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[
"How does a cold make us produce more snot and or mucus?"
] |
[
false
] |
[deleted]
|
[
"The short answer is cytokines.",
"The longer answer is that the immune system releases IL-13 and IL-6. Macrophages that are in the infected area pump out a LOT of IL-6 (T cells make some as well) which causes goblet cells to increase mucus production.",
"Th2 cells will produce IL-13 which has the same effect. This cytokine is also associated with allergies. While IL-4 is the cytokine responsible for getting B cells to make IgE, IL-13 is responsible for every other physiological change that occurs during an allergy response, the chief being (along with the effects of histamine) the increased production of mucus."
] |
[
"It flushes viruses, bacteria, and allergens out of the body. Even before flushing them out, it keeps them away from tissue surfaces and makes attachment and entry harder. Some bacteria have mucinase that overcomes this. "
] |
[
"Thanks!"
] |
[
"Did we always know that electricity was a physical phenomenon? If not, when did we find out?"
] |
[
false
] | null |
[
"I would like to encourage more history of science questions here. However, if you don't get an answer, try ",
"/r/askhistorians",
" or ",
"/r/historyofscience"
] |
[
"As I understand it, ancient cultures such as the Greeks knew that static electricity was a thing, mainly due to the shocks produced when rubbing amber and fur together, but it wasn't until the 1600s when we really started to begin differentiating and classifying different electrical phenomena and began understanding that they were related. And it would be another 200 years before the brightest among us would have a keen enough understanding to use electrical phenomena in a practical way (ala Faraday's electric motor)."
] |
[
"Thanks, I'll wait and repost in the morning on one or both of those subs."
] |
[
"(Repost) from r/pics. Bone cancer"
] |
[
false
] |
Why does the body do this to itself? What causes it?
|
[
"It's likely this is osteosarcoma, the most common primary malignant bone forming tumor. Although usually found in metaphyseal region of long bone it can occasionally occur here in the skull. Bone is laid down haphazardly in the periosteum, the outer layer of bone. This periosteal reaction in osteosarcoma is characterized by a 'sunburst' pattern because bone is laid down steadily but too rapidly. These connective tissue fibers that connect the periosteum to the bone are called ",
"Sharpey's fibers",
", and they eventually ossify - giving the 'hair on end', sunburst pattern you see here in the photo!",
"As for why the body does this to itself - in this case, it is due to mutations in tumor suppressor genes. Osteosarcoma is known for inactivating mutations of the retinoblastoma and p53 genes. These are genes that regulate the cell cycle (G1 to S phase) and if disrupted, the mutated cells proliferate/replicate too much and cause the bone cancer. This is a very brief summary of what happens but I hope it helps."
] |
[
"Is this as painful as I imagine it to be?"
] |
[
"Yes. Pain is also one of the most common symptoms of osteosarcomas."
] |
[
"Is Chess really that infinite?"
] |
[
false
] |
There are a number of quotes flying around the internet (and indeed recently on my favorite show "Person of interest") indicating that the number of potential games of chess is virtually infinite. My Question is simply: How many possible games of chess are there? And, what does that number mean? (i.e. grains of sand on the beach, or stars in our galaxy) Bonus question: As there are many legal moves in a game of chess but often only a small set that are logical, is there a way to determine how many of these games are probable?
|
[
"On mobile - it shows up as 1043. It's actually 10 raised to the 43rd. ",
":) just to clear up any confusion. "
] |
[
"Shannon has estimated the number of possible legal ",
" to be about 10",
". The number of legal ",
" is quite a bit higher, estimated by Littlewood and Hardy to be around 10",
" (commonly cited as 10",
" perhaps due to a misprint). This number is so large that it can't really be compared with anything that is not combinatorial in nature. It is far larger than the number of subatomic particles in the observable universe, let alone stars in the Milky Way galaxy.",
"As for your bonus question, a typical chess game today lasts about 40 to 60 moves (let's say 50). Let us say that there are 4 reasonable candidate moves in any given position. I suspect this is probably an underestimate if anything, but let's roll with it. That gives us about 4",
" ≈ 10",
" games that might reasonably be played by good human players. If there are 6 candidate moves, we get around 10",
", which is in the neighbourhood of the number of particles in the observable universe.",
"The largest commercial chess databases contain a handful of millions of games.",
" A lot of people have told me that a game could potentially last infinitely, or at least arbitrarily long by repeating moves. Others have correctly noted that players may claim a draw if (a) the position is repeated three times, or (b) 50 moves are made without a capture or a pawn move. Others still have correctly noted that this is irrelevant because the rule only gives the players the ",
", not the ",
" to make a draw. ",
", I have seen nobody note that the official FIDE rules of chess state that a game is drawn, period, regardless of the wishes of the players, if (a) the position is repeated ",
" times, or if (b) ",
" moves have been made without a capture or a pawn move. This effectively renders the game finite.",
"Please observe ",
"article 9.6",
"."
] |
[
"Bobby Fischer often said he was bored of normal chess because the game positions and strategies could be too easily memorized so that play on even the highest level was more about remembering the positions from prior experience and proceeding rather than having to rely on pure analytic thought and deriving the best move.\nIn fact, he felt so strongly that high level chess was just memorization for the best players and not true inherent skill that he favored a variation of chess that had the back row of pieces positioned in random order for each game so there could be no use of prior memory for the tactics that would evolve in that particular game.",
"I think it is interesting to point this out because the permutations of practical/logical games of chess, especially as the play level becomes higher, is much more narrow than this number. An easy example is the first 10-15 moves of chess rarely deviate from a collection of openings in high level play because the resulting game would confer a clear disadvantage and therefore, somewhat like evolution, have been naturally selected out of the potential game pool.\nSo its ironic, that as you get better at chess, it becomes easier to memorize the game and there are less unconventional positions you have to routinely consider as represented by this higher than astronomical number.",
"EDIT: I found more on ",
"Wikipedia",
" , including a quote from Bobby Fischer:",
"Fischer heavily disparaged chess as it was currently being played (at the highest levels). As a result, on June 19, 1996, in Buenos Aires, Argentina, Fischer announced and advocated a variant of chess called Fischerandom Chess (later known as Chess960). The goal of Fischerandom Chess was to ensure that a game between two players is a contest between their understandings of chess, rather than their abilities to memorize opening lines or prepare opening strategies.\nIn a 2006 Icelandic Radio interview, Fischer explained his reasons for advocating Fischerandom Chess:",
"\"In chess so much depends on opening theory, so the champions before the last century did not know as much as I do and other players do about opening theory. So if you just brought them back from the dead they wouldn’t do well. They’d get bad openings. You cannot compare the playing strength, you can only talk about natural ability. Memorisation is enormously powerful. Some kid of fourteen today, or even younger, could get an opening advantage against Capablanca, and especially against the players of the previous century, like Morphy and Steinitz. Maybe they would still be able to outplay the young kid of today. Or maybe not, because nowadays when you get the opening advantage not only do you get the opening advantage, you know how to play, they have so many examples of what to do from this position... and that is why I don’t like chess any more... It is all just memorization and prearrangement...\""
] |
[
"The Paradigm Shift!"
] |
[
false
] |
Paradigm shifts occur when substantiating, and validated, evidence has been accumulated to a degree that overcomes skepticism. New theories are normally considered fringe science until they reach this point, and are discouraged by journal editors and those who control scientific funding. My thoughts are that paradigm shifts are good for science, and help us get closer to fully understanding our universe. Wouldn't fringe science theories to find falsification or validation hasten our advancement? Why isn't this practical?
|
[
"Because fringe theories fail the first requirement, which is: reproducing the known experimental results. That's why they're fringe. "
] |
[
"Why isn't this practical?",
"Because in the ",
" majority of cases, 'fringe' science is a waste of time and money because it's wrong. ",
"Big, game-changing discoveries are exciting, but the number of these occurances in recent scientific history can probably be counted without taking your shoes off."
] |
[
"So we are too close to understanding ",
" for fringe science investment to be viable because the likelihood of a fringe theory finding validation is too low?"
] |
[
"I drop an object from a tower at the equator. In the direction oft earth's rotation, does the object land in front of, exactly at, or behindert the foot of the tower?"
] |
[
false
] | null |
[
"Due to the Coriolis force, the object is deflected slightly in the Westward direction."
] |
[
"westward? Are you sure? Earth moves west to east, shouldn't it be eastward?"
] |
[
"The equation for the Coriolis force is given ",
"here",
". If you evaluate the cross product of the Earth angular velocity and the velocity of a downward-moving object at the equator, you get a vector that points West."
] |
[
"What properties of a hexagon make it such a 'natural' shape?"
] |
[
false
] |
The hexagon is a pretty common shape in nature, with slime moulds, bee hives, crystal close packed structures, etc. almost as common as the natural logarithm. Why?
|
[
"Imagine dots aligned that way:",
". . . .\n\n . . . .\n\n. . . .\n",
"Now imagine a circle growing out of each of these dots at the exact same speed (or almost). Imagine that when they touch another circle they stop growing in that direction. So the shape keeps growing but keeps hitting other circles. Do you see the hexagonal forming?"
] |
[
"If you want to build a container with a special volume, an sphere has the lowest surface/Volume ratio and would be the best choice. Eggs for example are near orb shaped.\nBut if you need many containers, you could use the already existing walls of the first container to add the 2nd container directly to the first one. The 3rd to the 2nd one, and so on. ",
"If you have a regular Form that fits on an area without gaps, that would be nice. Possible are triangular, tetragonal, and hexagonal prisms, of which the hexagonal prism has the highest possible number of neighbours to share a side with. It simply is the cheapest (least material used) way to make a lot of containers with a certain volume, attaching each other. The construction plan is very simple, and it is stable too. What else do you want? The bee does not need to understand this. Evolution just prefered bees (or wasp like ancestors of bees) that built their honeycomb this way. "
] |
[
"If you want to pack the greatest number of circles in a 2D plane, you must use a hexagonal lattice (this is a mathematical fact). ",
"Just like circles are so common because they are the shape that minimizes circumference and maximizes area, hexagons are common because they create a pattern that maximizes the number of circles packed in the smallest area.",
"This picture",
" illustrates how packing circles lead to hexagonal lattices in nature."
] |
[
"How can a photon be \"massless\"?"
] |
[
false
] |
I've taken physical chemistry (quantum mechanics) and something I never got was how light was considered just a "wave". I understand in quantum mechanics that this is false since light exhibits particle and wavelike properties, but how can a photon/light be massless? Wouldn't it not be a particle then or even exist since it has no mass? What am I missing here?
|
[
"Wouldn't it not be a particle then or even exist since it has no mass?",
"No, there is no need for a particle to have mass. Humans are used to imagining mass as being made of \"stuff\", i.e. some kind of substance that exists and takes up space, and indeed this is a very useful picture in the real world. However, as far as particle physics is concerned, mass is just a parameter that determines part of the behaviour of particle, and there is no reason a particle can't be massless.",
"The reason that we have this idea that mass is \"made of stuff\" probably comes from the fact that for most human purposes mass is conserved, where here I mean \"rest mass\". So, if you have a system made of a bunch of pieces, the mass of the system is the sum of the masses of the individual parts. However, as we move away from the classical world into special relativity, we find that this conservation of rest mass breaks down. Total mass is still always conserved, but the mass of a system of particles can be different from the sum of the masses of the individual parts, as some of the mass can be due to the relative motion of particles and/or their interactions."
] |
[
"So my issue here is I'm looking at quantum mechanics from a classical mechanics point of view, which is counterintuitive, since it's quantum. In that case would you happen to know why particles produce wavelike behaviors? Thanks by the way. "
] |
[
"Can you elaborate a bit on what you mean by \"why particles produce wavelike behaviors\"? The fact simply is that at the level of quantum mechanics there is no such thing as solid point particles or classical waves as we understand them in the classical world. Instead, everything exhibits both particle-like and wave-like behaviour. Usually when we say \"particle\" in the context of classical mechanics we're always refering to these particle/wave hybrid things."
] |
[
"Is there a simple test to differentiate between copper and aluminum braided wire?"
] |
[
false
] |
[deleted]
|
[
"Copper looks copper-colored. Aluminum looks silver. There could be a coating on the wire, but if it's copper the core should look like copper. ",
"You could try dissolving some in sulfuric acid or nitric acid. If it turns blue, it's from copper salts. Aluminum salts are colorless, typically. "
] |
[
"Can be difficult to tell on small diameter wire. "
] |
[
"Melt a piece. Using a neutral flame copper will just melt while aluminum will slag. "
] |
[
"Are antibiotic resistant bacteria found in nature?"
] |
[
false
] |
So I was watching Grey's Anatomy tonight, and in the episode one of the doctors has an infection on her leg from being stranded in the wild for 4 days, and later the other doctors are talking about how the infection is resistant to Vancomycin. Obviously this television show isn't too realistic with the details, but as a Microbiology student it made me wonder if antibiotic resistant bacteria are found in nature? Or would the resistant infection have to come from a hospital setting?
|
[
"Remember where antibiotics come from... fungi produce them in nature to fend off bacteria. Antibiotic resistance didn't appear ",
" when we started using them to fight infections in humans - many of those resistance genes were already around in the bugs that compete with fungi in their natural environment.",
"That said, the fungus that vanco was isolated from was from Borneo - I doubt there's be much selective pressure to hang onto those resistance genes in the US..."
] |
[
"I'd add that it's the modern era, in which global travel is a reality. We take native samples from all over, geographically, so you can even find very specific types of resistance in environments where it might be a surprise otherwise (e.g., vancomycin resistance in a sample from a rural Sami encampment in northern Norway in the middle of winter). Humans have done a terrific job expanding the ranges of lots and lots of creatures."
] |
[
"Antibiotics are also often produced by bacteria themselves. For example, kanamycin is produced by ",
" and erythromycin from ",
". It is believed that antibiotic resistance developed ages ago simultaneously with the emergence of bacteria-secreted antibiotics as sort of an \"arms race\" for competing bacteria species for resources.",
"There is also emerging evidence that perhaps soil microbiota is transferring ancient antibiotic resistance gene cassettes to the strains found in hospitals, contrary to the common belief that antibiotic resistance is a result of widespread antibiotic use in the clinical setting.",
"Source:",
"http://www.ncbi.nlm.nih.gov/pubmed/22509370",
"http://www.ncbi.nlm.nih.gov/pubmed/22936781"
] |
[
"How many fundamental fields are there?"
] |
[
false
] | null |
[
"It's a little bit of a question as to how you count things, but here is a list of the fundamental fields:",
"Leptons:",
"electron, muon, tau",
"electron neutrino, muon neutrino, tau neutrino",
"Quarks:",
"up, charm, top quarks",
"down, strange, bottom quarks",
"Others:",
"Higgs",
"photon",
"W",
" Z",
" W",
" (here, I've spelled out the antiparticle of the W",
", while for the quarks and leptons, I've left that implicit)",
"gluons (8 kinds, but grouped into a single matrix)",
"These are the fields of the Standard Model. Something will be needed for quantum gravity, but what that is, isn't clear (might not even be a standard quantum field)."
] |
[
"To be precise, the basic field in general relativity is the metric (the object that determines how space is shaped at any point). If gravity were to be quantized like the other forces, it is quantizing the metric that would give rise to the graviton."
] |
[
"Is it the metric that's ",
" gravitational field in GR, or the Einstein tensor?"
] |
[
"Does light really make one lightyear per year, even though space is expanding?"
] |
[
false
] |
Let's say we had a star 1 mio lightyears away. While its light travels to us, the space itself in between is expanding, so the light has to travel a longer distance. Technically, the light therefore should take more than 1 mio years to reach us, even if the star was exactly 1 mio lightyears away originally. Am i correct or do i miss something?
|
[
"It's a very interesting question, and harder than you think. So I try explain, in local universe, low redshift, 1lyr is exactly the time the light make in one year. ",
"In cosmology we are some types of meansure distance, the comoving distance, that's depends on the grid of space time so the metric of space time, usually used FLRW, and how expansion affects that grid, an teansverse comoving, depended the same parameters of the last one and de curvature of space time, and luminosity distance, that's measure method use the light, obviously, ",
"And de relation of comoving(most used for cosmologist) and luminosity distance depends of Z ( the redshit) like dl=(1+z)dm where transversal comoving distance. ",
"And finally for light travel distance have some interal in redshift... ",
"In resume, in flar universe, only in the flat. Comoving and light travel distance are compatible. ",
"And all measure of distance disagree in high redshifts. ",
"You can see more searching for distance measures cosmology.( in Wikipedia probably have some interesting plots to visualize that). ",
"I hope helped. "
] |
[
"The distance traveled in the year by a photon remains constant while the matter taking up “space” is expanding.",
"It's not the matter that is expanding (that's not expanding), but spacetime (seen in the FLRW metric)."
] |
[
"The distance traveled in the year by a photon remains constant while the matter taking up “space” is expanding.",
"It's not the matter that is expanding (that's not expanding), but spacetime (seen in the FLRW metric)."
] |
[
"How come bodybuilders need to be infinitely precise with the types and amounts of food they eat, yet my horses just munch on some hay and are physical specimens?"
] |
[
false
] |
Have we just weeded out all the fat, slow, weak horses after thousands of years of domestication, or what causes this difference in how our bodies utilize resources?
|
[
"Well what about the fact that horse diets are so monotone? I've been around a lot of horses and never ran in to any that didn't mainly eat hay and then occasionally had a treat or some kind of oats. How does this one bland form of nutrients sustain their entire massive bodies while (as I understand it) it's very easy for humans to have deficiencies in our diets and suffer because of them."
] |
[
"There are many different ways to answer this. But ill give it my best shot. \nDepending on breed, level of exercise and work along with soundness of their legs and hooves there is a difference between a fat horse and a muscular horse. Yes there are still fat, slow and weak horses mostly caused by injury, issues at birth/development in the womb. Some horses are more high spirited than others which makes them burn fat more quickly like warmbloods and Arabians. Some slower breeds are appaloosas and draft horses. but with the right feed, amount of exercise any horse can become muscular and more spirited. "
] |
[
"....Well there are many different versions of feed for different horses. Some high spirited horses need feed with little sugar, no corn, molasses, or alfalfa meal which gives them what nutrients they need without the \"hyper-ness\" Its kind of like a sugar high, alot of racehorses are like this. Thoroughbreds, Warmbloods and Arabians are some examples.\n....Some horses are called \"hard keepers\" which means they could either have allergies, or have a hard time keeping weight on them. Most (but not all) hard keepers are senior horses, with being older most cannot digest hay or forages, nor can their bodies absorb what they need from regular feed so they get senior feed which has extra calories, fat and nutrients their bodies need to keep them healthy. (Most of them do not get the regular flakes of hay, but they get it in pellet form.) ",
"....Some horses are called \"easy keepers\" Which they can get just about anything and they will be same all the time and keep their weight/body in great condition.",
"....Some horses are \"grass fat\" horses, they maintain their bodies with mostly grass and get little to no daily grain. ",
"....Horses can have deficiencies in their diets just like humans can, And there are specialty brands of horse feed that help with all of them. All horses vary just like we do. :) ",
"You can go to the websites of some brand name horse feeds and they can probably explain in further detail too. "
] |
[
"If every multicellular life form suddenly disappeared, would singled celled life forms eventually re-evolve into multicellular ones again?"
] |
[
false
] | null |
[
"Probably yes. The removal of multicellular life would not be a \"reset to zero\" event. There is still complex single cellular life, some of which is actually very closely related to multicellular life. A really good example would be baker's yeast.",
"There's at least three origins of multicellularity across eukaryotes between animals, plants and fungi, so if any Eukaryote survived it's actually quite reasonable to assume it could happen again. Since there's plenty of single celled eukaryotes there's pretty good odds that multicellular life would reemerge from them.",
"The reset to zero event would be the loss of all eukaryotic life. Whether multicellular life could recover from that is far less likely."
] |
[
"Single cells appeared about a billion years after Earth's formation multicellulars took another 2-3 billion years. The mechanism is still unknown, so it's hard to speculate but since the Earth only has about 1 to 2 billion years left before it becomes uninhabitable the probability is low that multicellulars will evolve again.",
"It's weird to think about we're lucky that we evolved multicellular life within the last 20% of the Earth's life, time was running out."
