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[
"Assuming we had (nuclear?) power plants producing electricity at 'near zero' cost, - what technology or process would we then use to product a liquid energy store?"
] |
[
false
] |
Synthetic petrol, if you will, but not synthetic in the biomass/corn sense.
|
[
"Hydrogen is the easiest one to produce (but maybe not to use)."
] |
[
"So think about the fact that hydrocarbons are really really great stores of energy. They're stable (not really likely to explode), not particularly volatile (evaporate slowly relative to say, pure hydrogen), and have high energy density. Oh, and we already have an extremely well developed hydrocarbon infrastructure.",
"Now think about their downsides: they take buried carbon and combine it with atmospheric oxygen to release CO2. So wouldn't it be nice if you could take CO2, release the oxygen back into the atmosphere and put the carbon back into a hydrocarbon. (And thus not have to pull more carbon out of the ground) You kill 3 birds with a single stone. Granted they're 3 birds you created in the first place but whatever...",
"Lo, and behold, we already have an ",
" system that does ",
". And not only does it not require electricity at near zero cost, all it requires is light from the sun. Photosynthesis.",
"Now I'm fairly anti-current-biofuels because they're really entangled in legislative provisions. Giant corn farms get subsidies to convert food crops to fuel or whatever, but this is just my personal opinion. Don't take it as some sort of absolute truth. But it's ",
" a young area right now. We're working on algae that does the work many many times more efficiently than stuff like corn, without harming food supplies. "
] |
[
"BS hard to use. Just mix tiny amounts of it with regular air, light it on fire, produce electricity with a microphone."
] |
[
"How would gravity work with planet sized non-spherical object (for example a long cylinder)? Would gravity be stronger at the ends compared to the middle of the side?"
] |
[
false
] |
If you stand on the end you would have say 15km of material beneath you, pulling you down. But if you stand on the side you would have only 4-5km of material beneath you, pulling you down.
|
[
"No, the statement that gravity acts through the center of mass is incorrect. It is correct in some simple cases, such as spherical objects when you're located outside the sphere. But there are counter-examples.",
"One such example is a hollow sphere, where you are in its interior, but not in the center. While you're at a non-zero distance from the sphere's center of mass, you don't experience any gravity (due to the Shell Theorem or Gauss' Law).",
"Additionally, an infinite line has a gravitational field that is perpendicular to the line. This is, in good approximation, also true for a rod where the width is far smaller than it's length, like the 1m vs a few billion miles of your example. The gravitational force would be almost exactly the same (both direction and magnitude) at the middle of the rod as it would if you were at 3/4th or even 9/10th of its length."
] |
[
"If you're off from the end of the rod, the gravitational field is the same as a point-mass located at the centre of the rod.",
"If you're near the middle of the rod, and it's very long, the gravitational field will be twice that of what is felt from the end. You can think of this as being able to get closer to the centre of mass near the middle than near the end.",
"This is the same as the problem of the electric field of a charged rod, which is discussed here: ",
"http://www.phys.uri.edu/gerhard/PHY204/tsl31.pdf"
] |
[
"In the limit that the rod's length is much larger than its diameter, and you are close to the rod, the direction of the gravitational force is towards the rod's axis rather than towards the center of mass. This is because a very long rod can be approximated as infinity long and an infinitely-long rod has no center of mass because of symmetry.",
"Mathematically, an arbitrary gravitational field created by a localized object can be expanded into the sum of a series of multipole moment terms. The first term in the series, the monopole moment term, is equivalent to the gravitational field of a point particle, which happens to be equivalent to the field of a perfect sphere. Therefore, the closer a gravitational body is to a sphere, the more the monopole moment dominates and the more accurate is the approximation, \"gravity points towards the center of mass\". However, if a body of mass significantly deviates from a sphere, the higher-order multiple moments will become significant and the approximation \"gravity points towards the center of mass\" will become less accurate. "
] |
[
"Why is it that when one's eyes or nails turn yellow is it a sign of liver failure? Why yellow? What is taking place for this to happen?"
] |
[
false
] | null |
[
"What you're describing is called ",
"scleral (or conjunctival) icterus",
" (literally yellowing of the white of the eye), and it is a sign of jaundice, which describes a state of excess bilirubin in the body. Bilirubin is one of the breakdown products of hemoglobin, and is normally conjugated in the liver to make it water soluble, and then excreted in feces (as part of bile), as well as through urine. If that process is interrupted via liver damage (or if hemoglobin degradation increased, as with hemolysis), it may result in inability of the body to get rid of all that bilirubin, and its buildup within the body. Bilirubin and its metabolic degradation products are pigmented, and produce varying colors depending on which step along the degradation pathway it's on. (This is also contributes to the color of your stool and urine.) The ",
"wiki",
" section has more details on the steps and the colors they produce if you're interested."
] |
[
"This phenomenon is called jaundice and is associated with a number of diseases and there are different mechanisms involved. The main culprit is bilirubin - a breakdown compound from red blood cells. Bilirubin is insoluble in water and is transported to the liver where it is attached to a sugarish molecule, making the compound soluble and allowing for its removal from the body. ",
"Removal takes place through bile, a large portion is secreted through the intestines, where it is processed by your gut microbes producing the dark brown color of your stool. A small portion is removed through our urine, coloring it yellow. ",
"If any of the processes involved in removing the bilirubin is affected by disease or illness the concentration of bilirubin will rise. This will cause a higher concentration in most tissue, where it is easily noticed in the whitest, like the eye.",
"There is a lot of research being done with regard to neonatal Hyperbilirubinemia (hyper = high) ",
"Stanley ",
" - An Evidence-Based Review of Important Issues Concerning Neonatal Hyperbilirubinemia",
" ",
"Wikipedia has a nice list of related illnesses: ",
"link"
] |
[
"producing the dark brown color of your stool",
"A bit in the novel version of \"Silence of the Lambs\" has Lecter telling the FBI that they should go after one (non-existent) \"William Rubin\". Lecter was amusing himself by giving them such a shitty clue."
] |
[
"How do huge structures get buried?"
] |
[
false
] |
Huge structures such as houses, pyramids and whole cities that are hundreds or thousands of years old are often found below the surface, often while digging for construction. My question is how can these tho vs simply get buried? Esp. In places where humans have always lived and nature hasn't reclaimed the settlment.
|
[
"I would say that Kolmanskop in Namibia is a good example to bring up, with weathering, in how buildings, particularly those near deserts/loose sediment, can become buried from the weather. The straightforward process in this example being; sediment is carried by the wind into buildings, where it builds up against the walls, finds it's way through the doorways and windows; etc..",
"In this example though, there is sediment all around, easily visible. It's not a big stretch to think that the wind could blow it into mounds against the buildings until they are covered.",
"However, in other areas, with more solid earth, how likely is this to happen? Less so, probably. In Greece we have ruins still clearly visible; unburied. Yet they are experiencing some growth of plant matter.",
"-just to add to your answer."
] |
[
"I would say that Kolmanskop in Namibia is a good example to bring up, with weathering, in how buildings, particularly those near deserts/loose sediment, can become buried from the weather. The straightforward process in this example being; sediment is carried by the wind into buildings, where it builds up against the walls, finds it's way through the doorways and windows; etc..",
"In this example though, there is sediment all around, easily visible. It's not a big stretch to think that the wind could blow it into mounds against the buildings until they are covered.",
"However, in other areas, with more solid earth, how likely is this to happen? Less so, probably. In Greece we have ruins still clearly visible; unburied. Yet they are experiencing some growth of plant matter.",
"-just to add to your answer."
] |
[
"You are mostly describing how buildings get old and fall apart. He was specifically asking about getting buried. Where does this 5 meters of earth come from?"
] |
[
"Is it possible to think about a sound that cannot be created/replicated?"
] |
[
false
] | null |
[
"My favorite color is purplish-orange. My second favorite is greenish-red"
] |
[
"My favorite color is purplish-orange. My second favorite is greenish-red"
] |
[
"Do you mean Periwinkle? "
] |
[
"Are there any enzymes that catalyze inorganic molecules and hydrocarbons ?"
] |
[
false
] |
Can I get their names, if that is possible?
|
[
"I'm not sure what you're asking. Enzymes catalyse specific chemical reactions, like the synthesis or degradation of a molecule. I don't think that saying that an enzyme catalyzes a molecule makes sense. Also, inorganic molecules and hydrocarbons are different things. For chemists (and biochemists) organic molecules are basically most molecules made from carbon (",
"Wikipedia definition of organic",
".) Hydrocarbons are organic molecules to chemists. ",
"If you're thinking of hydrocarbons like oil, natural gas, and coal those are formed from the decomposition of organisms. I don't think there's an enzyme that contributes to this, it's just time, pressure and heat. The hydrocarbons in living organisms are the basis for many biomolecules and you'd need to look up all the individual reactions to find the enzymes involved in their synthesis and degradation. ",
"There are inorganic molecules that are important to life. Water, salts, carbon dioxide, etc. These are involved in chemical reactions in organisms as both reactants and products, so enzymes would both synthesize them and break them up. Again, you'd have to look at the many many different reactions in an organism to get the enzymes involved."
] |
[
"I would look into deep-sea vent biology and chemosynthesis for examples of inorganic biocatalysis and methane metabolism for leads on hydrocarbon biocatalysis."
] |
[
"Yes, there are enzymes which catalyze reactions involving those. An example off the top of my head is catalase, which breaks down hydrogen peroxide (H2O2), which is an inorganic molecule. From a quick google search, I found ",
"this",
", which seems to be able to break down the C-H bonds in hydrocarbons."
] |
[
"Why do vacuum-tube amplifiers sound so much louder, per watt of output power, than their solid-state counterparts?"
] |
[
false
] |
[deleted]
|
[
"Did you check if the 100-watt digital receivers are actually \"100 Watt peak-to-peak\" ? ;)",
"Old electronics were measured properly (RMS). Later marketing has turned output power to a lie.",
"In other words, if output is measured correctly then 100 watts is always 100 watts and should sound the same.",
"Edit: check ",
"this",
"."
] |
[
"Exactly, a 100Wpp receiver would only be around 35Wrms."
] |
[
"disclaimer- i am not a musician, and know very little about the specifics of guitar amps, so this is largely speculation- i do have a little background in electronics, though not professionally, so take my thoughts with a grain of salt...",
"i think this has more to do with the perception of sound than the actual sound pressure being produced by the speakers- tube amps tend to be simpler (in terms of circuit complexity, not their behavior) than solid state, mainly because of space and heat constraints- so a tube amp is not the most linear, it tends to distort somewhat. solid-state, on the other hand, being smaller, can pack in a lot more compensation circuitry to avoid distortion. the shape of a waveform can have a significant affect on the perceived \"loudness\", so the sound may only seem louder because of some difference in relative frequency content...",
"on the other hand, tubes might really be louder- i think tubes can exceed their ratings a little for brief periods without too much trouble, though that may shorten their life a little- so you might actually end up overdriving it, and it will sound ok, while solid-state amps tend to work up to the point that they exceed their ability to dissipate heat, and then they release their magic smoke and never work again- so they include circuitry to limit their power output before they reach that point, i.e. clipping, which is distortion- if it's a particularly sophisticated amp, i would guess it might back off the gain temporarily when that happens to avoid the distortion, which would explain it not quite reaching the \"max\" that the equivalent tube amp is capable of."
] |
[
"If your muscles are passively moved, would your heart rate go up?"
] |
[
false
] |
I remember an electric exercise bike from years ago and it made me wonder if you could be completely relaxed and your muscles were moved passively, would your heart rate go up? Would the muscles being moved (contracted and lengthened) respond in some way (for example, increase in bulk) similar to how it would if they were actively moving?
|
[
"Your heart rate would not increase as a result of the movement. If it were to increase, it would be due to you psychologically reacting to the situation or otherwise. But since you aren't using energy (ATP) to move your muscles and exert force on the bike, your heart rate isn't going to go up."
] |
[
"My thoughts were that movement of the limbs moves the muscles contracting the veins that are within which in turn moves an increased amount of blood back to the heart. This increased blood coming back to the heart forces the heart to do something with that blood, and so it pumps faster. "
] |
[
"If anything happened there would probably be a decrease in heart rate to compensate for the increased blood flow from squeezing the veins, all other things being equal."
] |
[
"What are the characteristics that allowed multicellularity to evolve on earth?"
] |
[
false
] | null |
[
"But cells in a multi-cellular organism live side by side. They don't engulf each other. How can a bacteria engulfing mitochondria(if that is indeed the reason for cells containing mitochondria) be evidence for multi-cellular organism evolving? A multi-cellular organism is nothing like a cell containing mitochondria. "
] |
[
"There is a nice explanation of how eukaryotic cells evolved, but the OP asked about multicellular life, which is a bit different. In some sense, multicellular life is pretty simple - you just need cells to decide it is easier to stick together than remain apart. Bacteria do this when they form a ",
"biofilm",
". However, many people don't define biofilms as multicellular life because they don't show nearly the level of specialization that animals, plants, and fungi do. ",
"So another question we could ask is why are eukaryotic cells able to form the complex multicellular organisms that aren't observed in bacteria and archaea. This boils down to the fact that eukaryotic cells seem to be capable of ",
"differentiating",
" into many cell types and these can form into distinct tissues and organs. So why can eukaryotic cells differentiate into so many cell types? Here we have to speculate, but one theory I heard proposed at a conference (can't remember the name of the speaker) was that ",
"nucleosomes",
" were a key factor. They are able to be modified through dozens of potential post-translational modifications, and that may provide more flexibility for epigenetic control. We really have a ways to go before we understand all the mechanisms that allow for ",
"stem cell differentiation",
" though, so we can't really prove that any one feature of eukaryotic cells was necessary for complex multicellular life to evolve.",
"Whatever was necessary, multicellular life has ",
"evolved more than once",
", even if you only count \"complex\" multicellular life. ",
"Plants and animals",
" all evolved into multicellular organisms independently."
] |
[
"As is usual in nature, all these challenges can be addressed in a slow creeping manner - eg by starting with just a two-celled species, then a 4-celled species, etc"
] |
[
"When a solid physical object is broken into two pieces. Why don't the pieces fuse back together when hold together tightly?"
] |
[
false
] |
My understanding is that molecules are attracted to each other by Van Der Waals forces, and the atoms in the molecules are held together by the strong nuclear force. So when you put the pieces back together, and they fit perfectly, shouldn't they fuse together again? what is preventing this from happening?
|
[
"A few reasons. As ",
"/u/airbornemint",
" said, you'll never get them back together perfectly. Further, even if you had two pieces of identical metal, polished to the highest tolerances capable and perfectly flat, you'd never actually get them close enough to reform those bonds, at least while in the presence of an atmosphere. This is for two reasons.",
"1: As ",
"/u/D-Evolve",
" mentioned, things oxidize in the air. As soon as the material is broken and exposed to air, it instantly begins to develop a layer of oxidation. Even if this layer were only 1 atom thick, it would prevent rebonding. In space, if an object is lacking oxidation to begin with, it will not develop it. So, if you have a tool, say a wrench, with no oxidation, and a bolt, of the same material and also with no oxidation, on contact, the two can fuse. This is called cold welding. ",
"2: Now let's say you have an atmosphere, but it is of only a noble gas. It will not oxidize anything, but the ambient pressure is 1 atmosphere, the same as Earth. Bringing two pieces of metal close enough to touch will still never occur, because you will never achieve a perfect vacuum between the two pieces. There will always be some amount of atmosphere between them, preventing them from bonding."
] |
[
"Yes, do it inside a vacuum chamber; it is already used in some types of nanofabrication."
] |
[
"Yes, do it inside a vacuum chamber; it is already used in some types of nanofabrication."
] |
[
"How big would a cube of Lead have to be for it to be unable to hold its shape?"
] |
[
false
] |
I would think that if you had a cube of lead that was big enough, the weight pushing down on the bottom half or fifth etc. would deform it into a trapezoidal looking shape. At what dimensions would this occur?
|
[
"A related question: if the cube were floating in outer space, how big before its own gravity would pull it into a blob? ",
"And the bonus question, how hot would it get in the process?"
] |
[
"Distortion occurs at any dimension. It depends on noticeable you want the effect to be. If you know Poisson's ratio and Young's modulus for lead the calculations for any size block are trivial."
] |
[
"I did some math and I got the same answer as PhatZounds.",
"Assume you have some column of lead with cross-sectional area \"A.\" Pressure is just force over area, or ",
". The maximum force experienced will be at the bottom of the column of lead of length ",
". Now, force is given by mass times acceleration (assuming acceleration to be uniform on the scale of the cube; acceleration being ",
", Earth's gravity); so pressure is ",
". Mass is given by density times volume, or ",
". With our variables, volume is a product of the cross-sectional area times the length of the rod, ",
"; mass is then ",
". Now substitute that in and our equation for pressure becomes ",
"; of course ",
" cancels out here and our pressure is then given by ",
". Of course, we're looking for ",
" (which is the height of the cube), so then we can rearrange: ",
"Now for numbers: density of lead is 11340 kg/m",
" , g = 9.8 m/s",
" , and our pressure given by PhatZounds is 5.52MPa or 5.52 MN/m",
" ; substituting that in:",
"x = (5.52 x10",
" N/m",
" 11340 kg/m",
" · 9.8 m/s",
" ) = 49.67 m",
"Hopefully that's right; and if not, I trust someone will point that out!"
] |
[
"Assuming a modern refrigerator of average capacity/efficiency; further, assuming standard use: would the presence of 0.5m^3 of water inside acting as a thermal \"battery\" have any effect on the system's efficiency?"
] |
[
false
] |
...or is this one of those "Newton's Second Law" things where you'd never fully recoup the energy you put into cooling the mass of water in the first place? If we need to define "standard use"; lets say we open the fridge five times a day for five seconds each time. Thanks for your time and your expertise.
|
[
"I don't think you are correct. Let's take this to the extreme...the entire interior of the refrigerator is filled with water (in a container). Now, when the door is opened/shut, there is virtually no influx of warm air, replacing cool air and causing the refrigerator compressor to do work to cool it. The water container is ",
" warmed slightly while the door is open, but this is a much lesser effect than the air exchange. "
] |
[
"As someone else stated, all you would do is add thermal inertia to the system. You would increase the amount of time it would take to change the system from one state to another, but you would not effect the steady-state operation. ",
"Assuming you disregard opening the door and allowing air to move in or out of the refrigerator, the efficiency of the system is just based on the power it takes to overcome the heat gained from the environment. Both of these things are based on temperature (and a few other things, but mainly temperature) and at steady state, temperatures wouldn't be changing. So the heat transfer into the refrigerator, and the efficiency of the system, would stay the same as long as you were at steady state.",
"Assuming you open the door a few times per day, the only ",
" difference you will make is that there will be less air to cool because much of the volume inside the refrigerator has been taken up by water. Then, the refrigerator will return to the previous state a little bit faster. This may seem to contradict what I said in my first paragraph, but what I meant before was more along the lines of testing how long it would take to drop the temperature in the fridge by (just as some random number) 10 degrees. The air in the fridge may cool down quickly, but it will still have to cool the water, so the overall average temperature of the fridge (by mass, for example) will take a lot longer drop."
] |
[
"Zero effect. ",
"The water won't change the amount of heat lost through the exterior. All it will do it add thermal mass, thus 'softening' the warm/cold spikes the interior will experience as the refrigerator cycles on and off, or the door is opened/closed. The presence of water won't affect the opening and closing, unless it's placed in such a way as to block airflow, but even then there will be the same amount of airflow on the front-facing side of the water container, so you'd just be 'protecting' the rear of the refrigerator from getting warmer, but you'd still gain heat on that side of the container, so it's all the same."
