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[
"How in the name of physics can ice cubes form these upside-down icicles in my freezer?"
] |
[
false
] |
It simply blew my mind when I opened my freezer door to see two upside-down icicles. I've seen them do this more since but this is by far the tallest I've seen them get. Can AskScience explain this to me?
|
[
"This",
" page at caltech.edu has a nice explanation of ice spikes."
] |
[
"These are called ",
"ice spikes",
".",
"The basic idea is that water expands when it freezes, so if the top starts to freeze first the water underneath gets displaced. But the only direction it can go is up, so it does so at the weakest spot in the surface ice (or an opening if the surface isn't freezing uniformly. Then it freezes, but the process continues as the ice layer moves down, until you've got a column of ice protruding out the top."
] |
[
"Wikipedia could certainly use an update from that page."
] |
[
"Are modern, engineered cigarettes MORE harmful or addictive than the relatively unprocessed tobacco of our ancestors."
] |
[
false
] |
Saw the top comment on this video, and I got curious. So far, everything seems to lead me to: 1. Smoking is bad. Let's not discuss this further. 2. Unsubstantiated forum posts Help me find some evidence!
|
[
"I worked at a cigarette factory for a few years. I'm not sure of the status of my nda, but basically most of the stuff they add is food products. Most of that is casing to make it able to be cut (otherwise it would turn to dust). The flavoring is a tiny percentage of the final product. ",
"That being said they also remove a lot of nasty stuff, particularly from burley varieties. ",
"The fillers include stems of the plant and recycled cigarettes. Some of it is expanded. If you don't want fillers get skinny brands. ",
"It probably depends on the brand, but I would say it would be a bit better, especially with current filters (back decades ago there were filters with asbestos in them). ",
"That being said I don't smoke and you should quit if you do. "
] |
[
"There are more than 100 additives, and upwards of 599 in some cigarettes. To, and I quote ",
"camouflage the odor of environmental tobacco smoke emitted from cigarettes, enhance or maintain nicotine delivery, could increase the addictiveness of cigarettes, and mask symptoms and illnesses associated with smoking behaviors.",
"Cite: ",
"http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2040350/",
"It seems that some of the additives, pertaining to nicotine, slow metabolism of nicotine and allow the nicotine to stay in the blood longer. Since nicotine is a known, although not explicitly proven, carcinogen, this is bad. It also has teratogenic properties.",
"That study should clear up some of your questions, since it is about additives to tobacco."
] |
[
"In direct studies of formation of precancerous cells in lab animals, HUGE doses of nicotine over LONG periods of time have no effect when nicotine is delivered in isolation. When nicotine is delivered in tobacco, there are huge effects. I feel quite safe in stating the existing scientific literature supports e-cigs are being less likely to cause lung damage than cigarettes. Of course, there are still blood pressure/cardiovascular system effects that are mainly from the nicotine - but you asked about carcinogenicity."
] |
[
"How much of the proteome and genome do we understand?"
] |
[
false
] |
I was just wondering about the overall set of knowledge humanity has and the equestion just popped into my head. In terms of percentage what's the rough guesstimate of how much we understand of the fields as a whole? What are the benefits of each field of research? ( Potential benefits too) and what do we have to look out for in terms of law/ ethical questions.
|
[
"In terms of percentage what's the rough guesstimate of how much we understand of the fields as a whole?",
"Not much. As a wildly optimistic esitmate, I'd put it in the single digit percentages. We don't know all the players, nor do we know how all the players interact.",
"We've sequenced the genome, but we still don't know what ",
"one in five",
" of the gene products do. And that's just the ones that make protein, not all of the stuff that's actually used.",
"And it doesn't stop there. Of the \"classified\" genes in that pie chart, many are known to have other functions. Many more are thought to have multiple functions. Then toss in all the interactions there are; many gene products have multiple roles (not just function; they can do the same thing in different pathways or cells) and they all interact with each other in a myriad of ways. ",
"Hell, we just discovered a whole new ",
"system",
" of gene regulation only 10 years ago, and we're still identifying molecules in the system.",
"What are the benefits of each field of research? ( Potential benefits too)",
"Damn near everything. From better zit cream to a cure for cancer to longevity drugs.",
"and what do we have to look out for in terms of law/ ethical questions.",
"Again, damn near everything. It's hard to predict ethical quandries in such a massively large field, but they would range at least as far as the potential benefits. If you can give someone a 95% confidence interval of their lifespan, do you tell them? If someone has a very high chance of becoming an untreatble homicidal maniac at the age of 23, do you lock him up pre-emptively? "
] |
[
"The genome is well on its way to confusing us for another few decades, and the proteome is just beginning to go from cool sounding to confusing. ",
"That said, there are a few things we do know.",
"1) ",
" (and by proxy, the \"exome\") of the human genome. On the other hand, we have no idea what a lot of it does, we are still learning about RNA genes, and much of the rest of the genome may be transcribed at low levels as well.",
"2) ",
" and we will arrive at a set of common variants within all populations as more genome sequencing is completed.",
"3) ",
" within the human genome/proteome. We are very far from understanding what many of these do or how variation within the families across species affects biology.",
"4) ",
" in the genome. The caveat from number 3 plays here as well.",
"5) ",
", but not individual cells. The relevance to interesting biology is there sometimes, but not always."
] |
[
"None of it, or more precisely, next to nothing.",
"This question is way too broad to get a meaningful answer as it depends on how you define \"understand\". It also sounds like you are holding a philosophical assumption that knowledge is finite, which many (most?) philosophers of science do not believe to be true. If knowledge is essentially infinite, there is no way to quantify any portion of it. Its like asking, \"of all the integers, what percent has been written in ink?\" Since the amount of integers (a) is infinite and the number of inked integers is finite (b) you calculate the percentage of inked intergers (x) like this: b/a = x/100, x= 100*b/a or in English x = some number of integers divided by infinity. Anything divided by infinity is as equal to zero as you can get without actually being zero. ",
"Therefore, we know next to nothing if you assume knowledge is infinite."
] |
[
"Has there been any study on the life span of the higgs boson and gravity?"
] |
[
false
] |
Pretty much, the more mass around it and its life span?
|
[
"It is still too early to know much of anything about the Higgs Boson. The physicists at CERN are now entering the characterization phase of a new particle where they create more particles, and carefully watch the results to figure out the characteristics of the new particle. Once they have the Higgs Boson characterized they will then start doing experimentation with it. Almost any question beyond \"Does the Higgs Boson exist?\" would be hard to talk about.",
"Source: The most recent ",
"Star Talk Radio.",
" They are talking to a physicist from CERN about the discovery of the Higgs and they mention that they are just entering the characterization phase of the new discovery."
] |
[
"What do you mean?"
] |
[
"There is an AMA about this exact question in ",
"/r/IAMA"
] |
[
"Which biotechnological barriers are currently preventing drug barons from genetically engineering potatoes that produce cocaine?"
] |
[
false
] | null |
[
"lol",
"The short answer is that there are no technical barriers to doing this. Others in this thread have speculated that the import of an entire biosynthetic pathway might impair the host or cause other difficulties, but in fact this kind of thing is the bread and butter of we metabolic engineers, and the technique is much more common and easier than one may think.",
"However, with that said, yeilds of the end product (cocaine, THC, morphine, whatever) will almost always initially be lower per unit cost in the transgenic host than they are in the natural host due to a variety of factors. The metabolic engineering only gives you a starting point from which to then begin a classic selection and strain improvement program which may or may not ever beat your production costs of your original organism (even with operating costs of smuggling and DEA interceptions figured in).",
"The other reason why this would be very unattractive to drug barons is that it would encourage much greater \"home brewing\" and this cut into your own profits. It would be very difficult to keep a yeast making cocaine quarantined. Once it got out of the baron's control, anyone could home brew thier own cocaine beer. The fact that the only places in the world where coca can be cultivated in large scale are high elevations with lots of rain is actually an ",
" to a drug baron that enables him to keep his production consolidated and relatively free of competition.",
"Lastly, if you can find a team of people with enough experitise to actually do this work, I expect all of the key people are generally very easily employable. The baron is competing for talent with legitimate organizations that can offer comfortable middle-class lifestyles to their employees without the risk of death or loss of freedom (from either law enforecement or an immoral drug baron himself).",
"All of the above lead to some fairly high barriers to getting these kinds of transgenics made, but in the end none of them are really technical in nature."
] |
[
"Yes, but the plant will only grow in Colombia and Bolivia, which is a bit of a drawback because those countries are pretty poor. You want to sell it to rich people, which means you have to cross a border with the stuff. This causes troubles. But if I have a herd of cows that give coca-milk, I can produce my cocaine right here, in broad daylight (until the police wizen up, of course). "
] |
[
"Yes, but the plant will only grow in Colombia and Bolivia, which is a bit of a drawback because those countries are pretty poor. You want to sell it to rich people, which means you have to cross a border with the stuff. This causes troubles. But if I have a herd of cows that give coca-milk, I can produce my cocaine right here, in broad daylight (until the police wizen up, of course). "
] |
[
"When two balls are released on a Newton's Cradle, why is the momentum transferred to the two at the end and not just one (giving it a greater speed)?"
] |
[
false
] | null |
[
"That would conserve the momentum term, however halving the initial mass while doubling the initial velocity gives the kinetic energy at the other end of the cradle as KE = 1/2",
"m)",
"v)",
" which comes out to KE =mv",
" or double what the initial kinetic energy was.",
"The only mass/velocity combination that satisfies both momentum and energy conservation is where mass and velocity are the same, hence the same amount of mass (2 balls) moves at the same speed."
] |
[
"What if the balls at the other end had a different mass?"
] |
[
"What if the balls at the other end had a different mass?"
] |
[
"If the visible light spectrum follows a straight line from ~400nm (red) to ~800nm (violet), how can it be represented as a color wheel?"
] |
[
false
] |
Related: How is purple a combination of blue and red, if purple and blue are on one side of the spectrum, while red is at the other side?
|
[
"Color is created by your brain by using three sets of cells called \"cones\" on your retina, which have response peaks that correspond to red, green, and blue.",
"Also it's worth mentioning that the primary colors are different if you're dealing with light (red/green/blue, all colors mix to form white), or pigments (red/blue/yellow, all colors mix to form black)."
] |
[
"It should be pointed out that the word \"purple\" refers to colors that do not lie on the color spectrum. The color that appears on one end of the color spectrum is called \"violet\" in the scientific literature, and the word \"purple\" is used exclusively to refer to non-spectral colors."
] |
[
"Color perception more about your eyes than it is about the spectrum.",
"The human eye has three color receptors...when the eye says \"red and blue receptors are firing, green is not\" the brains translates that as \"purple\". That's why color charts can be multi-dimensional...it is all about the interaction of three variables in your eyes."
] |
[
"How do my eyes \"know\" the difference between viewing a small screen close-up compared to a big screen from further away?"
] |
[
false
] |
In other words, why is the visual effect of watching a movie on a theater screen significantly different than watching on a TV screen, assuming both screens appear the same size in my field of vision?
|
[
"There are at least two ways. First of all, your eyes must turn inward slightly in order to both face the same part of the same object. To converge on a nearer surface they must turn inward slightly more, and to converge on a more distant surface, they must turn inward slightly less. Secondly, the muscles that stretch the lens must flatten it to focus on a distant object and let it bulge out to focus on a near object. In both cases, the muscle's position feeds back to the brain to give distance information. The brain also uses cues from parallax and composition to estimate the distances of objects, but this isn't really an \"eye\" thing, so it might not count, depending on how you meant the question."
] |
[
"theatre pixel resolution is usually a LOT bigger than tv pixel resolution.",
"(I think it's in the 4000s, but this is just going from memory.)"
] |
[
"Like any object you view (not just screens), your question is explained by what is called depth perception",
"http://en.wikipedia.org/wiki/Depth_perception",
"I haven't been here a very long time. Is it bad just to post a wiki link? Am I supposed to provide a more 'plain english' explanation?",
"Interestingly, I believe that people who only have vision in one eye do not have depth perception."
] |
[
"How do you calculate pressure at which a supported plate would break?"
] |
[
false
] | null |
[
"There are approximate analytical solutions for thin flat plates loaded by pressure, but finite element analysis is the quickest method for thick ones with odd boundary conditions, especially when using brittle (less forgiving) materials.",
"If you specify the materials to be used, the maximum expected pressure, the required safety factor, and some basic dimensions, I can design a pressure vessel for you, complete with finite element analysis to back up the conclusions."
] |
[
"With a viewing aperture only 1/8\" across, it shouldn't require a particularly thick piece of window material.",
"I need the following pieces of data:"
] |
[
"I don't know of a seal rated for 30,000 psi. A typical O-ring is rated only for about 3000 psi.",
"However, a high-durometer silicone O-ring should work at 6000 psi as long as the geometry is designed such that the pressure closes the gap through which an O-ring would extrude. This is easy to achieve for the seal between glass and steel viewport.",
"However, if the cap screws on to the tube, it becomes a problem to design this secondary seal in a way that prohibits failure by O-ring extrusion (the most common failure mode for O-rings). So I propose that the cap be welded onto the tube, even though this prevents dis-assembly or repairs.",
"Here is the design",
", including part dimensions and finite element analysis at the ultimate load of 30,000 psi. For the fused silica, I also checked that maximum principal stress didn't exceed about 7,000 psi.",
"For assembly, the high-durometer silicone O-ring and fused silica window plate are placed in the cap (annealed 4130 steel), then the cap is fillet welded (weld size of 0.188\") via GTAW to the tube (also 4130 steel), with care taken not to overheat the cap and damage the O-ring."
] |
[
"Does Polynomial interpolation work with n-1 times the same supporting point xi and 1 thats different?"
] |
[
false
] |
first, english is not my mother language... so dont hate me too much. So when i do polynomial interpolation, and i have n different supporting points, i can build a lagrange polynom(Li(x)) and do the standard interpolation fn(x) = sum(f(xi) *Li(x)) and if i have 1 supporting point, I could simply do a taylor approximation with n times the supporting point "a" but what if i have n-1 times the same point a and 1times b?` i learned that in general the system matrix that contains the base-funktions with the different supporting points, has to have full rank. so that i can get a unique solution, but why does it matter if i can solve it for 1solution i have a solution and dont have to care if ther are more?
|
[
"I'm not entirely clear what you're asking, but it sounds like you're generally asking why use a lagrange polynomial versus a Taylor expansion?",
"First, they solve different problems. With Lagrange polynomials, you know the value at discrete points, and you want to ",
", that is find the value ",
" those distinct points. Taylor expansions are somewhat the opposite: you have the value of a function and a number of its derivatives at a single point, and you want to ",
" this. That is, describe the function ",
" from that point. ",
"In numerical methods, this distinction can get a little unclear. Finite difference methods are based off Taylor series expansions, but in order to determine a gradient at a particular point to use in that expansion, you have to form an interpolation (lagrange or some other kind) of neighboring points. In other words, in order to ",
" a function from a point we first ",
" it from neighboring points.",
"These things are close relatives too: if you take a finite difference Taylor expansion about a point x",
"{i+1}, and another expansion towards i-1, and truncate the series, you end up with the unique lagrange polynomial through those 3 points. "
] |
[
"ok, sorry my technical english is a bit rusty,\nthx for your answer one more question, ist the hermite interpolation basecly just a finite taylor expansion?"
] |
[
"ist the hermite interpolation basecly just a finite taylor expansion?",
"I was going to mention that. It's not really a Taylor expansion because it requires values and their derivatives at two distinct points, whereas a Taylor expansion is about a single point. And it's not a lagrange interpolating polynomial either because it's using derivatives, not just values. But, you can take two first-order Taylor expansions, one at each point, and that gives you the unique hermite cubic polynomial.",
"This is exactly equivalent to just saying you have a cubic polynomial that is sum a_n x",
" from n 0 to 3, and then determine the four coefficients which satisfy the point values and derivatives. If you didn't have those derivatives, but happened to have two more point values that exactly sit on that cubic, then a lagrange polynomial will give you same polynomial. "
] |
[
"When an atoms electron drops an orbital and the atom shoots out a photon with momentum p, does the atom then have a momentum of -p?"
] |
[
false
] |
[deleted]
|
[
"Yes."
] |
[
"Yes indeed, it's called \"radiation recoil\"."
] |
[
"p = mv only applies to a nonrelativistic particle. In general, momentum is a property of any particle which is moving, whether or not it has mass."
] |
[
"Are a butterfly and a caterpillar the same animal genetically?"
] |
[
false
] |
How can an organism achieve such a drastic transformation using the same genome? Does a caterpillar's DNA undergo a rewrite when it metamorphoses? Is there some sort of inherent gene editing going on?
|
[
"They have the same genome yes. And it shouldn't be that surprising, the same genome that produces your eye is the same genome which produces your kidneys, two very different organs. One of the biggest discoveries from the human genome project was that the absolute number of genes is not that high, it's the regulation of expression and splicing which allows for the huge amount of diversity in tissues."
] |
[
"You would be interested in epigenetics. Your genome is essentially a textbook of instructions for building proteins, but in these instructions you have regulatory parts. Some parts are locked off in some organs, after all there's no need for your eye to tell cells to create all the cell transporter proteins that the kidney has. There's also no reason all the cells in your eye should have the \"grow and divide\" genes on, so that part is kept silent. ",
"The DNA itself has a series of switches that are not part of the code, but instead like little tags and bookmarks that go \"read me!\" or \"go away\" to proteins like polymerase. Then there are various other enzymes that go around and turn on/off these tags, or add them, depending on the cellular stressors and needs."
] |
[
"Can you explain regulation of expression further? I'm interested in how the genetic instructions translate to specific functions."
] |
[
"How do IR detection cards work?"
] |
[
false
] |
I recently saw this vid: . And it showcased an infrared detection card, which seemed like magic to me. How do they work?
|
[
"The reason these cards are surprising is that most of the time, when a photon interacts with matter it emits photons that are the same energy or lower -- that means you can't directly make visible light from infrared.",
"There are two types of infrared detection cards.",
"The most common type, the one shown at the start of the video, contains a phosphorescent material similar to glow-in-the-dark stuff. You \"charge it up\" by holding it under visible light: this excites the atoms and locks them in the excited state. When struck by infrared, the excited atoms return to their original state, releasing a photon. The energy for their glow comes from the visible light they were charged with: the infrared is just a trigger. Once the light is given off, that part of the card stops working until it's recharged.",
"The other kind (the green card in the video) doesn't need to be charged: these use the same rare-earth elements that the green lasers in the video use. They absorb two infrared photons and emit one with twice the energy (green). However, this process isn't very efficient in a thin layer, so these cards work best with higher-power lasers."
] |
[
"Thanks for the thorough explanation"
] |
[
"While gold is a good IR reflector, in order to shift the wavelength it would likely need to be at the nanoparticle level which would be quite ineffective. The manufacturer of some IR cards states that it is made from plastic and liquid crystals, but that's all the info I could get easily."
] |
[
"How do ionic solids like salt melt?"
] |
[
false
] |
NaCl is held together by an ionic bond. When in a solid, these molecules make a lattice of ionic bonds to stay together. So as I see it, a grain of salt would be a neatly ordered lattice of Na and Cl ions in a 1:1 ratio. Now when the solid is heated to the melting point, why do the NaCl molecules stay intact and just separate from each other? Since everything is held by the same ionic bonds why don't all the atoms disassociate and turn into a liquid of Cl and Na instead of a liquid of NaCl. I'd understand if the molecules were held by covalent bonds and the lattice had the weaker ionic bonds. Idk if I explained my question well, please help?
|
[
"The solution structure of ionic liquids is an active area of research. Evidence suggests a variety of intermolecular forces play a role, explaining the variability in electronic, ionic, and thermal conductivities seen experimentally."
] |
[
"Actually, liquid salts usually are ionic liquids and consist of disassociated cations and anions that move about independently. There will still be some order insofar as arrangements where you have a large cluster of (positive) cations or (negative) anions are both energetically and entropically unfavourable and therefore very unlikely. The ions usually won't move around in pairs, though."
] |
[
"The NaCl molecule is held together by the electrostatic force produced by the oppositely charged ions. As I understood the molecules are held together by forces of attraction which form a lattice network. The only thing I can think of is that the electro static force is far stronger than the forces of attraction between the salt molecules."
