudes of the northern hemisphere, weather systems most often approach from the west. Since high pressure generally brings fair weather, this type of red sky at sunset would indicate that clear weather is approaching, which would \"delight\" a sailor. If the sky is red in the eastern morning sky for the same reasons as above, then the high pressure region has most likely already passed from west to the east, and an area of low pressure may follow. Low pressure usually brings clouds, rain or storms, a warning for sailors.\""
] |
[
"To add to this, the saying would of been more true in the days of wind powered ships where vessels had limited maneuverability in getting out of potential storms that were forming. In today's navies, conventional ships are much faster and able to sail against the wind quicker and more efficiently than tacking would allow for wind powered ships and makes weather less of an issue as storms can sometimes be avoided almost all together."
] |
[
"Interesting. The saying in the UK is \"Red sky at night, shepherd's delight, red sky in morning, shepherd's warning\". So not necessarily due to stormy seas. But definitely to do with weather in which to work in. Or not, depending on the sky colour. "
] |
[
"Why don't cats get sick from licking their dirty feet all the time?"
] |
[
false
] |
If i stopped and licked my feet clean every 2 minutes I am sure I would be experiencing some gastrointestinal troubles.
|
[
"When humans learned to control fire and cook their food, about 125,000 years ago, they no longer had a need for a highly acidic stomach, since cooking kills most pathogens. Because a highly acidic stomach, when no longer needed, has its disadvantages and its maintenance is a drain on the body’s resources, it was gradually selected out of the population. ",
"As a side note, cooking food was a serious turning point in human development. Raw food, whether vegetable or meat, is harder to chew and harder for the body to extract nutrients from than cooked food. Modern apes spend five hours a day just chewing. So cooked food left more time and energy for other things. Modern apes (as did early humans) eat their food where they find it. After humans started cooking their food, they had to bring it back to the fire to cook and eat it. That meant they had to learn to trust each other not to steal food, which led to the development of a social structure conducive to advancement in other areas."
] |
[
"What reason is there that humans lack this? Is it something we had but lost, or that we never had?"
] |
[
"A cat's stomach is very acidic. This acid kills most dangerous bacteria; thats why it's OK for a cat to eat a live mouse but you should never even think about it. This high acidity is common among most predatory species and is even stronger among carrion eaters like buzzards and vultures."
] |
[
"Like animals, are there any food plants or fruit trees got extinct over the years or considered as endangered species which might go extinct soon?"
] |
[
false
] | null |
[
"Famously, most banana's today are all clones, and were bred because they were resistant to a local blight that killed off the last variety. If it adapts to the new variety ",
" it can/will wipe out the rest of them within a couple years."
] |
[
"Too late. A version of Panama disease (the disease that ",
"wiped out the Gros Michel",
") called TR4 has already adapted to ",
"attack the current strain",
" of bananas that we eat today (called the cavendish).",
"TR4 has ruined banana crops in Australia and Africa already. While it hasn't reached Latin America yet (where most bananas are grown and exported), the TR4 spores can ",
"live for decades in the soil",
" and it is believed that it's only a matter of time before it reaches LA."
] |
[
"Not an expert in anything really, but your question made me think of corn. The corn we have now is not anything like the corn found hundreds of years ago. We've selectively bred only the most productive strains, so other \"original\" strains are probably greatly diminished or possibly extinct due to cross-pollination with our new super corn. But I could be way wrong. Good question. "
] |
[
"My school's chem department threw this out, it was way too cool to trash so I took it. But what is it?"
] |
[
false
] | null |
[
"It's a roundbottom flask. You use it for certain types of organic chemistry reactions. The ones I've used were like 3\" across, so that one looks awesome.",
"And to my knowledge it's not illegal to own it, you're just not allowed to use it to make meth. SO- DON'T MAKE METH :D"
] |
[
"I don't know if anyone has mentioned this, and even if they have it bears repeating",
"You have no idea what might have been in it and residues could make you sick or possibly even kill you.",
"I wouldn't even have it in the kitchen if I were you. "
] |
[
"Betting someone's health on the idea that some grad student wouldn't improperly dispose of a piece of lab equipment is insane."
] |
[
"What about deep breathing makes us lightheaded?"
] |
[
false
] |
As in, how does deep breathing cause lightheadedness? If it's simply "Too much oxygen" what about all that oxygen results in feeling lightheaded? What mechanisms are at play/ what's going on?
|
[
"Hyperventilation removes more CO2 from the blood than is being released into the blood via cell respiration. This increases the pH of the blood, a condition called alkalosis, which in turn causes blood vessels to constrict, reducing blood flow. Alkalosis also reduces the amount of freely ionized calcium in the blood, which is essential for proper nerve functioning, and which also causes blood vessels to constrict, reducing blood flow to the brain further, which makes you feel lightheaded."
] |
[
"The blood needs to do two things to supply your brain (or any cells) with oxygen. First, the heme group needs to absorb oxygen in the lungs, and secondly, it needs to release oxygen in the cells. This two way equilibrium reaction is affected by the pH of the blood. Too low and your blood won't absorb oxygen (acidosis). Too high and the blood, although full of oxygen, won't release oxygen to the cells (alkalosis). The rate and depth that you breathe determines how quickly you expel carbonic acid, in the form of CO2, from the blood. Breathing too quickly or deeply, causes lightheadedness and possibly loss of consciousness as your brain is unable to take oxygen from the blood. A simple treatment of hyperventilation is to breathe into a bag, which causes you to absorb some CO2, lowering the pH of the blood and allowing your brain to acces the oxygen in the blood.\nThis brings up a common misunderstanding about diet and the pH of your blood. Drinking alkaline water won't change the pH of your blood. If your blood was outside of the optimal range of pH values it is immediately corrected by the urge to either breathe faster or slower. If it stayed out of the optimal range for more than a few minutes, you would be dead. You can't change your blood pH by drinking overpriced water."
