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[
"Assume you have something that generates heat at N degrees. If this heat source were stuck inside an oven and there was little to no way the heat could escape, would the temperature inside the oven eventually go above N degrees?"
] |
[
false
] | null |
[
"The second law of thermodynamics says that heat flows from hot to cold. If the system somehow found itself in a state where the temperature of the oven is higher than the temperature of the heat source, then the net flow of energy would be from the oven to the heat source. The oven would cool down and the heat source would heat up."
] |
[
"No, the oven can never reach a temperature higher than its heat source."
] |
[
"I believe you but something in my intuition isn't meeting you there yet. I guess I was thinking that if the molecules are moving around (which is where temperature comes from) and the heat source is bleeding heat into the oven then it's creating more movement (or maybe pressure?) inside the oven.",
"And since nothing can escape, then the molecules are getting faster, right?",
"Or am I just talking crap? What am I missing? Because it makes sense that you shouldn't be able to make the temperature above N degrees. But I just don't quite see why, yet."
] |
[
"Were Curiosity and its transport to Mars sterilised beforehand, and if not, is there a chance that microorganisms brought by it will thrive on Mars?"
] |
[
false
] | null |
[
"Hi Odenetheus thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
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" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Biology"
] |
[
"'Biology'"
] |
[
"What are the gravitaional forces on the inside of a spinning hollow sphere the size of earth?"
] |
[
false
] | null |
[
"A solid ball and a hollow shell of the same mass have the same exterior gravitational field. "
] |
[
"I'm talking about the interior, obviously all gravitational forces would cancel out, leaving a zero-g environment, but if you spin it, could you create an artificial gravity on the inside of the sphere?"
] |
[
"Yes. This is a commonly asked question. The centrifugal force mimics a gravitational force.",
"https://www.reddit.com/r/askscience/search?q=artificial+gravity&restrict_sr=on&sort=relevance&t=all",
"https://www.reddit.com/r/askscience/comments/51xg1l/physics_if_the_earth_wasnt_spinning_would_we_feel/?ref=search_posts",
"https://www.reddit.com/r/askscience/comments/2oms2h/are_the_effects_of_gravity_on_earth_different_to/"
] |
[
"Why do images flip in a magnifying glass at a certain point?"
] |
[
false
] |
So I was looking through a magnifying glass and I noticed that when I looked at an object that was about three feet from the magnifying glass (how close it was to my eye was irrelevant... I think), the image in it completely flipped.
|
[
"This",
" picture is helpful. The lens actually works the same in both directions. (In this picture an object way off to the left is giving off light.) Normally the glass would magnify things for your eyes because the object will appear larger (the light from the object takes up more of your vision) if your eye is between the lens and the focal point. Once you get to the focal point, all the light will be in one point on your eye (which can be very dangerous if you're looking at a light source, you can burn your retina). Once you get past that, you can see that the light hitting your eye will be flipped upside down. "
] |
[
"It has to do with how far you are from the lens in terms of focal distances. It's best to draw a small object and trace how one point of that object gets translated as an image.",
"Follow as I trace the tip of the arrow head to its image\n",
"http://i.imgur.com/maPpF.png",
"Assume the long line in the middle is the convex lens. The two smaller lines are one focal length away from the lens. The easiest way to trace light as it goes from the tip of the arrowhead is to follow it straight into the lens (top line) and then it goes to the focus on the other side.",
"Another line is the line that goes straight through the center of the lens. Another (for good measure) is one that goes straight through the focus on the side of the object and then goes straight across.",
"As you can see, the tip of the arrowhead ends up on the bottom, and the image is also enlarged. My high school physics education can't explain ",
" it does that, but that's how it goes.",
"I also apologize for the picture's sloppiness or if I messed the picture up because I haven't done optics since two years ago."
] |
[
"While this explains beautifully how the light coming through the lens is affected, it doesn't explain how/whether the distance from the object being viewed affects whether or not it flips. Does that distance have anything to do with it?"
] |
[
"What do moles do during floods?"
] |
[
false
] | null |
[
"Though I cannot find what I'd consider to be highly scientific sources (lots of gardeners answering), moles dig their tunnels deep enough and at specific angles to avoid water getting into their nests. The soil saturated with water only goes so deep, and established mole tunnels are deeper than this level. This is why \"flooding out\" moles doesn't always work; they're counting on water getting in, so they build their nests and tunnels accordingly. Some moles do just die though, due to being on or near the surface, or having relocated recently enough that they don't have established tunnels."
] |
[
"I don't know, but moles can swim very well and don't need much oxygen. The star-nose mole spends about as much time underwater as underground, and desmonds, a sort of mole (a talpid) is an aquatic animal. There isn't much oxygen in their tunnels anyway, so they are very good at going without much of it. So, all things considered, they probably do just fine, even though they might lose their tunnel networks if they collapse or don't drain."
] |
[
"So they dig water traps?"
] |
[
"How important are shoes to public health?"
] |
[
false
] |
[deleted]
|
[
"In addition to the things already stated, even in developing countries, proper footwear is an issue. ",
"In our country, a huge proportion of people (often african american, underprivileged, etc.) are diabetic. This can cause a condition called peripheral neuropathy, in which peripheral neurons effectively die off, and cease to relay signals such as pain, temperature, pressure to the central nervous system. This can lead to severe deformities as these people accumulate musculoskeletal injuries and fractures they are unable to feel, called Charcot Joints. They are also more prone to ulcers, infection of the soft tissue or bone, called osteomyelitis, which could lead to sepsis and worse. ",
"In my short clinical practice, I've seen quite a few homeless without shoes or with ancient shoes presenting with horrible foot deformities or ulcerations/infections. I check every patient's feet with diabetes, no matter what. "
] |
[
"Infection is the main public health risk. ",
"Notably: ",
"Parasites...",
"\n- Hookworm. Can cause anemia, intestinal discomfort, diarrhea, and growth delays. Severe or untreated forms (notably in the developing world) can lead to death. An infected individual also acts as a host for further hookworm spreading.",
"\n- Shistosomiasis. Found predominantly in many African countries where a freshwater snail is the natural host. The parasite will attach to the skin when you are in water, but cuts to the feet (via the snail shells, rocks, etc.) also pose a significant risk that footwear can reduce. Causes a variety of symptoms including diarrhea and gastrointestinal upset, and is associated with significantly increased rates of bladder cancer and liver failure. Life expectancy in endemic regions tends to be quite low.",
"Bacteria...",
"\n- Tetanus. Severe forms can lead to death.",
"\n- Any other. With increasing diabetes prevalence there is also an increase in diabetic peripheral neuropathy that results in decreased sensation in the feet (as well as decreased bloodflow and therefore decreased healing response). ",
"Things like fungal infections and viral infections (like plantar warts) are more of a hygiene concern, and would register rather much lower on a public health priority list."
] |
[
"Why is tetanus always mentioned in association with ",
" nails? Isn't the risk of tetanus infection the same regardless of what broke the skin?",
" Thanks everyone for the answer! It's not the rust, it's two factors related to the rust: 1) The nail is rusty because it has been exposed to a moist environment long enough to oxidize; 2) because it's been exposed for so long, and the rough, flaky surface is a cozy habitat for bacteria, it probably has bacteria. Yay science!"
] |
[
"Cell Respiration"
] |
[
false
] |
Alright maybe this should be in biology but it’s a question so I put it here. In school I have to make my own lab for cell respiration. We had done a lab that if you activated yeast and put it with molasses in a test tube with a stopper and "U-tube"? it would release CO2 (I think) and you would see bubbles in the water. So when I created my own lab I decided I would change the molasses with other things and see if the yeast still did cell respiration. So I tried it with yeast and corn syrup, and a yeast-sugar solution. So my question is should the yeast have done cell respiration with those things. I'm asking because this lab is a worth a huge part of my grade and I want to make sure it wasn't human error for not working. If cell respiration shouldn’t have occurred then I’m fine. I have made a quick drawing of what the lab was like to hopefully help you understand what I was describing. Sorry if my grammar is not the greatest. Help would be appreciated thanks!
|
[
"Well, firstly, yeast will die if it is too warm. I think that room temperature is ideal but i definitely wouldnt go over 40C.",
"Secondly, you need to make sure there was no preservative with the corn syrup. Preservative preserves by killing microbes, such as yeast. Check the label on the side of the bottle.",
"You should see bubbles in this set up provided you have enough yeast and dont overload the solution with sugar. Too much sugar and the yeast will die.",
"You could collect the CO2 in a test tube and then identify it as CO2 using by seeing if a small flame is extinguished when placed inside it. Remember that CO2 is heavier than air, however."
] |
[
"Pretty much anything with sugar should do it."
] |
[
"Check what kind of corn syrup you are using.\nFrom wiki:",
"Corn syrup is distinct from high-fructose corn syrup, created when corn syrup undergoes enzymatic processing that produces a sweeter compound containing higher levels of fructose.",
"This would complicate your reaction: for a very simple explanation ",
"look here",
"\nSo how about just leaving your reaction going for longer?\nAlso, it would probably have been a good idea to collect the CO2 in a tube and compare the volume you get with corn syrup to the volume you get with molasses."
] |
[
"What stops water from continually sinking through the ground? (Primary school science question)"
] |
[
false
] |
My year 4 class started looking at soil composition today and one of the students asked why water doesn't keep sinking through the ground. I promised them I'd have an answer by tomorrow (Sydney time), so I'm hoping the kind people at can help me help them! Apologies if this isn't the subreddit to ask this question. Feel free to advice of a more appropriate subreddit if there is one. Thanks!
|
[
"Well, there's a number of things at play here. Pick and choose which bits you want to use in the explanation at their level.",
"Chemical wetting. Soil can have lots of clay minerals in it, and these will hold on to water molecules when they are available.",
"Capillary action. Fine pore spaces within the structure of the soil enable water surface tension and adhesion (how well water sticks to a particular substance) to be a powerful enough force that the moisture remains in the porous structure. This is the same thing that will draw water up a capillary tube ",
"https://en.wikipedia.org/wiki/Capillary_action",
"Impermeable bedrock. Soil sits on top of a solid bedrock, and water can flow into the soil much faster than it can flow into the rock. It's like having a sponge sat on a brick. If you keep pouring water on the sponge, yes some water will gradually seep into the brick, but the sponge will start losing water out of its sides before the brick is completely wet. ",
"Through motion. Related to point 3, when there is rainfall or groundwater uphill, that water will take the easiest path downhill, and that is usually through the soil. So even through it may not have rained where you are, if it has rained upstream the soils downstream will moisten after time.",
"All of these things are quite easy to demonstrate in the classroom, and you can even do some experiments. If you have access to an oven and a mass balance you can even calculate water amounts in an object; wet the object, weight it, then dry it in the oven over night and weight it again. The lost mass is the mass of water. This is how we do it in the lab, and it can tell you all sorts of things about a rock. FOr example, if you soak a rock for a day or two, weight it, dry it, then weight it again the amount of water you'e lost is equal to the amount of space in the rock. You'll get really big values for sandstones, and relatively small values for igneous rocks and clays and shales."
] |
[
"The simple answer is that the soil can only absorb so much water, and after that absorbing water is going to be much slower as you get closer and closer to the saturation point. For a 9-year-old, an analogy with salt-water would probably work.",
"You could also explain that quite some water ",
" in fact seep through the ground, which is called groundwater and can be harvested. If you want, you could even do an experiment, taking some amount of soil and seeing how wet it is already(works better the less dry the climate is.)"
] |
[
"That explanation works against the question. If soil could absorb infinite amounts of water, then all water would always be contained in a very thin layer of soil on top of the ground. But since there is a saturation, water sickers further down just like the salt in a saturated water container will sink to the ground. ",
"The key is probably to realize what soil does with water. It absorbs water like a sponge. I guess that in this state gravity is not affecting the water much and far less than differences in water concentration of neighbouring soil mass. Meaning, that if you placed two cubes of aoil next to each other in a container such that they are in contact with onranother,, and one cube contains zero water and the other is saturated at 100%, then iver tine the dry cube would absorb water fron the wet cube. But like I said, just my guess that gravity has a snaller effect than what I just described. "
] |
[
"Wavefunction collapse is faster than the speed of light. Doesn't this just mean that they used math to answer the question?"
] |
[
false
] |
I keep reading about how researchers are measuring the speed of the collapse of the wavefunction by sending entangled particles to two different locations, measuring one, and then checking the other. I have recently had a conversation where it was explained to me that a wave function is not just math. My questions are so: 1. At its most naive, entanglement just means that if I know the identity of one, by the magic of math, I know what the other is. How do we know that the collapse of the second is an actual physical event. My spider sense goes crazy when people tell me that they can only prove a freaky experiment works by using a bunch of random numbers and classical conservation laws, but I know that a lot of people have worked on this that are smarter than me. edit: deep dyslexia sucks. Spiders and bats are not the same thing
|
[
"You're asking questions at the very heart of Quantum Mechanics. People disagree on how to interpret QM. So when you say ",
"How do we know that the collapse of the second is an actual physical event.",
"the answer is we don't. Some consider the wave function physical 'real'. Some don't. If the wave function is not real, then clearly its collapse is not real either. Niels Bohr famously threw out realism. That is, it's a mistake to think physics describes som underlying realty, it's simply a tool to predict the outcomes of measurements. To ask what is ",
" happening is simply a non sensical question (according to him).",
"the standard collapse of measuring particle 1",
"Not familiar with the term 'standard collapse', but I think you're suggesting is known as a hidden variable interpretation of QM. That he outcome was already predetermined before your measured. This is certainly possible, but there's a result known as bells theorem that shows that if that is true, then the universe must communicate faster than light(non local)."
] |
[
"Believe me, I have a phD in soft condensed matter, and most of quantum physics still sounds like bull unless I really think about it, which is almost never as I spend all my time pretending to understand biology!",
"But I still failing to see how collapsing the wavefunction is anything but already knowing the answer from the math and the one measurement you have already done. "
] |
[
"Are you asking if there's something special about EPR pairs that's impossible to find in classical physics? If so, the answer is a clear yes. ",
"Bells Theorem",
" says that the outcome of a measurement is not pre-determined (unless the world is non-local). ",
"Super dense coding",
" allows you to communicate two classical bits by only one quantum bit given an EPR pair. ",
"A non local box",
" can be implemented with greater correctness using an EPR pair than what is classically possible. It's a good example because it's trivial to see you cannot do better than 75% classically.",
"Whenever you measure half of an EPR pair you can no longer do any of this. Measuring half of an EPR destroys that connection. Something fundamental happens at that moment. "
] |
[
"How do bugs actually stick themselves and walk on walls and ceilings, y'know, like Spider-Man?"
] |
[
false
] | null |
[
"They’ve usually got little claws on the ends of their legs and they grab onto the texture of the surface. ",
"They’re also extremely light, so it doesn’t take much friction to hold them to a surface. ",
"You’ll note that the larger the insect is, the rougher the surface needs to be for it to climb.",
"Consider this ",
"image",
" to see the claw I’m talking about."
] |
[
"Certain insects have a ",
"crazy fractal-like design to the fur/material on their legs",
"(this image is from a gecko, but similar principle applies to insects), they have hairs that split into two hairs which split into four hairs etc.. This exponentially increases the theoretical contact patch with the surface. ",
"If you could figure out a way to reproduce that pattern with the same level of fidelity artificially, you'd be a billionaire. It's practically impossible to create any type of mold to create something like this at the moment."
] |
[
"Nano technology in short. Basically the same effect of when you hold say, a serving tray or any smooth flat surface. You can tilt it sometimes almost vertically without it sliding or falling off of a flat hand depending on how much it weighs. This is due to the surface area of your hand being in contact with the surface of the tray creating friction (the greater the surface area, the greater the friction). Many insects have evolved microscopic hairs on their “feet” that makes the ratio of surface area to weight much much higher than that of my earlier example of humans however things like geckos are also very good at this. If it weren’t for our finger prints adding surface area, we would probably be a lot worse at climbing things."
] |
[
"What is it about a digital camera's sensor that results in noise artifacts in low light settings?"
] |
[
false
] |
I understand that stronger lighting means more information to outdo the noise, but why does the noise appear in the first place?
|
[
"Part of it is thermal noise. The electrons in your sensor have some thermal energy associated with them, and can trip the sensors. When you have a high light intensity, the signal generally outweighs the noise. But in low light conditions, the noise is much greater in comparison to the signal."
] |
[
"These guys do an excellent job answering your question: ",
"http://photo.stackexchange.com/questions/11910/what-types-of-noise-can-be-present-in-digital-photographs"
] |
[
"This is actually a great introduction to stochastic calculations.",
"Let's say I want to measure the value of pi. So I draw a square on the ground, and inscribe a circle into that. Then, I sit above the whole thing and drop grains of rice. I drop the rice in such a way that the rice has an equal probability of landing anywhere in the circle.",
"So how does this let me calculate pi? Well, after a while, I count up the number of grains of rice that have fallen inside the circle, and divide by the total number I dropped. I know that this ratio should be equal to the ratio of the area of the circle to the square, and that THIS value is equal to pi/4. ",
"Let's say I drop 10 grains of rice, and 7 fall inside the circle. Since the area of the circle is pi*r",
" and the area of the square is (2*r)",
" , my ratio of 7/10 is roughly equal to pi/4. So my estimate of pi is 3.1. Now let's say I drop 100 grains of rice, and 78 of them fall inside. Now my estimate is pi=3.12, which is getting closer. The more rice I drop, the better my estimate gets.",
"So how the hell does this relate to a camera? Your camera is probably around 10 megapixels, or 10 million pixels. There is a tiny aperture in the front of your camera, and when you take the picture light streams though it and hits the pixels inside. Each pixel makes a stochastic estimation of the ",
" image by capturing some finite number of photons. The total number of photons that make it through the aperture are split between all 10 million pixels. If you are in a dark environment, the total number of photons is lower, and your estimate of the true value becomes worse. To put it another way, when the total number of photons is lower, the measurement each pixel makes is much more sensitive to random variations in the number of photons which happen to hit that pixel. This manifests as noise.",
"Another takeaway here is that this isn't a property of the camera's sensor - this is an intrinsic property of performing a measurement by recording a finite number of discrete events."
] |
[
"How is a mosquito proboscis physically capable of puncturing human skin?"
] |
[
false
] |
Human skin should be way too dense and strong for something so small and fragile like a mosquito. How is this possible?
|
[
"It uses two maxillas to cut its way into the skin so the fascicle can enter while the labium remains on the surface of the skin.",
"Think two little rotary saws that cut their way into you while a syphon gets slowly lowered down. ",
"Its not even a puncture at the scale the mosquito is working at."
] |
[
"Video here: ",
"https://www.npr.org/sections/health-shots/2016/06/07/480653821/watch-mosquitoes-use-6-needles-to-suck-your-blood"
] |
[
"That link’s staying blue for me thanks."
] |
[
"What happens if a gun is fired inside a pressurized cabin? (Like in an airplane)"
] |
[
false
] |
Today my military friend was trying to tell me that if a gun was shot at a high altitude in a pressurized airplane, that passengers would die from the force of the blast from the muzzle. (Not the bullet, unless of course it hits someone). He also went on to say that if the cabin is open to the air (depressurized) that the gun would act normally.
|
[
"I do not think that would be correct. The cabin is not extremely pressurized to allow for major changes (like what you might think of as the exploding safe episode of mythbusters).",
"Airplane cabins are generally kept at pressures similar to high land altitudes. See here from wiki:",
"A typical cabin altitude, such as the Boeing 767's, is maintained at 6,900 feet (2,100 m) when cruising at 39,000 feet (12,000 m)",
"So what they are saying is that the cabin pressure is the same as the pressure at 6,900 ft elevation.",
"So if what your friend was saying is true, you should be able to kill someone with just the force of the blast at a mountain altitude of 6900 ft. We all know you cannot do this."
] |
[
"Ok thank you. I tried to explain that to him! He was trying to make a point that force is much more powerful in a pressurized environment, specifically an airplane as we are both aerospace engineers. ",
"Are there any physics equations or a relationship between force from an explosion and a pressurized environment?"
] |
[
"I don't quite get where that train of thought came from. \"Pressurized environment\" doesn't automatically mean \"higher pressure\" - in fact, as stated above, the pressure is ",
" - maybe the term is confusing him.",
"I can understand if your friend thought a higher pressure environment can conduct a shockwave some more (or something along the lines of that), but in ",
"?"
] |
[
"How do photons interact with eachother?"
] |
[
false
] | null |
[
"Generally photons don't interact with each other, but in a non-linear medium it is possible. For example, two photons can combine to excite a molecule to an excited state with an energy difference equal to the sum of both photons (two-photon absorption TPA, a third-order process), or two photons can combine to result in a third one, and many other interactions become possible.",
"Answering \"how\" is not very easy without a lot of math, and quantum mechanics. The ",
"wikipedia page",
" on NLO is a good place to start."
] |
[
"Thank you for the reply. Will read up on it further. :D"
] |
[
"Photons can interfere with each other."
] |
[
"If the gas in a solar nebula is blown away as soon as the star becomes hot enough for hydrogen fusion, why are there different-sized stars?"
] |
[
false
] |
It's my understanding that all stars, at least ones that weren't formed in the early universe, were born in solar nebulae. The gas cloud spins around, and at the very center a star begins to form from accumulating dust and ices. Eventually this young star becomes so massive that the pressure its weight creates causes its core to begin fusing hydrogen atoms. Once this happens, most of the free-floating particles in the gas cloud get blown away, and most star and planet growth ceases. Since hydrogen fusion begins at a specific temperature, this would imply that all stars formed in this manner would have roughly the same mass, as they stopped growing once they became main sequence stars. However, this is clearly not the case, as main sequence stars can range in mass from a few percent the mass of the sun to ~100 solar masses. What's causing this size difference? The one thing I could think of was chemical composition, because it would cause a difference in density and therefore pressure, meaning a star would need a different mass to achieve H-fusion. However, it doesn't seem likely to me that this would single-handedly account for the vast range of possible star masses. Either there's something else causing the difference, or I simply don't understand how great an impact chemical composition makes.
|
[
"Once the hydrogen cloud is disturbed, the force of gravity causes different-sized clumps to form. Each of these may become a star. The arbitrarily-sized pocket of the cloud begins to collapse.",
"The hydrogen molecules (",
" atomic hydrogen) which comprise this cloud are all attracted to the center of mass of this clump before even the proto-star core is formed. So they all gain velocity towards it proportional to the total mass of the cloud. The bigger the cloud, the greater the speed at which they are racing towards the core when the core finally reaches the temperature at which fusion begins. When the core ignites, it exerts this \"blowing out\" outward force on all the incoming particles, however, this force must overcome the attractive force of the mass of the core ",
" the total velocity towards the core that they already attained. That part of the remaining cloud which is moving too fast or already too close will add to the mass of the star, and this amount of trapped gas is what varies."
