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[
"What would happen to my body if I were hit by an atom from an atom smasher?"
] |
[
false
] |
Lets say I was able to stand in front of the path of an atom traveling at Large Hadron Collider speeds. Would it obliterate my body to pieces or would the atom pass through my body without incident? Thank you guys a lot, extremely informative. So from has been said; a single proton would most likely have 7 TeV of energy; which would likely cause no damage at all, or even pass right through you as many particles do constantly. I have also learned that particles can be used at high speed in a medical oncology as a form of cancer treatment. I think I shall go out under the stars tonight and bathe in the particles raining down from space!
|
[
"As a researcher at the Institute for High Energy Physics in Protvino, Bugorski used to work with the largest Soviet particle accelerator, the U-70 synchrotron.[2] On July 13, 1978, Bugorski was checking a malfunctioning piece of equipment when an accident occurred due to failed safety mechanisms. Bugorski was leaning over the piece of equipment when he stuck his head in the part through which the proton beam was running. Reportedly, he saw a flash \"brighter than a thousand suns\", but did not feel any pain.[1]",
"The left half of Bugorski's face swelled up beyond recognition, and over the next several days, started peeling off revealing the path that the proton beam (moving near the speed of light) had burned through parts of his face, his bone, and the brain tissue underneath. As it was believed that he had received far in excess of the radiation dose that would normally kill a person, Bugorski was taken to a clinic in Moscow where the doctors could observe his expected demise. However, Bugorski survived and even completed his Ph.D. There was virtually no damage to his intellectual capacity, but the fatigue of mental work increased markedly.[2] Bugorski completely lost hearing in the left ear and only a constant, unpleasant internal noise remained. The left half of his face was paralyzed, due to the destruction of nerves.[1] He is able to function perfectly well, except for the fact that he has occasional complex partial seizures and rare tonic-clonic seizures.",
"Source"
] |
[
"This happens to you already, all day every day. We usually call subatomic particles freely traveling around by another name - radiation. You are exposed to radiation every second from the ground, the air, the walls of your house, and space.",
"The protons in the LHC have 7 TeV, which is a unit of energy. This is roughly equivalent to the energy that a flying mosquito has. This is so little energy as to not be noticeable if it were to hit you."
] |
[
"Yes, this story never fails to be brought up whenever anyone asks anything related to human exposure to particle accelerators. This example is really only applicable if we are talking about massive cranial exposure to radiation. The OP is asking about the effect of one particle, which is so small as to not be noticeable."
] |
[
"Given that the majority of calculations performed by a computer are some sort of matrix inversion, solution of a linear system equations, or solving some partial-differential equation, are there known Quantum Computer algorithms that actually provide speed-up for these problems?"
] |
[
false
] | null |
[
"but quantum many-body calculations are only the tiniest sub-set of the numerical calculations that we do in our society.",
"For now, because they are hard to do.",
"Quantum computers are not supposed to replace classical supercomputers. They are supposed to supplement them - take over some work that is difficult for classical computers, and do some tasks way beyond their capabilities."
] |
[
"Your statement about the types of computations being done on computers isn't really accurate, but even if it was, it's missing the point. Quantum computing has the potential to revolutionize a few specific areas of computing that are really important, which is enough to be interesting and worthwhile, even if it won't enhance every type of computation.",
"For example, you cite prime number factorization. The security of many modern encryption and authentication techniques depends on prime number factorization being hard. If quantum computing makes that easy, then the entire security apparatus of the modern internet will need to be overhauled.",
"Even though encryption and decryption is a tiny fraction of the total computation your computer does, if that one little piece is compromised it would change your life in a major way."
] |
[
"You're taking one of the most high-profile uses of quantum computing and saying it doesn't matter. Of course you're going to be left saying that quantum computing doesn't satisfy. If you've already decided (against the general wisdom) that these things don't matter then I'm not going to be able to convince you, but still quantum computing research is a good thing. Here's one more try for you. ",
"I'll respond in three parts:",
"Part 1) Justifying that trying to break public-key cryptography is a worthwhile goal.",
"Part 2) Describe two other specific applications we think quantum computing can be good at, even if we don't have specific proof of this right now.",
"Part 3) Describe the broader impact of quantum computing on our understanding of computation. ",
"First, trying to break public key cryptography is a good thing. Breaking cryptographic algorithms shows us how they're weak, and shows us how to improve things. Even without functional quantum computers the research in quantum computing has inspired a new generation of quantum-resistant encryption algorithms. Even if QC breaks classical encryption techniques we already have proposed alternatives currently being researched. ",
"Why do we care about protecting ourselves against hypothetical threats? Lots of people do. Put yourself in the shoes of a government official or corporate officer. You have information you want to keep secret, so you use encryption. The time-horizon for secrecy might be many years, and if you want to upgrade to a stronger encryption in the future then you have to decrypt the information first which carries its own risks. You'd rather not do this. Suppose you want to encrypt something once and keep it secret for the next 30 years- you of course are going to be keenly interested in whether or not quantum computers are going to become a reality in those 30 years. That's eons in the technology world: 30 years ago there was no Linux, there was no Google or Amazon, and your high end desktop computer had a 386 processor in it.",
"Research effort into breaking cryptography with quantum computing is useful regardless of the outcome. If we do break our standard cryptographic algorithms then we learn something about how those algorithms are weak. If we can't break our algorithms after hard years of effort, then this tells us something else: those algorithms may not be susceptible to quantum attack after all, either because quantum computers just aren't feasible, or because the original attacks that were envisioned aren't workable in practice. ",
"For part 2, here are two specific applications that we foresee for quantum computing. The first is physics modelling and chemistry modelling. This is another application domain you seem to discount offhand, but the reality is that these have strong implications for huge, billion dollar industries. For example, accurate and fast modelling of molecules could help with computer simulation of chemical and physical interactions, and could mean big money in pharmaceutical, chemical and materials research. These are areas where you only need one or two high-profile success stories to generate huge value, and researchers in some of those fields are already hurting for better ways to do things. For example, one of the standard ways pharmaceutical research is conducted these days is by synthesizing a novel molecule (very expensive in itself) and then doing hundreds or thousands of micro-assays to check for certain kinds of reactivity (super duper tremendously expensive). If you could use efficient computation to better target what kinds of assays are likely to be successful or at least discard the assays that are unlikely to be successful then you're talking about billions and billions of dollars in efficiency gains. ",
"A second major application is accelerating optimization problems, and by extension accelerating machine learning. Lots of quantum computing researchers think that acceleration of optimization should be feasible, even though we don't have great general purpose algorithms to do this at the present. Machine learning is basically the next computer revolution and is again an industry worth billions of dollars. What this would amount to is faster training times, and many useful models have training times of hours and days simply because there is so much data that must be sifted through. Even if you don't care about machine learning, many useful computations can be posed as difficult optimization problems, which we then think would be susceptible to acceleration through quantum computing. ",
"Part 3 is that quantum computing is a useful but radically different model of computation from classical computation. There are deep, fundamental, and unsolved problems in our understanding of how computation relates to the universe we live in. For example, the Church-Turing Thesis essentially supposes that all physical processes must be efficiently computable (i.e. simulatable) on a Turing machine. For a long time many people held this conjecture to be probably true, but quantum computing may end up being a big glaring exception. ",
"You might have heard of the \"P=NP\" question, which essentially (under one interpretation) asks whether the set of all problems we can efficiently solve with a regular computer (P) is equal to the set of all problems we can efficiently solve with with an infinitely parallel processing computer (NP). In addition to these two sets (which are called complexity classes), there is the quantum complexity class called BQP, and how this relates to classical computing is unknown. For example, it's possible that P=BQP, or NP=BQP, or it's possible that BQP is strictly bigger than NP, or it's possible that BQP sits between P and NP, with BQP being strictly larger than P but strictly smaller than NP.",
"What this all means in plain English is that quantum computing proposes a new model of computation that appears meaningfully different from classic computation, but we don't really understand how. Further investigations here could help us better understand the fundamental nature of quantum computability, and possibly even better understand traditional P/NP computability. This brings us back to prime number factorization, because this is something that is expected not to be in P (i.e. we think it's a harder problem than we can do on normal computers), but it appears that it should be in BQP, but it's anybody's guess if BQP is strictly larger than P, or whether BQP and P are partially disjoint, or what. ",
"The only way that we make progress in these questions is by continuing to ask:",
"1) Are large quantum computers physically realizable? If not, what laws of nature prevent it? This would be a radical shift in our view of the world (i.e. maybe Church-Turing is right). We know that small-scale quantum behavior exists, and we think that large-scale quantum behavior does not exist (i.e. Schrodinger's Cat), and large-scale quantum computing in part is going to really push our physical understanding of what constitutes small and large quantum phenomena.",
"2) What kinds of quantum algorithms can be developed? Is quantum computing only valuable in specific cases, or will it be broadly applicable to many problems? How do quantum algorithms compare to the existing and more studied traditional complexity classes like P and NP (and many others)? "
] |
[
"Would a microwave heat up heavy water (deuterium oxide) just like regular water?"
] |
[
false
] |
I tried to find the answer on Google but couldn't come across anything.
|
[
"Yes, they have almost the same electrical dipole moment. It wouldn't be ",
" the same, since H2O and D2O have ever-so-slightly different properties (specific heats and so on), but that applies no matter how you heat them."
] |
[
"Generally, no. The heat capacity of an ideal gas is independent of the weight of the gas molecules. For noble gases it's 20.78 J/molK for Helium and 21.01 for Xenon, and the latter weighs 32 times as much as the former. ",
"The difference between H2O and D2O is more indirect, as the relative difference in mass between oxygen and the H/D atoms changes the vibrational energies of the molecules."
] |
[
"It's not a misconception. Water is usually the part of your food which absorbs the majority of the radiation. The relative permittivity of wafer is ~80 whereas most plastics are around 3."
] |
[
"How can super low frequencies of electromagnet radiation (eg. radio waves) and super high frequencies of electromagnetic radiation (eg. gamma rays) pass through walls, but the frequencies in between can't?"
] |
[
false
] | null |
[
"Has to do with the wavelength. High frequencies have short wavelengths, small enough for the electromagnetic waves to pass through the empty space in the matter. This is why high frequencies are damaging to living cells - the wavelength is literally short enough to pierce DNA like a knife, slicing it apart.",
"Low frequencies, like HF radio, have long enough wavelengths that they pass around objects like walls unimpeded, in the same way that a small rock sticking up from the ocean floor doesn't disrupt a large wave crashing into the shore.",
"Many frequencies have wavelengths that are too long to penetrate the spaces between atoms/molecules, but not long enough to pass around the entire object unimpeded. So they get blocked.",
"edit: spelling"
] |
[
"Don’t photons need exactly the right amount of energy to be absorbed by an atom? Is it not because the atoms in the wall just don’t accept the specific frequency of the light?"
] |
[
"Yes! There are specific sets of wavelengths (or frequencies, or energies if you like) that any given atom can absorb. Because these are specific, explicit sets of energy levels, we call them ‘quantized’, which is when quantum mechanics was born out of. (Very simplified, but it’s the idea). "
] |
[
"Is there a uniquely \"Human\" protein, or a unique aspect of a Human protein that exists in humans and no other species?"
] |
[
false
] |
Asking for a television script I'm writing. Thank you!
|
[
"Sure, though it depends on exactly what you mean by \"unique\". ",
"Bitar et al. 2019",
" examined over 800 genes with at least some human-specific features, and might be a good resource to read further into. Probably unsurprisingly, ",
"a lot of them are known or predicted to be involved with the nervous and immune systems",
".",
"It's worth noting though that their methodology was to search through other literature for genes described as human-specific, so the actual definition of this can vary a lot. A large majority of the genes there still have orthologs in other species, with only minor alterations that are unique to humans. While even small alterations to DNA sequence can have major implications for the resulting proteins, these don't really sound like what you're looking for.",
"Of the ~870 genes they studied, only 28 are listed as being of ",
" origin, meaning that they are actually brand new rather than just representing human-specific modifications to older genes. Of those 28, only 12 are actually protein-coding. Of those 12, 4 are listed as \"hominoid-specific\" rather than being specific to ",
", so honestly I'm not sure why they are included at all. That leaves 8 remaining candidates, but out of curiosity I decided to plug them into ",
"OrthoDB",
" to check if any of them have known orthologs in other species, and the results are kind of disappointing:",
"I didn't look further into the original source publications from which these 8 genes were initially identified as \"human-unique\", but it seems like there has been a mistake or at least confusion at some point between their discovery and their classification within the Bitar et al. paper. At the very least, even if they have human-specific features, they do not seem to have appeared ",
" in humans, with the exception of DNAH10OS (which is supported by the ",
"Uniprot page",
" for the corresponding protein). So I guess go for that one if you want a real example, though I'm sure others exist too."
] |
[
"Thanks for the sources you listed! That's incredibly interesting."
] |
[
"You might be curious to know that author and former marine-mammal biologist Peter Watts explored this idea in his book ",
"Blindsight",
". The full novel and copious background notes are ",
"available online from the author himself",
". There's also a short ",
"in-universe lecture on the subject",
". (The original webpage ",
"here",
" uses Flash, unfortunately.)",
"It's definitely a rather out-there idea, but he puts together a fairly well-described account of vampires being an extinct branch of the human evolutionary tree who are obligate cannibals due to requiring protocadherin-Y. The vampires are important to his story for other reasons, and it's a good book that I'd recommend in any case - it's probably my favorite work of fiction."
] |
[
"When a person suffers a severe case of amnesia, will they have interests in the same things that they had before their amnesia?"
] |
[
false
] | null |
[
"It depends. Retrograde amnesia (the most common type of amnesia) only impairs ones memory for events. Skill related memory (muscle memory) is not affected. That is why a person with amnesia can still speak English.",
"So, if ones preferences come from a particularly traumatic event, then they might not have the same hatred for that thing because they may not remember this event. On the other hand, if a particular preference has been had since birth because of a genetic predisposition, it will not be affected."
] |
[
"The area of the brain thought to play a major part in sexual preference--a subregion of the hypothalamus--is not involved in conscious memories. Also, it's a wiring thing (disclaimer, believed to be), so not really something that can be forgotten. There is some evidence (in lab animals) that you can lesion this area of the brain to change sexual preference, but the chances of such a localized lesion in a human, without any damage to the rest of the hypothalamus and thus some drastic side effects, is highly improbable."
] |
[
"how about sexual orientation, is it possible for one to forget that he is straight, or vice versa and forget he/she is gay?"
] |
[
"If you remove a verruca/wart from your body, does that remove the virus, or will it always remain in your system?"
] |
[
false
] |
[deleted]
|
[
"No, because I don't have genital warts. I have a verruca on my foot that's about 2mm across."
] |
[
"I'm consulting ",
"/r/askscience",
" because I want a serious "
] |
[
"Don't get your warts in a bunch, I was just kidding. Perhaps you should consult a doctor if you want a a serious opinion and can't take a joke."
] |
[
"AskScience AMA series: I am a neuroscience researcher who pokes brains all day."
] |
[
false
] |
I'm a postdoc doing basic research into auditory brainstem and olfactory systems using electrophysiology and laser imaging techniques. I have a free evening and a bottle of wine. I'll be hitting F5 periodically so go nuts. Edit: The questions seemed to have dried up so I'm for bed. If there's anything else, I'll get to it on the morrow. Thanks for a nice evening reddit! Edit 2: after a nice long sleep I'll be around sporadically today if there're any more questions, so feel free to AMA else.
|
[
"It's a cliche but - the brain. It's just really amazing. The way millions of tiny subcellular processes are going on constantly within every cell (neuron and otherwise). Each neuron is connected to an impossibly complicated network via hundreds or thousands of synapses. Each part connected just so so that you can move, breathe, do mental arithmetic, remember last week's dinner and plan for your future. And its not static: these connections grow and adapt and are lost and reformed. In some parts of the brain (dentate gyrus and olfactory bulb) new neurons are being constantly born, transported and integrated into the network. It's mindblowing and I love going into work and seeing something noone else has ever seen every day. "
] |
[
"I did a bachelors degree, then a masters and a PhD. Then I looked for post-doc positions. I guess I never really left university ;)",
"Pay isn't great (I work at a university), but I'm doing ok."
] |
[
"Can you explain in more detail what you do? And what questions you are examining?"
] |
[
"Does a strained rubber band have more mass than an unstrained one?"
] |
[
false
] | null |
[
"Does a strained rubber band have more mass than an unstrained one?",
"Yes, very slightly."
] |
[
"How is that shown though? How much mass would it gain "
] |
[
"It gains a mass equal to the elastic potential energy, divided by c",
"."
] |
[
"Is it possible for a Plesiosaur breeding population to live in a large lake?"
] |
[
false
] |
Disclaimer: I am NOT a cryptozoologist! All I wan't to know is: Is there enough food and habitat in a lake of similar size to Lake Champlain or Lake Oakanogan to support a breeding population of lake monsters?
|
[
"Absolutely, I'll do so tomorrow evening when more people are online. I have no idea why all my questions are snared in the spam filter, but I really appreciate the help."
] |
[
"I know we have some panelists that would probably love to answer your question!",
"I went ahead and approved your question, and gave you an upvote, but since you posted this 6 hours ago, you might have better luck posting it again.",
"If you decide to repost it, shoot me a PM and I'll approve it for you!",
"Good luck."
] |
[
"I have my doubts. The best analogy might be with marine mammals...they share the closest niche. And only extensive river systems hold breeding populations of dolphins. Lake Baikal has a breeding population of seals, but lake Baikal is ",
". And note that both dolphins and seals are quite a bit smaller than the standard plesiosaur. The largest fresh water fish are about the same size...and again, they live in extensive river systems. ",
"On longer time scales, both those lakes were (I believe) scooped out during the last glaciation by the North American ice sheet. "
] |
[
"Can carbon dating be affected by unusually high levels of radiation during a certain time?"
] |
[
false
] |
I understand that carbon dating is the measurement of the degradation of Carbon14. If, in the case of human remains, an individual received extra radiation due to atomic bombs, mercury poisoning, etc, could that skew the dating process? This is not a creation/evolution related question.
|
[
"Heck yes.",
"C-14 dating has been noticeably impacted by human-produced C-14, mostly from nuclear testing since the 1950s. People who actually do C-14 dating use a ",
"calibration curve",
" to adjust the naïve results given by their tests to better match the actual history of C-14 production on our planet. That's why the curve isn't a perfectly smooth line; several different effects cause ",
"variations",
" in the amount of C-14 present in the atmosphere, and if you don't account for them, your measurements can give you dates that are off by thousands of years.",
"I believe that the calibration curve itself has been painstakingly generated by comparing C-14 results from the results of different dating methods. The best is to do C-14 measurements on objects with a historically known age, e.g. wood samples that can be authoritatively dated using [dendrochronology(",
"http://en.wikipedia.org/wiki/Dendrochronology",
"). Older stuff can be measured by any of a number of other radioisotope decay ratios, and lots of other kinds of tests as well. Eventually, with enough samples measured enough ways, you can build up a pretty good picture of the historical C-14 levels going back a few tens of thousands of years ago. That's about all you really need, because C-14 decays fast enough that it's not really useful past about 50,000 years."
] |
[
"C-14 decays by beta emission, which occurs with basically a continuum of energies up to 149 keV ",
"(link)",
". If you were using a geiger-type counter (which can't determine the energy or type of radiation) to determine the sample's radioactivity, then absolutely any other ionizing radiation would trigger the detector and prevent an accurate age determination.",
"I'm not sure, to be honest, but I assume typically a spectroscopic detector is used for C-14 dating. In this case, depending on the quality of the instrument (the energy resolution), you should basically be able to determine which types of radiation are present in your sample's energy spectrum.",
"So, if you have another radioactive isotope in your sample that emitted gamma rays at an energy higher than 149 keV, you should be able to separate those counts from the counts that are due to C-14 (which will be 149 keV or less). This isn't entirely true, as higher energy gammas will produce some background at lower energies due to compton scattering, but in theory you could subtract this out.",
"If you had contaminants that were low energy gamma emitters (less than 149 keV), or other beta emitters (which will also produce a spectrum of energies up to some cut-off value), this will complicate things more worser.",
"I would guess the answer is that you could still estimate it, because you can always estimate anything, but you would probably lose some precision, even using the best equipment."
] |
[
"To add to this, mass spectrometry is often used for C-14 dating like you said, where the measurement doesn't rely on release of radiation but rather the amount of C-14 can be quantitatively measured. This is typically done with some version of a particle accelerator like a cyclotron so that rare isotopes to give better separation of the lower concentrations of C-14 amidst a strong background signal of C-12."
] |
[
"How much resources do huge AIs like AlphaGo and AlphaZero take up?"
] |
[
false
] |
Just wondering exactly what it takes to run these very strong AI program that can learn to beat world champions in a matter of hours. I don't actually know of any other big/commercial AIs, but feel free to mention anything!
|
[
"When they defeated Lee Sedol, those components were replaced by 48 TPUs. (Tensor Processing Units optimized for neural networks)\nAlphaZero only uses 4TPUs."
] |
[
"I read the paper and answered my own question.",
"\"AlphaGo uses an asynchronous multi-threaded search that executes simulations on CPUs, and computes policy and value networks in parallel on GPUs\""
] |
[
"I don't have a complete answer for you, but AlphaGo in particular has two variants implemented:",
"quoted from their Nature paper ",
"here",
". They both played with a 5 second 'thinking time' per move (\"Extended Data Table 6\")."
] |
[
"Can intermittent light be as effective as continuous light for plant photosynthesis?"
] |
[
false
] |
Lets say you had a plant grow under a light-bulb that was on continuously for 8 hours and a plant under a bulb that was on for a second/off for a second for 8 hours ( for a total of 4 hours of light). Would the later plant be similar to a plant grown under continuous light of 4 hours? Lets say you had the same experiment but the light that switched on and off was doubled in intensity (so the plant gets roughly the same energy of light as the continuous 8 hour bulb only via double intensity bursts.) I suppose the root question i'm asking is if you only have X units of light (lux?)(sorry dont even know what the right word is) to give to a plant whats the optimum way to deliver it?
|
[
"Let's consider your first example, where Plant 'A' is grown under conditions in which it is exposed to eight continuous hours of light and where Plant 'B' is flashed with light for eight hours, but receives half amount of light energy. In this scenario, both plants will absorb different amounts of light, but express similar physiological response. Plants \"detect\" light using a protein called ",
"phytochrome",
". This is protein which exists as two conformational isomers: red and far-red (these refer to the wavelength of light most easily absorbed by the isomers. The far-red isomer is created when the red isomer is exposed to red light, and the red isomer when the far-red isomer is exposed to far-red light. The far-red isomer will slowly change back into the red isomer too, if it is not exposed to red light. (Welcome to the convoluted world of undergrad botanical science! Basically: if the plant is exposed to light the biologically active form of this signalling protein exists, when the plant is not exposed to light the biologically active form converts back into the biologically inactive form). If you imagine a graph of concentration of phytochrome far-red (biologically active) vs. time, we can understand that this will look like a series of peaks, it is literally the amount of time between these peaks that determines the circadian rhythm of plants. SO. What does this mean in the case of experiment #1? Well: All of the phytochrome in Plant 'A' will exist in the biologically active far-red isomeric conformation for a period of eight hours and then slowly change back into phytochrome far-red at night. What this means is: Plant 'A' is \"aware\" that it is receiving eight hours of light a day and will have the appropriate responses for its particular species. Plant 'B', which is being flashed with light for a period of eight hours, on the contrary, will \"think\" it's receiving eight hours worth of light (because the phytochrome will still be in its far-red isomeric conformation for those eight hours) and will express the same genes as Plant 'A', but will have collected only half of the energy. If eight hours of light is enough to induce responses like flowering and other energy costly responses Plant 'B' will most likely die. The second experiment, where plant 'B' is flashed with high intensity light for half the amount of total time is an interesting consideration. If the light was not too intense that it would damage the tissue of the plant, Plant 'B' would be ok. It would have received the amount of energy it \"thought\" it had. However, plants can be damaged and die from overly intense light (I wrote a lot about plant responses to high light intensity in another ask-science question, I'll find it and link it. Some of the responses are on the molecular scale! Neat!"
] |
[
"Here's some neat stuff I summarized about plant responses to high light intensity!"
] |
[
"Thank you! This is an amazing answer to which i have no follow up questions!"
