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[
"What is the maximum amount of hours you can spend in the same date?"
] |
[
false
] |
If you could travel fast enough. What is the maximum amount of hours one could spend on a specific date? Say i went 24 hours in one time zone, then had the speed to go to the edge of the next on and repeat as many times as possible to stay in today.
|
[
"The time zones go from UTC -12:00 to UTC +14:00, as can be seen on ",
"Wikipedia",
". That alone is enough for a 50 hour day. You could get an extra hour if the Line Islands used daylight savings time, but it seems they don't. You don't have to go that fast for this. You basically just have to cross the international date line.",
"Edit: ",
"Here's the path",
", using ",
"this map",
"."
] |
[
"Stupidly pedantic, but +1 second if you pick a leap second day to do it on."
] |
[
"Theoretically I believe 47:59:59 hours:minutes:seconds. It's all based on the international date line. If you view a world map and image it is segmented into 24 equal time zones. You could travel through all of those zones and then back around to the international date line theoretically getting you back to the start of the day you wanted.",
"I'm sure someone else will come up with a much more eloquent way of explaining this win images but I'm on mobile so it's a hassle. My tip would be to google the time zones and imagine your starting in one time zone and hop each time zone every hour. So you technically maximise the day.",
"Start at GMT 00:00am leave GMT at 1:00 and hop back a time zone until you end up back where you started.",
"Hope that answers it.",
"Edit:\nTo add to my comment the link below explains it very well, but to make the most of your time you would keep travelling back in time for a full 24 hours cycle and then sit the rest of that day out partying on the international date line until the day ticks over. ",
"Monday 00:00am travel back a time zone every hour until you've completed your last time zone so it remains Monday 00:00am then you have a the whole of Monday on the date line and it ticks over to Tuesday 00:00am. ",
"http://science.howstuffworks.com/science-vs-myth/everyday-myths/question618.htm"
] |
[
"How likely is it that there are undiscovered elements in different parts of the universe?"
] |
[
false
] | null |
[
"Despite its name, the island of stability isn't theorized to be stable. It is just theorized as less unstable than other nearby elements."
] |
[
"We can create those heavier elements artificially in the lab and they may form spontaneously in the high-gravity, energy-rich centers of stars, but they don't last. Their nuclei are too large for the nuclear forces to hold them together, so they're highly unstable."
] |
[
"That's the thing about the periodic table of elements. It tells us what elements are possible based on their structure. Since there are no \"holes\", we know we're not missing anything.",
"That's not to say that we can't find heavier elements, which scientists are continually working to create in the lab, or other isotopes of existing elements."
] |
[
"Question about zero voltage"
] |
[
false
] |
Say you have a circuit. At a point where the voltage is zero, does that mean there is no difference in potential between that point and the ground? Could you touch that 0V point and not get shocked even though there is current flowing through it? Does AC or DC make a difference?
|
[
"Voltage is the potential difference between 2 points. If you make one reference point ground and some other test point not ground and the potential is zero then current will not flow because there is no motive force. AC is a different beast. If neither side is grounded current won't flow to ground. ",
"Edit: to clarify and add"
] |
[
"First, voltage \"at a point\" is an invalid statement. Assuming you mean ground as a reference point and voltage to groung is 0V it means this point is effectively ground. If you would insert yourself between ground and this point, no current would flow through you, therefore no shock."
] |
[
"I would take issue with calling it effectively ground, because a floating point that has the potential of ground will not sink and source current the way ground does."
] |
[
"Can your body adapt to hot temperatures over time like exercising a muscle increases it’s strength?"
] |
[
false
] | null |
[
"Yes, ",
"\"These physiological adaptations include:",
"To acclimatize workers, gradually increase their exposure time in hot environmental conditions over a 7-14 day period. New workers will need more time to acclimatize than workers who have already had some exposure.\"",
"https://www.cdc.gov/niosh/topics/heatstress/acclima.html"
] |
[
"Additionally, some people are genetically predisposed to be able to handle heat better. As far as I am aware, it's mostly through anthropometric characteristics (IE how your body is shaped). Your body dissipates heat through your skin so if you are tall, lanky, and skinny, you'll have more surface area per lb of body to get rid of heat. ",
"The article below also goes into some other genes that may play a role but it's not well understood yet.",
"https://link.springer.com/article/10.1007%2Fs40279-019-01067-z"
] |
[
"Yes as someone who worked in an industrial forge you do adapt to hot temps over time.",
"My first summer I had several bouts of heat exhaustion and overall had high heat stress all summer. ",
"By my last year there (7 years) summers were more of an annoyance than a possibly deadly situation.",
"Average temp in forge during summer months was 140 degrees Fahrenheit and during winter was 85-100 degrees Fahrenheit. ",
"We worked ten hour shifts. Not only did we physically adapt to the hear you also become more aware of your bodies signals during exertion in the heat.",
"As mentioned above I did tend to sweat earlier and sweat more while at the same time I did not experience symptoms of dehydration as bad in my last year.",
"Muscles did not cramp as much and overall heat stress did not affect me as bad during my last year.",
"Now almost 10 years removed from the forge and I do not handle heat well almost as if I rebounded farther than my original base line."
] |
[
"Why shouldn't you extinguish a beach bonfire by burying the fire with sand?"
] |
[
false
] | null |
[
"In terms of intrinsic properties, sand has a decently high heat capacity and a rather low thermal conductivity. The former property means that sand can absorb a large amount of thermal energy and the latter means that hot buried sand can retain this energy for a prolonged period. In practical terms, this means that even an extended time after a fire is covered there will be hot sand hidden beneath the surface such that if someone unwittingly steps into it he may sustain serious burns. "
] |
[
"sand is such a good insulator in fact that some cultural foods involve cooking large pieces of meat by burying the meat and coals underneath sand and cooking for hours."
] |
[
"Burying the fire may smother it, but you have a lot of hot coals now insulated by sand. You risk something flammable which comes in contact with the sand or with the material lighting on fire long after you've left. Similarly, this is a bad idea if you expect anyone may be on that beach in the next day or so. They would probably be upset stepping into your fire."
] |
[
"There were once less than 30 California Condors left. How does this affect the species, genetically?"
] |
[
false
] |
All future California Condors will necessarily originate from those few. Is there enough generic diversity with those 30 subjects for the species to recover and thrive?
|
[
"Yes actually! There were three distinct families that were left over and when breeding programs were started they made sure to breed condors to those who were least like them. Condors were transfered between breeding facilities on a regular basis and the condors that are alive now have the broadest \"range\" of genetic diversity. The condors that survived would also, theoretically, be the strongest and most able to survive meaning that any of their offspring have the greatest chance of survival.",
"The bad part is diseases which arise when both parents are carriers. By testing the population for these diseases and only breeding pairs that would select against this, the condors alive now are very healthy and stand a great chance of recovery."
] |
[
"This is a concept called ",
"\"Genetic Bottleneck\"",
". If the limited number of surviving members of the population happen to have genes that made them more likely to survive the bottleneck in the first place, the population as a whole may become heartier. But if the bottleneck resulted in a small population with a random assortment of genes and there happened to be a high proportion of individuals with \"bad\" (disease-causing/something leading to poor adaptation to the environment/etc), then the population might have a greater chance of extinction. "
] |
[
"20,000 and 30 are very different numbers when you're trying to assess the genetic diversity of a species."
] |
[
"How much longer will the Hubble Space Telescope remain operational?"
] |
[
false
] |
How much longer will the Hubble Space Telescope likely remain operational given it was launched in 1990 and was last serviced in 2009,9 years ago?
|
[
"BFR could potentially bring it back in one piece with an acceptable cost.",
"I really hope they do this. Hubble was such a revolutionary instrument, it should be in the Smithsonian, not charred scrap at the bottom of the ocean."
] |
[
"As long as NASA finds a way to use it. They are expecting that it will fall back to Earth ",
"between 2030 and 2040",
". It could fail due to other issues before, of course. ",
"BFR",
" could potentially bring it back in one piece with an acceptable cost."
] |
[
"A good resource is ",
"this Hubble Status presentation PDF from 2017.",
"The HST's most vulnerable component is its gyroscopes, which are used for precisely pointing the telescope. It needs three gyroscopes for normal operations, and it has six on-board for redundancy. ",
"The second gyro of those six failed in April of this year.",
" Once two more fail, it will start to affect operations. Operations can continue in a more limited capacity all the way down to one gyro (which would get Hubble very solidly into the 2030s, where its orbit would become the limiting factor). But the question once we reach sub-three-gyro operations (estimated at ~2023) will be if a limited Hubble is worth $100M a year, which is what it costs to run.",
"Right now, it is *very* worth it.",
"And as you can see from ",
"that PDF I linked",
", folks are working hard to develop innovative plans that keep all these instruments going, all so it can keep being worth the upkeep as we go forward into this uncharted territory.",
"* Edit for clarity: It's important to note that these gyroscopes are not like the ",
"control moment gyros",
" that the ISS uses the momentum of to rotate. The Hubble gyroscopes just help you know which way you're pointing. For a complete picture of how Hubble points itself and knows where it's pointing, check out ",
"this page",
" (the magnetic momentum dumping is pretty cool)."
] |
[
"Is the future of Internet speed more closely in line with hardware or software advancements?"
] |
[
false
] |
I'm not very knowledgeable with technology, so forgive this question if it's stupid. I'm aware that advancements in hardware allow us to send information at incredible speeds through the series of tubes that is the Internet. My question is, will future speed increases be based upon advancements in the materials and physical technology used to transfer information, or is it a software issue, in which the programming behind how information is sent could be improved, allowing much faster speeds? Thanks in advance for helping me out.
|
[
"Its primarily in line with business decisions than technological decisions"
] |
[
"This is pretty much the best answer. If you have the money the sky is the limit in terms of raw throughput. Throw enough cash at a teir-1/teir-2 provider and you can have your very own dedicated multi-fiber bundle that basically guarantees you will saturate the connection of whomever you're communicating with before your own connection becomes a limiting factor.",
"There are fundamental limits to how fast you can send information but limitations of everyone else's hardware will become an issue long before you ever reach that point; not because better hardware doesn't exist but because companies don't deploy bleeding-edge tech the moment it becomes available."
] |
[
"I am currently working for an internet provider that is make a shift to faster internet speeds. They are doing it in two major ways. This company supplies TV and Internet which share the same cables. Until recently we still offered analog cabler service. Analog uses wave signals were as digital uses binary and requires a digital converter box. Analog signals take up as much \"space\" as 10 digital signals. So by eliminating the Analog we were able to provide more digital channels and more bandwidth for the internet. The next which we are currently in is switching the copper wiring to fiber optics. Copper wiring uses electricity which has a limited speed, and loses power over long distances, were fiber optics use ligth and is faster, more consistent, and allows for a higher data transfer rate."
] |
[
"What really kills you when you die of thirst or hunger?"
] |
[
false
] | null |
[
"For starvation, you first run out of carbohydrates (sugars) as an energy source, then you run out of lipids (fat) as an energy source, and finally your body starts breaking down proteins for energy. Since proteins are essential to all your cellular function, this means that your body starts breaking down your organs, starting with muscles. As parts of your vital organs are broken down, you die, usually from heart failure.",
"For dehydration, you end up with an electrolyte imbalance in your blood, which leads to seizures and heart failure. "
] |
[
"Yes. That is one of (not the only) the biological/evolutionary reasons that our bodies tend to store excess food as fat. As a battery for scarce times."
] |
[
"Does this mean that if you are twice as fat as person A (by % of fat in the body) does that mean you would live twice as long without food (with normal access to water)?"
] |
[
"What are the differences between Antimatter and Matter?"
] |
[
false
] | null |
[
"From ",
"the Wikipedia page",
":",
"antimatter is material composed of antiparticles, which have the same mass as particles of ordinary matter but have opposite charge and quantum spin.",
"Normal matter is made of Neutrons (with a neutral charge), Protons (with a positive charge), and Electrons (with a negative charge). Antimatter has Positrons (the opposite of an electron with a positive charge) and Antiprotons (the opposite of a proton with a negative charge).",
"When the two combine, they can annihilate (explode) and release lots of energy."
] |
[
"The quarks and anti quarks would annihilate and anything that doesn't will hadronize. This would still be a very energetic event."
] |
[
"What do you mean by \"combine\"? Does that mean low speed physical contact? High speed accelerator?",
"How is it stored? How is it transported from wherever it is made to wherever it is stored?"
] |
[
"I know that through evolution one species can become another species, but at what point does one species turn into another?"
] |
[
false
] |
I also don’t know what flair to put, so I put chemistry
|
[
"It's a new species when people agree that it's a new species. ",
"There's no dividing line, because \"species\" is just a human definition that doesn't line neatly up with biology. There are many different definitions of \"species -- the one that's most widely known is the ",
"\"biological species concept\"",
", which uses fertile interbreeding as its definition; but that's just one definition of many, and it isn't particularly useful in many cases, including this one.",
"People talk about ",
"chronospecies",
" when talking about changes over time, but mainly that illustrates that there's no clear demarkation. ",
"Of course, there's no reason why there should be a clear demarkation. With contemporary species, there is at least sometimes a reason for speciation (as defined by interbreeding, for example). If say two overlapping populations exist -- say, small-beaked bird that specialize on seeds, and large-beaked birds that specialize in nuts -- and their offspring were intermediate (medium-beaked), then they'd have a selective disadvantage to interbreed. Medium-beaked birds might not be able to eat seeds well, or nuts well, and would be less fit than either extreme, so a bird that preferred to breed only with its own kind would have more successful offspring, and you'd eventually evolve reproductive isolation. (Obviously this is super simplified.) But there's no selection for speciation over time, and it's just random chance. ",
"So there's nothing except chance driving speciation, and so there's no reason to expect a nice neat dividing line, just many many generations of gradual intermediates."
] |
[
"Some conditions apply, your results may very.",
"Animals can be different species and still produce fertile offspring, mostly ones that are geographically seperate."
] |
[
"There isn't really a single point you'd be able to identify where the species changed. With a few exceptions, like ",
"polyploid speciation",
" in plants which can theoretically happen in a single generation, speciation is a continuous process that takes some time. Many people make a distinction between two main patterns of evolutionary change. Cladogenesis is evolutionary change that occurs as one lineage splits into two or more separate groups, which may eventually become distinct species. In contrast, anagenesis is change that occurs within a single lineage that remains a cohesive group during this time. Here's ",
"some",
" ",
"diagrams",
" that show the difference pretty well. (Note: personally, I don't really think there's a particularly meaningful distinction between these two patterns, but I don't want to get too off-topic).",
"The situation you're describing sounds more like anagenic speciation, since we're thinking about an ancestral species and a descendant species that are separated by ",
", rather than two species that coexist in time diverging from each other in ",
" (or at least phenotypic space), which would be more akin to cladogenesis. The problem here is that we're restricted in what aspects of these two species we can actually study. Even with the assumption that the descendant species is alive at present, the ancestral species will only be represented by fossils or historical specimens, depending on the time frame we're talking about. This means that there won't be any way to test if these two species are different under the ",
"biological species concept",
" (check out the last point there especially), since we can't try interbreeding them. So, the only way to tell if two groups that exist at different points in time are different species is typically to compare morphology, and these methods are somewhat prone to subjectivity and disagreement about where exactly a line separating species should be drawn. A good example of this is the confusing taxonomic history of ",
", a genus which over time has gone from having almost a dozen species at one point to just one at present, with some being moved to the genus ",
" partially because of temporal separation (",
"source here",
", though this is still something of a contentious issue).",
"On a final note though, even when discussing cladogenic speciation, where both putative species are around at the same time, there's still no clear threshold to determine when speciation has truly occurred. ",
"This figure",
" (",
"source",
") does a great job of showing how different species concepts will disagree on the exact point at which two species are fully separated, and so we can only really say two groups of organisms represent \"good\" species some time after their initial divergence."
] |
[
"So if you cannot create or destroy energy, does that mean there's a constant amount if energy in the universe?"
] |
[
false
] | null |
[
"Sort of but not really.",
"To keep a long story short, the law of conservation of energy only applies for any system which is \"time-translation invariant\" -- meaning, if you did an experiment, the time you choose to do the experiment would have no effect on the outcome. For any system that is time-translation-invariant, energy is always conserved, and the total amount of energy is constant -- yes.",
"However, it turns out that the universe is ",
" time-translation invariant. The universe is expanding at an accelerating rate, which is causing the density of ordinary (baryonic) matter to decrease (at the rate you'd expect -- the total amount of energy in ordinary matter remains the same), and the density of electromagnetic radiation to decrease even faster (photons are losing energy over time) -- but the density of dark energy appears to be remaining the same. Consequently, photons are losing energy through redshift as space expands, and the total amount of dark energy in an expanding region is increasing. These changes do not cancel eachother out (so it's not as simple as photons being converted into dark energy, or anything exotic like that).",
"Also, there's the strong possibility that the universe is ",
" infinite in spatial extent, which would mean the total amount of energy would also be infinite. So no matter how much it expands, if it is infinite, then it will always be infinite, and the question of how much total energy is in the universe is moot.",
"Hope that helps!"
] |
[
"True, although whether the universe is infinite or not, you can still write conservation of energy for a small volume by saying any change in the amount of energy in the volume must be due to energy leaving or entering the volume through its edges."
] |
[
"Oh yeah, no doubt about that. :) Though the OP was asking about the universe as a whole, and not a small volume of it -- so that's the question I answered. :p"
] |
[
"What defines male and female in a Seahorse?"
] |
[
false
] |
I have been told many times that with seahorses, the males hold the fertilized eggs and give birth to the offspring. But doesn't that make them the female? So what makes them male? Is it a Y chromosome? Is it the difference between sperm and eggs?
|
[
"Females have the ova (eggs). Males have the sperm. For some reason, in seahorses, the females insert their eggs into the male and he fertilizes them inside himself. After gestation, all the hundreds of babies burst out.",
"Biological life is weird, haha."
] |
[
"Seahorses just don’t care about our arbitrary concepts of gender and sex. ",
"To a seahorse, the only thing that matters is who’s making sperm (male), and who’s making eggs (female). The idea that the one who carries them, or the one who gives birth, is a specific gender or sex doesn’t matter to a seahorse. ",
"So, basically, a male, scientifically, produces sperm. A female produces ova (eggs). ",
"Most species have the male deposit, insert, or otherwise give his sperm to the female where it fertilizes her eggs. Seahorses have females that give their eggs to the males, and it becomes fertilized at that point. ",
"The aquatic world is wonderful and strange, and it’s not just seahorses. Female fish and a number of invertebrates release their eggs instead of carrying them. Either they’re just a cloud of eggs floating that gets fertilized by the male, or they’re carefully laid somewhere and gets fertilized by a male. ",
"To sea creatures, the idea that a female has to be the one to actually carry the babies inside her is absurd, and they think humans are very simply stupid. I mean, all the fuss over who carries what, and most of ",
" don’t even bother carrying anything at all!"
] |
[
"The larger of the two gametes is the ova. The smaller is the sperm. Same size gametes get arbitrarily assigned. "
] |
[
"Why is there so much controversy surrounding GMOs?"