] |
[
"How are hazard ratios interpreted?"
] |
[
false
] |
I am curious about the interpretation of hazard ratios, particularly from this study: . I thought it used to be open access, but if it was, it isn't now. Their conclusion was that a high intensity of exposure to formaldehyde leads to a much higher risk of ALS death. It's somewhat confusing because they never address the risk of developing ALS. My main question is how do you interpret hazard ratios? And why does it look bimodal here, meaning a medium risk leads to lower risk of ALS death according to the HRs? One group from Table 1 is shown below. Adjusted HRs* and 95% CIs for ALS mortality by level of occupational formaldehyde exposure, National Longitudinal Mortality Study, men ages 25 years and older, 1973–2011
|
[
"I don't know too much about this, but this seems like a nice explanation: ",
"www.medicine.ox.ac.uk/.../what_are_haz_ratios.pdf",
"Essentially, a hazard ratio is the probability of an event (in this example, ALS mortality) in some experimental group (respondents exposed to some level of formaldehyde) at a given time, divided by the probability of the same event in a control group (unexposed respondents, who are identified as the reference group). The confidence interval takes the place of a p-value. If the 95% confidence interval includes 1, the HR is not significantly different from 1.",
"In this case, it looks like they found that in the \"Low\" group, there was no heightened risk compared with unexposed. In the \"medium\" group, I agree that it does look like there's actually a decreased risk compared with unexposed respondents. Without seeing the full publication (my institution says it offers free access, but then doesn't--very annoying) i can't confirm that this is what the authors say they found, or see if they suggest any reasons why this might be. It would be interesting to know what types of jobs are captured by this category, and what possible protective factors might be specific to this group.",
"I would not call this bimodal; it looks like the \"high' group had relatively too few respondents, and as a result too few ALS deaths (not that any ALS deaths are good :-/ ) to draw any conclusion. The confidence interval goes from ..4 to 5.80, meaning that the 1.53 HR is not significantly different from 1.0.",
"This may be way too simplified, but this website breaks hazard ratios down and offers self-quizzes: ",
"http://www.students4bestevidence.net/a-beginners-guide-to-interpreting-odds-ratios-confidence-intervals-and-p-values-the-nuts-and-bolts-20-minute-tutorial/"
] |
[
"My main question is how do you interpret hazard ratios? And why does it look bimodal here, meaning a medium risk leads to lower risk of ALS death according to the HRs?",
"Hi. Hazard ratios determine the likelihood of a negative event (ex: ALS mortality) compared to some reference group (ex: unexposed people). So for the medium intensity exposure, you'd say that someone with medium intensity exposure to occupational CH2O is 27% less likely to die from ALS compared to unexposed people. Those with high exposure are 1.53x MORE likely to die of ALS than unexposed people.",
"The point estimate is essentially useless if the confidence interval crosses one. The 95% confidence interval tells you with 95% confidence that the real HR lies within that range. So you can imagine that if < 1 means less hazard, > 1 means more hazard and 1 means same hazard, a confidence intervals that spans the entire range of < 1 to > 1 tells you that the results are essential non-significant statistically.",
"The fact that medium exposure is less likely to result in ALS death tells me the author probably did not account for some confounding factor in their adjusted HR."
] |
[
"Thank you. I spent a good amount of time even figuring out what HR stood for, because they don't define it in the publication.",
"You can find a pdf of the publication online.",
"Are hazard ratios the same as odds ratios? I know how to calculate and interpret odds ratios. If so, that clears things up. I use them for analyzing species presence/absence data, not in this context.",
"Edit:I believe they are using this to make these categories.",
"The NLMS is a multistage probability\nsample of the civilian non-institutionalised\npopulation (response rate ∼96%). We\nincluded the 794 541 men and 674 694\nwomen who were at ages 25+ when surveyed.\nParticipants were asked about their\ncurrent or most recent job. We used a formaldehyde\nexposure matrix constructed\nby industrial hygienists at the National\nCancer Institute and previously described.",
"\nIntensity and probability of formaldehyde\nexposure were calculated for each occupation\nand industry, and coded as none, low,\nmedium or high.",
"3 - Wang R, Zhang Y, Lan Q, et al. Occupational exposure to solvents and risk of non-Hodgkin lymphoma in Connecticut women. Am J Epidemiol 2009;169:176–85."
] |
[
"What kind of events/circumstances would it take to cause a world-wide winter/another Ice Age?"
] |
[
false
] |
I am aware of nuclear winter and gamma ray bursts possibly causing it, but is there other non-nuclear/non-radioactive ways that another Ice Age-like event could occur? Edit: I'm asking because I'm writing a novel centered around Earth turning into a frozen wasteland.
|
[
"A sure fire way to cool rapidly is an impact event or super volcano eruption. Throwing billions of tlnes of ash and smoke into the atmosphere causes cooling. However, the timescale of the cooling may not be long enough to create the world you are imagining. Also, if the impacter is much larger than 1-2 km in diameter the immediate effects would be lethal enough to kill everyone. Maybe a multi-strike event of a few 1 km objects simultaneously hitting would suit your scenario best. "
] |
[
"How poles reversing can affect climate? \nSerious question."
] |
[
"They've been watching too many disaster films. There is zero evidence that a magnetic pole reversal would cause any climactic weather events and being that its a process that is thought to unfold over half a million years no human has ever been alive to challenge that theory.",
"Now a physical pole reversal would definitely have some climactic events associated with it, but that's mostly because anything catastrophic enough to cause the Earth to move that much that quickly would very likely destroy the planet anyway. "
] |
[
"Why is it that some particles interact with the higgs field and some don't?"
] |
[
false
] |
I have a very VERY basic understanding of what the higgs field is and what it does but I'm not sure sure I understand what makes particles react with it. So... what makes particles react or not react with it?
|
[
"There is currently no known theory that explains why the various higgs couplings have the values that they do. All we can do is go out and measure them.",
"The Standard Model of particle physics is built out of gauge symmetries, which means that when we create the theory we impose some specific mathematical structure to it. The specifics of this structure ensures that some particles, such as the photon, do not gain a mass by interacting with the higgs. So some people might like to say that these mathematical structures explain why some particles don't interact with the higgs field, but that just raises the question of why the universe admits description by these gauge theories and not others.",
"As far as I know, for particles that do interact with the higgs, there's no way to determine the values the coupling strengths will have."
] |
[
"dern questions... be there no end to them?!?!"
] |
[
"I would like to think that's the true glory of science and existence as a whole."
] |
[
"What stage of sleep are people in when they are in a coma?"
] |
[
false
] | null |
[
"They are not in a stage of sleep.",
"Here is a good chart describing different mental states relative to each other:\n",
"http://www.google.ca/imgres?um=1&hl=en&biw=1920&bih=926&tbm=isch&tbnid=ko1yWxKam3VoOM:&imgrefurl=http://www.sciencenews.org/view/feature/id/337940/title/Emblems_of_Awareness&docid=f4-q1QapJ171rM&imgurl=http://www.sciencenews.org/pictures/021112/consciousness_graph_zoom.gif&w=960&h=834&ei=jSi4T77ZK8-M6QGt7pDuCg&zoom=1",
"In a coma you have no primary sensory responses (meaning your brain does not register sensory input) which means you have no awareness, you also have no cerebral activity in general which means you have no wakefulness.",
"During sleep, you have full primary sensory response although secondary sensory responses are heavily reduced (meaning you do hear and register sound, you do register smells, light and touch and temperature, but you have few emotional or cerebral responses). You also have cerebral activity, your brain is coordinating all necessary systems such as breathing etc and you have the ability to dream and process both memories and thoughts."
] |
[
"In Catatonia you are fully aware meaning you have primary and secondary responses to sensory stimuli, for instance if someone calls you name your brain will respond very differently than if someone calls out the word spoon (your brain will recognize your name being spoken and trigger the emotional and cerebral responses associated with that). However you have no thought processes at all, there is no cerebral activity that does not result from stimulus of some sense.",
"The main difference is that your body and brain is fully aware of itself and the outside world in a Catatonic state, whereas in a coma the brain has no sensory responses."
] |
[
"i mean like stage 1, stage 2, REM, etc"
] |
[
"Can the stomach digest calcium-rich foods such as egg shells, bones, etc and would eating those be beneficial to the human organism?"
] |
[
false
] | null |
[
"Yeah, definitely. I know of a nutrition professor that highly advocated buying canned salmon ",
" the bones because they aren't super hard and are an excellent source of calcium. ",
"It seems like using eggshells in powder form are useful and can be absorbed as well. I'd assume if you can or...want to even chew on eggshells there'd be a benefit from it.",
"Bones source: Professor and ",
"here",
"Eggshell: ",
"Here"
] |
[
"Eggshells commonly have salmonella and other bad bacteria on them though, right? Might be a good reason to avoid eating them without taking proper safety precautions. "
] |
[
"Yeah it's definitely more common on the shell than inside. ",
"The CDC says that about 1 in 20000 eggs may be contaminated.",
"That statistic was from the 1990s though, so that could have possibly changed. "
] |
[
"Vacuum Walls as insulation?"
] |
[
false
] |
Theoretically, wouldn't a wall that was vacuum-sealed be the best possible insulator, because there is no medium (other than the wall) to transfer the heat?
|
[
"This is how a thermos works."
] |
[
"This is what we use to store cryogenic liquids like liquid nitrogen and liquid helium for weeks or months without it all boiling off.",
"The primary method of heat transfer is the thermal radiation traveling from the warm surface to the cold one, and it turns out that this can be drastically reduced by inserting additional opaque layers of material between them. Very thin layers of aluminized mylar is often used for this.",
"Fun fact: If you've ever had an MRI and heard the constant throbbing sound in the room, that's a type of vacuum pump called a ",
"cryopump",
" maintaining the ultra-high vacuum around the liquid helium which cools the superconducting magnet coils. ",
"Strangely the TV show House used the sound for that of the MRI doing its imaging",
"But as for using this as insulation for a building, you would run into difficulty having large flat surfaces under vacuum. Atmospheric pressure is about 14 pounds per square inch, so a 8' by 16' wall would be crushed inward by 130 tons of force. A house would have to be built like a submarine for the vacuum walls to not bow in and make contact with each other."
] |
[
"http://en.wikipedia.org/wiki/Vacuum_insulated_panel",
"Surprisingly, yes. It's actually structurally feasible using aerogels, which are the usual answer to impossible problems. Unfortunately it costs a lot, can't be cut to size, and deteriorates over time. (Speaking as someone who's pulled water-damaged insulation out of a wall post-flood, these are very real issues.) Vacuum insulation is incredibly efficient in terms of thickness, but most people don't care about a few inches of wall thickness in a normal home. A thicker wall with a greater volume of conventional insulation is considerably cheaper and easier. ",
"For specialty applications, though, or perhaps in colder climates, it has real promise. It's also pretty effing cool."
] |
[
"What determines the placebo for a vaccine's clinical trait?"
] |
[
false
] |
Why is saline solution the choice of placebo in control groups? What determines it to be used? Are there other placebos and what are differences?
|
[
"Generally it needs to be:",
"Known to be safe and if a drug, licenced in the area that the trial is taking place. ",
"Able to be made up to be indistinguishable from the trial drug - this is harder than you think: things like colour, consistency and even smell are critical. Without this either the participants or investigators may be unblinded.",
"Cheap to make and easy to store. ",
"Saline is most of these things, although the absence of colour and smell can make it a poor choice for placebo. ",
"In some vaccine trials a licenced vaccine against another infection was used - I. E. Oxford/astra trial in UK used menACWY vaccine. This was a criticism of the trial as in the parallel trial in Brazil they used saline."
] |
[
"Especially for Corona Vacs most people get a reaction afterwards (e.g. headache, fever). Saline, etc. does not have it. This significantly reduces the quality of the study because most test persons know if they got the vac or the placebo."
] |
[
"It's hard to know for 100% certainty. Placebos can cause psychosomatic symptoms that can present with real physical findings. I wouldn't say that \"most\" test subjects know which one they got."
] |
[
"Does a helium tank get heavier the emptier it gets?"
] |
[
false
] |
I know that it would get progressively less massive, but would it weigh more on a standard scale as it got empty?
|
[
"Now a partially filled tank, one that has gaseous helium in it but no liquid, technically would be lighter, but we are splitting hairs at this point :D",
"Just to be clear: it would be lighter than if it had air in it, but not lighter than if it were empty."
] |
[
"Now a partially filled tank, one that has gaseous helium in it but no liquid, technically would be lighter, but we are splitting hairs at this point :D",
"Just to be clear: it would be lighter than if it had air in it, but not lighter than if it were empty."
] |
[
"If you mean empty by filling in atmospheric air, then yes, it's possible.\nBut! Actual mass is proportional to the particles inside, so if the pressure inside was significantly bigger that the 1 Atm pressure outside, it can actually be lighter when you let it out.",
"\nWiki: \"Helium gas cylinders have the highest pressures possible when full, around 1000 atmospheres.\"",
"\nSo He seems to be 4g/mol, air around 29g/mol, but in a tank you can have up to 1000 times more per volume."
] |
[
"Has there been any evidence to suggest that improvements in cellular technology (in terms of quality and quantity) has led to more lives being saved in emergency situations?"
] |
[
false
] |
I realize that the answer should be an obvious yes, but I was curious what the data actually shows. Has there been a significant improvement in recent decades?
|
[
"There's a lot of data and research in this area, though it's scattered across a number of different fields depending on the particular kinds of benefits you're after.",
"Some studies have looked at the use of cell phones in ",
"reporting accidents more quickly",
" or being ",
"able to call",
" if you need help. That said, I'm not familiar with much work that looks at these questions in a more systematic way, including possible opposing effects from things like the bystander effect or entering more risky situations because of having a phone with you (which the later link touches on).",
"Another massive chunk of the research focuses on the use of cell phones in things like providing distributed data on infrastructure damage, missing people, and local needs post disaster (e.g., see Google People Finder in Nepal right now, among others). Using similar principles, there's also significant interest - and work being done - in using mobile phone and social media reporting to be able to track the spread of diseases as well.",
"Finally, there's a set of issues around the technical dimensions of network reliability and connectivity during disasters. Take, for instance, the ",
"GETS program",
" (Government Emergency Telecommunications Service), which prioritizes available telephone infrastructure for emergency responder use during major disasters. Again, lots of research in this vein.",
"(Source: Sociologist of science & technology, and have worked in emergency medical response for 7 years, including several years in oversight & administrative roles)."
] |
[
"I'm a 911 dispatcher, and I'm just going to hijack the (currently) #1 comment to add one thing. No matter how good our technology gets, it won't replace the human element. GPS and cell tower triangulation are only so accurate, and even less so inside. If you don't know where you are, the chances of getting help are significantly reduced.",
"If you're traveling from Chicago to New Orleans and roll your car, knowing that you're on I-55 will be good enough to find you. If you're visiting a friend in downtown Chicago, and someone kicks in the door and starts murdering everyone while you're in the bathroom, if you don't know the building, floor, and apartment number you're in we aren't going to find you. ",
"Every time I have a citizen sit in dispatch with me, I have them call 911 from their cellphone. The top of the line phones, like iPhones and Galaxys can usually get within a couple block radius. Others can only pull the tower you're using, which can be very far away. If you're on an interstate between cities, that's fine. If you're inside a building we may only be able to narrow it down to a few hundred, or in a good scenario a few dozen, buildings. This will not get you help.",
"tl:dr technology is great but you should always know where you are"
] |
[
"Isn't this why the fcc recently passed the indoor mandate? ",
"Although, I hear there is a loophole and the carriers can basically do nothing and get away with it, something about how indoor and outdoor locations can be mixed. ",
"I agree, the tech exists, but the indoor solution isn't here yet. "
] |
[
"Are there any practical uses for trying to get a Noble gas to react with other elements/compounds."
] |
[
false
] |
I know there was an expirament in which Xenon was successfully forced to react. But why? What's the point, an is there any use for this?
|
[
"You ",
" if there's a use for something or not until you find it and learn about it. Open inquiry is what got you the technological advances you enjoy every day. If it was obvious that studying nature would give us technological improvements that would make life better, then science would've developed a lot earlier than it did."
] |
[
"Noble gas compounds have fairly niche uses, in general. Many are very strong oxidising agents and could be quite useful because there's little chance of any side reactions happening - ",
"xenic acid",
" can oxidise other compounds without introducing any impurities into the reaction, since it liberates stable xenon which is very unlikely to spontaneously react with any other species in the system.",
"Noble gas compounds can also be easier to handle than the gases themselves, which can be handy when you're dealing with radioactive isotopes."
] |
[
"Xenon difluoride is used for aromatic fluorination (this be the overall theme here) as its very handy for this (especially as impurities aren't possible and the Xenon will simple evaporate). (while this is a nice option though this by no means is used large scale it would be far to expensive)",
"Krypton difluoride this ones kinda special KrF2 isn't all that interesting and it breaks down quickly. However KrF+ now this ones interesting. This is currently the strongest Oxidizing agent know (beats Oxygen difluoride and elemental Fluorine). its currently the only known compound that can force gold into a +5 oxidation state (as AuF5).",
"KrF is also used in ",
"Excimer Laser",
"I'm not aware of any current use for the oxides (XeO3 and XeO4) both are highly volatile however their Perxenates are stable (except for the silver one) only use for those I could find (taken straight from wiki): Sodium perxenate, Na4XeO6, can be used for the analytic separation of trace amounts of americium from curium.",
"but as has been pointed out, just because we have not much of an idea what to use it for right now doesn't mean we'll never find a use for it and Science at its core is about gaining knowledge not necessarily usefulness. ",
"edited for missing a word"
] |
[
"Is the 'radioactive days' real and do explosions on the Sun's surface affect our health?"
] |
[
false
] |
I've been hearing this for a while in my country. I've even experienced stuff like that. By that I mean headaches on the same days with other people, high blood pressure, etc. I've also heard from many people that it's 'radioactive days', explosions on the Sun burst out huge energy and it does affect our health. Sorry for a bit of gibberish and thanks in advance.
|
[
"From what you're describing, no.",
"People misunderstand the concept of radiation, but basically there are two categories of things we think of as \"radiation\": electromagnetic waves and energetic particles.",
"EM waves are the same thing as light, and they include radio, microwave, infrared, visible light, ultraviolet, x-rays, and gamma rays. Of those, UV, x-rays, and esp. Gamma can be harmful to humans at relatively low intensities. The atmosphere mostly screens them and protects us. Some UV slips through, which is why sunscreen is a thing. ",
"The other category of \"radiation\" is the emission of charged particles: electrons and protons, mostly. Whether these are harmful just depends on how fast they're going.\nThe sun sprays out charged particles, but the Earths magnetic field catches most of that before it reaches the surface.",
"Of both kinds, if the radiation has enough energy to knock electrons off of atoms, it is called \"ionizing\" radiation. Non ionizing radiation is literally incapable of harming you. Ionizing radiation can, but your body heals itself, so to do lasting damage, you need either long or intense exposure.",
"The sun's output varies a bit, but not THAT much, and Earth's atmosphere and magnetic field screens most harmful radiation. The symptoms you're describing couldn't come from solar output. More likely the shared headaches are either the result of airborne allergens or just coincidence. "
] |
[
"One tiny correction to a mostly accurate statement: non-ionizing radiation cannot harm you in the way we think of radiation poisoning/cancer, but it can still give you RF burns."
] |
[
"The sun sprays out charged particles, but the Earths magnetic field catches most of that before it reaches the surface.",
"What reaches the surface is mainly induced by cosmic rays - which means from sources outside the solar system."
