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[
"Is there any promise in the idea of sonofusion or bubble fusion or is it absolute bull? And is this still an active area of research?"
] |
[
false
] | null |
[
"Thread from yesterday: ",
"http://www.reddit.com/r/askscience/comments/290k88/is_bubble_fusion_feasible/"
] |
[
"Not really..it's weird that it came up twice in a row."
] |
[
"Not really..it's weird that it came up twice in a row."
] |
[
"How was the first virus found?"
] |
[
false
] |
What methods were used to distinguish viruses from other pathogens so that we knew it was something different than all the known stuff?
|
[
"It was found because of its size. Viruses are much smaller than bacteria.",
"The experiment that discovered viruses involved taking plants infected with ",
"tobacco mosaic virus",
" and passing a puree of the plants though very fine filters which should remove any bacteria. The filtered liquid was still capable of infecting plants demonstrating the infectious agent was smaller than bacteria.",
"It’s also more difficult to culture viruses since they require specific host cells. So after this experiment viral diseases were notoriously difficult to culture (and therefore identify). For example, influenza was mistaken for the bacteria Haemophilus influenzae for a long time simply because it was reproduced in culture while the virus was not. The problem is that while that bacteria was found in many flu patients, injecting it into animals didnt cause flu, so it couldn’t be the infectious agent.",
"Edit: ",
"Koch’s postulates",
" were the original requirements to identify a disease causing agent. They are no longer accurate but it shows the mindset of researchers when identifying (or failing to identify) viral diseases."
] |
[
"Adding to this, because it couldn't be cultured and couldn't be filtered, they assumed it was a self-replicating poison of some kind, hence they called it virus from Latin meaning ‘slimy liquid, poison’."
] |
[
"By the late 1880’s, Scientists already knew that bacteria could cause disease, and scientists had filters fine enough to filter out bacteria in a liquid. When he was doing research to isolate the pathogen for tobacco leaf mosaic disease, Dimitry Ivanovsky noted that the liquid from homogenized infected tobacco leaf tissue that passed through the fine filter was still infectious. So, the pathogen could not be a bacterium. He coined the term ‘filterable virus’ or ‘filterable agent’, though work to understand what a virus actually ",
" would have to wait until the 1930’s and 1940’s. ",
"More info here.",
" and ",
"here",
" and ",
"here",
"."
] |
[
"If spent nuclear fuel requires constant cooling before it's stored, why don't they use it to keep powering turbines while the waste is still hot?"
] |
[
false
] | null |
[
"The heat produced is very small. By the time the fuel is removed from the reactor it is only a few megawatts. ",
"Using the spent fuel to produce electricity means you need to keep the spent fuel in a boiler or pressure vessel, in order to allow it to get hot enough to efficiently produce steam. If you put nuclear fuel in a pressure vessel, you now have all the same nuclear safety requirements as you do in the actual reactor itself, meaning you need an emergency core cooling system, safety systems, containment, etc. this is very complex, and the heat output of the spent fuel is extremely low and keeps decreasing over time. It's not economical or efficient. It would not justify the cost of building all this new equipment to try and harvest power from decay heat. ",
"http://en.m.wikipedia.org/wiki/File:Decay_heat_illustration2.PNG",
"Sorry it's a mobile link. But as you can see the heat output of the spent fuel drops drastically in the first week post shutdown. A full refuel outage takes no shorter than 15-20days, so it would be at least 3 weeks to get the spent fuel into a pressure vessel. By that point it's down below 0.5% of the reactor's full power output. For a large 1000 MWe reactor, that means it's less than 5 MWelectric output at best, before accounting for feedwater, control system, circulation system, and other requirements. And as I said, within the next few months this drops even more drastically. It's just not enough heat to justify a steam production cycle. ",
"While the fuel could technically be used for heating applications like in a radioisotope thermal generator, the fuel is extremely radioactive during this time, and can deliver lethal dose rates in seconds or minutes. A normal RTG uses a radiation source with low penetrating capability, and very little shielding is needed. The radiation from spent fuel from a power reactor can penetrate up to 7 feet of water, meaning you need a massive amount of shielding to use it in an RTG application. This makes it not practical for RTG use (not to mention you need to keep it covered and cooled to ensure no loss of fission product material in the fuel rod cladding). ",
"What we do see, is while the fuel is still in the reactor we can use this decay heat for lowering certain pieces of equipment. For example, the turbine driven auxiliary feedwater system can run for days on reactor steam, providing adequate makeup to the steam generator or pressure vessel. Some plants also installed miniature electric generators that use the reactor's decay heat to power critical instruments during an extreme accident, as only a small amount of power is required to run indicators and alarms. "
] |
[
"I just added a little to my first reply on that.",
"So here are some issues. First is to get 470watts of output, voyager's RTG operated with a hot temperature of 1832 degF. At this temperature, the zirconium cladding around spent fuel embrittles and is highly susceptible to damage. If you try to operate the spent fuel at a lower temperature for an RTG application, you would drastically reduce the already low power output of the RTG. ",
"An RTG utilizes Plutonium-238, which is primarily an alpha emitter. You do not need much shielding to block this radiation. Spent nuclear fuel has hundreds of different isotopes, many are radioactive, and shortly after fuel is removed from the reactor (when it still has a lot of decay heat), the radiation is significant enough that it can deliver a lethal dose in seconds to minutes. It is highly penetrating radiation. You would need significantly more shielding to use spent fuel in this abnormal application.",
"During the first year after being removed from the reactor, spent fuel requires consistent cooling to prevent melting or igniting into flames. So this would be a huge additional hazard beyond a simple RTG application.",
"To have spent fuel above boiling temperature, you need to either have it in a pressure vessel, or have it exposed to air, as stated previously during the first year, the fuel has the potential to melt or ignite if exposed to air. And a pressure vessel is pretty much out.",
"Is it technically possible? Yes. Is it feasible, safe, or efficient? It's not. If you want to use spent fuel products in RTG applications the best thing to do would be to reprocess the fuel to separate the highly penetrating radioactive material, and to mix the fuel into something more suitable for that application."
] |
[
"What about electricity generation without turbines? Similar to how RTG's get power."
] |
[
"Why Oxygen?"
] |
[
false
] |
I have always wondered why did we evolve to use oxygen instead of Nitrogen? If the atmosphere is roughly 78% nitrogen, 20.95% oxygen, 0.93% argon, 0.038% carbon dioxide
|
[
"Not much useful chemistry can take place with nitrogen. Nitrogen fixation in legumes, for example, needs to happen in an oxygen depleted root nodule by Rhizobia bacteria. It is extremely difficult, as nitrogen (N2) is an extremely stable, inert gas, and requires a lot of energy to split. ",
"The ultimate purpose of aerobic metabolism is to rob electrons of potential energy and then dump them. The source of these electrons comes from carrier molecules (ie NADH) reduced in Krebs Cycle. These electrons provide a potential across the inner membrane of the mitochondria, allowing protons to migrate through special transmembrane structures producing ATP. These electrons need to go somewhere, and are dumped onto oxygen, reducing it in the presence of hydrogen to form water. Of the gases present in the atmosphere, Oxygen is the only one that makes sense to reduce in this way. It is much more electronegative than nitrogen, and reducing N2 to amonia would produce a toxic intermediary as well as require incredibly harsh, hypoxic conditions. "
] |
[
"I'll add that the \"toxic\" intermediary and \"harsh\" conditions are only described as such because we don't use them. Oxygen-rich air was toxic to most life back when it first appeared. ",
"But the point that oxygen is more electronegative than nitrogen is correct. Also, the activation energy required to break divalent oxygen is smaller than that required for trivalent nitrogen, so biochemistry can go faster with oxygen."
] |
[
"Another reason, which I learned from david attenborough's doc about the origins of life last night, is that the origin of multicellular life is thought to be due to an increase in the concentration of oxygen in early earth's atmosphere, because it enabled these rogue single cells to produce the molecule collagen. This made them glob together, and wala, our earliest eukaryotic ancestors were born. ",
"Like Lickitysplit said, Oxygen makes it easy for our body to harvest energy, as it is very electronegative atom, and so it easily accepts a extra electrons. Therefore, it can be reduced easily. This is why it's called the ",
"final electron acceptor in the electron transport chain",
" in aerobic respiration, which all of your cells undergo."
] |
[
"Is there a name for words are are universal or required for language, and are there any notable linguistic exceptions?"
] |
[
false
] | null |
[
"What do mean by a word being universal or required for language? Do you just mean a word that appears in all languages? "
] |
[
"Words that, from an English speaking perspective, seem like basic requirements, words like: the, a, or. Or words that seemingly every langue should have, like sky, or eat."
] |
[
"Not all languages have articles (the, a); for example, Russian does not. ",
"I think the term you are looking for is ",
"linguistic universal",
". "
] |
[
"There is a debate on the \"Squirrel biting\" video as to whether or not squirrels can transmit rabies. Maybe someone here can shed some light?"
] |
[
false
] | null |
[
"Small rodents (like squirrels, hamsters, guinea pigs, gerbils, chipmunks, rats, and mice) and lagomorphs including rabbits and hares are almost never found to be infected with rabies and have not been known to transmit rabies to humans. ",
"http://www.cdc.gov/rabies/exposure/animals/other.html"
] |
[
"Care to share a source on that second part?"
] |
[
"The issue with bats is that you can be bit by a bat and not know it, especially when you are sleeping. If you are bit by a larger animal and are in a developed country, you are likely to seek treatment."
] |
[
"Can planets in the habitable zone have moons that also supports life?"
] |
[
false
] |
I was just thinking about our moon and how cool it would be if it was green and lush when we looked up at it. But it has no atmosphere since its too small, also, its too near the sun for its size, i guess? Also no magnetic shielding. Would this also be true for other moons around planets in the habitable zone?
|
[
"I think that the magnetic shielding would be a big issue. Even larger planets like Mars have their atmosphere stripped away by the solar winds, and Mars is much larger than our moon."
] |
[
"What if the planet had a very large magnetic field, or the moon was still geologically active?",
"That can happen right? moons be active I mean"
] |
[
"Jupiter has a very strong magnetic field. Unfortunately for its moons this magnetic field accelerates charged particles and bathes them in radiation.\n",
"http://en.wikipedia.org/wiki/Magnetosphere_of_Jupiter"
] |
[
"I woke up at 3 a.m and noticed it was raining heavily and the sky was green. Why is this?"
] |
[
false
] |
[deleted]
|
[
"The tornado doesn't need to be particularly close. I grew up about 70 miles from Detroit, MI, and I distinctly recall one hitting Detroit and the sky was Bright Goddamn Green.",
"The other possibility is that the clouds feeding the rainstorm were bloody enormous. ",
"Source"
] |
[
"Huh. Didn't know that. Thanks."
] |
[
"It's because of tornados, which you obviously seem to know already... I don't actually know, but there's this: ",
"http://www.news.wisc.edu/15301"
] |
[
"The Problem with the Specious Present"
] |
[
false
] |
[deleted]
|
[
"I don't think this technically has anything to do with science, much more of a philosophy question, but I will take a crack at it. ",
"It defines all time as a series of instances which take up no time themselves, so since no given instance takes up time, time doesn't exist. I would just view that as word play more than an argument, since I would define time as the distance between two instances, in between which lie an infinite number of other instances. ",
"It doesn't make sense to define time in a frame that it doesn't fit (a single instance), so this paradox would just be improperly defining \"time\". ",
"Edit: Just to add an analogy- This is akin to taking the derivative of a point on a curve, finding it to be zero, finding that all other points on the curve derive to zero, and stating that the derivative of the equation for the curve is zero. However, its not, the person doing so just improperly used the derivative."
] |
[
"So all in all, you are saying that this is cleverly disguised faulty logic?"
] |
[
"In my opinion, pretty much. I feel like the same thing happens when people try to make sense of things with analogies (ironic given the fact I used one earlier). It is easy to misinterpret thing A when it is compared to thing B in a situation when thing B does not actually represent thing A, even if you can phrase it to sound like it does. "
] |
[
"Why do you need eye protection when welding and why can you watch a video of someone welding without this protection ?"
] |
[
false
] | null |
[
"Sparks can fly into your eye when you weld and blind you."
] |
[
"Then why can't you see anything with a welding mask ? You could use a clear visor if it was only the sparks ?"
] |
[
"Oh, I see what you mean. Welding arcs emit a ton of UV and IR light. Intense, prolonged exposure can damage your eye. That's why welding helmets use a tinted shade (like sunglasses). "
] |
[
"Why don't we create synthetic gasoline?"
] |
[
false
] |
Why hasn't anyone created synthetic gasoline? Can it not be created by a similar process that synthetic motor oil is created? Or is that a completely different process. It seems like a no brainer to try and create as it would reduce dependency on foreign oil. Oil companies then could create this instead and still keep their profits. Obviously there is something preventing us from doing this, so I thought I would ask.
|
[
"The difficulty with creating a fuel is that you have to put the energy into it that you are going to extract later when you burn it. For something we only make a little of like motor oil, that's not a big deal. Replacing all transportation fuel, however, is a very big deal."
] |
[
"Why hasn't anyone created synthetic gasoline?",
"They have. Various commercial level processes exists for creating synthetic liquid fuels, notably ",
"Gas to liquids",
" processes which convert a gas (typically 'syngas', a mixture of H_2 and CO) into liquid fuel, and ",
"Coal liquefication",
" which converts coal into liquid fuels. Companies including SASOL (the South African oil company) and Shell have production facilities using these process, and in some cases have had for a considerable time.",
"It seems like a no brainer to try and create as it would reduce dependency on foreign oil.",
"That's the downside. You still need a very good supply of carbon, hydrogen and oxygen and a large amount of energy. Syngas, can be created from water and CO_2, but that takes even more energy. At a very high level, you can synthesize nearly any of the fuels that we use from a variety of base products, but you need a large amount of energy to do it. Because of the amount of energy used, these processes are only really used when there is a very convenient source of cheap raw materials available (like coal or various gasses), and investing the energy to turn these into liquid fuels is profitable. ",
"Without abundant, clean and cheap energy sources, these processes are not an environmental or energy-independence panacea."
] |
[
"Doesn't the fact that motor oil is used for lubrication rather than as an energy source make a huge difference here?"
] |
[
"You are standing on the moon. Your friend is standing on the Earth. He shines a special laser pointer at you. Is it true is true that you will see the dot from his laser pointer appear next to you before he does because you're already at the destination and he is not?"
] |
[
false
] | null |
[
"No -- perception is the result of photons entering your eye. They physically have to get there (at the speed of light)."
] |
[
"Yes because the light has to travel from his flashlight to the moon and then a very short distance to your eye and this is a much shorter distance than to the moon and to the eye of the observer on earth."
] |
[
"Light from the laser and light from the person's hand as they push the button will essentially arrive at the same time since both travel at the same rate and are right next to each other in space."
] |
[
"If matter cannot be created nor destroyed , then what happens to the matter that falls into a black hole?"
] |
[
false
] |
[deleted]
|
[
"It becomes part of the black hole.",
"Also, matter can be created and destroyed; for example, a free neutron can decay and turn into a proton, an electron, an antineutrino, or an electron and positron can annihilate and turn into two photons. Various properties have to be conserved (unchanged), such as the total energy, total momentum, total electric charge, and so forth, but particular particles can cease to exist or start to exist."
] |
[
"The conservation of mass is only applicable in classical mechanics ie most of the things we do on Earth in kinematics, engineering, etc. ",
"However, when we start to delve into the quantum or relativistic realms, mass becomes a little for volative. Einstein's famous mass-energy equivalence formula (simplified as it may be) is one of the most famous equations ever. E= Mc",
" ",
"That states that mass is actually just energy, but in a different form. That's why in nuclear reactors for example, the output masses are lower than the input masses because some of the input mass was converted into pure energy. Thus the actual law is conservation of Energy and is applicable everywhere (as of now. Who knows what's out there)."
] |
[
"Huh, interesting. Thanks mate."
] |
[
"Do animals actually understand each other's calls like humans understand speech?"
] |
[
false
] |
I know they can understand each other, but do animals interpret each other's calls as intricately as humans can with our speech using words and such?
|
[
"Like humans? Yes, maybe. We think dolphins actually have a complex language with syntax. There is evidence that they even each have individual names that they get from their mother's name. But we haven't made much headway in learning their language if it's there. ",
"Other animals certainly recognize conspecific calls. Song birds find mates using their songs, so wouldn't be very successful at reproducing if they didn't recognize each other. Other animals have other forms of complex communication. Vervet monkeys have predator calls that identify the type of predator they see. There is a call for 'eagle' that will tell all of the other monkeys to look up and maybe duck, a call for 'leopard' will let the group know that they should run into a tree, and the call for 'snake' tells everyone to look down. Other monkeys have similarly different calls for different predators. Most animal mothers will also recognize their own offspring calls and distinguish them from the other young in the group. ",
"Whales will recognize each other's calls from far off. Because whale songs travel in water they can be heard up to 3,000 kms. from the source. One whale, called the 52 Hz whale, has for decades been singing in a vocal range that's too high-pitched and is undetectable by other whales, so this lonesome whale cannot elicit a response from other whales. "
] |
[
"There is evidence that they even each have individual names ",
"I hadn't heard about that bit. Link to where I could read more?"
] |
[
"I absolutely love the idea of some breakthrough team cracking dolphin speach and using advanced communicators to talk in real-time with a dolphin. The thought alone is a poshy of mental masturbation"
] |
[
"How do exchange particles know which way to go?"
] |
[
false
] |
Whenever you see diagrams of something like neutron decay, the exchange particles always know where to go or what type to be. How is this possible?
|
[
"That is because Feynman diagrams are just graphical representations of algebraic terms in a computation of how likely a specific collision or decay process is to occur.",
"The positions of all vertices and internal lines are completely irrelevant. The only thing that matters is which lines connect to which vertices, and which lines represent incoming or outgoing particles.",
"To determine the probability of an interaction, a physicist (or more likely computer) makes a sum of the terms corresponding to every valid diagram with the specified incoming and outgoing particles. Since there are is in principle no limit to the number of vertices, the calculation will be cut off at some \"order\" or maximum number of vertices. The idea is that each vertex significantly decreases the probability contribution for that diagram and one can get a good approximation of the true probability from the partial computation.",
"These diagrams are useful on their own without calculating anything to determine:",
"If a given interaction is possible",
"By counting the minimum vertices required, approximately how likely the interaction is to occur or roughly what the decay rate should be (to an order of magnitude or two).",
"EDIT: There is a funny story around the fact that you can draw the lines in whatever shape you want. A few physicists made a bet to see who could use the word \"penguin\" in their next paper. The bet was won by specifically drawing a Feynman diagram for a process in the rough shape of a penguin, and calling it a ",
"penguin diagram",
". The word \"penguin\" is still common in particle physics to refer to a specific class of interactions that have these diagrams."
] |
[
"It was the other way around actually! Ellis lost the bet and therefore had to use the word 'penguin' in his next paper."
] |
[
"Feynman diagrams aren't an attempt to illustrate an actual interaction, they're instead a neat hand-writing short hand for the mathematical integrals one has to solve. In the actual math one sums or integrates over all possible positions and/or all possible momentum (I.e. directions). So it's in the math, but not the little short-hand"
] |
[
"Do microwaves kill bacteria?"
] |
[
false
] |
I've always wondered if a microwave oven could be used as a disinfectant. Does it kill bacteria outright? Or is it the created heat in food/other elements that does the trick?
|
[
"To some extend a microwave can kill bacteria, but not all bacteria can be considered equal in terms of conditions required to inactivate or kill them. As you might understand there are many factors in play to consider such as the material, thickness of the material and the type of bacteria so it's not possible to give you a generalised answer that will apply to everything you stick in the microwave.",
"Perhaps you've heard of this tip before. Stick a sponge in a microwave to disinfect the sponge. Going by this example the following has been found. ",
"NYTimes - The Claim: You Can Disinfect a Kitchen Sponge in the Microwave (2007)",
":",
"In recent years, at least two studies have put the claim to the test, and both have confirmed it. The most recent, published in the December 2006 issue of The Journal of Environmental Health, found that microwaving kitchen sponges and other scrubbing pads for one to two minutes at full power could reduce levels of bacteria, including E. coli and other common causes of food-borne illness, by more than 99 percent.",
"A previous study in 1999 found that many bacteria are eliminated within the first 15 seconds of being heated by microwave, and that only E. coli survive longer than 30 seconds.",
"To avoid fires or overheating, the authors of the 2006 study recommended that only damp sponges and those without metal be zapped. But some experts say the practice poses a safety hazard and should be discouraged. Some news accounts have described cases in which kitchen sponges caught fire while being cooked by microwave.",
"Other studies have found a safer alternative: soaking soiled sponges in diluted solutions of bleach, which is just as effective as heating. Then again, there is an even simpler option: tossing the sponge out and getting a new one.",
"BBC - Microwave 'sterilisers' warning (2007)",
":",
"Professor Gabriel Bitton, a expert in environmental engineering at the University of Florida, and colleagues contaminated kitchen sponges and plastic scrubbing pads in dirty water which contained faecal bacteria, viruses, protozoan parasites and bacterial spores.",
"After two minutes on full power, 99% of bacteria were inactivated. And E. coli bacteria were killed after just 30 seconds. Bacillus cereus spores - which are largely associated with vegetables or foods in contact with soil and are normally quite resistant to radiation, heat and toxic chemicals - were completely eradicated after four minutes in the microwave.",
"Professor Britton said it was likely to be heat, rather than radiation, that proved fatal ",
"The team also looked at whether the microwave oven could be used to sterilise contaminated syringes. It was found to be an effective method but took far longer - up to 12 minutes for the Bacillus cereus spores.",
"Professor Hugh Pennington, a food safety expert at the University of Aberdeen said heating was an effective way of sterilising kitchen equipment.",
"He said heat was an obvious method of sterilisation.",
"EDIT: ",
"How Microwaves Work",
". "
] |
[
"It should be mentioned that even though most bacteria die the toxins produced by them may remain, so you can still become sick by ingesting spoiled food that is microwaved."
