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[
"What is rayleigh scattering? Why isn't the sky purple or green or yellow? Is the air really blue?"
] |
[
false
] | null |
[
"Rayleigh scattering is the classical scattering of light off of tightly-bound charged particles. The scattering cross section (probability) is proportional to (frequency)",
", which means that higher frequencies are more strongly scattered.",
"That means that when white light travels through air, more of the high frequency part of the spectrum scatters into your eyes.",
"You may ask why the sky isn't violet then, and that's because if you convolve the response of human vision with the distribution of light scattered into your view, the resulting distribution peaks in the blue region. In other words, our vision is more sensitive to blue than violet."
] |
[
"True violet does stimulate our red cones, though. They have a little peak down there. That's why it looks like it's on the way to magenta (red+blue) instead of just a deeper and deeper blue."
] |
[
"Red cones have a small peak in responsiveness down at the blue end of the spectrum. That's the violet we see in a rainbow."
] |
[
"How cheap a space rocket can be made?"
] |
[
false
] | null |
[
"First question is what is your definition of \"space\"?",
"http://en.wikipedia.org/wiki/Outer_space"
] |
[
"You may be interested in ",
"Copenhagen Suborbitals",
", a non-profit which is trying to launch a manned spaceflight above the Karman line on a shoestring budget. I can't find their budget information right, but I believe it was around 100,000 dollars per year."
] |
[
"You can get a weather balloon 'near' space in the outer reaches of our atmosphere for pretty cheap. People do it all the time."
] |
[
"Vacuum Airship?"
] |
[
false
] |
We're familiar with airships using lighter-than-air gas (Hindenburg, Goodyear Blimp, etc). But, if the balloon/ envelope could maintain an airtight rigid structure and have all the air removed from inside (creating a vacuum), would it float as long as the envelope was lighter than the generated lift? Is such a method or such a structure even theoretically possible?
|
[
"Yes, the problem is that the envelope would need to be impossibly light and rigid. A secondary issue would be with such a light material and pressure differential you'd have diffusion of atmosphere into the envelope, so you would need some sort of pump to keep the balloon a vacuum."
] |
[
"In theory yes, the problem lies in the structure of the lighter than air transport. Providing the rigid structure that can resist the air pressure around it ends up weighing more than just filling the balloon with a lighter gas. The helium or hydrogen end up acting as part of the structure resisting the air pressure acting on the outside of the balloon. So it just ends up being cheaper and lighter to fill a balloon with a lifting gas. "
] |
[
"I have considered this often before, and my idea is that you couldn't possibly build or deploy such a machine for near sea level deployment but if you designed it to somehow float at a higher altitude where there is much less pressure you could potentially deploy a cheap high altitude platform. I would suggest using a conventional airship to carry it to high altitude, a rocket that drops from said airship to lift it to deployment altitude, and a mylar based collapsed airship that can be opened with a mechanism similar to an umbrella. Deploy this at apogee (vertical launch, no sideways orbital speed maneuver means a much smaller rocket and much less fuel). If deployed at a high enough altitude you could potentially deploy a long term observatory water you could deploy communications equipment, or telescopes or whatever. "
] |
[
"What specifically keeps viruses from moving from human to animal or vice versa in most cases?"
] |
[
false
] |
It seems like most of the core components are there for mammal to mammal virus transfer, viruses speciality is adaptation, why can’t I get my dog sick and vice versa? thanks!
|
[
"It's very crudely similar to the reason you can't get an organ transplant from your dog despite sharing the same organs. There are certain molecules (mainly proteins) that exist on the surface of animal cells that allow other species to recognise them as foreign. By and large the same ",
" of proteins (we say they are homologous) exist on the surface of your dogs cells and yours but they are sufficiently different that your body will recognise them as \"not mine\".",
"Viruses exploit their hosts by binding to proteins on the surface of cells. Often these proteins are sufficiently different between species that a virus cannot recognise \"Protein X\" in a human, even though it operates by binding to the homologous 'Protein X\" in a dog. However, it is certainly possible for viruses to evolve to recognise both dog ",
" human Protein X. This can happen most easily when humans and populations of sick animals live closely together for long periods of time. It's one of the leading hypotheses of the emergence of covid, HIV and ebola (to name a few high profile but far from comprehensive examples).",
"The viruses don't do this on purpose of course. They're mutating randomly all the time. But if a few virions by chance develop a mutation that makes them less selective wrt the differences between Protein X across species AND they have the opportunity to spread to that new species, they can jump the \"species barrier\" and become a new infectious agent in a new set of hosts."
] |
[
"It's more like covid evolved in its host species to a form where it was able to affect humans.",
"To oversimplify things:",
"Picture a virus as a really funky key. Your cells (animal cells) are covered in funky looking locks. These locks are meant to allow good things in while generally keeping bad stuff out, all throughout your body. When a virus mutates, it is finding a way to spread more efficiently and effectively. One of these methods is by changing binding protein shape to fit more locks.",
"Similar situation with swine flu, avian flu, and many other zoetic viruses. We keep an eye on which animal viruses are getting dangerously close to making the human jump by taking animal cell lines, replacing the receptors (locks from earlier) with human versions, and then seeing if the virus is able to bind and replicate."
] |
[
"Wow first answer is a champion!! So detailed and really makes sense. Thanks so much. ",
"Follow up question, for something like covid. Was it just waiting to find a human with a similar enough protein match to make the jump?"
] |
[
"Similarity between gravity and acceleration"
] |
[
false
] |
I have some understanding that gravity can be explained as the effects of a time gradient. I am wondering if it is possible to also look at acceleration in a similar way. My understanding is that the effects of a gravitational field are very similar to the effects of acceleration. I think I've read if you are in a sealed chamber it's impossible to determine whether you are under constant acceleration or within a gravitational field. When you accelerate, an outside observer sees your clock as getting slower and slower. Therefore could it be said that while you are accelerating you are pushing through a time gradient? Possibly that this time gradient is resisting your change from one velocity to another? I have my doubts and I do know that gravitational time dilation is quite different to relative velocity time dilation. Can anyone set me straight?
|
[
"Okay so let's start with special relativity. If I am moving (uniformly: straight-line, constant speed) relative to you, you will see my length contract along the direction of motion and you will see my time dilate relative to you. All of this happens to make sure that we measure the speed of light to be c.",
"Now let's think about accelerated motion. If I'm accelerating, I'm moving at a speed relative to what I was ",
" moving at. So my new frame measures time and distance differently than the previous frame. So we treat acceleration as a bunch of very small steps in speed that are maintained briefly, and then jump to the next speed. When we stitch together all these short-lived frames, we get a picture that we can call a \"curvature field;\" a continuously varying set of rules for how to make measurements of distance and time as a function of \"where\" I'm at along that path of acceleration. Again: this is all done to make sure that at every point in my motion, I measure the speed of light to be c.",
"So now we get to Einstein's famous \"",
"equivalence principle",
".\" If I'm in an elevator car (with no windows, and too small to feel any tidal effects of gravity) I cannot tell whether the elevator is stationary on the ground, or has a rocket affixed to its bottom accelerating me upwards through empty space at 1g of acceleration. No experiment I perform will notice a difference. Similarly, if I'm floating about in the elevator car, I do not know whether it is free floating far from any source of gravity, or whether it is free-",
" down the shaft. Therefore, the curvature field we derived from considering accelerated frames ",
" of gravity. ",
"A bunch of math follows here that's bloody difficult at best, but the conclusion is that the representation of the curvature field",
" is equal to",
" a representation of energy called the ",
"stress energy tensor",
". Now again remember that so far all we've said is that measurements of space and time must change to accommodate motion, and accelerated motion is physically indistinguishable from gravity so observers in a gravitational field must have these changes in measurements of space and time in order to keep c constant. ",
"The next step is subtle. If we follow the rules of these changes of measurements in space and time to keep c fixed, we can ",
" construct the force of gravity on other things. The logic sounds very circular, but isn't entirely so. Our premise so far is keeping c fixed for all observers, including those under acceleration. So how does gravity come about?",
"Well we take a mathematical representation of a particle's motion, say the ",
"Lagrangian",
", and construct it for a particle ",
". ",
", we construct it in a curved spacetime, one that's obeying the rules we've outlined above that keep c fixed for all observers. And what happens is that the rates of change of motion in various directions ",
" to accommodate this curved spacetime. Out of this force-free initial condition, a potential energy (another, more fundamental way of representing a force) ",
" in the equation. So we start with a set of rules about keeping c fixed and we find that \"free\" motion now becomes gravitational motion. And that gravitational motion affects even massless things like light. And it is a more accurate description of gravitational motion than Newton's F=GMm/r",
" . It gets the orbit of Mercury correct, which Newton does not. It predicts things like black holes. It predicts a gravitational effect of rotation, frame-dragging, that has been measured. It predicts redshifting of light as it loses momentum leaving a gravitational well, even though it maintains the same speed throughout. And so much much more that has all been experimentally confirmed to a remarkable degree over the years."
] |
[
"What do you mean by time gradient?"
] |
[
"There are no tidal forces to due accelerating through space out side of a gravity field so you would not detect the differences there. As far as an elevator on the ground, there is a difference, I am not sure that is has been measured experimentally for the height of an elevator, but I seem to recall differences have been measured at a distance of 10 meters. So, in theory, yes, you could tell the difference in an elevator."
] |
[
"Do electrons, or really any observable object, have compact support?"
] |
[
false
] |
This is a bit of a silly question, but it stems from a silly I read. Much of it seems to me a profound example of the misapplication of mathematics and physics, specifically the idea of a compact support. Anyway, it got me thinking, do the location of objects in the real world have compact support? Since the probability distributions that describe the location of electrons and all other quantum phenomenon probably don't vanish, then it seems that you couldn't say that the location of any total object had compact support in the strict sense. Thoughts?
|
[
"Radial wave functions of electrons for instance vanish as r -> ∞ and r -> 0 so have bounded support.",
"Wait, what? I thought that the radial wave function remains nonzero for arbitrarily large values of r (at least for hydrogen 1s), although they do tend to zero in the limit, so as to remain integrable. But this would mean that the support is both unbounded and not compact."
] |
[
"No, \"vanish at infinity\" is the correct term - it's necessary for a function to vanish at infinity if it's square integrable. But the support isn't bounded, so it can't be compact.",
"Edit: Compact requires closed and bounded."
] |
[
"Right, this is a one-point compactification, where we add a point \"at infinity,\" which then (under the map t --> arctan(t)) fills in the circle - because without it, you'll get the circle minus a point. This then makes the real line look just like a closed interval, so it's compact now.",
"In 2 dimensions, this is just the ",
"Riemann sphere",
"."
] |
[
"Radiation energy can damage DNA. Can any other energy applied to cells damage DNA?"
] |
[
false
] |
Looking for insight into what lifestyle choices can lead to (or avoid) cancer. It seems like cells structures would be safe from kinetic energy at the micro level, or am I wrong? Would Sound energy be an exception to this? Thermal energy damages if high enough, but can constant low-level above-average heat, like 100F lead to more damage over time?
|
[
"Beside what G8r and tisvigil specified, mechanical energy can also damage DNA. Asbestos is one of the example where it causes illness mostly by mechanical means. ",
"As a silicate mineral, asbestos is a member the group of minerals that make up as much as 90% of the earth's crust. It is incredibly common, it is not toxic, but that is one of the reason why it was unexpected. ",
"It is a type of fiber, which is why it is so flexible and so easily woven into many type of composition, but the fibers are not just fine, they are incredibly fine. The ends of the natural fibers taper down to nano-meter sharpness. With a tip that is no more than a few atoms across, it is capable of damaging DNA without killing the cells. In result, when lodged within living and sensitive tissue like lung, will eventually damages some DNA in a way where it will become cancerous. "
] |
[
"Genetic damage due to electromagnetic radiation is an all-or-nothing deal, as a single photon of the radiation has to be sufficiently energetic to break a chemical bond in the DNA chain. Wavelengths longer than visible light, such as infrared, don't have the required energy, and neither do sound waves, unless either is intense enough to mechanically destroy the DNA, which of course would be intense enough to kill you outright.",
"If you're considering lifestyle choices, the ",
"genotoxicity",
" of the chemicals in your environment are a significant determining factor in whether you might eventually get cancer. Awareness and avoidance of major ",
"carcinogens",
" should be high on your to-do list.",
"First and foremost, though, eat healthy and stay fit. That won't prevent all cancer, but it ",
", and vastly improves your prognosis should you ever be diagnosed.",
" Added sermon at the end"
] |
[
"This is actually a chemistry/physics question, so you could try reposting there if you want more answers.",
"Basically you should be concerned about any type of electromagnetic radiation with a ",
"wavelength that is shorter than visible light",
". Shorter wavelength = increasing frequency = more energy = more damage.",
"This means that a lot of radiation, like radio waves, won't damage your DNA."
] |
[
"Will all races and ethnicities eventually interbreed enough to have the same basic phenotypes?"
] |
[
false
] |
Will humanity all one day be the creamy mocha of Tiger Woods or Barack Obama? This is a repost from AskReddit, and I guess I'm looking for a slightly more detailed response.
|
[
"Nope. Let's say (to really simplify things) that skin color is determined by a couple of co-dominant genes: A and B. Someone with aabb alleles will be pure white, someone with AABB will be very dark, while someone with AaBb will be somewhere in the middle.",
"Let's say the aabb person breeds with the AABB person; all their children will be AaBb. So far so good - we're getting more uniform. But if the AaBb person breeds with another AaBb person, a eighth of their kids will be very white (aabb), an eighth will be very dark (AABB), and the rest will be varying shades (Aabb, aaBb, AAbb, aaBB, AaBb, AABb, AaBB). In table form:",
"AABB AABb AaBB AaBb\nAABb AAbb AaBb Aabb\nAaBB AaBb aaBB aaBb\nAaBb Aabb aaBb aabb\n",
"If race isn't being selected for, there's no way that all the genes will eventually get out of the gene pool. Skin color is actually a lot more complex than the above, with lots of different quirks (it's not really a white-black spectrum), but the principle stands.",
" Genes shuffle around instead of blending.",
"Edit: The discussion on these topics isn't as robust as it might be, but similar questions were answered ",
"here",
", ",
"here",
" and ",
"here",
"."
] |
[
"Well if you look at the above example, you start with two populations, one of which is completely white and one completely black. In the first generation, they're all the same mixed skin tone. However, in the second generation, you again have a proper curve of skin tone:",
"Assuming a population of infinite size and random mating, these ratios will stay the same - this is the ",
"Hardy-Weinberg principle",
". So if we make some broad assumptions about the human species, it would be that we'll trend towards everyone having a similar skin tone, but that it'll make a curve of skin tone probability rather than a blending. Note that they ",
" get more probable for a generation or two ... and then they hit equilibrium and stay there, without everyone having the same skin tone."
] |
[
"Well if you look at the above example, you start with two populations, one of which is completely white and one completely black. In the first generation, they're all the same mixed skin tone. However, in the second generation, you again have a proper curve of skin tone:",
"Assuming a population of infinite size and random mating, these ratios will stay the same - this is the ",
"Hardy-Weinberg principle",
". So if we make some broad assumptions about the human species, it would be that we'll trend towards everyone having a similar skin tone, but that it'll make a curve of skin tone probability rather than a blending. Note that they ",
" get more probable for a generation or two ... and then they hit equilibrium and stay there, without everyone having the same skin tone."
] |
[
"If an air bubble is accidentally left in a syringe for a vaccine or any other medicine can it kill me? Or is it rare?"
] |
[
false
] |
EDIT : I have been supplied with answers so thank you people who commented and goodbye EDIT 2 : Wow I didn't expect this post to blow up I woke up and saw my phone was filled with notifications and when I saw why I got extremely happy so thank you!
|
[
"No a simple air bubble won’t kill you, either in the muscle or even in the IV. ",
"If somebody grabs a huge syringe and fill it completely with air and inject it in your veins, it may cause problems. But small air bubbles get commonly injected with no side effects"
] |
[
"For those who, like me, were unfamiliar with these words:",
"An echocardiogram is a way to check out your heart with ultrasound. ",
"A bubble study is a non-invasive technique where they put a handful of small bubbles in your blood and then watch it circulate through your heart, basically to check for holes. Basically, if everything's healthy the bubbles wind up in one place (your lungs), but if there's like a tiny hole somewhere in your heart where it shouldn't be, the bubbles will show up in places they shouldn't be able to get to - the bubbles are important cause they can see and distinguish them with the ultrasound.",
"A \"PFO\", or \"patent foramen ovale,\" is that tiny hole. In this context, patent means unobstructed or open and affording free passage; foramen basically means hole and a foramen ovale is a hole between the upper chambers of your heart that's present during fetal development, but should close. Thus, a patent foramen ovale is what you call it when it never closed up all the way.",
"Of course, if I'm wrong, someone please correct me. I'm just a dude with Google and free time.",
"You know, I knew my heart pumped blood, but for some reason the fact that it was like literally full of blood hadn't occurred to me. For some reason I guess I imagined it was dry inside, which obviously doesn't make sense. Never had reason to really think about the specific operation of it before. Neat."
] |
[
"To add to this, t's actually pretty common to have a couple CC of air in a saline syringe for a bubble study during an echocardiogram to check for a PFO."
] |
[
"Are there any human bloods types that we know of, that no longer exist?"
] |
[
false
] |
Please forgive the grammatical error in the title.
|
[
"Blood decays without a trace quite early in the process of decomposition, well before any fossilization sets in. It would be a stroke of pure luck to find remains even from a few hundred years ago, let alone hundreds of thousands of years on which the bllod type can be determined. "
] |
[
"If you read the article I posted below it goes into the history of blood groups. There's no reason to believe there weren't others, but they were clearly not as successful. Again, blood group is a very artificial classification used to make transfusions easier.",
" none of my posts containing the link are appearing. Google a brief history of blood groups and it's the ncbi link."
] |
[
"Is there any reason to suspect/rule out other types having existed in humans?"
] |
[
"Why do we feel pain near our chest region when we are emotionally hurt?"
] |
[
false
] | null |
[
"Hi, just putting out here, this isn't my native language and I am in no way an expert, so in advance, I apologise if I'm not clear.",
"From what I can mostly recall (and explain in English) from the short time I studied in med school, the pain in the chest region (which I assumed would be the heart) caused by an emotional source is actually due to an overwhelming number of \"information\" (I think the term is stimuli ?). ",
"The brain isn't able to pinpoint where the body is hurting (i.e : there isn't any reason to feel hurt since there isn't a cleat cut for example), then the brain kind of goes into overdrive trying to process it, sending back, in turn, conflicting \"information\" to the rest of the body in trying to protect it from \"harm\". ",
"The pain in the chest area is actually/mostly the heart (see it as an electrical circuit) applying the contradictory information. So it will speed up its rhythm just to really slow it down the next second. The heart being a muscle, can tire and even hurt itself, which can lead to a heartbreak or cardiomyopathy (this isn't a heart attack, they're two very distinct heart failures). On this subject, I would suggest looking up the Takotsubo syndrome (often referred as takotsubo cardiomyopathy or TC in English I think ?). ",
"So for most people experiencing an emotional pain, the brain can't find what's wrong, kind of panics, leading to the heart in turn going crazy in response (to simplify). The emotional pain eventually becoming a physical one. While a minor disturbance in most case, it can be a really damaging one depending on the intensity and medical antecedent."
] |
[
"In some cases, it may be literally due to \"broken heart syndrome.\" Its poorly understood, but surges in stress hormones like adrenaline in very very traumatic events leads to damage/weakening of the heart tissue which in turn leads to angina. I have seen a few cases in my career on cardiac MRI."
] |
[
"Thank you. This was very informative."
] |
[
"What physiological adaptations would best suit fictional humanoids living in an arctic climate?"
