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[
"Why is my frosted notebook cover transparent when close to an object, but opaque at distances?"
] |
[
false
] |
I was in class and I realized that as I opened my notebook cover, the text underneath became rapidly out of focus. The cover to the notebook is a frosted plastic. When the cover is closed and the plastic is directly above the text, everything is easy to read. Once the cover is a distance of a few centimeters from the page, nothing below can be made out. I assume this is based upon some refraction principle, but I could not find a good explanation anywhere.
|
[
"Imagine two of the letters that are near each other each producing two light rays at a slight angle to each other (like a <, but with a much smaller angle, coming out very near perpendicular to the page). These rays hit the plastic, and are scattered a bit (the frosting effect). Now, if the distance between letters and the plastic is quite small, the rays from two different letters won't overlap: they won't have traveled very far from the perpendicular (in terms of linear distance). However, if the plastic is very far from the letters, the rays from different letters can fall on the plastic at the same point, which means when they are scattered, you can't tell which ray originated from which letter, resulting in them becoming blurred together.",
"In reality, each letter \"emits\" many many rays: the more that can be traced back to each individual letter, the more distinct the image will be. The farther away the plastic is from the paper, the more letters will have rays that fall on a given point in the plastic (when they are pressed together, only rays from one letter can fall on one particular point in the plastic).",
"Since the rays travel straight after the plastic, the observer-plastic distance is irrelevant: only the plastic-object distance determines blurriness."
] |
[
"the cover refracts light at different angles (most likely due to surface roughness). thus, at close distances, rays aren't bent much, but when the distance between the medium and the subject are increased, increased refraction blurs the image."
] |
[
"Why then, is it a function of the distance from the object, but not of the distance from the observer? Sorry, my optics knowledge is REALLY fuzzy (no pun intended)."
] |
[
"I don't understand how a microwave can cook food at different rates of speed if briefly stopped."
] |
[
false
] |
If I microwave hotpocket #1 for four minutes it will come out lava. If I microwave hotpocket #2 for two minutes open the microwave check the hotpocket and cook it for another two minutes to will come out warm but not lava. These are hypothetical examples.
|
[
"Most microwaves basically cook at full blast. The different heat settings you can set cause the microwave to take breaks at intervals like the break you gave your hot pocket at the two minute mark. This allows the hot and cold parts of your food to interact with each other longer; the cooler parts get more time to become warm while the hot parts give their heat up to the cold parts instead of overcook and burn. Some microwaves (like the Panasonic in my kitchen) have a so called inverter technology that actually reduces the intensity of the heat instead of taking breaks like most microwaves do and this can be particularly useful for thawing things gently."
] |
[
"I think he was asking why nuking something at full blast (say 750w) at 2 minutes, two times, with a small break in the middle doesn't make it as hot as nuking it at full blast (still 750w) for 4 minutes straight."
] |
[
"I have a purely speculative answer. This is mostly story telling, but it does agree (except with one caveat at the end) with what I know about how microwaves work.",
"Microwaves work on the principle of dielectric heating. Essentially what you're doing is rather than making molecules vibrate faster (which is what infrared radiation does and why sunlight feels warm) microwaves excite rotational motions...aka, make molecules rotate faster. In the case of warming up food, the broadband microwaves emitted by a microwave oven do a good job of making proteins, fats and to a limited extent carbohydrates rotate quite efficiently.",
"This warms up your food by friction. Seriously, that's it. Except for the frictional dissipation mechanism, microwave energy does a very poor job of being heat. It's a low energy excitation, you're just not putting enough energy into the food to generate heat in the absence of the frictional release mechanism. Which is called dielectric heating.",
"So my speculative answer to your question: Rotational motions are very sensitive to the environment that the molecules are in (which is why it is used for things like ",
"dielectric spectroscopy.",
" At first the microwaves aren't doing a particularly good job of heating the food because the temperature is relatively low and the motions of the molecules are relatively constrained. As the food gets warmer through dielectric heating, rotational motions become easier and easier. This is why it's so easy to go from too cold to lava -- because the temperature of the food is not a linear function of the amount of time spent in the microwave oven. In the field I work in, the temperature dependence of rotational motions is a well studied phenomenon. ",
"When you interrupt the microwave, the rotational motions of molecules inside the Hot Pocket dissipate quite rapidly. I can only assume (and this is the part that doesn't agree with what I know about how spectroscopy works) that when you turn the microwave back on, it has to re-activate all of those rotational modes and that this is not an instantaneous process, even though the temperature is higher than it was before. So, that's how you get not lava."
] |
[
"What is the 4th dimension and can you possibly explain it in layman's terms?"
] |
[
false
] |
I am not sure what category this falls into, but I think physics or mathematics are the closest ones. EDIT: Thanks for all the answers and thanks for making things clear to me, especially you
|
[
" fourth dimension isn't a thing, though I suppose time is often referred to as the fourth dimension.",
"You should just think of dimension as \"the number of pieces of information needed to uniquely specify a point\". So to uniquely specify a point in physical space, you need three pieces of information (for example on earth, its latitude, longitude and altitude). To uniquely specify an ",
" you need four pieces of information: three spatial coordinates and a time. That means that spacetime, the space whose points are events, is four dimensional. ",
"Another example with which you maybe more familiar is the space of polynomials in one variable x of degree less than four. That is, the collection of all functions that look like ax",
" + bx",
" + cx + d, for a, b, c, and d real numbers. ",
"Such a function is precisely specified by the values of a, b, c and d. They don't depend on each other, and every such function can be described by some choice of their values, so the space of all such functions is four dimensional.",
"The thing that can be mind-bending is trying to imagine what shapes like cubes and spheres might look like in four spatial dimensions. That's cool and all, but that's not an especially worthwhile or necessary thing to think about. "
] |
[
"Instead of thinking of \"the fourth dimension\" as a place or as time (although it's often, not incorrectly, used to refer to time), think of the number of dimensions as characterizing how many ",
" you can go.",
"In our spacetime, we can uniquely locate an event by where it happens and when. So how do we do that? If we have some reference event - say, my laptop the moment I press \"save\" - we can identify any other event by saying how far it is in front of or behind that event, above or below it, to the left or to the right of it, and before or after it. That's four numbers, because there are four independent directions you can move in spacetime. So that's what it means to be four-dimensional."
] |
[
"Are there continuous bijections from ",
" to ",
" ? I didn't think so. There definitely aren't from [0,1] to [0,1]",
"In any case, vector space structure is more natural to think about for a definition of dimension. I can get into an explanation of Hausdorff dimension if necessary.",
"EDIT: Actually it's a pretty easy exercise to show that there do not exist any continuous bijections from ",
" to ",
" . Yay Baire Category Theorem!"
] |
[
"How bright is humanity's electromagnetic footprint today, on all parts of the spectrum?"
] |
[
false
] |
One way we might detect life on an exoplanet might be the EM radiation that it emits from artificial sources. So to an outside observer, what regions of the EM spectrum would we be emitting and how would the radiated power compare to other objects in space?
|
[
" The electromagnetic 'footprint' of humanity, as you call it, is pretty much nothing when compared to the sun. ",
" This is probably the hardest question on askscience I've tried to tackle in a long time, so let's go on an adventure :D",
"For reference, the power output from the sun is about 3.9 x 10",
" Watts. I don't really have a reference for how big that number is compared to anything on earth. Actually, I do. If you like TNT equivalents, (4.2x10",
" Joules/kg) then it's like ",
"every day.",
"I know you asked about humanity, but I wanted to start by giving you some benchmarks about the sun because that's what our electromagnetic 'footprint' is competing against, at least in the alien's telescopes. The sun is going to outshine any amount of energy humanity puts out, and I'm going to spend the rest of this post trying to figure out by how much it wins. ",
"Ultimately, all the energy humanity uses ends up as heat. That's just thermodynamics. If you burn coal in your power plant to make electricity, and a lot of that energy goes to heat, and some of the energy goes to the turbine to generate electricity. Some of that electricity dissipates in the power lines, warming them a little bit. When it gets to your laptop, it makes your processor run, heating it up. Basically, ",
" If we consider the annual energy usage of humanity as going entirely into heat, then we can call that power output of humanity in all parts of the spectrum. Of course, in reality the bulk is infrared (heat), while there are sizable portions in parts of the radio and visible, but let's keep it simple and not try to divvy it up into different parts of the spectrum. This calculation I'm about to do is for the ",
".",
"If we say that ",
"humanity consumes out 5x10",
" Joules a year",
" then we put out that much in radiation, in all parts of the spectrum. ",
"As a power, that's 1.5x10",
" Watts.",
" ",
" and again that's using our most generous estimate for humanity. And honestly, that's pretty impressive that we even come ",
" to a fucking star. Good job, mankind. ",
"I want to give you another number, and that's the power that the earth's core radiates as it cools. You know, geothermal energy? Wikipedia gives that number as about 4.4x10",
" Watts. That means that all of humanity's signal doesn't even outshine the heat produced by the earth's cooling. ",
"You do ask another question, which is:",
"So to an outside observer, what regions of the EM spectrum would we be emitting",
"Mostly heat, with some radio waves, and not much visible light. All our streetlights and lamplights may be visible from space at night, but it's still nothing compared to to the sun. We put out a lot of radio waves and other signals too, and those might have a better chance of getting noticed by aliens since they contain information and therefore have a pattern to them, but we don't broadcast with the kinds of intensities to send messages across the galaxy. The average transmission is only as strong as it needs to be to get to it's destination, which is usually no further than a communications satellite in geosynchronous orbit. ",
"Maybe our best signal to space so far has been the Arecibo message, a three minute radio blast at 10",
" W. This post is getting long, but I highly encourage you to check out the ",
"Wiki page on the Arecibo message",
". I mean, how do you encode information so that aliens, who have never seen human language or numbers before, can understand it? But like I said, this post is getting long, so in the words of Feynman, I'll just have to leave you with something to imagine"
] |
[
"I was under the impression that our TV and radio broadcasts became sufficiently powerful to ",
" out of the solar system some time around the start of World War 2. I understand that the sun outshines anything we could ever send in visible light, but aren't the bands we used for communication used precisely because they're otherwise ",
" bands? I mean that they aren't bands of the spectrum that the sun strongly radiates?"
] |
[
"Is that to say that from that distance the light from the Sun would block out the ability to see Earth or was that just in terms of the electromagnetic footprint? The quality/capability of the telescope aside.",
"Well it's going to certainly depend on the quality of the telescope (and the distance to the aliens... the further away you look, the better a telescope you'll need). A cheap telescope will only be able to resolve the sun. A better telescope might be able to resolve the wobble of the sun due to the gravity of the planets, and might even be able to observe a change in apparent brightness of the sun when it is eclipsed by a planet, giving the aliens a good measure of the size of the earth and it's distance from the sun. ",
"An even better telescope could resolve the earth directly, and might even be able to get a chemical spectra, noticing an atmosphere with abundant oxygen, nitrogen, and water vapor. ",
"But again, the universe is big and the signal we put out is small, so unless those aliens are looking really close for signs of life as primitive as us then there's a good chance that they'll miss us. "
] |
[
"If I have a string that is one light year long"
] |
[
false
] |
[deleted]
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[
"Assuming the string is rigid (no elasticity), the speed of sound. If it's elastic (stretches), then I think it depends on the modulous (Young's? Help me out, materials science ppl)"
] |
[
"Good enough - no need to talk about young's modulus, just speed of sound is correct. "
] |
[
"Right. The rate at which the \"stretching\" travels down the material is the speed of sound in that material."
] |
[
"How is nutritional caloric content calculated? Particular with regard to items which the human digestive system doesn't break down/get energy or nutrients from"
] |
[
false
] |
When calculating the caloric content of foods, do the calories contained in substances indigestible by humans count? How is the caloric content of food calculated in this regard? I am familiar (more or less recall) the chemistry concept of caloric content based on the energy released as it heats water of a known volume by a measured amount - but surely calorie-free items such as artificial sweeteners would have a caloric content by this definition, but in fact have no caloric content as processed by the human digestive system. Same for roughage/cellulose materials in foods, etc etc. So is this discrepancy taken into account in nutritional information provided with foods? If so, how is it determined?
|
[
"The standard energy densities for macronutrients take digestibility into account. In general, the digestive system is highly efficient (~95%), but there are additional adjustments for fiber (only about 2 kcal/g are available out of the theoretical 4.2 kcal) and protein (there are substantial losses due to incomplete metabolism such that the combustion energy of ~5.5 kcal/g turns into the typical value of 4 kcal).",
"As for artificial sweeteners, some are metabolically inert, while others are technically carbohydrates, but the amounts are so small that they don't meaningfully contribute to energy intake."
] |
[
"Another question, what is up with zero-Calorie \"energy\" drinks? A Calorie is a unit of energy, what gives?"
] |
[
"many of them contain caffeine, taurine, and vitamin B which lend themselves towards being the \"energy\" aspect of the energy drink.",
"Also, zero-calorie means that there are fewer than 5 calories per serving, so they might have an unreported gram of sugar in there too. "
] |
[
"What is at the center of the Milky Way galaxy?"
] |
[
false
] | null |
[
"Yes. Also the one recently discovered wasn't recently discovered. It was known to be a black hole for some time, but researchers just now managed to create an image of it, the first ever picture of a black hole.",
"There's plenty more on this subject in the recent AMA thread with the scientists that created this picture. I suggest you look that one up for further reading."
] |
[
"Sagittarius A*, a supermassive black hole with a mass of approximately 4 million times that of the Sun."
] |
[
"So this is a totally different black hole that was just recently discovered?"
] |
[
"Why do our eyes turn red when there is a camera flash?"
] |
[
false
] |
[deleted]
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[
"Your pupil is transparent and only looks black because it is the only point of entry for light in the eye. It's similar to standing outside of your house in the daytime and trying to look inside one of the windows while the inside lights are off.",
"A camera flash increases the light intensity and allows a more prominent reflection of light off of your retina back into the camera lens. The normal color of your eye looks like ",
"this",
"."
] |
[
"it's the flash reflecting off your retinas"
] |
[
"Because the red light is the result of the reflection of it off our retinas"
] |
[
"Why exactly do the tectonic plates move in different directions?"
] |
[
false
] |
I fully understand that tectonic plates are just pieces of crust that move because of the convection cells of lava and rock beneath the surface moving them towards a certain direction. But my question is do the different convection cells all move in different directions, what determines that? So for example, the Indo-Australian and Pacific plates have a convergent border, so my question is why does the Indo-Australian plate's convection cell move east and the Pacific Plate's convection cell move west rather than both of them just moving in the same direction?
|
[
"There are a few different forces driving the motion of tectonic plates.",
" is thought to be the main one. The part of the plate that is subducting is old, (relatively) cold, making it dense, making it sink in the mantle. It pulls the surface part of the plate along. Like a tablecloth sliding off a table because of the weight of the part already hanging down.",
" is also associated with the subduction. The sinking slab drives flow in the surrounding mantle which then acts on other parts of plates. Slab suction means that even if the slab breaks it can still drive plate motion.",
"The fastest moving plates are the ones with most subduction, and this is taken as a major piece of evidence for subduction-related forces being dominant.",
" is from mid-ocean ridges. The plate near the ridge is new, warm, so it's less dense and sits high. Away from the ridge it's colder and more dense and sits low. So the plate basically slides downhill. Ridge push is estimated as 5-10% as strong as slab pull plus slab suction.",
"Mantle convection acting on the underside of the plates was once assumed to drive the motion, but it's now thought to be a very minor part. For it to be significant the convection cells would need to be comparable in size to the plates themselves, but evidence based on density measurements of the mantle by seismic waves indicate any convection cells are actually much smaller. Thus to the extent they exert forces on plates, they'll be pushing different bits of the same plate different ways with little overall effect."
] |
[
"The other answers are good, but I think they leave out an important point that would help you understand plate motion. ",
"Because the earth is a sphere with a curved surface rather than a flat disc, plate motion is better described as a rotation, rather than linear movement from one place on the planet to another in a straight line. ",
"Look at the video of plate motion in this link and look for rotation of the plates.",
"Notice how the plates appear to be rotating as they move around. All plate motion can be described as a rotation around an imaginary axis that intersects the center of the earth and the surface of the earth. The place where that axis of rotation comes out the surface of the earth is called an Euler point or Euler pole. The Euler point doesn't always have to come out within the plate itself. It's just the point about which the continent is rotating. ",
"This video does a decent job of showing the rotation of two plates on either side of a spreading center.",
" You can think of the two plates as spreading away from each other, but you get different spreading velocities at every point where you measure along the spreading center. But if you identify that Euler point, you'll see that all points have a constant rotational velocity relative to that point. It's just that the parts of the plate that are farther from the Euler point have to rotate farther in the same amount of time compared to points closer to the Euler point. Kind of like how the outside of a wheel travels faster than any given point closer to the center. ",
"So plates are tugged down by forces like slab pull when parts are subducting. Other parts of the plate are pushed by spreading centers. And those different forces at different parts of the plate boundary all add up to an overall net rotation. Sometimes plates appear to move in a very linear way, but in reality they're just rotating around an Euler point that's relatively far away from the plate itself. Kind of like how you can zoom in on a really big circle until a part of the circle looks a lot like a straight line. When you zoom out, you actually find that any point on the plate that you think is moving in a straight line is actually moving in a circle around the Euler point. ",
"Look at all these transverse faults along the Mid Atlantic Ridge.",
". That's all those parallel faults that are perpendicular to the ridge itself. Close up, they look like straight faults, but when we look from a distance we find that they're actually ",
"arcs which transcribe a section of a circle around a central pole of rotation (Euler point) like so.",
" These transverse faults are actually one good way of finding Euler points or Euler poles. It's a common exercize for plate tectonics students. ",
"You just draw perpendicular lines to all of the transverse faults and see where they intersect. That's your pole of rotation.",
"As for your specific question of why do convection cells move, the answer is they don't really move all that much. The plates just move in relation to the convection cells if they're affected by some other force besides the convection cell (like slab pull or a stronger convection cell somewhere else for instance).",
"Take Hawaii as an example. The Hawaiian islands are formed by volcanism from a mantle plume (convection cell) under the Big Island. Hawaii is a chain of islands that runs roughly NW-SE. When we date the islands we see that the biggest one toward the SE is the newest, and they get older as you go NW. ",
"Here's a helpful diagram.",
" This is because the Pacific plate is subducting mostly in the NW and there's a lot of spreading going on in the SE. ",
"So the overall motion of the plate is toward the NW",
". If we go back to our rotational definition of plate motion from earlier, it's actually rotating around an Euler point that's somewhere around northeastern Canada or Greenland.",
"The Pacific plate simply moves over the Hawaiian mantle plume, forming a chain of islands over time in the direction of plate motion, but the convection cell itself hasn't really moved relative to anything deeper inside the Earth. ",
"I used a mantle plume for that example, but spreading centers are the same way. They tend to not move too much. They do the pushing that causes the plates to move, but they don't move as much as the plates. They can move a bit, because spreading centers are related to convection in the mantle that's more shallow than the kind of deep mantle convection that causes plumes like the Hawaiian hot spot, but they don't just wander all over the planet like the plates can. ",
"This lava pool video is a perfect analogy on a smaller scale.",
" Notice how some of the \"spreading centers\" move around but overall they tend to be more stationary than the \"plates\" themselves. Some of the spreading centers get pushed around a bit when stronger spreading centers (stronger convection cells) push plates quickly over the top of them and force the weaker convection cells to take a new path of least resistance. But that really strong convection cell toward the left side for example really doesn't move all that much over time. Even when a plate temporarily covers it, you can see the convection cell keeps opening a spreading center right over that spot again. Once a spreading center starts, it can get pushed around a little bit, but if you disrupt it too much you'll stop the convection. You're not going to be able to push a convection cell all the way to the other side of the planet the way you could with a tectonic plate."
] |
[
"I would run \"tectonic plates convection currents\" through a google image search for a visual stylised 2d representation of what is going on. Broadly speaking what is happening is this:",
"Its all very circular, with the mantle processes driving the movement of the plates, and sinking plates driving the mantle. Its not perpetual motion ofc, because heat from the core is lost and when that heat runs out, no more plate tectonics. I'm generalising heavily here at all times ofc."
] |
[
"Topographers: how is topographical data stored?"
] |
[
false
] | null |
[
"Digital topographic data largely comes in one of two types, point clouds or rasters. ",
"Point clouds are what the name implies, i.e. \"clouds\" of individual points represented by x, y, z coordinates. These are typically raw data, i.e. points represent individual returns from some electromagnetic radiation bounced off the surface of the earth (e.g. lidar, radar) or points generated from photogrammetry. Point clouds are usually irregular, i.e. the spacing and azimuth between points are not fixed. These can get very large in terms of file sizes if you have dense points because you need to store all three coordinates for every point, though there are some compression schemes designed specifically for point data that can help significantly.",
"Rasters are basically images, i.e. a rectangular grid of pixels with (typically) uniform pixel dimensions, but in this case the value of each pixel represents an elevation. There are some file formats specific to topographic rasters, but because they are images there are also special forms of common image file formats (e.g. tiff, jpeg) that store topographic data. As with images, the raw data are the pixel values, but there is supplemental data like the number of rows and columns and the size of the pixels. Image file formats for topography data are a little different than regular image file formats because they need to store a little bit of extra data, like what coordinate system and projection the data is in, e.g. are the pixel dimensions given in degrees of latitude and longitude or in meters? Just like with images, there are a variety of compression schemes that work well with topographic rasters. ",
"Both types of topography data have their advantages. As mentioned before point clouds can be very large files, where as the same area can be covered by a much smaller (in terms of file size) raster because less data needs to be stored, i.e. you only need a single value for each grid cell and then just a very small bit of data indicating the numbers of rows and columns, size of the pixels, and how the values are ordered with respect to the rows and columns. Because point clouds are irregularly spaced, there are a lot of things we might want to calculate from topography data that are annoying to do (e.g. calculating slope), so rasters are much easier to deal with for these applications, and basically any image processing method can be applied to raster topography. The big issue with rasters is that they are interpolations, usually derived from a point cloud. Depending on the density of the point cloud and the resolution of the raster being made (i.e. size of the individual pixel in map units), a single elevation value in a raster pixel might represent multiple (potentially different) closely spaced points and thus the value in that pixel will represent some average, whereas other pixels might have zero points and are based solely on interpolation with neighboring points/pixels. This means that the quality and \"truth\" of the raster depends on how dense the point cloud is and the way you interpolate between points. Similarly, as you start doing operations on the raster, e.g. projecting from one coordinate system to another, you start interpolating the original interpolation and you get further away from the \"true\" data and errors can start to compound. For most purposes, these errors are small and don't matter, but in some cases, dealing with underlying point cloud is preferred."
