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[
"How we know that how kreb cycle actually happens in the cell?"
] |
[
false
] |
How do scientists study microscopic biochemical mechanism at cellular level like Na/K Pump, glycolysis, kreb cycle etc. In cycles products keep changing/converting so how do they keep a track of all of them? Considering they are so so minute and so so less in amount in comparison to average lab samples and experimentation.
|
[
"One powerful technique is isotopic labeling - a compound that is known to be part of a process is labeled with either a stable isotope or a radioactive one, then the label is tracked through the various transformations. For instance 13C or 14C labeled pyruvate could be fed into the citric acid cycle, producing labeled citrate and subsequent constituents over time. Varying the position of the label can show which parts of molecules are being transferred through the cycle. ",
"In the mid-20th century radioactive labeling was particularly useful because the compounds could be detected through simple techniques like thin layer chromatography, whereas we can observe stable isotope labels in a much more fine grained fashion now using LC-MS/MS."
] |
[
"Yes, and after that we can look at genetics - if we delete a gene does respiration cease?",
"And then knowing which genes are involved in respiration we can do microarray (or other expression assays) that can show us when in time different genes begin to be expressed after, say, giving a starved cell sugar."
] |
[
"To amplify the point about gene deletion, that has the added benefit of enriching the intermediate preceding that enzyme in the cycle. The system may still crank through, but everything backs up at that point, making it easier to find the compound."
] |
[
"Is there/was there a selective animal breeding program focused purely on intelligence?"
] |
[
false
] |
I ask because I have never heard of such a program, and the little bit of research I have done has only provided me with abstract information about the feasibility of the idea, not its implementation.
|
[
"We've been doing that for a while with dogs that need to be intelligent in some way to do their jobs.",
"http://en.wikipedia.org/wiki/Border_Collie",
"http://pets.webmd.com/dogs/features/how-smart-is-your-dog"
] |
[
"Interesting question but what kind of intelligence exactly? "
] |
[
"I was thinking in terms of problem solving ability."
] |
[
"Do insects experience pain in the same way we do?"
] |
[
false
] |
For instance, would a bee have a similar experience to a human if their leg was torn off?
|
[
"One problem with the question is that pain research often tosses \"perception of potentially harmful stimuli\" in the same pot as \"suffering\". ",
"Many very simple organisms have ways to perceive and react to things that might hurt them. A bee doesn't like to be squeezed and will sting in defense if it gets too bad. A simple coral will notice touch and withdraw from it. Even plants react to damage.",
"What they don't have is the higher capacity to think and worry about those experiences. It happens, seems to be uncomfortable, the animal tries to get out of the situation, but they don't seem to develop a lasting \"fear\" or often even just a strategy to avoid the same situation from happening again. ",
"A big part of what turns pain into suffering is the brain's ability to simulate the future. We can expect that something will hurt, we can fear it, we can imagine how bad things could get. We worry. Simple animals don't.",
"Context matters a lot to humans. The pain after a good workout can feel good, while the same amount of pain after an accident can have us suffering. It's very difficult to test for such processes in animals. You can check their bodies for special pain transmitting nerves, or chemical changes to damage, but that doesn't say anything about their ability to interpret the sensation beyond reflexes to move away."
] |
[
"Those animals seem to not fall under the category of \"simple animals\" and definitely ",
" perceive both pain and suffering, because we can clearly observe suffering in those more complex animals. Dogs, cats, etc. can learn to wince away from a human's hand if they've been hit before. They yelp and cry if they injure themselves badly. They experience mood changes if they've been inflicted pain. Personally I don't know at what \"level\" an animal moves from that field into the \"simple\" category that doesn't experience this, but as far as I can tell it's just a matter of neurological complexity and whether or not they exhibit the capacity to express those experiences in ways we can observe. "
] |
[
"Interesting topic. ",
"The current theory is that there is a correlation between complex and non complex organisms and the interpretations of pain. More complex organisms feel pain similar to humans. ",
"For example vertebrates, like a dog or human, are more complex then a spider or bumble bee. ",
"An experiment took place with two groups of bees. One group had their leg pinched, simulating their leg being cut off, while the other group had nothing done to their legs. Two solutions of surcrose were also placed near the bees. One mixed with morphine and one mixed without.\nIn theory, the bees that had the pinched leg should be drawn to the morphine solution. However, this was not the case. The \"hurt\" bees did not consume more morphine than the control group, thus showing that less complex organisms do not react to pain the same way that humans do. The \"hurt\" bees did consume more of the normal surcrose and the morphine mixed surcrose so they were prone to some type of hyperactivity. Whether or not they feel the pain and experience the same things, we do not know. ",
"Tl;dr: No. but they still feel something. ",
"http://www.realclearscience.com/quick_and_clear_science/2017/04/08/do_honeybees_feel_pain.html"
] |
[
"Is it possible to diffract bacterium?"
] |
[
false
] |
In a similar fashion to electron diffraction, is it possible to diffract bacterium?
|
[
"Actually, yes. I'm not sure about bacteria specifically yet, but a couple of techniques let us get that kind of data from other small things. ",
"Some of the earliest work done at the Stanford Free-electron laser was ",
"obtaining the diffraction pattern from a single virus.",
"This is an image of diffraction from a single viral particle",
". ",
"Additionally, ",
"soft X-rays have been used to image whole human cells using X-ray tomography",
" (like a CT scan):",
"http://www.ncbi.nlm.nih.gov/pubmed/23086890"
] |
[
"Very informative, loving those diffraction patterns. Just out of curiosity, is diffraction a useful tool for studying cells or microscopic processes?"
] |
[
"Depends on how you frame it. If you're looking at entire cells, that's brand new science and we haven't got far with it yet. It could be very promising, but there are huge technical challenges to get by before it becomes easily applicable. ",
"However, the field of ",
"x-ray crystallography",
" (that I happen to work in) uses diffraction from crystals of isolated molecules to determine their structures and model their behaviour. So in that sense, diffraction has been in use in biology for 60 years, and heavily so for the last 30"
] |
[
"Why are there so few species of mammals?"
] |
[
false
] |
It seems like mammals can have a lot of variance before we call them seperate species. There are more species of frogs and toads than all species of mammals. Is Mammelia just a younger Class? Are they better at breeding with more distant relatives? (And why are there so many species of bats? They take up like 20% of mammalian species)
|
[
"So species arise through divergent evolution. Evolution essentially occurs as genetics are altered from parent to offspring whether by genetic \"mistakes\" or by more purposeful routes such as combining DNA from multiple parents as with sexual reproduction.",
"More species would arise from a single progenitor species under various circumstances, most notably would be the number of offspring produced and the rate that the offspring are produced. ",
"So two extreme examples would be:",
"Mammals: A broad generalization, but tend to reproduce very slowly, reach reproductive age later, and be long lived, thus having fewer young throughout their lifetime. As a result, evolution of new species would occur much more slowly.",
"Insects: Have massive amounts of young, (thousands to hundreds of thousands in some cases), reach reproductive age quickly, and tend to be short lived. Thus, evolution of new species would proceed quite quickly in this group.",
"This is a broad generalization and many other factors can effect evolution of species, but in my opinion as a research biologist, this is likely the most impactful variable in reference to your question."
] |
[
"The bats thing isn't surprising to me. There are like 9-10k species of birds. There's a lot of niche space for \"flying things\". I wouldn't be surprised if a similar fraction of dinosaur species were birds 70 million years ago. Bats are also pretty small. You can pack more small species into a given area than you can pack big species. I mean 40% of all mammals are rodents. ",
"That may also have something to do with relatively low mammal numbers...mammals tend to be relatively big compared to most of the other clades out there. ",
"It is also definitely true that different groups of researchers studying different types of animals tend to split them up in different ways.. \"lumping\" or \"splitting\" to a greater or lesser extent. I don't know enough to say how that plays in here though."
] |
[
"The physical size of mammals is larger, on average, than anurans. That might have something to do with it. On the flip side, mammals occupy a much wider range of ecological niches. I bet you are correct about geographical isolation as well. Freshwater fish are incredibly diverse for just that reason."
] |
[
"Which agency has more accurate typhoon wind estimates: JMA or JTWC?"
] |
[
false
] |
[deleted]
|
[
"Converting the JMA's estimate from 10- to 1-minute winds gives an intensity of about 165mph, which closes less than half of the gap. ",
"Can you explain what you mean by \"converting\" a 10-minute wind estimate to a 1-minute wind estimate? How are you doing this conversion?"
] |
[
"I don't think that conversion is a useful estimate. 1-minute average wind-speeds, especially when searching for the maximum winds in a hurricane, are wildly chaotic. The ",
" departure of the 1 min wind from the 10 min wind may be a 1.14 multiplier, but I don't know how useful that is case-by-case. What's the variance of that metric? ",
"It's difficult to compare the accuracy of the JMA vs JTWC maximum winds for two reasons. First, the 1 min and 10 min winds are different quantities, which ultimately measure different things. There are processes that operate on 1 min timescales that can greatly influence the 1 min wind, but are too fast to play a significant role in the 10 min wind. It's a bit of an apples/oranges comparison, and both the 1 min and 10 min winds may be more-or-less equally accurate. The other issue is that the actual ",
" sustained wind speed is, I believe, always an inferred quantity - that is to say, it is never measured, but rather calculated based on the observations collected during reconnaissance."
] |
[
"I don't think that conversion is a useful estimate. 1-minute average wind-speeds, especially when searching for the maximum winds in a hurricane, are wildly chaotic. The ",
" departure of the 1 min wind from the 10 min wind may be a 1.14 multiplier, but I don't know how useful that is case-by-case. What's the variance of that metric? ",
"It's difficult to compare the accuracy of the JMA vs JTWC maximum winds for two reasons. First, the 1 min and 10 min winds are different quantities, which ultimately measure different things. There are processes that operate on 1 min timescales that can greatly influence the 1 min wind, but are too fast to play a significant role in the 10 min wind. It's a bit of an apples/oranges comparison, and both the 1 min and 10 min winds may be more-or-less equally accurate. The other issue is that the actual ",
" sustained wind speed is, I believe, always an inferred quantity - that is to say, it is never measured, but rather calculated based on the observations collected during reconnaissance."
] |
[
"How would I give myself the best chance at becoming a fossil once I die?"
] |
[
false
] |
What sort of preparation, if any, would increase the chances of fossilization? Would calcium or other mineral supplements help? Where should I have my bodied buried? Near a river? In the arctic? Would a casket hinder this goal? To be clear, I am not talking about mummification. I want my bones preserved in stone to be dug up millions of years from now.
|
[
"What you're interested in looking at is ",
"taphonomy",
", which is the study of what happens from the time an organism dies until it is discovered as a fossil. ",
"Here",
" is a journal article about it. You'll find this stuff if you go through some taphonomy papers or sites like the ones I linked to above.",
"There are some general conditions ideal for fossilization:",
"Ideally you'd like the remains to be complete and articulated, and maybe preserve soft tissue like hair or stomach contents. You also presumably want the remains to be found someday. ",
"The first step is to have them buried quickly. You don't want them to be exposed to the elements or to things like scavengers. They could get swallowed by a collapsing sand dune or sink to the bottom of a lake that has a lot of fine-grained sediment being deposited in it.",
"You want the environment to be low-energy, so no fast-moving water like rivers or strong ocean currents. You don't want big pieces of debris, like large pebbles, to potentially damage the remains. The smaller the sediment particles the better. ",
"Lithographic limestone",
" is ideal.",
"You want the environment to be low in oxygen to prevent decay. This will keep the skeleton together if nothing else. In ideal scenarios, this can preserve soft tissue.",
"You want them to be in a fairly stable area. No major earthquakes or igneous activity that will disturb the strata or metamorphose it. It's no good if the limestone the remains are in turns to marble. You don't want them to erode out of a hillside too soon or have faulting break apart and overturn things. You don't want there to be a lot of freeze-thaw cycles because when ",
"water gets into cracks and freezes",
" it can cleave things apart.",
"So I'd veto a river and the Arctic. I'm not sure about the effects of using a casket, although if you want the remains to ",
"permineralize",
" then a sealed casket might not be ideal. If there are microbes or mold spores in there they could potentially cause damage.",
"I'd suggest a lake or backwater lagoon that had an influx of sediment. If the bottom of the lagoon or lake is anoxic, even better. Swamps and peat bogs would work well. Or you could go for something terrestrial. Aim for a geologic region that is relatively stable. Less likely possibilities are volcanic ash or tar pits.",
"Above all, there are no guarantees in the fossil record. ",
"Taphonomic bias",
" is certainly an issue that paleontologists have to account for. There are ",
"lagerstätten",
" with absolutely exceptional preservation, but they're not common.",
"Examples of great fossilization:",
"Solnhofen limestone",
"Messel Shale",
"Djadochta Formation",
" (e.g. the Flaming Cliffs in Mongolia)",
"Jehol group",
" in Liaoning Province, China",
"Burgess Shale",
"Mazon Creek",
" in Illinois, US",
"Green River Formation",
"Chinle Formation",
" (e.g. Petrified Forest National Park)",
"Also, if you like this kind of stuff, you'll probably love the book ",
". It's a fictional book by renowned paleontologist George Gaylord Simpson."
] |
[
"Someone over at ",
"/r/geology",
" might be able to help you more with this. A paleontologist would know more details on the matter.",
"From my understanding, the best naturally occurring conditions for fossilization is deep underwater in mud or silt where there is little oxygen. ",
"The best example of this we know of is the ",
"Burgess Shale",
" where quote:",
"The Burgess Shale animals lived on or near the vicinity of a massive submarine carbonate wall, referred to as the Cathedral Escarpment which bounded a shallow warm carbonate seaway extending eastwards in to what is now Alberta. At the time the Burgess Shale fossils were formed, during the Cambrian period (about 505 - 510 million years ago), the North American continent straddled the Equator, and the surface of the land was completely devoid of complex life forms; that is, land plants and animals did not yet exist. Life on earth consisted only of marine plants and marine invertebrate animals.",
"Diagram",
"Periodic mudslides would overcome the animals, transporting them in a turbulent cloud of mud to the base of the reef, where they were buried and died. Over the course of many millions of years, the animals were buried by sediments, and their delicate remains turned into fossils. The fossils were at one time covered by up to 10 kilometres of overlying rock, and would have been subjected to great heat and pressure at those depths. Beginning about 175 million years ago, mountain-building forces bulldozed and transported the fossils from their ocean burial-ground many kilometres eastward on faults, to their current position high on a mountain ridge in Yoho National Park.",
"The special thing about being fossilized in this manner is that it would fossilize the soft parts of your body as well as the bones. ",
"Just remember that fossilization pretty much never occurs in the open or anywhere oxygen is present. Fossilized land animals are generally buried by mud or something along those lines which allows for the process to take place.",
"Sorry for my limited knowledge, but hopefully that helps some.",
"(Source: Geology bachelors)"
] |
[
"Have your body tossed into a peat bog. Or be buried in the desert. No casket. To last the longest you'd probably wanna go with peat bog "
] |
[
"How high would the lunar return module of the Apollo lander be able to go if it left from the surface of the earth?"
] |
[
false
] | null |
[
"The ascent engine could only lift the ascent stage in lunar gravity, where is had 1/6 of it's earth weight. On earth, the stage and fuel weighed around 10,000 pounds. The engine had a thrust of 3,500 pounds. So, the answer to your question is it would not even lift off."
] |
[
"0 m. With only a ",
"2.1 thrust-to-weight ratio",
" on the moon, and lunar gravity being only 1/6 of the earth's, it would not be able to overcome earth's gravity.",
"If we ignore TWR, the ascent stage has a delta-V (kinda like a measure of how 'far' it could go) of 2.2 km/s. Space Ship One's sub-orbital flights up to 100 km requred ",
"about 1.4 km delta-V",
", so that would be in the realm of possibility. For reference however, the delta-V needed to get into low earth orbit is around 10 km/s - far out of reach."
] |
[
"Do you mean the ",
"Lunar module",
" or the ",
"Command Module",
"?",
"The LM would get nowhere. It has a TWR (from Earth) of about 0.2 initially, and 0.5 when empty. It wouldn't be able to lift off the surface. The Ascent stage of the LM would get up as high as 0.3. Remember that the moon's gravity is about one sixth of that on earth, so the TWR of those engines on the moon is about six times higher, giving them plenty of oomf to fight the moon's gravity.",
"And actually now that I look at at, the CM wouldn't get any further with a TWR of 0.3 initially, up to 0.7.",
"They don't require much thrust while in space, they have the time to burn for very long times changing their velocity slowly, and without having to fight gravity to move around.",
"TL;DR The would wiggle a bit."
] |
[
"If used often, could a cup go without needing to be washed?"
] |
[
false
] |
[deleted]
|
[
"From",
" the Department of Physics - University of Illinois at Urbana-Champaign:",
"Here's a short and probably incomplete listing of ways to kill germs: ",
"1) Heat them up. Many germs fall apart when they are too hot, and perhaps more so when they are too hot and wet. Boiling water kills most germs in it and makes it much safer. ",
"... 9) Why kill them at all? Usually just washing stuff off with soap and water gets rid of them plenty well, and doesn't involve nasty chemicals or other hazardous, expensive methods. ",
"The regular use with boiling water will help to stop germs from getting a foot hold in your cup. "
] |
[
"I suspected as much. Thank you kindly, nobleman of the askscience page!"
] |
[
"I suspected as much. Thank you kindly, nobleman of the askscience page!"
] |
[
"What causes water rings on cups?"
] |
[
false
] |
When you leave a glass, why do your contents, end up in a ring around the glass, when there was no liquid outside the cup?
|
[
"Are you talking about ",
"water rings on the surface the glass was resting",
"? That's due to condensation, most prominent when you pour a cool drink onto the glass. Water vapour from the air condenses onto the surface of your glass because it is cooler, and when enough water has condensed it rolls down the side of your glass to the bottom. That usually doesn't include contents of whatever that's ",
" your cup.",
"Of course, it's possible that, in the process of sipping your drink, some has gone outside the cup."
] |
[
"Thats odd. My almond milk was all over the table. But what really confused me, was how there was water under the main spot, like you know how there is ridge all around the rim, on the underside of the cup, and then it hollows out a little bit? Anyways, thanks for the answer"
] |
[
"If you're convinced it's your almond milk, you're either spilling it when drinking (some liquid is left on the outside after you take a sip, and rolls down), or it is leaking."
] |
[
"Can a stray balloon make it to space?"
] |
[
false
] | null |
[
"No, for most definitions of space. ",
"Balloons don't really push themselves up, it's more that the air around them is pushing down harder than they do, and the air pushes them out of the way, thus up. As you get higher, there's less air to push the balloon higher. Eventually one of two things happen:",
"/u/mosskin-woast"
] |
[
"Months ago this same questions was asked and I was bored that day so I ran some numbers and I think I found that, under some extremely unrealistic expectations for material strength and weight, it is technically possible. I'll see if I can find the post but it was a while ago.",
"If I don't, basically what people's first response to the question is going to be is that a balloon can only rise as high as its effective density, so even if its filled with a vacuum, the balloon material itself has mass and thus the total mass divided by volume (i.e. effective density) isn't zero and thus, by Archimedes principle, it will rise to the point where the density of the atmosphere is equal to its effective density and then stop.",
"The problem with this, is it is saying that the point where the net upward force equals zero, is the same as the point where the ascent stops, but that's not correct, that's just the point where the acceleration switches signs and the balloon stops accelerating upwards and starts decelerating. What's missing is the question of how much velocity does it have to burn off when it reaches this point. Put another way, the REAL question is:",
"Does the balloon have escape velocity for a radius R when it reaches R, where R is the radius where the atmospheric density equals the average density of the balloon.",
"So it's not forbidden by the laws of physics. However, if I recall I showed using something whose mass to area was something like graphene, and if one could magically have a 3 km radius sphere which was at the same time somehow magically aerodynamic, and the entire things was a rigid structure, then it would be possible.",
"Which is an engineering impossibility, but not really a physical one.",
"EDIT: Found it!",
"https://www.reddit.com/r/askscience/comments/67v46d/is_it_theoretically_possible_to_reach_space_in_a/dgv1o9i/"
] |
[
"Not to mention the balloon would pop once it reached a point in the atmosphere where the pressure in the balloon was so much greater than on the inside that it would explode."
] |
[
"Why does my microwave mess up the (wi-fi) internet when it's on and is there any way to stop this?"
] |
[
false
] |
other than buying a new microwave
|
[
"Some quick googling landed me with the following information:",
"Approximate frequency of Microwave Oven: 2450 MHz (2.4 GHz)",
"Frequency of type b,g,ad protocol for Wifi: 2.4 GHz with channels taking the range from 2.4 to 2.5 GHz.",
"So you have either a b,g or ad type router (probably g) and your microwave has poor shielding (probably old). The emissions from your microwave are interfering with the signal to/from your router because they are of the same frequency. (Other frequencies don't matter because they are filtered out). This is happening because the channel that your router is using falls in the same frequency as your microwave. The 2.4-2.5 GHz frequency band is divided into smaller 20MHz sized channels that allow for multiple wireless signals following the same protocol to exist in the same area.",
"Since the oven frequency is an approximation I cannot say for sure what channel you are operating on, but the easiest fix would be to change your communications channel on your router. I've never done this so I can't say for sure how to (I'm sure google can).",
"I would also advise getting a new microwave as I do believe that they are supposed to shield against emitting radio waves."
] |
[
"The fact that his microwave causes WiFi disruption doesn't mean his oven is defective. Virtually all electronic devices emit radio waves. It should not emit so much as to violate the FCC class C power requirements, which are designed to avoid interference that disrupts radio communications. But the FCC isn't that interested in WiFi reception. ",
"In fact, microwave ovens disrupting WiFi is reported quite often. And the general fix is to try using a different channel. 7-11 are likely the worst. A lot of people say try channel 1. Of course, if your neighbor is using channel 1, this might not be the best choice either. "
] |
[
"Thanks for that. I was unsure of the power of the emitted radio waves from a microwave oven, I just assumed that it wouldn't violate FCC requirements. "
] |
[
"Why do we base attractiveness on such seemingly trivial factors? Why do fetishes exist?"
] |
[
false
] |
Couldn't a fat woman birth a child as efficiently as a skinny woman? Do the size of breasts serve any evolutionarily beneficial purpose? In short, WHY does the factor of attraction vary so much on seemingly trivial factors, ones that seem to serve minimal survival purposes?
|
[
"I'm going to be contrary to what other people in this thread are saying, and point out that things like attractiveness and beauty vary hugely over time and space. That is to say, different cultures have different concepts of beauty, whether its different because its somewhere else in the world, or different because its a past version of your own culture. For instance, you ask about fat women or small-chested women, but fat women ",
" considered attractive once, and small breasts ",
" preferred once. ",
"."
] |
[
"For one thing, a narrow waist indicates the woman is not already with child, which is clearly desirable since a pregnant woman is not available for procreation. Also wide hips indicate an easier and more successful birthing. I've seen it suggested that large breasts imply more milk for the child although I've never seen much proof and have read counter arguments. Furthermore these aspects are what we judge ALREADY possible candidates on their fitness, if a woman is green with illness you don't find her attractive clearly."
] |
[
"What easily visible factors would you consider to be non-trivial?"
] |
[
"How is having such dependent offspring selectively advantageous for humans?"
] |
[
false
] | null |
[
"Well, first of all, humans are extremely K-selected in comparison to most mammals. We put a lot of effort and care into each individual which is born. You can have a supremely dependent offspring when you put a lot of care into it. Additionally, our babies are born in what we call a secondarily altricial state. We are less developed at birth than what you'd see in most primate species. Basically, we are born before you would be expected with regards to our brain (and body) development. Much of this is related to brain size. We are born relatively large-brained, but have neonatal brains that are in a less developed state (relative to final brain size) than seen in our primate relatives. It has been hypothesized that this is due to the \"obstetric dilemma,\" where you can only manage to squeeze out a head of a certain size through the pelvic outlet (although there are some researchers who indicate that this might not necessarily be the case). ",
"It is also interesting to note that humans are really good at taking care of our kids after they are weaned. Most primates do not engage in significant direct care of offspring following weaning. Primate juveniles are pretty much on their own in terms of finding food following weaning -- and have correspondingly high rates of mortality. In contrast, humans engage in significant food sharing and direct care for individuals after weaning. This period called \"childhood\" (see work by Barry Bogin and friends) not only increases offspring survival, but also reduces interbirth interval by lowering the amount of time spent in lactation. As females demonstrate reproductive suppression during lactation, reducing this period allows us to resume cycling faster and allows us to have additional kids while still having dependent offspring. In contrast, other ape species have extremely long interbirth intervals as their period of lactation (and thus reproductive suppression) is longer than found among humans. "
] |
[
"It's a tradeoff. We can walk in two legs and have big heads at the cost of having needful childrens who take a lot of time and effort to raise.",
"The start is more difficult, but the potential to develop is higher. That's why it works."
