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[
"How does putting whisky on a mouth ulcer heal it?"
] |
[
false
] |
[deleted]
|
[
"Alcohol is a good disinfectant. It kills a wide range of micro-organisms and is mostly benign to healthy tissue. Whisky is about 40% ethanol, a good concentration for this purpose, although 60% would probably be better.",
"The ethanol kills off the surface micro-organisms that are hindering healing thus allowing your body to repair itself. Alcohol also numbs and even kills nerve endings, so this treatment will also provide some pain relief."
] |
[
"Both alcohol and salt are excellent disinfectants, they dry out cells, which is a major problem for single celled organisms (while us multicellular organisms can easily recover from a few dehydrated cells!). Viruses are also susceptible to drying out from these processes. I can't speak for TCP but it may have a similar effect. Either way, these products will help kill any opportunistic micro-organisms that take advantage of the damage and lessen the time taken to heal. Alcohol is also a mild topical anaesthesia and will numb the area for a short time, as well as kill off any pathogens. One of the main ingredients in most mouthwashes is alcohol, because it's excellent at sterilising the mouth in relatively small amounts.",
"As for what a mouth ulcer is, it is essentially a break in the cell wall that lines your mouth that protects the underlying tissue known as the mucous membrane. There are two recognised types, one of which is caused by abrasion - such as with dry, sharp foods or by rubbing on a tooth filling/dental fixture. The second type is known as ",
"aphthous stomatitis",
" and is characterised by recurrant ulceration with no primary identifiable cause. In some individuals, bacteria and viral pathogens have been shown to exacerbate the problem. ",
"The short answer is we don't know what causes many mouth ulcers, but many anti-septic products will work wonders for letting your body heal without interruption."
] |
[
"100-120 proof Whiskey are fairly common, although dwarfed by the number of 80 proof varieties out there. So it is pretty easy to the better concentration of alcohol. "
] |
[
"Is there an evolutionary reason that aquatic reptiles (such as ichtyosaurs) moved their tails horizontally, while aquatic mammals move their tails vertically?"
] |
[
false
] | null |
[
"Marine mammals and reptiles do not only use their tails for swimming, they use their whole body. The direction of undulation (lateral in reptiles and dorso-ventral in mammals) came from their respective terrestrial ancestors. Reptilian locomotion on land retained the ancestral state of the early tetrapods and is, interestingly, constrained by their breathing pattern-- one side of their lungs get compressed while they walk. The terrestrial mammals solved this problem by having an erect stance, so they can run and breathe at the same time. When members of each of these groups went back into the ocean, they retained their locomotion pattern. ",
"Source",
"PS. Unlike what has been said, the aquatic mammal tails did not come from fusing hindlegs. In the case of the pinnipeds, their tails have been lost; in the case of the cetaceans and manatees, they lost their hindlimbs but retained and modified their tails."
] |
[
"No. It's totally wrong. Look at a skeleton: whale tails look like vertebrae because they are an extension of their spine, just like reptile tails. They even have vestigial legs remaining about 2/3 of the way along their bodies, with leg bones and foot bones and everything (but the structure is inside their bodies, so you only see it in a dissection)",
"These people talking about fused limbs need to go to a museum and look.",
"link",
"There is a difference in the way the hips work for mammals and reptiles on land, and that carries over to cause the change in movement. I'm not sufficiently knowledgeable to explain beyond that",
"The difference "
] |
[
"No. It's totally wrong. Look at a skeleton: whale tails look like vertebrae because they are an extension of their spine, just like reptile tails. They even have vestigial legs remaining about 2/3 of the way along their bodies, with leg bones and foot bones and everything (but the structure is inside their bodies, so you only see it in a dissection)",
"These people talking about fused limbs need to go to a museum and look.",
"link",
"There is a difference in the way the hips work for mammals and reptiles on land, and that carries over to cause the change in movement. I'm not sufficiently knowledgeable to explain beyond that",
"The difference "
] |
[
"If temperature is merely a measure of kinetic energy, what exactly is the colour temperature of blackbody radiation?"
] |
[
false
] |
I'm a little confused by the concept of temperature, so perhaps someone could clear this up for me. On one hand, temperature is merely a measure of molecular vibrations. Our brains interpret these vibrations as temperature, and when the kinetic energy in two substances is different, placing these substances together causes the kinetic energy between them to average out, which is the basis for the concept of heat transfer. Is that all correct? (Also, if all of that's the case, does that mean that there's a simple conversion factor between joules and Kelvin?) But then on the other hand, temperature is also this more abstract concept related to blackbody radiation and Wien's law, where every colour has an associated temperature and these colours are the wavelengths whose energy is equal to the energy released in an atomic deexcitation. Is that also correct? I'm having trouble unifying these two concepts of temperature in mind. In one case, we're talking about kinetic energy in classical physics and in the other case, we're dealing with quantum mechanical principles. On top of that, I'm guessing that true blackbody radiation doesn't actually exist, as light can never be perfectly thermalized, so where does EM radiation that is true blackbody radiation fit into the whole colour/temperature discussion? Perhaps someone can help make sense of these seemingly disparate ideas and help me understand the concept of temperature. Thanks.
|
[
"The temperature as molecular kinetic energy explanation is ok but not the best. The actual definition of temperature has to do with the relationship between energy and entropy.",
"To relate the molecular motion picture to blackbody radiation, consider an atom with an electron that jumps between energy levels, emit a spectral line. If the atom is moving around in a gas, sometimes it is moving towards a given direction, sometimes it is moving away from that direction. Because of the Doppler effect, this spectral line will shift in frequencies, either red or blueshifted, depending on which way it moves relative to the observer. This has the effect of broadening out the line into a continuous spectrum."
] |
[
"The example I gave is basically to demonstrate that a continuous spectrum can arise from thermalization of discrete spectra. It's not a derivation of Planck's law."
] |
[
"If this really is accurate, then I'm confused.",
"From this subreddit and other resources I have gathered that blackbody radiation is generated by the rapid oscillation of charges in the hot matter. Thus, the spectrum is continuous because the particles' energies are distributed that way. The Doppler effect, in contrast, would only be responsible for the widening of the discrete spectral lines of elements.",
"In this view, OPs question would be answered by stating that thermal radiation is a completely different thing than the emissions that arise from electrons returning to their lower orbits.",
"How can I reconcile these bits of information?"
] |
[
"When a wound heals, does it grow just as fast as your other skin?"
] |
[
false
] | null |
[
"I got a small, but deep wound last Sunday, when a piece of burning wood got stuck on my finger. It was maybe 7-8 mm wide and 2-3 mm deep. Five days later, it is almost healed. This got me thinking:",
"Does skin grow this fast everywhere else? ",
"If not, how does the cells \"know\" that they have to grow back? ",
"How does it \"know\" how to stop? "
] |
[
"Skin usually grows at a common rate, depending on location. They just grow until they die, forming your epidermis.",
"So it's an ever-growing layer of skin, up to your outermost layer where they flake off into dust, making it pretty constant."
] |
[
"No, the growth depends on several factors.",
"From ",
"The Pathogenesis of Burn Wound Conservation-",
"\"The ability of the skin to heal largely depends on the dermis. The contained macrophages produce growth factors, fibroblasts, and extracellular matrix, which control epidermal regeneration. Since the highest concentration of cells and matrix resides in the upper aspect of the dermis, it follows that the deeper the burn, the less rapidly healing will occur.\"",
"and ",
"The healing-promoting effect of saliva on skin burn is mediated by epidermal growth factor (EGF): role of the neutrophils."
] |
[
"Why are LEDs (Light Emitting Diodes) only capable of producing a few colors?"
] |
[
false
] |
I asked this question in AskReddit without knowing about AskScience. (See: ) There were some replies, but not the clarification and simplification of answers that I'd hoped for. The best answer there indicated that the "band gap" of the material used determined the color of the LED. I thought maybe AskScience would be the place to go. So, here goes: Why isn't there an infinite number of colors of LEDs? Why are there only a few colors that are commonly produced? For example, Wikipedia lists ten colors of LEDs: What's the long and short of it? What's the scientific explanation for this? -- Please explain your reasoning in detail and then again like you were speaking to a 5-year old. Thank you! I understand that you can take the commonly offered LEDs and combine them to produce a rainbow effect and possibly the entire spectrum of colors, but the question still remains: Why aren't LEDs offered in more colors? Is it just cost prohibitive to research the science behind creating less common colors? LEDs are very cheap, so the cost prohibitive argument for only a few colors seems flawed. Unless it's just the original research that is so expensive, because manufacturing obviously isn't. Is it an issue of what material is used, and the "band gap"? (As mentioned above) EDIT: Thank you for the awesome answers and discussion! Very informative and thorough.
|
[
"The band gap first:",
"Electrons exist in atoms in very specific, discrete energy levels. Electrons cannot - absolutely cannot - have energies in between these 'allowed' energy levels. They can move up energy levels if you give them a bit of energy that exactly equals the difference in energy between those two levels. The electron can move itself back down if it gets rid of a bit of energy exactly equal to the difference in energy between the old level and the new level. These bits of energy are more commonly known as photons. ",
"When you move into molecules, these energy levels mix together to make new energy levels, half at lower energy and half at higher energy. The electrons go to the lowest ones they can, though, so the lower energy levels get filled up with electrons. Those higher ones are still kosher, though, and if you give an electron in one of the lower levels the right amount of energy (a photon with the correct wavelength) then it'll move up to a higher energy level. There's a 'no man's land' of energies between the lower and higher energy levels. That higher energy level has to be unoccupied (can't pile more electrons than there is space to hold them) but that's a detail we can forget about. ",
"Moving from molecules to a material, like silicon, you pile so many energy levels together that they start to blend together. The lower energy levels are getting close to a continuum, as are the upper energy levels. The electrons naturally want to exist in the lower states, but we can still move them to the upper energy levels if we give them a bit of the right amount of energy. The lower energy levels are known as the 'valence band' and the upper levels the 'conduction band'. The difference in energy between the two is known as the 'band gap'. The band gap is the amount of energy it takes to move an electron from the valence band to the conduction band. It is also the amount of energy an electron in the conduction band will release if it drops to the valence band. The conduction to valence transition (often) results in an emission of a photon with exactly the amount of energy of the band gap (plus or minus some spread thanks to thermal energy, but don't worry about that). In the end, the only photons that come out - the only photons that ",
" come out of the LED - are those with an energy exactly equal to the band gap of the material. ",
"In an LED we can use a current with sufficient voltage to pump electrons into the conduction band from the valence band, let them drop down to the valence band across that band gap and spit out a photon with an energy equal to the band gap energy of the material. ",
"Now why can't we have infinite colors of LED's? Because we don't have infinite different energies of the band gaps. We have to make the LED's out of matter, which have electrons in defined energies already. We can mix and match between materials that have energies in the right place, but still have a gap the right size, and can be processed into devices. Since everything is discrete on that scale we only end up with discrete colors of LED's. There's some fudging with the exact energy thanks to doping the semiconductor and such, so the colors that are available aren't like gas lasers with a single transition wavelength. Still, it's a narrow range around a central peak that you end up with.",
"Bonus fun trick - you can change the energy of the band gap (and the color of the LED) if you get the LED really cold. Try it the next time you have some dry ice or liquid nitrogen lying around. You can watch it return to normal as the temperature returns to RT, too. "
] |
[
"Wow. Thanks for your thorough explanation. This seems to make a good deal of sense.",
"So, from your explanation, it is an issue of materials and their physical properties, rather than research costs, etc. ",
"It seems interesting that the discrete colors produced are almost those of the standard rainbow. Wikipedia lists the standard colors as:",
"White, Red, Orange, Yellow, Green, Blue, Violet, Purple, Ultraviolet, and Infrared.",
"Ultraviolet and infrared aren't visible to the human eye, so the remaining 8 colors, more or less, make up the standard rainbow. (I guess all colors combined make white, so really the remaining 7 make up the ROYGBIV)",
"Oh, and now I really want to try your fun trick. I'm going to have to go find some dry ice and give it a shot!"
] |
[
"The problem with InGaN is that mixtures near 50% each have very poor quality crystalline. It becomes hard to tune near the center of the range."
] |
[
"At what size does quantum mechanics replace general relativity as the governing set of rules?"
] |
[
false
] |
So I know quantum mechanics are the laws that describe the interactions between subatomic particles and general relativity describes the interactions between macroscopic things. What I wanted to know is at what size does the switch between these two theories occur? And possibly why?
|
[
"They don't ",
" each other, strictly speaking. GR is a theory of gravity and QM (or, more accurately, quantum field theory) is a theory of electromagnetism, strong, and weak nuclear forces. This means that one theory doesn't turn into the other as you cross some size threshold - rather, they are two complimentary theories describing different forces. ",
"The reason we need two separate theories is because the mathematics of the two tend to not play nicely together. It goes something like this:",
"QFT relies on a mathematical trick called \"renormalization\" that effectively takes calculations that result in infinities and turn them into sensible, non-infinite answers. GR says that what we experience as gravity is actually a curvature of spacetime induced by the presence of matter and energy. The basic idea of a combined theory would be to take the mathematics of QFT (which are valid in flat spacetimes), and put them onto a curved spacetime as described by GR. It turns out, however, that many calculations from QFT that are renormalizable in flat spacetime are ",
" when done on a curved manifold. This is at the root of the so-called \"quantum gravity\" problem.",
"That being said, let me rephrase your question into one that has a better answer - at what scales do GR and QFT individually break down? The answer is roughly the ",
"Planck Scale",
", which is far smaller than current experiments are able to explore. Thus, as far as any experiments we can perform on earth are concerned, both QFT are GR are completely valid theories describing their own separate forces."
] |
[
"It's not that it's wrong, exactly, but rather that it's not the whole story. QFT is the best-tested physical theory in human history, and it works ",
". However, it's probably a limiting theory - there exists a more complete theory (i.e. one that incorporates gravity) that looks a lot like QFT on scales where gravity is negligible.",
"A similar example would be Newtonian mechanics vs. relativity. It's not that Newtonian mechanics is wrong, exactly - it's not ",
" true, but it works perfectly fine for low energy calculations. It's the low-energy limit of relativity theory. In other words, relativity theory looks a lot like Newtonian mechanics at low energies."
] |
[
"Good answer, but I think you're describing the problem of quantum gravity a bit wrong. We can put a renormalizable QFT on a curved background and still compute things (which is how one finds the Hawking radiation, for example). The problem of quantum gravity is rather when you quantize gravity itself. Which might have been what you meant, but not quite what you wrote. Sorry for nitpicking..."
] |
[
"What do we know about the supernova that created all the metals in the solar system?"
] |
[
false
] |
Is anything known about the supernova remnant that ended up being the solar system? I've tried looking around for some info, and if there are any papers that people know about, please pass them along. EDIT: Thanks for all the responses.
|
[
"It's not just one, atoms come from all over."
] |
[
"I've wondered about this too. But when you consider that it takes ~1/4 billion years to rotate around the galactic center, and the sun is about 5 billion years old, we've gone around the galaxy about 20 times. That system may just be too chaotic over that long of a time scale to accurately plot back in time to which stars were birthed in the same neighborhood as our own, or which supernova remnants (if we could even see them at all) contributed to our own."
] |
[
"That's a good point, but I guess my question is might then be does anybody know how many supernovas contributed to the solar system?"
] |
[
"Is it possible to make a magnetic alloy from nonferrous metals or semiconductors?"
] |
[
false
] |
My (vague) understanding is that what makes a material magnetic has something to do with how stable electrons are in their orbits and how resistant those orbits are to change. I know that magnetic disk drives read using semiconductor chips that change their electrical resistance in the presence of a magnetic field. Is a non-ferrous, non-electrical magnet plausible?
|
[
"Of the pure elements, ",
" (ferrum) is the best-known magnetic metal, of course. It's so prototypical that 'ferromagnetism', the best-known kind of magnetism, is named after it",
" also are sometimes considered to include ",
" and ",
" in addition to iron. All of them are highly ferromagnetic and also have similar chemical and metallurgical properties. However, they are not iron and there are many alloys that use Ni and Co which are magnetic.",
"There are also other metals that are ferromagnetic but not similar to iron. Some of the lanthanides (rare earth) have this property, notably ",
", ",
", and ",
" (though the latter two are not ferromagnetic at room temperature). Rare-earth magnets are the strongest permanent magnets, but these are alloys that contain iron, nickel, or cobalt too (in order to make them magnetic at room temperature). ",
"When it comes to alloys, there are indeed ferromagnetic materials that do not contain any ferrous element. ",
" is ferromagnetic but has no ferrous metal in it - if you are old enough you may remember that magnetic cassette tapes used this substance. ",
" (Ga,Mn)As is both a semiconductor and ferromagnetic. "
] |
[
"Doping some semiconductors with impurities has been shown in recent years to sometimes create ferromagnetic effects. I know you said no semiconductors, but this doesn't depend on an electromagnetic effect to work, so I think this might be what you had in mind.",
"Here's ",
"one example",
" that I found quickly. By doping zinc oxide with elemental zinc, aluminum, or platinum they were able to create materials with room-temperature ferromagnetism from non-ferromagnetic materials.",
"From my cursory look through the literature, there's no simple textbook answer for how this comes about. The best explanation I found for this is that the spin required for ferromagnetism arises from a \"donor impurity band\" in the semiconductor, which in the case of n-type doped ZnO might involve trapped electrons in the lattice's oxygen vacancies."
] |
[
"How are you defining nonferrous here? Not iron? Then yes, definitely. Hard disk drives use a cobalt chromium alloy. Both cobalt and nickel are frequently used to make ferromagnets."
] |
[
"Do cars with smaller tires use more gas than cars or trucks with larger tires?"
] |
[
false
] |
I hope I put this in the right category with the right flair. I apologize if not. My thinking on this was that cars with small tires need more revolutions per mile than cars or trucks with larger wheels, and therefore, smaller revolutions would utilize more gas to maintain the speed to go the distance needed. Am I thinking this correctly?
|
[
"No. Though certain factors like friction increase at higher engine speeds, engines are not always more inefficient at higher speeds. Ultimately, a truck requires more power and thus, more fuel to drive at a given speed than a car.",
"There are two factors in engine power, speed and torque. Speed is the speed of the engine, usually measured in RPMs, and torque is proportional to load at a given speed, but you can think of it more simply as the amount of fuel being injected. The engine speed is directly coupled to the wheel speed, which is controlled by the driver. At a given engine/vehicle speed, the load is dictated by the other driving conditions--things like road grade (level vs. uphill), vehicle weight, and vehicle drag. If you have a manual transmission, the engine speed at 30 mph in second gear will always be the same, whether you're driving level or going uphill. So to maintain 30 mph going uphill, the engine has to increase the torque by opening the throttle and injecting more fuel into the cylinder. Even though the engine is turning at the same speed, you're burning much more fuel going uphill because the load on the engine is much higher. ",
"Based on the example above, we can see that fuel consumption is only weakly proportional to engine speed and much more dependent on engine torque/load. To drive a large, heavy vehicle like a truck will require more torque than a car, even if the engine speed is lower. A car with a higher engine speed and be injecting fuel more often than the truck, but the truck is going to be injecting more fuel volume per revolution than the car. But if I'm a smart engineer, I'm going to give the car a transmission with gearing that is optimal for the car's tire size so that the engine is operating at optimal engine speeds for common driving speeds."
] |
[
"Thank you! I am not well versed in this, but I actually understood most of what you are saying. So, then, what you are saying, is a lighter car would actually use less gas because it would have less engine load or torque. I have a Toyota Celica and my gf has a Subaru Forrester, and her car eats up gas, where my car I can go pretty far without refilling. I would assume tank size would enter the variable on this level, but generally speaking, my car goes a lot farther than hers on a full tank of gas."
] |
[
"The kind of driving you do will have a large effect as well. The two main things that limits the motion of a vehicle are it's mass and drag. Mass will effect how much energy it takes to accelerate the vehicle, thus her smaller, lighter car will take less gas to get up to speed. Drag is proportional to velocity and dependent on the shape of the vehicle, a more aerodynamic vehicle will experience less drag and will take less gas to maintain a particular speed, we can also consider the efficiency of the engine, most engines are designed to be most efficient at a particular RPM/load and the transmission is heard so that RPM equates to a common driving speed, such as 50Km/hr, or 100Km/hr. If your GF tends to drive longer distances without stopping, such as a long freeway drive vs you driving though a downtown area then it's likely that we will get better mileage even in a vehicle that is normally less efficient."
] |
[
"Are there any animals that naturally have three ears? Or any with three eyes?"
] |
[
false
] |
I'm curious about the seeming (to me) lack of threes - is there a reason why aren't there more animals with three limbs, organs, etc?
|
[
"Many squamates (lizards) have a photosensitive third eye at the top of their head. it's not a fully evolved eye, but a cluster of light-sensitive cells.",
"http://www.amnh.org/exhibitions/past-exhibitions/lizards-and-snakes-alive/squamate-fun-facts"
] |
[
"Many fish, amphibians, and reptiles have a parietal eye, though it rarely functional. The tuatara's is particularly well developed, retaining its lens, but is only visible in hatchlings, and is quickly overgrown. The primitive lamprey also has a developed third eye (two different ones, actually), and fossil evidence suggests older species had a fully developed eye socket in this location. This may have been the first eye that evolved in vertebrates, and was eventually replaced by the pair we have now.",
"But to answer your question, most animals you encounter exhibit bilateral symmetry, so everything comes in pairs."
] |
[
"Symmetry is important because it allows you to do more with less genetic code.",
"Bilateral symmetry is so prevalent because while up and down, and front and back are different enough to warrant different adaptations, left vs. right is not. "
] |
[
"Has the discovery of martensite principles been at all important? Is this useful in any way, has it led to anything?"
] |
[
false
] | null |
[
"(Also, is this 'physics' or 'chemistry'?)"
] |
[
"Since Martensite appears to be ",
"some sort of crystal structure",
", I'd say chemistry."
] |
[
"Changed flair. Thank you."
] |
[
"Is time smooth? Or are there \"gaps\" in it? What is in those \"gaps\"?"
] |
[
false
] |
[deleted]
|
[
"You're referring to the quantisation of time. The general consensus is that time is continuous, although there is a fairly significant group that thinks it's quantised. As of now, there are no observations that suggest that time is quantised. "
] |
[
"What implications could come out of time being quantized?"
] |
[
"Quantized time would most likely be naturally coupled with quantized space as well. Also, there's some very interesting implications for the big bang and the concept of ",
"action",
" in physics."
] |
[
"Why can we drown after only a minute or two, but then get resuscitated a while later and still live? Why can't we just survive a few more minutes without breathing?"
] |
[
false
] |
Probably a stupid question, but I'm curious
|
[
"Here's a very simplified explanation. When you drown:",
"You're unable to get enough air into your lungs, because of the water.",
"You aren't able to get oxygen into your body. Your body continues to consume oxygen, and so the level of oxygen in your body decreases.",
"At some point, you stop breathing and your heart stops beating. I think the usual order is: stop breathing, followed by loss of consciousness, followed by cardiac arrest.",
"After this happens, if you're on your own, you're pretty much screwed. Even if the water were cleared out, your body generally doesn't have enough oxygen distributed throughout your heart muscle, diaphragm, and brain for the body to start going again by itself. It's sort of like, if your car runs out of gasoline and shuts down. You need to refill the tank, but just putting more fuel in won't automatically turn the car back on. Again, this is over-simplified, but it gives you some idea.",
"However, a person performing CPR can use artificial respiration and chest compressions to help move air in and out of the lungs and circulate the somewhat-oxygenated blood through the body.",
"Actually getting the heart and lungs working on their own again usually requires more advanced intervention, performed by a trained professional, in addition to CPR. However, performing CPR while waiting for more help to arrive increases the overall odds that the drowning victim will ultimately survive.",
"I'm basing this off my memory from a first aid class about a decade ago, so if I got anything wrong or left any gaps, hopefully someone can make corrections or provide more detail."
] |
[
"Just certified in Washington state last Saturday. 30 seconds of chest compressions, 2 rescue breaths is what we were taught."
