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[
"Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"In Larry Niven's book ",
" a hypothetical planetary system is explicated: a gas giant orbiting inside the Roche limit of a neutron star, such that it is unable to retain its atmosphere, which has subsequently gone into orbit around the neutron star as a torus of gas. The core of the giant planet is still there, chugging around the star. The densest part of the torus is called \"the smoke ring\" and here is where life has taken hold, uniquely suited to an existence in orbit where tidal forces rather than gravity are paramount.",
"To me, this has always seemed one of the most far-fetched ideas in sci-fi. Even if one allowed for the notion of a gas giant atmosphere that's breathable by humans (which I think is a pretty big gimme), wouldn't the radiation and magnetic field of the neutron star simply cook anything that tried to take up residence in the torus, regardless of whether or not it evolved there?",
"I don't want to say anything is impossible, but I've wanted some fact-checking on the idea for a while now."
] |
[
"We know Mars is mostly dead with a weak magnetic field. We also know it has about 1/3 the gravity of Earth.",
"Would it be possible using the asteroid belt and the Oort Cloud objects to not only increase the mass of the planet to match Earth's gravity but to also ensure that the right kind of metals were delivered to restart Mars' magnetic field?"
] |
[
"Besides the obvious point that the Moon would look a lot bigger in the sky, the ",
"tides",
" would have increased amplitude - at low tide the water level would decrease more than it already does and at high tide the water level would increase to a higher level compared to now.",
"In order for the Moon to have a stable orbit it would also need to orbit the Earth faster, so the ",
"lunar month",
" would decrease. The ",
"tidal locking",
" of the Moon would also cease and we would be able to see the far side of the Moon from the Earth."
] |
[
"What exactly is a flavor made up of?"
] |
[
false
] |
What is making something taste like it does? solved! Thanks so much for your answers guys!
|
[
"A large variety of chemical compounds. ",
"Esters are commonly used as flavoring.",
" Aldehydes and phenols are also important flavorants."
] |
[
"It's a combination of taste receptors and olfactory receptors interacting with molecules in your food. As langfan mentioned, esters are especially aromatic and tasteful."
] |
[
"Though a large number of ",
"functional groups",
" in molecules can change the way something tastes, our tongues have evolved to be particularly good at detecting chemicals that are important to our survival. These chemicals are detected by receptors on our tongues that bind with the appropriate chemical and send a signal to the brain. Acids taste sour, while bases taste bitter; either of these can be a sign that we are putting something in our mouths that we shouldn't eat. Free ions in solution taste salty, while sugars taste sweet; these are chemicals that most species need to survive. The fifth flavor, ",
"umami",
" (or savory), is related to the concentration of glutamates, and is often associated with the presence of proteins--again, a source of nutrition."
] |
[
"How does an ovary decide which egg to drop?"
] |
[
false
] |
When the body drops an egg from the ovary in anticipation of being fertilized, how is the specific egg chosen? Is there a queue of eggs waiting in a funnel-like system that switches every other month? Is it completely random?
|
[
"Humans aren’t meant to have litters- we are meant to have a single one to maximize our success with available resources. Whereas animals with large groups of offspring go for a “make a lot and hope some live” type strategy, the larger animals have just one or two to devote all the resources to that.",
"Evolutionarily, the ones that produced a single offspring at a time probably had more offspring survive to maturity, so that trait was the one passed on. Production of twins does seem to have a genetic link, but it’s not necessarily an advantageous trait (babies are often smaller)."
] |
[
"They don't necessary drop in order, as if they were on a production line. Multiple eggs begin to start towards the path of \"dropping\" at a time. The egg that gets to drop is the first one to grow large enough to rupture (corpus hemorrhagicum). That rupture release hormones that revert the other candidates. "
] |
[
"The number of mammary glands a species has is related to litter size. The relationship generally follows the \"one-half rule,\" which states that the average litter size is equal to half the number of mammaries. The number of mammaries also tends to put an upper limit on litter size. It's not necessarily a hard limit, but survival tends to drop noticeably when number of offspring being nursed exceeds number of mammaries."
] |
[
"Someone else asked about what would happen to Earth's orbit if the sun were to all of a sudden disappear. I have a related question?"
] |
[
false
] |
My intuition tells me it would take 8 minutes for the Earth's path through space to change, and someone in that thread said the same thing. This would seem to me that gravity behaves like information, i.e. like moving a long stick, and the other end doesn't feel the force until enough time has passed for that information to arrive at that point. Like the idea that information doesn't travel faster than light. Where this confuses me, is in general relativity. How does relativity explain this? Is it simply in that spacetime can't "deform" faster than light can travel? I have a basic working knowledge of general and special relativity, so feel free to dive into the physics of it, if that's what it takes to answer my question :)
|
[
"\"Where this confuses me, is in general relativity. How does relativity explain this? Is it simply in that spacetime can't \"deform\" faster than light can travel? \"",
"This is correct. Gravity propagates at the speed of light. (Brian Greene's The Elegant Universe)"
] |
[
"The answer is actually a little more complicated as ",
"AaronHolland44",
" makes it to be.",
"It turns out that ",
". That is, the vector that tells you the gravitational force on an object always points to the ",
". That is, Earth orbits ",
", not where it was eight minutes ago.",
"But that's against your intuition, right? It turns out there is something called ",
" that, ",
"with some complicated math",
", cancels out the velocity-dependent terms in Einstein's field equations, such that the Earth ",
" like it is orbiting the retarded position of the sun.",
"Now this also means that, if the sun were to \"suddenly disappear\", the Earth will continue to orbit where the sun ",
" (as if it were moving inertially) for eight minutes.",
"That seems crazy - but that's because it is. By positing a scenario where the sun suddenly \"disappeared\", you're breaking the laws of physics - conservation of energy and angular momentum being two of them. So it's hard to answer the question, because the scenario necessitates the removal of the laws that govern the universe. At the end, it is most accurate to say that gravity is instantaneous, but the changes in gravitational fields propagate at the speed of light.",
"For more information see ",
"this post"
] |
[
"In your magnetic example you have to think of individual particles and not whole objects.",
"A light year long stick, when pushed the other end will not react instantly, but why? Well simply when you push one end, you are really pushing atoms, the first layer of atoms move forward, which then tells the second layer to move forward, and repeat. Electromagnetism which governs how matter interacts and bonds together has a force carrier, the photon. Photons as you know travel at the speed of light, they don't travel faster, or slower, they are locked to the speed of light. So imagine 2 atoms locked due to electromagnetism, you move one atom and the force carrier for electromagnetism the photon must now \"communicate\" the change in position to the second atom to change it's position to remain locked together. So in a very long stick, we have a wave of \"information\" or electrmagetic wave communicating the change. However this change does not even occur in materials at the speed of light, it occurs at the speed of sound in a material.",
"With your magnet example, you are moving a magnet around a needle, that needle is comprised of atoms, and so is the magnet, when there position changes the eletromagnetic field which also governs magnetism must propogate the new information for the needle to align.",
"With gravity if gravitons are found to exist I find this fits perfectly, gravitons would be massless particles, massless particles are locked to the speed of light, thus any change in in an objects mass can only be communicated at the speed of light for how the spacetime geometry changed."
] |
[
"I have a heavy cold right now. How come, I can't last 5 minutes through the day without a heavy coughing attack, but sleep perfectly peaceful at night without ever getting the urge to cough or blow my nose?"
] |
[
false
] | null |
[
"I believe the urge to cough us actually a mental thought process, the same process as pain sensing. When you sleep as you progress through your cycles, specifically your REM cycles, you probably are just in such a deep sleep your mind doesn't receive the signal to cause the sensation of a need to cough. I could be wrong though.."
] |
[
"Usually coughing gets worse during night (not sleep). So you can feel lucky, I guess. While coughing is a ",
"reflex",
" it can be influenced by psychological factors as well. ",
"So Sweet_seduction69 is right basically. You probably think too much about your illness and don't get enough distraction."
] |
[
"Maybe it's allergies. "
] |
[
"Where in Natural Selection did the Photic Sneeze Reflex come from?"
] |
[
false
] |
How would sneezing from looking at a bright light help a human in its survival?
|
[
"Just because it exists doesn't mean it was necessarily beneficial. I can't really speak to this so I'll let experts answer your question for sure. I would just like to bring up that point since it seems to be a common misconception."
] |
[
"This is just a story though. It's very unlikely that we can actually know what the selective pressure was that drove the evolution of [insert random human trait here]."
] |
[
"This is just a story though. It's very unlikely that we can actually know what the selective pressure was that drove the evolution of [insert random human trait here]."
] |
[
"Since a singularity is infinitely small, can 2 singularities be in the same place?"
] |
[
false
] | null |
[
"Singularities in general aren't infinitely small points, it's more common for them to have the structure of instants in time - this is the case for the Big Bang singularity or that beyond a black hole. In those two cases respectively the singularity is in the past of any observer and in the future of any observer who has crossed the horizon.",
"The exception would be given by naked singularities such as that in an overextremal charged black hole, but these are not thought to be realizable in our Universe. These singularities look indeed like point in space - i.e., they have the structure of a time-like wordline (in some sense). But, again, these probably don't exist, and also are repulsive, not attractive.",
"In any case, the question is ill-defined because \"being in the same place\" means that it's understood that there's a coordinate system (t,x) defined on your manifold, and these two objects at fixed coordinate time t have the same coordinate position x. However a singularity is not part of the manifold, it's informally outside. Formally it's just what the name suggest, a singularity in the behaviour of the Riemannian structure itself as you approach an edge of spacetime. The presence of a singularity will at the very least influence the construction of a coordinate system close to it. In particular, for the singularity of a normal BH, it's impossible to choose the time and space coordinates such that the singularity can be understood as something that is in some place."
] |
[
"You're too young to worry about spacetime."
] |
[
"in the real world, singularities can't \"be in some place\". They are an instant in the future of some unlucky people."
] |
[
"Why is only half of my pine tree wet?"
] |
[
false
] |
Three different trees, and only half of the tree is wet after a couple days of rain.
|
[
"Obvious follow-up questions for clarification:",
"Was there a prevailing wind in the direction of the wet side?",
"Is there a heat or significant source of radiation on the dry side?",
"I don't know much about trees, but these details seem relevant if the answer isn't biological."
] |
[
"Is there a correlation to the amount of direct sunlight each side of the tree gets? Also, have we ruled out sap, or some form of secretion from the tree itself?"
] |
[
"No significant wind, but the dry side seems to mostly the west and south side of the trees. There are probably a dozen or so with this going on."
] |
[
"Why do atomic explosions require such specialized circumstances/equipment?"
] |
[
false
] |
The best example I can think of is rather mundane, so bear with me. In laymans' terms, the atomic bomb causes an explosion by "splitting the atom," right? Why doesn't something like cutting a loaf of bread, shooting a target, or swinging a wrecking ball cause the atom to release its energy? All of these things can cause divisions in materials which are made up of molecules and atoms. Is their resistance to force really that high? Is it just an inexpliccable fact of life? Again, sorry for the wording. It's late, I'm tired, and I'm also not the most intelligent individual when it comes to nuclear physics. Any and all answers are greatly appreciated!
|
[
"The nucleus of an atom is held together by the strong force. If you split the atom, you'll need to tinker with it.",
"If you cut bread, shoot a target, or swing a wrecking ball, you only encounter electrostatic forces. Much, much weaker than the strong force."
] |
[
"As others said, you're separating atoms in those cases as opposed to actually splitting them. The atomic bomb actually causes an explosion by splitting a whole bunch of atoms though. It creates a chain reaction in which one atom is a split by a neutron, which then splits to release more neutrons which in turn cause other atoms to split and so on. The nucleus of an atom is held together by very powerful nuclear forces that are actually fairly well understood."
] |
[
"The way this works is with a certain isotope of Uranium. When you shoot neutrons that aren't too fast on that Uranium, it can capture a neutron, which makes the nucleus highly unstable such that it splits. The result is two lighter nuclei (like Caesium) and two or three more fast neutrons. If you manage to slow these down, they can again be captured by Uranium, causing it to split and releasing two or three more neutrons each. If you have enough Uranium around (an over critical mass), this causes a chain reaction, which, if not controlled like in a reactor, blows up.",
"When you slice bread or shoot a target, you will never split an atom, only molecules, because the forces involved are not nearly high enough. Plus, you usually don't deal with heavy nuclei. You can't really split light nuclei like carbon into three Heliums, or one Helium into two Deuterium. I mean, it's physically possible, but it pretty much never happens and would be really hard to achieve. As far as I know, it's never been done before in the lab, but I could be wrong.",
"Certain configurations of protons and neutrons are more energetically favorable than others, which is why some of them decay. On top of that, there is a turning point at iron where having more nucleons is less favorable. That is why fusing Hydrogen to Helium releases energy, but splitting Uranium into lighter elements releases energy too, even though it is the opposite of fusion. "
] |
[
"On a molecular level why is inhaling Cyanide (HCN), even in small amounts, so dangerous to humans?"
] |
[
false
] |
At least with Carbon Monoxide it takes a lot to really do damage but Cyanide seems like one whiff is enough.
|
[
"Cyanide poisons by stopping cellular respiration - specifically, by inhibiting ",
"cytochrome c oxidase",
" in the electron transport chain. It stops the cellular machinery that's responsible for generating energy with oxygen.",
"Carbon monoxide, on the other hand, binds to hemoglobin much more strongly than oxygen does, so it will displace oxygen in hemoglobin. In addition, the binding of one carbon monoxide molecule ",
" the affinity of the remaining hemoglobin sites with oxygen, preventing the release of oxygen. The end result is the decrease in available oxygen to tissue.",
"So these two gases kill via different mechanisms, but similar end result of stopping cellular respiration. In an analogy of disrupting mail service, carbon monoxide does so by stopping the postal delivery workers from picking up and delivering mail. Cyanide does so by shutting down the mail processing facility itself.",
"Do note that similar amounts of both gases can still be quite lethal. ",
"Here it says 3500 ppm of hydrogen cyanide kills in about 1 minute",
" , while ",
"similar concentrations of carbon monoxide kills in 30 minutes",
"."
] |
[
"This is it exactly. Cyanide is basically poison for all carbon-based life. Which is why a lot of plants have a defense where biting or crushing the plant mixes specific chemicals that generate cyanide, in order to deter feeders.",
"There are literally a handful of species of mammals capable of eating cyanide rich diets, most of them are Bamboo Lemurs who live on what should be enough cyanide rich bamboo to kill them 12 times per day. No one yet knows the mechanism that protects them."
] |
[
"It is more complicated than the story told so far. This is a super old source, but it covers this exact topic. ",
" ",
"http://mmbr.asm.org/content/40/3/652.full.pdf",
"I'm not sure if that is behind a paywall, but it is ",
" from Microbiology and Molecular Biology Reviews 1976. ",
" ",
"Here's the relevant bit:",
" \n \n ",
"MECHANISMS OF CYANIDE RESISTANCE\nAND DETOXICATION",
"It is a common myth that cyanide is a specific\ninhibitor of cytochrome oxidase. In fact, cyanide\ninhibits a wide range of enzymes, many of\nwhich, though by no means all, are hemoproteins\nor other metal-containing oxidases or oxygenases.\nDixon and Webb have listed some of\nthe enzymes known to be inhibited by cyanide\n(41). Cyanide is a very reactive molecule, and it\nis not surprising that it is catholic in its inhibitory\ntastes. It forms stable complexes with\nmany metals, reacts with keto groups to form\ncyanohydrins, and reduces thiol groups (136).\nAt concentrations of about 10-4 M or lower,\ncyanide is usually highly inhibitory to cytochrome\noxidase but has little effect on other\nenzymes, which require 1O-4 to 10-2 M cyanide\nfor significant inhibition; there are, of course,\nmany exceptions to this generalization. Therefore,\ntreatment of cells with \"low\" concentrations\nof cyanide often results in an apparently\nspecific inactivation of respiration.",
"How, then, do some microorganisms manage\nto adapt to growth in the presence of cyanide?\nThey can either induce enzymes for degradation\nand detoxication of cyanide or form cyanide-resistant\nenzymes. Because cytochrome\noxidase is sensitive to cyanide poisoning and\nrespiration is central to functioning of the cell,\nthe development of cyanide-resistant respiratory\nsystems is of particular interest and, consequently,\nthere have been several studies of\ncyanide-resistant respiration, but there has\nbeen, to my knowledge, no research on the\nadaptation of other cyanide-sensitive enzymes\nto cyanide resistance.\nDifferentiation between cyanide-sensitive\nand cyanide-resistant organisms has been used\nas a taxonomic test. Moller developed a cyanide-containing\nmedium (116), which has been\nimproved by inclusion of an indicator (56) and a\nhigher concentration of cyanide (119). It has\nbeen shown that the Enterobacteriaceae can be\nsubdivided into cyanide-sensitive (Escherichia,\nShigella, Edwardsiella, Salmonella, Arizona)\nand cyanide-resistant (Citrobacter, Klebsiella,\nEnterobacter, Serratia, Proteus, Providencia,\nAeromonas) species (79, 119).",
"Preliminary studies in my laboratory have\nshown that the active component of complex\ncyanide differentiation media is probably cysteine\n(N. Porter, D. E. F. Harrison, and C. J.\nKnowles, unpublished observations).",
" \n \n "
] |
[
"I'm flying from Seattle to Australia tomorrow, are there any cool experiments I can do to show that I'll be rotating roughly 90 degrees due to the latitude difference?"
] |
[
false
] |
I was just thinking how I'll be rotating nearly 90 degrees. If I had a gyroscope or something, would I be able to see it slowly rotate as I fly south? Any cool experiments that could be done to show this difference in latitude?
|
[
"Get a protractor, tape or glue a straw to the straight edge, and tie a weighed down string to the middle. When you get on the plane, look down the straw at a star that you can easily pick out from the night sky (hope you're travelling at night!) and is viewable from both hemispheres, and mark where the string hangs. Once in Australia and landed, repeat and notice the difference in where the string hangs.",
"I'm pretty sure this will work, have a fun trip :)"
] |
[
"Theoretically it's possible: but you don't have a casing that's friction-free enough to hold the gyro in, and you don't have a good enough power source to spin it. \nIf I were you, I'd get a star chart and see which constellations are only visible on either side of the planet. (assuming the cloud cover clears up enough)"
] |
[
"Foucault's pendulum",
" behaves differently at different latitudes and in an opposing manner in north vs south latitudes. ",
"The underlying principle is the same as that that causes ",
" bodies of water (and air) to drain / swirl in differing directions when isolated from other larger outside sources. "
] |
[
"Spin in particle physics?"
] |
[
false
] |
I know that Fermions have half-integer spin and Bosons have integer spin. I can visualize a spin of 1/2, 1, etc. but what would a spin of 0 or 2 look like? I know that 1 means it looks the same after 360° of rotation, would 2 be after 720°?
|
[
"As you said, one way to look at spin is in terms of rotational symmetry. If you can rotate something 360 degrees and have it look the same, that is equivalent to spin-1. Something that is spin-2 has 180 degree symmetry, and something that is spin-0 is invariant under any rotation.",
"How do you visualize spin-1/2? There are geometric analogies, like ",
"holding a coffee cup backwards and rotating it until you can drink it."
] |
[
"In a certain basis (which can always be chosen), the state of a spin-S particle picks up a phase factor e",
" as you rotate it through a constant axis by an angle θ radians. So if you rotate a particle by an angle 2pi, the state picks up a factor (-1)",
". So as you can see, half-integer spins pick up a minus sign under a full rotation. But more generally, the function e",
" is periodic with period θ ~ θ + 2pi/S, so you could think about the phase \"wrapping around a circle\" as you rotate from 0 to 2pi, where it wraps around S times by the time you get to 2 pi (and wrapping around halfway corresponds to picking up a minus sign, as e",
" = -1).",
"(Though I'm not sure you'll find any of this is intuitive if you're not familiar with QM...)"