] |
[
false
] | null |
[
"Two things I'd suggest, an increase in volume relative to surface area, a more carnivorous diet."
] |
[
"Just at the inuit: more adipose tissue, a larger liver for gluconeogenisis, adapted to a diet consisting out of mostly animal fats, etc."
] |
[
"Sure, short and fat doesn't necessarily specify a particular size. They're relative measures. Since you're overlooking the square-cube law, I suppose you could scale a human up to achieve this goal rather than shorten/fatten one, however at that point you're pretty much dispensing with the science anyway."
] |
[
"Why don't potential Mars settlers simply wear heavy suits to increase gravity's effects?"
] |
[
false
] |
Hello all, The problems associated with lower gravity both in orbit around earth and long term settlements on mars are huge for the human body. Whilst i understand why a suit wouldn't work in orbit, would a heavy suit work on mars? For example, giving an 11 Stone (on earth) Human a suit weighing ~18 stone (on earth) whilst on mars could keep the same force applied to the person's muscles downwards. The suit could be taken off temporarily to perform any needed other functions, of course.
|
[
"if someone stays in microgravity for too long",
"Right, but Mars does not have microgravity (near-zero g). We do not know what the effects of living in Martian gravity (0.38 g) are, because it has never been tested on humans. It may be that with regular exercise, the health risk is minimal, and they may even be able to return to Earth and readjust to the high gravity after years on Mars. We won't know until we've tried it."
] |
[
"It's not clear what the effects of prolonged exposure to Martian gravity would be. Microgravity is clearly problematic for human physiology, but some think that low gravity could be just fine, or have minimal negative effects. We'll have to see. Your idea is one way of dealing with it if it becomes problematic."
] |
[
"There's no evidence that exposure to Martian gravity causes heart atrophy, or anything else. As I said, it hasn't been tested."
] |
[
"Idea from r/highdeas"
] |
[
false
] | null |
[
"I don't get it?"
] |
[
"Because it's been removed. I'm saying there are none."
] |
[
"I had a feeling that's what you meant. If I submitted the same thing without mentioning highdeas would you of left it up?"
] |
[
"Why do we define the point of no return from a black hole (Schwartzchild radius) with a speed, instead of total energy required?"
] |
[
false
] |
I've asked this several times, but never got a reasonable answer. Why is speed used to define the point of no return for black holes? Escape velocity is a concept thus: the speed at which you have to go to escape a gravity well . On earth, for instance, we can escape Earth's surface by never actually reaching or exceeding the escape velocity : you just need enough kinetic energy at the surface to get farther away (and that speed is far lower than the escape velocity); the farther you go, the lower the escape velocity gets. To really completely escape, at some point you do have to exceed the escape velocity, but that velocity keeps getting lower the farther you go. So you can push yourself beyond the moon, and then at some point your speed is greater than the escape velocity, and boop! you've escaped. It seems like escape from a normal gravity well is a question of energy to overcome the gravitational potential, not just instantaneous speed when you start to leave. BUT with black holes, all we ever talk about is the Schwartzchild radius, which is only defined by speed. Why? I don't see a reason why a sufficiently powerful spacecraft with huge thust just inside the SR, couldn't push enough to move slightly outside the SR, given a significantly large black hole.
|
[
"In general relativity, the curvature of spacetime sort of flips when you cross the horizon. Space becomes timelike and time becomes spacelike. A consequence of this is that the only paths through spacetime are towards the center. Moving away from it is equivalent to going back in time. This is independent of the fact that the escape velocity on the surface is light speed."
] |
[
"Contrary to popular belief, the Schwarzschild radius is ",
" defined by speed. It just happens to ",
" the distance at which a calculation of Newtonian escape velocity predicts that a value of c. ",
", the Schwarzschild radius is the value of Schwarzschild coördinate \"r\" (which can be interpreted as radial distance) at which there is a coördinate singularity in the Schwarzschild metric; this value of \"r\" corresponds to the location of the event horizon as seen by an observer very far from the black hole."
] |
[
"and close to the horizon, is it still defined?",
"where can I read more on this?"
] |
[
"Have we physically measured time dilation in a real time experiment before?"
] |
[
false
] | null |
[
"Yes, there have been experiments with planes carrying highly accurate atomic clocks being flown around. Upon arrival, the difference in time on the onboard clock and the ground clock matched what was predicted.",
"In addition, satellites that have highly time-sensitive functions are being corrected for the effects of time dilation. An example would be the GPS satellites. GPS is as accurate as it is because the time dilation experienced by these satellites is very close to the amount of correction being applied."
] |
[
"This guy",
" loaded a few atomic clocks into his minivan, brought them on a camping trip into the mountains, and successfully measured the slight difference gravitational time dilation caused by being at a higher elevation than another atomic clock back at home."
] |
[
"As is often alluded to, GPS satellites need to make regular corrections to account for both general relativistic (the large effect) and special relativistic effects like so:",
"https://upload.wikimedia.org/wikipedia/commons/3/36/Orbit_times.svg"
] |
[
"[Biology] Is it theoretically possible to clone someone from their own gamete cells?"
] |
[
false
] |
Cloning is generically described in lay terms as taking a cell from a living organism and then using its DNA to create an identical copy of that organism. My question is, can a gamete (someone's own sperm or egg cell) be used to clone a person, or do gametes have "incomplete" DNA relative to any other cell in the person's body?
|
[
"Not a clone, but you could duplicate each of the chromosomes to create a diploid cell, and that would work to create a single-parent organism. It would have to be a female, of course, since you'd need either XX or XY, and XX is the only one of those that can be done by duplication."
] |
[
"A gamete contains only 1/2 of an individual's genome. You have two sets of chromosomes: one from you father, one from your mother. The processes of ",
"meiosis",
" and ",
"genetic recombination",
" produces gametes that contain only one set of chromosomes. However, each chromosome in a particular gamete is a mixture of the two you inherited from your parents."
] |
[
"Thank you. So does this mean that an egg, but not a sperm, could be turned into a complete organism? "
] |
[
"What kind of stuff actually affects our immune system (in a good or bad way)?"
] |
[
false
] |
[deleted]
|
[
"Stuff that effects your immune system:",
"Sun exposure, burns",
"Sleep deprivation or interruption of circadian rythms",
"Acute cold exposure",
"Vitamin D deficiency",
"Here's an interesting one that is emerging: ",
"Acupuncture",
" can impact specific parts of your immune system such as increasing certain types of antibodies after stress along with positive immune effects in some autoimmune diseases. There needs to be more study on this, but the information out there does look promising."
] |
[
"I don't know about cold, but I'm fairly sure stress supresses/reduces immune responses. Cortisol and other stress hormones do suppress the immune system- that's why you see anti-inflammatory drugs with cortisone in them."
] |
[
"Another thing that really appears to weaken the immune system is sleep deprivation."
] |
[
"Is there a way we could take a picture of the Milky Way by sending something like the HST \"up\" the galactic plane for a few decades and have it take pictures?"
] |
[
false
] | null |
[
"Hi, I'd repost this on ",
"/r/AskScienceDiscussion",
"."
] |
[
"Will do so in a moment.",
"\nThanks.",
"\n",
"EDIT: Done."
] |
[
"Cool, looks good. I'd also look into why it's harder to launch something perpendicular to the plane of rotation for the solar system. "
] |
[
"Why are super-clusters the largest objects in the observable Universe?"
] |
[
false
] |
After recently watching a video about the Laniakea supercluster, a question arose about what prevents super-clusters from forming ever larger structures. Why for instance don't they form into spirals or discs made up of many super-clusters? Is it simply that the distances involved are too great? Any insights are much appreciated!
|
[
"Essentially, because 1) the universe hasn't had time and 2) the universe is flying apart rather rapidly, which makes it harder for structure to grow indefinitely. ",
"If you had a static (meaning neither expanding nor contracting), infinite universe with a fairly smooth density distribution, then yes, you would expect structure to continue growing over time. However you would not expect gravitationally bound structures to have gotten very far beyond the supercluster scale, since the age of the universe is a pretty serious limiting factor. In reality, of course, our universe is not just expanding but expanding faster and faster, so it's getting pretty late in the game for large-scale structure to be really growing. Even the Great Attractor is actually receding from us. The matter in our supercluster will never all collect in the same place, we're receding too fast. The diagrams only represent the deviations in galaxies velocities from the Hubble Law (i.e., the change in their motion due to the tug from other matter). For most of our supercluster, the Great Attractor is only causing a moderate decrease in the rate at which the galaxies are flying apart."
] |
[
"It doesn't really look like the Big Rip is going to happen. It's only going to happen if dark energy happens to be of a variety called ",
"quintessence",
", and at present there's nothing to indicate that that's the case."
] |
[
"Structures that can be thought as larger than superclusters do exist; see for example the great walls such as the ",
"Sloan great wall",
", structures observed by galaxy survays that span appreciable fractions of the observable universe. These structures are thought to form inside 'filaments' of dark matter which are observed to form in simulations starting from an initial conditions similar to those corresponding to the CMB taking into account cosmic expansion.",
"At very large scales the universe is thought to be fairly uniform; in time cosmic expansion will separate large structures further and further away, until - in the distant future - only gravitationally bound structures will exist separated by enormous expanses of empty space. Unless the nature of cosmic expansion itself displays additional dynamics noticable only at timescales much greater than the current age of the universe."
] |
[
"Why does glass appear transparent?"
] |
[
false
] |
It's made from solid matter and even when very thick appears clear. What's the transparent property? And do other animals also see it as transparent?
|
[
"https://www.youtube.com/watch?v=Omr0JNyDBI0",
" this video will answer your question. apparently it has to do with how the atoms (and therefor the electrons) are arranged. ",
"There are lots of cool physics videos on this channel."
] |
[
"To add, glass is NOT transparent to non-visible light, specifically ultraviolet light. That's why you can't get a suntan through a window."
] |
[
"From ",
"Cancer Research UK",
":",
"People often think that glass windows protect us from sunburn and skin damage. Although most glass windows do offer some protection, they are definitely not completely sun proof. So we would not advise that you think of them as sun protection.",
"Most glass used for windows blocks UVB but not UVA. This means that although glass might reduce the risk of sunburn, it does not prevent long term damage from UVA. So, if you are driving long distances or sitting in your conservatory every day for long periods of time, you need to make sure you are using sun protection on sunny days."
] |
[
"What does the orbit of Earth look like?"
] |
[
false
] |
I know this depends on what it's relative to, but I'm still having trouble picturing it. What I'm looking for is how it travels relative to the universe as a whole, just the plane of the solar system, and just the Sun. Relative to the Sun does it go around in circles or does it make more of a flower pattern? Does the Sun stay in the same spot compared to the solar system or does it wobble?
|
[
"The Earth's revolution around the sun is described as an ellipse. This is a shape very similar to an oval.\nThe Sun's revolution around the Milky Way is also elliptical (roughly). Therefore, the earth's revolution around the Milky Way is a kind of spiral-flower shape."
] |
[
"Nearly. The orientation of the ellipse rotates very slowly, once every 112,000 years. This is called ",
"apsidal precession",
"."
] |
[
"Does the ellipse come back to the same point relative to the Sun every time?"
] |
[
"What is the best way to divide up voting districts?"
] |
[
false
] |
Is there a formula that is agreed upon by mathematicians to be the most fair way to divide up voting districts?
|
[
"Like any question relating to optimization, you would have to first define \"fair\". It's not generally agreed upon what a \"fair\" voting district would even look like. Is it based on closest geographic proximity? Similar income levels? 50/50 distribution of some kind of political leaning? School districts? Distance to nearest waffle house?",
"After you define what \"fair\" means, there is a field of ",
"clustering algorithms",
" that will accomplish what you want. In particular there are ",
"graph partitioning",
" problems; I use these to break up discrete domains into nearly-equal segments in order to parallelize computations.",
"Edit: I have no opinion on voting districts, and ",
"/r/askscience",
" isn't the place for political debate, I was merely answering the question in the spirit of graph partitioning =)"
] |
[
"I'm sure you know this, but for the rest of the folks out there, this system is in place in many democracies. It's called proportional representation, and it has its own set of problems.",
"First, there's no filtering. What if a joke slate of Morning Radio Hosts get 2% of votes? Should they really get 2% of the seats?",
"Second, there's the problem of candidate selection. Imagine we amend the Constitution and switch the U.S. House of Representatives proportional representation. In the next election, the Libertarian party gets 11% of votes, entitling them to, say, 47 seats in the U.S. House of Representatives. Now the important question: Which 47 Libertarians get to sit in those seats? In places that use this system, this is usually decided by the party leadership creating an ordered list: the first 47 people on that list get the seats. But ",
" didn't vote on who those people would be.",
"Third, there's no voting ",
". In the example above, what if you ",
" person 12 because you know he's an evil Raxacoricofallapatorian hell-bent on galctic domination. But you like the rest of the top 50. There's no chance to vote ",
" someone.",
"Fourth, you have no one to call in government. When you live in a district, you can call ",
" congressperson to express your views and encouragements. And she's much more likely to care about your opinion than some random jack who owes more to his party leader than the voters of West Bumblebee, Iowa.",
"Finally, majorities. When no one party gets over 50%, there's no clear choice of who gets to govern. Parties have to negotiate and divvy up ministries and jobs among themselves to \"form a government.\" Multiple parties vie to be in a \"coalition\" with the top vote-getters so their leadership can get the job as foreign minister or whatnot. Your vote for who should be in charge can end up mattering less than the parties' post-election horse-trading.",
"There are procedural ways of dealing with these problems. ",
"Germany's electoral system",
" does a notably good job of addressing these concerns. I'm a huge fan, in fact. But it's not perfect. None of these systems can be since they all involve trade-offs."
] |
[
"Wouldn't it be good to just make a single district and give the parties seats according to the rate they got votes? So with 45% of the votes you'd get 45% of the seats."
] |
[
"Do the yearly flu vaccines vaccinate against the latest version of H and N according to the virus's antigenic drift, or the virsus's antigenic shift?"
] |
[
false
] |
I've been reading about the difference between antigenic shift and antigenic drift (I think I understand the difference) in regards to flu vaccines but can't find an answer to this question. Does a flu vaccine have an H1N1 (or any other combinations of H and N, just using H1N1 for an example) flu virus with a specific hemoglutenin 1 protein, and also an H1N1 with another specific H1 that has a gene sequence for the H1 which is slightly different than the other but is still considered an H1 (an H1 that has undergone antigenic drift)? For example a trivalent vaccine with 3 slightly different versions of H1N1, each with an H1 and N1 that has enough antigenic drift difference from the others that the protein is shaped differently but is still an H1 or an N1. Or would a typical trivalent vaccine have 3 different flu strains with different combinations of H and N subunits? For example a vaccine with H1N1, H2N2, H3N3 as the three different strains. Or are the vaccines some combination of these two?
|
[
"Minor point, the seasonal vaccines aren't made by reverse genetics; they still use classical reassortment. It's a regulatory/patent thing."
] |
[
"Keep in mind that the trivalent flu vaccine is made up of different strains that are predicted to be circulating throughout the population in the coming flu season, so it's not always representative of what you might actually be exposed to. The Trivalent Influenza Vaccina (TIV) is the injectable form of the vaccine consisting of killed flu virus containing two Influenza A strains, as well as one Influenza B strain, but in the future I believe they'll be including another flu B, to make the vaccine quadrivalent. The Live Attenuated Influenza Vaccine (LAIV) or \"FluMist\", is already quadrivalent.",
"As for your question, the HA (hemagglutinin) or NA (neuraminidase) proteins obviously differ between the strains that are used in each version of the vaccine, but it doesn't really matter whether these proteins are drifted or shifted, since the strains included are predicted from those already circulating in the southern hemisphere. Those particular strains have been sequenced and their HA and NA subtypes are known. Using a reverse genetics approach, the viruses for the vaccine can be produced ",
" with a different influenza backbone, but will still include the HA or NA proteins from the strains predicted to be circulating. Generally there is a combination of HA and NA subtypes, like H1N1, or H5N1 - something like that, though again it depends on what's been predicted to circulate. Hope that helps, but feel free to ask if you need clarification."
] |
[
"ah cool, thanks for the info!"
] |
[
"If you gather up all the asteroids in our solar system, flung them somehow to a galaxy far, far away ... Would there be a noticeable impact on the orbits of planets or their moons in our solar system?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"It is hypothetical or speculative in nature. We do not allow hypothetical questions because questions that cannot be confidently answered with any available data often invite non-scientific speculation. For more information regarding this and similar issues, please see our ",
"guidelines.",
"A good home for this question is our sister subreddit ",
"/r/AskScienceDiscussion",
" because of its open-ended or speculative nature. Please feel free to repost there!",
"Please see our ",
"guidelines.",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"Physics"
] |
[
"Physics"
] |
[
"If one were to bring an open mason jar into the deep ocean and place an animal suited to a high pressure environment into it, what happens to the creature? What happens when you close the mason jar with the creature inside of it? What happens if you bring that jar to the surface?"
] |
[
false
] |
Assuming the mason jar is indestructible. Sorry if this has been asked before, but I've searched and I couldn't find it. Sorry I couldn't word it more eloquently, and I'm sorry if I missed any typos, I'm on mobile. Edit: Thank you guys for answering. Honestly, I don't know why the answer wasn't obvious based on what I'd already known, and now I feel a bit silly. Either way, thank you again for answering my question!! Merry Christmas and have a happy New Year!
|
[
"No, not if the jar was indestructible as you say. The bubbles would form when the jar was opened releasing the pressure.",
"A real jar would of course stretch a little as the pressure around it reduces, and might even shatter at some point."
] |
[
"Nothing much. The creature will not explode as long as the jar is able to withstand the pressure. How long it will live, depends on the relative size of the creature and jar, and how careful you are about not exposing it to light. Eventually it'll run out of oxygen and die."
] |
[
"The pressure increases as you descend, and the water in the jar being exposed has the same pressure as the surrounding water because it has the same weight of water above it pushing down on it. Then if you were to scoop a passing creature in to the jar and close the lid the same pressure would remain, because as you ascend, it cannot expand due to the lid being closed and the jar being so strong. The creature would be fine (in terms of pressure but maybe not oxygen etc if it required it) until you opened the lid. At which point it would likely die, but depends on its physiology."
] |
[
"When the surface of a body of water freezes, what is preventing the water beneath the ice from freezing too?"
] |
[
false
] | null |
[
"Heat transfer through water can proceed through two mechanisms. One is diffusion, where the kinetic energy from one molecule transfers to its neighbors through random collisions. While the molecules collide enough that diffusion from one molecule to the next is pretty fast, this transfer becomes slower and slower as you work on larger and larger scales.",
"The other mechanism is convection. Since water is a fluid, you can have large currents of water moving molecules up or down in the lake or pond even when the net flow is zero. Convection currents are hard to model but are driven by density fluctuations (because of temperature), gravity, and inertia. Convection is much more efficient than diffusion on almost any length scale you would worry about.",
"Once the water freezes at the top of the lake, the ice will stay in place since it floats. In a solid there are no convective flows, so heat transfer is only going to take place by diffusion. The diffusion in ice is a little faster than diffusion in water, but it is still slower than convection in water. So when the air gets very cold, ice will form on the surface relatively quickly. But the thicker the ice gets, the more slowly heat will be able to leave the water underneath. The ice is essentially insulating the water more and more as it gets thicker. Since the rate of ice growth is proportional to the rate of heat transfer, it takes about four times as long to form an ice layer twice as thick. "
] |
[
"I'm going to answer a very similar and related question in hopes that it'll give you the information you were looking for: why does the water on top freeze first? Ice is less dense than water (a very unique property that most substances dont have) this allows any ice crystals that form to float to the top, also most of the time water is losing its heat energy to the air above it causing the top layer to cool first bus freezing on top. To answer your question more directly nothing is stopping the water below the ice layer on top to freeze other than the fact that the top layer will freeze first."