] |
[
"since the raster maps are usually projections from straight upwards, you can't have overhangs or -laps in them whereas point cloud can have these"
] |
[
"Rasters are relatively easy to work with, largely because there are so many tools designed for image analysis/manipulation. Point clouds are a bit more niche. Both tend to be dealt with in GIS because in almost all applications, topography data that are not tied to their geographic coordinates and projection are useless. GIS is designed specifically to work with this kind of data."
] |
[
"Was cold dark matter always cold, or was it hot in the early universe?"
] |
[
false
] |
If the latter, at what point did the HDM turn into CDM?
|
[
"Assuming thermal production: It was hot in the early universe and cooled in the same way everything else did - from the expansion of the universe."
] |
[
"For thermal pair production the temperature needs to be in the same range as the mass (kT ~ mc",
") or higher*, which implies the particles are relativistic at that time. As the universe expands pair production stops, things cool down, and interactions get less common as the particle density goes down. The decoupling time influences the final temperature, which then influences how dark matter clumps form. The hotter the dark matter the larger the clumps, with smaller clumps only forming later when dark matter is colder. That's not what we see, galaxies formed early, so dark matter needed to be colder earlier. This is also where people get educated guesses for dark matter cross sections from. ",
"Here is an example",
", they arrive at decoupling at 23 MeV for 100 GeV particles in their model.",
"*sometimes much higher. Neutrinos are very light but there is no efficient way to produce them below the MeV scale."
] |
[
"When we speak of CDM are we referring do the particle being non relativistic at present time or already at time of decoupling?"
] |
[
"How can time pass differelty for 2 objects in relative motion if it doesnt depend on the sign of the speed?"
] |
[
false
] |
[deleted]
|
[
"You have described the ",
"twin paradox",
". The resolution comes in the fact that the two twins cannot continuously stay in two inertial frames if they ever want to meet up again - someone must turn around.",
"Also, keep in mind that this is for kinematic time dilation only. The main reason for the time differences you see depicted in Interstellar is ",
"gravitational time dilation",
", which isn't relative. Both observers will agree that the clock closer to the massive body ticks slower."
] |
[
"The time dilation in the movie was provided by the force of gravity of the black hole, not the landing process. Gravity acts locally like an accelerated frame (see the Equivalence Principle).",
"For example, we are currently experiencing a small amount of gravitational time dilation just by sitting here on Earth."
] |
[
"I understand its a movie, but one thing I was wondering that I haven't found much discussion on. Wouldn't the ship that is trying to land on a planet that is effected by time dilation as much as the one in Intersteller have to accelerate to incredible speeds in order to land. My understanding of relativity is that there must be an acceleration of the an object relative to another for it to experience time dilation relative to the other.",
"\nSo in the movie a big concern was fuel, but just getting to the planet that's experiencing that much time dilation would require massive acceleration and again when taking off and re docking with the ship (except negative)",
"On the wiki page you linked it one of rules is: ",
"\"According to General Relativity, gravitational time dilation is copresent with the existence of an accelerated reference frame.\"",
"Is my understanding of this concept correct?"
] |
[
"Paradox in the speed of light?"
] |
[
false
] | null |
[
"When you're talking about special relativity (which is this field), you need to be careful about who's observing what.",
"Imagine we have two people, A and B. A is sitting in a spaceship floating in space, and B comes rocketing by at constant velocity. Suppose that they also each have one of a pair of identical clocks. Now what happens here is not that A notices time going slowly, or that B notices time going slowly - that wouldn't make sense. Rather, A measures B's clock to be going slower than his, and B measures A's clock to be going slower than his.",
"Now, as B moves faster and faster relative to A, this slowing gets more and more extreme, and as B approaches the speed of light relative to A, A observes B's clock approaching a stop.",
"The question is then what happens ",
" the speed of light (let's say B's mass is dropping to 0 so that this can happen). The trouble is that it's not clear that it makes sense to talk about this in the same way. In particular, it doesn't really make a lot of sense for a photon to carry a clock in the same way. If you just extrapolate the math, what you find is that, ",
", it travels zero distance in zero time. This does not mean that A observes the distance traveled to be 0 (due to length contraction, which I didn't mention but is a similar effect) and the time taken to be 0. Rather, it means that some hypothetical observer which is at rest relative to the light (which isn't possible, which is the problem!) will observe the emitter and absorber of the light to be in the same place and thus the light travels zero distance in zero time. And A observes the light as traveling a finite distance at the speed of light."
] |
[
"Any discussion of this should mention that there's no such thing as a photon's reference frame. ",
" if you're going to write things like \"the photon in its own reference frame.\""
] |
[
"Thanks, good point. I should've made this clearer."
] |
[
"If I took a spoonful of matter from a neutron star and moved it away from the star, would it expand or stay compacted?"
] |
[
false
] |
Pretty much the title. A how and why would be pretty cool
|
[
"It would explode and fly apart. It's super hot and the only reason its stuck together is the total gravity of the entire star."
] |
[
"how hot are we talking?"
] |
[
"That depends on if it's newly formed or not, they emit so much energy within a few years they're sitting at around 10",
" or rather 1,000,000 (one million degrees kelvin) which is about 1799540.33 fahrenheit ",
"when they're just born it's closer to 1,000,000,000,000 one trillion degrees kelvin, or 1.79 trillion degrees and some change in fahrenheit"
] |
[
"Hey AskScience, what's your reaction to Roger Penrose's \"The Emperor's New Mind\"?"
] |
[
false
] |
I've finished reading it, and it was pretty tough going at times, despite my familiarity with most of the physics involved. I know that people who believe in "strong AI" and think the "singularity" will occur around 2030 have strong misgivings about the idea that consciousness cannot arise out of a sufficiently complicated algorithm. I'm inclined to agree with Penrose, but as the book is 20+ years old now, some of his stuff is probably outdated. Your thoughts?
|
[
"I read tENM and first half of SotM ~10 year ago.",
"My thoughts? I really liked his 2 page with the three way test showing Bell's theorem. ",
"Thought he presented interesting, but unproven hypotheses that QM plays a large role in consciousness and that human thought can't be replicated algorithmically with no strong evidence to back it. Seemed mostly just we don't understand A (intelligence/consciousness), and B (QM) produces lots of weird effects, so maybe B explains A.",
"That said, I recently read some research claiming quantum mechanics does play some role in biology ",
"[1]",
", so there could be something to it.",
"If you are looking for another good book of similar vein, I'd recommend Hofstadter's Godel, Escher, Bach."
] |
[
"I read the sequel to \"The Emperor's new mind\"; \"Shadows of the mind\", in which he puts forward an extensive argument for why true intelligence and free will can’t be emulated with anything short of quantum computations. AFAIR, all of it is based on the assumption that all that a human mind is can not be simulated on a computer. ",
"I do not think that the fundamental assumption is correct, making the rest of the argument somewhat superfluous. ",
"This is getting more into ",
"/r/philosophy",
" territory though. I am not aware of any rigorous scientific claims based on experiments that say anything about \"free will\". Well, there are some... but then the discussion shifts and that particular thing is no longer necessarily \"free will\". Define it, and then we can start testing if it exists."
] |
[
"Oh hey, this is my field, sort-of (quantum chemistry applied to biochem). Quantum mechanics ",
" play a role in biology, via chemistry - which is intrinsically quantum-mechanical (something non-chemists just don't seem to know). These are considered 'trivial' examples of QM, since they're entirely to be expected. (E.g. photoactivation of the receptors in the eye - there's no 'classical' theory of how light and molecules interact. ",
" it's quantum)",
"Unfortunately there's a lot of bad science going on under the \"quantum biology\" moniker. Ranging from over-sensationalizing expected QM effects, to bad/overly speculative science, to pseudoscience to Deepak Chopra. I would count 'quantum consciousness' as ranging from 'extremely speculative, and very unlikely given what we know so far' to outright nonsense. It's safe to say it's ",
" something which is mainstream QM, mainstream within quantum chemistry/chemical physics, or mainstream neurology. ",
"The reference you linked to, I would put in the 'bad science' category. It's a flawed model (and likely inconsistent with existing experimental results. Not to mention the entire field of protein folding, which almost exclusively utilizes classical models, to great success). It's hard to explain to the layperson what's likely and legitimate and what results aren't. But in general, if it deals with chemical reactions/bonding, energy transfer, light/matter interactions, electron transfer (and motion) and proton transfer and motion, then it's quantum mechanical. If they're talking about giant protein structures acting quantum-mechanically, it's BS. If they're talking about the brain or anything else being a 'quantum computer', it's BS. "
] |
[
"If alcohol is a toxin, does that mean that inebriation and the after-effects of drunkenness is basically the body's response to a poisonous substance?"
] |
[
false
] | null |
[
"I don't feel you've had a very good answer here at all.",
"Alcohol is a toxin but like most (all) toxic substances toxicity is a function of dose. By and large irregular, moderate inebriation is not sufficient to bring on most of alcohol's toxic effects (damage to the liver, heart, pancreas, increased cancer risk, birth defects and so forth). Habitual drinkers and those drinking heavily are at increased risk of the toxic effects, because it is a dose-response effect. Low risk consumption is a fairly low dose and quite a lot less than a great many people will drink in a single session. To avoid detrimental effects, in the UK people are advised to drink no more than 14 units in a week (about 1 drink a day) and to avoid binge drinking (consuming more than 6-8 units in a single session)",
"https://www.drinkaware.co.uk/alcohol-facts/alcoholic-drinks-units/latest-uk-alcohol-unit-guidance/",
"Alcohol inebriation is caused by alcohol's acute effects on the central nervous system. Exactly how it achieves this effect is still not fully elucidated though alcohol is understood to be able to affect a large number of receptor ion channels across the brain. Most importantly, at recreational concentrations, alcohol interacts with GABA receptors and it is currently believed that alcohol's disinhibition of these receptors is the principal mode of action for alcohol. I am not aware that this effect is regarded as a toxic effect of alcohol, I don't believe this effect causes neuro-toxicity with irregular, recreational doses of alcohol.",
"https://en.wikipedia.org/wiki/Alcohol_(drug)",
"https://en.wikipedia.org/wiki/Alcohol_intoxication#GABAA_receptors",
"https://en.wikipedia.org/wiki/GABAA_receptor",
"Hangovers have in general received little research attention. A number of hypotheses have circulated for years (alcohol withdrawal, acetaldehyde toxicity, dehydration etc...) but none of them have compelling evidence. A single session of inebriation likely isn't enough to cause sufficient physical dependency to trigger withdrawal. Acetaldehyde is toxic and is produced in the liver but it is not clear that it can induce hangover like effects. Dehydration will cause headaches but people with hangovers typically don't have lower electrolyte levels.",
"Somewhat recent evidence suggests the alcohol disregulates the control of cytokines, which are immune system signalling molecules. High levels of cytokines in the blood induce many of the sensations we associate with illness; fatigue, nausea, headaches, and general malaise. These are also the same symptoms commonly seen with hangovers and it is now known that people with hangovers have high levels of cytokines circulating. I'm not aware that a causal mechanism through which alcohol achieves this cytokine disregulation has been demonstrated. Possibly it is an immune system reaction to alcohol as a toxin, alternatively it may be that alcohol directly stimulates cytokine release through its known interactions in the nervous system. These lines of evidence suggest that a hangover is a form of inflammatory response and this also implies that the best treatment is with NSAID drugs such as ibuprofen and paracetamol.",
"https://www.ncbi.nlm.nih.gov/m/pubmed/14693266/",
"https://academic.oup.com/alcalc/article/43/2/124/122754"
] |
[
"The withdrawal hypothesis for hangovers has very little evidence to support it. ",
"The acute hangover effects are now known to be because alcohol disregulates cytokine release. Sufficient cytokine release brings on nausea, headaches and fatigue in people",
"There are long term neurological effects for heavy drinkers and alcoholics but they are not relevant to describing the hangover (except in so far as they compound one another)",
"https://www.ncbi.nlm.nih.gov/m/pubmed/14693266/",
"https://academic.oup.com/alcalc/article/43/2/124/122754"
] |
[
"How can you call methanol, CH3OH more complex than ethanol, CH3CH2OH? My understanding is methanol is far more poisonous because it's ",
" and doesn't break down as easily as ethanol."
] |
[
"Why does a spacecraft re-entering the atmosphere appear to be 'on fire', then when it gets closer to earth the 'burning' stops, even before parachute slowing?"
] |
[
false
] | null |
[
"In the outer atmosphere, the atmosphere is very thin and therefore causes a lot less air resistance, allowing the craft to achieve much higher speeds. As it reaches the denser atmosphere, it still has the previous speed but is now experiencing greater atmospheric friction, causing the hull to heat up and start glowing.",
"Eventually, the increased air friction slows the craft down so much that the friction is no longer sufficient to heat the hull up so much that it starts to glow.",
"Additionally, denser gases more easily conduct heat away from the hull, but i'm not sure how big of a difference that makes."
] |
[
"It's the effect of shockwaves. As the spacecraft that comes back from orbit is moving through the atmosphere it has to push air out of the way. Any moving object will push air in front of it, and cause pressure waves to propagate; but in this case, as the vehicle is much faster than sound, it moves faster than the pressure waves it creates (sound itself is just a pressure wave). A shockwave forms a few cm in front of it, and ahead of that the presence of the vehicle is not felt yet.",
"From the point of view of molecule that is colliding at a normal rate with its neighbors, suddenly the shockwave arrives and collision rates increase violently. Air molecules acquire a lot of kinetic energy this way, which is what we define as heat. The ultimate source of this energy is the spacecraft, which is slowing down as the energy is dissipated into the atmosphere.",
"What you're seeing in pictures and videos is a layer of plasmised air glowing because of its intense heat. It can reach 25000°C (4 times hotter than the surface of the Sun).",
"The burning stops, gradually, simply because the spacecraft has slowed down to a less extreme speed. Conventionally we say that the hypersonic regime (\"burning up\") is Mach 5 or higher, but it's actually a smooth transition. From Mach 1 to Mach 5 (supersonic) you still have a shockwave but the heat is not high enough to threaten the structure of the vehicle, and below Mach 1 there isn't even a shockwave."
] |
[
"Thank you. Does terminal velocity play a part?"
] |
[
"Is the nucleus of an atom a sea of quarks without clear boundaries between protons and neutrons?"
] |
[
false
] |
I am aware of the quantum stuff that means we can't know exactly where the protons and neutrons are but that's not what I mean. Since both are made of quarks, ups and downs I think, are the quarks just all together in one big soup instead of being bonded to two others like in diagrams?
|
[
"No, it’s more of a sea of nucleons/quasiparticles (nucleon pairs, alpha clusters, etc.). It’s not simply a homogeneous sea of quarks."
] |
[
"Every nucleus has a well-defined A (mass number). That’s the total number of nucleons that make it up. It’s not necessarily trivial to partition them into clusters. For example, certain states in carbon-12 are well-represented by clusters of three alpha particles. Other states in carbon-12 might be better described as 6 protons and 6 neutrons. In general, they’re somewhere in between."
] |
[
"So when you say \"sea\", are we talking a concrete number of particles? Like \"48\"? Like \"roughly 3 million\"? Or is it really just a noisy mess of an uncountable amount particles bouncing around randomly (aside from some rough clustering or something)? "
] |
[
"What is the temperature of steam off the surface of boiling water?"
] |
[
false
] |
Realistically when I boil water, can the steam go over 100C?
|
[
"For the most part, steam immediately above the surface of boiling water will be exactly 100C, or whatever the boiling point is at your particular air pressure. The steam will be in thermal equilibrium with the liquid water, so it won't exceed its temperature.",
"If you want to get steam that is hotter than 100C, you would have to isolate the steam and heat it. You could create these conditions inside an oven, but not on a stovetop."
] |
[
"Yes, if the lid forms an airtight seal. If the steam periodically lifts up the lid fully, you can divide the weight of the lid by the surface area to get the difference in pressure with the atmosphere. (If the lid is partially lifted up the pressure doesn't support the whole weight, so the calculation is a bit more complex).\nFrom there you look up the ",
"phase diagram",
" of water to find the boiling point for that pressure. Note that when the lid goes up, the temperature has to go down, so the steam production rate goes up till the temperature is brought down (due to the ",
"energy required for vaporization",
")",
"This is also how pressure cookers work. They are able to cook at a temperature greater than 100C because of the weight that stops the steam escaping."
] |
[
"Which is how automatic rice cookers work... By detecting the increase in temp when the liquid water is all gone. "
] |
[
"Assuming all else equal, why do women find it harder to get pregnant as they age?"
] |
[
false
] |
I know a couple of my friends (late 20s - early 30s) are finding it really difficult to conceive, and now they are taking herbal tonics to try to "produce more sperm or make the womb 'fertile ground'". Some have even taken 1-2 yrs just to conceive. But yet, some of my friends (between 19-23) can conceive without batting any eye lids. EDIT: Any advice for women who are around late 20s to early 30s on how to conceive easier? Aside from medical enhancements.
|
[
"While I agree with your stance on alternative medicines, your response isn't helpful or constructive."
] |
[
"Women's eggs form before they are born. A 32 year old woman's eggs are older than she is (her age goes from her birth). Those eggs have been sitting there \"cooking\" for a long time. In contrast a man's sperm is just weeks old."
] |
[
"Panzer is correct when they say that women have a set number of eggs throughout their life and as they age this decreases. However that directly doesn't affect their ovulation, which is the real problem when discussing pregnancy.",
"There are two main reasons why the older a women is the more difficult it is to become pregnant. First your body needs regular hormone cycles, this more applies to people post menopause. When going through the menstrual cycle, a woman's body is constantly having monthly spikes in estrogen and progesterone and slowly decreasing those hormone levels throughout the month. This spike stimulates ovulation and without the proper spike no egg will be given off. Along with that you need to maintain those hormone levels to sustain your uterine lining to allow for embryo emplantation. So when aging, especially after menopause, keeping these hormone levels regular and sustained is difficult. So that is when you must seek out hormone treatment.",
"The other reason relates to the fact that women have a set number of eggs after puberty. Since women are working with a set number of eggs, the longer one waits, the more likely it is that something will happen to them. This could be something as complicated as a error in completely meiosis, since all eggs are stuck at metaphase 2, or the physical destruction of the eggs. This is why the longer you wait to have baby, the more likely it is to have Downs syndrome, because eggs that have waited to long to be ovulated will more likely have a nondisjuntion event in cell division (which is where one cell gets too many chromosomes due to improper cell division). Other events like this can occur which can cause termination of the pregnancy, adding to the fact that the older you are, the harder it is to have a viable conception.",
"There are plenty of other answers to this question but what I said gave some major answers. "
] |
[
"If I was floating in the vacuum of space and I threw a credit card or a rock by me, would it orbit around me like a moon?"
] |
[
false
] | null |
[
"Let's just say it's you and the card/rock, nothing else. If your mass is, say, 100 kg, and you are a sphere of radius 30 cm, then the escape velocity for a particle on the surface of your body is about 200 μm/s.",
"When you simply let go of an object, you don't let go of it perfectly. You give it some velocity, and my guess is that it is typically much much greater than 200 μm/s. Certainly if you ",
" the card or rock, the velocity of the object is about 4-6 orders of magnitude greater than the escape velocity. So the object just escapes to infinity. It does not orbit around you."
] |
[
"To put 200 μm/s in perspective, an object that can travel about an inch in 2 minutes and 7 seconds."
] |
[
"That's not true. Although it's common to treat objects as point masses when dealing with gravity, this only works for objects that are reasonable approximations to spheres. For a more complicated object, you have to include higher order multipole moments, and the solutions you get for the motion of the orbiting body won't be simple conic sections."
] |
[
"How to determine if someone has received a vaccine?"
] |
[
false
] |
Noticed a news report today about a state of emergency being declared in New York because of a measles outbreak. In the article it mentioned that “Rockland County, on the Hudson River north of New York City, has barred unvaccinated children from public spaces after 153 cases were confirmed. Violating the order will be punishable by a fine of $500 (£378) and up to six months in prison.” (BBC News) I was wondering if you can test a person for a vaccination, or whether in this case the parent trying to avoid a fine would just have to provide paperwork documenting it had occurred? And are there any circumstances where you’d need to test for a vaccine for medical reasons?
|
[
"Yes, you can. Basically, they draw blood and then put bits of virus/etc. in the blood sample and test to see if the immune cells react by producing antibodies.",
"However, usually they just ask parents to provide official forms signed by their doctor that they've received the vaccination."
] |
[
"It is directly determined by how well immune cells can remember it, which in turn depends on the nature of the specific virus. Some viruses are harder to generate effective immune responses against than others. People can also be genetically better or worse at generating immune responses to certain viruses.",
"It also depends on the nature of the vaccine. Attenuated vaccines (with \"live\" virus that is altered so it can't cause serious illness in someone with a healthy immune system) are generally more effective than killed vaccines. Subunit vaccines contain just an immune-activating piece of the virus, and their effectiveness completely depends on what that piece is.",
"It also depends on the dosing of the vaccine. It's very common for a vaccine that provides only limited short-term protection after one dose to provide strong lifetime protection after 4-5 doses spaced out over the course of months, as each dose builds on the immunity generated by the last."
] |
[
"Thank you! Do you know why some vaccines last longer than others? Does it have to do with how well immune cells can remember it, or is it more about the nature of the specific virus?"
] |
[
"What really causes death when you die of \"old age\"?"