] |
[
"Complex numbers are numbers of the form z=x+iy, where x is a real part and y is the imaginary part. We can imagine that z is a vector on an abstract plane called the ",
"Argand plane",
", where its real part is the x component and the imaginary part is y.",
"Just like you can rotate a vector in the Cartesian plane by some angle, you can rotate a complex number lying in the Argand plane by an angle. To rotate a vector ",
"=(x,y) in the Cartesian plane, we use:",
" = R(θ)",
"where R(θ) is the matrix",
"cos(θ) -sin(θ)\nsin(θ) cos(θ)\n",
"so",
"x' = xcos(θ) - ysin(θ)",
"y' = xsin(θ) + ycos(θ)",
"Euler's identity says that e",
" = cos(θ) + isin(θ), so let's see what happens if we multiply z=x+iy by it.",
"e",
"z = xcos(θ) + ixsin(θ) + iycos(θ) - ysin(θ)",
"Collecting terms, the real part and imaginary parts are now:",
"Re{z} = xcos(θ) - ysin(θ)",
"Im{z} = xsin(θ) + ycos(θ)",
"So multiplying by e",
" rotates complex numbers in the Argand plane in the same way that R(θ) rotated them on the Cartesian plane.",
"We call the direction that the state is pointing in the Argand plane its phase. The phase of a particle cannot itself be measured directly (it has no effect on the particle's observable properties because e",
" is unitary), but a difference in phase between interacting states can be measured."
] |
[
"How do Scientists derive formulas and constants?"
] |
[
false
] | null |
[
"It depends on the equation. Some, like F=ma are basically just mathematical expressions of an experimentally observed fact. Others, like say your kinematic equations, like, v_final = v_initial + at, are just derived from the definitions of velocity and acceleration and using Calculus.",
"As for experimental constants, there's a reason they're called EXPERIMENTAL constants, because you find them by doing experiment.",
"Most equations beyond the \"basic\" ones are mathematically derived though."
] |
[
"From experiments.",
"F=ma is a definition of force, but you can observe that forces always come in pairs: If body A exerts a force X on B, then B also exerts a force X on A in the opposite direction. You can test this with thousands of different objects and mechanisms for transmitting the force until you are reasonable sure that this is always the case.",
"To find G, measure the force between two masses in the lab. F=G m1 m2 / r",
" or G = F r",
" / (m1 m2). Repeat this with as many objects as possible to verify that it always works."
] |
[
"I teach physics and the way we do it in class is collect a bunch of data from an experiment. Then we graph the variables we are interested in. Then we compare graphs from our slightly different experiments and try to figure out the meaning of the slope and y-intercept. The slope often has a physical meaning, like mass or velocity, and other times it's part of the equation, like GmM. Many of the constants are those values because of how we've defined things like what 1 newton means, and those constants would be different if our units were different. "
] |
[
"Is brushing your teeth with toothpaste truly the only way to maintain them ?"
] |
[
false
] | null |
[
"Related: I've heard recently (pretty sure it was on reddit, maybe askscience even) that there was a study that actually suggested brushing your teeth ",
" tooth paste was more effective and got them cleaner.",
"Any truth in that?"
] |
[
"I also heard this on ",
"/r/askscience",
" by a dentist. I believe the reasoning he gave was that toothpaste vastly improves the experience of brushing your teeth so it increases occurrence in the population."
] |
[
"Weird thing, but I actually hate toothpaste. I'd much prefer to brush without it. So is this really true? "
] |
[
"Ask Science: How do we know that the gravitational constant in our galaxy, is the same in other galaxies?"
] |
[
false
] |
I am very new to studying the sciences so this may be a dumb question. But if galaxies are all spinning at different speeds and expanding away from us could the gravity be different in other parts of the universe. If they were different what does this actually mean? How could we even measure it? Is there any point to measuring it? Could this explain why galaxies that collide seem to interact in ways we wouldnt expect them to?
|
[
"Layman here.",
"Stars life cycle is dependent on their mass. Astronomers know enough about the lifecycle of stars to be confident that the stars in other galaxies are behaving the same as the ones in ours.",
"Also the evolution of the universe is shaped by gravity. You wouldn't expect the universe to be homogeneous and isotropic if gravity would be different in other regions of the universe."
] |
[
"WMAP is very close to isotropic. Also, we've observed galaxies on large enough scales to see that on scales greater than about 100,000 megaparsecs, the Universe is essentially smooth and uniform."
] |
[
"\"Modified Newtonian Dynamics,\"",
" or \"MOND\" is the theory that attempts to explain observed discrepancies in galactic motion with the idea that we have the gravitational equations wrong. ",
"As I understand it, two major problems with MOND are:",
"In other words, it's a formula derived out of observation that hasn't been used to successfully predict any behavior, and has no basis in other observed quantum phenomena. ",
"From here I defer to our cosmological experts. "
] |
[
"Some plants are known for absorbing toxic chemicals from contaminated soil, and are said to be good at soil remediation. But where do those chemicals go after they're absorbed by the plant?"
] |
[
false
] |
For example I've seen articles that say that cattails absorb a lot of toxins from wetlands, so they have a positive impact. But when the plant dies, doesn't it just fall down in the same environment and release everything back into the soil? What is the benefit of things like this?
|
[
"They’re sequestered in the plants material. The stem, the leaves, whatever.",
"Unless the pollution is some kind of organic molecule that is actually used and transformed by the plant, then the pollution just sits in the plant.",
"Those plants can then be chopped down/harvested and then properly disposed of.",
"It’s a lot easier to let the plants absorb the pollutant and then harvest the plants and take them away, then try to artificially absorb the pollutant directly from the ground sometimes."
] |
[
"I knew of a company called Phytoteck. They planted mustard plants on contaminated soil (heavy metals), harvested them when fully grown, and then trucked them away for burial/ The EPA shut them down saying they were afraid of wind blown distribution of contaminants if the plants dried out before being buried."
] |
[
"Thank you, that's really interesting!"
] |
[
"What happens when your body encounters a pathogen that it has no antibody for?"
] |
[
false
] | null |
[
"This happens routinely and is part of the normal immune defence to a pathogen you've never seen before.",
"1) Pathogen enters the body by whichever route you prefer - let's say you stand on a thorn or something.",
"2) The pathogen triggers the innate immune system which detects highly invariant molecules which are ",
" found within your body such as lipopolysaccaride, a component of bacterial cell walls. ",
"3) The innate immune system kills the pathogen through various methods which I won't explain here",
"4) Bits of the pathogen are digested by your immune cells and presented on the surface. They then travel from the site of infection to your lymph nodes or spleen. Here they wander about waving their bit of pathogen they have on their cell surface to all the naive T cells present in the lymph nodes. ",
"5) One of the T cells will recognise that bit of pathogen, activate, and clonally expand producing millions of identical T cells specific for that bit of bacterium",
"6) One of those activated T cells will go and find a B cell also specific for that antigen and activate that B cell. The B cell receptor is a membrane bound antibody and upon activation, the B cell also undergoes clonal expansion, becoming an antibody secreting plasma cell.",
"7) Antibodies are secreted on a huge scale and clear the pathogen from the system, again by various methods."
] |
[
"That doesn't really happen. That said viruses and bacteria put a lot of effort into evading the immune system, both innate and adaptive but by methods other than no corresponding T cell. ",
"Have a look at viral escape (there's a review ",
"here",
") in addition to specific bacteria like TB which hide within macrophages or viral Hepatitis which has all sorts of clever tricks!",
"Edit: CMV is an amazing case and is, in some regards, the perfect virus. It infects most of the human population - the vast majority are asymptomatic. When it infects cells it causes them to downregulate the cell surface protein which CD8 T cells scan for signs of viral infection. So the T cell can't detect if there's anything wrong. But the body's smarter than that and Natural Killer cells will kill cells when they fail to display MHC Class I. But the virus is even more amazing - it expresses a viral protein which looks like MHC I without any of the functional capabilities. CD8 T cells think there's nothing wrong because it can't read the MHC, but is satisfied that they've read something, and NK cells don't kill it because MHC I like protein is expressed."
] |
[
"So interesting! Thanks"
] |
[
"A planet orbiting two suns"
] |
[
false
] |
is it possible for a planet to orbit 2 suns (like in star wars) and if so what would its orbit look like
|
[
"It's perfectly possible to have a binary star system - either with the planet orbiting one star and the other star significantly more distant, or with the two stars relatively close together and the planet orbiting the centre of mass of the system.",
"Systems like that have now ",
"been observed",
", so yes, it's perfectly possible."
] |
[
"This",
" applet can show you what an orbit like that could look like, select the 'binary star, planet' preset."
] |
[
"When two stars are part of the same solar system it is called a binary star. The center of these type of solar systems (where our sun is in ours) is actually the center of mass between the two stars which both the stars orbit around. So if there were any planets also included in the system, they would either also be rotating around the center of mass of the system like the stars, or depending on their location just orbit one of the stars akin to a moon around a planet."
] |
[
"Would a dead body get sunburnt?"
] |
[
false
] |
I'm asking if there would be any differences between an exposed corpse and live individual. Does the body react differently to solar radiation during decomposition? Would the length of exposure produce differing results between a corpse and a living body. I know it sounds like a silly question, but while watching Psych I noticed one of the investigations found a nude dead body out in the sunlight, and it was pale despite several supposed hours of exposure.
|
[
"Skin turns red due to increased blood-flow as your body tries to fix the damage caused by the UV radiation. A dead body doesn't try to fix anything."
] |
[
"Adding to this; there'd still be UV damage, but in the time it would take, the heat from the sun would be helping along the bacteria eating the body, and you'd probably see decomposition before anything else."
] |
[
"Not only is the redness from increased blood flow to the region, but the burn itself is actually due to UV damage to non-coding RNA, which then triggers an immune response from surrounding cells.",
"So if the biochemical reactions within the cell have come to a stop, no sunburn will be present.",
"http://www.biotechniques.com/news/Sunburn-Results-from-Damaged-Noncoding-RNA/biotechniques-332812.html?utm_source=BioTechniques+Newsletters+%26+e-Alerts&utm_campaign=c806788767-Weekly&utm_medium=email#.UDnNQaN3FBm"
] |
[
"Anyone Help maths-algebra? Thanks"
] |
[
false
] | null |
[
"Not the right sub."
] |
[
"Where should I post it?"
] |
[
"/r/homeworkhelp"
] |
[
"Why are there little holes in the metal prongs of power adapters?"
] |
[
false
] | null |
[
"The holes are to fit little bumps on the inside of the socket to prevent the prongs from slipping out. Type A & B plug types are detailed ",
"here",
". See also the description for plug type A ",
"here",
"."
] |
[
"You can purchase extension cords that slide pins into those holes. They mechanically latch and you cannot remove the plug. ",
"I have a \"Husky\" brand cord with a little switch on the outlet. That engages the pin to mechanically lock the plug. They work really well, particularly when you're pulling multiple extension cords plugged end to end. "
] |
[
"Dude, uk have the greatest and safest plugs in the world. Until you stand on one of course. "
] |
[
"Were there feathered 4-legged dinosaurs?"
] |
[
false
] |
I've done some searching but I'm not sure on the terminology to search effectively.
|
[
"Here's a sort of family tree of dinosaurs",
"http://biology.unm.edu/ccouncil/Biology_203/Images/Phylogeny/cladogramDino.gif",
"It's not known exactly when feathers show up, but to the best of my knowledge the group including everything to the right of T. rex (and including T. rex) probably had feathers or protofeathers of some sort. Feathers aren't known from any others, though some may have had fibers or hollow quills of a sort on their skin. We have probable featherless skin-prints from some sauropods and hadrosaurs. Pterosaurs aren't dinosaurs, but they are fairly closely related, and they were furry.",
"Hope that helps somewhat."
] |
[
"Well, it's a matter of semantics what's a \"leg\" and what's a \"feather\". ",
"A lot of dinosaurs had shaggy fur-like feathers like a modern ",
"emu",
" or ",
"cassowary",
" or ",
"kiwi",
" bird. ",
"e.g. ",
"- the therizinosaurs",
"https://upload.wikimedia.org/wikipedia/commons/7/71/Nothronychus_BW2.jpg",
"https://upload.wikimedia.org/wikipedia/commons/c/c6/Nothronychus_SIZE.png",
" ",
"http://whatsinjohnsfreezer.files.wordpress.com/2013/03/therizinosaur.jpg",
" ",
"- the early tyrannosaur ",
"Yutyrannus",
" ",
"- and others: If you search for \"feathered dinosaur\" you'll see images. ",
"Microraptor",
" was a small dinosaur that's usually described as having had four wings, but it had toes and claws on all its limbs and ",
"probably used them all for climbing locomotion",
", so we could just as well say that it had \"four legs\" that it also used for flying. "
] |
[
"Thanks, this actually probably best answers my question (which I asked poorly I think :P) The diagram was helpful. "
] |
[
"Can you freeze water while it is conducting electricity?"
] |
[
false
] |
As the title asks. If water is currently conducting electricity, can it be frozen?
|
[
"Water is not actually a conductor ",
" which makes the premise problematic.",
"Ions dissolved in the water can conduct electricity though and it is basically impossible to keep ions out of water so even highly distilled water still conducts (if only a little).",
"To answer your question, the freezing water would impede the movement of the ions in the water and the impedance between your two electrodes would rise and the current would diminish. However, the current would not keep the water from freezing (I assume we are talking relatively weak currents)."
] |
[
"The current would being to heat the water (due to the natural effects of nonzero resistance), and could potentially out-do your proposed freezing method."
] |
[
"What if we increased the strength of the current?"
] |
[
"I'm a EE student but I just realized my love of physics, what should I do?"
] |
[
false
] |
[deleted]
|
[
"Yes it is possible. I know a few engineers who have pursued physics at the graduate level. With an electrical engineering degree you should have the mathematical background for it (PDEs and linear algebra mostly), which is the most important thing for theory. My advice would be to take a quantum mechanics class if you can, and read some textbooks. Talk to professors that you're interested in working with, and see if you can work with them.",
"A good textbook for someone with an EE background would be Griffith's Electromagnetism textbook; see if you can understand it, particularly the later chapters on relativistic E&M."
] |
[
"I went the opposite, physics undergrad into engineering grad school. both tracks are very doable because they build off similar concepts.",
"Good luck and have fun."
] |
[
"I struggled with something similar while in college. Here's what I came up with, though your mileage may vary. I was studying computer science, but had a real passion for cosmology and theoretical physics, still do actually. There were two big revelations that helped me decide on sticking with CS.",
"1) I knew lots of people who developed software that were making good livings doing it, while I knew personally zero theoretical physicists.",
"2) I made the realization that like my mother who really enjoys going to Church (it's not for me at all) yet had no interest in joining the clergy or being a Biblical scholar, so too, I had (and still have) a real love for theoretical physics. But like my mother, my yearning for that passion is a qualitative one. I love that folks that are probably way smarter than me are out doing the hard math on Riemann Curvature Tensors and then just presenting me with the information necessary to have a good qualitative understanding of how the universe works. I'm perfectly happy making my living writing software while reading as many books on the current theories in cosmology as possible and picking up enough of it that I can draw and explain the famous \"light clock\" experiment for time dilation.",
"Anyway, you may decide to pursue a career in physics instead of EE, but the TL;DR is that maybe what you're really facing is a false dilemma. You can certainly have a day job as an electrical engineer while spending most of your free time enjoying learning about M-theory."
] |
[
"Putting space garbage on the moon?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"/r/AskScience",
"guidelines",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"Can you give an actual reason why? I don't see how it's a theory to be vetted or debunked. And I'm not asking for peer review. I'm asking if space junk can be sent to the moon and why or why jot? "
] |
[
"Hi, feel free to send a message to modmail to have another mod review the removal:",
"https://www.reddit.com/message/compose?to=%2Fr%2Faskscience"
] |
[
"What research is being done on animals and their inbred \"instincts\"?"
] |
[
false
] | null |
[
"This is too broad of a question. There is tons of research done on a variety of animals and behaviors. The keyword you are looking for is \"innate\". You can do an advanced Google scholar search for whatever animal you are interested in + innate and exclude things like \"immune\" \"immunity\" and \"resistance\" since there are also a bunch of articles on innate immune response which isn't what you're interested in."
] |
[
"Right, but I'm asking people to share some things that maybe people don't know about. Or maybe they do. There's no wrong answer or specific question that needs answered, I'm asking what's out there."
] |
[
"In that case, I would recommend posting to our sister-sub ",
"/r/asksciencediscussion",
". We don't really do \"what are some cool facts/examples\" posts on this sub."
] |
[
"Why does Covid-19 affect your taste and smell?"
] |
[
false
] | null |
[
"The olfactory support cells, which surround the neurons and help them function, are susceptible to the coronavirus. It is believed that the virus causes the olfactory epithelium to lose the cilia that detect smells."
] |
[
"Short answer yes. However the stratified squamous epithelium (the lining of veins) does not typically come into contact with the virus. Currently it is thought to be impossible to spread through blood. A considerable amount of cases have had cardiovascular issues, such as strokes, bruising, encephalitis (brain swelling) and a lot of other atypical symptoms. Covid is a very strange virus, and quite unlike any seen before."
] |
[
"Doesn't the virus affect the epithelium of veins all over the body too?"
] |
[
"Why do some animals have slit pupils and some round pupils (e.g. cats v. dogs)?"
] |
[
false
] |
Why do some animals have pupils that form slits when closed (like cats, for example, or some snakes) while other animals have pupils that stay round (like us, or dogs)? Is there a functional difference? Does it relate to the animals' origins as a primarily nocturnal or daytime species? I am working on a boring project this morning and, looking at my cat's eyes as he sat in the sun, I just started to wonder.
|
[
"Imaging scientist here. The answer has to do with the resolution that can be achieved through different apertures (i.e. pupils).",
"The narrower your aperture is, the higher the frequency response is in that direction. To first order, resolution is the Fourier transform of the aperture. However, it is a tradeoff, infinitely small pupils give you infinite resolution (ignoring diffraction), but don't let any light through.",
"That is, cats have higher spacial resolution in the horizontal plane than in the vertical one, because their pupils are narrower in that direction. Cats are hunters and hunt their food seeing it in that plane.",
"Analogously, goats and sheep have square (horizontal slit) pupils because they evolved in mountainous regions and threats came from uphill or downhill.",
"Humans and many other animals saw threats/food from all directions.",
"Cuttlefish have ",
"w shaped eyes",
". According to the pedia, this lets them see the polarization of light."
] |
[
"Slit pupils are an adaption to multifocal lenses.",
"Because light is dispersive, a monofocal lens cannot focus all wavelengths equally. This is a problem called chromatic aberration. For many animals, it isn't much of an issue. For small animals with large eyes, and a very low f-number, it's a big problem that would limit the clarity of their vision.",
"The solution is to have a multifocal lens. The lens is made up of concentric regions, each of which focuses a different range or wavelengths.",
"Now if you have a multifocal lens of this sort, you can't have a circular pupil. Contracting the pupil would cut off some of the wavelengths. The solution is to have a slit pupil. This means that even in bright light a domestic cat can use all the regions of its multifocal lens.",
"The general pattern is that larger animals have monofocal lenses and circular pupils, while smaller animals have multifocal lenses and slit pupils. For example domestic cats have slits, the lynx has a kind of oval pupil, and all the big cats circular pupils. Foxes have slits, wolves have round pupils. There are however some exceptions, like mice (multifocal, circular pupil)."
] |
[
"And the craziest eyes of the animal kingdom belong to the ",
"mantis shrimp",
"."
] |
[
"Is there an explanation or at least widely accepted theory behind gluten intolerance?"
