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[
"What is the slowest speed the human eye can observe to see its movement?"
] |
[
false
] |
For example, a plant is always growing but in most cases we can’t observe that growth with our eyes in real time. What is the speed of something before it is impossible for the human eye to recognise that it is moving? I have tried to search this up many times but it has never answered to my liking. Thanks. 🙂
|
[
"What we perceive as apparent motion is created by sequences of frames portraying a stimulus at different locations. Our brains do not view the world as one continuous motion but rather the combination and processing of \"percepts\". You can think of it like a film, where each frame is combined and processed to produce one smooth continuous image/motion.",
"When we view stimuli, we categorize them in \"orders.\" Examples of first order motion stimuli are related to luminence, and second order would be related to contrast. The third order revolves around features. We are very sensitive to first order motion, and are also able to detect second order motion even without the presence of first order cues (Chubb & Sperling, 1988). Due to this, it has been suggested that separate motion systems exist.",
"Three different models",
" for detecting motion for each system have been suggested. ",
"There has also been a ",
"proposed model",
" for ",
"th order motion that generates a motion signal. This is a combination of several orders, and it a bit simplified and does not account for all kinds of motion, such as stimuli with motion energy at different places."
] |
[
"Depends on what you mean by observe movement.",
"Persuade a plant to grow with a ",
"vernier scale",
", and you'd probably be able to notice movement. Over the scale of minutes to hours, you'd notice growth in some types of grass if you had a vernier scale on it.",
"OTOH, stars that are far away may move at a fraction of the light speed, yet seem stationary due to perspective."
] |
[
"I think what they’re asking is more about being able to watch it and see it grow in the moment. Kudzu grows a foot a day so if you waited a few hours you’d see the growth, but I think the question is about the minimum speed you can be able to see the motion of its growth, rather than just notice the growth. I just looked it up online and for example, the fastest growing plant grows 0.00002 mph. I think the question is would that be fast enough to perceive the actual motion of its growth? If not, what speed would we be able to perceive?"
] |
[
"Why are marine mammals so intelligent?"
] |
[
false
] |
Why are the majority of mammals which live exclusively in water (whales, dolphines, porpoises) so highly intelligent? From beluga whales blowing ring bubbles to entertain themselves, to the whale putting on a show possibly as a reward to its human helpers ( ), to dolphins using sea sponges to protect themselves while getting food on the sea floor - they seem like abnormally intelligent mammals. Are there theories around this? I've done some preliminary googling and the best reason I've found is: "They have larger brains". So...why? Is this a product of evolution, in that it takes lots of smarts to survive in the very chaotic, dangerous sea?
|
[
"The evolution of cetacean (dolphin, whale, porpoise) intelligence is poorly understood due to the relative difficulty of determining brain characteristics from fossils until very recently. I should point out that the higher level of intelligence is mostly contained to the suborder of odontoceti (toothed whales) and the highest levels of intelligence are contained to individual species within the superfamily delphinoidea (dolphins, porpoises, belugas, and narwhals). However, there have been attempts at piecing together the evolution of their brains.",
"The results show that encephalization increased in two critical phases in the evolution of Odontoceti. First, the origin of odontocetes from archaeocetes near the Eocene-Oligocene transition occurred contemporaneously with a significant increase in encephalization. Furthermore, because there was no significant increase in brain size over the course of archaeocete [now extinct suborder of cetaceans] evolution, these findings rule out the hypothetical possibility that large relative brain size was associated with the invasion of aquatic habitats.",
"Source",
"It seems unlikely that the evolution of high levels of intelligence is simply due to living in an aquatic environment.",
"Another major hypothesis regarding the high encephalization in toothed whales focuses on the neural processing needs associated with either echolocation per se or its elaboration into a complex perceptual system in the suborder Odontoceti (Jerison, 1986; Ridgway, 1986; Oelschläger, 1990). Results here show an increase in encephalization at the origin of Odontoceti that may be related to the emergence and elaboration of the ability to process high-frequency acoustic information associated with echolocation. Echolocation is an ability found in all modern odontocetes, thought to have existed in all known fossil odontocetes (Fleischer, 1976; Fordyce and de Muizon, 2001) and to have been absent in all archaeocetes (Uhen, 2004).",
"Increases in brain size seem to at least correlate with the emergence of echolocation.",
"The conventional wisdom holds that increased encephalization confers a selective advantage and that increases in encephalization should be pervasive across groups and their component lineages (Gould, 1988). The shift to higher encephalization levels within Odontoceti at the origin of Delphinoidea, however, and the continued expansion (toward both higher and lower levels) within Delphinoidea suggests the absence of an overall drive toward higher levels of encephalization for Delphinoidea as a whole.",
" Basically, it seems that the initial increase in brain size in toothed whales may have been a result of a need to process high frequency sounds involved in echolocation. The second period of growth in brain size may have had to do with the emergence of social structures within some toothed whale species. Because the increase in brain size didn't seem to happen until the emergence of toothed whales, an aquatic habitat seems like an unlikely selective pressure for intelligence. However, there is plenty more research into this area that needs to be done."
] |
[
"This isn't a reddit post, this is a goddamn one-man wikipedia article. My hat off to you good sir."
] |
[
"This is not a satisfying answer though. ",
"Why do tigers have stripes?",
"Which is the better answer: 1. Because having stripes helped them survive to produce more offspring, or 2. Because having stripes breaks up their outline against their background, making it harder for their prey to see them, and thus easier for them to catch dinner.",
"Evolution absolutely can have a cause. Some evolution proceeds randomly (via ",
"genetic drift",
"), but all adaptation proceeds by natural selection, which is very much a cause --> effect process. Evolution does not have ",
", or ",
", but it very much has a cause."
] |
[
"How is norovirus able to withstand the low pH of the stomach?"
] |
[
false
] |
In order to infect the GI epithelium, norovirus would have to survive the low pH of the stomach. I thought most proteins denature at a much higher pH. What is special about norovirus that makes it so resilient to acid?
|
[
"Well yes, most proteins we know of do denature at very acidic (or basic) pHs. The key word though is 'most'. The norovirus capsid is pH stable down to a pH of about 1 and the stomach typically approaches a pH of 2 IIRC. The virus capsid proteins do unfold at about a pH 10 though.",
"Here's a nice paper looking at the mechanical stability and recovery of the virus capsid across a range of pHs",
"https://www.ncbi.nlm.nih.gov/pubmed/20592107",
"In theory proteins can be synthesised or evolved to be stable for any given physio-chemical environment. We typically encounter proteins or do research on proteins that are evolved for the kind of environment we live in; 1 atmosphere of pressure, low-salt, neutral pH and easy water availability. Part of the reason for this is we don't have to look very far for organisms (and their proteins) that live in the same environment as we do. But plenty of organisms live in much more extreme environments and their proteins have evolved to cope. So we shouldn't be too surprised that something like norovirus is uniquely adapted to survived the environment of the stomach.",
"Most interesting I think is how do thing like virulent strains of e.coli or salmonella survive the stomach to cause in infection."
] |
[
"I vaguely recall that h.pylori also has a proton pump protein in it's cell membrane to pump H+ out of it's cytoplasm and back in to the environment as well.",
"I think a lot of GI bacteria get to the GI through sheer weight of numbers. If 99.99% get destroyed in the stomach then a couple might still make it through. Someone with more knowledge of this might be able to clarify."
] |
[
"Thank you! This is a great answer. I recall from microbiology h. pylori is able to buffer H+ by producing ammonia via urease. It also burrows into the mucus lining of the lumen to protect itself. I'm not sure how e. coli and salmonella does it, though. That's an interesting question."
] |
[
"Could I eat my own arm or leg to stay alive longer?"
] |
[
false
] |
[deleted]
|
[
"Yes, assuming that the energy lost from amputating a leg (I am going to assume leg, since a proper amputation needs two hands) is less than the energy gained by consuming it. As far as how long your leg would last you, it depends all on your body, both your metabolism and how nutritious your leg is. You can survive with very few calories per day, especially if you have water. 2000 calories is the recommended daily amount for a healthy adult, even a quarter of that would be sufficient for that last day. How many calories your leg has might be a question for your doctor."
] |
[
"Gak! Actually, you could survive without food for much longer. Gandhi lasted 21 days and hunger strikers have lasted well over 40 days. Perhaps you should hold off removing your leg!"
] |
[
"I realize this doesn't provide any actual evidence, but you should read Stephen King's short story called \"Survivor Type.\" It's about a very similar situation, and he claims he had discussions with a doctor and everything in it is at least plausible. "
] |
[
"The space program has used CO2 scrubbers for ~50 years. Why can't we use this same technology to help clean the atmosphere?"
] |
[
false
] |
I don't understand why we don't have some capture device on our vehicles to collect CO2. I'm kind of thinking a cartridge type filter, perhaps similar to the ones made famous in Apollo 13. I have some ideas, but I don't really want to push the discussion in any direction before it begins. Edit 1) I'm thinking of an unpowered system that is designed to capture CO2 from air that passes through the filter - not something that will capture all of the output from a car.
|
[
"My understanding is that the production and recycling of CO2 scrubbers takes a significant amount of energy, greater than the amount of CO2 that is absorbed from the production of a similar amount of energy. IE it still leads to a net increase in CO2, it just decreases it locally. "
] |
[
"Then why not just use the clean energy directly and not generate the CO2 in the first place?"
] |
[
"It is largely an issue of size, temperature and time scale, though price cannot be discounted. Here is a link describing the method used on the space shuttle:",
"http://web.archive.org/web/20071031085108/http://www.hamiltonsundstrand.com/hsc/proddesc_display/0,4494,CLI1_DIV25_ETI5338_PRD776,00.html"
] |
[
"Could covid antibody tests be more efficient from blood mixing?"
] |
[
false
] |
Just an idea I was thinking over. Since covid antibody tests would be positive if EITHER of 2 mixed blood samples but negative if NEITHER did, theoretically, by using a method of mixing 2 blood samples and then one person come back with equally certain results for 1.5 average tests rather than 2 (if 50% of the population were effected at random). I'm not sure if I explained it well enough, an example. A household of 4 people has one suspected covid case and then it passes. If everyones blood was mixed and tested, it could come back positive showing at least 1 person had it or negative for noone. If negative, 1 test has tested 4 people but if positive, blood of 2 sets of 2 could be mixed and the process repeated. The worse case scenario, 4 tests are required but best case only 1 is. For tested individually, it needs 4. On top of this, because it is more likely for either everyone to have it or not have it, the method becomes better by a greater chance of a full negative reply. So the question, if I have explained myself, would this practically work? If it would, what statistically be the best method, binary spliting? Something else? This is poorly worded, sorry, but it was an interesting concept I wanted to share.
|
[
"It's called pool testing , they just started rolling out limited testing using this with the CoVid test, not the antibody test. Obviously testing and validation must be done prior to approving pool testing with a given test , that's basically what were waiting on.",
"https://www.cdc.gov/coronavirus/2019-ncov/lab/pooling-procedures.html"
] |
[
"This can be done and in certain circumstances it is but there are so many considerations it's probably not worth it for this use case. This is the sort of thing that sounds good to e.g. a computer science student because the overhead that applies to clinical samples does not (generally) apply to data.",
"For one, this method becomes less efficient as the prevalence increases. The tests that are widely available frequently rely on a set input of e.g. serum, so you lose sensitivity by having to combine and thus dilute everyone's samples. They are also already fairly high throughput, and having to manually mix many samples is time consuming in practice. There's also a time sink associated with storing and retrieving the individual samples for subsequent re-testing. When it's feasible to test thousands of samples per day in a single clinical lab the return on the added labor is not that great.",
"Where this IS applicable is in testing for low-frequency diseases in situations with limited diagnostic capabilities. Where these limitations still exist for the current coronavirus pandemic it's largely a political issue."
] |
[
"Thats pretty cool, didnt know about this and I'm glad theres a name for it"
] |
[
"How does Obama's basic research budget compare to Bush's?"
] |
[
false
] |
I was watching the PBS documentary The Atom Smashers and a lot of the interviews focus on the budget cuts for basic research which crippled Fermilab during Bush's second term. I was wondering if anyone could tell me or point me to an easy place to find out if Obama had done anything to increase basic research funding in the US. Thanks!
|
[
"Courtesy of the Obamameter:",
"http://www.politifact.com/truth-o-meter/promises/subjects/science/"
] |
[
"The Obama stimulus was pretty generous to science, though may hurt hard when it disappears and there are more scientists competing for less grant money.",
"That said it is a myth that \"Bush\" was bad for science budgets as opposed to it just being a horrible time for budget funding. It is true that the FY08 budget was devastating to scientists--I was doing experimental particle physics at the time and our lab shut down the experiment early, had layoffs, and I had to TA while writing my thesis (having to TA while doing experimental particle physics due to low grant funds had been unheard of in the past 30 years at my school). ",
"That said, I do not blame Bush for it (and I am a democrat and campaigned for Obama and think the Bush administration was horrible in a lot of other aspects). The story the lab director told us (who was totally caught off guard by the budget and frequently went down to Washington to try getting emergency funding to reduce layoffs) was the following. Bush wanted to increase the science budget as one of his hallmark initiatives (the \"American Competitiveness Initiative\") and had wrote in ~3% budget increases in the FY07 and FY08 budgets. In FY07 the increase couldn't get through congress, and so in FY08 he wrote in a ~5% increase. The community was happy, but there was some midnight decision around December 2007 where the science funding was decreased by about 10% in the FY08 budget and no one was aware who gutted what. It seemed that democrats wanted Bush to put more into other programs, reduce the deficit, and cut military spending and were going to veto his budget, and in the back in forth science got cut hard. So politics as usual; cut something someone values to hurt them. E.g., when push came to shove both sides agreed on cutting science, specifically fusion and high energy physics. ",
"For High Energy Physics, well, the situation is dire, and I am not exaggerating. The numbers are:",
"FY07 current operating budget is $751.8M",
"The Bush Administration’s request for FY08 was $782.3 M.",
"The final bill (with the mandatory rescission) provides $688.3 M ",
"[1]",
"Also Clinton was president when funding stopped for the SSC. Republicans are usually kind to big science (e.g., particle physics), despite being widely perceived as being anti-science (from their rhetoric that caters to the evangelical religious republican base). A professor once told me that its because the Republicans think that particle physics may contribute to some next big weapon somehow or just help give the US a technological advantage in war through the developments necessary to do particle physics. He didn't think these assumptions were correct, but liked getting the funding anyway."
] |
[
"Well there's a huge gulf between modern particle physics and weapons development and virtually no area of overlap. I've never met a modern particle physicist who thinks their research will have an iota of an impact on weapons development. Many actually go into the field, simply because they see no applicable use for it. Results are not top-secret, you can order all our experimental data for free from the US government funded ",
"Particle Data Group",
". This is in contrast to information on how to build atomic weaponry which is all classified and based on much simpler well-understood physics. Other possible rationale for republicans being kind to science, is (a) no one wants there party to be the anti-science and have our country be left behind, or (b) if scientists develop technology through federal dollars thats a huge stimulus to the big business world that can patent the technology or grow large off supporting the government research, and republicans often have closer ties to the world of big business.",
"I often see politics overly simplified into our side is good, the other side is stupid and evil. Its worth the effort to learn why your opposition thinks the way it does, and to attempt to see and appreciate their value system. E.g., I like strict handgun laws in cities, but can easily see how some republicans can think if more law-abiding citizens had concealed handguns on them, it would be easier to prevent crime (like this reddit story today where a mugging was stopped)."
] |
[
"Can a quantum observation be undone?"
] |
[
false
] |
I was reading about the various interpretations in quantum mechanics and about the wave function collapse and was wondering whether the process can be reversed. If an observer is rendered incapable of transmitting the result of an observation (e.g. destroyed immediately after), would multiple observers, theoretically, observe the same results (before being destroyed)? Would the system revert to its indeterminate ("superposition") state or does the first observation permanently lock any other subsequent measurements to a certain result?
|
[
"http://en.wikipedia.org/wiki/Quantum_eraser_experiment"
] |
[
"Is there a formula for the time a state takes to revert to a superposition?"
] |
[
"After a quantum system is measured, it's wavefunction collapses to that of one of it's eigenstates (essentially one of the many possible 'answers' to the measurement). If you continually re-measure the system faster than it can return to it's original quantum state that was a superposition of many eigenstates, it will return the same answer forever. You can even leverage this property in order to prevent the decay of particles (which is akin to radioactive decay) which is called the ",
"quantum zeno effect",
".",
"So yes, the process can be reversed, by allowing the system enough time to return to it's original quantum state."
] |
[
"We know world's fastest creature both on land and sea, in terms of distance/second But what is the world's fastest being in terms of body lengths/second?"
] |
[
false
] |
I was watching a Nat today while I was brushing my teeth and I thought holy shit, that tiny tiny tiny bug is hauling ass compared to its size. Like I'd imagine if a human we're able to cover it's equivalent body length/sec we would be super Sonic. Am I wrong? Is it truly not that fast? I would assume the smaller the animal the faster it could go in BL/S or "Body Lengths/ second.
|
[
"I don't know if it is the record but here is 1000 times the body length per second: ",
"Copepod"
] |
[
"Borg et al. 2012",
" is the original article on this if anyone's interested. The ",
"relevant figure",
" does indeed show some of the smallest individuals just barely hitting 1000 body lengths per second in the top left corner, though most individuals are significantly slower.",
"I think another contender worth mentioning is the mite examined by ",
"Rubin et al. 2016",
", which is able to sustain very high speeds just by running, rather than jumping (averaging around 200 body lengths per second, but over 300 in some cases)."
] |
[
"If you were curious about Air - then its Annas Hummingbird!",
"“ Scientists calculated that the 50mph speed of the hummingbird at the fastest point in its descent is equivalent to it moving 383 times its body length each second. The G-force as it turns out of its dive is nearly nine times the force of gravity – the same as the maximum G-forces experienced by fighter pilots“"
] |
[
"To the best of our knowledge, with which Earth species do humans share the least DNA in common?"
] |
[
false
] |
I remember learning in an introductory biochemistry course several years ago that share ~97% of our DNA with bananas, and ~99.9% with chimpanzees. Today I read on this from February, 2013, that the notion of our DNA being so similar to chimps is, in fact, false, now that we've had more time to dissect the human and chimp genomes for comparison. The article concludes it's possible only 70% of our DNA is in common with our "closest" relative on Earth, much lower than previously thought. Well this got me thinking: Which species, extinct or still living, contains a DNA strand that deviates most from our own? Would it be life on Earth's oldest known ancestor, from which all other life has stemmed; or something that's evolved radically different from ours over time? Or maybe this is a null and unanswerable question until we've analyzed the genomes of more species.... ? Thank you all beforehand!
|
[
"There are an awful lot of bacteriophages and archaephages with which you share zero sequence homology. ",
"That said, among cellular organisms, you wouldn't really be able to generate a properly satisfying answer with the kinds of data and statistical analyses we have available - where measuring relatedness is non-intuitively tricky in a bunch of ways. One would logically expect to find our most distant relative in some strange branch of the Eubacterial domain, but flipping the question to measuring unrelatedness invalidates a lot of the assumptions that we make while trying to measure relatedness in standard ways. "
] |
[
"Thanks for the answer, that's what I was worried about encountering as a boundary with this question... guess I'll repost in 20 years or so...."
] |
[
"Also, keep in mind that DNA sequence is only part of the picture. DNA is chemically modified to control expression. So even though chimps and humans share so much homology, it doesn't mean the genes act in the same capacity since this epigenetic modification is different.",
"I question that we have 97% sequence identity with bananas. I think that is way over stated. Primates is also less than 99.9, but much closer to that number."
] |
[
"Why are Neanderthals classified as a different species from Homo Sapiens?"
] |
[
false
] |
If they can mate and form viable genetic offspring, what makes them a separate species? Please feel free to apply this same line of logic to all the other separate species that can mate and form viable offspring.
|
[
"I don’t believe they are always considered a separate species anymore. IIRC they are often classified as ",
" (with anatomically modern humans being ",
"). ",
"Part of the confusion stems from how species work. We’ve applied a relatively rigid system of classification to something a lot more fluid. For instance, one of the more common definitions of a species is a population of organisms which can breed together to produce fertile offspring. Therefore, if the offspring of two animals aren’t able to reproduce the parents would be considered separate species. However, hybrids sometimes are fertile, which further muddies the waters.",
"Species and subspecies are more approximate classifications that solid categories. It’s also worth noting that it was once assumed modern humans and Neanderthals couldn’t interbreed, which is why they were originally classified as a separate species.",
"Also, looking through the literature, you’ll often see both ",
" and ",
" referred to, occasionally within the same paper, so it appears they’re quite commonly used interchangeably as a result of the ambiguity over whether they’re a separate species or not."
] |
[
"Speciation can happen both from inability to have viable offspring and from behaviors or geographic locations that create barriers to having viable offspring.",
"Speciation is also considered a more gradual thing than a lot of people realize.",
"Finally, there is evidence that surviving Neanderthal genes in modern humans are the result of male Neanderthal-female human pairings, one possible explanation for which is infertility of offspring of the opposite pairing."
] |
[
"Ring species",
" are a good example of how the underlying biology is much more fluid than our definitions"
] |
[
"What are the effects on your health of cold and warm showers?"