] |
[
"Basically, the earth has a fairly regular temperature. If you're out camping and it's 75 degrees out, the ground beneath you will be around 60. That's why you never want to sleep on open ground, it will suck up your body heat and never actually warm up. ",
"Because of this, most of the energy lost in a body of water is to the surface, and once the surface has a layer of ice the air can no longer directly affect the water beneath it, so every drop in temperature has to either go through the layer of ice which is a slow process. OR through the ground which is an even slower process. Basically in order to freeze all the way through a lake has to be pretty shallow, or be in really cold weather for a long time."
] |
[
"Does the uncertainty principle just pertain to velocity and position, or are there other \"quality pairs\" that it stops us from getting perfectly?"
] |
[
false
] | null |
[
"There is a ",
"generalized uncertainty principle",
" which gives the lower bound on the product of the variances of two observables in terms of their commutator.",
"Any two observables whose operators don't commute obey a similar uncertainty relation.",
"This includes position and its conjugate momentum, one component of an angular momentum with another, etc."
] |
[
"Observable quantities are represented by Hermitian operators. You can think of them as matrices.",
"When you multiply two matrices, A and B, their product in one order",
"AB",
"is not necessarily equal to their product in the other order",
"BA.",
"If these were numbers, obviously these would be equal to each other. Because multiplication of numbers has the commutative property.",
"But multiplication of matrices does not have this property.",
"You can define something called the ",
":",
"[A,B] = AB - BA.",
"If AB is the same as BA, then these matrices commute, and their commutator is zero. Then that means that these observables do not have a minimum uncertainty product.",
"However if [A,B] is not zero, then they do."
] |
[
"Can I get a tl;dr on what commute means?"
] |
[
"Is there any possible way of generating electricity on a large scale from algae-produced adenosine triphosphate (ATP)?"
] |
[
false
] |
For example, is there a way that we could get a bunch of green algae massed in a bucket (the size of a nuclear power plant cooling tower) and harvest ATP from their chloroplasts? If it were possible to get energy in the form of electricity from the phosphate groups leaving adenosine triphosphate (ATP), how much green algae or plant material would you need to produce, let's say 1kW? Is there another ATP-producing organism that would be more effective?
|
[
"Realize that the energy coming from Algae (well, actually nearly all energy short of geo-thermal and nuclear) is really solar energy.",
"So the question really becomes, is Algae more efficient / cheaper than solar panels for a given surface area. ",
"For the specifics, I don't know.... but it is a more accurate way of viewing the question. I'm sure you ",
" generate electricity on a large scale from algae, however the problem is efficiency / cost. "
] |
[
"ATP is unstable outside of a cell. It's present in low concentrations and gets used up fairly quickly. There's not a significant store of ATP (in terms of concentration) in the cell. You'd be better off trying to get energy from the electron carriers (NAD+/NADH), but even those are transient. The compounds that are stable enough to be extracted and are present in significant concentrations are all energy storage compounds that we already target like sugars, lipids and proteins.",
"Some numbers on ATP storage/usage in humans:\n",
"http://en.wikipedia.org/wiki/Adenosine_triphosphate#ATP_recycling"
] |
[
"This is a different approach compared to what I would consider. Its not by extracting the ATP or the NAD+/H that you would best harvest the energy from these molecules. I was picturing the use of shuttles or transporters or something that drove an electric current. You could hook this up to a circuit made of graphene or whatever the materials science of the day was.",
"My go to would be to use bioengineering to fuse characteristics of an electric eel cell with a photosynthetic organism."
] |
[
"How do trees know it's time to prepare for winter?"
] |
[
false
] |
While strolling across a yellowish-orangish-reddish park recently, I was wondering how do the trees "know" it's Fall already and it is high time to drop the leaves and prepare for winter? Is it simply connected with the temperature or is the mechanism behind that much more complex?
|
[
"Plants can sense ",
"photoperiods",
". They balanced the expression of several genes that counteract each other in the light and dark. As the days get shorter they express more of the dark genes which are able to overwhelm the light genes.",
"In a lot of plants, they modify their genome packaging to wait for summer. Then when the temperature rises they unpackage their springtime genes."
] |
[
"This is also a problem for herbaceous plants and seeds underground that want to grow in the spring. The idea is that after the plant shuts down based on day length it unlocks some genes that will respond to warm temperatures. Coupling these two mechanisms lets the plant be sure that it is only unlocking these genes when the temperatures are lower as the days are shorter (and it won't flower in the fall).",
"Now that the genes have unlocked the plant will only activate them when it senses sustained warm temperatures. After it expresses the genes with warm temperatures it will lock them back up and wait for short days to unlock them again. In many plants, this is called ",
"vernalization",
". There is some nuance in what people call it based on the behavior of the plant (I think the tree people refer to it as dormancy), but I am not a plant physiologist and am very under-educated in the nuance here.",
"There is also a lot of variation in how exactly the plant times this, as they are often evolved for a specific location."
] |
[
"I've never though of it in terms of a process like photoperiodism and gene balance. Thank you for the reply!"
] |
[
"During brain formation in a foetus, what makes each part of the brain different ? Is it a specific neurones organisation ? Why for example speech ability is always located at the same place for each individual ?"
] |
[
false
] | null |
[
"The the identity of different areas (for example, visual, auditory, motor, sensory) is established during the formation of the brain by diffusible proteins that form gradients from high concentration to low concentration over the length and width of the brain. ",
"Essentially, there are different molecules secreted by each of four poles of the brain (front-center, back-center, front-outside, back-outside), and a cell can read its position based on the concentration of the secreted molecules in its environment; see ",
"this graphic",
" for more details.",
"Based on the concentration of secreted molecules in its environment, the cell goes on to express different amounts of identity-determining genes, and area specialization continues for about two weeks in mice (and longer in humans)."
] |
[
"Thanks this is useful ! But then how are these differences expressed at cellular level, I mean what physically differentiate the bunch of neurones in the olfactory area than an other bunch of neurones in the audition area ? What are the physical effects on brain cells nature and structure of the presence of several chemical gradients during brain growth ?"
] |
[
"This was a very good question and a great response. He just explained the physical effects on brain cells structure during the presence of these chemicals. These molecules activate transcription factors which literally give direction to neurons as they grow, and thats how the matter accumulates. These transcription factors though, are based off of genes and the modification of those genes by epigenetic factors. These genes are very specific, and encode the olfactory area within a specific neurohormone that can only be used once the chemicals have reached the proper destination. At a cellular level once the brain is developed and even during development, its simple difference in histology that differentiates where the next group of direction-giving chemicals will travel.",
"These chemicals can detect difference in histology, and give direction for growth and thats how these regions grow to be different."
] |
[
"How do particle detectors work? What do quarks look like on on such a device?"
] |
[
false
] |
[deleted]
|
[
"iorgfeflkd describes the ",
"bubble chamber",
" and the ",
"cloud chamber",
", which were some of the first particle detectors. With them, we discovered particles that revolutionized our understanding of everything, such as the ",
"positron",
" (first antimatter particle we found).",
"Nowadays, most of the particle detectors used at large particle accelerators like the ",
"Tevatron",
" and the LHC come in one of three flavors, as far as I know.",
"The first is the ",
"silicon tracker",
". When a high energy particle goes through a doped silicon strip, some energy is deposited in the silicon, which is read out by electronics. (Unfortunately, this is as detailed as my understanding goes in this area.)",
"Secondly, some ",
"calorimeters",
" make the particles go through massive materials that they'll strongly interact with, like iron or lead. This produces collisions, which create secondary particles that can be picked up by sensors and silicon trackers.",
"The third way I know of is the ",
"muon",
" drift chamber. The ATLAS experiment at the LHC, especially, uses these in the outermost layer of the detector. It's pretty much a long pipe with a wire running through the middle of it, lengthwise. The pipe is filled with a gas, and the wire is slightly positively charged. (The gas might be argon? I forget.) When a muon goes through the pipe, it will smack into the atoms of the gas and ionize it. The freed electrons will be attracted to the wire and will go to it, producing a signal you can pick up at either end of the wire. ",
"How do we tell what's what? These detectors tend to be immersed in a known magnetic field produced by a giant magnet, so charged particle tracks curve, much as you've seen in the bubble chamber. (Much larger curves, though, for the much higher energy particles we're producing today.) Because of how the magnetic force works, the radius of curvature is directly related to the charge/mass ratio, which makes it pretty easy to pick out energetic charged particles, tell what they are, and tell how much energy they have.",
"Sometimes, we don't care what each individual particle is, because they spray out in a jet. This mostly applies to hadronic matter like quarks and gluons, because they spray out in jets due to the peculiarities of the strong force. What we care about is the total amount of energy in the jet. By reconstructing the event and accounting for all the energy and momenta, and with our knowledge of particle physics, we can turn the clock back and figure out what fleeting, ephemeral particles we created in the collision.",
"I recommend the ",
"ATLAS experiment website",
" for awesome images of what it all looks like when we run it through tons of computers and reconstruct what happened. There's also some pretty cool videos there that explain stuff about particle accelerators.",
"Aside from what goes on in our biggest budget particle accelerators, there's also some really awesome work being done in neutrino physics. ",
"Neutrinos",
" have extremely little mass and they very very rarely interact with anything. Trying to detect them really sucks - it used to be that the only way we knew they existed was that we were missing some energy and momentum in one direction, when we accounted for everything else.",
"Ingenious experimentalists have found ways though, such as putting a gigantic piece of steel in their way and detecting the products of their collisions with scintillators, which light up when a particle hits them (the ",
"MINOS",
" experiment) or putting a large tank of some chemical in their way and detecting collisions. Of course, the collisions are still very rare, but they can be detected.",
"Super-Kamiokande",
" is one of the latter type of experiments. It's a gigantic tank filled with ultra-pure water and lined on its surface with a large array of photomultiplier tubes, which amplify signals from individual photons. If a neutrino comes in and interacts with the water, sometimes an electron will be ejected at speeds that are faster than the speed of light in the water (which is slower than the speed of light in vacuum, which is the fastest possible speed, if you were wondering). The electron then emits a ring of ",
"Cherenkov radiation",
", which is pretty much the light-equivalent of a sonic boom, and those photons are picked up by the photomultiplier tubes. ",
"Fing awesome."
] |
[
"We never actually see quarks on their own. They are always in groups of two (mesons) or three (baryons). This is because it costs more energy to separate quarks than to create two new ones out of the vacuum. So, if you ever did manage to separate two quarks, new ones would quickly be created for them to buddy up with. ",
"Because of this we can only see the result of quark decays. When two particles hit each other at very high energies they very briefly form a bunch of quarks, and then these quarks ",
", which is to say they quickly buddy up to form mesons or baryons. The result of the collsions looks ",
"pretty messy",
" in a detector. Each one of those lines is the path of a particle that's been reconstructed from the collision. This takes an immense amount of modelling and computation. The program that does this is called ",
"PYTHIA",
".",
"You might wonder if we've never seen a quark, why do we believe they exist? Quarks were mathematically predicted by Gell-Mann, but the observational verification came from the ",
"Fields-Feynman parton model",
". The idea was that if a baryon (like a proton) is made of three quarks, then we should be able to detect the point-like scattering of three object inside of the proton. The Fields-Feyman model included something called form factors that allowed experimenters to determine that there are indeed three pointlike objects inside baryons and that they had the properties of Gell-Mann's quarks. "
] |
[
"Basically there's a cloud of gas or bubbles, that undergo a phase change when a particle goes past them (for instance, going from liquid to gas). By following the path of the phase changes, you can see various particles. If you put the whole thing in a magnetic field, charged particles start going in circles, so you can learn about the properties of the particles by the circles.",
"Here's what an image might look like"
] |
[
"How does the instant frozen beer/water trick work? Is the liquid below the freezing temperature and if it is why is it not solid?"
] |
[
false
] |
There are loads of Youtube videos of this trick but I wasn't sure if Ask Science had to be self posts.
|
[
"First for the Askscience rule- they have to be self-posts but you can put the links in your description. ",
"Now, for the science. The process you are seeing is called ",
"supercooling",
" and it arises because of a somewhat complex scenario which I will do my best to describe. First, yes, supercooled water is well below freezing temperature. So why isn't it frozen? Well, the reason water freezes in the first place is because of the principle that matter will generally try to go into the lowest energy state available to it. It turns out that above 0 C (32 F) it is a lower energy state for water to be a solid than a liquid, so there is freezes. But while freezing is a lower energy state, staying as a liquid is locally, a lower energy state. ",
"The best way I know to explain this is imagining a rollercoaster. So a rollercoaster will always want to, in general, head down hill. But imagine that you're on a rollercoaster that is heading downhill, then there is a small bump before it goes down further. If the rollercoaster has enough speed, it will roll down, pop over the bump, and then back down. That is what water does when it freezes. But when water supercools, in is in a state where it doesn't have enough speed, so it goes down, and then can't crest the hill in order to make it over the bump. Basically, it takes a little energy for water to move from liquid to solid. ",
"Where does this energy come from normally? Well, normally it comes from one of two sources. Either a.) actual physical motion. As it is cooling down, it gets moved about a little bit, which gives a molecule enough energy to hop over that bump. Or b.) you cool down the water fast enough that it doesn't all cool uniformly, so there is some cold water ready to freeze, and then some water a little hotter, which can transfer energy to a colder water molecule, bumping it over the edge. This first bit of ice that forms is called the nucleus of the ice, and once it forms, then the ice will spread very rapidly, as it gives a nice, easy path for the rest of the water to enter into the solid state. Going back to the rollercoaster, the nucleus of the ice is like the first cart getting over the bump, and then it can pull the rest of the carts across the hill. ",
"When water is supercooled, it is cooled slowly so all of the water reaches the same temperature at the same time, and it is cooled in a way where it isn't shaking/moving. So then, no ice nucleus can form. But as soon as you impart a little energy, bumping it, etc- suddenly some of the water will get enough energy to hop over that bump, form a nucleus, and freeze. The rest happens so quickly because all of the water is cold enough to freeze, it was just waiting for the little push it needed. "
] |
[
"If you get distilled water in a perfectly scratch-free glass, there's no nucleus for ice crystals to form around."
] |
[
"Thank you, got it now."
] |
[
"Why are there diamond patterns on the beach?"
] |
[
false
] |
I was at the ocean shores beach and noticed some diamond patterns in the sand. . What's the deal?
|
[
"That occurs when you have wave energy coming in from two different directions. Typically, these two directions are when waves wash up onto the beach at an angle, and then wash back into the ocean.",
"See this as another example"
] |
[
"From these papers (",
"one",
", ",
"two",
") it sounds like they are a flow effect and are not related to the waves hitting the beach other than that the waves are what set up the thin sheets of backflowing water where the flow instabilities that create the pattern occur."
] |
[
"Yep, that's my understanding of it - it requires backwash in a different direction than the uprush. This ",
" happen if you do indeed have waves coming in at different angles... but that's only a rare exception to the rule and any such ripples formed in such a location will not last long. It was just easier to talk about \"wave energy' in general terms than to break it down into different types of swash.",
"Regardless, you ",
" need some sort of angle involved in the waves hitting the beach."
] |
[
"What's the deal with \"i\", as in imaginary numbers?"
] |
[
false
] |
Besides finding the square root of a negative, what can you do with i?
|
[
"In physics, imaginary/complex numbers, especially in their exponential form, eg. e",
", are very useful for describing waves and oscillations, because they make the algebra much easier. When finding the speed of an oscillation, you needn't mess around with cosines and sines when you can use complex-exponentials."
] |
[
"The main use I've seen for imaginary numbers is that they make it easy to represent a point on a ",
"2-dimensional plane",
" with one complex number made of a \"real\" part plus an \"imaginary\" part. Or similarly, to represent a 2-D vector. ",
"Once you are representing such things using complex numbers, it is relatively easy to do mathematical operations on that 2-D quantity. ",
"If you think of these complex numbers as a real part on the X-axis and the imaginary part on the Y-axis like ",
"so",
", then if you want to rotate a vector by 90 degrees CCW, you just multiply it by i. ",
"Try it. Take the complex number 2+0i. Draw the vector from the origin to that point. Now multiply (2+0i) by i. You get 2i+0i",
" = 0+2i. Draw that vector. ",
"Now do it again. (0+2i) times i = 0+2i",
" = -2+0i . (Remember that i",
" = -1.) Draw that vector. ",
"This kind of thing is useful at times. For example, in electrical engineering we can use complex numbers to represent the amplitude and phase of a signal. "
] |
[
"As afcagroo says, complex numbers are always useful when dealing with quantities that vary in two dimensions, because these often vary in a sinusoidal manner. Algebra, especially integral and differential calculus, can get a bit fiddly when working with sines and cosines, whereas it is fairly simple when working with exponentials."
] |
[
"How does file compression work on computers?"
] |
[
false
] |
How can you make a file smaller and still be able to get all the information back? How can you compress a video and still see the same thing (for example, I can compress a 3.5 GB fraps recording into 500 mB and still see the same thing)? If you end up with the same information anyways, why isn't everything compressed all the time to save space?
|
[
"There are two types of data compression: lossless, and lossy.",
"Lossless compression is the simpler of the two, though implementations of it are deceptively complex. The basic idea is that, most data contains patterns that can be discovered, then encoded away into smaller representations of said patterns. for instance, consider this sequence:",
"\"grape banana apple banana cucumber\"",
"A simple compression algorithm would detect that the word \"banana\" occurs multiple times, and decides that it will replace each instance of the word \"banana\" with a special symbol, let's say \\b",
"\"grape \\b apple \\b cucumber\"",
"The compression algorithm would have something like a lookup table stored with the compressed data, to make it possible to revert the process:",
"key: value:\n\\b banana\n",
"When the data is to be de-compressed, the algorithm simply reverses the changes.",
"There are many approaches to finding these patterns. I recommend losing a few hours to wikipedia on the subject. An easy place to start is \"run length encoding\".",
"\"Lossy\" compression is a technique that takes a set of data with a known purpose, like audio or video, and rendering a smaller piece of data that will produce results ",
" to the original when interpreted by an application at a later time. The original data is lost, but what you end up with is usually \"close enough\". This is why, sometimes, you see \"artifacts\" when watching videos on the internet, like blocky parts of the image, or why you hear squeals, clicks, and pops when listening to some compressed audio, or the famous ",
"\"jpeg effect\"",
"Many audio, video, and image formats actually use a combination of both lossy and lossless effects to achieve better results.",
"As for why everything isn't compressed all the time... there is a cost! That cost is paid in CPU time. On modern desktop PCs, this is hardly an issue, as those machines have CPU time to spare, but on more constrained devices that need to consume data, like cellular phones, or set-top boxes, this cost can become a problem."
] |
[
"I'll try to give a toy example.",
"Suppose my file looks like this: \"aaabbbaaabbbaaabbbaaabbb\"",
"The compression algorithm might do something like identify that \"aaabbb\" repeats, and call it \"0\"",
"So the compressed file is:",
"(compression table)\naaabbb : 0\n(data)\n\"0000\"\n",
"which is somewhat smaller than the original.",
"However, because it is compressed, the file looks totally different than before. So programs that could use the original file can't use it anymore because it is in a totally different format. In order to use the file again, it needs to be decompressed.",
"A real world example is a telephone, sort of. When you speak into a telephone, your voice gets converted into electric signals and then sent over to the target phone you are speaking into. But if they just \"left it as electric signals\", the other person wouldn't be able to understand what you are saying. So it needs to be converted back to sound again."