] |
[
false
] |
I recently met a girl who up until she left for college was able to eat all the bread she wanted. However, during her first semester she became gluten intolerant. Is it genetic? or something more? I have found lots of material on it and even explanation on why the body can't process gluten in intolerant individuals. Though, I have found nothing explaining how the body gets like that or what causes it to emerge late in life. Thanks for reading!
|
[
"Mm no, there is a pretty well established etiology for gluten intolerance. Now whether everyone who SAYS they have it actually has it, that is another question. ",
"I would urge you to keep an open mind and not fall into the trap of assuming something is made-up simply because it has increased in prevalence. "
] |
[
"Hi I'm an immunology grad student and I may be able to help you with your question",
"I guess the first thing to say is that gluten intolerance still hasn't been completely figured out. Gluten intolerance is a strange occurrence because our immune system is usually pretty good at not reacting to food proteins because of something called \"Oral Tolerance\". The idea is that constant exposure to a foreign substance (for example, gluten) in our intestines will condition our immune system to not react against it and cause inflammation. This is a major idea in mucosal immunology and it also is involved with how we can co-exist with huge amounts of bacteria in our gut. For some reason people with gluten insensitivities have a breakdown of this \"oral tolerance\"",
"When it comes to gluten sensitivity, it is now seen as a spectrum of disorders. The one we are taught most about is Celiac's Disease. This is a disease characterized by an immune response against gluten, and it has a very strong genetic correlation. More than 95% of people with Celiac's Disease also express the MHC allele HLA-DQ2 (MHC molecules are very important in the immune system. They bind to foreign proteins and present them to your immune cells, which is how you develop immunity against specific pathogens)",
"When you digest gluten, you break it down into smaller proteins. It turns out that one of these proteins, alpha-gliadin, just happens to bind very well to HLA-DQ2, which means that your immune system could potentially see that protein as foreign and mount a response. What this means is that the next time you ingest gluten, your immune cells will think that anything that contains gliaden is infected with something and needs to die. So the cells in your gut, not knowing any better, will show this gliaden to your immune cells only to have them \"Oh no! This cell is infected and needs to die\" You immune cells then proceed in causing the innocent cell to die and will release other proteins that promote inflammation and further cell death. This will be the start of a chronic disease and everything you ingest gluten you are triggering your immune cells to attack your body. All this leads to an overall inflammatory gut and just basically an all-around bad time for the victim. That is a very simplistic view of the subject but I hope it makes a little sense",
"What's interesting is that most individuals who express HLA-DQ2 do not develop celiac disease even though in the western diet gluten is everywhere. So there must be other factors, genetic or environmental. It's probably both. As of now it's not completely known why this \"oral tolerance\" breaks down. Some studies have shows that other immunoregulatory genes could be involved and people with mutations in some of these genes could make them more susceptible",
"Also, people without the HLA-DQ2 gene can still have other gluten insensitiveness. There is evidence now that the gliadin proteins themselves can stimulate an immune response, even without using HLA-DQ2. I think the actual disease is a little different than Celiac's, but it still results in inflammation in the gut triggered by gluten.",
"I hope this helps some. Gluten insensitiveness can be developed as we age, but people still don't know exactly why they develop when they do. It may just be a case of 'wrong place at the wrong time' where several factors come together to set up a chain reaction leading to a chronic condition :(",
"mucosal immunology is crazy"
] |
[
"What's interesting is that most individuals who express HLA-DQ2 do not develop celiac disease even though in the western diet gluten is everywhere. So there must be other factors, genetic or environmental. It's probably both. As of now it's not completely known why this \"oral tolerance\" breaks down. Some studies have shows that other immunoregulatory genes could be involved and people with mutations in some of these genes could make them more susceptible",
"I've heard some speculation that infection might be involved, somehow. Like, if a strand of virus or bacterial DNA shares some coding with gluten, those with HLA-DQ2/DQ8 might mistake one for the other?",
"I know there isn't much conclusive evidence to support any of the theories, but how plausible does that sound?"
] |
[
"Does the Quantum Uncertainty Principle and the CPT symmetry mean that the past is also uncertain?"
] |
[
false
] |
Since in theory there is a CPT symmetry, would Quantum Uncertainty also hold if we reverse the arrow of time? Does the Quantum Uncertainty Principle hold for the past, or only for the future?
|
[
"CPT symmetry says that the laws of physics are ",
" symmetric in time. For everyday events you might as well call it symmetric. Our direction of time is given by the fact that the past had very low entropy. Some interpretations of quantum mechanics give an additional direction of time by the measurement postulate (like Copenhagen Interpretation or GRW model). ",
"The uncertainty principle is not really a time dependent statement. You could freeze the universe in time and it would still be true. Adding a direction of time is irrelevant in the basic notion of the statement. It's a mathematical fact about the mathematical representation of a particle in quantum mechanics. The name \"uncertainty\" is somewhat misleading with our modern understanding of QM. The name implies there's some information we can't access, but most interpretations of QM would just tell you you're asking a bad question when you're asking for the exact position and exact momentum at the same time."
] |
[
"|The name \"uncertainty\" is somewhat misleading with our modern understanding of QM. ",
"To be fair it's catchier then Heisenberg's Necessary Relation Between Position Distribution And Position Evolution Which Prevents The Position Distribution And The Momentum Viewpoint From Both Being Sharply Concentrated At The Same Time Principle "
] |
[
"Yes-and-no. Ultimately this is a very very philosophical question regarding how you interpret the ",
" of the physics we use to describe the world. ",
"I would roughly argue, in the vaguest terms (to somewhat avoid my own sympathies on the matter), that the past is ",
" as the future is. Ie, in the several ways to answer the question, you'll likely find that the future is just as uncertain in ways that the past could be, or that they're both certain in the same ways. ",
"Which isn't to say anything about determinism or epistemology (what we can know about the world). The world may be ontologically (truly/really) \"certain\" and yet epistemologically undeterministic (it is not possible, in principle, to calculate the future knowing present conditions)."
] |
[
"What are ways to back up computers in a manual way which would be unaffected by EMP and would still allow for data recovery to a computer?"
] |
[
false
] | null |
[
"You could put your storage device in a Faraday cage and it would be protected from the EMP, although that's probably not the answer you wanted.",
"Optical media would be unaffected, however they do degrade over time.",
"Paper or punch cards could be used, but the amount of data would be fairly small, and they can still degrade if stored poorly. The standard IBM punch card that was popular in the early days of computing had 80 columns and 12 rows, which can contain 960 bits (125 bytes) of information. A 8.4GB DVD is equivalent to about ",
"90 million",
" of these punch cards. ",
"Relevant XKCD What-if",
".",
"With modern technology the amount of data able to be stored on paper or punch cards could be significantly higher than this, however I don't think this has been used or seriously attempted."
] |
[
"It depends on how long you want to keep the data. CDs and DVDs are not affected by EMPs because the bits are actually burned into a polymer substrate. And I read about some archival DVD technology a while back that would work. The only issue with CDs and DVDs is that the data will degrade after 5 to 10 years."
] |
[
"Do \"pressed\" optical discs last longer than ones that are burned? "
] |
[
"Do you happen to know any good math theory books?"
] |
[
false
] |
I am looking for advice on good math theory books, a similar one i've read was Zero: The Biography of a Dangerous Idea by Charles Seife. I'm also interested in physics books, but any will do. Thank you reddit
|
[
"Do you mean \"math theory\" in a popular-science kind of way? Or real, serious, balls-to-the-wall academic stuff?",
"Because I have to warn you... Most of it is pretty damn dense.",
"EDIT: To assist us, can you give us an idea of your level of formal mathematical education? In particular, have you done any rigorous calculus (i.e. does the phrase \"Let epsilon > 0\" mean anything to you?) or abstract algebra?"
] |
[
"i'm currently reading this: ",
"http://en.wikipedia.org/wiki/G%C3%B6del,_Escher,_Bach",
"if you like math, physics, logic, music, and anything with patterns that might have something interesting to say about the nature of the universe, give it a shot."
] |
[
"There's no such thing as math theory, there is just math. If it's not math, it's nonsense."
] |
[
"Why do allergies occur only in certain parts of the body?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"/r/AskScience",
"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."
] |
[
"Hi there, ",
"Thanks for letting me know what was causing it to not be submitted. I have resubmitted but it still doesn't seem to have been approved?"
] |
[
"I think in that case, it was just missed by us. If you resubmit it again (sorry!) and let me know here, I'll try to take care of it ASAP."
] |
[
"Calcium Channels... What does \"Q\" stand for in Q-type? L=Long Lasting, R=Resistant, N=neurotranmitter, and P=Purkinje...but I can't find the meaning of Q!"
] |
[
false
] | null |
[
"I will attempt to answer this as I think the original nomenclature was designated \"Q\" because it fell just after \"P\" in the alphabet. As you mention, the P Type CA2+ channel was discovered because it was in high concentrations in Purkinje neurons and thusly labeled in 1989. As scientists continued to discover different calcium channels, the above labels began to emerge, just as you mention. However, in 1995 Randal et al started to describe a disparity of the P type calcium channel that varied its voltage response to Funnel Web Spider Venom. ",
"Randal and Tsien then labeled this variant \"Q\" (no apparent reason given). As more research was done, it was discovered that both the P and Q type calcium channels arose from the same gene and only post-transcriptional splicing caused the differences(",
"http://en.wikipedia.org/wiki/Post-transcriptional_modification",
") if you are interested. Here is an article written by the co-author(Tsien) of the 1995 paper detailing the history of calcium channel discovery(",
"http://www.ncbi.nlm.nih.gov/books/NBK6465/#A32920",
")",
"Sources:\nRandall et al 1995 paper: ",
"http://www.ncbi.nlm.nih.gov/pubmed/7722641",
"\nTsien History of Ca Channel: ",
"http://www.ncbi.nlm.nih.gov/books/NBK6465/#A32920",
"\nAlso: I am an MD",
"TL; DR It was after P in the alphabet."
] |
[
"I just had a chat with Andy Randall, and he confirms, it was just the next letter after P...",
"I can also say that R was chosen the same way, and has nothing to do with \"Resistant\""
] |
[
"I'm pretty sure he's getting confused with the iQ cardiac current, what is now called iH."
] |
[
"If water is hardly compressible, how do sound waves propagate through it? Do they propagate faster in water?"
] |
[
false
] | null |
[
"They propagate much faster. The speed of sound in water is about 1500m/s, compared to 342 m/s in air."
] |
[
"So since the water is hardly compressible, the movement is faster? Does this also mean they are dampened? (edit: compared to air)"
] |
[
"Sound speed is given by c=sqrt(B/ρ), where B is the Bulk Modulus (inverse of compressibility ß) and ρ is density. Water is 1000x denser than air, but it's also 15000x ",
", so the overall effect is that the speed of sound in water is considerably higher than in air.",
"An easy way to think about this is that the water has a lot of molecules packed closely together, so if I move one molecule, it will very quickly run into another molecule to transfer its energy to. In air, however, the molecule will have to fly for a little ways before it runs into another air molecule to transfer its energy to.",
"A fairly good simple model is billiard balls in a row. If the balls are far apart, then when I hit a ball it has to move some distance before it hits the next ball, which then has to move some distance before it hits the next, etc. If the balls are closer together, the wave will move faster because it doesn't have to hit anything. If we connected the balls together with a rigid rod (like in a solid) then the energy would propagate almost instantaneously."
] |
[
"Is there any way to test products meant for humans that could potentially be harmful on non-living substances?"
] |
[
false
] |
After reading about rats showing empathy I wondered what it meant for ethical testing. Is there anyway to test products meant for humans on non living or "unconscious" organisms?
|
[
"There are in-vitro tests, that test substances on tissue samples from humans that are still 'alive', in that the cells are still doing their basic functions and are dividing. You can get detailed information about the effect the substance tested has on the cells, but as you are not actually testing in a real human being, or any being at all, you will have to put that information in context. ",
"A summary is to be found on [Wikipedia][",
"http://en.wikipedia.org/wiki/In_vitro",
")."
] |
[
"For studies that look at animal behavior, like the rat empathy study, there isn't really a good way to get around using live animals. But even still there are guiding principles that scientists follow (especially if they receive federal funding), and virtually every research institution has an Animal Care and Use Protocol committee that reviews animals research proposals and considers whether adequate steps were made to reduce animal suffering, with attention paid to the ",
"\"",
"\"",
" of animal research: ",
"eduction (using as few animals as possible to still get statistically significant results), ",
"efinement, (minimizing pain or discomfort to animals) and ",
"eplacement (using tissues or cell cultures, mathematical modeling, or less-sentient species like insects)."
] |
[
"Johns Hopkins School of Public Health has a Center for Alternatives to Animal Testing; ",
"CAAT's Publications Page",
" has a lot of reading material on the subject, and it looks like your best bet is ",
"this overview brief",
". The topic of the paper is the state of alternatives as of the beginning of 2011, and the bibliography is -- holy crap -- 10 pages long."
] |
[
"Why is it currently less common for the earth to encounter a large comet or asteroid than it was millions of years ago?"
] |
[
false
] |
I was reading Astrophysics for People in a Hurry and one of the lines gave me pause "earth's occasional encounters with large comets and asteroids, a formerly common event" NDT doesn't explain why this is, simply that it was formerly a common event. I assumed that it was either the universe was expanding and now there is more room and less collisions. Or perhaps that there are now less comets and asteroids since over time they have collided and been destroyed? Or something else I didn't think of at all? Thanks!
|
[
"Asteroids and comets are predominantly remnants leftover from formation of the solar system. Over the billions of years that our solar system has been around, these leftover bits have mostly had an unsteady orbit which caused them to collide with the sun, or have already collided with another object in the solar system. "
] |
[
"these leftover bits have mostly had an unsteady orbit which caused them to collide with the sun, or have already collided with another object in the solar system. ",
"The most common result is getting ejected out of the solar system.",
"Anyway, most things with unstable orbits are gone now, and everything that crosses the orbit of Earth is unstable."
] |
[
"Objects in orbit tend to stay in the same orbit until they either collide with another object, or pass closely enough that gravity between them alters their trajectory.",
"So most of the stuff in an orbit that could collide with earth has either collided already, or been pulled into an orbit that either can't or is unlikely to collide, or launched out of the solar system."
] |
[
"How are animal toxicity studies related back to humans when different species find different things toxic?"
] |
[
false
] |
Let’s take raisins for example. If you were testing raisins in dogs, the LD50 would be really low compared to the LD50 in humans. How do we account for these differences? Are there animals that have consistently had similar toxicities as humans that are used (mice? pigs?)? Are compounds tested in many different species? I know they can be tested on human cell lines, but that doesn’t necessarily equate to the whole system.
|
[
"Even though it's true that different species may have different response to a certain toxic substance, it's something that we are aware of and can adjust for in toxicology studies. It's also a matter of which model is more suitable for each case. As a rule of thumb, the closest the animal is to us, the more reliable the results will be. So the best models would be large apes, like chimpanzees, gorillas or orangutans, but they are rarely used for obvious reasons. Instead, one common technique is to use two animal models, one rodent (rat, mouse, guinea pig) and one something else (dogs or pigs, for example). If both show the same toxic effect its more likely that humans will suffer it too. In any case, any LD50 should always include the model used to determineit."
] |
[
"This occasionally happens. It's one of the major arguments against animal testing."
] |
[
"Thanks for your response. That all makes sense, I just wonder about the hypothetical situation in which both animal models are fine and humans are not, or vice versa."
] |
[
"Do \"photonic booms\" happen?"
] |
[
false
] |
I suppose there's no way to know for sure, but if something moves faster than the speed of light, would it create a "boom" of light like a plane does when it moves faster than sound?
|
[
"It is no different from light in the way that a sonic boom is just a pressure wave. "
] |
[
"Hmm interesting. Is there any real difference between Cherenkov Radiation and regular Electromagnetic Radiation?"
] |
[
"Hmm interesting. Is there any real difference between Cherenkov Radiation and regular Electromagnetic Radiation?"
] |
[
"How do we find the distance between the Earth and stars?"
] |
[
false
] |
We know Proxima Centauri is 4.2 light years away. We know Sirius is 8.6 light years away. How do we find and calculate these distances?
|
[
"There are several ways to calculate the distance of stars:\nParallax: for stars relatively close by we can look at their position relative to “fixed” background stars (not truly fixed but so very far away they may as well be) and wait 6 months until the earth has completed half an orbit round the sun. When that is done we can use some trig to determine the distance as we have the angle of the triangle and distance of one of the side (the diameter of earths orbit). This method can only be used and near by stars as the further away the more they move relative to the fixed stars.",
"Redshift/recession velocity: Hubble’s crowning achievement was finding the relationship between the speed at which something is going away and it’s distance (expanding universe supported the Big Bang and shattered the still universe theory) he came up with the equation v=H0 * d and we can calculate v using the redshift equation, and re arrange to get d, (the value of Hubble’s constant has change a lot since Hubble started due to better equipment)",
"Mainly doing distance galaxies now but can apply to stars",
"Cepheid variables : an out of date but still cool technique. A cepheid variable star is a type of star that pulsates rapidly they are very bright and pulse with very similar amplitudes and frequencies, when calculating the absolute magnitude of these stars (ie how bright they are at a distance of 10 parsecs) we find they are in a very small range, if we spot a star pulsating with the same frequency we can assume it’s a cepheid variable and compare how bright we know it is and how bright we see it as and then determine the distance (using the inverse square law)",
"Last but not least brightness and estimation of a galaxies distance can be calculated by seeing how bright a galaxy is as dimmer things tend to be further away (this isn’t accurate for many reasons but can give a good estimation)"
] |
[
"I saw a YouTube video the other day where they talked about another method as well. I think it had something to do with a binary system where one star ate the other and turned into a black hole. And since we knew the exact mass the star would turn into a black hole, we could determine the distance to it by analysing the red shift."
] |
[
"You're talking about ",
"type Ia supernovae",
", I think. As you describe, they occur when one star (a white dwarf) accretes matter off a binary companion, gaining mass until it reaches a critical threshold of 1.44 solar masses. At this point the white dwarf becomes unable to support its own weight, and it starts to collapse.",
"This triggers a violent nuclear explosion, which blasts the star apart in a supernova (no black hole is formed by this process). Because this always happens at the same mass, the supernovae should always release a similar amount of energy (i.e. should always have the same luminosity).",
"By comparing this absolute value with how luminous the star appears, we can work out how far away it is."
] |
[
"Why do radio signals of the same frequency not mix, but rather, one overpowers the other?"
] |
[
false
] |
For clarity: I live in between the ranges of two radio broadcasts of the same frequency, often when I am listening to one, the other takes over; why wouldn't the signals always combine to form an amalgamation of both broadcasts?
|
[
"This is called the capture effect, and only works with FM radios. An AM radio would actually work as you imagine. ",
"The FM capture effect isn't really a natural physical phenomenon, it's an engineered design feature. It can vary depending on how the signal chain is made. When a lower level signal and a higher level signal hit the limiter in an FM receiver, the weaker signal ends up not contributing much to the instantaneous frequency at the detector so has no impact on the output audio. In effect, the limiter is blocking the weaker signal and letting the stronger through. "
] |
[
"Do the FM signals interfere naturally? If they do, will the receiver chose the signal formed by constructive interference over the individual signals? "
] |
[
"Interfere could mean physical E-M wave interference, audio signal interference or frequency mixing in the radio.",
"Two radio signals will superimpose in space or air, like light from two flashlights. A spatial interference pattern can exist, like light diffraction. Two radio signals can mix in a non-linear device to make sum and difference of the original frequencies. A heterodyne mixer works this way.",
"FM is a modulation method, not the physical layer. FM modulated signals propagate same as any other wave of the same frequency. As noted by KF7LZE, the FM receiver is designed to select the stronger signal. The limiter circuit trys to remove all amplitude variation (no AM). The output of the limiter is almost digital (discrete amplitude). The strongest signal wins at the FM detector.",
"Two AM signals will beat at an AM detector. This often results in a strong whistle. The whistle is the frequency difference between the two signals. FM radios are designed to block this."
] |
[
"How much of fire's kinetic energy is released via photons vs. thermal conduction?"