] |
[
"Really? I am CPR certified and we used rescue breaths."
] |
[
"Why do physicists say that a photon has zero rest mass instead of saying that a photon doesn't exist at rest?"
] |
[
false
] |
At rest, a photon wouldn't actually represent any sort of force or material, so why talk about it in this way? Is it a form of potential energy and so considered something?
|
[
"A better term than \"rest mass\" is \"invariant mass\", or just \"mass\" (since \"relativistic mass\" is an outdated concept). You may have seen the equation for the relativistic energy of a particle, E",
"=m",
"c",
"+p",
"c",
". If we re-express this equation as E",
"-p",
"c",
"=m",
"c",
", we find that we can express the mass of a particle as a function of the particle's energy and momentum. The important point is that, even though the Energy and momentum will be different in different frames, this calculated mass will always be the same, hence \"invariant mass\". For photons, the energy is always E=pc, so their invariant mass is zero."
] |
[
"Photons (or light) were not considered to be particles at all for a long time, so the concepts of momentum and energy were developed for \"traditional\" particles with rest mass, and only later were the equations rewritten to include photons. By that time it was necessary to describe the rest mass term as 0 to fit the traditional language. "
] |
[
"I was speaking more at a historical level about why we can't write .5*mv",
" as the kinetic energy, etc., so the term \"rest mass\" doesn't apply. ",
"Maybe it's just the order I learned things, but it's my impression that the term reflects a transition from classical massed particles to the modern approach. "
] |
[
"How does Paracetamol toxicity work?"
] |
[
false
] |
Okay, this is a bit of a strange one I know. There is a lot of rubbish regarding paracetamol out there. Many believe that using it long term can be bad for your liver for example. However the truth is that you're fine as long as you stay within the 'therapeutic' range. I was at work today (Admin at a GP surgery) and I scanned a letter regarding a patient that attempted suicide by consuming 30 paracetamol tablets and went to sleep. Apparently she was annoyed to have woken up seemingly fine. So what happened to this patient? Did she get lucky? Also, if it's safe to have up to 8 in a day does it matter how you divide the dosage throughout the day? For example could one take 3 two times a day instead? Why is the suggested dosage 2 four times a day? What if an individual took 4 twice a day? Would this be dangerous? It seems to me that paracetamol toxicity works quite differently to a lot of other drug overdoses? But that is basically my main question. If it's okay to have 4000 mg of paracetamol a day, does it matter how that is divided throughout the day? What may be the long term effects of taking more than 1000 mg every 4 hours?
|
[
"This is one of my favourite toxicity questions!",
"The reason it seems different to 'other' cases is because of how easy it is to do despite the fact it's a commonly used, easy to obtain drug.",
"Paracetamol is taken up by the body and relieves pain, high temperature, etc. 'After' that, like many drugs, it's metabolised, in this case in the Liver. That means that the chemical structure is changed, inactivating it and/or making it easier to excrete. It's a foreign compound so your body is going to remove it.",
"In this case, paracetamol itself is ",
" toxic. However, one of the 'metabolites' (something it gets metabolised into) is. Paracetamol is metabolism ",
"into three different compounds",
" initally. NAPQI is toxic, and damages the liver.",
"NAPQI is usually detoxified quickly in the liver (\"GSH conjugation\" in the graph), so normal use of paracetamol is not necessarily dangerous. For individuals with ",
" low body mass it can be.",
"There are different types of overdose. You can accidentally take more than recommended, for example taking lemsip ",
" paracetamol tablets. There are excessive single doses, such as taking 30 tablets at once. And there are also excessive ",
", which is what you're referring to with \"4 twice a day\". This wouldn't necessarily be bad on its own as a one off, as people taking lemsip ",
" cocodamol ",
" paracetamol effectively do this. Sadly people do do that when they're unwell.",
"Now, back to NAPQI. It's usually removed very quick so you only get toxic doses when you go above the recommended dosage, but this can be as low as 75mg/kg to start seeing toxic effects. It's normally 150mg/kg. For 75mg/kg, thats a dose of 5250mg for an adult, or around 11 500mg tablets. Doses of 10-15g are when it typically starts to get lethal. This is because the liver cannot work fast enough to clear out NAPQI, so it continues to damage your liver. ",
", as the packages say.",
"15g of paracetamol is 30 tablets so it could be lethal, but not necessarily. People survive massive overdoses by chance. ",
", though, it ",
" matter how you spread the doses and the dose regimen (how many and how often) is designed around making it work but stopping it killing you. You shouldn't double up doses of paracetamol to \"make it work longer\". ",
"Interesting side note, alcohol use can lower the amount of damage your liver can take and so alcoholics should avoid paracetamol use."
] |
[
"I claim no special expertise on the matter, which is why I defer the case to my wife, a certified poison information specialist which has worked the emergency phone lines at a poison information hotline for 15 years.",
"While it is true that at therapeutic doses, acetaminophen is safe, beyond the threshold of about 7.5 to 10 g (ie, 24 regular-strength or 15 extra-strength caplets or tablets) over a period of 8 hours or less, you get serious risk of hepatoxicity. ",
"The actual mechanism of the toxic reaction is complex, but understood (see ",
"reference 1",
", ",
"reference 2",
", ",
"reference 3",
", ",
"reference 4",
"). The potential outcomes may include acute liver failure. This is common enough that some countries have introduced legislation to limit the size of commercially available packages, which have resulted in notable decreases in observed fatalities from suicide (",
"reference 5",
").",
"Normal procedures in such cases involves the intravenous ",
"administration of N_acetylcisteine",
". There are various protocols.",
"The effects in the context of acute overdose are quite different from those of long term such as you suggest (1g/ 4 hr) over extended periods. However, the line dividing the 2 regimes of action is a fuzzy one when one factors in interactions with other substances and variations in overall state.",
"In the case of your patient, the questions is really one of dosage, her outcome will have depended on the overall dosage in terms of her overall weight (Those 30 tablets may have been low dosage, the patient may have been overweight). Also, my wife mentions that in a day-to-day emergency setting, one must always be cautious about establishing the actual events associated to a suicide attempt (cry for help, need for attention, etc.) - the patient may have lied about the actual # of tablets. And there also are factors of individual metabolism of course. She may have been lucky.",
"My wife adds (and I quote) \"Damn those salicylates\" (she isn't a fan of Tylenol). "
] |
[
"BTW, Tylenol is not a salicylate. "
] |
[
"If you recycle an envelope with a clear plastic \"window\" on it, does the plastic part interfere with the paper recycling process?"
] |
[
false
] |
Basically I'm wondering if it's worth the effort to manually remove the plastic window before recycling a windowed envelope.
|
[
"I work in a single stream recycling plant, it will most likely get rejected by the machines. "
] |
[
"The entire envelope will be rejected and added to a waste or a low quality% fiber mix. ",
"The only thing that can have 2 materials are metals, such a concentrated frozen juice as the paper/cardboard burns off in the incinerators and the metal ends will remain. You should also separate plastic lids from bottles as they are different plastics.",
"neat fact: recycling glass is a loss of dollars and is subsidized by the government. At least where I live...",
"also: this is from a single stream recycling facility perspective, not a 'fiber processing plant'"
] |
[
"I am a plastic recycler and this is completely wrong. Everything is chopped up then put in a wash tank. The bottle tops are HDPE/PP and float while the bottle is PET and sinks. No need to separate beforehand. "
] |
[
"How does a Pulsar star let us determine distance to it accurately?"
] |
[
false
] |
I remember hearing this somewhere, but I forgot, and couldn't find it by googling. What is the calculation to determine distance to a pulsar star? How does its fixed period help us determine that?
|
[
"I think you might mean estimating distance to the pulsar using the pulsar dispersion measure. To put it simply:",
"The Pulsar emits light over a certain range of [radio] frequencies. As the photons travel towards us they interact with [mainly] free electrons in interstellar space. This interaction slightly prolongs their travel time. The kicker here is that lower frequency photons get slowed down more than higher frequency ones resulting in frequency dispersion of the measured signal. By carefully measuring the degree of this dispersion we can calculate the total mass/number of interacting electrons between us and the pulsar. If we then make educated assumptions about the average density of these free electrons in the space between us and the pulsar we can calculate the distance."
] |
[
"Thank you, this is what I was looking for."
] |
[
"I think you're half remember som facts about the plaque on the Voyager space probes. This map was designed by Frank Drake to shown the location of the Earth relative to 14 pulsars. Pulsars are rapidly rotating neutron stars which emit beacons of radio waves. The precise timing of the resultant radio pulses provide markers observable in radio wavelengths across broad stretches of the galaxy."
] |
[
"Why did every single species in the Homo genus except for Homo sapiens sapiens go extinct?"
] |
[
false
] |
From what I can gather Homo neanderthalensis for were intelligent enough to make tools out of bone and rock for example, so why couldn't they evolve alongside what would eventually become modern humans? Did our species' "merge"?
|
[
"To a first approximation, every species that has ever lived is now extinct, so the unusual thing is that H. sapiens is still around. ",
"Species don't last all that long, geologically. The average is a couple of million years, but much shorter periods are not unusual. Most of human ancestors and cousins probably did last around that long. Homo sapiens is only a couple hundred thousand years old, and Neanderthals probably lasted about twice that long before going extinct. So neanderthals were arguably more successful than sapiens so far; we have another 200,000 years to show we can do better. ",
"What's more, for the majority of H. sapiens species' lifespan, multiple Homo species did coexist. Neanderthals and sapiens coexisted for about 150,000 of the 200,000 years sapiens has been around; probably so did Denisovans, and \"hobbits\" were around for a fair bit of that too. So it's only the most recent quarter of our species lifespan that we've been alone. ",
"H. sapiens and H. neandertalis did interbreed, but the species didn't merge. Successful interbreeding was extremely rare, on the order of one or two successful interbreeding per generations (interbreeding per se was probably rare, but the hybrids were probably subfertile at best -- male hybrids were probably completely sterile). That's nowhere near enough to merge the species. ",
"No one knows why Neanderthals went extinct, or why sapiens succeeded them. There may well have been interspecies conflict, but one most important point was the Neanderthals and sapiens needed different ecosystems, and climate change led to Neanderthals running out of the denser forest they needed for their ambush-type hunting, with sapiens preferring the lighter forests and the half-open savannahs that were left behind. Quite possibly it was a combination -- in previous climate changes, Neanderthals were able to cope with the new environment reasonably well, but this time there was a smaller, faster, better-adapted cousin already there, competing for food and resources, and that may have been enough to push them over the edge. "
] |
[
"It's hypersimplistic to just say we outcompeted them. For fifty thousand years, sapiens and neandertalis took turns with Europe. When it was cold, the Neandertals dominated; as it warmed up, Neandertals moved North and sapiens moved up; then it cooled down again, and sapiens retreated to the sun and Neandertals moved South again. Finally, one climate swing was too much, and neandertalis disappeared forever. ",
"So it's probably technically true that sapiens outcompeted neandertalis, but the opposite is also true; in other cycles, neandertalis outcompeted sapiens. It's not some intrinsic virtue in H. sapiens that let us survive while Neandertals disappeared; we just got the climate breaks at the right time. As you say, it is all about niche partitioning; Neandertals and sapiens used different niches, and the Neandertal niche was taken away -- just as the sapiens niche was periodically taken away at intervals too. ",
"We know almost nothing about Denisovans, so we can barely speculate about them. Apparently they co-existed with Neandertals for quite a while; did one or the other out-compete each other, were sapiens involved, or what? Did they use different niches? We know almost nothing about their physical appearance, though maybe they were Neandertal-like and similarly cold-adapted, so maybe they lost their niche at the same time? "
] |
[
"Sure it's simplistic to just say Homo sapiens sapiens outcompeted other humans, but that doesn't make it inaccurate. My issue is that when people discuss humans they try to personalize things, overcomplicate arguments, and/or ignore biology. My argument is that biology and the inherent competitive nature of biological systems is what's really important when answering this question. ",
"We aren't just discussing our species, but rather our subspecies which isn't nearly as old. While the species Homo sapiens has been around for about 400K years, Homo sapiens sapiens only emerged 100 KYA, and only began spreading out of Africa around 50 KYA. In that 50K year time period all other humans disappeared. Climate shifts (ie rapid --on geologic scales-- switches between ice ages and warming periods) were happening since a few million years before the first human populations evolved (and may in fact have been crucial in creating an environment for Humans to evolve in in the first place), and there was always pretty decent diversity of human species (at least since Homo erectus started spreading across the world 2 million years ago)... until modern humans arrive. I think it's more likely than not anatomically modern humans played a crucial role in the disappearance of other human species; and the most likely role that would have been is being a better competitor for resources.",
"The rise of anatomically modern humans didn't coincide with the extinction of just Homo neandrathalensis but also all the other human species on the globe. Homo erectus and it's descendants had spread all over the old world, yet none of them last longer than a few millennia after modern humans enter the area; Homo neandrathalensis hangs on the longest for 30K years or so side by side with modern humans and interbreads with them, but most other human species disappear rapidly: Once the first modern human bones appear in an area there are no further traces of non modern populations within a few thousand years (even other H. sapien groups disappear once H. s. s. emerges on any given scene). There is an off chance this rapid decline in human diversity that coincides with anatomically modern human migration is due to climate, but I think it's more likely H. s. s. has a genetic predisposition for language and social skills (my pet hypothesis, arguably it could be memmetic or any range of genetic traits unique to H s. s., I just think we are hyper focused on language and social interaction so I think these are the key adaptations of modern humans that causes their succes) that gave them an advantage over other human groups causing them to outcompete other human populations. Maybe it's a combination of the ice age and human migration since they coincide (and there would be even less resources to compete for during an ice age), but nevertheless modern human migration seems to be a key player in the disappearance of other human populations.",
"My argument is that the fossil record shows the most likely explanation for the disapearance of most human populations over the past 50K years is that anatomically modern humans simply outcompeted other humans. They were better at procuring the resources. Also the historical record of human behavior demonstrates it's likely modern humans weren't averse to the use of violence in procuring resources and eliminating competition, which could have been devastatingly effective to other human species. I don't agree climate change was likely main cause in the extinction of non modern humans. Rapid climate shifting was part of the long term environment humans as a larger group developed and diversified in. Without modern humans climate shifts would have done what they had done before, eliminate some groups but cause the rise of others; modern humans alone and their capacity to outcompete other human groups is the best explanation for why Homo sapiens sapiens are the only ones left on Earth today."
] |
[
"How can Antiprotons annihilate with Neutrons?"
] |
[
false
] |
I thought annihilation requires a particle and its specific anti-particle but I read in a book about antimatter that antiprotons annihilate with neutrons. How so?
|
[
"Hadrons are made of quarks. A neutron has valence quark content of udd and a proton has valence quark content of uud. So an antiproton has antiup and antidown quarks which can annihilate with up and down quarks in a neutron. They can’t fully annihilate each other; there will still be some quarks in the final state (probably in the form of pions)."
] |
[
"Its possible! Pions are a combinations of quarks and antiquarks. ",
"",
"https://en.wikipedia.org/wiki/Pion",
"",
"There are three types and have been widely studied."
] |
[
"So it would be possible to keep matter and antimatter closely together with no annihilation happening if you make sure that they have no quark type in common?",
"Not sure if any kind of matter/antimatter combination exists which satisfies that condition."
] |
[
"Does light always move?"
] |
[
false
] |
Are there any conditions where light can become stationary? I'm thinking maybe at the event horizon of a black hole? Would there be any way to detect that this was occurring?
|
[
" Yes.",
" It's a neat consequence of special relativity that light ",
" move at the speed of light. ",
"Einstein's two postulates that form the basis of special relativity say that (1) the laws of physics are the same in all inertial frames, and (2) the speed of light is the same in all inertial frames. One key idea of an inertial frame is that when you are in one you feel like you are at rest. For example, a plane at cruising altitude or you in your car at highway speeds or you sitting at your desk - these are all inertial frames, and if you close your eyes, these all feel the same to you. A ",
" If light was to have such an inertial frame associated with it, it breaks the second postulate- that light is always moving. Because of this contradiction, we have to conclude that light has no inertial frame (where it can be seen at rest). It's an odd consequence- light ",
" move at the speed of light!",
"I'm thinking maybe at the event horizon of a black hole? ",
"This is actually a very good question; a photon emitted at the event horizon is a funny thing. A part of you thinks that it might be stuck there, and as fast as it tries to go up it makes no progress, as if it was on a treadmill. The reality is a little different from this, but for practical purposes it's a good analogy. The core physics actually depends on whose frame you are observing the photon in! Since the photon doesn't have a frame, we have to decide who is observing it. In the frame of an infalling observer, who will pass the photon on their journey across event horizon into the black hole, the photon will appear to be moving out and away from the black hole at the speed of light, as it should. In the frame of an observer distant from the black hole the photon will appear to be infinitely redshifted because of this sort of 'treadmill' analogy I tried to make. Effectively, they won't see the photon. ",
"An interesting piece of the black hole, which I like to tell people about a lot on askscience, is the photon sphere (not to be confused with the photosphere of a star like the sun!). The photon sphere is the distance where the required orbital velocity for a circular orbit is equal to the speed of light. A photon traveling parallel to the event horizon will actually end up orbitting the black hole at this distance. If an astronaut were to be at this point, they could look forward and see the back of their head!",
"Would there be any way to detect that this was occurring?",
"Aside from observing redshifts and setting up fancy clocks on rockets like I described above? I guess that's a better question for an experimentalist, which I am not. "
] |
[
"Light always moves at the speed of light ",
".",
"Light in a medium can be much slower. One way to look at it is that the photons are constantly hitting atoms of the medium, being absorbed, and then being re-emitted later, which takes time."
] |
[
"Is it correct to say that the individual photons are moving at light speed within the medium, but the average velocity (group velocity?) is very low or zero? "
] |
[
"What do non-human primates do with their dead? How do they mourn them? What do they do with their bodies?"
] |
[
false
] | null |
[
"Chimpanzees mourn their dead and even have what could be described as rituals. Other primates seem to experience grief as well. This article describes ",
"death rituals in the animal kingdom",
". Warning: it's very sad. I still don't know what they do with the bodies. Apparently, it's pretty rare for humans to actually witness a natural death in the wild."
] |
[
"Hello,",
"Turkish guy here. Magpie's are very common here and i really love them. i know they are not primates but i have a cool fact about them that seems relevant. ",
"https://www.eiu.edu/humanitiescenter/pdf/The%20Dying%20Animal.pdf",
"According to a report by the\nCornell Lab of Ornithology, yellow-billed magpies\nreact to a death by descending on the carcass and\nhopping around and squawking (Dickinson and Chu\n2007). Ethologist Marc Bekoff observed “funeral be-\nhavior” among a group black-billed magpies: “One\napproached the corpse, gently pecked at it, just as an\nelephant would nose the carcass of another elephant,\nand stepped back. Another magpie did the same thing,”\nBekoff reported. “Next, one of the magpies flew off,\nbrought back some grass and laid it by the corpse.\nAnother magpie did the same. Then all four stood vigil\nfor a few seconds and one by one flew off” (The\nTelegraph 2009, ¶5–¶6).",
"TL:DR magpies inspect their dead and decide what is the cause of death. i read somewhere that if they do not like the cause of death then they abandon an area but i do not have source rn."
] |
[
"Primatologist here! ",
"This is kind of a tough one to answer for a number of reasons. ",
"First, any reaction seen is really going to depend on the type of primate and the social system of that primate. In more social species you’re probably more likely to see something interesting than in less social species. Simply, there’s more opportunity for an animal to encounter a dead conspecific. Moreover, in such species there is often a hole left in the social life of the group (and that of its individual constituents) when an animal dies. This can lead to changes in, or a reshuffling of, group dynamics and/or individual behaviors following the death of an individual - particularly if the dead animal was central to the group. In solitary species this isn’t going to be as much of a factor. ",
"Second, when observing primates, it is actually really rare to witness the death of an animal and following group responses. Primates are long lived, and the odds that you will be there on the day one dies is pretty low if they are an adult - although you are more likely to encounter a dead immature due to high infant/juvenile mortality in many primate species. In several thousand hours of observational time following primates, I’ve encountered dead study animals on 5 occasions. Of these, I’ve only seen one actually die. Usually, animals pretty much just disappear, and we’re often we’re not sure if they are dead or have transferred out of their social group. In the case of predation, it’s likely there will be no body, although you might find parts later. Basically, recording what goes on after a death is hard since it is so rare to observe.",
"That said, I can provide a few anecdotes about what I’ve seen with wild primates interacting with dead conspecifics. I’ve seen two mothers with dead infants -one a macaque and the other a ring tailed lemur. The macaque basically carried her dead infant around for a day or so before finally letting it go. Primatologists don’t like to infer mental states to animals, but she definitely seemed confused and down about the situation. With the lemur, I actually saw the infant die. Mom attempted to carry the infant with her hands while walking bipedally, but dropped the dead infant after 5-10 minutes so that she could keep up with the rest of her group. Once the group stopped some distance away, she returned to the body of the infant (which I was inspecting and preparing to take back to the lab). She basically stared at me from a few meters away while I took photos of her dead kid. Again we don’t like to infer mental states of animals, but she seemed to be in a bad way, or at least hoping that maybe the kid would be alright when she came back for it. I personally felt kind of embarrassed to be doing my job while she sat there.",
"I’ve also seen macaques checking out the body of a dead young adult male. These seemed to mainly be members of the “bachelor” group he was hanging out with at the time. While I noticed they were interested in his body, I didn’t get any good observations as they came after me aggressively when I went to see what was going on. I basically had to get out of the area to avoid being mobbed. I don’t know if they thought I had killed him, or if they were protecting the body, or something else. Interesting behavior though.",
"Edit: Wow! Thanks for the gold!"
] |
[
"Is the gravitational attraction pulling us constantly with the same amount of force in different locations or it differs, what about if you're on a boat in the ocean?"
] |
[
false
] | null |
[
"It varies by up to 0.7%",
". Some of the variation (0.3%) is not, strictly speaking, due to variation in gravity, but due to the earth's spin creating a centrifugal force which is greatest at the equator. If you want to weight the most, stand on the north pole. To weight your least (on the surface of the earth) you need to climb a high mountain in Peru. Also, if you start digging a hole you move closer to the centre of the earth which makes you heavier."
] |
[
"It differs. Gravitation is towards mass, so mass distribution affects the distribution of force in the gravitation field. Same in the ocean. And, of course, celestial bodies affect the sum total of gravitational force you experience."
] |
[
"That is what I was looking for and it's what I thought too, makes sense, thank you!"
] |
[
"Is there something like the \"double dabble\" algorithm, for trinary/base 3?"
] |
[
false
] |
[deleted]
|
[
"It looks like it could be modified pretty easily. First off, instead of adding three to numbers that are at least five before the left shift, you add six to numbers that are at least ten (taking them to at least sixteen) after the left shift. The end result is the same, but it makes it a bit clearer and makes it generalize better.",
"Binary coded decimal uses four bits for each digit, so there's 16 possibilities. Ternary coded decimal would use three trits, so there's 27 possibilities. Instead of bringing it from 10 to 16 , you have to bring 10 to 27, so on the step where you add 6, you instead add 17."
] |
[
"Quick note, relized base 3 is probably called ternary, not trinary."
] |
[
"Thanks! Very clear explanation."
] |
[
"If a planet is no longer rotating but still revolving around a star, will the planet start rotating again?"
] |
[
false
] | null |
[
"How does it transfer it's rotational momentum?"
] |
[
"How does it transfer it's rotational momentum?"
] |
[
"The star's gravity will raise a tidal bulge on the surface of the planet: as the planet moves in its orbit the bulge will become offset from the star-to-planet radius line. The star's gravity then pulls on the bulge, creating a net torque which causes the planet to rotate.",
"It's exactly the same as the usual ",
"Tidal locking",
", except it speeds up rotation rather than slowing it down."
] |
[
"Is time discrete or continuous? What would help to indicate that it is one vs. the other?"
