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[
"How do strong nuclear forces create mass?"
] |
[
false
] |
I came across the sentence, "Most of the mass of a common proton or neutron is the result of the ; the individual quarks provide only about 1% of the mass of a proton." in the But it also says that they're caused by Gluons which have no mass. I thought conservation laws meant that mass couldn't be created or destroyed. How does this work?
|
[
"Gluons are a very special case, because they carry color charge, and QCD is non-perturbative/confined at low energies. QCD is a lot like QED, except for those two important points. But you have no problem thinking of situations with real photons. You can distinguish in your mind a real photon from a virtual photon. It works the same for the gluons, it’s just very hard to come up with a situation where there are real gluons around (something like a QGP at very high energies, above the deconfinement scale). You don’t encounter these situations in your daily life, so real gluons are not something you can intuit like real photons."
] |
[
"I mean, what's inside, then?",
"You might be interested in this enlightening article from Matt Strassler",
"https://profmattstrassler.com/articles-and-posts/particle-physics-basics/the-structure-of-matter/protons-and-neutrons/"
] |
[
"The gluons being referred to here are virtual particles. There are no literal gluons inside of a proton/neutron.",
"But anyway, kinetic and potential energies contribute to the masses of physical systems. The kinetic and potential energies of the interactions between the quarks in the proton/neutron contribute to the mass of the proton/neutron. And the interactions are very strong, and the quarks are “moving” very fast, so they end up contributing much more than the sum of the bare masses of the quarks."
] |
[
"Why do dogs lick our faces, but not each others?"
] |
[
false
] |
I know they have a second olfactory gland in their mouth. Do they get the best scent out of us by licking our face as opposed to smelling another dogs bum?
|
[
"http://en.wikipedia.org/wiki/Dog_communication#Tongue_.28Licking.29",
"\nTongue (Licking)",
"A very common form of communication is for a dog to lick another dog, or a person. Dogs lick other dogs' faces and mouths when they greet each other to indicate friendliness. Dogs like to lick human skin not only for the salt from the sweat, but also as a form of greeting, such as by briefly licking a person's hand after sniffing it.",
"Licking is also used as a social bonding analogous to primate social grooming and stroking. This can indicate intimacy. Such licking is longer and slower, as compared to the brief licking of faces during a greeting."
] |
[
"Just a heads up, but this subreddit is pretty unique and has some special rules about posting. Look over to your right to learn more. Posting anecdotes or unsourced claims are not typically allowed, and the rules are more stringently applied for top level replies such as yours. "
] |
[
"Just a heads up, but this subreddit is pretty unique and has some special rules about posting. Look over to your right to learn more. Posting anecdotes or unsourced claims are not typically allowed, and the rules are more stringently applied for top level replies such as yours. "
] |
[
"When we look at a picture of the surface of the sun, how much of that represents actual fusion, and how much is merely \"hot gas\"?"
] |
[
false
] | null |
[
"On the surface it's all hot gas and plasma."
] |
[
"Most of the fusion is deep in the core. To sustain thermonuclear reactions like fusion, you have to have a combination of high density and high temperature. The center of the Sun has a density similar to that of solid rock, and a temperature of millions of degrees K (the surface is pretty cool at only 6,000K -- not much hotter than the arc in a typical arc lamp). So that's where the thermonuclear reactions take place.",
"\"Hot gas\" is a good way to describe the outer layers of the solar interior, which are cool and tenuous compared to the core. The material in the Sun is so hot that it's actually ",
"plasma",
", which means that it is electrically conductive -- so it has lots of interesting electrical phenomena mixed in. Below the photosphere (the visible surface) the material acts mostly like a gas and the electric currents and magnetic field sort of go along for the ride. Above the photosphere (in the chromosphere and corona) the magnetic field steers the show and the gas acts like it's nailed to particular magnetic field lines, more or less. ",
"Plasma has a way of concentrating energy in both space and time. The photosphere is heated by convection from below -- hot material (heated by conduction fusion in the Sun's core) rises to the surface, cools (by radiating sunlight) and sinks again. But since the material is a plasma, that process induces titanic electric currents all over the place. Occasionally those currents collapse dramatically, releasing all kinds of energy as heat, as coherently accelerated particles, and as kinetic energy of material hurled from the surface. Those sudden energy releases are ",
"solar flares",
", and they drive ",
"coronal mass ejections",
" through space. Inside a solar flare fusions occur, but they're not energetically important compared to the ongoing fusion in the core of the star.",
"(Incidentally, the Sun makes antimatter too -- a large solar flare may create as much as a few kg of antimatter, which immediately annihilates on contact with all the other matter around)."
] |
[
"Fusion reactions occur in the central regions, where pressure and density are highest. Heat produced in the core, where temperature reaches in the millions of degrees, is transported to the surface by radiation and convection currents. What you see is plasma glowing from heat produced hundreds of thousands of kilometers below."
] |
[
"What happens when a hypothetical black hole would exist that's so big that metric expansion becomes noticeable across it's diameter? Would this affect its Schwarzschild radius? It's temperature? Anything else?"
] |
[
false
] | null |
[
"i can't tell you anything specific about it, maybe someone else can expand or correct me, but it seems to me what you are looking for is something like the ",
"https://en.wikipedia.org/wiki/De_Sitter%E2%80%93Schwarzschild_metric",
"which describes a black hole in expanding space (cosmological constant). maybe that's good enough for a first read until someone gives you a proper answer."
] |
[
"you're right about the pure schwarzschild metric. this is about the ",
" schwarzschild metric though",
"de Sitter space is the simplest solution of Einstein's equation with a positive cosmological constant. It is spherically symmetric and it has a cosmological horizon surrounding any observer, and describes an inflating universe. The Schwarzschild solution is the simplest spherically symmetric solution of the Einstein equations with zero cosmological constant, and it describes a black hole event horizon in otherwise empty space. "
] |
[
"which describes a black hole in expanding space (cosmological constant)",
"It does not. The Schwarzschild metric is a ",
" solution of the Einstein equations."
] |
[
"Why do birds have white feces?"
] |
[
false
] |
Title
|
[
"Basically this comes down to the fact that birds (and reptiles) don't urinate (there are some rare ones which do but it is not common at all). All animals have to deal with the nitrogenous (containing nitrogen atoms) waste products of protein metabolism. You eat food, you make proteins and then you breakdown those proteins and excrete the waste parts.",
"In mammals one of these waste products is the nitrogen containing urea. Urea is conveniently soluble in water, so it is fairly straight forward to get rid of the (mildly) toxic urea via urination.",
"Birds on the other hand convert the nitrogenous waste of protein metabolism to uric acid. Uric acid is nowhere near as soluble in water as urea is, so instead it is excreted with the faeces. It is the uric acid is what gives birds and reptiles the white colouring to their faeces.",
"There are likely a variety of reasons for this but by far the most significant is that secreting uric acid directly instead of using urine is a great way to conserve water."
] |
[
"Your kidneys can very efficiently get rid of all other water soluble waste from your blood simultaneously as they filter out urine, which is a huge benefit. ",
"And urea is biochemically simple to generate (the urea cycle) greatly streamlining protein breakdown. And urea, as it is water soluble, can be directly dumped in to your blood stream by the liver which makes urea disposal somewhat less complex."
] |
[
"Also uric acid is much less toxic than ammonia or urea, which comes into play as birds spend time in an impermeable shell"
] |
[
"Are smoke and ash composed of the same chemicals?"
] |
[
false
] |
Are the chemicals in ash and smoke the same, and are they present in the same ratio? By "smoke" I'm referring to the particulates, not any gases. If the answer depends on the material being burned, answer for cigarettes.
|
[
"Typically ash contains the unburnt elements, with ",
"wood ash",
" this is mostly potassium, calcium, sulphur and iron sometimes.",
"Smoke on the other hand when it is visible is mainly water vapor, and partially burnt hydrocarbons. In a well controlled fire, it should be nearly clear until the water vapor condenses, and be mostly carbon dioxide.",
"Cigarettes are designed not to burn, so many different unburnt organic compounds are in the smoke, most of which would have completely combusted into CO2 and water had the tobacco been burnt in a fire. The main element of ",
"smoke",
" is unburnt carbon, ",
"Cigarette ash",
" is still mostly Potassium and Calcium like wood ash."
] |
[
"Interesting. What happens to nitrogen when proteins burn? Is it released as N2? In my ignorance I always thought ashes were nitrogen compounds.",
"edit: reworded to avoid ambiguity"
] |
[
"Depending on the flame temperature you can get various NOx released, even when burning pure methane. I'd assume that at a high enough flame temperature to breakdown the proteins would leave the nitrogen free to form nitric oxides in the same way.",
"NOx on Wikipedia",
"Although the complete mechanism is not fully understood, there are two primary paths of formation. The first involves the oxidation of volatile nitrogen species during the initial stages of combustion. During the release and prior to the oxidation of the volatiles, nitrogen reacts to form several intermediaries which are then oxidized into NO"
] |
[
"Can we transfer information through UV, Xray, and Gamma waves?"
] |
[
false
] |
In class, we are currently learning about the physics of energy - Our definition for a wave is 'an oscillation/vibration that transfers energy/information through the medium in which it travels.' so is it possible to transfer information through UV, Xray, and Gamma waves?
|
[
"You could, but those frequencies are not as good as radio for data transmission as they are readily absorbed by solids or air. Also, they all give you cancer.",
"They're good for imaging though. Near-UV photography is a thing, in fact a very interesting thing. X-rays are obvious. Also, there's UV astronomy, X-ray astronomy, gamma astronomy."
] |
[
"Higher frequencies give you faster maximum bitrates. The faster you can vary the signal the more bits you can send. ",
"So why aren't we using gamma ray routers? For one, we don't need to. You can send ",
"stupid amounts of data",
" through fiber optic cable without bottlenecking on bitrate. Visible light has a frequency of 430-770 terahertz and the maximum bitrate for a single-stranded cable is about twice the frequency. The bottlenecks are in routing."
] |
[
"Oh yeah! I forgot about optic fiber! I was concentrated on wireless."
] |
[
"Is space infinite because it's round/a sphere?"
] |
[
false
] | null |
[
"Well, yes, you've definitely got some misconceptions there. Our ",
"Milky Way galaxy",
" is most definitely NOT infinite. It is a bit over 100,000 light years across and has hundreds of billions of stars. These are large numbers, maybe incomprehensibly huge... But if you can put a number to it, then it might as well be zero when comparing it to infinity.",
"A solar system is a collection of planets around a star, a galaxy is a huge collection of stars, and the observable universe is the sum total of all stars, galaxies, and planets that we could theoretically see.",
"Consider that in a tiny speck of the sky, ",
"we can see literally thousands of galaxies",
". Surely there are many we can't see for whatever reason.",
"What is hypothesized to be infinite is the ",
". Because of expansion and the finite speed of light, the parts of the universe that we can see are limited. What is beyond that is still a mystery -- but scientists have figured out clever ways to make guesses. I recommend that you research on curvature of the universe. That might tell you what you want to know.",
"The most important thing to take away from this is that a galaxy is a spinning disk of stars and gas and dust. The universe is the sum total of space, energy, and time."
] |
[
"Because of expansion and the finite speed of light, the parts of the universe that we can see are limited",
"Could you elaborate on this? How exactly is lights speed finite? I don't understand how it relates to how far we can see in the universe. "
] |
[
"It is a fundamental truth about the universe that anything which lacks mass will travel at 299,792,458 meters per second. This has been confirmed by both experiment and through ",
"derivations",
" starting from Maxwell's equations.",
"If you have a light that you can turn on with a remote control, it may seem like the light turns on at the same time you press the button. But really it takes time. Imagine the light is 5m away. Your infrared signal has to go to the light, the light will turn on, and the light has to reach your eyes. There and back is 10m, so the time required after you push the button will be 10m/(299,792,458m/s) = 33.4 nanoseconds. But what if the light you are seeing is coming from a star 10 Billion lightyears away? The light you are seeing was emitted from the star 10Billion years ago, so you are literally looking back in time. When you looked at the lightbulb, you were looking merely nanoseconds into the past. When you look at the sun (don't it's bad for your eyes) you're looking 8minutes into the past, and when you look up into a starry sky, you are looking eons into the past. If you look at something far enough away, you are actually looking at the first light that was emitted after the birth of the universe. This is called the cosmic background radiation. But for some reason, light from things very far away tends to be faint and reddish. Why?",
"The universe is expanding. Gravity holds things together locally, but the distances between galaxies and superclusters of galaxies are too great for gravity to counteract the expansion of space. This was first ",
"observed by Edwin Hubble",
". All space is expanding equally and the speed at which it is expanding is actually ",
"increasing",
". Over very large distances, this expansion can stretch light. When light gets stretched, it gets fainter and redder because its wavelength is getting stretched longer. If there is enough distance between two objects, the expansion can actually cause things to move away from each other at speeds greater than that of light. This does not contradict the cosmological speed limit because the objects themselves aren't moving -- the space in between them is expanding. But if they are expanding away from each other at greater than the speed of light, then light from one object can never reach the other object, so they will never be able to see each other."
] |
[
"Is Recycling spent nuclear fuel the ultimate solution for the US?"
] |
[
false
] |
This link explores some of the issues. What are the risks?
|
[
"This comment is not entirely accurate. All isotopes of both uranium and plutonium are fissionable, that is, they are capable of undergoing fission following a neutron absorption. Not all fissionable isotopes are fissile however.",
"A fissile isotope is capable of supporting a chain reaction. Not all isotopes of uranium are fissile, but not all isotopes of plutonium are fissile either.",
"Plutonium must have a very specific isotopic purity to be used for making nuclear weapons. One could not simply separate out the plutonium from the other actinides and make a bomb from it. The presence of Pu-240, which has a high rate of spontaneous fission, will make the material unsuitable for weapons as it will tend to fizzle (predetonate).",
"However, walkingagh is correct in saying that the proliferation risk is the main thing holding back spent nuclear fuel recycling and fast reactors. Most technologies being pursued today involve processes that don't require the separation of plutonium from other actinides."
] |
[
"Liquid Fluoride Thorium Reactors can \"burn-up\" both Uranium and Plutonium into \"safe\" nuclear remnants. They are the best answer to fix our nuclear crap-pile and also the energy needs of the future."
] |
[
"This makes me so happy to hear that at least someone in the US is considering Molten Salts again.",
"Please tell me they are intending to use Thorium as a potential fuel source?"
] |
[
"Why does air feel cooler when it blows past you, like from a fan? The air is the same temperature."
] |
[
false
] |
Thought of this last night, as I sat near a fan. Thanks in advance.
|
[
"Because it increases the rate of heat transfer. If the air is cooler than your body temperature, increasing the air flow will cool you down faster. If the air is hotter than your body temperature, increasing the air flow will heat you up faster. To gain an intuition, think of the extreme case of absolutely still air. Then the air would form an insulating pocket around your body and there would be little heat exchange."
] |
[
"Exactly. Body temp is around 36°C, room temp is like 22°C. So the layer of air around you will gradually connect these two temperatures. If you blow it away, you get contact with 22°C air and you feel colder. Also hair helps keeping warmer air close to your body."
] |
[
"Your skin does not really feel temperature. It feels heat gain or heat loss. When the air is cold you lose more heat, and you think \"it is cold\". When the air is really hot, or sunlight is strong, or you touch something very high temperature, you gain heat and think \"it is hot\".",
"Your skin is usually about 34C. If the the air is less than 34C, then a wind will increase heat loss. If you are slightly sweaty, there is extra heat loss. Heat loss of skin from wind is proportional to the wind speed,to about the 0.7 power. Heat loss --> v",
"If the air is higher than 34C, then you will gain a little heat from the air, but still be losing heat from sweat. At a fairly high temperature, the heat gain and the sweat heat loss balance, but this is rare except in really hot and humid conditions, or if you are wearing heavy clothes. At super high temperatures, your sweat is not even enough, and hot wind will make you hotter. This is super rare. A sauna could maybe do this, but there is usually no wind or fan in a sauna."
] |
[
"How does the flu actually kill people?"
] |
[
false
] | null |
[
"They are often at risk populations like the elderly, children, or immune-compromised. What typically kills them isn't \"flu\" exactly but that it causes potentially fatal situations such as pneumonia, sepsis, electrolyte imbalances triggering arrythmias or seizures, worsening existing health problems such as COPD, CHF, etc. "
] |
[
"Influenza infections can kill directly, or through various stages of indirect effects.",
"Influenza infection can cause pneumonia (damage to the lungs) directly. Most normal human influenza virus infections mainly infect cells of the upper respiratory system (the trachea and upward), but sometimes the virus will move down further and infect the cells that line the lung airways and alveoli (the pockets where oxygen is actually exchanged):",
"The alveolar epithelial cell lining is as much a target of influenza infection as the epithelial covering of the bronchi and bronchioles. Three characteristic alveolar changes are seen in early influenza virus pneumonia: capillary thrombosis, focal necrosis of the alveolar wall, and development of hyaline membranes.... Alveolar lining cells also undergo necrotic changes and desquamation. ",
"--",
"The Pathology of Influenza Virus Infections",
"Severe strains of influenza, like avian influenza strains that have jumped into humans, are much more lethal (30-70% mortality rates). These not only cause massive damage to the lungs, but also spread throughout the body and can infect the brain and other organs. ",
"It's believed that at least in some cases of \"normal\" influenza infections, and many cases of avian influenza, a lot of the damage to the lungs is caused by a massive, unregulated inflammation responding to the virus, as opposed to just viral replication directly. ",
"The term \"cytokine storm” to describe an immune response to influenza infection was first used in late 2003 in reference to influenza-associated encephalopathy [3] [4]. Thus far, the influenza-induced cytokine storm has been linked to uncontrolled proinflammatory responses, which induce significant immunopathology and severe disease outcomes",
"--",
"New fronts emerge in the influenza cytokine storm",
"Secondary bacteria pneumonia is probably the most common pathway leading from influenza infection to death. For reasons that aren't really well understood, influenza infection makes people much more susceptible to bacteria infections. That means that after even a fairly mild influenza infection, bacteria that are normally fairly innocuous can cause pneumonia, which of course can be fatal:",
"The most famous reports of bacterial colonization after lung viral infection stem from the 1918 influenza pandemic where between 20 and 60 million deaths were due to bacterial co-infection (110). It is estimated that ~25% of all influenza-related deaths are associated with co-infections, particularly during seasonal outbreaks (111, 112). Viral respiratory infections elevate nasopharyngeal bacterial density (113, 114), which may promote their colonization in the lower airways, though the precise mechanisms are unclear.",
"--",
"Innate Immune Cell Suppression and the Link With Secondary Lung Bacterial Pneumonia",
"One other factor that's probably important but that really isn't understood well is that influenza infections are correlated with other problems, especially heart attacks. This has been known for a long time; here's a paper from 1892:",
"One of the chief characteristics of an influenza epidemic is the effect it produces on the mortality from other diseases. The disorders most conspicuously affected are, as is well known, those of the respiratory system; but others are influenced in an almost equally marked degree. The annexed table gives details of the relation between the mortality due to various causes of death and that attributed primarily to influenza during the course of the 1892 epidemic. ... Besides the rise in the mortality from the respiratory diseases, the augmented fatality of phthisis, diseases of the circulatory system, and whooping-cough is noticeable, as is also the increase in the number of deaths attributed simply to “old age.”",
"--On the Influenza Epidemic of 1892 in London :: BMJ 2:353-356 (1892)",
"We still see this correlation today:",
"A spectrum of cardiovascular complications has been reported in association with influenza infection. ... Cardiovascular mortality is also increased during influenza epidemics in patients with pre-existing coronary artery disease. Rates of myocardial infarction have been shown to increase following influenza outbreaks, whilst decreases in cardiovascular mortality have been demonstrated following influenza vaccination in high risk patients.",
"--",
"The cardiovascular manifestations of influenza: A systematic review",
" ",
"Side note, when people measure the effectiveness of influenza vaccination (which is often relatively low -- 50% efficacy is common; of course this is a major benefit at the population level for such a common infection) -- most of these secondary effects are not measured. In particular, it's increasingly clear that influenza vaccination reduces heart attacks, but that's not considered when most epidemiologists calculate the benefits of vaccination. It turns out that influenza vaccination is just about as effective in preventing heart attacks as most of the other interventions that doctors recommend:",
"Influenza is one of the leading infectious causes of morbidity and mortality globally, and evidence is accumulating that it can precipitate acute myocardial infarction (AMI). ... There is a large body of observational and clinical trial evidence that shows that influenza vaccine protects against AMI. Estimates of the efficacy of influenza vaccine in preventing AMI range from 15% to 45%. This is a similar range of efficacy compared with the accepted routine coronary prevention measures such as smoking cessation (32-43%), statins (19-30%) and antihypertensive therapy (17-25%). Influenza vaccine should be considered as an integral part of CVD management and prevention....The incorporation of vaccination into routine CVD prevention in patient care requires a clinical practice paradigm change.",
"--",
"Influenza vaccine as a coronary intervention for prevention of myocardial infarction"
] |
[
"One of the common causes of death is not the flu itself, but a secondary bacterial infection causing pneumonia. The influenza virus will cause damage in the respiratory tract, setting up a good environment for bacteria to grow. ",
"However, the flu can kill people all on its own. You can get rapid and severe pulmonary edema (fluid leaking into your lungs keeping you from getting enough oxygen) and you can get sepsis (severe body-wide inflammatory response). "
] |
[
"How and why are complex numbers used when calculating things like impedance and power in an AC circuit?"
] |
[
false
] |
To expand slightly: Why is a complex number needed to represent impedance, admittance, etc.? What kind of influence does the imaginary part of Z=R+jX or Y=G+jB have in practice? How do complex numbers describe the real, actual values, can they be measured? Why does the impedance of inductors and capacitors have only the imaginary part? I know a little bit about all this, but I just can't get the reasoning behind it. How did the concept of using complex numbers in AC circuits come about even?
|
[
"Short(ish) answer, you can generalise the Ohm law (V = R * I) by replacing the resistance R with the complex impedance Z, writing V = Z * I.",
"In the case of AC signals, both the voltage V and the current I can be represented by sinusoidal functions that have the same frequencies but different amplitudes and phases.",
"If Z is purely real (Z = R) two sine functions describing voltage and current have the amplitudes Vmax and Imax such that Vmax = R * Imax (Ohm’s law). The phase shift between the two sine functions of V and I is zero, meaning the peak of the voltage occurs at the same time as the peak of the current.",
"If the impedance Z is purely complex, Z = jX, the reactance will induce a phase shift of π/2 (in the complex plane, j corresponds to π/2) between the voltage and the current (see ",
"https://en.wikipedia.org/wiki/Electrical_impedance#/media/File:VI_phase.png",
")",
"In general case, we can describe an electrical component by its complex impedance Z = R + jX. That will lead to an arbitrary phase shift (an angle between 0 and 2π) between V and I. Remember, you can write a complex number Z = R + jX under its exponential form, Z = rho*exp(j*theta), where theta is the angle that represents the phase shift (lag or lead) of the voltage sinusoidal function with respect to the current sinusoidal function.",
"As for your question about the use of complex numbers, the simple(istic) answer is that rather than writing two equations (one for amplitudes, another for phase shifts) we can combine them into a single equation using the concept of complex impedance. Once we are in the formalism of complex numbers, the oscillating quantities can be represented with exponential functions (Euler’s formula). The benefit is that the algebra happens to be much simpler with exponential functions than with trigonometric ones.",
"There is also a concept of phasors in electronics for which the use of complex numbers makes a perfect sense, but that is a tad more complicated subject to explain in a single post, see for example ",
"https://www.electronics-tutorials.ws/accircuits/phasors.html",
"In the case of capacitors and inductors, which are purely reactive components (only imaginary part), the sinusoidal voltage across those components is in quadrature (a π/2 phase difference) with the sinusoidal current through the component. What that means in practice is that such purely reactive component will alternately absorb energy from the circuit and then return that same energy to the circuit without ever dissipating it (contrary to what happens in resistive components like resistor R). If capacitors and inductors had a real part in their impedance, they would dissipate some energy; but this is not how they behave in reality, thus the real part of their complex impedance is strictly zero."