] |
[
"That makes a lot of sense. I figured the \"blowing out\" force would overpower the gas particles, but I guess not.",
"You make it sound like it's happening on a really short timescale if the gas is moving towards the star at such a high velocity. Are there any good estimates on how long it takes for the gas to begin fusion, and then for the rest of the cloud to collapse?"
] |
[
"These clouds can be tens or even a hundred lightyears in diameter, so it definitely doesn't happen in a short time, you could say it takes a very long time but most of the events are disproportionately packed towards the end of that time, since it's an accelerating process.",
"Once the molecular cloud loses the kinetic energy to resist gravity, it generally takes a few million years for it to collapse. It actually depends on how hot (increase here increases time it takes to collapse) and dense (increase decreases time to collapse) the cloud is."
] |
[
"Is there a correlation between 1 cal = 4.184 J and water’s heat capacity of 4.184 J/g°C?"
] |
[
false
] |
I’m in an online introduction class to chemistry. Today’s lesson covered energy, temperature, heat capacity and such. There was one part of the lesson that said 1 calorie is equal 4.184 joules. Later in the lesson there was a part that said water’s heat capacity is 4.184 J/g°C. I noticed that numbers were the same between the two. No where in the lesson did it address this similarity. So I was wondering if there’s a reason that these numbers are the same or if some there is some kind of correlation out side of having joule as part of the measurement? Or is this just coincidence?
|
[
"It's not a coincidence at all. The \"calorie\" unit is defined to be the amount of energy required to increase the temperature of 1 gram of water by 1 Kelvin (or °C, which represents the same temperature increment). As such, it is directly linked to the heat capacity of water.",
"The heat capacity of water depends on the pressure and starting temperature, so the amount of energy that 1 cal represents changes slightly with these variables. The conversion value of 4.184 corresponds to water at atmospheric pressure with a temperature somewhere around 18 °C. It was picked as the standard conversion rate between calories and Joules."
] |
[
"Water has some very interesting physical properties. Enjoy your studies.",
"For instance, its density is highest at 4 C. This means that as water approaches the freezing point when below 4 C, it rises as water slightly warmer is denser and sinks.",
"What does this mean? Water freezes top down. Most compounds freeze bottom up because density generally increases with decreasing temperature.",
"It can be argued that life on this planet wouldn't exist, at least as we know it, if water froze bottom up. Freezing top down can protect aquatic life as the top layer is insulating and warmer water lies below."
] |
[
"My lesson didn’t mention this at all. It didn’t even really explain what a calorie was outside of a measurement of energy. So thank you a ton!"
] |
[
"Can you compare torque and horsepower?"
] |
[
false
] |
I am kind of confused by were one reddit user suggests you can directly compare torque and horsepower, yet another user says you cant. In the discussion only the users you say you can compare them have the upvotes, although my intuition would say you cant. Who is right here? Is this reddit being stupid or is it me just being dumb?
|
[
"You have to very careful, while they both share similar units, they are expressing different quantities. Horsepower is a unit of power, or energy per time. Torque is a psuedovector with units of energy per radian (degrees in a circle), because it's a psuedovector, it has direction as well as magnitude. You can think of torque as the energy needed to change angular momentum, so if you integrate torque through some angle, you get energy. If we have an angular frequency, then the inner dot product of torque and angular frequency gives you the power, which we can freely express as Horsepower if we want to.",
"In short, they are different, but related quantities. Comparing them is only appropriate if you know the rotation of the system or commonly in engineering, the RPM."
] |
[
"This article explains how to read a dyno chart:",
"\n",
"https://www.amsperformance.com/resources/technical-articles/56-hp-tq-dyno-chart",
"\nIt's a real graph that's useful in characterising a vehicle's performance. Since the torque is directly tied to your vehicle's acceleration (remember Torque = r x F and F = ma), the relationship between how much energy your car needs to use to maintain the same acceleration at different RPM is important.",
"I wouldn't say the point where they're equal fundamentally ",
" anything. They're not separate measurements on the chart. For the measured car, the dynamometer measured torque, once you have the torque, you have the power.",
"What makes the chart ",
" is how torque changes with RPM, to quote the article, ",
"Ideally, the TQ curve should be as flat as possible. This gives you the same acceleration rate at all RPM's in each gear. With a flat TQ curve, HP will continue to climb all the way to red line.",
"This means each engine has a unique torque-RPM curve which is the car's performance, check out this graph,",
"\n",
"https://i.imgur.com/XoUHD67.jpg",
"\nHere's three idealized engines, each with a different torque-RPM relationship. From this, we see the power responds different to the different engines. Especially compare the flat and decreasing engines. For the flat dashed curve, at higher RPM, we're still accelerating the same amount. For the decreasing dashed curve, our engine can't accelerate as much at higher RPM, its power starts dropping unable to handle the high RPM."
] |
[
"The formula for Tq is:",
"Tq = HP * 5252 / RPM",
"Where HP is in lb-ft.",
"Which is why those plots will always meet at 5252 RPM."
] |
[
"What exactly does a scintillation counter measure?"
] |
[
false
] |
I've done a bit of gamma ray spectroscopy, and I'm trying to interpret my results, but I don't know enough about scintillation counters. So lets say a gamma ray comes in, generates and electron-positron pair, and then undergoes a few compton scattering events. The positron annihilates with an electron. So, what gets measured by the photomultiplier? There are several different things all with different energies. There might be 3 or 4 gamma rays with different energies (traveling in different directions), a few electrons with different energies (also traveling in different directions), and maybe theres some interactions between the compton electrons and the scintillator that gives off some lower energy photons. Can the detector "see" high energy gamma rays that don't undergo any scattering? Can it see the compton electrons? What about gamma rays and electrons that get scattered at some large angle (say, backwards and out of the detector)? Are these partially detected in some way, or are these completely invisible? At first, I thought the scintillation counter was literally counting the number of photons with particular energies, but if that were true I cannot explain my results.
|
[
"When thinking about radiation detection, I like to start at the end and work backwards. At the end, you have a device that measures an electrical impulse. This impulse represents one detection event - also since you are taking an energy spectrum, the size of the impulse represents how much energy was detected.",
"The impulse is generated by the photomultiplier tube. This takes visible photons and converts it into an electrical signal.",
"The visible photons are generated by scintillation events. This happens when a free electron roaming around inside your scintillator falls into a lower energy state.",
"Free electrons are generated from ionization events. Usually, you have one very energetic electron that comes crashing through your scintillator, ionizing hundreds or thousands of atoms along its path.",
"These very energetic electrons were generated through interactions between your gamma rays and the atoms of the scintillator - compton scatter, photoelectric effect, and pair production.",
"So the only thing your detector is able to see is ionization energy left behind by the gamma ray. Let's say one of your gamma rays undergoes compton scattering, and subsequently escapes. Your detector would see a signal equal to the energy of the compton electron, but not the gamma ray.",
"In pair production, you often see \"escape peaks.\" This is when one or both of the 511 keV annihilation photons escapes. You would have a full-energy peak (representing the full gamma ray energy), and two smaller peaks at 511 keV and 1022 keV behind it.",
"So to sum it all up - take the energy of the photon entering the detector, and the energies of all photons that leave. The difference of these two values is the signal that the detector records."
] |
[
"Exactly.",
"The thing with a detector like this is that you don't measure the absolute energy deposited in each event - just the relative energy. So a 500 keV detection event produces a pulse that has twice the voltage of a 250 keV detection event. That is why you have to calibrate your spectrum with a known source of photons in order to establish the relative energy scale."
] |
[
"Your detector would see a signal equal to the energy of the compton electron",
"So how exactly does it see this energy?",
"The compton electron blazes through, knocking a whole bunch of other electrons loose, and when those eventually fall back into place they give off low energy photons, which the detector then sees a whole bunch of and \"adds them up\" and counts it as one event with total energy roughly equal to the kinetic energy of the compton electron? Won't some of these photons end up never entering the photomultiplier?"
] |
[
"How do we keep track of human genetic change? How much change would need to occur before scientists could say a new species of humans has evolved?"
] |
[
false
] |
I recently saw an exhibit about the brief period when neanderthals and homo sapiens co-existed, both of which could be classified as humans. I've been fascinated with the prospect of different species of humans coexisting ever since. How much would some homo sapiens have to change before we would classify them as a different species? Do we currently measure this change in any way? Does increased mobility prevent any one group from deviating so substantially that it would become a different species?
|
[
"This is a good question, and it's one for which you would find a lot of contention among biologists. The problem is that we do not have a single definition for species. As humans, we like to put things into discrete categories, but real organisms don't necessarily obey our rules. Now, for mammals like ourselves, we are generally ok with defining a species as a group of individuals that can produce viable, fertile offspring. However, given current genetic evidence we would consider our own species and neanderthals as a single species under that definition. ",
"Moreover, there isn't really a strict genetic cutoff for what defines a species. In the plant and fungal kingdoms, we see many organisms lumped together as the same species when, on average, they might have less genetic identity than a human and a chimpanzee. This means that we couldn't really put a number on the amount of change that would be required to produce a new species of humans - rather, it would likely depend on key changes occurring in specific genes required for successful reproduction to take place. ",
"With respect to your second question, increased mobility (and mating) will ensure that groups are less differentiated from one another genetically. Speciation requires that groups stop exchanging genes and thereby undergo evolution (mutation, genetic drift, selection, recombination) separately. So, yes, increased mobility (if accompanied by the production of fertile offspring) will prevent speciation."
] |
[
"Yes, our current global interconnectedness probably makes it difficult for any group to evolve to the point of speciation. As was already stated, species can be very tricky for scientists to determine, but a good rule of thumb is that the offspring of two separate species tend to be nonviable or sterile. This is NOT always true (in fact, recent DNA evidence suggests that Homo Sapiens and Neanderthals mated and had viable offspring). That being said, the sort of racial variations that we see now (Asian traits, African traits, European traits, Native American traits, to simplify) indicate that there was a potential for speciation if these groups had continued to be isolated from each other for hundreds of thousands of years. ",
"Speciation requires more than just isolation from the parent group-- natural selection pressures must also be present, and the DNA has to mutate. In today’s society we have gotten rid of a lot of selection pressures through technology and medicine, but that is not to say that NEW selection pressures are not changing us (as a whole species) right now.",
"In order to let a mutation become prevalent in the population, it has to confer a benefit that would make mating more likely. Problematically, culture can also interfere with the spreading of desirable genes. For example, in modern Western society it is “better” to have fewer offspring with a single mate, which reduces the spread of paternal genes.",
"An interesting idea for the future that has been brought up is that of genetic manipulation a’ la the movie Gatica. In theory, “designer” children could be made without diseases and with specific mental and physical traits. Manipulation at this level would be quite expensive, allowing only the wealthy class to afford it. After only a dozen generations of this type of manipulation, it would be entirely possible that there would be two separate human species living at the same time (the rich and the poor would literally become separate species). Creepy and unlikely, but technically possible with the science we have today, and one of the only ways that I could see two separate human species 'evolving' in the future. "
] |
[
"The evidence for anatomically moden humans and Neanderthals interbreeding is not as strong as previously thought and is explained by human population structuring. Here is the ",
"PNAS article",
". I agree that it would probably be most appropriate to use the biological species concept to define different human species. We must also be careful to out right say that gene flow with fertile offspring would prevent speciation. There are multiple ",
"examples",
" of speciation taking place with gene flow. A species that spreads across an environmental gradient is a good example of this. We have two populations of the same species that exchange genetic material and produce fertile offspring, but each population is slightly adapted to their position in the environmental gradient. The offspring of a cross between both populations produce offspring that are not well adapted to either environment and are outcompeted by offspring that are a product of individuals from the same population. This scenario can lead to speciation even though gene flow is taking place. "
] |
[
"What is the physical significance of a commutator in Quantum Mechanics?"
] |
[
false
] |
It is my understanding that you can use commutators to determine the uncertainty relationships between some observables but I am still having a hard time understanding what the physical meaning of the expression [A,B] is. Also, in addition to the one application above, what else can they be used for?
|
[
"Hm. It's a mathematical construct which literally tells you whether two operators commute. IMO, it doesn't have a \"physical\" meaning beyond that on its own, just like there is no particular physical meaning behind the \"+\" or \"-\" operator beyond the literal meaning of \"add\" and \"subtract\". "
] |
[
"The commutators can however tell you something about the eigenstates of the operators. If two operators commute, there are states that are eigenstates to both of the operators. If their commutator is nonzero, there exist no such states. This is a very obvious and straightforward result, but usually not the reason you are interested in the commutators.",
"For one, when doing any QM calculations involving operators, you will often need to rearrange the order they are applied, leading to the commutators coming into play. (AB |phi> = BA |phi> + [A,B] |phi>)",
"The commutator with the Hamiltonian (Energy operator) is also often used to write down the ",
"von Neumann equation",
".",
"So alltogether they simply appear very often in QM and pre-calculating them makes other calculations thus much easier."
] |
[
"This isn't really a 'physical' interpretation, but it kind of shows that there's something deeper and more interesting about commutators.",
"Proper maths students will probably slay me for this, but commutators (by using them as Lie brackets) can tell you about the structure of the operator Lie algebra you're using and allow you to generate a Lie group on your Hilbert space.",
"http://en.wikipedia.org/wiki/Commutator#Ring_theory",
" is probably helpful.",
"You can get something useful out of knowing the commutators of operators even if you don't know e.g. the products of operators.",
"Another place commutators come up in QM is ",
"http://en.wikipedia.org/wiki/Ehrenfest_theorem"
] |
[
"Why is human beard hair so much coarser than either body hair or head hair?"
] |
[
false
] |
Is it simply a matter of evolution? As beard hair shields a hunter's face against the elements while hunting, it would obviously be an advantage to have facial hair that is stiff and loose to mitigate wind chill or precipitation. What proteins are in beard hair which aren't found in other types of hair? I would love to have any information you can provide on this topic.
|
[
"Hair coarseness is a function of the thickness of each individual shaft of hair. Beard hairs are coarser than scalp hairs because they are individually thicker than your head hairs. One of the main things that influences hair thickness is the size of the dermal papilla, the space the root of the hair shaft sits in at the base of the follicle. Dermal papilla size is characterised both in terms of the space afforded within the dermal (skin) matrix and the number of cells at the dermal papilla.",
"Table 2 in the following paper shows that the dermal papilla in male beard hair follicles is around 4 times the size of dermal papilla in male scalp follicles. So we might expect that beard hairs are thicker than scalp hairs",
"http://ac.els-cdn.com/S0022202X15406700/1-s2.0-S0022202X15406700-main.pdf?_tid=d76ae1b6-3561-11e7-a265-00000aab0f01&acdnat=1494408180_3ef85226c926ada6bdd37aae4e068499",
"This paper (figures 4 through 7) show that follicle size is roughly correlated with hair shaft thickness at different body sites, although they don't specifically measure the dermal papilla size (which would be rather invasive).",
"http://ac.els-cdn.com/S0022202X15306291/1-s2.0-S0022202X15306291-main.pdf?_tid=6e7ddb36-3561-11e7-a5ee-00000aacb362&acdnat=1494408004_b8c74d07766baecfbeff46a1f8d98c18",
"That's the proximal, specific reason beard hair is coarser than scalp hair. Also worth noting that follicle density is lower on the face than the scalp and that likely increases the perception of coarseness as the fingers can better resolve each individual hair when the face is stroked.",
"http://onlinelibrary.wiley.com/doi/10.1111/j.1529-8019.2008.00214.x/full",
"Is it simply a matter of evolution? ",
"It certainly appears to be an evolved trait. Beard growth shows strong sexual dimorphism; males have obvious beard growth and women very little. This kind of marked sexual dimorphism is usually taken as evidence that the trait is primarily influenced by sexual selection rather than some other environmental selection. Another piece of evidence that this is a sexually selected trait is that beard hairs come in around the onset of sexual maturity, which strongly suggests they are a signal of sexual maturation.",
"https://en.wikipedia.org/wiki/Sexual_selection",
"It seems unlikely that exposure (wind chill, precipitation etc...) is the cause. We have no evidence that males spent less time sheltered than women in the Paleolithic period during which Homo sapiens evolved. For many hunter-gatherers men do typically hunt but women spend significant time out gathering (fun fact: grandmothers gather significantly more calories per day than the men acquire through hunting). Also humans evolved near the equator and I'm not aware of any evidence that extant hunter-gatherers living on or near the equator show any gender based differences in sheltering. ",
"Worth noting that women do hunt in some hunter-gatherer groups but I don't think they've started growing beards. Although perhaps they've just not had enough evolutionary time... ;)",
"What proteins are in beard hair which aren't found in other types of hair?",
"Beard and scalp hairs are both constructed from type 1 and type 2 keratin. There's no specific proteinaceous difference between beard and other hairs.",
"Edit: In case people revisit this answer. Some people are asking what is the evolutionary reason beard hairs are thicker than scalp hairs. I'm not aware of any work on this nor on how we could assess this. The above answer is kept largely to what Science does know about beard hair thickness and the evolutionary drive for beard presence. Coming up with an evolutionary Just-So story about the Why of it would be much too speculative. Not all traits are under strict evolutionary selection so beard hair thickness may just be an artefact of the process which matures pubic and beard follicles"
] |
[
"A very thorough and well explained response. Thank you. "
] |
[
"Just to clarify, sexual selection is a type of natural selection not a different process."
] |
[
"How were heavy vehicles steered before the popularization of power steering?"
] |
[
false
] |
Manual steering requires a lot of force even with a moderately heavy vehicle such as a mini-van, but power steering wasn't really around commercially until the 1950s. How did heavy vehicles such as cargo trucks get around this problem?
|
[
"Many older vehicles used what is called ",
"\"worm and sector\"",
" steering which used a worm gear to turn a meshing section of the Pittman arm, which in turn moved the wheels. Today, this has been replaced with recirculating ball steering which operates on a similar principle, only the worm gear moves metal balls which mesh with the Pittman arm, instead of the worm meshing directly.",
"To counteract the increased force, large trucks usually have larger diameter steering wheels as well as a smaller effective gear ratio, so you will sometimes see that semi drivers will have to turn the wheel more times to make a turn as compared to a car."
] |
[
"Two things... First, when the vehicle is moving, steering without power is relatively easy. Before power steering, people just made sure the car was rolling before turning the wheel. On top of that, steering wheels were larger. Having a larger wheel has the same effect on it's ability to turn as using a longer lever."
] |
[
"This. You can also have a higher gear ratio between the steering wheel and the wheels (it takes more rotations of the wheel from lock to lock)"
] |
[
"Can black holes be used as giant space mirrors?"
] |
[
false
] |
Black holes have strong enough gravity to prevent light from escaping. Could they also have light orbit them, such as how planets orbit stars? If so, would it be possible for black holes to have a slingshot effect on light, essentially sending it back in the direction it came?
|
[
"I read an article that explained that being next to the black hole the light would bend so much that you would be able to see the back of your head in front of you. I thought that was interesting anyone want to do some scientific poetry on that ?"
] |
[
"Black holes do bend light; it's an example of ",
"gravitational lensing",
".",
"This is outside my field, so hopefully someone will double-check my math, but I don't think it's possible for a black hole to deflect light 180 degrees ",
". Light inside the event horizon won't be coming back in the direction it came, for obvious reasons.",
"Wikipedia says the deflection is 4Gm/rc",
" in the direction of the mass. The Schwarzschild radius is 2Gm/c",
" . So, no matter how massive the black hole, light at the event horizon will only be deflected about 115 degrees. I think."
] |
[
"What about rotation? This drags spacetime in strange ways."
] |
[
"Do babies need to breathe after birth if the umbilical cord is not cut?"
] |
[
false
] |
Babies clearly breathe after birth since they cry, but if the umbilical chord were left alone, would they to? Does the mother stop supplying the baby with nutrients/oxygen after birth?
|
[
"There is so much to this, so I’ll try to be brief, but also cover the gist of what occurs. ",
"If placenta is still pumping ",
" attached to baby, baby will continue receiving oxygenated blood for awhile, but that varies on a case-by-case basis. Some of baby’s blood volume gets squeezed back into the placenta during birth, so those moments after birth give baby time to get some of their blood volume back from the placenta. That extra blood that goes back into the placenta is also making the placenta heavy, which helps to encourage the process of detaching from the wall of the uterus. ",
"If it’s still attached to mom and baby and still pumping, baby will continue receiving oxygenated blood from mom via the placenta even if baby is born. The placenta can take varying amounts of time to detach—usually within 10-15 minutes. It can take much longer (even hours), although in most hospital settings they won’t let it go on for more than 15-30 minutes without intervention. This time where baby and placenta are both attached gives baby time to transition and clear the lungs of fluid. ",
"The first 3-5 breaths that baby takes are actually pushing that fluid into the alveoli where it will be absorbed. During those first breaths (or first few helping breaths provided by a bag/mask in the case of baby needing some help with transitioning), baby is using the oxygenated placental blood. Only after that occurs is baby even relying on room air. Once baby starts breathing room air, the whole circulatory system changes. The blood that was bypassing the lungs entirely up until that point now enters the lungs where it gets oxygenated and gets circulated through the body. ",
"I’m a midwife who primarily does homebirths, but I have also spent several years doing birth center births. At home and in the birth center environment, we usually practice delayed cord clamping/cutting, which means that baby stays attached to the placenta for as long as the parents want. I’ve seen a placenta keep pumping for 2 hours on more than one occasion even after it was no longer attached to mom. It is unlikely that there is any useful amount of oxygen available to baby in the placental blood after the first few minutes, but it doesn’t hurt to keep them attached. Most of the time the placenta is done pumping by the time it comes out. ",
"When doing a resuscitation, most midwives will leave baby attached to the placenta. In the hospital the cord is typically cut within 30 seconds. If a delayed cord clamping is requested, it usually happens in under 3 minutes. They will always cut the cord before resuscitation in the hospital setting."
] |
[
"This is a very in depth summary, but just to further clarify for others, the placenta does not pump. The baby's heart is what moves the fluid around the fetal/neonatal circulatory system. The umbilical cord will have pulsations in its artery, but this is because it is attached to the heart, like any other artery."