] |
[
false
] | null |
[
"It’s continuous, as far as we know."
] |
[
"It's possible that time is discrete on a scale too small to probe experimentally using current technology. Experiments sensitive to phenomena on shorter timescales could change the status quo.",
"I imagine there's no way to prove it experimentally other than to directly show that time is discrete. But even with a negative result, it's always possible that the discretization is just too small to measure with that particular experiment."
] |
[
"What would help to support this argument? Is this something that could be testable in theory, and we just don't have a \"precise enough\" way of measuring time as a unit yet?",
"Would this be something more likely to be proven directly or proven indirectly (by eliminating the other possibility)?"
] |
[
"How can you lose members because of diabetes?"
] |
[
false
] | null |
[
"Diabetes causes problems with the circulation. ",
"The metabolic differences in uncontrolled diabetes, like high levels of glucose and fatty acids in the bloodstream, trigger changes in the cells that line the walls of blood vessels. Over time those walls stiffen, thicken, and contract, leaving much less room inside the vessel for blood to flow. ",
"Lack of blood flow starts to affect the nerves first. The lack of oxygen causes slow damage over time. ",
"As the nerves start to become damaged, they stop transmitting signals correctly. The feet and toes become numb. Numbness makes the person more likely to injure themselves by accident. It also means that if the person does get an injury, they might not feel it. A bump, scrape, or cut on the affected extremity can go entirely unnoticed unless the person inspects the area and sees it. ",
"The lack of circulation also makes it very difficult to heal from any injury. There are no resources getting there to grow new tissue, and white blood cells cannot reach the area to fight off bacteria. Any small bump or scrape can lead to an infection-- especially if the person didn't notice it and therefore didn't clean the wound. ",
"So an infection starts. Bacteria take up residence. Because there's no blood getting to the infected area, the body's defenses cannot get there to fight them. The infection worsens over time and works its way deeper into the body. Eventually it reaches the bone, and settles in to start eating it. ",
"A bone infection, called osteomyelitis, is very dangerous and tenacious even in a healthy person. In a diabetic person with bad circulation it's practically impossible to treat. It will steadily continue getting worse, spreading further up and further in, until it becomes life threatening. ",
"The only way to stop the infection is to surgically remove the affected body part."
] |
[
"Peripheral neuropathy is one of the long-term consequences of uncontrolled diabetes because high blood glucose damage nerves among other things, and people lose sensation in their feet (higher parts can be affected too, but feet are most common) and don't realize when they get an injury -- could be from stepping on something sharp or slow development of pressure sore from wearing ill-fitting shoes. It gets infected, gets worse, and eventually the infection spreads to the bones and end up with amputation. ",
"It's just one of the many consequences. Uncontrolled hyperglycemia messes up other organs too. They can lose their vision (diabetic retinopathy). Their kidneys can get damaged and end up with hemodialysis."
] |
[
"Another aspect of hyperglycemia is that it effects the capillaries. Unhealthy necrotic growth of capillaries occurs which lead to hemorrhaging of lymphatic fluids and blood with poor oxygen transport leading to tissue damage and infection. That's why exercise is so important for any diabetic. Exercise improves insulin sensitivity and promotes healthy capillary beds, improving circulation."
] |
[
"Do other elements occasionally fuse in our sun? Elements like Helium, Lithium, etc.? Or is it strictly Hydrogen only?"
] |
[
false
] | null |
[
"Well, yes and no. The sun gets its energy from the chain of reactions that leads from 4H to 1He. But there are actually several different chains that lead to the same result. It's not just like 4 hydrogen atoms all meet up and the same time and out comes helium.",
"Most of the time you're getting the energy from the ",
"p-p chain",
", which consists of fusing H, a light isotope of He, Li, and Be. But the sun does get ~2% of its energy from the ",
"CNO cycle",
" which involves (obviously) fusing C, N, and O atoms in a reusable cycle.",
"So there's actually a lot of different elements that are being simultaneously fused in the Sun's core to end up with the net result of 4H -> 1He."
] |
[
"Our sun is a main sequence star. What that means is that it is burning only (with perhaps exceptionally minor deviations) Hydrogen in it's core. Hydrogen is the easiest element by far to fuse, starts fusing the earliest. As a star collapses from a cloud of gas, it's interior heats up and the pressure increases more and more. Eventually, it becomes hot and dense enough to fuse Hydrogen into Helium in the core. The act of doing so stops the contraction, and cuts off the need for burning heavier elements (which require hotter temperatures and pressures, and are less efficient) until the star runs out of easily fusible Hydrogen in the core. Once that happens, the star will leave the main sequence, and either die, or start burning Helium in the core (and Hydrogen in a shell around the core), depending on how massive it is."
] |
[
"A much more in depth answer. Thanks."
] |
[
"What exactly is gluon fusion and why is it the primary means of Higgs production at the LHC?"
] |
[
false
] |
I'm studying the Higgs for a highschool course and I'm more or less just curious as to what gluon fusion is other than just the union of two gluons. As well as why this is used so exclusively at the LHC? If anyone had the time to explain other methods such as proton-proton collisions etc that'd be great.
|
[
"This is an extremely intricate and complex process. So instead of trying to paraphrase and give you an explanation that probably won't satisfy your curiosity, check out ",
"these",
" ",
"links.",
"They have some good explanations of the process, along with some math. The math may be too over your head, but it is very interesting to see the process worked out. Hope this helps."
] |
[
"Like ",
"/u/IKinetic",
" said, it's and intricate and complex process. But I'll give it a try. The explanation won't be mathematically rigorous, but it should give you a rough idea. And it aligns with the intuition of an experimental particle physicists (theorists might cringe a bit though, but psh, who needs 'em).",
"So first, you have to know how we would ",
" to make Higgs particles if it were possible. And for that you need to know about pair annihilation.",
"So when matter and antimatter meet (that is, when a matter particle and antimatter particle collide), they ",
" each other. What does that mean? As an example, let's take an electron, and it's antimatter partner, the positron. When an electron and positron collide, they usually produce photons, particles of light, and we say they annihilate into photons. The energy that was locked up in the mass of the electron and positron turned into the energy of the photons by E = mc",
" (energy = mass).",
"Now in some cases, it is possible that an electron/positron pair could annihilate into other particles, such as a Z boson, though is is very unlikely except under very specific circumstances.",
"In principle, it is possible to produce a Higgs via electron-positron annihilation like this. However, the Higgs is a bit different and this method won't easily work. The problem is that the lighter the particle-antiparticle pair, the less likely you are to produce a Higgs. And electrons and positrons are basically the lightest particles out there.",
"So we want to annihilate heavy particles. The heaviest particle we know of is a ",
". It is about 340,000 times heavier than an electron. So a thing that we would love to be able to do is take a bunch of top quarks and a bunch of anti-top quarks and smash them into each other. The Higgs would get produced all the time, and everyone would rejoice!",
"One problem: the top quark decays (turns into other lighter particles) in a tenth of a billionth of a billionth of a billionth of a second. So it disappears immediately after we make them, and we can't directly use it for anything.",
"However, particles that we do have that are stable are protons. They're everywhere. But protons aren't fundamental particles (they're made of other particles), and we don't really talk about collisions unless it's between fundamental particles. Protons are basically bags of three quarks (two up quarks and one down quark) held together in a sea of gluons. ",
"Now the LHC collides protons and protons. But with two protons and no antiprotons, there are no antiparticles in sight! How are we going to get a Higgs without them?",
"Well there's a way around this. Let's take a snapshot of our ultra-fast moving proton. There is a chance that one of the gluons in the sea that holds the quarks together happens to have a lot of energy. It's just random chance that one gluon could happen to be moving really fast inside the proton. ",
"If two protons collide and in each one there is a gluon that has a lot of energy, these two energetic gluons can collide with each other. This is ",
" generally.",
"There can be ",
" in this gluon collision collision that they can actually ",
" some top quarks (again via E = mc",
" In fact, they can even create a top quark and anti-top quark together. Then these two top quarks will quickly annihilate with each other and have chance of producing a Higgs. So ",
" we've managed to produce a Higgs via with top quarks!",
"A similar thing happens in another central Higgs production method: vector boson fusion. In this case, it's not top quarks that get produced, but W and Z particles (which are together called the ",
"), which are the next heaviest particle we know of. If you get a W and anti-W, or if you get two Z's (the Z is actually it's ",
" antiparticle), then they can annihilate and produce a Higgs. Remember the Higgs like to be produced from heavy things. Usually the W's and Z's for vector boson fusion come from a quark collision, rather than a gluon one. At the level I'm explaining it, Higgs production via gluon fusion and vector boson fusion are otherwise similar.",
"The reason these processes are primary Higgs production methods are because, as I've said, we really need heavy particles around to make a Higgs. The issue is that the heavy particles we need (top quarks, W's and Z's) are themselves produced relatively rarely. But it balances out that these methods are ",
" better than producing a Higgs directly with collisions of lighter particles that we have around.",
"These difficulties are why it was so hard to make the Higgs, and why it wasn't discovered until 2012, when the particle itself was suggested in 1964, nearly 50 years earlier.",
"Note to physicists: I know that the top quarks in glue-glue fusion are virtual particles in a loop. I didn't want to bring in virtual particles, since they're weird and don't really exist and this is an explanation at the high school level. Calm the knee-jerk reaction to point this out: trust me, I feel it too. I also know that you wouldn't be resonantly producing Higgs at a top-antitop collider if the tops are on-shell, but that's not the point I'm trying to make.",
"EDIT: If you have any questions, certainly feel free to ask. This is complicated. I also often forget to explain concepts and words that I use everyday and forget that most people don't know."
] |
[
"These are things you learn perhaps at the end of an undergraduate physics major, or at the beginning of a physics PhD program in particle physics, depending on what schools you're talking about. A lot of this knowledge comes from doing research in LHC-related experiments and often not so directly from classes. Many of these things are rather specialized, so it won't be covered in a general physics curriculum without a particle physics focus.",
"The subject that underlies all of particle physics (among other things) is ",
"Quantum Field Theory",
", which is a notoriously difficult subject, requiring years of preparation to begin to really tackle. The physics you'll cover in high school is an absolutely necessary foundation to ever reach a good mathematical understanding of particle physics.",
"That begin said, if you want to start learning about these kinds of things, there are tons of non-mathematical popular science books available. Pick one that sounds interesting and give it a shot! That's what I did all those years ago in high school!"
] |
[
"Why do cars make a \"whooshing\" sound when you drive past them, even if they are stationary?"
] |
[
false
] |
When a car drives past, you can hear a whoosh sound because (I assume) the displacement of the air. However, why would this sound occur when you are driving in a car with your window open, and you pass a stationary car? My friend suggested this was do to the interaction of the displacement of the air with a large, stationary object, but I've heard this sound even from a few lanes over when you wouldn't expect the displacement of air as you drive by to affect the parked car. I'm guessing that this is some sort of echo effect, echoing the sound of my vehicle passing theirs. So, what's the truth?
|
[
"Its the Doppler effect of the sound that you're making bouncing off the other car."
] |
[
"It's just the sound (of the air turbulence around your car) bouncing off the other cars. If I have a noisy brake, for example, I'll notice it more when I've got my window down, drive by a pack of cars, or drive near a high curb.",
"You friend is somewhat right, though. As your car moves, it does displace air, and that air does get pushed around nearby stationary cars, but the sound that you hear is almost surely due to your own car's turbulent wake. The sound pressure is proportional to some not-small power of the velocity gradient (is it 4 or 5?), and the velocity of air around your car is always going to be significantly more than the induced velocity around the stationary cars that you pass."
] |
[
"No worries! I have been fooled by much simpler stuff."
] |
[
"Why is the universe Accelerating in expansion?"
] |
[
false
] |
[deleted]
|
[
"But one tinier than what we'd expect by a factor of 10",
" and that's just assuming that no Planck-scale physics adds to the vacuum expectation value. So it's a possibility but certainly not the only explanation for the acceleration."
] |
[
"That's a good question. If the Universe's energy budget were dominated by normal matter or radiation then yes, the gravity of all the stuff in the Universe acting on the rest would cause it to decelerate. This is why we were so surprised to find that the opposite is happening!",
"So obviously the assumption in the question must be wrong, that gravity is universally attractive. I can think of two major possibilities (plenty of others exist, though most can be put into one of these two forms): either the energy density of the Universe is in something which ",
" have attractive gravity (such as the quantum vacuum, which has a constant density even as the Universe expands), or gravity isn't necessarily attractive on large scales, usually due to the presence of a \"fifth force\" which pops up on cosmic distances.",
"Sadly, I don't know of any proposals which are elegant, natural, and match the data. Well, perhaps it's not so sad, because it keeps folks like me employed."
] |
[
"Short answer, but i am sure someone will correct me or fill in the blanks, if needed:",
"Back in the day, someone found out that the density of the universe, would tell the shape and the ultimate fate of the universe. They tried to measure the density of the universe, but found that the measured density could not alone explain the acceleration of the universe that was seen by experiments. By measurements of the cosmic microwave background, they found out what the shape of the universe should be, and were able to calculate the expected density of the universe. They found that they could only account for around 30% of the mass needed to explain the acceleration. ",
"The rest of this needed mass, and thus the acceleration of the expansion of the universe, was then explained by the introduction of dark energy. And noone knows that dark energy is, but we can see that it should be there."
] |
[
"Did the earth form from the Sun \"spitting it out in the form of a meteorite?\""
] |
[
false
] | null |
[
"All of this is pure insanity. Please disregard that entire paragraph. If you're curious to our best understanding, simply search around for AskScience posts or Wikipedia articles on the formation of the solar system, the sun, the earth, dark energy, meteorites and basic chemistry."
] |
[
"That's what I thought...thanks. Now how to break it to him?"
] |
[
"Very gently?"
] |
[
"Is there any scientific consensus regarding the longterm effects of smoking marijuana?"
] |
[
false
] |
[deleted]
|
[
"The appropriate answer to OP's question is that no, there is no strong consensus on the long-term effects of cannabis use (I avoid saying \"smoking\" because the smoke part is another health risk altogether, and we'll leave this strictly up to cannabis).",
"I certainly agree that there is a lot of promising research showing potential medical uses for THC and other cannabanoids, however you've chosen to review a select few in your post, and have also selected excerpts in a way that somewhat misrepresents the actual state of the science. ",
"Your bias on this subject is pretty apparent and bias is a major problem in cannabis research. So much of the research is clearly either \"pro\" or \"anti\" cannabis and it really influences the methods and results of some of these studies. It makes finding a clear answer very difficult because we become skeptical of the agenda of many researchers. As I'm currently involved in a study doing fMRI scans on patients immediately after smoking THC (we have a bong that works inside the MRI machine) I'd say I'm in a pretty good spot to comment on this.",
"Furthermore, to draw the conclusion that it is not only safe but is also \"healthy\" is irresponsible and extremely unfounded in my opinion and I'd argue that this statement:",
"So please, keep enjoying your cannabis while also enjoying the fact that you're helping your body heal itself.",
"is not only inaccurate and misleading, but bordering on medical advice and should be removed from your post. "
] |
[
"The appropriate answer to OP's question is that no, there is no strong consensus on the long-term effects of cannabis use (I avoid saying \"smoking\" because the smoke part is another health risk altogether, and we'll leave this strictly up to cannabis).",
"I certainly agree that there is a lot of promising research showing potential medical uses for THC and other cannabanoids, however you've chosen to review a select few in your post, and have also selected excerpts in a way that somewhat misrepresents the actual state of the science. ",
"Your bias on this subject is pretty apparent and bias is a major problem in cannabis research. So much of the research is clearly either \"pro\" or \"anti\" cannabis and it really influences the methods and results of some of these studies. It makes finding a clear answer very difficult because we become skeptical of the agenda of many researchers. As I'm currently involved in a study doing fMRI scans on patients immediately after smoking THC (we have a bong that works inside the MRI machine) I'd say I'm in a pretty good spot to comment on this.",
"Furthermore, to draw the conclusion that it is not only safe but is also \"healthy\" is irresponsible and extremely unfounded in my opinion and I'd argue that this statement:",
"So please, keep enjoying your cannabis while also enjoying the fact that you're helping your body heal itself.",
"is not only inaccurate and misleading, but bordering on medical advice and should be removed from your post. "
] |
[
" comments as of this post.",
"Very few scientific answers. Even fewer cited ones. And a lot that list cited benefits but not the downsides.",
"Basically, IntoTheMystic, you're going to have to go to a completely different website because this one is too biased to ever be a reliable source of information.",
"However, when it comes to cannabis, you're going to have bias problems no matter where you go, unfortunately.",
"I used to be a huge pothead, loved it. Quit completely for 3 years. Now, I only smoke occasionally. I would love to see it legalized. But, am I the only one that would be capable of being completely unbiased in my answer? It's really not that hard.",
"I love this subreddit and its intended purpose, but I often find myself disappointed."
] |
[
"How cold would it have to be to slow data packets transmitted over wire? Does temperature even have an effect on this?"
] |
[
false
] |
My friend and I were joking about the cold weather in Canada. I remarked that it was "so cold packets were freezing and ping was timing out." While humorous, it got me thinking -- is this possible? How is our data transmitted over wire? Can it be affected by temperature? If I cooled a section of the wire to just above absolute zero -- what would happen to new data as it flows into that area? Would it just be a giant traffic jam?
|
[
"Many metals become more conductive at lower temperatures, which would reduce the voltage or wattage requirement in order to transmit.",
"Although not all materials become superconductors when cold, all superconductors must be cooled to be superconducting.",
"So, no. There would not be a traffic jam. It would make things easier."
] |
[
"At absolute zero, the average velocity of an ideal gas, solid, liquid, whatever - becomes zero. When you get really really really close to absolute zero, strange stuff starts to happen. But for all intents and purposes, electrons move from one atom to another. ",
"Imagine atoms are like pingpong balls in a box that are constantly in motion, these pingpong balls have a bunch of fleas stuck to their outside. The fleas are like electrons, and they can jump from one ball to another. Now if you slow down these pingpong balls, the fleas have an easier time jumping from one ball to another, right? This is (in very simple terms) why stuff becomes more conductive at lower temperatures."
] |
[
"This is a good question! I know everybody likes to say \"electricity moves at the speed of light!\", but this is not quite true and it leads to interesting contradictions like the one you have mentioned here. Electrons in an ordinary metal conductor do not move at the speed of light, they move at a very slow speed called the ",
"Drift Speed",
" which is independant of temperature, but still nowhere close to the speed of light. The IMPULSE of the conductor becoming charged, however, does travel at the speed of light from one end of the conductor to the other. Unfortunately, my analogy kindof breaks down at this point. So i'll use another.",
"Imagine you have a wire that's like a big long frictionless plastic tube, and inside of this tube there are frictionless ball bearings stacked one next to another all the way down the tube. These ball bearings are like electrons. You can shake the tube up all you want, or cool it as cold as you want, but when you stick another ball bearing in one end of the tube, it's going to force one out the other end at (basically) the speed of light. "
] |
[
"What makes viruses only survive in water droplets, on surfaces, or in air? What about temperature?"
] |
[
false
] |
In this video this doctor says the virus can live on a surface for 9 days, does that mean that surfaces must have moisture on it? Can a virus live in anything that's fat, like oil? What makes other viruses survive without water droplets? (What sort of viruses are airborne?) What makes the HIV virus only survive in blood? Can the HIV virus mutate to live in water droplets?
|
[
"Biological things are quite delicate, and there are many things that can damage any biological matter, for example, oxygen, UV rays, high temperatures, low temperatures, high salts, low salts, the list goes on. The reason why certain viruses only survive in water droplets or blood depends on how delicate the viral capsid (the outer coat of the virus) is. Without the outer coat, viruses do not have the machinery to infect cells and their genetic material is very easily damaged. This is especially true for RNA viruses like COVID-19 - RNases are literally everywhere in the air, and any unprotected RNA can be degraded in minutes and is very unlikely to survive more than a few hours when exposed to the elements. ",
"Anyways, back to the fragility of viral capsids. As I said before, biological things are delicate. Blood and water provide protection against the harsh elements, thus protecting viruses from harmful things like UV radiation and oxygen. Generally, blood and saliva also have some salts dissolved in them, which also helps biological agents \"survive\". Survival in this case meaning maintenance of structure and function. Depending on the composition of the viral capsid, some viruses can be relatively more robust while others can never survive outside of blood. Relatively robust viruses generally are smaller and less complex - this is also why they're airborne - they're small enough to be able to float in the air and be carried away by the wind. This is untrue for COVID-19, since coronaviruses generally are quite large and heavy, hence it will sink fairly soon after it's projected and won't truly be airborne - it will reside in respiratory droplets. ",
"With the background now said, I'll try to answer some of your questions: ",
"does that mean that surfaces must have moisture on it? Can a virus live in anything that's fat, like oil? ",
"It depends on the surface and the virus. Some surfaces have been said to have antimicrobial activities (like sterling silver), though I'm unsure of how this functions and to what extent this is true. Viruses can survive on most solid surfaces at least for a bit though, it really depends on how delicate the viral capsid is. In the case of COVID-19 I believe they won't survive for more than a couple of hours, especially in outdoor environments where there is significantly more UV radiation. ",
"Can a virus live in oil? That's a good question and I can only give an educated guess, which is probably not. Oil can do many things to viruses, including denaturing (inactivating) the capsid proteins, dehydrating (and therefore also inactivating) the proteins, or preserve the virus in a micelle (I believe this is unlikely but happy to be challenged on this with sources). ",
"Like I briefly mentioned, airborne viruses are much smaller (and therefore lighter) than coronaviruses and therefore can be pushed by wind. Most viruses can survive for at least a couple of minutes without water droplets, but whether the survival time is meaningful depends on the virus and how robust it is. ",
"",
"For this questions I'll just address the second part, which is whether HIV can mutate to live in water droplets. For me the answer is almost certainly no. Never say never, but it is HIGHLY unlikely. Mutations are more likely to make any biological agent weaker rather than stronger. Think about it this way - in humans, how often do mutations create cancer (very often), and how often do mutations create the X-men?"
] |
[
"I agree that oils can denature capsid proteins, dehydrate them, but the preservation in a micelle doesn't make sense to me.",
"I think viruses can be preserved in a micelle if its surrounded by water and that tiny water droplet gets trapped in a micelle. Though this happening is pretty unlikely so my answer was probably not, but the possibility exists. Nevertheless the amount of viruses that could survive in oil is likely to be minuscule and oil is terrible for cleaning things, so it shouldn't factor into day-to-day life. ",
"Physical stress, unless microscopic, doesn't really affect viruses. Microscopic physical stress only really occurs pointedly or in extreme conditions both of which only occur in laboratory conditions, so it's unlikely that a virus can be killed by wind blowing on it. ",
"To elaborate more on the stressors - these are all factors that can render either the spike protein denatured or the genetic material unreadable. UV rays do both: they damage the nucleic acids as well as the capsid proteins, probably one of the best if not the best way of sanitizing things, but of course effectiveness depends on strength of radiation and time of exposure. Heat: also extremely effective, depending on how much heat there is either the proteins can get denatured (50C) or chemical bonds get broken (200C). Either way almost nothing survives. Oxygen: our atmosphere actually has quite a high concentration of oxygen which is very reactive and not very conductive to life, it can oxidate and therefore damage the capsid proteins. This is also the same chemical reaction by which bleach and hydrogen peroxide works, just in a less concentrated form. Dehydration/too much salt: these are very similar things - proteins require specifically placed charges to be able to keep their shape, which is aided by salt and water. If there's too much or too little of either, the specifically placed charge interactions disappear or there are too many interactions, and the proteins become misfolded and useless. Acid/Base: also changes the charges which hold a protein together and render it misfolded. Depending on the strength of the acid/base it can also rip apart the molecules. Interesingly and perhaps relevantly, RNA degrades itself in mild bases in a matter of minutes."