] |
[
"How much energy/heat does the moon block from reaching the Earth during a solar eclipse?"
] |
[
false
] |
The moon is blocking sunlight from reaching a small portion of the Earth during a solar eclipse, so how much energy does it actually block that would have otherwise traveled to the earth? Could an eclipse cause a measurable difference in temperature on the Earth?
|
[
"If the eclipsed area has a radius of 100 km and lasts 7 minutes, and the sun gives 1460 watts/m",
" , that's about 2 x 10",
" joules blocked.",
"If it blocks a 100x100x10 km region of the atmosphere, according to my rough calculations it should drop about 6 degrees, but I'm not sure that's accurate."
] |
[
"I don't think too much apparently ",
"http://www.aaadelhi.org/files/eclipse99_mir_big.jpg"
] |
[
"Yes, because everyone knows how stuff freezes over every night only a few minutes after sunset, even in summer in the Bahamas."
] |
[
"r/AskScience, I have a question about odds.."
] |
[
false
] |
Is there a way to calculate random events? Or is there no such thing as a random event given the proper information and time to process? For instance, if you were breaking in a game of pool and the balls traveled at exactly the same speed until they went in a pocket would you: A. Be able to calculate the exact time it takes for all the balls to fall in a pocket? B. Be able to calculate which ball falls in which pocket? I'm not asking to actually do those calculations, but I want to know where modern science sits on be able to predict random occurrences.
|
[
"No, there is no way to know exact positions and exact behaviour (momentum, a measure of motion) simultaneously. In fact, you can think of the universe ",
" things don't ",
" exact positions and momenta. We've even accounted for the fact that \"well suppose there ",
" something but we don't know how to measure it.\" We actually came up with a way of measuring the possibility of unmeasurables, and the results ",
" to indicate that our universe does not have them. To go into more detail, this is called Bell's Theorem, and ignoring some counter arguments for the moment, it says that the universe can either be local, where information is not transmitted faster than light; or it can have quantum things we can't measure, called \"hidden variables;\" but not both. Well since FTL information transfer can break causality for things that are known to have cause-effect relationships, we assume that our universe is local and without hidden variables. There are of course people who think that we occupy a non-local universe with hidden variables, but the bulk consensus seems to be local non-hidden."
] |
[
"So the two calculations you suggested aren't actually random. They are going to depend on a lot of different factors.",
"The easiest scientific example I can come up with is radioactive decay. Say you have a lump of uranium. We know it's going to decay but can't accurately say, ok...one decay will happen ",
". What we can describe is the statistical behavior of the decay process. We can describe decay with a half-life, where we calculate that in one half-life, half of the sample will have decayed. But there is no way to know when individual decay events will occur."
] |
[
"True randomness is unpredictable by definition. If we were able to calculate a random event then the event would not be, in fact, random.",
"For your question about the pool scenario, the answer is yes. Although the calculations would be extremely tedious using fairly basic physics of angles and momentum one could figure out which balls would go into which pocket given a break at a particular speed and angle. "
] |
[
"If honey bees aren’t native to North America, why aren’t they treated like other invasive species?"
] |
[
false
] | null |
[
"As a bee researcher, I have to say I disagree with several of the answers here to varying degrees. But to first address your initial question, honey bees are treated differently in North America because they are essentially livestock. There is at least some evidence that people were intentionally managing honey bee hives as early as 9000 years ago (",
"Roffet-Salque et al. 2016",
"), which is older than the domestication of many other animals such as chickens, ducks, horses, camels, and llamas. While truly wild populations of ",
" definitely still exist in some parts of the world, all honey bees in North America live in either managed hives or feral colonies descended from the same. (Some people use \"wild\" interchangeably with feral\" for such cases, but personally I prefer to reserve this term for unmanaged ",
" in their native range, since in North America all honey bees can trace their ancestry back to managed hives brought over by Europeans, even if they have lived independently of humans for generations).",
"Honey bees are of course very important for human agriculture, pollinating a large percentage of the different crops that we eat. As a sidenote though, statistics related to this and claims that we would starve to death without bees are often misrepresented. Honey bees definitely pollinate a large ",
" of crops, but the major staple crops that account for a large proportion of agriculture (and most human diets) are not actually insect-pollinated. However, it is important to emphasize the difference between these ",
" pollination services (i.e., making food for us) and ",
" pollination services as discussed by ",
"u/madchad90",
".To be fair, honey bees definitely do perform ecosystem services of this type. However, native bees are often more effective at pollinating native plants (especially those which require ",
"buzz pollination",
"), so in many ways honey bees kind of just provide quantity over quality as a result of their very high abundance (see ",
"Hung et al. 2018",
" for example). Keep in mind that North America's native flora got along absolutely fine without honey bees for many millions of years!",
"But the primary negative impacts of honey bees come from their interactions with other pollinator species. I'm really not sure where ",
"u/svarogteuse",
" is coming from in their comment, because the claim that competition between honey bees and native species has already reached some kind of equilibrium is simply not true. Yes, honey bees were first brought to the East Coast about 400 years ago, but they didn't arrive everywhere at once, (e.g., there weren't any in California until the 1850s). Furthermore, modern apiculture and the use of honey bees in agriculture more generally is much more intensive than anything that would have existed in colonial North America; California's almond industry alone makes use of something like ",
"1.6 million hives every year",
"!",
"It is admittedly difficult to draw any direct causal links between honey bees and native pollinator declines, which are surely the result of multiple drivers, but that certainly doesn't mean that they can be absolved of any culpability! Recent work by ",
"Angelella et al. 2021",
" has provided some pretty good evidence of the negative impacts of honey bees on wild bee communities, and the fact that many pollinator species have seen declines over the past few decades while honey bees have seen an upwards trend over the same period (",
"Zattara and Aizen 2021",
"30651-5)) also does not bode well. In further contradiction to the suggestion that 400 years is enough time for interactions between honey bees and native species to settle, recent work by ",
"Herrera 2020",
" has in fact reported that ",
" has been supplanting other native species ",
", where it has obviously lived for millennia. Finally, an important but often overlooked consideration is the fact that even when they don't directly cause native species to go extinct, the presence of honey bees still disrupts general ecosystem dynamics, for example by greatly reducing historically common plant-pollinator interactions (",
"Valido et al. 2019",
").",
"To summarize, honey bees aren't usually thought of as invasive for the same reason as, say, chickens, or any other species of agricultural significance. We intentionally brought them here for a purpose, and they are beneficial ",
". Their impact on ",
" is more complicated, however, though I would argue that the net effect is negative and shares similarities in many ways to that of other species which are considered invasive. Of course, that doesn't mean I think we should get rid of them all or anything, I like food too! I just think it is important to be aware of their effects, as with any major agricultural practices."
] |
[
"Honey bees are one of the few non native species that have become “invasive” that we’ve introduced that don’t have cons that outweigh the pros, so to speak.",
"As a matter of fact, many types of modern agriculture DEPEND on pollination from honey bees.",
"They are incredibly precise individually and amazingly cohesive as a hive. The rabbit hole on the incredible things honey bees do runs very deep."
] |
[
"I don't know how beneficial honey bees are outside of pollinating large agricultural fields. Honey bees are invasive and displace native bees that have evolved to pollinate specific types of native pants. I think they are treated differently because they produce honey which is a commodity."
] |
[
"What is actually going on in those salt-on-a-vibrating-plate \"resonance\" demonstrations?"
] |
[
false
] | null |
[
"Vibration of plates occurs in a predictable fashion based on the boundary conditions of the plate, the properties of the plate, and the induced vibration. The sand or rice or salt or whatever will tend to accumulate in regions of low displacement and leave regions of high displacement because it will get \"tossed away\" by the vibrations."
] |
[
"If you had the salt on an infinite plane, and put vibration under it, the wave would expand in circles.",
"When you instead do it on a square plate, the properties change when the wave reaches the edge of the plate in one area, but is still moving into the corner of the plate in another. ",
"The wave essentially reflects, but unevenly, and the reflected wave interferes with the initial wave. ",
"For a much more boring example of the same phenomenon see this video using a circular plate: ",
"https://www.youtube.com/watch?v=CGiiSlMFFlI",
"Since the wave gets reflected straight back, the interference is just circles. It's simply interference. Where waves constructively interfere, you get the sand moved away, where waves destructively interfere, the sand doesn't move. ",
"It's the shape of the plate that makes the interesting patterns. "
] |
[
"Let's simplify this and just look at a sine wave for a second.",
" Imagine a string that is excited in that manner. If you were to first place sand evenly across the top of that string (ignoring the fact that it would all fall off), where would the sand go? It would be pushed away from the points with maximum displacement, and settle on the \"nodes\", where the string isn't moving.",
"Now let's go back to your plate example. The plate is excited at a given frequency (it also has some noise and harmonics of that frequency). Those vibrations are hitting the boundary of the plate and reflecting back. The result is that you don't get a super simple shape like a sine wave with nodes at even distances. You get nodes in really strange patterns that result from the differing phase and wavelengths of the reflected waves.",
"So the vibration pushes the sand off of the points of maximum displacement, and the sand settles where at the node points, just like in the sine wave example."
] |
[
"Rather than retiring the last two space shuttles on Earth, why aren't they being permanently integrated into the ISS?"
] |
[
false
] |
My impression is that they are still perfectly spaceworthy, with re-entry posing the only significant danger. Considering they have fully-functional life support built in, not to mention the massive expense inherent in building and deploying new space station modules, why not give the shuttles a permanent home in orbit where they can continue to serve a useful purpose?
|
[
"I'm going to guess that a) it's because the space shuttles are designed to be in space for a period of a few days only, b) the space station has a limited number of docking ports and they can't really spare them, and finally, c) the altitude/attitude control thrusters on the ISS weren't designed to handle the extra load of two space shuttles hanging off the ISS.",
"Points a) and c) will probably cause a faster depletion of resources onboard the station, requiring more expensive supply missions, which will have trouble docking because of point b).",
"Also, ",
"cassander",
" raises an interesting point about the power consumption of the space shuttles. I believe at the moment they use fuel cells to produce onboard power. This would require supplies of H₂ and O₂ for the shuttle as well..."
] |
[
"Well, they're already 30+ years old. Aside from wear and tear, they must be filled with a lot of obsolete equipment. Plus keeping them up there and turned on has got to take power, which they probably don't have a whole lot of. "
] |
[
"I think smhinsey is talking about using them for stationkeeping. Use them for thrust to keep the orbit from decaying. ",
"This is currently already done by the zvesda or whatever the hell it's called though...so I don't see why they need more engines. ",
"Regardless, it's a moot point. The plan of de-orbiting it in 2016 has been scrapped...it will be around until 2020 or beyond thanks to the Obama administration. "
] |
[
"Does the surface of the Earth \"flatten out\" to any extent due to space-time curvature?"
] |
[
false
] |
I apologize, I know it sounds like a stupid question. I'm thinking of that pithy line, "mass tells space how to curve, space tells mass how to move." I remember visual gravitational models that suggest that heavy astronomical objects acts a little like dimples on a canvas, drawing objects to them and "curving" straight line motion. My question is, how does this apply to us here on Earth, much closer to the center of our planetary mass? Do we perceive the Earth as more "flat" because of this? EDIT: awesome! Thank you all for your comments. I'm absolutely fascinated reading through them. You invested some real time explaining this to me and I really appreciate your effort!
|
[
"The answer is yes or no depending on exactly how you phrase the question. Let me explain:",
"Let me just specify first that these effects are ",
". Basically Earth's mass curves spacetime, sure; the components of curvature relating time and space are pretty large and are what gives you the gravitational force, etc etc. But there's also space-space curvature, meaning that at every given instant in time, space is curved itself too. But this is a very, very small effect. It's only perceptible in the context of precision experiments. But let's talk about it anyway.",
"Let's assume Earth is perfectly spherical and smooth, and is not rotating.",
"So you want to know about the curvature of the surface of the Earth, which is a sphere, a 2d surface. Curvature in general is indubitably complex to quantify and explain, but for surfaces becomes very simple: it's describable completely by a single number, the gaussian curvature K. When K > 0 at a point, your surface looks sphere-y, when K=0 it looks flat, and when K < 0 it looks hyperbolic-y.",
"The Earth is as we said spherically symmetric and so whatever the value of K, it has to be constant over the Earth.",
"The fundamental piece of math I am going to use is called the Gauss-Bonnet theorem. For our specific case, it tells you that if you have a surface of constant curvature K, of area A, then this formula holds:",
"A * K = 2π * χ",
"χ is an integer called the Euler characteristic of the surface. You can look up what it is (it's easy!) or you can also not and I'll just tell you the sphere has χ = 2.",
"So we know that our curvature has to be",
"K = 4π/A",
"No escaping this. Even though space can be severely curved, this relationship has to hold. It's a theorem and bears a very important person's name, so yeah. Note that A is the area as measured by someone living on the surface. If you use a tape to measure the length of the equator, you can also compute A (divide by 2π, square, multiply by 4π).",
"Now, if space was flat, we would use A = 4π R",
" and so conclude K = 1/R",
", which is the usual formula for the curvature of a sphere. However, A = 4πR",
" is ",
" in curved space. R would be the proper radius, that is the actual distance from the centre of the Earth to the surface, measured by actual rulers. Freaky but true. A is actually a bit less than 4πR",
" iirc.",
"So here we have this situation. Let's say you define an \"effective\" radius r through A = 4π r",
". As we said R=/=r. The curvature is then K = 1/r",
". Your question could be phrased as \"if we add the effects of general relativity, does the Earth gets a variation in curvature as compared to what we would expect?\". ",
"Well, ",
" do you expect? You cannot fit the normal flat-space Earth, with A=4π R, in the curved space created by its own gravity - you need to change something. Either you keep the radius fixed and make the surface area smaller than 4πR",
" to accomodate, or you keep the surface geometry fixed and increase the radius.",
"In case one the area gets smaller so K gets bigger, so the Earth would be ",
" flat than usual, not more. In case number two, K is unchanged. As you can see, it's really just a question of defining what you want to keep unchanged."
] |
[
"Well, what do you expect? You cannot fit the normal flat-space Earth, with A=4π R, in the curved space created by its own gravity - you need to change something. Either you keep the radius fixed and make the surface area smaller than 4πR2 to accomodate, or you keep the surface geometry fixed and increase the radius.",
"In case one the area gets smaller so K gets bigger, so the Earth would be less flat than usual, not more. In case number two, K is unchanged. As you can see, it's really just a question of defining what you want to keep unchanged.",
"I interpreted the question like this: whether space is curved or not, we can measure two \"radii\", ",
" and ",
". The radius ",
" is really the circumferential radius we get by measuring the circumference ",
" of Earth and simply defining ",
" = ",
"/(2π). The radius ",
" is the proper radius that we would get by directly measuring the distance from the surface to the center of Earth. (Of course, how you do that is a different story, but let's just say you can.)",
"We have two \"candidate\" values for the curvature of Earth's surface: κ",
" = 1/r",
" and κ",
" = 1/R",
". Of course, the ",
" curvature is always κ = κ",
". In general, ",
" ≥ ",
" (with equality holding only if space is not curved within Earth's interior), whence κ",
" ≥ κ",
". So I interpreted the question as asking whether (and how much) general relativity tells us κ",
" exceeds κ",
". So if Earth's interior has any mass at all, GR tells us that κ",
" is strictly larger than κ",
". That is, Earth's surface has a larger curvature than expected.",
"But I agree that the interpretation of \"expected\" is very difficult. Although I call both κ",
" and κ",
" \"candidate curvatures\", we know that the curvature of Earth's surface is always κ",
" no matter what. (This makes sense too since it is calculated using only measurements that can be performed within the surface itself.) So we have no reason to expect that κ",
" is meaningful at all. The uninteresting, yet correct, answer to the OP's question would just be \"there is no deviation from what is expected\". But then you don't get to have fun invoking the Gauss-Bonnet theorem or explaining the difference between a proper radial coordinate and a circumferential radial coordinate.",
" For those interested, the deviation between ",
" and ",
" for Earth is very tiny as ",
"/u/rantonels",
" noted. To calculate ",
" exactly we would either have to do the measurement directly (and I don't know of a way to do that) or we can propose some reasonable density profiles for Earth and do all the nasty integration. The simplest assumption is that the density of Earth is constant. (This is actually a really bad assumption because it then implies that the speed of sound in Earth is infinite. But we can use it to at least get an order of magnitude estimate.)",
"If you go through all the math to compute ",
", you should find that to first order, we get ",
" = ",
" + ",
"/6, where ",
" is the Schwarzschild radius of Earth, which is slightly less than 9 millimeters. The value of ",
" is about 6 x 10",
" millimeters. So you can see that the relative difference between ",
" and ",
" is about one ten-millionth of one percent."
] |
[
"What would you say about the intuition that, if you lie near the photosphere around a blackhole (where the geodesics are closed), you can are going essentially \"straight\" while remaining on near sphere. Which would imply the area of the photosphere is 0 (which is not the case?), so is the problem in the definition of \"straightness\" or does the intuitive definition of curvature not match the one you mentioned?"
] |
[
"A little simple, but- Why do basketballs bounce so hard when they hit a corner?"
] |
[
false
] |
If you've ever dropped a basketball, or any other kind of bouncy ball on an edge or corner, you know what i'm talking about. Why do they do this?
|
[
"Why does this matter, though? ",
"The ball is carrying the same amount of energy whether it hits a corner, edge, or flat plane. My instinct would be to say that there should be no difference in total \"bounce\": in hitting a flat plane, you use the ball's energy to cause a larger section of the ball to deform and bounce back a smaller amount; in hitting a corner, you use the same amount of energy to have a smaller section of the ball deform and bounce back a larger amount. ",
"Assuming that OP is right, could the difference simply be that edges and corners have less \"give\" in them than flat surfaces, and therefore the ball bounces more because the collision is more elastic rather than because it matters whether the target's resistance is focused on a point? ",
"If not, could you give a more detailed explanation of how focusing the same amount of energy on a smaller part of the ball causes it to fly off at a higher speed? "
] |
[
"A good basketball will rebound off the floor with ",
"about 75%",
" of its original energy. Hitting a corner can't do more than 33% better than this under any circumstances."
] |
[
"The quastion was, \"Why do basketballs bounce so hard when they hit a corner?\" I was simply pointing out that they can't bounce more than 33% harder than from a flat surface without violating conservation of energy."
] |
[
"How do we communicate with satellites?"
] |
[
false
] |
Motivated by about dropping pictures. Satellites are essentially computers in space, correct? Do normal actions apply? Can I "drag n drop" an image by connecting remotely?
|
[
"Modern satellites communicate via radio waves. If you have an antenna or dish with the correct shape and electronics, you can easily receive the signal sent by the satellite. With a similar or larger dish correctly positioned you could probably send a signal to the satellite, but you would need the correct code/password for it to actually accept any commands from you. "
] |
[
"Satellites are essentially computers in space, correct?",
"This is arguable, because they have lots of systems/devices that are not computers. But if you say they ",
" computers then yes, your assumption is almost correct.",
"But it's computers understood like an electronic circuit that has a processor, memory and can run programs. It's not like the computers we're used to with graphical environments.",
"Can I \"drag n drop\" an image by connecting remotely?",
"No. They don't use typical desktop operating systems. In most cases they use software developed specifically for their purposes.",
"Sending a command for the satellite typically will be writing a command in a text terminal. ",
"This image",
" is actually not a satellite system but linking just to show what a text-mode terminal looks like. In some cases they have a graphical application where they click some buttons for common tasks, but it doesn't look at all like the applications you normally use when copying pictures in your PC.",
"edit: googling a bit found a picture from real systems: ",
"http://upload.wikimedia.org/wikipedia/commons/4/45/ISS_Flight_Control_Room_2006.jpg"
] |
[
"That depends on each particular case. Probes going very far away in interplanetary space sometimes do not have any security at all, simply because the parabolic antenna needed to communicate that far is not something that a hacker may have in his garage (actually I asked this to a professor who works in the industry, he said they were more concerned in the times of the cold war but nowadays nobody cares).",
"But Earth orbiting satellites need stronger security, some of them use RSA or DSA."
] |
[
"I always read about the diseases western Europeans settlers brought to American when they settled here wiping out Native Americans. Why didn't these diseases exist in NA?"
] |
[
false
] |
Did the Native Americans have other diseases to contend with that were more specific to that region? If so, did those affect the Europeans? I never hear about diseases in Native American culture pre-colonization, which makes me wonder if the lack of industrialization in NA made it less of a breeding ground for diseases
|
[
"Native Americans did have their own set of diseases to contend with actually. It's been ",
"addressed previously",
" in ",
"/r/AskHistorians",
". People here like to cite the recent CGP Grey video, despite it just summarizing Jared Diamond's book ",
", which has been widely criticized by historians and anthropologists alike. You can find a nice criticism ",
"here",
". To add to their criticism, the book and the video cite smallpox as having arisen from cattle. This is likely not the case however, as molecular clock analysis of variola virus clades combined with historical records indicate that it is likely the virus ",
"diverged from an African rodent enzootic pathogen approximately 68,000 years ago",
", probably ",
"before the domestication of animals",
".",
"It's also been mentioned here that ",
"syphilis probably originated in the New World and spread to the Old World through the Columbian Exchange",
". Although it never spread to the old world, a disease called cocoliztli, proprosed to have been caused by a hantavirus, created two large-scale epidemics in 1545 and 1576, killing between 7 and 17 million people in modern-day Mexico. Overall though, I recommend reading the aforementioned ",
"/r/AskHistorians",
" answer for a more in-depth description of the diseases Native Americans had to contend with."
] |
[
" is a funny one, in that it caused a number of major plagues amongst the indigenous inhabitants of Mexico, some leaving whole towns with nobody alive to bury the dead, and yet it didn't seem to affect people of Spanish blood. Spanish monks were closely involved with the sick and the dying, yet never seemed to catch the disease. That's backwards to the normal way, with immunity and co-evolution leaving people less vulnerable to diseases from their locality, and open to infection by exotic pathogens; however, as this was a highly discriminatory society with the Spanish as the colonial overlords, it might be just a matter of protection through better nutrition and living conditions.",
"I've seen some convincing arguments that it was a haemorrhagic fever, and I'm sure I read a relatively recent paper that had isolated a strong candidate (was it an arenavirus?) from rats in an area coincident with focal points of past epidemics; but I can't track it down now. "
] |
[
"thank you!"
] |
[
"what does \" no two electrons in the universe can have the same energy state\" actually mean?"
] |
[
false
] |
Does it mean there are an infinite levels of states an electron can be, like an infinite rungs on a ladder?
|
[
"This is correct. The four quantum numbers specify the \"address\" of the electron within an atom. No two electrons can hold the same probabilistic model specified by the quantum numbers within the same atom. However, electrons can absolutely hold the same quantum numbers in different atoms. Not sure if this is what the op is asking for but konzahiker's answer is correct."
] |
[
"This is correct. The four quantum numbers specify the \"address\" of the electron within an atom. No two electrons can hold the same probabilistic model specified by the quantum numbers within the same atom. However, electrons can absolutely hold the same quantum numbers in different atoms. Not sure if this is what the op is asking for but konzahiker's answer is correct."
] |
[
"It should actually be \"have the same state\". Energy or not doesn't matter.",
"The state of any quantum system is a normalized vector in a Hilbert space (well, it's typically called a ",
", but they're essentially interchangeable). Like a normal 3-d vector, we can describe this vector by a list of numbers saying how much it goes in some fixed set of \"basis\" directions. For two states, both where a given observable has a fixed value, but different in one then the other, the two vectors will be \"orthogonal\", at right angles to each other. This means that values for observables can be used to pick out a standard basis for a system. Energy is often used as a factor in picking out a convenient basis.",
"The actual rule is that any two electrons must have orthogonal vectors. (Well, actually the full rule is that the entire global \"tensor product state\" must be antisymmetric under exchange of any two electrons. But it gives the first as a consequence.)"
] |
[
"Why do people with Down's Syndrome look very much alike?"