] |
[
"OK. The real answer. IT DOESN'T. Deep breathing does not cause lightheadedness. The deeper answer.... ",
"The rate at which you breathe controls the clearance of CO2 from your blood. The level of CO2 in your blood controls the drive for breathing. So, while you are breathing heavy, your blood gets plenty of oxygen, clears more CO2 than normal, and drives your respiration to a low level. So you get lightheaded - not while you are deep breathing, but after you stop. ",
"Now, when you STOP DEEP BREATHING, your respiratory drive is too low, and you will starve your brain of oxygen. This phenomena at altitude leads to Cheyne-Stokes respirations, which happens spontaneously (instead of the intentional deep breathing-lightheadedness you ask about). ",
"The relation between hyperventilation and getting lightheaded is all about breathing being controlled almost only by CO2 levels, and not by O2 levels. ",
"Don't they teach respiratory physiology properly anymore?"
] |
[
"A concussion is the impact of the brain on the skull. Do animals with an exoskeleton experience a similar phenomena when their exoskeleton receives an impact?"
] |
[
false
] | null |
[
"Animals with exoskeletons in general do not have brains. They have multiple ganglia which are knots of nerve cells that together act like a brain but are nowhere as complex and large in comparison. On the plus side, since they aren't as heavy they do not \"bounce\" around. Concussions are a problem that not many animals have to fear because you need a brain with a mass big enough to damage itself when accelerated."
] |
[
"Its a mix of a few things:",
"If we think on natural movements and falling:",
"now if you smash or flick an insect against a hard wall or hit it with a fly swatter that is of course a different thing but then you will mostly also break the exoskeleton and damage the whole body."
] |
[
"So is it not possible for them to receive damage to other organs from them moving around, or are they typically so packed in that there is no room for movement?"
] |
[
"How much of a bottleneck is protein folding in the drug development process?"
] |
[
false
] |
I'm a total layman but I've been really excited to read about the Alphafold breakthrough. Assuming it does what they claim it does how much time and money would this save? From my understanding starting a drug from scratch and releasing it to the general public takes about 15 years (not sure if this is accurate). How long would it take now?
|
[
"Kind of a null question. Some drugs target proteins whose structure is already known. Overall, start to finish, determining the structure of a protein can take anywhere between a month and a few years, if it can even be done (some are tricky). The longest part of drug development is testing the drug itself in clinical trials. Don't forget, many drugs have an \"unknown mechamism.\" It's not even known what proteins they target until years after it's on the market. Having a protein structure can help, but it's not an absolute requirement for a large number of meds"
] |
[
"Basically, it's (maybe) a game changer for determining protein structure (but standard crystallography will never go away). It helps drug development, but not entirely sure I would say its a game changer for drug development."
] |
[
"Protein folding is not currently a mjaor step in the drug development process. However, being able to accurately fold proteins- which this program is much better at but still not perfect- is the first step on simulating more complex processes, which eventuality will allow us to speed up effectiveness and toxicology determination of new drug candidates."
] |
[
"How does an immune system combat toxins (like snake venom)?"
] |
[
false
] |
I understand (at least crudely) how our immune system reacts to viruses, bacteria, and mold, but I'm ignorant as to how exactly it fights toxins. The recent TIL about Bill Haast developing a strong resistance to various snake venoms made this thought jump into my head. Does our immune system simply treat a toxin in whatever way it treats a standard dangerous protein/molecule/peptide (or is any dangerous protein/molecule/peptide automatically considered a toxin by the mere fact that it's dangerous)? How does one actually resist things like specific venoms or poisons? Do we actually keep antibodies around to fight against these chemicals like we would for something like chickenpox? Or do the affected tissues of a specific toxin somehow build up their own resistances to its effects? I feel as though I'm conceptualizing toxins in a way that makes them seem difficult to "fight off", when in truth the methods of stopping them are very similar to the methods of fighting off harmful bacteria or whatnot, and I just can't get over my own mental block. Herpetologists, unite!
|
[
"It should be noted that these days you rarely make mass quantities of antibody by injecting things into horses - nowadays (actually since the 70s) we make them by fusing cultured B-cells with melanoma cells and making hybridomas, which pump out monoclonal antibodies like nobody's business."
] |
[
"Your body can't really tell whether a protein is a toxin or not, it just knows that it shouldn't be there in the first place. The immune system will usually recognize and try to neutralize any proteins that it identifies as foreign. That's why organ transplants are problematic; your body knows that it's foreign and tries to destroy it.",
"Protein-based toxins are neutralized by antibodies. The toxins are recognized by our immune systems and antibodies are produced against that specific protein. These antibodies, once made, have the ability to bind to the toxins and prevent it from interacting with the body, thus rendering it harmless and allowing the body to dispose of it. This is true of any foreign proteins, be it snake venom or cholera toxin. It can take up to a week to develop these antibodies, so obviously this won't help you if a snake has injected you with a lethal dose that will kill you in hours. However, if you give yourself small non-lethal doses, it allows the body to produce the antibodies and give you a certain level of immunity over time.",
"This is actually the basis of antivenom production. Venom is collected and a non-lethal amount injected into a large animal like a horse (or Bill Haast). The horse does the same thing we do and produce copious amounts of antibodies against the venom. All that's left to do is purify the antibody and injected into someone who's been bitten. The antibodies will neutralize the venom in the same way. "
] |
[
"Thanks!"
] |
[
"Prolonging laptop battery life"
] |
[
false
] |
I have already made certain changes to my laptop usage to help prolong my battery life, such as lowering the screen brightness and changing certain other appearance settings. But I remember hearing something about how fully charging the battery, and then using it until it is almost fully drained before recharging somehow helps to preserve battery life. Is there any truth in this, and if so why? Edit: Thanks for the helpful responses all! Just thought it was an interesting piece of info and had to check out the truth in it.
|
[
"I believe it depends on the construction of the battery. An Apple Store representative told me in 2008 that the \"use it until it's drained\" advice was accurate for older batteries, but newer ones are worn out by any change in their stored charge. That is, the battery is worn through expenditure and charging, so going from 100% to 0% and back to 100% would be 200% worth of wear on the battery. It would be the same for going from 100% to 50% and back twice."