] |
[
"Thanks a lot. This is really helpful."
] |
[
"What's happening when you break in an engine, and how do different break in methods effect the engine's performance and longevity?"
] |
[
false
] |
Also, what effect do cylinder coatings such as nikasil or SCEM have on break in?
|
[
"Breaking in an engine is about making sure that all of the bearings and moving parts settle in together and wear evenly. If you don't do it, the engine will fail sooner, but there are so many variables you can't really say for sure how much damage you'll do. ",
"You could end up with piston rings that don't seat correctly and the car will burn oil, or you could get piston slap (when the piston head rocks back and forth in the cylinder rather then sliding straight up and down.)",
"Camshaft lobes could wear incorrectly. leading to valves opening and closing at the wrong speed/time. ",
"A crankshaft bearing could spin and destroy itself, seizing the entire engine. ",
"The crankshaft itself could begin flexing as it rotates, and eventually snap. ",
"Every car manual I have ever read has said that you should break in an engine by running it at various RPM, and avoiding heavy loads for the first few thousand miles. Once an engine is broken in, if you take it apart, it has to go together exactly the same way, as the parts have \"mated\" together. Engine assemblers use journaling marks to make sure that they have no excuse for mixing parts up or getting something backwards. ",
"Now, these are all pretty extreme examples. Modern machining is pretty good, and you have to abuse a car pretty hard during it's break in period to do damage that will be immediately apparent. If you don't hoon your car, but simply ignore the break in procedures and drive to work and whatnot, you'll probably sell your car before anything goes wrong with the engine. ",
"In older engines strictly following the break-in procedures was far more important due to less advanced materials and less consistent tolerances.",
"I really don't know anything about nikasil or SCEM, but I've got a car with a rotary engine, and nikasil is mentioned as a material used in apex seals for them. The break in procedure for my RX-8 was no different from my bog standard Honda , so I doubt it changes much of anything.",
"Someone with an ASE certification should be able to provide a lot more technical terms and info then me. you can find them on ",
"/r/mechanicadvice",
" and ",
"/r/cartalk",
" You can find photos of horrible engine failures on ",
"/r/justrolledintotheshop",
" "
] |
[
"Motoman needs more then entirely anecdotal evidence. ",
"Did yo notice the part where he said you could port your intake and exhaust to restrict airflow and improve power? ",
"He only talks about piston rings. There are plenty of other parts in an engine effected by the break-in period.",
"He's also trying to sell magazines.",
"I would take his site, with a very large grain of salt. The only thing that rings 100% true to me on that entire page is the importance of warming your engine up before driving it hard, and that is something that must be done for the entire life of the engine. Cold oil is thicker and will not lubricate parts properly, leading to excessive wear.",
"Edit: One more thing. What interest could an automaker have in having you break your engine in improperly? engine replacement warranties go out to 100,000 miles on many cars. Giving improper break in instructions would do nothing but cost the company money in warranty engine replacements. Auto companies paid a lot of money to smart people to design and build that engine. Do you really want to trust some guy who says his process works on every engine regardless of construction or type? Of do you want to trust the guys who made the engine?",
"EDIT2 More thoughts: Serous racing engines are torn down and rebuilt on a extremely regular basis. Their tolerances are different. An F1 engine revs all the way to 18 thousand RPM. Tolerances are so tight on an F1 engine that they are essentially seized until you inject heated oil and coolant into it, the thermal expansion of the metal being enough to allow it to spin. They are much different animals then an average car engine, and I've heard F1 commentators talking about how they pretty much know exactly how long an F1 engine is going to last down to a few miles because of the level of precision involved and the number of sensors used to monitor the engine. They HAVE to know this stuff as F1 only lets a team use a limited number of engines in a season, so they need to wring every last lap they can out of the engine so they have more spares in case of catastrophic failure. Also, the engine alone is worth more then your car. Yes, even you Mr. \"I have a $100,000 car.\" An F1 engine costs something in the range of $230,000 and rumor has it that engines are going to get even MORE expensive next season.",
"Edit3: Spelling grammar, minor factual corrections and expanding on things.",
"Edit4 Help me! I literally cannot stop posting about this:",
"Lets say this process works. How many horsepower are you really gaining? How many do you stand to lose? ",
"5 horsepower? That's what mechanics call butt dyno territory. It's impossible to really feel that when you're driving. It's within a margin of error it's hard to say what's causing it.",
"Finally, I hate how the guy states a bunch of questions and answers it with \"Good question!\" then moves on without actually answering it.",
"We should really just go over to ",
"/r/Mechanicadvice",
" and ",
"/r/cartalk",
" then watch the subreddits explode into a fight over this. :)",
"http://www.reddit.com/r/MechanicAdvice/comments/1dfiu4/the_motoman_engine_break_in_method_fact_or_fiction/"
] |
[
"Breaking in an engine effects only two major components. The camshaft and the piston rings. It polishes the camshaft against the lifters and the piston rings against the cylinder walls. ",
"There are only 3 types of break-ins, too soft, just right, and too hard. When replacing parts, the manufacturer will tell you how they must be broken in otherwise the warrenty is void. Cue ",
"r/conspiresy",
".",
"New cams and piston rings are rough. If the break-in is too soft, more ware happens because it takes a minimum amount of force to ware them smooth. If you don't give that force the parts will stay rough causing orders of magnitude more ware. A cam can ware out in 1000miles if not broken-in. Providing the correct break-in gives enough force on the moving parts to ware smooth but not so much that causes excessive ware. Break-ins that are too rough cause excessive ware to parts before the smooth out. Like polishing the paint on your car by standing on your hood and moving the polishing pad with your foot. ",
"When I replaced my camshaft I had to run the engine at 2000rpm for 20min without load and then at 3000rpm for an additional 20min. Then I was able to break-in my piston rings by accelerating from 45mph to 55mph at full throttle and letting the engine slow me back to 45mph a minimum of 15times."
] |
[
"If Gravity Is Not a Force, but the Curvature of 4D Spacetime, Why Do We Want to Unify It with the Other Fundamental Forces?"
] |
[
false
] |
Gravity always seemed to be the hardest force to tie into the bunch of the 4 fundamental ones, but gravity is also the only force for which we go out of the way to claim that it's just a result of curvature in 4D spacetime and that it isn't really a force. So, if it actually isn't a force, why are we so keen on unifying it with the three leftover forces in the pursuit of a "Theory of Everything"?
|
[
"Because this curvature is still describing a classical phenomenon. ",
"Think of this. Maxwell's equations describe electromagnetic interactions as interactions with fields and charges. That's the classical view. But quantum electrodynamics (QED) describes it as charged particles exchanging photons (quanta of the electromagnetic field). How do we know QED is better? Experiments see discrepancies from the classical interpretation. ",
"The curvature of space-time is related to the gravitational field, again a classical field. We expect this to be an exchange of gravitons between masses(quantum gravity), but we haven't noticed any discrepancies between reality and Einstein's equations yet because these things would occur in very strong gravitational fields which we don't have access to."
] |
[
"If we had a Saturn-sized detector in close orbit around a neutron star, we would detect a graviton per century. However, it would be drowned in a neutrino background; the required neutrino shield would be massive enough to make everything collapse into a black hole.",
"But hey, maybe you'd see a graviton."
] |
[
"Physics is not in the business of determining an objective, underlying reality; it's in the business of providing models that describe observed behavior.",
" of our models, including relativity and the standard model of particle physics, are essentially just \"a nice way of looking at things\" that may be \"actually not representative of reality\". This is, for example, why we haven't settled, and probably never will settle, on a \"correct\" interpretation of quantum mechanics; the ",
" work, but they don't give us any direct insight into ",
".",
"What they do represent is our best ",
". That is, we've developed a model that accurately describes some range of phenomena in a certain language, and it does so to a better degree than any other model, so we adopt the position that the language used in the model is, provisionally, an accurate description of reality.",
"To take gravity as a particular example, you can formulate it as a curvature in spacetime. In this picture, physical spacetime is described as a four-dimensional Lorentzian manifold with curvature determined according to Einstein's field equation, and \"objects\" are assigned physical spacetime coördinates in such a way that they trace out paths in spacetime determined by the curvature. Alternatively, one can treat the so-called \"metric\" as a dynamical field on a flat, non-physical background that couples to other fields in a particular way so that the paths of objects are determined by their interactions with this field. In either case, the resulting description of each object's motion is the same (at least insofar as present experimental bounds allow us to check); the only difference is in the language they use."
] |
[
"Why can particles such as muons pass seamlessly through matter, such as humans?"
] |
[
false
] |
[deleted]
|
[
"Wow, this is exactly the answer I was looking for! Thank you very much! :) I'm surprised I've never heard of the Bethe-Bloch formula, but I'm very glad I was introduced to it. "
] |
[
"Wow, this is exactly the answer I was looking for! Thank you very much! :) I'm surprised I've never heard of the Bethe-Bloch formula, but I'm very glad I was introduced to it. "
] |
[
"No, I am specifically talking about muons. Areas of research such as muon tomography lead me to this question. "
] |
[
"[Biology] Is the inside of a resting neuron negative, or just MORE negative (a.k.a. less positive, but still positive) than the extracellular fluid surrounding it?"
] |
[
false
] |
I've been looking at YT videos and various websites for a while now and they seem to use vague language in describing this
|
[
"You may find the wording vague because as with any other discussion of potential difference, it is the ",
" in electric potential that matters; the absolute value can be anything you want.",
"We know that real cells are aqueous systems, and by the law of electroneutrality we know that the system is overall neutral to begin with - you can point at any random flask of solution and expect it to be basically electrically neutral. This means that if we were to set up an electrochemical gradient, say, with NaCl, across some membrane in this system, it must do so via charge separation - one side of this membrane has an excess of Na",
" and will be positive, the other negative with an excess of Cl",
" and be negative. So you can build an arbitrary membrane potential of -70 mV by having one compartment sitting at +35 mV, and the other -35 mV, both relative to our original, electroneutral solution. In a one-ion scenario, the voltage difference is given by the ",
"Nernst equation",
".",
"Real cell systems, however, are a lot more complex, and are full of charge-carrying species. So whenever you find a potential mentioned like this, the number only applies to the ions we're investigating. For example, in a cell there are potassium, sodium, chloride, sulphate, phosphate, carbonate, etc. ions, but not all of them are permeable. It is only the cell-permeable ones that we consider in coming up with the membrane potential - see the ",
"Goldman equation",
" - because those are the only ones that can actually be used to do work.",
"So basically, there are so many other species (such as charge-carrying proteins) that can neutralize any \"net\" charge, it's really not too meaningful to discuss any given compartment to be \"positive\" or \"negative\", because it could be either or both. The membrane potential exists as a local phenomenon that is only found across that membrane, generated by ions that can permeate that membrane. The only thing we can say for certain is that if you consider the solution in bulk you can consider it as basically neutral."
] |
[
"You're discussing membrane potentials while I think OP meant to ask something akin to \"if we count all the positive and negative ions according to their charge ",
", will it be a net positive or negative?\"."
] |
[
"You're discussing membrane potentials while I think OP meant to ask something akin to \"if we count all the positive and negative ions according to their charge ",
", will it be a net positive or negative?\"."
] |
[
"so, i have some questions about solar power"
] |
[
false
] |
[deleted]
|
[
"I'm no expert on solar power, but I have done a bit of research into the matter. ",
"First, a solar panel is made up of photovoltaic cells, which simply put convert energy from the sun into useful DC voltage. (Google how they do that if you wish.)",
"The energy will then either be stored or sold back to the grid. In the case of your streetlight, it is more likely stored in a battery. The amount of energy captured depends on a variety of things. Solar panels are rated for their power output in Watts and have an efficiency rating. Typically the designer would try and match this output with the load requirements. Same idea to power a house. Using say 30 200W solar panels will ideally yield 6kW of power.",
"As for weather, solar panels are pretty picky. In fact, not having them at a proper angle can greatly decrease power output. Clouds or snow build up will reduce power output dramatically. ",
"Finally, there are a few reasons this hasn't picked up. For one, it's pricey. For something like this to be beneficial, the price of electricity would have to skyrocket, the solar panels would need to become a lot more efficient, or solar panel prices would need to drop. "
] |
[
"This is a very good answer.",
"To add to this I was listening to a podcast on alternative energy with a journalist and a scientist and they were talking about how one of the main problems with the main types of renewable power sources (wind, solar tidal etc...) is that they cannot be controlled as easily.",
"Power stations can very quickly turn up output when \"Eastenders\" finishes to match the power demand when everyone switches on their kettle. Or at 7-8am when everyone gets up for work and makes themselves a coffee and some toast. It is really important to brring the supply up and down to match the demand or people's light bulbs blow out or don't switch on.\nThis is quite difficult to do with Solar power. They can't make the sun shine brighter at 4.30 for 5 minutes then dim again.",
"A lot of R&D is going into storage methods to store the energy more efficiently so they can create these supply spikes. One such method for wind power is ",
"compressed air energy storage",
" and ",
"here"
] |
[
"I know that where I live, the majority of generation is not renewable, and may account for only 10% of the total generated electricity, so this would not work. Even if this number increased dramatically, it still wouldn't be feasible. Your typical coal generator doesn't simply turn on with a switch, it can require hours to ramp up. Consider that you rely heavily on solar, and there's a cloudy day you didn't expect. You're stuck scrambling to boost output from your standard generator. ",
"Edit: With better means of storing energy, such a problem could be overcome."
] |
[
"silly math regarding supermassive black holes and average density."
] |
[
false
] |
So, regarding the new largest ever black hole that's been discovered... I was doing some math. Badly, likely. Can someone proof this? This is not homework, and was done for fun on another thread. The diameter of the event horizon for the new black hole was estimated to be about the size of the orbit of Neptune, or 4 light-days, which would give us a radius of... r= 51,804,136,742,400 m (299,792,458 m/s x 60sec x 60min x 24 x 2) and pi is 3.14159265359 so the volume of the event horizon would be 26,486,747,264,016,772,492,836,761,361 cubic meters. If that's correct, we can move on. The current heavyweight comes in at 17 Billion solar masses. 1.9891 × 10 kg (suns mass) x 17,000,000,000 = 33,814,700,000,000,000,000,000,000,000,000,000,000,000 kg. So, the average density of that event horizon volume would be 1,276,664,879,342 kg/m3 if my shitty math is correct. It probably isn't. Now, this conflicts with things I've heard, that the average densities of supermassive black holes are in fact very light, some even lower than water. That doesn't jive with my ad-hoc calculations. Any input?
|
[
"Now, this conflicts with things I've heard, that the average densities of supermassive black holes are in fact very light, some even lower than water.",
"I thought this was totally wrong at first, but then I ",
"ran the numbers myself in wolfram alpha",
" and got a density drastically lower than water. Things I never knew before!",
"As for your math, I think you may have made an error in calculating the volume. Since the radius is about 5 x 10",
" m, and the volume V = (4 pi r",
" )/ 3, the volume should be something like 6 x 10",
" cubic meters, which is way higher than what you have in your post.",
"This refers only to the average density within the event horizon; it is thought that the mass actually all piles up in the center (possible/probably in a singularity with infinite density).",
"edit: in general, since the Schwarzschild Radius of a black hole is 3 km per solar mass, the volume is proportional to the cube of the mass, so higher-mass black holes will have lower densities."
] |
[
"As for your math, I think you may have made an error in calculating the volume. Since the radius is about 5 x 1013 m, and the volume V = (4 pi r3 )/ 3, the volume should be something like 6 x 1041 cubic meters, which is way higher than what you have in your post.",
"Ahhhh. I see. I used the area of a circle instead of the volume of a sphere. That's my problem, thanks. "
] |
[
"Das_Mime already answered your question, but I wanted to direct you to my comment ",
"here",
" regarding the notion of black hole density and, in particular, my response ",
"here",
" regarding the fact that the volume of a black hole isn't particularly well defined. As such, any discussion of the density of a black hole should be taken with a grain of salt."
] |
[
"Sucking hot air out or sucking cool air in - what's a more effective way to cool down a room?"
] |
[
false
] |
I have a fan I put on my window sill, and I have the type of windows that open horizontally (so there's a large patch of open window that the fan does not cover. I'm guessing heat pump, but all the physics I know was from my chemistry courses so I can't say for certain. My reasoning is that the air in my room is hot and the air outside is cool, so having a fan that moves air along the gradient in a thermodynamically-favorable direction would take less work (from the fan) then the reverse. I don't know if there is a significant difference in air pressure between my room and the outside environment when a window is opened. I think that in the overall system, the total air pressure of the room VS the outside world moves to equilibrium quicker then the temperatures, possibly mitigating the effect of pressure (if my assumptions aren't too flawed). Also, the fact that the opening to the outside is not completely sealed by the fan may have an effect that I'm unaware of. Just something I've wondered about. Curious to know if someone has a more conclusive answer.
|
[
"Time to do some science!",
"Given what I can tell about your current setup, I'd recommend putting the fan at the bottom of the window, and move your bed/desk so it's pointing at you. Sure, it may seem obvious, but here's why:",
"If you want to get really fancy, go get a smoke machine, smoke bomb, or something really dusty and cloud up your room before turning on the fan in a bunch of different positions. Take some video to see where the smoke goes and test your hypotheses about the fan's flow lines.",
"For other people with hot room problems, if you have access to an attic, stick your fan in the ceiling to blow the hot air out. Drawing cool air in with this method can be even better than the solution I offer above, but it depends on your fan, room size, geometry, etc. Heat transfer problems are nasty that way: hard to solve analytically for complicated geometries and funky boundary conditions. But at least they're easy to experiment with! I look forward to hear how it goes."
] |
[
"anytime you can justify lighting off a smoke bomb indoors gets my upvote"
] |
[
"I think it's less about thermodynamics than about the circulation of the air within the room. ",
"When you point the fan outward in a window that's only half covered by the fan, you create a low pressure area behind the fan. Assuming that the room is pretty well sealed, there will be an equal volume of air coming in from the other half of the window. However, this incoming air is immediately adjacent to the low-pressure area behind the fan, so much of it will just get sucked right back out the window. (If you're on the other side of the room, you don't feel much moving air, right?)",
"If you point the fan inward, you still have an equal amount of air moving in and out, but the air coming in is reaching more parts of the room. This results in greater circulation, which promotes efficient heat transfer. Presumably, this will cool the room off more quickly.",
"(This is my informed guess, feel free to prove me wrong if you know more about the topic than I)"
] |
[
"Why must the electrode of a pH meter never be removed from a solution while the device is on?"
] |
[
false
] |
Hello scientists! Every lab manual I've ever run across insists quite vigorously, often in italics, that one must remove the pH meter's electrode from solution while still on. I've dutifully followed these instructions, but answers as to why this an imperative aren't easily available online. I'm sure there is a simple explanation, and the strong warning language makes me curious as to what it is. Presumably it ruins the device and/or data, but as a man of the world, I simply need more answers (which you lot are overqualified to provide.) What's the deal?
|
[
"I'm not too sure about this, but i think it might have something to do with drying out the electrode's glass coating which would results in unreliable results being detected. So it should always remain in the solution or in a specific container with electrolytes which keeps it moist and prevents drying out.",
"I could be wrong, though. "
] |
[
"I would say that the electrode can be taken out of solution while the instrument is on. I do all the time. I do not however encourage leaving the electrode out in open air for more than about 30 seconds. This is where you start running into the problems that Tanukki has described."
] |
[
"If you let it dry, salt crystals or contaminants could accrue inside the instrument and cause blockage or errors later on. Well, it's probably only a concern if you measure more viscous things, but the maintenance routine exists as a preventative measure.",
"Fischer Scientific also says this: ",
"Allowing the bulb to dry out may change the resistance of the glass, rendering the electrode useless."
] |
[
"Why do larger elements (e.g Moscovium) have such short lifespans - Can they not remain stable? Why do they last incredibly short periods of time?"
] |
[
false
] |
Most of my question is explained in the title, but why do superheavy elements last for so short - do they not have a stable form in which we can observe them? Edit: Thanks to everyone who comments; your input is much appreciated!
|
[
"A contributing factor is that we probably haven't synthesised the most stable isotopes of many superheavy elements. The higher the atomic number, the greater the neutron/proton ratio required for stability, and since superheavy elements are synthesised by fusing two lighter ones together it's hard to get enough neutrons.",
"For example the first isotope of Copernicium (element 112) synthesised, in 1996, was Cn-277 with a half-life of under a millisecond. A few years later Cn-285 was synthesised and that has a half-life of about 30 seconds. Still very short in human terms, but many thousands of times more stable than the first isotope discovered.",
"It's likely the same will apply for the newest elements discovered, and indeed unconfirmed results indicate this. Even in the predicted \"island of stability\" half-lifes are still likely to be minutes at best though."
] |
[
"Interesting.",
"I am wondering if we'll ever see a stable isotope of Roentgenium, the fourth precious metal. And I wonder what color it would be."
] |
[
"Just because it is in the same group/column as copper, silver, and gold on the periodic table."
] |
[
"longest eartly shadow possible?"
] |
[
false
] |
the empire state building blocked the sun from me from 20 miles away where I grew up...whats the longest possible shadow that you could possibly observe (and distinguish)
|
[
"Strictly speaking, I think an object can cast an infinite shadow, albeit not for very long.",
"Consider a single ray, moving from the sun to the earth, and assume that this ray misses the earth by a tiny margin, say 3 feet or so. If we ignore the effects of gravity, then this ray will move past the earth and out into space, and will travel (for all intents and purposes) an infinite distance. Now say that you place an object in the way of that ray. This means that the object will cast a shadow, in the place where the ray was going to be, and since the ray was aimed in such a way as to travel an infinite distance, so will the shadow be of infinite distance. This is still true when gravity is brought into the picture, it just means we have to tweak the angles."
] |
[
"Well, if we imagine a structure built to cover the whole earth, it would be casting a shadow from the sun on 50% of the earth at any given time. ",
"A single vertical structure? Depends how thick? Still. Imagine a pole extending out to the sun. Move it a few degrees either way, it will cast a shadow on almost 45 percent of the diameter of the sphere. It won't go further because the sphere will then be curving away. "
] |
[
"But that shadow would be caused by an earthly object. I think the OP wants to know how long could a shadow be on earth. So, what is the longest shadow that could be cast by a vertical object on a sphere?"
] |
[
"At what point if at all, do an exotic species become a native species?"
] |
[
false
] |
Can an exotic species become so well intregrated into the local ecosystem that it can be consider a native to that system?
|
[
"Once a non native species establishes a sustainable population it’s pretty much a part of the ecosystem. This happens a with a lot of organisms. If it’s overtaking ecological established niches it’s an invasive."
] |
[
"There is no strict and universal definition of what counts as native vs exotic (or invasive), it is controversial and debated in science. ",
"Here",
" is a paper discussing the lack of consensus in science and government and possible solutions."
] |
[
"Native is less a biological definition and more of a human one. Terms like \"predator\" refer to how species relate to other species in their environment. On the other hand, terms like \"weed\" refer to how species relate to humanity (or how humanity relates to the species). Native is more like the second type of definition. It basically means the species was already there before human influence....although often in practice this means it was there around the time when Europeans showed up. It can't really become native, because native is just our way of talking about the history of a species rather than its relationship to its environment. ",
"Now, a species can become naturalized and basically become a settled component of the local ecosystem, but that's using slightly different terminology."
] |
[
"If an electron has a non-zero chance to be a very long distance from the atom, then doesn't the amount of atoms in the universe makes a certainity that there is at least one electron out there orbiting meters away from it's atoms?"
] |
[
false
] |
Also, does this even matter, or the whole concept of the electron as a point particle that "is" somewhere is stupid?
|
[
"the whole concept of the electron as a point particle that \"is\" somewhere is stupid?",
"I think that a better way of imagining the electron is as a localized wave. It does, after all, behave according to a modification of the wave equation.",
"Although people tend to talk in terms of the probability of finding an electron over here or over there, most actual physical processes do not resolve the position of the electron a volume much smaller than an atom. If you want to force the electron to collapse into a state where the entire wave is effectively localized into a very small volume, you have to hit it with something of very high energy, such as an x-ray or gamma ray. ",
"Getting to your main question, if you did shoot an x-ray at an atom but 'missed' by a few bohr radii, you would still have a small chance of the x-ray scattering off of the electron. This probability decreases exponentially as one moves away from the center of the atom.",
"When people talk of the electron as a point particle, what is meant is that there does not appear to be any internal structure, or if there is, it must be contained in a small volume with a radius under 10",
" m. So far there are no major indications of internal structure."
