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[
"During the first nuclear bomb test, how did they know how far away to observe the blast? Did they already know how many tons of TNT (or TJ) it was?"
] |
[
false
] |
I tried some google-fu, but nothing showed up. How did the scientists that made the bomb know where to place their observation cameras and bunkers? From what I've seen they were fairly close enough to the blast to see it without using binoculars or other things. There were bunkers 10,000 yards away and observation things 20 miles away. I also read that there was a betting pool as to how many tons of TNT or TJ the blast would be. Is there a way to figure this out mathematically? (the TJ and distance of the blast wave)
|
[
"The question of how large a nuclear blast can be is a function of the total energy release possible multiplied by the expected efficiency of the weapon. ",
"So in the case of the first nuclear weapon, they knew that it contained 6.2 kg of plutonium. 1 kg of plutonium, completely fissioned, releases 18 kt or so of energy. So the absolute upper bound is around 112 kilotons. ",
"But they also knew their method was not going to be very efficient. The \"safe\" estimate was that it would release about 5 kilotons worth of energy — an efficiency of only about 5% (that is, only about .28 kg of plutonium would fission, in a weapon that had 6.2 kg of plutonium in it). The most optimistic estimates (e.g. in the betting pool) was around 50 kilotons — an efficiency of 45%. But this was unusual — most thought it would be lower, maybe even less than a kiloton. ",
"In reality, it was around 20 kilotons, which is an efficiency of about 18%, which is considerably higher than the \"safe\" guess (4X more). ",
"They had a pretty OK idea of how the blast wave would react at different distances and kept anything really sensitive well outside of those distances. They were aided in the fact that damage does not scale linearly with increase of explosive yield: because the explosive energy is released as a sphere, it scales as a cubic root. To put this simply, in order to double the area of destruction, you have to increase the yield by a factor of eight (so a 8 kt bomb destroys twice the area of a 1 kt bomb). So just because it was 4X more energetic than they predicted, that did not mean they had to be 4X as far away to be safe. ",
"There were many uncertainties, however. They tried to keep things as safe as they could under the circumstances, but there were many unknowns. They kept all personnel at comfortably safe distances, and tracked the spread of radioactive fallout. They even prepared for grim eventualities such as people accidentally dying during the test (which sounds fanciful, but it is worth noting that during several Soviet nuclear weapons tests there were inadvertent deaths due to unusual unanticipated phenomena, such as reflection of blast waves off of inversion layers in the atmosphere)."
] |
[
"They had blown up a test explosion of 100 tons of TNT earlier in the month, to help calibrate the effects. They did not have good reliable understanding of what thousands of tons of TNT would do, though — that's a ",
" of TNT. But they could guess for some aspects of it, like how the shock wave would work. A lot of it was theoretically determined, but with big error bars. ",
"They greatly increased efficiencies in the early Cold War. By 1948 they could use more or less the same bomb and the same amount of material but get 50 kilotons out of it, by implementing a number of tricks to increase the efficiency. By the early 1950s they had fission bombs that could get in the 100s of kilotons, and had developed thermonuclear weapons in the tens of megatons. ",
"As for safety issues, when they started using thermonuclear weapons (fission+fusion+fission reactions), their early weapons were sometimes many times greater than predicted (e.g. Castle Bravo was 2.5X more energetic than expected), and this did create some significant safety issues (in particular with regards to radioactive fallout). They also made errors the other way, thinking weapons would be bigger than they ended up being. "
] |
[
"Castle bravo - the reason bikini atoll is ",
"missing a chunk",
"Apparently it has been deemed 'habitable' again, long before half lives would lead us to expect which is rather interesting."
] |
[
"Why do the same voltages appear frequently?"
] |
[
false
] |
3.3v, 5v, 9v, 12v and so on. Is there something inherently advantageous about these numbers or are they just somewhat evenly spaced out arbitrary numbers to try to keep things standardized?
|
[
"As far as batteries go you are limited to using multiples of the cell voltage of the system used in the battery. For example alkaline batteries are around 1.5V/cell, so AAA, A, C and D batteries use a single cell. 6V and 9V batteries use 4 and 6 1.5V cell in series. Other cells produce different voltages that you might also see commonly: NiMH and NiCd ~1.2V, Li-ion ~3.7V, Lead-acid ~2V (6 in series for a car battery to give 12V).",
"That doesn't exactly address your question, but batteries are the power sources for a lot of portable electronics and provide the base or starting voltage from which the device operates. There will usually will be some circuitry that changes the voltage to the proper level for that device. For digital logic, there are specific voltage levels which represent a low or high voltage (see ",
"/u/cyrusm",
"'s post)."
] |
[
"In regards to digital electronic circuits, which it kind of sounds like what you are referring to, the voltages are determined to suit the ",
"logic family",
" or the communication protocol being used in the design. These standardized logic families were created so that chips and circuits could more easily interface with each other in designs without additional, and fairly complicated/unreliable voltage conversion circuitry being included. As technology progresses, these voltages are becoming lower and lower (12V to 9V to 5V to 3.3V and so on) because transistors are becoming more capable of operating at these voltages, which uses less power. The wikipedia article linked has a ton more info on the topic."
] |
[
"There are some good answers here. To embellish, I'd imagine part of the reason there is such a drive to lower operating voltages on ICs has to do with ramp up and fall off delays for high speed digital circuits. ",
"No node voltage can instantaneously change from 0 volts to X volts or from X volts to 0 volts. Given some degree of parasitic capacitance -which all circuits have - the amount of time it takes to charge up a line to a valid voltage or decay to a valid voltage is small, but definitely real. Therefore, as operating frequencies increase, this \"analog\" behavior becomes more of a problem as the decay/charge times become significant with respect to the mark(high)/space(low) times on a digital bus. When the valid voltage range is tightened, less time is needed for rapidly changing voltage swings to settle, be sampled, then change again, only to be sampled again.",
"Also, different technologies require different voltages. The closer the input voltage is to the output voltages of local linear regulators on a given device - the less power is wasted to heat. Heat is a big concern for many applications. "
] |
[
"If your brain releases melatonin when it gets dark, is it the opposite for nocturnal animals, and it releases when it's light?"
] |
[
false
] | null |
[
"The answer is: melatonin is released during the night in both diurnal and nocturnal species, but it is not sleep-promoting in nocturnal species.",
"In both diurnal and nocturnal species, there is a daily rhythm in the firing of neurons in the central circadian clock, the suprachiasmatic nucleus (SCN). The neurons tend to fire most during the day and least during the night. Low firing rates are therefore associated with sleep in diurnal animals, but wake in nocturnal animals. For more details on how the SCN promotes wake vs. sleep, see my other post.",
"The effects of melatonin on sleep are in part mediated via the SCN, since SCN neurons have melatonin receptors. Melatonin suppresses the firing of SCN neurons. In diurnal animals, this has the effect of promoting sleep. In nocturnal animals, this has the effect of promoting wake.",
"In summary, the effect of melatonin during night is to enhance the natural night-time state of that animal, be it sleep or wake."
] |
[
"No. Melatonin is released from the pineal gland into the blood during darkness, regardless if the animal is diurnal or nocturnal. "
] |
[
"Then what is the primary regulator of the sleep-wake cycle in diurnal and nocturnal animals?"
] |
[
"Why aren't we growing square trees?"
] |
[
false
] |
The article says that the original scientist moved onto other things because "inertia and distractions delayed implementation." Still though, this seems like a hugely beneficial idea given that only 50-60% of trees are actually used for lumber - the rest goes to pulp, paper or waste. So what gives?
|
[
"The method discussed appears to promote a specific growth pattern via an artificial scarring response. Perfecting the method, training a workforce and artificially maintaining millions of trees throughout their long lifetime would be labor intensive and wouldn't reap any potential benefits for decades. Given lumbers' relatively low cost the logging companies likely perceive it as too much risk for not enough reward at this time."
] |
[
"Sure - but it seems that they had the process down where you basically cut the tree down like grass. Cut off the top 3/4 and the tree regrows itself. I'm guessing it probably has to do with the already low-cost of lumber. It's a shame though, less forest cutting seems like a pretty good idea. "
] |
[
"Indeed; I personally find it fascinating. Unfortunately migrating between large-scale systems involves an inherent cost of time, money and risk that is often not justifiable until the existing system becomes unviable."
] |
[
"Why are we carbon based?"
] |
[
false
] |
[deleted]
|
[
"Carbon is in group 14 of the periodic table. It has 4 valence electrons, and so can form 4 bonds, allowing for very complex large molecules. 4 is also halfway between 0 and 8, both of which form a stable octet of valence electrons, so carbon can bond easily with nearly any atom, regardless of electronegativity. Carbon is also relatively common as nearly every ignited star produces it. All these make carbon a good element to use as the basis of life.",
"If you're asking why other chemically similar elements like silicon aren't the basis for life, silicon just can't bond so easily with many different atoms, and it's huge compared to carbon. In addition, redox is very important for most energy-releasing and absorbing processes. Carbon's fully reduced oxidised state is a gas, easily expelled. Silicon's fully oxidised state is sand. There are some obvious inconveniences associated with this"
] |
[
"A little background, first: in general, the properties of all matter around us, from living things to rocks, are determined by the outer, or valence, electrons in the atoms making up those things. It is these valence electrons (their number and how they're arranged) that determine how atoms bond and interact with one another.",
"Carbon just so happens to sit at a spot in the periodic table that gives it four valence electrons. It also just so happens that, at this spot, there are four valence orbitals (essentially, slots for electrons to occupy). Each orbital, though, wants two electrons in order to be satisfied. This means that carbon wants to form exactly four bonds to other atoms in order to stabilize itself. Carbon also sits high enough on the periodic table that all of its electrons are held fairly close to its nucleus, which means that when it bonds to things, those bonds are typically very strong. Finally, carbon is attractive to electrons (electronegative), but not too attractive, which means that it will usually share electrons equally rather than ripping them off or giving them up entirely.",
"Together, these properties allow carbon to link up with up to four other carbons (or atoms other than carbon) at a time, and those bonds tend to stay together well. Alternately, carbon can bond to the same thing twice or even three times. It's this ability to bond well to so many other things, in so many ways, that allows carbon compounds to form up into all different shapes and sizes (organic compounds). Carbon is also abundant on this planet, which is good news if you want a bunch of complicated carbon-based molecules to come together in the right way to form a system (life).",
"Problems with other elements: they may have too many or too few electrons, they may be further down on the periodic table and form weaker bonds (like silicon), or they may prefer to form different types of bonds that don't give you the freedom to form such complicated structures."
] |
[
"As mentioned elsewhere, Carbon is very versatile when it comes to forming chemical bonds. It can bond to form stable molecules with many different atoms including other carbon atoms. This allows it to form the long chains and polymers that are vital for something as complex as living organisms. ",
"Another point unrelated to Carbons actual properties is that it occurs everywhere. Carbon is one of the elements produced in ordinary nuclear fusion in stars, as opposed to the Supernovae that form most heavier elements. As a result of the way nuclear fusion progresses Carbon the fourth most common element in the universe (After H, He and O). Thus even if another type of atom could form molecules complex enough to constitute life, it would still be unlikely to occur simply because Carbon is so comparatively common."
] |
[
"Could an audio speaker demolish a large structure (like a bridge or building) via sonic resonance?"
] |
[
false
] |
Imagine the following system: Would that even work? I've seen old videos of bridges torn apart by resonance, and I've had neighbors crank their car stereos up loud enough to rattle the floor in my apartment. I'd like to think it wouldn't actually be that easy to take down a building, though.
|
[
"In order to get the structure to fall apart, you would need to generate a big enough wave inside the structure to overcome the structural integrity. In theory, there's no reason you couldn't do that. However, wave propagation through any medium is always a little bit lossy (sometimes a lot lossy). That means that the amplitude of the wave gets attenuated as it travels. Additionally, that attenuation is somewhat proportional to the amplitude itself. That means that the minimum power to make the building collapse at the resonant frequency is dictated by the lossiness of the building resonating at that frequency and at the collapse amplitude.",
"Given current technology, I'm fairly certain you can not produce this much power with an audio speaker, not to mention the frequencies would be very low. You would need something more akin to repeatedly hitting the building with a wrecking-ball."
] |
[
"The resonant frequencies of buildings are generally too low for speakers to reach, well below the human hearing range, so it would be a difficult technological feat to build a speaker capable of accomplishing this.",
"Edit: Relevant ",
"Myth-buster's test of Tesla's Oscillator"
] |
[
"Yeah, the issue is power. Finding the right frequency is the same as asking what's the minimum power I need to make speakers that can knock down a building, but that minimum might be really big."
] |
[
"What does radioactive decay actually look like? If you had a gram of an element with a short half-life (maybe an hour or so) what would you observe?"
] |
[
false
] |
[deleted]
|
[
"If you had a gram of an element with a short half-life (maybe an hour or so) what would you observe?",
"Typical decay energy is on the order of tens of thousands to a million electron volts per decay. To put this in perspective, ",
"the burning of sodium in chlorine gas",
" to form table salt, releases a puny 4.7 eV per atom. So the energy released would be hundreds of thousands of times more than any mundane ",
" reaction.",
"If the isotope only had a half life of an hour, the sample would melt and then vaporize extremely quickly. This would probably also melt the container holding it in short order.",
"If the sample was in a solution, the solvent would boil away rapidly, followed by the vaporization of the sample itself. the solution would heat rapidly even if quite a small amount was dissolved, a few micrograms, for example.",
"This would be particularly true of alpha an beta emitters, which is how the vast majority of radioisotopes decay. Alpha and beta particles have poor penetrating power, so the decay energy would be deposited inside the sample itself, or very nearby. ",
"In the case of gamma emitters, this would not necessarily be true, because gamma rays have high penetrating power. So the energy given off by the sample would be distributed over a much larger volume surrounding the sample. The air surrounding the sample container would give off a ghostly blue glow as a result of the gamma rays ionizing air molecules.",
"One gram of a gamma emitting isotope with a very short half life would be almost impossible to handle. Nobody could get anywhere near the sample container without receiving a life threatening dose of radiation, and the gamma rays would rapidly damage any electronic devices such as cameras and robots used to handle it remotely."
] |
[
"Nuclei are really, really small. The smallest feature a microscope can see is ",
"slightly less than half",
" the wavelength of the light it focuses.",
"Visible photons have a wavelength of 400-700 nanometers, and are much too \"big\" to image a uranium nucleus - which is about 266 million times smaller than the wavelength of purple light.",
"So on the microscopic level you'll see nothing, and I'm not sure it makes sense to ask what happens with a no-limit microscope because it involves quantum tunneling and just sort of goes from intact nucleus to broken nucleus.",
"On the macroscopic level you'll see ",
"a chunk of glowing-hot metal",
"."
] |
[
"Yup, it'll be warm to the touch. If you insulate it— so that the heat it generates doesn't escape— it'll get hotter and hotter.",
"A blob of plutonium and some thermocouples and a heat sink makes a fairly long-lived power source, a \"nuclear battery\" which is very simple and reliable. These are used in deep-space probes, Cold War Russian arctic lighthouses, and once upon a time they were used in pacemakers."
] |
[
"What is it exactly that makes your throat hurt?"
] |
[
false
] |
Bonus question, why does it dry out so quickly when you swallow or take a drink?
|
[
"I assume you are asking about sore throats during infections. When viruses or bacteria infect your throat, your immune system responds by inducing a localized inflammation. This is primarily mediated by ",
"granulocytes",
" and the cytokines/chemokines they release. One of the effects of inflammation is pain and that is why your throat hurts.",
"You might ask, since viruses and bacteria usually do not cause the pain directly themselves, why would your own immune system want to cause pain to your own body? The answer is that inflammation is a process whereby your immune system attempts to fight off the infection. The exact details are extremely complicated and are still being researched on but in general, inflammation serves to recruit various types of immune cells to the site of infection. It does so by causing localized increase in blood vessel permeability (this results in swelling and redness) which in turn promotes ",
"leukocyte extravasation",
". The pain that results from inflammation is thought to bring attention of the organism to the affected area.",
"Besides the acute recruitment of immune cells to the inflammation site, pro-inflammatory molecules released by the immune cells also enhances ",
"antigen presentation",
" to ",
"lymphocytes",
" that will eventually be the ones responsible for fully neutralizing the infectious agent(s)."
] |
[
"Great reply. On a side note, if you're experiencing inflammatory pain and you take an anti-inflammatory like ibuprofen to reduce it, does that also lessen your immune response to the infection? And so, would taking anti-inflammatories actually cause you to recover more slowly?"
] |
[
"This is a question I occasionally wonder about too. Off the top of my head, I can't think of any studies that addressed this directly but I would imagine that taking NSAIDs or immunosuppressants does affect the immune response against pathogens although the extent of the effect will probably depend on a wide variety of factors. However, we typically recover without any issues because the immune system has a lot of redundancy and it is not surprising considering how pathogens often try to suppress the immune system themselves. "
] |
[
"Is it possible for a human being to condition themselves to hibernate throughout the entire winter like other animals and insects do?"
] |
[
false
] | null |
[
"Sort of",
"http://www.nytimes.com/2007/11/25/opinion/25robb.html",
"They aren't hibernating, of course. But then, neither are bears."
] |
[
"We could certainly adjust our metabolic rate to use less energy and require less food, but we wouldn't be able to hibernate. The biggest problem with hibernation is warming the body rapidly upon waking. Animals that can truely hibernate have large stores of brown adipose tissue to produce a large amount of heat quickly in key parts of the body. Humans start with this tissue at as infants, but lose the majority of it as they age. "
] |
[
"You would really have condition yourself to deal with the tappen too. (the fecal plug that builds up and prevents a bear from soiling itself, very painful poop upon waking)"
] |
[
"Why can i not see the exhaust from a bus, but i can see its shadow"
] |
[
false
] |
The bus i take to school everyday has the exhaust pipe on the back of the bus, when i look at it, i see nothing(except the occasional puff if black), so why can i see the shadow of this invisible gas?
|
[
"Its a ",
"shadowgraph",
" caused by the difference in index of refraction between the hot exhaust and cold air."
] |
[
"The reason is really because the light casting the shadow is collimated. I.E. it is all coming from the same direction. However, when you are simply looking at the exhaust, light is coming from multiple directions, so it hides the distortion. If you look closely, the exhaust will still blur whatever it is in front of still."
] |
[
"The refractory index of the exhaust is markedly different to the surrounding air. "
] |
[
"Is baldness more prevalent now than it was years ago?"
] |
[
false
] | null |
[
"Yes, it's much more prevalent today than it was in the past.",
"Androgen hormones, the cause of male pattern baldness, are elevated in hyperinsulinemia, the pre-cursor to type II diabetes. Formerly called \"adult onset diabetes\" until it started appearing more and more commonly in younger people. (sources: ",
"hyperinsulinemia elevates serum concentrations of free insulin-like growth factor-1 (IGF-1) and androgens",
" and ",
"Type 2 diabetes has been described as a new epidemic in the American pediatric population that has been coincident with the overall 33% increase in diabetes incidence and prevalence seen during the past decade.",
")",
"Balding is not unknown among tribal populations, but it is quite rare and usually limited to a receding hairline. (source: observations of australian aborigines, ",
"little baldness was seen even in the very old.",
").",
"Androgen isn't the only hormone thought to present a part in hair loss, hormones such as serotonin, estrogen, cortisol and many more can play a role. Diet and environmental factors can throw these hormones way beyond normal ranges. Phytoestrogens in soy (a food newly introduced in the human diet in any significant quantity) can increase estrogen effects beyond normal ranges, consumption of only the tender cuts of meat without consuming the cartilaganous and tougher parts ",
"creates an amino acid profile that favours excess serotonin",
", cortisol production is triggered by stress, which modern lives certainly are more stressful, but also by white light (invention of electricity) and lack of sleep (alarm clocks). For more reading on this stuff, check out ",
"Danny Roddy's",
" site using hormonal panels to determine imbalances and then make dietary changes which are known to increase/decrease specific hormones."
] |
[
"Androgen hormones, the cause of male pattern baldness, ",
"Only if they carry the allele for male-pattern baldness. Androgens by themselves will not cause male-pattern baldness.",
"Balding is not unknown among tribal populations, but it is quite rare and usually limited to a receding hairline. (source: observations of australian aborigines, [3] little baldness was seen even in the very old.).",
"That doesn't say anything except for the rate of male-pattern baldness in aborigines. Allelic frequencies vary between populations. ",
"which modern lives certainly are more stressful",
"Eh."
] |
[
"Well, ancient and medieval art depicts tons of bald men. And since we lack any sort of epidemiological records for the bulk of human history, I'd say \"We don't know, but probably not.\""
] |
[
"Is there a name for when you review a mental list and you almost always forget 1-2 items?"
