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[
"Is every black hole surrounded by a spinning disk of matter and heat?"
] |
[
false
] |
Im wondering if humanity could ever come close to a black hole, or if we would get killed by the radiation, heat etc.?
|
[
"Nope, their are black holes with no disk but they are nearly impossible to find them since the disk is the reason we can see them, their are also theoretical atom sized dark holes all over the universe. As for your other question, it depends on the size of the dark hole and the amount of mater around it. If the plasma disk is to large it will cook you beffore you enter, some black holes are so large that scientis believe you can \"fall\" past the event horizon and survive but then you red shift and slowly fade away (it can take a long time), but the gravity will most likely stretch you like gum."
] |
[
"Theoretical dark holes atom sized. I've never heard anything about that, do you have a source explaining what you mean?"
] |
[
"/u/ODISY",
" may be referring to WIMPs (",
"Weakly Interacting Massive Particles",
"). One possible ultimate end to black holes. Although they would be much much smaller than an atom. "
] |
[
"If North Korea got a missile with nuclear material into the shallow water near one of it's targets (Hawaii, Japan, Guam) would this still be dangerous for the people nearby? What about the marine life and food chain?"
] |
[
false
] |
So the test fires from North Korean missiles have proven to be inaccurate, but lets say that there was a lucky shot and a missile hit the shallows near one of the above territories and it contained nuclear material. Would it have to detonate to have any noticeable effect. What would be the best course of action to clean it up if it were to happen.
|
[
"Would it have to detonate to have any noticeable effect.",
"Hard to say with certainty, because people who have that kind of knowledge of NK's missile program are probably forbidden from sharing their knowledge publicly. One of ours (USA) would almost certainly have to detonate (barring a manufacturing flaw which allowed for a leak) before it did much of anything. We have actually had accidental releases of our nuclear weapons before, and they often just fall to the ground and sit there until we go get them. We've also had nuclear weapons on board airplanes that have crashed, but that often doesn't turn out quite as well - the forces of the crash can break open the weapon and cause radioactive contamination (search under \"broken arrow\" for more info).",
"I would guess that, political insanity aside, NK's scientists have had at least enough sense to properly contain and shield the nuclear package, but that doesn't mean it would survive a missile impact intact. Additionally, the missile would presumably be armed, and so if it didn't detonate, it would be because it was a dud, not because it wasn't supposed to. ",
"In short, assuming the missile works as it should, if NK fires it at something, it's probably going to detonate.",
"If it did blow up, it would be pretty devastating to any marine life that happened to be in the area. We detonated a nuclear bomb in shallow water during the Bikini Atoll tests, so we have a pretty good idea of what would happen. In addition to the under water shockwave, the shallowness of the water would allow for an airborne shockwave as well. How deep the explosion happened would determine how intense the above-water blast would be. ",
"Radioactive water and steam would be dispersed over a large area which would devastate sea life. The underwater explosion itself would be attenuated fairly quickly, because water doesn't compress, which means the explosion has to move it out of the way. As the bubble from the explosion expands, it encounters more and more water, which means a hell of a lot of the energy from the explosion will go into just pushing water. ",
"Of course, the worst effects from this would be on a geopolitical scale, as it's not outside the realm of comprehension that it would start WWIII unless China declined to defend NK based on the egregiousness of the missile attack, but that's beyond the scope of this subreddit."
] |
[
"Do some reading on Operation Crossroads for a more detailed answer. The short answer is that the Bikini Atoll tests involved two detonations.",
"The first was an air burst, in which a bomb exploded fairly high above the testing area. You don't get a whole lot of radioactive ",
" off of an airburst, but as to the spread of radiation, it goes all over. The burst is high enough that the plume is carried into the stratosphere, where the radioactive particles are blown all over the world by the upper-level winds. Local fallout isn't all that intense, but the direct answer to your question is that the air burst will scatter radioactive fallout farther, though at lower concentrations.",
"In this first test, they tied a bunch of animals (mice, guinea pigs, goats, etc) to the ships that were part of the test (no humans on board). Some were penned on the decks, some in various compartments throughout the ship. Around 1/3 of the test animals died either directly from the explosion or later from radiation exposure. ",
"The second test was the shallow test we've already talked about. The bomb was dangled from one of the boats (that particular boat apparently vaporized, because they never found any of it after the test). Local fallout was quite a bit worse - they ended up having to sink most of the ships that were still floating after the tests because they couldn't decontaminate them enough to scrap them. ",
"As with the first test, they tied animals to the boats (though they only used pigs and rats this time). Most of the animals died - only a few rats survived. ",
"Water bursts are particularly fun because the blast emits neutrons, which transform the regular sodium in salt water into radioactive sodium. Unlike most radioactive products, sodium doesn't sink, but remains where ever it is - which means it sloshes up against the ships and contaminates the hell out of them. Even though the bomb didn't produce much by weight of the radioactive sodium, it was enough to contaminate the test ships, the ships that sailed in after the test to check things out, and the decontamination water (which, I suppose, should really have been called recontamination water at that point) with which they tried and failed to salvage the ships enough to scrap them. "
] |
[
"I went and looked up the Bikini Atoll tests,",
"http://www.youtube.com/watch?v=-l6Q8Q1smwg",
"The wall of radioactive spray that was produced, how far would the radioactive steam and spray spread, would it be carried further than if it had detonated over the surface of the water?"
] |
[
"Nephew asked this question and I didn't know how to answer succinctly (he's 7yrs old) - \"If hot air rises, why doesn't hot water rise too?\" He means in a body of water, why doesn't the hot water sit on the top of the bath, and the cold at the bottom?"
] |
[
false
] | null |
[
"You should explain that things don't rise because they rise, they rise because they are less dense. That's why air rises through water, and why soap sinks to the bottom of the bathtub.",
"Then you can explain that a hot water balloon would rise in a pool as well because it is less dense than cold water. ",
"You could probably also make a glass of hot water and mix some food coloring with cold water. Pour some of the cold food colored water into the hot water and it should (mostly) sink. Just do it down the side of the glass to avoid mixing it. "
] |
[
"Or sprinkle something light, but which sinks, into water (probably wet ground black pepper would do) and put it on low heat on a stove. You'll see the particles moving as the water circulates."
] |
[
"Normally when things heat up they expand and become less dense, causing them to rise above the more dense liquid/gas. This is called thermal expansion. Some substances undergo negative thermal expansion where they actually expand when cooled. Water does this between approximately 0 and 4 degrees celcius."
] |
[
"What causes the variability in malleability between metals?"
] |
[
false
] |
For instance, copper and gold are much more malleable than, say, iron. All three are cubic, though iron is body-centered versus face-centered. Is that what causes the difference or is there something else? Why is gold even more malleable than copper - does it have something to do with increased density?
|
[
"Malleability is mainly influenced by the energy required for planes of metal atoms to slip past each other. As you said, copper and gold assume a face-centered cubic structure. In this structure, the atoms are packed in such a way that there are four sets of close packed layers that can easily slip past each other. In the other common structures for metals, ",
"hcp and bcc",
", there are 1 and 0 sets of close packed layers, respectively.",
"So if you are trying to deform a piece of metal (which consisty of many crystallites in many different orientations), it is easier to deform one that is face-centered cubic. Regardless of the direction of the force you are applying, there is almost always a cp plane that can be moved. In an hcp metal, you will encounter crystals that are oriented in a way that allows no easy deformation. ",
"It's of course still possible to deform metals along other planes, but this takes more energy, which leads to higher hardness.",
"Obviously, there are other factors in place here, particularly in alloys or hardened metals, but the difference in hardness for fcc, hcp and bcc metals comes down to crystallography."
] |
[
"Copper and gold are FCC, not BCC."
] |
[
"You're right, thank you. I changed the mistake. Wasn't paying enough attention when writing my answer."
] |
[
"What makes some medical conditions (such as cancer) genetically transferable while some conditions that would seem to be genetic, totally random?"
] |
[
false
] | null |
[
"I'm not sure I understand your question. Some diseases are genetic, some have a genetic component but interact with the environment, some come from the environment and have no genetic component. "
] |
[
"Well, I tried to give some context but you said not to. Then you said the question was ok, but not the extra text. ",
"rom albasri[M] via ",
"/r/askscience",
" sent 23 hours ago",
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"We do not offer medical advice on /r/AskScience. Please see our guidelines. If you have concerns about your health, you need to speak to a medical professional.\n\nThe general question is ok, but the text of the post is inappropriate\n",
"If you disagree with this decision, please send a message to the moderators."
] |
[
"Sorry I missed this message. I don't recall your original post. What are you trying to ask exactly? Maybe we can work on a good phrasing together"
] |
[
"Is p53 mutated in every Triple Negative Breast Cancer Tumor?"
] |
[
false
] |
If not, how is TNBC treated in this case?
|
[
"p53 inactivation does not, as far as I know, have much of a bearing on treatment. I think p53 inactivation confers a poorer prognosis in general, but then again most cancers inactivate p53 at some point.",
"The current treatment for breast cancer is targeted at the receptors the specific cancer uses to grow, but there are other more primitive options. Herceptin and Tamoxifen are wonderful drugs, but before them there was traditional cytotoxic chemo. These drugs are much less specialised and are used to treat a variety of different cancer types, so, as you can imagine, they are much more unpleasant with more side effects, and usually less effective. This is why TNBC is so difficult to treat. I can't give you an exact list of drugs, and, besides, I imagine there is more than one available regimen, but I do know Paclitaxel is used for breast cancer. If I had to guess I would say an anthracyclin like Doxorubicin will also feature in most of the regimens, since the anthracyclins are some of the best available cytotoxic drugs."
] |
[
"The p53 gene remains normal in many triple-negative breast cancers. Although the loss of p53 is a strong factor in the development of cancer, it is not required for the development of a malignant tumor. Although this is oversimplifying a complex topic, you can imagine that p53 by itself is not strong enough to prevent cancer if there are multiple other mutations that impact the regulation of cell growth and development."
] |
[
"Thanks, so basically general, wide use treatments would be used to treat TNBC? I found a paper on a small molecule called DPCPX which inhibited A1 receptors found in TNBC tumor cells, which would result in an increased rate of apoptosis. I was just wondering if p53 was ever capable of being functional in TNBC tumors.",
"Sorry if I am unclear, I'm still a undergrad :D"
] |
[
"What is physically happening in an electric generator when the torque of the rotor is increased?"
] |
[
false
] |
Speaking of a synchronous generator with a constant RPM rotor. As far as I know, the increase in torque translates to an increase in current in the coils. What is physically happening? Put another way: How is mechanical energy physically translated to electrical energy?
|
[
"As far as I know, the increase in torque translates to an increase in current in the coils.",
"It's more meaningful to think of it the other way around -- to say that an increase in coil current requires an increase in torque to maintain the same rotation speed. A generator operating at a constant RPM must increase torque to maintain the same rotation speed when faced with increased power demands.",
"An AC power generator must maintain a constant RPM to remain synchronized with the required line frequency. When the load power increases, the coil current increases proportionally, and to maintain the required constant RPM the generator must produce more power at the same speed. This is accomplished by increasing the torque, the rotational force on the generator's shaft.",
"In a hydroelectric generator, this increased-torque requirement is met by increasing the water flow through the driving water turbine. In a gas or diesel powered generator, this is accomplished by increasing the throttle setting and fuel flow. This is obviously all performed automatically, using a feedback system to maintain a constant generator RPM."
] |
[
"For a given electron current flow in a coil of wire, the surrounding magnetic field is proportional to the current. ",
"Diagram"
] |
[
"You're pretty much right. Increased current in the generator stator coils due to increased load leads to a stronger magnetic field in the bore. A stronger field means a stronger force opposing the rotation of the rotor, so more torque is required to balance out this force or the rotor will slow. "
] |
[
"How do materials both refract and reflect light simultaneously?"
] |
[
false
] |
[deleted]
|
[
"When an EM wave hits a boundary between two media, the transmitted wave has a different speed and wavelength than the incident wave. However, Maxwell's equations, which describe EM wave behavior) require that the fields be continuous at the boundary. Not surprisingly, these requirements are called \"boundary conditions\". It's a bit complicated, so I won't go into the details.",
"The solution that satisfies the boundary conditions contains both a transmitted wave that satisfies Snell's law, and a reflected wave that satisfies the law of reflection. The solution also tells us the intensities of the reflected and refracted waves."
] |
[
"In terms of light photons rather than wave theory, each individual photon can either refract (go through the boundary) or reflect (bounce off it). It is purely a probabilistic process."
] |
[
"That's true, but the boundary conditions in the photon problem are the same. It's just the meaning of the wave that differs."
] |
[
"Why are specific heat capacities of unknown substances important? What are uses of low/high specific heat capacities?"
] |
[
false
] |
I admit this is for homework, but because I don't want to act like I came here without doing any work I will tell you what I know about specific heat capacities. A specific heat capacity is the amount of energy required for an object to go up(or down? Someone confirm this please?) by 1 K or C. So if it's lower it heats up faster than a higher one(assuming the rate of energy input is the same). That's all the relevant stuff that I can think of. I haven't learned too much about energy yet so I'm at a loss as to how to answer the questions. If anyone could please help that would be great.
|
[
"The oceans are a ",
"major heat sink",
" for the planet, due to the high specific heat of water."
] |
[
"Say you put a dish in the oven and let it cook for a while. You take it out and let it cool for a bit. When can you handle the dish with your hands?",
"If the dish is made of a high heat capacity material like glass, it is storing a lot of energy. As it cools it gives off this energy as heat. It will take a long time for the glass to cool to a temperature you can touch without injury.",
"If the dish is made of a low heat-capacity material like aluminum, it doesn't store as much energy. Aluminum also is a very good heat conductor so it can transfer its 'heat energy' to the surrounding air quicker. You could touch the aluminum without injury much quicker. If you've ever heated up something in the oven and covered it with aluminum, you may have noticed you can handle the aluminum within seconds without getting burned."
] |
[
"Space ships create a lot of heat from friction with the atmosphere",
"This isn't quite correct. Most of the heat comes from the (incredibly) rapid compression of the air below the spacecraft, not friction. These are not the same thing.",
"[I wish I had a better citation for this, but ",
"here it is",
"."
] |
[
"why you DON'T develop resistance to some medications?"
] |
[
false
] |
I know people who take drugs for HTN for years or Anti-depressants and etc. so why don't you develop resistance to them? or why do some side effects go away but the main effect of the drugs persists without increasing the dose? (i think side effects are because of the same receptors but in a different part of the body. (also I know all the drugs don't work by blocking a receptor))
|
[
"Often, the meds are either interacting directly with the body systems as a substitute for missing/tiny titers of the natural active component, or act as an antagonist for the same, so metering/shutting down the target system. This isn't quite the same as other systems that can develop tolerances (thereby requiring higher doses for the same perceived effect). Honestly, we'd have to take this on a case-by-case basis as no blanket statement is correct. Nor does this function in a natural selection format like antibiotics with bacteria that either evolve of die, where plasmids xfered via sex confer resistance for survivors.",
"There are plenty of other metabolic considerations. Some drugs are useless in their taken form, and only modifications/metabolism in the gut biome or liver or elsewhere generate the active physiological daughter products."
] |
[
"I’m a doctor. Medications act on enzymes or receptors. These medications can activate receptors, de-activate them or turn on/off chemical pathways. ",
"The question becomes which pathways, when activated/inactivated cause I disruption of homeostasis (the bodies ability to regulate itself). If a drug turns on/off a receptor and the body senses that as a disruption of homeostasis, then the cell will make more receptors so there is more activation or stop\nproduction of those receptors. These are the medications that cause tolerance. ",
"Some medications don’t affect a pathway where upregulation or down regulation by receptor expression is possible, these are the drugs that do not cause tolerance."
] |
[
"We do know that SSRIs cause a withdrawal of sorts if stopped abruptly, this implies some sort of adaptation in the brain's serotonin system, or some other downstream effect. To really answer why you don't generally grow resistant to SSRIs would require to understand exactly why SSRIs work for depression, and we don't yet. One hypothesis is not that the additional serotonin is the direct way they work, but that the presence of more serotonin downregulates certain serotonin receptors and that downregulation is ultimately what gives it therapeutic benefit."
] |
[
"What happens in our brains and chemistry when we control an emotion like reigning in fear?"
] |
[
false
] |
[deleted]
|
[
"In the absence of someone specialising in this area, the frontal lobes are responsible for most emotional responses, but the cerebral cortex (the 'thinking' part) can override this part of the brain where the emotional response is inappropriate. For example when you hold back tears to save face when something upsets you, your frontal cortex is firing off an emotional response that you're using your cerebral cortex to inhibit. A similar thing occurs when you need to pee; the lower, subconscious part of the brain is demanding action from the higher cortex saying \"we need to pee, right now\", whilst your cortex inhibits the urge to pee because urinating in public is a big no. The shuffling action is the result of the lower brain attempting to control the motor functions and demanding action."
] |
[
"I'd like to clarify a couple of things in here. ",
"First, the frontal lobes are part of the cerebral cortex. The cerebral cortex is the layer of folded brain tissue on the outer surface of the brain that is divided into frontal, parietal, occipital, and temporal lobes. ",
"There are many parts of the brain that are broadly involved in emotion. Because emotion involves the collection of the body's responses to maintaining itself in the face of danger and various deviations from homeostasis, these structures tend to be located in the oldest parts of the brain that regulate body functions, including the brainstem, other subcortical structures such as the amygdala, and older cortical structures like the insula integrate information from the viscera of the body. ",
"Emotion regulation tends to involve interactions between these emotion-related structures and higher/newer regions of the cerebral cortex. It is generally thought that frontal lobe structures are important for emotion regulation. For instance, people with damage to the orbitofrontal cortex often become emotionally disregulated (see ",
"the famous case of Phineas Gage",
", for example). Neuroimaging studies have implicated the ventral lateral prefrontal cortex in particular as important for certain emotion regulation processes. Kevin Ochsner's work is relevant here, and you can watch this youtube of him explaining it: ",
"Kevin Ochsner on emotion regulation",
". "
] |
[
"Many of the feelings we have such as fear and extreme happiness are due in part to the balance of neurotransmitters such as serotonin, dopamine, and adrenaline. This is also why many designer drugs give you that high, because they can mimic the natural compounds in your brain chemistry."
] |
[
"Can physicists capture a gluon particle on its own, or even collect a pure sample of gluons, and would it be massless?"
] |
[
false
] | null |
[
"Gluons and quarks are subject to the strong force. This makes them special because they can never appear by themselves. Their attraction to other strongly interacting particles is so large, that if you were to try and pull them apart to examine one by itself, the field lines connecting them would snap and create more particles which then serve to pair up the particles you were trying to pull apart. [Sort of a cartoon explanation obviously.]",
"Another answer mentioned glueballs. It is true that this is a particle in the standard model which would be made of nothing but gluons However, in practice, it is not really a particle so much as a \"intermediate broad resonance\", Because as a particle it is so unstable that its existence itself isn't really a sensible way to describe it. It is more like an intermediate state in a long near-instantaneous decay chain of QCD hadron states, which decay their way towards sort of stable particles like pions and truly stable particles like protons.",
"However, interestingly, it is possible to imagine theories of QCD [The strong attraction] which do not have a light quarks. In that case, the glueball would kind of be the equivalent of the proton, meaning it is the stable form of matter in this theory sector. Furthermore, it is possible that this is realized in nature, but that we just do not yet see these interactions and particles. They could be related to dark matter, or be part of a meta stable \"hidden sector\" of particles and forces co-existing with our own, but only extremely weekly coupled to us (I.e. Standard Model particles)."
] |
[
"Their attraction to other strongly interacting particles is so large, that if you were to try and pull them apart to examine one by itself, the field lines connecting them would snap and create more particles which then serve to pair up the particles you were trying to pull apart. [Sort of a cartoon explanation obviously.]",
"I can maybe elaborate on this in a non cartoony way most people can understand fully. ",
"A quark and a gluon are bound together by a certain energy. To pull them apart, you need to use energy to overcome the energy holding them together. Like using energy to stretch a rubber band. The energy holding a quark and gluon together happens to be equivalent to the mass of a quark and a gluon. So if you added enough energy to this particle pair to overcome the force holding it together, you've also added enough energy to create a new quark-gluon pair. Once the quark and gluon ",
" get pulled apart, this energy has to go somewhere. Because its exactly equivalent to the mass of a quark and gluon, the most stable state is for that energy to manifest as a quark and a gluon. Your new quark and gluon just bind to their now lonely original counterparts, and you now just have two quark gluon pairs. ",
"All of this is near instantaneous. Without closer inspection, it would just look like your energy turned into another quark. Kind of like a high speed particle collision; where two particles can collide and create particles with a collective mass higher than the original two, because some kinetic energy turns into mass. You'd see one quark splitting into two. ",
"Also, interesting side note for anyone interested in this: ",
"Three quarks, two up and one down, form a proton. The rest masses of all three quarks, combined, is 9.4 MeV. The proton's total mass is 938.3 MeV. Meaning 1% of the mass of a proton (or neutron) is the actual mass of the quarks. The rest, 99% of the mass of every proton and neutron, is just binding energy from the strong nuclear force. 99% of the mass of an atom is contained in the nucleus. ",
"Youve been taught your whole life that everything around you is composed of particles. Turns out the particles themselves at less than 1% of the mass of everything, everything you know is Quantum Chromodynamic binding energy. "
] |
[
"The closest thing to this is the currently-hypothetical ",
"glueball",
", which is a bound particle made only of gluons. It is expected to have a mass 3-5 times that of the electron. There is currently an American experiment called Glue-X which is developing the capability to produce and detect these (larger experiments like at the LHC are probably creating them but not detecting them)."
] |
[
"Is all organic life involved in symbiosis of some sort?"