] |
[
"Actually, the two are different. Most data file compression are designed to be lossless while movie compression is lossy. ",
"For file compression, what you get out is ",
" what you had in. Here, the trick is that most human readable data files are rather,... empty....",
"One obvious exemple is if I have an image of 2000 pixels by 2000 pixels that is all black. In image format, I would use 2000x2000x8 bits, or ~4megabytes. But I can describe it by just four numbers (2000,2000,8,0), a handful of bytes, as long as the program that reads it in and reads it out knows your convention. A more practical exemple is to realize most languages have limited combinations of letters. \"ion\" is pretty common, \"zft\" is rather rare. So if I extend my character set to 12 bits (instead of the 8 bits used for 256 ascii character enchoding), I can still have my regular 256 characters, and a lot of \"common letter combos\" (3840 of them). Now, as I compress text, everytime I replace a two letter combo by its 12 bit equivalent I save (2x8-12)=4 bit or ~25% compression. If I also get 3 letter combos in the mix, I can get (3x8-12)=12bit or 50% compression. ",
"Not bad. And I haven't lost any info. I have just benefited from the fact that my original information wasn't that \"rich\". As an interesting play, look one of these days how much compressing a ten megabytes .txt file gives you and how much compressing a ten megabyte .exe file gives you. You should notice massive differences in the compression ratio. The .txt is actually rather hollow, lots of repeating patterns in human languages. The .exe is actually rather full, not many repeating bit patters. ",
"Ok, now for video/sound/images, most compressions are (variably) lossy. We ",
" information. You will not get out exactly what you put in. Many techniques here...Again, the idea is that much information is extra. Potentially every pixel counts if you are an astronomer. But if you are watching a movie, meh, maybe you don't need every little pixels. Then it can be removed...for exemple, a \"raw movie\" is a full frame for every frame. ",
"But what if you only store one frame, then store for the next five frames \"only\" the pixels that changed, then store a new reference frame, then again, only the pixels that change and so on...you could throw away a lot of data...and since most movie scence don't completely change all the pixels from one frame to another (the scenery is mostly static), you'd be mostly good. ",
"Also, why not describe a picture not as pure pixels, but in \"blocks\" of variable size, so that a large swath of uniform color can be represented as a single block...again, huge gain, the blue sky becomes one big block instead of occupying all those pixels...",
"There are many algorithms out there to create lossy or lossless compression. I have only described some (not very good to be honest) methods one could think of using...but hopefully it gives you a sense for it. After that, it is just a lot more math to try to squeeze as much size out while retaining as much information in as possible. "
] |
[
"Do lymph nodes and kidneys have a common ancestor?"
] |
[
false
] |
It can be difficult to differentiate one from the other unless you know what you're looking for, so I'm wondering whether someone knowns whether they share an ancestor. They're both basically used as filtration units--would it too much of a bound to suggest that they were once the same?
|
[
"First, common ancestor is not really the correct term because lymph nodes and kidneys are not organisms in themselves. You could ask if at some point in evolutionary history there was an organ that combined the function of these two.",
"Second, the lymph nodes and kidneys are actually quite distinct. I'm not sure what makes you say that it can be difficult to differentiate them. A large lymph node is, at best, 1/10th the size of the kidney, they have different colors, and are located in quite distinct areas of the body. And those are just the gross differences. Microscopically, they are as different as can be. Lymph nodes have a two layered structure punctuated by follicles while the kidney has multiple pyramidal structures with quite unique nephron morphology.",
"As for any shared function, there essentially is none. The lymph node isn't really a filtration organ. It is involved in displaying various antigens to immune cells so they can decide whether or not to promote inflammation. The kidney on the other hand is a filtration organ that is involved in maintaining proper chemical homeostasis in the blood. The only time the kidney can be said to have any immune function is during a brief point in embryonic development when hematopoiesis takes place there rather than the bone marrow."
] |
[
"1) You have to decide if you are using the word \"ancestor\" in a scientific sense or a common language sense. If want to be scientific, then, no, two daughter B-cells are not ancestors of the cell from which they divided; they are clones. Even cells that give rise to more differentiated cell types are not ancestors of those progeny. That is because the term ancestor applies specifically to an evolutionary relationship. Individual cells of the same organism don't have an evolutionary relationship to one another.",
"2) At this point I wasn't saying their distinguishing qualities make them evolutionarily unrelated. I was asking what makes you think they are hard to differentiate, because they aren't.",
"3) Antigen presentation is essentially the whole story. The function of macrophages in the lymph node is to take up antigen to be used FOR antigen presentation, not simply clearance. Clearance of cellular debris by macrophages occurs primarily in peripheral tissues where cell death is occurring. ",
"4) Again, not an argument for why they aren't evolutionary related, just that you can indeed tell them apart, in the same way I can tell your left axillary lymph node apart from your right one because I can find one on the left side of your body and one on your right. Similarly, as the only red, curved, retroperitoneal structures located on either side of midline, I can distinguish the kidneys quite easily from lymph nodes.",
"5) You do not need to show me diagrams of the kidney and lymph nodes. I am well aware of what they look like on paper and in vivo. "
] |
[
"By that logic, two daughter B cells of the same father cell don't share an ancestor. (Hint: They do.) ",
"Why do distinctions make a common ancestor impossible? I agree that they are morphologically differentiated for differing purposes, but that's kinda the point of evolution. ",
"Lymph nodes are most definitely filtration units. Providing a meeting place for lymphocytes and APC's is only half the story. Cellular wastes are transported through lymphatics and into the lymph nodes, where macrophages clear the debris. I'll agree that the kidney has no other immunological function but that's beside the point. Evolution changes things. Even if lymph nodes didn't functionally filtrate anything they'd still be a potential ancestor to our kidneys, or a distant cousin. I really don't know why it's hard to think that organs have ancestors. Do individual cells have ancestors? Of course. Do tissues have ancestors? Of course. Then so do organs.",
"Location doesn't count as an argument. By that logic, the lymph node in my left armpit is not at all related to the lymph node in my right armpit.",
"All objections have been properly met. Here are pictures that make the two look similar. ",
"Lymph node: ",
"http://i.imgur.com/b3k68.jpg",
"Kidney: ",
"http://i.imgur.com/TsYrX.jpg"
] |
[
"When I squint my eyes at night, why do I experience the 'lens flare' effect?"
] |
[
false
] |
Is it just because my pupils are to large or don't react quickly enough? Why would squinting accentuate this? In case it's relevant, I am also near sighted, with slight astigmatism.
|
[
": downvote only those comments which detract from the discussion (distracting memes, off-topic jokes, pseudo-scientific mumbo-jumbo, and anti-science rhetoric)."
] |
[
"Wild speculation alert: I always thought it was because of light refraction through your eye lashes and/or through tears/eye moisture. This and the fact that you should notice flares a lot easier at night because of the increased contrast due to the lower-light conditions."
] |
[
"More Wild Speculation Here: I see this effect on almost all light (real pain in the ass w/ driving into headlights) with it notably worse at night and I have astigmatisms in both eyes. My guess has always been that the two are related."
] |
[
"Are there specific areas where meteorites are more likely to fall or is it completely random?"
] |
[
false
] | null |
[
"We find new ones that won't orbit us again",
"Meteorites are meteoroids which enter Earth’s atmosphere and make it all the way to impacting with the Earth’s surface. So of course there are no meteorites that are orbiting us again. ",
"ones that we won't see for a very long time",
"Are you thinking of objects like ",
"Halley’s comet?",
" it’s not a meteorite. ",
"and random ones from past explosions from far away stars and solar systems",
"all together we have about 38,000 or so confirmed meteorites in collections around the world. Exactly none of these are from outside of our own Solar System. We’ve only ever even observed a single object travelling through our Solar System which came from somewhere outside of it - ",
"Oumuamua",
". ",
"Luckily, we have a high chance of spotting anything life threatening with enough time to keep everyone safe and clear from ground zero.",
"No, we really don’t. We have a high chance of spotting anything really large that would threaten life world wide, on the scale of the asteroid that wiped out the dinosaurs for example. We wouldn’t really have enough time to do much about it or get people safe though. It’s difficult to even imagine how people could be kept safe from something on that scale. ",
"Then there are ‘medium’ sized impacts - big enough to cause widesparead damage where they hit, but not on a global scale. Not only can we not do much about those, but we often can’t see them coming until the last minute. The ",
"Chelyabinsk meteor",
" was quite a small one (though still thought to be the largest one entering the Earth’s atmosphere since 1908) and as such, we didn’t see it coming at all. Luckily it exploded in the atmosphere many km above Chelyabinsk rather than smashing into it directly, but this still caused a shock wave which shattered windows across the city and hospitalised many people.",
"For objects which are a bit bigger that impact, the blast would be like a small nuclear weapon being detonated - not the sort of thing you want in a city. If they impact over the ocean then they could cause a tsunami to be generated."
] |
[
"We find new ones that won't orbit us again",
"Meteorites are meteoroids which enter Earth’s atmosphere and make it all the way to impacting with the Earth’s surface. So of course there are no meteorites that are orbiting us again. ",
"ones that we won't see for a very long time",
"Are you thinking of objects like ",
"Halley’s comet?",
" it’s not a meteorite. ",
"and random ones from past explosions from far away stars and solar systems",
"all together we have about 38,000 or so confirmed meteorites in collections around the world. Exactly none of these are from outside of our own Solar System. We’ve only ever even observed a single object travelling through our Solar System which came from somewhere outside of it - ",
"Oumuamua",
". ",
"Luckily, we have a high chance of spotting anything life threatening with enough time to keep everyone safe and clear from ground zero.",
"No, we really don’t. We have a high chance of spotting anything really large that would threaten life world wide, on the scale of the asteroid that wiped out the dinosaurs for example. We wouldn’t really have enough time to do much about it or get people safe though. It’s difficult to even imagine how people could be kept safe from something on that scale. ",
"Then there are ‘medium’ sized impacts - big enough to cause widesparead damage where they hit, but not on a global scale. Not only can we not do much about those, but we often can’t see them coming until the last minute. The ",
"Chelyabinsk meteor",
" was quite a small one (though still thought to be the largest one entering the Earth’s atmosphere since 1908) and as such, we didn’t see it coming at all. Luckily it exploded in the atmosphere many km above Chelyabinsk rather than smashing into it directly, but this still caused a shock wave which shattered windows across the city and hospitalised many people.",
"For objects which are a bit bigger that impact, the blast would be like a small nuclear weapon being detonated - not the sort of thing you want in a city. If they impact over the ocean then they could cause a tsunami to be generated."
] |
[
"It is not completely random, but it does form a distribution. There are areas, which \"shouldn't\" be at risk of impacts, but nonetheless become impacted. However, a few characteristics will significantly raise the likelihood of a meteor crash.",
"So, while it's not an exact science, because there is some level of randomness to the arrangement of the universe, it's not a completely random phenomenon.",
"Edit: ",
"Sourced from Cornell University"
] |
[
"Could a fusion power plant be used to manufacture plutonium?"
] |
[
false
] |
Fusion between deuterium and tritium of the sort envisioned in near future reactor designs tends to release high energy neutrons. If you exposed U-238 to these neutrons would it be possible to slowly turn it into plutonium, as in a light water reactor? If not would it be possible to use normal water or graphite to slow the neutrons down enough for transmutation to occur? And if so, would this make nuclear fusion reactors a proliferation risk?
|
[
"You could in theory do it, but if you already have both uranium and the capacity to separate isotopes (which you will need to get the forms of plutonium you want) it seems like an insanely inefficient way to go about things. Who would bother? It would be far easier to build a conventional fission breeder reactor."
] |
[
"Plutonium is made in fission reactors, not fusion reactors."
] |
[
"If you exposed U-238 to these neutrons would it be possible to slowly turn it into plutonium, as in a light water reactor?",
"Technically, yes. Capture is much more likely with a thermal neutron than a fast neutron though.",
"Moderating the neutrons could help. Whether it’s a serious proliferation risk depends on what the neutron flux is, and the rate at which neutrons are captured, which depends on whether there is moderator, etc."
] |
[
"Which animals are considered extant dinosaurs?"
] |
[
false
] |
I am familiar with the fact that a lot of birds are evolved from dinosaurs but what other animals out there are less known for this fact?
|
[
"That's pretty much it. Birds "
] |
[
" birds are descended from a group of bipedal dinosaurs called maniraptorans, (see the far right of ",
"this tree",
"). No other dinosaur lineage besides birds survived the end-Cretaceous extinction. Other prehistoric reptiles (e.g. pterosaurs, plesiosaurs, ichthyosaurs) similarly did not survive."
] |
[
"At least one other prehistoric reptile survived; the ",
"Tuatara",
":",
"The tuatara is famous because it is the only survivor of an ancient group of reptiles that roamed the earth at the same time as dinosaurs. It hasn't changed much in over 225 million years! "
] |
[
"What is happening to the electrical signals from one's brain when one's muscles are too tired to obey? In other words, what does \"too tired\" mean physiologically in this context?"
] |
[
false
] | null |
[
"The electrical signals are just fine. They are simply arriving at muscles which have exhausted their ability to respond, either by using up all their available ATP or through injury."
] |
[
"Assuming that the muscle has not been poisoned (ie, by VX or another cholinesterase inhibitor), the electrical signal reaches motor endplates and causes acetylcholine release, just like usual. It's just that the muscle doesn't respond, likely because the actin and myosin can't slide due to ATP depletion."
] |
[
"There is a bit more to the story.. There is a central component to muscle fatigue. Motor neuron firing rate decreases as muscle fatigue is approached, but attempts to correct it with nerve stimulation haven't reversed the fatigue, so it's thought to be only part of the story.",
"And its most likely not ATP depletion that directly causes the fatigue, though it may contribute(ATP concentrations remain much higher than that required for contraction at fatigue), it's much more likely to be the increase in acidity from lactic acid that inhibits sarcomere binding and calcium release from the sarcoplasmic reticulum.",
"So the signals still reach the muscle, they still release the acetylcholine, but the altered biochemistry in the cell stops the contraction after that. As well, afferent(going out) nerve fibers from the muscle may signal the CNS to slow down firing."
] |
[
"If only 4-5% of the air we exhale is CO2, how many times can we breathe the same one breath? And at what point would we pass out."
] |
[
false
] | null |
[
"Interestingly, your body registers suffocation not by the lack of O2 in the air but by the concentration of CO2 in your blood. Without a way to get rid of CO2, you would still feel the same as if you were holding your breath."
] |
[
"The mechanism that drives your body's respiratory system is the difference in concentration between O2 and CO2 at the blood/air barrier within the lungs.",
"I can't estimate the answer to your question, but I can say that your lungs would transport less and less as the O2 and CO2 levels in the two areas began to approach each other."
] |
[
"Not so easy to answer (for me at least). I think the easiest way to go about answering the question is to look at an average breath (450ml) and look at the O2 contained therein (94,5ml). The average body uses about 200ml of O2 per minute and breathes 10 times. That means after 5 average breaths the O2 is gone (not really, it asymptotically goes toward 0) and has been replaced by CO2. So my best guess is that you have about 30 seconds longer than you can hold your breath without fainting. Whether you keep on breathing in and out does not really make too much of a difference at this point, only that your muscles produce more CO2 and hasten the inevitable.."
] |
[
"Would an ocean of honey still have waves?"
] |
[
false
] | null |
[
"Well the premise is a hypothetical, and it's a bit open-ended. The closed-ended answer is just that you'd be changing the density and viscosity of the ocean, but not the underlying fluid dynamic equations that govern the ocean and atmosphere. So the same kind of wave phenomena should exist, just maybe with a modified dispersion relation, and a rescaling of the relevant lengths, times, etc.",
"But I assume you want something more in-depth than that, and I think you'll get a good open-ended discussion over there."
] |
[
"Hello,",
"This would be more appropriate for ",
"/r/AskScienceDiscussion",
".",
"Best."
] |
[
"Hey thanks for your help! Just curious why it would be better there though. I get the gist of why most of the things in that sub fit there but I can't quite see why my question is more fitting for the discussion sub!",
"Is it not just as much of a yes or no question as anything here? Or is it because I gave a few of my ideas in the subtext of the question"
] |
[
"Why does total resistance decrease, as you add resistors in parallel to eachother in a circuit?"
] |
[
false
] | null |
[
"When you add resistors in parallel, you add additional paths for the current to flow through. You increase the conductance (G), and the conductance is related to the resistance by G = 1/R."
] |
[
"conductance\nI get this but in terms of what is actually going on what do you mean"
] |
[
"There are more paths for the current to flow through."
] |
[
"How is energy conserved in wave interference?"
] |
[
false
] |
Whilst reading a pop science book on physics and metal, I got to wondering where does the energy go in destructive interference. It had a bit on this in the appendix, which mentioned: A) you have to consider the energy globally for energy conservation to apply. Fair enough i understand this But that doesn't explain what if the sources are as close as possible to one another. B) The oscillators will be coupled in such a way as to require more/less energy. The book referencing a 2014 paper on it, and says to quote: The resolution lies in realising what happens when 2 sources get so close together than their separation is lower than the wavelength of the wave... what happens under those is that the two sources are coupled together- one affects the other... But then consider this: EDIT: The lasers are just a placeholder here for an ideal wave restricted to a line. I am aware real lasers aren't like this. We set up 2 identical lasers, their beams have a power 'E', very far away from one another. And these have been placed in such a way as to be aligned and all that jazz so that the light they emit is aimed at the other perfectly (so that their beams will interfere). Now we get the lasers to fire simultaneously. The laser beams go forth and at the midpoint they meet. They interfere, so the wave has power of 4E (as power is proportional to the square of amplitude, which just adds linearly no?). But because the source of the laser beam is so far away, they are not yet causally connected. So how can they couple to explain the extra energy from 2 laser beams, if there is no non FTL way for the lasers source to communicate that they are on even?
|
[
"You always have both types of interference, constructive and destructive. You cannot have one without the other.",
"In your example with counter-propagating beams the energy density varies between 0 and 4 times the energy density of a single beam, with an average of 2."
] |
[
"No matter how exactly the waveforms look like energy is always conserved."
] |
[
"I think pooling your discussion with me and with ",
"/u/mfb-",
" there's kind of two different questions going on. The first is the fact that lines of destructive interference aren't a violation of energy conservation because there are also lines of constructive interference in any beam.",
"Your second question seems to basically be, say in 1D, if I have two pulses that are opposite amplitude that pass by each other so that they briefly destructively interfere AT SOME POINT, where did the energy go? A wave is the result of basically coupled oscillators, like an array of springs where at any given point:",
"https://en.wikipedia.org/wiki/File:Simple_harmonic_motion_animation.gif",
"Something is oscillating because it has some kinetic energy but also a restoring force back towards it zero point. There is a potential energy associated with this restoring force. It's trading back and forth between kinetic and potential energy. The \"ripple\", the deviation of the wave from 0, is about the potential energy. If it's zero at a point then that means the energy is currently all in the kinetic. If two ripples are currently destructively interfering at a point x then that just means that the kinetic energy at the point x is basically twice the typical kinetic energy maximum for either wave in isolation and that kinetic energy will turn back to potential momentarily.",
"So if I have sin(kx-wt) at x=0,t=0 that is zero, that doesn't mean the energy is zero, that means the POTENTIAL energy is zero and the energy is totally kinetic. Later when the wave is at its maximum potential is maximum, kinetic is zero and total energy is UNCHANGED."
] |
[
"Why is the speed of light different when it travels through different media?"