] |
[
false
] | null |
[
"Hi Papapadopoulos thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
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" ",
" "
] |
[
"‘Psychology’ "
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"listed in our wiki!",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"What do they mean when they say that electromagnetism, the strong nuclear and weak nuclear forces all unify into one force at high temperatures? Is it one force or three forces?"
] |
[
false
] | null |
[
"Yeah, sorry about that. It’s quite a technical subject and I don’t know of anything to point you to"
] |
[
"The fundamental forces all arise from symmetries. There is a lot of mathematics I don’t think I can cover here but basically there two types of symmetry:",
"a trivial kind where you do nothing to everything and a non-trivial kind which does something to multiple things such that the effect cancels out.",
"For a certain type of symmetry, if you want that to be a symmetry of nature, you have to have a force.",
"The larger the symmetry, in a specific sense, the more degrees of freedom that force will have to have. ",
"Unification is the idea that there is a large symmetry of nature with a corresponding force, and all the symmetries and forces of the standard model are contained within the larger one.",
"An example of this which we know to be true is electroweak unification. There is some electroweak force, which comes from some symmetry, part of that symmetry has been broken, and the remaining parts make up electromagnetism and the weak nuclear force"
] |
[
"Hmm this is still sort of hard to grasp",
"Are there any videos you'd recommend to make things easier?"
] |
[
"I'm trying to get into illustrating extinct mammals. Is my drawing of Hyenadon gigas anywhere near accurate?"
] |
[
false
] |
Hey, Askscience! I'm a concept artist and thought it would be fun to try my hand at illustrating extinct critters, but I'm not entirely sure how to go about doing it accurately. I thought I'd draw a hyenadon first, so I went ahead and drew it over a picture of a skeleton I found while looking at lots of reference of modern hyenas and previous hyenadon illustrations. According to Wikipedia, Hyenadon gigas, one species of hyenadon, was 10 feet high! I added in the human silhouette and it was absolutely dwarfed and didn't seem right at all, so I shrank the hyenadon down a little to perhaps reflect hyenadons in general or a younger hyenadon gigas. Does this seem OK? Also, could any of you recommend any good blogs or resources that I could look at to get better estimates of the metrics of extinct critters in the future?
|
[
"Edit - Your last statement is bogus - extinct critters in the future...",
"You misread OP. They were asking for resources where they can, at a later date, find references for the body dimensions of extinct animals. They were not asking about extinct animals in the future, but rather their future studies of extinct animals."
] |
[
"He means look at in the future. . . "
] |
[
"Hi! This is not my field of expertise, but since no one gave you any kind of answer I'll just try to help. I believe 10 feet is probably not how high they were, but the end of the tail to tip of nose measure. Usually when talking about sizes of similar animals that measure is used (alongside weight). 10 feet high is indeed way too much."
] |
[
"Do airline crews suffer a higher ratio of radiation illnesses?"
] |
[
false
] |
It seems to me that even a marginal exposure, over a large number that work in the business would result in a higher incidents of cancer or other illnesses vs the average population.
|
[
"The amount of radiation received by airline crews is small roughly 2 mSv per year. It's not known with certainty whether these levels are harmful or not. According to the linear no-threshold model, any amount of radiation increases the risk of cancer, however, according to the radiation hormesis hypothesis, small amounts of radiation actually decrease the chance of cancer. If the linear no-threshold model is correct, then the effect would still be small, 1 Sv increases the chance of developing cancer by 5%, working for 20 years would receive roughly 40 mSv. Which would result in a 0.2 % higher chance of developing cancer.",
"There are studies underway in areas with high levels of natural background radiation to determine the effects of long term exposure to low levels of radiation. The city of Ramsar, Iran has the highest natural background radiation levels in the world, with some people receiving doses great than 100 mSv per year. Wikipedia has this to say about the area",
"Early anecdotal evidence from local doctors and preliminary cytogenetic studies suggested that there may be no such harmful effect, and possibly even a radioadaptive effect.[8] More recent epidemiological data show a slightly reduced lung cancer rate[9] and non-significantly elevated morbidity, but the small size of the population (only 1800 inhabitants in the high-background areas) will require a longer monitoring period to draw definitive conclusions.[10] Furthermore, there are questions regarding possible non-cancer effects of the radiation background. An Iranian study has shown that people in the area have a significantly higher expression of CD69 gene and also a higher incidence of stable and unstable chromosomal aberrations.[11] Chromosomal aberrations have been found in other studies[12] and a possible elevation of female infertility has been reported.[13]"
] |
[
"Does 5% mean if you had a 1% chance of developing brain cancer, you now have a 1.05% chance? Or does it mean you now have a 6% chance?",
"Whenever I see results of studies given in that form, I'm never sure what is meant. Is there a grammatical standard or way to tell?"
] |
[
"Ideally, you should say that 1% to 1.05% is a 5% increase, 1% to 6% is a 5 percentage-point increase. Wikipedia says:",
"the incidence of cancers due to ionizing radiation can be modeled as increasing linearly with effective dose at a rate of 5.5% per sievert.",
"I take that to mean that it's a 5.5 percentage-point increase per sievert. Obviously the model falls apart at high doses (20 Sv = 110% probability of cancer? What does that mean?!), but since an acute dose of 8 Sv is ",
"invariably fatal",
", that's not of too great a concern."
] |
[
"Why are homosapiens the only organisms still alive in the homo... ehh I forgot the word. Family? Also, how would life be different today if the population was a mix of homo species?"
] |
[
false
] |
Edit: it was genus! Genus, right? Genus and species make up the name? I remembered this right after I submitted.
|
[
"Yes, Homo is the genus name. The homo genus arose about 2.3 mya with ",
", humans evolved 200,000 years ago. We are the only living representatives of this genus. Not so long ago 3 species co-exsisted: ",
"neanderthals",
" and ",
"floresiensis",
". The other species like erectus, or habilis were extinct before we evolved and it is thought that these species are our direct ancestors. e.g. H. habilis -> H. erectus -> H. heidelbergensis -> H. sapiens (but this is not a hard linage in the sense that many people would debate this exact order/timing of events etc.)",
"Neanderthals went extinct ~24,000 years ago. That is pretty recent in the context of the history of the human species.",
"Three major hypothesis why these species (neanderthals specifically) went extinct:",
" ",
"We out competed them for resources, and we hunted or killed them to into extinction",
"We interbred with them, 'blending' the two species. Not a lot of evidence for this one. A paper came out a while ago which provided evidence that humans and neanderthals interbred but how many interbreeding events there were and how pervasive it was remains a question. ",
"Their environment changed and they were not able to adapt and went extinct.",
"A combination of 1 and 3 are probably the best answer we have to date.",
"You may be interested in this wiki article on the ",
"homo",
" genus and ",
"human evolution",
"."
] |
[
"Is there? I have never heard this before at all. Infact, Austalopithecines appeared after the pan/homo lineage split so you would have to include all Australopith precursor species such as ardipithicus and the other handful of species who's names escape me in Homo too."
] |
[
"Some argue that neanderthals were not a separate species, but rather a subspecies of human and should be therefore classified as H. sapiens neaderthalensis. We could get into a lengthly discussion about speciation and what a species is, but the long and short of it is - not every case is a species defined by the ability interbreed and produce viable offspring. If you want more information on speciation let me know."
] |
[
"Reinterpreting the Drake equation, I call it 'Edens Everywhere'. Could it hold up?"
] |
[
false
] |
Every time I see someone go through the steps of the Drake Equation, they get to the part where they put in the number for how long a civilization exists they use ourselves as an example, and put in between 2000 and 40 years. The result is that there should be very very very few civs at our level. However, life has been on this planet for 500M years. If you use that number, there should be a crapload of planets with complex life (monkeys / dinosaurs... whatever). Everywhere, there should be planets with 'jungles', 'oceans', and rich biomes. Edens everywhere. Is there any reason this cant be the case, and would it maybe explain why we have found no signals from ET?
|
[
"Actually life is believed to have been on earth for up to about ",
"3.8 billion years now",
". ",
"edit: apparently even longer, read the comment below"
] |
[
"I took the \"up to\" to mean that is the earliest estimate (I apologize if I misunderstood), but that number comes from direct fossil evidence, and so is the latest estimate. It is very possible based on what we now know that life had existed on earth for up to 4.2 billion years, assuming the various conditions that may have led to life and when they were first present. and there are a lot of research papers that examine the possibility. ",
"The late heavy bombardment happened about 3.8 billion years ago, and devastated the earth. The oldest rocks on the earth are from this time period, and so scientists used to assume the earth was molten up until this point, but now know otherwise. Fossils appear in those rocks, and so either life predates the event or life arose spontaneously immediately afterwards. Either way this is relevant to the OP's question because it means that life basically came about as soon as the earth had oceans, and says a lot about how easy it is for life to spring up and how much life there could potentially be outside of our planet."
] |
[
"Thanks for the reply, I was siding with caution on the dates given that it is very much not my area but I knew the OPs 500 million was way off."
] |
[
"Why are batteries arrays made with cylindrical batteries rather than square prisms so they can pack even better?"
] |
[
false
] | null |
[
"First of all, some packs are made with prismatic cells. The pros and cons of cylindrical vs prismatic cells themselves are more important than packing efficiency. Notably, cylindrical manufacturing is more mature, and cylindrical cells tend to be better (in energy density and cost per kWh) at lower capacities, which most packaged battery packs are.",
"Here's an in-depth article on the cylindrical vs prismatic question: ",
"https://www.sciencedirect.com/science/article/pii/S0378775316315981"
] |
[
"Mostly historical now.",
"Originally many mass-manufactured batteries were made by rolling flat sheets of material, inserting a rod, and filling the space with an electrolyte. It made for a fairly simple method of manufacture and was pretty reliable. By rolling a sheet around a tube you easily got a known size without needing spacers and rods were pretty simple to extrude. You could also cast or extrude the tube pretty easily.",
"If you went with two flat sheets you'd need several spacers to make sure the sheet was evenly spaced all around and a flat item is less structurally-sound than a round one. Look at the strength of an arch vs the strength of a square opening. ",
"In addition, you have the highest ratio of volume to surface area with a round container. But if you go with a sphere you lose a lot of volume when you pack them. It turns out that a great balance of volume to surface area and packing units comes from cylinders instead of spheres or square prisms.",
"So most battery manufacturers settled around making cylindrical batteries rather than any other shape. The exception is when you really need to maximize volume, then they go with whatever shape does that best - such as in a cell phone, you'll see that the batteries will often be a flat rectangle which uses every bit of space possible."
] |
[
"Another thing to note is pressure. Cylinders are more able to withstand overpressure, and batteries tend to produce hydrogen (which is catalytically recombined and/or diffuses out).",
"Additionally, packing of cylinders in a hexagonal lattice is pretty close to packing of hexagons, so the gains are relatively minimal and if you need cooling channels regardless, may be non existent.",
"edit: according to wikipedia (and easy to verify geometrically), hexagonally packed circles fill up slightly over 90% of the area: ",
"https://en.wikipedia.org/wiki/Circle_packing",
"so for it to make sense to go with hexagons or squares, the space (rather than weight) has to be an extreme premium."
] |
[
"What is an anaerobic environment?"
] |
[
false
] |
[deleted]
|
[
"An anaerobic environment is one in which there is little to no breathable oxygen. The Earth is mostly made of aerobic environments and features few anaerobic areas. Perhaps unsurprisingly, most of the life on Earth inhabits aerobic environments while avoiding anaerobic anomalies. However, anaerobic environments are often of great interest to geologists, zoologists and biologists due to the unusual insights they provide into nature.",
"Your container would initially not be an anaerobic environment until the available oxygen is used up or removed. ",
"Source: ",
"https://sciencing.com/anaerobic-environment-10003906.html",
" "
] |
[
"Nope. Much of the seafloor and deeper ocean has low enough concentrations of dissolved oxygen to be considered anaerobic. And that's to say nothing of anoxic lakes and other freshwater features."
] |
[
"Nope. Much of the seafloor and deeper ocean has low enough concentrations of dissolved oxygen to be considered anaerobic. And that's to say nothing of anoxic lakes and other freshwater features."
] |
[
"Is there an electronic component that can change its resistance based on the current that flowed trough it? A bit like air ionization just more permanently."
] |
[
false
] |
Basically satisfying the following equation: R(q) = C * sum(q) where R is the resistance, C is an arbitrary constant and q is the charge that traveled trough the device with a negative and a positive direction.
|
[
"Sounds like a \"",
"memristor",
"\" - its resistance varies depending on how much charge has flowed through it previously, and in which direction.",
"It doesn't satisfy your equation though, because a memristor's characteristics are non-linear; you can't vary the resistance all the way from zero to infinity just by flowing charge."
] |
[
"Thermistors are sometimes used this way, exploiting the fact that when current flows through them, the power dissipated causes them to heat up and change resistance with either a positive or negative temperature coefficient.",
"Positive coefficient (PTC) types are sometimes used as current limiting devices.",
"Negative coefficient (NTC) types are used as inrush current limiters with initially high resistance at turn on, and as it heats up, resistance drops.",
"Neither have the linear behavior to are describing and behave exponentially.",
"I don’t think any single component has the behavior you are describing, but technically you could probably use a small circuit combination of an Opamp, a FET (or a current regulator) and some resistors and capacitors to approximate what you describe, depending on the application"
] |
[
"Within its range and a range of currents, (if my shallow understanding hasn’t betrayed me) a thermistor between power source and load would also vary resistance depending on how much its own resistance heated it. Again, not a linear variation."
] |
[
"I take a sheet of plastic and rip it. What's happening at the chemical level?"
] |
[
false
] |
Is it mostly just disrupting some type of intermolecular force holding the separate molecules together? Or does the force actually break the covalent bonds within the polymers? If covalent bonds are breaking, what happens to the electrons that were once in those bonds? Any interesting analogues to other substances (paper, skin, graphite, etc) would also be appreciated.
|
[
"It's not favored energetically. You can use bond dissociation energies to determine this."
] |
[
"I don't believe it would be intramolecular forces that are being broken, but intermolecular forces. Intermolecular forces (hydrogen bonding, London dispersion, etc) are bonds that hold a paper molecule to another paper molecule. "
] |
[
"Sorry, I mixed the two up. But why can't you easily recreate the bonds by pressing the torn sheets together? From my understanding of it, the proximity could set up the system again, 'reforming' the paper."
] |
[
"Could someone please explain (like I'm 23) how the rotational motion of a turbine shaft produces electricity?"
] |
[
false
] |
[deleted]
|
[
"suppose you have a magnetic field passing through a loop of metal wire. When you change how much field passes through that loop, the wire responds by creating a current that would generate a magnetic field that opposes that change. So at the end of this shaft is a magnet, which as it rotates near coils of wire, generate currents/voltages within those wires."
] |
[
"A conductor and a magnetic field in relative motion create an electric current in the conductor. Properly arranging magnets and coiled wire, you can make a generator which converts rotational motion into electricity."
] |
[
"The turbine doesn't produce the electricity, it converts the water, steam, wind, whatever to rotational mechanical energy.",
"Then we connect that rotational mechanical energy (via a shaft or pulleys or whatever) to a generator, and ",
" produces the electricity. ",
"- ",
"http://en.wikipedia.org/wiki/Electric_generator",
" - "
] |
[
"Intuition of Wave Function"
] |
[
false
] |
According to Wikipedia, the wave function describing a particle in one dimension is Ae . Why does it take this form? Why is there a need for a complex valued function? I understand Euler's formula and that it is cos(kx-omega*t) + isin(kx-omega*t), but why does it need a cosine and sine term, and why is the sine term imaginary? Is it just the way the math works out, or is there an intuitive way to understand this? Thank you.
|
[
"The only good answer to the \"why\" is due to symmetry arguments. If you get higher into physics and learn some group theory, you learn how to approach a physics problem from scratch.",
"We assume that we are looking at a particular type of field/particle and we try to find it's governing set of equations. (If you have some mechanics background, we start with a Lagrangian.) ",
"From here, we assume anything can happen; that is, any term possible can be a part of this Lagrangian. We could say it's psi x the magnetic field x the shape of the shoes I'm wearing to the power of their size. Whatever you'd like.",
"Then we realize that physics must agree with certain symmetries. IE rotational, 4 dimensional space time boosts and translations, global U(1) gauge invariance, local SU(3) gauge invariance, the fact that my shoe size can't effect what is happening to a positron in Bangladesh, whatever. Plus the units must work out properly. And some other basic arguments. ",
"Eventually what you find is that there is only a few possible terms that could exist in the real world. The one representing a free particle gives us a divergence of a gradient. And it just so happens to have solutions of the form Exp(i(kx-wt)). ",
"We are stuck with a wave function of that form because nothing else works. If we were to assume some other form of the wave function, we'd find weird things like the wave function preferred to travel left rather than right, independent of what is happening otherwise. And since we know that nature doesn't actually do weird things of this sort, we end up with an equation that says Exp(ikx-iwt).",
"If you know UG physics, I could go further. If not, it probably would be a bit too mathematical to understand.",
"If you are asking why do we have fields in the first place? That's rather philosophical and I don't know how to answer it."
] |
[
"I'll vouch for the technical correctness of this answer, but I have a few problems with it.",
"1) Who decides what the Lagrangian is supposed to be, and how? This is at some point an ",
" choice, and all the fanciness with symmetry is just about keeping the set of assumptions to a minimum.",
"2) The free particle solution is actually unphysical. To see why, just try to come up with a consistent answer for the as-yet unspecified number ",
". The issue is not the differential equation, but with the choice of measure on phase space. That's why the usual pictures for quantum mechanics involve ",
"wave-packets",
", rather than the free-particle solution.",
"3) The intuition I find the most helpful about why complex numbers are needed (I think this is OP's primary question) is that quantum mechanics is, in some as yet poorly understood way, the ",
" of probability theory. You get complex numbers because they are necessary to interpret square-roots properly."
] |
[
"quantum mechanics is, in some as yet poorly understood way, the square-root of probability theory.",
"I don't know if it's that poorly understood. As Scott Aaronson points out, it can be thought that as straight forward generalization of probability theory: ",
"This is from nice lecture where Aaronson teaches QM this way:",
"\n",
"http://www.scottaaronson.com/democritus/lec9.html"
] |
[
"Do all blue eyes really come from ONE person? See description for more."
] |
[
false
] |
[deleted]
|
[
"Yeah, two people had to carry the gene to make a blue eyed baby. Those two people were descended from that original ONE person with the blue eyed mutation.",
"(This is purely hypothetical, assuming easy stats with no bernoulli trials, etc...)",
"Let's say the guy/gal was particularly successful, and had 6 kids. By your notation, he's Bb. He/she has 50% chance of giving the blue eyes gene to his kids, so let's say 3 of them end up being Bb.",
"Those 3 kids each went on to have 6 kids each, 18 total, and 1/2 will be Bb -> 9. So they had 6 more kids each, half of which will be Bb -> 27. Another generation -> 27 * 6 * 1/2 = 81 Bb peoples.",
"Then these 81 carriers decide to start making babies with each other, and now BOTH of them are Bb. There's now a 1/4 chance of having a bb kid with blue eyes.",
"This kind of spread is not uncommon even in recent times. Read up on the ",
"Founder Effect",
", it'll give you an idea and some examples of how a few people's genes can spread throughout a larger population.",
"tl;dr: original blue gene person had tons of babies, and at some point, some of his babies carrying the blue gene decided to get together and have blue eyed babies.",
"EDIT: Thanks for the suggestion, Surf!"
] |
[
"So it only spread due to inbreeding?"
] |
[
"Sure, if you want to call it inbreeding. The parents who made the first blue-eyed baby would both be able to trace themselves back to this original individual at some point. It could've been one generation ago or twenty."
] |
[
"Newton's Third Law of Physics - Why does anything move at all if there is an equal reactionary force?"
] |
[
false
] |
So the rule to my understanding and Googling is that for every action there is an equal and opposite reaction. What I can't wrap my head around, is that if I'm playing pool, and I knock the white ball into another ball, why is the white ball not knocked backwards an equal amount to the ball it knocked into? I can understand in a lot of cases gravity or other forces diminish the reactionary force, but in this case.. when one ball rolls into another the energy transfers to the other ball without an equal reaction visually. This video you can see him applying force to the ball, but no matter what way it hits the yellow ball.. at least visually to me there doesn't seem to be an equal reaction of speed from the white ball. Is it a case of diminishing returns? That the white ball after it transfers all energy to the yellow ball, the reactionary force from the contact is only so big as to move it a little bit? Where as the yellow ball has the energy from the cue plus the reactionary force from the white ball that gives it the greater speed?
|
[
"If the white ball transfers some of its momentum to the yellow ball, the yellow ball will speed up and the white ball will slow down. That is what you see in the video."