] |
[
false
] |
[deleted]
|
[
"Well, it could be argued that all eukaryotic life ",
" symbiotic, since according to endosymbiotic theory, organelles like mitochondria and chloroplasts are actually bacteria that figured out how to survive inside another cell."
] |
[
"ok fine, bad example - use those bacteria individually as the example. pre-hookup. the point is if you follow back far enough, to the first life form, there were no other life forms to be in symbiosis with"
] |
[
"How could you even tell what the \"first life\" is? Is a nucleotide alive? Probably not, it can't self-replicate. Is a strand of self-replicating RNA alive? Maybe by some definition, but the standard answer is no because it doesn't exhibit all the characteristics we associate with ",
"living organisms",
". But if you wait until you can find the first organism that ",
" have all those characteristics, you'll probably find that there are already millions of very similar organisms that are very close to being considered \"alive\" as well. So if it's co-dependent with any of those not-quite-living organisms, is that not a symbiotic relationship?",
"You can try to make distinctions about what life is and isn't, but ultimately it just isn't very meaningful because nature didn't happen in a rigidly-defined framework. It just ",
", and kept happening until ",
" happened. Don't like that conclusion? Too bad, that's life."
] |
[
"Is it easier for an exhaust fan to pull air through a duct rather than pushing it into the duct?"
] |
[
false
] |
I'm planning on adding a new bathroom exhaust fan and somehow I'm thinking that it if it were mounted closer to the roof (in the attic) it would be able to pull the humid air out of the bathroom through the duct more efficiently. As opposed to being ceiling mounted, it would have a harder time pushing air through the duct. Is there any basis for this?
|
[
"This might be a better question for ",
"/r/AskEngineers",
" but I think in most cases it won't be different enough to matter. You are playing with three basic paramters: suction pressure, discharge pressure, and fan speed. Assuming fan speed is constant then you might just be playing with the first two. Therefore the bigger the pressure difference on the upstream and downstream side the greater the airflow.",
"Locating the fan on the ceiling gives you basically no suction pipe which means very little draw down of the pressure. However you have the greatest run of pipe on the discharge side which means the biggest discharge pressure of all the locations.",
"Locating the fan on the roof gives you the opposite case, unobstructed outlet for lowest possible discharge pressure but you are sucking through a long tube so lowest possible suction pressure as well.",
"Now is where you need the math that I don't have on hand. I don't want to speculate on which case is mathematically better, I just wanted to give you an idea of the factors involved in the problem.",
"However, without doing the math there are other things you can also consider for the best performance:",
"\n-remove as many bends in the vent pipe as possible (especially 90 degree elbows, those increase your pressure drop incredibly)",
"\n-mount the fan in a place that is easy to access in order to clean the intake (clogged intake or dirty blades significantly impede flow as well as pose fire risks)",
"\n-upsize the fan if worried, the difference in power consumption will be minimal unless you are running the thing constantly"
] |
[
"From a volume flow standpoint, the location of the fan does not matter. In a given section of duct or pipe the pressure difference between the inlet and outlet is proportional to how fast the fluid is moving. This pressure differential will be the same if the fan is at the inlet, outlet, middle, or if the duct section is part of a larger system and pressurized elsewhere. A fan in the duct will generate the pressure differential with higher than atmospheric immediately after the fan, and lower immediately before the fan.",
"Accessibility, I would think, is more important in locating a bathroom fan than how the location of the fan affects flow rate. The duct itself also has an affect on flow rate. A larger diameter duct will (to a point) generate less pressure loss. On the air flow I expect a bathroom fan moves, going from a 4\" duct to a 6\" duct could be noticeable, but going from a 6\" to an 8\" would have much less difference. (I am guessing on the sizes though. I usually designed to 30 ft/s for air, but that is probably too fast for HVAC.) Reducing the number of bends also decreases pressure loss. (In the math a bend is treated as a length of pipe that causes the same pressure loss.)",
"There are a couple of other considerations for fan placement, though. Leakage needs to be considered. On a bathroom fan duct leakage is not much of a concern unless there is a there is a need to keep humidity out of the attic space. A gas furnace is a better example. The combustion gasses (CO, CO2, etc.) need to be kept out of the room air. The two streams meet in a heat exchanger to warm the air. The air fan is placed ahead of the heat exchanger to slightly increase pressure, and the combustion fan is placed after the heat exchanger to slightly decrease pressure. That way any leak in the heat exchanger will push air into the combustion gasses instead of pulling gasses into the building.",
"Another thing that gets considered is if equipment has a preferred pressure range. The fan may need to be before, after, or both to keep equipment in the desired range. Computer case fans might be the best well known example."
] |
[
"I would certainly think that reducing pressure in the duct by sucking would decrease resistance in the duct."
] |
[
"Why do we get hungry if we have excess calories already stored in our body."
] |
[
false
] |
If our body stores excess calories as fat cells, why do we get hungry again when our body could instead burn off some fat cells first which would also reduce health problems associated with carrying too many fat cells?
|
[
"The short answer is evolutionary history - it's only been in the last few thousand years (arguably the last thousand) that we've had an abundance of food. Before that, we were just like other foraging animals - we had to constantly be looking for food. Because of this, it would be entirely possible that we may have to go days, even weeks with little to eat if the food supply was short. Essentially, our bodies wouldn't want to \"waste\" the fat we have stored up - it would be better to save it for when we really need it. Hunger likely evolved as a way to ensure a constant supply of food when it was available so fat stores could be saved for dire circumstances."
] |
[
"Apparently, an obese man once fasted without food (but consumed water and vitamins) for 1 year and two weeks. So, under the right conditions, your fat store could keep you going for quite some time.",
"Source: ",
"http://pmj.bmj.com/content/49/569/203.abstract"
] |
[
"Hunger also has to do with low levels of sugar in the blood. When you have low blood sugar, your pancreas and stomach secrete glucagon and ghrelin. These hormones are responsible for the breakdown of stored energy and hunger stimulation. The response is an increase in circulating glucose in the blood, which raises enough to support tissue function but not enough to suppress the hunger response. This is why, if you haven't eaten in a while, you're more likely to crave energy-rich foods. ",
"Interestingly enough, this also partially explains why we sometimes can eat and eat and never fill up. Essentially, if you bumrush your bloodstream with sugar, your insulin levels will spike. Your body will respond by shuttling all glucose into storage, which will cause blood sugar to plummet much faster than if you had eaten fewer carbohydrates more slowly. However, endocrine responses are not immediate, which means there's a period where your blood sugar is low but your insulin is still moderately high, which means that you'll crave energy-rich foods, but no matter how much you eat you'll have a hard time raising your blood sugar, since insulin is still present in the bloodstream in such force. "
] |
[
"Is the Columbia River Gorge a Fjord?"
] |
[
false
] |
The Gorge is on the border between Washington and Oregon, USA and is very similar in appearance to some fjords.
|
[
"The Columbia River Gorge is considered a canyon, but the way it was formed is basically the same as a Fjord. ",
"Several lakes attached to the gorge are referred to as \"fjord-like\" on ",
"Wikipedia",
"."
] |
[
"Fjords are typically formed by glacial erosion. The Columbia River Gorge was actually formed by floodwaters, during glacial periods, in events known as the ",
"Missoula Floods.",
" ",
"The damming of river waters in Montana by glaciers formed massive lakes. Periodically, the ice dams collapsed, releasing huge volumes of water that rushed through eastern Washington, carving out the Columbia Gorge and creating the scablands of eastern Washington. The Willamette valley of western Oregon was also generated by these floods.",
"You can still see the ancient shorelines of the lakes, high up on the mountain sides, in the town of Missoula, MT. And those pretty waterfalls that flow into the Columbia Gorge were once feeder streams, until the floods tore out the bottom of the Columbia River, reducing its altitude by hundreds of feet."
] |
[
"Wow! Amazing info, thank you so much."
] |
[
"Could wireless electricity enable us to build solar farms in space and then let us use the power back on earth?"
] |
[
false
] | null |
[
"Yes",
". Actual wireless power tends to degrade quickly but we could set up solar farms in space and use things like microwave transmitters to send the power to special receiving stations and have them sent out via more traditional power lines from there."
] |
[
"People have proposed ways to transmit power from space to the ground, such as focused microwave beams. But any such scheme likely has some major concerns associated with it. For example, if you have a powerful microwave beam, how do you ensure that it is impossible for it to go \"off target\" and harm people/livestock/landscape/etc. ? How do you make certain that punching little holes in the ionosphere won't cause some negative consequences? How do you quickly repair it in the case of a failure? How do you make certain that it couldn't deliberately be turned into a weapon? How do you distribute the resulting energy in a way that the power loss isn't so great as to make the whole scheme inefficient? ",
"I believe that none of these challenges are insurmountable, but they aren't necessarily trivial either. "
] |
[
"Interestingly enough, the Japanese company ",
"Luna Ring",
" has proposed an ambitious plan to do exactly this."
] |
[
"10th Grade Chemistry Teacher needs help, actually, questions."
] |
[
false
] |
[deleted]
|
[
"This sat in the spam filter all night. I can release it, but since it is 9 hours old, no one will see it. You should repost it, and message the moderators if you don't see it in the \"new\" queue."
] |
[
"Just a suggestion/thought (I'm a Spanish teacher, so my topic-specific usefulness to your question is limited, but...):",
"\"Is biodiesel a promising new energy source?\" is a closed-ended question. They will find sources that say \"yes\" and stop researching."
] |
[
"15-16 year old kids are very interested in science that is bordering science fiction, but still somewhat scientific. I know I was - I went into materials science because I thought nanotechnology = nanobots + molecular manufacturing. Turns out it's not, but it's just as cool, you just need to know a little more math to appreciate it. ",
"Some things that can be very interesting:",
"Why was the 19XX Nobel Prize in Phys/Chem/Med awarded? How did it transform its field?",
"What is an interesting technology that could happen in the next 10 years and what scientific/engineering developments are necessary to make it happen? (Star wars holograms, space elevator, AI, anthropomorphic robots)",
"Then there are some interesting science 'paradoxes' you can try:",
"etc. ",
"There are a lot of a questions that are very interesting and require a lot of understanding of very broad scientific topics to be able to appreciate, but I am biased with my choices. I would think about what you've heard that really excited YOU when you heard it, and devise questions around that to help students explore those topics. "
] |
[
"Does Photon Redshift (and blueshift) violate conservation of Energy?"
] |
[
false
] |
So, according to the laws of physics, energy cannot be created or destroyed, meaning the amount of energy stays constant, however, Photon redshift has the photon losing energy, but wouldn’t that violate energy conservation? Because what exactly would the photon be losing energy to? If there’s nothing for the energy to be transfered to, the only way for the photon to lose energy would be to destroy energy, which according to the laws of physics, isn’t allowed, but since the photon is losing energy and it’s not being transfer, is energy being destroyed as the photon redshifts?
|
[
"This is a violation of the traditional way conservation of energy is explained, which is not really a problem with the conservation law, but a problem with the more simplified version we learn (which works for pretty much any reasonable situation we're in).",
"The easiest way I know to discuss this is by looking at ",
"Noether's Theorem",
". This theorem states that for every symmetry there is an associated conservation law. What does that mean? Take for instance transnational symmetry. That means if I do an experiment ",
" and you do an experiment ",
", all else being equal (e.g. in the same gravity and EM field) our experiment will yield the same result. From the fact that translation symmetry exists (translation just meaning I can move my experiment from one place to another) you can prove conservation of momentum (the proof is well beyond the scope of this write-up). ",
"Now, energy on the other hand, is paired up with time symmetry. That means, if I do an experiment ",
" and you do the same experiment ",
", all else being equal we should get the same result. And for all practical applications, this is true. But, once you start dealing with applications which span local galaxy superclusters (aka- the scale where the expansion of the universe is happening. Our solar system isn't \"expanding\", it is gravitationally bound. But galaxies not in our super cluster are expanding away from us) suddenly time symmetry is no longer true. This is because the place in which you are doing the experiment has changed. ",
"But this isn't really a fault of conservation of energy, because the conservation law only applies in situations where time symmetry applies. It's just normally we don't mention the full law (sort of like how when teaching momentum, we don't first teach the entire relativistic definition)."
] |
[
"If it's due to expansion of the universe: Yes.",
"If it's due to motion in a gravitational potential: No. The difference comes from the energy in the gravitational field.",
"If it's due to you changing your reference frame: No. Different reference frames can assign different energies to the same objects."
] |
[
"what exactly would the photon be losing energy to?",
"The gravitational field.",
"Gravitational potential energy (and, to a lesser extent, kinetic energy as well) is a tricky business in arbitrary spacetimes (no distance parallelism, no covariant expression for gravitational energy density, potential lack of time-like Killing vector fields, Noether's first vs. second theorem, ...).",
"While the answer above can be argued to be correct 'morally', due to the subleties involved, one can also reject that perspective and instead abandon energy conservation in the general case of evolving spacetimes."
] |
[
"Do microchips implanted in the body require energy to function? Do they absorb it from the bloodstream?"
] |
[
false
] |
[deleted]
|
[
"Yes they require energy, no they don’t absorb it through the blood stream. Blood supplies mostly oxygen to the different systems of the body but not directly energy. Oxygen is a key component in the chemical processes our body uses to break down storage molecules in order to create useful molecules that release energy into our various systems. Implanted devices require separate power sources which is what often requires the device to be serviced after a specific period of time"
] |
[
"They either require their own power or don't need power at all. An example of something that might not need power would be something like a Radio Frequency IDentification (RFID). The tiny bit of information it's carrying is read by providing energy to it via a reader and reading the response. So it is only \"powered\" by the reader itself.",
"It's worth point out that self-powering biological chips ARE a subject of current research. Typical ideas are based around things like thermoelectric, piezoelectric or osmotic/ion gradient power sources."
] |
[
"To go deeper into this, an RFID chip is basically just a specifically designed mirror, reading an RFID chip with the reading device works not that different from how SONAR works.",
"The device emites a specific pulse of small, weak, EMR waves at the RFID chip, which has a small antenna inside of it. The chip receives the waves, they get changed in shape a bit, and reflected back.",
"The reflection back is decoded and, the way it changed is mathematically turned into data."
] |
[
"How is Hawking Radiation possible if nothing \"escapes\" a black hole?"
] |
[
false
] | null |
[
"Hawking radiation originates from outside the horizon."
] |
[
"Ok, thats good to know. I still dont get how it could exist. Unless i misunderstand its from the black hole emitting particles, correct?"
] |
[
"It's a complicated effect. But to summarize it as briefly as possible, an observer far away from the black hole sees the spacetime just outside the horizon as having a small but nonzero temperature. And anything at nonzero temperature radiates thermally.",
"So particles are created just outside the horizon and radiated away."
] |
[
"How did the first humans with 46 chromosomes breed?"
] |
[
false
] |
[deleted]
|
[
"I asked a ",
"very similar question",
" about a year ago, ",
"r/askscience",
" was very helpful. ",
"I'm not going to try and explain it all now as pretty much all the info is in the link, but in essence you just have to accept the epic scale of evolution. Though the probability of such an event seems miniscule, given the time span of evolution the probability does go up. And even now there are people occasionally born with ",
"44 chromosomes",
" that are doing just fine "
] |
[
"The TL;Dr of the link is basically that how the DNA is arranged in chromosomes doesn't matter so much, what matters is that the offspring gets a complete set of DNA from the parent. A merged or split chromosome makes it easier to get a complete set of DNA, but it is not required. So a person with a fused chromosome wouldn't have to find a partner with a fused chromosome, she and her offspring would just have to get lucky with the chromosome shuffle until her fused chromosome dominates the population."
] |
[
"I would answer this on my own but PZ Myers has done such a great job I don't think I could improve on it. Here is the ",
"link",
" explaining how the change in chromosome number could happen and still allow interbreeding that could eventually lead to speciation."
] |
[
"How hard is it to create high speed rail systems?"
] |
[
false
] |
With creating loads and loads of highspeed rail systems very fast (2-3 years each) I was wondering how hard is it to make these things? They don't seem to have a problem with making them. Why can't we have these in the US and Canada or even spanning the EU from end to end? How much does a highspeed rail system cost /km compared to a normal one?
|
[
"Unfortunately I can't answer your question, but last night as I was falling asleep on a high speed train in China, I was wondering exactly the same thing. I would imagine that it's not the initial investment of capital that is the barrier here, it's simply that Americans are more attached to their own cars and the highway system than Chinese people are. This is compounded with the fact that in a lot of US cities the public transit system is somewhat lacking, so that once you get to your destination city you would still need to rent a car. Again this is all just my own speculation, but I think it is lack of demand that is the barrier here."
] |
[
"In the UK at least the problem is investment and actually putting down the network. Purchasing land will be ridiculously expensive so existing track will have to be upgraded. Of course, no one wants such a large disruption to service so it isn't going to happen very fast. In china it's quite possible to bulldoze through people's houses as we saw with the Olympic stadium.",
"Rail has a lot of problems with profitability in this country, and it's not helped by the strange private-public hybrid they've got going on with Network Rail."
] |
[
"I've read that it's something like 20 million $/km to do it in North America."
] |
[
"If scientists eventually observed proton decay, how would this affect the Standard Model? Would evidence of proton decay force us to change any current theories?"
] |
[
false
] | null |
[
"The Standard Model does not allow for proton decay, so it would definitely force us to change the current theory. That said, we already have set a very high lower limit on the lifetime of the proton, and I don't know if there are any models being discussed currently that allow for proton decay but with a longer lifetime than that."
] |
[
"Quite a few so-called GUTs -- Grand Unified Theories -- predict proton decay. The Standard Model on the other hand does not allow it. ",
"If proton decay is observed we require to extend the Standard Model such that it includes the process. This has happened before with processes such as neutrino oscillations, electroweak unification and now very likely the Higgs effect.",
"One way in which proton decay can be understood, while still having the Standard Model describing be approximately valid, is through use of the before mentioned GUTs. What GUTs usually do is bundle all the different particles and forces in the standard model together, such that they fall under the same umbrella. To be more specific, the Standard Model consists of three fundamental forces (electromagnetic, weak nuclear and strong nuclear). GUT theories unifies these forces into a single \"grand force\" which on low-energy scales decomposes into the forces that we know. This is known as symmetry breaking. It usually requires the introduction of new symmetries, such as supersymmetry and larger gauge groups. ",
"The grand force very typically predicts a number of new particles (I don't know of any that don't). Inclusion of new particles also means some particles which appear to be stable (like protons) can decay into these new particles, or alternatively use these particles to decay into particles that we know; a process which is normally forbidden by the Standard Model. These would then be the mechanisms behind proton decay. ",
"An example would be a proton decaying into a positron and a pi-0 meson via some \"new\" force. The force only manifests itself in the real world through the three forces that we know. ",
"Measurement of proton decay and the corresponding lifetime would rule out a large number of these GUT proposals, as some cannot be correct if proton decay does not occur or if the lifetime is too far off. Keep in mind, however, that any GUT that is proposed ",
" to include the Standard Model in the low-energy limit. That is the biggest criteria we have. ",
"Eventually we would hopefully be able to rule out most GUTs and obtain a single unified theory. This would then replace the Standard Model as the theory of particle physics. But this GUT theory might not be easy to tame and could be difficult to work with, and so the Standard Model would still be used as a very successful approximation to particle physics."
] |
[
"I don't know if there are any models being discussed currently that allow for proton decay but with a longer lifetime than that.",
"Believe it or not, there are! :) Many ",
"grand unified theories",
" allow ",
"protons to decay",
" (by allowing violations of baryon number symmetry), and many of them predict a very long but finite average lifetime for the proton, generally longer than 10",
". At least some (maybe most or almost all?) also allow the neutron to decay on similar timescales via similar processes.",
"The current experimental for the lower bound of proton decay (if it exists) is at least 10",
" years, so to be consistent with observation, any GUT must predict a lifetime for the proton of at least that long."
] |
[
"Is there a point of no return associated with dehydration while still being alive?"
] |
[
false
] |
Can you be so dehydrated, while still being alive that no amount of liquid however administered will save the person from death?
|
[
"According to ",
"this",
", there is a point at which ",
" water will not save you from death, but apparently you can still survive if you are re-hydrated intravenously.",
"So, no. You are either dead, or can be re-hydrated intravenously. There doesn't seem to be an in-between. And even if there were, you'd probably be dead pretty quick anyway. Like, within seconds."
] |
[
"Any idea why you cannot be hydrated orally?"
] |
[
"Yes, it's possible to be alive, very ill, but so dehydrated that it causes fatal kidney damage. There was a recent case where a women survived a car crash but was not found for 3 days (her boyfriend was killed in the crash). She died of kidney failure 3 days after she was found.",
"Ms Bell, who was a mother, had been in a medically-induced coma at the Queen Elizabeth University Hospital in Glasgow having suffered kidney damage from dehydration from lying in the wreckage for so long. She died at about 06:50 on Sunday.",
"http://www.bbc.com/news/uk-scotland-33497318",
"Dehydration - complications",
"Kidney failure. This potentially life-threatening problem occurs when your kidneys are no longer able to remove excess fluids and waste from your blood.",
"http://www.mayoclinic.org/diseases-conditions/dehydration/basics/complications/con-20030056"
] |
[
"If Crude oil is made from decaying plant and animal matter, wouldn't the fact that the moon Titan has large crude oil deposits suggests that life at some point existed on this planet?"
] |
[
false
] |
[deleted]
|
[
"Titan doesn't have crude oil, at least not in the way you'd picture it. On Earth, much of our oil is resultant of the geological deposition of biomass in sea beds. This process produced a hydrocarbon mixture we call oil. However, there are many kinds of hydrocarbons, it's not a single molecule.",
"On Titan, you have enormous quantities of natural gas, but since it's so cold on Titan (-180 Celsius!), the methane (still gaseous too), ethane and propane have condensed into their liquid states. Here's a picture of ",
"lakes on Titan.",
" The hydrocarbons on Titan are hypothosized to have formed via inorganic processes. This isn't too far fetched because there are plenty of inorganic channels which produce hydrocarbons from sunlight without the need for life."