] |
[
false
] |
I just don't understand it. I work in molecular biology/biophysics. Although I don't do any work on food production, it seems common sense that we would want to genetically modify our food to produce the traits we want, and not the ones we don't. This seems like a no-brainer. So why is there so much controversy over GMOs? Is it actually a controversy over the practice itself? Is it a controversy over the practices employed by the corporations making GMOs? If it's the former, I can't help but categorize the anti-GMO people as ignorant and impulsive. If it's the latter, why can't we frame the debate as anti-Monsanto rather than anti-GMO? Thanks. Sorry to anyone I offended. Please educate me on the matter, if you can. Edit for clarity: Is there an actual scientific problem, or is the problem ignorance of science, or is the problem mostly political?
|
[
"Are you asking what the controversy surrounding GMO ",
" is, or are you asking about GMOs broadly? To many people, the word GMO means food, but we really have engineered a whole bunch of organisms beyond just foods.",
"When I talk to people, the responses fall into one of the following categories, all paraphrased:",
"\"",
"\" -- The problem here is typically twofold: (1) the casual citizen doesn't know how much scientists know about genetics and protein functions, so doesn't understand what we are doing to make a GMO, usually imagining we are just trying random things until we get something we like and (2) they don't know who regulates the outcomes. They know the FDA does drugs and FDA approval makes them feel safe, but they think no one is regulating GMOs, so who is protecting us?",
"(",
") \"",
"\" --This is a nuanced social argument and, when pressed, individuals either can't name a single specific GMO product or can only name roundup-ready corn. The argument is valid and just, but they often can't support it with details.",
"(",
") \"",
"\" -- again bringing up issues of safety and not understanding the regulatory process",
"(",
") \"",
"\" --this is probably the strongest argument I hear, because it's based on solid reasoning that no amount of scientific logic or government regulation can refute. My personal opinion on this one is that the benefits often far outweigh the risks, but it is always true there will be unmitigated risk involved in synthetic organism release, because of the beauty of evolution.",
"(",
") \"",
"\" --this is similar to the above argument, and often these people have heard of the problems with invasive species, leading them to think adding species to an ecosystem always causes havoc. ",
"There is one final argument I've heard once or twice, which goes something like, \"",
"\" --This is a very broad philosophy vs science argument and another one that not much can change.",
"Of those arguments, the loudest and most popular are the (A) anti-corporate and (B) 'scientists don't know what they are doing' arguments. I tend to be able to sway the (A) type by explaining that we have failed so far in GMO production by letting it be dominated by big profit makers, but that the promise of GMOs is a possible solution to many health, medical, and ecological problems that go far beyond profits. The (B) type tend to be swayed by a long explanation of the process of genetic engineering: how focused, targeted, tested, and difficult it is, giving them an understanding that we aren't just mixing organisms willy nilly. ",
"I also like to tell people that the current regulatory framework is a mess, with several overlapping agencies responsible for approving different parts without clear standards of what a GMO is or an understanding that some GMOs need more scrutiny than others; they always agree with me that more oversight and a clearer process is needed.",
"And I like to conclude by saying that companies like monsanto fight against GMO labeling because they are afraid you won't buy the product if it says 'contains GMOs'. I tell people this is wrong, because a corporation shouldn't be able to sneak something in you don't want and that, as a scientist, I want people to have full knowledge of what's going on so they can have an informed opinion about where the science should take us. If all of a sudden 50% of what's in the grocery store has a GMO label on it, it will both shock people into questioning what's going on and remove some of the stigma with the acronym-- \"if all of these GMOs are already out there and no one has gotten sick or died, they must not be nearly as unsafe as I was assuming.\"",
"Here is an earlier post I made on the same topic that contains a partial list of some of the approved GMOs out there"
] |
[
"It seems to me that you are brushing off the last argument and painting it in a very non-scientific way when it can really be a legitimate argument. When you take away all the philosophical stuff, the actual argument goes something like this (using corn as an example):",
"If we completely monoculture corn across the globe, what happens when corn fungus adapts and kills 75% of the global corn crop in a single year?",
"I don't know if this type of issue is already being addressed in GMO research or not, but things like the collapse of honey bees show that even just similar organisms, even if they are not genetically identical, can be completely decimated on a global scale. It seems like identical organisms would exacerbate this problem."
] |
[
"Its not a scientific question really because the reasons are mostly political.\nThe #1 pusher for GMOs is ",
"monsanto",
" who have an incredibly bad name. They manufactured agent orange in vietnam and have a hand in manufacturing lots of food you buy in supermarkets.",
"They also have a practice of suing farmers when bees cross polinate monsantos seeds with the farmers crop because they have patented the genetic modifications.",
"So in general I don't think people distrust GMOs but they do distrust monsanto.",
"Sorry if this answer was not scientific enough but it seems that the answer was more political."
] |
[
"Breathing in high altitudes with compressed air?"
] |
[
false
] |
Hi all, The other day I was reading about mount Everest and how a bunch of dead bodies remain up there because no one have the strength to get them down from above 8.000 m. I know we breathe on high altitudes (inside airplanes) thanks to air compression. The oxygen don't diminish with higher altitude, only gets separated because of the lack of pressure. So why use pure oxygen? What if I made a hand pump connected to a light container and some filters and simply compress the air and breath as I go? Would it work? it would be lighter than carrying an oxygen tank and limitless. Buts something tells me is not that simple... Thanks in advance!!
|
[
"To answer your question in parts,",
"1) Why use pure oxygen? This is because what matters is the partial pressure of oxygen. In the atmosphere, oxygen comprises roughly 20% oxygen. This means that you could breathe air at 20% of sea level pressure if it was 100% oxygen. So carrying oxygen to high-altitude environments is the most efficient way to bring your own air with you.",
"2) Why not simply compress the air at Everest? First of all, you can't breathe compressed air directly. This is because if there's a pressure difference between the air your breathing and the environment, this could cause major damage to your lungs (think of over-inflating a balloon). Secondly, compressing air is actually a lot of work. A person simply doesn't have enough energy to compress that much air in order to breathe."
] |
[
"Nevermind the compressing part, even if you had the energy to do it. Lungs work on a somewhat minute pressure gradient established by expanding the volume of the cavity in which they reside, thus causing a lower pressure within said cavity. As a result, air rushes in. Regardless of the altitude, this is going to happen. Compressing the air in this way is akin to turbo charging a car. YES, you can jam more air into the system this way. However, as was previously stated by ",
"/u/shadydentist",
" the effect of this is going to be catastrophic for the subject trying this."
] |
[
"Nevermind the compressing part, even if you had the energy to do it. Lungs work on a somewhat minute pressure gradient established by expanding the volume of the cavity in which they reside, thus causing a lower pressure within said cavity. As a result, air rushes in. Regardless of the altitude, this is going to happen. Compressing the air in this way is akin to turbo charging a car. YES, you can jam more air into the system this way. However, as was previously stated by ",
"/u/shadydentist",
" the effect of this is going to be catastrophic for the subject trying this."
] |
[
"Could we find opportunity?"
] |
[
false
] | null |
[
"We know exactly where Curiosity is. The hard part is getting there."
] |
[
"Planetary sci"
] |
[
"Planetary sci"
] |
[
"The photons sent after the big bang must have bumped into millions of galaxies, stars, planets, ... If matter absorbs photons, how is it possible that we still see the cosmic background radiation?"
] |
[
false
] |
The main reason why I can't figure this out is because the universe expands faster than the speed of light. So all matter that came into existence somewhere in space, must have been there before the light from the big bang reaches it
|
[
"Most of it actually hasn't been absorbed or scattered significantly, because space is really mostly empty. However, a fraction of it is scattered as it passed through the hot ",
"intracluster medium",
" plasma around galaxy clusters. This results in a change in the spectrum of the light called the ",
"Sunyaev–Zel'dovich effect",
". There are cosmic microwave background telescopes including ",
"the South Pole Telescope",
" and the ",
"Atacama Cosmology Telescope",
" that look in great detail at sections of the CMB to find clusters using this effect."
] |
[
"It's already incredibly dim, sitting at around 2.7 kelvin and will continue to cool, fade and become harder to detect that is correct. In about 10 to 100 billion years in fact it'd be impossible to tell the big bang happened. Any modern proof of the big bang becomes undetectable around those time frames. "
] |
[
"The simple answer is: because they literally come from everywhere. ",
"They are the light that was bouncing about at the Big Bang, which happened everywhere that was, that light is from everywhere in the universe and has been bouncing around for 13.7 billion years. It ",
" get absorbed, but there is simply so much of it in so many places that there's still so much left. ",
"If you think about it, it's just like the light from the sun. Even though you have walls and doors and things in your house, there's still plenty of light to see, so it gets everywhere anywhere. And the universe doesn't have those things; for the most part, it's completely empty."
] |
[
"How does transparency work?"
] |
[
false
] |
As far as I can tell, there aren't little holes for the photons to jump through in my window. I'm curious to know the mechanism behind transmitting light through a transparent material in addition to the obvious case of how it gets through the air we breathe.
|
[
"So there are two different primary mechanisms for transparency.",
"1) Materials have what is called a \"bandgap\". In this bandgap, electrons in the material cannot have certain values of energy. That is, imagine a ball - you can give the ball any energy you want. But in a material, if you pretend the electrons are balls, they can actually only have certain energy values.",
"Now in order for a material to interact with light, the light must be absorbed. So lets say you have an electron at some energy which tries to absorb the photon. If the total energy of the electron after the absorption was not allowed in the material, then the photon can't be absorbed at all, and the photon just passes through. This is the mechanism of transparency for many everyday materials.",
"Also aside from just the energy, the momentum of the light must be conserved. This leads to a more complicated process, but sufficed to say that absorbing X energy and Y momentum from a photon can be prohibited in a material, meaning that the light won't be absorbed at all.",
"2) The second mechanism of transparency is where the photons have too much energy to interact with the electrons. In order for the electrons to interact with the photons, they have to pick up the photon energy.",
"Imagine you are sitting on a swing. If someone pushes you nice and slow, you will start swinging and absorb their energy, and your swinging frequency will match up with their pushing frequency. But if some asshole comes up to you and starts quickly hammering on your back then you're not going to go swinging really quickly, you're going to sit there and vibrate while all that energy in your back dissipates and rattles up the chain.",
"The same process happens in electrons - if the incident photon has an energy too high then the electron can't respond fast enough to capture that energy. Therefore, the photon will pass right through the material. This is the mechanism of transparency for things such as x-ray beams going through your bones.",
"As you can see, transparency is actually a very difficult topic and is quite complicated."
] |
[
"I'm sorry but the 'little holes' description wholly misses the point. Your second description is more correct. ",
"Edit: While an electron can be localized to an incredibly \"small\" space, it is most certainly NOT ",
" a golf ball whizzing around in the context of an atomic structure. That's why the 'holes' argument is completely wrong. The wave-particle \"duality\" must always consider the wave part. ",
"In order for light to be absorbed, it must be able to interact with the object. This interaction occurs when the energy in a photon is sufficient to excite an electron in an atom of the material. When this cannot happen (e.g. if the first excited state available is above the energy of the photon) light will pass through the material without interacting. ",
"60 symbols has a good description:\n",
"http://www.youtube.com/watch?v=Omr0JNyDBI0"
] |
[
"There are three things you need to consider to understand transparency:",
"There is a property of matter called the index of refraction (yes, which can be derived from other physical quantities). This index describes how matter behaves when an electromagnetic wave such as light impinges on it. The index is generally different for different frequencies. In general, when an EM wave hits a material, the oscillating electric field causes the atoms in the material to oscillate in time with it. These atoms pass the vibrations on to their neighbors and so the light propagates through the material. Notably, the index of refraction tells us that the speed of propagation varies in materials (when compared to a vacuum) such that for a given frequency, the wavelength gets shorter with increasing index of refraction. This also has implications for how light is bent by lenses and how antireflection coatings work.",
"The index of refraction can have a complex value (i.e. contain imaginary numbers) which indicates that the E-field is absorbed by the material and usually turned into heat (special exceptions like solar panels exist). By knowing how thick your material is and how strong the absorption is, you can determine how much light will be left after it passes through. Remember the index is different for different colours of light, so some may be absorbed faster than others.",
"The index of refraction need not be uniform throughout a material. Whenever light encounters variations in index, its path is bent/deflected. So if you have billions of tiny imperfections in your material, your light will be scattered and so it becomes difficult to hold on to any information contained in the light. This is sometimes referred to as the \"shower curtain\" effect.",
"Specifically for air, its index is very close to 1 (the vacuum value) and so light passes through it mostly like there's nothing there. The exception is water vapor and dust which you'll see when you shine a green laser pointer into the sky at night (but not at planes).",
"So in summary, consider three pieces of acrylic plastic: clear, white and black. The clear one has uniform index with a small complex component, the white has a highly varied index also with a low complex component and the black has a high complex component (we can't tell how varied it is with just our eyes).",
"You can try this at home with two laser pointers if you have light skin. Compare holding your finger on the end of red laser pointer and a green one. With a strong enough red laser pointer, you can illuminate all the way through your whole finger, but note that you can't see the bone like you would in an X-ray. This is due to scattering in and between all of your cells etc. With a green laser pointer, notice that you don't see light spreading through you in the same way even though the green pointer seems might brighter to your eyes (that's another story). That's because the complex component of the index of your tissues (largely blood) is larger for green light. That's also why you look like a pink-ish colour in normal light."
] |
[
"Why do distorted, fuzzy lines appear when viewing a computer screen through a phone camera?"
] |
[
false
] |
[deleted]
|
[
"You may also be thinking of the ",
"Moire pattern",
". This is because of something called ",
"aliasing",
" (this thing that video cards are anti). Because both the screen and the camera are made up of arrays of pixels, the differing alignments cause these patterns. If you increased the resolution of the camera, eventually the pattern would go away."
] |
[
"Because both screens actually flicker with the ",
"refresh rate",
"Here",
" is a quite easy to understand article about it."
] |
[
"I'd say that the phones screen refresh rate has little to do with it, its rather the difference between the cameras frame rate and timing, and the refresh rate of the screen, than that of the computer screen that does it.",
"Cameras are typically 30 fps while the screen refreshes at 60 Hz (60 fps). If they were perfectly timed at this interval there wouldn't be any flicker."
] |
[
"What is the difference between cane and beet sugar?"
] |
[
false
] |
From what I understand, there is no way to distinguish cane sugar from beet sugar other than some small C4 vs C3 marker that is irrelevant nutritionaly. Yet, you see food packages that advertise "made with pure cane sugar" as if it's superior.
|
[
"A lot of those packages specify \"pure cane sugar\" to differentiate from high fructose corn syrup, which IS nutritionally different. ",
"That being said, packaging says whatever sells, and people like to think that cane sugar is somehow \"purer\". Same way that a lot of cereal mention that they're low in sodium/fat, implying that they're healthy and ignoring the massive amounts of sugar in them. "
] |
[
"Also, I'd like to point out that even when comparing HFCS and cane sugar, the actual nutritional differences are very small. "
] |
[
"Hmm is it that cane sugar is sometimes turned into char bone sugar vs beet sugar generally being organic and raw? I'm not sure tbh. But I know when I was looking into animal product-less sugar, that kept coming up on google. "
] |
[
"Are there any long term health threats from regular but low exposure to CO?"
] |
[
false
] | null |
[
"I could probably drag up the paper again if needs be, but there is a reported ",
"increased incidence",
" of aortic aneurysms in firefighters that is thought to have been caused by exposure to carbon monoxide.",
"Now, these days, firefighters use SCBA to minimize their exposure to smoke, so the study is quite old. They also had to counter for how many firefighters used to smoke back then."
] |
[
"No it was more that my friends do it and i was checking out if the health risks were significant before like joining them. I know that low oxygen levels in the blood can cause brain damage what with brain cells inability to respire anaerobically and all, but I was wondering if the low levels (10-20 ppm) relatively infrequently would cause any lasting damage because the short lifespan of red-blood cells would surely mean it wasn't cumulative damage?"
] |
[
"Even though RBC's have a short lifespan, body organs need oxygen constantly so there is the potential for some cellular damage.",
"\nBut if the CO levels are infrequent, then I doubt it's doing any more damage than walking alongside heavy traffic in a city would do. "
] |
[
"How do Jet engines work?"
] |
[
false
] |
I was reading about the internals of jet engines earlier and a diagram showed two small compressors behind a turbine, which then seems to put the compressed air in a combustion chamber, and after combustion it just chucks it back out again... surely pressurized air that's been combusted can't provide that much thrust? what am i missing? (sorry I really have no clue about thrust or aerospace engineering, however I hope to take it for university....)
|
[
"There are many different type of jet engine but simply put the purpose of the compressor is to suck in as much air as possible into the small space of the combustion chamber. You then combust the gas and it expands ",
". This expansion provides the thrust but also powers the turbine which connect the compressor so more air is sucked in and so forth.",
"A jet engine like a Turbojet operates similar to a joule cycle turbine like you'd get in a gas powered power plant. You might want to google \"Joule Cycle\" for more info!"
] |
[
"I explain the basics of turbojets like a 4-stroke internal combustion engine in your car. ",
"See diagram.",
"First you have an intake: draw air into the engine, like the intake stroke in an IC engine.",
"Second you have compressors compressing the air, like the compression stroke in an IC engine.",
"Then you inject fuel and combust it. This expands and provides the power stroke. In a car engine, this expansion helps to power the other cylinders compression strokes. In a jet engine, some of this energy is used to make the turbine rotate, which is connected by a shaft to the compression fans at the front of the engine to provide the power needed for compression. The rest is going very quickly out the back to provide the actual thrust.",
"Then you exhaust it out the back.",
"surely pressurized air that's been combusted can't provide that much thrust?",
"Surely it can, and it can be extremely efficient. Works for your car!"
] |
[
"Good question. Have you ever seen one of those jet sprinklers with nozzles that point in opposite directions? They spin once you put some water through because the nozzles are providing thrust.",
"The thrust force of a jet is equal to the rate of mass flowing out of the nozzle (kg/s) multiplied by the velocity of the jet (m/s). Mass continuity tells us that the mass flow rate is m=rho * A * V (mass flow=density * area of cross section * velocity). After some algebra we find that the Thrust= density * area * velocity",
"So if you want to generate a ton of thrust to move a airplane you need to accelerate the flow to a high velocity. After the engine pressurizes the air and then heats it with a combustor, the flow goes through a turbine expansion. This turbine is only generates enough power to run the compressor. So the flow is still hot and has some pressure. That is why the last component of a jet engine is a nozzle. It takes the gas which expanded across the turbine and constricts it again with a converging nozzle. The nozzle converts a portion of the excess heat into kinetic energy, ramping up the velocity of the flow and the thrust. "
] |
[
"I found this big tooth washed up on the beach (Hilton Head Island, SC) on vacation last week. Does anyone know what it's from?"
] |
[
false
] |
I it's a tooth, though I could be wrong. edit: I think you guys have nailed it as coming from an Atlantic horseshoe crab (and not a tooth after all!) Very cool to know! Good chance it is likely a tail, it certainly smells like it was near something's asshole.
|
[
"Everyone, could we please keep this discussion civil and mature? This is a legitimate question that deserves a legitimate answer. Keep it scientific please. "
] |
[
"Long enough rolling around in the sand because of waves motions will smooth out those serrated edges. ",
"The fact that the walls of this thing are so thin point to a chitinous exoskeleton. If you try to bend it, is it a little resistant but still bends a bit?"
] |
[
"Long enough rolling around in the sand because of waves motions will smooth out those serrated edges. ",
"The fact that the walls of this thing are so thin point to a chitinous exoskeleton. If you try to bend it, is it a little resistant but still bends a bit?"