] |
[
"Is there any way that you could send a signal through space, bounce it off of something, and receive it many years later?"
] |
[
false
] |
It could be like a radio-time capsule, or more like a delayed back up system. We could transmit as much of our accumulated knowledge as possible, and aim for the signal to return a few thousand (or however long) years later. That way, if there is some catastrophic incident that wipes out most of the population, not only will our knowledge be preserved but it would help rebuild society. Just a thought.
|
[
"The power required to bounce a wave off an astronomical object thousands of light years away would have to be ",
". Your idea works in principle, but would be extremely hard to put into practice. A better idea might be putting a space probe into a stable but distant position (so whatever wipes us out doesn't get the probe too), a solar orbit would be a good example. This probe would then constantly transmit such information back to Earth. "
] |
[
"Well, if I want to send some sort of signal out there and have it bounce back, I'd want a really good reflector. Otherwise, I'd just get back weak and/or garbled signals, like the difference between standing in front of a mirror and standing in front of a normal wall.",
"I can't think of anything out there that would be a good reflector for EM waves or gravitational waves... sorry. 2x4b's space probe is a better idea, although I'd be concerned about the survivability of the probe. Maybe if we launched a lot of them, there'd be an okay chance that at least one would survive the debris/micrometeorites, radiation, cosmic rays, etc. for when we need it."
] |
[
"Yes, if you could make a whole star go boom."
] |
[
"How can sound waves escape from a black hole of light cannot?"
] |
[
false
] |
[deleted]
|
[
"They don't escape from the black hole. It black hole is moving throughout the giant cloud of gas and causes the gas to swirl, and that movement and swirling causes the gas to ripple."
] |
[
"I would also think that sound waves could come from the destruction of the star that formed the black hole. When the star collapses, it heats up the gas around it, causing it to explosively expand. So I assume this would produce a pretty loud sound front."
] |
[
"Just a quick note: It isn't \"sound\" coming from the black hole. Sound requires a medium to travel through because it works based off of vibrations in molecules. There are many videos on youtube such as \"Sounds of Saturn\", etc. where you can listen to what a planet/celestial object \"sounds\" like. But really, it's just different types of waves (not sound) that are being translated ",
" sound."
] |
[
"Are anti-perspirant deodorants harmful to humans in any way?"
] |
[
false
] | null |
[
"That didn't hold up under further research. Aluminum has nothing to do with Alzheimer's. "
] |
[
"That didn't hold up under further research. Aluminum has nothing to do with Alzheimer's. "
] |
[
"please dont post nonsense to Askscience"
] |
[
"How do aquatic plants in places like the Chesapeake bay resist algae buildup on themselves?"
] |
[
false
] |
I was at the bay 2 weeks ago working on a project, and I accidentally left some wire fencing in the water. When I returned a few days ago and took the wire out, there was a huge build up of algae and slimy stuff on it. How do aquatic plants, like eelgrass for example, not get covered in this and die?
|
[
"Marine biologist here. Submerged aquatic vegetation (SAV) actually has a very hard time dealing with epiphytic algae growing on them, as they are outcompeted for light. This is actually one of the major causes of the loss of SAV beds in many areas, as eutrophication increases the prevalence and growth rate of said algae. ",
"Tldr; they don't"
] |
[
"Believe it or not, plants wage extremely intense biological warfare. Most plants secrete compounds that are toxic to other plants and organisms, which helps them establish their roots so that they can obtain nutrients. I don't know what type of plant you are referring to, but this can be seen with terrestrial plants as well. Next time you're talking a walk through the park, stop and look at the base of a tree that is planted in the middle of some grass. Many trees will have a zone around the base where no grass grows. This is because the trees produce compounds that kill the grass to prevent it and other plants from settling in it's territory. "
] |
[
"The presence of aquatic plants is normal, but an overabundance of algae usually is associated with nutrient/fertilizer/organic waste runoff (eutrophication) allowing the faster growing organisms to have large blooms where it could not normally be supported. SAV beds are a very valuable part of the ecosystem: fish habitat and erosion protection, among others. The fouling communities you see are a result of watershed pollution, either nitrogenous waste from agricultural inputs or phosphates from industrial runoff. Both of these are usually pretty limited in aqautic systems, so when there is an increase in N and/or P the algae especially grows like crazy. "
] |
[
"Do the shapes on the border of a rectangular voronoi diagram tend to have greater area than the shapes that are not touching the border?"
] |
[
false
] | null |
[
"Yes and no. Voronoi tessellations are a way to distribute space to a set of points. The border can be arbitrary : if you only have a set of points in 2D, for example, what you have is just a collection of points. Then, if there's no border, the shapes on the outside are infinite in size.",
"If you're taking the tessallation of the points on, say, a piece of paper, where there is a boundary, then the size of the outer polygons depends on how close your points are to the edge. If you define a border on an arbitrary space ( again, imagine 2D as an example ) as being as close to the points as possible, then they might be smaller - it also depends on the space between the \"inner\" points."
] |
[
"For a given point distribution, there should be some statistical relationship between the \"inner point spacing\" and the \"point-edge spacing\". This relationship should directly answer OP's question, in terms of the distribution. I believe this relationship could be determined theoretically, at least for a uniform distribution. It could also be estimated via a Monte Carlo simulation, which would be a little easier."
] |
[
"Yeah, I was thinking about doing a Monte Carlo simulation myself and to measure the areas directly, but I'm not so clever with programming. "
] |
[
"Do mirrors have a resolution?"
] |
[
false
] |
Whats the quality of a mirror I guess I mean, and if the answer is different depending on the mirror, then what would a car mirror's reflection quality be?
|
[
"As far as I'm aware, the resolution of optical systems is related to the wavelength of light, so the smallest features that can be \"displayed\" or reflected are a few hundred nanometers across.",
"It's not unlikely that imperfections in the mirror will reduce this though. In any case, you can't actually ",
" any imperfections in a good mirror."
] |
[
"I'll start with the short answer then get into more detail. Since you asked for the quality and resolution I'll try to explain both. I'll then start ranting because there are some very interesting things relating to this. ",
"The short answer is that if your mirror is diffraction limited resolution will be limited by the rayleigh criterion (and thus wavelength and size of mirror), if not it will be limited by the larger point spread function coming from a distorted wavefront. Google Rayleigh criterion and optical aberrations/Wavefront error if you want. A car mirror probably doesn't have a very good resolution as the size of the mirror causes it to have a really small f/#",
"----Rambling explanations-----",
"For resolution a decent rule would be that it depends on the wavelength of the light and the aperture (diameter/size) of the mirror. In your case the mirror will likely have significant scattering from imperfections and the air and the best way to determine resolution in this case would be from an experiment such as using a USAF resolution test (locate the closest resolvable bars and calculate resolution.) Calculating the resolution would be very difficult without knowing the curvature of the surface, quality, ect.",
"You also asked for quality, in optical lenses and mirrors quality is can be generalized by peak to valley (distance from highest point to lowest point, not the best), RMS (sort of like an average of distances between peaks and valleys in the lens), or MTF(calculates resolution of the system) you can look at some lenses or mirrors from a vendor like edmund optics to see how they describe the quality of their mirrors.",
"For mirrors and optical systems in general, the best resolution is generally related to the rayleigh criterion. ",
"D~= 1.22",
"focal length/Entrance pupil diameter. ",
"What this means is that light from a point that is focused has a distribution of light pertaining to some point over some distance (we'll say its a gaussian) Now when there are two of these gaussians from two different points on whatever you are imaging are far apart, we can clearly see that they are separate, it becomes tricky when they start overlapping two bumps next to each other can still be resolvable or non resolvable. The rayleigh criterion descripts how overlapped they can get.",
"What the relationship means is that generally resolution becomes limited by how big your EPD is aka how big is your mirror. There are other things that effect resolution such as the quality of the wavefront coming in and leaving the system.",
"The other important part is also the size of the point spread functions, two PSF might be very large and thus unresolvable very far away. Now we are in the realm of aberrations and wavefront error.",
"Light can be modeled as a plane wave, a perfect plane wave has a flat wavefront while travelling \"at infinity\" such as the light coming from a car behind you to your mirror, and follows a perfect circular shape as it is being focused to the image. If this wavefront is perfect, it will be limited by the rayleigh criterion, if the spot size is bigger than something called the airy disk, then the resolution will be effected by this messed up wavefront.",
"The wavefront is usually messed up by imperfections in the mirror, or trying to move it through an optical system. One example is that bending a ray a lot causes one type of aberration called spherical. The wavefront also usually does not come in perfect.",
"Extreme cases of this are easy to see while driving on a hot humid day. You may look ahead of you and see a mirage, the shimmering is occuring from the wavefront being messed up from turbulance in the humid air. ",
"Both correcting wavefront error and the diffraction limit are very things people have to think about as they build better telescopes on land. A better resolution requires a bigger primary mirror which is why some of the new telescopes being built have 80ft + primary mirrors. Google large magellan telescope. It also requires a good point spread function which requires adaptive optics to counteract the turbulence of the atmosphere. A short summary of how it works is they irradiate the sodium layer in the atmostphere to make a fake star, calculate the wavefront shape from that and correct it with a deformable mirror 1000s of time a second.",
"Also well balanced optical systems must be designed to eliminate aberrations such as spherical from the optical system.",
"That was long and disorganized but maybe someone will find it interesting haha."
] |
[
"This is actually a good question. Do the light rays on the mirror have to something like \"bounce off recognisably far from each other\"? I mean, if I for example use some big convex lens to focus the image of my face into a micrometer on the mirror (just >wavelength for the whole face), and then magnify it back, perhaps with the same lens, will I see my eyes blur together, just because their rays were less than a wavelength apart when they reached the mirror?"
] |
[
"Does the shape of the end of a pipe affect the fluid dynamics of fluid coming out?"
] |
[
false
] |
I am wondering if the exit shape of a pipe (cut perpendicular to flow, or angled to stream of flow) affects how smooth a fluid comes out of a pipe. I have an air pipe that carries a material and exits the end. One of the pipes is angled and one is flat at the end and they appear to have different spreading as it exits. I'm wondering if there is any science behind this or other variables affecting it?
|
[
"The longer any section of pipe is in contact with the fluid, the more time the fluid will exert viscous drag on the walls of the pipe. This drag has the effect of slowing the particles nearest to the pipe wall, with a decreasing effect the further the fluid particle is from the wall.",
"This means that any section of pipe that sticks out a bit further (e.g. an angled section) would slow the fluid down more and lead to an increased spread of fluid.",
"This would certainly contribute to the difference."
] |
[
"I was seeing the wider spread on the flat pipe, not angled. There must be something else affecting the stream."
] |
[
"In short, yes. It's been a few years since I studied fluid flow through pipes and air flow was not one of the areas we focused on but the outflow from a pipe can be affected by a number of things including the shape of the exit. Sorry I couldn't be more helpful but that is about all I remember from my pipe flow courses concerning this.",
"Edit: just a thought and no math to back it up but it might be possible that the additional spreading you have observed in the pipe cut perpendicular is caused by turbulence in the exit environment while the angled cut offers some slight stability or shelter to the outflow. Like I said this is just a wild ass guess so don't quote me on it."
] |
[
"when I shine a flashlight at Mars, does a small amount of the light actually reach it?"
] |
[
false
] | null |
[
"Yes, you need to be careful with phrases like \"a small amount\". ",
"Mars is around 225 million km away at ",
" average distance. Lets say you have a 1W flashlight and aim it at Mars, the intensity very far away from this flashlight will drop off as the distance squared (also a little extra from absorption and scattering in the atmosphere). Without doing any exact calculations, if we assume scattering is negligible we can say the intensity that hits Mars will be larger than",
"I > 1W / (2 pi * (225 million km)",
" ~ 3 × 10",
" W /m",
"Mars has a surface area of 144.8 million km², so the power hitting Mars will be around",
"I * A/4 ~ 2.3 × 10",
" W",
"This isn't a lot of power, but a single photon at optical wavelengths has an energy of around 3 × 10",
" J, so this is still billions of photons a second hitting Mars. ",
"Edit: Lots of people are pointing out the beam divergence and scattering I ignored. Scattering I still don't think is very significant, ",
"about a fraction 10",
" of the light will be scattered for every meter of travel",
", most of earths atmosphere is within 20 km of the surface so the intensity is reduced by a factor of around",
"I/I_0 = exp(-20000*10",
" ~ 0.8",
"which is a 20% loss and thus not significant. If you aimed the beam through more atmosphere or if you had a blue flashlight this gets worse, but never significant.",
"The beam divergence depends heavily on how wide a flashlight you have to start with, if you had something which is quite compact the divergence is worse than something with a large output. Most of the power is actually in a spherical segment which is, say, 30 degrees in size, where as my calculation assumed this was closer to 90 degrees. To compensate the intensity on Mars would be bigger by a factor of (90/30)",
" = 9 ~ 10. "
] |
[
"That would be the case for something like a laser, but a flashlight would have a beam wide enough to cover a sufficient swath of the sky to not need such precision. "
] |
[
"I would think you would you have to lead the target, to use a hunting term, since Mars is so far away, you'd have to aim the beam to where Mars will be in about 20 minutes. Just thinking aloud."
] |
[
"Why does wearing high-heels increase pressure on one's feet and cause foot problems?"
] |
[
false
] |
[deleted]
|
[
"It is very damaging to feet over time, and yes, it does cause foot AND leg problems. The simple fact is that for hours at a time, the foot and its supporting muscles and tendons are forced into a ",
"very unnatural position",
" that is normally reserved for going on tip-toe, something we only do for a few seconds.",
"By balancing the whole body weight on the ball and toes of the foot, you put excess pressure on knees, over time creating bone-to-bone contact and friction whereas when standing flat, the cartilage in the knee joint can cushion between the bones. ",
"Additionally, without the balance of having the foot flat on the ground, the ankles are destabilized, which is why it's very easy to fall and twist your ankles since they are forced into an upright position without any support. Heels also force the achilles tendon to be constantly shortened, making them tense without the opportunity to stretch out. The shorter and tenser a tendon becomes, the easier it is for it to get damaged or snap."
] |
[
"Also, the angular shape of a heel also can affect the toes, causing ingrown toenails and bunions. ",
"Here",
" is a great image comparing what your foot looks like in heels and in a normally fitted shoe."
] |
[
"Good addition and good graphic- thanks."
] |
[
"Do you technically see air? I mean, it looks a lot different than space."
] |
[
false
] |
Are you technically seeing it, but your so used to looking through it, you don't really think anything of it? Thanks in advance!
|
[
"This is an interesting question.",
"One of the ways that we \"see\" transparent things is by the way light reflects/refracts through it. For example, have you ever noticed how the angles of things look odd when you're in water? It looks like your leg is at a different angle in the water than it is outside of the water. This is because of something called the \"index of refraction\" of a medium.",
"The same thing happens with glass, but it's harder to notice because panes of glass are often quite thin. The effect appears stronger with \"thicker\" stuff.",
"Anyways, the point here is that the index of refraction of a vacuum is defined as 1. The index of refraction of air is almost 1. It is 1.000277 according to Wikipedia. So, in that respect, space and air would \"look\" similar. That is, if you were standing on some magic boundary that perfectly separated a normal atmosphere from a vacuum, you would not see that \"weird angle\" like you do standing in water."
] |
[
"A better way to frame the question might be to refer to an Earth denuded of atmosphere, or being on the moon. The answer is yes; without the intervening atmosphere, distant objects look much clearer. Look at a distant mountain range and you will see they look blurred and fuzzy due to the photons being diverted somewhat by all the air molecules they have to go past. On the moon, distant mountain ranges look quite sharp, and your brain would perceive them as closer than they actually are as a result. "
] |
[
"Ok, so that answers the refraction part. What about other characteristics like color or clarity? Does space look \"clearer\" than air? Perceptively?"
] |
[
"All of the planets in our system orbit in the same way. What about other solar systems?"
] |
[
false
] |
All of the planets including the asteroid belt, Kuiper belt, and dwarf planets orbit the sun on the same plane, like a nearly perfect disc going around our star. Is this a Normal thing? Is there any other solar systems out there that orbit in a more chaotic way?
|
[
"Given the vast number of other planetary systems, it's entirely likely there is at least one planet that is orbiting retrograde compared to the rest. It's incredible unlikely, as it would pretty much have to be a captured rogue planet(oid). Planets and asteroids form out of the planetary disc that will all be rotating in the same direction. Due to the conservation of momentum, it would take an extreme amount of energy to cause it to go in the other direction."
] |
[
"In single star systems it's pretty common. Gravity tends to flatten things out, and angular momentum caused from the original gravitation collapse of dust into a star is what gives all planets their direction they orbit. But they're finding that it's quite possible for there to be say, polar solar planes in binary systems and stuff. In all honesty it just depends on what and how other objects besides the main star influence the planetary disk/planets gravitationally."
] |
[
"It is normal, but we know examples where the orbital planes are different. ",
"Upsilon Andromedae",
" is an example (that star is visible to the naked eye, by the way)."
] |
[
"How/why does pouring a carbonated drink into ice make the drink lose its fizz?"
] |
[
false
] |
I have noticed that pouring coke, ginger beer, and pretty much every other carbonated beverage over ice in a glass causes the drink to lose almost all of its fizz. If I make a Moscow Mule with ice, it inevitably ends up flat; without ice, I have no such problem. I've tried pouring the ginger beer slowly into the copper with ice, and it still loses 90% of the carbonation. What is happening?
|
[
"Ice that is freshly taken from the freezer has a pretty rough surface. It is rough enough that it provides tons of nucleation sites for the CO2 in the carbonated liquid to come out of solution, much like the mentos do in the coke + mentos demonstrations but to a lesser extent.",
"To reduce the carbonation loss you need to remove the nucleation sites from the ice before adding the carbonated liquid. Once the surface of the ice melts a little most of the nucleation sites should be removed, though there will be some no matter what you do. You could leave the ice sitting out of the freezer before making the drink or wash the ice with water before using.",
"Beyond that you need to limit the transient nucleation sites from air-liquid interfaces and mixing, and that can be achieved by slowly pouring along the side of a tipped glass. Additionally, the solubility of the CO2 is better at lower temperatures, so getting the liquids as cold as possible before pouring would help to retain the most carbonation."
] |
[
"They have the ice laying out of the freezer. So they melt a LITTLE, but still is ice.."
] |
[
"Thank you. I wonder how restaurants and bars manage to make carbonated alcoholic drinks over ice without losing the carb. I will try rinsing the ice first from now on."
] |
[
"Why do classical objects behave classically and not quantumly?"
] |
[
false
] |
Seeing as visibly large objects are a collection of smaller systems that behave quantumly, how come as a whole these large objects do not behave quantumly?
|
[
"They do. Everything does. The quantum effects are just insignificant compared to the classical effects, which is the average result. Same deal with relativity. Everything experiences the same transformations all the time, it's just below the threshold of being meaningful. "
] |
[
"The law of averages. A single coin toss is completely unpredictable. But flip a coin a thousand times and you can make very good predictions on the average outcome.",
"Trying to measure the exact speed and position of tiny particles are like those single coin tosses. The behavior of the large objects comprised of millions of them can be estimated quite accurately even if you don't know what each individual particle is doing.",
"The catch is chaos theory where certain systems allow the tiny amount of randomness inherent in the individual particles to eventually propagate upwards in scale to alter the future predictions of global phenomena (like weather)."
] |
[
"Please read our guidelines and FAQ before posting",
"A good example of this is quantum tunneling: A quantum particle has a non-zero probability to go through an energy barrier (a wall) which is higher than the energy of a particle. However, the probability of multiple particle (an object) tunneling at once goes down exponentially with the number of particle, making it so unlikable for classical objects (with many particles) that we wont need this possibility in our classical laws of motion."