] |
[
"The apparent power S is the combination of the true power P and the reactive power Q. When powering a load whose impedance is Z = R + jX, only the resistive part will participate in power dissipation, the reactive part will reflect a fraction of the power back to the source.",
"Take the example of a device (load) that requires 100 W of power to function and has the impedance Z such that 80% of power is dissipated through R (true power P), and 20% of power is reflected back to the source (reactive power Q). You will need to ensure that your power supply can provide 125 W of apparent power S. That will allow 125 W * 80% = 100 W of useful true power to be dissipated in your device, while 125 W * 20% = 25 W of reactive power will be bounced back toward the power supply (and eventually lost through the cables that connect the power supply to the load after multiple bounces).",
"If on the other hand, your device had a purely resistive impedance Z = R (best case scenario), all the power would be dissipated (no reactive power) and a 100 W rated power supply would be sufficient for your application.",
"For more details see ",
"https://www.allaboutcircuits.com/textbook/alternating-current/chpt-11/true-reactive-and-apparent-power/"
] |
[
"Thank you for answering a bit more in-depth to my questions!",
"To follow up with a short question in regards to power; if the real power P is the amount of electric energy dissipated as heat and the reactive power Q is the amount that returns to the source, what does apparent power S represent?"
] |
[
"What are some interesting topics for infectious diseases?"
] |
[
false
] | null |
[
"My best friend is doing his Masters of Infectious Diseases currently. I can ask him when I get to the computer. ",
"I do know that he has done his thesis on a few strains of a local disease. I dont know what it was called, as I only proofread his thesis and don't fully understand all of the terminology. It's not my field :)"
] |
[
"Histoplasmosis",
"The life cycle is the cool part.",
"Just a taste: Just about any mammal that has lived in the US Mississippi River Valley area for an extended period of time (months to years) has inhaled the spores of this fungus, and have a deposit currently sitting somewhere in their lungs. If that spore ever reaches a certain lower threshold temperature (IIRC, it's ~25C) it will start to grow. ",
"It's basically a head start decomposer. It's waiting for your body to cool as an indication that you are dead, and then it will eat your corpse from the inside out.",
"Most clinical cases are in immunosuppressed people, but there are other cases as well. It manifests as anything from a flu-like disease to a disseminated fungal infection."
] |
[
"Four words: ",
"mathematical modeling of zombies",
". ",
"Warning: link is a PDF (some folks seem to get bugged about that)."
] |
[
"Does geology play a part in showing the average temperature of the Earth in a certain time period, like the chemical makeup of the rocks? Or is there more to it in determining geologically what the climate was like in the past?"
] |
[
false
] |
Had someone mention in another thread that we have historical data on temperatures obtained by geology studies that shows the climate currently doesn't match with the general trend we'd expect to be naturally occurring, so I'm curious as to if there's something geologically that shows the Earth's average climate in comparison to now, and how that shows it's much warmer now than it should be by natural progression.
|
[
"The rocks generally just offer insights to the climate of the time. Showing us if it was deep sea, continental shelf, delta, beach, grassland, moorland, mountainous, jungle, forest etc",
"Fossil evidence can show the cycles of population booms and falls over millions of years, pointing to ecological instability through many factors such as climate.",
"Now, Ice... Ice can offer much more, over a much smaller time period ",
"Ice traps air, and we can find the chemical composition of that air to determine the global temperature. Through this method we've been able to track Carbon concentrations over thousands of years."
] |
[
"There's a few ways of determining temperature in the geologic past. ",
"The most common is something called δ18O, which involved looking at the ratio of light to heavy isotopes of oxygen in carbonate. The broad description of how it works is that in warmer climates the ocean contains less light isotopes of oxygen as that evaporates more easily, so there's a larger amount of heavy oxygen in the carbonates that form. The downside of this is that heavy isotopes are also more likely to fall out of vapour and get trapped in ice so δ18O is also affected by global ice volume.",
"To correct for this, you can look at other measures. A well established one is the ratio of Magnesium to Calcium in the same carbonates. Basically, Magnesium can substitute for Calcium in CaCO3 and it's easier for this to happen in warmer temperatures, so you can look at the Mg/Ca and δ18O in the same carbonates and remove the temperature effect from the δ18O to work out ice volume.",
"The temperature effect of these is estimated using modern day samples to calculate the size of the effect. It means that absolute temperatures should generally be taken with a pinch of salt as ballpark-correct, but the size of changes can be trusted reasonably well.",
"There's some new proxies out there now like \"clumped isotopes\" that I'm now too far removed academia to understand. Suffice it to say all of this is subjected to the normal rigours of peer-review. There's also proxies for carbon dioxide levels and other metrics.",
"One thing to be aware of is that ice-sheet records and sediment records are different. Everything I have talked about is appropriate to sediment records. Ice sheet records are great because you can basically just sample air bubbles trapped in ice from the time and measure everything except temperature pretty directly. They only go back to 400,000 years ago. Sediment records you have to rely almost exclusively on geochemical signals. They go back to about 70 million years ago continuously; occasionally you have to do a bit of \"signal matching\" to see where two records overlap to make one longer record.",
"There's a few legends out there who are able to look at geochemical signals fossils from 300 million years ago, but the chances of putting them into any continuous timeline are slim to nill."
] |
[
"Just wanna say: you can also say a lot about the temperature from oxygen isotope ratios, but a reply to a comment isn't the place to explain differential sequestration of heavy isotopes which correlates strongly with temperature and other useful climate data.",
"Basically, the oxygen bound by some processes doesn't take an even slice of the natural mix of oxygen isotopes, ",
" other processes record the atmospheric concentrations of the light and heavy oxygen, so you usually have data to calibrate your models...",
"But, not my area, I just listened to a lot of talks by colleagues doing work in this subdiscipline. I may have some basics wrong, but that's the gist."
] |
[
"At what point do we call a data set Qualitative?"
] |
[
false
] | null |
[
"Your example of color is spot on, but it fails to demonstrate why qualitative data might be preferable to quantitative for certain research questions. ",
"What most of what people call \"qualitative\" differences are really differences that come about because of vast complexity. Groups of people form based on differences in so many ",
" variables that it becomes impossible to model. Instead of trying to solve the ",
"computationally intractable",
" problem of identifying and measuring all of these variables, it becomes more productive to just refer to them as entirely unique groups. ",
"EDIT: Couple things to add:",
"A lot of the time researchers will discover what some of the important quantitative variables are between groups by interviewing members and just listening to their responses. Early sex research was done this way and I wouldn't be surprised if most quantitative variables were first defined based on intuitions that researchers had through these kind of interviews."
] |
[
"A good example of a truly qualitative data set is one that uses focus groups or semi-structured interviews with participants. These are sometimes used in the social sciences. They are typically used to explore an issue beginning from a participants point of view. So instead of the researcher making assumptions about why a phenom might happen, listing those reasons, and asking the participant which of those reasons applies to him/her, the participant just tells the researcher and the researcher pulls apart what participants say later.",
"For example, in ",
"this",
" article, they interview 40 homeless youth with a series of open-ended questions pertaining to maltreatment, parental substance use, criminal activity, and prior living situations. They record the interviews, transcribe them, and code for instances of abuse, living transitions, and groupings by theme. Then they just report what they find using excerpts from interviews as examples. It's not meant to be really rigorous science in the way that large-scale, quantitative studies are, but it's meant to figure out what's happening straight from the source, without imposing any preconceived notions on that source.",
"In essence, yes, the qual data in this case is turned into numbers (e.g., every time a participant describes emotional abuse, it is coded numerically), but the numeric codes still represent qual data, so it is all still considered qualitative. "
] |
[
"Color is actually less quantitative than you may think due to the way your eye works. Consider: you can achieve \"yellow\" either by using something like 440 nm sodium light, or by mixing green and red in appropriate quantities. ",
"Which one is \"true\" yellow? Your eye cannot necessarily distinguish it because you only have cones for red and green, but no specific receptor for yellow. Sure, we have spectrometers that can do this, but color is actually a subjective qualitative measure, not a faithful representation of the spectrum. What actually goes on in your brain to create the colors in the world is still a bit of a mystery and it's in no way guaranteed that what you call \"red\" and what I call \"red\" are the same thing.",
"This can be most-easily understood for people who have some sort of visual impairment, for example inability to distinguish red and green. They obviously must have a different perception of color. Did you ever try to describe to someone what \"red\" looks like who can't see it?"
] |
[
"What exactly does \"relative to C-12\" mean? A question regarding atomic weight."
] |
[
false
] |
So I'm trying to understand the definition of atomic weight (? a bit confused with the names as well). Here's what I understand so far: - masses of atoms are cumbersome to express in kilograms, so scientists came up with a more simplified way of expressing them: - by using the stable and abundant C-12 isotope, containing 12 nucleons, they defined the atomic mass unit as 1/12 of the atomic mass. Since the mass of the electrons is negligible, this essentially gives us an approximate mass of one nucleon (a proton or a neutron) - by using C-12 as a baseline we can now define other isotopes' atom masses relative to C-12. The thing I'm trying to understand is why other isotopes masses aren't integers like C-12. I thought the whole idea was to get integer numbers as an easy way of measuring atoms masses. My google searching found the following, which I'm struggling to understand: - due to isotopes' different binding energies they all have different mass defects. The mass defect is defined as the sum of the components' masses minus the experimentally measured mass. I sort of get this, but: - because the masses are relative to C-12 they will not be integers. ^ This is the thing I'm struggling with. Relative how? So the C-12 experimentally measured mass / 12 equals 1 amu, meaning that the C-12 mass defect is "baked into" this unit. How do we determine the masses of other isotopes then, relative to C12? Do we just experimentally measure the weight of the isotope atoms in kilograms, and then express them in amu? Is this what "relative to C-12" means? Any insights are appreciated!
|
[
"So what's the mass of a CO2 molecule?",
"12 u + 2*16 u = 44 u, easy.",
"12*1.66 yg + 2*16*1.66 yg = let me get my calculator. Sure, 1.66 =~ 5/3, and 44/3 is about 15, so the result will be somewhere around 74, but what's the point of this extra effort for nothing?"
] |
[
"You can just express everything in kilogram, but it's awkward. Atom masses have ratios that are close to integers. If you don't need a high precision it's perfectly fine to treat a nucleus with x nucleons as having a mass of x u.",
"It's not exact because there is the binding energy, and based on the mass/energy relation that energy impacts the mass. We could choose the hydrogen atom as standard - make it 1 u. But hydrogen has an exceptionally small binding energy (0, because there is nothing to bind), so this choice would make many atoms deviate quite notably from their integer values. Carbon-12 has a more typical binding energy so choosing that leads to atom masses being closer to their atomic number.",
"How do we determine the masses of other isotopes then, relative to C12?",
"Put C-12 in your penning trap, then put whatever isotope you want to study there, and compare their masses experimentally. There are no kilograms involved because measuring things in kilograms would come with larger uncertainties - but in principle you could do that, too."
] |
[
"That's still awkward because you have this factor of 1.66 everywhere."
] |
[
"If we think in our own voices, how do we sometimes read things in other people's voices?"
] |
[
false
] | null |
[
"Our neocortices are believed by many neuroscientists to extract statistical regularities of our environment. Speech patterns are a part of this regularity. Our ability to reconstruct patterns, such as those of speech, internally is likely due to a mechanism that allows us to predict what is going to occur around us.",
"It is easy to demonstrate this process. If you cover up an object so that one bit sticks out at one end and another at another end, you still see the object as complete. The \"hidden\" part of the object is predicted through this mechanism to exist even though it is occluded. When you are listening to someone speak (or reading something someone has written) you are predicting what you are going to hear next constantly. You are constructing an internal model of the pattern you are receiving. What you experience is a mix of your internal model and the actual sensory input you are receiving.",
"Imagine that I were to speak some sentences containing the ending \"aw\".",
"The long arm of the aw.\nThe carpenter reached for his aw.\nHe ate them aw.\nThe dog hurt its aw.",
"If you heard them out loud, you would likely insist you heard law, saw, raw, and paw, even though I said \"aw\" each time.",
"Through this process we build extensive repertoires of internal models of patterns. The speech patterns of yourself and others are built through this process, and this is why you can reproduce them internally.",
"If you think this sounds strange, remember what happens when you meet someone speaking in a way very strange to you. Gradually, you become accustomed to their speech pattern. Their speech--the actual sensory input--has not changed in any way. You are the one who has changed. You have constructed an internal model of their speech pattern.",
"It's no wonder, then, that we can mimic other speech patterns internally and \"think\" with these patterns."
] |
[
"wow, very informational. it all makes sense now. thank you!(:"
] |
[
"Wow I watched a video of people with heavy indian accents and at the start I barely understood but then I started easily understanding them, this is why! Thanks"
] |
[
"What is a practical way to form a moderate acidic solution using strong acids?"
] |
[
false
] | null |
[
"Just do successive dilutions. Take 1ml of your concentrated acid into 999ml DI water to make solution X (you should have instruments precise to 0.1ml at least). Repeat the same procedure on solution X to make solution Y. Y is already a million times less concentrated than your stock acid. Titrate your Y against a dilute strong base of known concentration to precisely determine concentration of your dilute sulphuric acid if necessary.",
"If the pH 4 is crucial, you shouldnt be using strong acids anyway. Fluctuations in atmospheric CO2 will cause problems. You should look at acetic acid, citric acid etc."
] |
[
"take 1ml of your very strong acid and put into 999ml (that's manageable I hope) water. now you have 1L of acid 1/1000 original concentration.",
"Then take 1ml from this 1L and put into FRESH 999ml of water. Now you have 1L of acid 1/1000000 original concentration. Hope that helps.",
"You only need 2L of water for this."
] |
[
"I'm not sure how strong your acid is, but you should probably consider diluting the acid with distilled water to a more appropriate molarity. I had a similar problem while acidifying samples for my research dissertation - the lab only had ~37M H2SO4 in stock which would have been impractical to use, i subsequently used distilled water to dilute it to 0.01M.",
"Unless you have to use H2SO4 for methodological reasons, i was always told that hydrochloric acid (HCl) was generally better for reducing pH of solutions - HCl is far weaker than H2SO4 at the same molarity.",
"Edit: Just to add, 1*10",
" litres = 1 microliter which could pretty easily be pipetted using a micropipette, the ones labelled P20 are usually good for 0.5-20 microliters."
] |
[
"Why does the sound of water filling change while the bottle is filling up?"
] |
[
false
] | null |
[
"What you hear is air resonating in the cavity between the top of the water and the top of the bottle. The frequency of this resonance depends inversely on the height of the cavity (you can imagine one wavelength fitting between the water and the top, and that wavelength getting smaller as more water is added). So as it fills up, the frequency increases."
] |
[
"This is a similar question why does a small hand drum sound different from a massive 6ft bass drum: the resonating cavities are different sizes and shapes. ",
"Sound is a pressure wave, and that pressure wave is created by air particles bouncing off the bottle and each other. As those change, so does the resulting sound. "
] |
[
"The best analogy I can think of is a slide trombone. ",
"When the trombonist buzzes his lips in the mouthpiece,it generates sound waves inside the tube of the instrument. This causes the column of air inside the t-bone to resonate at certain wavelengths in the same way a guitar string will vibrate. This is able to suppress certain frequencies in the player's lips while amplifying others. This is due to constructive and destructive interference.",
"These wavelengths are directly related to the overall length of the t-bone. ",
"Kicking out the slide increases the length of the instrument which increases the wavelength of the sounds produced. Note that lower pitched sounds have a longer wavelength. Pulling the slide back in decreases the wavelength and raises the pitch.",
"Filling a bottle with water has the same effect as a trombone slide. The rippling surface of the water generates vibrations. The air column inside the bottle can resonate at certain frequencies, as demonstrated by blowing over the lip. ",
"As the bottle fills It reduces the length of the air column which reduces the wavelength of the resonation producing higher pitched sounds."
] |
[
"Doesn't the burning of fossil fuels actually return elements to the atmosphere that were there originally?"
] |
[
false
] |
I was wondering about this today. Fossil fuels are made of carbon and hydrogen which is locked inside the Earth. This carbon and hydrogen was pulled out of the atmosphere by plants during photosynthesis. I understand that we're doing it at an extremely fast pace, but aren't we really returning these elements to their original state? This leads me to a couple of followup questions: I'm in no way trying to refute the ill effects of using fossil fuels with these questions, I'm just very curious about this and wondering if anyone had any insight.
|
[
"Coal and oil were generally laid down well before the dinosaurs. The Carboniferous period was like 360-300 Million years ago. The earliest dinosaurs show up in the Triassic, around 250-200 Million years ago.",
"Anyways, yes it is true that the carbon in coal and oil was once absorbed from the atmosphere and trapped in plants, that were then buried. But this process itself was an extremely long, gradual one. Then when it is burned, what may have taken thousands or millions of years to store is released in a much shorter time scale of tens or hundreds of years. (no I don't have numbers, this is just the qualitative argument)",
"Finally, plants would absorb co2 but animals create it as well. (ie, they release the carbon stored in plants). For a plant to truly store away carbon out of the atmosphere it must be buried (and even this has some caveats if I recall correctly). ",
"I really don't want to talk about the projected effects of co2 in the atmosphere, that inevitably turns into a shitstorm. But the above is the data about historical natural carbon sequestration."
] |
[
"As I reread this is seems poorly written and with a low quality analogy. Instead try this unprofessional ",
"mspaint",
" drawing."
] |
[
"Valid points, but some caveats we must think of:\n1. Its possible that fossil fuels have attained some sort of equillibrium levels over the eons. This would not be the case if becoming a fossil fuel was a one-way trip. Some geologists here?",
"We do not know (or I do not know) if during the time of Dinosaurs the earth was slightly cooler to begin with (because of distance from sun or something?). Its not entirely unlikely, we're talking about millions of years. If that were the case releasing the same amount of CO2 into the atmosphere might exacerbate green-house effects.",
"It would also be good if someone could find out whether the composition of the atmosphere (in terms of other greenhouse gases AND CO2) supports this data. If it is true that all the carbon thats buried now used to be in the atmosphere then we must be able to find it through some measurements? (Don't know if ice-core drilling can go back to 65million years though).",
"Releasing the same amount of CO2 as jurassic era also assumes everything else was the same. It could haven not been. Even traces of methane can have bigger effects. I don't know if we have clues about how the ozone layer was in those days. So there many more variables I think.",
"Nevertheless, its a very interesting viewpoint indeed."
] |
[
"Why are papercuts so painful?"
] |
[
false
] |
[deleted]
|
[
"Paper cuts are superficial injuries (they don't go very deep into the skin) and thus don't cause much nerve damage. A sharp knife, on the other hand, can cut deep enough to sever or damage the underlying nerves."
] |
[
"TIL being cut with paper hurts more than being cut with a knife."
] |
[
"I always figured paper cuts hurt worse than deeper or more serious injuries because there is less nerve damage with such a shallow cut. Also, there are a whole fucking lot of nerve endings on one's fingertips, which is where most of them happen. A paper cut on the arm, say, would also likely sting, but not as badly as on the fingertip. I wouldn't want a paper cut on my genitals either."
] |
[
"What is it about catnip?"
] |
[
false
] |
[deleted]
|
[
"wiki",
"The nepetalactone in catnip acts as a feline attractant. This chemical enters the feline's nose.[15] Cats detect it through their olfactory epithelium, not through their vomeronasal organ.[16] At the olfactory epithelium, the nepetalactone binds to one or more olfactory receptors. "
] |
[
"Not all cats are affected by catnip.[12] Roughly half to two thirds of cats are affected by the plant.[17][18] The phenomenon is hereditary.[12]",
"That is also from the wiki. From that, I would infer that it is a genetic factor, and some cats carry the genetic information necessary to produce such a receptor, while other species do not."
] |
[
"Interesting! ",
"Would you happen to be able to find why nepetalactone attracts only cats and not humans or even dogs or other animals who have a strong sense of smell?"
] |
[
"When/How did Earth get water?"
] |
[
false
] |
From my understanding of the history of the Earth, it started out as just a big rock covered in lava (magma?) some-billion years ago. And then, a few billion years later, it had some water, which then held life. Now, where the life came from is a question for another time. But, where did the water come from?
|
[
"There are two main possibilities for the origin of water on Earth: an extraplanetary source - comets, meteorites etc, and an internal source - water contained in the structure of minerals in the mantle. The main problem that has to be dealth with by both is of volume, and of reconciling the geochemical signatures of modern water with that of both internal and external sources. ",
"But let's start with age. The oldest rock on Earth are thought to be greater than 4.0 billlion years old. This can be measured reasonably well using Uranium-lead (U-Pb) radiogenic isotope systems (very similar to the techniques used in radiocarbon dating, though the U-Pb system has a much longer half-life and can see events further into the past). Other systems include Samarium-Neodymium (Sm-Nd) which is of particular interest in the formation of the first continents due to Nd being more likely to enter a melt phase when a rock is being melted. Using this system and other extinct isotope systems we can estimate some early, and later episodic formation of the continental crust. ",
"Kemp et al. 2006",
" This is important, because before rock formation, we have no records of what the surface of the Earth was like, but we can infer that it has a composition similar to that of the mantle today. ",
"Once we have a rock record, we can start to preserve some information. Direct evidence of water comes from the formation of Banded Iron Formations ~ 3.8Ga (billion years) which requires both water and biological activity. ",
"Cazja et al., 2012",
". If we push further back to the oldest surviving material, we can only see minerals such as zircon. These are exceptionally resistent to metamorphism and alteration, and therefore are the oldest surviving original components of the original continental crust. The remaining rocks have been either eroded, deposited as sediments, subducted into the mantle or metamorphosed to high grades (such as the granulites at the centre of old 'cratons'). ",
"Nutman, 2006",
" These zircons are up to 4.4 billion years old (U-Pb dating) and record temperature through their Oxygen-18/Total oxygen isotopic ratio (d18O). These suggest that the planet was cool enough to support liquid water on the surface at ~4.4Ga (billion years before present). ",
"Valley et al. 2014",
" In addition, they suggest that minerals such as clays and carbonates (which preferentially uptake O-18) were present in the early Earth, inferred from the d18O ratio. If clays and carbonates existed on the early Earth, only ~120 million years after formation, then so should liquid water. ",
"When it comes to origin, there are several schools of thought. Water can be stored in the structure of minerals common in the mantle, such as ringwoodite. The water isn't in liquid form but trapped within the physical structure of the minerals (common examples today include hydrated copper sulfate, blue crystals commonly used in school science experiments). Both ringwoodite and garnet can hold significant quantities of water, and it's possible that the lower mantle, thought to be at least partially isolated from the upper mantle from which the continents formed, may still contain significant ",
"quantities of water",
" . It is possible this water was emitted from the mantle during melting events that generated the continental crust. ",
"The other proposed source of ocean water is from water-rich meteroites that bombarded the Earth and inner solar system early after its formation, but after initial crust formation. The scars of this are seen in crater on the moon and other inner rock planets. These chondrites contain water with a similar isotopic ratio (Deuterium/Hydrogen) to that of water on Earth, however other sources thought originally to have delivered water, such as comets, are now thought less likely, as their D/H ratios are much greater than that of Earth oceanwater. ",
"Altwegg et al., 2015",
" ",
"The water stored in the mantle has been estimated to be isotopically lighter (low D/H ratio) than that of ocean water on Earth, from glass inclusion in old basalts (primitive melts), but that may not rule out a contribution from mantle waters, as lighter water is also lost ",
"preferentially to space over time",
". The origin of this water may be due to incorporation of water-rich chondrites into the early Earth, before crustal formation, due to similar isotopic composition of these bodies to that of ",
"Earth's water today",
"In short, we're not totally sure, however it is possible that a mix of both orbital bombardment and mantle devolitisation processes during early melting produced oceans we know today. It's also possible there was some contribution to the oceans from biological activity during the Great Oxygenation Event ",
"Holland et al., 2006"
] |
[
"Earths hydrosphere, along with it's atmosphere, came from gasses being released by the lava left over after volcanic eruptions. When earth was forming into the massive sphere that it is, it trapped many different elements inside itself. Star dust coalesced into an object with enough mass to develop a strong attractive gravitational pull, and it grew larger to the point that it became a big target for all sorts of space projectiles containing even more elements. At this time the earth was less solid. Anything that hit it got absorbed. After billions of years the earth solidified with a ton of elements which are responsible for almost everything we see on earth today, including water. "
] |
[
"Actually, the Earth is 4.5 billion years old, and scientists suspect that there was a solid crust (because we have evidence of liquid water) when the Earth was only 120-200 million years old."