] |
[
"Relevant information: ",
"http://www.apple.com/batteries/",
"The documentation for my MacBook Pro (2010) recommends completing at least one charge cycle per month (as described in the above link). In other words, don't let it sit plugged in, or completely drained, for weeks at a time. ",
"Apple also recommends letting iPhone batteries complete a full charge cycle at least once a month (they use the same type of lithium ion batteries), by charging it to 100% and then letting it drain completely. Source here: ",
"http://www.apple.com/batteries/iPhone",
" ",
"It's true that older nickel-based batteries required this full discharge. I don't know how necessary it is with lithium batteries. Perhaps a scientist could shed some light!"
] |
[
"while in theory li-ion battery should work forever, shelf life, cycling and temperature would affect its lifespan. every charge therefore weaken it capacity. that said, partial discharge would prolong it life by reducing stress.",
"How much? let say at 100% discharge, your battery life is about 3 times shorter than at 50% discharge, 5 times at 25% and about 9 times at 10%.",
"other factors is the charge voltage. it is recommended to maintain at 4.2V, a slight increase in voltage (4.3) would shorten the cycles to half.",
"for storage, it is recommended to store at 40% at low temp. to give you an idea, at 0C and 40%, a 2% loss would occur within a year. but at 60C, you would see a 25% loss. the figures gets worst if you are storing a full charge. with 60C, you get 40% loss in 3 months"
] |
[
"What results in me getting more wet, walking or running in the rain? Or would it be the same?"
] |
[
false
] | null |
[
"It depends on the rate of rainfall, angle of rainfall, your speed, your direction, and the shape of your body. If rain is",
"and you are",
"and",
"then the net rainfall on you consists of",
"and the amount of time it will take you to reach your destination is D/Z, so the total amount of rainfall you will encounter is",
"D/Z (X * Ah + sqrt(Y",
" + Z",
" + 2YZ cos alpha) * Av)",
"which doesn't have a simple relationship to your speed Z."
] |
[
"You can split the amount of rain hitting you in two components:",
"So it is best to run as fast as you can to minimize the time spent in the rain.",
"Here's a Minute Physics video explaining this very well: ",
"Is it Better to Walk or Run in the Rain?"
] |
[
"You will get more wet walking. The more time you are under the rain the more wet you get. Running doesn't make you get hit by more rain. You are just traveling faster so the impact is harder so it can trick you in to thinking you are getting hit by more rain."
] |
[
"Is there a such thing as a material that does not absorb light? What would happen if you built a room out of it and turned a light on inside the room? Would light just bounce around it forever?"
] |
[
false
] | null |
[
"Light will either interact by absorption or reflection, a combination, or passing through. No ideal reflective materials exist though there are very good reflecting surfaces or non-interacting materials. What would define these greatly depends on the wavelength of light. Let us consider a microwave. The wavelength is much greater than the distance between particles so we consider only waves. Let us consider a perfectly conducting material such that there is no energy lost in the surface and no electric field. A room made out of such materials will then simply invert the electric field. If enough waves occur the light will superimpose and lets say it fills the entire room. No electric field is inside the boundary, and the field at the surface is orthogonal to the surface. There is thus a boundary condition forcing that the fields take on certain allowed discrete modes. This forms a microwave cavity analogous to well your microwave. Similarly one can do this with perfectly reflecting mirrors, though your index would have to have to be infinite. From here you can think of fiber optic cables. For visible light, you have to consider absorption through excitation rather than current generation. In this mode you need to reflect off of a material with good conductivity below the workfunction where the light gives the electron enough energy to leave it's state, while not passing through the materials. The modes are no longer macroscopic so we will consider photons for metals. Molecules and atoms can absorb and re-emit light causing losses. For gamma radiation much of the light will pass through the material and not reflect having wavelengths much smaller than the atom sizes or similar. There will thus always be losses depending on the mode of interaction. All light will still lose energy to heating and imperfections as well though. If you consider an extremely low chance of loss in a 1 meter cubed box you would still lose all the light extremely fast due simply to the rate of light traveling, having ~10",
" interactions per second. This didn't answer your question exactly but I hope gave a better look at considerations to be made. To strictly answer your question no, and in the ideal case yes without considering any interaction beyond simple electromagnetic. If any of this didn't make sense to you ask about any part of it- as it was a very general overview and I wish to save typing if I can. \n Dark matter has no electromagnetic interaction as well so it does not absorb light. "
] |
[
"What if you left the light on in the room? Would the room ever \"Fill up\" with light where no more light can fit into the room? "
] |
[
"If light interacts with a medium, there are three possibilities: reflection, absorption and transmission. ",
"If there was a material, that had a 100% reflection rate (which there is not), then, yes, the photons would keep bouncing off the walls forever."
] |
[
"How and why is a RadioCarbon (14C) date calibrated?"
] |
[
false
] |
I am looking at several AMS 14C dates and cannot for the life of me understand why they are being used uncalibrated in the literature or why calibrating a date is necessary. A date of 8030 ± 160 turns into 6974 ± 233 after calibration (CalPal) What is the process behind calibration? Which is the more correct number? Thanks everyone.
|
[
"Just to add on, the uncalibrated date is given in case readers wish to compare to other artifacts using a different calibration method as well as leaving a good record of the process used for data workup."