] |
[
"The real kind as opposed to the imaginary kinds your spa treatment is supposed to purge. ",
"Lots",
" and ",
"lots",
" of different classes of toxins."
] |
[
"Does it take an infinite amount of time to fall towards an event horizon of a black hole?"
] |
[
false
] |
Closer you get to the event horizon, greater is the time dilation. So for an outside observer an object will take more time to cover the same distance as it approaches the event horizon. Technically at the event horizon dilation if infinite, well, we do not yet know clearly what happens at that point, but we can see that time dilation is very high at a point which is really really close to the event horizon. So, for an outside observer it would appear that it takes infinite time for an object to fall into the event horizon. Is this right?
|
[
"Say we have two observers, Alice and Bob. Say Alice is stupid enough to cross the event horizon of a black hole described by the Schwarschild metric (symmetric, non-rotating, zero net charge). Bob is hovering outside the event horizon observing Alice falling into it. What do Alice and Bob see from their own reference frames?",
"Alice sees nothing special. In fact she may not even be aware of the moment where she actually crosses the event horizon. Nothing special is going on for Alice until she is obliterated by the singularity at the center r=0.",
"Bob sees Alice more and more slowly falling towards the event horizon. From Bob's perspective, he never sees Alice actually crossing it. From his view, Alice will \"eventually\" become infinitely redshifted and approach the horizon at an infinitely slow infall speed. It would take an infinite amount of time for Alice to cross the event horizon from Bob's perspective."
] |
[
"The redshift beyond detectability would actually happen very rapidly. It would be measured in milliseconds, with the last photon reaching Bob in less than a second."
] |
[
"That's my understanding. You would see Alice appear to slow down slightly, but she would become undetectable to any distant observer in a very short period of time. ",
"In proper time (i.e. from Alice's perspective), she would cross the event horizon as if she were crossing any other imaginary barrier. From the perspective of a distant observer, there would be no way to observe her crossing the horizon. There are no light paths from the horizon to an observer, and those photons released just outside the horizon would take nearly infinite time to reach the observer.",
"The paradox about objects stopping short of the event horizon stems from a coordinate singularity at the Schwarzschild radius. But this is not a true singularity. We can't observe an object crossing the event horizon, but it does happen. The \"when\" is a tricky question because time is relative."
] |
[
"What threat does glacial melting pose to the gulf stream?"
] |
[
false
] |
As in, if global warming were to go out of control, and the glaciers in antarctica melt, would the flow of water disturb the gulf stream to any large extent, and if so, what would the consequences be? I heard that it would plunge northern Europe into an ice age, but what credibility does this theory actually have? Thanks in advance.
|
[
"The Gulf Stream primarily exists because of the action of winds blowing across the subtropical Atlantic. A good (but small) map of the surface currents is ",
"here",
". Unfortunately, many people are taught this ",
"image",
" of ocean circulation which both dramatically simplifies the Thermohaline Circulation and makes it appear that the Gulf Stream primarily exists as a limb of this circulation.",
"The freshwater input from melting polar ice will certainly effect the global thermohaline circulation by decreasing the formation of deep waters at high latitude. But since most of the Gulf Stream transport (80-90%) is due to the wind and not thermohaline effects, The Gulf Stream itself will persist but perhaps with a slightly weaker transport."
] |
[
"It turns out I meant the arctic, not antarctica. My apologies."
] |
[
"The biggest consequence for the Gulf Stream would come from arctic melting in Greenland and northern Canada. All that cold and less saline water would barge into the north atlantic where it might both slow thermohaline circulation and shift the path of the Gulf Stream further south; say towards North Africa. It would also turn the Davis straight into an \"iceberg cannon\" shooting into the north atlantic. This would have severe climatic consequences in Northern Europe. "
] |
[
"Implying this is true - Why did the menarche occur earlier and earlier?"
] |
[
false
] |
I heard that women used to get their period after 16 or so, now the average menarche occurs between 12-13, and girls as young as 9 are getting them. Why is this?
|
[
"The answer is we don't know. There is no solid evidence showing why this is occurring just that it is. Some believe it's environmental insults; some believe it's BMI related; some believe it's genetic; and some believe it's psychological or a combination of these.",
"BMI: ",
"http://www.ncbi.nlm.nih.gov/pubmed/24466641",
"An example of genetics: ",
"http://www.ncbi.nlm.nih.gov/pubmed/24438044",
", ",
"http://www.ncbi.nlm.nih.gov/pubmed/23599027",
"An example of environmental insults: ",
"http://www.ncbi.nlm.nih.gov/pubmed/23569194",
"Socioeconomical minus nutrition (I believe a large confounding factor would be psychological in this study): ",
"http://www.ncbi.nlm.nih.gov/pubmed/22641520",
"TLDR; we don't know"
] |
[
"BMI is the theory I subscribe to mostly (with a host of other contributing factors but it's my primary factor). There is solid evidence that a reaching a weight triggers menarche (and indeed is necessary to trigger menarche)"
] |
[
"How could it be psychological? Is the hypothesis that girls were hiding their \"early\" onset back in the day thus skewing the data? I cannot come up with any other possible \"psychological\" reason."
] |
[
"Why do particles that are not noble gas atoms want to become ions? If the reasoning is to maintain a ground state or low entropy then why aren't more electrons transferred to minimise the space between sub-atomic particles and minimise the entropy of the atomic system?"
] |
[
false
] |
Looking at sodium metal and a sodium ion in NaCl, when sodium metal reacts with water it violently gives off its valence electron and causes a massive exothermic reaction after which the remainder sodium is now stable with its new valence electron shell filled. But what is the benefit in this? I understand that they want to have a ground state but what's the benefit of that? I've heard one view on Quora suggesting that it's to do with the universe favouring less entropy in a system. So by becoming an ion there's less entropy within the sodium atom because the sub-atomic particles are closer together but.... by that logic why doesn't the atom give off MORE electrons so the remainder sub-atomic particles are closer together to minimise the system entropy? If only I could personally ask the sodium atoms :').
|
[
"It is not favoured for the sodium atom to give up its electrons. It takes energy. Copared to other atoms the energy reqired to remove an electron from the shell is lower, however, still existent. The reason to form the salt is that chlorine \"wants\" the electron and that afterwards, the lattice energy from solid salt formation is released. Without lattice energy, the salt formation would not be favoured, because the the positive effect of clorine ionization Cl-->Cl- does not outweight the energy required to form Na+ from Na.",
"EDIT: For the entropy consideration: You need to differentiate between enthalpy and entropy. The favoured states are basically given by enthalpy. Enthalpy is like it is and derives from the electron wave functions. We can describe them, calculate values and find soulutions, but they are a basic principle like the fundametal realtions that give e or pi. If you ask why is pi pi, you wont get a sufficient answer. I hope that answers your question.\nFor formation of solid salts, entropy is not the driving factor. Entropy would indeed favour ions that are free of their electrons in a mixture with free electrons, which only happens at very high temperatures (plasma), because then the entropy would be the main driving force. Of course anions like Cl- would not be favoured in such a system, so it is not a very suitable answer."
] |
[
"I'll give a go at some quick answers for you since you seem to have a decent understanding of the underlying concepts. ",
"First, the energy required to remove the valence electron in a neutral sodium atom is very low compared to other atoms. This is largely due to electron shielding. Basically the electron shells beneath the valence electron cause the nucleus of the atom to have less of an effect on it. This is also the response to your last question about why an atom doesn't shed more electrons. ",
"Second, I'm not so sure about your use of the term ground state. Typically ground state refers the lowest energy level of an electron, contrasted by an excited state. You are referring a molecule with a lower energy being the preferable system. For instance, dynamite has a very high chemical energy. When it reacts, the products are a much lower energy with the remainder being transferred to the explosion. At no point in this reaction is anything in an excited state. Don't confuse a higher energy transition state with an excited state (transition states can be excited states, but it's not required). ",
"Third, you are mixing up entropy and enthalpy. Remember that entropy is the disorder of a system. It can be decreased in a local system, but must always increase for the universe. This is immutable. Enthalpy is more simply the energy of a system. As you said, a reaction is genrally favored if it lowers the enthalpy of the system. Likewise, a reaction is generally favored if the entropy increases. For instance, burning butane will do both. It lowers the energy of the system (water and carbon dioxide are both lower energy molecules than butane) and increases the entropy in the form of creating more molecules (for every molecule of butane burned, 4 carbon dioxide and 5 water molecules are generated). ",
"Last, why does the energy of a system always move towards the minimum? That's due to the physical laws of the universe. You'll get better answers from a physicist about that. ",
"As always, if anything is incorrect or not correct enough, let me know!"
] |
[
"Thank you for the brilliant reply! Could you expand a bit more into your edited part? As in why the electron change is enthalpy driven and not entropy driven?"
] |
[
"How does hypothermia kill?"
] |
[
false
] |
So how exactly does hypothermia kill? Is it something like enzyme reactions getting out of their 'operating temperatures', or the body's temperature-regulating mechanisms spiraling out of control once they get too far out of wack, with fatal effects?
|
[
"Below 34C the heart tends to stop beating properly. We cannot accept any rhythm an ECG provides when the body is below this temperature, they're simply not appropriate rhythms and require treatment, we wouldn't declare someone dead on the basis of an ECG finding while they're cold (not that an ECG alone is ever enough to declare death). It's why the phrase \"No one's dead until they're warm and dead\" is popular in medicine.",
"Once the heart stops beating cells begin the apoptosis and necrotic processes that lead to tissue death, but this can be slowed by the decreased temperature. Beyond temps of 0C the freezing can mechanically lyse cells and tissue due to the expansion and crystallization of water as it transitions to ice."
] |
[
"They follow a progression. Initially they become tachycardic (high heart rate) then quickly become extremely bradycardic (under 40 bpm if I recall hard numbers appropriately, but it varies as always in medicine.) They present a specific J wave on ECG below 28C, again if I'm recalling hard numbers right, and then progress rapidly into V-fib and asystole around 20C.",
"As for the reasons this occurs, it's going to be due to electrolyte imbalances brought on by failing metabolism."
] |
[
"Are the arrhythmias a primary result of low temperature, or are they results of other systems getting wacky from the cold?",
"If a primary result, do we know what causes the problem? Is is an electrical issue, or a cardiac muscle issue?"
] |
[
"I am currently learning about resonant circuits, and there is discussion of current leading voltage and voltage leading current. How can current and voltage not be happening at the same time? Aren't there always electrons? How can this be possible?"
] |
[
false
] | null |
[
"Think of current as flow of water and voltage as pressure of water.",
"First of all, it's obvious you can increase pressure without increasing flow (if water has nowhere to flow to — for example, increasing pressure in a closed container). ",
"Second, it's obvious you can increase flow without increasing pressure — for example, water flowing downhill can flow faster and faster without any change in pressure.",
"In various other scenarios you can have various other relationships between flow and pressure, such as situations where flow changes and pressure follows (current leading voltage), or pressure changes and flow follows (voltage leading current). Wikipedia's article on ",
"hydraulic analogy",
" is a good place to start."
] |
[
"Fair enough. I meant obvious not in the sense \"you should have seen this\" but in the sense of \"now that I am telling you, I am sure you see it\"."
] |
[
"Good explanation, but I think what you're saying is obvious actually isn't obvious. That's actually where the question was solved (at least for me)."
] |
[
"If the world's most powerful telescope was pointed towards the moon how closely could we examine the moon's surface?"
] |
[
false
] | null |
[
"It would be on the order of 10's of meters. If you're asking if you could see the American flag planted by the apollo astronauts, then no, there is no telescope capable of doing that. (For reference, it would take a reflecting telescope 1/4 mile wide to resolve the flag on the moon to a few pixels on a monitor where the video feed was coming in from an imaging telescope. -source wikipedia calculations of Dawe's Limit, Rayleigh Criterion, and angular resolution).",
"shavera, you seem to be thinking that angular resolution and magnification are not as strictly tied together as they are. In order to resolve 2 point sources that are extremely close in terms of angular separation, you not only need a very large light bucket like a newtonian reflector, but you also need to be at or near the telescope's maximum usable magnification. An example of this is a personal one. I have a 10\" reflector and if I just stick my camera in the focuser, and point it at the north star, I only see 1 star on the computer screen. However, when I increase the focal length of my imaging setup via using multiple barlow lenses, and I again point it at the north star, you can resolve both Polaris A and Polaris B. My telescope is not large enough to resolve Polaris Ab though, the 3rd star in the group, at it's maximum magnification aka focal length. It would require a significantly larger telescope to do that. "
] |
[
"Small note, ",
" cannot resolve the moon landing site. Some of Nasa's crafts have taken pictures of the site.",
"http://www.space.com/12796-photos-apollo-moon-landing-sites-lro.html",
"I got chewed out on this a while back."
] |
[
"Correct, I should have noted that. I have seen the photos, you can see the landers as very small objects, and moreso the shadow that they cast. I will see if i can find them. ",
"Here's one from nasa.gov ",
"http://www.nasa.gov/sites/default/files/images/369234main_lroc_apollo11labeled_256x256.jpg"
] |
[
"My science teacher doesn't believe in global warming because of volcanoes and their CO2 levels after they erupt. Is this credible, and is it possible that he is right?"
] |
[
false
] |
My science teacher is a very smart man, but there are several things that I question with him. For example, he does not believe in global warming. He says it is a normal cycle in the history of the world. He backs this up by talking about volcanoes and their carbon dioxide. Apparently, when a volcano set off a couple years ago, they measured the CO2 in the atmosphere and saw that it was almost 400% higher than it was used to. (I'm not sure if it was 400%, I'm just repeating what he told us.) Now, he says that if people are worrying about global warming - then why did the CO2 in the atmosphere have no ill effects? He then says that the CO2 went back down to 'normal levels' in a short amount of time. So, that means that if the earth was really bogged down with all this carbon dioxide that we humans are making, it could easily stop it and reverse it. Now, my teacher is persuasive and well spoken. He did convince a lot of people in my class, and even made me doubt my beliefs. Can someone explain to me if he is right/wrong? And why?
|
[
"Skeptical Science",
" has a ton of facts and figures (with citations) that are aimed at addressing most of the common misconceptions about climate change. I highly recommend it in addition to the answers that were given here."
] |
[
"The ",
"Keeling Curve",
" has shown an incredibly consistent rise in atmospheric CO2 over the past 50 odd years. A 400% sudden increase in atmospheric CO2 from any single event would just be ridiculous."
] |
[
"Here's the ",
"link",
" to OP's question on that site, for the lazy. Good find. :)"
] |
[
"Mechanism for Type 2 Superconductors?"
] |
[
false
] |
Is there a generally accepted mechanism for the function of Type 2 superconductors? I've been reading about BCS theory for Type 1 superconductors and have a decent understanding of the formation of Cooper Pairs and the overall mechanism. I have however, been able to find nothing on how Type 2 superconductors work other than "it's different from Type 1".
|
[
"(It's been a while since I did this particular theory, but I think my explanation is correct).",
"Type 2 superconductors superconduct by essentially the same mechanism as the type 1s, so far as we understand, though the factors affecting cooper pair formation may be different and more complicated. The difference is in the way they behave with respect to increasing the incident magnetic field. This magnetic field may be caused by an applied current...the important thing is that it represents a source of energy which may be transferred to the superconductor. If this energy cannot be dissipated in the superconducting state, the state will collapse.",
"In a type 1 superconductor, you're probably aware that there's a sudden superconducting cutoff at a critical magnetic field. That is to say, as you turn up a magnetic field, suddenly the superconducting state collapses and the field penetrates the material entirely.",
"In a type 2 superconductor, this doesn't happen. As you ramp up the magnetic field, the state doesn't suddenly collapse, but instead vortices penetrate it and slowly reduce its superconducting properties. These vortices consist of a magnetic field line penetrating the sample, circled by superconducting current which protects the rest of the sample's superconducting state. As you increase the field, more and more vortices form, until eventually the superconducting state does vanish entirely.",
"The behaviour of vortices under different conditions is an area of interest in itself. For instance, they may have a stationary state which is stable, and this may affect the properties of the superconductor."
] |
[
"The Ginzburg-Landau theory",
" is a phenomenological theory (does not propose a mechanism) that boils a superconductor down to a couple numbers. The coherence length is about how far the superconducting state extends in a solid. The penetration depth is how far into the solid a magnetic field can penetrate. If the penetration depth over the coherence length is small you have Type I, if it's large then you have a Type II.",
"I'm just pointing out that the same equations with different values can give both behaviors. Having a vortex state is a function of whether or not it lowers energy/maximizes entropy."
] |
[
"I'm afraid I don't know the details, but it probably comes down to the particular structure of the material. In some, it will be energetically be favourable to have a vortex state, but in others it's simply a lower energy state to cease superconducting."
] |
[
"Could wormhole travel make us go beyond the observable Universe?"
] |
[
false
] | null |
[
"Show me a wormhole - and then we can experiment and see.",
"Since nobody has yet to discover a wormhole, we can but at best speculate."
] |
[
"I love healthy debate on the internet. Now there's a sentence I thought I'd never use.",
"To be sure, the question of wormholes does lend itself to some speculation and depends on certain assumptions and definitions. The following is my understanding of the situation. ",
"The wormholes they speak of arise from toy solutions of the Einstein Field Equations. The EFE can be solved two ways: Either taking the Stress Energy Tensor and seeing the resulting curvature of space-time, or taking some arbitrary curvature of space-time and seeing what distribution of stress energy creates it. The second of these two methods often results in nonsensical solutions that may have no meaning in physical reality. ",
"For example, what is negative energy density? This is a term that pops up a lot when one brings up the idea of wormholes, but is it something that can actually happen in reality? What does it even mean? Well, that's open to interpretation.",
"There is no hard data on the existence of wormholes. They are just possible solutions based on the math of the models of how we describe the universe. The question then is: Are we abusing the models?",
"If you say yes, then wormholes don't exist. If you say no, then the possibility of wormholes are not ruled out. Still, there is no hard data on wormholes, and the specific conditions that give rise to them are speculative at best.",
"Still, the math say they may be possible, so we can't completely rule them out. Of course, our interpretations of these 'wormhole solutions' is really what causes the uncertainty. And still, no hard data exists which is the tipping point for me.",
"There are highly respected scientists on both sides of the debate, which just goes to show that the question isn't completely moot. The best scientists are the ones that know how much they don't know. In my opinion, there isn't enough evidence to give them serious thought yet. It's mostly speculation of things that could be. Of course, I could be wrong, and will be the first to admit it. Still, I'm pretty sure that if wormholes do exist, they won't be at all similar to the fictionalized versions described in pop fiction."
] |
[
"Some very highly respected scientists like Carl Sagan and Neil deGrasse Tyson have voiced support for the idea that wormholes might exist. I'm not trying to make an appeal to authority, but rather curious as to why these seemingly smart and rational people accept the possibility wormholes might exist, while seem to suggest they don't exist and their popularity is the result of a lack of understanding of relativistic physics. ",
"Just to stress, I'm not trying to make a case against your argument, just curious."
] |
[
"How does light give objects their colors?"
] |
[
false
] |
[deleted]
|
[
"Materials can absorb or reflect the radiation from light, or they can do both. If you hit a green object with white light, the object absorbs most of the spectrum, but reflects the light of the frequency range that corresponds to the color green. That reflected light hits your eye and you see the color green."
] |
[
"Check out the ",
"guidelines for r/askscience",
"."
] |
[
"Oops.. Well I apologize on that one. Better?"
] |
[
"How did vacuum metallurgy develop? Is it possible to actually locate part of the metal-making process in deep space, like the bay of the space shuttle for instance?"