] |
[
"Can someone help clarify electric vehicles?"
] |
[
false
] | null |
[
"Another genuine problem with this is, what are they going to do with the batteries when they are no good anymore? This is no widely known way to salvage the innards of a lithium ion battery. They can replace the insides, but still need to dispose of whats used. There have been studies on the environmental impact of factories per vehicle, but the results are inconclusive."
] |
[
"Another genuine problem with this is, what are they going to do with the batteries when they are no good anymore? This is no widely known way to salvage the innards of a lithium ion battery. They can replace the insides, but still need to dispose of whats used. There have been studies on the environmental impact of factories per vehicle, but the results are inconclusive."
] |
[
"Trying to measure a hybrid or electric car's environmental impact is tough. I've seen articles (link below) that claim the Toyota Prius is worse than a Hummer H3, due to the sheer amount of energy to make the car (mining in Canada, processing in Indonesia, packaging in China, installation in Japan).",
"http://www.pacinst.org/topics/integrity_of_science/case_studies/hummer_versus_prius.html"
] |
[
"Why can we not accept the null hypothesis if p>=0.95 but we can accept the alternative hypothesis if p<=0.05?"
] |
[
false
] |
Let's say we obtain a p<=0.05. We can say we reject the null and now accept the alternative hypothesis as reasonable. But why can we accept the alternative but not accept the null if we obtain p>=0.95? It seems by accepting the alternative hypothesis we are committing the same fallacy than if we accept the null.
|
[
"Um. I think you're thinking about P-values incorrectly. If P > 0.05 then you fail to reject the null hypothesis. Frequentest statistics are based on the assumptions of refutationism. This assumes that you can only prove things WRONG by providing refuting evidence. The null hypothesis is the hypothesis that there is NO effect, so your typical statistical tests seek to refute them."
] |
[
"To keep it simple, p values are used to reject a null hypothesis, namely that two samples are from the same population. Take two samples, find their p value and if it is less than 0.05, then you'd say they are, with statistical significance, NOT from the same population (you'd reject the null hypothesis that they are from the same population). If the p value is above 0.05 (or other values of interest), then you would not reject the null hypothesis and would conclude that they are not significantly different (and may be from the same population).",
"To your question, if your p value is 0.95, it is above 0.05 and you would fail to reject the hypothesis. In these scenarios, you actually are 'accepting the null'. However, it doesn't prove that the null is true because you should have devised the hypothesis that 'accepting the null' essentially means that nothing happened. You do not become more confident in 'nothing happening' by having a larger p-value, only more confident that the experiment showed that you should not reject the null."
] |
[
"The difference lies in the definition of p-value, and the reason why we accept or reject the null hypothesis.",
"The level of acceptance/rejection, aka the threshold of p-value, refers to the type-1 error of the experiment, which is defined as the probability that you reject a null hypothesis given that it is in fact true, denoted as P(rejecting null | null is true). Naturally we want to have a small value of this probability as we want to minimize the chance we reject a true hypothesis.",
"So a small p-value simply translate to the statement that \"given the evidence in hand, it is safe to say the hypothesis is wrong because the probability we wrongly reject the hypothesis (when in fact it is true) is so low\". On the contrary, a high p-value actually mean \"given the evidence in hand, the chance we reject the hypothesis (which is indeed true) is so high. We couldn't afford to reject it.\" It says nothing about the chance we accept a wrong hypothesis, which is P(Accept Null | Null is wrong). this quantity requires additional information outside of p-value, such as marginal probability of null is true (or false).",
"Now, if this still does not clear your doubt, let me give you an example. Suppose the true mean of the population is 0. We collect data and do a hypothesis testing under the null that the mean is 0, then the p-value would be very large. Now imagine instead of testing the mean being 0, our null test the mean being 0.0000001. Naturally, the p-value is still very high. But obviously this null is wrong. Indeed as we collect larger and larger sample, the p-value will decrease and eventually goes to 0, which demonstrates the notation of \"we do not have enough evidence to reject the null\"."
] |
[
"Does your DNA alter throughout your lifetime?"
] |
[
false
] |
Does everything you come in contact with in your life alter your DNA chemistry in any way? All of your experiences? All of your emotions? Physical damage? Healthy or poor eating? Hygiene? UPDATE: All of this is amazing you guys. I appreciate all of the effort you all put in to explaining. It’s truly amazing; the human body.
|
[
"By and large your cells are doing their level best to prevent your day to day experiences from having any impact on your DNA. Just about all chemicals you ingest/inhale from whatever sources (food stuffs, drugs, smoke, oxygen, bacteria) will have some impact on your cell's DNA. Plus some other sources of damage such as ionising radiation like UV light or skin contact of chemicals. ",
"Any time any foreign chemicals can get to your DNA they have the potential of reacting with it and causing changes (damage). Because this is an ever present and continuous risk your cells contain a whole suite of repair systems that detect any damage and put things back as they were. But these systems are not perfect so over your lifetime your cells will pick up random changes just from your day to day exposure to your environment.",
"This is also the cause/basis of most cancer, if you're unlucky some cell(s) in your body will end up with the right pattern of damage to send the cell cancerous. In large part the DNA repair systems are there to prevent this happening.",
"All that being said there are some legitimate changes to you genes that happen in your lifetime. Our immune system has a cassette of genes used to generate antibodies. In our antibody producing cells this cassette of genes is randomised and this allows us to produce cells with near infinite variations of possible antibodies.",
"Alongside this we also have epigenetic changes. These aren't changes to the DNA sequence, instead these are tags that can be added to genes to control how they are expressed. This pattern of tags is available to be edited during your lifetime and it does respond to environmental stresses. One good example, starvation has been shown to have a marked epigenetic impact on people's genes and it has been shown mother's will pass on their epigenetic markers to their kids. "
] |
[
"There is also a relatively new science called epigenetics. This science looks at alterations to epigenes, which don't ",
" but they do ",
" So your DNA may contain a sequence to make you susceptible to infection; as a child the epigenes keep this sequence suppressed, then when you turn 40 your epigenes change and activate this DNA sequence so you start getting sick more often. This is called gene expression.",
"Gene expression is affected by just about everything you do: exercise, diet, sleep, occupation, daily habits, and friendships.",
"Puberty, aging, aggression, focus, ability to learn, ability to problem solve, social habits, how much sleep you need at night are all influenced by your epigenetics.",
"Epigenetics are coupled with your DNA and you inherit epigenes from your parents, so having a child at 20 will pass down different epigenetic markers than having a child at 40 - and this is one theory of the increasing prevalence of autism in America."
] |
[
"That’s amazing. Thank you so much."
] |
[
"Does focusing our eyes affect the our eye’s “refresh rate”?"
] |
[
false
] | null |
[
"Maybe ",
"this",
". Which is actually an online book. You can find chapters on the right-hand side."
] |
[
"The resolution of your eye, light sensitivity, and motion sensitivity is not uniform across the retina. The periphery of the retina is more sensitive to light and motion but has lower resolution. That's why it is easier to see stars out of the corner of your eye at night than looking directly at them. "
] |
[
"Very cool!! Do you have any papers on this to recommend? :) thanks btw!"
] |
[
"Are humans allergic to mosquito saliva? If so, does that favor mosquitoes somehow?"
] |
[
false
] |
Layman here, who hates mosquitoes with a passion. Yesterday I stumbled upon a factoid picture that says humans are allergic to mosquito saliva and that's why we get red spots. Does that somehow make the mosquitoes' jobs easier?
|
[
"I believe it's because of the body's immune response which creates histamine. I, too, have been a buffet for hundreds of mosquitoes. Mosquitoes also have an anesthetic in their saliva. The effectiveness of that anesthetic seems to vary because sometimes I feel the bites and smash the bugs while other times I don't know I'm bit until I scratch the wheal."
] |
[
"Two reasons for the swelling:\n1. Mosquitos secrete anti-bloodclotting factors that allow it to fully extract a blood meal without the host immune system stopping it in its tracks. These factors will sort of bump around and eventually \"stick\" to host antibodies that will create an immune response with either histamine or more antibodies etc"
] |
[
"I don't think it makes their job easier; in fact I don't think it affects their job at all, seeing how the itching usually starts a short while after the mosquito has finished feeding and flies off. Most mosquito bites aren't noticed by the victim at all while the mosquito's there, partly because they inject an anaesthetic.",
"It appears to be a side-effect of the stuff the mosquito injects (anti-blood-clotting agents, as someone else noted, and also I guess whatever dirt or bacteria or what-have you happened to be on the mosquito's mouthparts). Basically a small, local inflammation."
] |
[
"What pattern would a flat mosquito net have in order to be as material-efficient as possible?"
] |
[
false
] |
I tried to solve this on my own, but I don't even know where to start... It doesn't matter if the final result is impractical to build or if it requires the wires to be cut into smaller portions. Pretend that the material used in this case is so expensive that every femtogram spared is worth the effort. Also, to simplify things, the mosquitoes could be considered solid spheres with a fixed radius and the wires could be treated as geometrical straight lines.
|
[
"I haven't come up with an answer, but I've got a few extra questions that might help you out.",
"I'll make some additional simplifying assumptions: ",
"Assume the net must cover a bounded (finite), flat region in space, for example a doorway or tent entrance.",
"Assume the wires are rigid, so we don't have to worry about them deforming under gravity or wind.",
"Since the mosquitoes are traveling through a flat region, only their widest cross section matters, so we can model them as circles with radius ",
".",
"So writing up the problem in mathematical terms:",
" ",
" ",
"To summarise in non-mathematical terms, S is the region we're trying to fill and N is to be the net such that any mosquito trying to pass through S must be blocked by some part of N.",
"There's still a bit of the question that isn't entirely rigourous - I haven't said what 'smallest' means in this context. There are two \"answers\" I've come up with for this question and they use different senses of size.",
"Apologies for the upcoming speculation, but I thought this was an interesting question and would like to see an answer. Perhaps you could ask it on ",
"/r/learnmath",
" or ",
"/r/math",
"?",
"The less satisfying of the answers is the one that directly answers the question above. Here we don't really need any length of wire since if it were possible to suspend infinitesimal points of wire in the air, it would be possible to block mosquitoes with a finite smattering of points in S.",
"For example, draw a grid with spacings of r/2 across S and place a piece of wire at each crossing of horizontal and vertical lines. This solution uses zero length of wire, but we could clearly use less. In this case I think it makes sense to say 'smallest net' means that it uses the fewest tiny pieces of wire (or formally, the cardinality of N).",
"Even with such a boring-looking answer, I think true minimisation will be difficult for a general shape S. Away from the edges the dots may look something like ",
"this",
", r*sqrt(3) apart.",
"For mosquitoes that are much smaller than S, drawing such a pattern with the wire is likely to be pretty close to optimal (though not save every femtogram possible).",
"I think the more interesting question is when we demand that the net N is ",
" (or better, when the union of N and the boundary of S is connected but this requires additional assumptions on S), so that there are no magically floating bits of wire.",
"In this case it makes sense to talk about 'smallest' in terms of length of wire. Using a grid of wires with spacing of r/2 we see that solutions with finite length exist, so this is a sensible thing to optimise.",
"I suspect an optimal solution will look something like a set of parallel lines, spaced ",
" 2r apart, starting from one side of S and stopping r away from the other side.",
"The orientation of these lines depend greatly on S. For a rectangle l long and w wide, wires running the length of it would have total length around ",
" (w/2r)(l-r).",
"Edit: If the mosquitoes have radius r, the lines need only be spaced 2r apart."
] |
[
"That... that was incredibly useful! And for some reason it only appeared today in my inbox. This said, I can't complain!",
"Again, this was all beautifully said, and I don't see why it classifies as speculation (especially in regards to the second more \"interesting\" question, which is exactly what I was looking for). My guess was also a set of parallel wires, spaced r apart. The stopping r away from the other side is a very clever thought I would've never gotten. Very nicely done.",
"The orientation of these lines depend greatly on S.",
"I figured the same, but how we determine that? For example, if S is a rectangle with l>w we have (w/r)(l-r)>(l/r)(w-r) and hence the most efficient is clearly the latter (i.e. running the wires on its width). Would it be possible to determine a formula that would allow to find the right orientation in an any given shape? Or just in any given regular shape? And in the case of a rectangle (which I imagine would be the simplest irregular shape to tackle), how would we know to or not to consider oblique orientations?",
"I apologize for the many questions, and you're right, I should consider posting this on ",
"/r/learnmath",
". Thanks again, and I hope it doesn't take a week for my answer to be properly posted too."
] |
[
"Would it be possible to determine a formula that would allow to find the right orientation in an any given shape?",
"For a general shape, I suspect not. Consider a rectangle and suppose the parallel lines solution is right. Then add a bump to one of the sides, with the bump much bigger than r, but much smaller than the side length.",
"Clearly the optimal solution near the bump must change drastically. It's not unreasonable to claim the 'change' to the solution will propagate out from this point with diminishing effect. In the middle of the rectangle, the solution will probably look much like it did before, but maybe with the wires ever so slightly deformed.",
"This slight deformation is probably very hard to describe, and was caused by only a very simple change to the original shape. A formula that takes in shapes and outputs patterns of wires (which mathematically would be most easily written as a (finite) collection of parameterised paths) would look very weird indeed.",
"(If you're feeling very brave, you could try applying ",
"calculus of variations",
", but this can get difficult when analysing only relatively simple paths and constraints.)",
"Or just in any given regular shape?",
"I think even this is hard. What would a solution look like for a circle? For circles much larger than the mosquito, I think the wires will look similar to the parallel lines solution away from the circle's edge. At the edge, this solution is obviously suboptimal. What would the transition look like.",
"how would we know to or not to consider oblique orientations?",
"This is a good question that I don't yet have an answer to."
] |
[
"Why does it require so much data to process a photo of a black hole?"
] |
[
false
] |
So, I don’t understand why you need 7,000 petabytes of data (approximately) to take a photo of a black hole. Can someone explain?
|
[
"A number of factors come into play here. ",
"Some more detail here: ",
"https://www.livescience.com/65203-black-hole-why-so-long.html"
] |
[
"Because it's not actually a photo. The input was never pixels, they are too small to tell left from right directly. All the telescopes put together are just seeing a single point of light each. They need to correlate them together, to see when each wave hits different telescopes to try and figure out where each part came from.",
"And to get any meaningful resoltuion, needs to record high fidelity from each telescope, and from a lot of telescopes.",
"The thing you want to look into is VLBI (very-long baseline interferometry); but It's quite in-depth if you want to dig into it. Aside from wikipedia, I couldn't find any good neat summary; but here's an unrelated thing, how planetary radar works, which works differently since we're sending and receiving a pulse from one telescope, not passively receiving at many telescopes, but it gives a neat starter on how interferometry works: ",
"https://www.youtube.com/watch?v=AAJTHsjYoPA"
] |
[
"Thank you very much"
] |
[
"Is there a condition where a person doesn't get excited about anything?"
] |
[
false
] | null |
[
"Major Depressive Disorder... Anhedonia, or a general disinterest in things that used to give you pleasure, is a characteristic symptom.",
"Being bummed out can also have a similar impact. Doesn't need a fancy name."
] |
[
"I am not bummed out or depressed or anything, I just can't find anything to make me say wow - its the same with hobbies too; I can't find anything that I am crazy about."
] |
[
"Maybe you need to find something that challenges you optimally, gets you into ",
"flow."
] |
[
"100% this is a scientific experiment"
] |
[
false
] | null |
[
"Rememberful"
] |
[
"Rememberful"
] |
[
"rememberable"
] |
[
"Are several copies of the same memory stored in the brain?"
] |
[
false
] |
Is there just one single copy, or are there several. If so, are they all stored in the same hemisphere?
|
[
"Memories, contrary to popular belief, does not work like a video record. There are, in effect, no \"copies\" of memories at all.",
"The brain is a cluster of neurons, roughly 100-150 billion neurons, or that is the estimate (to put that into context, that is a higher number than there are stars in our milky way). Memory, or everything else, for that matter, is when a cluster of neurons fire together. So a memory is only a pattern, so to speak. That pattern can, and will change, usually just a tiny bit, everytime it's fired. ",
"This is why creating false memories is so easy, and why our memories are an extremely fallible source of information. ",
"For more information about how fallible our memory is, I recommend the book \"Suggestions of Abuse\" by Dr. Michael D. Yapko, and here's an excerpt from and interview, which you might be interested in: ",
"https://www.youtube.com/watch?v=91XQsJLfcJM"
] |
[
"Ok. This thing with \"therapists bringing out memories that have been suppressed\" is usually, in most cases, a matter of the therapist unknowingly suggesting things to a receptive patient, and thus bringing about the recollection of false memories. As I say, memory is extremely fallible, and it's SUPER easy to influence it. By subtle wording of a sentence, you can get a completely different outcome from someone that's browsing his/her memory. So if a therapist starts intently digging around for \"suppressed memories\", I say: run, this is a bad therapist and not qualified for the job.",
"Research into this area has indicated that on the contrary to what was once believed, it is actually more likely that we REMEMBER the bad things that happen in our lives rather than \"suppress\" them. That makes sense in evolutionary terms, as you, as an organism, definitely don't want to forget something that has proven dangerous to your life or wellbeing in the past.",
"However, that is not to say that we can't have experienced things that are not accessible to our conscious mind. There is a thing called dissociation, which is a defense mechanism used, by us and other animals, in the face of danger when it looks like we have no escape. Fight or flight response is pointless when you're completely backed into a corner and/or powerless. So at that time dissociation can kick in, making the experience often feel unreal, sometimes described as an out of body experience, or a feeling of disconnection. A person in essence \"flees into her mind\" with the help of our opiod system. ",
"Dissociation is often used by children that experience chronic maltreatment/abuse at the hands of caregivers, as they need to find a way to protect themselves, and \"their selves\" from the abuser which also happens to be their lifeline. They somehow need to make sense of the world, like we all do, and if you know what cognitive dissonance is, then you realize how powerful that need is. And here you have a situation where you are afraid of the thing you love the most. Your sense of safety is also your source of danger. And in those cases we often see dissociation used as a form of coping mechanism. \"Split\" yourself in two, have two realities. And shove the painful part away, so the rest of you can function.",
"This pattern will produce symptoms that often have profound effects on a persons' functioning, especially in relation to other people, and thus people often (well, sometimes) come into therapy for that. So, in these cases, it actually can happen that memories that maybe weren't \"consciously recollected\" can become more vivid. But the thing is though, that it's not even that common, as the thing is, the hippocampus, the thing that \"records\" or \"makes\" our memories, that thing often goes offline when we experience high intensity emotions, SUCH for example intense fear, anxiety and horror, all of which can lead to dissociation. So.... ",
"TL:DR: Supressed memories are highly unlikely, although they can exist.",
"Edit: Even though the hippocampus goes offline, making the experience not accessible to our conscious mind, i.e. in explicit memory, the event is recorded by other mechanisms of the brain, f.x. the amygdala, and becomes part of our implicit memory (the thing you use when you ride a bike - our \"muscle memory\" and the \"things we know\" without having a special memory, you know). Thus you have the symptoms, as even though you can't explicitly remember, your body and your brain does, and you react accordingly. Your past, in essence, bleeds into your present, in a dysfunctional way.",
"I may be getting a little off track here, for your question though... :)"
] |
[
"I'm sorry if I sound patronizing, but you sound like you're not very familiar with the brain as an organ. The brain is in essence nothing but a cluster of neurons. Everything we do, translates from a pattern of firing in our brains.",
"So, memory is still just a pattern of firing, even though that pattern has grown robust through long term potentiation. "
] |
[
"Is it theoretically possible to surround the sun with solar panels and “harness” the sun?"
] |
[
false
] | null |
[
"There's a thought experiment, called a ",
"Dyson Sphere",
" (after physicist Freeman Dyson who popularized the thought experiment), that does this.",
"The engineering required to achieve this is far beyond our current capabilities, making it a highly theoretical concept."
] |
[
"From what I understand, the Dyson Swarm is a better and more realistic alternative.",
"Edit: yes, Swarm, not sphere again :P"
] |
[
"automated self-replicating factories",
"What could possibly go wrong?"