] |
[
"Why is there dangerous radioactive waste left over from nuclear reactors?"
] |
[
false
] |
If the waste that comes out of a nuclear plant is still dangerously radioactive, why can't we keep using it to provide energy until it's no longer significantly radioactive?
|
[
"It no longer becomes energy profitable to keep \"burning\" those very radioactive nuclei in a power plant.",
"Lets go to basics of nuclear fission: Neutrons are the currency of a nuclear reactor. They cause fission reactions, which in turn make more nuclear reactions. There are certain nuclei that are have large \"targets\" or cross sections for neutron based reactions in a reactor. The bigger the cross section the more likely the nucleus is to fission when it sees a neutron. We choose uranium 235 to run our nuclear reactors due to its large cross section and natural abundance (.07% of all uranium on earth is this isotope). ",
"The next part of fission that you need to understand is that energy is let off which is just determined as (with a few assumptions)",
"E=Mass of first nucleus+Mass of Neutron-(Mass of Fission Products).",
"These are all linked due to E=MC",
"Let's put the basics together now. The waste from the nuclear power plants is just a mixture of Uranium 238, unspent Uranium 235, and fission products. First, if you look up the fission product cross sections and the uranium 238 cross sections, you will find its very small---meaning a low chance of a neutron reaction. Secondly, you'll find that burning up the fission products through neutron reactions releases less and less energy, remember capital E, due to the ",
"Binding Energy Curve",
". As you get to the top of the curve, which all fission/fusion based reactions move towards, you release less energy per event.",
"Lastly, there is a size factor. Nuclear reactors have several TONS of material in them and a same scale level of waste (let's not get into a CO2-Rad Waste talk here). To completely deplete that using basically modern-day alchemy would be very difficult......not to say it cant be done.",
"TLDR: Economics."
] |
[
"I don't think any of your points answer his/her question.",
"Also:",
"Radioactive decay heat accounts for 5% of a nuclear reactors power at steady state....so it makes a huge impact!"
] |
[
"\"The mass of a nucleus is mostly made up of the binding energy of the neutrons and protons in the nuclei.\"",
"No its not, the rest of the explanation is great but this statement is false. The mass of the nucleus is mostly made of gluon-quark interactions in the protons and neutrons.",
"The binding energy is essentially an energy deficit, the energy given out in creating the nuclei or also the energy needed to split it into its parts. The higher the binding energy is the more tightly the nuclei is bound as it needs more energy put in to split it.",
"You gain energy from fission/fusion because you move to nuclei with higher binding energys(high energy deficits which was given out in the reaction)."
] |
[
"Is blood doping with white blood cells possible to create a super Immune system?"
] |
[
false
] |
As I understand Lance Armstrong style blood doping extracts red blood cells then puts them back in to increase the amount of oxygen available during an event. So could we take out white blood cell at intervals while healthy and store in a bank and then when we get sick put them back in?
|
[
"It would be quite pointless if we were using our own white cells. If you ever encountered am given pathogen before your immune system \"remembers\" it and relevant white cells multiply when it's encountered again. When a new antigen is found your immune system just needs to learn it. But a \"doping\" like that is used sometimes ... But with antibodies. For example when someone is infected with rabies a horse serum with anty rabies antibodies is used. You can't count on immune system in this case, this disease is usually developing too severe symptoms before your immune system can fight it well, so you need to get antibodies from somewhere else. "
] |
[
"So it wouldn't help speed recovery or possibly your immune system adapting to a new pathogen to have an rapid increase in white blood cells that your body didn't have to produce?"
] |
[
"Using antibodies is cheaper and carries less risk of strong immune response than using white cells. Remember, our immune system reacts to most things that are not marked as part of our body and is not used to, including cells from other people/animals. Whole white cells would probably trigger an inflammation or something worse,resulting in more harm than good. And as I said, using our own white cells would be pointless. Also I might have used wrong words concerning body producing relevant cells - it's not our body producing new cells, it's our own white cells that remembered the antibody (or just learned about it). They divide and because their number doubles with every division adding a few more cells won't speed up the process that much. "
] |
[
"What happens to a metal baseball bat when \"it dies\"."
] |
[
false
] |
In most non-pro leagues expensive, metal baseball bats are used that typically last for 1-2 years (less if used by a whole team) before they are considered "dead." This means the bat no longer seems to have the pop as the ball comes off the barrel and typically results in the baseball flying slower and shorter and becoming easier to play. So what changes inside the baseball bat from when it is brand new to when it is considered "dead"?
|
[
"High-cycle metal fatigue. Collisions between a new bat and the ball are mostly elastic and lose little energy, transferring most of the kinetic energy of the bat into the ball. Over repeated collisions, the metal fatigues and the collisions become increasingly plastic, losing more and more of the kinetic energy into plastic deformation of the bat. Most aluminum alloys lack a fatigue limit and will eventually fracture even under weak repeated stress."
] |
[
"While this makes sense its a little disappointing as answer as I still feel like I don't know any more than I could reason going into the question, so I looked a little harder at what I could find out about this.",
"What does High-cycle metal fatigue mean is happening beyond just wearing down after many at bats? ",
"Wikipedia/Fatigue (material)",
" is somewhat useful here as it tells us what factors apply, that it doesn't reduce over time and that at a high enough threshold microscopic cracks begin to form (not sure if the last one applies or not).",
"A couple of websites also showed that an aluminum baseball bat is ",
"actually hollow",
" which actually surprised me although I'm not sure it should have in hindsight.",
"And then ",
"this website",
" from a Penn State professor goes into a lot more detail about the physics of a baseball bat. The ",
"sweet spot section",
" seems particularly useful but so far I've only skimmed/looked at the diagrams. It essentially says that hitting a baseball in the sweet spot of a bat ",
" is hard to define as there are many definitions of sweet spot. ",
"So is it reasonable to assume that these microfractures are causing more vibration and absorption of energy throughout the bat reducing the force pushed on the ball? Also would these microfractures change the way the sweet spot works, eliminating it all together, or would that part still cause the least vibrations on a dead bat? Or does fatigue not even impart microfractures on a baseball bat as it doesn't exceed a certain threshold and my understanding of how fatigue works is wrong?",
"edit: (I based my striked out part about the sweet spot on a diagram I had looked at which ends up also being part of the definition he uses however there are many definitions of sweet spot. It is also the definition that causes minimal vibration on the hands which is a common feeling of hitting the sweet spot)."
] |
[
"Okay, so High Cycle fatigue works as such: metals are made up of a bunch of tiny crystals. There are so called \"dislocations\" in these crystals, basically places where the metal doesn't line up properly. Once you hit them with a stress such as a baseball bat hitting a ball, you move these dislocations to the edges of the grains, or to the \"grain boundaries\". Once these reach the boundaries, which are places that are already stressed because of the discontinuity of the material (the grains are lined up differently), they begin to coalesce, or form longer chains. Once these chains become large enough, they create high enough stresses that they create cracks. These cracks expand as the bat is fatigued more and eventually you get a crack you can see that really affects the bat's performance. Hope this helps.",
"I am a researcher in static crack analysis and propagation...and am also a bit drunk at the moment. Hopefully this all makes sense."
] |
[
"Bond strength between amphipathic molecules and air in saltwater?"
] |
[
false
] |
This question is related to protein skimmers. How strong is the bond between the amphipathic molecules and the air in a protein skimmer chamber? I understand that some molecules will be more hydrophobic than hydrophilic, but what is the window that they operate in? From instance, how strong is the strongest bond with air versus the weakest? What would be required to break the strongest bond versus the weakest?
|
[
"It's just surface tension, which is ",
" the molecules don't bind to air. A molecule at the surface will have higher energy compared to one in solution, because it's only forming intermolecular bonds on the sides facing the solution. Now, if you put some amphiphilic molecules in the solution, they have a hydrophilic part that bonds to water and a hydrophobic part that doesn't. If you move that molecule to the surface, it can keep the hydrophobic part facing the water and the hydrophobic part facing the air. It's not binding to the air there, but it wasn't binding strongly to anything in the bulk either, meaning it costs relatively less energy to put the amphiphile on the surface than to have it in the bulk solvent. So that's where they end up. "
] |
[
"What bonds? There's no bonding of air molecules to anything there, to any significant extent."
] |
[
"I guess I misunderstood what I researched. If that's the case, then how is the organic compound attached to the air bubble? I was under the impression it was a chemical bond."
] |
[
"How would time dilation affect the decay of elements?"
] |
[
false
] |
[deleted]
|
[
"Then it'll appear to decay at its normal rate to anyone on the ship, and slower to someone on the planet."
] |
[
"People on Earth would see it decaying at a reduced rate. People on the ship would see it decaying at the normal rate.",
"Let's say the ship leaves Earth at 0.8c and flies for 1.25 years before arriving at a deep space station, all as measured by people on Earth. Then the ship is now 1 light-year away, and it's clocks show only 0.75 years to have passed. On this ship is a radioactive material with a (rest-frame) half-life of .25 years. Since 0.75 years have passed on the ship, it has passed three half-lives, so 1/8 of the sample remains. Thus, the half-life as measured on ",
" has increased to 5/12 of a year (so that 1.25 years is three half-lives)",
"Now, what does the ship see? Well, it sees Earth take off at 0.8c and fly away for 0.75 years. It also sees the deep space station approaching at 0.8c. Now, thanks to length contraction, the other major consequence of the special theory of relativity, the space station is only 0.6 light years away. So, after 0.75 years of flying at 0.8c, the deep space station arrives at the ship. The on board radioactive sample has passed three half-lives, and so is down to 1/8 the original amount.",
"Thus, all observers agree on the final state: upon arriving at the space station, the ship is carrying 1/8 the material it had when it left Earth. But whether that works out because time dilation increased the half-life (how Earth sees things) or because length-contraction shortened the distance traveled (how the ship sees things) depends on which observer you ask."
] |
[
"Is the element on the ship or on the planet? The decay rate of an element is given in the frame-of-motion of that atom. So if it's moving very fast relative you, it will have a longer lifetime. (Which is indeed seen all the time with fast-moving cosmic muons and such things)"
] |
[
"Can a bright light outside the visible spectrum hurt your eyes?"
] |
[
false
] |
For that matter, what exactly's happening when a bright light "hurts"?
|
[
"Yes. Absolutely light outside the visible spectrum can be harmful. Both visible and other than visible light can be harmful, but in both cases, it depends on the intensity. The reason outside-visible light (such as UV/IR) can be much more harmful is because you can't see it so you don't blink to shield yourself and it can cause much more harm before you even know it. "
] |
[
"Latching on to the top comment - UV and IR light ARE quite dangerous due to the fact that they don't have the aversion effect (blinking) that visible light does. However, the reason ambient UV and IR have less of an effect (damage wise) on the retina is very much due to the cornea's absorption spectrum. ",
"The cornea's absorption spectrum is dominated by its water content, which has relatively high absorption in the UV and Mid-Far IR ranges (above 1.5 micron wavelength). This means that instead of transmitting to the retina, these wavelengths of light will largely be absorbed and the energy dissipated as heat in the cornea. ",
"High power and concentration of this light, however, can cause excessive heat build up - this is actually how laser ablation in Lasik eye surgery works! Along with specific focusing of the laser, it allows you to 'select' the cornea topology for ablation without light continuing through the optical cavity and damaging the retina. ",
"I have ~3 years of research experience involving light-tissue interaction in the eye and love answering questions about it, let me know if you have others!",
"EDIT: Quick notice - people keep asking about the safety of different types of IR lights. I've done my best to give informed advice, but it's really difficult to be concrete without looking at the specifications of an individual device. Know that these devices are usually designed to be entirely safe in normal operating conditions, but that using them inappropriately they can be harmful! Consult the manufacturer for the best information possible."
] |
[
"Absolutely! Ultraviolet and (near) infrared can both cause pain and eye damage similar to a bright visible light because they will still be focused onto your retinas with enough intensity to cook them.",
"Infrared lasers can be dangerous to work around because the beam is invisible and often quite strong. Wear your goggles. Looking into a blast furnace or a bonfire is also rather uncomfortable due to the infrared and is not really recommended.",
"Ultraviolet can sunburn your retinas and cause clouding of the cornea (cataracts) even when unfocused due to the higher energy level of the individual photons. The most common laboratory threat that emits a lot of ultraviolet is the germicidal lamp; basically, don't look at it while it is on. Normal black lights you see in nightclubs are different (partial phosphor coating vs no phosphor coating) and emit much less ultraviolet."
] |
[
"Where does the electricity go when it's \"grounded\"?"
] |
[
false
] |
[deleted]
|
[
"This is a pretty poor answer. The earth is at a potential of 0V only with respect to itself, as is ",
" any other point you want to choose as \"ground\". ",
"The correct answer to OPs question is that \"the electricity\" returns to the source from which it came. This is always true when current flows. See ",
"https://en.wikipedia.org/wiki/Kirchhoff%27s_circuit_laws",
"Often, a short or leakage path in an electronic device does not actually go to \"the earth\" at all, it simply goes back to the chassis or the ground of the power supply in the device. But if it does go to \"earth\", it only results in current flowing if the earth also connects back to the power supply, not due to any ability of the earth to absorb power.",
"Another simple way to see the error in this explanation is, touch the positive end of a battery to the earth. Note that the battery does not discharge. Now connect both ends of the battery to the earth. Now, the leakage path created by \"the earth\" causes energy to flow from one terminal of the battery ",
". You're not \"pumping electricity\" into the earth."
] |
[
"This is a pretty poor answer. The earth is at a potential of 0V only with respect to itself, as is ",
" any other point you want to choose as \"ground\". ",
"The correct answer to OPs question is that \"the electricity\" returns to the source from which it came. This is always true when current flows. See ",
"https://en.wikipedia.org/wiki/Kirchhoff%27s_circuit_laws",
"Often, a short or leakage path in an electronic device does not actually go to \"the earth\" at all, it simply goes back to the chassis or the ground of the power supply in the device. But if it does go to \"earth\", it only results in current flowing if the earth also connects back to the power supply, not due to any ability of the earth to absorb power.",
"Another simple way to see the error in this explanation is, touch the positive end of a battery to the earth. Note that the battery does not discharge. Now connect both ends of the battery to the earth. Now, the leakage path created by \"the earth\" causes energy to flow from one terminal of the battery ",
". You're not \"pumping electricity\" into the earth."
] |
[
"You just described closing a circuit when you said bring one sphere into contact with another. Static discharges when it finds a path (circuit) to take.",
"Even a capacitor must have a path to ground in order to charge it. If you don't believe me, try charging a capacitor with one lead disconnected."
] |
[
"If the Hubble Space Telescope can view images of galaxies 13 billion ly away, why can't it take photos of extrasolar planets?"
] |
[
true
] |
[deleted]
|
[
"To elaborate on some of the half truths here so far:",
"Luminosity is only somewhat of an issue. Though its true a planet would appear extremely dim as long as it still reflects some light it would be possible to integrate on a signal long enough to produce an image. Now its also entirely possible that the integration times would be unfeasible but that would depend largely on the size of the planet,distance, and albedo. ",
"The primary reason is angular resolution. The Hubbles angular resolution is ~0.05 arc seconds. For scale, the moon is ~30 arcmin, and Mars is ~3arcmin. Thus if hubble was on earth looking at mars the planet would only be about 3600 pixels in width (30*60/0.05). Now imagine some planet that is millions of times further from us its going to be impossible resolve given it will be far less than a pixel with in angular diameter."
] |
[
"Correct. And then distinguishing it from other sources becomes the trick using motion."
] |
[
"Let's estimate it! The limiting factor will be angular resolution. Hubble has an angular resolution of about 0.05 arcseconds. So if something is smaller than 0.05 arcseconds, it can't be resolved, if it is bigger than that, it can be resolved. The angular size of something is (Physical size) / (Distance away).",
"Now let's see how big galaxies are, and how big planets are. Let's say we have a spiral galaxy about 10 billion light years away, and 50 kiloparsecs in diameter. Then it is about 3 arcseconds big. Easy for Hubble to resolve. Now let's say we have a Jupiter-sized planet, 10 light years away. Then it is about 0.0006 arcseconds big. Way too small for Hubble to resolve!",
"Disclaimer: Of course, you can use certain methods to detect planets even if you don't resolve them. But by \"take photos of extrasolar planets\" I assume you're resolving the planet."
] |
[
"Why does biology/evolution favor a 50-50 gender split in humans and other mammals even though from a reproductive perspective the male is not necessary after successful insemination?"
] |
[
false
] | null |
[
"The 50:50 split is favored in most species due to the benefits of producing offspring of different sexes.",
"We'll use an example population of 100 individuals and we need to start at some unbalanced sex ratio. Let's use 70 males and 30 females (you'll see by the end that it doesn't matter what our starting point is). Think of yourself as a parent with children born into this population. Your son is able to mate with 30% of the population and your daughter can mate with 70% of the population. You can easily see that its better to be female in this situation because they can find a mates more quickly (and then have more time/energy for other things). Here's the tricky bit: PARENTS that have more daughters will have their genetic code favored in this situation because female children do better than male children. Those successful children will also be predisposed to have more daughters than the base population. In this way, the sex ratio of the population will begin to favor females. You may see some overcompensation where females begin to outnumber males but the same process will direct the sex ratio back towards 1:1 where neither sex has a mating advantage over the other.",
"source/more details",
"Disclosure: self repost from ",
"this related question"
] |
[
"if those societies have a 50-50 split, a significant portion of males have to fail to reproduce, whereas if they were female they could have",
"Assuming 'ideal' polygamy, where you have 1 man with a group of N women and reproduction only happens within the group (with no 'cheating'), you'd find that the smaller number of males who ",
" reproduce have more children, which makes up for the lower odds of having ",
".",
"From the perspective of a parent \"deciding\" which sex of child to produce, it might look like a choice between a daughter with near-100% odds of 1 grandchild or a son with 1/N odds of N grandchildren.",
"If you modify the scenario so that there exist more females than males, those odds would change - the odds of being a successful many-grandchild-fathering male would go up and the odds of being a failed non-reproducing male would go down and the expected genetic 'reward' for having a son would increase."
] |
[
"Since I've thought about similar to OP, I can understand why a male sex-skew would be discouraged, but not a female one. If a population was 30 males, 70 females, there would be some reward to parents who produced more males, but wouldn't there be the same reward for parents who simply produced more promiscuous males? 30-70 ratio still allows for all females to reproduce, and the higher offspring count of the males seems like it would reward them. I mean, polygamy isn't really a theoretical exercise, humans have done it throughout history. And unless I'm missing something, if those societies have a 50-50 split, a significant portion of males have to fail to reproduce, whereas if they were female they could have."
] |
[
"A few physics around the house questions..."
] |
[
false
] |
A few things have always perplexed me. How come when I put down a gallon of milk, it sometimes seems to "slide" a half an inch or so after it was at rest? How come when put ice in a cup and fill up the cup with a liquid, sometimes the ice stays near bottom, but rises to surface when I pick up and put down the cup? Also, how come when I look in my rear view mirror I can see a reflection of what's behind me on my cars' ceiling? I am perplexed and very curious to know!
|
[
"Gallon of milk: it's likely that the you have jostled the liquid in the container when you set it down. When this mass of liquid then rushes to the other side of the container, it has some momentum. When it hits the side, the milk jug will move slightly, since it was essentially struck by a moving mass.",
"Ice: If you leave the cube at the bottom of the glass for a few minutes, the bottom of the ice might melt, and then refreeze to the bottom of the glass. When you pour in the water, it remelts, and since ice is less dense than water, it floats.",
"Car mirror: your rear view mirror has two different angled mirrors - one for day time, and one for night. I'm not sure if the night time one is just tinted or is polarized, but in any case, this second angle could cause the phenomenon you describe. "
] |
[
"Wow that's interesting about the angled mirrors. Mucho Gracias!"
] |
[
"(muchas gracias)"
] |
[
"Why don't loud sounds travel faster than quiet sounds?"
] |
[
false
] |
It seems to me that if loud sounds 'have'(i can't really think of a better term to use) more energy than quieter sounds, then they should travel faster. Why is it that they don't?
|
[
"Sound propagates in the form of pressure variations in fluid mediums and molecular vibrations in solid mediums. So the speed of sound depends on the properties of the material and the surrounding conditions that it travels on. Louder sounds have got a greater amplitude of vibration ie. the pressure variations are larger and the molecular vibrations have got a greater amplitude (they oscillate farther away from their original position). How these oscillations get transferred from one molecule to the next is dependent on the properties of the material. The energy of sound is 'stored' in the form of its frequency and amplitude and not its speed."
] |
[
"You are probably thinking of sound like a ball, where a higher kinetic energy corresponds to a higher speed. Sound is actually a wave. It is a waving oscillation in the pressure of a material. For all waves, the propagation speed of the wave is determined by the properties of the material or field it is passing through. In rough terms, the more a medium is able to snap back to its equilibrium point after being displaced as part of the wave, the faster the wave will propagate. For all waves, the amount of energy carried is proportional to the amplitude of the wave, which is how strong or far each displacement is in the medium. For sound, a louder sound carries more energy, meaning that the pressure is higher in the peaks of the wave and lower in the troughs of the wave than for the sound wave of a quieter sound."
] |
[
"Just to add a bit more to this... The reason why the speed of sound is constant regardless of its amplitude is very closely connected with the reason why a mass and spring system will oscillate always at the same frequency, regardless of the amplitude of the movement. ",
"If this latter statement doesn't chock you, maybe the first one will become a bit more intuitive. To understand this thoroughly you need to go to the maths I think."
] |
[
"Is carbonated water still acidic after it has gone flat?"
] |
[
false
] |
Additionally I guess I would like to know if there's any difference between still water and water that was once fizzy but is now flat.
|
[
"\"Still\" water is just a term meaning \"non-carbonated\"; it doesn't necessarily refer to distilled water."
] |
[
"'Flat' carbonated water is just water that is no longer supersaturated with carbon dioxide. It would still contain some residual CO2, depending on temperature, and would therefore still be very slightly acidic (ph 6 or so).\nI'm not sure what you mean by still water. If you are talking about distilled water, it would probably have less CO2 than flat carbonated water. This is because the CO2 is driven off when the water is heated to boiling, and it is likely that the water would then have been condensed and bottled without having time to reabsorb much CO2 from the atmosphere. Nonetheless conventional distilled water still has some dissolved gases and for lab work that requires water with ",
" dissolved gases, further degassing is typically needed."
] |
[
"Yes, though not strongly so. When carbon dioxide dissolves in water, some of it becomes carbonic acid. However carbonic acid is not a strong acid so it's not going to be as acidic as say, a soda (to which citric acid has been added for flavor)."
