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[
"There are thousands of seemingly isolated bodies of water all throughout the planet which happen to have fish in them. How did they get there if truly isolated?"
] |
[
false
] | null |
[
"Massive floods",
", ",
"changes in river flows",
", ",
"freak weather events",
", ",
"historically very different climate",
" with larger or interconnected lakes."
] |
[
"Do birds have some role?"
] |
[
"There are some fish whose eggs can tolerate drying out. Killifish of the genus ",
"Nothobranchius,",
" for example, are a seasonal fish which live in temporary pools. The eggs survive in the mud when the pools dry. In captivity, killi breeders have to mimic that dry spell in order to get the eggs to successfully hatch. "
] |
[
"Does your vision's depth of field change with your pupils' level of dilation, as in photography?"
] |
[
false
] |
I've been wondering this since I got into photography. With a camera lens a wider aperture corresponds with a more narrow depth of field. Do human eyes have a narrower depth of field at night (for example) because the pupil enlarges to allow more light in?
|
[
"Physically, I'm sure it does. However, physiologically I think the eye is designed to focus on relatively small areas. Which means that while the light may be focused correctly, the rods and cones don't have the resolution to make use of that information. "
] |
[
"Perhaps, but if so, it wouldn't make much difference. At night (or low light conditions in general), there isn't enough light for the cones to function, and cones are responsible for most of our visual acuity (ability to see detail)."
] |
[
"Yes, they do. You can test this out on a sunny day: everything will be in focus (assuming your eyesight is sharp)."
] |
[
"Question about how Stem Cells work?"
] |
[
false
] |
[deleted]
|
[
"With a few caveats, every cell in your body has the genetic material required to recreate your entire body exactly. This is your DNA genome contained in \"all\" (the vast majority) of your cells. However as you develop, different chemical signals communicate to different groups of cells that they need to activate specific genetic programs. This is called differentiation and it is how a stem cell can become a skin cell (epithelial cell), heart cell (cardiomyocyte), brain cell (astrocyte, neuron, glial), liver cell ( hepatocyte), bone cell (ostocyte, chondrocyte), and every other cell type. ",
"Once a cell is signaled (and beings to send signals to its neighbors) it typically cannot become a stem cell again. We call this terminal differentiation. I should say that a very active (and heated) area of research is discovering how to convert various terminally differentiated cells back into stem cells. It has been done, but its only skeptically accepted by the scientific community. There is a lot we still have to learn to really understand what happens on a cellular or chemical level to these cells. ",
"True stem cells are what we call omnipotent, meaning that they can (under the right conditions) become every possible cell type. Much more common are the pluripotent stem cells, which still have the ability to become many cell types, but not ",
" cell type.",
"The general theory regarding stem cell therapy has to do with replacing damaged or dead tissue that cannot repair itself. The stem cells would sense the chemical signals from the surrounding tissue and react by differentiating into that tissue. It works but since we don't understand the process on a step by step level, we need to exercise caution in using it. ",
"The same goes for growing new body parts. The stem cells could be induced to activate the development process just as it did the first time that tissue or organ was made. Again the problem is that we don't fully understand the chemical and genetic processes on a step by step level. This makes it difficult to know what to do to guide or direct the stem cell growth and differentiation.",
"Essentially the medical side of stem cell therapy is to trust that they will know what to do, and do it correctly once they are in place. The research side of stem cells is to figure out how stem cells \"know\" or \"decide\" to do what they do, and then be able to manipulate their grown with much greater precision and specificity. ",
"Here are a few reviews on the subject I tried to find open access articles, but the abstracts are all available:",
"http://onlinelibrary.wiley.com/doi/10.1002/stem.1999/epdf",
"http://www.mdpi.com/1422-0067/17/6/982",
"http://link.springer.com/article/10.1007/s40778-016-0037-5",
"http://www.ncbi.nlm.nih.gov/pubmed/26941361",
"http://onlinelibrary.wiley.com/doi/10.1111/hepr.12747/abstract",
"http://www.sciencedirect.com/science/article/pii/S1357272514003100"
] |
[
"Stem cells do have the ability, albeit to a certain medical practice. Like CharlesOSmith said above, the stem cells would respond to the signals released by their neighboring cells, and they in turn \"fill in the gap\" and respond appropriately. But this is where it gets a little tricky...",
"If you wanted to use true, totipotent (can turn into ",
" and ",
") human embryonic stem cells, you run into problems like donor rejection, since you yourself do not have any left because you are born and out of the womb, and we'd have to harvest it from a 6-9 day old embryo which leads to moral issues. ",
"If we use Induced Pluripotent Stem cells, we run into things like tumors/cancer and low success rate of induction. This is performed by taking your adult cells and turning them back into an embryonic stem cell like state by turning on specific genes; however, one of the genes typically used is c-myc, a tumor gene. (Note: it doesn't ",
" to be used, but success rates are even lower without it.) Another thing to remember is that your body has accumulated a decent amount of mutations by now; the radiation from the sun constantly bombarding your skin, all the crap that's in the air, carcinogens, and more can all up the chance of mutations - and bad ones (most mutations are neutral and don't do anything). ",
"So where does that leave us? Well, it's completely possible and plausible, but funding for it has been rocky and unpredictable. \nAlso, there's the moral dilemma. But we are moving forward, and with ",
"3D printing of human organs",
", there's other options. ",
"But, there are things involving stem cells and their healing abilities that we do know: ",
"we know human embryonic stem cells can heal a mouse's injured heart",
" and we also know that ",
"the fetus can send stem cells to its mother during pregnancy, and it will target sites of injury and heal the injuries at an accelerated rate"
] |
[
"Stem cells do have the ability, albeit to a certain medical practice. Like CharlesOSmith said above, the stem cells would respond to the signals released by their neighboring cells, and they in turn \"fill in the gap\" and respond appropriately. But this is where it gets a little tricky...",
"If you wanted to use true, totipotent (can turn into ",
" and ",
") human embryonic stem cells, you run into problems like donor rejection, since you yourself do not have any left because you are born and out of the womb, and we'd have to harvest it from a 6-9 day old embryo which leads to moral issues. ",
"If we use Induced Pluripotent Stem cells, we run into things like tumors/cancer and low success rate of induction. This is performed by taking your adult cells and turning them back into an embryonic stem cell like state by turning on specific genes; however, one of the genes typically used is c-myc, a tumor gene. (Note: it doesn't ",
" to be used, but success rates are even lower without it.) Another thing to remember is that your body has accumulated a decent amount of mutations by now; the radiation from the sun constantly bombarding your skin, all the crap that's in the air, carcinogens, and more can all up the chance of mutations - and bad ones (most mutations are neutral and don't do anything). ",
"So where does that leave us? Well, it's completely possible and plausible, but funding for it has been rocky and unpredictable. \nAlso, there's the moral dilemma. But we are moving forward, and with ",
"3D printing of human organs",
", there's other options. ",
"But, there are things involving stem cells and their healing abilities that we do know: ",
"we know human embryonic stem cells can heal a mouse's injured heart",
" and we also know that ",
"the fetus can send stem cells to its mother during pregnancy, and it will target sites of injury and heal the injuries at an accelerated rate"
] |
[
"How does the brain know how much pain to feel?"
] |
[
false
] |
Example: Why does getting a limb chopped off hurt more than a paper cut?
|
[
"Pain is an experience that is heavily modulated, processed, and interpreted before getting to the part of your brain that goes \"Oww\". Some structures that are understood to be critical in this function are the ",
"periaqueductal gray",
" and the ",
"rostral ventromedial medulla",
"."
] |
[
"Do nerve receptors send a different strength of signal for differing amounts of pain? Or is there something else going on here?",
"Thinking about it now it may be the quantity of nerve endings in pain?"
] |
[
"If I remember anything from my physiology class, I believe there are different types receptor that are at different depths in the skin. The stronger the stimulus the deeper it would go therefore activating the deeper receptors. I would agree that more never endings that are stimulated would increase the pain response as well thats why being slapped on the back I believe feels more painful than a pinch. "
] |
[
"What is beyond the edge of our universe?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"This question is based on fundamentally flawed premises. Please conduct some background research and revise your question if you wish to resubmit.",
"As far as we know the universe has no edge. It is either infinite or closed onto itself.",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"So if it´s closed onto itself, what is the current theory as to what lies beyond it?"
] |
[
"If it is not infinite there is no need for something to be \"outside\". See ",
"this answer",
" from our FAQ. ",
"This one",
" could also be useful."
] |
[
"About to get a demo confocal microscope in our lab. Any suggestions for some fun/interesting things to do with it?"
] |
[
false
] |
[deleted]
|
[
"Do tissue Fluorescenct staining (avoid green channel due to auto-fluorescence) and do a Z stack on it. Many can do a 3D modeling after the Z-stack.",
"Also see how many antibodies you can do at once. (violet, Dapi, green, yellow, red, far red, far far red) without bleed through, but you might need conjugated antibodies for this."
] |
[
"If you're in a neuro lab, doing some cell fills and taking a z-stack of a well-filled cell to turn it into a 3-D image leads to spectacular images."
] |
[
"These guys",
" in my old honours lab do some pretty cool live cell imaging of endocytosis-related pathways. Watching a cell swallow something, and then have the endosome mature and change colour as it matures into a lysosome is pretty cool."
] |
[
"What do people mean when they say things like \"math is the language of the universe\"?"
] |
[
false
] |
[deleted]
|
[
"I'll try to convey to you why I think the statement is true. This is a very popular sentiment because of what is now called ",
"The Unreasonable Effectiveness of Mathematics in the Natural Sciences",
". It's an article published in the sixties but the sentiment goes farther back.",
"In summary: In our attempt to translate the world into mathematics, we establish some equations which seem to fit the world pretty well. Then we look at the equations closely and we notice that they accept some inputs that we hadn't thought of before and the result of the equations makes sense, but no one has thought of it before. Then it is experimentally established that the conclusion, which was based solely on mathematics, is correct. So by describing the world in mathematics, we also seem to be exploring the universe because what we're finding isn't just a description of one process or object or any one thing. It is ultimately, a generalization that holds true in many domains.",
"Perhaps an example would be appropriate, but the only one I can think of right now is fairly advanced, and truth be told not in my expertise at all. Maybe you have heard of the name ",
"Paul Dirac",
". He is synonymous with genius though he is not quite the superstar that is Einstein when it comes to fame and glory. He postulated the existence of anti-matter, an absolutely groundbreaking development in 20th century physics. He did it while he was trying to come up with an equation that would describe the behavior of electrons in an atom. So he came up with his equation, and he noticed that if the equation were to be true, there must be this other kind of object called anti-electron (another solution to the equation), that behaves exactly the same way, but when it comes into contact with an electron, the two annihilate. To that day there had never been any reason to believe there is this form of matter. There was no experimental evidence for the existence of stuff we haven't seen yet, but the equation said otherwise, and some time later when particle accelerators could be built, the existence of anti-matter was proven experimentally.",
"Sometimes this is referred to as beauty because it captures vast swathes of the universe on paper and in a format that makes it understandable to mere mortals.",
" — Albert Einstein",
"i.e. it seems to follow very general rules and a relatively small number of them and all of these rules are mathematical in nature. By relatively small I mean that there isn't a rule that says how an apple should fall from a tree as opposed to how a human falls from an airplane. It's the same rule.",
"I apologize if I started to ramble. This is a highly personal sentiment and so it lends itself to disconnected thoughts, but I would love to elaborate. In terms of recommended reading, it's not reading, but I highly recommend watching the ",
"Feynman lectures",
" at Cornell University. Feynman is always listed as a favorite because he could convey the kinds of things I have been trying to in the last 4 paragraphs with ease and passion."
] |
[
"Mathematics is the language by which we make qualitative statements like \"gravity pulls things together\" into quantitative statements like \"F = ma = G(mM)/r",
"By using quantitative statements, which relate physically measurable quantities to one another, we can develop theories and make predictions from them. These theories are often expressible in qualitative ways, but if you want to actually determine the real, physical result of some process, you have to use the quantitative, mathematical formalism."
] |
[
"anti-electron (another solution to the equation)",
"I'm sure this is an offensively simplified version of what happened, but did Dirac's equation have something like a square root which resulted in \"+/- n\" which led to the theory of antimatter? ",
"Because that's fucking cool beyond belief."
] |
[
"Why does a hair sometimes suddenly sprout in places where there is no hair?"
] |
[
false
] |
I had a single hair grow underneath my collarbone, and the surrounding area is completely hairless. This hair was also really strange: it was completely white, significantly thinner, and very long compared to the rest of my body hair. This has happened before on my foot (the top of my foot), although it wasn't quite as long, and after I pulled it out (more than a year ago), no hair has ever grown back there. I'm not really familiar with how hair follicles work, so if someone could explain that, it would be greatly appreciated!
|
[
"A hair follicle has multiple kinds of cell involved. There are cells that product the keratin follicle itself, cells that give the hairs its pigment, cells that sweat and secrete oils for the hair, and cells that pull the hair up. \nAll hair follicle units are developed more-or-less at birth. Their turning on-and-off are what gives rise to puberty's hair growth and normal baldness. \nWhat you have is probably ectopic and spontaneous hair growth - it's a lot like a mole that has overly active pigment cells (melanocytes). These things happen a lot with skin because skin is very proliferative (you turn over an entire layer every 28 days) and is subject to rare changes that activates these out-of-place functions.\nIt's likely that some of your proliferative cells in your skin turned into hair-producing cells, divided a bit into a large enough mass, and then started producing keratin. Because these cells randomly became this way all of a sudden, the accompanying pigment cells aren't there. Therefore, the hair follicle you have is white."
] |
[
"C'mon people! Only 16 down votes? You can do better than that!!"
] |
[
"You can't explain that."
] |
[
"What percentage of our own galaxy have astronomers cataloged? How are names for stars selected?"
] |
[
false
] | null |
[
"Names for stars are generally given by their constellation and then a greek letter corresponding to how bright they are in that constellation (so Alpha Centauri is the brightest in Centaurus). Stars that aren't part of a constellation are generally given names corresponding to the order in which they were catalogued in some sort of survey (so Gliese 581 is the 581st star in the Gliese star catalogue)."
] |
[
"The USNO B catalog (the largest to date) contains about 1 billion stars and galaxies. There are roughly 300 billion stars in our galaxy, so we've cataloged about 0.3%. You can see about 6000 stars with your naked eye from a dark site with no moon. The vast distances, extinction from interstellar dust, and the fact that the vast majority of stars are smaller and dimmer than the Sun explains why we've cataloged so few. ",
"The stars are typically named numerically, either by their coordinates or with just a counter (though the details depends on the survey that catalogs them). Each survey assigns their own name to the same stars, so they have many names. For example, there are 16 names for this one (the first transiting hot jupiter host):\n",
"http://simbad.u-strasbg.fr/simbad/sim-id?Ident=hd+209458&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id"
] |
[
"Most names are selected as their \"brightness\" in the constellation. IE \"Alpha Orionis\" would be Betelgeuse. However, it should be noted that the star of the highest magnitude in Orion, today, is Rigel. ",
"Most stars have names that catalog their brightness in a certain constellation. That makes them easy to find. For example, \"alpha canis majoris\" would be Sirius, the brightest star in Canis Major. Easy!",
"A lot of stars have proprietary names, like Betelgeuse and Antares. These are relics of the past. Betelgeuse was named from Arabic Northern Africa (as are a lot of stars). Antares is \"opposite\" (ant-) the sky from Ares (Mars). This is, of course, relative.",
"On star charts stars can, more often than not, be identified by their \"brightness\" within a constellation, e.g. Alpha Orionis, Gamma Scorpius, etc.",
"EDIT: I use \"brightness\" in quotation marks because it tells us nothing of the star. Stars are measured in ",
", not brightness. Luminosity is a function of surface area and energy output. \"Brightness\" is a judgement."
] |
[
"Can a virus mutate to be less deadly?"
] |
[
false
] |
[deleted]
|
[
"Sure. A virus’ “goal” is to survive and multiply, not kill. That could mean that it becomes less deadly, so people take it less seriously and spread it more easily. If the virus is too deadly, the host could die before passing the virus on. This is why ebola is not a huge widespread problem compared to COVID-19–it kills too quickly and isn’t very infectious, so it tends not to really spread."
] |
[
"Virulence factors are genes that give pathogens their pathogenic properties. These include genes that allow for attachment or invasion of cells, or productions of toxins.",
"Pathogens can mutate to be less virulent, as mutations can be deleterious to an organism. Mutations are random, and the effects of mutations can be beneficial, neutral, or deadly. Selection acts on these mutations in various ways. changing their frequency in the population. And thus, random mutation may decrease effectiveness or completely disable virulence factors.",
"However, for pathogens, being less virulent and pathogenic often can be a detriment to the pathogen because it will be out-competed by the more pathogenic organisms of its strain. Thus, its frequency in the population would decrease.",
"However, it is possible for a pathogen to become less deadly. For example, a pathogenic bacteria could mutate to become symbiotic with its host, and have a mutualistic relationship. A hypothetical example of this could be the bacteria within our guts. Additionally, a virus could become a transposon, degrading over time, and ",
"here is an example of a transposon that is hypothesized to be beneficial.",
"Pathogens that are most deadly are often not a good survival strategy. A pathogen such as the common flu can be spread among many people because people with the flu often still go about their daily business, shedding more viral particles and exposing more people to these particles than they would if they were bedridden."
] |
[
"Pathogens that are most deadly are often not a good survival strategy. A pathogen such as the common flu can be spread among many people because people with the flu often still go about their daily business, shedding more viral particles and exposing more people to these particles than they would if they were bedridden.",
"This selection pressure was inverted during WWI. Soldiers with mild strains of the flu stayed in the trenches, while the deadlier strains got loaded into an ambulance and driven hundreds of miles away from the front.",
"And 9 months later we got the Spanish Flu."
] |
[
"Will it ever be possible to measure the true size of an electron?"
] |
[
false
] | null |
[
"The electron is governed by quantum mechanics, for which we need toss the concept of \"size\" in the definition we know it traditionally. ",
"Consider the following scenario: Before you've made a measurement on the position of the electron, it's in a superposition of various position states. Making a measurement necessarily knocks out a whole bunch of these states (e.g. we knew it could have been anywhere in the room until we made our measurement, and when we made our measurement we became sure that it was in a small corner of the room), narrowing where we know the particle was when we made the measurement. More precise measuring apparatuses will eliminate more and more of those states in a given measurement until, in the limit of perfect empirical resolution, you resolve the electron to be at a single point in space, and its description becomes that of a Dirac-Delta: zero at all points except exactly where you've measured it. The Dirac Delta is an infinitely high spike and is infinitely narrow, so, to the truest meaning of what we know classically (we've pinpointed the electron to a position, now we measure its size) the electron has a volume of zero!",
"All subatomic particles, in that sense, have no size. ",
"We could also ",
" size to be the full-width at half maximum of scattering experiments, the same way we do with atomic nuclei, but scattering off an electron to determine properties like its dimensions is impractical: what smaller particle are you going to scatter off an electron to determine these properties? ",
" No, because the question isn't appropriate."
] |
[
"Quantum Mech is not an easy subject. If you get confused by it, well, so does everyone. Atomic and subatomic world is probabilist. Things aren't in a certain place, they can be somewhere and somewhere else at once. So how can you know something about it? You know where it most probably is, where it is ",
", and that is related to the particle ",
". You can calculate where a particle is most likely to hang around. The thing is, before you measure it, it's in neither place, its position is undefined and the probability is actually the most accurate way of describing its state. It's a silly thing, but it's how the quantum world behaves."
] |
[
"Could be worth mentioning that this is true for elementary particles only. For composite particles, such as a proton, it gets more complicated because of the interactions between the quarks and gluons it is made of. Thus it does not behave as a Dirac-Delta function in high energy experiments. "
] |
[
"Are there any experiments I can do myself to prove Einstein's STR?"
] |
[
false
] | null |
[
"That's a good idea, but now I have to prove to him that the decay rate of muons isn't what it seems and that it should be shorter.",
"See what I'm getting at? \nCan STR be shown and explained plainly so anyone can understand, or is a certain leap of faith required until people's brains become accustomed to a different kind of universe? "
] |
[
"That's a good idea, but now I have to prove to him that the decay rate of muons isn't what it seems and that it should be shorter.",
"See what I'm getting at? \nCan STR be shown and explained plainly so anyone can understand, or is a certain leap of faith required until people's brains become accustomed to a different kind of universe? "
] |
[
"That's the problem. My grandfather's life revolved around the Bernoulli equation, he designed water pumps all his life and had a tenure at a construction engineering college here in Croatia and he is convinced that he knows everything there is to know about energy. And from a classical standpoint maybe he does, but no way in hell can he be convinced that the speed of light is the same for every observer no matter the speed of the source because that breaks the law of conservation of energy. ",
"So I guess I came to the real question that I want to ask, is there a way to show that the the second postulate is true? How can we observe that the speed of light is the same in every reference frame?"
