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[
"What's considered to be \"normal\" weight fluctuation for a healthy person, based on water/food intake and other factors?"
] |
[
false
] | null |
[
"The biggest difference is sweat. If you think about it, A pound of food is A LOT of food, like a 10 inch plate with some mashed potatoes, side salad, and a chicken breast or something. It's the amount of food in a decent meal. ",
"Water is heavy. A standard bicycle water bottle is 650-700mL. that's nearly 1.5lb. That's how much you lose an hour just from sweating and water vapour lost in your breath. ",
"The best time to weigh yourself is in the morning, before or after your morning piss (as long as you keep it consistent). ",
"Your weight can fluctuate by 2-5lb (variance is higher if you are larger) either way from a baseline. You get to know your baseline pretty well from these morning weigh-ins. "
] |
[
"My weight fluctuates 2-4 lbs each day, depending on when I weigh myself. I use the morning, right after my shower, to look at my weight. Usually it's the same weight as the day before plus or minus 2 lbs."
] |
[
"try and poop at the same time each day, weigh yourself after that. 2-3lb sounds right from my experience. go from monday to monday to see actual progress"
] |
[
"Question on hypothesis of space time, dark matter and dark energy."
] |
[
false
] |
From the things that I have read, dark matter exerts a gravitational force, but doesn't seem to interact with anything else. Dark energy on the other hand appears to be pushing the universe apart. Has anyone much more educated and learned than me posited the following: Dark energy, or rather the lack of dark matter, causes spacetime to break down, make it more difficult to traverse, while the presence of dark matter simplifies the universe? What if the distances haven't (and aren't) actually any longer, but rather they have simple become harder to travel along? The more broken and ambiguated these spaces become, the longer anything takes to travel through them, the more red-shifted light becomes. What if dark matter keeps the universe in check, stopping it from falling apart? Can someone tell me why this idea is totally wrong, why it couldn't be as simple as that? This would be a neat way to explain expansion, maybe even inflation - so it is clearly wrong, but how?
|
[
"There's this concept in the physical sciences. I'm going to tell you about it, and ",
" you to take it in the spirit in which it's intended, and not as an insult.",
"The idea is called \"not even wrong.\" The phrase goes back to a guy named Wolfgang Pauli — of the Pauli exclusion principle, among many other things — who was once shown the work of a young student of physics. \"This isn't right,\" Pauli was heard to say. \"This isn't even wrong.\"",
"What's meant by that, other than an amusing turn of phrase, is that there are known facts about the universe, and also well-tested theories and models. None of these is inviolable — any of them could turn out to be wrong or incomplete — but they're ",
"To be merely wrong means to be inconsistent with something trusted. If I told you that it's possible for apples to fall ",
" you'd say I was wrong. Because apples are not observed to fall upward. They are only observed to fall downward.",
"But if I told you that apples can because apples have wings and can fly, it follows that they don't actually fall at all, that's ",
" It demonstrates that I'm not even aware of what an apple ",
" and in fact I have confused it with a ",
"So to be not even wrong is to advance an idea that is not merely in contradiction of observed phenomena, but that contradicts basic principles.",
"Does that mean any person who's not even wrong is stupid? Of course not. The modern history of the sciences is ",
" with ideas that were advanced by obviously brilliant men and women that just happened to be nutso. There's no ",
" in being not even wrong; that's why I say again that this is not an insult.",
"Things in our universe make sense, and they are all to a greater or lesser extent understood. The properties of spacetime, gravitation, dark matter and dark energy are all understood — not completely! But they're all ",
"The idea you've advanced here is not just incompatible with observation, but it's inconsistent with everything that's currently known to be true about this stuff.",
"Again: That is not an insult. It's ",
" to think \"outside the box,\" as it were. But the fact remains that there actually is a box, and before thinking outside of it it's best to at least be aware that a box exists, and that certain things are inside of it. If nothing else, it saves you time that would otherwise be wasted trying to justify the nonsensical or struggling to prove the already-known.",
"I do hope this has been an encouraging comment and not a discouraging one."
] |
[
"your little \"hypothesis\".",
"Please don't do this. The guy at least wants to learn."
] |
[
"Okay, my idea is this:",
"Lets say that Point A and Point B are a set distance apart, and moving between them requires a travel along the shortest path, which is 100 vertices of \"space/time\". What if Dark Matter kept these 100 verticies stable? What if the lack of dark matter allowed the verticies to degrade, to become more complex, therefore making the number of points between A and B 120 rather than the initial 100? As time wears on - or as time breaks down - what if the physical distance between objects doesn't change, what if it just becomes harder to get from A to B?",
"What would this idea explain? It would tie up Dark Matter and Dark Energy as a simple cause and effect rather than things we don't understand. It would explain why galaxies are ",
"flying apart at ever increasing speeds",
" from one another, it would explain why the ",
"rotating arms of a galaxy",
" seem to be drawn in by far more gravity than the galaxy can exert."
] |
[
"What is the physical mechanism that causes multi-pendulum behavior?"
] |
[
false
] |
[deleted]
|
[
"The behavior is chaotic. This is the most famous chaotic system. The behavior cannot be described in a formal way, because it is impossible to predict what it will do in the future (small pertebations will make it take a different path ).",
"How would you use it for energy generation? The only reason this keeps spinning for a long time is that it is well oiled. It is not a perpetual motion machine."
] |
[
"If you add up the kinetic energy of the thing, it is the same as the kinetic energy of a normal pendulum release from the same height; it just looks like it has more energy."
] |
[
"If you add up the kinetic energy of the thing, it is the same as the kinetic energy of a normal pendulum release from the same height; it just looks like it has more energy."
] |
[
"What are the differences, if any, (chemically, activity-wise, etc.) in the brain between when having a dream and when having a nightmare?"
] |
[
false
] |
I'm aware it's all REM, but are there any differences? Side question: without access to my heart rate, respiration rate, etc. but with access to a brain scan, would an expert be able to tell if I was having a nightmare as opposed to a dream? (In case you're wondering: yeah, I just had a nightmare and am trying to calm down so I can go back to sleep...)
|
[
"Hi! I'm an expert in this field. I'm the guy who looks at the raw squiggly lines and interprets them. I'm called a polysomnographic technologist.",
"Short answer: no.",
"Long answer. It's actually not all REM. Dreaming can occur in any stage of sleep. It's most common in REM, and the dreams are most vivid, but other stages have had reported dreams. ",
"For example, in stage N3 sleep, dreams are often reported which are very boring and mundane. ",
"Stage N2 sleep is thought to have a huge role in memory consolidation, which means that the alternating 2 and R that you get toward morning help you remember your dreams. And like everything you did the previous day. I'd love to go in depth about that, but I'm on mobile. And at work.",
"As far as the original question, the brainwaves are what you'd think would be the hallmark indicator. Unfortunately, we are only looking at the surface of the brain, and there is a lot of noise in the signal. So really we make determinations based off of patterns. If we could do a sleep study where we could stick needles deep into your brain and look at a bunch of different systems, then maybe. But with standard PSG equipment? Not really. ",
"We might, of course, make a determination based off of heart rate, blood pressure, perspiration, and the like, but those things change like crazy anyway during REM, so it's tough. ",
"So the answer is possibly, if we can stick needles into your limbic system, match those readings with your other vitals, wake you during REM and have a good account of the dream, and do this enough to have enough data."
] |
[
"I'm so self-absorbed, I completely forgot that there are other ways to look at the brain. You're absolutely right!"
] |
[
"I disagree! Given access to a brain scan taken during dreaming (I assume he means fMRI), you'd expect to see differences in \"nightmare\" vs \"not nightmare\". Off the top of my head, I'd predict greater amygdala activation, though I'm positive that the story is more complex than that. (I'd agree you wouldn't see this with EEG -- the amygdala is about as bad as it gets for source localization for you guys, I'd imagine...)",
"In addition to the other physiological methods you list, I'd think a fairly reliable signal of \"nightmare\" would be a cortisol spike."
] |
[
"How do we know the speed of light"
] |
[
false
] |
Because relativity affects everything and as far as I know everything in the universe is moving in some way shape or form, how do we know the exact speed of light. And is it relative?
|
[
"We can measure it by bouncing it off mirrors and timing the delay."
] |
[
"Doesn't that just tell you the wavelength?"
] |
[
"I believe the earliest measurment of the speed of light was by observing ",
" ",
"Jupiters moon Io",
" and comparing where it ",
" to be and where it ",
" to be. Since 1983 the meter is actually defined in terms of the speed of light, so in a sense you can't measure c any more... you can only redefine the meter. ",
"There are many practical ways to measure the speed of light. Most involve using an electromagnetic wave of known frequency and measuring it's wavelength. My personal favourite involves a ",
"microwave owen and marshmallows",
". "
] |
[
"Layman's question, what hard evidence is there against an oscillating universe?"
] |
[
false
] |
I'm just a regular person with no education in science that wants to confirm a hypothesis and I hope you guys can either tear my idea apart and spit on it in a constructive and hopefully educational comment, or confirm it as valid. It is my understanding that the big bang theory is based on two things a layman can easily understand. First of all the observation Edwin Hubble made of the shift to the red spectrum as things move away from us in the 1920's and 1930's. The second thing being the microwave background radiation discovered in the 1960's. All I know about this is that the big bang theory is the only one so far to explain the background radiation, I would love to know if the radiation is decreasing or increasing in any way, wavelength or frequency variations over time? So with this information in hand, as a layman, I wonder is it not possible that the universe is oscillating? That in fact what we think was the creation of the universe at the big bang was merely the universe starting an expansion after having finished a contraction? Reading more about the background radiation, for example that it has the same nature of a gas filling a void, even leads me to draw parallels with human lungs. The reason I ask this is because I have my own ideas that I play around with when smoking weed with friends and they're all based on the idea that the universe is just another ecosystem. That it resembles our natural ecosystems on earth in many ways, but of course is an ecosystem that cannot sustain human life on its own without encapsulating it in isolated spots as we have on earth. TL;DR: Is it naive of humans to write the big bang theory in text books as fact when we've only observed this entity we claim to be almost 14 billion years old for 100 years in the way we do today? Could the universe in fact be oscillating instead of just expanding into nothing for no apparent reason? We have so many things in nature that are seasonal, come and go, expand and contract, or breathe.
|
[
"I would suggest that we set the drug-fueled speculations aside and concentrate on actual observed facts. That's just me, though.",
"There is this thing called the ",
" If you measure some arbitrary coordinate distance in space at some instant ",
"₁, then measure it again at some later instant ",
"₂, the two measurements will differ by a multiplicative factor ",
" That's why ",
" is called the ",
"The scale factor is related to … stuff. It's a function of time, but the nature of the relationship between the scale factor and time is a function of the content of the universe. If there were nothing in the universe but cold matter, the scale factor would go by the ",
" to the two-thirds power, where ",
" is whatever duration you're interested in. If there were nothing but radiation in the universe, the scale factor would go by the square root of ",
" And if there were nothing in the universe ",
" just a pure vacuum, ",
" would go by ",
" to the ",
" where ",
" is Euler's constant; it'd be an exponential relationship, in other words.",
"In the real universe, the relationship between the scale factor and time is a combination of all three of these idealized relationships, and ",
" At different periods in the history of the universe, the relationship between the scale factor and time has been subject to different dominances. Early on, the universe was radiation-dominated. Then it was matter-dominated. We're either in or approaching and era in which the universe is vacuum-dominated.",
"But the point is, none of these three relationships, nor any combination of them, could result in a ",
" relationship between the scale factor and time. In other words, no matter how big you let ",
" get, ",
" will never get ",
" Which means metric expansion is never going to reverse itself, and the universe is never going to contract, and therefore the oscillating-universe idea is definitely not a good description of reality.",
"Everything I told you is a mixture of about six parts observation to four parts theory, greatly simplified."
] |
[
"This was very helpful, very well put and you made it easy to understand. Well written. ",
"So in other words would you agree that the leap of faith here, if one were to involve blind faith and spirituality, is that something has to activate a function that would reverse the expansion and this something is not explainable by any modern theory and it would most likely break the law of thermodynamics as we know it today? ",
"At least that is how I've perceived it. ",
"In that case, let's hope humans are again proven wrong as they have been so many times before in science. ;)"
] |
[
"Yeah, it's natural for some to seek comfort in spirituality. And where's the harm really as long as they respect their fellow man and live a good life contributing to society without trying to brainwash others. "
] |
[
"Astronomy question: you suddenly find yourself in a random star system somewhere in this galaxy. Could you figure out your exact location, relative to earth?"
] |
[
false
] |
You've probably used some kind of wormhole, without prior knowledge where it would lead. You arrive comfortably in a new part of space. Let's say you have the entire knowledge of the human race in your data banks, everything that's been written and researched in astronomy and related fields is readily available to you. You also have access to all sorts of equipment you might need. Now, would it be possible, through observation of the galaxy, to locate your current position as well as our own little solar system? I have a feeling that, through smart science, this wouldn't be so hard, but I might be totally wrong. Now, on to the next question: what if the wormhole let you to another galaxy, at random? It might be Andromeda, and it might be billions of lightyears away. Could you still locate yourself relative to earth? If you could, would you be using known entities like pulsars, or something else altogether?
|
[
"You could locate various pulsars, which have a characteristic radio pattern, and triangulate."
] |
[
"So what is your book about?"
] |
[
"You could really use any set of stars with known positions, but unless they have some very unique property you'd probably have some trouble locating them at the alien system.",
"Pulsars are used because they have a characteristic pattern and are hard to miss. \"Find the thing that oscillates at X Hz\" is a lot easier than \"Find the star that has X composition, Y satellites, and Z spectra\""
] |
[
"I'm a teenager with relatively dark brown hair. Why do I have a scattering of blonde, black, brown and even red facial hair."
] |
[
false
] | null |
[
"dark hair absorbs more radiation from the sun, head hair is slightly lighter in the front (forehead) because it's farther from your head and you don't need to waste pigment, hair has some photo-absorption properties so that may play something into it",
"there's evidence that sometimes your beard color is part of one of your recessive traits from the link below, wikipedia led me there but i can't find anything better than an abstract",
"http://www.ncbi.nlm.nih.gov/pubmed/7581459",
"http://sciencefocus.com/qa/why-do-so-many-men-despite-hair-colour-have-ginger-beards",
"so maybe you're half ginger or something..."
] |
[
"My father and myself both have multi coloured beards and have put it down to having a ginger grandfather."
] |
[
"I have dark black hair and bright red spots in my beard. I've heard a red beard is a sign of divinity in India. Let us pack our bags in search of furious glory."
] |
[
"Does the amount of energy a creature requires contribute to the length of it's life?"
] |
[
false
] |
Learning that a whale can live up to 150 years made me think of this. They're obviously huge, which requires a ton of energy to survive. Humans require a lot of energy for their brains. It seems the smaller the creature, the shorter life expectancy they have. Insects have the shortest life spans, and I would assume need less energy than mammals.
|
[
"There are many things that can contribute to life spans, lifestyle, metabolism requirements, genetics.",
"Telomeres are one genetic control on life span, and is specifically why ",
"lobsters can live for such a long time",
".",
"In some cases, it may be a ",
"single gene",
".",
"If you're interested in a thorough read, it's a book from 2003, so it might be a tad outdated, but ",
"Mattson",
" has a volume on the topic.",
"Energy can play a role, but it's not a clear linear relationship. Coral colonies have been found to be 4000+ years old, sponges can live a long time, koi fish can live 200 years, which obviously don't need as much energy as a whale.",
"The short answer is, it's complex and a lot of interplay between factors."
] |
[
"Aw, that's very interesting, Ill check it out. Thanks, this definitely cleared it up"
] |
[
"There is a ",
"definite correlation between heart rate and length of life",
", and if you think about it, something small like a hummingbird or a shrew is using up a great deal more energy ",
" than a human is. That seems to be playing the biggest role there, at least among mammals."
] |
[
"Is it true that charging a battery with induction is faster as with a traditional cable?"
] |
[
false
] | null |
[
"Inductive charging is just a different way to pass the energy from the source to the device, it won't make battery charge faster. "
] |
[
"You can increase the current induced or the current delivered by the wire. Both are just providing an over voltage to top up the battery. In general the charge time has way more to do with the battery than the source of electricity.",
"It is like asking is it faster to fill up a bucket with a hose or a pitcher, either one can be faster, just matters on how much water comes out of each one.",
"Edit: Grammar"
] |
[
"You never specified the current. More current(within bounds) will charge the battery faster, regardless of whether you are using induced current or charging directly from a dc source. "
] |
[
"My dad had a question that I couldn't answer about slingshots, maybe you guys could answer it"
] |
[
false
] |
He asked "If you had a slingshot with 2 pieces of 6-foot tubing pulled back to 12 feet, is it the same force as 4 pieces(2 on each side) of 3-foot tubing pulled back to 6 feet? Also, would the object go the same distance (with same components of course)?
|
[
"The elastic potential energy is 1/2.k.x",
" where k is Hookes constant and x the stretched distance. You've doubled up the tubing width and halved its length, so stretching it say, 1mm, requires 4 times the force because each part of the tubing has the stretch twice as far and is twice as wide. So ",
" the spring constant is increased by a factor of four. ",
"The stetched distance, x, is halved. Half squared is a quarter so overall it is the same energy, same speed, same flight distance. However it takes four times as much force to pull back the object."
] |
[
"I think you've made an error. x should be the difference between stretched distance and relaxed distance. Not the stretched distance.",
"So, in the first case E = 1/2.k.(12 - 6)",
" . 2 = k.36",
"In the second case, E = 1/2.k.(6 - 3)",
" . 4 = 2.k.9 = k.18",
"So the first case imparts more energy to the object you're shooting.",
"When you double the amount of cords, you're effectively doubling k. That means to empart the same energy you only have to stretch by a factor of sqrt(2) less (not 2)."
] |
[
"Yes, but k2 in the second case is different from k1 in the first case. k is the string constant of the whole spring in this equation, not the elasticity of a unit length of spring. By halving the length of the tube (i.e. spring) they've changed k. I guessed k2 = 2 . k1 but I haven't provided proof.",
"Edit: ",
"http://en.wikipedia.org/wiki/Hooke's_law#Multiple_springs",
" shows the half as long & twice as wide case. "
] |
[
"How does a multi-plug extension cord work? Does it split the electrical current between the plugs? Are there items that shouldn't be plugged in together?"
] |
[
false
] | null |
[
"Current isn't split, you end up drawing more of it. The danger there is drawing more current than the wiring can handle, in which case you will trip a circuit breaker, blow fuse, or worst case start a fire (highly unlikely but possible, especially if you have older wiring). So don't wire several high-draw devices into a multi-plug cord, although the draw would have to be very high to cause problems, and like I say, the circuit breaker will almost certainly trip before you run into any problems."
] |
[
"All home wiring is connected as a ",
"parallel circuit",
". Because the wiring is parallel, all devices see the same (theoretically constant) voltage. You do not \"split\" current, because the current is not constant. Each device draws as much current as it requires. There is an upper limit on current imposed by the circuit breakers to prevent wiring from overheating (and burning down your house). ",
"The circuit breaker (current limit) is chosen for the gauge of wire used inside the walls. So it is possible to overload an extension cord without tripping a breaker. Read the specs for the cord, don't chain extension cords, etc."
] |
[
"Power strips are basically parallel circuits for all the appliances plugged in. Some have fuses to prevent current overload. Either way, make sure your power strip is UL certified, as cheaply manufactured powers strips can lead to fires when internal resistance or shorted connections spark.",
"The only things I'd recommend not plugging in together would be multiple high current devices (because of the aforementioned hazard)."
] |
[
"How can VY Canis Majoris have a density lower than hydrogen?"
] |
[
false
] | null |
[
"Pressure of a gas is temperature dependant- PV=nRT, the pressure times the volume is equal to the number of moles of gas x the gas constant x the temperature.",
"\nThe inner sections of a star are very hot and very dense, else nuclear fusion can't occur. But most of the volume of a sphere is in its outer reaches, where it's cooler and less dense. It also depends where you define the outer reaches of a star, the Sun's corona extends far beyond the Photosphere (what we 'see'), and is incredibly sparse."