] |
[
false
] |
[deleted]
|
[
"I won't bore you with the specifics regarding aetiology, but essentially Down's is due to a an extra chromosome leading to significant neural and physical defects, one of which is their 'similar' appearance as you term it.",
"Those with Down's appear to have a significant degree of deficiency in midfacial area, mandibular area, and endocranial area",
" perhaps due to muscular atrophy caused by the disease.",
"Otherwise, why they look similar is down to human conditioning. In simple terms, we are very adept at noticing facial differences in our own race, however often, we look at other races, black, asian etc. and cannot differentiate as well between the faces",
" This is what occurs with those with Down's syndrome; we see a similar trait and assume they all 'look the same'. This is obviously not the case as those with Down's syndrome often have very different features, but we can't see past this human trait of recognising those similar to us, far better. ",
" "
] |
[
"Intersting that the comparison to differentiating among Asians comes up - Dr. John Langdon Down, first English physician to describe the syndrome, named the disorder Mongolism as he thought these patients were simply expressing traits that made them more like ethnic Asians. When that theory was later proven incorrect the disorder was renamed after Down himself.",
"Source: ",
", Daniel Kevles."
] |
[
"Plenty of disorders have both neurocognitive effects and physical developmental effects. For example, ",
"Dubowitz syndrome",
" causes severe retardation as well as microcephaly (small hands and feet) and specific facial features.",
"Often one major mutation can cause more than one phenotypic effect. Traits are frequently linked and inherited together during meiosis.",
"In the case of Down's syndrome, you have a partial or complete third copy of Chromosome 21. That's a pretty massive mutation, so it effects both neurocognitive development and physical development. We've learned a lot about different coding regions of Chromosome 21 by studying the effects of Down's.",
"As for why \"people with Down's syndrome look alike\", they don't. They have a series of shared facial features, but they have as much variation within their facial features as neuro-normatives do. It's like how \"all Asians look alike\" to other ethnic groups, despite plenty of in-group variation. Anyone who has spent time with Down's individuals can tell you they are all distinct individuals.It is proposed that when human beings recognize other humans, we focus on the differences between their facial features, the features of those nearest them, and our own. When someone neuro-normative looks at someone with Down's (or someone in an out-group ethnic group) we instantly recognize the features that are the most different from our own. This is also proposed to be the mechanism behind the ",
"flashed face distortion effect",
" and why we have difficulty recognizing faces in crowds.",
"Edit: Microcephaly is reduced head size. I was trying to remember the phrase for reduced hands and feet (still can't think of it) and when I couldn't I removed the wrong half of the sentence. Perils of editing on a tiny screen."
] |
[
"Why are coastlines crinkly near the poles but smooth in the tropics?"
] |
[
false
] |
I've noticed from playing that you can instantly tell how close an island is to the poles by how crinkly its coastline is. Everything in the Arctic or Antarctic has intricate crinkly edges: Svalbard, Ellesmere, the Falklands, the Kerguelen Islands. Tropical islands look totally different, smooth and rounded: Sri Lanka, Barbados, Nauru. Why's that? Edit: I'm getting notifications every few minutes about glaciers, erosion and Slartibartfast, and almost all of the comments vanish so no one but me can see them. But thank you for all of the answers, I am feeling thoroughly educated!
|
[
"Jagged coastlines near the poles are caused by glaciation cutting through the landmass and isostatic rebound.",
"Smooth coastlines in the tropics and as you near the equator are due to heavier weathering from rain and liquid water.",
"Ice cuts, water erodes.",
"This is just the simple explanation from what I remember. Credentials- B Sc. Geology.",
"Edit: Additionally, I'd also like to point out that there are exceptions to this. Abundance of \"jagged\" toward the poles and \"smooth\" near the equator is just describing prevalence. Citing a smooth coast near a pole or a jagged pole near the equator doesn't discredit prevalence. For example, Hawaii, being relatively recently created by magma plumes it will take lots of time due to the mineral composition and youth of the islands for them to either smooth out or erode away. Another example is the tectonic uplift along the US west coast.",
"Edit 2: There are some top level comments that are more descriptive than mine with some good additional information. Don't just read mine because its higher and forget to scroll down for the more in depth comments."
] |
[
"Because of the way that glaciers and waves shape the land.",
"In the polar regions, glaciers advance and retreat over thousands of years, carving out fjords and other features in the coastline. The glaciers erode the land, creating valleys, and deposit the rock and sediment they have picked up in the process, building up landforms like moraines. This process creates a crinkly or jagged coastline.",
"In tropical regions, waves are the main agent shaping the coast. The waves erode the land primarily through a process called longshore drift, in which waves hit the coast at an angle and push sediment along the shore. This process creates a smooth coastline because the waves tend to erode the land evenly, not carving out fjords or creating other distinct landforms.",
"Climate and sea level changes also play a role. In warmer climates, sediment is transported more quickly, leading to a less-pronounced coastline and sometimes sediment deposits forming barrier islands or lagoons"
] |
[
"There's also a lot of rounding and smoothing from biomass -- soil erosion depositing deltas, for example."
] |
[
"Do lower rates of photosynthesis necessarily mean lower rates of carbon intake in trees?"
] |
[
false
] |
Or more specifically, do trees use carbon dioxide as it comes in, or do they have a way to store it before actually using it in photosynthesis?
|
[
"Trees can't. Cacti can.",
"Plants need CO2 and get it by opening little valves called stomata on their leaves. This lets CO2 in but also lets water out.",
"If you are a cactus or a jade plant you open your stomata at night when water loss is slower and store CO2 as ",
"crasullacean acid",
". During the day when the sun would bake water out of you, you close your stomata most of the way and photosynthesize with stored carbon while losing 6x less water.",
"Maple trees are C3 plants. They can close their stomata when low on water, but have no stores of CO2 to use. This is more efficient so long as there is surplus water. C4 plants like corn can very briefly store CO2 as malate, but they do this to move it around in the leaf and not to amass a huge stockpile."
] |
[
"Might mention the existance of CAM photosynthesis as well. CAM plants also can store CO2 in form of organic compounds during the night and use it for PS during the day."
] |
[
"Thanks for the answer! Thanks for the link as well -- that was quite helpful."
] |
[
"Does medicine really absorb into your system faster if placed under your tongue?"
] |
[
false
] |
I've heard this before as for with heart medication to place it under your tongue so it gets directly and more efficiently into your blood stream. If so then why and how does it work? Also wouldn't the same go for alcohol if you hold it under your tongue, it should get absorbed into your blood stream quicker? I know that you can get drunk by placing alcohol in your rectum for a similar reason.
|
[
"I've heard this before as for with heart medication",
"That is nitroglycerin. It is one of the few medications which is administered sublingually (under the tongue). Once absorbed, nitroglycerin is converted into nitric oxide (NO), which is a naturally-occurring vasodilator (expands blood vessels). It is absorbed quickly and has a quick effect, which is one of the advantages of the medication.",
"Medications absorbed through the mouth has one other property: it doesn't travel to the liver first. When medication is absorbed by the intestines, it first travels to the liver. There, it is subject to ",
"first pass metabolism",
". The liver can either reduce the amount of active drug, or in drugs that need to be metabolized into an active form, it can increase the amount.",
"Alcohol can also be absorbed through the mouth, as it is membrane permeable. Its membrane permeability also allow the breathalyzer test to work: a little bit of alcohol evaporates out of your mouth, which you can clearly smell or detect with a breathalyzer."
] |
[
"This does produce an erroneously high value. I believe people have actually tried this defense in court, but don't quote me on that.",
"When I was in middle school, we had an inventor of one of the breathalyzers come in. He had a student swish mouthwash and tested them right after. Their calculated BAC was very high."
] |
[
"At least in Finland breathaliser results are not used in court. If you blow over the limit you get bloodtests."
] |
[
"Will the asteroid belt eventually become a planet?"
] |
[
false
] |
Figure that seems like a logical step in the formation of planets (a bunch of small pieces forming larger and larger chunks of matter), but then I'm wondering if there's some counteracting that the outer planets do that might keep them in a more uniform distribution.
|
[
"No. The current thinking is that the asteroid belt is matter that never formed a planet, but there is no mechanism that would cause it to merge into a single object. It's also worth noting that the entire asteroid belt has a mass equal to about only 4% of the mass of the Moon."
] |
[
"Purple tags aside (although I might have to change my username to \"purple tag guy\"), ",
"here",
" is a source, which includes this:",
"The total mass of the Asteroid belt is estimated to be 3.0 to 3.6×10",
" kilograms, which is 4 percent of the Earth's Moon."
] |
[
"Larger than Mars? Were do you get your info from? I don't know about initial masses of the ring that didn't coalesce due to the gravitational influence of Jupiter or whatever mechanism, but I cannot believe that the asteroid belt currently contains any magnitude of the mass of Mars in it. I would be absolutely amazed to see your source for this."
] |
[
"Are there any mammals or reptiles that evolved into the water and then back out again (or vice versa with amphibians)?"
] |
[
false
] |
More specific, is it possible for an animal to change phylum and then back or different one?
|
[
"This is one hypothesis for the origin of snakes-they came from marine ancestors. See: ",
"http://en.wikipedia.org/wiki/Snake#Origins",
"\nBut no one really knows for sure.",
"Also, changing phylum is something entirely different. Amphibians, mammals, fish, and reptiles are all in the same phylum. And you can't really change phylum because a phylum is defined as an ancestor and all of its descendants, no matter what environment they live in."
] |
[
"I don't know of any examples where a terrestrial vertebrate evolved to be fully aquatic and then evolved to be terrestrial again. There is a hypothesis that this is true of humans (",
"http://en.wikipedia.org/wiki/Aquatic_ape_hypothesis",
") but most scientists consider it to be unlikely. In any case, if an animal did this, it would not change its phylum or even its class. Whales are still vertebrates and mammals even though they live in the ocean, and this would still be true even if they evolved to live on land again.",
"There are lots of examples of species evolving to resemble a more ancestral state. Whales of course evolved from fish that came onto land then returned to the water. Flightless birds like ostriches evolved from a flightless running dinosaur that became a flying bird that became a flightless runner again."
] |
[
"The aquatic ape hypothesis is nearly universally considered nonsense, mind you."
] |
[
"What’s the largest star system in number of planets?"
] |
[
false
] |
Have we observed any system populated by large amount of planets and can we have an idea of these planets size and composition?
|
[
"There is some speculation that most/all star systems (after sufficient time) ",
"self-organize",
" themselves into systems of 7-10 planets. This would be accomplished through Harmonic-Resonance which would cause all matter in an accretion disk to get pushed/pulled into bands at specific intervals from the parent-star.",
"Evidence of this process exists in our own solar-system, as material between Mars and Jupiter has never coalesced into a planet of its own, but instead is constantly agitated by the bodies around it leaving the matter strewn about in an Asteroid Belt. "
] |
[
"There are several systems that are known to have at least 6 planets. TRAPPIST-1 has 7 known planets. Kepler-90 is reported to have 8. HD 10180 has been reported to have as many as 9, but all the exoplanet catalogs I've looked at (",
"NASA exoplanet archive",
", ",
"exoplanet.eu",
", and ",
"exoplanets.org",
") only list 6 planets as confirmed."
] |
[
"Probably not, it is just easier to find planets here than elsewhere."
] |
[
"Is an encrypted disk volume more susceptible to becoming completely unreadable if some of its bits are altered or lost?"
] |
[
false
] |
[deleted]
|
[
"Your answer will depend on what type of encryption algorithm you use and what kind of corruption you mean. For example, using AES encryption in ECB mode would be generally resistant to \"bit flipping\" data corruption, while CBC mode is less so.",
"With AES in ECB mode, the encryption procedure takes fixed-size blocks (for example, every 16 bytes) and applies an encryption procedure that only depends on the encryption key and those 16 bytes, meaning that the decryption process of those 16 bytes is independent of the rest of the encrypted disk. In this case each instance of data corruption would lead to at most 16 bytes being destroyed.",
"However, AES in CBC mode (chained mode) is different. The encryption of a particular 16 bytes depends on those bytes, plus the encryption key, ",
". This means that cipher blocks are dependent on one another. Here the decryption is such that only the corrupted block and the subsequent block will be destroyed (for a total of 32 bytes). This doubles the theoretical loss rate due to errors. ",
"Why would you ever use CBC over ECB? Since each 16 byte block is independent of every other 16 byte block in ECB mode, this encryption mode leaves a significant amount of statistical data intact, even though the exact data is obscured. CBC mode (and later modes) are designed to destroy this statistical residue.",
"There's an absolutely fantastic picture of a penguin encrypted with ECB and CBC modes showing this over on Wikipedia, as well as a better explanation of ECB, CBC, and other block cipher operating modes.",
"https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Common_modes",
"However, you're specifically asking about hard drives. A consideration when discussing ECB vs CBC for hard drives is that these drives do not read and write 16 bytes at a time. Instead, the basic unit of read and write are 512 byte sectors. Because of this, data integrity is often enforced in chunks of 512 bytes at the hard drive level. If ",
" data in a 512 byte sector is corrupted then the ",
" 512 byte chunk is considered corrupted. It doesn't matter if 16 bytes are corrupted due to ECB, or if 32 bytes were corrupted due to CBC, or if just a single byte was corrupted, the entire 512B block would be considered unreliable.",
"But here's the thing: Data corruption on unencrypted plaintext would also cause the loss of that 512 byte sector. It doesn't matter if that sector happens to be encrypted or not, the data integrity mechanism discards it either way.",
"The one exception to the above statement is that a CBC error may propagate across two hard drive sectors instead of one. The block at the end of one sector may be corrupted, which causes the block at the start of the next sector to be corrupted, in which case a total of 1024 bytes would be considered unreliable and thrown away. Since a block is 16 bytes and a sector is 512 bytes there are a total of 32 blocks per sector... assuming that your data corruption strikes randomly then you've got a 1/32 (or approximately 3%) chance that a corrupted block happens to be the last block of a sector. Thus, 3% of the time a data corruption error in CBC mode will cause the loss of 1024 bytes, and 97% of the time it will cause the loss of 512 bytes. In the original ECB mode a data corruption will cause the loss of 512 bytes 100% of the time. ",
"This cross-sector corruption is the only place where either ECB or CBC is more vulnerable to \"bit flip\" data corruption than their unencrypted counterparts. ",
"But the story isn't over yet. Yet another dimension to your answer is that there are different types of data corruption and not all encryption algorithms deal with all types of corruption the same. What I said above applies to \"bit flip\" errors, where some of the data is permuted unexpectedly. There are also \"bit slip\" errors, where bits are accidentally added or removed from the ciphertext. These are much more problematic for block ciphers, because block ciphers rely on everything being aligned to neat 16-byte boundaries. If you add or remove bits then suddenly none of your data is neatly aligned, and decryption will fail for ",
" encrypted block, not just the block that contains the slip.",
"But again, adding random bits to unencrypted data causes problems there as well, so it's hard to single this out as a specific vulnerability of encrypted hard drives. The encryption would make data recovery a pain in the tuckus compared to unencrypted drives, but a savvy data recovery tech could fix bit slip errors in either an encrypted or unencrypted situation. "
] |
[
"It depends upon the implementation. Many encryption schemes also employ compression in one form or another, and many compression algorithms employ varied notions of integrity checks and recovery records (the latter of which is often configurable, to allow the user to increase the amount of data in the archive devoted to redundant recovery record data, to allow for more corruption before the archive is lost forever). The simplest form of recovery is the computation of/inclusion of a parity bit for each semi-arbitrarily-sized record.",
"Of course, there's nothing preventing an encryption implementation from directly implementing integrity checks and recovery records; I only bring it up in the context of compression algorithms because the features are prominent in mainstream familiar applications like 7zip and winRAR."
] |
[
"One thing seems worth adding: Compressed disks generally have some sort of metadata that can be crucially important. For instance, Linux's dmcrypt has a special block where it keeps the actual key your data is encrypted with, and your passphrase then encrypts that key. This allows for multiple passwords that unlock the same drive.",
"However this means that if this data were to become damaged, the entire disk would become impossible to decrypt. ",
"That can be either a good thing (if you want to have a way to quickly render the whole disk unreadable without writing over the entire drive), or really bad, if something causes that particular bit to be lost."
] |
[
"Have humans evolved in the last two thousand years and if so how?"
] |
[
false
] | null |
[
"Humans are always evolving. However, 2,000 years is a very tiny length of time to be looking for evolutionary changes. You need to bump that up to at least 5,000, preferably more like 10,000 years to see significant evolutionary changes. "
] |
[
"The disease response things mentioned would be the most recent evolutionary changes. Which makes sense if you think about it, the quickly evolving pathogenic microbes and viruses are the only persistent challenges to human fitness (across all human populations). I'll throw in a few of my favorite examples when I'm asked about this (they're older than 2,000 years ago though).",
"Lactase persistence",
"--the ability for humans to drink milk after infancy. It's a very unique mutation, pretty specific to humans; there's a few different mutations with a few different timelines. ~7,500 years ago if memory serves.",
"Blue eyes",
"--This has actually been traced back to one individual who lived ~6,000-10,000 years ago and has been heavily selected for (especially recently). That individual lived in a population around the black sea, if memory serves."
] |
[
"that's not always true. humans are being tossed into a radically new environment which is a catalyst for rapid evolutionary change. ",
"for instance, the hippos closest cousin is the whale, which has evolved so rapidly upon becoming buoyant we required substantial genetic evidence to discover this. ",
"it is also the case that genetic diversity typically leads to sudden but limited rapid adaption. until the relevant genetic diversity has run dry. after which we must rely on more on mutation than our current genetic diversity.",
"one thing worthy of note is that humans have been filtered through a bottleneck, so we might have rather limited genetic diversity compared to other species. ",
"anyways, if i had to guess, the major changes are probably our newly evolved substantial resistances to the foods provided by agriculture. such as grains and milk, alcohol, which are not part of the hunter gatherer diet. however resistance is a far cry from healthy. ",
"keep in mind the crux of evolution is reproduction, especially considering humans don't die very much. so we have probably evolved to cope with the increasing density of competing humans in our environment, as well as city life/reproduction. ",
"for this same reason, we probably still do not have many resistances to modern poisons, such as lead and other heavy metals. these are dramatically different from poisons encountered in the wild which are designed to be fast acting and easily recognizable as a result. and evolution doesn't care about long term damage very much anyways. "
] |
[
"[Astronomy]Why does space not have random visible light noise?"
] |
[
false
] |
If the universe has random noise and background radiation from the big bang, why is nobe of it in the visible spectrum?
|
[
"The temperature of the cosmic blackbody radiation that fills space is between 2 and 3 kelvins. As a result, the thermal photons are concentrated at wavelengths much longer than those of visible light. This temperature is so low because space has cooled off as it has expanded, and it has been expanding for a long time."
] |
[
"Also of interesting note is that the anisotropy of the CMBR - i.e. how much it varies from one location in the sky to another - is less than one part in 100,000, so even if it was visible it would look pretty damn uniform."
] |
[
"Additionally at one time in the past this background radiation would have been in the optical, but as already said it has 'cooled' since to microwave wavelengths. Prior to this it would have had shorter than optical wavelengths."
] |
[
"What are the difficulties with algal Bio fuel, biodiesel specifically?"
] |
[
false
] | null |
[
"Very interesting...keep us updated on how it goes.",
"The main problem in industry is balancing cost and yield. If you dont control their environment (farming them in the ocean), then they spend all their energy fending off disease and the like, rather than producing lipids which can be turned into biodiesel. If you DO control their environment, the organisms yield more lipids. But so far, not in a cost effective way.",
"If you are going to do this in your backyard, I would recommend figuring out how to avoid contamination. Viruses and other microbes that could out-compete your algae are your biggest threats.",
"Also, make sure you get the right genetics for your algae. You want a strain that has been engineered to produce as much lipid as possible."
] |
[
"I looked into producing biodiesel some years back, the chemistry is pretty easy, so long as you have access to the right things. A few of them wont be readily available come the zombie apocalypse."
] |
[
"I'm curious about how do you plan to do it. I can help you out (I make setups to carry out chemical reaction engineering all the time) with tweaking your design if you share.",
"Forgetting the actual process for a second, you need to figure out how you're gonna test the product. My labmates do this with a DSC to measure the heating value of the fuel. If you look at papers they provide an Oxygen to Carbon ratio of the product so if it's low you're doing well. Biofuels are plagued by high O content. ",
"Caveat: My expertise in hydrothermal processing of biomass rather than biological/fermentation techniques. "
] |
[
"Could one say that our body is basically a biotechnic robot controlled by our brain?"
] |
[
false
] |
I started to think about it after watching
|
[
"This view overemphasizes brain states and neglects the contribution of body states, which are implicated in emotional responses that have been shown to be involved in human decision making. See \"the feeling of what happens\" by Antonio Damasio and research on embodied cognition, and affect. ",
"This also downplays social aspects of learning and thought."
] |
[
"I should clarify and elaborate. You can get some background on ",
"embodied cognition from Wikipedia",
"George Lakoff's writing is often accessible: ",
"http://www.qwiki.com/q/#!/George_Lakoff",
"Lakoff, for example, talks about how metaphor plays a role in thought, and how important the body is in those metaphors.",
"Describing the body as a robot controlled by the brain is a metaphor that obscures the interrelationship between body and brain, or the brain as a part of a body, that helps to form the mind.",
"So, my problem was with the description (note: that's what OP's question was about: \"Could one say\"). Of course, one could say this; I am merely noting that if you do say that, you're choosing a perspective that downplays a lot of research on the role of the body in the mind."
] |
[
"As a student of neuroscience, I think that you are either misinformed or misconstruing the information you have. As far as my education has shown me, thought is an activity that happens solely between the neurons of the brain. ",
"Thought is profoundly effected by stimuli from the outside world. These stimuli can be as simple as a sound or a flash of light, or as complex as having a conversation with a good friend. From the brain's perspective, they are all stimuli. ",
"It is from how the brain processes the stimuli that we get complex conceptions such as language and conversation and other people's minds. But every thought of yours in an activity that takes place within your skull, and is based on the stimuli you receive through your sensory systems.",
"So I conclude with a rephrasing of your \"Thought is purely brain-based\" postulate. I'd say that 'Thought is purely brain-located, and is based on the senses.'"
] |
[
"Does freezing and thawing store-bought bread affect/retard mould growth?"
] |
[
false
] | null |
[
"First of all, most bread mold won't really hurt you. However it is obviously undesirable to eat. You can definitely keep it in the freezer to prevent mold from growing, if you don't mind the loss in quality of the bread. The fridge will slow down mold growth quite a bit, but in the fridge your bread will go stale much faster (the starches are crystallizing faster). This doesn't happen in the freezer, as long as the bread freezes quickly enough.",
"TL;DR go ahead and freeze that shit."
] |
[
"Thanks you for your reply. ",
"Please let me clarify the question. If you freeze and then immediately defrost the bread, is that series of actions beneficial to bread shelf-life, all things being equal?",
"Thanks, ManofMystry"
] |
[
"Gotcha. Good question. I really don't know for sure, but I'd guess probably not."
] |
[
"Why do flesh, tissue, muscle, bone, skin all heal on their own but Teeth don't?"
] |
[
false
] |
You break a bone and it will heal. Tear a Ligament or muscle, it will heal. Cut skin, it heals. Why do bad/cracked teeth not heal and go back to normal after a while?
|
[
"There are two cell types responsible for making teeth. The ameloblasts and the odontoblasts. The ameloblasts make the hard enamel that protect your teeth and the odontoblasts make the softer dentin that makes up the core of your tooth. ",
"Enamel is deposited on your tooth like frosting. Inside-> outside. This means that the ameloblasts are on the outside of the tooth when it erupts. As a result, they all die, and you lose your ability to generate new enamel. The odontoblasts live on after eruption, so you can generate new dentin, but it is the enamel which makes your teeth what they are, so if you lose that, you are SOL."
] |
[
"In addition, to answer the other ",
" (Why did we evolve like this?):",
"Because there hadn't been enough evolutionary drive to make proto-teeth develop in another way, and since then we're stuck at a local maximum in DNA-space. In non comp sci terms: As teeth are \"modified\" scales, they were \"intended\" (excuse the ID-like metaphor) to be continuously replaced - such is the case in many animals, most famously sharks, but happens in different forms in mammals - we have two sets of teeth, elephant's have 6 sets of molars, lagomorph incisors grow continuously (but only new dentin is produced). ",
"Why do we have only two sets and not six like the elephants? Because two sets are enough to bring us to breeding age, what happens after that offers no evolutionary pressure.",
"Evolution is a ",
" and does things like this all the time."
] |
[
"What?"
] |
[
"Some materials are better erasers than others, why do graphite particles stick better to some materials than others at a molecular level?"