] |
[
"On the cellular level why does certain foods like black beans and pasta go hard and other foods like bread and apples go moldy?"
] |
[
false
] | null |
[
"Black beans and pasta are dehydrated."
] |
[
"Clearly you have never been a college student. Pasta and beans will mold."
] |
[
"mostly depends on the water content"
] |
[
"How true is it that male baldness is inherited from your mother's side?"
] |
[
false
] |
[deleted]
|
[
"When a male trait is said to be \"inherited from the mother's side\", what is generally meant is that it's linked to a gene on the X chromosome; because men only get one copy (from their mother), a man with the trait will gave inherited it from his mother. She could have inherited it from either her mother or father, as she received an X chromosome from each of them. This is why some traits that are not otherwise sex linked are found much more commonly in males - things like the most common form of colour blindness, haemophilia, etc. A woman can have them, but it requires her to receive the same mutation on both of her X chromosomes. ",
"With reference specifically to baldness, a quick google 'literature review ' suggests there is an X chromosome component but the overall picture is more complex. I don't have the background to pick out the reliable sources from the medical clickbait though. "
] |
[
"Hi MinArbejdsBruger thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Male pattern baldness is an X-linked trait, meaning it is found on the X chromosome.",
"An XY male receives one copy of X from his mother and one copy of Y from his father. So a male can get this gene only from his mother (since it's on the X gene, not the Y gene.)",
"An XX female receives one copy of X from her mother and one copy of X from her father. So a female can get this gene from her mother, her father, or both.",
"The expression of this gene is male hormone-mediated, so most women with this gene do not go bald, even if they have two copies. "
] |
[
"in the FAQ it is stated that one proof of the universe's expansion is that \"more distant galaxies are packed closer together\". What sort of measurements have been made to show this?"
] |
[
false
] | null |
[
"Telescope observations were done to establish two things. ",
"1) The distance to galaxies using Supernova Light curves and redshifts.",
"2) How seperated the galaxies are (basically galaxies \"per square inch\")",
"Its found that at larger distances, there are more galaxies per unit area at that distance.",
"So at 10 billion ly we might have 5 galaxies per unit area. At 12, the average is 8, at 13 the average is 14 per unit area.",
"",
"Its essentially a matter of sectioning off a portion of the sky and counting. Then comparing that to the distances for each galaxy."
] |
[
"Exactly, we are not seeing them as they are now, but as they were back then. So we can observe they were closer in the past."
] |
[
"Is the reason this tells us its expanding is because the ones farther away are being seen further back in time?"
] |
[
"If I made a giant wheel, and spun it at 100rpm how large would it need to be in order for the outer edge to be traveling at the speed of light?"
] |
[
false
] |
I am aware that an object this large would start to 'bend' as well, but let's just assume that the object is made out of an unbreakable material and this factor won't come into play.
|
[
"Relativistic effects aside, let's live a little and consider we are in a Newtonian universe (linear approximation of reality)",
"100rpm is the angular velocity\nrpm = 2",
"pi radians /(60s) = pi radians /(30s)\n100rpm = 100 * pi radians /(30s)",
"speed of light is 299,792,458 m/s",
"relevant angular velocity formula w * r = v\n100 * pi radians /(30s) * r = 299,792,458 m/s\nsolve for r",
"r = 28,628km",
"I hope I did that right. But in the future a better place to ask this would probably be ",
"r/theydidthemath"
] |
[
"For reference, this is like a planet 91 times larger than Earth (by volume), spinning 144,000 times faster."
] |
[
"yes, but you'd have a sweet looking planet from a spaceship's perspective."
] |
[
"If space is essentially a vacuum, how do planets cool off over time? Where does the energy disperse to?"
] |
[
false
] | null |
[
"More mathy, the ",
"Stefan-Boltzmann Law",
" which describes the radiation heat flux from objects as a function of temperature to the forth power for black bodies. Using the law, you can actually get a decent estimation for the surface temperature of the Sun or the temperature of Tungsten wires in incandescent light bulbs which can be approximated by a black body."
] |
[
"Yep. To be more specific, the energy radiates away into space in the form of photons (electromagnetic radiation). "
] |
[
"Yep. To be more specific, the energy radiates away into space in the form of photons (electromagnetic radiation). "
] |
[
"Questions about behavior of electrons in an atom?"
] |
[
false
] |
Hello I’ve been learning about Quantum Physics recently, it’s super interesting, and it seriously has left me with more questions than answers. Crazy to think that matter is probabilistic on the most fundamental level. I’ve been thinking about some of the features of the quantum mechanical model of the atom for a little while, and I’ve tried to combine all questions that I had in my head over the past month into one post. I’d really like to get some intuition on this mind bending topic (full disclosure: contains a lot of questions beginning with “what exactly”). First off, what exactly does it mean for an electron to behave both as a particle and a wave? I know that by calculating the de Broglie wavelength of an electron we get a wavelength that is pretty significant at the atomic scale, but what exactly is the ‘wave’ that we are referring to here? What exactly is the quantum wave function? Is it a mathematical representation of the probabilities of the electron’s position at any given time, or is it referring to the electron as a physical wave in space? What do people mean when referring to an ‘electron cloud’? Is it the probability of the position of a single electron, or the electron ‘wave’ being spread throughout the atom? If it’s a physical ‘wave’, what exactly is it made of, and does it mean that the charge and mass of the electron is distributed across the wave? These are some of the questions I have for now. Just for context, I have a pretty intuitive understanding of Bohr’s model of the hydrogen atom, and a basic intuitive understanding of spectroscopy (The photoelectric effect, transition of an electron across energy levels after interacting with a photon of a certain frequency, emission and spectra, etc.). I really don’t get the intuition behind electrons treated as ‘standing waves’. Thanks for your time!
|
[
"The electron isn't really both a particle and a wave, it's really neither. It's a metaphor, really; the wave/particle duality business is just a way of saying that the electron sometimes has behaviour that's a bit like a classical particle, and sometimes has behaviour that looks like a classical wave, but it's not a classical particle, and it's not a classical wave.",
"As to the wavefunction: it's a mathematical object which describes the state of a quantum system. A basic notion in quantum mechanics is that you measure observables of a system (for example: position in space, or momentum, or...) by applying operators to the state of that system. The state can be written down in terms of a basis that's associated with an operator.",
"A really simple example of an operator is spin along an axis; an electron, for example, can either be spin up or spin down. In this case, the basis is those two spin states, and you can describe the electron as being in a state which is a sum of those up and down states, and that encodes the probability that the electron will be found in either the up or down spin states when you measure the spin.",
"Ok, but what has that to do with wavefunctions? Well, a wavefunction is the state of an electron expressed in the basis of the position operator. Because, unlike spin, position is continuous, the basis has an infinite number of states. Instead of a sum of states, you've got a function which has a value at every point in space. Broadly speaking, that function at each point encodes the probability that, when the position of the electron is measured, that the answer you get will be the point. (Technically, you get the probability by applying the ",
"Born rule",
")",
"When people are talking about probability clouds and suchlike, this is pretty much what they're talking about. Until you actually measure where an electron is, all you can talk about is probabilities of where it might be. If you measure repeatedly and plot the points, it'll trace out a cloud of points.",
"Right, the last point is that the shape of the wavefunction is determined by the fact that they have to be solutions of the ",
"time-independent Schrödinger equation",
". The equation itself is simple-looking; you operate on the wavefunction with the Hamiltonian operator, and you get out the energy. Because of maths, the form of the wavefunctions that can satisfy this equation tend to look like waves (in that they have e",
"-like terms in them). The precise nature of the Hamiltonian is dependent on what form potential energy takes in your system, which affects the shape of the wavefunctions.",
"In free space where there's no potential well, (IIRC) it's a plane wave (hence de Broglie wavelengths and such) and you've got a continuous range of energies. When you solve it for a situation like an atom (that is, a Coulomb potential), there are only a discrete set of possible solutions, and those solutions are related to a set of functions called the ",
"spherical harmonics",
". ",
"It's a bit like Bohr's model, in that when you wrap something wave-like around in a circle, only certain configurations are possible. It's a little bit like that, sort of. ",
"I hope that's helpful; I've tried to express a little of the mathematics in what's going on, but by necessity I've had to gloss over a ",
" of detail. I think the main notion to dispel is that waves or clouds are whatever are physical things made of stuff, which they're not, and it's not that electrons are smeared out across space. It's actually that the position is indeterminate and probabilistic until measured."
] |
[
"Oh wow, thank you so much for such a detailed answer! Really, the first and the last paragraphs really cleared the confusion about when electrons really are, understanding that they’re neither particles nor waves makes so much sense! And I never knew that the clouds are only pictures traced by measuring the position of an electron multiple times, I always used to think of it as the ‘electron wave’. So that’s basically what an orbital is right? ",
"Seriously, that answer was incredibly helpful, and I’m actually starting to get an intuitive grasp on the topic. Thank you so much! I really do appreciate it!"
] |
[
"First off, what exactly does it mean for an electron to behave both as a particle and a wave?",
"You are familiar with the idealized concepts of particles and waves. The truth is that electrons (and everything else) displays properties that you would typically associate with particles and properties that you would typically associate with waves. You can't say that anything in quantum mechanics is purely a particle or purely a wave. Everything is both.",
"I know that by calculating the de Broglie wavelength of an electron we get a wavelength that is pretty significant at the atomic scale, but what exactly is the ‘wave’ that we are referring to here?",
"The wavefunction.",
"What exactly is the quantum wave function? Is it a mathematical representation of the probabilities of the electron’s position at any given time, or is it referring to the electron as a physical wave in space?",
"It's both of those things.",
"What do people mean when referring to an ‘electron cloud’? Is it the probability of the position of a single electron, or the electron ‘wave’ being spread throughout the atom?",
"Yes, although it's not necessarily just one electron. In a multi-electron atom, you have some many-body wavefunction describing all of the electrons.",
"If it’s a physical ‘wave’, what exactly is it made of, and does it mean that the charge and mass of the electron is distributed across the wave?",
"Yes, the mass and charge are distributed. There is some continuous mass and charge density function, both proportional to the squared modulus of the wavefunction."
] |
[
"What causes someone to talk in their sleep?"
] |
[
false
] | null |
[
"Somniloquy (Sleep-talking) usually occurs during transitory arousals from NREM sleep, which is when the body does not move smoothly from one stage in NREM sleep to another, and they become partially aroused from sleep. Further it can also occur during REM sleep at which time it represents a motor breakthrough of dream speech, words spoken in a dream are spoken out loud.",
"Sleep-talking can occur by itself or as a feature of another sleep disorder.",
"Source"
] |
[
"Follow up; sometimes friends/ girlfriend have reported me humming in my sleep, a high pitched \"hmmmmmm\" with my mouth closed or a more opera-esque \"ahhhhhh\" with my mouth open. Sometimes I can almost be aware of this happening. Is this related to sleep talking, or something else entirely?"
] |
[
"What causes sleep talking?",
"You might think that sleep talking occurs during dreaming. But scientists still are not sure if such chatter is linked to nighttime reveries. The talking can occur in any stage of sleep.",
"Sleep talking usually occurs by itself and is most often harmless. However, in some cases, it might be a sign of a more serious sleep disorder or health condition.",
"REM sleep behavior disorder (RBD) and sleep terrors are two types of sleep disorders that cause some people to shout during sleep. Sleep terrors, also called night terrors, usually involve frightening screams, thrashing, and kicking. It's hard to wake someone having a sleep terror. Children with sleep terrors usually sleep talk and sleepwalk.",
"People with RBD yell, shout, grunt, and act out their dreams, often violently.",
"Sleep talking can also occur with sleepwalking and nocturnal sleep-related eating disorder (NS-RED), a condition in which a person eats while asleep.",
"Other things that can cause sleep talking include:\nCertain medications, emotional stress, fever, mental health disorder, substance abuse.",
"This WebMD article has some general information:",
"http://www.webmd.com/sleep-disorders/excessive-sleepiness-10/talking-in-your-sleep?page=2",
"I know I sleep talked because of sleep apnea. Sleep talking was my body's way of jump starting my breathing again, and annoying my wife. Now that I have a CPAP, I haven't had an episode in two years."
] |
[
"How do animals with such different evolutionary trees have similar skeletal structures (example: chickens and humans both have a humerus upper arm/wing bone and radius/ulna lower)?"
] |
[
false
] | null |
[
"Broadly, it seems that the general body plan of chordates (animals with spinal chords) works really well. Having a central spine, four appendages, and a head with a brain in it has led our lineage to a lot of success. As a result, any time in natural history when a mutant was born with an extra set of limbs or a different body plan, they were less successful than their four-limbed brethren, and those mutations didn't stay in the gene pool very long. Everything that has evolved from the first species that had this body plan still generally has it. ",
"While it is simple to say this is just because that body plan was more successful, there are some complicated molecular reasons behind this too. When we develop as embryos, the shape of our body is made by molecules that are VERY important. A relatively small number of genes is responsible for making everything important in our bodies - our vital organs, our bones, our muscles, etc. Modifying these genes that even slightly is then very likely to kill the embryo, so to a certain extent babies with mutations that would cause their general body shape to be different likely would not even live long enough to be born. On the other hand, very rarely, relatively mild mutations (such as those that turn an arm into a wing but preserve the general skeletal structure) don't screw with those molecules enough to kill the embryo. Thus, if the wing mutation arises in a population where it is beneficial, it can be subjected to natural selection and propagate through the gene pool."
] |
[
"Humans and chickens are on the same evolutionary tree. We share a common ancestor with chickens that already had single bones in their upper limbs and double bones in their lower limbs. This is called homology, anatomical identity by descent.",
"Organisms that evolve anatomical traits independently generally do it in different ways. For example birds and bats evolved their wings independently, meaning they did not inherit their wings from a common ancestor that had wings. So even though their wings are both modifications of the front limbs (made up of the humerus, radius, ulna, and carpals since their common ancestor did have front limbs made up of these bones), the modifications that make those bones into wings are entirely different. This is called analogy, convergent function but non-identical descent."
] |
[
"What do you mean by different? Humans and chickens are both vertebrates. In the broad scheme of things birds and mammals are pretty similar. Arms are switched out for wings, and hair is switched out for feathers"
] |
[
"Say I take a stretched rubber band, clamp it into a vice, and then melt it. What happens to the potential energy?"
] |
[
false
] |
[deleted]
|
[
"An elastic band actually doesn't store any potential energy when you stretch it. When you stretch a band, then release it, it relaxes back to its original shape due to entropy. ",
"This",
" explains that process quite well.",
"When you stretch a rubber band, the work you do actually heats up the rubber band and ",
"none of your work is stored as potential energy",
". Conversely relaxing a stretched band actually cools it down.",
"Therefore, if you melt it in such a way without causing it to fracture, then all the heat you put in goes into heating up the polymers and there was no potential energy in the first place to worry about."
] |
[
"Most people don't believe the cool down bit, but here's a cool experiment: Stretch two bands equally. Release one immediatly, and leave the other to cool to room temperature before releasing. The first one will retract far quicker, and releasing the second will cause it to very slowly retract and become noticeably colder."
] |
[
"When polymers are sufficiently cooled they surpass the \"glass transition temperature\" where the polymer chains that could previously slide other eachother to provide an elastic effect become fixed in a more crystalline structure. It varies between polymers but you could probably find a list of common ones.",
"\nIgnoring the material the band is made of, i would say the likelihood of it retracting actually depends as much on the surrounding temperature of the band and the band itself. If both temperatures are below the glass transition temperature it won't retract. ",
"They actually have to bear this in mind when engineering rubber or plastic componenets subjected to temperature extremes: you need to keep them below melting point and above the point where they become brittle."
] |
[
"How realistic, even in theory, is an artificially induced teraforming event? (Think Firstly/Serenity)"
] |
[
false
] |
Watching all these sci-fi shows, you always hear about humans or other races teraforming a planet to make it suitable for habitation. Assuming a planet was in the habitable zone of its parent star, would even be possible to teraform a planet for human habitation?
|
[
"It is possible with the proper amount of progress in the genetic modification or chemistry fields. However it would probably be a 100+ year long project, if not thousands of years. It would all depend on the planet we are trying to teraform and its climate/biochemistry. ",
"Edit: As far as the genetic mod. goes, I was talking about modifying plants to survive the initial process."
] |
[
"Searched",
"Relevant ",
"discussion",
"Original question by ",
"blueatlanta",
"What challenges are we presented with if we were to terraform Venus or Mars?",
"Are there valuable resources from either of these planets?",
"Can we find gems, fuel, undiscovered elements?",
"What is stopping us from pursuing this path?",
"Relevant comment courtesy ",
"therealsteve",
"What's stopping us? Oh, nothing really. Just that it would be a megaproject on a scale several orders of magnitude larger than anything we have ever even attempted, to date. For the love of Hawking, we can't even terraform earth to stop it from changing climates! Turning a whole different planet to look like earth? WAY outside our league.",
"You'd need a way to get a lot of mass into space. Either a ",
"launch loop",
" and/or a ",
"space elevator",
" and/or maybe just (ha, \"just\") a lunar city with a ",
"mass driver",
". Either way, you'd need a cheap, scalable way to launch and/or construct huge spaceships in space. Any of this would require decades of R/D, not to mention construction time.",
"That'll let you set up heavy industry on mars. That's step 1. There are like a billion other steps. Maybe you build an ",
"orion drive",
" cometary tugboat. An orion drive is a space-ship engine that is basically a giant metal plate mounted on the end of a set of HUGE shock absorbers. You set off a nuclear bomb on the far side of the plate, and once you've re-attached your retinas you do it again. It's very, very efficient by mass. You could use it to redirect comets. Assuming you have technology a few dozen decades more advanced than ours.",
"But really, we have no idea how this would be done. Conventional engineering cannot help us here, because it's so far beyond the current scope of our technologies that any speculation is useless. It's like asking a ",
"middle-ages metallurgist",
" how he would go about constructing ",
"the Apollo mission",
". His suggestions will not be helpful. (\"Oh, clearly it would have to be bird shaped, or else it couldn't possibly fly, and you'd need some kind of pen for the draft animals, which you'd use to power the wings . . . \")",
"Until the technology is developed, we can't possibly know which parts will be hard and which parts will be easy. Maybe we'll have crazy ",
"von neumann",
" ",
"nanomachines",
" making it trivial to put heavy industry on the moon. Maybe we'll have ",
"brain uploaders",
", allowing us to send a team of 5 million brilliant engineers in a ",
"holographic hard drive",
" the ",
"size of a can of tuna",
". Maybe we'll have cheap, long-chain ",
"carbon nanotubes",
" or other ",
"super-strong materials",
" that let us litter the equator with elevators. Maybe we'll have crazy ",
"genetically engineered",
" plants that can grow on mars somehow. Or ",
"uplifted",
" space ",
"octopi",
" to do all our dirty work.",
"Maybe we'll have ",
"frakking",
" ",
"transporter beams",
".",
"My main points are thus: Speculation is fun, but not particularly useful here, and isn't really ",
"science",
" as much as it is ",
"science fiction",
"."
] |
[
"Thanks. Truth be told posting from my phone and the mobile app has a very bad time performing a search. Thanks for the info!"
] |
[
"Are animals capable of having “obscure” dreams? Eg. flying, being a different animal, etc"
] |
[
false
] | null |
[
"We don't have a way of knowing at the moment"
] |
[
"Do we know if they dream the same way humans do? As in, do dogs go through the same type of sleep cycle as humans?"