] |
[
"To add to this, the density of hydrogen in your link is only true at Earth-like conditions. As it mentions after that number, this is at about 1 Barr, 15 degrees C. Based on ",
"the wikipedia page",
", VY Canis Majoris has an average temperature of 3490 K, or 3217 degrees C. So, given the ideal gas law provided above, clearly the density, framed as n/V, decreases as T increases. So with a basic assumption of constant temperature, density and pressure throughout the star, you can start to see how the density can be lower in the star. ",
"This assumption is pretty wrong, but conceptually it still works. In reality, the star has different layers of density, and as a red supergiant, these vary drastically in temperature and pressure. At its core, VY Canis Majoris is probably incredibly dense, around neutron star density, surrounded by a massive gaseous atmosphere still hot from its old days as an O type star. This atmosphere is collapsing, heating up, and then expanding , slowly blowing off more and more material, and isn't dense enough to be considered opaque. According to the wiki, it seems to be in debate as to what is going on with this specific star, as it seems to be far too large, but the density is fully within acceptable ranges.",
"Hope that helps."
] |
[
"I'm sure the Khan academy have some, otherwise the wikipedia pages on the Gas Law/Boyle's law are probably pretty good coverage."
] |
[
"If SARS went away and hasn't been seen since 2003, does that mean COVID-19 (since it's caused by SARS-CoV-2) will be the same?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"guidelines.",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"do you know if there's a sub where i can ask this question? since i can't find an answer anywhere."
] |
[
"Sure, try ",
"/r/AskScienceDiscussion",
" perhaps. It is the sister subreddit of ",
"/r/askscience",
" but allows theoretical questions."
] |
[
"Is it possible to get a marble into \"orbit\" around the center of a funnel?"
] |
[
false
] |
To clarify: Given a funnel and a marble, is there a way to throw the marble in with such a trajectory that it would effectively travel in an ellipse around the hole in the center? I'm sure it would eventually fall in, but that happens with regular orbits anyway, to my understanding.
|
[
"The marble experiences both drag and rolling friction, which I'm pretty sure those formulas aren't accounting for. No matter what you do, unless you are setting up the orbit in an airless, frictionless environment, it will immediately begin to degrade."
] |
[
"I think you'd be better off using some super hard polished metal for the funnel and marble. Greased stuff doesn't like to roll. "
] |
[
"I think you'd be better off using some super hard polished metal for the funnel and marble. Greased stuff doesn't like to roll. "
] |
[
"The average lifespan of an adult monarch butterfly is 2-6 weeks. However, during migration one generation has a lifespan of up to 8 months. What allows this?"
] |
[
false
] | null |
[
"It appears to be due to ",
"Diapause",
"And you probably read about ",
"monarch butterflies",
".",
"From what I've read on wikipedia it seems that the generation that begins the move enters diapause. Thus removing the daily need for procreation upon reaching a more habitable place in which they resume mating.",
"Hopefully someone with more knowledge about butterflies can answer this better. "
] |
[
"That's not exactly what I was asking.",
"I'm asking why the migratory butterflies have a lifespan 6x longer than their non-migratory counterparts."
] |
[
"That's not exactly what I was asking.",
"I'm asking why the migratory butterflies have a lifespan 6x longer than their non-migratory counterparts."
] |
[
"Would wearing weights on your arms and legs throughout the day or during a workout benefit you in any significant way?"
] |
[
false
] | null |
[
"Moderator's note: fitness related threads are not an open invitation for people to speculate or share personal experience. Please wait for the experts."
] |
[
"Quick question my good sir, I just got my B.S. in Bio-Chemistry would that be sufficient to be on said panel of experts; if not what else would be required? "
] |
[
"The panel is an informal group of Redditors who are professional scientists (or plan on becoming one, with at least a graduate-level familiarity with the field of their choice). ",
"The official panelist thread",
"Edit: Even though you're not eligible to become a panelist, you can still give answers if you know them. You just have to make sure your post is well-sourced. "
] |
[
"If H./A. Floresiensis is a descendant of H. Erectus, how do you explain the substantially smaller sized skull and brain when compared to H. Erectus?"
] |
[
false
] |
I know the brain and skull can shrink due to Foster's rule; (The island effect). However this can only be to a certain extent. Floresiensis had the brain capacity of 400 cubic centimeters, while H. Erectus had a substantially larger capacity of 600 cubic centimeters. These Differentials transcend the possible capabilities that the island effect can have, so how can you explain this contrast? [EDIT] Thanks everyone for clarifying. My biology teacher drilled this concept into my mind and with a lack of sources, I was led to believe it was entirely true.
|
[
"How do they transcend 'the possible capabilities that the island effect can have'? I wasn't aware that island based selection had limits.\nThey hunted pygmy elephants on that island were scaled down roughly the same amount they were. They clearly had some sort of adaptation, in which their brain was consolidated to a smaller size without sacrificing any or much of its function. Precisely how evolution managed to do this is beyond anyone at the moment. There was a large following (that for some reason had a lot of traction) saying that the individuals on Flores were just 'diseased'.\nRegardless, at this point that has been ruled out. They were as advanced as any other hominid at that time and the evidence supports it (i.e. dwellings, fire pits, hunting tools, etc.), just because people don't want to believe or necessarily understand how island dwarfism can take a brain, that we thought was contingent on its size, and shrink and maintain its function means its impossible-because it's not, we're looking at all the evidence.\nWhat happened is a neural reconfiguration of the brain. We don't 100% understand it, which is why you're asking this question and it's still a hot topic, but Homo floresiensis shows that a brain can be drastically reduced and still maintain \"advanced\" functions."
] |
[
"This link",
" references a study that showed that a pygmy hippopotamus from madagascar had a brain 30% smaller than a simply scaled down version of its ancestor would have. This definitely supports the possibility that insular dwarfism could have an increased reductive effect on brain size.",
"I definitely agree there there are morphological similarities between Homo Floresiensis and both Homo Erectus and Australopithecus, but I don't think that brain size is as compelling a factor as you do. Throughout human evolution we see such a steady increase in brain size that it's easy to assume this is a natural progression, but there are definitely selective pressures that can reduce brain size, so a small brain is not necessarily evidence of a more primitive ancestor. Add to that the similarity of structure between the skulls and brains of H. Floresiensis and Homo Erectus, such as a large Brodmann's area, mastoid fissure, and thick cranial bones, and the fact that the timing and location of the appearance of Homo Floresiensis, suggest that Homo Erectus is probably a better candidate for the ancestor based on the present information.",
"EDIT: I just reread this and have concluded that I have to stop using the word \"definitely\". "
] |
[
"This link",
" references a study that showed that a pygmy hippopotamus from madagascar had a brain 30% smaller than a simply scaled down version of its ancestor would have. This definitely supports the possibility that insular dwarfism could have an increased reductive effect on brain size.",
"I definitely agree there there are morphological similarities between Homo Floresiensis and both Homo Erectus and Australopithecus, but I don't think that brain size is as compelling a factor as you do. Throughout human evolution we see such a steady increase in brain size that it's easy to assume this is a natural progression, but there are definitely selective pressures that can reduce brain size, so a small brain is not necessarily evidence of a more primitive ancestor. Add to that the similarity of structure between the skulls and brains of H. Floresiensis and Homo Erectus, such as a large Brodmann's area, mastoid fissure, and thick cranial bones, and the fact that the timing and location of the appearance of Homo Floresiensis, suggest that Homo Erectus is probably a better candidate for the ancestor based on the present information.",
"EDIT: I just reread this and have concluded that I have to stop using the word \"definitely\". "
] |
[
"As temperature increases, molecular structures that are less thermodynamically stable form in greater numbers. Why?"
] |
[
false
] |
[deleted]
|
[
"For rearrangements, it's often a case of ",
"thermodynamic versus kinetic reaction control",
". So in this case, the starting material is stable at room temperature, but as you add heat it allows it to obtain the activation energy necessary to go to the thermodynamically more stable product. This is caused by the heat adding vibrational and rotational energy to the molecular bonds."
] |
[
"As an aside, in computer science, there is a search algorithm called simulated annealing (SA). The idea is to escape local minima or maxima, depending upon the goal being sought. At the start, a \"temperature\" variable is set to a high value. In each search iteration, the likelihood of dropping a current solution for a worse one is randomly determined, with the temperature playing a role in the calculation. Higher temperatures result in more frequent changes in search of new solutions. As the search iterates, the temperature is reduced exponentially, meaning that as the search progresses, good solutions are retained more often. That is, the search gradually turns into pure hill climbing.",
"SA is a general \"goto\" search strategy, outperforming most alternatives in most situations, according to at least one author, Skiena. SA can approach within a reasonable percentage of an optimal solution even when the space is far too large to search exhaustively.",
"SA has a direct analogy to annealing a metal, such as iron. Increasing the iron's temperature and letting it cool slowly results in larger crystals with reduced defects. To say it a different way, slower rates of cooling result in a greater decrease in the iron's thermodynamic free energy for a given temperature. ",
"Skiena's example was a skier waking in a resort hotel. She wants to get to the top of the mountain. The greedy algorithm would direct her to the roof of the hotel. She needs a strategy to avoid the local maximum in order to find the global one. With SA, the initial high temperature causes the hotel's roof to be rejected, at least temporarily, allowing her to discover the mountain. Once on the mountain, as the temperature cools, she is increasingly likely to stay on the mountain and begin seeking that local maximum, which also is the global one.",
"The direct analogy between SA and physical annealing may provide an insight into your chemistry question. At higher temperatures, molecules are in faster motion. Thus, it may be harder for them to \"stick\" in configurations that are thermodynamically preferable at lower temperatures. By analogy, they reject the locally-best solution. ",
"I would love to hear from a physical chemist, or whoever knows, about what is known about the chemical bonding OP discusses. What are the energy transitions when forming each of the two structures OP mentioned? How long does each take to form? How close, at given temperatures, do the molecules or atoms need to approach, and within what range of relative velocities? How much time is needed within the approach window for the bond to form?",
"All analogies break down at some point. I suspect the real answer to OP's question comes from questions like I asked in the prior paragraph. However, I find it fascinating that Boltzman's Constant plays a role not only in physics but also in computer science, and that the analogy has proven so successful. It makes me wonder about the possible deep connection between the motions and behaviors of molecules and the abstract properties of searching a discrete space.",
"The wiki article on SA is ",
"here",
".",
"For more information on Skiena, see ",
"here",
"."
] |
[
"What's are the thermodynamic parameters (enthalpy, free energy, entropy change) of the reaction between the isomers? Unless I'm missing something a shift in the equilibrium constant with respect to temperature is described by the ",
"Van 't Hoff equation",
". If the net reaction is endothermic it will tend toward the product side as you increase the temperature."
] |
[
"In string theory, the ninth dimension has randomized laws of physics. If this is so, how can we determine that there's a tenth dimension?"
] |
[
false
] | null |
[
"Dude you just came with something like \"you know how cats have 13 paws?\", offered not only no explanation of why that would be true, but also not even an explanation of where you got that, no context, and you would like us to explain to you why cats have 13 paws? They don't, that's all I know.",
"I'm trying to help, but you need to at least make the effort of clarifying where you're coming from."
] |
[
"this is completely insane. Who told you this?"
] |
[
"If by the ninth dimension there are varying laws of physics",
"Why? Where did you get this? What's special about the number 9?"
] |
[
"How is \"order\" (as opposed to chaos) defined in physics?"
] |
[
false
] |
I've always heard entropy explained as the overall decrease of order within closed systems. But how is order determined? Is it that the position of the group of particles within the system tends toward a uniform distribution? Or is there something more interesting behind it?
|
[
"That's a bad explanation for entropy. Entropy is the number of microscopic possibilities (atomic configurations) that correspond to a single macroscopic quantity (like pressure, temperature).",
"There's another usage of \"order\" in physics, which is used to separate phases from one another. The \"order\" in each phase is different. This type of order refers to how organized the system is. If I know one atom is here, how confident am I that another particle is some very large distance away? If I'm very confident, then it's ordered. If I'm not, then it's not ordered."
] |
[
"There are a few different kinds of entropy that you can define, which are all related to not knowing something for sure. If you have a probability distribution, p(x), where 0 < x < 1, then the entropy is defined as:",
"S = k [integral from x = 0 to x = 1] p(x) log (p(x)) dx",
"where k is some constant depending on how you defined entropy."
] |
[
"Imagine you have a little box with some gas particles. Each particle has a position and a momentum (let's pretend for the moment that the universe is classical and not quantum, but the same will hold true for quantum systems). Place that little box inside a bigger box. Open the little box. Now there are a lot more available positions within the system for the particles to occupy. Let the system spend some time to ",
" (settle down), and ask yourself, just how likely is it that all of these particles are ",
" in the little box? Sure maybe a few are, but it'd be very bizarre to imagine that they wouldn't take advantage of all the other possible locations in the big box. ",
"So we can say that the small box is a more \"ordered\" scenario because there are fewer ways to arrange the particles into that volume than there are ways to arrange the particles in the much larger volume."
] |
[
"Why do your palms gets so sweaty when you are nervous?"
] |
[
false
] |
When most people get nervous, it seems that only their palms get sweaty. Unfortunately, for me, my whole body gets sweaty :(
|
[
"What is the actual function of having sweaty palms? I fail to see any benefits that the human body can achieve from having this"
] |
[
"What is the actual function of having sweaty palms? I fail to see any benefits that the human body can achieve from having this"
] |
[
"Why do your knees get weak, or your arms heavy?"
] |
[
"I am in orbit around a neutron star. I've a very powerful searchlight, which I point at the neutron star. What do I see? Shiny mirror-like surface? White matte surface? Pitch-dark surface? Something else?"
] |
[
false
] |
Assume it's a very very old neutron star, so it's cool enough that it's not "smoldering" anymore in visible light. It's not clear to me how it would look like. Would the atmosphere be dense enough to absorb light? Would the surface be smooth enough to be mirror-like? Also, see Q #5 here:
|
[
"Neutron stars are believed to be good reflection surfaces for high energy photons (x rays) due to the density of the magnetic surface matter. The higher the frequency, the greater the reflection, but it really depends on photon polarization. Lower frequencies like the visible spectrum... I have no idea about.",
"http://adsabs.harvard.edu/abs/1978Natur.271..216L",
"http://adsabs.harvard.edu/full/1973SvA....17....1L",
" ",
"If anyone else has contradicting data, please post it and correct me.",
"Edit: I've been looking around, and I can't quite give you a decent answer to your question. Sorry OP."
] |
[
"A neutron star would shine brilliantly with its own light for a very long time indeed*, especially if it were being heated by matter falling onto it. The emitted light would be dominated by blue, with decreasing intensity towards the red end of the spectrum. The net result overall is bluish white, but not a perfect blue mixed with a perfect white.",
"But you specifically want to know what a neutron star's incident-light properties are? That is much more difficult to answer. Because a neutron star is so dense, only its outermost layer is going to matter to its optical properties. A neutron star has a thin atmosphere of extremely hot gas, but due to the extreme surface gravity, it will only be about a meter thick. Neutron star atmospheres are currently an active area of research. I'm not sure if that is enough to be opaque ala Venus, or if the true surface would be visible.",
"In any event, in the top layer of the crust, the density drops below the neutron drip density and the nuclear saturation density, so the composition will have the normal distribution of precisely equal numbers of protons and electrons, which will probably be approximately equal to the number of neutrons. The reflective properties will therefore be like hot, ionized iron, helium, or hydrogen, depending on which is actually present.",
"*White dwarfs are cooler than neutron stars and have a larger surface from which to emit radiation, yet even their cooling time scale is longer than the age of the Universe. Unless I'm missing something important about a neutron star, a neutron star should be much much hotter than the surface of a normal star for as long as you could possibly care to watch or wait.",
"http://physics.stackexchange.com/questions/26595/if-i-shine-a-bright-light-on-a-neutron-star-what-would-it-look-like"
] |
[
"A neutron star still has structure - it's not ",
" neutrons, and the outer layers still have atomic nuclei and electrons floating about."
] |
[
"What kind of safety controls are in place to protect doctors working in high-risk areas from infection (Re: the recent Ebola outbreak and the doctors being infected)?"
] |
[
false
] |
I understand that many different medical environments are very high risk for the physicians and other medical staff but I am curious how this risk is managed. I know that the places these physicians work are severely resource-limited so they can't expect to work under US hospital standards, but there have to be some limits on what the doctors are allowed to do. It seems horrifically counterproductive since dead doctors: Who is responsible for overseeing doctors on the front lines of outbreaks of highly contagious diseases and how do they put in place controls to keep the doctors safe?
|
[
"Typically, healthcare professionals working in high-risk environments execute caution and common sense practices to minimize the risk of infection. Which specific ",
"personal protective equipment",
" (PPE) are necessary depend on the specific pathogen, but generally covering the body with a lab coat, gloves, face mask, eye goggles or protective shield, etc. are in order. Also, frequent hand-washing, glove changes, and limiting patient contact with the world at large are also essential to minimizing the spread of infection. \nI'm not well-versed in Ebola specifically, but, for example, tuberculosis standard precautions include an N95 respirator and positive pressure airflow (if available), as its primary route of infection is inhalation. ",
"Generically-speaking, for very high-risk pathogens more coverage is needed. For example, one might wear a lab coat with an apron and arm covers or a ",
"bunny suit",
", double gloves, shoe covers, an N95 respirator, goggles and a face shield. They would likely change the outermost layer of all that PPE frequently and segregate it for separate disposal from the routine biohazard trash. ",
"Maintaining the cleanest possible exam space is also essential to reducing the risk of infection, and again those precautions may change depending on the specific pathogen being studied. That said, exam rooms and laboratories should, at a minimum, have ",
"broad-spectrum disinfectants",
" capable of killing viruses, unicellular parasites, fungi, and bacteria, including ",
"mycobacteria",
" like tuberculosis. All surfaces should be thoroughly wiped down before and after each patient or sample to minimize contamination. ",
"EDIT: I forgot to answer the second part of your question, w/r/t who's responsible. At a typical hospital the safety officer and/or safety committee is responsible for ensuring compliance with safety standards and practices. For people working in remote or ad hoc situations, they're largely responsible for policing themselves. Healthcare workers undergo extensive safety training and, while that doesn't ",
"ensure compliance",
", it does at least create a base of knowledge about best practices for infectious disease safety. "
] |
[
"What about the human factors component of that?",
"Is there someone there with authority to tell the doctor \"you are too tired and need a break otherwise you are putting yourself and our entire treatment center at risk\" ?",
"How does this work in a 3rd world country or crisis zone?"
] |
[
"Theoretically clinicians in a hospital setting have a supervisor they report to who could tell them to go home if they're not fit for work, but obviously in very small and/or bare bones settings the attending physician is probably the top of the food chain, and would have to rely on his or her own judgment to know when to stop. Of course, ",
"it's not like we put any effort into keeping our physicians well-rested",
" in the American medical system, either. Working very long hours in high-stress environments is ",
"part of medical training",
", so theoretically an experienced physician working in a war zone or remote clinic has some knowledge of their personal limits. "
] |
[
"Do safety/regulatory tests degrade the durability and lifespan of a new product or piece of machinery?"