] |
[
"There is a natural instinct when the baby is born to take the first breath. This first breath leads to an increase in oxygen and when oxygen enters the baby’s body a great deal of things occur. One of primary things is the closer of the parent ductus arteriosus and dilation of arteries in the lungs. Essentially that first breath literally kicks the lungs into gear and closes off some of the perinatal blood vessels. Umbilical cord is no longer needed. ",
"Also the science behind oxygen being a direct pulmonary vasodilator is quite interesting and a whole discussion in its own right."
] |
[
"What happens to bodily waste in people who have very infrequent bowel movements?"
] |
[
false
] |
[deleted]
|
[
"My experience here comes from human gross anatomy, so stuff at small scales may be best explained by someone else.",
"There's a pretty wide range in defecation frequency in humans. ",
"Here is one study",
" looking at a limited demographic in a single city that found a lot of variation in bowel movement habits that were otherwise considered normal. So when we talk about these rates being \"infrequent\" it's kind of a relative thing, and it doesn't necessarily mean constipation, which is I think what most people are assuming in their responses. As that source notes, defecation rate is also not a great measure of intestinal transit time, because the rates of movement through the parts of the digestive system can vary. ",
"In these instances food is going through the normal digestive process, with some portions of digestion taking longer. ",
"Here is a brief explanation of various transit times",
" within different parts of the digestive tract. It takes long enough that several meals are moving through at a time, and again each portion of the digestive tract takes different amounts of time. ",
"The gut tract is long enough to accommodate this, because the small intestine averages ~22 feet long, while the large intestine averages ~5 feet. This can vary from person to person, or can even change based on how muscles in the intestines are contracting. ",
"The main thing about the lower digestive tract is how much water gets absorbed. Even if a large portion of a meal can't be broken down, it contains a lot of water. Our intestines absorb a lot of that, both passively (via diffusion) and actively. Exactly how much depends on the osmotic gradient, particularly in the small intestine. ",
"Here's the water content in fruits and vegetables",
" and ",
"meat",
". So by the end you've still lost mass in the form of water even if there was a lot of indigestible material. ",
"Of course as others have mentioned, there can also be health issues that lead to infrequent defecation that is not due to normal variation."
] |
[
"It just stays there. Its volume is reduced by recycling the water. Which means the eventual bowel movement is more difficult, because the fecal matter, lacking water, is more stiff."
] |
[
"Thanks for the interesting reply. I assume you mean 'small intestine' instead of 'short intestine' though?",
"Currently laid up with a bit of stomach flu/food poisoning, so the water extraction part isn't doing it's thing. Not asking for medical advice, but the graph of transit times made me wonder if it's more likely that the meal of that evening caused this, or the meal of the evening before? Do you get ill when it reaches the stomach, or later in the digestive tract?"
] |
[
"What's the most fun or interesting thing you scientists do with chemistry/your knowledge of chemistry?"
] |
[
false
] |
Just thought it'd be fun to hear or maybe do.
|
[
"extracting illegal drugs from readily available and legal plants"
] |
[
"Precipitating DNA, making H2(g), and of course making dry ice fog."
] |
[
"Not a scientist, but I've had some fun with things during my years. Making liquid nitrogen ice cream is a winner with kids, and throw in a reverse flame blower show for added fun.",
"Also we used to make tennis ball cannons shooting several hundred meters with a mineral that made an explosive gas when immersed in water, but I can't for the life of me remember what it was named."
] |
[
"Why did Nordic people evolve to have thin bodyhair and blonde hair while people in hotter regions have thick bodyhair which would be better suited to colder climates?"
] |
[
false
] |
In terms of heat insulation, why didn't people in colder climates evolve to have thick and dark bodyhair which would help you keep warmer. And on the contrary, shouldn't people in hotter regions have blonde hair which would reflect sun and perhaps no bodyhair to keep cool? Or does the sun have an effect that makes hair darker?
|
[
"The differences in hair has a negligible effect on your ability to survive northern climates: humans won't survive the winters anyway without clothing, so your hair matters little.",
"What ",
" matter is sunlight. Near the equator the intense sunlight is a problem, causing sunburns and skin cancer, so darker skin and hair that absorbs the sunlight before it can cause damage is beneficial. Near the poles the lack of sunlight during winter months is a much bigger problem, as ",
"vitamin D is synthesized in the skin",
" when it is exposed to sunlight. When ",
" sunlight is the bigger problem, having lighter skin is beneficial."
] |
[
"The vitamin D hypothesis is a well-supported notion of how light skin developed, but hair color is only weakly influenced by alleles for skin or eye color. It is more likely that variation in hair and eye color was the result of ",
"strong sexual selection at northern latitudes",
" (link to another comment).",
" On the topic of skin color, things do get interesting. As pointed out, the ability to utilize sunlight to synthesize vitamin D favors lighter skin pigmentation. However, hunter-gatherers had adequate vitamin D in their diets anyway (lots of meat), so they didn't need to make much endogenously. Northern Europe is a very unique place because it is at high enough latitudes to receive weak sunlight, but is warmed enough by the gulf stream to allow the advent of agriculture. When people there began farming, their diets changed substantially, and they lost much of the vitamin D they used to get through food. It was at that point that those two factors (low dietary vitamin D and weak sunlight) interacted to exert a strong enough selective pressure to promote light skin color."
] |
[
"The reason that hair color/thickness and skin pigmentation evolved the way it did is not due to thermal insulation, but rather protection of skin from the sun. The reason people in, for example Africa, have such dark skin and thick hair is that it allows their body to be less susceptible to sun damage such as sunburn and the development of skin cancer. Because this is not a necessary trait for survival in northern regions, their skin and hair pigmentation became much lighter.",
"EDIT: As several others have pointed out, lighter skin is also advantageous in that it allows for better synthesis of Vitamin D, which is important in northern environments where there is less sunlight"
] |
[
"Does it take the same amount of energy to slow down a space craft as it did to get to that speed?"
] |
[
false
] | null |
[
"That depends. It can take less, more or the equal amount of energy due to gravity assists.",
"But let's imagine there is no matter around you. To move forward you need propulsion, and to stop you need the exact same amount of propulsion in the exactly opposite direction.",
"However, in real life there are several things that makes this not this easy. There is no such thing as stopping in space, because you're always pulled towards mass, be it the Earth, the Sun or any other object. In fact, the spaceship is also pulling the Earth towards it, even though it's a microscopic pull that can't be measured.",
"Due to the amount of entities in space, scientists often use gravity assists to adjust the velocity of spacecrafts, and gravity assists do actually take a small amount of the planet's orbital energy and you can decelerate relative to the Sun (assuming the planet is orbiting the sun.)\n*Completely forgot about the fact that you have fuel with you. Thanks -KR-"
] |
[
"There are multiple layers of reality to that question.",
"1st layer: Yes, it takes the same amount of energy. If you shift your frame of reference to the accelerated space craft, you see that to get to the previous \"null\" velocity, you have to make the same acceleration as to get to that velocity.",
"2nd layer: In reality you have to take your fuel with you. That means you leave some mass behind to accelerate yourselve [1]. On your deceleration burn you don't have to decelerate the mass you previously expended, which means it takes less energy to decelerate.",
"3rd layer: There is probably some drag in the interstellar medium, so probably you could decelerate with some ginormous magnetic \"drag chute\" or something like that.",
"[1] Rocket equation, ",
"http://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation"
] |
[
"Not necessarily. The main determinant of power for a rocket is the delta-v, or the total amount the rocket can change it's velocity by.",
"The Oberth effect says that impulse added when your velocity is higher, ie at the apogee of your orbit near the gravitational body, can result in greater final velocities than any other segment of the orbit.",
"http://en.wikipedia.org/wiki/Oberth_effect",
"Rockets produce the same force, regardless of velocity, and thus the same acceleration. If you increase your velocity while you are at the fastest point of your orbit, you greatly increase your kinetic energy (KE=1/2mv",
" )."
] |
[
"What is in between galaxies?"
] |
[
false
] |
after seeing this picture ( ) I became curious about what is in between galaxies. I know it's a bit of a silly question but is it just empty space or is there more to it? Any info is greatly appreciated.
|
[
"The 'intergalactic medium' (IGM) is mostly a rarified plasma. The heating mechanism depends on the particular environment -- the gas between galaxies in clusters tends to be very, very hot indeed (millions of kelvin), and emits in the X-ray. This is generally heated via gravitational shockwaves, as the gas falls into the massive gravitational potential of the cluster. ",
"Other galaxies, with very active central black holes, can also dump energy into the IGM (which heats it up). ",
"(EDIT... some people are taking issue with 'gravitation shock waves'. I was trying to say 'shock heating' in a non-fancy way). "
] |
[
"Much of it (at least the baryons) was ejected from galaxies from either Supernovae or Active Galactic Nucleii. That stuff tends to be moving fast and since the IGM is so sparse, it's hard for particles to interact and potentially cool."
] |
[
"Just ask your questions here. If you can't think of any specific questions the AMA would in fact not be fascinating."
] |
[
"How much Carbon does an acre of trees offset each year?"
] |
[
false
] |
Specifically, in a rainforest that is fairly well established (roughly 100 years old, some trees older, and found in Northern Australia).
|
[
"That's the thing though; all trees are collecting carbon from the air and depositing it."
] |
[
"Well, of course that is possible, which is why I mentioned it. However, in a well established environment, there is very little net burial. It does not just accumulate forever, but rather reaches a state where as much organic material is released by decay as is sequestered by photosynthesis.",
"The balance and cycling is all about storage. An old forest is not adding to its store of organic carbon, on overage.",
"It is the same in the ocean. Efforts to fertilize High-nutrient low-productivity zones by adding essential micronutrients, such as iron, are not likely to sequester much CO2. The phytoplankton will die, decay, and release the CO2 they took up in the first place, with only a tiny fraction being buried in deep sea sediments."
] |
[
"Unless the forest is increasing in size, or creating a deposit of buried organic carbon, it releases as much CO2 as it absorbs. It is in dynamic equilibrium."
] |
[
"Why aren’t waterfalls just eroded to slopes?"
] |
[
false
] |
I can understand that water needs some place to go and sometimes the easiest path is over a ledge. However, I would think that the power of erosion would convert these waterfalls into smoother inclines. Are waterfalls usually just the result of recently redirected water where the forces of erosion haven’t worn it down yet? Are tectonic plates moving faster than the forces of erosion can act? Are the rock found at many waterfalls more resistant to erosion? Thanks!
|
[
"The most powerful weathering happens in two places in a waterfall system. The critical edge, the place with the least support. And the vertical edge, where falling water has a lot of force and there is not much vertical support.\nThese two places happen to be where the defining features of the waterfall are (edge before the drop and the cliff face). Since these places experience much stronger weathering than anywhere else, the general shape of the waterfall remains. It just recedes up the stream over time (see the erosion of Niagara Falls).",
"For example: picture a waterfall with big rocks at the edge before the water tumbled down. In the event that these rocked get swept down what do you expect to happen? Generally the water creates a new critical edge some distance back and now the water begins falling directly onto rock/sediment that is clinging to the side of the cliff."
] |
[
"I looked up Niagara Falls erosion and found this: ",
"\"What is the future of Niagara Falls?\nToday, the falls continue to erode, however, the rate has been greatly reduced due to flow control and diversion for hydro-power generation. Recession for at least the last 560 years has been estimated at 1 to 1.5 metres per year. Its current rate of erosion is estimated at 1 foot per year and could possibly be reduced to 1 foot per 10 years.",
"The current rate of recession is unclear; assessing its value remains the responsibility of the International Joint Commission. The International Boundary Waters Treaty stipulates the minimum amount of flow over the falls during daytime, nighttime and the tourist season.",
"Erosive forces include the action of frost from the spray, the dissolving action of the spray itself, and abrasion action of the softer shales by fallen limestone boulders.",
"No one knows when the next major rock fall will occur in the Horseshoe Falls; the effect could be to speed up erosion. A stable position is abandoned when the crest line develops a notch configuration and the Falls retreats relatively rapidly until a new stable position is attained. It’s also possible that the current or future flow and volume of the river will not be sufficient to carve out a deep enough plunge pool to accommodate rock falls; in this case, the Canadian Falls could be supported by talus in much the same way as the American Falls.",
"The Cascade Rapids above the falls are about 15 metres (50 ft.) higher than the falls today; once that ledge has been breached, the falls will have an extra 15 metres of force.",
"Climate change is also an influencing factor on the future of the Niagara River as an integral part of the Great Lakes Basin; models indicate a drying up of the Basin. Isostatic rebound continues to affect the Great Lakes Basin and consequently the flow of water through the Niagara River.",
"All things considered, scientists speculate that perhaps 2,000 years from now the American Falls could dry up. It is a stationary feature collapsing by rock falls and landslides, carrying less than seven percent of flow before diversion; this bit of water is shallow and spread out, therefore ineffective as a major erosive power. As a dry falls, it could appear like the Niagara Glen does today.",
"The Horseshoe Falls will notch back for about 15,000 years, traveling back about four miles to a softer riverbed (from the southern end of Navy Island to Buffalo/Fort Erie the riverbed is no longer the erosion-resistant limestone but soft Salina shale) after which the rate of erosion will change significantly (remember the bedrock tilts downward to Lake Erie). The falls could be replaced by a series of rapids.",
"50,000 years from now, at the present rate of erosion, the remaining 20 miles to Lake Erie will have been undermined. There won’t be a falls anymore, but there will still be a river at work.\"",
"-",
"https://www.niagaraparks.com/visit-niagara-parks/plan-your-visit/niagara-falls-geology-facts-figures/#:~:text=Its%20current%20rate%20of%20erosion,1%20foot%20per%2010%20years",
"."
] |
[
"If you explore the woods downstream you can see signs of the previous positions of the falls. Giant boulders, bowls ground out of the stone, etc.",
"Niagara Escarpment"
] |
[
"If electric cars become the norm, is it likely it would be economically feasible to own a gas powered car?"
] |
[
false
] |
Let's say would it be feasible for a middle class guy?
|
[
"It takes a while to change production of large scale oil fields. What would happen is that as people started switching to electric cars, the demand for fuel would fall relative to supply, causing a glut of inventory and leading to lower prices. The lower cost of fuel would serve to stem the tide of people switching to electric. ",
"A similar thing happened with alternative fuels in the mid 80's when the threat of development pushed gas companies to produce more gas, keeping inflation adjusted prices BELOW where they were in 1979 for TWO DECADES. ",
"Eventually, either 1) oil companies would reign in and eventually phase out production (but don't weep for them, they are all heavily invested across the board in energy production), or 2) we would reach some sort of medium between the cost of energy and the cost of gas, with a decent number of each on the road. ",
"This is, of course, ignoring any government intervention to push vehicles from one energy source to another."
] |
[
"With #2, at some point in time the cost of gas (and very well maybe electricity depending on our supplier) would go up just due to the difficulty in drilling for it, given traditional drilling methods. At a certain point in time usable oil will become to low yield to be worth drilling for."
] |
[
"Do you mean gasoline, or natural gas? "
] |
[
"I'm just a lowly at student, uninitiated in the way of physics. Explain the holographic principle to me in one of those over simplified metaphors."
] |
[
false
] |
[deleted]
|
[
"Imagine watching a movie. The screen is flat, but your mind kind of interprets it as three-dimensional! This has nothing to do with the holographic principle."
] |
[
"The maximum amount of quantum state information that can be contained within a region of space is equal to the area of a sphere with the same volume as the region, measured in square Planck length units.",
"There's not really a metaphor required, because it's really just that simple. If you try to cram the maximum possible information into a given volume, eventually a black hole will form that fills that volume, and the surface area of the black hole's event horizon in square Planck length units will be equal to the number of bits of information contained inside the volume. If you add any more information, the black hole's event horizon will have to grow, which means you can no longer get it all into the volume you started out with."
] |
[
"If you're coming at this from the point of view of what I call a \"computer person\" — those admirable and infuriating young people who find computers to be natural and intuitive rather than backwards and infuriating, and who thus tend to see everything in terms of how it could be computed with a computer — then it's likely you're going to be frustrated. In this context, a bit of information is not unambiguously defined. It can't be, because of the nuances of entanglement and other quantum weirdnesses.",
"But the fuzzy, comfortable definition is that a bit — more properly a \"quantum bit,\" also called a \"qubit\" — is the minimum amount of information necessary to describe the state of a two-state system. You might imagine that this is just an ordinary binary digit, zero or one, A or B, heads or tails or whatever. But in fact, two-state quantum systems are not always in either of their two possible states. Sometimes they're in a superposition of states — a little from column A and a little from column B. So a quantum bit must include that degree of nuance. It's not necessarily zero or one, or A or B. Sometimes it's ",
" + ",
" where ",
" and ",
" are complex numbers.",
"But when you talk about black hole thermodynamics, it's customary — ever since Jacob Bekenstein did it the first time — to think about the most reduced case possible: that of just a ",
" falling into a black hole. The idealized scenario that comes closest to that is of a photon with a wavelength exactly equal to the black hole's diameter. Since your ability to localize a photon within a given volume goes inversely with the photon's wavelength, a photon with a wavelength exactly equal to a black hole's diameter represents exactly one bit: Either the photon is localized within the black hole's volume, or it isn't. No other information can be extracted, because that's literally all the information there is.",
"A photon with a wavelength equal to a black hole's diameter will of course have a certain specific energy; there's no uncertainty relationship between a photon's wavelength and its energy. If you know the wavelength exactly, you know the energy exactly, and in this case we know the wavelength exactly because we defined it exactly.",
"So if you imagine a photon of wavelength 2",
" (where ",
" is the Schwarzschild radius) falling into a black hole, you can calculate the total energy that will be gained by the black hole in the process, from which you can determine by how much the black hole's event-horizon radius will grow. It turns out to be something like ten-to-the-minus-seventy meters, give or take a couple of orders of magnitude; I haven't worked through the maths recently so I don't exactly recall. But the interesting thing about all this isn't the amount by which the radius grows; that's just a very very small number. The interesting thing is the amount by which the ",
" of the black hole grows. That turns out to be one square Planck length unit.",
"Which gives us the holographic principle, basically. If you add one bit of information to a black hole, the black hole's surface area grows by one square Planck length unit. Which means the number of bits contained within a black hole is equal to the black hole's surface area in square Planck length units. Which means the surface area in square Planck length units of a black hole of volume ",
" is exactly equal to the maximum number of bits of information you can cram into a region of space with volume ",
" You can have ",
" bits of information in that volume, of course. But you can't ever have ",
" That's the maximum information density, in quantum bits per unit volume, that the universe will permit, due to the relationship between geometry and energy that we call gravity."
] |
[
"Why could this PVC I am analyzing have endothermic peaks near the melt point when PVC is an amorphous solid?"
] |
[
false
] | null |
[
"This is run on a DSC. I think I solved the problem. I looked at the pan my tech have me and there is a brown line around the ridge of it indicating some off gassing has occurred. I'm guessing that was the problem. "
] |
[
"Not the right sub for such specific / idiosyncratic questions. Try ",
"/r/askchemistry",
" or ",
"/r/labrats"
] |
[
"Solved my own problem anyways. The mini cups were popping open because of the volatiles and the \"endotherm\" was caused by the sensor reading an open cup vs a sealed cup. "
] |
[
"Will running a humidifier in a warm, dry, closed room cool the room?"
] |
[
false
] |
Specifically, does increasing the humidity of a closed system affect the temperature? What about an open system (window opened in the aforementioned room, for example)? I suppose the humidifier produces some kind of heat while running, but I'm not sure if that's important for this question.
|
[
"With a usual swamp cooler setup you will have positive pressure inside the residence with a cracked-open window or door in the region where you want cool air to flow through the building. If the humid air can't escape then you will saturate the air which may marginally reduce the temperature at first but then you're stuck in a still-pretty-hot and, even worse, humid room. I've done this with a portable evaporative cooler I own and it is not pleasant and does not produce a measurable difference in temperature on my thermometer. It just makes it feel like you're in a swamp."
] |
[
"yes, it's very important. since humidifiers are not 100% efficient, you will be adding excess heat to the room. Similar to why leaving your refrigerator door open won't cool your room, it will in fact heat it."
] |
[
"A dehumidifier will always warm a room. Heat is removed from the water molecules upon condensation. Additionally, waste heat is always produced by the motor. ",
"Increasing the humidity has the opposite effect; it cools the room. See ",
"swamp cooler",
". Water molecules absorb heat during the state change from liquid to gas. ",
"Edit: I mistakenly read your question as DEhumidifier. My information above is correct, but only answers your question in a round-about way. "
] |
[
"How tonal languages such as Mandarin sung without changing the meaning of the words?"
] |
[
false
] |
[deleted]
|
[
"To start, in Mandarin tones are not sung. The tune follows the melody and context is all you need.",
"However, this is ",
" the case with all tonal languages. Cantonese is a good example of a tonal language in which singing preserves some ",
" of phonemic tone, but not the actual original tone from the normal spoken form of the word.",
"If you feel like reading a proper paper on this, there's ",
"The Realization of Tone in Singing in Cantonese and Mandarin by Murray Henry Schellenberg",
" which compares Mandarin and Cantonese in this regard. A shorter version of the study ",
"is here",
".",
"I'm repeating myself from an earlier comment on this topic, but to quote from the abstract:",
"Cantonese singers included a rising contour when singing words with rising tones and Cantonese listeners were attuned to this. Mandarin singers did not add in contour information and Mandarin listeners had difficulty recognizing the words out of context. The thesis also expands the discussion of singing in tone languages by examining some of the sociological and political factors which appear to have influenced the ways in which tone is expressed (or not) in these two varieties of Chinese.",
"And also:",
"[Cantonese singers] do not appear to include a falling contour when singing a falling tone",
"What's interesting is ",
" Cantonese has the tone and Mandarin does not, and it's most likely extralinguistic. One possible reason is that Cantonese opera is relatively new and only dates back to about the 1920s. Beijing (Peking) opera and Kun Opera (from around Shanghai) are both older. Quoting again from the above sources:",
"One may be purely aesthetic: given the uses and re-use of a limited set of melodies, the use of 58 the linguistic tones of the lyrics provides a greater variety of melody. The other reason he suggests is expediency. Heavy reliance on linguistic tone limits the need for musical notation and rehearsal – singers may be relied upon to produce good theatre without needing a lot of outside rehearsal.",
"Then, finally, another important factor that likely contributes to this difference has to do with sociological factors and issues like group identity. That is, tone was retained on purpose as a means of distinguishing the singing from the more common styles to reinforce cultural cohesion. Page 59 of the linked paper begins to go into this in more detail, if you're interested.",
" In many cases, phonemic tone is disregarded in song. In languages where it's not, there may be non-linguistic reasons for the tone's appearance, such as aesthetics or sociological factors. When it is present, it may be only a representation of the tone and not the tone as it would be as spoken.",
"Sources:",
"Schellenberg, Murray. ",
". 2011",
"— ",
". 2013"
] |
[
"This is at best an oversimplification on many many points, and at worst just flat out incorrect.",
"It's actually ",
" entirely up to context in Cantonese, where tones are in fact still represented in song. See my longer response to OP about that.",
"\"Japanese has fewer tones than Chinese\". To say that Japanese has tones is just not accurate. Many dialects (but not all) of Japanese follow a pitch accent system, but this is not a tonal system as the term is used in linguistics.",
"\"when … whispering, tones can be less noticeable\". Voicing is absent when whispering. That's why it's whispering. So I'm not sure what you mean by \"less noticeable\", but if you're actually talking about changes in pitch, it's not noticeable because it's not there. However, to a native Mandarin speaker, tones are still represented in whispered speech through duration and stress, and so are ",
". ",
"I don't even know what to say about the claim about understanding Japanese being spoken faster. That's just a baseless claim unless you've got something to back it up. Something more than syllable frequencies across language, because those studies are reporting on something completely different than what you're making claims about.",
"Please don't make claims based on speculation and hunches."