] |
[
"Radiocarbon dating can date material by comparing the quantity of C14 in a sample of previously-living-but-now-nonliving matter to the concentration of C14 in the atmosphere. Though the rate of C14 decay is a constant (",
"though the mechanism requires some advanced physics",
"), the amount of C14 available in the atmosphere has not been consistent over time. (In essence, the assumption of initial C14 based on today's atmosphere would be incorrect.) By calibrating, the C14 content of samples that can be accurately dated by other methods is used to build a model of what C14 content was like at a particular time.\nTherefore, you should expect the calibrated value to be more accurate.",
"Source: Aitken, \"Science-based Dating in Archaeology,\" pp. 82-85."
] |
[
"And, in case you are curious, the principle mechanism for changing ratios of 14C:12C in the atmosphere is fluctuation of the earth's magnetic field. Stronger fields reduce penetration of cosmic rays. weaker fields allow greater penetration. Cosmic rays interact with N to form 14C in the upper atmosphere. Greater penetration results in higher production of 14C and vice versa.",
"(The central issue here, often unstated, is: why is there any 14C on earth if it has a half life of 5730 years and the earth is >4 billion years old? The answer is, it is constantly being produced, but not at a completely steady rate. Hence calibration is needed)."
] |
[
"Will anything terrible happen if I walk or play on a lawn that's been treated with herbicide, pesticide, or fertilizer?"
] |
[
false
] |
Can the chemicals cling to your shoes more than three days after spraying? Can you track them into your home, where pets and babies may lick them or absorb them through skin? Should such lawns be avoided forever? I have a close friend who avoids walking on these lawns, everywhere, to the point where we can't enjoy some activities together at all: I wonder whether her concerns are rational or scientifically validated.
|
[
"Contact poisons: ",
"http://en.wikipedia.org/wiki/Contact_poison",
"You can only be sure by checking the ~cide used.",
"Meanwhile, organic fertiliser (ie shit) can infect cuts/sores for as long as it remains on the lawn. Artificial fertiliser: check the label."
] |
[
"My Yates (r) Glysophate weedspray says, among other things:",
"DO NOT allow children and pets to enter treated areas until spray has dried."
] |
[
"Short answer: no. I used to spray this stuff on commercial properties as a summer job. Basically the EPA has very strict laws on what kinds of chemicals can be sprayed on lawns that pets and humans come into contact with. Of course don't lick the grass, but feel free to play."
] |
[
"when a limb gets amputated, how do they stop the flow of blood?"
] |
[
false
] |
Do they somehow connect the artery to the vein, up the limb past the amputation?
|
[
"Surgeon here: You wouldn’t want to connect a major artery to a major vein — that would result in high pressure oxygenated blood pouring rapidly into the vein, raising pressure in the venous system and wasting oxygen. For large blood vessels we tie them off with ligatures (surgical thread, basically) or clip them shut with metal or plastic clips. Bleeding from smaller vessels is handled with cautery, usually electrocautery or sometimes ultrasonic cautery."
] |
[
"Depends on the size of amputation. A pinky toe? No different. Both legs at the hip? Yeah they can run into some cardiac issues which there are theories about why. I've attached a very topical paper on this if you'd like to read.\n",
"https://pubmed.ncbi.nlm.nih.gov/18281705/"
] |
[
"Would an amputee (or double, triple, quadruple amputee for eg) have increased blood flow to the rest of the body since there is less \"body\" that the heart needs to pump to? Or does the heart just work less hard?",
"\nAre there positive/negative side effects because of this?"
] |
[
"Is water really tasteless or are we just so used to the taste of water we don't give any thought to it?"
] |
[
false
] | null |
[
"There is evidence that mineral content in water affects the flavor we perceive. Bottled water manufacturers add in the desired minerals rather than selling distilled water, which some say tastes \"flat.\"",
"Here's a study about the chemometric analysis of bottled and tap waters that had been through blind taste tests. It was determined that many testers disliked the flavors of high concentrations of certain minerals and liked others. ",
"http://www.ncbi.nlm.nih.gov/pubmed/23200507"
] |
[
"You have 'taste buds' in your mouth that are you 'taste', they detect five things. Salty, sour, bitter, sweet and umami(savory). If the thing you are eating or drinking does not have any of these elements in it, it will not have a taste because is not taste to detect.",
"If water has nothing we can taste it is tasteless."
] |
[
"idk, but how would you know if something is tasteless? There's so much stuff in your mouth, if water would really be tasteless, 'tasting water' might actually be 'tasting the stuff in your mouth', and how would you really know?"
] |
[
"Ask Anything Wednesday - Biology, Chemistry, Neuroscience, Medicine, Psychology"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"No cephalopods (octopus or squid) have evolved to survive in freshwater, but Gastropods (snails) and bivalves (e.g. mussels), which are in the same phylum, have been able to do so. Why might this be?"
] |
[
"???",
"From calendar:",
"9 Aug Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science",
"This is the 2nd time I recall this happening. I had written out multiple astronomy questions already :("
] |
[
"Yeah, this is a good question. There have been a number of site-wide reddit issues with AutoModerator for awhile now, which does the scheduling of things like Ask Anything Wednesday. I'm not sure if that's the actual cause though but it seems possible. If you have questions, I'd be happy to attempt to answer them (or try to get someone who can)!"
] |
[
"[Warning: Transfinite numbers] Regarding the cardinality of rational vs real numbers"
] |
[
false
] |
If the cardinality of the set of rational numbers is aleph null, and is countable, is there a set of numbers that is not countable with a cardinality of aleph null? If the set of real numbers has a cardinality of c, and c is > aleph null, does that mean the cardinality is >= aleph one (or however you say it)? Is there a cardinal number between aleph null and aleph one?
|
[
"The definition of being countably infinite is to have cardinality aleph null - all sets with cardinality aleph null have the same cardinality, so it makes sense that you shouldn't go from 'countable' to 'uncountable' by staying the same.",
"Is there a cardinal number between aleph null and aleph one?",
"This is essentially the ",
"continuum hypothesis",
".",
"Edit:",
"See comments about definition of aleph one. I had actually meant to respond to the question ",
" it, and copied and pasted wrong late at night.",
"If the set of real numbers has a cardinality of c, and c is > aleph null, does that mean the cardinality is >= aleph one (or however you say it)?"