] |
[
"Excellent answer. I just wanted to add that there are also some chemical inorganic processes which produce methane ",
" sunlight as well. The serpentinization of olivine for instance (Olivine + water + carbonic acid → serpentine + magnetite + methane).",
"Such a process could act throughout large volumes of planetary crust and might account for largish amounts of short chained hydrocarbons.",
"Anyways, it would be quite straightforward to tell biogenic hydrocarbons from abiogenic ones. Those resulting from biological processes show strong isotopic fractionation of carbon, while the abiogenic one do not."
] |
[
"No oxygen, so without an oxidant, you wouldn't get the burning world your heart desired. The hydrocarbons in Titan's environment might as well be as inert and boring as water."
] |
[
"Is there good reason that the many worlds interpretation of quantum mechanics is so popular?"
] |
[
false
] |
The underlying issue I’m having is that science is terrific at not giving anything value without evidence, but I hear about the many worlds interpretation of quantum mechanics all the time. So I’m wondering first, is there some conceivable method of testing this someday that I’m not aware of? I get that it’s only an interpretation, and could explain what we see in a way, but I worry that this interpretation is just a lot of fun and that’s what’s making it popular. Second, let’s assume we could devise some experiment, and it turned out that everything that could happen indeed does, what could we do with this knowledge? Or maybe that’s not even possible to speculate about.
|
[
"MWI is popular for a few reasons.",
"It is the most direct and simple reading of quantum theory. Many worlds are just the inevitable consequence of the basic equations of quantum mechanics. All other interpretations should then be understood as efforts to get rid of all but one world. So, unless MWI is unworkable, making any of these moves is unnecessary extravagance.",
"To paraphrase Churchill, many worlds is the worst interpretation, except for all the others. By which I mean that among the major interpretations, the problems one can raise against MWI are the least severe. The big issue in MWI is the nature of probability, but there are strong defenses of this from David Wallace, Lev Vaidman, Carroll/Sebens, etc. Meanwhile the subjective collapse interpretations (Copenhagen/QBism) have profound internal inconsistencies where different observers cannot even agree about the contents/dimension of the Hilbert space (see Wigner's friend). Objective collapse (GRW) is not even technically an interpretation as much as a whole new, more complicated theory. Hidden variables (Bohmian mechanics) is only workable for simple nonrelativistic problems and doesn't allow you to reproduce the full content of modern QFT. ",
"MWI applies generically and easily to any sort of quantum theory (particle mechanics, fields, qubits, whatever) and can be applied to early universe cosmology (where there are no classical observers). The other options will fail at one or both of these tasks. "
] |
[
"CI is probably still the most popular in general because of how it taken for granted in many textbooks and courses, but it is relatively less popular among folks who have done a deeper dive into philosophy/foundations of QM."
] |
[
"Would you say that MWI is the most popular interpretation of quantum mechanics these days? If so, when did it become the predominant interpretation? My understanding (mostly from reading Wikipedia) is that the Copenhagan interpretation was originally the predominant interpretation, but I don't know when that changed."
] |
[
"Are lighter eyes more sensitive to light?"
] |
[
false
] | null |
[
"You're approximately right, but get a few details wrong:",
"Different shades of blue, and in irises with a limited amount of melanin, different shades of grey, green and hazel, are deter- mined by the thickness and density of the iris itself and the extent of accumulation of white collagen fibres, as well as patches of tissue loss in the anterior border layer and stroma.",
"As for the propensity for lighter eyed folks to have eye problems later in life: I too have read this, but I have yet to confirm if it's due to the iris itself or if the iris is poorly pigmented for some reason that also predisposes to degenerative processes in the eye.",
"EDIT since this comment is getting more views than my actual answer, ",
"I will link it here",
". I answer OP's question in full with research to back it up. Check it out and learn about eye color, contrast, and acuity. "
] |
[
"You're approximately right, but get a few details wrong:",
"Different shades of blue, and in irises with a limited amount of melanin, different shades of grey, green and hazel, are deter- mined by the thickness and density of the iris itself and the extent of accumulation of white collagen fibres, as well as patches of tissue loss in the anterior border layer and stroma.",
"As for the propensity for lighter eyed folks to have eye problems later in life: I too have read this, but I have yet to confirm if it's due to the iris itself or if the iris is poorly pigmented for some reason that also predisposes to degenerative processes in the eye.",
"EDIT since this comment is getting more views than my actual answer, ",
"I will link it here",
". I answer OP's question in full with research to back it up. Check it out and learn about eye color, contrast, and acuity. "
] |
[
"Waaay too many anecdotal and unsourced things being said here. Let's clear things up:",
"It isn't that you're more ",
" per se. It's more complicated than that. The experimental evidence for what I'm going to exlplain is largely from this paper: Graefes Arch Clin Exp Ophthalmol. 2013 Jan;251(1):195-202. doi: 10.1007/s00417-012-2006-8. Epub 2012 Apr 12.",
"Basically, people with very light eyes (not just blue, but ",
" blue) have more intraocular straylight (IOSL). ",
"This image",
" shows you what that means: brighter light from point A in the real world scatters before hitting the retina, causing the image of dark point B to be less dark. This is often mainfested as difficulty seeing faintly illuminated things at night when bright headlights are off center from the field of view. It also means that more photoreceptors are being hit by a light source than \"should\" be. The result is not that bright things are brighter (i.e., the eye is simply more sensitive) but rather that dark things are not as dark, and the brain processes this as overall increased brightness in the scene.",
"Back to the data: only the fairest eyed of those tested had increased IOSL. Once you get past the lightest of eyes, the differences don't really matter. Brown and hazel and \"blue\" eyes had no statistically significant difference.",
"Next, the authors measured contrast sensitivity. With more IOSL, contrast sensitivity should go down, right? Well... kinda. It varied a lot from person to person. Why? Because contrast is not just sensitivity, but also corneal and lens effects. Contrast is the ability to resolve differences in brightness ",
" space. It's hard to separate the two without manipulating the physical architecture of the eye. Age comes into play here, and people vary so much that it's hard to separate out the isolated effect. From the paper:",
"In our present study, we showed that iris color is also associated significantly with differences in visual functions such as IOSL or CS. Persons with light-blue-colored eyes have significant higher IOSL values than persons with darker-colored irises (blue-grey, green-hazel, and brown). Light-blue-colored eyes had 0.07 to 0.08 log units higher IOSL values, which is an increase by a factor of 1.2. In regard to CS, subjects with light-blue iris color showed also lower CS values than subjects with other iris color, but this difference was only statistically significant for persons aged 40–59 and 60–80 years with light-blue and brown iris color. However, even if statistically significant, we do not think that the small difference in regard to CS is clinically important.",
"They go on to say why:",
"We suppose that the main causes for these findings are the higher translucency of light pigmented irises, the higher fundus reflectance due to lower fundus pigmentation and, to a smaller part, light passing the pigmented ocular wall, which all result in an increase of intraocular light scattering. This is supported by Ijspeert and van den Berg who looked at the causal relationship between iris color and IOSL in previous studies and found that the pigmentation dependence is caused by different transmis- sion of light through the iris and by variations in transmission of light through the ocular wall.",
"And here's your question answered:",
"Since light-blue-colored eyes showed a mean IOSL in- crease by a factor of 1.2 (0.07 – 0.08 log units) compared to the other groups, we think that this difference is clinically important and that subjects with light-blue-colored iris may report more complaints from increased straylight than other subjects of the same age. ",
" If concomitant retinal pathologies exist as macular degeneration, retinal dystrophy or glaucoma, these problems are much worsened, calling for extra attention on straylight in such patients.",
"(emphasis added)",
"EDIT: one last thing: They found no difference in visual acuity overall. Why? There's a weak association between IOSL and CS, and a weak association between CS and acuity. Two weak associations in a chain basically make no meaningful association at all.",
"EDIT 2: Just to add an anecdote as to why I have read about this so much- I have ",
" light eyes despite having olive skin of a more sunny heritage. So do many people in my family, and we all have a lot of difficulty driving for long periods at night. Once I became a doctor, my family kept asking me about this stuff. I finally decided to learn about it properly. Basically, I feel your pain."
] |
[
"Possibility of large deepsea monsters"
] |
[
false
] |
I remember reading that we have explored less then 10% of the sea and it gives me chills to think about what may lurk in the icy depths of the sea, especially concerning giant monsters like the colossal squid. However, due to the very high pressure in these depths would it be possible for such things to exist or would all the creatures down there be minuscule in size?
|
[
"While the first live giant and colossal squids were only sighted in recent years, we've known about their existence for a long time. They're beaks have been found throughout the ocean, inside whale stomachs, and their carcasses have been hauled out of the sea and found on the shorelines.",
"However, we also know from observation that a number of bizarre and monstrous looking creatures exist at the crushing depths in the abyssal zone. We don't normally see them because of their inability to survive at depths even a human would consider deep. In addition to that, they're carcass is usually devoured when they expire because of the complete and utter lack of food at such deep depths, meaning anything easily acquired disappears quickly.",
"Finally, as was mentioned in a separate response, the biggest factor in determining the size of an animal is its ability to acquire food. As we've seen with blue whales, you don't have to eat big food to be a big animal, but you do have to eat a lot of it or have a significantly lower metabolic rate. This is important because, as I've stated, there is a harsh lack of food near the bottom oceanic layers. The floor is actually more heavily populated than the layers between it and the surface, but the odds of a creature as massive as a colossal squid or larger existing at those depths is unlikely. The average depth of the ocean is about 3700 meters, while adult colossal squids are only known to exist at depths of 2200 meters, at most.",
"At odds to this is the existence of \"",
"Deep-sea gigantism",
"\", which provides a number of reasons behind why these deep dwelling creatures are so large. It's worth consideration, but is limited in its existing examples.",
"To answer your actual question, it's a mixed bag between both the big and the small. Just like life near the surface, some if it is amazingly large and others of it are quite tiny. Pressure doesn't have a significant role on the maximum allowed size of an organism, as we've seen with a number of whales diving to crushing depths and returning again to the surface with ease.",
"There are no doubt more interesting creatures, both big and small, still waiting to be discovered across the entirety of the ocean, but for right now we can only go on what we've seen."
] |
[
"I've read that there have been squid beaks discovered in the stomachs of sperm whales that are much bigger than those found on actual giant and colossal squids."
] |
[
"Source:",
"\"The beak is considerably smaller than some found in the stomachs of sperm whales, suggesting there are Colossal Squid much larger than this one.\"",
"\n",
"http://en.wikipedia.org/wiki/Colossal_Squid#Defrosting_and_dissection.2C_April-May_2008"
] |
[
"P-47 Thunderbolt Propellor Damage. What would this do in flight, if anything?"
] |
[
false
] |
Hey , I saw this picture on another sub and was curious what effect this would have in flight, if anything at all. Also let's say, hypothetically, that if he could eject the damaged propellor blade, what effect would that have in flight also? Thanks! Here's the Picture:
|
[
"Purposefully jettisoning a prop blade in flight will lead to an uncommanded jettisoning of the rest of the prop blades, followed by a catastrophic and likely explosive failure of the rest of the engine due to a massive prop balance failure.",
"The blades will also take out whatever is in their path; control cables, fuel tanks, pilots, control surfaces.",
"Also, a pilot isn't going to be able to troubleshoot a blade failure down to a single blade unless he first shuts off the engine and feathers the prop so that it sits static in the air stream. Even then, it's 50/50 that the blade damage will be in his field of sight.",
"Actually, less because out of the 8 blade surfaces, he can only see 3 even in optimal circumstances.",
"So nothing good, basically. "
] |
[
"The P-47 was one of the largest 4-stroke single engine planes ever. They couldn't feather that engine during flight and land with another. They likely flew back with it at minimal power. ",
"Damage of that sort will cause less pull from that blade. That's not the problem. The offcenter distribution of rotational inertia could destroy the bearings in the motor. It didn't happen and likely they tested the bearings with missing blades at full power before they built the thing."
] |
[
"Friend of mine actually lost a propeller blade in flight on his Bonanza at 6000. The other two blades flew off immediately due to the inbalance. Because there was no drag of air on the blades (it was a lot like throwing your car in neutral while holding your foot to the floor), the engine went past redline faster than the prop governor could hold it, and the engine blew. That whole process took about a half second.",
"Had the other blades not flew off, the inbalance likely would have ripped the engine from the motor mounts, possibly causing the aircraft to crash, due to the sensitivity of weight and balance and the telegraphic shockwaves the vibration would send down the airframe. ",
"The pilot in this picture got lucky. I'm sure the propeller was unbalanced. However, so long as the mass of the damaged blade remains close to equal as the other blades, as well as the distribution of that mass, then you'd probably be ok (for a short time anyway)."
] |
[
"What are the current and historical uses for desert sand?"
] |
[
false
] |
All I can find is glass. I imagine it was used historically for bricks as well, though Beach sand is better for construction and other products. I can only find article after article talking about how it "could" be used for concrete after this or that new production technique, but I'm not invested in potential uses, I'm interested in current and historical. There's a ton of it, and we've been around it for thousands of years. I have to believe there are some other good uses for it
|
[
"That much I know. But any google searches are populated immediately by dozens of pages talking about some new 'miracle procedure' that will make desert sand good for concrete. I don't believe it, i don't think it's going to happen. But I am curious if there have been historical uses for it."
] |
[
"Desert sand is the product of aeolian erosion, meaning it is created by the wind moving and colliding sand particles. \nThis sand has small, homogeneously sized particles, that are well rounded. All of these things are bad for concrete, where you want sand particles with structures that \"lock in\" to each other to create more strength. ",
"So basicall, with current technology, desert sand is pretty useless for construction. More information here: ",
"https://youtu.be/t5fv9h2scME"
] |
[
"The ",
"Wikipedia article on sand",
" lists several dozen different uses, including current and historical ones. Some of them would have similar issues as with concrete, but many others, for example filling sandbags, would not. Most of the applications have links to articles that discuss those applications in more detail. To take the same example again, the article on",
"sandbags",
" discusses about eight different applications for sandbags.",
"However, the quantity of sand needed for most of these other applications is quite small compared to amount used for concrete. And many of the uses are predicated on the assumption that sand is inexpensive, and it wouldn't be worth shipping a long distance."
] |
[
"What type of clouds are these (picture link inside) and why do they form this way?"
] |
[
false
] |
We just had a small storm pass over us here in Dayton, Ohio and I've never seen anything like it. I've seen the "egg carton" type clouds, but these I can't describe vaguely enough to search using Google. Anyone care to explain?
|
[
"It's a ",
"\"new\" cloud type (i.e. one recently categorized, although informally)",
"But the cloud fan has proposed a \"formal,\" Latin name: Undulatus asperatus--roughly, \"a very turbulent, violent, chaotic form of undulation"
] |
[
"They haven't in 60 years. :)"
] |
[
"I didn't know they were adding cloud classifications. Elementary school science be damned"
] |
[
"If there are exactly 2 animals left of a species and they are to repopulate, how do successive generations not turn up with all sort of genetic diseases from inbreeding?"
] |
[
false
] |
I would guess that some gross shit gotta go down like father/dtr, mother/son, bro/sis, 1st cousin etc for the population to rise. How the hell you not get a bunch of TIMMAYS out of this?
|
[
"Genetic diseases from inbreeding aren't a guarantee, they're just slightly more likely. Inbreeding reduces genetic variation and also brings to light more recessive genetic traits, some of them harmful. Successive generations will be harmed by this but if they can survive long enough to generate a large enough population then natural selection can cull a lot of the more harmful traits and work back towards a more healthy population.",
"Cheetahs, for example, are believed to have passed through a genetic bottleneck fairly recently."
] |
[
"I doubt he's going to get the kind of answer he's looking for (with an emphasis on evolution/genetics) from another subreddit.",
"I know many scientists see religion and science to be incompatible, but many others would argue that they can coexist. Without getting into a debate on religion, OP's question seems to be an interesting enough hypothetical, and \"it'll never happen\" is not the kind of answer I would expect from askscience."
] |
[
"I don't think you'll ever find any examples of an entire lineage arising from just two animals, much to noah's dismay, but such a thing could feasibly be possible if the two animals have no detrimental genetic traits. ",
"The only problem, aside from societal stigma, with inbreeding is that it magnifies recessive traits by increasing the likelihood of them being expressed. But inbreeding occurs quite often in the animal worlds with little effect. At some point though, some X generations, where I don't know what X is, you'd want to breed as far away from the line as possible (so 'cousins Y times removed). There's some pretty screwed up dog lineages out there due to heavy inbreeding with no regards to genetic well being, but there's some good ones too. ",
"So the possibility lies entirely with the genetic health of the 'founders' of that species. ",
"But again there's no data to back this up. Even with dogs it's all just isolation, not really the 'last of the two' scenario or anything. It may be that this has already happened, was non-viable, and we don't see it because of that. But again we don't know that that has happened so, who knows?",
"Fun Fact: Due to careless breeding and poor genetics, the English Bulldog is no longer capable of giving birth naturally. You have to do C-sections. There's also a chicken breed (doublebreasted leghorn or something like that) that, through over selection for breast size, is no longer capable of naturally breeding on their own. The male cannot fertilize the female and the line is propagated solely through AI. Not the most popular breed since it's expensive. ",
"So that's what poor genetic monitoring and variability gives you eventually. "
] |
[
"Can a large enough static charge move an object?"
] |
[
false
] |
[deleted]
|
[
"Can a large enough static charge move an object?",
"Yes; this is how the ",
"mass-to-charge ratio",
" of the electron was determined in the famous ",
"Millikan oil drop experiment",
". If you want to try this for yourself, try putting small paper shreds on a table, then take a balloon and rub it against your hair. The excess charge on the balloon will move the paper around.",
"As for the case of your watch, it probably fell off the stand because of vibration. There are two arguments for this: (1) the watch building up static charge is unlikely because the exterior is metal and because Apple would likely have designed against this, and (2) assuming a 125g watch is displaced 1mm above the charging pad, it would need a charge of ",
"about 11nC",
"+1+mm+mm)), which is larger than typical charges exchanged in static shocks."
] |
[
"Can a big static charge move an object? Yes definitely! It happens all the time, and you can test it ",
"yourself pretty easily",
". But can it move your smart watch? Probably not.",
"Electrostatic forces \"scale\" proportional to the surface area of the object. That means that if you have two similar objects, but one has twice as much surface area, you can generate twice the electrostatic force on that object compared with the similar one. ",
"But the mass of objects scales with volume. In general, if object 1 is twice as big as object 2, it might have 4 times the surface area, but 8 times the volume (and 8 times the mass). ",
"So the ",
" of electrostatic force to the mass of an object gets smaller as an object gets bigger. And that means big objects, like your apple watch, are not easily moved by electrostatic forces. ",
"Things that we can move easily by electrostatic forces tend to be very flat and very thing, or very very small. Like hair, or bits of ",
"plastic",
". ",
"Static forces are useful when we're making very tiny machines, like the ",
"tiny mirrors used in digital projectors",
". ",
"But to move a large object like a watch you would need an enormous amount of charge, more than you could accidentally generate without meaning too. ",
"A lot of modern electronics have very smooth surfaces, maybe your watch is just sliding very slowly across your smooth desk? "
] |
[
"U.S. Patent 633,829 from 1899 describes a static electric machine. Not only does it exist, it has been around for a long time.",
"The rule of thumb is that for a air gap of greater than 1 mm, electromagnetic motors are more effective. For sizes less than 1 mm, electrostatic motors are more effective. Electrostatic motors and other motion inducing devices have a dominate place in motion for MEMS and NEMS due to their small size. For example a typical MEMS gyroscope uses a vibrating structure in order to measure the angular velocity. This vibration is induced with electrostatic force."
] |
[
"How is it possible that wifi routers have such bad signals"
] |
[
false
] |
A serious question, why is it that, even though a good connection to satellites across miles and miles of space can be established, if I moved my laptop about a couple walls closer in my house to my internet router I'd get much better signal?
|
[
"Another aspect of this is that consumer-grade wifi equipment is built to be just \"good enough\" while staying within very strict and severe cost constraints, while satellite systems make reliability of signal transmission a very high priority, with consequent added cost. "
] |
[
"Different power ratings and frequencies. Longer wavelengths travel further at lower power outputs."
] |
[
"The use of parabolic antennas for satellite transmissions means you can get away with weaker signals, as well."
] |
[
"What property of food determines the length in which something can safely be left out of the food temperature safety zone?"
] |
[
false
] | null |
[
"I believe it's the type of bacteria that are normally found in it at low numbers, and their speed of replication when temperatures are right. Some bacteria produce nasty stuff and if you let them live in meat for a while they can produce enough toxins to be a problem even after cooking. ",
"Different foods host different bacteria and let them grow at different speeds. ",
""
] |
[
"A wet, neutral pH, and sugary environment is best for growing bacteria, so foods like melons are a bigger risk than dried crackers or a glass of pure water. These are generalizations, but useful ones. Bacteria like E. coli and salmonella prefer uncooked meat, and diseases like norovirus and staph can be transferred from sick people via foods without necessarily thriving on the food itself. ",
"Natural barriers like skins of fruits are very effective at keeping germs out, so I would eat a peach that had been sitting out for days, but not a sliced peach. ",
"https://www.cdc.gov/foodsafety/symptoms.html#symptoms"
] |
[
"Water activity is one important factor:",
"https://en.wikipedia.org/wiki/Water_activity",
"Substances like honey, dried fruit or grains, and cured meat have lower water activity than something like fresh meat or fresh fruit which can spoil more easily.",
"At least that is my laymen's understanding. "
] |
[
"Is there a reserve of animal DNA in case of exctinction?"