] |
[
false
] | null |
[
"The direct effects are seen as a constricting of the blood vessels under cold conditions due to the affinity of the post junctional alpha-adrenoceptors for norepinephrine. \nWarm showers do the exact opposite with the end result being net vasodilation.\nLook into the work of Shepherd and others"
] |
[
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"If you would also like to protect yourself, add the Chrome extension ",
"TamperMonkey",
", or the Firefox extension ",
"GreaseMonkey",
" and add ",
"this open source script",
". ",
"Then simply click on your username on Reddit, go to the comments tab, scroll down as far as possible (hint:use ",
"RES",
"), and hit the new OVERWRITE button at the top."
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[
"Upon review of the literature it would seem that both have their benefits. Though not many people have conducted studies that include both variables. There has been some independent research done on one or the other variable. The literature would seem to suggest that both can be used in medically advantageous ways. "
] |
[
"Why does sunlight cause the colors of objects to fade over time?"
] |
[
false
] |
[deleted]
|
[
"Most of the pigments we use to give colour to objects are organic pigments. Organic pigments happen to have lots of chemical bonds in them that can be broken by exposure to visible and ultraviolet light. So put enough light into them for a long enough time and the compounds that give the object its colour in the first place will be destroyed. So the colour fades."
] |
[
"It may be because red needs to fewest amount of bonds to make, thus breaking any of them gets rid of the color. Also more bonds increase the stability of the system."
] |
[
"Speaking as an ex organic chemistry tutor, the answer is ",
" stability.."
] |
[
"Has there ever been a period of time (however brief) other than now, that humans lived through a temperature change as rapid as the one predicted to occur?"
] |
[
false
] |
I remember hearing somewhere that humans once lived through a brief period where the temperature rapidly changed like it is now, and the we survived. Is it possible this could happen again?
|
[
"One common theory of human evolutionary history says that our intelligence is a product of a rapid cycle of climate change and the adaptability that survival required. Ice ages and warm periods do happen. In fact, after Neandethal man had left Africa and was doing well in Eurasia, between something like 200, 000 and 70, 000 years ago, the climate jn Africa cycled wildly between warm, wet and jungly and deserts caused by huge glacial caps sequestering the water and affecting weather worldwide. At one point 70-75, 000 years ago, there may have been as few as a few thousand modern humans that survived a terrible drought hundreds of years long in Africa.",
"At this point humans began sporadic, but frequent migrations throughout the world, and culture and technolovies exploded. So, we have survived some bad times. ",
"However, we don't know how bad it's going to get. Species survival may or may not be the biggest worry surrounding global warming. Human suffering on a colossal scale, wars, disease, societal upheaval, destruction of resources, displacement, starvation, etc are more likely. Remember, a few thousand survivors could save the species, but that would still mean you that 7 billion died horribly."
] |
[
"Indeed, homo sapiens wouldn't be that dominating if not for the constant climate changes and his adaptability. "
] |
[
"This also assumes a problem though. I mean the temperature has been increasing before humans began to have an affect, and has been higher in the past.",
"Unless the goal is to keep the temperature ideal for humanity, climate change isn't a real problem."
] |
[
"Why is the light frequency spectrum cyclical like the audio frequency spectrum?"
] |
[
false
] |
EDIT: *NOT. Why is the light frequency spectrum NOT cyclical like the audio frequency spectrum? I'm not sure if all my terminology is correct or my explanation makes any sense, so apologies. I'm calling the audio frequency spectrum cyclical in that when a frequency doubles (eg from 220Hz to 440Hz) the pitch heard is more or less repeated (ie, an octave from A0 to A1). The cycle continues with octave stacking on top of octave as frequency increases and pitch rises. My question is simply: Why does light not do the same thing? For example, green light has a wavelength of roughly 510nm. Why is the wavelength of 1020nm similar to green? Thanks in advance, please feel free to ask me to clarify anything.
|
[
"Light and sound are both waves, but we detect them in very different ways. When a sound wave comes in, it vibrates the ear drum, which, through a linkage of bones, vibrates a fluid in the cochlea, which then vibrates a nerve. This nerve is then sending an electrical signal to the brain telling it exactly what frequency it is hearing. The frequency resolution is actually pretty good, and most people can differentiate within a few Hz at 1 kHz.",
"When light is absorbed in the eyes, however, the frequency information is lost; the eye does not actually record the frequency information. Instead, the eye has three types of cone cells that are sensitive to light within a certain frequency range. These three different cell types (called L, M, and S) are centered at roughly 590 nm, 535 nm, and 430 nm. When monochromatic light is absorbed in the eye, each type of cone cell gives off a certain strength of response, and this combination of responses is unique to each color. For instance, the L cell responds equally to light at 500 nm and 650 nm. If you only had L cells, you wouldn't be able to distinguish between those two colors (this is hinting at how color-blindness happens). Luckily, the M and S cells respond very differently to these two colors, and so your brain can use the relative signal from each type of cell to define each color. This method of differentiating between colors is very good, and most people can distinguish between several million colors. Incidentally, this is a frequency resolution on the order of 20 MHz or so at 500 THz.",
"TLDR: your ear records the actual frequency it hears directly. Your eye takes three sort of crappy measurements, and then uses a lookup table to accurately determine the correct frequency. The first method is very amenable to things like a simple frequency doubling (just vibrates twice as fast), whereas the second is not at all (it's just a totally different combination of three numbers when you double). Hope that helps a little."
] |
[
"the only answer i can give you is because light isnt really a wave.",
"i mean in some ways it does behave as you describe, we just dont perceive light and sound the same way we cant even perceive directly more than a fraction of the total spectrum. but you can often treat them similarly.",
"individual quanta like photons, electrons, and all the other quantum particles that are said to be both waves and particles are really neither. they exhibit some aspects of being waves. but they are not waves. ditto for particles. so analogies like comparing light to sound dont work all the time."
] |
[
"We can perceive sound from approximately 20 to 20,000 hertz. We can see light from 4x10",
" to 8x10",
" That's a frequency range of 400,000,000,000,000 Hertz. Octaves are tools used mostly by musicians. They are not a unit of measurement. The radio spectrum covers more octaves than audio. I'm rambling....",
"If humans can detect more discrete audio frequencies than light wavelengths, that is a function of their physiology and psychology. "
] |
[
"How did scientist/mathematicians come up with things such as fourier/z transform?"
] |
[
false
] |
How did they prove it at the time? Was there a need to come up with something like this to solve an existing problem or was it to simply test correctness of proof and optimizing existing methods? Are there any books or videos which go through how some popular theorams and proofs were derived an stories behind them?
|
[
"The main theorems and proofs we see today are not what would have been seen when the ideas were first coming around. The idea for Fourier series had been teased at by people like Euler, Lagrange and Gauss, but not enough to recognize a more general theory. This was in the context of physics problems governed by differential equations like elasticity or orbital mechanics (see ",
"this",
"). But the Fourier Series was really first used by Fourier to analyze the Heat Equation, and (according to ",
"this MSE post",
") was used as a kind of \"calculus\" (rules for symbolic manipulations) for solutions to these differential equations. Fourier used it to approximate solutions via trigonometric functions, which is a first natural step to what is going on. After Fourier figured out that integral transformations are a cool thing, many others jumped on the idea and you really start seeing them pop up all over the place in the early/mid 1800s.",
"As for a progression on the proofs, it's probably best to not follow how things originally went. Hindsight is 20/20, and so we know what the important and useful properties of Fourier series and transforms are, and can address them naturally from basic principles. Whereas, these ideas were being developed alongside things like proper Real Analysis, and can lack the direction. If you are interested in the historical progression on its own right, then I would say it's best to know the modern theory first and then look back into some history of math work done on the subject to get that perspective. Sometimes keeping historical progression in mind can help clarify certain concepts in math as you're learning it, but other times it can get in the way of a first understanding. I'm no math historian, but my opinion is that Fourier analysis (and much of calculus and analysis) is in the latter camp. But the links provided can lead you to some historical stuff, and ",
"here",
" is a treatise on the subject written by Fourier."
] |
[
"Regarding the need for discovering the transforms: I sometimes think of solving problems in physics as trying to find the \"correct\" coordinate basis to work in. If you try to solve a problem naively, it's almost always very difficult, but if you find the \"correct\" coordinates to work in, the problem becomes relatively easy. Here, I'm using the term \"coordinates\" in an abstract way - I'm using the term as a general word for the variables you're working with in a given problem.",
"This is essentially how Fourier or Z transforms arise - as a need to convert functions to a different basis, where the preferred basis has nice properties when studying certain mathematical problems. In particular, Fourier transforms make wave equations much easier to solve and work with, and Z transforms have the same application to certain finite difference equations. ",
"Of course, the hard part is finding the correct basis (aka finding the transform which makes everything easier). But the application of these transforms to interesting problems was clear."
] |
[
"It is also interesting how much of the modern* formalism around Fourier series and transforms is inspired by physics. For instance the Dirac delta function was concieved out of physical needs, and later made rigourous through distribution theory.",
"The desire to unify the \"wave function\" aspect and the \"matrix\" aspect of quantum mechanics was a big influence as well. With finite dimensions and matrices, it is natural to use linear algebra concepts such as base vectors, projections onto a vector, and base changes etc. ",
"In the modern formalism, the Fourier series is a natural set of \"base vectors\" to express solutions of every periodical problem in. And the Fourier transform gives the base change from the \"position coordinate\" to the \"momentum coordinate\". ",
"(This is also how the uncertainty principle arises: the fourier transform of a delta function is a constant function. In other words, if we know exactly where the particle is, we don't know its momentum.)",
"Footnote: \"modern\" = 1940's. The actual contemporary theory concerns C*-algebras and other kinds of abstract stuff."
] |
[
"Why do slick tyres give more grip when they are hot?"
] |
[
false
] |
Never made sense to me...tyres are tyres. I am not talking about all kids of tyres though, obviously wet groved ones are going break away when they are super hot, but I am talking about slick racing tyres with no grooves.
|
[
"Rubber gets \"stickier\" when its hot, for lack of a better term. Physically, a cold piece of rubber will be less elastic and more brittle, which means its not going to grip as well.",
"This is not just for slick tires either. All tires function better when they are warmed up."
] |
[
"If you look at a slick tyre when it's cold, it's almost shiny. It has a 'waxy' feel and is quite hard. You can make a mark with your thumbnail. It's hard to describe - almost like a stiff plastic barrel. The tyre is absolutely useless when it is cold. That's why they have tyre warmers before they even attemt to drive - on things like Le Mans and F1. The drivers often weave back and forth across the track on the warmup laps. Working heat into the tyre also helps it achieve it's design pressure - which translates directly to ride height. Once the tyres are properly warm, they are literally melting on the outer surface. This provides fucking insane grip, which is helped by downforce. The tyre sticks to the track, and more importantly, sticks to the rubber already on the racing line. Sometimes the tyre gets too hot and 'blisters'. This is disastrous to grip and renders the tyre completely useless."
] |
[
"Ah, I honestly thought they were weaving back and fourth because either A: They didnt want someone to pass them (even tho they arent allowed to), or B: They didnt want to hit the brakes while pacing."
] |
[
"Why doesn't the water in rivers, streams and lakes just go into the ground?"
] |
[
false
] |
I guess I'm asking how the does water stay above the ground and not seep in? Does it have to do with the water table? Thanks for all the great answers everyone!
|
[
"Geotechnical Engineer here. Holy hell, I'm relevant on reddit? ",
"As some have pointed out previously, soil has a saturation limit. Varying types of soil may have greater infiltration rates than others. Such as sand versus clay. Sand is a much larger particle than clay and as the particles settle, sand will create greater voids per unit volume than clay. These voids allow for water to filter through more readily, increasing the hydraulic conductivity of the soil type. So the larger the particle = the easier water can flow through the soil.",
"In the case of a stream bed, it becomes a bit more complicated. The stream bed is the physical representation of water collecting from a massive watershed. For instance, the Mississippi River's watershed collects from the majority of the eastern United States. At the starting points of these watersheds, typically the larger particles; cobbles and gravels, and sands are located here. It is likely that in these areas the infiltration rates are higher allowing more water to drain into the ground, but because the water is continually being fed from melting snow pack and rain and other sources, the stream bed is continually being saturated beyond its maximum infiltration rate and capacity. Thus standing water will begin to form, and if the water eventually finds a way to move downhill, streams begin to form.",
"Now follow these streams downhill until you get to a resevoir or a lake. As the water finds flat terrain and builds up, it creates a stilling basin that allows even the smallest clay particles that have been previously suspended in the stream's current to settle to the bottom. These smaller clay particles can create a barrier that makes it more difficult for the water to seep into the ground. As a matter of fact, clay is commonly used as a barrier to keep contaminated water or leachate from spreading, such as a landfill.",
"Edit: Thanks for the gold! ",
"Edit 2: There has been quite some hubbub about the void per unit volume statement of sand versus clay and the ability of a clay to hold water. Clay is a peculiar material in that it has varying degrees of arrangements. In its under-consolidated arrangement it is likely that clay will have more voids per unit volume than sand. However, in it's highly over-consolidated arrangement it is likely not so. Imagine you have a deck of cards and you build a house of cards by placing cards in a sort of \"T\" fashion. This is how a clay is arranged in its under-consolidated arrangement. A lot of voids between very thin small plates. Now take that house of cards and collapse it down so they are all laying on top of each other. This is the over-consolidated arrangement. Now keep pressing these cards together with an insane amount of pressure to the point they nearly start to make a brick. This is the highly over-consolidated formation. A clay shale is the result of over-consolidation. ",
"This is not the only reason water is restricted from moving through clays. Because of the small particle size of a clay, the geometry of a clay particle, and what clay particles are made of, clay particles has a tendency to attract water molecules. They will attract water molecules and these water molecules will hold on to the clay particle to some degree, filling what voids are left.",
"The point is not about permeability or porosity but ",
"hydraulic conductivity",
". Hydraulic conductivity is simply how fast can the water move through the clay versus the sand. Sand will have a much higher hydraulic conductivity than under-consolidated clay (~10",
" cm/s) and many orders of magnitude more than a over-consolidated clay (~10",
" cm/s)."
] |
[
"Just to supplement this, the level of water that lies below the ground is called the \"water table.\" "
] |
[
"Just to supplement this, the level of water that lies below the ground is called the \"water table.\" "
] |
[
"If an obese person attempts to lose weight and starts eating healthy, would the plaque on their arteries decrease and/or disappear over time?"
] |
[
false
] |
[deleted]
|
[
"Point of clarification, just being obese doesn't mean that there are plaques in arteries (arteriosclerosis). Being obese only raises the risk for developing plaques. ",
"That said, a healthier diet and weight loss in a person that does have plaques can slowly decrease the natural progression of the plaques. "
] |
[
"http://www.sciencedaily.com/releases/2008/09/080922155916.htm",
"Aspirin. "
] |
[
"There are two major players in the formation of the plaques, cholesterol and platelets (there are others but those are the major two). We have medications that decrease cholesterol (statins, fibrates, etc.) and we have antiplatelets (aspirin). ",
"The body doesn't do anything about them on its own. The plaques form as a result of too much cholesterol and platelet activity, often coupled with blood vessel damage, which can happen as a result of high blood pressure. The body is designed to fix obstructions and damage with platelets. So the short answer is that the body does what it knows how to do but actually makes the problem worse. ",
"Right now there are several means with which plaques can be removed. With the aforementioned medications or with stents, which are tiny metal nets that are expanded to destroy the plaque and improved the vessel's integrity. See: ",
"Angioplasty"
] |
[
"Rude/sexist STEM internship interviewer???"
] |
[
false
] | null |
[
"Ugh, this is awful. I'd post in ",
"/r/LadiesofScience",
". I think you'll get good advice there. "
] |
[
"Thanks! I totally appreciate it!"
] |
[
"That's absolutely infuriating and I'm sorry to hear your experience. Unfortunately, AskScience is not the place for this post. I suggest one of the other biology or biotech subreddits.",
"On the bright side, don't think of it as a failed interview, but as bullet dodged. This sounds like a terrible place to be employed at. I'd look elsewhere immediately. Perhaps leave a complaint to the company president."
] |
[
"Why do human beings and dogs have such a great interspecies relationship? Are there other examples in nature?"
] |
[
false
] |
Can anyone cite research about human beings and dogs and their relationship? Are there other animals that do this? Why? Thank you.
|
[
"The current relationship between man and canine is known as symbiosis. There are different kinds of symbioses: mutual, parasitic, and neutral or commensalistic. In a mutual symbiosis, both partners benefit. In a parasitic, one benefits, and one is harmed. In a commensalistic, one benefits, and the other is neither harmed nor benefits.",
"Symbiosis exists in every niche and nook and cranny of the earth. Without symbiosis, life would not exist. Basically, the relationship between man and dog is analogous to the relationship between you and the bacteria living in your gut. At least, for some people who like dogs.",
"The relationship between man and dog is considered a mutual one, because the dog is gaining food, shelter, caring, etc., while the man is gaining companionship, and possibly other help, like warding off predators (burglars) or helping with hunting, per se.",
"Think of the mimosa fish and sharks, how the mimosa fish feed the bacteria off of the skin of the shark, and in turn, the shark doesn't eat the mimosa like it would other fish (though sometimes it does...whoops).",
"Since you asked for citings, here is an online e-book (Google books) on the relationship between man and domestic animals. Please let me know if this answers your question, and if you may have other questions.",
"Man Meets Dog by Konrad Lorenz, Marjorie Wilson"
] |
[
"I feel like this is a bad example of an interspecies relationship. We domesticated the modern dog. We breed the dog based on traits that we found desirable and I will assume that those dogs that obeyed their owners got breed over those that didn't. This steady path of domestication would lead to a dog with a more natural affinity towards us. I doubt if you ran into a dog's wolf ancestor, you would be able to simply adopt it."
] |
[
"I think you are referring to the Remora Fish...I don't think a mimosa fish is real...unless there is a fish in the mimosas I like to chug down..."
] |
[
"Do carbon-fiber prosthetics give South African runner an unfair advantage?"
] |
[
false
] |
[deleted]
|
[
"At present it is largely a moot point, given that Pistorius himself was too slow to make the individual qualification times - he is not exactly a threat to the likes of Usain Bolt at present."
] |
[
"I'm not sure in this case, but I've read that prosthetics are a huge advantage in long distance races where fatigue plays a role."
] |
[
"I'm not sure in this case, but I've read that prosthetics are a huge advantage in long distance races where fatigue plays a role."
] |
[
"After seeing the images included on the voyager, would we still include similar images and information today?"
] |
[
false
] | null |
[
"The messages on the voyager spare craft are practically a novelty, an amusing side project. Yes it may well last for thousands (millions,billions?) of years floating throughout our universe, but the odds of anyone or anything encountering this probe are so low as to be considered zero.",
"Even if an alien species came across the probe this event would be so far removed from our time scale as to make all information and cultural changes between 1977-2013 irrelevant. ",
"It is more a part of nasa's PR work to ensure public favour with the public in regards to their budget than a serious scientific venture.",
"\"the record is best seen as a time capsule or a symbolic statement more than a serious attempt to communicate with extraterrestrial life\"",
"http://en.wikipedia.org/wiki/Voyager_Golden_Record"
] |
[
"Ah okay thanks for the answer!",
"\"Even if an alien species came across the probe this event would be so far removed from our time scale as to make all information and cultural changes between 1977-2013 irrelevant. \" ",
"This is actually a good point i didn't think of before. ",
"I just thought there are maybe some very important physical findings like the higgs boson, which help at least us humans t understand our perception of the universe."
] |
[
"But IF NASA were to make a new \"golden record\" to ensure public favour, what would have changed as compared to the public favour record of 1977?"
] |
[
"Is it possible for vaccines to spread like normal colds/flu? (Through coughing or sneezing)"
] |
[
false
] | null |
[
"No, vaccines are either fragments of the external portions of viruses/bacteria (i.e. dead bits and pieces), or they're inactivated, meaning that key virulence/reproductive factors have been removed/destroyed/inhibited. Vaccines with dead viruses/fragments can neither spread, nor revert. ",
"Having said that, any ",
" vaccine has a non-zero chance of reverting to the wild type in the host, and in that case they can spread the disease, but not the vaccine. Remember, a vaccine is just a harmless form of the original pathogen designed to elicit an immune response, without causing infection. The virus itself will do the same, but it will also potentially make you ill, so in that sense simply spreading a disease is not spreading the vaccine for that disease."
] |
[
"A few vaccines use a live, weakened form of a virus. For example, the oral polio vaccine. These can potentially spread to other people.",
"See: ",
"https://www.who.int/features/qa/64/en/"
] |
[
"The nasal flu vaccine (discontinued I think?) was also a live attenuated vaccine. ",
"The CDC's info sheet says that people who received it should stay away from the severely immunocompromised for seven days, so I assume there is some small chance it could be spread from person to person."
] |
[
"What is the best way to plot the geometry of multiple intersecting magnetic and diamagnetic fields?"