] |
[
"Your question is a good one but not stated well. It doesn't make sense to say that an electron \"is orbiting meters away from its atoms,\" because an electron can't be considered to be following a definite path. Ever. This is Heisenberg at it's finest. (If you want more details, go ahead and ask, I don't think it's really the main point of your question.)",
"I think what you mean to say is something to the effect of, \"If we measured the position of every atomic electron in the universe at the same time, isn't it extremely likely that one of them would be measured to be meters away from its nucleus?\" ",
"Let's do a rough calculation. The probability of observing an electron at that radius falls off roughly like e",
" with a_0 the Bohr radius. Now, the Bohr radius is roughly 10",
" m, and we want to know the probability of observing the electron to be 1m away. So it's about e",
" which is a really, really tiny number. ",
"How tiny? Well, I think the current estimate is that there are somewhere around 10",
" ish electrons in the universe (citation needed, couldn't find a good source). And 10",
" is about e",
" We're talking about an ",
" 8 orders of magnitude larger. So actually it's very improbable that you would measure an electron to be 1m away from its nucleus, even if you measured the positions all the atomic electrons in the universe at once. Your probability is something on the order of 1 in e",
"EDIT: Prettied up my exponents."
] |
[
"he's right. I'm not a english born speaker but this is no excuse – I wasn;t paying attention to the title."
] |
[
"Is there a common explanation why people who took LSD describe similar visual experiences e.g. colorful, fractal, vibrating strings/stripes ?"
] |
[
false
] | null |
[
"LSD affects a specific neurotransmitter receptor in the brain called ",
"5HT2a",
". Activation of this receptor leads to many changes in activity across the brain. A recent ",
"study",
" looked at how taking LSD affects the part of the brain that processes ",
"visual information",
" using a technique called ",
"fMRI",
". They showed that brain activity in people who closed their eyes after taking LSD mirrored the brain's response when people saw real images. They figured this out by comparing patterns of eyes-closed fMRI activity under LSD vs. without LSD. Here's a quote from the article: \"This result may indicate that under LSD, with eyes-closed, the early visual system behaves as if it were seeing spatially localized visual inputs.\""
] |
[
"Well, what other stimuli? Presumably the answer is because the two groups they are comparing are people on LSD looking straight ahead at a blank screen in an MRI scanner, and people in the same condition except not on LSD. We have overwhelming evidence for the specific role of neural activity in early visual areas (though even this is complicated), so what other stimuli could be causing the LSD group to have fMRI activity there?"
] |
[
"Those fractals are actually called Form Constants! They're a result of (often) psychedelic stimulation to your visual cortex. They've also been heard of in patients with severe migraines.",
"Wikipedia's explanation is a follows: It is believed that the reason why these form constants appear has to do with the way the visual system is organized, and in particular in the mapping between patterns on the retina and the columnar organization of primary visual cortex. Concentric circles in the retina are mapped into parallel lines in visual cortex. Spirals, tunnels, lattices and cobwebs map into lines in different directions. This means that if activation spreads in straight lines within the visual cortex, the experience is equivalent to looking at actual form constants."
] |
[
"How do you invent a programming language?"
] |
[
false
] |
I'm just curious how someone is able to write a programming language like, say, Java. How does the language know what any of your code actually means?
|
[
"Designing a computer language is a pretty tricky business, really. There are a lot of tradeoffs to be made, which explains why there are ",
"so dang many",
" of them. When starting a new one from scratch, you ask yourself a lot of questions. Ultimately, the question that matters most is, \"What do I want to be ",
" in this language?\" You might even call it the First Question of Computing.",
"That's only half the problem, however. To understand the second half, let's take a little detour into the mid 20th century, and look at computers themselves.",
"Now, ever since ",
"the first computers",
" came online, we brave and foolish folks who program them have had a vast number of varied answers to this question. Some folks wanted to ",
"make war simpler",
", some wanted to ",
"make intelligence simpler",
". But in general, the early computers were often single purpose machines.",
"Enter ",
"ENIAC",
", which is often called the first \"general purpose\" computer. All of a sudden, we had a machine which could do a lot of different things. This was exciting! And terrifying at the same time. How do you tell a computer the size of a small house that you want to calculate the logarithm of any number you give it, just as a simple example?",
"The answer was to have a very small number of very simple instructions that the computer could perform, and then build up from this small ",
"instruction set",
", combining them in various orders, until you eventually make a \"program\" that does what you want. Amazingly, this still holds true today! Your typical PC running what's called the ",
"x86 instruction set",
" is basically just performing a bunch of the same small(-",
"ish",
") number of instructions over and over, until you get ",
"what you wanted",
" to get.",
"[As a brief aside, mathematicians had already attempted this reduction of an algorithm to the most ",
"basic set",
" of operations and postulates - let's just say it ",
"didn't go so well",
", and both mathematicians and computer programmers are struggling with some ",
"fundamental problems",
" that fell out even today.]",
"One key feature of almost all instruction sets is their emphasis on arithmetic. There's a reason we call computers \"computers\", after all. The designers of the earliest computers answered the First Question of Computing with \"I want ",
" to be easy.\" So computers got really good at math, ",
"really quickly",
".",
"Unfortunately, as the things we asked computers to do became more and more complex, it became very tedious to construct programs using that very small set of possible instructions. One particularly ",
"forward thinking programmer",
" decided one day to add a ",
"layer of indirection",
" between the program writer, and the machine. Basically, she decided to answer the First Question of Computing with, \"I want to make ",
" easy.\" The first of the truly great computer programming languages, ",
"FORTRAN",
", was finally born.",
"FORTRAN allows the programmer to type things like \"do the following thing ",
"10 times",
"\", written not in instruction-set codes, but in plain old ",
"English",
". This was an enormous step forward, but involved some sleight of hand behind the scenes. Basically, the FORTRAN compiler would read in the program which was nice to human eyes, and for each line of code, it would create a bunch of those instructions from the instruction set that ",
"preserved the intent",
" of that line of code, but could now be executed by the machine. This truly was wizardry of the highest order.",
"Very much like a growing baby, FORTRAN changed and grew as the years went by, as different people asked it to answer the First Question of Computing in different ways. Computers started to get smaller and faster, and made their way into the home. All of a sudden, folks much like myself started to give ",
" different answers",
" to the First Question of Computing. We were playing with the computer, exploring what it would let us do, what it could be pushed to do.",
"With this large set of new things that people wanted to be ",
" to do on a computer, a whole slew of new languages popped up. Some of them let you ",
"manipulate lists",
" really easily, some of them let you ",
"manipulate hardware",
" really easily. In each language, it was easy to do some things, but remember those tradeoffs I mentioned right at the beginning? They were right about to bite us programmers in the butt.",
"In C, for instance, it is in fact very easy to manipulate hardware. Many ",
"operating systems",
" are written in C for just this reason. Unfortunately, making it easy to manipulate hardware makes it really hard to ",
"manage your computer's memory",
", among other things. C programmers spend a lot of time worrying about where ",
" they stored this variable or that string, how to get rid of it, how to let other parts of the program know where it is. Needless to say, if you're not answering the First Question of Computing with \"I want to make hardware manipulation easy\", C is going to give you a rough ride.",
"The designers of ",
"Java",
", for instance, answered the First Question of Computing with, \"I want to make ",
"running on lots of different machines",
" easy\". While the jury may still be out on whether or not they succeeded, they did have a clear vision because they succinctly answered the First Question of Computing. (A few other global principles went into the design as well, of course.)",
"Now for each of these new computer languages, you'd have a different ",
"grammar",
" that defined what a legal line of code looks like, much like English grammar is different than Finnish grammar. Both let you speak and ",
"convey meaning",
", but they sound pretty darn different.",
"What's the same, however, is that for each line of code in the \"high-level\" language, we use a compiler or interpreter to transform our friendly code into the kind of instructions the machine likes to read. This constant, this fundamental purpose of the compiler, is the second half of designing a computer language. First it ",
"parses",
" your friendly code, then ",
"generates",
" machine code.",
"We can now hopefully answer what it means to create a new programming language. First, you need to answer the First Question of Computing. Once you have decided how ",
" want to answer that question, then you write the grammar that fulfills your answer, and the compiler that translates your grammar to the grammar of the underlying machine instruction set.",
"This process, this mapping between two different levels of representation, but a map that ",
", is far and away one of the most amazing ideas I've ever learned about. It has applications in a huge number of different ",
"endeavors",
", across all ",
"walks of life",
". It is the idea of a ",
". The fact that you asked this question means you've taken your first step into a truly amazing journey. Stay curious :)"
] |
[
"At the bottom, as ",
"/u/somethingpretentious",
" said, it all has to be translated to 1s and 0s, or machine code, as that's the only thing the computer can understand.",
"So to see how a programming language tells the computer what to do, we should first look at how machine code tells the computer what to do. It does that by connecting certain sequences of those digits to certain actions.",
"This might be what a piece of machine code could look like. (I just invented these particular sequences, though. I've grouped it up in 8 digits because machine code is typically made up of bytes.)",
"00001100 00100100\n00001000 00010000 00010011\n00001011 00010000\n",
"The computer gets meaning out of this by sending these sequences through complicated arrangements of logic gates. Here's what this sequence ",
" mean: (Register A is a place for storing a single number in the processor. Let's assume A is zero at the beginning.)",
"add the following number to Register A (00001100) 36 (00100100) \n -- The value in A is now 36. (00100100 is 36 in binary)\nstore in this address in the RAM that number (00001000) Address: 00010000 Number: 19 (00010011) \n -- The RAM is basically a series of Registers, each of which have a number (or address) instead of a name, and in each of which you can store a number.\nsubstract the number in the following RAM address from A (00001011) Address: 00010000 \n -- The value in A is now 17. \n",
"You could now do other things, like printing the number in A onto the screen, for which there would be another sequence of digits.",
"The first thing you can do to make it easier for humans to read and write code is to write the numbers in hexadecimal instead of binary. This is very easy to translate back and forth. The code would then look like this (still grouped in Bytes):",
"0C 24\n08 10 13\n0B 10\n",
"That is a little bit easier to read, but still pretty much meaningless for a human without a lot of practice. The next step is to translate these numbers to words, which would be Assembly (0x means that it is a hexadecimal number):",
"ADD A 36 -- we need to write 'A' here, because the sequence 00001100 was only used for adding something to A, but 'ADD' is also used for other additions\nSTORE [0x10] 19 -- we use [x] to say that x is an address, not a number\nSUB A [0x10]\n",
"The translation of this is still fairly straightforward, though slightly more complicated. Though from here on out, it gets much more difficult to make improvements. That is because we want the user to get away from the level of the machine. He should, for example, be able to introduce variables and give them names, and then refer to these names instead of the address in the RAM. He should also be able to write his own functions (or methods, if you prefer). This is quite a bit more complicated, but can be expressed in Assembly. Functions are just sequences of instructions which can be saved in the RAM, which might refer to specific addresses for getting their arguments.",
"He should also be able to have variables which store not just numbers, but Strings and Lists and Pictures. That means you have to encode them to look like numbers, and they will likely need more than one byte of RAM.",
"Many modern programming languages end at this step. Some go one step further: Their code is translated to code of other modern programming languages, which is then translated to assembly.",
"I hope this is somewhat understandable and gives you an insight."
] |
[
"This is one of the greatest posts on reddit! A beautiful summation of programming languages and compilers (I studied comp sci)"
] |
[
"If i put a candle in a box, then put a candle and a mirror in another box, will the one with the mirror be brighter inside?"
] |
[
false
] |
thought about this as i put a mirror up in my room. i flicked on a flashlight in the dark and it shone through the mirror to reflect back into the room. then i wondered if the room was actually any brighter now than it was without the mirror.
|
[
"Yeah, as JushiBlue pointed out, it depends where you're looking. Some of the first \"flashlights\" (or torches you crazy Brits you) were basically this principle. Stick a candle in some type of enclosure and a bunch of reflective mirrors to focus the light outward very brightly. That outward light is much brighter than just the candle by itself, but only because it's focused much like a lens.",
"An easy way to think of it is that a candle in an open enclosure emits light radially, if you use mirrors you're \"moving\" some of the light that would have gone in other directions into the same direction, thus making it brighter!"
] |
[
"It depends on where you measure the intensity of the light. Assuming you have a setup like Mirror----Candle-----Wall, then the wall will be brighter than just a candle----wall setup. This is because the wall will receive the intensity of the candle as well as the intensity of the reflected light. It will be approximately twice as bright as the set up with no mirror. "
] |
[
"I'll further add that if the box had no lid and you looked into the box, it would definitely look brighter. This is because more light is being reflected from the mirror surface out of the top of the box and into your eye. Presumably the box has a fairly matte surface which scatters and absorbs light more than a mirrored surface."
] |
[
"How exactly do geologists know the number of supercontinents that have formed in the past?"
] |
[
false
] |
[deleted]
|
[
"To understand the reconstruction of paleocontinents (and supercontinents), one must delve into the basics of paleogeography. There are 2 main Toolsets in this discipline:",
"1 - ",
" When continents break up, they carry with them rocks with similar géologies, sedimentary environments and fossil faunas. These stand out and demand explainations, such as for instance the Avalonian trilobite faunas of Tethyan affinity in Easternmost Newfoundland, which just do not jibe with the trilobite faunas of the rest of N America; or the very similar geological environments in Eastern Brasil and Western Africa.",
"2 - ",
" When igneous rocks cool down, magnetic minerals they contain will orient in the 3-D magnetic field they are exposed to. There is both a horizontal component to this and a vertical one, and this information gets locked in. As a result, these magnetic minerals provide a record of the attitude of the magnetic field to which they were exposed when they chilled, which points to where the paleo-pole used to be back then. Also keep in mind that igneous rocks are usually relatively easy to date accurately through isotopic methods.",
" since continents migrate and rotate through the workings of plate tectonics, they usully do not point to the current magnetic poles and the trajectory of their migration can be reconstructed by backtracking. Thus, by combining the apparent position of the pole for a given area from igneous rocks of different ages, it is possible to reconstruct a the apparent pole wander path for that crustal segment.",
"You can refer to ",
"this paleomagnetism primer for the basics",
" and to explore how paleocontinents are reconstructed with more detail, actual data and actual calculations.",
"Coming back to your primary question, the correct answer would be \"we don't quite know\"... The problem with the question is that we are limited by the state of the geological record, and that beyond a certain age horizon there just aren't that many rocks avalaible which may be used for paleomagnetic investigations. You need a certain number of puzzle pièces to be able to build a meaningfull picture, and they just aren't there. To compound that problem, the further one goes back in time with these reconstructions, the greater the uncertainty becomes, as initially small measurement uncertainties add up.",
"Currently, there is pretty much no doubt about the supercontinents of ",
"Pangea",
" and ",
"Rodinia",
", although the exact fitting of the pièces may be somewhat open to debate (less so for Pangea, more so for Rodinia). You've mentionned Gondwanaland, which is technically not quite a supercontinent (a supercontinent is, by definition an association of most of Earths continents), although it was certainly impressive (roughly S America + Africa + Antarctica + Australia). Gondwanaland was running away from Laurasia (roughly N America + Europe + Asia) back then, after the breakup of Pangea."
] |
[
"I would like to add to ",
"u/Gargatua13013",
"'s excellent answer, and also add that the closing of oceanic basins creates what are called paired metamorphic belts.",
"Paired metamorphic belts are parallel stripes of what are called greenstones (high temperature, low pressure facies) and bluestones (low temperature, high pressure facies) that indicate previous subduction zones. Subduction zones are the areas where oceanic crust is thrust beneath continents. Examples are the western edge of South America where the Andes are being built, as well as the island arc that forms Japan. ",
"When supercontinents are accreting (coming together), there is usually a piece of oceanic crust that is attached to one or both continental plates. As they collide, the oceanic crust is subducted, producing paired metamorphic belts, until the density contrast is low enough to move into a style of deformation that is more crumpling of crust and large thrust faults.",
"These paired metamorphic belts, such as the one that runs through Ontario from the Grenville, and the one in Appalachia from the assembly of Pangea, record the cycles of supercontinental accretion. So we know that because there are at least two paired metamorphic belts in North America, there have been at least two supercontinents assembled and then separated in the last billion years.",
"I could have missed something, but that's just the info that was in my brain.",
"Cheers!"
] |
[
"Some proof of this. I'm an engineer/machinist. A company I do work for makes kettles (furnaces for extracting precious metals). These things normally go to Siberia, Africa and North America. We was doing one for Ireland which was unusual. The reason he told me was, whilst mining a very rich seam in Canada a very clever geologist surmised where the seam ended around Canada's coast and predicted where that part broke away from Europe. His prediction was in Ireland and within a mile of the seam. Always remembered it because it was a proof of something that happened 300 million years ago (or more). Thought it was pretty cool. "
] |
[
"Is there a drug that induces sorrow as its primary effect?"
] |
[
false
] | null |
[
"Alcohol often induces this effect in people, it is a depressant of the central nervous system."
] |
[
"There is a class of hallucinogens called deliriants that, in contrast to more popularly used recreational drugs, most often cause feelings of dread, anxiety, and dysphoria.",
"Anti-psychotic drugs very frequently induce dysphoria as well. You could maybe say it is one of their 'primary' effects even though it's obviously not administered for this purpose."
] |
[
"yes, source - ",
"http://en.wikipedia.org/wiki/Depressogenic"
] |
[
"Why are American aircraft carriers flat, while British aircraft carriers sloped upward?"
] |
[
false
] |
Surely there must be an internationally agreed upon method for launching an aircraft into the air from a very short distance, especially with the aircraft being so similar? What explains the disparity?
|
[
"British carriers are designed for Harrier jets which can take off under their own power off a sloped deck. Their engines can be turned downward to assist takeoff.",
"US aircraft are launched off the carrier with a catapult that accelerates the plane from zero to flying in 2 seconds. US carriers can fly a range of aircraft using this system."
] |
[
"These guys are obviously having fun, but for the rest of us:",
"LHA = ",
"Landing Helicopter Assault",
", \" general purpose helicopter-carrying amphibious assault ships\"",
"LHD = ",
"Landing Helicopter Deck",
", \"multipurpose amphibious assault ships which are capable of operating helicopters and have a well deck\"",
"VTOL = ",
"vertical take-off and landing",
", \"fixed-wing aircraft that can hover, take off and land vertically as well as helicopters and other aircraft with powered rotors, such as tiltrotors\"",
"I think?"
] |
[
"That's just one portion of the carrier design to consider. The larger size, angled deck, catapults, and arresting gear of the US carriers allow them to accommodate a variety of aircraft and allow for simultaneous launching and recovery operations. Ski-jump carriers have been smaller, and do not support simultaneous operations.\nThat might be one of the reasons why the UK's next generation carrier(s) will be larger, use catapults, arresting gear, and no ski-jump.",
"http://en.wikipedia.org/wiki/Queen_Elizabeth_class_aircraft_carrier"
] |
[
"Is Delta T (Temperature) subject to momentum?"
] |
[
false
] |
[deleted]
|
[
"The greater the difference in temperature between two things, the faster heat will conduct between them. So hot water in cold air will initially lose heat faster than lukewarm water ... but by the time it cools down to lukewarm temperature, all other things being equal, it will cool at the same rate as the lukewarm water did. ",
"Heat capacity is the property that determines how much energy you need to raise temperature of an object. It does change with temperature, but not, as far as I know, with rate of heating. ",
"I don't know what causes the awesome boiling water to snow effect, but I would look, as a starting point, at the way the size and shape of water droplets changes between warm and very hot water. Tiny droplets will cool much, much faster than large ones, which might mean they can freeze very quickly. "
] |
[
"Hot water freezes faster than cold water given equal size droplets and temperature of air; this is quirky but 100% true fact."
] |
[
"That sounds bizarre but interesting! What's the reason behind it? What mechanism is going on?"
] |
[
"Is the latent heat of fusion of water altered with different crystalline structures of ice? (Ice formed under very high pressure vs STP) If so, is there a formula?"
] |
[
false
] |
The thought is, because ice formed under high pressure cannot optimize for hydrogen bonds (why it normally expands when frozen), that it would require less energy to undergo the phase transition
|
[
"Yes. Latent heat is the difference between states A & B at the conditions of phase transition, in terms of energy stored in the configuration of molecules (internal energy including sum of all intermolecular interactions).",
"There are 18 known phases of crystalline solid water, so I don't think there's a simple formula I can find for you. The normal variant is hexagonal, but you also get cubic, tetragonal, rhombohedral, etc. Many of those won't have a \"heat of fusion\" because there won't be a direct phase boundary with liquid water, but there will be some latent heat associated with transition to other forms of ice."
] |
[
"The other answers have done a good job here but I wanted to mention that you can harness the latent heats associated with different crystallization states to make self-thermoregulating materials (much like ",
"coffee joulies",
" use a phase-change material to achieve the same style of thermoregulation). If this interests you, check out ",
"Outlast’s website",
" (their polymer material uses different crystallization states for energy storage and release) or read academic reviews like ",
"“A review of materials, heat transfer and phase change problem formulation for latent heat thermal energy storage systems”",
" (Agyenim et al., ",
", 2010) or ",
"“Optically-controlled long-term storage and release of thermal energy in phase-change materials”",
" (Han et al., ",
", 2017)."
] |
[
"This is all correct, I would only add that it's not necessary that states A and B be directly adjacent on a phase diagram to speak about a heat of fusion. To modify your statement the heat of fusion is defined where A & B have the same free energy, if you get rid of all the other phases of ice other than the one you're interested in then you can construct a new phase diagram which will touch water and talk about it's heat of fusion in this way. This is a valid way of thinking about heats of fusion of high pressure phases even if in reality they would turn into other phases of ice before they turn into water."
] |
[
"Why is there mist that covers the skyscrapers in Dubai, when it is a desert city?"
] |
[
false
] |
I was watching The Arrivals and they mentioned that since the building of the Burj Dubai Tower, there has been a mist that surrounds it and other skyscapers. EDIT: I understand it's on a sea-shore, but the mist never used to be there, it showed up after the Burj Dubai became the tallest in the city. Why did the mist suddenly show up?
|
[
"It's on a sea-shore. "
] |
[
"Well... that didn't take much science to solve."
] |
[
"That's where she sells sea shells"
] |
[
"Do stars have lagrange points?"
] |
[
false
] |
Since our star is orbiting the centre of our galaxy, does it have it's set of L-points? is there some far off L4/L5 position of just some colossal clump of debris never to have a star of it's own to orbit? If so, could a sufficiently large enough star hold entire other star systems in it's L4/L5? and should you be some astronomer to evolve in such a star system, would you be able to tell that you were in the L4/L5 of a larger body and not infact independently orbiting the central mass of the galaxy? would that have any implications? Thanks!
|
[
"For most of the galaxy the gravity of the center is very small relative to the gravity of all the other stars in the galaxy. So any stellar Lagrange point would be swamped by the effect of gravity from other stars."
] |
[
"Just a note, our star isn't really orbiting the center of the galaxy, at least not in the same way the earth orbits the sun. Our star's path around the center of the galaxy is determined by gravitational pull of all the mass that has a smaller galactic radius than us.",
"Basically, galaxies are not point masses and so the same rules don't really apply."
] |
[
"I've never seen Lagrange points used in the literature to discuss anything other than ",
". Basically, to have Lagrange points you need a massive object and a satellite- so the Sun-Jupiter points are good for asteroids, the Sun-Earth points are good space telescopes, etc. ",
"For extended distributions of mass like the clusterfucks of stars we see in galaxies and clusters we tend to use different, more statistical ways of modeling bulk behavior (i.e. the Virial theorem). "
] |
[
"Are there any materials in this world that are impenetrable by gamma rays?"
] |
[
false
] |
[deleted]
|
[
"It all depends on thickness of the material. Air can effectively stop gamma rays from outer space. The 100 km of atmosphere make a very good shield. The Earth itself stops them. But if you are looking for a thin material, I would have to say no. Gamma rays are just high energy light and subject to the same Beer's law for absorptions, so some will get though for arbitrarily thin materials."
] |
[
"Like he said, it depends on the thickness. ",
"But 'dimming' the intensity doesn't make the individual photons less energetic, it just means less photons are getting through. So the radiation getting through the shielding is still dangerous to anybody there."
] |
[
"It depends on the gamma ray energy. In general gamma rays don't get deterministically stopped, some of them always pass. There's an exponential law describing the percentage of photons stopped depending on the thickness of material traveled. \nWith low energy photons (10 keV or less) some half of the photons get absorbed every tenth of mm of lead (approximately). But if you increase the energy even only to 500 keV some mm of lead are not enough to absorb half of the incoming photons. If you keep increasing the energy things get even more difficult. You need very huge amount of dense, high Z matter to stop them. Luckily, the amount does not keep on increasing as dramaticaly like from 10 keV to 500 keV, because electromagnetic showers start to happen. For a 10 GeV photon some 20 cm of lead are enough to stop most of the flux. (20 thousand time the energy, only 10 times the thickness)",
"Anyway gammas (and neutrons) are the hardest to stop. That's why radiation-therapy rooms need incredibly thick walls of full concrete loaded with barium.",
"Note: the numbers are quite rough, I didn't check the tables. But the orders of magnitude are correct."
] |
[
"Why do green house gases not stop as much light from entering the atmosphere as they keep from exiting the atmosphere?"