] |
[
"If blood cells don't have DNA, how do the police use blood for genetic testing?"
] |
[
false
] | null |
[
"Mature red blood cells don't have a nucleus (thus no DNA), but white blood cells do."
] |
[
"If I recall correctly, red blood cells don't have nucleuses in order to carry more oxygen. Blood cells themselves don't reproduce. They are produced from bone marrow. "
] |
[
"And you don't need very much DNA for genetic testing so the small proportion of white blood cells is enough. "
] |
[
"Just found out I have to drink Barium for a CT on friday. Is Barium actually safe to drink?"
] |
[
false
] | null |
[
"Barium is not radioactive. It is used because it is opaque to x-rays and isn't poisonous like Lead. Please speak with your doctor about associated risks and any other questions you have. They really are the best resource for this as we can't give you advice about your medical situation. They will be able to tell you if you need someone to drive you to and from the appointment, etc."
] |
[
"Yeah, I realize nobody can give medical advise online, and I wouldn't really take it. I'm not looking for medical advice.. just facts about the liquid barium, trying to understand what the possible risks and what to do afterwards. My doctor won't be there, it's a radiologist and I'm not admitted to a hospital, my doctor also hasn't been the most thorough at explaining things or looking into things, it's been like pulling teeth at times. So, I'm just looking for more information to hopefully put my mind at ease a little bit."
] |
[
"We really can't give you that information. Do a web search on it, there's patient information readily available. Search WebMD or The Mayo Clinic's site. "
] |
[
"Is required delta-v to reach mars polar and equatorial landing sites different?"
] |
[
false
] |
My intuition tells me it harder to land on pole vs equator. But hence I can't find definitive confirmation (also, I don't have skills to make calculations...), maybe I'm wrong on this. Or maybe the difference is totally insignificant. So: I am trying to understand if, lets say, 1000 kg of cargo needs exactly the same amount of fuel to safely land on poles vs equator. And if not, whether the difference is more like 0,5% (rather insignificant) or closer to 5% (significant).
|
[
"Not significantly, no.",
"In terms of the orbital insertion, hitting Mars in the first place takes enormous precision, and changing the target from the equator to the pole is a rounding error in fuel usage. Mars and Earth both orbit the Sun in ",
" the same plane, but there are small variances, so it's a toss up as to which option will take (a tiny amount) less fuel. Either way, mid-course corrections are needed to get the orbital insertion path to an acceptable tolerance.",
"In terms of the landing itself, if you were doing a fully powered descent (like with Moon landers), you could get some fuel savings by landing at the equator (as long as your initial orbit was in the same direction as Mars' rotation), just like how we get an initial boost by launching from the Earth's equator. In practice, Mars has an atmosphere, so any efficient lander will shed, the vast, vast majority of its orbital speed by aerobraking, rather than by spending fuel. So, again, this is going to wind up as a rounding error in terms of fuel savings."
] |
[
"As the other person said, we aren't going to save in heat shield by using a more efficient aerobreaking anyway.",
"For reference, if you aim at the pole, you will have to kill 200-300 meters per second more. That's very insignificant compared to 10+ kilometers per second that you need to kill anyway. It's 2-3%, but it won't translate directly into fuel anyway."
] |
[
"However, if we could calculate the thickness of heat shield our vehicle was going to need, with the same kind of accuracy as we can budget our propellant, then we could save a few kilos by landing with the planet's rotation. I have no clue if we can do this today, but my guess is no."
] |
[
"What would happen to my body if I were somehow physically prevented from urination/defecating?"
] |
[
false
] | null |
[
"In that case, I'll cover the defecation side!",
"Essentially, what we're looking at is bowel obstruction. We can categorise it by the cause (mechanical obstruction, non-mechanical obstruction), or by the location (small bowel, large bowel, or outlet). ",
"One way to think about it is that the bowel is a hollow tube which receives food from one side and transports it out the other. Kinda like piping. In fact, the entire gastrointestinal system can be seen this way, but we'll focus on the bowels.",
"Mechanical obstruction occurs when the 'tube' is 'kinked' or there's something within the lumen, walls, or pressing from outside of the 'tube', which obstructs passage. If you have a blocked up tube receiving material from one side and unable to pass it out, there's going to be an increase in pressure inside that tube. ",
"Going back to our tube analogy, the level of the obstruction will determine the onset of symptoms, as there's more of the tube to 'fill up' before the pressure starts to increase. Anatomy-wise, our small intestine is higher up and has a much smaller lumen compared to our large intestine. This means that obstructive symptoms tend to develop earlier.",
"Now we can start going into symptoms. With the increase in pressure we get bowel distention, which is experienced as pain and bloating. This pain is \"colicky\", coming and going with the waves of peristalsis (our squeezing/propulsion mechanism). The increased pressure on the intestinal wall will also start to impair its blood supply, leading to ischaemia/necrosis. The damage to the integrity of the intestinal wall allows bacteria to get across into the bloodstream, causing sepsis, and can lead to bowel perforation - where the intestinal contents are released into the abdominal cavity (causing peritonitis and high mortality).",
"As the material within the bowels continues to build up, we also start to get backflow. In small bowel obstruction, intestinal contents are released back into the stomach and vomited out. As the intestinal contents are stationary for an extended duration, bacteria will have a field-day and begin converting the food into faecal matter. This can lead to complications such as aspiration of the vomitus, causing very nasty pneumonia. This isn't such a common symptom for large bowel obstruction. ",
"In complete obstructions, there will also be constipation - as nothing will be getting through.",
"So in a scenario where you are \"physically\" prevented from defecating, presumably by someone bunging you up (hehh), and you continued to eat a normal diet, your colon would fill up, become distended and eventually perforate, spraying faecal matter around your abdominal cavity and causing sepsis and peritonitis. ",
"This is why in cases of bowel obstruction, patients are often given clear fluids or TPN (total parental nutrition), so they can obtain some nutrition/hydration without exacerbating the condition. That and surgically correcting the cause of obstruction.",
"TL;DR - Don't bung it up! "
] |
[
"I will cover the urination side of this question. ",
"There are two main categories of urinary obstruction. There is acute urinary retention (all of the sudden not being able to pee) and there is chronic obstruction (narrowing making it harder to pee for a long time). ",
"In the presence of acute urinary retention (such as with someone with an enlarged prostate that has cut off the flow of urine), you will see an acute swelling of the bladder such that it can be easily felt through the skin on a non-obese person. Eventually, this can result in a back-up of urine higher in the kidneys. This can be seen on imaging such as ultrasound or CT scan and is called hydronephrosis. A kidney in this setting can lose some of its ability to properly filter solutes such as sodium. This can lead to disturbances in the solutes in the body. The kidney can also become compressed by the fluid in its central portion.",
"Chronic obstruction (such as with benign prostatic hyperplasia or a urethral stricture) can result in a deformed bladder which has many folds. This occurs due to the bladder having to push against a higher resistance for long periods of times and is adaptive similar to how a heart changes when it pushes against a deformed valve. This can result in problems in the one-way valves that urine passes through to the bladder. Again we can see dilation of the kidney and the tube that carries urine from the kidney to the bladder (ureter). Kidney problems can again occur. ",
"Interestingly, a fetus can have urinary obstruction as well. The amniotic fluid that surrounds a fetus is formed from the fetus's urine. Without urine, this fluid is not present as much as you would want it to be (called oligo- or anhydramnios). Amniotic fluid helps with lung development, so babies with this problem can have poorly functioning lungs. Also it is a buffer against the uterus, so babies can have deformed faces. The back-up of urine can also permanently damage their kidneys. One such disease that leads to this is posterior urethral valves. ",
"Also interesting, is that severe constipation can lead to urinary obstruction."
] |
[
"The sodium would be an issue. But the potassium would be the real problem....",
"You wouldn't excrete potassium, it would go up and it would cause arrhythmia's and death"
] |
[
"Is there any evidence that ancient humans might have danced or sang to impress a mate?"
] |
[
false
] | null |
[
"What do you mean by ancient humans? We know modern humans do this. Dance and (less frequently) song are used in courtship rituals across virtually all cultures, throughout history; and therefore certainly humans have been doing so at least since the start of recorded history, and we have no reason to believe it's a recent phenomenon. I am able to find ",
"some papers",
" (which themselves have underlying sources) that directly conclude that courtship ritual is a primary, or even ",
" primary source of dancing, predating recorded history by a wide margin."
] |
[
"Maybe the user is referring to the Homo genus or even Hominidae when we were (closer to) animals and less self-reflecting in our decisions and actions."
] |
[
"Don’t even some birds dance for a mate?"
] |
[
"Can equations that model motion (eg. F=ma) be derived from first principle, ground-up?"
] |
[
false
] | null |
[
"It depends on what you take to be your \"first principles\". If you take F = ma to be a first principle, then there's not need to derive F = ma. If you take the principle of stationary action to be a first principle, then you can \"derive\" F = ma from that."
] |
[
"Sorry, it’s hard for me to explain what I mean. I mean to say that, F = ma isn’t true per se. Wouldn’t you say that the most accurate form of F=ma for, say, a person pushing on a block, would be a direct solution for all the interactions between each individual molecule/atom? If you get what I mean"
] |
[
"F = ma applies for classical, nonrelativistic systems. You can modify it to include relativistic effects, but to treat quantum systems, you have to fundamentally change the way you do things."
] |
[
"Why isn't the steam released from nuclear reactors radioactive?"
] |
[
false
] |
So unless my understanding on how the reactors work is wrong, don't they use the radioactive material to create steam to turn the turbines? Wouldn't this cause some radioactive material to be released with the steam?
|
[
"Massive oversimplification, but:",
"A.The fuel is clad in tubes, so there isn't any direct contact between the fuel and the cooling water. ",
"B. the cooling water isn't directly turned into steam. It is kept under pressure to prevent it from boiling.",
"C. The superheated cooling water is pumped through a heat exchanger. The water in the heat exchanger then boils, and that is where the steam in generated."
] |
[
"Now to complicate things a little.",
"You described a PWR but some of the US plants are BWR where your point \"B\" is not applicable. The fuel heats the water at a lower pressure (still ~1000psi) which directly becomes steam and then runs a turbine.",
"Additionally, sometimes fuel leaks (and steam generators leak) and radioactive gases get into the water. ",
"Additionally additionally, sometimes there are particulates in the water like rust that can become irradiated from neutrons. ",
"However, all that being said, the steam is never radioactive but sometimes radioactive particles/gases can get into the steam. ",
"Lastly, the steam is typically in a close loop but seals leak (because they are man made) and sometimes certain mechanical failures can require steam to be released into the atmosphere (after it's been scrubbed and filtered).",
"All, in all it's a pretty minor amount and federal law 10 CFR 100 (i think) dictates how much radiation can leave the plant (the answer is very little).",
"Happy to expand/clarify if necessary."
] |
[
"In a boiling water reactor, where the steam we send to the turbine comes from the reactor, it is radioactive. There are trace amounts of fission products and other activation products, but the majority (95%) of the radiation in the steam is from nitrogen-16, which has a half life of 7 ish seconds. ",
"N-16 makes the drywell hazardously radioactive, makes the turbine heater bay/steam bay have dose rates up to 2 rem/hour (that's equal to the yearly international radiation limit in 1 year for a rad worker, in 1 hour) and is the reason BWR heater bays and turbine decks have massive shield walls when we are online. ",
"When we shut down, after a couple minutes the dose rates are down to 1-2 mRem/hr in the heater bay. ",
"For pwr plants, there typically is some tritium in the steam and extremely minute amounts of other fission or corrosion products that may have leaked out of the reactor coolant system. It's virtually negligible in the grand scheme of radiation emitters. ",
"Remember as others have said, the radioactive fuel is held inside fuel rod cladding. But the radioactive material can diffuse or leak in very small amounts, and sometimes fuel cladding fails releasing larger amounts of radioactive material. ",
"I work in the nuclear power industry. Please feel free to ask questions. "
] |
[
"My mom always says \"if women ran the world there would be no wars\". From Cleopatra to Thatcher, how many female leaders have started wars and how does it compare to male leaders (in percent)?"
] |
[
false
] | null |
[
"This is a very broad question. Percentage of male leaders, across the world and over the course of 2000 years that have started wars vs women who have started wars? Would anyone be able to calculate that, even just focusing on major powers and not the thousands of piddling principalities that have existed in that time frame in Europe alone? Plus any comparison using real numbers wouldn't be very useful as for most of human history only a few extraordinary women have been able to wield any real, direct power in most cultures.",
"If you want to argue with your mother just read up on the few famous female leaders in history. Catherine the Great, Isabella of Spain, Elizabeth I of England, Indira Gandhi, Dowager Empress Cixi of the Qing dynasty.... Joan of Arc wasn't a ruler (for the most part wasn't even really a military leader from what I understand), but I guess you could argue she helped incite the French to fight against the English? Boudica would be a good one. Although based on my very limited knowledge most of the famous female leaders have fought defensive wars against foreign aggressors, Boudica and Joan included.",
"Going off on a bit of a tangent, but a problem you'll run into when learning about historical powerful women is they're never really portrayed in a positive light (with a very small number of exceptions, like Elizabeth I, Boudica). I'm pretty certain every great man has done awful things, but women who have either wielded power or have been the power behind the scenes are more often than not portrayed as awful, conniving and power-hungry while men who do the same things or worse to attain their goals are seen as great heroes. Look at Augustus and his wife Livia. They were both hungry for power, both worked to consolidate their power over the Roman state. But Augustus is portrayed as the benevolent father figure who founded the Roman Empire while Livia is portrayed as his scheming bitch wife who just wanted power for herself.",
"TLDR while your mom is almost certainly wrong there aren't enough unbiased sources from before the 20th century to properly answer your question and give you ammunition to use against her. "
] |
[
"Additionally, we need to consider the fact that women rose to power in the classical and middle ages almost entirely in periods of time of incredible instability and conflict; otherwise a male heir would be more likely. From this, many of the female leaders are cast into war almost upon taking the throne. ",
"Examples off of the top of my head:",
"Part of this, of course, stems from the fact that states (or proto-states and kingdoms) often need to employ force a lot, as force is the basis factual of legitimacy for any government. Still, I have much more trouble naming a single female leader from pre-1600 that didn't go to war at some point. "
] |
[
"..but a problem you'll run into when learning about historical powerful women is they're never really portrayed in a positive light..",
"Can you give scientific evidence that powerful women are \"portrayed in a negative light\" more than their male counterparts? ",
"I haven't read about a single powerful leader (man or woman) who was portrayed in completely positive or completely negative light. There clearly is a spectrum there. Has there been scientific research (and not feminist research) into this that allows you to make this statement?"
] |
[
"I just received a telescope and discovered that it is not sighted correctly. How do I fix this?"
] |
[
false
] | null |
[
"Try ",
"r/astronomy",
". They are usually very helpful with this sort of question. "
] |
[
"You need to be more specific. Read up on telescope collimation."
] |
[
"Some more information would be helpful, but I assuming that what you mean is that when you look through the finderscope that is not what you see when you look through the optical tube eyepiece.\nIf that is so, you will need to adjust the finderscope. Focus the optical tube on some faraway object during the day. Then look through the finderscope. There should be a way of adjusting it to move the crosshairs so they are lined up on the same object you have sighted the optical tube on- there are often adjustment screws that move it horizontally or vertically for example."
] |
[
"How can Rabies still exist and be as prevalent as it is, if it's lethality is 99.99% and it's disease cycle is relatively short?"
] |
[
false
] | null |
[
"Because rabies can infect a lot of different animal hosts, many of which can live a long time or indefinitely after being infected. These are known as reservoir hosts because they provide a stable source for infections of more susceptible hosts. Reservoir hosts for rabies generally include Carnivoran mammals (raccoons, skunks, canines) and bats.",
"Human-to-human transmission of rabies is incredibly rare. Almost all infections come from animals, either directly from a reservoir host or from another animal that was recently infected by a reservoir host."
] |
[
"Most human to human cases of rabies over the past decade or so have been a result of organ/tissue transplants!",
"https://pubmed.ncbi.nlm.nih.gov/20205588/",
"https://pubmed.ncbi.nlm.nih.gov/28411355/",
"https://pubmed.ncbi.nlm.nih.gov/27331337/",
"Dogs are also the most common vector species in human infections."
] |
[
"Besides what others have said the cycle in humans is only short once symptoms appear. You can be infected for months before you become ill. Once symptoms show you have maybe a week to live, a little longer if you're lucky. Depending on how you define \"lucky\" since your existence will be torture."
] |
[
"\"Try to drink your juice or smoothie straight away. After 15 minutes, light and air will destroy much of the nutrients. \" What is happening here?"
] |
[
false
] | null |
[
"Any antioxidants will quickly degrade if they react with oxygen in the atmosphere -- it's their job to sweep up excess oxygen ions to prevent them from oxidizing other molecules. Vitamin A, vitamin C, and melatonin are some major antioxidants that come to mind."
] |
[
"Isn't the oxygen introduced when it's blended? Why would ingesting it make a difference? The process would continue regardless I would think "
] |
[
"There is only a limited amount in the blender and only a short period of exposure. Also, atmospheric oxygen is O2 so it's not as quick to react, but it will eventually. If you leave it sitting out then there is more time for oxygen to work its way through the mixture. I don't know exactly how long it takes to happen.",
"You ",
" the process to continue after you ingest it, that's the whole point of antioxidants."
] |
[
"Magnetic Spin of Electron, +1/2 or -1/2, does one state have a lower energy?"
] |
[
false
] |
Let's say a subshell is half-filled, will the electrons have a magnetic spin number +1/2? Or can they all have -1/2? Do atoms have a preference of + or - here? Is the +1/2 or -1/2 purely a conventional thing? Or is there an empirical way to look at a single electron and say, that's UP! Thanks Edit: Thank you all for taking the time to answer my question, it has answered clearly AND I learned something! Upvotes for all!
|
[
"There is also a slight difference in energy of spin up and spin down states of electrons in atoms compared to the spin of the nucleus. Since the nucleus produces a weak magnetic field of its own, the electron spin direction that is anti-aligned with the nuclear spin will be slightly lower energy.",
"This is the origin of the ",
"21 cm radio emission line",
" of hydrogen, which is extremely useful for astronomical observations."
] |
[
"There is also a slight difference in energy of spin up and spin down states of electrons in atoms compared to the spin of the nucleus. Since the nucleus produces a weak magnetic field of its own, the electron spin direction that is anti-aligned with the nuclear spin will be slightly lower energy.",
"This is the origin of the ",
"21 cm radio emission line",
" of hydrogen, which is extremely useful for astronomical observations."
] |
[
"This effect also comes into play in couplings observed via nuclear magnetic resonance. "
] |
[
"How does muscle atrophy occur among bed-ridden adults but new born babies that keep lying down for most of the day build muscles good enough to help them stand up?"
] |
[
false
] | null |
[
"I seem to recall a study, done many years ago, in which some college athlete volunteers (all presumably in good physical condition), were paired with infants and asked only to \"mirror\" the babies' actions. At the end of the day, the athletes were totally exhausted."
] |
[
"I seem to recall a study, done many years ago, in which some college athlete volunteers (all presumably in good physical condition), were paired with infants and asked only to \"mirror\" the babies' actions. At the end of the day, the athletes were totally exhausted."
] |
[
"There's a similar thing floating around Facebook now where a dad mimics his daughter's movements. It would kill me to keep up with even a tiny infant!"
] |
[
"Why does squinting improve my eyesight?"
] |
[
false
] | null |
[
"It has more to do with excluding the high-angle light rays from coming into your eye. Those are the ones that are the most out-of-focus. Cutting down the iris towards a pinhole with your eyelids will cause things to be more in focus. "
] |
[
"I don't see how this can be correct. For a squint to affect the view of objects in the distance in this way, the eyelids would have to at least partially cover the pupil. Mild squinting doesn't do this, as one can confirm by looking in a mirror and squinting a bit. ",
"I believe that the stress you are putting on your eye when you squint is changing the shape of the lens in your eye (affecting the focus) and the roundness of your eye (affecting the astigmatism). If you go into \"extreme squint mode\" then the mechanism that Staus described may also come into play. ",
"When someone has had lens replacement surgery (cataract surgery) and the natural lens is removed, the new artificial lens is not connected to the muscles and mild squinting is no longer as effective at improving myopia. "
] |
[
"While we're on the topic, does it actually negatively affect your vision?"
] |
[
"Why is it that if I squeeze an \"empty\" plastic bottle with water droplets covering its inner surface, that the water droplets do not change?"
] |
[
false
] |
[deleted]
|
[
"You could do that if you had a good way to force the air to do it. The trouble is that as you squeeze the bottle and put a pressure on the system, the air reacts and tries to exert this pressure back- but it does so from all directions equally. If you could force the air to put all the pressure on a droplet on one side only, then the droplet would definitely roll away, or at the very least deform to best counteract the distribution of pressure on its surface. But what you see in the bottle is already the best configuration- by adopting that hemispherical shape (with minor adjustments for the base), the water has adapted to the distribution of pressure that the air was already exerting. When you squeeze the bottle, you only change the magnitude of the pressure, and not its distribution across the surface of the droplet.",
"That's also why a nitrogen gun/air gun is so effective at removing water/liquids from my lab surfaces. The gas from the gun is in a nice jet, so the target liquid fouling up my sample has very little choice but to roll away or be carried away altogether. I couldn't do that just be putting the sample in a giant pressurized chamber- it would just sit there until it evaporated."