] |
[
false
] |
I've heard that you can basically make crystalline metals that have amazing properties using this technique. Is this true? If so, what are some of the neat properties these metals/alloys display?
|
[
"When you say nearly all metals are naturally crystalline, do you mean polycrystalline or single crystal? The former, right?"
] |
[
"When you say nearly all metals are naturally crystalline, do you mean polycrystalline or single crystal? The former, right?"
] |
[
"When you arc melt, what pressure do you work with? To strike an arc there has to be at least ",
" gas to ionize, right? I always wondered what near-vacuum pressures were considered normal when arc melting. I've seen the process before, but have never done it."
] |
[
"What's the most complex parasite life cycle that we know of?"
] |
[
false
] | null |
[
"I am almost sure someone will one-up me, but the ",
"Lancet river fluke",
" deserves at least an honorable mention. Their cycle is mammal -> poop -> snail -> snail-eating ant -> herbivore mammal accidentally eating ants while eating grass. It passes through three totally unrelated creatures. Mammals are also the definitive host, the host where sexual reproduction happens.",
"Three hosts is not unusual for a fluke; Chinese liver flukes (source of an enormous amount of gall bladder cancer) go snail->fish->mammal. There are tens of thousands of parasites. Anybody got four or more?"
] |
[
"Toxoplasma gondii",
" has a very interesting mechanism behind its life cycle. The full life cycle can be seen ",
"Here",
". It can reproduce in most warm blooded animals but it can only sexually reproduce in cats. There is evidence of induced behavioral changes in infected mice that make them less afraid of cats, making them easier prey and transmitting the parasite. It’s also very common in humans, ",
"~11% of people over age 6 in the US have it",
", fortunately it’s fairly benign. Toxoplasma infection is hypothesized to cause behavioral changes in humans but this is not yet proven (despite the existence of crazy cat people).",
"Another very interesting parasite is ",
"Cordyceps",
", which turns ants into zombies, David Attenborough explains it in ",
"this Planet Earth clip"
] |
[
"I doubt it's the ",
" complicated, but the ",
"life cycle of ",
" (the cause of malaria) is pretty convoluted.",
"So I count 5 distinct parasite stages that live in two different human body sites (liver, blood) and two different mosquito body sites (gut, salivary glands). I only gave the names of the extracellular stages here too; there are a number of other names for developmental stages of the parasite that occur as they grow inside liver and blood cells."
] |
[
"At what speed does glass break?"
] |
[
false
] |
If I were the throw a rock through a window, how fast would the glass break from the point of contact (with the rock) to the outer edge of the windowpane? Also, what defines what path the fracture will take from the contactpoint to the outer edge of the window?
|
[
"The speed at which waves travel through a material is the same as the speed of sound in that material. The speed of sound in a material can be estimated by knowing that material's density and bulk modulus. The formula is ",
"c=(K/p)",
"where c is speed of propagation, K is the modulus of elasticity, and p is the material's density. One may also use a materials shear modulus in place of the modulus of elasticity. The type of breaking that occurs likely dictates how fast the break will propagate and hence, which modulus should be used in the above formula. ",
"If one applies the above formula to glass, (taking the shear modulus of 26.2 GPa and a density of 2.5*10",
" kg/m",
" we get a speed of sound of ~3200 m/s. "
] |
[
"Could you explain why you think a crack should move as fast as a pressure wave? Microscopically, a crack must be caused by breaking of bonds, and while there are certainly the same interatomic forces involved that also play a role in wave propagation, I would be surprised if there wasn't some difference in velocity for the much more complex crack propagation than for elastic wave propagation. ",
"This paper",
" lists some experimental results which put the velocity of crack propagation at between 10% and 60% of the Rayleigh wave speed (surface waves, whose velocity I think should be close to the sound velocity in isotropic media)",
"Edit: ",
"This paper",
" also puts it in the 100 m/s range than in the 1000 m/s range you can usually find sound velocity"
] |
[
"/u/nepharan",
" touched on this, but I think it's important to highlight the difficulty of the mathematics here: You're dealing with bulk material (the glass pane) with defects (which make it hard to apply quantum mechanical modelling to everything). So you think, oh, I'll use some kind of mechanics model. But as ",
"/u/nepharan",
" mentioned, a crack involves the breaking of bonds which is a ",
", i.e. there is no satisfactory classical/continuum treatment for the \"tip\" of the crack where it propagates, but you're dealing with large-scale materials, so you can't just try and solve the quantum mechanical problem! This is a very interesting and active area of research in multiscale modelling/applied mathematics. The general field you are looking for is fracture mechanics (",
"Wiki",
"). Your scenario would most likely be an opening mode fracture.",
"I can't find any very accessible academic papers on these types of fractures, unfortunately. Just a bunch of inaccessible ones on shears."
] |
[
"How/where does immunity to disease live in my body? Before starting a new job, I had blood tests to confirm immunity to many diseases. Does that mean my blood is forever changed every time I get a flu shot, or is it stored elsewhere?"
] |
[
false
] | null |
[
"White blood cells, also called leucocytes, are the cells which fight diseases. They are produced in the bone marrow from the same stem cells as red blood cells.",
"Leucocytes live everywhere in the body, especially blood, lymphatic nodes, spleen and thymus. In a time of need, they migrate to tissues where they fight an infection.",
"Everytime you get a flu shot, your body develops antibodies against the given strain of a virus. Cells producing antibodies against flu from the past remain in the blood as a form of immunologic memory, but they are not active as long as you dont get the same virus again. Basically yes, your immunity is stored in blood and lymphatic tissue."
] |
[
"Although not an expert on immunology, I'll hopefully try and clarify. Basically there are two components of the immune system, they are variably classified as either innate and adaptive immunity or humoral and cell-mediated immunity. ",
"As mentioned, the immune system is made up of many type of cells that derive from particular systems. The two basic divisions are lymphoid and myeloid lineages. The lymphoid lineage includes T lymphocytes which can be broken up into CD4 Helper T cells and CD8 cytotoxic T cells and B lymphocytes. The myeloid lineage is simpler and includes neutrophils and macrophages. ",
"Most vaccines are to viruses. Viruses function by hijacking cellular machinery. Antigen presenting cells like macrophages or dendritic cells take up antigen and present them to CD4 T cells. These cells basically lend a hand everywhere but they activate the B cells to produce antibody. They activate many B cells and through a variety of genetic rearrangements, the B cell will produce a functioning antibody to combat that antigen. The antibody will bind to that antigen which labels the cell for destruction and phagocytosis by cells like macrophages. ",
"The B cells after the infection is over then enter a senescent state and create a plasma cell that can be reactivated if an infection occurs. Most vaccines function in this way by stimulating the humoral immune system and causing antibodies to form. Blood tests for common vaccines look for these antibodies. ",
"Other tests or vaccines rely on different parts of the immune system. For example, the test for tuberculosis relies on the activity of the CD8 cells rather than B cells. "
] |
[
"The immunity of our body is taken care of by the cells called WBCs( white blood cells) .Some of which float around in the blood looking for signals that indicate the invasion of body by any microorganisms.",
"When there is a Microorganism where its not supposed to be, the tissues around it ( infected or dead) release chemical signals which attract the WBCs to the site.The WBCs then engulf the microorganism( phaocytosis) and break it down through enzymes eventually killing it.Simultaneously they are also taking samples from the microorganisms, mainly it's surface molecules ( antigens) and give it to a different type of WBCs called plasma cell that make antibodies against the antigens. Now these antibodies go and bind to the antigens on the surface of the microorganisms and mark them ready and start signalling other WBCs to come over and engulf the organisms/ kill it.",
"The body then stores some of these antibodies for future reference.So next time you are infected by the same organism, your body doesn't waste time again designing the antibody.Instead, it directly starts making multiple copies of the old antibody it had created last time you were infected by that particular organism.",
"So the immunity in your body is stored in form of these antigen recognizing antibodies.",
"And the reason you get yearly flu shots is because of the Influenza virus whose molecular structure keeps changing very rapidly so the body has to keep creating new antibodies against it. But by giving the vaccination, we are introducing the inactivated virus into the body. That way the body is still able to recognize the surface molecules and start creating antibodies even before the actual disease causing organism infects us."
] |
[
"Does any species have a symbiosis with viruses?"
] |
[
false
] |
Many species including humans have formed symbiosis with some other lifeform. One example being humans and gut bacteria. Does any species have a symbiosis with viruses? And if so, how does it work? And if not, why are viruses so special in this regard? Thanks in advance!
|
[
"The coolest example of viral symbiosis in my opinion is seen in some parasitoid wasps. Lots of wasps have venomous compounds that they use to paralyze or otherwise incapacitate prey, but a few actually use viruses instead. Certain ichneumonid and braconid wasps have entire, intact viral DNA within their genomes, which they can use to produce viruses whenever they want. The wasps ",
"inject these viruses into their hosts",
" (usually caterpillars) along with their eggs, where the viruses will weaken the immune system. Then, in classic parasitoid wasp fashion, the larvae eat their host from the inside until it eventually dies.",
"Interestingly, this form of viral symbiosis actually evolved independently in the two groups of wasps mentioned above, with ichnoviruses and bracoviruses pretty clearly showing distinct origins (",
"Volkoff et al. 2010",
"). It's not uncommon for viruses to integrate their DNA with their host's; this has been documented in many animals (see, for example, ",
"Johnson 2019",
"). Our own genomes are composed of something like 5% endogenous retroviruses, but these are mostly inactivated remnants, and certainly don't show the same symbiotic relationship in our case.",
"If you want some more examples, check out ",
"Roossinck 2011",
", which describes several other instances of known viral mutualisms."
] |
[
"Yes! ",
" (baker's yeast) has a virus (technically, it's a satellite but w/e) that encodes a toxin that kills other yeast cells that don't have the virus. So in this example the virus increases the host's ability to compete with its neighbours."
] |
[
"Retroviruses, like HIV, synthesize DNA fragments from their RNA once inside the cell. These DNA fragments can become incorporated into the hosts genome and, if it’s a germ line cell, passed on to offspring. The human genome contains about 5-8% retroviral like genes, some of which have been shown to be involved in normal human function (because mutations to these genes are seen in disease). These have been theorized to be a source of accelerated evolution in complex life, by making “gene swapping” possible naturally. Not only that, there are genes that encode for viral-like capsids in which human RNA is packaged and transferred between cells (look for Arc capsids in neural tissue). These packages look indistinguishable from viral capsids and seem to function the same way, just without causing disease. These findings really blur the line that actually defines a virus as a virus. To give one answer to your question, I would say we as humans have at least several symbiotic viruses which have been incorporated into our genome. Are these still viruses, however? That’s a harder question."
] |
[
"Sodium halides"
] |
[
false
] |
[deleted]
|
[
"There's no health reason",
"Except that bromide salts can cause ",
"bromism",
"."
] |
[
"We do need the Cl ions. There are specific Cl conducting ion channels in our neurons, which regulate in part the resting potential. Check ",
"http://en.wikipedia.org/wiki/Serum_chloride",
" for other physiological functions.",
"Cystic fibrosis is also cause by misregulation of Cl absorbance in the lungs.\nThe brominism point of langfan is also relevant.",
"Finally i think that the simple abundance of Cl salts is the reason that organisms have adapted to it. Bromine is relatively less abundant."
] |
[
"Evolutionarily we are adapted to dealing with chloride ions, mostly because they are such a dominate anion. Fluoride, bromide, iodide and other anions all have health issues if taken in anything more than trace amounts. Polyvalent anions are more difficult for active transport mechanisms to handle. The ion size and structure greatly effect how biochemistry handles anions, and there are biochemical routes for maintaining and controlling just about every ion or compound in your system.",
"TLDR; Biology is tuned for chloride through evolution."
] |
[
"How do headphones change volume, whether plugged in or with Bluetooth? If the electrical energy is changed into sound, does the amplitude and strength of the electricity determine the volume?"
] |
[
false
] | null |
[
"A Bluetooth signal is digital - the amplitude of it doesn't matter as long as it is large enough to be detected clearly. The volume is transmitted digitally as well. The speakers then produce sound with the right volume.",
"Headphones you plug into the headphone jack: That is analog, louder just means more voltage and current."
] |
[
"There's a bunch of different profiles/versions for bluetooth audio-- if memory serves, I think if the headphones/speaker/whatever doesn't support AVRCP v1.4 or later, that the volume control happens by making the signal smaller (and less precise as you point out) at the source side. If it does, then the device is essentially remote-controlling the volume settings at the speaker side. In general, that would probably be implemented by increasing or decreasing the gain of the amplifier in the output device, but it would even then still be possible to do it any number of other ways.",
"If anybody has had to read through the standards more recently than me, let me know if I've missed or flubbed anything. I ",
" AVRCP 1.4 is where they added \"Absolute Volume,\" and I ",
" that's what they called \"controlling the output device volume instead of scaling the signal sent.\"",
"TL;DR: #3 is probably the most common, but \"it depends.\""
] |
[
"Yes, that's it exactly. ",
"The speakers don't change anything, you just send them a weaker signal. ",
"With bluetooth, there is essentially a whole radio included with the headphones. I don't know if the volume is done by scaling the data in the radio signal, or by adjusting the gain in the receiver. "
] |
[
"Besides being cut or menstruating, how does the body dispose of old, used blood cells?"
] |
[
false
] |
[deleted]
|
[
"They ",
"get eaten",
"."
] |
[
"The lysosomes break apart and release digesting enzymes which break down the cells and allows the different base compounds to be reused "
] |
[
"Enzymes break down your red blood cells and tries to keep as much useful parts as it can like iron and the protein parts. Others is just excreted via urine like bilirubin (this stuff is what makes your pee yellow and your poop is brown/yellow)!"
] |
[
"In a house with no air conditioning, would it be better to keep the windows closed or open during the day?"
] |
[
false
] | null |
[
"I actually designed systems for passive cooling. Option 1 is correct, but there's another big angle to this... if you want the house to keep cool, don't let sunlight in. Radiant energy from the sun still passes through those windows, but if you shutter them, a lot less gets in. A house that's more reflective of heat is best, but either way, if you have patches of sun, that's heat getting in."
] |
[
"Yes. Heat flows from higher temperature to lower temperature. So the basic idea is if it's cooler outside, open the windows. If it's cooler inside, keep the windows closed."
] |
[
"Yes. Heat flows from higher temperature to lower temperature. So the basic idea is if it's cooler outside, open the windows. If it's cooler inside, keep the windows closed."
] |
[
"If the theory of Thia colliding with Earth created the moon was true. Would it have been possible for the Moon to developed an atmosphere and harbor life?"
] |
[
false
] |
What conditions would it have taken for this to happen? And how likely/unlikely would it be to happen after 2 planets collide
|
[
"The Moon ",
"does have an extremely thin atmosphere",
", which its extremely low gravity allows to escape (be blasted away by the solar wind). It is continuously replenished, but continuously blown away. If the Moon were ",
" heavier, its gravity would enable it to hold a more substantial atmosphere.",
"Apollo 17 studied the Moon's atmosphere."
] |
[
"Continuously replenished by what?"
] |
[
"Answer is in the linked Apollo 17 article."
] |
[
"Is sea salt chemically different from table salt?"
] |
[
false
] |
If table salt is NaCl, is sea salt that you buy at the grocery store any different?
|
[
"If you mean the salt (as in all the different salts in the package you buy) then I can note a single major difference.",
"No Iodine is added to Seasalt... This can be problematic for many people who do not eat enough foods rich in iodine and depend on the added source in table salt. Also seasalt can generally contain more impurities before purified.",
"Otherwise beside the different mixture of salts that may occur there isnt any reason sea salt is better for you than salt which is mined from the earth. The truth is some old salt deposits are formed from old seabeds."
] |
[
"Close, it's MgSO",
" that's used as an anti-caking agent, not MgCl",
"."
] |
[
"Im sorry but you are mistaken.",
"According to the Mayo Clinic:\n\"Sea salt and table salt have the same basic nutritional value, despite the fact that sea salt is often promoted as being healthier. Sea salt and table salt contain comparable amounts of sodium by weight.\"",
"No salt has Iodine naturally in it. Many sea salts are less likely to have it at all. It doesnt lack nutrients (Nutrients: a substance that provides nourishment essential for growth and the maintenance of life.)\nWhat you are referring to is minerals. Minerals do not denote nutritional value. The same arguments that are used for sea salt are used for Himalayan Rock salt (which contains trace heavy metals).",
"I not going to post all the sources but this is pretty good.\n",
"http://blog.fooducate.com/2011/08/12/sea-salt-vs-table-salt-the-truth/"
] |
[
"Why isn't there two-photon imaging using x-ray probes for imaging of the entire mouse brain?"
] |
[
false
] |
In optical imaging of mouse brains (with a cranial window) two photon imaging has penetration depth of hundreds of microns. This limits imaging to cortical regions only. Why haven't fluorophores been developed which are excited by higher energy photons (x-ray for example) which would allow penetration to deeper regions of the brain? I understand higher energy photon are potentially damaging to tissue. Is this the main reason?
|
[
"Two reasons.",
"One is contrast. Two-photon fluorescence imaging is typically done with near-IR photons, which your body is mostly transparent to (losses mainly due to scattering, not absorption)- this means you only get two photon emission ",
" where the beam is focused. ",
"Que the famous picture.",
"Typical imaging with x-rays is due to scattering, not fluorescence, which has no simple two-photon analog (you could do x-ray Raman, a four-wave-mixing process, but that's far from simple). If you want to do two-photon x-ray fluorescence, you'd need to find a dye that is transparent to one wavelength of x-rays, but can absorb two photons of that wavelength and fluoresce. That's tough, but not a deal breaker.",
"The real problem is, as you point out, tissue damage. You need high pulse energies per unit time to do two-photon imaging. Typically that's done with femtosecond lasers. If you put that much energy per unit time of x-rays onto ",
" the current thinking is that you get ",
"Coulomb explosion- que famous pic #2",
".",
"(Aside- despite this explosion \"feature\", high energy x-rays have actually been proposed to determine the structure of single proteins. ",
"See here.",
")"
] |
[
"Another reason, we have no good way of building an x-ray lens and no material from which to build one with (though new metamaterials may get around this). This is why x-ray experiments are relient on scattering or diffraction - the sample image is only later reconstructed. Though scattering experiments are being performed on whole cells or organisms in this way, the work usually requires a tremendous dosage at a syncrotron at a national lab, and always on fixed samples (I.e. not living), because as you guess of radiation damage",
"Xray fluorescence is used all the time in biophysics, usually from inner shell electrons from a heavy metal like mercury or iron. It would be possible to chemically synthesize a probe relying on a heavy metal, but the signal from it would be very weak and it would likely abosrb enough energy to obliterate your sample. "
] |
[
"You're right. Big schools are good if you just want to throw yourself in the mix and be sure to find a little of everything and lots of talent in one place. If there's something in specific you're interested in, then go for it."
] |
[
"Why is the dirt around anthills so different from the dirt around it? As if the anthill dirt is uniformly size and dried"
] |
[
false
] | null |
[
"As they dig out new tunnels and chambers the ants carry the dirt out of the nest. They drop the removed soil at the mouth of the entrance, and it builds up into the mound. So the anthill is made of soil from below the surface, which may have a different makeup than the topsoil, packed into discrete balls of an optimum size to be carried by a single ant. All those discrete balls of dirt dry faster than packed soil that air can't move through as easily."
] |
[
"I believe it is because when the ants excavate their home, they use their jaws and cut out little bite size pieces of dirt and carry them one by one to the outside. And because the ants are all roughly the same size, they all cut out roughly the same size chunk of dirt."
] |
[
"don't they also spit on the chunks to make them stay together when being carried?"
] |
[
"How does hair know when to stop growing?"
] |
[
false
] | null |
[
"Please do a search beforehand to find other threads like ",
"this"
] |
[
"Sorry about that! Taking my question down now. "
] |
[
"no worries, just leave it up or else all your other submissions will go to the spam filter\nI've removed it :) Happy learning!"
] |
[
"What gives Blood that distinct smell?"
] |
[
false
] | null |
[
"See ",
"this thread",
" and ",
"this thread",
"."
] |
[
"It's the iron in your blood, actually. That's what gives it the metallic, tangy smell and taste.",
"Your blood has proteins called hemoglobin, in which iron is used to transport oxygen throughout your body. That was to just explain why it's there."
] |
[
"It would be a pretty imperceptible change. The iron levels in someone's blood don't fluctuate that much, even when they're considered to be deficient."
] |
[
"Is there anything in our universe that is truly random?"