] |
[
"That's a different question. I recommend making a new post for that, although you can find plenty of information about sleep stages in animals with a simple google search and perhaps you should look there first."
] |
[
"Where did the first anaerobic bacteria on earth come from?"
] |
[
false
] |
I'm reading Origins by Tyson and Goldsmith and the first anaerobic bacteria on Earth are mentioned in the first chapter, but not where they come from. Based on commonly accepted scientific theories, where did these simple anaerobic bacteria come from and how did they end up on Earth? Were these bacteria present in the pre- big bang state of the universe? And no, God did it is not an acceptable answer. Edit: I know that one theory is that this bacteria came from a meteorite. What I want to know is where the bacteria on the meteorite came from.
|
[
"Early life (if not the first life) on Earth would have all been anaerobic due to the lack of oxygen in the Earth atmosphere until roughly 2 billion years ago when oxygen became prominent via production by cyanobacteria which are photosynthetic. ",
"This is called ",
"the Great Oxidation-Event",
" and is regarded as one of the largest extinction events in Earth's history. If you're asking about where did these first organisms come from, then I'd have to say that we don't know, but there are ",
"some ideas.",
".",
"This may be dramatic, but oxygen is poisonous to all life, including us and modern life that utilizes aerobic respiration have all sorts of biological safety features to combat that. While some modern anaerobic life can life in the presence of oxygen, it is still deadly to much anaerobic life."
] |
[
"Yes that's true, but I want to know where the bacteria on the meteorite came from"
] |
[
"True, but I think you misunderstood OP's question. Now you explained that anaerobic life came first and how it evolved into aerobic life.",
"OP, however, was aiming more in the direction of \"where did the bacteria come from ",
"\", i.e. ",
"abiogenesis",
" (see also ",
"here",
")"
] |
[
"When I push down an air-filled ball in a pool of water, I can feel a lot of energy being built up the deeper it goes. What exactly is happening?"
] |
[
false
] |
I understand the basics - water is denser than air, so air is trying to float up. I'm kind of amazed at the seemingly huge amount of force that builds up this way though. Why does the amount of potential energy stored in the ball (is it even potential energy exactly?) seem to increase the deeper I try to push the ball and what makes the force so strong?
|
[
"That energy turns into increased pressure inside the balloon i think. Good question though."
] |
[
"Your observation is true, up until the object is completely submerged as the buoyancy force is proportional to the density of the water and the volume of the object submerged. If you had alot of water and you pushed very deep there might be some force resulting from the density change of the compressing water but it would likely be negligible. ",
"But to better answer your question if you have a 1 ft diameter balloon underwater the force of it pushing up is the same at 1 ft as at 10 ft, in theory. (This is only true if the volume of the balloon is held constant)",
"In fact, the force at 10 ft would likely be less than at 1 ft because the additional water pressure compresses the balloon so it has less volume. the Buoyant force is proportional to the submerged volume so when you reduce the submerged volume you proportionally reduce the force. "
] |
[
"In fact, the force at 10 ft would likely be less than at 1 ft because the additional water pressure compresses the balloon so it has less volume.",
"This brought up another question in my head. If I was right in my assumption that I'm storing potential energy in the ball by pushing it down, and if that energy decreases if I manage to push it deep enough to compress the ball as you say, where does the \"lost\" energy go? Does it work towards compressing the ball?"
] |
[
"Are cellphones always transmitting signals?"
] |
[
false
] |
Are cellphones always emitting a wireless transmission to the towers, if so, are the waves "bouncing" or a direct path? And finally, if the theories are true that cellphones cause cancer, if you're inside a mall for example, isn't everybody just in a huge wireless signal mass?. And if the signals do bounce everywhere, wouldn't it not matter if you have a cellphone or not, everywhere outside would technically be covered in signals correct? So why are people so paranoid of getting cancer by keeping a cellphone? just living is giving you cancer if its true?
|
[
"They're only in constant contact with a tower when you have an established connection such as an active phone call or data connection. Otherwise, it generally sits idle and occasionally 'polls' to see what's available in the area. The waves' path to the tower is line of sight (although this applies to what microwaves can see through, like buildings). ",
"There is still ",
"no solid link between cell phone radiation and cancer",
". If you're in a mall, yes you are bombarded by cell phone signals (actually pretty much everywhere you go), but the energy level of those waves is tiny even when it's all added up. Also keep in mind the inverse square law... the strength of the signal is inversely proportional to the square of the distance from the source.",
"The hysteria surrounding cell phone radiation and cancers is mainly due to the misunderstanding about how the electromagnetic spectrum works, and what energy level you need in order to start making some harmful changes to your body. Microwaves on a milliwatt energy level aren't going to do the trick. "
] |
[
"Good, solid answer but just to add to it there can always be a ",
"multipath propagation",
" where the signal does bounce around and cause inter symbol interference. Frequency division multiplexing helps get around this."
] |
[
"Thanks for the answers guys :D"
] |
[
"In this rapidly innovating world, how to scientists stay on the same page?"
] |
[
false
] | null |
[
"One answer is that we have no perfect system for this. This isn't as much of a problem as it seems, as repetition (or reproduction) is a good thing, in that it confirms the results.",
"We have a few imperfect methods. In order of faster to slower dissemination, they are personal contact, conferences, journal articles and rumor. Which is more important depends on the field. In particular, I think that the pace of progress and size of the field are important. Personal contact is only really effective in small fields. In fast moving fields, the field will have moved on before an article has been published, so conferences becomes more important."
] |
[
"This answer gets to the nub of it.",
"And it's important to highlight that scientists are generally only really up-to-date in whatever tiny subfield they're working on at a time. And even then some of them are not as up to date as they could be.",
"Before you start any experiments you're going to take some time to see what else has happened in the field (assuming you're not very familiar with it already). This search through the litereature should identify any people who have done the same or similar work before. "
] |
[
"When a research group discovers something new, they'll typically submit a paper to a relevant ",
"academic journal",
" for publication. Other researchers in the field can read these journals to make sure they stay on top of recent findings."
] |
[
"The flu vaccine contains 4 variants. Why do they limit it to only 4 varieties?"
] |
[
false
] | null |
[
"Influenza is confusing. ",
"Let’s start with the word “variants”. Why are there four variants in the vaccine? Because there are four major influenza subgroups that circulate among humans each year. They are influenza A(H1N1), influenza A(H3N2), and two subsets of influenza B, the Yamagata and the Victoria subsets. ",
"These subgroups have almost no immune interaction with each other. You can be infected with H1N1, have terrific strong protective immunity to it, and still be infected with influenza B or A(H3N2) next week. ",
"Within these broad groups, there are smaller differences that gradually change over years. The H3N2 in last year’s vaccine is probably the same as this year’s. Because the circulating strains gradually change, the vaccine strains gradually change to match them, but it takes several years, as a rule, before the changes are big enough that they’re not a great fit. (Because there are 4 viruses in the vaccine, the vaccine as a whole changes pretty much every year, but individual components are much more stable.)",
"Also because the changes are gradual, it takes a long time before you lose all immune interactions. The H3N2 vaccine from 6 years ago may still give ",
" protection today, though not much. The one from 12 years probably won’t, but you do have some wiggle room. ",
"So you need one representative for each major group, but adding a second member within that group doesn’t gain you much in terms of protection - even if your first choice is a little off, you still gain something - whereas it increases cost and prep time significantly. ",
"And in general the surveillance organizations are pretty good about identifying the main strains. They do miss, but in the past decade (40 vaccine viruses) there have only been one or two significant misses. And in those years, they probably didn’t have the actual circulating virus as one of the options (because they appeared too late to be used in the vaccine, which needs around 6 months of lead time to prepare the hundreds of millions of doses that are needed). ",
"So adding more strains would add little or nothing to the protection, while increasing cost and complexity. The main thing is that they have to cover each of the four major subgroups."
] |
[
"Cost and efficacy for the most part.",
"Adding an additional strain increases cost, there was a lot of discussion when the move from a trivalent (three strain) to a quadrivalent (4 strain) vaccine.",
"The health organisations look at strains present in different parts of the world, as well as strains occurring locally outside of the traditional flu season (when people congregate indoors).",
"https://www.scientificamerican.com/article/how-are-seasonal-flu-vaccines-made/",
"http://apps.who.int/gb/pip/pdf_files/Fluvaccvirusselection.pdf?ua=1",
"So more strains could be added, but is it beneficial?"
] |
[
"There are a lot of different technical reasons (economics, size of dose, delivery method, risk of complications, supply chain issues) such that each additional strain included in the vaccine has real costs. Thus, designing a vaccine is always a trade-off between cost and benefit.",
"The ",
"CDC does extensive flu surveillance",
" in order to keep track of what flu strains are prevalent in the population and what they predict will be prevalent come flu season. The flu vaccine is designed to target the few high-profile strains that are most likely to cause people harm."
] |
[
"Why is it that semiconducting materials have lower resistances the hotter they get?"
] |
[
false
] |
[deleted]
|
[
"A material that conducts electricity well (a conductor) has lots of charged particles that can move around, allowing electrical current to flow. A material that doesn't conduct electricity (an insulator) has no movable charged particles (either there are no charged particles, or the charged particles are locked in place). A semiconductor is in between these two. There are some, but not many charged particles that can move around. One common way of having this condition is to have a medium-sized gap between the energy level of the highest energy electrons (in the ground state) and the lowest unoccupied energy level. If the gap is very small, then it's easy for electrons to jump up and move around, so you have a conductor. If the gap is very large, it's incredibly difficult for electrons to do so and you have an insulator. But with that medium gap, you have some-but-not-lots of electrons that can make the jump. Increasing the temperature increases the energy that the electrons have and therefore increases the fraction of electrons that can successfully make the jump up. With more electrons able to move around, electricity flows easier (resistance is lower)."
] |
[
"Ohhh, that makes sense. Thank you, very well explained!"
] |
[
"All of the metal’s outer electrons are already delocalised, they all can already carry charge. Increasing the temperature only increases the rate of vibration of the positive metal ions and electrons, which means there are more frequent collisions, slowing down the flow of charge."
] |
[
"Whats the yellow stuff next to our eyes that's there after we've slept?"
] |
[
false
] |
And why doesn't it appear during the day?
|
[
"It's called ",
"rheum",
". When you're awake, you blink, and tears carry it away. When you're asleep, you're not blinking, and it accumulates in the corners of your eye"
] |
[
"Sorry, if you follow the wiki through, it's mucus plus skin cells and dust"
] |
[
"Oh, ok! Thanks! "
] |
[
"Humans have created so many different plastics and plastic waste, what is the likely-hood that a microbe will adapt and begin eating the plastic waste, and eventually plastic we use on a daily basis? Could this be catastrophic?"
] |
[
false
] | null |
[
"there already is a fungus that eats plastic. \"Gusse fed chips of phenolic resin to five different species of white-rot fungus to see whether they could eat it. The team found that one species (Phanerochaete chrysosporium) turned from white to pink after a few days, suggesting that it had broken down the resin into smaller chemical components of the polymer known to be pink.",
"The team confirmed this by feeding the fungus phenolic resin containing a heavier isotope of carbon, and found that the isotope was incorporated into the fungus after it had feasted on the plastic. To nail the case, they used an electron microscope to show that the resin was pitted with craters after being semi-digested by the fungus. \"It's clearly breaking it down,\" Gusse says.\"",
"http://www.bioedonline.org/news/news.cfm?art=2575"
] |
[
"http://m.gizmodo.com/5880768/amazonian-mushroom-eats-indestructible-plastics"
] |
[
"I guess my main question is what are the chances that something like that becomes a serious problem in our daily lives since nearly everything is in some part made of plastic?"
] |
[
"Can the human body survive breathing pure oxygen at lower pressures?"
] |
[
false
] |
I know that pure oxygen is poisonous at atmospheric pressure, but wasn’t sure about the question in the title. I’m reading the new Artemis book about the moon colony - the book explains they breathe pure oxygen at a lower pressure and I wasn’t sure if it was true, and if it is true, what the difference is that allows people to be fine in this situation. Thanks!
|
[
"Yes, surviving with pure oxygen at low pressure is perfectly feasible. The problem of oxygen toxicity at high pressures was discovered in the late XIX century, and there was much research about this during the first half of the XX century (in the context of divers and submarines) and at the beginning of the space era.",
"In fact, astronaut EVA suits are inflated at 0.3 bar 100% oxygen. It would be hard to contain higher pressures, and they would feel very rigid.",
"This is not without disadvantages e.g. for a spacecraft or a Moon colony as you were asking. Human respiration relies on the ",
" of oxygen at 0.2-0.3 bar, and on top of it you can add as much as you want of a diluent inert gas like Nitrogen or Helium. But fire propagation speed depends on the oxygen %. In a pure oxygen environment it's a serious concern. You may try googling the Apollo 1 incident. In the ISS they just decided to have 1 bar with 20% oxygen, and I wouldn't expect this to be any different for a hypothetical Moon colony.",
"As for what allows people to be fine I'll let the medicine experts describe the mechanism of action."
] |
[
"Why are you using Roman numerals in 2017?"
] |
[
"Roman numerals are often used to label centuries in Romance languages (e.g., the beer Dos Equis means two X and celebrate s the beginning of the XX century when it was founded). Judging by OP's history, they speak a Romance language or two."
] |
[
"Why can the nerves in limbs be reattached and still function but not the spinal cord?"
] |
[
false
] |
It is possible for surgeons to reattach severed limbs and have them recover functionality. What is physically different about the spinal cord that makes it impossible to successfully reattach like can be done with the nerves in arms and legs?
|
[
"As you can imagine, the spinal cord is an extremely complex bundling of neurons that interconnect with every nerve in your body. It's simply too difficult to identify and re-connect each nerve to where it originally was prior to the injury. Additionally, injuries that typically occur in the spinal cord are often due to high force incidents (car accidents, sports, etc) so the damage can cause irreversible death of the neurons (so surgery wouldn't help). On the other hand, extremities have a lot fewer nerves and their individual roles are pretty well understood; this makes it much easier to simply reattach them. "
] |
[
"How do you reconnect a nerve anyway? Just push them together and hope for the best? Glue? "
] |
[
"Its usually done by physically sewing the nerves back together. The surgeons will often use the assistance of microscopic cameras and robotics to help ensure maximum precision."
] |
[
"What would the result be of 2 identical AIs played chess?"
] |
[
false
] | null |
[
"Google's ",
", trained solely by reinforcement learning from\ngames of self-play, took 4 hours to beat the previous world champion chess program, Stockfish 8. ",
"Paper",
". (PDF)"
] |
[
"Most likely a draw, as is the most likely outcome whenever two strong engines or players play one another. Keep in mind that chess is not a perfectly balanced game, White has an advantage in going first. Black simply replicating all of White moves will not go well, so you will not see an engine playing the identical moves on both sides. ",
"Here",
" are some example games where someone played Stockfish against itself. Playing an engine against itself is also part of how they are developed. ",
"Here",
" are details of Stockfish runs against itself. I don't understand everything on that page but it does show the win, loss and draw rate for every test, looks like about 70% draws."
] |
[
"And AlphaZero as well.",
"Many draws with some wins, the stronger the AI is the larger the fraction of draws tends to get."
] |
[
"Does the human body use stored (old) fat or newly digested fat for energy first?"
] |
[
false
] |
[deleted]
|
[
"Not quite right. Fats, especially triglycerides are hydrolyzed into fatty acid monomers in the GI tract, remade into triglycerides in your enterocytes, and packaged into chylomicrons for transport to the liver. "
] |
[
"Newly digested fats go to liver before being stored. If your body then needs energy (this generally means your creatine phosphate and glycogen stores are depleted), the liver will use the recently digesed fatty acids since they are more available (adipose fats are less available because a catabolic hormone has to signal adipocytes, esterases break triacylglycerols to glycerol and FAs, which then have to travel through blood to liver). The hepatocyte uniquely has special enzymes to carry out process known as ketogenesis to break down the fat into usable energy. "
] |
[
"If you mean fat straight out of the stomach, that fat is not digested. In order to get those huge fat molecules into your bloodsteam, your digestive system has to break the fat down into sugar in a similar process to when you burn fat. The sugar, now moved into your blood from your intestines, can be used immediately with no processing. However, if your blood sugar is made too low, glycogen stored in your liver will be converted to sugar. Once your glycogen stores are depleted, the fat metabolisation begins."
] |
[
"Do fetuses sleep?"
] |
[
false
] | null |
[
"Yes, that is ",
"when sleep develops",
"."
] |
[
"Only read the abstract, but this bit \"There is evidence for episodes of wakefulness in the fetus. \" made me wonder whether the baseline pre-36 week, pre-organization of behavioral modes state is most similar to sleep? If so, have there been EEG studies in preterm infants that early or perhaps in utero that would tell us if the brain states at that time are sleep-like (or perhaps even cycle through something like the NREM phases)?"
] |
[
"Yes they do, I am speaking as a mother of 3, so slightly layman, (apologies mods) but in utero babies often get into a cycle of waking and sleeping as indicated by the amount of activity felt. The cycle changes at different stages in the 2nd and 3rd trimesters, but often they baby follows the same wake/sleep pattern for a while after they are born. This is reported by mothers, and midwives/health visitors. (wish I had a paper on it!) \nI'd be fascinated to know whether they do cycle through the sleep stages in the same way as older babies.children and adults do. "
] |
[
"Why has bad eyesight not been 'evolved out'?"
] |
[
false
] |
I read but it didn't really answer my question, which is why do so many people need glasses to see even reasonably well? Surely this would be selected against by natural selection? I understand the argument that people in the distant past didn't live long enough for age-related myopia to kick in but I know many people who've had bad eyesight their entire lives so this doesn't make sense. Also, I've heard the argument that it may be related to eye strain related to modern living (books/monitors/other screens) but, apart from apparently being an , I've read in dim light, sat 'too close' to the TV and used computers for my entire life and still have 20/20 so this must be a minor effect at best. Can anyone explain this to me?
|
[
"Evolution doesn't lead to perfection. If you can see well enough to eat, not get eaten, and fuck something, your genes get passed down.",
"Also, there could be recessive genes for myoia that are leading to two healthy parents having a myopic child. Your question is no different from any other question about how less-than-perfect organisms are born. Why asthma? Why diabetes, leukemia, warts, and albinos?"
] |
[
"\"Survival of the fit enough.\"?"
] |
[
"Stephen Jay Gould suggested \"Survival of the barely adequate\"."
] |
[
"What could be causing purple smoke seen in the photos of the Tianjin blast?"
] |
[
false
] |
[deleted]
|
[
"Potassium. Probably from potassium nitrate, a common oxidizing agent used in munitions. The violet color is from the atomic emission of potassium. like this: ",
"http://fineartamerica.com/featured/potassium-flame-test-andrew-lambert-photography.html"
] |
[
"\"The White Helmets @SyriaCivilDef: (...) barrel bomb doesn't explode, then leaks gas which discolors the soil. Ideas? 1/3\" ",
"https://twitter.com/SyriaCivilDef/status/577191496627175424/photo/1",
"\nThe White Helmets @SyriaCivilDef · 15 mrt.",
"\nThis from barrel bomb in Hayyan - 5-10kms from Hreitan, several weeks ago. Same discoloration + symptoms of cas \n",
"https://twitter.com/SyriaCivilDef/status/577213158663831552/photo/1"
] |
[
"\"The White Helmets @SyriaCivilDef: (...) barrel bomb doesn't explode, then leaks gas which discolors the soil. Ideas? 1/3\" ",
"https://twitter.com/SyriaCivilDef/status/577191496627175424/photo/1",
"\nThe White Helmets @SyriaCivilDef · 15 mrt.",
"\nThis from barrel bomb in Hayyan - 5-10kms from Hreitan, several weeks ago. Same discoloration + symptoms of cas \n",
"https://twitter.com/SyriaCivilDef/status/577213158663831552/photo/1"
] |
[
"How does the 2nd law of entropy apply to an emulsion?"