] |
[
"This is at best an oversimplification on many many points, and at worst just flat out incorrect.",
"It's actually ",
" entirely up to context in Cantonese, where tones are in fact still represented in song. See my longer response to OP about that.",
"\"Japanese has fewer tones than Chinese\". To say that Japanese has tones is just not accurate. Many dialects (but not all) of Japanese follow a pitch accent system, but this is not a tonal system as the term is used in linguistics.",
"\"when … whispering, tones can be less noticeable\". Voicing is absent when whispering. That's why it's whispering. So I'm not sure what you mean by \"less noticeable\", but if you're actually talking about changes in pitch, it's not noticeable because it's not there. However, to a native Mandarin speaker, tones are still represented in whispered speech through duration and stress, and so are ",
". ",
"I don't even know what to say about the claim about understanding Japanese being spoken faster. That's just a baseless claim unless you've got something to back it up. Something more than syllable frequencies across language, because those studies are reporting on something completely different than what you're making claims about.",
"Please don't make claims based on speculation and hunches."
] |
[
"What are the differences between multi-core and GPU computing? When would you use each?"
] |
[
false
] |
[deleted]
|
[
"With a multi-core CPU, each core can do its own thing. To a programmer, it works exactly like you'd expect a multi-core system to work: you can launch threads on all cores and run completely different, individual tasks on all of them. The biggest multi-core CPUs from AMD have about 16 cores (while I believe the biggest Intel CPUs have 12 cores), and with high-end server motherboards you can usually cram several of these into a single computer, giving you a maximum of around 60 or so cores on a conventional machine.",
"With a GPU, you instead can have hundreds or thousands of cores running hundreds or thousands of threads at once. However, there is one important limitation: you can't run different code on each thread concurrently. GPU architecture limits you to running the ",
" on all your threads at once. You load your data into memory and run one operation at a time (small pieces of code called \"kernels\" or \"shaders\") on the entire data array. The scheduler launches thousands of threads, one for each core, and then executes the kernel. If you have 2880 cores in your GPU, you can load an array of 2880 floating point numbers and have a kernel multiply all the numbers in the array by 2 at the same time. And the GPU will do this extraordinarily quickly compared to a multi-core CPU, which has to essentially loop through all 2880 numbers after you divide the work across its cores.",
"The major limitation on the GPU side is that each thread can essentially only perform the same operation at a time, just on different parts of the data set you load into memory. The threads are \"dumber\" compared to CPU threads. There are unique programming challenges when working with either architechture. With CPU threads, you have to worry about concurrency and synchronization, so you need to prevent two threads from modifying the same piece of memory at the same time, and (usually pretty bad) problems arise if two CPUs disagree. With GPU threads, synchronization is less of a problem, and the challenge lies in optimizing your algorithm to operate on massive arrays of data a little at a time. Some algorithms work better on GPUs than others because some algorithms just don't benefit from massively parallel computations like this. As others have mentioned, certain steps of some hashing algorithms (used in mining Bitcoins and cracking passwords), graphics rendering, and video post-processing all benefit greatly from GPU acceleration. Algorithms where the next step depends heavily on the output of previous steps, like compiling code, are difficult or impossible to parallelize on a GPU and still yield better performance.",
"Of course the line is blurred all the time. SIMD instructions (MMX/SSE/NEON/etc) allow you to run a single instruction on a large piece of data at once on a CPU (like a GPU). And NVIDIA is integrating an ARM CPU into their next-generation GPUs."
] |
[
"While this is a decent description of modern ",
", it's a bit misleading.",
"GPUs can be MIMD",
".",
"In reality the difference is simply the multicore vs. manycore argument.",
"In a multicore, you create a processor that's as powerful as you can make it, and then, when you can't make it any better, you stick a couple more copies of it down to take up the rest of the die space.",
"In a manycore, you deliberately create relatively weak processors, but a ton of them.",
"Multicore is generally better at MIMD, and manycore at SIMD, but that does not mean that multicore cannot do SIMD or that manycore cannot do MIMD. ",
"I feel that too much of your post was spent elaborating the difference between SIMD and MIMD, and that you may confuse others into thinking that manycore ",
" SIMD and that multicore ",
" MIMD."
] |
[
"Very well explained! I've heard bits and pieces of this before but never seen it all wrapped up so coherently."
] |
[
"Why do we develop tolerance to certain drugs? Why don't we develop a tolerance to others, antidepressants for example?"
] |
[
false
] | null |
[
"Tolerance is caused when a drug blocks a specific receptor on a cell, we'll use morphine and the mu receptor which is located throughout your body as an example, a cell that has all of its mu receptors blocked for an extended period it will try to compensate by increasing the rate at which it produces more mu receptors, once more receptors are being made it will take more drug to ensure all the receptors are being blocked.\nAntidepressants generally act by blocking specific proteins on nerve cells that act as a pump, technically called reuptake transporters, for neurotransmitters (seratonin, dopamine, norepinephrine) this results in more neurotransmitter being left outside the nerve to bind to receptors on other nerve cells. What the nerve cell detects from this is lower levels of neurotransmitter being brought back into the cell. Rather than producing more pumps the nerve compensates by producing more new neurotransmitter, with a net result that more neurotransmitter is released, which is what is ultimately responsible for most of the antidepressant effect of the drugs; this process can take a few weeks which is why when you look at studies antidepressants typically take a few weeks to reach full effect.",
"I'll admit objectively it may seem that people build up a tolerance to antidepressants but this is mostly because they aren't terribly effective to begin with and depression is very recurrent so many patients will relapse even if still taking the antidepressant",
"Hope that helps"
] |
[
"Are you trying to say that reuptake inhibitors don't build tolerance? Because cocaine for example is a reuptake inhibitor and is generally considered to build tolerance.",
"\"Tolerance\" is probably a pretty complex process, though. And dose has a lot to do with it."
] |
[
"I'm in pharmacy so cocaine is a bit outside my realm of expertise but I thought the tolerance was more a result of a psychological change, with continuous activation of the mesolimbic reward pathway resulting in the brain in an requirement for even more activation in order for the brain to recognize the activation as significantly above baseline"
] |
[
"If our skin cells die and regenerate so much, as well as most of the other cells in our body, why are tattoos still visible after so many decades?"
] |
[
false
] | null |
[
"Our skin has several layers, the top being composed of the epidermis (keratinized dead layers of cells) and the dermis (where your nerves, blood vessels, and epithelial progenitors are). These layers are held together and the cells are positioned by the extra cellular matrix, which is comprised of carbohydrate fibers and proteins. All tissues in your body have this as it helps organize and hold your cells in place.",
"The ink from a tattoo is deposited below the dermis and into the extra cellular matrix. Some of it gets into cells, and when they die the ink fades. This is why tattoos will fade with time. What remains, however, is the ink that has dyed the matrix. ",
"This is also why tattoos are so hard to remove: you can't just kill the cells because the dye is not contained in any cells. It's part of the matrix surrounding your cells, so lasers are used to break down the dyes directly"
] |
[
"Is that not what the henna style tattoos do? Those due your skin and last a couple weeks"
] |
[
"Is that not what the henna style tattoos do? Those due your skin and last a couple weeks"
] |
[
"When touching something without looking at it, why is it difficult to distinguish cold from wet?"
] |
[
false
] |
I first noticed this the other night while in bed, I reached my hands across my sheets and thought I felt something wet. It turned out to just really cold. It got me thinking and I tried out a few objects blindfolded, such as a cold ceramic dish, a cold glass, and porcelain. Is there anything to this or is it purely anecdotal?
|
[
"Maybe a better question is, do we have the ability to detect 'wet' directly or is it only through a combination of temperature and texture that we determine that something is 'wet'? "
] |
[
"To my knowledge, we have no sensory mechanism to detect 'wet' directly in the short-term."
] |
[
"Also, our sense of hot and cold is not actually a sense of temperature, it's a sense of heat flux. We \"feel\" energy out (cold) or energy in (hot), and how cold or hot it feels depends on the rate of transfer. ",
"How \"cold\" something feels depends not only on its actual temperature but also on its thermal conductivity. Water is a good conductor, and the contact between your skin and the water is excellent, so it tends to \"feel\" warmer or colder than other substances that are at the same temperature.",
"That's also why warm water feels ",
" if your hands are freezing, but you get \"used to it\" as your hands warm up. As the difference in temperature is reduced as your hands warm up the heat flux is lower, and the water doesn't feel as hot (even though it hasn't actually changed).",
"The opposite is also true. You can get an excellent insulator red hot and hold it in your hand."
] |
[
"Is it possible that the end of the sunspot cycle could significantly slow down global warming?"
] |
[
false
] |
Sunspots, the enormous magnetic storms that erupt on the sun's surface as the cycle builds, might disappear entirely for the first time in approximately 400 years. If the reported trends continue—a big if, other researchers note—a hibernating sun would have only a slight cooling effect on climate I'm not entirely so sure about that "slight cooling effect on climate"... We know SO little about the Sun's cycles and solar variability ( over timescales lasting more than several decades, since we barely monitored the Sun before a few decades ago). And assuming that this IF happens, then the last time this happened was the time of the Maunder Minimum, when you had snowfall and freezing temperatures (in both Europe and North America) during SUMMER. I would hardly call that "a slight cooling effect" (see ) - although if it happens again, I don't think it will be as severe as what happened during the Maunder minimum. In fact, my fear is that it would entirely discredit the climate modelling community just because they neglected solar variability. Already, I'm afraid that the climate modelling community (along with the broader scientific community, which has vehemently defended the modelling community) might be discredited (by the popular opinion) in 5-10 years, because there are other cycles that can cause an apparent lapse in global warming for around a decade (it's just that the warming in the 1990s was superimposed upon a warming part of the possible cycle, and we now might be heading towards the cooler phase of that cycle, which explains why the last 10 years haven't really seen much of a strong warming trend): But it might give us a lucky break of several decades. That being said, I'm definitely not counting or betting on that happening, and do not think the argument should be a factor towards laxer policies towards CO2 mitigation. Even if it did happen, I highly doubt it would result in anything similar to the repeat of the Maunder Minimum. I'm just anticipating that this be possible, and that if it is possible, then we must at least prepare for its slight possibility (and that maybe we can't completely be 95% confident that global warming is going to be as catastrophic as the IPCC thinks it is). By the way, I actually work with climate modellers, and am in no way sympathetic to skeptics of anthropogenic global warming (although I do have a fair amount of respect for both Dyson and Lomborg, though I don't like it how Dyson also tries to use some of the more scientifically irresponsible arguments). I am open to alternative sides of the data and interpretations, since I'm still just learning (and haven't gone through the entire IPCC pdf yet). With all that being said, does anyone think that the emerging field of could help us better quantify variations in the solar output (especially in the past?) See for a recent science paper (conducted on stars SIMILAR to the sun)
|
[
"Considering how low sunspot activity was the last few years (It was a very deep minimum) and yet we still had extremely hot years (indeed the 2000's were a good deal hotter than the 1990's I'd say I wouldn't count on it."
] |
[
"You dropped this:",
")"
] |
[
"\"The temperature change associated with any reduction in sunspot activity would likely be minimal and may not be enough to offset the impact of greenhouse gases on global warming, according to scientists who have published recent papers on the topic.",
"\"Recent solar 11-year cycles are associated empirically with changes in global surface temperature of 0.1 Celsius,\" said Judith Lean, a solar physicist with the US Naval Research Laboratory.",
"If the cycle were to stop or slow down, the small fluctuation in temperature would do the same, eliminating the slightly cooler effect of a solar minimum compared to the warmer solar maximum. The phenomenon was witnessed during the descending phase of the last solar cycle.",
"This \"cancelled part of the greenhouse gas warming of the period 2000-2008, causing the net global surface temperature to remain approximately flat -- and leading to the big debate of why the Earth hadn't (been) warming in the past decade,\" Lean, who was not involved in the three studies presented, said in an email to AFP.",
"A study in the March 2010 issue of Geophysical Research Letters explored what effect an extended solar minimum might have, and found no more than a 0.3 Celsius dip by 2100 compared to normal solar fluctuations.",
"\"A new Maunder-type solar activity minimum cannot offset the global warming caused by human greenhouse gas emissions,\" wrote authors Georg Feulner and Stefan Rahmstorf, noting that forecasts by the Intergovernmental Panel on Climate Change have found a range of 3.7 Celsius to 4.5 Celsius rise by this century's end compared to the latter half of the 20th century.",
"\"Moreover, any offset of global warming due to a grand minimum of solar activity would be merely a temporary effect, since the distinct solar minima during the last millennium typically lasted for only several decades or a century at most.\"",
"~ Taken from the ",
"yahoo article",
"."
] |
[
"Are comets constantly shrinking? That is to say, are they losing mass through their dust trail?"
] |
[
false
] |
That is to say, are comets like Halley's comet going to disappear one day?
|
[
"Comets are constantly losing mass. There is a finite number of passes a comet can do before it \"turns off\". However, common belief is that the comet won't just disappear but rather change. Comets lose ice more than they lose dust. It is assumed that eventually a comet could develop a surface that is a good enough insulator to allow it to stop the mass loss. However this would fundamentally change the comet into something else that does not behave or look like a comet. "
] |
[
"Indeed, there are such objects that have orbits we expect of comets but have spectra more like an asteroid. We call these \"comet-asteroid transition objects.\" ",
"944 Hidalgo",
" is among the most well-known."
] |
[
"Comets lose mass when they're near the sun. They heat up, which sublimates/boils ices, causing gas to stream out (and it will carry rocks and dust along with it). Comets are visible to the naked eye when they're outgassing like this (the comets themselves are too small/dark to see, it's the surrounding gas and dust you see).",
"Comets far from the Sun don't really do this. Oort cloud comets ten thousand times as far from the Sun as the Earth is don't lose significant mass.",
"Halley loses mass (because it comes close to the sun). This could cause it to become invisible (if all the ices boil away), although it's more likely that a close encounter with a planet will eject it from the solar system, or that it'll collide with a planet, than that it'll just run out of ices."
] |
[
"If Thorium is so abundant and cheap, why is it so hard to get a sample of?"
] |
[
false
] |
video from "Periodic Table of Videos" stresses how hard to get Thorium is, but every proponent of Thorium ever has noted that a major benefit of thorium is that it is so abundant and cheap to mine... So which is it, and if it's both, then how is this inconsistency settled? Are people just throwing away Thorium because it has no use currently? I would still expect there to be SOMEONE selling nice thorium spheres or cubes for classrooms... Edit: I'll clarify that I'm not asking about Thorium reactors or LFTRs or MSRs.... Just why is it so hard for a to get a , and when he does why is that sample so tiny? As far as I understand Thorium emits only alpha particles which are easily stopped by the lightest of shielding and might even be safe to handle with only gloves... I'd assume would be selling chunks of it!
|
[
"Thorium is abundant and cheap to mine compared to other similar elements, but it is still extremely rare compared to common metals like iron and aluminum. The main problem is that if there's no industrial use, there's no proper market and no economy of scale. A mine isn't going to be profitable if the only demand for their product is from people who think it's neat."
] |
[
"Im a mineral collector, so i speak from that viewpoint.",
"\nMonazite, the major ore, is traditionally minded as sand. To buy a nice Monazite crystal (like, 1-3 cm) can be a bit pricey. A thorianite crystal (1cm is big) can be REALLY PRICEY. So, specifically, in terms of crystals, the rarity is the cause of the price. As an ore, it is typically unremarkable."
] |
[
"To buy a nice Monazite crystal (like, 1-3 cm) can be a bit pricey. A thorianite crystal (1cm is big) can be REALLY PRICEY. ",
"Can you give rough numbers? This can mean anything from few hundred bucks to millions"
] |
[
"A question about redshift"
] |
[
false
] |
Okay, redshift. The distance between me and a galaxy far, far away increases because the universe is expanding, and this shows up as a redshift. In analogy: if I have a magic box from which an ant shows up every second, i get one ant per second if I put it on my desk. If I glue the box to a balloon, and I blow the balloon up, I get less ants per second. Even though the ant still move at their maximum speed-of-ants, they arrive slower. So, the ant-delay (redshift) is a measure of the speed with which the balloon is inflated (the universe expands). Yes? Now, we know that the speed with which the universe expands is increasing. So, younger objects in the universe exist in a faster-expanding universe, and should have a higher redshift. But instead, the really high-redshift stuff is truly ancient. What am I missing?
|
[
"I feel you are complicating things:",
"If a light source moves away from you the wave length of light you observe from it gets longer - this is red shift - and if it moves faster it gets more red shifted. The universe is expanding everywhere and all the time thus the more distant objects are more red shifted",
"Attempt at clever analogy: Take a balloon and make an x on it, then make a y close to the x, and a z on the other side. Pretend you are x, y a near by galaxy and z a far away galaxy. Inflate the balloon and y will move away from you, but z will move faster away from you. Works?"
] |
[
"Your ant metaphor is apt. What is important to remember is that each ant box emits ants at the same rate locally. The fact that the ants are walking across the balloon as it expands is the reason why the ants show up at your door at a different frequency than when they left the box. The ants from farther galaxies have to walk across the balloon while it expands for longer so they end up redshifted further."
] |
[
"So, younger objects in the universe exist in a faster-expanding universe, and should have a higher redshift. But instead, the really high-redshift stuff is truly ancient.",
"Redshift is a function of two things... the rate of expansion, and the distance to the object.",
"So while the rate of expansion is higher now than it was 10 billion years ago, the distance we measure to objects 10 billion years ago is really, really high. So their redshift ends up being large. ",
"The rate of expansion is only ",
" higher now than it was 10 billion years ago - a factor of a few, say. Whereas the distance to the ancient things is thousands and thousands of times greater than 'young' objects near to us. So the distance factor ends up dominating. ",
"Make sense?"
] |
[
"Is it possible that there are stable super-heavy elements (beyond atomic number 100)?"
] |
[
false
] |
Is there a law against it or is possible just taking a large amount of energy?
|
[
"Probably not. There is a proposed ",
"island of stability",
". However, this is a relative descriptor, as being able to work with something that might last for minutes to days would allow much greater depth & breadth of study than something which decays in fractions of a second.",
"It might also be of interest that some physical models propose the notion of ",
"proton decay",
", so as to temper the notion of \"no decay at all\" that you seem to be working with here. "
] |
[
"Mendelevium and nobelium have an atomic number of 101 and 102 and are stable.",
"Um ... no?",
"Mendelevium",
":",
"\"Sixteen isotopes of mendelevium from mass 245 to 260 have been characterized, with the most stable being 258Md with a half-life of 51.5 days, 260Md with a half-life of 31.8 days, and 257Md with a half-life of 5.52 hours. All of the remaining radioactive isotopes have half-lives that are less than 97 minutes, and the majority of these have half-lives that are less than 5 minutes. This element also has 5 meta states, with the longest-lived being 258mMd (t½ = 58 minutes).\"",
"Isotopes of mendelevium and their half lives",
"Nobelium",
":",
"\"Twelve radioisotopes of nobelium have been characterized, with the most stable being 259No with a half-life of 58 minutes. Longer half-lives are expected for the as-yet-unknown 261No and 263No. An isomeric level has been found in 253No and K-isomers have been found in 250No, 252No and 254No to date.\"",
"Isotopes of nobelium and their half lives"
] |
[
"There are legitimate and reasonable theories about the so-called ",
"Island of Stability",
". However, the hypothesized super-stable elements have not yet been synthesized. It is of course possible that there are fundamental reasons for this, thought it might also just be the technical difficulties (alluded to at the end of the article). ",
"So, yes, it is possible (in that there isn't anything we currently know that explicitly forbids this). The two most likely scenarios are that we either find some or that we come up with new physics that tells us why they don't exist.",
"*"
] |
[
"Why aren't airplane fuselage and/or wing surfaces dimpled?"
] |
[
false
] |
If dimpling significantly reduces drag on a golf ball, why can't a similar principle be applied to airplanes? If I remember correctly, Mythbusters tested dimpling on cars and concluded that it did improve fuel efficiency.
|
[
"Before adding some other factors I'd like to add to what ",
"u/cantilene",
" said; turbulence reduces flow separation and thus adverse pressure gradient. BUT, it increases skin friction significantly, the other form of drag along with adverse pressure gradient. With a golf ball you have no choice but to accept the possibility of adverse pressure because it is so \"blunt\", but an aircraft wing is generally not (except extreme conditions). So if you add dimples you add a whole lot of skin friction and drag vs. laminar or even transitional flow.",
"To add to this, think about the weight and manufacturing involved with dimpling something. The surface area of a dimpled object is MUCH greater than that of a flat object. That is more material and thus more weight. Aircraft usually have to be very careful with their weight. In addition, the manufacturing process to create sheets like that would add significantly to the already high cost of large aircraft.",
"And finally a slight rant, mythbusters is not a scientific source. They do not follow the scientific method and several of their \"conclusions\" have been misleading and perhaps even down right wrong. "
] |
[
"Just to further add onto the topic of the turbulent boundary layer:",
"At the Reynolds numbers most aircraft operate at, the boundary layer is almost completely turbulent. So adding dimples to that would really only give you more skin drag."
] |
[
"A lot of airplanes these days have vortex generators on the wings which do essentially the same thing. As to why all planes don't have them, the answer is that planes are built to be aerodynamic whereas golf ball are just spheres. The dimples on a golf ball help prevent flow separation because turbulent flow sticks to the surface better. But on a properly designed wing at the appropriate angle of attack, you wouldn't have that much flow separation to begin with."