] |
[
"Why is a Neutron star considered a star when it has a very similar make up to a planet?"
] |
[
false
] | null |
[
"How does it possibly have a similar makeup to a planet? ",
"Neutrons stars are remnants (primarily the cores) of particularly massive stars that undergo supernovae. During the star's collapse, the gravitational pressure in the core is sufficiently high to overcome electron degeneracy pressure and cause the core to collapse further into what will become the neutron star. This is the only reason they are considered stars - they are the leftover cores of dead stars. ",
"The fact that neutron stars consist primarily of a dense sea of neutrons and electrons, it has little resemblance to planets. Even in size, neutron stars have radii of ~10 km, which is far too small to be classified as a planet. T"
] |
[
"Neutron stars form because higher mass stars have undergone such decay that they consist only of neutrons. This is unlike a planet ",
" a star.",
"The nomenclature is most likely due to the fact that the Neutron star is the result of a star collapsing. "
] |
[
"Neutron stars are nothing like planets, they are very ",
" stars. I don't know any planets that have the mass of a giant star compressed into something the size of Brooklyn. "
] |
[
"When engineers work with devices emitting electromagnetic radiation, how do they control the frequency of the EM Radiaiton?"
] |
[
false
] |
Specifically microwave radiation... I don't understand how frequencies can be controled and manipulated the way they are.
|
[
"Inductors and capacitors are the two rudimentary \"reactive\" circuit elements in basic circuits. They are essentially resistors whose resistance depends upon frequency. With these elements, you can create a sort of logic in analog circuits.",
"With inductors and capacitors, one can create filters that accept or reject certain frequencies. This is how the frequency in the circuit is regulated. Inductors themselves also will radiate the energy off - they serve as both radio transmitters and receivers. There are other types of antennas and receivers, of course. Antenna theory is a rich subject.",
"This question is very broad and this answer applies in a general way. The subject of reactive circuits using inductors and capacitors is itself a very rich topic. Check out LR, RC, LC, LRC circuits. Perhaps \"VCO's\" or voltage controlled oscillators - but these require some knowledge of transistors. Feel free to ask more specific questions if you have them."
] |
[
"I will try.",
"To control the frequency of E/M radiation, you simply have to control the frequency of the ",
" in a circuit. The circuit will radiate away the same frequency that it has inside it. ",
"There are two pieces you can put in a circuit that respond to frequency. They respond to frequency simply because of what shape they are made into. ",
"One of them is the ",
". It acts as a high frequency killer. It will kill the high frequencies in a circuit. ",
"The other is the ",
". It will kill the low frequencies in a circuit.",
"An engineer can decide how strong to make the inductor or capacitor. He can ask himself \"how much do I want to kill the high frequencies?\" and make an inductor that matches up. He can ask \"how much do I want to allow the high frequencies?\" and make a capacitors that goes along with that. ",
"Again, the key is in the shape of the inductor or capacitor. If it's the right size and shape, it will do what the engineer expects.",
"An engineer can also combine lots inductors and capacitors to make a circuit ",
" - that is, it can allow or reject whatever frequencies the engineer wants. ",
"Once the circuit is done, the engineer can attach an antenna and it will naturally radiate E/M waves away at the same frequencies he designed it at. The radiation part is easy - nature takes care of that (although, antenna theory is an ongoing research topic. How to make the BEST antennas is hard - but it's simple to make an antenna that radiates a bit - just attach a piece of metal, and you're set).",
"The hard part is making the circuit out of inductors and capacitors to select the frequencies you want. These are called ",
". Hope this helps! Edit = touch-ups."
] |
[
"You also need an oscillator--something to produce the frequency in the first place. If you simply connect up some LC circuits to form a filter, generally nothing happens. AltoidNerd already mentioned Voltage-Controlled Oscillators (whose output frequency is tuneable with a voltage, generally across a fixed range specified when you design the oscillator), but there are a lot of other types of oscillators, such as ",
"crystal oscillators",
", purely solid state amplifier based circuits, magnetrons, and even far more sophisticated methods involving waveguides and resonance (a laser could be considered an oscillator, for instance, because it has all of the same basic properties, except at a far higher frequency).",
"In general, you generate a signal at a specific frequency using a tuned filter and nonlinear feedback. If you were to take a narrowband LC filter, for instance, hook up the output to an amplifier, and use it to drive the circuit's input, then (assuming lots about the amplifier's capabilities) you would eventually see a square wave at the amplifier's output, corresponding to the peak resonant frequency of the LC circuit (it'd be shifted in frequency very slightly due to the addition of the amplifier, but that's not really important for now). The feedback is nonlinear because eventually the amplifier's output exceeds the power supply's voltages and it is clipped, forming a square wave.",
"Just in case, the ELI5 version is to imagine a slinky in your hand. The weight and spring constant of a slinky are analogous to an LC circuit. If you hold one end and let the other end move freely, in a vertical arrangement, and then move your hand up and down, the entire slinky will react. If you move too fast, the slinky doesn't move very well, and if you move too slowly, it follows your hand precisely, at a fixed length. But, when you're moving your hand up and down just right, the slinky will oscillate with a nice amplitude, and the entire arrangement of you \"feeling\" for when it is moving the best, combined with the weight and spring properties of the slinky forms a tuned filter (the slinky dynamics) and nonlinear feedback (you adjusting your hand's speed to maximize the slinky's amplitude).",
"If you wanted a sine wave instead, you would need a way to limit the gain of the amplifier based on the amplitude of the circuit--several approaches exist to do this directly (such as the wein bridge oscillator), but there is also another, better approach: add additional filtering. You'd produce a square wave as before, and then introduce extra filtering stages (another LC circuit, tuned the same way as before) that removes the additional harmonics, leaving you with a signal that is approximately sinusoidal, depending on how much filtering you have and how sinusoidal you need your signal to be.",
"Also, while LC circuits are great for explaining the ideas of tuned circuits, in practice people use crystals, VCOs, frequency multipliers, waveguides, and other things that are modeled as LC circuits, but do not necessarily use inductors or capacitors, to generate signals, because they tend to have design advantages. For instance, qaurtz crystals tend to have a size (and cost) advantage over inductors and capacitors, but they form very narrowband filters. However, unless the environment is tightly controlled, they do not have good frequency stability (vibration especially poses a problem, because quartz crystals work on the piezoelectric effect). In multi-frequency applications, like cell phones, a fixed inductor and capacitor is not suitable for handling multiple frequencies with high selectivity, so circuits with voltage-controllable capacitance are used instead (generally, these are reverse biased diodes or transistors, whose parasitic capacitance is a function of the applied voltage, allowing them to be tuned).",
"But yes, you'd need to have the appropriate tuned circuit (more general than just LC, for the reasons above and several others, relating to bandwidth and a property called Q), and then you could build something operating at a specific frequency."
] |
[
"Benefits of sleep after the snooze button?"
] |
[
false
] | null |
[
"It can actually make it worse. The best option is to actually wake up without an alarm and then stay up. ",
"Your body goes through a natural sleep cycle going in and out of deep (rem- rapid eye movement) sleep. You will feel the most refreshed if you wake up while not in REM sleep. ",
"By hitting the snooze and going back to sleep you may wind up going back into REM sleep making it even worse when you wake up. "
] |
[
"*depends on if you peed"
] |
[
"well now nobody knows what I'm talking about "
] |
[
"Why does 65 mph in a car feel nothing like going 25 mph on a roller coaster?"
] |
[
false
] |
What I mean is, why can you feel the speed on a roller coaster, but not get that same feeling in a car going twice as fast?
|
[
"Acceleration, my friend. Roller coaster accelerate both by changing direction and by changing speed. This creates a strong feeling of acceleration in directions which are atypical for driving on a flat surface. Essentially, you merely aren't used to that kind of motion, so it feels different, and thus exciting."
] |
[
"Yeah, adding to mloewen's answer, you actually never \"feel\" speed, you only ever feel ",
". Airplanes, going at hundreds and hundreds of miles per hour, are just as comfortable as cars. ",
"In a roller coaster, you are subject not just to abnormal accelerations from sharp turns and loops and such, you are also feeling wind in your face, which is, in essence, accelerating some parts of your face backwards."
] |
[
"Cars are designed for comfort, roller coasters are designed for that \"feel\". Also because cars are closed(mostly) and run on flat surface and can't make turns at high seed. Coaster turn at high seed and you fell the centripetal(centrifugal?) force. Also many of them go up side down. "
] |
[
"How much energy does an electron/beam of electrons have to have before it becomes dangerous to human health?"
] |
[
false
] |
I was wondering in the context of a particle accelerator. For example, some of the largest particle accelerators can produce beams on the scale of GeV or TeV, which is obviously very dangerous. What's the lower bound of that scale? How energetic can a beam be before it gets dangerous?
|
[
"It's not just the energy that matters, it's the intensity as well. A single electron with a TeV of kinetic energy is not going to be as physically harmful as an intense beam of 100 keV electrons.",
"In terms of harm to your body, if you believe the ",
"linear no-threshol model",
", then ",
" amount of ionizing radiation exposure is somewhat harmful to your body.",
"Electrons with kinetic energies at least on the order of 10 eV or so are ionizing."
] |
[
"Suppose a crazed physicist offered me the choice of standing in a beam of photons of with energies of 10 eV, or an equally intense beam of electrons each with 10 eV of kinetic energy. By equal intensity I mean each beam delivers to its target (me) the same number of photons or electrons per unit area per unit time. ",
"If I'm not mistaken, these photons are referred to as Extreme UV. On the other hand, the electrons will be pelting me at 2000 km/sec. Assuming no skin protection, is one of these choices obviously preferable to the other?",
"I'm leaning toward the electron beam, because I could find much discussion of beams of such low energy. Whereas EUV sounds nasty. "
] |
[
"If I was faced with this situation, I would look into the dose equivalent deposited into human tissue by these two types of radiation and choose the one which is smaller.",
"I would probably also look into the range of both kinds of radiation in human tissue (or water as a decent substitute). Neither will penetrate very far since they're both pretty low-energy. But if one is more likely to be stopped in your epidermis than your dermis for example, that's worth considering."
] |
[
"Why do eukaryotes have introns?"
] |
[
false
] |
Why do prokaryotes not? Introns early? Late? Somewhere in between?
|
[
"An intron is cut out during splicing. This allows the exons that are between them to arange in many different ways, bacause they don't have to reconnect in the same order as they were before. This allows the cell to create multiple different proteins (or RNA in that matter) from a single sequence. If you meant to ask how they appeared, I am not 100% sure, but it is plausible that transposons were involved, as some new similar mutations due to them are still discovered, where they insert a non-coding sequence into a coding one."
] |
[
"Though their function is not 100% clear yet, many scientists believe that non-coding areas in our DNA have something to do with the high adaptation rate in eucarya during the evolution.",
"A gene is an Intron until it get's a specific starting and end codon which will make it work. The resulting Proteine can be either good or bad. If it's good it stays and if it's bad it will go extinct (oversimplified!)",
"Did you ever notice the big gaps in the development of multifunctional organs? Like the digestive system? There are multiple building plans in eucarya for a digestive system but did you ever wonder how the big changes were made to allow eucarya to evolve into a more specific lifeform, without leaving much mosaic animals?",
"That's probably due to many introns at once getting a new function and thus building new proteines in that changed these building plans to make them more specific.",
"Sorry for my bad english, I'm still a learner. "
] |
[
"There is no clear-cut biological answer to this question, and there probably never will be. Lots of people will propose various explanations, such as introns allow greater complexity, they play a regulatory role by affecting the expression of neighboring exons, etc. (see the other answers in this thread, for example; the internet is full of explanations like these). But many organisms do perfectly well without introns, and as a molecular biologist I strongly doubt there is anything organisms can achieve with introns that they absolutely couldn't achieve without them. ",
"In fact, even among eukaryotes, many don't have introns, or have very few (yeast are a great example: they have all the machinery necessary to splice out introns, but the vast majority of their genes have exactly 0 introns, and the few they do have are quite short). So it's not just about prokaryotes vs. eukaryotes; the more general trend is that bigger and more complex organisms tend to have more (and longer) introns. ",
"Some people might argue that more complex organisms require more complex and flexible genomes, and introns play a part in that. Some might even claim that introns allowed these organisms to evolve their complexity to begin with. But I think it's simply a matter of negative selection, or lack thereof. Higher organisms don't pay a significant fitness penalty by having lots of DNA in their cells, so they are not selected for genomic efficiency like most microorganisms tend to be. They accumulate a lot of junk in their genomes simply because evolution isn't pressuring them not to. Look at humans: 99% of our genome is total junk. Don't believe all these people who say \"there is no such thing as junk DNA\", \"most of the human genome has annotated function\", etc. The fact is, a huge percentage of the human genome is totally unnecessary BS. Sure, much of this junk has evolved some (often marginal) functionality over time, but we would have been perfectly fine if we didn't have it to begin with. Most of our DNA, including our numerous and lengthy introns, is there simply because evolution hasn't bothered to get rid of it. ",
"Compare our genome to that of bacteria: there is nothing there that isn't absolutely necessary. Protein coding sequences, some (very short) promoters and terminators, a few more minimal regulatory sequences, and that's it. There is no inefficiency there, because bacteria can't afford it. Any extra DNA means more energy wasted during DNA replication, thus lowering their highly-optimized fitness. Evolution has sculpted bacteria towards maximum efficiency, so if they can do without introns (and I believe ",
" organism can, in principle) they just won't have them. Keep in mind, it's not as if bacteria lack complex and flexible regulatory mechanisms that control gene expression and such. They have plenty of regulatory complexity. They've just figured out how to achieve this without long stretches of mostly-useless DNA. "
] |
[
"Dear r/askscience, how plausible would it be for the universe to be a sphere?"
] |
[
false
] |
I was thinking about the universe, and how plausible would it be if the universe was in the form of a hollow sphere, where the sphere is constantly "inflating" like a balloon. I have theorized other things but this will go first. I'm 16 so sorry if this is a dumb question.
|
[
"this was the way we thought of it for a long time. But look on a globe, notice how you can make a triangle from (0,0) latitude longitude, walk north to the north pole, turn 90° walk down to the equator, turn 90° and walk back to where you start to find yourself 90° with respect to your original path. You've made a triangle with ",
" 90° interior angles. The point being that if it does curve back around, it's likely to have a geometry different than the kind you learn in elementary school (for example, triangles with more than 180° in their interior angles). ",
"So if the universe was like a sphere, in that it wrapped back around on itself, it should likely have a specific kind of curvature. ",
"but our best data doesn't seem to support this curvature",
", so the universe doesn't likely do this."
] |
[
"I wouldn't think that the shape of the universe as a whole would affect us, just as we don't notice the Earth is round when we walk on it."
] |
[
"but if we do very precise tests of the Earth, we do find that it's curved. The same of our universe. We do very precise tests and don't see it to be curved. Unless it's greater than 251 times the size of our observable universe. Which then leads physicists to wonder why the curvature should be so small, but not exactly zero. (also note the error bars also go the other way into negative curvature, so...)"
] |
[
"Does sound travel farther/more quickly in cold air then it does in warm or humid air?"
] |
[
false
] |
I’ve noticed that it sounds different outside when it gets cold, like I can hear more ambient noise, so I was wondering if this is just in my head or if this is actually something that occurs.
|
[
"Speed of sound is directly influenced by the tenperature of the air.",
"Acoustic speed is equal to the square root of gamma (ratio of specific heats, usually 1.4) times R (gas constant of air, 1716 using Rankine or 287 using Kelvin) times the temperature of air (Rankine or Kelvin). ",
"The higher you go in the atmosphere, the slower the acoustic speed is, so the inverse of what you said is correct. ",
"Warmer = faster acoustic speed, Colder = slower acoustic speed"
] |
[
"I would say depending on the area the cold would help someone hear better outside due to less critters making noise."
] |
[
"I would say depending on the area the cold would help someone hear better outside due to less critters making noise."
] |
[
"My kitchen sponge is smelly. I pop it in the microwave for a minute, rinse it off, and the smell is gone. Is this really because the bacteria are killed?"
] |
[
false
] |
Surely the "smell molecules" are inanimate and will just hang around until washed regardless of whether the bacteria that created them are alive or dead Also, are there any reasons (toxicity etc) why you shouldn't microwave a sponge? Sponges need to be wet before being microwaved or they are apparently a fire hazard.
|
[
"When answering this I am making two assumptions:\n1. it is a moist or wet sponge when you are heating it.\n2. it is steaming and really hot when you are done heating it. ",
"What you are doing is increasing the temperature of the sponge to boiling (100 C). This is a relatively high temperature for aroma chemicals (many are considered 'light' volatiles) and this volatilizes (boils) a number of aroma chemicals from the sponge. Aroma chemicals are released based on a number of physical properties of the specific smell molecule and the matrix the aroma chemicals are in. Some 'stick' more and some less. ",
"As aroma chemicals are heated above certain molecule specific temperatures they leave the sponge and enter the air (or headspace) of the microwave. As this happens you reach the boiling point of water and any compound that has a boiling point lower than that of water is essentially in the headspace of the microwave and is no longer associated with the sponge. When you take the sponge out you allow all those compounds to escape in the air, and have significantly fewer molecules 'attached' to the sponge, and so it does not smell as bad. "
] |
[
"Yes. Microwaving is also more effective in ",
"killing yeasts and molds",
" than cleaning products like bleach. "
] |
[
"Because microwave radiation is extremely effective at boiling the water in any mixture away; no moisture, no mold."
] |
[
"Is it possible to train your brain to recognize the other eye as the dominant eye?"
] |
[
false
] |
[deleted]
|
[
"This reminded me of how lazy eyes are treated in children; an eye patch is put on the STRONG eye. This means that the weaker or 'lazy' eye now has to compensate and provide vision for the whole of the brain. Over time, the lazy eye becomes stronger, until it functions as a normal eye. This theory uses neuroplasticity: the ability of the nervous system to develop and strengthen new connections between neurons. A system such as this is used by Edward Tuab to treat stroke patients (the normal limb is put in a sling/cast, requiring the patient to use only their damaged limb) ",
"It is possible for someone to 'retrain' their brain to recognise the other eye as dominant, by covering the currently dominant eye with an eye-pach. However, in adults this will take a lot longer than in children, (as children have far more plastic brains than adults) and requires the use of an eye patch at all time for months on end. Furthermore, the results would be varied, and the weaker eye may only be strengthened to a small extent. For best results, i'd couple wearing the eye patch with rigourous 'training', so playing games/doing activities designed to strengthen the eye: things like Where's Waldo, Eye Spy, games requiring depth perception etc etc, anything that requires good vision will help. "
] |
[
"You're completely right, depth perception is best achieved with two eyes; this makes it a good task for strengthening one eye. The harder the activities the better. \nIf you've already had problems with depth perception maybe just stick to finding tasks with your weaker eye, and then build up to using both eyes for the depth perception.",
"Remember these tasks need to be very difficult, or improvement is limited. If you're interested, try looking up Barbara Arrowsmith-Young. While her work is centered around learning difficulties, the same principle apply. ",
"Most importantly though, I would definitely see you doctor/neurologist before doing anything."
] |
[
"I have a pretty significant astigmatism in my left eye and was forced to use an eye patch over my right eye for several hours every night as a young child. According to the doctor, my astigmatism was so severe I could have gone blind in my left eye without the eye patch treatment.",
"Question, how could you perform depth perception based activities using one eye? I thought depth perception was a product of stereo vision. I ask because I've always felt that the my drastic right-eye dominance made depth perception based activities difficult, such as shooting a basketball. Maybe I should get an eye patch and keep training my left eye!"
] |
[
"What exactly causes the pain from a static spark?"
] |
[
false
] |
Is it due to direct electrical stimulation of the nerve endings? Is it due to a change in temperature? Or is it something else?
|
[
"Source?",
"The timescale of a shock-induced pain response is much shorter than one corresponding to temperature-induced pain and qualitatively distinct as well.",
"EDIT: due to the lack of any better answer, I'll weigh in with a bit of evidence-based speculation. The pain experienced is most likely the effect of all voltage-sensitive neurons firing at once, be it temperature, pressure or damage sensitive neurons, they all require minute changes in voltage (in the order of millivolts) to fire and so it's very likely that a localized electrical current creates enough of a difference for the shock to simultaneously activate all those sensations, even though none of the proper corresponding stimuli are present.",
"Additionally, other non-sensory cells can also release molecules that signal damage and this acts on a much slower timescale given that neurons have to translate the chemical message into an electrical one. This delayed harm-indicating signalling is probably what causes the lingering pain associated with electric shocks."
] |
[
"The pain is actually a heat response. Static sparks are hot, that little zap you hear is from the air being super heated (like a lightning bolt). That heat will affect the tiny point of contact, giving a pain sensation."
] |
[
"The typical energies in a static shock range from 100-500 mJ ",
"source",
".\nIf you take the highest energy (500 mJ) and assume local heating effects only (lets say 1g of finger tissue is heated) then you get a temperature rise of 0.12 C."
] |
[
"Why do photovoltaic cell graphs level out?"
] |
[
false
] |
I recently did an experiment similar to this one: When discussing my graph and data I wasn't sure why the graph of a photovoltaic cell's voltage output in relation to LUX levels out. Is this because pv cells have a maximum capacity or some other reason? And if so, what is it?
|
[
"If this is for a class, you need to warn your teacher that the experiment in the link is fundamentally incorrect.",
"The author has you measure the open-circuit voltage, i.e. the voltage under zero-current conditions, with no load resistor connected across the solar panel. This is wrong, since the voltage isn't directly proportional to light intensity, instead current is. Therefore, the entire experiment is teaching a misconception and breeding confusion. And it also misses an excellent opportunity to discuss how solar cells actually work.",
"In photovoltaic cells, it's the short-circuit current which is directly proportional to light intensity. That's the output current at zero voltage. A solar cell is a sort of \"charge pump.\" It's a pump where the rate of photon-absorption in the PN junction determines the rate of charge carriers being forced to cross the potential barrier. So, twice the light intensity, twice the incoming photons/second, twice the number of charges per second, and twice the milliamperes. This, while voltage remains close to zero. Simple, no?",
"To properly perform a simplified PV experiment, you'd connect a current meter across the panel, not a voltmeter. A current meter acts as a zero-ohm resistance, so this configuration measures short-circuit output current of the panel. Then, as you turn up the brightness of the bulb, the current will rise in proportion. You'd get a smoothly sloping graph which looks nothing like the one in that article.",
"In answer to your original question, the potential of 9V is created by the junction potential of the stack of many PV cells in the panel. It's produced by the built-in electric fields inside the individual solar cells. In theory, for an ideal solar panel connected to an ideal voltmeter, the open-circuit voltage should always be 9V, even in total darkness. (In other words, we don't need to explain the 9V, instead we need to explain why the voltage falls to zero at all!) In your real-world example, the shape of the graph is probably determined mostly by the parallel (not series) resistance found across each PN junction in the cells. Even the resistance of the voltmeter may affect that curve."
] |
[
"I have stuff to add to that.",
"People build solar panels to get power, which is measured in watts and is volts multiplied by amps. People also always want as much power as possible from their cells.",
"So you plot a graph of voltage vs amperage (called an IV curve) and find the point where power multiplied by voltage is highest (called the peak power point). This is the elbow joint on the right side of the graph.",
"More info on how to do IV curves, and examples",
"."