] |
[
false
] |
[deleted]
|
[
"It does seem that way macroscopically! Droplets of oil will coalesce until you have a water-only phase and an oil-only phase, which looks more ordered.",
"This doesn't look like such a paradox at the microscopic scale. A water-only phase will form an extended hydrogen bonding network, like ",
"this",
". Oil cannot form hydrogen bonds and so it appears like a roadblock. ",
"Here",
" is the best picture I could find. This roadblock ",
" the ways that water can form hydrogen bonds. Since- as you are saying with entropy- at constant energy the system moves towards the state with the most \"conformational freedom\", it's the drive to make an extended hydrogen bonding network that is the drive for phase separation.",
"I'm disappointed that some of the other answers in this thread (including from a \"mod\" named Chemomechanics) display poor knowledge of thermodynamics. Please be careful with what you read on the internet!",
"BTW- What is a hydrogen bonding liquid? Well, water is a very good example because it can donate two hydrogen bonds (2x H) and accept two hydrogen bonds (two lone pairs of electrons on the O). Liquid ammonia, for example (NH3) can accept one and donate three, so it's ok. Oil has many CH bonds which, at best, in a stretch, can donate one weak hydrogen bond and accept none, so it contributes negligibly to the hydrogen bonding network."
] |
[
"It requires energy to break hydrogen bonds, so forming emulsions don't \"release energy\", as the user said, but it ",
" absorb energy."
] |
[
"Great answer. Now I have always been fascinated by the apparent violation of the second law that happens in miso soup, where if you stir it up, after a while all the particles will gather in the middle of the bowl. Not sure what is going on there. Here's an ",
"exaple",
" which kinda shows it, but it stopped too soon."
] |
[
"Is my Y chromosome identical to my dad's?"
] |
[
false
] |
I was reading on and I came across , and I was wondering whether it was real.
|
[
"Well, the part about the Y is true, it's the same as your dads Y* and that is that same as his dads Y* andsoforth. ",
"In this statement he/she is wrong: \"So you don't know whether your X chromosome comes from, but you know where your Y chromosome comes from, and therefore you know that you share no genetics with your paternal grandmother!\"",
"You do not share any genetics with your paternal grandmother on the sex chromosomes, but you do share her genetics on all other chromosomes, as she gave a copy to your dad, who partly passed them on to you, so except the XY you're genetically 25% identical to any grandparent.",
"Also in the psychology-department ther's the bit of sleeping with your grandma, which I do not wish to think about at all.",
"*Except for the rare genetic mutation that may occur"
] |
[
"Yes!"
] |
[
"So would this imply that all males have the exact same (baring mutation) Y chromosome in common? Couldn't you trace back (way, WAY back) to a common ancestor?"
] |
[
"Why must a runner go for long distances to increase their endurance?"
] |
[
false
] |
I have no solid points against a buddy of mine. He argues that he can train just as well through 4 minute stints of running his hardest (I think it works something like 20 seconds 100%, 10 seconds rest, repeat for 4 minutes) as I can by running for 45 minutes at a time - assuming we do this equally as often. He keeps bringing up VO2 Max as a good indictator of aerobic stength and his program claims to significantly increase VO2 max, and therefore it is just as good as mine. But I, with a less scienctific background argue that I would love to see him run his program for the winter and try to join me on one of my 45 minute runs and I bet he can't do it. I tried googling this, but googling around for anything about fitness seems to just bring up a lot of weight loss advice...
|
[
"If you want a place to start reading, ",
"here",
" is a reasonably comprehensive literature review.",
"The single most important factor in distance running is how much oxygen can be taken from the air and delivered to mitochondria in the muscles. There are lots of other factors (removing waste products, structural, fuel supply .. ), but oxygen delivery is the big one. With oxygen, muscles use efficient aerobic respiration, and the rest of the body has no problem clearing up the waste. Without oxygen, muscles use inefficient anaerobic respiration, and clearing up all the waste products becomes a huge problem.",
"So if oxygen transport is the most important factor, how do we train it? As far as we know, simply lots of running. This process takes a very long time, but is the single thing that most differentiates a world class runner from a novice.",
"I want to emphasize again that oxygen transport is the single most important long term factor that requires training. A world class 1500m and a world class marathon runner will both have outstanding oxygen transport. They differ in other less important factors, which is why they couldn't just swap distances.",
"One of these less important factors is how fast the lungs can get rid of CO2. This is what causes the urge to breathe, and someone to feel out of breath when running fast. The faster CO2 gets removed, the faster waste products can get cleaned up, and the faster you can run. Fortunately, this factor can be trained remarkably quickly, on the order of weeks rather than years. Tabata training is especially good at it.",
"CO2 removal can be trained quickly, but also reaches a peak quickly. The total benefit achievable simply is nowhere near as large as training oxygen transport over a long period of time.",
"So in the short term, tabata sprints are very good, and provide fast improvement. However in the long term, they aren't a substitute for lots of running. They are training a different factor, one that isn't as important overall."
] |
[
"VO2 Max is a confusing concept that's been consistently misused by coaches and sports scientists for decades. Oxygen transported to the mitochondria is what matters most, VO2 also includes oxygen that never gets to the mitochondria, but is instead used to clean up waste. Two people with identical VO2 might be totally different, if one is using the oxygen mostly for aerobic respiration, and the other is using it mostly to clean up after anaerobic respiration. There are lots of other problems with the \"VO2 is everything\" approach to training, the paper I linked has a whole chapter on it."
] |
[
"It's called high-intensity interval training. Tabata method, specifically."
] |
[
"How long would a scent last in a glass jar?"
] |
[
false
] |
Could it last forever?
|
[
"If you had a vessel that could be sealed and would not allow any exchange of material between the internal and external environments, and didn't absorb or react with any of whatever molecules that produced the scent, then the only thing that would limit how long the scent remained would be the rate of decay of the scent molecules.",
"Its highly improbably, if not impossible, that any complex, scent-producing molecule would last forever, and I am not a physicist or chemist, so I don't have a whole lot of knowledge about the decay rates of individual elements, but it is highly likely that with the right containment vessel, you could keep a smell stored in it for a very, very long time."
] |
[
"Butyryl chloride, which hydrolyses in air to butyric acid (the essence of rancid butter, or, a month of non-shower)."
] |
[
"Its highly improbably, if not impossible, that any complex, scent-producing molecule would last forever",
"What if you froze it to near absolute zero?"
] |
[
"Is there any difference in getting vitamins and minerals from a multivitamin as opposed to actual food?"
] |
[
false
] |
For example, could one live a healthy lifestyle by eating a a good mixture of whatever fats, carbohydrates, and proteins they prefer plus a multivitamin?
|
[
"One possible difference is something called bioavailability. This is a measure of how effective your body is at absorbing the nutrients (vitamins, protein, whatever). Some sources have better bioavailability than others. E.G. milk has excellent bioavailability for protein and calcium."
] |
[
"Just the normal vitamins are the same in pills and in fruits/veggies. What you won't get with vitamin pills are any other, possibly not-yet-identified potentially good ingredients that are in fruits and veggies. It's quite a limited number of substances that are supplemented through vitamin pills, so it's a lot better to eat varied and get your vitamins through your food.",
""
] |
[
"Im not an expert but as someone who is into fitness and according to my pediatrician, multivitamins don't really serve purpose to the general healthy population. It typically is most useful for people deficient in certain nutrients"
] |
[
"Do human beings refrain from inbreeding because of an evolutionary trait OR because it is not socially accepted in society?"
] |
[
false
] | null |
[
"Yes.",
"The social taboo developed in response to evolved mechanisms to prevent inbreeding. Both act in concert to prevent it in modern humans."
] |
[
"Humans have a genetic predisposition to avoid mating with people they knew as children. Even people who know they are unrelated are less likely to become romantically involved if they spent time together as children, it's called the Westermarck Effect. ",
"http://en.wikipedia.org/wiki/Westermarck_effect"
] |
[
"Sometimes I really wonder how much of what we do today in society is just some evolutionary behavior that's manifested in that particular way."
] |
[
"Why/how does fire create light?"
] |
[
false
] |
What exactly causes fire to emit light?
|
[
"It's a mixture of atomic/molecular excitations and thermal radiation. In short, gaseous atoms and molecules will become less excited by emitting light. These emissions will result in ",
"discrete peaks in the spectrum.",
" Incomplete combustion which creates soot will glow incandescently, this is thermal blackbody radiation and results from the property that bulk materials behaves as if described by simply oscillators. These emissions will be a wide spectrum which depends on emissivity and temperature."
] |
[
"Whenever a charge changes states or its motion, it must produce a self propagating \"disturbance\" in the electromagnetic field. This happens because changes in the EM field do not travel at infinite speed.",
"These disturbances are light. ",
"When you shake a fan, a wave of wind is produced. Same idea, without the medium of air."
] |
[
"...My head hurts. ELI5?"
] |
[
"A question about centrifugal force in a weightless environment?"
] |
[
false
] |
After reading 'Rendezvous with Rama' by Arthur C Clarke, I have been stumped by a thought about centrifugal force in a weightless environment. In the book a character attempts to fly in a winged craft along the central axis of a massive closed spinning cylinder with a gaseous environment. As they go along (If I am remembering correctly) they lose power and end up being pulled down to the inside surface. So I have been thinking about what particular set of circumstances are required for the centrifugal force to act on a body. Say for example, if I am floating in space and a completely open-ended massive spinning cylinder were to pass around me i.e., I pass through the cylinder, however I am not on the central axis but closer to the inside surface. Would I be pulled down to the surface by the centrifugal force? I am deliberately excluding the gravitational force from this thought experiment.
|
[
"If you are not in contact with the wall of the cylinder at all and it starts to spin, you won't suddenly feel a centrifugal force pushing you outwards in your frame of reference.",
"However if you hold onto the side of the cylinder while it spins up, your rest frame is now non-inertial. And now there ",
" a centrifugal force pushing outwards on you."
] |
[
"In that scenario the skybike fell because the atmosphere of Rama rotated with the structure of the vehicle. As soon as the aircraft started to break up, it got pulled around with the atmosphere, which introduced centrifugal force and created pseudogravity, so it fell and crashed.",
"Great book. If you are interested, Blindsight by Peter Watts is almost the same story told from a different perspective.",
"Edit: without an atmosphere you could fly around the inside of a spinning cylinder with no problems, just as Apollo 10 orbited over the moon at ten thousand feet without crashing."
] |
[
"The centrifugal force is only acting on you if you're holding onto the wall. The reason that you fall down when you jump is because the cylinder is curved.",
"Take a look at ",
"this animation",
", which shows a red ball being thrown in a rotating environment. You can see that after it's thrown, no force acts on the ball, and it travels in a straight line (that's the red line). However, from the perspective of someone in the rotating frame, the ball appears to rise up and then fall back down, because the edge of the disk curves round to meet it. The blue line shows the object's path in the rotating frame.",
"From this, you can hopefully see that an object stopped in space above the edge of the disk would not be attracted to the edge of the disk, but would just float there. In that Arthur C. Clarke example you gave, the atmosphere (or possibly atmoring?) would be spinning too, since friction would drag it along with the edge of the cylinder. The plane would not then be able to remain suspended above the edge of the cylinder, since the drag from the air would pull it along, and once it starts moving, it'll drift towards the walls."
] |
[
"Why do men seem to want to do more sexually or physically than women?"
] |
[
false
] |
[deleted]
|
[
"Can you give a reliable source for that?"
] |
[
"Libido tends to be linked to androgen levels, especially testosterone. These are generally higher in men than in women."
] |
[
"That is not always true. Women can have just as high a sex drive as men, we just tend not to act on it as often as men."
] |
[
"Do animals know when to stop eating or eat less since their prey can't reproduce quick enough?"
] |
[
false
] |
We have a lot of trouble with overfishing the ocean for example. so I asked myself If animals may have such a problem as well and stop before it's too late.
|
[
"Starvation culls predator numbers when prey are in decline, when there is a glut of food then the population increases with it, when the prey are scarce the predators decline. ",
"There was a study done on rabbits and foxes and the population numbers of both fluctuate in very similar trends over time, with the prey numbers advancing first and predators following. "
] |
[
"Question is not about feeling full but being aware of prey population declining meaning less food food in the future"
] |
[
"Why are you asking me. I was notifying you of your misperception of the question. I doubt they do as well."
] |
[
"Evolution of defensive poisons"
] |
[
false
] |
How can a defensive poison (such as that of a poisonous frog) evolve if the selective pressure depends on its predator knowing it's poisonous? That is there no advantage to the individual to being poisonous if you die anyway. Is that why poisonous animals are colourful, because only the distinctive ones are remembered by the poisoned predator as being poisonous? (that is only animals that evolve a poison and a distinctive colour simultaneously can pass on a benefit to their kin?
|
[
"A frog can have a hundred matured offspring before it gets eaten, and so can they, in turn. This would give time for the whole process to take place. The mutation does not necessarily die with the eaten frog. I hope I did not misunderstand your statement."
] |
[
"The selective pressure doesn't depend on the predator knowing it's poisonous. The poison kills the predator, regardless of whether it knows what it ate was good for it or bad for it - however, those predators that don't eat the poisonous prey will live, while those that don't will die. Eventually, you select for the predators that avoid the poisonous animal - if it happens to have a distinct colouring, that's ok.",
"The distinctive colouring would, by expectation, be secondary, as the predators have stopped eating the animal that isn't camouflaged so well any more. Otherwise, if the fancy colour evolved before the toxin, the brightly coloured prey would be easier to see, and thus would have been depleted faster, favouring those that are better camoflaged."
] |
[
"There is also good documentation on organisms, specifically insects, that produce toxic compounds and are not eaten by larger organisms. This happens because, unlike what you might imagine, the large organism actually \"samples\" the insect before it fully commits to eating it. ",
"For example, if a toxic insect is about to be eaten by a frog, the frog actually will use its tongue and place the insect into its mouth, but will spit it back out unharmed because it detects the toxin. So no, the predator does not have to actually kill the organism to detect the poison and avoid the insect."
] |
[
"I am NeuroBill. I'm a neuroscientist who had worked Down-under, in Europe and back down-under again. Ask me anything about cellular neuroscience, working in three countries or having two passports!"
] |
[
false
] |
My name is Dr Bill Connelly. I've been selling my skills as a neuroscientist for a decade. My skill is using an (admittedly old) Nobel prize winning technique to understand the electrical properties of the brain and combining that with computational modelling of these things. I've used what I know to probe the cellular results and causes of epilepsy, why some brain cells talk to themselves, what histamine is doing in the brain and many other things. If you've got a question about how the brain works on a cellular level, I might be able to answer it. Feel free to get in contact on twitter at @NeuroBill or on my website I can start at 2300 UTC (7 PM EDT), and hang around till 700 UTC.
|
[
"What is happening in an ADHD persons brain? And what are the best treatments for ADHD?",
"Thanks! "
] |
[
"I can answer some of that! ",
"Regarding what is going on in the brain of someone with ADHD:",
"The brain is... Really ludicrously complex. The tools we have available to us are very limited in their ability to look at the fine details of what's going on in a living human brain. You can do fMRI studies of people with and without ADHD, sure, but even if you DO observe a difference in activity, the area you're seeing that difference in probably contains a hundred million neurons, and you have no way whatsoever of knowing which neurons in that area are acting unusually (since different subgroups of neurons in a given brain structure usually have very different jobs). So our best guesses about what's going on in ADHD are really quite limited.",
"Here's what we DO know:",
"The neurotransmitter dopamine (which is often, stupidly, referred to as \"the reward chemical\") is used by many different brain systems, including some relating to reward or motivation, others relating to movement, one system relating to lactation.. The list goes on. But some of the important dopamine pathways that we believe might be abnormal in people with ADHD are dopamine pathways relating to motivation and attention. This is supported by the finding that certain versions of certain genes that are related to dopamine function are associated with increased risk of ADHD, and also by the fact that drugs that affect dopamine tend to affect ADHD symptoms.",
"But, there is probably a lot more to it than that. It is almost certainly NOT a simple matter of \"too much / too little\" of some particular neurotransmitter. The \"too much / too little of this neurotransmitter\" way of thinking about mental disorders is commonly used to explain things because it's easy to understand, but it's pretty much always wrong. I know of perhaps 1 or 2 disorders that are actually legitimately caused by an overall excess or deficit of a particular chemical in the brain (e.g. phenylketonuria).",
"Some more nuanced evidence for the pathology of ADHD comes from EEG studies. Among other things, EEG can be used to assess temporary connections between brain areas, in the form of synchronized brainwaves between brain areas. There is some evidence that people with ADHD have abnormal communication between brain areas, particularly involving the frontal cortex, a part of the brain particularly associated with making decisions and evaluating choices, which may be related to the impulsivity and difficulty sticking to a task that people with ADHD often experience.",
"I think we will find out more within the next couple decades, as methods for both examining the activity of live human brains AND for creating and studying animal models of ADHD (which can potentially assess the role of ",
" neural circuits in the disorder) improve."
] |
[
"Hello everyone!\nSorry I'm a little late to the party, but they fired this thing up at 1am local time. However, it's 6:44am, the coffee is poured, my beard is oiled and I am ready to answer."
] |
[
"Did this once 50 mile wide sea in north west China (40.5 N,90.84 E) evaporate down in size to become just a salt farm?"
] |
[
false
] |
I was thinking that it might have seasonal variations that I'm not seeing in
|
[
"Your link goes to the panama canal. You meant to link this : ",
"https://maps.google.com/maps?oe=UTF-8&q=40.5%20N,90.84%20E",
" .",
"Edit: For a better view of what he is talking about go back and forth between maps and satellite."
] |
[
"Thanks, I changed the link"
] |
[
"Gogole maps kindly names the nearest town: Ruo Qiang Xian, Bayinguoleng, Xinjiang, China @ 34 km (20 miles?) distance.",
"Putting that into the web produces travel guides that explain the nature of the area",
"http://www.wiki86.com/view/6978.htm",
"http://www.travelchinaguide.com/attraction/xinjiang/korla/lop_nur.htm",
"They say it was once a lake, but desertification occured in 1972 and now it's a salt lake."
] |
[
"When a bird returns to its nest and see that either the nest itself or the egg is missing how does it react? Does it realize that it may have been eaten?"
] |
[
false
] |
I know some birds are surprisingly smart so I just wanted to know how they handle that situation.
|
[
"Excellent question! I was talking about the same thing because watching a documentary i saw some birds invade nests and place their eggs leaving their babies behind \"for adoption\". It always baffled me that the adoptive parents just accept that. So I don't know if they are not smart on that level or if they just decide to keep going regardless. Also because some of these invasive chicks hatch early and literally kill the siblings to avoid competing for food and protection."
] |
[
"I'm fairly certain that on that level of cognition the natural mothering instinct is more powerful than physical recognition. Their brains are just not big enough."
] |
[
"This is called brood parasitism. Tricking a different species to raise your own offspring. The cowbird is the textbook case for this behavior, where the chick hatches early and instinctually rolls the competing eggs out of the nest. The reason why the parents don't react is because they recognize their eggs by color, and the cowbird has evolved eggs of a similar color. To boil it down, yes the parents are simply not smart enough to know that something is wrong."
] |
[
"What's the smallest change in temperature a human can detect?"