] |
[
"Does the auditory nerves activate, when we hear the voice of our thoughts?"
] |
[
false
] |
I was wondering whether the nerves that are firing when we process sound activated, when we "hear" sound in our mind. Same could be asked for visualizations.
|
[
"Higher order auditory and visual regions of the brain can get activated, but not really the primary auditory/ optic nerves. Those sort of need to funnel in physical stimuli (sound/ light stimuli), so they're not active if nothing is coming in. But they're connected to other regions via synapses that are involved in making sense of those incoming sights/sounds. Those regions can become active if you're imagining, rather than physically receiving those signals."
] |
[
"I read something that said that they did an FMRI study for people with Schizophrenia and that the brain was activated in the same ways when hearing auditory hallucinations as when listening to someone else speak. However, it did not go further into if this is normal for anyone when \"listening\" to an internal voice not related to hallucinations. If not, it could make sense why auditory hallucinations are perceived by the individual as coming from outside of their own head so to speak."
] |
[
"I read something that said that they did an FMRI study for people with Schizophrenia and that the brain was activated in the same ways when hearing auditory hallucinations as when listening to someone else speak. However, it did not go further into if this is normal for anyone when \"listening\" to an internal voice not related to hallucinations. If not, it could make sense why auditory hallucinations are perceived by the individual as coming from outside of their own head so to speak."
] |
[
"Why do dogs have a \"wet dog\" smell?"
] |
[
false
] |
I have had several dogs over the years and it does not matter what kind of fur they have they all have that same or similar smell that just stinks. What causes this?
|
[
"Dogs have sweat glands, just not for the purpose of thermoregulation. The distinct \"wet dog\" smell is from apocrine glands which are associated with every hair follicle on a dog. The purpose of these glands is to seal the outer layer of the skin (which is why it's an oily secretion) and also acts as a pheromone."
] |
[
"This is only a partial answer - it doesn't explain why a dry dog doesn't smell quite as a wet one does. The evaporation of water from the dog carries the smell. Most of the smells (the volatiles) are from bacterial decomposition of oil secreted by the apocrine glands as well as anything else the coat/skin has picked up (urine etc). A dog's paws will smell a lot like 'wet dog' even when dry."
] |
[
"Fun fact: Purebred huskies don't have that stinky dog smell."
] |
[
"If mRNA translation errors are relatively common, how do cells prevent malformed proteins from getting out of control?"
] |
[
false
] |
I read that one of the challenges with the mRNA COVID-19 vaccines is that mRNA breaks down pretty quickly. That made me curious what happens if a cell begins to translate mRNA that has already been partially degraded. While researching that I learned that translation errors are actually quite common. Presumably cells must have a way of dealing with this. Can anybody fill me in? EDIT: thanks for the informative answers! And just in case it's a different answer, my original question was: what, if any, danger is there in mRNA from COVID-19 vaccines becoming partially degraded and still translated by a cell?
|
[
"Cells have various mechanisms of correctly both transcription errors and translation errors by helper proteins. ",
"Even after translation it still has to fold correctly and possibly be modified further to be useful. ",
"Even if a bad one gets through which doesn’t work correctly, that doesn’t mean there aren’t tons of other copies to do the work. It’s not the end of the world.",
"EDIT: As far as the COVID vaccines many times they are already degraded before they get into you if sites are aren’t following temperature guidelines. After it gets into your body it’ll immediately be incorporated and use your cellular machinery to build spike proteins for your cells to express and get attacked, after a while the mRNA will naturally degrade. Two weeks later you’ll get another shot."
] |
[
"There are various systems of control in the endoplasmatic reticulum and in the Golgi apparatus. Also, in the citoplasm I think. \nChaperon proteins control the protein multiple times and if it doesn’t fold properly it’s discarded.",
"Also, when mRNA breaks down it just can’t be used anymore, it’s like if you have a recipe and the paper gets shredded.\nYou see, mRNA has an approximate life of 30mins to 24hrs on the norm if produced by us.",
"But also, it’s not like there is only one copy in the vaccine. So we should be good.",
"Edit: grammar"
] |
[
"They idea of for your own body to learn to recognize those spike proteins. ",
"After the exposure your body will generate antibodies to the antigens on the spike proteins. Those antibodies will stick around in your body. While they exist, you no longer need a source of spike proteins."
] |
[
"Whats the current scientific thought on how humans learn, and how to apply that to learn efficiently?"
] |
[
false
] | null |
[
"This is a very broad/vague question. You can take an entire semester-long college course on Learning. Do you have a more specific question?"
] |
[
"Tackle what you personally think is most important about it",
"The issue with the science of learning as far as I can tell is just that; its broad, vague and not very cohesive. It's something everyone uses but there doesnt seem to be a discipline dedicated to it. I was hoping that someone could summarize the knowledge on the topic and perhaps lift forward what they think is the most important pieces, or the biggest recent verified discoveries. "
] |
[
"This sub isn't really geared toward summarizing entire fields of study. It's like asking \"what happened in Europe in the 19th century?\" I recommend trying to narrow down to a more specific question. If you want a general understanding, you can try to find free pdfs of textbooks on human memory or learning. "
] |
[
"If you did drugs, then 'groundhog dayed' back a day, would you still be addicted?"
] |
[
false
] | null |
[
"Groundhounding a day back isn't a real thing so we can't answer this question. "
] |
[
"The question is whether or not the memory of a drug's effect is enough to hook one on the drug, despite no physiological changes."
] |
[
"What is a realistic scenario in which that could happen?"
] |
[
"Do we know of any micro-organisms that could possibly survive space travel via asteroid?"
] |
[
false
] |
A made it to the front page today that said that rocks thrown into space by the impact that killed the dinosaurs may have had enough force to get to Mars or Europa, potentially seeding them with life. It seems implausible that any micro-organism could possibly survive the varied conditions caused by the impact, prolonged space travel, re-entry, impact again, and then survive long enough to adapt to an alien world. Do we know of any micro-organism that could possibly survive that kind of kinetic force, heat, cold, vacuum, radiation, food and water scarcity, and foreign atmosphere?
|
[
"I am not exactly qualified to answer this question, but I did read an article the other day regarding Tardigrades. From what I understand they are the closest microorganisms that humans know of that could survive each of those kinds of environments. Here's a link to more information about them. ",
"http://tardigrades.bio.unc.edu/tardigrades/"
] |
[
"A species of cyanobacteria survived in space for 553 days. So some of them can certainly survive in space. I believe they are unable to reproduce in space, however. Source below, apologize for it not being the best source.",
"http://news.discovery.com/space/record-breaking-microbial-star-trekkers.htm",
"I took a course on coursera with Prof Charles Cockell (a leading astrobiologist) and he went into a good analysis of this exact question. The short answer was that we don't know. We know that some meteorites that are large enough can have core temps that stay below 50 degrees (Celsius) leaving the atmosphere. So it seems possible that if you had a very hearty bacteria at the center of an asteroid it could theoretically survive exiting the atmosphere, and again we know they can survive the vacuum of space. ",
"Whether or not it is plausible that this could occur given the multitude of factors required to launch it into space is another question, and well above my knowledge in the area"
] |
[
"The trouble I see with tardigrades as they are described by that article is that while they can totally survive all of that stuff in their hibernation mode, they need water in order to wake up. Mars is pretty dry, but Europa may be a decent habitat for the little guys providing they're ok with an average temperature of -160C. Mars also has some water, so they might be able to make it if they landed in the right spot.",
"Also, according to this ",
"wikipedia article",
", they can last up to ten years in their hibernating state. ",
"Voyager 1",
" got to the Jupiter system in about three years, but that was specifically aimed and propelled in order to get there. I have no idea how long a tardigrade would have to survive on a rock ejected by an impact before it got to Europa. The ",
"Mariner 4",
" got to Mars in about a year, but again it was pointed in the right direction to start with.",
"So, based on that Wikipedia research, I think that tardigrades have a decent shot at surviving the trip and the destination, but I still have no idea if they can survive the arrival or departure."
] |
[
"If inflation inflates space, why doesn't it inflate the speed of light?"
] |
[
false
] |
I don't understand how stretching space would physically increase the subjective distance between two objects. Wouldn't the observer and the two objects increase in size too, as well as all particles, forces and natural constants, thus rendering the change invisible to the inner observer.
|
[
"That's kinda implied by the fact that we can measure the expansion. But isn't an inflation that ONLY affects the distance between objects not actually an inflation of space, but rather a simple relative movement of objects, thus it should not violate the speed of light ?"
] |
[
"But isn't an inflation that ONLY affects the distance between objects not actually an inflation of space, but rather a simple relative movement of objects, thus it should not violate the speed of light ?",
"No, it actually is an inflation of space. From an inertial reference point they are not accelerating at all, yet they still move apart."
] |
[
"Wouldn't the observer and the two objects increase in size too",
"The fundamental forces completely overpower the effect on a local scale, negating any tendency to become larger. Natural constants are unaffected."
] |
[
"What would happen, gravitationally, if the sun suddenly ceased to exist?"
] |
[
false
] | null |
[
"The problem - and I realize you might not know this - is that matter simply doesn't \"cease to exist.\" That is not permitted in relativity.",
"If you want to model it classically, then the Earth will continue in its inertial path. This means it will continue it's current velocity - Newton's first law.",
"If you really ",
" to force it into the relativistic model, the Earth will continue to orbit where the sun is headed for 8 minutes until the information of its appearance gets here. But again, the reason for this somewhat absurd answer is because of the unrealistic premise."
] |
[
"I understand that it is not a possible scenario, I just sought the answer to what would happen if this somehow were to occur."
] |
[
"You're not getting my point. You're asking someone to disregard some law of physics, then analyze the scenario using the laws you just broke. That's why the set up is meaningless. However, often one forms these questions to understand some relationship in those laws, and I was attempting to figure out what you're interested in. Newtonian physics or relativity? I provided an answer to both.",
"If we treat gravity as a force, then it's no different from any other force. So we can rephrase to letting go of a bucket after swinging it around. You remove the centripetal force, the object maintains its inertial path tangent to its previous, circular path.",
"If you're asking about the propagation of gravity in relativity, then the changes in gravitation propagate at the speed of light, but because of aberration, the earth actually orbits the \"future\" location of the sun."
] |
[
"If you have an organ transplant, will your body gradually replace the DNA in it with your own, or will the cells continue to regenerate with the same external DNA?"
] |
[
false
] |
[deleted]
|
[
"By and large the transplanted tissue will retain the donor DNA. This fact should not be too surprising considering that you are taking a complex slab of tissue with millions of cells, which are not going to be readily replaced. From the point of view of these cells, they won't \"know\" that they are now in a foreign body and will largely continue to grow, replicate, and function as they did before.",
"Having said that, the picture is not completely static. With time cells from the host organism will interact and/or modify the transplanted organ and its surroundings. Such interactions can take a detrimental turn when the host's immune system recognizes the donor tissue as foreign and effectively starts to attack the cells in the donor tissue. This process called ",
"transplant rejection",
" can lead to complete organ failure in acute cases as well as to long-term chronic tissue damage. In order to reduce the risk of rejection, transplant patients are generally given ",
"immunosuppressive drugs",
" in order to reduce how much damage their immune system can cause to the new tissue. Finally, cellular fragments from the donor tissue can also be released into the host. In fact, detecting free DNA from donor tissue ",
"appears to be a strong indicator of organ rejection",
"."
] |
[
"Can confirm, I also have had a Bone Marrow transplant. I now have two types of DNA. My blood DNA is that of my donor, however, my tissue DNA (such as skin etc) is all mine. Also interesting is I was O- prior to transplant but am now A+ due to the donors blood type. Pretty crazy stuff they can do these days. "
] |
[
"I've had a bone marrow transplant. Does that mean if the police do a DNA test on my blood, I'll have the DNA of my donor? "
] |
[
"With the continued development of antibiotic resistant strains of bacterial infections (e.g. Gonorrhea currently heading toward superbug status) why does there seem to be so little pursuit of viral phage medicine?"
] |
[
false
] |
has been known about and established for some time primarily in Eastern European countries and yet there seems to be very little talk about it outside of those areas. Is there some prominent issue preventing a heightened development of this type of medicine? Edit: gives a good overview about phage therapy and its history and application.
|
[
"First a history lesson: Phage therapy was pioneered by the Soviets and Eastern European countries. However, in the West they heavily favored antibiotics. Antibiotics are broad spectrum, require no need for specific identification of the organism and are cheap. Phages are expensive, narrow spectrum and require specific identification of the organism. This lead the west to largely ignore phage therapy while we developed novel antibiotics more powerful than the last.",
"However, as antibiotic resistance has become more widespread there has been more interest in phages. But there are several drawbacks. First, phages are extremely specific with many phages only infecting one species of bacteria. So a patient coming into the ER with a bad infection is not going to be prescribed a phage since you'd have to definitively identify the bacteria causing the infection before starting phage therapy, a process that can take a few days during which your patient is dying. A doctor will prescribe a broad spectrum antibiotic and then if the clinical micro lab identifies the pathogen, the antibiotic therapy will be modified. ",
"Secondly, whole phage will stimulate the immune system. This means that you will develop an immune response to the phage either rendering further treatment with the phage useless or worse upon your next treatment you'll have a massive allergic response. Thus, any phage you use will be quickly neutralized so if you come down with the same infection you cant use the same phage you did the first time. ",
"Thirdly, phages are expensive. They have to be cultured, purified and tested for efficacy. They cannot be synthesized like antibiotics can. This requires very expensive processes. This will also render phage therapy a treatment of last resort meaning as a pharma company your market is extremely limited.",
"Together, phages present a very poor market for pharmaceutical development. Your product will only be used in very limited cases, be very expensive and be a one time application with no repeat customers. ",
"However, phage therapy does have some attractive properties. First, there is investigation of using phage lysin rather than whole phage. Lysin basically punches holes in the bacterial cell membrane weakening it and allowing unregulated flow of water and solutes into the cell causing it to burst. Lysins can be applied externally to a bacteria and cause lysis(they do not need to be produced in the cytoplasm) and seem to have weak immune stimulation. One study showed them to be effective against MRSA and VRSA, synergistic treatment with both lysin and antibiotic can also neutralize strains that are resistant to either and can protect mice against lethal challenges with S. aureus without stimulating much of an immune response. ",
"Some reading on lysins:\n",
"http://www.ncbi.nlm.nih.gov/pubmed/21048011",
"\n",
"http://jid.oxfordjournals.org/content/196/8/1237.long",
"Second, the narrow specificity of lysins also presents an attractive option for people that need to take lots of antibiotics continually(cystic fibrosis, immune suppressed, etc). Broad spectrum antibiotics target both the pathogen and your normal microbiome. Continued use of antibiotics is associated with yeast infections, GI distress and C. difficile infections which are extremely different to treat and can be fatal plus many other infections. Also, non-specific targeting of other organisms increases the chances of bacteria developing resistance. A non-pathogenic organism harboring resistance to an antibiotic can transfer this resistance to a pathogenic organism giving rise to antibiotic resistant human pathogens. The high specificity of lysins greatly reduces this since they will only target the pathogen and can even be specific to a certain species meaning you wouldn't even target related species. "
] |
[
"Bacteriophages are ",
" specific. Most anti-biotics are broad spectrum. This means we not only need to swab and confirm species and genus of infection, but then identify the strain, and provide the appropriate phage for that strain. These would be susceptbile over time to the same mutations that protect bacteria from antibiotics. Determining a specific strain and tailoring the phage to that individual strain is taxing from a development standpoint. You would constantly have to be changing the forumlation, and that could alter delivery, side-effects and efficacy, as well as requiring new testing and validation processes each and every time.",
"I'm sure there is more, but these are the ones of the top of my head."
] |
[
"There's also risk that the virus could evolve and itself become a pathogen",
"Unless you have a citation, then I am going to say that is certainly not true at all. Phages have co-evolved with bacteria likely since the origin of cellular life and have highly specific receptors for attachment and entry. Phage jumping from infecting bacterial cells to human cells would require an enormous amount of evolution, evolution with no benefit since humans provide a very hostile environment to viral growth. ",
"SIV which infects primates only jumped to humans twice that we know of, giving HIV-1 and HIV-2 and yet SIV infects a genetically very similar host. So the jump between about as evolutionarily divergent hosts as possible would be astronomically slim. Phage jumping from bacteria to humans is the equivalent of a human evolving the ability to breathe underwater. ",
"Thats not to say phage has no role in human disease, cholera toxin is encoded by a phage that infects Vibrio cholera but the phage itself does not infect human cells. "
] |
[
"If the moon fell to Earth, what would happen to the ocean as it was falling? Like what would happen to the tides as the moon got closer?"
] |
[
false
] | null |
[
"Such hypothetical / speculative / open-ended questions are better suited for our sister-sub ",
"/r/asksciencediscussion",
". Please post there instead."
] |
[
"Okay sure! Should I delete this or leave it up?"
] |
[
"Already removed"
] |
[
"How much are the personality traits of alcoholics caused by alcohol?"
] |
[
false
] |
Mid and late stage alcoholics are often described as being self-centered, grandiose, manipulative, self-pitying, anxious, easily frustrated, impulsive, dependent, and more. Is this correct? If not, I would still like to know which of their character traits can be said to be caused by alcohol alone? How does alcohol abuse change a person's brain and thus their personality?
|
[
"Alcoholism is also comorbid with anxiety, depression, antisocial personality disorder, personality disorders, and a type of dementia known as ",
"Korsakoff's syndrome",
". All of these may affect personality presentations, and may be related to frontal lobe pathology, which is ",
"strongly correlated with alcoholism",
". Frontal lobe damage is commonly accompanied by ",
"changes in personality",
", among other things, and certain prefrontal damage in particular is associated with a disorder now known as ",
"pseudopsychopathy",
".",
"In these cases, we are talking about neuronal damage and atrophy stemming directly from alcohol abuse. These factors may play a role, combined with the substance abuse and dependence issues another poster commented on."
] |
[
"Thank you very much for these links. The article ",
"FRONTAL LOBE CHANGES IN ALCOHOLISM: A REVIEW OF THE LITERATURE",
" had the information I had been looking for.",
"While I have you attention, do you know of any reliable estimate for the percentage of alcoholics in any given population? I know the answer to this must depend on how alcoholism is defined, but is there some sort of rough estimate? How different is it for different populations? I remember hearing estimates of one-in-seven people being susceptible, or one-in-ten.",
"Also, are there any studies of the effects of alcoholism on history?",
"Thanks again for those highly informative links, especially the one mentioned just above."
] |
[
"This behavior is typical of addicts in general, and results from the addiction rather than the direct affects of the drug.",
"So yes and no.",
"http://en.wikipedia.org/wiki/Substance_use_disorder",
"\n",
"http://en.wikipedia.org/wiki/Substance_dependence"
] |
[
"Why can't we stimulate tooth growth, and why can't teeth repair after being damaged?"
] |
[
false
] |
[deleted]
|
[
"This comment has been overwritten by an open source script to protect this user's privacy. ",
"If you would like to do the same, add the browser extension ",
"GreaseMonkey",
" to Firefox and add ",
"this open source script",
". ",
"Then simply click on your username on Reddit, go to the comments tab, and hit the new OVERWRITE button at the top."
] |
[
"So how does the common man go about having the ultrasound treatment?"