] |
[
false
] |
Example of some practical questions to tackle are those presented in these demonstrations: Essentially how could you plot the path that electrons are taking when a magnets interact with eachother or when they interact with a diamagnetic. Georgia State University hosts a basic example of magnetic fields which likely we have all seen before: But how do we mathematically plot and predict how a magnetic field will behave when subjected to multiple sources in various amounts of Tesla units and their interactions with diamagnetic material? Thanks Science!
|
[
"A field is a mathematical description as much as it is a physical one--it describes something that has a certain value (or values) at every point in space. Each point is described by a vector, which in the broadest sense is an ordered list of numbers.",
"The most basic kind of vector that we're familiar with in classical physics is a simple one that consists of two numbers--one specifying strength, and one specifying direction, often represented as an arrow with a length indicating strength.",
"The magnetic field can be thought of as consisting of one of these little arrows at every point in space, ",
"like this",
". The neat thing about vectors is that they can be combined linearly, meaning they can be added together and the resulting vector is pretty simple to calculate. Say you have a point in space and two magnets, A and B. If you know what the field strength and direction at that point from A is (call this vector ",
"), and the field strength and direction from B is (vector ",
"), you can find the total field strength and direction at that point by just ",
" + ",
"Because you're adding vectors and not simple numbers, the rules are a little more in-depth but not particularly complicated. Here's a brief overview: ",
"http://www.emfs.info/what/adding/"
] |
[
"I'm not sure what your getting at here, he never said you can ignore one magnet. You add the vectors to find the combined effect from both fields."
] |
[
"Ah ok, I understand the confusion now. The article is worded for general readers so it's a little vague.",
"I think what they mean to say is not the biggest SOURCE, but the source with the largest contribution at that point in space. As you say, distance plays a large role with the inverse square falloff, so in most cases the field with the greatest strength at a given point outweighs other fields."
] |
[
"Is there a cost-effective way to return spent nuclear fuel to a safe \"ore form\"?"
] |
[
false
] | null |
[
"You can downblend fuel, but that doesn't change the total amount of activity it has. And anyway, the fuel itself is not the biggest concern with spent rods; there are lots of fission products produced by the operation of the reactor, which are often far more radioactive than the fuel itself.",
"Just some way to make it so the rods are no longer so radioactive so they could be stored in far safer and cheaper ways.",
"By far the safest and simplest strategy would be to ",
" open the fuel rods and try to separate out the waste. Just leave them as they are, encase them in some kind of shielding medium, and place them somewhere safe for long-term storage. This is already what is done."
] |
[
"Thank you for the insight. ",
"What got me thinking about this was Thunderf00t on youtube made a video where he was walking around in Colorado and just picked up some ore from the ground that was radioactive. I didn't understand why we couldn't chop up the fuel back into such a broken down state that it would go back to that relatively harmless form. ",
"",
"I guess that's what you mean by downblend? ",
"",
"But yeah, it might be just ridiculously dangerous and difficult (expensive) to do. ",
"",
"Anyway, thanks again! "
] |
[
"Downblending is mixing enriched uranium with depleted uranium to make it less radioactive per unit mass, and less able to go critical. Or generally, you could downblend with anything, it doesn’t have to be DU, but that’s what’s common."
] |
[
"Why does fluid in an IV bag infuse faster the higher it is placed?"
] |
[
false
] |
[deleted]
|
[
"The pressure difference between the bag and the iv inlet increases as you raise the bag resulting in a faster flow."
] |
[
"It should be noted for clarity that it's the delta between the bag and the patient. (This kind of implies altitude plays an effect in respect to this question - which it does but not for the purpose of this question.) ",
"The liquid is free flowing and effected by gravity separately to the bag/drip feed line. Therefore a greater \"altitude\" will have more time for gravity to increase it's force; following 9.81m/2",
" "
] |
[
"https://en.wikipedia.org/wiki/Fluid_statics#Hydrostatic_pressure"
] |
[
"Questions regarding the expression and inheritance of the X chromosome."
] |
[
false
] |
This may be outdated or inaccurate but when I was in high school I think we learned that a female has 2 X chromosomes and that when genes that are controlled by the X chromosome are expressed they can be expressed differently depending on which X chromosome is used. It was the current understanding then that there was a 50/50 chance so basically random one X chromosome would be chosen over another. I was wondering what our current understanding of this process is. How does our body "decide" which X chromosome controls the expression of X-linked traits. More specifically I want to know what mechanism(s) are responsible for allowing this either random or controlled expression of both X chromosomes. My next question is about how the X chromosome is inherited. When a female forms an egg she can only pass off an X chromosome. Is this chromosome just a carbon copy of one of her X's or a "mixture" of the both of them?
|
[
"You are mostly correct. Generally, we all have two copies of each chromosome, and there is a phenomenon called genomic imprinting in which one copy of a gene is turned off and the other is expressed. For some genes the paternal allele is silenced, and for others the maternally inherited allele is silenced, and there can be severe consequences if things go wrong. Most genes are not imprinted, though (pretty sure). ",
"The X chromosome is a special case. Since females have two X chromosomes and males have only one, one whole X chromosome is \"turned off\" in each cell of a female. Which X gets turned off is random and is decided early in embryonic development. While the choice is random, it is random in each cell, and so the result is a person with mosaic expression of the X chromosomes throughout the body. That entire chromosome stays turned off for the lifetime of that cell and is passed to its progeny. If you want to know more about X-inactivation, start here and then you can decide where you want to go with it: ",
"http://en.wikipedia.org/wiki/X-inactivation",
"The \"turned off\" genes (or whole X chromosomes) are silent, meaning that the DNA is tightly bound up in proteins (=heterochromatin) and gene expression is prevented, and this is largely due to post-translational modifications (methylation, acetylation) of the histone proteins that package the chromosome's DNA. ",
"For part 2, see the first post. The X chromosomes swap DNA with each other first (meiotic recombination) and then segregate randomly, so each egg gets one. "
] |
[
"That would be the job of Mr. ",
"Xist",
", a huge RNA gene (it doesn't get translated) that gets expressed only from the copy of X that gets inactivated. If I remember right this RNA coats the inactivated x-chromosome, preventing transcription and is required for x-inactivation. How is the inactivated-copy chosen? As far as I know of the literature the consensus is that its randomly chosen by some limiting factor produced from another chromosome. Another player in this game is Tsix, (xist backwards), which is an antisense RNA coded in the same region as Xist but in the other direction. You can read more about it in the ",
"wikipedia page",
" which seems to be quite current.",
"For your second question, yes, the X chromosome can undergo recombination in females, so it will be a mixture of both the copies. The Y can't (mostly). ",
"Further reading"
] |
[
"for your first question, ",
" ",
"this link",
" is a good start. ",
" ",
" should be able to clear it up for you if you don't want to sift through wikipedia.",
"for your second question, it's a mix of the two. during gamete (ova, sperm) formation, pairs of chromosomes line up and undergo ",
"chromosomal crossover",
", so each x chromosome in ova are a copy of one of the original x chromosomes, but with sections swapped out for sections from the other x chromosome.",
"disclaimer: haven't studied this in 12 years, and that was at a high school level.",
"edit: yeah, i was wrong about some stuff. see disclaimer."
] |
[
"How do species evolve new organs?"
] |
[
false
] | null |
[
" 600 million years ago. The sea sponge eventually evolved to communicate between cells so they can pump in unison allowing for an even higher rate of food gathering. This gives rise to the predecessor for muscles, the hydrostatic skeleton which operates by having dedicated cells contract in unison to fill tiny water chambers changing the overall shape. (they started off individual cells that figured out how to contract in unison, from there specialization takes over) While this is the precursor to muscles, they really first started 530 million years ago in the first vertebra Pikaia because bones are needed for muscles to have leverage.",
" 550 million years ago. Flatworm like creaturs still without a circulatory system need a way for food to get to the inside layers of cells since food can only diffuse a few cells through. A generation eventually had a hole in the front which helped survival and it turned into a mouth from there.",
" 550 million years ago, eyes started as cells capable of detecting light levels. Animals that had these cells had better survivability, eventually these simple light detectors evolved into complex eyes once blood supply reached them.",
" 530 million years ago. The cambrian explosion is the first time calcium appeared in the oceans, animals that could deposit it along their spine or on their skin to make shells survive much better and evolves from there.",
" 530 million years ago. The cambrian explosion also was the first time with abundant oxygen in the water. Gills started off as rows of appendages near the head. All it took for this is some cells capable of absorbing oxygen out of the water and into the animal, and any animal with it excelled. Eventually these appendages improved into gills.",
" 375 million years ago. Started off when the fins for stabilizing fish began being used to shuffle around in shallow water. Titaalik was one of the first to use these muscular fins. Bones grew into these to continue to help support the weight of the animal.",
" Fish at first had to gulp air up to maintain buoyancy. The iterations of evolution capable of holding air better survived better, eventually this expanding need to hold air for extended periods without other issues grew into a cavity near the mouth, that pouch got bigger and more complex and more self contained slowly. 100 million years later the circulatory system merged with swim bladders using hemoglobin was able to fill the swim bladder using only oxygen from the blood instead of having to surface. Then 365 million years ago in our ancestor named Acanthostega the swim bladder developed cells capable of sharing oxygen the other direction. Eventually this grew more complex and capable and especially more so when it replaced the gills entirely.",
" 308 million years ago. Developed when the nerve that connects to the jaw bone joint became more sensitive to vibration. Early ears were simply vibration sensing nerves near the surface of the skin where the joint for upper and lower jaw is. Ear drums were not developed until later as this simple development became more complex."
] |
[
"This is very informative, thank you!"
] |
[
"I'm no scientist, but from what I understand a lot of it is random gene mutations combined with adaptability (survival of the fittest).",
"For example, take eyes. Let's say that a species has no eyes. Eventually a random gene mutation occurs that creates tiny, barely formed eyes. Because the creatures with eyes (albeit not vey good ones) can see better than the ones without eyes, they avoid predators and therefore reproduce more.",
"Over time, further mutations occur, changing the shape/color/placement of the eyes. Each time an improvement is made, the trait is carried on (again, because the better eyes ensure better survival, which ensures reproduction).",
"This also works the other way. Random mutations can be detrimental and never be passed on."
] |
[
"Was the Speed of Sound ever considered a theoretical speed limit?"
] |
[
false
] |
This might be more of a history question, but I'm curious about scientific opinion of the speed of sound. The general consensus is, knowing what we know now, the speed of light is the ultimate speed limit of the universe. Before we could routinely break the sound barrier, was it considered a theoretical speed limit? Were people ridiculed for thinking they could go faster than it? Thank you.
|
[
"The 'sound barrier' was never considered a theoretical speed limit while the term was being used. The tips of airplane propellers had been brushing up against it for a long time. Bullets has been breaking it for a long time. The V2 bomb broke it during every flight.",
"The term referred to the many disparate problems that pop up when you pilot an aircraft designed for subsonic speeds (M<<1) at transonic speeds (M~1). Drag increases, your controls could become ineffective or even reversed, shock waves could create aerodynamic loads that cause your plane to break up. It was a 'barrier' to pilots because trying to go past it often killed you. Understanding and solving all these issues and packaging the solutions together into a plane that could be piloted all the way from M=0 to M>1 was a daunting challenge, but one that was met in 1947. ",
"It was kind of like how nuclear fusion is today. The science all says it's possible, but engineering around the practical problems involved is proving extremely difficult. "
] |
[
"This entire post is massively incorrect and totally at odds with actual history. Why did you even post this?",
"Yes, or better, it was considered a practical speed limit, in the sense that it was strongly suspected that large objects travelling faster than sound in air were bound to explode.",
"There was absolutely no way to guess in advance a possible design for a supersonic aircraft.",
"Bullshit. For starters, ",
"the Germans had a supersonic wind tunnel in the early 30s.",
" Secondly, projectile studies had been done for 100+ years on how to shape rifle/cannon rounds. ",
"Look at the cartridge for this 1903 springfield rifle.",
" Parabolic or sharp ogive shapes were used 50+ years before breaking the sound barrier, same nose cone shape as the Bell X-1.",
"On the more pure science front, shockwaves and expansion fans were extensively studied (lots by the germans) in the 20s and 30s (c.f. Prandtl.) ",
"Supersonic nozzles were patented in 1888",
" and used on rockets ",
"in the 1910s and 1920s.",
"The method of characteristics for designing supersonic 2D and axisymmetric bodies (the way the wings and fuselage respectively of the X-1 was designed) was known for 20+ years before the X-1.",
"There also was a brief period of confusion around WWII because measurements of airspeed with the known methods become inaccurate around the speed of sound, since they are based on linear aerodynamics. ",
"However the correction was known by Rayleigh and every other aerodynamicist by at least the 1910s.",
"t was known perfectly well that meteors were supersonic - that's why they explode. It was also known that most muzzle velocities of weapons since the 1800s were supersonic - bullets don't explode because they aren't supersonic for long, and they're also solid metal",
"I have to delete your post. This is way too egregiously wrong on a pretty important topic. Hell it's downright offensive to anyone that's actually studied aerodynamics. I haven't been this annoyed by a wrong ",
"/r/askscience",
" answer since someone said \"scientists don't actually know what creates lift\", and at least that person wasn't a panelist."
] |
[
"This entire post is massively incorrect and totally at odds with actual history. Why did you even post this?",
"Yes, or better, it was considered a practical speed limit, in the sense that it was strongly suspected that large objects travelling faster than sound in air were bound to explode.",
"There was absolutely no way to guess in advance a possible design for a supersonic aircraft.",
"Bullshit. For starters, ",
"the Germans had a supersonic wind tunnel in the early 30s.",
" Secondly, projectile studies had been done for 100+ years on how to shape rifle/cannon rounds. ",
"Look at the cartridge for this 1903 springfield rifle.",
" Parabolic or sharp ogive shapes were used 50+ years before breaking the sound barrier, same nose cone shape as the Bell X-1.",
"On the more pure science front, shockwaves and expansion fans were extensively studied (lots by the germans) in the 20s and 30s (c.f. Prandtl.) ",
"Supersonic nozzles were patented in 1888",
" and used on rockets ",
"in the 1910s and 1920s.",
"The method of characteristics for designing supersonic 2D and axisymmetric bodies (the way the wings and fuselage respectively of the X-1 was designed) was known for 20+ years before the X-1.",
"There also was a brief period of confusion around WWII because measurements of airspeed with the known methods become inaccurate around the speed of sound, since they are based on linear aerodynamics. ",
"However the correction was known by Rayleigh and every other aerodynamicist by at least the 1910s.",
"t was known perfectly well that meteors were supersonic - that's why they explode. It was also known that most muzzle velocities of weapons since the 1800s were supersonic - bullets don't explode because they aren't supersonic for long, and they're also solid metal",
"I have to delete your post. This is way too egregiously wrong on a pretty important topic. Hell it's downright offensive to anyone that's actually studied aerodynamics. I haven't been this annoyed by a wrong ",
"/r/askscience",
" answer since someone said \"scientists don't actually know what creates lift\", and at least that person wasn't a panelist."
] |
[
"Can somebody explain an event horizon in a non technical way?"
] |
[
false
] |
[deleted]
|
[
"When you fall into a black hole it's the region after which you can't get out of the black hole."
] |
[
"Yep so the event horizon refers to exactly that. Events are logged by what we can see so if we can't observe within the even horizon, it's the boundary at which nothing can escape. Referring specifically to light is because nothing can go faster than the speed of light and so if light can't escape, nothing can."
] |
[
"I thought event horizon referred specifically to when ",
" couldn't escape?"
] |
[
"Does external pain have a \"resolution\" based on the density of pain receptors in the body?"
] |
[
false
] |
Similar to the resolution of pixels on computer monitor, is there a resolution of pain on the skin due to the density of nociceptors? If so, why do we feel pain exactly where we get pricked by a needle, for example?
|
[
"There is a test that can be done that looks like a stick with two adjustable pins on it. By poking (gently) the doctor can determine whether you feel one prick or two and the ability to resolve the pricks varies over the body. So the answer to the question is \"yes\" and the second answer is that you don't feel \"precisely.\""
] |
[
"That's quite interesting. What is this test called and what is the purpose of this test?"
] |
[
"Two point discrimination test. Its to determine the sensory density of a particular area, which is loosely resolution. You can do it for different types of stimuli as well, like vibration, not just pain. This image may help:",
"http://dundeemedstudentnotes.files.wordpress.com/2012/04/untitled1.jpg"
] |
[
"How true is it that cell phones can cause infertility if left near a man's testicles for an extended period of time?"
] |
[
false
] |
Along with that, if true, how long would it generally take for you to become infertile? What about more than one phone?
|
[
"the level of radiation put out by a cell phone is incredibly low.",
"nobody realizes it, but cordless phones put out much more radiation than a cell. now granted, you don't carry this in your pocket. ",
"and cell phones put or less and less power all the time. as technology advances, the ability to decipher signals from noise increases, this lowering the required output. ",
"a modern cell puts out somewhere around 1/4 of a watt at full power. in urban areas, they are generally more in the 1/8 watt range. that's nothing. ",
"but, to be on the safe side, carry your phone screen side facing you. nearly all of the radiated power goes away from you."
] |
[
"Plus, it makes the screen less likely to be damaged.",
"Also, don't phones emit really low levels of non-ionizing radiation? Doesn't that pretty much make them harmless to biological life?"
] |
[
"Cell phones (and wifi) emit radio waves. Radio waves are non-ionizing radiation, and only weakly interact with tissue, so they don't cause tissue damage or sterility, even at high power. ",
"There is no possible way for any number of cell phones to cause sterility or tissue damage via radiation, even if you swam in a sea of cell phones. All of the research has proven this."
] |
[
"Can humans pant like dogs to cool off?"
] |
[
false
] |
[deleted]
|
[
"Yes, but the effect would not be as pronounced as it is in dogs because not as much blood flows through your mouth and the surface area is smaller relative to body size. Your saliva would evaporate leaving your mouth cooler, the same mechanism that sweating uses. ",
"I'm not sure about how much cooling this would provide, but I am sure that it would provide some (the moisture loss would not be as efficient as sweating)."
] |
[
"You do lose moisture through your lungs... just take a breath in and exhale on something and witness the condensation. If the air is dry enough and cooler than your body, you would lose some heat this way. Exhale on your hand and you can tell with the heat of your breath. However, the volume of air is not great and the air will quickly become saturated with vapor. The cooler and dryer the air is going, the more heat that will escape. ",
"In the reverse, if the air is extremely hot and humid, sweating (and breathing) will have little effect in cooling your body."
] |
[
"You do lose moisture through your lungs... just take a breath in and exhale on something and witness the condensation. If the air is dry enough and cooler than your body, you would lose some heat this way. Exhale on your hand and you can tell with the heat of your breath. However, the volume of air is not great and the air will quickly become saturated with vapor. The cooler and dryer the air is going, the more heat that will escape. ",
"In the reverse, if the air is extremely hot and humid, sweating (and breathing) will have little effect in cooling your body."
] |
[
"\"72% of Americans this...\", \"\"25% of Americans that...\" Where do these statistics come from, who checks them? No one ever asked me anything..."
] |
[
false
] |
Also what if lets say the surveys are optional, those people who take the surveys are statistically more open minded, etc? Is there a "Department of Facts"?
|
[
"I worked for Statistics Canada for a while as a student job. I would assume in the U.S. data is collected in a similar way. They either randomly phone somebody or send an in-person interviewer. ",
"With a large enough sample size you can make reasonable valid extrapolations as to the larger population. ",
"In Canada certain surveys are mandated by law. You can be prosecuted for non-compliance. Such legally mandated surveys include the labor force survey, which produces public information like the unemployment rate, and the national census. These are fairly reliable and valid, I think ... ",
"(Stats-Can has to my knowledge only ever turned one person over for prosecution. That was a Quebec woman who took a very public stance against doing the census. Usually what they do is just call you endlessly until you're battered into complying, which isn't harassment at all since they have the legal right :p. Almost everyone complies ...) ",
"I will say that there is a whole range of \"optional\" surveys that ask a lot more personal things, which the news media report on I'm sure, including stuff like sexual history, mental health, really nearly anything you can imagine. I wonder just how valid the results of these really are, since the participants are all people who decided themselves to be in the survey (rather than being truly random).",
"Same would go for any private survey from a company or public interest group, which I doubt would have the force of law behind them ... ",
"Edit: **I was told that there are certain mathematical formulas used to correct for expected biases and such or problems with the data, but I do not know what these are or how they work."
] |
[
"As an interesting aside, a few thousand people, if perfectly randomly selected, will be just as representative for a million people as a hundred million people. That is, you don't need a larger sample to have representative results from a larger population. ",
"What this means is that it's highly unlikely for you to be one of the few thousand chosen in their survey. "
] |
[
"For those interested, check out the Wikipedia page on ",
"confidence intervals",
". Using some simple math on your data set, a statistician can say \"I am X% confident that the number you are asking for is between A and B.\" E.g. \"I am 95% confident that the unemployment rate is somewhere between 7.6% and 9.1%.\" As we get a larger number of data points, we can make X% get closer and closer to 100%.",
"If you look at the math on the Wiki page I linked, you will also notice that the total population size is irrelevant to the accuracy of the poll. If 1000 data points is sufficient to provide a given confidence interval for a population of 1 million, it is also sufficient for a population of 100 trillion. This is a little counterintuitive for most people, but is easy to prove in a Stats 101 course. This means that the number of people polled can be surprisingly small (hundreds or thousands), as adagietto said."
] |
[
"What exactly is a linear transformation?"