] |
[
"Aleph 1 is defined as the first cardinal that is different from aleph 0, so by definition,\nthere is no cardinal strictly between aleph0 and aleph1.",
"(The aleph numbers are defined as equivalence classes on the ordinals, two ordinals being equivalent if there exists a bijection between them.)",
"I have to think about the second question, whether c >= aleph1. This would mean\nthat there exists an injective function from aleph1 into the continuum. It may be possible that there are models of set theory, in which the cardinality of the continuum is not even in the aleph sequence. ",
"Axiom of choice would imply that all sets are well-ordered. Since the aleph sequence is defined\nthrough ordinals, this would imply that every cardinality is somewhere in the aleph sequence, hence AC\ndoes imply that c >= aleph1. Without AC, it is probably false in some models."
] |
[
"Is there a cardinal number between aleph null and aleph one?",
"This is essentially the ",
"continuum hypothesis",
".",
"Nah, it's just the definition of aleph one. CH says that aleph one = |",
"|, and that's probably model-dependent."
] |
[
"Is a sphere rotationally symmetrical across all 4 axes in 4 dimensions?"
] |
[
false
] | null |
[
"A sphere in N dimensions is symmetric under rotations in N dimensions."
] |
[
"The surface defined by r",
" = Σ",
" x",
" is invariant under SO(N) rotations."
] |
[
"I have no idea what that means."
] |
[
"Is it possible for the moon of one planet to have satellite of its own?"
] |
[
false
] | null |
[
"Gravity does not have rules about what is allowed to orbit what. Also the phrase \"moon \" is just a label for a body that is orbiting something that is also orbiting a star. So yes, it is possible. Bear in mind that orbits are not stable like an eternal clockwork mechanism, so given enough time things will either collide or escape each other's gravitatonal influence."
] |
[
"The Earth is a 'moon' to the Sun and we have a moon of our own. Its certainly possible, as others state, but gravity likes stability and will force all gravitational relationships into a stable state (eventually). This makes it hard for moons of moons of moons to exist, but its possible. In fact.. interesting scifi 'scenario'."
] |
[
"It's also worth noting that a few of the Apollo and Luna missions were artificial moons for our moon for some length of time, so we have examples that prove it's possible.",
"To restate the stability thing in another way, the only real issue hindering how many levels you have is that for every level you go down, the more likely it is that there are larger objects around to perturb the orbit and threaten long-term stability. Minimizing these perturbations means \"grandparent\" bodies need to be much further away from a moon, or child body, than a parent body to keep the parent body's gravity dominant. It also governs how closely the planets' orbits can get to each other."
] |
[
"Why can't we harness the electricity in lightning?"
] |
[
false
] | null |
[
"(I'm reposting this from here ",
"from a similar discussion",
") ",
"It's simply not enough energy and very hard to transport. I used to have a fun dream to think about ...move to Florida, mid-peninsula which has one of the highest rates of lightning strikes in the world, and try to earn a living catching lightning bolts. Sounds like fun?",
"So I looked into the approximate value of electricity in lightning strikes.",
"So let's say you could \"catch\" a bolt, with a tower, a model rocket or maybe a heavy duty kite. If you succeed you get a burst of energy in the megawatt to gigawatt range...but only for a brief fraction of a second. You can't just throw a pulse like that onto the energy grid so you would need to also have local storage. Can't use batteries though because they need time to charge. Your best bet is probably a huge farm of capacitors. And even then it would be tricky as capacitors \"leak\" away storage very rapidly compared to batteries.",
"So that's hard too...but let's just pretend it all works---how much energy does it make? How much in dollars?",
"Well browsing a few different sources we get maybe 1MJ (megaj-joule) to 500MJ per strike. Once again erring for the best case scenario lets say you can catch 10 bolts a day at 500MJ a bolt. So you make 5,000MJ a day....How much does 1MJ of electricity cost?",
"A kilowatt-hour is the energy that results from using 1,000 watts over an hour. 1 watt = 1 J/s. So 1 kWh = 3600s*1000J/s=3.6 MJ (million joules).",
"A typical kWh in the U.S. cost between 7 and 15 cents or 0.07 USD to 0.15 USD.",
"A 100 watt light bulb uses 1 kWh in 10 hours. 10 kWh cost roughly $1 and has 36MJ.",
"So our super fancy lightning catcher and storage system catches 5,000 MJ a day at best. Convert to kWh --- 5,000,000,000J=1389 kWh. So now we can use an average kWh cost of 10 cents or $ 0.10 USD to find that 1389 kWh * 0.10 USD/kWh gives $139.",
"So now you've got just $139 dollars of energy per day and presumably you need to pay a few people to help with all the tasks around your hi-tech station and buy stuff etc... it's just not enough money to sustain the machinery and labor required to harness it...Wish we could...it would be a cool place to work..."
] |
[
"I, too, am not an expert but the brevity of lightning is the difficult part. Imagine trying to charge a battery from 0% to 100% in ",
"30 microseconds",
". At this time, there is nothing that can store that kind of energy that quickly."
] |
[
"What if you flew a kite high enough that you could grab electricity directly from the clouds before it forms into lightning? Then you wouldn't have to figure out how to store all that fleeting energy, you'd just distribute it right away."
] |
[
"Why hasn't the car industry explored a diesel/electric car instead of hybrid drive with gasoline?"
] |
[
false
] | null |
[
"Because it's not a function of Diesel/Electric vs Gas/Electric, it's Diesel/Electric vs AtkinsonCycle/Electric vs. OttoCycle/Electric. An Atkinson Cycle engine is as fuel efficient as a Diesel, it just lacks the torque (made up for by the electric) and uses cheaper fuel."