] |
[
false
] |
In learning more in depth about mutations in genetics, it sort of came to me that not even a mutation is sort of random. It happens as a result of physical interactions and not an arbitrary event. Could an omniscient being (with unlimited powers of observation and processing ability) be able to predict everything, or is there truly randomness at a subatomic level?
|
[
"As far as we know, quantum mechanical processes are truly random- certainly they are random to the extent that we have no mechanism for predicting the outcome of a quantum process with certainty (we can only predict probabilistically), and there is strong evidence (Bell's theorem) that any theory which is able to predict such processes must be nonlocal. Since nonlocality has its own problems, it's reasonable to conclude that there is likely no theory which can exactly predict the outcome of quantum processes.",
"Interestingly, quantum mechanics also challenges the premise of your question, since by the Heisenberg uncertainty principle your 'omniscient being' would still be unable to simultaneously access position and momentum information to arbitrary precision for a particular particle (or any other pair of measurements with a nonzero commutator.) So in terms of modern physics the question isn't totally well-posed."
] |
[
"Nuclear decay is a good example. "
] |
[
"It's reasonable to treat some things as random for practical purposes, but proving true randomness is impossible. A process would have to be observed forever in order to decide it has no pattern. Randomness is not required for fundamental unpredictability. Something which is part of the universe, cannot precisely predict the totality of events within it. One place their predictive powers breaks down is in predicting their own predictions. There's a simple way to demonstrate this. If you meet something that claims it can predict anything, ask it, \"Will this universe not be one in which your answer to this question is yes?\""
] |
[
"Why is it that HIV/AIDS and cancer are so difficult to cure?"
] |
[
false
] |
Is it because they are relatively new?
|
[
"Variability.",
"HIV mutates in the body with a very high rate, making it difficult to eradicate it with a single agent. ",
"more info",
"\"Cancer\" is actually an umbrella term for hundreds of different diseases. Every cell in the body which replicates has a chance to become cancerous, so there are hundreds of types of cancer. Also, it takes 5 to 10 independent DNA mutations in a single cell to lead to cancer, and so each cancer of each cell type has countless variations depending on which specific mutations it carries.",
"Add that to the fact that cancer is composed of tissue from your own body, which makes it difficult to target without harming healthy tissue. One famous researcher likens it to trying to create a drug or therapy which kills your left ear without hurting your right ear."
] |
[
"Vaccines also prevent disease, not infection",
"No, vaccines boost the immune response, thus practically avoiding ",
"."
] |
[
"Slash, burn or poison."
] |
[
"How can a parrot imitate human language and why can't other species do so?"
] |
[
false
] |
[deleted]
|
[
"Birds have a structure called a syrinx located at the base of the trachea that they use to make noise. All birds have it, however in some birds (like song birds parrots and mynahs) it is extraordinarily complex and can be used to make more than one noise at a time. In other birds (herons geese and raptors, for example) it is pretty simple, and can only make a few sounds. \nParrots can imitate human voices because imitating sounds they hear is important in their social structure. They aren't adapted to imitate humans, they have very precise muscular control over their syrinx and can pretty much imitate whatever they hear within reason. When surrounded by humans, they make human noises. Parrots aren't even the best at it, Mynah birds can imitate humans with precise accuracy and Lyrebirds can imitate just about anything, including chainsaws and camera shutters. ",
"http://en.wikipedia.org/wiki/Syrinx_(biology)",
"\n",
"http://www.youtube.com/watch?v=VjE0Kdfos4Y"
] |
[
"But we can! We have the most complex vocalization of any mammal. We can imitate dogs, cats, cows, horses, chickens, etc. Some people are better than others though.",
"The thing with birds is, the males who are best at a specific task tend to get all the females. If all women wanted to have babies from that black guy in Police Academy, we'd evolve in that direction really fast."
] |
[
"The chainsaw and camera shutter sound too good to be true. Is there some way to confirm the video's claims other than David attenbourough is in it?"
] |
[
"How does inflation solve the flatness problem in the big bang theory?"
] |
[
false
] |
I realize that the amount of e-foldings inflation caused would really flatten out a universe sort of like a pancake. However in a cosmology book I have it says we can use the Friedmann equation to extrapolate backward to before inflation even happened, and see that the universe was already extremely flat at that point, so inflation doesn't really seem to resolve that issue to me. Am I interpreting something wrong here? Since I've never actually seen or heard anything about this. Been struggling with this question for a while now, don't really know exactly where to ask this so I hope this is a good place.
|
[
"Since you asked a technical question, I hope you don't mind if I give you a slightly technical answer. Inflation's resolution to the flatness problem - as well as its other miracles, solving the horizon, relic, and structure formation problems - lies in the simple fact that during inflation the ",
" shrinks with time rather than growing.",
"Comoving means that we're talking about coordinates in which we ignore the expansion, so that particles are more or less stationary. The horizon size is, as the name suggests, roughly the size of the observable universe (it's the distance at which two points are receding from each other at an apparent velocity equal to the speed of light). Normally, in a decelerating expansion, the horizon size in comoving coordinates is growing, so that more and more galaxies come into view over time. However, during inflation, it shrinks, meaning more and more of the Universe ",
" our view, and things which were once small-scale are quickly blown up to cosmic scales. This is how quantum fluctuations on tiny scales during inflation become density perturbations which eventually seed the growth of galaxies. The famous horizon and cosmic relic problems, two of the main reasons for the development of inflation, are also solved because of this behavior.",
"The flatness problem turns out to be solved due to this as well. If you want to visualize it, you might think of the Universe as \"zooming in\" during inflation on a small patch, which is going to be flatter than a larger patch much the way that the Earth's surface looks flat on human scales. If you work out the mathematics, you find that while in a decelerating universe the curvature deviates away from flatness as time goes on, during inflation it deviates ",
" flatness, even if it started out in some highly curved state. So what we mean when we say that inflation requires a certain number of e-folds (60 or so) to \"solve\" the flatness problem is that inflation needs to have lasted that long in order for it to",
"a) Start from some generic initial curvature (deviations from flatness of order one, i.e., quite significant deviations!), and",
"b) End inflation with the curvature around 10",
" away from flatness, which is the value which would evolve by today to a deviation of 10",
" from flatness, which is the \"least flat\" our Universe could be, as determined by the errors in observations like the CMB data."
] |
[
"I'm sure I could look this up somewhere, but for the interest of brevity, do you know how much time the inflationary period lasted, with respect to, say, the Quark-Gluon Plasma era? There's been a lot of talk in our field about the hadronization freeze-out of the QGP leading to the overdensities in the early universe and it occurred to me that if the time scales between these two events are way off then that could be problematic."
] |
[
"Off the top of my head, probably about 10 to 20 orders of magnitude. Inflation would likely not have lasted much longer than the Planck era."
] |
[
"I read that nicotine stimulates ADH release. Does this mean that during times of temporary water shortage, it may be beneficial to smoke? Or are the effects to small?"
] |
[
false
] |
So ADH makes your urine more concentrated, and makes you pee less, helping you retain water in your body more easily, right? If nicotine stimulates its release, then if I was hypothetically in the desert, would smoking or chewing nicotine gum help me preserve water any significant amount? I know the chances are pretty low of me being stranded somewhere with nothing but 20 cigarettes, a nicotine patch and a packet of pretzels, but I'm still curious. EDIT: Sorry about the grammar derp in the title.
|
[
"Here's an article in the British Medical Journal from all the way back in 1945 called \"",
"The Antidiuretic Action of Nicotine And of Smoking",
"\". The entire thing seems really interesting and worth the read, but just to keep it short...",
"I found this sentence right on the first page: ",
"Now, who knows if any of this stuff is scientifically sound after 67 years? Nonetheless, it's very interesting.",
"Now for your question... if what this article says is true, then I could see using nicotine in a very specific situation to conserve your body water. But smoking is a bad idea because it's hot and full of tar and makes your mucous membranes all dried out, which would probably far negate any antidiuretic effect of the nicotine."
] |
[
"Doesn't help that nicotine itself is a carcinogen, and you should probably limit exposure."
] |
[
"There are other articles, more recent, that discuss ",
"cigarette effects on vasopressin",
". Interestingly, nicotine alone has no effect.",
"However, if I were in the desert, I'm not sure an antidiuretic would be that helpful, since it might cause hyponatremia, or low blood sodium. It also raises the blood pressure, which may actually make it more uncomfortable in the heat. ",
"Sounds like you should carry a Camelback instead. Besides, smoking causes cancer."
] |
[
"Why does having both an inductor and a capacitor make a circuit AC?"
] |
[
false
] |
I had it described to me like a slinky bouncing above and below it's resting level, and this represents the back-and-forth of inductors and capacitors, but I'm still having a hard time understanding.
|
[
"AC is typically used to describe the type of power supply (or voltage source) for the circuit. Inductors and capacitors will behave differently if driven by an AC power supply. You can find more info here:\n",
"http://web.mit.edu/viz/EM/visualizations/coursenotes/modules/guide12.pdf"
] |
[
"The other comments are correct in that you can drive an alternating current with a power source, but I think the point being made is that ",
" a power source and assuming no loss of energy (e.g. through resistance of the wires), a circuit with just a capacitor and inductor has the ability to oscillate at a natural frequency determined by the inductance and capacitance, namely 1/sqrt(LC).",
"Here's a wikipedia article that explains it well",
". The back-and-forth analogy of the spring refers to how the energy is being stored. With a spring, you can store potential energy by either compressing or stretching the spring. In an LC circuit, the potential energy oscillates between being stored in the magnetic field of the inductor and electric field of the capacitor."
] |
[
"A follow up question then would be is it this characteristic which led to AC being an initial choice for domestic circuits?",
"\nI can kind of intuit a mythical notion of stability and distance as a result of ossiclation at a specific frequency (60khz for instance).",
"[ to clarify -- by initial choice I mean purely why did those in the AC camp feel it had technical merit over DC, not why did they object to DC as a result of the socio-political choices of inter-personal issues of their respective advocates.]"
] |
[
"With the advent of an asteroid flying by, what would be our plans for an asteroid heading directly towards us?"
] |
[
false
] | null |
[
"A little off topic here, but with them hitting the earth all the time and not doing much damage...",
"Isn't the theory on how earth had such large oceans due to constant bombardment by thousands upon thousands of asteroids containing ice?",
"If this is so... what happened to them all? I'm not knowledgeable at all in this field but my professor got me curious!"
] |
[
"citation neeeded :)"
] |
[
"Realistically, though, the plan is to hope it's not large enough to cause an extinction event and a lot of us will probably die. We simply don't have the technology or resources to detect and divert asteroids soon enough.",
"However, asteroids hit the earth all the time, most of them are quite small and don't cause any significant damage. "
] |
[
"What is the \"Pseudo-gap\" and how does it relate to every day life?"
] |
[
false
] |
Not long ago, there was a news brief about the discovery of evidence that the Pseudo-gap was real. The pseudo-gap sounded not like a fake clothing retailer, but was instead something responsible for blocking the conduction of electromagnetism. Can someone explain a bit more about what the pseudo-gap really is and if it can be overcome, how will it change our technology?
|
[
"The recent news said something rather different, actually - the pseudogap has been well-known to exist for quite some time.",
"Before we get to the pseudogap, I need to explain what a(n energy) gap is. In materials, electrons can occupy lots of different states with lots of different energies. However, in some cases, there are energies that have no states, that is, electrons cannot have those energies. If there is a range of such energies, then the system \"has a gap\" which encompasses those energies.",
"From now on, we're going to assume that there's only one important gap.",
"Now, there are lots of ways that you can get a gap. Generically, the crystal structure of a material causes gaps to appear. Why does this matter? In simple cases, if you fill up all the states below a gap and none above, this means that you have an electrical insulator - a small kick to an electron won't be able to get it to reach an unoccupied state because it needs the energy to get across the gap. If you don't fill up the states below the gap all the way, then the material is a metal, because there are empty states available whose energy is arbitrarily close to the energy of a filled state. We talk about this as there being a \"band\" of energies (the set of energies below the gap) which is either filled (insulator) or partially filled (metal).",
"One more thing before I get to the pseudogap. Another way to get a gap is to have superconductivity. One way to think about this is to start with a metal, with a partially filled band. Now start cooling the system down. This allows the effect of the electrons interacting with each other to become more important (actually it's a little more involved than that, but that's besides the point here). It's possible for those interactions to create a new gap inside what used to be a band, and sometimes the way that this happens is by pairing up electrons and forming a superconductor. A superconductor is kind of strange, in that all the states below this new gap are filled and the ones above are empty, but it's a perfect electrical conductor, which goes against what normally happens.",
"Now, the pseudogap. In the materials superconductivity appears at the highest temperatures that we know of, something strange happens at temperatures between superconductivity and the \"normal\" metallic state. A gap starts to appear, but only certain electrons see the gap. More precisely, at a given energy, if we start from a normal metal and cool to the pseudogap, then states at that energy with certain momenta are gapped out (no longer allowed), but states at that energy with other momenta are not removed. This is extremely strange, and there is, to my knowledge, only one other example of anything that looks even vaguely like this (and the physics there is almost certainly completely unrelated).",
"What causes the pseudogap to appear is still extremely controversial, but there are two main interpretations of how the pseudogap relates to superconductivity. One is that the pseudogap occurs because there is \"extra\" pairing as you cool down that ",
" superconductivity appear earlier. The other interpretation is that the pseudogap is actually the material trying to be a full-blown superconductor, but something else is ",
" the electrons from pairing up.",
"The recent article you saw, if I'm thinking of the right one, was about a paper that claimed to have experimental evidence for the latter interpretation, that is, it claimed that the pseudogap interferes with superconductivity.",
"Why this matters: right now, the very highest temperature superconductor has to be cooled by liquid nitrogen. But if we didn't have to cool superconductors at all, we could use them in everyday life, which would be fantastic because heat doesn't get wasted when current runs through a superconductor. If the pseudogap is getting in the way of superconductivity, then we need to figure out how to get rid of it in order to raise the temperature at which these materials go superconducting.",
"If we had room temperature superconductors, you could imagine, for example, superconducting power lines which don't waste any heat as they transfer power from the power plant to your house. If we were to get really lucky with materials issues, we could also imagine MRI machines (which use superconductors to create huge magnetic fields) that don't require liquid helium to cool them, alleviating an enormous part of the demand for our increasingly-depleted reserves of helium."
] |
[
"Do you think generating a material that superconducts at higher temperatures is feasible or still out of range? Apart from the applications, the principle is remarkable on its own too. Is there a general class of materials that people are thinking could exploit this?",
"This is extremely well-written and easy to understand. Thanks."
] |
[
"High-Tc (critical temperature) superconductors are something that people have been searching for for decades. We've made some incredible strides. Initially, we only knew of materials with critical temperatures in the liquid helium range (4 Kelvin, ~-270C), but now we have materials (BSCCO, YBCO) that are in the liquid nitrogen range (70 Kelvin, ~-200C). I think that we will see materials with even higher Tc in the coming decades, it's just a matter of understanding superconductivity better, and giving the search enough time."
] |
[
"Could there be life in oceans deep under the crust?"
] |
[
false
] |
[deleted]
|
[
"These \"oceans\" are a misnomer. There are not oceans deep under the surface. There is a vast amount of \"water\" in the mantle of the Earth, but it is in the form of hydrous minerals. These are just minerals with Hydrogen and Oxygen in them - not literally water. And only as a very small % of the elements in mantle minerals.",
"This is still important because it is why volcanic activity releases water (H and O are combined into water as the mineral melts and erupts), which helps offset water lost by metamorphism of oceanic rock which is later subducted into the mantle. ",
"It is also important because even though H and O are a small % of the elements in mantle minerals, the mantle is ",
", so it adds up to a lot. Which is why it was reported a while back that \"oceans\" worth of water was under the surface. And by especially egregious misrepresentations of science by some news outlets, that literal oceans were beneath the surface.",
"Hydrous minerals can't be used as a water substitute by life as far as we are aware, and combined with other problems life would face at those depths, it is pretty reasonable to assume there isn't any."
] |
[
"For now the known thermal limit of life is ~120°C. But it is not expected to be much higher, there are some claims that it could be possible for slightly higher temperatures, but the current limit already only exist under laboratory conditions.",
"\nYou have the problem that DNA degrades faster with increasing temperatures and anything well over the current limit would require an insane recovery rate.",
"\nSo the answer would be no, as the stability of DNA is unsustainable in such high temperatures."
] |
[
"they are not literal oceans, due to subduction zones a lot of water gets pulled into the mantle so the mantle naturally contains a lot of water - therefore, you also encounter very water rich minerals and rocks in the vicinity of subduction zones",
"\nand to counter evaporation you just need enough pressure, that's why hydrothermal waters in deep sea vent systems (e.g. black smokers) have temperatures of well over 300°C and still are in liquid form"
] |
[
"If we stopped an object's orbit in space, would it \"fall\" towards the sun?"
] |
[
false
] | null |
[
"Yes, that is correct, unless the object is under stronger influence of another body. For instance, if you stopped the Moon from rotating around the Earth, it would collide with Earth. Likewise, if we stopped Earth, it would fall into the Sun.",
"So the \"reach\" of gravity is basically defined by an object's Hill sphere - inside an object's Hill sphere, that object dominates the gravitational attraction to any satellites. Putting this in context of my previous example, the Moon is inside Earth's Hill sphere, but farther from Earth, you leave Earth's Hill sphere and enter that of the Sun. The Sun's Hill sphere is huge compared to those of the planets."
] |
[
"An orbit is essentially falling towards an object with enough lateral motion to continually miss. If we remove the lateral motion, then you are simply falling toward it."
] |
[
"By my math, it will take closer to 1/6 of its orbital period, as the acceleration increases as distance decreases."
] |
[
"Does a caterpillar retain it's \"Identity\" when it become a butterfly ?"
] |
[
false
] |
In other words, is it the same individual or does the caterpillar "dies" when it undergoes metamorphosis for a new butterfly with no prior memories or experience to be born ? If yes it means that the nervous system of the caterpillar is preserved during metamorphosis ? Thanks for your answers !
|
[
"There is probably no clear answer to this, since there is a lack of a clear definition for \"identity\" as you use it in this context.",
"The nervous system is changed in the metamorphosis, but it is not completely destroyed and rebuild, see here for example ",
"https://www.frontiersin.org/articles/10.3389/fnsys.2010.00007/full",
" ",
"Als there seems to be a certain degree of memory retention through the metamorphosis ",
"https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0001736",
" ",
"",
"If this means that its still the same individual is probably a philosophical question."
] |
[
"Yes, the nervous system persists during metamorphosis, although it is also greatly extended and remodeled - the adult insect has very different senses than its juvenile self, and responds to them with very different behaviors. But an adult insect can still respond to cues it was taught to respond to as a larva.",
"Whether or not this constitutes \"memories\" or \"identity\" depends a bit on how much credit you want to give an insect brain. It's very difficult to say whether insects are conscious of their environment in anything resembling the way that you or I are conscious. If we embrace a practical definition where \"memory\" is just the retention of information and \"identity\" is a collection of memories, then yes, it's the same little guy before and after metamorphosis.",
"Anyway, my research is about butterfly life cycles, although I don't study the mechanics of metamorphosis as such. Do PM me or ask here if you have any follow-up questions. :)"
] |
[
"I listened to a segment about this on NPR several months ago, and it was absolutely fascinating to learn this."
] |
[
"Geologists of reddit: what is this rock I found?"
] |
[
false
] |
Neither a fingernail nor a penny seems to scratch the rock. The penny leaves a streak of metallic shine on it, but since the side of the penny is also damaged, I am concluding that the penny, not the rock, was scratched, and the penny just left some residue on the rock.
|
[
"That could be a few things. Realgar, or Cinnabar. Looking from the fracture and what I can see though, the likely hood it is Chert is very low. In my opinion, it is Realgar. ",
"@ Freezer: BIFs are dominantly from 3.7 -> 2.6Ga. Although, BIFs can form anytime the ocean/sea is \"choked\" off from surface air. This makes them not able to to gather enough oxygen to oxidize the iron, and ferrouginous hydrates fall to the sea floor and create BIF's. ",
"The BIF's around my area sometimes contain gold and are closely related to the Komatiites around the area. Check out Timmins' Geology for BIF's. I am a local geologist working in that gold camp."
] |
[
"Cool, you're right. I should have checked the range, I was working from memory. If it's chert, I still doubt this originated in Iceland, but I'm not familiar with Realgar. How is it formed?"
] |
[
"You don't need BIFs for chert. Chert is simple a chemical sedimentary rock that can be found in many environments (from river deposits to limestone to BIFs etc). My guess is some hydrothermal fluid dissolved some iron and silica and deposited as chert. ",
"Edit- I am on my phone so I can't see the pictures very well but as of right now my guess is chert. You can also submit to ",
"r/geology",
" and we will be happy to examine it there too. "
] |
[
"Would it be possible to selectively breed dogs back into a wolf, or is the process completely irreversible?"