] |
[
false
] |
I'm thinking about cars, for example, when companies claim that their cars have been "tested in advance" of a new sale, or of nuclear waste receptacles, which must pass regulatory inspection (which can include dropping the container from some height to ensure that it is safe). Wouldn't dropping something--even if it's being done to ensure the product's safety--degrade the overall durability of the thing? When a company claims that a product has been 'tested,' do they mean that ALL products have been tested, or just one?
|
[
"Quality testing such as what you are describing is usually done on a specimen or a sample rather than every single item. other testing is done on every single machine, but this is testing which will not degrade the machine or make it unsafe.\nFirstly, the sample testing, using statistical methods, results can be obtained every 5 items on a production line to build up a bell distribution curve. from this it is easy to see if any machine or process is moving outside of the tolerance specified.\nFor drob testing and things, the ROPS and FOPS tests carried out on construction machinery is conducted on a test sample using the manufacturing process used on the scaled up version. If this passes, then provided that the design is within the tolerances, all of the machines are built to that standard, and manufacturers can say that the design has been tested.\nSometimes a test is carried out on every single machine. Where i work, hydraulics are tested by using them for a short while without any load to see if any leaks out. this is inspected under UV light, with UV particles in the hydraulic oil which glow, to make leaks obvious.\nIf a leak is spotted, then it is fixed, cleaned up and retested until it is good.\nSo when a company says a product has been tested, you need to use common sense to decide if it is likely THAT product has been tested, or if the product overall has been tested.\nIn the case of cars and crash testing, a production car has to be used for the tests, and if it passes, then every car has that pass certificate, unless the manufacturing process or design changes.\nor, in the case of cars again, every 1 in 20 cars might be taken off the line once fully built, and measured to a few microns of accuracy all over and compared to the CAD model. In this case the car is undamaged, but it can be seen if the previous set of cars has serious geometrical defects. technically, driving the car off the production line once built is a test, because if it doesn't start, its failed!"
] |
[
"Nuclear engineer here.",
"With regards to nuclear safety-grade equipment, most of the testing of equipment is done on the design of the equipment. For example, we do not test every spent fuel cask, instead we test that design of spent fuel cask ad naseum, to prove the design is sufficient. Then out of the first lot or two of casks, we may test a select number of them to make sure the manufacturing process is properly building the casks in accordance with design.",
"For parts in the plant, it all depends. For example, one safety function of the reactor vessel is that it must have the ability to withstand at least 1 emergency blowdown. The stresses on the vessel from performing an emergency blowdown are massive and will degrade the vessel's ability to withstand subsequent blowdowns, and as such, only the first few boiling water reactors actually ran an emergency blowdown test. My reactor never ran an emergency blowdown. The first BWRs proved that the reactor vessel of that design can withstand an emergency blowdown, and instead of having to re-test, we instead prove that the vessel we built and installed was created in accordance with the design which was successfully tested for blowdown.",
"For things like nuclear safety grade fuses and bolts, we will order them in lots, then we will destructively test a percentage of each lot to prove that the lot is capable of meeting its design requirements. This is on top of the QA process which assures that the lot was manufactured in accordance with a pre-tested pre-approved design.",
"For equipment in service which can be tested, if that equipment performs a safety function, radiological release function, or an important to safety function, we have mandatory testing we do on a regular basis as part of our operating license. For example, emergency core cooling system pumps are started every quarter to demonstrate that they meet their safety functions (can produce ample flow, pressure, start in the required amount of time, no leaks or other deficiencies), and comprehensive tests are performed every 2 years. Emergency generators are started monthly and loaded onto the power grid, and every 2 years we perform a cold-emergency-quick-start, which is stressful on the engine/generator but proves it can and will start under worst case conditions. The reactor vessel gets a hydrostatic pressure test to show it can hold pressure every time we re-assemble it. The turbine gets a mandatory trip any time the emergency trip system has been touched immediately following turbine startup. These tests do put fatigue on the equipment, however these components were designed with a certain amount of expected testing and wear/tear in their life. We we exceed those fatigue limits, we need to either re-analyze the equipment using the actual test data (Rather than assumptions when we started the plant), or we need to refurbish the equipment.",
"So it all depends. Generally with components, you do not do tests on every piece. But with full systems, you do system functional testing on a regular basis."
] |
[
"Thank you!"
] |
[
"How risky is surface transmission of COVID-19?"
] |
[
false
] |
At the beginning of the pandemic, I remember an oft-cited study that showed the coronavirus surviving on surfaces for a number of days. If I remember correctly, non-porous surfaces, such as metals and plastics, were worse. In the meantime, I remember reading about a study where it survived on a smartphone for a month, but I think that was under quite rigorous lab conditions. What is the current consensus: * Does coronavirus survive for extended periods (days/weeks) on various household surfaces? * If it does, how much of a risk of transmission does it actually present? (That is, presuming one doesn’t increase personal hygiene beyond what would be considered normal.)
|
[
"When SARS-CoV-2 was first identified, with no solid data the best guess was that it would behave like many other respiratory viruses for which surface persistence and transmission is important. As more data came in, it’s become clear that SARS-CoV-2 is closer to pure respiratory transmission than these other viruses, and surface transmission is less important than the original guesses. ",
"That’s why recommendations have changed - from an early emphasis on surface decontamination to the current focus on masking and social distancing, which protect against droplet transmission. That’s not to say you should ignore disinfection, but it seems to be less important than with some other viruses. ",
"Recent evidences suggest that the most common route of transmission for SARS-CoV-2 is likely via droplet, aerosol, or direct contact in a person-to-person encounter, although the possibility of transmission via fomites from surfaces cannot be ruled out entirely. ... Based on recent evidences from the literature, decontamination of hospital surfaces should constitute an important part of the infection control and prevention of COVID-19.",
"—",
"Current understanding of the surface contamination and contact transmission of SARS-CoV-2 in healthcare settings"
] |
[
"How do they measure the survivability of viruses on surfaces? I keep reading that they think most transmission is via respiratory routes, but I never see reasoning or data to suggest why."
] |
[
"They measure viruses on surfaces in two ways: By detecting the genome through PCR or similar approaches, or by culturing the virus on infectable cells. The former is far more sensitive, but it doesn’t distinguish between live and dead virus. In experimental scenarios, culture testing does show that the virus can survive for some time on surfaces, but in real-world situations it’s much harder to find. Importantly, even then it doesn’t demonstrate that surviving, infectious virus on surfaces can actually infect people efficiently. That’s where actual epidemiology and case tracking come in. ",
"Although several experimental studies have cultured live virus from aerosols and surfaces hours after inoculation, the real-world studies that detect viral RNA in the environment report very low levels, and few have isolated viable virus. Strong evidence from case and cluster reports indicates that respiratory transmission is dominant, with proximity and ventilation being key determinants of transmission risk. In the few cases where direct contact or fomite transmission is presumed, respiratory transmission has not been completely excluded.",
"—",
"Transmission of SARS-CoV-2: A Review of Viral, Host, and Environmental Factors"
] |
[
"Are songs on the outside of a vinyl more detailed than those closer to the rotation axis?"
] |
[
false
] |
Since the rotational speed doesn't change, the linear speed on the outer part of a vinyl is greater, right? So more information is being within a given time. Y'know, the needle will meet more "bumps" in one second when it's far from the rotation axis than when it's closer. Does this mean the music is more detailed?
|
[
"I'm sorry, but you are incorrect on the first part of this. Vinyl records are by definition a CAV (constant angular velocity) recording medium. LPs, for example, spun at 33 1/3 RPM, no matter where the pickup was located. ",
"Back when the gramophone was developed they were driven by a clockwork mechanism, requiring no electricity at all. The mechanism had a mechanical governor that limited its rotational speed to the standard. As the technology progressed into the electrical age, the platter was spun by a synchronous motor, operating off the local AC voltage. A synchronous motor rotates at a speed precisely related to the line frequency feeding it. This in turn is connected to the turn-table through a pulley and belt system, resulting in 33 1/3 RPM for an LP record.",
"Audio CDs, on the other hand, operate based on CLV (Constant Linear Velocity). As the laser/read head moves out towards the edge, the rotational speed of the disk slows down, such that the linear speed of the disk passing over the laser is more or less constant. This requires a fairly complex servo-mechanism, which wasn't possible for reasonable prices until the modern age. The purpose for CLV vs CAV is that it allows more data to fit on a given sized medium. It's also important to know that optical drives, once they went above something like 8x, switched back to CAV, and compensated for this in software.",
"Other examples of this was ye olde LaserDisc format for movies. On the author's choice, LaserDiscs could either be CAV or CLV. CLV discs allowed more time per side of the disc, but had various downsides. CAV disks allowed for direct frame references, stable pausing etc... but reduced the time per side of disc.",
"You also had a similar effect in the days of 3.5\" floppy disks. IBM/PC double-sided/double density disks were a CAV device, and permitted the storage of 720KB per disk. Apple, with their SuperDrive (and thanks to the Integrated Woz Machine), could drive the mechanism to achieve CLV, and could store 800KB on the same medium. That was a big deal back in the day."
] |
[
"To answer OP's question, yes, the information density of a vinyl does increase towards the outside of the disk, however, this does not change the quality of the music. Record players are designed to operate at speeds which are orders of magnitude lower than the point where needle-reading capabilities would be diminished by, for instance, needle bounce or lag in needle drop off the top edge of a bump in the track. ",
"Essentially, the audio track near the outside is just somewhat stretched compared to the inside. Because it's an analog system, you don't lose any resolution or clarity. The same information is just slightly denser per length."
] |
[
"So this explanation, While accurate, doesn't necessarily answer OP's question. ",
"Y'know, the needle will meet more \"bumps\" in one second when it's far from the rotation axis than when it's closer",
"Indicates he understand the basics of what you are explaining already I think. I think what he is actually asking is does the actual audio quality degrade as you get closer to the center of the record. The information on the record is certainly much closer together the closer to the center the pickup gets, but that doesn't necessarily indicate the quality is \"Lessened.\"",
"I don't know the answer but it seems that we would need someone who understands what the maximum information capacity a record has and if records were designed to utilize that volume of information at the center most part where \"compression\" becomes an issue and outside of that the same data is simply more spread out. That said, its also possible that a record is capable of capturing more data for playback than the amount that would ever cause a \"Compression\" problem especially for the time period Records were really used for mostly.",
"TL;DR the question is less \"does the quality CAPACITY diminish the closer you are to the center of the record,\" which is an obvious yes, and more, \"Does the lessened quality capacity at the center of a record actually matter? Or is it still capable of replaying music at qualities higher than other bottlenecks (period microphones/record makers etc)\""
] |
[
"Is there just one single molecule of DNA in a cell nucleus, or are there many individual copies of DNA in a nucleus."
] |
[
false
] |
If many, about how many DNA molecules would there typically be in a cell nucleus?
|
[
"Duplicate chromatids only exist during cell division and most human cells aren't dividing most of the time. So most human cells contain only 46 chromosomes, and no chromatids.",
"But each chromosome is double-stranded, and since the strands are only held together by hydrogen bonds, you could consider them separate DNA molecules. There are 92 DNA helices in most human cells, in 46 double helices.",
"Of course there are exceptions: some cells have no nucleus, like red blood cells, and sperm and egg cells are haploid (only one chromosome from each pair, so 23 total). During early pregnancy, trophoblast giant cells go through a sort of partial cell cycle where DNA replication occurs but cell division doesn't, so they can accumulate tens or hundreds of copies of the 23 chromosome pairs. And don't forget that mitochondria have their own DNA. Meanwhile, in any female cell, one of the X chromosomes is crumpled up in a corner somewhere by X-inactivation."
] |
[
"I assume your question was asking about human cells, or at least eukaryotic cells - seeing as you mentioned a nucleus. But because everyone else has left you very good answers let me answer this question for bacteria and viruses!",
"Between bacteria and viruses, pretty much any arrangement of nucleic acid is possible: single piece of DNA, multiple pieces of DNA, circular, linear, RNA genomes, etc.. They're a diverse bunch.",
"The \"norm\" for most bacteria that people study is a genome composed of a single circular DNA chromosome, i.e. one molecule of DNA per cell. I study a bacterium just like that, one molecule of DNA per cell, strictly. I said 'strictly' because stuff can get loosey-goosey.",
" is the most widely studied bacterium. It has a single circular chromosome of DNA, but it doesn't necessarily have one DNA molecule. When times get good for an ",
" cell, it will start to replicate its DNA, and before the new copy is done being made it'll start making a new copy again. I learned that when the cells are growing at maximum speed it can have upto ",
"! It does this as a trick. It takes about 45 minutes to replicate all of its DNA, front to back, but it doesn't wait for one replication to finish before starting the next. So, when a new piece of DNA is replicated, its already halfway done on its next replication. With this trick, ",
" can split its cells every 20-26 minutes! Which is a good thing, microbiologist aren't too patient. Here's an article I found that is hopefully more eloquent than my rambling: ",
"http://sandwalk.blogspot.ca/2008/05/dna-replication-in-e-coli-solution.html"
] |
[
"There are 2 chromatids per each of the 46 chromosomes. Different species have different numbers of chromosomes in the nucleus. "
] |
[
"At what frequency does a repetitive sound become a solid sound?"
] |
[
false
] |
For instance, if you were able to beat a drum fast enough, at what BPM would it sound like a continuous noise?
|
[
"At 0-10Hz, you hear individual beats. Between 10-~60Hz, you'll hear it as a tone but your brain more or less just gets annoyed, which you'll recognize as dissonance. Above 60Hz, you'll hear a tone. ",
"Much more info at this link:\n",
"http://www.phys.uconn.edu/~gibson/Notes/Section5_5/Sec5_5.htm",
"For a good demonstration of this, check out the beginning of \"One\" by Swedish House Mafia. They begin by playing a bass drum beat in time, then slowly crank up the tempo until it becomes its own tone, which becomes the bass line for the song.",
"https://www.youtube.com/watch?v=PkQ5rEJaTmk",
"This question has some answers that get into why this is the case:",
"https://www.reddit.com/r/askscience/comments/17dt7b/do_brains_have_a_sampling_rate_that_they_operate/",
"You can experiment using this tone generator. Set it to square wave and see what happens at 5, 10, 20, 40, and 60Hz.",
"http://onlinetonegenerator.com/"
] |
[
"Speakers become less efficient as the frequency gets lower so you have to compensate with more power. It's uncommon to get headphones that can produce sound below about 20Hz or even 100Hz for low quality ones. By turning it up you're compensating for the drop off in efficiency. Unless you have some amazing headphones it's unlikely they will be able to do any damage. ",
"In theory, if you had really good headphones or a subwoofer that could go right down to 0Hz, it could result in damage. Sound is changes in air pressure. From an air pressure point of view, taking off and landing in an aircraft is very low frequency sound. If you can't equalise your ears they will be damaged. "
] |
[
"The suggestion to try the online tone generator is excellent. That really brings out the fact that it's gradual transition and you can hear some signals either way, or perhaps even as both simultaneously.",
"Some other interesting things to observe about that:",
"If you set it to a sawtooth, it will sound like a slower series of clicks in that range, and it will transition to a tone at a higher frequency. In a sense, that's a fairer test--if you have the saw tooth set at 20 Hz, you get 20 clicks per second, whereas with a square wave you get 40 clicks per second a 20 Hz.",
"If you set it to a sine wave, with most computer speakers, you'll hear nothing at all until a much higher frequency--on my laptop about 180 Hz is just barely starting to make a bit of very quiet sound. That means that if you hear it as a tone at, say, 50 Hz, you aren't necessarily hearing any acoustical energy at 50 Hz, but you are instead hearing harmonics of 50 Hz, which your brain uses to figure out that it's a 50 Hz tone. That shows that the ability to hear low frequencies in the 20-80 Hz range is not necessary to perceive sounds that repeat at 20-80 Hz as tones."
] |
[
"Why are symptoms caused by Mononucleosis only temporary when the virus is with you for life?"
] |
[
false
] |
[deleted]
|
[
"Once your body produces a sufficient quantity of antibodies, the virus has a much harder time infecting cells (as the antibodies bind the virus, interfering with its normal function, and marking it for destruction), and thus the acute symptoms disappear. However, it remains latent in certain cells, and virus particles continue to be produced; if antibody levels drop off for whatever reason, symptoms might return, or the virus particle quantity might rise to the point where you are infectious."
] |
[
"Mononucleosis is caused by Epstein-Barr virus, a member of the herpes family of viruses (which also includes Herpes simplex virus, that causes coldsores). After initial infection an immune response is raised and this produces the symptoms associated with the disease, also referred to as the acute infection.",
"However, the virus infects B cells, which produce antibodies, and here they cannot be attacked by the immune system as the immune system does not attack self cells. Once it infects a B cell, it integrates it's genome into the host cell's genome, allowing it to express it's own genes without itself being active, allowing the virus to persist even after the viruses that have caused the initial infection are removed by the immune system."
] |
[
"Can this virus be passed on to someone else? I mean, like through giving birth? I'm curious because in high school I had gotten mono, and the only fathomable way for me to have gotten it was through my boyfriend at the time. Now, his mom had gotten twice in her life, so because it might have a been a bit stronger, or her immune system was too weak to really fight it off the first time, and she got it a second, would she be able to pass that to him, and then he gave it to me? ",
"Sorry if this is a stupid question, and sorry it's so long."
] |
[
"Metabolics of Alcoholic Drinks?"
] |
[
false
] | null |
[
"Ethanol is not a sugar. Sugars are mostly burned immediately but some times stored as polysaccharides, or converted into fat. Ethanol gets converted into acetyl-COA and from there can be converted into ATP or fat."
] |
[
"There is something called the citric acid cycle, and it is how most of the ATP and other Molecules used as energy are created. Sugars and fats are metablised into acetyl-COA and converted into energy on there own seperate pathway. Sugar alcohols are basically sugars that have functional group with an extra hydrogen on them (reduced). The first step in the metabolism of sugar alcohols is to remove the hydrogen and turn the functional group form an alcohol to an aldehyde (oxidized). Once the hydrogen is removed they are a sugar and are metabolized the same way other sugars are metabolized. This means they can form ATP or Fat. ",
"The reason they have fewer reported calories probably has to do with them accounting for the sugar that is not absorbed."
] |
[
"And to clarify a point OP made, alcohol cannot be converted to sugar. In fact, when you consume alcohol, it competes with the resources required to metabolize sugar. Your body's reduced ability to metabolize sugar while drinking is a contributing factor to hangovers."
] |
[
"How are viruses weakened in vaccines"
] |
[
false
] |
I have read about how vaccines are sometimes made using weakened live viruses. How exactly are living viruses weakened?
|
[
"There actually is a distinction between vaccines made from killed viruses as opposed to attenuated (weakened) viruses. Killed viruses are composed of individual viral proteins and particles that are incapable of replicating at all. Attenuated viruses are weakened but not killed, meaning that they are capable of still infecting cells; just not enough to cause illness. ",
"There are attenuated viral vaccines such as MMR and varicella (chickenpox), and then there are killed viral vaccines such as the annual influenza shot and the Salk polio vaccine. There is also another polio vaccine called the Sabin vaccine that uses an attenuated virus. The annual influenza vaccine also now comes in a nasally-inhaled form called FluMist which contains attenuated virus; the presence of attenuated (as opposed to killed) virus allows it to \"infect\" a person nasally and activate the immune system. ",
"Attenuated vaccines are theoretically more effective because they mimic the actual infection cycle of a live virus, allowing the immune system to react to a simulated \"real\" threat rather than the individual proteins that compose a killed viral vaccine. However, there is some risk that attenuated vaccines can still \"re-activate\" and cause illness, especially in those with compromised immune systems. This is why attenuated viral vaccines are contraindicated in patients with AIDS, pregnant women, and others in whom an attenuated vaccine is more likely to activate and could be devastating. "
] |
[
"Just replying to say that qxrt has the accurate description of attenuated vaccine. There is a bit of confusion in the post above by quophnix. His description of a virus was pretty much correct. However, an inactivated vaccine is ",
" the same as an attenuated vaccine which you were asking about. ",
"Inactivated vaccines do not actively reproduce and do not produce an IgA response. Therefore you require booster shots. His claim that your immune system learns what the virus looks like through inactivated vaccines is misleading in this sense. Antibody memory is a tricky thing that still isn't fully understood. ",
"An attenuated vaccine actively reproduces and produces a full antibody response therefore you get a more lasting protection against the virus.",
"A attenuated virus is weakened because its virulence is reduced. It's still very much \"alive\". Virulence is what is modified when producing an attenuated vaccine. These virulence factors include things like how easily a virus can transmit from host to host, how easily the virus can adhere to target cells, how easily the virus can evade the immune system etc. Once these factors are weakened in any way, the virus is considered attenuated and used in vaccines. ",
"Obviously a virus that can't transmit or attach to target cells is not going to be as lethal as the original virus. That isn't to say that complications can't occur though. Take for example the attenuated Yellow Fever vaccine. This produces a response so very similar to the actual disease that most recipients of the vaccine are hospital ridden for 2-3 weeks."