] |
[
false
] |
I've wondered if there are specific organs/body function which tend to just fail when you are old or if it's rather a general weakness your whole body can't deal with
|
[
"The term \"death from old age\" itself isn't very scientific, as it can point to death from any number of causes, which may be associated with aging. ",
"As people age, we begin to see deficits in cellular function throughout the body. Normal, healthy cells which have been isolated from patients tend to reach a limit in the number of divisions they can undergo in cell culture, known as the ",
"Hayflick limit",
". Cells isolated from a fetus can divide around 50 times in culture, but those isolated from adults or the elderly divide far fewer times, showing there is something of a molecular timer on life. There was an ",
"excellent discussion on /r/science",
" about a month ago that delves further into this, and I recommend reading it for a nice layperson-friendly overview on the putative molecular mechanisms by which aging, or senescence, occurs.",
"The aging of the immune system, or ",
"immunosenescence",
", results in dysregulated immune responses, elevations or decreases in certain immune cell populations, dysregulated cytokine signaling, diminished antigen receptor repertoire diversity, decreased ",
"lymphopoiesis",
", etc.... In short, the immune system of the elderly is prone to react inappropriately or poorly to any type of infection or even to vaccination. There is ongoing research looking at ways to boost the efficacy of the flu (or other) vaccinations specifically for the immunocompromised or the elderly, as they're less likely to develop immunity after inoculation.",
"Cancer incidence also increases with age and is a major contributor to “death from old age”. Immunosenescence offers a likely explanation for the increase in the incidence of cancer that we see with age, though direct evidence for this is still scanty. Our immune system normally identifies and destroys cancerous cells throughout our lifetime, termed ",
"cancer immunosurveillance",
", but the dysregulation associated with age could mean that cancerous cells could escape detection by the immune system. Interestingly however, there is also evidence that in the oldest of the old, the ",
"incidence of cancer either plateaus or even decreases",
". This may be due to the establishment of an immune environment unfavorable for the growth of pre-metastatic cells (known as neoplastic growth). ",
"Epigenetic modifications",
" also ",
"have been proposed to play a role in increased cancer incidence",
" as we age. So it may well be that immunosurveillance is not so dysfunctional as we think, but rather our cells experience a decreased threshold for malignant transformation, resulting in an increased number of cancerous cells in our bodies.",
"Mutations and cellular damage occur as we age, and the ability to repair or deal with these adverse events decreases significantly. As a result, you see an impact on cellular function ",
", and depending on one’s lifestyle, genetics, exercise, etc… it’s a matter of time before you begin to see dysfunction in certain organs or other areas of the body. In conclusion, the term “death by old age” really refers to the underpinning molecular mechanisms contributing to cellular senescence, and based on lifestyle or environmental/genetic factors, can point to the development of defects in one or more parts of the body."
] |
[
"Doctor here. Couldn't compete with ",
"/u/Kegnaught",
"'s response, but more simply: death from \"old age\" is a layman's term. When we sign death certificates we try to put in a cause of death that is more specifically proximate: in my experience, most often kidney failure. When you get very weak and frail you typically lose the drive to eat and drink, and the kidneys fail without water. This causes a buildup of toxins which lead to respiratory depression and eventually failure of your brain and heart."
] |
[
"Thanks very much for your explanation! Seems like aging processes are far more complex than I imagined... "
] |
[
"Sometimes if I open a non-.txt file in Notepad, I see what appears to be a collection of random characters. What exactly am I looking at?"
] |
[
false
] | null |
[
"You're looking at the content of the file converted into readable characters. For example, let's say you open a ",
".exe",
" file in Notepad. You'll see a lot of seemingly \"random\" characters, which appear to make no sense. However, what you're seeing isn't designed to be displayed as text. Instead, it is binary code designed to be interpreted by a computer.",
"Now, you might ask, if the binary wasn't supposed to be text, why is it? The answer is simple: Notepad doesn't care. It just reads in a stream of data and converts it into text. So, if the ",
".exe",
" you opened contains the binary values ",
"1001000",
", Notepad will display it as \"H\". Why? Because text, just like the executable, is also just a series of binary values which applications can display however they want. Notepad uses ",
"ASCII",
" codes for text if one isn't specified, and the ASCII code for \"H\" is ",
"1001000",
", so that's what will show up. If you added the ",
".exe",
" extension to a text file, the computer probably wouldn't run it because it's not interpreting it as text, it's interpreting your file as instructions to send to the CPU. The binary values in your text probably don't correspond to valid CPU instructions, so nothing happens, although, interpreted differently (as a text file), you see your text displayed on the screen."
] |
[
"Fun fact: All executable files in Windows, and in MS-DOS before that (all .exe, .sys, .dll files, etc.) start with two printable characters: \"MZ\". You will see them if you open the file in Notepad or a hex editor. Why? Because the Microsoft developer who created the file format in the early 80s was named Mark Zbikowski."
] |
[
"All files on a computer (be they text, programs, images, or whatever) are a stream of bytes. Each byte is a value from 0 to 255.",
"On their own, bytes are ",
" but they aren't ",
" [1]. To be useful information, you need to ",
" the data in the correct way. Depending on what your binary file is, the correct way may be to interpret the file as a ZIP file or an EXE file or a JPG file. The program will read the file according to its internal logic and that interpretation will produce a meaningful result.",
"When you open in Notepad, you're forcing an interpretation of each byte as text (if the language on is set to English, Notepad will probably interpret the text as CodePage 1252, aka Windows Latin 1). This works by looking up each byte in the following table:",
"http://msdn.microsoft.com/en-us/library/cc195054.aspx",
"and showing the character found.",
"However, since these bytes are not intended to be interpreted in this way, it looks like nonsense. Of course, the bytes are probably not nonsense but the ",
" is, so it's not useful (except in cases where there is ",
" part of the file that is still legible when interpreted as text).",
"Usually, when we open a binary file that isn't text, we use \"Hex\" editors. These simply open the file and display each byte as a pair of base 16 digits (e.g. 01 4F C3 80 45 DE 74 81). This can be very slow to read but it is clear (unlike text which may hide certain characters or make others hard to see) and if you know roughly what you're looking for (i.e. you already know or suspect what the file format may be), it is a way to examine arbitrary bytes.",
"There's a trend in many file formats – particularly among media files like video, images or audio – of having the first 2 or 4 characters of a file indicate the data type (known as a Four Character Code) to help you guess what the actual type of the file is so you can get the interpretation correct.",
"http://en.wikipedia.org/wiki/FourCC",
"For example, PNG images start with bytes with the hexadecimal representation 89 50 4E 47. If an arbitrary stream of bytes starts with this, there's a high probability that it's a PNG file. However, most files do not use a FourCC so you will need to know in advance (from the filename extension or other information stored elsewhere) what the type of the file is and how to interpret it because blindly looking at a file without knowing the format will not usually reveal anything helpful.",
"[1] Terminology note: communications engineers and economists may use \"data\" to mean usefully interpreted values (i.e. not noise). In computer science, \"data\" is just a number of bytes (a quantitative not qualitative measure)."
] |
[
"Does salt accelerate rust formation?"
] |
[
false
] | null |
[
"On plain carbon steel and irons yes very much. Especially salts with chloride. ",
"Oxidation (rust) by itself on steels and irons is self limiting. The oxide layer prevents more oxygen from getting to the pure Fe. Chloride fucks up the formation of iron oxide films and constantly exposes fresh Fe to the environment. Also chloride can combine with hydrogen that is released during iron corrosion and forms HCL acid which greatly increases corrosion rate due to low pH condition. "
] |
[
"One of the most important conditions is also abundant free oxygen which, in reaction with water, can form iron oxy hydroxides (rust).\nIf you have a sunken ship lying in the oxygen poor deep sea then it takes couples of decades for it to break down. And even then (in case of the Titanic) it's mostly driven by anaerobic, iron eating bacteria."
] |
[
"If you mean salt in an aqueous solution, yes very much so. Corrosion is an oxygen-reduction reaction, this process involves a transfer of electrons. Therefore, the presence of salt or electrolytes in water increases the electrical conductivity of the water and thus accelerates and promotes corrosion. ",
"This is why metal components in/near saltwater are either protected by paint or other coatings, replaced frequently, or very rusty."
] |
[
"Why did CPUs stopped at around ~3-4GHz?"
] |
[
false
] | null |
[
"That top answer gives part of what is happening, but doesn't put it into the right context for a layman.",
"There is nothing magical about the number 3-4 GHz. IBM developed a part which exceeds that (",
"http://en.wikipedia.org/wiki/POWER6",
").",
"What is happening is as much limited by economics and engineering as it is the underlying materials.",
"It is a big engineering challenge to produce high frequency parts (there is a large amount of risk). Also, there is less payoff for producing faster parts (market acceptance). These two things have combined to make it less risky (a better investment) to continue developing one line of parts (the Core line at Intel, and the K7 line from AMD).",
"Also, the market is moving more towards lower power (higher battery life). Lower frequency parts do better in this space.",
"So, there is a true limit, but it is much higher than 3-4 GHz. We don't go past where we are because no one is willing to take a risk and build the parts, because they don't think enough people will buy them."
] |
[
"See:",
"http://www.reddit.com/r/askscience/comments/ngv50/why_have_cpus_been_limited_in_frequency_to_around/",
"\n",
"http://www.reddit.com/r/askscience/comments/y8anh/why_do_i_have_cpu_with_8_3_ghz_cores_and_not_1_24/"
] |
[
"Why? Clock speed is an arbitrary and not particularly good measurement of usefulness, just like the number of I/O ports or the number of cache lines. Computers are tools just like cars, hammers, and guns; designing and building them is particularly capital-intensive too. Bringing a CPU to market is a hundred-million-dollar project, even for something as small and low-featured as a smartphone processor[1]. Developing one for the sake of it is a substantial sunk capital, so companies need to get something out of it.",
"IBM uses the aforementioned POWER6 CPU (which is almost certainly an unprofitable product in isolation) to help keep customers on IBM mainframe hardware, which keeps customers buying IBM mainframe software, and most importantly, keeps customers buying IBM mainframe consultant hours, which can be sold at a huge margin.",
"Desktop processors are seemingly stagnant between 2GHz and 3GHz because the R&D focus is on other ways to improve their speed; now that all the common operating systems support multiple processors, chip designers are free to work on making multiprocessing more efficient space-wise, make existing clock cycles more useful, and so on.",
"1: ",
"http://venturebeat.com/2012/09/18/more-details-shake-loose-on-apples-a6-chip-including-a-500m-development-effort/"
] |
[
"Is it possible that two people have the same fingerprint? Or at least that they're undistinguishable?"
] |
[
false
] |
I know that every kid in elementary school learns that every human has a unique fingerprint, easily distinguished from other's but there isn't an infinite number of patter on a tiny fingertip, is it? So is there a chance that two humans actually have fingerprint that e.g. the police could mix up?
|
[
"As far as we know, fingerprints are unique, but they can be very similar. Especially when you consider the fact that the latent prints found at a crime scene are often just partial prints that are smeared, smudged, and missing information, it's certainly possible that a false positive could occur. Most famously and recently this happened with the 2005 Madrid train bombings where multiple agencies matched a print found on a grocery bag to someone in the US, but it wasn't them."
] |
[
"To add to this, it might be useful to understand how fingerprints are formed. When an individual is still a foetus inside their mother's womb, they are very subject to pressure. When the baby makes contact with anything, be it through their fingers touching or their toes, the resulting pressure forms \"friction ridges\". These are the faint lines we can see on our fingers and toes, otherwise known as \"fingerprints\".",
" ",
"Because every baby touches in unique ways, the pressure always creates different fingerprints, that aren't present on any other individual. Moreover, this is also why identical twins do not share fingerprints, even though their DNA matches. However, this is not to say that similar circumstances cannot occur, and therefore lead to identical fingerprints. "
] |
[
"Interesting topic. Hope this helps."
] |
[
"What do different refractive indecies affect light?"
] |
[
false
] | null |
[
"Hi TheDiamondOr1 thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Physics"
] |
[
"'Physics'"
] |
[
"What exactly does blood type mean?"
] |
[
false
] |
Does your blood type affect any aspects of your personality, physique, health....etc?
|
[
"You need to understand two concepts for blood type:",
" are special immune proteins that float in the plasma of the blood and attack foreign particles (anything that doesn't exist in the body itself). ",
" is a general term that signifies what the antibody is attacking. ",
"On our red blood cells some of us have particular molecules. These are called antigens because if you give them to someone who doesn't have them their antibodies will attack it. ",
"The most well known blood antigens are \"A\" and \"B\". Someone with either of these will be A or B, someone with both is AB someone with neither is O. Another minor antigen is called Rhesus, if you have it you are Rh+ if not you are Rh-. This is often written as A+, O- etc.",
"If you give blood from someone with an antigen like A or B to someone who doesn't (e.g. O) their body will attack the blood and make them very sick. In general, someone who is O- can donate to anyone but only get O- blood, while someone who is AB+ can receive from anyone and only donate to AB+ people. ",
"That is the main clincal relevance, as well as a more complicated ",
"disease",
" involving Rhesus and pregnancy. The blood type in general does not affect other aspects such as personality etc. It is essentially a natural variation between people that probably wouldn't have had much significance before we started swapping blood."
] |
[
"There are 8.\nA+\nA-\nB+\nB-\nAB+\nAB-\nO+\nO-",
"which, by your nomenclature, would be ARh, A, BRh, B, ABRh, AB-, ORh, O. The nomenclature is different because people noticed the difference for the A/B/O types first. A and B are co-dominaint, and O is recessive to either A or B (or AB). Rh is only relevant during pregnancies, and that does have to do with an immune response mounted by the mother. Rh+ and Rh- are pretty simple dominant/recessive relationships. In short, the names differ because they act differently."
] |
[
"Haha I was waiting for someone to bring up the Bombay type. I'm not sure that Bombay type will make a lot of difference for anyone practicing outside of India, it's more a curiosity for most non-medical personnel practicing outside of the area but yes you are absolutely correct. They will show up as \"O\" on a type but will have a reaction when you transfuse them (I had a preceptor who did part of his residency in Mumbai, they actually went to a nearby village and got blood from his family to transfuse this patient after nearly killing him with O blood)."
] |
[
"Does nicotine have any merit as a pharmaceutical drug?"
] |
[
false
] |
[deleted]
|
[
":",
"Nicotine, as well as other nicotinic drugs, may provide useful therapeutic treatment for a variety of cognitive impairments including those found in Alzheimer’s disease, schizophrenia and attention deficit hyperactivity disorder ADHD . We have found that nicotine skin\npatches significantly improve attentional performance in people with these disease states as well as normal nonsmoking adults. Animal\nmodels are critical for determining the neurobehavioral bases for nicotinic effects on cognitive function. We have found in lesion and\nlocal infusion studies with rats that the hippocampus is an important substrate for nicotinic effects on working memory function. Both a7 and\na4b2 nicotinic receptors in the hippocampus are involved. Further work has investigated the relationship of nicotinic systems with\ndopaminergic and glutaminergic systems in the basis of cognitive function. Nicotine has proven to be a useful prototypic compound for\nthe family of nicotinic compounds. It produces cognitive improvements in both animal models and clinical populations. Recent work with\nmore selective nicotinic receptor agonists and antagonists in animal models is providing important information concerning the neural\nmechanisms for nicotinic involvement in cognitive function and opening avenues for development of safe and effective nicotinic\ntreatments for clinical use.",
"http://academicdepartments.musc.edu/psychiatry/research/cns/upadhyayareferences/Levin_2000.pdf"
] |
[
"According to many current studies the process for such gastrointestinal diseases as ulcerative colitis can be inhibited by the use of nicotine. Patients with ulcerative colitis who stop smoking have a substantial increase in flairs. The use of patches and a reintroduction of the habit see an immense reduction as well. "
] |
[
"http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2014383/"
] |
[
"Since the Earths orbit is elliptical shouldnt the seasons be slightly shorter or longer?"
] |
[
false
] |
Does the elliptical orbit cause a sort of "slingshot" effect that increases acceleration? I've noticed that spring and fall seem to last a bit longer but that could be due to geographical location (Massachusetts)
|
[
"Earth’s orbit is technically elliptical, but only barely. The difference between its maximum and minimum distances to the sun is only ",
"about 3%",
". That’s not enough to significantly affect the seasons."
] |
[
"The main cause of seasons is the earth tilting on its axis when the northern hemisphere tilts away from the sun that's when you get winter because the days get shorter and the sun's rays have to travel longer through the atmosphere. I'm not aware that the distance from the sun has too much bearing on this."
] |
[
"I think the other answers have misunderstood your question. Earth’s orbital speed at perihelion is about 3.4% faster than at aphelion (30.29 km/s vs 29.29 km/s), using values from ",
"this Wikipedia article",
". This has a small but significant effect on the time spent in each part of the orbit, but if you look at this ",
"highly exaggerated diagram",
", you can see that if anything, summer in the northern hemisphere will be ",
" (and on that note this also clearly demonstrates that distance to the sun is not a factor in the seasons, since the Earth is ",
" from the sun during summer in the northern hemisphere).",
"Because spring and fall more or less align with when the Earth is in between apsides, their lengths are least affected by the (already tiny) eccentricity of the Earth’s orbit, so to answer your question: no, it is entirely down to geographical factors or just plain cognitive biases."
] |
[
"Does the ring around Saturn actually have an effect on the climate of Saturn?"
] |
[
false
] | null |
[
"This is currently not well known, but is a very active area of study.",
"The rings cast a fairly significant shadow on the planet",
", meaning there's less sunlight absorbed in the winter hemisphere than would happen without them. However, it remains unclear how important that sunlight is to the climate.",
"Like most giant planets (except for Uranus), Saturn generates a good deal of its own heat. We believe the source of this heat is the helium settling out of the mostly hydrogen atmosphere; having denser helium below lighter hydrogen is a lower energy state than the two being well-mixed, and thus provides a source of thermal energy.",
"With that said, there's still not a whole lot of energy to work with. With Saturn roughly 10x farther from the Sun than we are, sunlight on the planet is about 100x weaker. The internal heat generated by helium separation adds an additional ~80% to that.",
"What may be important, though, is where that heat is distributed. The internal heat is a bottom-up heating, while sunlight generally causes a top-down heating. After a long winter season of very little sunlight due to ring shadowing, but still significant internal heating from below, this has the potential to set up a strong vertical thermal gradient.",
"It's possible this thermal gradient could be enough to generate strong convection by early spring. Perhaps coincidentally, or perhaps because of this thermal gradient, this time period is when we often see the ",
"big storms on Saturn",
" that occur roughly once every Saturn year.",
": We don't really know...but there's some very tentative speculation that this could be responsible for the big springtime storms we see on Saturn."
] |
[
"Just being in a lower energy state doesn't produce any energy (remember, energy's never \"produced\", only transferred). ",
"When the hydrogen and helium are mixed, they are in a higher-energy state than when they are separated. It's very similar to holding a ball up in the air and letting it fall. The ball in the air has more potential energy than the ball on the ground. Likewise, the helium is \"heavier\", and thus wants to \"fall\" down past the hydrogen. ",
"So, mixed, the H and He are in a \"higher energy state\", and separated, they're in a \"lower energy state\". To go from one to the other, they must lose energy - where does that energy go? (we can't create or destroy energy, remember?) Like many, many other examples, that energy shows up as heat, or thermal energy. "
] |
[
"Never have I seen this concept so well explained! Thank you very much!"
] |
[
"Seeing colors from a black-and-white strobe?"
] |
[
false
] |
Today I was in the showers at the gym - white tiles on the walls - and one of the overhead lights was flickering. After about five minutes, all of the sudden my vision became overlaid with red and blue spots and lines. It went away pretty quickly if I looked at the better-lit half of the room, and would start again when I was under the strobing effect. So I'm wondering, what causes this, and why such a significant time-delay?
|
[
"You probably experienced a ",
"Fechner color effect",
" similar to ",
"Benhams's top",
". It's not really understood, and vision scientists have long debates about both what's happening and where it's happening.",
"Try buying or making a Benham top. They're really amazing to see IRL.",
"My guess is that it happens due to the different response rates of different pathways through the ",
"LGN",
"."
] |
[
"I'll definitely have to check out the Benham top. Thanks for the answer!"
] |
[
"No problem. Cool observation!"
] |
[
"Is it common for other animals to have their closest biological relative be as distant as chimpanzees are from humans?"
] |
[
false
] |
Chimpanzees are the closer to humans than any other extant species in terms of shared DNA and where they would fall on a taxonomy chart. But just looking at the two species, they seem to be very, very different. Is the biological distance between humans and chimpanzees as wide as it seems when compared to the distances between other animals and their "relatives"? Are humans and chimpanzees actually really close, and it's just bias because I'm one of them? Or is this distance par for the course, and all the animals that look similar are in fact as different as humans are from chimpanzees?
|
[
"The bigger reason for the perceived difference is that the other, closer groups to modern humans are extinct. Humans and chimps diverged between 4 and 13 million years ago. So broadly speaking, the answer to your question is no, it isn't particularly common for a species to have its closest extant relative be in a different genus, with the divergence between them occurring 4-13 MYA.",
"There are some species that are very 'lonely', though. ",
"Aardvarks",
" are the only living species of their ",
", let alone their family and genus. They're separated from their nearest relatives, ",
"elephant shrews",
" by around ",
"81 million years",
" of evolution. ",
"For the comparisons I'm about to make, I want to point out up front that it would be better, I think, to try to make comparisons based on sequence divergence of complete genomes, since people like to point out that humans and chimps differ by ",
"~1.24% of their genomes, on average",
". Unfortunately, most species in the world have not be exhaustively sequenced, so that sort of comparison really isn't possible. Instead, I'm going to give some examples of things that diverged a similar amount of time ago.",
"Coatis",
" and ",
"Olingos",
" diverged ",
"~10.2 MYA",
".",
"Lutra",
" and ",
"Melogale",
" diverged ",
"~11 MYA",
". Alternatively, ",
" and ",
" diverged 4.9 MYA while ",
" and ",
" diverged 3.7 MYA.",
" and ",
" had their last common ancestor ",
"~5.1 MYA",
".",
"\nAs brought up by ",
"/u/danby",
", the way I framed this number was a little misleading. I'll be clearer:",
"Genome-wide nucleotide divergence between humans and chimpanzees is 1.23%, though it is more likely to be ~1.06% when you account for polymorphisms within each species. A more significant source of difference is insertion/deletion events, which accounts for ~3% of each respective genome. Also, human chromosome 2 is the result of the fusion of our common ancestor's chromosomes 2A and 2B. There are also 9 pericentric inversions. The differences were not spread randomly throughout the genomes, but were unevenly fixed in particular sites and chromosomes."