] |
[
false
] |
[deleted]
|
[
"Depends on what you mean by that question.",
"Could we selectively bread dogs to physically appear like wolves? Yes, it would take a while but simply selecting for more wolf like characteristics and breeding them will eventually lead to an animal that looks like a wolf. Something similar was tried in Germany which created the Heck Cattle, in an attempt to \"breed back the Auroch\".",
"Genetically though it would not be possible to breed back wolves. If you did a genetic analysis of dogs you attempted to \"breed back in to wolves\" there would be clear evidence in your breed showing their decent from domesticated dogs, plus you'd lack alot of genetic diversity found in wild wolves. On the molecular, genetic level, your breed would most certainly not be wild wolves no matter how much they looked the part, and it would be impossible for them ever to be. The breed would have their own unique ancestry and this would remain in the breed's genome for perpetuity in the breed's decedents."
] |
[
"Technically yes they wouldn't be wolves, but it would be possible to breed dogs that look and behave much like wolves. It might not even be too difficult."
] |
[
"Genetic recombination means genes will be lost from a population in favour of the genes you selected for artificially. So the basic answer is yes it would be theoretically possible to return a dog breed to what is essentially a wild wolf without involving wolves again to reintroduce lost genetic diversity. Genes don't typically lay dormant unless they are transposable elements (genes that are basically inserted by viruses, to oversimplify it), you can only have copies that are expressed or not expressed, or genetic code that does not function for anything. If you were to mutate genes you could render them non-functional, but selectively breeding will not render genes non-functional (although recombination might disrupt compensatory pathways), only mutation can do that. You can then breed the mutations, so that the dysfunctional gene is passed on. Thus you get different phenotypic traits based on this, but you cannot un-mutate the defective gene."
] |
[
"Sand that’s beneath the sand at the deepest part of the ocean - is it wet too or is it dry due to some kind of intense pressure barrier?"
] |
[
false
] | null |
[
"It's still wet. ",
" It is possible to completely dry an ocean sediment, but (1) not through pressure alone and (2) not under conditions that exist in most sea-floor sediments.",
"Sea-floor sediments are (obviously) water-saturated at the point of deposition so to obtain dry sediment, some process has to remove the water. This could be a physical or a chemical process, so let's work through them. Before we do that, I'd like to introduce some important terminology. In a sediment, we have grains (i.e. the small fragments of rock that make up a sediment or sedimentary rock, be it pebbles, sand, or mud) and porespace, which is the gaps between grains. Porespace is filled by a fluid which is usually air or water, but could also be oil or gas. The proportion of the rock that is made up of porespace is called the porosity, so if I talk about a sediment having a porosity of 50%, that means that 50% of the volume of that sediment is solid grains and 50% of the volume is gaps between the grains. Another related, but different, parameter is the permeability, which describes how ",
" the porespace is and therefore how easily fluid can flow through the rock. ",
"When you mention a \"pressure barrier\", I think you're imagining a situation where the pressure is so high that all of the water is squeezed out of the sediment. To some extent this does happen - as sediments are buried to greater depth, sediment particles (in the case of deep-sea sediments this is almost always mud rather than sand) undergo compaction (i.e. they get closer together). This therefore reduces the porosity and it is well-documented that sediment porosity decays with depth (e.g. ",
"Hamilton 1976",
"). Since water is practically incompressible, this reduction in porosity is accompanied by the expulsion of the fluid (e.g. water, usually). Importantly though, whilst the porosity declines with depth, it practically never reaches zero. Even sediments well over a kilometre beneath the seafloor will usually have a porosity of >30%. The reason for this is simple - if you perfectly pack spheres, the lowest possible porosity can you physically achieve is ",
"~25%",
". Sediment grains are not perfect spheres of constant size (although deep-sea sediments usually do not have a large grain size variation) but perfect packing is also difficult to achieve so the result is that it is very difficult for a sediment to physically compact to a lower porosity than this (sediment grains can deform, but the pressures required for this are high compared to the typical pressures experienced by marine sediments). Furthermore, reductions in porosity are usually accompanied by reductions in permeability, which makes it increasingly difficult to expel the water and therefore to compact the sediment further (this increases the water pressure and in extreme cases this can result in the rock hydraulically fracturing itself and dewatering that way, but again this does not result in complete dewatering). ",
"So pressure alone can reduce how much water there is in a sediment, but it can't make it dry. It is in fact, however, possible to dry a sediment chemically. Compaction is not the only way to reduce porosity - you can also precipitate new minerals within the porespace from ions dissolved in the water, e.g. calcite or quartz. Just like pressurisation, this reduces the porosity of a sediment and therefore how much water it can hold. However, similarly to pressurisation, this process is also self-limiting. The more the porosity is reduced through mineral precipitation, the lower the permeability of the rock. Dissolved minerals only make up a relatively small mass fraction of porewater so to continue precipitating minerals, you have to have a steady flow of water through the rock to keep providing ions to drive precipitation. The lower the permeability, the more this supply is restricted and the lower the rate of mineral precipitation, so it is practically impossible to completely eliminate porosity through low-temperature mineral precipitation alone. ",
"The only way to completely eliminate the porosity is to chemically react the water with the rock and/or recrystallise the rock. ",
"The sediment thickness",
" and geothermal gradient in most of the ocean is too small to reach the pressures and temperatures required for this to happen. An important exception is at ",
"subduction zones",
". Here, extremely high pressures are reached, eventually resulting in the complete expulsion of water from the sediment. This is very important because it is this flux of water from subducting sediments (and the hydrated basaltic crust below) into the overlying mantle wedge that is thought to drive melting that causes volcanic arcs behind subduction zones.",
"There is one last mechanism, which is the reason why a typical sedimentary rock you find at the Earth's surface isn't wet. If tectonic forces exhume a sediment or sedimentary rock above the water table, then as long as the sediment has permeability, the water will eventually drain out."
] |
[
"Fantastic answer! Explained the simple terminology so well I was actually able to follow and understand."
] |
[
"I always thought it was the heat that did this. Does heat still playa factor there though?",
"Yes, but the pressure is more important. ",
"This is the most famous form",
" of the metamorphic phase diagram which essentially tells you key mineral assemblages that start forming at different temperature-pressure conditions. The path labelled (4) is a typical subduction-zone path, where the pressure increases significantly more than the temperature. ",
"When/how deep is the water extracted from the oceanic floorplate? ",
"I'm really not an expert on subduction zone dynamics but ",
"this diagram",
" from a ",
"2014 review paper",
" illustrates the process quite nicely. There are several processes that can result in the release of water from the subducting slab and these occur over a range of conditions so there isn't one single depth where fluid is suddenly released en-masse. Some key points are when certain hydrous minerals suddenly become unstable and release their water, such as serpentine (which is formed by the hydrothermal alteration of basalt at the sea-floor) which occurs at relatively shallow depths and amphibole (which occurs at much greater depth). ",
"Wouldn't this process cause massive water vapor bubbles in the (I assume) molten rock?",
"This process doesn't create water vapour, because water vapour cannot exist at these high pressures. At a typical dewatering depth of 50km, the pressure is approximately 1.5GPa, which is far beyond the ",
"critical point for water",
", which means it exists as a phase known as a ",
"supercritical fluid",
". ",
"Is this the phenomenon you're talking about that drives the melting causing the volcanic arcs?",
"Yep! In schools, the model that is typically taught is that when the subducting slab enters the Earth, it melts due to the high temperatures and it's that resultant magma which causes arc volcanism. This is actually not true - due to the relatively rapid rate of subduction, the subducting slab simply doesn't have the time to heat up enough to melt. We know this (1) because of thermodynamics, (2) by analysing the chemistry of volcanic arc rocks and realising that they don't correlate well with the chemistry of the downgoing slab and (3) because through experimentation we know that volcanic arc magmas can't really be formed by the melting of sediments. ",
"The overlying mantle wedge is much hotter, but the pressure-temperature conditions still do not enable melting",
". However, when volatiles (mainly in the form of water) are released from the subducting slab into the overlying mantle wedge, this reduces the melting point (or to be pedantic, the solidus) of the mantle wedge and partial melting is able to occur. As you can see in that diagram, the zone of partial melting ",
" occurs where the hottest part of the mantle wedge (shown by the isothermal contours) coincides with volatile fluxes from the slab."
] |
[
"How do we know the \"stable\" isotopes don't just have absurdly long half-lives (as in several magnitutes times the age of the universe)?"
] |
[
false
] |
I know bismuth was formely considered stable until it was discovered it just had an extremely long half-life.
|
[
"We don't really, it is theorized that protons even in stable atoms may decay over long enough timescales, in this case no atom would truly be stable. There are also the tiny probabilities that collections of stable atoms may slowly undergo spontaneous fusion events which isn't radioactive decay but would mean that no sample of atoms would remain stable over unlimited periods of time."
] |
[
"As has been pointed out, the best we can do is to set lower limits on the half-times of various nuclei and even protons which we believe to be stable. To put some numbers on it, the age of the universe is about ",
"10",
" s",
" and limits on the lifetime of the proton are ",
"tau_p > 10",
" s",
". So we are talking about more than several orders of magnitude here. Experiments are currently being performed to push this limit further, as many theories predict that protons will be unstable, especially theories that unify the strong nuclear force with the electroweak force."
] |
[
"The standard model predicts infinite stability - this is because it conserves baryon number, and there are no lighter baryons for a lone proton to decay into. ",
"In contrast, grand unified theories often do not have that conservation law, and predict that protons can and do decay."
] |
[
"Are the cells of donor organs replaced by the recipients cells over a long period of time or do they remain..?"
] |
[
false
] |
To elaborate. Let's say I donate my heart to somebody after my death. Through mitosis my cells should be replaced and supply the hearth tissue with healthy new cells. Does this continue to go on or will the recipients body start to send out totipotent or pluripotent cells / or earlier heart cells of some kind to start to replace my cells. The real question to me is, will re recipient still have genetic material of me inside him when he passes away? Thanks in advance, sorry if this question sounds weird.
|
[
"To my understanding of developmental biology, the organ will always be composed of cells from the donor. The cells that would divide in your heart to replace old/dead/damaged cells would come through the mitosis of other cells also within the heart as opposed to the liver or the immune system.",
"The real question to me is, will re recipient still have genetic material of me inside him when he passes away?",
"Yes, for as long as they live with that organ."
] |
[
"Your understanding is correct, which is why solid organ transplant recipients require lifelong immunosuppression, to prevent rejection of the foreign cells."
] |
[
"Histidine's response is largely correct, but being a heart researcher I figure I'd provide some specific info regarding the heart -",
"The heart is a very special organ in that most of the heart cells are not replaced throughout your lifetime. There's extremely limited regenerative potential in the heart, which replaces maybe 1% of your heart cells per year when you're young and have better regenerative potential. The heart cells are replaced either by a cardiac stem cell or through mitosis of the heart cells, although individual contributions (as heart cells are largely seen as post-mitotic and may only undergo mitosis after severe injury) are under intense debate. So regarding your heart cells, most of these cells don't turnover, period - donor or not. ",
"Regarding stem cells, the adult body has zero naturally occurring pluripotent or totipotent cells. Most of the stem cells that are responsible for replacing certain organs or tissues generally reside within/near that organ, so whatever little cell turnover you'd have within the heart, for instance, would still remain cells from the donor tissue, rather than the recipient. "
] |
[
"Do all male mammals have useless nipples like humans do?"
] |
[
false
] | null |
[
"Platypi and echidnas do not have nipples, true. They have broader glands under the skin, and suckling occurs through the skin proper and not a mammary.",
"However, all eutherian, placental mammals (non monotreme, non marsupial) have nipples regardless of gender, and these are functionally identical save that male ones are much under developed and can even produce a mucus much like milk. Fatty tissues that develop the breast or teat in female animals are also present at a much reduce amount and morphology."
] |
[
"Platypi and echidnas do not have nipples, true. They have broader glands under the skin, and suckling occurs through the skin proper and not a mammary.",
"However, all eutherian, placental mammals (non monotreme, non marsupial) have nipples regardless of gender, and these are functionally identical save that male ones are much under developed and can even produce a mucus much like milk. Fatty tissues that develop the breast or teat in female animals are also present at a much reduce amount and morphology."
] |
[
"females (XX) and males (XY) initially develop the same.",
"in the womb all babies develop as female. then the Y kicks in by producing a protein that changes the genital tubercle from a clit to a penis. hence leaving nipples because the baby initially developed as female."
] |
[
"How much, if any, Vitamin D can I get from indirect sunlight?"
] |
[
false
] | null |
[
"This article is very informative ",
"http://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/",
"\"The factors that affect UV radiation exposure and research to date on the amount of sun exposure needed to maintain adequate vitamin D levels make it difficult to provide general guidelines. It has been suggested by some vitamin D researchers, for example, that approximately 5–30 minutes of sun exposure between 10 AM and 3 PM at least twice a week to the face, arms, legs, or back without sunscreen usually lead to sufficient vitamin D synthesis and that the moderate use of commercial tanning beds that emit 2%–6% UVB radiation is also effective [6,19]. Individuals with limited sun exposure need to include good sources of vitamin D in their diet or take a supplement to achieve recommended levels of intake.\"",
"Also, if you are using sunscreen or if you are inside and getting sunlight from a window you do not get Vitamin D."
] |
[
"I would like to point out that you don't get vitamin D from light, you make its precursor which is converted to active vitamin D by light."
] |
[
"Would it dramatically change depending on latitude and season?"
] |
[
"Why don't dipole-dipole interactions induce a spontaneous chain reaction and align all molecules in a polar liquid/gas?"
] |
[
false
] |
My best guess is that the random motion of the molecules due to their kinetic energy prevents them from organizing like that. Is this true/ the whole story? Do MRIs work by overcoming this kinetic energy with a strong magnetic field? Is this what is going on when a polar substance like water freezes?
|
[
"I'll talk about something similar: small particles that are longer than they are wide (anisotropic colloids). These are sometimes known as liquid crystals.",
"There are various benefits to having them aligned. Perhaps due to a dipole interaction, or because they're being squeezed together. However, the entropy of the system is maximized when they are all pointing in different directions. Thermodynamics favours a system with greater entropy.",
"So depending on the energetic benefit of being aligned, a liquid crystal may either be aligned to minimize energy, or disordered to maximized entropy. (",
"compare red to green",
")",
"I am not a chemist, so perhaps wait for someone else to make the connection with molecules rather than anisotropic colloids."
] |
[
"My best guess is that the random motion of the molecules due to their kinetic energy prevents them from organizing like that. [..] Is this what is going on when a polar substance like water freezes? ",
"Yes, that's essentially correct, with a slight caveat. For a simple dipole (say, NaCl), there's only really one way it can organize itself (a cubic crystal checkerboard pattern), but water can have several equivalent orientations. Even at absolute zero (theoretically), water can still have more than one way of aligning itself, giving rise to what's known as 'residual entropy'; it's still got some disorder at absolute zero.",
"A perfect crystal (which has exactly one way of arranging itself) has zero entropy at absolute zero.",
"Do MRIs work by overcoming this kinetic energy with a strong magnetic field?",
"No, MRIs don't align the molecules; a dipole moment is electrical, and it's a magentic field. The magnetic moment is much smaller. In fact, it's required for NMR/MRI to work that the molecules have random orientations relative the field. ",
"The thing that gets oriented relative the field is the magnetic moment ('spin') of the (typically hydrogen) nuclei of the molecules. This doesn't correspond to any spatial re-arrangement."
] |
[
"I've spent time hanging out with the members of the ",
"Whaley group at UC Berkeley",
", who study interactions in arrays of cold, dipolar molecules. For more than I give here, check out some of their recent publications.",
"At zero temperature, there are definitely a variety of systems in which fluctuations can lead to spontaneous alignments of the systems. This typically leads to a sort of \"phase behavior.\" Just as heating water above a particular temperature results in a phase transition from liquid to gas, tuning the coupling strength between dipoles can result in a spontaneous switch from random to aligned.",
"In practice (e.g. outside of physics labs), this never happens. The chief reason is thermal motion--that is, at the temperatures found on earth, there is so much vibrating and \"bouncing around\" happening in the system that the energy gain from dipole-dipole alignment is not high enough to enforce that alignment, relative to the phonon (vibration) energies of the surrounding system."
] |
[
"Can a material be both electrically conductive and an isolator?"
] |
[
false
] |
I mean, for example, you flip a switch and make a material an isolator, and than flip it back so current can flow through it. Is that physically possible? Could you make that?
|
[
"Superconducting electromagnets often make use of a powdered superconducting material, embedded in a thin tube of metal like silver or copper. (The SC itself is often quite brittle, hard, and otherwise very difficult to shape into wires, strips, or coils. )",
"These magnets have the advantage that, once a current is introduced into the superconductor, it persists indefinitely due to zero electrical resistance, and an external source of power can be switched off.",
"Although sver and copper are normally thought to be the best conductors, in this case the copper or silver cladding is an effective insulator, by comparison to the SC. The embedded SC has resistance of zero and the metal cladding has resistance of much greater than zero. It may be thought of in the same way as the plastic insulation on a conventional wire. Effectively zero current travels through the metal cladding.",
"The other common example is semiconductor devices like transistors or diodes.",
"In diodes, they are decent conductors if the current flows in one direction, but they switch to being good insulators if the current is ever reversed.",
"The difference in forward vs reverse conductivity may be as high as a factor of 10,000 times."
] |
[
"I think you're kinda missing a big one here, which is the entirety of semiconductor and computer technology, which involves flipping something from an insulator to a conductor and back by applying a voltage at the transistor gate."
] |
[
"Yes, this is how computer chips work, they're just trillions of MOSFET transistors that flip the conductivity of the transistor channel electrostatically. You also control conductivity through applying strain and by inserting impurities. There are also things like phase-change memory where you can literally re-order the atomic arrangements of the material at will to act as a \"0\" or \"1\""
] |
[
"Is there a Universal base number system?"
] |
[
false
] | null |
[
"Whether a number is whole or not has nothing to do with the base of the number system used. Pi will never be a whole number, because it is not an integer. ",
"There's no reason, I suppose, that you couldn't use a base-pi number system... Except that then all the integers would be infinite non-repeating decimals, and that would kind of suck. "
] |
[
"Not really. The (interesting) properties of numbers should generally be independent of how we write them."
] |
[
"I found this cool ",
"Radix Converter",
", along the lines of what I'm pondering."
] |
[
"Is it correct (Scientifically) to refer to Humans as Omnivores?"
] |
[
false
] |
Not all of us eat meat, not all of us eat plants and some of us enjoy both. We've got a couple of sharp teeth for tearing meat (I assume) and some flat ones for chewing greens (I assume). Whats the verdict askscience??
|
[
"We are omnivores by design, even if we arent all by habit. Same way that someone with backwards sleep habits would not put our status as diurnal as any different."
] |
[
"Evolutionarily speaking, we are omnivores. Biochemically, we have the means of obtaining nutrients from both plant and animal matter. Culturally, or by habit as IamPolaris_247 says, it doesn't means we HAVE to eat both, but we certainly are capable of it. "
] |
[
"So you are saying that a human can live with either plant or animal matter without really ",
" the other?\nThen why is it a nutritionist recommends that we have both in a balanced diet?"
] |
[
"If I have a quad core CPU, what consumes more power - running one core at higher frequency, or a multiple cores at lower frequencies?"
] |
[
false
] |
To be specific, what consumes more power - Running one core at, say, 1.4 GHz Running two cores at 700 MHz, or Running four cores at 350 MHz?
|
[
"Really depends on the internal details, but there are simple arguments that says running multiple cores at lower frequency is better for power usage. I recall nvidia specifically using this argument behind their claim of improved battery life in one of their Tegra chips.",
"The basic idea is that in order to run at higher frequency, the chip must have a higher voltage. Power usage increase linearly with frequency, but quadratic with voltage. Increased voltage required for high frequency is therefore extremely expensive in terms of power usage. "
] |
[
"CS MS here. Note that your options are not necessarily computationally equivalent. Depending on the actual parallelism of the algorithms being executed on these cores, which depends (among other things) on the intrinsic parallelism of the problems the algorithms are trying to solve, you may have four cores at 350 MHz performing as well as one core at 350 MHz."
] |
[
"So there's no way if knowing for sure? Considering the same load? "
] |
[
"Question in Cosmology: Wouldn't the big bang have produced a completely homogenous universe? Wouldn't objects exist at ~equal distance from one another and all look relatively the same?"