] |
[
"I was talking with my dental hygienist yesterday, and he mentioned that there was a study done, where they took stem cells from the bone marrow and induced bone formation 90% of the time. I'm having the hardest time finding the study, but I guess it's possible ",
" ",
"This",
" is the closest I've gotten!",
"Sorry for the lack of my knowledge! I only found out about this just yesterday, and thought I would offer what I heard through my hygienist."
] |
[
"What are the potentials of Antarctica?"
] |
[
false
] |
I hadn't realized that Antarctica was once warm and temperate. There could be tons of fossils there. We've used it to study the level of carbon in the Earth, but imagine if we could look deeper? The continent also has an ancient lake (Vostok), which could still have extremophile bacteria / viruses and organisms. Opening it could contaminate the lake, or the earth. What other potentials for Antarctica are there for research?
|
[
"It is one of the best places on earth to collect meteorites. Basically any rock sitting on the ice has a high chance of being a meteorite so every year teams go there to collect them."
] |
[
"Opening it could contaminate the lake, or the earth.",
"Maybe the lake, but not the earth. The extremophile bacteria would be easily outcompeted by ordinary bacteria (who don't have to spend energy supporting all the bells and whistles that the extremophiles use to survive in harsh conditions)."
] |
[
"Aww, I guess that X-Files episode will never become a reality :)."
] |
[
"On a wave level, what is the difference between two sounds that are identical except for their timbre?"
] |
[
false
] | null |
[
"Well, if the timbre is defined as the sound when pitch and loudness are equal ",
"http://en.m.wikipedia.org/wiki/Timbre",
", then it must be the frequency content that differs.\nThe instruments do not play only one frequency per note. They play a note and range of harmonica of that note defined by the shape and construction of the instrument. The harmonics are of various intensity relative to the lowest dominant frequency. This combination of dominant and harmonic frequencies, as well as each components amplitude will give you a timbre. For instance, you cannot say a guitar and a trumpet will resonant with the same characteristic harmonics even when you make both produce the base frequency of a note, say 440 Hz. The physical dimensions of the vibration cavity and construction materials are different, so the harmonic content will be added differently to the base note because the waves will be reflected differently in the two cavities.\nEven two of the same instrument will rarely be so identical with two players to match all the frequency harmonics. You could argue that even the construction of the instrument may vary enough to change that slightly, but the manufacturers of most instruments would try to minimize that as much as possible.",
"You asked about at the wave level, similar things apply to acoustic chambers and even EM waveguides and resonators, but they are usually specifically designed with a frequency range in mind and they are operated within that limit so they do not become overmoded. Instruments, by definition, are overmoded because you desire that harmonic acoustic content."
] |
[
"A sound source is a structure that for some reason is going through mechanical vibrations. Air going through the pipes and holes of a wind instrument, a bow or a pick vibrating a string, a stick hitting a drum. These vibrations excite the elastic medium through which sound propagates (air in most cases) which then reaches your ears.",
"The mechanical structure that is your sound source has an eigenfrequency: a natural frequency in which it vibrates when excited. Its overall shape, size, and material properties define which one it is.",
"A frictionless, strictly 1-dimensional perfectly elastic string will vibrate when plucked in one frequency, determined by 3 factors",
"1.) ",
" how tightly it is pulled by its anchor points",
"2.) ",
" its material property which gives you the mass of the string when multiplied by its length",
"3.) ",
" Self evident, how long the string is.",
"The formula then for frequency f[Hz] is",
"f = sqrt(T/μ)/2L",
"this produces a pressure wave in the form of",
"p(t) = Pmax",
"t)",
"which we call a harmonic tone.",
"Any combination of L, T and μ that gives you a value of f will produce the same tone. There is absolutely no way for you to distinguish one set of L, T, and μ from another, if they both produce the same f.",
"BUT",
"these conditions I have just described are ideal mathematical constructs. In reality, no structure producing sound is THAT simple. Producing a purely harmonic tone with strictly 1 frequency is impossilbe. But the sound source's size, shape and material properties mean that when you give it energy, some frequencies vibrate more than others.",
"We can now use a mathematical trick called \"Fourier Transform\" to describe a sound signal as an integral of its harmonics. The actual meaning of this is that Fourier Transform gives us an idea about which frequencies vibrate more and which vibrate less. In other words, the overall energy distribution across the whole \"spectrum\" of frequencies",
"The frequency which has the most energy is called \"pitch\" or \"tone\". A violin and a human singing the some note, will have the same \"dominant frequency\" That is, most of their energy will be in the same frequency.",
"But the rest of of the energy will be distribuited differently in a human, compared to a violin. This is because they have different shapes, size and materials, therefore some frequencies that resonate in a violin structure don't resonate as much in a human strucure and vice versa",
"The overall \"shape\" around the dominant frequency each sound source has is called \"timbre\""
] |
[
"Not OP, but follow-up question:",
"The elements you mentioned, if I understand correctly, are basically the harmonics (over- and under-tones) that accompany the main tone. As a guy who started his music composition and programming on a C-64's SID chip, I became very familiar with the concept of the ADSR sound envelope (attack, decay, sustain, release). ",
"I have heard and seen mentioned elsewhere and here on Reddit where if you mask the attack, it becomes harder to discern the source of a note (e.g. it's much easier to tell a piano from a guitar if you hear the beginning of the tone). ",
"Since that recognition of the instrument playing the note seems to rely on the timbre, it would seem that masking part of the ADSR envelope masks some of the difference in timbre.",
"So, to what extent does the envelope contribute to it vs. the elements you have cited, and is the envelope really just a way to describe that information or is it additional information about the sound? You mentioned the \"shape\" as the timbre, and I have seen the ADSR envelope also described and represented as the \"shape\" of the sound. ",
"(Note: long-time musician here, but didn't take acoustics in college, which I regret now...)"
] |
[
"What happens when the speed of expansion of the universe passes c?"
] |
[
false
] |
Well I guess the first question would be, can this happen? The expansion of the universe is accelerating, so do we know what would happen when it accelerates to the speed of light? What about faster than that? Isn't it impossible for anything to go faster than light? Also, if that happened, would we at one point not be able to see any other galaxies because they're receding from us faster than their light can reach us (assuming we'll be here, of course)? Sorry if this is a dumb question. I only have basic knowledge of physics, I'm a high-school student getting interested in astronomy.
|
[
"The expansion of the universe and the speed of light have different units, therefore you can't compare them.",
"The Hubble Constant is the fraction by which a given parcel of space will grow in a given amount of time. It has units of inverse time, s",
". The speed of light, of course, has units of distance/time, m s",
".",
"The Hubble Constant is usually given in units of kilometers per second per megaparsec, but the two distance units just cancel out and you get the result that the universe expands by about 0.00000000000000002% per second.",
"Also, if that happened, would we at one point not be able to see any other galaxies because they're receding from us faster than their light can reach us (assuming we'll be here, of course)?",
"There will eventually come a time when there are no other visible galaxies in our observable universe (except for nearby ones that are gravitationally bound to us)."
] |
[
"We in fact know that far-away parts of the universe are receding from us faster than the speed of light. However, this is not a problem. It's better to think about the expansion of the universe as an change in space itself rather than the motion of the things in that space; think of it as extra distance appearing between far-off objects. In this way, nothing is moving faster than light in the sense of any actual motion; instead, the distance between us and such an object increases faster than light can traverse that distance (i.e. more than 1 light-year of distance is added per year).",
"Also, if that happened, would we at one point not be able to see any other galaxies because they're receding from us faster than their light can reach us (assuming we'll be here, of course)?",
"Yes indeed. It will be a dark and dismal universe that day far, far into the future!"
] |
[
"That dark and dismal scenario is called a ",
"big rip",
".",
"The really fun part will be when the acceleration becomes great enough to pull atoms apart. This could happen as soon as ",
"16.7 billion years",
" in the future. How dark energy works and how strong it is are a bit uncertain though, so there is no guarantee that the universe will end like this at all."
] |
[
"Why is it that armpit sweat smells different than foot sweat, and that smells different from ballsack sweat? How are these different musks produced?"
] |
[
false
] |
See title.
|
[
"Sweat is odorless. Body odor is produced by bacteria that break down the sweat (basically bacteria poop). ",
"There are different bacteria on different parts of your body and they produce different smells.",
"One recent study published in the journal Science found that at least 18 different phyla of bacteria dwell in 20 different skin habitats. (",
"SOURCE",
")"
] |
[
"This sounds like a take-home experiment. Let us know the results, and thanks for volunteering! ;P"
] |
[
"Ok, legit question; if one is having smelly/sweaty armpits and a clean ballsack then rubs his hand (or something sufficient) under his armpits and then rubs his sweaty/smelly hand on his ballsack, "
] |
[
"Is there any evidence that a caloric deficit doesn't help some percentage of the population lose weight?"
] |
[
false
] |
Specifically, what individuals cannot lose weight through a simple caloric calculation and restriction? What factors influence success through this specific medium? Hormones, genes, age?
|
[
"This would be physically impossible. If your calories in are less than you calories out, and you don't lose weight over time, one or both of these values has been mis-measured. Anything else would literally violate the laws of thermodynamics. Not to mention conservation of matter.",
"Hormones and genes and age and all of that can influence both how many calories you burn, and how efficiently you use the calories you eat, but it cannot somehow create energy and mass from nothing."
] |
[
"There are people who get fatter despite calorically negative diets because their body actually cannibalizes their organs and muscles to produce fat. If they don't change their diet they starve to death. Of course, they are still losing weight. ",
"Source: ",
"http://video.google.com/videoplay?docid=4362041487661765149"
] |
[
"I don't think it's necessarily true that it never goes back to normal; some research has shown that continuing a vigorous exercise regimen (at least an hour of moderate exercise a day, 5-7 days a week) for over a year will help your body adjust to its new weight. You can lose weight without ever exercising beyond what it takes to get through a normal day, but it's very hard to keep it off without beginning an exercise regimen."
] |
[
"Question from r/loseit - do fat cells go away when you diet or just shrink?"
] |
[
false
] | null |
[
"Shrink"
] |
[
"That's actually not true. When you gain a lot of weight, you exhibit both an increase in the size of fat cells as well as the number of them (your body releases certain chemicals to stimulate the production of more fat cells). Unfortunately, diet and exercise will only shrink the fat cells, but not reduce their number. This is (one of the many) biological reasons why it's so tricky to maintain weight loss."
] |
[
"I'm thinking of this in a normal body working out type persepctive. What exactly is meant by 'a lot of weight'?",
"are we talking about 20 points, or more like 200?"
] |
[
"Is \"quantum probability\" the same as \"real probability\"?"
] |
[
false
] |
If I roll a die, as it's rolling, there's a probability if it being a 6 (1/6). This isn't actually whats happening, because we can theoretically analyze the conditions of the roll to determine the result before it stops rolling. Just when I roll it, im not perfectly examining it, so there's a probability. If I set up an quantum experiment, is the same "type" of probability happening? If we could theoretically analyze everything without interfering with the particles, could we determine the result? Or are superpositions literally and physically a particle splitting into multiple other particles?
|
[
"This is actually exactly the right question in a certain sense. There IS actually a difference between classical and quantum probability.",
"Classically, events have a probability of happening that is a real number between 0 and 1. If we add together the probability of every possible event, we should get 1 ( there's a 100% chance that SOMETHING happens if we account for every outcome).",
"In quantum things are slightly more complicated. We have probability ",
" rather than probability. So instead of an event having probability .5 it could be -.5 or .5i. These amplitudes are complex numbers meaning they can be part imaginary or negative. Rather than adding all the amplitudes to get 1, we add their magnitude squared to get 1. If you take the magnitude squared, you get back a classical probability. This is the probability of that event.",
"So if event A has amplitude .5i, then it has probability .25 ( the magnitude of .5i squared).",
"So you might think this was a pretty worthless addition. What does using amplitudes give us if we just convert back to probabilities? Well in quantum you only convert back to probabilities when there's a collapse. So up until that point, when things interact, we're adding together amplitudes NOT probabilities. And amplitudes can be negative. So in some situations (Google two slit interference for a specific example), you can get two events effectively canceling each other out because they had opposite amplitudes. At the end of the day you still get back to good old fashioned probability for your observable events. . It's what happens in between that can behave differently.",
"Rereading your question, you also seem to be asking if quantum is truly \"random\" as in: do the probabilities (of observable events, so after we squared our amplitudes. No complex numbers here) represent what we don't know but in ",
" could know about the system, or is it truly unknowable. As in is it like rolling a dice where we could predict the outcome with certainty if we knew all the angles and masses and velocities perfectly, or is it fundamentally unknowable.",
"The answer is up to (some) debate, but most physicists would say it's truly unknowable. Theories that say there's more info we just haven't found yet are called hidden variable theories. They aren't that popular because in order to accept a hidden variable theory we have to reject what is called locality (effectively the basis of Special Relativity)",
"Locality says that there's no way for me to do something here on Earth and have it instantly effect something on the moon. The result of any action has to travel at a finite speed (less than or equal to the speed of light). ",
"Physicists really like locality. Without it, physical predictions become effectively impossible. Without it, we have to account for every other thing in the universe when we run an experiment. It's an assumption, but it's one we're reluctant to get rid of, and one that experiment has held up remarkably well.",
"Hidden variable theories that have locality are called local hidden variable theories. And local hidden variable theories are mathematically impossible by Bell's Inequality theorem (with a few other complicated assumptions). It's one of my favorite bits of physics because it took what we thought was a purely philosophical question and gave it a rigorous mathematical answer.",
"So to answer your question, most physicists would say it's a different type of probability (not just us not knowing things), but the question is technically open"
] |
[
"I just want to say that people like you and the effort you just put into this post is what makes Reddit an enjoyable place to be. Have an awesome day. "
] |
[
"The answer is up to (some) debate, but most physicists would say it's truly unknowable. Theories that say there's more info we just haven't found yet are called hidden variable theories. ",
"Not exactly. Even proponents of hidden variable theories will tell you it's unknowable. While it's not truly random, the information needed to predict it is impossible for us to find. There's no way to \"theoretically analyze everything\" as OP is asking."
] |
[
"Could someone help explain the second law of thermodynamics to me? What is disorder?"
] |
[
false
] |
I've read about the second law of thermodynamics a lot, and it seems to pop up in all sorts of places, especially discussions of the flow of time. But I just don't understand how it works on a conceptual level. My understanding (so far) is that everything in the Universe tends toward disorder. That's why you can't have a self-perpetuating machine (a machine that uses its own energy output as an input to run), because it will descend to disorder. But disorder is subjective. How can we quantify "order"? How do you tell how much entropy something has?
|
[
"I have studied general relativity, quantum mechanics, quantum field theory, the theories describing black holes and Big Bang cosmology, and I have never in my life struggled with a concept as long and as frustratingly as I've struggled with entropy.",
"I'm sure someone else will come along and define the concept much more precisely and clearly than I can. But here's how I finally resolved it for myself:",
"Entropy is hidden information. It's a way of quantifying how much information is ",
" within a system.",
"Consider a bathtub inside a very, very cold room. The water in the bathtub has frozen. For sake of argument, let us stipulate that it has frozen into a single, perfect crystal of ice. Furthermore, and again just for the sake of argument, let us assume that the ice is at ",
" zero. ",
" absolute zero; there is absolutely no molecular motion at all.",
"The entropy of that system is zero. There is ",
" hidden information. We know exactly where every single molecule in that system is and how it's moving, with no room for doubt.",
"Now let the temperature of the room rise until the ice melts. We now have a bathtub full of water. The entropy of that system is fairly large. There is a lot of information ",
" inside the bathtub. We know how many molecules there are, because we know the precise mass of water in the tub, but the ",
" of those molecules is quite uncertain. There are a great many possible arrangements of molecules that could ",
" a bathtub full of cold water.",
"Now let the temperature rise further until the water all evaporates. We now have a bathtub full of water vapour. The entropy of the system is now even larger; there's an even greater degree of uncertainty. There are even more possible configurations of molecules — positions and velocities — that would all look the same to us. So there's a lot of uncertainty about how that system is arranged.",
"The different arrangements of molecules that all look the same are called ",
" For the frozen bathtub at absolute zero, there's just one microstate, just one possible arrangement of the system. For the bathtub full of water vapor, there is an enormous number of possible microstates.",
"The entropy of the bathtub — of any system — can be quantified in terms of how many possible microstates there are. There's a formula for this involving a summation sign and a logarithm, but I can never remember it. The point is the more microstates there are — the more possible configurations that all look the same — the higher the entropy of the system. In other words, the less certain you are about how the various elementary parts of the system are configured, the higher the system's entropy.",
"As I said, there's sure to be someone who can offer a better, clearer, more rigorous definition than that. But I am not that person. This is just the notion of entropy I have to carry around inside my head in order to get through life."
] |
[
"I know next to nothing about mathematics or anything beyond high school physics, so my apologies in advance if this is a waste of y'all's time, ",
", how does the second law of thermodynamics--loosening arrangements of microstates in a system--figure with the picture we have of the expansion of the universe, where an infinitely dense \"system\" has, through time, expanded, coagulated, and cooled...? ",
"I guess I just find the temperature metaphor counterintuitive..."
] |
[
"When it's said that the average temperature of the universe is three degrees Kelvin, that means the universe is filled with radiation corresponding to what would be emitted by an ideal black body with a temperature of three degrees Kelvin.",
"Was that your question?"
] |
[
"if only mass-energy consenves, does that means energy balances in engineering are wrong?"
] |
[
false
] |
if so, what other property should i balance in my sytems in order to keep degrees of freedom at 0, because if that is wrong, my momentum balances are wrong too, what are the properties that can be balanced?
|
[
"In all but the most extreme of cases, your energy balances are just fine. It's true that technically it's mass-energy which is conserved, but most systems especially in engineering do not experience significant mass changes--any changes that would be present, say from heating or chemical reactions are much ",
" too small to make a noticeable difference in an industrial setting.",
"Think of it this way, we ignore the gravitational effects of Venus when designing the trusses for a skyscraper--they are just too small care about."
] |
[
"Well, technically, even energy is not conserved since the universe is expending.",
"According to Noether's Theorem, conservation is linked to symmetry, which expansion breaks."
] |
[
"Well, technically, even energy is not conserved since the universe is expending.",
"Energy is not conserved under certain contexts. All space outwards to the galaxies in our local group are ",
" experiencing expansion from each other. So if you're figuring out the energies involved in constructing a building, you're a-okay. Energy is conserved.",
"Sure it's not conserved in a nebulous sense, but that a nuance for another day."
] |
[
"Why am I (with an AB+) blood type a universal blood recipient, but a universal plasma donor?"
] |
[
false
] |
I do understand antigens and why I am a universal recipient, but I just came across something on the red cross website that indicates I'm a universal plasma donor.
|
[
"Antibodies in blood plasma are the opposite of the blood type, so if you have type A blood your plasma has type B antibodies and vice versa. If you have type AB blood, though, your plasma has ",
" antibodies and can be safely given to anybody."
] |
[
"your antibodies are created to attack foreign cells. if your RBCs are A, then your antibodies will attack the foreign B cells, and vice versa, to prevent contamination. If you are type AB, you can't have antibodies against either of those sets of proteins, or else you'll attack your own RBCs, which is not evolutionary advantageous"
] |
[
"Furthermore, if you have type O, your own RBCs have no antigens to recognize, so you safely produce antibodies against both A and B RBCs."