] |
[
"Diesel is actually a lot cheaper in some markets btw."
] |
[
"The problem with diesel was that until 2007, good clean diesel fuel wasn't widely available and diesel emission control system of passenger cars couldn't satisfy emission standards in all 50 states. However, you will see the diesel revolution soon: GM, Mazda, Chrysler and some others are bringing passenger cars with a diesel engine to the US and the diesel electric hybrids are not too far behind."
] |
[
"If black holes bend space-time, do they bend time too?"
] |
[
false
] |
[deleted]
|
[
"Space and time are connected insofar as gravity and the fabric of space-time goes. When a large mass, like a black hole, exists, it bends the space-time around it. This pulls things in to orbits, just like the Earth is in orbit around the Sun, but also \"bends time.\" If you were to watch something fall in to a black hole, you would see some very interesting effects with time due to General Relativity, just like you see weird things with time when you watch something move ultra-relativistically due to the effects of Special Relativity."
] |
[
"Yes. In fact, this is why black holes are inescapable. An observer near any massive object has its future time axis bent towards the object. If the object is massive enough, and the observer is close enough, then the observer's entire future ",
" — the bundle of places they can possibly go to or affect — points towards the center of the black hole. Escaping the black hole would require traveling into the past.",
"A spinning object also bends time around itself in the direction of spin; this is called ",
". This is a smaller effect. But it is measurable around the Earth, for example. And a rapidly spinning black hole can theoretically produce all sorts of extreme effects on the time-axis of observers near it.",
"I've seen some good explanations and diagrams of this in books but I couldn't find any online just now (it's really hard to draw a non-misleading diagram of the dynamics of things in 4-dimensional spacetime!). Maybe someone else has a link handy."
] |
[
"You're probably right but I don't get it. What does bending time mean? What are these effects you speak of? What's a ultra-relativistically movement?"
] |
[
"What does \"Earth-analog outgassing rates for surface pressure\" mean?"
] |
[
false
] |
I'm reading this paper: page 8, 10 lines down.
|
[
"Gas leaving the rock and going into the atmosphere, probably - here modeled to be at the same rate as for Earth. They explicitly discuss outgassing of CO2 in the following paragraph."
] |
[
"I’m not sure if you’re just parsing the sentence strangely in your mind - in addition to what mfb- said, it’s worth mentioning that the sentence as you quoted it is incomplete. ",
"“These two atmospheric models assume Earth-analog outgassing rates for surface pressure... ",
"”",
"The authors are discussing different atmospheric models, which have incorporated outgassing rates (flux of gases from interior of the planet to the atmosphere, an important aspect of planetary evolution) as similar to those calculated for Earth (this is what is meant by Earth-analog, presumably they are doing this because it is an Earth-like, potentially habitable planet) for surface pressure ",
", this is plugging two different pressures for their models, as this will produce varying end results. They’re trying to get a picture of what the atmosphere could look like over a range of conditions."
] |
[
"Thanks"
] |
[
"Why does squinting or partially closing one's eyes make vision clearer?"
] |
[
false
] |
I don't quite have to squint to notice a difference, often I can just close my eyes a little and distant text becomes much more clear. Why does that help, when glasses do something so different to my eyes to make things clear?
|
[
"The way I understand it, if you squint (or look through a pinhole - try it), you are effectively just using the center of your lens. Very little focussing needs to be performed in this situation; the center of the lens is barely curved and the light mainly goes straight through. ",
"As a result, the image is dimmer but will be in surprisingly good focus, even if you have quite poor eyesight. "
] |
[
"There are two different ways this works.",
"The first one involves the way images are formed in the eye. Light rays entering the eye through the lens ideally converge on the retina. However, due to refractive defects, these rays may converge at a point closer or further than this ideal spot.",
"Here's a relevant image.",
" The top image shows light converging on a point further than the retina (this is what happens when someone is far sighted). The bottom one shows how this is corrected using a convex lens, with the rays focusing exactly on the retina.",
"Now, when you squint your eyes, your eyeball changes shape just a little bit due to pressure, giving your eye a more oval shape. This changes the distance from the lens to the retina, and thus, the light rays are able to converge at a point that is closer to the retina, which results in a clearer image.",
"The second way squinting helps has been described by ",
"/u/64vintage",
". As light passes through your lens, the rays passing through the center are deflected more accurately than the ones passing through the outer areas. When you squint, you reduce the amount of light entering the lens, and the majority of this light is through the center. This also leads to sharper vision.",
"TLDR: Squinting helps in two ways: 1) Allows light to focus on retina more easily 2) Lets more light in through center of lens."
] |
[
"This is correct. By squinting you are removing the paraxial rays, which create the most blur on the retina. Myopia derives its name from the proclivity of a myope to squint. A downside if this is you get less light into the eye. This trade-off is apparent in the pinhole eye of the Nautilus. "
] |
[
"Kepler Exoplanet Megathread"
] |
[
false
] |
Hi everyone! The team just announced 1284 new planets, bringing the total confirmations to well over 3000. A couple hundred are estimated to be rocky planets, with a few of those in the habitable zones of the stars. If you've got any questions, ask away!
|
[
"Woohoo! Exciting stuff! I understand that this is a very small region of the sky and Kepler can only detect planets in the orbital plane that matches our line of sight. How much of an effect do these new detections have on the estimate of the total number of exoplanets in our galaxy? Do they fall within expected values? Or does this exceed expectations?"
] |
[
"The bigger point is that this is HOW we're constraining that number. Kepler is only looking at a small patch of sky, but much of what Kepler was designed to figure out is the frequencies of various planets, particularly earth-sized planets in earth-like orbits.",
"So these results will be what are used to figure out what our expected values are for planets in the galaxy."
] |
[
"I wonder how many of these it will be possible to make ",
"surface maps",
" of, and whether we can get good spectroscopy data with the next generation of telescopes."