] |
[
"Are all electrons and protons in the universe a product of beta decay?"
] |
[
false
] | null |
[
"No. Many of them are left over from the Big Bang."
] |
[
"Thanks, what percentage of them would you say are beta particles? "
] |
[
"I have no idea."
] |
[
"How is our body able to create the material our nails are made from?"
] |
[
false
] | null |
[
"Hair and nails are composed of ",
"keratin",
". Keratin is an extremely stable protein that is made as a very long, coiled fiber (sort of like a stretched-out slinky). The subunits of proteins, including keratin, are added piece by piece - imagine linking shower curtain rings together, one-by-one. These subunits are called amino acids.",
"The properties of the amino acids and the overall 3D structure of the coiled keratin cause multiple strands of keratin to aggregate together! The base of your nail makes new keratin all the time, and it sticks to the rest of the keratin being made until you get a (finger/toe)nail!"
] |
[
"That's called the lunula, it's the visible part of the keratin-making matrix that fingernails protect. Your grandmother might have just lost them with age (aging does weird shit to your body), but fingernails are also a good indicator of overall health, so it might be something worth checking out.",
"Fun fact - my dad is a physician, and he once diagnosed a stranger at the airport with cystic fibrosis because his fingernails were doing something called clubbing (my dad is pretty much House)"
] |
[
"Maybe, probably just compared to people who don't have enough protein in their diets. The enzymes that propel reactions forward, creating your nails, have a limit to how fast they can work. They can only string together so many amino acids (AA) in a given amount of time. If the concentration of AAs is low, the enzymes will work slower than if they had as many AAs as they could get their hands on. What this means is, after a certain threshold of dietary AA intake, the nails will be growing as fast as they'll ever grow. Below that threshold, as you become more and more deficient in dietary AAs, I bet you could see some decrease in nail production. Probably not terribly noticeable until you were super-deficient in protein intake."
] |
[
"Undiscovered Mathematics"
] |
[
false
] |
So as the legend goes, Newton discovered differential and integral calculus to describe planetary motion. Is it possible that there is more math to discover that is necessary to describe the universe? eg. Algebra, Trig, Calculus, ??? For example, might there be quantum mathematics?
|
[
"The answer is of course ",
", if history is any indication at all.",
"Physics has always been a (the?) major source of new mathematics, and it is as true today as ever. Roughly what tends to happen is that physics is written down using some mathematics that already exists (more or less), but a deeper study of the physical theory leads to a deeper study of the mathematics. This in turn may lead to a nicer formulation of the physical theory, which then leads to more mathematical development and more physics, and so on and so forth, and the subjects feed off of each other in this way.",
"Calculus and Newtonian mechanics is one example. It is of course ",
" the case that Newton just came out of nowhere, developed all of the principles of classical mechanics and calculus himself, and that the theory was somehow \"finished\" right then and there. Newtonian mechanics led to its reformulations ",
"Lagrangian mechanics",
" and ",
"Hamiltonian mechanics",
"--the mathematics here is well beyond what Newton came up with, and it is difficult to overstate the importance of these ideas to current math and current physics both.",
"More recent examples include relativity and the ",
"subsequent development",
" of differential geometry, quantum mechanics and the development of, among other things, ",
"functional analysis",
" (by ",
"Von Neumann",
", for example), string theory and the development of, for example, ",
"Gromov-Witten theory",
" and its influence on the study of ",
"moduli of curves",
", ",
"Chern-Simons theory",
" and its influence on ",
"knot theory",
", etc (much of this from ",
"Edward Witten",
", a ",
"Fields medal",
" winner), and about a billion other things.",
"So my point is, the ",
"interplay between physics and math",
" has always been strong, and still is, and the distinction between the fields is often blurred. There is more physics to be discovered, which ",
" there is more math to be discovered, and vice versa. The answer to all of your questions is yes."
] |
[
"True in what sense? You need to define your terminology better."
] |
[
"I think you have to account for our admittedly small capabilities of perception as modern humans.",
"We can't travel that fast, see that well, of a multitude of things. Few of us ever live in circumstances where we experience nuances like shifts in relativity in ways that we can directly and obviously observe. ",
"This is a popular argument by those who like to say \"well you only use XX% of your brain\"...And its somewhat unfounded.",
"The best way to approach your answer is to ask, if something exists out there and you can quantify it or even prove it to exist, what are you attempting to do? ",
"Any thing you even attempt to describe would be subjected to only your perception, your color spectrum, your main senses. ",
"You might as well ask if there are other forces we are unaware of...For example, humans can't detect magnetic fields or hear very high/low pitched sounds like other animals...there could be entire modalities of understanding that we haven't discovered because they aren't directly accessible to us.",
"The point is to keep trying to figure things out using what we have to create other things. Calculus wouldn't be possible without trig which wouldn't be possible without geometry which wouldn't be possible without algebra. Likewise, we couldn't detect the extent of the electromagnetic spectrum without scientists accidentally melting chocolate in microwaves or describing the eerie radioactive glow of their fine china at the last turn of the century with concepts of atomic decay.",
"I say all of that to say that yes, there could be some other way to describe the universe...just as there could be ANYTHING out there...but until you can prove it and test it and confirm it, then speculation is only going to get us no where. "
] |
[
"Do we possess the computational power to simulate the origin of a single celled organism from non-living material?"
] |
[
false
] | null |
[
"Essentially no. Not in the sense that you are probably asking the question. \nWe almost certainly don't have enough computing power to simulate enough molecules and a large enough environment to go from non-living material all the way to cells.",
"But even if we did have the computing power there are many, many steps in that process where we literally have no information. So building a simulation would be something of a lot of guess work."
] |
[
"Funnily enough I work on protein folding and the evolution of protein folds. I have to say that in 10 years the field as barely progressed and that's with all the advances around distributed computing, faster computers and gpGPU calculation. The biggest and obvious problem is that the models we use, complex as they are, remain far, far too simplified but we don't have a clear idea of where the simplification is acceptable and when it isn't.",
"We recently wrote a paper that was the first marked breakthrough in one of the sub parts of this problem in 15 years. The only problem is our work only applies to a tiny, tiny niche subset of the proteins that we know of"
] |
[
"There's a scientific field called \"Molecular Dynamics\" that deals with computer simulations of molecules.",
"The state of the art is simulating maybe 10",
" molecules over 10",
" seconds. So, it is no where near the level of simulating evolution.",
"Here's an example of a molecular dynamics simulation of ",
"ice melting",
"."
] |
[
"Where can I get some Renografin 60? Help me, Reddit Ask Science, you're my only hope."
] |
[
false
] | null |
[
"I'm not sure about asking for prescription medications, even one that is just a radiopaque substance with no clinical effect, on reddit.",
"Doesn't Bracco make it any more? If not, then I would suggest contacting distributors like Cardinal, McKesson, or Owens & Minor. If you're not using this for human use, but just for experimental purposes, they may have expired supply they may be able to contribute for your use. If you're using it for human use, I know it has 2 year shelf life, and you're probably out of luck."
] |
[
"One other suggestion. I don't know where you're located, but you might want to contact hospital pharmacies or radiology/cardiology cath labs in your area for expired ionic contrast agents. They are going to be really paranoid about giving away expired product because they will be concerned it will be used in humans. But if you're in an academic lab, and you contact the manager, and meet them in person with the appropriate credentials with the appropriate not for human use labeling, I'm sure they'd love to have you take it off their hands.",
"This will take some work, but you might be able to score cases of it. I remember having to take expired ionic contrast agent back for nonionic versions on many occasions. Yeah, I was in the industry for a long time."
] |
[
"Also, what about Isopaque from Mallinckrodt? It's essentially similar, but I'm not sure what you're doing for your work."
] |
[
"How would the Earth be different if it had three moons of equal size, equally spaced on the same orbital plane?"
] |
[
false
] | null |
[
"That's not a stable configuration, it would decay and eventually at least one of the moons would either be kicked out of the system or fall to Earth, and another would either suffer the same fate or have to move to a higher or lower orbit. Having two massive moons on the same orbit doesn't work."
] |
[
"Of course not, I knew the first answer would make me feel dumb. And I also realized that trying to evenly distribute mass would make the bulge less prominent since it's due to the gravitational imbalance caused by the moon's presence.",
"Hmm, I'm trying to write a story that somewhat hinges on the sea levels at the equator being much higher than the poles. I've always wanted to write something in the \"At The Mountains of Madness\" realm but I was trying to figure out a way to explain why with our current technology we didn't notice the enormous Antarctic mountain range. The only thing I could think of was to lower the sea level at the poles so that the mountains gained their height that way. But then the water has to go somewhere, I'm just not sure how to offset the distribution without causing massive tectonic (I don't mind flooding, I'd like to avoid rampant volcanism/earthquakes) or atmospheric problems. I could just write it and say forget the science but I can't bring myself to do that entirely. And I assume that shifting the weight of the water that much could cause that sort of problem. Really the more I keep thinking and writing on this particular problem the more ridiculous the proposition becomes. I just can't change that much without it pretty much wiping us out, which doesn't work well with a story that involves humans. I can drop the moons idea but it felt like introducing other massive objects was the only way to prompt some change. "
] |
[
"I feel like there are probably some simpler ways to get to the intended goal of un-noticed Antarctic mountains, starting with the currently known mountain ranges and mile-thick ice sheet."
] |
[
"Is sexual anxiety a new human trait or has it been around for centuries?"
] |
[
false
] | null |
[
"Short answer: Yes (probably). ",
"Science answer: A study on macaques revealed that males had difficulty achieving orgasm (less than 2% of time) if the female didn't make noise during sex. When they did shout, ejaculate rates rose to 86%. Source: (It had to be the Germans) ",
"http://rspb.royalsocietypublishing.org/content/275/1634/571",
"This directly shows a relationship between males ability to perform sexually based on reaction from the female, albeit in monkeys. However! More science tells us monkeys are relatives to apes, which I would relate to humans with confidence. ",
"I'm unaware of sexy studies in closer related species, or of any psycho-historical study with the foundation (see what I did there?) that related the males performance to social factors. Sounds most interesting. ",
"My condolences, things will get better."
] |
[
"You might want to consider specifying which of the two options in the original question you are saying \"Yes\" to."
] |
[
"You may have some success asking this question in ",
"/r/askhistorians",
" if you're looking for historical context in connection to current society (porn use and whatnot). It's not a scientific answer, but it may answer some of your questions. "
] |
[
"Does the method of loci/ memory palace technique really work? Are there any notable examples?"
] |
[
false
] | null |
[
"http://www.usamemorychampionship.com/"
] |
[
"The loci method is relatively well documented and has been shown to work moderately well for new learners. It is interesting to note that older people who may have age-related memory deficits don't benefit as much from it as young and healthy individuals (",
"ref",
").",
"An interesting point to note is that these kinds of techniques seem to be immensely beneficial some people and not-so-much for others. For an interesting (and rather bizarre) case of extreme memory feats, check out ",
"Solomon Shereshevsky",
", also known as Luria's patient 'S."
] |
[
"Here's an interesting TED talk on the subject: \n",
"http://www.ted.com/talks/lang/en/joshua_foer_feats_of_memory_anyone_can_do.html"
] |
[
"What would happen if you uniformly increased the pressure inside a perfect sphere of perfectly consistent material?"
] |
[
false
] |
If the material of the sphere was perfectly consistent, such as that there are no areas weaker than others, would the sphere ever break? In what manner would it break? I realise that an argument could be made for air pressure resulting in a rupture at a point where more force is exerted for a moment, so assume that the pressure provides uniform force in all directions.
|
[
"Well, the sphere will break once the pressure is high enough to push apart the bonds. ",
"As long as the material is not perfectly stretchy or something to that effect.",
"Same as with a chain where all the links have the exact same strength, each link is still breakable."
] |
[
"Well, the sphere will break once the pressure is high enough to push apart the bonds. ",
"As long as the material is not perfectly stretchy or something to that effect.",
"Same as with a chain where all the links have the exact same strength, each link is still breakable."
] |
[
"Yes, but for anything to break it has to start somewhere. In a real material, this happens at the tiniest imperfection, or even molecular bonds are not perfectly spherical.",
"In OP's imaginary universe where everything is perfectly smooth and spherical and not even composed of atoms, there is no single place for an initial perturbation to start the failure process."
] |
[
"Can a person get the same strain of Norovirus within a week or two of getting rid of it?"
] |
[
false
] |
I work in an aged care facility, and we are at the tail end of a disatrous Gastro outbreak. Now we have some residents getting it for the second time supposedly, and I'm a little skeptical regarding the legitimacy of these seconds bouts. I've looked online for an answer to this, and only found conflicting opinions with no sources (yahoo answers etc...) Furthermore, if you can get it twice, can someone please explain what the mechanism is? Does the virus mutate? Can it lay dormant? Thanks! edit: Thanks so much for the thorough answers, everyone! Both I and the RN here found this all fascinating. The nurse in particular (@64yrs old) found 'the reddit' to be amazing... just to touch on some questions: Yes, at the onset of the outbreak a Doctor (whoever it was) tested for and confirmed Norovirus. And there seemed to be some concern regarding why any resident here would be getting gastro twice... unfortunately all I can say about that is there has been an influx of very young and poorly trained new staff making many observable errors... making this outbreak drag on and on... I'm trying hard train them etc, but I'm night staff and barely see any of them! And I certainly know how bad the Norovirus is... I was the first Staff member to get it this time! Anyway, thanks again Science community!
|
[
"Yes you can. But it's highly unlikely and shouldn't happen but is completely possible.",
"You should be immune to the strain you just cleared for a short period (if you weren't then how would you ever get over it!) but this doesn't last long a few months in very fit and healthy people, the elderly probably have less effective immunity that doesn't last as long.",
"So how can you be infected again? This can happen for a number of reasons. 1) It's a different strain (completely different, a different bug, or slightly mutated). 2) Your immunity has passed.",
"The immunity doesn't last very long but the elderly aren't able to mount a great immune response (especially right after a d&v outbreak!) So I suspect that they could well be getting the same bug twice or even a lightly mutated version noroviris is a fairly fast mutator.",
"There's no point doubting it you'll never get rid of the outbreak if you don't put in place rigorous controls at the first sign of trouble."
] |
[
"Med Student here",
"Apparently you can ",
"http://www.cdc.gov/mmwr/preview/mmwrhtml/rr6003a1.htm",
"\nScroll down to immunity section, about 1/10th way down",
"Susceptibility seems to have host genetic factors.",
"Take away message: ensure infected patients are isolated and vigorous hand hygiene is instilled in everyone. Wash hands in hot water and soap between contact, ensure kitchen and bathroom surfaces are cleaned down with bleach or chlorhexidine (remember door handles!) "
] |
[
"That sounded sketchy. ",
"If you go to the CDC articles original sources it says \"",
" and five of the 10 who remained well had a ",
"What the article is saying is the host-genetic factors could cause you to asymptomatically clear the infection without developing an antibody response. That being said ",
" of those who became symptomatic 4 weeks later still had a serum response. ",
"Thus ",
"The one obvious exception might be if you received a dose that cause you to be symptomatic for a short period (say 1 day), but was insufficient to cause a longer infection and then you later received a much higher dose. "
] |
[
"Can you find the Mona Lisa in a Mandelbrot fractal?"
] |
[
false
] |
Apparently when one goes deep enough into any arbitrarily coloured Mandelbrot fractal one can find amazing structures. Is it possible to find the Mona Lisa painting in there when given enough time and resources? for reference:
|
[
"No. Just because something is infinite doesn't mean it will have every possible permutation of values.",
"For example, imagine a pattern like 10100100010000100000...",
"It could go on forever and never repeat. No where in that sequence of numbers will 123 ever appear. In spite of the infinite complexity of the pattern, it isn't guaranteed to have every combination of numbers."
] |
[
"It's not random. That's the problem."
] |
[
"It's not random. That's the problem."
] |
[
"What other things like seeing our nose and breathing we ignore by default?"
] |
[
false
] | null |
[
"We do this all the time with things that aren't changing in our environment. For example, when you first put your clothes on in the morning you feel them on your skin, but, very rapidly you stop noticing them. Now that you've read this, you might become aware of your clothing again! The same applies to ambient noise like traffic from the street or the ticking of a clock in your room. "
] |
[
"Generally speaking it's almost impossible to tickle yourself. Your brain filters the sensation of touching ourself to prevent the response another's might provoke. There are exceptions to this.",
"Someone's going to mention you're schizophrenic if you can, but having an ailment like that is a lot more complicated than passing one simple test."
] |
[
"There is actually a hole in your sight. Close one eye and take your thumb and, keeping your open eye facing directly forward and focused on a point in the background, move it across your field of view. Eventually, you will noticed that a portion of your thumb will disappear. This is completely natural and present in both eyes. Your brain compensates for this whole in the center of your vision."
] |
[
"Why are the noble metals so unreactive?"
] |
[
false
] |
From what I have gathered so far it seems that the inner electrons have more energy than the outer electrons. But I don't know how this all ties into it. If you are explaining it could you explain it in the most layman terms as possible so I can grasp the concept.
|
[
"Because we live on a planet covered in water.",
"The best way to understand this, look at the ",
"electrochemical series",
", and scroll down to 0, which corresponds to Hydrogen. Now, observe the metals below that point - Your \"noble\" metals.",
"Basically, the \"noble\" metals stay in their metallic elemental form because anything that ",
" react with them will preferentially react with water to give back the noble metal. But anything that ",
" react with them would typically react with water ",
", so that first condition doesn't even typically need to happen."
] |
[
"Not sure why this got voted down - It counts as the \"right\" answer.",
"If we lived on a planet dominated by free fluorine, we would have ",
" \"noble\" metals. If we lived on a planet with no free hydrogen or oxygen, we'd have \"noble\" sodium and calcium.",
"Although ",
"/u/cosmotravella",
" gave an answer possibly more like what the OP wanted, that reasoning doesn't work well in practice. Once we start dealing with D orbitals, you just can't explain the observed reactivity purely in terms of energy states. In the real world, we simply ",
" see ground state transition metals, ",
".",
"Why do we have gold just lying around on Earth? Because ",
", plain and simple."
] |
[
"While the other answers are very correct, I'll try and answer your question as well.",
"I'm assuming what you want to know is 'why are the elements at the bottom right of the transition metal series so much less reactive than those at the top left?'",
"This answer will be no good for a degree level course, if you are taking a chemistry degree then you'd probably be better off asking one of your tutors as things get very complicated very quickly. ",
"Now, in general a metal reacts by losing electron density from its valence shell (either wholly or partially losing electrons, think of the ionic and covalent character of bonds), if we think about the problem under this assumption then we can say that a metals reactivity will in some way be dependant on the ease at which it loses electrons to some attacking species.",
"An important concept is that as we add electrons into a given d subshell , e.g., the 4d shell, each additional electron is not getting further away from the nucleus, meaning that as we go from left to right along the transition series we are adding protons to the core (+1 charge each time) and are adding electrons into a level that is (roughly) the same height as the level we were at when we were one step to the left. For this reason as we progress to the right of the series along a given row the valence electrons of each element are held progressively tighter by the nucleus. (we say the effective nuclear charge increases).",
"Similarly, as we go down the series, the effective nuclear charge also increases, this is because each additional electron doesn't block the charge of the nucleus 100%. By the time we reach gold and mercury, the valence electrons are held nice and tight (there are also relativistic effects which mean they are held even more tightly).",
"Now while the effective charge of mercury/gold is strong enough to bind the valence electrons nice and strongly it is not enough to grab electrons and hold them in the 6p shell. So species that we call the nobel metals are not attractive enough to steal additional electrons but are strong enough to keep the electrons that they already have."
] |
[
"A question on nuclear decay and the number of nuclei."
] |
[
false
] |
The number of nuclei of a number of atoms after a time t can be defined with the equation: N = N(0) e The half-life (T) is therefore when N = N(0)/2, and so: N(0)/2 = N(0) e ; ... ; T = ln/λ If we were to represent N(0)/2 vs time on a graph, we would get this graph: As can be witnessed, there's a horizontal asymptote of x = 0. Since the y axis represents the number of nuclei left, this means that there will always be (an ever-decreasing) radioactivity. That is all fairly simple and such, however, if that is right, that means that no matter how long you leave a sample out to decay, you will literally never run out of your sample, and furthermore, it implies that you can even never get to N = 1 because if you can't run out of your sample, you would also suddenly lose the radioactivity. AND IF the sample could ran out so that N = 0, it would mean that there won't be any radioactivity anymore in any case. This has confused me, because obviously this is physically impossible, but the math states this is so. So what is the actual scenario in real life cases?
|
[
"The maths is statistical, it's describing a totally perfect situation where arbitrary amounts of radioactivity are allowed, including fractions.",
"In real life, this is of course not the case. The mathematical model is a very good match when you have many radioactive nuclei because on average everything works in the ideal way. But when you have few nuclei left, they can no longer quite fit this curve. Since the decay of any particular nuclei is totally random, the last few atoms could stick around for a long time, or all decay at once, or anything in between. On average, they'll show the ideal behaviour from the curve.",
"Also bear in mind that this is all statistical. That mathematical curve ",
" perfectly describes what really happens, even in the ideal case with loads of nuclei. It's only ever a good prediction. The idea of averages is very important, because that's what the maths is ",
" telling you the behaviour of."
] |
[
"Radioactive decay is modeled on a Poisson distribution. One of the assumptions of a poisson distribution is that there are a large number of \"events\" - or in other words that there are a large number of nuclei to decay. The equations don't hold exactly when you get down to very tiny decay amounts, and the results are distributed stochastically.",
"Here's an example. Take 10 pennies, and put them on your desk heads up. Then go through and flip each one individually. If it comes out tails, remove it. Continue until all the coins have been removed. The \"half-life\" of a penny is one cycle, since each one has a 50% chance of being removed with each flip. But if you applied the equations exactly, you would have 10 pennies, then 5, then 2.5, then 1.25, then 0.625... etc. Obviously this isn't accurate, since you can't have 0.625 pennies. What you would see is that the number of pennies left depends on the random chance of flipping the coins - maybe 10, 5, 2, 1, 0; maybe 10, 8, 4, 2, 1, 1,1,0. Radioactive decay of a small number of atoms works the same way."
] |
[
"Right, that actually make sense considering decay is random.",
"So, lets speak hypothetically, that you put a single atom of a radioactive isotope in a perfect quantum vacuum, it would decay right? What if it were directly observed the whole time?"