] |
[
"Why do tattoos on the inside of your lip fade, while ones on external skin stay permanent?"
] |
[
false
] | null |
[
"Would this be because of constant contact with moisture? I would like to know as well.."
] |
[
"If I had to guess, I would think it's because the inside of your mouth replaces cells at a much faster rate, therefore the ink would be pushed to the surface much faster."
] |
[
"I tried finding a 'scientific' explanation and the best I could get was that the tattoo doesn't go as deep as others, and hence can wear out as the skin regenerates.",
"For three years, though? Anyone? "
] |
[
"Red light interferes the least with night vision right? So why do automobile dashboards always use blue/green/white variations?"
] |
[
false
] |
[deleted]
|
[
"I imagine it's a negligible effect compared to the headlights of other cars, so people go with more aesthetically pleasing lighting."
] |
[
"They don't always. My car has red lighting (Audi)."
] |
[
"My 1970 Dodge Challenger R/T had orange dash lighting."
] |
[
"Would this homemade volcanic fog filter work to reduce sulfuric acid in the air - bubbling household air through a solution of baking soda?"
] |
[
false
] |
I live in Hawaii and we have problems with volcanic fog (vog). The vog causes numerous health problems which seem to come mainly from the sulfur dioxide content of the vog. The sulfur dioxide turns to sulfuric acid on contact with moist air or moist lungs. I had this idea to use a blower fan to suck household air through a container of water that included some sort of alkaline substance such as baking soda. The idea is that the action of bubbling the air through the baking soda solution would neutralize the sulfuric acid. Would this work? Are there dangers of breathing air that has been bubbled through baking soda (sodium bicarbonate)? Are there other substances that would work better in the bubbler? Are their other more effective (but still inexpensive) methods of scrubbing the sulfur dioxide and sulfuric acid from household air? My worst fear is that the above described contraption would just moisten the remaining sulfur dioxide that is in the air and convert that to more sulfuric acid.
|
[
"It sounds like this would work. Note that baking soda is not technically a base. I think it is a buffer or a salt. (I don't know if it is an alkaline or not).",
"Sodium hydrogen carbonate (NaHCO3) breaks down with any acid HX to make H2CO3 + NaX. H2CO3 (carbonic acid) then decomposes to make H2O and CO2. As long and NaX is not volatile (NaSO4 and NaCl would not be), then there is no trouble doing this.",
"I don't think that NaHCO3 can decompose into anything else. When heated it become 2 NaHCO3 → Na2CO3 + H2O + CO2. Again, very safe."
] |
[
"The problem is that you could have large bubble of gas still that contain sulfur dioxide. I don't know how you mix the gas bubbles thoroughly with the baking soda water. I would think that someone has invented something like this already, given that it seems to be a problem where you live."
] |
[
"You could use a diffuser, which is a bunch of tiny holes in the downstem (pipe going into the water). Just like a bong!",
"Or you could pipe the gas to the bottom of the solution's container, fill the container with something to break up bubbles (like glass pieces) and let the bubbles break up as they flow past."
] |
[
"Why; a coffee cup with a little milk in it froze in my fridge but the container of milk next to it was still fluid?"
] |
[
false
] |
something about the way different materials radiate away and conduct heat; but i would have guessed that it would have come to some equilibrium; all materials arriving at the same temperature in their own time. ~help me science!!!
|
[
"Over time you are right, but over a short time in a fridge I wouldn't expect things to get all the way to equilibrium. Because of that we need to consider items starting at different temps, tons of different materials with different thermal conductivities and heat capacities, and more.",
"In your particular case you have a container of milk vs a cup with minimal liquid. The container is probably closed which means the only contact with cold air is on the surface of the container, and there is an insulating layer of air in the headspace of the container. The container also has (presumably) a lot of milk inside. In contrast the cup is open on top which means free contact with the fridge air and relatively small amount of liquid.",
"Now why does any of this matter? Firstly, the cup has a relatively low heat capacity compared to the container, just by virtue of the amount of liquid. Practically that means that the heat will be removed much more quickly from the cup as there is less total heat there to pull away. Secondly, the cup being open means that the dry fridge air can not only directly contact the liquid and speed cooling by avoiding an insulating layer, it can also cool the liquid through evaporation. In contrast the container will experience no evaporative cooling. It probably also has a much lower volume/surface area ratio which slows down heat transfer.",
"Put these together and you would expect that given equal environments the cup would freeze much faster than the container.",
"All this being said, it isn't uncommon for fridges to have drastic temperature differences in different places so it could entirely be an effect of placement of the vessels. Without some experimentation we don't have enough data to tell."
] |
[
"The milk has a significant amount of dissolved sugars, proteins, and minerals which together will lower the freezing point compared to water. This is a phenomenon called freezing point depression. If the coffee wasn't sweetened this could explain the difference "
] |
[
"interesting things to think about and explore further. thanks."
] |
[
"Is there a \"natural\" way that the human body wakes itself up in the morning? If so, does drinking coffee in the morning lessen the effect of that process?"
] |
[
false
] |
[deleted]
|
[
"Your body has a circadian rhythm and wakes itself up at a certain hour. Your body temperature rises, various hormones are released or stopped, particularly the sleep related hormone melatonin which is controlled by the Suprachiasmatic nucleus and to a lesser degree blue light. It's not secreted during your day cycle so you are more awake in the day and its level should drop before you wake up.",
"http://www.sciencedirect.com/science/article/pii/0024320579904983",
"Cortisol is also released, a stress hormone, which helps you have the strength to deal with the day. Many people awake just before their alarm thanks to ",
"http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1402564/",
"http://www.ncbi.nlm.nih.gov/pubmed/14592218",
"Coffee can make you sleep lighter, and reduces melatonin secretion.",
"Thank you to Whatthefat for explaining the secretion of melatonin better. He is the expert."
] |
[
"Excluding environmental stimuli (e.g., light), the transition from sleep to wakefulness in the morning is due to two physiological process.",
"One is the ",
"circadian rhythm",
", which promotes wake during the daytime and promotes sleep at night. The circadian drive for wakefulness typically begins to increase ",
"a couple of hours before regular awakening",
". This includes telling the pineal gland to stop producing the sleep-promoting hormone melatonin in preparation for awakening.",
"The other factor is ",
"sleep homeostatic pressure",
". Across the night, sleep pressure dissipates due to the clearance of sleep-promoting substances from the brain. This means there is less and less drive to remain asleep.",
"Together, these two factors promote the onset of wakefulness in the morning.",
"The brain is not able to immediately transition from sleep to fully alert wakefulness. In the first minutes of awakening, people typically feel very groggy and their cognitive performance is exceptionally poor. This phenomenon is referred to as sleep inertia.",
"Normally, ",
"it takes around 1-2 h to fully dissipate sleep inertia",
". The reason sleep inertia exists is not known, but it has been hypothesized that different parts of the brain may take different amounts of time to transition from sleep to wakefulness. Certainly the opposite is true: ",
"the thalamus falls asleep several minutes before the cortex",
".",
"Caffeine acts as a competitive antagonist of adenosine, which is one of the sleep-regulatory substances that accumulates in the brain during wakefulness. In effect, it makes people temporarily less sensitive to (or \"masks\") the sleep-promoting effects of the adenosine. This can help people to stay awake or make the transition from sleep to wakefulness more rapid.",
"Taking caffeine has been shown to reduce the effects of sleep inertia following naps",
". Unfortunately, it is more difficult to achieve this in the morning, since it takes ~1 h for ingested caffeine to reach peak levels in the blood, by which time the worst of sleep inertia has already passed.",
"Long-term caffeine use has been shown to ",
"increase the number of adenosine receptors in the brain",
" and ",
"increase their sensitivity",
". This means that more caffeine is required to elicit the same response. It also means that the brain becomes progressively more sensitive to the regular levels of adenosine. For somebody who suddenly stops drinking caffeine, this can result in caffeine withdrawl and higher levels of sleepiness (and presumably greater difficulty transitioning from sleep to wakefulness) than prior to the caffeine use."
] |
[
"They did compare caffeinated coffee to decaf, so it's probably the caffeine. But I don't know enough about the process of decaffeination to say whether it significantly changes the chemical composition of the coffee with regards to things other than caffeine."
] |
[
"If muscles shiver for warmth, and the heart is a muscle, why doesn't it shiver?"
] |
[
false
] |
Or does it under extreme cold temperatures?
|
[
"Skeletal muscle (the muscles attached to your bones that allow you to move) are the ones that shiver. The heart and other organs like those in your digestive system are a different type of muscle (smooth muscle) and are controlled by separate portions of the nervous system (sympathetic and parasympathetic nervous system) that don't utilize shivering because it would disrupt important body functions."
] |
[
"Thank you very much! Very informative!"
] |
[
"The tongue doesn't shiver either."
] |
[
"What causes the observed interaction between matter and a vacuum?"
] |
[
false
] |
[deleted]
|
[
"Thanks for the reply. I still don't quite understand though, what kind of forces are acting on matter around a vacuum?"
] |
[
"Thanks for the reply. I still don't quite understand though, what kind of forces are acting on matter around a vacuum?"
] |
[
"Atmospheric pressure. The weight of the air creates a certain pressure at sea level. When you have a perfectly closed container, there would be no interaction, but once you open it the surrounding atmospheric pressure starts rushing in. It's very similar to opening an empty container underwater, just that you're in air, not water.",
"When other stuff (not just air or gas) also rushes towards the vacuum, that's a secondary effect created by the rushing air."
] |
[
"Is there any sound in nature that can cause deafness in humans?"
] |
[
false
] |
I mean something naturally occurring that would be on the decibel level of a jet, concert or explosion.
|
[
"You would need a sound at 140 dB or higher in order to cause instant irrevocable hearing loss (not necessarily deafness). The blue whale can generate sounds up to 188 dB. When Krakatoa exploded, it made a 180 dB sound. Meteors and eathquakes can generate even louder sounds. "
] |
[
"You would have to be unreasonably close to those things for that to happen though, correct? IE that close to Krakatoa and you are dead anyway."
] |
[
"Excellent point. "
] |
[
"When will Iceland split because of the movement of the Eurasian Plate and the North American Plate?"
] |
[
false
] | null |
[
"Iceland is constantly expanding due to the expansion of the ",
"Mid-Atlantic Ridge",
". This expansion, in conjunction with the ",
"Iceland hotspot",
", manifests as a ",
"large number of volcanoes",
". New land is constantly being formed by volcanoes, so as long as the Iceland hotspot remains over this area, Iceland will never \"split apart\"."
] |
[
"So Iceland is actually getting bigger over time due to the movement of the plates? "
] |
[
"Yes. The island is gettin ",
"about an inch (2.5 cm) wider each year",
", not to mention the ",
"new islands",
" that occasionally form."
] |
[
"What is the limiting factor on how fast I can tap my finger on my desk?"
] |
[
false
] |
When I try to tap my finger on my desk as fast as possible I can't go any faster than 4 or 5 beats per second. Is it my muscles, my brain or something else that won't let me change the direction of movement any faster?
|
[
"The guy in that video is tapping with his whole hand though and only using the relatively slow movement of his fingers to change which keys the movement of his hand causes him to hit. When I only move my index finger and keep the rest of my hand still, the fastest I can tap is 8 times per second. If I move my whole hand, keeping my index finger locked, I can get 12-13 taps in a second. This is what everyone does when they play fast paced button mashing video games. You play with your whole hand, not just your fingers.",
"On the other hand (",
"), ",
"/u/markpsp",
" is mentioning an experiment performed in the lab in a lot of intro human physiology class. By using a switching power supply with variable frequency (not a car battery) and electrodes placed on the underside of your forearm you can induce rapid flexion of just your fingers independent of your wrist. My memory of this experiment, though, was that at a relatively low frequency my fingers began to tetanize. Rapid repeated stimulation of a muscle causes what's called summation, where instead of just repeating the same contraction at higher frequency, each additional signal increases the tension of the contraction and decreases the level of relaxation inbetween. At a high enough frequency you get tetanus of the muscle where it's rigid and doesn't relax at all.",
"It seems like the muscles that control our fingers have a relatively low threshold for summation and tetanization. That might be a constraint their physical structure, being really long and narrow muscles, or it might be an evolutionary adaptation since gripping strength in our fingers has always been much more important to survival than rapid tapping.",
"Since this tapping relies on the full relaxation of flexion (as well as extension), you have to avoid any summation at all or you wouldn't be able to keep tapping for very long. So it might be the summation threshold of your finger flexors that's the limiting factor. Of course, there must be something in your brain that's preventing you from going faster because it knows you want to keep tapping rather than enter a summation type contraction cycle."
] |
[
"The guy in that video is tapping with his whole hand though and only using the relatively slow movement of his fingers to change which keys the movement of his hand causes him to hit. When I only move my index finger and keep the rest of my hand still, the fastest I can tap is 8 times per second. If I move my whole hand, keeping my index finger locked, I can get 12-13 taps in a second. This is what everyone does when they play fast paced button mashing video games. You play with your whole hand, not just your fingers.",
"On the other hand (",
"), ",
"/u/markpsp",
" is mentioning an experiment performed in the lab in a lot of intro human physiology class. By using a switching power supply with variable frequency (not a car battery) and electrodes placed on the underside of your forearm you can induce rapid flexion of just your fingers independent of your wrist. My memory of this experiment, though, was that at a relatively low frequency my fingers began to tetanize. Rapid repeated stimulation of a muscle causes what's called summation, where instead of just repeating the same contraction at higher frequency, each additional signal increases the tension of the contraction and decreases the level of relaxation inbetween. At a high enough frequency you get tetanus of the muscle where it's rigid and doesn't relax at all.",
"It seems like the muscles that control our fingers have a relatively low threshold for summation and tetanization. That might be a constraint their physical structure, being really long and narrow muscles, or it might be an evolutionary adaptation since gripping strength in our fingers has always been much more important to survival than rapid tapping.",
"Since this tapping relies on the full relaxation of flexion (as well as extension), you have to avoid any summation at all or you wouldn't be able to keep tapping for very long. So it might be the summation threshold of your finger flexors that's the limiting factor. Of course, there must be something in your brain that's preventing you from going faster because it knows you want to keep tapping rather than enter a summation type contraction cycle."
] |
[
"You can hook yourself to a car battery and see how fast your muscle can expand and contract.",
"Won't work. It's a direct current so your muscles will only contract and stay that way.",
"Also, don't do it anyway."
] |
[
"Is string theory an actual scientific theory?"
] |
[
false
] |
[deleted]
|
[
"Dude, sure it is. It's still in its nascent stages, but it's certainly a valid physics theory just like any other. One problem is that we haven't fully formulated the theory, so many of its predictions are still ambiguous. But the main problem is that its predictions require energies far greater than those we can probe on Earth; so it's testable, but not by us!",
"Most string theorists I know believe that if we find evidence of string theory in our lifetimes, it won't be through a particle accelerator like the LHC (they'll never have enough energy) but through cosmological observations. The early Universe had extremely high energies just after the Big Bang, and at early enough times quantum gravity, whether or not it's string theory, would certainly come into play. With luck that era might just be observable in the future.",
"I would say the best possibility for doing this is likely through the cosmic background of gravitational radiation. Events in the early Universe such as cosmic inflation will produce distinct signatures of gravitational waves. By measuring those we would have a direct window onto the early Universe, nearly untouched since a tiny fraction of a second after the Big Bang, since gravitational radiation doesn't interact strongly with matter. Unfortunately, however, gravity wave observatories sensitive enough to measure this background are likely decades off.",
"The fact that string theory isn't fully developed yet isn't a reason to give up on it, it's a reason to work harder on it, figure out what the final theory should look like, and then determine how to test it so that one day, we, or our kids or our grandkids or great-grandkids, can see if it's on to something."
] |
[
"I submit to you the following article, published in Physics Today, written by a string theorist:",
"Article"
] |
[
"From what I understand the only concepts in String Theory that are falsifiable are shared by general quantum mechanics, Lorentz invariance and General Relativity.",
"Claiming String Theory is falsifiable because of that foundation sounds like bullshit to me, if you cannot test the unique aspects of String Theory that by definition, make it String Theory, how can you claim it is falsifiable?"
] |
[
"As the universe expands, will the fundamental forces change such that matter cannot exist?"
] |
[
false
] |
[deleted]
|
[
"We don't think the fundamental forces will ever change. We do like to think that they are all the same force at certain high energy levels but that isn't proved for gravity. Regardless no change.",
"You may be thinking of the Big Freeze or Big Rip theories for the end of the universe. It is noteworthy to point out that neither of these are proven. In the first you get infinite entropy with fundamental particles and in the second you get similar but matter and space itself may be \"torn\" apart. We just don't know.",
"Try reading this...",
"https://en.wikipedia.org/wiki/Ultimate_fate_of_the_universe"
] |
[
"We do like to think that they are all the same force at certain high energy levels but that isn't proved for gravity.",
"It should be noted that it has been experimentally observed only for two out of four forces. "
] |
[
"However, our data on the curvature and makeup in the universe seem to strongly suggest one of these two \"fates\""
] |
[
"When we see the night sky, we're basically looking at the stars that are on the opposite side of the sun at a moment in the year. Are modern telescopes able to see the stars that we can't see during the day? Has the sun been an obstacle to observing a specific area of outer space within our range?"
] |
[
false
] | null |
[
"I don't quite get what you mean... the earth spins on its axis and goes around the sun at the same time, so you can be on one \"side\" of the sun facing away and then, half a year later, on the other side facing the other way..."
] |
[
"Thanks, I know this and agree with you, added some text in order to make my question a bit clearer."
] |
[
"I guess the answer is no then. The galactic core obscures part of the milky way for us... but there's no equivalent for the sun because in 6 month's time you will find yourself on the other side"
] |
[
"What actually happens when I lower the volume in my smartphone using the volume slider?"
] |
[
false
] |
And further, if my device is connected to a Bluetooth speaker, what is the correlation between the volume control from my phone, and the physical volume control on the speaker? Are they actually performing the same operation, or can I get a lot more volume steps using controls on both the devices?
|
[
"In both cases, the smartphone contains a digital signal (the audio) and information about the volume setting, both of which are transmitted to an audio controller, which drives a digital-to-analog converter, which drives a speaker.",
"In the case of playing through wired analog speakers or earphones, all of that control and conversion circuitry is inside the phone. In the case of a Bluetooth speaker or headphones, the audio controller and the DAC are inside the Bluetooth device. ",
"In the case of analog output, the two volume controls are typically multiplicative, so that setting your volume to half on both will result in audio that is 1/4 as loud as setting both to full.",
"In the case of digital output, the two volume controllers are typically linked, so that setting one to 1/2 is the same as setting the other to 1/2."
] |
[
"When you lower the volume on your smartphone, pretty self explanatory hehe, uhm, the screen picks up the signal and cpu calculates and lowers the volume, aka the amplitude decreases. If you connect to the bluetooth speaker, it is different, your phone sends bluetooth signal to speaker and telling speaker to decrease amplitude. \nAs for \"Are they actually performing the same operation, or can I get a lot more volume steps using controls on both the devices?\" the answer is: you could get a lot more volume using both controls. If you are some kinda maniac and want more, you can download apps on phone to make it louder."
] |
[
"That explains a lot. Thanks. "
] |
[
"Why doesn't neutron reflection cause a fission reaction?"
] |
[
false
] |
So I just stumbled upon the "Demon core" story about the plutonium core going critical via neutron reflection. I was wondering though, why didn't the core undergo a fission reaction when the tungsten carbide bricks were placed around it? Wouldn't it just take 1 single neutron bouncing off the shielding to collide with the mass and cause it to go into fission? To my understanding that's how the atomic bombs in Nagasaki and Hiroshima were detonated.
|
[
"A single neutron can only fission at most one atom, releasing a tiny bit of energy. If the neutron splits an atom then more neutrons are released. What happens then depends on the geometry.",
"If - on average - the neutrons from one fission reaction produce more than one fission reaction you get a chain reaction. If the neutrons produce less than one fission reaction then you do not get a chain reaction. That number is called criticality.",
"Neutron reflectors can increase that average, more plutonium closer together increases it as well.",
"You can make a nuclear weapon by simply increasing the criticality to above 1 and then waiting for a random neutron to start the chain reaction but that is unreliable. All nuclear weapons come with a small neutron source to start the chain reaction at the right time - normally close to the point where the criticality reaches its maximum, but in some cases lower yields might be preferred."