] |
[
false
] |
I'm trying to build a tabletop RPG in the likes of D&D and I'm making a spell, "Darkness." I'm trying to go about it a little scientifically (as scientifically as you can get with magic) and I want to state that the spell simply "deletes" photons entering a certain area, therefore making it dark. I figured that the area would be much cooler than the surrounding area since solar radiation is mostly gone, like being in the shade of a tree vs. directly under the sun, but what about fire? If I brought a torch into this area how much cooler would it get? Is the electromagnetic radiation an insignificantly small part of the heat energy that it would feel pretty much the same, or would it feel noticably cooler?
|
[
"Kind of a tricky question, depends on the circumstances. Conduction is practically none in this case, it's more radiation vs convection.",
"Radiation accounts for most, if not nearly all, of the heat transfer from e.g. torches and bonfires in an open environment, e.g. outdoors, because the hot flue gas escapes the surroundings. The heat you'd normally feel from a bonfire is almost completely radiation. If the flue gases hit you e.g. if you're above a bonfire or wind blows towards you, the flue gas or the air heated by flue gases or fire would naturally feel hot and would transfer the heat via convection. So in conclusion, \"deleting\" photons would make it cold in an open environment if the flue gas or heated air doesn't hit you.",
"In a closed environment, e.g. tent or small room, most of the heat you'd feel instantly is from radiation. However, over time the fire would heat up the surrounding air and objects from convection as well. In other words, if the heat can't escape, the overall temperature of the system would increase. So in this case, deleting photons would most likely delay the warming effect of fire, but not completely erase it. Keep in mind, that if the flue gas exits the system via chimney, ventilation or something, most of the heat would escape as well because the flue gas doesn't cool off as fast due to lack of radiation.",
"EDIT: by cold in the first example (outdoors), I mean it would feel as if there was no fire or sun. The air temperature wouldn't change"
] |
[
"Thanks for the answer. So the heat that you feel from a campfire is nearly all radiation? Thinking about it that makes sense. Since hot air rises, all of the air heated by convection is going up into the atmosphere. So if there was a torch in this spell you wouldn't know it was there until you placed your hand directly above the flame. Interesting. ",
"Now I have another question, lol. What proportion of the energy is released as radiation vs. convection? If you have a closed room and cast this spell in it and threw a torch in after, would the room only heat up half as much? It's hard to search for on google as I only ever find the generic chemical equation, carbon chain + oxygen = water + co2 + light. What proportion of the energy is light?"
] |
[
"Yes. In our normal environment, huge numbers of photons are being emitted by everything. You don't notice because just as many are generally being absorbed. If you \"delete\" those photons, everything would freeze very very quickly.",
"I read a story once where one wizard made a spell that acted like a one-way force field for photons. It would instantly cook something like a dragon."
] |
[
"How do we know what the earth's mantle and core are composed of if we haven't directly observed them?"
] |
[
false
] |
When I was a kid I would often page through encyclopedia books, and one of the images that really made me stop and wonder was the picture of a cross section of the earth, with core and mantle in labeled circles. Today I realized that I've never learned the answer to how we know these things, so I'm asking you guys: How are we so confident about what's underneath the earth's crust if we haven't seen it?
|
[
"A few ways, but most importantly - seismic waves.",
"Every time there's an earthquake those seismic waves travel through the earth and are detected by seismometers around the globe. As well as letting us work out where exactly that earthquake happened, and what kind of fault movement it was, the arrival time of the waves at different places gives us a lot of information about what they have passed through on the way. There's a lot of refraction and reflection events. Some of the main boundaries are even associated with what we call 'mode conversions' - when a P or S wave is converted into an S or P wave respectively.",
"We can also get information from other methods. For example, we know that Earth accreted in the Hadean from planetessimals orbiting the sun. Those same bodies are now smashed up and form many of the asteroids that hit us. By analysing their geochemistry we can get a vvery good handle on what the bulk earth chemistry is like. Pair that with high temp/pressure physics and the mineralogists can get some awesome data.",
"We also have inclusions brought up from depth by some volcanic activity (e.g. ",
"http://en.wikipedia.org/wiki/Eclogite",
").",
"Finally, the presence of our magnetic field forces us to draw certain conclusions about the structure of the geodynamo."
] |
[
"It comes up every now and then.",
"But you're right. It could be this giant piece of alien technology in the center of earth that replicates the gravitational and magnetic forces of a solid core of molten iron. "
] |
[
"In that case, what kinds of data or evidence have we gathered to determine that it's whatever amount of spinning molten iron? How do we know about the composition and volume of things inside the earth?"
] |
[
"Why does outer space look black?"
] |
[
false
] | null |
[
"This is called ",
"Olbers' paradox",
". More or less, the universe is quite bright. But at frequencies our eyes can't see. Everything's red-shifted too much.",
"The cosmic microwave background exists in every direction we look, a remnant of the big bang."
] |
[
"It appears black because except for stars there isn't enough visible light coming from space to be detected by our eyes.",
"There isn't enough visible light because only the nearest stars are close enough to be distinctly visible. You can see the plane of the milky way where the stars are dense enough to be seen. The only galaxies we can see are the dwarf galaxies the lesser and greater Magellanic clouds. All the other ones are too far away and so too dim to see.",
"It's also true the because the universe it expanding, it's expanding faster than the light from stars can fill it. And the light from the oldest most distant stars is red shifted into the infrared. Finally the light from the big bang has been red shifted down to a few degrees above absolute zero and can only be detected by microwave telescopes."
] |
[
"You've have to go back quite far to see an appreciable difference. Some galaxies might be brighter than others than they are now, when things were much closer together.",
"Starting around 7 billion years ago, expansion started speeding up.",
"However, we've undergone a lot of galactic mergers over time. We're about to smack into the Andromeda galaxy in about 4 billion years. The sky then will look about like this due to strong star formation:",
"https://www.nasa.gov/mission_pages/hubble/science/milky-way-collide.html",
"And our sky would've looked like that on and off in the beginning as well during galaxy formation and collisions.",
"There's a very famous picture of cosmic inflation here to give you an idea of how bright everything would have been once the universe thinned out enough for stars to start lighting up:",
"https://helpfulcolin.com/2014/03/cosmic-inflation-and-expansion-of-the-universe/",
"Hope that helps!"
] |
[
"What were the theories about the nature of stars before we began to understand nuclear reactions?"
] |
[
false
] | null |
[
"Prior to understanding nuclear reactions, identifying the energy source of the sun was an issue. Probably the best attempt (late 1800s) was the ",
"Kelvin-Helmholtz mechanism",
", which proposed the energy source of the sun came from gravitational collapse. This would require that the sun be slowly shrinking in order to continue to output energy, and implied that the age of the sun was somewhere around roughly 10 million years. During the late 1800s early 1900s, geologists were beginning to understand that the age that the earth was much older than 10 million years, so the energy source of the sun remained an open question until nuclear fusion came along."
] |
[
"It is worth adding that nuclear fusion was proposed as a possible thing in the world ",
". That is, it was proposed by theorists as something that might exist, and might power stars, as early as 1920. People are sometimes surprised by this, because they expect that nuclear fusion is a younger than that, in particular younger than nuclear fission. It, of course, took several decades to work out exact what fusion reactions were fueling stars of different sorts."
] |
[
"Arthur Eddington was the first to theorize it I believe, at least on paper. Einstein had already proposed the connection between mass and energy in his famous equation e=mc2 back in 1905, so the fact that a small amount of mass could create a large amount of energy was already known. Eddington took another recent discovery - the measurement of the mass of helium, which turned out to be 0.8% less than the combined mass of 4 hydrogen atoms - and proposed that this missing mass had been converted to energy and would power the stars."
] |
[
"How close could two stars be to each other?"
] |
[
false
] | null |
[
"If he's looking for how close stars can be ",
" colliding, then that depends strongly on the mass and radius of the stars.",
"The mass and distance between stars defines what's called the \"Roche Lobe\". If any material of a star gets beyond the Roche Lobe (say if the star expands), then it is no longer bound to that star and will then accrete onto the other star.",
"There's a good picture of that ",
"here",
"."
] |
[
"I think you may need to clarify your question perhaps? There is no limit to how close two stars can be to each other, as ",
"stellar collisions",
" do occur. So close enough to collide and merge."
] |
[
"The system PSR J0737-3039A/B has two stars that orbit each other every 2.4 hours and are a bit farther from each other than the Earth is from the moon."
] |
[
"What happens to a person's system if they are given the wrong blood type?"
] |
[
false
] | null |
[
"Their immune system recognises it as foreign, and the blood agglutinates (clots)."
] |
[
"Then the person has a lot of infarction, because the blood clots clog the arteries and veins of the body. ",
"Strokes are infarctions of the brain, heart attack of the heart, etc. you can get them in any part of your body and they're never good. ",
"Edit:",
"I should rephrase. All of those things CAUSE infarctions. Infarction refers to the tissue death caused by an interruption in blood flow. "
] |
[
"The type of blood is named so after the markers present on the red blood cells (ie. type A blood as A markers, type B has B markers, type O has no markers and type AB has A and B markers). Each person has the antibodies to recognise the markers they ",
" present. So a type A person will have A markers and anti-B antibodies -- therefore their blood can only go to people ",
" anti-A antibodies (that is to say: to type A and type AB people), and can only receive blood ",
" B markers (that is to say: from type A and type O people). This is why type O are universal donors (they present no markers, so their blood will not cause an immune reaction in the receiver), and type AB are universal receivers (they have no anti-markers antibodies so will not have an immune reaction to the received blood).",
"If you are given the wrong bloodtype and present an immune reaction, antibodies will bind the markers on the blood, and clots will form -- see LULBASAUR's thread from hereon."
] |
[
"Why do our bodies seem to be so inefficient at absorbing water?"
] |
[
false
] |
When we urinate, a huge percentage of what makes up the urine is just water. Why is so much of the water we take in completely wasted?
|
[
"You're not just urinating your water away for no reason. Water in urine is a ",
" that carries all your water-soluble waste. Your kidney basically partitions out a portion of your blood as a dilute solution, then meticulously release and reabsorb constituents to control the level of ions, salts, other organic compounds, and water before it is released into the bladder.",
"Under normal operation your body does try to reabsorb water using passive means. If you want to make your urine ",
" concentrated then energy is required.",
"So the water is no more wasted in urine than your garbage bag is wasted in carrying garbage."
] |
[
"It's not wasted, actually. The water is there as a solvent for waste products. Urine production in animals is a tradeoff between using up water and dealing with very concentrated waste. Some animals excrete much more concentrated urine, especially if they're in ecological niches where water is more precious, but their kidneys and bladder then have a much harder time of it, and more metabolic energy has to be spent generating the waste (and presumably in cellular turnover as they deal with the progressively more toxic sludge)."
] |
[
"When we urinate, a huge percentage of what makes up the urine is just water. Why is so much of the water we take in completely wasted?",
"Sorry if this sounds dickish, but I laughed a little. First, your intestines are really good at absorbing water, unless you constantly have diarrhea (in which case I am sorry, get well soon!). From the intestines on, the water enters your system and distributes in the intracellular fluid rooms and extracellular fluid rooms, including your blood stream. From there on, water is filtered and excreted via the kidney. The thing is, it looks like you lose a lot of water via your kidneys and the urinary tract, but your kidneys are INCREDIBLY INCREDIBLY efficient in retaining water. 180 liters of your blood plasma (the liquid portion of your blood) get filtered in the kidneys per day. You pee 1 to 2 liters per day! A healthy adult weighing 75 kg has about 45 liters of water in their body total. You would lose your entire water content within less than a day if your kidney wouldn't reabsorb the vast majority of what is filtered. Believe me when I tell you that our body is incredibly good in managing water, and I will demonstrate why that is the case.",
"There are 2 reasons why you lose a perceivably \"large\" amount of water within a day. The first is elemination, the second is water and electrolyte balance.",
"1) your body consistently produces metabolites that it can't break down anymore, but that become toxic in some way or shape. You also constantly ingest stuff that would become toxic after prolonged exposure. Your body produces enough of these that it might become a problem in the short term if it can't get rid of it ASAP. The solution is pretty simple and beautiful: throw every molecule in the blood stream (including water) up to a certain size OUT of the blood (through a specifically built molecular sieve called the glomerulus, which contains the blood-urine barrier), and the filtered fluid then travels along a very long system of tubes where everything the body needs to retain (water, electrolytes, glucose, some proteins etc.) is actively drawn back with highly energetic processes. Additionally, some endogenous toxins that bypass the sieve are actively excreted in these so called tubules. The residue of the tubular fluid that didn't get reabsorbed, now urine, leaves your kidney via open ends into the renal pelvis and gets transported to the bladder in the urinary tracts. This process is really useful because our kidneys can just get rid of every substance the body has never seen before and isn't evolutionarily adapted to in no time. However, in order to properly get rid of these substances, they need to be solved in a solution (urine) and transported out of the body - the body doesn't know any other way other than regulating fluids. Because of this, for proper kidney function you need to excrete a basal amount of 500 ml per day. We're probably not the most extreme concentrators though - camels for example have an even higher concentrated urine for obvious reasons.",
"2) You constantly ingest stuff. That pizza you just ate had a certain amount of water content, that cola you drank was of course full of water, and when your cells burn nutrients for energy, a small amount of extra water is also produced. You even need to drink a basal amount of liquid because of detoxification and because you constantly lose water outside of your kidneys (sweating, exhaling water from the lungs, gall fluid etc.). The thing is that the water contents within your body need to be very tightly regulated - for one, in case of too much water your circulatory system suffers because the heart needs to pump harder the more liquid it receives, leading to pretty bad stuff like hypertonia and cardial hypertrophy. the excess water needs to stay somewhere and collects not only in your blood stream, but also the fluid compartments surrounding your cells (extracellular) and also within your cells (intracellular). The fact that cells shouldn't be bloated with water should be fairly obvious. However, this also disrupts one of nature's most important mechanisms, and that is electrolyte control; virtually all of your cells depend on transmembrane potentials in some way or shape in order to be functional, and transmembrane potentials depend on the concentration of electrolytes (ions), which is decreased with a higher water content (total amount of ions stays the same while water increases - or in other words, the ions get diluted). and on top of that improper electrolyte concentrations leads to nasty osmotic effects (drawing too much water into places that shouldn't be overly hydrated) that may be lethal to your survival by themselves. Thus, it is very important for the organism that any irrelevant excess amount of fluid gets out before any such problems arise, and for that reason the exact amount of water resorption and thus urine concentration is also very tightly regulated depending on the amount of fluid available in your system. Your kidney acts as the central effector of water homeostasis within your body by \"deciding\" how much water is urinated, if you will. In non-pathological situations (and when not receiving certain medications), the kidneys (and associated regulatory structures like the hypothalamus in the brain or your heart) are really good in gauging and regulating the exact amount of fluid that needs to get out of the system. And if you lack fluid, you will only urinate the obligatory 500 ml (for detoxification) while you are motivated to drink by your brain - because you feel thirsty."
] |
[
"With a tree pollen allergy, is it better to open my windows and air out my bedroom or keep them shut up for a few more weeks?"
] |
[
false
] |
In the Northeast, apparantly we are in for a record pollen year. My wife is allergic to tree pollen up here and is absolutely miserable. I think it would be better to air out the bedroom, open windows and let whats in here out. She thinks letting any more pollen in would kill her. Further evidence, she seems to get worse at home than outside. We took a walk in the ark yesterday and she didn't seem that bad until we came home and the nose kicked it up a notch.
|
[
"As a fellow allergy sufferer, keep the windows closed. \"Airing out\" will expose more pollen into the room. Instead, try vaccuming well and cleaning surfaces that come into contact with clothes that have been outside. I always take a shower when coming home to wash off the pollen that might be on my hair and skin. ",
"Also, there are foods/drinks that are high in histamines, especially fermented alcohol (not as bad with vodka and gin). ",
"http://www.ncbi.nlm.nih.gov/pubmed/10344773",
"http://www.urticaria.thunderworksinc.com/pages/lowhistamine.htm"
] |
[
"Everything I've read says to keep windows closed, and if you want to air out do it quickly and open all windows so the air rushes through.",
"Pollen count lessens in damp weather. So air out on days when it is raining. I believe cold temperature also makes a difference, but I can't remember right now. Hot sunny days that are windy are the worst from my experience, since the pollen can travel very far.",
"My experience is that it takes a while before the allergies kick in, so if you were out walking and came home if could be that it hadn't really started until then."
] |
[
"I have heard there are many natural remedies for spring allergies as well. The ones that I have tried and seen work best are local and totally natural honey (can be used in tea, sandwiches, etc.), and mint. I grow mint in my garden and if you eat about one or two stalks a day, the allergies almost completely disappear. ",
"Here's an article if you want to know more.\n",
"http://www.earthclinic.com/CURES/allergies.html"
] |
[
"How does a black hole exhibit electric charge?"
] |
[
false
] | null |
[
"Electric fields don't \"move\" and don't need to escape. ",
"A charge has electric field lines extending all the way to infinity. Think of them as threads connecting the charge with a point at infinity. When the charge falls into the black hole, the field lines still have one extremity \"tied\" at infinity, while the other is tied to the black hole. So the black hole is now charged and it has the same external electric field the charge had.",
"Charges don't continuously \"generate\" an electric field. They ",
" an electric field, it's something they carry around always.",
"To be more precise, in the \"far-away\" perspective (which means using Schwarzschild coordinates) the charge takes infinite time to reach the event horizon and only gets closer and closer to it. In that case, you can prove that the field lines emanating from the charge tend to first spread around the horizon, and then turn outwards radially (I'm not sure if there is a picture of this around...). So not only do all field lines escape to infinity (which they must, because you cannot change the total number of field lines that do, because that's the total charge in the Universe), but also they are spherically symmetric and the field is what you'd expect if the charge was actually in the middle instead of in one point in the surface - as if the black hole itself was charged."
] |
[
"Let's try this way: the charge is not really associated with the volume occupied by the field, so that you could cut out a chunk of it or smth.",
"The charge in a region is actually related to the surface bounding the region, in fact it is equal to the flux of the electric field through that boundary surface. This is just Gauss' law.",
"So for example take a very large sphere centered on your neutron star or whatever. The flux of the electric field through the sphere (pictorially: the number of field lines crossing it) is equal to charge inside, which is the charge of the electron. Now, anything can happen inside, black holes, fairies, anything, but that flux will not be changed, because the surface of the sphere is very far (arbitrarily far), so it can not be affected. So the charge inside ",
" be constant. For roughly this reason conservation of electric charge is a very strong law (it's called a superconservation law) and black holes will not break it. You make a box, and if no charge enters or exits, then you will always measure a constant total charge for the box (by measuring the E field around) no matter what crazy physics (even unknown physics) goes on inside the box.",
"In this case the black hole \"eats\" one extremity of the field lines (with a different meaning to this depending on the coordinates) but the other extremity always extends outwards to infinity, and you cannot change things at large distances (and you cannot cut the line!), so the black hole becomes charged with the same charge as the electron.",
"Compare to other \"normal\" or \"accidental\" conservation laws, like baryon number: black holes don't care, and can change baryon number, lepton number, etc... but electric charge is a gauge charge, it's off limits."
] |
[
"Thanks! That explains some things. The second part is quite illuminating (and unexpected) actually. But there are more questions as well...",
"If an electron finds itself inside of the event horizon, wouldn't the interior \"trap\" some volume of the electric field? Would that prevent it from interacting with the outside world? Imagine this scenario: a neutron star with a charge of exactly 0 and being on a brink of collapse. Then an electron falls on it and triggers the collapse: now we have a black hole with an electron inside of it (at least that's what I'm assuming). Would it leave the rest of the universe dealing with a fraction of the electron charge associated with the part of the electric field outside of the black hole? I'm guessing not, but what mechanism would the Universe employ to avoid this situation?"
] |
[
"How difficult is it to damage or kill microorganisms mechanically? If I strike an anvil with a hammer, do I leave a briefly sterile surface behind?"
] |
[
false
] | null |
[
"Simply put, no. Basically surfaces are not smooth enough to physically crush bacteria. In fact, bacteria can actually squeeze themselves into spaces that are only a fraction of their normal width. ",
"Here",
" is a video taken at a Harvard lab that was growing ",
" under the microscope in time lapse. The bacteria were supposed to grow within the horizontal channels, however, what ended up happening was the bacteria were squeezing out of the channels into a tiny space between he glass coverslip and the solid support. The result was bacterial \"pancakes\" that continued to grow. There is a more detailed explanation in the video description.",
"That all said, there are surfaces that are able to mechanically kill bacteria. ",
"Here",
" is a link to a recent publication about it. Basically, cicada (insect) wings have nano structures on them that are able to tear bacterial membranes apart simply by contacting them. The link contains a video illustrating this phenomenon."