] |
[
"Thank you, this was a great answer.",
"The aardvark is so lonely! And is exactly what I was looking for. That and ",
"the answer to your question is no, it isn't particularly common for a species to have its closest extant relative be in a different genus",
"that part are the kind of thing I was hoping to learn. And thank for the examples too."
] |
[
"Keep in mind that a taxanomic genus is a wholly human construct and we have no consistent (objective) definition of how far apart two species must be before they should be considered to be in different genuses.",
"Chimps are in a different genus to humans for a combination of reasons: historical, scientific utility and a degree of human speciesism. "
] |
[
"Why does Ethylene Glycol freeze at -12.9 °C, water freeze at 0 °C, but the mixture of the two freeze (depending on composition) below -60 °C?"
] |
[
false
] |
Maybe I am remembering college wrong, but shouldn't the freezing point end up somewhere between the two individual freezing points?
|
[
"I will take the liberty of changing your example, to make it more illustrative. Suppose you mix water and dimethyl sulfoxide (DMSO), instead of ethylene glycol. DMSO has a freezing point of +19°C. Thus, if your memory was correct, mixing DMSO and water should result in a freezing point ",
" than 0°C (but lower than 19°C). This is not what happens: in actuality, the mixture will be stable as a liquid at ",
" temperatures.",
"As ",
"/u/rupert1920",
" mentioned, this is due in part to the phenomenon of colligative freezing point depression. When you add a reasonably small amount of a water-soluble substance (a \"solute\") to a volume of water, the freezing point of the water will be reduced by an amount that is approximately proportional to the number of molecules of solute that was dissolved into the water. Here's the kicker: the degree of lowering of the freezing point depends ",
" on the number of dissolved solute molecules, and is independent of the chemical and physical properties of the added chemical. Thus, whether I add 1 mol of ethylene glycol or 1 mol of DMSO to a 1-L volume of water, the new freezing point will be the same (–1.86°C). Thus, the solidification temperature of the solute does not affect the temperature at which ice can form in the mixture.",
"Now, another side to this is that when I mix water and a solute (say DMSO) at a room temperature (so that both substances are liquid), what substance is being added to the other? Above, we took the view that DMSO was being added as a solute to the pure water, thus lowering the equilibrium ice crystallization temperature. However, equivalently, we can think of the water molecules as being the solute, and the pure DMSO being the solvent. Thus, dissolving water molecules into liquid DMSO should lower the crystallization temperature of the DMSO — and it ",
" (by ",
"4.07°C",
" for every mole of water that is added to a kilogram of DMSO). However, it is important to remember that this \"freezing\" point of the DMSO mixture represents the temperature at which DMSO is able to crystallize (i.e., precipitate) from the solution.",
"In summary, if small amounts of DMSO are added to water, then the ice freezing point will be reduced to below 0°C. On the other hand, if small amounts of water are added to DMSO, then the DMSO \"freezing point\" (precipitation temperature) will be reduced to below 19°C. When the amounts mixed are more even, then both substances can crystallize at the same temperature, which can be as low as –70°C (if the proportions are right).",
"TL;DR: You remembered college wrong. :-/"
] |
[
"The phenomenon is known as ",
"colligative properties",
", specifically ",
"freezing-point depression",
"."
] |
[
"You may find this of interest as it gives a pretty good explanation of what goes on when you cool and freeze a mixture.",
"https://www.uwgb.edu/dutchs/Petrology/beutect.htm"
] |
[
"How effective is CPR if applied immediately after cardiac arrest?"
] |
[
false
] |
So, according to the statistics, the vast majority of patients don't make it, despite CPR (<5 percent survivors), and I wonder if that's the case because it's simply administered too late to be effective. Are the chances significantly higher if emergency measures are taken immediately?
|
[
"One way to look at this is to compare the survival rates of cardiac arrests which happen outside of hospital compared to those that happen within the hospital. Although the in hospital population may be sicker, it is also reasonable to assume that CPR will be started sooner, and be more effective, for an in hospital arrest. ",
"Not surprisingly, outcome for in hospital arrest is better; survival to hospital discharge has been given at around 17%, compared to 8% for out of hospital arrest ",
"(source:BMJ 2012;345 Published 3 October 2012)"
] |
[
"It depends on the cause of the arrest and the comorbidities.",
"If somebody is having myocardial ischemia which triggers ventricular tachycardia, CPR (with defibrillation, the most important step) is very effective. Of course this needs to be followed with opening the blocked blood vessels, or it will return.",
"The fundamental concept is reversing the cause, and quickly. Most things that cause the heart to stop are more difficult to reverse. In other words, if things are so dire that your heart has stopped, the heart stopping is just one more thing to add to an already dire situation.",
"Again, myocardial ischemia is one of the few exceptions."
] |
[
"One has to take into account the quality of CPR given, which in most cases is atrocious. In areas where serious efforts to improve CPR have been taken, the survival rate is much higher. Seattle regularly reports survival rates which double or triple the national average. "
] |
[
"I want to get back into shape. Is it better to workout over a period of couple hours with short breaks or is it better to work out over a short period of time until you are exhausted?"
] |
[
false
] |
I've seen some articles and studies that cover the efficiency of long and short workouts but I can't find them now. To explain the title: I am wondering if it will be more efficient to go "all out" for 15-30 minutes until I am exhausted and can't move a muscle or if it's better to work out over a longer period of time (1-2hrs) while taking breaks every 15-20 minutes. Any information on this would be appreciated.
|
[
"Your question would be better asked in the ",
"fitness subreddit",
"."
] |
[
"Thanks."
] |
[
"I can't speak as much on physically which is more effective at burning calories, but research shows that people trying to get back into shape have much higher success rates, and keep weight off better, when they break their exercise into small 15-30 minute daily routines, rather than long sessions.",
"Long sessions are tiring and make for a large amount of failed weight loss. Short sessions are more manageable and more likely to be followed long-term."
] |
[
"Is earth's electric potential growing or decreasing?"
] |
[
false
] |
[deleted]
|
[
"The larger the Earth's net charge gets (whether + or -), the more it repels particles of the same charge and attracts ones of opposite charge. This has the effect of lowering the charge again. It's a self-regulating system."
] |
[
"OK, so I didn't know anything about this question beforehand but found it interesting so googled it a bit and you are not the first one asking it. I found these two questions on stackexchange: ",
"http://physics.stackexchange.com/questions/91556/is-the-earth-negatively-or-positively-charged",
" and ",
"http://physics.stackexchange.com/questions/3955/what-is-the-net-charge-of-the-earth",
".",
"From what I can read it turns out to be a hard problem to solve due to several reasons:",
"(1) We can measure a large electric field in the atmosphere which correspond to a negatively charged surface. However this is believed to be cancelled inside the Earth by a positively charged core and a positively charged upper atmosphere (this is what causes lightning). If we try to measure the electric field from a charged Earth directly we will have to subtract the contributions from the atmospheric potential gradiant which is many order of magnitudes larger and the current methods simply cannot do that with high enough precision.",
"(2) The Earth is not a finite ball and the atmosphere extends far out to the Allen radiation belt - should we include this?",
"(3) The solar wind carries both positively and negatively charged particles and Earth repels those with opposite charge than itself so that it seeks to be charge neutral. However, magnetic fields and complicated atmospheric effects might hinder this to some extend.",
"In ",
"this paper",
" they make some estimates and say that the \"frequently quoted\" value of -500 kC is not unreasonable. But they also say that the estimates may be completely wrong and there are no measurements to back it up so the net charge may as well be completely or very near exact 0.",
"In another more recent ",
"paper",
", he makes some model calculations taking the magnetic field of the Earth and the van Allen belt into considerations and estimates that the total net charge is -1 C, which is very very small. However he cites that the charge of the naked Earth without atmosphere is -4.5x10",
" C, which should be a generally accepted value(?).",
"TL;DR: If the Earth (solid + atmosphere) has a net charge it is very, very small and practically impossible to directly measure."
] |
[
"It should be, although it's difficult to measure or calculate"
] |
[
"[Weekly Discussion Thread] Scientists, how do you stay motivated?"
] |
[
false
] |
This is the twelfth installment of the weekly discussion thread (we took a break last week due to Curiosity landing) and this weeks topic comes to us from the suggestion thread (linked below). Topic: What about your science keeps you motivated on a daily basis? Or more generally, how do you stay motivated while researching? Here is last weeks thread: Here is the suggestion thread: If you want to become a panelist: Have fun!
|
[
"I work in theoretical high energy particle physics: coming up and evaluating theories for new physics beyond the standard model, comparing their predictions to data from the Large Hadron Collider, etc. ",
"I personally get a big kick out of solving tricky technical problems, which our field has aplenty, and understanding a big complicated physical picture/relationship/theory is even more satisfying. I still find it mind-blowing that we as humans can come up with these abstract, intricate mathematical structures which somehow end up describing the universe at almost every level. It gives me the chills. There are plenty of mysteries left, and now that the LHC is running there's finally lots of data to actually figure out what the missing puzzle pieces are, so I guess I'm in it for the thrill of understanding and uncovering the basic laws of the universe, as well as my personal obsession with technical detail that makes the humdrum day-to-day work very satisfying as well. It's science in its purest form, with (right now) no practical application (apart from the many technologies that get developed as a side-effect, e.g. internet & medical imaging), but who knows where this could lead? I feel incredibly grateful that society supports this kind of research -- good things happen when you let scientists just explore and do their thing. "
] |
[
"I hate not knowing. All the motivation I need."
] |
[
"As a cancer researcher I try to focus on the fact that my work may one day improve the lives of people suffering for an absolutely disease. I think in general focusing on how your research will improve humanity can be a great motivator; especially when things can be frustrating or certain political aspects of research get in the way."
] |
[
"Why are earthworms more prone to going on the sidewalk during and after rain?"
] |
[
false
] |
I have noticed they also like to go on the sidewalk in the morning, too. Why is that?
|
[
"Apparently there are two theories on this, but the both theories are based upon the fact that earthworms do not have lungs to breathe, but rather they breathe through their skin, in a process called diffusion. For diffusion to occur, the earthworm’s skin must be kept moist, so they release mucus to keep their skin moist. ",
" or ",
" soil also helps this process as it prevents them from drying out.",
"So the first theory is that they surface so that they don't drown! After/during a rainfall the ground becomes saturated with water (far beyond the point of it being moist). Too much water doesn't help the process of diffusion as the air in the soil is replaced with water.",
"The second theory is that the earthworms use these periods as an optimal time for \"migration\". The higher moisture content in the air provides an opportunity to move greater distances across the soil surface than they could do through soil. It is less work to move on the surface than burrowing through the soil.",
"This second theory appears to be gaining more ground and also helps explain why earthworms make their appearance at night when the moisture in the air is higher."
] |
[
"To elaborate on the drowning bit: earthworms can breathe oxygen through water just as well as air. Worms can live days or even weeks in water. If the oxygen content of the water is low they will drown but rainwater would be oxygen rich."
] |
[
"Isn't drowning just a fancy word for asphyxiation in a fluid?"
] |
[
"How can 2 things traveling away from each other at the speed of light both be traveling at less than (or equal to) the speed of light?"
] |
[
false
] |
So if the "speed limit" of the universe is the speed of light. And all speed is relative. Then what is the relative speed of 2 objects traveling away from each other at the speed of light? surely that's 2x the speed of light? How can that be possible and since its probably not, how am I wrong?
|
[
"Speed does not merely add linearly. It adds according to ",
"this equation",
", which means thats no matter how fast the two objects are going, they will never appear to be going faster than the speed of light.",
"In your case, each object will see the other object as traveling at the speed of light. "
] |
[
"Let's deal with things moving at speeds v very close to the speed of light, but not quite there (just because it's easier to work with). Here's the subtle difference. ",
"Suppose you have two cannons which shoot out people moving at v. You point them in opposite directions and fire. Now in your frame of reference, what exactly do you mean by the relative velocity? If you mean the (signed) difference between the velocities, then yes, by definition it's 2v > c, but this isn't a meaningful number; nobody is actually observing any object traveling at 2v. This isn't what we mean when we talk about relative velocity.",
"Now let's look from the point of view of one of the people, say person A (and the other is B). In your own reference frame, you're at rest, so now relative velocity has meaning - we can say the relative velocity is the velocity which A measures B to have (in A's frame). Now the funny thing is that relative velocity is NOT equal to the difference in velocities observed in the third frame; it's actually a more complicated formula which doesn't allow the relative velocity to be c. This arises from special relativity, and it's simply an observable fact of the universe.",
"Though I can't explain without the math why the formula is exactly what it is, here's a little intuition on why such a relation arises from special relativity. SR takes as a postulate that the speed of light is a constant in all frames. This may seem reasonable to your intuition, but it's actually highly nonintuitive. Let's take A and B again, but this time we only shoot B out of a cannon (a little easier to think about). We'll have A and B start at the same location. Now, at the instant the cannon fires, A shoots out a photon in the direction B's cannon is pointed.",
"Now, A observes the photon moving at c. What the postulate of SR says is that B observes the photon to be moving at c, NOT at c-v! So just subtracting velocities doesn't work given this postulate (which has been tested empirically to very good precision), so plain old subtraction just plain can't work."
] |
[
"Thanks to the Lorentz transformation, lightspeed isn't additive in the way you're suggesting. Special relativity can be strange and almost illogical at times."
] |
[
"Why are some animal droppings always in such uniform shapes and sizes?"
] |
[
false
] |
Why do animals, for example a rabbit have such uniform shaped and sized droppings? They look like raisins. Do they have a cookie cutter in their bums?
|
[
"In the colon there are band-like structures called taenia and out-pouchings of the colon called haustra. There are varying numbers of taenia along the length of the bowel and also between species. As liquid is absorbed from the colon the faeces begins to take shape and the number and size of the taenia and haustra have an influence on this. ",
"It isn't all down to taenia and haustra - the diet of the animal plays an important role too. If you eat a lot of cellulose you are predisposed toward firmer, pellet-like stools. If you think of horses, they are a species designed to graze poor-quality pastures for a large part of the day, but often required by us to eat small quantities of highly digestible carbohydrate-based diets. On the mostly fibre diets (without other pathology) their stools should be well formed and pebble-like. On rich carby diets or when turned out on lush pasture (water and sugar) they lose all ability to form nice pellet stools and develop diarrhoea. ",
"Last, but not least the sphincter function gets to place the final artistic flourish on a stool. If you are disturbed mid poop, you may get a few walnut whips."
] |
[
"Wow can't believe someone got back to me after three days. Very thorough response. Thank you"
] |
[
"Hullo, you are welcome! I was struggling to get out of bed and go running and writing that answer gave me a whole 5 extra minutes of excuse!"
] |
[
"Why does a human body has the need to throw up when it is aware of something disgusting?"
] |
[
false
] |
[deleted]
|
[
"The Psychology of Revulsion"
] |
[
"This is only from a quick read from Wiki but:\n\"The central nervous system mediates vomiting that arises from psychiatric disorders and stress from higher brain centres\". In this case the stress of being surprised and hit in the face, the need to understand the situation quickly in order to deal with it would cause a high amount of immediate stress.",
"Then once the tampon has been recognised the brain naturally does what it does best and uses association to bring up information. In this case that would likely be a smell, and not a very nice one.",
"The area postrema when stimulated causes vomiting. and: \"The chemoreceptor trigger zone at the base of the fourth ventricle dopamine D2 receptors, serotonin 5-HT3 receptors, opioid receptors, acetylcholine receptors, and receptors for substance P. Stimulation of different receptors are involved in different pathways leading to emesis, in the final common pathway substance P appears involved.\".\nWhich as far as I can tell means really bad smells will stimulate the area postrema and cause the vomiting effect.",
"I can see this was a survival trait as we take so much foreign substances into the stomach a system to evacuate all that at a moments notice is crucial. Of course evaluation as good as it often turns out can be tricked. "
] |
[
"Other answers are correct. Here is a shorter answer: vomiting is a simple attempt to discard things that might be poison, and the controls are not very precise."
] |
[
"How is the Sun's corona hotter than the photosphere?"
] |
[
false
] |
[deleted]
|
[
"We're not sure",
". "
] |
[
"That's probably the best answer, although we're fairly certain that it has something to do with magnetic fields.",
"Magnetic fields, on the other hand, is the astrophysicst's ultimate cop-out answer. "
] |
[
"Thanks, guys. It's good to know that we're just still working on the answer."
] |
[
"Why do the sex of the parents matter in creating a liger or tigon?"
] |
[
false
] |
A is a cross between a male tiger and a female lion. A is a cross between a female tiger and a male lion. As you can see, these two animals look different. Ligers are much bigger. Why would switching the breed of the parents cause such differences?
|
[
"Great question! This is what I've been trying to address for my PhD dissertation.",
"Short answer: it's probably something to do with genomic imprinting, but the X chromosome plays a big role in all species tested so far.",
"Long answer: There are actually many mammal hybrids that show growth patterns similar to ligers and tigons - where one hybrid is much bigger than the parents while the other is much smaller. We call this parent-of-origin dependent growth (or POE growth) because the size of the offspring depends on the which species is which parent. For a complete list of all the ",
" species with POE growth, check out Brekke and Good (2014), specifically supplemental table 1. ",
"As for why many mammals show this pattern, it could be for a couple reasons. The most intuitive explanation is that an epigenetic process known as genomic imprinting is involved. Genomic imprinting is a parent-of-origin dependent regulation of around 200 genes where one copy of the gene is silenced depending on which parent it was inherited from. For example a gene called ",
" is only ever expressed from the fathers copy while another gene ",
" is only expressed from the mothers copy. Hopefully you can begin to see how the direction of the cross (i.e. tiger female x lion male or lion female x tiger male) matters - the offspring will be using different versions of each imprinted gene depending on who the mother and father are. To further complicate the story (because that's how biology goes) imprinted genes generally play a major role in fetal development - so when something goes wrong with imprinted genes, the growth ",
" and ultimately the adult size of the individual is messed up. In addition to all those complications here's another: genes where mammals tend to use the fathers copy often increase offspring growth while the genes where the maternal allele is used tend to repress offspring growth. Thus normal mammal pregnancies can be thought of as a balance between the fathers alleles promoting larger offspring and the mothers alleles repressing offspring growth.",
"So now that we have a background in imprinting: what exactly is \"going wrong\" to result in POE growth of mammal hybrids? The Brekke and Good (2014) paper explains this as well, but I'll summarize here. There are two things that may be going on. ",
". This may be a problem because of the interaction of growth promoters and growth repressors. For example, back to ",
" and ",
": The fathers copy of ",
" is used and acts as a growth promoter. It is known to interact with maternal allele of ",
" (the \"r\" stands for \"receptor\") which inactivates ",
" and thereby represses growth. In a hybrid, say a lion x tiger (females always come first), the allele of ",
" that is turned on is from the tiger, whereas the allele of ",
" is from a lion. These two alleles have not been tested together evolutionarily and may not play well together. Perhaps the lions version of ",
" doesn't inactivate the tigers version of ",
" - now the balance is off between growth promoters and growth repressors and the offspring may be quite large. Alternatively ",
" Genomic imprinting, as I said is an epigenetic phenomena which we thing may be prone to disruption in hybrids. What do I mean by \"breaks down\" and \"disrupted\"? I mean that the silencing of one allele fails - so instead of only using the fathers copy of ",
", if the imprinting of ",
" is disrupted then both the maternal and paternal copies will be turned on. If this happens at ",
" and not ",
" then the balance between the two will be skewed (there will be too much ",
" for ",
" to inactivate). A excess of growth promoter will lead to large offspring, and an excess of growth repressor will lead to small offspring. ",
"While no one has studied genomic imprinting in the hybrids of lions and tigers, imprinting seems to be involved in POE growth in the hybrids of deer mice and hamsters, and possibly house mice too. Furthermore, in many of these hybrids genomic imprinting seems disrupted at some genes (i.e. option 2 above) but that doesn't rule out option 1. ",
"In addition, the X chromosome has been implicated as playing a major role in POE growth too (at this point you may be thinking -\"wait a minute where did the ",
" come from, what does ",
" have to do with growth\" - good. that's what we thought too). It turns out that not only is the X chromosome subject to imprinting (specifically in the placenta - which is what matters for offspring growth) but it has genes that are crucial to proper placenta function and thereby growth. It also houses genes that are critical for the proper maintenance of epigenetic marks - for example the ones that silence imprinted genes. It has been directly implicated as causing POE growth in deer mice and house mice and (though as yet unpublished) hamsters too. In the end it actually looks like an interaction between the X chromosome and the disruption of imprinting is the culprit, but there are certainly differences between all the species that have been studied.",
"To answer your question: we have no idea what causes POE growth in Ligers and Tigons, but it probably has to do with genomic imprinting and the X chromosome. ",
"~~~~~~~~~~~",
"Brekke, T. D., & Good, J. M. (2014). Parent-of-origin growth effects and the evolution of hybrid inviability in dwarf hamsters. Evolution, 68(11), 3134–3148.",
" or ",
"here",
" for one without a paywall"
] |
[
"Dang! How long have you been waiting for this particular question to crop up?"
] |
[
"I was always taught it was just a naming convention for hybrids: first part of the name is from the male and second is from the female. Is this just not true or oversimplified?",
"Also, I'm a semester away from an undergrad in Conservation Biology and am looking at Hybridization as a possible area of research for grad school. Mind if I message you with some questions?"
] |
[
"Why is New Horizons not flying closer than 7750 miles from Pluto's surface?"