] |
[
false
] |
This is a basic question I know but I cannot wrap my head around it. I understand the conditions under which a transformation is linear (although I could not tell you exactly what the significance of it is) given here. What I don't get it this. The transformation y = ax + b is non-linear but it is the equation of a line. It seems to me that if you took all of the x points and scaled them then shifted them that should be a linear transformation. Please help me. I stumbled upon this question when looking into the relation between Celsius and Fahrenheit (F = (9/5)C+32). Both Fahrenheit and Celsius scales are linear correct? If they are, how can the transformation between them be non-linear?
|
[
"Linear transformations preserve addition and scalar multiplication (as you've said you already know). ",
"Let's see what happens when we try the transformation f(x) = ax + b. ",
"We need f(x1 + x2) = f(x1) + f(x2)",
"f(x1 + x2) = a(x1 + x2) + b ",
"f(x1) + f(x2) = ax1 + b + ax2 + b = a(x1 + x2) + 2b",
"We need f(kx) = k f(x)",
"f(kx) = a(kx) + b = kax + b",
"k f(x) = k(ax + b) = kax + kb",
"So f(x) = ax + b doesn't meet either of the criteria for a linear transformation. You are right, though, in saying that it describes a line. As you can see from the calculations above, the problem in both cases is the constant term (b). Without the constant, the transformation f(x) = ax would be a linear transformation. ",
"f(x) = ax + b describes an ",
", which is not linear, but does still map lines to lines. "
] |
[
"Homomorphisms are important because they preserve structure. ",
"eh, yes, but I would be careful here. Generally, a particular type of morphism preserves a particular kind of structure when mapping one instance of a category of mathematical objects into another instance of the same category.",
"So, a homomorphism preserves ",
" structure, but not other types of structure (which I'm sure you're aware of and is implied, but I just want to clarify for OP and other less-experienced readers). ",
"For instance, f(x) = 2x is a homomorphism, but it does not preserve ",
" (so it is not an ",
"), since, e.g. the (usual Euclidean) distance between 0 and 1 is 1, but the distance between f(0) and f(1) is 2.",
"Similarly, in ",
", a general linear transformation will not preserve area."
] |
[
"In general, these are called homomorphisms. Homomorphisms have the following properties:",
"f(a#b)=f(a)#f(b)\nf(a^-1 )=[f(a)]^-1\nf(e)=e\n",
"Where e is the identity and # is a binary relation like multiplication or addition.",
"Homomorphisms are important because they preserve structure. (e.g. If we have a group of inputs filtered by a certain property like divisibility, the group of outputs will have the same property.)",
"Think about how linear transformations in ",
" deform the unit square."
] |
[
"Why don't the veins in the inner elbow crease or pinch when you fold your arm?"
] |
[
false
] |
I would think it has something to do with blood pressure keeping the walls of the vein pushed out but there's more. What keeps it intact when you bend your arm?
|
[
"I can confirm that \"wibbly-wobbly\" is the correct scientific term given to the appearance of veins."
] |
[
"Veins do crease and pinch shut. Venous blood-pressure is pretty low, and the walls of veins aren't reinforced like those of arteries. Doesn't really matter, though. Veins are the capacitive vessels of your body. The bulk of your blood is in veins at any given time. ",
"If you look at histological slides of veins and arteries, the arteries are nearly always nice and circular, but the veins are always flimsy wibbly-wobbly looking.",
"It's a bigger issue when you have poor venous return in your legs, and blood pools down there. Generally, you move your arms enough that muscle contraction constricts your veins mechanically and forces the blood out of veins. ",
"But, I guess if you managed to lock your arms in a manner such that venous return became abysmal, you might be able to make yourself pass out."
] |
[
"Two different things. Not only is the course that veins take sometimes convoluted and meandering, but what we are referring to here is the cross-sectional appearance. Cut an artery in twain and it is a very thick, near-perfect circle. Do the same with a vein and it is not nearly as thick-walled and the shape that it makes is only loosely circular. ",
"http://www.sciencephoto.com/image/115288/350wm/C0051126-Normal_human_vein_cross-section._LM-SPL.jpg",
"http://www.sciencephoto.com/image/115283/350wm/C0051121-Normal_human_artery_cross-section._LM-SPL.jpg",
" "
] |
[
"If someone consumed only sugar water, what nutritional deficiency would be the first to cause them major issues or be the biggest contribution to their death."
] |
[
false
] | null |
[
"Long before that, the loss of potassium, then probably sodium would cause death. "
] |
[
"In a normal, healthy adult with no genetic predisposition, insulin resistance may occur in a ",
" hyperglycemic (overfed) setting, but your pancreatic beta cells will compensate by increasing insulin. It is only when there is combined insulin resistance and beta cell dysfunction (may also see concomitant alpha cell dysfunction) will you see the problems associated with chronic high sugar intake.",
"Salt derangements would cause more immediate problems."
] |
[
"This. This question is a variant of the starvation /dehydration question "
] |
[
"Why does restmass prevent things standing still or moving with c?"
] |
[
false
] |
I was thinking about how particles that posses restmass never can reach the speed of light and the same particles can never stand absolutely still, which is implied by quantum-mechanics. Is there a deeper relationship between these two limits for massive particles? I find it interessting that photons (0 restmass) can never stand still and always move at c, hence according to relativity they don't move in time, only in space. Now since particles with restmass are limited to move somewhere between 0 and c, ought there be a particle, maybe similar to the photon, that can never move faster than 0m/s and hence only travels in time, not in space?
|
[
"First off- relativity. ",
"There is one \"axiom\" of relativity- the speed of light is constant in all reference frames. While this is an axiom, it has been experimentally verified, so you don't have to feel bad accepting it. It is from this one axiom that all of the other \"cool stuff\" of relativity comes from- time dilation, length contraction, etc. So, accepting this one axiom, the fact that no particle with mass can go faster than light can be derived. ",
"Now, quantum. ",
"The uncertainty principle doesn't so much say that \"a particle cannot be at rest\" as it says \"a particle does not have a definite position.\" This is a small, but important distinction. It isn't that we don't know exactly where it is, it is that it isn't in any one place. ",
"And back to relativity- ",
"The statement \"an object is at absolute rest\" doesn't even make sense. Relativity says \"all inertial frames are equivalent\" which means that if you and I are both in spaceships, not accelerating to me it seems as if I am at rest and you are moving, and to you it seems as if you are at rest and I am moving, and to a third person we could both be moving and they are at rest. All of these are the right, none of them are wrong. So- as long as you are not accelerating (which we are on Earth, rotating and all) you are traveling \"zero through space, and c through time.\" ",
"Now remember, in all inertial frames, the speed of light must be measured at 'c' so there is no inertial frame which is traveling at 'c' as measured by anyone. 'c' is a very \"special\" speed in that regard. "
] |
[
"This video",
" is an excellent answer"
] |
[
"could you expand on that distinction between being at rest and not having a definite position? I am still under the impression something as an inertial frame cannot truly exist, since uncertainty in position to me sounds just like moving, more specificly brownian motion which is like random acceleration in all sorts of directions. But what i'm more interested in is if maybe there is particle that would be at rest in all inertial frames."
] |
[
"49,999 readers! Because reading AskScience was also cool before hitting 50k!"
] |
[
false
] |
Alrighty, we're officially pretty darn huge by now. 55th largest subreddit, half-way to the big 100,000. Excellent! Since the last State of AskScience post, we have seen a few exciting changes: Slim and improved side-bar, enabled by the nifty that explains our house rules, mission statement, and so on. Improved panel tags! Easier to administer, unlimited slots, a sharp new look, and more colors. We're continuously growing, and that means there are more and more people who are new to . For the most part, I'm happy to see all the traffic. I see lots of really interesting and novel questions, and many really awesome scientific responses, from both old-timers and newcomers. However, the amount of non-science commenting is (again) on the rise, so I ask of you: please think before you submit! Try not to comment if you do not know how to scientifically back up what you are saying. Asking a question, or simply up-or-downvoting is most often a much better way of interacting with and contributing to the community. We're trying to run a valuable service here, please help us keep it as awesome and on-target as it has been in the past. For example: Bad: I'm not a physicist but if I had to guess I'd say that the magnets would fly off... Good: According to my understanding, the magnets would fly off because of the [redacted] principle. Is this correct? Finally, if you have a source handy, please provide it. If you know where your knowledge and wisdom came from, please cite it. Thanks! We're branching out into other social networks, so that everybody can benefit from the wisdom in these pages instead of just redditors. Spread the wealth: and . The concept is that it's a user you can add to an appropriate Google+ circle, or "like" the Facebook page, which adds a feed that links to the best few AskScience questions every day. - short and sweet!
|
[
"Another thing:",
"Don't just post questions like \"explain acid-base chemistry to me like I'm five.\" Ask a specific question, and someone will answer it but will treat you like an adult."
] |
[
"And if you don't understand the answer, you can always ask for clarification on the part you don't understand."
] |
[
"Yes, this is actually a matter that should be addressed, and in a positive light:",
"http://www.reddit.com/r/explainlikeimfive",
" is a really nice subreddit which is meant to give you answers that children can understand. They really make no claims about how accurate the answers are, and that's also not the main point of that subreddit.",
"AskScience is very different: our main point is ",
", and while the scientists here do an absolutely splendiferous job of making themselves understood, I like the atmosphere here to remain as grown-up and serious as it always has been."
] |
[
"Does the melting of the polar ice caps contribute to cooling in the atmosphere, similar to how evaporative cooling works?"
] |
[
false
] |
[deleted]
|
[
"Yes but...",
"the amount of extra heat absorbed this way cannot exceed the amount of extra heat supplied, that would violate the 2nd law of thermo",
"water absorbs more sunlight than ice because water is darker than ice; over time the additional heat absorbed this way will dwarf the enthalpy of melting",
"it sounds like you are under the impression that the polar vortex is an isolated storm that did not exist before this month. The polar vortex is always present; most of the time it is confined to the stratosphere above the north pole. What happened in this case is, a big mass of tropical air rolled up and knocked the polar vortex off its perch. As a result, the polar vortex splintered apart into masses of extra-cold air which drifted down over North America, Europe, and Asia.",
"As for how sea ice melting plays in to that, ",
"the loss of arctic sea ice makes the polar vortex weaker",
", and ",
"the weaker the polar vortex is, the more vulnerable it is to these sorts of disruptions",
". i.e. sea ice melting makes storms of this kind more likely, but probably does not make them colder than they otherwise would have been. "
] |
[
"Polar cooling events are mostly about containment and redirecting cold that already exists ",
"https://www.businessinsider.com/polar-vortex-dangers-why-it-happens-2019-1",
"The main local arctic thermal variable is color. Dark dirt doesn’t reflect heat as well as bright snow and ice. "
] |
[
"I'm in no way able to answer this, but I find it pretty interesting. And just thinking about it: it seems like it wouldn't contribute because ice melts at 32+ F. But the temps in the vortex are well below zero. The ice would have to warm up, then the air would cool the air way back down..."
] |
[
"Given the right conditions and diet, is extremely prolonged life (i.e. significantly greater than 122 years or whatever the confirmed record is) theoretically possible?"
] |
[
false
] |
Someone posted this link in the TIL subreddit, describing a man who allegedly was at least 197 years old when he died, and lived that long by using his knowledge as an herbalist. I'm obviously skeptical to an degree, but I know next to nothing about biology and aging so I figured I'd askscience. My basic question is just whether it is theoretically possible to extend human life anywhere near that much without advanced medical technology that doesn't exist yet.
|
[
"Our telomeres, which break off in parts after each cell division, dictate how many times our cells can divide. They are only long enough to support about 140 years of life. After that, when cells die, they aren't replaced.",
"However, cancer will almost certainly occur during that time. Every time a cell divides, it runs the risk of a mutation occurring in its DNA. The longer you live, the more times your cells divide, and thus the higher the risk for cancer. Cancer cells are immortal; they mutate in a way that expresses the enzyme telomerase, which prevents the telomeres from shortening. One of my professors has some cancer cells that were donated from a woman who died in the 50s.",
"So, even if you somehow avoid getting cancer (and heart disease, and bus accidents, and bad falls...), you can't live much more than approximately 140 years."
] |
[
"You have an odd definition of proof."
] |
[
"The only regimen I've heard of that ",
" achieve meaningful life extension is ",
"caloric restriction.",
" It has been shown to extend the lifespan of many creatures, but the jury is still out on if it can meaningfully extend ",
" lifespan. There are ",
"some signs",
" that it can but nothing conclusive. I seriously doubt any diet could get the kind of increase you're talking about."
] |
[
"Why does water evaporate off of ceramic quicker than plastic?"
] |
[
false
] |
Well I imagine it's because water sticks to the plastic more cohesively. So why? I imagine it has something to do with the electrons. The electrons with H20 and plastic must share some sort of bond that is more cohesive than the random bond-breaking force of evaporation?
|
[
"Most likely because of higher thermal conductivity.",
"When water evaporates, it cools, which makes it less likely to evaporate. On ceramic, the material can transfer heat back into the now cooler water faster, but in plastic it can't, so the water has to wait longer to get enough thermal energy to fully evaporate."
] |
[
"Evaporation happens at the water/air surface, far away from the material the water has contact with. A different surface can influence how a drop of water shrinks, which has a small effect on the surface tension, but I would be surprised if that is relevant. The different thermal conductivity is a more interesting point."
] |
[
"As they said; thermal conductivity. ",
"Water binds to itself much more strongly than to either a plastic or ceramic surface, and it's the water-water bonds that are being broken in evaporation. As things evaporate the liquid cools though, slowing further evaporation, so all other conditions being equal (temperature, humidity, air pressure) the rate of evaporation will depend on how fast heat will flow to the liquid to compensate for the evaporative cooling.",
"However, even if the water molecules ",
" bind much more strongly to the surface than to each other, all that'd mean is that the evaporation would leave a single-molecule layer (monolayer) of water behind. Which is a dry surface as far as we can see and tell at the human scale. Under ordinary conditions there's usually some water molecules stuck to most 'dry' surfaces around you.",
"(Hence why laboratory glassware needs to be heated in an oven before it can be used for chemistry where no water can be present, such as Grignard reactions)"
] |
[
"Are certain speech impediments restricted to particular languages? eg: lisps and English?"
] |
[
false
] | null |
[
"I would say yes.",
"For example, a \"lisp\" commonly refers to misarticulation of ",
"sibilants",
". If a language does not have sibilants, its speakers obviously won't have a lisp (dunno about L2s though...). Examples of languages without sibilants (or voiceless fricatives, in fact): ",
"Hawai",
", ",
"Dinka",
", ",
"Lango",
", and almost all ",
"indigenous languages of Australia",
".",
"Another example is the inability to articulate an alveolar tap [ɾ] or trill [r]. People with that disability which speak a language with such a sound will often eplace it with something else, e.g. [ʁ]"
] |
[
"If, by \"lisps\" you mean \"replacement of one sound with another\", then the answer is \"no\". ",
"A \"lisp\" commonly refers to ",
"any articulation problem",
" involving ",
"sibilants",
".",
"French, for example, has the word susseyement[...], which refers for the impediment where /ʃ/ (\"sh\" as in \"ship\") is replaced by /s/ (so chien becomes sien)",
"The page you linked actually says ",
"Le susseyement [...] est ",
". Ce vice de prononciation consiste aussi à donner au « j » le son du « z », au « ch » le son du « ç »",
"(emphasis mine)",
"this is distinct from the English lisp that replaces /s/ with /θ/ (\"th\" as in \"think\") and /z/ with /ð/ (\"th\" as in \"this\")",
"I doubt that people with lisps actually merge these phonemes, for two reasons: 1. The \"lisped\" /s/ and /z/ are not necessarily actually [θ] and [ð] (i.e. they are phonetically distinct from /θ/ /ð/). See also ",
"here",
". 2. Even people who produce these phonemes phonetically exactly the same, I mean it's not like they don't ",
" the difference between e.g. [s] and [θ], they just can't produce the sounds. So assuming that they somehow ",
" is misleading.",
"which does not occur in French because French does not have /θ/ or /ð/. The same is probably true in other languages as well.",
"Huh. Interesting. There are ",
"German speakers with a lisp",
", but German doesn't have /θ/ or /ð/."
] |
[
"If, by \"lisps\" you mean \"replacement of one sound with another\", then the answer is \"no\". One way of answering this question is to look at whether other languages have come up for words for speech impediments for their own speakers. French, for example, has the word ",
" (also called ",
" and ",
"), which refers for the impediment where /ʃ/ (\"sh\" as in \"ship\") is replaced by /s/ (so ",
" becomes ",
") and /ʒ/ (the \"zh\" sound in the middle of \"vision\" and at the end of \"beige\") is replaced by /z/. This is distinct from the English lisp that replaces /s/ with /θ/ (\"th\" as in \"think\") and /z/ with /ð/ (\"th\" as in \"this\"), which does not occur in French because French does not have /θ/ or /ð/.",
"The same is probably true in other languages as well."
] |
[
"How does one represent concepts, such as looping, stopping, storing, etc through electric signals (created by binary)"
] |
[
false
] |
[deleted]
|
[
"The most basic programming languages are ",
"machine languages",
", which define numerical codes for very basic commands. In a machine language, each instruction is some fixed number of bits long, determined by the processor (",
"). Those bits are then broken down into the opcode, which tells the processor what to do, and then several references which tell the processor which values to do that operation to.",
"So when a processor goes to execute the next command in a program, it gets the command, feeds the opcode into a piece of circuitry that sets the value of various control bits based on the value of the opcode, then it pulls the values out of the specified registers, does some math and stores the resulting value in a target register.",
"Of course, this is a simplified description and many commands don't follow this exact model, but the idea is basically the same. To go a little more in-depth, I can tell you that branching works by performing a test on a given value which returns either 0 or 1. Then, depending on this value, the next instruction it fetches is either current instruction + 1 (as usual) or the branch target instruction."
] |
[
"In a machine language, each instruction is some fixed number of bits long, determined by the processor (this is basically what the \"64-bit\" refers to when we say \"64-bit processor).",
"When we say 64-bit processor, that number can refer to a number of things (e.g. virtual address size, data bus width, size of accumulator and/or general purpose registers), but rarely to the instruction size. Moreover, few processors have such ",
"large instruction sizes",
", and not all instruction sizes are fixed. Fixed instruction size is a property of ",
"RISC architectures",
", while ",
"CISC architectures",
" have variable address sizes."
] |
[
"The size of the accumulator and other general purpose registers might be a better indication of how many bits the processor is. The 8088 for example had a 20 bit address bus and an 8 bit data bus, but was a 16 bit processor."
] |
[
"Does a hot metal bar lose heat in empty space?"
] |
[
false
] |
Afaik heat is the cumulative kinetic energy of the metal atoms. If it does get cold, how is this energy lost? There is no matter to transfer this kinetic energy to. I suspect the bar may radiate energy as the (various kinds of) light. But how exactly is an atom's kinetic energy converted into light? The only processes that I know produce photons are nuclear changes and electronic jumps.
|
[
"Yes, due to radiation. It doesn't lose heat due to conduction or convection, as it would in normal circumstances."
] |
[
"It can become excited in a collision with another atom and then emit radiation as it de-excites."
] |
[
"http://coolcosmos.ipac.caltech.edu/cosmic_classroom/ir_tutorial/images/irbody.jpg",
"keeping that in mind, you can understand how will the metal object 'lose' it's heat in space. if u would look at it with infrared goggle, u would see it as red and turning to blue"
] |
[
"Do we have vestigial psychology, just like we have vestigial organs like our appendix?"
] |
[
false
] |
Felt like a really stupid question to ask but wanted to know if there is any real data on it, or if im just not looking at it from the right angle.
|
[
"Insofar as we share emotional responses with \"lower\" order sentient beings, yes. Human brains have different components you can sort of think of as stacked on top of each other.",
"One of the more basic components is the amygdala. It functions similarly to the entire brain of reptiles. We experience fear and anger at a basic level the same way reptiles do (not that there isn't also \"higher\" brain activity that doesn't correspond to what a reptile experiences).",
"It's not 'vestigial' in the sense that we still use it. But it is part of an evolutionary progression that reaches back at least as far as the dinosaurs.",
"In another sense, human intelligence appears (at least superficially) to be adapted to environments we generally don't live in any more. People like to assume that we are rational logic processors whose overall behavior has to fit into a comprehensible order of some kind.",
"Instead, we're pattern-matchers and risk-avoiders. The amount of time necessary to reason out an accurate opinion on whether a rustle in the grass is a tiger or a bird based on observation and deduction would leave you no time to avoid the tiger. So we see the rustle -- it closely resembles things we've experienced or things we've been taught to fear, so we assume it's bad, and escape. Most of the time we're escaping something harmless.",
"Especially in the modern world. That same process of figuring out \"What does this experience resemble that I remember or have been taught?\" applies to the way ordinary people evaluate probability (gambling, stock markets, etc). \"The last time I made this and this and this bet on the roulette wheel, I won a bunch of money. So this time, doing the same thing will lead to a similar result\"",
"But the pattern-matching process is hurting more than helping, in situations where actual probability comes into play."