] |
[
false
] | null |
[
"Let's consider this from an intuition perspective (For rigor, you can reference any of the billion books that have been written about light-matter interactions).",
"The basic principles we need to agree on first:",
"\n1.) \"Light\" is an electromagnetic wave that propagates through things (and also through vacuum).",
"2.) Matter is made up of protons, neutrons, and most important for our question, electrons. Electrons are charged particles. Charged particles have electric fields. (and if moving, magnetic, but we're not worried about that here) ",
"Okay great, so we agree on the above two points. ",
"Now, when light (an electromagnetic wave) moves through a vacuum, there is no matter around, and hence no electrons. The light sees no other electric fields, and so has nothing to interact with, and thus keeps its constant speed. (See where I'm going yet?)",
"When light enters a material that ",
" have electrons (i.e. all real things), the electric field of the light interacts with the electric field generated by the electrons in the material. This interaction is complicated, but in general will \"slow\" down the light. It slows down the light because the electrons in the material try to respond to negate the effect of the applied electric field from the light. The magnitude/strength of this interaction (how much the light is slowed down) is encoded in a material parameter called the \"Index of Refraction\". It is a material-specific quantity, and in general varies with the frequency/wavelength of the incident light.",
"EDIT: ",
"This",
" PDF by Andrei Tokmakoff has just as much rigor as required. On a side note, I'm also a huge fan of his work, he's a legend in spectroscopy!"
] |
[
"Thanks for the explanation!"
] |
[
"Wooo thanks for the explanation, that was fascinating!"
] |
[
"What is the average distance between where a human is born and where it dies?"
] |
[
false
] |
I'm interested in both variations of this question: The total amount of distance traveled in a person's lifetime and the absolute distance between the location of their birth and the location of their death. EDIT: Jesus christ, I mean on the surface of the earth. I'm not referring to the Earth's revolution around the center of the galaxy.
|
[
"Mean = Average",
"Median = Typical",
"Mode = Most Common"
] |
[
"Mean = Average",
"Median = Typical",
"Mode = Most Common"
] |
[
"I'm not sure that there would be much data on this, the studies that you could undertake would be historical.",
"Also the variation would be massive; geographical occupational and socioeconomical factors would impact majorly.",
"You would have spikes for the wars over the years in terms of distance travelled and distance between life and death.",
"And then we get some of the physics minded people here that declare the centre of the solar system as the reference point and hence any person to person variations are insignificant and negligable."
] |
[
"Head shapes. What causes them?"
] |
[
false
] |
Are they caused by genes, development in the womb, post-birth events (e.g. sleeping positions), a combination of these, or something else? Historically, some groups have deliberately shaped infants' heads. There was a "northwest head" in China where the infant (male) was tied to a board to flatten the back of the skull. The Mayans did something similar to the forehead. Did these techniques, or ones like them, harm the brain? Is there an ideal head shape? What is the current thinking in science on this general topic?
|
[
"All of the above. As with everything in biology, this results from a combination of genetic and environmental influences. ",
"You will have to specify what you mean by ideal. Aesthetics? Brain power? Fitting under doorways? You need a defined purpose to evaluate suitability and ideal-ness. ",
"Remember that the head has a long evolutionary history and many many constraints because it contains multiple organ systems and functions in many different ways (feeding, breathing, sight, smell, hearing, balance, hormones, information processing etc.). So you have to balance all these equations to answer your question (or even ask it in an answerable way)."
] |
[
"I do not have many specific answers for these questions. In part it is because the experiments they would require are unethical to perform on humans. But generally, within the bounds of normal human behavior, I speculate that most of head size and shape is genetic. You could alter that by letting a baby sleep on one side all the time or what have you, but for the most part that is not happening. I have never heard that brain shape affects cognitive ability. The debunked pseudoscience of phrenology was interested in the lumps and bumps of the braincase as a way to assess personality and smarts, but well, it just wasnt true. I will go with my better judgement and refrain from speculating further on the rest of your questions."
] |
[
"Some people have narrow heads, some wide. Some people have high foreheads, some don't, some have a large upper-back portion of the skull, some don't. How much of this is genes, how much due to treatment during infancy? For example, I have heard it said that if infants sleep on their sides too much, their heads will be narrower.",
"As for ideal, I mean best for the brain. So, if an infant's head is narrowed by sleeping on its side, is this bad for its brain? Does it decrease cranial volume and thus the size of the brain?",
"To my knowledge, parents no longer try to create the \"northwest head\" in China because, I have heard, it came to be believed that it harms the brain.",
"How much do the sinus cavities contribute to head size and shape? In older books we can often find head shapes and sizes correlated with racial, or even ethnic, differences. Is any of that true? Can we say that a certain ethnic group in Europe, say, generally have larger or wider, or narrower heads than another European group? Are people with large heads generally smarter?",
"Sorry for the sort of messy questions, but that's the kind of thing I want to know. If you can think of a better way of asking that, please do so!"
] |
[
"Do light and sound have acceleration"
] |
[
false
] |
I take a crappy middle school pre-physics class but this question that came up in class sort of fascinated me. Please explain
|
[
"physics guy here",
"yeah light always travels at the speed of light (lol) ~3x10",
" m/s because all massless \"particles\" (photons) must ALWAYS travel at c. The reason it appears to travel slower through a medium is because the phase of the wave is retarded by passing through the charge density of the electron orbitals. So the individual waves continue to move forward at c, but the wave envelope is slowed and as such a beam of light will appear to be slowed."
] |
[
"Light changes speed depending on the medium it travels through. It's what makes refraction happen. The speed of light is constant in a vacuum is what you meant to post I'm sure.",
"http://en.wikipedia.org/wiki/Speed_of_light",
"The speed at which light propagates through transparent materials, such as glass or air, is less than c. The ratio between c and the speed v at which light travels in a material is called the refractive index n of the material (n = c / v). ",
"And since you let the layman speculation out of the bag, I'm pretty sure that the acceleration of light at the boundary would be infinite. I'm sure some physics guy will chime in and hopefully validate my intuition based on what I know about physics (I'm a senior year EE student)."
] |
[
"The important thing to know about wave speeds is that there are 3 different kinds:",
"1) The phase velocity is the speed at which a single point on the wave moves. Like if you put your finger on a certain point on a wave (like a crest or a trough) and then follow it forward, that's the phase speed. It's always c.",
"2) The group velocity is the speed at which a group of waves move together in an envelope. In a non-absorptive medium, this is what carries the energy/momentum/information of the wave and can travel at different velocities depending on the medium (even superluminal velocities or backwards ones 0.o). And to clarify what I said before, the phase retardation I was talking about was the retardation of the group envelope, not the phase speed.",
"3) The front velocity is the very beginning part of the very first wave envelope. In an absorptive medium, this is what carries the signal, and it always travels at or less than c, depending on the medium. In a lot of cases the front velocity is equal to or approximately the group velocity. You might be wondering how part of the envelope can travel at a different speed than the envelope itself; that's because the envelope can change shape in some media, compressing or expanding and causing the endpoints to move at different speeds than the overall envelope.",
"In RF the velocities you usually care about are the signal/front and group velocities of the electromagnetic waves because those are the ones that are going to carry your signal and are the ones that change velocity when they go through different media. ",
"To answer your question in the middle of your post, the photon is the envelope and is composed of various EM waves with different frequencies but all moving at c. The description of a photon as a particle is somewhat confusing because its location is smeared out over all of space. In my opinion, it's always a wave and the particle idea is just a good approximation when the envelope is very narrow.",
"I'm sorry if this sounded long winded or confusing, quantum physics is not intuitive at all and wave mechanics is not something people can identify with easily. If you have any more questions I'll try to clarify to the best of my ability :/"
] |
[
"Why do chemical reactions go with the square of temperature, but diffusion goes with the cube?"
] |
[
false
] |
I dissect tissue in 4% formaldehyde, and my PI told me that if I were to dissect thicker tissue, I should do so on ice, which would allow the fix more time to diffuse into the tissue but without over-fixing the peripheral tissue. He said something like chemical reactions go with the square of temperature, but diffusion goes with the cube. It makes sense to me that diffusion might go with the cube of temperature (volume of a sphere involves a cube, so maybe cubes are inherent to thinking about three-dimensional space?). But it doesn't quite make sense why chemical reactions might go with the square of temperature. Chemical reactions aren't a flat plane. I'm guessing it has to do with multiplying the probabilities of each step of the reaction? Would a more complex (e.g. enzymatic) reaction go with the cube of temperature? Edit: thanks everyone for answering my question!
|
[
"Chemical reactions increase in rate at an exponential rate. The Arrhenius equation is a reasonable approximation for most chemical reactions at a small range of temperatures and somewhat describes how they work, and temperature is exponential under it. Diffusion and chemical reactions can both be described by a version of it.",
"An increase of 10 degrees will double the rate of reaction normally, from around 0-100C with many types of reactions. It's an extremely complex field at higher levels and with less standard conditions it's more complex what the relationship is.",
"http://pubs.rsc.org/en/Content/ArticleLanding/2008/CS/b704257b",
"Your friend was wrong."
] |
[
"Maybe it's the holiday season or something but I can't think of anything that sounds like this T",
" dependence. There is the ",
"van't Hoff equation",
" or the ",
"Gibbs-Helmholtz equation",
" where it's possible to rearrange these equations to have T",
" appear somewhere, but that's about it."
] |
[
"All I know about Chemical Reactions I know because of Fogler. "
] |
[
"I was thinking about tattoos, and I started wondering about my dermis."
] |
[
false
] |
I know your epidermis is continually shedding and being replaced by new skin. I have this notion that my skin in a month will be completely different than my skin today (same structure but a different origin of the materials). I also know that tattoos are deposited below the epidermis. My question is how does the epidermis regenerate? What fraction of the material (amino acids, chemical elements, etc) in your epidermis are recycled locally and what materials must be excreted and replaced systemically? When I eat a steak, besides extracting energy, doesn't that cow meat (proteins, elements, amino acids) become incorporated into my tissues, meaning I have replaced old tissue with new tissue from a completely different origin? I also though that, while neurons do not die and get replaced, the materials that compose them are being recycled continuously, so I imagine this is how the epidermis works. Are tattoos stuck because their is no mechanism to excrete the ink specifically (because it is foreign) or are most of the things in your epidermis similarly static? TLDR: Are the materials in our epidermis pretty much static? EDIT: Are the materials in our pretty much static?
|
[
"From my perspective as a non-dermatologist, the dermis is just bland connective tissue. A dermatologist would disagree.",
"What happens to tattoo ink is indisputably cool. ",
"Immune cells ingest them and fibroblasts lay down collagen around them",
". This is a \"classic\" image of a macrophage with tattoo ink. ",
"http://foreyesonly.tumblr.com/post/3926231853/ohscience-tattoo-source-submitted"
] |
[
"Cool! That is what I was wondering. That's really weird. I guess when the macrophage dies, a new macrophage eats it, but it wouldn't be able to break it down either. Thanks a lot :D"
] |
[
"The outer layer of skin is just dead skin cells interlaced with a protein called keratin. Keratin kills skin cells, but also gives the outer layer its protective qualities (waterproof, etc). It does this via a process called kertatinization, in which skin cell precursors continue to express keratin until they lose their nucleus, and metabolism ceases. Around that time they're on the outer layer of the skin. These cells are continuously regenerated by skin \"stem\" cells (not stem cells in the way you're thinking of, but they're undifferentiated and continue cell division throughout life). ",
"So to answer your first question, everything in your skin is replaced. The Keratin, which is made up of amino acids, and the cells themselves. All materials that make up cells must be replaced, including lipids, the essential chemicals, everything. And yes, you get these material from food you eat. ",
"Neurons work differently, they don't actually divide throughout someones life, but the components of the individual cells do get replaced (fairly certain) over many years. Like I said before, skin doesn't work like this. The actual skin cells are dead, and fall off your skin, and then get replaced by other dead skin cells.",
"As for tattoos, I'm pretty sure the ink is deposited below he epidermal layer, which prevents cell division and loss of dead cells in the epidermis from removing the tattoo ink. "
] |
[
"Does an octopus have a dominant tentacle?"
] |
[
false
] | null |
[
"My brief googling showed that Ruth Byrne seems to have done some research in this area based on what she told the National Wildlife Federation in ",
"this article",
" Then when I went to try to find anything published by her the best citation I found was in a 2017 post on ",
"/r/askscience",
" which I have quoted here:",
"From \"The Soul of an Octopus\" by Sy Montgomery: \"University of Vienna researcher Ruth Byrne reported that her captive octopuses always choose a favorite arm to explore new objects or mazes... Tank-bound octopuses, at least, are known to have a dominant eye, and Byrne thinks this dominance might be transferred to the front limb nearest the favored eye.\" However, as others have stated in the thread, all eight limbs act somewhat autonomously. The author in this section actually refers to the possibility of \"bold\" and \"shy\" arms, describing how some arms will display curiosity when presented with a new object while others retreat.",
"here is the rest of the reddit thread",
" if you are interested in the other responses",
"edit: after some more looking around ",
"here",
" is an article that at least in the abstract does suggest that octopuses have specialized limbs and ",
"here",
" is an article that looks into if the ",
"dominant eye of an octopus",
" influences which limbs are used and says in the abstract that they did not find lateralized behavior. ",
"This is I believe where the conclusion quoted in the reddit post comes from that speculates that octopus arms are specialized but not like left vs right hands and more like the arms are autonomous with some being 'shy' vs 'curious.'"
] |
[
"It is so weird to me... If each tentacle is independent from the others, how can a octopus coordinate so well every tentacle when each tentacle does what it wants ?"
] |
[
"This question was asked previously, ~4 years ago, ",
"here",
"Here's what I said 4 years ago: \nApparently, they do indeed have a \"favorite arm\" they use when exploring new things (",
"source",
"). They also exhibit favored combinations of arms for various tasks as well. As ",
"u/vickinick",
" mentioned, this may be related to the fact that it is known they have a very strong preference for using one eye over the other (",
"source",
"), and octopuses use their highly developed vision to get a better sense of what their arms are doing (their arms exhibit some degree of autonomous behavior)"
] |
[
"What are the hurdles for using the Fischer-Tropsch reactions for liquid fuel production?"
] |
[
false
] |
Liquid fuels are great and I don't think we will every really get away from them because of the energy density. I'm wondering why we are spending so much money into biofuel research, which I feel is a waste of time. The Fischer-Tropsch reaction allows you to produce carbon based fuels from carbon monoxide and hydrogen. We can produce hydrogen through the S-I cycle. We can produce carbon monoxide from a reverse water gas shift reaction with carbon dioxide. You can get some nuclear plant to power all of this. Basically, you can make fuel from air and water. I'm wondering what the major hurdles are besides simply cost and whether or not this idea is potentially feasible. EDIT: Evidence that it is not economically unfeasible.
|
[
"Fischer-Tropsch isn't always uneconomical, but it ",
" is if you're getting both your carbon monoxide and hydrogen out of CO2 and water. ",
"In some places it's economical to burn oil for electricity, too. But just the step of producing hydrogen from electricity is less than 50% efficient by current methods. ",
"The disparity here is that electricity, oil, gas and coal all cost about the same, within an order-of-magnitude. Which is why it's seldom coal is cheap enough and gasoline expensive enough to warrant using the FT process on coal in the first place. There's absolutely no chance of doing it economically using CO produced by RWGS, no matter where you got the hydrogen from, much less if you got it from water. Not to mention there's no possibility of even doing that reaction without first getting the CO2 into a purer form than the 0.04% that it has in the atmosphere, which requires further expenditure of energy.",
"Of course, we already have another, not very efficient but exceedingly cheap catalyst that'll produce fuel directly out of sunlight, and which produces itself at little or no cost, namely plants, algae and bacteria. I.e. biofuels."
] |
[
"What do you mean besides cost? Cost is ",
" to do with why this (and any number of other existing processes) are infeasible. Every chemist and chemical engineer knows about the Fischer-Tropsch (and there are other processes as well). If it was economical, we'd be doing it. ",
"We're spending money on biofuel research because those things aren't uneconomical, or at least have the potential to be economical."
] |
[
"That's not a paper, it's an engineering magazine article. It's not peer-reviewed, nor does it reference anything that's peer reviewed. It doesn't even give any way of knowing how those numbers were arrived at, in particular there's no detail at all about how much energy would be required for the RWGS reaction, which is not something that's been done at all at the industrial scale, so there's no way of even guessing what their assumption might have been. It also appears to be written by three retired engineers, none of whom were actual chemical engineers or otherwise experts in this area. And you can tell, there are no energy and material balances or any of the sorts of calculations you'd expect from a paper (or even just a undergrad Chem Eng assignment), or indeed any way of knowing exactly how they arrived at the numbers given.",
"And no, it's not exactly what you're talking about, because even these nuts aren't proposing getting the CO2 from air."
] |
[
"Could living things sink or dive into lava? Or is it simply too dense?"
] |
[
false
] |
This link is near the top of right now: The comments are full of people talking about diving in. Would a human actually sink or even be able to get below the surface? Or is molten rock too dense for that? I've wondered this since I was a kid and saw Arnold lowering himself into molten steel at the end of Terminator 2!
|
[
"Kilauea lava is about 2.6 times as dense as water; the human body is slightly less dense than water. Lava is also significantly more viscous than water.",
"If you jumped off the edge of the crater you'd sink a little because of momentum, but you would easily float in lava. The net force pushing you to the surface of lava is stronger than the force of gravity on your body in air."
] |
[
"Can we make any estimate about how much the gas disolved in, and erupting from, the lava would affect how much you would sink?"
] |
[
"Are you in the right thread? "
] |
[
"What would happen if we were to channel vast amounts of electric current into the Earth?"
] |
[
false
] |
I understand that we ground our electrical circuits into the earth to 'dispel' the charges, but what would happen if we were to ground circuits with large amounts of current? And when I say large, i'm talking millions and millions of times stronger than currents we are used to seeing. Would anything happen? How many Amps would it take to do anything?
|
[
"This is one of those cases where knowing to ask the right question counts. Grounding is not a matter of current per say, it is a matter of charge. Ground in a circuit is defined as 0 voltage, the entire circuit has an offset to. If ground had a large amount of charge >>than the circuit current would flow out from it until no more disparity existed so the main current would be out from it until equilibrium at which everything is at the same potential. Near the surface if it was a conductor there would be a large uniform field to be used as an offset and it would be the same thing. Now if you are saying there is a current consistently moving through the system then you have to deal with large forces applied to everything which would make any electronics impossible. A current must be linked to a force remember and lets define it by points. For example if it was an AC current there would be an oscillating voltage which is common in some experiments. If it was millions of times greater and over a short enough period of time, all other circuits would be impossible once again. If long enough just the base would change. Anything between those two is situational. You will also have to define your current better as it is in fact moving charges so direction and everything changes this, and there are in fact more than one sort of \"current\" effectively. "
] |
[
"You need to remember that the charges that make up the current need to come from somewhere. Generally, they came from the ground in some fashion, so sending them back isn't going to do a whole lot."
] |
[
"Have you used a ",
"Van de Graaff generator",
" before? If we are getting charge from an outside source I imagine the earth would behave like aVan de Graaff generator. Even though the earth isn't hollow, the charge would still accumulate along the surface (Well, depending on how conductive the material is there). There would just be way more/fewer electrons contained in the earth than usual. I imagine we wouldn't really notice until we (Earth) got near something with a very different amount of charge (the planet we stole the charge from). Then you would probably get a giant lightning bolt between the two."
] |
[
"What chemical (if any) dictates the release of fat from fat cells?"