] |
[
"the reason they say weakened virus is because they have to leave enough of the virus intact so that there is an immune response from your body. without the immune response from your body, your body wouldn't learn what the pathogen looks like and be able to use that information to defend you from infection in the future.",
"This is false. Attenuated viruses produce the full antibody response meaning that you get production of IgA as well as IgM/IgG. This means that you do get longer lasting immunity. An inactivated vaccine is what you're thinking of.",
"Attenuated vaccines actually last for a relatively long time because they produce the same immune responses an actual infection would produce. See Salk vs Sabin Polio vaccine and how replication boosts immunity."
] |
[
"Theoretical math question: What shape of cake would maximize icing per piece?"
] |
[
false
] |
[deleted]
|
[
"Make a cake in the shape of a Menger sponge. Ice all surfaces. Done."
] |
[
"Note at all, a Menger sponge fits in a finite volume. Then assuming that icing is never more than a given thickness, the iced sponge should also fit in a finite volume.",
"What you can't do is coat every surface with the same thickness of icing, for the simple reason that not every surface has enough room above it."
] |
[
"Warning: If done properly, requires an infinite amount of icing ..."
] |
[
"What if all the missing mass in the universe (dark matter) are just stars hidden within Dyson spheres ?"
] |
[
false
] |
So, I was crunching numbers with a friend using the drake equation, and it turns out that 3000 one billion year old civilizations might exist within our galaxy alone, so automating the construction of Dyson spheres shouldn't be that difficult of a task for them, and well, they've been around longer than us, so they had the time to build lots of'em, and if they're energy efficient they won't be detectable at all. I'd like to hear your thoughts on that fellow Redditors.
|
[
"The idea that dark matter is in the form of condensed objects that we can't see (like brown dwarves, black holes, in an extreme circumstance, Dyston spheres) is called the MACHO hypothesis (Massive Compact Halo Objects, in comparison to WIMP, Weekly Interacting Massive Particles). This has largely been ruled out by observation, particularly with microlensing where a diffuse distribution of mass would be very different from a compact one. Warm objects like Dyson spheres we would additionally see as infrared radiation.",
"http://www.epj-conferences.org/articles/epjconf/pdf/2014/07/epjconf_icfp2012_00025.pdf",
"However, the Dyson sphere idea is a bit more troubling: it implied of all the hundreds of billions of stars in our galaxy, about 80% have of them developed civilizations powerful enough to enshroud their host stars."
] |
[
"That still wouldn't make them look like they were made up of dark matter.",
"And yeah, it's possible aliens are all over the place and really good at hiding from us, but we have no evidence to suggest that that is the case."
] |
[
"But what if they wanted to make them stealthy to avoid detection?",
"Well, that's the thing: they can't be. The energy the star releases has to come out some way, somehow. Eventually, it will get turned into heat. Assuming the beings are similar to us in temperature preference, and their machines have similar operating temperatures, their civilization would be emitting a star's worth of infrared energy.",
"This doesn't matter for the purposes of dark matter, though, because as ",
"/u/iorgfeflkd",
" said, microlensing results rule out MACHOs being a significant contributor to dark matter, and there's no hiding your mass."
] |
[
"What makes it so that a new COVID-19 mutation is able to 'get around' our vaccinations?"
] |
[
false
] |
I apologize for the frequently asked question. I'm sure everyone wants to know.
|
[
"Since the vaccines all target the spike protein, when the virus changes the spike protein in a region that antibodies bind it will lead to some immune escape.",
"There are many different antibody binding sites on spike -- at least 17 or 18. A single change, leaving a dozen other sites for antibodies to attack, might give a ",
" reduction in vaccine effectiveness, but only very slight. Actual ",
" would likely need mutations in three, four, six sites at once. ",
"It's really hard for the virus to change all of the binding sites -- it's exponentially less likely to mutate in two spots simultaneously than one, exponentially less likely than that to change in three, etc. So superficially, it should be extremely difficult for the virus to experience selection for immune escape. ",
"There are two points that change the equation a little bit. ",
"One -- so far, by far the most important -- is that selection for ",
" also leads to some accidental ",
". That's almost certainly the driver for all the variants we've seen so far -- the reduced immunity is just coincidental, and the selection is for increased transmission. ",
"It's well known that selection on pathogens is almost entirely at the level of transmission, so this isn't at all surprising. It's not surprising that the various variants that have sequentially dominated have each sequentially been better at transmission than the previous, whereas there's little change in their immune evasion ability. Really, the only variant that had a drastic immune evasion ability was the beta variant (B.1.351), which didn't have much improved transmission and so far hasn't really spread. (I haven't seen any data for e.g. the lambda variant, either in terms of transmission or immune escape.)",
"Conversely, of course delta only has moderate immune evasion and all of that seems to be mostly incidental to its functional changes (",
"Molecular basis of immune evasion by the delta and kappa SARS-CoV-2 variants",
"). ",
"The reason this happens is that spike is very important for virus spread and entry (though it's not the only factor), and as a zoonotic virus it started off, a year and a half ago, as quite poorly adapted to humans. As it's adapted to humans (optimized binding to its receptor, optimized fusion and entry and so on), coincidentally that's also changed the regions that the antibodies bind to.",
"Again, none of this is surprising. Delta arose in a population with very low immunity and almost no vaccination, so there would be little or no selection for immune evasion whereas there is always selection for enhanced transmission. If there is any surprise, it's probably how poorly adapted the ",
" virus has turned out to be -- I don't think many virologists expected it to have sequence space to adapt to this much enhancement of transmission. ",
"In the future, is there likely to be direct selection for immune evasion? Considering the large number of vaccines we have experience with, including many that target viruses with a much higher mutation rate (measles, mumps, yellow fever, etc etc) -- none of which show significant immune evasion over periods of many decades -- it seems a ",
" unlikely. ",
"The one exception is influenza (although even there, it's been proposed that the antigenic drift that's seen is actually selection for transmission and not immune evasion (",
"Hemagglutinin Receptor Binding Avidity Drives Influenza A Virus Antigenic Drift",
" -- though that's a minority opinion), and that's unique in its ability to tolerate mutations in its hemagglutinin (",
"Deep mutational scanning of hemagglutinin helps predict evolutionary fates of human H3N2 influenza variants",
") which other viruses can't do (",
"Mutational analysis of measles virus suggests constraints on antigenic variation of the glycoproteins",
").",
"Still, there have been a number of variants of spike protein over the past 18 months, so it does suggest that spike is at last intermediate in its tolerance -- perhaps more like influenza B than A (",
"The Influenza B Virus Hemagglutinin Head Domain Is Less Tolerant to Transposon Mutagenesis than That of the Influenza A Virus",
"). Influenza B throws out antigenic variants every few years, but much less often than A, so if that's an analogy then immunologically significant variants might arise every few years. ",
"The best way to avoid this, of course, is to reduce the overall pool of viruses, thereby reducing the number of variants (",
"Full vaccination is imperative to suppress SARS-CoV-2 delta variant mutation frequency",
"). Again, since the variants are being selected on transmission and not immune evasion, the real concern is that there will be sequential selection of highly transmissible variants that will eventually, coincidentally, have more immune evasion ability. ",
"That's why vaccination is the best way to avoid immune evasion. Reducing the pool overall, reduces the number of variants that can lead to sequential selection. Since all the variants so far have been well controlled by the vaccines, the best approach is obvious."
] |
[
"I mean we can look at history. Did that happen with measles? Mumps? Polio? Rubella? Yellow fever? Smallpox? Anything else in the hundreds of years of experience we have with vaccination? Obviously it has not.",
"I realize that for many people this is the first time they’ve ever had to think about vaccines in their lives. Realize that that’s because vaccinologists, virologists, immunologists do think about vaccines a lot, and are actually very good at doing their job."
] |
[
"Well, the article you linked raised the concern, then tempered it with the fact that it’s unlikely, and the mutations observed thus far in SARS-CoV-2 aren’t really surprising, it’s normal and within expectations.",
"And while the article said something about how we could end up back where we started with a fresh, new virus, it followed up right away by explaining how modifying current vaccines to fit new variants is much easier than developing new vaccines against a new disease. So overall, it told the same message as iayork’s explanation, just focusing more on saying it’s possible than saying it’s unlikely.",
"As for the comment from ‘someone’, many studies such as ",
"this one published just a couple days ago",
" report very little difference in vaccine effectiveness against the delta variant compared to alpha, a drop of around 5%, when you have the recommended two-dose regimen. Far from what I’d call ‘considerably less effective’. We saw a spike of delta cases mainly because it’s more easily transmissible, not because it ignores vaccination."
] |
[
"Does light stop moving at absolute zero?"
] |
[
false
] |
I know that absolute zero signifies that all matter stops moving. So, can a photon still travel through 0 K?
|
[
"absolute zero signifies that all matter stops moving ",
"This actually isn't the case. Quantum systems almost always have energy of motion which is still nonzero as you approach absolute zero temperature. For instance, electrons don't stop moving around their atoms because it's cold. What absolute zero does mean is that your system no longer has any excess internal energy it can lose.",
"So, can a photon still travel through 0 K? ",
"The is more complicated. Temperature does not just exist on its own, it's a property—a substance has a temperature and different substances interact with light in different ways. So a medium at one temperature might impede light while a different medium at the same temperature lets it travel through just fine. Being close to absolute zero doesn't have anything to do with it."
] |
[
"To add to this: by definition, a system at zero temperature is in its quantum mechanical ground state. So for example, in a common metal at zero temperature, there are electrons moving at an average of 10",
" m/s, so saying that motion stops at zero temperature is certainly false."
] |
[
"Also, if a system at absolute zero absorbed a photon, then the system wouldn't be in its lowest energy state any more. In other words, it wouldn't be at absolute zero after it absorbed the photon. "
] |
[
"What happens when we run out of space on the radio frequency spectrum(s)?"
] |
[
false
] | null |
[
"The radio frequency spectrum is a finite resource. If we \"run out of space\", we're out of luck. But certain ",
" of the spectrum, allocated by agreement to specific purposes can and do \"fill up\". In that case, new national and possibly international regulations have to be written to reallocate portions of the spectrum involved.",
"Each portion of the ",
"Radio Frequency Spectrum",
" from 3 Hz. to 3000 GHz. (3 THz.) is allocated for use (or non-use) international agreement under the auspices of the International Telecommunication Union.",
"Each parts of the radio spectrum is apportioned by the ITU for different radio technologies and applications; some 40 radiocommunication services are defined in the ",
"ITU's Radio Regulations",
".",
"The drafting, revision and adoption of the Radio Regulations is the responsibility of the World Radiocommunication Conferences (WRCs) of the ITU, meetings of which are typically held every three or four years, most recently in Geneva in 2012."
] |
[
"Although it's important to note that we can shrink the wavelengths that we use to create virtually infinite more radio channels. It would require better hardware, but we wouldn't exactly \"run out\" ever.",
"Edit: as some people pointed out, what I meant was to reduce the range of frequencies for each channel. It's also been pointed out that doing so would reduce the bandwidth and is this not useful beyond a certain extent (certainly not \"infinite\"). I'll be more clear in the future about my level of expertise on the subject :)"
] |
[
"Yes but Doppler shifting would eventually become an issue at velocities that humans tend to move at. As is all the other factors such as multiple reflections and scattering. If you look at a signal on a spectrum analyzer it really is more like fuzzy than you might expect. The hardware could be perfect but the path would still be non-ideal. So there is a finite limit. "
] |
[
"Is there a scientific basis for homosexuality, bisexuality, etc.? or is sexuality just a choice someone can change for whatever reason?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"/r/AskScience",
"To check for previous similar posts, please use the subreddit search on the right, or Google site:reddit.com",
"/r/askscience",
" ",
"Also consider looking at ",
"our FAQ",
".",
"For more information regarding this and similar issues, please see our ",
"guidelines.",
"If you disagree with this decision, please send a message to the moderators."
] |
[
"I assume you are being sarcastic. There is an entire section on causes in the homosexuality wiki. Start there."
] |
[
"I assume you are being sarcastic. There is an entire section on causes in the homosexuality wiki. Start there."
] |
[
"Does breathing through your nose reduce the amount of air you can take in compared with your mouth?"
] |
[
false
] |
I mean they both lead to the same throat anyway
|
[
"Your lungs hold the same capacity. The rate of inhalation/exhalation, however, is different. Breathing through the mouth is quicker."
] |
[
"The anatomical dead space of the mouth is comparable to that of the nasal cavity; with a deep breath, you'll get the same amount of air in your lungs by breathing through your nose as you would by breathing through your mouth. However, the mouth has a (potentially) larger diameter than the nostrils. It will take less effort to expand the lungs when the air that's moving in to fill them has a larger passageway to move through. So while the amount of air you get per breath won't change, the ",
" of air you can take in (breaths/minute) will be higher if you breathe through your mouth. ",
"Short answer: per breath, no. Per ",
", yes."
] |
[
"It's also more work to breath through your nose!"
] |
[
"Why is it we do not feel pain while unconscious?"
] |
[
false
] |
And for that matter, why is it our brains have the ability to be unconscious? What unconsciousness?
|
[
"To some degree, it's tautological. If we could feel pain, we'd be conscious, because being able to sense is part of what it means to be conscious. But the other questions are far more mysterious. The first of the two is almost philosophy, and the second ",
" is philosophy. The fact that you can even ask what consciousness is exemplifies how little we really understand: it's not that we can pick out consciousness and say look, there it is, but I don't know what it is, like we can with dark matter. The problem is more that we don't even know how to pick it out in the world. We think that it exists, but we can't even get enough of an idea of what it is to point to it. The more we learn about cognition the truer this becomes."
] |
[
"Pain is used as a mechanism to alert us as to what can be damaging to our body. When asleep we will still feel pain and awaken suddenly to halt the cause, but our bodies will enter an unconscious state (not sleep) generally from some incident which has disrupted blood flow to the brain (fainting, head trauma, blood loss) as to protect the brain, or it cannot function. In this state one wont feel pain in the memorable sense (pain is still transmitted from the source to the brain through the nerves) as the conscious brain cannot/wont interpret this signal.",
"As for unconsciousness, I'm not too sure. I suspect it is simply the brain \"turning off\" in a way that conserves brain power and energy, such that a reduced blood flow can help lessen the extent of any possible injury that may have occurred (in the sense of brain swelling)."
] |
[
"We don't always wake up tho. This is one of the things that is raised in the consciousness literature. When you're asleep, and you've twisted your arm, you react just as you would when you're awake, but you don't ever ",
" the pain. You just react to it. That's actually one of the deep puzzles of consciousness: if you can do everything without it, why's it even there? And how can we tell if other animals have it, since it's clearly not necessary? Noone's got a good answer for this."
] |
[
"If I went skydiving, and instead of a parachute, I landed in a large pit of those little foam cubes, would I be okay?"
] |
[
false
] |
This was a tremendously silly question that popped into my head this morning. Thanks for indulging me, /askscience. I expected one sincere reply and two insults, but here we are.
|
[
"Assuming that the foam cubes would decelerate you more or less evenly then you would need 7.7 meters of foam to make the fall survivable (20g), about 15.4 meters to be able to just walk it off (10g) and about 154.1 meters in order to make the landing smooth as a cushion (1g).",
"In reality the foam is probably going to be of very little resistance at first but then rapidly decelerate you near the end of your landing so I wouldn't want to land on anything less then say 25 meters of foam. :P"
] |
[
"Essentially what matters is how fast you will decelerate upon approaching the ground. From what I could find the terminal velocity of a skydiver is about 56m/s (200km/hr). Obviously hitting the ground with such a speed means your chances of surviving are small. Slowing down, e.g. by falling through those foam cubes would extend the time over which you could decelerate, thus reducing the maximum (g) forces acting upon you at any given time. In principle, having enough such cubes should work just fine. In fact, by playing with the material properties and the thickness of the layer you can continuously reduce the final deceleration you will experience to arbitrarily low levels.",
"Tl;dr: Yes if there are enough foam cubes with the right material properties. "
] |
[
"Cardboard boxes, actually.",
" That being said, his webbed suit slowed him down a considerable amount, so doing this sort of thing with a typical skydiver would require far more cushioning. "
] |
[
"Does data have weight? Ex If I were to weigh a USB before and after loading it with data, would there be any difference (no matter how minute)?"
] |
[
false
] | null |
[
"Yes, but only technically. A “0” bit in a flash drive is a low voltage state, and a “1” bit is a high voltage state. The high voltage state has a higher potential energy, so it also has more mass by E=mc",
" . With that known, a drive that is completely full of “1”s will be heavier than one completely full of “0”s. For a 4GB drive, it’s on the order of 10",
" g. This is an attogram, which is 1 millionth of a nanogram. Or put another way, it’s the equivalent of about 3000 ",
" of gold. ",
"However, a drive filled with actual data won’t be all 1s. There will be roughly as many 1s and 0s. So really, it will be about half as big of a difference. And an “empty” drive won’t be all 0s either, since any data that was on it previously would still be there just delisted. Bits in the high voltage state weigh more than bits in the low voltage state. But an empty or full flash drive can weigh more, less, or the same as each other."
] |
[
"There's no need to actually erase the data, the drive just allocates that space as \"free\" so it can be written over. Writing to 0 then writing actual data takes twice as many operations."
] |
[
"Depends on the media. Imagine an old punched card. Adding data to them obviously make them lighter because you are actually punching holes in them. Adding data to a piece of paper makes it heaver because the ink adds weight. For many other type of electronics, such as harddisk drives, data is just magnetic orientation, so they don't change in weight, but there probably are some that add and subtract weight."
] |
[
"Why do mirrors never seem to ice up?"
] |
[
false
] |
I just noticed this winter time that the mirrors on my car never seem to ice up, and when I think back on it, I can never remember a time during the winter that the mirrors have ever iced up. Why is this? Why is it that ice never seems to build up on mirrors?
|
[
"They do ice up. Mine were this morning. Its quite common, though not as much as the windows. "
] |
[
"I think the mirrors might be aided in that they tend to be vertical and suspended, so it's harder for downward falling precipitation to collect on them significantly to begin with, and there's not much to keep it from falling off. ",
"That being said, I concur with kev92715. Mine have been quite inconveniently icy a time or two this winter alone."
] |
[
"Mirrors are also embedded about a half inch inside their housing which also helps keep any precipitation off of them. Of course, Murphy's Law dictates that the wind will always blow towards them."
] |
[
"How _exactly_ do we feel temperature?"
] |
[
false
] |
I'd like details down to the interactions of atoms, please. Do nerves that sense temperature detect the vibration of the atoms in the body? If I remember chemistry right, temperature is the speed that particles vibrate at, no?
|
[
"Unfortunately we don't understand thermoception entirely. Over the last decade the picture has become much more clear, and so I will say what I know.",
"Temperature sensing comes from free nerve endings that are found in your skin and other areas. These neurons that sense temperature are thought to sense it by the expression of a class of ion channels called TRP channels. These ion channels open when they sense a particular temperature, which subsequently activates the neurons and so that's how you know that you are feeling some temperature. The most famous of these, TRPV1, is a ion channel that responds to painfully hot temperatures- it is also a receptor for capsaicin, the chemical that makes hot peppers spicy, and the reason why we sense this hot spiciness is that it binds to these heat channels and activates our sensation of hotness. There are an entire family of these channels, and different channels have different temperature sensitivities, and they cover a spectrum of temperatures so you can sense when it's warm, cool, or painfully hot/cold.",
"As to the exact specifics, I don't think it is known exactly how the channel is activated. From a theoretical perspective though, it must somehow sense the temperature. You are right that temperature is related to the speed at which particles vibrate, but it is more accurate to say that the temperature is a result of the average kinetic energy of the particles. When you touch something hot, the particles have high average kinetic energies and will transfer some of these kinetic energy into the skin, and thus raising the temperature of the particles in the cells and the environment they are in, reaching the thermoreceptors in the neurons. Somehow, these channels undergo some structural change when they have a particular temperature that allows a pore to open and cause the influx of ions. The actual atomic basis of how this occurs is probably not known."