] |
[
"What is the psychological mechanism that causes things like songs or food to \"get old\"?"
] |
[
false
] |
If I listen to a song I like a lot, after a while I get bored of it, and eventually I'll start to downright dislike it. The same thing happens to everyone with certain foods, movies, even places and people. I just wonder why something I really enjoy can turn to something I actively avoid simply through being exposed to it too much. What drives this change?
|
[
"While you wait for the scientists to show up, here is the Wikipedia entry on ",
"The Coolidge Effect",
":",
"In biology and psychology, the Coolidge effect is a phenomenon—seen in nearly every mammalian species in which it has been tested—whereby males (and to a lesser extent females) exhibit renewed sexual interest if introduced to new receptive sexual partners, even after refusing sex from prior but still available sexual partners."
] |
[
"This is from a sociological perspective (I have a Soc. degree from UCSB). I am at work right now and don't have access to my old notes/books, so it is from memory. I do recall this very phenomena from my socialization class.",
"Habituation. These are actions we perform, or in this case things we do every day. You get diminishing returns after each listen/taste/ viewing/ what have you (basically any kind of stimuli). You'll likely notice that after you go without it for a given amount of time and then experience said stimuli again, you will notice it feels \"fresh\" again, but not to the same extent as the first couple times. Think of it like a graph constantly going toward zero.",
"EDIT: spelling change of habitualization to habituation. "
] |
[
"I think you mean the law of diminishing marginal utilities, not returns. And although the law holds true, it only gives a name to what OP was asking, not an explanation. "
] |
[
"Why is there only one species of human?"
] |
[
false
] | null |
[
"There are a variety of reasons, but here are two: ",
"1: Due to our technology and general intellect, humans around the world have been able to live in far more similar conditions than another, equally distributed species.",
"2: We are a relatively young species . Since the migration from Africa and the general distribution throughout the world, we didn't have enough time to develop to many unique genetic traits in various isolated populations. Now that the world is so much smaller due to technology, that will never happen.",
"It should be noted that various groups did undergo independent evolution leading to changes in skin colour, sand slight changes to things like bone and muscle structure, certain desease immunities and other minor differences, some of which we were directly responsible for, such as lactose tolerance which is more prevalent among populations who historically milked cows."
] |
[
"This is a tremendous claim to make as fact without citing supporting evidence. What about the hypothesis that humans and Neanderthals interbred, leading to the eventual genetic swamping of the Neanderthal genome?"
] |
[
"Because the other species of human (Neanderthals, ",
", etc.) were eventually driven extinct by competition from ",
"."
] |
[
"What caused the super-continent Pangea to split up in the first place? Is that same force still driving the plates in their movement?"
] |
[
false
] | null |
[
"Just a wee piece of general mislabeling that really grinds my gears as a student of geology, There is absolutely, categorically, completely, no layer of liquid (or boiling) magma in the mantle. There is a liquid outer core, which is composed of iron and nickel, which is not magma.\nThe mantle may behave as an incredibly viscous liquid over geologic time, but it is not magma. Magma/melt will only form under certain geologic conditions of temperature and pressure, and is very localised. (a good thing too or volcanoes would erupt everywhere)"
] |
[
"Pretty much, and Pangea didnt even come around until pretty late in Earth's life span. There were other supercontinets and little proto continents smashing into each other and breaking apart for millions of years before Pangea. Really interesting stuff "
] |
[
"Yes. One major example is the ",
"mid-Atlantic ridge",
" which started as the fault line that created South America's east coast and Africa's west. This is still active and expanding even today.",
"You might ask whether there are any current landmasses which are still together today but will likely split in the near geological future, and the ",
"East African Rift",
" is possibly the most active example.",
"It could be that, for as yet unforeseen reasons, the rift will fail. There's an example of this, believe it or not, in North America. The Great Lakes between the US and Canada owe their existence, at least in part, to the ",
"Midcontinent Rift System",
" which failed a ",
"illion or so years ago.",
"Had it succeeded, the world would be a very different place today.",
"Edit: million -> billion"
] |
[
"How would I determine how long it takes my apartment's stale air to be replaced by fresh air with all the windows open?"
] |
[
false
] |
Every weekend and some weekdays as well I have an argument with my wife about opening the windows and letting out all the warmth and letting in as much frigid fast flowing wind as possible. She's convinced it's necessary and it is nice to have fresh air but I at least would like not to prolong the torture if possible. What would I need to do to determine how long it takes for the complete volume of air in the apartment to be replaced by the air from outside? I'm guessing it really couldn't take that long because as we're on the third floor up and as soon as the windows are opened, very strong winds come in and blow every object in the house on to the floor and shake the bathroom mirror on it's fixtures. How do I approach this question?
|
[
"In scientific settings you'd seal up the house and add a tracer to the air. A tracer is inert (no reaction/adsorption), doesn't separate (no condensation/settling), and is originally present at a constant quantity (usually zero). Once you mixed the tracer in, and you were sure it was distributed evenly through out the house, you could start the flow and sample the concentration of the exit air periodically. You could then keep track of how long it would take to remove all the original air, since its removed in proportion to the tracer. If you wanted to do this experiment in a fish tank, you could use red food coloring to give you a water analogy. A common gaseous tracer is SF6 (sulfur hexafluoride).",
"I'm guessing like most people you don't have easy access to the analytical tools necessary to measure gas concentrations, so you can't perform a tracer test. Whether or not you run a tracer test, there are several other things you may be able to measure that might help you (some already mentioned in other comments):",
"air changes per hour (ACH)"
] |
[
"This is probably the most scientific approach to it I could think of as well. I would just get a smoke machine, fill my apartment. Open all the windows, start a timer, and stop the timer when you feel everything's cleared out. This isn't as rigorous and accurate as ramk13's idea, but it is fairly easy to do."
] |
[
"How do I approach this question?",
"The question is",
"How would I determine how long it takes my apartment's stale air to be replaced by fresh air...",
"My first knee jerk reaction is that you must define a satisfactory working definition of what is meant by this. What specification do you require? How fresh do you want it - ",
" Without such a definition, you'll never be able to test it."
] |
[
"Curvature of Earth and its effect on travel."
] |
[
false
] |
On a trip from India to US recently, I saw the path that my flight took, because they display it on your monitors. In image, the yellow line is the path that it actually took, but from what I understand, red should be the shortest path. So, I told this to a friend and he was like, "Well, it's the curvature of the earth that makes this the shortest path.". I was all like, "Oh OK.", but when I got around to thinking about it, I couldn't actually understand why. Could somebody explain why? OR did my friend not know what he was talking about?
|
[
"The shortest path between points on the surface are ",
"great circles",
". Due to the way the globe is projected on the map, they appear as curves. This is, of course, barring any other aviation considerations such as jet streams."
] |
[
"As otgers have said, it's all about great circles. If you want a more tabgible answer, grab a globe and some steing and place it between India and US."
] |
[
"It's because of the \"great-circle distance\"",
"Basically, the yellow arc is the shorter distance when viewed on a sphere, rather than a two-dimensional map.",
"Flat, 2-dimensional maps tend to be greatly distorted at their edges.",
"If you were to take a globe, and place one end of a string at your starting point, and pull it tight to your destination, you will get the great-circle distance, which will be shorter than the path that the red line takes.",
"http://en.wikipedia.org/wiki/Great-circle_distance"
] |
[
"Do humans (or other animal species) give off ultra-violet colors similar to flowers that we can't see?"
] |
[
false
] |
Is that why bees circle us? Or is it merely our scent? Or is it just a warning for us to get the fuck out?
|
[
"Apparently, they look like they've been smeared with pitch.",
"Here's a link to two pictures",
"one is taken using a regular RGB camera, and shows a person with sunscreen applied to half his face - this is not visible, and he just looks like a regular joe.",
"the other is taken with a UV-sensitive camera, and shows how this sunscreen ",
" UV light in one half of his face. ",
"(For fairness sake, I should note that mechanical sunscreens, based on ZiO or TiO reflect and scatter UV light, and chemical sunscreens absorb UV light..)"
] |
[
"As a photographer who did some experimentation with Infrared imaging a while back, I can say that the world, including people, looks very different. ",
"Here",
" is a link to the wiki, which includes a portrait done under ambient UV light."
] |
[
"The sun emits into the UV frequency range, and some proportion of that light is reflected off of everything that doesn't absorb the UV photons. Humans (and most animals) have ",
"melanin",
" which does absorb some amount of UV light (meaning that it would appear darker to UV sensitive eyes), but even the most melanin heavy skin does not absorb anything close to all the UV rays.",
"This means that bees, and any other UV seeing animals/machines/sensors will detect a person as having some amount of UV color. ",
"I am not nearly enough of an expert to even begin to approximate what the magnitude of that light would be, and how that would compare to something that had evolved to grow UV patterns. However, humans have never in our evolutionary history been hunted by or sexually selected for UV colored patterns, so whatever the bee does see is probably just a constant formless pattern. Think how tree bark is brownish, but not a single unified color anywhere and not generally patterned.",
"AFAIK, a bee can see us, and see the UV component of our skin color, but I rather doubt it reacts specifically to that information. Any circling bee is probably reacting most strongly to our sheer size and/or motion patterns."
] |
[
"How does radiation cause mutations?"
] |
[
false
] | null |
[
"Simply put, radiation breaks the strands in your DNA. The DNA can repair itself, and it usually does this quite well. A fraction of the time though, the repair process isn't done properly. This means the DNA is now slightly modified, which can affect the next generation of cells."
] |
[
"Technically the same as the other two answers currently up, different phrasing:",
"Certain types of radiation can get inside of your cells and then hit an atom with enough force to cause an electron to bounce out, which changes the charge of the atom and creates an Ion (thus the name, ionizing radiation)",
"This changes the chemistry of the atom drastically (example: Fluoride is good for you, Fluorine is bad, the difference is one electron). If that Atom happens to be part of a DNA molecule, this can rapidly cause a mutation in DNA.",
"If in turn that DNA is in a germline cell (cells that become sperm cells or egg cells), then that mutation can be passed on. Otherwise, it probably won't do much unless it causes a cell to behave poorly, in which case the cell dies.",
"This is basically radiation poisoning, lethal levels of radiation simply means to much cumulative damage has been taken to different cells, and your body can no longer keep up with the repairs. Also, healthy mutations in one cell can cause it to be read as foreign by other cells, which can lead to internal 'fights' between cells that are producing slightly different proteins. "
] |
[
"Otherwise, it probably won't do much unless it causes a cell to behave poorly, in which case the cell dies.",
"Or rarely it disables the cell's capability of committing suicide because something went wrong. Then at a later time another mutation comes along and deactivates the regulation of that cell's reproduction, and suddenly the cell starts dividing uncontrollably and has become cancerous."
] |
[
"Does Hydrogen Peroxide kill bacteria?"
] |
[
false
] |
Hi, So I got into a debate elsewhere about whether H2O2 can actually kill Bacteria. There was also suggestion of it "promoting healing" etc. of which I am more dubious. Peroxide breaks down into Water and Oxygen free radicals, and my understanding is that this breakdown is catalysed by biological matter, and the free radicals screw up chemical structures in the cell walls. Anyone got any citations they can offer, alongside a TL:DR? Obviously I am referring to the low percentage stuff you can get in brown bottles from a pharmacist.
|
[
"Neutrophils and macrophages actually make their own H2O2 (really starts as superoxide ion, O2",
" --superoxide dismutase--> H2O2) to kill bacteria as part of their oxygen-dependent killing mechanism. So yes this is a pretty good approach to killing bacteria. ",
"Another enzyme, catalase, is present in our bodies that breaks down the dangerous H2O2 into H2O + O2. Some bacteria also have this enzyme and therefore may be resistant to killing with H2O2.",
"Source: Murray, Patrick R., Ken S. Rosenthal, and Michael A. Pfaller. Medical Microbiology. Philadelphia: Elsevier/Saunders, 2013. Print."
] |
[
"That's great, thanks!"
] |
[
"I think you might be mixing a few things around here. NADPH oxidase makes superoxide ion which is the first step for production of reactive oxygen intermediates (ROIs) that kill bacteria. Without this enzyme a person would develop chronic granulomatous disease. In this disease the phagocytic cells can engulf bacteria normally but can't kill them with ROIs once engulfed which leads to T-cells walling off the ineffective phagocytes and forming a granuloma.",
"I can't say if all things make H2O2. Always and never statements are dangerous in science. But I'm sure that NOT ALL things have catalase, which would be needed to protect against H2O2."
] |
[
"Are there any methods of recording uncertainties without observing them?"
] |
[
false
] |
Quantum Mechanics has many particles and functions which are in a state of uncertainty until they are observed, where they collapse into a single state. My question is, are there any methods, theoretical or real, to record such things for future observation? For example, is it possible to freeze a quantum state in time so that it may be observed later on, and the data recorded? And as a further question, in quantum mechanics, what exactly counts as observation? Is it only human observation, or can it also be animal observation? What about mechanical? And does changing the observer create a difference in the observed state?
|
[
"There's a lot of questions in this post and some things you seem confused on, so I'll try to address each thing one by one. Let's start with the confusion.",
"Quantum Mechanics has many particles and functions which are in a state of uncertainty until they are observed, where they collapse into a single state.",
"You're confusing ",
" with ",
". An \"observable\" (a property that you can measure, like position, momentum, spin, etc.) has \"eigenstates\", which are quantum states corresponding to a definite allowable value of the observable. You can put a quantum system in a superposition of multiple eigenstates. A superposition is just a linear combination of multiple states. (For example, a chord of CEG on the piano is just a superposition of the sounds of C, E, and G.) When you measure the superposed system, it will collapse to one of the eigenstates with a probability proportional to \"how much\" of the eigenstate was in the superposition.",
" is a related, but separate concept. The uncertainty between two observables describes how much information you can simultaneously gather about both properties. Mathematically, two observables do not share a common set of eigenstates, they will have an uncertainty relation between them. Conceptually, let's take the classic example of momentum and position. Suppose I have a slinky and I make waves in it that travel down the slinky. If I measure the wavelength of the waves that I make, I actually get a distribution of values centered around some dominant frequency. The only way that I can get an ",
" value for a wavelength is if I make a ",
"standing wave",
", which has an exact wavelength. But this gives me no information about the position of the wave, because it is spread out over the entire slinky! This is a very close analogy to how things behave quantum mechanically - uncertainty is not specific to quantum mechanics, it describes general scenarios where knowledge of one property precludes knowledge of another one.",
"Okay, on to your remaining questions.",
"My question is, are there any methods, theoretical or real, to record such things for future observation? For example, is it possible to freeze a quantum state in time so that it may be observed later on, and the data recorded?",
"There are quantum states that have observables which do not evolve over time, but the \"phase\" of a quantum state evolves at a rate proportional to the energy of the system, so to \"freeze\" a state would involve cooling it to absolute zero, which isn't possible.",
"And as a further question, in quantum mechanics, what exactly counts as observation? Is it only human observation, or can it also be animal observation? What about mechanical? And does changing the observer create a difference in the observed state?",
"This is actually an open question in physics and there isn't a single answer that is universally agreed upon. However, as much as pop-sci media would like to have you believe otherwise, an observation doesn't have anything to do with consciousness, so a human observation or an animal observation or a mechanical observation are all the same. Changing the observer with another macroscopic object makes no difference.",
"The actual process of wavefunction collapse is also poorly understood. There are a lot of theories with varying degrees of credibility interpreting this, including ",
"the many-worlds interpretation",
", ",
"GRW theory",
", and the (most popular) ",
"Copenhagen interpretation",
"."
] |
[
"My understanding is more like \"use\" of the information (with \"use\" not being anthropomorphic).",
"That is to say any subsequent situation in which it matters what the state was at some point prior will cause the collapse. That would include, but theoretically isn't limited to, a scientist taking a measurement. It also (to my not-scientific brain) helps to explain some of the interferometry experiments where detection of one particle's state causes the partner particle to have ",
" been filtered by a polarizer at some point prior to that at which state was measured. "
] |
[
"My understanding is more like \"use\" of the information (with \"use\" not being anthropomorphic).",
"That is to say any subsequent situation in which it matters what the state was at some point prior will cause the collapse. That would include, but theoretically isn't limited to, a scientist taking a measurement. It also (to my not-scientific brain) helps to explain some of the interferometry experiments where detection of one particle's state causes the partner particle to have ",
" been filtered by a polarizer at some point prior to that at which state was measured. "
] |
[
"How can gene modification work in a fully mature adult?"
] |
[
false
] |
I understand how we can change the DNA info in a single cell and all but how does this spread to the rest of the body? It makes sense with a zygote because the single cell will split and become all the cells in the body but how does this work with a living breathing adult organism? How would injecting a shot containing genetic info into my arm cause the cells in my feet to get the same cancer blocking (just an example) genes that go to my scalp and lungs etc?
|
[
"A key thing to remember is that many tissues such as the intestinal lining, various immune cells, and red blood cells regularly replicate. If you can genetically change the stem cells that then divide and differentiate, you can change those downstream cells.",
"The methods used to induce the genetic modification can, theoretically, target all cells in the body that express a given receptor or other mechanism to provide specificity. Just like a flu virus infects a large number of cells, the genetic modification technique can do the same."
] |
[
"Has this ever been done with humans or other large mammals?"
] |
[
"Thank you. Very interesting. Hopeful and also a little scary."
] |
[
"Is it possible for an anion to exist in solution without a cation and vice versa ?"
] |
[
false
] | null |
[
"Yes, this is actually the basis for bioelectricity used in our nervous systemand muscles. Our cells actively seperate ions to create electric and chemical gradients that can be used to power other reactions (typically transport accros the membrane). The inside and outside of the cell are separate solutions seperated by a membrane. If there is a difference between total charges (cations-anions) inside and out then a voltage difference is created. In extreme cases like electric eels these voltages can be added in series to potentially deadly levels. "
] |
[
"I don't believe there is. The electric force is so strong that even if it were possible to separate the ions on a large scale your pure ions would become like a black hole for anything with the opposite charge. Plugging in the values for seperating the positive and negative ions from one mole of sodium chloride salt placed 2 meters apart into Coulomb's law tells me that the beakers of positive and negative ions would be attracted to each other with 2.09",
"10",
" pounds. I'm not entirely sure that's correct, its been a while since physics class but I remember a similar extreme example from class. That same force would resist the separation of the ions the entire time, getting more intense the more ions are separated so accomplishing this would require a huge amount of energy."
] |
[
"Thank you for the informative reply.",
"In that case how exactly is the anion separated from the cation?",
"EDIT: what i mean by that is how could this process be replicated in a lab"
] |
[
"How is CPU or GPU usage calculated and reported? How does a piece of hardware \"know\" how much of its maximum processing capacity is being utilized?"
] |
[
false
] |
[deleted]
|
[
"Every process is given time on the CPU by the kernel. This means that you can 'ask' the kernel how much time each process gets and from that, the usage. Take a look at this code if you want to see the nitty gritty details:",
"https://github.com/hishamhm/htop"
] |
[
"Game dev here - while true that this is how it works it can actually result in it being easy to misunderstand usage. For instance, one thread can be deadlocked waiting for another thread, and can report usage even though it is not conceptually busy. So knowing the difference between “actually busy” and “reported usage” is important once you are doing lower level programming.",
"In that respect, usage doesn’t actually represent “useful calculations” or “percent of processing power “ but literally just what % of residency the given task has, whether or not it’s doing anything useful with that time. whether the task is actually fully using the processing potential of the cpu is an entirely different matter that requires more precise tools (often a sampling based performance tool like VTune) to discover."
] |
[
"Any time-sharing operating system has, in its kernel, a bit of code called the ",
", whose job is to co-ordinate the different programs that want to run. (A single-core computer can only do one thing at once; it switches between tasks rapidly to give the illusion of multiple programs running simultaneously. Multi-core computers do the same thing except they can run up to (e.g.) four tasks at once. Each brief little bit of run-time is called a \"time slice\".)",
"Anyway, the scheduler has a list of all the currently active processes in the system. It chooses one to run next, sets up the CPU to be in the same state as it was last time it was run, and transfers control to it. After a while, either a timer goes off, or the running process makes a system-call like \"wait for a network event\"; either of these will transfer control back to the kernel. After the kernel handles the request, the scheduler gets told to suspend that process for a while and run another one. So it records the current state of the CPU to restore it next time, and also it updates a bunch of book-keeping info like how long the process had been running.",
"That book-keeping info can be used to figure out how much of the total CPU time is being given to one process or another, or to unused time when there's nothing to do. That number is what shows up when you look at a \"CPU utilization\" number in a process listing."
] |
[
"Do ants (and other small bugs) take fall damage?"
] |
[
false
] | null |
[
"Technically yes, since they are falling downwards, but their terminal velocity is not nearly high enough for any real damage to occur.",
"Plus, most bugs have strong exoskeletons or squishy bodies that can absorb impacts very well relative to their size."
] |
[
"So then if we were able to scale ourselves down 1:1 to the size of an ant, would our exiting skeleton now be able to withstand a very high fall?"
] |
[
"Doesn't even need to be as small as an ant. A mouse is (for our purposes) physically very similar to a really, really small human, and they can survive a fall from virtually any height."
] |
[
"Do we have a man-made satellite with a big elliptical orbit around the earth?"
] |
[
false
] |
And if we do what would be the purpose of this orbit?
|
[
"Yes! A good example of a very useful large elliptical orbit is a ",
"Molniya orbit",
". It serves the same kind of purpose that a geostationary orbit does, however it's designed so that most of its orbit is spent being directly over a much higher latitude. ",
"This is very useful for countries like Russia which are far enough north that a geostationary satellite would see it as \"slanted\" due to the curvature of the Earth. A Molniya orbit allows the satellite to spend most of its time looking directly down at high latitudes, while also staying generally over the same spots on Earth all day.",
"EDIT:",
"Another example would be a ",
"Tundra Orbit",
" which has a period of one day, instead of half a day."
] |
[
"What about in non-simple terms? What about 63.4 degrees prevent disturbance by the second zonal coefficient? What would happen if the inclination was another angle, would we see precession moving the apoapsis away from Russia or what? And what about higher order terms and tesseral coefficients, must they be accounted for or do the denominator r",
" grow so fast that they're irrelevant?",
"And as somebody without much familiarity with this particular math, I'm curious, must any object admit such an angle like 63.4 if the object is close to an oblate spheroid with close to a radially symmetric density function, or is it conceivable the Earth could be so constructed as to permit no such solution, and if so, what's special about our geology that permits it?"