] |
[
false
] |
I understand how greenhouse gases prevent light from exiting our atmosphere, but why do they not prevent an equal amount of light from entering?
|
[
"The big greenhouse gases on the Earth (water, carbon dioxide, methane, oxygen, etc) work because those molecules have specific bands of wavelengths where they absorb light. These are greenhouse gases because those bands are most effective at absorbing infrared light.",
"The light coming into the Earth from the sun is (roughly) ",
"a blackbody at 5800K",
". Thus, most of the light (energy) from the sun is in the visible wavelengths and a lot of it gets through to the surface (the red part in the figure) because the greenhouse gas absorption bands aren't as good in the visible (you can see in the image where the bands still work).",
"Meanwhile, the Earth is much colder, something like 280K. Its blackbody emission is therefore ",
"almost entirely in the infrared",
". This happens to be where the greenhouse gases are extremely effective at absorbing light and therefore don't let the Earth's light escape back into space (you can see lots of yellow where the greenhouse gases eat up all the light trying to escape and then reradiate it back at the Earth).",
"Basically then, the greenhouse gases work because the wavelengths of light coming in are different from the wavelengths of light going out, and the greenhouse absorption bands are more effective at preventing the light from getting out than preventing the light from coming in."
] |
[
"The big greenhouse gases on the Earth (water, carbon dioxide, methane, ",
", etc)",
"Just to be clear, the oxygen we breathe (O2) is not a greenhouse gas, although ozone (O3) does have a slight greenhouse effect."
] |
[
"The energy coming in and the energy going out are not in the same form. The energy coming in is mostly around the Sun's peak blackbody emission frequency, which is to say, the visible light range. The blackbody radiation coming back off the Earth's surface is mostly at much lower frequencies, the deep infrared range."
] |
[
"The Mars Perseverance Rover's Parachute has an asymmetrical pattern to it. Why is that? Why was this pattern chosen?"
] |
[
false
] |
Image of Parachute:
|
[
"The asymmetry in the coloring makes it easier to study the video and assess the parachute's performance. In multi-chute systems, you'll see that each parachute has a different pattern so they can tell them apart.",
"Edit: more explanation: the parachute is able to twist with respect to the vehicle (and therefore the camera). If there's any strange behavior in the parachute, they can track it visually and then go back and look at photos of the folded and packed chute, the fabrication process, etc, and the markings help them to make a direct comparison."
] |
[
"Any patch of about 10% of the parachute is enough to identity the orientation.",
"This would be especially useful in a failure situation where there might be a just a few frames of vision to work with. If it all works, it's just a pattern."
] |
[
"High contrast color patterns are far easier to see from a far distance at low resolution than some shapes.",
"Here, I drew A B C on it, then shrunk it down to 50x50.",
"https://imgur.com/a/uFe0qNH",
"You can still clearly see the red/white pattern, but the letters are basically invisible. Good luck trying to tell apart IJL and DOQ at a distance too."
] |
[
"Now that a piece of wreckage from flight MH370 has been confirmed on Réunion Island, is it possible to use our understanding of direction and speed of currents in the Indian Ocean to narrow down where it likely crashed?"
] |
[
false
] |
Confirmation the wreckage is from MH370 can be found here: The crash occurred 515 days ago. If this points an area out, where would it be? Is the area outlined by this method an improvement of the previous search perimeter on the one where search parties were operating? Are they even close?
|
[
"There's a pretty good summary ",
"here",
". What I took away from that was that it'd be insanely hard to pinpoint an exact starting location since planes aren't really Lagrangian drifters and ocean flow is more turbulent than it is laminar. What say you, ",
"/u/sverdrupian",
"?"
] |
[
"I agree. The ocean is full of eddies. Over the course of a year those eddies stir and mix the ocean so much that back-tracing the path of any single piece of flotsam is impossible. We know for sure now that the plane crashed in the southern Indian Ocean but this finding isn't going to narrow the search area any better than the previous estimates based on fuel consumption and satellite pings.",
"Also, things washed up on beaches are notoriously difficult to track since typically no one is there to see it wash up. It could have been last week or several months ago. Without that timing information, it is even harder to back-trace a trajectory since the specific patterns of ocean eddy currents is always evolving and changing over time. "
] |
[
"There are likely several oceanography modeling groups gearing up to do this right now. Some probablistic information may be better than no information. My gut (based on years of working with ocean data) is that the resulting estimate is unlikely to eliminate any of the areas where they have been searching: ",
"map link",
". As one of the news articles says, the ocean is like 'a pinball machine' on these scales. You can do a pretty good job of representing that behavior with a stochastic random-walk model (representing the eddy effects) sumperimposed on a slow westward drift (from the gyre circulation). The only thing really certain now is that the plane went down in the Indian Ocean south of the equator and somewhere between Australia and Reunion Island. ",
"Happy cakeday, btw!"
] |
[
"What ever happened to the hole in the ozone layer?"
] |
[
false
] |
Are my poor little phytoplankton going to be okay?
|
[
"Since 1981 the United Nations Environment Programme has sponsored a series of reports on scientific assessment of ozone depletion, based on satellite measurements. The 2007 report showed that the hole in the ozone layer was recovering and the smallest it had been for about a decade.[62] The 2010 report found that \"Over the past decade, global ozone and ozone in the Arctic and Antarctic regions is no longer decreasing but is not yet increasing... the ozone layer outside the Polar regions is projected to recover to its pre-1980 levels some time before the middle of this century... In contrast, the springtime ozone hole over the Antarctic is expected to recover much later.\"[63]",
"http://en.wikipedia.org/wiki/Ozone_depletion"
] |
[
"The problem was actually handled. Much like the acid rain problem.",
"This is what regulation solving problems looks like."
] |
[
"The fact that we got our shit together on this gives me hope for the future."
] |
[
"If energy cant be created or destroyed. How can it be here?"
] |
[
false
] |
Existence and creation are different things but how it can be here if in coudnt be created?
|
[
"There are basically two options:",
"The total energy is constant, has always",
" existed and will continue to exist forever",
"Energy is created in some process that we aren't sure about yet. One candidate for such a process that may violate energy conservation is cosmic expansion of a space with a positive vacuum energy. If the cosmological constant is indeed constant, but space is expanding, this implies that vacuum energy is actually created. It's also possible that the total amount of energy was simply created at or near the big bang through some physical process we have no access to.",
" for a suitable definition of always and forever, which might, as far as we know, include that time started after or with the big bang"
] |
[
"Yes, but be aware that this is a bit of a point-of-view matter. If space-time changes, energy of systems inside the space-time need not be conserved. The other view is to interpret the maths in such a way as saying that energy is actually conserved, it goes into (or out of) the gravitational field.",
"See this blog post for an overview: ",
"http://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/"
] |
[
"I think it answers it pretty well. The question was asking how energy exists if it can't be created. The answer given was \"Nobody knows, but it must have either always been here, or it can be created through some process we haven't figured out yet.\"",
"Remember, scientific discovery is an ongoing process, sometimes the answer to a question is simply \"We don't know, but we're working on it.\""
] |
[
"I thought electrons didn't actually orbit the nucleus, but this SciAm article talks about possible relativistic effects in large atoms from their \"orbits\". Please help me understand."
] |
[
false
] |
My previous impression was that electrons sat in a "probability cloud" around the nucleus of the atom, and they didn't actually orbit the atom a la planets, as the old simplified models talked about. In the latest Scientific American article titled "Cracks in the Period Table" (Edit: the article is about the properties of synthesized super-heavy atoms), there is a paragraph in the intro that says, "But as the atomic numbers -- the number of protons in a nucleus -- reached higher, some of the added elements no longer behaved the way the period law requires; that is, their chemical interactions, such as the types of bonds they form with other atoms, did not resemble those of other elements in the same column of the table. The reason is that some of the electrons orbiting the heaviest nuclei reach speeds that are a substantial fraction of the speed of light. They become, in physics parlance, "relativistic," causing the atoms' behavior to differ from what is expected from their position in the table." So, can someone help me understand exactly what orbiting means when it comes to electrons, and why there is a speed involved if it's a probability cloud? And if there is some sort of orbit involved, what path do the electrons follow, and how does the path twist into an orbital shape?
|
[
"Ah yes! That's the problem with describing them as a 'probability cloud'. See, if it was ",
" a cloud of electron density, one might wonder what quantum mechanics is for, since classical EM has no problems modeling a 'charge cloud', so to speak. ",
"But that's not the whole story. The probability of where the electrons are behaves in a \"wave-like\" manner. The 'cloud' doesn't change its position, but it still has kinetic energy, it's behaving much like a ",
"standing wave",
". ",
"The more tightly concentrated the cloud is, the higher the kinetic energy, and the more spread out it is, the lower the kinetic energy. It's very much at odds with classical physics - the electrons are ",
", and yet the 'cloud', the probability of where they're likely to be (which is all you can say about their position), ",
". Not while the atom/molecule is in its ground state, anyway. ",
"Quantum particles don't follow classical trajectories. In fact, when you have a 'node' in an orbital (again, analogous to nodes in standing waves), that's an area where there's an exactly ",
" probability density of finding the electron. They can get from one point to another without necessarily having to pass intermediate points. ",
"Anyway - in heavier elements, the attraction from the nucleus is stronger, since it has a larger positive charge. The innermost electrons therefore get probability clouds more narrowly centered on the nucleus of the atom. But in response, they also get that much more kinetic energy. And they end up with relativistic effects on their momentum, because they have 'velocities' that start to get up to a significant fraction of light speed. (You normally only talk in momentum terms here, because 'velocity' is not a well useful concept for something that doesn't follow a trajectory!)",
"So relativistic effects become increasingly important for heavier elements. (It's ",
"what gives gold its yellow color",
" and ",
"what allows your car to start",
", among other things)"
] |
[
"Electrons might not have a classical velocity associated with their orbitals, but they do have well-understood values of momentum, which (combined with the known rest mass of the electron) gives them effective velocity values. When these are high enough, as in heavy elements, you begin to see relativistic effects that warp the trends and patterns that previously applied."
] |
[
"Thinking of momentum and mass is probably more correct - in particle physics, you often describe particles by their total energy, their momentum, and their rest mass. All three are related by E",
" = m",
" c",
" + p",
" c",
" You could work back from those to get the speed of the electrons, but it probably wouldn't make much sense to do so (once you become highly relativistic, you can gain a lot of energy/momentum but barely change your speed).",
"Edit: I forgot how to relativity."
] |
[
"What defines measurement which affects quantum outcomes? Or what is wrong with my understanding?"
] |
[
false
] |
It's my understanding that when one "measures" results in a quantum experiment, it will affect the results. That is, if I fire buckyballs though some slots, they will take every possible path and these paths will interfere and create an interference pattern. I may be mistaken, but I understand that measuring the buckyball impacts will affect the experiment's outcome. This must be my misunderstanding, as eyeballs and testing equipment (amplifiers) should not affect the interference pattern. But the original experiment consisting of a single buckyball resulted on a well defined path, or so I thought? My base question, besides how is my understanding flawed, mis what defines the measurement that will affect this outcome? Perception? Sensation? I'm very confused. Help!
|
[
"You are misunderstanding what it means to observe/measure in quantum physics. ",
"This has been addressed before",
" (",
"try this search too",
"). It's worth checking out previous threads."
] |
[
"Thanks for the links. They better defined my question and I realize now that I understand the uncertainty quite well. I also realize it is quite uncomfortable for me to understand. "
] |
[
"I also realize it is quite uncomfortable for me to understand.",
"It's uncomfortable to everyone. Don't fret. :)"
] |
[
"What happens to the light that strikes a solar cell but is not converted into electricity?"
] |
[
false
] | null |
[
"If it's absorbed it's turned into heat [just like any other light that is absorbed], if not it's sent packing back into space or wherever.",
"Ironically heating up a solar cell makes it less efficient so the ideal solar cell is highly reflective."
] |
[
"When light hits the IC and it cannot be converted to free electrons it's converted to heat. That heat \"slows down\" (makes more resistive) the circuit which then drops the efficiency of the circuit.",
"The ideal ratio is to have 100% of the capture photons converted to electrons and the rest reflected but that's not possible given the object is opaque...",
"Basically, you want to keep the solar cell as cool as possible to drop the resistance of the circuit. But cooling takes energy ... so uh ... you deal with it."
] |
[
"That is the most simple way to explain it, that our primary losses are due to heat losses and reflections. ",
"Absorption is what happens when an electron absorbs the photon and is liberated from the atom to which it is bonded. As we have a bandgap in the semiconductor, the absorbed energy must be enough to promote the electron from the valence band to the conduction band. ",
"Not enough energy and the electron relaxes back to the conduction band, the energy is lost to radiative recombination (hey, that's kind of how LEDs work) or heat losses due to collisions with the lattice (think heat from friction). Much more energy than the bandgap and the same thing happens, but the electron settles into the lowest unoccupied state in the conduction band.",
"The book is expensive, but if you can find a cheap copy of: ",
"http://www.amazon.com/Crystalline-Silicon-Solar-Cells-Applications/dp/0471971448",
" it has a very practical approach.",
"Its really quick to say 'heat and reflections', but its slow to say where all of that comes from.",
" I did a research paper on PV in grad school. The theoretical maximum efficiency of any type of solar cell? 88%",
" The wiki article on solar efficiency only slightly disagrees with my comment, stating the limit is 86% and citing a Harvard article."
] |
[
"What causes a random long white strand of hair to grow?"
] |
[
false
] |
[deleted]
|
[
"This question was asked recently (not complaining, but the search function might give you some additional responses to your query). "
] |
[
"Please reserve top level comments for answers to the OP's question, or futher, related questions"
] |
[
"Please reserve top level comments for answers to the OP's question, or futher, related questions"
] |
[
"What exactly are the new states of matter?"
] |
[
false
] |
We all know the big three but now there's bose-einstein condensates and dropletons? I have read a few articles on them and their discovery but I still don't quite get what they are.
|
[
"Since this is a physics question, I have to say first: no one REAALLY knows what they are. But in terms of my knowledge I believe I might be able to help on the BEC side. Bose certain materials when cooled to extremely low temperatures the energy in their atoms/molecules and it is no longer made up of fermionic mater, which follows Fermi-Dirac statistics, follow the pauli exclusion principle, and half half-integer spins. Instead it is now made of Bosons, which do not obey the pauli exclusion principle and have integer spins. One of the main properties that characterizes this would be no viscosity, making them as slippery as possible. Because of the bosons that comprise this matter at the lowest quantum state, it additionally can behave strangely and therefore also represents what is called a macroscopic quantum phenomenon. Of course there are more technicalities and mathematics involved but thats the basics (as far as I know). I'm sure someone with more knowledge could explain it better."
] |
[
"So BEC are what is present in superconductors during quantum locking?",
"EDIT: What differentiates BEC's and Dropletons from the other states of matter?"
] |
[
"I think the big difference is mostly that liquids, solids, and gases exist in everyday life. You breathe air, drink water, and eat food. Additionally many of the lesser known states of matter are either hard to create in a lab, or hard to observe even when they're there. Plasma is not as rare as some states of matter that are more like quantum based events. ",
"And for the quantum locking thing, I don't think so. BEC's appear a bit more like what we would intuitively call liquids. Superconductors are just when they slow down the atoms of the material to the point where electrons do not collide with them, which would decrease the energy transfered."
] |
[
"What is mild hyperexpansion of the lungs?"
] |
[
false
] |
I had chest X-ray done a while ago, and while flipping through my records, I noticed that the doctor had left a note "Lungs are mildly hyperexpanded..." What is it?
|
[
"You need to ask your doctor. We can't interpret exactly what he meant, and anyway the internet is a bad place to be looking for medical advice."
] |
[
"Take all of that with a grain of salt.",
"Don't take it at all. ",
"If there was reason to suspect disease, your doctor would have informed you and pursued it clinically. If you have more questions, talk to the doctor that ordered the x-ray.",
"EDIT: OP shouldn't be asking medical advice, Fmeson shouldn't be giving medical advice, and in general, someone who has no knowledge of the subject matter should not link a Yahoo answers response. This subreddit is not Google, and your ability to find an unreliable source using Google-Fu does not make you an expert."
] |
[
"Take all of that with a grain of salt.",
"Don't take it at all. ",
"If there was reason to suspect disease, your doctor would have informed you and pursued it clinically. If you have more questions, talk to the doctor that ordered the x-ray.",
"EDIT: OP shouldn't be asking medical advice, Fmeson shouldn't be giving medical advice, and in general, someone who has no knowledge of the subject matter should not link a Yahoo answers response. This subreddit is not Google, and your ability to find an unreliable source using Google-Fu does not make you an expert."
] |
[
"Does the heat index actually correlate to a specific dry air temperature well?"
] |
[
false
] |
With the heat rising in the northeast U.S., the topic of heat index keeps popping up on my radar. What I'm trying to figure out is whether a heat index of 110 deg F is actually comparable to a dry air temperature of 110 deg F. I'm basing this off of experiencing I've personally had while living in NJ where the heat index is 105 deg F vs. an air temperature I've experienced of 110 deg in Las Vegas. To me, I felt significantly warmer in NJ than I did in Vegas, despite the heat index being lower in NJ. From what I've read, the correlation is based off of relative humidity and the body's ability to reject heat to the atmosphere. Obviously perspiration is the primary method of heat removal, which is inhibited when the ambient humidity is increased. The amount of heat removal is apparently directly related to how hot we personally feel. I still don't understand how this determination is made, since I feel much warmer in a humid environment than in a warmer, dryer one. OR, am I confusing discomfort of sweat with heat, making this question useless?
|
[
"The calculation is a curve-fit to a specific set of data from the 1970s but each individual experiences heat differently. The data for the classic heat index assumed a 5'7\" man weighing 147 pounds, wearing long pants and short-sleeved shirt while walking 3 mph in the shade with a slight breeze. Your results may vary.",
"source"
] |
[
"That is ridiculously specific.",
"Isn't science meant to be ridiculously specific?"
] |
[
"That is ridiculously specific.",
"Isn't science meant to be ridiculously specific?"
] |
[
"For something as medically useful and clinically important as Lithium, how do we not yet know its mechanism of action?"
] |
[
false
] | null |
[
"Most drugs, especially those as old as Lithium, were discovered serendipitously. ",
"In 1849, a researcher named John Cade, wanted to see if any chemicals in urine from manic patients were toxic, so he dosed guinea pigs with urine samples from patients with mania. To solubilize uric acid crystals as control, he used a lithium salt. He noticed it had a profoundly sedative effect. Initially, he tried to chase down various chemicals causing the effect, before he realized it was the lithium itself acting as a tranquilizer.",
"This started lithium's long history of use in the clinic and many patent medicines, and it's one of the first drugs to be used to treat psychiatric disorders. It was even in the original formulation of 7-up called \"Bib-Label Lithiated Lemon-Lime Soda\". Unfortunately, lithium has a low therapeutic index (a little is good, a little more is toxic), so use as a patent medicine or in drinks caused many cases of chronic lithium toxicity, presenting as tremor and mild confusion in most cases. ",
"Now it's use is much more restricted and closely monitored. However, to this day, it remains one of the standbys for treatment of mania, especially bipolar disorder. ",
"But none of this has answered your question, which was why do we not know how it works.",
"The answer is relatively simple: we don't know how many things work, including the brain itself. Most treatments are evaluated for safety and efficacy, and a mechanism of action is not required for FDA approval (though this is now ",
" changing as pharma requires it).",
"Add to this fact that lithium is mind-bendingly simple - it's literally just the ionic form of an element. You can find salts in rocks. If I had to give you a complete list of what sodium did in our body, another ion closely related to lithium, you and I would both tire of the endeavor long before we covered every topic in depth. ",
"And that relationship could be key, because though lithium is present in all life, it is not required and you do quite well without it. Most theories on lithium's MOA that I find plausible suggest subtle modifications on sodium ion channels in the brain. But this could be way off. I've been wrong before."
] |
[
"To put things in perspective, deorphanizing a drug (finding the target) is one of the hardest problems in the biological sciences. The workings of a cell are like a setup of dominos, you knock one over and everything changes. How do you tell the difference between what happened directly and what happened as a consequence? It gets exponentially more complicated when a drug is discovered by the effects it has on a complex organism like a human."
] |
[
"OP should know that the same can be said about a lot of drugs, especially those used to treat psychiatric or neurological disorders. As an earlier poster mentioned, serendipity is often how many were discovered. Amytryptiline was first tested as an antihistamine/decongestant. Viagra as a treatment for hypertension. The theories that are used to explain their effects are discovered after the fact, and often those theories are based on fairly thin data sets."
] |
[
"Are there any animals that don't sleep?"
] |
[
false
] | null |
[
"Some animals with simpler brains like worms and insects don't sleep, at least not the same way we do."
] |
[
"Worms",
" and ",
"insects",
" do sleep."
] |
[
"I don't know if this is what you are looking for, but ",
"this",
" article talks about dolphins, and their ability to rest half of their brain at a time. So, while they are still technically sleeping, never fully unconscious. "
] |
[
"Why aren't siblings of the same gender genetic twins?"
] |
[
false
] |
Ignoring random mutation of gametes, why don't brothers with the same parents have the same genome? The way I understand it, each parent contributes half of the genetic code, in the form of half of the 46 chromosomes. If a specific set of chromosomes (eg the odd numbered from dad, the even numbered from mom) are in each gamete, copied from the parent's genome, the resulting offspring are identical. If each ovum had a different set of chromosomes, that's a huge number of possible combinations (2 to be exact, for humans), and the fertilizing sperm would have to match up identically, otherwise bad things would probably happen. Not saying that they don't, but those bad things would be far more common. So, obviously I'm missing something, because my brother is not my twin genetically, but he managed to be granted a relatively normal set of chromosomes, just like me.
|
[
"I think the main thing you are missing is the fact that humans are ",
". This means that we have two copies of our DNA that are very similar that make up our entire genome. Each of the 46 chromosomes has a twin making 23 pairs of closely matching chromosomes. When a gamete is formed one of each of these pairs is ",
" sorted into the gamete and only one of these chromosome sets (the sex chromosomes X and Y) determines the gender. ",
"Thinking of it as 'mom gave me the odd ones and dad the even' is not really correct and it may help to look at what's called a ",
"karyotype",
" which is just a visualization of the chromosomes. Their are only 22 non-sex chromosomes and every normal human has two of each. You are actually getting one full copy from your father ",
" your mother. This means that you are getting two copies of every gene, one from each parent and this is a good thing because one copy might have a deleterious mutation that could harm fitness. All of these non-sex chromosomes are what determine morphological features, what you look like hair color, eye color, height etc. Their is very little information (comparatively) stored on the sex chromosomes (Y especially being very small) so that means that someones sex is not closely linked to a whole lot of traits (hence, for the most part you and your brother are different because you got different non-sex chromosomes from each parent). Some traits that are found on the sex chromosomes are sex-linked like one particular form of red-green color blindness.",
"This is also really just the beginning as not only do chromosomes (one of each of the 23 pairs) get randomly put into an egg or a sperm, but genes can also swap places with their counterparts on their twin chromosome. "
] |
[
"Nope. So your mom has 2 copies of each chromosome and your dad has two copies of each, and you already seem to know you get one of each from your mom and your dad. ",
"Now lets just look at chromosome 4. You get one chromosome 4 from mom (who has two to give, A and B) and you get one chromosome 4 from your dad (he also has two, lets call them C and D). ",
"You might have chromosome 4 versions A and D, while your brother might have A and C meaning you have one chromosome in common but aren't identical. He could also have B and D meaning you don't share any similarities in your chromosome 4 at all!",
"Now apply this to all 23 chromosomes. You could have exactly the same ones, 1 in common, or two entirely different ones for each of the 23 sets. That's why you and your brother aren't identical. "
] |
[
"If each ovum had a different set of chromosomes, that's a huge number of possible combinations (222 to be exact, for humans), and the fertilizing sperm would have to match up identically, otherwise bad things would probably happen",
"Wait, what do you mean bad things would probably happen? There they do not match up identically, and bad things DON'T happen. In fact, if all the alleles are exactly the same, then bad things are probably more likely to happen because of homozygosity in deleterious alleles (which is why incest can cause problems).",
"Unless you mean they don't match the actual type of chromosomes, which in that case is because you are misunderstanding how the chromosomes are distributed in gametes.",
"You have 23 different \"types\" of chromosomes, (well, 24 in males), and you have two of each type of chromosomes in adults. When you make gametes, you select one of EACH \"type\" of chromosome, contributing half the number of chromosomes, but importantly still having each type of chromosome. So every gamete has a whole set of chromosomes. They are however, all different, because there are 2",
" types of possible different combinations of chromosomes from a single parent, more if you include recombination between chromosomes, so that is why every gamete is genetically different, BUT still has a normal set of chromosomes. No gamete is ever identical to the parent because of this, and the offspring resulting from different fertilization likewise are not genetically identical to the parents or their siblings."