] |
[
"I would say no solely in the fact that if we were dropped in a situation that is outside the norm of our day-to-day lives are primitive like old school ways of thinking kick in. It's like fight or flight, how often is that get triggered? But when it does it's life-saving. I think the brains a lot faster and adapting and evolving then our physical bodies are, so there's probably not a lot of vestigial stuff if any"
] |
[
"The closest things I can think of are some infant reflexes like the Moro reflex. A speculative idea is that it helped baby primates grab their mothers when at risk of falling. Humans don't climb trees of course.",
"https://www.urmc.rochester.edu/encyclopedia/content.aspx?ContentTypeID=90&ContentID=P02630",
"This reflex drops out after a few months in a typically developing infant.",
"There are many aspects of psychology that are not well adapted to the modern world e.g. craving for lots of fatty sweet food which makes us overweight; or the stress response when doing exams and the like. But these are not so much vestigial as mismatched to the current environment."
] |
[
"Is there a statistically significant difference in any variable depending on the season of the year you were born?"
] |
[
false
] |
Like a stronger immune system? A higher likelihood of having certain traits?
|
[
"This is more sociological than biological, but there is something called the Relative Age Effect where the arbitrary dates placed on age groups for youth sports leads to children born towards the earlier dates to be more successful and likely to become professional than the kids born later in the date range. ",
"For example if you have a youth hockey league with teams based on kids born in each year, starting with kids born in the year 2012 (just for example) the kids born close to January will have about a year's growth mentally and physically more than the kids born in December, and will see more playtime and get more experience in games. The effect diminishes with age, for example ",
"this study",
" found very little evidence of the effect among Canadian NHL players (contrary to the popularly cited book Outliers by Malcolm Gladwell, which brings it up)"
] |
[
"There was a study done in Africa where they monitored the life span and health of individuals. They found that people lived longer when they were born in a certain time of the year. The later concluded that this was due to the harvest been present when the mother was carrying the child so nutrients from veg and other sources were absorbed in the early stage of pregnancy"
] |
[
"Seasonality is a strong predictor of air pollution (its higher in winter) and we now know that pregnant mothers exposed to air pollution can transfer some of it to their developing babies, so in a round about way, season can potentially change things like neurodevelopment through air pollution as a mediator."
] |
[
"Can neural impulses (electrical signals) in a human body be connected to a computer?"
] |
[
false
] | null |
[
"Sure. See for example braingate."
] |
[
"So would it be possible to store memory, think faster, and process information using a computer connected to our brain? Ik this sounds ridiculously sci-fi but is there potential?"
] |
[
"We don't know how a lot of information is encoded and stored. For many of these applications, what is happening is that a person is able think of something that produces a clearly identifiable signal. We can then pair that signal to some response in a computer. But it's not necessarily that we know what the person is thinking about, we are just saying \"when we see this pattern, do X\". ",
"There are certain brain regions that are organized in a fairly straightforward way like motor and somatosensory cortex and we can actually know things like if this group of cells is active then the person is moving or is thinking of moving their arm. ",
"However, all of this recording of neural activity is very different from sending signals ",
" the brain. That's a whole other can of worms and we can't do that very well."
] |
[
"Why are everyone's voices different from each other?"
] |
[
false
] |
I mean since pretty much everyone have the same designed organs and such, why are our voices all different?
|
[
"Everyone has ",
"vocal folds",
" which generate roughly sawtooth shaped buzzy tones. We can control the frequency of these tones to a greater or lesser range with a bit of practice and training.",
"On their own, the sound made by these folds would pretty much sound the same for everybody in the world, but the sounds are filtered by the mouth and nasal cavities and resonances in the skull which changes the level of some frequencies and harmonics.",
"The greatest difference though, is the personal control we make of the lips, teeth and tongue which create all the different vowel and consonant sounds. This is a complex learnt behaviour and involves a lot of imitation of our peers and family to create regional accents.",
"If you think about a good impersonator, you will realise that there is very little physical difference in the vocal tract sounds between individuals. ",
"One Elvis sounds pretty much like another",
" (although you can always recognise the real king)."
] |
[
"Is it possible for everyone to be a good impersonator? Or do you have to be lucky enough to have a more neutral resonance in your skull cavities and stuff?"
] |
[
"The vocal folds, explained previously, buzz. On their own they sound like a kazoo. These, along with the cartilage surrounding them, vary in size, rigidity, and capability. Trained singers have a very dense, calloused, and durable set of folds. Smokers have a destroyed set after heavy use. Alcohol users have theirs changed as well. This means vocal folds are varied both genetically and due to environmental factors. ",
"The emphasis though is more on the vocal tract as a whole.",
"http://en.m.wikipedia.org/wiki/Vocal_tract",
"The differences in humans of arm length, hair color, and head shape also manifest in the different parts of the vocal tract. By modifying the different parts, you are altering the sound. This is exactly the same reason that a saxophone sounds different than a clarinet. Both have a vibrating reed at their source, but their material they are made from, overall shape, and length vary the sound a lot."
] |
[
"Why don't the heavier elements fall in to the center when solar systems are forming?"
] |
[
false
] |
As the title says, why is it that hydrogen goes to the center when solar systems are forming?
|
[
"there wouldn't be fusion happening in the core, would there? ",
"Well, fusion is happening in the sun, isn't it? So the assumption that there would be no fusion at all, isn't correct. You're right however, when comparing two stars of the same mass with different metallicities. A star with less metals will have a higher compression, thus it will produce more energy and be brighter than the star with same mass but more metals. ",
"So the reaction rate decreases with higher metallicity. The sun is a population I star with high metallicity. Roughly 2% of its mass do not account to hydrogen and helium, but to heavier elements such as oxygen, carbon and iron. 2% is pretty small compared to the overall mass, but the sun accounts for 99,86% of the solar systems mass. That means, the 2% are still 14 times more mass than all the other stuff together. "
] |
[
"They do. The sun holds more heavy elements than the mass of all planets combined. Furthermore, the sun was at the center of the primordial nebula. The huge amount of mass gathered even more mass and so it gorwed. The planets on the other hand formed from the leftover after the sun has already formed. The reason why the earth and other inner planets are rock is, that surrounding gas was blown away by the solar wind. Further out it was not as strong as in the inner solar system, so the gas giants could collect alot of gas. "
] |
[
"But stars are made up of hydrogen, helium and only trace amounts of everything else. If there was that much of the heavy elements, there wouldn't be fusion happening in the core, would there? "
] |
[
"Can diesel explode due to suction rather than compression?"
] |
[
false
] |
Could suction pressure be enough to set off an explosion if enough oxygen was mixed in the chamber?
|
[
"Not really. Diesel requires compression to raise the pressure (and as a consequence the temperature) of the air to their combustion levels. This is why the pistons exert pressure on the gas in the cylinder. The vacuum you'd create by applying suction to this gas would neither compress nor heat it, therefore combustion wouldn't occur without some type of ignition source."
] |
[
"No. Inside an engine diesel ignites because of the increased pressure of the compressed air. ",
"\"Suction pressure\" is negative pressure. If pressure decreases, air temperature goes down and therefore there is nothing to ignite the fuel. "
] |
[
"Suddenly decreasing pressure will reduce the temperature",
"You would have invented a way to chill diesel fuel (mostly useless), and if you try a different fluid such as freon and loop the fluid around so you compress it outside your house (producing heat) while allowing it to expand inside your house near a fan (sucking in heat) you will have reinvented air conditioning."
] |
[
"How complex of a computer could someone build by hand?"
] |
[
false
] |
Basically, let's assume all the giant manufacturing plants in the world shut down. Humanity is limited to building things using relatively simple tools, with the most complex being something like a soldering iron. If we limited the computer to being, say, the size of an average car, how complex could someone make it?
|
[
"This fellow built a computer out of relays. Relays are nothing more than electromagnetic switches, and can be built by hand from basic parts such as wire, nails, and metal sheet.",
"http://www.electronixandmore.com/project/relaycomputertwo/index.html"
] |
[
"There are current projects where hobbiests are making microchips with pretty low-tech tools. ",
"http://code.google.com/p/homecmos/",
"\n",
"http://hackaday.com/2010/03/10/jeri-makes-integrated-circuits/",
"\n",
"http://hackaday.com/2010/05/13/transistor-fabrication-so-simple-a-child-can-do-it/",
"with that tech, we get a desk sized 386 with enough work, but check this:",
"http://code.google.com/p/homecmos/wiki/SQUIDfab",
"While the experiment was a failure, the basis for a quantum computer was functioning for a while."
] |
[
"Hmmm? You can build a processor from individual transistors. Unless the premise is that transistors no longer exist, in which case vacuum tubes wouldn't either. "
] |
[
"How can a computer program can prevent the computer from \"knowing\" its code? (like closed source programs)"
] |
[
false
] |
In non open-source programs, you can't check the source code from the program, but it still executes and runs on the computer. Shouldn't there be a way to know what that code is? From what I understand it works like a blackbox, you feed it input and it gives outputs acording to the code. But how can it prevent me from checking the code?
|
[
"There are ways of viewing the code of an executable program, using tools called decompilers, disassemblers, or debuggers, for instance. The thing to remember is that you won't be looking at source code, but rather machine code. Unless it was intentionally compiled with debugging symbols intact , you're not going to get anything like clean variable and function names. ",
"There are also many anti-disassembly techniques in common use these days (they overlap often with security techniques to avoid stack attacks and the like, too) , like randomized memory addresses and even checks for known debuggers that will cause the execution to abort. "
] |
[
"Just to add to this. Op you could view the machine readable code inside an executable with a text editor, but it would just look like a bunch gibberish. If you had a program that displays the hexadecimal interpretation of the file you might be able to reverse engineer it, but it would take a lot of time and effort. The thing is you could never really figure out exactly the human readable source code since there might be multiple ways to express the same thing in a language, and you would probably lose things like variable names since the computer doesn't need that sort of information."
] |
[
"Just to add to this. Op you could view the machine readable code inside an executable with a text editor, but it would just look like a bunch gibberish. If you had a program that displays the hexadecimal interpretation of the file you might be able to reverse engineer it, but it would take a lot of time and effort. The thing is you could never really figure out exactly the human readable source code since there might be multiple ways to express the same thing in a language, and you would probably lose things like variable names since the computer doesn't need that sort of information."
] |
[
"Why does my nose get all runny when it's cold outside?"
] |
[
false
] | null |
[
"Your nose serves two purposes: to warm and humidify the air. When it is cold and dry outside, your nose works really hard to add moisture to the air coming in through your nose, however some times some of that fluid may start to run out of your nose. Additionally, when breathing out through your nose, the warm and moist air from your body hits the cold air and causes the moisture to condense on the outside of your nose, further increasing the amount of fluid running out of your nose."
] |
[
"In addition, the cilia (little hair-like projections) that beat to move the mucus (produced in the nose) away fail to work in the cold, stopping the natural mucus flow and causing it to drip out instead."
] |
[
"The nasal cavity is highly vascularized, that is, it has tons and tons of blood vessels, and they are relatively close to the surface. That's why medications (or drugs) taken through the nose work relatively quickly. Like someone else said, one of the nose's functions is to warm and moisturize air as it enters the body, and when it's cold outside, it has a harder time warming it to physiologically acceptable temperatures. The nose uses the heat from the body, carried by the blood, to warm the air. So when it's cold outside, you get increased blood flow to the nose, which causes an increase in capillary hydrostatic pressure, which causes more fluid to leak out through the capillary walls and into the inside of your nose. ",
"Have you ever noticed that when you're sick and you have a stuffy nose, it seems like only one side of your nose is clogged? And then it randomly switches sides? That's due to the large venous plexuses called \"swell bodies\" that are really close to the surface and function to occlude the nose to give it time to re-moisturize after the air has sucked all the moisture out of it. When those swell bodies swell up, fluid leaks out and you get a run. Hope this helps a little. "
] |
[
"Would you do more work on Mars or less?"
] |
[
false
] |
Watching the film The Martian, we see Mark (Matt Damon's) character breathing heavily after shoveling some dirt. With the low gravity field on Mars should he be that fagged out?
|
[
"Acceleration is force/mass, so as long as mass is constant, the two are directly related. In fact, the integral of acceleration is velocity.",
"But more to the point, lifting a mass requires an acceleration. By the definition of work, moving a body against a gravitational field requires work."
] |
[
"It requires work against gravity and also work against intertia. Have you taken dynamics or just statics? The force transmitted by the shovel to the dirt is eccentric. It is off-center thus requires both a linear acceleration component and a rotational component.",
"My argument is that the work required for both these accelerations are much higher in order of magnitude than the work against gravity."
] |
[
"Have you taken dynamics or just statics? ",
"Analyzing dynamic problems and evaluating forces is what I do for a living. If you work out the kinematics, you'll find that the moment required to rotate the shovel scales linearly with gravity. So presuming the geometry of the two situations is identical, the factor is .38."
] |
[
"How do climate scientists correct for historical date from less precise instruments?"
] |
[
false
] |
I'm not a climate change denier; I accept the broad scientific consensus. There has been one bothersome argument that I can't find specifics on how it is quashed. I originally heard it from that bastion of facts, Dennis Miller, when he said something to the effect of "How can we possibly trust the accuracy of the data from the 1800s and early 1900s? There's no way their thermometers could have been accurate enough to properly record the global temperature." So my question is, given that instruments have been made more precise over time, how does one correct for the possibility of imprecise historical data? Is it as simple as an ever-decreasing error bar? (mods: If this question has been asked and answered, please direct me there before deleting this post. I did try to find a thread first.)
|
[
"Your question come from the premise that old (1800s and 1900s - which is in reality not very old for weather and climate science) instruments are less precise. But, as I see weather sciences, it's not really the case. ",
"Actually, we can trace back the invention of alcool and mercury-based thermometers somewhere around 1740. Since there, and as these thermometers were calibrated on physical properties of water (which are somehow immuable at controlled conditions), reading from them are accurate and precise. The more limiting factor is the fact that these data should have been noted and archived properly. It's obvious that temperature models are based on less meteorological stations in 1800 than today, this limit the resolution of them. But where data exist, they are accurate enough and I think there's no need to correct them. "
] |
[
"I'm not sure question of OP concern this kind of data. As I read is, he talk about climate for the 2 past centuries (1800s - 1900s). ",
"On of the interests in dendrochronology is modelling of much older climatic trends (in the order of 10,000 B.P. and even more). To achieve this, scientists rely on old specimens of wood (fossils, sub-fossils, old constructions, art, furnitures) and use a technique call inter-datation to build long series of data. The purpose is to model climatic ",
" which is sure not as precise as digital thermometers, which is not the goal. "
] |
[
"I'm more familiar with ocean measurements than atmospheric. From the late 1800s to circa 1970s, ocean temperature measurements were taken with high quality mercury thermometers which could routinely measure to an accuracy of 0.05°C and in the right hands could be as accurate as 0.01°C. [",
"source",
"] So the accuracy of individual measurements is not much of an issue. The larger problem is sparse sampling and the paucity of data from 100 years ago. The biggest organized collection of ocean data in the 1800s was the ",
"Challenger Expedition",
" which over the course of 4 years collected 362 profiles of temperature from the world ocean. Today the ",
"Argo float program",
" collects a comparable amount of data ",
". So the biggest issue when trying to detect temperature trends is to be conscious of how the sampling statistics have changed over time. The magnitude of ocean warming (0.59 °C±0.12 over 135 years) is large enough to be statistically significant despite the sparseness of early data. [",
"source",
"]."
] |
[
"Does the growth rate vary between fingernails?"
] |
[
false
] |
[deleted]
|
[
"Since fingernails actually grow with a rate proportional to the to the length of the terminal phalanges (outermost finger bones) [",
"Source",
"], yes, your nail on your little finge should grow a little slower.",
"With the same reason, some people's nails are going to grow faster than nothers'."
] |
[
"Weird, I always assumed that the thumb nail would grow slower, but the outermost finger bone there is longer than on the other fingers, so it must grow faster. Well, TIL."
] |
[
"Some do grow faster than others, and the older you get the slower they grow. "
] |
[
"Is there a term for the set of valid 'letter groupings' in a language that correspond to one or more words?"
] |
[
false
] | null |
[
"A list of heterographs. See ",
"this",
" wiki page."
] |
[
"That's almost what I'm looking for, but it appears to exclude words that only ever have one meaning (e.g. \"logarithm\", as far as I know, has no homonyms or heterographs, yet is included in this hypothetical list because it is a valid 'ordered group of letters' that can make up a word)."
] |
[
"Perhaps I'm not entirely sure what you are asking then. Why would a list of English words include multiple copies of the same word? You could just say a \"a list of all English words such that each word appears only once on the list (i.e. homographs appear only once)\""
] |
[
"Are there any adverse effects that can result from drinking fluoridated tap water?"
] |
[
false
] |
I ask because I have a somewhat sketchy landlord who tends to buy into all these conspiracy theories. The other day my roommates and I ran into him downtown where he was protesting the municipal government's decision to fluoridate the tap water. He subsequently advised us not to drink the tap water because we'll end up with mutant children. I was curious to see if there is any legitimacy to his claims.
|
[
"There really are no proven dangers. Throughout the years many a person has claimed that fluoride in the water leads to more children with Downs, more bone cancer in males and thyroid problems, along with a few hundred other complaints. None of these claims have been backed by any meaningful research, a few relied on animal (rat) testing, but the testing was flawed. "
] |
[
"At the concentrations used commonly, there is no danger to a healthy person. ",
"http://en.wikipedia.org/wiki/Water_fluoridation_controversy#Safety",
"There does, however, seem to be a real reduction in tooth decay."
] |
[
"Technically speaking, the wiki page is off on average, daily ingestion amounts. It fails to take into account fluoride present in foods, watered with fluoridated water. But, still not really an issue. ",
"The wiki article also doesn't address the ion interactions that we get with fluoridated water in most communities. Many places uses cheaper fluoride salts or compounds, which can react with the clearing agents (things like aluminum to make your water less murky). Again, not really a big deal but something that people think is the end of the world."
] |
[
"How much alcohol is safe to drink while pregnant? Is it safe at any time during pregnancy?"
] |
[
false
] |
From a speech I saw from 2 professors from Duke (Bloom and Schwartz-Bloom), many physicians and people still have the notion that drinking during pregnancy is okay in moderation. You can see for yourself the recent discussion on this topic (which severely lacked recent evidence). [1] However, guidelines within many countries say no amount of alcohol is safe during pregnancy. [2] I believe these recommendations are based on a rat study that showed neurodegenerative effects on rats during development. [3] What does askcience think? (Please no anecdotes about my mom drank and I turned out fine) Sources: [1] [2] [3]
|
[
"http://www.bjog.org/details/news/2085661/Danish_studies_suggest_low_and_moderate_drinking_in_early_pregnancy_has_no_adver.html",
"http://news.discovery.com/human/alcohol-drinking-pregnant-women.html",
"Telling someone to drink nothing is just so much easier then saying moderation may be fine. Mostly because the people who tend toward dangerous binge drinking don't see themselves as having a binge drinking problem. They may considerate it\"moderate\". "
] |
[
"From what I gathered, the UK study surveyed women when the babies were 9 months old. That casts big doubt on the accuracy of the data used here."
] |
[
"Most of the problems will be apparent when the child is born, especially the facial malformation associated with FAS. However there is also heart defects, spinal defects and mental defects associated with alcohol consumption during pregnancy. And even though most children will turn out okay you should never risk it. The consensus amongst my professors are: Pregnant or planning to become? Then no alcohol for you ",
"There are studies showing that diabetes, drinking during the pregnancy and obesity is linked to several birth defects. ",
"One of several studies",
" I have read during my teratogenesis course in medicine. ",
"Also ",
"FAS"
] |
[
"Pterosaurs are my favorite class of dinosaurs. Quetzalcoatlus had a wingspan of 40 feet and was the largest flying animal to ever live. Are there any theories on how it actually managed to achieve flight?"
] |
[
false
] |
They are, to me, probably the most fascinating animal that there's ever been. They were . Their size is actually comparable to small planes. But of course, in order for them to actually be able to fly, it would have required major anatomical adaptations. They had to somehow be lightweight despite being such an incredibly large animal. I imagine that they must have been incredibly fragile. Is there even any indication that they were capable of powered flight? Did they just live their whole lives on the tops of huge cliffs?
|
[
"The big pterosaurs are indeed incredible animals. Here's the TL;DR of the articles I'm going to cite in this post.",
"Azhdarchid pterosaurs were huuge. They could ",
"look a giraffe in the eye",
" is how huge they were. Probably weighed in at a good 250 kg. In terms of ecology they were probably ",
"something like giant storks",
" in behavior, capable of walking around on the ground using their long, stiff necks and long bills to reach around and pluck prey from the ground. They seem to have been capable walkers, probably better than many other pterosaurs on the ground. They have fairly short wings for their size, which means they weren't specialized gliders. ",
"This plays into one of the reasons pterosaurs could get so big in general: unlike in birds, where hind limbs have to scale up because birds launch standing on their hindlimbs, pterosaurs seem to have launched using ",
"all four limbs",
" (see ",
"this video",
"). This means that instead of having to carry around useless heavily muscled hindlimbs in flight, they could use their forelimbs both to fly and to boost themselves off the ground, getting double use out of the muscle and saving weight. ",
"Check out pterosaur.net, also, for lots of info "
] |
[
"The strongest argument I can make for them being flyers (Petrie, haha) is that evolution and natural selection does not support redundant characteristics. Q. northropi had all the physical characteristics to be a flyer. It's physiology is similar to many current long ranging birds like ",
"albatross",
" and ",
"frigatebirds",
". Their wingspan is drastically bigger in proportion to their bodies and their wings are thin and streamlined, perfect for gliding long distances with minimal effort. If they could not fly, growing such gigantic, well defined wings would be an enormous waste of energy, so natural selection would not allow it to persist. They also have a beak that does not fit together perfectly. The lower jaw has a bit of a downward curve, which has led some people to suggest they were like ",
"skimmers",
" in their hunting methods. ",
"The strongest evidence, however, came with modern technology and biomechanical modeling. After factoring in weight, wingspan, aerodynamics and body structure, computer models deemed northropi capable of flight. It was estimated that they were capable of flying up to 80mph, to 15000 feet and that they could stay airborne for several days. These facts are also true, curiously enough, for the birds that it resembles most that I mentioned earlier (except altitude, that varies). As for why they have such well developed legs, if I had to guess, I'd suggest it had something to do with the method of takeoff. Large birds cannot just leap into the air, they need a running start, wind help, or a cliff to jump of off (or all of them). Since pterosaur wings are part of their walking mechanism, I don't see them being able to really get much of a running start. They may have needed better legs with which to jump and propel themselves into the air. But that last part is just a guess."