] |
[
"From that Wikipedia link for Molniya orbits:",
"\"The reason that the inclination should have the value 63.4° is that then the argument of perigee is not perturbed by the J2 term of the gravitational field of the Earth but stays at −90°.\"",
"Details?"
] |
[
"What do you catabolize first during starvation: muscle, fat, or both in equal measure?"
] |
[
false
] |
I'm actually a Nutrition Science graduate, so I understand the process, but we never actually covered what the latest science says about which gets catabolized first. I was wondering this while watching , where the contestants frequently starve for 21 days. It's my hunch that the body breaks down both in equal measure, but I'm not sure. EDIT: Apologies for the wording of the question (of course you use the serum glucose and stored glycogen ). What I was really getting at is at what rate muscle/fat loss happens in extended starvation. Happy to see that the answers seem to be addressing that. Thanks for reading between the lines.
|
[
"Finally something in ",
"r/askscience",
" where my degree can be of use (PhD in muscle biology)",
"Whenever you stop eating, your substrate preference will be about 2/3 fat and 1/3 carbohydrates. Those carbohydrates will come from stored glycogen in your liver and muscles.",
"When those glycogen stores run out, the liver will try to defend the blood glucose through gluconeogenesis, synthesizing glucose from amino acids from protein broken down elsewhere in the body and glycerol from triglycerides. This metabolic phase is characterized often by decreases in blood sugar and associated tiredness and hunger. It is also the phase in which muscle catabolism progresses at the fastest pace.",
"However, 12-24 hours after running out of glycogen, the body will gradually go into ketosis, in which the liver synthesizes ketone bodies from fatty acids. These ketone bodies can substitute and/or replace glucose in the metabolism, reducing the need for breakdown of protein for amino acids for gluconeogenesis. After a couple of days the substrate preference will have changed to 90% fat and 10% carbohydrates, thereby reducing muscle catabolism strongly. This state can be maintained for as long as there is enough fat. The longest documented therapeutic fast was 385 days during 100+ kg weight loss in an obese patient. Mind you that a kg of bodyfat contains enough energy to go for 3-6 days depending on body size and activity level.",
"Ketosis and relying predominantly on fats will continue until only the essential bodyfat stores are left at approximately 5-7% in men and 10-14% in women. At this level the substrate preference for fats disappear and muscle catabolism increase sharply again. At this point death will usually occur within very few weeks."
] |
[
"Just going off of this: There was a case of a very obese man who ",
"literally starved himself for a year",
" to lose weight. Granted, the fact that his heart ",
" wasn't damaged by doing this was due to very careful monitoring by a team of qualified doctors. ",
"EDIT: The muscles of your heart need potassium and a variety of other important nutrients to continue beating. Not eating, period, usually depletes those nutrient stores very quickly. Heart failure is the usual cause of death when a person is starved for too long. In people who should be fat enough to survive, this is brought on by a lack of vital nutrients that are needed to sustain the heart. In this particular case, the team who worked with this man monitored his nutrient levels in his blood and urine and tried to ensure that even though he wasn't eating, he was still getting those vital nutrients. "
] |
[
"Just going off of this: There was a case of a very obese man who ",
"literally starved himself for a year",
" to lose weight. Granted, the fact that his heart ",
" wasn't damaged by doing this was due to very careful monitoring by a team of qualified doctors. ",
"EDIT: The muscles of your heart need potassium and a variety of other important nutrients to continue beating. Not eating, period, usually depletes those nutrient stores very quickly. Heart failure is the usual cause of death when a person is starved for too long. In people who should be fat enough to survive, this is brought on by a lack of vital nutrients that are needed to sustain the heart. In this particular case, the team who worked with this man monitored his nutrient levels in his blood and urine and tried to ensure that even though he wasn't eating, he was still getting those vital nutrients. "
] |
[
"If there's no ultimate frame of reference, how do we know the Universe's age?"
] |
[
false
] |
Could some other civilization in a different galaxy measure CMBR and derive an age other than 13.7 billion years?
|
[
"The age of the universe is given as measured in the CMB frame, which is the unique frame in which the CMB appears isotropic. In all other frames, the age of the universe is strictly smaller."
] |
[
"I take it you have heard of the Doppler effect, where when you travel towards the source of an EM wave, it appears more energetic, and vice versa.",
"Suppose there are two observers, one sees an isotropic CMB, ie same from every direction. The other observer is moving relative to the first observer, thus he will observe a Doppler shift in the CMB, depending on his direction of travel. Thus the second observer will see a non-isotropic CMB. Reverse the logic, and you can see how requiring an observation of isotropic CMB fixes a unique reference frame."
] |
[
"Could you explain this a little more?"
] |
[
"Question about possible containment methods for Japan's Fukushima nuclear plant."
] |
[
false
] |
Probably stupid, but.... Is it possible to contain the Fukushima nuclear plant with a sort of temporary sheet-like cover using the coordinated efforts of helicopters and/or cranes? I realize the plant is right on the shore which would make it quite difficult as there are many obstacles, but wouldn't it work if there were some sort of a "clamp/brace wall", if you will, built just off shore in order to hold whatever would be used as a cover? Any other possibilities? What, exactly, is even being done/discussed in regards to figuring out how to contain it?
|
[
"They actually are doing this. They are building outer structures with new overhead cranes and a system for fuel cask transfer to the ground level. They are additionally adding more structural supports and putting in HEPA level or greater air filtering to prevent radioactive particulate from escaping. ",
"Here is one article: ",
"http://www.world-nuclear-news.org/RS_Fukushima_fuel_removal_buildings_1904121.html"
] |
[
"Unit 1 has already ",
"been covered",
", more pictures ",
"here",
". There is work being done to remove the debris from the upper parts of the other damaged units. If you dig into some of the roadmap documents, they have installed a higher tsunami wall, and are planning on placing barriers to reduce further groundwater and ocean contamination, in addition to the measures Hiddencamper mentioned."
] |
[
"Hey, thanks. Even though this is an 11 day old post, I'm still interested. Do you also happen to know the current U.S. radiation exposure? I can't seem to find anything on it."
] |
[
"How do you prove the uncertainty of an observable related to an operator is zero?"
] |
[
false
] |
So, I'm struggling to prove this identity: ∆α=( < Q >−< Q > ) =0 for an operator Q representing an observable α. I assume it has something to do with expanding < Q > and < Q > as integrals, but I can't quite seem to get it :(
|
[
"Ah I see, that was much simpler than I thought. Cheers!"
] |
[
"The idea is that you are operating in a basis set, where the wavefunction |F> is an eigenfunction of the operator Q with the eigenvalue a:",
"Q|F>=a|F>",
"Next, remember what <Q> represents, it can be written in bra-ket notation as <F|Q|F>. This expression reduces to ",
"<F|a|F>=a<F|F>=a, making the assumption that F is orthonormal. ",
"As for Q",
" remember that what that expression means is that you are using the operator twice in succession, so",
"<Q^2>=<QQ> = <F|QQ|F>= <F|aQ|F>=<F|a^2|F>=a",
" * <F|F>=a",
"Putting it all together:",
"da = (<Q>",
" - <Q>",
" = ((a)",
" - a",
" = 0"
] |
[
"Note that your claim ∆α=( < Q",
" >−< Q >",
" )",
" =0 is not generally true of any observable operator in an arbitrary state. It is only true for an eigenstate of that operator, |F> (such that Q|F> = a|F>).",
"This is clear from the uncertainty principle alone: ∆x ∆p ≥ ћ/2 , where both x and p are observable operators."
] |
[
"Can dams be built in series?"
] |
[
false
] |
[deleted]
|
[
"The amount of energy you can derive from a dam is proportional to the pressure of the water, which is determined by the height. If you have dams in series, you lose that effective difference in height. That's why dams like the Hoover Dam and Three Gorges are all massive structures - that height allows them to hold back a large height (and thus pressure) of water, and allows more electricity to be generated."
] |
[
"It is actually rather common! Some examples are:",
"The Colorado River",
"The Columbia River",
"The Tennessee River",
"There's also others, such as ",
"the Upper Mississippi",
" and ",
"the Ohio",
" are also dammed, but more for navigational reasons, I believe."
] |
[
"There is a curve though. Massive dams like Grand Coulee and Hoover are simply not built anymore because it is more effective to have smaller (still quite big, just not monumental) dams in sequence.",
"Three Gorges dam in China is a mega-monster. It was not built to be the most efficient, it was built to be the most impressive. To me at least, they succeeded."
] |
[
"How close could a manned spaceship get to the sun?"
] |
[
false
] |
The astronauts must be able to survive and return to Earth, in a ship designed specially for this mission - not just a normal one that for some reason comes into course with the sun. Also, what about an unmanned no returning probe? Could one be built that could even get to the surface before burning up or being crushed by gravity?
|
[
"First, things do not simply fall to the Sun. Or they do but they constantly miss the Sun. When you leave Earth, you're going about 30 km/s, 90 degrees off of the Sun. If you intend to get to the Sun, you need to cancel most of this speed somehow. So far the probe that has left Earth with the greatest speed is the ",
"New Horizons",
", with a speed of 16.26 km/s, relative to Earth. Had we launched that in the opposite direction of Earth's orbit, it would have gotten an orbital speed of about 14 km/s around the Sun and would have made a new record in closest approach to the Sun at about 0.1 AU away, but that's still 20 solar radii away.",
"But actually, New Horizons did have enough propellant to make it into the Sun had we wanted it to go there. Because there's a more energy efficient way to go there than cancelling all the orbital speed of Earth right away. The way to do it is to first fly as far away as you can, theoretically infinitely far for the optimal case but something a bit less will do for us. So you get to the solar system escape velocity and fly away. New Horizons had even a greater velocity than this. When you're somewhere way past Pluto, your velocity will slowly approach zero, but never quite get there, if you had escape velocity when you started. Then you use your engines just a little bit to cancel your remaining velocity. Now you're stationary relative to the Sun and will indeed just fall in it.",
"So, it turns out that the most energy efficient way to get into the Sun (without using gravity assist tricks) is to first escape the solar system and then fall into the Sun. In other words it is easier to send something completely away from the solar system than to send it into the Sun.",
"Then with a little bit of finesse, you could loop around the Sun instead of hitting it with a velocity of about 600 km/s. And now we need to worry about shielding against the heat of the Sun. And also about getting the astronauts back home, although that turns out to easier than you might think. When you're at the closest point to the Sun you can make huge changes to your orbit with only a small amount of fuel. So the orbit there could be changed to meet up with Earth again half an orbit later.",
"Do note that this method of getting to the Sun is very time consuming. We're talking several decades here."
] |
[
"I know and I can't answer that without taking some wild guesses. However, I have a feeling he thought that getting there was no problem at all when in fact it's probably a bigger problem than the heat shielding, at least unless you go ridiculously close to the Sun."
] |
[
"There isn't really an answer to this question, because no ship like this has ever been designed. The way engineering works is, you specify design parameters, and engineers design a device that will operate within those parameters.",
"Now that we've gotten past that, a ship could certainly be designed to operate well within the orbit of Mercury. It would need a very well-designed heat shield though, to reflect heat away from where the crew is. The heat shield would probably be made from a very reflective metal with a reasonably high melting point, like silver or beryllium. A well-designed polished-metal conical heat shield could reflect virtually all of the energy away without absorbing enough of it to reach its melting point. Silver's melting point is 960 C, and beryllium's is 1290 C, which are well above the surface temperatures of either Mercury or Venus.",
"As long as the ship doesn't enter the Sun's corona, or get hit by a solar flare though, it would theoretically be possible to design a spaceship that could survive a brief period of orbiting very close to the Sun."
] |
[
"If I am allegic to house cats, am I also allergic to big cats (lions, tigers, pumas, etc)?"
] |
[
false
] |
Do all cats carry the protien that makes me unable to be around cats, or is it specific to the domestic house cat? It would sound cooler to say "I'm allegic to panthers and cheetahs" instead of "keep that little cute kitten over there away from me!"
|
[
"According to ",
"this",
" test of IgE and IgG4 reaction to Fel D 1 from many of the big cats - it looks like your answer is yes...you can say \"Get that Beast away from me! I am allergic to its relative Lions, Pumas & Siberian Tigers!\""
] |
[
"Reddit doesn't actually display accurate upvote downvote counts as an anti spam prevention measure. More than likely no one down voted it at all."
] |
[
"I wonder what 6 people think when downvoting the correct and cited answer. Maybe they are just angry you ruined their dreams of owning a \"big\" cat."
] |
[
"How does the concentration of sugar affect the fermentation in beer?"
] |
[
false
] |
Will more alcohol be produced with more sugar? Or less? This is for an EEI I am doing at school, thanks in advance :).
|
[
"Up until a point, the more sugar there is the more alcohol will be produced. Basically alcohol is a byproduct of the bacteria's respiration, so the more sugar they have to metabolise, the more alcohol they will produce."
] |
[
"You are able to fine tune the result of your fermentation by adjusting the sugar levels you start with, as well as the time spent fermenting. If you start with a higher level of sugar (you measure it with a hydrometer), you are able to end with a higher alcohol content. If you stop the fermentation early, you hold on to whatever sugar hasn't been fermented. In this way, you are able to adjust the final alcohol level, and final sugar level."
] |
[
"Consider posting this question in ",
"/r/Homebrewing",
" as well :)"
] |
[
"Graphene surface area."
] |
[
false
] |
I was reading an article on graphene supercapacitors when I came across this line The resulting graphene electrode is highly porous. A single gram of this stuff has a surface area bigger than a basketball court. It is from this article in the MIT review of technology. The electrode to which they refer is in a "coin shaped cell" so presumable its about the size of a quarter, give or take a bit. How is it possible to have such a large surface area if the coin size electrode is made up of graphene, which I understand to be a hexagonal lattice. What surface are they referring to? The surface of the sheets of graphene themselves? or the surface area of the constituent atoms? Are there as many sheets of graphene in the cell as there are quarters covering a basketball court? Thanks.
|
[
"When discussing porous materials surface areas, we normally speak of gas-accessible areas. This is the \"real\" surface area, that stuff can actually get to and interact with.",
"More formally, we measure the amount of gas adsorbing to surface of the sample, then back-calculate the area using the size of the gas molecule and the mass/volume of the material. This is normally measured as an isotherm, and modeled with Langmuir or BET theory.",
"Edit: It's probably relevant to mention that if your surface is electrochemically active, your can use this to determine surface area instead. It's more practical for very small samples (<25mg), but is somewhat poorly defined."
] |
[
"This is a great answer. What we do is we force a gas into the porous substance, so that it sticks to whatever it can. Each molecule of the gas is kind of like a pixel of a certain size. If we know how many pixels we can fit onto the substance, and how big each pixel is, we can work out how much surface area there is inside the sample.",
"However, you'll note that there are limitations to this technique depending on what your 'pixel' molecule is. Something relatively big and bulky, like CO2, isn't going to fit into as many nooks and crannies as something tiny like H2. So if we want to be really accurate when talking about surface areas of porous materials, you also need to explain how that surface area was measured, so other scientists and engineers know what sort of limitations there were in your methods."
] |
[
"I actually did my thesis on this exact topic. For a visual understanding, here are some electron micrographs of my electrode material:",
"http://s1359.beta.photobucket.com/user/norsoulnet2/library/Graphene",
"The above answer is 100% correct and the SA is measured by BET with N2 gas. This particular graphene you are looking at was made by thermal exfoliation of graphite oxide and resulted in a surface area of 600 m",
" per gram. This is about average surface area for graphene made with this method, and is probably the best way to make graphene in bulk."
] |
[
"photosynthesis equation tattoo"
] |
[
false
] |
so i have been thinking about getting the photosynthesis equation as a tattoo for a while now. and just saw a post of all the other awesome science tattoos. but my question is can you use E in the equation and it still be correct? (6CO2 + 6H2O + E --> 6O2 + C6H12O6) instead of writing out energy? i know its light energy but ive never seen a symbol for light. most of the equations i see use the word energy or nothing at all. but its a very important factor in the process and i want to include it just looking for the most scientifically accurate answer i can find.
|
[
"The correct symbol would be \"hν\"",
"h= Planck's (J.s)",
"ν= Greek letter nu = frequency in Hz",
"hv = J.sXHz = J.sX1/s = Joules = energy"
] |
[
"This is correct. (to OP) Also, rather than having it as +hv in your equation, this is generally written above the --->"
] |
[
"I would just put the word 'light' over your arrow.",
"Sure, not the most correct way to do it, but anyone who sees it will understand what you mean"
] |
[
"[Astronomy] How close can we get a man made probe to the sun before it becomes inoperable with today's technology?"
] |
[
false
] |
I understand that Helios I and II are the man made objects that have the distinction of being the closest, but I'm curious as to how close we can get with an unmanned probe using today's technology before it would begin to take enough damage that it'd be rendered inoperable.
|
[
"Here's",
" a good article that addresses your exact question.",
"For a spacecraft, the ability to fly safely near the sun depends entirely on its material, its design, and its fly-by trajectory.",
"Helios 2's perihelion (closest approach to the sun) was ~42 million km. The perihelion of that proposed probe is just under 6 million km, and the probe is scheduled to launch in 2018.",
"Solar Probe Plus pushes the limits of materials science and engineering, and will actually orbit within the corona of the sun, enduring temperatures of 2,600 °F (1,400 °C). "
] |
[
"Nice article, but all of the designs discussed were with longer term survival of the probe (much more scientifically useful from my point of view). However, OP seems to be interested in a possible destructive venture (e.g. the Soviet Венера 7-12 find more info on those in the ",
"Venus wiki",
" ). ",
"You could, conceivably, get much closer to the sun; with a non-orbital trajectory you could use the sun's gravitation field to increase the velocity of the probe, ablative and reflective technology increase the life expectancy of the sensing/sending equipment. This would in short order become a destructive maneuver for the craft, what you could detect in this suicidal death plunge is outside my ken, and getting that useful data back out would be difficult.",
"I tried to set up a calculation to actually answer your question, but the variables are numerous enough to make this not worth it. I'm just too lazy. Now if you paid me a salary and gave me time for research I could give you this answer; closer than we ever have. Then if you had me try again the answer would be; a little closer than last time. Ad infinitum with quickly diminishing returns."
] |
[
"Wow thanks, that was an excellent article."
] |
[
"Alternative method for space launch?"
] |
[
false
] |
I have little idea on the practicalities of this idea so I thought I'd throw it out there and see if anyone with more knowledge on the relevant subjects might be able to offer some insight. A big part of the cost and risk associated with space launches is the rocketry. As we know if the payload increases the amount of required fuel increases which increases the payload and so on.. Would it be possible to drill a circular hole in to the earths crust several kilometres deep, much like a geothermal well then at the bottom build a massive pressure chamber for the purposes of firing a payload directly up in to space? I would imagine the interior of the circular well would be lined with a kind of super conductive rail to reduce friction and any human passengers would be held inside some sort of inertia dampening gel bubble (now I'm stretching it!). Thoughts?
|
[
"Also wouldn't gravity be stronger the closer you get to the center of the Earth?",
"No it becomes less due to mass overhead. Check out ",
"Newton's shell theorem",
"."
] |
[
"This is a very cool idea that has been discussed in the scientific community for a long time, but there are several problems with the concept of using a ballistic/gun-type launch system to put large payloads into space - particularly manned payloads. ",
"The system you are describing provides all the initial delta-v requirements to the projectile prior to it exiting the muzzle, so the initial g-forces that the payload/passengers would be subjected to during the acceleration phase would still be extreme, even with a kilometer-long launch tunnel/barrel. ",
"You can lower the air pressure within the tunnel to help limit projectile drag, but once that projectile is accelerated and it exits the mouth or muzzle of the vacuum tunnel, it will immediately impact 14.7 psi worth of air pressure (assuming a muzzle location that is at sea level here). That would cause the ballistic payload to immediately begin decelerating upon muzzle exit as soon as it makes contact with the outside atmospheric environment, which would subject both the projectile and any hypothetical passengers aboard to further severe g-loads, this time in a direction directly opposite the velocity vector. Designing a man-sized capsule capable of handling all those extreme forces would be difficult, and designing it to be able to keep a human being alive inside throughout the launch phase would be considerably harder. Because of that, this gun launch system you are describing could function easier if it was utilized on a celestial body that lacks an appreciable atmosphere (like the Moon or an asteroid for example), as that would remove atmospheric loads on the projectile from the equation. ",
"If those g-force and structural integrity issues were worked out however, you could theoretically use this kind of system to ballistically throw payloads on either a sub-orbital trajectory or, if your delta-v is high enough and you can get above Earth's escape velocity, you could make your payload escape Earth's gravity well and head off into space. Unfortunately though, you cannot put a payload onto orbit above the Earth through a ballistic launch alone. In order to achieve a stable orbit, your capsule/projectile must have its own on-board rocket motor that is also capable of handling the rigors of launch acceleration, because you would still have to do a controlled prograde burn at or near apogee in order to raise your projectile's perigee high enough to allow it to enter a stable orbit. Without that on-board course correction capability though, your ballistic capsule will not be capable of achieving orbit, and will re-enter the atmosphere prior to completing a single revolution of the Earth.",
"While small suborbital payloads have been shot into space on purely ballistic trajectories (the US HARP project has done so already), as of yet we have not been able to design a small or large scale projectile with a functional rocket motor aboard that is capable of surviving the initial acceleration loads and allow you to execute the required course correction burn at apogee to achieve a stable orbit above the Earth. "
] |
[
"Very informative, thank you."
] |
[
"Do we really need to bend over when exiting an helicopter?"
] |
[
false
] |
I mean when walking away, not while exiting the hall.
|
[
"I have a helicopter private pilot license so I can probably give you some additional insight. \nThe rule that you mention is just one out of several rules when passengers approach or leave a helicopter with the rotor blades turning. The point here is that no one wants to have their head chopped off by a helicopter, and while the rotors blades should be parallel to the ground and higher than you, it is not always the case for whatever factors (land inclination, wind gusts, human error, etc). There is also things that could be blown out of your head, pieces of clothes, papers, your actual hair if you have long hair, and you need to be careful with those things as well. You should also never run to get an object if it was blown away. The way you approach a helicopter should always be by the front as well, you should never be close to the rear rotor since it will most likely be at your height as well, unlike the main rotor. \nMost aviation accidents happen because of negligence or human error, and these rules are in place for security and to try to avoid that accidents so they should always be followed."
] |
[
"I'll just add a note that one of the most dangerous times to approach/retreat from a helicopter is when the blades are spinning down. Most chopper blades are fairly flexible, and droop significantly when they loose the centrifugal force pulling them out straight."