] |
[
"What Newton's third axiom says is, that the center of mass of a closed system cannot be accelerated.",
"That means, if you are in space, you cannot accelerate in any direction without emitting mass into the opposite direction (technically anything with momentum, so shining a flashlight in the opposite direction will also propel you forward ever so slightly).",
"This video you can see him applying force to the ball, but no matter what way it hits the yellow ball.. at least visually to me there doesn't seem to be an equal reaction of speed from the white ball. ",
"In the center of mass frame of reference, both balls simply change their direction while maintaining the same speed (in idealized conditions of course.)"
] |
[
"The white ball is indeed knocked backward an equal amount. Think of it in terms of the overall momentum. Before the collision you had one ball moving forward and one ball at rest. After the collision you have one ball moving forward and one ball at rest. ",
"The white ball was moving forward at we'll say 1 m/s. It met the yellow ball and they acted on each other. This made the white ball push the yellow ball and the yellow ball push the white ball. ",
"The white ball was pushed such that it was accelerated 1 m/s backward and the yellow ball 1 m/s forward. Since the white ball was moving forward at 1 m/s and then pushed 1 m/s backward it is now at rest (1 - 1 = 0). The yellow ball was at rest and then pushed forward at 1 m/s (0 + 1 = 1). Our total momentum is the same since we started with one ball going 1 m/s . ",
"If you're so inclined you could also think in terms of the reference frame of the white ball. It \"sees\" a yellow ball coming at it at 1 m/s and then bouncing off of it at 1 m/s in the opposite direction. The same as bouncing a ball off of the floor or a wall. You don't really consider the wall moving to hit the ball, but you just as well could draw up a reference frame from the point of the ball which makes the wall or floor hit it."
] |
[
"Why does a protoplanetary disc not stay?"
] |
[
false
] |
From my understanding, a protoplanetary disc is a disc of dense gas and material orbiting a newly formed star. My question is the disc only around young stars? I presume the matter falls into the star, but why? Does it not have enough speed? IF anyone could give me some insight into what happens it would be much appreciated!
|
[
"It's called a protoplanetary disk because it forms into planets. Material that collides and sticks together will create a gravity field, pulling more debris into itself."
] |
[
"Here is a quick article that talks about Micro-gravity and how planet building gets started",
"The disc is the gas that wasnt close enough (also Pushed away by stellar winds from the new star) to fall into the star during its formation. As far as I know if a old star was to orbit into a gas cloud it would be pushed away by stars outward winds creating a bow-shock. (I think I remember seeing that our solar system is going to or is currently traveling through a gas cloud) ",
"Im sure someone else can give an more in depth answer, this is what I remember from College astronomy classes and reading articles about similar stuff online. "
] |
[
"The ",
"Wikipedia article on accretion disks",
" discusses the process of matter falling into the star. Matter in the orbiting disk must lose angular momentum in order to spiral inwards towards the star. Angular momentum is conserved, so it has to be transferred from one portion of the disk to another in order to allow part of the disk to fall inwards. The ",
"magnetorotational instability",
" is an important mechanism that allows this to happen. Obviously, if planetesimals form and accrete into planets, some of the material in the disk ends up in said planets. The ",
"Wiki article on protoplanetary disks",
" also mentions that the stellar wind from the central star blows some of the gas out of the system entirely. "
] |
[
"Is there anywhere in the universe where energy is being converted to matter?"
] |
[
false
] |
In my Introductory Astronomy class, the professor said that the large amounts of energy produced by stars is the result of nuclear fusion converting some matter into energy. Is there anywhere that energy is converted back into matter or is the net amount of matter slowly diminishing? I guess a different approach to asking this is "Is it possible to convert energy to matter, and what are the conditions required?" Additionally, what form would this new matter take? Edit: Just to clarify, I am asking about matter, not mass. I understand that energy has a relativistic mass.
|
[
"The Large Hadron Collider converts the kinetic energy of protons into a series of massive particles.",
"The expression \"energy converted into matter\" doesn't quite make sense, because energy is a quantity and matter is a description of something. But there are examples (like the one above) where things with energy lose some of it when things with mass are created."
] |
[
"Particles, e.g fermions and hadrons, are formed whenever enough energy is available. So two 511kEv Gamma rays could collide and form an electron-positron pair. This however leads to a big unsolved conundrum of the big bang theory, why does their appear to be so much more matter than antimatter.\nWhat I think you are asking about, is whether the everyday low energy radiation coming out of stars could somehow combine to get enough energy to create particles. This would require an energy accumulator that would store up loads of small amounts of energy and release them with enough at one time to create particles.",
"Don't know of anywhere in the universe where this is thought to happen, but if the big bang theory was wrong and the universe was steady state this is a possible mechanism for sustaining it."
] |
[
"In the CNO cycle and pp-chains some positrons are emitted by nuclei in beta decay, which then annihilate with electrons. This is not the dominant part of the energy output, but it is significant.",
"Edit: Also, beta decay in general can be seen as turning energy (nuclear binding energy) into matter (electrons or positrons, and neutrinos)."
] |
[
"Commutators (QM)! How do they work?"
] |
[
false
] |
Saying two things, A and B, commute ([A,B] = AB - BA =0) always struck me as a totally arbitrary operation. Where did the idea for a commutator come from, and why is that relation special/what does it tell us? When two observables don't commute, they can't be measured at the same time (x & p, Lx & Ly, etc.), but why is this determined by their commutators?
|
[
"The way I think of it is that it doesn't matter which ",
" you make the associated measurement with. Say you measure x and momentum in the y direction. These operators commute so you can measure x first then y or y first then x and get the same result. But something like x px will give a different result than px x. Because measuring whichever one first in time order changes the state for the second measurement in time order. And since time ordering matters now, they can't be done simultaneously."
] |
[
"In the cause of angular momentum the commutators generate the algebra. So from the idea of group structure angular momentum is closed under this operation. IE [L_i,L_j] will always give you another element of the group. In particular these groups are called Lie Groups and the Algebra, Lie Algebra."
] |
[
"Touching on the Lie Algebra of angular momentum, considering certain operators as the infinitesimal generators of motions (J for rotation, p for translation) it becomes obvious why certain observables would fail to commute. NOTE: I've ignored the factors of -i when considering the momentum operator in the position basis.\nConsider the momentum operator p on our initial state ket |a> ( or in wave mechanics, we have our wave function f(a) ) which is an eigenket for the position basis (x|a> = a|a>). However, don't think of this as something to be bra-ketted to measure the expectation value, think of p for what it really is, an operation by which we send our initial ket |a> to a new ket |a + dx>. Thinking of p as an infinitesimal movement dx in a certain direction, we'd expect that the position expectation value would change as well (and in this basis, x|a + dx> will of course return (a + dx)|a +dx> )",
"Ah, but now lets return to the initial state |a> and lets act in the opposite order. x|x> will obviously be an eigenket the position operator x acting on |a>: x|a> = a|a>. Wonderful, but now lets let p act on it as well. p(a|a>) = a(p|a>) = a|a +dx>.",
"Here's where we see why something like the commutator is so powerful. We've arrived at our new position for both of them, but acting with p first causes the state to move infinitesimally, which is then picked up when x acts on it. The commutator picks up on this and suggests that the relationship between the x and p operators is more intimate than just two useful observables. It tells us that the notions in the Hamiltonian formalism of mechanics have been preserved under the process of going from coordinate to operator."
] |
[
"Do women with big boobs have more estrogen?"
] |
[
false
] | null |
[
"I have no idea why the top comments here are all people idly speculating about it when real answers exist one google search away. Breast development and size is a complex interaction between genetics and ",
"several different hormones",
" which includes the steroid hormones, estrogen and progesterone, growth hormone,insulin-like growth factor 1, and prolactin. Estrogen alone is not solely responsible. The best (but not the only) predictor of your breast size will be your female relatives. ",
"Having high estrogen, just like having high testosterone, is not even necessarily a good thing. It’s associated with increased risk of depression and anxiety, hair loss, thyroid disease, heart attack, stroke, blood clots, breast cancer, and ovarian cancer. It also doesn’t make you more likely to conceive as it causes decreased sex drive and irregular periods."
] |
[
"When taking estrogen based birth control pills these are the side effects to watch out for. You are messing with your hormones and can end up with higher than intended estrogen levels."
] |
[
"I don't know about breast size, but facial features are correlated:",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1560017/"
] |
[
"If an object with mass is moving near the speed of light towards me. Does the light reflected from that object \"blue shift\" into dangerous gamma rays?"
] |
[
false
] |
So it is my understanding that the light coming from objects moving toward an observer is "blue shifted" and the wavelengths compressed. If this is true can the light be so shifted that it is harmful to an observer? For example, if say "the flash" was holding a flashlight and running toward me at relativistic speeds, does the light get compressed to gamma rays?
|
[
"If this is true can the light be so shifted that it is harmful to an observer?",
"Yes, it can be.",
"For example, if say \"the flash\" was holding a flashlight and running toward me at relativistic speeds, does the light get compressed to gamma rays?",
"If he's running fast enough, yes."
] |
[
"And not only that, but thanks to relativistic beaming, the light will be focused into a narrow beam ahead of the object, so not only will you be hit by higher energy radiation, you'll also be hit by more of it."
] |
[
"/u/RobusEtCeleritas",
" is right, the answer is yes. But the gamma rays from The Flash's flashlight are the least dangerous thing in this scenario. To blueshift from visible light to gamma radiation, The Flash would need to be moving at at least 99.99999992% the speed of light. At this speed, his relativistic kinetic energy will be about 25,000 times his E=mc",
" mass-energy: should he collide with anything (including the air you're standing in), this energy will be released to the environment in an explosion. This would release about 30,000 times as much energy as all the nuclear weapons in the world.",
"https://en.wikipedia.org/wiki/Kinetic_energy",
"\n",
"https://en.wikipedia.org/wiki/TNT_equivalent",
"\n",
"https://en.wikipedia.org/wiki/Relativistic_Doppler_effect",
"\n",
"http://hyperphysics.phy-astr.gsu.edu/hbase/Relativ/reldop3.html"
] |
[
"How can exchange of photons generate attractive force?"
] |
[
false
] |
So I read that electromagnetic interactions are carried out by exchange of photons, but I can't understand how can that generate attractive force between electron and proton for example.
|
[
"Static forces are brought about by an exchange of ",
" particles. Virtual particles are not really particles (hence the name), but are mathematical pieces of the overall equation describing the fields. Static forces are brought about physically by static fields. The \"photon\" does not describe every possible electromagnetic field configuration. It just describes an asymptotically-free fluctuation of the EM field. Static fields are another possible configuration of the EM field. In static fields, there are no literal little particles shooting off from a proton, carrying away momentum, and then smashing into the nearby an electron and thereby causing and electron. You are right that this makes no sense. "
] |
[
"There's a good description of it ",
"here."
] |
[
"\"Exchange of photons\" and \"exchange of virtual particles\" in general is a terrible term in my opinion. In my opinion, it's people mistakenly thinking of a mathematical approximation scheme as a physical process, just because it can be formulated in terms of Feynman diagrams (",
"http://en.wikipedia.org/wiki/Feynman_diagram",
").",
"Really, what happens is that both electron and proton have an electric field attached to them because they both carry electric charge. When two electrically charge objects are brought close to one another, their electric fields adds up, resulting in a change of energy of the electric field, or equivalently, a force between the charged objects. At least that's how I like to think about it.",
"Virtual particles get their name from the mathematical formalism of Feynman diagrams, used in the framework of perturbative quantum field theory.",
"When you calculate scattering rates or other quantities, you can approximate these quantities by a (usually infinite) sum of contributions, where each contribution is usually much smaller than the previous one. This way you can just stop calculating at some point and ignore any further small contributions.",
"Now, each term in this sum, can be represented by a Feynman diagram. You can construct Feynman diagrams according to really easy rules:\n* You have one type of line for each fundamental particle in your model. E.g., in Quantum Electrodynamics (QED), a wiggly line for a photon, and a solid line with an arrow for an electron or antielectron (depeding on the direction of the arrow)\n* You have one type of vertex for each type of interaction in your theory. E.g. in QED, you only have the interaction vertex consisting of a solid line with arrow pointing towards the vertex, a solid line with arrow pointing away from the vertex, and a wiggly line connected to the vertex.",
"In order to calculate a scattering rate, you draw all diagrams you can think of with the correct set of incoming and outgoing particles. The more complicated the diagram is, the smaller the corresponding term, so you can neglect really complicated diagrams.",
"The incoming and outgoing particles are ",
" particles, that you can see with a detector. Any internal lines of the diagram are called ",
" particles, because they are also represented by lines, but aren't actually particles.",
"The reason that this makes sense is that you can consider each real particle, each virtual particle, and each interaction vertex as a factor in a term in the sum you're trying to calculate. Since the interaction vertex between e.g. a real electron, a real photon, and a virtual electron is the same as the vertex between a real electron, a real positron, and a virtual photon, you use the same line for both real and virtual particles.",
"But that's all just a very simple graphical representation of a mathematical approximation scheme, there is nothing physical about it!"
] |
[
"What's the best thing to say to someone when you're talking about evolution and they bring up the missing link?"
] |
[
false
] | null |
[
"Then we best wait for an expert to come along if I’m to be responsible :)"
] |
[
"I won’t directly answer because it is not my field but in general you have to really ask yourself if it is worth engaging with this kind of thing. If somebody is educated in science and says something like this they are being wilfully ignorant and no actual ",
" will change their mind."
] |
[
"She wasn't really that educated in science though. I'm pretty sure the only reason they hired her was because she had a teaching degree. She mostly just showed videos and gave worksheets. Now got the school year is over though I probably won't see her again I just want to know what to say if I ever hear that argument come up again, or if the opportunity ever comes up to debate with her about it. Also my soon-to-be step dad doesn't believe in evolution."
] |
[
"Why does the Earth have an axial tilt?"
] |
[
false
] | null |
[
"No one is sure! The most frequent theory that I have heard is that during the formation of Earth, it was struck by a very large object, such as another planet, at an angle. This would have caused Earth's rotation to have been altered. This theory is often coupled with theories about the formation of the Moon. See ",
"this article",
" for further information on the subject."
] |
[
"The Chicxulub impact did not produce enough force to give the earth an axial tilt. Like the other commenter said, it's thought to be a product of the moon formation impact. Also the moon stabilizes our axial tilt! Without such a large moon, the axis would sway more and seasons would be very unstable over the years compared to how they behave now. The earth is actually not unique in having an axial tilt. Mars has a similar yet unstable tilt since it has no large moons. Uranus is completely tilted on its side in fact! Uranus has extreme weather patterns throughout a Uranian year due to the extreme tilt"
] |
[
"could it have been the Chicxulub asteroid? or do we have reason to believe the earth has been tilted for longer. ",
"Also is earth unique in its axial tilt?"
] |
[
"Is it theoretically possible to have a set of entangled photons to interact with each other, even if one part is in a black hole?"
] |
[
false
] |
If you entangled a set of photons and sent one part into the hole, is it theoretically possible to have the entanglement survive the forces of the black hole and still interact with the other pair? Like, would one theoretically be able to entangle a pair, keep one in a sensor and send the other into a black hole and observe the interaction between the black hole one and the one in the sensor, thus getting data from inside a black hole?
|
[
"Imagine four playing cards: two Aces and two Kings. You select two cards at random; these are placed in envelopes, the envelopes placed in boxes, and one of the boxes is chosen at random and mailed to your cousin in Ontario. The remaining undrawn cards are destroyed. Now, you and your cousin each have a card, and each of you has either an Ace or a King with exactly 50% probability; you can have a look at your own card to see what it is, but it is impossible for you to determine your cousin's card without sending him a letter. This is a four-state system; each card can have an independent value of Ace or King.",
"Now imagine the same situation, except from the four you deliberately choose one Ace and one King. You place the two in envelopes, send one of them on their way, and destroy the rest. Now, when you open your box and see an Ace, you ",
" immediately that your cousin has the King; you don't need him to tell you what his card holds, indeed you might know this information before he even receives it! Your careful selection has reduced the problem to a two-state system; though there are still two cards, their values are no longer independent.",
"Similarly, quantum entanglement does not involve any interaction or transmission of data the way you're thinking; it is just that what looks like two independent systems is actually one -- each particle's state encapsulated in the other."
] |
[
"You place the two in envelopes, send one of them on their way",
"To anyone else reading this, it's an analogy. In quantum entanglement, there are no local hidden variables and the quantum states are not pre-determined."
] |
[
"That is orthogonal to what I was trying to illustrate, but it is a very important point; I couldn't think of a way to incorporate that in a simple analogy. Thanks for clarifying."
] |
[
"What are the oldest species that we could (in theory) bring back from extinction, given the half-life of DNA?"
] |
[
false
] | null |
[
"I do not believe that we are capable of truly bringing any species back. With out a parental cell then even if a \" \" was cloned, by using using an egg from a common ancestor, it would be a hybrid and not a pure \" \". DNA is not the blueprint of a creature, it is more like the library of information, of which a cell can draw from. DNA only makes the creature when released into the context of a the maternal cell. This is rooted in cytoplasmic inheritance, and addresses the misconception of DNA being the blueprint. This line of thought is rooted in a prior believe of a linear relationship from DNA to protein and to gene expression.",
"Also as a side not a species is not an individual but a functioning population. Genetic information can survive but memes can not. They don't exist as a tangible substance. ",
"I hear a lot about bringing species back, and not enough about not causing extinctions to begin with. "
] |
[
"It's not the half-life of DNA that's the real concern. DNA needs to preserved, and most DNA will not preserve well enough to even approach it's half-life. Some study specimens that have been preserved in alcohol for hundred of years provide viable DNA, but that's only a few hundred years we're talking about. The best way to preserve DNA is to freeze it, and that is what a lot of scientists are doing now with specimens of critically endangered species, in anticipation of a world where de-extinction is commonplace. The oldest species we could feasibly bring back is the Mammoth, because (by coincidence) we have some specimens that have been conveniently deep-frozen for us by nature for the last 10,000 years or so. ",
"When it comes to de-extinction, there are thee techniques: ",
" - This is what we do with things like heirloom tomatoes, selectively choosing for species with more primitive traits. This doesn't really bring species back, but you could end up with an end product that looks a lot like the ancestor of what you started with, and could fill the ecological niche left behind (assuming there is such a niche). They've been working on this method with cattle.",
" - A little more difficult to explain. Basically you sequence the genome of an extinct animal, compare it to one of an extant animal that it's closely related to, and then generically modify an embryo of the extant animal, changing the sequences that differentiate it from the extinct species. Assuming the extinct animal and it's extant relative are closely related, their genomes would be extremely similar, so you wouldn't need to change much. This is what they're doing with the passenger pigeon, and I expect that they will be successful in the near future.",
" - This is when you take ancient DNA, and using IVF, implant a cloned embryo into a surrogate of a closely related extant species, then wait out the gestation period and see if it's viable. We clone individuals of living species all the time, the only difference here is that the donor DNA will be coming from an extinct species. This is what Korea is currently attempting to do with a Mammoth. They may not be far off from achieving this, though they could (and should, in my opinion) be prevented from doing so due to ethical concerns surrounding the Asian Elephant (the Mammoth's closest extant relative, individuals would be subject to painful procedures and general misery associated with the IVF). ",
"Edit: I am a Zoologist, and admittedly unfamiliar with the current progress on de-extinction of plant species. So I should clarify that a mammoth is the oldest ",
" species we may be able to bring back."
] |
[
"There's the ",
"ice age flowers",
" (that's the first search result i got, if someone has a better article I would be interested in seeing it.)",
"If you're talking about animals, every few years I hear talk of resurrecting mammoths using elephant DNA to fill in the gaps like in Jurassic Park, but haven't heard much about that lately and like ",
"/u/ktreektree",
" says, it wouldn't be a mammoth, but a hybrid."
] |
[
"Do antibiotics kill all healthy gut bacteria and if so how does the body return to normal after treatment?"