] |
[
false
] | null |
[
"Not a certified scientist but how I understand it, graphite is comprised of covalent carbon bonds that exhibit mainly London intermolecular bonding with other substances. This means that it won't stick as well to more polar substances (i.e. glass, some plastics, etc.) while it bonds well with materials like drywall paint and paper which I'm guessing are oil/lipid based and would exhibit London bonding."
] |
[
"I believe so. I'm really spitballing here but I think the eraser is more attracted to the simple carbon bonds of the graphite than the the lipid bonds of the lapsed. I'm assuming the paper chemical bonds are lipid soluble because it comes from tree bark which is an organic substance and cells have a lot of phospholipids. ",
"Edit: also this: \"When you rub an eraser across a pencil mark, the abrasives in the eraser gently scratch the surface fibers of the paper to loosen the graphite particles. The softeners in the eraser help to prevent the paper from tearing. The sticky rubber in the eraser grabs and holds on to the graphite particles.\n",
"http://wonderopolis.org/wonder/how-does-an-eraser-work/",
"Actually this previous askreddit is way more accurate than everything I've posted: \n",
"https://www.google.com/amp/s/amp.reddit.com/r/askscience/comments/2kp9m9/how_does_graphite_bind_to_paper_and_how_does_an/?client=safari"
] |
[
"I believe so. I'm really spitballing here but I think the eraser is more attracted to the simple carbon bonds of the graphite than the the lipid bonds of the lapsed. I'm assuming the paper chemical bonds are lipid soluble because it comes from tree bark which is an organic substance and cells have a lot of phospholipids. ",
"Edit: also this: \"When you rub an eraser across a pencil mark, the abrasives in the eraser gently scratch the surface fibers of the paper to loosen the graphite particles. The softeners in the eraser help to prevent the paper from tearing. The sticky rubber in the eraser grabs and holds on to the graphite particles.\n",
"http://wonderopolis.org/wonder/how-does-an-eraser-work/",
"Actually this previous askreddit is way more accurate than everything I've posted: \n",
"https://www.google.com/amp/s/amp.reddit.com/r/askscience/comments/2kp9m9/how_does_graphite_bind_to_paper_and_how_does_an/?client=safari"
] |
[
"How are artificial flavors that mimic natural flavors made?"
] |
[
false
] |
Fruit flavored candy, BeanBoozled, ect.
|
[
"In some cases there is a very specific molecule that gives a majority of the characteristic to a natural flavor. If that happens to be true and if the molecule happens to be fairly simple then it can be manufactured in huge quantities for low costs using chemical industry. For example, limonene provides a citrus taste, ethylvanillin tastes like vanilla, cinnamaldehyde tastes like cinnamon, etc. Not exactly, because the natural flavors contain a whole family of other molecules that subtly affect the overall taste, but enough for artificial flavorings to seem very similar to the natural examples.",
"Fun fact, artificial banana flavor comes from isoamyl acetate, this is the core flavor compound in ripe Gros Michel cultivar bananas. Of course, modern bananas are of the Cavendish strain, which taste different and don't have as strong an isoamyl acetate smell, which is why artificial banana flavor tastes different to modern bananas."
] |
[
"Even if the molecule is quite complex it can be mass-produced. This is most commonly done using modified yeast cells. And because it's are produced by living organisms, the product is considered 'natural' and not 'synthetic'. "
] |
[
"Adding onto this:",
"Another factor in synthetic flavors (all flavors, really) is actually smell",
"(1)",
" and color",
"(2)",
".",
"One of the ways that Skittles saves in production costs is by changing the colors and smells of their skittles, but the actual flavor remaining the same.",
"I know that you asked about the ",
" specifically but there's much trickery involved, especially when it comes to artificial things."
] |
[
"Why do birds, insects, squirrels, and other animals move in short, jerky motions?"
] |
[
false
] | null |
[
"It's a matter of size. It takes a lot more energy for a large animal to accelerate/decelerate a limb or such. On the scale of an insect, beating their wings is relatively easy. Here's the wikipedia article on the ",
"Square-Cube Law",
" in regard to biomechanics."
] |
[
"Survival would be the main focus. They move short distances and check for any dangerous situations or predators. Hence you always see a bird when eating to pick to the food a few times, and then look around a few times, rinse and repeat."
] |
[
"Fast movement allows the organism to be still more often, and movement attracts predators."
] |
[
"How are food calories scientifically measured, and how well does this reflect what is actually biologically available in living systems?"
] |
[
false
] |
What I have read suggests that basic values for caloric content are derived from bomb calorimeter studies, which seems to just represent how much heat energy can be given off by the substance through igniting it making careful measurements. Obviously this would not be a perfect surrogate for calories available to all living systems. For instance humans are unable to digest cellulose, so although it could give off energy on ignition, it would not be biologically available to humans. So how did we figure out calorie content for various complex foods and what its functional impact would be on human nutrition?
|
[
"This Link",
" might provide some usefull information. It states that the bomb calorimeter is an out-dated technique and not used anymore.",
"most of the calorie values in the USDA and industry food tables are based on an indirect calorie estimation made using the so-called Atwater system. In this system, calories are not determined directly by burning the foods. Instead, the total caloric value is calculated by adding up the calories provided by the energy-containing nutrients: protein, carbohydrate, fat and alcohol. Because carbohydrates contain some fiber that is not digested and utilized by the body, the fiber component is usually subtracted from the total carbohydrate before calculating the calories.",
"More information can also be found ",
"here",
".",
" ",
"the wikipedia page",
" gives also some more detailed information."
] |
[
"To expand, the values used are:",
"4 Cal/gram usable carbohydrate",
"4 Cal/gram protein",
"9 Cal/gram fat",
"7 Cal/gram alcohol",
"It's not exact, especially when it comes to the large variety of carbohydrates that exist, but it's good enough for government work."
] |
[
"There's this device called a bomb calorimeter, which is a chamber pressurized with oxygen and filled with whatever you want to measure. ",
"You put this chamber in a very specific (well measured) amount of water, ignite it, then measure the change in the temperature of the water. ",
"From this, you are able to say how many calories are in whatever you burned. ",
"How does this relate to your ability to metabolise the food? ",
"I don't know, but that first part is what I understand. ",
"Edit: I'm sorry, I just answered what I know, which you also seem to know. "
] |
[
"What will happen to the frequency and wavelength of the sound wave if we directly change the speed of sound? How will they change?"
] |
[
false
] | null |
[
"The sound wave will ",
"refract",
", similarly to how light would. The frequency stays the same and the wavelength changes."
] |
[
"Is that what causes your voice to sound funny when you inhale helium?"
] |
[
"This already happens with refraction. If a light wave enters another medium, the velocity of that photon will change according to the index of refraction.",
"When this happens, the wave length changesbut the frequency stays the same. V is proportional to wavelength, so when velocity increases, so does wavelength."
] |
[
"Could a railgun projectile reach low Earth orbit? The ISS?"
] |
[
false
] |
I understand that a railgun projectile could reach speeds of over 7000mph(high estimate) or 5000mph(low estimate). I was unable to find a range of the projectile or a definitive answer on the weight but one article from 2012 mentions it being around 40lbs. I know it would not be able to STAY in orbit however is there a possibility of the projectile reaching LEO and damaging satellites or even the ISS?
|
[
"No.",
"The speed that you mentioned is enough to reach the ",
" of the ISS and many satellites, even though not fast enough to remain in orbit. If your objective is just reaching it (based on your use of the word \"damage\" I guess crashing isn't a problem) this could be enough, if sent in a trajectory where the satellite is expected to hit it.",
"But this is only if we neglect atmospheric drag. In real life the projectile will burn up like a meteor",
" , and even if it were designed to resist the heat, the viscosity of the atmosphere will slow it down until it falls back before reaching any meaningful altitude.",
" The low estimate of 5000mph is equivalent to Mach 6.5. This is moderately hypersonic. It may not be as fast as a spacecraft returning from orbit, but on the surface atmospheric density is a lot higher."
] |
[
"In real life the projectile will burn up like a meteor",
"Just thought I'd add a visual for anyone interested. ",
"Here's some text footage",
"."
] |
[
"For a roughly circular projectile, atmospheric drag is a huge problem. It's proportional to the square of the velocity if the velocity isn't very low. This gives you the differential equation v'=-kv²-g, which has the solution v=tan(atan(k v0/q)-tq)q/k and x=log(cos(qt)+sin(qt)v0 q/g)/k. where v is the velocity, x the position, g the gravitational acceleration and q=sqrt(gk).",
"Solving for the turnaround point v=0, we find t=atan(k v0/q)/q. Arcus tangent asymptotes towards pi/2, so unless k/q is very small increasing v0 has very little effect. In this limit, the maximum height is x=log(v0/g), so the velocity required to reach a given height grows exponentially with the height. It is an extreme case of diminishing returns. Based on this it should be very hard for a meteorite impact on Earth to knock free pieces of rock that could impact other planets. The impact fireball basically needs to be as thick as the atmosphere.",
"The way around these problems is to make the drag as small as possible compared to other forces. A good shape is a long, ",
" rod (rocket shape) that has high momentum compared to its drag. A rocket loses only a small fraction of its energy to drag. So if you want your railgun to reach satellites, it should fire rails.",
"Using railguns to launch objects into space",
" has been considered, and could potentially be cheaper rockets.",
"Edit: katinia points out that aerodynamic shapes result in very high heat absoroption that will be problematic for reasonably-sized objects. In order to avoid losing enormous amounts of energy to drag, the shape still has to be long enough.",
"Newton's impact depth approximation",
" states that an object will stop approximately when it has displaced mass equal to its own mass. We can use this to get a rough estimate for how long the projectile needs to be. Our atmosphere has a scale height of about 7.6 km, which means that if it were compressed into a slab the same density at at sea level it would have that height. A projectile with surface area A, length L and density rho will have pushed air equal to its own mass after moving a distance x given by AL rho = Ax rho_air, giving x=L rho/rho_air. Air density at sea level is about 1.23 kg/m³, so if your projectile is made of steel (8050 kg/m³), the length needed to just barely exit the atmosphere (completely ignoring gravity) is 7.6 km * 1.23/8050 = 1.1 m. To only lose a small fraction of its momentum, it should be several times this length, for example 10 m.",
"The width of the projectile will be a tradeoff between the energy required to accelerate it, which is proportional to its mass and hence its width given a fixed length, and to heat dissipation considerations that drive it towards a blunt shape. I'm not sure what the optimal shape would look like, but it would probably be longer than in reentry vehicles, since those don't rely on preserving momentum to make it through the atmosphere."
] |
[
"How does exercise affect mood, and what is the best type of exercise for mental acuity?"
] |
[
false
] |
As a programmer, and before I had this profession; I noticed it was harder and harder for me to sit down and concentrate and work through a boring, but necessary task. I've also been, not necessarily a couch potato, but definitely not getting my recommended allowance of exercise. I had known, in theory, that exercise can help improve concentration. However, after starting running, I noticed I could work much more efficiently than usual; tasks that I couldn't bring myself to do before fell easily. I did some research (of the google variety) and it seems there is a general pop-sci consensus that exercising is affecting dopamine and endorphin levels; and this would probably account for my ability to concentrate. I read somewhere else that aerobic exercises were more associated with dopamine and endorphins than anaerobic exercises; so things like jogging would be better than weight lifting; for increasing dopamine production. In any case; it seemed to me that this is actually not really well understood at all (despite the pop-sci confidence). I am hoping someone with some expertise can give me a way to think about the exercise <-> concentration link, and maybe give some clarity as to what is really understood on the topic. At a high level, I am looking for a way to optimize my fitness routine around a sense of well being and being able to concentrate.
|
[
"OK. Here's what science can tell you to do wrt using exercise to improve executive function. ",
"30 minutes, hard aerobic exercise, 3X per week. This is what most studies use. It has a clear, unambiguous impact on executive function over a time period of months. You will become a more effective programmer. I recommend Monday-Wednesday-Friday noon workouts, as there is also a boost for a few hours after exercise, and putting the three workouts in the middle of work days will let you take advantage of that. ",
"Whenever you workout in a day, it will impact you energy at other times in the day. Early morning workouts lead to sluggishness late in the day. Late day workouts lead to sluggishness early, etc. ",
"The relationship between exercise and executive function is thought to exist because the aerobic stress boosts neurotrophin levels (especially BDNF), which promote the health of neurons in the brain in a pattern dependent on metabolic usage. The neurons most used in executive function also have the largest metabolic needs. ",
"The only other thing to mention is that executive function also depends on insulin resistance. If you drink a lot of sugar drinks (sodas or juices), it will make you insulin resistant and have a negative impact on executive function. Don't do that. ",
"hth"
] |
[
"Thanks, I have been doing that.",
"What I have learned is that running is better than lifting; and also better than stationary biking of similar intensity. ",
"It also seems that longer is better (for ability to concentrate) but worse for recovery.",
"I'd like to know more though because I am sort of bouncing around; mostly running. I don't mind experimenting, but I'd rather reduce my search set if possible."
] |
[
"Thanks, I have been doing that.",
"What I have learned is that running is better than lifting; and also better than stationary biking of similar intensity. ",
"It also seems that longer is better (for ability to concentrate) but worse for recovery.",
"I'd like to know more though because I am sort of bouncing around; mostly running. I don't mind experimenting, but I'd rather reduce my search set if possible."
] |
[
"How much propylene glycol would it take to kill you?"
] |
[
false
] |
I saw the news story on Fireball being pulled from European shelves due to a high amount of propylene glycol. Is there enough in it to kill someone? If not how much would someone have to drink before there were any harmful effects?
|
[
"an additional comparison would be to the ethanol in the beverage:",
"LD50/LC50:\nCAS# 64-17-5:\nDraize test, rabbit, eye: 500 mg Severe; Draize test, rabbit, eye: 500 mg/24H Mild; Draize test, rabbit, skin: 20 mg/24H Moderate; Inhalation, mouse: LC50 = 39 gm/m3/4H; Inhalation, rat: LC50 = 20000 ppm/10H;\nOral, mouse: LD50 = 3450 mg/kg;\nOral, rabbit: LD50 = 6300 mg/kg;\nOral, rat: LD50 = 9000 mg/kg;\nOral, rat: LD50 = 7060 mg/kg;\nCAS# 7732-18-5:\nOral, rat: LD50 = >90 mL/kg;",
"http://www.nafaa.org/ethanol.pdf",
"So, essentially, the lethal dose of propylene glycol is two to three times higher than the alcohol. ",
"Just because it is \"in antifreeze\" doesn't make it extremely hazardous. Ethylene glycol is the dangerous material in antifreeze, but is a different compound. "
] |
[
"A common way to measure the toxicity of a substance is the ",
"LD50 test",
". A population of laboratory animals receive the same dosage of the substance. The amount of killed animals is counted and the test is repeated with higher/lower dosages until half of the population is dead. The result is influenced by the route of administration (oral, intravenous, dermal etc.), as well as by the chosen species. For obvious reasons, there are no LD50 measurements for humans, so we can only get an approximation by testing human cell cultures or species that have similar biochemical features. Clinical evidence may put that in perspective, however, we rarely know the exact dosage of accidental, homocidal or suicidal intoxications, though we can gather clinical evidence in elaborate studies about pharmaceutical drugs (however, this is a complex and problematic aspect that is probably off-topic).",
"So the best numbers I can give you are the LD50 for orally administered propylene glycol (1,2-Propylenglycol) in different species:",
"Source: ",
"Toxnet database"
] |
[
"Thanks!"
] |
[
"In movies, when a patient is about to pass out, a common cliche is the first responder saying \"stay with me\" or something to that effect, is there actually any medical benefit to trying to keep a person awake in such situations?"
] |
[
false
] |
The only context I know of where this is helpful is in surgeries where a patient is kept conscious and doctors want to make sure they haven't injured their brain. I don't see how this would help when a patient is losing blood and is entering hypovolemic shock (which is one of the most common context of this). Recently I saw this interview with where she recounts her experience with a ruptured brain aneurysm, she says she tried to keep as active as possible and started repeating lines from memory with the host stating that this is something that you should do in that situation. Is there any scientific basis to justify all this?
|
[
"It's really useful to be able to ask someone what's wrong. It's also helpful to be able to talk to someone to assess them. Keeping an injured person awake until they can be assessed is easier and probably less harmful than trying to wake a person with unknown injuries. "
] |
[
"Doubtful, but keeping them as alert and oriented as possible (read: conscious) will help them maintain airway patency if nothing else."
] |
[
"Yes, but is there evidence that talking with a patient slows down their loss of consciousness? if you are losing blood, for example, the rate at which you lose consciousness depends on the amount of blood lost. "
] |
[
"Why will cocoa powder only mix with warm/hot water but won't with cold water?"
] |
[
false
] |
So I noticed when mixing cocoa powder with water than when I pour cold water into the powder it really resist mixing up properly and it leaves a lot of cocoa powder dross on top even after lots of stirring. But when I pour warm/hot water it mixes up with little to know stirring. I suppose this is a food science question so I will tag it chemistry without that as an option.
|
[
"Warmer liquids in general have a greater ability to dissolve solids, and less ability to dissolve gasses in solution. ",
"A good way to remember this concept is by thinking of the energy in the liquid. A hot liquid, or gas, has lots of energy. All of the molecules are moving around quickly, and they all want more space for themselves. This allows for more space between the liquid molecules, and therefore allows more stuff to be ‘in’ the water. Gassed that are trapped in cool water escape when the water is heated because everybody now has more energy and everybody is moving more quickly and needs more space. The gas escapes water because it is moving quickly and now has room and energy to get out. ",
"This is not always technically accurate, but is a good way of remembering the general concept."
] |
[
"On top of the general answers already given, cocoa powder also contains some amount of fat. The fats will not easily dissolve in cold water, so cocoa is even more resistant to dissolving in cold water than many other substances."
] |
[
"The whole dissolution thing is absolutely correct, ",
". With cocoa powder it's a lot more about the fact the small amount of oils and fats only melt at higher temperatures. If you put a stick of butter in cold water, it's... Not doing a lot. If you heat that water up, the butter can more easily melt. ",
"Plus, most of the cocoa powder doesn't actually dissolve. It ends up being thoroughly mixed through, but if you leave it out for long enough, you'll get a residue at the bottom, and the top bit tastes watery. At first, the particles are in suspension, but over time the larger ones sink to the bottom. Give it long enough, and a good amount will separate out, with only some of it remaining in the water due to the ambient energy and intermolecular forces. ",
"Here's an experiment you can try, of which I have no idea what the result will be. Try to mix cocoa powder with a very small amount of cold water, about equal in volume to the cocoa powder you have, and mix it very thoroughly. Then, once the cocoa powder has turned into a weird, thick paste, add a little bit more water, until it's a thinner paste. Then, try to mix that thin paste into the rest of the water. This is a technique used for corn starch and other thickening agents. I think it won't work perfectly, so you'll still notice imperfect mixing with cold water, but it should be better than normal mixing."
] |
[
"How can two lasers combine to create white light?"
] |
[
false
] |
Two complementary colors, let's say red and cyan, can be combined to create white light. I also know that white light consists of all frequencies. How is it possible that all frequencies can be created from a superposition of just two single frequencies? If this is the case, this is very counter-intuitive.
|
[
"There is a tiny bit of confusion here: color is a psychological property, not a physical one. While it is the case that light composed of all wavelengths in the visible range is experienced as white, so is light made up of just the wavelengths we experience as red green and blue (that's how your monitors and tvs make light that appears white). In both cases, the light is stimulating all three cone receptors in our eyes to an equal extent. This is experienced as white. ",
"The ",
"sensitivity spectra",
" of the three cone types are quite broad. It is therefore a bit misleading to refer to them as \"red\", \"green\", and \"blue\" because each cone actually responds to a wide range of wavelengths. Their peak sensitivities are to wavelengths which we experience as those three colors though. A more accurate name often used is short, medium, and long to describe the wavelength that they are most sensitive to. ",
"The medium and long cone sensitivity functions overlap. So there is certainly a particular frequency at which both kinds of cones would be stimulated equally. You can find combinations of two frequencies that could stimulate all three cone types equally, but it is easier to do with three lights -- you could just swamp all three cone types with high intensity light and they will respond maximally and therefore have the same activation.",
"Because of this organization, it is also possible to find different combinations of lights at different wavelengths that are experienced in the same way. These are called ",
"metamers",
". For example, you could have one light made of two wavelengths and a second from two completely different wavelengths, but we would see them as identical in color and brightness."
] |
[
"That's a good answer, Just one thing to add regarding the addition of wavelengths:",
"To see how different hues could be reached by combinations different wavelengths, one can use the ",
"color gamut",
". pure wavelengths are on the edge, combination of two wavelengths form a line between them, where the ratio of their intensities determine the hue along that line, and the total intensity determines the brightness. In the middle it's white, so any line that passes through there represents 2 possible wavelengths who's correct ration would produce white.",
"Using 3 wavelengths creates a triangle, any color inside that triangle can be reproduced by the combination of different ratios of these 3 wavelengths, red green and blue creates a big triangle which to a good approximation spans the whole color space. Some displays use 4 or 5 different wavelengths to span even more of the color space.",
"I highly recommend ",
"this chapter from Feynman's lectures",
" which explains this whole thing in detail, and even goes into color illusions, for example that the distinction between ",
"brown and orange",
" is not a physical one, but a ",
"psychological",
" one. "
] |
[
"Thanks for solid answers both of you, it helped my understanding a lot!"
] |
[
"Why don't waterfalls get worn down to gradual inclines?"
] |
[
false
] | null |
[
"Waterfalls form where a layer of hard rock lies on top of a layer of soft rock. The soft rock below erodes faster, creating a steep drop, sheltered by a ledge of hard rock above. Eventually, the soft rock starts to erode beneath the hard rock, creating an overhang, which breaks off when it gets too long, creating a new vertical face, so the waterfall gradually moves upstream."
] |
[
"Thank you, that makes perfect sense."
] |
[
"Yeah, more or less. They divert water into reservoirs at night, which is used to power the hydro plant during the day so the falls can be going at full-volume when tourists come by. At night, they're reduced to a trickle.",
"Also, one time the water was fully diverted away from the American falls.",
"For such a dramatic symbol of nature's raw power, the falls are pretty intensely managed."
] |
[
"How do Virtual Machines handle Memory Caches?"
] |
[
false
] |
Let's say I have a multicore processor with three cache levels. On it, there is a hypervisor with two virtual machines running. As I understood it the hypervisor kind of to be a computer with smaller memory to each VM. I also know that a cache is a faster and smaller type of memory, like RAM relates to the harddrive, but a cache can't be explicitly targeted by an application programmer. Does an operating system programmer handle cache accesses? Or is the cache behavior determined by a even lower level, like directly in hardware? If the OS on one VM wants to write to the cache, does it tell the hypervisor "Hey I want to write to this specific line/address of my own virtual cache!"? A "virtual cache" sounds weird, because indirection is slow and caches are supposed to be fast. Also, when multiple VMs each have a dedicated space in the cache, these spaces would be rather small. Therefore, maybe the VM doesn't concern itself with caches and just tells the hypervisor on which vitual adresses it wants to read and write and lets the hypervisor decide when and where to access a cache. Probably I have misunderstood something about operating systems and it works differently altogether. The background to this question is that I'm reading the paper . They explain that the cache opens a side-channel, where information can leak from one process to another. They write that this also works for cross-VM attacks. I want to have a clearer understanding on how the caches of two VMs on the same host interact. I would be grateful for even some pointers.
|
[
"Caches are usually managed entirely in hardware, with no input from the software. This is true in both traditional (single-OS) systems as well as virtualized systems. There is only one set of caches for the entire system (though multi-core processors will usually have a separate L1 and L2 cache for each processor).",
"The cache is a side-channel precisely because it is shared between processes (or guest OSes) on a single system. This means that the data from two different processes can reside next to each other in memory. The recent Spectre and Meltdown attacks both demonstrated side-channel attacks that could be used by a malicious process to extract the data belonging to another process.",
"For example, in the Meltdown attack there is a cache line you want to read the data out of. The hardware is supposed to prevent you from reading this data, and it does, but it can be exploited (tricked) into revealing the data itself. This is done by attempting to use the data and timing how long that process takes. The CPU hardware ultimately denies the request to use the data, but the attacker meticulously arranges memory ahead of time so that the access time reveals the actual contents of the forbidden data. If each byte (eight bits) is one of 256 possible combinations, they need to try 256 possible scenarios, and the one scenario that executes quickly implies the actual value of the forbidden memory.",
"You can read a lot more specifics in the papers at their websites:"
] |
[
"Thanks for the explanation! That’s the first high level detail that I was able to quickly grasp"
] |
[
"I think an additional detail that would help is that most modern cpus have physically indexed caches. Meaning, they are caches of physical memory after virtual address translation. This means that the different VMs will compete for space in the cache but the CPU does not confuse them because they are using unique physical addresses.",
"This requires the operating system and hypervisor to properly setup page tables but they aren't involved in individual memory accesses so long as there is not a page fault.",
"There are systems with virtual caches that require more direct operating system intervention. The virtual addresses include some kind of address space tag which is unique per-process. They require more cache flushes for changes in translation as well.",
"There are also systems where you can more manually manage and partition caches. This is more common in the embedded space where you want to give a stronger guarantee of completion time for a specific process."