] |
[
"If a spaceship is in the dead of space, unaffected by gravity, will firing the rockets increase the ships speed indefinitely?"
] |
[
false
] | null |
[
"An object moving with constant proper acceleration will technically continue accelerating forever, however its speed will asymptotically approach c.",
"There's a derivation ",
"here",
"."
] |
[
"Just to make an addition to ",
"/u/RobusEtCeleritas",
"' answer, if one imagines a trip from, say, Earth to the nearest star system Alpha Centauri - a distance of ~4 lightyears - it is a result of relativity that from the perspective of the Earth and the perspective of Alpha Centauri, as you constantly accelerate, your speed for them will approach c and never exceed it meaning that from their perspective your journey will always take longer than 4 years (it takes light 4 years to go 4 lightyears). From this simple reality we get all our bummer statements that faster-than-light travel is impossible. ",
" it is important to note that there is a very important ",
" to this situation which is that from ",
" perspective on the ship it is entirely possible for you to make the trip in less than 4 years. ",
"For example, if we let our imaginations run wild the \"ideal\" spacecraft would yield a constant acceleration of 1G at all times. Side-stepping the question of how such a ship could carry such an outrageous amount of fuel, this would have the advantage that the people on the ship would feel \"Earth gravity\" of 1G due to the uniform acceleration (like how you feel heavy when a descending elevator slows down). In such a ship you can look at ",
"this plot",
" and see what would happen. The right y-axis is the crappy reality of relativity, to get to say the center of the Milky Way would take ~10",
" years(or 100,000 years) from the perspective of the Earth and the center (well technically this graph is for a round trip but we're just talking order of magnitude here so it's not a big different). HOWEVER, the left axis is how long the trip took from your perspective in the ship and to get to the center of the Milky Way and back with a 1G accelerating ship, which is ~100,000 light years away takes... ~",
". Everyone you ever knew would be already dead for eons but you'd only have experienced a few decades and could make the trip there and back."
] |
[
"The lack of particles to push against in space will mean that acceleration will be slower because the rocket exhaust will need to push the ship forward from other particles emitted from the exhaust.",
"Say what now? The accelerating force provided by a rocket's exhaust does not require the presence of a medium to 'push against'. The mass and net velocity of the exhaust gases (or ions) define the force of acceleration imparted by the engine."
] |
[
"How does a ground/earth pin work on a plane?"
] |
[
false
] |
I was on an American Airlines flight and noticed that there were power plug holes on the backs of the seats, 110v 60hz, they had earthing ports, how did they work?
|
[
"The ground pin doesn't have to connect to the actual ground: what matters is that it connects the case of the electronic device to something else the user is touching, so the device and the user are at the same voltage. No voltage difference, no shock.",
"In a car, for instance, the ground is the metal frame of the car. For an airplane, the ground pin presumably is in contact with the frame of the plane.",
"The vehicle might have a very different voltage than the actual ground, but so long as all the objects the user can touch are at the same voltage, no shock can occur."
] |
[
"One question. The user is almost definitely not directly in contact with the plane's frame, how is it guaranteed to work? The seat is cloth, the user's shoe is rubber, etc."
] |
[
"The user gets shocked. It's no different that when you touch something in your house or car and you have a static built up that hasn't been grounded through other means. This however usually doesn't happen, as it doesn't take much to discharge. Humidity can do it. Also, it merely a static change difference from ground which holds very little energy even if high voltage. ",
"The main issue though is the user will not be a path between the device casing shorted to the live wire and the ground (be it actually ground or a chasis/frame) thanks to the ground wire being a much better path. It doesn't matter if the user has a solid insulation between them and the ground or not, either way they aren't getting shocked if they touch the device while there's a short to the live wire or any other voltage build up. "
] |
[
"In basaltic magma, how much is recycled crustal material and how much is mantle material?"
] |
[
false
] |
I'm curious about both mid-ocean ridge and mantle plume/hot spot magmas, and potential differences between the two. From what I can gather, granitic magmas usually result from recycling of crustal material at subduction zones; but I'm not so clear on the composition of basaltic magmas. How much of the material at mid-ocean ridges/hot spots originates deeper in the mantle and is brought up by convection, and how does this interact with the astenosphere and moho? Thanks!
|
[
"I believe that the magma that has the greatest amount of crust recycling is in a subduction zone such as the one around Oregon and Washington states. The oceanic crust slips underneath the continental plate, melts in the mantle, and then feeds into the volcanoes in the area."
] |
[
"In both the scenarios you outlined the crust is oceanic in origin anyway. You will get some remelting on the way up but its essentially the same composition as the melt you already have. My geology degree was 20 years ago and I sucked at it so I am sure someone will come along soon with a more wordy explanation."
] |
[
"Magma usually forms in the Asthenosphere. There is almost no convection in the asthenosphere, just some vertical movements of themperature.\nThe difference in magma formation are: ",
"These three processes form a basaltic melt in the Asthenosphere which is less dense than the Asthenosphere and therefore rises. The basic composition of the melt of all three is not that different at all. The big differences between the three processes are the physical properties of the magma. \nWhen the magma rises in the crust, the pressure on the magma lowers and the temperature stays almost the same (magma cools really slowly, except at earths surface)! The magmas without fluids when rising in the earths crust will stay fairly 'liquid' and not lose a lot of material by crystallization, because decompression and the same temperature favor a liquid state of the magma. \nMagma which formed with fluids (Subduction Zone) has other properties. It's temperature is lower and it could only become a magma because of the polymerization by the fluids added. When this magma rises it also suffers a decompression and the temperature stays almost the same. But the fluid in it will lead to a magma differentiation because by rising the magma gets closer to the solidus curve. The wet solidus curve has a completely different shape than the dry solidus (",
"https://en.wikipedia.org/wiki/Partial_melting",
"). Therefore by rising the magma crystallizes and loses some minerals leading to a granitic melt in the end. This is also the reason why we have continental crust and why continental crust can not be subducted (less dense)."
] |
[
"What is it called when the products of a chemical reaction inhibit further production of the same chemical? Same with when the products of a chemical reaction facilitate more production of the same chemical?"
] |
[
false
] |
The phrase sympathetic and parasympathetic keep coming up, but I an't find them in the right context.
|
[
"In biology and especially when talking about metabolic pathways, you would use the terms negative feedback and positive feedback, where a metabolite allosterically regulates the activity (positively or negatively) of an enzyme earlier in the pathway. For example, the first step of glycolysis is the conversion of glucose to glucose 6-phosphate by hexokinase (in muscle). Hexokinase is inhibited by a G6P, an example of negative feedback.",
"When metabolites impact the activity of enzymes 'downstream' on the pathway, we call that feedforward activation or inhibition."
] |
[
"There are two ways to interpret this question - from a kinetics standpoint, or from a thermodynamic standpoint.",
"A product can ",
" the reaction that produced it, so in that way it is \"facilitating more production\". This is known as ",
"autocatalysis",
". Likewise, there is ",
"autoinhibition",
" as well.",
"From the thermodynamic side of things, you can say that in all equilibrium reactions, the presence of products \"inhibit\" further production, because the formation of products brings the reaction closer to equilibrium. There isn't really a strong analogous situation for the opposite case thermodynamically speaking. The closest I can think of are reaction products that don't stick around for equilibrium to establish - so they don't facilitate more production, per se, but simply don't inhibit it. An example of this are ",
"decarboxylation reactions",
". Usually the reaction occurs in a solvent, so the carbon dioxide that forms bubbles away, leaving \"room\" for more carbon dioxide to form and the reaction to proceed. Such a reaction is considered entropically driven."
] |
[
"You described the chemistry--I might chime in with some biology as well.",
"While not directly thermodynamically inhibited, certain proteins synthesized in organisms follow whats called a ",
" substrate-level inhibition system. I can't remember if all organisms have this, but certain organisms produce enzymes and proteins that are involved with the synthesis of Tryptophan.",
"Tryptophan itself inhibits the first or second step in its own synthesis. It self-regulates by slowing down its own production after it'd been produced."
] |
[
"Why does Venus rotate in the opposite direction to the other planets in our solar system?"
] |
[
false
] | null |
[
"This is due to the impacts by asteroids in the early years of their formation.",
"No, this is generally ",
" the consensus answer any longer in planetary science.",
"Some 30 years ago, this was the standard explanation why Uranus' and Venus' odd axial tilts were the result of giant impacts. Bear in mind, though, that this was relatively soon after the Apollo missions had confirmed that our Moon had formed via giant impact (although there's evidence now that even this may not be so straightforward).",
"So, this may have been a case of \"when you have a hammer, everything looks like a nail.\" Giant impacts started being used to explain everything a bit odd in the solar system. Uranus is weirdly tilted? Must've been hit by something! Huge cliffs on Miranda? Must've been hit by something! Weird two-tone coloration on Iapetus? Must've been hit by something! Neptune has a mysterious source of internal heat? Must've been hit by something!",
"This hypothesis started waning about 15 years ago when impact simulations were getting good enough to show that it's exceptionally difficult to produce an impact that's large enough to tilt Uranus but not completely obliterate the planet. It's a little more likely to do this with multiple impacts, but still not exactly easy.",
"The most likely scenario at this point is that Uranus had some kind of gravitational near-miss, enough to induce a tidal torque that could turn its axial tilt. There's also some evidence that this scenario would require ejecting some mass in the process, possibly a big moon. The remaining moons would eventually fall in line with the new inclination angle of Uranus' equator due to tidal forces acting over billions of years. This explanation also has the neatness that it may explain why Uranus doesn't have a big moon, which we'd expect from most formation scenarios; moreover, there are at least some formation scenarios that suggest Uranus and Neptune swapped orbits early on, providing ample opportunity for this gravitational near-miss to occur.",
"For Venus, meanwhile, it turns out you can get the planet to slow down to almost a standstill with just solar tides acting on the thick atmosphere when applied over the age of the Solar System. (Not only does Venus rotate backwards, but it also does so exceptionally slowly, with one rotation every 243 days.) Explaining the slight backwards motion imposed on top of this virtual standstill is still a little tough, though there's some hand-wavy explanations that additional tidal torque induced by Earth might do just that."
] |
[
"This is due to the impacts by asteroids in the early years of their formation.",
"No, this is generally ",
" the consensus answer any longer in planetary science.",
"Some 30 years ago, this was the standard explanation why Uranus' and Venus' odd axial tilts were the result of giant impacts. Bear in mind, though, that this was relatively soon after the Apollo missions had confirmed that our Moon had formed via giant impact (although there's evidence now that even this may not be so straightforward).",
"So, this may have been a case of \"when you have a hammer, everything looks like a nail.\" Giant impacts started being used to explain everything a bit odd in the solar system. Uranus is weirdly tilted? Must've been hit by something! Huge cliffs on Miranda? Must've been hit by something! Weird two-tone coloration on Iapetus? Must've been hit by something! Neptune has a mysterious source of internal heat? Must've been hit by something!",
"This hypothesis started waning about 15 years ago when impact simulations were getting good enough to show that it's exceptionally difficult to produce an impact that's large enough to tilt Uranus but not completely obliterate the planet. It's a little more likely to do this with multiple impacts, but still not exactly easy.",
"The most likely scenario at this point is that Uranus had some kind of gravitational near-miss, enough to induce a tidal torque that could turn its axial tilt. There's also some evidence that this scenario would require ejecting some mass in the process, possibly a big moon. The remaining moons would eventually fall in line with the new inclination angle of Uranus' equator due to tidal forces acting over billions of years. This explanation also has the neatness that it may explain why Uranus doesn't have a big moon, which we'd expect from most formation scenarios; moreover, there are at least some formation scenarios that suggest Uranus and Neptune swapped orbits early on, providing ample opportunity for this gravitational near-miss to occur.",
"For Venus, meanwhile, it turns out you can get the planet to slow down to almost a standstill with just solar tides acting on the thick atmosphere when applied over the age of the Solar System. (Not only does Venus rotate backwards, but it also does so exceptionally slowly, with one rotation every 243 days.) Explaining the slight backwards motion imposed on top of this virtual standstill is still a little tough, though there's some hand-wavy explanations that additional tidal torque induced by Earth might do just that."
] |
[
"Another theory is they may have completely flipped 180 degrees. Moons stabilize planet tilts and Venus has no moon to help with that. "
] |
[
"Does exercising in the morning really increase your metabolism all day vs exercising any other time?"
] |
[
false
] |
I've asked this question before and got no responses (~1 month ago), so I figured I'd try again. I hear this claim often spouted here on reddit and is "common" knowledge among gym goer's, but it never made sense to me. I don't see how the metabolic response induced by exercising would be any different depending on the time of day.
|
[
"Nope. It's a myth, like locational fat burning (eg. doing crunches to burn tummy fat) or burning more calories at a lower heart rate. ",
"Metabolic rate spikes after exercise but then tails off after a few hours back down to slightly above the BMR for up to a couple of days regardless of time of day you start the exercise. The amount it spikes by is pretty closely related to how hard you exercise. You perform better later in the day (optimally around 6pm), and you have the best mix of temperature and hormones at that time to avoid injury in comparison to training with cold muscles first thing in the morning too.",
"HOWEVER ",
"There are a bunch of studies that show that exercise first thing in the morning is more habit forming than exercise later in the day. Personally I don't believe in relying on some motivation or inspiration to achieve an ends. I think you have goals and you train yourself to have habits that satisfy those goals. You don't need to motivate yourself to get out of bed and hit the gym, it's just what you always do. Which is why I tend to train first thing, despite the slightly elevated risks. "
] |
[
"Myth Confirmed : ",
"http://www.ncbi.nlm.nih.gov/pubmed/20837645",
"\nTLDR:while the morning isnt a factor, working out in a fasted state is and that is most likely to be true in the morning. Only the group that exercised before breakfast gained almost no weight and showed no signs of insulin resistance. They also burned the fat they were taking in more efficiently.",
"All your injury prone worrisomeness can be eliminated by properly warming up and stretching. You should be doing this morning, noon, or night anyway."
] |
[
"I think the emphasis should be on ",
" and not stretching, in my personal experience. Muscles don't really ",
" all that much, only your ligaments. You don't want \"loose\" ligaments."
] |
[
"How are temperatures as high as 4 trillion Celsius contained?"
] |
[
false
] |
Doesn't a temperature that hot melt everything around it?
|
[
"Searched",
"Relevant ",
"discussion",
"Original question by ",
"speed_is_all_I_need",
"Take the ",
"Z-Machine",
" for example. How do you contain 6.6 billion degree temperatures? I feel like it would melt nearly anything in an instant. What materials would be needed to create a heatsink that could deal with those incredible temperatures?",
"Top comment courtesy ",
"iorgfeflkd",
"These things are generally confined by magnetic fields in vacuum. Heat doesn't transfer through a vacuum, so the interior of the chamber doesn't get melted by the heat of the plasma.",
"In collisions at CERN and Brookhaven National Lab, temperatures have reached the trillions of degrees, but it's only in the volume of an atom that things get that hot."
] |
[
"Since Temperature is an average quantity over many molecules, how can they have a temperature over the volume of one molecule? I understand a huge kinetic energy but not a Temperature."
] |
[
"It says the volume of an atom, not referring to a single molecule. The proton beams at CERN send many protons around at once, not just one. The average kinetic energies of these protons define the temperature. ",
"All this is saying is that these protons only take up the volume of about 1 atom, which is a little vague but makes sense, since common atoms contain many neutrons and protons. "
] |
[
"Is it possible to know things in your dreams that you don't know in real life?"
] |
[
false
] | null |
[
"The second one. It's possible to access memories/knowledge that you might not be able to access (or at least not find yourself in the correct context to access) while awake."
] |
[
"That is essentially what our friend darwin2500 said."
] |
[
"That is essentially what our friend darwin2500 said."
] |
[
"The Mormon Church Released pictures of the \"Seer Stone\" reportedly used by Joseph Smith. Can you make a geological analysis of it?"
] |
[
false
] | null |
[
"I'll give this a whirl, it's not everyday that one gets first pick at looking at a sacred relic.",
"First, the shape. That is a prolate ellipsoïd with very well devellopped rounding. There is definitely no faceting such as you'd find on a glacially derived cobble. The shape, roundness and exteranal smooth texture are consistent with transport in a fluviatile system (in other words, that pebble was picked out of a stream or from fluviatile deposits).",
"Also a word about the polishing and patina. Either that rock was waxed, laquered or varnished in some way, or else it was handled ",
", enough to acquire that shiny yellowish patina.",
"Now, the material. The quality of the picture is so-so. I'd be all over that pebble with a handlens before I said anything with confidence. From what I see in the pix, I'm thinking more along the lines of metamorphic than straightforward sedimentary (although I'm leaning towards meta-seds). That comes mostly from the wispyness of the lamination, the sharpness of the contacts on both sides of those quarto-feldspathic laminations (no grading). But I'm not setting this down as a definitive ID. So: ",
" metasedimentary (Say, a metawacke or somesuch), conditional to a ",
" examination with a handlens. What I'd be looking for with the handlens is whether it is made of rounded grains (And thus a Sandstone) or whether it was made of interlocking crystals (which would make it metamorphic in this case). I'd also look for evidence of deformation and a comple of other processes (is that ",
" sedimentary lamination? could it be metamorphic ribboning or even migmatisation?)",
"You may also want to give the rock a whirl on ",
"/r/geology",
" and see what we might have to say about it there. Perhaps some of my colleagues which are more familiar with the geologic particulars of the american mid-west will feel some familiarity with that specific lithology and have an Eureka moment. I'm pretty sure ",
"/r/askhistorians",
" might have a ball commenting on this as well.",
"Finally, I'm by no means well informed on Mormonism, but you metionned this is called a \"Seer Stone\"? Any chance that might be in relation with the fact that when looked at perpendicular to the laminations, the intersection of these laminations with the surface of the pebble generates a concentric pattern of ellipses, somewhat like an eye? Would you perchance happen to know if early Mormons had any cultural dealings with the \"Doctrine of signatures\" (the belief that the properties of things were influenced by their appearance)?",
"EDIT/UPDATE: ",
"To all users mentionning the stone is supposed to have been picked up in NY state and not the american midwest; thanks for bringing that to my attention. As previously stated, I claim no familiarity with the history of Mormonism, just geology. ",
"From what I've been made to understand, the provenance of the stone is a matter of historical interest as it is referred to in Smiths texts. What I make of that is that it's sourcing in a well upstate NY is a hypothesis to be tested. But there is only so much one can say without direct access to the specimen. Let it just stand that while there is nothing I can see from OPs pix which is inconsistent with a sourcing of that pebble in upstate NY (or a well for that matter), there is nothing either to exclude other origins. ",
"Some users have suggested other origins which might perhaps be testable. One of the most intriguing was set forth by ",
"/u/WRCousCous",
", who suggests based on his experience with amerindian artifacts that the patina and general aspect of the pebble might be consistent with a type of artifact known as a \"thunder egg\". Apparently this would fit in with a documented fascination by Smith with native artifacts and culture.",
"Anyways, this is a quite enjoyable discusssion for I which I thank contributing users, and an excellent exemple of something I have always deeply believed: even the smallest stone can be an object of intense interest and fascination."
] |
[
"\"I will now give you a description of the manner in which the Book of Mormon was translated. Joseph Smith would put the seer stone into a hat, and put his face in the hat, drawing it closely around his face to exclude the light; and in the darkness the spiritual light would shine. A piece of something resembling parchment would appear, and under it was the interpretation in English. Brother Joseph would read off the English to Oliver Cowdery, who was his principal scribe, and when it was written down and repeated to brother Joseph to see if it was correct, then it would disappear, and another character with the interpretation would appear. Thus the Book of Mormon was translated by the gift and power of God, and not by any power of man.\""
] |
[
"RE patina: not a geologist, but I have worked on a lot of antique wooden objects, and the thing really does look like it's been varnished, and that varnish has , typically, yellowed with age. Whether it's shellac/ spirit varnish, a long-oil varnish, or simply years of being shined with a bit of linseed oil, I don't know. And I doubt they'd let me in to dab at the thing with some cotton swabs and solvents to find out. But it'd be very common for somebody to varnish this, so they could wipe it clean every so often."
] |
[
"What stops an electron from falling into the protons within an atom?"
] |
[
false
] |
what stops the negatively charged atom from being attracted and falling towards the positively charged protons?
|
[
"Because of quantum uncertainty, the electrons are already as close as possible to the nucleus.",
"People sometimes explain this as an ",
" consequence of quantum mechanics. This is far from obvious; for example it would be false if our Universe had 4 spatial dimensions, and electrons ",
" fall into nuclei even with quantum mechanics.",
"For simplicity, let's consider the hydrogen atom. I'm gonna work with orders of magnitude here, so I'll leave out some numerical constants.",
"So, the hydrogen atom essentially wants to lose energy. It will lose energy by emitting radiation until it has reached its lowest possible energy state, if such a state exists. In classical electrodynamics, such a state doesn't exist: the electron and proton continue spiraling in emitting greater and greater amount of energy. In a finite time p and e join having emitted an infinite burst of energy. This clearly does not happen IRL and is quantum mechanics that comes to the rescue. But before we deal with it it's important to understand that e does not necessarily move towards p because there is an attractive force. e just wants to lose energy, that's all, and it will do so until it has energy left.",
"Energy is potential + kinetic. Potential energy is what yields the attraction; between electron and proton at a distance Δx this energy is",
"E_p = - e",
"/Δx",
"Note this energy is ",
" and decreases as the electron is brought closer to the proton. So if we were to just make this as small as possible we would obtain that the e wants to get near the p, which makes sense.",
"But there's also kinetic energy. This is",
"E_k = p",
"/2m",
"Where p is the linear momentum of the electron and m is essentially the mass of the electron (you can derive this from E_k = 1/2 mv",
" and p=mv).",
"Now, since classically we can change Δx and p to pleasure it looks like we can make E_k zero by sending p to 0 and E_p arbitrarily negative large by shrinking Δx. So the atom should be able to lose infinite energy and e and p join, just like I said above.",
"In quantum mechanics, however, we will reach a limit in the form of uncertainty. Heisenberg's uncertainty principle is something like Δx Δp > hbar. So trying to confine the electron in a small space is gonna bound p to have a typical value not smaller than p ~ hbar / Δx. ",
"This changes things. Rewriting the total energy using the HUP:",
"E = E_p + E_k = - e",
"/Δx + hbar",
"/(2m (Δx)",
")",
"= - A (Δx)",
" + B (Δx)",
"I've defined the positive constants A and B; their value is not important. You can see that this function attains its minimum at a distance Δx different than zero. You can just plot it in Wolframalpha, choose any random (positive) values for A and B and you'll see what I mean. So the electron will not join the proton; it will lose energy through emission of radiation until it is in the lowest energy state which has it at a nonzero distance from the proton. If you did all the calculations, this nonzero distance would be on the order of the Bohr radius.",
"Intuitively, to recap, the electron will get closer to the proton until it's localized in a region so small the uncertainty in momentum grows, and this makes the kinetic energy higher much faster than the potential energy gets lower. So this \"uncertainty force\" pushes back against the Coulomb attraction. Equilibrium is found at around the Bohr distance.",
"That's of course a very heuristic argument. You redo the calculation in actual QM (instead of what we did here, which is a semiclassical/orders of magnitude analysis) and more or less the same comes out, but you also know the exact values. But all the essential reasons for the electron not to fall in the proton are above.",
"(Bonus round: why doesn't uncertainty prevent collapse if there are 4 or more spatial dimensions? Well, because the Coulomb potential has a different form. It has behaviour (Δx)",
" where D are the spacetime dimensions. The \"uncertainty energy\" always goes as (Δx)",
". So the thing above does not work. In general one should be wary of handwaving the \"uncertainty fixes all divergences\" argument because in many physical systems it can be completely wrong.)"
] |
[
"Wow!!"
] |
[
"Am I being annoying if I ask how?"
] |
[
"Why can I tell when a tv has been turned on from really far away, even when nothing is playing on it?"
] |
[
false
] |
In sixth grade we would often watch a short educational film after returning from "specials" (gym and the like) and the tv would alread by setup when we got back. I began to notice that I could sort of 'hear' that the tv was on in the classroom, long before we got there. The best way I can describe it is that there's just sort of a buzz that I'm aware of, and that means a tv is on somewhere. remember nothing is playing on the tv. This happens even if the tv is just on a black input/line/tv-video screen. Anyone know what's going on here? Can everyone do this?
|
[
"A TV's electronics generate around 500 lines at 30 frames per second, or ~15000 Hz, which is at the upper threshold of human hearing. Lots of adults can't hear the noise due to high frequency hearing loss.",
"Edit: I'll add that this is similar to the noise of power transformers - i.e. the so-called \"60 Hertz Hum\""
] |
[
"This effect pisses me off so much. People who can't hear it often end up leaving their TVs on and it drives me mad. But then I look like a nutter turning off an off television!"