] |
[
"Single cells appeared about a billion years after Earth's formation multicellulars took another 2-3 billion years.",
"since the Earth only has about 1 to 2 billion years left before it becomes uninhabitable the probability is low that multicellulars will evolve again.",
"It depends, there is a huge variety of single celled life forms on Earth today, occupying just about every niche. That's a big head start on when the first single celled life first appeared. ",
"I'd think that for at least some of the current single cell life the evolutionary jump to multi-cellularity is not ",
" great, eg: ",
"https://en.wikipedia.org/wiki/Caulerpa",
", ",
"https://en.wikipedia.org/wiki/Dictyostelium_discoideum",
".",
"So IMO: yes, multi-cellular life would evolve, on a time scale far below a billion years.",
"Edit: Also apparently multicellular life evolved independently at least 25 times, source: ",
"https://en.wikipedia.org/wiki/Multicellular_organism"
] |
[
"In formulations of string theory which posit \"extra\" dimensions, are these dimensions considered to be orthogonal to \"normal\" dimensions?"
] |
[
false
] |
This is all a little over my head. Please help me understand dimensional compactification, and whether, with such compaction, those dimensions are still considered to be orthogonal to "non-compact" dimensions.
|
[
"Yes, they are. There's not really much to it at all, you don't even have to think of the compactified dimensions as real physical dimensions if you don't want to, you could imagine just that the vibration modes and winding modes in the extra dimensions are like some extra internal quantum numbers that particles can carry.",
"If you imagine a particle moving through spacetime, then to describe when and where it is, you need to specify four numbers: 1 for time and 3 for position",
"(t,x,y,z)",
"You can write a physical theory down in terms of this list of numbers. But then you can ask, why stop at 3? Once a theory is written down, it's typically no problem at all to just write down a completely arbitrary number of dimensions: everywhere you had (t,x,y,z) before, replace it with",
"(t,x1,x2,x3,x4,...,xd)",
"You don't need to be able to imagine it, you just see that the equations that work for our spacetime work just the same no matter how many dimensions appear in the equation.",
"Have you seen the Brian Green documentaries on YouTube, such as this one where he tries to give an intuitive understanding of compactified extra dimensions? E.g. ",
"here",
"? "
] |
[
"Thanks. I'll check some of those videos later tonite..."
] |
[
"A dimension is just a measurement. The number of dimensions something has is the number of measurements required to describe it. To describe where you are in the world, you would need latitude, longitude, and altitude. To add when you were there, you would need to add date/time. Then add the temperature, humidity, wind reading, your age, height & weight, and you have 10 dimensions.",
"To plot them on a graph, draw a long horizontal line, with 10 vertical lines running through it. Above each vertical line write each of the measurements. Define minimum and maximum values, and plot your result on each line. Join the dots and you have a 10 dimensional line - not a line that exists in 10 dimensional space, but a line that requires 10 measurements to describe it"
] |
[
"Why do pens magically fail to work on some small areas of a piece of paper, yet work fine elsewhere on the same page?"
] |
[
false
] | null |
[
"To combine the other posts, it's due to a portion of the paper having reduced friction. Friction is necessary for most writing utensils to function. "
] |
[
"Combine this, ",
"mjbat7's answer",
" and the notion of how a ",
"ballpoint pen",
" works, and you have a pretty good explanation of the problem: if the ball in the tip of the pen doesn't find enough friction to roll it quickly runs out of ink on the part of its surface that's touching the paper."
] |
[
"The Lamy Safari is $35. I believe a 3-pack of Pilot Varsities can be had for around $5 at Wal-Mart."
] |
[
"Where do animals' basic intuitions come from?"
] |
[
false
] |
I've been watching a lot of Attenborough's nature documentaries recently. Often in the commentary, he says that such or such animal (or plant) adapted to have a certain behavior. For instance, you've got these fascinating capuchins who collect palm nuts; let them dry three days; transport them to the cracking site; cleverly counter jaguar attacks; and pass knowledge over. It is absolutely amazing to see an animal being able of planning so complex strategies. But it is learning from generation to generation that gave them this adaptive behavior. My problem is different. I cannot start to comprehend where are possible. I'm thinking about the baby mammal that somewhat that if he wants some food he needs to find his mother's breast first (and how does he know that his mouth is made to eat, anyway?). I'm thinking about the freshly born baby turtles who are going to the ocean instead of further inside the island. I'm thinking about how this insect (stalk-eyed fly) that he needs to begin a transformation. This behavior does not come from learning. It seems more to be a behavior on par with breathing. But I don't understand what allows to trigger such level of sophisticated reflexes in nature. Anyone?
|
[
"Evolution. The baby turtles that got to the ocean had a better chance of mating, so they had baby turtles that had a tendency to go to the ocean. ",
"The baby mammal that drank more milk grew stronger and had more babies than the ones that didn't get as much milk. "
] |
[
"Well with the capuchins they're taught by their parents. Those that don't pick up the necessary skills die. ",
"With things like metamorphosis and migration, it's hormones. ",
"As to how a calf knows immediately to go to the udder, I don't know, but I'd be willing to bet it's based on scent. It probably smells good to them in the same way that rotting flesh smells good to a dog, so they know it's OK to eat."
] |
[
"I'm no expert by any means, but I would imagine that it's something like the way that you automatically jerk your hand away from a hot stove-top, or a sewing machine begins to stitch when provided power. The makeup and arrangement of neurons in the brains of each of these creatures has evolved over time to trigger a specific behaviour in response to specific stimuli. It occurs somewhat below the level of what we would term conscious choice, and can be viewed as far more mechanical in nature.",
"As for how complex reflexes are created, it is done in the same way that complex analyses are performed by computers using very simple components (e.g., and/or gates). That is, the sophisticated response is built up from a large number of simple operations, arranged in a certain order. You could even think of it as similar to the way in which a Rube Goldberg machine takes an initial input and transforms it, over many steps, into a completely different output. Evolutionarily, this is the result of many, many beneficial mutations occurring as a result of random mutation, each building on its forbears (see my post below for a more detailed description of the process by which such mutations occur and accumulate). This, of course, usually requires a very long time-frame in which to occur - that's why the discovery of so-called \"deep time\" has been such an important step in our understanding of the natural world.",
"So, yes, it is an expression of genes, but genes that have mutated into very specific forms over a very long period of time."
] |
[
"While driving today right before a storm was about to take place, all of my car windows and the cars driving around me, immediately fogged up. Explain how this happened, please."
] |
[
false
] |
[deleted]
|
[
"Condensation forms when warm, moist air comes in contact with something cold. The air is cooled below its dew point near the surface and so some of the water condenses making fog. Do you know if the condensation was on the inside or outside of your window? Usually in a car what happens is that the air inside the car is warmer and wetter than outside (thanks to heating and breathing), so the windows make some of the water condense. But based on the association with the weather you described, my guess is that what you saw occurred when you drove a relatively cool car exterior into a warm wet air mass and so condensation formed on the outside of the car. But I am just guessing, I would have to know more."
] |
[
"Yes. It was on the outside. I know this because my windshield wipers were effective in removing the condensation."
] |
[
"Makes sense then. I'm going with the outside of your car windows were cool, and you drove into a patch of warm humid air."
] |
[
"COVID/Flu transmission: Is \"don't touch your face\" just code for \"don't touch mucous membranes\" or is there more to it?"
] |
[
false
] |
Much of the public health messaging I see around COVID, Flu, and other common sicknesses emphasizes not touching your face with dirty hands. When I hear that, I hear "don't touch your eyes, the inside of your nose, or your mouth"/your mucous membranes. Is this right or is your cheek genuinely a dangerous place to touch and if so, why? Is there some way that things move from your cheek to your eye easily? Is your cheek significantly riskier than touching say, your shoulder? I understand that we now know that formite transmission is not the dominant mode of transmission for COVID (seems to be quite rare), but for other similar sicknesses, I still have this question.
|
[
"What you're observing is the difference between generalized advice and specific advice. There is no direct infection mechanism for SARS-CoV-2 that is deposited on the skin, but you could think of the virus's journey to your mucous membranes as a trip with many stops.",
"You touch a surface that is freshly infected with SARS-CoV-2.",
"You touch your cheek.",
"You wash your hands.",
"You rub/swipe your cheek in the direction of your mouth/lips.",
"SARS-CoV-2 has now found a pathway to your mucous membranes.",
". One of the reasons that fomite transmission is not common with SARS-CoV-2 is that the viral load is not sufficient, and the virus is not easily delivered to a region of the body where it thrives.",
"Put another way, you are far less likely to actually exhibit COVID-19 symptoms as a result of this transmission method than you are by directly touching a mucous membrane, but the \"don't touch your face\" advice is given because it is easily understood, and it's less crass than saying, \"Don't pick your nose, everyone.\""
] |
[
"Thank you, I figured the answer was something like this and you hit on both points: what you put on your cheek by touching it doesn't necessarily stay there (because you move it later), and it's just more palatable/commonly understood messaging than don't pick your nose/touch mucous membranes."
] |
[
"First, most viruses require contact with preferred mucus membranes to infect people: nasal passage, eyes, genitals, digestive track are common. The skin serves as an excellent barrier against viruses.",
"There are some common fomite transmitted diseases: hand foot and mouth (spreads from contact of objects especially among children), norovirus (common cause of gastroenteritis), rhinovirus (common cold), rotavirus (diarrhea in children) and most STDs are considered fomite transmitted.",
"However, coronavirus and influenza (the two you explicitly mention) spreading through fomites vs \"airborne\" is a story of confusion amongst public health experts. If you look at scientific papers from early 2020 or before you hear about the concept of influenza spreading through \"aerosolized fomites\". Wait... That sounds like influenza is airborne or at least partially airborne so why even call it a fomite?",
"The story behind this weird wording is pretty long. But the summary is in the 1930s, Wells discovered the general rules of small droplets behaviour (varies slightly with temperature and humidity), but basically, droplets larger than 100 microns fall to surfaces quickly. This became the \"line\" between airborne and not airborne. That is, until some scientists accidentally swapped 100 micron size for 5 microns size (the size a droplet must be below to enter deep in the lungs, as TB needs to.) This mistake persisted, moving what was considered \"airborne\" to be much more restrictive: many larger droplets were not considered to be possibly airborne, but they were!",
"This framed the research of many scientists into fomites instead, because they assumed most larger droplets with high viral load dropped to surfaces and had a hard time being \"airborne\". But to explain the weird behavior of apparent \"airborne\" transmission of certain viruses between people who don't touch the same things, you get weird names like \"aerosolized fomites\".",
"Fast forward to COVID Pandemic. Aerosol physicists notice public health keeps saying 5 microns as cut off for airborne. Physicists know this number is actually closer to 100 microns from Wells and other work. Multiple physicists write an open letter asking public health to please call coronavirus airborne! After it gets publicity and public health researches a bit, they finally call coronavirus airborne. Those large droplets do stay floating in the air for a while!",
"Aerosol physicists later clarified that \"airborne\" is not really well defined. If someone sneezes directly on you, very large droplets can still infect you. Is that airborne? If large droplets are sucked into an HVAC system, they can still infect someone really far away is that airborne?",
"But anyway, the old \"wash your hands to prevent coronavirus infection\" is kind of older information and fomite transmission of coronavirus is now believed to be very unlikely.",
"But wash your hands anyway because there are plenty of viruses and bacteria that ",
" make you or others sick via your hands."
] |
[
"The ban of chlorofluorocarbons (CFCs) is known to be the most successful international intervention ever. How did we successfully convince politicians worldwide that CFCs was damaging the ozone layer, but today we are still having a hard time convincing politicians about global warming?"
] |
[
false
] | null |
[
"Unlike CO2, which is just about unavoidable for any form of combustion, a lot of CFC usage was relatively easy replaced",
"This is really all it comes down to. If CO2 emissions could be easily ended, they would be. Unlike CFCs, the entire world depends on burning fossil fuels in order for civilization to function.",
"While there is some progress being made towards moving away from them, it's going to be a long, difficult, expensive road."
] |
[
"Unlike CO2, which is just about unavoidable for any form of combustion, a lot of CFC usage was relatively easy replaced",
"This is really all it comes down to. If CO2 emissions could be easily ended, they would be. Unlike CFCs, the entire world depends on burning fossil fuels in order for civilization to function.",
"While there is some progress being made towards moving away from them, it's going to be a long, difficult, expensive road."
] |
[
"Environmental social scientist here.",
"The TL;DR version is that far, ",
" fewer ",
"paychecks depended upon",
" using CFCs than depend on using fossil fuels.",
"CFCs were only used in a relatively small number of products, and already at the time the environmental damage CFCs cause was identified there were technological substitutes available that were not prohibitively expensive.",
"The same cannot be said for fossil fuels (which emit CO2, which in turn is the primary driver of anthropogenic climate change). The entire global economy is utterly dependent upon the cheap energy and industrial inputs provided by fossil fuels. And only recently have we begun to develop cost-competitive renewable alternatives to fossil fuels as sources of energy and hydrocarbons. As a result, resistance to admitting that CO2 emissions from fossil fuels is a serious (read: ",
") problem has been enormous from a huge range of vested interests - industrial, economic, and political.",
"Other \"advantages\" CFCs had were the fact that CFCs and the hole in the stratospheric ozone layer over Antarctica are not naturally occurring (unlike CO2 emissions and the greenhouse effect), and so there was a fairly clear and incontrovertible smoking gun right from the outset.",
"This case is very well understood in the literature (political economy of the environment, political ecology, environmental politics, etc.). The ",
"wikipedia article on the policy history of CFCs",
" is pretty solid. ",
"But for folks who want to understand the story behind the ",
" around ozone depletion and climate change - and yes, there ",
" denialism about the link between CFCs and ozone - then here are some sources to check out:",
"Merchants of doubt",
" (book).\n",
"http://reports.ncse.com/index.php/rncse/article/viewFile/71/64",
"\n",
"http://www.tandfonline.com/doi/abs/10.1080/00139157.2011.588553?journalCode=venv20#.VBvCgfldVzo",
"\n",
"http://mitpress.mit.edu/books/business-global-environmental-governance"
] |
[
"If black holes can form because of the Schwartzchild radius, then why did the early universe at all expand?"
] |
[
false
] | null |
[
"The Big Bang was not all the universe concentrated at a point. As far as we know, at the moment after the Big Bang, the universe was infinite in extent, just as it is now. Energy DENSITY was arbitrarily high EVERYWHERE. This is not the ingredients of a black hole, which is a small region of high energy density surrounded by empty space."
] |
[
"The blackhole energy density is defined by the density needed to keep light from escaping. So anywhere with that density is by definition inside a black hole",
"No, things that are solutions to the GR equations within the Schwarzschild metric with radii less than the Schwarzschild radius are by definition blackholes. The Schwarzschild metric is that of a single spherical mass inside an empty universe (with no special cosmological texture). ",
"The Big Bang is described by the Friedmann-LeMaitre-Robertson-Walker metric which tells a story of a universe of uniform density parametrized by a time dependent scale factor."
] |
[
"This is covered in the Ask Science FAQ\n",
"After the big bang, why didn't the universe re-collapse under its own self-gravity?"
] |
[
"Where do we get raw elements from? Ie. Neon, helium."
] |
[
false
] | null |
[
"There are two ways I can interpret your question: 1. How do elements form in our universe? and 2. Where are pure elements found on Earth?",
"For 1, it depends on which elements we're talking about. Very basic elements like hydrogen and helium were formed in the Big Bang. Some other smaller elements like carbon, nitrogen, and oxygen, among others, are formed in stars like the sun through fusion and the appropriately-named CNO cycle. Some larger elements, such as copper, are formed in larger, supergiant stars, but the majority of these elements are formed when these stars undergo supernovae. And finally, for the heaviest elements of all, these are formed in laboratories by humans performing experiments.",
"For 2, it also depends on which elements. Because the Earth has a lot of oxygen which readily reacts with many metals, there are a ton of elements that are rarely found in their pure state. The so-called \"noble metals\" of copper, silver, gold, and platinum are relatively stable and unreactive compared to metals like sodium, calcium, and iron, and that's why we find these native metals on the Earth and not others. The other pure elements that are found on Earth are mostly gaseous and make up part of our atmosphere, such as oxygen, nitrogen, and argon. These are found in native form because they are plentiful and relatively stable (oxygen is the exception being fairly reactive). Nitrogen forms a diatomic molecule with itself and is fairly unreactive in this state and the noble gases are famously inert, due to having a full electron shell. Noble gases can be formed by radioactive decay: Potassium-40 decays into Argon and many radioactive elements emit alpha radiation (helium nuclei). Neon is present in a very small amount (less than 20 ppm) in at atmosphere but is important for many scientific and technological applications. To produce pure neon, air is fractionally distilled by cooling it and removing liquids as they condense. Eventually you're left with helium and neon and you remove the helium using activated charcoal to adsorb the helium atoms."
] |
[
"Sorry, but I have to correct a few facts in your post.",
"First of all, nucleosynthesis to helium occurred in the first 10 minutes after the big bang. This has been known since George Gamov's work in the 1940s. The timescale is set by the decay of isolated neutrons, and it is easy to derive from this the ratio of H and He. In greater detail, big bang nucleosynthesis has been extremely well understood since around 1970. What you're alluding to in the decoupling of radiation and matter is the point when protons and electrons can form neutral hydrogen. But that's at a temperature of around 6000 K, which is far too cold for nuclear fusion.",
"For the more massive elements, the basic picture of nucleosynthesis of elements in stars has been around since 1957, when one of the most famous papers in astrophysics, the so-called BBFH or B^2FH paper, after the initials of its authors, Burbidge, Burbidge, Fowler, and Hoyle. The paper is so famous it has its ",
"own wikipedia entry",
" and it is still worth a read as it is extremely well written. It defines the main fusion channels to go to iron and beyond, the s- and r-process (among other channels). The paper clearly lays out the nucleosynthesis of elements heavier than Fe in the s-processes during the post main sequence phase of stellar evolution. It also shows that neutron rich elements must be formed by neutron capture (the r-process) and it has been clear since that time that the elemental abundance pattern is a mixture of stellar nucleosynthesis (s-process and related processes) and nucleosynthesis in supernovae through the r-process. Work in the 1980s and 1990s showed that while r-processes in neutrino rich winds in supernovae work for elements like Sr, Y, Zr and others, neutron star mergers are required for some of the heavier elements here. The first computations for this were done by Freiburghaus, Stefan Rosswog and Frieder Thielemann in Basel in 1999 and was fairly quickly accepted, so this has been known for 20 years now, and is not recent news."
] |
[
"We thought for awhile that supernovae were the main ways that elements above iron were created, in the past decade or so the general consensus has shifted to thinking that these heavy elements are primarily created through neutron star collisions, although supernovae still contribute.",
"And to expand a little on the lightest elements, the universe wasn’t cool enough for atoms to form until ~370,000 years after the big bang. At this point primordial nucleosynthesis was able to occur and created the hydrogen and most of the helium we still see today, with trace amounts of lithium and beryllium.",
"As a fun side note, the cosmic microwave background, which is the oldest light we can see, is from this period."
] |
[
"A blue shirt reflects blue light, a green one reflects green light. Is it possible to make infrared shirts and would they be effective at keeping us cool in summer?"
] |
[
false
] | null |
[
"That shirt might also be pretty effective at trapping your body heat."
] |
[
"Not if it was made of a nice unidirectional metamaterial. Reflects IR from one direction, and lets it pass right through from the other side. Added bonus, turn it inside out for a very effective sweater."
] |
[
"Yes and no. The thermal jackets you find in survival kits effectively are designed to reflect IR but keep in mind if you're reflecting it from your body, you're also keeping your body from radiating its own heat. I did the research a while ago but what I can recall, 1/3 - 1/2 of your body's cooling is from radiation. ",
"Also, higher frequencies of light still add energy to your body (hence why greenhouses work). This is why you'll see white being used for clothing in some middle eastern countries, which is the practical way to use your proposed concept."
] |
[
"Have we observed any EM waves from space that were originally radiated as a non-visible EM wave but redshifted or blueshifted into a wave within our eyes' measure of perception? Or is this even possible?"