] |
[
"If the Earth was tidally locked to the Sun (like the Moon is to the Earth), would it still be able to sustain life?"
] |
[
false
] |
I'm curious to know what it would be like on Earth if we had no day-night cycle at all. Are scientists able to predict what the implications of that might be?
|
[
"If the Earth were tidally locked that would mean that one side the planet is perpetually in sunlight, and the other in darkness. This would result in continual heating of the one side from solar radiation, and cooling of the dark side from radiative loses to space. The atmosphere and ocean current may move some of this heat around a bit but likely not enough to make a difference. The tilting and precession of the Earth's axis may also affect the amount of heating, but again not enough to make a difference. The day side would become literal hell, with temperatures well above boiling,a nd the night side would become Hoth, nothing but Ice. Assuming that the atmosphere and other factors were unchanged (unlikely) the only habitable area would be the terminator (the boundary of night and day where it is perpetually dusk."
] |
[
"I can't recall the source, but I read in an article somewhere that not even the terminator would be habitable, because (and don't quote me on this): If the planet was tidally locked, solar winds unhindered by the Earths rotation would cause winds of up to 1000mph on the surface, effectively killing anything there. ",
"IIRC This was from a previous Askscience thread, if anybody wishes to dig it up."
] |
[
"The earth is protected from solar winds by the magnetic field, which isn't created by the earths rotation but rather the rotation of the earths core. So whether or not the solar winds would blow off the atmosphere, depends on whether or not the core of the earth stops spinning the same time as the earth does."
] |
[
"Why does blowing on a lit match cause it to go out?"
] |
[
false
] | null |
[
"Your intuition that it would burn brighter is good one, because fire needs oxygen to breathe. Fire also needs a fuel and a heat source. When you blow on a match (quite a small flame compared to bellows on a fire pit), which of those three things (oxygen, heat source, fuel) are you taking away?"
] |
[
"Your intuition is correct. You get flames when you have flammable vapors in the air, and they get a source of ignition. I thought it was really interesting when I learned how candles work: the wick of a candle \"sucks\" up wax from the body of the candle by capillary action, and once in the wick, the wax vaporizes relatively quickly. So when you light the wick of the candle, the fire you see comes almost entirely from the vaporized wax. If you have to hold a lighter to the wick for a few seconds before it catches, it's because the concentration of vapors from the wax in the air wasn't high enough at the original temperature. The flame from the lighter/match heats up the wax, vaporizes it to within its flammability limit, and then it catches fire.",
"But when you blow it out, you displace that vapor. Now you're missing fuel for a moment, until enough of it vaporizes again to be within its flammability limit. But by that point, it needs to be ignited again to start the combustion reaction back up."
] |
[
"You can also blow out a fire pit with a bellows and make the coals hotter in doing so. They ignite when you stop blowing. In this case you've got constant fuel, more heat and more oxygen but no fire.",
"What's fire made out of? I think maybe the bellows blow away the stuff that the fire's made out of."
] |
[
"Why did biological creatures evolve to be symmetrical?"
] |
[
false
] |
I understand the biological process that leads to symmetry to a certain extent.. But why did this happen? What's the evolutionary advantage? Is the coincidence due to universal forces and constraints?
|
[
"Bilateral symmetry has evolved many times. Within the echinoderms, which are generally considered pentamerally symmetric, bilateral symmetry has subsequently evolved in at least two groups, the irregular echinoids (sand dollars) and the holothurians (sea cucumbers).",
"Both those groups - as well as most bilaterally symmetric organisms - benefit from the fact that your front end is constantly being pushed into new terrain, with fresh food, and all your sensory organs concentrated there. Waste is generally deposited at the other end, where you just left from, which is another advantage (some gastropods have problems with this since their anus is restricted in location). ",
"Compare to things that have different symmetries. Pentameral echinoderms tend to be realtively awkward in movement and limited sense organs. Sponges are just extremely limited in how they can make a living. "
] |
[
"If they weren't macro symmetrical they would find it harder to move in a straight line, also senses such as hearing and sight would be skewed making it harder to avoid attack and also harder to pinpoint prey."
] |
[
"I think the symmetry is directly linked to the way that creatures move (or do not move) and the medium they are in. Let's look at the three dimensions for a creature on land. Up and down are significantly different due to gravity (parts of the creature are usually in contact with the ground, while others are not). Left and right are not different, so it makes sense that most creatures that move have left-right symmetry. The other dimension (forward and back) might be more of a toss-up: there's probably an advantage to specializing in motion in one direction rather than having a kind of radial symmetry that allows movement in all directions. But I think given these constraints, it would not be surprising to see either left-right symmetry or complete radial symmetry. ",
"Note that plants do not exhibit the bilateral symmetry most animals have because they do not move in a preferred direction. Also, think of how the medium of water affects marine life: because creatures are more suspended in the water, you might expect more spherically symmetrical life forms."
] |
[
"How do poisonous/harmful gases dissipate into the atmosphere?"
] |
[
false
] |
After seeing some news regarding chemical weapons recently I've begun to wonder/worry how exactly poisonous gases become non-lethal. I understand lethality is often a matter of how concentrated the gas is. But does that theoretically mean enough gas can be released into the atmosphere to make it entirely harmful? Or are there other processes which break down the gas into its components and render it harmless?
|
[
"As someone who has sat through a lot of atmospheric chemistry colloquia, let me add that ",
"hydroxyl radicals",
" are (one of?) the major degradation pathways for organic molecules in the Earth's atmosphere (so there's at least some radical chemistry that doesn't ",
" involve UV reactions)."
] |
[
"You could never poison the whole atmosphere, even if you tried.",
"The most potent lethal substance known to man is the Botulinum toxin, with a median lethal dose via inhalation of ",
"3 ng/kg",
", or 186 ng for the average human (about the weight of a large pollen grain). The average human breathes about ",
"10 liters of air per minute",
", or 14,400 liters=14.4 cubic meters per day, which . So even if you could somehow get humans to perfectly absorb every molecule of poison from every breath they took over the course of a day, and every breath was air that wasn't breathed by someone else already, you would need to have a concentration of 186 ng/m",
" which corresponds to a mass mixing ratio (weight of substance in a certain volume divided by weight of air in that same volume) of 1.05*10",
" Now this probably does not seem like a lot, but consider this: the atmosphere weighs ",
"5.3*10",
" kg",
", which means you would need to somehow get over 55000 kg of botulinum toxin (about the weight of the ",
"largest dinosaur ever known",
", which needless to say is many times the amount that exists in the entire world). And remember all the ridiculous assumptions that went into formulating this estimate, so the actual amount needed to \"poison\" the atmosphere is probably millions of times more than this.",
"In addition, most toxic substances are unstable in the environment. This makes sense from an evolutionary standpoint: if there was a substance commonly found in the atmosphere that killed us our species wouldn't make it very far. If you're talking about sarin gas, which I assume is at the heart of your question since has been in the news due to to rumors of its imminent use in Syria, once it is released into the environment it quickly breaks down (",
"with a half life of about 10 hours",
") due to ",
"hydroxide ions",
" in the air."
] |
[
"wazoheat covered dilution pretty well. But as for the processes, there's (broadly speaking) two ways things can go; photodegradation and biodegradation. Gases in the atmosphere can/will be picked up by living things (or dissolve into rain and get into the ground that way, in order to be picked up) and then converted into other things as part of their metabolism. Not that there are bacteria that 'eat' mustard gas or such (AFAIK), but the metabolic pathways aren't necessarily that specific, and will still often turn them into other (ultimately harmless) compounds. Although they can actually become ",
" harmful in the intermediate; there are many substances toxic to humans that are not actually so toxic in-themselves, but are 'inadvertently' metabolized in our body into toxic substances.",
"Photodegradation is essentially just the bonds being broken due to the UV light in the atmosphere, although it can also occur indirectly, where other molecules are broken by the UV light and then react with it. The things that persist for a long time in the atmosphere are things that are chemically quite inert and UV-resistant, such as sulfur hexaflouride - which is biologically harmless as it's so inert, but an environmental danger since it's so very persistent in the atmosphere and a potent greenhouse gas. Toxins, on the other hand, are seldom very chemically inert. (on the contrary, many toxic substances, such as halogen gases, are dangerous simply because they're so very chemically reactive)"
] |
[
"What is dark matter? (More questions inside)"
] |
[
false
] |
Do we even know what it is? If not, where does it come from? Who "found" it? Also, how is it created? Thanks
|
[
"DarthBarthus is correct; dark in this case means two things. 1) we don't know what it is... it's mysterious, and 2) it does not emit (or absorb) light. ",
"We don't know yet what it's made of. There are a number of plausible ideas out there, and lots of experiments working on figuring it out. As far as we can tell, it only interacts with other \"regular\" kinds of matter through gravitation. ",
"It was created, as far as we know, via the same processes that created the \"regular\" (baryonic) matter and radiation in the universe. i.e. it came from the big bang.",
"If we can't directly detect it or see it, how are we so sure it's there? Well remember it does interact gravitationally. So we can watch its effect on how baryonic matter moves. ",
"It was first discovered/postulated by Jon Oort, an astrophysicist studying orbital velocities of stars in the Milkyway in the 1930s. From the basic laws of gravitation, you can calculate how fast you expect objects in a galaxy to be orbiting if you know the overall distribution of mass in the galaxy. It turns out that the orbital speeds of stars don't match up with what we'd expect if the only mass in the galaxy is the stars/gas/dust we can see. Not even close. It was off by enough that there was no way to account for it just from mis-counting, or reasonable errors in estimating star masses or anything like that. There had to be something else out there, and a LOT of it. Franz Zwicky observed a similar kind of thing with the movement of galaxies in galaxy clusters also in the 1930s. ",
"There are other ways to \"see\" it as well. Gravitational lensing is a popular method used today, especially with the advent of good computers, allowing for statistical analysis of weak gravitational lensing to subtle to measure by eye. "
] |
[
"The existence of dark matter was first inferred by ",
"Jan Oort",
" and ",
"Fritz Zwicky",
". Dark matter was first identified by looking at how the stars in a galaxy rotated around the center of their galaxy. If the only matter present were the stars we can see, we should see stars further from the center of a galaxy moving at a slower speed than those closer in, based on how gravity works. In fact, the speeds are pretty much the same regardless of distance (once you get away from the central part). From this, one can conclude, again, based on how gravity works, that there must be much more matter that we can't see, and that it must be in more of a ball shape rather than a pancake shape. Since it's matter that we don't see, we call it ",
" (in constrast to ",
", which is what we can see).",
"There have been other methods to measure the presence of dark matter (via gravitational lensing -- i.e., the deflection of light by the gravitational effect of the dark matter), and people have also developed models of cosmology that constrain the possibilities for dark matter.",
"At this point, we don't know what dark matter is. We know it interacts gravitationally, and it is possible that it interacts via the weak force (no evidence for that, but it wouldn't pose a problem), but it does not interact via the other two forces (electromagnetism and the strong force). We know there is about five times as much dark matter as luminous matter. Beyond that, there are proposals and ideas, but nothing definitive."
] |
[
"Thanks, long and detailed answer!"
] |
[
"Could weapons grade uranium melt into some geometry that could explode?"
] |
[
false
] |
Basically does 95%+ U-235 need to be compressed by an explosion or theoretically could a cube say 50m per side explode? I guess my question is does the metallic lattice of the uranium need to be compressed further. If it does need to be compressed what depth of water would a cube need to be under for it to go super-critical? Follow-up are there any rarer fissionable elements that could do this?
|
[
"The critical mass of U-235 is about ",
"50 kg",
" for a sphere in empty space. The radius of this sphere is less than 10 cm. Anything larger will \"explode\". ",
"I put \"explode\" in quotes, because the U will begin to explode but, because it will no longer be critical, the explosion will fizzle. A nuclear bomb requires a method for holding the U together for some time (a few microseconds, IIRC)."
] |
[
"U-235 on its own will not just explode. Assume you have more than a critical mass just sitting there. Don't ask how you got it to that condition, but assume you have 1.5 critical masses just sitting there. A fission chain reaction would begin and would rapidly increase in power. It would heat up rapidly and eventually melt or possibly blow apart if it was two hemispheres. It would not be a nuclear explosion like you see in videos. For that to happen you need to contain that material for a microsecond and have a strong neutron source to start the reaction. That doesn't happen if you have uranium sitting in a room.",
"This second question is a bit more complex since it is lacking a lot of detail. If I have a chunk of U-235 that is exactly at critical, or even slightly below, throwing it in water would make it go super critical. This is because the water acts as both a moderator and a neutron reflector. So it helps slow the neutrons down, which increases the probability of fission. It also reflects neutrons back towards the uranium. Going super critical doesn't always mean explosion. Reactors go slightly super critical all the time. That is because the definition of critical is basically when this value called the multiplication factor equals 1. So if it equals 1.0001, it is super critical.",
"First, I would just mention that there is a difference between fissionable and fissile. You mean fissile. U-238 is fissionable, but it is not fissile. Fissile basically means it can sustain a chain reaction. Fissionable means it can fission. Even with all the other \"rarer\" isotopes, they will act similar to uranium. The major difference would be the critical mass and neutron yields."
] |
[
"Ah OK. So basically you'd need some external pressure greater than the internal pressure the uranium sphere generates. Otherwise it will be a splat rather than a boom."
] |
[
"What biological differences in some mammals allow for advanced movement very soon after birth?"
] |
[
false
] |
[deleted]
|
[
"That's awfully anthropomorphic. A lot of mammals give birth to babies that are highly non-independent, this has nothing to do with being human. Horses are the special ones here.",
"But you're right one one thing; there is a fundamental evolutionary trade-off between the impact of pregnancy on the mother and the viability/survival chances of the baby. Horses, sheep don't nest or burrow (obviously) and generally don't have many options to support their young, so it's more efficient if babies are born quite independent despite the problems that a longer pregnancy poses."
] |
[
"We have a longer development time after birth because evolutionarily we can afford to. It was sort of a biological arms race to see how small a child woman could have so that she could increase the physiology, pelvis and whatnot, to be able to walk upright. As those creatures increased their social cohesion, children could be born less and less developed allowing for women to have better and better physiologies. This is less of a problem for mammals like fowls because their own physiology isn't limited as much by offspring size and the fact that they do not need as long of a developmental period to allow for bigger brains."
] |
[
"Simply put, the biological difference is genetic. Mammalian embryos start out seeming quite similar and gradually differentiate as they develop due to genetic traits. For some mammals, like dolphines, the need to be carried along by their parent(s) is outweighed by the benefit and convenience of being independently mobile; i.e. if dolphines had to carry their babies, then everyday tasks like hunting and protection would become more difficult. They inherited this way of life from their genetic ancestors. The key here is that their ancestors followed an evolutionary tradition because it worked for their offspring more often than not, and those benefits werw continually passed on to new species."
] |
[
"How do we know that the sedimentary rock on Mars was formed by water, and not wind?"
] |
[
false
] |
This article (and others) are claiming that the sedimentary rock was created by water, but how do we know it wasn't from wind blowing sand into a desert, then the climate changing, and the desert moving. By desert in this case I just mean sand dunes, not just lack of water.
|
[
"In general, the process that transports sediment leads to characteristic differences between various aspects of deposits of sediments including the shape of grains, the distribution of sizes of grains, and the size and type of ",
"bedforms",
" within the deposit. For Mars, certainly eolian (wind blown) deposits and processes are important, but for the particular deposits that are considered to be likely deposited by flowing water the observed characteristics are more consistent with fluvial (water) deposition. At the simplest level, this is done by comparison between deposits on Earth and Mars, for example ",
"this Science paper",
" or this ",
"longer and more detailed Journal of Geophysical Research paper",
". There are also mathematical arguments based on calculations of the necessary shear stress to entrain (pick up, essentially) and transport observed grains sizes, shapes and densities to demonstrate that for many of these deposits, wind is not a feasible mechanism.",
"TL;DR - Not all sediment is the same, distributions of sizes and shapes of sediment can tell us whether grains were moved by water, wind, or other processes."
] |
[
"If I understand your question, I believe the answer is that the sand or dry dirt needs some other mechanism to help hold together the grains. If you think of the Sahara desert, you can picture all of the dunes. These dunes are representative of the structural limits of loose dry particles.",
"No matter how much wind you have in the Sahara, without any mechanism to hold the grains together you will never see little balls.",
"You can think of tumbleweeds too. They don't have moisture, but they have the tangled web of branches as a mechanism for cohesion. ",
"It might be possible to get a small amount of dry particular material to form a ball from static electricity, but I can't think of a naturally occurring example of that."
] |
[
"Not exactly, I was thinking of the rock itself. The balls (concretions) are formed by precipitating minerals in the sedimentary rocks, before it becomes solid rock. But I guess for the minerals to precipitate in a significant amount, there would have to be water present, even if it was just a little bit of ground water. The articles suggest that all sedimentary rock is formed by moving water, but earth there are large areas of sandstone formed by ancient deserts."
] |
[
"Would an atomic bomb produce two mushroom clouds in opposite directions if the bomb was released in the sky?"
] |
[
false
] |
[deleted]
|
[
"When an atomic bomb goes off, it creates (in the remnants of the fireball, which becomes the \"head\" of the mushroom cloud) something like a bubble of very hot, low-density gas. At most altitudes it is going to be much less dense than the atmosphere around it. So like a bubble released at the bottom of a jug of water, or a hot-air balloon, it is going to rise. If you create an atomic detonation at a very high altitude, it might already be the right density to stop rising, but that's about the only thing you would imagine having. At altitudes sufficiently high above the ground, the cloud will consist only of the mushroom head, not the stem. ",
"So, in short, no. You will not get a downward-moving mushroom cloud under any circumstances."
] |
[
"It's spherical, but with weird fringes as it comes apart and isn't being held together the way it would be in an atmosphere. There are photographs of this, as the US and USSR both tested nuclear weapons in outer space in the late 1950s and early 1960s: ",
"Starfish Prime cloud, 1962",
". This was an exoatmospheric nuclear detonation, viewed from below (the black line is the cloud from the rocket that took it up). ",
"For a nuclear weapon explosion in space, you don't have much of a shock wave/blast wave to speak of. Almost all of the energy of an initial nuclear explosion is in the form of radiation and heat. In an atmosphere, a lot of this is converted into blast/shock by being absorbed by the atmosphere. In outer space, it would not be converted, so you would get almost exclusively radiation and heat. You would still have a fireball (the remnants of the bomb material being turned into a gaseous blob), and that's what you're seeing in that photo. ",
"The radiation released can be absorbed and re-emitted by the upper atmosphere, which can cause a large-scale electromagnetic pulse (EMP), which is the most significant effect of an outer-space detonation of a nuke on Earth, as an aside."
] |
[
"When a nuclear bomb goes off, the amount of material involved is initially very small - after all it has to fit inside a warhead! ",
"The explosion produces a tremendous amount of energy in the form of radiation at many wavelengths. So the first thing we see when any bomb goes off (anywhere) is the intense white light. ",
"When we can see again, what we see is the impact of all that energy on the material surrounding the bomb when it went off - the amount of material in the bomb itself is tiny so will hardly be noticeable. The energy of the explosion superheats the air around it, generating the mushroom cloud as described above. ",
"If the bomb went off in space, we'd still see the radiative output from the explosion, but after that it would be pretty boring. With no material around the bomb to be affected by it, you'd just get the small amount of bomb material scattering into space. ",
"A shockwave requires a medium to travel through - as space is (for the purposes of this question) empty, there is no medium, so there can be no shockwave. And yes, whenever they show a shockwave in space in the movies, it's because they're ignoring or ignorant of Physics."
] |
[
"With the increase in population and decrease in trees, would we see a noticeable increase in CO2 in our life time?"
] |
[
false
] | null |
[
"We are already experiencing some of the most high levels of co2 the world has seen in recent history. This is due to burning of fossil fuels etc. ",
"Respiration in one human releases 900 grams of CO2 according to Wikipedia. So :",
"0.9 * 365.25 = 328.725 kg per year per person.",
"The united states census bureau suggests there will be a world population of 7.2 billion in 2015. So:",
"328.725 * 7200000000 = 2.37 * 10",
" ",
"Or according to this \n",
"Source",
": 2.168 x 10",
" tonnes/year ",
"I can't find any info on trees, but for comparison, here's what we produce from burning fossil fuels: ",
"8365000kg",
"Source",
"Or 24.9 * 10 ",
"\n",
"Source",
"So it looks like breathing has a sizeable impact. ( I'm not entirely sure this result is correct though, if some other redditors could double check my working). According to the other source, breathing contributes about 5% of co2 emissions."
] |
[
"What do you mean noticeable? We notice it enough to get warming. Do you mean enough to affect our respiration?"
] |
[
"Wow it means we lose a pound sleeping every night just by breathing "
] |
[
"Is a bar of soap always clean?"
] |
[
false
] |
Do bars of soap actively fight germs and bacteria even when they're not being "used" or do they simply collect the bad stuff? Or does the bad stuff get washed off with the top layer of soap and go down the drain, hence why soap bars get smaller over time?
|
[
"Actually soap in of itself is not clean, nor is it necessarily anti-bacterial. In fact, it is the mechanical action that is largely responsible for removing the little creatures living on you, not necessarily directly killing them either.",
"Soap's active ingredient is usually Lauryl Sulfate which is an amphipathic molecule. Amphipathic means that one part of it sticks to water and one part sticks to oil. When you scrub with soap in the shower, you dislodge the microbes, dirt, dead skin, and detritus off of your body through the process of scrubbing. The soap is more like the tool you use to get them off. Lauryl Sulfate can stick to the microbe's membrane as well as destabilize adhesive molecules they have on their exterior. Then, when you pass a sponge or washrag over your skin, they more easily detach. The mechanical action is key.",
"Stronger amphipathic molecules can poke holes in the membranes of microbes and kill them by doing so, but this can damage your body's cells as well. I believe anti-bacterial soaps have more sophisticated mechanisms of action, like ",
"Triclosan",
" which inhibits a key pathway in microbe metabolism.",
"Here's an experiment to observe amphipathicity at a higher level, and the importance of mechanical action in efficiency of amphipathic solvation.",
"You will need",
"Mustard (amphipathic, like soap) ",
"Vinegar, preferably balsalmic (its like water)",
"Olive Oil (self explanatory)",
"Glass cup (must be clear/see-through)",
"Now, pour the vinegar and oil in a 1:1 ratio, or 4 tablespoons each. See that the dark vinegar does not mix with the Oil for a very long time? Even if you stir it, they separate very quickly. This is because they are (nearly) pure hydrophobic (doesn't stick to water, nonpolar; this is the oil) or hydrophilic (sticks to water, polar) and cannot electrostatically associate with each other.",
"Next for the fun/delicious part. Add a spoonful of mustard or two to your concoction and stir it. Watch as the vinegar and oil now merge together and no defined line exists between them anymore. Molecules in the mustard act as intermediates and can interact with both molecules at the same time, allowing the mingling of the previously separate liquids.",
"Make a second concoction but after adding the mustard DO NOT STIR. See that the effect is completely different.",
"Finally, throw in some salt and pepper, possibly minced garlic and put that on a salad/dip bread in it/etc. Its a good sauce or dressing.",
"Science, it's fun and delicious.",
"TL;DR Soap is not clean on its own, scrubbing + soap removes bacteria. Anti-bacterial soap has ingredients that actively kill bacteria that come in contact with the ingredients. The antibacterial ingredient kills microbes through a sophisticated mechanism of action usually by blocking an important step in a metabolic pathway. If you only read the TL;DR you missed a fun kitchen experiment."