] |
[
"In many cases, when you squeeze the bottle, what you're squeezing most is the air in the bottle, which is a reasonably compressible fluid. Water is generally considered an incompressible fluid, so when you put the two together, your compressible air is going to compress instead of the droplets, which aren't going to do anything.",
"Of course, if you go and squeeze the bottle right on the droplets, then you will end up deforming them, but it won't be the squeezing so much as the fact that you physically stuck something else into the droplet, or you changed appreciably the bit of plastic it was sitting on."
] |
[
"Pretty much. The air exerts a pressure on the surface of every droplet, but the droplets are really quite resistant to compression.",
"http://en.wikipedia.org/wiki/Properties_of_water#Compressibility",
" starts getting into exactly how poorly this fight will go for the air in the bottle. That section mentions that in the deep oceans, you can observe 1.8% compression of water, but as you would expect from the deep ocean the pressure is substantial. If you don't have a reference for 40 megapascals, it's equal to 394.8 atmospheres worth of pressure, or 5802 pounds of force per square inch, which despite being an imperial unit may still be more meaningful. Chances are very good that your plastic bottle will be torn open before you manage to put that much pressure on the trapped air, and even if you put that much on it, all you'll get back out is a 1.8% volume compression. Even with all that, you'd be hard pressed to see it. Really, the odds are just completely stacked against the air."
] |
[
"Are calories calculated the same for animals as they are in humans?"
] |
[
false
] |
[deleted]
|
[
"Calories are measured by burning a food in something like a liter of water and seeing what the temperature rise of the water is. Caloric qualities of a food are independent of who or what is going to it eat it. "
] |
[
"Calories are measured by burning a food in something like a liter of water and seeing what the temperature rise of the water is. Caloric qualities of a food are independent of who or what is going to it eat it. "
] |
[
"Calories are a unit of energy. One thermodynamic calorie is the amount of energy that heats one gram of water by 1° C: 4.1868 joules. The calories that you see on nutrition labels are actually kilocalories (4,186.8 joules), labeled \"Calories\" for historical reasons.",
"An easy-to-measure upper bound on the amount of energy that's available from a food item or substance is the amount of energy obtained by burning it in air (",
"https://www.youtube.com/watch?v=UDgeaAMdYIY",
"). That upper bound is independent of what species you're considering.",
"The amount of energy actually obtained by organisms is less than the upper bound. There are substances that burn in the calorimeter that not all species digest; e.g. humans don't digest cellulose. The calorie values shown on nutrition labels have had corrections applied based on measurements of typical human digestion. (Further reading: ",
"https://www.ars.usda.gov/ARSUserFiles/80400525/Data/Classics/ah74.pdf",
") Those corrections would be different in other species."
] |
[
"How common is it for animals to starve to death in the wild?"
] |
[
false
] |
I've always wondered if it's a common thing or not. As in they starve simply because they failed to find food not because of human involvement
|
[
"Well, listening to BBC Radio 2 this morning, they were discussing the \"chubby squirrel epidemic\" seen this winter. Temperatures have been mild and thus there has been an overabundance of food for the squirrels. As a result, we have fat squirrels this year. A representative from the Wildlife Trust came on as a guest speaker and stated that under normal circumstances, most squirrels wouldn't survive their first year as they'd die in winter due to starvation.",
"(For what it's worth.)"
] |
[
"In temperate areas, it is extremely common for animals to starve to death during winter. It probably ",
"occurs most often",
" in fishes, then dinosaurs (birds), then mammals. With some species, u",
"p to 90%",
" of the individuals die as a direct result of starvation."
] |
[
"Watch some national geographic... it is extremely common.",
"Very few populations are stable, and instead have repeating patterns of highs and lows.",
"For instance a high population of deer can cause a low population of wolves to rise, and as they mature, they overhunt the deer, resulting in many of the wolves starving, which drops their population and then lets deer start growing again.",
"This isn't even mentioning the patterns caused by droughts and other natural weather related phenomena.",
"In many of these cases, the \"low\" portions are usually caused by either predators or starving, depending upon where the animal in question falls into the food chain."
] |
[
"Why do we presribe prednisone instead of prednisolone?"
] |
[
false
] |
Why does prednisone exist? Why would you prescribe it? Prednisone is converted by your body to prednisolone (active form). This conversion is so efficient that a 25mg tablet of prednisone is equivalent to 25mg prednisolone in a healthy individual. In people with hepatic insuffiency, the conversion is less effiecent and prednisolone is a preferred drug. Why do we still bother with prednisone? Are their any benefits for prescribing prednisone?
|
[
"Mostly it's because prednisone is cheaper. ",
"As you say, they have similar biological effects in most cases. Prednisolone is available in some forms that prednisone isn't, such as eyedrops, but outside of those special cases they are pretty much equivalent. ",
"They are even the same age, both having been introduced to the market in 1955. ",
"But, for equivalent tablet doses, prednisolone may cost five times more than prednisone. In some cases the difference could be even greater."
] |
[
"pharmacology aside, there's a lot of potential reasons",
"method of delivery? prednisone comes in tablets, prednisolone seems to only be available as a liquid -- i suspect liquids and syrups are more annoying to transport, dose correctly, etc.",
"cost? per mg, prednisone seems to be less than 1/5 the price ($0.049 per mg at retail in the US, versus $0.27 per mg for prednisolone)"
] |
[
"These are called “prodrugs” and there are many other examples of this. There are a few reasons why prodrugs are used. Sometimes it’s just more cost effective. But a more interesting application is its use as an extended release version of the drug that can’t be tampered with. Often times the drug is broken down into the active drug more slowly than if you just took the active drug, and since this breakdown is usually enzyme dependent you can’t easily convert it to the active form and bypass this ‘pseudo extended release’ mechanism. This is quite useful for drugs with abuse/addiction potential a prime example of this is the drug Vyvanse (lisdexamphetmine) it functions very similarly to extended release amphetamine (Adderall XR), but with one big caveat, for many extended release formulations there is some way to extract out the drug (crushing/dissolving the pill etc.) so that people who want to misuse the drug can get it all at once, you can’t do this with prodrugs. Occasionally two drugs will be combined into one molecule that once ingested will quickly degrade into both drugs, Vyvanse breaks down not only into amphetamine, but also L-lysine which can help mitigate some side effects. Another example of this is the discontinued drug Amphecloral which breaks down into amphetamine and chloral hydrate (a strong depressant) the idea being that the depressant would counteract some of the stimulant’s side effects, it was very addictive and discontinued. ",
"However, it should be noted that since the mechanism for prodrugs is enzyme dependent the effects can vary by quite a lot for different individuals and for some don’t work much at all. A prime example of this is codeine which is a prodrug for morphine, which depending on your genetics can vary in effects from person to person by 15-20% more so than if they had been given the equivalent dose of morphine, however morphine can be more easily abused (is 3X more potent when injected) so most doctors don’t prescribe morphine. ",
"So prodrugs can help reduce abuse potential, ensuring they’re taken as prescribed, can be cheaper, last longer, and can even incorporate two different drugs. However do to the enzyme dependent mechanism the effective dosage absorbed can also be less predictable."
] |
[
"How does deep oil well drilling work? Is the pipe the same diameter all the way down? Why doesn't friction impede progress?"
] |
[
false
] |
Saw a news article today on a new 7000 ft below sea floor record for drilling. This got me to thinking: how is it possible to overcome the friction between the pipe and the material being drilled through over long distances? Does the entire pipe consist of the same diameter, and is slowly being pressed into the earth? Or is there a technique where smaller diameter pipes are used?
|
[
"The diameter of the bit is larger (about 2-3x) than the diameter of the pipe. The \"walls\" of the hole and inside of the drill pipe are pumped full of drilling fluid that reduces friction and heat as well as holds the pressure of whatever you are drilling in to below the surface of the hole (preventing a blowout)."
] |
[
"The amount of power that a rigs topdrive (engine that pipe is connected to and spins) is enormous in comparison. Where I am from it is typical to drill 5000m holes (half straight down and then kicked out on a long 90 degree turn). Depending on the rock formation you can drill 100m/h or 0.01m/h. As the bit wears down the rate of penetration slows and the bit will eventually need to be replaced. To answer you question though, the pipe is the same diameter the entire way down to make for easy tripping in and out of the hole when bits or downhole tools need to be changed."
] |
[
"The part I'm still having trouble understanding though is how friction between the pipe and the surrounding rock doesn't keep it from spinning after getting to a certain depth. That has to add up to a point where the force necessary to keep the pipe spinning is equal to the power output of the engine driving it?"
] |
[
"Would it be possible for something to exist that actually repelled space/time as opposed to attracted it like normal mass? What would be its characteristics?"
] |
[
false
] |
Like a reverse black hole maybe? something that would kick away from it anything that came close? I would think that such a thing would also be invisible or maybe even narrowly reflective as it shot back light that tried to approach it.
|
[
"I don't think you've asked this question in a way that other people understand. What do you mean by \"space/time\" here? Because I don't think most people think of mass as \"attracting space-time\". I think some people might say something more like \"mass attracts mass, with large masses, and repels mass with tiny masses\". From what I understand, gravity is one end of the spectrum, with the attractive force working at the large masses, and the electromagnetic force working on small masses. Though I'm still trying to get someone to explain this to me in a clear way, so I'm not totally sure if that's what the general consensus is these days. If true, the electromagnetic force seems to be what you're talking about, as in repelling things.",
"You also seem to be asking the more clear question (in your text, as opposed to your post title), if there is an opposite of a black hole. You might want to try asking that as your whole question. That might generate some good responses."
] |
[
"i said 'space/time' for completeness i guess since both are tied together but i suppose it makes a bit more sense if you take 'time' out of it."
] |
[
"Do a google for kirkwood gaps. ",
"If you imagine mass as creating \"gravitationally attractive valleys\" in space/time, then kirkwood gaps are \"gravitationally repellent mountains\" created by the opposing masses of Jupiter and the Sun. ",
"Good enough?"
] |
[
"how long after I \"die\" would my mind stop working?"
] |
[
false
] | null |
[
"I don't think you are dead UNTIL your mind stops working. "
] |
[
"Just to be more specific, your explanation pertains to the brain not the mind. Although observations highly suggest that the two are very closely related, it's still uncertain what will happen to the mind after brain damage as the mid is not directly observed. One may still choose beeline that the mind is independent of the body and will continue to exist past the biological death of the body. Hence his is more of a metaphysical of philosophical question and not a neuroscience one."
] |
[
"Just to be more specific, your explanation pertains to the brain not the mind. Although observations highly suggest that the two are very closely related, it's still uncertain what will happen to the mind after brain damage as the mid is not directly observed. One may still choose beeline that the mind is independent of the body and will continue to exist past the biological death of the body. Hence his is more of a metaphysical of philosophical question and not a neuroscience one."
] |
[
"Evolution: Can a creature's traits change during it's lifetime?"
] |
[
false
] |
[deleted]
|
[
"Epigenetics",
" is not exactly what you're asking for but it might interest you."
] |
[
"Many animals have fur coats that change in thickness and color to match the seasons, like an ",
"arctic fox",
" (first one I thought of).",
"Or an example closer to home: If a human moves from a cloudy place to a sunny place, you get a tan (bodily adaptation to account for local environmental conditions)."
] |
[
"No, an animal cannot change its traits within its lifetime (nor pass those traits on to future offspring) unless it is an animal that is already adapted to a changing environment where it changes it coat colour depending on the seasons (arctic fox mentioned below, hares - the ones we have in canada do this too). ",
"The type of evolution you are referring to was already thought of by the scientist ",
"Lamarck",
" who thought of ",
"Lamarckism inheritance",
". No substantial support, evidence of any kind has been found for this.",
"In Lamarck's theory he postulates that if an animal uses a trait in a more useful way, and that trait changes it can be passed on. For instance, if a young giraffe must stretch and stretch its neck to reach foliage, its neck becomes longer over ",
" lifetime. At the end of its life its neck is much longer, then say if it didn't have to stretch it neck so much. This longer necked giraffe passes this long-neck trait onto its offspring.",
"But this is not how it works, no matter how much a giraffe stretches its neck it does not change the trait, encoded within the genes in its gamete cells. Variations in the coding of the gene of the gamete cell, will determine if its offspring will have long necks or short. But this is predetermined within the gamete cell, not by how much the trait is used or disused by the adult.",
"That being said, if you got a blast of radiation to your gametes (cells which develop into eggs or sperm) you could damage the DNA within, causing mutations which could lead to serious diseases in future offspring.",
"And another area is epigenetics, mentioned in another comment.",
"I must also add, Lamarck thought of many other aspects of the theory of evolution that still hold to this day. First that traits are passed on...however, his mechanism of passing them on is incorrect, but we can't blame him, he never knew what DNA was, nor genes nor any other unit of inheritance."
] |
[
"Are computers just as efficient as electric heaters if you want to warm up a room? Does all of the energy used end up as heat or does a tiny bit used in calculations?"
] |
[
false
] | null |
[
"Here are relevant questions. Hopefully they are helpful.",
"[1]",
"\n",
"[2]",
"\n",
"[3]"
] |
[
"in computers, there are often moving parts, as well as lights, that translate energy into things other than heat, so literally, no. \nbut i think the heart of your question is what the actual energy requirements/release of computing itself are. and this is where i start to speculate a bit, but i believe that the actual operations of a computer are done via changing the electrical current through resistance, capacitors, etc. in such processes, (from my admittedly limited knowledge of physics) i believe that any energy lost in the electrical circuit would be lost as heat. so ignoring auxiliary components (moving parts/lights) i wouldn't think it would matter if the resistance which results in energy loss as heat came from a heating coil or a computer circuit."
] |
[
"This is not correct. The fans eventually stop when you turn off the computer and is turned into heat by friction. True for all moving parts. The light from display hits the environment and turns into heat as well. If you have windows, a tiny bit of light might escape that way. "
] |
[
"What is the smallest planet/moon that still has a detectable magnetic field?"
] |
[
false
] | null |
[
"I just want to add that two kinds of magnetic field exist. \nIntrinsic magnetic fields and induced magnetic fields.\nMercury, Earth, Jupiter, Saturn, Uranus and Neptune have intrinsic fields. It is usually due to them having metalic cores. (Iron for Earth and Mercury and metalic hydrogen for the giants.) \nThey spin fast (especially Jupiter which has a rotation rate of 10h!!) and because their core is a giant conductor they create a magnetic field around the planet. \nVenus and Mars only have an induced magnetic field. This field is created by the solar wind, which is essentially a lot of charged particles flying at very high speeds. These create a magnetic field which interacts with the planets and creates a bow shock. (The bow shock is basically decellerating the solar wind to subsonic speeds.) \nand like the other guy already said, the mercury is the smallest planet with an intrinsic field and also has the smallest intrinsic magnetic field. Jupiter has by faaaaar the biggest field. It is MANY orders of magnitude bigger than the others. This is due to Jupiters size and his ridiculously fast rotation. (seriously 10h is more than twice as fast as Earth while Jupiter is also more than 20 times as large as Earth. utterly ridiculous)\nAnd the last factor making his magnetic field so strong is plasma coming from its moon Io. The plasma follows the magnetic field of Jupiter and actually adds internal pressure, weakening the effect of the solar wind.",
"This strong magnetic field is actually a big problem for spacecraft that want to explore jupiter. The strong field creates extremely strong radiation belts around Jupiter and its moons. The radiation is so strong it will actually destroy any spacecraft that stays for too long and it will definitely kill any human who would enter the radiation belts. Unfortunately Europa is directly within these belts, so that an exploration of its ice and (probable) sub-ice ocean will be very difficult. "
] |
[
"Better to ask: which planet or moon is the smallest - the EM field is everywhere and of course anything with an electric charge (protons and electrons) interacts with it at some level.",
"I'm going to take some liberties here, and talk about detectable ",
" effects that can be detected by near-Earth instruments.",
"Firstly, Mercury is the smallest planet. It has a moderately strong field, which has been measured by passing probes and could in some circumstances be measurable from Earth by its interaction with flares and other Solar matter.",
"Venus's magnetism is negligible, Mars has a weak field which affects atmospheric conditions.",
"Our own moon has a weak but detectable field, provided you're in orbit or watching it during a solar flare and it's nearly full.",
"The gas giants have very strong fields. Saturn's field even changes the appearance of the planet's rings, similar to the way iron filings outline a bar magnet. Many moons of these behemoths orbit ",
" the planetary field, but have virtually no magnetism of their own due to tidal locking and other conditions. (Titan is a spectacular example of this)",
"Edit: \nMercury: Smallest planet, has magnetosphere\nDeimos: Smallest moon, technically has a field (weak)\nGanymede IIRC has a native magnetic field (not induced by parent body)."
] |
[
"Thanks for such a detailed answer!"
] |
[
"Light from distant stars and galaxies reaching earth?"
] |
[
false
] | null |
[
"I have no idea what you are trying to say."
] |
[
"Understandable. I can try and do it step by step. A galaxy would take at least 13 billion years to get 13 billion light years away right?"
] |
[
"Actually with the expansion of the universe it could look like a galaxy is 20 billion light years away even tho the universe is only 13.7 billion years old. ",
"See our in FAQ for more info: ",
"https://www.reddit.com/r/askscience/wiki/astronomy/theobservableuniverse"
] |
[
"\"Blood Doping\" is when professional athletes artificially increase their number of red blood cells to gain endurance. If this helps, why wouldn't the body naturally have that higher blood count?"
] |
[
false
] | null |
[
"To add to what has been noted so far adding additional Red Blood cells to the human circulation system introduces certain health risks. It increases blood viscosity and decreases cardiac output and blood speed. It can increase the risk of stroke, heart attack, phlebitis, and pulmonary embolism. ",
"even when soldiers do blood dope they only get a temporary boost in performance, I believe that the excess blood cells are reabsorbed by the body and their performance reverts to normal. Blood Doping is essentially fooling the body into having more red blood cells than it needs so it will revert to the required amount in time anyway."
] |
[
"Producing red blood cells takes energy, so your body only does it when it detects that you need them. This regulation process is relatively slow. One of the ways that blood doping works is that athletes put themselves in situations where this natural production of blood cells (hematopoiesis) is stimulated, then have their own blood drawn and stored for later, when it can be transfused into their system in circumstances when their body isn't producing as many red blood cells."
] |
[
"To add many of the components of blood cells, and the degradation of blood cells are toxic and pro-inflammatory (ex. heme). "
] |
[
"How does interferential current, used on the body, cross in the middle, instead of forming two parallel currents?"
] |
[
false
] |
[deleted]
|
[
"I can't be authoritative on the effectiveness of the treatment -- just on the physics. The idea is to make two ~4kHz A.C. signals interfere, producing heterodyning at the right frequency (~10 Hz) to muck about with the nervous system. If the two voltages are applied across the body (e.g. the \"carrier\" is from the right shoulder to the left hip and the \"variable wave\" is from the left shoulder to the right hip), then when the waves are in phase the two shoulders will both have positive voltage simultaneously, and current will run up and down the body, changing direction four times per millisecond. When the waves are out of phase, the two left side electrodes will have positive voltage simultaneously, and current will run sideways across the body. As the carrier and variable waves drift relative to each other, the current will slosh in funny directions, tending back and forth between those two end cases.",
"I'm only an astrophysicist, not a biophysicist -- but it all seems pretty hokey to me. To make it effective at stimulating nerves, the overall system would have to include a mixer or a rectifier (something that allows current to pass one way but not the other), to remove the \"high\" 4KHz frequency and decode the beating back down to the 10 Hz range where it affects the nervous system. It is, I suppose, possible that the ion pathways through the nerve cell walls could rectify the current somehow -- but I couldn't tell ya whether they do or not, without hitting Google for more than 30 seconds.",
"The idea seems to be that skin tolerates higher currents at kHz frequencies than at near-D.C., so you can run more current into the hapless patient (without burning him) than you could by direct stimulation in the tens of Hz (which is the band where nerves operate).",
"Edit: I got interested and spent the 30 seconds on google. ",
"here",
" is an interesting review from the 1990s of how it seems to work. Wow, never woulda guessed."
] |
[
"Thank you very much! I guess I'm really just asking a more basic question, however. The desired effect is to create a point in the middle where the currents cross. The current from one lead travels only to its corresponding lead (far). Why does it do this instead of going to the other lead (parallel formation instead of an \"X\"), which is closer? "
] |
[
"Current spreads out as it travels through a resistor with spatial extent.",
"Even if it didn't, when the two signals are in quadrature (90 degrees out of phase) the shortest conductive path goes right through the centerpoint a couple of times per cycle: when one pair of electrodes is at full voltage and the other pair is at zero."