] |
[
false
] |
I have a general idea of how the Doppler effect works in terms of light as well as with the expansion of space. I'm wondering if an infrared or ultraviolet wave could ever cross the "threshold" of visible light due to the Doppler effect. Thanks!
|
[
"Yes. ",
"You could have looked up and seen this in 2008",
" if you were lucky enough to do so at the right time. The light you would have seen did not start out as visible light."
] |
[
"Of course. Think of it like this: Anything with mass has a temperature and therefore emits some light. (See black body radiation.) Even though the radiation emission from an object has some peak wavelength, there is still some emission across the EM spectrum. This means that by observing distant objects with a variety of different temperatures, we can superimpose these radiated wavelengths and deduce that the entire visible spectrum and beyond is present. Now it's just a matter of velocity and calculus. If some radiation is just beyond (like infinitely close to) our visible range on the ultraviolet side, then any non zero velocity in a direction away from us would shift it into our visible range. Same goes the infrared side of things. Any movement toward us would result in a blueshift into our visible range.",
"Sorry if that's hard to follow. Typing on a phone and I'm dead tired. I'm happy to explain differently or more quantitatively if need be."
] |
[
"Why? What about near-IR/UVvis sources?"
] |
[
"If a foreign object was in orbit around the earth, how long would it take for us to realize it was there?"
] |
[
false
] |
This isn't about aliens or anything, I'm just interested in how aware we are of the objects in the sky above us.
|
[
"If it was bigger than a baseball and radar-reflective, at most about 2-3 orbital periods. Earth orbit is monitored pretty closely by NORAD - in the particular band they use for their \"radar curtain\", we're the brightest known object in the galaxy."
] |
[
"Oh, I meant by intrinsic spectral radiance -- measured in total watts per unit frequency per unit area.",
"Now that I think about it I no longer have the numbers handy, so I can't properly defend the assertion -- but with a handy envelope: one must figure they radiate something like 10",
" Watts at something like 10",
" Hz (to capture baseball-sized objects), with a stability of order 10",
" and a radiating area no larger than, say, 1km",
" So that is something like 10 W sec/m",
" . The Sun, by contrast, emits 4x10",
" Watts spread across the visible band, which is 10",
" Hz, and has a surface area of 1.5x10",
" m",
" So that is 2.7 microW sec/m",
" , far less than NORAD."
] |
[
":-) No, I mean as in luminous flux."
] |
[
"Does Mitochondrial DNA expression vary?"
] |
[
false
] |
Given that they are not multi-cellular organisms I wouldn't expect individual mitochondria within a cell to have different roles. However within different cells on a multi-cellular organism (neurons, skin, eye, etc) do the mitochondria contained express differing genes of their own DNA to make proteins specific to that cell? Or do all Mitochondria in each cell perform the same function?
|
[
"As tempting as ",
"/u/Mitaines",
"'s logic is, a quick search shows that expression from mitochondrial DNA (mtDNA) does in fact vary between tissue types in humans. This actually becomes less surprising when you discover that many of the proteins encoded in mtDNA are involved in oxidative ",
"phosphorylation",
" (you know, the process that makes the mitochondria \"the powerhouse of the cell\"). If that's the case, it doesn't really make sense for every tissue type to express from mtDNA the same, since there's no way that energetic needs for different cell types are the same, and they're ",
"not",
". ",
"And that's not even to get into expression in other organisms, like ",
"plants",
". "
] |
[
"Different genes as in gene A is expressed in tissue X but not at all in tissue Y, no. ",
"Different levels of the same gene? Yes, absolutely. High energy tissues will have comparatively higher expression of the mitochondrially encoded components of the electron transport chain. Mitochondrial mRNA and tRNAs are also post transcriptionally regulated with respect to demand. So while ",
"u/Mitaines",
" is correct is saying that the origin and character of mtDNA transcription necessitates roughly equal levels of transcription. However, if you go in an quantitate different mRNA/tRNA levels you might get different ratios between tissues due to post-transcriptional regulation. In fact, there is extensive literature showing this occurs in disease states and mouse models of mtDisease, where levels of specific mtDNA derived RNA transcripts are down/up regulated compared to others, in a post transcriptional manner.",
"Bear in mind mitochondria have other roles beyond simple energy production, although the mitochondrial genome only contains components of the electron transport chain and associated translational machinery. ",
"However, in mitochondrial disease you can actually have cells with different mitochondrial DNA. Some mitochondrial diseases are what we can heteroplasic, in that, above a certain threshold, a % of mutated mtDNA in a particular mitochondrion, cell or tissue can cause disease. So you could say in this case they have 'different' genes (the majority are just point mutations). You can get different ratios of mutated:wt mtDNA due to the nature of mitochondrial replication (i.e. genetic drift occurs, as well as certain bottlenecks during zygote/blastocyst development) and this can change during life and development."
] |
[
"Thanks for the correction ",
"/u/dazosan",
"!",
"You can find exactly what dazosan said in this paper here: ",
"http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2408405/",
"\n\"...signaling pathways must exist to coordinate the activities of these distinct genetic compartments (the nucleus and mitochondria) to maintain and modulate mitochondrial gene expression and OXPHOS activity, not to mention the many other functions of these amazing organelles.\"",
"So differences in concentration is definitely not the only way to differ energy production in different cells."
] |
[
"Hypervelocity Impact on front page got me thinking... (speed + gravity question)"
] |
[
false
] |
People in the post started talking about a "Rods from God" weapon system devised in science fiction, where objects where hyper-accelerated in orbit towards the planet. My question is, once something is going several times the speed of sound, from orbit, does the Earth's gravity really do all that much to speed it up further? At that point are't you essentially shooting with the wind? Sure it doesn't slow the projectile down, but does it really speed it up meaningfully? Does being in orbit have an advantage other than ease of "line of sight" to target?
|
[
"Sure it doesn't slow the projectile down, but does it really speed it up meaningfully? Does being in orbit have an advantage other than ease of \"line of sight\" to target?",
"I can think of 2 advantages to launching a projectile from orbit: ",
"You won't experience any drag until you are close to the target (in atmosphere), so you can continue to gain energy almost until impact. ",
"No matter how hard you accelerate it in orbit, all of your projectile's gravitational potential energy will become kinetic energy as it falls. No matter how fast you shoot it initially, it will still continue to accelerate as it falls. "
] |
[
"I recognize this, but I'm curious if the gain in speed is significant. I realize every bit of increased speed will increase the power of the kinetic impact, I'm just curious how much.",
"I guess the root of my question is: If you have a tank 10 miles from your target that can fire a slug at mach 10 at the target, and you also have a satellite in orbit that can fire a slug at mach 10 at the target, does the satellite have a ",
" advantage over the tank?",
"On a target by target basis, deploying the tank is arguably more cost effective given current technology, I'm curious why one would go with the satellite option, other than it's capability of striking more targets from it's position."
] |
[
"The thing is if a tank launched a projectile at Mach 10 on the ground, by the time it hit the target it would have slowed down significantly by the time it hits the target.",
"However, from space (let's say geostationary orbit - 250km) the projectile might reach up to Mach 15-16 before starting to slow down. ",
"Have a look at this XKCD what-if for an example of the calculations involved",
". It's actually a very complex calculation to have to do to figure it out.",
"This is because the energy spent getting it up there is transferred to ",
"gravitational potential energy",
", so let's say we raise something by 250km, we 'give it', using ",
", ",
"1.594 gigajoules of energy",
". This is roughly 1.1x the energy found in a lightning bolt. Even if only 10% of this energy was kept on impact (the rest having gone into compressive heating, etc), it would make a significant difference.",
"A 1kg projectile moving at mach 10 has just 5.7 ",
"joules of KE, for comparison.",
"TL;DR ",
" it would make a significant difference to the final impact if launched from space."
] |
[
"How big of an object would we need to create an artificial atmosphere in space?"
] |
[
false
] |
[deleted]
|
[
"It wouldnt need to be that big, they create a breathable atmosphere in the space station at all times, major problems would be scale, the bigger the ship the bigger the air cleaning systems would have to be"
] |
[
"He means an atmosphere ",
" an object, not ",
" a hollow one.",
"I'm not sure on the requirement of gravity, but I do know that it depends on location as well - Titan has a heavy atmosphere, but Mercury, which has a much higher mass, hardly has any atmosphere because it's closer to the Sun. The closer your object is to the sun, the heavier it will have to be to counteract the solar wind."
] |
[
"Solar wind has no effect on atmo it never touches it, the magnetic fields shield it, which is something you would have to create as well if you wamt to live on something as opposed to in it. Gravity also has a role here, the amount of atmosphere an object can maintain depends on its gravity. More gravity meams you can hold onto the gasses preventing them from venting into space, so creating a man made object to hold atmosphere (with out artificial gravity or other gas retention system) woukd require building a ship either as large as, or as dense as, a planet, for example if you could create and contain a black hole with proprtionately the same gravitational pull as a planet and keep it in the cemter of a ship, then flood the area around the ship with carbon dioxide and other heavy atmospheris gasses you could pull it off"
] |
[
"What happens to black holes during universal heat death?"
] |
[
false
] | null |
[
"If Hawking is right, they'll eventually \"evaporate\" due to Hawking radiation, where they slowly lose mass due to quantum processes near the event horizon. This takes a really long time for really really massive black holes; if a supermassive black hole that was a billion times the mass of the sun never gained another once of mass again, it would still take 10",
" years to evaporate. ",
"If Hawking is wrong, then they'll probably just sit and chill and sweep up what's left of the mass of the universe, occasionally gobbling up another photon or electron. ",
"Of course, this question cannot be fully answered without a theory of quantum gravity, which we don't currently have. "
] |
[
"The rate of energy loss due to evaporation today would be less than the rate of absorbtion of light from stars, so any black holes existing today, even if they're not near any mass to absorb, will not be decreasing in mass.",
"Even after the stellarluminiferous era, the rate of energy loss from Hawking Radiation will have to compete with the rate of absorbtion from the cosmic background radiation. Black Holes will have to wait until the cosmic expansion has increased the wavelength of the CMBR to a low enough level for the balance between it and Hawking's radiation to have a net loss."
] |
[
"The rate of energy loss due to evaporation today would be less than the rate of absorbtion of light from stars, so any black holes existing today, even if they're not near any mass to absorb, will not be decreasing in mass.",
"Even after the stellarluminiferous era, the rate of energy loss from Hawking Radiation will have to compete with the rate of absorbtion from the cosmic background radiation. Black Holes will have to wait until the cosmic expansion has increased the wavelength of the CMBR to a low enough level for the balance between it and Hawking's radiation to have a net loss."
] |
[
"Why is it that a lit candle doesn't produce any smoke until after you blow it out?"
] |
[
false
] | null |
[
"This was answered by errantdog a few months ago: ",
"here",
"."
] |
[
"thanks"
] |
[
"You're welcome. I hope that answered it sufficiently for you?"
] |
[
"Why are iron (Fe) and cobalt (Co) good catalysts for creating hydrocarbon chains?"
] |
[
false
] |
I've been reading on slurry bed reactors, and i know that cobalt is more power efficient (less heat required) than iron in reactors, but what i don't understand is the mechanism which Co or Fe allow Carbon Monoxide (CO) and Hydrogen (H) to do this: (2n+1) H2 + n CO → Cn H(2n+2) + n H2O I have no chemistry background, so be gentle! Oh, and if the explanation explains where "coke" comes from in this reaction, that would be excellent, too. Thank you!
|
[
"There are at least three possible mechanisms, and which one predominates may depend on temperature, pressure and catalyst. As to why these metals (and nickel and ruthenuim) are good, other metals would give either different, less useful products or nothing at all, or not be stable under the conditions. All these metals absorb CO and H2 well on to their surface, which is a key prerequisite to getting them to react. The precise steps after these two molecules absorb is still being studied."
] |
[
"In general terms, transition metal catalysts act by two methods. First the metal centre is very highly positively charges and very electronegative - it will attract the electrons forming bonds and in other parts of the molecule. This polarises C-C bonds in the growing chain and allows insertion of another group. The other effect is that the metal coordinates the molecules in a small area, greatly increasing the local concentration of reactants, speeding up the reaction. ",
"A similar reaction, Ziegler-Natta polymerisation to create polyethylene is a good demonstration",
"If you want a bit more in depth detail the reason Co is lower energy and Fe is that these reaction involve two main types of ligand exchange, oxidative addition and reductive elimination. These change the electron count at the metal centre (18e being the optimum) and Co has a lower energy barrier for these transitions. "
] |
[
"i think i saw a video of a guy with a weed wacker and gasoline...",
"but seriously, what you're asking is more of a non combustion temperature bake off of impurities so the forged metals dont absorb any of those gases. hydro carbon chains though? idont remember that from the video"
] |
[
"Can the material taken with nasal swab test for CoV-19 also be used to look for other viruses after testing for CoV-19?"
] |
[
false
] |
We're taking more samples from people than ever. I'm wondering if the samples taken could also be used to monitor other infections to improve our understanding of other pathogens. Also, is human DNA also being unintentionally collected with these swabs? It's a dark thought, but are we surrendering our DNA unwittingly when we submit to these tests? I hope that there is some oversight preventing this kind of breach of privacy. It seems to be a tremendous opportunity for a controlling government (say China) to gain a huge genetic dataset on their own population.
|
[
"Yes. For example, the CDC lists a bunch of assays that can simultaneously test for COVID-19 and influenza (",
"Multiplex Assays Authorized for Simultaneous Detection of Influenza Viruses and SARS-CoV-2 by FDA",
"). A couple of these are commercially available. At the research level, there are ways to test for dozens of different pathogens at once. ",
"However, most if not all these assays are more complicated and harder to run than the simple single-pathogen tests, so it’s not done for everyone who walks up to a testing facility. ",
"Yes, of course human DNA is being collected with these samples. You’re giving up your DNA every time you get a haircut. It’s hard to imagine any kind of modern assay that doesn’t include human DNA, from blood samples to nasal swabs to saliva samples. ",
"Because it’s so ubiquitous, there are laws about testing for human DNA without specific permission. I’m not a lawyer, but some of the many laws that regulate human DNA analysis can be searched at ",
"LawSeq",
", at the National Cancer Institute’s ",
"50-State Survey of Laws Regulating the Collection, Storage, and Use of Human Tissue Specimens and Associated Data for Research",
", in ",
"The law of genetic privacy: applications, implications, and limitations",
", and in ",
"Protecting Your Genetic Identity: GINA and HIPAA",
"."
] |
[
"However, most if not all these assays are more complicated and harder to run than the simple single-pathogen tests, so it’s not done for everyone who walks up to a testing facility. ",
"Nah. Multiplex PCR tests are generally very automated. BioFire's FilmArray system, for example. 21 targets, bacterial and viral, on the respiratory panel, including SARS-CoV-2. Luminex's Verigene RP has 16. So it's actually used for a lot of screening, especially now that we have more rhinovirus and paraflu showing up for the season.",
"The real reason they aren't as common as other PCR tests is because they're very expensive, have an order of magnitude lower throughput, and have lower sensitivity than singleple, tests. I'll get some citations later if you'd like."
] |
[
"Testing complexity has a specific definition for the US FDA. \"High/moderate\" means a test must be operated by a qualified individual, i.e. someone with a specific clinical laboratory science education or significant training. The alternative, \"waived\" testing, can be done by anyone, and has pretty tight restrictions proving the test is \"foolproof\" enough. Any test authorized by emergency use is by definition ",
" moderately complex, and must be done in a clinical lab, performed by qualified professionals and overseen by an expert director. But virtually every clinical laboratory in North America satisfies that.",
"CMS actually has ",
"a great all-in-one portal",
" for CLIA guidance. There's even an FAQ for the Abbott i-Stat testing platform that illustrates just how strict waived testing is."
] |
[
"When a video game runs at 60 frames per second, does that mean only the display shows what happens every 60th of a second, or does the game have markers that take inputs and produce outputs only at those times too?"
] |
[
false
] |
For example, I know that the CPU that's processing everything can make a cycle every couple billionths of a second, and all though it would take a lot of them to produce a result, taking an input and sending it to the game should be very fast, and be able to happen in between frames, right? So for instance say there's a certain game that runs 60 fps, where the simple objective is to press a button before your opponent. If you press it after exactly 101 ms, and your opponent presses it after 115 ms, since the next "marker" for the game would happen at 116.6 ms, would this produce a tie, or would you win? I would imagine that the CPU could tell you pressed it first, but when working with emulators and such, everything is cut into individual frames.
|
[
"It depends on the game.",
"Minecraft will draw frames as often as your GPU and your monitor can handle, but the physics system only \"ticks\" once every 1/20th of a second. Time happens in 50 ms slices. If you and a friend both hit two buttons to start two redstone clocks at the same time to within a few milliseconds then they will be perfectly simultaneous.",
"If you are interested in breaking things for fun or testing purposes then the weirdness of discrete time is a good place to start looking for bugs. "
] |
[
"You can move your view faster than 20 fps but the world is rerendering yes."
] |
[
"Missing some details. You would have to explicitly code the engine to note the time of the keypress as well, that is not a standard feature. Most games ",
" just go to the basic \"The key has been pressed since last frame and then result in a tie. Unity engine by default, for example, merely tracks that inputs have been pressed between frames. ",
"Games are very limited in what input they can process during the loop because of the nature of 3d graphics. Typical loop is ",
"1) Check inputs",
"\n2) Perform AI",
"\n3) Render ",
"Recently, threading can run bits of each step in parallel but those steps ",
" be performed in that order. Imagine if you allowed the camera to move partway through rendering a frame. You'd get models torn apart as an arm rendered with the old position and a head with the new position. Same if the AI kicked in mid render. ",
"If your physics engine is tied to your frame rate, as in some old games, the game will run at a very high speed on modern hardware: gravity will be much stronger, everything will move faster, etc.",
"That's where you use a fixed timing loop so that doesn't happen. If the loop finishes early it waits. "
] |
[
"Why are some liquids easier to blow bubbles in than others?"
] |
[
false
] |
Like milk for example. Every child knows that if you put a straw in a glass of milk and blow it produces a bunch of bubbles, yet if you do it to water, it only produces smaller bubbles which pop really easily. So what is it with milk, and any other liquids like milk, that makes it produce these kind of bubbles?
|
[
"In essence yes this is right, but more in depth it is due to the increased viscosity and increased surface tension in milk and other liquids that provides the increased bubble ability. Similarly if you look at the long chain molecules of soap its essentially the same thing as long chain fats and proteins that are used to make bubbles."
] |
[
"Simple answer: due to proteins and fat present in the liquid. "
] |
[
"Ah, makes sense, thank you! :D"
] |
[
"Some species don't breed in captivity. Why? What's keeping them?"
] |
[
false
] |
[deleted]
|
[
"It depends, which species are we talking about? Some are lacking the proper natural and biological signals they would get in their natural habitat signaling breeding season, or for other species just a general depression from being held captive. Other species may just reject the mate chosen for them or be unable to find a suitable mate among the limited number of potential mates in their vicinity. Yet others, like rabbits or dogs for example, will hump and try to impregnate anything that moves and has a heartbeat regardless of if they’re in a natural ecosystem or a 4’x4’ wooden box with no food or windows. And don’t even get me started on "
] |
[
"Behaviors specific to the species that can't take place in a confined environment. ",
"Honey bees ",
" can be raised in complete captivity, fed sugar water and pollen or pollen substitutes. This is not how we normally raise them however, under normal conditions they have open access to the outdoors. They will never mate under those confined conditions however. ",
"Honey bee queens fly soon after emerging from the pupal stage to ",
"Drone Congregation Areas",
" (DCA) and mate there. DCA are areas where drones from the surrounding hives gather and await virgin queens. Drones typically fly only about 900m (0.5 miles) to one but queens fly to ones further away so they won't mate with their brothers. The mating takes place 15-40 meters above the ground and involves all of the drones chasing the queen in flight. She will mate with on average a dozen or more drones before returning to the hive.",
"Drones will show no interest in mating with a queen outside of a DCA. We are not entirely sure why but believe various pheromones are involved. ",
"Keeping honey bees inside a giant enclosure with acceptable distances and height won't work either. Honey bees do the vast majority of their navigation using the sun and they do badly in spaces where they can not see it and use it properly constantly trying to get out. They tend to get stuck in the corners.",
"The requirement for flight, the distances involved, the height above the ground, and the release of pheromones to trigger mating only under the right conditions all means honey bees will not breed in captivity."