] |
[
"You can kill some cells with mechanical forces, but you won't create a sterile field by doing it. ",
"In tissue culture, you'll lose thousands (##,000) of cells every time you harvest a flask, just from the mechanical stresses of pouring or pipetting the culture media containing the cells. For reference, a 175cm",
" flask can easily contain a single layer of 5-10 million (##,000,000) cells. If you centrifuge this amount down, the pellet formed will be about the size of your fingertip. The few thousand you lose mechanically are negligible.",
"If you want to clean a surface, a spray bottle of 70% ethanol is great. If you need to be REALLY sure, some dilute bleach will kill basically anything. :)"
] |
[
"According to the ICAL team at Montana State University you can literally stab bacteria multiple times with an Atomic Force Microscope (AFM) tip and they remain viable. (skip to pg12 \"3.3 Investigation of mechanical properties of living Salmonella\" for the stabby bit)\n",
"http://cdn.intechopen.com/pdfs/26471/InTech-Immunoimmobilization_of_living_salmonella_for_fundamental_studies_and_biosensor_applications.pdf"
] |
[
"Is there a substance that you can taste(with your tongue) while it is in contact with your skin?"
] |
[
false
] |
I think I read somewhere about this substance (can't remember if it was a liquid or solid) that you can taste while touching it with your fingers. I don't know if the information is accurate as I remember it. My reason is that if it exists and is non-toxic I would have its use be part of a hypothetical new dog training method. So if you know of any such chemical/substance, just give me the name(and/or any other info) so I can research. tx
|
[
"Sorta. Things mixed in DMSO (dimethylsulfoxide) cross into the body very easily. The thing I've seen mixed with DMSO most often to show the taste effect is peppermint essence.",
"This effect is also useful practically. Drugs mixed with DMSO are painted onto the skin of horses as a painless way of dosing very high-strung animals."
] |
[
"This! I read this question and nothing came to mind, but after reading your comment it reminded me that I had a stem cell treatment with an IV fluid that was preserved with DMSO.",
"It's hard to say if I 'tasted' it, but the sense of taste and smell are so closely related it might be incorrect to separate the two entirely. If you couldn't smell, you wouldn't taste food the same way you're used to.",
"But anyways, I didn't get DMSO topically, but rather it was infused into my bloodstream via a needle. After a bit, it smelled kind of sulphur-y and tasted the same. I read another patient's description as it smelling like 'truffles', if that gives any indication(?) It actually sort of seeped through my skin so people in the same room as me would be hit with the smell. It's rather unique, I think I'd recognize it easily if I smelled it again.",
"I also know you can get altered taste from other IV medications (it happens a lot in chemotherapy) such as a 'metallic' taste, but I don't know much about skin-contact."
] |
[
"DMSO has a slight as well. Get it on the skin, and you will taste it in your mouth."
] |
[
"How (un)healthy is it for one to work nightshift?"
] |
[
false
] |
[deleted]
|
[
"For all requiring citations.",
"A Directly related article: ",
"James FO, Cermakian N, Boivin DB. Circadian rhythms of melatonin, cortisol, and clock gene expression during simulated night shift work.\nSleep. 2007 Nov;30(11):1427-36.",
"Evidence of variation in blood pressure, heart rate and onset of cardiovascular events. ",
"Muller JE, Tofler GH, Stone PH. Circadian variation and triggers of onset of acute cardiovascular disease. Circulation. 1989;79:733-743",
"Muller JE, Stone PH, Turi ZG, Rutherford JD, Czeisler CA, Parker C, Poole WK, Passamani E, Roberts R, Robertson T, et al. Circadian variation in the frequency of onset of acute myocardial infarction. N Engl J Med. 1985;313:1315-1322",
"This is the molecular clock mechanism that keeps time in each and every type of your cells. Hope you have access to Pubmed!",
"Circadian Rhythms - Keeping Time Fact Sheet from National Institute of General Medical Sciences: ",
"http://www.nigms.nih.gov/publications/factsheet_circadianrhythms.htm",
"\nHere are some references, not sure if you have access to PubMed: 1. Reppert SM, Weaver DR. Coordination of circadian timing in mammals. Nature. 2002;418:935-941 - ",
"http://www.ncbi.nlm.nih.gov/pubmed/12198538",
" 2. Cuninkova L, Brown SA. Peripheral circadian oscillators: Interesting mechanisms and powerful tools. Ann N Y Acad Sci. 2008;1129:358-370 - ",
"http://www.ncbi.nlm.nih.gov/pubmed/18591495",
"\nWikipedia - ",
"http://en.wikipedia.org/wiki/Circadian_rhythm"
] |
[
"For all requiring citations.",
"A Directly related article: ",
"James FO, Cermakian N, Boivin DB. Circadian rhythms of melatonin, cortisol, and clock gene expression during simulated night shift work.\nSleep. 2007 Nov;30(11):1427-36.",
"Evidence of variation in blood pressure, heart rate and onset of cardiovascular events. ",
"Muller JE, Tofler GH, Stone PH. Circadian variation and triggers of onset of acute cardiovascular disease. Circulation. 1989;79:733-743",
"Muller JE, Stone PH, Turi ZG, Rutherford JD, Czeisler CA, Parker C, Poole WK, Passamani E, Roberts R, Robertson T, et al. Circadian variation in the frequency of onset of acute myocardial infarction. N Engl J Med. 1985;313:1315-1322",
"This is the molecular clock mechanism that keeps time in each and every type of your cells. Hope you have access to Pubmed!",
"Circadian Rhythms - Keeping Time Fact Sheet from National Institute of General Medical Sciences: ",
"http://www.nigms.nih.gov/publications/factsheet_circadianrhythms.htm",
"\nHere are some references, not sure if you have access to PubMed: 1. Reppert SM, Weaver DR. Coordination of circadian timing in mammals. Nature. 2002;418:935-941 - ",
"http://www.ncbi.nlm.nih.gov/pubmed/12198538",
" 2. Cuninkova L, Brown SA. Peripheral circadian oscillators: Interesting mechanisms and powerful tools. Ann N Y Acad Sci. 2008;1129:358-370 - ",
"http://www.ncbi.nlm.nih.gov/pubmed/18591495",
"\nWikipedia - ",
"http://en.wikipedia.org/wiki/Circadian_rhythm"
] |
[
"Working night shifts has the many negative affects on the body. It changes gene expression, protein levels including hormone levels in many organs, including the heart. The processes that happen in your body at night and during the daytime are very different. During the day you are more active, need to eat, etc, this includes higher blood pressure and heart rate during the day, but when activity levels are low during the night the heart rate and blood pressure decrease. By staying awake during the dark, you are forcing your organs to work harder when they are used to working lower, and they aren't particularly flexible in that way. Eventually, cardiovascular diseases develop as well as depression. This field is termed circadian rhythms. "
] |
[
"How did the first polar explorers know they had reached the pole and they weren't actually off by kilometers?"
] |
[
false
] |
[deleted]
|
[
"Astronomy. They used sextants to measure the positions of the sun (expeditions were made during the summer, so stars couldn't be used). In theory, if you are standing at the exact pole, the sun should stay at the (almost) exactly the same angle with respect to the horizon (it technically moves a tiny bit up/down the sky every day to the change of the seasons, but not at all due to the daily rotation). Sextants are pretty accurate (down to a few hundred meters in ideal conditions).",
"Apparently the first explorers to the south pole made a bunch of measurements are the pole itself, to \"box\" it in and prove they definitely, at some point, were on top of the pole proper."
] |
[
"Or in the case of Robert Peary, you just claim you got there (because he had no way of really knowing) and then proceed to bully everyone into accepting your claim. ",
"http://tierneylab.blogs.nytimes.com/2009/09/07/who-was-first-at-the-north-pole/"
] |
[
"Magnetic north and the north pole are not in the same spot. In fact the magnetic north pole moves around over time (it looks like it can wander around 25 miles/year). At magnetic north I ",
" the compass would try to point down."
] |
[
"Why doesn't New Year's Day coincide with the Winter Solstice?"
] |
[
false
] | null |
[
"This isn't a science question; more of a history of calendar question. According to ",
"wikipedia",
", it used to be March 1st (which sort of makes sense--celebrate the new year in the spring and start of a new harvest), but in 46BC a Roman emperor moved it to January to honor the two-faced roman god Janus.",
"Probably observed on March 1 in the old Roman Calendar, The World Book Encyclopedia of 1984, volume 14, page 237 states: \"The Roman ruler Julius Caesar established January 1 as New Year's Day in 46 BC. The Romans dedicated this day to Janus, the god of gates, doors, and beginnings. The month of January was named after Janus, who had two faces - one looking forward and the other looking backward.\""
] |
[
"We need an ",
"/r/AskHistory",
" subreddit."
] |
[
"It is the start of new year in Iran and most of central Asia at exact moment of Spring Equinox, i.e. start of spring.",
"http://en.wikipedia.org/wiki/Norouz"
] |
[
"Why is Fahrenheit used in America, even though Celsius seems to be the generally accepted measure of heat in international science? Are there certain pros/cons to each measure?"
] |
[
false
] |
[deleted]
|
[
"Anyone who goes to high school will learn Celsius. Anyone who decides to enter science will use Kelvin."
] |
[
"Celsius and Fahrenheit have no real benefits or downsides in comparison, except for ease of memorization. It tends to be easier to remember that boiling is 100C rather than 212F, and that freezing is 0C rather than 32F. ",
"The Kelvin scale, however, has real mathematical advantages in terms of simplifying formulae. "
] |
[
"Celsius is still commonly used in the biological sciences."
] |
[
"Does Liquid Nitrogen behave as a Bactericide?"
] |
[
false
] |
Let's say I have a pair of jeans covered with bacteria from daily usage. If I pour Liquid Nitrogen and flash freeze them in this manner, will it kill practically all of the bacteria? Will it preserve them? Also, will the jeans be okay if I don't touch them while they're frozen and let them thaw out on its own?
|
[
"Freezing bacteria is mostly bacteriostatic, and as others have mentioned, is frequently the preferred method of long-term cell storage. You do typically store them in a cryo-protectant, like glycerol, as ",
" freeze-thaw cycles will start to lyse cells. This causes enough cycles of ice crystal formation to disrupt cell membranes."
] |
[
"Bacteria are small. The speed at which liquid nitrogen freezes things would not allow large ice crystals to form."
] |
[
"According to ",
"this",
" and other guidelines I found, Storing in liquid nitrogen is a recommended method for bacteria preservation for several species."
] |
[
"Do humans host viruses that used to be deadly to us but no longer are? How do we know they used to kill us?"
] |
[
false
] |
Building on the notion that HIV is becoming less deadly to us over time - how do we know what used to kill us?
|
[
"The remains of ancient retroviruses litter our genomes, accounting for about 8% of our total genetic material, if not more. If you count other ",
"transposable elements",
", that percentage increases dramatically. Human endogenous retroviruses (ERVs) are the remains of viruses that managed to integrate into the DNA of a germ cell (which divide into sperm or eggs). This is a very rare occurrence, since retroviruses we know normally target somatic cells.",
"We don't necessarily know that these viruses used to kill us, but it can be said with some confidence that anytime a virus is introduced into a new population, there tends to be increased mortality and morbidity until two things happen:",
"The virus attenuates itself to become less virulent, and persists longer in the host, thereby facilitating its own transmission to new hosts.",
"The host adapts to the virus, in terms of its own genetic (ie. ",
"innate",
") immunity.",
"Both of these occurrences are well documented, so really the notion that HIV is becoming less deadly over time is to be expected. A really nice example of these two things occurring together was the introduction of ",
"myxoma virus",
" into the Australian rabbit population in 1950. Myxoma virus causes the disease myxomatosis in European rabbits (which were the type found in Australia) and is associated with very high mortality (>70%). The natural reservoir of the virus however is the American cottontail rabbit, where it causes only benign skin tumors (much like a wart). The Australian government decided to release this virus because the rabbit population had gotten out of control (around 600 million in 1950). In only two years, the population was reduced to 100 million - about an 83% reduction in population. Needless to say, there was some pretty severe evolutionary selection pressure going on in these rabbits.",
"Over the period of about a decade (or less!) both attenuated versions of the virus were found to be circulating, as well as increased genetic resistance to a highly pathogenic lab strain of the virus (known as Standard Laboratory Strain - super original, I know). In 1950, approximately 90% of wild rabbits from Australia died from SLS in the laboratory, but by 1961, the lethality of the same strain of the virus had decreased to about 20%, representing adaptations in the rabbits' innate immune systems to compensate for the introduction of this virus ",
"[1]",
".",
"Viruses are not necessarily harmful either. There's a really nice review in nature (",
"www.nature.com/nrmicro/journal/v9/n2/full/nrmicro2491.html",
") about mutualistic viruses in many different animals.One of my favorite examples of symbiogenesis (where a viral integration event into genomic DNA results in a new species) is the development of the placenta in mammals. The envelope gene from an ancient retrovirus which integrated into an animal's DNA far in the past was able to induce fusion of neighboring cells. This gene eventually became necessary in the development of the mammalian placenta, and in time led to us!",
"So as you can see, the remnants of integrated viruses can actually become beneficial. It may also go the other way though, as some human ERVs may be implicated in autoimmune disease progression, such as in MS. We can't really deny though, that viruses have and continue to play a big role in the evolution of all species."
] |
[
"Human DNA certainly contains DNA from viruses that has incorporated itself into our genome, and is now perfectly harmless. These are called Endogenous retrovirus (ERV), and could account for as much as 5% of the human genome. I suppose it's highly possible that current ERV could have descended from more dangerous progenitors, but it would be hard to say definitively that they used to be deadly. ",
"http://www.bbc.co.uk/news/science-environment-17809503",
"http://en.wikipedia.org/wiki/Endogenous_retrovirus"
] |
[
"Thanks! I am not in the field and had no idea about this."
] |
[
"How do ELISA assays work?"
] |
[
false
] |
[deleted]
|
[
"E.nzyme L.inked I.mmunoS.orbent A.ssay... ELI5 version:",
"Antibodies are small molecules that can recognize and stick to different substances, very specifically.",
"In ELISA, you stick these antibodies to a plastic plate. Then you put the tested sample on the plate. If the searched substance is present, it will stick to antibodies.",
"After washing all that didn't stick, you use another antibody to check if the stuck antibodies are \"free\" or bond to something. This secondary antibody is coniugated with a revealer (fluorescent). So if the plastic plate becomes fluorescent, there is no substances. If it's dark, there is plenty. If something between, there are traces.",
"This is VERY simplicistic. There are a lot of ELISA techniques, but all (more or less) are based on this principle. You can stick the substance to the plate, and check if a sample (like your blood) has antibodies against that. If the substance is a viral protein it can be used to check if you have an infection.",
"There are many others (indirect, sandwich, competitive..) whose details are explained on wikipedia.",
"If you read them, remember: the Y shaped thingies are the antibodies. They recognize other substances (or other antibodies) and stick to them. Soon or later, there will be a detecting antibody (radioactive, fluorescent, etc) to show the result.",
"If you have other questions, feel free to ask."
] |
[
"ELISA, or Enzyme-linked immunosorbent assays, work by taking advantage of the ability of antibodies to bind an antigen with both high specificity and high affinity. For this reason it is necessary to know what Antigen you are testing before ahead of time, so that monoclonal antibodies against this antigen can be generated. ",
"These antibodies are then coupled to an enzyme which is able to convert a colorless substrate into a colored product.",
"The antigen is first attached to the sides of the microtitre plate in which the experiment is conducted. Then the antibody-enzyme complex is added to the plate. This antibody binds with both high specificity and high affinity to the antigen if there is antigen present in the well. Excess antibody is washed away so that only wells containing the antigen contain the color-changing enzyme. The colorless substrate of the antibody-coupled enzyme is added to the well, and the wells that contain the enzyme (and therefor the antigen) will noticeably change color."
] |
[
"Minor point, this is capture ELISA, or sandwich ELISA, which is a modification of traditional ELISA that is probably the most commonly used form of ELISA in biological research nowadays. "
] |
[
"Which has more gravitational pull on me... girl sitting across from me on a bus, or the nearest star?"
] |
[
false
] |
NINJA EDIT: I wasn't thinking of the sun... but that comparison would be interesting as well!
|
[
"Gravitational force is given by f = G m1 m2 / r",
" . I'll assume a mass of 90kg for you (although it is irrelevant to the answer).",
":",
"F = 6.67x10",
" x 50 x 90 / 2",
"F = 7.5x10",
" N",
":",
"F = 6.67x10",
" x 90 x 2.4x10",
" / ( 4.0x10",
" )",
"F = 9.1x10",
" N",
":",
"F = 6.67x10",
" x 90 x 4.00x10",
" / ( 4.1x10",
" )",
"F = 1.4x10",
" N",
":",
"F = 6.67x10",
" x 90 x 1.99x10",
" / ( 1.5x10",
" )",
"F = 0.53 N",
"So the sun by far, followed by the girl!",
" (credit to mutatron for the comparison idea): Attraction of ",
" is 7 million times stronger than ",
" who is 5000 times stronger than ",
" which are 15 times stronger than ",
". (Alpha Centauri is a ",
"binary star",
".)",
": There are a few questions on why we can't feel the gravitational attraction of the sun. We are in freefall around the sun, just as an object in orbit is in freefall around the earth (an astronaut on the ISS doesn't feel the still significant pull of the earth).",
"In order to move in a circle a centripetal force, that acts towards the centre of rotation, must be applied to an object. In the case of our spinning with the rotation of the Earth, a little of the force of gravity is used to supply this centripetal acceleration and keep us rotating. For an object in orbit, the centripetal force is equal to the force due to gravity.",
"You can feel this effect when you drive quickly over a sharp crest on a hill (circular motion) on an otherwise straight road. The faster you go, the more gravity needs to contribute to keep you in circular motion over the crest of the hill, and the lighter you feel. If you go fast enough, gravity can no longer supply sufficient centripetal force and your vehicle leaves the road: in which case you would feel weightless until you hit the road again!",
": For those wondering, about half of the deleted comments are comments about the deleted comments! The large block deleted below was mainly about ways the guy and girl could get closer together to increase their gravitational attraction, combined with numerous comments on deleted comments... "
] |
[
"We don't have any sense for being pulled by a force. ",
"The feeling of being pulled down by gravity is actually the feeling of compression from being pushed up by the ground while being pulled down by gravity. It goes away in free fall or orbit."
] |
[
"An interesting point is that the sun's attraction being this big is counter-intuitive (to me at least); we don't feel it as we are effectively in orbit around it. "
] |
[
"Architects or engineers of reddit, mathematically, how can you tell if a structure will be stable?"
] |
[
false
] |
Are there a set of equations that are used to determine how much force is applied an how much force certain parts of the structure can take?
|
[
"Yes, there are equations used to figure out how strong a structure is. At a fundamental level, the discipline of determining how materials respond to applied force is called ",
". Continuum mechanics is a very broad discipline that takes the fundamental laws that govern the motion of bodies (e.g. Newton's Laws and conservation laws) and apply them to general materials - continuum mechanics approaches can be used to model fluids as well as solids, for example. ",
"But solid mechanics is what you're after - the branch of continuum mechanics that deals with the general behavior of solids. A constitutive law is what provides the relationship between stresses (forces applied) and strains (material deformation). In general, this constitutive law is quite complicated. For solids in the elastic range, (small deformations, which is what you design your building to undergo - in general, if your bridge or skyscraper sees plastic [permanent] deformation, something's gone horribly wrong), under the linear assumption (i.e. stress is proportional to strain) there can be as many as 21 different constants that describe how the strain changes with the stress (or the stress changes with the strain). In very simple cases, under simple applied loads, however, you can reduce everything down to something that might be familiar to you: analogous to Hooke's law (F = -kx), σ = Eε.",
"But a fully continuum mechanics approach is impractical in general to take for a structure (indeed, it's inapplicable to a structure, since the structure isn't one continuous piece). What happens is that these constitutive relations that describe how stress and strain interact are applied to each component of the building in much-simplified forms under various assumptions. Bending stress is given by σ = -My/I; torsional stress is given by τ = Tρ/J; tensile or compressive stress is given by σ = F/A, and all these stresses are combined (typically using a formula to generate what's called the \"von Mises stress\") to see whether the structure can support the loads required without \"yielding\" (experiencing plastic deformation)."