] |
[
"How do rovers such as curiosity maneuver in space?"
] |
[
false
] |
I would expect internal combustion rockets to be out of the question since they need both heat and oxygen to work. How would rovers adjust their flight path in space?
|
[
"As an example, the launch vehicle for the Opportunity Rover was a ",
"Delta II Rocket",
". The rover is actually a payload in the rocket - so the standard rocket motors are used to launch and maneuver. ",
"The fuel depends on which stage/booster it is and the actual Delta II model - but most of them appear to be solid fuel.",
"Edit: I see that Curiosity will be launched by an ",
"Atlas V",
" rocket."
] |
[
"I was looking for more on how they actually change course once in space. After I did some searching on the best search engine in existence, I came across some pretty satisfying answers. ",
"Resistojet",
"\n",
"Reaction Wheel"
] |
[
"Though I'm not completely certain, I expect the system to be much like adjusting the orbit of the International Space Station. It's a combination of gyroscope flywheels like you mentioned, and rocket thrusters needed for more immediate and drastic changes.",
"The course taken by the vehicle containing said rover is mostly unpowered though. It is an orbit set using the gravitational pulls of the Earth, Moon, Sun, et. al. to ultimately rendezvous with the target. Changes in trajectory are done using small rocket engines. Usually it's never needed due to thorough calculative planning - usable energy in space is so scarce, it's quite costly to change course."
] |
[
"Why does the shadowed part of the moon appear to be invisible even during the day? Wouldn't we see some faint part of it?"
] |
[
false
] | null |
[
"If you look closely at the moon at night, you may be able to see the circle be completed by a faint glow. That is earthshine -- sunlight that has bounced off the earth, illuminating the shadowed (night) side of the moon. ",
"During the day, however, our atmosphere scatters so much blue light at us that it all but drowns out the difference. While we may be able to see the difference between pitch black and earthshine-illuminated-moon-shadow at night, during the day it's just two extremely close shades of blue. "
] |
[
"Yes, it's most visible on a small crescent Moon because at that point in the Moon's orbit, the Earth is nearly full from the Moon's perspective."
] |
[
"Doesn't earthshine particularly visible at dawn and dusk, when the light reflected from the illuminated part of the Earth lights the Moon, and the brightness of the sky is not sufficient to fade it ?"
] |
[
"Mercury's orbit with the Sun?"
] |
[
false
] |
I was reading on wikipedia that Mercury is tidally locked with the sun with a 3:2 ratio. Meaning it rotates 3 times on its axis for every 2 rotations around the sun. But then it says that 1 day on Mercury is equal to 2 Mercury years. Wouldn't that be a 1:2 ratio. If someone could clarify this to me thank you.
|
[
"Okay. The planet spins at such a speed that its Prime Meridian passes the sun once every two years. In order to do that, the planet has to be spinning in such a way that the sun appears to set in the direction of planetary travel. A minor, but important distinction.",
"As the planet goes around the sun, it makes what appears to be a half revolution over the course of the year, but it is actually moving farther than that, spinning a full turn and a half during that year. Two years makes 3 rotations in space to complete one day.",
"Edit - It should be noted that Mercury doesn't have a two year day, which changes the numbers.",
"A Mercurial Day is equal to 58 days, 15 hours on Earth, and a Mercurial Year is 88 days.",
"That means that the planet moves 239.77 degrees around the sun before completing a day (about 2/3 a revolution), and the planet would have spun about 600 degrees total (5/3 rotations)"
] |
[
"There are two ways to measure rotation, one based on the local star (what we normally consider as a rotation) and one based on the galactic center (basically a lot closer to the absolute motion of the planet).",
"Imagine the planet for a moment, and assume it does not spin at all. Under the first idea, looking at the planet from above it would appear to spin as it moves around the sun. But under the second idea, the planet appears not to spin, but the sun still rises and sets on the surface.",
"Now, we introduce a slow spin, like Mercury has, \"noon\" (the time when the sun is directly overhead) is 58.6 hours apart. Two thirds of a year. But the planet spinning 360 degrees isn't enough to face the sun again, it has to spin around an extra 240 degrees (approximately) to hit noon again.",
"http://imgur.com/gtuifg3",
"Crude drawing to illustrate the positions.",
"But yes, Mercury spins incredibly slowly."
] |
[
"I'm still having a hard time picturing this. What do you mean when you say 2 years makes 3 rotations in space to complete one day. Wouldn't that be three days.\nIs it spinning on it's axis at a rate just slightly faster than it orbits the sun so the day just lasts really long?\nIs there any simulator where I could see this to understand it better?\nThank you"
] |
[
"Would a hot dish of food have significantly more energy/calories if eaten than the same dish served cold?"
] |
[
false
] | null |
[
"It has more calories in the sense that hot things have more energy than cold ones. But it wouldn't have more usable calories. Not directly at least since the body cannot directly convert heat into a usable calorie source for metabolic action.",
"Indirectly though it might give us a little more energy. When you eat something it enters your stomach and rapidly changes to body temperature. In the case of something cold this means it absorbs heat from your body. This heat has to be replaced and the body does so by burning calories.",
"If the food you ate was warm then the heat energy would be absorbed by your body which would not need to burn as much to keep warm, for a few minutes anyway.",
"I'm on my phone so I can't do any calculations right now to see what exactly the difference is, but its not a lot. Not what you'd consider a 'significant amount.'"
] |
[
"Eat the soup at room temperature; keep the stove and fuel handy to melt snow for water--a much bigger worry than food during the winter."
] |
[
"Most foods have specific heats around 0.6 to 0.8 kcal/kg*C. A steak has around 2000 kcals/kg in chemical energy. If we look at a +40C change in temperature (reasonable), we're looking at 26 kcal/kg (for steak).",
"That's 1.3% more energy, which I'd say counts as \"not significant.\" ",
"That's neglecting any consideration of how the body uses thermal energy. I'd be reasonably comfortable assuming it's far less than 100% efficient. "
] |
[
"What keeps electrons in \"orbit\" (lazy, inaccurate word) around a nucleus?"
] |
[
false
] |
I realize that electrons actually exist in s, p, d, and f orbitals, and that these orbitals are not actually newtonian orbits, but rather areas of space around a nucleus that an electron is statistically likely to reside in at any given moment in time. In a newtonian orbit, such as the moon around the earth, say, what prevents gravity from pulling the orbiting object into the earth is the momentum of the object around the earth. What prevents the positively charged nucleus of an atom from pulling the electrons surrounding it into the nucleus?
|
[
"Just wanted to say thanks for this explanation! It's the best I've heard for describing the Hamiltonian in a concise way while still explaining the mathematical concepts behind it."
] |
[
"lets take a look at the wave equation and compare it to the old school for the case of hydrogen with one electron and one proton. First the old school charge equation...",
"F=K",
"(charge of the proton)/r",
"F= force pulling the electron and proton together\nK=random constant\nr= distance between the proton and the electron",
"What you'll notice is that the closer the proton and the electron the smaller r",
" gets and as r approaches 0 the force becomes infinite and like wise the energy released becomes infinite. This obviously doesn't happen as you might have guessed. furthermore once the two are right on top of each other it becomes impossible to detect the charge at all due to the net charge being zero, and hence to exist. As you can see these \"classical\" equations break down on atomic scales and are no longer useful. This is where quantum mechanics comes in to play.",
"At the beginning of the 1900s people began to realize that electrons (and protons) are not neat little point charges with all there charge packed into one place. They are diffuse waves of charge density spread out over molecules. this waviness drastically changes the math involved so that the old equation above no longer directly applies. no longer are two neat little points interacting but two diffuse waves and everysingle point on the wave is interacting with every single point on the other wave. This is where the calculus/dif.eq. so now I present to you the wave equation and the Hamiltonian operator. since the electron can't be represented by and a single (x,y,z) coordinate we're going to use a function psi(x,y,z) . A function where you plug in a location and you get the amplitude of the wave at that location. ",
"Wave Equation: an operator(the Hamiltonian) applied to the wave function returns the energy of the system time the wave function.",
"H",
"Psi(x,y,z)",
"H=the hamiltonian.\nPsi(x,y,z)-the wave function that describes the diffuse charge of the electron or the proton\nE= the energy of the system",
"When we stick the hamiltonian in there ",
"(d/dx)",
" Psi(x,y,z) + U(x,y,z)",
"Psi(x,y,z)",
"(d/dx)",
" Psi(x,y,z) = the second derivative of psi(x,y,z) or how bent and wavey the equation is\nU(x,y,z)*Psi(x,y,z) = the potential energy part of the equation or how much energy is involved in getting the positive and negative charge close to one another.",
"The Hamiltonian is where the answer to your question lies. The energy of the wave(and the electron) is dependent on two things. first is the U(x,y,z) function. this is exactly the same as the old school classical charge equation. the closer the negative and the possitive charges over lap the more energetically favorable the system is. The second part is where the wave mechanics comes in(the (d/dx)",
" part). this part describes the second derivative of the wave function, or how bendy and warped the function describing the electron density is. The more bent up and wavey the wave function is the more energy is stored up in the fluctuations of the wave and the less energetically favorable the system is.",
"And so there's this competition between the charge wanting to bring The electron and the proton together and the wave equation that wants the wave equation not wanting to be bunched up and highly bent out of shape(having the electron collapse into the proton would require the wave equation for both to be packed into an infinitely small area, hence and infinitely bent out of shape wave equation) .",
"If you have any questions feel free to ask."
] |
[
"Perfect! I haven't encountered the Hamiltonian in my chemistry or physics classes yet. I just figured there had to be ",
". Thanks much. Quantum weirdness strikes again :D"
] |
[
"Will my stove always reach the same end temperature - only slower on a low setting?"
] |
[
false
] |
This may be a somewhat stupid question. I'm supplying heat over time by turning my stove on, correct? If I did this with a high setting on my stove and then later with a low setting but for a longer period of time, wouldn't the total amount of heat be the same? How would that work with regard to temperature?
|
[
"Short answer: no. The key point is that energy is leaving the burner/food system as well. The hotter the food/burner is, the faster it loses energy. To maintain a high temperature, then, you have to add energy in faster. So a \"high\" setting ",
" have a higher equilibrium temperature than the \"low\" setting. You can verify this on an electric coil range by leaving the burner on at a given setting and observing the color the burner reaches. At \"low\" it stays how it looks at room temperature, emitting light in the infrared. At \"medium\" it looks a dull red, still emitting mostly in the infrared but with a tail of the light distribution reaching noticeably into visible wavelengths. At \"high\" it appears a bright orange, as the higher temperature gives a much stronger tail into visible wavelengths. The relevant physical laws are Wein's displacement law which essentially says \"hotter things are bluer and colder things are redder\" and Planck's law for thermal radiation, which describes the spectrum of light emitted by an object at some given temperature. "
] |
[
"I assure you I do not. The taps in your bathroom associate cold with blue for reasons that have nothing to do with thermal radiation. Hotter objects produce a spectrum that peaks at shorter wavelengths (bluer). "
] |
[
"The question specifically asked about \"end temperatures\". The only physically meaningful interpretation of that is \"equilibrium temperature\". Otherwise, it's just whatever the temperature has reached when you turn the element off. "
] |
[
"How do objects leaving Earth overcome their rotational momentum due to the Earth's rotation?"
] |
[
false
] |
I couldn't find the answer on google because I can't really phrase my question right. This started with me thinking about what if the Earth stopped rotating? Everything would be thrown in a certain direction due to the momentum from the rotating Earth... But what about rockets for example? While they are within the atmosphere, they should still be rotating along with the Earth, but once they leave the atmosphere I imagine they shouldn't be affected so much by the Earth- but still retain some momentum? Maybe they lose their rotational momentum slowly and have negligible rotational momentum by the time they leave the atmosphere, or is it some other reason? Thanks for reading!
|
[
"For things to orbit, they have to be going much, much faster than the rotation of the Earth. At the equator the tangential velocity of the Earth is about 150 m/s, whereas a low orbit requires about 7 km/s. So really, they have the opposite problem. Spaceships tend to be launched Eastward from a location close to the Equator, to maximize the velocity the Earth gives them (Baikonur is an exception)."
] |
[
"The speed required for orbit decreases as the radius of the orbit gets larger.",
"Orbital velocity isn't the same as escape velocity; it's about 71% as fast."
] |
[
"Thank you! I see now that the momentum is constructive to spaceships."
] |
[
"Are there any common transparent substances with a high dependence of index of refraction on temperature?"
] |
[
false
] |
And where would I find this kind of information? I can only find a few examples online of dn/dT (eg near room temperature water and mineral oil are around 10 / K at 633 nm, fused silica around 10 / K at 633 nm). I'm curious if there are any above 10 / K in the visible range.
|
[
"Are you OK with a phase change?"
] |
[
"dn/dT is called the thermo-optic coefficient.",
"Here's a ",
"whole book",
" about these coefficients in optical materials."
] |
[
"No, I'm contributing to some undergraduate labs and I was curious if I could have them measure the temperature of a substance through the index of refraction, so I was looking for a substance where the effect would be large (but I think a phase change would be too obvious an effect). "
] |
[
"Why are faces easier to scan than words?"
] |
[
true
] |
[deleted]
|
[
"There is a brain region dedicated to facial-feature recognition (fusiform gyrus in the inferior temporal lobe [usually right hemisphere]). Even infants can discriminate between [upright] faces and scrambled facial features (showing activation of the fusiform gyrus when exposed to the upright face). This is a process thought to be evolutionarily and genetically pre-programmed within deeper [evolutionarily older] brain structures, and has become a very SUBCONSCIOUS process that happens automatically. ",
"Text on the other-hand requires a bit of processing and decoding. Words themselves, once sight-word phonics is established, require that a symbol be decoded before it is processed and understood. This process is not nearly as ingrained and is a LEARNED behavior that takes practice. You've probably noticed that you've become much better at recognizing words as you've practiced. The eye stops on each word for approximately 1/4th of a second, and conceptualizes it as a picture (sight-word reading, and phonetic awareness [eg. Nonsense words are able to be read such as: \"hathcampter\" << that requires some processing, but you're able to associate the sounds that these letters will make when combined). For exmalpe, tihs is not extmrely dififlct to raed, becuase yov'ue estbalshed sgiht-wrod reocgniiton alraedy, and each wrod deosn't need to be decdoded indvidually anyomre. So reading words is faster than it once was, but you've been able to \"read\" faces since you were an infant and developed sight. ",
"All-in-all, recognizing text is actually more complicated than recognizing faces. "
] |
[
"Basically, you have a dedicated face coprocessor."
] |
[
"tl;dr Reading words needs to be learned, your brain is just awesome at reading faces by itself."
] |
[
"Can water be compressed to a solid?"
] |
[
false
] |
The 'normal' solid form of water is crystal, leading to a lot of 'negative' space and the common trivia about ice being more voluminous than liquid water. It seems like though, the crystallization is almost just getting in the way of what could be a more normal (to other molecules) solidification process. So is it possible to either compress water until it's solid, or cool it in such a way that its viscosity increases to solid?
|
[
"Keeping it at room temperature, you'd have to compress it to a pressure of about 10,000 atmospheres before it solidified. It wouldn't form regular ice, it would form something called Ice-VI with a different structure."
] |
[
"Surprisingly no! not like most other substances. That's why water's so cool. Almost every other liquid can do that. Here's the crazy part; for the same reason, if you have ice just barely cold enough to be frozen, you can compress it into a liquid! If I try to push those molecules closer together, it would turn into a liquid. Water is more dense as a liquid than as a solid under reasonable pressures! That's why ice floats, and lakes freeze over instead of freeze under. If it didn't work like that, every winter, freshwater life would be destroyed (for the most part).",
" when you get over a 2 hundred million pascal water ",
" compress into a solid, but its not the ice that you know. Its a different configuration of the molecules. But to put that in perspective, the bottom of the Mariana's Trench is under 1070 atmospheres of pressure, and is around 1 degree Celsius. That's an unfathomable amount of pressure. At that temperature, if the water was completely fresh, you would need 6 times that amount of pressure. That's an extra 5000 atmospheres of pressure.",
"Edit: bad math"
] |
[
"Adding on to the other answers, you might be interested to know that at one point we thought the exoplanet Gliese 436b was largely composed of ice at around 250 degrees C. I'm not sure if that's still the consensus, though.",
"http://news.nationalgeographic.com/news/2007/05/070517-hot-planet_2.html"
] |
[
"If we could somehow measure the capacity of our memory in terms of how we measure a computers memory, how much would the average brain have?"
] |
[
false
] | null |
[
"I tried looking for this before. you will see articles from back in early 2000's saying it's ~140 gigs (no idea where they got that number)",
"The problem is we don't fully understand memory storage yet, so can't really measure. It's briefly mentioned in this ",
"Scientific America"
] |
[
"This isn't quite correct. Memories (of a sort) can be stored in the synapse (e.g., see ",
"here",
") or in single neurons (or at least small groups of neurons -- ",
"paper",
" and ",
"summary",
")."
] |
[
"As far as we know effects like memory and thought are not localized to single neurons but are collective, emergent effects. So it's difficult to give a direct analogy to computer storage."
] |
[
"Has science demonstrated that whales have degenerate genes for mammal legs?"
] |
[
false
] |
It would be beautiful to link the phenological evidence to genomic evidence about the reason for those vestigial leg bones.
|
[
"PZ Myers explains what cetacean limb genes are doing ",
"here",
". Basically, the genes are the same as for land mammals but the execution of them has differed."
] |
[
"Nice summary (one expects no less from PZ). The money-shot is at the end:",
"How do you make a whale? Clearly, you don't just \"lose\" the genes required to make hind limbs. You have to revise and add to the control information for existing banks of regulatory genes involved in limb formation.",
"Clearly, whales can make perfectly good limbs at the front end, so you wouldn't really expect them to have lost any leg-making genes. They just don't switch on part of the leg-making program at the back end."
] |
[
"Thank you. Excellent stuff."
] |
[
"Why can we 'feel' someone staring at us?"
] |
[
false
] | null |
[
"You mean if we actually see a face why do we look at it? We need to put objects into our fovea to resolve details and faces draw our attention as objects in the environment that are important, partly for social reasons and partly because whenever there is a face we usually look at it (which sounds circular, but all I mean is that we rapidly learn that faces are important stimuli; very young infants (within the first few weeks of life) have a preference to look at face-like stimuli)."
] |
[
"You can't. This is called the psychic staring effect and there is no conclusive evidence that it exists."
] |
[
"There are some on the wiki page or you can search Google scholar for the term"
] |
[
"If the fusion reactions in stars don't go beyond Iron, how did the heavier elements come into being? And moreover, how did they end up on earth?"
] |
[
false
] |
I know the stellar death occurs when the fusion reactions stop owing to high binding energy per nucleon ratio of Iron and it not being favorable anymore to occur fusion. Then how come Uranium and other elements exist? I'm assuming everything came into being from Hydrogen which came into being after the Big bang. Thank you everyone! I'm gonna go through the links in a bit. Thank you for the amazing answers!! :D You guys are awesome!
|
[
"There are a couple of processes that create elements heavier than iron. The s-process (s for 'slow') happens in large stars, where atomic nuclei capture free neutrons, increasing their mass. Occasionally they'll undergo beta decay, increasing their atomic number. This takes a long time, but because there's just so much stuff inside stars, it works out, and is responsible for about half of the atomic nuclei heavier than iron.",
"The other half are typically created by the r-process (r for 'rapid'). This occurs when there are a lot (and I mean a lot) of free neutrons around and nuclei just soak them up. Conditions like these tend to only happen in core-collapse supernovae, and so many of these elements are created during supernovae.",
"EDIT: Others have pointed out that we now also have evidence that suggests many heavier elements are created within neutron star collisions. I figured I should add this here since it has become a popular answer."