] |
[
false
] | null |
[
"They certainly deplete the gut microbiome and in fact stomach issues are common with abx. Some bacteria escape due to a combination of factors, some are replenished from the appendix (turns out it is now thought to be a reservoir), and food. In bad enough cases some doctors even tell people have to eat probiotics (yogurt, live sauerkraut, otc high-dose).",
"\nSidenotes: the gut microbiome impacts us a lot, from mood to metabolism. ",
"Edit: I am getting several questions that relate to whether someone should take or not take or when to take probiotics. I ain't an MD and while I am a scientist with sufficient working knowledge on this subject given what I do (metabolism and chronobiology; yes, that involves the microbiome as well), my focus isn't probiotics. So I do not feel comfortable given any sort of advice. ",
"Edit 2: Yes, there is debate about the efficacy of oral probiotics, I am well-aware, with a huge argument being survival of bacteria in the stomach being long enough to make it to the intestines. My understanding of this is that that is why most off-the-shelf probiotic cfu counts are too low to be effective, and why fecal transplants are a thing."
] |
[
"Depends on the antibiotics. For most of them, no they don't kill ALL gut bacteria, but still result in dysbiosis. You would need a very high dose of a very powerful antibiotics to delete all your microbiote. The body returns to normal through the alimentation."
] |
[
"It's real. Most common right now is with people that have had C-diff infections that keep recurring and need good bacteria to re-colonize and cure their infection when antibiotic treatment isn't effective."
] |
[
"Using acceleration to achieve artificial gravity on spacecrafts?"
] |
[
false
] |
As the feeling of gravity is created if a spaceship is accelerating or spinning around in a centrifuge á la 2001: a space odyssey, one could achieve the feeling of gravity in a micro gravity environment. How fast does the spaceship have to accelerate in order to achieve near-earth values though? Is it 9.82 m/s And then would this method be useful for any sort of missions or would there be too big a energy demand so that we're better of with a centrifuge?
|
[
"To calculate the \"centrifuge-style\" acceleration, the formula to use is ",
". This formula is also equivalent to ",
"You can plug in your own figures into this - ",
" would be 9.81 in your example. If you are imagining a spaceship rotating end over end, then ",
" is the distance between the centre of mass and any given spot on the ship, for which you'd like to calculate ",
".",
"The nice thing about space is that once you've gotten your ship rotating, it won't stop until it hits something. So the energy needed isn't a huge problem. ",
"If you wanted to create gravity by accelerating linearly, you would need to continuously accelerate at 9.81 m/s",
". This would be very impractical for long periods of time, due to the amount of energy you'd need to expend to do so. You would also end up going extremely fast, which may be undesirable."
] |
[
"The \"less nice\" thing about rotating to produce gravity is that if your rotating section is small (think Discovery from 2001 sized) the acceleration on your head will be a lot less than the acceleration on your feet. Not sure what this would do to your circulation over time!",
"Plus, huge coriolis effects whenever you drop or throw anything!"
] |
[
"Forces aren't particularly useful at relativistic energies. This thread has a good talk through of the ideas. \n",
"http://www.physicsforums.com/showthread.php?t=552219"
] |
[
"If someone was born blind and suddenly gained their vision 20 years later could anything bad happen?"
] |
[
false
] | null |
[
"This does happen with individuals who born with congenital cataracts and who live in places without easy access to surgery. Project Prakash is an oeganization that does this in India and there are a number of research articles published on the vision of such people post surgery. I'm not sure what you have in mind about what sort of bad thing can happen."
] |
[
"Any type of sensory overload or anything like that"
] |
[
"Yes in the sense that things are brighter. But they continue to have poor visual acuity for a while and only slowly gain visual function."
] |
[
"What is happening when my nose clogs up?"
] |
[
false
] |
So, it's allergy season again, and it seems my sinuses have clogged up completely. It also seems no matter how much I blow my nose or rinse out, there's more to come. What is going on, and why does it seem to never end?
|
[
"The reason your nasal congestion \"never seems to end\" has more to do with the swelling and inflammation in your sinuses than with mucus production.",
"The allergic reactions you're having cause your sinuses swell, thus blocking the airways. Blowing your nose can help remove mucus, but it does nothing to decrease the inflammation (and can actually make it worse if you go overboard)."
] |
[
"You're nasal passages get inflamed due to the irritants in the air, whether they be smoke, pollen, or animal dander. The mucus built up is to protect your sinuses from coming in contact with the irritants. Blowing your nose can help relieve some pressure but if you blow to much you can cause your sinuses to come into contact with the irritants causing more inflammation and more sinus pressure so take it easy on the kleenex"
] |
[
"Netipotting has always helped for me. What you do is take a pot (in my case I always used a syringe without the needle as it was easier) and place it in one nostril and make sure it is a near 100% seal and pour water into the nose. This will cause the water to either run down your throat or out your other nose which can help clear up your sinuses. "
] |
[
"What happens to all the random particles that are inhaled into our lungs?"
] |
[
false
] |
I'm thinking particles of sand, dust, bugs or any other random particle. Do we just cough them out over the course of a day? Do they get lodged in there? Like that guy who had a pine tree growing in one of his lungs! From a seed!...
|
[
"what the.....",
"\n",
"http://www.mosnews.com/weird/2009/04/13/firtree/",
" ",
"I've never seen anything like that!"
] |
[
"Stores of energy in the seed?"
] |
[
"Similarily, ",
"a guy had a pea plant growing in his lung."
] |
[
"Are there any naturally occurring lasers?"
] |
[
false
] |
Either organically or in places like stars or small scales minerals? Where do materials lase without man?
|
[
"There are masers (microwave lasers) in galactic centers. "
] |
[
"Well, the \"a\" is for \"amplification\". The coherency is due to the \"se\"."
] |
[
"Certain star and planet atmospheres contain masers. The CO2 atmospheres of Mars and Venus in particular do. Not sure why that wasn't mentioned. I don't know if any solid state material has been found to naturally lase, but it's entirely conceivable to me that a particularly pure crystalline mineral of some sort on Mercury, for instance, where the intensity of sunlight would be strong enough to achieve a population inverson, could be capable of some lasing off the reflective, naturally cleaved surfaces of the material."
] |
[
"What is the mechanism behind optical fresnel losses?"
] |
[
false
] |
Even a perfectly polished glass surface can exhibit ~4% loss per surface when bombarded by orthogonal incident rays. I understand that optical coatings form layers of increased density, therefore decreasing the "step density" between air and glass, but I don't understand the actual mechanism behind the Fresnel less. In a vacuum would the effect become more pronounced?
|
[
"The backreflection arises from an impedance mismatch between the two media. In this case the impedance is related to the electrical permittivity, which exhibits a discontinuity at the interface. The permittivity of air is very close to that of vacuum, so there wouldn't be a significant difference between air and a vacuum.",
"By adding one or more layers of material at the interface, the impedance can be matched over a specified wavelength range such that the back-reflection can be well below 4%. This is how anti-reflection coatings work. "
] |
[
"Index matching is common with fibers however AR coatings for optics normal work by interference (like a DBR in reverse), by having a layer on the substrate that is quarter of the wavelength thick and a refractive index that is the sqrt of that of the substrates you can eliminate the reflections at that wavelength."
] |
[
"Different materials have different refractive indices (optical densities). As we move from one material to another, some component of light is reflected and some component is transmitted (the remainder is absorbed, but that's not really relevant to Fresnel loss). The Fresnel loss is the fraction reflected from the glass surface, when you're interested in the light transmitted. The ",
"Fresnel Equations",
" describe the fraction reflected, and also take into account polarisation.",
"If we ignore polarisation and consider a glass with refractive index 1.5, we can see that we expect R = |(n1-n2)/(n1+n2)|",
" = |(1-1.5)/(1+1.5)|",
" = 0.04, the 4% reflection we were looking for.",
"In reality, air has n =1.0003 and vacuum has n=1 so the Fresnel loss would be slight larger for glass in a vacuum than for glass in air (but only slightly)."
] |
[
"What would happen if a living brain was exposed to light?"
] |
[
false
] |
Please humor my silly hypothetical. What if you could twist off the upper portion of your skull and replace it with a transparent, temperature-controlled dome. Would light have ANY effect on the brain? Positive effects? Negative effects? or would it only get a sexy tan just in time for swimsuit season?
|
[
"The brain has no melanin, so it wouldn't get a tan. As to the effects, I can't imagine UV radiation having a terrific effect on it. It has no natural defenses to it, the way your skin does (see the aforementioned melanin). I'm betting you're looking at cancer, one way or another."
] |
[
"Only you wouldn't feel the inevitable burn as the brain doesn't have any nerves. Thinking about it, it could be a really deep question due to the brains nack for adjusting itself, would the brain in question be able to compensate for the \"cooked\" parts of the lobes?\nEdit: assuming of course that the light mentioned is sunlight and periodically applied as would happen in the course of days."
] |
[
"What if you could twist off the upper portion of your skull and replace it with a transparent, temperature-controlled dome.",
"Ain't no \"what if\" about it: it's called a ",
" and it's used for chronic recording. See, for example, ",
"Figure 1",
" (warning: pdf - the only direct links I could find were firewalled)."
] |
[
"[PHYSICS]What is a particle?"
] |
[
false
] |
I have often heard that particles are possibly just highly condensed/organized space-time or vacuum or something, but I don't know how much traction that thought has in the realm of modern physics. Basically I need to know some hypotheses (I'm not asking for objective truth here, just the current thoughts on the subject) on the nature of matter.
|
[
"Things like protons and neutrons are composite particles - collections of more fundamental particles.",
"As far as we know, electrons, quarks and photons (among others) are fundamental, indivisible, particles.",
"In Quantum Mechanics these particles are a bit point-like (zero dimensional) particles and a bit wave-like. The lighter the particle, the more apparent the wave-like nature. At the extreme, photons appear predominantly wave-like.",
"This tells us more about the mathematics that describe them than it does about the particles themselves. This leaves a fair amount of room for speculation in what gives rise to the mathematical descriptions of Quantum Mechanics.",
"Particles might be no more or less than that mathematics that QM describes. They might be a product of some underlying behaviour.",
"Since you asked for speculation: particles are particular knots (shapes) in a (graph theory) graph in which each node is connected through two uni-directional vertices."
] |
[
"Actually, that is an incredibly useful description for the paper I'm writing. I'm comparing Vedanta philosophy (specifically the concept of Brahman) with Minkowski-esque conceptions of space-time, and one of the problems I had was that matter isn't \"ineffable\" enough. From your description though, it sounds like I can easily argue that like the Hindu concept of Maya (or the Kantian phenomenological realm if you prefer that formulation) is still present in our understanding of particles, in that while we have semi-predictive models of their behavior we cannot understand their true nature (Brahman/numinological properties). You wouldn't happen to know of any scholarly sources I could cite as to the mysterious nature of particles, do you? Probably a review of various hypotheses that leaves the question open-ended would be excellent. If not, thanks for your help thus far!"
] |
[
"Pretty much all of Quantum Mechanics is a description of the mysterious nature of particles.",
"Most of particle physics is an effort to understand particles better. As such scholarly articles are heavy on the math and tend to avoid the word 'mysterious'.",
"Perhaps something along the lines of ",
"M-Brane",
" theory would help. It is a speculative (but serious) attempt at a better theory of particles (it includes string theory as a sub-set)."
] |
[
"Does sun-burned skin absorb Vitamin D at the same rate as normal skin?"
] |
[
false
] |
[deleted]
|
[
"Umm... I'm pretty sure skin doesn't absorb vitamin d at all. "
] |
[
"I think wackyvorlon meant that the skin doesn't ",
" Vitamin D directly from the sun. ",
"Instead, skin uses the energy absorbed from the sun to ",
" Vitamin D."
] |
[
"I think wackyvorlon meant that the skin doesn't ",
" Vitamin D directly from the sun. ",
"Instead, skin uses the energy absorbed from the sun to ",
" Vitamin D."
] |
[
"If the 2028 asteroid collided with the moon... what would happen? How would it effect life on earth?"
] |
[
false
] |
If the asteroid is estimated to be between 1.3 km and 2.8 km in diameter, what kind of damage would it do if it impacted the moon? Would it cause any problems here on earth? Give me any info you got on this thing! Edit: Responses are disappointing :(
|
[
"A 3km asteroid slamming into a 1700km moon would knock it out of its orbit? I find that very unlikely."
] |
[
"Armchair science does not belong in ",
"r/askscience",
"."
] |
[
"(layman here) It'd make a nice big explosion on the Moon (barely visible, maybe), and a nice-sized new crater, and maybe kick up enough moon dust fast enough to make a faint little invisible temporary ring around Earth (that'd disappear pretty quickly). ",
"But otherwise, not much. The Moon's much bigger than that. And it's pretty far away from our satellites and things.",
"That'd actually be a pretty good scenario in terms of impact on humanity, if I'm not mistaken. It would be MUCH better than it, say, hitting an ocean."
] |
[
"How do you convert energy into cold like in a fridge?"
] |
[
false
] |
I get how you convert energy into heat in an oven, but how do you convert energy into cold in a fridge?
|
[
"Without going into much details, the basic refrigerating cycle (in a closed loop) looks like this:",
"1) compress the refrigerating gas. The gas temperature and pressure rise as a result.",
"2) cool down the gas to (almost) room temperature. Heat exchangers do that, they are usually placed on the side and the back of the fridge. Pressure in the gas remains the same as after (1).",
"3) expand the gas. This reduces the gas pressure, and it's temperature drops from room temperature to a lower value. Use this cold gas to absorb heat from inside the fridge (another heat exchanger).",
"Rinse and repeat."
] |
[
"In case this explanation did not make it obvious, a refrigerator does not \"convert energy into cold\". Cold is by definition, the absence of thermal energy. You get cold temperatures in a given volume by ",
" thermal energy from this volume, not by converting it or destroying. A refrigerator sucks the heat out of its interior and spits it out on the outside. "
] |
[
"That's the way it's actually done, because using change of state extracts much more heat. But in principle it works fine even without this."
] |
[
"What is happening in my skin after a mosquito bites me?"
] |
[
false
] |
Can anyone explain what is happening, why it itches, why a lump forms, why it takes so long to return to normal? Thank you!
|
[
"When a mosquito bites it will inject its food source with its saliva, which acts as an anti-coagulant. The presence of this foreign material triggers a localized inflammatory response, resulting in the characteristic redness and swelling; and the localized release of histamines which causes the itching.",
"This sort of response typically subsides within a matter of hours, however if the bitten individual has a more serious allergy to the proteins present in the mosquito saliva the inflammation can be more severe, and also result in diffuse hives/rash."
] |
[
"And what does ammonia in things such as Afterbite do that cause the inflammation to die down?"
] |
[
"Honestly? I have no clue. I even asked an entomologist PhD friend of mine and she didn't know how ammonia works for mosquito bites either."
] |
[
"What stops a helicopter in forward flight from automatically rolling?"
] |
[
false
] |
In forward flight, the counter-clockwise spinning blades of a helicopter would encounter more drag and lift on the right hand side, and less on the left hand side, due the variation in relative wind-speeds passing over the blades. There would be then, I assume, more lift on the right hand side side of the helicopter than the left. This would cause a rotation of the helicopter about its longitudinal axis, a.k.a rolling. Do helicopters have a mechanism for dealing with this, or is the effect just negligible?
|
[
"The effect isn't negligible. In fact, this was a major engineering problem that had to be overcome in early helicopter designs. Early prototypes would flip over fairly easily. I read a very readable, in-depth article on this in (I think) Popular Mechanics about 20-25 years ago, but I can't seem to find anything comparable to reference right now. The mechanism you're looking for is called a ",
"\"teeter hinge\" or \"flapping hinge\"",
" and it allows the blade to basically teeter back and forth by a small amount as each side of the blade produces slightly different lift. I wish I could find some more in-depth information to link you to, but I'm drawing a blank.",
"EDIT: formatting",
"EDIT 2: ",
"Here's another link",
". Still pretty anemic, but a little more readable."
] |
[
"I did look it up. It turns out some of them have a system similar to variable pitch propellers on aeroplanes, whereby the advancing blade has a lower angle of attack whereas the returning blade has a higher angle of attack, the AOA being the 'flapping' whereas feathering is from what I can gather is in 'copters with three or more blades re-space themselves during rotation. E.g a two rotor helicopter would have an angle between blades of 180, but during rotation at some points it would be more or less than that.",
"http://www.copters.com/aero/lift_dissymetry.html"
] |
[
"The tips on a helicopter wing are generally traveling close to mach 1 (~761mph), Helicopters typically don't go more than 150MPH, so the difference is generally negligible. However it is worth noting that many faster/larger helicopters have dual rotors which spin opposite each other. I'm not sure that this would be what they are trying to combat, but it would counter any effect that had."
] |
[
"Are there any mobile, multi-cellular organisms that utilize Chlorophyll?"
] |
[
false
] |
Mobile as in creatures that actively move around in a controlled manner, not those which travel and replicate through spore-like methods.
|
[
"There's the sacoglossan sea slug, which practices ",
"kleptoplasty",
", utilizing the chlorophyll it obtains from algae it eats."
] |
[
"The spotted salamander gets some energy, it seems, from a symbiotic alga in its skin: ",
"http://www.nature.com/news/2010/100730/full/news.2010.384.html",
"I know this doesn't strictly fall within OP's definition, but I thought it was worth mentioning."
] |
[
"This is pretty cool:",
"Although Elysia chlorotica are unable to synthesize their own chloroplasts, the ability to maintain the chloroplasts acquired from Vaucheria litorea in a functional state indicates that Elysia chlorotica must possess photosynthesis-supporting genes within its own nuclear genome; most likely acquired through horizontal gene transfer.[5] Since chloroplast DNA alone encodes for just 10% of the proteins required for proper photosynthesis, scientists investigated the Elysia chlorotica genome for potential genes that could support chloroplast survival and photosynthesis. The researchers found a vital algal gene, psbO (a nuclear gene encoding for a manganese-stabilizing protein within the photosystem II complex[5]) in the sea slug's DNA, identical to the algal version. They concluded that the gene was likely to have been acquired through horizontal gene transfer, as it was already present in the eggs and sex cells of Elysia chlorotica.[6]"
] |
[
"Why can we see Mercury and Venus in the sky if they are within our orbit?"
] |
[
false
] |
I don't understand why we can see Mercury and Venus if their orbits are inside of our own? Surely we are looking out of our solar system thus couldn't see them unless during the day but then the sun would make it to bright to observe. Assuming it has something to do with refraction/geometry.
|
[
"The answer does have to do with geometry.",
"Consider the following arrangement:",
" Sun Venus\n\n\n\n XXX\n XXXXX\n EARTH\n XXX\n",
"Imagine you live at the 'H' on the above diagram of the Earth. In this configuration, the Sun will not be visible from that spot, so it'll be night time, but Venus will be -- so you'll be able to see Venus in the night sky.",
"Because Venus and Mercury have orbits inside that of the Earth, however, neither can be seen all night. At best, Mercury can be seen for about an hour after sunset or for about an hour before sunrise, whereas for Venus, the most is about 4 hours before sunrise or after sunset, if memory serves me correctly. "
] |
[
"We can see them because their maximum (angular) separation from the sun is large enough that we can see them as separate objects in the sky from the sun, especially during sunrise/sunset when the sun is obscured. ",
"Maximum elongation for Mercury is ~20-30º, which comes out to being visible for 1-2 hours before/after sunset/sunrise; for Venus, it's ~45º, which comes out to being visible for ~3 hours before/after subset/sunrise.",
"Oh, for context, the angular diameter of the sun is about .5º, which means that Mercury can be as far as 40-60 sun-diameters away from the sun, and Venus can be as far as 90 sun-diameters away from the sun, as seen from Earth.",
"You may ",
"this diagram on Wikipedia",
" useful."
] |
[
"Thank you so much!"
] |
[
"How important is it that I refrigerate my eggs?"
] |
[
false
] | null |
[
"The low temperatures do indeed inhibit bacterial growth, but there are several other factors.",
"First of all, the egg, when it is laid, is covered in a transparent protein coating. This coating keeps out bacteria and most gas exchange, and serves to keep the egg hydrated for it's month-long sit under a chicken butt. This coating is removed from processed eggs in the wash/bleach cycle.",
"The low temperatures serve to keep the proteins within the egg from breaking down as well. The yolks of refrigerated eggs are much more firm, as are their whites. ",
"From experimentation I've done with ",
" ",
" freshly laid eggs, I say that (for processed eggs) they age approximately seven times faster outside of the refrigerator than inside. If they still have their protein coating intact, this factor is reduced to about 3.",
"Source: I have a lot of chickens.",
" : Clarity as to source of eggs."
] |
[
"My favorite part was his source."
] |
[
"It would be beneficial. Also, it is best to wrap any potent foods (such as fish) since eggs have slightly porous shells and so can absorb the smells of other foods in the fridge. We had a final exam in food economics which was completely on eggs - it wasn't very ",
"xhilarating..."
] |
[
"How did Quantum Mechanics change science?"