] |
[
"Can you get cancer if you eat cancer tissue of an animal?"
] |
[
false
] | null |
[
"Transmissible cancers do exist. Probably the most famous one is the kind that causes ",
"Tasmanian devil facial tumor disease",
", which is transmitted by direct contact between individuals. However, almost all transmissible cancers only affect animals within a particular species. The only evidence I was able to find of clear interspecific cancer transmission is from ",
"Metzger et al. 2016",
", who identified cancers in carpet shell clams that appeared to be from a different (but closely related) species. I was going to say that this is probably dependent on some quirks of the immune system in bivalves or something, but surprisingly I did find one case in ",
"Muehlenbachs et al. 2015",
" where a person was found with some tumors that appeared to have come from a tapeworm they were infected with (probably worth noting they were also immunocompromised due to HIV). Since they presumably got the tapeworm from food... I guess the answer is a very, very tentative \"maybe\"."
] |
[
"No. It's technically possible to get certain types of cancer from another humans under very, very rare circumstances (via organ transplants rather than cannibalism). Cancer spreads effectively because the immune system cannot tell the difference between your normal cells and cancerous ones; the body would recognize cancerous cells from an unrelated species as foreign, non-human, non-self cells."
] |
[
"Wanted to add this ",
"sexually transmitted cancer in dogs",
"."
] |
[
"can you recommend an intro anatomy textbook?"
] |
[
false
] |
I start medical school in September, have never taken an anatomy course, and want to play a little catch-up to the rest of the field. Recommend a good textbook, AskScience!
|
[
"Netter's is the best IMO. Awesome diagrams and clear illustrations. "
] |
[
"Seconded. Netter is just an atlas though, not a text."
] |
[
"I used Gray's Anatomy when I took anatomy in med school. It was a good book, explained things well."
] |
[
"Woken up so suddenly that your body \"wakes up\", but you yourself don't? What is this phenomenon?"
] |
[
false
] | null |
[
"If this is true, it sounds like an extended state of sleep walking. Sleep walking occurs when the brain is in a disassociated state shifting to/from waking/sleeping. Basically, the whole brain does not wake up--part of it can remain in sleep signal patterns. ",
"Severity and symptoms of sleep walking differ between person to person. Some people may just move from the bed to a couch. Some sleep eat. Some sleep talk excessively. ",
"Probably, because of the violent nature by which he was yanked awake, only part of his brain successfully made that jump. It's not very common, and usually is a rarity for even casual sleep walkers, but I've seen much stranger things in sleep walking studies. "
] |
[
"Well, any abnormal movement/actions during sleep are considered parasomnia. I did a big research project on it back in my abnormal psych course. Basically, this is a whole big web for abnormal sleep behavior (and will probably be reclassified with the next DSM comes out). Anyhow, sleep walking can be a relatively tame example of a parasomnia. ",
"My interest was first piqued when I had a very severe night terror several years ago. It was my sophomore year of college and I was stressed. My roommate woke up to me screaming at the stop of my lungs, cowering in the corner of the room, completely unreachable by all attempts to wake me. It wasn't until a parent (who was in town) came in and calmly told me (without trying to wake me) to get back into bed and that everything was ok. I have no memory of this event--night terrors are different from night mares because the 'bodily reaction' is unconscious. I had sleep walked before and I wanted to explore more into parasomnias. ",
"I've read studies about a rare weight disorder where the individual eats in his/her sleep. It's called ",
"nocturnal sleep related eating disorder",
". Another disorder is is sexomnia, where individuals engage in sexual activity while sleep walking. Women have been essentially raped because they sleep walked into a neighbors apartment, started undressing, and the men (whether or not aware of sleep walking) went along with it. Thankfully, there are enough honest people out there to keep this from happening too often. There are other incidents when people cook full meals, drive their car, walk about window. It's pretty intense. ",
"One of my favorite psych subjects. I'm in neuropsych so I really like studying brain sleep stages and activities, etc.. "
] |
[
"Really? This is very interesting. And you say you've seen stranger things? Any examples?"
] |
[
"What is the driving force for osmosis?"
] |
[
false
] |
I have been taught that osmosis is driven by the molar concentration of solutes in a solution across a selectively permeable membrane. Pretty basic to me. What puzzles me is how there is no relationship between osmotic pressure and size of the solute since osmotic pressure is a "colligative property". I've been told that cells can reduce osmotic pressure by combining many molecules of glucose into one large molecule of glycogen, for example. How is this possible?
|
[
"All colligative properties are manifestations of entropy and the second law of thermodynamics. That is, they neglect all enthalpic contributions to the effects (these lead to deviations from ideal behavior). ",
"Osmotic pressure derives from the driving force of a solution to become more dilute, because spreading solute out results in higher entropy. ",
"Osmotic pressure can be reduced by making glycogen from glucose because you're simply reducing the number of things available to create pressure. Glycogen would still be subject to concentration gradients, though glycogen may be large enough of a molecule that you never have a statistical sample in solution and different factors could take over."
] |
[
"To further this wholly correct point - osmotic pressure depends on the concentration of particles in solution. It doesn't matter what those particles are. So if you take 100 glucose molecules and combine them into a single glycogen molecule, you have gone from 100 particles to 1 particle in solution. The osmotic pressure across the membrane from low to high solute concentration similarly reduces. "
] |
[
"So is osmotic pressure a physical pressure?"
] |
[
"Do photons (and other C travelers) experience an acceleration to C or is the velocity instantaneous?"
] |
[
false
] |
Or does it not even make sense to define an acceleration to such things? If so, why? For examples sake, say I have an interaction that results in an emitted photon, at what point is it traveling at C? And where does this energy to travel such speeds come from, simply from the system as it goes to ground state which in turn is the energy to fuel the emissions? How can that be enough?
|
[
"There is no acceleration, because photons always travel at c. This is just an intrinsic property of massless particles in general.",
"And where does this energy to travel such speeds come from, simply from the system as it goes to ground state which in turn is the energy to fuel the emissions? How can that be enough?",
"Photons do not have kinetic energy, so it takes no energy to send them flying off at c. Instead, energy imparted to a photon changes the wavelength of the photon, and the energy of the photon is simply however much energy the system has lost in producing the photon."
] |
[
"Just to add, the frequency of the photon/wave is dependent on the energy the photon carries, via planck's constant. Furthermore a photon does have momentum, which is related to the frequency and thus the energy of a photon. Therefore if a photon were to hit a surface after being emitted, and is adsorbed, it will give momentum to the object, but the photon will instead of slow down simply disappear."
] |
[
"It doesn't seem like anybody has actually answered you. The momentum of a photon is proportionate to its frequency, instead of its mass and velocity, both of which are constant.",
"I'm sure you are familiar with E=mc",
" but you might not realize that that is not the complete equation. It is only the part that describes the energy of an object with mass at rest, where m != 0 and momentum is greater than 0. The complete equation is E",
" = m",
" c",
" + p",
" c",
" . The second term has a p which is momentum. For an object with mass that is p=mv. But for a photon it is p=hv/c, where v is the photon's frequency and h is the Planck constant and c is the speed of light. So when we set m=0 in the equation from before we get E",
" = p",
" c",
" and then E = pc.",
"As for the light not having kinetic energy, that is because it is pure energy already. Kinetic energy is the energy component of an object due to its mass and motion. It is the representation of the energy required to produce that motion or stop it. Photons don't have a rest form. They are always moving and so they represent energy themselves."
] |
[
"Is it probable that the solar panels from the Mars rover get cleaned by a storm or anything else?"
] |
[
false
] |
[deleted]
|
[
"Yes - actually, this happens quite a lot, and this is part of why Spirit and Opportunity lasted for so long. The Martian wind partially cleans the solar panels, so although they quickly became fairly dusty, they still ran fairly decently for quite a long time."
] |
[
"Especially Opportunity! That little rover belongs in the Mars Museum of History when we build it. That was by far the best bargain we US taxpayers ever got."
] |
[
"Yes. They didn't think this was possible when they launched Spirit and Opportunity but quickly discovered it did actually happen which is why those plucky little bots kept going for so long",
"It's not a perfect solution because the robot has to recharge it's batteries during the day and conserve power at night or during minor dust storms. NASA sometimes had to park the rover in the best angle to catch the sunlight and put it into low power sleep mode waiting for a storm strong enough to clean the solar panels so it could get a full charge again. ",
"The newer rover, Curiosity, is nuclear powered so it can run at night and doesn't need to worry about darkness or going into low power modes or hoping a good storm comes at the right time. Also if a rover ever gets too cold the electronics are ruined and Opportunity spent a lot of its power running electric heaters in the Martian night to keep itself warm. Curiosity didn't have that problem because it's nuclear thermoelectric generator keeps it warm. (IIRC Spirit and Opportunity did have nuclear thermoelectric generators too that acted mostly as hot-water-bottles rather than electricity sources but their heat output decreases over time as the nuclear isotopes decay and they weren't intended to be used for 14 years)",
"The downside of Curiosity's nuclear source compared to Opportunity's solar power is that when Curiosity's nuclear batteries run dry there's no alternative. No dust storms are going to add more plutonium or other radioactive isotopes into Curiosity's thermoelectric generator. When the fuel runs out the rover is dead, it's a fixed deadline for Curiosity unlike Spirit and Opportunity's opportunity to continue working. "
] |
[
"If Prince Rubert's Drops are stronger than steel, can we make materials using the same idea?"
] |
[
false
] |
I know they are very fragile since they detonate if you break the tail, but could we make something using the same tension idea?
|
[
"We do it all the time - that's exactly what ",
"tempered glass",
" is. Some everyday examples: the side and rear windows of your car, most windows in commercial buildings, and a lot of glass baking dishes. ",
"They have the same failure mode as Rupert drops, as a small crack will cause them to fail all at once. ",
"Here's a high-speed video",
" of cracking a tempered window.",
"Edit: ",
"Here's another one",
" that is more violent and shows some of the issues with it. "
] |
[
"As an aside, shattering is not a bug but a ",
" of tempered glass. A million tiny shards are much safer than a few big ones. In my town you're not allowed to put untempered glass at floor level in a house for this reason.",
"Bonus: if you wear polarized sunglasses you might have noticed a diamond pattern on the rear windshields of cars. This is caused by the grid of compressed air nozzles that blow on the glass to temper it."
] |
[
"Bonus: if you wear polarized sunglasses you might have noticed a diamond pattern on the rear windshields of cars. This is caused by the grid of compressed air nozzles that blow on the glass to temper it.",
"Hah, that explains that. I thought it might've been an artifact of some sort of coating process."
] |
[
"Can complex or imaginary numbers be irrational?"
] |
[
false
] |
I know that imaginary numbers and real numbers are different sets with no intersection, and rational/irrational numbers are are a subset of real numbers. That leads me to believe that there are no irrational numbers, but would the square root of negative pi or pi times i be irrational. Also, could complex numbers with an imaginary part be irrational, like e + i?
|
[
"I know that imaginary numbers and real numbers are different sets with no intersection",
"I suppose by \"imaginary numbers\" you mean purely imaginary numbers, i.e., complex numbers of the form z = b",
" with b real. If so, then z = 0 is both real and purely imaginary.",
"and rational/irrational numbers are are a subset of real numbers",
"Yes, the set of rationals is defined as the set of quotients of integers, which are real numbers. So for complex numbers we usually just refer to whether their real or imaginary parts (which are real numbers) are rational or irrational. It's sometimes convenient just to say a \"rational complex number\" is a complex number with rational real and imaginary parts, although the terminology is not standard.",
"(For instance, should an \"irrational complex number\" be a number that is not a \"rational complex number\" or a complex number with both irrational real part and irrational imaginary part?) I believe the standard term for \"rational complex number\" is actually \"Gaussian rational\", but I have honestly read both \"rational complex number\" and \"Gaussian rational\" in about equal amounts. Maybe \"Gaussian rational\" is more common in algebra or number theory, fields outside my expertise.",
"For the math-inclined, the \"rational complex numbers\" are perhaps the most natural extension of the rational numbers to the complex numbers in the following sense. The \"rational complex numbers\" form a subfield of the complex numbers and is the smallest subfield that contains the rational numbers and the imaginary constant ",
". In other words, the \"rational complex numbers\" precisely form the simple field extension Q[i]."
] |
[
"smallest subfield that contains the ",
" numbers and the imaginary constant ",
"I assume the bolded word is a typo for \"rational\"?"
] |
[
"Ah, yes, thanks. Otherwise the field would just be all complex numbers. D:"
] |
[
"Do you have a preferred lung/kidney?"
] |
[
false
] |
I know it sounds weird to ask, but I was wondering since we have a preferred hand/eye/foot, does our body prefer our organs as well? Are there any parts of our body that get preferred that you wouldn't think would?
|
[
"Every two or so hours your body switches which one of your nostrils is “dominate”. The majority of the air you inhale goes into one nostril or the other. Cover one nostril and breathe in through your nose, then cover the other. One will be significantly easier to breathe through."
] |
[
"No, the body works at the same time both lungs and kidneys functioning to work together for efficiency and efficacy. If only one worked at a time or back to back then it would take a while to start up again. The lungs would develop atelectasis from not being filled and empty, decreasing the amount a person can breath and overall tidal volume (increasing work of breathing) and the kidneys would create crystals inside from not being filtered, resulting in inflammation or kidney stones. Both systems need to work together continuously to prevent problems. And you dont have any other dual paired organs. It may seem counterproductive to constantly be powering these systems but think of it as a company. Your body works best when more are working together. 2 employees working at half pace is way better than 1 at full pace."
] |
[
"Outside of some pathology, no. Your body does not use one lung or kidney more than the other. Your lungs basically operate on pressure differentials - when you inhale, it expands your lungs, reduces the pressure inside the lungs, and atmospheric air rushes in towards that low pressure area - unless you can selectively expand part or one side of your thorax, than that pressure differential will be more-or-less evenly distributed in your lungs, so air will go everywhere. Caveat: Some areas of the lung have airways which offer more or less resistance to others (primarily as a function of airway diameter), which might impact which parts of the lung fill faster/first/more often. ",
"I'm not aware of any non-voluntary bodily activities which have a sided 'preference' - the only thing that we tend to develop 'sidedness' is voluntary movements, which is probably (almost certainly) more of a cognitive result than a physiological one."
] |
[
"how would you explain x^-1 and x^1/y?"
] |
[
false
] |
How would you explain taking a number to the negative power? I don't understand how that would be the reciprocal of x!! I also don't get taking a number to the reciprocal of something like 4 how is that the square root of 4?
|
[
"Well, for the first one think about it this way. If you multiply two numbers with the same base raised to an exponent, you simply add the exponents: a",
" * a",
" = a",
" Now what happens if you divide by a? Lets say a",
" / a = a",
" But that's exactly the same thing as saying a",
" * a",
" = a",
" So by comparison a",
" must be the reciprocal of a , if we follow the rules of multiplying two numbers with the same base.",
"It's the same kind of idea with raising something to the fraction of a power. See if you can prove it to yourself."
] |
[
"In general, x",
" * x",
" = x",
". Following this, whatever you define x",
" to be, it should satisfy x",
" * x",
" = x",
" = 1, but then x",
" = 1/x just by manipulating that equation.",
"Similarly, in general you have (x",
")",
" = x",
" , so whatever you define x",
" to be, it would be nice to satisfy (x",
")",
" = x",
" = x, but this means that x",
" is a number which when taken to the mth power gives x, the definition of the mth root of x."
] |
[
"I like this approach, called ",
". ",
"First, I show students 5",
" 5",
" and 5",
" We discuss what it means to go 'up' a power - to multiple by 5. So what does it mean to go down a power? It means to divide by 5. ",
"So now we have: ",
"5",
" = 125",
"5",
" = 25",
"5",
" = 5",
"5",
" = ???",
"5",
" = 1/5, meaning to ",
"5",
" = 1/25, meaning to ",
".",
"This leads to a really intuitive and memorable understanding of 5",
" If we start at the top and go down one exponent, we divide by 5. And this leads us smoothly through 25, 5, 1, 1/5, 1/25. "
] |
[
"Can someone please explain the Ecliptic Coordinate System (Heliocentric)?"
] |
[
false
] |
To practice my coding, I wanted to write up a very rough, very basic navigational computer type program that would track the orbits of every planet. Given a time, a destination, and point of origin, the program would report back the distance between the two points. I understand there are various coordinate systems for tracking celestial bodies, but decided on the heliocentric ecliptic coordinate system because it made the most sense to put the Sun at the center of the map. I don't understand how positions are given, however. Could someone please explain how the coordinates are read/determined? Or point me to a simpler method of tracking the planets' positions? Thank you!
|
[
"Elliptical is fine. Since you're doing heliocentric, your focal point is the Sun, so just assume everything is orbiting on separate planes. If you want to really get an exact estimate each time without adjustments, do the Lambert's method or the Gauss method. Lambert is when you know the distances."
] |
[
"I don't understand how positions are given",
"Could you please be more specific about this point?",
"I assume you're asking how to convert angles and radii to x,y,z coordinates. Take a look at ",
"spherical coordinates",
". In your case it may be simplified if you consider one plane at a time, so you can just work with 2D coordinates:",
"x = r cos θ",
"y = r sin θ",
"However if you're using the ecliptic plane as a reference you'll have to use 3D."
] |
[
"Ultimately I'm not sure how to plot the other planets. Since I'm going heliocentric, I imagine the sun is at coordinates (0,0,0). If I then wanted to plot Mercury on this virtual map, how would I do that?",
"Ideally I would like to turn this into a simulation of some sort where I could keep adding data on other celestial bodies, like comets, but I just don't know how to plot it all out within a map."
] |
[
"Is there any way to predict when a particular star will go supernova?"
] |
[
false
] |
I'm curious if the nighttime sky will be lit up with the beauty of a supernova within my lifetime. Is there any way astronomers can predict (within a certain time frame) when a star will go supernova?
|
[
"Betelgeuse in the Orion constellation is about to/already gone supernova. It's only about 700 lightyears away, and is predicted to go within 10-1000 years. This means it could go within our lifetime, and may have already, the light just hasn't reached us yet. When it does it'll basically be a second moon in terms of brightness, the night sky will be constantly bathed in supernova light similar to the intensity of a full moon, for months.",
"We can observe Betelgeuse in enough clarity to see that its surface is very unstable and turbulant, and indeed its mass has decreased by something like 30% in the past few decades. We already knew it was a red giant long ago, and it's only a matter of time now.",
"I am not a professional astronomer, just an amateur with an interest in astronomy."
] |
[
"Do you have a citation for 10-1000 years? Wikipedia says \"Betelgeuse is expected to explode as a type II supernova, possibly within the next million years.\" The other four top google results of \"Betelgeuse Supernova\" also give million year ish predictions."
] |
[
"It seems the 10-1000 years was anecdotal, I'm sure I remember seeing it somewhere, but nevertheless, ",
"Dr. Brian Cox on Betelgeuse",
", this was from a recent live stargazing thing he appeared on, and I would be inclined to trust what he says as a reputable source, plus it's the BBC, they're generally reliable."
] |
[
"How much of the current climate trend is actually due to humans? Aren't we coming out of an ice age, and this would naturally change the climate in its own?"
] |
[
false
] | null |
[
"Our current data and models suggest that ",
" of the temperature change over the past 100 years is due to humans.",
"We are not \"coming out\" of an ice age: the last ice age ended 12,000 years ago, and these warm periods typically last 8000-15,000 years. So we're probably nearer to the end of a warm period than the start.",
"We can estimate how much climate change is natural vs artificial using computer simulations. If we put both artificial climate change drivers (greenhouse gases and other pollutants) and natural ones (solar brightness, Earth's orbit, volcanic eruptions) into the simulations, we can match the observed climate trend very well. If we use only natural climate drivers, we see no long-term trend in the models.",
"https://science2017.globalchange.gov/chapter/3/"
] |
[
"Thank you. I have secondary questions now, not sure if that's allowed but whatever. I've heard this argument made recently; how much of an effect on the current extreme weather, at least in America, is due to ocean currents like El Nino? Or is it mostly the slowly changing climate causing more and more extreme weather patterns over time? For instance that major cold snap in the Midwest in January. "
] |
[
"The climatic maximum was roughly 7000 years ago, so without human influence, we should be cooling and approaching glacial conditions again."
] |
[
"In simple language, what's the distribution of mass of a galaxy (i.e. % of total mass as a function of radius)? I actually googled an article on the topic (see text) but it's too technical for me and I'd appreciate a simple explanation."
] |
[
false
] |
The article:
|
[
"Look at the bottom panel of Figure 2 on that page - I've rehosted it ",
"here",
".",
"This gives mass as a function of radius for a galaxy. The radius is in kiloparsecs, where a kiloparsec is about 3000 light years (in astronomy we tend to prefer parsecs to light-years). The mass is in 10",
" solar masses. That means that a mass of \"1\" means the mass within that radius is 100 billion times the mass of our Sun, a mass of \"2\" means the mass within that radius is 200 billion times the mass of our Sun and so on.",
"The next confusing thing here is that there are two separate lines here. The dotted line shows the mass of the visible matter - the disc of gas and stars. The solid line shows the total mass, which is calculated from looking at how fast stars move in circular orbits around the galaxy. This gives a much higher mass, which suggests that most of the mass is not visible - it's in a big puffy halo of dark matter."