] |
[
"Yes, I know. But it's the only way I know at least to indicate to anyone else reading that they existed ",
" the dinosaurs, if that makes sense. Just like how people may not know that there's a difference between Pterosaurs and Pterodactyls."
] |
[
"What would be the scale limits of Nano Quadrotors (flying robots) while maintaining their intended function? Videos inside."
] |
[
false
] |
[deleted]
|
[
"Nano is a complete misnomer... ",
"The smallest you can make a Quadrotor is dependent upon the size of the motor to drive all the propellers. So the question is how much money are you willing to spend? You could very well have a very tiny motor, but it would need to provide enough lift to support the weight of the battery, wireless receiver, circuits and frame and whatnot which can be done if you use very lightweight materials like carbon fiber and low density batteries.",
"You could probably do some ballpark calculations, find a motor, find the power it needs to work (find the mass of the lightest battery that can supply that voltage and current) and google the formulas for the force 4 rotors (never taken any fluid dynamics/aerodynamics courses so i can't tell ya) would exert with that one motor supplying the energy. If that force is greater than the combined weight of the frame, battery, motor etc, then it'll work."
] |
[
"Honestly, i'm pretty sure it becomes primarily software dependent in diverse weather conditions assuming you have a good enough quadrotor. All you need is good software and gyroscopes to make the adjustments when the wind tips it over. As for rain, there are a lot of commercial hydrophobic sprays available now i'm sure you could apply to make it pretty damn waterproof.",
"The problem with using them in swarms like they use in a lot of the youtube videos is they don't tell you there are cameras EVERYWHERE. These cameras are the ones guiding them. Your construction ground would have to be littered with cameras to guide the robots to do whatever you want to do. Not very practical assuming a large area."
] |
[
"The limitation is having world sensors integrated onto the vehicle. GRASP only has their vehicles flying in a room with IR sensors mounted on the walls. "
] |
[
"How do we know that the Mariana Trench is indeed the deepest point on earth, if we’ve only explored/mapped 15% of the ocean floor?"
] |
[
false
] | null |
[
"We've only looked at a little bit of the ocean floor in detail.",
"We've seen the whole thing in a general view, though. ",
"And while that's not enough for really intricate information, it's more than enough to know that there aren't any other 11km deep chasms out there. Those are kinda hard to miss."
] |
[
"The entire ocean floor has been mapped. Just look at google maps, open the satellite view and look at the oceans. We know the bathymetry of the oceans very well. But we don't have perfect resolution everywhere. We don't have meter-scale resolution of the ocean floor everywhere. But our resolution is easily good enough to say with certainty that the Mariana Trench is the deepest point of the ocean.",
"For more information, look at this old post that is still perfectly valid. ",
"https://www.reddit.com/r/askscience/comments/6d1x6p/if_weve_only_explored_something_like_5_of_the/dhza552/"
] |
[
"This is a very common misunderstanding that keeps cropping up. The entire ocean floor has been surveyed to about kilometer accuracy, which excludes the possibility of any unknown superdeep trenches.",
"This 15%, sometimes 5% figure comes from various reports about ",
" scale survey data. ",
"Deep trenches also can't just happen, their location is constrained by plate tectonics."
] |
[
"If colors come from light, as part of the spectrum, then how is it possible that non-luminous objects can have color?"
] |
[
false
] |
[deleted]
|
[
"How do we perceive objects? You don't directly detect an object when you look at it. The way yours eyes work is as a photon detector. Photosensitive cells in your eyes are struck by photons (quanta of light), and are capable of \"recording\" both the number and frequency that they receive. Number translates to how much light is hitting them, and frequency of the photon translates to how much energy is in it, i.e. what color it is.",
"For example, ~400x10",
" meter wavelength photons (400 nanometer) correspond roughly to blue light and ~700x10",
" meter wavelength photons (700 nanometer) correspond roughly to red light.",
"So what's happening when you see an object is that white light from the sun or a lamp is reflected off of it. White light is composed of all frequencies of light (technically some are missing because of atomic absorption in the outer layers of the sun, but that's a technicality that doesn't matter here). An object, due to it's composition, will absorb certain frequencies of light. Only those that are not absorbed reach your eyes.",
"Other objects will work in the reverse: they generate light by exciting electrons, thus releasing photons. Only certain frequencies are excited and so only certain frequencies of light are emitted. "
] |
[
"Because the object absorbs certain wavelengths of ambient light, and reflects other wavelengths. The combinations of wavelengths that hit our eye are somewhat arbitrarily converted into 'colors' by the brain."
] |
[
"when any form of visible light hits it, it will appear that color.",
"This isn't true. Go put a blue object under a red light. It will appear black, not blue. This is because red light doesn't have any blue light in it for the object to reflect. Similarly, a yellow object will appear red under red light, and green under green light. White light contains all visible colors, which is why objects can appear many different colors under white light, by absorbing different combinations of colors. (yellow objects absorb blue but reflect red and green, for example.)"
] |
[
"If an Ephemeris data updates every two hours, how does GPS finds its position accurately?"
] |
[
false
] |
I just downloaded a set of Ephemeris data and I realised that the satellite position updates every two hours. Does a navigation message includes the same Ephemeris data and if so, how does one find an accurate position with the time information obtained in the nav message? I'm quite confused with the time info in the Ephemeris and nav message.
|
[
"GPS signals contain both the emission time and satellite orbit data.",
"https://onlinelibrary.wiley.com/doi/abs/10.1002/j.2161-4296.1978.tb01325.x",
" Table 2-1 has the message structure"
] |
[
"Oh thanks, I'll check it out!"
] |
[
"The ephemeris data is NOT the position of the satellite. It is the *description* of the satellite's elliptical orbit. Using the ephemeris data you can calculate the position of the satellite at any time. Each satellite has an atomic clock that is precisely synched to GPS master time. The time the signal is transmitted is in the satellite's signal. The GPS receiver also has a clock. The receiver calculates the difference between the time it received the signal and the time the signal was sent (from the time in the signal). This difference, in nanoseconds, is called the \"pseudorange\". If you have the pseudorange from 4 satellites, and you have calculated the position of each satellite, AND you have a model of the shape of the Earth (an oblate spheroid) , then you can determine your own coordinates on the Earth and also correct your local time. When you are receiving MORE than four satellites (and thus have more than four pseudoranges) you can use the additional data to correct for measurement errors and obtain a more accurate answer. ",
"In addition, GPS receivers do not only use the GPS data to determine the pseudorange. They also track the phase of the signal, and they use the tiny differences in the phase to more accurately determine the time the satellite signal was received. Finally, there are very expensive \"reference\" GPS receivers that are used to monitor the GPS signals and do research. These reference receivers have their own atomic clocks that are also synched to the GPS master time. This drastically reduces the errors in the received pseudorange and allows a much more accurate position calculation. ",
"I am a former GPS SW engineer that worked for a GPS receiver manufacturer that supplied high end receivers used in the GPS monitoring stations and at research labs. I also worked for a government contractor associated with GPS system research for the FAA."
] |
[
"Why aren't lymph nodes impervious to tumours?"
] |
[
false
] |
This is to do with lymphomas. So why are areas so abundant in Immune receptors so susceptible to tumour growth? Shouldn't areas with high immuno-surveillance be practically impervious? Thank You
|
[
"Simple answer is because cancer cells look very similar (to your immune system) to normal cells. ",
"Longer answer is that there often is immune recognition of cancer cells (often by natural killer (NK) cells). NK cells pick up more on \"stressed\" cells and cells where things just aren't quite right than do other more specific immune cells (like T and B cells)\nAnd that does often have an effect which slows down cancers in general (immunosuppressed people/animal models get more cancers partly due to this (also because of viruses etc.))",
"But there are also other factors at play.\nSome cancers secrete immunosuppressive factors and cytokines which your body naturally produces in other situations and the cancer hijacks it and tones down the immune system re:the cancer. This can often only be local so you don't get opportunistic infections.",
"There's also this thing called immunological editing (I think that's what it's called, might be receptor editing) whereby the cancer cells are under selection pressure from the immune system. Most of the cancer cells don't look too wrong to the immune system (as they are your own cells, just out of control). The immune system kills them though because they are still wrong looking. The cells which are the least wrong survive and proliferate. Rinse and repeat until you have a cancer which isn't recognised by the immune system",
"It's also worth thinking about the fact you only \"hear\" about the potentially cancerous cells which make it through the lymph nodes defences. The rest get killed and you're none the wiser; it only takes one in a million cells to get past the defences :)",
"(Sorry for lack of references, on my phone, but I'm an immunology student studying for finals ATM for background)",
"Tl:dr\nCancer cells do get recognised, but its sometimes not enough to completely stop them, and they have various methods to stop the immune system or evolve away from recognition."
] |
[
"I like this answer.",
"Also, I'd like to point out that while OP says that the question is about lymphomas specifically, it's important to note that cancers of non-immune origin also can metastasize through the lymph nodes. So immune evasion, even within a lymph node, is not specific to lymphoma. ",
"I'd also like to state, just for the record, that a cancer that metastasizes from another area TO a lymph node is not characterized as lymphoma, it is still a cancer of the tissue of origin. I am not suggesting that the OP didn't know this, I just wanted to make it clear as I have seen this question/confusion more than a few times recently.",
"edit - added a word for clarification"
] |
[
"I couldn't have said this better myself. A++"
] |
[
"How is energy conserved when photons are red-shifted by their emission towards us from objects moving away from us?"
] |
[
false
] |
I've read other questions that have been asked about when photons which are red shifted by the expansion of the universe, energy isn't technically conserved, but I was wondering if energy is conserved when red shifting is happening solely because an object is moving away from us. If it is conserved, how is it conserved? Where does the energy the photon loses when its frequency is lowered go? If it is not conserved, why is this? Is it because of all this space time invariance stuff I read about? One extra question: When looking at the absorption spectra from stars, the spectral lines are shifted to a higher wavelength. Absorption spectra occur when photons of a specific frequency are absorbed from light emitted by the star. What confuses me is, if the stars are emitting light, which I assume is red shifted as soon as it is emitted, then why do the spectral lines occur in different places? I would assume that atoms would just absorb photons of the wavelength they usually do, red-shifted or not, and we would see those spectral lines in their usual place.
|
[
"I'm not moving relative myself, but I'm moving rather fast relative the Sun. So I have different kinetic energies depending on what my coordinate system is. This holds true both for classical mechanics (Galilean relativity) and with Special Relativity. ",
"But it doesn't matter if you measure things relative one point in space, or another point in space, or a point moving at a certain constant linear velocity (these are 'inertial frames of reference'). You cannot tell the difference, nothing changes physically, it's just a change of coordinate systems.",
"Within the same inertial frame, energy is conserved. The fact that energies can be different in different inertial frames doesn't change that. There is no absolute energy, what the energy is depends on what you're measuring against. If you're standing still and I'm running towards you, and you throw a ball to me, the ball will be moving faster and have more kinetic energy relative me than relative you. ",
"Here's where Special Relativity comes in: With photons, it is no different. Emit a photon instead of a ball and it will still have higher energy if you're moving towards the emitting object. The only difference is that light always moves at the same speed, its kinetic energy is related to its frequency instead. So it is the ",
" of the light that changes with your frame of reference, rather than its velocity.",
"But there's no energy being added, lost or not-conserved here. You're merely comparing energies that are measured in different reference frames. The shift is not some physical process, but a choice of coordinates.",
"When you talk about absorption/emission, then the natural, convenient frame of reference is that where the absorbing/emitting is at rest. If you're moving towards or away from that object, then the spectrum will be shifted. As it ",
" be, not just because the emitted photons must have a different energy in your frame of reference, but the electrons that emitted that photon were moving at different velocities in your frame of reference, and their change in kinetic energy when they transitioned and emitted the photon was different. But whichever frame you measure in, the emitting electrons lost the same amount of energy that the photon carried away. It all works out, the energy is conserved as long as you're measuring everything in the same inertial frame, whichever one you choose. ",
"It only seems like energy isn't conserved when you compare different inertial frames. But as I explained in the first paragraph, there's no reason to assume the energy should be the same, as that's not true anywhere."
] |
[
"Energy is generally not conserved under change of (inertial) frames. One way to see this is that energy is the temporal component of the energy-momentum vector (\\omega, cp) and/or the purely temporal component of the stress-energy tensor. So under for instance Lorentz transformations the energy transforms covariantly. See for instance\n",
"http://galileo.phys.virginia.edu/classes/252/energy_p_reln.html",
"The thing that is conserved is E",
" - c",
" p",
" but for a photon that quantity is zero."
] |
[
"Wow, that's actually really clear! That makes a lot of sense. I suppose the problem is that it is represented as a sort of physical process, e.g. when people say the wave is stretched, it makes me want to think that it occurs like that no matter what perspective you take, whereas it is actually a matter of reference frames. That analogy with the ball is very good!"
] |
[
"How would having a giant planet in close proximity affect Earth's gravity and the people on the surface?"
] |
[
false
] |
The thought came up when my roommate and I were watching a Sucker Punch ad on TV. There is a shot that shows a ringed, Saturn-like planet very close to wherever they are in that movie. I have no interest in seeing Sucker Punch, and in talking about how stupid it looks, I wondered how a huge planet's gravitational pull would affect people living on Earth. I would assume that something as small as the moon has enough pull to affect tidal action, so a larger object would have an even greater effect. Anyway, please answer. I'd love to know.
|
[
"For starters, the Earth-Moon distance is about 1/100-th the Earth-Mars distance. The moon's mass is 1/10 that of the Earth. The pic in question might indicate another Earth sized planet at a moon-like distance. The effects of two large mass in such proximity would show its effects during the planet formation stage. So I'll claim without any proof that in the time precluding planet formation, the two large masses in question will coalesce into a single larger one. i.e. having two planets in such proximity would be a rather contrived scenario.",
"Apparently, the ",
"Roche limit",
" tells you whether the Earth is likely to disintegrate under these massive tidal forces. The moon is apparently at 40 times the radius that would cause its disintegration. Decreasing the moon's orbit radius by 40 means a factor of 1600 increase in gravitational pull, and the above situation corresponds to a 100x increase. So things would be unlikely to just break up and fly off into space, but it might cause issues for satellites orbiting Earth. Also, monstrous tides that consume most low-lying land, increased volcanic activity and tectonic instability. ",
"That wasn't very useful was it...",
"All this considered, Sucker Punch is a mindless fun movie with bad dialogue that makes you facepalm, you'll enjoy it if you like stuff like Death Proof and Machete."
] |
[
"Visit ",
"Io",
" to find out what it is like. ",
"I guess we would have a lot of trouble with towering tidal waves, earth quakes and volcano activities. "
] |
[
"(non-professional)",
"\nhuge tidal shifts, very likely stronger tectonic movement, climate shifts as a planet that size/proximity would likely alter the orbit of the planets around it. "
] |
[
"Why do babies try and put everything in their mouths? This seems like a huge evolutionary disadvantage."
] |
[
false
] |
Without constant supervision, almost every baby ever would kill itself within minutes. Is there some sort of advantage to this I'm not seeing?
|
[
"It is actually an evolutionary advantage.",
"Think of it like this: The process kick starts their little immune systems into getting into fighting shape by putting things in their mouths and exposing it to all kinds of bacteria and interesting micro organisms. You wouldn't want an immune system thats never had to fight a battle before, would you?",
"We tend to think dirt, and being dirty is bad for us, but thats just not true 99.9% of the time. It actually has a ton of physiological benefits that we just don't really understand.",
"source: ",
"http://www.nytimes.com/2009/01/27/health/27brod.html?_r=4&ref=health&",
"Edit: took out source pointing to the wrong article"
] |
[
"Human babies learn an incredible amount in a short amount of time. They don't come prebuilt with a bunch of species instincts, but are instead staggeringly adaptable to different environments/cultures. This constant testing of all objects is part of that. It's the major evolutionary advantage of our species, but the cost is a long period of helplessness (a deer can walk almost immediately after birth).\nTo protect babies, we have a far more intense bonding than most animals, both between mother and child and between adults of the species (so the baby is never unsupervised).",
"But basically yeah its part of why we're so good at learning"
] |
[
"I think you are failing to appreciate the selection landscape. Human babies are dependent on their mothers and are helpless. It is not the case that babies have this trait and are free range. An instinct to suckle is a pretty good thing for a mammal. One could certainly imagine that babies without a suckling trait (assuming here some simple Mendelian trait) would be out competed by babies that suckle even if some choke on items."
] |
[
"Why are robots still so \"jerky\"?"
] |
[
false
] |
After many years, most robots I see demonstrated/operating still have very jerky movements - it seems odd that they aren't built with motors capable of much finer/more delicate control, and it would be very surprising if such motors weren't available (there must be applications for them somewhere!). Are smoother, finer motors just too expensive to be used for robotics, or are such motors not widely available?
|
[
"Robots have been used for remote surgery since 2001. There are many motions an artificial structure can make that are much more efficient and more accurate than any human could do.",
"You are considering 'jerky' with respect to humans which are limited by requiring slow steady movement for accuracy. Robots can do it quickly and even more accurately.",
"edit: It's like asking why a calculator is so hasty in its answer to a calculation while a human can perform the calculation so nice and steadily."
] |
[
"The robots ",
" moving smoothly. It's just that they are often programmed to move efficiently, which often means perfectly straight lines and a high acceleration, so it doesn't look smooth compared to say a human moving a human hand around."
] |
[
"I guess it's only a problem if you're trying to emulate human movements, then, although quite often it does look quite unstable - e.g. the robot stops moving suddenly, causing it to wobble, such as when ",
"this red robot",
" comes to a stand. I'd also imagine it puts more stress on the structural components - or is the acceleration far too low to be an issue with the materials being used?"
] |
[
"How long does it take for asphyxia related death to take place?"
] |
[
false
] |
In movies and TV shows, anytime a character is choked, s/he always passes out in under a minute and is presumed dead. I understand that temporary loss of consciousness can occur as a result of suboptimal brain oxygenation, as is the case in some fainting spells (or that fading feeling one has when standing up too quickly), but physiologically, how much time (I understand it would probably be a range based on metabolic conditions) would elapse before one dies? Furthermore, is the cause of death unrecoverable brain damage from CNS hypoxia, myocardial infarction, something else that I can not think of, or some combination thereof? In the event of multiple system failure, what is the order in which each system would occur? OR does it really take only a brief moment of time, due to, for example, either panic inducing an increasing metabolic need (from arm flailing and/or other SNS based response -- endocrine or otherwise) depleting the residual oxygen in the lungs, or other factors? Edit: Actually, as I think about it more, I am probably oversimplifying the whole matter in my head. Therefore, any and all input would be appreciated!
|
[
"Can't really address the specific causes of death, but I will say that the vast majority of tv and movie portrayals of asphyxiation are unrealistic. You would need to continue choking someone for a significant period of time AFTER they lose consciousness in order to kill them. Doesn't make for good television though."
] |
[
"Physician here.",
"Short answer: the brain will die in 5-10 minutes.",
"Long answer: If the person has had training or preparation, they can hold their breath for ",
"up to 20 minutes",
". Also, if they are immediately cooled... like a drowning in a frozen lake, then they could recover almost completely after 20-30 minutes of no oxygen.",
"Short answer: Yes. In lack of oxygen, ALL deaths will be due to brain death.",
"Long answer: All death is essentially due to lung failure, heart failure or brain failure. Everything else is a circumstance. You either can't oxygenate your blood, can't pump your blood (deliver the oxygen), or your brain is not functioning.",
"Your brain will go first. The heart will suffer irreversible damage at 4-6 hours. The rest of your organs at 6-8 hours. Organ transplantation is possible because of cooling and treating the organs with certain stabilizing solutions. Then, they can survive up to 18+ hours."
] |
[
"Understandable about TV. It's an acceptable concession, methinks. Do you think one passes out (or drowns for that matter) with their eyes opened like in TV, or rather with their eyes closed (as I'd imagine most blackouts to occur -- I'm thinking g-force induced blackouts experienced by untrained fighter pilots[soon to be trained of course])?"
] |
[
"Is there a way I can safely remove the Americium-241 from a smoke detector?"
] |
[
false
] | null |
[
"The activity of the americium-241 in the smoke detector is less than 1 μCi, so as long as you don’t swallow it, it won’t really harm you."