] |
[
"Wouldn't it just take 1 single neutron bouncing off the shielding to collide with the mass and cause it to go into fission? To my understanding that's how the atomic bombs in Nagasaki and Hiroshima were detonated.",
"No, these are not initiated with one single neutron. There are ",
" fission reactions occurring at the same time.",
"(By \"fission reaction\" in the title, I'm assuming you're referring to criticality.) Adding a reflector helps keep the neutron flux around the fissile material, and generally lowers the critical mass of the system. But just adding reflection doesn't automatically guarantee that the system will go critical. If the mass of fissile material is still below the reflected critical mass, it won't reach criticality."
] |
[
"It is, very fortunately, not so easy to sustain a supercritical configuration of fissile material long enough to release nuclear-bomb-level amounts of energy. Otherwise we would not have (relatively) safe nuclear power but nuclear ",
" would be everywhere. The demon core underwent a \"criticality excursion\", that is, parts of the core became supercritical for a brief moment. But only for a ",
" brief moment: enough power was produced to move/throw the reflector away from the core, at which point the core immediately became subcritical again and the chain reaction stopped.",
"This is the big problem you face when designing a nuclear bomb: supercritical configurations very much like to tear themselves apart and become a rapidly expanding cloud of small, subcritical pieces of uranium or plutonium. Somehow you need to keep the core in one piece for several milliseconds to get even a small fraction of the fissile material to have a chance to actually fission. In a real-world fission bomb maybe a few percent of the available nuclei undergo fission before the bomb vaporizes itself."
] |
[
"Pterosaur flight?"
] |
[
false
] |
[deleted]
|
[
"That depends on how high a bar you want to set for proof. They have all the proper adaptions for flight: wings for a start, hollow bones, strong muscles for flapping (even stronger for taking off is a recent discovery). Computer simulations with reasonable assumptions show them capable of it. Is that proof? It's as close as we can get at this remove most likely."
] |
[
"I guess my main problem is that after reading a few papers on it, very few of the paleontologists are agreeing on the weight of the animals. Take quetzalcoatlus for example, (I know, the largest of them all is not really the best example) I have seen weight's ranging from 80kg to 200kg. So, how much of the computer simulation is guess work?"
] |
[
"Here are a couple links to previous discussions: ",
"Demonstration of how pterosaurs might have taken flight",
" ",
"AMA from a dinosaur paleontologist"
] |
[
"What exactly is meant by \"quantum information cannot be destroyed\"?"
] |
[
false
] | null |
[
"if you knew every piece of quantum information there is to know, you should be able to perfectly reconstruct the entire history of the universe",
"How do you reconcile this statement with the fact that the mathematics of quantum physics is non-deterministic?"
] |
[
"if you knew every piece of quantum information there is to know, you should be able to perfectly reconstruct the entire history of the universe",
"How do you reconcile this statement with the fact that the mathematics of quantum physics is non-deterministic?"
] |
[
"Quantum information can only be rearranged. This is due to the time parity of quantum physics. The physics has to be the same if time were to play backwards (need other parities too). With classical physics, there is no time reversal symmetry. Information can simply be lost (to heat, sound, etc.) in classical physics. Time is a one-way street with classical physics, so what is lost may never be found again."
] |
[
"flair:Physics If colliding matter and antimatter can annihilate each other to produce a photon, how is momentum conserved when photons are massless?"
] |
[
false
] |
Or is conservation of momentum a special case of conservation of energy which doesn't always apply? Bonus question: it occurs to me that a massless particle could have momentum if it had infinite velocity; is it fair to say that at the speed of light, time is effectively stopped, so from the photon's frame of reference it's velocity is infinite (i.e. it covers a finite distance in no time)?
|
[
"Photons still have momentum, despite not having mass. In fact, all their energy is due to momentum. Momentum=mass x velocity is just a low velocity approximation that breaks down in relativistic cases."
] |
[
"Additionally, when a particle anti-particle pair annihilate they produce two photons (at least). A single photon alone could not conserve 4-momentum of the two particle system."
] |
[
"Because the full equation isn't E=mc",
" but e",
"In the case with photons, you need relativistic physics as Newtonian formulas start to breakdown. In this case, the energy is entirely conserved through the momentum , p, of the massless photons because when mass is zero, the equation simplifies to E=PC where p is momentum and c is a factor up to the speed of light. ",
"This short Minutephysics video can help answer your question. \n",
"http://youtu.be/NnMIhxWRGNw"
] |
[
"How did Einstein go from the equivalence principle to gravity being the curvature of spacetime?"
] |
[
false
] |
[deleted]
|
[
"So, the equivalence principle implies that tidal forces are the true signature of gravitation (not free-fall.) In terms of spacetime geometry, these forces can be understood as following from a lack of distant teleparalleism (geodesics not remaining parallel) in turn resulting from curvature."
] |
[
"Because the EP says that the local effects of a gravitational field cannot be distinguished from an accelerating frame, i.e. just an artifact of choosing a particular coordinate system in spacetime, and not a real physical effect. The real physical effects of gravitation are nonlocal - tidal forces. These cause relative acceleration between nearby points and cannot be transformed away by change of coordinates."
] |
[
"Because the EP says that the local effects of a gravitational field cannot be distinguished from an accelerating frame, i.e. just an artifact of choosing a particular coordinate system in spacetime, and not a real physical effect. The real physical effects of gravitation are nonlocal - tidal forces. These cause relative acceleration between nearby points and cannot be transformed away by change of coordinates."
] |
[
"How is \"you only dream of people you've met in life before, and your mind can't make up new people\" even testable? Is this really true?"
] |
[
false
] | null |
[
"This is a common, but annoying, claim. There's no way of testing its veracity, for several reasons.",
"First, the question is ill-posed: what does \"make up new people\" mean? If a person is composed of pieces of others, then do they qualify as \"new\"? In any case, that's not an accurate representation of how memories work -- instead, some salient details of an event or person are recalled and then the brain fills in the blanks on the fly.",
"Second, we don't remember most of our dreams and have imperfect recall of those that we do, so there's no way of comprehensively studying all of the people that appear in dreams.",
"Third, we have no way of cataloging everyone that we've ever met, and certainly no way of comparing such a catalog to people that appear in dreams (even if such a catalog did exist)."
] |
[
"Where did you ever hear of such a statement being advocated? "
] |
[
"I've seen it trending around -- usually on \"random fact\" lists. I've even seen it on a list from the front page of reddit. Unfortunately I can't find the link though."
] |
[
"What is the difference between soap, detergent, and other cleaning products such as citrus oil?"
] |
[
false
] |
What does each one do on a molecular level to dirt, grease, microbes? Bonus question: how does each one react to greater/lesser concentration, agitation, contact time? I.E, when are you better off letting something soak vs scrubbing harder vs. using a stronger solution?
|
[
"Both soaps and detergents are ",
", molecules that have both a water-hating (hydrophobic) and a water-loving (hydrophilic) portion. Both clean the same way: when they contact a piece of grease, the grease becomes attracted to the hydrophobic part, detaches from wherever it is, and can float off into the water because of the hydrophilic part of the surfactant.",
"Killing viruses and bacteria is a little different. These critters have an outer shell made of molecules that are very similar to surfactants. So the soap/detergent molecule comes along and decides it will nestle down inside that virus/bacterium outer wall since it is chemically similar. When it does, this disrupts the wall so much that it falls apart and all the innards of the virus/bacteria spill out into the water and lose activity. Think of hammering a wedge into a brick wall. Far enough and the wall will crack open.",
"Historically soaps form soap scum in water and detergents do not. This is due to the exact chemical nature of the hydrophilic part of the molecule.",
"The rest of your question is pretty detailed. Just keep in mind that a stronger soap/detergent solution will become very irritating to your skin as it wants to disrupt your skin cells just like the viruses."
] |
[
"Oh yeah, about citrus oil. It by itself does not dissolve in water. So the idea is that it will simply contact that piece of grease and dissolve it. Sometimes it is mixed with soaps/detergents and water to form an ",
", like salad dressing. This basically works like the soaps do."
] |
[
"Although soap and detergent kind of do the same thing (removing non polar substances and particles), they are made with different materials and processes, and therefore they have different chemical formulas and purposes. Detergent is much stronger and better at collecting substances than soap, and most detergents have extra chemicals added to them to make them better at doing their inrended purpose.",
"As for killing viruses on your hands, regular soap is enough to kill most germs. Once the soap come in contact with the germ, the cell membrane will break and the germ will be killed, so scrubbing your whole hand around every nook and cranny (including fingernails) is advised, but you don't need to wait for the soap to break down the germ."
] |
[
"How do bugs survive winter by hiding in tiny cracks, when big animals like us are so vulnerable to it?"
] |
[
false
] | null |
[
"They are poikilotherm, they just don't die as easily when their body temperature drops, and if they have this kind of behavior, they are pretty adapted to cold weather or high temperature changes. \n Also, small bodies are way way way easier to heat up after getting cold. If you are a bear and you body temperature drops to 0°c, you have to spend an ungodly amount of energy to get above 30°c again (i.e. you die), but if you are a small squirrel, you body can reach lower temperatures and go back to normal without much problems.\n That explains why they have different ways to hibernate",
"Edit: sorry, the right name is poikilotherm, was confused by a false cognate. Also, not sure if it applies to invertebrates the same way, am not a zoologist, if someone can clarify, I would appreciate"
] |
[
"I'm an insect scientist. We do use the word poikilotherm to apply to invertebrates. What it means more specifically is that the animal's body is built to tolerate different temperatures. The opposite is a homeotherm, which can only operate so long as its body stays within a certain narrow range (humans are in this category)."
] |
[
"A lot of cold-blooded animals like insects and amphibians in colder climates create a sort of anti-freeze when they go in to hibernation. This allows them to essentially stop their body processes until it warms back up again. Cold-adapted animals also have modified protein structures that allow their bodily functions to happen at very cold temperatures, compared to warm-blooded animals where our bodies can only operate in a small window of temperatures. ",
"Here's a review: ",
"https://scholar.google.com/scholar?hl=en&as_sdt=0%2C30&q=hibernation+antifreeze&oq=hibernation+anti+free#d=gs_qabs&u=%23p%3DQktZO85Q8iEJ"
] |
[
"What exactly happens when you delete a file on your computer?"
] |
[
false
] |
Let's say you have a simple text file with a paragraph on it that you want to delete - what exactly happens to it once it's "permanently" deleted? Is it ever fully removed from the hard drive? If not, does it go anywhere on the computer? Also, what sort of processes happen when a computer deletes a file?
|
[
"The inode (metadata block where the file's description is stored) is removed from the filesystem's btree (database of all files on the disk) and all disk blocks that were identified as belonging to the inode are marked as empty.",
"Other than that, nothing happens. The file's information is not overwritten (unless you select \"Secure Delete\" of some kind). Technically, the file's data is still exactly where it was but it is ignored by the system and may be overwritten whenever the system next needs disk space since the file's former location is now viewed as \"empty\".",
"Remember, the concept of \"information\" in a computer is two fold. There is the \"data\" (binary 1's and 0's) but there's also the \"interpretation\". The disk blocks that store your file only have value if they are interpreted as a file and then, only if it is interpreted as the correct file type. If you interpret a block of 1's and 0's as \"empty\" then it doesn't matter that the 1's and 0's are there.",
"There are programs that will search empty blocks on your disk and attempt to undelete them. They work because they are asked to interpret empty blocks as \"text\" or \"images\" or \"Word Documents\", etc. If they don't know how to interpret the empty blocks then they won't be able to recover any useful information."
] |
[
"The file's information is not overwritten (unless you select \"Secure Delete\" of some kind). Technically, the file's data is still exactly where it was but it is ignored by the system and may be overwritten whenever the system next needs disk space since the file's former location is now viewed as \"empty\".",
"Would a disk defrag overwrite the data?"
] |
[
"Probably, but there is a chance that the deleted data is not used during the defragmentation, specially if you also deleted lots of other files."
] |
[
"How much force does it require to snap wood?"
] |
[
false
] |
So I'm a mathematics student trying to help out my younger brother build a bridge for a high school project and I can't find any formulas online to help with this quetsion. I'm sure there has got to be a formula along the lines of Length*Width*Height*constant for specific wood*torque > 0 But I cannot find it anywhere! The wood he's using is balsa wood. I'm sure there has got to be a formula out there I'm looking for. Thanks guys
|
[
"It's a fairly complicated problem that depends on the shape of the wood (known as the second moment of inertia) and how it's being bent. The simplest case would be a piece of wood fastened on one end, held horizontal, and weighted on the other. From this you can calculate the strain, and compare it to the breaking strain of wood.",
"It generally requires a knowledge of calculus and university-level physics, but here's an article: ",
"http://en.wikipedia.org/wiki/Bending#Quasistatic_bending_of_beams"
] |
[
"Not a civil engineer here, but I am a Mechanical. The best way to have a beam resist pure bending is to have as much material on the outside of the profile as possible, as the top and bottom edges are under the most stress, that is why I-beams have very little in the middle of the beam and the most at the extremes. ",
"Here",
" is a image that depicts the stress (blue=lower red=higher) profile for a simply supported I-beam."
] |
[
"Okay honestly that went way over my head. I sort of understand what it's getting at but I don't think I'll be able to calculate it. It's rather frustrating as it seems to me like it should be a pretty simple calculation.",
"If I had a piece of say 1x1x10cm wood at a 60degree angle to the horizontal then placing a Force Fz vertically downward on the end of the wood would result in the wood snapping. Surely this force Fz would be near identical for all pieces of balsa wood under similar conditions (humidity, temperature etc.).",
"But thanks for your reply mate it was a great read!"
] |
[
"Do bacteria have a meaningful \"top\" and \"bottom\"?"
] |
[
false
] |
That is to say, if I had a tiny spatula and flipped over some bacteria, would it continue about as it was before, or would it reorient itself back to its previous bearings?
|
[
"Well, this is an interesting question. At the size scale of bacteria, gravity has a much less drastic effect on organisms—the fluid that the bacteria is in exerts much more of an effect on the bacteria. So \"up\" and \"down\" as we know it, defined by our relation with gravity, isn't really a way that bacteria orient themselves. HOWEVER, it appears that many bacteria have some form of orienting themselves based on chemical gradients or even magnetism. Those known as \"magnetotactic bacteria\" orient themselves along the lines of Earth's magnetic fields, and even commonplace bacteria can exhibit similar effects. For example, the ones that cause ulcers (Helicobacter pylori) figure out which way they're going by way of chemical gradients in your stomach, while the bacteria on the roots of plants (Rhizobium lupini) tend to form 90-degree angles to the root that they attach themselves to.",
"So, tl;dr, some bacteria have a sense of direction (though it's different from humans'), and they would reorient themselves if you turned them opposite to the way they were going. ",
"Sources: ",
"http://www.pnas.org/content/101/14/5024.full",
" , ",
"http://mic.sgmjournals.org/content/journal/micro/10.1099/00221287-91-1-198?crawler=true&mimetype=application/pdf",
" , ",
"https://en.wikipedia.org/wiki/Magnetotactic_bacteria"
] |
[
"Well, this is an interesting question.",
"That's exactly what I said!",
"From the world of infectious bacteria (my field of expertise), there is also another directional consideration: some of these bacteria will attach to host cells. For example, certain types of bacteria use active mechanisms to attach to the cells lining the intestine. (",
"Certain pathogenic ",
" do this",
", to give just one ",
"example",
".) What's going on in that bacterium?? Is there something different happening on the \"top\" (the side away from the cell) and the \"bottom\" (the side closer to the cell)?",
"Probably. Almost definitely. But it's really hard to say. We're just now on the forefront of discovering that bacteria have subcellular spatial organization that's more sophisticated than \"a big bag of homogenous goo.\" Technology has historically been a major barrier to answering this question -- until recently, microscopes didn't work well to look at things that are a lot smaller than the wavelength of visible light, which forced us to go to great lengths in order to try and get a good look at what was happening spatially inside a bacterium. Recent advances have made this easier and easier, though, and from what I see people are really starting to make a dent in the problem (so stay tuned...)!"
] |
[
"Well said! Very interesting, thank you very much."
] |
[
"What force causes the Earth's tectonic plates to move?"
] |
[
false
] |
Additionally, how can this force be so consistent in vector that events like a megathrust earthquake occur?
|
[
"Ultimately there are two possible causes of why plates move and it is not yet known which is the correct mechanism:",
"1) Slab pull: In this scenario the down going slab pulls the rest of it along and thus causes movement including mantle convection.",
"2) The mantle is convecting due to a temperature gradient and this drives the plates at the top.",
"Which scenario is the one that is happening depends largely on what the coefficient of friction between the plates and the mantle is. If it is really low (like some people want) then scenario 1 is correct and if it is high then it's scenario 2.",
"Large earthquakes occur because two plates are locked and can't move relatively until there is enough stress to break them apart. "
] |
[
"It's been awhile but the estimates I recall seeing are that slab pull dominates. There's also 'ridge push' but it's pretty nominal. Not quite sure what the OP is on about with the second question. Changes in plate driving forces happen over a much longer time scale the the buildup for stresses that cause earthquakes so the local strain vectors should be 'consistent' on the latter time scale."
] |
[
"No arguments from me. I haven't looked at this stuff for maybe 20 years and so I'm not sure if there have been any more advancements but I'm guessing not. :-) Kind of reminds me of a comment a prof of mine once made. He was going to write a paper with the world's shortest abstract. The title was \"What have we learned from mantle convection that we didn't know from plate tectonics?\" The abstract: \"Not much\". :-)"
] |
[
"Why does ice melt slower in water with a higher salt concentration?"
] |
[
false
] | null |
[
"I assume you're asking about this:",
"http://en.wikipedia.org/wiki/Freezing-point_depression"
] |
[
"The water is colder. "
] |
[
"I'm confused. You mean vs water of a lower salt concentration? It shouldn't melt slower either. Assuming both waters are the same temperature, the total kinetic energy is higher in the high concentration water."
] |
[
"Can you compress a gas into a solid?"
] |
[
false
] | null |
[
"Most of the time, no. If you compress it AND drop the temperature, then yes, almost all gases will form a solid at some point.",
"The reason a thing is a gas is becuase it has enough energy to overcome the molecules attraction to one another. This attraction is fairly weak for things that are gases at room temperature (hence why they are gases). If you take many gases and compress them, but keep the temperature around 70F (25C), they will form a ",
"superfluid",
". Superfluidity is a special and weird and very cool form of matter. "
] |
[
"Wow, I love the graphs! Thanks!"
] |
[
"Yes, but you have to have the right gas and then the right conditions. I assume you are asking about a gas going directly to a solid, because going gas->liquid->solid is the trivial answer. Take a look at this ",
"phase diagram for CO2",
".",
"If you take CO2 from the pink area directly to the blue/purple area, then it will freeze from a gas into a solid. You can do this at atmospheric pressure by dropping the temperature, or by bringing the temperature down and then increasing the pressure like you asked. Phase diagrams are different for every compound, so you'll have to look at your compound of interest to see where the solid-vapor transition boundary is. Here's another example with ",
"water",
"."
] |
[
"Ask Science Scientists: When you review papers do you review anonymously, or do you sign off?"
] |
[
false
] |
A little while ago I decided I would sign all of my reviews and did so. Of course, now I'm giving a somewhat unfavorable review to someone who might be considered a giant in my field. It's not a good paper, but I might want to work with this person later on on a different project and I'm a bit worried that this might not be good for me. I'm still finishing up my Ph.D but I've got lots of experience writing reviews. I think the review is fair and the paper does show promise, but I am really thorough in detailing all the things that are wrong with the paper. (I do praise it too. . .) So what do you think? What do you do? Are you flexible in your anonymity? Why are they letting me review papers?!?!
|
[
"I write reviews assuming they could figure out who I am but usually dont actually sign. Best of both worlds- keeps me honest but dont have to worry about fragile egos. "
] |
[
"The editors know who I am but the journals I have done this for use a double blind. I do not know who the author is and they do not know who I am. ",
"In a close knit field it is not that hard to guess about either side.",
"I am never flexible with anonymity. You need to be able to honestly review people but still be able to collaborate later, or simply have a beer and discuss things."