] |
[
false
] | null |
[
"I can detect milliKelvins using an EPR temperature probe."
] |
[
"i think it might depend where on the spectrum between \"hot\" and \"cold\" we're talking. i think it's easier to detect a change in temperature when things are fairly moderate as opposed to if the same amount is changed while it's already either hot or cold while approaching the pain threshold. also it might depend on whether or not the heat is felt ambiently in the air or directly by touch (and if directly what the material is made of)."
] |
[
"I read once that 1 degree Fahrenheit is supposed to be the smallest unit of temperature that a human can detect, but that doesn't seem correct, based on what everfalling mentioned. Maybe it's the smallest unit that can be detected in a reasonable ambient temperature range (-10F - 110F)? "
] |
[
"Different spacetime curvature for different objects?"
] |
[
false
] |
Spacetime curvature accounts for how stars work as gravitational lenses for light. When explaining gravity as spacetime curvature, does it explain it completely - without the need of additional factors? Imagine shining a light beam vs. throwing an apple on earth? Obviously, there is hardly any curvature affecting the light beam, but quite a lot affecting the apple. Can spacetime curvature be different at the same place (even in the same intertial frame) for different objects?
|
[
"Imagine shining a light beam vs. throwing an apple on earth? Obviously, there is hardly any curvature affecting the light beam, but quite a lot affecting the apple.",
"The difference is that light is moving at ludicrously fast speeds compared to the apple. If you threw the apple at near the speed of light, it would move almost like the light would. The faster you throw it, the more its motion would resemble the motion of light.",
"So the curvature is affecting both in the same way, but one is moving quickly and one is moving slowly. The slower-moving object has low momentum, and stays in the gravitational field for a longer amount of time, so changes in its momentum due to gravity are significant compared to the original momentum -- that is to say, Δp is roughly the same order of magnitude as p. But the faster-moving object has high momentum, and leaves the gravitational field more quickly, so the changes in its momentum due to gravity are much smaller than its original momentum -- Δρ is much smaller than p, and so the change is not as noticable. The reality is that Δρ might actually be roughly the same order of magnitude for both a slow-moving and fast-moving body, but it's the ratio of Δρ/p that determines how much the velocity and trajectory appear to change to a human observer.",
"Btw I don't mean to imply that light is somehow the \"limiting case\" -- there are important differences between light and matter, but for the spirit of your question I don't think it's necessary to address these.",
"Can spacetime curvature be different at the same place (even in the same intertial frame) for different objects?",
"No, it can't, at least not in the most widely-accepted models. Moving between reference frames can affect the location of points and the sizes of distances between those points, but at that point, the curvature will be the same for every observer.",
"This follows from the idea that the stress-energy-momentum tensor in general relativity is Lorentz covariant.",
"Hope that helps!"
] |
[
"It's somewhat technical, but the \"curvature of spacetime\" (the metric) affects the motion of massive particles, massless particles, and tachyons* in three different ways. There's a certain quantity that is equal to 1, 0, or -1 depending on which you're dealing with. The faster objects are moving, the more their trajectory is similar to that of light.",
"See for example Hartle's Gravity, chapter 8."
] |
[
"Since you mentioned tachyons...",
"Are you saying that the trajectory of a tachyon resembles that of light the ",
" it gets, rather than the ",
" it gets, as one might naively assume? "
] |
[
"When recalling a memory, does it make the memory stronger/more imprinted once you remember it or does it actually become more \"used up\" causing each recollection to become distorted each time?"
] |
[
false
] |
[deleted]
|
[
"\"There are two main methods of accessing memory: recognition and recall. Recognition is the association of an event or physical object with one previously experienced or encountered, and involves a process of comparison of information with memory, e.g. recognizing a known face, true/false or multiple choice questions, etc. ",
"Recognition is a largely unconscious process, and the brain even has a dedicated face-recognition area, which passes information directly through the limbic areas to generate a sense of familiarity, before linking up with the cortical path, where data about the person's movements and intentions are processed.",
"Recall involves remembering a fact, event or object that is not currently physically present (in the sense of retrieving a representation, mental image or concept), and requires the direct uncovering of information from memory, e.g. remembering the name of a recognized person, fill-in the blank questions, etc.",
"Recognition is usually considered to be “superior” to recall (in the sense of being more effective), in that it requires just a single process rather than two processes. Recognition requires only a simple familiarity decision, whereas a full recall of an item from memory requires a two-stage process (indeed, this is often referred to as the two-stage theory of memory) in which the search and retrieval of candidate items from memory is followed by a familiarity decision where the correct information is chosen from the candidates retrieved. Thus, recall involves actively reconstructing the information and requires the activation of all the neurons involved in the memory in question, whereas recognition only requires a relatively simple decision as to whether one thing among others has been encountered before. Sometimes, however, even if a part of an object initially activates only a part of the neural network concerned, recognition may then suffice to activate the entire network.\"",
"Source:",
"http://www.human-memory.net/processes_recall.html"
] |
[
"Rather than try to repeat what they said, I'll give you this instead: ",
"Relevant Radiolab"
] |
[
"it is my understanding that you would not \"use up\" a memory in recalling it, at least not in the sense your checking account can be used up by unchecked spending. your memory will not become distorted ",
" from usage. to try to fully answer this question, i would say there are two big possibilities:",
"so where recalling a memory does not use it up, and in fact will likely strengthen it, the memory may become indirectly distorted by a cognitive error. our memory is remarkable incredible and efficient, and such errors are the cost we pay for the efficiency of the network of associations that our memory seems to consist of. \ni really tried to keep this semi-short, but i tend to rant. hope this helps",
"tl;dr? recall will likely strengthen a memory due to priming, except for when memory errors sneak in, then recall may distort said memory. "
] |
[
"Why are atoms with too many neutrons radioactive?"
] |
[
false
] |
I understand that having too little neutrons means the electromagnetic force repelling the protons from each other outweighs the strong nuclear force, but why does having too many neutrons make it unstable? Wouldn't adding neutrons increase the strong nuclear force while the electromagnetic force remains relatively the same?
|
[
"Now, I don't claim to be an expert in nuclear physics, although I did my undergraduate thesis project on a topic in few-nucleon systems, so I'm ",
" sure that what I'm saying here is accurate. If there is a nuclear physicist please correct me if I'm wrong.",
"For systems with few nucleons (say < 6 for the sake of argument), the electromagnetic force is mostly irrelevant. In other words, if you model the nuclear force as an interaction between protons and neutrons that satisfies isospin symmetry, the diproton system is unstable even without taking into account the electromagnetic repulsion. In such a theory, there is a so-called \"triplet\" state of pairs of nucleons that are completely identical as far as the nuclear force is concerned, and therefore can be treated as a superposition of all three. These three states include the two-proton system, the two-neutron system, and an excited version of the proton-neutron system. All three of these states are unstable (edit: actually, unbounded) for the same reason, although they probably have very slightly different binding energies due to the fact that the electromagnetic force does have a small effect. There is also a \"singlet\" state made of an unexcited proton-neutron pair that is stable (called deuterium). The electromagnetic force becomes important for nuclear stability when you start to add lots of nucleons into the nucleus, but for small numbers it does not play an important role. "
] |
[
"What about larger atoms? Why are heavier isotopes of mercury unstable?"
] |
[
"I always look to the semi empirical mass formula. Increasing the number of neutrons makes the system larger. Nucleons on the surface interact with less nucleons and are thus less bound. So you essentially have a weakening of the strong force. In addition, due to Pauli exclusion, too many neutrons would occupy higher levels compared to the protons. Thus, it would be energetically favorable for the neutrons to turn into a proton. This is the asymmetry term in the SEMF."
] |
[
"Probability question"
] |
[
false
] |
If there's a 6 sided die, 4 sides with an F and 2 with an M and I roll the die 3 times, am I more likely to get an M on the third try versus the first?
|
[
"no.",
"Every time you roll the dice you have 33% probability of getting \"M\". The dice don't keep track over how many times you roll, or what you rolled previously. They're just dice. "
] |
[
"Suppose that you throw once, decide do go to the toilet and return, then start again and throw twice. Was the last one the second or the third?"
] |
[
"Further information for OP / anyone else: this mistake is called the ",
"Gambler's Fallacy",
"."
] |
[
"From my six-year-old: why do roosters crow in the morning?"
] |
[
false
] |
They crow at other times of course, but I didn't really have a good answer for him. Is it some kind of aggression/dominance behaviour?
|
[
"Are any lights on? The roosters may be confused by environmental cue."
] |
[
"He is six, though. You think he really wants someone talking down to him like he is five?"
] |
[
"I used to live in a small town in China where many of my neighbors kept fighting cocks, as well as ordinary domestic chickens. I can attest that those fuckers crowed at any and all times of the day and night. Contrary to what I expected I didn't notice any uptick in crowing frequency at or around dawn. (And I was in a position to notice, having been kept up all night by the incessant crowing. After a few weeks I got used to it though.)"
] |
[
"How are ribosomal proteins synthesised?"
] |
[
false
] |
Ribosomes build proteins right? But how are the proteins, that make up the ribosomes built in the first place? Or are ribosomes automatically given to daughter cells?
|
[
"Ribosomal proteins are manufactured by ribosomes just like every other protein.",
"Ribosomes are indeed inherited by daughter cells from the parent cell."
] |
[
"Only the egg. ",
"Source",
", ",
"source",
". "
] |
[
"Yep. A daughter cell inherits ribosomes, and then can make their own. Ribosomal proteins aren't special, they're proteins like any other. "
] |
[
"Do computers slow over time, or is an old computer only slow due to increased software resource usage?"
] |
[
false
] |
Ignoring malware, let's say a PC from '95 was run today on the exact same applications, websites, etc that it was run on in '95. Would it run at the same speeds as it did back then?
|
[
"The CPU is clocked at the same speed, yes - assuming there have been no changes to any of the software installed on the PC, it should run at the same speed",
"In the more general case, there are mechanisms that cause the maximum speed a CPU could run at to decrease over time - nbti is the biggest contributor and increases logarithmically over time when the device is powered. If design and test guard bands were not set strictly enough when the part was manufactured, then it's possible that it would no longer work properly at its intended condition. This would not manifest itself as the computer running slower though, just crashes"
] |
[
"What is NBTI?"
] |
[
"In general, it would run at the same speed. There are however a handful of things that can make a computer slower (like a higher error rate from various parts, especially a hard drive) which can cause it to redo some work (like re-read a file). But as byrel said, these types of things are far more likely to just result in a crash (if you increase the correctable error rate, then you would increase the uncorrectable error rate, which will cause crashes)"
] |
[
"Why are bruised spots on fruit sweeter than the rest of it?"
] |
[
false
] | null |
[
"Bruising on fruits occurs because parts of the fruit cells' cell wall are ruptured, releasing the enzymes. This causes accelerated ripening, a process that involves breaking down enzymes, but more importantly, hydrolyzes storage polysaccharides. Those polysaccharides convert to smaller sugars (glucose, fructose, sucrose) which have a sweeter taste than the originals."
] |
[
"Your saliva and digestive enzymes would break down those same starches, so the caloric value should be the same.",
"I would imagine it’s ",
" that other compounds we consider nutrients (vitamins etc) might also be broken down by enzymes in the bruise, but I don’t know for certain. Certainly not enough to impact the overall nutritional content. Probably."
] |
[
"Awesome response- thank you!!!"
] |
[
"Have we contaminated space with life from earth?"
] |
[
false
] |
For example, do we know if the Voyager probes or the Curiosity rover did not carry (living or dead) bacteria, viruses, or other microorganisms (e.g. tardigrades) into space or other planets? Are there normally steps taken before launch to prevent this?
|
[
"We almost certainly did include those microbes on Voyager, since cleaning protocols are only used on probes going to places we expect to find life. Since Voyager did not land/crash anywhere, no cleaning.",
"NASA has a protocol for cleaning these probes and rovers and the program is overseen by the ",
"NASA Planetary Protection Officer."
] |
[
"Yes. But so has nature. It's likely that some big impacts have thrown Earth rocks into interplanetary space that could still have contained living Earth micro-organisms, and some of those could have landed on other planetary bodies (certainly Mars, possibly the moons of Jupiter and Saturn)."
] |
[
"The sun releases a lot of UV radiation that our ozone layer shields, as well as our magnetic field for solar wind.",
"Both are effective methods of destruction of organic molecules.",
"Are organic molecules present on the Voyager? Very likely. Can any self replicate as life does? Likely not."
] |
[
"Why did the Shuttle start to move forward upon takeoff?"
] |
[
false
] |
I was watching some space stuff and I noticed that the Shuttle moves forward on takeoff. Not as in roll, yaw or pitch, it goes up as it should but goes forward ever so slightly. In the video below, it just goes to the right. (Example - ) What makes this happen? Is it due to the SRBs being more powerful than the Shuttle's main engines?
|
[
"The Space Shuttle Main Engines, attached to the Orbiter, are not directly under the assembled vehicle’s center of mass. As such, the SSMEs are angled to thrust through the center of mass instead of vertically. This keeps the vehicle from pitching nose-down uncontrollably during flight."
] |
[
"This is perfect, I didn't know about that angle. Thank you!"
] |
[
"They start the Main Engines first to make sure they are spooled up and working before the SRBs are lit. Since, once the SRBs are lit the Shuttle is lifting off one way or another. So what are you are seeing is the the ME thrusting and the Shutting rocking forward and back to vertical from the thrust. Only then do they light the SRBs."
] |
[
"Is there any chance of there being an undiscovered simple machine?"
] |
[
false
] | null |
[
"Well - I'd say there are perhaps some chances as we work out the basics of nanotech. Some of those microminiaturised machines might exploit some small-scale properties of matter which are irrelevant at the macro scale."
] |
[
"If you're asking whether there is a probability greater than 0, the answer is, \"Of course!\" For a long time we believed we had all the components necessary for a basic electronic circuit, then in 2008 HP created the ",
"Memristor",
", which was a fundamental circuit element that had not existed except in theory. I don't know of any theory about hypothetical simple machines, but the beauty of science is that we're always happy to look for more!",
"changed the wording slightly for accuracy's sake."
] |
[
"I think that means HP invented it. I can talk about the general concept of a machine that uses ice cream as fuel and spits out gold bullion, but nothing has really been invented until there's a working device."
] |
[
"Why were the cameras on the Voyager 1 turned off?"
] |
[
false
] |
I was reading an article and read they were turned off as it heads into the unknown.
|
[
"Because everyone bullies NASA for their lunch money :( "
] |
[
"what if there was something to see?",
"What if there's something interesting to detect, but only if we turn off the camera to power the probe long enough to detect it? NASA isn't turning off the cameras because they're giving up, they want to make the most of limited resources."
] |
[
"Nothing to see, and Voyager has a limited amount of power and data storage. Additionally it'll get harder and harder to continue transmitting images as it gets farther away from Earth. "
] |
[
"could you drink some sort of ATP liquid for calories?"
] |
[
false
] |
What would your digestive system do with it?
|
[
"You certainly can drink ATP.",
"I include that link only to show that oral ATP supplements are available. I would be very hesitant to make any claims on what (if any) effects these supplements would have.",
"In my opinion, your body would digest the ATP and use it for its component parts as it does with all food. I don't think ingesting it in its charged form would provide much advantage, but I haven't looked into it thoroughly."
] |
[
"I think It would break down immediately in your saliva since it's not too stable in water. It might produce a strange sensation on the tongue in doing so. "
] |
[
"Good point. I think that's why they gave it an enteric coating in the study cited."
] |
[
"Did Bipedal Dinosaurs Hop?"
] |
[
false
] | null |
[
"From what can be guessed from the fossil record and their characteristics, it's very unlikely they could, hopping as a whole is a very energy inefficient system of movement, and presents a huge stress on leg muscles and bones",
"Small birds can get away with hopping, as their mass is negligible, and their legs very strong for their weight, adapted not to get worn down by the impact of landing, still, do note that the big birds (birds of prey, most flightless birds...) do not hop, at least not as their usual ground locomotion, which shows how energy inefficient such a process is",
"Kangaroos and some steppe/desert rodents cheat the system, as they adapted to favour hopping as a medium of transportation (while being very inefficient, it can be faster), their legs are unique to maximize jump height, are their tail functions as a \"spring\" to aid movement (at least in kangaroos), some of their vital processes do also use the excess energy from hopping to minimize the energy loss ",
"Meanwhile, the fossil record shows that dinosaur tails were held parallel to the ground, as they would be used for balancing, while their size and weight would heavily discourage any hopping besides some burst movements, like jumping onto prey or hopping to change their direction after a surprise threat",
"Unsurprisingly, there's not many scientific papers on the subject, ",
"but here's a more in-depth answer"
] |
[
"I watched a nature show recently that stated the kangaroo leg tendon is springy. This allows energy reuse while hopping. I believe they claimed the resulting hopping was more energy efficient than human running. "
] |
[
"There's not any good evidence to support the idea. We have quite a few trackways showing dinosaurs running with a typical alternating stride, but there are only a handful of trackways that could potentially be interpreted as those of a hopping dinosaur, and consensus is that those were made by other animals (in the most notable case, a swimming turtle). Links below to a couple relevant parts of books",
"https://books.google.com/books?id=xCrSL48cho0C&pg=PA44&lpg=PA44&dq=dinosaur+trackway+hopping&source=bl&ots=W2OSVWXpXH&sig=oKTLBfhrvm3DFAi7dnbk4_OporQ&hl=en&sa=X&ved=0ahUKEwjDlJrKz6_TAhXjslQKHRfrBdgQ6AEIJzAB#v=onepage&q=dinosaur%20trackway%20hopping&f=false",
"https://books.google.com/books?id=kji6fde5g-gC&pg=PA177&lpg=PA177&dq=dinosaur+trackway+hopping&source=bl&ots=g1kpqXuOi1&sig=CDie4Bc8wIN9SqOIqCfUyLWkChY&hl=en&sa=X&ved=0ahUKEwjDlJrKz6_TAhXjslQKHRfrBdgQ6AEIIzAA#v=onepage&q=dinosaur%20trackway%20hopping&f=false"
] |
[
"Largest Possible Atom?"
] |
[
false
] |
[deleted]
|
[
"We don't know!",
"There are two limiting scenarios, the atomic one and the nuclear one. The atomic limit, somewhere between 137 and 179 (sometimes called \"Feynmanium\" is the point the ionization energy of an electron is equivalent to its rest-mass energy, so if you ionize the atom it can create another electron-positron pair out of the vacuum.",
"The nuclear limit occurs roughly when neutrons and protons \"drip\" off the atom simultaneously and you can't add any more nucleons to even create an unstable bound nucleus (like 118); they simply will not stick together as a nucleus, the ",
"binding energy",
" will never be negative. I'm not exactly sure where this occurs but I think I've read it being around 150. Maybe ",
"/u/verylittle",
" knows.",
"Before this, there is the hypothesized Island of Stability, around 126 (maybe?), where superheavy elements are more stable than their neighbors."
] |
[
"Depending on whether you allow gravitational binding, you might consider a neutron star to be a single enormous atom. The size limit would then be Chandrasekhar's Limit, the mass at which the neutron star would collapse into a black hole."
] |
[
"*Nuclear force (or residual strong force), not electromagnetic. The electromagnetic force actually destabilizes nuclei with protons in them, because it'll push them apart. Neutrons are neutral and don't really interact with the electromagnetic force anyway."
] |
[
"Is there any scientific reasoning behind the fact that momentum is the derivative of kinetic energy with respect to velocity?"