] |
[
"I don’t advise you to play around with the source in your smoke detector, but when I handle similar sources, I make sure to follow ALARA (dose As Low As Reasonably Achievable), use gloves when possible, avoid touching my body with contaminated gloves, and wash my hands after. There is no food or drink allowed anywhere near where sources are being handled, so there’s no possibility of ingesting anything contaminated. If you’re worried about inhalation, you can get one of those filtered masks that cover your nose and mouth."
] |
[
"So just keep far away from food, cover my skin and wear disposable gloves, essentially? Thanks :)"
] |
[
"Is it possible to improve one's vision without glasses or surgery?"
] |
[
false
] |
[deleted]
|
[
"I am an American board-certified ophthalmologist. Let me clear a few things up. In general, nearsightedness is caused from the eye being too long, and farsightedness is due to the eye being too short. There is no way to change this with any type of activity or medication. However, as we get older the lens of the eye begins to change shape, density, and even it's refractive ability, leading to a secondary cause of vision changes – lens changes. There is also no activity that will cause the lens to change, with the exception of a few medications which speed up the development of cataracts. The only exercise that is considered at all effective is for one particular condition known as convergence insufficiency. This is where the eyes are unable to converge for reading. Continually trying to converge the eyes has been shown to be effective. All other exercises are totally bogus, despite being promoted by some optometrists."
] |
[
"I have amblyopia, a fairly common vision disorder in which the brain ignores input from an eye that is otherwise physically healthy. ",
"A few years ago a VR game called Diplopia was successfully crowd funded, and today it's been renamed Vivid Vision. The VR game forces the brain to incrementally utilize more input from the weak eye. They seem to have had some success, and are now distributing an oculus rift package to vision centers across the U.S.",
"They did an AMA here: reddit.com",
"/r/IAmA/comments/40surh/we_are_james_and_dr_tran_from_vivid_vision_we_are/",
"I'm really excited about this potential treatment, but with the Rift at $599 and Vive at $799 it could be years before I can afford it."
] |
[
"He et al. (2007)",
" showed renewed plasticity in adult rats and ",
"Duffy and Mitchell (2013)",
" found the same in adult cats following deprivation during adulthood. In humans: ",
"Zhou, Thompson, and Hess (2013)",
". See also ",
"Mitchell (2013)",
" and ",
"Mitchell et al. (2016)",
".",
"More generally, a number of studies recently have found experience-dependent plasticity in amblyopia such as ",
"Polat et al. (2004)",
", ",
"Huang, Zhou, and Lu (2008)",
", and ",
"Thompson et al. (2008)",
". See ",
"Sengpiel (2014)",
" and ",
"Hubener and Bonhoeffer (2014)",
" for reviews.",
"These links are mostly dealing specifically with amblyopia, but if we're talking about perceptual learning in general, there are of course plenty of changes that the visual system can undergo during adulthood (although oftentimes perceptual learning is task and retinal location specific)."
] |
[
"Why is it that planets don't 'twinkle' when viewed from earth?"
] |
[
false
] |
Why do planets, as opposed to stars, not 'twinkle' when viewed from earth even thought the light from both passes through the same atmosphere? Is it that stars, due to their relative distances, behave as point source of light?
|
[
"Yes, basically. It has to do with the relative ",
"angular diameter",
" (width) of the two bodies in the night sky.",
"Jupiter",
", at ~140,000km in diameter and ~700,000,000km away has an average angular diameter of ~40 arcseconds, which is right at the limits of resolution for the human eye.",
"Sirius",
", on the other hand, has a diameter of approximately 17 times that of Jupiter, but is approximately 100,000 times farther away. So it's angular diameter is ~.006 arcseconds...about 6000 times smaller. When disturbances happen in the upper atmosphere, they tend to get averaged out over the width of Jupiter's disc...much less so with that of Sirius. This would be like comparing the seafaring ability of a ",
"Maersk Triple E",
" with a little bathtub toy. ",
"This seems absurd, but it's because your perception of the size of a star in the night sky is limited to the size of the rods and cones in your eye and the focusing power of the lens. If you held a red blood cell up at arms length, that would be roughly one arcsecond in diameter. Sirius is 166th of that...on the order of larger molecules.",
"(many edits to fix an error. For what it's worth, Wolfram Alpha is really cool for figuring out some of this stuff ",
"width of Sirius if Jupiter was the USS Ronald Reagan",
")"
] |
[
"It has nothing to do with the number of photons ",
". If Sirius appeared as bright as the sun, we would be receiving the same number of photons per second from it as from the sun, but it would still appear to twinkle because of its small angular diameter."
] |
[
"In other words, stars are basically point sources."
] |
[
"Why is there no medical approach based on how plants fight infections?"
] |
[
false
] | null |
[
"What a douchelord"
] |
[
"What a douchelord"
] |
[
"Questions based on discussion, speculation, or opinion are better suited for ",
"r/asksciencediscussion",
"."
] |
[
"If we dropped an atomic bomb into a hurricane at the right spot, could it \"kill\" the hurricane?"
] |
[
false
] | null |
[
"Similar question asked earlier in the week (I think) this is the only one I could find on it (3 months old): ",
"http://www.reddit.com/r/answers/comments/hpb8b/could_you_disrupt_a_weather_pattern_with_a/",
"also just found this ",
"http://www.reddit.com/r/AskReddit/comments/fcebk/if_an_atomic_bomb_was_dropped_right_in_the_eye_of/",
"Hope this is of some help."
] |
[
"Thanks! Apologies for the repost-ish. :)"
] |
[
"No props :)"
] |
[
"The boiling point of carbon dioxide is -57 °C. The coldest recorded temperature in an inhabited place is almost -68 °C. Does this mean that carbon dioxide condenses out of the air in these places?"
] |
[
false
] |
This is what got me thinking: . Furthmore, the lowest recorded natural temperature anywhere on earth is -89.2 °C , colder than the freezing point of CO2. Would carbon dioxide ice freeze out of the air under those conditions?
|
[
"At 1 atm it wont form a solid until -78.5 C.",
"CO2 Phase Diagram"
] |
[
"I don't want to rain (CO2 frost) on the parade here but Vostok Station is at an altitude of 3,488 meters (or 11,444 feet) and ",
"this site",
" describes \"atmospheric pressure here is very low comprising 624.2 hPa on average for a year.\" ",
"So about 62% of standard temperature pressure. The CO2 phase change line for sublimation slopes such that lower pressures means the phase change takes place at ",
" temperatures than the -78C at STP.",
"Wolfram Alpha says CO2 sublimates at -84C at 624.2 hPa.",
"But wait, it gets ",
" because all the above assumes we are dealing with pure CO2 at 1 atmosphere (or 0.6 atmosphere at Vostok.) ",
"CO2 in the earths atmosphere is only about 0.036% (",
"creeping up on that 400 ppm",
", go climate denial!) so the partial pressure of CO2 is ",
" lower. Plugging ",
" into Wolfram Alpha gives you a ",
"much chillier",
" -144C.",
"But wait, there's more! -144C is how cold it would have to be at Vostok ",
" for CO2 to sublimate out. The -89.2 °C was almost thirty years ago in 1983, back when ",
"CO2 was about 10 effing percent lower than today at 340ppm",
". Putting the lower partial pressure into Wolfram Alpha ",
"gives us -145.1C",
" as the temperature that it would have to have been at Vostok in 1983 for CO2 frost.",
"Figuring out the likelihood of Vostok Station ever seeing -89.2 °C again in the face of CO2 growing at ",
"about 2ppm per year",
" is left as an exercise. "
] |
[
"The freezing point of CO2 is really only valid when going from liquid CO2 to solid and at a specific pressure, probably sea level or one atmosphere. The same thing with water if you have water that has impurities it affects the freezing and boiling points the 0 C and 100 C freezing and boiling points of water are really only valid in distilled water at one atmosphere. ",
"The concentration of CO2 in earths atmosphere is ~.0387% or 387 PPM. That is really too low to cause it to condense and fall to the ground out of the air like snow. ",
"Source on carbon dioxide in earths atmosphere",
"Also you point out the boiling point. This is only where CO2 goes from a gas to a liquid at standard atmosphere. it's melting point (when going from solid to liquid) is -78 C which is colder than the -68 C in an inhabited place. ",
"http://en.wikipedia.org/wiki/Carbon_dioxide"
] |
[
"How do antibiotic creams work compared to antibiotic pills, and is there also a risk for over using it as well?"
] |
[
false
] | null |
[
"Depends on what you’re treating, the drug that is applied, etc. typically you don’t use the same antibiotics as creams and pills. You would use a topical cream for most skin infections, but if you needed to treat a pulmonary infection, you wouldn’t want to slather someone’s lungs in cream. There is a risk with overusing. If you’re asking the difference in how the body absorbs the antibiotic, cream is absorbed through the skin into the immediate area, and usually isn’t absorbed systematically, while pills are absorbed via the gastrointestinal system and circulated through the bloodstream."
] |
[
"As for the second part, yes, there is a big risk for overusing it, but not in the way you think. Using antibiotics all the time will start triggering evolution within bacteria, creating strains that are completely resistant to antibiotics, eventually creating a superbug. This is already going on, and the best example of a superbug is MRSA. And by the way, this process is over using it amongst many many people over a relatively long period of time."
] |
[
"Antibiotic creams is specially formulated to work on applied area. Antibiotic pills need to be ingested and some drugs (pro-drug) will need to be metabolized to its active drug before it can circulate the body and do its work.",
"Antibiotic cream is prescribed especially for local skin infection (e.g skin ulcer). A popular misconception that is still commonly practiced is crushing an antibiotic pills to be applied topically. This is so wrong as it won't work as intended.",
"Risk of antibiotic cream is less than systemic antibiotic since it is applied topically. However, with misuse, risk of resistance can also increase."
] |
[
"i found a mysterious science object. what is it?"
] |
[
false
] |
i was walking down the burke-gilman trail, close to the university of washington, and i found this odd thing hidden in a wooded grove. it comes up to my knee, and weighs maybe 30 lbs. does anyone have any idea what it is?
|
[
"I believe you're right. It's a picture of an eight quartz lamp heater array mounted to a custom made flange with huge heat sinks. This is a furnace that could have been a part of a chemical vapour deposition setup. Hard to tell. There are many applications that would require this type of heating.",
"Those golden coloured things look like modified Be-Cu barrel connectors. The screws are not gold plated screws, the sheen looks off. If those screws are vented, the piece of equipment is definitely vacuum related.",
"The 16+8 holes at the very bottom are for feedthroughs to the lamps. The top 8 holes are for mounting the flange. They are worn from repeated over-tightening. The two larger holes are probably for alignment with dowel pins to another part of a chamber. At first this looked like a differentially pumped flange, but probably not.",
"EDIT: clunky wording."
] |
[
"It reminds me of a lot of the ultra-high-vacuum equipment I've seen, but... is it open at the sides, or does it have thick solid walls?",
"edit: Example of what an UHV chamber might look like: ",
"right here",
"The roundness, the stainless steel (possible gold plating?) and screw holes remind me of this kind of equipment.",
"Whatever it is, it looks expensive... or at least, it looks like it would have been expensive originally (but could well be worthless now). Definitely hang onto it until you've got an identification."
] |
[
"What's on the slabs of PCB at the center of the parabolic reflectors? A great honking set of LED emitters? ",
"I have no idea. But from looking at it, we can see a few things:",
"In general, it looks set up to do ",
" with a lot of power, probably involving light aimed at the center. If the other end was open, I'd guess maybe it was for UV water sterilization in a huge flow-through setup. "
] |
[
"With solar panels being so \"shiny\", doesn't it affect their ability to absorb the sun light?"
] |
[
false
] |
I saw this picture and was puzzled how their surfaces could be so shiny: Does the material have other benefits which makes up for the glossy effect of it? Is any sun light lost because of the shinyness?
|
[
"The picture you posted is taken at an oblique angle. As you increase the viewing angle, the reflectivity grows until it reaches 100%. If you looked at those same panels straight on, they would look almost black.",
"For that reason, you always want solar panels to be facing the sun. One of the main areas of research in solar tech is figuring out cheap ways to make panels track the sun.",
"EDIT: As Yakooza1 points out, the maximum reflectivity is not 100%, but it does increase with angle of incidence."
] |
[
"One of the main areas of research in solar tech is figuring out cheap ways to make panels track the sun.",
"What do you mean by this? I'm imagining we have enough information about orbits to accurately predict the Sun's position in the sky on any given day, so it simply using that information that is being researched?"
] |
[
"Tracking for a single panel with clearance around it increases daily output only marginally, whereas tracking panels packed adjacent in an array will actually REDUCE the array output dramatically.",
"Say you have 1000 sq ft of south-facing roof. The panels are all packed together. The ROOF can't turn to face the sun. That 1000 sq ft only receives so much sunlight... cos of incident angle, actually. ",
"If you tilt the panels individually on that roof, it will do nothing to increase the net sunlight striking that 1000 sq ft. No, what happens is one panel starts to partially shade its next neighbor, which is a really problematic situation because the cells are in series. ",
"Plus it makes installed panel costs like 5x more over the lifetime. Makes more sense to put 5x more panels out there."
] |
[
"Why do my computer speakers occasionally pick up AM radio stations?"
] |
[
false
] |
I went to plug my computer speakers into my laptop today, and if I only half plug in the line-in cable, I can hear a local AM radio station (specifically WLS890 Chicago) playing under static on my computer speakers. What's the explanation there?
|
[
"http://en.wikipedia.org/wiki/Antenna_%28radio%29",
"Something in your computer or case is acting as an antenna that is matched to that local station. ",
"For some reason when the cable is only half plugged in, the circuit is delivering that station to your speakers. Not sure why this is the case here though."
] |
[
"AM = Amplitude Modulation. So there's a frequency in the air that's getting stronger and weaker to directly model the waveform of a sound. (This is important, because FM doesn't do this)",
"Your computer case is acting as an antenna. When the cable is plugged in halfway, this is probably connecting the signal pin to ground - and your ground is likely picking up the AM signal.",
"When a radio wave is picked up by an antenna, it translates directly into voltage along the wire. If your speakers are picking up this antenna voltage where the audio signal should be (as it would if you plugged it in halfway) then the speakers are doing their job properly - you're just giving it a signal you didn't know about!",
"For fun, try turning up your speakers and touching the tip with your finger. On my systems, often I could produce a soothing 60Hz tone overlaid with a 30Hz one. After much exploration, I figured it out - it was the hum from the fluorescent lights, transmitted through the air and picked up by the \"antenna\" that is the human body!"
] |
[
"This would be more fitting in ",
"/r/electronics",
" or ",
"/r/AskEngineers",
"."
] |
[
"If two astronauts are indefinitely moving away from each other at a constant speed, who is aging slower?"
] |
[
false
] |
Was reading about the twin paradox earlier and I can accept the age difference resulting from the acceleration needed for the twin to turn around. But what would happen if the twin just didn't come back? Assuming they are already moving away at constant speed from the start
|
[
"Each twin would determine that the other twin was younger than themselves. No one would be able to determine which twin was \"really\" younger, because there's no such thing. This is one of the consequences of the relativity of simultaneity, which is the idea in special relativity that there's no way to uniquely determine the order of events that happen far enough away from each other that they're not causally connected."
] |
[
"That's completely incorrect. Time dilation ocurs between any two reference frames that are moving relative to each other, including constant relative velocities. Acceleration greatly complicates the matter, but is not necessary for time dilation."
] |
[
"That's completely incorrect. Time dilation ocurs between any two reference frames that are moving relative to each other, including constant relative velocities. Acceleration greatly complicates the matter, but is not necessary for time dilation."
] |
[
"Why do transformers only work with alternating current?"
] |
[
false
] | null |
[
"Transformers make use of the fact that a changing magnetic field can produce a voltage - this is Faraday's law of induction. It's not the absolute value of the magnetic field but its rate of change which is important.",
"Direct current has a constant electric (and hence magnetic) field across the coils and so is incapable of inducing any voltage in the secondary coil. Alternating current rapidly changes direction and is therefore suitable for this kind of transformation."
] |
[
"So, basically, what is ",
" happening is the same thing as moving a magnet relative to coils of wire?"
] |
[
"A good answer is provided ",
"here",
". Basically, the reason is that DC cannot create an alternating magnetic field which is needed to make the electrons in the second coil move."
] |
[
"What would happen to an object that fell onto a gas planet?"
] |
[
false
] |
Lets assume theres a planet fully made of gas, like neptune just without the massive core. What would happpen if I threw a rock at that planet? The planet should have gravity but because theres no solid core, the rock cant really hit anything and therefore land. Would it just fall through the core and then return to eventually become the core? Im so confused...
|
[
"There might not be a solid core, but there's plenty enough gas for it to ",
"go through and burn up in!",
"There's a thought experiment that wonders what'd happen if you managed to bore a tunnel straight through the centre of the Earth to the other side. If you just jumped in, the assumption is that you'd end up on the other side of the earth, but not quite make it all the way through due to air friction, and because you'd lose a little more height each time through, you'd end up at rest at the centre of the earth (damped harmonic motion--assuming you'd survive the 'fall' and that the molten core at the centre would be obliging enough to maintain the tunnel). ",
"In a similar fashion, if your gas planet were completely gaseous and was impacted by a big enough meteorite that it'd survive re-entry--it'd probably come on through on the other side, assuming it wasn't captured within the gas planet's gravity well (it'd also lose some of it's kinetic energy). If it ",
" captured, your completely gaseous planet would no longer be completely gaseous!"
] |
[
"I'd imagine the gravity of a planet the size of Neptune, even ignoring that compression of particles due to gravity nearing it's centre, creating a denser core, would still have enough gravitational mass to crush the rock, and have it begin orbiting the centre of mass and burn. "
] |
[
"Thanks for the answer :)"
] |
[
"Were protohumans able to reproduce year round, or did they have seasonal mating? How far does this trait go back on our evolutionary tree?"
] |
[
false
] | null |
[
"Well, pretty much all monkeys reproduce year round, so it's probably a reasonable bet that our most recent common ancestor with new world monkeys probably did too. That puts us at least at 40 million years. That said, year-round reproduction in mammals probably more a factor of climate than lineage. If you live in the tropics (like many primates do), there aren't major seasonal variations that you could reproduce according to."
] |
[
"Followup: is the incidence of seasonal mating proportional to latitude?"
] |
[
"Yes, almost certainly. Off the top of my head, I can't think of any terrestrial mammals that natively live in northern latitudes and don't have seasonal reproduction. So I would say that seasonal reproduction is highly correlated to latitude. Exceptions might be animals that are more capable of controlling their environment, like burrowing or communal living animals."
] |
[
"Chloroplasts into humans."
] |
[
false
] | null |
[
"It would in my opinion be technically possible... eventually. A plant respires like we do so it would seem to be possible although I am sure there are many things I've overlooked (I'm not saying in any way that this is feasible without a huge amount of research).",
"\nHowever, the real question is why you would want to. As you may be away from looking at a food chain, the animals at the bottom have to eat huge amounts (herbivores) and the energy gets more concentrated as you go up the predators to the point where lions and especially reptiles such as alligators, can go a long time between meals. The energy demands of an animal are far higher than a plant though, which is why they can get enough energy from photosynthesis, but we would come nowhere near our energy demands."
] |
[
"Energy isn't concentrated as you go up, it is lost as you go up the energy pyramid to higher trophic levels - I believe the rule of thumb is that only 10% of energy at each trophic level is passed on to the next."
] |
[
"Yeah, that's what I've heard, between 10-15%. And to answer his question, you could do it in order to stop muscle meltdown (catabolising proteins for energy, when glucose and lipids are unavailable) in nations where there is no or very little food."
] |
[
"Would it be possible to propel a spaceship using only nuclear radiation?"
] |
[
false
] |
I know this is only theoretical, but would it be possible to design a ship capable of being propelled using only nuclear radiation as it's method of propulsion? I realize the specific impulse of an engine like this would be extremely high, but theoretically, even if only one particle left the original mass we are using then that exerts a minute amount of force against the mass. Right?
|
[
"Yes",
"http://en.wikipedia.org/wiki/Fission-fragment_rocket",
"\n",
"http://en.wikipedia.org/wiki/Fusion_rocket"
] |
[
"While i appreciate the links, this is not the radiation i meant. When a piece of plutonium is sitting on a table, it is emitting radiation. I was talking about using that radiation to propel something. The thrust would be almost infinitely small, but it would still be there, and it would last thousands/millions of years so eventually it might lead to a decent speed."
] |
[
"That would be the propulsion scheme from my first link."
] |
[
"Why is there bacteria everywhere? What does bacteria feed on to survive and multiply on the floor for example?"