] |
[
"That was a great answer - like one you might expect from Bill Nye. "
] |
[
"A luffa or a washcloth will probably increase the amount of stuff you wash off. However, the goal of washing is not to end up 100% sterile, that's impossible and ultimately detrimental - the vast majority of microorganisms that colonize your body are benign or even helpful.",
"Using antibacterial soap in the shower is ",
" overkill and actually harmful over the long run (at a population level, not a personal level). If you're going to be performing surgery, antimicrobial hand soap might be a good idea - for daily use, definitely not."
] |
[
"Why does salt/lime dissolve in water and why is the amount dependent on the temperature?"
] |
[
false
] |
So let me begin by telling from which direction I'm coming from. After using my water boiler in the kitchen for a couple of days, lime will settle at the bottom of it. Why does this happen? As far as I know warm water is capable of holding more salts and lime then cold water. Is this right? And my question then is, why is that even the case, why is there a difference in the amount of slat/lime, water can hold with different temperatures. I was wondering that because I don't understand why the lime settles down if it more it can dissolve in warm water. Is it only because of the steam that can't hold the lime? But then, why does there is no lime at the top of my boiler but only at the bottom?
|
[
"The reason lime deposits mainly at the bottom is that the heating element is where the highest temperature is found, and where water actually boils by direct contact with this surface. The rest of the body of water heats up by conduction/convection and, when boiling, by the bubbles of vapor flowing up the water.",
"Now, as you said, salts are usually indeed more soluble in water at higher temperatures. The thing is, the carbonate salts, specifically calcium carbonate (the main component in limescale) is in an equilibrium with the calcium bicarbonate form. It's hard for me to format the actual chemical equation because I'm on mobile, but basically the much more soluble calcium bicarbonate (one calcium ion and two bicarbonate ions) is always partially dissociated as calcium carbonate (one calcium and one carbonate ion) and a molecule of carbon dioxide. Calcium carbonate is very insoluble and precipitates, and carbon dioxide is a gas.",
"Because for gases dissolved in water it works the other way, and a higher temperature means lower solubility, heating up water to its boiling point basically means getting rid of all dissolved gases. When you boil water and push the dissolved carbon dioxide out of solution, you are shifting the equilibrium towards the carbonate side, causing more calcium carbonate to precipitate.",
"Basically, although for dissolved calcium bicarbonate in water it holds true that the hotter it gets, the more soluble it is, by boiling carbon dioxide away you are forcing the calcium bicarbonate to become calcium carbonate, which is very insoluble."
] |
[
"This is a really good answer. Thanks for the great explanation. Do you by any chance know where I can find a table of the solubility of salts in Water?"
] |
[
"table of the solubility of salts in Water?",
"Most common salts should be in here : ",
"https://en.wikipedia.org/wiki/Solubility_table",
"For a more scientific approach, or mixtures of various salts (common ion effect!), best look into solubility product constants. Tables for common salts in water at 25°C are readily available. ",
"https://www.periodni.com/solubility_product_constants.html"
] |
[
"If an air conditioner was locked in a (somehow) heat-sealed room, with it's air intake, would the room (not the internals of the aircon) get hotter or colder or stay the same?"
] |
[
false
] | null |
[
"Warmer. Even if the transfer of thermal energy from its intake to its outtake can be considered equal, the fact that it has to use energy to run will result in a net growth in temperature.",
"This is similar to the question of: \"If a refrigerator is thermally isolated in a sealed room, then would that room warm or cool if its door is left open?\" The answer there is still the same; since the refrigerator would require an input of energy to run then the room will, on average, warm up."
] |
[
"The room would get hotter. Think of it this way: to pump out colder air, you need to create at least as much hotter air (to obey the laws of thermodynamics). So that alone balances out. However, on top of that there's also a motor running to achieve this process, so you get additional heat from that."
] |
[
"Cool, thanks :D"
] |
[
"Basic heat exchange question"
] |
[
false
] | null |
[
"You can have liquid water at 100 C."
] |
[
"You are correct, with no temperature difference there will be no heat flow. If there were it would be a violation of the second law of thermodynamics."
] |
[
"The phenomenon is ",
"vapor-liquid equilibrium",
". There is a different phenomenon known as a ",
"superheated liquid",
" where a liquid remains a liquid well above its boiling point until it is disturbed, but that isn't really related to the question at hand."
] |
[
"Say the Continental US is a flat object and population density determines its actual density. Where would it's Center of Gravity be?"
] |
[
false
] |
For instance, if you were to balance it on top of a pole, where would you put the pole, somewhere in the midwest? But where specifically?
|
[
"For the whole of the US, this location would be near Plato, Missouri.",
"The US Census Bureau has an animation of how the mean center of population has moved from 1790 to 2010 ",
"here",
".",
"There's also a news story ",
"here",
"; excerpt:",
"The Census Bureau calculates the center of population after each decennial census. It determines the center based on where an \"imaginary, flat, weightless and rigid map of the United States would balance perfectly\" if all 308,745,538 residents weighed the same amounts."
] |
[
"Did this compensate for alaska and Hawaii? Since they are detached it would skew the results westward."
] |
[
"It does include Alaska and Hawaii.",
"The Wikipedia article on this subject ",
"states",
":",
"The addition of Alaska and Hawaii to the union moved the center about two miles (3 km) farther south and about ten miles (16 km) farther west in 1960.",
"The citation for this statement isn't there any more, but this does give one a sense of the size of the impact of Alaska and Hawaii. "
] |
[
"If someone or something could move faster than the speed of light, what would happen to its shadow?"
] |
[
false
] | null |
[
"That’s fair. Just was disappointed. Have a good day."
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"guidelines",
"Please see our ",
"list of related subreddits",
" for other options for your question.",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"Lame."
] |
[
"What exactly is a “panoramic view” in astronomy maps and images?"
] |
[
false
] |
For example, I understand a panorama when taken from my phone. I understand that, if it is a 360 panorama, the sides will wrap around. However, astronomy maps and images (e.g. the cosmic microwave background images) are ellipsoidal. Does this imply the image wraps around at all the edges? Why is it ellipsoidal instead of circular? Are we looking at a pre-specified projection? Is there an article where I can learn more about the history of them? I really have not been able to find an answer on google. Panoramic space images or maps link to many beautiful photos, but not to the answer I’m looking for. Thank you in advance, not easy to put this question into words!
|
[
"Looking at a map of the whole sky is similar to looking at a map of the earth, like the ",
"Mollweide projection ",
". A sphere is 360° around its equator but only 180° from top to bottom, which is why the projection isn’t circular. Because of the rotation of the earth it’s easy to pick a top and bottom, but in principle you could pick any direction as “vertical” and the orthogonal direction would be “horizontal”."
] |
[
"Thank you! This is what I was looking for."
] |
[
"This is the ",
"Mollweide projection",
", and is easiest to understand by looking at a Mollweide map of Earth. It is ellipsoidal because it is a projection of the surface of a sphere onto a 2d map while keeping area correct and without too much distortion."
] |
[
"What’s the mechanism that causes sore throats due to viral infections?"
] |
[
false
] |
I cannot find anything about this online. I know that viral infections, and to a lesser extent, bacterial infections, cause sore throats. But WHY? Is it beneficial to the body in fighting infections somehow? Is it inflammation of the lymph nodes? Can’t figure it out!
|
[
"Many viruses/bacteria first encounter our nose/throats/upper airway when we inhale them from other infected people. The probable combination between the upper airway being the first tissue inhaled pathogens encounter and an evolutionary adaptation towards that specific type of tissue means the upper airway is where the infection starts.",
"When our immune system cells encounter foreign pathogens (viruses or bacteria) they begin releasing special signalling molecules that recruit more immune cells to the area (i.e. backup) and increase blood flow (swelling/inflammation) to expedite their travel.",
"In slightly more detail, when our immune cells encounter virally-infected cells they can tell those cells to \"self-destruct\".",
"Also, many virally-infected cells end up producing a ton of viruses until the cell literally bursts open. If cells die this way their contents spill out, which our immune cells also do not like. So, they again want to release signalling molecules to increase blood flow and recruit more immune cells to the area to clean it up.",
"A sore throat is the result of your immune system doing it's job and causing inflammation/swelling where it's needed and the fact that there's a fairly significant amount of your cells dying in that area. It's worth mentioning those signalling molecules your immune cells release also increase pain sensitivity via your neurons.",
"TL;DR immune system causes swelling (pressure) and nerve sensitization in response to pathogens.",
"Edit: here's a video showing some of the immune system processes - ",
"https://youtu.be/wHCJUMBKgyo&t=12m58s"
] |
[
"<recruit more immune cells",
"Some of these immune cells are literally like bouncers shoving through a packed crowd. The push between cells that normally do not have any space between them, and in their wake extra plasma may flow in. ",
"Imagine a packed club, and then 50 or 100 huge bouncers show up and begin push through the crowd, interogating people. No one can leave. People get pressed against the walls. That is your sore throat. (And yeah, sometime some of the zombies who look like real people explode and then everyone who got goo on them becomes a ticking time bomb zombie unless the bouncers blow their heads off first. But still - no one gets to leave)"
] |
[
"https://www.wikidoc.org/index.php/Pharyngitis_pathophysiology",
"Essentially viruses can directly invade the cells, bacteria can release toxins and things that irritate nerves, all of this can cause immune cells to come and cause inflammation, and your mucous can also be irritating."
] |
[
"Orbital Trajectories and Error?"
] |
[
false
] |
I first appreciated what a free return trajectory was when I watched where a science teacher uses a lycra sheet and weights to demonstrate gravity (free return is at the 6:20 mark). The trajectory makes sense to me and I guess you could say you "fall" all the way to the moon and fall all the way home again. What I don't understand is that ideally the whole path is predetermined by the velocity of the object when it leaves the earth. How is this done so accurately? I know that mid course corrections are possible but I assume they must be minimal. Maybe a better question is how accurate does the initial velocity need to be? That is an earth/moon question from the Apollo era. I had the same sense of "how do they achieve that accuracy" this year when New Horizons not only reached Pluto but passed between Pluto and Charon.......wow
|
[
"It's simple: they don't have the needed accuracy at launch (for some trips you might need to be unpractically precise). You might know that in general, the error in the configuration of a mechanical system grows exponentially, so no matter how good you are, you often aren't able to calibrate everything in advance. They just make adjustments mid-flight. If you've been smart, the adjustments won't be large.",
"A minimalist plan of periodic orbital reassessment and corrections is enough to bring that exponentially small precision requirement at launch into something reasonable."
] |
[
"When shooting for the moon, you can normally get within 2-3km/s and still be very close to the trajectory you were aiming for. ",
"The change in velocity required to go from low earth orbit to the moon is 3 km/s, according to Wikipedia. Your numbers aren't entirely correct."
] |
[
"When shooting for the moon, you can normally get within 2-3km/s and still be very close to the trajectory you were aiming for. ",
"The change in velocity required to go from low earth orbit to the moon is 3 km/s, according to Wikipedia. Your numbers aren't entirely correct."
] |
[
"Can someone become un-allergic to something?"
] |
[
false
] |
[deleted]
|
[
"Sure, the process is called ",
". It can happen naturally, after extended exposure to an allergen (this can also aggravate symptoms), or therapeutically, through ",
"immunotherapy",
" (where patients receive repeatedly, and over a long period of time, small doses of modified allergen)."
] |
[
"Thanks much, this is the type of response I was hoping for"
] |
[
"I was allergic to nuts (and a bunch of other stuff) for ~7 years, but now i can eat nuts again except cashews."
] |
[
"If I see a fly land on my food, should I ignore it and go ahead and eat the food?"
] |
[
false
] |
When a fly lands on my food I always feel kind of revolted and I wave it away, but I don't know if I am being hyper-fussy by not eating that bit, or being sensible because I could get ill. I suspect I'm being fussy. But then, why do we go to such lengths to keep food fresh and covered up if there's no risk? So how much risk is there of the fly passing on some kind of bacterium that might do me harm?
|
[
"Your immune system is pretty beastly. Keep in mind the environment in which the human body was conditioned for included ravaging diseases and general filth. Our immune system has adapted to combat common environmental microbes and pathogens through built up passive immunity. Unless the fly transmits something specific ( typhoid, cholera and dysentery etc) you shouldn't have any problems if you're a healthy adult. If you're immunodeficient, things might be different. I also think some parasites are vectored through their eggs, but your stomach acid should take care of that. ",
"Source:",
"http://en.wikipedia.org/wiki/Innate_immunity"
] |
[
"You might not like this answer... You likely consume many flies during an average year without harm.",
"\"it is not possible to eliminate pest insects from the human food chain. Insects are present in many foods, especially grains. Food laws in many countries do not prohibit insect parts in food, but rather, they limit the quantity.\" -- ",
"Entomophagy",
"According to the U.S. Food and Drug Administration's The Food Defect Action Levels booklet, contamination on the average of 150 or more insect fragments per 100 grams poses no health hazard.",
"So to answer your question, if eating the fly isn't a health hazard, how is eating something a fly landed on an issue?"
] |
[
"Yes, it's true. They eat by regurgitating enzymes onto their food, letting the food dissolve into a soupy mess, and then sopping it all up with their sponge-like mouthparts."
] |
[
"At a small enough scale, visible light wouldn't register as such since you'd be smaller than the wavelength. Are there types of energy too large for us to experience in a similar manner?"
] |
[
false
] |
I've read that we can't see objects that are smaller than the size of the wavelength range of visible light. I hope I'm getting that right? Are there types of energy with wavelengths that are so large that we cannot register them?
|
[
"Not really. Radio waves are the longest type of electromagnetic radiation. They range from centimeters to kilometers and larger in wavelength. Despite their large wavelengths, we stull use them all the time. As long as you have an antenna long enough to emit or receive these long waves, you can still use them. ",
"A nice part about radio waves is that they're so long that they don't get \"scattered\" by things like the atmosphere or interstellar dust!"
] |
[
"Random fun information: Very long wavelength radio waves are used as an extremely low-bandwidth way to communicate with submarines:\n",
"http://en.wikipedia.org/wiki/Extremely_low_frequency",
"This requires an antenna that is thousands of kilometers long, for which purpose the earth itself is used."
] |
[
"This is not entirely correct. An ionized plasma will not transmit waves with a frequency higher than its \"plasma frequency\", which for the Earth's ionosphere is about 10 MHz - in the middle of the radio/TV spectrum."
] |
[
"[META] - AskScience Journal Club!"
] |
[
false
] |
Hello AskScience! Today we're rolling out the AskScience Journal Club as a new trial feature. Basically, this thread will be a dedicated space for discussion of interesting research studies in a variety of fields. This presents an opportunity for our panelists to talk about interesting topics that may not be asked about very frequently, as well as a chance to demonstrate how scientists read and critique journal articles. Meanwhile, our readers get exposure to both the cutting edge of research as well as some of the lesser-known aspects of science. This initial post can range from a simple "here's this cool article on the topic of X, which basically found that Y, which is important because Z", to something more elaborate that be included in a . AskScience users are encouraged to engage in a dialogue about these studies: don't understand a paper's methods? Disagree with the overall significance? Want more info on the background context of this study? All are great questions to ask the panelists! We also welcome discussion between people other than the OPs for each paper - while the panelist who originally posted the paper likely has expertise and interest in the area, I'm sure that none of them will claim to be the final authority on any topic. Many similar "I read this article in the NYT about a research study, can someone tell me more?" questions are posted to AskScience, and we absolutely want to discuss topics that are of interest to you as well. Because these topics involve providing analysis on published literature we understand that not everything can be sourced, but as always try to keep everything as factual as possible and make it clear when you are offering your opinion vs established facts. Please feel free to message the mods with any feedback or suggestions you may have, but let's keep those comments out of this thread to avoid clutter. If this experience is well-received we may continue this as a regular (weekly?) series, so let us know what you think! Lastly, a big thank you to everyone taking the time to discuss papers! Our success is largely dependent on our user base and our panelists, so keep up the good work, both with asking and answering science questions!
|
[
"I'm a biophysical chemist, and so I've chosen a very recent (presently in press) paper that touches upon protein-membrane interactions, membrane biophysics, and some interesting (NMR) spectroscopy. All of this is right up my alley, so I was actually interested enough to do more than just skim through the figures here. I've attempted to write this for an interested although non-specialist audience, and less for fellow scientists. I've avoided all NMR acronyms, for one. If you see me mention \"proton\", I mean \"the hydrogen nucleus.\" You can tell me where I've went wrong/utterly botched it on this effort. ",
"Title: Solid-State 13C NMR Reveals Annealing of Raft-Like Membranes Containing Cholesterol by the Intrinsically Disordered Protein α-Synuclein",
"Authors: Avigdor Leftin, Constantin Job, Klaus Beyer and Michael F. Brown",
"Link",
" - ",
"; 2013; Article in Press",
"Protein aggregates - termed ",
"Lewy bodies",
" - are found in the brains of people suffering from various neurological disorders, most notably ",
"Parkinson's disease",
". These large insoluble aggregates are primarily composed of the ",
"intrinsically disordered protein",
" ",
"α-synuclein",
". It's been proposed that α-synuclein - while basically unfolded in solution - adopts a more structured conformation when binding to the membrane surface, by which it can control the local structure of the membrane, which subsequently mediates communication between neurons. The working hypothesis in this paper is as such - in the healthy brain, the α-synuclein protein stabilizes membranes and modulates fusion of small vesicles involved in neurotransmission, and when this process is interrupted due to protein aggregation, the result is disregulation of signal transmission and onset of the neurodegenerative symptoms. This idea is graphically portrayed in ",
"Figure 1",
" from the paper.",
" - ",
"\"…local structure of the membrane\"? ",
"Well, this is a good question. In model membranes, you can get separation of different components (or particular mixtures of components), and has been demonstrated by any number of experimental techniques, and is well supported by what's known of theory. The evidence for this sort of structuring in actual cells is not clear-cut in the same manner, but it's a useful working hypothesis, at the least, for many. These separated domains have 'recently' been termed ",
"lipid rafts",
" in the literature.",
" ",
"The authors wanted to see the effect of α-synuclein binding to model membranes that have a tendency to form rafts. To do this, they used ",
"solid state NMR",
" to measure the chemical shifts and proton-carbon dipolar couplings of the raft-forming mixture (POPC, egg yolk sphingomyelin {EYSM}, and cholesterol). In short, the idea is to determine the (ideally) unique marker signal (the chemical shift) for each carbon atom in each of the three lipids, depending on the (in principle) unique chemical environment of each atom, and then measure an associated parameter (the proton-carbon dipolar coupling) which is sensitive to motion at that particular carbon atom. The advantage of how they did this experiment is that it did not require any isotopic enrichment, in contrast to what most people tend to think of when one discusses biological NMR. Given the sheer number of lipids one can cram into a sample holder, the ",
"natural abundance 13C",
" is enough to get good data in this case. ",
"The individual lipids POPC and EYSM were first studied separately (",
"Fig. 2",
") and then together with cholesterol (",
"Fig 3",
".). The data becomes messier, as signals begin to overlap on top of one another, especially in the area around 30 ppm. This is where all of those carbon atoms in the middle of the lipid chains tend to show up, as they're not near or at the end, nor are they up where the head groups are located. There are other differences, of course, but that is perhaps the most noticeable. To help correct for that, the authors essentially did a set of experiments where they attempted to build up to this three-component mixture in ",
"figure 4",
". In addition to the one-component data from figure 2, they did a mixture of those two, each one with cholesterol, and then simply added the two spectra of each with cholesterol to compare to the three-component mixture. As it turned out, the sum of the lipid + cholesterol spectra yields something reasonably close to the three-component mixture data. ",
"Onto the protein binding and how it affects the membranes! The authors tested the full-length α-synuclein (which is ~ 140 amino acids long) on these membranes. In ",
"figure 5",
", you see the data from the membranes with the full-length protein. It looks quite a bit like the data obtained from just POPC and EYSM in figure 3. (Snarky remarks - the infamous weasel words \"not an effective experiment to detect a particular species\" is used to explain why we can't see the majority of cholesterol signals, yet those rather clear-cut signals at ~ 18/19 ppm are still right there, which were attributed to cholesterol earlier. I suppose that they are the minority who snuck on through. And they cut off the data below 15 ppm in figure 5b, in contrast to 5a. I suppose the methyl groups were giving them nightmares in the three-component mixtures. They also did this in figure 3.) In essence, the congested signals that were there in figure 3…seem to vanish.",
"My attempt to keep things somewhat non-specialist is failing me for figures ",
"6",
", ",
"7",
", & ",
"8",
", so I'm going to engage in some hand-waving. The authors basically use the proton-carbon dipolar coupling (remember, insofar as we're concerned in this case, the proton and carbon nuclei are little magnetic dipoles) as an indicator of the order or disorder in the membrane, and then use a model to make some estimations of how thick the membrane is, in the absence and presence of the protein. Basically, they find that the long carbon chains that form the interior of the bilayer become more disordered, while the surface becomes more ordered (since it's presumably interacting with the protein). They extend that to a calculation which indicates that the bilayer becomes thinner and the lipids aren't packed quite as tightly. ",
"The authors wrap up with arguing their case for α-synuclein serving as a way to counter the formation of rafts (and membrane defects) by cholesterol, and that this is a process that is dynamic and needs to be responsive to a number of factors. The conformational flexibility of the protein is critical to this process as well, and aggregation of these proteins is not conducive for maintaining proper function. This is the fairly standard \"big picture\" connection that most papers in my field tend to do, IMO, and as everyone has their own pet topic or three, I am not tremendously qualified to address the details of Parkinson's disease or related pathologies. ",
"Overall, I thought it was a solid paper, and was interesting to read along with giving me some ideas for my own work. I think it's a fine addition to the protein-membrane interaction literature, and it's always good to see people going after the lipids themselves. There are some things I noticed, of course, that have me thinking.",
"1.) These experiments were run at 48 deg. Celsius, given the solid to liquid transition temperature of EYSM (38 deg. Celsius). I am not an MD, but my understanding is that if the human brain was held at a temperature of 48 deg. Celsius for any period of time, it is not a good thing, nor is it something that would likely preserve proper functioning. Perhaps alternate lipid mixtures might make for more interesting models given our typical temperature range…..",
"2.) Everything was done in water without any additional buffering. Now, there are practical issues here (high ionic strengths can cause sample heating in these sorts of experiments to varying extents), but when the authors mention \"Fusion events are highly dynamic, whereby the protein is required to respond rapidly and reversibly to changes in membrane phase, shape, and electrostatic environment\" in the text, I have to wonder. There was a mention of wanting to avoid salt-screening effects on the protein-lipid interaction, which is understandable, but putting that given the aforementioned text makes me shake my head.",
"3.) Related to # 1 - just what are good model membrane systems, in the end? While I think ",
" NMR is what we'd all like to see sooner rather than later, compromises will have to be made in the meantime. And how can we reconcile this with phase separation of lipids in model systems being well-estabished versus the ",
" dissent? ",
"4.) That they put a whole bunch of material in the supplemental info drives me crazy, but has me reading, and attempting to think through some stuff I haven't thought through in a while. I may have more to write later. "
] |
[
"I thought it'd be interesting to talk about the paper ",
"Use of azithromycin and death from cardiovascular causes",
" by Svanstrom et al, published in the New England Journal of Medicine (one of the larger journals in the field) this past May. ",
"To provide some background, ",
"azithromycin",
" is a type of ",
"macrolide antibiotic",
", commonly used for various ",
"upper respiratory infections/sinusitis",
", ",
"atypical pneumonias",
", and ",
"some sexually transmitted infections",
". It is very commonly prescribed - in 2011, around 40 million people in the US received at least one outpatient prescription. This is despite the fact that major organization guidelines have recommended ",
"against using azithromycin as first-line treatment for sinusitis, given high resistance rates",
". This high prescription rate is likely partly attributable to high patient demand, since many subjectively report that a ",
"z-pak",
" is easy to take and rapidly makes them feel better (likely more due to the ",
"anti-inflammatory properties",
" of macrolides rather than their antimicrobial effects).",
"This issue is clinically relevant because other drugs in this class of antibiotic (in particular erythromycin and clarithromycin) have been shown to have cardiac conduction side-effects that can lead to ",
"increased risk of sudden cardiac death",
". Azithromycin as classically been thought of as safer to user from a cardiac perspective, but a paper published ",
"last year in NEJM",
" suggested otherwise, with an extra 47 cardiac deaths per million courses of azithromycin as compared to amoxicillin (a ",
"penicillin derivative",
"). This was obviously concerning, though the study was limited by its retrospective nature and the effect size is fairly small.",
"Now that all that background info is out of the way, on to this new paper by Svanstrom et al. ",
"Study design: ",
"prospective cohort",
" ",
"Subject pool: all individuals living in Denmark from 1997-2010 from 18-64yo ",
"Inclusion criteria: at least one use of either oral azithromycin or penicillin; control group consisted of group with no antibiotics ",
"Exclusion criteria: hospitalizations or antibiotics within 1mo prior to index date (date that they took azithromycin or penicillin); filling multiple antibiotic prescriptions on index date; not living in Denmark at least 2yrs or not having filled at least 1 other prescription in the year before index date ",
"Matching: they used a ",
"propensity-score matching",
" between azithromycin and no antibiotics to try to account for ",
"confounding variables",
" ",
"Outcomes: cardiovascular deaths; secondary outcome is all-cause deaths",
"Results: with ~1 million episodes in each group, they found a relative risk of 2.85 for increased cardiovascular death with current (within 1-5 days) use of azithromycin vs no antibiotics. The absolute risk increase is 0.7/1000 patient-years. They found no significant difference with more distant (>5 days) use, and no significant difference between azithromycin and penicillin. ",
"Subgroup analysis: risks did not differ significantly based on age or sex, but did trend towards being higher in patients with history of cardiovascular disease (nonsignificant) ",
"Sensitivity analysis",
": again, no significant difference between azithromycin and penicillin ",
"Take-home: this study seems to show that azithromycin is associated with increased cardiovascular deaths as compared to no antibiotic, but is no different from penicillin. This study used a very different population from the earlier Ray et al. study so they're a bit hard to compare directly. Overall, these two studies seem to ",
" that azithromycin may be associated with significant increases in cardiovascular death in at-risk populations (such as those with underlying heart disease). There are enough flaws in both of these studies to keep me from buying into them entirely. I'm a bit torn because I do believe that azithromycin is overused (due to overtreatment of viral disease and bacterial resistance patterns), but the low effect sizes in these studies suggest that you'd need to prescribe a ton of it before you actually caused any harm. ",
"This is my take on the article; I'm eager to hear others' thoughts as well! Any questions are also welcome, though I likely will not be able to answer them during the day so please excuse the delay (alternatively, anyone else is also welcome to chime in with answers). "
] |
[
"1) Speaking as someone with zero experience in SLF or DROSS (in the spirit of keeping initialisms and acronyms to a minimal, they stand for \"separated local field\" and \"dipolar recoupling on-axis with scaling and shape preservation\"... yeah...), could you explain what those techniques are and how the residual dipolar coupling information is extracted?",
"I'm curious as to the source of what seem like sinc wiggles in Figure 6, which is the reason I'm asking the question. I know, I'm forcing you to do more than hand-waving. =P",
"2) MAS (\"magic angle spinning\") in water?",
"3) I think I'm going to give up my panelist tag now."