] |
[
false
] |
Did Quantum Mechanics really have an impact on science, or is it just over-blown? Did the new ideas that were introduced actually change the way we do science or think about stuff (especially with atoms), or is it really not used that much?
|
[
"I do not believe it is an overstatement to call Quantum Mechanics the biggest revolution in both Physics and Chemistry since the work of Newton and Lavoisier.",
"There is a reason why we talk about \"classical physics\" and \"modern physics\", usually referring to the developments in the first half of the 20th century as the turning point. A ",
" short list of highlights from that period:",
"black body radiation",
"special relativity",
"Brownian motion",
"the photoelectric effect",
"atomic model",
"Lewis notation",
"matter wave",
"Pauli exclusion principle",
"Fermi-Dirac statistics",
"Bose-Einstein statistics",
"wave equation",
"theorem",
"uncertainty principle",
"The Dirac equation",
"The Copenhagen interpretation",
"electronic band structure",
"phonons",
"theorem",
"Let me give you a little overview of the most important developments, and then go into the implications and the impact.",
"Planck solved the problem of black-body radiation by introducing the notion of photons, discrete packets of electromagnetic radiation energy. He considered them mostly to be a mathematical curiosity, yet they inspired Einstein to consider them as real physical particles. This concept helped him explain the photoelectric effect. Furthermore, at the turn of the century, the atomic hypothesis had still not been fully accepted. Support for it was great, but not unanimous. Einstein's explanation of Brownian motion showed not only that a fluid consists of many tiny moving particles, but also provided a way to estimate their size.",
"With the concept of discrete particles and energy levels as a backdrop, and with clear empirical guidance from atomic emission spectra, Bohr formulated his atomic model, in which electrons only occupied specific energy levels by quantizing their angular momentum. An assumption which turned out to be correct, though at the time, there was no way to explain this postulate. This changed when de Broglie considered the idea that if waves could behave as particles, particles might also be able to behave as waves. Formulating this matter wave concept in his doctoral thesis, he provided a natural explanation for the quantization of angular momentum in the Bohr model: if the electron matter wave would not \"fit\" neatly around the orbit, it would destructively interfere with itself, so it provided a clear restriction on which orbits the electron can inhabite.",
"Schrödinger subsequently worked out the governing equation of motion for such a matter wave, and by doing so provided what is essentially Newton's laws for quantum mechanical particles. In fact, Ehrenfest explicitly showed that Newton's laws can be ",
" from the Schrödinger equation! Using this equation, he could suddenly explain all of chemistry. Let me say that again: ",
" How's that for importance and impact. ",
"Assume you are a late 19th century physicist. Aside from being a bad-ass, awesome and bearded, you also consider yourself to have a fairly firm grasp of how all of reality works. Reality consists of atoms and electromagnetic fields, of which you know the governing equations. All of the universe is governed by Newton's and Maxwell's equations, and any problem can be cracked by solving those. The universe is neatly deterministic, and given full information about a system, you can predict everything it will ever do for all time. Then comes along these fellows like Einstein, Bohr, de Broglie, Schrödinger, Heisenberg and others that tell you that all particles are really waves, all waves are really particles, and all you can know about any of them is only statistical in nature, and you can't predict any single event with 100% accuracy.",
"Think of the philosophical shock. All of standard human intuition breaks down at this point. Particles are at multiple places at ones, they behave as waves, they can tunnel through barriers they shouldn't be able to cross, knowledge about position destroys knowledge about momentum, particles don't even ",
" a well-defined position or momentum. But it works. It's crazy, it makes no sense at all, but it works. It even explains Mendeleev's periodic table, that's how well it works.",
"Einstein strongly resisted the notion of a non-deterministic universe, but Bell's theorem of 1964 proved without a shadow of a doubt that any local theory could not be compatible with quantum mechanics. Meaning: there is no patch for quantum weirdness, it is an integral part of how reality works. If that's not a hard pill to swallow, I don't know what is.",
"And think of the implications for chemistry. Suddenly, all inter-atomic interactions (chemical reactions) could be calculated from first principles! Just plug the problem into Schrödinger's equation and it'll spit out what molecules with react with each other, and how violent the reaction will be. Of course, it's not so easy. Schrödinger's equation is very hard to solve exactly, but in recent years (from the 1980's onward) we've been able to use computers to tackle these problems. ",
" computational chemistry is quickly becoming a routine activity at universities and companies around the world. Especially pharmaceutical companies use these calculations to predict what molecules might perform a desirable chemical reaction in the body.",
"And then there is solid-state physics. Without quantum mechanics, none of solid-state physics makes ",
" sense. It's no surprise that the field only really took off in the 1930's. Using the concepts of quantum mechanics, we can now determine the properties of solid materials, much in the same way we now predict chemical reactions. We can calculate how electrons will behave in a conductor, how the band gap works in a semiconductor, how to build transistors and other electronics, we can even calculate the thermal expansion of a material without ever having to make it!",
"There is no comparing 19th century to 20th century physics. Classical physics still has its uses, but quantum mechanics permeates everywhere. And I haven't even mentioned developments like nuclear physics, the standard model, superconductors, superfluidity, nanotechnology, quantum information transfer, quantum computing, ...",
"I could go on for hours, this is only a glimpse of the impact modern physics has had on our understanding of the universe, and it's here to stay."
] |
[
"Good, long list! I came here about to answer \"all of chemistry\" but you beat me to it. I'm biased as a quantum chemist, but I really do think it's one of the most underappreciated triumphs of QM. Even your post understates it! ",
"It's not just that we could calculate things - as you say, that's only been something we've been able to do accurately (for all but the simplest reactions) in the last few decades. But that's the quantitative theory, the much more significant thing is that it lead to a ",
" theory. Quantum mechanics immediately led to the development of Valence-Bond theory and Molecular Orbital theory, the two main approximations and conceptual frameworks within which chemical bonding is discussed and understood today. ",
"Prior to this, there simply ",
" any coherent \"theory of chemistry\". It was ",
" rather ad-hoc empirical rules. Sometimes bonds 'oscillated' as in benzene, sometimes not. You had models like the 'cubical atom' which are now almost completely forgotten, because all the old models that couldn't be justified from quantum mechanics were thrown out when QM revolutionized everything. Pretty much the only pre-quantum chemical bonding concepts still taught are ionic/covalent bonds, and Lewis structures. All thanks to Pauling coming up with how the concepts (with slight modifications) could be justified in terms of QM, which is how and why they'd worked. ",
"Prior to QM, you just couldn't predict anything reliably, even qualitatively, because the models weren't based on the underlying physics. You had no way of knowing when or why you were wrong. QM changed all that within 15-20 years of its creation. Chemistry hasn't been taught the same way since the 1939 publishing of \"The Nature of the Chemical Bond\". ",
"Even though you couldn't calculate that much, since they had these models, they could make qualitative predictions, and when those failed, you'd have a model that could explain what'd happened instead of what you expected. Back when an empirical model failed, you were left with nothing."
] |
[
"I honestly don't know where to start. Quantum mechanics is our best understanding of fundamental reality. Basically everything we understand about the universe is quantum mechanical, except einstein's general relativity. Its broadly agreed the biggest problem with general relativity is that it's not quantum mechanical.",
"If you've ever visited a hospital, used a computer, talked on a cell phone, looked at a flat screen tv or a million other things I can't think of right now, you've taken advantage of the understanding quantum mechanics have given us. It's underlies modern society.",
"it's the best tested theory in the history of science. ",
"I hope this is not too soon, but I'm pretty sure the people of Hiroshima and Nagasaki didn't think it was \"over-blown\". "
] |
[
"Can someone explain to me the fine structure constant?"
] |
[
false
] |
For context, I know a decent amount of physics (at least more than the average joe). I have an equivalent bachelors in physics (my college didn't offer it as an accredited degree) and I love reading about it. However, this is the first time I have read about it and I can't seem to figure it out. I understand that it is a constant between EM Waves and charged particles. But, when you have a quark (I know they cannot be isolated in standard energies but just go along with it) you have a charge of 1/3 so shouldn't the constant 'change'? Or does this not apply to all elementary particles? Also what else does this constant apply to? I read we have seen it pop up in many different arenas. I don't need the super dumbed down version, but dumb enough for someone with only a bachelor's.
|
[
"The fine structure constant is related to the coupling between charged particles (",
" of them) and the electromagnetic field. Gluons don’t couple to the EM field, so the fine structure constant isn’t really relevant for them. The strong force has its own coupling constant, which is qualitatively and quantitatively different than the electromagnetic coupling constant."
] |
[
"It just means interacting."
] |
[
"Particles with more charge (in magnitude) have stronger coupling to the EM field. The fine structure constant α is the coupling constant for particles with |q| = e, the elementary unit charge. For particles with charge e/3, the coupling constant is a constant multiple of α. No matter what the charge is, the coupling is still proportional to α."
] |
[
"Do astronauts - or any scientists - have a written protocol for dealing with extraterrestrials?"
] |
[
false
] | null |
[
"Yes"
] |
[
"I once read something on this actually:",
"If we were to meet extra terrestrials, they probably wouldn't look like us, and most likely they would send machines in their place. Biological creatures don't travel well for millions of light years, we get old. Machines don't.",
"These aliens will be advanced, ",
" advanced. More advanced than you can even comprehend, they cracked interstellar travel, that means they've rectified some of the greatest quandaries in physics. ",
"They will certainly not speak our language. But there is one thing they will understand: Math. The first person to come in contact with an alien should actually draw a triangle. Just a simple triangle, then maybe some simple trig and phythag's theorem. This is because the triangle is so crucial in math and science, they'll recognize that we know it's significance. After that, you can move into more complicated mathematics, of course using symbols instead of numbers. ",
"After that, they will hopefully understand that we are indeed an intelligent species as well, and understand science and the universe around us. ",
" they are peaceful, and don't melt us and use our planet for resources, seriously. After that, maybe we can share our knowledge and they could share theirs. It would be a wonderful opportunity once the language barrier is broken. "
] |
[
"Check whether it's true. If it is, tell other people."
] |
[
"Why do crops need rotation and/or leaving the field fallow to prosper, while trees are able to grow and prosper in the same exact spot for years?"
] |
[
false
] | null |
[
"We don't usually care how fast or how well the trees are growing on a year to year basis. However we are ",
" interested in making sure that a crop yields the maximum amount of food every single time we spend money to plant it."
] |
[
"Crop rotation",
" is performed to fix nitrogen in the soil. Trees can also benefit if low growing, nitrogen fixing plants are placed between them as in ",
"meadow orchards",
". But it's not feasible to uproot trees on an annual basis."
] |
[
"Crops need certain nutriients to grow and produce good yields. One of the most important nutrients is Nıtrogen. Crops are rotated historıcally with a cycle of one grain crop, one root crop and one nıtrogen fixing crop or leaving the field fallow. Nitrogen fixing crops include legumes, clover, peanuts and Alfalfa. I'm sure more efficient rotations than the ones I learned in history class when I learned about Turnip Townsend and his patent crop rotator (I just looked him up and it was 2 grain crops (wheat & barley) followed by a root crop (TURNIPS!) and then clover).",
"As to trees - at a guess they sap nitorgen from the soil at a slower rate than grain crops or have a similar method to the legume family to fix nitrogen back to the soil. I am affraid I don't know on that score. "
] |
[
"Medicine: What actually kills someone with cancer?"
] |
[
false
] |
You often hear that someone "died of cancer", be it breast cancer, prostate cancer, melanoma or something else but what is it that actually kills them? Is it the immune system going havoc and killing all living cells it can find? Do you starve to death as the tumour grows and all nutrients you manage to ingest are seized by the cancerous cells? Infections, like pneumonia?
|
[
"The easiest way to think of cancer is to think of the effect of weeds in a garden.",
"Weeds grow quickly and wherever they like, and they will choke out the plants you've intentionally put in your garden and either impede their function or kill them entirely.",
"In some cases, the weeds suck all the nutrients out of the soli and consume all the soil's water. Plant dehydrates and starves and dies.",
"In other cases, especially with vines, the weed simply grows on top of the existing plants, preventing them from growing properly by simply occupying the spaces they would grow into - and in some cases, physically kills leaves and branches by squeezing them.",
"Metastatic cancer is when tumor cells from one area migrate to another area of the body - the bad ones are typically liver, brain, and lungs. Metastatic breast cancer, for example, can cause malignant breast tissue to start growing in your lungs. This means that normal lung tissue gets essentially choked out by the fast-reproducing cancer cells, and your lungs stop functioning as they should.",
"This is why chemotherapy has the side effects that it does. Chemo targets fast-growing cells, like tumor cells and kills them. But you have many other fast-growing cells in your body like hair folicles, stomach lining, etc. Those tend to die too, so you lose your hair and have trouble eating. It's also why cancer treatment follows the general course that it does. You try to excise the tumor before it goes metastatic and migrates around the body. Once it metastisizes, you can't surgically remove all those tiny tumor cells so you have to poison them, either chemically or by applying radiation in the areas that the tumors are detected. If the poison doesn't effectively kill them all, you will eventually die."
] |
[
"As a medical student I once had this very same question, but basically here are several physiopathologic ways it can happen.",
"\n1. Tumoral lisis syndrome. Cancer cells sometimes die quickly in big numbers, releasing potassium into the bloodstream, among other (toxic) byproducts of cellular degradation, wich can cause acute renal failure, metabolic acidosis, and eventually leads to heart arrythmias and asystole (heart stops beating).",
"\n2. Brain cancers can compress and invade the brainstem, leading to either brain death or dysfunction of the respiratory control center (patient stops breathing).",
"\n3. Multi-organic failure, the cancer can affect several organs (liver, heart, blood, kidneys, lungs...), and once several are affected, the body can't keep up the delicate balance needed to sustain life. Liver failure leads to accumulation of toxins (patient can develop brain edema, see number 2) and lack of coagulation proteins (patient bleeds). Heart failure leads to inadequate blood and oxygen supply. Blood failure, lack of platelets also lead to bleeding (sometimes spontaneously) or severe anemia (also inadequate oxygen supply). Lung failure it's kind of self explanatory. Renal failure same as tumoral lisis syndrome. And so on.",
"\n4. Infections. Cancer patients are usually immunosupressed (usually from chemo), and are prone to severe infections.",
"\n5. Malnutrition/dehydration.",
"In the examples you give, melanoma is usually brain metastasis (2), breast cancer can either be 2, 3, 4, 5; prostate cancer I'm not sure but i think also 3, 4 and 5. Overall, AFAIK, 3 and 4 are the most common."
] |
[
"It depends on the cancer. With leukemia patients will die from infection or disease due to a compromised immune system, other leukemia patients die from internal bleeding from low platelets, some die from the stress a low red blood count places on the heart. With a cancer like bone cancer the death is completely different, such as tumors growing in and causing a collapse of the lungs leading to death"
] |
[
"At the peak of infection if all cold or flu viruses could be taken out of the body and put into a cup, how much volume would they consume?"
] |
[
false
] |
I don't know how many viruses are typically involved in an infection or how big they are, but I suspect the things that consume our body with sickness would not take up very much space at all.
|
[
"This is some fun sounding math, I'll take a crack at it. ",
"Peak viral load titers for RSV (Respiratory Syncytial Virus - a common source of winter colds) have been estimated as high as 10 million plaque forming units (i.e. viable viral particles) per milliliter of respiratory secretions (statistic taken from ",
"this paper",
").",
"RSV is part of the paramyxovirus family, with the size of viral particles ranging from 120-300 nm. (I'm too lazy to find the average actual size of RSV, but it shouldn't throw off our math by more than a factor of 3.)",
"In a well person, about one liter of respiratory secretions are produced each day. In a sick person, that roughly doubles to two liters daily.",
"So let's do the math: Taking the upper bound on size, a 300nm spheroid particle (converting for volume) with X 10 million particles per milliliter X 2 liters/day gives you... (drumroll please) ...",
"2.828×10",
" liters of virus particles/day. Less than a microliter of total volume. According to Wolfram Alpha, that volume is roughly comparable to four medium sized grains of sand. So there you have it. Viruses are small, and I honestly expected the final volume to be smaller. This estimate likely even lowballs the actual number since it only accounts for secretions and not viruses actively inside cells replicating and infecting. ",
"EDIT: Units"
] |
[
"It's possible to make an estimate, using the same math, we just have to swap in different numbers. Viral load titers in those dying due to Ebola ",
"have been measured up to 10⁹ plaque forming units",
" per ml of serum. ",
"Serum volume in an average adult male would be roughly 2.5 - 2.75 liters. ",
"Volume estimates are where things get hard. ",
"Look at this thing",
". It's not a nice sphere like our RSV example above. It's a long, thin, filament. However, if we know the mass and the density (and we do - molecular mass of ≈3.82 x 108 and a buoyant density in potassium tartrate of ≈1.14 g/cm3 per Wikipedia) we can use these to estimate volume - which comes out to 5.6 x 10",
" cc's per viroid particle. This isn't actually that far off from our estimate of volume for RSV - though I didn't include it, it came to roughly 1.4 x 10",
" cc's per viroid particle. ",
"Time for some numer crunching. 5.6 x 10",
" cc's per viroid particle X 10",
" particles per ml X 2.75 L gives you....",
"Roughly 1.5 ml. Using our previous analogy (thanks again to Wolfram Alpha), we have the equivalent of 25,000 or so medium-sized grains of sand (or 2.4 M&M candies) floating around the blood of someone experiencing massive (and ultimately fatal) ebola viremia. Again, this is likely a low estimate due to the difficulty in calculating viral loads in those cells hosting actively replicating Ebola. ",
"EDIT: Corrected a three-orders-of-magnitude mistake."
] |
[
"Would it be possible to replicate this with something like ebola, where the virus has completely taken over?"
] |
[
"When we say the universe is 13.8 billion years old, is that with respect to some particular reference frame?"
] |
[
false
] | null |
[
"Hi ",
"/u/moon_physics",
",",
"When we say the universe is 13.8 billion years old, is that with respect to some particular reference frame?",
"It is! In particular, when physicists say the universe is 13.8 billion years old, it is with respect to the ",
"cosmic microwave background rest frame",
". [To learn about the cosmic microwave background, look ",
"here",
".] This frame is useful because it is the frame in which the CMB \"dipole term\" vanishes. When we observe the CMB from Earth, we measure a nonzero dipole term because we possess a \"",
"peculiar velocity",
"\" with respect to the CMB. We have to account for this dipole term in order to get an accurate handle on the features of our universe: how much is dark energy, how much is dark matter, and so on.",
"Hope this helps!"
] |
[
"I always hear that there is no \"true\" or \"basic\" universal reference frame (not sure how to put it but I think you know what I mean). Can you explain to me why this wouldn't be it?"
] |
[
"It would make sense if laws of physics were different in that frame, but they aren't, it just gives us a more convenient one to use for some things on the scale of the observable universe (just like the Sun is a better reference frame than Earth when looking at the solar system)",
"http://en.wikipedia.org/wiki/Preferred_frame",
"http://en.wikipedia.org/wiki/Inertial_frame_of_reference"
] |
[
"What would prove the many-worlds interpretation? What would disprove the many-worlds interpretation?"
] |
[
false
] | null |
[
"We know of nothing to either of those answers. Physics and experiments can't touch the results of the many-worlds interpretation. It's entirely in the realm of philosophy and completely detached from any physical meaning."
] |
[
"The various mainstream interpretations of quantum mechanics all make the same predictions. (",
"http://en.wikipedia.org/wiki/Interpretations_of_quantum_mechanics",
") That means that there's no scientific way to tell them apart or 'prove' them against each other."
] |
[
"The various mainstream interpretations of quantum mechanics all make the same predictions. (",
"http://en.wikipedia.org/wiki/Interpretations_of_quantum_mechanics",
") That means that there's no scientific way to tell them apart or 'prove' them against each other."
] |
[
"What is the nutritional value of an average human being?"
] |
[
false
] |
Average would be around 5'10" and 190ish pounds. Nutritional value being vitamins, protein and all those too.
|
[
"http://onlinelibrary.wiley.com/doi/10.1525/aa.1970.72.1.02a00140/pdf",
"Garn, Stanley M., and Walter D. Block. \"The Limited Nutritional Value of Cannibalism.\"American Anthropologist 72:106",
"Notable quote:",
"A 50 kg man might yield 30 kg edible \nmuscle mass if well and skillfully butchered, \nand 30 kg edible muscle would yield about \n4.5 kg (4500 gm) protein, or 4.0 kg protein \nassuming 9 0% digestibility. \nAssuming quality protein requirements as \n1 gm per kilogram of body weight, this \nwould provide one-day’s protein require- \nments for approximately 60 60-kilogram \nadults. One man, in other words, serves 60, \nskimpily. ",
"Whelp, that doesn't really answer the caloric question, but it definitely proves the existence of research on the subject. ",
"EDIT: More info",
"http://www.enotes.com/cannibalism-reference/cannibalism",
"On the other hand, human tissue has the same nutritional value as any other mammalian tissue when it is eaten, whether by a human or nonhuman predator",
"I've been trying to find more articles, but ninety percent of all the useful-looking ones aren't free.",
"One last EDIT: More information can (probably) be found in Mary Roach's ",
". There is a chapter about cannibalism, and I vaguely recall being amazed that someone had done nutritional research on human flesh. The specifics I don't remember, and I don't know if it went any more in depth than the items I've already posted.",
"Either way, great read."