] |
[
false
] |
I know there are reserves for diseases and plant seeds in case we need to repopulate certain species. Is there something similar for the DNA of endangered animals in case we need to clone an animal to revive it from extinction?
|
[
"I have made a conscious decision to never doubt King George can do something.",
"I would also add that we save seeds from all the plants we can get our hands on. This has a very practical benefit for modern breeding a genetic manipulation as some plants possess traits (like disease resistance) that are very useful to incorporate into modern crops."
] |
[
"I have made a conscious decision to never doubt King George can do something.",
"I would also add that we save seeds from all the plants we can get our hands on. This has a very practical benefit for modern breeding a genetic manipulation as some plants possess traits (like disease resistance) that are very useful to incorporate into modern crops."
] |
[
"Thank you for the detailed response! Thats fascinating that theyre attempting to revive a woolly mammoth. I wonder if it will be a wierd hybrid of the asian elephant and mammoth like a mule or liger."
] |
[
"Are there any limits to time dilation?"
] |
[
false
] |
Let's say that there was a spacecraft that had practically unlimited amounts of delta-v, high thrust, decades of supplies, radiation shielding, and protection against any particles that it might hit. Its crew decides to go out and keep burning until they're going as close to light speed as possible. Assuming that they never have to worry about fuel or anything else, then how extreme could the time dilation end up getting? Could it even get to the point where they're able to experience the heat death of the universe within their lifetimes? Or is there something that limits time dilation to a certain rate?
|
[
"There is no limit. As your velocity approaches c, gamma (the time dilation factor) approaches infinity.",
"E: ",
"Like so"
] |
[
"So if one were to answer OP's question as basically, \"given enough energy and speed, time dilation could get so large that the heat death of the Universe would happen in a few minutes of flight in this spacecraft\", then one would not be incorrect?"
] |
[
"Well yeah, I know that you can never actually get to c, but I'm talking about just getting close enough to experience significant amounts of time dilation."
] |
[
"What happens to the last remaining atom in a lump of radioactive material?At which point does it disintegrate?"
] |
[
false
] |
(from an article in the Journal of Heuristics)
|
[
"Half life is just a a way to represent the probability of an atom to decay. No matter how many or how few atoms you have in a system, each atom has a 50% chance of decaying in one half life. These events are all independent, so one atom doesn't change based on the other atoms in the system. However, since there are around 10",
" atoms in a common object, statistically very close to half of the nuclei will decay with one half-life. ",
"When you are only left with one atom, it has a 50% of decaying in one halflife, the exact same as it did when there were many atoms. it's possible for it to never decay, but each half life passed reduces those odds 50%. ",
"So for radioactive decay, 'singleness' or 'manyness' is irrelevant, there is no difference. "
] |
[
"The atom will decay with the same probability distribution in timing as the others, starting now...",
"Longer version:\nRadioactive decay is (to close approximation) a Poisson process. What that means is that each atom has the same chance to decay in a given period. The half life of an element is the length of time for which that probability is 50%, ergo approximately half of a given sample will have decayed by then. However, the probability of any particular atom decaying over any future interval is not effected by how long it's waited up till now. That's why of the remaining 50%, approximately half will decay in the next half life, leaving about 25%. If a particular atom has a half life of 1 year, and has gone 100,000,000,000 years without decaying, the chance of it decaying in the next year is still exactly 50%.",
"As you get down to a countable number of atoms, the statistics becomes much more probabilistic, and much less about large averages. For two atoms, you can calculate seperate probabilities of still having 2, 1, or 0 particles at any given future time. They are always probabilities though. Indeed, there is always a non-zero probability of any one, or even all the atoms remaining in one state or the other. As the number and time increase, this probability quickly shrinks to become negligible.",
"If you plot the probability distribution for 2 or three atoms, it looks like a shaded checkerboard, growing thinner with time along a roughly logarithmic decline.",
"As you increase the number of atoms, the distribution actually becomes more uncertain in raw number-of-atoms terms, but more certain as a percent--the number of atoms grows faster than the variability. This common when taking any sum of independent probabilities. It's this statistical averaging effect that covers the ground between singleness and manyness. So effectively, if we continuously \"zoom out\" to see our whole plot, then it will appear to become more detailed, and the sides more focused until at very high particle count, it would appear to be a line, when all the way zoomed in.",
"To answer the final question: Half life defined as \"when half the particles decay\" is an emergent trend. Half life defined more rigorously as \"the time after which a particle will have a 50% chance of having decayed\" is very much a directly measurable quantity, from which the aforementioned emergent effect arises."
] |
[
"thanks for your reply .",
"However the author also speculated on the (admittedly far-out) possibility long -lived particles-electrons ,protons....- are in this state simply as the remnant-particles from the big bang ,and thus may decay eventually.What's your take ?"
] |
[
"Angular Momentum Question"
] |
[
false
] |
I tried posting this to askreddit, needless to say I didn't know this subreddit existed. Anyways, my modern physics teacher again disappointed me in lecture with a poor explanation. I understand that the question is not really answered, but can someone explain how electrons have angular momentum without spinning on their axis? Orbital angular momentum is easy, but spin angular momentum makes no sense to me.
|
[
"I'm going to have to disagree with RobotRollCall here. We don't really know what spin is. It's ",
" intrinsic angular momentum. It 's an intrinsic property. It ",
" angular momentum, but it's not actually \"intrinsic angular momentum\". An electron does not spin on its own axis.",
"We know it's not angular momentum because it doesn't ",
" act that way. If you take an ordinary object that's spinning and rotate it 360 degrees, it'll still be rotating the same way. Angular momentum transforms as you'd expect it to under three-dimensional rotations.",
"Spin doesn't behave that way. Take a spin-1/2 particle (fermion) such as an electron, rotate it 360 degrees, and it 'spins' in the opposite direction! It takes two full rotations to get back where you were. ",
"Why is that? Well, because fermion spin just isn't a three-dimensional property, it's two-dimensional. Spin is described by a complex-valued amplitude (like most quantum properties) in two dimensions. So the \"intrinsic angular momentum\" you measure is a projection of that in real, three-dimensional space. ",
"But a two-dimensional thing in three-dimensional space doesn't rotate according to the same rules as a three-dimensional things. Do the math (nasty spinor stuff) and you end up with the aforementioned weird property that it takes a 720 degree rotation to get back to where you were. ",
"Tangloids",
" make for a sort of visualization of that, which ",
"this guy demonstrates",
". ",
"That still doesn't answer what spin ",
". I don't think anyone really knows, it's a question of interpretation. The Standard Model basically says that you have certain fields with certain symmetries, which give rise to particles with corresponding properties, such as charge and spin. And from that you have the electrons with their two-dimensional, 1/2-spin, property. (I'm not a particle physicist so that's about all I know about that) But as for ",
"what the math means",
", I'm pretty clueless. ",
"But from this weird rotation property, you have the spin-statistics theorem, which gives the Pauli principle, which causes electrons to behave the way they do in atoms, which gives us chemistry, which gives biology, which is the reason why we're here in the first place. So I guess it's good for something. "
] |
[
"The universe is under no obligation to make sense to anybody.",
"Spin is intrinsic angular momentum. It just is. The fact that we only encounter classical angular momentum in the context of something rotating doesn't matter. Spin is angular momentum in the absence of rotation."
] |
[
"I think the best way of explaining this is with an analogy. Imagine the only type of energy you knew to exist was kinetic energy, i.e. you live in completely free universe where no potentials exist. This would all be fine, you'd have a law of conservation of energy, where the only type of energy is kinetic energy (so you wouldn't even have the distinct words \"energy\" vs \"kinetic energy\"). Then, all of a sudden, you gain a potential (someone turns on a gravity field, something like that). Now, to get a conserved quantity, you have to add your kinetic and potential energies. But since you're so used to the only type of energy being kinetic energy you can't get a feel for how you can have non-zero energy for zero velocity. It's just the same as how we can't get a feel for having non-zero total angular momentum for zero orbital angular momentum. "
] |
[
"BLACKHOLES: Is it possible there are blackhole cores made of different atomic structure?"
] |
[
false
] |
[deleted]
|
[
"I'm afraid I don't understand the question; there are no elements crucial to the formation of a black hole. All that matters is that you have an object of sufficient mass undergoing collapse. In a stellar collapse process, the star will fuse elements up to iron before undergoing its supernova phase, and then a whole slew of new elements will be made during the supernova, but those aren't in any way critical to the collapse toward singularity."
] |
[
"No, because the properties of an atom are determined by its atomic structure, and the material that collapses into a black hole ",
" its atomic structure. During the collapse, all atomic identity is wiped out and you're left with an object that has no measurable properties other than mass, angular momentum, and charge (and related quantities, like Hawking temperature, which only depends on mass)."
] |
[
"Not really.",
"The gravitational interaction even at the neutron star level is sufficient that there is no ",
" structure to speak of (at least in the interior regions). All of the protons start binding to the free electrons or tossing off positrons, so you're left with just a bunch of neutrons. Since the element to which an atom corresponds depends on the number of protons in the nucleus, and all of the protons are gone, there are no atoms ",
"."
] |
[
"What role does Insulin have in memory?"
] |
[
false
] |
this is in conjunction with an article im reading about the link between type 2 diabetes and alzheimers, it says there is a link but doesnt go any further as to say why.
|
[
"I can think of a few reasons that type 2 diabetes and Alzheimers may be linked, and none have to do with insulin directly...",
"Diabetes can cause damage to your blood vessels. Types of dementia may occur due to brain damage that is often caused by reduced or blocked blood flow to your brain. Many people with diabetes have brain changes that are hallmarks of both Alzheimer's disease and vascular dementia. Some researchers think that each condition fuels the damage caused by the other.",
"People with type 2 diabetes also have chronically high blood sugar, and while neurons are some of the more demanding cells as far as glucose goes, too much glucose with kill them. That's why diabetics get diabetic nephropathy in which peripheral neurons die and they get numb, tingly, painful extremities. If this happens to central neurons, it's very bad, and could definitely lead to cognitive deficits.",
"Also, as ",
"u/glarn48",
" pointed out, Glucocorticocoids, like cortisol, are high in type 2 diabetes. The glucocorticoid hypothesis of brain aging and Alzheimer’s disease proposed that chronic exposure to GCs promotes hippocampal aging and Alzheimers. "
] |
[
"My first thought when I read this question about type 2 diabetes and alzheimers actually wasn't insulin but glucocorticoids (GC), which are hormones involved in glucose metabolism, but they also have many psychological effects. Exposure to high levels of GCs for example can lead to cognitive impairments especially in older adults (see ",
"here",
" ).",
"I don't know much about type 2 diabetes, but I suspect that there would be endogenous changes in GC levels. I did find an ",
"article",
" that links glucocorticoid ",
" for diabetes with cognitive impairment. "
] |
[
"A little bit of a late response but I think this is an interesting question. Before talking about the link to Alzheimer's be aware insulin is actually an important signaling molecule/growth factor in the brain. In fact, the brain produces its own insulin (rodents even have a brain specific isoform) as well as being able to respond to peripheral insulin. In addition, neurons in culture will die without insulin. Insulin's exact function is still being worked out but it seems to play an important role in the ability of neurons to have a proper shape and form connections with each-other. ",
"There have been several papers on possible effects of amyloid-beta on insulin receptors - ",
"for example",
". The upshot seems to be that amyloid-beta oligomers (thought to be an important pathogenic agent in alzheimer's) negatively impact the function of insulin in the brain. In type II diabetes many tissues in the body are already insulin resistant which, combined with a potential effect of amyloid-beta, may have an especially detrimental impact on the ability of these neurons to respond to insulin resulting in cell death... dendritic spine loss... etc",
"Anyways, this last part is just a guess - exactly how a potential effect of amyloid-beta on insulin receptors may relate to type II diabetes is up in the air as far as I can tell. Maybe some aspect of hyperglycemia ramps up amyloid production, or the detrimental effects of diabetes on the brain impair the ability to clear amyloid, or maybe it is part of an initiating event unrelated to amyloid beta... there are a lot of possible explanations but hopefully this answer at least provides some sort of a link between the DMII and alzheimer's."
] |
[
"What are the properties of the amplitude of a lightwave?"
] |
[
false
] |
I know that the frequency (length) of a lightwave is measurable spatially and that frequency affects our perception of the wave's color. Is the amplitude of a lightwave measurable spatially? Is amplitude a function of length? Does amplitude affect any perceptible properties of the lightwave (brightness/some other thing I don't know about)?
|
[
"The transverse components are ",
"an electric and a magnetic field",
". They do not have an intrinsic length-scale. The amplitude determines how much energy the wave transfers to something when it interacts, for example a higher power laser that can do more damage to your eye has a stronger electric and magnetic field."
] |
[
"The amplitude of (the electric component of) a light wave is measured in V/m, which has no meaning in terms of a spatial amplitude. It's proportional to the amount of force a charge would experience when subjected to the field/wave.",
"The energy density of a field/wave is proportional to",
"E",
" + B",
"where E and B are the field amplitudes. A wave with greater amplitude has more energy, which corresponds roughly to our perception of the light's intensity/brightness, but not in a linear way. You'd need to talk to someone more familiar with how the eye works to get more detail on how we perceive it."
] |
[
"Thanks! That link is useful in explaining the separate components of a light (electromagnetic) wave."
] |
[
"Does heat from a candle in space move gradually and spherically away from it?"
] |
[
false
] |
So I saw this post about a candle in space which is round because there is no "up" in space. Does this mean that all the heat moves gradually and spherically? And what happens when the heat reaches a wall. Does it get reflected in some kind of way? Bonus question: If so, does it mean that a candle in space burns out faster because the heat is staying closer to the candle/wax itself?
|
[
"I believe what you meant is a candle in 0 gravity, since space has no air, thus no oxygen to fuel the fire. ",
"Good question, though. \"Heat\" (actually, it's hot air) moves upward in normal gravity since hot air is less dense than cold air. If you have no gravity, it will stay around the light. This is why the candlelight is spherical too, I believe. ",
"I hope I didn't write some complete nonsense there. "
] |
[
"Yes, the hot air would not change direction as it would if there were gravity. But the heat would still be transferred to the cooler air, much the same way as the sun heats earth."
] |
[
"I am interpreting this issue as if you were on board a spacecraft, such as the ISS, in freefall, rather than if you were in a vacuum.",
"So if we ignore the oxygen issue for the candle then you have pretty much worked out how it would go.",
"Any radiative heat transfer will remain unchanged. Without gravity there is no convection but we do still have conduction. The heat source can heat air molecules directly and those will bump into adjacent molecules transferring energy as they do. This energy will spread out randomly but spherically in all directions slowly. Slowly because after all, air is a very poor conductor of heat."
] |
[
"Why do eyeglasses \"work\" even when held at arm's length?"
] |
[
false
] |
My understanding is that myopia makes images focus in front of the retina. Let's say that in my case it's 1cm. If I pulled my glasses forward 1cm, shouldn't it be the same as having uncorrected vision? Instead, I can see things clearly (even if a little distorted) if I look through eyeglasses even if I hold them a metre away from my eyes. How does that work?
|
[
"I'd venture a guess that you don't have a very strong prescription. I have a fairly strong one, and I can't move my glasses any more than 10 cm from my face without my vision becoming quite blurry.",
"Glasses correct myopia by diverging the light slightly before it enters the eye. This causes the image to focus slightly further back than it would without the glasses. The further the glasses lens is from the eye, the more the light will diverge before entering the eye, causing the light to focus even further back. So your understanding is correct, except it's not a one to one relationship. Moving the glasses one cm from your eye won't change the focal point by one cm, much less than that actually. But, it'll change the focal point more for someone whose prescription is stronger, which is why I'm theorizing your prescription is much weaker than mine."
] |
[
"The strongest prescription I ever had was about -3.0 diopters, so not particularly strong. Now it's -0.5 so even weaker. I guess this makes sense."
] |
[
"The eye actually has a total power of about +60 diopters to focus the image on the retina. If your prescription is -3 then it means your eye has an extra +3 that needs to be neutralized to get the image to focus properly. As you pull the lenses away from your eye, it's still bending light coming through that lens, though the further away, the less effective power it has... One reason contact prescriptions are slightly different. If your eye needs -6 contacts then 10 mm away where your glasses sit will need only slightly stronger but the higher the power, the steeper the climb. A -1 at arms length probably only needs to be stronger by-0.5 diopters but a -3 might need to be stronger by an extra -2 diopters, -6 needs to be way stronger! Regardless, pulling that lens away from your eye getting a slightly under powered lens is still mostly going to correct things.",
"An extra tidbit about some of the newer fancy \"digital\" lenses many optical shops offer is they can take measurements of how your glasses sit on your face and tweak the grinding of your lenses so the light going through the tilted lens in your frame matches the light the doctor measured in the exam room with the lenses vertical at a set distance from your eyeball. Most (if not all) chain eyeglass shops tout the best digital lenses (they aren't at all) but generally for single vision, unless you have over -4/5 sph or -1.5 cyl it won't be noticeable at all. With private offices, it depends on what product they use, the lab they use, and many other factors whether it'll make a difference. For progressive lenses it's a whole different story.",
"Edit: found the equation... The formula for vertex correction is Fc=F/(1-xF), where Fc is the power corrected for vertex distance, F is the original lens power, and x is the change in vertex distance in meters."
] |
[
"What does p-value really mean?"
] |
[
false
] | null |
[
"The easiest way I know to explain p-value is by thinking of an experiment like this: I have a coin and I want to know if it's a fair coin or not (aka- if when I flip it, it is actually a 50/50 chance of coming up heads vs tails). So, let's say I flip a coin 6 times, and I get all 6 of them heads. That would indicate that the coin is weighted, but obviously it ",
" happen even with a fair coin, so the question is, how do we capture that information, and how do we compare it instead of 100 flips of a coin, and they all come up heads (which obviously is a larger indicator that the coin is weighted)?",
"We use a p-value, which is supposed to answer the question \"given my hypothesis is false (aka, the coin is not weighted), what is the likelihood that I would have gotten this same result?\" With our example, is really easy to calculate. If you flip a coin 6 times, you would expect to get 3 heads/3 tails (\"expect\" just meaning most likely outcome, but really you would only actually get 3 and 3 31% of the time). And you would only expect to get all 6 of them heads 1.5% of the time (This is just ",
"using the binomial formula for a 50/50 outcome",
"*0.5",
" So, your p-value in the experiment \"I believe this coin is weighted to be more likely to come up heads, and I flipped it 6 times, and all 6 times were heads, so I say it is weighted, with a p-value of 1.5%.\" If instead you flipped the coin 10 times, and all 10 were heads, then your p-value would be reduced to 0.1%, which is lower, showing you are even more confident. ",
"Now, this makes it seem super easy, and like there shouldn't be any confusion around them. But the reason p-values get so confusing, is in real life, it's normally not so cut and dry like my above examples. So instead of a coin weighted so heavily it always comes up heads, we instead have a coin that is just ever so slightly weighted, so it only comes up heads 50.5% of the time. Then, you would have to do many, many experiments, to try to find some signal. And even after you find it, sometimes it doesn't look super convincing- since you're barely getting any more heads than tails, and maybe there's just something wrong with your experiment. ",
"Or a bigger problem still ",
"p-hacking",
". Perhaps the easiest example of this would be switching from a coin to a 20 sided die, and you say \"well, I believe that one of these sides is slightly weighted\" so you do a bunch of rolls of a 20 sided die, and then whichever side happens to come up more, you say \"that's the side it's weighted towards.\" But when you don't have a theory before you start (aka- I think this is weighted to come up as a '6' more often than not), then you are likely to find something that happens more than expected."
] |
[
"Yeah, that is kind of the classic example, and captures it probably more succinctly than I did."
] |
[
"would this be considered p-hacking?"
] |
[
"Does the speed at which you pass through a metal detector effect its sensitivity?"
] |
[
false
] |
*affect Say I have a 20g iron nail in my pocket, and this is right around the threshold of a metal detector in a security line. Would it matter if I ran through the detector at top speed or walked through the detector slowly? In my mind there are two considerations. One, running through may give the detector a short enough signal that the software filters it out as an anomaly (here I'm talking about speeds attainable by humans, I'm not trying to say that the piece of metal is going so fast that it exceeds the sampling rate of the detector, just that there are software controls to exclude false positives but in this case they would be filtering out a true positive.) Second, going through faster actually will generate a larger signal (like a magnet passing through a coil more quickly generates a larger current), so it's the person who walks through very slowly that is not detected. I am asking these questions with little understanding of the engineering or physics behind metal detectors, and was hoping you all could provide some insight.
|
[
"If the magnetic field of the metal detector were constant, then moving slow enough would not set it off. However, most, if not all metal detectors use oscillating magnetic fields, which you can basically think of as a magnet moving back and forth. In this case, it doesn't matter how you moved.",
"Addendum: A metal detector works by using an oscillating magnetic field to set up electric currents in a metal. It only works on metals because metals have electrons that can move around freely (that's why they conduct electricity). The electric currents, then in turn set up their own magnetic field. Since the whole thing is driven by the first magnetic field, you look for a second magnetic field that oscillate at the same frequency as that first field to determine if there's metal around."
] |
[
"The more impressive feat would be flying it through an airport metal detector with no one noticing. "
] |
[
"about 2000mph. so no you cant."
] |
[
"How does something like Chantix NOT produce withdrawals/nicotine cravings if it binds to nicotine receptors?"
] |
[
false
] |
. This isn't medical advice, just a random thought. I've considered trying Chantix but I hear it's expensive and I'm a little scared of the side effects... can't be any worse than smoking though! Anyway, thanks in advance. I love being able to ask scientists questions, I can't think of anywhere else I would be able to. :)
|
[
"chantix is a ",
" agonist, which means it binds to the same receptors, but doesn't elicit as strong a response. the response is weak enough that it doesn't lead to a lot of dopamine release downstream, so it won't really have withdrawal effects."