] |
[
false
] |
Wouldn't flying closer yield more/better data/pictures?
|
[
"because 7750 miles is extremly close for a planetary flyby. there is the chance that any closer would cause the ship to go of course due to the gravity of the planet, or that a slight miscalculation would place the ship closer than expected. the windows of tolerence would then be smaler as to not allow the craft to acutally hit the surface. there may also be dust, or other debris. But one of the main reasons is that New Horizons is going really fast. it's only doing a flyby. it will not go into orbit. so if the flyby was too close you would have a very small field of view. possibly too small to do anything useful because the surface will pass the craft by so fast."
] |
[
"it's final goal is the Kupier belt. placing it in orbit would mean it needs a lot of fuel to slow down and then even more to escape the gravity of pluto again. just not feasible."
] |
[
"What will it visit there? "
] |
[
"Why are there states of matter (like solid, liquid, etc) instead of just smooth gradient from solid to gas?"
] |
[
false
] | null |
[
"There's a number of things to consider with this. The existence of discontinuous phase transitions can be predicted by characterising (or grouping) the states of matter by their symmetries. A gas has continuous translational symmetry while a solid crystal doesn't. So if you want to transition from a solid to a gas you will always have to encounter a discontinuous phase transition. On the other hand, both liquids and gases share the same symmetries (they're both ",
" aperiodic!!). Following the same reasoning, this would tell us that you can go from a liquid to a gas without undergoing a discontinuous phase transitions. This is achievable by transitioning from a liquid to a gas via a supercritical fluid - such a transition is continuous (or smooth as you put it).",
"This is why some people say glasses or plastics are super cooled liquids. Both liquids and glasses are anisotropic and so share symmetries. So you can undergo a smooth phase transition between them (the glass transition)."
] |
[
"To complement \\u\\Appaulingly's excellent answer, succinctly: The constituent molecules are either fixed in place or they're not (classic distinction between solid and liquid). The surface tension is either positive or it's not (classic distinction between condensed matter and gas).",
"Edge cases: Maybe many of the molecules are fixed in place, but many aren't (very compliant materials, complex fluids). Maybe the molecules are undergoing very slow rearrangement (creep, extremely viscous fluids). Maybe the surface tension is right around zero (the critical point). And many other edge cases exist that blur the standard distinctions."
] |
[
"What about that drop of pitch that seems like a solid but it dribbles a bit once every 20 years?",
"See the very last part of my comment. The pitch is an amorphous solid or equivalently a very viscous liquid and so you can transition between them via a second order glassy phase transition (continuous phase transition).",
"",
"You can have solids that have translation symmetry if you average the positions of atoms over long time scales",
"Of course solids have translational symmetry. They don't have continuous translational symmetry or continuous rotational symmetry which is what amorphous solids and fluids have."
] |
[
"Where do the symbiotic bacteria in human gastric systems come from?"
] |
[
false
] |
So, I understand that we have quite a few different little microbes that we co-exist with, like the various bacteria and such in our intestines and gastric systems. My question is how do these things get there? Do we carry the genetic information to create them in our genes? Are they passed from mother to child during pregnancy?
|
[
"We don't completely know. Yet. As unwarranted_happines mentioned, we do know that some of it comes from the mother. The birth canal is certainly not sterile, and if the baby is born via a vaginal birth, that can be the \"start\" of colonization. Breast milk is also not sterile, so if the baby is breast fed, that is a second easy route of colonization. Beyond that, most people currently caulk it up to \"environmental exposure\". But there are a few things that still don't quite fit that. We do know that there are certain types of bacteria that are only found in the lower sections of the intestinal tract. They aren't in the vagina or breast milk. So how do we get colonized with those? Additionally, we're finding the uterus isn't quite as sterile as we had previously thought, so perhaps some colonization happens even prior to birth?",
"We also know that colonization happens through a series of successions. A brand spanking new newborn has a different gut bacteria profile (a different microbiota) than that of even a one month old, which is different from a six month old, and so forth. We know that bacteria get introduced over time, and that different types dominate at different points in time. ",
"Along with all this, we also know that your gut community is more likely to be similar to that of your immediate family. We know that obviously genetics likely plays a part, as does the fact that you likely get a large portion of your inoculation from your family, in addition to eating similar foods as they do. For me, this leads to questions about obesity. We know that obese people have different microbial communities than thin people. Can this be passed on? Does something trigger one person to get obese, and can they then inoculate future children to become that way too? Which comes first, the excess calories or the different gut microbiota (or is it a succession)?",
"\nI'll stop know, as I fear I'm straying too far from your question. But one last answer, we do not carry the genetic information to create them in our genes. But we may carry the genetic information that tells our body which ones are \"good\" and which ones aren't."
] |
[
"Twin studies actually formed the basis for most of todays human microbiota/biome studies. But to my knowledge, those studies are based on twins who lived together for at least their biological formative years. The problem with the \"separated at birth\" idea is that we don't know which portion of the environment is important. It would be so many variables that we wouldn't know which one(s) really mattered."
] |
[
"Before birth, the gut of a fetus is sterile - no bacterial colonization (and human cells do not possess genes to create bacteria). Shortly after birth, bacteria colonize the newborn gut. Studies like ",
"this one",
" and ",
"this one",
" suggest that the majority of newborn bacterial strains are acquired from the mother. I think the rest are hypothesized to come from other environmental factors."
] |
[
"How much of a humans diet is made up of bacteria? Cheese & yogurt, plants and animals?"
] |
[
false
] | null |
[
"My i also add chemistry and medicine?"
] |
[
"My i also add chemistry and medicine?"
] |
[
"Hi ",
"/u/MeanderingWarrior",
" ,",
"Unfortunately Reddit only supports one flair per submission. Sorry!"
] |
[
"How can we see the bigbang's light if, as matter, we go slower than the light it emits?"
] |
[
false
] | null |
[
"Thank you"
] |
[
"Thank you"
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"/r/AskScience",
"To check for previous similar posts, please use the subreddit search on the right, or Google site:reddit.com",
"/r/askscience",
" ",
"Also consider looking at ",
"our FAQ",
".",
"For more information regarding this and similar issues, please see our ",
"guidelines.",
"This question is based on fundamentally flawed premises. Please conduct some background research and revise your question if you wish to resubmit.",
"The big bang was not an explosion from a single point.",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"Can we align the direction of an atom's electrons?"
] |
[
false
] |
, it is stated of the magnet's construction: In a magnet it is the unpaired electrons, aligned so they spin in the same direction, which generate the magnetic field. Is it not true that our understanding of electrons has progressed to the point where we now know that they are quantum variables, that they are mathematically in all places at once? How, then, could we be aligning their paths to create a magnetic field?
|
[
"Atoms are quantum systems, but the directions of the spins of an ensemble of atoms follow some probability distribution. If you make the external magnetic field very large or the temperature very low (μB/kT >> 1), then the majority of the atoms in your sample will have they magnetic dipole moments aligned with the external magnetic field, and the material will be magnetized.",
"In the case of a ferromagnet, you don't actually need an external magnetic field, because the interactions between neighboring atoms are strong enough for the object to spontaneously magnetize, even without any external field."
] |
[
"If you cool you magnet from above the Curie temperature in zero field, each atomic spin wants to align with its neighbours. However, since your magnet is pretty big, you will get multiple domains aligned along different directions.",
"The way you can magnetise a magnet (i.e. make its magnetic domains align) is either by heating it above its Curie temperature and then cooling it in a bias field, or by applying a field stronger than the so-called \"coercive field\" of the magnet, forcing the domains to align with the field."
] |
[
"It's a little to misleading to say the electrons \"spin in the same direction,\" electrons don't \"spin\" as a verb, they ",
" spin, which is a property. Spin does not refer to the electron orbiting around the atom or spinning around its own axis, it is a quantum of angular momentum that an electron possesses, the same way it has charge and mass. The spin of an electron, in the context of an atom, can be defined as being either up or down. Paired electrons have opposite spins that cancel out, but unpaired electrons tend to all have their spin in the same direction, which results in a net magnetic moment of the atom."
] |
[
"Is there a textbook on special relativity?"
] |
[
false
] | null |
[
"Yes, absolutely there are many excellent texts.",
"You say you understand calculus, set theory, vectors, etc. So that's great. I'd absolutely recommend learning a bit of linear algebra before attempting to touch special relativity. There's a lot that won't be necessary - singular value decomp, jordan form, etc. But you should be familiar with basic concepts from linear transforms, because special relativity is all about Lorentz transforms. So if you're going to teach yourself linear algebra just to get to special relativity, there's a ton you can skip. But if you're gonna read half a linear algebra textbook, why not read the other half while you're there? The hands-down single best linear algebra textbook I know of is Sheldon Axlers ",
" After you read that, you'll have to go look up the word determinant, because he won't use it. ",
"Once you've learned linear algebra, you can do special relativity. When it comes to relativity teachers, there is no name bigger than John Archibald Wheeler, and with good reason. Wheeler published a book with another author, Taylor, and it's called ",
". It's an excellent, excellent text for somebody who wants to learn special relativity.",
"If you're interested in continuing on to general relativity after that, you can pick up \"Gravitation\" by Misner, Thorne and Wheeler (although everybody just calls it ",
" or MTW). It is simply THE introductory text to general relativity, but the first section is just special relativity. General relativity relies on a few new areas of math that you'll need - differential geometry, partial differential equations, some light low-dimensional topology - but MTW includes all the math you'll really need in the text, except for the partial differential equations (PDEs). I'd HIGHLY recommend MTW. The go-to text for PDEs for non-mathematicians is Habermans ",
". I won't rave about it like I will Axlers book or MTW, but it's a very adequate book for learning PDEs. I wouldn't recommend learning everything there; just like with Axler, there's a lot you can skip if your goal is getting acquainted with general relativity. Perhaps use it as a reference if you come across material in MTW that is unclear.",
"If you're more interested in the mathematical background, look at Naber's text, \n",
" It spends a great deal more time on mathematical structure, like the Lorentz group, the Poincare group, the EM tensors and the classic tensor-rephrasing of the Maxwell equations, and the causal structure of space-time. This is not an intro text; don't pick it up until after you've down your time with either one of Wheeler's books above.",
"Whatever you do, steer clear of anything from Dover (the publisher). Their texts are usually hit-or-miss, and every SR text I've seen from them is a miss."
] |
[
"There are tons of books.",
"The final chapters of Kleppner & Kolenkow, ",
" do a nice job of introducing special relativity. Purcell's ",
" (vol. 2 of the Berkeley series) has the most easily acessible introduction to how relativity plus electric fields leads to magnetic fields.",
"Taylor & Wheeler, ",
" is good. Misner, Thorne, and Wheeler, which zelmerszoetrop recommends, is indeed wonderful, but is also highly idiosyncratic. I don't think it's where I'd recommend starting, but rather save it for down the line a bit.",
"Weinberg's ",
" is also a general relativity book that introduces special relativity in the tensor notation first. I think it's a great resource. Weinberg's book is deliberately algebraic, while Misner, Thorne, and Wheeler have written an aggressively geometric book. The combination of the two is really nice, but I think starting with Weinberg's book and then reading Misner, Thorne, and Wheeler on special relativity would be the best way to combine them.",
"Most textbooks entitled \"Modern Physics\" while have a couple of chapters introducing special relativity. ",
"Finally, let me point you to John Baez's ",
"recommendations for books on special relativity",
", in the middle of his larger page on relativity books more generally. (FYI, Baez is a mathematician with a keen understanding of physics. I think it's safe to say that anything he writes is worth paying attention to.)"
] |
[
"Thanks for the help. I should have mentioned that I understand Linear Algebra quite well, as well as PDE's, tensors, ect. I am an engineer, after all. I guess I just assume everyone knows what math engineers know."
] |
[
"Does the colour of clothes you wear affect whether or not you attract insects?"
] |
[
false
] |
Well?
|
[
"some (many) insects LOVE yellow! We used yellow plates filled with ethanol to catch insects in the field. Our prof assured us that the yellow plates work much better than other colors.\nAlso I've made the experience myself that yellow stuff tends to attract more insects than lets say brown stuff.",
"A quick googling brought ",
"this",
" up..."
] |
[
"It isn't just flowers insects are attracted to. I live in a temperate region, we grow a lot of crops. Many crop pests must find the crop each year (because they \"hibernate\" somewhere else or just move up from the south). They also often rely on color for this. Insects like aphids will fly more-or-less randomly through the air until they spot their preferred color below, at which point they will try to fly to that color, at which point they'll test it with tasting it. ",
"This is why pan traps, like what OnlyOnePairOfShoes described, work. Pan traps are usually yellow or green, reflective of the crop they are emulating. ",
"But it goes beyond flowers and grains - some insects are attracting to contrast or another pattern more than any specific color. For instance, a ladybug I worked with was shown to fly to dark spots on a lighter background preferentially. This species, in its native habitat, overwinters in caves (in NA it overwinters in our houses - Harmonia axyridis). The thought was that the dark on light spots might be indicative (to the ladybug) of a cave-like habitat."
] |
[
"Insects that do like these colors are usually ones that flowers want to attract, and as we know flowers give themselves bright colors and even \"landing pads\", black lines pointing to the center of the flower, to grab the attention of pollinators. They can't always tell the difference from you wearing a bright, flower colored shirt (bright orange, pink, yellow, etc.) and an actual flower so they go to investigate and in the process annoy the hell out of you. "
] |
[
"Do local sea levels in the ocean change with the seasons? In other words, is there a \"tidal\" high and low that is driven by temperature instead of the moon?"
] |
[
false
] |
The ocean's mass will remain about the same, I understand that. But water's density is a function of temperature, so given a difference in the temperature of a region of the ocean in winter and a region of the ocean in the summer, the density of the ocean will vary. Assuming the following conditions (one being ocean in absolute winter, one being ocean in peak summer) consider the difference in volume between the two conditions: This is a mere .31% change in volume, but consider the total volume of the ocean is Does that mean that the 'summer' side of the globe has 93 million more cubic miles of ocean than the 'winter' side? If the earth's surface is 196.6 million cubic miles, that would mean temperature can raise or lower sea levels by almost half a mile! I know this doesn't happen, I know there are thermal gradients that connect the peak high and low temperatures of ocean, and I know that the ocean is an open system and will want to self level. But do we see sea levels rise and fall slightly with average temperature? I would assume that shore lines would not notice this change because of ocean depth being small, and this difference being tremendous when the ocean is deep. Thanks in advance.
|
[
"Surface temperatures ",
"don't really change that much",
" either - maybe 40 degrees F / 22 C in a strongly seasonal place like Wood's Hole. This is because the ocean is an incredibly good heat sink.",
"The seasonal swings are also more or less confined to near the surface. Seawater is densest around 4 C. Water that is warmer or colder will head towards the surface. As a consequence you can get pretty close to 4 C whether you're near Hawaii or Alaska.",
"There is still ",
"a detectable effect",
" though! "
] |
[
"First of all, where are you getting these numbers? 32 degrees C is almost body temp and 80 degrees C is almost boiling. Your densities also don't match what I looked up for both 80C and 80F",
"Second, you can't really work out new radii like that for spheres. Using a very simple approximation of the Earth as a perfect sphere, with the oceans uniformally distributed around it, then applying an increase to the total volume of 0.31%, I get an increased average height of 8 metres. This is assuming that the entire ocean is warmed up so you could say the \"summer side\" is 4m. Then you also need to consider that the \"winter side\" is denser and decreased in height. In this very simple approximation, less dense water from the hot side would flow to the cold side so the change would be even smaller.",
"But yeah, in isolated bodies of water like lakes, you might see a difference in surface height between winter and summer. You would then have to look at factors like rain and evaporation though (larger volume of water in summer but also increased evaporation so less water in total)"
] |
[
"As noted by the others, ",
"1) your estimates of sea surface temp are mostly likely meant to be Fahrenheit and are a pretty extreme (unrealistic) seasonal change for any one location and ",
"2) the seasonal cycle in temperatures only really stays within the ocean mixed layer (top ~50 meters or 150 feet of the ocean).",
"It turns out that when you do things properly and include the physics of ocean mixing, currents, and the rotation of the Earth, you get a ",
"maximum seasonal change in sea level of about 15 cm (half a foot)",
", which happens in strong western boundary currents like the Gulf Stream off the east coast of the US. Sea level change is found to be caused by a combination of surface heating (as you guessed) but also how the winds (and the currents they create) change with seasons."
] |
[
"Why do some people have straight creases on the insides of their forearms, even though they aren't fat?"
] |
[
false
] |
A couple of my friends and I have a straight line on both forearms near the "elbow pit" (related I found online). Thing is, neither of us are, or ever were, fat enough to have fat folds in that area, and there is no way to bend our arms in such a way that the crease starts to wrinkle/fold. Is this a lasting result of baby fat, or could it be some kind of hereditary characteristic?
|
[
"I have it too. No idea why."
] |
[
"There is no published scientific research suggesting hypotheses that could explain this phenomenon, nor can I think of a means to test any such hypotheses that one could propose."
] |
[
"I was formerly fat (320 @ 5'6\") and I ",
" have one. "
] |
[
"Could you imagine an equivalence between mathematical models and computer models in natural science?"
] |
[
false
] |
I have found myself fiddling with the idea of representing what we know about our physical universe in computational terms. I'm not talking about adding the governing equations to a program, or monte-carlo simulation, no I'm thinking about representing it in a pure object-oriented way. Say you define some objects, that can act in some metric defined by interconnections between these objects. Elements such as the ranges of forces (or perhaps easier described as gauge bosons for the "enlightened ones") would be message-passing with some protocol structure. In a structure such as this, the idea of inheritance would be a great way to let composite objects, such as atoms, molecules or hamsters be super-structures of simpler concepts. Does anyone work on these ideas, I really haven't found any clear references. What do you all think, could we gain anything from this approach, perhaps cheat the three-body problem by multi-processing for instance? My education tells me I'm moving into pseudo science, but the more intimate I get with my own field (Particle physics) the more convinced I become that it could be possible.
|
[
"I'm not quite sure what you're talking about, but maybe you'd like this article:",
"http://arxiv.org/PS_cache/arxiv/pdf/0903/0903.0340v3.pdf"
] |
[
"I think I get what you are saying... but I'm not sure how useful it would be.",
"\nThe major issue with this is that it would rapidly become far too computationally intensive to be of any use.",
"\nFor any system of interacting 'objects', the time taken to simulate them will rise with roughly the square of the number of objects. This makes the problem infeasible to compute for large systems."
] |
[
"It sounds like you are describing a discrete event simulation. They've been around for a while; Simula67 was the first Object-Oriented language, and it was designed to do simulations of object interactions. I'm guessing this is not interesting to you though. However, if you would like to see something interesting, google for ",
". Formal Systems are deductive models which can be used to conduct scientific studies via proof systems. "
] |
[
"Where does it go?"
] |
[
false
] |
When a living organism dies, where does the energy dissipate too? Can someone give a detailed explanation of the process?
|
[
"The energy? If you mean the heat, it dissipates into the surroundings. If you mean the chemical energy in the molecules that make up the organism, then those are incorporated, digested and used by whatever decomposes the body. This, also, eventually will end up as heat energy. If you mean something else, then this might not be the right subreddit for this question.",
"Soo you want a detailed explanation of ",
" process?"
] |
[
"The actual energy goes into the ground, while the organic remains will nourish other organisms that will be lucky enough to stumble upon the remains. Quite beautiful if you ask me.",
"Neil De Grass Tyson had something very interesting to say about this ",
"video"
] |
[
"The energy is in the form of electrical chemical bonds throughout their body, and those bonds get broken as things, mostly bacteria, eat the organism."
] |
[
"When a rocket lifts off, is the entire weight borne by the nozzle assembly?"
] |
[
false
] |
If so, what specific part of the nozzle(s) bear the weight? How big is this connection compared to the bell of the nozzle? And due to acceleration, do G-forces cause the weight to be greater than the rocket weighs at standstill?
|
[
"Yes, the entire weight of the rocket (and extra based on the g-force) is borne by the engine bell and combustion chamber. One way to look at the force generated by a rocket engine is to look at the pressure of the gasses in the combustion chamber and in the engine bell, sum them up, subtract the external pressure, and that's your total upwards force. So the force is distributed along the entire interior surface of the engine. This link has an image that shows how the pressure is distributed across the inside of the engine: ",
"http://www.braeunig.us/space/propuls.htm"
] |
[
"If you ever first get a look at an engine, the top of the combustion chamber is incredibly beefy, and there's a very, very strong u-joint (or sometimes just a hinge, depending on the configuration and control strategy) that attaches it to the rocket structure."
] |
[
"however, one has to be very careful to make clear that this is mostly ",
" forces .. in other words, engine is pushing against the stack, and thats much easier to bear without squishing, while the same forces if they were ",
", equivalent of say lifting the rocket upside down by grabbing the nozzles, would quickly tear the rocket apart!",
"yet another way of visualizing whats going on is to think of it like the difference between a bridge pillar vs a bridge beam .. the pillars can easily be made of things like stone as they're just bearing compressive forces, while the beams holding a bridge are much demanding on the materials and need high strength steel to avoid being pulled apart .. the goal in designing lightweight rockets is to try and get as much of the structure in compression as possible as materials to withstand compression are a lot easier to find .. (on the flip side, materials that handle tension well commonly get fashioned into belts and cables, and find use to make e.g. bridge suspension cables, embedded belts in tires, fiber wrapping around pressure vessels etc)",
"*[And to clarify further, think again of the stone pillar of the bridge.. the stones there might be held together by just cement or in ancient roman ones by nothing at all other than the weight above them .. turning such a bridge upside down would quickly have all the stones come apart .. same with building a rocket .. since we're only mostly dealing with compression, you can get away with much weaker joints and connections which would quickly come apart if weight of the massive rocket were to be hanging on the nozzles rather than just pushing the nozzle onto the rocket]"
] |
[
"What is stopping the vacuum of space from pulling everything off of the earth?"
] |
[
false
] |
[deleted]
|
[
"The Earth has a gravitational pull due to its collective mass. Vacuums are the absence of particles and do not have a force associated with them. Perhaps you are thinking of opening a box full of air in a vacuum and all of the particles escaping. That's because the pressure inside the box is forcing the particles out, not the vacuum pulling them out."