] |
[
"See above, \"In answer to your original question.\"",
"Ideally the graph should be 9V at ",
" light intensities. I don't know the type of solar panel you have (probably amorphous thin-film on glass?), but probably contains eighteen cells in series, each of which produce 0.5V. That 0.5V comes from the PN junction of the cell, and the 0.5V is almost identical to the turn-on voltage of a common diode. (So, search for info about the nature of a diode's Vf voltage.)",
"The 0.5V (and hence the total 9V) is a built-in electric field which appears when the solar cell is first manufactured, when the movable holes and electrons at the PN junction each get trapped on the \"wrong\" side. Or, you could imagine a piece of p-doped semiconductor touching a piece of n-doped, and at the instant of contact some holes and electrons flood across the junction, and the two pieces start charging up. (This happens in darkness, light plays no role.) This spontaneous charging process slows and stops when it hits a value of around 0.5V, since (after a couple more stages of explanation) that's the potential needed to keep any more electrons from falling into holes. The complexity of explanation grows, since Quantum Mechanics and band theory is actually the cause of the 0.5V. For lots of accurate but advanced info, look up: diode potential barrier, depletion layer, diode Vf voltage, semiconductor band-gap.",
"Specifically, when light shines on a solar cell, pairs of electrons/holes are created, and they get pulled in opposite directions by the built-in half-volt electric field. They build up on opposite sides of the PN junction, and cause the cell to act like a charged-up capacitor. If there's no load connected to the solar cell, then these opposite charges will only build up to a voltage of 0.5V, and they should just sit there forever. This newly-created voltage opposes the built-in voltage in the PN junction, canceling it out. With zero electric field now in the PN junction, any more hole/electron pairs created by light-absorption won't be pulled away from each other, and will quickly experience recombination (and create some heat, heat rather than electrical output.)",
"In other words, your solar cell is only a source of electrical energy when a load resistor is pulling the voltage somewhat below 0.5V, and the cell is producing significant current through the resistor circuit. Since there's no load resistor connected to your panel, you're basically measuring the electric field of the stack of PN junctions. In theory it should always be 9V, regardless of light intensity. So, as I mentioned earlier, the real problem is to explain why the graph isn't just flat everywhere at 9V, all the way to zero Lux.",
"To try: the 9V and 50mA panel rating suggests an ideal load resistor of 9/0.05 = 180 ohms. You could repeat the experiment (for extra credit? grin!) with a 180-ohm resistor connected across the panel. Then the voltage across the resistor should rise in a smooth slope, probably hitting about 4.5V at a light brightness equaling full sunlight."
] |
[
"Do we have any idea why there's a correlation between a nation's cancer rate and economic development?"
] |
[
false
] | null |
[
"This is one of those \"there is way more than one significant reason\" questions. ",
"One of the most significant reasons is almost certainly longer lifespans. ",
"Cancer incidence increases incredibly dramatically with age.",
" So even a small in average lifespan may sharply increase your cancer incidence. "
] |
[
"To put it bluntly: We all die of cancer, unless something else gets us first.",
"So by reducing other causes of death (accidents, preventable and treatable diseases) you inflate the number of cancer cases. Richer countries generally have higher safety levels and better healthcare, so they see higher rates of cancer."
] |
[
"First World countries, particularly those with public health care systems, are far more likely to notice cancer because of the wider availability of superior technology to pick up and diagnose tumours. This is either in life using various imaging methods or in death via autopsy. Unfortunately much of the world does not have access to these so the prevalence of many diseases are artificially low.",
"What's more is that some cancers, such as those of the prostate, can carry no symptoms at all with the patient often dying of another comorbidity. In countries where there aren't screening programs, it's very unlikely that these would ever be picked up. "
] |
[
"Why is the International Space Station is kept at 14.7psi?"
] |
[
false
] |
I read today that the International Space Station is kept at 14.7psi. This seems odd, commercial aircraft don't even pressurize to this level. if I recall they generally choose something higher to avoid airframe stress. Why would NASA choose this pressure when obviously trying to minimize the weight of bulky payloads. edit: higher altitude thus lower pressure.
|
[
"I think it is for compatibility with the long standing practice on the soyuz, and more recent practice on the shuttle. Now that you mention it it does seem strange that they don't event go for 10 psi, with the same partial pressure of oxygen. You would need more gear to handle the transition, but your structures would be lighter."
] |
[
"The obvious answer is 14.7 psi with 21% oxygen is the same total atmospheric pressure and partial pressure of oxygen as is the atmosphere on Earth. However, after the pure oxygen debacle of Apollo 1, NASA still used a lower pressure, higher oxygen content atmosphere on the Apollo space missions. The numbers I've seen are 70% oxygen at 5.5 psi which gives a partial pressure of 3.85 psi for oxygen (the same as 21% oxygen at 14.7 psi). While human flesh might not spontaneously combust at 70% oxygen, it is still a pretty damn high content. The ISS has a lot of stuff in it with electrical contacts, motors etc. One suspects there was a risk assessment that concluded it would be too hard to keep rigorous control of everything that got onto the space station from the various sources including the shuttle, soyuz, progress, columbus, dragon and other craft visiting the station to ensure something that generated a spark wouldn't ever get there. "
] |
[
"14.7 psi is 1.00027 atm, (almost) the same as sea level pressure on Earth. ",
"Reportedly",
" this results in benefits for crew comfort, and is much safer than the alternative, a pure oxygen atmosphere, which has cause problems in the past."
] |
[
"When I look up into the night sky how far away into space am I actually seeing before my eyes cannot detect light anymore?"
] |
[
false
] | null |
[
"GRB 080319B",
" was a gamma-ray burst whose emissions arrived at Earth at 0612 UTC on March 19th, 2008. Its peak visual magnitude was 5.8, roughly comparable to the average brightness of the planet Uranus. While not visible from sites such as inner cities, this brightness is easily achievable from a rural location by a dark-adjusted observer.",
"The GRB was within visible range for approximately 30 seconds. Its redshift was measured to be z = 0.937, which corresponds with a ",
"lookback time",
" of ~7.5 billion years. This distance is approximately 2.3 Gpc, making it the most distant object seen visually by humans (by a huge longshot)."
] |
[
"How far away you can see is dependent on the absolute magnitude of whatever you are looking at. The most distant object that you can see is the Andromeda Galaxy, which is about 2.5 million light years away.",
"However, the only reason that you're able to see that far is because it's the combined output of billions of stars. You can't see any individual stars that are anywhere near that far away. All of the stars in our night sky are within our local region of the Milky Way.",
"The most distant well-known star that you can see is Deneb, which is about 1800 light-years away. Most of the stars in the night sky are within a couple hundred light years of us."
] |
[
"When and why are gamma-rays dangerous? If we could see that gamma-ray it must have hit us surely?"
] |
[
"How much of a role does aerodynamics play in a car's performance? Why is every modern car shaped like an egg?"
] |
[
false
] | null |
[
"So my follow up question would be, how much of a difference would the performance of a car from say 50's/60's, if only it's body were to be redesigned with modern aerodynamic? Would it be a drastic difference or just slight?"
] |
[
"Short answer: It makes a massive difference.",
"Long answer: Aerodynamic forces are extremely complex and difficult to deal with simply, but the classic drag equation (an approximation) tells us that the drag force experienced by an object moving through a fluid is proportional to the square of the object's speed. This means that as a car goes faster and faster, aerodynamic drag quickly becomes the dominant force against which the car must work to maintain its speed or accelerate. This also means that at low speeds, the aerodynamic forces are much less noticeable.",
"As for the egg shape... there are two kinds of fluid flow, ",
" and ",
". Laminar flow is \"attached\" to the surface, with velocity smoothly decreasing to zero as you pass through the boundary layer towards the surface, and turbulent flow is characterized by \"separation\" of these layers from the surface and a chaotic, random flow behavior. Abrupt edges and features tend to produce turbulent flow, while a smooth teardrop shape can allow flow to remain laminar over its entire surface. ",
"Producing turbulence takes a lot of energy (manifested as a certain type of drag) so aerodynamic bodies are generally designed to have the flow stay laminar over them, from airplane wings to car bodies. However, in practice, you need a perfectly smooth surface to have completely laminar flow, which is unrealistic for a car, and other design considerations might (do) require that the vehicle's shape not be an ideal form. However, there ",
" such an ideal form, and that's what's been influencing car designs so much lately.",
"edit: I should mention that sometimes, inducing turbulence can actually decrease the ",
" drag. Often this is done intentionally... like I said, aerodynamics is very complex and often unintuitive."
] |
[
"Thanks for answering by the way. What I'm trying to find out is, if modern body designs of sedans actually improve car performance alone as compared to older car body designs, and by how much. Is there somewhere to look up the aerodynamics of the bodies of cars alone? Would there be comparative data? Can we compare the drag force of the 1965 Impala's car body to a 2013 Impala's car body? "
] |
[
"Does light decay?"
] |
[
false
] |
Edit: Jesus. You all made my brain hurt.
|
[
"As far as we know, it doesn't.",
"If it does, it must have a lifetime of over three years in its own rest frame (which it would have if it had mass, which it would need to decay), but because light moves so fast it is dilated to much longer than the age of the universe in our rest frame.",
"http://arxiv.org/pdf/1304.2821.pdf"
] |
[
"Can someone re-word this sentence so that it makes sense?"
] |
[
"At relativistic speeds particles with certain lifetimes (i.e. times before they decay into other particles) appear lengthened to us because the lifetime would be measured in their frame.",
"Imagine a particle that decays after 10s, and now imagine this particle going maybe 0.8c. I don't have anything near me to do the math, but because of relativistic effects what would appear to 10s to the particle may be something like 16 seconds to us.",
"Now imagine a photon, going the speed of light, which does not experience time in its frame--this is because it's going at the speed of light. If it had a decay time it would never decay because it never experiences time. And I think what this person was saying is that even if it did experience time it would be so minute that because of the dilation it would be much longer than the universe's age before it would finally decay"
] |
[
"WHY do antimatter and normal matter annihilate?"
] |
[
false
] | null |
[
"That is a great question, but it is really difficult to explain to someone without basic knowledge of quantum field theory, so I hope my explanation makes at least a little bit of sense, even though it's really long.",
"Quantum Field Theory models the behaviour of fundamental particles, and it incorporates quantum mechanics (necessary for particles) and special relativity (necessary for changing mass to kinetic energy as E = m c",
" , and thus for creating and annihilating particles).",
"In quantum field theory (QFT), all elementary particles are considered as quanta of waves / oscillations in a field. The frequency of the oscillation is proportional to the energy of the quantum by Planck's constant, and (inverse) wavelength is related to the momentum.",
"Photons are the quanta corresponding to electromagnetic waves. Similarly, electrons are the quanta of oscillations in the \"electron field\".",
"I know this sounds really abstract so far, because it is, but let us just accept that for now and bear with me.",
"If a type of quantum or particle carries any type of charge, like the electron carries electric charge, then there must be another type of particle which has opposite charge but the same mass, called its antiparticle. This is due to a fundamental symmetry of QFT.",
"Let us just consider the simplest example of an annihilation reaction: the annihilation of an electron and a positron (= antielectron) to two gamma ray photons. We need (at least) two photons because energy and linear momentum is conserved. All other annihilation reactions are conceptually similar.",
"The electron positron pair have a total energy given by 2",
"c",
" (+ kinetic energy + potential energy), where m is the mass of a single electron. They also carry no total linear momentum (in the centre-of-mass reference frame). Therefore, you need two photons, going in exactly opposite direction, and each carrying exactly half of the energy of the initial electron-positron pair (in the centre of mass frame).",
"The relevant QFT model is called Quantum Electrodynamics (QED). It describes the interaction of the electron field and the electromagnetic field with one another.",
"Calculations in QFT can be done using Feynman diagrams, which are really simple to draw and quite understandable, but where each graphical element also has a precise mathematical meaning. In your sketch, you say one axis is time, and one axis is \"space\". Each particle is represented by a type of line. Each type of interaction is described by a vertex, i.e. where line meet. To calculate the probability that from some initial state (an electron and a position), you get some final state (two photons), you draw the simplest diagrams that take your initial state to your final state via some interactions.",
"The rules on how to draw these Feynman diagrams, i.e. which particles there are and what vertices are allowed, and how to convert them to mathematical expressions are called the Feynman rules.",
"The Feynman rules for QED are:\n* There two types of lines: wiggly lines corresponding to photons, or the electromagnetic field, and solid lines with arrows, corresponding to electrons and positrons, or the electron field.\n* There is one type of vertex. It has a solid line with arrow pointing towards the vertex, a solid line with arrow pointing away from it, and a wiggly line attached to it.\n* A photon in the initial or final state is represented by a wiggly line.\n* An electron in the initial or final state is represented by solid lines with an arrow pointing in the \"+ time\" direction of your diagram.\n* A positron in the initial or final state is represented by solid lines with an arrow pointing in the \"- time\" direction.",
"You can have any number and any type of intermediate lines connecting the internal vertices in a Feynman diagram.",
"Obeying these rules, the simplest diagram for electron + positron -> 2 photons you can draw is the second figure in ",
"http://en.wikipedia.org/wiki/Electron%E2%80%93positron_annihilation",
"That Feynman diagram shows that, within quantum electrodynamics, an electron and a positron can and will with a probability greater than zero annihilate to two photons.",
"By the way, notice how you can rotate this diagram, to get a diagram describing (Compton) scattering of a photon and an electron (or positron) off of one another. This rotation of Feynman diagrams also corresponds to a symmetry of QFT, that can mathematically relate very different physical processes like in this example.",
"Within the Standard Model of Particle Physics, which is another famous QFT model, you get the same result as long as the energy of your electron and positron isn't too high (otherwise Feynman diagrams due to the Weak Interaction become large)."
] |
[
"The simplest way to think about it is that the particle presents +1 of something and the antiparticle -1, and when you put them together you have zero of that particle.",
"For example"
] |
[
"Electrons are not the anti-particle of protons, even though they have opposite charge. In simple terms, an anti-particle is not just a particle with the opposite charge to another, it a particle that is exactly the same as another except for the sign of some of its properties (in the case of electrons and positrons, they are identical but the former has a charge of -1 and latter a charge of +1)."
] |
[
"Why do humans have a full head of hair?"
] |
[
false
] |
Apologies in advance to the follically challenged among us for the incendiary title. I have read the on hair evolution, but it's not completely satisfying, so I was wondering if anyone here had thoughts on the matter. I can see the UV protection being important, but would the UV light really penetrate through the skull deeply enough to cause brain damage, even in infancy, making the head the main priority? Then it seems like we should have kept the hair on our faces too. Also, I don't quite understand why head and facial hair regrows so rapidly, and doesn't stop growing at a certain length. And I'm also curious about the sexual differences in hair growth, eg why male hormones cause more hair growth, why women don't bald as much, why females don't have facial hair (sexual selection I'm guessing?). Please do your best to answer these questions and any I forgot, even if the answers get a little hairy.
|
[
"In evolutionary biology, a Spandrel is a phenotypic characteristic that is a byproduct of the evolution of some other character, rather than a direct product of adaptive selection."
] |
[
"UV light doesn't need to penetrate to the brain to do damage. It would make sense that the skin on the top of your head is the most exposed to UV damage and that it would be advantageous to have skin on your head."
] |
[
"If I recall my anthropology classes correctly, we're not quite sure but we can give some guesses. The most prominent factor is probably sexual selection. Basically, chicks don't want to bang hairy dudes and dudes don't want to bang hairy chicks. This of course brings up the question of why such a trait has remained desirable across basically the whole of human history, and we don't know. But if you review the literature of almost every society that ",
" literature, people like hairless people, head excepted.",
"Now, that might help explain why there's less body hair, but it wouldn't exactly explain more head hair. Unless there was a similar sexual selection process for head hair, which would be straining credulity. ",
"One possible explanation (again, this is basically informed speculation) can be formed by looking at the difference between \"African\" hair and non-African hair. African hair is kind of nappy. European, Asian, and Native American hair is smooth. This would suggest an evolutionary benefit for people in the more northerly climates to grow longer, smoother hair (which makes sense; more dense hair keeps you warmer). It's possible that a combination of evolutionary pressures (more hair) and sexual pressures (less hair, except on the head) brought us to a point where we have less body hair but more head hair.",
"Speculating on the \"causes\" of stuff we've evolved in the past is usually a murky business."
] |
[
"Does the length of sleep affect the perceived length of dreams?"
] |
[
false
] |
Time in dreams is a bit scooty, but I'm sure it's a pretty common experience that we sometimes have dreams which seem to go on for much longer than others. Is this at all related to the amount of time we're asleep? Can we have dreams which feel like they're longer than the time we actually slept for?
|
[
"Your sleep cycles vary. You will have shorter, shallower sleep cycles later on in your sleep, so you will have more dreams per hour the more hours you sleep that night.",
"As to each dream itself, no. You might remember 20 seconds of a dream and feel like it was a 3 minute experience, or vice versa."
] |
[
"As to each dream itself, no. You might remember 20 seconds of a dream and feel like it was a 3 minute experience, or vice versa.",
"This concept of how we perceive time while dreaming is so fascinating. Sometimes I’ll take short naps and have dreams that feel like feature length movies lol."
] |
[
"I doubt there's a satisfying answer to this.",
"Personally, my state of mind has a lot to do with the perceived length of a dream. In times of distress or melancholy, I'll have anywhere from feature-length dreams to the kind where you feel like you've woken up from living some other life. Whether it's a nap, 8 hours at night, or a 12 hour coma, the length of my dreams will vary wildly and arbitrarily."
] |
[
"Is there a link between high IQ scores and disorders like ADHD and Asperger's?"
] |
[
false
] | null |
[
"Short answer? No. People with a high IQ score do not, as a population, have a higher incidence of ADHD or Asperger Syndrome. You will find no major study specifically tasked with finding such a link (but many debunking the notion) for the reasons listed below.",
"Long answer? Still no, but for a pretty wide range of reasons. ",
"Let's look at ADHD first. First and foremost, ADHD is a spectrum disorder. ADD's spectrum covers nine different classifications of \"inattention\" symptoms and ADHD's spectrum covers nine different classifications of \"hyperactivity and impulsivity\" symptoms. To receive a formal diagnosis of ADD or ADHD, the individual must manifest six of those nine symptoms over a period of at least six months. This means that the title of \"ADD/ADHD\" does not imply a uniform ",
" because an individual can manifest all 18 of the criteria in major form and be noticeably impaired, or only manifest 12 in minimal form and present normally - but both are technically ADD/ADHD. ",
" because we hear about ADD and ADHD so often, many people think they know what the disorder entails and are ready to label someone (or even themselves!) as ADD/ADHD without a clinical diagnosis. The real culprit is this bit of language in the DSM-5, however: \"elevated novelty seeking.\" The smart child in the classroom who already knows 2+2=4 and is bored with it is not \"novelty seeking\" by trying to figure out what 3+3 is before the rest of the class - but that is what often gets called ADD/ADHD. This leads to the belief that ADD/ADHD is a \"smart\" disorder.",
"Unfortunately, ADD and ADHD diagnoses are predictors of lower intellectual ability later in life, particularly regarding things that people with high IQ scores are typically good at: tests of attention, executive function and memory. In adulthood, persons with ADHD typically experience: \"poorer occupational performance, attainment, attendance, and higher probability of unemployment as well as elevated interpersonal conflict.\" ",
"What all this means is that a person with ADD/ADHD is not only going to perform badly on something like an IQ test, but even if they manage the test well enough to score highly, they are unlikely to be regarded as an \"eccentric genius\" when they reach adulthood because of all the problems mentioned above. So, long answer for ADHD is no. ",
"Now, on to Aspergers. I think this is a fairly interesting disorder, because from my point of view, it's our first step towards getting rid of the autism \"spectrum\" and replacing it with a specific, definable disorder at each stage of impairment. That being said, Aspergers is on the low end of it, but comes with a particular fatal flaw to anyone who wants to be a genius - \"Restricted, repetitive patterns of behavior, ",
", or activities.\" (Emphasis mine.) ",
"\"Genius\" is the product of many individual threads of knowledge coming together to solve a larger problem. Restrictive thinking of any kind would necessarily impair that. Even for someone who is a \"genius in their field,\" their interests are not limited to only that field. This, combined with the problems in social communication and social problems in general, is not a great predictor of future success. ",
"And to compound this problem, Aspergers is just like ADD/ADHD in terms of public awareness and willingness to diagnose without qualification. People who are depressed, socially awkward or who just want to be a little \"different\" without being ",
" different are very ready to slap a label on themselves and Aspergers is one that looks fairly comfortable. ",
"What's important to keep in mind when asking questions like \"Does X disorder imply Y attribute\" is the word \"disorder.\" If someone is clinically diagnosed with these problems, they are ",
" that impede one's ability to move forward in life, not small quirks that can be easily ignored. For every 100 bored kids on dextroamphetamines to keep them from fidgeting (one of whom may be a person with a high IQ) there's some poor kid who's zombied-out on bupropion and ",
" can't focus long enough to memorize their multiplication tables. The former may \"have\" the same disorder as the latter, but who is genuinely suffering?",
"Source is my trusty DSM-5. (And college and textbooks and experience ;0, but quotes and such are all from the DSM.)",
"TL;DR: Spectrum disorders often have charismatic individuals that technically \"have\" the disorder while appearing to suffer none of its ill effects. This is not the norm. ",
"Edit: Clarity"
] |
[
"That's not what that article says. It only says that most mentally ill people aren't creative geniuses, and vice versa, but that's not what I was asking. If (randomly making up numbers here) 15% of everyone with an IQ within the 99th percentile have ADHD, compared to 5% of the population in general, that would mean a higher rate of ADHD, even though the vast majority wouldn't have the disorder. "
] |
[
"That's not what that article says. It only says that most mentally ill people aren't creative geniuses, and vice versa, but that's not what I was asking. If (randomly making up numbers here) 15% of everyone with an IQ within the 99th percentile have ADHD, compared to 5% of the population in general, that would mean a higher rate of ADHD, even though the vast majority wouldn't have the disorder. "
] |
[
"Where does water come from?"
] |
[
false
] |
I feel like this is a really really dumb question but recently i was thinking about aquifers and for some reason it made me wonder how the sea level rises every year if that’s where our water supply comes from. Pls don’t roast me ❤️ :)
|
[
"Water from the oceans evaporates creating clouds that drop water on the land filling rivers etc that eventually make their way back to sea. It’s called hydrologic cycle, they often get you to do diagrams of this cycle a few times through school. \nGenerally our water supply comes from creating dams at points in these rivers that collect large deposits of water. There are places that use other methods such as bore water. For example here in Australia we have the largest artesian basin in the world and that is the only supply of water other than rain tanks for a lot of inland Australia. (predominantly in Queensland but it stretches into the Northern territory, South Australia and a little bit into the top of NSW). ",
"Also just to add, i believe originally our water came from asteroids mostly. And now it just cycles through the earth. The total amount of water on earth never really changes, just the location of that water. ",
"P.s this is my understanding and i’m no expert, i’m sure someone else here will have a much better and more in depth explanation :)"
] |
[
"Hydrogen was created after the big bang as subatomic particles collided with eachother. Stars fuse Hydrogen atoms together for fuel and make more complex atoms as a result- one being Oxygen. After the star lives out its life and goes super nova, it leaves behind the elements within the nebula. The elements are unstable and react with each other to form water. Gravity continues to aggregate the molecules together until you get meteors and asteroids. There are several theories explaining why so many of them would have hit Earth. Some examples include Jupiter's orbit may have once been much closer to the sun, bringing in asteroids because of its gravity; or Saturn and Jupiter had an orbital resonance which pulled in asteroids and didn't allow them to have stable orbits."
] |
[
"Speaking generally at a global scale, sea level rise is caused by two main things: Temperature increase of the liquid water, causing it to expand in volume, and melting glaciers resting on land, adding to to total water in the ocean. Aquifers are made up of water that long ago fell as rain and soaked into the rock and soil. That water originally (ok, ignoring the whole big bang/stars/comets part) was part of the ocean and heat from the sun caused it to evaporate and form clouds which created rain over land. The water we're pumping from aquifers doesn't substantially add to what is already in the ocean."
] |
[
"What tasks are faster to do with a computer that uses quantum processing (aka qubits) ? How faster it is compared to normal bits?"