] |
[
"There's still dark matter in the centre - there's actually a higher concentration there than in the outer parts - but there's an even higher concentration of visible \"baryonic\" matter which dominates there.",
"Most of the baryonic matter (stars, gas, & dust) is in a disc. The density of this stuff is quite high. By comparison, the dark matter is roughly spherical in shape. Its density is quite low, but it makes up for it by covering a much larger volume, which means the total mass is higher.",
"When you look in the centre of a galaxy, a lot of the volume you're looking at is taken up by the disc, so the high density disc can often win and dominate the mass and dynamics. But as you go to bigger and bigger scales, the disc becomes a smaller and smaller fraction of what you're looking at, and the high-volume dark matter really starts to dominate.",
"The baryonic matter can also be more strongly concentrated in the centre than the dark matter is. Dark matter drops off roughly like 1/r",
" while baryonic mass drops off exponentially. You can also have a bulge of stars in the middle."
] |
[
"There's still dark matter in the centre - there's actually a higher concentration there than in the outer parts - but there's an even higher concentration of visible \"baryonic\" matter which dominates there.",
"Most of the baryonic matter (stars, gas, & dust) is in a disc. The density of this stuff is quite high. By comparison, the dark matter is roughly spherical in shape. Its density is quite low, but it makes up for it by covering a much larger volume, which means the total mass is higher.",
"When you look in the centre of a galaxy, a lot of the volume you're looking at is taken up by the disc, so the high density disc can often win and dominate the mass and dynamics. But as you go to bigger and bigger scales, the disc becomes a smaller and smaller fraction of what you're looking at, and the high-volume dark matter really starts to dominate.",
"The baryonic matter can also be more strongly concentrated in the centre than the dark matter is. Dark matter drops off roughly like 1/r",
" while baryonic mass drops off exponentially. You can also have a bulge of stars in the middle."
] |
[
"How come light that comes from other stars is not scattered ?"
] |
[
false
] |
So i was thinking that if light from other stars can take light years to get to earth how come it reaches us? Why don't other planets or other stars come in the way and scatter it? or does light travel straight through objects?
|
[
"Space is empty. Really, really, really empty. The average cubic kilometer of interstellar space in the galaxy has maybe a nanogram of matter in it, and outside of galaxies we're looking at an even lower density, by a factor of a million or so. Planets and stars are utterly tiny. Even when Earth and Mars are at their closest, there are 10,000 Earth radii between the two planets. Planets are little specks of dust in space, and stars are not that big either. Between the Sun and Proxima Centauri, the next closest star, there are about 600 million solar radii. There just isn't all that much stuff out there. What's known as the ",
"mean free path",
" for a photon, the average distance it will travel before hitting something, is longer than the width of the observable universe. Most light will just continue on into the void, not hitting anything.",
"That said, there are some regions of space which do block light effectively. Molecular clouds in particular are very good at extinguishing light, although infrared can pass through more easily, and microwave/radio waves more easily still. In addition to these, free-floating dust grains (by which I mean anything from very large organic molecules to small silicate grains) also scatter and absorb light quite effectively. The plane of our Galaxy has a lot of gas and dust and so it it hard to see through it to extragalactic objects. If we look to the Galactic north or south, however, the path is quite clear, because the disk of the Galaxy is quite thin. For this reason, most extragalactic surveys tend to look at the Galactic polar regions, with the exception of radio surveys which can see through gas and dust quite easily."
] |
[
"You're not quite fathoming how huge and precise \"unfathomably huge and precise\" is."
] |
[
"Stars are much bigger than planets; so even when a planet ",
" get in the way, it only blocks a little bit of the light—not enough to tell with the naked eye. But very sensitive telescopes can detect the difference, and that’s actually one of the main ways we find planets outside the solar system."
] |
[
"If I squeeze a bottle of water in space, what would happen to the bottle? Would it become reinflated like it would on Earth due to displacement of liquid with air?"
] |
[
false
] |
[deleted]
|
[
"You mean an open bottle than you empty by squeezing the water out? There would be no difference in space, the bottle will go back to it's original form due to elastic deformation of the plastic. It has nothing to do with pressure from inside (because there is not pressure difference between inside and outside the bottle, if we consider the case where the bottle is opened)."
] |
[
"This was the answer I was looking for. Thank you, the question has been on my mind for the past few days."
] |
[
"We you squeeze a bottle on ear you are pushing out a large fraction of the air inside. In the vacuum of space the bottle would actually move back to it's original form faster as it wouldn't have to suck air inside to keep its internal pressure balanced with the external pressure because there would be no external pressure. Think about how a bottle won't expand on earth if you squeeze it and then plug the spout. I suspect this may have been the motivation behind your original question. "
] |
[
"For psychologists... what exactly do you do?"
] |
[
false
] | null |
[
"I'd refer to my response. You're asking why can't the entire discipline of psychology be replaced simply with neuropsychology. Similarly, one can ask why can't biology be replaced with physics or chemistry. It's a different scope of things, and you can't always stick a simulation into a computer when you're dealing with highly complex systems that interacts with many external influences (the environment, the people around us). Ask any physicists about simulating the entire human brain with the Standard Model, even if its possible, it will rely on a lot of psychological expertise in order to model the process correctly.",
"That being said, I think there's a general trend for bridging psychology and biology as of late, there's no harm in keeping up with the trend within the discipline, at the end of the day, neuropsychology is still psychology. You seemed to categorised psychology as the like of talk therapy (I believe that's ",
"). There many exciting researches into the human mind, as we'll likely still be dealing with other humans and human errors in the next 30 years, I believe psychology (a field no doubt is evolving) will still be relevant."
] |
[
"While a valid question, I suspect this post is more appropriate at AskAcademia or AskSocialScience. I spent a year studying psychology and I too, had the same questions and doubts before I moved onto biology. At the time, psychology as a discipline was too amorphous and abstract for me.",
"Now with a few years more experience in the big pool of science, I think I can appreciate psychology a bit more. It may seem strange for the subdisciplines or the different schools to be contradictory or completely unrelated to each other. However, I think the shape of the discipline as a whole came out from various necessities and problems that needed to be answered. The mind is a very tricky and complex thing, and most psychology is dealing with it at a pretty abstract level. Certainly, we can take a reductionist approach and conclude that everything is the result of nature (genetics and neurology) and nurture (culture, upbringing, and the surrounding environment), but that doesn't really help us with many questions at hand. Thus psychology is a \"softer\" science than biology (which is somewhere on the scale of the science \"purity\" scale, with mathematicians scoffing at everyone), but it doesn't make it less useful. In this sense, I admire psychologists and those in the softer sciences to be able to work in the fuzzier abstract level without going into a reductionist spiral as I tend to do.",
"Psychoanalysis, as far as I'm aware, is mostly considered as out of date and nonscientific by most respectable psychologist, even though it had a strong impact on our society and the popular concept of psychology. It will persist thanks to some practitioners, but then again, some people still hold quasi/pseudo scientific ideas about magnetism or toxins that should've died out centuries ago.",
"A good friend of mine studied management and psychology and is now working for the equivalent of the ",
"IRS",
" in my country."
] |
[
"Group therapy is a world away from 'just talking' with friends and family, and has different effectiveness. Just because disorders have biological correlates doesn't mean the biological approach is the best. Psychology also has nonclinical applications. ",
"Psychoanalysis was applied philosophy in Freud's time, not so much now. Psychoanalysis has a very specific meaning, and therapy is a separate concept. I could go on, but I think it sounds to me like you're not personally enamoured with the psychological approach, which is fine, it's one of many. Look seriously into the biological side of things and see if their approach is any better. The mind is complicated and any study of it is unlikely to be conclusive."
] |
[
"Are there scientists that study other scientists?"
] |
[
false
] | null |
[
"A number of anthropolgists did a study of physicists at the Large Hadron Collider by embedding themselves in the population:",
"http://www.nature.com/news/2010/100324/full/464482a.html"
] |
[
"I know a guy doing a PhD in Philosophy of Science. I don't understand it, but basically he studies flow of information between scientists and how different factors such as reputation, impact of work etc.. control the flow and direction of fields and research. Really confuses me to be honest. "
] |
[
"But who studies the scientist studying scientists?"
] |
[
"How do the Japanese Snow Monkeys dry off without dying once they leave the hotsprings?"
] |
[
false
] |
[deleted]
|
[
"The snow monkeys (macaques) have a thick layer of fur close to the skin that effectively protects it from getting wet. If you watch them climb out of the hot springs they’ll often shake the water off the fluffy outer fur and then they’ll be essentially dry."
] |
[
"Of course they do. They also feel cold too, which is why they hang out in the hot springs.",
"Their fur is designed to prevent them from staying wet and becoming popsicles in the cold weather when they leave the hot spring."
] |
[
"Their real issue with the cold is not getting dry, but staying warm at night while they sleep. They sleep in the trees, and if they can’t find a group to huddle with they freeze to death."
] |
[
"Did neanderthals breed with homosapien?"
] |
[
false
] |
[deleted]
|
[
"A similar question was just asked a few hours ago, but I will answer yours with the same answer I gave the previous OP. The simple answer for you is yes, certain populations of humans (non-african populations) and neanderthals interbred and yes these offspring were fertile because we still have 1-5% Neanderthal DNA within ourselves. ",
"A little background on the two species. Neanderthals evolved in Europe about 600,000 years ago and lived independently from humans for many hundreds of thousands of years, developing their own culture, languages, tool systems etc. Humans evolved in Africa about 200,000 years ago and then migrated out of Africa about 100,000 years ago. We encountered Neanderthals when we began to move into the Eurasia region and into Europe. Known interactions began about 30,000 to 50,000 years ago and could only have lasted until Neanderthals went extinct, about 24,000 years ago.",
"(From the other OP) Did Humans kill them off, or did we breed with them?",
"Well there are two main hypotheses, and a third less likely hypothesis. But more importantly a combination of factors led to their extinction (i.e. hypothesis 1 + 2, and perhaps a little of 3). Local conditions may have also played factor like disease, malnutrition or a particularly harsh season. Sometimes even factors like distance between groups can be enough to cause extinction because their isn't enough gene flow. If their isn't enough migration between groups then the groups may be too small to flourish. This can be especially hard for k-selected species like humans / Homo species where we usually only produce one offspring every year. If all available females die, or are unable to raise offspring because of bad conditions that could be disastrous for already dwindling populations. Anyway, the two main contributing factors that likely most groups were:",
"Climate change: Neanderthals could not adapt physically or behaviourally to the changing climate, where as humans could. We were more innovative and could rapidly build on old ideas or invent new technologies. On the other hand as far as we can tell Neanderthals were pretty stagnant in terms of culture and ability to innovate. They had the same tool technologies for hundreds of thousands of years, they had the same hunting techniques, they lived the same kinds of lives and they never migrated out of Europe. If a prey species moved out of their territory they may not have been innovative enough to adapt to new food sources, this may have led to the extinction of certain populations. ",
"Humans out competed them. As we moved into Europe we either extirpated or killed off the Neanderthals. They could not compete with our better tool technologies, our ability to adapt and innovate. Also behaviourally we may have been more cohesive. Humans engaged in trade and even long distance trade, that same type of cohesion between Neanderthals is less evident. So we simply moved into their territory and there wasn't enough room for two highly intelligent species. One had to go. It is not clear whether this is the result of direct competition - aggressive interactions (i.e. we killed them) or indirect competition - passive interactions (i.e. we stole their resources, extirpated them etc.)",
"We mated with them and they blended into our species or the ",
"admixture theory",
". We know that human populations residing outside of Africa have between 1-5% Neanderthal DNA. ",
". First, I would like to say that a few selected studies have been blown out of proportion by the media / sensational documentaries. That is not to say that their findings are not important, or not interesting. They are very interesting, but we have to make sure we interpret the results correctly and we can't jump to conclusions about the nature of human and neanderthal interactions. ",
"\"The genomes of all non-Africans include portions that are of Neanderthal origin, due to interbreeding between Neanderthals and the ancestors of Eurasians in Northern Africa or the Middle East prior to their spread. Rather than absorption of the Neanderthal population, this gene flow appears to have been of limited duration and limited extent.\"",
"We can account for the 1-5%DNA with just a few interbreeding events. This 1-5% DNA does not mean that whenever and wherever we encountered each another we had sex. It may have been infrequent and inconsequential to the populations at the time. ",
"Humans and Neanderthals only overlapped for a short period of time in selected areas of our ranges. That means that the majority of Neanderthals probably never encountered humans. ",
"We don't know the types of these interactions. Just because we interbred does not mean the interaction was nice. I.E. It could have been preformed in the context of rape. We may not have wanted to interbreed, which is very important when we think about defining species lines. ",
"While modern humans share some nuclear DNA with the extinct Neanderthals, the two species do not share any mitochondrial DNA, which in primates is always maternally transmitted. ",
"TL;DR We were very different, both morphologically and behaviourally. It is more likely that we competed for resources then shared them. It was more likely that we were two separate species then subspecies. It was more likely that Neanderthals went extinct because of an inability to adapt to a changing climate and compete directly/indirectly with human populations than being absorbed into the larger human population.",
"Neanderthal Coexsistance with Humans"
] |
[
"This observation has prompted the hypothesis that whereas female humans interbreeding with male Neanderthals were able to generate fertile offspring, the progeny of female Neanderthals who mated with male humans were either rare, absent or sterile.",
"Or there could have been a small number of matings and the mDNA lost by drift. Or Neandertal mDNA might have been inferior (in the context of a mostly human rest of genome and selected out of existence. "
] |
[
"Or the small amount of neanderthal DNA could be explained by a common ancestor. There are many unknowns. The point is that evidence to date points to human-neanderthal hybrids being: infrequent, not ubiquitous across the two species, and probably infertile in some cases. Which indicates that hybrid vigour was low, which would lead to the conclusion that these two species were indeed speciating. "
] |
[
"How exactly did we determine that a mole = 6.02214179(30)×10^23?"
] |
[
false
] | null |
[
"The Avogadro constant is defined by ",
"NIST",
" as 6.022 141 29 x 10",
" mol-1. It is the relationship between constituent particles of a substance and the mass of said substance. ",
"The way we \"determine\" the value right now is making the assumption that an Avogadro's number of Carbon 12 atoms weights 12 grams (to clarify: 6.022 141 29 x 10",
" Carbon-12 atoms weighs 12 grams).",
"There's a whole history covered on the wikipedia page for the ",
"Avogadro Constant",
".",
"There's another great summary of the history ",
"here",
".",
"Today, there is a global effort to accurately measure the number. It's called, the ",
"Avogadro Project",
". They use high purity 1kg spheres of silicon, which are accurate to the spacing of 1 atom!",
"The website has some cool info. Check it out. \"The roundness delta of the finished sphere (being held above) is about 50 nm on a 93.6 mm diameter. It is believed to be the roundest object in the world.\""
] |
[
"I was under the impression that, as OrbitalPete said too, Avogadro's constant is defined as the number of atoms in 12 grams of carbon-12. Which means that it's not defined as any specific number but instead measured. And the number you have is an accurate measurement of that. Even the page you linked gives the uncertainty of the number which would suggest that it is indeed measured and not defined. I mean if you define something to some number why have any uncertainty there at all.",
"This could possibly change with the redefinition of units. Instead we could define Avogadro's constant to be some specific number and then mass would depend on that."
] |
[
"NIST is a defining body for the constant. Of course, NIST did not just make the number up. If you search their bibliography, you can find 69 citations that reference the word Avogadro. It is a highly measures constant, but at some point, someone has to define what the value is. NIST defines the value based on the available data. ",
"This is why I said that NIST defines the value as 6.022 141 29 x 1023 mol-1. It is to give a reference for where I get the number. It would not be erroneous to say that my chemistry book defines it as 6.022 x 10",
" mol-1. ",
"EDIT:",
"Check out this link ",
"PDF",
". Page 23 takes about the proposals of the fundamental definitions for the Avogadro constant:",
"The unit of amount of substance is called the mole, symbol mol, and the mole is \ndefined by specifying the mass of carbon 12 that constitutes one mole of carbon 12\natoms. By international agreement this was fixed at 0.012 kg, i.e. 12 g.\nFollowing proposals by the IUPAP, the IUPAC, and the ISO, the CIPM gave a\ndefinition of the mole in 1967 and confirmed it in 1969. This was adopted by the\n14th CGPM (1971, Resolution 3; CR, 78 and Metrologia, 1972, 8, 36):",
"\n",
"\n",
"\n",
"\n",
"It follows that the molar mass of carbon 12 is exactly 12 grams per mole,\nM(12C) = 12 g/mol.",
"In 1980 the CIPM approved the report of the CCU (1980) which specified that",
"\n",
"The definition of the mole also determines the value of the universal constant that\nrelates the number of entities to amount of substance for any sample. This constant is\ncalled the Avogadro constant, symbol NA or L. If N(X) denotes the number of entities\nX in a specified sample, and if n(X) denotes the amount of substance of entities X in\nthe same sample, the relation is n(X) = N(X)/NA."
] |
[
"What determines a \"match\" for a kidney transplant?"
] |
[
false
] |
I figure that blood type plays a huge rope but im sure there are other factors too
|
[
"Blood type and the HLA (human leukocyte antigen) alleles. HLA is expressed on all cells and is recognized by your immune system to distinguish 'self' and 'non-self' cells. HLA locus can vary between individuals and are more likely to be a match the closer related you are i.e. direct siblings, parents.",
"general explanation: ",
"http://www.ucdmc.ucdavis.edu/transplant/livingdonation/donor_compatible.html"
] |
[
"Hi, I work at a histocompatibility lab. tinyping, cmuadamson, JStanton617 are all correct. I just want to elaborate a bit more. ",
"In our lab, we do genetic testing to see what HLA alleles the patient and donor have. To evaluate compatibility, we look at a total of 10 alleles (A, B, C, DR, DQ). The patient can have 0 out of the 10 alleles that match with the donor and the transplant can still be viable. In my experience, the match mostly depends on donor-specific antibodies.",
"We also do antibody testing. Our antibody assays tell us what antibodies the patient has and the quantity. If a patient has an antibody to a donor antigen, then the transplant is said to have a high risk associated with it (ie more of a chance that the organ will be rejected by the patient). ",
"We also evaluate the risk of organ rejection via flow cytometry (Crossmatch). We extract lymph cells (T and B cells) from the donor sample and crossmatch it with the patient's serum. If the donor lymph cells react with the patient serum, then there is a high likelihood that the organ will be rejected. ",
"And as I mentioned above, a 0/10 allele match is OK, but we have to pay close attention to the patient's pre-transplant antibodies because there is a high chance that the patient will develop antibodies post-transplant (A delayed or chronic organ rejection can occur). Development of antibodies can also significantly lower the organ's survival rate inside the patient.",
"So, in summary, a PERFECT donor match includes: a 10/10 allele match, no donor-specific antibodies, and a negative flow crossmatch.",
"Hope that answered your question!"
] |
[
"Some alleles of the HLA are more common than others. If you have more common alleles you may find a match in 1:10,000, while others with rare variants could be up to 1:500,000"
] |
[
"Why do low pressure areas form at warm places if pressure is directly proportional to temperature?"
] |
[
false
] | null |
[
"You're referencing the ideal gas law. We use that law in a lot of our derivations for the behavior of the atmosphere, but you should remember local regions are not constrained to a constant volume. Subsequently, sometimes our observations are somewhat counter-intuitive.",
"In regards to your question, I usually have to think about it with two principles focused on a column of air. First, we ask what actually warmed the column of air? The warming of the column is usually related to solar heating. When the sun heats the air, it warms and, given the right conditions, it will rise. Rising air in effect leaves an absence of air below it, which is a low pressure region. Surrounding air will then fill in, lest a vacuum would occur.",
"We add that knowledge to the second principle: atmospheric pressure is essentially the weight of the air above you. When you have a warm column, the air expands upward. Air moves out of the column (usually at the height of any inversions). With air moving out, your reduce the amount of air above you, thereby reducing the pressure. I confess this also assumes the ideal-gas law works here too, but paired with the first principle, provides a good picture of what's going on.",
"Note, at the top of the warm column is a relative high pressure region due to convergence. The whole column in general though has reduced in pressure as long as air has moved out of it."
] |
[
"The volume of the air increasing due to the higher temperatures will mean that there will be less of it above you. The air cant keep going up the atmosphere forever so it'll move aside and you'll end up with less air in total above you."