] |
[
"Can a virus live in oil? That's a good question and I can only give an educated guess, which is probably not.",
"Could you give an update to your comment if you've come across any new information?",
"I agree that oils can denature capsid proteins, dehydrate them, but the preservation in a micelle doesn't make sense to me. There has to be some level of physical contact between the surface proteins of the virus and the oil. The outward-facing portion of the surface proteins is hydrophilic. How could this lead to the preservation of the virus?",
"airborne viruses are much smaller (and therefore lighter) than coronaviruses and therefore can be pushed by the wind. ",
"How does physical stress affect viruses? I'm wondering about how delicate the entire thing is. Say, if blows in the wind, face stress, break open and is degraded quickly. What other events can provide enough stress for them?"
] |
[
"A black-body with a temperature above 8,000k appears blue. Is it still blue at 100,000k or more?"
] |
[
false
] |
Neutron stars appear white, and they have temperatures above 100,000 kelvin. What's the reason for this?
|
[
"Since a 100,000K star is outputting approximately the same amount of each color of light, it appears white.",
"This is wrong. The problem is that at 100,000 K, the spectral energy distribution is so strongly dominated by incredibly short wavelengths in the ultraviolet/X-ray region that you don't have the dynamic range on that WolframAlpha graph to see the difference in visible wavelengths.",
"What you really need is either a log plot that can simultaneously show very large and very small values, or some math. For example, ",
"here's a log plot",
" of the Planck function for a variety of temperatures...note that on the right side of the graph, all the spectral energy distributions have the same slope. In other words, everything 8,000 K or hotter will look blue.",
"This can also be explained in mathematical terms by the ",
"Rayleigh-Jeans Law",
". This function describes the Planck Law for wavelengths much longer than the blackbody's peak wavelength. Note that this scales as 1/λ",
" , i.e. inversely proportional to wavelength to the 4th power. That means something that's very red (750nm) that has a wavelength about twice as large as something very blue (375nm) will be emitting 16 times as much blue light as red light. This is what explains the right side of all the spectra in the above log plot having the same slope.",
" The above answer is wrong because the plot can't properly show the visible wavelengths. Everything above 8,000 K will be blue, and as you get hotter, it approaches the exact same shade of blue."
] |
[
"I'm not sure, and unfortunately the statement is unsourced. I see a number of people in discussions of this making the same argument I did, but that seems to be naive. ",
"If we consider the ",
"ratio of red to blue light emitted",
", then blue light does continue to be about an order of magnitude higher for even very high temperatures.",
"The only other explanation I can think of is different sources are using different definitions of what the 'color' of something is. The astronomy pages we're looking at might define the color as 'the wavelength in the visual spectrum at which the most light is emitted'. Wikipedia (and myself in my previous answer) might have been working off a definition of color as 'what color the human eye would see if it were to look at the star'. That could explain the different answers here."
] |
[
"We have ",
"Planck's law",
" to describe the light output of a black-body at a particular temperature over different wavelengths."
] |
[
"I have an introductory Physics Question..."
] |
[
false
] |
I'm not sure if this is the right subreddit for this, so let me know if I'm in the wrong place. We are doing the physics unit on Energy, Power and Work, and I am having some trouble figuring out how to work a pretty basic problem. I have linked the problem and my attempted solution below. If anyone could explain how to do this problem, it would really help me understand the rest of the unit... Thanks everyone!
|
[
"In the future you might also try ",
"r/homework help",
" for this kind of question. "
] |
[
"You're attacking this problem the wrong way. Instead of thinking about forces, think in terms of energy. Moving the car forward at a certain speed movies it upwards at a related speed, which can be found using the angle. Using the formula for gravitational potential work=mass*9.8*height, you can then relate its upward speed to a change in energy, which you know to be 35kW."
] |
[
"I am sure that instead of energy, you meant power."
] |
[
"a question involving physics"
] |
[
false
] |
i have a question in regards to ballistics... im looking for an equation(or even a site that i can go to) that i can imput the mass of an object, the speed of said object, and other certain variables... like density wind and thickness of target, to get all the projected paths... NO I AM NOT AN ASSASIN(assasins would know shit like this) im just looking for a computer model im trying to put together
|
[
"If there is no wind, you can solve this directly with the kinematic equations (which I can explain if you like).",
"If there ",
" wind, it's easiest to write a computer program to solve this really. You mentioned computer model - are you comfortable with programming in any one particular language? I can teach you the basics of how to perform this type of simulation if you like - it's fairly simple, provided you know a language already."
] |
[
"Can I ask for clarification on what you're looking for with \"all projected paths\"? What are you projecting exactly? Would it be correct to rephrase your question as \"For a target of a certain size in a certain position, what are all the points I could shoot it from (for a certain muzzle velocity and drag force), and what angle would I need to shoot it at?\""
] |
[
"Well, if there's no drag, then it's just a whole bunch of parabolae.",
"If there is drag, you're going to have to simulate a whole bunch of firings. Each of these will make a line, and you can plot these.",
"For each shot, you start with the initial position & velocity of your projectile. This is six numbers, three for position - x,y,z - and three for velocity - v_x, v_y, v_z. Your programmer will want to do these as an array. You then calculate the acceleration on these objects. There are many equations for drag, but it will be in the opposite direction to the motion (i.e. -v_x,-v_y,-v_z). Gravity will always be -g in the y direction. Then you need to calculate what happens to the bullet as it steps forward. The best combination of simplicity and accuracy is probably the ",
"leapfrog",
" method. You then keep repeating this until your bullet has gone as far as you are interested in."
] |
[
"How would the sky look if viewed from a planet closer to the center of our galaxy?"
] |
[
false
] |
I was just wondering that since the center of our galaxy seems at least to us pretty bright, would it also seem as bright if viewed from a planet orbiting some star there? Or are the distances between starts there still long enough that the the sky would look something resembling a little brighter version of our own night sky?
|
[
"Being closer to the inside of the galaxy, the biggest effect would be that the white band that makes up the Milky Way would be thicker and extend further around, until once you are fairly deep in it would appear to wrap all the way around the sky (although you'll still a lot of individual stars, since only the more distant ones will get all mixed together in a \"milky\" fashion)."
] |
[
"There would still be a day/night cycle provided the planet you were on was rotating sufficiently.",
"The night sky would appear brighter, but still recognizably night and not as bright as day."
] |
[
"Would the stars at the centre of our galaxy be so close to each other that the night sky a would actually be lid up by other nearby stars? So would the be a \"night\" at all?"
] |
[
"Is there any potential for non-random genetic mutation? Is feedback driven evolution possible?"
] |
[
false
] |
Consider if the legs of newborns were amputated at birth. Could this lead to human populations without legs, with stunted, malformed or even huge legs? Intuitively, it seems there might be evolutionary changes relating to traits which provide improved fitness given lack of legs. Leg related selection would be impossible (given you can't tell what your mate's legs were like), unless leg traits are related to, for example, arm traits that are selected for (e.g. huge, long arms, which would be useful without legs, might be associated with huge, long legs, or smaller legs, or whatever). But is there any potentially direct mechanism for altering a genetic trait passed to your offspring in a behaviorally moderated fashion? In short, is there any way genetic traits unrelated to any significant selection process can evolve as a result of behavior, or will they only change due to an association with other selectively significant traits?
|
[
"i know, but it was related to what the OP was asking. i thought maybe reading the article could have answered his question better than me just saying \"not really\" in response to his question."
] |
[
"It seems to me that there are at least two questions here:",
"Consider if the legs of newborns were amputated at birth. Could this lead to human populations without legs, with stunted, malformed or even huge legs? ",
"Yes. Absolutely. For the same reason that cave dwellers are born without working eyes.",
"http://www.talkrational.org/showthread.php?p=1205417",
"Intuitively, it seems there might be evolutionary changes relating to traits which provide improved fitness given lack of legs. Leg related selection would be impossible (given you can't tell what your mate's legs were like), unless leg traits are related to, for example, arm traits that are selected for (e.g. huge, long arms, which would be useful without legs, might be associated with huge, long legs, or smaller legs, or whatever). ",
"I think you're still on the same question as above. I think.",
"Then you switch to a totally different question:",
"But is there any potentially direct mechanism for altering a genetic trait passed to your offspring in a behaviorally moderated fashion?",
"Which is where Lamarkism and Epigenetics become relevant."
] |
[
"this could be of use to you:",
"http://en.wikipedia.org/wiki/Lamarkism",
"also this:",
"http://en.wikipedia.org/wiki/Epigenetics"
] |
[
"Why is that both nuclear fission and nuclear fusion release energy? Shouldn't one release energy and the other absorb energy?"
] |
[
false
] | null |
[
"The reason is that iron is the most stable element. ",
"Why then is iron the most stable element? When lighter elements combine, the net attraction between the nucleons due to the strong force exceeds the net repulsion due to the Coulomb force. Once the nucleus starts to be too big, however, the attractive forces due to the strong force start to level off because they can only go a very short ways. To greatly simplify, for elements larger than iron, the nucleus becomes so big that nucleons on one side of the nucleus don't really feel the attraction from nucleons on the other side of the nucleus. The result is that each proton only feels attraction from nearby nucleons, not the entire nucleus.",
"The Coulomb repulsion has a much weaker distance dependence, however, so even in very large nuclei every proton feels the repulsive force from every other proton, making the nucleus less stable. The larger the nucleus, the more protons are repulsing each other, and the less stable the nucleus is. ",
"This can be mitigated by adding in more neutrons in order to distance the protons from each other further, but there is a limit to this. If there are too many neutrons compared to the number of protons, the neutrons will leak out of the nucleus (this is known as the neutron drip line). ",
"So, since iron is the most stable element in all of this, being the ideal size where every proton feels the strong force from every nucleon, it becomes clear why both fission and fusion release energy. Any reaction which produces an element closer in size to iron will make the element more stable and release nuclear energy."
] |
[
"They do. Either fusing element A and B into C will produce energy and fissioning C int A and B will consume it or vice versa. But people are interested in using nuclear reactions to release energy, not consume it, so they only talk about fusing light elements and fissioning heavy ones, which are the reactions that release energy."
] |
[
"Fe56 is the most stable element and nuclear reactions that move closer to this point release energy. Fusion releases energy until iron is produced, at which point energy must be added back in to produce heavier elements. Fission is the opposite, releasing energy as heavier elements are split until iron is produced, at which point energy must be added back to produce lighter elements."
] |
[
"Is there a genetic disease where the heterozygote has more severe disease symptoms than the homozygote?"
] |
[
false
] |
So we hopefully know that people can carry some genetic mutation as a heterozygote and have minimal (or no) symptoms, but potential offspring who are homozygous will then show the associated disease with worse symptoms, this is common. But I wonder if there are examples of genetic diseases where the heterozygous condition is actually more severe than the homozygote? Say if a single mutant allele incorrectly activates some pathway relative to wild type, whereas in the homozygote this creates such a large change that the cell responds and the net effect is minimal? Or if two different protein variants interfere with each others’ function, whereas again this potentially does not occur in the wt or homozygote? This could be a loss of function or gain of function effect on the protein. I am not thinking about sex linked genes, only autosomal, or compound mutants where the other allele is affected by a second variant.
|
[
"Yes; the best studied mechanism for this is cellular interference. ",
"PCDH19 is the classic human disease example. It's a protocadherin (cell surface protein that affects migration, signaling, etc) on the X chromosome. When both normal and abnormal PCDH19 is present (XX heterozygotes) affected individuals have epilepsy and developmental delay because neurons with different variants behave differently and have trouble forming networks with each other. XY males, regardless of whether there is a mutant or wt allele are normal. XXY males or mosaic males have the same phenotype as heterozygous females. ",
"This is an illustration: ",
"https://www.ncbi.nlm.nih.gov/books/NBK98182/figure/depienne.f4/",
"EFNB1 is another example: ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3605834/",
" ",
"OLD paper postulating this: ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1686061/",
"Edit: I know you said you're not interested in sex chromosomes, but this disease mechanism applies just as easily to autosomal genes. We can predict based on males that a true mutant homozygote would be unaffected while a compound heterozygote would be affected. ",
"The problem with finding an autosomal example is being homozygous outside of a consanguinous situation is exceedingly improbable. Not only do both alleles need to develop a disease causing mutation, but they need to mutate in the same way by chance. Most recessive diseases we see are caused by a compound heterozygous state; which while not wild type, it also not homozygous."
] |
[
"Maybe. ",
"In sheep and pigs, there’s a complex scenario (“polar overdominance”) in which only heterozygotes with a particular mutation show the phenotype:",
"A single nucleotide polymorphism in the DLK1-DIO3 imprinted gene cluster alters gene expression … muscle hypertrophy only occurs in heterozygous animals that inherit a normal maternal allele and the callipyge SNP on the paternal allele (+/C).",
"—",
"New insights into polar overdominance in callipyge sheep",
"The details of how this works don’t seem to be well understood and I’m not going to try to summarize the complicated tentative explanations. In sheep and pigs, the muscular hypertrophy phenotype is at least somewhat desirable, but in humans there may be a similar mutation that, in heterozygotes, is associated with severe obesity. ",
"In a study sample of 1025 French and German trio families comprised of both parents and extremely obese offspring we found a single nucleotide polymorphism (rs1802710) associated with child and adolescent obesity. Analysis of the allelic transmission pattern indicated the existence of polar overdominance, an unusual mode of non-mendelian inheritance in humans previously known from the callipyge mutation in sheep.",
"—",
"Preferential reciprocal transfer of paternal/maternal DLK1 alleles to obese children: first evidence of polar overdominance in humans"
] |
[
"A bit indirect, but some forms of achondroplasia are so severe that homozygotes are incompatible with live birth, and thus heterozygous (or homozygous would type) are the only observed.",
"A better example: ABO blood types in terms of blood contaminagion (whether available acceptable blood types, or maternal-fetal hemolytic anemia). Diversity of heterozygous actually works against a “phenotype” of immune acceptance."
] |
[
"Does relativity have any effect on temperature similar to how length becomes contracted and time gets dilated?"
] |
[
false
] | null |
[
"So first to clarify your question. Temperature is a number a number that becomes useful when we are talking about a box of particles, in fact only if the box of particles is in something called thermal equilibrium. By saying a box of particles is at temperature T we are really saying that the distribution of particle velocities (or energies sometimes) in that box has a certain shape.",
"There are two possible cases I think you could be talking about. The first is where you have a box at a non-relativistic temperature (which we will get to shortly) and it moves past you at a relativistic speed. This case is simple, we always define temperature as only being due to the random thermal motions of the particles, not the bulk motion, otherwise running water would be \"hotter\" than still.",
"So if you wanted to know the temperature of a box of particles that flew by you, it would have to be the same as if it were at rest as all you have done is added an \"offset\" that you could easily account for using your lorentz transform for velocities.",
"The second case is a bit more interesting; (but probably not what you meant to ask) what if you have a temperature that is hot enough that some of the particles are moving at relativistic velocity ",
"?",
"Now, the relationship between the energy of a particle in a distribution and the same particles velocity is a simple matter of 0.5 m v",
" but only when at a non-relativistic velocity. If particles start to move at relativistic speeds then the relationship grows less simple and the lovely math that tells us the shape of the distribution is not the same.",
"For electrons the temperature at which this happens is approximately 300keV or 3GK (3 billion K). For more massive particles it requires it to be much hotter, 5TK (5 trillion K) for protons. At these temperatures approximately 10% of the particles have a lorentz factor of 2 (v=~0.9c). Any element would be fully ionized at these kinds of temperatures making anything this hot a plasma. A plasma this hot could only ever be transient, perhaps the result of a relativistic beam hitting a stationary target or in the core of a supernova.",
"In this case the nice distribution and laws of thermodynamics become a bit skewed to the side but temperature has really become a no-longer-useful concept anyway since these are hardly nicely behaved distributions sitting at equilibrium.",
"At these kind of energies much most the physics is slightly modified and we have access to some cool new effects such as pair production."
] |
[
"An interesting fact is that the EM blackbody radiation spectrum of a cool object looks exactly like a redshifted spectrum from a hot object, and that of a hot object looks like a blueshifted version of a cool object. Which is to say, if you measure temperature with one of those temperature-sensor guns you won't know how hot something actually is until you know how fast it's moving towards or away from you. With starlight you can do this by finding absorption spectra and matching the redshift, so you can still measure the object's \"real\" temperature (the temperature in its rest frame).",
"When you try to hover near a black hole, the gravitational redshift means the black hole's hawking radiation seen from a distance is much cooler than if you try to hover close to it, and if you try hovering near the event horizon you get fried (but if you fall right in without resisting you don't see any radiation). ",
"These effects are mostly about how temperature is seen by other objects, but that does have physical relevance because that's what determines how much energy gets exchanged. A cooler object could be in thermal equilibrium with a warmer object if the warmer object is lower in a gravitational field. "
] |
[
"Actually the OP could be thinking of a third case: the fact that time dilation shifts the velocity distribution of a box of particles. In other words is temperature a relativistic invariant, and if not, what is the transformation. This is something Einstein and Planck attempted to work out in 1907, arguing that temperature is lowered by the gamma factor, but since then the issue has been fraught with disagreement, with many, such as Ott/Eddington/Moller, arguing that it is in fact ",
" by the gamma factor. This has a rich history. As far as I know there is not a consensus on the matter. "
] |
[
"Cysteine to help metabolize the highly toxic 'acetaldehyde' that accumulates during a night of drinking."
] |
[
false
] |
Dear Science, I am wondering if you'd care to comment on the proposal that taking cysteine supplements while drinking alcohol can have a positive effect on the breaking down of the acetaldehyde that accumulates when one metabolizes alcohol. I have heard that people who suffer with the particular enzyme deficiency that leads to the 'Asian flush' while drinking have reported some success with the use of cysteine (paired with vitamin c). However, such people have also reported success, I believe, with taking Zantac or Pepcid AC. Since reading this article I have been taking cysteine and vitamin c very diligently whenever I drink. I started the process originally not because I would suffer any sort of Asian flush reaction, but rather that alcohol tended to make me feel sick to my stomach every morning after drinking (but, oddly, never during the actual night of drinking). Is there any credence to this claim? The rat test described by the article is interesting (that it protected rats from dying after being administered lethal doses of acetaldehyde. I do find it seems to help with my morning-after-drinking nausea, but I am also open to the possibility that I am just building up a tolerance for alcohol. Thanks science <3
|
[
"hangover causes",
"I'm not sure the cysteine and vitamin C are actually helping. The wikipedia article seems to say that most hangover symptoms are caused by a decline in NAD+ concentrations, which is caused by alcohol dehydrogenase and acetaldehyde dehydrogenase activity. Water and food, however, do help."
] |
[
"I thought the same thing. Because of the use of acetic acid as an energy source from the oxidation of alcohol, your blood sugar crashes due to low glycogen release from the liver. This, coupled with dehydration, makes you feel hungover.",
"The old wolf-down-a-poutine-and-drink-three-glasses-of-water-before-passing-out always worked for me."
] |
[
"If you really wanted repeatability in your experiment, you might try Steel Reserve instead of the Natty. Worst hangover/fl. oz. ratio of just about any beer."
] |
[
"Is there anything capable of withstanding direct contact with lava?"
] |
[
false
] |
So, is there anything capable of withstanding direct long-term contact with lava? Like some type of metal or something?
|
[
"You might want to see ",
"my thread here",
" about some of the cool things (pun intended) we do with lava (like ",
" in lava, ",
" lava, etc). You will see shovels, gloves, etc - all handling lava.",
"People are always surprised at how lava does NOT just melt everything. Toss a rock onto a surface flow and it bounces and gets carried along.",
"We tossed small propane tanks into a lava tube (with a magma river flowing in it) - and it took about 20 seconds before the container blew.",
"The gloves we use are Kevlar and Spun Glass and can withstand direct contact to lava (2000 F) for up to 20 seconds without breaching. With those gloves I have actually lifted molten lava with my hands - it is like lifting taffy off the ground. The interesting thing to note is the hard rock under the surface flow is not molten.",
"Once lava hits the surface, as in a surface flow - once the flow stops moving all it takes is 1 inch of solidified lava on top of the liquid lava to support human weight (we regularly walk over molten lava, as long as it has a crust).",
"Lava exploding into the air - where it can rain molten lava around you, also is rather surprising. I've had a couple of blobs hit my jacket and just bounce off (burning the jacket of course). You really don't want to be anywhere where the lava explodes, goes over your head, and lands behind you.",
"That said... any material that has a melting point higher than 2000 F will withstand lava."
] |
[
"If you look at the 3rd picture on my linked post: ",
"http://i.imgur.com/vlbCP.jpg",
"Look at the lava on the ground - I had just lifted that up to show some tourists, and dropped it because I held it for about 20 seconds or so and it was getting pretty hot. Look at my glove and you can see some lava stuck to the finger. Now this is a bad situation because you instinctively want to get that lava off - so you flail your arms - which of course can fling hot lava in all directions.",
"Yes, it is imprecise - because it depends on the amount of contact, the viscosity, etc. In the case of a ",
" lava - it is very fluid and pouring out of a rock like water. In this case you can actually let the lava flow through your gloved fingers. But in the case like my picture - the lava is very thick and taffy like - and it tends to heat things up a lot faster with direct contact.",
"As per the walking over lava - yes... it is an instinctive aversion. We usually wear denim jeans and rugged hiking boots. As you approach a hot flow, your legs will tell you pretty fast whether or not this is a safe enough flow to cross.",
"It is like you describe... as you approach - if it is hot enough you instinctively turn away just like opening a super hot oven door.",
"If you can step up on the flow and take a few strides and don't feel too uncomfortable, you're fine.",
"Since we carry pyrometers - we know that the ",
" point is around 700 F. Past that you can't take too much more."
] |
[
"With the temperature of lava (That is, above ground and not magma, which is below ground) being between 1300 - 2200 degrees F, any alloy or material with a melting point above that will withstand contact. Magma can reach much higher temperatures in subduction zones however. ",
"Here",
" are some melting points of metals if you are interested",
"Edit: I should add that some lava CAN reach temperatures of over 2900 degrees but it is uncommon and requires a high amount of magnesium oxide to reach those temperatures."
] |
[
"How did the moon landing spacesuits survive the ridiculous temperatures?"
] |
[
false
] |
I’m not a conspiracy theorist I just need to know
|
[
"The short answer is that astronauts survive the cold with layers upon layers of insulation and survive the heat by reflecting most of the light that they come into contact with. That's why spacesuits are bulky and also white."
] |
[
"Internal tubing and a pump flow’s coolant between the outer space suit and the astronaut."
] |
[
"Thank you, I was hoping someone would provide a more technical answer"
] |
[
"How much of a threat is space debris?"
] |
[
false
] |
[deleted]
|
[
"The short answer is yes. It is a Threat. ",
"Is it overstated by the media? Yes and no. ",
"Kessler syndrome is a real worry, There is a critical mass that needs to be floating up there before that happens though. NASA , ESA, CNSA and everyone with a space agency have their predictions about that, since they talk id guess that they are all pretty close to the same positions on it. That doesn't mean that we don't have other opinions on the math, Kessler syndrome is theoretical, and people are working on solutions for cleaning up space so it may not happen at all. ",
"One of the problems is we are in the position right now, of \"Look how big the ocean is, how can the bit of trash that we put in affect it?\" except with space. \"There is so much space, how can every orbit be in danger of debris, when the debris is so small and there is so much sky?\" ",
"And to a certain extent, thats true, there is a lot of sky, and its hard to pollute it all. But we dont need to to cause huge problems. We dont have launch sites everywhere, there are places where it is easier to launch and places where it is really really hard to. Some orbits are pretty useless to us, some are used by more then one thing. The biggest problem with this is that the debris that is the most problematic is the small stuff, the pieces that cant be tracked by radar (like those plastic satellites, if they were to shatter) that are all traveling at orbital speeds. ",
"This is the opening to a 2003 Anime that explores the idea of a future where cleaning orbits of debris is a job. its a really good example of what the problem with debris is. ",
"https://www.youtube.com/watch?v=heESAW2addo",
"edit,for correcting names"
] |
[
"But that debris also stays put in its orbit. Except for the ",
" small pieces, we know where most of them are. For the most part, the odds of getting hit by one without even seeing it coming are minuscule.",
"But yeah, nobody wants to be responsible for making more. Launches have gotten good at ensuring most of their non-payload-related things end up back on Earth in a relatively quick timeframe"
] |
[
"But that debris also stays put in its orbit",
"Debris in LEO will eventually de-orbit in a reasonable timeframe, more or less. Geostationary satellites are boosted to higher orbit called the graveyard orbit at the end of their lifespan, and there they will stay for millennia. However, the orbit itself is also much bigger than any low-altitude one."