] |
[
"Ocean fish are really bad with breeding in captivity. Salmon has been figured out, Sturgeons on a smaller scale and progress has been made for the important Bluefin Tuna.",
"\nMost of the rest... no one knows. There is big, big money to be made for people who figure out how to breed an economically important fish species on a large scale. Looking at the examples above, individual allowances have to be made for every species in question so it's an uphill battle. "
] |
[
"On the cellular level, would animals be more \"complex\" than plants?"
] |
[
false
] |
Im sure that is a vary naive way to word my question, so ill try to elaborate. If we look at a substance, on the cellular level, would the cells/bacteria/microorganisms be more evolved, on a plant substance (leaf, grass etc) or on a Animal substance (muscle, flesh tissue, blood etc)?
|
[
"There's ",
"a type of fern",
" with over 1000 chromosomes, if you want to consider that in your definition of complexity. "
] |
[
"\"Evolved\" is a loaded term that begs the misconception that evolution always progresses by some measure. But if you just ask about complexity, there could be a good case for plants being more complex at the cellular level. They are little friggin chemical factories, making tons more complex molecules than animals."
] |
[
"I'd argue that plants are more complex on a cellular level. They have structures like cell walls and chloroplasts that animals don't have, and they have pretty complicated biochemical abilities. Animals (usually) deal with the environment by moving around, sensing, and responding. Plants are (mostly) stuck in one spot, so their cellular machinery has to be able to handle a lot of environmental impacts.",
"Bacterial cells are less complicated than eukaryotic cells, but many single celled eukaryotes have the most complex cells of all. Unlike multicelled eukaryotes like animals and plants they have to cram all the machinery of life into just one cell."
] |
[
"A question about Firesticks, Space Canoes and Explosive Decompression (asked in AskReddit, not a lot of interest)"
] |
[
false
] |
Spaceship (et al) decompression is widely portrayed in sci-fi, and I was just wondering how realistic the various portrayals are. Like in Alien Resurrection when the hybrid gets sucked through the tiny hole - would that happen? Or would it be more akin to a hoover sticking out of the wall? Or somewhere in between? What variables would the resulting force depend on? Would a golfball-sized hole suck more or less than a basketball-sized hole? Obviously (I think) the internal pressure would make a huge difference, but what about the size of the decompressing compartment? If it was cupboard-sized or warehouse-sized, would it make a difference? Cheers guys
|
[
"Atmospheric pressure is only about 100k newtons per meter. So, a hole of 1 meter square can only have a maximum force of 100k newtons, which is not actually that much.",
"Explosive decompression/compression in deep water dives is much more dangerous, because the pressure differential can be much greater. There was this terrible incident where a diver got sucked out of a pressure chamber through a 2 inch gap... not pretty to think about."
] |
[
"extremely fatal"
] |
[
"Just thinking about this as a semi-science-literate layperson -",
"In our everyday experience, water pressure produces much greater force than air pressure. (Tens of kilometers of air on top of us produces a pressure of a couple of kilos, whereas we can't dive deeper than a few dozen meters in water without suffering pressure damage.)",
"I can't imagine someone being forced through an arm-sized drain at the bottom of a swimming pool, or even at the bottom of a well. ",
"I therefore have to assume that air pressure suitable for human environments wouldn't produce greater forces, even in a large compartment.",
"I suppose that one could also try thinking about decompression as the equivalent of an explosion - what force do you think would be necessary to force a certain object / being through a certain hole? I imagine that a human-sized being through a golfball-sized hole is theoretically possible, but again, would require forces way stronger than what we'd expect by decompressing a human environment. "
] |
[
"It rains sulfuric acid on Venus. Is there a constant fog of sulfuric acid in the atmosphere, or occasional storm clouds of acid?"
] |
[
false
] |
Could you occasionally use an acid proof umbrella or would you constantly require an acid proof suit if you were in the upper atmosphere? If you had a floating habitat high enough in the atmosphere to have a survivable temperature, could you walk around unprotected with an oxygen mask?
|
[
"The clouds of sulfuric acid that obscure our view of the surface only exist above an altitude of around 48 km and rapidly thin out with increasing altitude. In the upper atmosphere, photolysis of carbon dioxide by UV radiation from the sun gives carbon monoxide and atomic oxygen, the latter of which oxidises sulfur dioxide to sulfur trioxide. Being aggressively hygroscopic, sulfur trioxide rapidly reacts with any water present to form tiny droplets of sulfuric acid. These then precipitate towards the surface, encountering increasingly hotter conditions and becoming increasingly concentrated as a result. When formed in the upper atmosphere, the acid has a concentration of around 75–85%, but at the base of the cloud layer it exceeds 98%.",
"Below 48 km, sulfuric acid boils off and increasingly dissociates into sulfur trioxide and water. Water diffuses away while sulfur trioxide is destroyed by thermochemical reactions. The main channel for this destruction ",
" to be reaction with carbonyl sulfide, itself produced from reaction of carbon monoxide with either sulfur dioxide or disulfur near the surface. However, there is a serious lack of observational data from the lower atmosphere, and even the clouds themselves are not well-characterised, so many other processes could contribute.",
"To answer your other question: the densest cloud layers have an aerosol mass loading of ~100 mg m",
" with a particle number density of ~1000 cm",
". These numbers are quite similar to those found in storm clouds on Earth, to give you an idea of what they might look like up close. An average human has a frontal area of around 0.7 m",
" in an upright position. Assuming the atmosphere is completely still, at an average walking speed of 1.5 m/s, you will pass through about 1 m",
" of atmosphere each second. Making another assumption that all the droplets you encounter stick to you, ten seconds of walking will evenly cover your front with about a gram of sulfuric acid, and after 15 minutes you will have soaked up nearly 100 grams of sulfuric acid. Suffice to say, you will not have a good time walking through these clouds without any protective equipment.",
"Information largely taken from the following four reviews (all open access) and references therein:",
"Bézard and de Bergh (2007). Composition of the atmosphere of Venus below the clouds. J. Geophys. Res., 112:E04S07",
"Taylor et. al. (2018). Venus: The Atmosphere, Climate, Surface, Interior and Near-Space Environment of an Earth-Like Planet. Space Sci. Rev., 214:35",
"Titov et. al. (2018). Clouds and Hazes of Venus. Space Sci. Rev., 214:126",
"Mills et. al. (2007). Atmospheric Composition, Chemistry, and Clouds. In: Exploring Venus as a Terrestrial Planet. Geophysical monograph series, No. 176, American Geophysical Union, Washington, DC, pp. 73-100"
] |
[
"The one atmosphere line (the altitude where humans would be most comfortable without a pressure suit) is 50 km above ground.",
"You'll have to make some compromises to live anywhere except Earth, but Venus is asking a lot."
] |
[
"Venus is constantly obstructed by sulfuric acid clouds. The sulfuric acid rain on Venus never reaches the ground. As it falls it warms up and evaporates again.",
"The optimal altitude for a floating habitat (based on atmospheric pressure) is right between the sulfuric acid clouds and sulfuric acid haze. Thus you would constantly be experiencing acid rain.",
"The atmosphere of Venus contains a significant amount of sulfur dioxide which dissolves in water to make sufurous acid. I'm pretty sure that having your skin exposed to this for long durations would kill you. But that's irrelevant because the atmosphere on Venus is really hot and that would definitely kill you first.",
"You would need a suit that is refrigerated and acidproof to survive in the Atmosphere of venus."
] |
[
"What is that high pitched ringing sound you hear when you turn on a television?"
] |
[
false
] | null |
[
"My friend didn't believe I could hear this, so we ran a series of trials where I backed into the living room with my eyes closed and told him whether the TV was on or not. I achieved a perfect record but he still didn't believe me."
] |
[
"Thanks, I always thought it might be some form of tinnitus caused by being close to electronics. TIL otherwise! "
] |
[
"Thanks, I always thought it might be some form of tinnitus caused by being close to electronics. TIL otherwise! "
] |
[
"Do all living things use electric impulses throughout their bodies to move and do everything else?"
] |
[
false
] |
From my (admittedly limited) understanding of human beings' bodies, I assume that we use electric impulses throughout our entire body to move and do pretty much everything else that is required to be alive. Is this true of other organisms? Are there any creatures out there that manipulate their bodies in some other way that does not involve electric impulses? Specifically, I'm curious if it is accurate to say: All living things send electrical signals throughout their bodies and this is how most functions (from "brain" to body) are carried out. I appreciate any help that is offered! Edit: I also don't know if this would fall under Physics, Chemistry or Biology, so I have no clue what flair to attach to this question. Any help with that would be greatly appreciated too!
|
[
"The neural system, in evolutionary terms, is a pretty recent invention. It allows for very fast communication between different cells within a multicellular organism. It allows an organism to integrate stimuli from the environment and produce a single response to them. ",
"For any unicellular organism, there is no need for this fast communication, because the organism is a unit by itself and hence all coordination required for survival is intracellular. They don't use electrical impulses to communicate. ",
"I'm sure if you look at simple organisms that are 'less evolved' they would not have a nervous system. However, I'm not a biologist, so I can say for sure what they are! But the basic idea, electric impulses allow quick communication between cells that have to work together for the survival of the whole organism :)"
] |
[
"Exactly, a multicellular organism that does not use nerve mediating communication between cells is theoretically possible but I could not envision it surviving for long in an environment where it was competing for a niche against an organism with nerve mediated intracellular communication. The response time of this organism would be orders of magnitude slower (this would worsen drastically as the organism increased in size). ",
"Slime mould are the most complex unicellular organism that I am aware of; they communicate using a cAMP cascade and are able to perform complex tasks that other unicellular organisms are not capable of (forming a 'slug' that has a definite anterior and posterior orientation, that reacts to stimuli such as heat and light and can migrate, as well as forming a fruiting body capable of dispersing spores). They do not possess nerves and while they are capable of these feats, their response time is lacklustre when compared to a more complex animal, but a large part of this is due to their nature as a temporary aggregate of individual cells rather than a true multicellular arrangement. "
] |
[
"Cyclic AMP acts as both a paracrine signal and an intracellular signal, with cAMP detecting G-protein receptors being present on the outside of the cell. The receptor upon binding cAMP triggers the activation of Adenylate Cyclase, producing cAMP inside the cell that also diffuses out of the cell. That amplifies the signal and transmits it in a paracrine fashion. Inside the cell however, the presence of high concentrations of cAMP activate a G-protein that disables the external receptor for cAMP, and activates Phospholipase C, releasing IP3 and calcium ions which then trigger the cytoskeletal changes. Phosphodiesterase lowers the cAMP concentration inside the cell, the external receptor becomes active again and this repeats cyclically. This cAMP signalling is used to draw the cells together, so with each pulse of cAMP they will contract slightly.",
"I'm not sure how prodding it would work, as I am not sure if they have a mechanism of detecting that but if they were placed near a food source then they would use a similar method of chemotaxis to move towards the food source. ",
"I'm not an expert on slime mould, just a biochemist that thinks they are pretty damn cool. So if I'm saying anything wrong here anyone, please correct me and add to this discussion!"
] |
[
"Why do we assume so much about Quantum Physics?"
] |
[
false
] | null |
[
"Anybody who describes entanglement as \"instantaneous communication\" has no idea what they're talking about. Not only is that not at all what entanglement is, but the no-communication theorem actually says that that's impossible."
] |
[
"Correct. I'm not referring to an ability for US to transmit information instantaneously. Rather, I was referring to the idea that information about their state IS transmitted instantaneously upon observation of one particle. Hence the \"strange behavior at a distance\" phrasing. "
] |
[
"There is no instantaneous transfer of information whatsoever."
] |
[
"How is my computer password (eg. log in) stored on my computer and how safe is it compared to how a website would store that password?"
] |
[
false
] |
I've seen videos on hashes and and the correct and safe ways for websites to store your username and password, but what about on my PC? Back when I had a macbook I used to be able to access pretty much every password I'd saved with a built in app called 'keychain access' or the likes I don't know if that's a thing with windows now but in hindsight that doesn't feel very safe. Whats stopping a hacker from say accessing that Application and seeing what my stored password is for my bank account or email? How securely are my saved passwords stored on my PC? Edit: this video by is what I mean, also
|
[
"Log-in passwords to access a computer and \"stored passwords\" inside an application can use two different mechanisms.",
"Typically the password you use to log-in in a computer is not stored in a way that allows to be recovered. A function (a kind of hash) of the password is computed and stored and when you try to login the same function is applied to what you submitted to see if the results match.",
"This is pretty safe, if your password is long enough. If it is short or trivial, and if computing that function is fast, then somebody can try all the combinations of few letters (short password) or try all the password from a database of commonly used passwords (trivial password), or combine the two approaches.",
"Anyway, if the password is something like fv3g04g!!zY you are probably safe. The downside of this approach is that it is not usually possible (if the system is well programmed) to recover the password if you forget it. What you can do is to generate a new password.",
"The passwords that are stored in an application like Chrome, that allows you to recover them, clearly cannot use this approach. They must store the actual password is a way that can be decrypted, not a one-way hash function of the password.",
"Clearly it depends on the good will and competence of the programmer of the specific application to come up with a way to store encrypted password that is safe."
] |
[
"The website will request your PC to send the password in clear text (over an encrypted connection - don't type your password if that is not the case). This is a security requirement so that any leaked hashes can't be used by the bad guys to impersonate you.",
"So if you have any passwords stored in your PC, ",
" they are encrypted then it is in a decryptable form, not a hash. At this point we can distinguish 3 types of local password storage:",
"1) Non encrypted. As ",
"/u/Ummgh23",
" said, this is bad programming, but I'm not excluding that some apps may do it.",
"2) Encrypted, but the key is stored on disk. You can use the stored password without typing a master password every time.",
"3) Encrypted, but the user needs to type a master password to use it. This is the most secure way. You mentioned macbook, which I don't know well, but I've seen some Linux apps to do this (e.g. gnome-keyring).",
"Any app or web browser that remembers your password for a website or service without asking you to type a master password is either type 1 or 2 in the above classification (though some may use your OS account's password as an encryption key?). Trojans, or anyone having physical access to your hard drive, may be able to get your password and the encryption key. Type 3 is safer.",
"Also be wary of leaked hashes. It's extremely difficult, but with massive parallel computation it may be possible to find a colliding string so that it can be used in place of your password. That's why reusing passwords between different websites is generally a bad idea - when one of them is leaked all others are exposed."
] |
[
"And again, security of the keychain depends on the strength of the password used to encrypt it.",
"The mathematics behind any modern cryptosystem can be assumed to be unbreakable, so you have to look at\nsurrounding factors: besides the weakness of simple passwords to brute force, there would also be the obvious\nattack vector of installing a key snooping application in the operating system and in thus security of the passwords\non a modern computer depends on whether the system can be kept free of malware. Even though that does not mean\nmalware is out there to get at your keychain first and foremost. Most malware is simply used for DDOS attacks or email spam. That is anonymous malware from an attacker that does not specifically targets you (I am assuming you don't have a well organized enemy with technical knowledge).",
"If your harddisk is not encrypted it would be trivial to install targeted malware with physical access to the machine. An encrypted harddisk is a pretty solid defense against any physical access attacks on the computer, because it's impossible to install malware to a computer that you cannot boot.",
"Security depends on a whole lot and it is not the cryptosystem implementation that is the weak link nowadays."
] |
[
"What would we see if there was an object that absorbed 100% of the light photons that hit it? Just a black space?"
] |
[
false
] | null |
[
"It would be black, no matter what spectrum of light/electromagnetic waves you are sensitive to (radio, visible light, microwaves). A black hole would do that (though with a black hole there are additional effects due to its strong gravitational field, such as the bending of light that passes close to it.)",
"Interesting side note: black holes aren't entirely black, they radiate via a process called \"Hawking Radiation\": in the vacuum of space, so-called virtual particle pairs (e.g. an electron and an anti-electron = positron) are constantly created for a brief amount of time before they annihilate, due to the Heisenberg Uncertainty Principle. These virtual pairs are constantly being created and then annihilate each other, but near a black hole it is possible that one of these spontaneously created pairs lands inside the event horizon of the black hole while the other one does not. This can give the outside particle the energy needed to make the transition from 'virtual' to 'real', and it flies off into open space. The black hole donated some of its mass energy to this particle, shrinking a tiny bit in the process. This process is fast for light black holes (subatomic black holes evaporate in seconds or less), while large black holes take trillions of times the age of the universe to evaporate. But, nevertheless, no black hole is actually truly black. (Though in practice the hawking radiation of an astronomically-sized black hole is undetectable.)"
] |
[
"A black holes event horizon absorbs 100% of the photons that hit it. ",
"We see nothing, essentially, but it's outline against anything it occults and anything that may be in front of it. "
] |
[
"Note that the whole \"virtual particle pair near the event horizon\" explanation is purely heuristic and may not (in my opinion, probably does not) actually correspond in any way to what's \"really going on\" at the particle level. No one has ever worked out a complete particle description of Hawking radiation (doing so would almost certainly require a complete quantum theory of gravity), and the relevant calculations and models that we do have say nothing at all about virtual particle pairs."
] |
[
"Is talc really the softest substance? What is 'softness' anyway?"
] |
[
false
] | null |
[
"Substance? Probably not but it's the softest mineral according to the ",
"Mohs scale",
"."
] |
[
"The hardness scale is based on what can scratch what. Diamond can scratch everything, corrundum everything but diamond, etc. Everything else on the scale can scratch talc."
] |
[
"Poor talc. :("
] |
[
"Could a blood transfusion potentially help coronavirus patients who are in critical care?"
] |
[
false
] |
Apologies if this is a ridiculously stupid question but curiosity got the better of me. From my very basic understanding, severe cases of Covid-19 result in breathing difficulties and not being able to circulate oxygen to organs in the body. So it got me wondering, if the patient received oxygenated blood whilst removing blood that isn’t carrying oxygen, could that at least help along ventilators and other care?
|
[
"Short answer: a blood transfusion would probably help only a little bit—and probably not enough to make it worthwhile except if the patient already needed blood for other reasons. This is because providing more blood doesn't fix the apparent underlying problem in severe COVID-19, which is lung failure.",
"Long answer: we give people blood for several reasons. The most common ones are acute blood loss (hemorrhage), anemia or other low blood cell counts, and certain clotting or bleeding disorders. In most of these cases, the blood that is given serves to directly replace something that the patient was missing—blood cells or hemoglobin (the main oxygen-carrying molecules in the blood), platelets or certain factors in the blood that help in clotting, or simply a sheer volume of blood.",
"Now let's consider COVID-19. In severe disease, SARS-CoV-2 infects the cells in the lungs that produce surfactant (a substance that helps lung units stay open and thus allows you to breathe) and that help regenerate new lung cells when damage occurs. If infection becomes severe enough, the patient will lose enough lung function that they will not be able to breathe without a mechanical ventilator. The key problem is that, even though blood is making it through the lungs, not enough gas exchange can take place—that is, not enough oxygen can actually get into the blood regardless of how much blood there is.",
"Unfortunately, simply providing more blood—based on what we know right now, at least—doesn't do enough to help the body get oxygen to the cells in the body. The best we can do is (1) provide mechanical ventilation and other measures to improve lung function, (2) give medications to see if the viral infection can be slowed or stopped, and (3) wait for the patient's immune system to respond in a productive way (as there is some evidence that an abnormal immune response can actually make COVID-19 worse). This is not to say that patients who need a blood transfusion for other reasons (i.e., anemia or active hemorrhage as above) wouldn't get one. It's conceivable that patients with certain low blood counts may be affected more by COVID-19, but I'm not sure that we have enough evidence to make that claim yet.",
"Two additional notes: "
] |
[
"I think you underestimate the quantities that would be necessary. Breathing takes in about 8 litres of air every minute and extracts about a quarter of the oxygen. So that's two litres a minute. Maybe you could reduce that a bit by cooling the patient down but it still needs significant amounts. It is done for things like heart surgery but it takes large, expensive equipment to supply the required amounts and it's very invasive."
] |
[
"Thank you for a comprehensive and thorough reply. I really enjoyed reading it and I’ve definitely learnt something new."