] |
[
"In the case of things on the surface of the earth, they are surrounded by gas from all sides except on the bottom, so the end result is that gas (atmosphere) on the top side pushes them towards the side with no gas (bottom side), resulting in what we call atmospheric pressure.",
"This is not correct. Atmospheric pressure is the pressure in the atmosphere itself, it has nothing to do with objects being pushed by the air (they're not). All objects, even ones sitting on the ground are surrounded by air. The layer of air underneath an object sitting on the ground is very thin, but it ",
". Objects do not get pushed downwards by the atmosphere when they're sitting on the ground. If this was true, an object sitting on the ground would feel heavier than the same object held in the air. ",
"It would also be hard to move from the ground, since there essentially would be a vacuum under it. A 1x1x0.01 meter steel plate would weigh (assuming 8 g/cm",
" 80 kg, but when sitting on the ground be subjected to a downwards force of ~101 kN (standard pressure is 101.325 kPa, the unit Pascal is defined as 1 N / m",
" so on a 1x1 meter object, the force in Newtons is equal to the pressure differential in Pascal) plus ~785 N which is the force due to gravity. "
] |
[
"Vacuum doesn't pull on things. It's gas that pushes on things, and if you have gas on one side of a thing (for example, atmosphere pushing on liquid in a glass) and less concentrated gas on another side of a thing (for example, on the end of a straw that you are sucking on), then gas will push the thing from the side with more gas to the side with less gas (up the straw).",
"In the case of things on the surface of the earth, they are surrounded by gas from all sides except on the bottom, so the end result is that gas (atmosphere) on the top side pushes them towards the side with no gas (bottom side), resulting in what we call atmospheric pressure. ",
"And what is causing all that gas to stick to earth and is earth's gravity."
] |
[
"Why, in times of life-threatening danger, do humans oftentimes have more fright about siblings or loved ones over their own safety?"
] |
[
false
] |
From an evolution point of view to, me, saving themselves would increase their fitness and their ability to reproduce successfully.
|
[
"Taking care of others is selected-for, from an evolution standpoint. As a species that has only one incapable offspring per year, the mothers and fathers that chose to \"drop everything and run\" in the face of danger simply didn't pass on their genes.",
"Since we see this affection in many lower mammals, from lemurs to housecats, I presume that the care and concern for family members was hardwired in long before humanity became distinct from other primates."
] |
[
"This is largely what the book \"The Emperor's Embrace\" is about (emperor penguins). Note, a lot of that book is wild speculation, but some of it is still quite sciency. There are probably better resources but I'm not expert.",
"Reproducing successfully means that one's offspring need to reach maturity, not just be born, and since it takes many year for human young to reach maturity, it is a huge evolutionary advantage to defend our children. ",
"As for \"loved ones\", I think its it probably very hard to tease apart nature and nurture. The \"Emperor's Embrace\" argues that in this case the best strategy is working together as a community, because young mammals are vulnerable for a long time before marriage.",
"There are also other curious things, such as cuckoos, which fool other birds into caring for their young as their own."
] |
[
"Hi! Welcome to ",
"/r/AskScience",
"!",
"In this subreddit, we enforce a policy where top-level comments (direct replies to the original post) must be factual answers to the question, preferably with citations, or follow-up questions.",
"Check out the sidebar and ",
"guidelines",
" for more information! Or take a look at the ",
"Welcome",
" thread."
] |
[
"[Physics]What is Quantum dot?"
] |
[
false
] |
What makes them so special? How are they created? How do they work? What are the future applications for them? Just interested in everything about them! Thanks.
|
[
"Basically it's a small...thingy where electrons are confined and can't escape. They are usually made of tiny (nanometer sized) crystals of materials like silicon or cadmium. Electrons within the dot can have different energy levels, like electrons around an atom. That's why they're often called artificial atoms. They can absorb and emit photons when the electrons change energy levels, so they're useful for ",
"fluorescence imaging",
". They're also potentially useful for devices where it's necessary to have electrons changing energy levels in a controlled manner, like solar panels or quantum computers."
] |
[
"Thanks a lot, that was really useful!"
] |
[
"Too add more on the fluorescent properties, quantum dots have a wide absorption spectrum, high quantum yield, narrow emission spectrum, and is resistant to photobleaching. This makes it either a good energy donor for FRET, or a superior fluorescent label over organic fluorophores. One unique characteristic is that the absorption/emission characteristics are dependent on size of the quantum dots."
] |
[
"Why are Herbs tasty? No plant benefit..."
] |
[
false
] |
After making an awesome curry tonight, I was wondering why some plants have flavors that we find palatable. Fruits I understand - consuming them potentially spreads the seeds, but I can see no evolutionary benefit to Thyme, Rosemary, Mint, etc. I'm sure the percentage of 'tasty' plants to 'non-tasty' plants is tiny, but I cant see the evolutionary basis of making your leaves taste nice to animals (humans in this case). Note: I understand that once a plant is deemed as desirable by farming humans, that it will then become more successful - see us planting great fields of an ex-wild grass called wheat. My question is to whether the plants evolution did this intentionally, or it was blind chance that we like to eat herbs, but don't like to eat the bajillion other plants out there.
|
[
"The main factors break down like this:",
"Some of the tastes we like mimic more dangerous tastes This is especially true of some of the more pungent and/or bitter herbs, where the taste is fairly similar to what you'd get if you ate other plants that are poisonous. In general, animals will avoid those, but humans have the advantage of a long life, a good memory, and the ability to share stories. This means we can learn which strange tastes are associated with actual harm, and which ones aren't.",
"Because we are large compared to something like an aphid, we are able to dissolve the chemicals we get in herbs to much more dilute levels than the aphid eating them would, and at lower levels they may be much less toxic. Rhubarb, for example, is slightly toxic if you eat a lot of it raw, but rarely causes any real danger to humans. The same chemicals that make it toxic to us though make it quite dangerous for insects.",
"In other cases, the purpose of the chemicals providing taste was completely unrelated to the fact that we eventually ended up finding them tasty. A chemical which is an antibacterial which just happens to taste minty to us, for instance, is useful to the plant because it makes it less suitable for bacteria to infect it. The fact that we eventually came along and ate it wasn't enough to reduce the evolutionary history of usefulness of that minty-tasting antibiotic."
] |
[
"Those are both true, but the phrasing of the initial question made me think he wanted the logic that applies where neither of these are the case."
] |
[
"Those are both true, but the phrasing of the initial question made me think he wanted the logic that applies where neither of these are the case."
] |
[
"Can Moons Have Rings?"
] |
[
false
] | null |
[
"If they can, they'd be very short lived. Rings require a very stable orbit, but with moons, the gravitational effect of the planet is stronger on one side of the moon than the other. This will distort the ring orbit, and without the stability, the debris that makes up the ring will either crash into the moon or be pulled out to space"
] |
[
"Rings require a very stable orbit, but with moons, the gravitational effect of the planet is stronger on one side of the moon than the other.",
"This answer is not quite correct. The same reasoning would say that planets cannot have rings, since the Sun's gravity is stronger on one side than the other, destabilizing the rings.",
"The more correct answer is that moons can have stable rings if the extent of those rings is much smaller than the moon's ",
"Hill sphere",
", which you can think of as the region over which the moon's gravity dominates. ",
"Being much smaller than the Hill sphere is not a sufficient condition for ring stability, of course. Rings that are highly inclined relative to the moon's equatorial bulge, or highly inclined relative to the moon's orbital plane, would also be unstable even if well inside the Hill sphere."
] |
[
"I love how you explained this and how it sounded in my head when I read it. "
] |
[
"why don't women get facial hair like men?"
] |
[
false
] | null |
[
"Androgen levels in men and women differ, and there are areas on the body that are more sensitive to androgens that have hair growth in the same areas in men and women (armpits, genital area). Men produce more androgens. Dihydrotestosterone (DHT) is in much higher concentrations in men, which is mainly responsible for facial hair growth, if I remember correctly. Also can be the cause of losing hair on top of the head.",
"\nSome women do have some facial hair, whether its fine, downy kind, sparse, or dark stubble."
] |
[
"So it's not \"like men\", since it's vellus hair, not terminal hair. ",
"The difference is testosterone. "
] |
[
"So it's not \"like men\", since it's vellus hair, not terminal hair.",
"They get terminal hair too. Some women grow more than others, but you don't see it because they wax, pluck, or shave it off."
] |
[
"When did humans start to use names to refer to each other?"
] |
[
false
] |
I am asking in the context of the tradition of passing down names and using first and last names or middle names.
|
[
"I'm going to have to disagree with your reasoning.",
"Names are a part of language: a referent that points to a single individual and can be used in that individual's absence to refer to him/her and only him/her. This sort of behavior more or less requires long-term referential processing (that is, being able to identify a referent with an object and use that referent even when the object is not there). This sort of processing seems like it would be a direct antecedent to the symbolic processing that underlies human language (being able to group objects into classes and assign a referent to that class), but really the symbolic processing probably came first and brought the referential thing with it, since it's only one step from animal calls to long-distant referents (that is, animal calls where the thing being called about isn't actually around but still being referred to anyway), whereas no animal we know of has individual names for things that are only useable when that individual thing is around.",
"My guess is that pretty much as soon as our symbolic language capabilities became to any degree generalizable (that is, we went from having a few long-distance referents to being able to assign new referents to newly-defined classes of things), individual names were one of the first things we used that power for. Purely a gut guess, but it would make sense being social animals that one of the first things we'd want to talk about or directly address would be others in a group.",
"Anyway, I don't think that guessing based on anatomy is really the way to go about this. Language use probably predated any large change in terms of brain anatomy, because once we had symbolic processing we had a new evolutionary force selecting for types of intelligence that had never been selected for before (this is called the Baldwin Effect, when a learned behavior beings exerting evolutionary force on the species who has learned it). I'm with those who suggest that very simple language (probably symbolic speech with little syntax, looking closer to a pidgin than a language) evolved in ",
" first and became more complex. ",
"Derek Bickerton",
" tries to date this fairly exactly using certain kinds of tool manufacturing and different hunting techniques which all happened in ",
" around the same time, but I can't remember what the date he gave was. His book ",
" is well worth picking up if you're interested in the evolution of language, although there is a fair amount of just-so storytelling going on. Anyway, ",
" was around much earlier than ",
" went extinct (speciation events don't usually involve the entirety of a species evolving into something new, but often just an isolated group), so 1.4 million is probably too late for a maximum estimate: I'd give it closer to 1.8 or so, when ",
" began migrating out of Africa (which wikipedia tells me is now not the preferred hypothesis and that ",
" is distinct from ",
"? Just two years ago this wasn't what I was learning in my biological anthro courses and readings. Whatever, s/erectus/ergaster if that's the case -- whichever pre-",
" homonid was in Africa at the time).",
"Also, regarding first and last names, that's a bit easier of a question to answer: family names most likely originated around the time agriculture, herding, and civilization were first popping up, when humans first started having private property and thus inheritance became important. Of course, the specific Given-Name Given-Name2 Family-Name structure of modern English is much newer than that. Family names don't have to take the modern English way of everyone in the family having the same name: in some cultures one's surname is one's father's name (Iceland still uses this convention, and it's where the \"son\" in Johnson, Wilson, etc. comes from), in other's a family title or profession is used (thus \"Smith\" means \"metal smith\", etc.), or even where a person was born if there is a tie to that land (usually ownership; thus the French \"de ",
"\" names).",
": A better answer than just giving a time and possible anatomical reasons is thinking about why names would come into use. Thus, we began using names most likely around the same time that we learned to refer to individual objects or classes of objects with a specific sound, even when they weren't around -- the first step towards human language.",
"The whole family name, and particularly the modern English first/middle/last name system, comes from a much later time -- the former around the advent of civilization, and the latter was probably brought to us by the Normand Conquest of the 1080's."
] |
[
"No one knows, but you can narrow it down a little.",
"50,000 years ago there was relatively modern behavior, so it is likely earlier than that. Anatomically modern humans were around 200,000 years ago, so I suspect it was earlier than anatomically moderns. The Neanderthal-anatomically modern human ancestor was around 650,000 years ago. Neanderthals were likely capable of complex speech, so my guess would be that it's earlier than that. ",
", at about 2.3 to 1.4 million years ago, had a brain about the size of a chimps. I would guess this is way too early for any names, let alone names with structure (first, middle, last). So, if I had to guess, I would say about 650 thousand to 1.4 million years ago, likely closer to 650 thousand."
] |
[
"My guess is: as soon as we started using language. I find it hard to imagine that our ancestors, living in small communities where personal relationships were everything, could have had any significant period where they had words for ",
" without having words for individuals."
] |
[
"How many parameters are needed to describe the complete state of a photon? For a beam of photons?"
] |
[
false
] |
I was reading today in Slashdot about (optical) Orbital Angular Momentum being used to encode information on a light beam to acheive incredibly high data throughput rates . I had never heard about OAM, and it occurred to me that light might have a few more properties than I had really thought about. So, how much information do you need to give a complete description of a photon? I think you could also ask this in terms of "how to construct an eigenspace for a photon". I could imagine that you'd need at least the direction vector, then either frequency or energy, polarization state ( is four parameters?). Is that it? 8 parameters? How much information would you need for a uniform monochromatic beam of light? The 8 previous parameters, plus intensity, coherency, initial diameter, spread, then I guess the OAM parameters? I'm not sure how coherency is modeled, so I'm not sure I can even take a stab at this. I have to admit, photonics is not my primary field of study, but I'm kinda curious about this and how it relates to wireless technologies What say you, photonics scientists of reddit?
|
[
"Direction of propagation is part of the wave vector. Beyond that your reply is somewhat misleading since it implies that there are only 3 parameters (2 if you had lumped in propagation direction with wave vector). It's true a photon can be described using only the wave vector and it's polarization state, but I think by parameters the OP means scalar values, of which these terms contain several. \nIf you were to break it down the state of a photon is given by:",
"Polarization state",
"2 & 3 together contain the same information as the wave vector. So, all told 5 scalar values can completely describe a photon (unless I missed something). This of course doesn't include universal constants like the speed of light, just what varies from proton to proton."
] |
[
"For a beam, at least in X-ray optics, we usually use energy/wavelength, divergence, intensity per unit area at a given plane, and coherence. ",
"The coherence has two parts, temporal and spatial; the temporal (or longitudinal) coherence is a measure of the monochromaticity, whereas the spatial (or lateral) coherence documents the largest distance between two points in space that have a fixed phase relationship -- the latter has a lot to do with the source size and its distance to the plane of interest (van Cittert-Zernike theorem)."
] |
[
"No. ",
"http://en.wikipedia.org/wiki/Photon#Physical_properties",
"A photon can be described entirely by its wave vector, polarization state and direction of propagation."
] |
[
"How can astronomers differentiate spectroscopic red shift and the expanding universe red shift while looking at a star?"
] |
[
false
] |
Just came to my mind. It might be two completely different things tho.
|
[
"We don't. Motion is motion, and all you can record is the velocity in the direction of your line of sight. Locally, peculiar motions of objects vastly dominate the Hubble flow, but at greater and greater distances, motion from the expansion of the universe builds up and dominates local motions. The Hubble constant is about 70 km per second per MEGAPARSEC, so it takes millions and millions of light years to become dominant. Earth moves at about 35 km/s around the Sun, just for scale. When you have a cluster of galaxies, you can say what the average velocity of the cluster is and know that differences from that are local to the cluster, but a single measurement will always just tell you the total motion in your line of sight: peculiar velocity in its local frame plus Hubble flow. Also, motion from the expansion of the universe is constant (at human timescales anyway :P) so any ",
" you measure are local (e.g. a binary star orbiting around something else, or a cluster of stars around a central black hole)."
] |
[
"Awesome thanks :)"
] |
[
"70 km per second per MEGAPARSEC",
"To be fair, though, a megaparsec is really not that big in the cosmic distance scale. It gets you out as far as only the very closest galaxies (Andromeda, M33) in our local neighborhood. The closest galaxy cluster is 16 megaparsecs away."
] |
[
"Are emotions a possible requirement for an organism to have human level intelligence?"
] |
[
false
] | null |
[
"Emotions are not only a possible requirement for an organism to have human level intelligence, they are ",
" for for an organism to have in tact reasoning and successful decision making. Individuals with damage to critical \"emotion\" centers of the brain can no longer live normal lives due to impaired reasoning and decision making. However, their performance on IQ tests remains perfect. This had been a paradox since the classic patient Phineas Gage displayed this pattern in the mid-1800's.",
"The eminent neurobiologist & neurologist Antonio Damasio has recently solved the paradox, highlighting the central role that emotions play in uniquely human traits (i.e., decision making, reasoning, moral reasoning, etc.)",
"If you are even remotely interested in this, I would recommending checking out his classic book, ",
". Fascinating stuff."
] |
[
"All of those things you just listed are behaviours. Ergo, it is a behavioural motivator.",
"But I think we're using different definitions of intelligence. Intelligence is simply the capacity for more complex reactive behaviour. So more intelligent creatures, like humans, can do more complex things like learning based on cues, planning ahead, or following a thought train through more levels of indirection. You are talking about the mind in some vague way that I'm not sure about."
] |
[
"What I am proposing is that an emotion is a precursor to any set of behaviors, intelligent or not. An emotion is characterized by its physiological profile. The body reacts in a certain way, and it expresses the emotion in a very concrete and measurable way. To be sure, some components of the emotion process are not visible to the naked eye but can be made \"visible\" with current scientific probes such as hormonal assays and electrophysiological wave patterns. The emotion itself ends there. Then, comes the emotional response (qua behavior).",
"The behavior (i.e., running away from danger) only follows the enactment of the emotional program. You can call it a behavioral motivator if you'd like, but it is a survival mechanism. That is why every animal, no matter the degree of its intelligence, possesses a set of emotion programs that acts to promote its survival, although every animal does not possess a complex level of intelligence as we do. That's because complex intelligence is not necessary for survival (although it surely enhances it). That is what separates us from animals: Our adaptive response, which builds upon our emotional response or appropriately adjusts our emotional response, is a big part of what we call intelligence. And it can only happen as a result of the initial emotional trigger."
] |
[
"Is there such a thing as UVC-resistant bacteria?"
] |
[
false
] |
Most news articles about harmful bacterial evolution talk about antibiotic resistance. Is there a similar danger to using UVC to disinfect things, developing bacteria that is impervious to UV damage? Is there something similar for hand sanitizers (alcohol)?
|
[
"You mean like ",
"? Yep, there's such a thing. Fortunately, not all bacteria are dangerous to humans.",
"https://www.newscientist.com/article/2252786-radiation-resistant-bacteria-could-survive-journey-from-earth-to-mars/"
] |
[
"You can still kill it with UV, you just need more of it. In this particular case the bacteria only survived when largely shielded from UV:",
"Although the bacteria in the outer layer of the clumps were destroyed by the UV, these dead cells seem to have shielded the bacteria in the innermost layers, which survived.",
"UVC causes all sorts of chemical reactions, that's unavoidable in living matter. Enough of it ",
" kill everything."
] |
[
"An organism that is resistant to UV or alcohol needs expensive mechanisms to resist those broad spectrum hazzards. Those organisms would put a lot of energy into being resistant to those dangers, and would have less resources allocated to rapid reproduction or to evade the immune system.",
"Antibiotics usually attack a specific molecule in an organism, so resistance can be achieved by changing or protecting just a small part of the organism. That change might cost hardly any resources for the resistant organisms.",
"This is why UV or alcohol resistant pathogens are more rare than antibiotics resistant pathogens."
] |
[
"How is it possible for a plane to fly when it is upside-down?"
] |
[
false
] |
I know that the wings of a plane are airfoils, which causes slower moving air under the wing with a higher pressure to force the wing up. I don't get how an airfoil that is upside-down can still keep a plane in the air. Edit: thanks for everyone who replied!
|
[
"While wings do typically have camber (the curved shape that causes air over the 'top' of the wing to move faster than the bottom, resulting in a pressure differential providing lift), this is a relatively small component. The biggest contributor to lift is the simple fact that air hitting an angled wing on the leading edge gets pushed downward, creating an equal and opposite force on the wing. There's a lot of complications about vortices, stable flows, etc etc - but the core of it is just simple conservation of momentum. You can feel this yourself by sticking your hand out of a car window - even if your hand is flat, if it forms a slight angle against the wind, it'll be pushed up or down, until you reach the critical angle at which it stalls.",
"As such, if you have a cambered wing and want to fly upside-down, you just have to adjust your angle of attack to counteract the lift from cambering (which is now pushing you down). On some planes designed for acrobatics, they'll simply not camber the wing at all to make this easier, relying solely on the angle of attack to generate lift - but this is not a necessary condition for inverted flight."
] |
[
"I upvoted your answer to the OP, but I'm downvoting this because bdunderscore is perfectly correct at the level of discourse that I think is appropriate given the OP's level of understanding. You are both correct, and though bdunderscore is simplifying a bit, I think this allows him to offer a bit more insight than you did in your post. The take home lesson I think you both should agree on is that Bournoulli's theorem is not the explanation of lift. This is basically what bdunderscore emphasizes, correctly."
] |
[
"A nice, clear post. Here's a nice link about lift from nasa (",
"http://wright.nasa.gov/airplane/lift1.html",
") it's basically what bdunderscore said but it's from nasa, with pictures of the Wright plane, and therefore better ;)",
"It's probably worth adding that many aerobatic planes do not have cambered wings (",
"http://en.wikipedia.org/wiki/Wing/",
") which makes flying upside-down easier."
] |
[
"Is there something comparable to blood types in other species?"