] |
[
"What is the difference between quantum entanglement and a classical analogon? (see description)"
] |
[
false
] |
Let's say we generate a pair of entangled photons and measure the state of one of the photons. It is often said that the other photon then immedietaly takes the opposite state, which is the "spooky action" that Einstein described. Now lets say I have two classical objects, one white and one black and throw them blindly in opposite directions. I don't know which object I threw where but if I find one of the objects and see its color I immediately know the color of the other object. Where is the difference to quantum entanglement? Why is quantum entanglement so spooky? Is it just in the maths or is there some way to describe it visually?
|
[
"What you're describing is not an entangled state, it's just a mixed state. There are mixed states in both classical and quantum mechanics, but entangled states are purely quantum; there is no classical analog."
] |
[
"Whether the states of the two objects count as entangled depends on whether or not there is (or has every been) any record, anywhere else in the universe, that would let one reconstruct their states (i.e., whether the states have been \"observed\"). For objects large enough for a human to interact with, the answer is basically always that they have left a trace somewhere. (Was an ant watching you throw the objects? Even without an actual ant, if there is a place on the wall where an ant ",
" seen what you were doing, then basically \"the wall was watching\", and thus your system has been observed, and cannot be entangled.)",
"The reason any of this matters is that whether a system has been observed, vs. being completely isolated from the rest of the universe, affects what kinds of quantum manipulations you can do to the system.",
"This is hard to explain without going into a ",
" more technical detail, but, at a high level, the main magic of quantum is that probabilities/possibilities can \"interfere\" with each other, canceling each other out. (In a non-quantum setting, different possible outcomes can only ",
" their probabilities together, instead of the quantum ability of subtraction/canceling.) But in order for a positive and negative effect to cancel out, they need to be the same effect: if I have a pile of gray rocks, and I add 50 gray rocks to it, and take 50 gray rocks from it, then the two effects have cancelled out; however, if I add 50 blue rocks to a pile but take away 50 gray rocks, then the two effects are very different, the rock pile changes, and no cancellation occurs. Analogously, in an isolated quantum system, I can get two different ways of producing the same outcome to cancel each other out (e.g., in the double slit experiment, the photon could have gone through either slit), but if ",
" else in the universe \"knows\" which slit the photon went through, then the two possibilities are distinguished, like gray and blue rocks, and we cannot cancel out +50 blue rocks with -50 gray rocks."
] |
[
"The difference is that in the classical example you already know that one is white and one is black. Their colours were set prior to the measurement, you just don't know which one is which (this is called a \"mixed state\"). In QM, the states are not individually defined prior to the measurement, there is just a superposition state of black and white (a \"pure state\"). The individual states only become defined once a measurement is made, and the state you get is inherently random.",
"That's what's spooky about entanglement: It's not decided which is white and which is black until a meaurement is made, the outcome is inherently random, and yet conservation laws (i.e. you always get a pair of black and white, not two whites or two blacks) are still respected no matter how far apart the two objects are situated. No signal (that we know of) can travel between them to tell one which colour to be if the other is measured, or else this would violate our understanding of relativity.",
"Actually it get's even crazier, because you are not just limited to black and white (you can change the axis of measurements). It's more like the two objects will always have colours that are on the opposite sides of a colour wheel."
] |
[
"What determines how much of an ingredient you have to add to a dish in order for the dish to have a noticeable change in flavor?"
] |
[
false
] |
For instance, you usually see chefs on shows saying add a tiny pinch of salt or pepper into a dish. But does that tiny pinch really make a difference in the overall flavor of the dish? I'm not sure how much of a difference an couple extra grains of salt or sugar can add to a dish's flavor. How much salt, sugar, pepper, whatever do you have to add in order for the dishes flavor to change? What determines this noticeable change in flavor?
|
[
"Taste is quite complicated so it is not always a linear 'more of X = stronger flavour', although that will generally be true if you are talking about something simple like adding more sugar to water.",
"It also depends on what the other flavours in the dish are already. For example if you over brew your coffee it will taste bitter. You can add a lot of (high fat) milk or sugar to hide this. However adding even a small pinch of salt to the coffee will mask the bitterness of coffee without you being able to taste any saltiness.",
"Similarly when cooking Italian food; it is common to add a small amount of sugar to a tomato based sauce, since the sugar hides acidity of the tomatoes without making the sauce taste sweet."
] |
[
"The factor that determines the amount of spice required to change the taste of a dish is the concentration of the spice. Many spices are concentrated to the extent that consuming the raw form will overload the sensory receptors in your taste buds, and cause an unpleasant response (e.g. the so-called cinnamon challenge). Therefore, we add a small amount of any particular spice to dilute the effect, to achieve a \"sweet spot\" where the concentration is neither too low to be detected or high enough to be uncomfortable. So, what determines the level of flavoring is the relative size of your dish to the amount of spice added, as influenced by the level of your biological response to the spice (varies between different individuals)."
] |
[
"Once you learn to cook and add certain amounts of salt and pepper you can and will taste the difference, I'd suggest cooking the same meal using different measurements to understand this concept as it is the only way to learn it it. "
] |
[
"If the universe (\"space\") is expanding (and we know that by observing the red shift phenomena of objects moving away from us), why don't we observe/perceive the same thing within our own solar system?"
] |
[
false
] | null |
[
"Hi! We have a bunch of questions on ",
"the universe expanding",
" in our astronomy FAQ, including a couple about the solar system and local effects of gravity. There may be similar topics in there that interest you, too. Check them out and let us know if you have more questions!"
] |
[
"Thanks. I wasn't sure whether to ask my question in the Physics or Astronomy section. I'll take a look over there.",
"For my future reference, I had read the recommendations for asking a question, but wasn't sure if I should have submitted it through a moderator or not. Should I submit future questions through a moderator first?",
"Love the site. I spent several hours yesterday (before registering to ask my question) just browsing the science questions area. There is a wealth of information here. My compliments to the staff and all that take the time to answer the questions!"
] |
[
"Nope, you're fine to just submit things. Sometimes submission rates go through the roof and we get backed up, so posts can end up buried. If you submit and a post doesn't show after a couple hours, let us know and we'll check into it right away.",
"We don't let similar questions out too frequently because our panelists often will ignore them. However, we know that these are common questions because they're really cool and interesting, and we want to direct people to somewhere where they'll get a good answer (like the FAQ). Then they can come back with additional questions.",
"Thanks for the kind words! We are very glad to have you here with us! If you'd like more discussion-based questions, check out ",
"/r/AskScienceDiscussion",
". Our panelists are there, too, but it's a much smaller sub and we have hypothetical or open-ended questions there."
] |
[
"What is the likely mortality rate of COVID without any medical treatment?"
] |
[
false
] |
I’ve heard about how lots of people die when there isn’t oxygen available for COVID patients in the icu. Like what happened in Egypt a few months ago.
|
[
"We can use death rate from overwhelmed hospital data in the early stages of outbreak as a proxy. In Italy, they had an uncontrolled outbreak in q2 2020 that used up the ICU capacity. With ventilators, 30% admitted died. Without ventilators, 60% died. About 10% of infected people got admitted, with a large age skew(old folks). Taking population. Distribution into account, covid is about 5ish percent deadly to total population without any medical intervention, +- 3% for uncertainty due to my inexact estimation."
] |
[
"Your question heavily depends on the demographic you are talking about, first of all. Young people with no health problems have about a 0.03% fatality rate. As a human ages, gains weight, and encounters other health problems, that risk dramatically rises. COPD, a disease that typically results from smoking and damages lung tissue for example, makes things much worse for a COVID patient. COVID is very much a cull the heard disease, but unfortunatly 0.03% is not 0%, and many people have tragically shocking deaths where they had no risk factors at all, yet seem to die out of no where. ",
"Right now, the overall fatality rate world wide is 2%. 146 million infected, 3 million dead. It's difficult to pin down the relative accuracy of this number. One contencious issue is exactly how a death \"counts\" for this purpose, especially since countries, hospitals, and individual physicians do it differently / have widely varrying degrees of adherence to national guidelines. For instance, in Florida, thd cdc admitted they had counted a young man who died in a motor cycle accident as a COVID death because his corpse was COVID positive. Some would argue that's fine, it's a COVID death, others would say not. A 97 year old lady with congestive heart failure, dementia, and a BMI of 42 dies of COVID. Some may argue this is hardly a body to place at the feet of COVID since she was in such rough shape already, while others (myself included) would argue a death is a death no matter if the infection was rather distial to her main health issues. ",
"Tl;dr - it's overall 2% for everyone, less than 0.03% for young healthy peopls, risk rises for individuals based on comorbidities.",
"Edit: I just saw \"without medical treatment\". I don't know the relative influence of medical intervention on outcomes, so if someone with more knowledge on that end wants to chime in, please do so."
] |
[
"48% of Covid-19 deaths in India, up to a few months ago, were younger than 60. This is not explained by its relatively younger population.",
"https://science.thewire.in/health/india-covid-19-mortality-comorbidities-age-health-ministry/",
"This is seen in most countries in the developing world, several reasons are proposed. ",
"Higher death rates in younger patients may be due to poor medical care, particularly in the recovery phase. Also, young people have higher rates of untreated chronic illnesses that makes then vulnerable to Covid-19.",
"And it seems that elderly people in India, if the figures are to be trusted, are considerably less likely to die from COVID-19 compared to elderly in developed countries. This is said to be linked to lower rates of infections in elderly in India; maybe they can isolate better because fewer live in care homes.",
"Demombynes, G. 2020. COVID-19 Age-Mortality Curves Are Flatter in Developing Countries. Policy Research Working Papers, ",
"https://doi.org/10.1596/1813-9450-9313",
"."
] |
[
"How is body air volume effected by water pressure with free divers? As opposed to an open system with scuba divers."
] |
[
false
] |
I understand the concept of air and nitrogen/oxygen levels in scuba diving but that's an open system. If a diver holds their breath at the surface and dives down to 20 m do they now only have a quarter of that air usable in their bodies even though it's a closed system? The record is around a 100m is the divers body working with 1/1024 of the original air they got at the surface? I am not sure if I am explaining the question correctly but any light that can be shed on this would be greatly appreciated!
|
[
"You just have to remember a very simple equation:",
"pV = nRT",
"When you take a breath of air, there is a specific number of air molecules that enter your lungs at a specific temperature (~ body temperature): that's the \"nRT\" side of the equation.",
"When you dive down, the number and temperature of the air molecules obviously doesn't change, as no air can go into or out of your lungs. So the right hand of the equation remains fixed. But since the pressure inside your chest cavity must balance the increasing pressure outside as you dive (lest your chest implode!), the equation becomes:",
"p_surface x V_surface = p_dive x V_dive",
"Rearranging,",
"V_dive/V_surface = p_surface/p_dive",
"You can thus see that as the pressure during the dive goes up, the volume during the dive goes down. ",
"Now, even though the total ",
" of air molecules hasn't changed, the usable number has. The reason for this is that the efficiency of your lungs is proportional to their ",
", not the sheer number of air molecules in their volume (this is why your lungs have such a fractal, branching shape: to maximize the surface area given the volume). The problem is that while the surface area ",
" is proportional to some characteristic length scale ",
" the volume ",
" is proportional to ",
" If the efficiency of your lungs is proportional to their area, then (if you do the math), you'll find that it is proportional to the cube root of the volume squared, ",
" This means that if your lungs are 0.25 their surface volume, then they only have about 0.4 times the usable air.",
"In scuba diving, however, the regulator is fed air from a primary valve ",
", meaning that you are breathing air at the same pressure as the water around you. This means that your lungs will expand and contract at normal volume levels. The danger, of course, is if you accidentally hold your breath and ascend, which will cause the high pressure air in your lungs to expand and rupture your lung cavity!",
"Source: Physicist and certified scuba diver."
] |
[
"I am having trouble believing the idea that your lung surface area decreases by so much.",
"In an ideal (one whose sides are lines or planes of zero width) geometrical shape, you can keep the surface the same and reduce the volume essentially to zero.",
"For example, the shape which results if you pinch a sphere as compared to a sphere. Both have the same surface area but different volumes.",
"Another easy to visualize example is a square and a rhombus. Both have the same perimeter but different surface area. You can easily extend this to a cube and a parallelepiped.",
"Cells and your lung walls will not really compress much if at all. I may not be accounting for the expansion that lungs undergo during inhalation, but I don't think it stretches the surface the way a balloon's skin is stretched when inflated.",
"Alveoli bending and closing off parts of the lung seem to be the only two mechanisms by which your lungs' surface area can get reduced.",
"I am not convinced that those effects are large enough to account for 60% surface reduction.",
"So, why is it that you think the number is so large?",
"EDIT: I realized that the 60% is specific for your example. But my question still remains. Why do you think there is proportional scaling of both surface and volume?"
] |
[
"You'll note that because we are talking about ratios of before/after area, we can highly generalize the problem. So when I say that surface area is ",
" to some characteristic length scale ",
" an example might be the surface area of a sphere, which is ",
" = 4pi x ",
" in which the characteristic length scale is ",
", and the ",
" is 4pi. Another example might be the the surface area of a cube, ",
" = 6 x ",
" in which the characteristic length scale is ",
", and the constant of proportionality is 6. But in any case, the area goes as some length squared, and the volume goes as some length cubed. Now, in the case of a very complex structure such as a lung, we don't know what the constant of proportionality is, ",
", because if you are comparing the efficiency of the lung before and after, you take a ratio, and the constant of proportionality cancels out."
] |
[
"How does ionization state affect radioactive decay rates?"
] |
[
false
] |
I was taking a stroll through Wikipedia and came across this: Technetium is a chemical element with the symbol Tc and atomic number 43. It is the lightest element whose isotopes are all radioactive; ...So there is one isotope of Technetium that is or is not stable depending on its ionization state. Is it normal for ionization state to affect the half life of radioactive isotopes? How does it work? And is that useful information or just a curious little detail?
|
[
"Certain kinds of nuclear decays involve the atomic electrons. One example is electron capture, which is similar to a beta",
" decay, but instead of producing a positron, the nucleus absorbs an electron. This can happen spontaneously in atoms because there are bound electrons available. Technetium-97 in the ground state ",
" decays by electron capture.",
"But since this decay requires atomic electrons to be present, if you remove all of the atomic electrons, the decay can't happen anymore. And because this particular isotope only decays this way, if you remove all of its electrons, it doesn't decay at all."
] |
[
"That is really interesting. Thank you. But I assume you would never realistically see it stripped of all 43 electrons, right? I mean at that point it would be so highly charged it would steal electrons from basically everything, right?"
] |
[
"Accelerators can strip all electrons from all elements they can accelerate. The LHC routinely creates bare lead nuclei, stripping all 82 electrons from the atom. Fully ionized uranium is common as well.",
"There are just a few cases where the stability changes based on the electrons. There is also one nuclide that gets unstable if you remove all electrons because it can then do bound-state beta decay (basically the inverse of electron capture)."
] |
[
"Are there glaciers on Mars' polar regions?"
] |
[
false
] | null |
[
"Mars has a southern polar icecap, which consist of water ice and carbon dioxide ice which shrinks and grows with the seasonal cycle. It has more in common with the antarctic ice cap, but without marginal spreading. Growth and shrinkage are controlled by sublimation. There is no northern icecap."
] |
[
"...and I'll post it again. Mars does indeed have a northern icecap.\n ",
"http://en.m.wikipedia.org/wiki/Martian_polar_ice_caps"
] |
[
"I recently talked to a planetologist who examines mega dunes on the northern ice cap on mars. She said it's still controversial whether there are flowing glaciers on mars since it is hard to trace movement, but the northern ice cap exists and follows seasonal changes, although small.\nThe northern Ice cap is also much smaller than the southern since it is about 3 km lower above 'sea level'."
] |
[
"Is this the right intepretation of Schrodingers cat?"
] |
[
false
] |
I feel this is a very misunderstood experiment, so ill try to explain it, and you guys can correct me in case Im wrong. Basicly the first misconception I see is that if you put the cat in the box, it is no longer observed. This is a misunderstanding of what 'observed' means in the quantum world. It does NOT mean that a human or other animal actually has to see the cat. It means an interaction with matter (or with the electrons that are 'floating' outside matter) or a loose electron or photon. For example in the double slit experiment, a photon is observed and collapses from the superposition if it hits the screen at the other end. The difference between being observed by a photon or by matter (the screen or 'end' destination) is that if a particle small enough is observed in midair by a photon it now behaves as if it was a particle all along. But if it is not observed in 'midair' and has the chance to hit the screen it has been a wave all a long. So it does not matter wether you put a box around the cat or not. Because if the geiger counter goes off, and the device to kill the cat is activated, the super position collapses. This happens before the cat dies. The moment the geiger counter is activated is also the moment the observation takes place. This is not my thought, but was Niels Bohr's observation fwiw. I think this is also the origin of the multiverse theory? Because the time of decaying, and the subsequent observation is truly random. So you cannot predict when the cat will die. It could be after 5 minutes, or after 20 minutes. It is TRULY random. Only the Radioactive substance on the microscopic scale does. And this is why physicists think that every bit of time on that time line of decay, a new universe splits off. So if the cat dies exactly after 20min , then you are in the universe where the cat dies after 20min. But there is another universe split off 15min ago where the cat died after exactly 5 min. And another one where the cat died after 7.23 min and one where it died after 9 min and so on. This seems to be an attempt by physicists to make the true randomness of quantum mechanics deterministic again? This is probably where my understanding ends :) . Thoughts?
|
[
"I feel this is a very misunderstood experiment, so ill try to explain it, and you guys can correct me in case Im wrong.",
"Among lay people yes, but not among most physicists.",
"It does NOT mean that a human or other animal actually has to see the cat. It means an interaction with matter (or with the electrons that are 'floating' outside matter) or a loose electron or photon.",
"This is correct.",
"It is TRULY random. ",
"Nothing is known to be truly random, but leading interpretations of quantum mechanics claim what you're describing would be.",
"But the cat does not exist in a superposition. Only the Radioactive substance on the microscopic scale does.",
"Assuming the cat and radioactive substance are isolated from everything else (i.e. the environment), then strictly speaking neither are in a superposition state since they are entangled. Only the global system of the cat and radioactive substance can be described as a coherent superposition. The individual subsystems of the cat or the radioactive substance are described by what are known as mixed states.",
"However, there is nothing in quantum mechanics that prevents a perfectly isolated cat from being in a superposition state. This might sound strange to you, and it did to Schrödinger, which is why he opened the letter where he describes his eponymous thought experiment with, \"One can even consider such ridiculous cases as a cat...\"",
"We now know that it is really really hard to perfectly isolate something like a cat, and due to the phenomenon known as decoherence (basically entangling interactions with the environment), the local system of the cat will not be a superposition. However, it is an active area of research to create superposition states of larger and larger things, such as C60 buckyballs and other large molecules.",
"This seems to be an attempt by physicists to make the true randomness of quantum mechanics deterministic again?",
"Quantum mechanics is a fully deterministic theory, they only randomness appears when you attempt to perform measurements."
] |
[
"With the exception of gravity, which isn't described in quantum theory, any interaction between two molecules could be considered observation. What's necessary for \"observation\" is that the interaction entangles the two molecules, so that now something you can measure about molecule 1 is correlated with something you can measure about molecule 2. This is sufficient to break the superposition in the original state of molecule 1."
] |
[
"Would any type of interaction between two molecules be considered observation. Like two hydrogen next to each other would feel gravity, electric, magnetic, and many other forces between each other"
] |
[
"How do we know how many protons are in an atom's nucleus?"
] |
[
false
] |
How do we know how many protons are in the nucleus of each element's atom? Do we have a way of viewing things that can magnify more than electron microscopy? If you can provide your source, that would be much appreciated, but it is not required. Thanks!
|
[
"Historically, first you had Berzelius and others making accurate measurements of (relative) atomic masses in the early 19th century, and in the late 19th century you had Mendeleev coming up with the periodic table by ordering the elements by a combination of their mass and properties. By that time they still didn't know anything about the inner structure of the atom, but a few years later one of the first pieces came into place when the electron was discovered, and removing electrons left a net positive charge on the rest of the atom. ",
"So that's where they stood around 1900, when Rutherford had the 'plum pudding model' of the atom where the electrons and positively charges were more or less mixed about like a pudding in the atom. He famously did an experiment where positive alpha particles were 'shot' at gold foil, and he measured how the positively-charged alpha particles deflected off the atoms. He did not expect much deflection (since he thought the charges were fairly evenly distributed) but he measured lots of it, even cases where the alpha particles reversed their direction, which he described \"as shooting a cannon ball at a piece of tissue and having the cannon ball bounce back\".",
"Rutherford figured out that the only way this could be explained would be if the positively charged part of the atom was quite small relative the rest of the atom. He called that the 'nucleus' and was able to estimate from the amount of deflection that it had a charge that was about half the atomic mass of the element. This was largely informed also by him having determined that alpha particles (which had a 2+ charge) were helium nuclei, but helium had a mass that was 4x that of hydrogen. ",
"Not long after that, van den Broek suggested that the charge of the nucleus was exactly equal to the atom's rank in the periodic table. So it was theorized before it was measured accurately enough to tell whether this was true. (Half of gold's mass is 98, its atomic number is 79, so that's a pretty significant difference in estimates of its charge)",
"The real test of this came with the Bohr model of the atom, which predicted the spectral lines of the element, the amounts of energy that the electrons could emit and absorb. Although it was only approximately correct for hydrogen and became a very crude approximation when applied to other atoms, it predicted a general trend where the energy levels of the electrons were proportional to Z",
" (the nuclear charge squared), which was a broad enough general trend that it could (and was) observed despite the Bohr model not being particularly accurate. ",
"So around that same time (1910s) you also have the idea being raised that the difference between Z and the atomic mass was being made up by some second element of the nucleus. But it wasn't until Chadwick ",
"discovered the neutron",
" in 1932 that it was actually known that the atomic nucleus was made up of protons and neutrons, and thus that the nuclear charge was the number of protons. ",
"Later these things would be measured and verified more accurately of course, not least through Rutherford's method of measuring how ",
"electrons scatter off the nucleus",
".",
"Do we have a way of viewing things that can magnify more than electron microscopy?",
"You're not really 'viewing' anything in an optical sense even with electron microscopy, you're essentially bouncing electrons off of stuff and recording where they end up. When dealing with things smaller than the wavelengths of visible light, it also doesn't really make sense to talk about 'seeing' things, so the question here is really what you want to count as 'viewing'. We can for instance 'see' the trails of subatomic particles in ",
"bubble chambers",
", but you're not seeing the particle, you have to infer the properties of the particles by doing calculations based on a model, much like Rutherford and Bohr were doing. Is it still 'seeing' something if you need to do calculations to understand what you're looking at? Chemists have very clear ideas of what molecules 'look like', but no way of really directly 'seeing' them."
] |
[
"That's completely wrong, everything you just wrote. Atoms don't have to be neutral at all times. Second, you ",
" tell in how many electrons there are in an atom from its properties in any straightforward manner, and they had neither the calculating power nor the quantum mechanics required to do such calculations when nuclear charges were first determined. The properties that can be predicted from the number of ",
" electrons determined an elements' place in the Periodic Table. The PT existed before they knew anything about electrons or that atoms had small positively-charged nuclei, and it is in no way obvious that the nuclear charge should be the same number as an element's place on the PT.",
"They could not and did not calculate anything, nor count electrons. Nothing you wrote has anything to do with how nuclear charges were actually determined."