] |
[
"If wood is suspended on the surface of a liquid with a higher boiling point than ignition, could the wood burn despite being wet?"
] |
[
false
] |
Assuming only the top surface of the wood is exposed to air.
|
[
"The autoignition temperature of wood is close to 300C, so you'd need a very hot liquid. If the wood is floating on liquid metal at a temperature of 400C (for example), then heat will transfer to the wood until it's at a high enough temperature that the portion exposed to air will catch fire.",
"If you had the wood completely submerged, it wouldn't catch fire, but would instead break down via pyrolysis, giving off bubbles of flammable gas which would ignite when they hit the air."
] |
[
"Wood needs oxygen to burn. If a liquid is hotter than the ignition temperature of wood, chances are, it is heating the surrounding air enough to ignite it. The \"wet\" side of the wood would probably not burn due to lack of oxygen, but would be converted to carbon (charcoal) with enough heat."
] |
[
"Do you sail? Curious what you do that you're near wooden sailworthy ships often :P"
] |
[
"Are stem cells really that \"next big thing\" as advertised? Why or why not?"
] |
[
false
] |
I don't really understand much about stem cell biology, only that it is very concentrated in the bone marrow, and that it can take the function of any other cell in the body. Is that it?
|
[
"The potential implications of stem cell based regenerative medicine are huge for medicine. While most stem cell therapies that go on today use adult stem cells like the hematopoietic stem cells in the bone marrow for blood cancers or ",
"immune related disorders",
" or ",
"mesenchymal stem cells",
" which are often what's used in treatments for multiple sclerosis or ligament injuries for instance, I believe the real renaissance in stem cell therapies will be due to ",
"induced pluripotent stem cells",
" which are embryonic-like stem cells that are derived from any adult cell, such as skin. ",
"These cells can make any cell in the body, and despite the advancement to do so being only 8 years old, these cells are already being used in clinical trials for ",
"age related macular degeneration",
". By turning these stem cells into different types of cells of the body, we have the ability to treat a wide variety of disease (liver, heart, diabetes, genetic disorders, etc) and injuries (spinal cord, muscle, etc). Additionally, since these cells can be derived from patients themselves, they allow for the ability to study genetic diseases in order to understand the underlying mechanisms of disease and develop new therapies. Combined with genetic engineering, a patient's own cells can be genetically corrected and re-transplanted back into the patient. ",
"So yes, stem cells offer huge potential and you will see in the coming years more and more therapies using stem cells. This post is really just scratching the surface, but research in this area is very exciting. "
] |
[
"Stem cell biology and the associated engineering is incredibly exciting, BUT",
"I'm skeptical of most therapies involving stem cells in the near to medium term future, with a few exceptions.",
"The thing is, diseases are complicated, multifacted, and incompletely understood. I'll list a few examples and give some thoughts about why I think stem cells will/won't make an impact. For the purposes of this, I'll talk about two classic treatment paradigms: inject/place stem cells, and place material/scaffold + stem cell.",
"Don't expect much from stem cells here. Cancer is an overgrowth of malignant cells. We don't know how to kill them and stem cells aren't really a solution here. If stem cell engineering gets ",
" at some point, you can imagine a surgeon being extra aggressive with surgery and replacing with new engineered organs. (\"Bladder cancer? Cut the whole damn thing out! We can put in a GlaxoSmithKline PeeBag 1200 back in once you're in remission.\") ",
"The exception to this is some types of blood cancers, where stem cell therapy is already a thing. In short, doctors wipe out the immune system with chemo/radiation, and \"reboot\" the immune system by infusing you with stem cells. ",
"Read more from American Cancer Society here.",
" ",
"Type 1 diabetes, chances are probably pretty good we can make some progress here. T1 Diabetes results from the immune system killing off specific cells in the pancreas. Stop the immune response, add in pancreatic beta cells, you might just have a T1 diabetes cure. Problem is, the more common type (type 2) is pretty different in cause (insulin insensitivity from poor diet/no exercise) and probably can't be affected much by stem cells. ",
"Don't expect much progress here, either. The heart is crazy complex, and so are blood vessels. It's not obvious how to actually repair a heart with stem cells. In a heart attack, you're looking at actual death of heart muscle cells. However, they're rapidly replaced with scar tissue. You can't really just cut out the damaged parts and replace it with new tissue. ",
"The liver is relatively promising! The liver regrows pretty nicely on its own after you cut part of it out, and the tissue is relatively homogenous with function. When an organ regrows on its own really nicely, you can imagine that the biology is relatively robust, if we can figure out the right materials and cell regimes. ",
"However, there's no treatment anywhere near clinical application yet. ",
" bone, skin, muscle.",
"Bone: You don't even really need stem cells here. There are some great biomaterials that recruit bone cells to do their thing and fully integrate the implant into bone, and remodel it over time. There are even a couple that are FDA approved.",
"Skin: Think next generation bandages, pitri dish grown skin grafts, etc. This is actually already done and it'll likely get even better. Stay tuned...",
"Muscle: Muscle is a tough one. Muscle fibers are REALLY long, and encouraging them to form their attachment sites might be a tall order. On the other hand, they aren't too complicated so someone might figure it out. There's not an obvious way to use them to fix muscular disorders though, so short of muscle tears or muscle cancers (rare), the impact may be limited. ",
"TL;DR: Stem cells aren't the end all, be all of medicine. However, they are an incredibly ",
" area, and at some point they (and related therapies) will be as exciting as news stories suggest. That point, however, may be year 2100 or beyond. We've really solved all the diseases that can be easily solved. ",
"TL;DR part 2: If you want something that can do everything stem cells have been promised to do and more, eat a healthy diet and maintain a healthy body weight, eat lots of vegetables, don't consume too much sugar or alcohol, exercise regularly (cardio AND weights), don't smoke, get your annual flu shot, and wear sunscreen and a seatbelt and don't live in a house with a gun. You've drastically ",
" from the ",
"top TEN leading causes of death",
" and you'll enjoy the remaining years of your life too. If you follow this advice, you'll reduce your risk of cardiovascular death, diabetes, preventable cancer of almost every kind, and you'll be strong enough and healthy enough to enjoy your later years too."
] |
[
"When a zygote is formed (i.e. when sperm and egg join) it divides over and over to form the cells that will eventually be the body of the new organism. These cells, up until a certain point in development, are called embryonic stem cells (ESCs). After the body is formed and development is well underway, most cells stop dividing quite as often as the ESCs were dividing. Specific populations of cells still need to be able to divide though, mainly because specific types of cells are quickly used/destroyed. Blood, skin, and intestinal lining are just a few examples of tissues that contain these populations of dividing cells, called adult stem cells (ASCs). ASCs continue to divide throughout the organism's life to replace broken/lost cells and keep those tissues healthy (you probably don't want to run out of skin, for instance, so it's a good thing we have skin stem cells).",
"The bone marrow contains one type of ASCs ",
"called Hematopoietic stem cells",
". Those are responsible for replacing red blood cells and several other blood-related cell types (as seen in the link)."
] |
[
"'Human Body' Would it be more beneficial for us to fuse with machine or to skip fusion and start development into gene modification?"
] |
[
false
] | null |
[
"This kind of conversation is very open ended and calls for speculative answers even from specialists. ",
"/r/AskScienceDiscussion",
" is better suited for this type of question."
] |
[
"Hi SpicyBeardedWarlock 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.",
" ",
" "
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"For more information regarding this and similar issues, please see our ",
"guidelines.",
"/r/AskScienceDiscussion",
"Please see our ",
"guidelines.",
"If you disagree with this decision, please send a message to the moderators."
] |
[
"Nuclear meltdown leading to critical mass?"
] |
[
false
] |
A friend of mine has said that if uranium rods in a damaged nuclear power plant meltdown, the uranium can pool together and reach a critical mass, causing an explosion. Is there any possibility of this actually happening? If so, what would the exact effects be?
|
[
"No, there is not enough uranium in a rod to create a nuclear explosion."
] |
[
"The fission chain reaction was stopped when the reactor was SCRAMed following the earthquake. But if all the rods melt, and the fuel pools at the bottom of the reactor, it could go critical again. This would lead to the generation of more heat, and exacerbate the problems they are already facing with heat removal. The core could also melt through the containment.",
"The heat could cause an explosion, but not a nuclear explosion. If the water were to flash to steam very quickly, you have a large pressure increase which could cause a steam explosion. Or oxidation of the zirconium cladding could produce hydrogen, leading to a hydrogen explosion."
] |
[
"In order to make a massive nuclear explosion, all that uranium has to be held together by precise force for an extended period of time. One explosion a few meters away might make all the uranium go together, but then a fission reaction would start, and the critical mass would rip itself apart before a REAL nuclear explosion could build up."
] |
[
"How long could you survive at absolute zero temperature? (−273.15°C or −459.67°F)"
] |
[
false
] |
I'm guessing we're talking second(s) (or less). Or would you just be damaged enough instantly that you wouldn't be able to recover?
|
[
"It's all in the rate of heat transfer. The vacuum of space (not near a star) is incredibly cold, but heat transfer only occurs through phase changes and radiation which would take some hours to kill you (assuming you had a pressure suit and air, but not proper insulation or HVAC). However, if we had a medium, like liquid helium with convective and conductive transfer at play you'd die very quickly within seconds."
] |
[
"Matter won't behave in any way at zero temperature, because it is physically impossible to get there in the first place. That's just like asking how matter would be have when going at the speed of light or faster - there's no physical answer because the starting assumption is already wrong."
] |
[
"For this reason, and since the OP didn't specify how the body would be cooled, I submit a paradoxical seeming answer that a person would survive indevinitely at absolute 0. There would be no functioning \"life,\" but provided there was no external influence, the body would remain exactly the same until the heat death of the universe. It would be fozen mid-synaptic-firing and between heartbeats."
] |
[
"Can we grow babies in labs?"
] |
[
false
] |
Since we can artificially inseminate a human embryo is it also possible to create an artificial womb and "grow" a human? If not is it a questions of ethics or technology or both that prevent us from doing it. If technology is the issue how long until we can do it?
|
[
"AFAIK, we are not there yet. Mother's placenta is an amazing evolutionary feat that is not going to be easily reproduced anytime soon. ",
"Artificial placenta is the key: ",
"http://en.wikipedia.org/wiki/Artificial_uterus"
] |
[
"TIL how important and complicated the placenta is. "
] |
[
"Thank you?"
] |
[
"What would Earth's climate be like with a zero degree axial tilt?"
] |
[
false
] |
I've always wondered what Earth's climate would look like without any kind of axial tilt. My understanding (though quite laymen) is that almost all weather is created by thermal differences in the oceans which is produced largely by the tilt itself. Now obviously there would still be thermal differences, even without a tilt, but I wonder how much of our current climate system is the ultimate product of the tilt. Would the Earth's climate be dramatically different? Would it be more arid, wet, or temperate? Would hurricanes and large weather systems be less or more powerful?
|
[
"Seasons would be nonexistent.",
"The Earth's axis remains tilted in the same direction with reference to the background stars throughout a year (throughout its entire orbit). This means that one pole (and the associated hemisphere of the Earth) will be directed away from the Sun at one side of the orbit, and half an orbit later (half a year later) this pole will be directed towards the Sun. This is the cause of the Earth's seasons.\nVariations in Earth's axial tilt can influence the seasons and is likely a factor in long-term climate change.",
"http://en.wikipedia.org/wiki/Axial_tilt#Earth.27s_seasons"
] |
[
"The earth's orbit is only slightly elliptical. We probably wouldn't notice a difference."
] |
[
"The issue with axial tilt is not added/decreased distance but the angle with which sunlight strikes the surface, and the amount of sunlight the hemisphere gets.",
"In winter days are shorter, yes? So there are fewer hours for the sun to warm the ground and air.",
"Additionally, take a flashlight and shine it straight on at a wall; it makes a small round spot. Now move the flashlight over and shine it at an angle. The flashlight's putting out the same amount of light, but covering a much larger area; clearly there's less light per square cm.",
"Put those factors together - less intense light for fewer hours of the day in winter, more intense light for more hours of the day in summer - and you can see where the temperature differences of the seasons come from even without any significant differences in distance from the sun."
] |
[
"Why is our blinking synchronized between both eyes?"
] |
[
false
] | null |
[
"Medical student here. Just finished neuroscience, so I feel like I should share so that least SOME of the minutiae they taught us is useful... ",
"The closing of the eyelid is controlled by the orbicularis oculi muscle, which is innervated by the facial nerve (cranial nerve 7). Many cranial nerve functions are bilateral (both sides), since the descending control of those nerves from their respective origins in the brainstem are themselves bilateral. This is exemplified by the fact that if you were to sever the upstream controller of the cranial nerve on one side, you'd see loss of function on only one side. ",
"Another interesting thing is the control of left and right eye movements (looking left and right) . It's MUCH more complex than I thought before reading about the pathways. When you look to the right, for instance, your cranial nerve 6 (abducens) is responsible for moving your right eye to the right. To get the left eye to move right, however, your brain must have a way to communicate with the other eye. It accomplishes this via a structure called the ascending medial longitudinal fasciculus, which passes a message to the left cranial nerve 3 (occulomotor). In this way, the eyes are able to move smoothly and coordinately in the same direction. ",
"I'm not certain if I answered your question satisfactorily. I'm writing on my phone, so I apologize for the lack of formatting. ",
"(edit--corrected a cranial nerve)"
] |
[
"Both eyes are connected via the ",
"Median Longitudinal Fasciculus",
" that runs in your brainstem. It gives the information to each eye so that they know what the other is doing and can make coordinated movements. It's why you can look right and both eyes will follow even though they use different muscles for that movement (lateral rectus for your right eye and medial rectus for your left eye).",
"Problems with it can cause one eye to move without the other following, you can get double vision even though the actual muscles work fine. Opening your eyes uses ",
"levator palpebrae superioris",
" muscles (I've always thought that sounded like a Harry Potter spell, but it basically just means \"upper eyelid elevator\"), which is innervated by ",
"oculomotor nerve",
", the same nerve that gets most of your eye movement muscles.",
"Closing your eyes when you blink actually uses your ",
"facial nerve",
". Your upper facial muscles have dual innervation (both sides of the cortex), but your lower ones have single side innervation, which is why you can't preferentially wrinkle only half of your forehead but you can raise only one cheek. Your eyes are in that upper division. Think about winking vs blinking. You can't easily wink without moving any other part of your face, eg. raising your cheek slightly, but you can when you blink."
] |
[
"Additional question: Similarly, does synchronized blinking have anything to do with the way we have synchronized eyeball movement?"
] |
[
"What does the ISS use to protect its solar panels?"
] |
[
false
] |
I understand that we track large objects and activate thrusters long before a collision that helps protect against major impacts, but what about the small stuff like bolts and nuts from failed space craft and other small rocks? It seems like we would not be able to track every single piece of debre out there, so what does the ISS do to protect there solar panels from impacts with these small items?
|
[
"On top of that, debris that would hit the space station should be travelling on the same orbit and therefore have a similar speed",
"Not necessarily. You can have similar orbits intersect, even if they have a similar periapsis and apoapsis, if you have one object in a different orbital inclination (such was the cause of the ",
"Iridium-Cosmos satellite crash in 2009",
") or if one object has a different Longitude of the Ascending Node. "
] |
[
"I don't think they use anything. Space is BIG and even if there are plenty of debris in orbit, they are really far between and the probability of hitting anything is still very low. ",
"On top of that, debris that ",
" hit the space station should be travelling on the same orbit and therefore have a similar speed, so the impact would be more of a bump than a crash. And if it's a fast-moving object that is not in orbit, like a meteor, then it's not something we can anticipate or protect against, but again, it's not likely to happen. The space station is a tiny target.",
"I think it would be more cost efficient to replace a damaged panel than to build stronger, heavier panels."
] |
[
" If you've been to ESTEC open day, they have a former panel from the Hubble space telescope that was replaced and is now exhibited there, when you look at it closely you can see it's full of impact craters. NASA must have similar things exhibited. You can also check here: ",
"http://orbitaldebris.jsc.nasa.gov/measure/surfaceexam.html",
"But we're not concerned on solar panels. They don't need special protection like pressurized environments because losing a few cells is tolerable.",
"Solar cells are connected in series in \"strings\" to give the appropriate voltage, then several strings are connected in parallel to give the appropriate power. Each cell is connected in parallel to a bypass diode. (",
"Source",
"). So even if a few cells are lost the overall panel will still be working.",
"Also panels are usually oversized to account for degradation, which is due in part to normal operation and in part to radiation from high energy particles. So even if some power is lost when there is an impact, they still generate more than enough to keep the station powered. They have been calculated for the EOL power requirements."
] |
[
"How would blood pressure and blood volume be affected by the loss of a limb?"
] |
[
false
] |
[deleted]
|
[
"tl;dr: Red blood cells are produced by marrow, and it responds to decreased oxygen delivery to the kidney. Volume is also controlled by the kidney, and it responds to changes in pressure in the arteries. Both of these systems can respond to loss of a limb.",
"You're right that blood cells are produced by bone marrow. But, in adults especially, most of the marrow in your arm isn't working very hard anymore. Most of the hematopoesis happens in your axial skeleton, which you can't cut off. They're produced in response to stimulating factors. Red cells, for example, are produced in part in response to release of erythropoeitin (EPO) from kidney cells into the blood. The kidney releases EPO when it senses low oxygen delivery by the blood. That oxygen-sensing system actually won the Nobel Prize this year.",
"The blood ",
" is determined largely by the fluid component of blood. This is closely controlled by your kidney in response to changes in blood pressure. If you bleed or sweat too much, the pressure in your arteries starts to fall off, and your kidney works hard to produce less urine relative to how much water you drink. If you drink too much water and your arteries become too full of volume, your kidneys will pee the excess off."
] |
[
"Very informative, thanks for taking the time to write that out!"
] |
[
"Very informative, thanks for taking the time to write that out!"
] |
[
"Several questions... How would a \"cloud\" of hydrogen gas behave in space, under various conditions? Would it expand or diffuse? Would it collapse under its own gravitational field? Also, If there was a big enough \"rock\" in space, would it collapse under its own gravitational field?"
] |
[
false
] |
Me and my friend are having a disagreement about how gravity affects matter (granted we both have a poor understanding of the subject). I am of the opinion that a big enough object would not necessarily collapse under its own gravitational field, and he is of the opinion that as long as sufficient mass is reached a black hole could be formed.
|
[
"Hydrogen at any reasonable temperatue would diffuse, since it's random motion due to the temperature would overcome the tiny force of any gravity. If you compress the gas enough, and there is enough of it, and it's cold enough, then it might collapse in on itself due to gravity.",
"As for the rock: every object has a Schwarzschild radius. If the entire mass of an object were to be compressed into a sphere with that object's Schwarzschild radius, it would collapse and form a black hole."
] |
[
"So a single hydrogen molecule in space at 3K will have a kinetic energy of 6.21x10",
" . The gravitational potential energy given by a single hydrogen molecule to another is (7.48x10",
" / r), where r is the distance between the two molecules. This means that for gravity to overcome the energy from heat, the two molecules would have to be about 1.2x10",
" m apart. That's smaller than the Planck length. Now, if there are more than two molecules then the gravitational field will increase in strength, but you would need a ",
" of molecules in close proximity and then they could form anything from a nebula to a star depending on how dense the cloud is.",
"For any object, the gravitational field is such that it looks like the entire mass is concentrated at the centre of mass (unless you're inside the object, then it's different). So, if an object was enormous, but not very dense, then you would probably be very far away from the CoM, and the mass would be small, so the gravitational force would be tiny. I don't know how this relates to the Schwarzschild radius, though..."