] |
[
false
] |
There are only a limited scenarios where quantum bits provide a improvement over conventional processing. When that applies how faster that computing is? It's like a quadratic or exponential function of number of bits? qubits are useful in brute-force attack in cryptography? (I have no knowledge over this, so the nomenclature may be all wrong!)
|
[
"RSA relies on integer factorization. On a classical computer, it's not actually exponential, but the time increases about exponentially with the cube root of the number of bits. It's still really fast. On a quantum computer, it's about the square of the number of bits. I think that's also around how much longer it takes to encrypt, so basically if your enemy has more computing power than you, no matter how big you make your key they'll be able to decrypt it faster than you can encrypt it.",
"I don't know exactly how it is with elliptic curve encryption, but I think it's similar.",
"That's just for public key encryption. If you're doing symmetric encryption, where there's one key for both encrypting and decrypting, then there's no great way to break it with a quantum computer. There is an algorithm that lets you invert a function in sqrt(n) time, so instead of taking 2",
" tries to break a 256-bit encryption it only takes 2",
". That's still 2",
" times faster, which sounds impressive, but the practical result is that everyone just needs to double the length of the key."
] |
[
"We don't always know how fast a task can be done. (The most famous example of this is the P=NP question.) A lot of the things that people are excited about for quantum computing are problems like that. There are specific examples where people are excited about possible performance improvements.",
"If you look at the wikipedia page (",
"https://en.wikipedia.org/wiki/Quantum_algorithm",
") you can see that the expected speed-up varies by task and algorithm, and ranges from relatively small amounts to exponential performance increases."
] |
[
"It's still really fast.",
"Think you meant 'slow'."
] |
[
"Helium balloons only deflate and drop because the helium leaks through the latex. Is there any material that is light enough to float without leaking the helium?"
] |
[
false
] |
[deleted]
|
[
"The helium still escapes through the seals and is still capable of escaping through microscopic defects in the mylar.",
"Sure, very slow leaks, but even mylar won't contain helium forever."
] |
[
"Yes, there is - a plastic called mylar. It is often aluminized - coated inside with a thin coating of aluminium. It is the stuff that potato crisps packets are made out of, and it is used for those shiny, metallic balloons. And, unless pierced by rough handling, mylar balloons last practically forever."
] |
[
"I'd use hydrogen rather than helium:",
"The best combination would seem to be mylar, as it is less permeable, and hydrogen, as it is less prone to permeate balloons than hydrogen, and more plentiful. But hydrogen is flammable."
] |
[
"In beta decay, how does a neutron turn into a proton, accompanied by an electron and a positron? In addition, why does having extra neutrons make the atom unstable?"
] |
[
false
] |
I have 2 main problems/questions I'm struggling to understand. + Additional Question: What makes the C14 atom go, "Let's change one of our neutron instead of getting rid of 2 neutrons and turning into C12"? To sum it all up, what's a beta decay? Thanks in advance!
|
[
"Why is the positron necessary? Why would you need a positron when charges of proton + electron = neutron ? Is it because of the spin, or something that I need to balance out?",
"To go from a proton to a neutron, electric charge has to be conserved. This can either be done by having an electron in the initial state (electron capture), or by having a positron in the final state (beta",
" decay).",
"Why does the decay happen in the first place?",
"Because it can. A lower-energy state exists, and this decay path allows the nucleus to reach that state without violating any relevant conservation law. ",
"Why is having 2 extra neutrons (in carbon 14) be a such a big deal?",
"Because carbon-12 has the lowest mass of all nuclides with 12 nucleons, but carbon-14 doesn't have the lowest mass of all nuclides with 14 nucleons. So ",
"C is unstable, but ",
"C isn't.",
"Additional Question: What makes the C14 atom go, \"Let's change one of our neutron instead of getting rid of 2 neutrons and turning into C12\"?",
"The two-neutron separation energy for ",
"C is positive, so it takes energy to remove two neutrons. That process can't happen spontaneously."
] |
[
"Beta- decay is a neutron turning to a proton, an electron and an antineutrino. No positron involved.",
"Beta+ decay is a proton turning to a neutron, a positron and a neutrino. This rarely happens naturally as there are not many mechanisms producing proton-rich nuclei.",
"There is also electron capture: electron+proton -> neutron plus neutrino"
] |
[
"Same thing. Charge has to be conserved, so there has to be an electron in the final state or a positron in the initial state. But unlike electrons, there aren't positrons around in normal matter, so there's no \"positron capture\" decay mode, just beta",
" decay."
] |
[
"How much electricity does a cargo ship use on an average day while making a journey?"
] |
[
false
] | null |
[
"The term you are looking for is \"Hotel Load\".",
"The term hotel load is used with respect to ships to describe their non-propulsion energy requirements. It can be thought of as the energy load required to operate all 'non propulsion' systems aboard ship - lights, air conditioning, computers, water purifiers, radios, etc. When a ship is in port, for instance, all of its energy requirements constitute* the hotel load. When a ship is underway, the excess in energy requirements over and above that needed to drive the ship is the hotel load. The term can be used to describe the actual electrical power draw, or to describe the amount of engine plant time and output required to produce that energy from the generators. Ships in port do, of course, have the option of accepting shore power to handle their hotel load and reduce time on their engine components, if sufficient power is available.",
"This is fairly easy to get for ships in port, since they genrally switch to port-based power, which is metered. To get an underway value you need a Chief Engineer."
] |
[
"Got some additional information from the boat owner. We have 2 navigation radars. One is 2 KW, and the other is 20 KW. The 50 KW load is with only the smaller one in operation."
] |
[
"I'm actually asking about electrical use. Navigation systems, lighting for the crew, stuff like that."
] |
[
"Is the human race becoming weaker biologically."
] |
[
false
] | null |
[
"The answer to your question lies in the definition of weak. If being plucked from an urban area an thrown into the wilderness then your theory would hold some water (note that this is hardly original). However, if successfully surviving in the human construct that we call society constitutes being strong then natural selection, albeit in a non-natural environment, should still hold true."
] |
[
"mutations that are beneficial to them and give them a better chance of surviving ",
"Careful, they don't have to give any particular ",
" a better chance of survival. You could for instance have a hypothetical gene that made 10% of the people with it infertile, while it made the other 90% much more fertile. It's not the ",
" survival that matters, but the group.",
"weaker on the biological scale ",
"There's not really any such absolute scale. You can't say one species is all-around 'better' than another. We're adapted to different niches and environments. It's not like evolution has a particular set 'goal'. It can go 'backwards' if you will - for instance, life evolved in the oceans, some animals moved to land, some of them (cetaceans) \"returned\". ",
"Evolution continues - there are still mutations, sexual reproduction, and natural selection. In fact, my understanding is that our genome is diversifying faster than ever now, due to a larger population. If anything we're evolving 'faster'. ",
"It's true that we're not evolving the same way if we'd maintained a hunter-gatherer lifestyle - because we don't need the same things as then. To give an example, there's the fairly recent (and unique to humans) mutation of adult lactose-tolerance. Which is clearly a survival benefit, but only if you've got domesticated animals you can milk.",
"A lot (if not most) serious disabilities aren't genetic. They're birth defects or the results of accidents, etc. Things that evolution can't easily do much about. Sometimes evolution has no 'incentive' to fix them, either - age-related diabetes or cataracts hardly matter, since they mostly occur in people who are past child-bearing age.",
"Purely negative genetic traits easily get weeded out by evolution. So serious genetic illnesses (",
"Sickle-cell disease",
" being the perennial example) typically have positive side-effects for the group that carries the gene. (in that case, malaria resistance) ",
"So whether those afflicted with sickle-cell disease live or die, there's still a reason for the gene to propagate. However, now that we're better at treating and preventing malaria, there's not as much need for it. (Nor was there a need outside malaria-afflicted areas, which is probably why that mutation was originally limited to west Africa) ",
"I don't see how you could say we're either \"stronger\" or \"weaker\" with or without that mutation. It's an adaptation to certain circumstances, which is beneficial in those circumstances, but not otherwise. "
] |
[
"Always thought about the same thing, with evolution and survival of the fittest the weakest of the species die out. So with society even the weakest can propagate forward, does this mean evolution has come to a stand still? "
] |
[
"Are we producing more atmosphere than we lose at this point in time?"
] |
[
false
] |
I guess my question is pretty simple. At this point in time is the planet producing more atmosphere than we are losing to solar wind or are we slowly losing atmosphere? What are some of the factors affecting our atmospheric production or decline? Is our atmosphere undergoing any kind of changing state? As in, more oxygen rich, less oxygen rich? Etc....
|
[
"So, what we know of climatology and the how the Carbon cycle works is inferred knowledge from a bunch of proxies.",
"Starting way back, we knew there was very little oxygen in the atmosphere, due to the presence of Pyrite in very early rocks. When iron is exposed to oxygen, you'll know that it forms rust. No oxygen, no rust. So, the earliest sedimentary rocks we look at were formed by water with very low oxygen content, but which held sulphur, producing FeS2, pyrite crystals.",
"With the emergence of Archaea, the earliest life which consisted of chemotrophs (things that eat chemicals and spit out different ones), not much oxygen was freed, but photosynthetic organisms eventually evolved, and Carbon Dioxide in the oceans started to be converted to usable carbon and free oxygen. As the oxygen levels started to climb in Earth's seas, it quickly bonded to the iron dissolved there, creating insoluble iron oxides that settled out to create Banded Iron Formations (between 2.4 and 1.8 billion years ago (Gya)). These banding events happened in stages as the earth's climate changed, so creating alternating layers of high and low Iron oxide content. Wikipedia's got a lovely article on it.",
"Once all the iron in the sea had been depleted, oxygen started to form a major part of the atmosphere, but Earth's landmases were still oxygen deprived, and so most new generation was now sequestered on land, as the iron and rocks there started to chemically weather. This meant that oxygen levels stayed around 0.8% for a further Billion years, to 0.85 Gya.",
"Eventually, of course, even the landmasses were fully rusted, and this is where oxygen levels really started to increase. Multicellular, Sexual life had evolved in the meantime, and once oxygen was no-longer being used up by chemical processes in Earth's rocks, life really took off.",
"It took a further 300 million years until the cambrian explosion happened 542 Mya, by which stage Oxygen levels were roughly where they are now, but as plants rapidly moved onto and colonised the land, atmospheric CO2 levels took a huge hit and oxygen levels skyrocketed to something like 35% by the end of the carboniferous period.",
"The reason the Carboniferous period is called this is because plants, up to this stage, had evolved to produce lignin, wood, and could now trap Carbon. Thing is, fungus, the primary CO2 regulator, hadn't caught up to using wood as a food source, so for a few million years none of the wood rotted. It just sat there, in swamps, getting buried by new plants growing on top of it. This period is responsible for basically ALL of our coal and natural gas deposits, as it locked up ENORMOUS amounts of carbon below the ground.",
"When fungi got their shit together and started to eat wood, finally, the rest of life started to catch up, since fungi is edible whilst wood isn't, so oxygen levels steadily dropped to where they are today as more and more living things came around to use it, and more and more of the continents were eroded to form new Iron Oxide deposits.",
"The thing is, most of the carbon dioxide buried in the Carboniferous period never made its way deep enough to become part of the Earth's mantle, or to be thrown up again in volcanos, so it's all just sat there, and life on Earth has trundled along without all that carbon in the cycle since then.",
"Levels of Atmospheric CO2 have rose and fell thousands of times since, during periods of glaciation and greenhouse, and we can measure them in fossils, limestone, gas bubbles in ice, stalagmites and stalactites (speleothems), but they've never strayed beyond certain margins, because the amount of carbon in circulation has been roughly constant.",
"Dumping more carbon into the system by burning fossil fuels now threatens that, since there's no guarantee that the current amount of life on Earth will be able to absorb the enormous amount of CO2 we've added, and so the atmosphere is getting more and more CO2 rich each year. We've risen from 320ppm in 1956 to just over 400ppm now, 25% increase in 60 years, and this has tied pretty closely to a steady increase in average global temperature too.",
"This is because the earth loses heat as infra-red radiation, which all objects give off when they're warmer than 0 degrees kelvin, but CO2 is very good at bouncing it back down to earth, where the energy is reabsorbed and heats us up again, like the glass in a greenhouse keeping the heat from escaping (hence \"greenhouse gas\"). The ocean will eventually, over a few hundred thousand years, be able to dissolve a lot of CO2 as H2CO3, carbonic acid, which can be turned into limestone by rock weathering, but by that stage the world will already be extremely hot if fossil fuel use isn't cut down to practically 0% of the level its at now, not to mention having a sea that tastes like sparkling water.",
"So yeah, that's a ",
" TL;DR on how earth's atmosphere has changed over time, how the carbon and oxygen cycle work and why fossil fuel use is potentially pretty bad for us if you like the idea of life still existing on earth's landmasses. Acid rain ain't fun."
] |
[
"We are always slowly losing atmosphere. As you mention, we do have solar wind stripping us, but there is also the spontaneous generation of free hydrogen and helium by radioactive processes to consider. These are usually trapped within rock or liquid, but once freed, the atoms experience buoyant force, and barring the occasional spontaneous reactions of hydrogen with oxygen, nitrogen and other molecules to form compounds in our atmosphere, each attains escape velocity and pops off into space. The earth does not produce any more of the elements present in our atmosphere, excluding some rare radioactive decays creating short-lived heavy noble gases (radon), so we are losing mass and atmosphere faster than we produce it."
] |
[
"And what about massive amounts of gasses from burning fuel?"
] |
[
"What happens to a weak electromagnet if you apply a strong magnetic field opposing it?"
] |
[
false
] |
If you have a massively large neodymium magnet and place it opposite a small electromagnet, would they repel? I've read Which implies that the electrons slow down but reading about drift velocity and propagation of wave speed, none of it implies lowering the overall number of charges/second So here's what I imagine happening: If the permanent magnet is sufficiently strong enough, the magnetic field 'overpowers' the electromagnet's core and realigns the charges with its' pole rather than with the field created by the current. At this point, the core has a magnetic field opposing the current and adds together with the magnetic field of the permanent magnet, subtracting the magnetic field of the current from the entire system? E.g. The solenoid gets attracted to the permanent magnet regardless of direction of the poles, but is slightly weaker than it would be if there's no current flowing through the electromagnet? Is that correct? What would happen if the electromagnet has no core?
|
[
"So i have a bachelors in electrical engineering so I will try to help out.",
"Things I know. The electric field around an electromagnet is proportional to the current at that time. ",
"If you alter that field you induce a voltage that changes the current and if you change the current you change the field strength /polarity. But its the change that induces the voltage so at steady state the voltage and current should be the same as at the start which means field strength will be he same",
"I want to think at steady state both magnets exist. At thier individual polarity but the flux lines in the space between the two would be secerely distorted. "
] |
[
"Magnetic fields are additive. An electromagnet like a solenoid is just a bunch of wires adding their fields. OP was correct in his assessment. It gets significantly more complicated when magnetically permeable materials are involved, but its still generally true that the magnetic fields simply overlap. The stronger field will overpower the other field.",
"In the situation I think you're describing, the magnetic field would have the same polarity at two sides and no opposite polarity, which would violate Gauss' law for magnetism."
] |
[
"I cant draw magnetic field lines in ascii but I was thinking more along the lines of first year physics if you placed two north poles next to each other the field lines dont comnect they repell. So the polarity of the poles remains. The path of the field lines through space are distorted. "
] |
[
"How much extra energy (if any) does it take to do hard mental tasks?"
] |
[
false
] |
Like studying all day, or taking an exam or anything that requires a lot of extra brain power
|
[
"It is very hard to quantify this. During baseline activity the brain uses around 20% of our body's energy supply making it the most energy dependent organ in our body. However, the beauty of it is that it is extremely adaptable. To use an example relevant to your question: if you didnt study a particular topic and then you decide to cram, the first day you will be exhausted after a relatively short period of time and hit a 'ceiling' when learning new information. However, each subsequent day things will be easier to comprehend and you will be able to spend more time doing the task. However, this is not infinte. The brain still needs downtime, especially deep sleep, to consolidate information.\nTl;dr Yes you will need extra energy initially but as your brain adapts to the task the energy demands will return to baseline."
] |
[
"are we talking a spike of a few percent or like an extra 10% total energy consumption?"
] |
[
"We are talking about a spike because higher energy demands are not sustainable. The amount of energy that can be redirected is limited because the body cannot afford to restrict energy usage of vital organs such as the heart, lungs etc. So thats why initally you feel tired. Your brain fulfils the extra energy demand from non-vital parts of your body."
] |
[
"If two radioactive atoms were entangled, would they decay at the exact same time?"
] |
[
false
] | null |
[
"Two particles may be 'entangled' - with respect to ",
". That means that that particular property (e.g. which spin state the particle is in) is correlated between the two particles. You cannot say that 'particles' themselves are entangled, it's really their states. In quantum mechanics, you can completely describe a system in terms of different states (a basis), and something which is entangled in one basis is not necessarily entangled in another. So another way of looking at it, is that the entanglement is a property of the physical description of the system, rather than the system itself.",
"So it's not clear what your question is supposed to mean. Which states are entangled here? Why would they decay simultaneously? Entanglement does not mean two 'entangled' particles suddenly act like each other's clones."
] |
[
"Sorry if I'm misunderstanding, but did you mean to say",
"Entanglement does ",
" mean two 'entangled' particles suddenly act like each other's clones.\n?"
] |
[
"Yes and sorta, respectively. Entanglement is well understood with math, but it's kind of tricky to translate that math into something a non-specialist will understand.",
"Consider this analogy: suppose you shuffle a deck of playing cards, you take 26 of them and your friend takes the other 26 to the Andromeda galaxy. Also suppose you wait a few million years for your friend to arrive, then look at your cards. If you see 11 red cards and 15 black, then your friend will definitely have 11 black and 15 red cards. But does the information that your friend will have 11 black and 15 red cards get instantaneously transmitted across two million light years from you to him? Of course not. And you can't use this to send him a message, either. It's just a statistical correlation which won't become evident until you get back together and compare results.",
"Now, I'm not saying that this is how quantum entanglement works; in reality it's more complex, and you have to know things about wavefunctions to really understand it. But this analogy does help explain ",
" aspect of quantum entanglement, namely why the collapse of an entangled state doesn't involve a transmission of information. (I'm sure someone is going to come along and complain about how the identities of the cards were determined all along, and that is indeed a difference between this analogy and real quantum entanglement, but it doesn't prevent the analogy from being useful for what it does.)"
] |
[
"If humans had wings, what wingspan would be needed for gliding and self-powered flight? Could the human metabolism keep up with the energy demands?"
] |
[
false
] |
I had this discussion with a friend once, but never reached a conclusion. Let's assume a 80kg human without aerodynamic clothing or hairstyle. Let's disregard the fact that the human body has no point where the needed bone structure and muscles could be be attached, although that, too, is an interesting subject (we'd want to keep our arms and hands as they are now don't we?) For mere gliding at a glide ratio of say, 5, what would the needed wingspan be? What about self-powered flight? Could it work? I doubt that the human metabolism is up to the job, and the wingspan for this would have to be even bigger. It seems the biggest specimen to ever achieve this is the , which weighed anything from 20 to 93kg and had a wingspan of 7 meters.
|
[
"I actually have a book that discusses such a thing. It's the Science of Supervillains, specifically the chapter about the Vulture.",
"I'll go get the book and scan you the part.",
"Edit: ",
"Here you go",
". It's actually a very cool book. Fun meshing of science with comic books.",
"TL;DR: ",
"he will need a wing area of approximately 800 square\nfeet to lift him off the ground*",
"Keep in mind the largest bird ever discovered, ",
"Argentavis",
", had a wing area of 75 square feet. A small plane, the ",
"Cessna 150",
", has a wing area of 159.5 square feet. ",
"The human Vulture would look terrifying if he ever glided over you, I imagine. He would blot the sun out for onlookers and probably couldn't navigate too terribly well in a cityscape.",
"Further reading",
"."
] |
[
"TL;DR: Now the numbers get interesting. If the Vulture weighs 90\nkilograms (fully equipped with wings and costume) and is sprinting at\n6 m/s (a record-setting pace, running a kilometer in less than\n2 minutes 30 seconds), ",
". Of course, that assumes he can keep\nmoving at 6 meters per second all the time he is in the air. Which leads\nus to conclude that the Vulture flying under his own power or even\nwith the aid of an electromagnetic booster is impossible. Still, he’s\nnot as outrageous now as he seemed nearly forty years ago.",
"Keep in mind the largest bird ever discovered, ",
"Argentavis",
", had a wing area of 7 square meters. A small plane, the ",
"Cessna 150",
", has a wing area of 14.82 square meters. "
] |
[
"His numbers are out by a factor of 10 compared to what we see in very small hang gliders. You can get a higher lift coefficient, run about 25% faster, and weighing less than 200 pounds helps.",
"I thought his math was wrong but was mistaken."
] |
[
"whats the shortest flash a human can register?"
] |
[
false
] | null |
[
"That post largely addressed a different question, though. A bright enough flash, no matter how short, will still be registered by the human eye because it will temporarily overload the sensors in our eyes, but we won't have a good impression of how long the flash ",
".",
"For example, I have an underwater camera flash that can fire for just 1 ms. Despite that thread you linked to indicating that our eyes can only distinguish temporal gaps down to 2-4 ms, I guarantee you if you look into this flash when it fires you will have the mother of all bright spots etched onto your vision for a few minutes."
] |
[
"[deleted]",
"\n ",
"This comment has been overwritten by ",
"this open source script",
" to protect this user's privacy. The purpose of this script is to help protect users from doxing, stalking, and harassment. It also helps prevent mods from profiling and censoring. ",
"If you would like to protect yourself, add the Chrome extension ",
"TamperMonkey",
", or the Firefox extension ",
"GreaseMonkey",
" and click Install This Script on ",
"the script",
" page. Then to delete your comments, simply click on your username on Reddit, go to the comments tab, scroll down as far as possible (hint: use ",
"RES",
"), and hit the new OVERWRITE button at the top."
] |
[
"This post already has some nice info!",
"https://www.reddit.com/r/askscience/comments/1vy3qe/how_many_frames_per_second_can_the_eye_see/"
] |
[
"Why Titan has atmosphere and other, larger moons don't?"
] |
[
false
] |
Larger celestial bodies have more gravity with which they can obtain and keep an atmosphere. Titan is not the biggest moon in our Solar System, why Ganymede, which is larger, does not have atmosphere?
|
[
"Larger moons? The only one larger is Ganymede and there is evidence of a thin atmosphere on Ganymede. Not to mention Titan is a million km from Saturn, while Ganymede is a million km from Jupiter. Being near Jupiter is probably a really bad place to be when collecting material from the gas cloud that the solar system formed from.",
"Take a look at the ",
"relative masses of objects in the Solar System",
" and be amazed. Looking in from outside there are only two things here: the Sun and Jupiter. With maybe hints of a third object: Saturn."
] |
[
"According to ",
"this",
" article, other factors besides size allow a body to retain an atmosphere. Titan has volcanic activity from Saturn's tidal forces. This is a continuous source of CO2, water vapor, nitrogen gas, and methane into the atmosphere. Titan's extreme cold ensures that much of these gas particles do not have enough energy to escape its relatively small gravity. "
] |
[
"As an atmospheres guy, jumping on board this comment to say the first explanation is far, far more likely. Daytime temperatures on Ganymede get up to around 160K, while Titan maintains an even 90K. That means it's much easier for gas molecules on Ganymede to gain escape velocity."
] |
[
"If blue eyes are recessive, how come the mutation can be traced back to one ancestor?"