] |
[
"Generally every material has ratings for how much force it can take in different ways. For example, let's say you have a steel beam. You could balance the beam on a fulcrum and apply force onto both ends (trying to bend it). You could also put the beam vertically and put a weight on top of it (trying to compress it). You could also suspend the beam in the air and hang a weight on the bottom (trying to pull it). Those are just three examples - you can apply force to something in many many different ways.",
"The equations that you'd use to determine how much force is exerted vary depending on what type of force it is and are sometimes situational. The easiest one would be the third example where the force is determine by just multiplying the mass of the object you are hanging times the force of gravity (f=ma=mg). I won't pretend to know the equations you'd use in each case.",
"The real crux of the situation is that there exist material engineers and scientists who determine how much force a material can withstand in different situations and then give you a rating for it. You use whatever equation relevant to determine if you would go over that rating."
] |
[
"Generally it heavily depends on who is selling it. Different manufacturing processes and material compositions can lead to huge tolerance differences. Usually when buying things like steel beams you would be provided a data sheet that an engineer could look at and determine the tolerances because you're probably ordering custom parts. I'm not sure you'd be able to just find general ratings online."
] |
[
"At what concentrations can hydrogen sulfide gas affect chrome?"
] |
[
false
] |
In my city, hydrogen sulfide gas has been pervasive in the air for the last month or two due to anaerobic digestion/decay of vegetation in a stagnant water channel. The smell the gas of the gas is like rotten eggs, which is a nuisance and has made a lot of people feel sick. The city released measurements, and the concentration of the gas is about 0.375 ppm on the low end and about 2.125 ppm on the high end. However, city residents have also been complaining about finding red/rust-like stuff staining their baths/showers even if they clean daily (so it's not mold or bacteria) and the chrome trim on their cars becoming oxidized or corroded. They said the timing of it coincided with the gas problem and think there's some huge public health crisis being covered up by the city. Our city's tap water system is not connected to the channel, so I thought it was just a ridiculous conspiracy theory based on confirmation bias. However, after Googling, it turns out hydrogen sulfide gas/liquid is actually corrosive to metals, though I couldn't find at what concentration. Now I'm curious: is it possible for hydrogen sulfide gas to affect chrome trim at the concentrations I mentioned above? Is it even remotely possible for it to affect pipes from the outside?
|
[
"Theoretically, corrosion of metal by hydrogen sulfide will occur at any concentration and the reaction will continue until equilibrium has been reached. Increasing the concentration will only increase the rate of the reaction depending on the rate law. Normally, in a closed system, the concentration of hydrogen sulfide decreases as it is consumed by the reaction, until equilibrium is reached. However, this is an open system where the concentration of hydrogen sulfide is nearly constant, and therefore, the reaction will continue until all the metal is consumed."
] |
[
"Uhh, wow, okay, that's a way more concerning answer than I was expecting. Thank you. Could you further explain what you mean by \"until equilibrium has been reached?\" ",
"Is the reaction that hydrogen sulfide gas has to metals similar to how salty sea air reacts to metals? Can the two effects be combined? My city is also only 20 minutes away from the ocean, and salt air can go ",
"pretty far inland",
"."
] |
[
"Well the study of equilibrium is a pretty heavy topic in chemistry, and I don't really want to get into it, so I invite you to read up on it here:",
"https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Book%3A_Chemistry_for_Allied_Health_(Soult)/08%3A_Properties_of_Solutions/8.02%3A_Chemical_Equilibrium",
"The reaction of hydrogen sulfide with metals is a completely different mechanism with different products than corrosion from salt. Reaction with hydrogen sulfide produces the corresponding metal sulfide, where as reaction with salt is a reaction with oxygen producing the corresponding metal oxide, the salt merely accelerating the reaction. ",
"The two reactions don't really combine, but rather compete for the metal surface, with the reaction that has the greater reaction rate winning out, since the reaction is essentially irreversible in an open system. If the reaction were reversible, then the product that dominates would be dependent on temperature, with the product that forms fastest dominating at low temperature, and the more stable product forming at higher temperatures.",
"If I had to guess, on chrome plated steel, the reaction with hydrogen sulfide would dominate because the chromium is already oxidized, so that reaction rate would essentially be zero."
] |
[
"Instead of other animals transmitting diseases to humans.. what diseases can humans transmit to other types of animals?"
] |
[
false
] | null |
[
"The rôle of humans in introducing chytrid fungus through several of their activities, including direct contact, into amphibian populations is quite well documented. ",
"see, for instance: ",
"Mendez ",
", 2008, \"Survival of the amphibian chytrid fungus Batrachochytrium dendrobatidis on bare hands and gloves: hygiene implications for amphibian handling\"",
"see also:",
"https://www.environment.gov.au/system/files/resources/279bf387-09e0-433f-8973-3e18158febb6/files/c-disease_1.pdf",
"http://www.amphibiaweb.org/chytrid/chytridiomycosis.html#spreading"
] |
[
"The rôle",
"Got a little French there for a second. I suspect you knew this because chytrid fungus jeopardized the frog leg industry. "
] |
[
"i work at a state health department and we recently had a case of person transmitting TB to his dog. Since there is no treatment for TB in dogs the animal had to be put down. :("
] |
[
"Do amputations improve the life of the body by having less material to care for?"
] |
[
false
] |
If you had a non functioning leg would amputation increase body health? You have full capacity of your organs but no longer have to pump as much blood and and other health maintenance.
|
[
"IANAD, but I have family members involved in medicine...",
"The problem with your assumption is that limbs require maintenance, so their absence would be a net gain. But limbs do provide some benefits with regards to regulating body temperature, blood pressure, etc.",
"But one thing you're missing is that mental health problems can easily enter into the picture through a complicated series of psychosomatic and somatopsychic responses to the loss. Roughly 2/3 of amputees suffer psychiatric symptoms, the most common of which was depression, followed by anxiety, crying spells, insomnia, loss of appetite, and suicidal ideation. (Source: ",
"Psychological Adaptation to Amputation",
") And all of those conditions are linked to decreased life span."
] |
[
"I was curious if there was risk of clotting in a non-functional limb, and to my surprise I found ",
"many",
" ",
"references",
" showing 10% risk of DVT ",
" lower extremity amputations. DVT can lead to ",
"pulmonary embolism",
".",
"So the risks associated with the procedure may outweigh any benefits. I am not educated, however, on the risks associated with keeping the limb (my original hypothesis that clots may form in a non-functional limb)."
] |
[
"IIRC, you can have trouble regulating temperature, blood pressure, etc., if you don't have enough periphery."
] |
[
"Is there a common structure or pattern in all things?"
] |
[
false
] |
[deleted]
|
[
"No. Certain arrangements are found in multiple domains because they're energetically favorable — spheres, tetrahedra and such like. But there's no significance to that beyond the fact that the same basic principles of dynamics apply at different scales."
] |
[
"I think these things all boil down to interactions with matter (i.e. each other). The spirals you described have similar forces that induce the particle in question into spiral and orbit-like patterns, because it is an energy-efficient pattern.",
"In mathematics, fractals are related to what you're looking at, and sometimes these also have real applications as well - see ",
"Hofstadter's butterfly",
".",
"As always, though, RRC has the most interesting answer."
] |
[
"Why is that not significant?",
"Because it doesn't ",
" anything. For example, if I dropped a bunch of satsumas on the floor and saw that they bounced a bit, then dropped a bunch of kittens on the floor and saw that they didn't, I might be tempted to imagine some relationship between satsuma-bounciness and kitten-bounciness. In fact, no such relationship exists. Both the satsumas and the kittens were interacting ",
"Droplets of rain in free fall tend to be roughly spherical. So do stars. That doesn't mean raindrops and stars are related in any way. They're just both governed by the same fundamental laws of physics.",
"I guess my inquiry is leading me into what the bigger picture of the universe looks like.",
"Astoundingly dull. Once you get up to a scale of about 300 million light years, it's all just a uniform smear of stuff.",
"Can we deduct what the shape of the universe is by seeing patterns in all things?",
"No. We have learned the shape of the universe by looking at the sky, but it's got nothing to do with patterns of the kind you're talking about.",
"Another question, can there be multiple universes?",
"No."
] |
[
"What is the neurochemical system involved with awareness or presence of mind?"
] |
[
false
] |
There's a neurochemical pathway involved with dopamine for the reward system, etc. But I haven't found any research involving physical manifestation of the pathway for mindfulness, etc. Which might provide information about how to exercise that pathway.
|
[
"You cannot think of the brain as a sack of neurochemicals and cells. It’s an extremely complex interconnected system that happens to have specific chemicals that affects some circuits more than others and can thus be used therapeutically. ",
"The default mode network, which is the one most clearly affected by mindfulness training, is not known to have such specific chemical dependencies."
] |
[
"I see. That makes sense. So would there be some electrical patterns or something that would give a clue as to how you can alter the state of mind to promote self awareness, apart from maybe just practice or repetition? I write it down on my to do list with everything else, but I don't check that often enough"
] |
[
"AFAIK this has only been observed recently with FMRI studies. But I understand that some attention patterns can be deduced from EEG measurements and the suppression if alpha waves. But ",
"the jury is still out on that one."
] |
[
"Why are some materials more hydrophobic than others?"
] |
[
false
] | null |
[
"Hydrophobicity depends on a variety of factors but the most often cited one is polarity. The basic principle is \"like dissolves like\" - polar solvents dissolve polar solutes and vice versa. To focus on the reason why, it's instructive to use water as the solvent and think about the solvations in thermodynamic terms. So say you have water and you're trying to dissolve something nonpolar like hexanes in it. So what are the processes happening here? First, the hexanes, which were previously surrounded by other hexane molecules, are now surrounded by water molecules. Second, the water molecules, which were previously surrounded by other water molecules, now have hexane molecules dispersed throughout, interrupting those former interactions. So you have three forces at play here - solute-solute interactions, solute-solvent interactions, and solvent-solvent interactions. The first and third are being broken and the second is being formed. ",
"Okay, so the hexane molecules were once able to interact with each other via van der Waals interactions and now interact with water molecules using those same forces. It's not clear whether there's a net stabilization or destabilization here. The water molecules were once able to interact with each other using dipole-dipole interactions and hydrogen bonding. Now the hexanes disrupt those interactions and replace them with vdW interactions, which provide less stabilization. So this destabilizes the system. Finally, solute-solvent interactions are van der Waals interactions - hexanes aren't polar. So this provides very little stabilization. So overall, you get something that's destabilized (thermodynamically unfavored) after mixing - so the two layers are better off staying separate. You would say that the solute is hydrophobic, or not willing to mix with water. "
] |
[
"Do the energy exercise and you will see. To help you, you should note that van der Waals interactions are inherently less stabilizing than dipole-dipole interactions, which are slightly less stabilizing than hydrogen bonds. To understand why, you must ask yourself how van der Waals interactions arise. They arise because as any two molecules approach each other, the electron clouds will repel and they will arrange themselves as to have a temporary dipole. On the other hand, polar molecules, by definition, have permanent dipoles. So the real question you're asking is why a permanent dipole is more stable than a temporary, induced dipole. ",
"Hydrogen bonds are a special type of dipole-dipole interaction that is especially strong. This is because a hydrogen atom bound to an electronegative element is basically a naked proton. This is the basis for most of organic chemistry. "
] |
[
"Why do non polar substances dissolve with each other? ",
"Why do polar substances dissolve with each other? I gather that polar substances roughly align their dipoles with each other, but what makes the interaction between, say, for H2O and NaCl, the hydrogen bonds between oxygen and hydrogen of different molecules weaker than the vanderwaals forces between the oxygen and the sodium?"
] |
[
"Is there a term that describes the psychological phenomenon of one person in a group of friends being established as the constant butt end of jokes?"
] |
[
false
] |
[deleted]
|
[
"\"The Omega Wolf is the male or female at the bottom of the hierarchy. The omega Wolf is usually the last to feed at the site of a pack kill. The omega seems to be the scapegoat for the other Wolves and generally slinks and submits at the least act of aggression by others. When the alpha is in a particularly grouchy mood he may not allow the omega to feed, or constantly dominate him or her. ",
" Omegas have been known to become stronger and literally fight their way back up the ranks to take a place among the subordinates; this can happen if they repeated win challenge against other Wolves.\"",
"http://www.runningwiththewolves.org/Behavior1.htm",
" "
] |
[
"That would be a sociological phenomenon, not a psychological one."
] |
[
"Social stratification",
" The animal equalivent is ",
"Dominance hierarchy",
".",
"I know there had been a lot of study in dominance in primates, they make some very interesting reading.",
"example"
] |
[
"How possible is it for a company with minimal polymer experience to start making useful polyurethanes?"
] |
[
false
] |
I work for a small ink company, and my boss has decided that we should start making our own resins (mostly the polyurethanes) since we can't find one with the correct properties. We have no polymer chemists on staff (or any PhDs, for that matter), but a few formulators. Is there any likelihood of success, and if people have any experience, how expensive would this likely be? We have very minimal equipment (although we do have a fumehood).
|
[
"This does not sound like a good idea, especially considering the lack of experienced personnel and equipment. First, you would need to determine the desired chemical structure of the polyurethane that you're interested in (or more probably, a variety of similar structures). Once you successfully devise a series of reactions to create the required precursors, you'll need to figure out how to polymerize them so as to produce the necessary molecular weights - something else that will have to be determined. Every step of the way, you'll have to purify things, characterize them, and then determine how to scale this into an industrial process. ",
"If you have to purchase characterization equipment that will function with a reasonable degree of precision (i.e., not just simple ",
"GPC",
"), then you'll wind up spending anything from tens of thousands to millions of dollars on equipment. It would be far easier to outsource the characterization - or better, outsource the synthesis as well. ",
"extremely dangerous"
] |
[
"I am a Polymer Chemist and I can tell you that your company will without doubt stumble badly. You cannot just willy nilly these reactions. Even if you succeed in making something useful or your desired PU you would still have to figure out how to sustain it and reproduce it. None of this can be possible without understanding of reaction chemistry and full analysis of the product. "
] |
[
"At first, let my clarify a few things. As far as I understand, your company is specializing in making some kind of items which have PU elements. You are purchasing these 2-pack compounds, mix them and then pour into molds for curing.",
"My next assumption is that your local PU supplier is unable to deliver product of required quality and you face either too fast gelling, or too strong heat evaluation, or the cured resin have poor mechanical properties, or any other undesired stuff.",
"You don't want (or don't have an opportunity) to change something in technological process or part design, so next logical conclusion is to change something in raw materials. Am I right yet?",
"Problem here is that your raw materials (polyols and isocyanates) are smelly liquids and chemically active substances, not the nice parts for assembly. And they have to react with each other first to form stiff crosslinked polymer.",
"Now, it is quite possible to mold good quality polyurethane articles without deep knowledge of how exactly polyols react with isocyanates. Your resin suppliers can do this part of job for you (and normally should). But still you have to understand that consistency of conditions at your plant (mostly air humidity and temperature) matter a lot for consistency of quality of molded PU parts. ",
"But without proper expertise you never should even think about \"cooking\" these components (polyols and isocyanates) yourself -- this is what your suppliers are for. These processes are prohibitively difficult, expensive and dangerous.",
"Molding polyurethanes is not that difficult if you have some simple formulations to begin with (and a hood). You will need also scales, simple glassware, and molds. If your market is not too much saturated I hope it could work for you."
] |
[
"What element do we consume the most?"
] |
[
false
] |
I was thinking maybe Na because we eat a lot of salty foods, or maybe H because water, but I'm not sure what element meats are mostly made of.
|
[
" Hydrogen, by number. Oxygen, by mass.",
" The stuff we eat is primary made up of three classes of molecules, and water. Those three molecules are fats, carbohydrates, and proteins and are made primarily of carbon, hydrogen, and oxygen, with a handful of other things sprinkled in. Water, on the other hand, makes up a variable percentage of what we eat, and depends on the food. The wiki article on ",
"\"Dry Matter\"",
" lists the relative water content of lots of foods: ",
"Boiled Oatmeal: 83% water\nCooked Macaroni: 78% water\nBoiled Eggs: 73% water\nBoiled Rice: 72%\nWhite Meat Chicken: 70%\nSirloin Steak: 69%\nSwiss Cheese: 37%\nBreads: 36%\nButter: 15%\nPeanut Butter: 5%\n",
"And additionally, they vaguely list fruits and vegetables being 70-95% water, which is cool. It's neat that things can be solid yet have such a high percentage of fluid in them- people for example are about 70% water. ",
"Anyway, on average, I'd expect that half the food you eat is actually just water. Since water is made of two hydrogen atoms and one oxygen atom, then hydrogen is very clearly the most abundant atom in our diet. It is also, coincidentally, the most abundant element in the universe. ",
"On the other hand, what I just said is only true if you're counting the ",
". You could easily count their combined mass, in which case the heavier elements actually stand a chance against hydrogen. Since oxygen, on average, is sixteen times as massive as hydrogen (8 protons and 8 neutrons), it will be the greatest contributor by mass. ",
"This cool plot",
" tells me that, by mass, humans are 65% oxygen, with carbon in a distant second place with 18.5%. ",
"So why are we called ",
" life forms when we're a majority oxygen by mass, and hydrogen by number? Well, it's just because carbon does the hard work- it has a very neat electron structure that enables it to do all sorts of cool bonds, which are the basis of all organic chemistry. "
] |
[
"Your answer is correct on a basis of quantity of atoms, but not on a basis of quantity of mass."
] |
[
"Good call. I've added some stuff. Thanks. "
] |
[
"False discovery rates and critical values for micro array data"
] |
[
false
] |
Hi Ask Science, So I realize this is a more specific question than is usual queried. I am looking at a micro array data set (as a noob), and I calculated a rough estimate of the FDR. But now I don't know what to do with it. How do I use these values (unique for each gene, based on the p-value*comparisons/rank) to determine a new critical value to account for false positives? For instance, Gene 1: p = 0.028203, FDR = 1.107459 Another: P-value = 5.61424E-06, FDR = 0.252641 Also, if I am only looking (a-priori) at a subset of genes, can I calculate the FDR based on (p-value*comparisons/rank)? Do I have to recalculate the rank? THANK YOU SO MUCH.
|
[
"My advice would be to to walk around your building until you find a lab that deals with microarrays a lot and then make a new friend. Or if your university has a genomics core they would probably be able to help you. ",
"I know i have received plenty of help from labs that have no stake in my work but were kind enough to help me. "
] |
[
"Thanks!",
"We just found something pretty neat using the advice here. We have a micro array set from a selected lines (naiive to a treatment), then a separate one with saline vs treatment. ",
"We found something pretttttttty interesting just now and are scrambling to find a lab that deals with the candidate gene (one we were interested in).",
"Off to make friends, then!"
] |
[
"You can read the original paper ",
"here",
". I think you will get it in a few hours based on the stuff you are describing. ",
"The gist of FDR is this: for one comparison, we use a p-value. For microarray data comprised of thousands of experiments, we know some of the data will be false positives, so we set a false discovery rate using a q-value which indicates what fraction of your positives will be false positives. The paper describes the relationship in greater detail."
] |
[
"At what \"level\" of development do creatures become conscious and is there anything other than humans that are conscious of their existence similar to us?"