] |
[
"10% body fat is no where near average for a male or a female",
"."
] |
[
"10% body fat is no where near average for a male or a female",
"."
] |
[
"Mitochondrial Eve"
] |
[
false
] |
What is the scientific relevance of the mitochondrial eve? I'm confused becuase the Wikipedia reference has this quote: Each ancestor (of people now living) in the line back to the matrilineal MRCA had female contemporaries such as sisters, female cousins, etc. and some of these female contemporaries may have descendants living now (with one or more males in their descendancy line). But none of the female contemporaries of the "Mitochondrial Eve" has descendants living now in an unbroken female line. So there were other females as this "Eve's" comtempories with descendants, so why is this one ancestor of any importance scientifically?
|
[
"What it's telling you is that we are all descended in an unbroken female line from the MRCA because everyone, male and female, gets their mitochondria from their mother. The MRCA's female contemporaries likely had children but if they only had male children, or at any point the contemporaries' descendents only had boys then they wouldn't have passed on their mitochondria only their nuclear DNA.",
"To answer your question about the MRCA's importance;",
"a) it was in and of itself an interesting scientific discovery that animals only inherit their mitochondria and their mitochondrial DNA from the female parent.",
"b) We can then use worldwide distribtions of mtDNA subtypes to map the divergence of and movements of humans",
"c) We can also use some of this information to estimate human evolutionary divergence times.",
"d) We can derive interesting haplotype information from distributions of mitochondria"
] |
[
"The other way around. \"Eve's\" contemporaries have no living descendants in an unbroken female line. There is only one oldest common ancestor."
] |
[
"No. It is/was a continuous on going process and as we no longer have those sequences we have no way of estimating a) how many alternative mtDNA types there once were and b) the rate that they were bred out of the population."
] |
[
"Linguists of Reddit, how likely or unlikely do you think it is people will still speak English 2000 years from now?"
] |
[
false
] | null |
[
"I think if we discuss patterns in english linguistical changes over the past 2000 years and understand why they occurred, we should be able to have an interesting conversation about this question in a hypothetical way. What do we think english will look like in 500 years? In 1000 years? In 2000?"
] |
[
"This isn't exactly my area and is slightly speculative.",
"Historical rates of language change would suggest that the English of 2000 years from now would be unintelligible to us. Certainly, the English of 2000 years ago would not be intelligible to us now. However, language is very much tied up with cultural change, and it may be that the constant recording and standardization of the language in modern times will slow down the usual drift."
] |
[
"It is possible to estimate the way language will change, based on the way it has in the past."
] |
[
"What is the difference between a zygote and a dikaryotic cell in fungi?"
] |
[
false
] |
[deleted]
|
[
"Here's a quick answer for you, but I'm sure a panelist will be around soon to give you a more detailed description.",
"Dikaryotic cells are formed when compatible nuclei from two different cells break down the wall between the cells to \"cohabit\" a compartment without sexual reproduction. ",
"From here.",
"However, zygotes are the result of fertilization during sexual reproduction.",
"I hope that helps some."
] |
[
"No problem, glad I could help."
] |
[
"No problem, glad I could help."
] |
[
"Watering with carbonated water?"
] |
[
false
] |
So let me know if I'm talking madness, but here's the question: If you were to water a garden/lawn/flowers with carbonated water during the daylight photosynthesis phase, would this be better than watering with just plain water? If so, does the mechanism have to do with delivering more CO2 to the soil, which the plants are trying to uptake in this phase, or does CO2 uptake not take place in the roots, but at the leaves? If this is not a beneficial thing for plants, why not?
|
[
"This is probably not a good idea. Carbonated water is more acidic than regular water because it contains carbonic acid and this will decrease the pH level of the soil. Changing the pH like this could be harmful or deadly for the plant."
] |
[
"This is correct, but to answer the rest of the question, roots do take up some CO₂. ",
"See my other comment ",
"here",
"."
] |
[
"You mean like fertilizer? It's usually in the form of nitrates, urea, ammonium. \nPlants can't break the N2 bond by themselves"
] |
[
"Are there actual wild horses in the Americas or are they all feral domesticated horses?"
] |
[
false
] |
Has anyone ever brought actual wild horses to the Americas? And are there wild horses still in Asia? Or have they been bred out with domesticated horses to the point that all the horses in the world are basically domesticated?
|
[
"Until recently, Przewalski’s horse, which lives in Mongolia was considered the last truly wild horse. As of a few years ago, though, ",
"DNA evidence suggests",
" they are actually descendants of domesticated horses, so likely there are no truly wild horses left."
] |
[
"To clarify, the DNA analysis showed they are related to horses associated to the Botai culture. Now whether the Botai had domesticated the horses whose remains are found around their settlements is an ongoing debate. It's quite possible they just hunted them.",
"EDIT: In any case, Przewalski horses are a separate lineage from today's domesticated horses, which is pretty cool I think. To clarify, if the Botai horses were domesticated, this would mean people domesticated wild horses on at least two distinct occasions."
] |
[
"From Wikipedia: While genus Equus, of which the horse is a member, originally evolved in North America, the horse became extinct on the continent approximately 8,000–12,000 years ago. In 1493, on Christopher Columbus' second voyage to the Americas, Spanish horses, representing E. caballus, were brought back to North America, first to the Virgin Islands; they were reintroduced to the continental mainland by Hernán Cortés in 1519. From early Spanish imports to Mexico and Florida, horses moved north, supplemented by later imports to the east and west coasts brought by British, French, and other European colonists. Native peoples of the Americas quickly obtained horses and developed their own horse culture."
] |
[
"Glovebox - backflow into positive pressure?"
] |
[
false
] |
We use a positive-pressure, argon-filled glovebox on a regular basis. There's a catalyst system which nominally removes trace amounts of water from the box - however, the moisture meter is wildly uncalibrated and unreliable. A situation has come up regarding the glovebox main vent. My lab-mates insist that if the vent is open (pipe ~ .5" diameter), then the positive pressure inside the glovebox prevents moisture from entering the box. I remember hearing that some backflow does occur, but I can't prove it. I've been looking for a report, book, or journal article which mentions this, but haven't had any luck. Any thoughts? Thanks! edit: The way that the backflow was explained to me was that the flow would be outwards for most of the pipe, but that along the edges, it would be inwards.
|
[
"If someone pulls their hands out of the gloves really fast, it's possible that you could suck some of the outside atmosphere in, but it shouldn't be standard procedure to keep the purge valve open while you're working. Otherwise, with an opening that small, you shouldn't get any backflow as long as the inside pressure is high enough (I wouldn't let it drop below ~6-9 mbar while purging).",
"There are other tests you can use to detect trace levels of oxygen and water in your box, like the light bulb test, or diethylzinc. "
] |
[
"The easiest way to tell if you have a leak is to turn off the circulator for about 10 minutes to let the temperature equilibrate, crank up the pressure, and listen for the box to refill. If you don't hear anything for about 10 minutes, you probably don't have a leak.",
"How long has it been since you regenerated you catalyst?"
] |
[
"Ah, I see. I think the best way to convince your labmates that they're wrong is to point out that a pressure differential only really saves you in a static system, but the air in the glove box is constantly circulating. If gas quickly rushes past a leak, it can create suction that ends up contaminating the box. This is especially true if your leak is somewhere along the circulation train (like one of the o-ring joints).",
"I think this, along with the fact that your box is clearly contaminated, should convince them. "
] |
[
"How closely related are the Y chromosomes in a male lineage?"
] |
[
false
] |
Since Y chromosomes must always be transferred from the male parent, how closely related should the Y chromosomes be when tracing the male lineage? I.e., comparing the Y chromosomes of the son to his father, grandfather, great grandfather, and so on?
|
[
"Because the Y chromosome is transferred directly from the father and it is not mixed with any other chromosomes it is almost identical to the father's chromosome (and his father before him...). Any changes would be due to mutation. Also note that it is possible for the Y chromosome to pick up VERY SMALL amounts of DNA from the X chromosome.",
"for more info: ",
"http://genetics.thetech.org/ask/ask295"
] |
[
"There are identical, save for mutations.",
"This naturally allows you to track ancestry. If you are a male, by comparing the Y chromosomes of groups of individuals, you can determine who descended from a common male ancestor. Because there are so many different Y chromosomes, this tends to lead at best to interesting family tree connections.",
"More interestingly: an inordinately large number of men in Central Asia tend to have identical Y chromosomes. The leading hypothesis for this phenomenon is Genghis Khan's widespread conquest and rape of Eurasia.",
"Source: a fantastic ",
"radiolab segment",
" on this very topic, and follow-up research."
] |
[
"Can't mild crossing over occur from the X?"
] |
[
"Have any wind turbines been able to break the Betz limit?"
] |
[
false
] |
I've seen multiple claims of new wind turbines that due to some characteristic, usually design, can output more energy than traditional wind turbines. Are these all hoaxes?
|
[
"The Betz limit is the theoretical limit. Real wind turbines are not reaching it, ",
"this modern one",
" (pdf warning) achieves around 45% max efficiency (compared to the 60% of the Betz limit). But if you look at the efficiency vs wind speed graph you can see that this maximum efficiency happen for a pretty narrow set of conditions (wind speeds of 5 to 8m/s). What unconventional designs often do is that they get their high efficiency regimes at lower wind speeds or they have (allegedly) a wider high efficiency regime."
] |
[
"No, they can't break the Betz limit as it is a limit in the strictest sense. It is a calculation of the energy extraction efficiency from a flow, and depends on the area of the rotor, as well as the area before and after the rotor. We have an imaginary 'tube' through which the fluid enters at one end, is slowed down by interaction with the rotor, and leaves at the other end. As the flow velocity decreases, the 'tube' widens. There is no flow through the 'walls' in this model.",
"Claims of breaking the limit usually are nothing more than a marketing gimmick, deliberately underestimating the initial input area and therefore the power of the wind. They either do not understand the theory, of they are lying for money. "
] |
[
"The Betz limit is a pretty strict limit; but not in the strictest sense - it has something of a loophole",
"Consider if we built our wind turbine to cool down the medium and chose a medium with a very low specific heat capacity where even a small change in heat leads to a large change in density (alternatively we could change the chemical composition of the medium using a reaction that requires minimal energy, but massively changes density). ",
"If density behind the rotor can be bigger than density before the rotor, then the law falls apart - you can have the same amount of medium moving through the same area with lower speed.",
"You could 'fix' that loophole by demanding that the outgoing airflow has the same density as the ingoing airflow, but that may not accurately describe reality in some circumstances - if you're in an elliptic geometry with one device generating the wind and another device drawing the energy out of the wind, you can have a stable flow with different densities on the path wind-producer to wind-consumer compared to the path wind-consumer to wind-producer; and you can extract an arbitrarily high percentage of the wind's kinetic energy with a small energy investment (that can, in theory, be arbitrarily small) for changing the mediums density at wind-consumer and producer",
"So yeah, the Betz limit is a pretty strong limit and almost definitely holds for the earth-atmosphere system, but there are different conditions in which it may be 'broken'",
"Edit: Forgot a word"
] |
[
"[Medicine - Dermotology] What is the latest research on acne? Are dermatologists getting any closer to finding a cure?"
] |
[
false
] | null |
[
"Everyone please remember that no one is allowed to give medical advice. Any comment advocating the use of medication or certain brand names will be deleted immediately. Please no more personal stories about what worked and what didn't. This is a science forum, and all answers should be scientific in nature. "
] |
[
"I'm not aware of anything groundbreaking just yet, unfortunately. The retinoids like Acutane are obviously very effective, but their side effect profile is less than desirable. (I dont think Acutane is even sold anymore, but I believe the generic still is)",
"http://www.ncbi.nlm.nih.gov/pubmed/10809858",
"Phototherapy sounds interesting, but I haven't personally seen any clinics using it. This study found mean 58% reduction in acne for mild-moderate cases w/o significant side effects."
] |
[
"Dermatology Resident here.",
"The short answer to your question is that no, there is no new groundbreaking research on acne. Acne is one of the most common dermatologic complaints, and one that people are willing to spend a lot of money treating. There is a lot of money invested in research for new products.",
"The problem is that acne is actually a very difficult condition to treat, and we really don't have a full understanding of the problem yet. We know there is increased inflammation in the setting of bacterial proliferation as well as enlarged sebaceous glands, but it is unclear the main driving factor behind all of it. We have a broad range of products ranging from antibiotics to anti-inflammatories to various formulations of topical and oral vitamin A. ",
"Aside from oral vitamin A (Isotretinoin - formerly accutane - which for severe, refractory acne can be almost a \"magic bullet\" albeit with side effects but can actually provide a \"cure\" by shrinking sebaceous glands), all of the medications we have tend to work best in combination. Hence, the modern trend in acne treatment been to combine various older, proven effective options into combo drugs. This is both for monetary reasons (length of drug patents and remaining non generic) and compliance reasons - we know from our studies that each additional medication you ask a patient to take or put on their face daily significantly decreases their chance of doing it.",
"The evidence for the effectiveness of phototherapy is mediocre at best and certainly no better than other easier treatments, and likely is just the company fishing for indications to sell more of their machine. You have to take new claims from these devices, or any new medication for that matter, with a grain of salt - remember you don't see all of the studies that showed little or no benefit, as they aren't published. Time will be the true test.",
"So nothing big. But in my and many other dermatologists experience, while acne may not be curable it certainly is treatable, and even the most severe patient with the appropriate motivation and medication compliance can ultimately be cleared. The problem most people make is trying numerous ineffective or only mildly effective over the counter treatments and suggestions before they finally come to see dermatologists."
] |
[
"If I started out naturally left-handed as a kid, then was \"trained\" to be right-handed, can I teach myself to go back to being a leftie?"
] |
[
false
] |
I started off always using my left hand. But in elementary school, I was told by my teachers/father that holding the pencil in my left hand was the "wrong way" and was harshly trained out of it. I'm not sure if this is a direct result of it, but my handwriting has always been EXTREMELY messy. Even when I try really hard and go slowly, it looks like a child hastily scrawled it. I still have many of the personality traits and attributes that lefties supposedly typically have: I'm fairly artistic, very high verbal and language-based IQ, but also diagnosed with a learning disorder (dyscalculia) and ADHD, etc... I can still use my left hand pretty well for everyday tasks if I need to. So I guess my question is: can a natural leftie who has been trained to be a rightie become a leftie again? Is it bad to have your natural handedness trained out of you?
|
[
"The previous answers are touching on whether your preference for using one hand can return, but in order to really get a hold of handedness, you need to consider actual ability, not just preference.",
"The answer is yes, you can train yourself to be proficient with your left hand again. You can, in fact, do this EVEN if you were not naturally a leftie. Whether or not you will prefer your left hand is a different issue, and it doesn't really matter. Because being able to write with your left hand just means that you can do it clearly, legibly, and efficiently. You CAN train yourself to do this with practice. Essentially, you are training your muscles in your left hand, along with your brain, for writing with your left hand. Then, you just need to make an effort to write with your left hand consistently, until it becomes automatic (if that's what you want to do). ",
"You can not have your natural handedness trained \"out of you\" per se. All that happened is, you stopped developing that muscle & you stopped practicing that skill. The skill didn't leave you, it just didn't progress. So all you need to do is put some time and effort into developing that skill & muscle again, until you don't need to remind yourself to use it every time."
] |
[
"So far, no studies have shown that you can truly \"shift\" your handedness.. Even if you get more used (through indoctrination or similar) to using the other hand, your brain will still be pre-defined to prefering the hand you were born to use. This is of course, if we accept the theory (most commonly accepted) that we are born into which hand we use the most ably.\n",
"http://en.wikipedia.org/wiki/Handedness",
"My point being that if you start using your \"natural\" hand for the task you want to be better at with that hand, my guess (sorry, sorry) is that you will fairly quickly revert to being a \"lefty\" (like myself)."
] |
[
"I was trained to be right-handed too, it resulted in me being ambidextrous. Its helpful at times but I'll always have bad handwriting."
] |
[
"How much does the expansion of the universe effect the approach of Andromeda?"
] |
[
false
] |
I know that the rate at which the universe is expanding is increasing, and I know that Andromeda is approaching us at some 2.35 billion miles a year (lifted from wikipedia). How much time does the expansion of the universe buy the two galaxies before they collide (as opposed to if the universe were static)
|
[
"It doesn't. ",
"Metric expansion doesn't occur within clusters of galaxies",
"."
] |
[
"So then in areas where spacetime is curved that curvature stops metric expansion, or slows it to imperceptible levels?"
] |
[
"it doesn't happen at all in mass-dominated regions of the universe. it only occurs in the vast voids between galactic clusters."
] |
[
"Are there any normal healthy parasites of humans?"
] |
[
false
] |
Multicellular organisms like ticks and fleas but are common in humans and perfectly normal/healthy like the bacteria in our guts.
|
[
"A parasite has a non-mutual symbiotic relationship with the host; the parasite benefits at the expense of the host. What you are actually looking for is mutualism - where both organisms benefit from their relationship. At the macro level we have domesticated animals like dogs, cats, sheep, etc. that one could argue are in a mutualistic relationship with us. At the micro level you mention gut flora but I am not aware of other types of bacteria that aid us. I hope this points you in the correct direction. "
] |
[
"As ",
"/u/stankyhankypanky",
" pointed out, a ",
" is not normal nor healthy. If you have one, then you've got a disease (depending on which parasite, e.g: ",
")",
"In a parasytic relation, the host (us) will ",
" get a downside. In the Taenia example, they'll eat what you eat, leaving nothing but leftovers for you, ending on severe vitamines deficit (mainly B6 & B12)",
"But, there are tons of bacteria, living in our organism which have very important functions, I'll point out some of them, for those of you who are curious:",
"This is only made by intestinal ones, but it is quite important for our survival; they synthesize some molecules which we need to survive, such as K vit or midchain fatty acids.",
"They make sure other bacteria don't grow up where they colonize (e.g: if a bacteria such as ",
" colonizes your skin, another one potentially harmful won't do it)",
"They have a very important role in our immunity development and in diseases so common as Allergy, Inflammatory Bowel Disease... ",
"So... No, no parasite is normal or healthy. You should stick to this. "
] |
[
"So are there any worm/insect like beings living on/within us that has a mutual symbiotic relationship with humans?"
] |
[
"How do the changing frequencies of music travel within one FM/AM frequency?"
] |
[
false
] |
And how are they played back accurately on a receiver/sound system?
|
[
"The carrier frequency (103.6 FM, for example) actually has a bandwidth of about 50 kHz (for FM broadcasting in the US). So, the station broadcasting at 103.6 MHz actually has a license to occupy the frequency range from 103.575 to 103.625 MHz.",
"This allows the changing frequencies to modulate the carrier frequency and carry an audio signal. ",
"Details on modulation are available on wikipedia."
] |
[
"The M stands for modulation.",
"To describe a periodic signal such as radio wave, we use its frequency (inverse to the period, or time it take for a signal to do its full \"travel\" from 0 to the top say 1, back to 0, then to -1 and finally to 0)\nand its amplitude, its \"height\". (we also use phase but please ignore for now)",
"In AM, Amplitude Modulation, carrier frequency stays the same, say 200kHz.\n",
"WolframAlpha to the rescue",
"However, the amplitude of the signal varies according to the signal we want to transmit. \n",
"see this image",
"On this image, the AM signal amplitude is modulated according to the message we want to send. When the message is close to -1, the AM signal amplitude is at its lowest. When the message is close 1, it's at its peak.",
"To receive the signal, we have to demodulate it. \nThat's easy: you want to only keep the envellope (the \"shape\" of the signal) and can be done with very simple component, basically, an antenna, a coil, a diode and you're almost there.\nThis why early radio transmitted only in AM.",
"In Frequency modulation, the carrier frequency vary very slighlty, in accordance with the signal we want to transmit.\nTo demodulate, you remove the carrier and you end up with the frequency variation which is your signal.",
"There are many other modulation modes, such as phase shifting where the phase is modified according to the signal (it's much harder to explain in layman terms but see ",
"wikipedia",
" if you want a nice headache)",
"The mode is chosen according to a number of parameters: is the signal digital or analog, do we need to transmit data at a high speed (see Nyquist and Shannon on that, another nice headache:-) ), do we need to transmit the signal far away, etc...?",
"The lower the carrier frequency, the farther the signal can go. AM is in the kHz range (HF, High Frequency Band). FM in the MHz(VHF, Very High Frequency). FM is said to travel \"to the horizon\". It obviously depends on power and antenna, but usually FM transmitter can't be received much farther than 200km.\nIn AM, you can easily receive a signal from more than 2000km at night with an off the shelf radio (I live in France, I routinely receive russian signals for example).",
"Other frequency range are used, for example in ",
"VLF",
" you can send data almost around the globe (which why it's used by submarines)",
"Hope this wall of text helps someone :)",
"Let's start with AM, which is easier to understand."