] |
[
"To add to the other comments, wheb people talk about \"volume\" in this context they are referring to molar volume, or the volume per mole of gas. This is like a sort of inverse density. If we consider the ideal gas law, PV= nRT, we can divide both sides by n to get PV/n= RT. This form has a number of advantages- the main one is that it now doesn't depend on the gas being in a closed container. The quantity V/n is an intrinsic value, meaning that it doesn't depend on the amount of substance. Thus, in many thermodynamic equations the term \"volume\" and the letter V refer to the molar volume (V/n), and so the ideal gas law is given as ",
"PV = RT"
] |
[
"Given what we know now about the coronavirus how big a role does asymptomatic transmission play in spreading the virus?"
] |
[
false
] |
[deleted]
|
[
"It’s been difficult to separate “asymptomatic” from “presymptomatic” and “mild symptoms”. The latest review I’ve seen determined that careful tracking found symptoms in most patients, with just 15-40% being completely asymptomatic (",
"Estimating the extent of asymptomatic COVID-19 and its potential for community transmission: systematic review and meta-analysis",
"). Earlier studies had much higher levels of “asymptomatic” patients, but mainly because they included presymptomatic as well - patients who were infected and shedding, who showed no symptoms at the time of diagnosis, but who would eventually develop at least some symptoms (and potentially serious symptoms). ",
"We know the presymptomatic patients are important sources of transmission:",
"Presymptomatic transmission is thought to be a major contributor to the spread of SARS-CoV-2. Modeling studies from China and Singapore estimated the percentage of infections transmitted from a presymptomatic individual as 48% to 62%. Pharyngeal shedding is high during the first week of infection at a time in which symptoms are still mild, which might explain the efficient transmission of SARS-CoV-2, because infected individuals can be infectious before they realize they are ill",
"—",
"Pathophysiology, Transmission, Diagnosis, and Treatment of Coronavirus Disease 2019 (COVID-19)",
"It’s harder to get a handle on exactly how much transmission comes from truly asymptomatic people, for obvious reasons, but the general sense is that they can and do transmit the virus, but not as much as presymptomatic patients. ",
"Five studies provided direct evidence of forward transmission of the infection by asymptomatic cases. Overall, there was a 42% lower relative risk of asymptomatic transmission compared to symptomatic transmission (combined Relative Risk: 0.58; 95% CI 0.335-0.994, p=0.047). … Our estimates of the prevalence of asymptomatic COVID-19 cases and asymptomatic transmission rates are lower than many highly publicized studies, but still sufficient to warrant policy attention.",
"—",
"Estimating the extent of asymptomatic COVID-19 and its potential for community transmission: systematic review and meta-analysis",
"This is a topic that’s being intensively studied, and so expect more information to keep appearing. Still, it does seem that much of the early confusion is settling down and experts are reaching a general agreement that asymptomatic infections are important, and a particular challenge for containment, but still represent a minority of infections and a smaller minority of transmission."
] |
[
"asymptomatic spread can be dangerous in the sense of ",
"- psychologically people think \"oh I don't have it, lets go party\" and this causes spikes which we witness when people organise huge events like a 400 guest wedding",
"- if you are careless and assume \"I will just avoid sick looking people\" you are just as likely to come into contact with an asymtomatic spreader and infect people in your close circle, since you saw nothing and assume therefor you also don't have the virus",
"the importance of making the public aware about asymptomatic spreading was, that the world has not seen such a highly infectious disease with such volatile symptoms (from death to being 100% unaware) and that when there is a new illness, scientists and doctors know very little of how to combat the virus.",
"This was a \"best case pandemic\", I look at it as a fire drill which severely crippled global economics - but in worst case this could have killed so many more people. Worst case, we could be looking at the shambles of humanity, if it was a more aggressive virus. Governments could crumble, first aid would be unable to respond, basically a societal collaps.",
"and if we are looking at a few countries, who were brought to their knees out of refusal to coorporate, listen to science and take simple precautions as to be aware of asymptomatic transmission, I'd hope that everyone out there is doing their very best to be part of the solution. Not the spreading"
] |
[
"well, first you need to separate asymptomatic cases from \"currently asymptomatic\" cases. It's turns out that the peak of the infectivity for symptomatic cases is 2 days before symptoms onset. ",
"It's also starting to become clear that people that will never experience symptoms ",
" will infect less people. But measuring exactly their contribution is hard. If you also account for pre-symptomatic spread... you realize that, while this might be a scientifically interesting question, it's not a knowledge that can help you in drafting policies.",
"There's a very comprehensive editorial on nature about the latest review on the topic\n",
"https://www.nature.com/articles/d41586-020-03141-3",
"Sharing the elevator with three people who have COVID, but are asymptomatic, is less risky then having dinner with a family member who has a cough.",
"Right conclusion for the wrong reason. Family meetings are dangerous because you are in the same room for a very long period of time (cough or not... of course in covid times no one is going to stay in the same room as someone with a serious cough!)",
"At the same time, riding in an elevator even pushed against a stranger is \"safe\" because in those 20 seconds there's no way that an infected person will emit enough viral particles for a virus with such a small attack rate. (unless they sneeze or cough on you maybe)"
] |
[
"[Medicine] What is special about peanuts that make some people extremely allergic to them?"
] |
[
false
] |
Why are some people allergic to peanuts in particular? Why is ingesting a peanut to these people akin to ingesting poison to others?
|
[
"Peanuts contain high levels of several heat-stable proteins, collectively known as Ara h proteins (from the scientific name ",
"), that can act as antigens. Some people develop IgE antibodies against these antigens, which causes a peanut allergy. Sources: ",
"https://link.springer.com/article/10.1007/s11882-014-0429-5",
" and ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4451826/",
"In particular Ara h1 is quite stable, ",
"and the IgE-interacting epitopes can survive digestion.",
"This is why peanut allergies are more common than allergies to other legumes (e.g. peas).",
"Also as ",
"/u/DocWsky",
" mentioned, peanuts are pretty common, so there are many opportunities for exposure."
] |
[
"If the antigens are proteins, why can't some people with peanut allergies eat peanut oil fried foods? Are there traces of the protein in the oil?"
] |
[
"If a chemist were to purify peanut oil it would be tolerated by an allergic person. Peanut oils that are comercially available are not \"pure\" and contain trace protein contaminants that are enough to trigger anaphylaxis."
] |
[
"In a desert, what is under all of the sand?"
] |
[
false
] |
I've always wondered, in stereotypical deserts with plentiful sand dunes, how deep does the sand go? And what's under the sand? Water? Dirt? Stone?
|
[
"I'm going to focus on the Sahara, because that lets me crib from ",
"this comment",
" I made a year ago. You can apply this same stuff to any desert, though!",
"First, I'm required to point out that deserts like the Sahara, contrary to popular belief, are mostly ",
" covered in sand dunes. ",
"Here's a map",
" of all the dune fields (in yellow) in the Sahara. Most of the Sahara looks something like ",
"this",
"- a rock-strewn sandy soil with a hard crust (\"desert pavement\"), like what you see in the Mars rover photos but with scattered bushes. The dunes covered places that look like that, so imagine a rocky soil a few meters thick at the bottom of the dunes. Then the groundwater level is usually somewhere above the old ground level, so imagine that it's soaking wet and muddy. That's what it's like down there. The dunes are not like glaciers- they don't rub rock formations smooth once they're buried. They mostly preserve it whole. (For an extreme example of this, see the ",
"camel thorn trees of Namibia",
" which were buried centuries ago and only recently uncovered as the dune kept migrating.)",
"Another thing to consider is where all that sand came from. You get sand dunes when the environment is producing more new sand grains faster than it can stabilize them into rock. The Sahara has so many dune fields because when the climate was wetter about 6000-10000 years ago, there were massive lakes covering what is now desert. When these lakes dried up, their sandy bottoms provided an ample source of sand to make dunes (and an ample source of nutrients in the form of wind blown dust to feed ",
"the Amazon rainforest",
"). ",
"Here's a map",
" (snipped from ",
"this paper",
") of all the huge lakes and alluvial fans (in blue and gray) that used to cover the Sahara. Notice how many of them are in the same parts of the desert that now have dune fields in that earlier image? In many places, the current dunes are directly over the old lake bed, so the bottom of the dunes is exactly what you would imagine a dried up lake to be like. See ",
"this radar image",
" from ",
"an earlier askscience",
" question. The top of the gray bar is the top of the dunes, and the red line is the bottom. It's so flat because it's an old lake bed. There probably aren't mountain ranges or other huge topographical features buried under the sand."
] |
[
"This is a great answer! I love that you punctuated it with links and relevant images, it really helped me visualise what you were talking about."
] |
[
"I've noticed my sugar do that when I pack it too tight. It got all chunky and not flowy"
] |
[
"Could the red tint of Europa's ice be cause by biology? Could this be confirmed without taking samples?"
] |
[
false
] | null |
[
"Possibly, this is an example on earth",
"http://en.wikipedia.org/wiki/Blood_Falls",
"It could just be minerals of iron in the ice, which don't have to come from a biological source at all. "
] |
[
"Good info, thanks. With the imagery/data we have - would NASA be able to tell the difference? Would some kind of spectra analysis help? I find it kind of mind blowing that maybe the surface of this moon is stained with life and we might not even realize it."
] |
[
"It is indeed interesting, I can't wait until they send a probe to some of the moons of Jupiter and Saturn that can send back some good data.",
"As for being able to tell the source of the iron etc, I don't think that any imaging techniques or spectroscopy that could determine that. It can tell you what is there, but not how it got there."
] |
[
"Why are bodies of water (such as lakes or ponds) calmer at night?"
] |
[
false
] |
I walk my dog around our complex's pond every morning and night, it seems a regular occurrence that the water is choppy during the morning/day and clear as glass at night. When I think about it, I've noticed this on lakes too (grew up living next to one). Is this just my imagination or is there some real science behind this?
|
[
"Its when they are sleeping. J/k. To really answer this question, you want to know what causes waves, and that is wind. So you then need to ask what causes wind... but here is my late night answer.",
"Waves are caused by winds blowing over the water. (we will leave out tidal forces for this discussion). During the day, the sun light warms up the land surrounding the body of water at an inconsistent rate, with the surface of the land getting warmer than the surface of the water. This temperature differential causes winds.",
"As night falls, the land cools, and the land and water surface areas become equal in temperature , the wind effect dies down.",
"Winds in general are also calmer at night due to the land surface temperature cools off and levels out quickly after sunset.",
"Edit:typos."
] |
[
"Wow, I totally overlooked the concept of heat causing wind (which obviously causes waves). Such a simple answer that I feel embarrassed for asking now!",
"I wouldn't be surprised to hear there are other minor forces at work here too, but I'm pretty satisfied with this answer assuming it's truly the primary factor. Thanks for the explanation."
] |
[
"As an addition to this. At night, it tends to be less windy the closer you get to the ground. Wind closer to the ground tends to find it origin in temprature differences on the ground, and wind higher up is due to pressure difference on a more grand scale. That's why windturbines even work at night, when it seems like there is no wind at all."
] |
[
"If energy can't be created or destroyed how much energy is there in the universe?"
] |
[
false
] |
Is there a way we could estimate this value ?
|
[
"It is not actually necessarily true that energy can't be created or destroyed (which, in more formal language, is the statement \"energy is conserved\"). While we can often define something called the \"total energy\" for a system, in doing so we're making certain technical assumptions about it (specifically that there's a sense in which it's 'time-translation invariant'). When you try to apply those assumptions to the universe as a whole, you have to jump into the mathematics of the general theory of relativity and you discover that you have to be more precise about definitions. While I could go into more detail, it's been done elsewhere by people who had the leisure of taking the time to do it right. For two of my preferred examples, see",
"Sean Carroll's article titled ",
"Energy is Not Conserved",
" and",
"John Baez's more technical article on ",
"energy conservation in general relativity",
".",
"The short version of the answer to the question of whether energy is conserved in the general theory of relativity is given in the first line of the Baez article:",
"In special cases, yes. In general — it depends on what you mean by \"energy\", and what you mean by \"conserved\".",
"Ultimately, I tend to side with Carroll in taking the position that",
"When the space through which particles move is changing, the total energy of those particles is not conserved.",
"Since our universe is expanding, this statement implies (as the article title states) that energy is ",
" conserved, in which case the \"total energy\" isn't constant.",
"That said, as alluded to in Carroll's article and worked out in some detail by Baez, there are other possible interpretations of the question and other possible answers. If you do it right, you can come to the conclusion that the total energy ",
" conserved, and that it's ",
". There's the positive energy of matter, radiation, et cetera, and then a negative energy of the gravitational field. But I tend to agree with Carroll's perspective in that",
"I personally think it’s better to forget about the so-called “energy of the gravitational field” and just admit that energy is not conserved..."
] |
[
"Lawrence Krauss explains a little bit about this in laymans terms in his book 'A Universe from Nothing'. Something something about how the total energy of space increases as space itself expands, and ultimately how he believes it is possible for something to originate from nothing because of quantum mechanics.",
"Did I already say I'm a layman when it comes to quantum mechanics?"
] |
[
"According to current theories, the total energy of the universe may be zero.",
"http://www.lifeslittlemysteries.com/1224-total-energy-universe-zero.html",
"http://en.wikipedia.org/wiki/Zero-energy_universe",
"http://www.astrosociety.org/pubs/mercury/31_02/nothing.html"
] |
[
"How did the icecaps end up so much higher than ocean level?"
] |
[
false
] | null |
[
"What do you mean exactly? If you're talking about sea ice, it's floating in the water just like and ice cube in a glass of water. If you're talking about continental glaciers, they form not from seawater but snowfall accumulated over many thousands of years."
] |
[
"The latter, oh that's so obvious now that you said it..."
] |
[
"There's a caveat to that, however.",
"East Antarctic ice fields are many thousands of feet above sea level, supported by very thick and strong cratonic crust. In West Antarctica, however, the earth's crust has undergone rifting and thinning, is no longer able to support the weight of its icecap, and has slowly sank into the mantle. The bedrock across much of West Antarctica is actually below sealevel by up to 200 meters.",
"This is why the West Antarctic Ice Sheet (WAIS) is very vulnerable to warming temperatures. Right now, the weight of the ice on the crust is enough to prevent any water from leaking downslope into the interior of West Antarctica; however, as the WAIS thins, pressure from the ocean can leak more and more water beneath the ice sheet, which can potentially lead to catastrophic ice sheet collapse.",
"If you're interested, here's a (hopefully) accessible discussion on the dynamics involved:",
"https://theconversation.com/the-west-antarctic-ice-sheet-is-in-trouble-but-the-ground-beneath-it-may-buy-some-time-98368"
] |
[
"Using dry ice to chill a drink?"
] |
[
false
] |
[deleted]
|
[
"I think there won't be a problem CO2 is used to carbonate drinks anyway. There are even DIYers who used dry ice in sealed containers to carbonate a whole bunch of weird things like fruits. ",
"The only risk is over chilling your drink and giving yourself brain freeze. You would also have to wait for all the dry ice to sublime before downing your drink if you want to avoid bursting your guts."
] |
[
"here's",
" the tutorial. Imagine pieces of fruits that fizzes in your mouth like alkazelsers."
] |
[
"Please explain carbonated fruit"
] |
[
"Does cooking meat for too long lower its nutritional value?"
] |
[
false
] |
My ex refused to use a crock pot because she was convinced that simmering meat for 8 hours broke down the proteins in it to the point that they were damaged in some way and less healthy than meat cooked in a more traditional way. Is this nonsense?
|
[
"Proteins are broken down in the digestive tract anyway. Generally you don't absorb intact proteins but rather the individual amino acids they are composed of.",
"For this reason the denaturation of proteins during cooking is not a problem at all. On the contrary, it will aid in their digestion.",
"However, if the amino acids themselves are decomposed, that will indeed reduce the nutritional value of the food. Fortunately amino acids are quite stable compounds. ",
"Glutamine",
" has the lowest heat tolerance and is destroyed at about 185 °C. Other AAs can withstand temperatures between 200–300 °C."
] |
[
"Actually, studies have shown that yes, cooking does break down proteins, but this actually allows humans (and mice) to absorb more usable energy from cooked meat. I believe the theory is that you don't have to spend as much energy digesting, and the proteins are more readily taken-in. In an experiment with mice, researchers gave one population cooked meat, and the other uncooked and they seem to get more energy from the cooked meat. ",
"I'm not sure about other species, but basically: proteins break down, but nutritional value goes up. "
] |
[
"I think this answers it pretty conclusively. Thanks!"
] |
[
"endangered species solution?"
] |
[
false
] | null |
[
"Komodo dragons actually have a ZW sex determination system, that is, females are ZW at the sex determining locus, while males are WW. In this case, females produce a haploid egg, then the chromosomes double to produce a male that is homozygous at every locus. Any recessive deleterious alleles are going to show up real quick..."
] |
[
"Chromosomes which determine gender are not universal. XY is limited to most mammals.",
"Many cold blooded (though cold blooded is a bit of an outdated term, that's another question) animals are either hermaphroditic or have gender determined by environmental factors. Because they have no sex chromosomes it's much more reasonable for them to switch genders at some point in their lives or to do tricks like parthenogenesis."
] |
[
"Irrelevant question: are the chromosomes actually in a shape which looks like a Z or W?"
] |
[
"Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"I see allot of questions unanswered, and it bothers me is this usual?"
] |
[
"How much energy do typical fast-breeder nuclear reactors produce compared to water reactors? Is fuel conversion a tradeoff for lower energy output, or are they just 'better' overall?"
] |
[
"No, flamethrowers need oxygen to burn. It might be possible to find the right exothermic mix that replicate what a flamethrower does but a regular flamethrower wouldn't work. It would just squirt fuel around."
] |
[
"Where is everything?"
] |
[
false
] | null |
[
"I concede that it's a philosophical question, but don't you consider where all things must be?",
"That isn't a philosophic question, it is a semantic one."
] |
[
"I think it really is more of a philosophical question. Sure, anything that exists is somewhere, but likewise, that place is only there because it exists. I'm really not sure that is a question that HAS an answer beyond the tautological one: Everything is where it is. Just being makes it there. To think that all that exists exists at a central location relative to something else is illogical - if there's something more than the universe, then that is the actual universe and we're simply measuring and deriving incorrectly.",
"As for our measurements... both time and space are measured relatively from reference points. On a planet, there's no shortage of reference points. On a planetary level, the obvious anchor is the nearest sun (or to be fair, the largest gravitational mass that things orbit around - assumed to be a sun.) In the Milky Way, it would be the ",
"galactic center",
", basically the axis of galactic rotation. I'm a far cry from an astrophysicist, but I suspect beyond that, there would either be another common rotational point, or maybe we'd lose our frame of reference or just attempt to measure things from the Milky Way."
] |
[
"Observers moving at different velocities can't even agree on the spatial location or velocity of other objects.",
"You're really talking about philosophy, not anything relevant to science."
] |
[
"Ask Anything Wednesday - Engineering, Mathematics, Computer Science"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"On the I.S.S. they are continuesly learning about space agriculture. I know that NASA has been doing experiments and trials with soils and different types plants.\nMy questions are, has NASA looked into self contained and sealed hydroponics systems? Other than no gravity and the proper seal of the fluids, what would be some other issues that would cause problems/concerns?\nIf someone could let me know it would be appreciated. Thanks."
] |
[
"You might be interested in ESA's ",
"citizen science hydroponics programme."
] |
[
"It still looks in in infancy stages and 5 years no updates. And isn't lettuce not very nutritious."
] |
[
"Is there a physical Limitation on how dense we can store data on a HDD Platter?"
] |
[
false
] |
Ok, from my understanding, correct me if im wrong, we are currently reaching the physical limitation of cpu transistors. But what about good old HDD's? They seem to manage to cram more and more data onto 1 platter, but is there a phyical limitation on how much information we can store on 1 platter?
|
[
"A key limit in magnetic storage is that random thermal energy alone can alter the magnetization of suitably small crystalline regions (grains, which constitute magnetic domains). Near this limit, we can no longer depend on the information persisting over the necessary operating time. This is discussed well ",
"here",
"."
] |
[
"is there a physical limitation on how much information we can store on 1 platter?",
"Of course. There is only a finite number of atoms in the readable part of a HDD platter, so even if we could assign one bit per atom (and we are very, very far from that) the storable information would still be finite (albeit enormous).",
"The total number of particles of any kind in the observable universe has been estimated to be around 10",
" so even there we have a limit on what we can ever hope to store."
] |
[
"A steady temperature alone is enough to randomly erase the data over time, if the grains are too small. So you could keep the hard drive at a consistently lower temperature. I don't know if this has been implemented in applications. You also look for materials that exhibit ",
"as high magnetization as possible",
". And you use ",
"geometric",
" ",
"tricks",
"."
] |
[
"how does chirality come into play when manufacturing pharmaceuticals?"
] |
[
false
] |
I understand what it is I just dont get how a mirror of a molecule would come into play. are they connected? do they come in pairs and the other molecule has to be flushed out? does it just happen by accident that a molecule chiral partner slips into the mix and isnt easily spotted because of its likeness? please explain.
|
[
"not quite, it's the difference between generic drugs and the brand's 'new and improved' drug -- eg omeprazole vs esomeprazole"
] |
[
"If a molecule has two chiral forms (enantiomers), laboratory synthesis will generally make a 50/50 mix of the two. That's just how it happens, because they're so similar. The R and L enantiomers have identical chemical properties across the board, and can be very difficult to separate.",
"It's only when you get into living things that chirality really starts to matter. Receptors and enzymes can be very finicky about handedness."