] |
[
"First of all, I applaud your commitment to transparency. I happen to think that peer review works better when reviews are signed, and even posted along with the article so that the whole process is open.",
"That said, you're still a grad student and may depend on some of these people for grants, jobs, or collaborations in the future. You're not going to change the world by yourself, so I'd err on the side of caution and stay anonymous on this particular review. Once you're a little more established, you'll be in a much better position to both make a difference and get through the process unscathed."
] |
[
"If I dug into the Earth 2,000 miles, (roughly 1/4 the diameter), and stood in that space, would I experience only 75% of 1G?"
] |
[
false
] |
If gravity is based on mass then all the mass above my head wouldn't be pulling me to the earths core so I would experience less G's. This is supposing that the tunnel I dug is straight down and there's no mass above me. Contrastly, would I experience even less than 75% of 1G if I was transported to a bubble 1/4 under the Earth's surface since the mass above me would be gravitationally pulling up (like the Moon does with the tide)? I hope this question makes sense. Thanks.
|
[
"There is a small caveat to add here in that this calculation assumes a uniform density for the Earth which is not strictly true."
] |
[
"Okay, first, there's a misconception in your question that I need to clear up: Even if you dig a tunnel straight down, the ground above you is still pulling up. You've removed the matter directly above you, but the matter all around the hole is still pulling up on you. In fact, in the grand scheme of things the tiny amount of earth you would have removed above you would be insignificant, so the pull of gravity whether you dug a tunnel or magically transported would be the same.",
"Whew, okay that wordy caveat is out of the way. Your line of thinking is partially correct; gravitational force does decrease as you get into the body which is producing the gravitational force. However, as it turns out, ",
"the decrease is completely linear",
"! When you do ",
"the complicated integration",
" out completely, the equations all sort out so that the gravitational force from the \"shell\" of earth outside of the radius you inhabit completely cancels out, just leaving the contribution from the earth below you. This means that if you go halfway to the earth's core, the force of gravity pulling you down will be exactly half of the force that was pulling you when you were at the surface. 30% of the way to the center means a 30% reduction of gravity, 99% of the way to the center is a 99% reduction in gravity, etc. Pretty cool, huh?",
"Edit: be sure to check out the other answers which are more correct: my answer assumes a planet of uniform density, which is not true for Earth."
] |
[
"As others have pointed out, this assumes uniform density, which is very far from true for Earth.",
"In actual fact, because the core is very much denser than the mantle which is itself denser than the crust, gravity actually gets stronger as you get closer to the core, and only starts decreasing as you start penetrating the outer core. ",
"https://upload.wikimedia.org/wikipedia/commons/8/86/EarthGravityPREM.jpg",
"For reference, the Earth has a radius of 6371 km",
"As far as the original question is concerned, a 1/4 diameter is equivalent to about 3185 km depth, which will put you just inside the inner core where the gravity will be slightly higher than it is on the surface."
] |
[
"If the universe is an hypertorus, is it possible that we receive the light from a star twice ?"
] |
[
false
] |
I recently read an article in a French science magazine stating that the universe might be an hypertorus (Euclidian, finite and borderless). They represented it using a cube in which when you exit through one side you actually come back in from the opposite one. I made a drawing to make my question clearer : The first 2 pictures are straight-forward the star lits us directly and we see it in the sky as it was at the moment the light was emited On the second line of the "comic" you can see the light traveling through the right side and coming back out of the left one and then hitting us. What we then see in the sky is a second star that appears to be way further than the first one and way older, when it is in fact the same one ! On the third line I was imagining a scenario where the light goes through the loop several times. We would then see the star as it was a very long time ago, or even maybe witness it's birth ? It sounds crazy but would it be possible that we see the same star at different moments of it's life span ? Christ this blew up over the week-end while I was away, I will try to read everything as soon as possible. Also thank you for the gilding ! Even if I have no clue what it does, I feel like someone now !
|
[
"Yep, if the universe is like that, then extremely distant things could be visible mulitple times. ",
"Researchers have looked for evidence for evidence of that",
" in the cosmic microwave background and haven't found any, which can be used to constrain the size of the potential torus that the universe might be."
] |
[
"Woaw, great article, thanks for sharing ! This is fascinating but also pretty hard to wrap my head around."
] |
[
"I think its worth pointing out that telescopes likely aren't powerful enough at the moment.",
"Let's assume its true. The cube with re-spawn on the other side (basically star fox multiplayer).",
"The first time the light from a star reaches you, it will have traveled simply the distance between you and the star. The 2nd time it passes you, it will have traveled the distance between you and the star PLUS the length of the universe. Since the 2nd is likely orders of magnitude larger, the lumonsity of the 2nd will be that much dimmer ie: likely on the order of a single photon per sq meter / year, or something absurd like that.",
"The photons aren't parallel, but near it, so over very large distances they slowly spread.",
"Also:",
"Olber's paradox"
] |
[
"Why do some animals get spotted fur as a result of domestication?"
] |
[
false
] |
Some animals that have a uniform coloured coat in the wild get a a spotted coat after X numer of generations under domestication. For example Cows and foxes. The frysian breed of cows here in the netherlands come from a uniformely clack/brown coloured bovine. The Russian domesticated foxes are a prime example. They started getting spotted fur after a couple of decades. What is going on here? Is this even a result of domestication? Is something even going on here?
|
[
"The prevailing thought is that this is due to ",
"gene linkage",
" between a major gene that influences aggression and at least one gene that influences color pattern. Gene linkage occurs when genes are very close to each other on a chromosome so the alleles for linked genes tend to be inherited together (so if you get the not-aggressive allele of the behavior gene then you are likely to also get the spotted allele of the adjacent color pattern gene).",
"It's also possible that this is due to a ",
"pleiotropic effect",
", caused by one gene that is somehow influencing both of these traits. Honestly, this seems more likely to me, since there are examples of domestication-associated color pattern changes in so many animal species:\n",
"The classic Russian foxes",
",\n",
"Finches",
",\n",
"Pigs",
",\n",
"Horses",
".\nSuch a diverse group of species all showing the same association suggests that the linkage is incredibly tight between the genes controlling the two traits. Particularly in the case of the fiches, the chromosomes containing genetic information in these species are very different; the finch genome divides information into a total of 40 chromosome pairs, while the pig has 19 pairs. There are also numerous rearrangements evident in comparing the sequence of genes between the chromosomes of these species. The likelihood of two genes staying so close together in the evolution of all these unique genomes seems low.",
"In all of these species the emergence of new alleles (or uncovering of existing alleles) seems to coincide with domestication events (the pig and horse papers I linked talk about this in some detail). There are more alleles controlling color in the domestic populations than in wild ones. Human selection certainly played a role in this by keeping the new color variants in the breeding pool, but the new alleles themselves would have resulted from mutations.",
"edit: formatting"
] |
[
"So if the alleles for coloration and aggression are either closely linked or dependent on some third gene, then would you expect solid colored house cats to be more aggressive than spotted or tortoise-shell colored house cats?"
] |
[
"Citing \"an unnamed French Army Surgeon\" as an authority hardly research. Rushton and Bogaert were using flawed methodology to promote racism. Period. ",
"here - ",
"read some of this",
"it gives some more information on why their studies were popular (racism) and why they were unpopular (racism, bad data, BS conclusions, etc etc) "
] |
[
"How did the photographers of the first nuclear test ever know what filter and film exposure combination to use to get a clear image of it?"
] |
[
false
] |
I'm thinking specifically of of the Trinity test, though I know there is a whole series. If it was the first test ever, how did they know in advance how to photograph it without over or under exposing the film?
|
[
"There was a large team of people working on photography of the Trinity test, and they had dozens of cameras recording the explosion simultaneously. These were set to different settings, filters, speeds, distances from the blast, and so on. So they purposely spread out their range quite a bit. They even had a few that were set for long-exposures, which produced ",
"bizarre, ghostly photographs",
". ",
"Even so, they ",
" over- and under-expose many of the shots, as you would expect. You're experiencing a selection bias here because you're looking at a shot that ",
" over/under exposed and the emulsion looks damaged (they had issues with radioactivity damaging some of the camera emulsions and \"fogging\" them; I don't know if that's what we're seeing here, or a more pedestrian dark-room problem). ",
"Here's an example",
" of one that didn't quite have the right settings — you can see what it is, but it's not a great shot; it's under-exposed. Here's one that is ",
"a bit over-exposed",
" — the fireball is hazy and indistinct (my photography teacher would have dinged me for that one, even though it's still not a terrible shot). Hence it's not one most people are familiar with. Think about how many photographs from Trinity you ",
" familiar with — two, three, four? And those are all pretty solid photographs... but that's why those are the ones you are familiar with.",
"I've seen hundreds, because I study this stuff, but even that is out of probably thousands of actual photographs taken (they had cameras that could photograph 10,000 frames per second there, so thousands is not a ridiculous number). (Edit: I looked it up, and they made over 100,000 \"photographic impressions,\" though most of these were from motion picture cameras of some sort.) The full range of photos that even got preserved includes lots of ",
"strange-looking ones",
" (those little white dots are where the fireball heat burned through the emulsion). ",
"Furthermore, they were mostly interested in the early progression of the fireball. There are very few photographs of the mushroom cloud. This is because this is the part that was most interesting to the technical people, and this photography was technical (scientific) photography, almost to a fault (as opposed to documentary photography, for the purpose of historical record). (The ",
"one decent color photograph",
" made was done with a scientist's personal camera, and as you can see, even labeling it as \"in color\" is a bit of a stretch given how limited its range is.) ",
"Lastly, it is worth emphasizing that this was not some quick little photographic attempt, but a major part of the test, with the full might of Los Alamos science behind it. There were different estimates as to how explosive the bomb would be, but all nuclear explosions in their range of predictions have pretty similar outputs, at least for the first few seconds that they were mostly concerned with. There is only so hot you can heat atmospheric air and have it transmit that as visible light; this is why nuclear fireballs have a characteristic ",
"\"double flash\"",
" light output, because at some point they overheat the air and it becomes opaque to visible light briefly. Which is only to say: you can figure out, theoretically, ",
"what the maximum perceived brightness is likely to be",
", even if the actual temperature of the fireball is a lot higher than that. You can use this kind of information to determine your shutter speed, filters, etc., within a reasonable range of estimates."
] |
[
"Pseudoscience, denial, conspiracies...whatever you wish to call it, it is not welcome here."
] |
[
"Pseudoscience, denial, conspiracies...whatever you wish to call it, it is not welcome here."
] |
[
"Measuring ecosystems: populations, biodiversity, biomass."
] |
[
false
] |
When I took zoology 101 in college we did a field study where we counted the number of species in a single square meter. What exactly do you call that type of measurement? More broadly. If you were to take a full inventory of biodiversity in a region, is there a standard set of measurements to take? For example. I know that to study microorganisms in the ocean you can take a DNA inventory from a cubic foot of water to describe the populations of bacteria and single cell organisms. What's that called? But on a macro level, in a forest for instance, you may also count the total number of observable species in a defined unit of area as well as the population distributions. What's that called? I am not looking for a narrow answer, but really anything, articles and examples of how these studies are done and what are the terms used to describe the various methods. I am hoping to contact field biologists about plans to take inventory of ecosystems in the Gulf of Mexico before and after the oil impacts on the shores as well as in various coastal waters. It would be nice to read up on the specifics and accepted methods for doing this so I can be current on the correct terminologies.
|
[
"Thanks...I'll be looking"
] |
[
"There's something called Mark-Recapture where you tag a certain number of animals in a given region (let's say moose in a square kilometer), release them, come back later, and count the number of moose in the same area. Based on the fraction of tagged moose that you count, you can calculate how many moose are in that forest."
] |
[
"Cool thanks for that... I was wondering how you handle the mobility of animals in such a study...or migrations too.. This should lead into some of that language I hope..."
] |
[
"If most people are vaccinated, what is wrong with people being non-vaccinated? Will the disease not stay isolated to those who are not?"
] |
[
false
] |
Just to be clear- IN NO WAY AM I AN ANTI-VAXXER, I AM UP-TO-DATE ON MY SHOTS, AND I FULLY SUPPORT VACCINATION AND MODERN SCIENCE.
|
[
"I'll add that the things we vaccinate against are subject to evolution, they can mutate in ways that would make the current vaccine ineffective. If enough people are vaccinated, the disease can be eradicated entirely, making future vaccinations unnessesary, however as long as there is some population where the disease can propagate it can evolve to affect those that have been vaccinated as well and we'd need to start the process all over again."
] |
[
"I'll add that the things we vaccinate against are subject to evolution, they can mutate in ways that would make the current vaccine ineffective. If enough people are vaccinated, the disease can be eradicated entirely, making future vaccinations unnessesary, however as long as there is some population where the disease can propagate it can evolve to affect those that have been vaccinated as well and we'd need to start the process all over again."
] |
[
"I think the issue, or part of it at least, is that some vaccines require that the child be a certain age in order for the vaccine to be administered. If a child who has not been vaccinated gets a disease, the other kids who have been vaccinated should be okay, but a smaller child who is not old enough to get the vaccine is now at risk to catch a potentially deadly disease. "
] |
[
"Explaining human evolution to a six-year old?"
] |
[
false
] |
My six-year old asked tonight: after the dinosaurs died, how did humans become alive? I said that after the dinosaurs died, there was a lot more food for the little mammals that were around at the time and were more like mice and rabbits, and these mammals were then able to have lots of babies. Some of those babies were a little different from the others and were able to get even more food and have more babies that were different. This went on for a long time until there were many different mammals like we see today...lions, elephants, horses, humans. I'm not totally satisfied with my answer, and lost him part way through but it was the best I could come up with on the spot. I also said I'd see if I could find an answer on the Internet. What would be a simple, yet accurate explanation for this age? a quick google search pointed to some resources for And Amazon turned up a couple of promising picture books: At any rate, I think a trip to the museum is in order.
|
[
"Hell we can't seem to be able to explain it to adults."
] |
[
"Here is my try, you will have to change the language to suit the child, but hopefully the gist behind it will be helpful. It is written from your perspective, talking to the child.",
"Have you ever noticed how my father doesn't look exactly the same as me? Well, you will grow up to look different from me as well! Every time a baby is made, it looks a little bit different from its parents. We don't notice the changes much, because people have only been around for a little while. But, animals have been around for millions and millions of years (billions? I should probably know that). Over these millions of years, all these little changes build up, and animals start to look very different.",
"It's very simplified, but hopefully it makes sense...",
"You could mention how similar we look to monkeys and apes, or horses and zebras or any group of animals."
] |
[
"Simple. Poignant. Refreshing. Well done. "
] |
[
"Will drinking beer or alcohol with a potentially tainted food kill the bacteria?"
] |
[
false
] |
I know that germs and bacteria cannot survive in an alcoholic environment, but could the alcohol from beer or mixed drink ingested at the same time kill it?
|
[
"The percent of alcohol in most beers (4-5%) is not enough to kill most bacteria."
] |
[
"It might. Cooking the food can kill bacteria too. But that's not going to stop food poisoning, that's often caused by the toxins the bacteria produce, rather than the bacteria themselves. (For instance Staphylococcus aureus - staph food poisoning, Clostridium botulinum - botulism)"
] |
[
"how much alcohol would it take?"
] |
[
"If you put enough of any kind of matter with hydrogen, like human beings, in a close enough space, would a star form?"
] |
[
false
] |
Or, could you render living material down to its component atoms and use only those materials to form a star?
|
[
"TLDR: Yes. If we define a \"star\" as a collection of material with sufficient mass to spontaneously ignite an exothermic fusion reaction, then it's true that bringing together a sufficient amount of material lighter than iron will form a star.",
"The Details: Stars form when clouds of dust and gas in space collapse under the force of gravity. As the gravitational potential energy dissipates, the gravity pulls the material closer and closer together. It would continue collapsing forever, except for the pressure forces which eventually counteract the gravity and create a hydrostatic equilibrium. In this equilibrium, it can be shown that pressures and temperatures must be very high at the core, and that the pressures and temperatures increase as the mass of the material increases.",
"Now, if you have a relatively small amount of mass (say, the mass of Earth or Jupiter), these pressures and temperatures are not high enough even at the core to cause a nuclear fusion reaction. As you increase the amount of mass, however, eventually the core temperatures are such that fusion will take place, beginning at around 10-20 times the mass of Jupiter (depending on the chemical composition of the gas/dust cloud). Even if you're bringing together solid bodies rather than the more typical gas and dust, this remains true: adding mass will eventually result in an exothermic fusion reaction, i.e. a star.",
"There's one caveat to this, however: elements higher than iron on the periodic table absorb rather than produce energy when their nuclei are fused (this is what makes fission bombs based on Uranium or Plutonium so powerful – it's the opposite of fusion!). So in order to form a \"star\" as we think of it, you'd need the majority of the mass to be comprised of elements lighter than iron, which humans are.",
"Assuming the average human weighs about 80kg, and that the smallest human star is about 10x the mass of jupiter, it would take about 1,000,000,000,000,000,000,000,000,000 humans squished together to form a star.",
"Edit: typos"
] |
[
"Might be worth noting it isn't until 13 M_J that you get deuterium burning, and about 85 M_J until hydrogen. Heavier elements will be require even more. So, way more humans."
] |
[
"Humans ",
"are mostly oxygen",
" (by mass, not count), and ",
"oxygen burning stars exist",
", so why not?"
] |
[
"Do cars accelerate better from a burnout or with traction control?"
] |
[
false
] |
Say, a tesla roadster is trying the 1/4 mile. Could it accelerate faster with traction control on or off? Also, how does this apply to gas powered cars? Is it better to apply the maximum ammount of torque before the tires start slipping or the maximum regardless?
|
[
"You want to apply the maximum, non-slipping torque. The reason being that the way you accelerate is by producing friction between the tire and the road. The greater that friction force, the faster you go.",
"It turns out for materials there are two \"types\" of friction, sliding friction or static friction. Sliding friction is the friction you get from, as you could guess, sliding an object across a surface. Static friction is the friction that stops an object from sliding when a force is applied. For all materials, the static friction is a larger force than the sliding friction (aka- harder to get an object moving that to keep it moving). For a tire that is slipping, you have sliding friction- but for a tire which is turning, no point of the tire is sliding across the surface, so you have static friction. Thus, by not sliding you are able to produce more force than by sliding. ",
"Side note: the reason you see racers burn out before the race start is to heat up the tires, which makes them stickier, increasing the amount of friction they produce. Also, this is why anti-lock brakes help you stop faster than sliding. "
] |
[
"the best acceleration is achieved with about 5% wheel slippage, on typical DOT-approved, street-compound tires.",
"The key is at what rate of slippage is the coefficient of friction highest? At what rate is the most energy transferred through the contact patch to the ground? ",
"It's going to be highly dependent on the rubber used, but the slippage creates enough friction heat to soften the rubber, increasing the coefficient of friction significantly.",
"Too much slippage rips off little pieces of the rubber, or pills... these act as tiny roller bearings and obviously reduce the overall acceleration.",
"This is known as \"roasting the meats\""
] |
[
"I would like to add to this that tire compounds on normal cars...are not meant to be warmed up to achieve maximum traction...so don't go doing burn outs in your mothers minivan."
] |
[
"Is \"sleep\" a particular defining characteristic for 'Animalia'? Are there animals that don't sleep?"