] |
[
"Bell peppers are full of water, which stores and conducts heat very well. So when you touch it, a lot of heat goes to your skin and this part of the skin feels a high temperature and yells to your nervous system \"hot, hot, hot\".\nWhen you eat a carrot, even it is at the same temperature, it gives less heat to your skin: it's just warm.",
"But that doesn't explain why bell peppers are so good compared to broccolis.",
"All these artifacts come from the fact that you can't wait for the thermal equilibrium between your skin and the object."
] |
[
"Its important to understand that you can only measure the temperature of your receptors, not the temperature of the object you touch. It means that you're more sensitive to how it is heated of cooled, i.e. to the heat flux more than to the actual temperature.\nThat's why wind can change the temperature you feel, or why a piece of metal (which is a good heat conductor) always seems hotter of colder than other objects."
] |
[
"Does heavy cognitive thinking burn extra calories compared to light brain processing?"
] |
[
false
] |
I'm curious to isolate the work that the brain does and how much calorie burning it undergoes. I've seen research that said it's negligible, but then I saw this video: Does anyone have any conclusive ideas about this?
|
[
"The brain's energy consumption is pretty constant, even while you're asleep. You're thinking of it like a CMOS-based FET transistor (e.g how we make most computers) which uses more power the more it switches, or like an engine which uses more fuel the faster it spins.",
"It's neither of these things. The work it does in processing is very low energy, it uses nearly all its energy budget in maintenance and respiration. Going back to the computer-based analogy, it's like emitter-coupled logic. It uses a lot of power, all the time, but no more when it's doing something consciously than when it's doing tons of things unconsciously."
] |
[
"I'm not sure that's entirely accurate.",
"When a person undergoes fMRI scanning of the brain, the scan picks up subtle increases in blood flow to certain regions based on the activities or even thought patterns of the patient - this is one of the main sources of evidence to support the theory that there are regions of the cerebral cortex, and that neuro plasticity can occur following brain trauma such as a stroke.",
"The increased blood flow is to supply more glucose and oxygen to the neurons and synapses as they have to actively transport neurotransmitter molecules and ions across their membranes in order to produce impulses.",
"I don't know what the actual increase of calorific load is in this situation, I suspect it's not particularly high."
] |
[
"so getting hungry after hour long exams are probably caused by stress or other factors?"
] |
[
"Had Isaac Newton not created/discovered Calculus, would somebody else have by this time?"
] |
[
false
] |
Same goes for other inventors/inventions like the lightbulb etc.
|
[
"Absolutely. There was a German mathematician named Gottfried Leibniz that discovered calculus simultaneously. In fact, a lot of the notation we use today (such as dy/dx instead of y') is due to Leibniz and not Newton."
] |
[
"Huge injustice similar to the injustice Tesla received. ",
"You know what is unjust? How everyone always talks about how Tesla got the short end of the stick, while he recieved enormous amounts of money, and even has an SI unit named after him, for mostly work done by Faraday before him and even though he misled people with impossible claims. ",
"Meanwhile, Oliver Heaviside is virtually forgotten by the world at large, even though his is the clear underdog story. Self taught scientist, ignored or suppressed by the scientific community during a large part of his lifetime, had his inventions stolen without credit, and died in poverty even though works are fundamental in current physics. ",
"Yet ask anyone on the street, they have no clue who Heaviside was, but they all know how Tesla is the one who was wronged. That is injustice imho."
] |
[
"In fact, he was the first to do it. Newton got more recognition because he was one of the leading men in the English Parliament. Huge injustice similar to the injustice Tesla received. "
] |
[
"What would the original domesticated dog have looked like in terms of modern breeds?"
] |
[
false
] |
If there isn't a modern breed that looks like that anymore, why didn't humans keep it around?
|
[
"Dogs",
" are a subspecies of grey wolves. The first dogs were domesticated from grey wolves. There have probably been multiple domestication events, some as early as about 33 000 years ago, but it appears as if those lineages died out. The current thought is that current breeds have been artificially selected for from a single domestication event about 15 000 years ago. ",
"Here is the article on the ",
"origins of the domestic dog",
".",
"Very likely the earliest dogs looked like their wild counterparts - e.g. wolves. There are many breeds which retain the physical and behavioural traits found in wolves, others have been bred to resemble wolves. Some breeds come to mind: huskey, american alsatians, malamutes, norwegian elkhound, siberian Laika, wolf hounds (irish, czech...), alaskan Klee Kai....",
"Also worth noting that many people have backcrossed dogs with wolves to create ",
"wolfdogs",
". Half-wolf half-dog, probably the closest you will get to an actual wolf while retaining traits from both lineages. "
] |
[
"This is a dangerous situation - the wog believes it is in charge of your home. It is protective of you, and listens to your commands most likely because it wants the rewards you train it with. ",
"You need to get in touch with a trainer and get to some training classes. The danger is that if, for example, someone came into your home that your wog considered a threat, it may attack them and you do not have the authority to stop it. If you are dominant, then it will cue off your behavior and be more subordinate to your commands. ",
"Most good dog training schools will evaluate your pet for free and give you advice. It's funny - normally when I'm advising dog owners I have to make the point \"there's a wolf living in your home\" but I guess you've got that part..."
] |
[
"So I own a husky that is half Siberian husky and half grey wolf (parents had a grey wolf around their house) and he is defiantly hostile around strangers but is completely loyal to me. Are these mixed traits of feral and domesticated canine? "
] |
[
"What would be the direct effects on climate from increased sea levels?"
] |
[
false
] |
[deleted]
|
[
"Depends why the sea levels increased. I don't know if any research has been done to confirm this, but I did read that if the greenland icecaps were to melt then it could drastically alter the behaviour of ocean currents that give Europe its mild climate.",
"Add to this changing the salinity of the oceans and other factors, it wouldn't be so much the rising sea that would be the main problem, it would just be one of the symptoms of something much bigger!"
] |
[
"Fun(?) Fact: While sea level rise is of course due in part to melting ice, thermal expansion is a much bigger component, as warming a lot of water even just a little bit, results in it taking up a lot more space."
] |
[
"thanks for the info!"
] |
[
"(Micro)Biologists! You've been tasked with doing a gram stain on bacterial slide. What steps / method do you use? (If you have an automated instrument, I'm jealous)"
] |
[
false
] |
[deleted]
|
[
"I always flooded with CV, then kinda dumped it off and flooded with iodine without rinsing. ",
"I also rinse by sticking the ",
" of the slide directly into the tap water stream. But that might be the way everybody does it, I dunno. "
] |
[
"Quite honestly, the last time I Gram stained something (and Gram should be capitalized, it's named after Hans Christian Gram) was when I was TAing. In the course of my research, Gram staining is useless. I'd rather just send it out for 16S sequencing.",
"But if you're having issues, you might need to up the crystal violet timing a bit, some things need a bit more time. The rest of your timing/technique looks fine."
] |
[
"I knew someone would correct my lack of the capital G just as I hit the submit button. I am shamed. ",
"I'm not (and probably won't end up in) research, so it's possible I may have to do these until the day I die, but I am TAing."
] |
[
"Is there a limit to how viscous intravenous medications can be?"
] |
[
false
] |
When administering medication intravenously, do drug manufacturers have to 'thin out' the medication with other solutions in order to bring it to a viscosity similar to human blood, or is there a fairly large range of viscosity that will mix well with blood? As a kind of bad example, could you get away with administering a medication with similar viscosity to honey?
|
[
"Thinning out a medication isn't necessarily an accurate depiction as most medications would not be delivered as a 100% solution in an IV. Many would be solids even. So, diluting them would be necessary for the IV in order to administer the medication slowly as opposed to as instantly as a shot or pill instead. Dilution in saline, for example, to a lower concentration of medication would result in a solution with a viscosity sufficiently similar to blood that it would present no deliverability challenges (at least I can't think of any example where this would not be the case). ",
"That said, viscosity alone would not necessarily be problematic, however, it would have effects on other aspects of the treatment. For example, if as viscous as something like honey, it may need to be delivered at a slower rate to ensure the bloodstream can sufficiently dissolve the medication which of course ultimately affect the treatment if it slows the delivery of medication. Significantly higher viscosities are also likely to be avoided due to deliverability (e.g. how much pressure does the nurse/doctor/machine need to apply to deliver the medication).",
"Just to be clear, viscosity, concentration, dose, etc are not interchangeable. You can change the viscosity of a solution by changing non-drug components. ",
"Edited to more clearly respond to the initial question."
] |
[
"In the case of iodine-containing radiocontrast agents, they are too viscous to be conveniently pushed through an IV line of normal dimensions that they are warmed first to thin them out before injecting IV or IA. That is why you experience a sense of warmth when they are injected.",
"More often a concern is either too high a concentration to be diluted in a peripheral vessel and so they injected into a major vessel such as subclavian or superior vena cave. This is the case for total parenteral nourishment and some toxic agents for chemo.",
"Thus viscosity ",
" is a plumbing issue more than anything."
] |
[
"Whoa, always wondered about that, thanks"
] |
[
"Sounds on Mars"
] |
[
false
] |
What affect does Mars' atmospheric conditions have on sound. Would the speed of sound be decreased, would the volume of the sound be decreased, the pitch?
|
[
"Um, density is in the denominator there, so",
"If a material is more dense... it will transmit sound slower."
] |
[
"It would be pitched lower due to the atmosphere being composed mostly of CO2 which is heavier than N2 (the main component of our atmosphere), and die off much more quickly due to the much lower pressure. Here's an ",
"article",
"."
] |
[
"Well.... for starters sound would travel slower, about 2/3rds of speed on Earth at normal conditions.",
"http://www.aerospaceweb.org/question/atmosphere/q0249.shtml"
] |
[
"Why is the fine structure constant called \"fine structure\"?"
] |
[
false
] | null |
[
"Atomic spectra have gross, fine and hyperfine structure.",
"The gross structure corresponds to the energy levels which result from non-relativistic solutions to the Schrodinger equation, with no allowance for the effects of electron spin.",
"Fine structure results from taking account of relativistic effects, and of interactions between electron spin and orbital angular momentum. This has the effect of splitting what would otherwise be single energy levels into closely spaced ones. It is the fact that these levels - and hence the resulting spectral lines - are closely spaced that leads to it being referred to as fine structure.",
"Hyperfine structure is an even smaller effect due to interactions with the nucleus.",
"The fine structure constant was given that name because it appears in the equations for calculating the size of fine structure corrections."
] |
[
"Wikipedia discusses them - is this what you're looking for?"
] |
[
"Wikipedia discusses them - is this what you're looking for?"
] |
[
"Is it technically possible for something to have a pH below 0?"
] |
[
false
] | null |
[
"Yes! The pH is defined as -log[H+], i.e. the negative logarithm of the concentration of hydrogen ions to the base 10. At pH 0, that means that the H+ concentration is 1 mol/L, and if you have a higher concentration, then the pH will be negative."
] |
[
"pH is defined as -log(aH) where aH is the activity of the hydrogen ion. At low concentrations this will be the same as the concentration, but at high concentrations the solution will behave non ideally and the activity represents an 'effective' concentration. ",
"A more general acidity function can be used called the Hammet acidity function, which can be used more concentrated solutions and can be use in solutions in non aqueous media (a so called solvent independant quantity). This can be used to compare the strength of acids in different media. The strength of the acid in this situation is defined by Ho and in dilute aqueous solutions this is equal to the pH. On this more general scale acidity can take -ve values eg. H2SO4 have an Ho of -12. One of the most extremely acidic compounds in existence is Fluoroantimonic acid which is 10",
" times more acidic than battery acid! It can even protonate hydrocarbons like methane!"
] |
[
"Ok, because I saw lemon rind is 2/3 and battery acid is 1, and so I couldn't figure out what straight up ACID is, like the good old-fashioned movie stuff that melts things. Thanks for your reply,very cool :D"
] |
[
"Is it theoretically possible that the Earth or its inhabitants could contain dark matter?"
] |
[
false
] |
Right off the bat I want to point out my profound ignorance of the subject. Given that 83% of the universe's matter is dark matter, it seems like it must be everywhere. Is it possible that it is all around (and inside) us but due to the quantities being so small we can't detect their gravity?
|
[
"Yes. It likely passes through your body every moment much like neutrinos do, and with little or no interaction. That's why dark matter detection experiments are often designed very similarly to neutrino detectors. Build a huge amount of mass and some detectors to see if a very rare thing happens within that mass."
] |
[
"well I don't know that you could calculate the ",
" per se. Or at least I don't know how to do that. I think we can make reasonable estimates of the average mass density of dark matter through the volume, but one would need to know the \"particle\" mass of dark matter to figure out the ",
" of dark matter particles. Usually though this problem is given as calculating neutrino flux through the body, as that's a more well known set of data."
] |
[
"Ah. I see. Well to follow up on that point, we think neutrinos are too light to be dark matter (they're so light that they'd probably zip away from galaxies rather than condensing into haloes around them). "
] |
[
"Will compressing a stream of air result in a lower temperature?"
] |
[
false
] |
This viral video (series of gifs) suggests that by using discarded plastic bottles to compress flowing air, users can lower the temperature of the air in their homes. This seems like a dubious claim; does it work as described or is a different cooling mechanic at work here?
|
[
"The air being forced through the smaller opening focuses the pressure from the wind, increasing airflow. You probably understand that part.",
"Humans radiate heat, creating a shell of warm air around them. This setup won't necessarily drop temperatures, but it will increase airflow in a room which allows for that heat shell to be blown away, as well as increasing evaporation of sweat which will also result in actual cooling.",
"It's just like a fan. If a room was thermodynamically sealed the fan motor will actually increase the room temperature, but by blowing your shell of heat and evaporation away from you it's still felt as a cooling effect.",
"Consider the difference in perceived temperature when you exhale slowly with an open mouth vs blowing with pursed lips. This is similar to that, with the breeze being the air in your lungs and the window or bottle openings being your lips.",
"All of this is also why at certain temperatures in varying humidities, the capability of a fan to cool you drops to basically zero. "
] |
[
"Those nozzles do not materially compress the air, because the wind is not moving fast enough to compress it. So the temperature of the air stays the same, but it is accelerated, which improves its ability to transfer heat from the occupants to the room and from the room to the outside (assuming it is a through breeze)."
] |
[
"The expansion described is an ",
"Irreversible adiabatic expansion",
". The system is irreversible because the fluid is allowed to change entropy from an unrestrained expansion into the environment (can be viewed as an infinite volume from the nozzles perspective). ",
"The exit temperature really depends on the pressure, temperature and volume differentials between the two systems. The system described above has what appears to be low differentials. Also, irreversible expansion depends on specific volume of a fluid (inverse of density). The density of air is low compared with other fluids such as CO2 or refrigerants, so the relative temperature drop is ultimately less. Lastly, the total efficiency of such a system is low.",
"Will it lower the temperature around the nozzles? Sure, marginally. Does it have the cooling capacity to lower the temperature of an entire home? Very doubtful. Is it better than a house AC unit? Not by a long shot, you’d be better off trying to cool your home with fire extinguishers (/s ...don’t try to cool your home with fire extinguishers)"
] |
[
"Where do the methyl groups used in DNA methylation derive from?"
] |
[
false
] |
When it's not part of a larger atom, methyl is highly reactive, so I'm guessing that it isn't just floating around before it is used for methylation.
|
[
"Cells use a carrier molecule, just like they use ATP to transfer phosphate, NAD",
" to move a pair of electrons, UDP-Sugars to move sugars, and CDP-choline to shuttle parts of lipids around. ",
"In the case of methyl groups, the cell uses S-adenosyl Methionine, or SAM. By linking an adenosyl group (ribose + adenine) to the sulfur of methionine, the methyl group becomes activated. This activated ",
" methyl group can be transferred from SAM to the target of interest, in your case to cytosine on DNA.",
"Edit: Mis-typed name of transferred group"
] |
[
"I think you need to think about it the other way around - why were those molecules selected over other ones? Well, using nucleotide derivatives is common, probably because you can have a protein that recognizes one nucleotide, tweak it a little bit, then it can switch to using another one. ",
"As for why small groups are linked into bigger molecules? This gives the cells a better way to discriminate between the specific molecules. It's hard to discriminate between amino acids, much easier to discriminate between two amino acids linked to distinct carriers. ",
"These carrier molecules also allow cells to subdivide pools of carrier molecules to do different things. The best example is the two electron carriers, NAD",
" and NADP",
" , one of which is used for catabolism, the other for anabolism, even though both carry out the same reaction. ",
"There also could be a random chance element, that if we ran evolution again, different molecules could play the same roles, in different combinations. But that's not an experiment we can easily carry out, running life from scratch again.",
"The Alberts Textbook has more info for the curious: ",
"http://www.ncbi.nlm.nih.gov/books/NBK26838/#A273"
] |
[
"How do cells evolve (if that's the right word) to know how to do all of this? Is it \"survival of the fittest?\" It always amazes me how they know exactly whch compounds and carrier molecules they need to interact with in order to achieve a certain task."
] |
[
"I need to do some form of chemistry experiment/investigation with my class of 10 year olds"
] |
[
false
] |
Hi guys, I'm trying to think of some way of showing a chemical reaction involving solids, liquids and gas to my 10 year olds. They obviously know a lot about melting/freezing etc, but I want to introduce to them that using chemical reactions we can also make gas escape etc. So, I've tried doing biocarbonate of soda + vinegar in a bottle with a balloon on the top, but to be honest i cant get it to work very well, it looks a bit pathetic. Mentos in diet coke is another, but again for some reason it just isn't working quite as well, and I don't wanna put a whole load of mentos/diet coke together infront of a load of kids incase it properly goes up! Problem I have is that I work in a primary school, not secondary (or high) school, so I literally have a pathetic amount of resources. Any ideas for a way I could show them (or they could investigate) some form of chemical reaction that shows gas maybe... escaping, or ... anything to do with gas really. Google has failed me! Thanks for any help
|
[
"With literally zero access to any lab chemicals I would recommend calcium carbonate being placed into water filled inverted film canisters to launch them. 10 year olds are old enough to be given a budget and a design aspect (like greatest distance per unit cost or time in the air).",
"Personally I would spring for some hydrogen peroxide and an oxidizing agent."
] |
[
"Electrolysis might be a good one. You can do it with a 9V battery, a water glass, some pencil lead, and some wire. You can also use regular wood pencils, just remove the erasers & sharpen both ends (so that the graphite is exposed). You can even hand out the pencils at the end of class as a reward, \"This pencil made oxygen!\"",
"Hook the wire to the pencil leads & the battery. Stick the other end of the pencils into the glass and wait for the oxygen & hydrogen to bubble up.",
"If the change can be physical and not chemical, another good one is the collapsing can. Get a heat source (hot plate, burner, even a candle will do), an empty soda can, some tongs and a bowl of ice water. Put some water in the can (about 1cm in the bottom is perfect) and get it boiling over the heat source. Now use the tongs to plunge the can into the ice water, open end down, the sudden change in pressure will cause the can to implode. This is more of a pressure change thing, but the water vapor may be playing a role here, too...give it a shot with and without the water in the soda can , see if there's a noticeable difference.",
"As for the bubbling thing...use wine corks. Get a plastic bottle that the corks fit snugly into. Tear a strip of tissue paper (5-6cm long) and staple/glue it to the bottom of the cork so it hangs back like a streamer. Fill the bottle ~halfway with vinegar, add the baking soda, and wedge the cork into the mouth. It should fly."
] |
[
"You can talk about sources of electricity by using the ",
"lemon battery",
"Acid/base concepts can be described with ",
"cabbage",
"A failproof way of describing the chemistry of carbonic acid in water (one of the most important polyprotic acid systems there is) can be obtained by dropping an ",
"Alka-Seltzer into 5% acetic acid solution."