] |
[
false
] |
If we figured out how aspirin and viagra work among other fantastic pharmaceutical milestones, how is it that we have still yet found a pill to release the fat from our fat cells?
|
[
"Increase burning fat when you don't need it = thermogenesis = a lot of heat = increase body temperature potentially to a dangerous level. There's a drug called dnp which burns brown adipose (type of fat) and creates a lot of heat and is used to lose weight (and to produce body heat. Was used by Russian soldiers in cold conditions to keep warm) but it's dangerous because you can die if you have too much (too much being a relatively low amount). There is also so much regulation with fat and carbohydrate metabolism that finding a one chemical that does that without crazy side effects would be very hard"
] |
[
"There are lots of substances that release fat from fat cells, (Adrenaline, stimulant drugs like meth) just none yet that do so without unpleasant side effects, risks of other long term harm or prohibitive expense. ",
"Just the absence of insulin does a pretty good job, see ",
"r/keto",
", but it's not pleasant. "
] |
[
"Glucagon among other hormones will result in fat release from adipose tissue. If the question you're asking is why haven't we made a drug to do this to make people skinny its like someone else said just because its in our blood doesn't mean we will use it. ",
"Having free fatty acids (what fat is outside storage in cells) can cause death in high concentrations as it is an acid.",
"Slightly higher concentrations are seen in heart attacks everyday from atherogenesis."
] |
[
"Is there any way, even theoretically, to conduct an entropy neutral process?"
] |
[
false
] |
I understand that you can decrease entropy, and any attempts to do so will only ever ultimately result in an increase. Instead, are there any processes (involving change, not just a sphere rotating in a frictionless vacuum for example) which could be entropy neutral, even in theoretical realms? I'm thinking there could be ways involving a point of singularity (infinite density) or massless particles (zero density), or radiation exchange, but I really can't think of any.
|
[
"(Sorry, that's a really sad story. I wish I'd never told it now)"
] |
[
"All unitary evolution in QM is (von Neumann) entropy neutral, which basically means that the entropy of an isolated system is always conserved according to the QM definition of entropy."
] |
[
"If a proton in intergalactic space meets another proton in intergalactic space and they repel each other, that would be an entropy-neutral process too."
] |
[
"If light is photons and photons are massless why cant light escape from a black hole?"
] |
[
false
] | null |
[
"Linked in the AskScience FAQ: ",
"https://www.reddit.com/r/askscience/comments/1heqk0/if_light_has_no_mass_then_how_is_it_affected_by/"
] |
[
"Sweet."
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"/r/AskScience",
"To check for previous similar posts, please use the subreddit search on the right, or Google site:reddit.com",
"/r/askscience",
" ",
"Also consider looking at ",
"our FAQ",
".",
"For more information regarding this and similar issues, please see our ",
"guidelines.",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"How can farming insects be more energy efficient than mammals?"
] |
[
false
] |
I have read that raising crickets would produce less of an environmental impact than cows, pigs or chickens. You can measure all of the impact into simple energy used to make a kilogram of meat. How can this be true considering economy of scale? One kilo of insects takes thousands of bugs, wouldn't having a single larger animal be more energy efficient?
|
[
"Insects are efficient at turning feed into bodymass 1.7kg/kg for crickets compared to 10kg/kg for beef. We can eat 80% of a cricket but only 40% of a cow.",
"Other environmental considerations in favour of insects: They do not require such large amounts of pasture or water. They do not produce as much manure (and associated pollution). Insects can also eat things that other animals do not further reducing environmental impact.",
"Data from ",
"http://www.fao.org/docrep/018/i3253e/i3253e00.htm",
" specifically ",
"http://www.fao.org/docrep/018/i3253e/i3253e05.pdf"
] |
[
"Among other factors, cattle grow more slowly than insects. Even in modern farming, where cattle can be slaughtered for meat at just over a year of age, while a field cricket is mature at roughly 12 weeks.",
"A lot of what a cow (or any animal) consumes goes into the activities of being alive, rather than simply growing-- things like maintaining a warm-blooded body temperature, walking around, mooing, and so forth. Since the cattle spend much more time doing this before they are ready for slaughter, there is much more opportunity for the animal to \"waste\" the energy it consumes. "
] |
[
"I have my lecture notes in front of me (I'm not sure if i am allowed to link them). Beef is 4.3% efficient. Pork is 8.5%, Chicken in 15%. Corn is 100%. Fish isn't listed, but 100% doesn't really make sense, unless they are photosynthetic."
] |
[
"Can some people be naturally immune to a virus without ever contracting or coming in contact with it before (vaccines included)?"
] |
[
false
] |
This might be a silly question that I just havent thought through and googled furiously enough but I read an article recently that said: "Scientists from the Institut Pasteur and the CNRS unraveled the immune responses of 200 African and European individuals. They show that there is indeed a difference in the way these populations respond to infection, that this response is largely controlled by genetics and that natural selection has played an important role in shaping such immune profiles. They also offer proof that the genetic legacy passed on by Neanderthals to Europeans has significantly influenced their ability to respond to viral challenges. This might just mean some are more susceptible to certain viruses than others but I was wondering if it can work to the other extreme, whereby someone's genetics or immune system essentially grants a predisposed immunity to certain viruses? Like in every zombie movie/show these days having that 1 person that just can't get infected for some reason.
|
[
"The HIV resistance is not immunity, it's resistance. Nobody in the field calls it immunity.",
"Immunity means a function of the innate immune system or the adaptive immune system. People with natural HIV resistance (i.e., the delta32 CCR5 gene) are not \"immune\" to HIV because no part of the immune system is preventing infection."
] |
[
"The HIV resistance is not immunity, it's resistance. Nobody in the field calls it immunity.",
"Immunity means a function of the innate immune system or the adaptive immune system. People with natural HIV resistance (i.e., the delta32 CCR5 gene) are not \"immune\" to HIV because no part of the immune system is preventing infection."
] |
[
"I agree with this except it’s wrong to say that someone is immune to COVID if they can spread it! If they can spread it, it means they are infected, which means they are not immune."
] |
[
"Has there been any research on methods for obstacles to identify themselves to an autonomous vehicle?"
] |
[
false
] |
I’ve been reading a lot of articles about artificial detection in AVs and all the research is focused on AVs using their onboard sensors to detect essentially uncooperative obstacles. What I’m wondering is if there’s any research related to signal emitters or other devices which could be attached to pedestrians/cyclists/other vehicles (or even signs, roads, etc.) to provide environmental data directly to the ego-vehicle.
|
[
"Yes, well sort of. Renault has developed what they call a level 4 autonomous vehicle, which can drive autonomously on a highway with sensors riddled along it so its as much the road knows the car is there as the car knows whats on the road ahead. In terms of something like say a littlee sticky or warning marker you could place on items I guess retroreflective markers could work quite easily but the concern isnt developing this tech, its justifying the implementation. eg why should I have to wear a sensor to keep me safe from autonomous cars, or place sensors on the walls of my house to stop a car crashing into it."
] |
[
"To be fair, you can do the same thing to people-operated cars with a box of roofing nails."
] |
[
"Also can I just start dropping stickies across the highway and watch all the autonomous cars come to a halt? Seems like an easily exploited system"
] |
[
"Is using an \"expired\" brita filter better than drinking straight tap water?"
] |
[
false
] |
I've been using the same filter for about 2 months longer than it's life expectancy. I would buy a new pack from Costco, but I don't have any more organs to sell. Should I just take it out and drink from the tap, or does it still provide some filtration?
|
[
"...I was with you up until the very end. You list a set of things that a Brita pitcher can accomplish that no one disputes, and then say its probably not doing anything anyway. Is this because the OP probably doesn't live in a place with very hard water that has some organic contaminants? I'm not sure that thats necessarily the case...a good portion of the midwestern United States falls into those categories."
] |
[
"I think you put the wrong word in quotations. Is drinking water from an unexpired Brita filter \"better\" than normal tap water?",
"In the vast majority of cases in the US or any other industrialized country, no. ",
"Brita filters have two basic components: an ion exchange filter, and a charcoal filter. The ion exchange filter is capable of removing metal ion contaminants, and could be useful if you have very hard water, or suspect heavy metal contamination (no guarantee it will work, though). The charcoal filter is good for absorbing organic impurities that can make your water smell or taste funky. There are usually also filters included that absorb chlorine. Britas do nothing for fluoride, though.",
"In a chemistry lab, it's possible to recharge ion exchange resin by passing a concentrated solution of some ionic compound (usually sodium chloride or hydrochloric acid) through the spent resin to drive out the metal ions and regenerate its efficacy. In principle, you could do the same with a Brita, but I don't know how well it would work. Regenerating the charcoal part is tougher, as you have to heat it in an oven, and it's not worth taking the filter apart to get at the charcoal.",
"So, is your filter still doing something? Probably. But it likely wasn't doing a whole lot to begin with."
] |
[
"Say what you want, but a Brita-like water filter makes tap water that tastes like a swimming pool acceptable and filtered water also doesn't have that skin on the surface of a cup of tea. As a tea enthusiast, the latter is reason enough for me to prefer filtered over non-filtered water. The tea tastes better, too, but I understand that this is subjective. ",
"On the other hand, a dental medicine student once told me that the charcoal filter has a ridiculously large surface area and is an ideal place for bacteria to live in. The toxins released by said bacteria might be bad for you. Is this really something to worry about, especially with \"expired\" filters?"
] |
[
"Do you think you'd be more intelligent if you had two brains?"
] |
[
false
] |
[deleted]
|
[
"And when one sleeps :P You can eliminate sleep and use that time to develop yourself ;)"
] |
[
"And when one sleeps :P You can eliminate sleep and use that time to develop yourself ;)"
] |
[
"Yes."
] |
[
"Why does the glare from the sun make me sneeze?"
] |
[
false
] |
[deleted]
|
[
"I didn't find any simple explenation in english, but found a few in my own language (Swedish) so I'll translate them roughly.",
"The simple answer is that the scientists don't know.",
"About 1 out of 4 suffers from this and it seems like it has to do something with the nerve system that over reacts when you transition from a dark environment into bright sunlight.",
"The scientific term for this is photic sneeze reflex, also known as photoptarmosis."
] |
[
"It is called Photic sneezing I believe. It is not something that all people posses. If I recall correctly your optic nerve is closer to your nasal nerves than is normal, therefore when your optic nerves are suddenly over stimulated by a bright light it \"jumps\" to your nasal nerves causing a sneeze. ",
"Source- I am also a photic sneezer and when I mentioned it to someone they said that light didn't make them sneeze, I was surprised that not everyone experienced this and did some research. "
] |
[
"Photic Sneeze Reflex"
] |
[
"Do gluons carry the strong force or only mediate it?"
] |
[
false
] | null |
[
"Carrying a force and mediating it are both the same thing. Gluons are to the strong force as photons are to the electromagnetic force. "
] |
[
"Ok. Thank you for clarifying. I hope someday to go into particle physics and this whole \"force carrying\" thing really threw me off"
] |
[
"No problem :)."
] |
[
"Can a counterbalanced lever be thrown further than an uncounterbalanced?"
] |
[
false
] | null |
[
"I realize this isn't super helpful, but the answer depends a lot on the specifics of the situation, eg:",
"To still give you a concrete answer, let's assume you take a modern throwing javelin (which if I recall correctly are symmetrically balanced) and replace the metal in the front half with a significantly lighter metal. In this situation, the front end of the javalin will be much more strongly effected by wind resistance and the whole thing will start tumbling end over end and go much less far. If you instead replace the front half I suspect the javelin will function normally, but the front end will start dropping sooner in the flight and you will still not go as far as with the regular javelin. "
] |
[
"Interesting, are ancient war javelin balanced in the same way?",
"Anyways, 1. Like 530 grams 2. Throwing knife throw 3. Adding extra weight"
] |
[
"I don't actually know how to to the math on this, but for 500g I suspect that heavier is better. The reason for this is that the limit of how fast you can throw a light object is largely determined by the speed at which you can move your arm, but a heavy object moving at the same speed as a lighter object will have more kinetic energy, so the original baton and the weighted one will leave your hand with the same velocity but the flight path of the latter will be less effected by air resistance.",
"Some quick googling suggests that the ideal balancing point for a throwing knife is in the centre of the knife, suggesting that the heavier, balanced baton has an advantage here as well. In the end though, these are just some educated guesses from my end. If you have a concrete use case you are looking at, I would suggest just trying both options and see which works better. "
] |
[
"Is it theoretically possible to be struck by lightning while inside your house?"
] |
[
false
] | null |
[
"Yes, it is. And I'm not speaking theoretically. The second time I was hit by lighting, I was in my basement.",
"(The first time was a bit of a shock. The second time, though, was revolting...)",
"I live on a mountain and have a tall pine tree next to my house. A very active storm blew in, and since I've lost electrical appliances to power surges from thunderstorms before I headed to the basement to turn off the main breaker to my house.",
"I was in bare feet on my concrete basement floor, reaching for the breaker box as a bolt hit the tree outside, about twenty feet from me. Electricity arced from the box to my right hand and from my right foot to the floor.",
"I got a few interesting burn marks (now faded and gone) and had some slight difficulties for a while, but I fully recovered. I lost my television, though.",
"So yes, it can happen."
] |
[
"Possible, but unlikely. If you are touching the plumbing (or the grounding conductor) with one hand, and touching a bare wire that goes to an antenna with the other, AND your hands are wet, then it seems possible that you could be used as a means to resolve the difference in potential that causes an electrical storm. By the way, I strongly recommend that you don't try this. Failing that, if you're not wearing shoes during a storm, and you're standing beneath a hole in the roof, or a place where metal passes through the roof, you could be struck this way, too. "
] |
[
"Yes. If the plumbing comes into contact with the ground, and there's continuity between one's self and the ground (through the water/plumbing), then yeah, it would significantly raise one's chance of being struck by lightning. Not a guarantee, by any means, but higher chances. In the end, it would depend on how high the plumbing raises up from the ground (like with bathroom in a two story house), and how exposed it is to the air outside the house. Also, dry skin has a resistance of something like 2-3 million Ohms, whereas wet skin has only 1-2 hundred Ohms of resistance. "
] |
[
"Is it possible to pass a very thin wire through a person's body without killing them?"
] |
[
false
] |
I had this thought the other day. Would it be possible to pass a very, very thin wire straight through a person's body, let's say around the middle, and have them survive despite technically being sliced in half? If so (considering very minimal damage would occur), would it be possible to pass 10, 20 or 100 wires simultaneously through the body at once without it resulting in a fatal injury? Is it purely the displaced cells that cause the fatal injury and if so, couldn't that be avoided by using a very thin wire, but still slice all the way through?
|
[
"You get cut in half, you die"
] |
[
"You're cells have proteins holding them together with other cells. It's more than displacement. No matter how thin you get, you'd have to pass through (and break) these proteins. You can't just slide in between cells."
] |
[
"Wouldn't it almost instantly seal back together?",
"Not really. You'd be severing many molecules in many cells, including polymers in the tissues and bones that hold our bodies together. Your cells and tissues are very dynamic structures, and would require time to repair themselves, if they could even survive the type of damage that would be caused by such a wound (slicing up lipids is one way of triggering apoptosis, programmed cell death).",
"In any case, the existence of a monomolecular filament with the properties necessary to do this is still something that lies only in science-fiction."
] |
[
"Are there any animals that are known/expected to exist based on remains and other evidence, but that we don't have any sightings of?"
] |
[
false
] |
[deleted]
|
[
"Charles Darwin predicted the existences of a moth with a 10 inch tongue based on the existences of a flower with a 10 inch nectar spurs.\n",
"http://faculty.washington.edu/jrw/110/darorch.htm",
":EDIT",
"http://en.wikipedia.org/wiki/Hawkmoth",
"\"[A. sesquipetale has] nectaries 11 and a half inches long, with only the lower inch and a half filled with very sweet nectar [...] it is, however, surprising, that any insect should be able to reach the nectar: our English sphinxes have probosces (sic) as long as their bodies; but in Madagascar there must be moths with probosces (sic) capable of extension to a length of between 10 and 12 inches!\""
] |
[
"Before only a few years ago, the only evidence we had of Giant Squid was a few washed up dead bodies, some whales with huge squid-like bite marks, and old fisherman stories. Now we have seen them in the wild and know that they exist.",
"As for your question, I can't think of any off the top of my head. You're getting dangerously close to cryptozoology when you talk about evidence for unseen animals, there are some people that think the shaky footage of Bigfoot means there has to be Bigfoot."
] |
[
"This moth named ",
" was recorded on infrared video in its natural setting for the first time by Phil DeVries. The footage was included in ",
"this PBS Nature video",
" uploaded in 2008."
] |
[
"Why is blue light the first to get absorbed into the atmosphere through rayleigh scattering, but it penetrates water deeper than other colors?"
] |
[
false
] |
I am out fishing and there are guys with lights that they use to light up the water in the back of the boat when it is dark out so they can see the fish, but all of the lights are either blue or more commonly green. I know from my stage crew days that blue is very hard to produce well, and that the human eye is most adept to see green, and when I did my scuba class they had a chart showing the depths that colors start to fade. This got me thinking however, why does blue light penetrate further than red light in water, shouldn't the same properties of Rayleigh scattering apply?
|
[
"Really good question!",
"In terms of scattering, yes, blue light is scattered more easily in water and in air. However, absorption is very different for water and even water vapor.",
"In water, there is a strong preference for absorption at the lower energy red end of the visible spectrum. The reason for this can be derived from quantum chemistry. Uniquely, water gets its blue color (of course a small amount of water is colorless, but if you have a large body of water, even without the reflection of the sky, there is a blue hue as OP discovered) due to the vibrational transitions of water molecules, unlike most media which get their color from electron-based interactions such as standard absorption/emission lines, Rayleigh scattering, etc.",
"This is because water is unique in its interaction with light being primarily determined by its OH bonds, whose symmetric and antisymmetrical vibrational stretching modes are at a very unusually high energy (spatial frequency). All of this means that an overtone transition happens at (symmetric spatial freq)+3*(antisymmetric spatial freq) = 14300 cm",
" . This corresponds to a red 698nm peak of absorption, whereas many common materials will peak in the infrared.",
"In water vapor, on the other hand, this red peak is shifted to lower energy, out of the visible range. This is again due to quantum chemistry; the relevant difference in structure between liquid and gaseous water is that hydrogen bonding is very strong in liquid water. This is why water vapor is colorless. I haven't look at what happens with air (nitrogen and oxygen), but I'm guessing they are colorless too.",
"So, basically, water is slightly blue because, unlike almost all other molecules, its strongest absorption peak is due to vibrational transitions. And these occur at 698nm - red.",
"Edit: misspoke by getting ahead of myself. thanks ",
"/u/richardmnixon42"
] |
[
"Interesting to add to this very complete answer is that heavy water (made from deuterium) is colorless since the overtone band is shifted in the infrared, confirming that this is the origin of water blue color"
] |
[
"This page has a copy of the image: ",
"http://www.dartmouth.edu/~etrnsfer/water.htm"
] |
[
"What the heck is toothpaste and why is it good for our teeth?"
] |
[
false
] | null |
[
"toothpaste is an abrasive. Like very fine sand paper, it rubs off the dirt and grime. You can also use it to polish metals like copper."
] |
[
"Toothpaste is a mixture of chemicals to clean your teeth effectively. However a common ingredient is fluoride, which prevent cavities. There are also anterbacterial angents in toothpaste."
] |
[
"I'd like to add that the fluoride prevents cavities by building the enamel back on the teeth. The outside of a tooth is kind of like a sponge with hard stuff filling in the spaces. Plaque eats away at that hard stuff and fluoride builds it back there, becoming harder than the original enamel."
] |
[
"particle spin"
] |
[
false
] |
How does a particle's spin affect its behavior?
|
[
"If it has integer spin, then it is a boson. It can occupy the same state as another identical boson. You can think of it in some cases as occupying the same point in space (and having the same velocity, and all other properties equal). Photons, gluons and compound particles like certain atoms (like Helium-4) fit this description. This doesn't work with fermions, particles with spin one-half (or three-half, five-half and so on). Examples for this would be electrons, quarks, protons, etc. ",
"They cannot occupy the same state. This becomes important for instance when neutron stars form. Before the star becomes a neutron star, there is a certain pressure keeping the star from collapsing. It's called the Fermi pressure and stems from the fact that if the star became any smaller, then some electrons would have the same position and velocity and their spin would have to point in the same direction, and so on. This can't happen due to the Pauli principle. If gravity is large enough, however, then the pressure can indeed be overcome by \"pressing the electrons into the protons\" such that they all become neutrons."