] |
[
false
] |
I'll add in any clarifications here, if needed.
|
[
"The kingdom ",
" includes animals without a developed central nervous system. \"Sleep\" is a function of the central nervous system (other than this fact I choose to not go into definitions of sleep at this moment.) ",
"From these two simple fact we can conclude there are indeed animals that don't sleep. Examples include such animals as sponges, starfish, sea urchins, jellyfish, hydras, tapeworms, roundworms etc.",
"All of these are animals and yet simply do not have sufficiently advanced central nervous systems to experience sleep. To be completely honest I am not quite sure about arthropods and worms because I am not familiar with the operation of ladderlike nervous systems, but fortunately your question doesn't require delving into such nuances.",
"It is possible to claim that some of these animals undergo periods of rest, but a) the argument doesn't work for all of them, e.g. sponges and b) this \"rest\" can be shown to be in a different category from what we call \"sleep\" (e.g. jellyfish are known to undergo periods of free floating \"rest\" but this is due to fiber fatigue, not neural processes, as far as I know)",
"tl;dr: "
] |
[
"Hmm, I meant is it a defining characteristic so that, for example, there's a large chunk of the evolutionary ancestral tree that \"sleeps\" and another chunk that does not?"
] |
[
"This has been asked before (try a search on the sidebar). There are some exceptions, but almost all animals that have been studied in-depth show sleep or sleep-like states, including worms and insects."
] |
[
"What is a neurotransmitter \"turnover rate\", with reference to acetylcholine? What does it mean if the turnover rate is increased or decreased?"
] |
[
false
] |
I'm learning about various neurotransmitters (especially acetylcholine) and I keep seeing "turnover" or "turnover rate" in academic papers. Any help would be much appreciated!
|
[
"Turnover rate is relevant for neurotransmitters which are degraded within the synapse. Some NTs are not (see serotonin- not degraded within the synapse to a significant degree, mostly reuptaken by the presynaptic side). Acetylcholine on the other hand is degraded by acetylcholinesterase within the synapse, and its components are then reuptaken. Turnover rate refers to the degradation rate (basically the amount of acetylcholinesterase in the synapse)"
] |
[
"Something about this response just feels like it's from ChatGPT... am I right, or just paranoid?"
] |
[
"Something about this response just feels like it's from ChatGPT... am I right, or just paranoid?"
] |
[
"How do medications cause weight gain?"
] |
[
false
] |
Does it throw off hormones and make you eat more? Does it reduces your metabolism so it allows more of the calories you eat to be stored instead of used?
|
[
"It depends on the type of medication. Some cause you to eat more because they stimulate appetite. Some do lower metabolism rate. Some cause you to retain water, which obviously doesn’t cause fat accumulation but it does affect how much you weigh. Others can even affect how your body stores and processes sugar. "
] |
[
"https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=56&contentid=DM300",
"That’s a link with some of the more common types that do. And with some specific names. For your viewing pleasure. "
] |
[
"I wish they would say exactly which one they did. Its become a pathetic excuse for people that just overeat."
] |
[
"Is there actually any evidence to suggest \"screens\" are bad for children?"
] |
[
false
] | null |
[
"A couple years ago I finished my degree in Human Development. There are quite a few studies on how TV effects kids behavior and learning. They basically go in the way you'd expect. If the kid watches violent shows, in the short term they are more violent. Similarly, if they watch educational shows, they have a short term advantage on their peers. However, both of these effects tend to wash out as kids get older. ",
"As far as other screens go, it's still to early to know. The kids who grew up with screens are still kids. Scientist can make all kinds of claims about short term impact, but the reality is there hasn't been enough time to see the full impact they have. ",
"My thoughts are, kids are really great at learning, and they learn by doing. If most of their \"doing\" is on a screen, they will become adept at navigating the electronic world. To me, that seems like a great skill to have in the world they will be living in. However, if a kid is in front of a screen his or her whole childhood, there may be weaknesses because of things the kid wasn't doing; for example face to face interaction. "
] |
[
"Agreed. There are a lot of studies on this. It is not the screen itself but the effects of having tv or other programming on that disrupts language development and parent child interaction. Even Sesame Street! See citations in this AAP publication ",
"http://m.pediatrics.aappublications.org/content/128/5/1040.full"
] |
[
"What do you mean by harmful? Physical, psychological, cognitive? Do you mean the screens as a device or the content played on those screens? \nSome perspective with all the supposed sensationalist research is that despite this ephemeral idea of \"children\", they are still just people and people are all different. Some kids would rather go out and run around or talk with friends instead of watching a tv show. Some kids would rather the opposite and couch potato, just like adult people. Some kids crave violent content, some kids are terrified by it. As to physical detriment, \"screens\" have been around for a generation. Is there a sudden epidemic in blindness? \nSo, for your friend (who probably secretly wants to tell you how to raise your own kids) the point is to know your own kids. Tablets, phones, televisions, computers, books, crayons and the like are just tools. How does this particular child use this particular tool? Is it positive and productive for your kid? "
] |
[
"Are the two electrons in the Helium atom in the same energy state?"
] |
[
false
] |
Are the two electrons in the same energy like two non-interacting electrons in a hydrogen atom (hypothetical) where the groundstate is degenerate due to spin? Or are the two electrons in different energy levels due to Coulomb repulsion?
|
[
"The single-particle orbitals that come from solving the TISE for non-interacting electrons in the nuclear mean-field potential do not accurately describe the ground state of the helium atom. The actual many-body state of the atom can be written as a linear combination of single-particle configurations. Since the angular momentum of the electron cloud is 0, this linear combination only includes configurations with total J = 0.",
"The ground state will be dominated by the configuration where both electrons are occupying the lowest hydrogenic orbitals, but you can in principle have admixtures of 2-particle/2-hole (2p2h) states, where both electrons are promoted to a higher single-particle orbital (the same one, so that they couple to J = 0)."
] |
[
"The single-particle orbitals neglect ee-interactions, but you are attempting to account for them by allowing the ground state to be an admixture of single-particle orbitals."
] |
[
"So, If you are asking if the electron in a helium ion has more or less energy than one of the electrons in neutral helium, the answer is less. One way to think about this is that in the helium atom, both of the electrons are are pulled toward the two protons in the nueclus, but because the electron wave function exists both close and far from the nucleus, there is some sheilding of the nuclear charge that occurs. Since the electrons repulse eachother, the idea is that the each electron sees some charge at the neucleus less than 2. So they are less tightly bound to the neucleus then they would otherwise be, and thus it takes less energy to strip one of them. But with only a single electron, it basically feels all of the charge of the nucleus and so it is held much tighter and it requires much more energy to strip that electron. So assuming that your reference for the energy of the electron is that a free electron with no motion has zero energy, then the energy of electrons bound to an atom is negative. And the energy of an electron bound to a helium ion in the ground state is more negative than the energy of an electron bound to a helium atom in the ground state."
] |
[
"Why do flies swarm at the top corners of my office building?"
] |
[
false
] | null |
[
"there may be stagnant water in the gutters. these insects look like mosquitoes so i am going to amuse they are and mosquitoes love stagnant water."
] |
[
"Are you sure they are flies? ",
"Bees swarm",
" like this; it is part of their re-productive cycle. They outgrow their current nest so a portion of that breaks off with a new queen and looks for a new nest; this is typically the swarm phase.",
"During the swarm most of the bees are huddled near/around the queen. Other bees are actively looking for a new nest site. It's a pretty elaborate process where bees find a potential site, then communicate back to location/size, get other bees to inspect and do the same. If enough bee's agree that their new site is ideal the entire swarm will relocate.",
"What you are seeing is most likely temporary, once they find an idea site they will dissipate very quickly. Unless that new site is in the corner of the building they are huddled around. ",
"This",
" is a pretty basic but good site to get more knowledge. I've personally caught two swarms but couldn't get them to settle into the new hive.... "
] |
[
"They're definitely not bees - they're small, so it's difficult to get a good photo, but I lucked out and found a spiderweb on the outside of a window near the corner, so ",
"here's a lot of dead ones on the web",
".",
"I've only noticed them this year, but my coworkers assure me they show up every year, and it's not just one swarm - they're on most of the corners of several buildings, so upwards of 10 individual groups.",
"I found them swarming near a tree round the back as well, which seems less weird - ",
"here's a crappy photo of that",
". The photos don't really capture how many of them there are - it's quite creepy."
] |
[
"Can corroded galvanized iron be visually distinguished from non-galvanized iron?"
] |
[
false
] |
I am currently working on a project without a conservator/chemist handy and need to answer the following question. Can galvanized iron fasteners be visually distinguished from regular, un-galvanized iron fasteners after 80+ years of corrosion. Most of the corrosion would be a result of exposure to sea water and coastal air. If so, how would I be able to tell?
|
[
"Corroded galvanized steel usually looks like white flakes/crystals over rusted steel. If you are unable to find any visible indication of either silver-colored zinc or white flakes, especially in the hidden areas of the bolt, it was likely never galvanized.",
"If you can remove a bolt, probably by cutting at this point, you should be able to look at the underside of the head, the washer, inside the threads, or the area that was between the bolted members. If the wind/water/whatever wasn't actively abrading away the zinc residue, it will still be visible.",
"-Source: I do structural and marine steel construction. "
] |
[
"Thanks. The fasteners are actually part of a shipwreck I am studying. ",
"The wreck is from the late 19th century and would probably have used plain iron. Do you know if the zinc would still have corroded white if applied to iron instead of steel? My knowledge of chemistry is pretty basic but I imagine it would be very similar right?"
] |
[
"Yes, it would look similar. It's the iron in steel that creates the iron oxide (Fe",
" O",
" If I remember correctly and the formatting works) known as rust.",
"The late 19th century was when steel started replacing wrought iron in most uses, so you might actually be looking at steel."
] |
[
"What would happen if a positron encountered a negative muon?"
] |
[
false
] |
As is common knowledge among the physics community when positrons encounter electrons they mutually annihilate each other into two high-energy gamma rays. Though what would happen if a positron encountered a negatively charged muon? Seeing as though they have opposite charges you would expect the same result. However, what would be leftover looking at how the muon is 207 times more massive than an electron? Would the new particle only be 206 times "heavier" than an electron? Would it now have a neutral charge? Would the particle still be short-lived and unstable like ordinary muons? If yes, what particle would it decay into? Why?
|
[
"Having opposite charges is not enough for two particles to annihilate, they have to be ",
" antiparticle. You can’t have annihilations between positrons and muons.",
"So what happens when they interact? There’s lots of possibilities, depending on the available energy. They could just scatter elastically, or at higher energies, all sorts of particles could be produced. B not annihilation."
] |
[
"Annihilation only occurs when a particle encounters its antiparticle, therefore a muon will only annihilate when encountering an antimuon. Most likely occurrences (depending on the system energy) are scattering, electromagnetic interaction (exchanging a photon) or weak interaction (exchanging a W/Z boson).",
"In addition to these first-order interactions, there are other more complex decay modes often relying on loop diagrams.",
"You may want to have a look at Feynmann Diagrams, a great way to understand which interactions are possible at quantum scale."
] |
[
"It decays with a half-life very close to the half-life of a free muon."
] |
[
"Could we test whether someone has been exposed to lead poisoning as a child, even if they are now an adult?"
] |
[
false
] |
If you were exposed to lead poisoning let's say, as a 5-year old, would it then be possible to do some kind of nerve biopsy, etc... to determine the of your nerves; in order to confirm or deny if lead exposure occurred? I don't know how difficult that would be, but theoretically, shouldn't it be possible to assess whether or not your nervous system is in a normal state or an abnormal one, with a view towards the cause? Thanks
|
[
"If they experienced lead poisoning as a child, it would probably be less invasive and ",
".",
"Before the epiphyseal plates fuse in adulthood (~20 years old), the long bones (i.e. proximal femur, right below the hip) growth very fast and are constantly depositing minerals inside the bone. In addition to the calcium crystal hydroxyapatite, other heavy minerals are incorporated and don't get removed as quickly (or at all).",
"Because lead is much denser than calcium, it can usually be identified radiographically by x-ray well into adulthood (there will be a clear darker line across the bone where there shouldn't be). I'm not sure how specific this Xray finding is for a history of lead poisoning, but is definitely a strong indicator if positive. If the person/family has saved a baby tooth, that fell out after the supposed age of lead poisoning, then that'd be a great diagnostic sample, as well.",
", which doesn't always show up in patients but is evidence of some recent long-term exposure to lead. It's a bluish/dark line that's present right where the gum meets the teeth.",
" - since it's used to clear the blood plasma and blood cells that may contain lead. However, liver cells have a relatively high turnover rate and may not show signs of earlier lead poisoning all the way from childhood.",
" about \"state of your nerves\" (though it's not a direct answer): this usually wouldn't be done medically. If it were, it's probably during a post-mortem autopsy.",
"The reason is because we'd need a good section of lots of neurons to identify gross pathological changes - and this is really only available in the brain. However, this is pretty invasive and has a lot of risks (hitting an important brain region, meningitis, etc.). We also cannot do anything about it since the damage has long-since been done. ",
"The diagnosis of previous childhood chronic lead poisoning would likely involve the following, though there's really nothing we can do now for the patient except supportive care:",
"Symptomatic (i.e. mental retardation, other neurologic problems like abdnominal pain, anemia)",
"Radiographic/physical (xray, Burtons Line as both previously mentioned, other physical findings, old baby teeth that were kept since childhood, liver biopsy)",
"Circumstantial (living near factory, use of groundwater, lead paint/piping in the homes, sibling/another family member, perhaps consider child abuse)"
] |
[
"Wow thank you for such an in depth response. ",
"Why does lead leave a dark bluish line between teeth and the gum line?",
"And oddly, what is the significance of child abuse? Meaning intentional poisoning?",
"And lastly is it really that fatalistic? Should there have been damage, there is no opportunity, even one based on some theoretical approach, to potentially reverse or heal damage?",
"Thanks"
] |
[
"I'm not sure about the Burton line, but it is probably attributed to a combination of bleeding, relatively inaccessible area (hence need good brushing), and external incorporation into the teeth (like coffee stains).",
"More relevant would be child neglect, but this would be brought up really only if there are other signs (like the child seems 'starved for attention' with the pediatrician, there are unusual bruises or broken bones, other things). Abuse is included in a pediatricians' possible list of diagnoses because it's something that should ",
" be missed in a clinical setting.",
"My choice of words of \"nothing can be done\" might have been a bit too grim. What I meant to say is that, given this exposure was several decades ago, there's not much we can do to reverse it. The patient has survived through that acute exposure already, so there's no real medical urgency, and other systems can be managed relatively well (blood transfusion, liver transplant, caretakers for neuropsychiatric deficits, pain medications, etc.)",
"For acute lead poisoning, where it's very high in the blood, IV ",
"EDTA",
" is used to draw the lead away, preventing it's \"active\" form from circulation, and then eventually be excreted. ",
"It might be theoretically possible to use this for a chronic/past case to ",
" pull lead out of tissues, but this would risk severe iron and calcium deficiency that's much worse.",
"In general, eliciting \"healing\" is very difficult, as it requires turnover of native tissue. Sometimes, such as in the liver, the native tissue cannot heal fast enough and other cells called fibroblasts come in and make their own connective tissue. This is the case with cirrhosis, where chronic liver damage surpasses the liver's ability of heal itself, and then the liver is eventually replaced with non-functional fibrous scars.",
"In the case with neurons, turnover is nearly impossible if large areas are generally damaged. While the brain ",
" readapt to some small injuries, something as non-selective as lead poisoning isn't really recoverable.",
"I should end with the point that this prognosis is based on current research. Other neurodegenerative diseases that deal with neuronal toxicity are being researched, and I hope to see progress in the near future."
] |
[
"How is there angular momentum in an electron when the Bohr orbital-movement model has been disproven and the static electron energy cloud is accepted?"
] |
[
false
] |
it makes sense to talk about angular momentum when there is a satellite circulating around a core but when you just have a negatively charged static/unmoving energy field emanating around a core, how do you interpret this? I've seen pictures in high school chemistry that show beautiful patterns in the probability density when you vary the angular momentum amount but I never got the term "angular momentum" in this context - is it a misnomer? What is it? How do I intuitively interpret it?
|
[
"In this case, momentum is a bit of a bad name. For an electron, there is always an angular momentum. Always. You cannot stop it. ",
"It sucks to accept, but it works to describe interactions and when you get into symmetry arguments in subparticle physics, the need for an intrinsic momentum for electrons is pretty noticeable.",
"You are referring to ",
" angular momentum, but I believe the OP is specifically reffering to ",
" angular momentum. It is the orbital angular momentum responsible for the \"shapes\" the OP is referring to.",
"That being said, spin is a good example of why you should not try to think of this classically. You are talking about quantum mechanics, but trying to interpret observables classically, which just wont work."
] |
[
"Very interesting that you mention this as I have just asked this question :D",
"http://www.reddit.com/r/askscience/comments/t0fj9/does_an_electron_cloud_vibrate_like_a_standing/",
"thanks for all the answers. I will write more questions as I try to understand the responses."
] |
[
"It isn't static in the sense that it has no motion, but that it stays in the same shape. It's a standing wave that oscillates, and it does have net motion around the center, in a sense.",
"Those probability clouds you saw were visual representations of the position wavefunction, which has complex values at every point in space and time (as in ",
"). It can actually change constantly without changing the chance that you'll see the particle in a given place. (the chance you'll see it in a certain place is actually the size of the complex number squared, which is a real number probability).",
"Are you familiar with Angular momentum defined as ",
" x ",
"? because it's actually the same in QM except that position and momentum take different forms. I've already mentioned the position wavefunction, and the momentum of the particle is the spatial derivative of position, scaled down by a constant (hbar) and multiplied by -i (a complex rotation).",
"This was about orbital angular momentum L. Spin S is a bit different, and not as relevant to your question about orbits."
] |
[
"How did the Gamma function arise?"
] |
[
false
] |
Taking the definition from : the factorial of a non-negative integer n, denoted by n!, is the product of all positive integers less than or equal to n. So how and why are we able to extend this definition into non-integer values or even complex numbers? Specifcally, how did we find the definition of the ?
|
[
"Integration by parts of the Euler integral of the second kind shows that:",
"Γ(t) = integral from 0 to infinity x^(t-1) e^-x dx = \n - lim x->infinity x^(t-1)e^-x\n + 0^(t-1)*e^-0\n + integral from 0 to infinity x^t/t * e^-x dx\n",
"The limit is 0, the expression on the third line is 0, and the expression on the fourth line is Γ(t+1) / t. Therefore what's left is t Γ(t) = Γ(t+1). This is the functional equation of the gamma function but it's also (apart from the sometimes annoying shift right by one) the definition of the factorial n (n-1)! = n!.",
"So to answer your questions:",
"Specifically, how did we find the definition of the Euler integral of the second kind?",
"There is no particular reason why the Euler integral of the second kind (which was \"chosen\" by Legendre) has to be the definition of the Gamma function. For example ",
"this",
" Wolfram Alpha link shows an alternative definition (that Euler himself used) of \"fraction factorials\". However Gamma is a special function, and you cannot express it using exponentials alone; all definitions will involve derivatives or integrals or series (or other special functions) in some way.",
"Still, the Euler integral of the second kind is perhaps the simplest starting point to prove that its solution satisfies the functional equation of the Gamma function (at least for t>0). How to come up with it? Difficult to say, but the proof is probably simple enough that you can do it backwards and come up with the integral.",
"So how and why are we able to extend this definition into non-integer values or even complex numbers?",
"Because we can build the analytic continuation of the factorial function, or equivalently because the functional equation n (n-1)! = n! has a solution given by the Euler integral of the second kind (with t=n+1). You can by the way prove that only one analytic function has f(1)=1, f(t+1) = t f(t) and also makes log(f(t)) convex. That's the ",
"Bohr-Mollerup theorem",
" (which I admit I have just learnt about).",
"More information: ",
"Leonhard Euler's Integral: A Historical Profile of the Gamma Function",
"."
] |
[
"So i guess that the wolfram alpha link also meets the f(1) = 1 requirement and the f(t+1) = t f(t) but not the log(f(t)) convex. ",
"It also satisfies the convexity of log(f(t)). It is just another integral (this time a definite one) whose solution is the Gamma function. Both integrals define the same function, just like",
"f(x) = lim x->infinity (1+n/x)^nx\nf(x) = sum x^i/i!\ndy/dx = y\n",
"all define e",
"The paper I linked has examples of functions that also interpolate the factorial but lack logarithmic convexity. The theorem explains what \"sets aside\" Gamma from all other interpolations of the factorial. A logarithmically convex functions f is \"really really convex\", since logarithm is \"pretty concave\" but still not concave enough to damage the convexity of f. For example x",
" is not logarithmically convex, while e",
" is. It makes sense that a function growing as fast as Gamma—which grows more or less like (x/e)",
" according to the Stirling approximation—is logarithmically convex, and indeed it is."