] |
[
"Sorry if this is too far off topic. I attended a manufacturing/automation expo as a field trip during my engineering undergrad. There was a guy showing off sonic welding equipment for joining plastic parts. As soon as he turned it on it sounded like a TV, but loud enough that I instantly recoiled and covered my ears. The guy chuckled and said something like \"all the kids do that\" and mentioned that he couldn't hear anything."
] |
[
"Do LCD monitors emit outside the visible spectrum?"
] |
[
false
] |
Chemist here, had someone ask me to tell them what wavelengths are emitted by a computer monitor. (They are doing research on eye disease) I don't have a set-up that will allow me to do emission spectroscopy on anything as bright as a computer monitor, or even an iPhone.
|
[
"LCD spectra would be limited to the type of backlight used. CCFLs are the most common, so you can look up the spectra for those. LEDs should generate even less non-visible light due to their higher efficiency."
] |
[
"Basically what Cookie has already said. The only light generating element of an LCD is the backlight. What's in front is a couple of polarizers, some liquid crystals that allow light through or not depending on applied voltages, and a small window over each 1/3 pixel of RG or B. ",
"http://www.youtube.com/watch?v=jiejNAUwcQ8"
] |
[
"Truthfully? Because I don't know how I'd explain what I was up to! ;) ",
"The main problem is the instrument I have access to does UV-vis absorption, not emission. I don't want the source light to reflect off the iphone and register on the detector. I also don't want to overload the detector. ",
"The other issue is that the person who asked me for the spectrum wants to use it to claim that the light from computer monitors caused their eye disease."
] |
[
"Physics and Psychology of Music Question: Why do the lengths between the frets on a guitar get smaller and smaller?"
] |
[
false
] |
So, I know that the sensation that humans hear as pitch corresponds to the frequency of the sound wave - a note that may considered to be high/low has a sound wave with a higher/lower frequency than the sound wave of the origin note. In western music theory the difference between pitches (or the interval between pitches) is quantized in units of whole steps and half steps (with two half steps making a whole step). To my ear, the half step (or semitone) between both A4 (440 Hz) and A4 (466.16 Hz) and, say, D5 (587.33) to D5 (622.25) is the same "distance," musically. But obviously, by either doing the math or looking at one's guitar fretboard* (example ), the actual frequency difference between those sets of notes are not equal. Why? What is the difference between musical pitch and physical frequency? Has spending my entire life listening to only music built on western music theory conditioned my brain to recognize those frequency differences as "half notes?" General comments on the connection between the physical phenomena of music, its theories thereof, and its perception by humans are also appreciated. *The frets on a guitar are equivalent to the keys on a piano. A specific fret or key corresponds to a specific note (frequency).
|
[
"Frequency is related to pitch on a logarithmic scale...each time you raise a pitch an octave, the frequency is doubled. That is why the difference between your A and A# is different than that of the D and D#. To compensate on a guitar, the fretboard must also be built \"logarithmically\". ",
"Guitar#frets"
] |
[
"Adding on to this, when we perceive pitch differences, we are actually looking at the ratio between the two pitches, rather than the difference between them. For example, the two notes of a P5 interval are in a ratio of 2:3. So A4:E4 would be 440:660, while A3:E3 would be 220:330. The difference between the frequencies of the pitches in each case is variable, while the ratio remains constant."
] |
[
"This doesn't answer the question, but is pretty relevant: ",
"https://www.youtube.com/watch?v=i_0DXxNeaQ0&feature=youtube_gdata_player"
] |
[
"Question about calories"
] |
[
false
] |
[deleted]
|
[
"You ask a good question, one I wondered and researched. First, let me say that this is a hard question to find answers on. But, I will share with you what I found. ",
"Today, the way it is found out is by referencing look up tables. Different \"ingredients\" are known to have certain calories (by ingredients, I mean things broken down to categories like fat and protein, etc). So, you know your food has a certain amount of fat, protein, sugar, etc and then you reference the table. But the question remains, how was that table made to begin with? ",
"People will say that the calories of a food can be determined by burning the food in a calorimeter and measuring the amount of calories is released in that burning process. However, while this is partially true, it isn't the entire story. For instance, cellulose is completely indigestible, thus is zero calories; however, it will burn and release heat. So, how did they work this out? In the grossest way possible. They burned some food, measured the calories. Then, they fed the exact same food to a person, collected his feces, then burnt his poop. The difference in the heat (calories) is how many calories your body absorbed. "
] |
[
"No no, a scientific endeavor like this takes the cooperation of ",
" researchers."
] |
[
"They burned some food, measured the calories. Then, they fed the exact same food to a person, collected his feces, then burnt his poop. The difference in the heat (calories) is how many calories your body absorbed.",
"What you're saying is: somebody probably spent 10 years getting their PhD in biochemistry and then proceeded to burn poop for a living. "
] |
[
"Where does the gas go when a person takes a bean-o?"
] |
[
false
] |
[deleted]
|
[
"Beano contains an enzyme (",
"Alpha-galactosidase",
"), which breaks down complex sugars into simpler sugars which can be more thoroughly digested, producing less gas."
] |
[
"Does this mean Bean-o helps you digest and absorb food more efficiently?"
] |
[
"Right. The gas comes from complex sugars making their way into your large intestine, where bacteria that naturally live in your gut consume them, producing carbon dioxide as a by-product. If the sugars are broken down, then they'll be absorbed by your digestive system, and there will be less food for the bacteria to consume, and they'll produce less gas. "
] |
[
"How do we know that the universe is expanding everywhere, as opposed to just around us?"
] |
[
false
] |
One of the ways that inflation is traditionally taught in schools is to half-inflate a balloon, draw "galaxies" on it, and then further inflate it. I realized suddenly recently that this "view" of the universe assumes that we, the observers, are at the center of the balloon. I mean this in the sense that all of our instruments with which we've gathered our entire understanding have only existed (roughly) within the confines of our solar system, and so instrumentally we've only established that the universe around us is expanding. I'm curious to know on what grounds we reason that the universe everywhere is expanding. It seems like a reasonable assumption to make, and presumably it matches with our observations and models. I guess I'm wondering whether the hypothesis of local inflation (or inflation only around large masses) is something that's been specifically tested/reasoned about. I.e. is inflation uniform at cosmic scales, or "spotty" (up to the extreme hypothetical limit of "only one spot, and you're in it").
|
[
"You've missed the point of the balloon analogy. In that example, we aren't at the center of the balloon, we're on the surface as well, in a curved 2D universe. Ignore the volume of the balloon. If you pay attention to the surface, you'll notice that every point on the surface is moving away from every other point, so regardless of where you pick the observation point, you will see all the surrounding points moving away from you."
] |
[
"Just, to start off, two quick points. \"Inflation\" and \"expansion\", despite being synonyms in English, are not actually the same thing in the lingo of cosmology. Expansion is the expansion of space that underpins Big Bang cosmology. Inflation refers to a specific epoch of expansion that is hypothesized to have happened in the first fractions of a fraction of a second after the Big Bang where the universe expanded in a very specific way (exponentially) driven by a quantum field (often called the \"inflaton field\"). ",
"Secondly, in the balloon analogy, we're not ",
" the balloon but rather one of the dots on the surface. Big Bang cosmology is all about the geometry of space and how it, and distances within that space, change in time and the point of the balloon analogy is to invoke an intuition of geometric structure changing in time by exploiting the everyday intuition of having a 2D object embedded in a 3D space. It is not an aspect of Big Bang cosmology that geometric expansion is tied to being embedded in a higher dimensional space, but such a conceptual trick does resonate very well with our fleshy, squishy little ape brains. Thus the utility of the analogy.",
"However, you are definitely on to something. ",
" of the key aspects of Big Bang cosmology is that the universe is expanding and thus any and all points in the universe are getting further apart and thus us, on Earth, see all distant points with an inherent recessional velocity (i.e. a velocity away from us) and that velocity getting greater, with a clear mathematical relationship, the farther away they are. There are then two conclusions to be made based on that data alone, either the universe is expanding, or we're somewhere special and everything is moving away from us. Maybe we have bad breath. Both equally fit that data. However, that isn't the only evidence we have for the former, in fact it's arguably not even the most compelling. The fact that at all points in the sky we see a distinctive type of light, called the Cosmic Microwave Background Radiation (the CMB) with a certain distinctive distribution (what's called Planck's Law), is exactly in line with the first picture but not the second. Furthermore, we have the relative abundances of the chemical elements and the time-dependence of the fundamental scale of \"clumpiness\" of things in the universe. Both fall not just qualitatively but quantitatively in line with the notion of Big Bang cosmology, and would have no explanation in the theory of \"we're in a special spot and have bad breath so everything is moving away from us, the further away the faster they're leaving... for reasons\"."
] |
[
"For starters, because our measure of cosmic expansion couldn't really tell the difference between the center of the universe being here on earth or it being some other planet in this galaxy, or indeed even in our galactic cluster.",
"Secondly, because there is really nothing special about 'here' that would lead us to think that it really is the center of the universe. By far the simplest explanation is that 'here' is effectively identical to everywhere else."
] |
[
"At what scale would the \"hold my finger over the tip of a straw and pick up water\" effect no longer work?"
] |
[
false
] |
All kids play around with the straw in their drink and hold their finger over the tip of it and pick up some of the fluid in the straw and then release their finger dropping it back into the cup. This is due to a combination of the vacuum created in the straw and the surface tension of the liquid at the end of the straw I presume. At what scale would this no longer work? Could a giant space alien with a giant straw dip into the pacific ocean and grab a bunch of water with its finger over the tip of the straw? For the liquid in question lets try using fresh water to keep it simple. Im not sure how much difference salt water makes in the question.
|
[
"At about thirty-four feet, which would correspond to about fifteen pounds per square inch of pressure at the bottom of the straw. Atmospheric pressure at sea level is about 15psi, and that is what is keeping the water up the straw; pull the straw higher than 34', and an empty space will begin to form above the water at the top of the straw.",
"EDIT: I answered the wrong question!"
] |
[
"OP, maybe you should clarify the question. I read it as though you're asking about the situation where you lift the end of the straw entirely out of the water, and the water in the straw stays in because of the narrowness of the straw. If you use a wider container, like if you cut the ends off a bottle, stick the bottom in water, put your palm over the top, and lift the whole bottle out of the water, then the water just runs out of the bottom. So how wide can the straw be before the water just runs out of the bottom when you lift it entirely out of the water. Is that your question? If so, everybody is answering the wrong question."
] |
[
"Thats exactly what I meant. I thought the phenomenon of kids playing with the liquid in their straw was clear. I'll add an edit to the post to clarify."
] |
[
"Biological question concerning the relationship between mitochondria and it's prokaryotic homologies."
] |
[
false
] |
If a prokaryote, let's say a bacteria, truly is closely related to the mitochondria, then would that mean antibiotics targeting the ribosomes of bacteria would also target mitochondria? Or is the genetic differences too great?
|
[
"Yes! See ",
"Zyvox",
" for one example. Mitochondrial ribosomes are actually quite similar to their prokaryotic brethren. It's true that there are some exceptions to the universal genetic code that we've only found in mitochondria, but this has nothing to do with the ribosome; rather, these differences are due to mutations in the tRNA and amino-acyl-synthetase genes, which actually do the work of interpreting codons and assigning amino acids. The ribosome itself doesn't have any defense against a mischarged tRNA."
] |
[
"If I remember correctly: Some potential antibiotics have been rejected because they hurt mitochondira too."
] |
[
"The differences are too great. The differences are so large that mitochondrial ribosomes have a different genetic code from the one that is found in prokaryotes and eukaryotes. However, the similarities in broad strokes between mitochondria and prokaryotes are still very large."
] |
[
"How do we determine and measure the average temperature of Earth?"
] |
[
false
] |
I assume that the average temperature of Earth changes based on multiple variables: Distance from the sea/ocean, altitude, hours of daylight, time of day etc. What are the criteria for measuring the average temperature of Earth? I also assume that each nation gives their own averages, but how do we determine the weights for each country? For example Russia is a lot bigger than Luxembourg, so Russia should have more variation in temperatures and their landmass should represent a larger proportion of the average temperatures.
|
[
"I would bet each principal investigator of global temperature changes would calculate that in a unique well-reasoned way. Your question may be best revised to be \"What well-regarded agencies and scientists are there that measure global temperature?\" And then looking into/asking them their methods.",
"Here's a good video on satellite measurements ",
"https://www.sciencelearn.org.nz/videos/118-satellites-for-atmospheric-measurements"
] |
[
"I think OP is interested in the averaging method more than the measurement method. In which case, you could interpolate to model a matrix of values across the whole earth surface at some resolution, then do arithmetic or geometric average. There are some other built in assumptions about time resolution, vertical profile, transport parameters, etc.",
"Example paper:\n",
"https://journals.ametsoc.org/view/journals/clim/31/5/jcli-d-17-0150.1.xml"
] |
[
"Exactly. ",
"Science is often really precise, but when you have multiple different organizations measuring temperature with different standards, how do we determine the average? ",
"For example, I imagine that we have more datapoints from land than oceans (because it is easier to stick a measuring tool on ground than in sea), would that give realistic estimate of global average temperature?"
] |
[
"What would the day/night cycle be like living on the moon?"
] |
[
false
] | null |
[
"There is no \"dark side\" of the Moon. There are permanently shadowed craters near the south pole (maybe the north as well, I'm not sure), but that doesn't really constitute a side. What's often called the \"dark side\" of the Moon is better called the far side of the Moon - the side not visible from Earth (it's actually less than half of the surface of the Moon that we can't see, but that's not important right now). This side has the same sort of day-night cycle as the near side: about four weeks.",
"No. That would be a lunar eclipse. A new Moon is when the Moon is located roughly between the Earth and the sun. The sun is shining on the far side of the Moon, and not on the near side. We can only see the near side, and that side is in the shadow of the Moon during the new Moon, making it dark and therefore difficult to see from Earth.",
"Yes. It's an even better source of light on the Moon because of its greater size and higher albedo (a measure of how much light is reflected by the object in question).",
"About four weeks long. The Moon is tidally locked with the Earth, which means that the same side always faces the Earth (with some very small variation that we'll ignore right now). The Moon therefore takes as long to rotate once around its axis as it takes to revolve once around the Earth - about four weeks. This makes days and nights two weeks long apiece. So the city in question would have two weeks of day and two weeks of night. "
] |
[
"Re: #2: The Earth is between the Moon and the Sun every 28 days. This is during a full Moon, and that's when a lunar eclipse can happen. The reason there isn't a lunar (or solar) eclipse on every orbit of the Moon is because the Moon's orbit doesn't put the Moon directly in the line of sight between the Earth and Sun every month. The orbit is slightly inclined to the Earth, and most of the time, it's either outside the shadow of the Earth or its shadow doesn't land on the Earth.",
"Re: #4. The Earth would be bigger, but I don't know how noticeably bigger it would be. The Earth is about 4 times the diameter of the Moon, so I suppose the Moon would appear to be about 4 times larger across the sky. While it sounds like a lot, I have to wonder if it wouldn't seem all that much bigger when actually on the Moon. I wonder if any Apollo astronauts commented on that..."
] |
[
"Thank you, very informative!",
"Re: #2 - I'm having trouble wrapping my mind around this (probably because I don't have a visual)... the moon orbits the earth every ~28 days, right? So how is it that the Earth isn't between the moon and the sun every 28 days?",
"Re: #4 - How much of the sky would the earth take up on the moon? Like the moon takes up a relatively small part of the sky on Earth... the Earth would be a lot bigger on the moon, right? Would that not have an effect on the day/night cycle, since the Earth literally never leaves the sky in that city? Would it not fairly frequently block out the sun?"
] |
[
"Why do banana peels turn brown so much faster once it has been peeled?"
] |
[
false
] | null |
[
"So I looked it up and apparently the contact with oxygen causes an enzyme called polyphenol oxidase (there are other enzymes too) to increase/start chemical reactions that produce melanin. Melanin is a strong pigment. Interestingly melanin is the same molecule that give people skin pigment, which protects us from UV rays.",
"http://www.ncbi.nlm.nih.gov/pubmed/6794984",
"http://en.wikipedia.org/wiki/Polyphenol_oxidase",
"https://suite.io/helga-george/3mq829r",
"Side note: I guess this means pigment was evolved and highly conserved a very long time ago, when animals and plants had a common ancestor.",
"Also, Im wondering if this rapid increase in melanin is a response by plants to produce melanin which can protect them from the harmful effects of UV rays (the oxygen being a signal that sensitive parts of the plants ar ein open air)"
] |
[
"Polyphenol oxidases (PPOs)! The same class of enzyme causes browning in a lot of soft plant tissue in response to damage, like the browning in apples, potatoes, etc. after bruising or cutting. The putative function is to protect the plant from pathogens that might enter during tissue damage. ",
"Somewhat related tangent: a company called Okanagan Specialty Fruits has actually developed ",
"a non-browning line of apples",
" by transforming them to induce RNA interference across a bunch of different enzymes in the PPO family. If you're not familiar with RNAi, the basic idea is that you induce the plant cells to produce a small piece of RNA that it thinks is a foreign piece of RNA. The cells degrade the small RNA, as well as similar looking RNA. So these apples are genetically engineered to produce extra RNA that looks like the PPOs, so the cells also degrade the RNA that would be translated into PPO proteins. I met the the founder of the company a few months back, and he was a really cool guy with a cool consumer-based approach towards biotech."
] |
[
"That is a very nice observation, I wonder if the same would happen in a vacuum. "
] |
[
"Can you create a machine learning algorithm to create a computer virus?"
] |
[
false
] |
So I have seen a lot of machine learning videos, including , , , . Then, I also saw . It made me think about since there are so many ways to produce machine learning algorithms in so many disparate fields and to do so many things, could you have an xkcd style virus-farm and try to use machine learning to look for security holes? The MarI/O simulator found a glitch in Mario, on so it might not be too far a jump to consider that a really advanced neural network might be able to evolve a way to hack computer systems? If so how would it work? Note: . I just thought it would be an interesting idea.
|
[
"Sure. Check out the DARPA cyber grand challenge for an example of fully automated exploit creation. They didn't use ml but in principle it would work.",
"But remember that ml isn't magic. It is sophisticated curve fitting. So I wouldn't worry about this having any worrisome implications about dystopias or whatever."
] |
[
"The successful teams in CGC used a combination of random fuzzing (trying random inputs to programs to see what happens) and a technique called dynamic symbolic execution, which tries inputs and then carefully considers how to change those inputs to force the code to do something different next time.",
"The details of dynamic symbolic execution are, unfortunately, complex. You aren't going to really understand what is going on without some serious background in SMT solvers and some knowledge of how your typical system exploit works. ",
"In principle, you could use machine learning driven fuzzing. This would train some ML model to produce input perturbations that maintain \"valid\" input patterns but hopefully test other stuff. This is useful for testing parsing code but generally isn't an incredibly effective technique compared to other approaches. "
] |
[
"Huh. I looked it up, but only found some simplified articles, that don't explain how the hacking boys work. So how do they?"
] |
[
"Did scientists know when the Trinity Atomic test occurred?"
] |
[
false
] |
Obviously the scientists involved knew what was going on, but what about other scientists monitoring other experiments? What did they think it was?
|
[
"If you don't get an answer here, you could try ",
"/r/askhistorians"
] |
[
"That is an excellent point about other explosions going on at the time. "
] |
[
"I thought of that, but I figured there might be more insight from the science community on how someone may have noticed this huge seismic event at the time. ",
"I'll give it a day here then head over that way."
] |
[
"What would the W and Z mass be without Higgs ?"
] |
[
false
] |
Just like technicolor, already in QCD the exchange of gluons in the spin zero, isospin zero channel is attractive, causing the formation of a quark condensate, which dynamically breaks chiral symmetry : SU(2)_L x SU(2)_R -> SU(2)_V The corresponding would-be Goldstone bosons contribute to the longitudinal components of the W and Z. In my understanding, the reason for introducing the Higgs is that the QCD condensate contribution is much too small for the W,Z phenomenological mass. Would anyone know of a reference were the QCD condensate contribution is evaluated ? My searches failed and I would be very grateful.
|
[
"Take a look at the following:",
"http://arxiv.org/pdf/hep-ph/0203079.pdf",
" (see p.14)",
"and this comment from Matt Strassler:\n",
"http://profmattstrassler.com/articles-and-posts/particle-physics-basics/the-known-apparently-elementary-particles/the-known-particles-if-the-higgs-field-were-zero/#comment-133"
] |
[
"Note that 93 MeV/175 GeV is about .05%, not .5%",
"But in addition, the contribution is actually smaller than this (see Matt Strassler's comment). The contributions add in quadrature; instead of just X, it is sqrt(X",
"+Y",
"); when Y<<X, this becomes X(1+Y",
"/2X",
"), and so the effect of the condensate is less than a part per million."
] |
[
"Thank you. The article seems excellent. It suggests a contribution of the order",
"\n93 MeV / 175 GeV ~ 0.5 %",
"\nIf this estimate were accurate, that would mean that the QCD condensate is ",
" than the present experimental accuracy. Because of that, I would imagine a more precise evaluation must have been preformed."
] |
[
"Can somebody slightly \"dumb-down\" the four levels of protein structure for me?"
] |
[
false
] |
[deleted]
|
[
"ELI5 version (Using Power Rangers):",
"Primary: The smaller parts that make up the zord (i.e. ball bearings, connecting rods, etc.)",
"Secondary: The specific structures of the Zord (i.e. arm + leg = alpha helices, torso = beta sheet)",
"Tertiary: Zord",
"Quaternary: Megazord",
"p.s. in case you didn't know the zords are their animal robots that they drive"
] |
[
"Ponies don't assemble into anything :( how about legos? or maybe Barbie Dolls?",
"EDIT: I'll just roll with Barbie dolls, with additional metaphor explaining the importance of structure on enzyme activity: ",
"Primary: Barbie's parts (i.e. legs, arms, torso head) The order they are in is meaningful. If they were not attached in the right order then Barbie would look silly and have no chance of picking up Ken. She probably also couldn't walk.",
"Secondary: The positions of Barbie's limbs (cross legged or cross armed = beta sheet, straight out = alpha helix). If these aren't normal she wil not be able to strike a good pose.",
"Teritiary: Barbie's whole body pose (is she walking like a model? sitting? laying down?) She needs to have the right pose for Ken to find her attractive.",
"Quaternary: Barbie's Accesories (her pink convertible, her Ray Bans, a Pony). Her accessories may make it harder for her to attract Ken (e.g. in the case of a gawdy hat), or they may make it easier( e.g. her pink convertible)."
] |
[
"Yes, Tertiary refers to the overall structure of a single protein. Secondary refers to specific structural elements of that protein."
] |
[
"If teleportation will be available for human transportation, will the individual that \"arrives\" at a certain location be the same but not the original that \"departed\" from another location?"
] |
[
false
] | null |
[
"That's one way to do it. Probably the only theoretically possible way we have right now. But I'm hoping for another way that actually transports your matter intact."
] |
[
"My argument is more philosophical than technical. In my oppinion there are two ways to \"teleport\". The first is to read all the atoms in a body, send that information to the other end and recreate that body. Even with perfect quantum replication it is still just a copy, and destroying the original is still murder. Any variation of this still ends up killing/destroying the original body.",
"The other way to teleport is to have two devices which hold two volumes of space. One with a person the other without. Then that hypothetical device would have to switch those two volumes of space, or transport that volume similar to a warp-drive somehow. That way whoever is inside doesn't move anywhere and nothing happens to him/her, with only the space in which he/she resides being transported."
] |
[
"Whether you consider the first kind of teleportation murder is dependent on how you understand personal identity. Keep in mind that all of the cells in our body die and are replaced over time and all the parts of each cell are constantly decaying and being rebuilt with new material. Thus if you held that continuity of your physical substance was necessary to maintain your personal identity over time, then you right now are not the same person that your mother gave birth to since you are not the same, atom for atom, as you were 10, 15 or 20 years or even a week ago. \nMany of the main arguments about personal identity outlined here if you're interested: ",
"http://plato.stanford.edu/entries/identity-personal/",
" "
] |
[
"Microbiologists and biologists of Askscience: Is it true that not washing hands will \"train\" one's immune system?"
] |
[
false
] |
I regularly get mocked for refusing to eat without hand washing. My friends assert that touching food with dirty hands is healthy because it will keep their immune systems in shape. I guess they mean that inoculating a fairly small amount of bacteria or viruses isn't harmful for the body because this will help it to recognize the pathogens. My idea is that they are incorrectly applying the idea behind a vaccine to live microbes; it is also proved that spending some time regularly in a wood or forest is a huge immune booster. Just not washing hands is plain stupid and dangerous. Am I wrong? Just to clarify, I am not a paranoid about hygiene. I just have the habit of washing hands before eating, because my parents told me so when I was young and I picked the habit up. again: thanks for all the responses!
|
[
"You're not wrong. Bacteria is good, but that's the non-pathogenic form. Most pathogens that cause disease in us have mechanisms that can specifically override our immune system. Just because you expose yourself to that bacteria doesn't mean you won't get infected. That's why they at least kill the pathogen before vaccinating you with it. What immunologists mean when they say germs are good is that you should get exposed to germs from a natural environment, where almost all of them will be non-pathogenic to us (like in the woods as you point out). One arm of our immune system gets activated by ANY microbe, pathogenic or not. And that arm apparently expects some amount of activation at all times, without which it kinda gets screwed up. But in an urban jungle, almost everything you find around yourself (especially your kitchen) is probably some kind of organism that can do something wrong to you, so the benefits of giving some stimulation to your innate immune system is outweighed by the risk of contracting some serious problem.",
"So the end-message is, go out and play in the ground, venture through woods. But WASH your hands before you eat while you're in any major human establishment!"