] |
[
"Physics ~If a tree (or any organic object) were placed in a vacuum...?"
] |
[
false
] |
So my friend and I were sitting at a table and he asked me this question. Hopefully Reddit will have an answer! Help solve this lunch break dispute. If one was able to place a tree within a vacuum, and then raise the temperature, would the tree melt? Honestly any organic object could be substituted but hey let's go with a tree. Edit: Many thanks!
|
[
"It wouldn't melt. Most organic structures would break down in what is known as thermolysis at a lower temperature than their melting point. ",
"Your tree would probably give off carbon dioxide along with water and sulfurous compounds and end up as a chunk of carbon. "
] |
[
"This is more or less how charcoal is produced. Manufacturers use a low-oxygen environment rather than a vacuum, but the idea is the same."
] |
[
"Heat within an enclosed space. No air in rather than complicate with vacuums or other gasses. "
] |
[
"What exactly goes on behind the scenes of an MRI to keep the liquid helium a liquid?"
] |
[
false
] |
I recently started a job as a Building Operator at a new hospital and we'll be getting 3 MRI's in the coming months. The best information I can get at this point is that we supply chilled water to the "MRI system" and liquid helium goes to the MRI. I've tried googling it to no avail. As the critical point of helium is -267.96C at 227kPa(absolute), there is most definitely something besides cooling water in there.
|
[
"Traditionally, the liquid helium is used to chill the superconducting wire down to ~ 4 K. This liquid helium dewar is set within a liquid nitrogen dewar, which slows down the boiling off of liquid helium by having one need more regular liquid nitrogen fills. Given that liquid nitrogen is dirt cheap relative to liquid helium, it was a pretty popular option. Plenty of other magnetic resonance spectrometers still use this method.",
"However, liquid helium is something of a precious commodity. It is likely that the chilled water is used by a refrigerator intended to capture and liquify the boiled-off helium. This cuts down the frequency of liquid helium refills and conserves helium. See, for example, ",
"this discussion",
" of MRI hardware at \"The Basics of MRI\" (Rochester Institute of Technology)"
] |
[
"On the subject of Liquid helium, its rarity, and techniques for capturing it and reusing it, a good discussion can be seen ",
"here",
". It's a video put out by the chemistry department of the University of Nottingham. "
] |
[
"If you have to supply chilled water, then it is not a liquid nitrogen cooled system like the other commenters are saying, but likely cooled with a cryo pump to even colder temperatures. This has the advantage that it does not require frequent filling with liquid nitrogen, and the LHe lasts even longer. The down sides are needing chilled water, having another thing that can break, and a lot of electricity being used.",
"Think of it as a heavy duty refrigerator. Instead of having a radiator for the removed heat, it will need chilled water.",
"Edit: As LongUserName pointed out below, in MRI magnets cooling water is also used to cool the normal-conducting gradient coils and their electronics."
] |
[
"Where do I begin to learn General Relativity?"
] |
[
false
] | null |
[
"It sounds like you have the basic mathematical prerequisites, but if you want to really get into it you're going to have to learn differential geometry. This is covered in most good relativity texts.",
"My school's General Relativity course, which is an upper-division undergraduate/first-year graduate course, used the material ",
"here",
" but assumed the material presented ",
"here",
" as a prerequisite.",
"For a more detailed treatment that follows a more standard approach, I suggest Sean Carroll's \"Spacetime and Geometry\". The majority of this book (certainly everything you need to get a foundation in relativity) is available free online (",
"here",
").",
"If you prefer a lecture format, Leonard Susskind has a video lecture series on the subject that can be found ",
"here",
". I'm not certain of the prerequisites for that, so you might want to start with his series on the special theory which can be found ",
"here",
"."
] |
[
"Bit meta perhaps, linking a discussion thread in a discussion thread, but I remembered ",
"this interesting thread on Slashdot when somebody asked the same question"
] |
[
"Assuming that you know special relativity already, I would check out ",
" by Misner, Thorne and Wheeler. It's big and thorough and probably starts at the right place. ",
"If you don't know special relativity, learn that first. "
] |
[
"Is there anyone on reddit that does research on aging? How close are we to extending our lives past 150, 200, 500?"
] |
[
false
] |
If your close, i would love to take part. TL;DR I really dont want to die lol
|
[
"Oh dear lord, please don't cite entropy as a reason we can't attain immortality..."
] |
[
"Opinion is divided here but if its possible we should be able to start doing some age-extension in some 20-30 years.."
] |
[
"As someone else in the biochemistry department, I'd like to respectfully remind you & OP that we were convinced it would be no more than a few years after cracking the Human Genome before we cured all disease and aging issues. That was back in the 90's. ",
"Also, as someone who spends WAY to much time on thermodynamic studies, I'd like to use ",
"this",
" as a counter argument to the entire concept of \"immortality\". ",
"This is not a full counter-claim, mind you. I actually think some counter-aging techniques may be possible SOME day. The problem is that our system is always more complicated than we at first assume it to be. So it seems like we always say \"In 20-50 years we'll be able to do XYZ!\" and then the universe goes and reminds us how little we actually know..."
] |
[
"Can Radiation (Nuclear or Otherwise) melt skin?"
] |
[
false
] |
I'm writing a story that's post apocalyptic and I want to be as realistic as possible, so I want to know that, if one were to survive radiation of some sort, would the radiation itself cause your skin to melt, or would it just be the intense heat?
|
[
"All kinds of radiation produce heat, but I guess you're asking about ",
" radiation like that coming from nuclear sources, X rays or UV. In this case heat is the least of your concerns as the ionizing effect damages your DNA.",
"It won't really melt, but a high radiation dose it can cause severe burns. Subsequent infections, blistering and hemorragia may make it look like dripping fluids but I wouldn't call this \"melting\".",
"If your character survives radiation then the dose wasn't extremely high, but it may still have been high enough to cause ",
"acute radiation syndrome",
". That wiki page has a table with symptoms and mortality rates for different doses.",
"In the long term survivors may still develop a cancer."
] |
[
"Acute radiation poisoning can cause intense damage to the skin including necrosis which would have the effect of skin sloughing off but it would not be an immediate effect instead it would occur after a few hours of exposure "
] |
[
"Sure. Radiation is just energy being deposited in your body. However, a radiation dose high enough to melt your skin is going to cause unconsciousness well before that happens, and acute death as well. So it's not very realistic.",
"Radiation basically damages the molecular machinery of your cells, including the data storage mechanisms that your cells use to tell themselves what to do and how to be (DNA). High enough doses will cause enough DNA damage to trigger programmed cellular death (apoptosis), which is your cells doing their diligent duty to avoid operating in a way that could harm you (e.g. causing cancer). But they don't know whether or not too many other cells are doing the same thing. The lower levels of a lethal dose involve basically all of your fastest replicating cells dying off. Those are your hair and gut cells, so you can't really eat or digest food properly. If you're able to undergo intensive medical care you might be able to survive that phase.",
"If you get a higher dose then some of your other vulnerable cells will die as well, those are primarily your internal organs, such as your liver. This is the worst way to go, your internal organs basically stop functioning and you slowly die over months. At higher levels you become incapacitated and die within 2 days or so.",
"As to your skin, at high enough doses you will get ",
"radiation burns",
", but these are blisters, reddening, ulcers, necrosis, etc, not melting.",
"Here's a pretty good overview: ",
"https://en.wikipedia.org/wiki/Acute_radiation_syndrome"
] |
[
"What are some failed traits that arrived due to evolution?"
] |
[
false
] |
If I understand it correctly, evolution is random genetic mutations that allow a species to out-compete other animals and gain in edge in the competition of the life cycle. Then shouldn't there be some random genetic mutations that ended up being either completely useless or actually hurting the animal? What are some traits from any animal that have this behavior?
|
[
"Not sure if this comes under your question ",
"but the Kakapo has lost the ability to fly but sometimes forgets this and when startled will run up a tree, jump and come crashing to the ground.",
". An interesting conflict of current evolutionary state vs instinct."
] |
[
"The obvious answer is any kind of ",
"vestigial trait",
", some notable part of the organism that no longer serves a purpose. There are many well known examples - animals in dark caves with eye sockets in the skull but no eyes, the appendix, snake leg remnants, and so on. The linked article lists many more.",
"Another exmaple that seems to fit your criteria is ",
"genetic disorders",
". Famous examples in humans include cystic fibrosis and Huntington's disease. In this case, the organism has genes that actively harm it in relation to most others of its species. Some such diseases are more or less plain bad, but for others the situation is more complex For instance, sickle cell anaemia is a disadvantageous trait when inherited from both parents, but having a single copy of the gene grants resistance to malaria."
] |
[
"humans useless - pinky, appendix, tailbone.."
] |
[
"Why does the sum of all positive integers equal -1/12?"
] |
[
false
] | null |
[
"You can find the basic answer with a simple Google search / on wiki. Please start there and come back with a more specific question."
] |
[
"I've been down that rabbit hole. This problem goes at least as far back as Ramanujan, maybe considerably further. I am trying to understand it's usefulness in physics and the redefinition of the equals sign in modern proofs. Mainly i want to understand the physical relevance of utilizing that value. The answers i have been able to find are either handwavey or highly technical. Was hoping for some expert insight."
] |
[
"That's a different question from the one you posted. I recommend a new post with a clearer title. Otherwise you'll get a bunch of responses that are just links to the numberphile video"
] |
[
"What is the pizza slice shape called?"
] |
[
false
] | null |
[
"Since it consists of two lines and an arc, it's a ",
"sector",
". Or more specifically, a minor sector, since it's smaller than a semicircle."
] |
[
"Don't it's angles measure more than 180 degrees on a flat surface? ",
"They do. If perfectly sliced from a perfectly round pizza, the sum of the angles of a slice will be 180 + 360x, where x is the fraction of the pizza, i.e. x = 1/8 = 0.125 if each slice is 1/8 of the pizza. Since the sum is greater than 180° for a non-infinitesimal pizza slice (due to the rounded side), any pizza slice that isn't infinitely small is non-triangular.",
"An infinitely small slice of pizza is arguably triangular, but it's also not an actual pizza slice, making the point moot."
] |
[
"I believe this is the correct answer. Now, if the sector is revolved along the axis between the origin and the center of the arc it would become a ",
"cone",
".",
"However, I am curious, would there be a name for a circular sector that is extruded in the z-direction, assuming the pizza is flat along the xy-plane?"
] |
[
"Graphene Applications - Hype or Real Promise?"
] |
[
false
] |
[deleted]
|
[
"I would say real promise, with a lot of engineering difficulties in the way. There are a lot of interesting effects that can be manipulated, creating new types of devices. Timescales are difficult to predict, but if you look at something like silicon, it took a few decades to really become applicable.",
"P.S. This is my thesis statement.",
"Since graphene was first isolated and functionally discovered in 2004, it has generated enormous amounts of interest in the condensed matter community. While graphene's potential for high quality electronic devices has all but ensured continuing interest as well as funding for years to come, this unique material also serves as a testbed for interesting and even unseen physical effects. A related, yet vastly different system is bilayer graphene, composed of two monolayers stacked together. Bilayer graphene hosts as much potential for applications and curious phenomena as its single layer cousin. This thesis will address some of the novel effects that can be realized in monolayer and bilayer graphene, and relate those effects to experimentally measurable quantities.",
"P.P.S. Can't you just go down to the second floor and ask the people there?"
] |
[
"What basis do you have for your 30 year timescale estimate? It seems like a wild ass guess as much as anything.",
"The discovery of graphene won a nobel prize not based on applications but because it was a newly discovered allotrope of carbon with quite unique and interesting properties.",
"As far as applications, it's hard to say, research is only beginning. The reason people are excited about graphene is that it has several remarkable properties that no other material has and may be suitable for unique application. Until we have more research it's impossible to say which way or the other whether such enthusiasm is completely warranted. That being said, if you see a lottery ticket trapped under a heavy rock and you can make out most of the digits and they all match the winning ticket, it's probably worth the effort to lift the rock and find out whether it's a winning ticket or not."
] |
[
"You keep your condensed matter experimentalists aboveground?!"
] |
[
"What happens to veins when an arm or leg gets amputated? (x-post from AskReddit)"
] |
[
false
] |
[deleted]
|
[
"As you move closer to the heart, veins get bigger. These bigger pipes are supposed to bring blood alllll the way down to your fingers and toes. When arms or legs go choppy-choppy, the bigger veins are tied off, or dammed up like rivers, because they no longer need to bring blood alllll the way down to your fingers and toes. But guess what? Brand new veins grow out! This way, blood isn't just hitting the new dam and sitting there, but actually gets to go round and round like all the other fun bloods do.",
"The human body: YAY!"
] |
[
"Surgeon. As the vein moves proximally it increases in size to accommodate a larger volume of blood from venous side branches. Similar to a river with its tributaries. This flow from \"tributary\" veins is not interrupted in the \"upper part\" of the remaining limb. However, there are many venous and arterial vessels that are ligated during the procedure. Through a called \"neovascularation\" new blood vessels begin to grow almost immediately. Hope this helps."
] |
[
"so does that mean the capillaries nearest the cutoff point of the artery start to expand and grow rapidly to deal with the increased pressure? Or is it part of the procedure to link the major artery and vein together to prevent what would be massive swelling?"
] |
[
"DNA tests usually take weeks to accomplish. The tests to prove that Bin Laden was killed took mere hours. In the field? What technology was this?"
] |
[
false
] |
Just surprising, that is all
|
[
"If you have the comparison sample the DNA test takes a few hours. It takes weeks when you send it into a giant lab that keeps thousands of other tests on back order because they have fewer technicians monitoring the reactions. All you have to do is extract the DNA from the cells, PCR out the RFLP/VNRs and then run a gel, should take about 12 hours max. I could do a diagnostic DNA assay in a day in the lab."
] |
[
"The US Navy has hospital ships which would be equipped with a full lab to run normal medical testing. A PCR machine would be pretty standard in this setting."
] |
[
"... And instead of running it on a gel running it on a lab-on-a-chip takes a few hours off, again.",
"In our diagnostics lab, it takes months, but that's only because it's cheaper AND, ultimately, more efficient to do batches of samples together instead of one sample at the time. Plus, as in diminutivetom's lab, there is a shortage of technicians and an overload of work..."
] |
[
"If I let go of an apple, does it immediately accelerate at 1g or does its acceleration also have a rate of acceleration?"
] |
[
false
] | null |
[
"If you let go of the apple instantaneously, it accelerates instantaneously. The real process of dropping an apple, however, involves reducing the grasping force over some short finite period of time, causing the apple's acceleration to itself accelerate up to ",
" during that short time your hand is still interacting with it. "
] |
[
"Without \"forces like air resistance\", there is no terminal velocity and acceleration continues indefinitely until collision. Terminal velocity is a function of forces like air resistance on a particular object, counteracting the acceleration of gravity.",
"Also, acceleration due to gravity at Earth's surface is 9.807 meters per second squared. This is convenient because it can be rounded off to 10 m/s",
" for quick-and-dirty calculations (and can help you remember it)."
] |
[
"Without \"forces like air resistance\", there is no terminal velocity and acceleration continues indefinitely until collision. Terminal velocity is a function of forces like air resistance on a particular object, counteracting the acceleration of gravity.",
"Also, acceleration due to gravity at Earth's surface is 9.807 meters per second squared. This is convenient because it can be rounded off to 10 m/s",
" for quick-and-dirty calculations (and can help you remember it)."
] |
[
"Iron is the element most attracted to magnets, and it's also the first one that dying stars can't fuse to make energy. Are these properties related?"
] |
[
false
] |
That's pretty much it. Is there something in the nature of iron that causes both of these things, or it it just a coincidence?
|
[
"Nope! Unrelated!",
"Stars can't fuse past iron because iron-56 has the lowest mass per nucleon, and so no energy can be released (by E=mc",
") from fusion- it's basically nuclear ash and all possible energy for nuclear reactions has been spent. ",
"Magnetism is not a nuclear physics phenomena, but an atomic physics phenomena. 'Ferromagnetism,' the kind of permanent magnetism you're used to experiencing in iron, is a consequence of the structure of the atomic electron orbitals and their occupations. ",
"Point being- one is a nuclear physics phenomena and the other is an 'electron' physics phenomena"
] |
[
"Nuclear ash is a beautiful description for iron. It makes it make so much more sense."
] |
[
"Excellent thought!",
"https://en.wikipedia.org/wiki/Iron_star",
"If you look at current theories regarding the far future of the universe, one of the main puzzles is whether or not protons decay. If they do, all matter will just eventually decay, leaving only black holes (which eventually will evaporate via Hawking radiation) and radiation. However, if they don't, then the formation of structures called \"iron stars\" becomes possible.",
"Given enough time, all stars that don't collapse to neutron stars or black holes will eventually cool to become hunks of dormant matter near absolute zero. Iron stars form when you wait long enough for random quantum tunneling events to induce cold fusion in these hunks. Given enough of these events, all the matter will eventually fuse to iron-56, which has the lowest energy state. Then if you wait even longer, iron stars will eventually collapse into neutron stars and black holes due to even lower probability quantum tunneling events.",
"The timescales for iron stars are insane:",
"There are some more details at this link:",
"https://en.wikipedia.org/wiki/Timeline_of_the_far_future#Earth,_the_Solar_System_and_the_universe",
"Edit: If you are interested in the far future, I highly recommend ",
"this 30-min video",
". Very entertaining and ",
" high production quality, as well as very educational."
] |
[
"What exactly are frequency and amplitude in radio waves? Do photons actually move up and down along a single plane as they travel?"
] |
[
false
] |
Radio waves are always visualized in 2 dimensions on an osciloscope. Is this how they actually travel through space as well, or do they just move in a straight line?
|
[
"You can think of the field being the sum of many many photons.",
"It's not really useful to treat radio waves in terms of photons."
] |
[
"The amplitude is the magnitude of the transverse electric field (measured in volts per meter) or magnetic field (measured in Tesla). The transverse fields oscillate as the waves propagates."
] |
[
"Does the photon cause the field to oscillate? Or is it just riding the wave of an already oscillating field?"
] |
[
"Can plants become obese?"
] |
[
false
] |
I tried a bit of googling, but all the results ended up pointing back to obesity in humans. From wikipedia, obesity is defined as "a medical condition in which excess body fat has accumulated to the extent that it may have an adverse effect on health, leading to reduced life expectancy and/or increased health problems." Are there plants that take in so many nutrients ("eat" too much) that they reduce their life expectancy? Does the concept of obesity even apply to plants or other flora?
|
[
"In a way, you could say that crop potatoes are wild potatoes bred to be obese: to store ridiculous large amounts of starch...",
"(ok this is not obesity, but it's nice to think about it that way.)",
"Nevertheless, drawing a broader parallel: obesity is storing so much \"reserve\" that it becomes very unhealthy. Many crop plants store so much \"reserve\" in their organs that it becomes interesting for us to harvest. This is also \"unhealthy\" for the plants: they are ",
" in that they wouldnt survive this way in nature. Thats why we need to use pesticides to kill the competion (weeds), to keep our plants alive in agriculture...",
"EDIT: grammar"
] |
[
"That's not the way plants work. They make their own energy rather than taking it in from the environment in their \"diet\". Plants store their energy in the form of starch rather than fat. They use this starch to either grow or reproduce. Some plants store lots of starch in their roots (eg potatoes), but the concept of obesity just does not apply to plants in the same way as it does for animals"
] |
[
"Right. I'd like to add that when when plants are making too much energy (more than gets used up for growth or starch reserves), they ",
"reduce their rates of photosynthesis",
". "
] |
[
"Why does ice melt faster in hot water than in hot air?"
] |
[
false
] | null |
[
"Heat transfer (in this case) is all about convection/conduction. This occurs when molecules of one medium collide with molecules of another. Water is much, much denser than air (almost 1000x denser), so it follows that there would be more contact between water and ice than between air and ice. More collisions/second mean faster heat transfer."
] |
[
"Water is a good conductor of heat; it transfers energy into the ice faster. Water has a high specific heat; it can give up a lot of energy without changing temperature very much. (The ice will be the same. It needs a lot of energy to increase in temperature and to melt. But the water is better able to provide that than the air.)"