] |
[
false
] |
I am not discrediting the theory by any means, but I obviously am misunderstanding something about the theory and would like some clarification. According to Newton's first law of motion When viewed in an inertial reference frame, an object either is at rest or moves at a constant velocity, unless acted upon by an external force That would mean all matter leaving the initial blast would have evenly distributed as there wasn't anything else to act upon it. Nothing would have caused one section to go further than another. So then, why when we look at the universe do we see so many different shapes of galaxies and why aren't galaxies (and the objects inside of them) pretty evenly distributed? The only answer I was able to come up with for this is that the "space" that matter occupied had to expand as well, and as we don't exactly understand how the edge of our universe works, maybe it doesn't expand evenly, leading to the differences we see in the universe? Thanks in advance. Also, I did read the rules and I realize that hypothetical questions are discouraged. I am not looking for personal theories or hypothetical answers, but to understand if this is a question that has already been explored and answered to some degree by scientists. Edit: Thanks for the answers and . This has really cleared up some confusion I had
|
[
"Surprisingly enough, the universe is quite homogeneous and isotropic.",
" The deviations in the CMB are very, very small amounts. While the picture you see of the CMB shows drastic colour differences (colour representing temperature), keep in mind that these differences are just tiny percentages over the norm. If you were to view it on a scale where the maximum/minimum values were the factors of 2 over the norm, the images would be a solid colour.",
"This link covers some of the basics.",
"Certainly, on the small scale the universe isn't homogenous. We obviously have galaxies, and clusters of matter, and what-not. This is an active area of investigation. One of the current hypotheses that I have heard about in cosmology talks is that perhaps it was a dark matter inhomogeneity that seeded the formation of local matter clumping.",
"Remember that gravity is only attractive, so wherever there is an increased density of matter, it will continue to increase.",
"In short, on large enough scales, the universe is homogeneous. And the reason why it isn't homogeneous at short scales is currently under investigation."
] |
[
"bertrussell is totally correct that this is still an unanswered question, but I thought I'd give one possible answer:",
"A high temperature gas means that the individual components of that gas have random motion. ",
"Furthermore, heavier objects (such as helium, lithium, etc) existing in that gas will exhibit:",
"http://en.wikipedia.org/wiki/Brownian_motion",
"So because of the random movement of atoms in a gas, you could easily see high pressure and low-pressure areas to form randomly, which would cascade via gravity to form clumps, which eventually form galaxies, etc etc.",
"This is not proven, however this random motion could be a mechanism for a homogenous gas cloud to form clumps. "
] |
[
"A high temperature gas means that the individual components of that gas have random motion.",
"Sorry, but this is a non-explanation. The question is: Where does the randomness come from in the first place? Heat isn't just magically \"random motion\". Every bit of this motion for every single particle/molecule was conveyed to them by other waves/particles/molecules, and they kept bumping into each other, spreading the randomness of heat all over the material. Heat is not \"magically random movement of particles\", it's just what we call the billiard chaos of billions of particles in combination.",
"But where did the randomness itself at the very beginning of the universe, when everything was hypothetically ",
" homogenous, come from?"
] |
[
"How are steel construction building beams allowed to get rusty and remain exposed to wet weather? Wouldn't that compromise their integrity?"
] |
[
false
] |
[deleted]
|
[
"Sea cans are made of a grade of steel that skins over a protective layer of rust that goes no further than the surface.COR-TEN, or Corten steel, is commonly referred to as weathering steel. The name Corten is the trademarked name. It may seem counterintuitive, but when exposed to the elements its chemical makeup allows for an early creation of light rust that adheres to the surface of the steel.",
"Corten still is typically used in bridges and towers, chimneys and rail cars, and even outdoor sculptures."
] |
[
"What is a sea can?"
] |
[
"The large 10x10x40 shipping containers you see on cargo ships and transport trucks. "
] |
[
"Where does the earths core get its heat energy from?"
] |
[
false
] |
from what I understand, the core of the earth is extremely hot. It's temperature is similar to the temperature of the sun's surface. The earth's core has been burning hot for billions of years. What are the sources of its perpetual energy? Also, how far would we have to dig to feel the temperature rise?
|
[
"The main contributors of the earth's internal heat are gravitational heating (dense stuff moves toward the core, trading gravitational potential energy for thermal), and radioactive heating (heat production by decay of unstable radioisotopes, particularly U, Th and K).",
"The top few tens of meters of the crust are mediated by environmental effects. Once you're below that, the rate at which temperature increases within the crust is highly dependent on how thinck the crust is (shallow crust gets hotter quicker with depth).",
"See here for examples:",
"http://www.mpoweruk.com/images/geo_temperature.jpg",
"Once you're down through the lithosphere, a more globally standardised temperature profile exists: ",
"http://upload.wikimedia.org/wikipedia/commons/thumb/c/c6/Temperature_schematic_of_inner_Earth.jpg/275px-Temperature_schematic_of_inner_Earth.jpg"
] |
[
"Every time an earthquake goes off on earth those seismic waves propagate through the planet. We have hundreds of seismic sensos lcoated around the planet, and that means that when they detect that earthquake we get hundreds of different signals from that one event. The difference in those signals is a function of the types and thicknesses of material that they passed through. So we can gather the data from all these earthquakes, and gradually put it together a lot like an ultrasound scan.",
"Doing that we basically get information that tells us how fast a seismic wave travels through a layer, and how thick that layer is. ",
"Now comes the modelling and experimentation. We also use lots of information gathered through things like gravity surveying (we know that gravity varies quite considerably around the planet because of changes in the material below, so we have measured it in great detail). By combining all this information we can start to build up a model of what pressures are like at certain depths. We can then start to conduct experiments in the lab, using extrmemly high pressure tools like diamond anvil presses, and look at how different minerals behave under those extreme conditions. Lots of experiments, together with computer modelling, and using geochemical analyses on things like meteorites (which we understand to have been fromed from early proto-planets), and we can gradually narrow down on what the specific minerals, temperatures and pressures are at a given depth.",
"The better that information becomes, the more precisely we can interpret the seismic data, and the better we can refine future experiments."
] |
[
"Something I've always wondered: how exactly do scientists measure the temperature and composition of the earth's core?"
] |
[
"Does Foucault's pendulum demonstrate that the earth is spherical or merely that it rotates?"
] |
[
false
] | null |
[
"The Foucault pendulum demonstrates that you are in a rotating frame of reference, so it shows that the Earth is rotating.",
"A collection of Foucault pendula at different locations could be used to infer that the Earth is spherical, as the pendula at different locations will have different periods."
] |
[
"Not a stupid question -- don't have a time for a long answer now, but take a look at ",
"Newton's bucket argument",
" and, more generally, ",
"Mach's principle",
". One way of framing your question is whether or not rotational motion only has a relative meaning.",
"The general view today is that you would be able to distinguish a rotating frame of reference from one that isn't rotating even if there were nothing else in the universe, based on what general relativity tells us, and so we expect that a Foucault pendulum would still work in that universe."
] |
[
"Possibly a stupid and/or meaningless question:",
"If the Earth were the only body in the universe, could it still rotate? In other words, is a second object required to define a frame of reference in which the first is rotating. If so, do Foucault pendula act like simple pundula in that universe?"
] |
[
"So broadly speaking, white reflects radiation and black absorbs radiation. Then why do paler people experience sun damage so much faster than darker people?"
] |
[
false
] |
I mean I know it's because of melanin but I guess I'm just approaching biology like the amateur physicist I am here and I'd like to reconcile the two! I mean why does melanin end up making skin darker to reflect more light? EDIT: Thank you all so much for your great answers! Really enjoyed reading the discussions that were started too :) I think the reality of biology tends to be so much more complex than the (relatively) simple scenarios examined in physics, and that's part of what makes it so interesting!
|
[
"The purpose of melanin is not to reflect light. Melanin actually absorbs the UV radiation from the sun. Without sufficient melanin the UV radiation penetrates our skin cells and damages the DNA. If you're out in the sun without protection long enough the DNA damage gets severe enough to kill the cells resulting in various degrees of sun burn. "
] |
[
"Actually, the cells damaged by the sun \"kill themselves\" so that they don't become carcinogenic cells."
] |
[
"Hopefully. When that programmed cell suicide goes awry, and they also happen be multiplying uncontrollably, you get a malignant tumor."
] |
[
"Is there any probably reason (other than pregnancy) for a woman with an irregular period, not on birth control, to be late by over a month?"
] |
[
false
] | null |
[
"The short answer is yes, there are a variety of reasons for irregular periods. Most of them are good reasons to visit the doctor."
] |
[
"My wife was on the depo for several years and once she stopped getting the shot, she had irratic periods for about a year and half with them sometimes coming within 2 weeks of each other and sometimes skipping a month or so. Other factors can come into play as well such as stress and diet. She might want to go see her doctor though, they will be able to tell her more about what is potentially going on."
] |
[
"Stress, underweight... a lot of things :/"
] |
[
"I have IBS: constant diarrhoea. How much nutrition am I likely to miss?"
] |
[
false
] |
Not here for health advice - have been seen by specialists etc, and the consensus is that I should just put up with it, which I do. My question is, how much of the goodness of the food I eat will go through without being absorbed? Oftentimes, the food I eat barely touches the sides - I'm on the throne within minutes. I eat good healthy food, and I get the sense I might as well throw it straight in the sewer without involving the middle-man. Follow-up question: If I do miss some nutrients, might that cause lethargy and malaise, in general?
|
[
"I have IBS and am extremely healthy. You have nothing to worry about aside from the inconvenience, pain, and embarrassment of constant shitting.",
"FWIW I got myself a medical marijuana card and it's a miracle cure, provided you can use it when necessary. "
] |
[
"Hey, thanks for the reply. I've heard other people say that the MJ helps, but there's no medical MJ here in New Zealand. \nIt's kind of easy enough to get anyway, but I'm getting too old to be dealing with drug dealers.",
"So I should be alright nutritionally though huh. That's good."
] |
[
"Sorry, another follow up question: Exactly how does the marijuana work, do you know? What does it do, physically?",
"I'm not talking about getting stoned, I was wasted through two years of my degree; I mean, what does the MJ do that makes it a miracle cure?"
] |
[
"If you had mugshots of a billion people, would current computer technology be able to sort them by appearance?"
] |
[
false
] |
The system would create a huge map of everyone, and the closer you were to someone the more they would look like you. Or maybe this has already been done by Facebook/NSA/etc.?
|
[
"https://en.wikipedia.org/wiki/Eigenface",
" is the reference you want."
] |
[
"Facial recognition software doesn't work the same as how humans recognize faces. If you don't tell the system what gender and ethnicity the face is, it might find a similarity between an African man and a Chinese woman - just because the distances between the facial features are similar"
] |
[
"Just wanna point out the simplest eigenface implementations have a bunch of issues.",
"Lighting, clothes, and facial expression can all be significant (so the algorithm might not recognize you at night, in a different shirt, or if you are smiling instead of frowning)."
] |
[
"Why don't we know the size of the entire universe?"
] |
[
false
] |
We know when it started and how fast it expands, so why are we unsure about how much 'space' there is beyond our observable universe?
|
[
"The Big Bang isn't an explosion of matter within space - it's the expansion of space itself. If the Big Bang was a classical explosion within some large or infinite space, you would indeed expect all the matter in the universe to be contained in a sphere, about 13.7 billion light-years in radius.",
"However, the expansion of the universe is actually about ",
". This works even if the universe is ",
" in size. It's possible that the universe has ",
" been infinite in size. We don't have great constraints for the extremely early universe. We know that the universe was once denser and more compact, but it could still have been infinite in size at that point.",
"To measure the size of the universe, we have to measure its curvature, which is connected to the expansion rate. We see no curvature, which is consistent with an infinite universe. However, a small (positive or negative) curvature is within the uncertainties. That is, the universe is either infinite, or so big that we can't (yet) tell that it isn't infinite. Unfortunately, if it ",
" infinite, then we will never be able to prove it - no matter how precise our measurements get, it'll always be possible there's a tiny curvature that's too small for us to see."
] |
[
"It's not mathematically necessary for a flat universe to be infinite, but for it not to be, you either have to defy the Cosmological Principle or allow especially \"weird\" topologies, like the universe is a higher-dimensional torus.",
"Defying the Cosmological Principle is effectively a non-starter for any theory without some groundbreaking revelation to support it. The universe could be analogous to a torus but in one more dimension, or some other finite-but-flat topology, but as far as I am aware there is no known reason why the universe might even possibly be that shape, and for the most part it's disregarded as an option. Not that people don't look at the possibility at least. For example, ",
"this paper",
" looks at the size a torus-like universe would have to be to be consistent with observations."
] |
[
"Thanks for this response. Does a flat geometry necessarily mean the universe is infinite? In other words, if we knew that the universe was flat, would that also mean it was infinite? Is it possible to have a flat geometry that is not infinite?"
] |
[
"Does the immune system remember it's last attempt at shuffling genes when searching for a better \"recipe\"?"
] |
[
false
] |
Hey guys, I know that the immune system is able to shuffle some genes around in the hope of finding a protein that binds on some part of the pathogen it's trying to get rid of. It's very simplified I know. I have no background. Here's my question. It will be a mess because I don't really know how to formulate it. Please bare with me! I was wondering about this : It finds a recipe that kind of work but it not a perfect fit. The system needs to shuffle the deck again. Does it remember that the last recipe only worked at 60% for example and it only needs to refine the last 40%, or does it starts from scratch hoping to find an event better solution since it can't really remember or feel how well it worked? Is it able need reiterate from prior attempt and knowledge gained?
|
[
"No, it doesn't \"remember\" anything. We like to imagine that biological systems are intelligent in some way and that the things that happen on a molecular basis have some kind of consciousness. For example: \"a cell grows and when it's big enough divides into two new cells\" or your example \"immune system fights pathogens\" like that the cell and immune system know what's going on. In reality that's just our wording for the explanation of a particular process. The immune system doesn't know what it's doing or why it's doing something and probably doesn't even know that it is an immune system. Biological processes are not intelligent in a sense that they have a certain will to carry out a function, but are just beautifully arranged puzzles of probability that form a whole process and that we're lucky to somewhat understand. When you really get into it it's all just probability of events. ",
"Anyway that's how I see these things."
] |
[
"You are actually describing two different processes that happen in the evolution of antigen binding proteins (antibodies or T-cell receptors). I will describe antibodies as I think people are a little more familiar with them, but T-cell receptors work in very analogous ways.",
"First, before any antigen is present, B-cells will undergo ",
" gene shuffling to create a large set of antibodies. Each cell will do so independently, without any input, and create some sequence of antibody that only that cell can produce. After the randomness, there is a process of selection, where cells that are making antibodies that don't fold right, or don't get expressed right, or bind something that is present on the surface of host cells will receive a trigger to kill themselves. Those cells die, new cells are created all the time, and ones that did not receive that trigger, stick around for a little while producing some amount of the antibody.",
"At some point an antigen gets into the system. There is interplay between cell localization, signals between different cell types, etc. but we can simplify. Some antibodies will bind antigens and start triggering whole cascades of signaling between different cell types. Eventually (simplifying a lot) the cell gets the signal that the antibody is binding, and to do two things. One, make more cells whose job it will be to produce a lot more of the antibody, and two, start replicating and making more of the B-cell. During that second step, the b-cells are set-up such that when they replicate, they have a very high rate of introducing mutations into the area of the genome that codes for the antibody. ",
"In this case, the cells again ",
" add extra mutations, but working off of the background of an antibody that has already had some function. So there is some \"memory\" but there is certainly no final goal. Simply random changes. After that set of antibodies is created, the process repeats. Antibodies with better activity are selected and more b-cells are created, more Ab is produced, and more variants are created. When the new variants get random mutations that don't perform as well, those cells get the message to kill themselves and not reproduce. In total, you end up with a large number of different antibodies against an antigen. In acute infections this can be easily hundreds of different sequences of antibodies that will all bind the antigen. Usually, only a few sequences will dominate around 2-3 weeks after presentation, which is when you have maximal immunity and clear the antigen from the blood.",
"As with all evolution, on the micro to macro scale, the variation is random and comes first, then selection pressure is applied, and more \"fit\" individuals (cells, clones, species, etc.) survive. There is no goal, so there can be no knowledge of how close or far you are from some specific thing, however, there is some \"memory\" in the sense that all biological entities come from other biological entities and the genetic code is carried over."
] |
[
"Exactly true. We far too often anthropomorphized processes that are purely chemical, purely probabilistic."
] |
[
"How much force does it take to stop a bullet?"
] |
[
false
] |
I use a Powdered Actuated Tool at work. It uses .22 caliber rounds to drive a nail into concrete. How much force is acting against me when I use it?
|
[
"Any finite force will stop a bullet eventually."
] |
[
"What kind of universe did I step into where joules are a unit of force?"
] |
[
"What kind of universe did I step into where joules are a unit of force?"
] |
[
"Why do nuclear reactions emit electromagnetic waves?"
] |
[
false
] |
Mass converted to energy through e=mc is in the form of kinetic energy and electromagnetic waves, now my question is why they form electromagnetic waves?
|
[
"Disturbances in electromagnetic fields manifest as electromagnetic waves. It's usually the movements of electrons that we associate with these disturbances. Protons, being charged particles, can also disturbe electric fields when they move/change in nuclear reactions."
] |
[
"E=mc",
" in fact refers only to the rest energy of a particle. In early physics, a box at rest would be considered as having zero energy if it was taken to be \"on the ground\". Einstein's famous equation simply says that mass itself is highly compacted energy, and as such, even a stationary particle with no other potential energies, will have some amount of energy, intrinsically.",
"The equation for mass increase is symmetric with time dilation in that you multiply the rest mass by the Lorentz factor."
] |
[
"Thanks for your comment! I have a question to add on to what you said, does the energy of the nuclear reaction influence how fast the proton accelerates, and therefore make the electromagnetic wave more energetic?"
] |
[
"Do we know what the core temperature of the earth was when it was formed, and do we know how much it has cooled since then?"
] |
[
false
] | null |
[
"I haven't been able to find a lot on the temperature of the core at the time of formation, but scientists estimate it will take 91 billion years to completely cool. In practical terms it may not get time to cool completely because the Sun will enter its Red Giant phase in approximately 5 billion years.",
"Based on this, I'd be confident in saying that the core temperature at formation would be reasonably similar to the current estimated temperature of 5,700 degrees K. ",
"https://education.nationalgeographic.org/resource/core",
"https://en.wikipedia.org/wiki/Earth%27s_inner_core",
"https://www.scientificamerican.com/article/why-is-the-earths-core-so/",
" (this is a pretty old article so some of the information within may no longer be accurate)",
"Edited to correct some mistakes."
] |
[
"Our sun is NOT going to 'go nova,' it's going to enter its red giant phase and maybe expand enough to include Earth's current orbit, maybe not. There's plenty of room in the uncertainty on the specifics of our star's future evolution for some or all of the inner bits of the Earth to survive the whole red giant phase (some tens or hundreds of millions of years, IIRC), and then resume the near hundred billion years of cooling in orbit of the white dwarf which will remain after that. Or, the scorched remains will be blown into interstellar space by the final blasts of gas from the terminal red giant.",
"Sorry, just a minor quibble."
] |
[
"No, thank you for the correction."
] |
[
"What makes copper (Paragard) IUDs safe?"
] |
[
false
] |
I read that copper IUDs work by releasing copper into the uterus and causing an inflammatory reaction. How could it be safe to have a constantly inflamed uterus for up to 10 years?
|
[
"To clarify, all IUDs (regardless of whether they are copper releasing, levonorgestrel releasing, or inert), ",
"cause localized inflammation",
". It's also important to acknowledge that the exact mechanism of IUD activity is not perfectly understood, though there are a number of likely pathways worked out. ",
"IUDs cause a marked local foreign body reaction, which turns the intrauterine milieu lethal for embryos [7], and except for the interference with ovarian function caused by LNG-IUS in some women [8], [9] and [10], they exert no obvious extrauterine effects [11], [12], [13] and [14]. The foreign body reaction is characterized by a marked increase in the number of neutrophils, mononuclear cells and plasma cells. The addition of copper significantly alters the metabolism of the endometrial cells, and with the LNG-IUS, there are massive decidual changes, atrophic glands and, sometimes, atrophy of the entire functional layer. ",
"Note that just because there is an inflammatory response ",
"does not necessarily mean there is any cellular damage (in animal models)",
":",
"This cellular response to copper persists for at least 7 months, without significant local tissue damage or detectable systemic effects on the test animal.",
"To correct some misleading information from other responses - though they share the word 'inflammatory', PID is not directly related to localized inflammation, but is rather related to infection. ",
"Risk of PID is usually related to underlying risk of STIs, and generally occurs in the first 20days post-insertion",
", which is consistent with the idea that the insertion process itself is what drives the risk of PID. Women at ",
"low risk for underlying STI have very little increased risk for PID from IUD insertion",
"."
] |
[
"Your citation does not support your statement that copper IUDs cause PID due to a low grade inflammation.",
"The concern that IUDs cause pelvic inflammatory disease is based on the hypothesis that insertion or maintenance of the IUD device \"may facilitate the ascendance of sexually transmitted organisms from the lower to the upper genital tract,\" not that inflammation itself causes PID. ",
"source",
"\nAlso, it's worth noting that this concern is universal to IUDs, and not limited to the copper formulations."
] |
[
"Does science have an understanding as to how the paragard causes increased cramping for many/most women who have it? Why does the cramping tend to go away with time?"