] |
[
"You should also never run to get an object if it was blown away",
"Why? I'm curious. Thanks."
] |
[
"1. How does Norovirus make your body vomit? 2. How does the virus leave your body? Does it die inside of your body and get expelled through waste?"
] |
[
false
] | null |
[
"Your digestive tract has its own specialized, semi-independent nervous system, called the \"enteric nervous system\". (It has more neurons than your spinal cord, and almost as many neurons as are in a cat's brain and body combined!) Its job is to coordinate all the muscle movements that go into making food move from one end to the other...helping push food along with smooth muscle contractions, and also responding to threats like poison (via diarrhea and vomiting). You have specialized cells in your intestines—enterochromatic cells—whose job it is to communicate what's happening in the intestines chemically to the enteric nervous system (and, via the vagus nerve, communicate to the brain itself).",
"Norovirus seems to be masterful at manipulating those enterochromatic cells (probably through chemicals it gets infected cells to release, ",
"as the rotovirus does",
"). First, the norovirus gets the enteric nervous system to ",
"slow down sending food from stomach to intestines",
". This loads the stomach up with extra food (for extra vomit), because the norovirus is spread to new hosts by vomit and feces. It also gives the norovirus time to reproduce, loading up the stomach and intestines with billions of norovirus to spread. Then the norovirus-infected cells (",
"\"tuft\" cells, apparently",
"...I had thought we still didn't have a good idea) release a chemical that tells the enterochromatic cells to tell the nervous systems (brain and enteric) that it's time to vomit. The enteric nervous system is pretty good at coordinating the vomit reflex from there, stimulating all the right muscles with the right timing so everything in your stomach (and all the new, waiting norovirus with it) comes blasting out.",
"Norovirus-infected cells also trick the rest of the intestinal cells to dump their fluids, ",
" Infected cells, as they explode and release new copies of norovirus, also release a toxin that communicates to neighboring healthy cells \"hey, instead of absorbing tons of water, why not expel all that water instead?\" The wave of extra water can't be reabsorbed by the intestine because all the cells are trying to eject their water instead, and so billions more norovirus ride the ensuing poo-tsunami (poonami?) out the back end in search of new victims. This is why you can continue to have diarrhea long after you feel you've run out of food that you ate...the virus has basically turned on a hose inside your body that continues to flush water out long after the intestines are otherwise empty.",
"Obviously the new, healthy, infection-ready copies of the virus leave with your massive quantities of vomit and diarrhea. I assume you mean \"where do the dead, defeated noroviruses go after they've lost?\"",
"Much the same as your body's response to any other virus invaders...your macrophages are killing them indiscriminately whenever they encounter a norovirus. Your B-cells, once they figure out how to make a norovirus antibody (and only if enough noroviruses have taken root that the macrophages can't keep up) start churning norovirus-antibodies out in large quantities. These antibodies bind to the part of each norovirus that let it hijack cells...once \"antibodied\", the virus is effectively neutralized and can no longer infect any cells in your body. The antibody also acts as a handshake for any of your T-cells that come across it, as a signal that the T-cell should ",
" destroy whatever the antibody is connected to.",
"Your immune T-cells are also on the hunt, destroying some viruses directly, and also destroying any virus-infected cells before they can release more virus. Cells usually signal the T-cells themselves if they are infected, although norovirus is good at finding rare sorts of intestinal cells that don't bother letting the immune system know they're infected, which can help norovirus infections last a lot longer.",
"So with antibodies gumming up new viruses and T-cells rounding up infected cells and old viruses, pretty soon your immune system is gumming/destroying noroviruses faster than they can make new ones. Eventually every norovirus is either gummed up with an antibody and destroyed by a T-cell, or just destroyed by a T-cell, or destroyed by a macrophage. The remaining debris is either washed out the gut, or eaten by clean-up macrophages on patrol."
] |
[
"Thank you so much for taking the time to reply, and for explaining it so well. "
] |
[
"You’re welcome! I only hope this question wasn’t provoked by recent personal experience!"
] |
[
"Why is the severity of the urge to urinate not always correlated with the subsequent volume of urine?"
] |
[
false
] |
I have noticed throughout my life that at times the urge to urinate can be quite severe, yet when I finally am able to relieve myself the volume urine expelled can be relatively small. However, other times the urge may be less severe yet the subsequent urine production be voluminous. What are the factors that influence the severity of the urge to urinate? Is it more than simply the volume of urine in the bladder?
|
[
"The neurobiology/physiology of micturition is very complex. The Wikipedia article overly simplifies. Certainly mechanical factors of volume and pressure play a large role, and mechanoreceptors do mediate reflexive voiding. However, there are other neurologic subtrates and signaling pathways involved.",
"Firstly, some basic neurobiology of how we pee:\n",
"The pontine micturition center",
", AKA Barrington's Nucleus, is the supraspinal region of the brain that is responsible for initiation of urination. ",
"This",
" diagram from Nature Neuroscience helps illustrate some of the signalling pathways involved. During bladder filling, the PMC is largely inhibited. One mechanoreceptors reach a certain critical level of stretch, afferent pathways to the PMC activate, leading to activation of the PMC, and increase in parasympathetic tone to the bladder and external urinary sphincter, which in turn leads to voiding. This is reflexive voiding. As we age, we learn to modulate and control reflexive voiding, so that we are able to hold our urine, despite being full. Typical first sensation of bladder fullness is between 150-200 mL, first desire to void between 200-250 mL, strong urge between 250-300 mL, and extreme urge at higher volumes.",
"So, what other factors influence desire to pee? Well, looking first at that illustration from nature, you will notice inputs to the PMC from several other brain regions, notably the periaqueductal gray, but there are also thalamic, hypothalamic, and frontal projections as well. This means emotional cues, fear/arousal, and homeostatic cues can all influence urination and alter the volumes at which we urinate.",
"Beyond neurobiology, there are other receptors within both the bladder mucosa and the detrussor muscle which will influence voiding. There are chemoreceptors within the bladder mucosa which will respond to bladder irritants, most notably within the bladder trigone. This is why people will have urgency when they have a UTI, despite low bladder volumes. Other dietary factors, notably artificial sweeteners, alcohol (beyond its effects on AVP and diuresis), and caffeine, all have direct irritant effect on bladder mucosa.",
"Additionally, the parasympathetic outflow to the bladder is acetylcholine, and the predominant receptors in bladder are M2 and M3. Our medications for overactive bladder, such as oxybutynin or solefenacin, predominantly are anti-muscarinics. Sympathetic outflow to the bladder is norepinephrine. We have less therapies targetted at this arm of the system due to undesirable side effects, but this is why sympathomimetics such as Sudafed will influence urination.",
"Innervation to the bowel also runs via the pudendal and pelvic nerves. This is why bowel conditions like constipation or IBS may also cause or inhibit frequency of voiding.",
"So how does prostate enlargement lead to urgency/frequency/nocturia? These symptoms develop from longstanding bladder outlet obstruction. In response to increased resistance, the bladder hypertrophies, as any muscle will. In turn, you get upregulation of muscarinic receptors, and notably an increase in density of M2 relative to M3. This hypertrophic bladder is both deconditioned, and overly sensitive to parasympathetic stimulation. As such, it will take longer for these symptoms to resolve either with medical or surgical therapy."
] |
[
"Just to let you know, I've added your post to the list of exceptional AskScience answers list."
] |
[
"It's called \"cold diuresis\". It is related to the fact that as you get cold, blood is shunted from your skin to your core, and your body adapts to this larger central blood volume by inhibiting anti-diuretic hormone, and you pee more. Many a chair lift ride up the mountain have been made uncomfortable by this phenomena. "
] |
[
"Have all of the nuclear detonations on Earth potentially shifted Earth's orbit around the Sun?"
] |
[
false
] | null |
[
"The answer ranges from ",
" to ",
"First of all, realize that for a nuclear explosion to have ",
" effect on the Earth's position or velocity, it would need to somehow kick up chunks of matter away from the Earth. Otherwise, ",
"Newton's laws of motion tell us",
" that if we consider the Earth and its atmosphere as one system, then any internal change of this system cannot change its overall momentum. To put it simply, when you throw a ball away from you, you are pushing on the Earth a tiny, tiny bit, but this change is compensated for by the ball's momentum. As a result, from an external perspective the overall momentum of the Earth doesn't change ",
" Nuclear explosions are far larger and messier, but the key idea remains the same.",
"So in other words, to push the Earth, we would need to cause the explosion to propel matter away from us, just like a rocket pushes gases away so it can move forward. In principle we could think of a way to use a nuclear bomb to this effect, where we would explode it right outside the atmosphere so it can push the Earth. But now we have a second problem: the Earth has a huuuuge amount of kinetic energy. The Earth has a mass of 6*10",
" kg and is flying around the sun at a speed of 30km/s. Now we can work out the total (translational) kinetic energy:",
"E = 1/2 m*v",
" = 1/2 * 6*10",
"kg * (30,000m/s)",
" = ",
"So we get a whopping 3*10",
"J of kinetic energy. To put that in perspective, the most powerful nuclear bomb ever tested, the Tsar Bomba, ",
" had a yield of 2*10",
"J. In other words, ",
" I think it's fair to say that we are pretty safe as it is... "
] |
[
"Thanks for that awesome reply! I was just curious after watching a show where they talked About changing an an asteroids trajectory by either exploding a bomb on it or hovering a large spacecraft near it in order to slow it down. "
] |
[
"That's not actually a terrible idea. If we know that some asteroid is on a collision course with earth, it only takes a small kick while it's still at a decent distance to turn a head-on collision into a flyby. Sure, it's not stopping an asteroid, but a few meters per second in the right direction is enough to get that job done. "
] |
[
"\"There is no Dothraki word for 'thank you.'\" We're all familiar with the \"Culture reflects language\" trope in popular culture, but are there linguistic differences to that extent in certain cultures in real life?"
] |
[
false
] | null |
[
"The trope you're describing isn't the one present in the example. Culture does not reflect language, in real life or in most fiction. The Dothraki are not aggressive and selfish because they lack a concise way to express thanks, they lack a concise way to express thanks because they are aggressive and selfish. ",
"This happens all the time in real life. Generally not with appreciation, because there's good reason to think that gratitude is a universal part of human nature, but, yes, when a culture doesn't have a thing, the language doesn't have that thing either. Because how could it? You can't name something that doesn't exist. ",
"So, when you have some particular practice that exists in one culture and not another, you get a word in one language and not the other. ",
"One example off the top of my head, there is a word that is present in a particular polynesian language, and no other language in the world. It means \"a curse upon a name or place, such that speaking it or entering it is bad luck\". No other cultures do this, at least not to such a degree, and so no other cultures have a word for it. The word is \"tabu\". In 1777, Captain Cook visited the island, thought the practice was cool, and brought it home to England, where it caught on and survived as a word for things that are forbidden to speak. ",
"This is also an example of how goddamn hard it is to find examples in modern languages that aren't absurdly specific, because of the unlikelihood that people would lack words for basic concepts common to all humankind, and because globalization had a flattening effect: all the cool stuff from every language was borrowed into every other language. "
] |
[
"In short, yes. For example, a word differentiating blue and green is a relatively modern invention. To the ancient Greeks, the sky was white and the sea was \"wine-dark\".",
"I remember this article that got passed around because of that Radiolab episode and this is wrong.",
"Yes, Homer did describe the sea as \"wine-dark\" but he also talked about the \"blue eyebrows of Poseidon\" (and purple sheep, Homer might have been high, who knows?).",
"The word \"κυανό\" was used by the ancient Greeks. It became cyan in English. ",
"For example: ",
"a selection from Homer's Iliad mentioning κυανό",
"And don't forget ",
"Caesar's memoirs on fighting blue painted dudes in Britain.",
"We definitely know for sure ",
"blue had Proto-Indo-European roots",
" and ",
"distinguishing it from green",
" wasn't a relatively modern invention."
] |
[
"In short, yes. For example, a word differentiating blue and green is a relatively modern invention. To the ancient Greeks, the sky was white and the sea was \"wine-dark\".",
"I remember this article that got passed around because of that Radiolab episode and this is wrong.",
"Yes, Homer did describe the sea as \"wine-dark\" but he also talked about the \"blue eyebrows of Poseidon\" (and purple sheep, Homer might have been high, who knows?).",
"The word \"κυανό\" was used by the ancient Greeks. It became cyan in English. ",
"For example: ",
"a selection from Homer's Iliad mentioning κυανό",
"And don't forget ",
"Caesar's memoirs on fighting blue painted dudes in Britain.",
"We definitely know for sure ",
"blue had Proto-Indo-European roots",
" and ",
"distinguishing it from green",
" wasn't a relatively modern invention."
] |
[
"What is this with my hands?"
] |
[
false
] | null |
[
"Hello,",
"We can't speculate about your personal experiences here."
] |
[
"Thanks!"
] |
[
"Where do i go then? What reddit should i ask?"
] |
[
"I know Newton believed in absolute time and relative time, I understand why he believed in relative time, but why did he believe in absolute time?"
] |
[
false
] |
What evidence did he have for absolute time? Why did he argue for its existence? Also could you also provide any readings on this if possible
|
[
"Here’s an attempt to begin an answer: from Newton’s ",
":",
"“Absolute, true, and mathematical time, of itself, and from its own nature flows equably without regard to anything external, and by another name is called duration: relative, apparent, and common time, is some sensible and external (whether accurate or unequable) measure of duration by the means of motion, which is commonly used instead of true time; such as an hour, a day, a month, a year.”",
"Relative time, says Newton, is derived by observing motion: so we can measure a day by the earth’s rotation relative to the sun. Absolute time is the underlying physical phenomenon that makes motion possible at all, which is not directly measurable without reference to motion. So by “relative”, it seems Newton means something different to Einstein. Newton assumed that time flows at the same rate for all observers, since he had no reason to assume otherwise given his understanding of the world."
] |
[
"The quotation says that relative time is a ",
" of duration. If nothing is in motion, time may pass, but we can’t say how much. We can’t “see” time passing directly, we can only infer it by observing things changing."
] |
[
"Relative time is empirical in that we measure it by observing change. Specifically, what we measure is duration—the time difference between one event and another. Absolute time, as I understand it, is like the framework those durations are attached to, perhaps a bit like a peg board with bits of string of various lengths attached to it. It’s a mathematical entity."
] |
[
"Can anybody on here describe what my grandfather's thesis is about?"
] |
[
false
] |
[deleted]
|
[
"From the patent for the strophotron, it says \"A strophotron is a mulitransit electron tube adaptable for use in the VHF and UHF frequency ranges\" and directed me to ",
"this",
" paper which I can't access right now."
] |
[
"Here's the abstrtact and first couple of paragraphs:",
"Summary-A new multitransit-electron tube is described, having\nhigh efficiency and an exceptionally wide electronic tuning range. An\nimportant feature of the tube is a trochoidal electron drift motion at\nright angles to the radio-frequency field, serving to remove electrons\nfrom the field at a favorable instant.",
"THE STROPHOTRON is a developmental electron tube that holds promise for a variety of\nuses in vhf and uhf communication. It is a highefficiency, wide-band device, easily frequency-modulated or electrically-tuned over an exceptionally wide\nrange of frequencies. In fact, strophotrons may be\noperated, without mechanical tuning, over a frequency\nspectrum covering about an octave. The electrodes of a\nstrophotron are few, of simple geometry, and do not require close tolerances.\nThe present paper will be limited to a general indication of the principle involved, the merits of the system,\nand some of the experimental results obtained with the\ntube operating as an oscillator. Development of the\ntube for amplification purposes is under way and will\nbe reported in due course.",
"PRINCIPLE OF OPERATION",
"Basically, the strophotron may be regarded as a Barkhausen-Kurz oscillator or a multireflex klystron, in\nwhich some of the inherent drawbacks of these and\nsimilar tubes of the prior art, such as poor efficiency and\nlow power, or narrow range of operating frequencies,\nhave been eliminated. This is achieved by a combination\nof frequency-independent density modulation of the\nelectron beam and a controllable drift velocity of the\nelectrons in a direction perpendicular to the oscillatory\nmotion, serving to remove them from the radio-frequency field at a favorable instant. This drift motion,\nobtained by means of crossed electric and magnetic fields\nor by an inhomogeneous magnetic field, is similar to\nthat present in trochotrons.2 The magnetic field at the\nsame time serves to prevent the electron beam from\nstriking the accelerator electrodes."
] |
[
"No idea on the strophotron, has things like coaxial cable tied to it. Probably a radio electronics piece.",
"http://link.springer.com/article/10.1007%2FBF01038829?LI=true",
"I love your username by the way!"
] |
[
"Could we start using older antibiotics again?"
] |
[
false
] |
[deleted]
|
[
"While this is mostly true, there is absolutely selective pressure ",
" antibiotic resistance in the complete absence of antibiotics. Unfortunately, most antibiotics are naturally occurring at concentrations high enough to avoid this selective pressure, so in practice we probably won't be able to use most of our old antibiotics again. "
] |
[
"It depends on the mutation, but usually bacteria hold on to these generic resistance islands even if they don’t express them all the time. Many carry SOS systems that cause them to rapidly express chains of genes (including resistance ones) in response to a life-threatening threat. "
] |
[
"Oh."
] |
[
"How does the brain know where each nerve ending is?"
] |
[
false
] | null |
[
"What do you mean?"
] |
[
"How does it know that the pain receptor on the end of my left finger is at the end of my left finger?"
] |
[
"Ah, see ",
"https://en.m.wikipedia.org/wiki/Axon_guidance",
" and related wiki pages. Is that what you mean?"
] |
[
"How do we know that all medicine isn't just a \"sugar pill\" with our brain causing the reaction it thinks should happen?"
] |
[
false
] | null |
[
"This is why you do double-blind studies where the doctors themselves do not know which patient is getting which kind of pill."
] |
[
"Mostly. The term you are looking for is \"double-blind clinical drug trial\"",
"Some exceptions include some surgery procedures. In those cases, surgery is still performed on the patient, but whatever is inserted into one patient is not inserted into another. In that case, the surgeon doing the surgery would know which is getting which. However, the doctor monitoring the patient afterward would not necessarily know."
] |
[
"You give some people medicine and some people a sugar pill. Tell both groups that they are getting medicine. See if the medicine group has better outcomes."
] |
[
"When I look into the sky how large is my field of view?"
] |
[
false
] |
I thought of this question while looking at an airplane. The plane appears to be barely moving obviously the plane is traveling very fast. My estimation is that my field of view on a clear day must be 1000 km
|
[
"First, we should clear up an issue that seems to be causing some confusion. Field of view is most appropriately expressed as an angle, not a distance. This is because we can see very very large objects if they are very very far away (like stars, which are in fact hundreds of times larger than the earth, but appear small because they're so far away). ",
"Having said that, Humans have an almost 180 degree field of view in the horizontal direction, and about a 130 degree field of view in the vertical direction (",
"source",
")."
] |
[
"You're not really asking a well-defined question here.",
"If you were ",
" ",
" ",
" at 10,000m, the distance to the horizon would be about 357 km, so you'd \"see\" about 400,000 km",
" of earth, and the ground would appear to be moving by at the same speed that you see the airplane moving.",
"But how much of the sky do you see? Well... about half of the universe.",
"http://en.wikipedia.org/wiki/Horizon#Distance_to_the_horizon"
] |
[
"I think an answer to OP could be the partial surface of a sphere centered at his eyes, extending to the distance of the airplane and covering his entire field of view.",
"Which would basically be a fraction (determined by the 180 by 130 degree) of the surface of a sphere with radius of somewhat over 10 km.",
"If we choose 15 km (airplane is away and above us), then the surface area is 1020 km",
" . It seems OP's estimation matches with this.",
"This is also somewhat arbitrary, since the airplanes distance will be changing and some things in the field of view will be closer or further away."
] |
[
"What do I hear when the world around me is silent?"
] |
[
false
] |
When there are no children screaming, no cars driving, no air conditioners blowing, when everything is as silent and motionless as is reasonable, what am I hearing? Can I hear things going on inside my head, and, if so, what?
|
[
"First off, you will never be in an environment that isn't permeated by some form of sound. However, when it becomes nearly silent your brain has the ability to cope by tricking you into thinking you are hearing sounds. With every image that you see, your brain registers a sound as well. When you see an event, say an explosion,even in complete silence, your brain will trick you into believing you heard the complimentary noise registered by that image. In this way, yes, you can hear things from inside your own head!",
"More information:",
"http://www.guardian.co.uk/science/blog/2010/may/14/brain-hears-silent-movies"
] |
[
"I seem to remember a post on reddit that used ",
"this gif",
" as an example. (Can't find the actual post because of the lack of decent reddit-fu...)"
] |
[
"Tinnitis :) That's what I hear..."
] |
[
"How do cows (and other herbivores) produce protein?"
] |
[
false
] |
Omnivores(like us) and carnivores obviously can easily build muscle by eating meat, beans, nuts, etc... to get their dietary protein and essential amino acids. How do herbivores (that don't eat beans and nuts, such as cows that typically only eat grass) produce the necessary amino acids to build all of their muscle? How are these animals able to synthesize all of the amino acids without relying on other sources, and why are we unable to synthesize the essential amino acids as they can?
|
[
"there are two basic types of amino acids, essential and non-essential. non-essential amino acids can be synthesized essentially from scratch by using various cellular byproducts from various pathways. essential amino acids are amino acids that an organism is not capable of synthesizing by themselves. cows have bacteria in their gut which do most of their amino acid synthesis or cellulose breakdown for them. these bacteria are able to synthesize amino acids from various sources of nitrogen (urea, ammonia, etc), and when each generation dies, the cow digests them and extracts the amino acids from them. having said that, i know that normal cattle on a farm are usually deficient in 2 amino acids: Lysine and Methionine. in a farm, a special type of feed is given to them which contains \"protected\" versions of those two amino acids. the amino acids are protected because if they were not, the bacteria in the gut would just break them down and make other amino acids from them. regarding cows in the wild, i am unsure as to what exactly they eat, but i imagine it would not be \"just grass\"."
] |
[
"the first link makes me ಠ_ಠ just a little. They completely knock \"complete proteins\" as if it's something completely negligible. It is important to note that proteins are made out of amino acids and some plants have more of some types of amino acids than others. It is important, if you're not eating any sources of animal protein, to balance the vegetable sources that you eat to make sure to get sufficient quantities of those amino acids."
] |
[
"It sounds like the cows are depending on bacteria in their stomachs that humans do not have to produce some amino acids.",
"This is very much true."
] |
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