] |
[
"My conceptualization of gravity entails that it emanates from every part of the mass of an object, not just the center. When you are outside of the object I understand why you use the center as a reference point to calculate the overall pull that a circular object will have on you, but once you are inside it you realize that you aren't being pulled from just the center, so why are you being pulled from only the center while on the outside?",
"It is true that you are pulled from every point. So, to work out the overall pull you integrate over all the points in the object. It turns out that (mathematically) this is exactly the same as treating the whole object as if it were compressed at a single point which we call the Centre of Gravity. Since inertial mass = gravitational mass, the CoG is the same thing as the Centre of Mass (which is used in rotational calculations).",
"For objects that are not of homogenous density (let's say one hemisphere of earth was of low density and the other hemisphere of high density), or not symmetrical (i.e oblong), would we still think of the gravitational energy as concentrated in the center of the object or would we calculate some sort of off center point based on distribution of density or shape?",
"The second option. Basically to find the centre of mass/gravity, you add up the individual masses of all the little bits of the object and then divide by the total mass (just like taking a mean).",
"Consider the very concept of a Swarzchild radius... If I compress any object beyond a certain point, it will form its own black hole because light cannot escape from it. The Swarzschild boundary represents that critical point where no force in nature can counteract its gravitational pull. Now imagine that instead of compressing this object you stretched it out, would its gravitational pull not become less and less until it is negligible? Is there a critical radius where ANYTHING (any force of nature at all) would be able to counteract the gravitational pull of this \"stretched object\"?",
"Right, so this is where conflicts appear :p. What the Schwartzschild radius is, is the radius at which the escape velocity is greater than the speed of light, ",
" the object is concentrated at a point. Now, real life objects aren't concentrated at a point, and when you're inside an object gravity behaves very differently (it decreases linearly with distance from the centre). So, for the Schwartzschild radius to represent something 'real' the radius of the object has to be less than the Schwartzschild one.",
"Forgive the run-on, and I hope I'm not making myself look silly with these ideas... I just have a really hard time forcing myself to think of an object of any size and composition as having a center where all the mass transfers its gravitational energy to, and then projects one gravitational field outside of the object, regardless of any kind of distance limitations... Thank you again and in advance for taking the time to inform me!",
"It's fine! Half the fun of science is explaining all this awesome stuff to other people!",
"The best way to think of the centre of mass is as a mathematical tool which we use to simplify calculations, so we don't have to do the whole integration every time."
] |
[
"After listening to RadioLab's recent episode about symmetry, a question about matter/antimatter has been brewing"
] |
[
false
] |
They mentioned that for every billion "pieces" of antimatter, there are like a billion and one pieces of matter. And that extra matter eventually accumulates and interacts and forms stars and planets and heavy elements and eventually life. But, if there had been a bias toward antimatter, would/could life still exist as we know it? Would we just be made up of antimatter instead of matter? And we would search the universe trying to understand this mysterious concept of matter? Or would a bias toward antimatter result in a wildly different universe?
|
[
"Well, not the exact same properties. Antimatter can behave differently under the weak force. This is what gives rise to CP-Violation and is believed to be why matter fills the observable universe instead of anti-matter."
] |
[
"Yes, antimatter has exactly the same properties, chemistry, etc. as regular matter; the only reason that one has primary status is because it's what we're made of. We could just as well call what we're made of \"antimatter\" and call positrons, etc. \"matter\"."
] |
[
"It kinda matters what the OP means by bias. If he means that CP-violation would favor anti-matter in the same way that it currently favors matter, then he would basically just be swapping their names. All the attribute which are unique to anti-matter would be transfered to matter and vice-versa.",
"However, if he meant that \"somehow\" originally the universe was filled with anti-matter and the laws are the same as they are now. Then, anti-matter would be slowly evaporating from the universe because of CP-violation. As, matter/anti-matter pairs are being created and destroyed constantly, which would favor matter."
] |
[
"Solid Rain is said to be a super-absorbent polymer that can soak up more than 500 times its own weight of water. Given that mountaintops have snow, if we make a very tall elevator, could we harvest humidity from the sky even in deserts?"
] |
[
false
] |
if these technology in the future could soak-up even more water in reasonable amounts of time, ¿could we bring down liquid (given that mountaintops have snow) by elevating these kind of polymers and leave them X time up there, all these in the middle of the desert?
|
[
"Based on the press release, you can't use these like millions small buckets to transport water from one place and dump it in another. That is, its not like a wash cloth that you wring out. Instead its like hair gel, that slowly dries out. But, I'm not really sure without seeing a paper describing its properties"
] |
[
"Yes, but there's limited atmospheric moisture over a desert, mountains near deserts have snow/ice on top because they form a ",
"rain shadow",
"."
] |
[
"I trust nothing like this until I see a peer reviewed publication. For all we know, there is 10 grams of this stuff. "
] |
[
"Does the same food have the same amount of calories as it is cold when it's hot?"
] |
[
false
] | null |
[
"More or less, yes. Especially for a processed food like a frozen pizza.",
"For fresh foods, cooking makes them both more and less nutritious, depending on the food and the cooking method. Cooking can break down hard-to-digest molecules and make them more available to you, but it can also break the structure of some molecules so they are not as nutritious.",
"Strictly speaking temperature, cold food and hot food are pretty much identical. Eating or drinking extremely cold things forces you to burn a tiny amount of calories to bring them up to body temperature for digestion, but this is miniscule compared to the calories in the food."
] |
[
"If it's the same object with no chemical changes, just at different temperatures, then yes, it's the same calories.",
"If the heating or cooling causes chemical change (which is a process we sometime call 'cooking'), then yes, the calories could change as the molecules change into thing that are easier or harder for us to digest."
] |
[
"Because of how the calories are defined if the chemistry is unchanged so are the calories. However if you eat cold food it will cool down your body slightly and your metabolism should increase to counter the change slightly."
] |
[
"How Feasible is a Nuclear Powered Locomotive"
] |
[
false
] |
I was looking over forum as I was google searching the answer, and only understood a small portion of the specifics mentioned. Can anyone shed some light in layman's terms?
|
[
"Feasible, but there's no particular need to build such a thing, and having a nuclear reactor racing around the countryside isn't necessarily a good idea. ",
"Relevant - ",
"http://en.wikipedia.org/wiki/Nuclear_marine_propulsion"
] |
[
"What warrickneff says is true of trying to miniaturize modern nuclear reactors. However there is another possibility in LFTRs (Liquid Fluoride Thorium Reactors). They ARE nuclear, but function VERY differently from what would be considered a traditional nuclear reactor. There were even plans in the 50s and 60s before ICBMs worked well to make a nuclear powered aircraft that ran off a LFTR so that it could deliver weapons systems to the USSR. ",
"Really cool stuff."
] |
[
"We already have electric subways and trams that are powered by rails or overhead lines. The problem is that installing the required infrastructure isn't cost effective for long distance rail transportation."
] |
[
"If astronauts lose bone mass in low gravity, do they gain it in high gravity?"
] |
[
false
] |
And what could the human skeleton look like after being exposed to high gravity for a prolonged period of time?
|
[
"I dont think anyone has done any LONG term studies. best i can find is maybe 24 hours in a centrifuge, considering its a box barely large enough to lay in, its not something you can really live in for weeks.",
"In theory though... yes, we should adapt, though perhaps not all of the adaptations would be healthy."
] |
[
"In the absence of evidence, it is probable to some limit. Having a high Body Mass Index is loosely correlated with Bone Mineral Density.",
"A simple formula used in clinical practice is the OST (Osteoporosis Self-Assessment Tool) which is used as a pre-screening for Osteoporosis, which is characterized by low Bone Mineral Density. The formula is (Weight in kg - Age) / 5 . Women who have a score under 2 and Men with a score under 4 are at higher risk of low BMD.",
"The more significant effect you'd probably see is the increased development of osteoarthritis resulting from the increased wear on joints."
] |
[
"Thanks for the detailed reply!"
] |
[
"Do animals with shorter life cycles have a faster evolutionary process?"
] |
[
false
] |
If the reproductive cycle happens in days instead of years, does the speed of evolutionary change increase.
|
[
"In a way yes and in a way no.Yes, in that a shorter reproductive cycle will allow for faster accumulation of mutations. All evolutionary change is the result of a mutation in the genome. But the major drive of the /speed/ of evolutionary change, as you asked, is the mutation rate - how often the process of DNA replication makes an error that could lead to evolutionary change. While you do often see a link between a shorter reproductive cycle and a higher mutation rate, it isn't necessarily always the case."
] |
[
"Here",
" is an article on those fruit flies which were kept in the dark for 57 years (1400 generations). Over 240 genes in the fly's genome showed point mutations."
] |
[
"Here",
" is an article on those fruit flies which were kept in the dark for 57 years (1400 generations). Over 240 genes in the fly's genome showed point mutations."
] |
[
"Is it possible to kill a star by introducing enough foreign iron to it?"
] |
[
false
] |
[deleted]
|
[
"Interesting question! For a low mass star, this will only lead to the star imploding once you reach 3 solar masses. Now, where will you get >2 solar masses of iron? For a high mass main sequence star, it will be difficult to add iron given the star will simply blow it away by powerful stellar winds. Say you can magically expel it into the photosphere of said star, we still don't know how long the iron will sink into the core to produce your expected supernova event. For an even higher mass evolved star, they will simply expel it violently through an episodic mass loss like that of a supernova impostor event due to a more violent spin like exceeding 450km/sec. "
] |
[
"I think the OP is thinking that since stars die out when they start creating iron, sending some iron in a star could be used to kill it. But of course it's not the iron that's killing the star in the first place. It's just that when a star is about to die, processes take place which happen to create iron. (Or at least this is my understanding, albeit I'm by no means an expert in this matter, do correct me if I'm wrong.)",
"Like say, people who die of old age usually have grey hair. Would dying your hair grey kill you? Of course not. It's not the grey hair that kills people, it's just something that tends to happen when people are close to dying of old age.",
"Furthermore, even if everything else in the solar system was 100% iron, all the planets, moons and so on, it'd still be less than the iron in the Sun already right now."
] |
[
"I think the OP is thinking that since stars die out when they start creating iron, sending some iron in a star could be used to kill it. But of course it's not the iron that's killing the star in the first place. It's just that when a star is about to die, processes take place which happen to create iron. (Or at least this is my understanding, albeit I'm by no means an expert in this matter, do correct me if I'm wrong.)",
"Like say, people who die of old age usually have grey hair. Would dying your hair grey kill you? Of course not. It's not the grey hair that kills people, it's just something that tends to happen when people are close to dying of old age.",
"Furthermore, even if everything else in the solar system was 100% iron, all the planets, moons and so on, it'd still be less than the iron in the Sun already right now."
] |
[
"Can we communicate via quantum entanglement if particle oscillations provide a carrier frequency analogous to radio carrier frequencies?"
] |
[
false
] |
I know that a typical form of this question has been asked and "settled" a zillion times before... however... forgive me for my persistent scepticism and frustration, but I have yet to encounter an answer that factors in the possibility of establishing a base vibration in the same way radio waves are expressed in a carrier frequency (like, say, 300 MHz). And overlayed on this carrier frequency is the much slower voice/sound frequency that manifests as sound. (Radio carrier frequencies are fixed, and adjusted for volume to reflect sound vibrations, but subatomic particle oscillations, I figure, would have to be varied by adjusting frequencies and bunched/spaced in order to reflect sound frequencies) So if you constantly "vibrate" the subatomic particle's states at one location at an extremely fast rate, one that statistically should manifest in an identical pattern in the other particle at the other side of the galaxy, then you can overlay the pattern with the much slower sound frequencies. And therefore transmit sound instantaneously. Sound transmission will result in a variation from the very rapid base rate, and you can thus tell that you have received a message. A one-for-one exchange won't work, for all the reasons that I've encountered a zillion times before. Eg, you put a red ball and a blue ball into separate boxes, pull out a red ball, then you know you have a blue ball in the other box. That's not communication. BUT if you do this extremely rapidly over a zillion cycles, then you know that the base outcome will always follow a statistically predictable carrier frequency, and so when you receive a variation from this base rate, you know that you have received an item of information... to the extent that you can transmit sound over the carrier oscillations. Thanks
|
[
"I think you are basically proposing the sort of thing discussed ",
"here",
". Your question is actually a good one and the explanations why it doesn't work are not general (",
" actually they are pretty general, see below), but every specific example studied has nonetheless found that no FTL communication is possible. The only way I could give you a better answer would be if you proposed a more concrete example. I suspect that your confusion is actually at a lower level, for example it is not possible to do exactly what you propose; when you have an entangled pair and you wiggle one, the other doesn't wiggle, that's not how it works. What happens is that when you ",
" one, your result is ",
" with what is ",
" in the other, but you can't control ",
" was measured, so there is no communication since the only way to know there was any correlation is for you to actually compare results. However going with an interpretation of your question in terms of rapidly turning on and off an interference effect through measurement on one side, or doing rapid measurements on one side which statistically change the spread of a complementary variable, is actually a very good question whose answer appears to depend on the particular setup.",
" At the request of ",
"/u/LostAndFaust",
" I would like to make clear that there is a no-communication theorem that ostensibly rules out faster-than-light communication in general. Nonetheless many serious researchers continue to take question's like the OP seriously, because it is interesting to see in each particular case how exactly faster-than-light communication is prevented, if at all. Also, not all researchers agree on the generality of the no-communication theorems and there is serious research still being conducted to test whether faster-than-light communication is possible (see John G. Cramer at U. Washington, for example). ",
" Just wanted to add a link to ",
"Popper's experiment",
", which is the basic idea I was interpreting the OP as asking about. It has a very interesting intellectual and experimental history!"
] |
[
"I was under the impression that the no-communication theorem was pretty general.",
"http://en.wikipedia.org/wiki/No-communication_theorem"
] |
[
"Look at it this way: Information wasn't sent FTL, the two parties just found out the same information at the same time.",
"Handing someone a note and saying \"Don't read this until you're across the galaxy\" is not the same as \"I'll text you the meeting place when you're across the galaxy\".",
"I don't know if either example helped or not."
] |
[
"Permeation of heavy water (D2O) through garments?"
] |
[
false
] |
My knowledge of chemistry is somewhat limited but I have a question pertaining to an project I'm working on. My question is: If you were to spill heavy D20 on some sort of cotton garment, would it permeate through to the other side at a faster or slower rate than normal water? If faster, approximately how much? Any answers appreciated. -bangbang
|
[
"As far as I know, wetting is related to surface tension and surface energy. I can't imagine that D2O acts that differently than regular water, and they have very similar surface tensions (~72mN/m). I would guess that the difference would be very small. The viscosities are different by a perceptible amount (~0.25 mPa*s) but I don't know if it would have an effect or not."
] |
[
"Alright now for the second part of my loaded question:",
"What would you have to do to water to get it to permeate through materials faster? even an educated guess is good.",
"edit* I should also mention that this substance would not be a corrosive or otherwise harmful to humans",
"-bangbang "
] |
[
"What are you trying to achieve? A little explanation would help a lot. If you're simply trying to filter it with a 'garment' you won't be able to isolate any significant amount."
] |
[
"Could it be possible for a species to have one sapient sex and one non-sapient sex (e.g. the Kzin)?"
] |
[
false
] |
Larry Niven writes some pretty fantastic aliens, including the not-just-your-everyday-cat-alien Kzinti. In his stories, the Kzin evolved with both sexes of equal intelligence, but after a very long time with serious eugenics (controlled breeding), the females were reduced to being of merely animal intelligence, while the males were of human-normal intelligence. I've come across this idea a couple of times since then in different SF contexts, of species with different average intelligence across the sexes (most recently in Bank's 'The Player of Games', where males and females have both been bred to be dumber than apices). Is this at all possible? Or would breeding for stupider members of the species necessarily dumb down all members of the species, regardless of sex?
|
[
"I don't see why not. There are lots of species that exhibit extreme ",
"sexual dimorphism",
", or where one sex is radically different than the other.",
"edit: in a totally unrelated note, after reading the article, TIL that there is a evolutionary biology theory called the ",
"sexy son hypothesis"
] |
[
"I've always thought that anglerfish were particularly interesting for this reason."
] |
[
"I read about a species of worm where the females are worms and the males are microscopic bugs inside them."
] |
[
"I drank a lot last night and went to sleep at about 11. At 8 this morning, I wake up and still feel drunk for about another hour. Surely I've processed the alcohol in this time and shouldn't feel drunk anymore. Whats going on?"
] |
[
false
] | null |
[
"How much is \"a lot\"?",
"And over what period of time?"
] |
[
"There was probably still alcohol in your system. I went to driving school years ago and the cop said that they have given a lot of DUIs in the morning when people were on their way to work. "
] |
[
"James May explains much better than I can:\n",
"http://www.viddler.com/v/eee6aa08",
"Probably best not to drive if you feel incapacitated in any way."
] |
[
"What causes sudden unilateral deafness?"
] |
[
false
] |
So I'm kinda of depressed that it's been almost 1.5 years since I woke up deaf in my right ear on January 2, 2010 and I just can't get this off my mind. What happened to my right ear? Why did it suddenly stop working? I just woke up one day and I wasn't able to hear anything from my right ear. I had tinnitus, which I still have till this day, and nothing else really. On the second day, for about an hour or so, I felt light headed and dizzy, but it went away very quickly. I've been to 4 or 5 ENTs (I've been to so many that I can't keep track of them) and they have all told me that they do not know the reason behind my sudden deafness. Here's something that I noticed: Whenever I get a blow to the head, there's this really high pitched noise that sort of explodes in my right ear followed by dizziness. My tinnitus varies in terms of loudness and tone. Furthermore, I occasionally experience clicking noises; they last less than a minute. When I'm tired (sleepy) and I move my head in a fast manner, I hear a loud noise I think this is the most interesting one: uncommonly, for about a millisecond or so, I am able to hear in my right ear, perfectly. Do any of my symptoms match a known cause for sudden unilateral deafness or am I to go on for the rest of my life not knowing what happened to my right ear?
|
[
"The ENTs where I work will tell you: it's idiopathic, meaning they have no clue. (As one guy says, \"it means we [doctors] are idiots, and we don't know!\"). There will probably never be a way to understand your specific case, but there are many possible explanations. Could be viral, could be inflammation, could be a change in blood supply, etc. You say you've been to the ENTs -- did they do scans or other tests to rule out neuromas? "
] |
[
"Yes, I got an MRI scan. Nothing showed up."
] |
[
"By co-incidence I just read this over on the BBC yesterday. ",
"Single Sided Deafness",
"."
] |
[
"Can the start codon be found in a non-codon triplet? Then can you start the codon sequence?"
] |
[
false
] |
Let's say that there is an mRNA strand that is like this: GAUUGACGAGAUGGUUGCCCAGU.... The start codon (AUG) is obviously there, but it is not in the codon triplet. GAU|UGA|CGA|GAU|GGU|UCC|CAG|U. My question is can you read the mRNA until the start codon and then create the codon triplets after? EX: GAUUGACGAG|AUG|GUU|CCC|AGU. Or do the triplets have to start at the beginning of the mRNA strand?
|
[
"The codon 'triplet' starts with the start codon. It does not matter how many bases are before it because the mRNA does not start getting translated until a start codon is reached. Therefore your second example is correct; however, to clarify, the mRNA is not being \"read,\" as you put it before the AUG - it is simply being threaded through the ribosome, the AUG starts the reading frame."
] |
[
"Another thing people are forgetting is that there is a lot that comes before the start codon on a mRNA. To start translation, you need more than just a start site, you also need the upstream sections for the various parts of the translation machinery to sit on to start the process. I'd suggest checking out the ",
"wikipedia",
") page on translation, and if you've still got more questions after that, come back and ask them! It took me a long time to realize that transcription and translation weren't quite as simple as it's presented in general biology, and really, knowing some of those details makes it make a lot more sense (at least to me)."
] |
[
"Yes. The portion before the start codon is the 5' untranslated region. The reading frame is defined by the start codon, not the first base in the sequence."
] |
[
"Why do human beings only have one set of teeth their entire lives, while other species such as sharks have the ability to regrow their teeth?"
] |
[
false
] |
Also, with genetic engineering and future medical advancements, is it possible that human beings could ever obtain this ability? Edit: I should have specified in the title that I meant the teeth we keep our entire adult lives after deciduous teeth. Sorry about that.
|
[
"I received two sets..."
] |
[
"Although it is quite rare there are cases about some humans having 3 or even 4 sets of teeth, but they're usually complicated. Humans don't really need more than 2 sets, our diet is relatively soft(we aren't chewing through bone or hard cartilage like a shark.) Some rodents have front teeth that never stop growing to chew through dirt/roots. Hope this answers your question."