] |
[
"Pharmacy student checking in. There are many many chiral drugs. Ibuprofen (Advil) is a great example. Advil's S enantiomer is more biologically active, but the R enantiomer is not toxic and is actually converted to the S enantiomer ",
", so Advil is sold as a racemic mixture because while chiral molecules can be selectively synthesized and/or purified, it is expensive. Then there are drugs like Naproxen (Aleve). Naproxen's S enantiomer is active, but its R enantiomer causes liver damage and has no analgesic effects. Then we get to everyone's favorite chiral drug example, thalidomide. Thalidomide's S enantiomer is an excellent morning sickness drug for pregnancy, but its R enantiomer causes severe birth defects, and this was not caught until after the drug was put on the market. ",
"As for the purity of these drugs during manufacturing, some drugs such as Ibuprofen are just synthesized in racemic mixtures and distributed. There is no harm in taking the R enantiomer, so why bother spending lots of money to purify it? Drugs like Naproxen generally utilize chiral reagents to selectively produce the active enantiomer (this is cheaper than synthesizing a racemic mixture and then discarding half the batch after enantiomeric purification, but more expensive than just a racemic mixture, which is why Aleve is more expensive than Ibuprofen). Then drugs like thalidomide are pulled from the market entirely because the enantiomers can interconvert in vivo via an acidic hydrogen. As for purity, the FDA and USP set purity standards for all medications, and the enantiomers (if they need to be excluded) have maximum levels with which they can still be in the final product as trace chemicals (these are very low concentrations). ",
"There are both chemical and physical methods for spotting enantiomers. Some chiral salts have one enantiomer that is more soluble than the other, polarized light passing through a mixture will be rotated less than it would if it was a pure enantiomer, etc. So it is not really possible for \"bad\" enantiomers to slip by IFF proper testing is conducted and the molecule cannot interconvert on its own."
] |
[
"My cooler is half full with a mixture of 50% ice cubes and 50% cold water. I want to add more ice. Should I drain the water first?"
] |
[
false
] |
This dilemma has plagued me since my freezer/fridge died a couple of weeks ago. Does the cold water help or hinder the future longevity of the coldness?
|
[
"The water definitely helps. Water has a really high specific heat. This means it can absorb a lot of energy without changing temperature much. Either way, you are going to lose ice at roughly the same rate (if we're talking about an ideal theoretical cooler). But at once all your ice melts, if you didn't drain the water, then you have a far greater heat absorbing (read: chilling power) capacity. Even after all the ice melts you still have a lot of water just above freezing temp, which is plenty to chill or keep cold a bunch of beverages.",
"The warm air taking the waters place contributes too but I think it's probably somewhat negligible. ",
"The only way I can think the water would decrease your cooling longevity is it increases the contact with the walls of the cooler, which could conduct heat into the cooler faster. But I would guess this is negligible unless your cooler isn't well insulated.",
"ASK MYTHBUSTERS!! I bet they would do it."
] |
[
"I have had the same dilemma. I think the answer is this: ",
"If the food is from the freezer (T< 0C), empty the water. If it is from the refrigerator (T> 0C), keep the water.",
"The water/ice mixture is going to tend to keep everything at a temperature of 0C. If your goal is to keep the temperature less than that, you can remove a substantial amount of heat from the system by dumping the water."
] |
[
"Yes, but air is such a terrible heat conductor compared to water. This is what mainly leads to my dilemma. "
] |
[
"Are there any known cultures where it is or was common to practice sex openly in front of others, including children?"
] |
[
false
] | null |
[
"You're thinking of the ",
"Etoro",
", a tribal group located in Papua New Guinea. "
] |
[
"I am not so sure about this one. Our anthropological sources, who were mainly missionaries or 'proper' 19th century men, were not so keen on recording sexual practices, and if they did, they often did it with an exotic message in mind (to show how 'uncivilised' or different other peoples were).",
"I read that in the Middle Ages in Europe, sex would have been openly practiced in the house, so in front of one's own children, as there was often only one bedroom. Also, in inns sex would have been public, again because of the single sleeping quarter available. Couple this with the double function of many inns as brothels, and you get almost roman orgy-like things going on in those places.",
"I think it would be safer to put the question the other way around, and question in which societies, and how strongly, the taboo on sex was maintained."
] |
[
"Could you post a source for this?"
] |
[
"With the introduction of vaccines, even if a variant isn’t strictly “covered” by the vaccine due to changes in proteins, would there be enough “training” of the body’s immune system on how to deal with a corona virus that the body would be more efficient if infected later?"
] |
[
false
] |
At the start of the Pandemic, a lot of the concern was about the novelty of the virus and the fact that the majority of humans would most likely not have contacted a coronavirus and so the body wouldn’t know how to efficiently “fight” it This is often cited as why the flu is no longer (generally) as bad, due to “people” having seen some form of flu at some point in their life.
|
[
"Short answer: Yes",
"Long answer: Probably",
"When you get exposed to an antigen (by getting infected or by getting a vaccine), your body generates B cells (generate antibodies) and T cells (recognize and kill infected cells). ",
"I'll focus on B cells: ",
"First, there will be a B cell that, just by random chance, has some affinity for the antigen. That B cell will divide like gangbusters but, in doing so, will undergo something called \"somatic hyper mutation\". This means that the DNA that codes for the \"recognition\" part of the B cell will be modified in countless ways. Invariably, some of these new B cells will be even better at recognizing the new antigen, and these will be selected for. In the end, you have a population of B cells producing antibodies that have been selected for their ability to bind the novel antigen really well.",
"Generally, these antibodies will also be good at binding other things that ",
" a lot like the first antigen so small mutations in the virus won't be able to escape.",
"",
"A (silly) analogy:",
"Gang of criminals from London moves into your neighborhood and your crime-fighting robot AI generates anti-gang drones. Some recognize the tattoos of Big Ben that all the members have, some recognize the Union Jack, some listen for their specific slang words (\"Bloody hell!\") or go after mini Coopers. The drones are, of course, tested first to make sure they don't accidentally recognize civilians (in the body this is called \"negative selection\").",
"Obviously, if a brand new Viking gang moves in and they're from Norway and drive motorcycles and wear furry horn hats, your crime fighting drones will not be much help. If, on the other hand, another gang from London moves in, your current drones might work pretty well and require few adjustments.",
"A bit more of a stretch might be a gang from Australia. Some of your drones might recognize just enough aspects of the new guys to keep them at bay while a new batch of drones that goes after cans of Fosters and dudes with crocodile teeth sewn into their hats comes online."
] |
[
"I would imagine it depends on the mutations that occur.",
"There are hundreds of \"variants\" since small microbes like viruses replicate so often. Mutations occur inevitably. I think its a matter of the spike protein of the virus and if that mutates.",
"Antibodies attach to the spike on the surfaces of viruses to stop them from attacking cells and signaling your immune system to kill them.",
"There must be a point where if there are enough mutations of the viral spike protein, that the antibodies no longer recognize the microbe and therefore do not attach and stop the virus. ",
"One analogy for example, if you start with a human and slowly replace its physical features with a monkey. There must be a point in between where you cant call this \"thing\" a human and instead consider it a monkey.",
"This point I imagine this isnt a clear boundry and instead is a gray area. \nSo I would assume the gray area for antibodies means some fight the virus and some don't. Which means only some \"protection\".",
"But these are just my thoughts.",
"Any other info to support or refute, or any feedback would be appreciated."
] |
[
"Lovely analogy.",
"What people don't realize is that antibodies bind to their targets partially even if they aren't a perfect match, but are close. Effectiveness fades gradually before it falls off a cliff to 0.",
"Now if a mutation causes the virus to bind to ACE2 more efficiently, enter the cell more quickly, or replicate faster, then the spread within the body will be faster and the viral load higher. But the immune system of a vaccinated person will already have a close match, so if that is the starting point for the somatic hypermutation to generate new antibodies, the immune system should ramp up more quickly than someone who has never been exposed.",
"It's an arms race."
] |
[
"If plants use water to produce oxygen, does that mean that over time the total amount of oxygen on earth slowly increases?"
] |
[
false
] |
As I understand it, photosynthesis in plants convert water to oxygen, and it converts carbondioxide molecules into sugar molecules. Plants don't actually convert carbondioxide into oxygen. The carbondioxide gets converted into sugars, which when the plants decay actually put carbondioxide back in the air, or which will end up in the ground. . So, considering that, does that mean that over time the total amount of oxygen on earth actually increases? Bonus questions: - What does this mean in terms of climate? - Does this mean that the earth's atmosphere slowly gets thicker, or does oxygen simply float out into space?
|
[
"Oxygen does increase over cycles, but then it falls back down.",
"In addition to producing oxygen by taking in carbon dioxide, plants ",
" animals take in oxygen and produce carbon dioxide through cellular respiration.",
"This process creates the compounds we use for energy storage.",
"Um, neither. To produce O2, CO2 must be absorbed. Thus we end up with a C and an O2 (putting it simply, the real reaction is quite larger). No new matter is created or lost, it just moves somewhere else. ",
" gases are produced, but they essentially have the same atomic composition, just chemically rearranged. Some are kept in the plant until it dies and is later digested."
] |
[
"The atmospheric balance is dynamic - it can and does change over time. However, there are various processes in action, some of which tend to stabilise atmospheric concentration and others that exacerbate it.",
"In the first instance, plants are one stage of a cycle. While plants do create both oxygen and sugars (among other things) the also respire - they use those sugars, 'burning' them with oxygen to fuel cellular functions. Animals eat plants for their sugars (and stuff) and 'burn' the sugars with oxygen (producing water and carbon dioxide).",
"The balance between photosynthesis and respiration is not automatically in balance - but if there are more plants that means more food for herbivores. So an increase in photosynthesis tends to be offset by an increase in numbers of animals.",
"Outside of that, volcanoes add gasses to the atmosphere and the oceans tend to act as a stabiliser (they absorb and emit gasses).",
"More Carbon Dioxide in the atmosphere tends to make it easier for plants to photosynthesise (higher partial pressure makes the gas more available). This encourages plant growth and given one source of CO2 is fossil fuels, puts both more carbon and oxygen into the system. It would seem plausible that the greater plant growth would offset the extra CO2 - if it weren't for all the other factors...",
"Oxygen forms about 21% of the atmosphere. CO2 forms about 0.04%. A small increase in CO2 has a disproportionate affect on temperature compared to oxygen. Oxygen is not a significant green house gas while CO2 is. Therefore we care about, and talk about very small absolute changes in CO2. A similar (absolute quantity) change in oxygen makes very little difference to temperature or other long term trends in comparison.",
"Hence, yes there are changes in oxygen composition of the atmosphere. We tend not to focus on these changes very much because changes in other gas proportions make hugely more difference to living conditions. But there are bounds on the degree to which oxygen can increase - one of them being the carbon supply.",
"TL;DR the system isn't static. It is complex with many influences. Oxygen levels cannot increase without limit but do vary and may be increasing now."
] |
[
"On a geologic time scale, yes, but it depends on the system and what is present to use, sequester, or release oxygen. There are many ways that the system is in flux, take a look at the ",
"Great Oxygenation Event",
", about 2.4 billion years ago. Bacteria slowly started to \"poison\" the atmosphere with oxygen, but gases are in constant flux, being absorbed, deposited, fixated, and released."
] |
[
"Is the universe as a whole \"heating up\" due to the stars everywhere outputting tons of energy (radiation, solar winds, supernovae)?"
] |
[
false
] |
Also, might this explain the accelerating expansion of the universe? ("dark energy")
|
[
"The universe is actually cooling, not heating up. Energy is conserved. Neither created nor destroyed. If you take a constant amount of heat and spread it over an increasingly large area, the temperature everywhere is dropping.",
"Also, might this explain the accelerating expansion of the universe? (\"dark energy\")",
"Nope, totally unrelated."
] |
[
"You can have a closed system heat up. Say I'm in a closed system and I have a match and some flammables. When I light the material on fire, the closed system will heat up. Energy is still conserved."
] |
[
"You're thinking of a closed system that has a fixed volume. Not a system that's expanding.",
"The heat you see at any one point will go down as the energy-density drops. And density drops when volume increases."
] |
[
"Why do we use three phase instead of two phase?"
] |
[
false
] |
I understand why we use three phase electricity instead of 4,5,6 etc but why don’t we use 180 degree shifted two phase systems? Thanks in advance
|
[
"The main benefit of 3-phase power is that the available power is never 0. ",
"A 180-degree shifted 2-phase system would actually be very similar to the 1-phase system that most household outlets provide. One of the downsides of this is flicker. Electric devices must contend with short periods of no power ",
" ",
" times a second."
] |
[
"120 times a second, actually. The wave crosses the x-axis twice from crest to crest."
] |
[
"In a 3-phase wye system, the neutral current is theoretically zero if each phase is loaded equally, ie ",
"sin(a) + sin(a + 120°) + sin(a + 240°)",
" is 0 for all a.",
"This is not true for 90° 2-phase, and 180° 2-phase has no inherent ",
" information that would compel a motor to always spin a certain way.",
"PS: stepper motors use 2-phase AC."
] |
[
"Scientists always say that most of the stars today were created when bigger stars died. I always thought bigger stars died when they ran out of hydrogen, where does the hydrogen for the new stars come from then?"
] |
[
false
] |
Thanks for the answers in advance, I am really curious since this question popped up in my mind several times over the last few months!
|
[
"Stars aren't created from the 'ashes' of dead stars. All stars pretty much form the same way: from collapsed clouds of hydrogen gas, which is itself left over from the big bang. ",
"These gas clouds get 'enriched' (or 'polluted,' depending on how you want to look at it) by the heavier isotopes/metals produced by earlier generations of stars. For example, we generally think older stars will be more metal poor because there is a good chance they formed from gas that was more pristine than gas that is available today. Observing the abundances of heavy metals in stars is actually one method of figuring out what 'generation' a star is and for figuring out what stellar processes were happening during different epochs. "
] |
[
"I would like to add that a star does not fuse ",
" of the hydrogen in it. In fact only the material in the core is fused. As the hydrogen in the core runs out they begin fusing heavier elements, which makes the star hotter inflating its size significantly. The outter layers of the star will eventually be shed as the star dies, regardless of the method of its eventual death. Therefore, a significant amount of hydrogen will be thrown back out into space, along with those heavier elements, that can be used to form new stars."
] |
[
"Most of the hydrogen in a star is only used for its weight, which enables the fusion in the stellar core."
] |
[
"Why did nucleosynthesis in the early universe allow neutrons to merge quickly with protons, but not allow protons to merge with each other?"
] |
[
false
] |
At the time, was the pressure and temperature too low for this to happen?
|
[
"Two protons merging forms Helium-2, which is very unstable and nearly always decays back to two protons. There is a (very) small chance that helium-2 might decay to hydrogen-2 (deuterium), which is stable. (This decay is what powers the Sun, incidentally)",
"Deuterium is stable, but only just and at temperatures higher than 0.1 MeV (about 1 GK) it will be destroyed. So when temperatures are hotter than this, nucleosynthesis essentially does not occur. Overall the time for big bang nucleosynthesis is about 17 minutes.",
"The cross-section for this reaction is about 10",
" b, and the proton density is about 1",
" /cm",
" during BBN. Combining these we can estimate a reaction rate of approximately 1",
" /s/proton. And so over the 17 minutes that BBN happens we get 1",
" reactions per proton. As you can see essentially we get no deuterium produced from two protons merging.",
"Edit: I tried to find for comparison the cross-section for proton+neutron fusion, and it seems to be on the order of 1",
" b for these energies. So as you can see, that's about 1",
" times more likely!"
] |
[
"I think it's because ",
"p + p -> d + e",
" + ν_e",
"Is a weak-mediated process, while ",
"p + n -> d + γ",
"Is EM. So it's many, many times faster. I think this is the main factor.",
"Primordial nucleosynthesis happens a while after the decoupling of the weak force, so weak interactions have already become \"frozen\" and literally weak as they are at room temperature."
] |
[
"Exactly the response I was looking for. Thank you very much. Also, do we estimate the time to be 17 minutes due to the expected conditions at the start of the Big Bang and extrapolate the conditions in which nucleosynthesis would occur and thus the time?"
] |
[
"Where does the energy for osmosis to work come from?"
] |
[
false
] | null |
[
"There is ",
" in having a membrane separating two compartments with a concentration gradient, and that's where the energy comes from."
] |
[
"Indeed, a system where both compartments have equal concentration has higher entropy than one with a concentration gradient."
] |
[
"Just wondering, would it have anything to do with entropy?"
] |
[
"Why do red letters on a blue background seem to shimmer or flash when viewed in peripheral vision?"
] |
[
false
] |
I have a t shirt that’s deep blue but has crimson letters on it. When I look directly at it nothing seems unusually but I’ve noticed that when it’s in my peripheral vision like when I’m using my phone for example, I notice the red letters seem to jump around and kind of flash when my eyes move. What’s causing this? I thought it might have to do with chromostereopsis but I was hoping someone might be able to give me an in depth explanation.
|
[
"Your peripheral vision is constructed by a bunch of very quick motions of your eyes. Your visual processing filters these motions out of your perceived vision, giving you the experience of a contiguous visual field.",
"When your eye darts over to look at red text on a blue background, it struggles to focus enough to cleanly distinguish the red from the blue. Instead of distracting you by making you look closer at the text, your brain does its best to guess at what it saw. As a result, the exact positions aren't quite settled until you actually focus on the text."
] |
[
"This seems to me to be less about psychology than about optics. Red and blue light have different focal lengths, which is why our eyes exhibit ",
"chromatic aberration",
" when looking at red things on blue backgrounds. You know how on a prism, red light bends the least and blue light bends the most, and all the colors between bend to various different degrees? That same effect happens in the lenses of our eyes. So when an image is just red and blue, you can't focus on both; when one is in focus, the other is necessarily blury.",
"Because of this, the edges of red letters on a blue background are where one color is in focus and another is blury. Your brain interprets that interference as shimmering, as it attempts to get the eye to focus the one that is out of focus, but in so doing, blurs the other."
] |
[
"When you look at how a prism splits light, blue and violet light bends significantly more than red. In fact, as far as visible colors go, red and blue have just about the most difference in how much they bend. (Only violet bends more, but the way we typically make colors that simulate true violet is by blending red and blue because of a quirk of our visual perception, so you won't see this effect from anything that is colored by ink, paint, nor computer monitors or phone screens, only \"true violet\" things like certain flowers.)",
"Now, consider a lens: a lens, to a rough approximation, essentially has a prism-like wedge wrapped around its center, which is fairly flat. Your eye lens is somewhat like this, even if the edges of your eye lens don't have a sharp edge. (The prism effect comes from two non-parallel surfaces on a light refracting material; it doesn't have to come to a sharp edge to have this effect.) As a result of this difference in how much a lens will bend different colors of light, a lens will have a different focal length for red light than for blue light. (This kind of color-dependent focal error is called \"",
"chromatic aberration",
"\".) Blue light will come in focus at a shorter distance than red. So if an image has colors from opposite ends of the spectrum, you can't just focus on the whole thing; if you focus on the red, the blue will be out of focus, and if you focus on the blue, the red will be out of focus. That's why you get that weird effect, because in your retina, where the red and blue meet, only one color or another will be in focus. The other will be blurry, and that blurry + sharp combo at the edges where two colors meet is perceived as shimmering. This is why chromatic aberration is most apparent at the edges of images where two highly contrasting colors meet. For example, ",
"this",
".jpg).",
"This effect is stronger toward the periphery because the periphery is where the light is coming through your eye lens at a steeper angle, where chromatic aberrations may be stronger due to the geometry of light coming into your eye near the sides and traversing your lens in a way that encounters more bending rather than down the middle where the prism effect is the weakest. For this reason, chromatic aberration is strongest with the most curvy lenses (which becomes really apparent for things like crystal balls) and for rays of light furthest from the axis of the lens."
] |
[
"If you had to cross a desert by foot, would it be better to walk or run?"