] |
[
"\"R-process only occurs in core-collapse supernova\" is a bit outdated. The ",
"recent double neutron star merger",
" showed evidence of r-process elements being formed in large enough amounts to explain ",
" r-process production, while simulations of core-collapse supernovae have had difficulties in making r-process elements (which could still be due to limitations of the simulations). It's likely some combination of NS-NS mergers and core-collapse supernovae, though."
] |
[
"As an addendum to this, the belief that heavier elements do not form during the life of a star is essentially correct. While in the s-process fusion of heavier elements does occur (very slowly and very infrequently), the r-process (that which creates the majority of heavier elements we see today) is accompanied by the “death” of the star, i.e. the collapse of a star into a supernova.",
"In essence, we are made not only of star-stuff, but of the corpses of stars. Neato! You’re a star zombie!"
] |
[
"Besides Human & Apes, do any other animals find certain things humorous?"
] |
[
false
] | null |
[
"Wikipedia has your back",
"."
] |
[
"That link goes to a 404."
] |
[
"Check out the title story from the book \"The Parrot's Lament\". Decide for yourself. I believe it. When people lie, they're generally not this creative. ",
"https://companionparrotonline.com/humor.html"
] |
[
"If the sun somehow captured an asteroid from outside the solar system would we be able to examine its composition and identify it as an extrasolar object?"
] |
[
false
] | null |
[
"Howdy! I've removed your post for its open-ended and speculative nature. I can redirect you towards ",
"/r/AskScienceDiscussion",
" which better suits such posts."
] |
[
"After giving it a second look, I let your second submission through."
] |
[
"After giving it a second look, I let your second submission through."
] |
[
"Since sound waves require a medium to travel through, and bone is a very dense one indeed, would you be able to hear yourself in space?"
] |
[
false
] |
Also, would you conceivably be able to hear someone if you held their hand or put your foreheads together and then spoke? Just a question out of morbid curiosity.
|
[
"Your vocal cords create pressure waves in the air surrounding them. Sound travels through bone by having a pressure wave come into contact with your body and the wave continues to propagate along the path. If there is no air, there is no wave to create. So nothing can cause the pressure wave to travel through your bones/body."
] |
[
"Not a scientist in this area or involved in science professionally at all, but I recently saw an interview with a veteran US astronaut who said that on EVAs if the communications went dead the astronauts could talk to each other by putting their heads together and the sound would travel through the glass(or whatever it's made out of) in the helmets. ",
"Sorry though, I can't remember where I saw it or who it was. "
] |
[
"You can try these things out here on our planet, Earth, and see if they work; get a friend and some heavy-duty ear muffs. Putting your heads together and talking is unlikely to do anything, but if you talked against a balloon and held it against their ear the pressure wave would still be able to propagate.",
"Most of the sound YOU hear when you talk comes from your mouth though, not the vibrations of your vocal cords.",
"Sound can be transmitted through bone if that's what you're interested in, there was a product called the ",
"bone fone",
" that used bone conduction to play music. My grandad used one to mitigate his hearing loss."
] |
[
"How is a three cylinder engine balanced?"
] |
[
false
] |
Take four cylinder engines, for example: you can see in how there is always one cylinder during combustion stroke at any given time, so there's never a lax in power. Engines with 6, 8, 10, or more cylinders are similarly staggered. So my question is how they achieve similar balancing with a 3 cylinder engine.
|
[
"you can see in this animation[1] how there is always one cylinder during combustion stroke at any given time, so there's never a lax in power ",
"Because of the way you phrased your question, I don't believe you are talking about how counterweights work. \nBriefly, counterweights are placed on the crankshaft essentially opposite the piston. The result is when the piston goes through its rotation, the mass of the piston wants to get thrown out and not come back. The mass of the counterweight counters this action and wants to continue rotating. It's the conservation of momentum. The most energy is conserved when the mass of the counterweight adequately cancels out the mass of the piston and connecting rod. ",
"Lets really answer your question, smooth power delivery.",
"\nSince you are looking at an inline engine, it's easy to see the operation in 2 dimensions.",
"\nThe reality is we want the pistons to fire at even time intervals to provide a smooth power deliver and \"never a lax in power\".",
"\nBefore we look at that, understand that we have a 4-stroke engine, so one combustion cycle is 4 strokes, or 2 revolutions.",
"\nIf we have one cylinder, it fires whenever it fires which is once every 2 revolutions.",
"\nIf we have 2 cylinders, we want them to fire evenly through the combustion cycle. We would like them to fire evenly through 2 revolutions. ",
"2 revolutions is 720 degrees (360 degrees x2) so to take two pistons, and evenly distribute their firing across 720 degrees, we fire one piston every 360 degrees. ",
"In your animation, focus on the inner 2 cylinders only. They look paired. They look like there is no difference in angle between them. A zero degree angle is the same as a 360 degree angle. They go up and down at the same time BUT when one is firing, the other is on the intake stroke and vice versa. So the provide power strokes at equally spaced intervals. ",
"If we have a 4 cylinder engine and we want the 4 cylinders to fire evenly across the combustion cycle, we need them to fire every 180 degrees (720 for a full cycle, divided by 4 cylinders).",
"\nThat's what your animation shows. When one piston is at the top, another piston is 180 degrees off at the bottom, another piston is another 180 degrees off at the top and the last piston is another 180 degrees off at the bottom. ",
"So now it provides smooth power flow.",
"\nThis formula (720/# of cylinders) is the ideal crankshaft angle between piston firing to achieve smooth engine operation.",
"\nFor a 3 cylinder engine, (720/3) we have the pistons fire 240 degrees apart from each other. \nThe crankshaft look almost like the letter Y. This way they can have even impulses from the power strokes of the 3 cylinders. ",
"Now, balancing a crankshaft is different from balancing the power strokes of an engine. That requires more explanation. ",
"Edit: Some rephrasing. "
] |
[
"That is a brilliant question.",
"\nWhile the power stroke lasts 180 degrees, the power obtained from that stroke does not.",
"\nMore specifically to answer your question, imagine each piston individually. ",
"If you have a one piston engine, and it has its power stroke, it then has 3 other strokes where it is not producing power. So for that single cylinder engine we essentially have \"on, off, off, off\" in terms of producing power and that can cause vibrations. ",
"We can reduce these vibrations simply by spinning the engine faster. Because when we spin the engine faster instead of seeing 1 on for 3 off's it spins so fast that it appears to us as 1 small on and no off.",
"\nBecause let's be real, considering the engine is not producing power for 3 of the 4 strokes, does it seem like the engine is off for 3/4 of the time? ",
"When you add on other cylinders, they each are following their four stroke cycle, and we time them to fire at intervals to smooth the power delivery but these angles don't have anything to do with one another. ",
"Each individual piston can follow a four stroke cycle, and the full cycle is complete in 720 degrees.",
"\nWe just change the point where each piston starts that cycle. ",
"Now, to correct a bit of your understanding, you should know that while we show the power stroke as 180 degrees of rotation, that actual power produce by that piston only occurs for a short part of that stroke.",
"\nIt doesn't occur across the entire 180 degree stroke.",
"\nSo the real way to think about the operation is that each time the spark plug fires we're getting a pulse of energy and we're just putting them all together to give us effectively uniform power distribution. ",
"Edit: I want to address the last point you made regarding 180 of power, 60 of nothing.",
"\nWhat's actually happening in one cylinder is \"180 of power\" and \"540 of nothing\"",
"\nIf we were looking at a 6 cylinder engine for example, it will fire every 120 degrees, so in the \"180 of power\" for one piston, by the time we get 120 through it we have another piston start firing and these two power strokes overlap. Then when the second piston is 120 through its stroke the first piston is already in its exhaust stroke and no longer contributing and the third piston begins its power stroke and overlaps. ",
"The result is the overlap, or the gap, between power strokes is consistent. When the engine spins fast enough these are imperceptible. "
] |
[
"Thank you for your response. You are correct in that I was not asking about counterweights (but I did get some interesting responses regarding them). ",
"Since a power stroke only lasts for 180 degrees and a three cylinder engine's strokes are 240 degrees apart, wouldn't the 60 degrees between the two make for some odd vibrations while trying to accelerate? There would be 180 degrees of power, then 60 of nothing, then 180 power, 60 nothing, etc. This seems like it would lead to a very rapid sort of pulsing in the power delivery."
] |
[
"Does an 8-hour sleep from 3-11 AM different from an 8-hour sleep from 10 - 6 AM?"
] |
[
false
] |
My dad keeps on telling me "Your immune system is weak because you always sleep late." However, I get full sleep but on a different schedule than them. I sleep for more or less 8 hours but from around 3 am onward. Does it make a difference than sleeping early?
|
[
"Yes it does differ. Our bodies are meant to be awake during daylight hours, and people who do things like work night shifts have been shown to have greater risk for heart disease and diabetes. ",
"http://healthhub.brighamandwomens.org/sleep-research-is-the-night-shift-bad-for-your-health#sthash.FsRd5q8x.mdWSnNib.dpbs",
"However, I'm not sure about how this affects your immune system. "
] |
[
"That study combines insufficient sleep as well as disruptions to the circadian rhythm (like having an inconsistent sleep schedule), right?",
"OP seems to be getting sufficient sleep, and his sleep schedule seems to be consistent... I don't think that study serves as sufficient evidence that there's a difference."
] |
[
"There are different chronotypes. Your circadian rhythm (peak levels of awareness, hormones, etc.) can be different than others. In some people it is very pronounced, and this is called Delayed Sleep Phase Disorder.",
"https://en.wikipedia.org/wiki/Delayed_sleep_phase_disorder",
"The short of it is that if you get a normal amount of sleep, just on a different schedule, it can be healthy. The main obstacle is conforming to what our society expects from us. Early chronotypes should be aware that they don't have superior willpower or energy. There's also evidence that late chronotypes are more creative thinkers."
] |
[
"Why are galaxies not spherical?"
] |
[
false
] | null |
[
"Because they're spinning."
] |
[
"Yes",
"The Earth is under the same force as it rotates on its own axis. That is why it's shape is approximately an oblate spheroid, rather than spherical (excluding local topography)."
] |
[
"Which in turn stretches it out?"
] |
[
"Why does wool/neoprene keep you \"warm\" when wet?"
] |
[
false
] |
I've taken several wilderness first aid classes now and spend a bit of time kayaking and whatnot. I keep hearing that wool or neoprene or a couple other synthetic materials will keep you warm even when you're submerged in water. I've also heard cotton called the "death cloth" in Search and Rescue, because it will get you hypothermic quicker. Anyways, why? And are there other materials I should know about in regards to this?
|
[
"The key concept here is thermal conductivity [abbreviated as k for some reason]. Water has a significantly higher k value than air does, so water can 'move' the heat much more quickly. Heat always travels from hot to cold [excluding systems with a power input, which your body is not]. So wet clothing will help you lose that heat much more quickly.",
"Things like neoprene [think wetsuits] do not allow the water to flow away from your body. They basically function as tiny reservoirs of water held near your skin. This allows you to heat up that layer of water next to your skin, which stays there. You don't feel cold, because the water surrounding you is the same temperature as your skin. And you don't lose your body heat as quickly, since there's little heat 'flow' due to your skin and the water being the same [or at least similar] temperature."
] |
[
"Also, neoprene is a solid foam, and inside it there are tiny bubbles of air, that act as an insulator. A side effect of that, for divers like me, is that, when you dive deep, water pressure compress the bubbles, the wetsuit becomes thinner and so less insulant."
] |
[
"Water drains the heat off your body about 25 times faster then air does. When cotton gets wet it no longer has insulating properties and simply lets the heat escape. On the other hand wool even when wet will help trap some of that heat from escaping. Neoprene on the other hand lets the water in when but does not let it leave. Given time your body heats up the trapped water and that is what keeps you warm. Hope that answers your question."
] |
[
"Can a fan blow air through a vacuum"
] |
[
false
] | null |
[
"Just to clarify, you're wanting to take the air out of a chamber with your wet item in it, and then re-introduce air, to blow through the chamber to dry it off? This sounds like an odd combination of two different methods, really - what's the point behind evacuating the chamber before passing the wind through?"
] |
[
"The plan is not to re-introduce air. The fans would be part of the vacuum chamber. In there with the wet beans. Thanks for reply!"
] |
[
"Well, if you've taken all of the air out of the chamber to create the vacuum, there won't be anything left to blow!"
] |
[
"I know this is a controversial issue, but what are your thoughts on genetic evidence for races?"
] |
[
false
] |
(or lack thereof) I'm a noob to genetics, having only had high school biology and a 100 level course on it so far (which didn't expand on it too much). I've seen the wiki article and some of the abstracts it's linked to. I'm under the impression that there's yet to be a definite consensus among population geneticists but maybe I'm wrong. I'm mostly curious to hear what those in relevant fields think about it.
|
[
"Not quite. Racial groupings are somewhat arbitrary but not analogous to the things you mentioned, because racial groupings come from large sets of genes and are in some sense closed.",
"For instance, two African parents will always produce an African-looking child. Two Asian parents will always produce an Asian-looking child. An African and an Asian parent will produce a child which looks a bit African and a bit Asian.",
"On the other hand, two brown-eyed parents can produce a green-eyed child and two right-handed parents can produce a left-handed child, and so forth.",
"Races are just groups of people that have been reproductively almost-isolated from each other for long enough that they have differing prevalences of a whole lot of genes -- for skin colour, hair curliness, eye colour, height, shape of certain facial features and so forth. Some of these have definitive adaptive advantages (sunnier places tend to have darker-skinned people, Europeans and Middle Easterners tend to maintain lactose tolerance into adulthood because they've been drinking cows' milk for many generations) and others seem to just be somewhat random drift with no particular advantage. "
] |
[
"Not quite. Racial groupings are somewhat arbitrary but not analogous to the things you mentioned, because racial groupings come from large sets of genes and are in some sense closed.",
"For instance, two African parents will always produce an African-looking child. Two Asian parents will always produce an Asian-looking child. An African and an Asian parent will produce a child which looks a bit African and a bit Asian.",
"On the other hand, two brown-eyed parents can produce a green-eyed child and two right-handed parents can produce a left-handed child, and so forth.",
"Races are just groups of people that have been reproductively almost-isolated from each other for long enough that they have differing prevalences of a whole lot of genes -- for skin colour, hair curliness, eye colour, height, shape of certain facial features and so forth. Some of these have definitive adaptive advantages (sunnier places tend to have darker-skinned people, Europeans and Middle Easterners tend to maintain lactose tolerance into adulthood because they've been drinking cows' milk for many generations) and others seem to just be somewhat random drift with no particular advantage. "
] |
[
"Of the 74 people who have run the 100 meter in less than 10 seconds, only one is white. All of the others are of West African/Caribbean descent.",
"I wonder how much of that is due to the majority of \"white\" people not training to be good at running. I mean, the vast majority of hockey players in the NHL are \"white\" but does that correlate to asians/africans being terrible at it?"
] |
[
"Why are the Great Basin, Mohave and Sonoran Deserts considered distinct?"
] |
[
false
] |
Looking at a map, these three deserts look like they are right next to each other. Why wouldn't they be known as one big desert?
|
[
"Mostly because of distinct plant life and weather. In the Sonoran desert you have several varieties of cacti that are not present in either the Mojave or Great Basin desert. The Sonoran also has two rainy seasons, summer monsoon and winter rains while the other do not. Also separting the Mojave and Great Basin is temperature. The Great Basin is considered a cold desert, whereas Mojave is a warm desert. There are also varieties of plant life, such as Joshua Trees which are plentiful in the Mojave but rarely occur in the Great Basin. Even though they are close different weather patterns cause a division of plant life in them and separate them."
] |
[
"Sounds like they are quite distinct. Thanks so much! I'll have to spend some time looking further into deserts, this is quite interesting."
] |
[
"Joshua Tree National Park connects the Mojave and Sonoran Deserts, and if you look closely you can see differences in the geology and topology along the boundary line. Among the many amazing reasons to visit Joshua Tree, if you're interested in deserts, the rangers and docents at the visitor centers can give you specific destinations and pointers on what to look for."
] |
[
"Has anyone ever invented a (non virtual) system of writing which is more efficient than the roman alphabet?"
] |
[
false
] |
We all know that there are many ways of writing, some of them still widespread in the world like the Japanese and Chinese pictographs. What i am wondering is, did anyone ever come up with a more efficient writing system than the one we currently use? If yes, why didn't it catch on?
|
[
"Consider ",
"stenographic systems",
", which allow people to write down information more quickly, at the expense of robustness.",
"The ",
"Shavian alphabet",
" was an attempt to create a alphabet for English that was ",
"featural",
" and had near-perfect ",
"phonemic orthography",
" - both features which would generally be considered improvements on our current alphabet.",
"Almost all common writing systems are developed through use, rather than designed. Large-scale reforms are difficult to institute (how would you go about organizing a widespread transition to the Shavian alphabet?) and thus don't happen, even if they would be \"more efficient\" than what we currently have."
] |
[
"It's difficult-to-impossible to objectively rank ",
"writing systems",
" by their efficiency. ",
"Another questioner got this response",
"; as you can see the conclusions were nowhere near definitive."
] |
[
"I've heard Hangul (written korean) is the most efficient, but I can't find any reliable sources online. ",
"Wikipedia",
" cites:",
"Numerous linguists have praised Hangul for its featural design, describing it as \"remarkable\", \"the most perfect phonetic system devised\", and \"brilliant, so deliberately does it fit the language like a glove.\"",
"(Cited in Taylor, Insup (1980). \"The Korean writing system: An alphabet? A syllabary? A logography?\". Processing of Visual Language 2: 65. New York: Plenum Press.)",
"Basically it has the best from both worlds. The individual letters are arranged so that each character forms a syllable. You can read it on two levels, either by syllable or by letter.",
"Here is a table of the characters to give you an idea:",
"http://www.hapkidoselfdefense.com/hangul_table.gif"
] |
[
"Why do I never see dead Pigeons in cities?"
] |
[
false
] | null |
[
"An article on this very subject: ",
"http://www.theatlanticcities.com/neighborhoods/2012/05/why-arent-cities-littered-dead-pigeons/2038/"
] |
[
"Thanks, what a perfect answer!"
] |
[
"Find a bridge with anti bird nets under it and look up. There will usually be at least one dead pigeon stuck in it. "
] |
[
"Are people executed via firing range able to hear the gunshot, or would they die before the sound reaches them?"