] |
[
"I would just like to add, the actual atomic numbers and which elements were still missing was done by using x-ray spectroscopy. The 1s electrons basically feel the full charge of the nucleus and the energy of an x-ray emitted when an electron from the n=2 level falls to the n=1 level is proportional to (Z-1)",
" . ",
"https://en.wikipedia.org/wiki/Moseley's_law"
] |
[
"Are there any differences in penis size based on race and nationality?"
] |
[
false
] | null |
[
"Hi Randomthrowayawayman thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Human Body."
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"/r/AskScience",
"For more information regarding this and similar issues, please see our ",
"guidelines",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"How much do our organs move?"
] |
[
false
] |
In addition to the heart and lungs, what's the extent and type of movement of our organs like the intestines, stomach, kidneys, liver, etc.?
|
[
"Each organ has its own little sack, and that sack is embedded inside a larger sack, so imagine everything’s pretty organized on where it is based on the sack system, with tissue allowing for some movement (like a few inches in any direction temporarily) but still having central locations for everything. Also some organs are not intended to move, and when they do move that’s very very bad (like the brain). ",
"If you are asking about movement in terms of proper functionality. Organs that do filtering such as the liver or kidneys don’t move at all. The stomach and intestines move constantly, expanding and contracting with smooth muscles."
] |
[
"So wait, the exterior of the organs that we see and are familiar with is basically a sack for the organ itself? With the exception of livers and kidneys since you said they don't move?\nSo are the intestines, for example, in a sack on their own or with other organs from the digestive system? And if they're on their own sack is it fitted around their shape or just again holding them in place, and what's the purpose of these sacks exactly?",
"Sorry for asking so many questions and thank you so much for answering!"
] |
[
"So for example, if you see a heart inside of someone, it will be surrounded by this thing called the pericardium. When you look at images of a heart, the pericardium will typically be removed or reflected to see the actual heart. The pericardium is the sac itself, it is multilayered and basically provides a little fluid cavity between the layers that secretes fluid to allow the heart to have reduced friction when it beats.",
"This is just one example, but a similar thing occurs in your lungs as well for example."
] |
[
"What's the basis of NMR spectroscopy?"
] |
[
false
] |
I've been doing some reading online and from what I've seen, there are two different explanations of NMR spectroscopy. One implies that the magnetic dipole moments can flip when hit by radio waves, and when they flip back, energy is emitted in the form of electromagnetic radiation. By analysing the emitted waves, we can determine their source, etc. The other explanation is that the sample is hit by a pulse, causing the dipoles to precess, and it is this precession that is used to determine the isotope in question. My question is, which of these explanations is correct? Is one a simplified version of the other? Or are both correct, and are simply different techniques for sample analysis?
|
[
"They are both kind of half right, but the precession is more right.",
"In an NMR, the large magnetic field creates an energy difference between the two different spin states of a nucleus (spin up and spin down). The short radio pulse creates a superposition of the spin-up and spin-down states (a \"coherence state\", think Schrodingers cat) that oscillates at a rate proportional to that energy difference. This effectively \"looks\" like the spin rotating in the x-y plane (perpendicular to the magnetic field).",
" The spin precession in the x-y plane creates an oscillating magnetic field which is picked up as an oscillating voltage. That signal has frequency components that correspond to atoms in different chemical environments, which each decay due to \"dephasing\" (similar isotopes will precess at slightly different rates, causing them to get out of phase and reduce the overall signal). You then Fourier transform that signal to pull out the different contributions from isotopes in different environments.",
"That's the simple FT-NMR experiment. You can then get arbitrarily more complicated by including more radio pulses. MRI for instance relies on the spin echo, which is usually two radio pulses. The first pulse does the same thing, but the second pulse reverses the direction of the precession so that all the spins eventually all end up at the same direction again. This makes a strong field that reproduces the original radio signal (a \"spin echo\"). By tracking how the intensity of that pulse changes for different duration between the first and second pulse, you get information about the dephasing of different isotopes. The differences in dephasing is what gives different signals for different body tissue in an MRI.",
"Edit: correcting embarrassing error"
] |
[
"The alternation between being more \"spin up\" and more \"spin down\" creates an oscillating magnetic field which is picked up as an oscillating voltage.",
"That is not quite correct. The oscillating voltage is induced by the precission of the spins. Spin up and spin down induce voltages of the opposite sign and therefore cancel each other out. If you excite some nuclei with down spin, you can measure the oscillating voltage."
] |
[
"Thanks, your answer was really helpful! Just to make sure I understand this correctly though, is the only signal we're interested in, a result of the oscillating voltage? Photons emitted during transition from one state to the other are not the source of our data?"
] |
[
"If we are constantly breathing in pathogenic microorganisms, why don't we get sick more often?"
] |
[
false
] |
I understand that microorganisms are everywhere. Therefore when we breath, we must breath them in. Why don't we get sick? Is it because the ones we breathe in aren't pathogenic? Or is it that the amount of pathogenic microorganisms is small and our immune system can handle it? As opposed to eating rotten food that has a higher concentration. Would that mean that pathogenic bacterias's effect is dose dependent?
|
[
"Our immune system is always working to fight off dangerous bacteria. I suppose when you say sick you mean why don't we get syntoms like fevers and pains every day from this fight, right? You only get symtoms when the immune system is not strong enough to fight off all the bacteria there is (causing an infection, for instance, when you cut your self and your immune system is not able to eliminate all the bacteria that entered through the cut) then it relies on other methods, like a fever. Inflamation and pus and side effects of the immune system fighting off bacteria. In other words, you immune system deals with all the bacteria and virus you have contact with every day just fine, yet sometimes it fails and lets some of them pass, which causes sickness like the flu (your symptons are usually side effects of your immune system fighting off the infection, as you can notice by the symtoms of allergies: the average particle that your immune systems reacts as if it was a pathogen is logically not provocking any of the syntoms, but rather your immune system is). While this happens the immune system continues to fight the bacteria/virus otherwise you would never heal.\nIt doesn't necessay mean that is quantity based, that there was too much bacteria to fight off, but rather that there was a certain type of bacteria which is harder to fight - usually a virus or bacteria that you immune system does not know. I don't know if you know, but we can never get the same type of flu twice, as your immune system already knows how to fight off that virus (and that's how vaccines works - or a simplified version). Your body is already expecialized on how to fight every day bacteria. \nEdit: I complement some stuff."
] |
[
"Virtually every pathogen you ingest will be located and dealt with by the innate response of the immune system before you ever notice any symptoms at all. This does not qualify as infection - it's simple routine entry and clearing of pathogens. The cells responsible for this (Primarily Neutrophils & Macrophages) are constantly circulating throughout your body & tissues searching for pathogens by scanning for common features - for example, Macrophages have a receptor that searches for peptidoglycan, a component of bacterial cell walls. When these cells identify a pathogen, they attack it either by engulfing and digesting it (if it's small) or degranulating (basically dumping neutralizing & digesting agents all over it) and the pathogen is dealt with.",
"The concept you're looking for is called an Infectious Dose. It's essentially how much of a given pathogen you need to be exposed to in order for that pathogen to overwhelm the innate immune system and actually cause an infection. These are typically expressed as ID50s, or the dosage that is sufficient to infect 50% of subjects. Influenza for example, has an infectious dose that ranges between 100 and 1000 virions (individual viral particles.)",
"Once the infection takes hold, the adaptive immune response (Primarily B and T cells) take over. The adaptive response is specifically targeted, significantly stronger, and also has capacity for memory. The downside to it is that it takes a little while to actually come online, due to the intricacies of how the T and B cells are actually produced. I can go into more detail here if you'd like, but it's not actually the answer to your question.",
"The answer to your question is the innate immune system. It does such a good job that virions have to achieve the infectious dose to overwhelm it and establish an infection before you ever actually get sick. "
] |
[
"I am a med student but very early in the course in a country where we get into med right after high school, so don't trust me very much, I wouldn't. I knew some things by head but I made some quick research in the internet to make sure before answering your question. I can send some links over. \n",
"https://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0072548/",
"\n",
"http://www.webmd.com/cold-and-flu/immune-system-fight-infection",
"\n",
"https://www.fsis.usda.gov/wps/portal/fsis/topics/food-safety-education/get-answers/food-safety-fact-sheets/safe-food-handling/molds-on-food-are-they-dangerous_/ct_index",
"\n",
"http://pediatrics.aappublications.org/content/101/4/712.short",
"\n(If I can't send links here please tell me, I'm fairly new). \nThose articles have good sources to them, you can look them up. :) Hope I helped. \nEdit: Forgot one. ",
"http://now.tufts.edu/articles/food-bacteria-smell-taste-bad-illness"
] |
[
"What is the minimum time needed to produce a verbal response?"
] |
[
false
] |
[deleted]
|
[
"This is very situation-dependent. In a lexical decision task (people see a bunch of words pop up on the screen and have to answer y/n to \"is this a word or not?\") the usual low-end of accurate response times on real words is about 200-300ms. In situations like this people are just reading a single word, making sure it's actually a word, and pressing \"yes\". If you make non-words that look like unpronounceable gibberish, people will usually respond more quickly than if your non-words are pronounceable, and people will respond slower the more similar the non-words are to real words. Unfortunately, I'm not aware of research that would reflect more naturalistic settings like conversations."
] |
[
" the more similar the non-words are to real words.",
"Does this include following common patterns like using real affixes or avoiding weird rhymes like /aUm/?"
] |
[
"Yes, phonotactically acceptable non-words will take longer to identify as non-words, and non-words with real morphology will too."
] |
[
"Noob question: Do the fundamental forces obey thermodynamics?"
] |
[
false
] |
First off I'm sure the answer is yes. I just can't wrap my hand around magnetism. It seems to always have it's magnetic properties so how is it still obeying the laws of thermodynamics?
|
[
"For clarification: what thermodynamic principles do you think magnetic fields violate?"
] |
[
"An object being attracted to an object by as magnet is the same as a rock falling downhill. No violation."
] |
[
"I think what I'm relally wondering is where is the energy input for the magnet?"
] |
[
"Why does a glass of water left for a while, have tiny bubbles on the inside of the glass?"
] |
[
false
] |
I guess this depends on what type of water you drink, but I've seen it in both Norway and Denmark. When I have a glass of water (tapwater) before I go to bed for example, but don't drink it all, the next day the inside of the glass is packed with tiny bubbles. And it seems like the longer it is left untouched, the bigger the bubbles get. Why is that?
|
[
"This is due to the temperature dependence of the solubility of gases in water. Colder water is capable of containing more dissolved gas (air) than warmer water. In the case of your tap water, the dissolved gases in the water reflect the two major components of the atmosphere: nitrogen and oxygen. Since you are getting bubbles overnight, I would guess that the source of your tap water is colder than room temperature. Therefore, as your glass of water warms up, it is not capable of maintaining all the initial gas in solution and some of it forms bubbles. "
] |
[
"This is correct, you are talking about the growth of the bubbles but the part you are missing is the formation of the bubbles on the glass. Bubbles (or crystals if the water were freezing) generally form on an imperfection or small radius object such as dirt or dust. This is the process of nucleation. Combined, the two process are referred to as nucleation and growth. These processes would occur with many phase changes in many different substances. ",
"A cool example can be made by supercooling a liquid. In that case, the liquid is below the freezing point but there is no imperfection for the bubbles to form (nucleate) on. Once the first bubble is formed, the process can be rapid, like in this ",
"example."
] |
[
"Not quite correct.",
"Yes, nucleation of crystals requires a solid seed, a piece of dust, a solid/liquid interface.",
"But nucleation of bubbles requires a vapor seed, a gas/liquid interface. Bubble nucleation involves microbubbles. In glass containers, the \"imperfections\" are actually pockets of air trapped in scratches, cracks, or dry surface dirt. Also see \"boiling chips.\"",
" leading to extremely rapid, even explosive phase change, almost anything can act as nucleation seeds. That's how bubble chambers work, but also it's why we don't see ion tracks from cosmic rays in our beer: the amount of dissolved CO2 is far too close to equilibrium.",
"[Edit: with the early cyclotrons, the question about beer bubbles came up. Eventually someone somewhere demonstrated that charged particle beams don't produce any bubble patterns in carbonated refreshments. I don't think they tried suddenly opening a bottle while holding it in a proton beam. Safer to just watch a full mug from behind thick lead-glass windows. I've heard the passed-along story, but I don't know if it resulted in any famous papers.]"
] |
[
"Why does a steady stream of water break up after some airtime?"
] |
[
false
] | null |
[
"The phenomenon is known as ",
"fluid thread breakup",
". The idea is the same as why water on a glass surface prefers to bread - water prefers to minimize its surface area to other fluids or surfaces. So if you dip your finger in water and drag it across a glass surface, initially you may have a long, continuous streak of water, but it quickly breaks up and beads to minimize surface area."
] |
[
"Going deeper, fluid is usually described in three manors: laminar, semi-turbulent, and turbulent. You know how if you turn on a faucet really slowly you get a stream of water that looks perfect and almost non moving? This is laminar. The paths that the molecules are following is very uniform. As gravity, air resistance, viscous forces, and surface tension phenomena act on the fluid it becomes more turbulent, which is disorganized. ",
"Reynold's Number is a metric for describing how turbulent a fluid is. ",
"Re = density * velocity * characteristic length / viscosity",
"Re from 0 to 2300 is laminar and beyond that it becomes more turbulent. ",
"So as that water comes out of the faucet, velocity increases due to the acceleration via gravity. The molecules get more chaotic and can no long keep a straight stream and so they bounce around and break up. "
] |
[
"I think this one is the answer you're looking for: ",
"Plateau-Rayleigh instability."
] |
[
"Can you identify/separate two mixed blood samples?"
] |
[
false
] |
If you mix two blood samples in a single vial, would you be able to identify that two individuals' blood had been mixed in a single vial? Could you isolate a single individual's blood or separate the mixture again once mixed? Could you identify from which two people the blood came from, or would mixing the blood prevent a forensic analysis like this? Thanks for the help!
|
[
"The red blood cells could, yes. As long as they are different blood types. This is based on the different antigens they present that make up the different blood types. Theoretically, you could create antibodies that bind each blood type individually, and tag them with a unique fluorescence. Cell sorting relies on these different fluorescent labels to literally sort the cells as they flow past the reading device. [If I'm not mistaken]\nWBC's would be harder to differentiate between people, but could be done based on MHC (HLA) typing. "
] |
[
"You can do DNA analysis on the blood and tell that the blood is from two people. There is usually DNA floating around in the blood.",
"They perform some fetal genetic tests that way. You just take a sample of the mother's blood and you'll see two types of DNA in there, her's and the unborn child's."
] |
[
"If they are of different blood type, cell sorting chromatography can tell you how many different blood types are present. If they are the same blood type, you would have to do DNA analysis to identify the number of individuals. This is done via SNP's. RBC's theoretically do not carry DNA, as they are enucleated. But if it is raw blood mixture, other cell types will be present for analysis. \nSeparating the mixture of RBC's would be difficult and time consuming, but could theoretically be done by chromatography cell sorting. \nTo identify the individuals precisely, you would have to have their DNA on record for comparison after sequencing or SNP patterning. "
] |
[
"I know that burning wood is a combustion reaction; is there anything different about the chemical changes going on in a glowing ember vs. a visible flame?"
] |
[
false
] | null |
[
"Yes. A glowing ember is an example of combustion happening via surface reaction. In charcoal, it is oxygen reacting directly with solid carbon. Visible flames are generally created by gaseous fuel that was either a gas to start with, like propane, or was vaporized by the flame's heat, like candle wax. Surface combustion (smouldering) is generally slower and has lower temperatures than gas phase combustion."
] |
[
"If we want to get technical, the combustion reaction of oxygen with solid-phase fuel (with no flame) is called \"",
"smoldering",
"\", while gas-phase fuel reacting with oxygen produces flames. I'm not sure if there's an equivalent for direct combustion of a liquid; most flammable liquids have a high vapor pressure, and it's the gas evaporating from the liquid that burns. "
] |
[
"Did you mean to make a top-level reply?"
] |
[
"Is there a non-geometric equivalent to Einstein's theory of general relativity?"
] |
[
false
] |
If I understand correctly, the geometric approach is what makes this theory so elegant. I wonder if there exists a theory that takes a non-geometric approach and agrees with the general theory of relativity on all (or most) findings at the expense of simplicity. Define "non-geometric" in specific terms?
|
[
"The short answer is yes. In the first half of the 20th century, we came to understand all the non-gravitational forces in terms of ",
", with the quintessential example being the electric and magnetic forces. In fact, it wasn't just the forces that came to be described this way, but the matter. Field theory came to underlie all of particle physics.",
"Not long after, people figured out that general relativity could be formulated in much the same way. In this picture, spacetime is flat, and gravity is carried by a ",
". That just means that, much the way that the electromagnetic field is described by a vector, the gravitational field is a matrix. And while it's not a geometrical theory, this particle-physics view of gravity is also very elegant: it turns out that, as long as you demand a few reasonable conditions (like special relativity), the ",
" consistent theory for a tensor field which describes gravity is general relativity!",
"Now this approach agrees with all the findings of GR for a very simple reason - it's the exact same theory, just in a different mathematical language. Instead of looking at things in terms of geometry, you look at fields and particles, just like in the rest of particle physics. Particles, in particular, come in when you introduce quantum mechanics - then each field comes with an associated particle, and the type of field (vector, tensor, etc.) turns out to correspond to how much spin that particle has. In natural units, vector fields have spin 1, tensors have spin 2, and so on. So the statement is that GR is the unique theory of a massless spin-2 field. The associated particle is called a graviton, analogous to the photon in electromagnetism."
] |
[
"This tensor field couples the same way to all matter, so there's no equivalence principle violation."
] |
[
"It haven't read the paper in complete depth, but they seem to be saying that theories which are not \"purely metric\" have a problem with the strong equivalence principle. For example, a scalar-tensor theory like ",
"Brans-Dicke",
" which has the metric interacting with a scalar field.",
"The formulation described by adamsolomon is purely tensor (and the tensor is the metric), so it is purely metric and shouldn't have a problem. The formulation is entirely equivalent to GR, which they claim to be the unique purely metric theory."
] |
[
"What digital synthesis techniques were used to originally create \"Chiptune\" sounds?"
] |
[
false
] |
I've been playing around with which features (among other things) several digital synthesis techniques, among them FM Synthesis, Additive Synthesis, and a few others simply listed as the type of sound they produce ("String", "Buzz" and "Noise"). Given the computational limitations of early computers and videogame systems, I was wondering, what techniques were the soundchips were actually using to create the sound?
|
[
"Generally chiptunes consist of basic waveforms, such as sine waves, square waves and sawtooth or triangle waves, and basic percussion, often generated from white noise going through an ADSR envelope or PCM samples.",
"It's a simple wave or static, followed by modifications. For instance, increasing or decreasing frequency or amplitude over time, or adding or multiplying these waves."
] |
[
"I'd love more detail. Especially if you have any insights on how I might duplicate this sort of modulation myself."
] |
[
"Sure, dude! I started writing chiptunes around 4 years ago but I've pretty much dropped out of the scene and moved onto experimental beat/bass-driven stuff.",
"There are so many ways to pull off chiptunes anymore. If you ",
" want to duplicate stuff well, or begin writing your own look into some trackers. ",
"A lot of chiptune tricks depend on what console or computer you're composing for. I guess I'll just elaborate a little on the ones I mentioned.",
"Quick note: I'm going to be referencing \"trackers\" a lot. A tracker is a music program that vertically sequences music and uses a lot of numbers to control things. If you need to know more ",
"this pretty much sums things up.",
"Example tune: Drax - Swamp Poo",
"The sound I'm talking about comes in around :20. That lead sound is what's known as a PWM. Essentially this sound is created by telling the C64 to modulate the waveform. If I'm not mistaken Rob Hubbard was really the first guy to use this sort of thing.",
"Over on the right side of the screen in the video you see a big mass of numbers. Those are all variables detailing the sound design of the song. Each instrument has its own little part in there. ",
"If you're more interested in this sort of stuff, definitely take a look at this ",
"GoatTracker tutorial",
". It gives a good intro on the basics of C64 sound design. (Also, GoatTracker has a similar layout to the tracker in the video.)",
"[Example tune: Janne Sunni - Acid Jazzed Evening](",
"www.youtube.com/watch?v=amXNbaRtLpQ",
")",
"This is a perfect example of how arpeggios can be used to simulate chords. Hopefully you can recognize it, but as you're listening just try to imagine you're hearing some jazzy chords. ",
"Essentially, an arpeggio is just a chord that's split up and each note is played separately. So with a C minor arpeggio, you'd hear c, then d#, then g. ",
"With early computers and gaming consoles, you couldn't really use chords as they'd use up all your sound channels! Typically computers of the 80s really only had maybe 2, 3, or 4 sound channels. A channel can only playback one sound/note at a time, so you can see how chords would be frustrating.",
"Somehow, people began speeding up arpeggios with their computers and noticed that it ",
" sounded like a chord. ",
"Most trackers have a special \"command\" for arpeggios. It's a bit harder to explain without a tracker right in front of us. Essentially it works by the root note of the chord being put in the sound channel and then with the command you go up by notes. so for a C major it'd look something like C-047. The c is the root, the 0 tells the tracker you want to make this note an arpeggio, the 4 is four notes above the C (so that'd make it an E), the 7 is seven notes above C (so that'd make it a G! see? easy if you know chord theory i guess haha.)",
"Alright, I'm getting tired, but if you have any other questions feel free to PM me and I'll try to answer to the best of my ability.",
"Hopefully this is sciencey enough for here haha. I apologize if it's a little informal or hard to understand. It's crazy how complex chiptunes can be. "
] |
[
"How does the Fermi Temperature exist if the temperature is reliant on the system being equal to zero kelvin?"
] |
[
false
] |
Hey guys, from my basic knowledge of Physics the Fermi Temperature is Tf = (Ef)/kB. I know that the Fermi Energy is found when the system is at zero degrees kelvin, such that there is no thermal energy, but how is it that there IS in fact a very high temperature that the electrons are actually at (usually 40k K). A follow up question is if there is a different temperature for each energy level (E = kB*T), why do they not equilibrate? I know these are probably pretty silly questions but I am not able to kind them online. Thanks
|
[
"My earlier comment was more confusing than it needed to be -- apologies for that. The Fermi temperature is the temperature at which average thermal energy is same as the quantum mechanical Fermi energy.",
"So when you calculate the Fermi Temperature, you aren't calculating an actual temperature of the system -- you are calculating a characteristic temperature which separates two regimes of the system's behavior. "
] |
[
"I listened to that last bit and I couldn't make sense of it...",
"Perhaps another way to think of the Fermi energy / Fermi temperature is like this.",
"Fill up the Fermi sphere with all your electrons in the solid. Now, pick one of the electrons right at the Fermi level, and remove all the other electrons. This lone electron is now clearly in an excited state. How much energy does it have compared to the lowest state that this single electron could possibly be in? The difference is the Fermi Energy.",
"If I wanted to excite a single electron from the lowest energy state to the Fermi level, how much thermal energy do I need? This is the Fermi temperature."
] |
[
"All the electrons in a solid are still fermions and so they all can't pile up into the lowest ground state with |k| = 0. This means some of them will be at a higher energy state than others. The electron in the highest energy state will be at the Fermi level. It has a corresponding wavevector and a corresponding temperature."
] |
[
"Ask Anything Wednesday - Economics, Political Science, Linguistics, Anthropology"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"Anything is \"testable\" though not necessarily in a scientifically rigorous fashion.",
"All you need to do is develop a hypothesis about an event and then wait to see if that hypothesis turns out to be right or wrong.",
"However, because this hypothesis was based around a real-world event rather than something performed in a lab it can only be done once with the exact same set of circumstances. ",
"So, for instance, you can hypothesize that Candidate A will win an election and then wait to see if you are right or wrong but you can never replicate that exact same election nor can you modify just one or two variables to see what effect doing so has on the outcome.",
"To get around this, you can use thing like polls or focus groups but those are unreliable in their own ways.",
"Another way would be to look at case studies, which is often how political scientists like to study an issue. So we might ask \"Are sanction effective in changing the behavior of a nation?\" And we can look at numerous historical examples and attempt to draw conclusions. But, again, we can't draw any firm conclusions because we can't re-run those case studies. ",
"So, in a strict sense of the term, you ",
" test a hypothesis but it would in no way be scientific. "
] |
[
"What sorts of things in Political Science are testable? It seems like there isn't much to test."