] |
[
false
] | null |
[
"First, the math:",
"s = speed",
"g = grade",
"Oxygen consumed during walking = .1s + 1.8sg + 3.5",
"Oxygen consumed during running = .2s + 0.9sg + 3.5",
"Basically, those formulas show that walking on a flat surface is much more efficient than running on a flat surface.",
"Our oasis is six miles away, running at 6mph I'll get there in an hour and burn roughly 750 calories to get there. That's an awful lot, let's try walking. Walking the same six miles at 3mph takes me twice the time but burns only 500 calories, much less.",
"Second, the thermoregulation and the math:",
"So my run to the oasis will burn 1.5 times the energy as walking, and in half the time. This means your body must thermoregulate at a much higher level than if it were walking.",
"In the running scenario your body must deal with the added heat from 750 cal/hour, whereas in the walking scenario thermoregulation is much easier considering your expenditure is 250 cal/hour. You're body is going to deal with this in the way it was designed to, sweating.",
"In the desert (high heat, low humidity) sweating is very good at keeping you cool because it will evaporate readily. It's a double edged sword because you'll be losing fluid very rapidly. So your best survival strategy would be to walk and conserve your body's water.",
"TL;DR: Walk.",
"edit: some grammar & wording issues",
"edit: always triple check your math",
"edit: more clarity"
] |
[
"I was referring to your body's water. Please note I'm not a desert survival guy, I'm a physiology guy. The math says walk, so I would walk."
] |
[
"take it slow and conserve your water",
"By \"conserve your water\", do you mean that you should ration whatever drinking liquids you have? Or are you saying conserve your ",
" water by exerting yourself as little as possible?",
"I've always been told to ",
" ration drinking fluids, but rather to drink whenever you need to as long as you have something to drink available."
] |
[
"Do lab workers/scientists have the option to take home lab rats as pets instead of euthanize them?"
] |
[
false
] |
I guess this can apply to psychology as well. Obviously you wouldn’t want to take home lab rats who’ve had regions of their brains ablaised or their neural circuits significantly impacted for purposes of the studies. But for studies that don’t require you to modify their brains, why do they have to be euthanized afterwards, and do the scientists/lab workers have the option to take them home as pets after the study’s conclusion? Are there safety and ethical concerns even with Wistars, Sprague-Dawleys, and Long-Evans?
|
[
"In all of the research protocols I’ve seen they call for euthanasia as the endpoint. My lab has to euthanize our mice because they are all transgenic. They wouldn’t necessarily cause any extreme changes if they were exposed to the wild population, but there are definitely strains out there that would!"
] |
[
"Depends on the experiments conducted and the breed, but generally yes. I even know some students that adopted rats from neuroscience labs.",
"In Germany it is not allowed to take transgenic rats home. Also some experiments require the scientists to kill the rats for further testing of some organs.",
"Although the scientists are allowed to kill the animals after the experiment, they can also be given away.Some are used as food for other animals or are actively given away to students or other intereste people.This usually applies for behavioral experiments, but I don't know if this would also apply to rats that were used for invasive experiments in neuroscience. If the rat has a hole in its skull it would require special treatments like antibiotica and a clean environment. I don't think you can trust people enough to provide that. (I don't work with rats, so I don't know about the exact procedures)",
"Edit: Corrected for some misinformation"
] |
[
"I also wonder how mice/rats kept in sterile conditions would do when exposed to microbes when brought home. Certainly there immune systems would have been impacted in some way."
] |
[
"Which is the stronger bond for platinum: oxygen or nitrogen?"
] |
[
false
] |
Would the oxygen bonded to platinum be displaced in the presence of nitrogen?
|
[
"If by Nitrogen you mean N2, then no. Molecular Nitrogen is fairly inert compared to Oxygen and from my quick research it doesnt seem to react much with Pt. Platinum will react with Nitrates (XNO3) to form Platinum Nitrate (Pt[NO3]4) but that decomposes into ",
"Adam's Catalyst",
" which is PtO2, leading me to believe the oxide is more stable.",
"Inorganic chemistry is not my strength so someone who knows more may correct me"
] |
[
"This is correct. Oxygen is more electronegative than nitrogen, meaning it will form a better bond"
] |
[
"Electronegativity is very important, but oxidation state is important too. So a not particularly electronegative element like Chromium can become a powerful oxidizer if you get it into a very high oxidation state."
] |
[
"How true is it that biology reduces to chemistry..."
] |
[
false
] |
Which reduces to physics, which reduces to mathematics? And math's axioms can't be proven. If this is true, does the scientific method change from top to bottom?
|
[
"Physics doesn't reduce to math, physics is described by math, as are chemistry and biology. Mathematics doesn't rely on the existence and characteristics of the universe, whereas sciences do."
] |
[
"I wouldn't say that physics reduces to mathematics. While physics is more or less just applied math, math by itself doesn't have inherent 'meaning'. I don't say that to demean math but the mathematical concepts are only applied to model the physics, not as the underlying reason for physics. Math is also used in the other sciences as well.",
"So while math is used in physics, you can't reduce physics down to math. The hierarchy you describe is more of which science can theoretically explain the others. Biology is the macro form of the individual chemical processes. Those chemical processes are a macro form of the individual laws of physics.",
"In the end, if we had a complete and perfect understanding of physics, we technically could describe every interaction of matter and as such, every chemical and biological process. A complete and perfect understanding of math would be great but it wouldn't be applied to anything and as such, wouldn't describe anything. A perfect understanding of physics WOULD imply a perfect understanding of all associated math, however.",
"We don't know or can't model accurately enough every process so we study more general fields like biology and chemistry and sociology when theoretically, they could all be explained with a complete understanding of physics and the capability to model such complex scenarios.",
"That's my understanding but I could very well be thinking about it too much..."
] |
[
"I think OP is talking about ",
"this",
" XKCD comic."
] |
[
"How flat is it possible to make something?"
] |
[
false
] |
And if scientist and engineers came together to try and make the flattest, straightest table (1 meter long) possible, would it be closest to absolutely flat, or the curvature of earth?
|
[
"\"Graphite sheet\" = graphene, a single atomic layer of carbon. It is theoretically very flat, but practical considerations come into play. It adopts the morphology of the underlying substrate. ",
"Producing a 1mx1m sheet of graphene is, currently, totally unfeasible."
] |
[
"\"Graphite sheet\" = graphene, a single atomic layer of carbon. It is theoretically very flat, but practical considerations come into play. It adopts the morphology of the underlying substrate. ",
"Producing a 1mx1m sheet of graphene is, currently, totally unfeasible."
] |
[
"50 micrometers is considered large and beyond 1mmx1mm is currently unfeasible. Sure you can make larger but then you start introducing grain-boundaries and all sorts of other defects that destroy the ballistic transport properties that make graphene so interesting."
] |
[
"Would it be possible to utilize Earth's magnetic field (possibly at the magnetic north pole?) to propel, or significantly aid propelling, a spacecraft into a near-orbital trajectory?"
] |
[
false
] | null |
[
"Such hypothetical / speculative / open-ended questions are better suited for our sister-sub ",
"/r/asksciencediscussion",
". Please post there instead."
] |
[
"How could I reword this to fit this sub? I am legitimately looking for an answer, not just Karma. I wanted to post it here because you all have millions of members willing to answer while discussion has 57k, and I would very much like to get plenty of good answers."
] |
[
"All people who have flair here have flair there as well. That sub is especially designed for discussion-based and speculative questions."
] |
[
"What is the latest in Classification?"
] |
[
false
] |
I am a hs science teacher going to teach the unit on Classification. Right now our 15 year old textbook teaches Kingdoms as Animalia, Planta, Protista, Fungi, Archaebacteria, and Eubactera. I know that this field is always changing but also heavily debated. I sort of feel bad teaching something that is no longer relevant, but at the same time there isn't really a consensus I can find to show what is the newest. I definitely teach that it is a man made science and not perfect but...
|
[
"I don't know the answer, but thank you for working so hard to provide the best education you can. Reading that there is a teacher who puts this amount of effort into their work made my day, from the bottom of my heart, thank you."
] |
[
"Teaching classification is always hard - I try to use Kingdom/Phyla when I can, but also like to use Domains (Eukarya, Bacteria, and Archaea) and Clades to indicate related-ness between and among organisms. The Protists are the hardest to keep track of since they're always regrouping them, so I teach them as autotrophic protists and heterotrophic and then break it down from there."
] |
[
"Monera....well at least I'm lucky we've moved past that. We had some faculty using that forever as well. Plus I saw that Chromalveolata may not be valid anymore - instead now Discicristates (I think)?"
] |
[
"Given that our vision is based on the reflection/refraction of light and light cannot escape the event horizon of a black hole, will we ever be able to capture in image past the EH or of an actual black hole?"
] |
[
false
] |
[deleted]
|
[
"No. We will never capture an image of what lies beyond the event horizon.*",
"We may capture an image of a black hole, though, which includes the event horizon.",
"* There is no confirmed information that negative energy is a practical quantity that can be used to access a black hole, even if it has been theorized that it is possible to expose a singularity using negative energy.\n"
] |
[
"I don't even think you can take a picture of anything that has gotten close enough to the event horizon for light to not be able to escape",
"That is the very definition of the event horizon. If light can escape, you are outside it. If it cannot, you are inside it. There is no outside where light cannot escape."
] |
[
"No known mechanism exists to convey information from within an event horizon to outside, including the sort of information we'd use to produce any image."
] |
[
"Is it physically possible to create a square wave (sound)?"
] |
[
false
] |
The speaker cone moves in and out corresponding to positive and negative amplitude. In a square wave, it instantaneously jumps from +1 to -1. Is there a way to create this sound pressure wave (not necessarily with a speaker)? And as a second question, could our ears even hear it given the fact that the timpanic membrane has to make the corresponding movement? Thanks
|
[
"To create a perfect square wave, you'd need a contribution from all possible frequencies of sine waves. But any real source has some finite range of frequencies (a \"bandwidth\") that it can properly produce.",
"So you can never get a perfect square wave, but you can get arbitrarily good by increasing the bandwidth of your source arbitrarily high."
] |
[
"Right, but not",
"all possible frequencies of sine waves",
"You'd need all the odd harmonics of the fundamental frequency. "
] |
[
"We can never create a perfect square wave, if that's what you are asking, in the same way that we can never draw a perfect circle. "
] |
[
"Some prime numbers, like 5, can be factored with complex numbers. Are there any prime numbers which can't be factored ever?"
] |
[
false
] |
If we allow factors from C instead of just R, 5 = (2 + i) * (2 - i). A little googling led me to a funky idea called "gaussian primes", or numbers which are prime on the complex plane. Many of the real number primes seem to lose their primeness once complex factors are involved. My intuition is that if you add another plane, j, many more of the primes on C and R will become factorable. Even more once you add k,l,m,n, and so on. Are there any "super primes", which won't factor no matter how many dimensions you add? If so, do they follow any patterns? Or, is the only way to tell them apart a brute force search? If not, how many dimensions do you need to make all of R factorable? what about all of C?
|
[
"Firstly, when you talk about factoring, we're not doing it in R, we're doing it in Z which is the set of integers. It doesn't make much sense to talk about factorization in R because there are no primes in R because every nonzero number in R is invertible and it only makes sense to talk about the primeness of numbers that have no multiplicative inverse (this is why 1 is not a prime). ",
"The Gaussian Numbers are then to the integers Z as the Complex Numbers are to the reals R. That is, you just throw in i=sqrt(-1) and we denote it by Z[i]. This is all numbers of the form n+im where n and m are integers. So its not the whole complex plane, a lot of numbers are missing. A ",
"famous theorem",
" due to Euler/Fermat says that the prime factors in the Gaussian numbers Z[i] exactly when it has remainder 1 after dividing by 4. So 5,13,17,29,37... all factor (so does 2=-i(1+i)",
"), but 3,7,11,19,23,31,... do not. ",
"Now, there are other number systems that we can make where different primes factor. But first, note that to obtain the Gaussian numbers, we're taking the integers Z and adding to them a root to the polynomial x",
"+1. It is worth saying that the primes that factor are exactly the primes p so that there exists an integer N so that N",
"+1 is divisible by p, in which case we say N",
"+1=0 mod p. So, in a way, i already exists \"mod p\" and so nothing happens \"mod p\" when we added in the i to get the Gaussian integers. Said anther way, the primes p that factor in Z[i] already think that there is a root to x",
"+1=0, its just that not all the primes agree about this. So this is all intimately connected to ",
". If we find a different polynomial that cannot be factored over the integers, then we can construct a new number system and how the primes factor will be determined by how the individual primes \"see\" this polynomial.",
"For example, instead of using x",
"+1=0, we could include roots to x",
"+x+1=0. The root of this are w=(-1+sqrt(-3))/2 and its complex conjugate and adding these gives us the ",
"Eisenstein Numbers",
" Z[w]. It should be noted that, just like Z[i], the numbers Z[w] are all contained within the complex plane. We've just chosen a different subset of the complex plane to look at, and this is the set of all n+wm, where n and m are integers. The primes that factor in Z[w] are exactly the primes that have remainder 1 after dividing by 3 (and 3 itself). So 3,7,13,19,31,37, etc all factor in Z[w].",
"Of course, there are tons of polynomials that do not factor over the integers. Infinitely many. And to each of these we can create a new number system by including its roots into the integers. If you then also look at the fractions of these things, then these are called ",
"Number Fields",
" and are a ",
" part of math. For simple number fields, like the Gaussian Numbers, Eisensten Numbers and others, we have a really easy way to know whether or not a prime factors and exactly how it factors. A prime factors in the Gaussians if and only if it has remainder 1 after dividing by 4 (or is 2), and a prime factors in the Eisenstein Numbers if and only if it has remainder 1 after dividing by 3 (or is 3). One of the crowning achievements in Number Theory, called ",
"Class Field Theory",
", is a way to do this in general for a large class of number fields (though the descriptions do get a lot more complicated). But we can't do it for all Number Fields, and we would like to and the ",
"Langlands Program",
" is a very advanced collection of conjectures that try to do this, but have yet to be solved.",
"So, now that we have a bit of context, are there primes that do not ever factor in any number field? No. If p is a prime, then we can include the root v=sqrt(p) to x",
"-p=0. In this way p factors as v",
" in this new number system. In fact, there are number systems where ",
" the primes factor in some way, and such a number system is actually not far off from the Gaussian Numbers. If you take the Gaussian Numbers and then include sqrt(i) into them to get all numbers of the form a+i",
"b+ic +i",
"d where a,b,c,d are integers, then every single prime factors in this new system in some way. This is the field associated with x",
"+1=0. ",
"Note that this has 4-dimensions over the integers (since it take 4 integers to determine one) and, in fact, the dimension over the rationals numbers of the number fields grows to be arbitrarily large. But, on the other hand, it is still contained within C. In fact, ",
" number fields, no matter their dimension over the rationals, live inside C due to the ",
"Fundamental Theorem of Algebra",
". So we can't really use number theory to extend number system beyond C.",
"EDIT: There may be typos, but I'm sick and don't particularly care to fix them atm."
] |
[
"You can't build quarternions or octonions in this way. In a way, I wouldn't consider them number systems at all because of this. And the fact that they tell us ",
" information, about rotations and such, without giving us any new arithmetic information about the integers would seem to suggest that they are more closely related to geometry than being number systems themselves.",
"The number field associated with x",
"+1=0 is 4 dimensional because it is 4 dimensions ",
". If you plugged real numbers into a+bi",
"+ci+di",
", then it could condense to a 2-dimensional thing ",
". The dimension we're working in depends on where we're coming from. If you come from the rational numbers, you can have any dimension you want, but if you come from the reals then the Fundamental Theorem of Algebra says that, through C, 2-dimensions is the most you can have when constructed in this way."
] |
[
"The Gaussian integers are the ring generated by Z and sqrt(-1). If you instead generated it by Z and sqrt(3), you'd be able to factor three. And if you just use all the reals, then there are no primes and everything is factorable. Every number is divisible by every number except zero."
] |
[
"Why are some CDs unable to remove something that has been burned onto it?"
] |
[
false
] | null |
[
"Precisely that. A laser heats a dye and permanently alters its reflectivity, \"burning\" the information into the physical structure of the disc."
] |
[
"This gives a fairly simplistic yet accurate description of both the answers you're seeking."
] |
[
"but how come some CDs can be altered?"
] |
[
"Is there actual benefit to breathing in 'fresh' air as opposed to sitting in a room?"
] |
[
false
] | null |
[
"Air pollution in homes can be much worse than outdoor air. So, depending on the air quality in your home or building, it can probably be argued that you lower your overall health risks by spending more time outside. Note that pollen and fungi levels tend to be higher outside than inside. ",
"From: ",
"http://www.cpsc.gov/cpscpub/pubs/450.html#Intro",
"\"EPA's Total Exposure Assessment Methodology (TEAM) studies found levels of about a dozen common organic pollutants to be 2 to 5 times higher inside homes than outside, regardless of whether the homes were located in rural or highly industrial areas.\"\n...\n\" Indoor levels of dust mites are higher than outdoor levels.\"",
"Indoor Air Pollutant Sources\n\"There are many sources of indoor air pollution in any home. These include combustion sources such as oil, gas, kerosene, coal, wood, and tobacco products; building materials and furnishings as diverse as deteriorated, asbestos-containing insulation, wet or damp carpet, and cabinetry or furniture made of certain pressed wood products; products for household cleaning and maintenance, personal care, or hobbies; central heating and cooling systems and humidification devices; and outdoor sources such as radon, pesticides, and outdoor air pollution.",
"The relative importance of any single source depends on how much of a given pollutant it emits and how hazardous those emissions are. In some cases, factors such as how old the source is and whether it is properly maintained are significant. For example, an improperly adjusted gas stove can emit significantly more carbon monoxide than one that is properly adjusted.",
"Some sources, such as building materials, furnishings, and household products like air fresheners, release pollutants more or less continuously. Other sources, related to activities carried out in the home, release pollutants intermittently. These include smoking, the use of unvented or malfunction-ing stoves, furnaces, or space heaters, the use of solvents in cleaning and hobby activities, the use of paint strippers in redecorating activities, and the use of cleaning products and pesticides in housekeeping. High pollutant concentrations can remain in the air for long periods after some of these activities.\""
] |
[
"Engineer from a Consulting firm here. We do building construction all the time. Particularly, I am in charge of HVAC, piping, and fire protection design for projects of various types including; institutional facilities, commercial buildings, medical campuses, educational facilities, laboratories, and government facilities.",
"Building ventilation is the process of bringing outdoor air into a building, circulating it, and later purging it to the environment. The main purpose of ventilation is to provide acceptable indoor air quality by diluting and removing contaminants from the indoor air.",
"Buildings are required, by state codes and ASHRAE 62.1 -Ventilation and Acceptable Indoor Air Quality, to maintain a certain CFM of outside air per person depending on the type of building and its usage. We do this for a couple of reasons. For one, quality of air outside is typically much better than indoor air, and we want occupants to be as comfortable as possible. Sometimes, such as when designing a medical facility such as a hospital, they have a ton of special rules and specifics, such as very high quality MERV filtration systems and 100% outside air (all new air in and vent out; no re-circulation) to minimize spread of disease.",
"Another big reason we bring in fresh air is a phenomenon known as ",
"\"Sick Building Syndrome\"",
". Occupants in buildings seem to come under acute health problems without outside air ventilation. One reason for this is because a lot of buildings are constructed with materials that emit ",
"VOCs",
" . Also mold, carbon dioxide, and ozone buildup can be a problem. These are all fixed by making sure one designs the mechanical HVAC system to have a high enough turn-over rate to bring in new air. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) recently revised its ventilation standard to provide a minimum of 15 cfm of outdoor air per person (20 cfm/person in office spaces). In addition, pollution from outdoors such as motor vehicle exhaust, can contribute to SBS.",
"SOURCES:",
"Bearg, DW. Building Systems: HVAC Systems. In: Spengler JD, Samet JM, McCarthy JF, eds. Indoor Air Quality Handbook. New York: McGraw-Hill; 2001: 7.1–7.18.",
"Orme, MS, Persily, AK, Rock, BA. et al. Ventilation and Infiltration. In: 2001 ASHRAE Handbook; Fundamentals (SI Edition). Atlanta, GA: ASHRAE, Inc.; 2001: 26.1-26.31.",
"http://en.wikipedia.org/wiki/Sick_building_syndrome",
"EDIT: spelling errorz"
] |
[
"Germ theory was pretty revolutionary. The whole idea of tiny animals that make you sick can take a little getting used to. I'm not trying to defend her for ignoring the science, I merely suggesting that it's a little unfair to judge her by todays standards. Some people think the Higgs boson doesn't exists, and some won't even after we find it. It takes a lot to fundamentally change someone's understanding of the world around them."
] |
[
"Is there a genetic basis behind genius-level intellect?"
] |
[
false
] |
Has research discovered any specific genes or alleles that are correlated with a higher level of intelligence? If so, have they been able to pair specific genes/alleles to specific skills (ie. math, visual-spatial awareness etc.)?
|
[
"Intelligence is a ",
": meaning that a LOT of genes contribute to your intelligence (there are also environmental factors but because you asked we will concentrate on genetic ones). Intelligence is also hard to measure and that field has all types of complexities of its own to deal with.",
"That said, there are some known polymorphisms that contribute to increased intelligence. These SNPs have a fairly modest (1-2%) association with increased intelligence.",
"China has just began a giant study to look for alleles/genes/marks associated with or likely to cause increased intelligence: ",
"article here",
"."
] |
[
"China is actually trying to find this out now, much to the chagrin of the remaining research community.."
] |
[
"Awesome thanks, I'll give the article a look"
] |
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