] |
[
"What are the benefits from bringing back resources from asteroids?"
] |
[
false
] |
I see what Planetary Resources is attempting but why would such great quantities of resources helps us? Are we currently limited by our resources, excluding oil I mean?
|
[
"the earth does not have an equal distribution of all elements so this causes some of them to be extremely rare and therefore expensive."
] |
[
"Such elements as?\nWould any of these be usable as an alternative power source?"
] |
[
"In particular the platinum group metals: ruthenium rhodium iridium osmium palladium and platinum. These are extremely useful in advanced electronics (things like electric cars, etc.) and are quite rare in the Earth's crust. ",
"In terms of power sources, some asteroids contain abundant water ice that can be extracted and split into hydrogen and oxygen and used for rocket fuel in space. "
] |
[
"Is the reaction of Silicon and Chlorine dangerous?"
] |
[
false
] |
[deleted]
|
[
"This reaction is producing silicon tetrachloride (SiCl4), a volatile liquid used in industrial silicon refining. It is a dangerous molecule because it produces hydrochloric acid when it touches water. The reaction producing it is also quite hazardous because you're heating chlorine gas up to a few hundred degrees. You couldn't do this in front of a classroom of students. I wouldn't even want to do it in my ventilated fume hood because the chlorine would corrode everything. I'd stick to the video. "
] |
[
"Chlorine gas definitely isn't something I would recommend using in \"my first ever Chemistry project for school\". When it comes in contact with water (including that in your cells) it creates hydrochloric acid. Having strong acid form in your lungs if something goes wrong isn't really a risk worth taking in my opinion."
] |
[
"Whenever you want to know the hazards of a chemical, google \"chemical name MSDS\"",
"Like ",
"silicon tetrachloride",
"and ",
"chlorine"
] |
[
"How can fruit ripen even after having being picked?"
] |
[
false
] | null |
[
"When the fruit is on its tree or bush, the roots are bringing up water and other minerals from the ground, while sunlight is being shined upon leaves. Very simplified, photosynthesis converts CO2 from our atmosphere with water to create glucose, which is the plant's energy source in order to grow. Inside each fruit are millions of cells present which are doing tasks such as toxin removal, photorespiration - all which require energy. If there is enough nutrients in the soil and enough sunlight, plants and especially trees, can maintain a long life barring any other natural causes that can harm it.",
"When you pick an apple off of a tree, you just cut of that apple's energy supply. However, there is still energy in that apple, allowing it to preform mitosis and divide. Thus, an apple can still ripen off the tree because energy is not localized to the trunk or branches, it is spread throughout the organism. Fruits change color when they ripen, and this is the result of pigments (already present in the apple from day one) being shown, as all the chlorophyll that was in the fruit has since stopped working from lack of energy. ",
"All fruits are not created equal, and some fruits go bad very fast after picking. There are two types of fruit: climacteric and non-climacteric. Climacteric fruits continue to ripen after being picked due to a chemical called ethylene, and examples of these fruits are mangoes, bananas, and avocados. Non-climacteric fruits do not ripen very much after being picked, and examples of non-climacteric fruits include almost all berries, oranges, and limes. ",
"This is a good page showing the chemistry behind the process of ripening: ",
"Fruit Ripening"
] |
[
"Ethelyne reacts or catalyzes?"
] |
[
"Ethylene is actually a plant hormone, much like testosterone and estrogen are for humans. When plants begin their reproduction cycle, ethylene production is increased, via the Yang (methionine) Cycle. Plants also produce ethylene during times of stress and physical damage. So, it would not be considered an enzyme nor something that catalyzes. As a fun fact, bananas are usually harvested when they are very unripe, and companies then subject the bananas to large amounts of ethylene in order to make them ripe faster.",
"This is a good link showing how ethylene affects plants"
] |
[
"Since plants have immune systems just like animals, is it possible for them to have allergies?"
] |
[
false
] | null |
[
"Yes! The plant immune system recognizes and responds to certain pathogenic proteins. These pathogenic proteins (called \"effectors\") are sometimes referred to as \"avirulence genes\" in the pathogen, because the plant immune system will efficiently recognize a potential infection by a pathogen with an \"avirulence gene\" and shut it down.",
"The way that this \"effector-triggered immunity\" (or ETI) works is called the \"hypersensitive response\" (or HR). During the Hypersensitive response plant cells around the potential pathogen die, creating a small \"dead zone\". These dead zones are very small, and cannot be seen with the naked eye. It may seem counter-intuitive for a plant to kill cells to prevent infection, but it prevents the potential pathogen from acquiring the nutrients and conditions it needs to replicate into a true infection. This is analogous to an allergic reaction, wherein an animal immune system overreacts and attacks its own cells. The primary difference is that in plant ETI the death of host cells is intentional and beneficial. ",
", if the plant tissue is exposed to an unnaturally high concentration of pathogens that trigger ETI, you can see a visible region of HR. Shown in ",
"this image",
" where a tobacco leaf was infiltrated with a protein that induces HR in tobacco.",
"Great question! I can answer any follow-up questions about plant immunity you might be interested in."
] |
[
"It's as analogous as you will find when comparing such diverse organisms as plants and animals. An allergy is an immune response above and beyond the \"helpful\" scope. Similarly we can create visible HR \"lesions\" by exposing plants to ETI-inducing proteins at a higher concentration than normal. ",
"Plant immunity is an innate immunity, whereas animals have an innate and an adaptive immune system. Allergies are connected to the adaptive immune system in a way that cannot occur in plants. So if you are looking for a perfect homologue of an allergic reaction, you will not find one in plants."
] |
[
"Does that still count as an allergic reaction, though? Those are a result of the body overreacting to a perceived threat and releasing chemicals into the bloodstream that cause a slue of problems. If it’s intentional, I don’t think it counts"
] |
[
"How do they know what colour dinosaurs were?"
] |
[
false
] |
They always seen to be brown or green. Are these just guesses, because fossils don't offer any clues to skin colour? Surely there were some variations to the brown/green dinosaurs, as there are variations in animals these days. Were there any brightly coloured dinosaurs?
|
[
"They've found that some dinosaurs were black, white, and red-brown! They worked this out by ",
"investigating the structure of dinosaur feathers",
". They may have also been ",
"iridescent",
".",
"Anything apart from that is purely speculative. Dinosaurs have often been portrayed as brown/green probably due to unimaginitive associations with lizards."
] |
[
"That's really interesting. It was actually a peacock that got me wondering about this. If you found a peacock fossil but had never seen a peacock would there be a way to tell it was coloured the way it is? So it seems you would be able too? "
] |
[
"Outside of the pigments we've found in feathers (which, as I recall, is a relatively recent development), we really have fairly little idea of what colors dinosaurs actually were, which is why there are ",
"so many",
" ",
"different interpretations",
" ",
"of what dinosaurs",
" ",
"looked like.",
"The popular choices of green and brown earthy tones is likely an association with modern lizards or camouflage, but given their relation to birds it's entirely possible that dinosaurs were in fact very colorful."
] |
[
"Do we know what the tallest mountain ever was?"
] |
[
false
] | null |
[
"Various flavors of this question are very popular on AskScience, so it might be worth checking out one of the more ",
"recent times a similar question came up",
".",
"With respect to our specific ability to determine what the tallest mountain ever might have been (or more generally, our ability to reconstruct paleoelevations at all), a relevant short comment was recently published by ",
"van Hinsbergen & Boschman",
". In this they nicely highlight that, no, just knowing the rates of plate motions is insufficient because the average elevation (or peak heights) of resultant mountains will be a product of the convergence rate, but also the details of the structural geometries (e.g. how distributed is the zone of deformation over which the plate convergence is accommodated, is it all converted to crustal thickening, etc), paleoenvironments (e.g. where is base level, what latitude are the mountains forming, how does this relate to glacial cover, etc), the types and nature of rocks exposed during the mountain formation (e.g. this will in part dictate the 'efficiency' of erosion and thus height), and the paleoclimate (e.g. the details of where and how precipitation is delivered to the mountain range will also control the efficiency of erosion). What this implies is that while this may not be unanswerable question, it is both an extremely difficult question to answer and extremely difficult answer to verify with data."
] |
[
"This is indeed a fun back of the envelope exercise, but fundamentally ignores some very basic aspects of how mountain ranges are built and supported. One of the best discussions of this is the classic ",
"Molnar and Lyon-Caen, 1998",
" paper (and ",
"here is a link to a PDF outside of a paywall",
"). The two important points highlighted here are that: ",
" The strength of the lithosphere that underlays the mountain range (not the material within the mountain range, that comes in for point 2) exerts a strong control on the maximum height and this is best expressed in terms of something like the ",
"effective elastic thickness",
" of the lithosphere. Going back to the original Everest/Himalaya to Mars comparison, this is arguably more important that the gravitational difference as the effective elastic thickness of the Martian lithosphere is much greater than that of most of Earth. If you go through the flexure calculations it works out to something like ~60% of the difference in height (assuming all other things equal, which is another very large assumption) can be accounted for by the flexural rigidity differences between Mars and Earth.",
" Peak heights are probably not particular diagnostic when you're considering the limits imposed by the mechanical strength of the material making up the mountain range. The argument in the Molnar & Lyon-Caen paper is that the average elevation of orogenic plateaus (e.g. Tibet, Altiplano, etc) are likely a good approximation of the maximum integrated height that is reflective of the mechanical strength of the material that makes up the mountain range. I.e. a mountain range grows in height until it is mechanically favorable to widen instead, growing a plateau, thus the height of the plateau represents the limit for the material in question. This means that if you wanted to do the above calculations (and ignore the flexural rigidity differences) the appropriate elevation to use for Earth would be the average elevation of the Tibetan plateau, not the crest of Everest. Another (not likely valid) assumption embedded in this is that the densities of the Earth vs Mars material is the same and that the failure criteria for those materials are the same (which is especially not valid for comparisons between Earth and other bodies as indicated in the comment by ",
"/u/loki130",
"). The Molnar and Lyon-Caen argument embeds some problematic assumptions of its own (namely that plateaus represent a progressive widening of mountain ranges, but a variety of evidence from Tibet especially suggests that may not be the case), but is probably a better starting point for back of the envelope calculations.",
"The ",
" version of the above is that when considering the mechanical limitations of range height, you should picture a pile of material on a trampoline. The absolute height attainable is a product of the thickness of the trampoline sheet (thicker = greater height because of less deflection) and the strength of the material (the same mass of pudding vs water will have very different maximum heights). Differences in gravity would be filtered through those aspects.",
"This also all of course ignores the variety of arguments for surficial controls on average elevations and/or peak heights, specifically that either glaciers (",
"Egholm et al, 2009",
") or rivers (",
"Hilley et al, 2019",
") exert a first order control on maximum topographic heights (for Earth)."
] |
[
"/u/CrustalTrudger",
"'s answer is more in depth than I could ever write, I'll just mention a point made by one of my teachers in uni giving some insight to your first question: how high has the tallest mountain on earth has ever been. This was an example he gave on the relevance on back-of-the-envelope calculations, so a lot of things are assumed and numbers are aggressively rounded.",
"Assuming the Everest is the tallest a mountain can be, a limiting factor could be how much stress the material (rocks) making up the mountain before failing – crumbling and rearranging itself in a more stable configuration. The stress to which the material is subjected is mostly due to the weight of all the material above it, and is a linear function of the height of material above and gravity.",
"Now, assuming the materials Mars is made of have roughly the same mechanical properties than those Earth is made of (similar rocks), then the highest possible mountain on Mars should be ",
"h_Mars = h_Everest * g_Earth / g_Mars",
", which is roughly ",
"9000 * 10 / 4 = 22500m",
". Further verification shows that it is indeed the height of ",
"Olympus Mons",
", the highest peak on Mars.",
"This hints that the Everest can indeed be close to the highest mountain that can possibly exist on Earth, if the mechanical yield of the material is indeed the limiting factor in both cases. However, this reasoning can't be used to validate completely that hypothesis: the limiting factor could be more linked to the peak growth rate vs. erosion rate, which would differ a lot on the different planets (thinner athmosphere and no liquid precipitation on Mars means a lower erosion rate, Olympus Mons is a volcano whereas the Everest is due to plate tectonics, which probably means its growth rate was much higher). In this case, the back-of-the-envelope calculation results is merely a neat coincidence."
] |
[
"How do deciduous trees know when to drop their leaves? What would happen to them if winter never came?"
] |
[
false
] |
Obviously temperature is super important to this process, but what actual patterns trigger dormancy, and how can these get messed up?
|
[
"It's not temperature that causes trees to lose their leaves, it's hours of sunlight.",
"Trees, as you can imagine, are pretty good at using sunlight. When they notice the hours of daylight per day start to get below a certain number, that triggers them to go into dormancy.",
"If winter never came, if temperatures never dropped below freezing, some trees would be fine, but most would be in trouble.",
"Some, indeed I would say most, trees require a certain number of days to be below freezing before they can be taken out of dormancy. Basically, they drop their leaves and enter dormancy due to triggers from the number of hours of sunlight in a day, but they wake up from dormancy based on temperature. In order to not wake up in the middle of a warm spell during winter, most will require that the temperature be below a certain level (typically freezing, but it isn't always) for a certain number of days (typically 30-60 days) followed by warmer temperatures for a certain number of days before they wake up.",
"This isn't always the case, but it is true of most trees.",
"After they leaf out and have their solar collectors deployed, they switch back to the number of daylight hours for most functions. For example, they'll flower based not on the temperature and not on the number of days it's been since their leaf buds first opened, but based on the number of daylight hours. This means that trees in different micro-climates (like climbing up a hill, where it's colder at the top of the hill than it is at the bottom) will all flower at the same time, thus increasing their chances of getting pollinated."
] |
[
"I recalled from my biology classes the phenomenon is called photoperiodism and experimentally proven that the receptor cells respond to night length.",
"To simplify things The photochemical Messengers generated requrie uninterrupted darkness to avoid being reverted to their base/inactive state . ",
"https://en.m.wikipedia.org/wiki/Photoperiodism",
"In 1920, W. W. Garner and H. A. Allard published their discoveries on photoperiodism and felt it was the length of daylight that was critical,[1][8] but it was later discovered that the length of the night was the controlling factor."
] |
[
"Isn’t it the length of nights that matter rather than daylight ?"
] |
[
"Would it be possible to invest so much money into a bank that it couldn't support the amount of interest it would owe you or wouldn't be in the banks best interest, as it would be too expensive?"
] |
[
false
] |
Do banks ultimately have an infinite supply of money? I'm thinking the answer would be that in theory, it's possible, but no one has that much money. What about if you went to a small rural town bank? I may be missing something completely obvious, but was just a thought I had.
|
[
"The more money you give to a bank, the more money they have to make investments and earn money.",
"So, assuming the bank was competent at making investments, no, you couldn't bankrupt a bank by over-investing."
] |
[
"Depositing a huge amount of money into a bank will cause problems, but not necessarily the one you're thinking of, because of the aforementioned need for a bank to earn money with your money, so they can pay you interest.",
"The bank needs to find people/firms to lend your vast amount of money to. To encourage them to take on debt, the bank might lend at a lower rate of interest than justified by the risk. Or, they might lend to/invest in risker clients than they otherwise would. The larger economy becomes distorted because there's an oversupply of credit.",
"What's the worst that could happen from this? Well, this sort of thing was a major contributing factor to the 2008 global banking crisis - and the worst global recession since the 1930s."
] |
[
"You have to remember interest you gain from the bank is lower than inflation. They don't even have to gain value from investing with your money to be able to pay you back."
] |
[
"Is there a limit to the size a planet can be and still be considered habitable?"
] |
[
false
] |
I mean could a planet be the size of jupiter and have life on it, under conditions similar to earth (water, oxygen, sunlight etc...)
|
[
"It could certainly sustain bacterial life and probably protozoans too. The question of more complex life is harder to answer.",
"Let's take Jupiter from your example. Gravitational acceleration at its surface is 24.79 m/s",
" or about 2.53g, where g is the gravitational acceleration on the surface of the Earth. So Jupiter's surface gravity is about 2.53 times higher than Earth. If you weigh 160 pounds on Earth, you would weigh a bit over 400 pounds on Jupiter. That wouldn't kill you. Certainly you'd find it harder to move around, you may run the risk of fractures or injuries if you fall, and your heart would probably not last as long. But even Earth adapted as you are, it wouldn't kill you.",
"It's quite possible that if you had evolved for Jupiter's gravity, even these problems wouldn't exist. Having a larger/stronger heart and thicker bones and stronger muscles aren't impossible things for evolution to produce, it does that all the time. Jupiter-evolved life would tend to be shorter and squatter (shorter because you're not fighting gravity as much to pump blood to the very top, squatter because of thicker bones and muscles), but there's nothing in biology that says it couldn't exist.",
"Let's make it more extreme. Jupiter doesn't have a solid surface, so let's imagine a Jupiter sized rocky planet. We don't know if such planets are possible, but let's assume one. It has the same diameter as Jupiter, but it's made of rocky material like Earth, with the same average density as Earth. We can calculate that its surface gravity would be about 10.9g. So a 160 pound person on Earth would weigh about 1740 pounds on this hypothetical planet.",
"Now we start running into problems of material strength. That's about the weight of a large bull, and you may have seen the thick bones a bull has to support its weight. Try packing them into a human sized body, along with the muscles needed to use them, and you have a problem. It can't be done. So at this point you have to re-imagine how critters would be formed.",
"Large organisms around our size would need stronger materials, maybe highly calcified bone embedded in some strong protein matrix. Locomotion could be re-designed so the center of gravity is lower, muscles are leveraged to produce shorter but stronger movements. Metabolism may need to be speeded up to provide more energy, or you could have a less energy-intensive lifestyle, like reptiles rather than warm blooded mammals or birds. No doubt there are lots of other adaptations that evolution could explore, given long enough.",
"So it's possible that organisms as large as us (or even larger) could exist on such a planet, without doing anything hugely different from what life does on Earth. They would look very different from Earth organisms, but they could probably exist. Gravity does set limits on maximum size, so you wouldn't expect to see elephants and giraffes there - the largest animals would probably be much smaller than those on Earth.",
"None of these problems matter much at small scales. Scientists ",
"can grow Earth bacteria at up to 400,000 g",
", which is far beyond the gravity possible on any planet. Protozoans and other small organisms could similarly survive at very high gravities even if they didn't evolve there, even if they're Earth adapted.",
"Marine life does not need to support its own weight, so it's possible that marine organisms could grow pretty big even on high gravity planets."
] |
[
"Related question - does this mean that there is an orbital distance from Jupiter where you would have exactly 1g of gravitational force, so that if you had a space station orbiting in that orbit, you'd have earth-like gravity?",
"No. There is some altitude above Jupiter where the gravity would be exactly 1 g, but if you were to put something there it would fall down to Jupiter, accelerating all the way. If you wanted it to stay up, you would have to give it an orbital velocity, in which case it would be like the ISS or any other space station - the occupants would experience zero g and be weightless."
] |
[
"So you don't have an actual source, just common sense?"
] |
[
"Do people actually die from a 'broken heart'?"
] |
[
false
] |
[deleted]
|
[
"Severe stress can actually cause a weakening of the muscle walls of the heart, which can lead to death.",
"Called Takotsubo cardiomyopathy"
] |
[
"Confirmed, I see this regularly in my line of work. Impressed this was in the first comment :-)"
] |
[
"There is also something called \"Failure to Thrive\" and a lot of older people get diagnosed with it after losing a significant other. ",
"Wiki",
"\n*Edit formatting "
] |
[
"Can weight lifting create more hormones in your body?"
] |
[
false
] | null |
[
"Yes, proper exercise with resistance will increase the levels of \"good\" hormones. Not only is there a increase in serum testosterone levels, but in Growth Hormone and IGF-1, a couple of other important anabolic hormones. A study published in ",
"Int J Sports Med. 1991 Apr;12:228-35",
" showed this hormonal increase after weight training in both men and women.",
"To examine endogenous anabolic hormonal responses to two different types of heavy resistance exercise protocols (HREPs), eight male and eight female subjects performed two randomly assigned protocols (i.e. P-1 and P-2) on separate days. Each protocol consisted of eight identically ordered exercises carefully designed to control for load, rest period length, and total work (J) effects. P-1 utilized a 5 RM load, 3-min rest periods and had lower total work than P-2. P-2 utilized a 10 RM load, 1-min rest periods and had a higher total work than P-1. Whole blood lactate and serum glucose, human growth hormone (hGH), testosterone (T), and somatomedin-C [SM-C] (i.e. insulin-like growth factor 1, IGF-1) were determined pre-exercise, mid-exercise (i.e. after 4 of the 8 exercises), and at 0, 5, 15, 30, and 60 min post-exercise. Males demonstrated significant (p less than 0.05) increases above rest in serum T values, and all serum concentrations were greater than corresponding female values. Growth hormone increases in both males and females following the P-2 HREP were significantly greater at all time points than corresponding P-1 values. Females exhibited significantly higher pre-exercise hGH levels compared to males. The P-1 exercise protocol did not result in any hGH increases in females. SM-C demonstrated random significant increases above rest in both males and females in response to both HREPs",
"Source"
] |
[
"Likely what you're experiencing is an increase in testosterone (T). This is probably in response to your weight lifting activities. T is also important in libido, which is why you're seeing an increase in sex drive. T is converted into estradiol (E2, which is the same hormone in women) and dihydrotestosterone (DHT) by different enzymes in the brain and other areas. All three are important in healthy sexual functioning. So, in short, you lifting weights causes more T to be released increasing libido. "
] |
[
"Alright, this is going to sound stupid, but would this be able to promote facial hairgrowth aswell as an extention of the greater amount of testosterone?"