] |
[
"Since the speed of light is the faster anything can go, is there a slowest speed something can go?"
] |
[
false
] |
Since there is a limit to how fast something can go, is there some kind of universal frame of reference? And, as a result, is there an absolute zero speed in the universe? I know that we are moving on a planet, moving in a star system, moving in a galaxy, moving through the universe. So we are not at that zero speed. I just finished reading this: If there is a zero speed, wouldn't time pass much faster? Edit: "fastest", not "faster" in title.
|
[
"is there some kind of universal frame of reference?",
"Nope. One of the biggest consequences of the theory of relativity is that there is no preferred frame of reference. All reference frames are equally valid.",
"Combine that with the speed of light being the \"speed limit\", and you get some very weird (or at least unintuitive) consequences. In a nutshell, light always appears to go the same speed in all frames of reference. This means that, if you're on a spaceship flying past a planet at 50% the speed of light, and you turn on your headlights (because all spaceships need headlights!) then you'll see the light moving away from you at the speed of light. Meanwhile, someone on the planet will see you moving at 50% the speed of light, and the light from your headlights propagating at 100% the speed of light (and not 150% as you might suspect).",
"The end result of this is that time itself changes based on your reference frame. Someone on the planet would see the people in the spaceship moving around as if time were slowed down for them, which explains how people on the planet and the people on the spaceship could both see the headlights as propagating at the speed of light while remaining consistent with each other."
] |
[
"Ah, well I should say, anything can move at speed 0, but that's only in one frame of reference. Not all observers will agree on that speed of 0 like they do all agree on the speed of c for light."
] |
[
"Sure, 0. "
] |
[
"Why doesn't the glass found within fiber optics break/shatter when the cord is bent?"
] |
[
false
] |
Glass is rigid and brittle, so how is it that you can bend it without it breaking (at least to some degree)?
|
[
"It's because the fiber is very thin. Suppose I had a glass rod ",
"=10 mm thick, and I tried to bend it into a circle with a radius of 100 mm. The radius of the curve is smaller on the inside edge, and larger on the outside edge. That means that the glass must stretch on the outside and compress on the inside of the curve, by about pi * d = 30 mm -- about 10%. Now, clearly if I took this glass rod and just pulled on it, it would break before I could stretch it by 10%!",
"But a real fiber optic cable has a diameter closer to 0.1 mm, so the stretching in this case would be about 0.1%: that's easily within the elastic strength of the cable."
] |
[
"It does break, which is why fiber has minimum bend radius specifications which are very important to follow.",
"Also, fiber cables have layers of cladding and sheathing which prevent you from kinking the fiber inside. Distribution cables have a rigid fiberglass “stick” down the middle of them that makes them quite stiff and difficult to bend."
] |
[
"It does break, which is why fiber has minimum bend radius specifications which are very important to follow.",
"Actually the bend radius specifications aren't just about breaking the fiber! The light rays are confined to the fiber by ",
"total internal reflection",
"; bending the fiber causes the rays to encounter the edge of the fiber at a steeper angle, which can let light \"leak out\" of the bend."
] |
[
"How many internal organs can be removed from a person, and they still lead a normal, un-medicated life?"
] |
[
false
] |
I recently had my gall bladder removed due to chronic gallstones and have had to make no real changes to my lifestyle or medical requirements post-op. Along with another obvious candidate, the appendix, how many organs from one person could be removed without having to take drugs or cause major, life altering issues afterwards? Edit: this sounds like an extreme weightloss program...
|
[
"You don't need your gallbladder. You can lose 70% of your liver (however it must be 70% loss in one area). You can lose your spleen. You don't need your appendix. Don't need 1 of the kidneys, don't need 1 of your lungs, don't need your stomach, don't need that 2nd eye or genital organ. You could keep going on. The problem with all this is that you don't know the implications of collectively losing these organs. Chances are this much loss is probably lethal because of complications."
] |
[
"So, you can live without your stomach and no medication, if you're willing to make dietary changes, but without the stomach, you're gonna probably have protein deficiencies, and your food won't be churned into chyme. You're also not going to have your secondary chemical digestion from hydrochloric acid. And, because you'll now very likely lack Intrinsic Factor, you're ACTUALLY going to need B12 shots, because you can't absorb it without Intrinsic Factor.",
"That said, people do live, pretty easily, with things like gastric bypasses. "
] |
[
"You don't need your stomach?"
] |
[
"Why is varicella more dangerous to get as you grow older?"
] |
[
false
] |
[deleted]
|
[
"Sounds to me as though you are attempting to confirm a bias, not learn something. If you already know everything about the answer, why did you ask the question?"
] |
[
"Sounds to me as though you are attempting to confirm a bias, not learn something. If you already know everything about the answer, why did you ask the question?"
] |
[
"Essentially what we know is that the reason varicella is worse/more harmful as you get older is because you’re more likely to suffer complications. ",
"By this I mean everything else other than blisters/rashes, like flu symptoms, high fever, loss of appetite, these kind of complications. Regardless if you’re immunocompromised or not. ",
"Scientists don’t actually know ‘why’ it gets worse, the assumption is that kids immune systems have a lot more phagocytes which will engulf any foreign body. Adults immune systems employ more antibodies rather than phagocytes. So in that aspect, kids immune systems are more aggressive, adults immune systems are less aggressive and rely more on storing information for longer immunity rather than immediate ‘killing’.",
"Hopefully this is somewhat of a reasonable answer.",
"(Edit: this information is slightly outdated and is what we knew in 2017, I haven’t really been able to find out anything more recent)"
] |
[
"Why is the nozzle on a rocket engine designed to reduce the gas pressure to the external pressure ? How is it more efficient ?"