] |
[
false
] | null |
[
"There are not just \"something comparable\" to blood types in other species, there ",
" blood types in other animals. ",
"According to a FAQ from the UC Davis vet school",
", blood types (and resulting transfusions) work pretty much the same way in dogs and cats as in people, although they don't have compatible systems (i.e., you wouldn't find a compatible blood-type in Fluffy or Snowball).",
"From the peer reviewed literature (",
"Avent & Reid, 2000",
"), there are descriptions of related (components of) blood type systems in invertebrates as well as 'higher animals:'",
"It was thought that Rh proteins were erythroid-specific and confined to higher vertebrates. However, the discovery of sequence-related RHAG homologs in invertebrates suggests otherwise. These homologs have been found as 2 different RHAG-like genes in Caenorhabditis elegans (a nematode; GenBank accession U64 847 and Z74 026) ",
" and as at least 1 in Geodia cydonium (a marine sponge; GenBank accession Y12 397).",
"So, not only do closely related mammals have blood types, but even very distantly related animals have similar or conserved genetic sequences coding for blood type factors. ",
"Apes and primates (including us) share the ABO blood-type system, and it appears to be at least 20 myo. However, we don't have a clear idea of why blood types evolved or what functions the system serves.",
" Most of the hypotheses have to do with disease resistance, and multiple blood types arising and persisting due to overlapping distributions of primate populations with pathogen and blood-parasite (like malaria) populations."
] |
[
"No, not at all. I mean they aren't compatible with humans. There are many different forms of blood-type ",
" in the animal kingdom. Humans largely share our blood type system with great apes and primates, but not with mammals as distant as canines. ",
"Blood types were actually discovered as a result of experiments with blood transfusion (including animal to person) between the 1600s and 1800s, many (or most or all) of which ended in the death of the patient receiving the blood.",
" Trying to determine why blood from another animal or another human had a high chance of causing coagulation and death eventually (around 1900) to the discovery and description of blood types."
] |
[
"I'm slightly confused by your answer. When you say that they don't have compatible blood-types, what exactly do you mean? Do you mean that you couldn't do something such as a blood transfusion between two dogs? "
] |
[
"If the Internet could be wholly redesigned from the ground up, what standards, protocols etc. would be implemented differently?"
] |
[
false
] | null |
[
"Assuming we know what we have learned from this internet, DNS would certainly be up for major overhaul.",
"The DNS protocol is responsible for a ridiculous percentage of DDoS attacks because of the quantity of poorly configured open resolvers and the design of the protocol itself, which makes it trivial to spoof a request that sends far more data to the victim as a response than is required in the request from the attacker.",
"this is known as an amplification attack and after working at an ISP for years it had my vote for single largest threat to the stability . the internet."
] |
[
"If we were starting from scratch, we would almost certainly skip ",
"IPv4",
" entirely and go straight to ",
"IPv6",
" or some variant with an equally large address space.",
"4 billion IP addresses must have seemed like an endless supply back in the 80's, but in the last few years we've finally started running out, and the demand for addresses is only going to get worse from here. At the rate things are going now, it's going to be years before it's viable to run a public site solely on IPv6."
] |
[
"We'd build in connection level encryption for a start.",
"SMTP would have authentication.",
"DNS would be fixed to prevent spoofing.",
"HTTP(S) is an amazing success that works astoundingly well, so I hope we'd keep that. "
] |
[
"Does drinking alcohol have any effect on the gut microbiome?"
] |
[
false
] | null |
[
"I'm a science writer who wrote a textbook on gut microbiota & diet with a dietitian and microbiologist... we recently did a quick summary of the effects of alcohol on the gut (see the end of the newsletter):\n",
"https://us19.campaign-archive.com/?u=238be946e37df7502dcf28e29&id=5640bf33be"
] |
[
"Thanks, very informative"
] |
[
"I don't know specifically about gut microbiome effects, however, I think that pretty much everything you consume has some sort of effect on your organs. Maybe we could ask a more specific question.",
"\"Does alchohol consumption decrease biodiversity in the human gut?\" \nMaybe even more specific for this one."
] |
[
"Will the virus causing COVID-19 disappear/go extinct after everyone gets the vaccine?"
] |
[
false
] |
[deleted]
|
[
"Unlikely? It would require mass universal vaccination AND for there to be no zoonotic hosts - no animals that can carry the virus. We were able to eliminate smallpox because there are no animals that carry it. Diseases that have animal reservoirs will pop up again whenever vaccination rates drop below the required level and exposures to infected animals occurs."
] |
[
"It is very unlikely SARS-COV-2 will go extinct. It is well documented that many different animal species like cats, dogs, bats, pangolins, minks and more can be infected and transmit the virus. Here's a ",
"USDA report",
" on animals they've identified in the US that were positive. It's impossible to vaccinate all of those animals. If an infected animal encounters a human who is not vaccinated at some point in the future, the virus could come back.",
"Also there are hundreds to thousands of related coronaviruses circulating in South East Asia, most commonly ",
"studied in bats",
". Many of these coronaviruses have the potential to cause a pandemic."
] |
[
"Smallpox is not really a good comparison, since smallpox had no known animal hosts and was very easy to diagnose and track overall. SARS-CoV-2 has many known animal reservoirs and can be very difficult to track. I think it's entirely possible for us to eradicate a virus like smallpox today, and in fact we're extremely close to eradicating polio, with only a couple hundred wild cases per year"
] |
[
"How do scientists know that they are assembling dino bones correctly when they often have only a few to go by?"
] |
[
false
] |
Has anyone ever done an experiment with modern bones to see how close they can get it with only a few frags of bone or mixed bones. I'm pretty skeptical that you can construct an entire animal from only a few broken and mixed up bones.
|
[
"You'd be surprised by how similar vertebrate skeletal layouts are. This, combined with the wealth of knowledge paleontologists draw on in order to compare the minutiae of a fossil specimens, means relatively few clues will give away details about how the species lived and what other species it resembles"
] |
[
"Because even in the most ancient of reptiles ",
"the knee bone is connected to the thigh bone,",
" the Thigh bone is connected to the hip bone, the Hip bone connected to the back bone, the Back bone connected to the neck bone and the Neck bone connected to the head bone. "
] |
[
"It's pretty rare to find the entire skeleton all laid out although that does happen at least some of the time for partial or full fossils embedded in sedimentary rock's especially.",
"Beyond that, they can actually look into the fossil to see where muscle and ligaments attached and get an estimate of how large these where which indicates what sort of muscle groups they belong to. They've also been known to use similar modern species when available to make comparisons.",
"Then there's models of locomotion they can run in simulations to ascertain how they might have moved, and they'll compare those results to other factors such as the muscle groups and so on."
] |
[
"What controls organ regeneration and why can't humans do it?"
] |
[
false
] | null |
[
"The human liver can regenerate.",
"The liver is the only human internal organ capable of natural regeneration of lost tissue; as little as 25% of a liver can regenerate into a whole liver.[14] This is, however, not true regeneration but rather compensatory growth.[15] The lobes that are removed do not regrow and the growth of the liver is a restoration of function, not original form. This contrasts with true regeneration where both original function and form are restored. In liver, large areas of the tissues are formed but for the formation of new cells there must be sufficient amount of material so the circulation of the blood becomes more active. ",
"This is predominantly due to the hepatocytes re-entering the cell cycle. That is, the hepatocytes go from the quiescent G0 phase to the G1 phase and undergo mitosis. This process is activated by the p75 receptors.[17] There is also some evidence of bipotential stem cells, called hepatic oval cells or ovalocytes (not to be confused with oval red blood cells of ovalocytosis), which are thought to reside in the canals of Hering. These cells can differentiate into either hepatocytes or cholangiocytes, the latter being the cells that line the bile ducts.",
"http://en.wikipedia.org/wiki/Liver",
"I also found this:",
"Simple animals like planarians have an enhanced capacity to regenerate because the adults retain clusters of stem cells (neoblast) within their bodies which migrate to the parts that need healing. They then divide and differentiate to grow the missing tissue and organs back. The process is more complex in vertebrates, but nevertheless, salamanders possess strong powers of regeneration, which begins immediately after amputation. Limb regeneration in the axolotl and newt has been extensively studied.",
"http://en.wikipedia.org/wiki/Regeneration_(biology)#Vertebrates",
"And, I know that you asked for organ regeneration, but humans are partly capable of limb regeneration as well.",
"http://en.wikipedia.org/wiki/Regeneration_(biology)#Humans"
] |
[
"You're partly right in that stem cells are a good starting point, but complexity is a big deal. As you suggest stem cells can become other types of cell, but need to be properly guided however the level of nuance required for that is not something we're even close to. Remember that human development takes a near minimum of nine months, and the reality is that babies are only half baked and require quite a bit more development once born.",
"Stem cells were (and to some degree still are) very big in the spinal cord injury field; people figured we could drop a bunch of them in the cord and they'd figure out what was wrong. Unfortunately, we learned that the adult spinal cord is not a very good place for stem cell development and growth, the body at this point has produced a number of signals halting development. I suspect this is the same in much of the rest of the body, because unchecked growth and development is a very bad thing (cancers and teratomas are good examples of this)."
] |
[
"Myostatin is just one of very very many growth factors. There's factors for everything. There are two problems with using these guys:",
"In my research I have seen problems with both; for the former, neurons will grow to where the growth factor is and won't leave that area, just squiggling around for a bit. For the latter, cancer can be a problem when you take away these brakes (like myostatin blockers)."
] |
[
"If Jupiter was a rocky planet instead of a gas giant, how difficult would it be to land a rover there with the much higher gravity?"
] |
[
false
] | null |
[
"I obviously should wait for proper authorities to jump in here but from a basic science background it would seem to me that it just wouldn't be possible to have a 'rocky' mass of those dimensions. The pressure alone would produce exotic states.",
"It would depend on the composition of the rocks of course but phase diagrams get pretty interesting for even the theorized pressures and temperatures present on the real Jupiter."
] |
[
"This is not the answer you are looking for, but here is a discussion of one hypothesis -- that it would turn into a star.",
"Jupiter's density is 1.33 g/cm3, iron is 7.8, so if it were a solid ball of iron it would have a mass under 10x its current mass.",
"This site says 75+ times bigger to become a star.",
"I looked this up because I recalled the (reported by that article) old hypothesis that it was pretty close to turning into a star already."
] |
[
"The problem on Venus is more the heat, isn't it?"
] |
[
"What happens inside the digestive system when a lactose intolerant person consumes dairy?"
] |
[
false
] | null |
[
"Your gut just lacks the enzymes to process the lactose, the bacteria that then meet the undigested lactose produce a bunch of nasty byproducts as they make efforts to devour the sugar. They produce lots of gas and the bacteria for the most part can't really handle it so the material just kinda gets shoved along the digestive tract as your bowels become filled with gas(at a rapid rate), causing diarrhea "
] |
[
"Most mammals, including most humans, stop producing lactase, a pancreatic enzyme that splits lactose (milk sugar) into a glucose and galactose after they are weaned. So lactose intolerance is the normal state. When lactose is consumed, it remains in the lumen of the bowel where it osmotically attracts water leading to diarrhea. Further, some bacteria can metabolize lactose and produce methane as a consequence. This gives the gas, the flatus. Avoid or reduce lactose consumption to avoid these physiological responses to lactose consumption. One way is to convert lactose to lactic acid. It curdles the milk and makes sour. Voila, yogurt and lebneh. Or make cheese and toss away the whey where the lactose remains. Cultural adaptions to retain the benefits of dairy without GI distress."
] |
[
"Well...that's how it expels it, gas forces fecal matter to move at a more rapid pace and to be pushed towards the exit. Also, as ",
"/u/alanmagid",
" mentions, lactose pulls water from the bowels causing it to further accelerate along. ",
"Basically it's like using a high pressure hose to clean a clog from a pipe. "
] |
[
"If I brew coffee with twice as much water but the same amount of grounds, how much more (if any) caffeine will be in the resulting pot?"
] |
[
false
] |
My intuition says it would contain somewhat more but less than twice as much caffeine. Is that right? Does anyone have a better idea of where in that range you would fall?
|
[
"It will have almost no effect on the amount of caffeine in the water. Caffeine has a very high solubility in water, especially hot water, so the limiting factor isn't the amount of water used, but the amount of coffee grounds added. Even at room temperature, one cup of coffee with its ~100 mg of caffeine is only around 2% of the saturation level. That's a good thing, because a cup of saturated caffeine solution (5 g of caffeine in 8 oz) is nearly enough to kill you. "
] |
[
"Partially. Espresso is a smaller volume of water being used to extract a \"normal\" amount of coffee, but one requirement of espresso is the pressure this extraction is done under (~9 bar). These conditions do result in a higher caffeine density than a drip coffee, yes."
] |
[
"So is it correct that a cup of espresso is just less water run through a normal amount of ground coffee, which therefore comes out stronger?"
] |
[
"If a new Hubble Telescope was to be designed today, how much more powerful could we make it?"
] |
[
false
] |
[deleted]
|
[
"The detectors being used by JWST are a pretty significant difference too. Hubble uses CCD technology, specifically ",
"SITe 2048x4096 sensors",
"(pdf) produced by Scientific Imaging Techologies (in its newer sensor packages). This is a ",
"backthinned CCD",
" with ",
"quantum efficiency",
" over 80% (in some frequencies) and ",
"dark current",
" in the neighborhood of ",
"0.1 e/second",
". By today's standards this would be the equivalent of an excellent, but ",
" sensor.",
"JWST is using Teledyne ",
"HgCdTe",
" based sensors (for most of its cameras) that peak at over 90% QE, with noise levels down around 0.004e/second ",
"pdf",
". The HgCdTe sensor is also much more sensitive to the infra-red than a CCD would be (important since that's what JWST is primarily going after), and is better suited to survive JWST's extremely cold operating temperatures than a CCD would be.",
"So yes, the larger mirrors of JWST do allow it to collect much more light than the Hubble could, but the camera technology has come a good ways forward too. Not only does it collect more light, but it can do more with the light it collects!"
] |
[
"The Hubble Space Telescope has actually been refitted several times in its life, so it's not just using the technology from its original designs in the 80s and its launch in the 90s. So it's not completely old technology.",
"That said, we don't need to be theoretical about the comparison, because its successor is already well under way - the ",
"James Webb Space Telescope",
". This is actually more of an infrared telescope, partially because adpative optics have made Earth-based telescopes much more competitive in the visible light range, but we sometimes still think of it as \"Hubble 2.0\".",
"The main difference is the size of the mirror that collects the light. JWST's mirror is 6.5m across, while the HST has a 2.4m mirror."
] |
[
"The main limiting factor is the size of the primary mirror. This was determined by what would fit in the Space Shuttle's cargo bay. Spy satellites have a similar size mirror (although curved differently for a smaller field of view).",
"The instruments are built with an extremely long lead time and are not off-the-shelf. If you built (i.e., finished assembling) a new Hubble today it would be using technology that was first started to be designed several years ago. The current instruments were installed five years ago which is not that long ago."
] |
[
"In winter, why don't lakes freeze through?"
] |
[
false
] |
Even if there are many consecutive days of sub-zero weather?
|
[
"Water has many unique properties, but one of the most important is the fact that the solid form is less dense than the liquid form. [This happens because the volume of the solid is greater than the liquid, due to the bonding as a result of the chemical structure.] The effect of this is that when some water freezes, it floats to the top of the body of water, and forms a sheet of ice on top of the liquid. This insulates the water beneath it and keeps it from freezing. Many evolutionary biologists argue that life would not have been able to evolve on earth if this wasn't true about water. "
] |
[
"In the mountains many do. Kills all the fish."
] |
[
"So if it's a big deep lake and really cold weather, it just doesn't have time to freeze through in a typical winter?"
] |
[
"Why does the body use RNA?"
] |
[
false
] |
When DNA is translated why is RNA used it seems like it would be easier to just use a copy of DNA and not have to have both "T" and "U" and only have to worry about having "T". Or am I missing some important reason as to why RNA is a better option to use? So instead you would have mDNA and tDNA and rDNA instead of mRNA, tRNA, and rRNA. I apologise if this is super obvious I'm somewhat new to biology.
|
[
"It's not \"super obvious\" and kudos to you to wonder about this instead of just taking it for granted!",
"There's a concept called \"RNA World\" where the genetic information was stored in the form of RNA and would resemble what you speculated in the question. However, RNA molecules are not very stable and somewhere along the way, DNA turned out to be a stable and better form of storage for genetic information. However, the protein translation machinery still requires RNA, and so the process we know: DNA to RNA transcription and then the translation of mRNA to protein."
] |
[
"You have to think about how large a single DNA molecule (a chromosome) is in comparison to the size of a gene that is getting transcribed... it would be an extreme waste (energetically inefficient) to transcribe all that genetic material (millions of base pairs long) for a gene encoding a protein that’s only a few hundred subunits long. ",
"Also you have to think spatially here. DNA resides in a different chemical environment with unique conditions (ph, solute concentration, etc.) that is separated from the ribosomal units outside the nucleus where transcription is taking place. ",
"You also have the issue of size of the nuclear pore where mRNA must travel through. (You don’t want DNA leaking out of the nucleus it would be chaos)",
"RNA has countless mechanisms by which it can regulate how genes are expressed, processed, and then transcribed. ",
"RNA is your “middle man” think of a huge enormous storehouse for books most of them pointless (this is DNA) and there’s multiple schools all around where the information from them is being thought (ribosomes transcribing or making proteins). RNA goes and gets the specific books that need thought in the schools and can even provide feedback on whether or not there needs to be more of them made. ",
"Hope this helps, good luck. "
] |
[
"Gotcha so it seems the theory is because the use of RNA evolved before DNA? and why reinvent the wheel (switch over to DNA) when you can just continue using what you already have?"
] |
[
"Why is forward, but not lateral, neck immobility a sign for meningitis?"
] |
[
false
] |
When considering meningitis, doctors check if a patient can tilt his head forward. Why is the forward movement (chin to chest) an indicator for meningitis but other neck stiffness (inability to turn or tilt head to the sides) is not? Disclaimer: of course the question arose from personal interest, but I have already been diagnosed by a professional as not having meningitis, so I'm not asking for medical advice. Just wondering what the physiology is.
|
[
"Meningitis is an irritation of the coverings of the brain, called the meninges. Forward neck movement will cause the meninges to stretch and because they're irritated, it will cause pain. Lateral head movement doesn't cause a significant stretch on the meninges and won't cause the same neck pain. ",
"Think of it like this. The brain and spinal cord all share one continuous covering. When you lean forward you're effectively making that covering longer, which will stretch it. When it's irritated, that stretch causes pain.",
"Hope that answers your question!"
] |
[
"Meningitis is an inflammation of the meninges, the membranes covering the brain. Any pressure or force applied to the meninges will hurt so the dorsal neck musculi get rigid to counteract any lenghtening movement of the membranes.",
"This is not limited to neck, for example there is the Laseque test in which one passively flexes the patients legs while he's laying on their back. This also extenses the membranes and thus is considerably restricted."
] |
[
"I think you meant Kernig's sign. The Lasegue test, aka Straight Leg Raise, is diagnostic of spinal stenosis. "
] |
[
"During early ambiogenesis is there really a need for stable lipid bilayer enclosures or can they extremely dynamic?"
] |
[
false
] |
My basic conception of early ambiogenesis is that early nucleotides were free floating in the "soup" and dynamic lipid bilayers would be rapidly forming and falling apart spontaneously. So the early life would basicly be more akin to a viral soup then a cellular soup with the nucleotides only transiently existing within lipid sacks. Then cellularization would have only occured many many (who knows how long ? millions ? billions?) years later only after the nucleotides were already highly advanced, possibly even already having some form of protein machinery.... The reason I want your take on this is because if seems like many people seem to think early life needed more stable lipid sacks that would spontaneously gloop apart in a sort of cellular replication system, which in my head isn't really necessarily. Anyways what are your thoughts?
|
[
"I am not a biologist, but here are my thoughts. Hopefully someone more knowledgeable on the topic will come along. ",
"There would need to be some sort of a boundary. It wouldn't necessarily have to be made of lipids perhaps it could be as simple as small pockets in a rock (really getting outside my area of expertise trying to come up with specific ideas). I can tell you that life requires a decrease in entropy (Wikipedia if you aren't familiar) because it leads to complex, ordered, improbable arrangements of atoms. This is only possible if it is coupled to a increase in entropy elsewhere achievable by the giving off of heat for example. It needs to take in materials it can consume to produce that heat and to eject waste. If there wasn't anything to contain the early nucleotides you described separate from the environment while still allowing the exchange of heat and nutrients, I don't think that indefinite growth of the level of complexity of the cellular machinery would be possible."
] |
[
"I am not entirely sure how to interpret your question. Ill give it a few stabs and hopefully something will hit the target. If not, feel free to keep asking or maybe somebody has a more helpful answer. Number 1 may be a bit hard to understand -- it certainly is hard to explain, but if you ever take a high level thermodynamics course, you will realize it is really cool :D",
"1) Entropy is more general than you present it. It is quiet simply a measure of the probability of the given state to all the other ones it could be in. Why to gas molecules not settle at the bottom of a container due to intermolecular attractions? Because of all the ways for them to fill the container, all sitting together at the bottom is a lot less probable than all the ways they could fill the container approximately uniformly. So entropy is in everything about science. In fact, materials don't like to lower their free energy just because, they do it because giving off heat lets materials access more configurations (increase their entropy) -- ultimately, every process in the universe is simply the kinetically favored pursuit of greater entropy.",
"2) Biological molecules even as simple as RNA are not probable arrangements of atoms. They are large molecules with lots of constituents and chiral centers all arranged just so to encode information, catalyze reactions, etc. Especially high concentrations of them would imply a system of very low entropy. This means that a lot of entropy needs to have been made somewhere else as a direct consequence of their formation. So to get life you need a high energy source which will degrade to a low energy source. There must also exist a kinetically favored pathway which produces the highly ordered cell machinery as a byproduct. ",
"3) Putting it all together, a lot of high energy fuel source would have to have been consumed and separated from the waste fuel. This leads to a need for a membrane.",
"Perhaps the simplest way to look at it is this. Life is a region of decreasing entropy; all physical process must create entropy --> life must have a barrier to separate the smaller decreasing region from the larger increasing region."
] |
[
"Abiogenesis?",
"Firstly, there are fossils of cellular structures from 3.5 billion years ago, so millions of years.",
"Secondly, are you asking what the overall order of molecules evolution is? *NA, proteins, lipids? One point that is missing concerns the nature of the cell boundary : it is possible that it was inorganic, not lipid.",
"In any case, one reason a boundary is necessary is that it separates metabolism from the inputs and outputs. Another is that it allows protocells to set up proton gradients to drive formation of energetic molecules (ATP, creatine phosphate, etc) as happens in mitochondria and chloroplasts today.",
"The main problem with an early formation of lipid boundaries is making the lipids themselves. I'm not sure what mechanisms have been proposed for chemical formation of these molecules."