] |
[
"But chemistry is so ",
" and has such a very large body of work behind it; people ",
" chemistry is complicated stuff and tend to shut off their sensory input when you bring it up. Meanwhile, neutron stars are exotic, sexy beasts that excite the imagination because \"whoa man, the universe is ",
"\"."
] |
[
"You can align the spin axis with a magnetic field then rotate the magnetic field."
] |
[
"What is causing the clearly defined line of bubbles part of the way up my glass of Coke?"
] |
[
false
] |
Quite a simple question this one, but I couldn't find the answer with a quick bit of googling. I poured a glass of coke straight from a bottle in the fridge yesterday, and as soon as I finished the pour, there was a very defined line of bubbles about a quarter of the way up the glass. There were just no bubbles in that part of the drink from the start which struck me as odd. The glass only water in it before this. - the line of bubbles isn't quite as clear as it was, but you get the idea! Thanks.
|
[
"For bubbles to form on a surface there needs to be nucleation sites. This could be some dirt or imperfections on the glass surface. So it could be that the manufacturing process of this glass caused a strip of the glass to be more rough than the other parts - causing more bubbles to nucleate there. Or whoever cleaned this glass did a half job of it and only cleaned the top/ rim and the bottom. Or maybe the glass wasn't cleaned at all and that line demarks the height of the previous liquid."
] |
[
"I’m actually thinking that area might be where another glass sits when they’re stacked in the cabinet. That would naturally lend itself to more nucleation sites by wear and tear from contact between the glasses."
] |
[
"In the restaurant/bar business, there are glasses that are clean enough for water, soda, etc., and then there's \"beer clean.\"",
"If a glass isn't cleaned well enough and a beer is poured in it then the head on the beer won't form properly.",
"I presume that these phenomenon are related."
] |
[
"If I drink enough blue food coloring, will my pee turn green?"
] |
[
false
] |
[deleted]
|
[
"As far as I can tell from my textbooks the only blue food coloring in use in the US is excreted in the feces.",
"You can turn your pee green if you eat too many Clorets, which contain chlorophyll. "
] |
[
"Try it"
] |
[
"You can turn your pee pink by eating red beetroot. So yes, certainly some pigments can pass through into the urine. Other pigments may be broken down, it would depend on their chemical structures I'd guess. "
] |
[
"Ask Anything Wednesday - Engineering, Mathematics, Computer Science"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"The FAQ for the ",
"/r/learnprogramming",
" subreddit has answers to these questions, and many more."
] |
[
"The FAQ for the ",
"/r/learnprogramming",
" subreddit has answers to these questions, and many more."
] |
[
"Computer Scientist here. It really depends on what you're trying to do. Do you want to have general foundational knowledge that will give you the tools to pick up pretty much any language with relative ease? Go get a computer science degree. It'll take 4+ years, it won't be easy, and if you don't like math you're going to have a bad time, but it does give you those tools I mentioned earlier and open up a lot of doors in the job market. ",
"Outside of that, it really depends on what you're trying to break into. Web dev is the easiest field to break into as self-taught. ",
"A good general language to start off with would be something like Python. "
] |
[
"What is happening in this nuclear explosion?"
] |
[
false
] |
a) There seems to be an initial explosion b) There seems to be a secondary explosion - what is happening here, why is there a second explosion? c) The center of the explosion seems to shift up and a little to the left, why? d) There seems to be some sort of vacuum that is filled, but how could this be if they are in space? e) what is the blue stuff?
|
[
"I am pretty sure a, b, and c are explained by the fact that this is actually two separate explosions spliced together for the gif without any fade or other way to separate the explosions. ",
"https://www.youtube.com/watch?v=KFXlrn6-ypg",
" has the same two explosions but in the reverse order.",
"The blue stuff is likely an aurora effect"
] |
[
"It is actual footage of the Starfish Prime test, but seems to be spliced together from two different views. It's pretty obvious that they're two different views since the latter part of the shot shows the smoke trails from some of the rockets carrying instrumentation that they shot up prior to detonation, but the earlier part does not. ",
"https://www.youtube.com/watch?v=KZoic9vg1fw",
" is declassified footage of the Operation Fishbowl test series that Starfish Prime was a part of."
] |
[
"The blue stuff is likely an aurora effect",
"Is it possibly cherkenov radiation? I read that prodcues a blue light when changing medium. I saw this on ",
"/r/space",
" yesterday and apparently this was detonated in the upper atmosphere. If this is being recorded from the ground the change from vacuum to air could be reaponsible for the blue light. Not saying its not an aurora effect, just womdering if it could be this instead."
] |
[
"How many neutrinos does it take in order to hurt/kill someone?"
] |
[
false
] |
Weird question.
|
[
"https://what-if.xkcd.com/73/"
] |
[
"I ",
" enjoyed this part, although it isn't relevant for the question:",
"Here's a question to give you a sense of scale:",
"Which of the following would be brighter, in terms of the amount of energy delivered to your retina:",
"A supernova, seen from as far away as the Sun is from the Earth, or",
"The detonation of a hydrogen bomb pressed against your eyeball?",
"Applying the physicist rule of thumb suggests that the supernova is brighter. And indeed, it is ... by nine orders of magnitude."
] |
[
"What is the relationship between brightness and neutrino emission density? If it is somewhat related, the comparison is sound."
] |
[
"Is the stereotypical \"vat of acid\" in movies really an acid? Or would it more likely be a base or oxidizer? Does such a substance exist? And If the movies messed up, how do you think this happened?"
] |
[
false
] |
So this requires a bit of an explanation. I was talking to a friend at one point and he mentioned that the stereotypical "vat of acid that will melt your skin off" is actually most likely a very powerful base. I asked my dad who is pretty good with chemistry and likes it. He works in the medical field so I trust what he says, but seeing as how maybe some things he might have learned in school may be dated or what not I wanted to see if anyone here could answer this? So far I've gathered that a powerful acid would cause some sort of scar or scab tissue (cant remember the name) to form after burning you for a wile which it couldnt burn through any longer. A powerful base will continually burn through substance by converting it to liquid? (I probably said that completely wrong but I know the word liquid had something to do with it) and will continually burn until it runs out. An oxidizer is what most likely would burn/dissolve/deteriorate metal substances. So when someone in a movie brings out a vat of acid to melt someone, which is it most likely? An acid, base, or oxidizer, or something else completely. And if its not an acid, how do you think the movie industry and entertainment in general messed this up so bad? Finally, what would be the closest substance to something like Aliens acid blood that can burn through pretty much anything? Sorry for the long question but I am really intrigued to hear more about this! I couldnt find anyone or anything that could help answer the question.
|
[
"This is a common misconception about HF. Yes it is highly corrosive and dangerous, but it's for specific reasons. ",
"It corrodes glass because glass is full of Si-O-Si bonds and HF can convert those to extremely stable Si-F bonds. Other common acids (HCl, H2SO4) don't have that driving force. The final product, if there's enough HF, is \"hexafluorosilicic acid,\" an equilibrium mixture with the composition H2SiF6. (The fact that normally tetravalent Si forms six Si-F bonds gives a clue about the stability of that bond.)",
"That reaction is the reason you have to store HF in a plastic bottle.",
"HF on skin is bad news for a whole different reason, and ironically half the problem is that it's a weak acid. The skin is good at keeping out charged species, we know this because you don't absorb salt out of the ocean. Neutral species--and HF, which is mostly not dissociated in aqueous solution--can pass through your skin more easily. This is a huge problem because large amounts of fluoride in your body are quite toxic, and HF for the reason I just mentioned is a highly bioavailable source of fluoride. In your blood and tissues, fluoride ions run into calcium and magnesium ions and form CaF2 and MgF2, which are very insoluble. This takes the calcium and magnesium out of circulation, which is a problem because you need them and also because you don't want deposits of insoluble minerals in your blood. The end result is nerve damage, pain and in major cases heart failure.",
"But dissolving your whole body is not really the way it goes down."
] |
[
"Yeah, even then. Fluoride doesn't have any special interaction with proteins, lipids, etc--the main stuff your body is made of. So you're just interested in the sheer strength of the acid/base. This paper, ",
"see if the link works (pdf!),",
" suggests that acids and bases are about equally good at hydrolyzing peptides. I think your best bet overall might be a large amount of concentrated sulfuric acid, which in its undiluted form is ~15 times stronger than an aqueous acid. (H2SO4 pKa -3, hydronium ion pKa -1.7). "
] |
[
"Hydrofluoric acid might be what you're thinking of. It is a highly corrosive and dangerous acid. Though technically a weak acid, it can burn through most things, including flesh and bone as well as glass. If you watch Breaking Bad, Season 1 that's what they used. A vat full will definitley get rid of a body. ",
"Small amounts on skin or clothing will burn a hole and create the scab/scar, but once it has be neutralized (or used up) it will stop doing damage. This is true of bases as well actually.",
"HF also damages nerves, so when its burning it may not cause pain. But even after it burns it is highly toxic and can cause damage to organs including the brain once in the blood stream.",
"Movies probably use acids because its what they and the public are most familiar with, but your dad is right bases and oxidizer can do the same job."
] |
[
"Did they have to bring the air up to the international space station?"
] |
[
false
] |
how did they get the air to the international space station?
|
[
"Sure. And they keep bringing up \"air\" - now mainly as water, which is split into hydrogen and oxygen at the station. The oxygen is needed for the crew, the hydrogen is used in the CO2 removal system. A bit of nitrogen covers losses to keep the interior at an Earth-like gas mixture.",
"It is part of the usual missions for new supplies and experiments."
] |
[
"There are prototypes, but it is difficult to get enough oxygen and to remove enough CO2 with that.",
"Most of the oxygen is recycled already, but the ISS needs the hydrogen from water to get rid of the CO2 (overall reaction: CO2 + 2 H2O -> CH4 + 2 O2, the CH4 is released to space). The ISS has a nearly closed cycle for oxygen.",
"A system to convert methane to carbon and to recover the hydrogen would reduce the water demand of the station a lot already, and (nearly) close the loop for hydrogen as well.",
"After that the next step is to grow food with the CO2 produced by the astronauts - closing the loop for carbon as well."
] |
[
"How far are we from having algae or plants in a grow module to produce air or would it require too much water to maintain?"
] |
[
"With the eventual arrival of colonists on Mars, would they be able to download content like movies/music from Earth? How would data transmission play out?"
] |
[
false
] | null |
[
"Hi Suddenly_Another_0ne thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Planetary-Sci"
] |
[
"Planetary Sci"
] |
[
"Why is it that morning dew only gathers on the front and rear windscreens, not the side windows, of cars?"
] |
[
false
] |
My best hypothesis is that it relates to surface area; I drive a wagon, so it's not the angle. I stepped outside just now (0630) and noticed all the cars fit the thesis question.
|
[
"I've noticed that if you park next to a wall the side next to that wall won't form dew while the exposed sides will. Are you parking next to other cars side by side?",
"I think it's related to radiative heat transfer: any windows that have a clear view of the sky will cool down faster than those seeing other objects. A window pointed at the open sky is a lot less insulated than a window pointing at a wall at ambient temperature. Here's a link describing this theory.",
"http://www.newton.dep.anl.gov/askasci/gen01/gen01425.htm"
] |
[
"This is the correct answer for this question. The front and rear windows are pointing toward the sky so they radiate heat to space and thus can be colder than surrounding air. ",
"The next thing about this is relative humidity. Colder air holds less water vapor than warmer air. For example a kg of air in temperature of 20C can hold 14,7 g of water vapor before the water starts to condensate 100% relative humidity). Now 0C air can hold only 3,8 g. ",
"Now lets assume at morning the air temperature is let's say 10C and has relative humidity of 95% and thus has 7,24 g/kg of vapor in it. The windshield radiates heat to space and gets one degree colder, this causes the air very close to windshield to be also 9C. But 9C air with 7,24 g/kg of vapor in it has relative humidity more than 100% and then the vapor starts to condensates and mist is formed to windshield.",
"Hope this helps and you are able to understand the phenomenon behind this. Feel free to ask if I there was something you didn't get!"
] |
[
"For the people that live in the atacama desert, specifically the residences of Lima, a advertising company teamed up with a university to build a billboard that takes advantage of the high humidity to generate clean water for residents. This is an active system unlike the passive one you described. ",
"http://phys.org/news/2013-02-lima-billboard.html"
] |
[
"What exactly is meant by ATP releasing \"energy\" for other chemical reactions to use?"
] |
[
false
] |
Does "energy" mean heat? If so, I am not sure what heat means at the level of individual molecules - velocity maybe, or vibrational energy? If so, how exactly can that help another reaction take place?
|
[
"The \"energy\" is basically chemical potential (or degree of chemical reactivity) that can be used to drive other chemical reactions (biologically, heat is just a waste product). ",
"Adenosine Triphosphate (ATP) has a reactive phosphate chain that can be used to \"easily\" add phosphate to many different molecules. Phosphate, in turn can catalyze other chemical reactions by adjusting the \"reactivity\" of metabolites and/or enzymes/proteins.",
"Here is a graphical overview of the chemistry that occurs",
" inside a cell and most of these reactions either directly involve phosphorylation (e.g. glycolysis or breaking down sugars) or are regulated by phosphorylation events (e.g. phosphorylation can turn off or turn on different enzymes, transcription factors etc.)"
] |
[
"The simplest way to think about how ATP can do work (or release energy) is to consider that there are three phosphate groups right next to each other. Each of these phosphate groups has a lot of negative charge, so they tend to repel each other, kind of like a spring. This means ATP stores a lot of potential energy, just like a compressed spring. And when an enzyme cuts one of these phosphate groups off, they strongly prefer to move apart, just like a compressed spring. That releasing of the potential energy stored in the \"spring\" can be used to do a number of things, like mechanical work, or catalyzing a chemical reaction. So in many ways, hydrolyzing the ATP is just like releasing a compressed spring."
] |
[
"To add to what ",
"/u/practically_sci",
" said, one way that ATP is used as an energy store is in DNA synthesis. Clipping together a DNA strand is a very high-energy process and would only happen very slowly (if at all) if left to go by itself. The body solves this problem by attaching ATP molecules - they're so eager to fall apart and become ADP that this drives the entire reaction to happen."
] |
[
"Why is it whenever you see powerful lasers used in labs or other areas they are almost allways green? Is this due to how they are produced or is green light a better wavelength for sensors to pick up?"
] |
[
false
] | null |
[
"A Nd:YAG laser is often used as as it can make ~10 nanosecond pulses at low frequency. (so it compresses all your power into a few short burst of very high power). Example: A 4W laser pulsed at 10Hz with a 10 ns pulse gives a 40 MW intensity during the pulse. Incidentally, this is why pulsed laser are so dangerous compared to continuous lasers. ",
"A Nd:YAG produces 1064 nm light (near IR). High power 1064 nm is very dangerous to work with as you cant see the beam, or reflections etc easily. So, if the wavelength isn't particularly important to the application, most applications will convert to the second harmonic of 1064nm. The second harmonic of 1064 (nonlinear optics) is 532 nm light (green!) Thus you often get green lasers for very high intensity applications. "
] |
[
"Side note: if you need high power pulsed red light, you can power a dye laser with the 532 nm light from a Nd:YAG, thus resulting in applications with red light also having green lasers present on the laser table.",
"For pulsed high power blue light you can use the third harmonic (UV) of a Nd:YAG to power a dye laser. But again, people like to avoid pulsed lasers in non-visible wavelengths so you will see less experiments done with pulsed blue light as they need pulsed UV to power the dye lasers. (That and you loose a lot of power going to the third harmonic) "
] |
[
"If you want to probe the dynamics of an excited state of a molecule that only lives for a very short amount of time (let's say 200 femtoseconds), you need to excite it with a pulse (10-30 fs long pulse for example) and get the hell out of there before you start \"looking\" at it. If your \"pump\" pulse isn't out of the way then you can't tell what's happening on a short timescale and you can only see what's happening on longer timescales, hundreds of fs, or picoseconds/nanoseconds. ",
"The field of science associated with these experiments is known as ultrafast spectroscopy :)"
] |
[
"Why is yellow so hard to see?"
] |
[
false
] |
[deleted]
|
[
"There are no valleys in the overall sensitivity (i.e., the luminosity function). The second figure in that link is (unfortunately) overlaying three different sensitivity functions, which makes it look like one function with peaks and troughs. Here are the three curves shown as separate lines: ",
"http://upload.wikimedia.org/wikipedia/commons/0/04/Cone-fundamentals-with-srgb-spectrum.svg",
"And here they are in a single weighted sum, which is the same as the third figure in your link: ",
"http://en.wikipedia.org/wiki/File:Eyesensitivity.png"
] |
[
"You're right that yellow is off-center, and that's precisely what you should be seeing. There is no rule that says your eye's response to stimulus in the visual spectrum must follow a perfect bell curve. In actuality, our eyes are most sensitive to the yellow-green area (a bit on the \"red\" side of pure green). In a way, this basically means that yellow doesn't need to try as hard to appear bright. Like I said, if you had a green crayon that was equally bright (emitted the same amount of energy), you'd have trouble seeing it too."
] |
[
"He gave the answer to that -- we use the yellow-green region to determine brightness in the first place, and we're most sensitive to individual colors closer to the center of each cone type's range."
] |
[
"With an electromagnetic wave, what is actually waving?"
] |
[
false
] |
Whenever an electromagnetic wave is depicted it's always an up and down motion over time. What is the vertical component? Is it actually moving up and down in space? Or, is the y-axis simply a measurement of some value?
|
[
"An electromagnetic wave is a coupling of an oscillatory electric field with an oscillatory magnetic field, the relationship between which is given by Maxwell's equations. Those ",
"3D depictions",
" we usually see are really just showing the propagation of a wave along a single dimension, with the amplitude along the other two axes representing the amplitude of the fields at that point. So there is nothing actually going up and down in space; as to which axes represent what, that depends on the actual graph, it's not standard."
] |
[
"Yeah, it's kind of confusing for beginners and laypeople. Even after studying Electrodynamics I sometimes have to stop myself from thinking of physical objects waving up and down in space."
] |
[
"Yeah, it's kind of confusing for beginners and laypeople. Even after studying Electrodynamics I sometimes have to stop myself from thinking of physical objects waving up and down in space."
] |
[
"In winter, do plants continue photosynthesis?"
] |
[
false
] | null |
[
"Plants has even a protection mechanism which is called photorespiration, that prevents from the (let's call it) \"overburning\" due to an excess of photons ",
"The protection mechanism is called ",
"non-photochemical quenching",
" with the help of ",
"xanthophylls",
". ",
"Chlorophyll florescence",
" also removes a tiny bit of energy.",
"Photorespiration, which happens in C3 plants and to a much less extent in C4 plants, is the protein/enzyme RuBisCo oxidizing a particular phosphate ester (RuBP) involved with photosynthesis which makes photosynthesis less efficient at higher light levels."
] |
[
"Afaik (and please correct me if I'm wrong) photosynthesis isn't something you can just \"stop\". Green parts which contain chlorophyll don't \"choose\" to photosynthesize or not, it's something very ...\"mechanical\": when chlorophyll is hit by a photon, it has no choice to react. Plants has even a protection mechanism which is called photorespiration, that prevents from the (let's call it) \"overburning\" due to an excess of photons (for example in very hot summers) and this happens exactly for this reason, because, unless the plant doesn't loses its green parts, it cannot choose to get the energy from the sun."