] |
[
false
] |
Does this mean it was only possible through incest? -sorry if this question has been asked before, i looked. and follow up question: if that mutation randomly occured, then isn't it possible that a person could also randomly have a mutation develop w/o being a carrier?
|
[
"We're all rather inbred. Humanity has a relatively low amount of genetic diversity compared to other species, from what I recall.",
"And yes, it's possible that the same mutation could arise indepently multiple times. But I believe it's incredibly unlikely given the sheer number of locations in the genetic code where a fairly random mutation might take place."
] |
[
"One published study claims that ",
"one mutation is responsible for blue eyes in all humans",
".",
"A carrier is someone whose genome contains one copy of a recessive allele, and thus does not show the outward signs of the trait that would be displayed by someone with two copies of that recessive allele, because they carry another allele whose functioning masks the recessive allele. The first person in which the mutation for blue eyes occurred would absolutely have been a carrier, because it is incredibly difficult and unusual to have two copies of a gene from one parent. Then some generations later, some child whose mother and father can both trace some lineage back to that one ancestor would be born the first human to show blue eyes.",
"Incest is a legal term, for sexual relations between individuals too closely inbred to be legally allowed to marry. However, everyone is somewhat inbred, and it doesn't require incest as it is defined legally in most of the world today. ",
"You can prove it mathematically. For each generation you trace back your ancestors, you will double the number of ancestors you find. So if you go back ",
" generations, you will have 2^",
" ancestors.",
"If you assume 20 years per generation (30 for those after 1900), you only have to go back 29 generations, to about 1400, to find a point in time where one has more ancestors than the population of earth. ",
"However, because of limited mobility in different times and places, most people who have ever been born had a much more limited pool of likely ancestors, meaning it would take far fewer generations before the probability of tracing two lineages back to one ancestor (i.e. inbreeding) because more likely than not. "
] |
[
"It depends on what you take to be incest. If you mean something like reproducing with your parents, siblings, or even first cousins, no, it's not a necessity. As you know, the gene is recessive. All humanity is inbred to some extent, especially if you trace your ethnicity to outside of Africa. If we had the knowledge and records, most people would be able to find a common ancestor with their SO.",
"The gene is recessive, so it can carry on, despite not manifesting itself outwardly. To use the simplified model taught in grade school, people will keep on carrying the Bb (Brown dominant/blue recessive) gene through 50% of their children, assuming reproduction with a BB person (Brown/brown). Those children will keep passing it on themselves. Eventually, maybe even 10 generations or more later, a Bb person will reproduce with another Bb person, and a blue eyed child is born. On a genetic level, what they did does not count as incest, even if they can trace a common ancestor back. For example, the risk of genetically diseased children with a second cousin is almost nonexistent, so you have no real worry if you're \"inbreeding\" many generations later.",
"And yes, it would be possible for a person to independently develop blue eyes. Blue eyes are not actually a \"color\", so to speak. It is the lack of melanin in the eye. If you have a mutation that turns off the switch to produce that melanin, you will have blue eyes. That's how surgery exists to turn one's eyes blue - they burn out the melanin (and the procedure is permanent). If it did appear, blue eyes are already a normal enough trait, so people may not even notice it when it spontaneously appears. They may assume they had the recessive genes for it, or a husband may assume the wife was unfaithful."
] |
[
"What's up with this study on fluoride?"
] |
[
false
] |
Some new review study about fluoride was published recently. It must be getting promoted on alternative health websites, because I've got some friends and family asking me for my opinion on it. (The abstract on Pubmed is here: ) Apparently, this study concludes that fluoride causes "significant damage to health and particularly to the nervous system", and that nobody should use fluoridated water or even toothpaste. That sounds like a rather loony overreaction to me, but I can't access the full text in English to see exactly what amounts of fluoride they're talking about. What does current research say about fluoride? Is there really growing opinion that it's dangerous, or is that just the conspiracy theorists gaining traction?
|
[
"Don't know about the current research on the subject but: \n- Journal with impact factor of 0.6 \n- Articles are not even in English\n- English abstract badly written",
"These are just hints -nothing would prevent an article with these features to be excellent- but I wouldn't give it too much credit at face value."
] |
[
"The full text is available but it's in Spanish and I can't get Google to translate it well. ",
"I'm just going to put this out there. The citations on this article are almost all from Chinese journals. I am ",
" saying that China doesn't do good research, however the way their publishing works makes a large amount of publications unreliable. Many institutions require a certain amount of publishing by their staff and it is pretty difficult to meet the standards they set. I'm not explaining this well unfortunately. I hope someone else can explain this well. ",
"In my opinion, until this information gets confirmed by a larger journal, I'd chalk it up as a little bit of hysteria. This is only my opinion and it is possible someone will come along and disagree, which is cool, especially if they can clarify the whole Chinese publishing situation."
] |
[
"I am not saying that China doesn't do good research, however the way their publishing works makes a large amount of publications unreliable. ",
"I am saying that ",
", China doesn't do good research. That means: They surely have excellent people and institutes, and Chinese students in the West tend to be exceptionally bright. Yet unfortunately all of that is swamped by a truckload of stuff that calling \"sloppy\" would be a compliment. I had the luck of being involved in the peer review of papers from China. Most of them were not even wrong: they were ",
".",
"This is unfortunate and I don't know why it is still that, but it's no secret."
] |
[
"Could an astronaut be rescued if they ever became detached from his/her spacecraft?"
] |
[
false
] |
After viewing this image it made me think what would happen if there was a mishap and for whatever reason an astronaut was lost in space. Could a rescue mission be launched and would the astronaut just sink back towards earth and die during re entry or would they just float endlessly?
|
[
"Check out this thread:\n",
"http://www.reddit.com/r/askscience/comments/m3ld5/what_are_if_any_the_established_methods_to/"
] |
[
"No, instead they have a smaller version called ",
"SAFER"
] |
[
"Same force, not speed. Since the magnet is many magnitudes less massive than the astronaut + equipment, the speed would be very different."
] |
[
"Would two extremely smooth pieces of metal stick together?"
] |
[
false
] |
I learned about metallic bonds in school a few years ago, and when I asked my teacher why two pieces of metal don't stick to each other when you hold them together, he didn't really have an answer. My hypothesis was that the surfaces might be too rough for the metallic bonds to be strong enough.
|
[
"So... Two flat, smooth pieces of gold (say, Avogadro-project-grade smooth) would indeed stick together?"
] |
[
"So... Two flat, smooth pieces of gold (say, Avogadro-project-grade smooth) would indeed stick together?"
] |
[
"That's awesome. Thanks for answering and sharing. I don't know if I'm allowed to thank people in ",
"/r/askscience",
" though, so I apologize if I'm not."
] |
[
"Why do hoarders hoard?"
] |
[
false
] | null |
[
"Asking people to take a survey is not absolutely appropriate on AskScience. We don't even allow posts that solicit opinions from people. We require answers to be supported by peer-reviewed research. "
] |
[
"Does this mean I can't post this? Even though it is based on empirical and theoretical research, and I am conducting empirical research that is aimed to be eventually published in a peer-reviewed journal? Could you please help me to understand how to adapt my post so that it is suitable for AskScience? Thank you :)"
] |
[
"No. We are not here to do original research for you, and you cannot post links to surveys.",
"Also, if all you do is ",
"spam this site with the same link",
", this admins of reddit will ban your account. The purpose of this site is to have users who contribute content to the community, not just mine it for data."
] |
[
"Why do animals have mating seasons, and why don’t humans?"
] |
[
false
] |
[deleted]
|
[
"Because you don't want to have a child in October and raise it through the winter when there's less food.",
"Since humans spend 18 years as a dependant it doesn't matter what time of year u have them as they are going to see a winter as an infant"
] |
[
"A proximal, mechanistic answer: because many wild animals are seasonally polyestrus, meaning they are only fertile several times in a particular season. This is controlled by hormones from the central nervous system acting within the central nervous system and on the gonads and uterus. These hormones are primarily induced by changing levels of light - eg through melatonin cycling. In animals who are nursing offspring, fertility may be repressed until the offspring slows or stops nursing. ",
"Some animals, like dogs and cats, are only fertile once or twice a year, but it's not necessarily seasonal. Others like cattle cycle continuously just like humans. Some larger mammals like elephants and rhinos may not cycle more than once every few years. "
] |
[
"It's also worth nothing that chimps and bonobos also don't have a breeding season, so it's not unique to humans."
] |
[
"I was microwaving some water, and it exploded all over the inside of the microwave with a loud \"pop\". What happened?"
] |
[
false
] |
The mug was about half full, and I had heated it up about half an hour earlier but left it in the microwave for too long, so I ran it for another minute and walked into the other room. At about 45 seconds I heard a loud pop, and when I went back to check it out I found water all over the inside of the microwave and hardly any left in the cup. What happened?
|
[
"Superheating happened.",
"Water normally boils at 100",
" C or 212",
" F, but that is only if there is a nucleation site for the first bubbles to form. A nucleation site can be a defect in the vessel (your mug in this case) or contaminates in the water. If you had relatively clean water, and a nice smooth mug, it's possible to heat up your water well above the boiling point. Some substances superheat easier than others.",
"Once a ",
" bubble forms, the surface tension of the water might be enough to hold that bubble in place and not let it grow too much. The temperature has to increase a bit above the regular boiling point for the bubble to keep expanding. When the bubbles grows a little bit, the surface tension decreases and then the bubble grows ",
" which causes that loud pop you heard.",
"Here is the wiki article",
"."
] |
[
"way too many"
] |
[
"Like others said, it's superheating. I got burned that way once, not fun. ",
"For the cooler (heh) and less dangerous flipside to it, try supercooling.",
"Take a sealed bottle of distilled water (not spring water; distilled water) and put it in the freezer. Place a roughly equal volume of tap water next to it (this is just to get the timing right). ",
"After 2-3 hours, check both. By then, the tap water should be frozen and the bottled water still water (you have to catch it at the right time; let it go too long and the distilled water may freeze, too). CAREFULLY remove the bottled water.",
"Now you can make it instantly snap to ice by:",
"1) Tapping the bottle sharply against a table\n2) opening the bottle\n3) Or the coolest one (if done just right): Set an ice cube on a table and pour the water directly onto the ice cube; the water will freeze up the stream and into the bottle. This one is hard to get right sometimes; it may take a few tries."
] |
[
"How did the underwater internet cables get there?"
] |
[
false
] |
[deleted]
|
[
"These underwater cables are deployed by boat. It essentially involves outfitting a ship with a large cable reel and sailing from one coast to the other while deploying the cable. The cable is dense enough to sink to the bottom.",
"More interesting is the process to repair such cables. Because defects happen from time to time and they need to be fixed. By measuring reflections in the signal emitted from the shore, it's possible to determine the location of a defect and a ship is sent out to that spot. The ship will use a long grapple to fish up the cable and the repair is done on board the ship. If the cable is relatively heavy, the ship will first deploy an instrument to cut the cable two pieces and then fish up each piece. Repair and reconnection are done on board. Finally, the repaired cable is lowered back into the ocean."
] |
[
"No one's swimming to the bottom, Specialty ",
"Cable Laying Ships",
" are used to roll out cables across expanses of water, including all the major oceans."
] |
[
"Repairing a cable is actually far more complex than that (and more interesting). I know you were trying to keep things simple, but I actually find it quite interesting.",
"Because of the way that the cables are laid, there's not enough slack to haul the cable to the surface. Instead, the cable repair ship drags a grapple along the sea floor until it snags the cable. They then send down a device which chops the cable. On one end, they tie off a buoy so that they can retrieve it towards the end of the process, and on the other they attach a haul line, and haul the end to the surface.",
"As they haul the cable to the surface, they have to sail along the line of the cable, ensuring that they don't pull too hard on it, and add additional strain or breaks to the cable. They basically have to control the droop and tension on the cable very closely. ",
"Once they get the cable end on deck, they then ensure they're on the correct end of the break. If not, they'll keep hauling the cable, checking until they find the broken section. Once they've isolated the break, they'll splice on a new section of cable (probably several miles long, and then play the cable out in a large U shape while they sail back to the other end.",
"They then haul the other end on deck, splice on the other end of the new section, test to make sure everything is good, before gently laying the whole thing down on the sea floor so that the cable lays in a large U shape away from its original path."
] |
[
"Can multiple optical telescopes be used in the same way as radio telescopes like the Very Large Array?"
] |
[
false
] |
Someone mentioned in a different thread that no (presumably optical) telescope can resolve either Voyager spacecraft any more, which got me wondering how large a lens would have to be to do so, and whether multiple, widely separated optical telescopes can be used to increase the effective resolution of the array, which is my understanding of how radio telescope arrays like the VLA work.
|
[
"Yes, it can be done.",
"Read ",
"this",
" from 2002 about a 6 optical telescope array and a little of what was involved in getting it working.",
"You can also find a list of ",
"optical and infrared interferometers",
" on Wikipedia, with a guide to the wavelengths ",
"here",
"."
] |
[
"The twin 10 meter ",
"Keck telescopes",
" in Hawaii can be operated as a single astronomical interferometer. They are about 40 meters apart.",
"Unlike with radio telescopes, optical technology is not yet able to do this over large distances. The wavelength of light is much shorter than radio wavelengths."
] |
[
"So for an optical interferometer to resolve voyager 1 at it's current position you would need it to be 1000 km across. A telescope would have to roughly double that size because interferometers do a bit better.",
"A second issue will be just how dim it is. Because all it's visible light is reflected from the Sun an absolutely tiny amount makes it all the way back from what little was reflected from the much dimmer sunlight. By my rough calculations to see just one photon per second from it you would need a telescope 43 km across. You really aren't going to see it.",
"So even if you use an interferometer you still need enormous telescopes. One of the major issues with optical interferometers is their terrible brightness limit. State of the art facilities are only now moving to objects just too dim for the naked eye.",
"Both of these calculations assumed 125.5 AU and voyager as a 3m disk."
] |
[
"Since newer cars have the general shape of an airplane wing (the profile of it), do they get lift when traveling freeway speeds (65-70) and does it affect gas mileage?"
] |
[
false
] | null |
[
"Traction doesn't impact gas milage, it impacts your control in corners but as long as the wheels don't slip nothing has changed, you have ",
" friction to continue on your way and you will never know.",
"Spoilers, like the wings on an F1 car, increase the weight of the car, but not the mass, so it gives you better traction but doesn't cost you more fuel to move. If the car served as a wing on the highway it would do the reverse, less traction but also no more fuel to move since inertia has remained the same."
] |
[
"Traction doesn't impact gas milage, it impacts your control in corners but as long as the wheels don't slip nothing has changed, you have ",
" friction to continue on your way and you will never know.",
"Spoilers, like the wings on an F1 car, increase the weight of the car, but not the mass, so it gives you better traction but doesn't cost you more fuel to move. If the car served as a wing on the highway it would do the reverse, less traction but also no more fuel to move since inertia has remained the same."
] |
[
"Road friction will slightly impact fuel consumption but its mainly because of the deformation of the tire. Softer road surfaces will also tend to create more resistance.",
"Also, spoilers do increase fuel consumption because they create drag, which is the main factor at higher speeds, more than mass."
] |
[
"Is there an understanding of how likely cooked foods that have \"gone bad\" are to contain harmful bacteria or toxins?"
] |
[
false
] |
I understand the answer may depend on many things such as the type of food (for example I am aware that heat resistant spores can be present in rice that multiply only after the rice is cooked), or whether it is in an oxygen-free environment, and so on. But generally speaking, or for specific food types, how likely is it that food which has been fully cooked, but allowed to "go bad" through age or lack of refrigeration, contains bacteria or toxins that are actually harmful? From anecdotes and experience, such as accidentally eating or trying moldy bread or milk, it is rare to actually get sick from consuming spoiled food. In fact, there are some people, I am told, who actually seek out and enjoy spoiled foods, including meat, without getting sick. Presumably most of the fungal or bacterial growth comes from very common, fairly benign kinds of fungus/bacteria, which get into the food via the air after the food is cooked, and begin to grow. Is it understood how common, and under what conditions, such benign bacteria will "loose out" to more harmful kinds of bacteria? Presumably all of this should be very easy to study scientifically, if a researcher were so inclined. Has this been done? Is there a reference cataloging the results for various types of food?
|
[
"Unfortunately the USDA's guide is too vague to satisfy my curiosity. It is possible that my question is too broad, but I would be curious if there is any quantitative information for even just one kind of food, such as milk or bread. For example: fungi {X1,X2,X3} is present above harmful threshold {Y1,Y2,Y3} in {Z1,Z2,Z3}% of bread when mold just becomes visible to the naked eye."
] |
[
"The USDA has a reasonable ",
"guide",
" that lists what do trust/not trust when it shows spoilage. The general consense appears to be that anything with higher moisture content and no hard surface should be discarded as toxins will have penetrated the food. ",
"They don't list sources, but I'm fairly sure the USDA should be reliable.",
"Every individual has a different risk in exposure to toxins or molds due to the risk of a severe allergy to the toxins it can produce, This is usually why a blanket 'do not eat' is issued.",
"In terms of whether or not beneficial bacteria are present, I'm certain they are, and it's likely that most mould and bacterial growth won't be deadly to an average person but I can't think of any way that this could be ethically studied."
] |
[
"Yes, I am aware that you didn't say it, I just wanted to point it out. However, penicillin is not a bacterium. It's a mould."
] |
[
"[Biology] Do trees and other plants, like animals, slowly lose the ability to heal quickly as they age?"
] |
[
false
] | null |
[
"Animals mostly lose their regenerative capabilities once their reproductive success rate is significantly dropped. This is because, there is very little selective pressure on genes required for longevity and tissue regeneration after an animal can no longer reproduce and pass on genes. In other words, you might have a perfect set of genes that allow tissue generation and longevity but if those genes cannot grant you reproductive successes, they won't be selected.",
"Unlike animals trees do not become less successful in reproduction with age. Actually an older tree is larger and can produce far more offspring. So genes required for tissue regeneration and longevity are selected for those. This is why many trees can live for thousands of years. Yet again mutation accumulate on DNA with time. This eventually wears them down. As a result they are not immortal. But evolution granted them with very long lifespans.",
"Edit1;According to the comments I wanted to point out that reproductive success does not only depend on the fertility or the ability to find and compete for mates, it is very strongly correlated to general survivability. For instance life span of rats in wild is about 1 year, as a pet rats can live up to 2-3 years and they are fertile and capable of reproducing during that period. Rats in wild have so short lifespans because they have many predators. So a rat is not likely to live much more than a year in wild due to predation even if it's genes would grant it 10 years lifespan. Since rats rarely live beyond a year in wild, they can only reproduce during that period. As a result, only the genes essential for survivability for the first few years are selected by evolution. Now even when we keep rats as pets, they can only go for 2-3 years at max because they lack the mechanisms that allow longevity."
] |
[
"Not necessarily, the pressure is for successful reproduction. So more effective cycles, cycles when there is less (or no) competition, longer cycles and more are all selected for. Whatever is actually most successful in the environment in which the individual finds itself in is what's most selected for."
] |
[
"Thank you!"
] |
[
"Is there any evidence that listening to something while you sleep will help you memorize/learn it?"
] |
[
false
] | null |
[
"In general, ",
"recall of material presented during sleep is very poor",
". People can retain some information if they are in a very light stage of sleep -- see ",
"this study",
" that linked EEG alpha activity to recall, for instance -- but not if they are deeply asleep.",
"However... there are two recent studies that might interest you:",
"Evidence that memory consolidation can be cued by sounds presented during sleep that were previously associated with those memories",
"Evidence that sounds (pink noise in this case) presented at just the right time in the slow-wave sleep wave can enhance slow waves and memory consolidation"
] |
[
"Went off what I learned in cog sci/psychology classes however I'll oblige:",
"The sleep boundary is fluid, my assumption that information gleaned in \"phase 1\" sleep (which people often assume is being \"awake\" but falling asleep) could be retained is based off studies that information learned just before sleep is retained better than information learned earlier in the day:",
"http://www.ncbi.nlm.nih.gov/pubmed/25515103",
"Recall is affected by pre-sleep information. Or, as the title says, \"Targeted Memory Reactivation during Sleep Depends on Prior Learning\"",
"Assuming you're not going to put on a tape and then instantaneously fall asleep my assumption about \"not being in Phase 2/REM\" (so \"pre-sleep\") is valid.",
"http://www.ncbi.nlm.nih.gov/pubmed/25429129",
"This presumes those motor sequences are learned outside of sleep, obviously. ",
"SOME associations can be made during sleep. I wasn't saying learning during sleep is entirely impossible. Just the idea that if you go to sleep listening to a french tape you won't wake up knowing french (in regard to how the question was phrased)",
"http://www.nature.com/neuro/journal/v15/n10/full/nn.3193.html",
"This suggests you are able to be conditioned during sleep however the authors explicitly point out that more complex learning (ex. learning a new language or a new skill) has not been shown during sleep. "
] |
[
"In regards to the question posed I think the lack of evidence that you can put on a tape and \"learn/memorize it\" while you sleep is proof enough.",
"There aren't a lot of studies published that say \"you can't learn something while you're in deep sleep for obvious reasons- the same reason why you don't see studies that say the sky is blue. ",
"The fact you can't find studies that say you learn from audio tapes during sleep should be proof enough that people have tried and there is no empirical evidence that it works. ",
"I was trying to answer the man's question, simple as that.",
"Cheers"
] |
[
"This question about gravity has been bugging me for a long time."
] |
[
false
] |
[deleted]
|
[
"We orbit around where the sun is ",
". More precisely, we orbit around where the sun's momentum 8 minutes ago predicted it would be now.",
"Change in gravity does take time to spread, but it doesn't change due to velocity.",
"See: ",
"http://www.reddit.com/r/askscience/comments/knlzm/do_we_orbit_the_sun_where_it_is_right_now_or/c2lp6ge"
] |
[
"In general relativity, the speed of gravitational waves is the same as the speed of light. See ",
"the Wikipedia article",
" for more info. ",
"Note that gravitons have never been observed nor is there a complete theory describing them."
] |
[
"Gravitational radiation consistent with general relativity has been inferred from the change in the orbital period of binary pulsars. The 1993 Nobel Prize in Physics was awarded for this discovery. Gravitons, on the other hand, don't even have a consistent theoretical framework to describe them, much less experimental verification of any type.",
"Regardless of what you want those terms to mean, they do have different meanings to the physics community. ",
"'Gravitational radiation' refers to continuous, propagating disturbances in space-time, usually in the context of a weak-field approximation within the framework of general relativity.",
"'Graviton' is used to describe a quanta of an as-of-yet-discovered quantum field theoretical model of gravity. It's not just that the particle is conjectural, the existence of a ",
" that could conjecture them is conjectural."
] |
[
"Can it be possible for a nearby star to be billions of years older or younger than our sun?"
] |
[
false
] |
Or does their relatively close proximity insinuate that their ages are also similar? Thanks askscience!
|
[
"Yeah, it's possible - the population of stars \"mixes\" fairly quickly (100s of millions of years), so a star that was born billions of years before or after our sun could totally be in the neighbourhood. We could also at some distant time in the future just happen to pass by a globular cluster or something, which are all made of real old stars."
] |
[
"Right. It should be added that it's not possible for a star much more massive than the sun to be much older than the sun. It would have already become a white dwarf or gone supernova."
] |
[
"In addition to what Astrokiwi says, it's totally possible that stars formed from the same cloud could be quite different in age and so, as well as an unrelated, differently aged, star just happening to be close by, it's feasible that a sibling star to the Sun could be very different in age. Their ages could certainly be different by millions of years and I could probably even go as far as 1 billion at a push, maybe, not billions plural though."
] |
[
"During the halogenation of propane with Chlorine, we can get two possibilities, Chloropropane and 2 - Chloropropane. How do we know which one will occur ?"