] |
[
false
] |
I've been learning on my own how rocket engines works (well approximately), and I've understood the part about the third law of motion and conservation of momentum. But I don't understand the pressure related aspect of such engines. I've seen that depending on what altitude you mean to use it, you have to elongate the nozzle so that the pressure reduces as much as possible until at the end of the nozzle, it is equal to the external pressure. But I would think that to increase the speed of the exhaust gas, one would need high pressure gas so that it wants to go even faster out of the engine ? Also I don't really understand the need for pressurizing the gas before the combustion chamber : is it to help combustion ? To reduce the size/weight of the combustion chamber ? Thanks if you answer !
|
[
"Your intuition of high pressure --> higher exhaust speed is valid, but to get the most out of that pressure you have to let it accelerate to that speed, i.e. expanding back to atmospheric pressure. Whatever pressure above atmospheric is left over at the end of the nozzle continues to accelerate the exhaust without actually providing more thrust."
] |
[
"To add to what others have said, there's an element of vector analysis involved. When the exit pressure is too high, the escaping gas blows outward from the nozzle, instead of straight back. When the exit pressure is too low, you get shock diamonds, which is the opposite (but similar in terms of lost efficiency).",
"Here's a ",
"Picture",
".",
"As the flow accelerates in the radial direction, that's acceleration that would otherwise be applied in the axial direction, and thus, applied thrust."
] |
[
"What makes you say that?",
"Because the density varies ",
" in a rocket nozzle. The whole thing is built around how compressibility fundamentally alters the behavior of fluid flow. Bernoulli is right out. The most fundamental aspect of ",
"de Laval nozzles",
" is that it exploits the fact that subsonic flows accelerate in converging sections whereas supersonic flows accelerate in diverging sections -- i.e. the exact opposite of what bernoulli states.",
"I've answered stuff about this a few times, ",
"here's one.",
"It's also not correct that you want to accelerate the flow to be as fast as possible. You want to accelerate the flow til pressure is equal to ambient pressure (of course in a vacuum that's the same as expanding the flow as much as possible and reducing pressure to a minimum.) If you expand the flow til the pressure is lower than ambient, you get ",
"overexpanded flow",
" that results in shocks that reduce the efficiency. For this reason the area ratio of nozzles is designed to be optimal at a target altitude ambient pressure -- the first stages of a rocket starting from ground level have a much different area ratio than the stages meant to operate in space. Supersonic aircraft have nozzles that vary in expansion in order to better match speed + altitude."
] |
[
"Why do we treat hyperacidemia in cardiac arrest patients, if hemoglobin has a higher tendency to release oxygen at lower pH?"
] |
[
false
] |
I work as an EMT, and I was pursuing my paramedic certification but got incredibly bored, among other things. In my biochemistry book, it states that "Oxygen affinity of hemoglobin decreases as pH decreases from a value of 7.4. Consequently, as hemoglobin moves into a region of lower pH, its tendency to release oxygen increases. For example, transport from the lungs, with a pH of 7.4 and as oxygen partial pressure of 100 torr, to active muscle, with a pH of 7.2 and a partial pressure of 20 torr, results in a release of oxygen amounting to 77% of total carrying capacity. Only 66% of the oxygen would be released in the absence of any change in pH." I know that part of the algorithm for treating cardiac arrest (outside of amiodarone and epinephrine) includes administration of sodium bicarbonate, even though recently it has gone out of style in favor of hypothermic protocols. My understanding was that the sodium bicarb was used to convert the lactic acid build up in ischemic tissues into carbonate ions that can then attach to hemoglobin and then be expelled through the lungs. Would this offset the oxygen-hemoglobin interaction that I previously mentioned? Or would the decreased PCO2 be more beneficial than the greater O2 unloading from the lower pH?
|
[
"One reason is that acidosis causes hyperkalemia and hyperkalemia causes impaired conduction and v-fib (prevented by amiodarone).",
"The heart is also already the most efficient organ at oxygen uptake from the blood, so the slight benefit is really outweighed by other factors."
] |
[
"This might help if you can get access. \n",
"http://www.ncbi.nlm.nih.gov/m/pubmed/2155764/?i=4&from=/2852199/related"
] |
[
"A couple of reasons. The heart probably won't pump as well in an acidemic environment, so maybe raising the pH will improve contractility if you bring the heart back. Some people think epinephrine is less likely to help a heart in an acidemic environment because it has poorer contracitilty in that setting, so maybe improving pH will improve the chance epi will work. Thirdly, if someone is hyperkalemic, raising pH will shift K intracellularly, which lowers serum potassium.",
"This part of ACLS (as are many parts) is not very evidenced based. It's important to remember that the things really proven in cardiac arrest are chest compressions and shocking. A lot of these other things are probably good to try, but what's important to think about (particularly for an EMT), is what will really help the patient. If you're out with very limited help, maximizing the quality of compressions and shocking any shockable rhythms is probably the best you thing you can do. Every compression is perfusion. Every time you don't do a compression to try to give some bicarb (if you're in the back while your partner's driving) is not perfusing the patient. That probably wipes out any benefit of bicarb. Then you roll in to the ED and there tons of doctor's and nurses. Then there's time to do compressions, intubate, bicarb, all the other fun things that may not work. So, when resources are limited, stick to what works. When not limited, try things that may work."
] |
[
"When firing a bullet out of a gun, at which point does the bullet reach its maximum speed? Is it at the point the bullet leaves the barrel or is it a couple of feet later?"
] |
[
false
] | null |
[
"Not strictly true, there will still be some pressure from expanding gases exiting the barrel, but since it can now expand radially the force will fall rapidly. "
] |
[
"It depends on the length of the barrel and other factors like rifling, twist rate, smooth bore. It's possible the bullet could reach its maximum velocity somewhere in the barrel if it's long enough. Short barrelled guns like pistols will have the bullet reaching maximum velocity at the point where they exit the barrel. This is known as Muzzle Velocity. "
] |
[
"All of the accelerating force happens inside the gun - when the bullet is out of the barrel there is nothing to make it go faster than it was going at the moment it left the barrel."
] |
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