] |
[
"A lot of processes can happen during photorespiration but the starting point is RuBisCo and the problem is too much oxygen in leaf tissue (there are studies on growing plants in chambers with lower oxygen levels to help get around photorespiration issues). The Calvin cycle then tries to make use of the oxygen instead of carbon dioxide which is where the photosynthesis efficiency hit takes place. It is not involved with \"overburning\" protection or plant thermal management.",
"http://www.plantphysiol.org/content/125/1/29.full",
"Most plants can also relocate chloroplasts to receive less light.",
"http://cdn.intechweb.org/pdfs/28376.pdf",
"Leaves have an emissivity of around 0.95 so they are good thermal radiators as well as ",
"transpiration",
" cooling of a plant since a phase change is taking place.",
"When stomata are closed then there is no gas exchange therefore little or no photosynthesis taking place. Drought conditions can cause this, for example. There will more chlorophyll fluorescence occurring which can be measure with my spectrometer and a thermal imaging camera show a lack of transpiration in leaves when the stomata close (I use this technique). The energy from the sun would be almost entirely wasted.",
"I have a lot of lighting information here.",
"edit- slight clarification and non-photochemical quenching kicks in at lower lighting levels than photorespiration. Perhaps 300-600 uMol/m2/sec or so of light for NPQ (this is wavelength and specific plant dependent) versus around 1200-1500 uMol/m2/sec for photorespiration in C3 plants."
] |
[
"Are there any synthetic materials that have the properties of a human thumbnail? Sometimes scraping things off of a surface my thumbnail works better than anything else I have."
] |
[
false
] | null |
[
"I do not know but I would like to point out that a possible reason for the efficacy of your own nail for scraping things is because it is attached to your finger quite rigidly. In contrast, any tool you use is being held by the soft pads of your hand and fingers and thus might absorb shock and be more prone to slipping or changing its angle of attack."
] |
[
"Guitar picks can be very similar. Pliable, but with resistance and not so hard that it will scratch most plastics. \nThey come in a number of different finishes & thicknesses so you would have to go to a store and lpay with them a bit to get the right feel. "
] |
[
"Curses! I came here to say this."
] |
[
"Does DNA ever switch direction mid-strand?"
] |
[
false
] | null |
[
"Wait, what? ",
"Bases in DNA are ",
" connected 5' - 3'. Or you can think of it as 3' - 5' if you prefer. It doesn't really matter, but retrotransposons or \"negative strand DNA\" or anything else aren't special in terms of how they're read or translated. We usually think in terms of 5' to 3' because that's the direction DNA is both synthesized and transcribed in and mRNA is translated in. ",
"By the way, I just wanted to point out that polymerase \"reads\" 3' to 5' and synthesizes 5' to 3'. "
] |
[
"I agree that DNA in the genome is always structurally linked 5' to 3'",
"RNA though, specifically messenger RNA or mRNA is (in eukaryotes) always capped with a 7-methylguanosine in a 5' to 5' way. ",
"http://www.nobelprize.org/educational/medicine/dna/a/splicing/splicing_endmaturation.html",
"\n",
"http://www.ncbi.nlm.nih.gov/pmc/articles/PMC316800/",
"video: ",
"https://www.youtube.com/watch?v=DoSRu15VtdM"
] |
[
"dazosan's right. DNA are always connected 5' to 3', and a 3' end can then connect to another 5' anyway, that's why circular plasmids exist in the first place! To answer the OP's question directly, a 5' cannot connect to another 5', neither would a 3' connect to a 3'. ",
"Concerning directions, I was thinking about something else.\nGenomic DNA is double stranded, and the structure goes like this:",
"\n5' ------------- 3'",
"\n3' ------------- 5'",
"\nIt consists of 2 strand that runs in opposite directions. So you can imagine there will be genes that runs from left to right on the top strand, but there will be genes that runs from right to left on the bottom strand. In this case, if you examine the double stranded DNA from left to right, you could say it \"switched direction\" mid strand, because you will bump into genes that runs in both directions (but on different strands). "
] |
[
"How well do we know physical constants?"
] |
[
false
] | null |
[
"It depends on the constant. The gravitational constant for instance is relatively poorly known because it is so weak. It's only known to about 5 decimal places. Atomic constants (elementary charge, atomic masses, boltzmanns constant, etc.) can be much more accurately measured because they relate to atomic transitions and those can be measured accurately to 1 in 10",
" or more. "
] |
[
"For particle-related properties, you can get that information ",
"here",
". As an example, it lists the mass of the proton (under \"baryons\", box \"p\") as m= 1.00727646677 ± 0.00000000010 u, where u is the atomic mass unit. This is quite high precision (as you can probably see)"
] |
[
"Well, it might soon be the case that the SI units are defined in such as way that many of the important physical constants are of a fixed, exactly known value (similar to how the speed of light is currently defined). ",
"Here is a link",
" to the wikipedia page about it."
] |
[
"Is Gene editing possible on adult humans or can only be done on embryos ? Why ?"
] |
[
false
] | null |
[
"That’s a huge open question in biology right now, actually. We have a few methods of gene delivery that are being tried on a clinical level, of which the most developed one is AAV. There is also stuff like nanoparticle-based delivery, which is very promising but less far along clinically.",
"AAV is adeno-associated viral vector delivery. We essentially take the genetic material we want to insert, pack it up inside a virus, and use retroviral mechanisms to get the gene we want into human cells. The issue with this is that each virus can only hit one cell-after a cell is infected by a virus, whether or not the genetic material is properly inserted, ",
" the virus is already used up. So, considering that we might need more than 1 virus per cell, we would need a TON of viruses to edit more than an embryo. It’s kind of dangerous to pump that many adenoviruses into your body, so for now we can only treat embryos and small cell populations. This is, however, the farthest developed technology.",
"More on AAV: ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5548848/",
"If anyone’s interested, I’m happy to elaborate more on AAV or NP delivery."
] |
[
"I'm interested. Why, or rather, how, does a cell become immune to the virus after being \"infected\" by it?",
"What kind of far-fetched mechanism can you speculate could circumvent this immunity?"
] |
[
"The cell itself doesn't become immune to virus, but your body will mount a strong immune response to the virus the next time it is encountered. That is what killed Jesse Gelsinger, the first recipient of virus vector gene therapy. I believe in that case the vector was was Adenovirus, not adeno-asociated virus, which the patient had apparently been exposed to previously.",
""
] |
[
"If gravity is a property of spacetime, why are we trying to explain it as a fundamental force?"
] |
[
false
] |
I feel like I sound like a complete idiot asking this. I should mention I have no real background in physics, so I probably am an idiot. From what I understand, we describe the strong force, the weak force, and the electromagnetic force as fundamental forces of nature, with each force being mediated by their own boson (or in the case of the weak force, two bosons). Also from what I understand, gravity is caused by mass bending spacetime around it. To me, it seems that gravity isn't something we should be describing as a fundamental force, and that it should be described as a property of the fabric of spacetime. Are we trying to explain it as a fundamental force because it fits better with the math?
|
[
"the other three fundamental forces are gauge theories, meaning that they also admit a \"geometrical\" formulation similar to, but not equal, that for gravity given by general relativity.",
"There are immense similarities between the other three interactions and gravity. Moreover, the geometric picture and the field picture (the one with the gauge bosons) are really equivalent - barring some global subtleties.",
"Finally, the unification of gravity with the other forces is almost a necessity, not just something that would be nice. It is likely necessary to build a consistent theory of quantum gravity. We write gravity and the other forces in all possible equivalent ways so that it's easier to understand possible connections when studying theories of everything. For example, understanding how gravity unavoidably arises as the theory of a spin-2 massless boson (the graviton) made it really easy at the time to recognize that string theory included gravitation.",
"(btw, the weak force has three bosons, and the strong force has eight)"
] |
[
"You can read general relativity entirely as a very complicated field theory on flat spacetime; you choose some particular coordinates and you treat the metric as just a tensor field with specific couplings to itself and to any other mass-energy. What you get is actually a gauge theory where the gauge symmetry arises from what originally were coordinate changes.",
"Writing gravity in this way puts it in the same form as electromagnetism & co. You have a graviton, and gravitational processes are described with series of feynman diagrams involving gravitons. For both gravity AND the fundamental interactions, this \"field\" picture is actually lacking because it misses global effects, for example respectively black holes or magnetic monopoles. But it allows the formulation of perturbation theory. You can go the other way and write the other forces in the \"geometrical\" picture, using differential geometry.",
"A different question is whether you could build a field theory of a spin-2 particle that ",
" admit an interpretation as a local section of a metric theory of curved spacetime, and this is well known to be not possible: as soon as you have self-consistent interacting spin-2 bosons, you have curved spacetime."
] |
[
"The fact that the other three fundamental forces are gauge theories being a tautology is possibly the greatest understatement I've heard this month."
] |
[
"If The Flash were real, would the friction between him and the air at certain speeds basically turn him into a big fireball?"
] |
[
false
] | null |
[
"If he's going fast enough, yeah! Not only that but sonic boom(s), wakes, and all sorts of atmospheric disturbances. ",
"This is all handled in the fiction by adding another layer of scifi/magic to account for all those problems:",
"\n",
"https://www.reddit.com/r/AskScienceFiction/comments/3ddjjx/dc\\_comics\\_how\\_does\\_the\\_flash\\_handle\\_friction/"
] |
[
"One of the cool things about \"the boys\" on Amazon Video was that their \"flash\" killed someone by bursting them in a run by"
] |
[
"The answer is yes, but the reasoning is actually interesting, in that it isn't really about friction. At a certain speed, it's not that he would be rubbing past the air which would cause him to heat up, it would be that the air would not be able to get out of the way in front of him, and it would therefore compress a column of air to such a degree that it would superheat and literally ignite. That's what's happening when a capsule or spaceship is entering the atmosphere and why they need a heat shield. It isn't friction, it's compression!"
] |
[
"Does the colour of ink affect its properties?"
] |
[
false
] | null |
[
"Yes. Different colors of ink are the result of using different dye chemicals. Different chemicals » different properties.",
"Anecdotally, I used to do test engineering at a manufacturer of ",
"huge, continuous-production printers",
" and inks. We had to do lots of testing of new batches of ink, and the differences in viscosity between different inks, and different batches of ink could often cause huge issues in the print nozzles. Additionally, some colors were more sensitive than others to changes in temperature, or temperature oscillations during storage.",
"Is there a specific property you're interested in?"
] |
[
"It's probably brand-specific, as ink manufacturers try to get uniform properties across all colors (though that might not be the case for pen mfr's).",
"If you were really curious, you could collect a large sample of ink of various colors and test the viscosity yourself using a flow cup viscometer. It's a pretty simple test - you just measure the time required for the fluid to flow through a small orifice. I doubt you care that much, but it would be an interesting experiment."
] |
[
"I was wondering about viscosity in particular because it felt like all my red pens wrote smoother than my black pens. Is this inherent for red ink or is it just for that particular brand of ink? "
] |
[
"Why do different animals taste different?"
] |
[
false
] | null |
[
"Diet plays a huge part in determining taste, even within the same species. Grain fed vs grass fed beef for example. This diet causes the fatty acid profile to be slightly different and that accounts for the majority of the differences. Fatty acids can oxidize into a variety of aromatic compounds, some good, some very very bad."
] |
[
"Aside from diet, other things such as the activity of the animal, what temperature they live at and how ey adapt to it, distribution of fat and muscl (which is related to both activity and temperature) as well as more unexpected things at indirectly affect diet such as what type of internal flora the animal hosts can affect its taste. Really almost anything that makes an animals physiology different from anothers can affect its taste. If they have physiological differences in the parts we eat and they arent too subtle, we should be able to taste a difference."
] |
[
"Got it... Should have thought of that myself. :) Thanks!"
] |
[
"What are stitches that dissolve made out of, and how do they dissolve?"
] |
[
false
] |
[deleted]
|
[
"\"Dissolving stitches\" (absorbable sutures) are nowadays mostly made of particular biodegradable polyesters. They are chemically related, though not identical, to poly(lactic acid) or polylactide (abbreviated as PLA -- the most common \"compostable plastic\" and also a common material in 3D printing).",
"They dissolve slowly in warm, wet environments (over a time-scale of weeks or months) as the water breaks down the chemical bonds that hold the polymer chain together. The same process happens in the body, but in that case, the presence of enzymes (released by cells reacting to the presence of the sutures) also speeds things up."
] |
[
"your body identifies them as a foreign body and attacks them",
"Here I have to disagree. The dissolution is just a function of normal proteolytic degradation, normal protein turnover. You don't want the suture to trigger an immune response."
] |
[
"your body identifies them as a foreign body and attacks them",
"Here I have to disagree. The dissolution is just a function of normal proteolytic degradation, normal protein turnover. You don't want the suture to trigger an immune response."
] |
[
"If water pressure is only increased with depth of water. Does that mean that you could have only 1 inch of water next to the Hoover dam from top to bottom and the stresses on the dam would be the same as a full reservoir?"
] |
[
false
] | null |
[
"Yes, if you build two dams back to back with only small gap between them and filled the gap with water the pressure would be the same as if there is whole lake behind the dam.",
"This is true as long as the gap is wide enough that water viskozity can be ignored."
] |
[
"No the water upstream isn’t being forced on the dam. That’s what he’s explaining in the video. ",
"this",
" video also says the same thing. Pressure doesn’t increase with the shape of the container or reservoir. Being it miles long like the Colorado river or just a thin sheet being held next to the dam."
] |
[
"Eh, yesish, but the water has to be held there somehow. This is done by the rest of the water in the resevoir. A 1 inch thick column of water needs some force to hold it in place, without that, it'd collapse. Making your dam wider or changing the dimensions of the reservoir would lower or raise the water height for instance. The force of the river is going to determine what your dimensions are and the resulting height."
] |
[
"Acidosis and oxygen injections"
] |
[
false
] |
I ran across this which claims that an injection of an oxygen laden solution (sounds like an emulsion) could oxygenate blood without the need for breathing for 15-30 minutes during a life threatening situation. Many people are speculating on the possibilities of using this for diving purposes to eliminate the potential of the bends. If you recieved sufficient oxygen for 30 minutes, but didn't ever exhale, wouldn't you suffer from some form of acidosis? Is there any way around this? How dangerous would acidosis be if this was used recreationally (away from a medical facility)?
|
[
"I actually just answered a ",
"very similar question",
" to this one last night.",
"Essentially, you would get respiratory acidosis very quickly. Keep in mind that the technique is being used in a hospital on a sedentary/sedated patient so the oxygen needs for that individual are extremely low. The technique in the article would be extremely ineffective for providing sufficient oxidation of the blood to perform an activity like swimming.",
"That being said, say this technique ",
" provide enough oxygen to the body. The way the body works, CO2 is moved to the lungs where it diffuses out. However, you need to exhale for the passive diffusion of CO2 to be effective at all. This means that you need to exhale. But then for the lung to reinflate so that you can exhale again, you need to inhale. Essentially, just this technique by itself would be absolutely ineffectual for diving.",
"There is a way around the acidosis and that is via a extracorporeal CO2 removal machine. It works by taking blood out of your body, removing CO2, and putting the blood back in. However, again, this is something that's used in a hospital for sedentary patients, so it would not be able to remove sufficient CO2 during any activity.",
"The resulting acidosis (last part of your question) would be extremely dangerous. In this it would be called acute respiratory acidosis. Your body is only able to buffer (i.e. control the acidity of your blood) your blood very slightly and only after several minutes. The resulting acidity, especially after 30 minutes, would cause shock, and respiratory along with other organ failure."
] |
[
"A rough guide to the rise in pCO2 (partial pressure of CO2) is 6 mmHg for the first minute and 3 mmHg for each additional minute of apnea. So for 30 minutes of apnea: pCO2 = 40 (normal) + 6 + 29*3 = 133 mmHg, which is not compatible with life (at least, I have never seen someone survive that, it would put your pH around 6.7). However, one could survive 15 minutes, where pCO2 would be 88 mmHg, although this is still very high (pH about 7.0).",
"One medical use I see for such an innovation would be as a rescue technique for unexpected difficult airway management after induction of anesthesia. In a situation where one is unable to ventilate or intubate a patient, one only has a few minutes to find a way to deliver oxygen prior to permanent neurological injury or death. This could buy you enough time for the anesthetic to wear off, in some cases.",
"edit: another idea could be to use such particles in some cases of respiratory failure (eg. ARDS), in combination with mechanical ventilation, to facilitate \"lung-protective\" ventilation strategies that aim to reduce the ventilator's driving pressure."
] |
[
"Just for the record, I've seen pcCO2's during arrest's on COPD'ers reach into the 150's. It's possible, but brutal to see, and they don't generally have good outcomes, because of what ends up happening to cerebral vasculature at the kind of acidosis/CO2 response."
] |
[
"If manure is all the waste from animals, why does it help fertilize soil?"
] |
[
false
] |
Always wondered how it could have any nutritional value to plants.
|
[
"Plants need Nitrogen, phosphorus, and potassium. Lucky for them, our shit contains lots of it."
] |
[
"Nitrogen cycle?\nNitrogen cycle.",
"The nitrogen in manure is in the form of either ammonium or organic compounds like proteins, urea, etc. Decomposers convert the organic material into ammonium as a product of metabolism (Ammonification or Mineralization), while plants and microbes use ammonium to synthesize organic compounds of their own (Assimilation). ",
"Microbes also oxidize ammonium during ATP synthesis, producing nitrates (Nitrification), which are interesting because, in addition to being assimilated for protein synthesis, they can be utilized as an electron acceptor for ATP synthesis under anaerobic conditions. "
] |
[
"One mans trash is another plants treasure.",
"Same as we breathe in what plants effectively exhale and they breathe in our exhaled chemistry."
] |
[
"Question regarding the Multiverse theory."
] |
[
false
] |
Let's assume each possible universe is the same size and that no two universes are exactly the same. That makes the possibilities finite, correct? Not infinite? My thoughts are this: What this all means is that there is a universe out there where the only difference between ours and its is that one single atom, say, 3,132,872 years ago moved a centimeter further away than that exact same atom did in our universe. Every kind of universe could be like this. Some with drastic changes and others with minor changes, comparing them to our universe, of course. There's a universe out there where Barack Obama is Spider-Man. And another universe where the only difference between that and it is that a blade of grass 2000 years ago swayed a millimeter further than it did in the other. Every different outcome of that universe exists just as every different outcome of any given universe exists. This number is...enormous. This number would break calculators and make numbers like googolplex look like the planck distance. But it's finite, right? Or am I missing something?
|
[
"There is a finite number of ways to arrange matter and energy in a universe.",
"Why would this be finite? As far as we know, the universe is continuous, not discrete, which immediately leads to an infinite number of possible universes, even for a very simple system with one particle."
] |
[
"There's a universe out there where Barack Obama is Spider-Man. And another universe where the only difference between that and it is that a blade of grass 2000 years ago swayed a millimeter further than it did in the other. Every different outcome of that universe exists just as every different outcome of any given universe exists.",
"Suppose A and B are two infinite sets Even if A is a subset of B, and they are both the same cardinality, it is still entirely possible that A is a proper subset of B. That is to say, just as it is not true that an infinite set of rational numbers will necessarily contain any other elements than prime integers, it is not necessarily true that an infinite set of universes will necessarily contain a universe where Barack Obama is spiderman. "
] |
[
"As in, can't the maximum possible information stored within a system be represented by the plank-area of a surface around that system?",
"We have no idea.",
"It's misleading to think of the Planck scale as the smallest possible scale or something like that. It's the scale where our understanding of physics breaks down. Period. End of story... at least until we understand how physics behaves at (and above) the Planck scale.",
"It might turn out it does imply some limit on information or that space is discretized, or it might not. For now, though, we can only speculate."
] |
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