] |
[
"Explain electron spin, how .5 spin gives objects mass, and why bosons have a spin of 1."
] |
[
false
] | null |
[
"Particle spin is an intrinsic amount of angular momentum that they have, i.e. something that is the same no matter what angle you look at it. Multiplied by Planck's constant, bosons have spins of 0,1,2,3 etc and fermions have spins of 1/2, 3/2, 5/2 etc. I'm not sure what you mean about mass."
] |
[
"Actually, just about all of this you can read about on Wikipedia ...",
"You're right, let's close this subreddit and leave a redirect to Wikipedia in its place."
] |
[
"To expand on this, Fermions obey the ",
"Pauli exclusion principle",
". This means that two identical fermions can't occupy the same quantum state at the same time (roughly, they can't be in the same place with the same energy at the same time). This is what gives matter (composed of fermions like protons, neutrons and electrons) it's \"solidness.\"",
"Bosons, on the other hand, can \"pile-up\" in the same quantum state. Some examples of this \"piling-up\" are lasers, superfluids, and superconductivity.",
"By the way, spins come in only integers and half-integers because we live in three dimensions. If we lived in a two-dimensional universe, then spins could come in ",
"any real number",
"."
] |
[
"When humans imagine an image in their brain, is the image we see being activated from the occipital lobe or somewhere else?"
] |
[
false
] |
[deleted]
|
[
"When we imagine movement, such as a batter hitting a baseball, our mirror neurons fire. This event resembles the activity that the motor neurons would exhibit we were to perform the action of hitting a baseball, however we will not move at all. It is hypothesized that this is one reason, among many, why humans enjoy spectator sports."
] |
[
"Just to clarify, mirror neurons would fire duirng both doing and seeing. Also, I think the question relates more to thinking about the sight of someone hitting a baseball compared to actually seeing it.",
"The occipital lobe is related to dreams and damage can cause them to cease, so it could be connected to conscious visualizing. "
] |
[
"Some of us do not have any visual images in our minds. Some of us think entirely in audio. This is worth consideration, perhaps."
] |
[
"Does milk really help you grow taller?"
] |
[
false
] |
My parents always used to say that drinking milk makes you taller. Is there any truth to this?
|
[
"A more accurate statement would be that drinking milk enhances your ability to grow taller. It doesn't necessarily make you taller. It's like saying eating protein makes you grow muscles. It can help you grow, but it doesn't do so automatically. It's only one part of a complex equation."
] |
[
"While your still very young, calcium is absolutely necessary to help strengthen bones and lack of calcium could indeed stunt growth and have negative effects. But this is only during the weening time period. After that it has not real benefit when it comes to bones"
] |
[
"Yes, but there is more to it than drinking milk. Overall nutrition during early development has a significant impact on height. Milk contains important nutrients, including fats, sugars, and proteins, as well as the calcium that is often focused on. Milk alone isn't sufficient for healthy developement, but the production of nutritious milk has evolved significantly, parents that produce good milk have more successful offspring.",
"Ultimately, your genes determine an upper limit on your height, if you get the right nutrition, you will reach that limit, if not, you will be shorter. This isn't particular to milk but milk is an important food, especially early on."
] |
[
"Is it possible to put out fire with Gasoline?"
] |
[
false
] |
[deleted]
|
[
"I'm sure someone will correct me if I'm wrong, but here it goes.",
"Gasoline burns as a vapor, but not very well as a liquid. So you could extinguish a flame if enough liquid Gas engulfed the flame so as to smother it out. Obvious risk that if it did not go out, it would be flooded with an accelerant."
] |
[
"I think the problem would be delivering the gasoline to the fire in a manner that would prevent it from separating or becoming and aerosol. As you said, the liquid isn't the problem, the vapor is. You can't simply spray it or pour it over the fire fast enough unless you could evacuate all the oxygen first. "
] |
[
"One way of extinguishing fires is with explosives - see videos of putting out burning wells in the Kuwaiti oil fires and other well blowouts. One firefighter started a company around this premise - Red Adair was known for putting out huge oil fires with explosives.",
"The premise is that if you have a large fire like an oil fire, it's extremely difficult to stop the blaze using traditional methods - it's just too hot and there's a massive fuel supply feeding the fire (which typically cannot be stopped without controlling the fire first).",
"So explosives are used to consume all of the oxygen around the fire. This temporary interruption of oxygen stops the fire, as long as there's not a nearby hot spot or other source of ignition.",
"I don't know if gasoline would actually work for this, since it doesn't burn as quickly as high explosives, but I would speculate that it could be used in the same manner - hopefully a chemist can elaborate here."
] |
[
"Why do some helicopters have 2 blades whilst others have 4 or 5?"
] |
[
false
] | null |
[
"The greater number of blades in a helicopter enables it to produce more lift, hence heavier helicopters, such as Sikorsky CH-53 has more blades. ",
"However, there will be trade offs from having more blades. The helicopter blades produce a wake of turbulence behind them, reducing the efficiency of the subsequent ones, resulting in a need to space them out sufficiently to prevent the turbulent wake from affecting the performance of the other blades to much. Furthermore, a greater number of blades will also complicate the hub, and overall increasing the cost. Hence it is not effective to increase the number of blades in small helicopters.",
"In order to further increase lift, the blades can be rotated at higher velocity. Then why can't heavier helicopters just rotate their blades faster? This is due to the tip of the blades limited to subsonic speeds, as supersonic blade tips will create extremely large amounts of drag and turbulence, greatly reducing efficiency. Furthermore, even before the blades reach supersonic speeds, there would be formation of local pockets of supersonic airflow, which also creates a large amount of drag. ",
"Hence, due to turbulence created by the blades, and the inefficiency of supersonic tips, there is a need for more blades in heavier helicopters. Small helicopters are better off with lesser blades to reduce the need for a complicated hub, as well as to save cost."
] |
[
"No. Counterbalancing (counterweighting you called it) a single blade would give a balanced rotation, but would require the same energy (fuel) to spin, while only creating half the lift, as you would only have one lifting blade. This single lifting blade also causes an issue where it is being lifted up, and prying on the center hub, without a counter acting blade lifting on the other side. ",
"Now this guy did an experiment with a toy..I'm not sure it would scale up very well. Most toys are made to just lift itself, not a payload etc.",
"https://www.youtube.com/watch?v=AD9juUWL5iU"
] |
[
"Your correct, thats exactly what would happen. But more blades means you need bigger engines to turn them. This increases fuel consumption, which means you would need to have bigger fuel tanks and cary more fuel. ",
"It all depends on the purpose of the chopper. If you want to fly faster or lift more weight then you add more blades. "
] |
[
"What is it that makes chemotherapy successful with some people but not others? (x-post from askreddit)"
] |
[
false
] |
This has probably been asked before, but my 2 minutes of pre-question research turned up nothing. I'm curious why chemo is successful with some cancer patients but seems to have little or no effect on others. What determines the effectiveness? If it's body chemistry, wouldn't doctors be able to determine whether or not it will work prior to beginning treatment? I lost my dad to esophageal cancer in '06 and watched him suffer through chemo for 2 months before he died. I'm wondering why he was subjected to the hell of this form of treatment when, in the end, it didn't improve his situation.
|
[
"First of all, I am sorry about your father. Cancer treatment is extremely complex and can cause horrible side effects to those receiving chemotherapy. I will try to explain my understanding of it.",
"There are many, many differences in the different types of cancer that occur in the human body. This includes differences in genes expressed, genes knocked out, rate of division, route of spread, speed of spread, etc. Different forms of chemo try to target various aspects of these cancers. For example, many chemotherapeutic agents target rapidly dividing cells by interrupting DNA synthesis or mitosis.",
"In a given cancer, a certain percentage of the cells are currently dividing. If you give a drug that prevents division, that percentage of the tumor will (hopefully) be killed. After that, another percentage of the tumor will begin to divide to continue growing. This is why there are \"rounds\" of chemotherapeutic treatment. The hope is to logarithmically decrease the number of cells in order to decrease the overall tumor burden of the patient. ",
"Targeting rapidly dividing cells has many drawbacks and accounts for many of the side effects unfortunately. Other rapidly dividing cells include hair cells (alopecia), cells lining the GI tract (diarrhea, nausea, vomiting), bone marrow (bone marrow suppression). ",
"There are also certain cancers that express receptors that we can target with chemotherapeutic agents. An example I will use is breast cancer. If a tumor expresses an estrogen receptor, then a drug like tamoxifen or raloxifene can be used on it. These agents block the estrogen receptor, which inhibits growth of the tumor (normally these tumors grow in response to estrogen). ",
"Unfortunately, some cancers simply don't respond to chemotherapeutic agents. This can be for many reasons, including various adaptations such as pumps to remove the drug from inside the cell, or stopping expression of a certain receptor that was the drug's target. These adaptations are (from my understanding) hard to predict and this is why many chemotherapeutic agents are often tried in cancer patients."
] |
[
"Wow, fascinating! Thank you for your thorough explanation."
] |
[
"no problem. Let me know if you have any other questions!"
] |
[
"Why is T wave on ECG (in most leads) of same polarity like QRS complex, despite having the opposite vector?"
] |
[
false
] |
The only explanation I could think of is that although the electrical axis of repolarization is of opposite direction than depolarization, the flow of ions through the membranes is opposite as well (positive ions go inside the cell during depolarization and outside during repolarization). So it's like double negative. Is that right? And, if it is, can you please specify the exact mechanism of how does this flow affect the ECG? I just feel it could be right, but can't support it with any logic.
|
[
"The last cardiomyocyte to depolarize is the first to repolarize. So it means that the endocardium is the last portion of ventricle thickness to depolarize, but it will be first portion to repolarize.\nThink of repolariation as being the opposite of depolarization. Whereas a positive deflection will be seen as a depolarized wave approaches a positive electrode, a replorization will show a positive deflection when moving away from a positive electrode"
] |
[
"Yeah I think understand this. The order in which the ventricle wall layers depolarize and the direction in which this action advances determine the mean vector of repolarization. At the same time this vector is approximately opposite to the one of repolarization. But still, my question is, ",
" will a repolarization show a positive deflection? "
] |
[
"Sorry that I'm a little unclear, I should probably have waited with answering this until I sober up tomorrow morning.",
"Repolarization begins in the epicardium and base, and spreads towards the endocardium, whereas depolarization does the reverse. As a result, the same polarity develops transiently across the heart during depolarization and repolarization. This is why the T wave is upright. I will find some find some explaining pictures as soon as I get home tomorrow."
] |
[
"how much energy would we save if we stopped lighting up streets, houses, and parking lots, and focused on cheap individual night vision?"
] |
[
false
] |
I hate light pollution and the energy used has to be a huge amount, but is it even feasible to get good enough night vision cheaply? Sorry kind of turned into a 2 part discussion...
|
[
"Hey, turns out that I work with night vision devices for a living. Couple things.",
"1) Yes, right now, the technology is pretty expensive. Military grade stuff is very expensive. To provide a pair of night vision goggles to all the 300+million (and growing) people in the country would be a monumental undertaking, in terms of both production and cost. ",
"2) You might not know that night vision goggles (the green vision stuff you see in all the movies) still require some amount of light to function. In true darkness (i.e. if you eliminated all other ambient light) they would be useless. Oh and as nofelix mentioned, these devices are currently monochrome, which is to say that they do not show color. Much work has been done to gain some kind of color, but without getting into it, it's somewhat of a physical impossibility. Not easily overcome.",
"3) Night vision devices are pretty power hungry themselves; right now they run off some AA's for example. You'd be swapping one kind of energy consumption for another, and probably be on the losing side of that battle. ",
"4) To the point above, light bulbs are pretty efficient these days. Especially with high efficiency CFLs or LEDs. And our infrastructure is set up to power all the things that you mentioned previously, so again, we're fairly efficient at it.",
"Hope that helps, glad to see you are thinking outside of the box!"
] |
[
"At an approximate population of 300 mil. I'd say the USA."
] |
[
"Night vision",
" is pretty crappy compared to illumination. You can't see colours or details for a start, so any task that required those would be impossible. And you're reliant on the goggles, so if you run out of batteries, or they get damaged then you can't see. Or if you just can't afford them. Luckily our society still considers lighting to be a public service worth providing.",
"So to solve these problems you'd need:",
"But you're right, we would save a lot of energy. It's an interesting idea."
] |
[
"What is the correct term for when the effects of an isolated variable cannot be accurately identified in the context of a large robust study? Esp. in relation to nutrition science."
] |
[
false
] |
Sorry for messy title but I'm not exactly sure how to ask this. ------------ Compound madeup123 has been shown to raise blood pressure. This has been shown in short-term, clinical experiments, by administering the compound to test subjects, and taking measurements. It turns out that the goofball fruit, which we have all been enjoying for years, has been shown to have relatively high levels of madeup123. Dr. Jon Smith, in his latest diet book, puts the goofball fruit on his list of foods to avoid, citing the experiments with compound madeup123, connecting it to increased risk of heart attack, stroke, and damaged arteries. ----------- I have a friend who seems to switch to a different diet every few years. Inevitably he has some book to show me, which "proves" that this diet is the best one. Sometimes its written by a medical professional, sometimes not. Littered throughout the book are examples like what I have written above. But here is the crux of my question: I understand this is different than trying to look at a large database of outcomes, and trying to draw some general conclusions. E.g. - a study of 300k coffee drinkers shows that drinking a cup a day extends your life by a few years. Ok, I'm skeptical of some of these, but I get it. This is different than the example I've given. But these fad diet books are rife with the kind of thing I'm talking about and sometimes it drives me bonkers. Either something wonky is going on here or I'm just not understanding something. If its the latter than thats fine with me, please educate me. What is the technical term for this sort of thing - statistical significance, or noise....or something else? What am I missing?
|
[
"First of it is important to make one thing very very clear. Nutritional science is despite its name not a an exact science. A lot in the field can not be proven due to the very problem you describe. It is almost impossible to downright impossible to without major concessions to get any result that is above error rate."
] |
[
"thought at first maybe you were thinking of \"confounding variable\" but maybe youre looking for this:",
"\"In an experiment, an extraneous variable is any variable that you're not investigating that can potentially affect the outcomes of your research study. If left uncontrolled, extraneous variables can lead to inaccurate conclusions about the relationship between independent and dependent variables\" (Scribbr)"
] |
[
"Yeah I'm not sure what the right words are, so I figured the best thing I could do was provide a hypothetical example.",
"Thank you for the detailed answer, very helpful."
] |
[
"Would it ever be possible to clone or create extinct animals out of fossil DNA?"
] |
[
false
] |
If so, why should or shouldn't we?
|
[
"There's interest in it, and there's been at least one ",
"partially-successful attempt",
". There's constant publicity about teams who claim they're going to clone mammoths, but group after group has been announcing that for decades and at this point the default assumption is that they're all full of shit. Even if it was possible, it's not very practical. ",
"First, \"fossil DNA\" is a non-starter for cloning. Although the state of DNA sequencing today means that genome sequences have been worked out for a number of extinct animals, up to 700,000 years old, that's not suitable for cloning; it's broken up into tiny fragments, it's degraded and chemically altered, and it's usually heavily contaminated with bacterial and other DNA. These things can be corrected by the computers that piece together the sequence, but they are absolutely impossible to overcome for cloning purposes, and will be for probably decades to come. We don't even know how many chromosomes Neanderthals have, despite knowing their genome sequence from several individuals.",
"(Two possible solutions that are decades away are synthesizing the full genome, where you'd need to worry about epigenetic effects, and massively mutating the genome of a modern relative, which has ethical as well as technical problems.)",
"Second, even if we're talking about relatively recent DNA, and even if there was a modern relative that could carry the embryo to term (say an elephant for a mammoth -- but you'd need to have a fairly close relative), it would be little more than a curiosity. It's not enough to clone one, or two, or even a dozen individuals of an endangered species, and it's hard to believe that this could be done for the hundreds or thousands of individuals you'd need for a minimal stable population. "
] |
[
"It takes 521 years for half of your DNA to decay",
". ",
"If you run the numbers:",
"...And so on.",
"Tyrannosaurus lived around 68-66 million years (My) ago. If we take 67 My, the number in-between, and divide it by 521, we get (rounded up) ~130 000 iterations of this decay process. As you can notice, there wouldn't be any DNA left to get any meaningful information, if any."
] |
[
"Yes and no. ",
"In theory you could potentially create, what looks and appears like, an extinct animal but one of the big problems is knowing what is important and what isn't. The most straight forward way of creating this mutant animal would be to use a construct, probably an animal, that shares a relatively recent common ancestor. Methodology aside, the biggest problem you're going to run into is not which genes are important, but rather which transcription factor are important and which regulatory regions are important. Most protein encoding regions of DNA are fairly well conserved in animal lineages, and most of the genetic diversity that we see is not so much a change in protein encoding regions of DNA but rather the cis-acting regions. ",
" Because it's difficult to say what's important and what's noise. ",
" Because we're building off of an existing DNA construct. ",
" The best way to do it would be to insert 1/nth of the genome into a construct, hope it doesn't kill the animal and everything is expressed perfectly (impossible) and then cross that lineage with another animal of a different 1/nth of the genome, and pray that you get a perfect homozygous cross. Then continue with the next lineage of 1/nth of the genome until you eventually mate a ",
" extinct animal, but at that point you don't really have an extinct animal as much as you just have some new weird mutant animal. ",
"As for whether or not we should do it, I say no. Whatever monster you create (it will be a monster, don't kid yourself) will not have any obvious natural predators and it's a problem if it gets out. ",
" Why are we making it in the first place?"
] |
[
"How do peripheral neurons receive oxygen?"
] |
[
false
] |
[deleted]
|
[
"The same way all your peripheral cells get oxygen.",
"The arteries from the heart divide and shrink as they progress from the aorta. From these, capillary beds spring, which are a maze of small vessels slightly smaller than an RBC. Across the walls of capillaries oxygen/CO2/nutrient exchange occurs, and these then diffuse into surrounding tissue.",
"Capillaries run in all living tissue, and peripheral nerves receive oxygen by diffusion from them."
] |
[
"So, do we see a decrease in neuronal conductivity when blood vessels are constricted? For example, will someone with hypertension have a weakened nervous system?"
] |
[
"When neurons do not receive enough oxygen they will quickly reduce their energy production and ion channel conductance. The latter will cause the neuron to have a higher excitation threshold which will lower the overall activity of the neuron. So yes, when there is not enough oxygen available to the neuronal population the amount of action potentials fired by the neurons will decrease. I do not know if having hypertension is sufficient to lower oxygen levels to such an extent that this effect will occur. Read Bickler & Donohoe (2002) for a review on this topic."
] |
[
"Why do strokes only happen in the brain?"
] |
[
false
] | null |
[
"That's the definition... Interruption of blood supply to other parts of the body has other names like \"heart attack\""
] |
[
"I was thinking about the specific cause, like a blood clot. Why don't those clots cause disaster elsewhere, like a finger or something?"
] |
[
"Ah, I recommend making a new post with that rephrased question then."
] |
[
"Would decompression have any affect on stopping or slowing a projectile in space?"
] |
[
false
] |
What prompted this question is the scene in Star Trek Into Darkness where Khan and Kirk perform a space jump first by being depressurized and pushed into the vacuum of space, and then guiding themselves to an entry port on the enemy ship... that also depressurizes when it opens. Wouldn't this exert the same or similar amount of force? If yes, would that not stop them instantly at the point of entry? Would that sudden halt kill them, or does decompression disperse air quickly enough that any incoming projectile (human or otherwise) has more than enough mass to pass right through? Are aerodynamics even at play in space? Hope that makes sense. I'm sure there are variations depending on the size of the projectile and amount of pressure on either end, but I was curious about the physics here - both if the depressurization is equal or unequal. The video in question:
|
[
"Sure, any projectile in a cloud of gas is going to experience \"air resistance,\" whether that cloud of gas is on Earth or in space. The same basic principle applies in both contexts: the projectile has to push the gas out of the way in front, and this takes energy. In your case, a moving cloud of gas will exert a force on any object it collides with.",
"First, how fast is that gas actually moving? The case where a spacecraft is leaking air to the vacuum is an example of ",
"choked flow",
", so called because the velocity of air is limited at the choke point. The short answer is that air will be flowing out of the spacecraft at roughly the speed of sound (mach 1, or about 343 meters per second).",
"Now, how much air is actually flowing out of the hole? One of the properties of choked flow is that the mass flow rate only depends on the pressure inside the vessel, and not outside the vessel. The mass flow rate on the linked page is complex, but just churning through numbers. ",
"Use a C_d of 1 as a worst-case scenario. In reality, the flow through an orifice never becomes truly fully choked.",
"Let's assume the discharge hole is 2 meters wide, so the area AS of the discharge hole is 3.14 meters squared. ",
"Use a lambda of 1.4 for air",
"If we assume that the air inside the spacecraft is at standard temperature and pressure, it will have a density (rho nought) of 1.225 kg per meter cubed, and a pressure of 101,300 pascals. ",
"So now we just plug and chug ( ",
"https://www.wolframalpha.com/input/?i=1.0*3.14*sqrt(1.4*1.225*101300*((2%2F(1.4%2B1))%5E((1.4%2B1)%2F(1.4-1))))",
" ), and get a mass flow rate of 757kg per second traveling at about 343 meters per second.",
"Now we can multiply the mass per second (757kg) and the velocity (686 meters per second) and get an ",
"impluse",
" of about 519,000 Netwon-seconds. If our explorer perfectly blocked the entire stream of air for one full second, the air would exert 519,000 Newtons of force and the explorer would experience acceleration of 662 g's, easily enough to \"blow them away.\" ",
"But, the explorer in the video clip is exposed to the air stream for maybe a half or a quarter of a second, and they don't block the entire stream. I'm not honestly sure how to figure out the hypersonic drag on the explorer, so let's say that they block 10% of the airflow on a rough size estimate, and only for a quarter of a second. At that point the force exerted is about 13,000 Newtons, or about 17 g's (162 meters per second squared). This is actually survivable based on the experiences of fighter jet pilots. Moreover, since our incoming velocity to the space ship is 343 meters per second, a quarter second acceleration of 162 meters per second squared results in a final velocity of about 303 meters per second entering the spaceship.",
"Lastly, now our explorers hit the inside atmosphere of the ship at 300 meters per second. I'm not actually sure what to make of this: we know for example that falling into water from a tall bridge is likely to kill you, because the water just doesn't move out of the way fast enough to accommodate your body. I think that something very similar will happen here, but I'm not sure how to calculate the initial shock or the drag forces involved."