] |
[
"Which i interpretate as that the Bohr-Mollerup theorem proves that no \"good\" interpolant for negative factorials can be found. Could you elaborate on the meaning of \"good\" here and why this is affected by the Bohr-Mollerup theorem?",
"If Γ(n) is meant to be an extension of the factorial function (n-1)!, then any reasonable extension should, at the very least, satisfy the functional equation",
"Γ(z+1) = z Γ(z)",
"Put z = 1 and you get Γ(2) = Γ(1), which means 1! = 0!. If we add the normalization condition that 1! = 1, then 0! also. Okay, now put z = 0 in the functional equation, and you get 1 = 0*(-1)!. So there's no way to define (-1)!. Note that we didn't have to talk about log-convexity.",
"So why is log-convexity the property that pops up? Interestingly, the gamma function Γ(z) is non-zero and meromorphic with simple poles at the negative integers. That means the ",
" g(z) = 1/Γ(z) is entire with simple zeroes at the non-positive integers. As a side note, it also satisfies the functional equation",
"z g(z+1) = g(z)",
"which is valid for ",
" complex numbers ",
". So now flip the problem of characterizing the gamma function to characterizing the reciprocal gamma function. You want a function ",
" such that:",
"The ",
" then uniquely determines ",
", up to some factor of the form e",
" where ",
" is an entire function. In particular, ",
" implies that you automatically know that ",
" must have the form",
"g(z) = z e",
" Π",
"(1 + z/n)e",
"(For reference, f(z) actually equals γz, where γ is the Euler-Mascheroni constant.)",
"The normalization condition ",
"(1) = 1 cannot determine ",
", but only that f(1) = γ. You can fix ",
" by fixing the genus or order of ",
", but that essentially means you are stating how ",
" grows at infinity. That should point you in a direction of why log-convexity is important for characterizing the gamma function, since you need to know something about ",
", i.e., the logarithm of ",
". (The relevant theorem for characterizing meromorphic functions by their poles is the ",
".)"
] |
[
"If there was a huge solar flare that hit the earth would everybody (or anybody) die or just the people on the daylight side?"
] |
[
false
] | null |
[
"The primary danger from solar flares isn't to us humans, but rather our infrastructure. A powerful enough solar flare can essentially destroy our electrical grid as well as knock out any satellites in the way. This could result in a loss of life due to a lack of power over an extended period of time.",
"Unless our magnetosphere was stripped, the majority of particles ejected during a solar flare will be caught up in the outer atmosphere and won't pose much risk to us individuals directly."
] |
[
"can essentially destroy our electrical grid as well as knock out any satellites",
"I would like to see sources about that. It could certainly, if powerful enough, have some effects on the power grid, but destroy it ?"
] |
[
"According to Dr. Phil Plait in his book ",
"Death From the Skies",
", a powerful enough solar flare has the capability to overload power lines and transformers, which is why I said ",
". Because obviously if every power line and transformer is blown out or snapped it's not going to be a simple repair."
] |
[
"Why do some viruses, such as influenza, quickly mutate (thus require different vaccinations annually), but other viruses, such as smallpox seem to barely mutate at all (or at least much more slowly)?"
] |
[
false
] | null |
[
"One reason why is that viruses like corona and influenza are single stranded RNA viruses and small pox is a double stranded DNA virus. ",
"If you have a single stranded genome, there is no repair mechanism and mutations occur much more frequently."
] |
[
"Another reason for some viruses such as influenza is that their genome is actually segmented! If a host has more than one strain of influenza, the segments can be mixed up and you have a rapid sudden form of mutation called antigenic shift. The other commonly known form of mutation that occurs over time due to replication errors is called antigenic drift.",
"Edit: It's actually antigenic shift/drift not genetic as I had mistakenly put before. Thank you ",
"/u/insulinjockey",
" for pointing that out."
] |
[
"You say “viruses like influenza”, but in fact it’s not viruses ",
" influenza, it’s ",
" influenza that does this. Influenza is unique in the virus world in its ability to evolve to avoid population immunity. Technically, influenza doesn’t mutate fast than other RNA viruses, but its surface proteins are more tolerant of mutations than other viruses are. See my answer in ",
"Why of some viruses mutate faster than others",
" for details and references. ",
"If you think about the vast majority of viral vaccines (measles, mumps, rubella, Yellow Fever, polio, etc etc etc) they do ",
" need to be updated annually. Even RNA viruses like measles and polio are antigenically very stable, in spite of having mutation rates that are very similar to influenza’s, and they haven’t needed to have their vaccines updated in the decades since they were introduced.",
"The question didn’t specifically ask about SARS-CoV-2, but since the other answers immediately turned to it ... Coronaviruses in general have slightly slower mutation rates than influenza, but they’re still very high. However, while they can and do readily accumulate mutations (",
"NextStrain.com",
" shows hundreds of mutations that the virus has made over the past few months) the default assumption - for good reasons - is that these mutations are neutral and don’t affect the virus function or antigenicity. ",
"If we look at the four endemic human coronaviruses, they show some signs of slow antigenic change, which hints that coronaviruses ",
" be able to tolerate ",
" changes in their proteins, but clearly not to anywhere near the extent of influenza. If we have to guess (and without data it’s mainly a guess) it seems likely that a vaccine against SARS-CoV-2 will be effective for many years, perhaps 5-10 years, before the virus drifts enough that it might need an update. Maybe not quite as good as measles, but hopefully much better than influenza."
] |
[
"What connection is there between the esophageal sphincter and your ears?"
] |
[
false
] |
Is there any nervous system or other connection between the esophageal sphincter and the area on both sides of your neck that run up it and behind your ears and into them? What would the reason or mechanism of why a person would experience pain in that region when getting an esophageal spasm? Is this "referred" pain from the vagus nerve? btw what exactly is "referred pain" - nerves nearby misfiring? And why would drinking ice cold water which presumably cools the esophageal sphincter halt the pain in the region and that referred parallel neck/ear pain? I know it's a lot of questions and this isn't asking for medical advice, it's genuinely trying to understand the biological connection between the parts in this circumstance. Thanks :)
|
[
"Are you referring to the upper esophageal sphincter or the lower?"
] |
[
"It's just that there are two of them, so it really depends which one. I'll try to get to this later today."
] |
[
"Alright here we go.",
"The esophageal sphincter is innervated by the ",
"vagus nerve.",
"This nerve does also have a branch called ",
"Alderman's nerve",
" which goes to the exact region of the ear you're referring to.",
"The vagus nerve is well known when speaking of referred pain, and would be the link in this case.",
"Referred pain is not well understood but the ",
"wiki",
" page has some information about theories, and some explanations for it.",
"The best way to explain the feeling you're asking about is likely to compare it to brain freeze. ",
"Does this answer your questions?"
] |
[
"There are many helpful bacteria inside the human body. Do we have any such viruses?"
] |
[
false
] |
[deleted]
|
[
"Maybe. ",
"Hepatitis G",
" might play a role in suppressing HIV. But generally speaking we don't have the same relationship with viruses as we do with bacteria. Bacteria we actually really need to survive."
] |
[
"Not on purpose. Viruses are bags of RNA or DNA. They float around with the sole purpose of reproducing. The viruses reproducing often hurts us. It takes over our cells machinery, eventually killing the cell. I don't think any virus could be beneficial or evolve to be beneficial on purpose.",
"Bacteria are different because many don't affect our bodies at all. They just live inside us or on us. Most bacteria aren't helpful at all, they may just make it so other harmful bacteria don't take up that space and hurt us."
] |
[
"Yes, countless billions, although probably not the ones you might have heard of. Every surface of your body, inside and out (skin, mouth, gut, genitals etc) is covered in microorganisms: mostly bacteria, but also fungi and viruses that infect bacteria, called phages. ",
"These microorganisms form complex ecosystems on your body. They eat stuff you eat or secrete (sweat, proteins, etc), and some of the waste products of microorganisms are eaten by other microorganisms - just like the life we can see with our eyes. Phages that infect bacteria are an important part of how this ecosystem works and can have effects on how these ecosystems develop. We also know that human diseases are associated with changes in these phages, although how and why isn't clear. For example, people with inflammatory bowel disease tend to have more phages in their gut - we already know that certain gut microbes have a critical role in this disease, so it's not that surprising to learn that viruses that infect these microbes can be related too.",
"https://www.eurekalert.org/pub_releases/2018-07/uoca-rfc072318.php",
"In another example, this study found that patients infected with C diff (a dangerous bacterial gut infection) have altered phages in their gut. A very effective treatment for C diff is to transplant healthy faeces from a donor into the patient. This study also found that the transplant treatment was more likely to be successful if the phages from the donor also successfully grew in the recipient, suggesting that phages might have a role in making the treatment work.",
"https://gut.bmj.com/content/67/4/634"
] |
[
"How to measure decibels in a MRI machine"
] |
[
false
] |
This is somewhere between DIY and AskScience. I have an (unpaid) internship and the doctor I'm working for is interested in measuring the decibels experienced by someone undergoing an MRI. I know that this has been measured to some degree already, but she wants a way of directly measuring in an active MRI. My plan was this: Use a long PVC pipe to conduct sound out of the MRI machine, then measure the decibels at the end of the pipe. Of course it would have to be calibrated using a known source to adjust for the absorption of sound by the pipe. I planned to use an old PC mic and some software on my computer to generate and record the sound for calibration. My question is this: The direction of the sound will certainly matter, so how do I accurately represent the human ear in the test? Consider that a pipe directly inserted into the tube will be perpendicular to the human ear in the same tube (the MRI machine's tube), so will I be able to get an accurate measurement? This project actually has nothing to do with my internship, but I thought it sounded like a good challenge. edit: Sorry for the large lag in replying, I posted this then got called away. All suggestions and comments are welcome, please tell me if you think there is a better community to post this in.
|
[
"I used to work in a lab where they made devices for delivering ultrasound inside an MRI. I can probably hook you up with some experts if it comes to that."
] |
[
"Do you need to make good measurements on the MRI while you're measuring the sound levels? If not then you don't have to worry about a recorder's electronics screwing with the signal."
] |
[
"Well, I think the concern is for the electronics of the recording device (and/or its attraction to the magnet)."
] |
[
"Does quantum mechanics prevent one from (hypothetically) measuring the gravitational field of a particle to determine its position and velocity?"
] |
[
false
] |
This is just a thought experiment. Could the path of a particle through a two-slit apparatus be determined using a device that could measure the gravitational field of a particle with unlimited sensitivity? Would there still be an interference pattern?
|
[
"There is no reason to suppose that gravity doesn't follow the rules of quantum mechanics to this basic order. So no, you cannot use gravitational effects to bypass the uncertainty principle. In fact, the uncertainty principle is probably the most certain part of quantum mechanics. It is incredibly unlikely that any new discovery will discredit it."
] |
[
"Correct me if I'm wrong, I've never worked in a laboratory with small scale gravitational effects, but the largest problem with your idea is what you mean when you refer to \"measuring the gravitational field\" of a particle. ",
"The way we measure gravitational fields is by observing their effects on other objects. Attempting to measure the gravitational field of a particle requires you to examine the movement of another particle in response to it. (Or some sort of equivalent measurement, see the ",
"Cavendish experiment",
".) ",
"In making ",
" measurements, you can see how the uncertainty principle affects your results in the usual way."
] |
[
"The influence of gravity can be detected in quantum mechanical systems. In fact, it can induce quantum interference. See ",
"Phys. Rev. Lett. 34, 1472–1474 (1975)",
"."
] |
[
"What would happen if you left a steak on the Moon?"
] |
[
false
] |
It doesn't have to be a steak - any cut of meat would work. Assume that it's not in a bag or any protective housing. How long would it last, and are there any circumstances where someone would be able to eat it afterwards? What would happen to them?
|
[
"It will freeze-dry at night and boil in vacuum during the day. ",
"With a bit of practice, salt and spices you could probably do a decent beef jerky. Be warned that the surface of the moon is rich in calcium oxide and other basic compounds, which are bad for you and will make the steak taste bitter. Use only clean surfaces for food preparation.",
"Repeated temperature swings and ionizing radiation are bad for organic molecules e.g. porterhouse. It will eventually be reduced to a lump of carbon. If you wait long enough, the resulting hockey puck may be struck by a micrometeor."
] |
[
"Steak in interstellar space is actually an interesting problem.",
"Going off Wolfram Alpha's phase diagrams, water is a solid even in vacuum if the temperature is low enough. Get a couple of AU away from the sun and even an impure \"comet\" like your steak should be very stable.",
"I can't guarantee total edibility (the exterior may freezerburn a little before it gets too cold for water to sublimate) but if it does happen you could cut the crusty bits off. The cosmic rays will get to it eventually, but destroying enough bonds to charcoalize it from radiation alone may take a long, long time."
] |
[
"I wanna go a bit furhter...if you just tossed a cut of meat into space, or anything biodegradable, away from the heat of any star, would it freeze dry and be good, theoretically, forever, since it is locked in a no oxygen vacuum of frozen space? Or, since there is water liquid in some materials to begin with from Earth, would it instantly have freezer burn from these leftover water/oxygen molecules?"
] |
[
"Could noise cancelling devices be built into machinery thus reducing damage to operators and noise pollution.?"
] |
[
false
] |
I was reading of the ways noise pollution is affecting marine mammals and birds in urban areas and kind of had this brain wave; would it be possible?
|
[
"The problem with noise cancelling is that it's immensely location specific. You have some environmental source of sound waves, and then you have a source of sound waves to destructively interfere. But if you look at a drawing of ",
"interference patterns",
", you'll note that there are points where they destructively interfere, and just as many points where they constructively interfere.",
"Noise cancelling headphones generate the interfering waves such that destructive interference occurs at the source of the interfering waves, i.e. at your ears. This is fine, since you only need a point of interference. But you can't cover a whole area with a noise-cancelling device. (Well, unless you could generate the interfering waves at precisely the same point as the waves you're trying to cancel, but generally you can't.)"
] |
[
"It depends on where the noise is coming from. You can put a muffler on a car engine but you can't exactly mask a concord's sonic boom. Any specific machine you had in mind? In general, making something quieter will usually be more expensive and less effective."
] |
[
"I think OP means noise canceling as in what is used in head phones and mobile phones..\nIt's interesting, \nI've wondered if we would ever see noise canceling devices for people who live close to railway lines and busy roads..\nIt could be done but I don't think it blocks the actual sounds from damaging our ears , It mutes them so we can't hear them.. \nIt's something to do with wave lengths and frequencies and I've never gotten into all that... "
] |
[
"If motion is relative, why is it (theoretically) possible for one massive object to move in 0.5c in one direction and for another to move at the same speed in the opposite direction?"
] |
[
false
] |
[deleted]
|
[
"It's perfectly possible for the relative velocity of two objects, as perceived by an external observer, to be greater than the speed of light. This is not a contradiction of the fact that nothing can travel faster than the speed of light because relative velocities are not the same in different reference frames in special relativity. Our classical intuition tells us that if the relative velocity of two objects is greater than the speed of light, it must be the case that one of the objects would see the other object travel faster than the speed of light in their reference frame. It turns out this is not the case in special relativity, even in the case where the relative velocity of two objects is greater than the speed of light in some external frame, in the frame of the objects themselves they will always see the other travel slower than light speed."
] |
[
"Length contraction/ time dilation (The reason I can answer with both is they're two sides of the same coin).",
"Person A will see the distance travelled by person B to be smaller in one second making B's speed slower, or equivalently they'll cover the same distance, but it will take a bit longer than a second."
] |
[
"There is a difference between ",
" velocity of a ",
" object and ",
" velocity as seen from some inertial frame. The maximum ",
" speed is c and the maximum ",
" speed between to objects is in the case of to massless particles moving in opposite direction and is in this case 2c.",
"Now let's consider your case of two objects A and B moving in opposite directions with speed 0.5c with respect to ",
" reference frame. Now changing reference frame to one of the object A we see that ",
" are moving with speed 0.5c. To find out what the speed of object B is in this reference frame we apply the ",
"relativistic velocity addition formula",
" and get:",
"vB' = (vA+vB)/(1 + vA vB/c",
") = (0.5c + 0.5c)/(1 + 0.5c x 0.5c/c",
") = 1/1.25c = 0.8c",
"Which is smaller than the speed of light as it should be."
] |
[
"Vaginas contain lactobacillus, which are needed for healthy digestion. Do we know if performing oral sex in one can have health beneficts?"
] |
[
false
] |
Sorry for the stupid question, but I couldn't get this out of my head. Also, sorry for the maybe weird phrasing of the question, English isn't my first language
|
[
"Shirt answer: no.",
"See my other reply for details.",
"Tl;dr: lactobacillus in vagina and gut are different at species and strain level (in healthy women).",
"Cunnilingus is no free probiotics treatment.",
"Also, don’t try to make “vagina yoghurt”. (Please...).",
"Source: I am an academic researcher on the human microbiome.",
"Edit: These are some papers on this, as requested repeatedly. I posted them in a different reply before which was subsequently deleted. Some of these papers were published literally two weeks ago, but the results were known in the field for some time.",
"https://www.ncbi.nlm.nih.gov/m/pubmed/30001516/",
"https://www.ncbi.nlm.nih.gov/m/pubmed/28144631/?i=2&from=/30001516/related",
" ",
"https://www.ncbi.nlm.nih.gov/m/pubmed/30001517/?i=15&from=/30001516/related",
" ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5880245/",
" ",
"https://www.ncbi.nlm.nih.gov/m/pubmed/29118049/?i=4&from=/30001516/related",
"https://www.ncbi.nlm.nih.gov/m/pubmed/27503374/?i=5&from=/30001516/related",
"https://www.ncbi.nlm.nih.gov/m/pubmed/28034306/?i=7&from=/30001516/related",
" ",
"https://www.ncbi.nlm.nih.gov/m/pubmed/28073918/?i=8&from=/30001516/related",
" ",
"https://www.ncbi.nlm.nih.gov/m/pubmed/29022384/?i=9&from=/30001516/related",
"Edit2: these refs are on the much discussed sub-question below whether babies keep their mothers’ vaginal Flora after birth. Not directly on the question of oral sex and gut health..."
] |
[
"Follow up question - is the bacteria in a birth canal related to gut bacteria in a healthy person?",
"How much of a person's gut bacteria depends on vaginal birth and passing through their mother's bacterial cultures?"
] |
[
"Apparently oral sex can have health impacts, but not positive ones. There has been ",
"some studies",
" that show that men who have had more oral sex partners are at an increased risk of throat cancer."
] |
[
"When a truck drives behind another truck to reduce drag, does it slow down the truck in front?"
] |
[
false
] |
I was just thinking about this on the highway yesterday and realized I have no idea how drag and slipstreams work. Does the truck in front create some sort of low-pressure zone that "pulls" the back truck along? Does that somehow require more energy from the front truck?
|
[
"The turbulence behind the un-aerodynamic rear of a truck adds to the drag on the vehicle. If another truck is close behind that turbulence is reduced, has less volume in which to operate. Therefore the presence of the second truck should actually ",
" the first truck. The second truck takes up the burden of rear-end turbulence but this can be expected to be more than compensated for by the slip-stream effect of following the first. edit:spelling"
] |
[
"Okay my brain just exploded.",
"Does this imply that, if/when inter-car communication matures, and vehicles are able to convoy on highways in very close proximity, ",
" fuel usage should decrease significantly, including that of the guy in front?"
] |
[
"Yes."
] |
[
"My wife is convinced that the full-body scanners that are now being used in some airports cause cancer, and thus refuses to use them. What is the evidence for or against this?"
] |
[
false
] | null |
[
"If the top scientists in the area are constantly arguing over it, I doubt we'll be able to reach any absolute conclusion here at askscience.",
"Personally, I always try to minimise my exposure to ionising radiation. I would not be keen to go through one of those backscatter scanners, however it is clear that if it does cause damage, the damage is not caused at the scale of the individual but rather the scale of the population.",
"How these devices were approved seemingly without empirical studies on whether they cause DNA damage is beyond me."