] |
[
"The thing to realize here is that the audio frequencies of music are completely unrelated to the electromagnetic frequencies of the radio transmission (much in the same way that the frequency of a wave on the surface of a lake has nothing to do with the frequency of the light that you use to see it with).",
"The actual details of radio transmission are fairly complex (and being a layman, I'm familiar with it to only a certain degree, so you may want an expert to chime in). But in general, the sound is encoded into a signal that is either frequency modulated (FM) or amplitude modulated (AM). For FM signals, you actually use a frequency ",
", and the offset from the carrier frequency is how information is encoded. AM instead encodes the information by keeping the frequency fixed and varying the amplitude of the carrier."
] |
[
"can a woman be pregnant with two different men's babies at once?"
] |
[
false
] |
sorry if this is a dumb question. i bet a coworker lunch that this was not possible. dont fail me reddit. baked ziti is on the line..
|
[
"Yes, it's possible, and it can happen naturally. It's called heteropaternal superfecundation. It's rare in humans but there have been documented cases. ",
"This article",
" has an overview. "
] |
[
"All fraternal twins are made from different sperm cells, so it isn't hard to imagine a scenario where the sperm come from different men. ",
"Even weirder, babies can be conceived days or weeks apart. It is called ",
"Superfetation",
", but it is very rare. ",
"Get cooking. "
] |
[
"thanks for the reply. bought 2 baked zitis and a pizza last week to honor the bet. i was wrong, but it was delicious. 🍛🍕🍜"
] |
[
"Why didn't this mixture of Conc. Sulphuric Acid and Cyclohexane react as expected?"
] |
[
false
] |
[deleted]
|
[
"Can you describe what reaction you're trying to make? Are you sure you don't mean cyclohexene?"
] |
[
"cyclohexene is not very stable in the bottle once it's been opened - they tend to form peroxides, and also polymeric contaminants, which might explain the multiple behaviours and the string-i-ness. Was it an old bottle? (supposed to dispose 12 months after opening if I recall) "
] |
[
"cyclohexene is not very stable in the bottle once it's been opened - they tend to form peroxides, and also polymeric contaminants, which might explain the multiple behaviours and the string-i-ness. Was it an old bottle? (supposed to dispose 12 months after opening if I recall) "
] |
[
"How does steel reduce the tension on concrete?"
] |
[
false
] |
I was recently watching a documentary where they said "concrete has an incredibly high strength when being compressed but it cracks with tension". Why is there a difference in the two and how does putting steel in the concrete inhibit the tension on concrete?
|
[
"Civil engineer here. Compression and tension are different in terms of the direction of applied forces, or loads. Compressive forces are loads acting inward on the element, while tensile forces are loads acting outward. Think of compressive forces as pushing and tensile forces as pulling. So saying concrete has high compressive strength but low tensile strength means it is easy to pull apart but difficult to crush. Steel, on the other hand, has a very high tensile strength. So it is added to concrete, typically in areas subject to tensile loads, to increase the overall strength. Typical rebar location in lateral beams, for instance, is at the bottom because this is where the beam experiences tension."
] |
[
"When tension -pulling - is applied to concrete, cracks form easily in the concrete lattice, and further pulling opens up the cracks breaking the concrete. To see how cracks affect the strength of material in tension, consider how easy it is to tear a plastic packet once a tiny notch is cut into it.",
"When the concrete is compressed, cracks are squeezed together, and this failure mode does not occur. Concrete is about 10 times stronger in compression than in tension.",
"Steel reinforcement reduces the tension in concrete in two ways:",
"the simple way: steel is ",
" than concrete, by about a factor of 10 (and stronger by a factor of ~100 in tension). So when tension is applied, the steel will take a higher proportion of the load. Sometimes, with simple reinforcement, the concrete cracks, and loses all strength in tension, but still works fine in compression.",
"the fancy way: the steel reinforcement is put into tension, and the concrete is allowed to set around it. Then, the external tension is released. The steel reinforcement springs back, and compresses the concrete (which is pretty strong in compression, ~10 times stronger than in tension, remember?). This is called pre-stressed concrete. Now, if you apply tension, it will all be taken up by the steel reinforcement, and the concrete will just experience a relief from the compression (and if the design is done right, will not crack).",
"Wikipedia has pretty thorough articles on both reinforced concrete and pre-stressed concrete if you'd like a thorough explanation."
] |
[
"Pre-stressed concrete is made even stronger by pouring the concrete over a lattice of steel rebar in tension and allowing it to harden. After the concrete has set, the tension on the lattice is released, further compressing the concrete. "
] |
[
"Since tectonic plates colliding form mountains, why aren't there mountains everywhere plates border?"
] |
[
false
] |
[deleted]
|
[
"Because not all plate boundaries are convergent. There are three basic types of plate boundaries, convergent (two plates moving towards each other), divergent (two plates moving away from each other), and transform (two plates moving past each other). Of these, convergent boundaries are where major mountain ranges are formed. At the simplest level, this is because of how materials respond to deformation. Imagine a pile of sand on two pieces of a movable substrate. If you were moving the underlying substrate material towards each other, the overlying sand would shorten and thicken (convergent). If you were moving the substrate pieces away, the sand pile would extend and thin (divergent). If you were moving the substrate pieces past each other, there would be limited change in extent or thickness, just a 'fault' that allowed the two packages of sand to move past each other (transform). If you look at a map ",
"of plates and boundaries",
" (the arrows show the sense of motion at the boundary), you can see that the major mountain ranges of the world occur where there is convergence across the boundary. Finally, not all convergent boundaries form mountain ranges and this largely has to do with the different behavior of ",
"continental",
" vs ",
"oceanic",
" crust. When the portions of both plates that are colliding are continental, a mountain range will form. If both are oceanic, ",
"a subduction zone",
" will form which may produce a volcanic island arc. When one plate is oceanic and one is continental, there will again be a subduction zone (with the oceanic plate subducting), and there may or may not be a mountain range developed in the continental portion depending on the detailed dynamics of the system."
] |
[
"The extension in the Basin and Range is internal to the North American plate and represents the early stages of rifting. If the process continued a new plate boundary would be created eventually with a new mid-ocean ridge along it. A more advanced state of rifting is in east Africa, which has split the African plate into the Nubian and Somali plates, with mountain ranges along the rift/boundary created by the associated tectonic movement and volcanism."
] |
[
"Exactly. And, at least on land, mountain ranges can form where plates diverge, as in the Basin and Range in the American West. There’s nothing like ascending the gently sloped side of a ridge or peak only to be confronted with a mile or more cliff on the steep side."
] |
[
"Happy Pi Day everyone!"
] |
[
false
] |
Today is 3/14/19, a bit of a rounded-up Pi Day! Grab a slice of your favorite Pi Day dessert and come celebrate with us. Our experts are here to answer your questions all about pi. Check out some past pi day . Check out the comments below for more and to ask follow-up questions! From all of us at , have a very happy Pi Day! And don't forget to wish a happy birthday to Albert Einstein!
|
[
"When did the Pi Day start being a thing? I mean, was Einstein asked by journalists \"Wow you were born on Pi Day?\""
] |
[
"I remember first hearing about it in middle school as it was probably a cute way for math teachers to have some fun with students. Late 90s?",
"Mind we also celebrated Avogadro’s Day in chemistry on October 23, but that doesn’t seem to have caught on the same way. "
] |
[
"There's also an algorithm to calculate an arbitrary binary digit without calculating the ones before it"
] |
[
"Does muscle make you more resistant to piercing wounds (shot, stabbed)? Does fat?"
] |
[
false
] |
Hypothetically, if we lined up a muscular person, an obese person, and a typical person, and had them shot in the same place, let's say abdomen, who would suffer less damage/trauma? Would it be different if they were stabbed?
|
[
"Doesn't entirely answer the question, but the MythBusters kind of did it:",
"http://mythbustersresults.com/coffin-punch",
"busted",
"Determining that the largest layer of fat around a human (Walter Hudson) would measure 16 inches, Adam and Jamie placed that amount of human-temperature cow fat in front of the dummy. The bullet made it all the way through the fat easily.",
"busted",
"Using the measurements of a man with 3-inch pectorals and 11-inch biceps, Adam and Jamie placed 14 inches of cow muscle in front of the dummy (assuming the man placed his bicep over his pectoral and the bullet passed through them both). The muscle failed to stop the bullet."
] |
[
"This would depend strongly on the type of bullet used. A frangible bullet, for example, will definitely not make it through 14 inches of muscle and probably not fat either. It's definitely not black and white like they are showing. Hollow points penetrate less than full metal jacket bullets. Smaller/faster calibers will penetrate less than larger/slower bullets, as the energy of very high speed bullets can literally tear the bullet apart into smaller pieces. There have been studies showing that large assailants are more difficult to incapacitate with a single handgun bullet. If you use an elephant rifle, though, it'll probably shoot through any human assailant of any size just about equally well. "
] |
[
"It's also worth noting that this is because the bullets have different lethality. Frangible and hollow points penetrate less because they are designed to impart more of their energy on the target rather than passing through and continuing past the target with energy that wasn't spent doing damage. Small bullets wounds like from a .22 will actually seal the wound pretty well and not bleed out through the skin as much as you would expect (Although internal damage is still possible).",
"The reasoning behind the hollow point is to create a huge wound tract, and either nick something that will take the person down quickly, or cause a blood pressure drop or spike enough to make someone pass out.",
"A frangible is meant to create lots of tiny wound tracks and nick something important; mainly they are self defense rounds for people who are in apartments or have close neighbors and are worried about a bullet continuing past the target to someplace it isn't wanted.",
"The key here is to realize that penetration, while an important aspect, isn't everything when it comes to how effective a round is."
] |
[
"If I took a deep-see creature, whose body is designed to withstand tons of pressure, and brought it to a spot with less pressure pushing down on it (such as the surface) and stood on it, would it support me, or would I squish it?"
] |
[
false
] |
I know that most of the time bringing any deep-sea creature up from the depths will kill it almost immediately, but I'm asking theoretically about the creature's body's ability to withstand pressure. It's a stupid question, I know, but I'm curious!
|
[
"I think the impression you have is that deep sea creatures are somehow super tough because the pressure in the deep sea is so high. (?)\nThat's not really the case since there are no particularly special body plans for pressure. Here is why. As was mentioned before, water is incompressible. Doesn't matter how much pressure is applied to it, it stays the same (be reasonable physicists and chemists,me are talking physiological conditions here). To survive, you just need to be made up of mostly water. Many of those creature look like goo when brought to the surface because their bodies are not well supported outside of the water. If anything, a deep sea creature is probably squishier when stepped on.\nAt depth, some creatures generate a bit of gas in body compartments or bladders to keep neutral buoyancy or whatever. Gasses, unlike the water in the body, is compressible, which means it will expand dramatically as the pressure around it is reduced (ascent from the depth). This is true of gases dissolved in body fluids too. Squishy creatures with internal gasses (both dissolved or otherwise) pretty much fizz and pop on their way up if their bodies are not allowed enough time to off-gas (gills, farting, or equivalent structures and processes). Quick ascents can therefore contribute to the squishiness factor."
] |
[
"This gets at the mechanisms underlying the ability to live in very deep water, so I find it to be a rather interesting question. I hope some marine biologists can chime in on this.",
"I recommend reading answers to a related question posted on the UCSB Scienceline page ",
"here",
".",
"My attempt at a short answer: ",
"You would squish the poor deep sea creature because while the water inside its body is effectively incompressible, it likely has pores/etc which would leak water when force is applied. In the deep ocean this is not a problem since that water would be replaced by the surrounding water coming through various mechanisms. At the surface, only air could replace the water and air is compressible."
] |
[
"It would depend on what kind of sea creature you would be talking about jelly fish, crustaceans, sharks, take your pick. I believe it has to do with the animals open circulatory system allowing water to pass through it. A controlled rise to the surface would not kill the animal. We often have unidentified sea creatures showing up after earthquakes at sea just to swim by and never be seen again for a Long time."
] |
[
"Why are some groups of animals, like rodents, not sexually dimorphic? (or at least as obvious as other mammals) How have social systems pressured changes in sexual dimorphism? How are species that aren't sexually dimorphic able to differentiate sexes before encounters?"
] |
[
false
] | null |
[
"How are you defining \"dimorphism\"? Are you approaching it with human bias towards visible differences?",
"Remember that there are other important sensory and behavioral clues to look for. Smell, in particular during estrus, is quite powerful, as are certain innate behaviors associated with mating, such as becoming more accommodating to the approach of a stranger.",
"Also, consider that even in dimorphic species there are same-sex encounters that lead to partial (or more) mating behaviors, from courtship up to pair bonding. "
] |
[
"Minor addition--it is sort of possible for sexes to evolve without each other, as in the case of termites. Most of their expressive genes have migrated to the sex chromosomes so males and females share little genetic material."
] |
[
"Minor addition--it is sort of possible for sexes to evolve without each other, as in the case of termites. Most of their expressive genes have migrated to the sex chromosomes so males and females share little genetic material."
] |
[
"How long will we survive if the Sun suddenly disappears?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"For more information regarding this and similar issues, please see our ",
"guidelines.",
"If you disagree with this decision, please send a message to the moderators."
] |
[
"I know the situation is hypothetical and highly unlikely to happen, but I was interested in the effects of suddenly losing the heat and gravitational pull from the Sun, and if we are able to sustain life somehow without solar energy. I do understand your reason for removing though, maybe the question should be asked a different way."
] |
[
"/r/AskScienceDiscussion",
" is your best bet!"
] |
[
"What is it about cockroaches that makes them famously able to survive radiation from a nuclear apocalypse?"
] |
[
false
] |
Are they really the only (land?) animals that would be able to make it? Is this specific resilience an evolutionary advantage or just some kind of quirk of their biology? Thanks
|
[
"DNA is most vulnerable, and most difficult to repair, when it is exposed in solution and being manipulated by enzymes. One reason is just that when it is being manipulated, the two rungs can be detached, reducing the number of chemical bonds available to support the molecule. Another is that there's more opportunity for confusion when many strands are in play and can potentially get mixed up.",
"When cells are not dividing, DNA is wrapped in/around proteins called histones. This reduces the exposure of the molecule, and givens repair enzymes time to fix it before it's used.",
"Cockroach cells spend most of their time not dividing, so the dna is less likely to be hit when radiation hits the cell, and the damage is more likely to be repaired before it's needed."
] |
[
"Study recently confirmed, that it's just because their cells divide slower than in other species, so they can survive longer. but when their cells divide, they are susceptible to the same mutations as any other species."
] |
[
"But there isn’t a phase in the cell cycle where radiation can’t enter a cell. It can always enter can’t it?"
] |
[
"Has a species of carnivores ever evolved from a species of herbivores?"
] |
[
false
] |
I'm curious about this because, if there were a case of this, that would mean that at some point, one of the members of the herbivore species, through some kind of situation or another, one day ate another animal. Might be a dumb question, I'm not sure.
|
[
"Lots of living herbivores will occasionally eat animals. Here's a deer eating a bird: ",
"https://www.youtube.com/watch?v=sQOQdBLHrLk",
"Whales (carnivorous/piscivorous) are most closely related to hippos (omnivorous, tending toward herbivory), and after that to ruminants (herbivorous), then swine and peccaries (omnivorous, tending toward herbivory), and camels and llamas (herbivorous). Whales and hippos probably had herbivorous ancestors (\"dichobunoids\")."
] |
[
"Generally speaking, a lot of lineages start off omnivorous, and then become specialized into either carnivory or herbivory. ",
"It's relatively rare that strict herbivores (",
"I say strict only in a broad sense, because many herbivores will on occasion eat meat out of necessity",
") can become obligate carnivores because they're so specialized for a herbivorous diet.",
"The reverse is rather common, though."
] |
[
"Off the top of my head there are two that come to mind Therizinosaurus and the Giant Panda. ",
"Usually theropods are considered omnivorous or exclusively carnivorous (think T-rex or velociraptors), but this and it's relatives are unique; they evolved from a common ancestor that favoured herbivore behavior, and these dinosaurs actually displayed theropod morphism with teeth designed to grind and chew like a cow rather than tear and strip like a lion.",
"As per the Giant Panda, yes it may have its sharp teeth, but we look at it's gut for indication; carnivores have a smaller intestinal tract; herbivores need a longer intestinal tract to allow plant material to break down as cellulose is indigestible if just met with stomach acid (goats and other animals eat stones to aide in this process of breaking down plant matter). Yet the panda's gut is unique as it is shorter, indicating that it was descended from a carnivorous species that has recently (in evolutionary terms) come to favour a herbivore diet. ",
"Sources on wiki if you're interested"
] |
[
"What is the largest nuclear explosion possible with the fissile/thermonuclear material Humanity has available?"
] |
[
false
] | null |
[
"Theoretically, yes. Practically, I don't know why you would. Since it is speculated that the fusion reaction is caused by ablative pressure from x rays, the x rays would travel faster than the blast wave. Thus, multistage devices can be built. However, the damage caused by the bomb is not linear with power. So doubling the bomb energy release does not mean you get double the explosion. "
] |
[
"Yes and no. It is not a matter of pumping it in. It is a matter of what is known as \"staging.\" What you are basically doing is using bombs to start more bombs to start more bombs. ",
"An atomic bomb (fission bomb) uses chemical explosives to start a nuclear fission chain reaction. This is put inside of a heavy casing and its radiation is drawn off to compress another component full of fusion fuel (you could use deuterium-tritium but it is kind of a pain; lithium-deuteride is a much easier fusion fuel to deal with). Compressing this with a fission bomb starts fusion reaction, which release neutrons. These neutrons can then induce fission in a natural uranium blanket. And in theory you could then have this whole thing compress another component of fusion fuel and more fission and so on, forever and ever.",
"What limits you is practical size of the thing. A 50-100 megaton bomb is already a bomb the size of a school bus. It's not an easy thing to get from here to there. A 1,000 megaton bomb would be somewhat larger. A 10,000 megaton bomb is probably well outside the size range that you'd be able to deliver anywhere useful. ",
"But yes, in theory, you can keep scaling them up indefinitely. As Dr. Strangelove put it, \"It requires only the will to do so.\"",
"During the Cold War, the largest bomb I've ever heard of any nuclear power seriously contemplating was a 10,000 megaton (that is, 10 gigaton) bomb. It never got past the drawing board stage, but it was taken fairly seriously."
] |
[
"Who was contemplating a 10000 Megaton bomb? I have never heard this in my life."
] |
[
"Why is the heliosphere elliptical or comet-like in shape?"
] |
[
false
] |
Is this because the Sun is rotating in the milky way creating a helio-tail?
|
[
"Yep. The Sun is orbiting the Milky Way at a different speed to the local gas, so the gas gets bunched up on the \"front\" side and streams out along the back. This is also true for the magnetic fields, which also get compressed on the front and stretched out the back. "
] |
[
"Actually results from the Cassini and Voyager 1 & 2 probes last year showed that the heliosphere only has few tail-like features and that the shape is mostly spherical and not very comet like. ",
"NASA release",
"Nature Paper"
] |
[
"thanks for corroborating that."
] |
[
"Which rodents have the largest territory?"
] |
[
false
] |
I know that beavers are technically rodents and have territories that can span up to multiple kilometers, but what about other (smaller) rodents - which species do have the largest territory? I hope someone can help me with this question, Google wasn't very helpful in that regard. Thank you! :)
|
[
"Gophers of any variety can take up large swaths of territory, and are organized amongst themselves.",
"Rats/mice by default are the most populace and can be found pretty much everywhere, but they don't really organize amongst themselves."
] |
[
"Rats absolutely do organize amongst themselves in groups called packs. Larger rats dominate the group and prevent other males from mating with the female rats."