] |
[
false
] |
[deleted]
|
[
"Your reasoning is incorrect. You have forgotten to take into account the reactivities towards primary hydrogen abstraction versus secondary hydrogen abstraction. For chlorine, the rate for secondary abstraction is 3.8 times faster. For this reason you get ~55% 2-chloropropane versus ~45% chloropropane.",
"If you extend to a more selective radical, such as Bromine, you will see major differences. As an example, take bromination of propane. You will obtain ~97% 2-bromopropane.",
"As a summary, it's not only a function of number of available hydrogens, but also a function of selectivity of the radical species.",
"Source: The chemistry of Radical Polymerization by Moad and Solomon, Second Edition, Elsevier, 2006.",
"Edit: The other posters are incorrect. They are referring to stabilities upon addition to unsaturated alkanes. The rules for radical \"addition\" for saturated compounds are rate dependent upon primary, secondary, tertiary hydrogen abstractions."
] |
[
"Radical stability describes thermodynamics, not kinetics. ",
"Kinetically, the primary hydrogens are more accessible (albeit only slightly), but the secondary radical is preferred thermodynamically, so hydrogen abstraction occurs preferentially at this position. Refer to ",
"/u/grapeNerds",
" post for specific data."
] |
[
"As far as I'm aware, this proceeds via a radical mechanism, so you need to have an unpaired electron on one carbon at some point. This intermediate species would be more stable on the central carbon, so kinetically substitution on the middle carbon is preferred. "
] |
[
"Do animals resort to incest?"
] |
[
false
] | null |
[
"As someone who has kept dogs over a number of generations, I can say that if the bitch is in heat, every male dog around will try and get at her, regardless of whether its his mother, sister, or daughter.",
"Disclaimer: I do not have a PHD, nor have I ever done experiments involving hundreds of animals on the subject. I have however observed canine mating habits from a rather early age simply due to having kept a full sized dog team."
] |
[
"Incest avoidance is commonplace in animals that live in families, such as wolves, lions, elephants, rodents, insects, etc."
] |
[
"Paraphrased from an old Nature article...",
"If we define incest as parent-child or brother-sister this accounts for less than 2% of observed sexual activity amongst birds and mammals.",
"I have no idea what you mean by \"resort to\" as it seems you are asking about some undefined situation."
] |
[
"How hard do your testicles need to be punched to render you infertile? I look at Steve-O from Jackass and have to imagine he cannot produce valid sperm."
] |
[
false
] | null |
[
"I hope you didn't rotate on Urology, because you clearly need to read further about the vasculature of the testes. ",
"This is my new all-purpose put-down."
] |
[
"I hope you didn't rotate on Urology, because you clearly need to read further about the vasculature of the testes. The testes have redundancy of blood supply. You can easily take out the gonadal artery and the testis survives on blood flow from the cremasteric and vasal arteries."
] |
[
"In order to answer you properly, you would really need to clarify your question. Infertility is a clinical disorder resulting from a broad spectrum of etiologies. It's such a wide ranging area that there is an American Urologic Association certified subspecialty with fellowship training.",
"Your question suggests that you are asking if it is possible to render a man ",
"azoospermic",
" by testicular trauma. To my knowledge, this is impossible, at least discounting disrupting the vas deferens, which has been mentioned several times elsewhere in this thread.",
"Most causes of productive azoospermia are congenital or endocrine in nature."
] |
[
"If photons travel at the speed of light, does that mean that time stands still from their POV?"
] |
[
false
] |
I know it's slightly meaningless to talk about the point of view of a photon, but if we were to make the ridiculous assumption that a proton is a conscious being... from their point of view, would they not experience all of time as a single "moment"? EDIT: I clearly meant photon. :P
|
[
"From a photon's perspective they travel 0.0 distance in 0.0 time. Length forward and behind is perfectly contracted to nothing and takes no time to traverse.",
"edit: Why are people downvoting her replies? They're not egregious errors of ",
" decorum, just amazement at some of the facts of Special Relativity. Let people think it's cool. It's cool to me."
] |
[
"I input that exact number into the formula and time goes 15 orders of magnitude faster, and distances are 15 orders of magnitude shorter. To put this into perspective, approximately ",
" would pass to the rest of the universe while 1 ",
" passes for you. And a light year would be approximately 10 meters in front of you.",
"edit: for clarity: don't divide the distance above by the time to get velocity, that doesn't really make any sense. I just picked some nice round numbers for each measurement."
] |
[
"So a photon is essentially static in time/space (from its own point of view)?",
"W.... T.... F."
] |
[
"How many counts per second is too many?"
] |
[
false
] | null |
[
"There's a lot of additional information necessary to answer this. If you were working around dangerous amounts of radioactivity, you would probably be trained on it."
] |
[
"Didn't get the training but only a warning not to spend to long around the marked boxes as they can be unsafe normally these boxes are kept in a hot shack but the area I am currently at is no longer occupied. what other info would i need ?"
] |
[
"You want to convert the count rate into a dose equivalent rate for it to really tell you how dangerous it is."
] |
[
"Why does temperature affect the appeal of food?"
] |
[
false
] |
[deleted]
|
[
"Temperature increases volatility, and taste is roughly 75% olfactory. On top of that it affects texture and color, which also play a role in flavor. Taste in foods with a temperature higher than 86 degrees F or lower than 68 degrees also becomes more difficult to distinguish- Hot coffees taste less bitter whereas slightly melted ice cream tastes sweeter. Other variables include time of day it was eaten, age, gender and degree of hunger of the taster."
] |
[
"Among many other factors, temperature affects the mouthfeel of fatty foods--lipids start to become waxy-feeling and hardened as a hot meat dish cools down, which is why things like stews and barbeque generally are served hot. Connective tissue/gelatin/etc. also starts to solidify as they cool, making even slow-cooked meat feel hard and tough again."
] |
[
"Hunger really affects it? I always said it as a joke \"hunger is the best seasoning\" had no idea it had science behind"
] |
[
"How come estrogen and progesterone protect women from heart attacks? What’s the connection?"
] |
[
false
] | null |
[
"A heart attack occurs when there is a blood clot inside the heart arteries. Usually, the blood clot is caused by a plaque that ruptured.",
"Estrogen increases the risk of blood clots. For example, ",
"birth control pills",
" (which contain estrogen) doubles the risk of heart attacks.",
"There is actually a good reason behind this. Estrogen increases during pregnancy, and it causes blood clots to prevent post-partum bleeding."
] |
[
"its weird how i never read about these and birth control pills. unquestionably it is very common in men but its deadlier for women maybe because of this? i really don’t know and understand why i have always seen the opposite and positive affect. btw are you saying the more you get pregnant more the chances of having a heart attack?"
] |
[
"Yes, that seems to be the case.",
"Although acute myocardial infarction is a rare event in women of reproductive age, pregnancy increases the risk 3- to 4-fold.",
"https://pubmed.ncbi.nlm.nih.gov/16534011/"
] |
[
"why does chicken pox and shingles cause different symptoms when they’re the same virus?"
] |
[
false
] | null |
[
"It's more the route of activation for the virus. During the first exposure of the Vzv(varicella-zoster virus) which is contracted through breathing or contact with the rash. The infection begins at the upper respiratory tract where it incubates for about 2 weeks before it enters the lung, travels to the blood stream and migrates to the skin to cause the rash of chicken pox. ",
"In contrast for shingles, after the first bout of chicken pox, some of the virus particles settle into nerve cells (neurons) of sensory ganglia (a group of nerve cells that connect the sensory periphery and central nervous system), where they remain for many years in an inactive, hidden (latent) form. The neurons in the sensory ganglia have nerve fibers that supply the skin and relay information to the brain about what the body is sensing—heat, cold, touch, pain. ",
"When the VZV reactivates, it spreads down the long nerve fibers (axons) that extend from the sensory cell bodies to the skin. As the virus multiplies, the telltale rash erupts. With shingles, the nervous system is more deeply involved than it was during the bout with chickenpox, and the symptoms are often more complex and severe"
] |
[
"chicken pox is the acute phase of initial vzv infection. shingles is reactivating a prior vzv infection that has laid dormant in the nerve root. the symptoms are different because it’s attacking the body in different ways at different phases in the “life cycle” of the virus. (airquotes cuz virus arent really alive per se)"
] |
[
"You shouldn't get shingles if your immunity is through a vaccine. This is why chicken pox parties are idiotic. Just give your kid the shot, otherwise they'll need the shingles shot later anyway."
] |
[
"If the Earth were in its nearest sustainable orbit around Jupiter, how big would the red giant look in the night sky?"
] |
[
false
] |
I've seen many posts regarding how big Jupiter would appear if it were the same distance away as the moon, but the consensus was that the Earth would be destroyed at such a distance, which then implanted this question into my head. Also, I would appreciate other details about the orbit, like average distance around Jupiter's surface, time required to complete one full orbit, and anything else deemed interesting.
|
[
"Let's say the earth is orbiting Jupiter at a distance of 750,000 km, any closer and the earth would be destroyed by tidal forces.",
"At this distance, Jupiter would have a size of 5.3° or about 11 times the Moon. The Earth's orbital period would be 4 days, 3 hours and 52 minutes."
] |
[
"Any idea what kinds of radiation we'd be subject to on the surface of the Earth?"
] |
[
"I think that the earth's magnetic field and atmosphere would shield us from almost all of it."
] |
[
"Does sanitizing less often, eating \"dirty\" things, playing in trash, etc. really boost the immune system?"
] |
[
false
] | null |
[
"Yes... and No.",
"...",
"The literature is very mixed. I will briefly describe the two sides in the field, as I know it to be. ",
"...",
"There are some sources that say yes: Eat Dirt! and in fine print \"only when you are young.\" There are others that say it has a completely different cause. ",
"...",
"The hygiene hypothesis states that eating dirt stimulates the adaptive and innate immune system to respond correctly to environmental pathogens. In a clean environment with no good targets, NK cells go rogue and kill healthy human cells, thus causing auto-immunity. B cells cells can also go rogue by responding to self or non-pathogens (allergies). An over-simplification of their argument would be the following: To make a machine work well, you have to use it. If you let your car sit around for 15 years, would you still expect it to run? ",
"...",
"There are several supporting articles. This is one:\nT. Olszak et al., “Microbial exposure during early life has persistent effects on natural killer T cell function,” Science, doi:10.1126/science.1219328, 2012.",
"...",
"However, there are skeptics of this. They argue that the immune system doesn't work that way. In childhood one is exposed to various pathogens. Those pathogens trigger a response from the adaptive immune system which sends out the army to kill them. In addition, it keeps some memory B and T cells. The next time there is an infection, there is a quick response. If there are no possible pathogens, the B and T cells eventually die. New B and T cells, with different active sites are created. This turnover in cells active sites increases the risk of self-reactive or non-pathogenic reactive (in the hygiene hypothesis). Except it shouldn't, in theory. There are many checkpoints in maturation/differentiation to stop self-reacting immune cells. The second camp believes that the immune problems of the new generation stem from the failures in this central check system. People in this camp tend to use genetics or environmental chemicals as causes. ",
"...",
"http://www.ncbi.nlm.nih.gov/pubmed/24763061",
"\n",
"http://www.ncbi.nlm.nih.gov/pubmed/25216337",
"Edit to add opposing article."
] |
[
"Doing said activities allows your body to come into contact with a greater number of pathogens. Your body recognizes those foreign bodies and combats them building up an immunity. If you've never been in contact with them and are suddenly exposed your body would freak the duck out. That is why if you live in a developed country and travel to a less developed one it is usually recommended you don't eat the local delicacies or drink unfiltered water."
] |
[
"Doing said activities allows your body to come into contact with a greater number of pathogens. Your body recognizes those foreign bodies and combats them building up an immunity. If you've never been in contact with them and are suddenly exposed your body would freak the duck out. That is why if you live in a developed country and travel to a less developed one it is usually recommended you don't eat the local delicacies or drink unfiltered water."
] |
[
"Sleeping with music playing"
] |
[
false
] |
Hi guys, i'm wondering. Almost 5 years I have been sleeping with my music on, not headphones, just playing it from my laptop, pretty silently, but still easy to listen to (chillstep mixes, trance and so on). I just hate that buzzing sound I hear when i'm trying to sleep and there is not a single sound around. It starts to drive me crazy and I can't fall asleep Does this kind of music sleeping ( not headphones) has any effects on my sleep cycles, rest, productivity ? Thank you
|
[
"In general, noise throughout the night is disruptive to sleep, especially if the noise level is highly variable, e.g., occasional loud noises. However, a steady background noise (e.g., white noise) can be beneficial to sleep quality if the environment is inherently noisy, e.g., ",
"the ICU of a hospital",
". Of course, if the white noise itself is very loud, ",
"sleep quality is adversely affected",
".",
"There have been several studies assessing the use of music to fall asleep. Most of these have involved listening to music for ~45 minutes around bedtime. For example, ",
"this study",
" in students with sleep complaints found that listening to classical music around bedtime could improve sleep, relative to listening to an audiobook or to nothing. ",
"This meta-analysis",
" found some beneficial effect of bedtime music interventions on sleep quality. However, it was based on only 5 studies in different populations, and found a relatively small effect. Many sleep/music studies have unfortunately been poorly designed, as discussed ",
"here",
". Note also that most studies involving music as a sleep-aid have naturally been targeted at groups that have sleep problems. ",
"This study",
" found no effect of listening to classical music for 45 minutes at bedtime in healthy sleepers.",
"I am not aware of ",
" studies where participants listened continuously to music throughout the night. Based on prior results, one could reasonably expect that sleep quality would be reduced if the sound level or quality changed frequently during the night (e.g., a playlist with many different types of music or high-tempo music). It is plausible that listening to calm relaxing music (e.g., classical music) throughout the night could be beneficial if there are already noise problems in the environment or if the individual has sleep problems. But without an appropriate study, it's not possible to say for sure."
] |
[
"Of course, if the white noise itself is very loud, sleep quality is adversely affected[2] .",
"In that study, the white noise was 93 ± 2 dB. Do you know what levels white noise should be at to not be disruptive to sleep? Is 60dB loud enough to disturb sleep quality?"
] |
[
"Are you asking if listening to an audiobook while asleep ",
" allows you to more easily recall the information?"
] |
[
"What, if any, are the differences between systemic nervous system synapses and those found in the brain or central nervous system?"
] |
[
false
] |
Different neurotransmitters? Structurally different?
|
[
"Hi there,",
"I am only a biomedical student so I may not be able to help you completely with this.\nI am going to presume with systemic nervous system you mean either the sympathetic nervous system and/or just the peripheral system.",
"First of it is important to understand that the central nervous system/brain neurons are on their own very diverse. Not every neuron can release every neurotransmitter nor does it have every receptor and even neurons that react to the same neurotransmitters can be different.",
"Neurotransmitters that are most prominent like GABA do play a role outside the brain/cns but this role greatly differs from the one inside the brain. ",
"I have no knowledge of the actual structure of the synapses outside of the CNS.",
"Someone else might be able to give you a more in depth answer but; yes there are different neurotransmitters but the receptors in these synapses can differ. "
] |
[
"To start, I am gonna make the assumption that the systemic nervous system you're referring to is the PNS - please correct me if this is wrong!",
"They are different in both ways.",
"Neurotransmitters: In the CNS, the main NTs are glutamate and GABA. In the PNS, the main NTs are acetylcholine and noradrenaline (thanks ",
"/u/FloatingNeuron",
")",
"Structure:",
"One structural difference can be found in the autonomic (involuntary) branch of the PNS. When the ANS synapses with smooth muscle, it does so in varicosities like ",
"this",
". The neurotransmitter is released to the ECF (fluid around the smooth muscle), rather than directly across the 'synapse', which is what you would \"expect\".",
"Another is in the specialised structure called the neuromuscular junction which is found only in the somatic (voluntary arm) of the PNS but doesn't exist in the CNS. ",
"Hope this helps some.",
"EDIT: I added the second part after finch1993 mentioned the NMJ so all credit to them."
] |
[
"Just what I was wondering thanks. "
] |
[
"If a fly flying north hits a train moving south will there be a point in time in which the fly's velocity is equal to zero?"
] |
[
false
] | null |
[
"Yes."
] |
[
"Can you elaborate? Why would the fly be at zero velocity? What would happen if the fly and the train would both be a single atoms? one heavier and faster than the other?"
] |
[
"The velocity of the fly is a continuous function of time, and it changes sign. So it must pass through zero.",
"Single atoms don't have well-defined positions or velocities, they should be treated with quantum mechanics."
] |
[
"Looking for material that forms needle-shaped crystals?"
] |
[
false
] |
[deleted]
|
[
"I recall MSG being rod-like crystals. It's certainly easy to get. I've never crystalized it from solution though. "
] |
[
"Salicylic acid aka Aspirin. ",
"Here's a procedure to make it in a lab",
"Edit: Solubility in water is a bit low 2 g/L at 20 °C"
] |
[
"In medicine, gout is partly diagnosed by finding microscopic needle-shaped crystals in joint fluid. This finding indicates increased calcium pyrophosphate or sodium monophosphate levels. Not sure if this is helpful at all, or whether these would form macro crystals on evaporation, but it could be a lead if all else fails. "
] |
[
"Why do solar flares seem to 'rewind' themselves along the path they traveled?"
] |
[
false
] |
This is a video of the sun in 4k resolution from October 14-30, 2014: Watch the far right side of the sun. Around 0:53 there's an explosion and that goes up (north), then it seems to suck the entire explosion right back into the path it traveled (south, toward the equator). This happens a few times in a row. Really, it happens all throughout the video with most of the explosions. Why do most of the sun's explosions travel back along the path they came from, instead of straight down toward the sun's center? It is atmospheric pressure giving the ejected matter no other path to travel against the force of gravity? EDIT: 1:42-1:52 especially. Mostly magnetism apparently! Thanks
|
[
"They're traveling back down magnetic flux lines. The flares you see consist of charged particles, plasma and the like, therefore they're affected by the suns intense coronal magnetism. Think bar magnet diagrams, these shots are an excellent visual demonstration of magnetic flux, similar to iron filings and a regular magnet. As for the exact reasons flares occur, it'll require someone smarter than I to explain. "
] |
[
"You're right in that the flares are a basic visualisation of the flux lines. The material is being ejected due to perturbations in the coronal magnetic field, said material is ejected at high speeds, but once it slows down due to inductive forces it travels back to the surface along the magnetic field. You'll sometimes see these looping back to the sun and flares will follow these in a big semi circular ring, but in other cases the magnetic loop is actually broken and ejecta can be sent out into space if it's energetic enough in what's called a coronal mass ejection.",
"Just a note about flux lines, they're not physical lines of magnetism, but they're visual representations we use to demonstrate a magnetic field, so there is no specific flux line these flares are traveling along, it's more that's the flares path through the suns magnetic field."
] |
[
"I'm just learning about about flux lines in one of my classes right now. So, from what I gather, the flares are kinda a physical representation of the flux lines? I know that's not really a proper way of explaining it, but the flares seemingly \"rewind\" because they are on a certain flux line?"
] |
[
"Could polar bears and penguins be introduced to their respective opposite poles (south, north) and survive?"
] |
[
false
] |
Would the conditions be similar enough weather wise to make it sustainable?
|
[
"Its unlikely that they would survive. ",
"Polar bears",
" are adapted to eating seals, but its very hard to hunt them in the open water so they hunt on land. Two common ways of catching seals include: crashing through the ice using their paws and kill the seals in their dens or stalking air holes and kill seals as they surface for air. These conditions are not as common in Antarctica because it is an area where land is covered in ice, with no seals under it but the Arctic is ocean covered in ice with seals under it. (There are seals in Antarctica, they would just be harder to hunt). Of course assuming you transferred the polar bears to areas with penguin colonies they would have pretty good (but seasonal) food source - unless it is the ",
"Emperor",
" which winters in Antarctica. But over time, the penguins being defenceless against polar bears would probably be exposed to intensive hunting pressure from which they may be extirpated from the region. ",
"Its probable that polar bears could survive Antarctica temperatures - they have many ",
"adaptations to the cold weather",
" - thick fur, lots of fat, skin that is black ",
". I do not know the absolute lowest temperature that a polar bear can survive but I do know that ",
"Antarctica",
" experiences colder temperatures than the ",
"Arctic",
". ",
"\"The temperature in Antarctica has reached −89 °C (−129 °F)...Temperatures reach a minimum of between −80 °C (−112 °F) and −90 °C (−130 °F) in the interior in winter and reach a maximum of between 5 °C (41 °F) and 15 °C (59 °F) near the coast in summer. And Antarctica is colder than the Arctic for two reasons. First, much of the continent is more than 3 kilometres (2 mi) above sea level, and temperature decreases with elevation. Second, the Arctic Ocean covers the north polar zone: the ocean's relative warmth is transferred through the icepack and prevents temperatures in the Arctic regions from reaching the extremes typical of the land surface of Antarctica.\" and from the Arctic article...\". Average winter temperatures can be as low as −40 °C (−40 °F), and the coldest recorded temperature is approximately −68 °C (−90 °F).\" So polar bears if transferred to Antarctica would possibly have to face temperatures as low as −80 °C which is colder then what they are normally exposed to at −40 °C. This could potentially be problematic, but not unsurmountable.",
"The problem with penguins is that they are essentially adapted to living in an environment where they have very few land predators - only sometimes are eggs/chicks killed by predatory seagulls. Adults main predator is killer whales from the ocean. Anyway... penguins in the Arctic would have a hard time of making it because of land predators like the polar bear, arctic fox or wolf. Even if they lived on cliffs like ",
"puffins",
" they can't fly so they would not be able to get to and from the sea. It would be better if they were transferred to a location - island - where no land predators can get them, but bare rock is available in summer for nesting (if the species requires). In terms of food there would be plenty of fish in the Arctic ocean for them to hunt, probably something like pollock. Also, temperatures in the arctic are warmer, so they wouldn't have to deal with being too cold so much as being too warm, especially in the summer months if they live in areas where it gets above what they might normally be exposed too. "
] |
[
"Wow that was more thorough than I had ever thought was possible, this is why i love ",
"r/askscience",
". Thank you for such an awesome response! "
] |
[
"Yes, I would assume that they would eat a penguin given half the chance - their diet isn't limited to just seals but they will also scavenge whale/seal/walrus carcasses as well as... \"Polar bears have also been observed to eat a wide variety of other wild foods, including muskox, reindeer, birds, eggs, rodents, shellfish, crabs, and other polar bears. They may also eat plants, including berries, roots, and kelp, however none of these are a significant part of their diet.[58]\"",
"Mostly polar bears will have a really hard time of it surviving in an ice free arctic (ice-free summers predicted as early as 2029) \"",
"Climate models give a range of predictions of Arctic sea ice loss, showing near-complete to complete loss in September anywhere from 2040 to some time well beyond 2100. About half of the analyzed models show near-complete to complete sea ice loss in September by the year 2100. More recently, the Catlin Arctic Survey concluded that summer ice loss would occur around 2029.",
"\". ",
"This is seriously bad news for polar bears because it takes them so long to reach the age of reproduction and finally when a female does have cubs she only has 2 or 3 and more then half will die before they reach 1. \"As of 2006, in Alaska, 42% of cubs now reach 12 months of age, down from 65% 15 years ago (because of a loss of ice - its harder to hunt). In most areas, cubs are weaned at two and a half years of age\". Also male bears kill infants, that are probably not their own in order to return the female into cycling.",
"There are four options for the polar bears at this point - some involve human intervention.",
"Survive indefinitely in captivity like in zoos.",
"Hybridize with grizzly bears, which has been reported in the past using genetic and morphological testing.",
"Remain separate from grizzlies but adapt to living off the land and not the sea - hunt birds, foxes, caribou, or become more omnivorous like other bears and change the diet to berries and vegetation. Both are extremely hard sets of adaptations to undergo/select for given the gestation length, weaning length and low number of offspring polar bear females have.",
"Try transferring them to Antarctica - but that will melt too eventually."
] |
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