] |
[
"I would start reading ",
"here",
". Looks controversial."
] |
[
"How these devices were approved seemingly without empirical studies on whether they cause DNA damage is beyond me.",
"It's troubling but not unexpected.",
"I remember reading about these X-ray machines that were once used to fit people's shoes decades ago. Eventually it was revealed they cause cancer and now people look back and wonder how dumb those people were.",
"I wonder if this is the same thing happening again."
] |
[
"Dear r/askscience panelists, what is a question you would love to be asked, and what is the answer?"
] |
[
false
] |
About your field of research, of course. I figure some of you must be dying for the right question to be asked here. Also, there are a lot of fields I didn't even know existed (historic cooking, anyone?) and would love to know more about them but I just wouldn't know what's a good question to ask.
|
[
"This reminds me of a story I heard. On a physics exam, a professor put \"Write a question appropriate for this class, and answer it.\" The student put down. \"Write a question appropriate for this class, and answer it. Write a question appropriate for this class, and answer it.\" Technically, he was correct."
] |
[
"Any question beginning with the phrase \"I think I've disproved\" and then something like relativity, quantum mechanics, the ideal gas law or the second law of thermodynamics. Cause I just can't get enough of those."
] |
[
"Seeing as the professor put the question on the exam, it must have been an appropriate question for the class, and so, the student answered with the same question to which the answer, of course, was the same question yet again."
] |
[
"What % of my weight am I actually lifting when doing a push-up?"
] |
[
false
] | null |
[
"Your question made me curious and a quick search yielded the study linked below, which looked at exactly this question.",
" The researchers found that the answer depends both on the variant of the exercise as well as the stage of the exercise. For example, in a traditional push-up the number is about 69% in the up position (at the top of the movement) and 75% in the down position (bottom of the movement).",
"It's also worth mentioning that the study also looked at a \"modified push-up.\" This modification ",
"as shown here",
" is essentially just an ",
" easier version of the exercise where the knees stay on the floor. Surprisingly (to me at least), even in this simpler version you still lift quite a bit of your body mass (54% in the up position and 62% in the down position).",
"edit: I corrected \"going up/down\" to \"up/down position\" to reflect the fact the body was kept stationary when the force was recorded in this study.",
" Suprak, et al. ",
" 2011: 25 (2) pp 497-503 ",
" ",
"Link"
] |
[
"You can also modify pushups in the other direction, making them significantly harder (mostly through increased leverage): ",
"Note: at no point do you lift 100% of your own body mass, since your hands and forearms are always at rest and all of the motion is above the elbow. ",
"Edit: body segment weight data as measured by Paolo de Leva says that hands and forearms average ",
"4.46% of body weight for men, and 3.88% for women",
". ",
"Source: "
] |
[
"To measure yourself: Put a bathroom scale under one of your hands while doing a push up. Double the maximum value the scale lists and divide that by your total weight (and multiple by 100) to calculate the percentage."
] |
[
"Is there an enzyme that could break down steel? Could you apply a certain growth medium to a steel girder and grow a bacterium capable of breaking it down?"
] |
[
false
] | null |
[
"Howdy! I've removed your post for its open-ended and speculative nature. I can redirect you towards ",
"/r/AskScienceDiscussion",
" which better suits such posts."
] |
[
"Oh man! I really wanted an answer. Could I resubmit it in a more concise manner?",
"\"Is there a biological way to break down steel?\""
] |
[
"I think that's a great rephrasing. Go for it, but message back so I can release it promptly. I'm curious to the answer as well.",
"To be clear, it was the second half of your post that got it removed."
] |
[
"I'm in a bad mood. Physiologically speaking, what's going on? Are there well-understood neuro-biological factors keeping me from enjoying my work? Is there a theory about the evolutionary benefits of being surly?"
] |
[
false
] |
[deleted]
|
[
"Usual disclaimer: I am not working in the field, but being grumpy in the short term is consistent with the game theory strategy called \"tit for two tats\". ",
"http://en.wikipedia.org/wiki/Tit_for_tat#Tit_for_two_tats",
"Basically, you try and take advantage of me once, and I let it go, because sometimes shit just happens, if you try and do it again while I'm still in a bad mood, I retaliate disproportionately. It's a evolutionary stable strategy that is more robust to noise and accidental insult than the standard tit for tat approach, and one which heavily penalises people who try and take advantage.",
"The thing about these \"evolutionary lite\" explanations is all they can tell you is a reason why being grumpy might be good. It doesn't have to be the actual reason that we're grumpy.",
"Hopefully, we can get a real game theorist/biologist to chime in on this."
] |
[
"First: your question and subquestions are all buzzwords and things that don't belong. Evolutionarily whatever is not required. Physiologically is pretty hard to answer (individual differences). Neuro-biological blah blahs. ",
"You're in a bad mood: that's emotion. There is a wealth of knowledge on emotion from psych, neuro and cognition studies. We need to firm up your question:",
"You're presuming that mood is aggregate chemical reactions",
"Re: Outlook: you mean someone who's just kind of a dick and always grumpy vs. someone who is often cheerful and oblivious? I don't think there is a way to set up a study to follow \"the grumps\" and \"the happies\" for a longitudinal study...",
"What is it exactly that you want to know about mood/emotion?"
] |
[
"Sure, let's clear away the confusion. Remember, I use \"all buzzwords\" because I don't know jargon.",
"RE: mood.\nI started here:\n",
"http://science-education.nih.gov/supplements/nih2/addiction/activities/lesson1_brainparts.htm",
"Where I acquire my first \"blah-blah\": neurobiology. Which says the frontal lobe regulates emotion, behaviors, etc. Vague.",
"Then here:\n",
"http://en.wikipedia.org/wiki/Emotion",
"\nWhere I acquire new funny words like \n\"Instinctual emotions (from the amygdala), versus cognitive emotions (from the prefrontal cortex).\" Instinctual?? That sounds like evolutionary theory might come into play (which I've learned now is not required). Being a layman, I dig.",
"http://en.wikipedia.org/wiki/Amygdala",
"\nVery cool. So base emotions like threat, fear, anger can be pinpointed. Understood.",
"Now I have the question: Without threat, fear, etc, why do negative emotions come around, persist, and what do these emotions do in the long / short term. So the reactions of adrenaline, the sympathetic system (",
"http://en.wikipedia.org/wiki/Sympathetic_nervous_system",
") and so on are short-term. ",
"I'm having trouble believing that long-term stress / anger ,etc hasn't been studied, and it's a bit more than \"the happies\" or \"the grumps\" as you put it. ",
"So are \"individual differences\" how we explain long-term mood or is there something else?"
] |
[
"Could humans survive in temperatures above 120°F?"
] |
[
false
] |
Considering that we can be comfortable in a hot bath around that temperature, I was wondering if that were applied to the air temperature, could we go on as normal (besides being pretty damn uncomfortable)?
|
[
"Humans have survived---amazingly---temperature of >250°F for tens of minutes, in temperature homeostasis experiments initiated by Sir Charles Blagden in the 18th century. The key was that it was a dry heat. The resulting sweating was abundant, but there were no permanent health problems. (A steak brought into the same test chamber emerged thoroughly cooked.)"
] |
[
"It depends on what you mean by \"survive\". You can be exposed to elevated temperatures like that for a while, but, eventually you will develop heat stress. How long it takes you to develop that heat stress depends on a number of factors, like how active you are, hydration, clothing, etc.",
"There are PHEL curves (Physiological Heat Exposure Limit) that basically capture what the exposure limit is for a given temperature and activity level."
] |
[
"I am going to assume that you are talking about sitting as you would in a bath, in the shade with an air temp of 120F. ",
"Yes. Provided that you are in a dry area and that you get a lot of water. Temperatures near this are common in Las Vegas, Phoenix, and Death Valley. People still work outdoors in it. Construction still goes on for example. It obviously helps to have shade and as little activity as possible.",
"The reason humans can do this is because of our sweat. Sweat evaporates quickly on hot days with low humidity. When it evaporates, it takes with it a lot of energy. You can look up psychrometric charts to see how much cooling you get. There is a form of air conditioning called a swamp cooler that runs off of this principle. It can take in 110F air at 10% humidity and pump out 64F air at 100% humidity."
] |
[
"How did the cowboys keep air conditions on their buildings for their saloons in when they use those butterfly doors?"
] |
[
false
] | null |
[
"Air conditioning didn't start being common until the 50's, half a century after when typical movie style saloons were common."
] |
[
"I know for sure place like movie theatres had them too. I assumed the regularplaces like restaurants and stuff had them aswell"
] |
[
"Depends on which era you are talking about. Classic \"far west\" cowboy saloons from the movies are usually depicting places from before 1910 with the peak of the Old West outlaw kind of period in the 1870's and 80's. The first air conditioning installations did not begin before 1906."
] |
[
"How does sodium nitrite sharpen a heated tungsten rod?"
] |
[
false
] | null |
[
"That was the flair bot bothering me for the chemistry label, if anyone is wondering."
] |
[
"That was the flair bot bothering me for the chemistry label, if anyone is wondering."
] |
[
"That was the flair bot bothering me for the chemistry label, if anyone is wondering."
] |
[
"What happens after a black hole is formed? Does it just grow and never go away? What will it be in the long run?"
] |
[
false
] | null |
[
"Currently black holes that form only grow. They emit Hawking radiation, however - very weak but still present. In the very distant future, when there is not much left that can fall in, Hawking radiation will win and the black holes slowly lose their energy (and therefore their mass) until they evaporate. It is unclear if they will go away completely or if there will be some sort of remnant left."
] |
[
"To elaborate, right now a black hole doesn't even have to be 'fed' with infalling stars, planets, dust and whatnot: what looks like empty space to us is energetic enough for that. That is, the black hole receives more energy from the cosmic microwave background than it emits due to Hawking Radiation. Over immeasurable times, space will cool off enough for Hawking Radiation to finally win."
] |
[
"Technically they are growing because they absorb photons that hit them and radiate very little energy but I wouldn't picture normal stellar mass block holes as some giant thing that just sucks up everything in it's surrounding and constantly grows ever larger. Mostly they just sit there and hangs out like most other celestial objects. It goes around it's orbit around the galactic center and attracts other objects gravitationally no special black hole suction. ",
"In the same sense Earth also pulls nearby asteroids and interplanetary dust towards it and some of that mass will collide with the Earth and add to Earth's mass. Every year about 40,000 tonnes of space dust get trapped in our atmosphere and 95,000 tonnes of hydrogen and helium is lost to outer space but we don't think of Earth as growing or shrinking even though this is happening. With black holes, yeah they are gaining mass but really they are just doing nothing if you look at them in the million or even billion year timeframe."
] |
[
"Can 241Am spontaneously generate 243Bk?"
] |
[
false
] |
As most of you may know, Berkelium was discovered after a surface of Americium-241 was bombarded with high energy alpha particles. This had got me wondering; as 241Am decays, it can occasionally produce a high energy alpha particle. If said alpha particle hits the nuclei of a nearby 241Am nucleus, wouldn’t that generate 243Bk (just as in the original synthesis)? So, would this mean that any given sample of Americium-241 potentially has a few atoms of Berkelium in it?
|
[
"Am primarily emits two alpha particles whose kinetic energies are around 5 MeV. The Coulomb barrier for ",
"He + ",
"Am is almost 30 MeV. So the probability of any given alpha particle actually undergoing a reaction with a ",
"Am nucleus is going to be very small."
] |
[
"If you start with a 100% pure sample? Probably zero.",
"Americium-241 + alpha = Berkelium-245 as an alpha particle has 2 protons and a total of 4 nucleons. Only alpha and beta will never get you to berkelium-243. And of course the probability of this reaction is tiny.",
"Americium-241 has a very small chance of spontaneous fission which releases neutrons. Beta- decays can increase the element number - but the first curium isotope to do so is curium-249. Collecting 8 neutrons in the same atom from the tiny spontaneous fission chance of Am-241? Forget it.",
"Am-241 + high energy alpha -> Bk-245 + 2 neutrons might be possible if a spontaneous fission process emits a high energy alpha particle. But that's an extremely obscure option."
] |
[
"So theoretically speaking, in say a 1 gram sample of Americium 241, how many atoms of Berkelium would be in there at any given time?"
] |
[
"What actually kills you when you are dehydrated?"
] |
[
false
] |
What goes on in your body that causes you to die from dehydration?
|
[
"The two most significant issues with severe dehydration are the loss of perfusion volume as well as the electrolyte abnormalities that develop. If someone is hypovolemic enough, they will not be able to maintain an adequate blood pressure to supply oxygen to their organs, which results in multi-organ failure (in particular, the heart, brain, kidneys, and liver are particularly vulnerable). In addition, changes in electrolyte concentrations in the blood (most typically sodium or potassium) can result in comas or seizures as well as cardiac arrhythmias."
] |
[
"If you don't drink enough water, your blood pressure can drop to dangerous levels. Because blood carries oxygen throughout your body, your organs, like your heart and brain, would start to fail due to the lack of oxygen. Additionally, lack of water would also cause the concentration of electrolytes, such as sodium, to increase in your blood, which would cause seizures and comas."
] |
[
"Can I have that in slightly more simplified English? No sarcasm, just a bit over my head."
] |
[
"Is it possible to have Auditory Hallucinations that are more positive than negative?"
] |
[
false
] |
this might be a dumb question, but has there been any recordings/ examples of people having auditory hallucinations, but they give that person a better outlook in life? all that i've seen are about people having horrible voices telling them to die or say how dumb they are.Thank you
|
[
"This is a bit anecdotal but there was an AMA on here a couple years back by a Schizophrenic who heard auditory hallucinations from 3-4 distinct voices, each with a different personality. One was very evil and demonic, one was a bit more childish and I think the other was friendly. If I recall correctly there would be some positive things said by the non-demonic ones. ",
"It was really interesting, she was fully aware they were just hallucinations, and basically ignored them and lives a fairly normal lifestyle. I'm going to try and find it.",
"Edit:",
"Here's the AMA. It's a really good read!",
"https://www.reddit.com/r/AMA/comments/1uts0g/schizophrenic_female_with_one_visual_and_two/",
"?"
] |
[
"For a good read on the subject I highly recommend Musicophilia by Oliver Sacks. Or for the lazy he has a few YouTube videos where he summarizes parts of his book."
] |
[
"Another example of auditory hallucinations that may be pleasant is musical hallucinations. Some people find them irritating or disruptive, but others may enjoy them.",
"Link that mentions pleasant musical hallucinations in passing: ",
"http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3105559/"
] |
[
"Why was the curiosity rover not landed at the poles where there is clear signs of ice water?"
] |
[
false
] |
Curiosity's main goal in to find out if Mars was ever hospitable to microbial life but is completely ignoring the opportunity to sample ice that may actually have microbial life. Why did they decided on Gale creator?
|
[
"That's a fair question with a few different answers. I am on the MSL science team and a major chunk of my PhD thesis was on Gale as a potential landing site, so I'll do my best to explain. If you want more detail, you can check the blog post I wrote when Gale was selected: ",
"http://blogs.agu.org/martianchronicles/2011/07/22/msl-to-land-at-gale-crater/",
"Or if you really want to get into the nitty-gritty, you can read my monstrous peer-reviewed paper about Gale:",
"http://marsjournal.org/contents/2010/0004/",
"Anyway, the first answer to your question is that MSL just can't land at the poles. Mars has a very thin atmosphere, so it is difficult to land at high elevations because the capsule just can't slow down fast enough. The north polar cap is in the middle of a huge basin, bit it is very tall, so it would be difficult to land there. It is also more difficult to land at the poles than at lower latitudes thanks to orbital dynamics. It takes more rocket fuel to change the spacecraft's trajectory to a polar orbit and land near the poles than it does to just aim for somewhere near the equator.",
"MSL is also limited in terms of the temperatures where it can operate. The motors in the arm and the wheels only work above a certain temperature. Some of the southern sites that were being considered (Eberswalde and Holden) would have been cold enough during the winter that MSL probably would not be able to move. So you can imagine the poles would be even worse.",
"Gale is the best of both worlds: it is a very deep hole in the ground near the equator, which means there is lots of atmosphere to help slow the descent, and it is warm enough to operate year-round.",
"In terms of science, we wanted to send MSL somewhere that was old and had evidence for liquid water and diverse environments. The polar caps are relatively young features, deposited millions instead of billions of years ago. So, they capture some great information about the recent climate of Mars, but they tell us very little about the period of time when it is possible that Mars was habitable.",
"Finally, MSL has a big lump of plutonium as a power source. That plutonium is very warm, which means that MSL will actually heat up the surface beneath it. If MSL landed on an ice cap, it would start melting/subliming the ice underneath it. This would have the potential to form liquid water that could then be contaminated by any earth microbes carried on MSL. NASA has planetary protection guidelines that specify how clean a spacecraft has to be to land in different environments. To be clean enough to land in an environment with liquid water, the entire spacecraft would have to be extremely well sterilized, which is extremely expensive. We can get away with a slightly less pristine spacecraft by going somewhere that is dry under current conditions.",
"I hope this long answer was helpful. If you want more information, another great source is the Marsoweb site, where all of the presentations from the 5 landing site workshop meetings can be downloaded. You'll get more information than you ever wanted about MSL and the landing sites! ",
"http://marsoweb.nas.nasa.gov/landingsites/index.html"
] |
[
"Why would you expect solid ice at less than -60 degrees to have microbial life? Any ice deposits at the poles are from precipitation (i.e., snow), whereas the equatorial target sites all have extensive evidence of ",
" water in the past. Gale crater was chosen for its diversity of aqueous minerals and its extensive stratigraphic section. It had nothing to do with methane, as the top answer claims. "
] |
[
"Someone will be able to fill in the gaps and give you the fine details, but basically Curiosity, from what I understand, is going to be checking out what is going on with the seasonal methane production on Mars which doesn't seem to be coming from the poles. Scientist have deduced it is \"produced\" and not just there because it breaks apart in the atmosphere and would need to be replenished as it lasts at most a few decades. It is a possible sign of life, but even if it isn't it will still be incredibly interesting.",
"Another gas targeted by TLS is methane. This greenhouse gas is a hot topic right now because trace amounts of it have been recently detected on Mars from Earth-bound telescopes. Surprisingly, this methane appears to come and go on a seasonal basis.",
"The TLS instrument should be able to detect methane in the atmosphere at the levels previously observed. And since Curiosity will operate for a full Martian year, the team should also be able to verify if any seasonal variations are occurring.",
"source",
"Hope that helps ;)"
] |
[
"How far away can the Earth's night lights be seen from?"
] |
[
false
] |
I was looking at some videos of Earth from space at night (or since you're in space, I guess it's more about what side of the planet you're on rather than what time of day it is) and I wondered how far these lights can be seen from. Can you still see them when you're halfway to the moon?
|
[
"With the unaided eye? With a telescope?",
"With a shield to block the sunlight or without?"
] |
[
"Can you answer each scenario?"
] |
[
"I can't figure out how luminous the artificial lights of the earth are, so I can't get to a complete answer for you. I will provide the means to answer your question, with the hopes that someone can find this missing piece.",
"I'm going to start with the assumption that either the sun is totally eclipsed by the earth, or that the observer can completely mask out the sun and the observer is viewing the earth from an angle where the lit portion is not visible (like a new moon--we'll call this the \"new earth\"). The reason for this is that the sun is so bright compared to night lights that neither the eye nor any instrument (as far as I know) has the dynamic range to see any night lights next to the overwhelming brightness of the sunlight.",
"An object in the night sky will be visible to the naked eye if it has an apparent magnitude of 6.5 or less (lower numbers mean brighter objects). To calculate apparent magnitude, use the formula m",
" = m",
" - 2.5 * log10( (L",
" / L",
") * (d",
" / d",
")",
" ),",
"where:",
"d",
" = 1.496e11 m / ( 10",
" * (5.493e25 W/L",
"))",
"So now we just need to figure out the visible luminosity of the earth. This is the hardest part, since googling for the luminosity of the earth at night turns up nothing. Help me, reddit!"
] |
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