] |
[
"Continuously growing new teeth (polyphydontia) is the ancestral state for vertebrates, and most non-mammalian vertebrates continuously replace their teeth throughout their lifespan. Mammals have exchanged this method for only two batches of tooth growth, and with good reason. Mammal teeth are highly specialized and intricately shaped...just look at a molar, and compare it to an incisor or a canine. They are very versatile and allow mammals to handle a wide variety of food types...there aren't many non-mammals who gnaw, for instance. And mammal molars are better for chewing and grinding than dentition in most other animals. However, all this specialization comes at a price...for the teeth to work properly, they have to be positioned just right. Continuously growing teeth can't be placed precisely, because they are constantly growing into position and falling out, and generally pushing each other around. This doesn't matter for other vertebrates, because their teeth are unspecialized and generally similar, and are used more for grabbing and holding food than chewing it. "
] |
[
"Can you Daisy chain vacuum pumps and compressors?"
] |
[
false
] |
This just something I was curious about; no particular application. Let's say you had access to many weak vacuum pumps, but no high performance pumps. Each pump really just represents a step in relative pressure, right? So if you ported the exhaust of one right into the inlet of the next could you effectively reach a much lower ultimate vacuum? Or vice versa with several weak compressors, reach a much higher pressure (if nothing explodes)? Is there a physics issue I'm overlooking?
|
[
"Pumps only operate on relative pressure in the viscous or transitional flow regime, which will get you down to a medium vacuum (~10 mTorr at best). I’m not sure if putting several pumps together in series in this situation would increase the effectiveness. However, if you want a high vacuum then it doesn’t matter how many pumps you put together if you just use roughing pumps. At very low pressures the gas enters the molecular flow regime where molecules mostly just bounce around on their own without interacting, so you can’t use a pump that “sucks” on the gas, you need to use a pump that traps any molecules that happen to fly into it like a turbomolecular or cryogenic pump. At this point the main limits on how good of a vacuum you can get are how long you’re willing to wait and how well you can eliminate leaks."
] |
[
"What you are talking about is essentially multistaging pumps/compressors. A thing to remember is that if they are poor pumps they will still perform poorly. You may be able to multistage them and get a lower pressure but it will work very inefficiently."
] |
[
"Multistage pumps are a thing because a lot of designs have a max practical pressure ratio they can achieve. Piston pumps and axial flow compressors have this problem. Part of the problem is as the pressure ratio goes up the flow rate goes down.",
"For high vacuum work multiple types of pumps are used to get to progressively lower pressures. Far as I understand molecular pumps won't work without being backed up by a roughing pump."
] |
[
"How much of Antarctica is actual land mass?"
] |
[
false
] |
[deleted]
|
[
"Here's a topological map of the bedrock."
] |
[
"See the legend on the side. Only the green, yellow and orange parts are above sea level. I couldn't find a percentage, but looking at the map it looks to me like very roughly half is below sea level.",
"However, that doesn't mean that the blue parts would necessarily all be underwater if the ice caps were to suddenly melt. Melting the ice caps would cause the sea level to rise by about 200 feet, so initially slightly more of the continent (some of the dark green parts) would be under water. But then over time the land would rise, as the weight of the ice is no longer pressing it down. The continent would rise about 1500 feet (more in some parts, less in others) so that maybe half of the light blue areas would end up above sea level."
] |
[
"Thanks, I guess that would have been a good place to start. I have basically zero experience with the subject and I'm not exactly sure what to do with what I'm looking at here. Care to give a rough estimate on square miles or a percentage of its total mass?"
] |
[
"Why is bacterial meningitis so deadly?"
] |
[
false
] |
I read that even up to 20% of people are carriers of this deadly bacteria. Can you ever be really sure that you or someone else you know got it before it is too late?
|
[
"A: bacterial meningitis is an umbrella term that describes any bacterial infection of the meninges.",
"B: Infections generally occur when bacteria grow in places they generally don't grow or over-grow the other bacteria in a site and are able to achieve toxic levels in that fashion.",
"C: You can't be entirely sure that you, or anyone else, for that matter isn't colonized with bacteria that could cause meningitis however you can, and should, be vaccinated against the age appropriate organisms"
] |
[
"Meningitis",
" is an acute inflamation of the protective membrane that covers the brain and spinal cord. This can result in brain swelling. The infection can also trigger sepsis, which can result in low blood pressure and excess clotting that can obstruct blood flow to the organs, and result in gangrene in the extremities.",
"I had a friend that got meningitis when she was a teenager, and she lost both her legs at the knee from the gangrene."
] |
[
"First on why:",
"Meningitis can be caused by different bacteria. The most well known are Neisseria menigitidis and Streptococcus pneumoniae. Both are opportunistic pathogens that are commonly found in the upper respiratory tracts, but can turn deadly if given the chance (hence a lot of people being carriers). Most people will not get anything more than bacterial cold symptoms even if they do become virulent, but menigitis is an exception that happens when they reach the meninges.",
"Meningitis is dangerous for two reasons. First, it is often a downstream infection from a larger problem such as sepsis. To be simple, once the bacteria reach the bloodstream, all bets are off. The immune response will happen throughout the patient's body and will be so violent that it will damage the patient as well in the process. Also, the pathogens have now gained access to blood, which is very rich in nutrients - especially limiting ones like iron.",
"The second reason is that, even if meningitis has skipped sepsis (which is possible), the immune response to what goes on inside the blood-brain barrier can be either quirky or limited. This barrier limits the entry of immunity-related molecules into the central nervous system, much less immune cells. Once bacteria are inside the cerebrospinal fluid, the resident immune cells there are easily overwhelmed, and in the absence of defence system, they can multiply within hours. Immune cells in the blood will try to enter this region, but in doing so, will compromise the blood-brain barrier. To finish it off, the bacteria often release endotoxins that initially make things worse as they are killed. So now you have a delayed raging reaction in the otherwise sterile and unprotected environment with disrupted homeostasis. Brain cells are generally delicate, and are bound to suffer, hence the deadliness.",
"Now for a quick detection of the disease:",
"The most obvious symptom is stiff neck accompanied by very high fever developing in less than two hours. Either can commonly happen in a normal situation, but both happening at the same time is rare. If this happens, calling emergency will be necessary to treat it before it is too late - unlike lesser bacterial infections, meningitis can kill in less than a day.",
"Having said that, the chances of an average first-world person encountering a meningitis-infected patient is low. It is not the kind of disease you need to be mindful of on a regular basis."
] |
[
"Do changes in the Earth's rotation influence earthquakes?"
] |
[
false
] |
This article claims that changes in the earth's rotation contribute to more earthquakes: On the surface this seems like junk science, but I'm not really qualified to say for sure. Can anyone clarify? If so, are there any ideas as to how this works?
|
[
"The link between the Earth's rotation and the number of big earthquakes was unclear,",
"Beyond the clickbait, there's your needle in the haystack. The Earth's rotation has been declining progressively since its formation due to the persistent influence of the tides, the wind, and the Moon. That is a glacially slow process involving more than 4 billion years. That is the scale of geological time involved. According to the scant details in the article, the research only looks at seismic events since 1900. That is less than the blink of an eye in the proper context. Paint me skeptical."
] |
[
"The Earth doesn't rotate at constant speed. Each day has a different duration depending on multiple factors. Here's the official site, and a table of average lenght of day (LOD) per year, since 1623. Before 1955 those figures were estimates; since 1955 the data come from atomic clocks:",
"https://www.iers.org/IERS/EN/Science/EarthRotation/LODsince1623.html?nn=12932",
"The US Geological Survey has a complete database of earthquakes. It's possible to build and download customized tables of earthquakes according to magnitude, location, and date:",
"https://earthquake.usgs.gov/earthquakes/browse/",
"Bilham and Bendick authored a paper: \"Do weak global stresses synchronize earthquakes?\" which was published by the Geophysical Research Letters, August 2017:",
"http://onlinelibrary.wiley.com/doi/10.1002/2017GL074934/abstract",
"Here's the abstract of Bilham's presentation at the GSA Annual meeting, October 2017:",
"https://gsa.confex.com/gsa/2017AM/webprogram/Paper300667.html",
"At the GSA presentation, as well as in several interviews with the meedia, Bilham claims:\n1) Increases in the annual number of strong earthquakes (maginute 7 or more) coincide with a slowing down in the rotation velocity of the Earth;\n2) Periods of high seismicity are preceded by deceleration episodes by 5-6 years.\n3) In periods of high seismicity, there are between 25 to 30 intense earthquakes a year; the rest of the time the average figure is around 15.\n4) The Earth is currently in a deceleration episode that began in 2011; therefore a period of high global seismicity of at least five years is expected.",
"By plotting the data obtained from IERS and USGS, we can test his assertions. What do we get?\n1) Nothing. No correlation at all.\n2) Nothing. No such thing.\n3) From 1900 to 2016, the average number of major earthquakes in a year was 11.4, and the maximum was 24.\n4) There was no deceleration episode that began in 2011.",
"Conclusions:",
"In their original paper, Bilham and Bendick were very cautious about their methods and findings. They even presented it as a question: \"Do weak global stresses synchronize earthquakes?\". In her webpage, Prof. Bendick acknowledges: \"I am working on temporal patterns in the global earthquake catalog, especially ones suggestive of earthquake cycle synchronization and entrainment. This is brand-new work, and we have lots to do on it!\".",
"http://hs.umt.edu/geosciences/faculty/bendick/research/subduction.php",
"On the other hand, Prof. Bilham has completely distorted the original paper's methods and findings, makes countless mistakes, and speaks in terms of absolute certainty. His assertions don't pass a basic test of scientific rigor. And his tone confims what his colleagues in India said of him: \"He's kind of a scaremonger\".",
"This is a terrible disservice to science and society.",
"All credit to 'tropic2's' comment on an ",
"article",
" reporting the same thing in The Guardian."
] |
[
"Yes, I missed that sentence, but that's what I thought, that the rotation slowing was a steady, extremely slow process."
] |
[
"Ask Anything Wednesday - Biology, Chemistry, Neuroscience, Medicine, Psychology"
] |
[
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!
|
[
"Is it safe to eat a pet that has been euthanized? I thought about that when a friend said they had to put down their kids' pet rabbit, and obviously that was not the time to make a joke, but still, I'm curious."
] |
[
"It is not. For many reasons actually.",
"1st: think about why we euthanize animals. Normally it's because of an illness or severe injury. If it's ill that in of itself can be cause for not wanting to consume it. However, you need to also think of the state of the body. Was there organ failure that may have released toxins into the blood stream? Is it septic (infection in the blood)? What drugs was it on before euthanasia? All of these are good reasons to not consume the body",
"2nd: Euthanasia drugs can be pretty nasty to ingest. Most euthansias are done IV with a phenobarbital sodium solution that stops the heart. This is toxic to ingest. The brand my clinic uses can kill you in as few as 2-3 grams. (Euthasol if you want to look up the data sheet) Many of the animals are also sedated first, that sedation can be toxic. ",
"Euthanized animals can actually be an environmental hazard as well, especially larger animals that have a high concentration of euthanasia drugs.",
"Source: veterinary assistant/pre-veterinary degree",
"Edit: I will say, there are probably cases where non-drug euthanasia was performed (bolt guns ect) on a mostly healthy animal I.E a horse that had just broken a leg that would probably be safe to eat barring any issues with the meat. But I would still stick to eat regulated butchered meat!"
] |
[
"Why do my antidepressants (mirtazapine) make me sooooooo tired?"
] |
[
"Are blood types linked to Genetics?"
] |
[
false
] | null |
[
"Hi penneewize 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.",
" ",
" "
] |
[
"Human body / biology"
] |
[
"Human biology"
] |
[
"Is there any truth to the fact that fast food is cheaper than healthy eating?"
] |
[
false
] | null |
[
"Fast food is not cheaper. It is easier, tasty and relatively low cost (this is not to imply healthy).",
"If you are a savvy shopper that pays attention to food costs and buy your own food and prepare your own food you can eat for less money than fast food costs.",
"This requires time and effort though and the price difference is not dramatic so fast food is an attractive alternative. You can cut coupons and spend time comparing prices in store and then lug it all home and spend time preparing the food and cleaning dishes or you can buy McDonald's food and spend a tiny fraction of the effort to acquire your food.",
"There is little doubt you are better off preparing your own meals but it is a lot more work (can be satisfying work as I see it but still more work).",
"If you include ",
"opportunity cost",
" it may be argued fast food is ultimately cheaper."
] |
[
"I agree with a lot of what you said, but I don't think you can factor in opportunity cost. This implies that you could be earning a wage in that time. Although we can attach value to leisure time, if we are looking at actual dollars spent as the main driver, then home cooked is the clear winner"
] |
[
"That assumes that we are talking about leisure time. There are people who work multiple jobs and essentially have very little time for activities other than working and sleeping. For these people, the opportunity cost of spending the time to plan meals and shop rather than simply buying fast food after working a double shift, for example, is very real."
] |
[
"Center of population math question: globe vs map"
] |
[
false
] |
Let's say you calculate the center of population (the point at which the total distance traveled by everyone is minimized) on a map, and find it to be somewhere near Bangladesh. Then, you calculate the center of population for the three dimensional Earth, and find it to be somewhere near the center of Earth's core, maybe up towards where Asia would be on the surface. My question is, is the center of population of the globe directly below the center of population of the map? To put it another way, if you draw a line segment between the two dimensional center and the geometrical center of the Earth, will the three dimensional center of population fall on that line segment? If the answer is yes, can this be proven? If the answer is no, but not always, can you show me the simplest example where the points do not line up?
|
[
"Assuming you are measuring distances on the surface of a globe when you say \"on a map\", the answer is no, even when the center of population is defined.",
"Consider the case of only three people on the Earth: one lives at the North pole, and the other two are at (0,0), the intersection of the equator and the prime meridian. On a globe, the center of population is 30 degrees north of the two people (one-third of the way along the angle between them). In three dimensions, the center is one-third of the way along a line segment joining them. These points do not line up in the way you suggest. See this ",
"Sketchpad diagram",
". We only have to consider a great circle rather than the entire globe in this example."
] |
[
"The answer is no. Imagine that the entire population of the Earth lived only in three places: ",
"In this case, your 3-D center is clearly going to located near the center of the Earth, but it'll be very slightly closer to the giant city in Argentina, and nearly directly beneath it. (The point on the Earth's surface above the 3-D center will be slightly to the north of the city in Argentina because of the hermit in Paraguay.) But your 2-D center will be somewhere very, very far from South America -- it'll be nearly between the two cities on a ",
"great circle",
" segment from one to the other that passes through the hermit's hut in Paraguay. ",
"If my calculations are correct",
", this puts the 2-D center in Europe, somewhere around France.",
"So, there's your counterexample. The points definitely don't line up, because France isn't in Argentina and there's a hermit in Paraguay."
] |
[
"Excellent answer. Thanks."
] |
[
"How do white blood cells attack a virus? Why does it take 3+ days to feel better after getting sick?"
] |
[
false
] | null |
[
"You mention viruses in the title and bacteria in the body of the post. They're very different. The common cold is not bacterial. Can you please clarify your question?"
] |
[
"That would be due to ignorance. Okay I'll delete and report when I understand what I'm asking better"
] |
[
"The post was never out on the sub, so you don't need to delete it. Let us know if we can help. People make this mistake a lot, which is why I mentioned it. Otherwise that's what most of the comments you get will say."
] |
[
"Is there any evidence that paleolithic humans were vegetarians or carnivores?"
] |
[
false
] |
[deleted]
|
[
"I'm no biologist but doesn't the fact that we have canines, incisors and molars tip you to the fact that maybe our ancestors were omnivorous?"
] |
[
"We had a long discussion about this a while ago: ",
"http://www.reddit.com/r/askscience/comments/hbkjx/question_for_the_historic_cooking_scientist_as/"
] |
[
"There's some interesting archaeological stuff in The Starch Solution video here: ",
"http://www.youtube.com/watch?v=4XVf36nwraw"
] |
[
"If I put a fan over my vent, will it circulate more heat into my room?"
] |
[
false
] | null |
[
"\"If the incoming air temperature from the vent is colder than your skin-body temperature, causing more air to circulate the room will amount to convective cooling. You'll lose heat faster and feel more cold.\"",
"This is only true if you're standing right under the vent. If the air is directed away from the occupants, the air only has to be hotter than room temperature to heat the room, so increasing the airflow will increase the heat to the room. However, there is an upper limit of how much air you can move through the space before the convective effects you describe take over."
] |
[
"If the incoming air temperature from the vent is colder than your skin-body temperature, causing more air to circulate the room will amount to convective cooling. You'll lose heat faster and feel more cold.",
"If the incoming air temperature is hotter, it'll help as heat is being transferred to you and at a faster rate. All of this is about mixing the air better in the room.",
"Generally vents already operate off a pressure difference to move the air into your room. The drop in pressure your fan with induce will be minimal. So you won't get any more hot air, but you might be able to make it more well mixed."
] |
[
"The problem is that fan blades are designed to work over a very small pressure change. Take your fan and partially block the inlet. Notice how it starts spinning faster? That's because it's not doing anything.",
"What you want is a blower fan. Like this. ",
"http://www.amazon.com/Lasko-Pro-Performance-Blower-4900/dp/B001DNGSCM/ref=sr_1_1?ie=UTF8&qid=1351341641&sr=8-1&keywords=blower+fan",
"These work much better across a change in pressure and are usually the type of fan you will find in most home HVAC systems."
] |
[
"Would a liquid-filled cockpit lessen inertia? (I'm thinking spacecraft specifically, not airplane)"
] |
[
false
] | null |
[
"'Physics'"
] |
[
"'Physics'"
] |
[
"'Physics'"
] |
[
"Would a Big Crunch reverse entropy?"
] |
[
false
] | null |
[
"This is a doozy of a question, and I think it's going to depend on the nature of the contraction.",
"One model that permits a big crunch begins by reversing the arrow of time, so the universe basically runs backwards from its present state with steadily decreasing entropy until some initial singularity is reached. Basically, the universe reverts (or evolves?) to the uniformity from its early history. This was ",
"discussed by Hawking",
", and while it's interesting it's important to remember that it is speculative and certainly not a mainstream idea. ",
"On the other hand, if the contraction is ergodic (you can take that to mean that matter in the universe just evolves 'normally' while the universe contracts), then I expect that entropy will continue to increase for a time. However, as this universe gets ",
" it will get both clumpier and hotter, until all that's left is black holes and eventually a lone singularity. I expect that the 2nd law of thermodynamics would be violated in this case as well, but it's hard to say exactly when or how. ",
"Speculations about the end (and beginning) of the universe are a dime a dozen, so don't worry too much on this. "
] |
[
"Actually, black holes are in a state of maximum entropy, so the 2nd law doesn't have to be broken if the whole universe collapses to a black hole."
] |
[
"That's because the black hole absorbs more background radiation than hawkings lets out. If there's no background to absorb,"
] |
[
"Is there any way a Non-Scientist can contribute to /AskScience?"
] |
[
false
] | null |
[
"If you find a question thats very interesting, do some research about it. Simple googling and a few tens of minutes can get answers to almost every question asked here in layman terms. Post what you found, with the links where you read them! There's no such thing as a \"non-scientist\", just people who have read stuff for too long and people who haven't :)"
] |
[
"Link reposted questions to well-answered threads on the same question.",
"Report inappropriate posts."
] |
[
"You could give back by asking interesting questions that haven't been answered before. The experts here are awesome about answering questions that are both legitimate and scientifically interesting, or questions that can help clear up common misconceptions. Try it out."
] |
[
"Us Japan the first to land a \"rover\" on an asteroid?"
] |
[
false
] | null |
[
"Hi PurpleMonkeyElephant 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.",
" ",
" "
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"Rosetta",
"You can find the basic answer with a google / wiki search. Please start there and come back with a more specific question.",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"By the way, feel free to post open-ended question like these in ",
"/r/AskScienceDiscussion",
"!"
] |
[
"A stupid question that I will never apologise for. Is the space in-between Earth and the Sun hot?"