] |
[
"Chantix is a what's called a \"partial agonist\" so while it activates the nicotine receptors (dulls craving) it also blocks the nicotine you smoke from binding to the nicotine receptor (uncouples the pleasure you receive from smoking). This second pathway of uncoupling the pleasure you receive from smoking a cigarette was actually just re-affirmed in a recently published paper, that I do not have on hand. In the paper they had people continue smoking cigarretes for 4 weeks while on Chantix and they had even higher quit rates than those that started Chantix and quit smoking at the same time.",
"This partial agonist class has a few other drugs that are used for similar situations. You may have heard of Suboxone (generic Buprhenorphine), this is a partial agonist at one of the opiate receptors (mu). It helps people quit using opiates in much the same way that Chantix helps people quit smoking. There is also one drug that falls into this class, Abilify (generic Aripiprazole) which is a partial agonist at D2 receptors in the brain and is used as an anti-psychotic."
] |
[
"Syntrik/waterinabottle explained it nicely. Im well aware that we dont give medical advice however, But I would like a very fast rant/warning.",
"<ENGAGE RANT>\n I want to warn you and anybody else considering using this drug of one thing which isnt fully documented in the usage guidlines yet. Im not going to talk about its efficiency /side effects / appropriateness whatever.",
"Varenicline ( chantix/champix) should not be used if you have any history of psychiatric illness , particularly depression / anxiety disorder and especially suicide. It was never trialed to any great extent on people who suffer from mental illness, and it carries a warning to say it is not recommended but various governing bodys may not have officially adopted this. A Varenicline Rep told me yesterday ( co-incidence , no? ) that a large multi centre trial is underway to see if its safe in mental health blahblahblah. ",
"Many case reports and my hospitals own anecdotal experience is that it is not. Just Last night a young man took an absolutely massive overdose of various pills, out of the blue no warning, happy guy, wife about to have her baby, great family, loved his hobbies etcetc... 1 week after starting champix. He had a hx of depression but controlled for a decade. ( very strange co-incidence that the rep was in that day !) I know its not scientific , i know there are all kinds of bias there, but I strongly suspect the champix is behind this suicide attempt.",
"</RANT>\nMy Rant is over now. I would hate to think that any redditor (or anyone) might be inappropriately started on this drug and suffer like that guy. Just be aware of it thats all."
] |
[
"Is it \"healthier\" to remove your wisdom teeth even if they are not bothering you?"
] |
[
false
] |
I was having pain with one of my wisdom teeth, and my dentist recommended that I remove them all. Are there any good reasons why I should/shouldn't?
|
[
"Caveat: I am not a dentist, but I am someone with a cool dentist who keeps me up to date on relevant research. ",
"Prophylactic removal has fallen out of favour in many places around the world. The UK are against it, with the NIH stating \"The practice of prophylactic removal of pathology-free impacted third molars should be discontinued. There is no reliable evidence to support a health benefit to patients from the prophylactic removal of pathology-free teeth”; the Australian Dental Association ",
"agrees",
". ",
"Here's",
" a literature review, and ",
"an overview",
" that come to the same conclusion. As long as wisdom teeth are not impacted or in some way likely to cause problems, it seems preferable to instead just keep an eye on them during regular check-ups."
] |
[
"I'm a dentist. Short answer is that you don't have to have the other wisdom teeth removed unless they appear to have the potential to cause resorption, decay or gum disease with the second molar forward of the wisdom tooth. This is another muddy issue. Not all dentists see it the same way. For more detail read on if you wish.",
"Insurance has screwed up the issue here in the US. Most 16-20 year olds have all four of their wisdom teeth removed because their parents dental insurance covers the procedure, which has become quite expensive. I was surprised when a patient came back recently to tell me that removal of the four wisdom teeth (with IV sedation) was $2000. In other parts of the US I'm sure it is significantly more. Many dental policies don't cover children once they're over 21 so parents feel they should take care of this procedure while there is coverage so that their children don't have to shoulder this expense later, given that fewer employers are offering dental (or even jobs). The rest of the world would say we're crazy and could easily solve this problem by simply ending the routine removal of wisdom teeth. Not so fast. I've tried to make case by case evaluations and recommendations in my office but by the time patients talk with the surgeons, they have them convinced to have all four done. I even had an oral surgery office call me to suggest that stop referring for selected removal and just tell them they need all four out. And I've had mothers bitch at me because their kid, now 26, has developed wisdom tooth pain, which is all my fault because I should have recommended removal back when they had insurance. For some reason, dentists who approach treatment conservatively are viewed as bad dentists here. ",
"On the other hand and in defense of the surgeons, healing and recovery does tend to be better for younger patients. In a lot of older adult patients, removal of an impacted lower wisdom tooth (lower wisdom teeth are much more difficult to remove than upper and cause far more post operative problems) results in bone loss and gum recession around the second molar in front of the wisdom tooth. Following a difficult removal second molars will often be sensitive to temperatures because of the gum recession. You rarely see this with younger patients. ",
"There is uncertainty as to how a wisdom tooth is going to eventually position itself. If it's clearly impacted, doesn't show evidence of pathology and looks like it will be super difficult to remove, I think it's best to leave it alone. If a wisdom tooth is erupting at an angle or is partially erupted, I think it is a good idea to remove because these often develop gum problems. I've seen partially erupted wisdom teeth cause severe resorption (the tooth eating itself), decay and gum disease that resulted in the removal of the wisdom tooth as well as the second molar.",
"Even if you have room and your wisdom teeth are erupted, very often the tissue around them is loose and susceptible to gum issues and people often bite their cheeks. They are hard to clean and often develop decay that is very difficult to impossible to restore. Sometimes I'll see the writing on the wall, that a patient isn't doing a good job keeping the wisdom teeth clean and they have decay or gum issues starting, and I'll recommend removal. They'll say,\"Geez, what's with you dentists, you're all wisdom tooth haters\", and they want me to fix the decay or fix the gum problem instead of removing the tooth. But again, because they can't clean well back there, new decay develops or gum problems never improve, and they ultimately have to have the tooth removed anyway. Despite what patients often think, most of the time we are trying to recommend a course of action that will prevent unnecessary expense and trouble down the road.",
"Hope this helps."
] |
[
"British children have healthier teeth than American children.",
"The difference here is that dental healthcare for kids is covered by the NHS, but cosmetic dentistry isn't. Historically this means cosmetic work (bleaching, straitening) wasn't as common as it was in the US. ",
"Cosmetic work is becoming lot more common over here, but the \"Hollywood smile\" is still not something everyone necessarily aspires to. "
] |
[
"[Physics] Is there a \"2012 update\" on the double slit experiment?"
] |
[
false
] |
Hello all It seems that the latest years, especially this one, were especially exciting for physics in general. This piece of news, for example: or this (since I'm a layman, I can't really get it) so the question that I bring today is: are there updates (that can be explained to those who are not physicists) on the understanding of the double slit experiment? Extra question: were there advancements or changes in the understanding of the wave/particle collapse? Thanks!
|
[
"What a negative view of scientists. Some discoveries are actually quite sensational. "
] |
[
"No and no. Scientists like to sensationalize their findings so that they get more grant money, and science journalists like to sensationalize their findings because it's easier than actually understanding anything. Our current understanding of basic quantum mechanical things like the double slit experiment is basically identical to what it has been"
] |
[
"I wasn't aware of this specific article you linked, but apparently there have been ",
"criticisms",
".",
"The first one is significant because they managed to protect a qubit from being influenced by 'noise' from its environment by using weak measurements and using the info gained from those to perform error correcting operations. It is by no means a contradiction to the fundamentals of QM.",
"In terms of the double slit, you can look at quantum erasure experiments and ",
"delayed choice versions of that",
". People have done double slit experiments with largish objects like ",
"buckyballs",
".",
"In terms of the wave/particle collapse business, you will find different opinions depending on whom you talk to. There are still people out there who claim that the decoherence picture can explain everything while there are others who thing the copenhagen interpretation is sufficient. There was ",
"this",
" paper that ",
"made",
" some ",
"waves",
" a while back. I have no idea what the state of the art is, might be interesting if someone knowledgeable could weigh in.",
"Overall, there is no fundamental, earth-shattering change of viewpoint. But physics, as they say, is an experimental science, and people these days know a good deal more about how to manipulate atoms or electrons or photons than their grandparents."
] |
[
"Do people who are constipated absorb more nutrition from the food they eat because it spends more time in their digestive tract?"
] |
[
false
] |
Whether that be calories or micronutrients.
|
[
"Almost all of the nutrients in food have already been absorbed before it reaches the lower intestines/colon, etc. So no."
] |
[
"Constipation results from food sitting in the large intestine, the colon, for too long. Large amounts of water get absorbed, and produce hard stools. Most of the food is already absorbed by then."
] |
[
"No as other have mentioned, constipation is really more of an issue with water content and \"bulK of the stool than it does with nutrients."
] |
[
"What did the ground of the cretaceous period look like?"
] |
[
false
] |
I recently found out that grass isn't too old of a development, so I was wondering what dinosaur-period terrain might look like. Was it covered with different kinds of plants? Were valleys and rolling hills all dirt brown and sparsely vegetated?
|
[
"lots of Ferns and mosses made up the majority of the ground cover. ",
"http://www.botany.wisc.edu/courses/botany_422/readings/Graham1993.pdf"
] |
[
"It is also worth noting that until the very end of the Cretaceous there were no ",
"flowering plants",
".",
"No cherries, lemons, limes, oranges, sunflowers, grasses (e.g. wheat, rice, maize, barley, rye), apples, pears, nuts, lilies, magnolias, orchids, palms, oaks, daisies, peas, pineapples, broccoli, potatoes, tomatoes, peppers, parsley, plums, apricots... well you get the picture. ",
"There were a lot of ",
"gymnosperms",
": e.g. pines (cone-bearing trees), cypresses, cycads, gnetophytes, and ginkgos."
] |
[
"thanks!"
] |
[
"Does quantum entanglement allow faster-than-light information transfer?"
] |
[
false
] |
[deleted]
|
[
"No. Full stop.",
"Previous discussions:",
"http://www.reddit.com/r/askscience/comments/hcrkw/why_cant_we_use_quantum_entanglement_to_send/",
"http://www.reddit.com/r/askscience/comments/galfv/is_entanglement_faster_than_light/",
"http://www.reddit.com/r/askscience/comments/gb77k/how_is_entanglement_able_to_move_faster_than_light/",
"http://www.reddit.com/r/askscience/comments/fuxw4/how_are_the_particles_linked_according_to_the/",
"http://www.reddit.com/r/askscience/comments/du7yd/quantum_entanglement_vs_special_relativity/",
"http://www.reddit.com/r/askscience/comments/ccuu7/since_the_topic_comes_up_whenever_a_quantum/",
"http://www.reddit.com/r/askscience/comments/ctk6u/quantum_entanglement_and_einstein/"
] |
[
"The article is incorrect, and I want to punch Geoff Brumfiel in the anus. There's a lesson here: science journalists don't always understand science.",
"While some people originally thought (many decades ago) that some information was being communicated, we now appreciate a more correct understanding of entanglement. You start out with a system where you know that, for example, particles A and B have to exit with opposite spin. If you measure particle A to be spin-up, you automatically know that B must be spin-down even though you haven't measured it. That's all there is to it - there isn't any faster-than-light communication, it's just inference based on your physical knowledge.",
"Indeed, if you measured a bunch of particle As, you'd get a random distribution. There's no way to influence what spin you measure, so there's no way to \"send\" any information through the system to your colleague who is measuring particle Bs. Only after you and your colleague come together and compare results do you find the \"spooky\" correlation, which is rather mundane."
] |
[
"Everyone knows that the anus is the organ responsible for coming up with interpretations of quantum physics."
] |
[
"If all dogs came from wolves, how did we get so many different breeds etc?"
] |
[
false
] |
Like how do we have pugs and Aussies and all of that jazz? Might be a dumb question but I would love to know!
|
[
"Selective breeding.",
"In the beginning we didn't have \"dogs\", we had wolves that didn't attack us, and protected us, in exchange for warmth & food. With time, as humans spread around the planet, we started setting them to different tasks like guarding or hunting. And each generation ",
" chose which dog could sire offspring, selecting those that had favorable traits, and/or were better accustomed to a certain climate.",
"And much later people got pretty much insane & wanted dogs that were fashionable, which is why we get breeds that wouldn't survive even 5 minutes without the comforts modern humans provide."
] |
[
"You have clearly not seen a greyhound when it spots a squirrel haha that instinct is definitely there but why bother hunting when human feeds you for free?"
] |
[
"There has been much less selective breeding for cats. They were domesticated like a farm animal, but didn't live as closely with humans as dogs do until very recently."
] |
[
"Why do electricity pylons make a loud buzzing sound?"
] |
[
false
] | null |
[
"Mains hum, electric hum, or power line hum is a sound associated with alternating current at the frequency of the mains electricity. The fundamental frequency of this sound is usually 50 Hz or 60 Hz, depending on the local power-line frequency. The sound often has heavy harmonic content above 50–60 Hz. Because of the presence of mains current in mains-powered audio equipment as well as ubiquitous AC electromagnetic fields from nearby appliances and wiring, 50/60 Hz electrical noise can get into audio systems, and is heard as mains hum from their speakers. Mains hum may also be heard coming from powerful electric power grid equipment such as utility transformers, caused by mechanical vibrations induced by the powerful AC current in them.",
"Electric hum around transformers is caused by stray magnetic fields causing the enclosure and accessories to vibrate. Magnetostriction is a second source of vibration, where the core iron changes shape minutely when exposed to magnetic fields. The intensity of the fields, and thus the \"hum\" intensity, is a function of the applied voltage. Because the magnetic flux density is strongest twice every electrical cycle, the fundamental \"hum\" frequency will be twice the electrical frequency. Additional harmonics above 100 Hz or 120 Hz will be caused by the non-linear behavior of most common magnetic materials."
] |
[
"Contaminates (usually bird poop or salt spray) on the insulators cause arcing which you can hear. Frequently you can also see it at night, especially during high humidity. If this gets bad enough, the power company will wash the insulators--search youtube for \"hot washing insulators\".",
"A side note--you hear the arcing as a 120Hz buzz (on 60Hz mains) because it arcs at both the positive and negative peak of the voltage wave. You hear transformers at 60Hz."
] |
[
"I'm not OP but, despite your informative answer, I think you've sidestepped the (intended) question - why do (power lines on) electricity pylons make a loud buzzing noise? ",
"I understand your arguments about transmission equipment, mains hum, etc. but I too would like to know the mechanism by which the HT power lines themselves both hum and crackle. I'm talking about the heavy duty stuff, at 132, 275, and even 400kV. I presume the hum is motion of the conductor induced by AC in the earth's magnetic field; perhaps the crackle is some sort of atmospheric ionisation?"
] |
[
"How does evolution work with chromosomes?"
] |
[
false
] |
All animals have a discrete number of chromosomes and can't reproduce with animals with a different number of chromosomes, right? So when an animal has a different number of chromosomes than its parent (as must have happened at some point), how does it reproduce?
|
[
"PZ Meyers has a pretty great explanation with pictures ",
"here",
". The short summary is that it is possible for two closely related organisms with different numbers of chromosomes to have fertile offspring. As the abnormal karyotype spreads and individuals with the abnormal number of chromosomes interbreed, speciation can occur."
] |
[
"Thank you!"
] |
[
"Yes, animals will have different numbers of chromosomes, but there are examples of different species breeding and producing offspring that are sterile. See the example of breeding donkeys and horses: ",
"http://en.wikipedia.org/wiki/Mule",
"Evolution works on a smaller scale operating on the gene level by affecting specific variations called alleles. Reference pundit squares for how alleles can mix. Evolution operates on the scale that certain alleles make for a 'better' or 'worse' surviving life form."
] |
[
"Why is glass such a good compound to store most chemicals in?"
] |
[
false
] |
I know some chemicals like HF can eat through glass, but in general most things can be stored in it without any reactions ir consequences. What properties does glass have that makes it so?
|
[
"As a chemist, I can tell you that basically nothing is kept in a metal container. The common choices are glass, for almost anything, polypropylene, which can be good if you have an acidic sample where you don't want the acid leeching metals out of the glass, or if you're dealing with HF. HF is really one of the few things you absolutely cannot keep in glass, as it etches the glass away. "
] |
[
"As a chemist, I can tell you that basically nothing is kept in a metal container. The common choices are glass, for almost anything, polypropylene, which can be good if you have an acidic sample where you don't want the acid leeching metals out of the glass, or if you're dealing with HF. HF is really one of the few things you absolutely cannot keep in glass, as it etches the glass away. "
] |
[
"See this thread and coniform's excellent answer.",
"http://www.reddit.com/r/askscience/comments/1894b8/why_is_glass_so_chemically_stable_why_are_there/"
] |
[
"Why do Chimps and Gorillas have insane strength and muscle mass?"
] |
[
false
] |
A couple of obervations of mine...I know there biology is different then humans but it seems Chimps and Gorillas eat poor nutritional greens and dont seem any more active then lets say a hunter- gatherer human lifestyle. Why did us humans go down such a different Evolutionary path? Why are the other Great Apes so damn strong?
|
[
"\"Biologists have uncovered differences in muscle architecture between chimpanzees and humans. But evolutionary biologist Alan Walker, a professor at Penn State University, thinks muscles may only be part of the story.",
"...Walker's hypothesis stems partly from a finding by primatologist Ann MacLarnon. MacLarnon showed that, relative to body mass, chimps have much less grey matter in their spinal cords than humans have. Spinal grey matter contains large numbers of motor neuronsnerves cells that connect to muscle fibers and regulate muscle movement. ",
"...Our surplus motor neurons allow us to engage smaller portions of our muscles at any given time. We can engage just a few muscle fibers for delicate tasks like threading a needle, and progressively more for tasks that require more force. On the other hand, since chimps have fewer motor neurons, each neuron triggers a higher number of muscle fibers. So using a muscle becomes more of an all-or-nothing proposition for chimps. As a result, chimps often end up using more muscle than they need.\"",
"Quoted from: ",
"http://www.biology-blog.com/blogs/permalinks/3-2009/why-a-chimp-is-so-strong.htm",
"Journal Source: ",
"Alan Walker. The Strength of Great Apes and the Speed of Humans. Current Anthropology, 2009; 50 (2): 229 DOI: 10.1086/592023"
] |
[
"Thin, lean bodies work very well for efficient locomotion."
] |
[
"It sounds like ",
"this is it",
"."
] |
[
"Why do orbits always rotate over time?"
] |
[
false
] |
I'm referring to , when an object doesn't take the same path each orbit around another object. What causes this to happen?
|
[
"That needs some context, orbits don't usually do that. The orbit of a perfectly spherical object about another perfectly spherical object will, when viewed in the reference frame of one of the objects, always have apsides in the same two locations. In the real world, planets, stars, and some moons are oblate spheroids, and some planets and moons have mass concentrations, and sometimes objects get close enough to a star to be noticeably affected by effects of general relativity. All of these variations perturb the orbit, and may cause the line of apsides to precess slowly over time, usually very, very slowly, only noticeable to the naked eye over very many orbits. Also, the pull of other planets will likely cause a small amount precession.",
"The image you've linked to needs some context to understand why it's behaving that way."
] |
[
"The orbit of a perfectly spherical object about another perfectly spherical object will, when viewed in the reference frame of one of the objects, always have apsides in the same two locations.",
"Isn't this only the case for Newtonian orbits? Wasn't the reason why ",
"the perihelion precession of Mercury",
" could be used to test relativity?"
] |
[
"That's correct. In a general relativity framework, the periapsis of an orbit is subject to the geodetic effect and the Lense-Thirring effect. These come from the rotation of the bodies."
] |
[
"Why Don’t we have fusion power yet?"
] |
[
false
] |
I was just wondering why we don’t have fusion power yet. I know that right now the reactors are highly inefficient but I was wondering if there was a specific reason? Is it the material that the reactors are made of or the amount of hydrogen and deuterium and tritium needed.
|
[
"ITER should be finished before 2025 (if things go relatively well) it will be the first complete industrial sized fusion reactor in the world. It's not supposed to be used to supply france's grid but for research purposes as à way to fine tune à reactor of this size.",
"It should theorically provide 10x more energy than is used to sustain the réaction.",
"After that it's supposed to be \"just\" à matter of constructing additionnal reactors and bringing them online.",
"Tl,dr : industrial pilots are under construction, it takes time to do so and to determine the best way of achieving fusion reliably."
] |
[
"Tl,dr : industrial pilots are under construction",
"ITER is not an industrial pilot. It's 100% a research experiment. The industrial pilot will be called DEMO, which will be designed once ITER is up and running, taking into account everything that was learned from the construction and operation of ITER."
] |
[
"Fusion generates a plasma so hot it would vaporize any material it touched. Controlled fusion therefore requires building a \"force field\" to hold the plasma. In modern parlance they tend to call it a \"magnetic bottle\". Since the particles of plasma are electrically charged, a magnetic field can, in theory, keep the plasma particles inside the field such that it never touches the sides. This has proved to be much more difficult than originally imagined. It is hard to keep the plasma in. As it gets hotter, turbulence mades it harder to adjust the field. The particles also start moving faster (temperature equals average kinetic energy equals averge particle speed), meaning you get a lot more leak through on the field. You'll see progress numbers for fusion experiments where they cite the length of time they're able to keep it confined, the temperature reached and the density of the plasma. For a working fusion reactor, the first number basically has to be infinite. There are also minimum temperatures and pressure/densities that have to be met in order to get a sustained fusion reaction. Right now a lot of test runs are trying to reach the temperature and density numbers independently, not necessarily at the same time AND keep the plasma confined. Last one I read, they were able to reach about 1/3 the required plasma density in one experiment. In another they're able to reach about 3/4 the require temperature, but at a very low density. Confinement times are on the order of 1000 seconds. Still a ways to go yet, but theory says they can do it with ITER. Some newer designs that are smaller than ITER are claiming to be able to do the job with sort of twisted up plasma paths (rather than the round donut of the traditional Tokamak design used in ITER). That name btw came out of Russian fusion research. I'd be interested if anyone has some context of what the russian means when translated. "
] |
[
"Do batteries change in mass at all when charged?"