] |
[
false
] | null |
[
"The developent of a neocortex similar to ours. I'm not an expert on the mental possibilities of other species, but I would assume that the next in line, so to speak, would probably be a dolphin, if we count primates out. ",
"I hate to say this, and I've never thought about it until now, but there probably wont ever be another creature from earth that develops evolves into something comparable to humans. Human involvement with nature makes it very unlikely for another species to be given the right circumstances for it to happen. Even if we did allow for that to happen, shifting human actions with the world would eventually end the process somehow, by either nuclear war, or some type of planetary disaster. ",
"But I like to stay positive, and say that when that disaster happens, something will emerge from the ashes of their perished fellow beings and thrive. That is inevitable. Imagine if cockroaches were to survive nuclear fallout that wiped mostly everything else out. They could evovle into something like us over time. "
] |
[
"I never thought about that but seeing how we have done with the gift maybe its best that no one else knows. It's a little embarrassing. "
] |
[
"Yeah,it is. I think about it a lot and it's probably in my best interest to stop, how I am ashamed to call myself human. To an alien audience, we probably seem horrific. "
] |
[
"Why do so many people dislike foods such as fish that have been eaten all throughout human evolution?"
] |
[
false
] |
Wouldn't we all have it hardwired into our DNA to like fish since it is one of the most eaten foods all throughout human history and needed for survival?
|
[
"In relation to fish and fish only:",
"As a pretty experienced cook I can tell you that in the case of the most fussy eaters - if you lie about what's in it, they will happily eat it. I don't recommend that, but it is proof that it's just some personal bullcrap in their heads.",
"There are some folk who genuinely don't like the taste, but that's quite rare.",
"Fish is actually hard to obtain fresh and cook properly, that might be part of the problem. Fresh fish doesn't smell, so all those \"smelly fish\" jokes you hear, or the smells at the fish market - that's all rotten fish. As for cooking, many people are afraid of cooking it as they are afraid to undercook it (due to food poisoninig), and find it sticks to the pan, and are afraid to overcook it as it turns into mush that is like eating pre-chewed babyfood."
] |
[
"I would say there's definitely a difference bw rotten fish smell and the smell/taste I would define as 'fishy'. Not all, or even most, fish smell fishy to me, but some definitely do no matter how fresh. ",
"Edit: Ok I just researched it, and apparently the traditional smell ",
" from the breakdown of trimethylamine oxide (don't try just searching for 'fishy smell' btw, totally different). So question - why do some fresh (as in, caught be me) fish smell that way to me?"
] |
[
"No, I mean they wont eat it if you tell them what's in it, and if you don't (or you lie) they eat it and like it.",
"You're the second type I mentioned, the people that actually dislike some ingredient because of its taste, not the people with imaginary food problems (the first type)."
] |
[
"How exactly do we perceive the color of a pixel?"
] |
[
false
] |
Since a pixel only emits red, green and blue: how do photons of these basic colors intermingle on the retina, making the eye perceiving wavelengths which differ from these basic colors?
|
[
"There are ",
"three types of cones",
", each of which has a slightly different ",
"frequency response curve",
". It's slightly more complicated because that graph is normalized, but the process works the same either way.",
"Look at that graph and pick a point in between the peaks - say, 500nm (aqua). Note the y-value of each curve at that point on the graph, and imagine that we have a light source of that wavelength.",
"Now pick three arbitrary points on the graph. If we have three light sources of those respective wavelengths, at intensities such that the sum of the responses of each cone type is identical to the 500nm responses, then you will be unable to tell the difference."
] |
[
"The colors we see are not a single wavelength, but a composition of different wavelengths. By changing the power level of three primary colors (because we have 3 types of color receptors in our eyes) we can reproduce different colors for out brain."
] |
[
"It is worth noting that this effect is known as Metamerism."
] |
[
"Are human bodies efficient compared to man-made machines like cars?"
] |
[
false
] |
[deleted]
|
[
"It depends on your definition of efficient. From an energy-in, energy-out perspective, not at all in any way. We eat a ton of energy, and what do we do with that energy? We turn almost all of it straight into heat. Some of it can go into altitude or speed, but that energy will very quickly be dispersed into heat again as we return home.",
"Also, we don't have wheels, so we can't store energy in motion. We have to constantly expend energy to go literally anywhere. Aside from this, a majority of our energy goes into generating heat, because we are warm-blooded.",
"About the only way that some energy would not just go straight to heat would be a person cranking a machine that stores energy.",
"On the other hand, our inefficiency helps us evolutionarily, as we don't need heat from the sun and can thus survive in cold environments provided insulation.",
"Also, gas engines are really inefficient. Most of the energy stored in gasoline just goes toward heating air. Only around 20 % goes to actually doing things mechanically. Humans, in comparison, spend nearly all of their energy making heat, and even make heat when doing no work at all."
] |
[
"Arguably. Some of our tissues like muscles, are pretty inefficient in terms of the mechanical work they do per unit of energy(as I recall, muscles are only 20-40% efficient). However, this underestimates the efficiency of the body in several ways(for example, in most machines any energy that is dissipated as heat is considered \"wasted\", but in a human body heat generation is neccesary to stay alive)",
"We also have some body parts(like the brain) that use at least an order of magnitude less energy than an equivalent machine would."
] |
[
"Well we do need all that heat so I wouldn't considered it wasted or inefficient. If you consider the heat we make that we are extremely efficient compared to other stuff. If we look at how much energy a computer uses to do one simple math problem (say 3x4) and how much energy we use, the computer is more efficient. But imagine now that we are going to solve a maze. Our brain uses less energy for that than the computer does (assuming it is a decently complex maze). Also computers make a lo of waste heat that requires even more energy to move away because they don't need the heat. "
] |
[
"Is it possible for some people to have a more/less saturated vision than other people?"
] |
[
false
] |
For example, can some people see more saturated colors than other people can?
|
[
"We can never be sure what the subjective nature of other people's experiences are. These experiences are termed ",
"qualia",
" and they play a big role in the philosophy of the mind. However, we can use self reported information when an individual experiences a change in the quality of their vision. People with cataracts that receive surgical treatment will attest that colors look more vibrant after surgery.",
"We can also measure objective differences in human vision and try to tie them back to saturation. If, say, oversaturated color perception led to a decrease in the ability to discriminate colors we could measure that. It would be hard to tease out an effect from saturation in particular though, since color discrimination can also be influenced by various forms of colorblindness and ",
"(maybe) language",
"."
] |
[
"With the level of genetic diversity amount humans, I would say it's extremely likely, but I have not heard about any particular studies being done.",
"The difficulty is that it's hard to compare the perception of two separate individuals without being able to see what they see. Even then, the observer would contaminate the results simply because they, too, would have a different perception from either test subject. This could be overcome by technology, but that technology would require the ability to plug into someone's brain or optic nerve, and we're not there yet."
] |
[
"Thanks, that was a good explanation :)"
] |
[
"Are there \"solar systems\" with planets at their center instead of suns?"
] |
[
false
] | null |
[
"You are right they are called rogue planets, not solar systems. ",
"http://en.wikipedia.org/wiki/Rogue_planet",
" ",
"Yes to having moons (example: ",
"http://en.wikipedia.org/wiki/Cha_110913-773444",
" ), not sure of any with moons that have moons. "
] |
[
"Thanks for steering me towards Cha 110913. It's been very interesting reading. Can you correct or confirm some new assumptions?",
"Apparently it was either ejected from a system or was formed in the same way that stars are formed. If similar to stars, a cloud of interstellar gas and dust collected and, through gravitational force, combined to create Cha 110913. Because it did not have enough mass, hydrogen fusion did not occur, so it did not become a star. But when it collapsed and formed, it had created a protoplanetary disk around it. That swirling cloud flattened out and by gravity of the particles and time eventually formed masses, or planets around it.",
"Now because Cha 110913 is not a star, it does not emit light like our sun. And because it is only 8 Jupiter masses, it's even too small to be a brown dwarf. I guess that makes it a planet. And the orbiting masses around it are therefore moons. Does that make it a planet at the center of its own system? And because it does not emit much light at all, any orbiting moons are cold and cannot support life, as we know possible? Also, since it is so small, it cannot support the orbit of a number of objects like our solar system?"
] |
[
"First, I'm an amateur not a pro, so you might want to ask these questions again in brand new posts to attract the real experts that askscience has to offer in this domain. But, I'll try my best: ",
"And the orbiting masses around it are therefore moons. Does that make it a planet at the center of its own system? ",
"Yes. Yes it does. Although I think that because since it's origin is more star like and the word planet connotes origin as a planet in a solar system, some people would like to call it a \"sub-brown dwarf\" to make the distinction from \"ejected planet\", although they could be practically the same thing in terms of composition. ",
"And because it does not emit much light at all, any orbiting moons are cold and cannot support life, as we know possible? ",
"Energy is fundamental to life, but solar energy is not the only source. If there were quite a lot of radioactive material in the core of the planet or moon for heat, it's very possible that could provide enough energy for life given other requisite conditions like water and organic chemicals (see the hypotheses about biogenesis at hydrothermal vents). ",
"Also, since it is so small, it cannot support the orbit of a number of objects like our solar system? ",
"Right. But there could be a pretty nice pile of interesting moons. Think of the diversity of worlds to be found around Jupiter alone."
] |
[
"Is 7 equal to 7.0 and 7.00?"
] |
[
false
] | null |
[
"Yes, they’re equal."
] |
[
"Mathematically, it’s true no matter what the precision is."
] |
[
"Thanks. Its true even when when we take precision into consideration right? Thats what the major opposing argument is. That they're not equal because the precision is different."
] |
[
"Is there such a thing as endangered plants???"
] |
[
false
] |
Do we have plants that are endangered, or records of plants that have gone extinct?? I am not knowledgeable on this subject. I know we find plants preserved in amber and stone, but the ones I recall seeing are things like wheat and ergot and flowers that we still have around today. I would also like to know if humans have ever purposefully eradicated a plant, or of that's possible.
|
[
"Endangered and extinct plants exist, just like animals. An example: the Arizona Agave with less than 100 plants alive in 1984. There are also plenty of extinct plants. The reason you never hear about them is probably because people care less about plants. They are also often closely related to other species which aren't extinct."
] |
[
"Yes! Most carnivorous plants, like the North American pitcher plants (genus Sarracenia), are endangered, mostly because of poaching. Basically, pitcher plants were so cool that people would pick entire fields clean. Nowadays, most botanists actually refuse to share the locations of new sites.",
"Additionally, a lot of construction projects are currently demolishing and building over things like bogs and peatswamps (which is where carnivorous plants naturally grow). The destruction of their natural habitat is aggravated by the fact that most carnivorous plants take years to develop flowers and produce seeds (which have <~25% germination rate)."
] |
[
"There is no reason why there would be endangered animals and not plants, but I feel that most of the general public finds animals more interesting, so you hear about endangered animals more.\nPlants are usually easier to grow healthily 'in captivity' than animals, and can be cloned (cuttings, tissue culture) meaning that they are easier to keep alive and renew the population. "
] |
[
"Can a radio antenna be used to detect visible light?"
] |
[
false
] |
Could I place a normal radio or TV antenna in sunlight, have a tuner that I could set to 'red' (400THz) and measure how much red light is present? (in watts I guess)
|
[
"Theoretically, yes. However, the antenna would have to be so small as to be realistically impossible.",
"At 400 THz, a half-wave dipole antenna would have to be 325 nm long, and thin enough to make that look like a wire (approx two-to-three orders of magnitude, or about 500 pm wide). Also the energy collected by this antenna would be so small, and the frequency so high, that it would be essentially unnoticeable."
] |
[
"Is this a description of the sensors in a digital camera or are those completely different? "
] |
[
"Sorry, misread the question.",
"No, a \"normal\" radio or TV antenna is designed for wavelengths orders of magnitude larger than a 400 THz signal. A tuner can compensate somewhat for a mis-matched antenna, but at these extremes, the tuner and antenna deficiencies would overpower the signal itself."
] |
[
"Does a spectrogram from a planet/non-light source get affected by the source of light which we obtain it from? For e.g., if we take a spectrogram of Jupiter, do we have to \"subtract\" the known spectrum of the Sun before we can determine the elements in Jupiter?"
] |
[
false
] |
To extend the example, since hydrogen from the sun produces a gap in the source spectrum, will it give us a "false positive" reading from the spectrum of the other planets?
|
[
"I believe I found the answer to my question. Please correct me if I'm wrong.",
"Analysis of the solar spectrum involves ",
"absorption spectroscopy",
". The hot sun acts as a ",
"black body radiator",
" which initially gives us a complete spectrum. As the light passes through the cooler gases nearer to the sun's surface, parts of the light spectrum gets absorbed by the elements present. This results in the formation of ",
"Fraunhofer lines",
", indicative of the composition of the sun.",
"Analysis of the planets in our solar system involves ",
"reflectance spectroscopy",
". The reflected spectra we obtain from the planets will include absorption lines from the sun, as well as from the composition of the planets themselves. In order to properly analyze the planetary spectra, a process called \"",
"deconvolution",
"\" is used so that the solar spectrum is separated from the planetary spectrum."
] |
[
"This is the correct answer."
] |
[
"It doesn't completely discount them, it discounts some relative amount of them. "
] |
[
"Why doesn't my body get better at fighting off infections with repeated exposures?"
] |
[
false
] | null |
[
"Hello,",
"We can't advise you about your personal medical situation."
] |
[
"Understandable; would my submission be accepted if I phrased it more generally?"
] |
[
"I think it would be very difficult to frame this question in a way that we can accept it. If you go into the specifics of your experiences, it's anecdotal. But if you leave that out and make the question general, it's a little open-ended."
] |
[
"How would you describe specific colors to someone who is blind?"
] |
[
false
] |
How can you accurately convey the image of the color red, for example, to someone who has never seen red? Let's say that this person was born blind, and therefore has never been able to see any colors (eliminating the possibility of using comparisons to things of that color/other colors).
|
[
"Best answer, synesthesia. "
] |
[
"Best answer, synesthesia. "
] |
[
"You can't. You can't even accurately describe the color red to someone who is sighted - that is, you can't be sure that what I call 'red' doesn't appear like a different color in your brain. All we can do is say that we both agree that a certain object looks red to ourselves. "
] |
[
"How does Europa still have water available to eject in Saturn's ring system?"
] |
[
false
] |
Firstly, am I correct in saying that part of Saturn's ring system is made by a sort of 'cryo-volcanism' of Europa ejecting water into space? If so: A) How long can this be maintained? I.e. it is spewing water at a rate of 'x' and we believe this can be maintained for 'y' years? B) What will happen to Europa in the future? Will it just be a waterless, earthy/rocky husk after all of it's water is ejected into Saturn's orbit? C) How long has this been going on for? D) How much water does it have to have been doing it for this long? E) What are the implications for the chances of life if its water is constantly being ejected? Sorry for so many questions, I'm really curious. I've sort of self-resolved in my own mind that maybe some of the water it ejects falls back onto the planet surface in a self-recycling fashion, extending the supply of water from the planet. But equally, I know the solar system has been in existence for billions of years, so I can't see how Europa hasn't already ran out of water! Thanks in advance!
|
[
"Europa is a moon of Jupiter, not Saturn.",
"Saturn's rings are most likely the result of a large moon which was torn apart by tidal forces millions of years ago.",
"cryo-volcanism wouldn't create a significant ring system there just isn't enough matter being ejected."
] |
[
"I think OP might be talking about Enceladus. ",
"cryo-volcanism wouldn't create a significant ring system there just isn't enough matter being ejected.",
"Actually, Enceladus' plumes cause Saturn's ",
"E ring",
". It is definitely diffuse, but it's a ring nonetheless."
] |
[
"Yes, you are correct, I meant Enceladus. \nWhen do you think it'll run out of water to keep topping up the E Ring? :)"
] |
[
"My dad asked me to look over the \"Blacklight Power\" site. It's got too much technobabble for me to understand completely (Related: What's a hydrino?), but I pretty much know it's bullshit. However, I need to need to explain it to him, so askscience, can you break it down for me?"
] |
[
false
] |
<- this is the main summary I tried to read. Couldn't make head or tail of it. Here's the text from the page for people who might not want to give them hits. BlackLight Power, Inc. - Executive Summary Business Presentation An overview of BlackLight's business, technology and market potential. This is a large file which may take a while to load. • BlackLight Power, Inc. is the inventor of a commercially competitive, nonpolluting new primary source of energy that forms a prior undiscovered form of hydrogen called “hydrino” which is very likely the identity of the dark matter of the universe. • Proprietary electrochemical reactants or solid fuels undergo reaction to cause hydrogen to form hydrino with energy released as electricity or heat, respectively. The net energy released from this "BlackLight Process" may be two hundred times that of combustion of the hydrogen fuel with power densities and performance comparable to those of batteries and conventional central power plants, respectively. • Water can be used as the stored hydrogen, generated on demand by electrolysis using less than 1% of the electrical output. With the elimination of fuel and fuel infrastructure costs, the operational cost of BlackLightPower generators is likely to be very inexpensive. Moreover, the process does not give rise to pollution, green-house gases, or radiation as conventional systems do. • The Company has developed three systems for producing electricity powered by forming hydrinos: one electrochemical and two thermal systems. A CIHT (Catalyst Induced Hydrino Transition) cell generates electricity directly from hydrogen. But, unlike a conventional hydrogen fuel cell, the cost is forecast at $25 per kW compared to thousands per kW for a fuel cell. This is in part due to the CIHT cell’s electrical energy released per hydrogen being over 200 times greater, and the CIHT materials being inexpensive. Moreover, fuel cells can’t use water as the source of hydrogen, since their product is water. For CIHT, no fuel infrastructure is required to provide on-site power allowing the CIHT cell to be autonomous. • BlackLight Power is focused on advancing CIHT technology to produce power to ultimately sell directly to consumers under power purchase agreements. Rapid dissemination at nominal historic cost is expected by deploying many autonomous distributed units that circumvent the huge barriers of entry into the power markets such as developing and building massive billion-dollar power plants requiring enormous thermally-driven mechanical generators with their associated power distribution infrastructure. This is especially advantageous in emerging markets. • Essentially all power sources of all sizes: thermal, electrical, marine, rail, aviation, aerospace, as well as, automotive sources become untethered from an electrical distribution or fuel infrastructure and are also independent of the sun, wind, or other external variable power sources. • A CIHT electric car is expected to have a range of 1500 miles on a liter of water. This direct application of the BlackLight Process to motive power has the potential of unsurpassed capability in terms of range, capital cost, power, logistics, and pollution abatement to zero, including zero carbon dioxide emission. Moreover, the compact automotive unit could be plugged into the electrical panel to power the owner’s home with enough power to spare to also power the neighborhood. BlackLight plans to pursue licensing, strategic partnerships, and leasing in motive power markets. • In addition, the Company has developed thermal producing solid fuel chemistries that in turn can be thermally regenerated. Thus, the Company believes that continuous generation of power liberated by forming hydrinos is commercially feasible using simplistic and efficient systems that concurrently maintain regeneration as part of the thermal energy balance. The system is closed except that only hydrogen consumed in forming hydrinos needs to be replaced. • Chemistries and engineering designs have been developed using the corresponding experimental parameters for power and regeneration for two thermal-Rankine systems. One comprises a multi-tube thermally interacting bundle of cells wherein cells producing power provide heat to those undergoing regeneration. As a system, the power output is constant. The capital costs are projected to be about $1400 per kW electric. The other comprises an array of reactor cells wherein power and regeneration chemistries occur synchronously, and each cell outputs constant power. The capital costs are projected to be about $1050 per kW electric. • BlackLight is non-exclusively licensing its thermal process to make power for a fixed royalty payment per kilowatt-hour of thermal or electric. To date, the Company has licensed the rights to produce approximately 8,250 MW of new electrical power to seven companies, including five electrical utilities and two independent power producers. Collectively, these utility companies own, purchase, or manage electric power production of approximately 7,600 MW and service nearly one million customers. The avoided fuel costs from these agreements could be in excess of $2 billion per year. • Electrical power from the CIHT cells, thermal power from the solid fuels and their thermal regeneration, hydrinos from both synthesis reactions and as a product of the CIHT cells and the solid fuels, as well as the light signature of the formation of hydrinos, and other signatures of the BlackLight Process have been independently validated and published in scientific journals and reports. • The theory upon which BlackLight's technology has been developed is based on the classical laws of physics. The Company recently released the finalized Grand-Unified Theory of Classical Physics that comprehensively addresses many of the basic problems in chemistry and physics using these physical laws without using approximations or pure mathematics, devoid of physics, as is the case for the incumbent atomic theory of quantum mechanics. BlackLight's wholly owned subsidiary, Millsian, Inc., is dedicated to developing computational, chemical-design software tools based on solving molecular structures using these laws. The essentially real-time, analytical solutions of the precise physical structure of molecules of boundless extent and complexity, not possible using quantum mechanics, further validates the classical theory relied on by the Company. TL;DR
|
[
"…new primary source of energy that forms a prior undiscovered form of hydrogen called “hydrino” which is very likely the identity of the dark matter of the universe.",
"At this point I stopped reading and skipped to the end, where I found:",
"The theory upon which BlackLight's technology has been developed is based on the classical laws of physics.",
"At that point, I was pretty convinced that my decision not to read the middle was a good one. This is pseudoscience, and is not worth the time it would take to make fun of it."