] |
[
"Although you didn't explicitly say this, someone might assume the implication of ice having the thermal properties of water, which isn't the case when they are at the same conditions. Iirc, specific heat of water is about double ice's at the melting point at standard pressure, and I think the thermal conductivity of ice is higher."
] |
[
"Why does the standard model have 3 versions of gravity and none of them are compatible with actual gravity (relativity)?"
] |
[
false
] | null |
[
"However, in an accurate model, the Higgs, the graviton, and the \"three generations of matter\" should all be fundamentally - \"the same\". How is this not \"dramatically bad\"?",
"None of those are the same thing. The Standard Model of particle physics doesn't include gravity at all. It includes the Higgs and three generations of fermions, but neither of those is related to gravity."
] |
[
"when you say ",
"The Standard Model of particle physics doesn't include gravity at all.",
"is it your position that mass is not directly related to gravity and that velocity is not directly related to mass? I mean - it seems to me that any model that includes mass or allows for movement \"includes gravity\". I would think anything else is multiplying entities without necessity."
] |
[
"Mass is relevant to gravity, but having particles with mass in your theory doesn't imply that you've included gravity."
] |
[
"How does a sphere of light (like the Sun) emit light in all directions?"
] |
[
false
] |
Say you have the sun as a light source and you place that sun/sphere in a spherical enclosure very far away and measure where light was absorbed. Since the enclosure is at a very large distance, shouldn't there be discrete points on the enclosed sphere that does not detect light because the source sphere would need an ever increasing angular precision to output light to reach every point on the enclosed sphere.
|
[
"Yes, if you try to measure x-rays from very distant sources, for example, they only arrive one at a time."
] |
[
"Right. If you have a uniform sphere emitting light (which the sun isn't with sunspots and such, but it's close), when people say it emits light uniformly in all directions, they mean that there is an equal probability that the next photon emitted will be headed in any one direction, not that it emits photons in all directions constantly or at the same time. (I think this is the point of the question?)",
"You just can't really tell because the sun is emitting something like 10",
" photons per second, which is a ridiculous number. In theory if you go far enough away from the sun you could set up a detector that would only detect one photon at a time. If the sun is uniformly emitting light, then it wouldn't matter where that detector was on a sphere, it would detect single photons at the same average rate, but not at the same times. The same can be said for uniform x-ray sources that emit photons at much lower rates."
] |
[
"the blips will get so close together as to seem ",
".",
"Continuous, not discreet?"
] |
[
"Why is 1080 poison (sodium fluoroacetate) so toxic to mammals but less dangerous to other animals?"
] |
[
false
] |
1080 is a pretty controversial subject here in New Zealand, but it's pretty widely used as a pesticide because it's pretty toxic to mammals (of which, we only have two native species) but less toxic to other kinds of animals (specifically, our native birds and reptiles that are often killed by possums). I kinda understand why it's toxic to mammals, but what's the difference between how mammals work and how, say, birds work that make it less dangerous to birds? Or is it something else about it? Thanks!
|
[
"I did a quick search on it. As a preface, I am a biochemist, so I approached the problem by looking at its toxicology.",
"So, the fluoroacetate ion is metabolized by mitochondria (which normally metabolize acetate at a certain point). This generates a toxin that binds to aconitase, one of the enzymes used in the generation of energy for cells. So, any obligate aerobic organism can be poisoned by this compound.",
"Why is this poison more robust in mammals? I couldn't find anything in a cursory search, but I will posit a few guesses (maybe this will spark someone else to dig a little more?) One possibility is the enzyme has a slightly different form in avians. The binding of the toxin to the aconitase probably has different mechanics if this is the case. Another possibility would be in the regeneration of the aconitase. All a cell has to do to \"detoxify\" is out produce the amount of enzyme that is being inactivated (I doubt this is the case, but isn't outside of the realm of possibility). Another possibility, though extremely unlikely, is that they have a way to inactivate the fluoroacetate before it reaches the mitochondria. This would require an enzyme that has been found in some soil bacteria. A more likely way for the toxicity i be decreased would be if avians had an enzyme that sequestered the fluoroacetate. This would never allow it to be metabolized into a toxin.",
"Sorry to leave such a response with no final answer. If I could find research comparing aconitase from different organisms, I would be able to give a more definitive answer. "
] |
[
"Might also be their Acetyl CoA synthetase having a lower affinity for fluoroacetate."
] |
[
"So fluoroacetate works by integrating into the citric acid cycle (Krebs cycle) by substituting for acetate to form fluorocitrate and then disrupting this key cycle by binding tightly to aconitase which prevents this critical cycle from functioning and killing the poisoned organism. It does affect birds as well although reptiles are much less susceptible. Generally birds aren't as attracted to the baits though - they are deliberately coloured to avoid birds eating them and DOC has determined quantities etc that minimise the potential bird effects. It still does effect them though - kea have a 12% mortality rate in areas that have 1080 drops but this is a significant improvement from their losses to rodents if the population explodes",
"Good review is ",
"here",
"(pdf) and DOC's FAQ is ",
"here"
] |
[
"Why did my red popsicles freeze before the others?"
] |
[
false
] | null |
[
"Different solutions freeze at different temperatures. A simple example is that water will freeze at 0 but salt water will freeze at -15. This is because of a change in the intermolecular bonding of the solution. The solutes (to add colour and flavour to the popsicle) that were included with the red popsicle increased the freezing point more than the solutes added to the other popsicles.",
"edit: It is technically also possible that EMR levels due to colour played a part, but if radiation heat transfer is dominating in your freezer you probably need to think about downgrading from the illuminated vaccuum freezer to a dark air filled one like the rest of us shmucks."
] |
[
"That's pretty neat. Thanks for the response."
] |
[
"From what I know about colligative properties, the red dye (and flavors, etc) probably decreased the freezing point less than the chemicals in the other popsicles. I've never heard of anything that raises the freezing poit of water."
] |
[
"Does the volume of gas in your intestines expand when on planes?"
] |
[
false
] |
[deleted]
|
[
"sure, but it all depends on how much intestinal gas is in each individual.",
"there are various types of \"",
"barotrauma",
"\" that can occur from the pressure change. the most interesting, for me, is your teeth exploding from the trapped gas in a filling. "
] |
[
"sure, but it all depends on how much intestinal gas is in each individual.",
"there are various types of \"",
"barotrauma",
"\" that can occur from the pressure change. the most interesting, for me, is your teeth exploding from the trapped gas in a filling. "
] |
[
"yes. even though most commercial flights are in pressurized cabins, the cabin pressure is less than that of where you departed. boyle's law explains the (inverse) relationship between volume and ambient pressure (",
"http://en.wikipedia.org/wiki/Boyle's_law",
").",
"this is one of the many things you are to learn during flight training/ground school."
] |
[
"Can you cool a room with candles?"
] |
[
false
] |
I recently read about a heat-sink table, the manufacturers of which claim that it can help cool a room to 71F. The table uses aluminum and wax to act as a heat-sink; the wax absorbs energy from the room as internal PE, decreasing the thermal energy of the room without increasing the temperature of the wax. This makes sense to me given my current understanding of thermal physics. But would this work the same way if you just placed a lot of candles in a room? I get that the surface area of the wax plays a role in the process (tiny wax balls in table have a much larger surface area/volume ratio), but could it theoretically work if you just had a lot of small candles? Table:
|
[
"say it was 80F in my house, and I moved one of those tables in, it should start to cool the room correct?",
"And the table will stop cooling when all the wax melts, and from then on it's just like an ordinary table.",
"In order for the table to work again, the wax has to re-harden, which only happens when the temperature drops below 71 F.",
"So if your room has constant cycles of temperature, like 68 F at night and 76 F during the day, the table will even them out so that the temperature remains within a narrower range.",
"But if your room temperature never drops below 72 in the summer, the table is useless."
] |
[
"That table does not cool or heat like an AC or heater. It evens out temperature fluctuations. The wax melts at 71F, taking advantage of the ",
"latent heat of fusion",
". Ideally, your candles would have to melt at 71F also, but any mass with a greater heat capacity than air would do the same thing to a lesser degree (that's sooo intended). "
] |
[
"I get that it doesn't act in the same way as an AC, in that you can't turn it on or off, but say it was 80F in my house, and I moved one of those tables in, it should start to cool the room correct? If we're taking advantage of its latent heat then we're in agreement that energy is being transferred from the room to the wax. The air certainly isn't undergoing a phase change, so it must be decreasing in thermal energy, and therefore must be dropping in temp. If we apply the thermal properties for parrafin wax, for example, then by my math 1kg of wax could cool a 125m",
" room by a little over 1.5C. Am I off on that?"
] |
[
"Are imaginary and complex electric charges possible?"
] |
[
false
] |
Charge as I understand it works like a number system; with increasingly positive charges on one end of the numberline and increasingly negative charges on the other end. However, when you think of charges as numbers you have to ask about imaginary and complex numbers. Could a particle have a charge of i?
|
[
"You can develop a theory of electromagnetics where imaginary numbers are used to represent magnetic charge. The math comes out surprisingly cleanly. In fact, Maxwell's Equations are invariant under rotation in the (q_e, q_m) plane - which is both surprising and cool, and unsurprising and boring, depending on how familiar you are with deep particle physics and the ties between symmetry and physical law -- and on how blasé you are about finding surprising symmetries in nature.",
"Given that symmetry (of Maxwell's Equations, between electric and magnetic charge) it's somewhat surprising that all the observed charge in the Universe happens to lie on a single line on that plane. (",
"There may be exceptions, but if so they are exceedingly rare",
")."
] |
[
"Charge is a physical property while imaginary numbers are an abstract numeric property. ",
"While complex numbers are ",
"useful in electrical engineering and Signal analysis",
" when doing calculations involving sine waves / alternating current, a physical property like charge can't be complex itself, it would be like having a mass of 2i kg.",
"I'm curious what got you thinking about it?"
] |
[
"Imaginary and complex numbers are just repesentation. If you think about it, there isn't such thing as \"negative\" numbers in nature either, but it is extremely usefull, and quite intuitive to use when describing things. Complex numbers are very usefull too, just not so intuitive to see."
] |
[
"I just read that the heat death of the universe is predicted to be approx 10^103 years from now, how was that number calculated?"
] |
[
false
] | null |
[
"Where did you read that?"
] |
[
"The heat death of the Universe occurs when there is no more practical thermodynamical differences left in the entire Universe. Every point in the Universe has the same energy, the same entropy, and as such no energy will be exchanged anywhere and no work can be done. For this to occur all objects in the Universe must radiate away all their energy through one process or another and then the radiated energy must have time to be distributed homogenously across the entire Universe. The longest lived objects in the Universe are black holes and those have a life time of around 10",
" years, only radiating through Hawking radiation.",
"Since parts of the Universe are separated by volumes of space that are expanding faster than the speed of light the only feasible way for a totally homogenous distribution of energy is to wait for all radiation to be red shifted until it reaches some theoretical lower limit, an absolute zero. This era of the Universe is usually called the Dark Era. It is very possible that quantum effects will have far reaching implications before things reach the absolute zero, which could prevent a total heat death of the Universe.",
"You would also have to wait for all elements to decay through radiation, but that happens in an instant compared to black holes dying out, so we don't have to worry about stray atoms lying around when tackling this question."
] |
[
"That's roughly the length of time that it will take for the largest supermassive black holes to completely evaporate. ",
"To put that in perspective: The amount of time required for those same supermassive black holes to emit even a single particle is much greater than the current age of the universe.",
"So yeah...10",
" years is a very very long time."
] |
[
"How are submarines always balanced?"
] |
[
false
] |
If the submarine is moving forward on the x axis (for reference), how do submarine crews and the engineers that build them avoid rotations around the x axis, or the y axis (e.g. too much weight in the front compared to the rear)?
|
[
"Submariner here; there are an equal amount of ballast tanks on both the port and starboard side of the submarine, usually found more forward and aft of the ship, these are carefully weighed and monitored on a regular basis, and depending on the weight of each individual tank, the ship has different trims and lists. Hope that answered your question. "
] |
[
"/u/Erxkeel94",
" is correct, but I will add just a bit from the deep-diving perspective.",
"Submersibles remain upright underwater by providing floatation ",
"syntactic foam",
" high on the vehicle and weight low. This generally keeps things vertical, but there are ballast tanks as well. Water can be pumped to maintain neutral buoyancy, since water becomes more dense at depth you need to be able to adjust. This is non-trivial at a few thousand meters.",
"In ",
"Alvin",
" mercury is pumped to control fore-aft trim."
] |
[
"They got many ballast tanks (front/back/etc) and they just adjust them until the ship is level. But that really only matters when they are stopped and hovering. Once they get moving their diving planes can provide lift and level out anything minor (and that's actually how the military ones surface, just point up and go up), the main ballast tanks are not normally pumped empty, they are drained empty when surfaced (except for emergencies)."
] |
[
"Do psychostimulants such Adderall, Vyvanse, and Ritalin, in a sense make you \"smarter\"?"
] |
[
false
] |
[deleted]
|
[
"Adderall is an Amphetamine yes, Methamphetamine No.",
"Its not the same.\nAs far as affecting people differently, as i understand it it does NOT affect people differently. It has the same effect on the brain but rather that Manifests differently on account of the existing brain chemistry its engaging. (i will try and find the article that explained this...but it may take me some time, i only hope someone else will beat me to it)"
] |
[
"Straight from the ",
"Adderall labeling info from the FDA",
":",
"Pharmacodynamics\n\"Amphetamines are non-catecholamine sympathomimetic amines with CNS stimulant activity. The mode of therapeutic action in Attention Deficit Hyperactivity Disorder (ADHD) is not known. Amphetamines are\nthought to block the reuptake of norepinephrine and dopamine into the presynaptic neuron and increase the release of these monoamines into the extraneuronal space.\"",
"It is known that amphetamines, or other stimulants like coffee, improve cognitive functioning. Making you \"smarter\" is not really an accurate measurement, but improved performance in certain tasks is.",
"This article",
" says the following:",
"Conclusions. Deficits in executive functions related to spatial working memory do occur in children with ADHD, although the magnitude of these deficits is not related to the child's age or the level of ADHD symptoms. These deficits were not present in the current sample of children who were receiving psychostimulant medication."
] |
[
"Methylphenidate (Ritalin) acts by decreasing reuptake of dopamine and norepinephrine from the synaptic cleft. The increased focus is thought to be mediated by the increased dopamine, but the NE effect tends to dominate and the end result is very similar to an amphetamine.",
"Among many worries with prolonged use of methylphenidate are tolerance and rebound, and serious complications can occur both peripherally (blood pressure, circulation problems) and centrally (psychosis, aggression, tics).",
"Like any of our nootropics, any benefit comes with a cost, so use should be reserved for patients who are unable to function without intervention. Recreational or frivolous use is severely contraindicated."
] |
[
"Is it possible to start producing large quantities of antimatter if the same amount of money that was spent for uranium enrichment back in the day was spent on antimatter production facilities today?"
] |
[
false
] | null |
[
"No way.",
"The current Antiproton Decelerator at CERN makes on the order of 10 million antiprotons once per minute by slamming a beam of about 10 trillion protons into an iridium target. The antiprotons are then steered into a beam in a holding ring. ",
"Just for the sake of argument, lets say we industrialized this process and increased the yield by a factor of one million, even though I can't even imagine the energy and resource cost to do such a thing.",
"Then you would be producing 10",
" antiprotons per minute, or on the order of 10",
" antiprotons per year. ",
"This means in a year you would have under 0.02 milligrams of antiprotons, assuming that you figured out a way to store them. Note that the current record for storing electrically neutral antihydrogen atoms is just 38 atoms at the CERN ALPHA experiment.",
"With that 0.02 mg of antimatter, you could release under 2 gigajoules (GJ) of energy. This is the same amount of energy as is available in a 15 gallon tank of gasoline."
] |
[
"He's also a wonderful person and a hell of a lot of fun to be around. But he lets his enthusiasm and his optimism get the best of him, and when he's speaking to an audience he ends up saying things that are, frankly, quite silly."
] |
[
"The production of antimatter with current technology simply takes more energy than the energy released in matter-antimatter reaction AFAIK."
] |
[
"Why doesn't ozone form as a 'triangle'?"
] |
[
false
] |
O3 forms a bent shape, with two single bonds, each of which are double bonds half the time. Wouldn't each of them being connected in a triangle of single bonds be far more stable?
|
[
"You would think right? But the problem comes in when you concider bond angles. To form a triangle the bonds would need to have an angle of 60° but according to VSEPR theory the bond angle on an atom with two bonding and two lone perfers to be at 104.5° (Edit: Note VSEPR is fairly simplistic but its in the right ballpark). This creates a situation known as ring strain. ",
"Ring strain creates instability, and the amount of ring strain in cyclic ozone makes it very unlikely to form and remain stable. "
] |
[
"Ah that makes sense, the three dimensional angles involved in VSEPR always confused me."
] |
[
"They’re based on the electrons repelling each other, therefore creating the most spaced out shape where all the “branches” are as far as possible from each other’s repulsion. Remember that the electrons all have the same charge, therefore want to be as spaced out as they can be."
] |
[
"Could micro black holes be used to simulate gravity on space ships?"
] |
[
false
] | null |
[
"Not really.",
"A micro black hole still only has the mass of the thing that formed it. So if I squished you enough that you became a black hole it'd be very small but its gravitational attraction would be no more than you as a regular person (which is to say not much at all).",
"To get 1g of gravity from a black hole you'd need to squish the earth into a black hole. That black hole would be about 2 centimeters across so pretty small. Of course now your space ship needs to move the mass of the earth...good luck with that.",
"Also, as black holes get smaller it is believed they will evaporate faster due to Hawking Radiation. Stellar mass black holes evaporate this way too but very, very slowly. The smaller you get the faster the process occurs. For really small black holes like an earth sized one it would not last long at all."
] |
[
"This isn't quite true, as the force of gravity depends on r",
" as well as M. You can get a force of 1g from a black hole with a mass of a mere 6×10",
" kg - peanuts compared to Earth's 6×10",
" kg! You just need to be stood two metres away from it. Of course, the tidal force is pretty severe here (if your feet are two metres from the black hole and your head is a further two metres away, the field difference from your head to your toes is about 7.5N/kg), and this is still a pretty ridiculous amount of mass to be hauling around.",
"There is, of course, also the minor practical difficulty of how exactly you fix a black hole in place and move it around, since you can't touch it or manipulate it by any method other than waving large masses around near it so it's attracted to them."
] |
[
"Interesting, thanks!"
] |
[
"Why did the I-5 bridge in Washington collapse?"
] |
[
false
] |
Can someone also describe "functionally obsolete?"
|
[
"It was designed in the 1950s and was an obsolete and dangerous design. Structural Engineering back then was downright primitive compared to today. That bridge design was \"fracture critical\" meaning failure in a single area could cause the entire bridge to collapse. Modern bridges are designed to sustain damage to multiple critical areas before failure. ",
"Think Jenga - if you build a tower without any middle blocks, removal of a single block anywhere will cause the tower to fall. Modern bridges have all 3 bricks and can survive lots and lots of bricks being removed. ",
"An oversized truck struck and damaged a crucial part of the bridge which caused it to collapse. This was a series of human errors. The truck had a lead car to look for obstructions and didn't spot the low clearance, the trucking company was issued permits for the route saying it was safe, and the bridge wasn't marked as a low obstruction. Only overhangs lower than 14' were required to be marked, this bridge was 14'7\", and the truck was 15'9\"."
] |
[
"The bridge is ",
"\"statically determinate\"",
" meaning the number of degrees of freedom is equal to the number of equations. This means that there is only one possible path the load is carried by. ",
"In contrast, modern structures are statically \"indeterminate\" with more degrees of freedom than equations requiring an approximate solution. The load in an indeterminate system will be carried through the path requiring the ",
"least amount of potential energy",
". When a part of the structure is damaged, the path of least potential energy will change and the load will now be carried differently. This will be true until the development of a mechanism in the structure."