] |
[
"What's preventing us from curing diabetes?"
] |
[
false
] |
Aside from things like lack of funding, what are some of the scientific/medical field obstacles? Are we just not at a high enough level of understanding? Does bioethics come into play anywhere? As a type 1 diabetic with some, albeit little, knowledge, I'm more than curious as to what's stopping us! Edit : To everyone who has participated, I am unbelievably grateful for your time. All this information is extremely helpful! Thank you! I have so much love and respect to everyone who has, has lost, or is losing someone to, diabetes. Love every second of your lives, guys. I'm here for anyone who is effected by this or other correlated disease. I am but a message away.
|
[
"Type 1 diabetes is an autoimmune disorder. This means that the patient's own immune system is attacking the cells in the pancreas that produce insulin. Why the immune system does this is related to genetic and environmental factors.",
"Because these cells are destroyed, the pancreas cannot make insulin, but the other cells of the body can sense and use insulin normally. \nTo cure this we need to:",
"a--help the pancreas recover it's damaged cells",
"b--find a way to block the immune system's attack.",
"We are working on this, and have made many promising strides with stem cells! ",
"Type 2 diabetes is an entirely different thing. That is mostly a metabolic disorder. Some genes and environmental factors can be involved, but usually it is caused by a Western diet. High sugar, high carbs, plus sedentary lifestyle will make your normal cells unresponsive to the massive waves of insulin they are being bombarded with. The pancreatic cells work just fine. They make insulin just fine (though as the disease progresses, the pancreas starts giving up). Your regular cells ignore insulin. The glucose stays in your blood and wreaks havoc on your nerves, kidney, heart, blood vessels, while your cells think that you are starving. ",
"You can sometimes reverse (but not exactly cure) type 2 early on by eating well, losing weight, and exercising. Once it has advanced, however, the condition becomes chronic with compounding issues (neuropathies, cardiac disease...ect) "
] |
[
"The primary reason is that the disease we commonly think of as \"diabetes\" is actually a middling large ",
" of diseases with a shared primary symptom - chronically high blood sugar. But each one of them is in fact the result of a different metabolic failing or external factor. Some of the best know factors and causes are:",
"DM (diabetes mellitus) Type 1 involves the pancreas ceasing to produce insulin altogether - sometimes very abruptly, perhaps over just a few weeks. We know the insulin-producing areas are actually attacked and destroyed by the body's own defence system, but ",
" this happens is - so far - unknown.",
"DM Type 2 involves ",
", a condition where the cells of one's body gradually become unable to process or to absorb insulin properly. It is, after all, a hormone, and ",
" diseases are a result of the body's inability to fully make use of its various hormones. Again, the process by which cellular resistance develops over time (unlike Type 1) is not well understood - though genetics, excess body weight, lack of exercise and high intake of simple carbs have all been statistically identified as factors affecting its development. ",
"Gestational diabetes, where pregnant women who had no previous signs of the disease develop it in parallel with their pregnancy, and lose it again shortly after giving birth. Again, the process is not well understood, but it may have something to do with certain hormonal changes that accompany pregnancy.",
"Assorted other causes (as many as two dozen) including autoimmune dysfunction, genetic mutation, acromegaly (too much growth hormone), hyperthyroidism (overactive thyroid gland), cystic fibrosis and even as a result of certain types of bacterial infections ... among others.",
"So trying to cure \"diabetes\" is just as much of a cluster as trying to cure, say \"the runny nose\", which as we all know, might be the result of a cold, influenza, other viruses, bacterial infection, adenoid problems, post-nasal drip, allergies, inflammation, and so on ...."
] |
[
"Research is certainly happening in that area, but the whole reason ",
" and ",
" ones' various organs even go about producing hormones ",
" is not well understood. Not the least reason for our current state of knowledge is that most hormones - including insulin - are ",
"chemically very complex",
", and the tiniest variation in their structure (say, an OH on a little chemical tail where there should be an H",
" ) can change the entire nature of: ",
" cells can metabolize it; ",
" cells metabolize it; and more importantly, what it ",
" once it begins to act on various body chemistry processes. ",
"In the case of insulin, it's not even the entire pancreas that ",
" it. It's only produced by one ",
" kind of cell - of many - which group together to form tiny sites on the surface of the pancreas called ",
". And it took over 50 years of research (1869 to 1921) after the islets were first noticed, just to realize what they did, to analyze the substance they produced, to identify it as a hormone, and to discover how important that hormone was to the way our body metabolizes nutrition. ",
"Heck, up until Dr. Banting's seminal discoveries, researchers didn't even know what the pancreas ",
" - just that if it suffered trauma or was surgically removed, subjects soon sickened and died. Can you imagine that? A human organ the size of a big kosher dill pickle, and everybody knew it was ",
", but nobody knew what it actually ",
"Now, if I start talking about how insulin's final form is ",
" two entirely different polypeptide chains, linked together in a chemically clever way by two specific disulfide bonds, but that it actually ",
" in the islets' beta cells as a ",
" polypeptide that is first split into ",
" and a ",
" with a free carboxyl... and so on, it'll either make your head spin right off ... or set you to earning your own doctorate in endocrinology. ",
"So how can one go about repairing a complex chemical ",
" like the pancreas, if one doesn't yet fully understand what its ",
" is? Or even what it's ",
"? Or how those components ",
"? Or how the product actually ",
" while it's being metabolized? Can one really fix what's gone wrong in a block-long computer factory, if one doesn't yet understand how or why the bad computers it keeps spitting out fail?"
] |
[
"If something travels at faster than speed of sound without generating any noise, then still there will be sonic boom?"
] |
[
false
] |
By something i mean anything like some rocket or airplane etc. but it is important that it must not generate any noise like from engine.
|
[
"A sonic boom isn't generated from the propulsion system of any machine.",
"Sound is pressure waves. A supersonic object creates a pressure cone where it is splitting the air. The boom you hear is when the cone intersects your ear. A supersonic bullet has a miniature sonic boom without producing any other noise. So, yes, there is still a sonic boom."
] |
[
"Supersonic is only 0.34 km/s. Orbital velocity is 7km/s so no, most supersonic things will just slow down and hit the ground. You are correct that in space, you can go as fast as you want without creating a sonic boom per se. There is very diffuse gas in space, but drag or pressure waves will be insignificant."
] |
[
"More specifically, it produces a shockwave by forcing the air in front of it to 'move aside' faster than the speed of sound causing a density spike. There is also a second shockwave originating behind it as the object leaves a partial vacuum behind it that collapses.",
"I suspect you could make an extremely tapered shape that would allow air to move aside and return behind it more slowly than the speed of sound even though the object is moving faster than the speed of sound and that would tend to suppress the formation of a sonic boom. "
] |
[
"Why do notes in chords fit together"
] |
[
false
] |
I'm doing a project in school which all students must do for their senior year in Sweden. The question I have chosen to answer is; I have a theory that it has something to do with the waves fitting together in some way. But other than that I don't know much. I don't really know how to proceed or how to test this. I also would need some easy-to-find literature on this subject and maybe some studies for validation.
|
[
"This is a good place to start. ",
"http://www.edly.com/mtfpp.html"
] |
[
"I don't feel comfortable answering this question for you since it's for a school project. However, here are some keywords you can read about on wikipedia to get started: ",
"dissonance",
", ",
"acoustic beating",
", ",
"harmonics",
", and ",
"octaves",
".",
"Basically, whenever any of the harmonics of two different notes lead to acoustic beating, the notes sound dissonant."
] |
[
"I would start by reading up on the Harmonic Series. "
] |
[
"Are NASA spacecraft transmissions encrypted?"
] |
[
false
] |
Could a layman intercept the signals from nasa satellites and get all the information? Or is it all done with.some secret protocol or something?
|
[
"This varies. In the past, information was transmitted in the clear. This reduced complexity and thus increased reliability. You would still need to figure out the communication protocol and/or file formats to understand what the information means.",
"However, there were several incidents in 2007 and 2008 when someone (not NASA) took control of a LANDSAT satellite for a few minutes. It is thought that the Chinese were responsible. No harm was done to the satellite.",
"Of course, NASA now has a focus on secure satellite communication.",
"See ",
"http://origin.www.uscc.gov/sites/default/files/annual_reports/annual_report_full_11.pdf",
" page 215-217, for information on the Chinese attacks (hacks?) on satellites."
] |
[
"I can't speak for NASA, but at ESA most spacecraft don't have any kind of encryption. There's an authentication mechanism though, which is standard and public. The only non-public thing is the signature of the spacecraft.",
"It is just too hard (and of very little value) to hijack a satellite. You need a ground station, some control system, to know how to command the spacecraft and how to interpret the TM. The communication protocols are pretty much standard (CCSDS is one of them, publicly available) and the frequency plans and modulations used are also public. But you still need to know how to command the spacecraft and how to interpret the actual telemetry coming down.",
"Military spacecraft, GNSS and telecom satellites ",
" use encryption, since those do have an strategic value and although they present the same problems for an \"attacker\" as a NASA/ESA scientific spacecraft, the value for the attacker can be such that it's worth to go through the trouble of obtaining the necessary information. As an example, the Galileo system is operated under encryption."
] |
[
"In the early days, it was PR point that NASA missions were in the clear.",
"\nPR was cuz USA is 'free', USSR wasn't. (I dont know if they encrypted). The\nreality was that computers weren't fast enough to do it on the fly, especially not\nthose on the spacecraft. For manned missions, so little was controlled from the",
"\nground it made no difference to safety. For unmanned, protocols were so arcane",
"\nand mission-specific, and ground equipment so big, t was unreasonable to even",
"\nworry about. I worked in Astronaut Training during shuttle program, and it was also",
"\nin the clear,except maybe some of the SDI stuff (I didn't work on that part at that",
"\ntime). Now I think comm spoofing / hijacking is enuf of a risk that at least some",
"\nParts should be encrypted."
] |
[
"The Rio–Antirrio Bridge spans the Gulf of Corinth in Greece. The Gulf expands by 30mm each year. How long could the bridge stretch to before breaking?"
] |
[
false
] |
It's a 2880m bridge now, how long would it be before it becomes unsafe? 2880.5m? 2900m? What technologies allow bridges to be "stretchy"? The does mention there being "provision for the gradual expansion of the strait over the bridge's lifetime". Does that mean that the bridge is expected to reach the end of its lifespan due to other factors before the expansion becomes an issue? What tends to be the limiting factor on longevity of bridges?
|
[
"Normally metal bridges are mounted on rollers on one side. Otherwise they would experience extreme forces due to normal thermal expansion and contraction which would increase the strength requirements significantly. "
] |
[
"I have crossed this bridge and i have noticed at some points it has a link between sections like 2 steel combs facing each other. Kinda hard to describe, but it only leaves some small rectanlge gaps if you stetch the bridge, which you can drive over with no issue. I thought it was pretty clever."
] |
[
"Good find, thank you! Wikipedia mentioned the supports being on top of gravel bases on which they can shift slightly, but my intuitions fail me when I try and consider what happens when you stretch another 8 or 9 centimeters out of each 100m length of driving surface."
] |
[
"Would pushing an object that weighs 100 pounds feel the same as pushing an object that weighs 1000 pounds if they are on a surface without friction?"
] |
[
false
] |
[deleted]
|
[
"The heavier one would move slower and appear bulkier/heavier to you and \"give way\" less to your pushing. Both would be pushable. Just the larger one would require more work to get it to an appreciable speed. This is because of inertia.",
"The funny thing is that if this were a truly frictionless surface in a vacuum (where you can ignore any random air currents), you could do wacky things like get the objects to move without even touching them. Stand next to them long enough and you will become attracted to the object (and it to you), and both of you will accelerate towards each other at an incredibly slow rate. After a few weeks I am sure the 1000 pound block would have moved an appreciable distance and begin to have a perceptible speed. This all assumes you are somehow bolted into place, of course, such that you aren't sliding around willy nilly on the surface yourself.... Otherwise even the act of breathing or a stray fart would cause you to slide around on such a surface!"
] |
[
"The explanation above explained what inertia is, with out using a technical and difficult word like inertia. Who cares what a word is, as long as the concept is communicated?"
] |
[
"If there is no friction, does pushing the blocks feel the same? Yes, in the sense that, no matter what push force you exert, however weak or strong, the block will begin to move. In other words, there is essentially zero effort to get either of the blocks moving, regardless of how massive they are. You can sneeze at the block and it will begin to move.",
"(Note that if you were also standing on the frictionless surface, after you push the block, you would rebound in the opposite direction as if the block exerted the same force on you.)",
"However, there are some obvious differences between the two blocks. If you exert the same push force F on both blocks, the acceleration of the block is",
"a = F/m",
"which is smaller the more massive the block is. Let's say you exert this force over some time interval T. Then the momentum you transfer to the block is",
"p = FT",
"So the speed of the block after you stop pushing is",
"v = FT/m",
"The more massive block ends up with a smaller speed. So when you ask the following question:",
"Would it require more effort to move the heavier block?",
"the answer really depends on what you mean. If by \"more effort to move\" you simply mean whether it takes more force to get the heavier block moving, then no. Like I wrote above, you can exert ",
" force on the block and it will move.",
"But if by \"more effort to move\" you mean to ask \"does it take more force to move the heavier block a certain distance in the same time\" or \"does it take more force to get the heavier block to a certain speed\", then the answer is yes. Say you want both blocks to end up with speed v, then the quantity FT/m must be the same for both blocks. So either you exert a larger force on the heavier block, or you push the heavier block for a longer time, or some sort of combination."
] |
[
"Why do neutrons interact differently with nuclei depending on their energies?"
] |
[
false
] |
So I was doing some reading on neutron radiation detection and shielding, and it appears to me that depending on the material used and the energy of the neutron, the neutrons are either bounces off the nucleus or is absorbed. What is the principle behind this?
|
[
"This is not only true of neutrons, it's true of photons and charged particles as well. In fact, I think a better question would be \"Why ",
" interact with matter the same way at different energies?\".",
"If you shoot a bullet at me it will hurt a lot, but if you throw it at me it won't. So even in very simple classical scattering there is energy dependence in how objects interact.",
"This carries over to quantum scattering as well.",
"At various energies you've got different processes which are possible, like scattering, reactions, and resonances all competing with each other, and the probabilities of which are of course energy-dependent."
] |
[
"It was that last line that made it really clear to me, so now I have some good starting points for further reading.",
"Thanks a lot!"
] |
[
"This same line of reasoning is why radio waves travel so freely (low energy) while visible light (higher energy) is so easily reflected off surfaces."
] |
[
"What does it mean for the Higgs field to be \"tachyonic\"?"
] |
[
false
] | null |
[
"To answer this question, one has to first understand something about how masses are determined in quantum field theory.",
"In quantum field theory, a scalar field like the Higgs field has a potential energy function. The vacuum is the state that minimizes this function, and so the field will settle throughout space to the value that minimizes the potential. Particles can arise as excitations around this vacuum value. The mass of these particles is determined by the curvature of the potential function at this point; in particle, the square of the mass is equal to the second derivative of the potential function at this minimizing value.",
"Now in the early universe, the potential for the Higgs field looks like a \"U\" (well, actually, a bowl), having its minimum at the origin, and so the Higgs field has a vacuum value of zero. There are also particle excitations around this value, and since the curvature is positive at this point, the mass of these excitations satisfies the relation m",
" > 0.",
"As the universe expands and cools, there is a critical temperature at which the shape of the potential energy function changes from a \"U\" to a \"W\" shape (well, actually, from a bowl shape to a Mexican hate shape). Now the Higgs field has settled to a value of zero throughout space, so we could ask ourselves what the excitations about this value look like now. Because the shape of the potential has changed, we are now at a local maximum (the central tip of the \"W\") rather than a minimum, and so the curvature of the potential has the opposite sign. Thus, if we calculate the mass of excitations around this point, we get the relation m",
" < 0, and particle with m",
" < 0 would be tachyonic.",
"But we don't actually get tachyons. As you see from the above, finding that the particle excitations would be tachyonic is an indication that we are looking for excitations around a local maximum rather than a minimum. What this actually means is that the vacuum value of the Higgs field is no longer zero, but is a value that takes takes you a minimum of the \"W\" (actually, Mexican hat). So the vacuum value of the Higgs field changes from zero to something non-zero. We are once again at a local minimum, and all the particle excitations have non-negative mass squared.",
"Edit: Fixed formatting."
] |
[
"*sombrero (not science, but this is as much as i can help :)"
] |
[
"Man. That was approachable and well-explained and it still hurt my brain."
] |
[
"How do I explain to someone that the relationship between the 3 sides of a right-angle triangle are the same across the whole universe?"
] |
[
false
] |
[deleted]
|
[
"...sure that if we took a circle on their planet, measured its circumference, measured its radius, and divided the two, we would get pi just like we do on Earth.",
"It should be said that we ought to separate theory from observation - in the presence of spacial curvature, circles ",
" have this property. Literally measuring a circle to absurd precision in earth's gravitational field would yield a value of the circle constant which is radius dependent; the sides of a triangle formed by a right angle and 3 geodesics would not exactly obey a",
" + b",
" = c",
"The theory of flat spaces ought to be the same in bizarre alien world however. The circle constant would ",
" the same if they were actually considering ",
" which exist on ",
".",
"This begs the questions as to whether an alien species would take e.g. hyperbolic space to be the setting of conventional elementary mathematics. I find it hard to imagine they would ignore the special case of spacial flatness and consider ",
" curved ones, but you never know. Suppose their world had some absurdly high gravitational fields, and to them, flat space didn't seem to exist whatsoever. Perhaps only their finest mathematicians would discover flat space as a notion. We can't really be sure..."
] |
[
"There are two different questions here - would an alien species necessarily discover all the same laws of mathematics we have, and are the constants like pi the same across the universe?",
"The first can be answered in the negative; aliens may have a dramatically different culture which emphasizes different things. They may find numbers and how numbers relate to each other fascinating, so they have a more highly-developed number theory than we do. Conversely, they may be bored to tears by geometry, and so they haven't discovered fundamental results like the Theorema Egregium.",
"BUT, we can be absolutely sure that they don't have an ALTERNATE Pythagorean theorem; it is not a",
"+b",
"=c",
" for them, that's not possible. The lengths of a triangles sides will not change as it is transported from here to there. Similarly, the constants of the universe will not change. They may not use pi - perhaps they use 2pi as their fundamental circle constant - but we can be absolutely sure that if we took a circle on their planet, measured its circumference, measured its radius, and divided the two, we would get pi just like we do on Earth. "
] |
[
"Well, we do assume that the laws of physics are the same everywhere.",
"The question is really more about the nature of math than about physics. Euclidean geometry relies on a small set of axioms, from these axioms everything that we consider euclidean geometry can be proven. The axioms of euclidean geometry seem very intuitive to us, but they don't have to be necessarily intuitive to an alien species. But in a way our intuition about their truthfulness isn't really all that important. Even if we wouldn't find them intuitive, but would still use them as axioms of a mathematical system, we would come to the same conclusions. A mathematical system exists separated from the laws of physics. It does not have to correspond to anything in nature. It just has to be consistent. "
] |
[
"About 410-290 million years ago the earth's atmosphere was 35% oxygen. If modern man existed in this era could our lungs breathe in this air?"
] |
[
false
] | null |
[
"Yes, oxygen toxicity is a documented problem for divers. It begins to occur when the partial pressure of oxygen being breathed is greater than 1.6 atmospheres. Because the pressure at sea level is only 1 atmosphere, even a pure oxygen atmosphere would be breathable to humans on Earth."
] |
[
"thanks doc."
] |
[
"That number is too high, oxygen can cause pulmonary damage at lower partial pressures too. 1.6 atmospheres is merely where the damage goes from being mainly pulmonary to being mainly cerebral.",
"The limit for pulmonary damage is about 0.5 atmospheres.",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2688103/",
"In healthy humans breathing more than 95% oxygen at normal atmospheric pressure (0.1 MPa), tracheobronchitis develops after a latent period of 4 to 22 hours"
] |
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