] |
[
false
] | null |
[
"Other bacteria. And then when they die, other bacteria comes to capitalize. Then (in water environments) when the process of cellular respiration depletes available oxygen, anaerobic bacteria comes and thrives while reducing sulfur instead (ever step in stagnant muck and it smells like rotten eggs?)",
"In short, bacteria were among the first living things on earth. They'll certainly be the last. Don't get me started on OP extremophiles 😅"
] |
[
"Prokaryotic or single-celled life has always been the dominant from of life on the planet. From free-floating algae that can alter the atmosphere over millions of years to polyextremophiles that survive the harshest of conditions.",
"Bacteria don't need much to survive but water of course is the most essential component. Without water, you won't have actively metabolizing (living) bacteria. There are saprophytic organisms that can make their own food which pathogenic bacteria can prey on. Even in a home, the dust is typically organic and mostly compromised of dander which the bacteria will readily consume.",
"Some pathogenic bacteria like listeria can be notoriously difficult to get rid of as they happy living in the soil and are quite hardy.",
"Not sure if you remember but Blue Bell certainly struggled: ",
"https://www.cnn.com/2015/04/04/health/blue-bell-ice-cream-listeria-plant-suspended/index.html"
] |
[
"Not just other bacteria, but all the organic dust that comes from plants, animals, people, etc"
] |
[
"Conservation of Kinetic Energy in an Inelastic Collision"
] |
[
false
] |
Experimentally, if a collision is inelastic, yet energy is still conserved, where might the kinetic energy go? Just got curious while studying physics.
|
[
"Usually inelastic collisions involve rearrangements of the pieces that make up each object. For example, in a crash between two vehicles that stick together, the vehicles will get crushed to some extent, and this will take energy to do. ",
"There are other effects to consider such as if the collision made any noise (energy carried in the sound) or if the collision generated any heat. I believe these are usually small contributors to the total kinetic energy loss, although I'm not completely sure.",
"In particle physics we refer to inelastic collisions as collisions where the things that come out are not the same as the things that went in. So at the LHC, if two protons collide and just deflect each other, that would be called an elastic collision. However, if they collide in such a way that the various types of quarks and gluons inside the proton get rearranged and/or new particles are created from the incoming energy, that would be referred to as an inelastic collision."
] |
[
"It might be transformed to heat, it might deform something involved in the collision... Sky's the limit, and it depends on the circumstances of the collision."
] |
[
"Usually inelastic collisions involve rearrangements of the pieces that make up each object. For example, in a crash between two vehicles that stick together, the vehicles will get crushed to some extent, and this will take energy to do.",
"Just as another example: For less rigid objects, some sort of deformation is still involved. Throw two bouncy balls at each other and watch it in slow motion, and you'll be able to see them deform and wobble and ripple."
] |
[
"If I consume undercooked beans (still kinda crunchy), do I obtain all the nutrients, or will my body just ignore some of the calories from the nutrients?"
] |
[
false
] | null |
[
"Don't consume undercooked beans, particularly red or white kidney beans. They have a toxin that is incredibly unpleasant. ",
"See ",
"this wikipedia article",
". Note that undercooked can be even worse than not cooked."
] |
[
"Dried pasta is safe to eat uncooked, but you should cook any fresh (or \"wet\") pasta before eating since it may contain raw egg. Dried peas are fine too (wasabi peas . . . drooooooool). Although, I can't guarantee you won't chip a tooth on the pasta."
] |
[
"I do cook the beans (usually pinto and chickpeas, the latter which are not beans) for about 30 minutes. But there is still some firmness to the beans. Even after 30 minutes of boiling. I do avoid red kidney beans because I had heard of their toxicity, which I am also aware is not just exclusive to kidney beans. Thanks for the info and URL."
] |
[
"How does the environment of space affect electronics?"
] |
[
false
] |
Specifically, how can electronics be protected from it? I know the temperatures are a major factor, but I understand that this can be stopped with insulation, cooling or just using electronics that operate in a greater range of temperatures. I'm more interested in the other factors, how they affect electronics, and how are space graded electronics different to survive them (what makes their price become so much higher than standard electronics).
|
[
"A relative of mine does this stuff for a living so I can tell you what I've learned by asking the same question. Note that this is a combination of ",
" and what makes sense.",
"Issues that you have to worry about when sending electronics to space:",
"wire bonds",
"As for the cost, there are two factors. The first is that making something with the right packaging and robustness against radiation means you aren't using your standard fabrication line. That means the price is higher just because of supply/demand. That aside, an enormous cost is ",
". When NASA builds a satellite they require not only that the parts in principle deal with the things listed above, but also that they are actually tested by",
"That means you need extra test equipment, people, and time. when you buy a mouse for your computer that's just a part off of a fab line that makes a million of 'em a day. Maybe a small number of parts from each batch are tested for quality control. When you build a satellite, you test every single part.",
"EDIT: I think a lot of contemporary parts use degenerately doped silicon, so I guess carrier freeze-out isn't a problem. Does anyone know if this was a problem ~30 years ago?"
] |
[
"part of radiation protection is a different layout for the memory.",
"in your home RAM the bits in a byte are physically next to each other and next to the next byte.",
"In spacecraft the RAM doesn't necessary look like this, apart from using EEC RAM it is also more spread out, so radiation most likely flips only one bit per byte instead of two or more (EEC can fix only single bit errors)"
] |
[
"Having adjacent bits in the same word/byte is almost never done in any IC memory. Not just to avoid soft errors, but because it doesn't make as much sense to lay things out like that on physical ICs. The most efficient ways to lay out the decoder circuitry that addresses the various bits naturally does not have bits next to each other. ",
"RAM used in spacecraft tends to be made using much larger memory cells, run at higher voltages. They can also use bit-cells that have more transistors in each to make them more robust against radiation induced errors. There are other things that can be done to help reduce the problem, such as using epitaxial silicon, using redundancy, using voting schemes, doing CRC/ECC \"scrubbing\", eliminating the use of B",
" etc. "
] |
[
"If something as small as an atom shot through your body would it be detrimental? Or even a string of atoms being passed, at fast speeds, horizontally through your body."
] |
[
false
] | null |
[
"The extreme example is ",
"Anatoly Bugorski",
" who had a high energy proton beam go through his head. He was injured, but survived."
] |
[
"It was actually a beam of protons, just one wouldn't be that big of a deal. You are kind of right though, in those kinds of high-energy collisions, a lot of energy gets released in the form of radiation. I don't know if the beam had enough energy to cause nuclear effects (essentially, when a proton hits the nucleus of some atom with enough energy to be absorbed, causing the atom to become radioactive) but if it did, you'd get a lot of gamma rays from nuclear decay.",
"Calculating exactly what would happen is very complicated though, it's why there are so many people working on the data from the LHC: high-energy physics is one of the most complex fields of physics at the moment."
] |
[
"Alpha particles are just that, they are equivalent to a He2+ atom. Which consists of 2 protons, 2 neutrons, and no electrons. Very few things are smaller than alpha particles including isotopes of hydrogen ( H ). Alpha particles are already too large to pass through your body. However, if the source which emits the alpha particle is already inside of you ( ingested or inhaled ) it will cause extreme amounts of damage, pending the amount."
] |
[
"What do ants do with their deceased?"
] |
[
false
] |
I was out on a smoke break today on the wooden staircase outside of my workplace. As I often do, I soak up the feeling of nature around me and enjoy the break from an otherwise hectic day. I noticed a line of ants marching along seemingly conducting business as usual. I noticed the lead ant was holding a deceased ant in his jaws carrying him along, with an escort of probably a dozen other ants. Made me wonder: what happens to the corpses of their fallen comrades? I could have answered my own question but I was chased off by a wasp so I ran back inside.
|
[
"Ant colonies operate rubbish heaps that are separate from the colony, but nearby. Any undesirable detritus from the nest goes there, carried by worker ants. This includes their deceased comrades. Even ants that have been terminally injured (such as their abdomen cut off) yet are still alive and moving are unceremoniously dumped there.",
"\nAnts aren't very romantic beings. "
] |
[
"Ditto. Well, not an ant farm, but I've come across several wild ant colonies that had a \"dumping ground\" with a pile of dead ants and other debris."
] |
[
"I don’t know the answer, but I can tell you this: I once was tasked to feed and water a co-worker’s ant farm. I forgot about it for several days and by the time I did remember, several of the ants had died. The living ants moved the dead ant bodies all to a specific area of the ant farm. ",
"I felt pretty bad about forgetting about them, just for the record. :-/"
] |
[
"Why does light travel the same speed for all observers?"
] |
[
false
] |
To my understanding, if something (say a ship in a vacuum) is travelling away from a light source it would observe photons reaching the ship in [time=d/c], while a stationary observer (with respect to the light source) could theoretically observe photons reaching the ship in [time=d/(c-v)] (where d=initial displacement from ship, c=speed of light, v=velocity of ship). I use this concept whenever I want to remember the implications of time dilation for something travelling near the speed of light, but I realized that I do not understand why this phenomenon should occur at all. My limited search on the subject found only that this is a mystery of nature and has been proven by experiment. Does any have some insight on this matter?
|
[
"I wouldn't classify it as a \"mystery\" of nature. But it is a postulate, something assumed to be true, based off of a lot of observations. ",
"The postulate arose because people were playing around with the equations that govern electricity and magnetism. You can test each of the 4 equations independently, they're called Maxwell's equations. And when you put them together in the right way, you get a wave that has some velocity that's equal to 1 divided by the square root of the electric permittivity constant multiplied by the magnetic permeability constant. But as you look at the equations, no where in there did it mention the speed of some observer. Each observer would necessarily come to the exact same conclusions based on the same laws of Electricity and Magnetism. ",
"So Einstein ultimately becomes famous for saying \"fine, let's just make this a thing. This speed of electromagnetic waves is a constant value for all observers. And no physical experiment can distinguish between a frame at rest and a frame in uniform motion.\" Take those two postulates and you get the whole of special relativity."
] |
[
"Well that's kind of my point about the story of this electromagnetism stuff. All observers will come up with the same laws of electromagnetism, regardless of their respective motions (so long as they're uniform and not accelerating). And out of the laws of electromagnetism fall the laws of light. Classically at least. If we want to deal with light quanta, then we could say that photons of light are massless and therefore travel at c, as all massless particles must."
] |
[
"Maxwell's equations clearly predict the speed of light, without reference to relative motion. There are two ways to interpret that; either the speed of light is the same for all observers, or the laws of physics are ",
" the same for all observers. The latter violates the principle of relativity, which states that physical laws should be the same for all observers moving inertially."
] |
[
"Would it be reasonable to consider the human species as Homo Domesticus?"
] |
[
false
] | null |
[
"No. Domesticus is a subspecies designation for a selectively bred subgroup of another species that has been domesticated. If a group of aliens comes to Earth, takes a small group of humans away and they are bred for certain traits that make them genetically and phenotypically distinct from humans on earth, then it would be fair to call them ",
". "
] |
[
"Welcome, thank you for asking. "
] |
[
"Thankyou."
] |
[
"Is it possible that an “earthquake season” could exist? Or are the earthquakes in my country just coincidences?"
] |
[
false
] |
I live in Mexico and earthquakes are fairly common here. They happen at any point of the year really but there’s a strange pattern a lot of us have been noticing recently. One of Mexico’s most devastating earthquakes happened on September 19, 1985. Then in 2017, a small earthquake happened on September the 7th. Then, just a few days later, on September 19th, another one of the most devastating earthquakes happened. Yesterday, September 7th 2021, another earthquake happened. Not as strong but extremely noticeable. 6.9-7.2 I think. I’m just wondering if there’s a reason why a lot of the most noticeable earthquakes here tend to happen during September. I know it’s probably just an interesting coincidence but if anyone knows of something, I’d appreciate them sharing!
|
[
"A general response to any question involving apparent periodicity, trends, clustering, etc in earthquakes are that apparent clustering of a variety of types in records of stochastic events (like earthquakes) are typically just that, i.e., apparent not real, and are actually an expected outcome of randomly distributed, but rare, events (e.g., ",
"Kagan & Jackson, 2016",
"). This means that demonstrating actual clustering or specific temporal trends in earthquakes records is pretty challenging (e.g., ",
"Daub et al., 2015",
"). More broadly, these tend to fall into the tendency for the human brain to look for patterns, etc (e.g., the ",
"clustering illusion",
" or ",
"apophenia",
"). ",
"Now, with specific reference to seasonality of earthquakes, this has been a long standing question, i.e., can there be seasonality within earthquake records and if there is, is it real and what are the mechanisms (e.g., ",
"McClellan, 1984",
"). There are some locations where there appears to be a seasonal signal detected in records of seismicity. For example, in portions of the Himalaya, there appears to be excess seismicity in the winter, with the idea that large loads imposed by the summer monsoons increase the normal stress on faults making them less likely to fail in the summer (e.g., ",
"Bollinger et al., 2007",
", ",
"Panda et al., 2018",
"). Alternatively, in Japan, the opposite is found with some areas potentially experiencing more earthquakes in summer with the normal stress provided by snow suppressing earthquakes in the winter (e.g., ",
"Heki, 2003",
"). Seasonal water load flucutations have also been argued to influence the statistics of seismicity in California (e.g., ",
"Johnson et al., 2017",
"). There are still other hints of seasonality in some seismic records without a clear mechanistic cause (e.g., ",
"Zhan & Shearer, 2015",
"). For all of the above, the challenge of isolating real clustering/periodicity as opposed to apparent signals exists, so all of these come with pretty big caveats. With reference to Mexico, I'm not aware of any arguments for specific seasonality in seismic records there with or without a mechanistic explanation. ",
" there are some places where it's been argued that there is a seasonal component to seismicity, usually tied to seasonal changes in water storage which influence the stress state in the shallow crust making earthquakes more or less likely during certain seasons. More broadly, most of the time that someone notices an apparent clustering or pattern, it's not actually real, and more a reflection of our brains tendency to try to find patterns in unstructured data and the real potential for actually random events to appear clustered. Given the lack of arguments in the literature for seasonality in seismicity in Mexico or Central America, I would guess the latter explanation is more relevant for this case."
] |
[
"I’ll let this paper by ",
"Hough, 2018",
" answer that question."
] |
[
"Yes. You can spend days sifting through the contradictory papers saying that they’ve confidently identified tidal triggering in a given seismic catalog vs the papers saying they’ve confidently rejected tidal triggering in the same catalog. Suffice to say, demonstrating clustering is hard, as described above."
] |
[
"What would happen to a bubble of carbonated water in space?"
] |
[
false
] |
[deleted]
|
[
"This is a video of Alka-Seltzer in a sphere of water on the ISS. ",
"http://www.youtube.com/watch?v=bgC-ocnTTto",
"Edit: Here is the same thing while rotating. ",
"http://www.youtube.com/watch?v=BxyfiBGCwhQ&feature=relmfu"
] |
[
"hope this answers your question.",
"http://www.youtube.com/watch?v=bgC-ocnTTto",
"(on a related note, how does one make a link out of something that is not a link? i.e. Platypuskeeper's \"like this\")"
] |
[
"there is formatting help on the lower right side of the reply box",
"but basically it is [like this]_(",
"http://www.youtube.com/watch?v=bgC-ocnTTto",
")",
"except remove the underscore between the ] ("
] |
[
"If the average human ear was a microphone, what would its specifications look like?"
] |
[
false
] | null |
[
"Ribbon microphone with huge fleshy ribbon. (DO NOT run phantom)",
"Cardioid with perfect off-axis rejection when installed in HUMAN HEAD mount (sold separately)",
"20hz-20,000hz for first 20-25 years of regular use",
"http://www.audioholics.com/room-acoustics/human-hearing-amplitude-sensitivity-part-1/clip_image001.gif/image_preview",
"Frequency response curve should look like the attached image, but flipped. Huge boost in High Mids and huge loss of Lows and Highs - gets flatter at higher SPL."
] |
[
"You ask a fascinating question, and one that requires a complex answer.",
"First, a lesson on what the ear is because I want to let you know exactly what you're asking and this is a topic about which I am very passionate. TL;DR at the bottom if you don't give a damn about science.",
"There are three sections of the ear: outer, middle, and inner. The outer ear is comprised of the pinna (colloquially: ear) and auditory canal (ear canal) with the tympanic membrane (eardrum) being the boundary between the outer and middle ear. The pinna, through its distinctive shapes and contours, creates phase cancellations in the acoustic waves as they enter the ear. These phase cancellations are what give us the ability to locate the source of a sound with one ear: monaural location. The auditory canal acts as a Helmholtz resonator, amplifying frequencies specifically important to human speech (approximately 3.4 kHz on average). At this point the modified acoustic energy reaches the tympanic membrane causing it to vibrate analogously to the incoming signal.",
"The middle ear is bounded by the tympanic membrane on the outside and oval window on the inside. Between these two points are three bones—the ossicles—that act as a pressure transformer between the ear drum and the significantly smaller oval window. These bones are called the malleus, incus, and stapes (colloquially hammer, anvil, and stirrup). In addition to acting as a pressure transformer (stepping up the pressure from the large tympanic membrane to the small oval window), the ossicles play a critical part in the auditory reflex. The auditory reflex is where you hear a loud sound and you feel your ears pang (like putting away dishes, someone playing drums, or firing a gun). The brain sends a signal to muscles and tendons attached to the ossicles and tenses them, attenuating some of the energy traveling through them. At this point, the acoustic energy from outside has been transformed into mechanical energy (through the tympanic membrane) and amplified by the ossicles. When the amplified mechanical energy reaches the oval window, it will be transformed again into hydraulic energy.",
"The inner ear has several parts relating to both balance and hearing, but the one that matters to the current topic is the cochlea. The cochlea is a helical organ that is filled with viscous fluids called perilymph and endolymph. As the waves of mechanical energy press against the oval window, the endolymph and perilymph move with it. The cochlea is a closed hydraulic system so at the opposite end of the cochlea and just below the oval window is the round window which moves opposite its oval cousin (oval window pushes in, round window pushes out and visa versa). As these waves travel through the cochlea the basilar membrane moves in conjunction with it, decoding the complex waveform. The basilar membrane has a mass/stiffness gradient along its lenth and it runs the full length of the cochlea. At its base—near the oval window and round window—it is at its greatest mass and least stiffness, meaning it is tuned to lower frequencies. At the apex of the cochlea it is at its smallest mass and greatest stiffness, meaning that it is tuned to higher frequencies. Think of this like a piano keyboard, where the left-most keys trigger low notes and the right-most trigger high notes. An organ called the organ of corti rests upon the basilar membrane and as the basilar membrane vibrates in response to the frequencies to which it is tuned little valves called hair cells are triggered. These hair cells release a neurochemical, changing the electrical potential of the perilymph in its section and sending an electrical signal via the 8th cranial nerve (also known as the vestibulocochlear nerve) to the brain. ",
"That is the Rube-Goldberg device that is our ear.",
"Now moving closer to answering your question.",
"Each ear operates omnidirectionally. We all can observe this: if you plug your right ear you can still hear things that happen on your right side in your left ear. The difference between the ear and a traditional omnidirectional microphone is that the ear is encased in a skull. The human head acts like a baffle, preventing some frequencies from making it around the head undamaged. These frequencies correspond to the size of the head. The average human head is about 6.5 inches across, ear to ear. This length corresponds with about 2 kHz. This is the critical frequency that divides the two components of binaural localization. I mentioned monaural localization earlier (localization with one ear). Binaural localization utilized both ears and it is divided amongst the frequency spectrum at 2 kHz, give or take. Frequencies lower than 2kHz are localized using a level difference. Literally, its louder in one ear than in the other. Frequencies higher than 2 kHz are localized using a time (phase) difference. Because our heads get in the way, higher frequencies take longer to arrive at one ear than the other because they have to reflect around the environment in an indirect path.",
"To properly recreate what the ear acts like you have to replicate much of what I listed above. This is actually an established recording practice, too. ",
"Just look up \"binaural recording\" and you find a wealth of recordings and information on the subject.",
" What those people use to recreate that is either a binaural recording microphone pair that are placed on a ",
"dummy head",
" or in the ears of the recordist.",
"The ear itself would have an extremely non-linear frequency response. ",
"This photo is a good approximation of that.",
" The auditory reflex would be like a built-in, frequency-dependent compressor/limiter with an attack time around 150 ms and a release time of maybe a full second (estimations). You would have to replicate the head and use a binaural pair of microphones as well. ",
" The quick and dirty way to get pretty close to replicating what our ears hear would be to take a pair of Shure SM57 microphones, put them inside a foam head, and hook them up to a stereo compressor with the attack and release settings as above and a threshold between 70 and 100 dB-SPL (a very wide gap, I know, but it's compensating for all of humanity). Then band-pass filter 6dB/octave at 80 Hz and 16 kHz. These frequencies are what are capable of being perceived by the basilar membrane inside the cochlea. Lower frequencies are usually felt more than heard and acousticians & audiologists kinda have no idea how we perceive super high frequencies since our ears don't seem to be able to hear them."
] |
[
"not omnidirectional, more like a figure 8 bent forward once you factor in the shape of the fleshy cartridge ear thing attached to your head"
] |
[
"How does rain come down diagonally with no wind?"
] |
[
false
] |
I suspect it has a simple answer such as wind at higher elevations? I've Googled and searched Reddit and couldn't find a definite answer.
|
[
"Your guess at a simple answer is correct. Rain will fall straight downwards unless there is horizontal wind blowing it in a different direction. It is not uncommon for there to be strong winds above ground that don't fully reach the surface, especially if you're in an area surrounded by buildings and/or trees. So if you witnessed this that's likely what was happening."
] |
[
"In a sail boat, I sometimes can have no wind at the deck but have wind just a few feet higher on the sails. Once the boat starts moving, I get apparent wind on the deck even though I can see from the surface of the water that it is calm. ",
"I imagine the rain keeps moving the direction it was going when it hits the calm air."
] |
[
"Thank you for taking the time to reply!"
] |
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