] |
[
false
] |
Is this just a sort of mathematical coincidence or are the principles of one's momentum and kinetic energy intertwined?
|
[
"It is definitely not a mathematical coincidence. When a body is being accelerated its gaining kinetic energy according to:",
"dE=Fdx=vdp. If we assume m is constant then we can do the following:",
"dE=vd(mv)=mvdv=pdv, and therefore dE/dv=p. ",
"Most modern physicists prefer to express KE as p",
" /2m because it makes the relationship between energy and momentum more explicit (and because this is how it occurs in the Hamiltonian formulation of classical mechanics.)"
] |
[
"This is only true for a free particle; introducing a potential which depends on the generalized coordinates or velocities will alter the definition of the generalized momentum"
] |
[
"In the ",
"Lagrangian formulation",
" of Newtonian mechanics this is more or less the ",
" of momentum.",
"In fact you can define \"generalized momenta\" in this way; for example the derivative of the kinetic energy with respect to the angular velocity is the angular momentum."
] |
[
"[Mathematics] The l_2 norm can be defined in a basis independent fashion, can other l_p norms be defined in this way?"
] |
[
false
] |
So I have a question I think I should've known from basic courses, but now I can't seem to find an answer anywhere. Say you have a vector space V, and assume that it is an inner product space (which for any physically meaningful situation I guess one can give V this structure). Then, the l_2 norm can be defined via the inner product without ever referring to a basis. Can one do this for other l_p norms? In particular, can one do this for the l_1 norm? What additional structure (such as the inner product in the l_2 case) does one need to be able to define the l_1 norm in a basis independent way?
|
[
"The important thing is that Lp-norms are only valid on function spaces, and in finite dimensions function spaces are very closely related to bases. In fact, choosing a basis for a finite dimensional vector space V is equivalent to choosing an isomorphism between V and the vector space of functions from {1,...,n}->F (where F is your field). So every finite dimensional vector space with a basis is naturally isomorphic to a function space with finite domain, and ever function space with a finite domain has a natural basis. For infinite dimensional things, it's not so simple.",
"But, in general, they Lp-norms are basis independent, but not measure independent. If X is any measurable set, then you can get the ",
"Lp-space",
" associated to X, which is the real (or complex)-valued functions so that the integral of |f(x)|",
" over X is finite (modded out by measure-zero functions). The norm is then just the 1/pth power of this. This is independent of any choice of basis, because it only depends on how the measure/integral works and this doesn't depend on a basis."
] |
[
"The Lp-norm is only defined on the function space, and on the function space it is basis independent, since it is just an integral on those functions. If V is a random finite dimensional vector space and R",
" is the set of functions from a finite set X to the reals, then an isomorphism V->R",
" will pullback the Lp-norm on R",
" to a norm on V. Strictly, I wouldn't then call this induced norm on V an \"Lp-norm\", because V is not a function space, rather it is a norm induced by an Lp-norm. This induced norm definitely ",
" depend on the isomorphism which, according to our correspondence, is the same as it depending on a basis for V. ",
"I think some of the confusion may be that we're assuming that R",
" has a natural choice of basis, namely the indicator functions of single points, but we don't need to do this at all. Under this basis f=f(1)I",
"+...+f(n)I",
", so it looks like we're invoking this basis to define |f|",
", but we're not, we're just using the measure. So we can forget that R",
" has a basis at all, and everything will still workout. We just say that having a basis ",
" there is an isomorphism V->R",
", dropping the equivalence, and I would say that this is probably a better way to think about things. Therefore, the Lp-norm on R",
" is independent of any choice of basis on R",
", but if we use a map V->R",
" to pullback this norm onto V, then the norm definitely depends on the choice of map V->R",
". If we're inducing this map via a basis, then this implies that the norm depends on the choice of basis.",
"While choosing a different basis will give you a different norm, the two induced topologies are homeomorphic (though, not necessarily isometric, they should differ by the absolute value of the determinant of the change-of-basis map). So there is still a bit of basis-independence going on at the topological level."
] |
[
"Hi thanks!",
"So I'm definitely staying within finite dimensional vector spaces. I still don't really see why these norms are basis independent though. I'm familiar with the fact that a vector space together with a choice of basis (indexed by X for example) is isomorphic to the space of functions over X. Then the lp norm of a vector is the lp norm of the function, agreed. ",
"But the form of the function depends on the initial choice of basis: the isomorphism is between a function space and a vector space ",
" a choice of basis. Different choices of bases will lead to different coefficients of the same vector. To be explicit, let {a_i} and {b_i} be two bases and v a vector, then",
"v = \\sum_i v_i a_i = \\sum_i v'_i b_i",
"where v_i ≠ v'_i in general. I see no reason why it should hold that",
"\\sum_i |v_i|",
" = \\sum_i |v'_i|",
"for any p other than 2. ",
"Or put in another way, a change of basis may be performed by a matrix M \\in GL(V). But GL(V) doesn't preserve l_p norms so the l_p norms are basis dependent. But then l_p norms should only be useful when one particular basis is 'more important' than the others, which is most commonly not the case. So there should be a loophole in the argument above, I just don't see where."
] |
[
"At what point can we no longer notice a difference in monitor refresh rate?"
] |
[
false
] |
[deleted]
|
[
"Ahhhh, this is tricky for lots of interesting reasons.",
"First off I'm going to go on a slight tangent and talk about g-sync (et al) and the heritage of monitor signaling standards going back to CRTs. You see, with a CRT the image was displayed by sweeping several electron beams across the display, lighting up different colored phosphors on the screen and \"painting\" an image one pass at a time. The signals that controlled those electron beams basically came directly from the signal from the computer \"live\" (more or less). This meant that the computer had to do all the work to avoid things like \"screen tearing\" where the image displayed on the monitor was changed part-way through it being drawn. Additionally it required the computer to display frames on the monitor at the frequency the monitor operated at. This necessitated keeping a buffer pipeline of rendered frames to avoid screen tearing or being left flat footed when for some reason a frame wasn't ready precisely when the monitor needed one.",
"But LCDs don't work that way, they have a maximum refresh rate but they don't have a minimum refresh rate. You could potentially send a frame to an LCD at 1 Hz or less and it'd still work just fine. This opens up the possibility for a new way of sending frames to LCDs. Instead of sending a raw signal, you can transmit the frame data (whenever it is available) and then tell the monitor when you're done transmitting the frame (which it stores in its own internal buffer) to display that frame. This means the actual frame rate of the display will match the actual rendering frame rate of the computer system, leading to a much smoother experience. And, more importantly here, leading to much less latency between input and display.",
"All of which is to illustrate that refresh rate doesn't tell you everything, depending on ",
" the computer and display are connected you can have different experiences in terms of how smooth and realistic the display feels as well as how responsive the display is relative to input. Studies have shown that around 100ms of latency is not perceptible by most people, though it's possible that some individuals (e-sports gamers, pilots, perhaps) are possible of perceiving latencies shorter than that. 100ms is only 10hz, and even 10ms is only 100hz, so it's likely that refresh rates higher than 100hz are not useful for humans in terms of perceived input/response latency.",
"However, there are some additional caveats here. One of them being motion blur. Humans have evolved to rely on motion blur to give cues on how things are moving (or not) so it's an important part of our visual system. Which means that realistic motion blur is important to produce realistic computer generated imagery (such as in first person video games). Computers can simulate motion blur using various rendering techniques but one of the easiest ways is to just generate and display a lot of frames faster than the eye can see, which will produce a natural motion blur effect, making higher frame rates potentially valuable. I don't know what the research says in terms of what refresh frequencies correspond to the most natural looking results though I suspect that even 60hz is probably good enough to make things look \"real\"."
] |
[
"A great write up! To me, this question is a rephrase of '",
"'. That would set the theoretical limit, and ",
"this graph shows",
" that most young adults seem to be able to discern ~15 ms (66Hz) temporal gaps. The extreme end are able to discern 5ms or less (200Hz+) temporal gaps.",
"Now, identifying temporal gaps is different from being able to discern fluidity differences of say, 100 FPS vs 200 FPS. Input lag is different again, because the monitor is not the only thing introducing lag. Your FPS indicate the ",
" input lag possible, with the total likely being much higher. It only really matters if that additional lag is actually crossing some sort of perception threshold. ",
"Overall, I think it's safe to say 240 Hz should be more than enough for the overwhelming majority of people, it would be hard to justify higher frequencies unless you get into ",
"use of strobes to reduce motion blur.",
" "
] |
[
"100ms is only 10hz, and even 10ms is only 100hz, so it's likely that refresh rates higher than 100hz are not useful for humans in terms of perceived input/response latency.",
"For latency, yes, but when you have 100ms to determine if the guy peeking around the corner is running, walking, or stopped, the more frames the better.",
"Also, mouse input hand-eye coordination is cleaner at higher refresh rates (for small, quick movements)."
] |
[
"Why don't our teeth heal?"
] |
[
false
] |
Why do we need fillings for our cavities, after all shouldn't evolution have caused that our teeth can regenerate like our bones and skin? Idk if this is the same but; We see this by some rodents who's ameloblasts don't die after their teeth grow. Though they need to constantly gnaw at things, to keep their teeth at the proper size and shape, this seems to be a much more practical solution ("evolution-wise") than not healing at all.
|
[
"For the purposes of evolution the most important thing was that we lived long enough to pass on our genes. Our teeth generally last long enough to accomplish this goal and likely would have lasted longer before humans started consuming soda and candy."
] |
[
"So your teeth do repair themselves. Only very slightly. Teeth can \"last\" until people are 60 and older without brushing their teeth or taking care of them. The main reason our teeth get broken down so fast is the high sugar foods and other weird bad for your teeth foods we eat. If we ate a diet closer to what cavemen ate, our teeth would not get broken down so readily. Evolution does not have a place it wants to go. Natural selection leads the way. If having rotten teeth at 60 years old does not stop genes from getting passed on, it doesn't really matter what happens to your teeth at that point. So In the end the main reason our teeth don't heal is because it doesn't hinder reproduction."
] |
[
"But damage to your teeth like smashing them against rocks and stuff? Being able to repair your teeth would have been a huge advantage, no? Or was it just so rare that there was no evolutionary pressure?"
] |
[
"What is a good metric to identify the \"uniformity\" of a distribution?"
] |
[
false
] |
[deleted]
|
[
"Entropy is nice if you can be sure that your distribution is continuous. Piecewise uniform distributions also maximize entropy.",
"I haven't done this personally but my gut feeling is that I would go with a simple error norm between the (unique) uniform distribution function on a certain domain and your measured function. Just make sure the scale is right. Depending on what you want to measure you can choose different norms (for example, if the heat transport is important you could choose a norm that measures derivatives, like H",
" — otherwise L",
" is good)."
] |
[
"Echoing the conclusion of ",
"/u/theBB",
", look elsewhere.",
"If I may make an alternative suggestion, why not find the discrete fourier transform of your data, normalize the energy to one, and then find the energy in the DC component? This would be akin to considering all data to to be constant, and the variation to be added noise. Further, for actually writing a paper you will not have to justify the intermediary step of approximating a probability distribution just to use a metric associated with them. I know I would not appreciate that as a reviewer. On the other hand, energy in dc vs energy in frequencies I can directly understand."
] |
[
"I think calculating the mean temperature and then finding the root mean square error about that mean should work pretty well. ",
"https://en.wikipedia.org/wiki/Mean_squared_error"
] |
[
"Theoretical Question about subatomic particles. The thought came to me when pondering solar system formation..."
] |
[
false
] |
We know matter is made up of atoms which are revolving around one another's subatomic forces. Just like gravity is draws together dust in the vacuum of space. Some particles obey gravity and some do not. So we're thinking there's an even smaller particle which for some reason defines gravity. Wouldn't it be safe to assume there could be even smaller particles influenceing or constructing the basis quarks and all of those super-tiny particles? Or maybe the simple rotation of a super-tiny particles or even atoms could define if the particle has mass or not. In the same way a gyroscopic motion effects the weight of an object but not the mass. If we knew a type of radiation or some other method to affect something so small maybe we could test for this So what am I missing which would disprove this? tell me askscience!
|
[
"This might be a lost cause, but here goes...",
"We know matter is made up of atoms which are revolving around one another's subatomic forces. ",
"Subatomic particles like electrons \"orbit\" protons and neutrons in some sense...",
"Just like gravity is draws together dust in the vacuum of space. Some particles obey gravity and some do not. ",
"All particles obey gravity.",
"So we're thinking there's an even smaller particle which for some reason defines gravity. ",
"What? Defines or defies?",
"Wouldn't it be safe to assume there could be even smaller particles influenceing or constructing the basis quarks and all of those super-tiny particles?",
"No, but it's not impossible that there are more than 4 forces at really high energies.",
"Or maybe the simple rotation of a super-tiny particles or even atoms could define if the particle has mass or not. ",
"In some sense you're right...binding energy is mass. Up quarks are ~3MeV, down quarks are ~5MeV, but proton = 2 up + 1 down = 940MeV.",
"In the same way a gyroscopic motion effects the weight of an object but not the mass. ",
"I don't think this is true, but I might have missed something in mechanics (highly unlikely, as I teach it every other year or so).",
"If we knew a type of radiation or some other method to affect something so small maybe we could test for this",
"I suppose... if we go so small (or equivalently very high in energy). However, what you're talking about is probably not achievable.",
"So what am I missing which would disprove this? tell me askscience!",
"I ",
" you're talking about a fifth force acting on a really small scale. In that case, it's just not testable and probably never will be."
] |
[
"Some particles obey gravity and some do not",
"Not true.",
"Anyway, there's no evidence to suggest that quarks and other particles have internal structure or sub-particles. There was evidence to suggest the same of protons and neutrons before quarks were discovered. Some people call the hypothetical particles you're talking about \"preons.\""
] |
[
"I was under the impression neutrinos disregard other matter and just pass right through. That led me to think they're unaffected by gravity too, or well, massless. The more I think about it the less that makes sense. So they just have extremely minuscule mass?"
] |
[
"Question about spinning spacecraft to produce artificial gravity. Does running backward make you lighter?"
] |
[
false
] |
So in the movie The Martian (or 2001 A Space Odyssey), they employ large spinning spacecraft to produce artificial gravity. My question is this: if you run/jog in one direction would you get heavier and if you run/jog the other direction would you get lighter and actually float if you match the speed of the rotation? I can't quite wrap my brain around this, but it seems like if you run backward and match the speed you would essentially be stationary and float. Can anyone help me out here?
|
[
"I answered a similar question ",
"here",
"."
] |
[
"Jumping would certainly mean that the ground is no longer exerting a force on you, so, yes, in that sense you \"cancel out gravity\". But you have a tangential component of velocity, relative to some non-rotating reference frame when you jump up. There are no external forces on you, so your linear momentum is conserved, and you just end up hitting the ground. It will appear to you that you just fall back down, albeit (likely noticeably) not in the same place from where you jumped.",
"You ",
" totally cancel out gravity by doing what the OP suggests: run against the rotation fast enough so that the effective force on you is zero. You will lift off the floor and just float there with the station spinning underneath you. Of course, if the station is not a perfect ring or has some other structure (like furniture or something), you can just grab on to a piece of the station and begin rotating with it again. (The air inside the station, assuming there is air, is also moving so it will slow you down too.)"
] |
[
"Awesome! Thanks for the answer! It looks like my intuition was correct. ",
"I wonder if with the 70 foot radius station you could reach 14.5m/s because as you get lighter you would be able to devote more energy to accelerating?"
] |
[
"What would be the effect of removing mosquitoes from the ecosystem?"
] |
[
false
] |
CDC said that there have been >100 instances of Zika in the U.S. so far, which reminded me that there is a company, Oxitec, which has been marketing that would eliminate mosquito populations through breeding in areas prone to mosquito-borne illnesses. Is anybody familiar with the outcomes/results of these efforts to date in the places where they have been tested? Have mosquito populations been eliminated? Have relevant infection rates decreased? Has there been other observable damage to the surrounding ecosystem? More broadly, how important are mosquitoes to their ecosystems? Does it vary significantly from place to place such that this is an impossible-to-answer question, or are there things we can say generally about the expected effects of using Oxitec's mosquitoes (or some other form of broad mosquito elimination) on surrounding ecosystems?
|
[
"Unfortunately it isn't really clear what the effect would be, and I believe the prevailing opinion right now is that it would be better to err on the side of caution by controlling their numbers rather than to eradicate them completely. Zika virus spreads via the mosquito species ",
"Aedes aegypti",
" and ",
"Aedes albopictus",
". There are over 3,000 different species of mosquitoes, and they do not usually feed on humans, normally preferring horses, cattle, or other large mammals. Some even feed on arthropods and other invertebrates. Since Zika and other flaviviruses are only transmitted by ",
" mosquitoes, you might be able to eradicate a few of these species without any major impact. Other diseases however, such as malaria, are transmitted by other genera of mosquito. To eliminate mosquitoes as a vector of disease transmission, you would need to take out numerous genera, and that's when you could run into a problem potentially disrupting ecosystems. The ",
"news article",
" everyone likes to quote in this matter is simply that - a news article, and should not be taken as gospel when it concludes that mosquitoes could safely be eradicated.",
"Mosquitoes are eaten mainly by other insects and fish, but also contribute to the diets of some birds and mammals. By removing mosquitoes altogether, you remove a food source (to varying degrees) for many animals. ",
"Studies such as this one",
" have shown a decrease in the number of birds being born shortly after the area was sprayed to reduce the mosquito population. This is impactful, since it does not require a complete loss of a population to create an unbalance in the food chain. This would likely also result in an increased number of other winged pests which would normally have been controlled by a healthy bird population. Disturbances like these could have potentially unforeseen and far-reaching effects on other species.",
"Additionally, only female mosquitoes actually bite people. Male mosquitoes have actually been found to be important in the ",
"pollination in some species of plants",
", which is also mentioned in the ",
"news article above",
". Eliminating them could potentially be detrimental to the ecosystem, but could also impact tropical crop production, resulting in a negative economic impact.",
"It is also not necessary to eradicate mosquitoes entirely to significantly reduce their global health burden. ",
"This study",
" shows that it is likely unnecessary to attempt to manage all aquatic habitats to reduce overall disease burden, but rather just treat a select few. Moreover, new vaccines are being developed against malaria and other mosquito-borne diseases. The vaccine candidate ",
"RTS,S/AS01, from GlaxoSmithKline Biologicals",
" showed 39% efficacy in a Phase 3 trial, far better than numerous other candidates. The only way to go from here is up. ",
"As you mentioned, mosquitoes could also be genetically modified to be sterile and reduce the overall population through breeding, or even to be resistant to certain diseases, such as malaria. This, and other approaches such as spraying areas with insecticides, are certainly much safer, more reliable approaches to improving public health than eradicating mosquitoes altogether, and ",
"have already been shown to work in reducing overall health burden",
". One of the methods by which the genetic modification of mosquitoes could be accomplished is through ",
"gene drive technology",
", which of course would require extensive testing before its introduction, as it carries its own risk of somehow being picked up by other species and spreading further. Gene drives are undoubtedly controversial",
"1",
"2",
" and it's possible it may not ever be safe enough for use this way. Oxitec's system is still under development, but other ",
"non-genetic methods of insect sterilizing have been utilized to successfully eradicate or reduce certain fly populations",
".",
"So unfortunately, we don't know exactly what the eradication of mosquitoes would do to the ecosystem. In my opinion at least, and I know there are ecologists who believe similarly, we would be better off utilizing other methods of control, as it behooves us to err on the side of caution, and be responsible about the environment in which we live."
] |
[
"thank you for the very informed response."
] |
[
"Excellent explanation. I was just going to go with the classic 'We can't predict what will happen, so let's not completely wipe them out yet' method."
] |
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