] |
[
"This is what I came here to post. ",
"*edit: I didn't have anything to add right when I made the comment. I only commented in order to lend the credence of the tag, otherwise I would have just upvoted.",
"Now for some additional quick info: Wash your hands before you go to the bathroom to protect yourself, wash your hands after to protect others.",
"Also, the idea of living in too clean of an environment is known as the hygiene hypothesis which is thought to be the reason allergies and asthma are higher in first world countries. Basically, not being exposed to as many antigens early in life leads to reacting strongly against innocuous antigens such as pollen and certain foods."
] |
[
"I think in this case, it's completely warranted. A backing from another voice in the field."
] |
[
"Can an average consumer find/afford solar panels that easily \"plug in\" to regular appliances (i.e. window air conditioner) AND provide adequate power?"
] |
[
false
] |
Is this possible? Its hotter than Satan's va-jayjay here but I feel so wasteful having the AC on 24/7. What equipment (size of solar panel, converter, etc.) would be needed to power the unit, which plugs into a standard U.S. three-prong outlet, for even just a couple hours per day? Along with environmentally friendly, I'd prefer to be wallet friendly too, if you know what I mean.
|
[
"Usually you'd hook your solar panel into your home energy grid - that way, if you make more energy than you burn on just an AC, you can use it for everything else in your house (things like the fridge and washing machine are big ones, for example, but even lightbulbs add up). It doesn't matter that a solar panel is attached to a specific appliance, just that it covers as much energy as possible/practical including, hopefully, an AC or more. I understand the associated guilty feeling of what seems like a willful burn of energy from the AC, but it all adds up to the same thing in the end, so don't worry about one specific appliance or the other.",
"Another advantage is that depending on where you live and how your power company operates, you can get paid to pump energy into the grid. I'm not too sure on the details of this but I know that it occurs on some level.",
"If you live in a sunny area (and it sounds like it), a solar panel can definitely help contribute to your electric bills and increase the value of your home. I think it's not too hard to get 150W per square meter (how much space do you have?), I don't know what your situation is but you could probably do better given climate conditions. You'd have to double-check that efficiency for whether its current, and both it and pricing are going to vary per model (the business has become much more competitive lately now that it's becoming mainstream). You can calculate if it's going to be worth it or not, which if I know a few more things about your house/region/utility rates I could give you a (very) rough estimate on, since I've done it a few times.",
"If it's the AC you're worried about, I don't know what model, setting, or time schedule you run it on, but if it's an old junker running frequently it can bang up to 1000W! This can vary a lot, so it's hard to say, but they're definitely extremely power-intensive.",
"It's always good to reduce your power usage in the first place, which is always superior to covering that with renewables - it's generally much cheaper and less of a hassle. Ceiling fans are much more energy efficient, but of course they also don't work as well - still, it means you could run your AC on a lower setting, or for less hours in the day. There's other various retrofits that you can do to your home in this vein that can be extremely cheap and easy (something like painting your roof white).",
"If you bring up the region you live in and your power usage profile/monthly power bill, I can go further on this tangent, but ultimately, yes you can certainly get a solar panel that could very possibly pay for itself and more, though it wouldn't function as a standalone unit and would instead help supply the entire energy needs of your house (which is easily the best way to do it, since if - say - it's early morning and you get sun but don't need the AC yet, you can use that to run your coffee machine)."
] |
[
"I met ",
"this guy",
" at a conference I attended for work. He told me he leases people solar installations for $0 down for home use and generally people start saving more money than it costs, starting in the first month. I am not backing this statement up, as this sounds like a typical elevator pitch. He also let me drive his Nissan Leaf. ",
"Probably the most in-your-face-liberal guy I've ever met that I still really liked. "
] |
[
"There are two problems with what you want to do.",
"To solve that second problem there are two approaches:",
"An offline system, which means you have a large bank of batteries that are charged by the panels. Much like a bank account, this lets you accumulate energy while you aren't running any electronic devices and then withdraw it when you need it, for example at night, or when you have a high load device like an air conditioner that you want to run for a short amount of time.",
"An online system, where you are still connected to the power company. Here you should visualize a Y-type connection: you have your solar panels on one branch of the Y, the power company's line on another branch, and everything else in your home on the third branch. The total current of all three branches has to sum to zero. If your panels generate more than you are currently using, the extra flows back onto the grid, and your utility pays you for that power. If you use more than your panels generate, then the difference is made up by taking from the grid, which you pay for as normal. This is convenient because at night you don't have to worry about running out of stored battery power but you can still reduce your dependence on the grid when there's available light, all without having to worry about storing any yourself through expensive batteries -- the grid becomes your battery.",
"Unfortunately number 2 does require participation of the electric company which is not guaranteed everywhere. I don't have a link handy but I think something like a third of utility companies nationwide currently have rules that allow you to do this.",
"Also unfortunately is that these systems cost a lot of money. Ballpark, maybe $5000 - $10000 parts and $2500 - $5000 labor to install them. There are a lot of tax breaks and incentives that can bring that down, and prices are always dropping. But it's currently something that's still an investment."
] |
[
"Relativity says that there is no \"right\" perspective. That seems to imply that the universe isn't in one particular state at a given point in time. What does that mean and how is this possible?"
] |
[
false
] | null |
[
"incorrect to say that the baseball exists at a finite location at a specific point in time?",
"No it's perfectly correct, the problem is that the numbers you get are unique to your reference frame and not values you should expect others to share.",
"it's actual location in the universe",
"There is no such thing. Relativity bans the notion of absolute space, the idea that the whole universe sits on some absolute immutable and ultimate stage that cannot change and retains primacy to all other viewpoints.",
"Also wouldn't this have to mean the baseball doesn't exist in one state at a time but rather infinite states and what would that even mean?",
"Take this idea. There is a baseball at rest (with respect to you) 5 feet from your left. Now I'm heading towards you and the baseball at 0.9c (with respect to you). You will say, the baseball is 5 feet to your left and I'm 1,000 feet away approaching the baseball at 0.9c.",
"Conversely I will say, the baseball is ~435 feet away and heading towards me at 0.9c. You are still 5 feet to the left.",
"Isn't this a weird disagreement we have? And it's how the world works. Now, we obviously can't have the baseball in two spatial coordinates at the same time, but then the phrase \"same time\" loses meaning--we disagree on each other's clocks too! What a mess!",
"Luckily, because of how Lorentz geometry works, when I slow down and come to rest with respect to you, we will now agree completely on spatial distances and the baseball will be in the same spatial distances we both measure. We will ",
" find ourselves in the same frame of reference, but disagreeing on whether or not the baseball is 5 feet to your left or not. Once I leave our shared reference frame however, I cannot make this statement anymore in general."
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"/r/AskScience",
"/r/askscience",
"For more information regarding this and similar issues, please see our ",
"guidelines.",
"This is a common question covered in the ",
"AskScience FAQ",
"If you disagree with this decision, please send a message to the moderators."
] |
[
"Relativity removes absolute geometrical relationships between reference frames. Using your baseball example, two different observers will both see a baseball, but disagree on how far away the other observer is from the baseball, the speed of the ball, how clocks move on the base ball and the other observer even the dimensions of the baseball.",
"All of this is ",
", because these geometrical disagreements are founded on mathematical law which preserves causality. If the baseball is caught by a player, we'll all agree that the player caught it--but we'll disagree on numerous variables and even the order of spatially separated events.",
"This is an old text, but it's written by Einstein himself on the topic:",
"\n",
"https://archive.org/details/cu31924011804774",
"\nAnd here's the special relativity chapter written by Feynman:",
"\n",
"http://www.feynmanlectures.caltech.edu/I_15.html"
] |
[
"What's actually happening to your rods and cones when your eyes are adjusting to the light/dark?"
] |
[
false
] |
I understand that when your eyes adjust to the light or dark that it takes time for your rods and cones to adapt to the change in condition, but what's actually going on with the cells for this to happen?
|
[
"When your rods and cones adapt to bright light, what is happening is they are \"photobleaching\". When rods & cones are bleached, they cannot process incoming light. Here's a short mechanistic description of photobleaching from ",
"this paper",
":",
"As a result of the work of G. Wald and his group\n[ 1 ] it is known that 11-cis-retinal, the prosthetic\ngroup of rhodopsin, undergoes stereochemical changes\nas a response to light absorption, leading eventually to\nall-trans-retinal. It is generally believed that retinal is\nthen removed from its apoprotein opsin; the original\nlight-sensitivity of rhodopsin is restored when, through\na cycle of reactions, 11-cis-retinal is again linked to\nthe protein. ",
"So essentially, light starts a process where 11-cis-retinal becomes detached from the rod or cone cell, and it eventually becomes attached again. However, since you're constantly being exposed to light many of your rods & cones are bleached since they can't be restored instantaneously. So since many of your rods & cones are bleached, the light doesn't overwhelm your retinas. In the dark, since there isn't much light to stimulate your rods & cones, more of them remain unbleached and you can more effectively pick up on the little bit of light that is there.",
"Fun facts: This is why when you open your eyes to bright light after having them closed for a while everything appears to have a blue tint! Rods respond to slightly blue light, but normally when you are in the light many of your rods are photobleached, and they \"unbleach\" much more slowly than cones. When you've just had your eyes closed for a very long time, all of your rods become unbleached."
] |
[
"Thanks! Perfect answer!"
] |
[
"The main effect is not in the cones and rods but you pupil which will close in reaction to bright light to let less light into you eye.",
"The rods and cones will react to constant stimulation by lowering their output. That is why when you take off colored sunglasses the colors seem off. This happens due to the limited rate at which nerves can fire. After a nerve has fired it needs some time to regenerate. So if a cone or rod is constantly on, it or its attached nerves can not regenerate neurotransmitters (pump the molecules that are released during an impulse back into the cell) fast enough and the signal will be dimmed down."
] |
[
"How did the Big Bang not form a super massive black hole?"
] |
[
false
] |
So, when a star's mass exceeds a certain threshold, it collapses into a black hole. In the beginning, all the mass in the universe was in close proximity. How could all that mass not trigger a black hole collapse? Surely there was more mass in the local area of the blast than exists in a black hole, and light (a massless particle) is a lot harder to suppress than actual mass. Therefore, it should have been impossible for any matter to have escaped the Big Bang (?!). What am I missing... EDIT: Front page! Thanks reddit!
|
[
"The Big Bang singularity isn't the same as a black hole. A black hole is a point in space time with infinite curvature. The Big Bang singularity was the entirety of space time. And the entirety of space time expanded. ",
"That being said. We have no working theory of black holes or the Big Bang. We just see that our models asymptotically reach these points. We can't explain what actually happens at these points, though. "
] |
[
"In the beginning, all the mass in the universe was in close proximity. ",
"No, in the beginning, all the mass in the universe was closer together, but still evenly distributed throughout all of space. ",
"How could all that mass not trigger a black hole collapse?",
"Since the density of the universe was, and is, the same everywhere, there is nowhere preferred to collapse to form one. ",
"Surely there was more mass in the local area of the blast",
"\"The local area of the blast\" is not a thing. The Big Bang happened everywhere. It was not an explosion sending matter out into empty space. It was all of space everywhere evenly and densely filled with matter expanding. "
] |
[
"A black hole is a point in space time with infinite curvature. The Big Bang singularity was the entirety of space time.",
"This is the first time an answer to this question has made sense to me."
] |
[
"what needs to happen for us to be able to colonize Venus?"
] |
[
false
] |
This question was brought up , but I'd like to investigate it further. What technological challenges do we face? What atmospheric conditions does Venus present now, and how bad would those conditions be for human life? Any estimates on when, if ever, we can start living there?
|
[
"I think that was \"The Jetsons.\""
] |
[
"Obscene surface temperatures and a toxic atmosphere both present challenges. No chance of agriculture unless the planet was terraformed. We could potentially do something like a \"city in a bubble\" but then the only advantage we gain is extra land, and almost nothing in the way of new resources."
] |
[
"Don't forget that a Venusian day lasts 116 Earth days since the planet is tidally synced with it's orbital period."
] |
[
"How long does it take a virus (such as Covid-19) to reproduce from the moment it enters a cell?"
] |
[
false
] |
How fast is viral reproduction on the level a single virus? Once it enters a cell, how long does it take for it to take over the cell, create more viruses and burst forth from the host cell? Does time vary significantly from virus to virus? Are ones with shorter time generally more dangerous/infectious?
|
[
"A complete viral replication cycle includes:",
"-Cell entry",
"-Unpackaging of genome and proteins",
"-Genome replication and protein synthesis",
"-Assembly of virions",
"-Release of virions from the host cell",
"The time required will vary quite a bit from virus to virus. Generally positive-sense RNA viruses (for example, coronavirus) are faster since their genomes can be directly translated into protein.",
"For the SARS coronavirus this takes between 7 and 24 hours: ",
"https://www.ncbi.nlm.nih.gov/pubmed/15170625",
"For SARS-CoV-2 it's more than 6 but less than 12 hours: ",
"https://wwwnc.cdc.gov/eid/article/26/6/20-0516-f4",
"Influenza virus is one of the fastest replicating, with a replication cycle of around 6 hours: ",
"http://www.euro.who.int/en/health-topics/communicable-diseases/influenza/data-and-statistics/virology-of-human-influenza",
"Herpes simplex virus 1 and 2 also have replication cycles of around the same time (hours). For cytomegalovirus (aka human herpesvirus 5), it's around a day or two (source: ",
"https://www.ncbi.nlm.nih.gov/books/NBK8157/",
")",
"Keep in mind that one infected cell can produce thousands of virions, so that even if it takes ~6 hours to produce them, the end result is extremely rapid replication."
] |
[
"To answer your question: yes, it varies from virus to virus. It depends on the host cell too. We probably ain't too sure of the exact time needed for the virus life cycle in our body, simply because the cell type and conditions in our body are different from those in labs.",
"Lethality is hardly correlated with time needed for life cycle. For example, ebola reproduce slower than herpes, but is more deadly. Some with very long life cycle, such as those with latency (eg. HIV), can cause a different set of problems altogether.",
"Sorry if the sentence structure is poor.. Typing on phone. Feel free to ask more if you have any more questions."
] |
[
"Reproduction time can be seen as a factor of spread, and possibly even incubation period before signs and symptoms appear, due to levels required before active disease such as the amount of the bacteria E-coli is needed before it passes a threshold to become illness causing, it is not a good indicator of much more. There are many factors that make a virus what it is. Time of reproduction is not usually a stand alone variable for much, especially in viruses."
] |
[
"What would happen if two stars merged together?"
] |
[
false
] | null |
[
"In some cases a nova or supernova would result. Some recent papers proposed for example the element gold could only be synthesized from the collision and merger of two neutron stars. Assuming some stars with considerable nuclear fuel remaining/time on the main sequence, there would be fairly massive explosion/outbursts from disruption of both stars structure before the combined mass reassembled into a new star. ",
"An event observed in 2008 is believed to be the first direct observation of a stellar merger",
". The paper makes reference to another astronomical object ",
"V838 Monocerotis",
". One theory is this is the remnant nebula from the explosion and combined star from a stellar merger. "
] |
[
"White dwarf collisions create something called Type 1A supernovae, which have a very unique emission signature. These events are more luminous than entire galaxies for a few days/weeks.",
"Neutron star collisions are thought to create certain types of gamma ray burst, which are the highest energy electromagnetic events we know of.",
"Source"
] |
[
"Seems doubtful that either would happen, but it is hard to really know. There are forces at work in the core of a star that we have an incomplete understanding of that would greatly matter for problem like this.. Lots probably depends on how exactly they are rammed together.",
"It is just educated speculation, but the majority of the time, with two stars the size of the sun ramming together, you will just end up with a larger sun like star. Most stars are boring main sequence stars like the sun, and between 1 to 10 solar masses or so they are all fairly similar and follow the same evolutionary course into a white dwarf."
] |
[
"Do rooms with hard reflective walls (such as a bathroom) leak less sound?"
] |
[
false
] |
I've recently been practicing my ukulele late at night in my apartment, and have wondered lately whether practicing in my bathroom (with its hard reflective walls) will leak less noise than playing in my living room. If I can hear myself more loudly inside, does that mean that outside the room there is less noise leaked?
|
[
"Depends on what you are comparing it to, but all else being equal: yes. If I have two closed rooms, one with hard tile walls and the other with sound-permeable drywall, less sound is going to leak from the tile wall room.",
"However, this assumes that all the sound is going through the walls. In truth, you have different paths that sound can take. For example, sound might travel through a window, through an open doorway, through a closed door, through the structure of the house, etc. In this situation, the fact that the sound is reverberating longer in the tile room might actually hurt you.",
"So, it's all going to depend on which paths for sound are most important. For a ukelele, which is fairly high frequency, the door will block a lot of the sound. For a tuba, it probably wouldn't do much. My suggestion is to get a sound level app for your phone (you don't need something great, just good enough to do relative levels) and test the sound level yourself.",
"If you do this, I'm curious to see what you find! Try playing with the door open, vs closed. Then try taking all the towels/rugs out of the room (since they absorb sound) and pulling the shower curtain.Then make a comparison with some other room."
] |
[
"It depends. In addition to the transmission and reflection you are already considering there is the possibility that the sound is absorbed in the wall. It's possible for a wall with high reflection and low absorption to transmit more sound than a wall with low reflection but high absorption."
] |
[
"One thing to keep in mind: When you move to a new apartment and experience the empty rooms, you experience much more echo/hall than now, where its fully furnished. The sound situation in your bathroom might still be something else, but I just want to call the attention to a possible misinterpretation regarding the cause for the different sound.",
"You might even have better sound absorption (Prevention that neighbors have to endure you.) in your living room than in the \"reflective wall bathroom\". I'm not saying that this ",
" so, though.",
"And another thought: In the bathroom, you usually have direct pipes to the bathrooms of the other apartments above and below you, which are good at carrying sound."
] |
[
"While sleeping, if nothing from the outside world triggers our wake-up, what most commonly triggers it?"
] |
[
false
] |
For instance, does something just sort of trigger in our brain and tell us it's time to wake up? Thanks
|
[
"First, it should be noted that sleep is not a continuous block. Even without any environmental stimuli, spontaneous awakenings are common during the night. For a healthy adult, it is typical to wake briefly about 20 times per night, with increasing frequency towards the end of the night. You don't remember most of these awakenings because short term memory does not function normally during sleep or shortly after awakening.",
"With that out of the way, I'll take your question to mean: What determines when we finally get up and start our day? The answer is that there are regions of the brain involved in controlling the overall arousal state of the brain (specifically, the ascending arousal system in the brainstem, and some neuronal populations in the hypothalamus and basal forebrain). The activity of these regions is primarily determined by two underlying processes:",
". We all contain a clock with a period close to 24 hours. This clock resides in a group of neurons in the suprachiasmatic nucleus of the hypothalamus. The clock promotes arousal during the circadian day and promotes sleep during the circadian night. Towards the end of the night, there is a progressively increasing arousal signal being sent from this clock.",
". While you are awake, certain substances build up in your brain, including adenosine, cytokines, and prostaglandin D_2. These substances make you feel more sleepy. During sleep, these substances are cleared from the brain. Towards the end of the night, the clearance of these substances results in an increasing drive to awaken."
] |
[
"For a healthy adult, it is typical to wake briefly about 20 times per night, with increasing frequency towards the end of the night. You don't remember most of these awakenings because short term memory does not function normally during sleep or shortly after awakening.",
"Do you have a citation for this?"
] |
[
"Sure! This study reports an average of 20.1 awakenings per night in healthy young adults, 22.9 in middle-aged, and 27.9 in older adults.",
"http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2817908/pdf/aasm.33.2.211.pdf",
"I can tell you from data from my own lab that a range of around 10-30 nighttime awakenings is typical for a healthy young adult.",
"Regarding memory being altered during sleep, that manifests in our inability to remember most dreams, and the frequent inability to remember events that occurred during brief awakenings during the night. The neurobiological basis for that is discussed here:",
"http://www.sciencedirect.com/science/article/pii/S0301008212000706"
] |
[
"Do learned behaviors have an effect on evolution?"
] |
[
false
] |
For example, there are pods (?) of dolphins that have learned special methods of hunting fish, like stirring up mud to trap the fish against the surface. The dolphins teach their offspring this method, increasing the chances of their offspring surviving because of this superior hunting method. It seems to me that even if a dolphin weren't particularly fast or healthy, it could still survive because of this "smart" hunting. Some species of monkey have also learned to use tools to open nuts/fruit, which is another behavior that is passed on through nurturing. Another (extreme) example would be humans and modern medicine. Have we "beaten" evolution because we can cure the people who otherwise would have died from Chicken Pox, etc.?
|
[
"While learned behaviors certainly influence evolution, it is important to remember that the specific learned behaviors themselves are not being passed on via evolution, and that there is a cost to learning. Nobody 'beats' evolution, but what exactly is under selection can change.",
"What you're talking about in most of these cases is cultural transmission (of information) as opposed to the transmission of genetic information. The difference between these types of information sharing is that as soon as you take an individual out of the social environment and raise it somewhere else, the advantage of learning is gone. Ie, if you took a human and raised them without ever letting them interact with another human being, they lose the benefit of all the accumulated knowledge.",
"What learned behaviors can do is change the selection individuals experience. In your dolphin example, learning to hunt by stirring up mud might reduce selection on swimming speed by reducing the need to chase fast prey, but it might increase selection on visual acuity (ie, to see prey in muddy water). It might also select on increased learning capacity, so that individuals who learn new hunting methods more quickly can start catching prey at an earlier age or with less practice. ",
"It's important to remember that increased learning doesn't come for free. Learning comes at the cost of time (using one of your examples, just think about the amount of time it takes to comprehend modern medicine..) and the cost of making mistakes before the behavior is perfected. They also have a physiological cost of increased brain size, which can feed back into increased gestation and development time, which then reduces the number of children a parent can successfully raise. In some cases it's worth the cost, but in many cases it's not."
] |
[
"Yes, as anything that increases an individual's fitness is going to increase the likely hood of passing on its genes to future generations. ",
"As for humans \"beating\" evolution, no you don't beat evolution, not with our understanding of genetics anyways. Certain factors, like inherent disease resistance, may have less of an effect on humanities' natural selection now then it did 20,000 years ago, but other mutations in out genetic code can still have a huge effect on our evolution. A mutation, for example, that inhibits something during fetal development is still out of our hands. ",
"As a side note, I believe people can still readily die from chicken pox and its more dangerous form shingles."
] |
[
"What you are asking about is actually a fascinating topic called the ",
"Baldwin effect",
", which describes how learning can affect evolution, and even, intriguingly, accelerate evolution - certain kinds of evolution are only possible in \"smart\" creatures. A related component, is a shift of behaviors that start out being learned but then gradually become innate after millions of years - certain creatures innately recognize predators (their DNA somehow hardwires predator recognition into their brains), whereas in the distant evolutionary past, these creatures had to learn to avoid predators the hard way. Biologists don't usually study learning, so this general area is an interesting interdisciplinary frontier that hasn't been explored as deeply as it might be."
] |
[
"Why is northern Alaska and Canada pockmarked with \"lakes\"?"