] |
[
"Hitting gas at sea-level pressure at 300 m/s should be survivable with a good suit. People have used ejection seats at various heights and speeds. Does it slow you down fast enough so you don't crash into the next wall? That is another question...",
"Do we know for sure these two reached 340 m/s relative to the initial spacecraft? Maybe the initial push was much weaker because there was not so much gas.",
"Also, what is the relative velocity of the two spacecraft and how much did they accelerate in between? They seem to enter the spacecraft at less than 300 m/s."
] |
[
"Thanks for both your answers. That’s also throwing me off about all this. The door opens, emits air pressure at a rapid rate, and even if that is survivable at the point of entry, would the atmospheric pressure when the door is closed create a cushion, a brick wall, or neither and they continue flying into the nearest wall? It sounds like the point of entry isn’t a killer, but entry at that speed is nothing to laugh at either"
] |
[
"Why do allergy shots help? Why can't I just be exposed the thing I am allergic to once a week?"
] |
[
false
] |
I have a decent knowledge of how allergies work, but what I still don't understand is how allergy shots actually work. I understand that the shots are exposure to allergens, and that the dose increases over time. Therefore, the patient can tolerate greater and greater amounts of the allergen until they have reached an acceptable level of tolerance. But what I don't understand is why continuous exposure doesn't do the same thing. If I am allergic to, say, cats and I am around a cat once a week, why does the allergy continue to get worse (or stay at a certain level of severity)? Why does the body build up a tolerance through allergy shots and not repetitive acute exposure? Does it have to do with the graduation of doses of allergy shots? Thanks!
|
[
"Actually, allergy shots ",
"don't cause a \"tolerance\"",
" in the way you are thinking. What they actually do is change the nature of the immune response from one dominated by IgE and eosinophils to an IgG/T cell immune response. These different immune mediators still respond to antigen, but they don't cause any of the allergic side effects that are so unpleasant to those of us plagued by allergies. ",
"So, the reason why continuous exposure doesn't do the same thing is that allergy shots contain factors that push the immune response in a certain direction while continuous exposure just causes continuous activation of the IgE/eosinophil dominated immune response. Good question, hope this helps! "
] |
[
"Ahhhhh, that does make sense, thank you! I think the disconnect was that I thought the allergy shots still produced a reaction via IgE/eosinophils and the body just became used to it, or bored of it, haha. But that exactly answers my question, thank you!"
] |
[
"Work the same way with Asthma allergy? If I get the shots will it only help the itching, watery eyes, sneezing. When I run into cats/dogs I really struggle to breath but didn't know if allergy shots would help that too... "
] |
[
"Why don't nuclear power plants use direct air cycle turbines?"
] |
[
false
] |
DACT were successfully spun up during the nuclear propulsion program but nuclear aircraft were not viable for obvious reasons. However they seem to make a lot of sense, why heat steam and run a turbine when you can run the turbine directly off the heat of the core? Wouldn't this be more efficient?
|
[
"No, so far we haven’t find anything is better than steam. You can look at the PV or TS diagram, steam give you the best result. Coal fired power plant do exactly that. But natural gas turbine will burn fuel at the turbine to generate power and send the exhaust to generate steam for more power, heat recovery steam generator (HRSG). If you use heat to do one task it will ended up losing too much heat (energy). "
] |
[
"The energy extracted from a fluid equals its pressure times its change in volume, so to get the most energy you want the volume to change as much as possible. The best way to do this is with a phase change, starting from a very dispersed gas and condensing it into a liquid.",
"There are a variety of condensible fluids you could use, but water has the advantage of having a convenient boiling point, a very high ",
"latent heat of vaporization",
", (so a small amount of steam can hold a lot of energy), plus it's cheap and nontoxic."
] |
[
"If you want to be horrified then that's not just an off-the-wall idea I made up. About half a dozen multimegawatt ",
"mercury turbines",
" were built in the U.S. for power generation, mostly in the 1930s and 40s. The site has old photos of workers floating calmly on top of pools of liquid mercury...",
"Mercury turbines were also used in some of the SNAP series of satellite nuclear reactors. The trifecta of rocketry, high-temperature mercury, and U-235 based reactors would make Captain Planet weep but the U.S. really needed something to power spy satellites at the time."
] |
[
"If trees did not ever exist, would homo sapiens even exist, if yes then what would humanity look like in that timeline's 2014 in comparison to our timeline's 2014?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"For more information regarding this and similar issues, please see our ",
"guidelines.",
"If you disagree with this decision, please send a message to the moderators."
] |
[
"Do you know a good place to ask this question besides askreddit? "
] |
[
"/r/AskScienceDiscussion",
" "
] |
[
"Why doesn't 2,4-Dimethylpentane have cis or trans isomers?"
] |
[
false
] |
[deleted]
|
[
"You're right in your last point. There's free rotation about all the bonds in this molecule so there's no way you can configure the atoms that isn't equivalent to all the others. ",
"It is possible to make some non-equivalent isomers if you for example replace half the hydrogens with deuterium. In that case, you can make two chiral centres at the 2 and 4 atoms, and if two methyl groups are deuterated, you can get four different arrangements of the molecule (R,R; R,S; S;R, S,S). Still not cis/trans, though as there's no double bond or ring to fix the conformation of the molecule."
] |
[
"Yeah, you need something to restrict the geometry so they can't easily interchange. This can happen a couple of other ways too, but they're not common."
] |
[
"Yeah, you need something to restrict the geometry so they can't easily interchange. This can happen a couple of other ways too, but they're not common."
] |
[
"How does 5G achieve speeds orders of magnitude faster than LTE if they’re both just using electromagnetic waves?"
] |
[
false
] |
[deleted]
|
[
"The TL;DR is: The speed of radio waves is often not important at all in wireless communication.",
"Long answer:\nFirst of all, in communication systems there are usually two important measures that relate to the \"speed\" of the system. One is called latency the other throughput and only the latency is directly related to the speed of the transmission medium as it denotes the time it takes to send a message from the sender to the receiver (you might have also heard of two times the latency referred to as 'ping'). However, most wireless communication is relatively short-ranged, at least when compared to the speed of light, and system delays dominate the latency (the next basetower for mobile communication is usually only a few kilometers away which translates to less than 10 microseconds in latency).",
"Now, the second measure of speed I mentioned earlier, throughput, is the really important number for most use cases. It relates to the amount of information transmitted in a given time period, a common unit is kbit/s. This tells you how fast your text, pictures and videos will load on your mobile phone. There are many ways to increase the throughput of radio communication, but here I will just take a short look at three of them: Increasing bandwidth, sensitivity or modulation speed (or a mix of all three).",
"Increasing bandwidth means, that more of the frequency spectrum is used by the system. Since there are very many wireless systems in use today, bandwidth is expensive as everyone wants some. That is why 5G and LTE actually mostly share the same frequency spectrum, the difference is that 5G can have additional bandwidth on a completely different frequency at the same time to increase throughput.",
"Higher system sensitivity is beneficial for increased data rates due to the fact that a more sensitive system can get more out of the bandwidth it has by using more advanced forms of encoding data onto radio waves. Each wave sent out can transmit more information if even the smallest difference between two waves can be picked up by the receiver. In the past, most advances in communication speed were due to increasing sensitivity.",
"Lastly, modulation speed is simply the speed at which the system can operate, e.g. how many waves can be sent and received in a given time period. Here, the trend towards ever increasing computational power plays an important role. The best communication system is worthless if new data cannot be processed fast enough.",
"I hope I could give answer your question and give you a short overview over the important factors determining transmission speed in wireless communication. Feel free to ask any clarifying or follow-up questions!"
] |
[
"The biggest change between 4G and 5G is the transmission frequency. The fastest 4G networks transmit at 2.5Ghz, and the fastest 5G networks transmit at 25Ghz and 39Ghz. This represents at least a 10-16 times increase in bandwidth- potentially more if you're used to 4G operating at 600 or 700 Mhz.",
"There are many nuances to encoding digital signals via radio, but the crudest possible explanation is that going from 2.5Ghz to 25Ghz packs 10 times more data in the same space and time as the 2.5Ghz signal. ",
"Changing frequencies requires a coordinated advance in the whole system: new transmitters, new computer equipment capable handling higher signalling rates, new software to manage the process, etc."
] |
[
"The biggest change between 4G and 5G is the transmission frequency. The fastest 4G networks transmit at 2.5Ghz, and the fastest 5G networks transmit at 25Ghz and 39Ghz. This represents at least a 10-16 times increase in bandwidth- potentially more if you're used to 4G operating at 600 or 700 Mhz.",
"There are many nuances to encoding digital signals via radio, but the crudest possible explanation is that going from 2.5Ghz to 25Ghz packs 10 times more data in the same space and time as the 2.5Ghz signal. ",
"Changing frequencies requires a coordinated advance in the whole system: new transmitters, new computer equipment capable handling higher signalling rates, new software to manage the process, etc."
] |
[
"Why does pure aluminum have such a high thermal conductivity, but such a low elastic modulus?"
] |
[
false
] |
[deleted]
|
[
"I knew keeping all my engineering textbooks would eventually have a use.\n\"Heat conduction is solids is moved by both lattice vibrations and free electrons. In high-purity metals, the electron mechanism is much more efficient than the phonon contribution because electrons are not as easily scattered and have higher velocities. Furthermore, metals are extremely good conductors of heat because large numbers of free electrons exist that participate in thermal conduction.\"\nSo we would expect any pure element to have a higher thermal conductivity compared to an alloy. ",
"Here",
" is a very similar graph that is in my textbook.\nThe elastic modulus does come partly from the strength of the metallic bonds, but once we start comparing metals, purity, grain size, and phase have a much greater importance."
] |
[
"Yes. Any material with free electrons will conduct both well. Then there are things like diamond that have no free electrons but conduct heat very well because lattice vibrations can easily move through the perfect crystal."
] |
[
"is this why good conductors of heat tend to be good conductors of electricity?"
] |
[
"Where did the name \"The milky way\" originate from?"
] |
[
false
] | null |
[
"The ancient Greeks were IRC the first people to call the galaxy the Milky Way. In fact, the Greek word for \"galaxy\" derives from the Greek word for \"milk.\""
] |
[
"Yes, it's Hera's breast milk that sprayed across the heavens when she breastfed Heracles."
] |
[
"Seen from Earth, the Milky Way is a gigantic arch across the entire night sky, visible with the naked eye, many times wider than the moon.",
"It's only hard to see in the modern world because light pollution from cities makes it difficult to see from where most people live. To the Greeks, it would have been the largest thing in the sky. If you ever have a chance to visit somewhere far enough from lights to see it clearly, it looks like ",
"this",
"."
] |
[
"When a Phase Change Occurs Because of Pressure Change (e.g. flashing of water), Does The Temp. Remain the Same?"
] |
[
false
] |
I was reading about the effects on the human body when exposed to near vacuum conditions (such as in space). When NASA testing this, their test subject reported the last thing he remembered before he began to lose consciousness was the water on his tongue beginning to boil. I assume this is because of the pressure of the water was below 1 atm and was beginning to change phase to a liquid? Would that be that be correct to assume? I imagine if, while the water was beginning to boil due to pressure, that if the temperature also changed it would probably be pretty painful.
|
[
"You are correct, the water on his tongue boiled because the pressure was so low. The ",
"phase diagram",
" of water shows the thermodynamically preferred state of water for a given combination of pressure and temperature. Assuming the test subject was in a near vacuum the boiling temperature of water in his conditions would have been about -60C. This doesn't mean the temperature on his tongue would have plummeted to -60C however, it does mean that the water on his tongue would continue to boil as long as the temperature was above that. Since boiling is an endothermic process his tongue would get colder as heat was absorbed by the boiling water. But i'm guessing his tongue would dry out before any painful amount of temp change occurred (assuming he was conscious...). Using low pressure to boil a liquid is actually frequently used to reach very low temperature, check",
" this video",
" out."
] |
[
"I'm not sure of the article is question since I'm on mobile, but I don't think it's necessary. I'm just a sophomore undergrad, but I may be answer your question. If you've seen a phase diagram before, there are usually three curves that distinguish different phases of a substance at various pressures and temperatures. I think it's possible to change one variable while keeping the other constant. The boiling sensation could have been due to lower atmospheric pressure in a vacuum. Although one way to boil water is to heat it, you could also lower the pressure above. If the pressure gets low enough, there will be less resistance for the water molecules to go against, and more will have a high enough energy to leave the surface. I hope someone with more experience could confirm or correct this! \nI'd also like to add, the same principle is on play in explaining why water boils at lower temperatures on Colorado compared to lower elevation states. "
] |
[
"In the scenario you described, what happened was that once the pressure in the ambient environment was reduced enough, it fell below the vapor pressure of the water in the subject's saliva. This caused the water molecules in his saliva to push harder than the air was pushing back, and the water began to vaporize. As the pressure drops, the temperature of the boiling liquid drops as well. There are interesting experiments where you can have a beaker of water in a vacuum chamber and then start pulling a vacuum. The water first starts to boil. Then, as the pressure drops further, and the water temperature drops, ice starts to form, and you can actually have all 3 phases of water in the same beaker instantaneously.",
"I hope that explains it. The thermodynamics of phase change can get pretty complex. "
] |
[
"What is the thin layer that forms on top of tea when it steeps too long?"
] |
[
false
] |
Well, title speaks for itself, I guess. I've noticed that when I let tea sit too long with the bag still in it, a transparent/white-ish layer forms on top of the water. The stronger the tea is, the more apparent it seems to be. For instance, it rarely appears with herbal teas, but with a strong Darjeeling, it takes no time at all. Can anyone tell me what that layer is and how/why it forms? Cheers!
|
[
"My guess would be various oils that are present in the tea leaves that sit on the surface of the water. "
] |
[
"Do you live in an area with hard water? Could be that combined with the oils in the tea"
] |
[
"It's a mixture of calcium carbonate from the water and complex organic molecules from the tea. Try filtering your water to soften it, or add lemon juice to lower the pH. "
] |
[
"Could Opportunity be in reach of Curiosity and see it?"
] |
[
false
] | null |
[
"Not really. Opportunity is ",
"here",
" and Curiosity is ",
"here",
"."
] |
[
"Thanks!"
] |
[
"Your question has been removed, but I'd encourage you to participate in the ",
"main thread",
" on the Mars landing. Right now, all Mars related threads will directed to that one."
] |
[
"If I were to stand in the middle of a completely sealed, spherical mirror with a light bulb in the middle, would the light build up to blinding levels, or just remain as bright as the bulb?"
] |
[
false
] |
Title basically says it all, but I imagine if you have a box full of bouncy balls, and you keep throwing them in there with infinite energy, adding more and more would increase the density of the balls in the box, so would the same thing happen with light?
|
[
"Short answer: for perfectly reflecting walls, it's gonna get hecka bright.",
"Let's start with what determines the brightness of an incandescent bulb. You've got some electrical power P being deposited in the resistive filament. The filament heats up to the point where that input power is matched by all the power it loses to conduction and radiation. The radiation it puts out is that of a rather imperfect blackbody... but let's just pretend it's a perfect little blackbody whose radiation is given by its surface area and temperature, T (maybe in the neighborhood of 4500F = 2500C).",
"As the hot filament fills the sphere with light, the energy density of that light grows, dE/dt = P, assuming you're not conducting any energy out of the sphere. Some of the light traversing the sphere impinges on the little filament, and is absorbed. That means the filament has to heat up so it can radiate more power (to balance the new input of absorbed light). Indeed, if you managed to fill up the sphere to just the right energy density (that associated with the temperature of the filament) you could turn off the electrical power and the filament (and radiation) would remain forever at the temperature T.",
"But, if you keep pumping in electrical power, the filament will heat up, the radiation energy density will increase... until something gives. For a practical filament, the material will fail when it gets too hot, opening the circuit... but then of course the whole system will remain at some high temperature, forever."
] |
[
"[EDIT: ",
"]",
"This is a point that begs for an estimate of timescales. ",
"First, let's estimate the timescale for radiation to fill the sphere so that it has the right energy density for a 2800K (say) blackbody. Since you're standing in it the room needs to be fairly big... to pick a round number let's say 100 cubic meters. The energy density of blackbody radiation is given by (4",
"T",
" where sigma is the Stefan-Boltzmann constant. Combining those two tells you that the total energy in blackbody radiation (at 2800K) is only about 5 Joules. So, it ideally would only take that 100W lightbulb about 1/20th of a second to fill up the room with that light.",
"If you're standing there absorbing photons, the light needs to heat you up until you're emitting at the same temperature as the filament. How long does that take?",
"Let's pretend (for round numbers) that you're 100kg of water. The heat capacity of water is about 4kJ/kg/Kelvin, so you need about 40,000 ",
"Joules to heat you up by 100K (or 100C) which gets you to boiling. Assuming all 100W from the lightbulb is heating you up, that takes about ",
" 400,000 seconds... which is about 4.6days. [",
"]",
"The heat capacity of steam is about half that (2kJ/kg/Kelvin), and we need to heat you by about another 2400K, so that's another ",
" ",
".",
"So, you're right in that the process is slowed way down... "
] |
[
"[EDIT: ",
"]",
"This is a point that begs for an estimate of timescales. ",
"First, let's estimate the timescale for radiation to fill the sphere so that it has the right energy density for a 2800K (say) blackbody. Since you're standing in it the room needs to be fairly big... to pick a round number let's say 100 cubic meters. The energy density of blackbody radiation is given by (4",
"T",
" where sigma is the Stefan-Boltzmann constant. Combining those two tells you that the total energy in blackbody radiation (at 2800K) is only about 5 Joules. So, it ideally would only take that 100W lightbulb about 1/20th of a second to fill up the room with that light.",
"If you're standing there absorbing photons, the light needs to heat you up until you're emitting at the same temperature as the filament. How long does that take?",
"Let's pretend (for round numbers) that you're 100kg of water. The heat capacity of water is about 4kJ/kg/Kelvin, so you need about 40,000 ",
"Joules to heat you up by 100K (or 100C) which gets you to boiling. Assuming all 100W from the lightbulb is heating you up, that takes about ",
" 400,000 seconds... which is about 4.6days. [",
"]",
"The heat capacity of steam is about half that (2kJ/kg/Kelvin), and we need to heat you by about another 2400K, so that's another ",
" ",
".",
"So, you're right in that the process is slowed way down... "
] |
[
"Is there a difference in the quality of gas based on where it's sold. Is exxon gas better than walmart gas,etc.?"
] |
[
false
] | null |
[
"I refer to Cartalk hosts, the Tappet brothers.",
"\"Is there a difference in the gas between the big names, and the El-Cheapo gasoline at my local Costco or Stupey-Mart?",
"There is. A number of years ago, some of the major auto manufacturers were ticked off with the deposits from gas that met EPA detergent standards. In other words, they were afraid they'd take the heat for problems, when their customer's engines clogged up from the twigs and dirt that was getting deposited on their fine handiwork.",
"So, they set their own guidelines, which they call \"Tier 2.\" All of the gas from the major gas companies meets the Tier 2 standards. The gas at your local Quickie Mart probably does not. The difference? In some tests, after about 10,000 miles, there was a minor amount of crud built up on engine components that ran exclusively on Quickie-Mart gas. Do we think this is an issue? Not really. But, would we advise running your car for 100,000 miles only on Quickie-Mart gas? Not if you're concerned about the longevity of your vehicle. We recommend switching back and forth between Tier 1 and Tier 2 - maybe every other tank full - to keep your engine running clean.\"",
"http://www.cartalk.com/content/premium-vs-regular-0"
] |
[
"As someone who has worked on software for a pipeline terminal, gas is gas. Far be it from me to disagree with Click and Clack, but I don't think this tells the whole truth: The only difference between these Tier 1 and Tier 2 fuels is the additives. An Exxon truck pulls up to a terminal, pushes a few buttons (on our system), and gets the Exxon blend of fuel, detergents, and additives. Behind him in line is a BP truck, and they get the BP blend. Then a truck going to Quick Trip (local convenience store that advertises that they have the 'best' gas).",
"Keep in mind, also, that these additives are just a small percentage of what goes into each tanker truck. 95%+ of it is just gas."
] |
[
"They call those 'Diesel' engines."
] |
[
"Is there a consensus on what is a dinosaur? How different were they from dinosauromorphs ?"
] |
[
false
] | null |
[
"Dinosaurs are defined as Triceratops, a house sparrow, and all descendants of their most recent common ancestor. You might hear a couple other definitions--sometimes Iguanodon and Megalosaurus are used the references instead--but they all amount to the same thing, which is basically ornithischians and saurischians combined (some people suspect that Herrerasauria is an outgroup--meaning either they would be excluded from Dinosauria or the definition would have to be altered--but the consensus seems to learn towards them still being Saurischians, and the same for Baron et al's proposal that Sauropodomorphs are further from therapods than ornithiscians).",
"If you compared them directly, the first dinosaur and its closest dinosauromorph ancestor wouldn't have been too different, but in general the earliest dinosaurs had a variety of improvements in their pelvis and limbs that gave them a more upright stance and a little more agility compared to their relatives."
] |
[
"No, which is typical for large groups. Even if we happened to find an example of that species, we wouldn't have the evidence to say if it was the actual most recent common ancestor or a close relative.",
"Of the dinosaurs we have found, different analyses still disagree on which species is the closest to the ancestor, but Eoraptor is a good example of something reasonably close."
] |
[
"This is not possible. Most species exist as chronospecies, they differ slightly over time. H. Sapiens is a chronospecies including H. Antecessor, H. Heidelbergensis, all the way back to H. Ergaster. There's no defining moment between any of them, and forms midway between different morphologies are common.",
"Let's say that the actual truth is that all members of Dinosauria are descended from the genus Eoraptor. Eoraptor lived for three million years. If we go back that amount of time, you were still a hairy walky ape. Eoraptor lived for a long time. Due to the Signor-Lipps effect, almost certainly for longer than this.",
"Did Dinosauria emerge from an earlier form of Eoraptor? A middle form? A late form? When exactly did it branch off? Was it allopatric speciation? Peipatric? What were the other branches? (Herrerasauria was one, most likely)",
"All we can say with confidence is that Dinosauria emerged from a group which probably included Eoraptor. Eoraptor itself may have been a basal sauropodomorph, and so already a dinosaur itself. Buriolestes is considered a very basal sauropodomorph, and it's older than Eoraptor is. Euparkeria was a similar animal, and lived at the same time as Eoraptor. Silesaurus, Lagerpeton, and Marasuchus also made up this group.",
"We have to ask all the question we asked Eoraptor of these genera too. Even if, as a godlike outsider, we know dinosaurs came from Eoraptor, Eoraptor is so similar to all those other animals that an observer 232 million years later cannot reconstruct the lineage any more accurately than \"That group.\""
] |
[
"How do center-surround receptive fields account for the Hermann Grid illusion?"
] |
[
false
] | null |
[
"They do not (in a lateral inhibition account). See ",
"here",
". "
] |
[
"Yes. I've looked up the site. Thank you for sharing.\nI understand that there is much more that we do not know.",
"Let's ignore the argument that it is the \"weak\" explanation. I'd still like to understand how RFs work in the Hermann Grid illusion. Particularly when it's reversed (White Squares; Black Lanes). ",
"Thank you!"
] |
[
"See the \"previous page\" in that link, which is ",
"this",
". It has an illustration of the mechanism / explanation. For white squares and black lines, it's just the opposite kind of RF (OFF-center instead of ON-center). "
] |
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