] |
[
"The ",
"Cot-Caught Merger",
" is something that is happening right now in American English. There are also other vowel shifts happening all over the place."
] |
[
"Not purely a science question but: Can you name a female scientist... who is not Marie Curie?"
] |
[
false
] | null |
[
"Jane Goodall. "
] |
[
"lise meitner",
"emmy noether",
"ada lovelace",
"barbara mcclintock",
"rosalind franklin",
"patricia goldman-rakic",
"hanna damasio",
"nancy kanwisher",
"nora volkow",
"judith harris",
"what's my prize?"
] |
[
"Watson and Crick probably ripped off Rosalind Franklin, and nobody gave much attention to Rosalind cause she didn't have a Y-Chromosome. That should help you remember her."
] |
[
"What makes rain clouds darker than other clouds?"
] |
[
false
] |
[deleted]
|
[
"Exactly. Fun fact: rain clouds aren't as dark as you think they are, they are in fact white but appear black because your eyes can't handle the contrast between the sunlit tops and the shadowed bottoms. You can see this if you look at a cloud through a narrow tube, so that you can only see a small part of it at once - every part of the cloud you look at through the tube will be white, even the parts that look black to you without the tube!"
] |
[
"A rain cloud would be denser (ie hold more water) and have a greater thickness because of the amount of water it holds.",
"Both these factors point to a rain cloud scattering more light than a 'normal' cloud, hence resulting in less light penetrating all the way through it"
] |
[
"Similar to the grey cube illusion concept?"
] |
[
"Two Questions. First, Black holes are said to have infinite density. If that's the case, wouldn't their gravitational influence instantaneously suck in the entire universe? Second. If a singularity just 1 dimension, how does a black hole have spin? Don't they need multiple dimensions to rotate?"
] |
[
false
] |
To further clarify. The first question. If they had infinite density, wouldnt that mean that an object at the event horizon would feel the same powerful pull as an object 50 light years away, or even further? The second question. I think i did a well enough job asking but if you need me to be more clear about the question, i'll gladly update with an edit.
|
[
"The characterisation of a singularity in any particular way is not very useful for knowing about what's really going on inside a black hole.",
"There are good reasons to expect that there are no singularities and the existence of singularities in General Relativity is generally taken to mean we can't trust it once we get close to the singularity. Additionally there is very little reason to expect the interior of a real black hole is anything like the interior in the non-dynamical black holes we often talk about.",
"Real black holes have to form, and they interact with their environment. So they are dynamical. There is good evidence, but it wasn't immediately obvious, that the exterior of the stationary black holes describes the exterior of real black holes well though.",
"When we talk about the rotation of a black hole, you do yourself a disservice by imagining that this has anything to do with a rotating object inside the horizon. ",
"To talk about what the rotation means from a physical point of view let me first give an analogy, Imagine you have some object that isn't perfectly level, so in some places it is higher and other places it is lower. If the object isn't changing this height is \"non-dynamical\" but if you are moving around the object the height you're at will be changing. We call a perspective where the height isn't changing under your feet a stationary perspective.",
"How does this relate to rotating black holes? Well something that is stationary closer to the black hole will be orbiting the black hole according to something stationary further away. Furthermore, if you throw something into the black hole which has some angular momentum the rotation of that closer observer will speed up. It will in fact speed up in exactly the same way as if you imagine the horizon was a rotating object which gained the angular momentum of what fell in."
] |
[
"Para199x is right, but let's talk about idealized non-dynamical black holes in General Relativity.",
"1) If you take a finite mass and squish it into a smaller and smaller space, its density goes up. Density isn't fundamental, it's a derived quantity equal to mass/volume. Singularities have no volume, they're points, so technically mass/0 will be undefined, but because negative volume doesn't exist, we can cheat a little and not be entirely wrong by saying black holes have infinite density. ",
"Given this, it's clear that black holes have a finite (but large) mass, like any other object, behave similarly, with gravity decreasing as you move away from it.",
"2) Rotating black holes don't have a point singularity, they have a ring singularity. This ring has no thickness, so it still has 0 volume, but it can rotate."
] |
[
"Sure. A stationary black hole is a particular type of solution to the ",
"Einstein Equations",
". In general the Einstein equations are stupidly difficult to solve, so to get a solution we can actually write down requires assuming some stuff.",
"The \"stationary\" part has some mathematical definition, the core of which is that the black hole is eternal and unchanging. A real black hole on the other hand started existing at some point, most likely after the collapse of something big. It also interacts with its environment, probably emits Hawking radiation etc. So nothing about a real black hole is actually stationary. Luckily there are very good reasons to think that the exterior (the only observable part) of a real black hole should be extremely close to that of a stationary black hole in almost all cases."
] |
[
"How does the blood test for food allergies work?"
] |
[
false
] |
[deleted]
|
[
"Tests have also expanded to now include IgA and IgM tests and MRT tests. ",
"In the case of these tests, the patient's blood is drawn and then put under microscope to observe if there is an immune response when exposed to a particular stimulus like say pollen. Antibodies and antihistamines are positive confirmation that there is a food allergy or sensitivity. ",
"The mediator release test uses the same idea but is more expansive. This test also tests for immune response when exposed to stimulus. The type of response may not indicate a true food allergy but can show a food sensitivity (any food that generates a negative reaction in your body). "
] |
[
"Tests have also expanded to now include IgA and IgM tests and MRT tests. ",
"In the case of these tests, the patient's blood is drawn and then put under microscope to observe if there is an immune response when exposed to a particular stimulus like say pollen. Antibodies and antihistamines are positive confirmation that there is a food allergy or sensitivity. ",
"The mediator release test uses the same idea but is more expansive. This test also tests for immune response when exposed to stimulus. The type of response may not indicate a true food allergy but can show a food sensitivity (any food that generates a negative reaction in your body). "
] |
[
"Nowadays you can test for allergies fairly easily with imunohistochmistry assay's. You create wells coated with the antigen you're testing for, run over your sample, and then run over something that will attach to the antibodies and show this through, for example, a color change. Thsee assays are used to quickly test for basic allergies such as pollen and food allergies."
] |
[
"Why is there discrete states of matter, as opposed to a continuous “spectrum” of matter?"
] |
[
false
] |
Why does matter go through discrete phases of solid → liquid → gas, rather than a continuous change going through a “buttery” or “syrup”-esque phase?
|
[
"At the atomic level, the temperature of a substance is a measure of how energetic it's particles are. The higher the temperature, the higher the average kinetic energy of the atoms or molecules that make up that substance. For most substances, these particles attract one another with a strength governed by the various attractive forces at play, such as electric forces, van der Waals (sp?) forces, and chemical bonds. At low temperatures (and high pressures) the particles don't have enough energy to break these bonds, and the substance is solid. At medium temperatures some but not all of these attractive forces can be overcome, and at high temperatures the particles become completely separated and exist as a gas. ",
"So why are there no in-between states? Because these bonds are binary; either they exist or they don't. Either the temperature is high enough to break the bonds, or it isn't. There is a very clear threshold above which the bonds are broken, and below which they remain intact. This translates into a clear division between states of matter. ",
"Interestingly, because temperature is an average measurement, it's possible (and indeed quite likely) for individual particles to have a much higher or lower kinetic energy than that average and break or form bonds independently of the rest of the substance. This is how water can evaporate without boiling, for instance. It's also possible for particles in a solid substance to gain enough energy to sublimate directly into a gas."
] |
[
"Although this is a nice understandable explanation for non-physicists, it isn't really correct. The phases of matter are a thermodynamic, statistical effect. The energy is not distributed evenly across all bonds due to (classical) probabilistic fluctuations, and so if this were the explanation, then we would expect there to be a large overlap at phase change boundaries with properties in between the two phases, but this isn't what happens. Instead, at phase change boundaries, accounting for latent energy, you get the coexistence of two completely separate phases. Matter doesn't end up in a mixed state between the two phases, but rather either in one or the other, subject to the values of the thermodynamic variables.",
"To give a concrete example, consider a lidded pot filled with water on the stove. When the water hits 100C, it doesn't uniformly dissolve into a liquid-gas hybrid fluid. Instead, it ",
": large but ultimately discrete bubbles of steam form inside the water. Inside the bubble, there is gas, and outside, there is liquid. There is no intermediary.",
"What might we expect if the phase boundary were not discrete? This in fact does happen for many liquid/gas* phase boundaries, it's called supercriticality. ",
"This video",
" contains footage (around 8 minutes in) of a supercritical fluid transitioning from \"gas-like\" to \"liquid-like\" phases, and you can see the non-discrete behaviour.",
"Why does evaporation occur, then? Although the microscopic picture of some particles gaining enough energy to jump off is useful, it doesn't capture the ",
" reasons for evaporation. To illustrate, consider the following question: there is water vapor in the air, so why don't the colder molecules of water condensate onto the evaporating water and cancel out the hot particles jumping off?",
"The answer is that this ",
" happen. This can be quantified using statistical mechanics. And it illustrates a fundamental point: evaporation is a ",
". It occurs because the plate of water you put out to evaporate is not at equilibrium with the atmospheric water vapor phase. If it were, for example if you try the experiment at 100% humidity, or you put the plate in a sealed box, then yes, water molecules would jump off and jump back in, but the two processes would occur in a ",
"detailed balance",
".",
"At equilibrium, the solid and liquid phases must co-exist (due to the fact that the liquid phase is inexpansible and so can only occupy a fraction of the available volume), and the gas will be at the ",
"vapor pressure",
". ",
"The key takeaway here is that phase transitions are a ",
" effect. They cannot be understood just by looking at the molecules under a microscope: they are emergent phenomena. They only arise in systems with large numbers of particles.",
"E: minor correction"
] |
[
"Are you sure that it doesn't? Sure, the four phases of matter that you learned in high school are a useful tool, but reality gets pretty complicated when we start carefully examining the boundary between solid and liquid. Highly viscous liquids can be indistinguishable from solids. Particulate solids behave like liquids in some situations. Elastic materials can deform to take the shape of a container. Liquid crystals exist. There are a lot of interesting physics happening in this area. Just look at wikipedia page for ",
"States of Matter.",
"On the other hand, the boundary between gases and liquids/solids has much less going on, basically because the difference between \"attractive forces are overwhelmed by kinetic energy\" (gases) and \"attractive forces hold molecules together\" is much greater than than the difference between \"attractive forces are opposed by other forces\" and \"attractive forces dominate interactions\"."
] |
[
"What technological advances need to happen before Satellite WiFi, accessible from an normal laptop, is possible?"
] |
[
false
] |
EDIT: ANY normal laptop.
|
[
"Iridium has ",
"Satellite Internet from a Laptop",
". I don't know much about it, though I would expect it to be expensive. And it looks like you need an Iridium phone with it.",
"Keep in mind that even current \"Satellite Internet\" isn't as good as it sounds, because of the latency of satellites. The speed of light unfortunately isn't that fast in the scheme of things when they're so high up.",
"An interesting solution Google is experimenting with is ",
"Project Loon",
", which is the idea of using a \"global balloon network\" for WiFi. That has the advantage that the balloons are relatively lower altitude, so you don't get as much of the latency. It's also a lot easier to make the network larger when you need to, rather than having to launch more satellites. I would say this has a better future as a truly global WiFi network, but I'm not an expert on the practical problems."
] |
[
"You would need to build in a ",
"satellite phone",
", something like Iridium."
] |
[
"Can you clarify what you mean by 'Satellite Wi-Fi'? I will assume that you mean a laptop capable of accessing the internet anywhere in the world using a dedicated piece of internal hardware that exchanges data with satellites in space. ",
"Issues #1 - Antenna\nWhile you need a big satellite dish to receive a TV signal, the same might not hold true for a laptop. I am not an antenna engineer, but have worked with them in the past and seen them get very creative. My friend holds a patent for making the metallic logo on your laptop into a wi-fi antenna, thus, I'm bet we could already creatively solve this problem. However, this is not really my area of expertise. ",
"Issue #2 - Cost\nIt costs an unbelievable amount of money to get a Satellite into space. This is, by far, the most prohibitive reason. Home ISPs that offer satellite internet service to rural customers already charge much more and offer much less in terms of bandwidth. 99% of people are happy walking to Starbucks down the block for some free internet. It would be almost impossible for this market to sustain itself given the cost of getting something into space.",
"Issue #3 - Demand\nThis relates closely to number 2. Who would want this? There is already free wi-fi in most places. In addition, there are 3G and 4G PIC-E cards available for laptops already. 3G and 4G connections are cheaper, faster, and definitely require a smaller antenna. The only advantage satellite would have over these existing technologies is that you can get satellite reception in very remote places (assuming enough satellites in the sky, etc...)"
] |
[
"Why does boredom feel the same as being tired?"
] |
[
false
] | null |
[
"I've been in lectures where I was so bored I could barely keep my eyes open, yet the moment it ends and I step out I'm wide awake"
] |
[
"I've been in lectures where I was so bored I could barely keep my eyes open, yet the moment it ends and I step out I'm wide awake"
] |
[
"I think it may have something to do with under stimulation of the brain. Perhaps your brain behaves as your computer does if left unactive for a certain period of time; in order to save energy, it 'wants' to go to sleepmode"
] |
[
"If a star cannot fuse iron atoms, what would happen if an large iron body collided with the star? Would it spell the end of the star?"
] |
[
false
] |
As far as I know, when a star begins creating iron, it basically is in the last stages before death since it cannot fuse iron. Would introducing iron in it cause this process to start prematurely?
|
[
"It isn't that stars cannot fuse iron - they can, and sometimes do. It's that iron cannot be used as an energy source for the star, because fusing elements lighter than iron releases energy, but fusing iron and heavier requires energy input.",
"You can see in ",
"this plot",
" that iron sits at the highest point on the curve of nuclear binding energies. Fusion moves you to the right, and past iron, binding energies of high elements begin to drop, meaning they can be fissioned as an energy source, but not fused.",
"Under extreme conditions (most notably supernovae), elements heavier than iron are produced, but not during the course of a star's normal life."
] |
[
"Also, a star just having iron sitting around isn't a problem. Stars are born with wide variations in their percentage of iron composition. Introducing extra iron wouldn't really matter as long as there's still plenty of H/He or other lighter elements in the core to fuse.",
"You only run into a problem for the star when all that's left in the core is iron/heavier elements that can't release energy with fusion."
] |
[
"Yes.... if you can find a chunk of pure iron large enough. Which would have to be like 10% the mass of the star or so (which is typically what percentage of the star is actively fusing).",
"People have actually thought",
" about what would happen if you had a neutron star merge with a normal star and displace the normal star's core. That would be about the closest thing to a real world application of this question.",
"Recently ",
"someone made a claim",
" they discovered such an object, but I'm not sure if it's been verified or what the consensus is yet."
] |
[
"Question about neanderthals."
] |
[
false
] |
Given the anthropological differences in the human phenotype, (i.e. shaq vs danny devito) Is it at all possible that neanderthals are a just as "human" as the homo sapien? By which I mean that the differences n body structure would be negligible enough to allow them to live as a human today with little to no issues?
|
[
"Shaq and Danny DeVito both have the same human DNA sequences and those physical differences you see are really in gene expression. Between a human and a neanderthal the DNA sequences are actually different. A neanderthal that looked physically the same as you would still be more different than Shaq to Danny DeVito. So how different we're they from us? I saw a presentation of the neanderthal sequencing project at MIT a few years ago and it was fascinating stuff:",
"http://bioinformatica.uab.es/base/documents%5CmasterGP%5CNeandertalGenome.pdf",
"Neanderthals and modern humans have a DNA divergence at about 516,000 years ago. Take that against modern human versus chimpanzee, which happened 6,500,000 years ago and you see how similar the two really were. Even according to the paper I linked, up until recent advances in DNA sequencing, even our understanding of modern humans was a little off. By increasing the sample size and using better technology to build out a basic understanding of Neanderthals, they compared again to modern humans and showed we share more DNA than previously thought.",
"As much as 4% of our modern human DNA might actually have been of Neanderthal origin. This is all from interbreeding that we only recently concluded (2010 recently). Now back to your point: sure our skeletons and muscle structures were extremely similar, but that's not all our DNA affects. At the end of the day two groups were competing for the same resources and something had to give. Modern humans simply out performed Neanderthals. Maybe the Neanderthals were less aggressive, less intelligent, or less responsive to danger. Maybe humans simply out bred them with no obvious advantage except numbers. Something about the Neanderthals made them unable to compete.",
"So could they survive today? I suspect not as a divergent group. The most likely scenario in my mind would be that if you magicked a population of Neanderthals to modern day and taught them to use iPods and drive cars, is that they would simply be reabsorbed into the human genome over time. I can't say if they have the capacity to do those things, but we know they are close enough to breed with humans and I doubt that the environmental factors that killed them in the first place would count for as much in today's world."
] |
[
"http://www.newscientist.com/article/dn18869-neanderthal-genome-reveals-interbreeding-with-humans.html",
"Sub-saharan african populations show little or no trace of it. The rest of humanity have it. "
] |
[
"Thank you for the informative reply"
] |
[
"My dad used to tell me that i couldn’t buy men’s products, even though they were much cheaper than woman’s products, due to the fact that the chemicals in things like body wash and deodorant reacted differently to afab and amab bodies. Is this true?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"We do not debunk or vet theories or offer peer review on ",
"/r/AskScience",
". For more information regarding this and similar issues, please see our ",
"guidelines",
"A good home for this question is our sister subreddit ",
"/r/AskScienceDiscussion",
" because of its open-ended or speculative nature. Please feel free to repost there!",
"Please see our ",
"guidelines",
".",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"Hey, we can’t speak to the health or safety of specific products, but I wanted to mention the ",
"pink tax",
". I would definitely encourage you to investigate the ingredients in different products and compare the differences. "
] |
[
"That’s not what I’m asking though. The pink tax is something I’m familiar with, in all its shiftiness, but my dads argument was that the chemicals in the different deodorants are inherently different because they were made for different kinds of bodies and they wouldn’t work they way they were supposed to if I didn’t buy the ones he wanted me to, straight up. Looking into it myself, I know that most deodorants carry similar if not the same kinds of things. But that’s not an argument I’ve only heard from him. I just was wondering if there was any scientific backing to it that reddit might know, since I haven’t been able to specifically find that answer. "
] |
[
"What causes gas flow exiting from a tube to become sonic upon exit into a large vacuum cavity?"
] |
[
false
] |
I was reading a where the authors assert that any flow (including subsonic flow) from a tube even of constant cross-section will become sonic upon being released into a large vacuum cavity: The exit flow cannot be subsonic given that it must diverge upon exit, and the pressure increase produced by this divergence would make it impossible for the jet to adjust itself to the zero pressure vacuum region. But why is this necessarily the case? If there are gas particles simply moving at some (subsonic) velocity in the tube, wouldn't they simply continue drifting at their instantaneous velocity as they exit the tube and enter the vacuum? What causes them to speed up to the sound speed and/or for the sound speed to decrease? Any explanations on why/how the flow becomes sonic would be appreciated since I seem to not quite understand the authors' arguments nor the physical mechanism(s) at play at the interface with the vacuum. I was under the impression that the gas will stream out at some angle based upon the collisions of the gas particles with the tube and other gas particles. Perhaps the gas density will decrease as it enters the vacuum and expands in the cavity causing the collision frequency to decrease. This would render a kinetic treatment more applicable, but I wasn't suspecting any sonic flow. It appears I am missing a fundamental insight here and clarity (through physical equations and/or intuitive explanations) would be appreciated.
|
[
"Any flow exiting a tube into a plenum will be supersonic of the pressure ratio is high enough to be ",
"choked",
", about 1.8 for air. This is independent of flow velocity when exiting into a plenum and happens all the time in everyday life with subsonic flows.",
"To answer your broad question, this phenomenon is a result of the internal fluid pressure. The molecules bouncing around inside a tube are colliding with each other and the walls. When they get to the opening, there are less collisions (both the wall and whatever gas is in the plenum) so the flow expands. If the pressure in the plenum is low enough relative to the tube, the flow exceeds the speed of sound. The exact pressure ratio depends on the nature of the gas (as does the speed of sound).",
"If the flow exits into a vacuum, the pressure ratio would be infinite and the the flow must be ",
"sonic at the exit.",
"Hope that helps."
] |
[
"That's a good question, not any \"easy ways\" that I'm aware of. Certainly ",
"shadowgraph",
" or ",
"Schlieren",
" are classic ways to verify or measure the a shockwave.",
"Though to be fair, that's where I probably made a mistake is saying supersonic vs sonic. Most of the everyday situations would end up subsonic after the sonic exit.",
"This image",
" from the wikipedia article on ",
"choked flow",
" shows various flow regimes that are possible. For a straight tube into a plenum (or think any pipe exhausting to atmosphere), A and B are the likely scenarios (considering the exit and throat to be effectively co-located).",
"However, in the case of exhausting in a vacuum, G is what will happen. The flow will be supersonic, but there won't be the shocks you think of with supersonic speeds, but expansion waves as the gas tries to fill the entire volume."
] |
[
"This is not choked flow, i.e. the cross-section of the tube is constant",
"It's constant until the plenum, then it's a diverging nozzle, where the flow will choke. It will effectively act as a converging-diverging nozzle, since there will be a discharge coefficient at the exit effectively making the tube smaller.",
"but there is no physical mechanism to change the velocity of the gas particles without collisions.",
"You can think of every single molecule in a flow going at or faster than the speed of sound (that's sort of what the speed of sound is, at least the collision frequency of molecules and their ability to hit the molecule in front of them and propagate a wave forward). So when a subsonic flow enters a vacuum, the molecules stop colliding with each other and travel at their full speed (supersonic). The molecules haven't accelerated, they just stop bouncing backwards, thus the average flow speed increases..",
"I don't believe the authors are making the same point of infinite pressure ratio that you're making for a vacuum where pressure on the outlet side is zero.",
"I'll go read the paper now to help with the exact wording. But to me it is implied by the setup since any flow has to have pressure and it's emptying to a vacuum, thus must exceed the sonic pressure ratio.",
"It also says just \"sonic\", not supersonic,",
"Yeah, that's probably right, I tend to use them interchangeably. Once you have sonic flow, you usually get supersonic flow in my world (see ",
"converging-diverging nozzle",
")"
] |
[
"Iron and cobalt have similar thermal conductivities (actually, cobalt's is higher) but cobalt takes longer to go from \"red hot\" to not glowing. Can anyone tell me why?"
] |
[
false
] |
I had both metals in the liquid state, and then they were rested on a chilled copper block. The cobalt took quite a few seconds to stop glowing, but when I melted and solidified the iron, it quickly returned to room temperature. I figure if it's strictly dependent on thermal conductivities, then iron should have cooled faster. If not, there was something else at play (maybe the iron was in better contact with the copper, or the cobalt wasn't fully melted onto the copper and therefore didn't create a good interface). That's pretty much all the information I have. Both metals were >99.5% pure, both were melted to a flowing liquid state with an arc melter on identical, chilled copper blocks. They were both liquidy enough to easily fill in the thin groove of the copper plate. It always seems the cobalt compounds take much longer to cool, but today I did it with just both pure iron and pure cobalt and cobalt still took much longer. edit: before anyone answers, maybe it has something to do with the crystal structure? Cobalt's thermal conductivity has to be different along the c-axis than the basal plane I'd assume, whereas iron's cubic system is more uniform.
|
[
"Actually, I'd think it'd be the different heat capacities. "
] |
[
"With the difference in density around 15%, that might be it. Unfortunately I never timed it, but it seems to be a much larger difference than that. Maybe I'll time it tomorrow."