] |
[
false
] |
I was looking over google maps when I noticed that northern Alaska and Canada had these dense "lake" formations. What are these from and why do they form that way? For example:
|
[
"I have been waiting for a geology themed question for AGES!",
"The answer to this is glaciers! During the last ice age massive multi-km thick sheets of ice covered canada, alaska and some northern parts of the lower 48. Think Antarctica, but in Canada! These super thick sheets of ice move very slowly, but over thousands of years these sheets scour every single feature off the surface. The glaciers plane off the hills and later fill the valleys with gravel (or till).",
"So how do these lakes form? Well, if you've planed off your entire landscape, you've destroyed your entire hydrologic network- the streams and rivers that carried water away are gone, and the water is stagnant. This is why Canada is covered with countless small shallow lakes. Over time, the lakes will fill in with sediment and streams will return. Eventually, it will look something like what northern indiana or iowa look like now. This explains what areas like ",
"quebec look like",
". Curiously, the exact location you pointed out is a different kind of landform, called kame and kettle topography.",
"To understand the difference between the area that you picked and the area that I linked in this post, compare the shape and pattern of the lakes. In Quebec the lakes are irregular, somewhat interconnected, and lie directly on the bedrock. In the spot you selected in alaska, the lakes are round, seem to follow a preferential direction and seem to lie on glacial gravels or soft sediment. These lakes are different! So how do glaciers work into this? Well it turns out that glaciers effect the landscape in different ways depending if you are near the start or end of a glacier. The beginning of a glacier is erosional, the glacier isn't carrying a lot of sediment yet and it carves deeply into the rock beneath it. The beginnings of glaciers form landscapes like in Quebec or northern minnesota. The ends of glaciers are totally different. By the time you get to the end of a glacier, it is carrying all the sediment picked up from the glacier gouging out the ground upflow. At this point the glacier is melting away, and as it melts it begins to become dirtier and dirtier and starts to turn into a pile of rocks. Check out ",
"this glacier",
" in alaska. See how it grades from a pure white snow to dirty and vegetation covered! As the glacier melts, big pockets of ice can be trapped under the sediment. As the glacier retreats, it leaves big blocks of ice buried beneath the sand and boulders. Over time these blocks melt away and the cavity where the ice was collapses, forming a small lake. These small, round lakes are called ",
" and form near the terminus of glaciers. These are the lakes you saw in alaska.",
"So the td;lr here is that these lakes were made by glaciers during the last ice age. The particular ones you pointed to are a type of glacial lake called a kettle. "
] |
[
"The other neat thing about glaciation also, is the rebound of the lithosphere due to the lifting of weight when the glacier melts. This is why Finland gains altitude of about 11 mm/year. So as you rebound the crust, if you don't do it at the same time, you can have migrating lakes. "
] |
[
"http://www.nationalparkstraveler.com/2009/10/melting-permafrost-may-help-explain-why-many-denali-national-park-wetlands-are-drying4724",
" \"The lakes and wetlands in this part of the world were formed about 8,000 years ago when the most recent glaciation ended, and many (but not all) owe their continued existence to the fact that permafrost helps to confine their water -- sort of like the sides of a bathtub – and keeps it from draining way.\"",
"Related: ",
"http://en.wikipedia.org/wiki/Thermokarst"
] |
[
"Is there any material that has a different melting and freezing point?"
] |
[
false
] |
i.e. is there any material that will tend to "stick" to whatever state it was in, whether that was solid or liquid, for some period? I know that there are other reasons that all snow doesn't melt as soon as it gets above 0 degrees (it takes time for heat to transfer, different specific heats of air vs. water, "above 0 degrees" on the weather doesn't account for shade vs. sun, etc.). But is there any substance where you can take a solid sample and a liquid sample, bring them into an environment with precisely the same conditions, and have them remain, respectively, solid and liquid? What about gas and liquid? I know that water vapor, liquid, and ice can continue to exist in the same room for a while, but again because of varying conditions... but I'm wondering if there's a further stickiness. Basically, a material that turns solid when it gets to temperature/pressure/etc. conditions X, but won't turn back into liquid again until it gets to X + 5 degrees, leaving a window where both states are stable. I hope I've explained my wondering sufficiently...
|
[
"What you're describing sounds like ",
"hysteresis",
", in which the state of a substance depends not only on current environment but also on prior environment. The example wikipedia lists is ",
"agar",
", which melts at 85C but freezes at 40C. Other '",
"antifreeze proteins",
"' and ",
"nonprotein macromolcules",
" also exhibit this effect. ",
"More info here.",
"edit: see ",
"EagleFalconn's",
" and ",
"coniform's",
" posts below, as they are more accurate than mine."
] |
[
"Even though the material \"knows\" it wants to be in a different state, it is sometimes easier said than done to get there. An ELI5 analogy: imagine you have 30 screaming kindergarteners in a classroom, all running around doing various things, and it is time for recess. Even though the kindergarteners would rather be at recess than the classroom, they might stay in the classroom for a while until you can run around pulling each kid off of whatever they are doing and communicating to them that it's recess time. While it might seem like you would never be able to find a kindergartener in a classroom at recess time, you very well might if the teacher in the classroom is slow and inefficient about rounding up all the kids and getting them organized, or if a particular group of kids is hard to pull away from what they are doing. Similarly, it is sometimes not so easy to organize enough of the atoms of a material to collectively change phase and \"get the ball rolling\" so that the atoms in the material figure out that it's time for a phase change."
] |
[
"No.",
"The situation being described by the OP is indeed hysteresis as stated by ",
"arumbar",
", and can ONLY occur for non-equilibrium situations. Agar is neither freezing nor melting because freezing and melting are explicitly ",
"first order phase transitions",
" which are equilibrium phenomenon. Agar is not in equilibrium."
] |
[
"Why do rotating black holes look so weird?"
] |
[
false
] |
So I found website from ESA where you can play around with a black hole and the rotating black hole (Kerr black hole) looks so weird. Why does it have that shape?
|
[
"It's because of an effect called 'frame dragging': The spin of the black whole ",
"twists the spacetime",
" with it. This means that trajectories of light look very different when orbiting the black hole clockwise in contrast to orbiting it counterclockwise. They are 'dragged' by the rotation.",
"For an outside viewer, this distorts light coming from behind the black hole differently, depending on wether it passes the black hole on the left or the right.",
"edit:",
"If you are talking about ",
", the reason why this actually ",
"looks rather weird",
" is because the gravitational field is much more complex. \"With hair\" is a bit of an inside joke, but refers to the fact that there's additional physical features on the outside of the black hole. In this case, there's a matter field swirling around the black hole, forming an equilibrium with the hole itself. In the image on ESA's site you can't actually ",
" the matter, only the gravitational lensing by it.",
"The reason that you can't see the matter is that it's only an rather abstract mathematical model of matter, a ",
". It's not defined what makes up this matter, if it could interact with light at all and so on. So for now let's assume it's transparent.",
"This black hole / matter combination has a more complicated gravitational field than an ordinary kerr hole, which can lead to chaotic orbits. You can still see that it's a spinning system, because it looks different on the left side than on the right side. But additionally there is some complex warping going on. The reason for this is, that the effective potential for the photons (considering all ",
" like gravity, centrifugal force etc.) forms intricate pockets, in which the photons can get trapped for a while. They'll bounce around in these pockets, eventually leaving in an arbitrary direction, which is extremely sensitive to the initial angle at which the photon approached the black hole.",
"It's very similar to the fractal pattern you see when looking at the ",
"reflections of four spheres",
", which is also a chaotic motion. You can try this for yourself with ",
"christmas tree balls",
".",
"The orbits of photons are not reflected by mirror walls, but are bouncing off potential wells, which leads to the highly chaotic regions you see in the images.",
"There's a detailled study of these effects in ",
"this paper",
", if you want to read more. The traps / pockets are visualized on page 20 for example."
] |
[
"Black holes have mass, charge and spin. If charge and spin vanish, it's called a Schwarzschild black hole. If it has spin, but no charge, it's called a Kerr black hole. The spacetime for a Kerr black hole is very different, for example it has an ergosphere, a region around it where it is impossible for objects to ",
" rotate. A charged black, non-rotating hole is called a Reissner-Nordström black hole, and if it has charge ",
" spin, it's a Kerr-Newman black hole. We think that almost all black holes in our universe are Kerr black holes.",
"Rotating a normal object, like a ball, will also lead to frame dragging, the gravitational field will change. Notice though that unlike for Schwarzschild black holes, the Kerr solution is not the outer solution for a sphere with finite density. "
] |
[
"I didn't see the Kerr black hole with scalar hair but thanks for explaning it too."
] |
[
"is there a name for ability to control the shape of the crystalline lens in humans, and is it common?"
] |
[
false
] |
I am able to blur my own vision by moving a part of my eye, that I assume is my crystalline lens. I'm able to control this consciously, as I would tense a muscle. I've never been able to find any evidence of this in another human.
|
[
"Your cornea is the external \"bump\" of the eye that lies above the iris and the lens. It is fixed and does not change in focus, though it can become occluded or scratched by things getting in your eye. ",
"The lens of the eye is comprised of layers of transparent, interlocking cells that are individually rigid bit collectively flexible. The muscles attached to your eyeballs are responsible for the overall movements of the eye but ALSO for flexing the lens, a process known as \"accommodation.\" This flexing allows for rapid adjustment of the focal length of the eye and enables you to quickly switch from far to near objects. It also allows you to deliberately unfocus your eyes to make your vision blurry. ",
"That you can willfully do so displays good control over you accommodative vision."
] |
[
"I apologise if my only evidence is of my own experience, but I have never been able to find any evidence of the phenomenon anywhere. I also did read the guidelines, and have done my best to abide by them."
] |
[
"It's a very common ability. When you tell people to 'focus far away' to do a magic eye picture or something they change the focus of their lens and the confocal point of their eyes at the same time."
] |
[
"How do we calculate rates of change mathematically knowing what we do about quantum mechanics?"
] |
[
false
] |
The obvious example is current. We know charge is a discrete value, so we can't use basic calculus to find the rate of change of charge as the derivative which, as I know it, can only be done on a continuous function.
|
[
"In many applications, we may simply assume that the charge can take arbitrary values, and this is usually a good approximation. For instance, in a wire, the elementary charge is negligibly small compared to the total charge in some cross-section of the wire. Precisely, in any cross-section, the charge is ",
", where ",
" is some integer and ",
" is the elementary charge. The value of ",
" is so small compared to ",
" (or ",
" is so large compared to 1) that the difference in charge between neighboring cross-sections is proportionately small as well. So we can approximate the charge as a continuous function of the position along the wire.",
"This type of approximation is done in other fields as well. For instance, in fluid mechanics, we know that the actual molecules are discrete and there can only be so many in a given volume (there may even be none). But for almost all applications we can approximate the fluid as a continuum. Typically, this means that the intermolecular distance is small compared to the characteristic length scale of the problem. There are some notorious examples where this approximation breaks down. For instance, for strong shock waves in some gases, the length scale of the shock (where the rapid change in density or velocity is) may be on the scale of the mean free path of the gas molecules. In that case, the continuum approximation breaks down and a kinetic theory may be more appropriate.",
"In plasmas, the intermolecular distance may be very large, but the continuum approximation may nevertheless still be good. There are other factors at play, like the relative strength of the self-electric, self-magnetic, and external magnetic fields, for instance, that may enter the scales of the problem in such a way to make fluid-like equations still a rather good approximation. But for general applications, I would say plasmas more often break the continuum approximation than traditional fluids, in that a full kinetic theory is more often required for plasmas than fluids."
] |
[
"Yes, as I mentioned, for plasmas or fluids, you need a full kinetic theory. Classical kinetic theory, for instance, is based on probability theory and the Hamiltonian and Lagrangian formulations of classical mechanics. (There are quantum and relativistic kinetic theories also.) A good analogy is \"statistical mechanics is to thermodynamics as kinetic theory is to fluid mechanics\". Some centralizing physical concepts in kinetic theory are the phase space distribution, Liouville's theorem, and the Fokker-Planck equation. Some key mathematical concepts from probability theory and applied mathematics are multiscale expansions, Markov processes, stochastic calculus, and the central limit theorem. (If you are familiar with financial mathematics, most of the same mathematical tools are used to model stock or option prices. The Fokker-Planck equation goes by many names, depending on who is using it.)",
"Depending on your exact problem, there may be other approximations you can make so that you don't have to use the full machinery of kinetic theory. For instance, there may be a time scale separation that lets you neglect certain terms in the relevant equations.",
"The main difficulty is obviously that it is impossible to follow the trajectories of each of the particles and make predictions. So some sort of statistical analysis must be done. It may be that you assume that the particles in a some sort of equilibrium and so their speeds follow a certain distribution. Or maybe you assume that the particles interact via short-range elastic collisions (which cause particles to exhibit random walks) in addition to some long-range interaction (which may cause particles to have an overall drift superimposed on the random walks).",
"You should definitely not get the impression that at any point we are making ",
" predictions. There are still some underlying assumptions we must make to make typical problems tractable, like the total number of particles being very large. If the total number of particles is not large, then a different theory must be used. If, for instance, there were only 3 or 4 particles total, then it is feasible (and probably required) just to follow the trajectories of the individual particles. Of course, you would need a computer to do that and still can't find the solutions exactly usually, but it's about exact as you are going to get."
] |
[
"I don't know what your professor said exactly or what he meant. But Euclidean geometry encompasses a lot more than circles and lines in a two-dimensional plane. The non-Euclidean nature of the universe is not important in the classical limit, but only in the relativistic limit. There is plenty of interesting physics, both well-studied and still unknown, in the classical limit.",
"(Also, our inability to follow individual particle trajectories has nothing to do with the failure of calculus or any other maths. It's just that solving ",
" = 10",
" coupled ordinary differential equations is extremely impractical on a computer. You also don't really get any deep understanding of why the particles behave the way they do.)"
] |
[
"Does the universe have total angular momentum different from zero?"
] |
[
false
] |
Is the total angular momentum if the universe zero? If not, wouldn't this determine a privileged direction in space?
|
[
"You can set up polar cosmological coordinates (FLRW basically) and in fact do compute said angular momentum with respect to some origin (say, Earth). It turns out to average to zero above the supercluster scale. If it wasn't so, you wouldn't have an isotropic Universe in those same coordinates, but you actually do.",
"Fun fact: as opposed to energy, total angular momentum is conserved in our Universe."
] |
[
"Thank you. I assume above the supercluster scale means huge huge scale, which is what I meant. Also, what you mean about energy is due to the constant accelerated expansion of the Universe thus increasing kinetic energy? If this is the case, does this increase vastly outscale the decrease in potential gravitational energy due to the separation between galaxies?"
] |
[
"There is no kinetic energy: in cosmological coordinates, we're all stationary (i.e., the derivative of the position coordinates wrt the time coordinate is zero). We are just getting further apart.",
"However, energy is being created because of other reasons. For example, dark energy is a constant energy density, but the volume of a given region is increasing; therefore the total energy in the region increases."
] |
[
"I was recently told that loss of antarctic ice was causing changes in the gravity of earth, how is this possible? if gravity is based on mass how can melting ice reduce the reduce the mass of earth?"
] |
[
false
] | null |
[
"It's not changing the mass of the Earth, it's changing the mass distribution. If you look at ",
"gravity maps of the Earth",
", it's not perfectly uniform everywhere because the mass of the Earth is not spread out perfectly equally.",
"Melting large amounts of ice basically redistributes mass from that area to other places, which can be measured by very precise maps of the gravitational pull everywhere on the planet.",
"Edit: The total mass of the Earth doesn't change, and the gravity of the Earth would still look the same from a large distance when it basically acts like a point particle, but when you're up close on the surface, moving the mass around can change the local gravity."
] |
[
"The earth's mass would remain the same. It could affect the distribution of mass. ",
"So if there is 1 million tons of ice at the poles... If it melted, the mass of the water would be distributed more evenly in the ocean. No longer just at the poles. ",
"It seems like the mass distribution change would be minimal, but would occur on a tiny scale when polar land ice melts and joins the ocean water. "
] |
[
"This",
" is what the earth looks like where gravity is equal.",
"\nRocks (Africa/Europe) is heavier with more gravity pull than the (Indian) Ocean, and that km's thick ice-sheet on top of Greenland (above sea level) is pulling the water upwards. ",
"(Google 'pictures' of \"gravity potato\" for more if you like this). "
] |
[
"Why +90% of people live in the northern hemisphere?"
] |
[
false
] |
[deleted]
|
[
"I don't know if the answer needs to be sciency enough, but this looks like it can be explained without it. ",
"First of all, most of the landmass is in Northern Hemisphere. Secondly, we also have the entirely to Asia in it, which contains two of the most populous countries - China and India.",
"Now, it doesn't look like that this would mean 90% of us live in Northern hemisphere, as we have Australia, half of Africa and South America in Southern, but I would think, that if your source is indeed correct about 90%, then it's simply because of that most of the extremely populous countries and cities are in Northern Hemisphere - Tokyo, Delhi, Singapore, New York.",
"Edit: Just went through google images, and it would be wrong to say that half of Africa is in Southern hemisphere - more like 1/5 or so.",
"Edit 2: More googling shows that 78% of landmass is in Northern Hemisphere (excluding Antarctica, cuz Penguins aren't people.)"
] |
[
"I like the landmass point, but the rest of your argument is kind of like saying \"90% of people live in the northern hemisphere because the northern hemisphere is where 90% of people live.\" \nI think the fundamental question OP wanted answered was why people are so concentrated in the northern half relative to the southern half. What factors contributed to the northern area being so populous relative to the other area? \nFrom what I understand, the answer is probably better answered by history than by science. Although there are other factors from ancient history that certainly played a role in whether/when societies underwent an agricultural revolution that would set those societies on the road to denser and denser population centers, I think one could explain much of the difference with the industrial revolution. The industrial revolution essentially created the modern economy complete with goods, factories, etc with strong economic growth capable of sustaining rapid population growth. Since the time when manufacturing began in earnest, the population has doubled several times in regions (mainly the northern half of the world) that experienced the industrial revolution. As for why it originated in Europe before being spread to North America and Asia: Britain had a strong demand for cloth, which was expensive and laborious to make at the time (which limited supply). Demand outpaced supply, ergo prices were extremely high. These high prices created a market opportunity for innovators who introduced machines and factory-style assembly in order to produce massive quantities of cloth both cheaply and quickly. On top of this, Britain had substantial coal and iron reserves, which were/are the bread and butter of industry. The idea of using machines to make things quickly and cheaply caught on pretty nicely, and became widespread in society. This allowed/demanded much denser urban centers to fit the workers in around factories, while boosting agricultural production, as well as creating the beginnings of economic growth. I'm less clear on why this revolution spread to some areas and not others. In the case of many African nations, imperialism focused mostly on exporting raw materials, and less on encouraging African countries to produce goods for themselves (which would have upset the trade imbalance that was benefiting Europeans so nicely), effectively delaying the spread of the industrial revolution to those countries. Asia on the other hand, while still very exploited (don't get me wrong) followed a different economic trajectory (courtesy of planned economics) that has let it grow incredibly quickly for the past 50 years, both economically and in terms of population. \nEdit: I know my model is simplistic, and I cannot account fully for the differences between Asia, vs Africa, vs Latin America, but as a general big picture explanation, it works. "
] |
[
"And even though Australia is a large landmass in the southern hemisphere a lot of it isn't very habitable. "
] |
[
"Why do we panic?"
] |
[
false
] |
I understand the fight or flight response, but panic seems to be somewhere in the middle and tends to cripple most people like a deer in headlights. All rational thought seems to go out the door.. Why?
|
[
"Not wanting to excite a predator has got to be at the top of the list of reasons, but there are other instances it can be useful.",
"\nYou freezing up in a dangerous situation might keep you from making a situation worse, or injuring yourself further.",
"\nIn a group scenario, having everyone running in all directions with different ideas would be chaotic.",
"\nFreezing and waiting for the emergence of a single to few leaders to direct the rest would likely be safer and provide more of a chance of remaining together for the group. "
] |
[
"There are interesting but speculative evolutionary theories on panic, depression, etc. Check out ",
"Randolph Nesse's",
" work in evolutionary psychiatry. Like you said, the fight or flight aspects are easy to understand but the debilitating aspects are harder. Why wouldn't selection weed out genes for crippling panic and depression if they're not adaptive? One answer is simply that there aren't genes for them; that the environment and other epigenetic factors are the main contributors. Another answer is that even if they are strongly genetically controlled, natural selection wouldn't have an effect unless they reduced reproductive success. Remember, reproductive success is more important than survival for natural selection. A genetic disorder that occurs late in life won't be selected against because it causes death after reproductive age."
] |
[
"Cite sources please.",
"edit: Downvoted for asking for supporting research? This place really has taken a nosedive."
] |
[
"Are proton-proton and neutron-neutron nuclear force interactions provide significant attraction? Can one hadron only 'bind' with another hadron via the nuclear force?"
] |
[
false
] |
[deleted]
|
[
"Are proton-proton and neutron-neutron nuclear force interactions provide significant attraction? ",
"Yes, their interactions are generally attractive, except at very short distances.",
"Can one hadron only 'bind' with another hadron via the nuclear force?",
"In principle you could have two hadrons of opposite charge form bound states due to their Coulomb interaction. For example, ",
"protonium",
".",
"Can these two bind with each other with any significant strength?",
"If you consider a system of two nucleons, there's four independent ways that you can couple their isospins: the singlet, which is just the ground state of the deuteron, and a triplet consisting of the diproton, the dineutron, and the first excited state of the deuteron.",
"The T = 0 singlet is the only one of those states which is bound. Even though there is an attractive residual strong force for the triplet, it's not strong enough for bound states to form.",
"Also can one neutron only bind to one proton and vice versa?",
"If you consider A = 2, as I did above, then yes. Of all the possibilities, only the ground state of the deuteron is bound."
] |
[
"Okay thank you so much for your reply. Since this isn’t my field of expertise there’s a couple concepts I just wanna reiterate to make sure I understand you.",
"Same-same hadron bonding is possible but the isospin pair (triplet state) to cause this is rare?",
"And only one hardon is bounded to another hadron. So does that mean in say a nucleus of carbon, there’s a “chain” where a proton is attracted to a neutron, which is attracted to a proton, which is attracted to a neutron...? Or does the proton feel an attraction to all neutrons is I think the strong interaction range?",
"edit: so I've been reading more and it seems a spin-pair is different from nonexclusive nucleonic force. So spin-pair bonds to form chains. But does the nonexclusive nucleonic force attract all nearby nucleons? I'm still reading but I still can't quite grasp where the nonexclusive nucleonic force comes from. It's simply a product of nucleonic charge? And is about 1/9th the strength of the spin-pair?"
] |
[
"The isospin triplet is unbound on its own.",
"In a nucleus with A > 2, every nucleon still interacts with eve ey other nucleon.",
"What do you mean by “nonexclusive nucleonic force”?"
] |
[
"How do our immune systems know not to attack healthy bacteria?"
] |
[
false
] |
I'm assuming it's some sort of chemical signal secreted by the bacteria, but what's the exact mechanism?
|
[
"According to ",
"Wikipedia",
" there are 1 quadrillion bacteria in the gut. That's ",
"10 times",
" the number of cells in the body. So even if the immune system was going to, I don't believe it would be successful. But there is ",
"information on how the immune system interacts with these bacteria",
". One of the functions of the protective flora is to train the immune system to recognize other bacteria in more harmful locations of the organism. Also ",
"this article",
" gives some information on how the two systems interact, but you need a little immune physiology knowledge before reading it. ",
"Also, this",
" is a study done on mice proving that the flora is there to train your immune system for other pathogens that it will encounter."
] |
[
" - ",
"I'll start this off by saying that my Immunology is a little bit rusty.",
"Inside the layers of our skin and mucous membranes there exists dendritic cells that detect bacteria and bacterial components known as Antigen Presenting Cells (APC's). These APCs present the components to other cells in the immune system and produce an immune response. This helps maintain a sterile environment for your body.",
"The bacteria located within the gut but are technically are outside of this protected barrier.",
"This is why stab wounds/trauma to the abdomen can be very dangerous. Damage to this protective membrane allows these massive amounts of bacteria to enter your body and start wrecking havoc leading to a systemic infection called Sepsis.",
"What you're thinking of is the chemicals secreted by bacteria such as Helicobacter Pylori. These chemicals counter-act the acids secreted by the stomach and create a more suitable environment for the bacteria to survive and multiply.",
"So what actually happens is that the bacteria live ",
" our skin/mucous membranes, but do not have the capability to penetrate it due to either the structure of the skin, or our immune system."
] |
[
"Actually lamina propria DCs (specificaly CX3CR+CD103+ if you are interested) project pseudopodia into the lumen of the intestines. They can sample antigen there an actually bring it back to the Peyer's Patches and mesenteric lymph nodes. I believe this process is important for the immune reaction against salmonella, for example, even before it traverses the epithelial barrier",
"A particularly popular thought regarding how pathogenic bacteria are distinguished from normal flora in the gut has to do with regulatory T cells. Regulatory T cells are a subset of T cells that are traditionally regarded to develop in the thymus and specifically recognize self tissue. However, instead of promoting inflammation like a normal T cell might when it encounters its antigen, regulatory T cells actually suppress immune responses. Since regulatory T cells recognize self antigens, you can see how this represents a way to combat autoimmunity.",
"Recently, it has come to be appreciated that regulatory T cells can develop outside of the thymus as well via direct differentiation from regular T cells. Why do more regulatory T cells form outside of the thymus? The thought is during the neonatal period, T cells populate the gut and survey the normal flora currently there. Any T cells that react to this flora are programmed to differentiate into immune suppressive cells rather than maintain their inflammatory phenotype. Thus, when these normal bacterial antigens are continually encountered later in life, you do not react to them. However, pathogenic bacteria, which hopefully were not present in the neonatal period, will be met by regular T cells who can respond as they do best and kill the bacteria."
] |
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