] |
[
false
] |
[deleted]
|
[
"Being shot is not instantaneously fatal. That's an artifact of movies and TV shows.",
"A gunshot wound to the thorax is generally instantaneously incapacitating due to the impact alone. But it does not typically result in an immediate loss of consciousness. There have been many, many documented cases of people suffering rifle wounds to the chest or abdomen and mistaking it for a blunt impact. What you hear most frequently is that it feels like being hit by a flying rock.",
"Even a gunshot wound that directly traumatizes the heart will not be instantaneously fatal. It can take anywhere from a minute to several minutes for an injury to the heart to reduce blood volume sufficiently to induce a loss of consciousness due to inadequate cranial perfusion. And gunshot wounds to the heart are ",
" rare, because bullets typically spall off the sternum. Most gunshot wounds that result in injury to the heart actually enter under the arm.",
"Even a gunshot wound to the head is not guaranteed to produce instant unconsciousness, though of course it can. I've seen patients arrive in the emergency room with small-caliber gunshot wounds to the head alert and oriented with a GCS of 14 or 15.",
"In general, the whole \"killed instantly\" thing is a load of bullcrap. While there are obviously situations in which it can happen, in cases where the brain is sufficiently traumatized in a short amount of time, in general it takes an absolute minimum of two to three minutes to die. While you will lose consciousness before death, getting shot isn't usually anywhere near enough to cause this to happen instantly.",
"So yes. You'd hear the shots."
] |
[
"Have a buddy who got shot in Iraq with a rifle (AK-47 I guess, or whatever the insurgents use) and he had no idea what hit him. He thought one of his squad mates just leveled him with a sucker punch and it wasn't until they started returning fire and one guy rushed over to drag him away that he realized \"huh, I was probably just shot.\""
] |
[
"Speed of a bullet",
": 180-1500m/s",
"Speed of sound",
": 340.29m/s",
"Then there's also the time it takes for a sound to register in your brain.",
"So, they'd probably get hit by it before they hear it.",
"But, whether or not they'd ",
" the sound before dying.. I do not know."
] |
[
"Could I increase the frequency of a radio wave emitted from an antenna to a point where it is in the visible light spectrum? Could I see it?"
] |
[
false
] |
I've always wondered this because the two different phenomena, emitting a radio signal and visible light, are placed on the same spectrum. I suspect no is the answer, but why?
|
[
"Well.. you can always try running towards the antenna is extremely high speeds. That should blueshift the emitted waves.",
"Otherwise, I'm afraid antennas stop behaving according to conventional antenna theory by the time you reach IR or terahertz frequencies. You cannot produce a conventional oscillator that drives a large antenna at those frequencies. You could always just try to boil the antenna and claim that the black body radiation it is emitting is the output but that seems like cheating. You could also build a particle accelerator to swing around electrons at high speeds and consider their synchrotron radiation as your antenna output, but that seems like cheating in the other direction. All in all, the physics of the real materials used to build an antenna tends to get in the way of you being able to do that.",
"Of course an \"ideal\" antenna with an \"ideal\" AC voltage source and \"ideal\" wires can do whatever you can dream up."
] |
[
"It is all the same thing but as the other responders point out, it's the assumptions built into the processes that start to break down - the technique itself should still work. The idea behind antennas is that you are using a wire (some ideal object with 0 resistance that transmits electric signals) and an oscillating AC voltage source (an ideal object that happens to produce a potential difference between its terminals) to produce an E/M field. As long as you satisfy all those constraints, you are good to go. From wide swathes of the E/M spectrum (well into microwave), you can work with those assumptions using conventional metal wires and oscillators. Once you get near the IR range, you get into trouble. Atoms and latice cells are on the size scale of nanometers. Visible light is ~500nm. You can begin to see how a wire isn't quite a \"wire\" any more. Wires don't really worry about electric signals bouncing back and forth in their cross section. Wires don't worry about lattice defects, band gaps and ballistic trajectories of electrons. If you somehow are able to get electrons to move in a nice orderly manner and still oscillate back and forth in this length scale (which is what a cyclotron does), then you can indeed get visible light. You can in fact produce X-rays and gamma-rays as well. The process just stops looking like a traditional antenna because you simply aren't able to engineer wires that both meet the mathematical assumptions of a wire and aesthetically look like wires that we are used to."
] |
[
"Well, they ",
" make radio waves via passing electricity through a gas: ",
"Spark Gap Transmitter",
".",
"It all ultimately comes down to physics - you can convert electricity to EM waves by a huge variety of different methods, but the efficiency will vary wildly. For low-to-medium RF ranges, a simple oscillator using more-or-less standard electronic components works really well. ",
"For higher frequencies, you might need something involving more-exotic semiconductors, or even ",
"a vacuum tube",
" that treats bunches of electrons as a working material for the oscillator.",
"As you get up into the visible range, you get different material interactions, so you have to switch to another method again, and once you start looking at higher frequencies than that, you're back to another method.",
"There do exist broadly-tunable light sources that can produce output over a huge range of frequencies. These are mostly \"electrons in a vacuum\" types of things, like the previously mentioned gyrotron, the free-electron laser, and synchrotron light sources."
] |
[
"What is the grey \"flesh\" between the salmon's skin and the pink flesh? Is it the same/edible as the pink flesh?"
] |
[
false
] | null |
[
"The grey flesh is slow twitch muscle and the pink fast twitch. Salmon move through a much denser medium (water compared to air) so it takes a lot more muscle to move quickly, say from a predator. This means that the ratio between slow and fast twitch muscles is very different in fish compared to humans.",
"One might assume that the fast twitch muscles are used more often because they make up most of the muscle. Most of the time salmon use the slow twitch muscles as they steadily and slowly move through the water. Only on those comparatively rarer occasions do they ever tap the fast twitch muscles.",
"This was all taken from the wonderful book \"The Story Of Sushi\" by Trevor Corson. "
] |
[
"Biologoy: the study of the non-Jewish human."
] |
[
"Although I am not a marine expert, I have, as someone that loves cooking, researched this. The white meat that you see in a salmon filet is pretty much pure muscle. The gray matter has a higher concentration of fats and such. That's why it's on the outside and why, if you smell it, it sellsbad - it's full of fatty products, some of which are aromatic.",
"It is just as edible as salmon's \"pink flesh\" as you call it. You could eat a bowl of it with a spoon and be fine aside from the fact that you ate a bunch of something gross. It is not the same, however; if you are grilling or otherwise cooking salmon, I suggest somehow stripping your filet of it.",
"Grilling tip: light up the grill and place your salmon on the grill with skin side down. Let it cook for a bit. After a little, go and flip it. After you flip it, you will find that you can take a fork or a knife, gently slip it between the salmon meat and skin, and lift up; the skin will peel right off. After you've peeled the skin/scales off, you'll see that \"dark meat\" in the middle of the filet. That \"dark meat\" is fatty and aromatic in an unpleasant way; use a fork, spoon, knife, or some other utensil to kind of scrape it off. If you do that, then, once your salmon is done, it will taste delicious and have very little of that \"intense fishiness\" that is unpleasant."
] |
[
"What is the carbon purity of cremated remains? (three part question)"
] |
[
false
] |
I have seen the places offering to have a diamond created out of the carbon remains after cremation, but I know that it can only take about 20 atoms of titanium to turn a synthetic diamond a brilliant yellow. I was just wondering if creating one out of cremated remains, how pure is the carbon content likely to be? Secondly, what other impurities are likely to be there? I would presume iron and zinc would be the main ones, since they are of higher concentrations (of the heavy metals) in human composition. I am unsure of which metals would be vaporized off since most cremation ovens run around 900 C. Thirdly, if approximate weight (give an average sized person) of the remains is roughly 5 lbs, what size diamond would that yield when condensed down?
|
[
"Cremation ash hardly contains carbon at all. It's mostly oxidized bone matter. It's practically ",
" minerals. Inorganic ash. If they're turning human remains into synthetic diamonds, they'd first be doing quite a bit of chemistry to separate out the carbon, so the \"purity\" of the ash isn't really relevant. I don't know what process they use for that, nor which synthesis process they use for the diamonds (which, except for CVD diamonds, ",
" the addition of catalytic metals, which is what discolors them)",
"Synthetic diamond size doesn't have much to do with the amount of carbon. If that was the case, we'd be making a lot more synthetic diamonds than we do. Most of the carbon likely goes to waste, but it depends on the process as well. But most processes for synthesizing diamonds do not produce large diamonds at all, and I'm guessing in this case that it's probably very small, industrial-size-and-quality synthetic diamonds. "
] |
[
"If you burn organic matter under the right conditions you can generate a lot of soot, which I assume is what they're doing."
] |
[
"It's not what you do in a crematorium oven; that's a pretty complete combustion. And it doesn't seem like these companies are doing the actual cremating, but just making diamonds out of whatever carbon they can get out of the ash."
] |
[
"Is there any scientific basis to claims that it's possible to influence the sex of your baby?"
] |
[
false
] |
[deleted]
|
[
"Some studies have shown that the sperm with the X chromosome live longer than the than the sperm with the Y chromosome. This means that 'female' sperm have a greater life span than 'male' sperm. However, 'male' sperm are considered 'better swimmers' as they have greater motility -- they live fast and die young (ha ha ha).",
"Therefore, having intercourse closer to ovulation you have a slightly greater chance of having a male, but if you have intercourse a day or two before ovulation you have a better chance of having a girl -- by the time you ovulate a lot of the 'male' sperm will have died leaving a greater percentage of 'female' sperm. Other studies (such as this one in the New England Journal of Medicine: ",
"http://www.nejm.org/doi/full/10.1056/NEJM199512073332301#t=articleBackground",
") have found no correlation.",
"Other research has shown a small increase in the number of male births to women who eat a good, potassium rich breakfast and ate more calories compared to women who skipped breakfast altogether. Not enough studies have been done to prove this is the case -- one study is not conclusive evidence.",
"EDIT: Grammar"
] |
[
"I don't think there are mega studies because a lot of the necessary controls would require conditions that wouldn't be ethical. Many (I would hope most) people who are trying to conceive are not willing to risk trying different things (like going through a starvation diet for example) in order to maybe get a child of one sex over another. ",
"edit: I used require three times in one sentence. I reworded."
] |
[
"I don't think there are mega studies because a lot of the necessary controls would require conditions that wouldn't be ethical. Many (I would hope most) people who are trying to conceive are not willing to risk trying different things (like going through a starvation diet for example) in order to maybe get a child of one sex over another. ",
"edit: I used require three times in one sentence. I reworded."
] |
[
"If you map hurricane Irene's path, you'll find it's been staying on the continental shelf, roughly skirting the border between it and deeper waters. Is this coincidence or is there a reason for that?"
] |
[
false
] | null |
[
"http://imgur.com/ELknQ"
] |
[
"It's because of the pattern of prevailing winds.",
"There's a ridge of high pressure that sits at approximately latitude 30N during the summer. It's called the ",
"subtropical ridge",
".",
"Winds south of the subtropical ridge are the ",
"trade winds",
", which blow east to west. Therefore, hurricanes originating in that area head westwards along the Caribbean towards Florida and the east coast.",
"The subtropical ridge is right around the north coast of Florida during hurricane season. So when the hurricane hits Florida, the westwards motion fades, since right on the subtropical ridge there are no prevailing winds. However, due to the ",
"Coriolis effect",
", the hurricane drifts ",
" from the equator, that is, northwards.",
"Once it crosses the subtropical ridge and goes northwards past Florida into the Georgia coast and the Carolinas, it comes under the influence of the ",
"Westerlies",
", or anti-trade winds. These winds blow from west to east. So the storm is pushed eastwards towards the Atlantic again. However, because of the curvature of the coast (which also curves eastwards along Georgia and the Carolinas), it tends to follow the coast. That is, as the hurricane is pushed eastwards by the Westerlies, the coast also curves eastwards, so the hurricane and the coast match tracks.",
"As it continues moving northwards (through the Coriolis effect) and eastwards (due to the Westerlies), it reaches the northern parts of the Atlantic, where the water is cooler, and as a result, the hurricane loses energy and tends to die out."
] |
[
"The eastern coast has outward ",
"prevailing winds",
". ",
"This also affects ocean waves.",
"I wager that hurricanes are channeled along the edge of the shelf because that's where the winds are the strongest. I also gather by looking at that picture in the wiki article that the Atlantic trades meet the coastal winds right around the continental shelf.",
"Hurricanes that make it through to Florida typically come in under the continental shelf; blowing hard through the islands, and then giving Florida and the rest of the states a swift uppercut. The Big Three in 2004 season had two fine examples of this in ",
"Ivan",
" and ",
"Charley",
" (scroll down to the charts).",
"Frances",
" did exactly what Irene did, but didn't meet the prevailing winds until she made it a bit further inland. A strong enough hurricane will hit the coast, touching down in Miami and just roll on up the side of florida on through Jacksonville and then dissipate over land or bounce off the coast."
] |
[
"Why do I tend to find people prettier if I like them and uglier if I dislike them?"
] |
[
false
] | null |
[
"Hi evilbutcut3 thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Hello,",
"We can't speculate about your personal preferences here."
] |
[
"Hi, I have actually talked about this to friends of mine and it seems that several of them also experience this. Thank you for answering though, I guess I'll remove this post :)"
] |
[
"If a superconductive wire can hold a current indefinitely, does that mean you can keep adding to the current and if so, how do you determine the capacity of a given length of superconductive cable?"
] |
[
false
] |
Forgive my ignorance. I would guess that "capacity" would be described in terms of amount of electrons?
|
[
"Superconductors have a \"critical current\" beyond which the superconductivity is broken, and you no longer have a superconductor, just a normal conductor."
] |
[
"What gives rise to this limit, some sort of saturation effect?"
] |
[
"the exact mechanism is unknown, but when the ",
"cooper pairs",
" is given enough energy it will break apart into two electrons resulting in the end of superconductivity. If the current is increased in a superconductor you don't end up with more carriers, but rather each carrier moves faster (remember I=dQ/dt). This mechanism means that at a high enough current we expect any cooper pairs to break apart. An interesting addendum is that the critical current is often of the order of magnitude to the current necessary to generate the critical magnetic field for a superconductor."
] |
[
"When white light hits a surface and reflects a color (and absorbs other wavelengths), what is happening at the reflection point?"
] |
[
false
] |
So if I take red paint, it's red because it absorbs everything except red. So white light has struck it, and reflected only the red. On a molecular level, why?
|
[
"Atoms have electrons orbiting the nucleus. These electrons move very fast and their position is not definite, so we will call them an electron cloud. When the cloud is centered around the nucleus, there is no net force on the cloud. When the cloud is pulled to one side, there is an electrostatic force pulling it back to center, like a spring. Seriously it operates very similarly to a spring. So when an incoming electromagnetic wave (light) had the correct frequency (color), there is a resonance effect in the spring and the light is absorbed. Other light reflects, and the net result is the color you see. "
] |
[
"So the energy from the non-red photons is transferred into the electron cloud and then that energy becomes what? Heat?"
] |
[
"Generally, yes. That is why a black surface out in the sun would generally heat up more than a white surface."
] |
[
"Approximately how fast is Sol traveling relative to the center of the Milky Way galaxy?"
] |
[
false
] | null |
[
"According to ",
"this NASA site",
", about 828000 km/hr, or 230 km/sec."
] |
[
"It does my head in when people use Sol and Luna trying to sound intelligent. "
] |
[
"It does my head in when people use Sol and Luna trying to sound intelligent. "
] |
[
"How does Mercury produce toxic fumes if it is a heavy metal?"
] |
[
false
] | null |
[
"Everything, including the metal mercury has a vapour pressure. The vapour pressure of mercury at room temperature happens to be greater than that of other metals. ",
"The actual toxicity of elemental mercury has, perhaps, been overstated in popular opinion. Mercury salts, however, and in particular organo-mercury compounds, can be quite a lot more toxic."
] |
[
"An important part that you mentioned, but perhaps not explicitly enough, is that the toxic 'fumes' from mercury are mercury vapor itself -- the gas phase of the metal."
] |
[
"I would like to add that mercury is naturally found in the environnment, in air, waters and soils. At room temperature, elemental mercury slowly forms vapor when in contact with air. Mercury vapor also comes from volcanic eruptions, erosion of rocks, and human industry."
] |
[
"Why don't we scale wind turbines down?"
] |
[
false
] |
[deleted]
|
[
"It is hard to measure everything's stress in a computer. Imagine that we test for 95% of the stuff, but BAM, we didn't check the sturdiness of the balls in the ball bearings, which creates a wobble and does damage to system A, which manages system B, which controls system C, which is the safety control for the whole thing, so the whole thing dies.",
"It's generally best to start small like we are, but then to slowly go up in size, until materials are either too weak to support it, or are to expensive to offset the benefits.",
"Good thing is that we are generally getting newer and better materials for cheaper, so improvements are always on the horizon (even if they are a speck on the horizon)"
] |
[
"The other reason turbines are as huge as possible is that short wind towers have less wind and more turbulence. A 120 foot tower will give you about ",
"double the power",
" vs ground level.",
"Small personal wind turbines tend to end in disappointment for many reasons. Go big or go home."
] |
[
"We're now testing 164 metre diameter rotors.",
"How is this not a fairly trivial thing to model or figure out? Like, honest question, why can't I just mock up a bunch of diameters in say a CAD program and check?"
] |
[
"Why does it sometimes take cold air and other times take hot air to defog my windshield?"
] |
[
false
] | null |
[
"it never \"takes\" hot or cold air. what it takes is \"dryer\" air.",
"when you use cold air either the humidity difference was VERY small or your AC compressor is kicking on to \"dry\" the air your using.",
"this is why older cars without AC have \"really\" hot heaters.",
"the other way to get the effect is with heat. Note I said dryer not dry. Hotter air can hold more moisture in it so if you heat 80% humidity air to twice the temperature its now \"lower\" humidity since the % is based on what it can hold not what it absolutely contains.",
"so hot air will hold more moisture and your giving it that moisture from your foggy windscreen. the hotter it is the more readily it will take on moisture.",
"SO to sum up. you need air DRYER than the surrounding and and enough of it to hold whatever is on your wind screen.",
"you can do this two ways. either DRY the air (turn on the AC) so it can hold more moisture or make the air HOT so it will hold more moisture."
] |
[
"While humidity is a factor, removing humidity isn't always a realistic solution. The cause of fogging is temperature differential. The air moving over the windshield tends to heat or cool the glass to a similar temperature, this can cause condensation. Condensation, which you likely know, is caused when air is cooled against a surface; the humidity condenses into a liquid out of the air, and fog is just a ton of tiny water droplets.",
"So, if the car is warm inside, but it's cold outside, the windshield is cold. The hot interior air condenses on the inside of the windshield, turning on the a/c cools the inside air and negates the temperature differential. If it's hot outside and cold inside, the outside may fog, heat will fix it. The key is removing the temperature difference on opposite sides of the glass.",
"Alternatively, if the temperature is similar, and humidity is high fogging can also happen. This is because of humidity getting trapped(or satan) combined with the windshield being cooled by air moving over it.. High heat should uncondense the formed water. Sometimes this doesn't work, but a/c can cool the air enough to discourage condensation. Swearing helps."
] |
[
"it never \"takes\" hot or cold air. what it takes is \"dryer\" air.",
"This isn't quite correct. ",
"\"Fog\" occurs when the temperature of the glass is below the condensation point, allowing water vapor to condense on the glass. Increasing the temperature of the glass such that it is above the condensation point clears the \"fog\". (This is how the rear defogger/defroster works in most cars. It uses resistive heating elements to heat the glass above the condensation point.)",
"In a very humid environment, blowing hot air at the cold windshield starts to increase the temperature of the glass, but until it exceeds the condensation point, the moisture in that hot air merely condenses on the glass. Turning on a hot defroster temporarily increases the \"fog\", but eventually (within a minute) eliminates the temperature condition that caused the fogging. ",
"Blowing ambient air on the glass works by the way you described, as evaporation rates are directly related to airflow. (effectively, moving air is \"dryer\" than still air) In some situations, blowing ambient air on the glass can immediately improve visibility, but the still-cold windshield can quickly refog while underway. ",
"Using the air conditioner to produce cold, dry air can exacerbate the fogging problem. Cooling the glass below the condensation point can cause fogging inside and out. If using the air conditioner to dry the air, also use heat to increase the temperature of the glass. ",
"tl;dr: for defogging a windshield, hot dry air is better than hot moist air; hot moist air is better than ambient air; ambient air is better than cold dry air. A lot of air movement is better than a little air movement. "
] |
[
"If I leave my phone charger plugged into an outlet, but unplug my phone from the charger, am I really \"wasting\" electricity?"