] |
[
"A hydrino is almost certainly a completely fictitious particle this company made up. We don't yet know (for sure) what dark matter is. No one does, much less some \"power generation\" company. The rest of the nonsense seems to fall into place after this.",
"And the last point. Particularly \"...without using approximations or pure mathematics...\" If it doesn't have math, it's almost certainly not true. "
] |
[
"Why don't you just read the Wikipedia article on the \"company\". ",
"http://en.wikipedia.org/wiki/Blacklight_Power",
"I especially like the following quote \"By 2009 BLP had raised about $60 million in venture capital, and claims to have seven commercial agreements to license BLP energy technology for the production of thermal or electric power to utilities and private corporations. By 2011 no known power generation has occurred.\"",
"Seems like this guy is a pretty good fraud. Considering he's been touting his magic free energy devices since 1991, you might want to ask why there is no real commercial product yet?"
] |
[
"How are memories stored? Could specific parts of the brain be targeted to erase specific memories?"
] |
[
false
] |
Are memories stored like files on a hard-drive where you can target the information directly, or are memories stored across the brain in a "holographic" type way where destroying parts of the brain would merely weaken memories but not destroy specific ones?
|
[
"See ",
"this thread",
" for some relevant information. There is no evidence to suggest that memories are stored in particular places in the brain. It is true that particular parts of the brain are involved in different types of memories, but there is no evidence to suggest that those are the places where they are stored.",
"Our best evidence suggests that memories are stored as complex ensembles of neuronal activity- which is described well by secondpolarbody's second paragraph. "
] |
[
"Different ",
" of memory are indeed stored in different parts of the brain, somewhat. For example, the hippocampus ( a part of your brain) is shown to store spatial memory (e.g. your knowledge of the roads in your neighbourhood). It has been observed that taxi drivers have on average larger hippocampi than the general population, presumably due to them being familiar with large areas of the city they work in.",
"However, actual pieces of long term memory are stored as strong connections between neurons, and your memory of a particular event may involve connections formed between many many neurons in different parts of the brain, covering the smell, sight, sound, emotional and other aspects of that memory. Therefore in this sense memory is also very spread out, and it would be impossible to delete specific memories by targeting a single part of the brain. "
] |
[
"Here are some links you may find relevant to your question. The short answers to your two questions are yes and perhaps, though it would be very difficult to parse the different aspects of single memories from other memories. \n",
"http://www.quora.com/Are-memories-stored-physically",
"\n",
"http://www.quora.com/How-are-memories-stored-in-the-human-brain",
"\n",
"http://www.quora.com/What-chemical-s-do-our-neurons-use-to-store-our-memories",
"\n",
"http://www.youtube.com/watch?v=HA7GwKXfJB0"
] |
[
"Is it easy to create a strong solenoid?"
] |
[
false
] | null |
[
"You think a power source that can supply 5 Amps is easy to find?"
] |
[
"Not sure. I was thinking just using the wall outlet and finding a low value resistor. Haven't actually tried to find it, though. That aside, is the calculation a good estimate given the conditions? There's probably overheating issues but I'll figure that out later."
] |
[
"Your wall outlet is not going to allow you to draw 5 Amps. 5 Amps is an enormous current, ",
" more than enough to kill you.",
"Creating a low-resistance path between the holes in your outlet will just trip the fuse."
] |
[
"Does exercise have any effect on height growth?"
] |
[
false
] |
I understand that height growth is basically genetics/environmental factors but what effect exercice like basketball or any sports can do to potentialize our height growth during puberty when you already have good nutrition?
|
[
"One study, it states that human growth hormone secretion can be stimulated by vigorous exercise and the conclusion is - \"We conclude that the GH response to acute aerobic exercise is augmented with repeated bouts of exercise\". The study can be seen here - ",
"http://jap.physiology.org/content/83/5/1756.full",
"And also, according to Wikipedia, \"Increased height during childhood is the most widely known effect of GH\" so I guess you could say that it is influenced by exercise, however the release in HGH due to exercise may only be for building bone and muscle, and not actual height growth.\nSo I think that exercise may only influence height growth to an extent. Swiftskill is correct in saying that genetics is the main factor contributing height growth."
] |
[
"Height can be affected by factors such as diet ",
", that point being genetics. Someone with poor nutrition will be shorter than someone who is well fed, all else being equal.",
"Basketball players are not tall because they play basketball. They play basketball because they are tall.",
"Therefore to answer your question, no, activity does not influence height. "
] |
[
"Workouts are mostly to increase your physical capabilities. Workouts will allow them to jump higher but not grow more. ",
"Increasing muscle mass is natural, increasing bone structure isnt."
] |
[
"Assuming we could live on the surface of the moon or Mars, how much radiation would we be exposed to?"
] |
[
false
] |
I've been reading some sci-fi books about colonizing the moon and Mars and was curious about the radiation load a human would experience over the course of a year in either of those locations. Also, what kind of radiation load would a human experience living a year in the International Space Station?
|
[
"The ",
"ISS Wiki article",
" states that astronauts in the ISS get the same radiation dosage in one day as someone on Earth gets in one year. So roughly 365 times more. ",
"The ",
"Colonization of Mars Wiki article",
" states that the dosage on Mars would be 2.5 times higher than on the ISS."
] |
[
"The colonies will probably have to be underground."
] |
[
"Why would it be higher on the surface of a planet? Is it the radiation shielding on the station, or the fact that the station is close enough to the earth's magnetosphere to shield the station?"
] |
[
"How can a supermassive black hole explode?"
] |
[
false
] |
I read an article that talks about the supermassive black hole at the center of our galaxy exploding relatively recently . How does a black hole explode? I don't pretend to know much in this area but I would think the energy needed for anything to escape a black hole would be impossible to reach, thus negating any "explosion" anything from escaping the event horizon. The article says it was "like a lighthouse for 200k light-years into deep space." How?
|
[
"It's a poorly written headline that's leading to a misconception. The black hole did not explode. You are correct, nothing can escape the event horizon. The ",
"original release",
" has the phrasing that the \"centre of the Milky Way exploded\" which is subtly but crucially different from the \"black hole at the center\" exploding. ",
"What DID happen was that some gas ",
" the black hole at a much higher than normal rate, and a large fraction of that material was ejected from very near to (but still outside of) the event horizon, at very high speeds, along with an incredible amount of high energy light. The study in the article found the impact of this event on the surrounding environment."
] |
[
"Yes, Hawking radiation does not originate from inside the event horizon, but just on its edge."
] |
[
"Classic newspaper article confuses more than helps people.",
"Black holes don't explode.\nSome can be active however. A galaxy with an active super massive BH at its core is called an AGN. \nSometimes these can produce flares.\nThat's what they were referring to.\nThe flare event."
] |
[
"Is it safe to fix my french press with super glue?"
] |
[
false
] | null |
[
"The polymer formed by the superglue curing process does not readily degrade when exposed to water, and it is low in extractables, you should be fine from a chemical exposure stand point. ",
"The bigger question is whether or not the glue will be sufficient to fix what you are attempting to fix, and that I can not answer."
] |
[
"Source? ",
"Cyanoacrylate polymerizes in the presence of and is insoluble in water.",
" How will using it have anything to do with burning yourself?"
] |
[
"I realise this is a fixit forum but after much personal experience, getting a quality replacement 'beaker' via ebay has stood up as the longest solution. Another common source previously used has been thrift stores."
] |
[
"Can cancer get cancer? E.g. can a cancerous tumor grow on another cancerous tumor?"
] |
[
false
] | null |
[
"Cancer usually refers to the uncontrolled and harmful growth of cells. Parts of a tumor can become malignant, metastasize, or become histologically distinct (and thus be different from the original tumor's pathological progression), but your assertion that cancer can \"grow on\" other cancer tumors doesn't make sense. It would be ",
" that tumor that's become different, that's all."
] |
[
"A tumor is a heterogeneous group of cells undergoing mutation and selective pressure from their microenvironment. In fact, within the same tumor, there will be subpopulations of cells with different mutations that are competing for the same resources. My point here is that a tumor can't really be thought of as a single entity, but rather a population of cancerous cells evolved from a common ancestor.",
"The closest real scenario to what you describe is when sub-populations of these cells evolve different mechanisms to, say evade cell death, and the group that does it better will ultimately win out and comprise more of the tumor's mass. "
] |
[
"I'd like to know if that second growth would be deleterious to the prior growth's health. "
] |
[
"Why are sinkholes almost always circular in shape?"
] |
[
false
] | null |
[
"Sinkholes occur when erosion has been going on below them; that much seems obvious. However, it's worth condiering that type of erosion.",
"The most common form is chemical weathering of limestone, caused by movement of groundwater, which in general tends to concentrate along particular weak joints or fractures within the rock mass. This creates a high-flow rate zone, which can transport more water, which can erod faster, so that starter zone now grows. What you end up with are large, complex cave systems which have some kind of linearity to them. ",
"https://virtuallandscapes.files.wordpress.com/2012/03/limestone.jpg",
"Now, as that image demonstrates so well, the rock mass has all sorts of pre-existing fractures and weaknesses in it along which subsequent erosion can preferentially channel. All that has to happen for a sink-hold to form is that erosion has to progress up toward the surface enough to remove the overburden strength so the roof collapses. Erosion doesn't happen in uniform sheets along these weaknesses, it is highly irregular, with variations in both rock structure and groundwater flow having a huge effect. And once a weakness starts opening, erosion tends to get concentrated there, rather than spread along an entire weak area. So it is far, far more likely that a single point will fail, rather than a sheet. That's ",
"not to say sheet-like erosion can't happpen though",
"."
] |
[
"Thanks for the reply.. I do get all of that, but why is it almost always a perfect circle? Why not just some weird misshapen hole, instead?"
] |
[
"Because what you have is a weak ",
". The failure is at a point location, and then a failure cone grows up from it."
] |
[
"Is it possible, once close enough to earth, to send a satellite into orbit around a comet? or to at least put a fixed beacon onto it?"
] |
[
false
] |
I say this because apparently we will be having a "once in a civilization" comet cruising around earth.
|
[
"There have been a number of ",
"comet rendezvous missions",
". Comets come fairly close to the Earth often, but that doesn't necessarily make them easier to rendezvous with. The big deal about this upcoming one will be its size and visibility."
] |
[
"This comet seems to have a velocity of around 50 km/s relative to Earth when its close to us. That's way too fast for us to catch it. And besides that, it doesn't even come all that near us. We could probably collide something with it or fly something through its tail if we wanted to but for a smooth landing you need to match the velocity of the probe with the comet. Same for orbiting around the comet. (I didn't find what the mass of the comet is so I couldn't calculate what orbiting it would be like, in any case it'll be a very slow orbit if it's practical at all.)",
"Nasa has this nice page that shows the orbits of stuff in 3d. ",
"Here's the orbit of this comet",
". And ",
"here's the orbit of a comet we've sent a probe to",
" (in 1985). In the overhead view it looks like the new comet comes very close to Earth when it's on its way out of the solar system but if you tilt the view a bit you'll see that it's not actually very close at all. On the other hand, the older comet comes both very close to Earth and its orbit is almost parallel with Earth's orbit, well not quite but much closer than the new comet. That's an orbit where it's practical to send something to the comet and do more than a flyby or a collision.",
"Edit: Actually, even the other comet I refer to, where we sent a probe, that probe was just a flyby. Even though that comet is a much more realistic target it's still quite fast relative to Earth."
] |
[
"seems like it gets VERY close to mars. thanks for the link!"
] |
[
"Do you burn more calories when you're sick?"
] |
[
false
] |
When you're sick you can experience symptoms like increased mucous production and fever. I imagine that since the body has to deal with these problems it would have to spend more energy. Anybody able to expand on this idea? Side question: when you have a cold, where the hell does all of that mucous come from? It's non-stop! Thanks for all the info guys. This subreddit is awesome!
|
[
"Yes, baseline energy usage increases ~15% with each degree increase in temperature.",
"Inflammation dumps a lot of chemicals into your blood that fire up the breakdown of fat and glycogen stores. Basically you mobilize your body's stored energy so that it can be used to fight infection.",
"Side question: Your respiratory tract from the nose on down is filled with \"goblet cells\" that create mucous secretions. These secretions trap infectious particles, which are then carried out of the respiratory tract by a \"mucociliary escalator\" -- basically, the other cells in your lungs have little fingers on them that push the mucus out of your body...onto your handkerchief. ",
"The fluid for mucous production comes from your blood. Goblet cells synthesize a substance called mucin, mix it with water from blood, and pump it into your respiratory tract."
] |
[
"Celsius."
] |
[
"baseline energy usage increases ~15% with each degree increase in temperature.",
"Fahrenheit or Celsius?"
] |
[
"why do our bodies need to maintain ~98-99 degrees?"
] |
[
false
] |
is there a scientific reason why our bodies need to be at around this range? why wouldn't we work as well at .. say 92 degrees, or 105? (if this has been asked before, I'll apologize in advance :) )
|
[
"You have proteins in your body that fold at certain temperatures and pHs. These proteins repair and replicate DNA, catalyze reactions, and run your metabolic systems. Any higher/lower, and the proteins would become unstable and denature, and you would die."
] |
[
"From what I remember of Biology:",
"This is due to Homeostasis.(Also known as maintaining a stable internal environment.) We are the heat we are because we're at the most optimal condition inside at this heat.(This applies to energy usage, protein conditions, et cetera.)",
"Only other reason I could find is that ",
"our body is constantly metabolizing food, and this releases energy which we take as heat, and try to get rid of.",
" This is thought to be another reason why we're the temperature we are. "
] |
[
"The body can be thought of as one giant test tube. At any given time, there are thousands upon thousands of reactions going on. Chemical reactions are very dependent on temperature. In addition to that, the body uses enzymes, which are proteins, in order to carry out the reactions efficiently. Protein structure and function are very dependent on temperature. If the proteins are misfolded or less active than usual, that could be very problematic. "
] |
[
"If you were in outside of the solar system with an apple. Would you have enough mass to have it revolve around you?"
] |
[
false
] | null |
[
"If you were a point mass of say 80 kg, an apple could orbit you at a distance of 1 m in approximately 24 hours. Orbital velocity would be about 27 cm/hour. There are terrestrial slugs faster than this by orders of magnitude. ",
"It would be impractical for two reasons: \nThe orbit would not be very stable because you are not a point mass. The apple will gravitate towards different parts of your body, uppsetting the orbit. ",
"Establishing the orbit in the first palace will be difficult. At a radius of 1 m, the difference between a circular orbit and escape velocity is 30 micrometers per second. ",
"Edit to say this: The gravitational gradient due to your body at the orbit of your apple is 67000 times stronger than the gradient in the suns gravitational field at the orbit of the Earth. What this means is that any disturbance from even your closest star would be neglible. You don't have to go through the trouble of leaving the solar system to try this experiment. You could just fail closer to home instead. "
] |
[
"In astrophysics terms, while there is no distant horizon where the apple will never return, there IS a set of speeds where you will not be seeing the apple again. There are three velocity regimes the apple can be in. In the slowest, the apple is not moving fast enough to escape (it is moving slower than 'escape velocity') and so it will orbit you forever. If the apple is moving precisely AT escape velocity, it will move away from you forever, slowing down all the time approaching zero velocity at infinity (though it will be more or less stationary at some point). If the apple is moving faster than escape velocity, it will also move away forever, but will not approach zero velocity and eventually will settle down to some speed or other depending on how fast it started.",
"Note that absolutely none of this depends on the direction the apple is moving initially, unless it actually HITS you."
] |
[
"If we had a large and roughly spherical spaceship do you think it would be feasible to have a few small cameras/probes orbiting it to monitor for surface impacts?"
] |
[
"How does cheatengine work? isn't it the job of the OS (ie, windows) to prevent programs from modifying the data of other programs?"
] |
[
false
] | null |
[
"Usually they use ",
"DLL Hooking",
". Basically, they trick the process into loading the exploit into its own memory space. Thus, they're not trying to modify another process's memory space which the OS does shut down. "
] |
[
"The point of the OS is to prevent programs from ",
" modifying the data of other programs. If a program needs to, there are APIs like ",
"ReadProcessMemory",
" that can be used to read & write the memory of other processes. ",
"These APIs also obey security restrictions, so for example, you can't modify the memory of another user's processes, or a system process, unless the cheatengine is also running with administrator privileges. "
] |
[
"What about statically linked binaries?"
] |
[
"Noether's theorem: Are there any simple physics problems that can solved by making a symmetry argument directly rather than by applying the corresponding conservation law?"
] |
[
false
] |
I'm not entirely sure this question makes sense. What I'm asking for is a simple textbook-type physics problem that would normally be solved by applying conservation of energy, momentum, or angular momentum that can also be solve by making an argument directly from the corresponding symmetry principle. Take, for example, the frictionless roller coaster problem where you can easily calculate its speed at any point by conserving energy. Is there a corresponding way to solve the problem directly from the principle of time symmetry without going through a fully general derivation of energy conservation via Noether's theorem? If this question doesn't make sense, or is not possible, could someone explain why at a level understandable by an engineer with a decent grasp of undergraduate physics?
|
[
"I think what you are imagining isn't really feasible. Here's why.",
"In Noether's Theorem, we are identifying a symmetry of the Lagrangian or, more properly, of the action. This does not lead to a conservation law until you invoke the equations of motion (the Euler-Lagrange equations).",
"While we can use symmetries of the action to generate new solutions from old ones, these symmetries are not overtly manifest in the individual trajectories of objects. Thus, for example, in a theory with rotational invariance, individual trajectories are not rotationally invariant; rotations turn one allowed path into another.",
"But the kinds of problems you are asking about -- problems which one solves by invoking conservation laws -- are problems about individual trajectories. These problems, either implicitly or explicitly, involve invoking the equations of motion. And once you are invoking the equations of motion, you are in essence bringing in the conservation law, since it is the equations of motion plus the invariance that produce the conservation law."
] |
[
"The symmetries you refer to here are not the kinds of symmetries involved in Noether's Theorem. Noether's Theorem refers to symmetries of the action, not symmetries of some particular physical system."
] |
[
"Very interesting, thanks, I will have to ponder this a bit but I think I see where you're going."
] |
[
"From a chemical and biological perspective, why and how does semen decompose from a gelatinous form to a viscous liquid after sitting for about 5 minutes?"
] |
[
false
] |
[deleted]
|
[
"It's because it's protein based, and high temperatures make protein structures go weird and congeal. (Similar to when you boil an egg.) This might be an evolutionary response that causes it to be harder to 'wash out' from inside the female, as it congeals after ejaculation into the vagina. ",
"It washes off perfectly OK in cold water, too. ",
"EDIT for spelling, thanks kabuto!"
] |
[
"Also, why does it congeal when exposed to hot water in a shower?"
] |
[
"Semen and ejaculate are composed of a very high concentration of proteins. Upon temperature change and pH change these proteins and cells will degrade and die. Denatured proteins and DNA turn into a gelatin like consistency (DNA turns into clear snot). It is exactly like egg whites. "
] |
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