] |
[
"\"Functionally obsolete\" does not necessarily mean old and worn out. It means it no longer meets the needs of the area/modern transportation while being perfectly safe structurally. This could mean it is too small: narrow lanes, low clearance, one lane only, etc. or it could have a low load-carrying capacity and not be able to support some semi-trucks or construction equipment etc. ",
"Edit: Link to ",
"ASCE description of conditions"
] |
[
"Can diamonds be manufactured by focusing a high power laser at graphite in a controlled atmosphere?"
] |
[
false
] |
The High Pressure High Temperature method uses a solid piece of graphite to create a diamond under conditions that simulate the natural process, whereas the Chemical Vapor Deposition method doesn't seem to need the high pressures, just high temperature plasma, a rather particular set of gasses, and rapid cooling. Industrial cutting lasers regularly vaporize steel and aluminum, which requires localized temperatures of 5000+ degrees F. Assuming an atmosphere (possibly pressurized) of Argon, Methane, and Hydrogen, could you use shoot an industrial laser at graphite (solid sheet, powder, whatever) and form a diamond?
|
[
"Just looking through the literature, it appears that low quality diamond can be produced this way, but not big sexy gemstones.",
"http://www.chm.bris.ac.uk/pt/diamond/pdf/drm13-661.pdf"
] |
[
"That's probably interesting more for the mechanism than the actual crystals. You can find diamond nanocrystals just in an ordinary ",
"candle flame",
". (although that discovery got some publicity, I don't think it really surprised many, not me at least) Vaporize a lot of carbon and some of them will statistically link back together as diamond, just as fullerenes are also produced in soot.",
"What we don't really understand well is how it all happens and how to influence the process. The whole thing occurs in situation far from thermal/thermodynamic equilibrium after all."
] |
[
"Just shooting a laser at carbon wouldn't produce a diamond in itself. But you would vaporize carbon atoms which ",
" re-settle to a diamond structure. But that is simply CVD with a different method of producing the plasma, which is the easy part. You can produce a graphite plasma from sticking a pencil lead of suitable length in a household microwave. ",
"The hard part is figuring out the substrates, pressure, gas mixtures etc that are conducive to forming a diamond film. "
] |
[
"Observation and quantum physics: What defines who or what is an observer?"
] |
[
false
] |
For example, in the classic double slit experiment, the wave form collapses into discrete particles when measured. Do we know if the physical existence of the inanimate detector causes the collapse, or does it happen only if the detector records the data, or if the collected data is observed? Some examples.. does the wave collapse if: The detector is not connected to anything? The data collected by the detector is not recorded? The data is recorded by not accessed? The data is accessed by a laboratory rat but not a human?
|
[
"There is a lot of confusion about the word \"observer.\" It sounds like it means \"dude looking at it\" but really it means something that forces the system into a definite state."
] |
[
"It's a correlation between the system, the detector, and the environment that makes the measurement irreversible. If your detector is small and isolated, it's possible to have your detector in superposition, entangled with the system it measured. So you could undo the measurement by reversing the measurement process ",
" your detector is very simple and very isolated, and it was the only thing recording the measured info. Then it's possible to basically run the detector backwards and undo the correlation process.",
"Once the info leaks from the detector to the environment, the process is effectively irreversible. It's like trying to unscramble an egg basically. Or a better analogy would be trying to delete a naked photo from the internet. It's out there, you're not getting it back. This process is called decoherence, it's essentially runaway entanglement that ensures that any future measurement of the system is consistent with the first measurement. It's not actually necessary to suppose that anything is collapsing, although that is often a simpler way to teach it."
] |
[
"The 'observer effect' basically means in order for us to measure something, we have to alter the state of it. If we want to see something with our eyes, we rely on photons emitted/reflected. This involves an interaction between a photon and the matter we are observing.\nThe same principle applies whatever your measurement method is.",
"So if you wanted to measure the position of an electron, we need to have a probe. We could use a photon, but in the interaction between the photon and the electron, energy is exchanged and the momentum of the electron changes, thus altering the state."
] |
[
"If doctors can fit babies with prescription eye ware when they can't talk, why do they need feedback from me to do the same thing?"
] |
[
false
] | null |
[
"Pediatric patients are fitted with eyewear based on prescriptions from mostly just the autofractors as jaimemaidana pointed out. This gives a really good estimation of the corrective lens prescription. A ballpark or rough estimation of the prescription.",
"Once someone learns his/her abc’s or sometimes shapes a phoropter may be used. The device that sits in front of your face, and you are asked if one or two, or a or b looks better as you are looking at an eye chart. This allows for an even better prescription to be determined. The phoropter may be used by itself or it may be used to fine tune the prescription that the autorefractor read, so you get the best possible vision.",
"It’s not that an adult’s autorefratcor generated prescription couldn’t be used, but your doctor wants your eyewear to have the best chance for giving you the best possible sight."
] |
[
"You will find most paediatric prescriptions are done with retinoscopy, a baby that young can't sit till for an autorefractor. "
] |
[
"As someone who used to work at an optometrists this doesn’t surprise me at all. Adults even have trouble sitting still for an autorefractor. I used to cringe when I had to do pretesting on kids, they just can’t sit still! "
] |
[
"Is there any way to release dopamine at will?"
] |
[
false
] |
I was thinking that maybe there is some way to release dopamine in order to enjoy doing tedious or otherwise stressful tasks. Anything? Preferably legal, but anything will suffice. Anything that you could use discreetly or easily without getting caught or maybe just being able to release it by just thinking about it or releasing it at will. Just curious
|
[
"Sure. Dopamine is the pleasure/reward chemical of the brain (in certain areas, in other areas of the brain it does other things as well, such as regulate movement. See Parkinson's disease).",
"Anything that makes you happy releases dopamine in your brain.",
"Think happy thoughts, dopamine will be released... simple as that. Think about your last great date with you gf, or think about the last time your dad and you went fishing, or whatever it is that is a happy memory for you. Or think about something happy in the near future... that next great date with you gf, that upcoming fishing trip with your dad, same concept.",
"Cheers!"
] |
[
"smiling releases dopamine "
] |
[
"To make this even stronger if you have difficulty focusing on the memory, try to tie a physical movement to the sensation. For example, smile and breathe out through your nose as you feel it (like, you're an idiot but I love you), rinse and repeat. Eventually, whenever you want a feeling, you can just vaguely remember the situation, perform the action and boom: emotion recall."
] |
[
"If you tattooed your entire body in ultraviolet ink, would it protect you from sunburn? What if you used infrared ink, would you feel less heat from heat lamps, fires, or the sun?"
] |
[
false
] | null |
[
"do ",
" inject sunscreen under your skin."
] |
[
"do ",
" inject sunscreen under your skin."
] |
[
"tattoo ink is put on the dermis, which is the layer under the layer that contains the melanin, called the epidermis (which protects against UV). melanoma developes on the area between the dermis and epidermis. when you get a tattoo, the ink is initially on top of this boundary, but will later migrate deeper inside. my best guess is that the tattoos would do nothing. that is assuming that UV ink actually blocks UV light, but UV ink just has ink which ",
" under a blacklight, i dont think it actually blocks a significant amount anyway.",
"tl;dr: i dont think it would help."
] |
[
"What sorts of experiments are possible in zero-G that are currently impossible or extremely difficult here on Earth?"
] |
[
false
] |
I've become fascinated with the International Space Station and I recently learned the the United States portion of the station is designated as a national laboratory.
|
[
"The Quest for the Most Spherical Bubble"
] |
[
"Certain details about the behaviour of fluids near the critical point can't be measured on Earth. You can find some examples if you do a search for \"microgravity critical exponents\"."
] |
[
"You can find a list of current and past experiments on the ISS ",
"on this NASA page",
" - it's far too long to summarise!"
] |
[
"What is different about kids’ biology that the COVID vaccine requires special testing for younger ages?"
] |
[
false
] |
The science behind the vaccine seems to be non-age-related. Do kids not produce antibodies fast enough or something?
|
[
"Not only are children usually smaller than adults, they have more active immune systems in general. There are also age-specific adverse effects possible - we have already seen that with the vaccines, since the (still very rare and generally very mild!) risk of myocarditis is almost entirely seen in younger men, and the risk of thrombosis from the adenovirus vaccines is mainly middle-aged women. With the virus itself, the risk of ",
"MIS-C",
" is almost entirely in children, while the other risks of the virus tend to be lower. ",
"So the whole risk-benefit equation is quite different between children and adults. Children got lower doses, because of their more active immune system (not so much because of their smaller size), and may be at less risk of some adverse effects (if myocarditis risk is affected by testosterone, as many think, then children under 12 should be relatively protected), but may in theory have more risk of immune overreaction. Is the lower dose safe and effective? Are there unexpected adverse effects? None of these are absolutely predictable from trials in older people, and in general the safety expectations for children are much higher than for older people. ",
"It’s worth pointing out that trials in older people do tell us a lot even for children. The extreme safety of the vaccines in older people tells us they’re ",
" also very safe in children. That’s why there’s almost always this kind of phased trial approach - start small, expand to the most at-risk populations, confirm safety at every stage, and then continue to slowly and cautiously expand the trials to include more people, checking at each step that the benefits outweigh the risks."
] |
[
"It’s about as conclusive as you can get with a rare condition. Don’t confuse the early caution about the link, with the current state of understanding - this has moved quickly, and in spite of the rarity and mild nature of the myocarditis it’s pretty confidently associated."
] |
[
"This is a great answer but I just wanted to point out that you need info on efficacy and longevity in that population also. Even though we think there is probably no reason it wont work in children, it is theoretically possible that it works better and no booster is needed, or that 3 spaced shots and not 2 are optimal or whatever."
] |
[
"If our ancestors had never left the ocean, would it still have been possible for our species to develop up to our current point?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"guidelines.",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"Okey that's fair enough"
] |
[
"You can try asking this to ",
"/r/asksciencediscussion",
" but I am. It sure you will get any satisfying answer."
] |
[
"Quick question about determining the ASA content in an aspirin tablet..."
] |
[
false
] |
[deleted]
|
[
"Usually, with titrations, you have the unknown in the beaker originally and titrate with the known."
] |
[
"Ask your teacher or lab assistant."
] |
[
"Unknown solution in the beaker, add some drops of the suitable pH indicator solution, probably Phenolphthalein and shake with your right hand. ",
"In the burette you should have your known concentration basic solution, in this case NaOH, and open and close the valve with you left hand going around the back of the burette, WHILE SHAKING THE BEAKER with the RIGHT hand.",
"This is what it should look like."
] |
[
"Do migratory animals born in captivity exhibit migratory instincts?"
] |
[
false
] |
For example, if a monarch butterfly is born and living in captivity, will it try to migrate along with wild monarchs? What about birds, mammals, etc?
|
[
"I don't know about birds, but I do know about monarch butterflies since I've raised many of them in captivity and then released them. Monarch butterflies have an internal compass that tells them where to go and when. When the seasons change, they know to migrate and their internal compass tells them where to go. It's been programmed ever since the first monarch butterfly evolved. There's even a group of monarchs that flies over the Great Lakes in North America and takes a several mile detour around the middle of one of the Great Lakes because when the butterflies started migrating that way, there was a mountain there. There's no mountain there anymore, but that route is programmed into their genetic code. That being said, that compass only works if they can see the sun/sky. This is why they don't do well in those butterfly conservatories - they get confused because they can't see the sun and they eventually die from stress."
] |
[
"Some of them do! There was a famous (older) study in behavioral ecology where migratory songbirds were kept in captivity, and during the migratory season, the birds became restless and tended to hop/move in the direction of their typical migration. That migratory restlessness is known as Zugunruhe! ",
"http://www.jstor.org/stable/4083048?seq=3#page_scan_tab_contents",
" ",
"https://en.wikipedia.org/wiki/Zugunruhe",
"This can be true even if the birds were captive-born. Here's an article about captive-born quail that includes a section on migratory restlessness.\n",
"http://onlinelibrary.wiley.com/doi/10.1111/j.1474-919x.2004.00313.x/full",
"I am not sure about mammals or insects, it might vary by taxa, but I wouldn't be surprised if you'd see some activity patterns change seasonally for highly migratory species, regardless of whether or not the individuals were captive born. ",
"I love migration questions, migration is so fascinating! :) "
] |
[
"The ",
"numbers at overwintering sites have dropped really dramatically",
"You can plant milkweed, which is what the caterpillars eat."
] |
[
"A question about water isotopologues - why does HDO fractionate more (i.e., 8x more) than H2(18)O"
] |
[
false
] |
See title! For example: During evaporation from a body of water, the water vapor will be "depleted" in the heavier isotopologues - HDO and H2(18)O - and "enriched" in the light isotopologue - H2O. However, when looking at the isotopic composition of the vapor (assuming that all of the liquid water didn't evaporate), the HDO will actually be much more depleted than the H2(18)O! I figure this has something to do with asymmetry of HDO compared to H2(18)O, but I cannot come up with a with a convincing explanation. [edit] Let me elaborate a bit, I was trying not to use esoteric terms to describe my problem and I think this lead to some confusion. Take a sample of naturally occurring water, fill a bottle about half way, close the bottle, and hold temperature constant at 25C. Most of the water will be H2O. The next two most common isotopologues of water are, as above, HDO and H2(18)O. When allowed to reach equilibrium (i.e., humidity = 100%), the vapor will have been fractionated both for deuterium and for 18-Oxygen. Based on mass, I would expect that the HDO (mass = 19) would have been preferentially evaporated and moved into the vapor phase when compared to H2(18)O (mass = 20). However, just the opposite is true. At equilibrium, there will be about eight times less HDO in vapor phase than the heavier H2(18)O. What this means is that if started with SMOW (standard mean ocean water, delta D = 0.00 per mil and delta 18-O = 0.00 per mil), our vapor would have delta D = -79 per mil and delta 18-O = -9 per mil (these aren't the exact fractionation factors, but close enough). Our heavy isotopologue is actually more common in vapor phase than our relatively lighter isotopologue! This is a commonly observed phenomena and is described in natural systems by the . [/edit]
|
[
"I would actually argue a differnt point. Evaporation rate should have no dependence on molecular mass (or extremely little). In general when comparing two different vapor pressures one has to look at intermolecular bonding energies. The weaker the intermolecular bonds the higher the vapor pressure.",
"So what is going on with isotopes then. Well of course the kinetic isotope effect. Given the frequency of some bond (yes even hydrogen bonds will have a vibrational frequency) that frequency v~sqrt(k/m) where k is the force constant of the bond and m is the reduced mass. Thus here D/H there will be a sqrt(2) depression of the vibrational energy of the ground state of the D bond relative to the H. Now the real trick is the absolute dissociation energy does not change thus D is now heavily stabilized relative to H. Where as in 18O/16O there is only a sqrt(9/8) stabilization in energy.",
"Thus given a temperature one could calculate the expected ratios of water isotopes in the liquid phase where D2O>HOD>H18O>H2O (though technically D2O would be rare to to rapid proton exchange in liquid water at reasonable temperatures)."
] |
[
"If I understand your question correctly, you are asking why water vapor from from HDO water has a higher proportion of lighter isotope than water vapor from H2(18)O?",
"Consider that a water molecule has two atoms of hydrogen to one atom of oxygen. Thus, water with deuterium (hydrogen with one extra neutron) may be H2O (no deuterium; mass = 18 amu), HDO (one hydrogen and one deuterium; mass = 19 amu), or D2O (two deuterium atoms; mass = 20 amu). In contrast, water with the 18-oxygen isotope may either be H2O (no heavy isotope; mass = 18 amu) or H2[18]O (mass = 20 amu).",
"Evaporation rate will be faster for lighter molecules of water and the resulting water vapor from either water source will therefore be more deplete (have a higher proportion of lighter molecules) than the water source. Deuterated water has the chance to exist in a \"hybrid\" molecule with only one heavy hydrogen atom (\"HDO\"; mass = 19 amu) that will evaporate more slowly than the lighter H2O (18 amu) but more quickly than the heavier D2O (20 amu). The 18O water can only exist as light (18 amu) or heavy (20 amu) molecules. Thus, I would expect to find fewer 20-amu water molecules in vapor from deuterated water than from 18-O water even though the molecular weights of the heaviest isotope are equal."
] |
[
"Good points about the hydrogen bonding between water molecules.",
"By the way, ",
"Cappa (2003)",
" wrote about the fractionation of water from a climate perspective. If you can access the article from your institution then it may help answer some questions."
] |
[
"How do ants breakdown/eat larger insects? Do they eat them on the spot or do they take pieces back to the nest. How does it work?"
] |
[
false
] | null |
[
"Antkeeper here. The short version is: Both!",
"A little background info: I feed my ants mainly pre-killed insects (some of them quite large compared to ants), sugar-water and honey, but sometimes they get what is left of a chicken-bone.",
"When the ants arrive at a food item (and after they have killed it if need be) they will eat if they are hungry and also fill up their social stomachs.",
"Ants have social stomachs that they can reguritate food from for other ants and thus feed everyone inside the colony. This is called Trophallaxis and is one way a Queen that never leaves the nest will get food. My impression from watching them is that they will always fill up themself first if the food is above a certain size, before starting to cut it into pieces and carry it back.",
"After filling up, they will try to carry the food into their nest, this is easy enough with small food items, but larger food or food that cannot be moved (like skewered cockroaches or chicken bones that are just too heavy to carry) they will try and cut into smaller pieces.",
"Ants have very powerful mandibles, they will try and cut up everything into smaller pieces until they can carry it around. Some things are too hard for them, but generally they are very clever in finding the soft sports at the joints or at the anus and work their way inside from there. In the end, a chicken bone will be gnawed clean and the only thing left from a cockroach will be the harder parts of the exoskeleton.",
"My educated guess is that they fill up first because they need the energy themself and because of the social stomach, they can easily feed the members that stayed behind. And they only begin carrying food home because if they are full, carrying it is really the only way to transport it back to the hungry larvae."
] |
[
"Do social stomachs have digestive enzymes to help turn most of the mass into immediately available nutrients in transit, or do they just barf it back up to whoever's hungry and let their regular stomach do the work?"
] |
[
"Such is life. Many thanks for the cool post!"
] |
[
"How does water form ice when under pressure?"
] |
[
false
] |
Traditionally, water freezes when the molecules are slowed down (due to freezing temperatures) enough for them to create stronger/stable bonds. However, I’ve recently been made aware that water can freeze under the right amount of pressure. From what I understand, if you pressurize water, you decrease the space for the molecules to spread out, actively lowering the melting point. Here’s where I’m confused. If it’s true that ice can form under pressure, does it form eventually when there’s not enough space for the molecules to rapidly bond/unbond? Is that what’s happening with ? Is the answer that simple or am I missing something? I feel like there’s a gap in my understanding.
|
[
"According to the ",
"phase diagram",
", if you pressurize water at room temperature, the solid phase will become the equilibrium phase at around 1 GPa or 10,000 atmospheres. This occurs because that particular crystal structure—ice IV—is denser than liquid water, so solidification becomes spontaneous to reduce the specific volume upon such extreme pressurization."
] |
[
"From an energetics POV, pressuring water increases its energy. And a simple rule of thumb is, any system likes to be at the lowest internal energy state that it can possibly be. ",
"If while pressurising water, you restricted the other possible ways of energy dissipation (kinetic energy, surface tension, heat, etc), water will prefer to lower it's internal energy by forming physical bonds (Vander Waals Bonds). This converts water to ice by making the molecular arrangement compact, regular and repetitive (that's what solids are)."
] |
[
"And a simple rule of thumb is, any system likes to be at the lowest internal energy state that it can possibly be.",
"If this were true, everything would be a solid. Systems instead tend to minimize their ",
"Gibbs free energy",
", which includes the internal energy but also a pressure–volume term that penalizes taking up too much space. As a result, pressurizing a system tends to drive it to its densest state—which for water is sometimes the (higher-internal-energy) liquid state and sometimes the solid state. This explains why compressing ice near room temperature can liquefy it."
] |
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