] |
[
false
] | null |
[
"Not significantly assuming the battery we are talking about is a closed system there will be a tiny weight difference because a charged battery has more energy and e=mc",
" But in practice you can't measure this. ",
"Some batteries however bind oxigen from the air when discharged these batteries are actually significantly heavier when fully discharged. See:\n",
"https://upload.wikimedia.org/wikipedia/commons/thumb/e/e4/Li-air-charge-discharge.jpg/1024px-Li-air-charge-discharge.jpg"
] |
[
"Math!",
"An 18650 li-ion battery weighs ~50 grams and stores around 11 Watt-hours of electricity. That's about 3,600 joules, which has a mass of 40 picograms, about the same as a small bacterium. It gets a trillionth heavier when its charged."
] |
[
"A lithium-ion battery is a sealed system (bad things happen if it is punctured) so it should not gain or lose any nucleons during a charge-discharge cycle. It also shouldn't gain or lose electrons as electricity always flows in a complete circuit; an electron cannot leave the cathode without another electron entering the anode.",
"Therefore, the only increase or decrease in mass would result from mass-energy equivalence, e=mc",
"So if a Tesla Model S battery pack weighed 600 kg and had exactly 100 kWh of usable energy (3.6x10",
" Joules), fully discharging the battery would cause it to lose ~4x10",
" kg, or 4 micrograms of mass. This is equal to the mass of 3.265 microliters of air at sea level.",
"If that Tesla battery has a total volume of 300 L and a volumetric thermal expansion coefficient of 50x10",
" /K, it would only need to cool down by 0.00022 C to displace 3.265 microliters less air, changing its buoyancy by exactly the same amount as the 100 kWh of mass-energy that was discharged.",
"So under any practical circumstances there's no way you'd be able to notice the mass-energy of a 100 kWh battery."
] |
[
"How strong is an electromagnet when it's not on?"
] |
[
false
] |
I work with a 3T magnet. It still has some magnetic field present even when there's no current turned on, right? How strong is that field?
|
[
"Well, most MRI magnets have superconducting wires cooled by liquid helium, which is more expensive to start up but uses much less electricity. You can only turn off the magnet by draining the helium, which is really really expensive so it's only done in case of emergencies, like the patient forgot to mention he has metallic prosthesis."
] |
[
"It really depends on the magnet. From the sounds of it, you have a magnetic core wrapped in wire? In that case the iron core still has a magnetic field. Is it an MRI magnet? Is that case it should probably never be turned off"
] |
[
"Superconductivity leads to the wires having zero resistance, so once you get the current going at temperature, you short the circuit and you have a constantly flowing current (i.e., an electromagnet that stays on).",
"Draining the helium will heat the wires above the critical temperature, in which case the magnet is quenched and no longer produces a field (as current quickly dissipates as heat when resistance is no longer zero)."
] |
[
"Is it possible to have a \"personal processing unit\" to carry around and help our devices process information?"
] |
[
false
] |
Hey Scientists of Reddit, I've been wondering this question for a while now and I just wanted to know if anybody has any insight on this. Some people's phones are a bit out of date and using a personal processor would help out with the processing power needed to keep up with apps that demand a lot more power to process. This could lead to other awesome applications for this technology. I've been fiddling with the idea that the processor could process the information and pass the already processed information through bluetooth to other devices. I'm not a computer expert and my expertise lies in software, so I thought maybe the scientists of reddit could shine some light on this idea. Thanks for reading :)
|
[
"The idea isn't ridiculous but...",
"Quite a lot of effort goes into keeping up with a processor - the memory and interface components are tied directly into the processor with dedicated high-bandwidth channels.",
"While a second processor can be useful in some circumstances, the data bandwidth between processors (and/or peripherals) will frequently be the limiting factor. This is especially true for graphic displays.",
"The next problem is maintaining compatibility. While there are a few standards for data - instructing another processor to do some work can be mildly tricky when that other processor is different to the first one. There are ways around this (Virtual Machines) and code prepared for multiple targets - but it involves extra work compared with running software on a single, known platform."
] |
[
"I'm not sure exactly what you mean. A computer processor (in your phone, tablet, or whatever) needs to be connected directly to hundreds of other elements in order to function correctly. ",
"Are you suggesting an extra processor like an extra battery pack? that could be plugged in as needed? Processing power is very hardware specific. ",
"You can already do things like run remote sessions on other hardware through a fast and consistent internet connection over ssh, but trying to combine the processing powers of two distinct processors would likely lead to a performance decrease from the compatibility issues.",
"EDIT: let me just add that if there was some situation in which there was a large block of information that needed some intensive processing, without any intermediate input or output, then this could possibly be sent to another device for processing. However this situation is extremely rare in most uses, and the time lost by sending/receiving would likely make up for the performance increase."
] |
[
"I guess I worded the idea wrong. I was imagining a device which has memory, processor, and a way to \"plug into\" it. I was imagining that this would allow for peripherals to be used instead of all of our devices to have their own dedicated processor.",
"Thank you for your response"
] |
[
"Another paradox within 'the twin paradox'?"
] |
[
false
] |
The paradox that the is named for isn't a true paradox, since it's based on the false assumption that both twins would age the same because each twin sees the other moving. However, considering the effects of time dilation as it becomes more extreme, I can't help but feel that a different sort of paradox arises. I'll give an example. Twin A departs from the location of Twin B in a spaceship that quickly accelerates to 0.995c. This would give a time dilation factor of just over 10, so for every second that passes from A's reference frame at this speed, just over 10 seconds would pass for B. Let's say that A does a short round trip of 10 lightseconds before quickly accelerating back down to being stationary right next to B again. From B's perspective, the journey would appear to have taken barely over 10 seconds, since A was traveling only half a percentage point below c. When considering A's perspective however, things seem to become paradoxical. According to special relativity, those ~10 seconds as experienced by Twin B would be for Twin A only experienced as ~1 second -- even though A has covered a distance that takes light 10 seconds to travel! Am I interpreting this correctly? Because it seems in this scenario that A would have had the experience of traveling at around 10 times the speed of light. Could it be a real consequence of special relativity that the faster you travel, the faster you to travel from your own perspective? If true, that would mean that an arbitrarily long journey could be experienced as taking place within an arbitrarily short amount of time if you were traveling a significant enough fraction of the speed of light. Or am I just seriously misunderstanding something about the effects of time dilation? EDIT: SOLVED - Thanks to all who replied! I hadn't considered that Lorentz contraction would actually allow this to happen. My mind is so blown.
|
[
"A would also experience length contraction, so that it would appear to him that he was only going 1/10th as far as B observes him to travel.",
"that would mean that an arbitrarily long journey could be experienced as taking place within an arbitrarily short amount of time if you were traveling a significant enough fraction of the speed of light",
"Yes, this is true. The traveller experiences this as a decrease in the distance to the destination."
] |
[
"Essentially, yes. People misunderstand that a lot, but given enough energy, you can reach everywhere in an arbitrarily short amount of time (well, there's some practical concerns), all according to relativity."
] |
[
"Yes, this is true.",
"The implications of that are mindblowing! With enough speed, you could travel any number of lightyears and also arrive at a point nearly as many years in the future, in just seconds. Provided you have an astronomical amount of energy and don't run into some cosmological horizon like the end of the Universe.",
"Though it's actually ",
" chilling to think that a near-instantaneous journey could transport you to a time after the Earth even exists. The entire remaining lifetime of our planet and maybe even our species, passed by in the blink of an eye, gone forever. Like... What?!"
] |
[
"A few questions about telescope technology and the expansion of the universe"
] |
[
false
] |
[deleted]
|
[
"Back in the 1990s, Silicon Graphics created a hardware-based random number generator using — I am not making this up — a lava lamp."
] |
[
"Back in the 1990s, Silicon Graphics created a hardware-based random number generator using — I am not making this up — a lava lamp."
] |
[
"1) Current data indicates that the metric expansion is accelerating.",
"2) Those radii correspond to times before the epoch of last scattering, which means that any light emitted during those periods was absorbed before it could traverse space; the universe was opaque.",
"3) The oldest we can see is light that was emitted roughly 380,000 years after the big bang. This is the CMB.",
"4) The CMB is extremely redshifted, relatively uniformly in all directions. We can't really look at it \"further away\" because the light we're seeing is, by definition, the light here."
] |
[
"How do astronomers know that the tiny 4 pixel dot on their photo is a galaxy and not a star?"
] |
[
false
] | null |
[
"photometry",
" and/or ",
"spectroscopy",
", because a (red-shifted) galaxy will have a different ",
"spectral energy distribution",
" from an individual star"
] |
[
"Even very distant galaxies will often appear a bit more spread out than stars. By looking at all the dots in the image you can model a point-spread function for that image and see if a particular object is a bit more extended (or fuzzier) than it should be, even if they appear identical to the human eye.",
"But very distant galaxies will be indistinguishable from nearby stars, in that they will both be \"point sources\" whose apparent size is below the resolution of the instrument, so you need to analyze the light from the object itself, as the other answer said. To expand on that a bit, spectroscopy is the best method and will usually clearly differentiate between stars in our local Galaxy and distant galaxies. The problem is that spectroscopy is time-consuming, and if you're doing a large survey it's not possible to follow-up on every galaxy candidate. Photometric studies are easier, and the more filters you observe an object in, the more confidence you can have in your identification. ",
"Astronomers use the term \"color\" to describe the difference in brightness of an object observed through two filters. So an object with a magnitude of 18.2 in the Red filter and 19.5 in the Blue filter would have a B-R color of 1.3. Let's add a V (green) filter to the mix, and now you get B-R, B-V, and V-R. A fourth filter would give you 6 colors, and so on. Each additional color lets you eliminate even more possibilities. Surveys using 5 or 6 filters are pretty common these days. And so a while a nearby star and a very distant galaxy may look similar in some colors, they won't look the same in all of them. ",
" That's why astronomers identify sources of contamination, propagate errors, and use terms like \"candidate\" and \"confidence level\" in papers, things which are sometimes lost or minimized when communicating with the public. It's less a matter of \"knowing\" that the 4-pixel dot is a galaxy, and more that it's highly unlikely it could be anything else."
] |
[
"I believe astronomers can “decode” the light being emitted by an object, and can deduce the components of that source of light through a tool called a spectroscope. Knowing which elements the light source is composed of probably gives scientist a better idea of what they are looking at. ",
"This was all from my astronomy courses 8 years ago so I may be wrong."
] |
[
"Is the natural state of human eyelids open or closed?"
] |
[
false
] |
I'm curious how the muscles in the eyelids works. When the muscles in your eyelid are relaxed, does that make your eyelids open or closed? I know if you die and your eyes are open, they stay open. When you are asleep you don't have trouble keeping them closed. I feel like the natural state should be open, but then why aren't there large numbers of people who suffer from their eyes opening while asleep?
|
[
"There is no natural state of the eyelid. That's like asking what's the natural state of your elbow, straight or bent?",
"The eyelid is closed by a muscle called the ",
"Obicularis oculi",
". It has an antagonist (or opposite pulling muscle) called the ",
"Levator palpebrae superioris",
" that opens the eyelid.",
"This is analogous to the biceps that bend the elbow and the triceps that straighten the elbow."
] |
[
"Actually levator palpebrae superioris ",
" the eyelid, and obicularis oculi ",
" the eyelid. ",
"From what I remember, obicularis oculi is really several muscles that are continuous. One part of it is constantly contracted (not under conscious control) so that when you sleep your eyes will remain closed. The other part(s) come into play when you have to blink or squint or close your eyes with force. ",
"Normally when you are awake most of the obicularis oculi is relaxed, and your levator palpebrae superioris is able to easily overcome the little contractile force the remaining part of obicularis oculi exerts, thus keeping your eyes open effortlessly. "
] |
[
"Perhaps what you mean by \"natural\" is essentially ",
", as in, no muscle contraction. ",
"If that is what you mean, then there really is no natural state since at any given time at least one of the muscles acting on the eyelid is contracted, with or without your conscious will to control it. ",
"In fact, many of the skeletal muscles in your body are actually in a state of \"tonic contraction\", even without your conscious input to contract them (but most of the time you can willingly contract them further). The nerves innervating these muscles actually input a constant signal to tell them to stay contracted to a certain degree. Examples include the muscles on your back that keep your posture, the muscles around your eyeballs, and the external anal sphincter muscle."
] |
[
"Could a sufficiently cold planet have real, flowing, liquid rivers of matter that is usually gaseous on our planet, such as nitrogen?"
] |
[
false
] |
What could its atmosphere be made of then? Could it rain or snow this "gas"?
|
[
"I can see some future cosmic redneck launching a flare into the atmosphere saying 'hey check this out'.",
"Is there enough oxygen for anything to happen from that? If not, would a source of flame built for use on Titan just carry an oxidizer and use the ambient atmosphere for fuel? Like an inverse of how we don't carry any oxidizer in our cars."
] |
[
"To add to this, we have seen features on Titan that are almost certainly created by precipitation. The only thing that fits what we know with Titan's atmosphere is if the methane itself is precipitating. There appears to be a full weather system analogous to that on Earth, but with methane instead of water."
] |
[
"To add to this, we have seen features on Titan that are almost certainly created by precipitation. The only thing that fits what we know with Titan's atmosphere is if the methane itself is precipitating. There appears to be a full weather system analogous to that on Earth, but with methane instead of water."
] |
[
"Would living on Mars over many generations, away from Earth’s environment cause our autoimmune system to be virtually nonexistent ?"
] |
[
false
] | null |
[
"Biology "
] |
[
"Biology "
] |
[
"Such hypothetical / speculative / open-ended questions are better suited for our newish sistersub ",
"/r/asksciencediscussion",
". Please post there instead."
] |
[
"How does diesel not combust in the high pressures of the high pressure fuel pumps of modern diesel engines?"
] |
[
false
] |
I know the pressures in most modern diesel engines for fuel rail pressure seem insane to a normal person, I know the one in my VW is something like 18,500 psi. That strikes me as higher than most of the pressures achieved in the cylinder. So that seems like it should be an issue but it isn't seeming to be.
|
[
"In this technical paper",
", P_max in a diesel cylinder is 180-200 bar (2600-2900 PSI)",
"However, in the cylinder it's a mixture of diesel ",
" that is compressed. Combustion needs oxygen! If the fuel pump is compressing just diesel by itself, it's not going to combust at any pressure because there's no oxygen."
] |
[
"All materials are compressible, their compressability just varies by many orders of magnitude.",
"Even things like steel and other metals compress with sufficient pressure (Terapascal range)."
] |
[
"There is no oxidizer (air or otherwise) in the fuel injection system - no way for the fuel to burn."
] |
[
"Can anyone help me with a modulus operation?"
] |
[
false
] | null |
[
"First consider 5555",
" mod 5555. What number is this? Then look at 5555",
" mod 5555. Then 5555",
" mod 5555. Are you seeing a pattern emerge?"
] |
[
"They all equal zero. What does that mean?"
] |
[
"I got a hold of my classmates who walked me through the same thought process. I feel dumb now, but thank you :)"
] |
[
"How can we understand where we are in our galaxy since we cannot see it from \"top down\"?"
] |
[
false
] |
This made me wonder this question. If we are in the disc, how can we be able to see past the center of our galaxy to know what lies on the other side, let alone where we are?
|
[
"Here are two very few basic clues we can use. First, ",
"we can see the Milky Way",
" from Earth pretty clearly. If we were near the interior it would be all around us (and much brighter). Second, we can look at the distribution of stars and their relative distances to determine a general map of where everything is."
] |
[
"That being said, it is extremely difficult to determine where we are in the Galaxy, with any precision. For example, the distance from us to the Galactic center has been the subject of controversy for many years, see for example ",
"this low-level review",
" of the subject. With the advent of sub millimeter VLBI, such as (for example) the ",
"Event Horizon Telescope",
" we can hopefully get a better measurement than the current ~10% uncertainties."
] |
[
"I have a question that goes along with this. How do we know the Milky Way is a spiral bar galaxy and not some other type?"
] |
[
"What would happen to forests if there were no wildfires?"
] |
[
false
] |
[deleted]
|
[
"Hey. I have a bachelors degree in rangeland management. It has a lot of overlap with any wildlands.",
"This question isn't necessarily as straightforward as It might seem. Different forests, and range lands have different fire regimes. And it all depends on fire return intervals. ",
"In Florida some forests have an almost annual fire return interval (historically) disrupting this has lead to a decline in habitat for a woodpecker species that inhabit the forests. They have a very specific forest structure requirement, there must not an any lower branches on trees for them to nest there.(lower branches allow snakes to climb trees) Lower branches burning in relatively low intensity fires creates this habitat. Stopping these fires has put this species at risk (and help create conditions for more intense fires)",
"\"Pando\" is a tree organism in Utah. It is an aspen tree forest made up of one organism... One of the largest and maybe oldest organisms in the world (rivaled by a mushroom in like..Oregon). Aspen trees without fires will eventually be overshadowed by shade tolerate fir trees. This reduces the successful recruitment of new trees. When there are fires, the aspen will regenerate. But it is often times in swathes of land so small that grazing animals put recruits in danger. Logging could help this, a lay person might call it \"clear cutting\" but in reality it would an called a \"coppice\" because we would do it with the intention that the trees resprout. This burn needs to be in a hard enough area (or with grazing and browsing heavily controlled). The lack of fires in any stand of this species puts that stand at risk (we humans need to decide whether we value this, or that, and decide to manipulate it based on our values, even if you say\"that's not our choice\" that's a values choice you're making)",
"The snow shoe hare needs a specific pine density and age, and it's aerial predator needs a different stand age and density. These are both directly affected by fire return intervals and a mosaic of a fire regime. Lodgepole pines need direct sunlight after being taken out, so the pine cones can open. OR a low intensity fire can be an acceptable way. The pine cones need heat.",
"On range lands sometimes our suppression of fire leads to juniper encroachment, which allows aerial predators to eat sage grouse, and shades out the shade intolerant sage brush. (Sage grouse are in and out of nearing endangered status) In other areas of range land, cheat grass has taken over and drastically reduced fire return intervals so that fire intolerant sage brush cannot return.",
"In other words, fire manipulation always has different affects... The fir build ups in redwood forests will almost certainly lead to fires that are hot enough to kill our tallest trees. Too much, and Too little fire is always a habitat manipulator. Logging and grazing can be tools to help fire regimes mimic nature, but they need to be done responsibly.",
"I'm a busy person, but I can dig up sources for all the things I just said if someone needs it. Though, pointing you in the right direction is my preference...These are all Googleable instances and claims! (And often very controversial)",
"Also, excuse typos...translate them. I'm on my phone"
] |
[
"Fire effects on forests vary hugely depending on forest type and fire type. Specific examples of different fire regimes:",
"Temperate rainforests (e.g., west coast of Canada and southern Chile): fire is not common and the ecosystem is not fire-adapted.",
"Conifer forests in the dry western US: ",
" fires are a regular part of the ecosystem. Lodgepole pines specifically require fires for their cones to open; other trees do not. Mature trees often survive low-intensity fires. However, recent fires have been far more intense than normal largely due to climate change and heavy fuel loads, and the ecosystem is not at all adapted to these destructive burns.",
"In general, fire acts as a disturbance that can reset the succession process--killing the mature trees and allowing fast-growing plants to thrive until slower-growing plants shade them out. Without fire or other disturbances (disease, insects, or clearing by humans) you'd see a lot more old growth. However, severe fires that are not part of the usual fire regime can be very destructive and hard to recover from."
] |
[
"For clarification I am neither a scientist or a forester. I do read a lot so have some unscientific information. First some species of trees only release seeds when they are in a fire situation so those species wouldn't propagate. \nSecond it was the policy of the federal and the state government for years to actively fight all forest fires and limit their spread. It has been discovered that this has led to brush buildup which increases fire danger, prevents some animals and plants that need the open areas between trees formally cleaned out by fires to go extinct or limited their numbers. \nThird trees eventually die and fall. If the forest is overgrown due to lack of fires then the seedlings don't get enough water and sunshine to grow meaning the tree isn't replaced."
] |
[
"Protein shakes for muscle gain. Are they needed?"
] |
[
false
] |
So I have a friend who is trying to put on a little muscle. Running and doing regular weight training. She has recently purchased pounds and pounds of these protein shakes that claim to boost muscle gain. I was wondering if there's actually any scientific evidence to suggest that it'll actually help. My gut is telling me that just eating a nice healthy balanced diet (which she does already ) will be enough in itself and that her body will get enough protein from that alone. I just don't see the point in wasting money on the stuff if it doesn't work. Thanks in advance for any help.
|
[
"Protein shakes just help you get the amount of protein you need without having to eat whole chickens everyday. You can get anything in a supplement from food. They just provide an easier way to get it."
] |
[
"It's like any other food. If eating protein shakes helps them get their daily protein intake, then it would be relatively equivalent to getting their protein from other sources."
] |
[
"Why is that? "
] |
[
"Should you keep moving or stand still in freezing water?"
] |
[
false
] |
I just recently watched the Titanic and it got me thinking about being in freezing water (around 4°C). Should you try to be still and increase the temperature of the water around you or is it better to try and swim towards the nearest rescue boat? I'm guessing that your body isn't able to increase the surrounding water that much and it's therefore better to keep moving? Any heat transfer experts want explain the pros and cons?
|
[
"You should get the fuck out of the cold water.",
"You are correct, that in still (or mostly still) water, you will lose less heat if you keep still. Moving will on the other hand produce body heat.",
"However, cold water will push you into hypothermia quickly mostly independent of how much you move which you generally won't be able to do for very long in any case.",
"So it depends on what your goal is. If you see anywhere safe, you best move is to get there as quickly as possible.",
"If you are hoping to be rescued at some point in the future and it is about maximising your survival time in the cold water, you should if possible curl into a ball and pray."