] |
[
false
] |
Right - as far as I understand, heat radiates from the sun, contacts our atmosphere and is filtered by the ozone layer. Going by the planetary order, Mercury -> Pluto is essentially hot -> cold. This seems to indicate that the radiation either loses effectiveness or dissipates over a distance - probably due to contact with space crap. Surely then, the closer to the Sun we get, the warmer it becomes? Is Space* actually hot, rather than cold? *at least the bit 'near' a star.
|
[
"This turns out not to be a stupid question at all, because it gets to the heart of what temperature is.",
"The space between the earth and the sun does not have a well defined temperature because it is not in equilibrium. There's lots of stuff carrying energy in the solar system:",
"There's lots of stuff there, but it just doesn't interact frequently enough to come to an equilibrium. ",
"The question you are asking should really be stated as \"at what temperature would an astronaut (or something else) equilibrate when orbiting the earth?\" depends on a lot of different factors. By far the most important of that list is radiation from the sun, including visible light, UV, and infrared. It's quite hard to calculate what temperature the astronaut would equilibrate at, but it would vary widely with a number of factors:",
"Now, let's take a look at the Wikipedia article on the ",
"Space Suit",
". It says that the space suit can withstand temperatures from -156 °C to +121 °C, so presumably a human in earth orbit is subjected to a range of temperatures inside that range with extra tolerances on either side.",
"A lot of people will tell you that the temperature of space is 4 Kelvin, the temperature of the cosmic microwave background. That's just wrong. There just isn't a place in the universe that it's equilibrium with the CMB (anymore) because of starlight or cosmic rays or the intersteller/intergalactic/intracluster medium."
] |
[
"This is just wrong. Space is neither cold nor hot since it is not in equilibrium. It does not have a well defined temperature."
] |
[
"Layman here. Great post! I remember last year my Physics professor said space was 4 Kelvin. Can you explain how the 4 Kelvin even came up in the first place?"
] |
[
"Why didn't I get nauseous as a child/teen as opposed to now ?"
] |
[
false
] | null |
[
"Hi, I like your question, but we are trying to limit questions that are asked referring directly to the OP, especially when it could be considered medical. Would you mind rephrasing your question to something like \"Why does motion sickness tend to increase with age?\" rather than \"Why do I experience more motion sickness as I get older\"? Also, if your question gets caught in the spam filter again and you don't see it in the new queue after a few minutes shoot us a mod mail and we'll let it out. Thanks!"
] |
[
"I initially didn't want to say \"why does it tend to\" because I've asked a couple of friends around and it seems like I'm the only one with that problem.",
"I guess I could just operate under the assumption and rephrase my question, thanks for the suggestion!"
] |
[
"Well that's exactly why we try not to let questions with \"I\" through. What you experience may be unique to you, in which case there would not be enough information to answer it properly and it would essentially be diagnosing a medical problem. ",
"I unfortunately have the same problem, so I did a bit of googling just to confirm it wasn't just some rare disorder. I can tell you now that it does happen to maybe 20% of people, but I'm still not sure why. ",
"Thanks for understanding!"
] |
[
"Can an individual actually \"fight to live\" or \"give up and die\"?"
] |
[
false
] |
[deleted]
|
[
"Research seems to indicate that willpower or despair does not significantly affect mortality.",
"Hospital nurses (me included) can give you lots of anecdotal evidence. We like to tell stories about patients who, on being told they had a terminal illness, apparently \"gave up\" and died before the illness seemed severe enough to be fatal. However we also have stories of people who had great attitudes, were bound and determined to beat the illness, and died early anyway. So anecdotes, including the Frankl one you quoted, are not much help.",
"There is some correlation between depression and poor outcomes, but it may be that the depressed patients are those who are sicker to begin with. That is, more serious illness may cause depression, rather than the other way around."
] |
[
"Do you have a citation for that first sentence?"
] |
[
"I suppose it would be more strictly accurate to say that research has not been able to show a correlation. It would be very hard to prove there is definitely no link.",
"Here's an article that reviews prior studies: ",
"http://www.ncbi.nlm.nih.gov/pubmed/15184701",
"Since we can't measure willpower and determination objectively, studies tend to look at the timing of deaths, comparing them to holidays and birthdays and other significant dates. The idea is to see whether the motivation to stay alive \"just until Christmas,\" or some other significant date, has any effect. There's no good evidence that it does."
] |
[
"Besides ice, what mineral has the highest percentage of oxygen by weight?"
] |
[
false
] |
I'm also curious to know which minerals have the highest percentages of other elements. So if anyone knows a good method/website/book, I'd love to hear about it.
|
[
"Interesting question; I never had a reason to think about this before. I don't know the answer, but it would have to be an aluminum- or silicon-bearing oxide or hydroxide. I did some quick calculations and the best candidate I could come up with is Gibbsite:",
"Gibbsite, Al(OH)3: 61.6%",
"Diaspore, AlO(OH): 53.3%",
"Quartz, SiO2: 53.3%",
"Corundum, Al2O3: 47.1%",
"There are a few things to keep in mind. First, ice is technically not a mineral; one criterion for calling something a mineral is that it must be solid at room temperature. Second, opal may beat out any of these contenders because it contains up to 21% water, but it's also not a true mineral because it lacks a longe-range atomic structure."
] |
[
"A great start-\nAs for \"ice,\" I have heard that this would considered an mineral if it is naturally formed. Which definition do you follow for \"mineral?\" I have not heard \"solid at room temperature\" before, though it makes a lot of sense.\nThanks again----"
] |
[
"Offhand I'd have to go with crystalline boric acid (mineral: sassolite, H3BO3). Helium doesn't bond, Li2O and BeO have lower ratios. After boron, you have to go down another row in the periodic table before you get to any oxides with four oxygen atoms, and it's not enough to offset the higher mass. Hydrogen is obviously the lightest counterion possible. So it seems right to me.",
"My arithmetic says 77% oxygen by weight."
] |
[
"Is pedophilia observed in nature?"
] |
[
false
] |
[deleted]
|
[
"The interesting point is that animals mate when they are physically ready to. Humans can start having children at a pretty young age (I think the earliest for girls is 9 and men are 12). The fact that we consider those ages to be too young for reproduction is based on mental abilities rather than being physically able to. As far as I know, I do not know of any animals that would have sex with one of its own species that was not old enough to be capable of reproducing. If there are, I'm on the same boat as you are in terms of curiosity. "
] |
[
"According to this article",
", both same-sex and adult-immature dyads engage in about as much general sexual activity as heterosexual adult dyads among bonobos and capuchins. And from other things I've read, it seems that only inter-family relationships occur less frequently among bonobos."
] |
[
"Pedophilia is not a willingness to mate with pubescent or postpubescent juveniles, it's a specific attraction to prepubescent (around 8 and below) juveniles. ",
"And if you are going to use this argument: ",
"Pedophilia might show up in animals based on selecting the most 'fit' mate which would naturally select for younger mates.",
"I'd like to see some citations, because I can just as easily tell you that animals do not attempt to reproduce with sexually immature mates because it would be impossible.",
"Also going to address this: ",
"Animals love to have sex and definitely don't care about age or even sometimes species.",
"Most animals have sex solely for the purpose of reproduction, age is ",
" a factor in reproduction because age determines sexual maturity, and when animals attempt to mate outside of their species it is not because of attraction but because they feel a need to mate, period."
] |
[
"How can something smolder without air? Is this a misconception, or is smoldering not a combustion reaction?"
] |
[
false
] |
I've always understood that oxygen was needed for combustion. I'm also under the impression that smoldering is a slow burn without a flame. So how is it possible for an underground fire to smolders indefinitely "without air". Further, in the process of making charcoal I was told that the wood is forced to smolder "without air". Something just doesn't seem right about this.
|
[
"\"Without air\" does not mean \"in a vacuum\". There is still a little bit of oxygen left. But since there isn't too much oxygen, whatever you are burning is undergoing ",
" combustion. These smouldering fires are very smokey because there isn't enough oxygen to convert all the carbon into carbon dioxide. You'll end up with lots of carbon-rich soot."
] |
[
"Thanks for the start, I'll build on your answer. Wood itself contains a lot of cellulose fibers. The molecular structure of these fibers consists of very long chains of glucose molecules linked together.",
"Each glucose molecule contains carbon, oxygen, and hydrogen. When you apply heat, you break up the molecular bonds that hold these atoms together. Under the correct conditions, the oxygen and hydrogen will recombine to make water, leaving the carbon behind. The result is charcoal.",
"If you heat the wood in an environment that has too much oxygen, you will start to convert a larger fraction of the carbon into carbon monoxide, and carbon dioxide. Both of these are gases and will escape. In any case, the essential idea of heating is to drive away the water, leaving the carbon behind. At the same time, you want to minimize the production of CO and CO2 so you'll have as much carbon left over as possible to form your charcoal bricks.",
"There is also ",
"destructive distillation",
" -- this is a kind of non-specific decomposition reaction in which you take an organic material and apply heat so that the larger molecules that make it up are converted into smaller molecules."
] |
[
"Particularly secondary organic carbonaceous aerosol, or brown carbon."
] |
[
"Today a yellow jacket landed on me and squirted some clear liquid on my coat. What was it?"
] |
[
false
] |
It was a lot of liquid. It landed, squirted it, then it flew away.
|
[
"Question: did the liquid have a smell to it? Bees, hornets, wasps, etc. excrete ",
"various pheromones",
" to communicate, and some of them have noted smells to them. My uncle works as a bee buster on the side, and he has had several incidents where fleets of hornets have sprayed so much alarm pheromone on and around him it was almost choaking him."
] |
[
"I had a bunch of ants get into my house several years back--they were swarming and many of them had wings. I recall that whenever I would squish one it had a ",
" strong odor to it. Is this a similar situation to what you described? Probably not alarm pheromone, but perhaps a pheromone related to the swarming behavior?"
] |
[
"It most definitely was some kind of pheromone. For exactly what I can not say. Nearly all insects use them. Ants in particular, and they have some of the most complex systems for it. ",
"The reason you could smell it, is some pheromones are rather small organic molecules which vaporize easily. There's simply more of it airborne to smell. Pheromones (alarm usually being one of them) that vaporize easily do so to if that signal needs to reach other insects quickly and strongly. Such as an ant dying (that's very bad for ants, and other ants need to know that fast).",
"Someone who studies entomology will likely be better suited for answering (I don't want to give mis-information). My knowledge on these matters is limited to what I have learned with natural product chemistry."
] |
[
"When I sleep with my contacts in, why are they dry when I wake up?"
] |
[
false
] | null |
[
"You got it almost right, except for the whole \"get behind the contacts\" thing. The more important part is keeping the contacts themselves wet. ",
"Tears need to lubricate whatever surfaces the eyelid is contacting, whether it's the eye itself (if you're not wearing contacts) or the contact lens. This ensures smooth movement of the eyelid during blinking. The wetness also allows oxygen from the air to diffuse through the lens and into the eye."
] |
[
"The act of blinking physically forces the tears behind the contacts. While sleeping, you stop blinking and thus no water can get behind the contact."
] |
[
"Thanks!"
] |
[
"What's currently the oldest living creature?"
] |
[
false
] | null |
[
"Depends on what you consider alive. There have been bacterial spores trapped in amber that were viable after 40 million years.",
"If you mean \"alive but not currently in some kind of stasis\" then probably weird seafloor or permafrost bacteria (can live tens of thousands or even millions of years).",
"If you mean \"not currently in stasis and also something that I can see and relate to\" then probably a clonal population of plants or fungi. There's an 80,000 year old forest in Utah (although it is thought to be dying) and some seagrass in the Mediterranean that might be 200,00 years old.",
"Finally, if you mean \"creature, like a thing that ",
" stuff\" then it's probably an arctic mollusk, which can live upwards of 500 years."
] |
[
"I can only find a news article about a presentation at a conference, but it appears that the individual bacteria themselves are millions of years old and divide only once every 10,000 years. ",
"https://phys.org/news/2013-08-soil-beneath-ocean-harbor-bacteria.html"
] |
[
"I cant recall of theres anything older and you could maybe argue this is cheating, but pando is actually an entire forest and one organism at the same time. Every quaking aspen in this forest is a clone and theyre all cknnected to 1 root system that is 80000 years old. The roots themselves are whats so old. The forest can burn down but the roots will soawn new trees when it needs more nutrients.",
"https://en.m.wikipedia.org/wiki/Pando_(tree)"
] |
[
"Are there alternatives to MRIs to do brain scans?"
] |
[
false
] |
I read that Helium is an important component to doing an MRI scan, but apparently the price of Helium is going to skyrocket because the amount of Helium that is going to be readily available will decrease. Is there any other technology to do brain scans without having to do an MRI?
|
[
"Let me start by assuring you that while MRIs use a good bit of helium at startup, it's stored cryogenically and very, very little is lost over time. Rising helium costs are not going to significantly affect the cost of MRIs.",
"Even if helium was completely unavailable, high temperature superconductors could be used to make MRI that only need liquid nitrogen.",
"Now, that said, here's a list of methods for brain imaging:",
"\n",
"http://en.wikipedia.org/wiki/Neuroimaging#Brain_imaging_techniques"
] |
[
"Yes, atmospheric escape is the process by which helium is lost. The predicted rise in helium prices is due to the selling of helium reserves, and not because of some significant decrease in helium production."
] |
[
"Gotcha. For the record I don't know what he's referring to either."
] |
[
"If we could transport to a planet very far away instantly, couldn’t we see how the earth was created and how life started?"
] |
[
false
] | null |
[
"Sure."
] |
[
"Elaborate?"
] |
[
"Light reaching a point 1000 light years away would have left the source 1000 years ago."
] |
[
"What will happen to a piece of wood, placed in a \"pot\"with no oxygen and then placed over a fire?"
] |
[
false
] |
also the same question but what if the "pot" was pressurised?
|
[
"That's basically a way to make charcoal. By starving the wood of oxygen you allow the moisture and volatile compounds to be burned off leaving you with a mostly pure carbon. It's important that it has some kind of vent though because the steam and volatile compounds will pressurize the container."
] |
[
"That's basically a way to make charcoal. By starving the wood of oxygen you allow the moisture and volatile compounds to be burned off leaving you with a mostly pure carbon.",
"This is correct: in a closed vessel (pot) you would get pyrolysis (thermal decomposition), rather than combustion. If wood were pure ",
"cellulose",
", it would decompose fairly cleanly, to give off ",
"levoglucosan",
" and eliminate water until there was basically just carbon left. But wood is also ",
"15-40%",
" ",
"lignin",
": a very ill defined, complex, resin that does not decompose cleanly. So things are a little more complicated.",
"Pyrolysis of wood has a long history, as a way to make liquid fuels, and is also known as “dry distillation of wood.” In addition to charcoal, the products “include a distillate comprising gases and condensible liquids. The gaseous components include carbon dioxide, carbon monoxide, hydrogen, methane and ethylene. The liquids that condense are mainly methanol, acetic acid, acetone, formic acid, propionic aldehyde and propanoic acid. They also contain components that condense to form wood tar. These are phenol derivatives, such as: cresols, guaiacol, catechol, pyrogallol, xylenol, turpentine ingredients: carene, pinene, camphene, terpineol, limonene, bornyl acetate.”",
"M. Lewandowski & E. Milchert, Chemik, 85(12), 1301-1306 (2011)",
"This technology is still being actively investigated, more so now as a potential renewable fuel source, and there is a recent review:",
"D. Mohan, C. U. Pittman, Jr., & P. H. Steele, Energy Fuels, 20(3), 848–889 (2006)",
"The full article is behind a paywall, but I found a reasonable introduction to Wood Pyrolysis ",
"here",
"."
] |
[
"If the container can stand it, not much, but there could be some danger when you go to open the pot."
] |
[
"Are there any neutrons floating through the cosmos by themselves?"
] |
[
false
] |
A lonely proton, with a positive charge, would attract lonely electrons. This, my general chemistry classes have taught me, is why protons and electrons group together into atoms. But if we took a neutron out of an atom, and watched it, what would happen? What forces would act on it? Furthermore, could any of you explain the strong and weak nuclear forces, or link to articles that would help me gain a better understanding of them?
|
[
"Neutrons decay into a proton, an electron, and an antineutrino after about 11 minutes. They have to be bound to other particles to be stable."
] |
[
"*On average they decay after about 11 minutes. Some may decay in a millisecond, some may last millions of years. "
] |
[
"Sure, neutrons decay... but if a neutron is ejected into interstellar space somewhere in the Universe more than once every ten minutes (which seems reasonable), then the answer is yes, there are plenty of neutrons floating through the cosmos.",
"What would happen to such a neutron? It could roll neatly into a nucleus and be absorbed, though that's insanely unlikely if it's floating through space. So not a lot, until it decays.",
"The weak nuclear force is what causes the neutron to decay. (Force might not be the best word - whatever intuitive idea of force you might have, it isn't that.)",
"The strong nuclear force acts equally on protons and neutrons, but only over a range of less than one ten-thousandth of the radius of the smallest atom. (At a fundamental level it's even less intuitive than the weak force, but at least it has the decency to pull things together.)",
"If you want to take a first step towards the strong force, ",
"the liquid drop model",
" is a good place to start. "
] |
[
"Is this correct about mitosis and meiosis?"
] |
[
false
] |
[deleted]
|
[
"I don't understand how the haploid cells are supposed to under go meiosis to make more haploid cells",
"They don't - the only thing the haploid gametes can do to reproduce (at least in obligate diploids) is to pair up into diploid zygotes.",
"Is it when the egg meets the sperm and a diploid cell will form?",
"Yeah, that.",
"But if that's true then wouldn't there be a limited number of diploid cells to make haploid cells?",
"No, because once there's a single diploid zygote, it reproduces by mitosis to make more and more diploid cells till you have a big organism with trillions of them, and then only some of them undergo meiosis to make more haploid gametes. (Actually, for females that happens while you're still in mom's womb.)"
] |
[
"I think you have it down, but the way you phrased that makes me cautious. When a zygote is formed (the fusion of two haploid cells into a diploid cell) there is a new individual. In multicellular eukaryotes (like yourself) you get more cells and grow for mitosis. Meiosis is ",
"."
] |
[
"I think you have it down, but the way you phrased that makes me cautious. When a zygote is formed (the fusion of two haploid cells into a diploid cell) there is a new individual. In multicellular eukaryotes (like yourself) you get more cells and grow for mitosis. Meiosis is ",
"."
] |
[
"What is the chemistry in an animal's coat is responsible for it's color?"
] |
[
false
] |
I understand that an animal's color is due to evolution and their genes, but there must be some chemical interaction that produces the color, isn't there? So there must be different interactions for every shade and color. What is that chemical interactions in blue-jays, chameleons, or tigers that gives them their characteristic colors?
|
[
"The colour we perceive in an object is due to the molecule's ",
"absorption",
" spectrum. Depending on what wavelength of light the molecule preferentially absorbs, we'll see different colours. This phenomenon is less a \"chemical\" interaction than a \"physical\" one.",
"It's the same with fur colours. The animals produce different compounds in their fur or hair, with characteristic absorption spectra. In humans (and many animals), the main molecule responsible for hair (and skin) colour is ",
"melanin",
".",
"Of course, the production of these compounds is very much regulated by genetics (via protein expression) - and that's the bridge between chemistry and biology.",
"Edit: There ",
" chemical reactions that produce colour (and light) - ",
"bioluminescence",
" is light produced from chemical/biological interactions (such as in fireflies)."
] |
[
"To add to that, some colors we see are due to pigments, such as melanins in mammal fur, for instance, but some of the colors we see on animals, such as butterflies and some birds are actually due to the microscopic structure of the surface being oriented such that certain wavelengths of light are visible. This is part of the reason that these organisms are able to produce such a wide pallet of colors, and why these often appear iridescent. If you were to crush a feather from a cardinal, what you would have left over would be red, because the color comes from caratenoids, which are pigments; whereas if you were to crush the iridescent feathers from a hummingbird, the result would be a drably colored dust. Same goes for butterfly wings, if you pick up a butterfly you just end up with some grey dust on your fingers, no matter the color of the butterfly. "
] |
[
"The camouflage of animals is a ",
" fascinating phenomenon. See ",
"this video",
", where cephalopods rapidly change colours and patterns (as well as texture) in less than a second.",
"I actually did not know the mechanism behind this, but after some research, I found this ",
"article",
" in Scientific American that explains that muscle contractions can control the surface area of chromatophores (pigment containing cells). Iridophores contain reflecting pigments that account for the metallic quality you see as well."
] |
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