] |
[
"VSEPR theory: T-shaped?"
] |
[
false
] |
[deleted]
|
[
"The repulsion between a lone pair and a bond pair is stronger than between two bond pairs. With trigonal planar each lone pair is at 90 degrees to three bond pairs. With a T-shape, each lone pair is at 90 degrees to two bond pairs, but is at 120 degrees to the remaining one. The average distance between bond pairs and lone pairs is therefore greater in a T-shape than in the trigonal planar arrangement."
] |
[
"Also, if you accept that d-orbitals are too high in energy to participate in bonding for main group elements, you cannot fit four unshared electrons in one p-orbital (that would be left over if the three sp",
" orbitals were occupied), so the unshared electrons must occupy sp",
" hybridized orbitals. "
] |
[
"With a T-shape, the lone pairs are 120 degrees away from one bond and 90 degrees away from the other bond. With a trigonal planar shape, the lone pairs are 90 degrees away from every bond. This ends up being more significant to the shape than having the lone pairs 120 instead of 180 degrees away."
] |
[
"What does Accutane do to get rid of your acne?"
] |
[
false
] | null |
[
"The simplest explanation I can provide (since I'm on my phone), is that it basically stops the production of the oils in your pores that causes breakouts. Everyone's pores produce oils, its when they are over-produced that pores become clogged and inflamed. Due to the way it works, you will have very dry skin (buy an oil free moisturizer) and most likely, chapped lips. This is very normal. It's when you experience any regular stomach pains that you should be alarmed.",
"Contrary to popular belief, acne is solely biological (assuming you regularly wash your face). It's all about hormones, which can change frequently.",
"I was on Accutane about 4 years ago, it worked very well, although its not a one time fix for everyone. I'm currently back on it, as of two days ago. The oily skin can come back years after completion, and it does for about 30% of people, but its severity will be diminished."
] |
[
"It works by reducing the sebum(oil) production by your skin, which otherwise fills the pores, becoming blackheads. If these become infected, they become spots. I don't know enough about dermatology past this. For your red skin though, get a chap stick and a moisturiser and use it daily or more regardless of how dry your skin feels at that moment. Also get into a good habit of washing your face when you shower. I just use whatever shower gel I have at the time rather than any expensive, face specific stuff. "
] |
[
"Accutane = Isotretinion",
"I would recommend reading the wiki article, ",
"http://en.wikipedia.org/wiki/Isotretinoin#Mechanism_of_action",
"It is informative and all that good stuff. I too used Accutane, did the job and some other stuff. Be careful with it and if you get depressed during the treatment, tell your doctor."
] |
[
"Why do mice experience senescence at such a greater rate than humans that their lifespan is almost around 1/40 of ours?"
] |
[
false
] |
It's not as if they have 40 times the metabolism, or that their cells divide 40 times faster than ours. Do they really accumulate free radicals, plaque, and genetic mutations at 40 times the rate we do? (thanks to Avedomni for rephrasing the question)
|
[
"Because of natural selection. ",
"It sounds like you are familiar with the idea that aging is the result of a cumulative physiological process, but that is not necessarily true. The current thinking is that aging is imposed by evolutionary pressures.",
"Here's a good ",
"talk",
" that gives a brief overview of the theory, by Michael Rose. ",
"Here's an article in the NY Times about him",
". He has not only a mathematical theory of aging, but he has also used it to breed flies that live 4-5 times longer than wild type flies.",
"According to him, humans age until about 90 years old, but after that point they cease to age. They just live on as the equivalent of 90 years olds. ",
"\"The common assumption is that young bodies work and then they fall apart during aging. Young bodies only work because natural selection makes them healthy enough to survive and breed. As adults get older, natural selection stops caring about them, so we lose its benefits and our health. If you don't understand this, aging research is an unending riddle that goes around in circles.\" --Michael Rose"
] |
[
"There's probably a lot of truth to that, but here's a paper dealing about the contrasting view--that metabolic activity has something to do with it. Just for balance. I'm not sure I agree with Rose on everything, but the flies are certainly cool.",
"edit: forgot the link like a fool\n",
"http://jeb.biologists.org/content/208/9/1717.full"
] |
[
"Mice do not appear to accumulate mutations at 40 times the rate as humans, nor do they accumulate that many more free radicals. ",
"Beyond that, I think ron_leflore is on to something. If you think about mice in the wild, it's unlikely they'd live that long, so the fact that they can even live 2 years in a laboratory or pet setting seems impressive. "
] |
[
"Do the spinning wheels on a vehicle create centrifugal force?"
] |
[
false
] |
I know that all rotating circular objects create some kind of centrifugal force but do the spinning tires on a car play any part in creating the grip to keep it grounded? Does the force generated vary at different velocities? Do engineers know when and how to utilize these forces in designing vehicles and tires?
|
[
"do the spinning tires on a car play any part in creating the grip to keep it grounded?",
"It's the friction between the rubber and the road that creates grip. The friction is due to the weight of the car. The centrifugal force doesn't add any extra grip.",
"Does the force generated vary at different velocities?",
"Yes. The faster something is spinning, the more force it takes to keep it from flying apart. In fact, the force goes up with the square of the velocity.",
"The sidewall of the tire is what pulls on the tire against the centrifugal force to keep the tire together. This is why damage to a sidewall almost always requires replacing the tire, and why tires have ",
"speed ratings",
". As the tire spins faster, it gets deformed more (since the sidewalls only pull at the sides, not the center) by the centrifugal force and the contact patch shrinks. Eventually it won't be able to keep grip, and might even come apart if the sidewall can't support the load.",
"Do engineers know when and how to utilize these forces in designing vehicles and tires?",
"Yes. For example, tire designers try to minimize the deformation at speed to keep the contact patch from shrinking. ",
"This page",
" has a discussion of one of the ways this is done.",
"Also, in some race cars where aerodynamics are important, like Formula 1, the car's suspension is tuned so that it's at the proper height when the tires are slightly larger from the centrifugal force pulling on them at speed. But for your everyday vehicle, it's such a minor effect that it's ignored."
] |
[
"Thanks. Got the answers I wanted :)"
] |
[
"Not that simple, there is such a thing as centrifugal force.",
"If a rotating object is being pulled towards the axis of rotation by centripetal force, why does it not accelerate towards the axis? There must be a component of force opposite to centripetal force pulling directly away from the axis of rotation... that is centrifugal force."
] |
[
"Why are our veins asymmetrical?"
] |
[
false
] |
I would think that since most things in our bodies are symmetrical, that our venous channels would be as well. I was looking at my arms today and found it strange that my veins are quite different in each forearm. Does this have something to do with development, or are veins just formed randomly? Do our veins change location throughout our lives (like rivers) depending on where they are needed?
|
[
"Veins aren't exactly formed randomly, but there are random elements in how they are formed. Identical twins will have different vasculature, for example.",
"This is because the body doesn't have a blueprint in the traditional sense, it is procedurally generated. Limb buds set up gradients of hormones that tell bones where to stop and start.",
"Many blood vessels are set in stone, like the aorta and vena cava, but farther out the vessels are procedurally generated, so left and right end up similar but different.",
"Veins do not move based on need."
] |
[
"I've never heard the term \"procedurally generated\" to describe human embryology and vascular formation. That's incredible. "
] |
[
"That's why the human genome is only three gigabits in size. You only need that and a bootstrap platform to build a human."
] |
[
"Can I say that future points downwards?"
] |
[
false
] |
Suppose a 2D flatlander orbiting the earth aligned in a plane perpendicular to its velocity. Can I say that his future points in the direction of his velocity? If thats's the case, then his velocity is already pointing somewhat towards his earth-facing direction (a direction he can point towards in his own sense if he knows where earth is). Will past also point downwards then? Edit: Edit 2 : When you're floating in space there's no way to tell which way the 4-velocity points (it point in future but you can't put your finger on it). But when under gravity, your future bends towards the mass causing that bend (is this correct?). So if I know where that mass is, I know what direction the space component of my 4-velocity vector points, right?
|
[
"But the flatlander doesn't have a downward to point in, in the sense you're using down. Just the same way, if we assume your analogy is sensible, then we'd not be able to point in the direction of our past. But the analogy itself doesn't make a whole lot of sense since you're just pointing in the direction the flatlanders were in the past. So saying that their past is down, is like saying your past is whichever direction you were in a few minutes ago (assuming you've moved). "
] |
[
"Uh.",
"I don't exactly understand what you said, but the future usually points futurewards. It can't point downwards, just like \"right\" can't point downwards.",
"And I don't think time can be \"aligned\" with spatial dimensions.",
"/layman"
] |
[
"...what? I don't follow your line of thought."
] |
[
"How does the human body digest water?"
] |
[
false
] |
I vaguely remember learning that the colon plays a key role in absorbing water, but I feel like I am misremembering something. Surely water doesn't travel through the entire body before being absorbed...? Also, are any chemicals involved in the digestion of water, such as stomach acid? Thanks in advance.
|
[
"When you talk of the digestion of water are you referring to how it enters the body? e.g. through the intestines.",
"I don't know of any mixing of chemicals with water. What I do know is that the water is absorbed through the intestinal walls using osmotic pressure gradients. ",
"It is A LOT more complicated than this explanation, however, effectively the cells in the intestine contain sodium ions (other solutes as well but lets focus on sodium). Water moves across cell membranes due to an osmotic pressure - moving from an area of low solute to an area of high solute (from intestinal path into the cells surrounding the intestinal path). This osmotic pressure is created by sodium pumps in the cell membranes that can provide a certain concentration of sodium ions in the cell. ",
"So basically the water is absorbed straight through the cell wall of the intestine into your body.",
"Someone can provide more indepth answers and can correct any wrong explanations. Again, this was A-level biology so I wouldn't be suprised if it was wrong."
] |
[
"Correct me if I'm wrong, but i think water is absorbed via diffusion not osmosis. It doesn't actually pass through the semi-permeable membrane of the cells, rather it is absorbed paracellularly passing between the intestinal cells. The concentration gradient you described is certainly the mechanism by which this gradient is established - using sodium pumps. I would add that a special sodium-glucose co-transporter is important in absorbing sodium to establish the gradient (this is one of the major reasons for sports drinks having glucose (the glucose for energy line is really only applicable to prolonged endurance events once glycogen stores are running low, however 'glucose for energy' is a sexier sell than 'glucose to help you absorb the water'). But i digress."
] |
[
"Although that's an impressive figure, roughly 7-8L of fluid will be absorbed in the small intestine before it gets to the ileocaecal valve. so in fact the colon only contributes ~15-20% of the daily GIT absorption of fluid"
] |
[
"Since both a WiFi signal and light are electromagnetic radiation, can I simulate the range of my WiFi Access Point by replacing it with a bright light in a pitch-dark night?"
] |
[
false
] |
I would probably need to leave all doors open since the WiFi signal has no trouble to shine through them, but it seems that concrete and brick walls are opaque for both WiFi and light.
|
[
"No. All materials have different absorption and scattering properties of electromagnetic radiation, and these properties are different for different wavelengths of light. Visible light and radio waves will not have the same behavior, especially since houses are such irregular objects made of so many different materials. Furthermore, you wouldn't simulate the correct power or signal-carrying properties of the light either."
] |
[
"I can highly recommend this set of blog-posts on the matter. Basically, the first post uses an approximation and simulates WiFi-signal using ray-tracing, while the second solves the more rigorous Helmholtz equations and the third gives you an app to do the same thing for you (which I haven't tried and therefore cannot comment on).",
"Highly readable, informative and enjoyable blog as well! Enjoy :-)",
"http://jasmcole.com/2014/07/12/wifi-strife/",
"http://jasmcole.com/2014/08/25/helmhurts/",
"http://jasmcole.com/2014/09/01/helmhurts-android-app/"
] |
[
"Ray tracing is only an approximation, and it doesn't handle things like wave interference or diffusion. That's OK for the things that ray tracing is used for, like images with reflective surfaces, but it's going to be a pretty bad approximation when you try to use it to model something like wifi in a house.",
"(Specifically, ray tracing relies on a \"ray theory\" model, while wifi or radio or similar EM models would require a \"wave theory\" model -- entirely different sets of equations.)",
"Think of it this way: if you wanted to make a simple model of a body of water, you might just create a perfectly opaque surface using some fractal equations and you'd get something that probably looked pretty good. But, if you wanted to figure out at what depth you might be able to see a shipwreck from a particular height given particular properties of the water, atmosphere, time of day, and so on, you'd have to use an entirely different set of mathematics.",
"Modeling wifi strength is like that. It depends ",
" on the properties of other surfaces to be modeled with any kind of accuracy with ray tracing.",
"If you're just standing in a room and you want to get a rough idea of how strong a signal might be from a particular location, sure, you can sort of visualize it as a light shining in another room. Glass would be mostly (but not completely) transparent, thin walls would be a little less transparent, dense wood would be dark, a fish tank would be opaque, metal would be opaque and reflective, a person walking through the room would look like a shadow with shiny metal bits, that sort of thing. It's good enough for guesswork if you're a field technician.",
"But once you get to an engineering level, there are too many inaccuracies in that guesswork. For example, wifi (and other radio signals) can do funky things you wouldn't expect, like develop a standing wave somewhere -- one or more \"bright spots\" hovering in the middle of the room. (A physicist should chime in here, but I think that would also be possible with visible light -- it would just require circumstances that we don't really encounter in daily life.)"
] |
[
"Do any plant cells undergo apoptosis in a similar fashion to animal cells?"
] |
[
false
] | null |
[
"To add about the damage to DNA and tumors: many plants are polypoloids, meaning they have multiple copies of their chromosomes creating redundancy if one set fails. With this 'backup' the need to kill off a cell is greatly reduced."
] |
[
"To add about the damage to DNA and tumors: many plants are polypoloids, meaning they have multiple copies of their chromosomes creating redundancy if one set fails. With this 'backup' the need to kill off a cell is greatly reduced."
] |
[
"also also, plants are generally way simpler than animals and can usually function pretty well even if they develop tumors - trees with massive growths can still function normally (and will produce beautiful burled wood when they're felled). since they don't really have a recirculating blood/circulatory system it's also not so easy for cancers to spread."
] |
[
"With satellite imagery, have we discovered every mass of land on the face of the earth?"
] |
[
false
] |
Or are there still islands out there in the sea we have not discovered?
|
[
"Islands are still ",
"being discovered",
" and will constantly be discovered (and lost) due to natural forces like erosion, ocean level changes, volcanic eruptions etc. "
] |
[
"There's a good Magic School Bus episode regarding volcanic island formation.",
"https://www.youtube.com/watch?v=D-JnSEPTlvc"
] |
[
"And some of the islands we thought existed never did ",
"http://www.huffingtonpost.com/2012/11/24/sandy-island-doesnt-exist_n_2184535.html"
] |
[
"How did the Ash tree develop a seed pod that could flutter down to the forest floor? How did it know what the best wing design was?"
] |
[
false
] |
[deleted]
|
[
"It didn’t know.",
"Survival of the adaptor. Random genetic changes and also response to environmental factors over eons caused the changes. Each incremental change enhanced that genetic line’s survival and gene proliferation."
] |
[
"It doesn't know. Seeds naturally vary, however slightly, in size, shape, mass and so on. This is partly due to their genes which, thanks to sex, they all have different sets of. Some varieties are, for whatever reason, a little more likely to germinate and survive to create seeds of their own. Their seeds will have sets of genes based on their own. And that's it. ",
"I guess there was some advantage to having seeds flutter: they'd land farther away and have better access to sunlight maybe. Some species of palm have nuts which fall in the sea and travel the ocean before germinating on a distant beach..."
] |
[
" stated, there is no \"why\" to evolution. In fact, some evolutionary traits aren't 100% positive, and are inefficient, like RUBISCO's oxygenase activity. Complete evolutionary flaw."
] |
[
"What happens if an anti-proton collides with, say, a normal neutron?"
] |
[
false
] |
[deleted]
|
[
"If they react, at low energy, the most probable result is hadronization into pions. For example, π",
" π",
" is a reasonable product. ",
"This happens, intuitively, if the two pair of corresponding quark antiquark annihilate leaving the resulting energy to the remaining antiup-down pair, which is a π",
" meson. It's however unlikely for only this meson to remain, for both a probabilistic and kinematic reason. It's more probable for only one pair to annihilate, which leaves both the π",
" and either up-antiup or down-antidown, a combination of whose is the π",
". You could also have photons in the final products or hadronization into more light mesons, depending on the energy. ",
"However, in the literature I only see bar p + n -> multiple π, so I think that should be the most probable outcome."
] |
[
"Most likely they will scatter electromagnetically (Rutherford scattering) being like-charged."
] |
[
"Most likely they will scatter electromagnetically (Rutherford scattering) being like-charged."
] |
[
"Do point-like particles have hawking radiation at their Schwarzchild radii?"
] |
[
false
] |
I know we've done some expiriments hinting towards stable or at least meta stable protons but is it possible? Intuitive logic tells me all the fermions would evaporate rapidly and none of us would be here but I'd love some other perspective.
|
[
"This is an area where the lack of a theory of quantum gravity is important. In theory an electron is a point-like particle, so it should have a Schwarzchild radius that is perhaps larger than it's physical radius (which is effectively 0). In reality though quantum effects dominate at such small scales and the result is that you don't end up with a black hole. The problem is that we don't have suitable theories to describe that behavior."
] |
[
"In reality though quantum effects dominate at such small scales and the result is that you don't end up with a black hole.",
"Well, to be a bit more precise, I would say that the result is that you don't end up with a ",
" black hole. It is possible that all \"fundamental\" particles are extremal black holes, but that they do not hawking radiate (ie decay) due to planck scale physics. This is essentially the picture that emerges within string theory due to the excited-string-black-hole correspondence."
] |
[
"In theory an electron is a point-like particle, so it should have a Schwarzchild radius that is perhaps larger than it's physical radius (which is effectively 0).",
"The schwarzchild radius for an electron mass is like 10",
" m, way way less than a planck length (even though the schwarzchild metric doesn't work for a spinning object anyway etc etc). So we really can't say anything about it at all until we get quantum gravity right."
] |
[
"what causes stiffness rather than soreness after physical exertion?"
] |
[
false
] | null |
[
"Drink more water."
] |
[
"i down bottles of water the whole day. but i didn't ask to stop it, I want to know the science."
] |
[
"Ah gotcha. My mistake."
] |
[
"How does Ampicillin act as a substitute for Penicillin?"
] |
[
false
] |
What are some reasons that say Ampicillin would be much more effective than Amoxicillin? Could this effect be even more pronounced when used in conjunction with Penicillin? Can drugs be exponentially effective?
|
[
"Both act via inhibition of transpeptidase, which is needed for bacterial cell walls. However, ampicillin's structure makes it more effective against Gram-negative bacteria than penicillin (Gram-negative bacteria tend to be more virulent). Due to this, they would be about equally effective against Gram-positive organisms, with ampicillin being better as a broad spectrum antibiotic."
] |
[
"Ampicillin and amoxicillin both go after the same enzyme that builds the bacterial cell wall. Both these drugs are members of the penicillin class of antibiotics, and as such there would be little benefit in combining them UNLESS there is resistance to one and not the other. Bacterial resistance is accomplished in MANY ways but the easiest thing for the bacteria to do is slightly change the structure of the enzyme such that the drug no longer inhibits its activity. ",
"While the drugs you mentioned would typically not be exponentially effective, many antibiotic combinations actually are complementary in their activity. For example, another way that bacteria derive resistance is by evolving penicillin binding proteins; compounds which bind penicillin and prevent it from inhibiting transpeptidase. By adding an antibiotic which inhibits bacterial protein translation, the creation of these proteins is halted/significantly diminished, and now penicillin works again. ",
"As another example, some bacteria actively pump antibiotic out of the cell. Adding an antibiotic like Daptomycin which disrupts the bacterial membrane into which these transporters are inserted will allow antibiotics to enter the cell more easily, and will also disrupt the electrochemical gradient that such transporters often use for energy. ",
"Combination therapy is used for several reasons. One, to increase efficacy. Two, to overcome resistance and to prevent new resistance from evolving. Three, to lessen the dose-dependent side effects elicited by one or more of the drugs. Multiple drug classes usually means you can use a lower dose of each drug."
] |
[
"UNLESS there is resistance to one and not the other",
"Ampicillin and amoxycillin are essentially interchangeable, resistance to one usually assumes resistance to the other"
] |
[
"Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"Theoretically, just barely crossing the equator is enough to change the direction of the Coriolis Effect, with the Coriolis Force equal to exactly zero at the equator.",
"Realistically, though, the Coriolis Force is so minimal when you're incredibly close to the equator that it's essentially impossible to detect it or see its influence. ",
"No hurricane has ever formed",
" within 5 degrees latitude of the equator or observed crossing it, so there's clearly some minimum amount of Coriolis Effect needed to support cyclogenesis and maintain a vortex.",
"I've seen videos of conmen in equatorial countries demonstrating to wide-eyed tourists how a basin of water will drain one way a few steps to one side of the equator, they then walk several steps across the equator to demonstrate it draining the other way. If you watch closely, though, this trickery is revealed in the direction they turn just prior to draining the basin - the inertia of that initial spin is far, far more important than the infinitesimal change of the Coriolis Force a few feet on either side of the equator."
] |
[
"Helium was also first discovered as an unknown spectroscopic line in the Sun's coronal spectrum during the eclipse of 1868, initially misidentified as sodium. By 1871, this unknown element was dubbed helium because of the Greek word for the Sun, \"helios\". It wasn't isolated in the lab until 1895."
] |
[
"The Coriolis Effect: Is there a fine line where in one location a vortex is spinning clockwise and if you move a certain amount of distance (either north or south) your outcome can change to counter-clockwise (or vice-versa)? In other words, what is the shortest distance between the northern and southern hemisphere where The Coriolis Effect gives the two different rotational outcomes. "
] |
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