] |
[
"or should he have done what he did, which is nothing?",
"Well obviously sitting there and dying isn't a good plan. He could have looked for more wreckage, maybe a piece of ice, or even pushed the door around."
] |
[
"If you can swim safely somewhere and get out of water you should do that. Otherwise you should not remove any clothes, you should always keep your head out of the water and you should cross your hands over your chest and your legs together, in order to lose as little body heat as possible. Also you can use your clothes as a floating vest, by tying the ends and blowing air in them.",
"Sources: I'm a lifeguard"
] |
[
"Why are triangles the strongest shape?"
] |
[
false
] | null |
[
"Given any three lengths, there is at most one triangle whose sides have those lengths. ",
"Presumably, the weakest part of a shape will be the joints, so if you have any shape and you put a force on it then it will likely prefer to deform at the joints than someone along one of the sides (not an engineer, just using this as heuristic). If you start off with an N-sided thing, then after a deformation like this you'll have another N-sided thing whose sides are all the same length as the original object. When N>=4, this is no problem and can totally happen. You can take a rectangle, and change the angles a bit to get a parallelogram that has the same lengths as the original rectangle but isn't the original rectangle. If you have something with a lot of sides, you can just imagine smushing it and deforming it in a way that doesn't change any of the sides, just the angles. Given any N sides (of valid length), then you can make infinitely many different N-gons with those sides.",
"Triangles are different, given any three sides (of valid length), then there is exactly one triangle that you can make from those sides. So if you try to deform it, you can't change the angles to get a new triangle with the same sides, as there is only one possible way to do this. Triangles then hold their shape.",
"This is all thanks to the ",
"Law of Cosines",
", a generalization of the Pythagorean Theorem."
] |
[
"Good explanation. I would add that for some designs, triangles are not the strongest shape. They are great for making trusses and towers, but make terrible pressure vessels. "
] |
[
"It's not that joints are weak, but that you don't want to be applying bending loads at them, because, like a lever, the distance magnifies the forces seen by the distant joint. With a triangle, you are converting the load applied at one corner to compressions and tension of the sides, and counter forces at the other two points."
] |
[
"How did they figure out antidotes to poisons?"
] |
[
false
] |
Did they just drink different poisons and try various things and hope they didn't die?
|
[
"Traditionally, that's probably not too far off the mark. I modern medicine, we know what we're doing though. In the case of each toxin, we can pretty quickly figure out its mode of action.",
"Most poisons tend to fall into broad categories. E.g.: there's broad metabolic poisons such as heavy metals, hemoglobin-binding toxins such as cyanide, hemolytic and neurotoxic poisons as well.",
"For each, there's usually a few antidotes that can counteract the effect of a given category. For example in the case of most heavy metals, you can inject chemicals called chelators that are good at binding and largely inactivating the metal ions. In the case of acetylcholinesterase inhibitors (a large class of very deadly neurotoxins), we have compounds that mimic the target of the poison, soaking it up.",
"Basically, since we understand chemistry well these days, it's pretty straightforward to design antidotes to poisons once we understand them."
] |
[
"Basically, since we understand chemistry well these days, it's pretty straightforward to design antidotes to poisons once we understand them.",
"Is it really so easy? Drug-discovery chemistry in other areas of medicine is very, very, very hard. With other diseases and disease processes, our understanding of biochemistry is good enough to design a compound that ",
" do what you want it to do...but finding a compound that does what you want it to do, doesn't have the solubility of brick dust, doesn't have significant off-target effects up to and including horrible toxicity, isn't broken down in the process of digestion, is manufacturable on a reasonable scale without having to spend a zillion dollars on exotic catalysts or a hundred-step PITA synthesis that takes a half ton of reagents to make one ten-milligram pill, all that good stuff- that's the kind of thing that can only be accomplished through billions of dollars' worth of trial, error, guesswork, toil and frustration. Is the biochemistry of toxins so much simpler than other areas of med chem? Why?"
] |
[
"If I had to guess I'd say being poisoned is more like stopping a bullet but diseases are more like fighting an all out war. If you can soak up enough of the toxin to make it non lethal you'll live. If you stop a bullet in the scheme of the war you've still got other stuff to deal with right afterwards."
] |
[
"If the liver can regenerate, how do people die from liver failure?"
] |
[
false
] | null |
[
"Liver failure can happen in two ways. First, the acute damage can simply be too serious for liver cells to deal with before the person dies. Second is a more protracted process, where damages accumulate.",
"Suppose that the liver has taken damages from infection/drug/alcohol/etc. ",
" Scar tissue is tougher than cushy liver tissue, so this leads to hardened liver with reduced function. (Cirrhosis) If this damage keeps piling up, the liver will eventually be overwhelmed and lead to chronic liver failure."
] |
[
"In cirrhosis, the fibrosis is diffuse, prohibiting surgical removal of scar tissue.",
"Fatty liver (steatosis) is essentially reversible but once the fibrous tissue forms, the extracellular matrix (the microscopic scaffolding outside the cells) no longer supports regeneration and the process is generally considered irreversible."
] |
[
"So if a liver is scarred, is a solution sometimes to cut away the scar tissue to stimulate new growth?"
] |
[
"Can crocodiles mate with alligators?"
] |
[
false
] |
[deleted]
|
[
"No, they can't. They may look similar, but they're quite distantly related, and they diverged a long time ago. Alligatoroidea and Crocodyloidea, the larger groups that contain modern alligators and crocodiles, respectively, extend back into the Cretaceous. However, lots of different croc species can successfully hybridize. And I'll head folks off at the pass on species definitions: crocs care not one whit for how we define a species. For more info on how biologists grapple with species definitions, check out ",
"this FAQ",
". ",
"Edit: I mention the divergence between crocodiles and alligators not because there's some hard rule about divergence dates or even taxonomic rank being the deciding factor in hybridization, but to illustrate that these animals are quite different despite the fact that they may look superficially visually similar. I mentioned weird bird hybrids in another comment, but I think it's worth pointing out that there have been hybrids between sand dollars and sea urchins ",
" (",
"source",
"). While kind of thing this is rare, it's worth noting that it can happen. Ultimately, rules about different genera/families/hybrids are infertile/etc. are not going to hold up. ",
"Okay, back to crocodiles. The American crocodile (",
") and Cuban crocodile (",
") can successfully hybridize. While their ranges overlap and hybridization can occur naturally, they're doing so more and more often. See ",
"this article",
" and ",
"this article",
" on the subject. The American crocodile is also known to hybridize with the Morelet's crocodile (",
"source",
" and ",
"source",
"). These are all New World croc species that are fairly closely related.",
"Also, the saltwater crocodile (",
") can hybridize with some of the Indopacific species. The Philippine crocodile (",
") is one of them (",
"source",
"). The Siamese crocodile, ",
" can hybridize with the saltwater crocodile as well. The weirdest croc hybrid I can think of off the top of my head is that ",
" can hybridize with the Cuban crocodile (",
"source",
"). ",
"So no, there are no gator/croc hybrids out there, but modern crocodylians ",
" do some wonky things. Some level of background hybridization is natural and expected where species overlap. However, as some populations are reduced, habitat is lost, and climate change impacts coastal habitat, these hybridizations seem to be on the rise. Many crocodylians are endangered, and some are critically endangered. Increased hybridization could put additional pressure on struggling species. Hybridization also occur in captivity, which can be problematic for captive breeding programs trying to preserve species."
] |
[
"Not to mention all the ",
"gamebird hybrids",
". Pheasants and chickens make some wacky hybrids. That article says they've even hybridized with chachalacas and guans, which are in a different family (Cracidae). I can't find a source for that, though. Birds have some ",
"crazy hybrids",
". Lots of cockatoos have hybridized in captivity across genera. If we look outside vertebrates, there have been hybrids between sand dollars and sea urchins in different orders (",
"source",
"). ",
"There's definitely no rule about Linnaean taxonomy that animals follow. As complicated as species definitions are, higher-level ranks are fairly simple: they're meaningful for classification, meaningless in terms of actual \"rank\". "
] |
[
"It's ",
", so you're not conserving the species. Hybridization is a mechanism for speciation. From a conservation perspective, if the hybridization is not a natural occurrence, it's generally not going to be what you want. There are exceptions, such as when genetic diversity is so low that a species isn't viable. "
] |
[
"How much influence do stochastic occurences have on the process of diffusion, and how much do deterministic?"
] |
[
false
] | null |
[
"Your question isn't clear - what do you mean by \"deterministic processes?\" Generally, processes at the molecular scale are all stochastic once you look closely enough."
] |
[
"I am sorry if I didn't word my question correctly. By 'deterministic processes', I meant steps in the diffusion process that are governed by deterministic laws. "
] |
[
"Hmm, ok, this question might be more of a physics question then, something to be tackled by statistical mechanics. ",
"I guess you might mean processes liike directed diffusion along an electrochemical gradient? "
] |
[
"Are modern humans stronger or more athletic than our pre-agricultural counterparts?"
] |
[
false
] | null |
[
"There is an argument using evolutionary theory that agriculture was only adopted to increase group fitness at the cost of indivual fitness.",
"Lots of civilisation diseases started with the adoption of agriculture.",
"So there is the argument that agriculture made civilisation possible but at the cost of pure indivual strength and physical prowess.",
"There is lots of evidence that early agricultural societies had less than healthy members compared to hunter gatherers. ",
"When you think about it, the indivual skills of a warrior in a large army is less important than pure numbers, most armies in the past were farmers called to war once a year, and yet the prevailed most of the time against nomad societies whos way of life made them formidable indivual warriors like the steppe people, just by numbers alone.",
"Edit:",
"If someone is interested where these theories come from, I recommend these books:",
"https://www.amazon.com/gp/aw/d/0452288193/ref=dbs_a_w_dp_0452288193",
"https://www.amazon.com/gp/aw/d/0996139516/ref=dbs_a_w_dp_0996139516",
"https://www.amazon.com/Secret-Our-Success-Evolution-Domesticating/dp/0691178437/ref=mp_s_a_1_1?keywords=joseph+henrich&qid=1558984106&s=gateway&sprefix=joseph+henr&sr=8-1",
"https://www.amazon.com/Not-Genes-Alone-Transformed-Evolution/dp/0226712125/ref=mp_s_a_1_1?keywords=not+by+genes+alone&qid=1558984151&s=gateway&sprefix=Not+by+ge&sr=8-1"
] |
[
"It depends on your viewpoint of the agricultural revolution and how you define stronger. Until very recently (within the last 200 years or so), the switch to agriculture had an overall negative impact on human health (Diamond 1987). Evidence for this can be seen in studies from western Ukraine on the Trypillia-Cucuteni(TC) culture (eneolithic, ~5 ka) (ka =calibrated c14 thousand years ago) which was the first farming community in that region. Previous archaeological cultures were mobile hunter-gatherers who subsisted on various plants and animals throughout the region. The TC had the common European domesticates such as wheat, barely, sheep, and goat. According to bioarchaeological studies on skeletons from Verteba cave, an archaeological site in western Ukraine with skeletons dating from both of the above mentioned groups, TC peoples are shorter, frequently have more dental carious lesions (cavities), and have more enamel hypoplasia. (Karsten et al. 2016). Enamel hypoplasia are used as proxies for poor health because they only develop during childhood and are markers of stress mainly due to starvation. Additionally, TC populations showed increased frequencies of violent trauma (~1/4 adults died violently!) and tuberculosis was common amongst the agricultural populations. ",
"Overall, I’d argue that prehistoric (pre-agg) hunter-gatherer populations were probably stronger because they were more mobile, had better diets (depending on region and temporal period), and lived in smaller groups which cut down on disease transmission. It is important to note however that the osteological paradox, the idea that skeletons could appear healthy because the disease that killed them worked so quickly that it didn’t leave a marker on the skeletal material, is a factor when comparing strength and health of two separate populations. Is what we see archaeologically representative of the entire population? Probably not but it’s a start. Finally, one of the greatest feats of strength (IMO) for pre-agricultural hunter-gatherer populations was the colonization of the south-central Andean highlands ~12.5 ka. One of the oldest archaeological sites in the new world is located at 4480 meters above sea level where only 60% of oxygen is available when compared to sea level (Rademaker et al. 2016). The populations that settled this area more than likely stayed up at these altitudes for extended periods of time (seasonally) which is downright incredible considering that when I when up there, the effects of hypoxia almost immediately took hold and I felt like death. I’m sure modern humans could settle high altitude and some still live in this area today but I think that it really speaks to the strength of pre-agg people who originally were colonizing these semi-harsh areas. ",
"Credentials: I participated in the excavation at Verteba cave in 2016 and 2017 and have a Masters degree in archaeology"
] |
[
"It's an interesting way to look at it but I struggle with language that suggests something occurred \"to\" achieve something else... which is language that often seems implicit in evolutionary theories.",
"",
"It could also be argued that the development of agriculture starts to take us out of \"Natural\" selection and moves our genetic development down more cultural routes...",
"",
"I don't dispute the individual genetic cost of course but it's worth remembering survivorship bias when comparing the health of early agricultural societies to hunter-gatherer / nomadic tribes. The health of the memberships of these tribes will be higher partially because the unhealthy won't have survived. So agriculture and civilization in general enables less resilient genomes to survive in the population while also creating new diseases in the animals we keep near us."
] |
[
"With all the tiny particles in the air (dust etc), do they accumulate in our lungs or anywhere in our body, and how does our body dispose of it?"
] |
[
false
] |
Currently laying face first on my pillow when I was struck with the thought
|
[
"The particles don't often make it into your lungs. Your nose is lined with hairs called cilia, these trap and filter out most particles, its why we have snot. The sinuses give the nose more time to filter out these particles as they travle down towards the trachea, and again, anything deposited in all but the smallest of airways is captured in sputum(mucus.) This is then moved out of the lungs by way of the cilia, and swallowed, 1/4 cup a day is actually a fairly normal amount to be swallowing, for those who cared.",
"Anything that actually lands in distal airways is removed by macrophages(a type of white blood cell) that roams our lungs, specificially for the purpose of keeping them clean! They engulf and break down the particles."
] |
[
"Our lungs do indeed have a mechanism for 'self-cleaning' to get rid of foreign dust particles and microbes etc. This is called ",
"Mucociliary clearance",
" ",
"The components of your respiratory tract from your nostrils to your trachea to your bronchi (although not your mouth) are lined with tiny hairs called 'cilia' which are kept moist and sticky by a specially produced mucus. Particles of dust are trapped within this mucus and the cilia move in a sweeping motion to constantly push this mucus, which is constantly being renewed, up toward your mouth and nose so that you can get rid of the foreign, unwanted, objects when you cough or sneeze. ",
"People with the condition Cystic Fibrosis can not do this effectively because they lack a gene needed to produce mucus of the correct 'recipe' this is why the treatment for the condition involves regular back massages to help clear the lungs and why sufferers are so prone to lung infections. "
] |
[
"Smoking damages/kills some of the cilia and makes this process of filtering incoming air much less efficient. So, long story short, yes."
] |
[
"If an infinitely powerful computer had a complete snapshot of the universe, by which I mean every possible datum about every bit of matter or energy, could a perfect simulation accurately predict the future, or is there some intrinsic randomness in the system?"
] |
[
false
] | null |
[
"This question has been asked, and it is known as ",
"Laplace's demon",
".\nUltimately you are asking if knowing fully the state of the universe at one time you can then predict the state at all future times.",
"In short, the answer is \"no\". You can make that argument in several ways, either through thermodynamics or quantum mechanics or information theory. ",
"A very readable lecture on this very topic was given by Stephen Hawking, and a transcript is ",
"here",
". The lecture was given in 1999 and focuses on the relationship between black holes and information. This may have been superseded (I recall a bet on the matter having recently been settled). I'm sure someone else will comment on this, but the way he argues the case is very well worth reading. "
] |
[
"You would however be able to assign a probability distribution over all possible futures.",
"Of course, it's important that this computer not be a part of this universe, or it would also have to simulate itself, simulating itself..."
] |
[
"Heisenberg's uncertainty principle",
" would make it impossible to predict the future. Indeed as I understand it, it would even make it impossible to have an infinitely precise model of the current state of the universe.",
"In particular note:\n\"the uncertainty principle actually states a fundamental property of quantum systems, and is not a statement about the observational success of current technology\"."
] |
[
"How does immunotherapy (allergy shots) work when regular exposure to pollen doesn't?"
] |
[
false
] |
I've searched this and every site gives some unhelpful answer about injecting the irritant and building up a tolerance. But we suffer from allergies every year and don't build up a tolerance. Is there something special about the delivery mechanism? The substance delivered? The exact dosage? Could I sniff exactly the right amount of tree on exactly the right schedule and get the same effect?
|
[
"That is an interesting question.",
"The exact mechanisms are unknown but the dominating theory is that the immune system switches from always releasing a lot IgE antibodies into the blood to producing more specific T-cells, which reduces allergic symptoms.",
"So could you recreate that at home? Sadly not, because the way of absorption plays a role for the immune system. Eating it, breathing it in and getting injections all stimulate different parts of the immune system. I fear, if you constantly expose yourself to the allergene, the allergy might get worse."
] |
[
"Allergen immunotherapy is NOT a quick fix. You are typically committing to years of therapy.",
"The intent is to receive just barely enough to \"stimulate\" your immune system without causing a full-blown immune response.",
"Simple analogy: training for a marathon. You run a little bit further every day to build up your fitness, both physical and mental. But try running a marathon today, right now at this second, and you're probably going to injure yourself.",
"The immunotherapy starts with about 3-6 months of buildup phase. You are injected with what is realistically the smallest amount they can dose. You don't want to see any immune response during this period.",
"Then slowly the dose starts to increase. More and more until an immune response is observed - then back it off. Continue the doses at a low level.",
"Typically, when the body recognizes a \"bad\" allergen, it is over-reacting. Your immune system (1) identifies the stimulant, (2) quantifies how much, and then (3) releases all the troops. Step (2) is the weak point that we are trying to manipulate.",
"Immunotherapy is teaching your body to ignore the stimulant. Maybe your body over-reacts when it detects 6 bad actors. Well, let's make 4 the background. Now it requires 10 bad actors to set off the alarm (4 background + 6 stimulants). Theoretically we can keep pushing the background higher and higher to train your immune system.",
"Self direction probably is not going to work. Sniffing the bad tree and you're probably going to hit that threshold and trigger an immune response.",
"Ideally, we do all the therapy in a controlled environment too. Then if you do have a bad reaction, you have trained staff and medication on hand to treat the bad reaction."
] |
[
"You want to have tiny shots that DON'T trigger a response. Note: can also be oral tablets or skin swabs.",
"Each time you trigger a response you are basically resetting back to the start.",
"Analogy time (2): lifting weights to build muscle. You want to continuously lift small weights and build up to heavier weights over time. Lift a big heavy weight and you injure yourself, need recovering time. Then you lose all your gains and have to start again."
] |
[
"How does Skype know not to send the sound of my own voice back when it is picked up by my friends mic.?"
] |
[
false
] | null |
[
"Skype, along with just about any telephony system down to and including the analog telephone system, has to do \"echo canceling\" so you don't hear your own voice. This is actually a REALLY hard problem, from a signal processing point of view, but it's so well studied that it's largely a solved problem at this point. Basically, the echo canceler takes your speech, delays it and the subtracts that from the output.",
"The trick is deciding how loud the echo is and how long the delay is. You can use knowledge about the whole transmission path if you have it, otherwise you have to measure and adapt. Bell Labs has been doing this since the 60s using analog techniques but pretty quickly moved to digital processes.",
"http://en.wikipedia.org/wiki/Echo_cancellation"
] |
[
"It's even more complicated, because the sent voice re-recorded will not just be altered by the microphone properties, but also by the speakers and the room's acoustic properties. Just subtracting the pure source sound at the right time-position would still leave all these alterations in place. That's an insanely complex problem."
] |
[
"At the heart of echo cancellation is cross-correlation. Basically you're looking for how similar your incoming sound is to the outgoing sound, once you find the offset of cross-similarity you can attenuate the echo. You can do this on the spatial domain [e.g. looking at PCM samples] or on the spectral domain [looking at FFT bins over time].",
"I'm sure there are a bazillion patents on effective techniques too ..."
] |
[
"What causes a “brain freeze” when eating ice cream or drinking something cold fast?"
] |
[
false
] | null |
[
"Well vasoconstriction is involved but it definitely is not the carotid arteries. If that was the case, we would have mini-strokes every time we ate some really cold. ",
"",
"What actually happens is there are capillaries on your palate which vasoconstrict when something really cold comes in contact. This isn't what actually causes the pain though and this makes sense because a brain freeze doesn't happen when you put something cold in your mouth; rather, it happens as soon as you remove the cold stimulus. When you remove the the cold stimulus, there is rapid dilation of those capillaries. This rapid dilation and change in temperature is picked up by the trigeminal nerve pain fibers (which are close by) as pain. That is why you get a brain freeze"
] |
[
"Well vasoconstriction is involved but it definitely is not the carotid arteries. If that was the case, we would have mini-strokes every time we ate some really cold. ",
"",
"What actually happens is there are capillaries on your palate which vasoconstrict when something really cold comes in contact. This isn't what actually causes the pain though and this makes sense because a brain freeze doesn't happen when you put something cold in your mouth; rather, it happens as soon as you remove the cold stimulus. When you remove the the cold stimulus, there is rapid dilation of those capillaries. This rapid dilation and change in temperature is picked up by the trigeminal nerve pain fibers (which are close by) as pain. That is why you get a brain freeze"
] |
[
"And put your tongue against the roof of your mouth, it warms the blood vessels there."