] |
[
false
] | null |
[
"\"Examples of work being done that isn't useful include leaving a light on in an empty room...leaving a cell phone charger plugged into an outlet when the cell phone is already fully charged, or is no longer connected to it...\" (",
"Green-Energy-Efficient-Homes.com",
")"
] |
[
"Great, thank you!:)"
] |
[
"Not all cellphone chargers are The same. Is there the same waste regardless of whether the charger is an old fashioned transformer, or a modern switch mode power supply?"
] |
[
"Is water the only chemical more dense as a liquid compared to a solid?"
] |
[
false
] | null |
[
"No, there are other examples of substances that display this property.",
"Density of Gallium (s) = 5.91g/cc , Gallium (l) = 6.1 g/cc",
"Also, germanium, silicon. Quite a few more."
] |
[
"Is there any common thread to explain why these and only these possess this shared property? "
] |
[
"Those are elements; are there any molecules like water that are most dense as a liquid? ",
"Of course, there is always ",
"amorphous ice",
" like HDA and VHDA that would not float (1.17 g/mL and 1.26 g/mL respectively). ",
"The common thread would be hydrogen bonding. You'd need a molecule with a good network of hydrogen bonding at its lowest energy conformation in the solid state. Then breaking some of those bonds randomly would cause the atoms themselves to take up less space and be more dense."
] |
[
"Why is slightly rotating things while pulling out easier, than only pulling without rotating?"
] |
[
false
] |
Sry for MY bad english. And thanks for any reply!
|
[
"For a variety of frictional and adhesive forces, the strength of the force is reduced once an object is in motion. Additionally, for a wide enough object, it's generally easier to exert a torque to produce twisting than a linear force for pulling, because torque increases with the radius of rotation, independent of applied force. The twisting motion makes the object move, reducing the adhesive force, which then makes pulling easier."
] |
[
"In high school physics class, you probably learned that static (unmoving) friction is higher than kinetic (moving) friction. This is usually true. What BoxAMu is saying is that it's often easier to break the static friction through a torque (rotational force) than by linear force."
] |
[
"Thanks to both of you! After 5 minutes of grinding gears in my Brain because of translating difficulties, i got it now! :)"
] |
[
"Is it possible for a planet to have an ocean without an atmosphere?"
] |
[
false
] | null |
[
"Yes, it's possible",
"No, it's really not.",
"If a liquid ocean existed without any atmospheric pressure, it would quickly boil until either the liquid was all gone, or there was enough boiled vapor to reach equilibrium pressure with the liquid. In other words, if you had a water ocean, it would very quickly create its own atmosphere of water vapor.",
"Both are larger than Earth and are expected to have water oceans, but no significant atmosphere.",
"Do you have a citation for this? Because the discovery paper (",
"PDF",
") makes no mention of the possibility of an ocean without an atmosphere - just that the atmospheric composition is unknown and assumed to be CO2."
] |
[
"Yes, it's possible",
"No, it's really not.",
"If a liquid ocean existed without any atmospheric pressure, it would quickly boil until either the liquid was all gone, or there was enough boiled vapor to reach equilibrium pressure with the liquid. In other words, if you had a water ocean, it would very quickly create its own atmosphere of water vapor.",
"Both are larger than Earth and are expected to have water oceans, but no significant atmosphere.",
"Do you have a citation for this? Because the discovery paper (",
"PDF",
") makes no mention of the possibility of an ocean without an atmosphere - just that the atmospheric composition is unknown and assumed to be CO2."
] |
[
"It all depends on your definition of ocean. Since the equilibrium point between a liquid and its vapor determines condensation and evaporation of said material, a liquid without a significant pressure of its own vapor (i.e., an atmosphere containing such vapor) would ultimately evaporate.",
"However, if you define \"ocean\" simply as a layer of water, whatever its state may be, there are a bunch of object completely covered in ice, and some even made almost exclusively of ice (like most comets and the rings of Saturn).",
"If you are asking this question with the purpose of colonization in mind, there's no doubt that icy bodies yield the relevant quantity of water needed, and some more."
] |
[
"Why are plants green and not black?"
] |
[
false
] |
[deleted]
|
[
"Actually, black objects DO reflect 'light' - they reflect parts of the electromagnetic spectrum that we can't see. Anyways, you're running on the assumption that evolution creates the most optimal possible solution to a problem, when what it really does is simply allow the most optimal existing solution to grow while other, less optimal solutions die out. Maybe some day, plants will be black. That requires that mutation to show up and thrive first :)"
] |
[
"yes, but i thought interacting with you fine people of science might have more interesting answers; thanks for the link, though! =D"
] |
[
"I was only thinking of the coloured light that we see, not the other wavelengths :D nice explanation of evolution, btw. I like it. "
] |
[
"Can you cook rotten meat enough, so that it becomes safe to eat?"
] |
[
false
] |
So you leave some meat in the fridge WAY past it's expiry date. You open it up just to be sure, and it's developed a rancid odour, and turns your stomach immediately. Lets assume its eat it, or die. Maybe I'm wrong, but I am under the impression, that the meat is now bacteria ridden. And I'm also under the impression that prolonged heat can kill bacteria. So Lets say I boil it to oblivion. For arguments sake, lets even assume we use a pressure cooker. Ensuring that the entire chunk of meat is well over 100 Degrees C. Can you heat it for long enough, that enough of the pathogens die off, and the meat becomes safe to eat? Thanks Reddit!
|
[
"You can kill the bacteria with heat, but there's no guarantee that toxins already produced by the bacteria will be destroyed by the heat.",
"Example is Staphylococcal Intoxication:",
"When Staphylococcus bacteria get into warm food and multiply, they produce a toxin or poison that causes illness. The toxin is not detectable by taste or smell. While the bacteria itself can be killed by temperatures of 120 F, its toxin is heat resistant; therefore, it is important to keep the staph organism from growing.",
"Source",
"."
] |
[
"That's exactly what I was looking for. I didn't realize pathogens can emit toxins.",
"Many Thanks!"
] |
[
"I should add for the sake of completeness that there will be some temperature high enough to inactivate the toxins. However, there is also the concern that the toxins could ",
"reactivate",
" after cooling. As a matter of pragmatism, it is safest to assume that once food is rancid it is not practical to try to make it safe again.",
"Of course your initial question stated it's eat this or die, so if the other option is (guaranteed) starving to death, then taking one's chance with excessively heated meat may be worth it. :)"
] |
[
"When you can't remember something why do you still know enough to recognize people's incorrect suggestions?"
] |
[
false
] |
For example: if you can't remember an actors name and people suggest a similar name you will know that it's not quite right. If you can't recall what it is to begin with, how does that work?
|
[
"The information may still be in your brain, you simply haven't yet been able to consciously access the proper memory. Or you have a partial memory, and it needs to be reinforced (for example, you can remember that the actor's name begins with the letter \"B\") to be restored. Long term memories need to be accessed to be \"refreshed\" or they will slowly fade away and become more difficult to access. This process also tends to change long-term memories over time. We don't remember the event, we remember the memory. It has been shown that people's long-term memories do change over time, and can be influenced by suggestion. ",
"An alternative could also be that you logically reject the suggestion without any involvement of the precise memory of the correct answer. For example, you ask \"What is the name of the actor in the Men in Black movie who costarred with Will Smith?\" and someone answers \"Justin Beiber\". You might simply recall that MIB was released in 1997, when JB was only about 3 years old and thus discount the suggestion as being inplausible. Or you might recall that Smith's co-star was a Texan, and know that JB is Canadian and hence not a match. "
] |
[
"Knowing something about one thing doesn't mean you know it about another.",
"I don't know who acted in the 1928s production of whatever, but I know it wasn't Keanu Reeves [or was it? He is immortal...].",
"So just because I can confirm one fact doesn't mean I know another."
] |
[
"One prominent theory of memory recall is that attractor networks are activated, are recurrent, and will ultimately fill in the missing blanks. The attractor network is a population of neurons. This population is self-activating in a loop. If you stimulate enough of the neurons, then all of them will get activated (and you will remember all of the memory). ",
"Anyway, following this theory, a clue to the memory triggers part of the appropriate attractor network. Of course, it is only a partial memory, so it also triggers a bunch of other, competing attractor networks. Someone makes a suggestion - and none of the competing attractor networks match the suggestion, so you know that is not the answer. ",
"One of my goals in life it to piece this puzzle together so I will know why a partially triggered memory can be remembers an hour or a day later, but cannot be figured out in real time. It pisses me off."
] |
[
"Our lungs are asymmetrical, and it appears that they have significantly different volume/surface-area ratios. Do they consequently absorb oxygen and transfer CO2 at different rates?"
] |
[
false
] | null |
[
"I used to be a respiratory therapist but that was more than thirty years ago and I did snooze through a few classes. Let's see what I remembrr.",
"Lungs are indeed asymmetrical. The right lung has three lobes, the left only two. The larger lung has more alveola (tiny balloon like sacs that share a membrane with the capillaries) than the left and therefore more surface area but, since the actual gas exchange happens at the level of the alveola it is likely a constant rate."
] |
[
"Exactly, gas exchange per unit volume of lung is equal, but total amounts are not. "
] |
[
"Exactly, gas exchange per unit volume of lung is equal, but total amounts are not. "
] |
[
"Is it possible to transmit wireless data at the frequency of visible light? In that case, we could see the data transmission."
] |
[
false
] | null |
[
"It's done all the time. We can see the pulse, but as humans in most cases, we can't read it. Some remote controls use visible light instead of infrared light too. Think of Morse Code flashing between ships. It being another form of visual communication with visible light. Remote controls just use a faster flashing and different dialect language.",
"Edit for more info: What makes microwaves so good for wifi routers is the very short wavelength and it passes through most things just like visible light passes through windows. The wavelength allows for faster bandwidth by many orders of magnitude than visible light. X-Ray and Gamma would be able to have higher bandwidth even still, except you know... radiation death."
] |
[
"Microwaves actually have much longer wavelengths than visible light (centimeters vs nanometers). They still go through walls better than visible light like you mentioned, but visible light would have a higher potential bandwidth."
] |
[
"There have been attempts to commercialize a WiFi-like technology based on light for a while. They rather creatively named it ",
"LiFi",
". ",
"Other terms worth chasing for more information are ",
"Visible light communication",
" and ",
"free-space optical communication",
".",
"There have also been some ",
"accidental visible-light systems.",
" There was a security bug with some ethernet routers in the 90s or early 2000s where you could actually read the network traffic by watching the Rx/Tx light blink. The router was actually \"blinking out\" the network signal by via the lights, even though it wasn't even wireless hardware. "
] |
[
"What do ants do when they are separated from the colony?"
] |
[
false
] |
I had an interesting experience with ants yesterday. They have been coming in through my kitchen window to feed on food in my kitchen. I closed the gap in the window that they were coming in through, but some ants were still inside the house. I found the behavior of these remaining ants interesting: They huddled into "groups," as if they were talking, and then they started to spread out, as if they were searching for a way back to the colony. I have two questions: What do ants usually do when they are separated from the colony (e.g., as above)? What were the ants who were trapped in my house probably doing? Thanks.
|
[
"I'm not a scientist, but I am an avid ant keeper. As a result, I've done a lot of ant research. ",
"Firstly, most ants navigate outside of their nests using two methods: pheromone trials, and counting their steps. ",
"Pheromone trails will be laid by ants when they find good, a danger, etc. They can follow these trails for quite some time, until the scent disperses. ",
"Ants, as mentioned, count their own steps. Scientists figured this out by giving ants stilts, and also, cutting their legs shorter. If they have the returning ants stilts, they would overshoot their nest. The reverse occurred for the poor cut ants. ",
"If ants lose the scent, and cant count their steps back, they will most usually begin to walk an ever-widening circle, in an attempt to find their nest or a pheromone trail. ",
"The ants in your house are likely grouping up because they realise they are unable to return to the nest by either usual method. The grouping is likely a natural response - they are attracted to others with the same smell. ",
"A few species of ants will allow outside ants of the same species to join their nests. However, most will kill outsiders. ",
"The ants in your house will eventually start to wander around looking for a new way to enter their nest. They will likely do this until death by misadventure."
] |
[
"that mean if the ant walk on a paper sheet and then you move it, she will be lost ?"
] |
[
"I've observed ants travelling about 100m crim their nests, so even during routine activity, they can move around quite a bit. ",
"I'd believe an ant will continue to travel in an ever-widening circle (it's an instinctual response) until it does of dehydration or other misadventure. ",
"So, if an ant was lucky enough to circle for, say, an entire day (not get smushed, eaten, etc) , it could probably find its colony even if it was\n2-300m.",
"The lost ant doesnt have to only find her nest - she will hopefully come across nestmates, or their pheromone trails. ",
"On that last point - ants will carry each other too! ",
"I've seen ants that appear to be lost meet a nestmate, and the nestmate will pick them up and carry them back!"
] |
[
"Why are high divers okay jumping into water from high up, but jumping off a bridge will kill you?"
] |
[
false
] | null |
[
"Technique is part of it but I think everyone is neglecting the fact that an Olympic high dive is around 33ft I believe. I'm not sure what the average bridge height is, but most people would picture a much higher drop when imagining a fall from a bridge. If you jump off a 33ft bridge youre going to most likely survive unless you land extremely awkwardly and drown."
] |
[
"All answers I've seen here are emphasizing technique. You have to hit the water right. And that certainly has a large effect. But there are two others that probably account for the large number of deaths (remember not everyone jumping off a bridge dies. I've seen \"It's a Wonderful Life)",
"1) Height is a big part. Olympic high diving is, I believe 11 meters. You wouldn't hit terminal velocity until you jump from about 167 meters. So the higher, the faster you are going up to that height. Most people wouldn't jump off of an 11 meter bridge to commit suicide. The Brooklyn bridge is about 135 meters above water.",
"2) Diving pools have water of a known depth, and it is still. Water under bridges has rocks, and pylons, and current. Even if you hit the water fine, you are likely to run into some solid object, or be swept away by current."
] |
[
"Bubblers obviously break the surface tension and reduce impact as a result.",
"Nope. The bubbles are simply to make the surface visible. The diver needs to know where it is so he can be in proper orientation when he/she hits it."
] |
[
"Since our moon revolves with the \"dark side\" always facing out, why did it form into a relatively perfect sphere?"
] |
[
false
] |
This is especially strange to me considering it was formed by collisions of multiple bodies. Since it isn't rotating on its own axis, wouldn't centrifugal forces stretch it?
|
[
"This was super helpful. We are all grateful that you were here to contribute. Your mastery of all things lunar has left us in awe. ",
"Your comprehension of etiquette, if any, is vague and fractional. You don't really know enough about being helpful to pose a decent answer, and you haven't done it. ",
"Tool. "
] |
[
"The moon ",
" spinning on its own axis. Due to tidal locking this spin is synronised with its orbital period.",
"The moon did not always show us the same face. It formed and then over millions of years it got totally locked."
] |
[
"Yes. Centrifugal force also stretches the earth. It's not obvious, but it is significant. The moon is further warped by the tidal forces from the earth. Earth is pulling more an the part closer and less on the part further, so it makes the moon somewhat football-shaped."
] |
[
"Why can't you donate blood after receiving eye surgery?"
] |
[
false
] | null |
[
"You may have received something like a corneal transplant and acquired a disease from that donated tissue. Rather than delving into the specifics of the operation they may simply disqualify you out of an abundance of caution."
] |
[
"Heck, they disqualify you if you've had gay sex anytime in your entire life, I get that question every time. I think that might be changing though."
] |
[
"They also disqualify all British people born before 1996 from ever donating in the USA, basically. ",
"EDIT: in Britain for more than 3 months between 1980-1996... sorry for oversimplifying"
] |
[
"How is the time component of spacetime expanding?"
] |
[
false
] |
Is it wrong to say that it's only space that's expanding, and not spacetime? Is it just that the two are so closely linked that the expansion of space on its own affects time, and therefore we say spacetime expands?
|
[
"Will do. Hopefully they won't notice me struggling to read it off my left palm as I explain it to them."
] |
[
"If anybody bugs you about it, just tell them that technically the scale factor only appears in the space components of the FLRW metric, but since the metric is an equation of ",
" it's fine to say \"spacetime.\"",
"That oughta shut 'em up."
] |
[
"There are currently no observations that can't be explained by assuming time ",
" undergo any kind of expansion, or other change in its geometry. More technically speaking, if you look at the FLRW metric equation that describes metric expansion, you see there's nothing funny going on in the time component. It's all in the space components. It's just - ",
" ",
" like you'd find in the metric equation in Minkowski space."
] |
[
"How, on a chemical level, does tempering chocolate work?"
] |
[
false
] |
I know tempering chocolate in the culinary world works by melting the chocolate, lowering the temperature and then raising it one last time to a very specific temperature, but what's going on chemically that makes the chocolate harden like that?
|
[
"I study material science and was once baffled by the similarity between chocolate tempering and steel tempering, here is what I remember from chocolate tempering:\nChocolate is made out of cacao powder, sugar and cacao butter. The cacao butter, when it solidifies, can adopt different structures with different organisations of its molecules. Those different structures are stable within different temperature domains recorded in a phase diagram much like for metals and alloys. If I remember correctly 3 of thoses structures ( also called phases) are of main interest: betaIV, betaV and betaVI. When you melt chocolate you \"destroy\" those crystalline structures and obtain a disorganised soup of molecules. By cooling it within a certain temperature range you encourage the development of certain solid phases over others: for chocolate the betaV is the one you want. Because the betaV structure is stable within a specific temperature range you want to adapt the cooling rate and maintain a specific temperature at which the chocolate will solidify. All of this is is mainly done for aspect and texture: a well tempered chocolate will look shiny, \"snap\" when you break it, and melt in your mouth without leaving lumps or granules: those are properties of the betaV structure. The betaIV structure looks dull and does not make the snaping noise when broken. Blooming is another issue from bad tempering, it results from the separation of sugar and cacao butter and forms white spots at the surface of the chocolate. \nI hope this could help, I am in no way a professional as far as chocolate is concerned so feel free to correct me if I am mistaken."
] |
[
"Seyler360 already explained it pretty well but I thought I'd add a source.",
"",
"https://acselementsofchocolate.typepad.com/elements_of_chocolate/TEMPERINGCHOCOLATE.html",
"",
"https://www.sciencefriday.com/educational-resources/chocolate-crystal-concoctions/",
"",
"Basically at certain temperature ranges, certain crystal structures can't maintain their geometry and change structures. The object of tempering is to make and 'Lock in' the favorable structures."
] |
[
"Thanks for the reply! I learned about metal tempering when I went to college for welding, but the thought never occurred to me that the same would apply to chocolate!"
] |
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