] |
[
"I should have been more specific.",
"Rats will organize themselv s.on this small of a scale yes, but there won't be thousands working in unison like gophers."
] |
[
"Can sound be predicted in a computer simulation?"
] |
[
false
] |
Suppose I wanted to make a computer simulation of a rubber ball hitting a wooden plank. There are many physics engines that could do this and would make an accurate reproduction of what it would look like. Would it be possible for a similar program to predict what sound would be made by this? As sound is just vibration, would it be possible to model how the ball and the plank vibrate, and use that to make a sound?
|
[
"Here is something from Cornell on the subject:\n",
"http://www.cs.cornell.edu/projects/sound/",
"You'd be interested in their list of related publications."
] |
[
"It's been done to some degree of success, I read a long article about it a few months back, I'll try to find it for you when I get out of work."
] |
[
"Yes it is possible, but it might be computationally more difficult. Finite Element Modelling might be required."
] |
[
"Why oil fries, while water boils?"
] |
[
false
] | null |
[
"To boil is to heat a liquid to point of vaporization. Like water to 100 °C. Oils boil much higher, like 300-400 °C.",
"Fry is a cooking term meant to heat something up, possibly with oil to cook it and maybe brown it. You could stir fry with water but I think that's more like sautéing."
] |
[
"When you put food in oil it's at s much hight temperature than boiling in water. As a result moisture in the food is boiled out which dies the food. Its also hot enough that browning (maillard reactions) and crisping can occur.",
"The bubbling when you deep fry is the water coming out of the food and vaporising. You can get pills to boil as well, although they aren't pure liquids boiling is generally accompanied by a lot of smoking, burning of components in the oil, and - because oils are generally flammable - the vaporised fraction often ignites."
] |
[
"The other responses have answered your question, but I wanted to mention this: You can cook in oil without boiling it, and you can cook in hot water without boiling it as well (like when you're using a sous-vide).",
"In both cases the liquid is being used to impart heat to the food."
] |
[
"Will I faint instantly if my heart stop beating?"
] |
[
false
] |
Or will I stay conscious until all the oxygen in my blood is depleted?
|
[
"If your heart suddenly stops, your blood stops circulating in your body, you don't have to wait for your blood to run out of oxygen because it doesn't matter if you still have free available oxygen in your blood or inside your red blood cells packed within the hemoglobin, it is stagnant.\nHowever you won't faint instantly. You central nervous system can maintain your consciousness level for around 9 seconds without oxygen, then you faint. This doesn't mean that you are experiencing brain damage from the instant you faint. You faint because it is a defense mechanism of your brain to avoid consuming energetic resources to keep you awake. Around 3 minutes after not receiving oxygen, you start experiencing brain damage.\nAnother different thing is if you suddenly stop breathing, then your blood will still be circulating and the available oxygen in your blood will be used."
] |
[
"There are things called pacemakers..."
] |
[
"Implantable Defibrillators (ICDs) exist, and are increasingly common.",
"They are more complex than pacemakers and have at least 2 wires - one in the Right Atrium (RA) and one in the Right Ventricle (RV). The RA wire can act like a regular pacemaker - ensuring the HR doesn't go below a minimum value - it gives a tiny shock that stimulates the atria to contract. The (RV) lead can also deliver pacing, forcing the ventricle to contract, however it's main function is defibrillation. (Other more complex lead arrangements are also possible).",
"If the patient suffers a dangerous cardiac arrhythmia, or has a VF or VT cardiac arrest (which would be fatal), the device delivers a shock to restore normal rhythm. Many patients report that it feels like being kicked in the chest. ",
"Interestingly, when these devices are implanted the cardiologist causes the patient to have a cardiac arrest on the table (VF), to ensure the device works correctly.",
"Here is a video of a footballer in Europe with such a device: ",
"https://youtu.be/UjZK4HgoY2Q",
"You'll see that he very quickly loses consciousness (seconds), then his leg twitches as he is defibrillated, and he comes round. Absolutely incredible! Although why someone with a potentially fatal arrhythmia is playing professional sport, I don't know."
] |
[
"Why does mold grow on tea but not on water, milk, or juice?"
] |
[
false
] |
Is it because the tea has more nutrients than the water and less sugar than the juice and milk? The mold seems to grow relatively quickly -- maybe after 3 days of leaving cold tea sitting. The tea that I drink in particular is Oolong tea boiled from the leaves (no teabag), if that makes a difference.
|
[
"Juice - too acid.",
"Milk - too much competition from bacteria.",
"Water - no food!"
] |
[
"Could be that you've boiled the water and killed off all the bacteria in the tea, while in the milk and juice, you haven't. Thus the bacteria in milk and juice cause spoilage much sooner than mold.",
"Though there are a number of other variables."
] |
[
"I've seen quite impressive mold growing on fruit juice.",
"Don't remember what specific type of juice."
] |
[
"How Can I *Safely* Watch the Transit of Venus?"
] |
[
false
] | null |
[
"Go to home-depot/lowes/Ace hardware and check out their welding section. They should sell welder's glass. It's a heavily tinted glass rectangle, about 2\" wide by 4\" long. A piece should cost no more than $5. It comes in different tints, which are designated by a number."
] |
[
"http://www.eclipseshades.com/safety.html#anchor138141",
"Basically, welding glass, highest grade you can get. That stuff got standards. ",
"Under no circumstances what so ever should you use crossed polarizers or black negatives or random stuff that looks dark or paints or various random dark stuff irresponsible people sell online and irl. The shiny stuff (metal coated) is mostly safe if dark enough, though. ",
"The issue is that the infrared light must also be blocked, and most 'black' filters do not filter infrared out very well."
] |
[
"No it's actually the ultraviolet that's the problem - infrared will cause heating but you'd have to stare for a very long time for thermal issues to arise. On the other hand, ultraviolet starts temporarily damaging the retina in a few seconds and permanently bleaching photoreceptors in the retina and damaging the cornea in less than a minute.",
"But welding goggles are the best for direct observation. If you have a telescope with a solar filter, that's safe but since I've had them jostle off at a bad moment, you'd want to use a digital eyepiece to view it on a computer screen. Lower cost, if you are at all handy (like can poke a pinhole in a paper plate) it's even safer to use an indirect projection onto a piece of paper from a pinhole held a foot or more in front of the surface. "
] |
[
"How do scientists determine the \"habitable zone\" for a planet to support life, if the surface temperature of the planet is highly dependent on its greenhouse gas composition?"
] |
[
false
] |
i.e. doesn't a planets ability depend on much more than just its distance from a star (given the stars solar ouput)?
|
[
"I answered a similar question here: ",
"How is the Goldilocks zone of a star defined, considering how much surface temperature can change due to planetary characteristics?"
] |
[
"Without a greenhouse effect Earth would be constantly ice bound and unlikely to have ever produced life (at least that moved beyond the deep ocean)."
] |
[
"Firstly we need to define what makes a planet habitable. The Earth it would appear is an almost perfect example, the presence of water and light and our planets surface temperature means that our planet is optimum for life to evolve and live.",
"There are two definitions of habitable zones around a star: the circumstellar habitable zone is the range of distances around a star that liquid water could exist on any planetary surface, and the continuous habitable zone is the range of distances in which a planet could reside and sustain liquid water for the majority of its stars life.\nRemember that these definitions don't give 100% accurate references for where a planet needs to be to be habitable. Also the main challenge in defining habitable, is that all we have to base our theories on is the examples of life and habitability of our planet. ",
"Lastly the assumption that a planets greenhouse gas effect defines its surface temperature is wrong, what determines a planets surface temperature is the amount of radiation (heat) received from its star. A planets atmosphere means that a planet can retain the heat received from its star through the greenhouse effect. "
] |
[
"Is there a name for the actual origin of the wind, like how a river has headwaters?"
] |
[
false
] | null |
[
"Rivers have a beginning and end that is clearly defined and generally permanent. Wind is ever flowing around the earth in ever changing systems of pressure driven by the sun and the earth's rotation. Thus, its hard to clearly define the starting point of wind. Wind is really more analogous to ocean currents, which we likewise don't generally consider to have a beginning or end.",
"So i dont think theres a word for the starting point of wind, rather, there's simply different drivers of air flow around the earth."
] |
[
"Ah, this makes a lot of sense. I figured that this was the case, but was wondering yesterday if there was some little-known term. Thank you!"
] |
[
"Wind doesn’t really have a beginning point but the geotrophic wind is kinda the origin of all ground wind. It is the wind of the higher atmosphere and everything “flows” down from there. It’s not the air itself that flows down from there but the wind speed which is a gradient with the geotrophic wind being the high end and zero wind speed touching the ground."
] |
[
"If a gas always fill it's recipient, wouldn't it's density be always determined by it's recipient?"
] |
[
false
] | null |
[
"Partially, it sounds like you are describing a scenario where you are controlling the volume and pressure of the system which both impact density. The other factor to consider is molecular weight, which is only dependent on the gas itself. If you had two identical containers and filled one with nitrogen and the other with oxygen the one filled with oxygen would have more mass (greater density).",
"You can also get into non-ideal situations if you use extreme temperatures or pressures and need to invoke the Van der Waals equation, at which point the gas density is even further changed by its composition."
] |
[
"The oxygen would fill the entire room for sure, and you would calculate its density based on pressure, volume and composition. Whatever density the original 1 mole was at would be reduced when you let it spread out. ",
"Another way to say it would be if you suddenly make the room bigger without adding any more gas the volume goes up, pressure goes down and thus the density would decrease. "
] |
[
"And what if we have let's say 1 mol of oxygen and you place it in a HUGE room with a normal pressure of 1atm. The oxygen would fill the whole room lowering its density so much or it has a \"fixed\" density for that pressure and would have a determined volume(lower than room's volume)?",
"I'm sorry if this is a pretty stupid question but I'm starting studying thermodynamics and sometimes the most elemental knowledge are avoided in college."
] |
[
"What is the opacity of air (average, of course)?"
] |
[
false
] |
How much visible light does, say, 1 metre of air block? How far is it physically possible for a human on a flat surface to see through an Earth-like atmosphere?
|
[
"I couldn't talk about air's transmittance over 1m, but ",
"here's",
" the solar spectrum measured in the upper atmosphere and at sea level.",
"Source"
] |
[
"I'm going to try re-submitting this with a different title.",
"Edit: ",
"It's not going well."
] |
[
"Please link me. I would love to know the answer."
] |
[
"From above water, why can't I hear someone yelling under water?"
] |
[
false
] |
I was playing around with my siblings at a pool and they were yelling messages under water to eachother. Why can't I, above water, hear them?
|
[
"The energy required to vibrate water molecules with sound is much greater. Sound is the vibration (within a range of frequencies) of molecules. I think the technical reason is the hydrogen bonds between water molecules that cause tension. Molecules in the air, for the most part, are not hindered by intermolecular bonds."
] |
[
"That doesn't make sense since people who are also under water can hear just fine. "
] |
[
"You can hear clearly under water? That's amazing. "
] |
[
"Are humans apes?"
] |
[
false
] |
So humans are primates. And we evolved from apes. But are we considered apes from a taxonomy viewpoint? Edit: Wow. Thanks for all the great answers. This got a lot more attention than I thought it would.
|
[
"This is an old essay from ",
"Talk.Origins",
":",
"A giraffe has never given birth\nto a horse, as far as we know it. An ape has never given birth to a man.\nI will give a million bucks to anyone who can observe an ape giving\nbirth to a human. Even your mother, if such were true.",
" ",
"As such, you are basically a collection of replicative proteins that function according to metabolic chemical reactions and processes. A virus is similar, in that it too is a replicative protein complete with mutable DNA and RNA, just as you have. But viruses lack metabolism, and so may not be considered to be alive in the same manner that you definitely are.",
" ",
"All remaining organic life is distinguished by structural differences at the cellular level between different groups of prokaryotes (which are essentially bacteria) and the eukaryotes (us). Unlike bacterial or viral cells, our cells have a nucleus. Hence, all non-viral / bacterial lifeforms are as we are; eukaryotes.",
" ",
"Now I've heard a few creationists argue that there are plants and there are animals and then there are human beings. And that none of them are actually related to one another other than through a common creator. They adamantly argue that we are not animals, as if there is some insult in that association. But you are one of only about a half-dozen kingdoms of eukaryotic life forms. Unlike those of most other biological kingdoms, you are incapable of manufacturing your own food and must compensate for that by ingesting other organisms. In other words, your most basic structure requires that you cause death to other living things. Otherwise, you wouldn't have a means of digestion. This, along with some very specific anatomical differences in the chemical composition of our metazoic cells, are the factors that define and distinguish an animal like yourself from all other kingdoms of life. Given the alternative choice between plants, molds, or fungus, animalia should seem reasonable even to the most adamant fundamentalist.",
" ",
"You have a spinal chord and every other minute physical distinction of that classification. You also have a skull, which classifies you as a craniate. Note: Not all chordates have skulls, or even bones of any kind. Once one of the chordates has enough calcium deposited around the brain to count as a skull, all of its descendants will share that. This is why absolutely all animals with skulls have spinal chords. And that is yet another commonality that implies common ancestry as opposed to common design.",
" ",
"Like all mammals, birds, dinosaurs, reptiles, amphibians, and most fish, you have a spine. Not everything with a spinal cord has a spine to put it in, but everything with a spine has a spinal cord in it, implying common descent.",
"Every animal that has a jaw and teeth (Gnathostomata) also has a backbone. And of course, you have both as well, again implying common descent.",
" ",
"You have only four limbs. So you are like all other terrestrial vertebrates including frogs. Even snakes and whales are tetrapods in that both still retain vestigial or fetal evidence of all four limbs. This is yet another consistent commonality implying a genetic relationship. There certainly is no creationist explanation for it.",
" ",
"Unlike turtles (which are anapsid) and \"true\" reptiles, dinosaurs and birds (which are all diapsid), your skull has only one temporal fenestra, a commonality between all of the vast collection of \"mammal-like reptiles\", which are now all extinct without any Biblical recognition or scriptural explanation either for their departure or their presence in the first place.",
" ",
"You are homeothermic (warm-blooded), follicle-bearing and have lactal nipples. And of course, not all synapsids are or were mammals, but all mammals are synapsid, implying common descent.",
" ",
"Or more specifically, you are a placental mammal, like most other lactal animals from shrews to whales. All eutherians are mammals, but not all mammals are eutherian. There are six major divisions in mammalia, only three of which still exist; those that hatch out of eggs like reptiles (monotremes), marsupials, that are born in the fetal stage and complete their development inside the mother's pouch, and those that developed in a shell-like placenta and were born in the infant stage, as you were. Your own fetal development seems to reveal a similar track of development from a single cell to a tadpole-looking creature, then growing limbs and digits out of your finlike appendages, and finally outgrowing your own tail. Some would consider this an indication of ancestry. Especially since fetal snakes, for example, actually have legs, feet, and cute little toes, which are reabsorbed into the body before hatching, implying common descent.",
" ",
"You have five fully-developed fingers and five fully-developed toes. Your toes are still prehensile and your hands can grasp with dexterity. You have only two lactal nipples and they are on your chest as opposed to your abdomen. These are pointless in males, which also have a pendulous penis and a well-developed ceacum or appendix, unlike all other mammals. Although your fangs are reduced in size, you do still have them along with some varied dentition indicative of primates exclusively. Your fur is thin and relatively sparse over most of your body. And your claws have been reduced to flat chitinous fingernails. Your fingers themselves have distinctive print patterns. You are also susceptible to AIDS and are mortally allergic to the toxin of the male funnel web spider of Australia (which is deadly to all primates, but only dangerous to primates, which is why you'd better beware of these spiders). And unlike all but one unrelated animal in all the world, your body cannot produce vitamin-C naturally and must have it supplemented in your diet, just as all other primates do. Nearly every one of these individual traits are unique only to primates exclusively. There is almost no other organism on Earth that matches any one of these descriptions separately, but absolutely all of the lemurs, tarsiers, monkeys, apes, you, and I match all of them at once perfectly, implying common descent.",
" ",
"Your tail is merely a stub of bones that don't even protrude outside the skin. Your dentition includes not only vestigial canines, but incisors, cuspids, bicuspids, and distinctive molars that come to five points interrupted by a \"Y\" shaped crevasse. This in addition to all of your other traits, like the dramatically increased range of motion in your shoulder, as well as a profound increase in cranial capacity and disposition toward a bipedal gait, indicates that you are not merely a vertebrate cranial chordate and a tetrapoidal placental mammalian primate, but you are more specifically an ape, and so was your mother before you.",
"Genetic similarity confirms morphological similarity rather conclusively, just as Charles Darwin himself predicted more than 140 years ago. While he knew nothing of DNA of course, he postulated that inheritable units of information must be contributed by either parent. He rather accurately predicted the discovery of DNA by illustrating the need for it. Our 98.4% to 99.4% identical genetic similarity explains why you have such social, behavioral, sexual, developmental, intellectual, and physical resemblance to a bonobo chimpanzee. Similarities that are not shared with any other organism on the planet. Hence you are both different species of the same literal family. In every respect, you are nearly identical. You, sir, are an ape.",
"And as I have witnessed the birth of both of my children, I have now met the criteria for your reward. Please make my $1,000,000.00 payable to L. Aron Nelson. Thank you. "
] |
[
"Yes. Ape (Hominoidea) is a superfamily and is made up of the families Hylobatidae and Hominidae. Within Hominidae there are four genera: Pongo, Gorilla, Pan, and Homo. I think you can take it from there!",
"As with all taxonomy, there is likely going to be some shuffling around and suggestions for reorganization based on DNA data. For example, ",
"this paper",
" suggests that the breakdown be:",
" Family Hominidae\n\n Subfamily Hylobatinae\n\n Hylobates\n\n Subfamily Homininae\n\n Tribe Pongini\n\n Pongo\n\n Tribe Hominini\n\n Subtribe Gorillina\n\n Gorilla\n\n Subtribe Hominina\n\n Pan\n\n Homo \n"
] |
[
"Adding to this in simpler words: the common name for hominidae is \"great apes\". This family includes gorillas, chimpanzees, and humans. "
] |
[
"What exactly is the spleen used for?"
] |
[
false
] |
A co-worker had said he heared some where that the spleen on an evolutionary scale was once used to help us drink water that was unsanitary. Since I had no idea I knew the people of askscience wouild know.
|
[
"The spleen is part of the reticuloendothelial system (now called the mononuclear phagocyte system.)",
"http://en.wikipedia.org/wiki/Mononuclear_phagocyte_system",
"Also see: \n",
"http://en.wikipedia.org/wiki/Spleen#Function",
"for a great summary of splenic function. Clinically, removing your spleen would cause a slight leukocytosis and thrombocytosis (increased white blood cells and platelets since fewer are being sequestered in the spleen's white pulp), decreased response to certain vaccines, and the ",
": susceptibility to encapsulated bacteria, like the pneumococcus, meningococcus, Salmonella, etc., all of which cause nasty infections. The spleen therefore plays an important role in protecting us against infections by these bacteria.",
"The speculation about helping to drink unsanitary water is mostly that, just speculation. Most of these encapsulated bacteria are transmitted by respiratory secretions or are present on the skin rather than being fecal-oral or waterborne, with the exception of Salmonella. An evolutionary biologist might be better equipped to compare the role of the spleen across species, however."
] |
[
"So pretty much maybe back a few thousand of years or more the spleen was larger and maybe helped us to drink dirt bad bacteria infested water? If we look at it our water supply it has gotten tremendously better over the years. What started this discussion was that back in the Ancient Greek times they would drink 3:1 water to wine mixture so he mentioned yeah the water was bad and we had larger spleens which helped aid in the bad water conditions. I came here to see what kind of back up I could find to this."
] |
[
"I doubt the spleen was larger thousands of years ago. The size of the organ wouldn't have anything to do with how efficient it is at getting rid of bacteria that have been coated with antibodies (which is its major function.) If the theory about \"bad water\" was correct, people in countries where the water supply is untreated (like India) would have larger spleens than their Western counterparts. They don't, and in fact an enlarged spleen is a sign of something gone wrong:",
"http://en.wikipedia.org/wiki/Splenomegaly#Causes",
"I personally think that the idea of our ancestors having larger spleens to process dirty water is BS. 1) There is no evidence of humans having larger spleens 2000 years ago than they do now. 2) 2000 years ago the average life expectancy was around 40-50, if not less, mainly due to infectious diseases, some of which were water and food-borne. Even if humans had larger spleens, they weren't helping them combat those deadly infections. 3) Drinking alcohol mixed with water, or boiling water before drinking it, was probably the only way people managed to drink uncontaminated water. Remember that the germ theory of disease is very recent."
] |
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