] |
[
"Why were animals so large in the past (Giant Sloth, Giant Leatherback Sea Turtle, other giant animals) but so small now?"
] |
[
false
] | null |
[
"The AskScience FAQ has some lovely things to say on this topic! ",
"Weren't insects huge in the past because oxygen levels were higher?",
" ",
"Could a dinosaur breathe in today's atmosphere? Weren't animals bigger when there was more oxygen to breathe?",
" ",
"Why are animals smaller today than in the past? Why were dinosaurs so huge?",
" (Also covers mammals) "
] |
[
"This comment has been overwritten by an open source script to protect this user's privacy. It was created to help protect users from doxing, stalking, harassment, and profiling for the purposes of censorship. ",
"If you would also like to protect yourself, add the Chrome extension ",
"TamperMonkey",
", or the Firefox extension ",
"GreaseMonkey",
" and add ",
"this open source script",
". ",
"Then simply click on your username on Reddit, go to the comments tab, scroll down as far as possible (hint:use ",
"RES",
"), and hit the new OVERWRITE button at the top."
] |
[
"Giant sloths lived ~10-15k years ago. The air isn't that different. It has more to do with habitat and food supply."
] |
[
"People talk about \"wasting\" water when we run the taps - is that a valid description of how water & sewage systems work?"
] |
[
false
] |
Clarification: I live in a Northern Ontario town with reasonably abundant fresh water. Most of our drinking water comes from two lakes. I'm under the assumption that, once the water leaves a house and goes back into the sewage system, it's treated and released. If that's correct, do we really "lose" the water? I'm sure the system isn't totally closed and therefore some of the water is lost (leaked, evaporated, etc.) But I'd imagine that most of it is reusable.
|
[
"It takes energy to turn dirty water into clean water; while the system is mostly closed quantity-of-water-wise, it is not energetically closed. If you are in an area where water is not supply-constrained, then using too much water is not causing someone else to have a shortage, but it is contributing to the carbon footprint of the water treatment plant. "
] |
[
"I'm from Los Angeles. We source our water from 500+ miles to the north, which has nearly destroyed several ecosystems, notable the Owens Valley and Mono Lake (see ",
"photos",
")\nAfter it goes down the drain, LA water is treated and flushed into the Pacific. It never recharges the water table up north- that's a waste!",
"In terms of energy consumption, the aqueduct is largely gravity fed and the city's main treatment plant captures methane gas from sewage to help power its operations. The main waste involves the resource itself."
] |
[
"I can see that having to ",
" all that clean water between the tap and the treatment plant would increase the energy cost, but how big is the impact on actual treatment? In other words: How much does the energy cost of water treatment depend on ",
" versus ",
"?"
] |
[
"What do irrational numbers \"mean\"?"
] |
[
false
] |
An irrational number is one that can't be represented as a fraction of two integers, but how is this reflected in real terms. I.e. 1.7 is one whole plus 7 out of 10 pieces of another whole. But is there any way to describe irrational numbers in terms like that? I can only imagine a whole object being divided infinitely, but I don't know how this would exist on real life. I hope this question makes sense.
|
[
"This is a very good question that deserves a very careful answer. This is going to be a long post, because I'm going to go into quite a bit of detail and using the simplest terms.",
"In order to understand an irrational number, it is very important to realize that this is just one level in a whole hierarchy of numbers. The starting point is the ‘natural numbers’: 1, 2, 3, and all the other numbers you get from those by adding one repeatedly. This is useful for things like counting apples or ten dollar bills. The important point about these numbers is that they were defined with respect to a mathematical operation: adding one. Every number ",
" we obtained could have been obtained from some other number ",
" using the formula ",
" = ",
" + 1. It is reasonable to write ",
" + ",
" as short-hand for ",
" + 1 + 1 + ... + 1 (",
" ones). So we can talk about trying to solve the equation ",
" + 2 = 5.",
"We quickly encounter a problem, however, if we try to solve ",
" + 5 = 2. We can’t do it with the natural numbers, even though it is quite reasonable to encounter this kind of equation in real life. For example, I put $5 in my bank account and the balance is now $2. This only makes sense if I owed the bank $3 to start with, but this idea of a ‘negative’ number isn’t covered by the natural numbers. There is some kind of missing piece when you try to use the natural numbers to keep track of money. The natural numbers, together with the negative numbers and zero, are called the integers.",
"This all seems a bit pedantic, but something historically and philosophically important happened when we accepted the negative numbers. We realized that different kinds of numbers need to be used to describe different kinds of situations. The rational numbers come from multiplication in exactly the same way that negative numbers come from addition. The rational numbers let you solve ",
" x 5 = 2 just as the integers let you solve ",
" + 5 = 2.",
"Now we come to the issue that we can’t find a rational number ",
" such that ",
" = ",
" x ",
" = 5. It turns out that no such rational number can exist. That is because such a rational number could be written as ",
". We have (",
") x (",
") = 5, which means ",
" x ",
" = 5 x ",
" x ",
". That means ",
" is divisible by 5 (say, ",
" = 5 x ",
"). If ",
" were also divisible by 5, we could have cancelled the 5 from the top and bottom (e.g. 5/10 = 1/2), so it is reasonable to assume that ",
" is not divisible by 5. However, ",
" x ",
" = 25 x ",
" x ",
" = 5 x ",
" x ",
", which means ",
" x ",
" = 5 x ",
" x ",
", which means ",
" is divisible by 5. A contradiction!",
"This is a completely convincing argument, and yet it is unsettling. Notice that 2.2 x 2.2 = 2x2 + 2x2x(2/10) + (2/10)x(2/10) = 4 + 8/10 + 4/100 = 4.84, which is pretty close to 5. In fact, 2.23 x 2.23 = (2.2)x(2.2) + 2x(2.2)x(0.03) +(0.03)x(0.03) = 4.84 + 0.132 + 0.0009 = 4.9729 is even closer. 2.232 x 2.232 = 4.981824 is closer still. Just as there was a gap in the natural numbers that prevented us from solving equations involving addition and there was a gap in the integers that prevented us from solving equations involving multiplication, so too is there a gap in the rational numbers preventing us from solving equations involving powers.",
"The numbers we have to add to talk sensibly about more complicated equations are correspondingly more complicated. One can spend entire lifetimes studying the so-called algebraic numbers and transcendental numbers and quaternions and Clifford algebras and all the other things you get by solving different kinds of equations. The intuition for the irrational number you are considering depends very much on where you got it from. It is a mark of the so-called ‘real’ numbers (a bad name, in my opinion) that they can all be approximated arbitrarily well by rational numbers, just as 2.232 was an approximation of the irrational number called √5.",
"So think of irrational numbers as being a kind of number that is not rational, but (usually) can be approximated by rational numbers. There are some obvious ones that can’t (like √-1), but you are unlikely to encounter these unless you are doing fairly advanced science or engineering."
] |
[
"If you can measure 1 inch with enough precision you can measure sqrt(2) inches with the same amount of precision: First construct a square with side lengths of exactly 1 inch (using your precise 1-inch ruler). Then cut the square in half along the diagonal, giving you two right-angled triangles. The lengths of these diagonals are now exactly sqrt(2) inches, by geometry."
] |
[
"You can not measure any physical length with infinte precision. So you can never measure a length to be exactly sqrt2 inches, but you can't measure something to be exactly 1 inch either.",
"For physical measurements, you can only measure up to some accuracy, so I am not really sure what you mean. Your zooming in argument applies for something 1 inch, just as much as it does sqrt2 inches, or any other number."
] |
[
"Why are the racks for test tubes 6x12 and 6x6"
] |
[
false
] |
I find this highly illogical in impractical and it seems no one can provide me with an answer as to why this is.
|
[
"Don't underestimate the power of \"it's always been that way\". Before metric was adopted, a \"dozen\" was often used as a unit. Eggs still come in dozens in many places, for instance.",
"Test tubes have been around for a LONG time, and after a university has invested in racks that hold them, of a specific size, and then all of the autoclaves hold them in those units, and they fit nicely on the shelves..... you get the idea. Buying a bunch of 5x10 units would just not stack nicely.",
"This is in the same department of why people use Qwerty keyboards, why Americans can't figure out metric and why newspapers still circulate - better ways might exist, but we're just used to the one we already have."
] |
[
"All my test tube racks are 4x10 or 5x12. Perhaps that's all you see because that's all your school/company buys."
] |
[
"That is just the size you're used to seeing wherever you do science. My lab uses lots of 4x10 and 4x5 racks. In grad school we used 8x12 all the time. "
] |
[
"Why does scratching an itch make it stop itching?"
] |
[
false
] |
Well, ive wondered this for awhile now. I appreciate any answers :)
|
[
"You may want to check out ",
"this",
" story. Not exactly scholarly but still interesting.",
"A brief synopsis (from my memory of reading it a few years ago) is that the brain might create some itches when it lacks sensory data from a region of the body. By forcing the hands to that area, in order to itch, it gets another sensory input on the area. The itch is relieved when it has sufficient information."
] |
[
"It's a reward for following instructions. ."
] |
[
"This seems right to me, anyway. The skin sends out an itch signal when it detects any sort of external parasite. Scratching is a behavior tailored to remove parasites. Scratching relieves the itch and (hopefully) removes the parasite in the process. If anyone has data on this, please chime in, I don't have time to go hunt for it. "
] |
[
"Are the superheavy elements well-mixed in the galaxy? Are there \"nuclear deserts\" where one might find the heaviest things (tellurium) absent?"
] |
[
false
] | null |
[
"To answer this, you must first consider the way different elements form in the first place - information that, fortunately, SDSS has compiled in this graph of the periodic table:",
"https://upload.wikimedia.org/wikipedia/commons/thumb/3/31/Nucleosynthesis_periodic_table.svg/2560px-Nucleosynthesis_periodic_table.svg.png",
"you'll see here that surprisingly, heavy elements aren't always produced differently to lighter elements: Both Carbon and Cerium are produced in majority by low-mass stars. As such you probably won't find any parts of the galaxy entirely missing these.",
"What's slightly more of concern are elements made by colliding neutron stars (purple on this chart) - in the halo of the galaxy these are triply hard to find:",
"As a result, we should expect to see that elements almost only synthesized by neutron stars (Iodine, Rhenium, Osmium, Iridium, Europium, Terbium, Holmium, Platinum, Gold, Bismuth, Polonium, Astatine, Radon, Francium, Radium, and Actinium onwards) should be extremely rare, or almost nonexistent, in the halo and other far outer parts of the milky way; although other heavy elements like Mercury, Thallium, and Lead should be counterintuitively fairly common, as low-mass stars still produce these."
] |
[
"Other than us being far enough from the galactic core for planet sterilizing astronomical events to be rare, but close enough for heavy elements to have some abundance, I haven't seen anything specific.",
"But it is really difficult to do detailed compositional analysis of every type of object in the Galaxy, and even the composition of comets and asteroids in our own solar system is still a matter of intense research. So lots of room for potential surprises."
] |
[
"Well, titanium is listed as .44% of the composition of the Earth, or 4,400,000 parts per billion. But it comprises only 3,000 parts per billion of the universe at large. (Both figures according to wikipedia.) So Earth has over 1,200 times the titanium we should compared to the universe as a whole. But this shouldn't be too surprising, since we're on a rocky planet and not a ball of mostly hydrogen."
] |
[
"What are quarks?"
] |
[
false
] |
My friend insists that quarks, leptons and bosons fall under the category of "quarks", while I say that quarks are their own subcategory, along with leptons and bosons, under the larger category of "subatomic particles". Who's right?
|
[
"First you have the fundamental particles. They divide into two main families based on their property of \"spin.\" Integer-spin particles are bosons, and half-odd-integer spin particles are fermions. Fermions have the property that no more than one can occupy any given state, so they form the structures that we think of as \"matter.\" Bosons can occupy a state multiple times, and their properties allow them to exchange momentum between fermions, or in other words, they exchange forces between the fermions.",
"Among the fermions there are again 2 major families, those that feel the strong force and those that don't. Those that do feel the strong force are quarks and those that don't are leptons. The leptons again divide into particles that feel the electromagnetic force (electrons, muons, tau leptons) and those that do not (neutrinos). ",
"So quarks are the strong force feeling spin 1/2 fundamental particles. But not all fundamental particles feel the strong force, nor are they all spin 1/2."
] |
[
"Yes, those are three distinct categories of sub atomic particles.",
"However, I think you mean \"gauge bosons\" or \"force mediators,\" both of which are used to describe the bosons in the standard model. The term \"boson\" is more general than you imply."
] |
[
"Yeah I showed my friend this, he still doesn't believe me.",
"EDIT: I absolutely love your username btw"
] |
[
"Communicating to past/future self?"
] |
[
false
] | null |
[
"Frequency of what? You can comminucate with you future self by just leaving a written/recorded message. They just can't answer back."
] |
[
"All organisms are made out of atoms and molecules, which means literally every living thing is radiating energy and vibration. Every living thing on earth vibrates at its own level with its own sound, determined by the velocity of its frequency. So what I’m getting at is maybe there is a way that we can find a frequency of the past and communicate with them or possibly the future."
] |
[
"All organisms are made out of atoms and molecules, which means literally every living thing is radiating energy and vibration. Every living thing on earth vibrates at its own level with its own sound, determined by the velocity of its frequency.",
"That's all more or less correct. You can listen to sound emitted by things and the electromagnetic frequencies they emit. But how would that help you communicate with something in the past? You cannot send signals back in time."
] |
[
"Did scientists notice empirical deviations from classical mechanics or classical electrodynamics before Einstein offered a theory to extend them?"
] |
[
false
] |
In other words, did scientists already think something was wrong with their theories? Or did they assume measurements were reasonably predicted by those theories?
|
[
"Yes. A good example is the ",
"Michelson Interferometer",
". There was a belief before relativity that there existed some absolute frame of reference against which all velocities could be measured -- some sort of cosmic \"ether\" in which everything was embedded.",
"By interferometry you could determine the absolute velocity of Earth. The experiment yielded NO motion against the absolute background. Since we know the Earth goes around the sun and the sun orbits the center of the galaxy, this made no sense at all.",
"Physics was clearly borked! Relativity was the solution."
] |
[
"Astronomers observed there was a mismatch between Mercury's actual orbit and its orbit as predicted by Newtonian physics. Because a similar mismatch had predicted the presence of Neptune before it was observed, ",
"one explanation was the existence of a planet even closer to the Sun than Mercury",
", but relativity solved the problem of Mercury's orbit."
] |
[
"The aether represented a specific model. That model was proven wrong. If it so happens that a modified aether model can explain things, it is no longer an aether by definition, but instead some new idea that was inspired by an aether model. "
] |
[
"Does the electromagnetic force have a similar affect on space-time as gravity?"
] |
[
false
] |
Or any other fundamental force. If not why is gravity the only one; and consequently identified as a “fundamental force”, when it would be more appropriate to call it a mere side effect of Existence?
|
[
"Yes, for a certain definition of \"similar\". The space-time curvature is related to the total \"stress-energy\" in a volume, and the EM force is part of that stress-energy. But most realistic densities of EM energies are very very tiny compared to gravity.",
"As for \"mere side effect\" ... I don't see what the point is of using that wording. EVERYTHING is a \"mere side effect\", so what is the main effect?"
] |
[
"If not why is gravity the only one",
"Go the opposite way: Find all ways a force can be described as change in spacetime. It turns out they all look like gravity. They don't have to look exactly like general relativity but they all lead to the same result in everyday life: A force proportional to the masses and the inverse square distance."
] |
[
"So since the em force is 10",
" times stronger than we should only need a 1/10",
" the mass to generate black holes with pure magnetism? This doesn’t seem to be right, because this would have been done by now surely.",
"If gravity alone is responsible for the bending of space time, then it would seem this doesn’t need a particle (to be quantized) carrier? Since all the other forces need particles and have limited effects, since they don’t bend space time the same as velocity/gravity"
] |
[
"Lobsters supposedly show no measurable signs of ageing and only die from external causes. Can we use this to increase the life-span of humankind?"
] |
[
false
] |
Repost from . I didn't quiet get the answer I was looking for. Is it possible and why/why not?
|
[
"It's thought that ",
"lobster longevity",
" is related to very high levels of the enzyme ",
"Telomerase",
"(",
"1",
"). By ",
"changing the levels of telomerase expression",
" in mice, ",
"it's possible to manipulate their longevity",
" (",
"2",
"). This is being looked into as a potential therapy for premature aging. It's ",
"unlikely that this could prove to be a good way to increase human lifespan",
", however.",
"In addition to telomeres, there are ",
"many other factors involved in ageing",
". I don't think there's any evidence that lobsters have any special mechanisms that counter these other aspects of senescence.",
"EDIT: This post is getting a lot of downvotes; if people would leave a note explaining why that might help me provide better answers. Is \"I don't know about lobsters but stem cells are cool so let's talk about that instead\" really so much better an answer?"
] |
[
"Turritopsis!"
] |
[
"Lobsters and selective other animals are considered negligible senescent, as far as we know do not display the typical signs of senescence. Humans age and die due to cell senescence and the failure of body systems (ultimate cause of natural death would be failure of organs). I don't think anyone knows why lobsters do not display signs of aging but for human beings many cells are not replaceable or decrease in their ability to regenerate which is why aging occurs in the first place.",
"\nThis whole stem cell research thing is what will allow us to increase the life span of humankind. By using stem cells, we are able to replace 'damaged' cells and allow the stem cells to differentiate and replace these cells. By replacing the cells we are essentially renewing our ability the regenerate cells and thus slowing down aging.\nNow with a highly metabolic creature as human beings, I don't think there is much comparison to a crustacean such as a loberster but I hope I somewhat answered your question to the best of my ability."
] |
[
"Why is Thorium three times more abundant than Uranium in Earth crust but it's radiation doesn't affect us much?"
] |
[
false
] | null |
[
"Uranium's radiation doesn't really affect us. The alpha particles it emits are easily blocked. Uranium's first use was in glassmaking: it adds a brilliant fluorescent green colour. In fact, depleted uranium emits so little radiation that it's an effective gamma ray shield due to its density. The main problem in terms of radiation comes from decay products like radon (which has a tendency to collect in one place since it's a heavy gas) and fission products like caesium-137 and strontium-90, which can bioaccumulate and whose gamma rays are bad for our DNA."
] |
[
"Natural Thorium is mainly Th-232, which has a half life on the order of ten billion years; Natural Uranium is primarily U-238 with a half life of about four billion years. Even excluding their relatively low abundance, these long half lives mean they have a low activity and don't really make too much of a daily radiation hazard."
] |
[
"Thanks!"
] |
[
"The situation with bee Colony Collapse across the world: Have bans against certain pesticides made an impact?"
] |
[
false
] |
I'm not fully informed on the topic, but to my understanding, EU banned certain pesticides and the US have not. What's the 2021 situation on pollinators in the EU vs the US?
|
[
"Neonicotinoid pesticides are seen as the most problematic for bees. The EU ",
"banned",
" the use of neonicotinoids on pollenator-attracting crops in 2013, and in open fields in 2018. However, there have been some significant ",
"loopholes",
", thus the risks to bees are ",
"persisting",
", but the population-level benefits of the bans are unclear. I unfortunately haven't seen post-2018 data on bee populations in the EU."
] |
[
"The Genetic Literacy Project is a corporate front group that was formerly funded by Monsanto. So excuse me if I don't take it as gospel that there chemicals aren't killing bees."
] |
[
"The Genetic Literacy Project is a corporate front group that was formerly funded by Monsanto. So excuse me if I don't take it as gospel that there chemicals aren't killing bees."
] |
[
"Why does salt water dehydrate you when salt helps you retain water?"
] |
[
false
] | null |
[
"Part of the problem is, seawater is really salty, about 3.5% salt by weight. An 8 oz (227 g) serving of seawater contains about 8 grams of salt. That's a lot of salt! The recommended maximum per day for sodium is 2.3 grams, which corresponds to 5.8 grams of NaCl table salt, about the same as in 1 teaspoon.",
"By comparison, bodily fluids like blood serum, cytoplasm, or interstitial fluid, are only about 0.9% salt by weight. When seawater comes into contact with cells in the intestines, where water is usually absorbed, osmosis pulls water out of those cells until the concentration is equal on both sides of the cell walls. So for every 8 oz serving you consume, your intestines want to supply 31 oz of water to equalize the concentration of salt.",
"So right there you're going to have problems, but in addition to your body dumping a bunch of water into your intestines, it's also going to absorb some of that salt and put it into the bloodstream. Your kidneys will be like \"Whoa! Too much salt!\" and try to get rid of it. But the only way they have to get rid of it is to concentrate salt into your urine, and they can only make that a little less salty than seawater. That means they're going to have to get rid of water to get rid of salt. They're expecting you to resupply your body with freshwater, and they don't have a backup plan when you don't do that. So now you've got diarrhea and your peeing too much, and you're probably vomiting too - you're probably going to die of dehydration.",
"When eating salty foods, it's a different story, usually. The mix of liquids and food in your intestines isn't going to be nearly as salty as seawater, so your body will be fine with just absorbing the salt and the water. But if you eat a lot of salt, it's still going to want to pull water out of your cells, so your cells end up a little dehydrated unless you drink a lot of liquids. So then you get a lot of liquids in your blood, and you get high blood pressure. Then your doc prescribes a diuretic so you'll pee some of that extra water out, and the salt you ate along with it."
] |
[
"Thanks for explaining the answer in a more understandable way than found though the Google."
] |
[
"about 0.9% salt by weight. ",
"Er, NS IV fluid 0.9% NaCl, but your body has many more solutes. the osmotic pressure of your serum is the same as normal saline, but the solutes are a cocktail of ions and organic molecules."
] |
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