] |
[
"edit: before anyone answers, maybe it has something to do with the crystal structure? Cobalt's thermal conductivity has to be different along the c-axis than the basal plane I'd assume, whereas iron's cubic system is more uniform.",
"The thermal conductivity of any polycrystalline material is isotropic (assuming that the grains are randomly oriented, which is the case if you froze macroscale amounts of molten metal). (In fact, any second-order tensor property -- thermal conductivity, resistivity, diffusivity -- is isotropic in polycrystals with randomly oriented grains.) So the single bulk thermal conductivity is the only one that's relevant for this question.",
"To return to which: Fe and Co have nearly the same melting temperature, density, thermal conductivity, specific heat, and thermal diffusivity (the key parameter controlling how fast a small sample will change temperature). Everything's within about 20%; would you say you observed a larger difference than that? Other things to consider: different rates of oxide formation, different emissivities of the metal and the oxide (i.e., does one sample radiate more efficiently than the other), possibly the oxides' thermal properties if they become thick enough."
] |
[
"What would be the gravitational effects of matter beyond the observable universe?"
] |
[
false
] |
My question assumes two things, first that there is matter beyond the edge of the observable universe, and second that gravity moves at the speed of light. If these are true, it would seem that for something halfway between Earth and the edge of the observable universe, we on Earth would not be able to see everything which is affecting it. Furthermore, it would be acted upon by gravitational forces which Earth is not. My question then is this, would this explain expansion? Would these forces be negligible? Do cosmologists study such things?
|
[
"I realize that. I'm sorry, but that didn't address my question. Presumably something which is not from our frame of reference, but billions of light-years away, would have a separate observable universe, one which could detect things which we cannot, and be affected by such."
] |
[
"I realize that. I'm sorry, but that didn't address my question. Presumably something which is not from our frame of reference, but billions of light-years away, would have a separate observable universe, one which could detect things which we cannot, and be affected by such."
] |
[
"Nothing, the observable universe is the bounds of all possible interactions with us, as the furtherst photons from the shortly after the beginning of time would have to cross the radius of the observable universe to get to us. You know what else would have to cross that, the gravitation / gravitational waves. They propagate at the speed of light too. ",
"All interactions happen through the sharing of particles, thus if the particle hasn't got to us yet, we cannot observe it, nor does it have ANY effect on us."
] |
[
"Could I request a professionally educated list of notable good/bad scientific journals, online news sources, etc?"
] |
[
false
] | null |
[
"Might want to try ",
"/r/askacademia"
] |
[
"I agree with iorg. Your question is better suited for ",
"/r/askacademia",
"."
] |
[
"Fair enough, thanks. :)"
] |
[
"AskScience AMA Series: I am byronmiller and I study the chemistry of protocells. Ask Me Anything!"
] |
[
false
] |
I am a chemist researching questions related to the origins of life. In particular, I'm interested in studying autocatalytic reactions, meaning molecules capable of replicating themselves, and minimal cells or protocells. I'm still early in my career and learn more every day about this huge, interdisciplinary topic. A current project I'm working on involves applying 'systems chemistry' approaches to autocatalytic reactions to see what we can learn about them with new techniques. I'll definitely be on from 9-11pm GMT (5-7 pm EDT) but might also check in at other times a bit earlier.
|
[
"I'm not too familiar with this field, but in a lot of the systems that I have heard about, the self-replicating structures or sequences that form are the most thermodynamically favorable ones. Obviously in a modern cell, the proteins that are expressed are not the most stable ones but the ones that are the most useful to the organism. What are some theories on how the \"function\" of a molecule becomes decoupled from its stability/ease of synthesis?"
] |
[
"What are the current theories regarding the precursors to highly complex biomolecules such as RNA/DNA, proteins etc? "
] |
[
"What is the coolest thing you've seen a protocell do? ",
"What are their current state, I remember reading about self assembling enclosures some years back, is that still where the field is going? ",
"This may sound dumb, but can I make simple ones at home and put them under the microscope?"
] |
[
"When performing a gravitational slingshot maneuver, does the direction the planet is rotating in relative to a spacecrafts trajectory make a difference?"
] |
[
false
] |
[Solved] I've probably worded this poorly, and this might seem obvious. I read some interesting comments on a post earlier and when speaking to my friend about it we disagreed on the above statement. While I was able to find lots of information about gravitational slingshots I didn't immediately see any that explicitly mentioned the rotation direction of the planet. I thought that it was the gravitational pull of the planet that accelerated a spacecraft and it wasn't really important what direction it was rotating in. He thought that it was entirely dependant on the rotational direction of the planet and a spacecraft would have to enter its gravity in the same direction. Please can you help me clear this up. Thank you!
|
[
"You're right, the rotation of the planet about its axis has no impact on a slingshot. What matters is the direction that the planet is orbiting around the sun and where the spacecraft crosses through its sphere of influence."
] |
[
"It only depends on the orbital motion, not on the rotation. For all planets apart from Uranus the two happen to be roughly aligned (although Venus rotates in the \"wrong\" direction).",
"Technically there is an effect from ",
"frame-dragging",
" but it is way too small to matter."
] |
[
"Normally no, however if you try to make a slingshot off an object with very uneven gravity, then it might make a difference. Imagine a planet where half of it is made of something very heavy, and the other half something very light, in such a way that you experience stronger pull when you're facing the \"heavy\" side. If this was the case, then rotation would influence the gravity assist."
] |
[
"If 1/3 in decimal form is .333 repeating, and 2/3 .666 repeating, why isn't 3/3 .999 repeating?"
] |
[
false
] | null |
[
"It is. 0.999... = 1 = 3/3."
] |
[
"But it isn't whole.."
] |
[
"https://en.wikipedia.org/wiki/0.999",
"..."
] |
[
"Is cancer immortal?"
] |
[
false
] |
I just read up on cellular senescence and from what I can tell, it would seem that cancer is immortal. I know that a normal human cell-line can only be passaged so long before it loses vitality due to senescence. Would it be possible to culture a tumor cell-line indefinitely?
|
[
"Some are. The HeLa cell line is perhaps the best example. ",
"link",
". It still needs nutrients to grow, but from a purely senescence perspective, they are immortal."
] |
[
"hallmarks of a transformed or immortalized (cancer) ",
"1- Growth factor independency\n2- No response to growth inhibitors\n3- Evasion of apoptosis\n4- Can promote angiogenesis\n5- Unlimited proliferation\n6- Invasive",
"basically there is a mutation that allows them to simultaneously produce their own growth signals (not need growth factors) and evade inhibition."
] |
[
"Yes, this is very useful in making monoclonal antibodies. By fusing a b-cell with a cancer cell, immortalized clones are produced which all make identical antibodies."
] |
[
"Are there diseases that actually directly cause people to gain weight?"
] |
[
false
] |
Ones that maybe prevent the body from processing fat?
|
[
"One that comes to my mind first is ",
"Cushing's Syndrome",
", which is caused by exposure of the body to high levels of the hormone cortisol, the hormone released by the adrenal glands in cases of long-term stress.",
"High levels can be due to high doses of cortisol as a drug (it is a steroid, so can be used to reduce inflammation), or due to tumours or over-activity in either the adrenal gland or the gland that controls the adrenal gland, the pituitary gland. The pituitary gland releases a hormone (adrenocorticotrophic hormone, ACTH) that stimulates the adrenal glands to produce cortisol, so if there is too much ACTH, the adrenals will produce too much cortisol.",
"Cortisol acts to increase the breakdown of our body's energy stores (proteins, fats, etc.), as our body effectively 'thinks' that we're starving and in stress. Since we're usually not using this energy, it then gets stored as fat in adipose tissue, causing truncal obesity (i.e. the trunk of your body, the torso, gets fat). The breakdown of proteins actually causes your muscles to waste away, making your arms and legs get thinner as your trunk gets fatter."
] |
[
"That does not sound pleasant. Thank you for the info! "
] |
[
"Heart failure can lead to decreased blood flow to kidney, leading to decreased production of urine, leading to a buildup of fluid in the body. This can cause someone to gain 3+ pounds in a day, and much more over the course of days to weeks."
] |
[
"Regarding solar power electrical grid storage issues. Why are gravity batteries (pumping water uphill during peak electrical accumulation and running it downhill at night i.e. a dam) not an option?"
] |
[
false
] | null |
[
"For that you need mountains, with two lakes above each other, and a river to replenish the evaporated water.",
"\nMost, if not all suitable sites are already used for that. ",
"1 kW",
" "
] |
[
"Pump storage does not necessarily need mountains. See Ludington, Michigan for an example. The idea of pump storage is not efficient storage, but rather generating at peak power rate times. These projects make billions of dollars by playing the energy market. Construction costs are not a deterrent, but rather environmental and other regulations. A recently rebuilt plant in Missouri cost $400M to build and makes $500M/year."
] |
[
"does not necessarily need mountains. ",
"Two large storage areas with sufficient elevation difference would indeed be a better description. ",
"In flat-as-a-pancake the Netherlands they dreamt up ",
"plan Lievense",
", a hollow island in the North Sea (considered too expensive). "
] |
[
"What is the basis for planets that are \"hospitable for life\"?"
] |
[
false
] |
Does that mean something that is Earth-like? Is any form of water enough? Does it have to do with oxygen or temperatures, or I guess probably a combination of these things? If so, I guess it "makes sense" that this is what we're looking for, but isn't there a chance that we could miss out on life in other conditions because of our bias?
|
[
"Basically all we know about extrasolar planets is a) what their orbits are and b) what their mass is. So they tend to say planets are habitable when they are about earth-sized (up to about twice as big) and about the same orbit (so liquid water can be formed). We aren't missing out on any possible life at all because we can't detect life on ",
" of these planets. The technology just isn't there yet. It's just a way for us to categorize planets according to what type they are. Once we can start taking atmospheric spectrum, we'll see if our ideas about hospitable are correct or not, because we'll get the spectra of all planets and see which ones show signs of life (IE, look weird and out-of-balance)."
] |
[
"We can't analyze atmospheres now?"
] |
[
"Not of extrasolar planets, except in a few exceptional cases. Maybe when James Webb comes online..."
] |
[
"Is drinking deuterium depleted water good or bad to your health? Is there any scientific evidence?"
] |
[
false
] |
There are a couple of papers out there, such as: Biological significance of naturally occurring deuterium: the antitumor effect of deuterium depletion [pdf]
|
[
"http://en.wikipedia.org/wiki/Heavy_water#Toxicity_in_humans"
] |
[
"Note the question is about deuterium ",
" water",
"http://en.wikipedia.org/wiki/Deuterium-depleted_water"
] |
[
"How depleted? HDO already only constitutes about 1 out of every 3,200 molecules of normal water, and D2O only about 1 in 41,000,000."
] |
[
"An Apophis impact event: Why is predicting whether or not this (or any observed asteroid) will hit the Earth so difficult?"
] |
[
false
] |
The orbits of the planets are well known, and the observations of Apophis appear to indicate that it "might" hit us (or more likely Venus).. but there is a large variation in the probabilities. Why are we still having a difficult time predicting something like an impact event for an observed asteroid? Is there a lot more noise and are there more orbital perturbations than are commonly believed?
|
[
"I guess the answer is \"Pretty Accurate\" given the power we have computationally at our disposal and the importance of the answer to the question...",
"I can understand the weather being difficult to predict, but I, at least, think of the solar system as somewhat uncluttered compared to particles of air and water in an atmosphere as dense as ours, and thought that vector calculations accounting for major gravitational wells in our solar system would be easier."
] |
[
"I guess the answer is \"Pretty Accurate\" given the power we have computationally at our disposal and the importance of the answer to the question...",
"I can understand the weather being difficult to predict, but I, at least, think of the solar system as somewhat uncluttered compared to particles of air and water in an atmosphere as dense as ours, and thought that vector calculations accounting for major gravitational wells in our solar system would be easier."
] |
[
"Awesome, this is what I was looking for. Thanks!"
] |
[
"Why are substance such as gasoline, liquor, and methane flammable?"
] |
[
false
] |
I don't really understand how certain substances such as gasoline can be highly flammable. Could you explain to me how these substance can be flammable? What happens at the molecular level to make it flammable?
|
[
"Flammability means that the atom when combined with Oxygen has less potential energy and therefore emits kinetic energy in the form of a flame.",
"When Hydrocarbons like Gasoline, liquor, and methane combine with oxygen, oxygen has very high electronegativity, or want of an electron (It has the 2nd highest electronegativity of any element.)",
"The bonds break, and form new bonds with oxygen, releasing tons of energy in the form of a flame."
] |
[
"Interestingly, some fuels are not flammable, but are combustible (e.g., kerosene, cooking oil, waxes, etc.) - they must be vaporized first before being able to efficiently combine with atmospheric oxygen. Throw a match in kerosene and it will go out. ",
"What this implies is that certain \"lighter\" fuels have a higher vapor pressure (they vaporize easier and/or at a lower temperature). Throw a match in gasoline and you're going to get a quick, exothermic reaction if the temperate is right (around 0-20C) but below -20C the vapor pressure disappears and that same match thrown into gasoline will extinguish it. "
] |
[
"Thank you for the response, I understand it better now"
] |
[
"I was always told that if you did LSD even once, traces of it would stay in your body forever. Is this even remotely true?"
] |
[
false
] |
[deleted]
|
[
"No, LSD has a half-life of between 3 and 5 hours. Within a day or two you would have essentially no LSD left in your body.",
"Are there ANY drugs that stay in your system forever?",
"There are things like Dioxins that will stay in your body for decades and heavy metals can become incorporated into your bones. But I cannot think of any drugs that stay in your body for years."
] |
[
"It is true that LSD itself will leave the body quickly, and even the metabolites of sd will leave the body within 24 hours. There is still more debate about the longterm effects of the drug itself. Now there are significant reports of the phenomenon of \"flashbacks\" from LSD use, which is normally what is referred to as the \"proof\" that the drug is still in your system. The current best theory of this phenomenon is that it is a type of post traumatic flashback incident caused by a bad trip. As far as flashbacks being caused by \"cracking\" your neck, there has never been any studies that show any connections ",
"Also, the marijuana is 10x worse than cigarettes is partially true. Smoked marijuana releases more tar than cigarettes to the tune of about ten fold. Therefor longterm marijuana use is more likely to cause COPD symptoms. That being said, most people that smoke marijuana are not smoking nearly as much marijuana as a cigarette smoker smokes cigarettes. If someone smoked the equivalent of 2 joints a day for 30+ years they would likely have significant bronchial problems. That being said, marijuana has been shown to actually reduce the rates of lung cancer. That particular line is more of a half-truth than a lie"
] |
[
"It is true that LSD itself will leave the body quickly, and even the metabolites of sd will leave the body within 24 hours. There is still more debate about the longterm effects of the drug itself. Now there are significant reports of the phenomenon of \"flashbacks\" from LSD use, which is normally what is referred to as the \"proof\" that the drug is still in your system. The current best theory of this phenomenon is that it is a type of post traumatic flashback incident caused by a bad trip. As far as flashbacks being caused by \"cracking\" your neck, there has never been any studies that show any connections ",
"Also, the marijuana is 10x worse than cigarettes is partially true. Smoked marijuana releases more tar than cigarettes to the tune of about ten fold. Therefor longterm marijuana use is more likely to cause COPD symptoms. That being said, most people that smoke marijuana are not smoking nearly as much marijuana as a cigarette smoker smokes cigarettes. If someone smoked the equivalent of 2 joints a day for 30+ years they would likely have significant bronchial problems. That being said, marijuana has been shown to actually reduce the rates of lung cancer. That particular line is more of a half-truth than a lie"
] |
[
"How does an irregular sleep schedule affect you?"
] |
[
false
] |
[deleted]
|
[
"There is actually a disorder to describe this: ",
"Shift-Work Disorder",
"The wiki describes it fairly well."
] |
[
"Great link, thanks for the info!"
] |
[
"Also, long term puts her at higher risk for metabolic disorder/diabetes."
] |
[
"Do we see with our eyes or with our brain?"
] |
[
false
] |
[deleted]
|
[
"I'll throw out two interesting examples: ",
"When blind people are given ",
"alternate means to remotely sense their environments, such as audio headphones that play certain tones when objects are in front of them",
", the part of the brain that \"lights up\" in response to the stimulus is the visual processing portion. They are \"seeing\" their environment in a very real sense, using the same mental hardware to process the signals as they would if their eyes worked.",
"Conversely, when the visual processing parts of the brain are damaged, subjects often report profound blindness. Yet when objects are placed in their field of view, ",
"they display responses that are typical of sighted people",
", such as side-stepping to avoid obstacles or turning their heads in response to flashes of light. But they are not consciously aware that it is happening, supporting the idea that some kind of low-level bypass processing takes place even if the brain's regular visual processing capabilities are impaired."
] |
[
"It depends what you mean by using the word 'see'.",
"Your eyes (skin, inner ear and other sensory surfaces) are 'just' receptors surfaces which act to map a sensory stimulus onto the body somehow. In vision, this is with photoreceptors which basically map incoming light into cells which then transfer this to electro-chemical information the rest of the brain can interpret (for hearing it's mapped by frequency in the cochlea and for touch it's using a combination of different sensors for different types of sensations mapped spatially in the brain). ",
"If what you mean by 'see' is not that, then it's in the brain. It's through different processing centres in different parts of the brain that individual parts of the sensory stimulus (brightness, contrast, relative motion, size, shape, etc) are pulled together to create 'visual objects'. This is the stage where you start to recognise patterns created in the eye and ascribe them to objects in your environment that you remember. This is all ",
" complicated and only superficially understood, but super interesting. ",
"Given that rough background, is there a more specific question you wanted to ask?"
] |
[
"to quote the ",
"Gorillaz",
", ",
"\"You don't see with your eye, you perceive with your mind.\"",
"Visual cognition researcher here.",
"Seeing (or more adequately stated, \"perception\") is an ",
" process, whereby you take external stimuli from the world and modulate and interpret them based on numerous parameters, including feature dimensions (e.g. orientation of stimuli, color, movement), expectations, and many other factors.",
"The belief that your eyes provide a \"direct awareness\" of the world out there ",
", without any interpretation or processing, is called ",
"naive realism",
". ",
"This is the most common-sensical and prevalent way of seeing the world, if only because your visual system is so robust that it very rarely fails to provide the impression of direct access to the visual environment. Or at least, as Daniel Dennett would say, it \"seems\" robust, if only because you have no reason to think otherwise. Once you do, you will see just how ",
" it really is.",
"Vision and cognitive scientists often study illusions because these highlight the occasions when vision and perception break down, usually because of some expectations that are not being met in the stimulus. However, notice that most illusions are artificially devised to provoke just such reactions, since most naturalistic stimuli (e.g., natural scenes) will conform to your expectations, thus you may never become aware of these limitations without external input from others.",
"There are many examples in the scientific literature that highlight the active and constructed nature of perception, but perhaps my favorite is ",
"this experiment involving the paralytic chemical curare",
" (",
").",
"This experiment was devised to demonstrate what happens to our \"visual world\" when we are not able to move our eyes.",
"You take it for granted that your visual experience is stable, although this is actively maintained by many mechanisms, including your vestibular system (balance) and others.",
"One mechanism that was under research at the time was whether eye movements were ballistic (i.e., fire and forget), or whether they were mediated by muscle feedback. Furthermore, scientists wanted to know the role of brain signals to the eye: did they just target eye movements (known as ",
") or were they involved in more thorough processing.",
"To test this, the subject was given ",
"curare",
", a chemical which paralyzes the body. This prevented the subject's eyes from moving, although the subject remained fully conscious. Under higher doses, curare paralyzes all muscles, so a respirator is required to pump oxygen, since the body is no longer able to breathe on its own.",
"Even though the subject was not able to move his eyes, he was still able to ",
" his eyes to move (i.e., to send signals to his eyes that he intended them to move).",
"To quote the article:",
"To recap: after being given a paralytic (so the subject's eyes couldn't move), the subject tried to move his eyes in a given direction. Since his eyes couldn't move, the signal he gave to move his eyes did not affect the eye muscles.",
"However, the visual system doesn't know this. Thus, the visual system ",
" for the eye movement as it normally would: by shifting our entire ",
" to compensate for our eye movements.",
"This happens ",
" you move your eyes. However, you don't realize this, because your visual world is moved in direct proportion to the signal your brain sends your ocular muscles.",
"As was stated in the article, this phenomenon was first discovered by Hermann von Helmholtz, who suggested the nature of the stability of our visual phenomenology, and thus our \"perceptions of space must in part be calculated centrally from a motor outflow to the extraocular muscles rather than from a sensory feedback.\" He suggested that if you press your eyeball lightly from the outside (i.e., put light pressure on your eyeball through your eyelid), you will notice your entire visual world moving. This is because your brain ",
" compensate for this signal, since it did not create it. However, for eye movements, your brain ",
" compensate, since it knows exactly where it is sending the eyes to.",
"This is just one example of the way in which our entire visual experience is built up from a myriad of calculations -- of the stimuli, of our expectations, and of other factors that we're still learning about.",
"To see more examples in action, have a look at some visual illusions. For example, this ",
"TED talk",
" with Beau Lotto has some good examples, as does ",
"this page",
"."
] |
[
"Does water in the atmosphere automatically conclude a strong magnetosphere when observing exo-planets?"
] |
[
false
] | null |
[
"Hi haydaldinho thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"‘Astronomy’"
] |
[
"Astronomy"
] |
[
"Was there a flight test of the Mars Science Labratory's Sky Crane descent system, and if not, why?"
] |
[
false
] |
In the waning hours before the Curiosity touches down [or not], I've spent my time looking up all the materials for the flight tests I can, and in particular the flight test of the entire sky crane system. All I can find is of the system. The utter lack of material covering a test of the sky crane stage leads me to suspect that no such test took place, either because the rockets are powered for mars gravity or because other tests were considered satisfactory substitutes. If it did not take place, it seems to me like a major step was skipped in the prototyping process.
|
[
"There's no practical way of simulating Mars' lighter gravity and less dense atmosphere here that they could use to test it."
] |
[
"The less dense atmosphere can be simulated in some of NASAs facilities.",
"That's absolutely incorrect. There's no practical way of simulating the conditions necessary for an all-up test of the skycrane system under rocket power. Can you point me to a 500m (or even 100m) tall building they could draw down to a near vacuum to try and fly the powered descent module? The largest vacuum chamber in the world is only 120 feet high by 100 feet in diameter. The blast from the rockets would reflect off the walls and floor making a test completely useless."
] |
[
"I watched a British science documentary 'Horizon, Mission to Mars' which aired last week. They filmed at JPL for the past year, there was footage of tests of the sky crane being tested in an aircraft hanger or similar building. "
] |
[
"Is there such a thing as \"good calorie\" vs \"bad calorie\"?"
] |
[
false
] | null |
[
"I believe one significant difference is the time profile of the metabolic energy that these different nutrients make available. Pure sugar causes a short-lived and extreme spike in blood glucose, which will send the blood insulin level soaring soon after it. Simple carbs have a slightly smoother time curve and complex carbs, fats and proteins are significantly slower-release."
] |
[
"There are calories which provide more nutrition and those that are \"empty.\" For example a calorie of refined sugar would be less nutritious than a calorie of avocado. You also have \"good fats\" and bad fats like triglycerides. A calorie of an omega 3 fatty acid is better than one of triglycerides. Finally, calories made up of fiber and protein can help you feel fuller longer than carbohydrate calories. So, while a calorie is a calorie, you are better off spending your calorie allotment on more nutritious calories than empty ones. "
] |
[
"But what do you mean by \"more nutritious\"? It seems a bit tautological to me: good calories are nutritious, bad calories aren't. What makes something \"nutritious\"?"
] |
[
"What is CECO?"
] |
[
false
] | null |
[
"That makes sense, thanks!"
] |
[
"Are you sure you are not talking about SECO (Second -stage- Engine Cut Off)?"
] |
[
"Maybe it was just a typo? The sentence says: “The LIFTOFF light is turned off at S-IC CECO.”"
] |
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